review article chondroitin sulfate proteoglycans in the...

Review ArticleChondroitin Sulfate Proteoglycans in the Nervous SystemInhibitors to Repair

Justin R Siebert1 Amanda Conta Steencken2 and Donna J Osterhout2

1 Lake Erie College of Osteopathic Medicine at Seton Hill 20 Seton Hill Drive Greensburg PA 15601 USA2Department of Cell and Developmental Biology State University of New York Upstate Medical University 750 East Adams StreetSyracuse NY 13210 USA

Correspondence should be addressed to Donna J Osterhout osterhodupstateedu

Received 10 May 2014 Revised 23 July 2014 Accepted 25 July 2014 Published 18 September 2014

Academic Editor Dragana Nikitovic

Copyright copy 2014 Justin R Siebert et alThis is an open access article distributed under theCreative CommonsAttribution Licensewhich permits unrestricted use distribution and reproduction in any medium provided the original work is properly cited

Chondroitin sulfate proteoglycans (CSPGs) are widely expressed in the normal central nervous system serving as guidance cuesduring development and modulating synaptic connections in the adult With injury or disease an increase in CSPG expression iscommonly observed close to lesioned areas However these CSPGdeposits form a substantial barrier to regeneration and are largelyresponsible for the inability to repair damage in the brain and spinal cordThis review discusses the role of CSPGs as inhibitors therole of inflammation in stimulating CSPG expression near site of injury and therapeutic strategies for overcoming the inhibitoryeffects of CSPGs and creating an environment conducive to nerve regeneration

1 Introduction

The limited ability of the human central nervous system(CNS) to repair itself following injuries has been knownsince the days of Ancient Egypt (3000ndash25000 BCE) asdocumented in the Edwin Smith papyrus [1] It had longbeen thought that neurons in the CNS were incapable ofmounting a regenerative response until the studies of Aguayoand colleagues in the early 1980rsquos [2 3] which demonstratedthat certain classes of neurons within the CNS particularlythose neurons which sustained an axonal injury in closeproximity to their cell body were able to regenerate theiraxons within a permissive environment such as a peripheralnerve graftAguayorsquoswork andmore recent studies [4ndash6] haveall demonstrated that supraspinal neurons (neurons arisingin the cerebral cortex or brainstem and which project theiraxons caudally into the spinal cord) are actually capable ofmounting a regenerative albeit brief and response followinginjury when provided with the proper environment Whileadvances in science have not solved the problem of this shortand often abortive nature of CNS neuron regeneration manyof the studies point to the same general theme CNS neuronsattempt to regenerate but the post-injury environment is

highly inhibitory to this process due to many moleculesexpressed after damage to the nervous system One familyof molecules the chondroitin sulfate proteoglycans (CSPGs)are of particular importance and have significant roles inlimiting the reparative response in almost every case of CNSdamage

Injuries to the CNS can generally be classified into twooverarching categories traumatic and neurodegenerativeTraumatic lesions to the brain or spinal cord are largelycontusive in nature and often result from falls sharp blowsor sudden deceleration style injuries rather than penetratingwounds [7 8] Unlike sharp lacerating wounds that severtissue contusion lesions occur when a physical force (com-pression shearing or tensile) is rapidly applied to neuraltissue without cutting [7 9ndash11] These sudden forces causerapid and focal compression and displacement of neuraltissue resulting in the disruption of multiple afferent andefferent neuronal fiber tracts Nontraumatic injuries to theCNS are often caused by degenerative pathologies such asmultiple sclerosis Alzheimerrsquos disease and Parkinsonrsquos dis-ease While research is progressing in all arenas of traumaticand degenerative CNS lesions one common attribute isobserved the expression of CSPGs in and around the areas

Hindawi Publishing CorporationBioMed Research InternationalVolume 2014 Article ID 845323 15 pageshttpdxdoiorg1011552014845323

2 BioMed Research International

G1

G1

G1

G1

G1

G1

Aggrecan

Brevican

Neurocan

Versican(V0)

G2 G3

G3

G3

Versican(V1)

Versican(V2)

G3

G3

G3

(a)

D2

D1

CAD

FN3D

CAD

FN3D

PhosphacanRPTP

(b)

ED1

ED2

Neuron-glial antigen 2

(c)

Figure 1 Schematic representation of individual proteoglycan molecules (a) Members of the lectican family aggrecan brevican neurocanand the three isotypes of versican all share a similar homology with a G1 domain at the N-terminus and a G3 domain at the C-terminusTheGAGside chain varies in number among the different lectican familymembers but is attached to the central core of the protein (b) Phosphacanis a splice variant of the RPTP molecule lacking the transmembrane and two intracellular domains found in the RPTP molecule (c) NG2is a transmembrane proteoglycan that lacks homology to any of the other CSPGs NG2 has two large extracellular domains separated by anextended region where the GAGs are attached a transmembrane domain and short cytoplasmic tail NG2 can be cleaved by enzymes at thecell surface and released into the extracellular matrix (adapted and modified from [16 18])

of CNS tissue damage It is important to understand thatupregulation of CSPG expression in response to an insult isthought to be a protective mechanism an attempt to walloff the area of damage and limit its spread [12ndash15] How-ever this creates a cellular microenvironment that inhibitsregeneration and repair It follows then that one therapeuticapproach to enhance CNS repair involves modulation ofCSPG expression which can change the cellular environmentto allow for neural regeneration

2 Chondroitin Sulfate Proteoglycans

Among the many CSPG molecules expressed in the CNS arethe lectican group which include aggrecan three forms ofversican (V0 V1 and V2) neurocan and brevican (Figure 1)All members of the lectican family consist of a central coreprotein that has an N-terminal G1 domain and a C-terminalG3 domainThe central domain binds the chondroitin sulfateglycosaminoglycan side chains (CS-GAG) [16ndash18]The aggre-can proteoglycan is the only member of the lectican groupthat has an additional globular (G2) near the G1 domainIndividual lectican molecules differ in the number of CS-GAG chains attached to their core proteins with over onehundred GAG side chains being found in aggrecan and aslittle as zero to five GAG chains being found in brevicanand neurocan [18] (Figure 1) The lectican family of CSPGsis largely produced by two major cell groups in the CNSneurons and astrocytes (Table 1)

Other proteoglycans that have major roles in the pathol-ogy of CNS injury are phosphacan and NG2 (Figure 1)

Phosphacan is a splice variant of receptor-type proteintyrosine phosphatase (RPTP) and lacks the two intracellulartyrosine phosphatase domains that are found in RPTP [18]This RPTP splice variant is secreted into the extracellularenvironment and contains attachment regions for CS-GAGchains Neuron-glial antigen 2 (NG2) is a unique CSPGthat lacks sequence homology to other known CSPGsNG2 proteoglycan is a transmembrane proteoglycan com-posed of a large extracellular domain (two large globulardomains separated by an extended region to which the GAGsattach) transmembrane domain and a short cytoplasmic tail(Figure 1) [18 19] Cells that express the NG2 proteoglycaninclude oligodendrocyte progenitor cells polydendrocytesactivated microglia and activated macrophages (Table 1)

The variations in the length of the core protein and thevarying number of GAG side chains attached to the centraldomain are major determinants of the biological activity ofan individual proteoglycan However the biological effects ofa proteoglycan are also affected by the sulfation patterns oftheN-acetylgalactosamine and glucuronate disaccharide thebasic unit that composes the CS-GAG [16 18] There are fourdifferent sulfation patterns that can occur based on eithermonosulfation or disulfation of the N-acetylgalactosamine(GalNAc) and glucuronate disaccharide (GlcA) of the GAGdisaccharide leading to the synthesis of the CS-A CS-C CS-D and CS-E CS-GAGs (Figure 2) [16ndash18 20] Sulfation ofthe chondroitin sulfate disaccharide can occur in the 4 and6 positions of the GalNAc and the 2 position of the GlcA[16 18 20] It has been demonstrated that a CSPG moleculecan be either inhibitory or permissive for axonal growth

BioMed Research International 3

Table 1

Cell Proteoglycan CNSspecific Location Inhibitory to axonal growth References

Neurons

Aggrecan No ECM YES [166 167]Brevican Yes ECM YES [22 105]Neurocan Yes ECM YES [16 22 105 168 169]Phosphacan Yes ECM YES [16 22 105 168 169]

AstrocytesBrevican Yes ECM YES [22 105 116]Neurocan Yes ECM YES [16 22 105 116 168 169]Phosphacan Yes ECM YES [16 22 105 116 121 122 168 169]

Activatedmicroglial cells

KSPGs No TM amp ECM YES [92 93 170]NG2 No TM amp ECM [92 108 109 121 122 171ndash174]

Oligodendrocyteprogenitor cells

KSPGs No TM amp ECM YES [92 93 170]NG2 No TM amp ECM [92 108 109 121 122 171]

Versican (V2) Yes ECM NO [106 108]Polydendrocytes NG2 No TM amp ECM [92 108 109 121 122]Activated vascularmacrophages

KSPGs No TM amp ECM YES [92 93 170]NG2 No TM amp ECM [92 108 109 121 122 173 174]

Abbreviations TM transmembrane ECM extracellular matrix

GlcA GalNAc

OO

O O OO

O

OO

OO O

OO

O

OOO

OO

O

O

OO

O

n

nn

nn

HONH

H C CO

Diasaccharide unit of GAG chain

Monosulfated Disulfated

CS-A

Sulfation at the 4-position of the GalNAc

CH OSO

OSO 3

CS-D

Sulfation at the 6-position of the GalNAcSulfation at the 2-position of the GlcA

CS-CCH OSO


CS-E

Sulfation at the 4 and 6 positions of the GalNAc

CH OSOO SO

CO2H R1 R2

R3

H3

H2

minusminus minus

minus

O3

O SOminusO3

H2H2

Figure 2 Diagram of the sulfation patterns of the disaccharide unit of theGAG chain Sulfation at different carbon atompositions in theGlcAandor GalNAc saccharide unit is one of the major factors that influence the effects of the proteoglycan Monosulfation can occur at position4 of the GalNAc resulting in synthesis of CS-A GAG or position 6 of the GalNAc resulting in the synthesis of the CS-C GAG Disulfationcan also occur with sulfation of position 6 of the GalNAc and position 2 of the GlcA resulting in synthesis of the CS-D GAG or sulfation ofpositions 4 and 6 on the GalNAc saccharide unit resulting in formation of the CS-E GAG (adapted and modified from [16 18])

based on themolecular position of the sulfationwhich occursin the disaccharide [20ndash22] For example when the sulfationoccurs at the 4-position (CS-A) the proteoglycan tends tobe highly inhibitory to axonal outgrowth [21 22] whereassulfation in the 6-position (CS-C) is more controversial and

has been found to be inhibitory to axonal outgrowth by somelabs [23] and permissive to axonal growth in others [20] Invitro experiments show that the disulphated GAGs (CS-Dand CS-E) promote the growth of embryonic axons [24 25]Taken together these observations reveal many aspects of


proteoglycan structure which can modulate their biologicaleffects on cells within the CNS

The majority of CSPGs can interact with growth factorscell adhesion molecules and other ECM molecules in thelocal environment and may regulate their biological activityCSPGs are widely distributed throughout the normal CNSboth during development and in the adult CSPGs expressionis especially rich in the embryonic brain and can directcell migration and axonal outgrowth by providing guidancecues [17 18] Phosphacan is concentrated in the regionsof cell proliferation such as the ventricular zone of theembryonic brains suggesting it may modulate cell divisionIn the healthy adult nervous system the soma and proximaldendrites of certain neurons are surrounded by a CSPG richstructure known as a perineuronal net This perineuronalnet stabilizes existing synapses and inhibits the formation ofaberrant synaptic connections [17 26] In terms of generalCSPG expression patterns white matter is rich in versicanand neurocan while brevican can be found throughout theCNS and NG2 is found expressed among meningeal cellsblood vessels and OPCs [27]

3 Traumatic Lesions

Vast strides have been made in characterizing and under-standing the complex orchestration of biological events thatoccurs following a lesion to the CNS Unfortunately it isnow widely known and accepted that the events occurring inbrain or spinal cord tissue post-injury create an environmenthostile to a regenerative response resulting in the abortivenature of the reparative process [9 28 29] This is due in partto a significant upregulation of CSPGs

The extreme forces applied to the CNS during trau-matic injuries result in disruption of axonal tracts bloodvessels and glial cells located at the epicenter of the lesion(reviewed by [10 12]) Immediately following injury thereis a marked swelling of CNS tissue caused by damage tothe local vasculature allowing for leakage of blood plasmafluid into the surrounding extracellular space [30] Thisvascular damage also creates an anoxic environment thatis accompanied by necrosis of tissue damaged during theinjury Dying cells release their contents directly into theextracellular environment resulting in a massive infiltrationof blood bornemacrophages andmicroglia the resident CNSimmune cell [31ndash34]

In healthy CNS tissue microglial cells exist in a nonactiveor resting state courtesy of microglia-neuronal commu-nications [35ndash37] However with an infection or traumamicroglial cells are activated taking on the role of a phago-cytic macrophage [38] Activated macrophagesmicrogliaplay an important role in the CNS response to injury andinfection because of the various products they secrete [37]including cytotoxic molecules (free radicals ie superox-ides) neurotrophic molecules (nerve growth factor eg)and a variety of pro- and anti-inflammatory cytokinesand chemokines [37] These cytokines can stimulate theexpression of CSPGs in a variety of cells in and aroundthe lesion Complicit in this process is the recruitment ofblood borne macrophages which invade the lesion site As

these cells perform their biological function of phagocytizingnecrotic cellular debris and any foreign pathogens theyfurther exacerbate the inflammatory response by releasinginflammatory cytokines which can also stimulate CSPGssynthesis from neighboring cells [38] Most important arethe astrocytes located at the border of the injury whichundergo a process known as reactive astrogliosis In responseto various cytokines astrocytes become hypertrophic andbegin secreting CSPGs leading to the formation of a glialscarThe glial scar serves as a chemophysical barrier to axonalregeneration [32 33 39 40]

4 Degenerative Lesions

While the etiologies of traumatic and degenerative lesionsare different during degeneration the CNS responds ina highly similar manner to that described for traumaticlesions complete with reactive astrogliosis and the depo-sition of CSPGs Hallmarks of Alzheimerrsquos disease (AD)pathology include the formation of neurofibrillary tanglesand extracellular accumulation of amyloid-beta (A120573) fibrils[41] This results in a loss of axonal integrity and a declinein synaptic connectivity that is believed to contribute todementia [42] Dystrophic neurites activated astrocytes andA120573 fibrils form senile plaques which are the key diagnosticcriteria of AD [43 44] These senile plaques appear tobe loci for inflammatory processes containing a variety ofmolecules such as cytokines acute-phase proteins and com-plement proteins which are secreted by reactive microgliaand astrocytes around the lesion [45ndash47] Microglia havebeen identified in close association with AD lesions andwhile their function is to phagocytize the lesions they areunable to do so With plaque deposition activated microgliaare present on a continuous basis and thus provide a constantsource of neurotoxic molecules [48] This mechanism hasbeen proposed to explain the toxicity of amyloid peptides(reviewed by [49ndash53])

Parkinsonrsquos disease (PD) is a neurodegenerative move-ment disorder of unknown etiology characterized by theselective loss of dopaminergic nigrostriatal neurons [54] PDpatients present symptoms such as resting tremor posturalinstability muscle stiffness and slowness of voluntary move-ments (reviewed by [55ndash57]) The selective vulnerability ofdopaminergic neurons observed in PD is thought to be dueto various interacting factors one of which is the microglia-mediated inflammatory response [57 58] A role for activatedmicroglia in neurodegeneration is supported by studiesusing PD animal models Dopaminergic neuronal degener-ation can be elicited by injecting the neurotoxin bacteriallipopolysaccharide into the rat substantia nigraThese exper-iments revealed a significant increase in microglia activationthroughout this subcortical area preceding marked neu-ronal death [59] Furthermore lipopolysaccharide-inducedneuronal death was blocked by inhibition of microglialactivation in this model Administration of the neurotoxins1-Methyl-4-phenyl-1256-tetrahydropyridine (MPTP) or 6-hydroxydopamine (6-OHDA) also mimics PD symptoms inmice and induces activation and proliferation of microglia aswell as increased expression of inducible nitric oxide synthase


(iNOS) and MHC class-I and II molecules [57 60ndash64] Theobserved increase in activated microglia is highly localizedand anatomically discrete limited to the substantia nigraFurthermore it is directly correlated with the neuronal death(reviewed by [57])

Multiple sclerosis (MS) is a clinically heterogeneousdemyelinating disease of the CNS [65] characterized byinflammation axonal degeneration and gliosis [66] Theetiology of this chronic inflammatory disease is unknownalthough an autoimmune response is thought to be involvedMS lesions are characterized by the presence of large regionsof demyelination commonly referred to as plaques Theseplaques contain reactive glial scar formation with infiltrationof activated T cells and macrophages [67] The blood brainbarrier (BBB) is disrupted and upregulation of various adhe-sion molecules has been reported on capillary endothelialcells during the early stages of disease [68] Increased BBBpermeability allows for inflammatory infiltrates like activatedmacrophages T cells and antibodies to invade the CNSparenchyma Tumor necrosis factor alpha (TNF-120572) is a keycytokine that may influence the progression of MS TNF-120572promotes the proliferation of bovine astrocytes and humanastroglioma cell lines which leads to reactive gliosis as seenin active MS plaques [69] TNF-120572 also stimulates productionof colony-stimulating factors from neighboring astrocyteswhich act as chemoattractants for reactive cellsThis results inincreasedmigration of activated cells to sites of inflammationand increases in the proliferation and activation of microglia[70ndash72]

Amyotrophic lateral sclerosis (ALS) is a rapidly progress-ing adult-onset disease that usually results in death within 5years of its initiation Clinical manifestations of the diseaseinclude initial muscle weakness and atrophy that progress toa spastic paralysis resulting frommotor neuron degeneration[73] About 25 of ALS cases appear to be caused by again-of-function mutation in the antioxidant enzyme CuZn superoxide dismutase-1 (SOD-1) which catalyzes theconversion of superoxide to oxygen and hydrogen peroxide[74] This disease shares some of the characteristic neuroin-flammatory changes observed in other neurodegenerativediseases like AD and MS [75] Neuroinflammation is a keymediator of the pathology observed in ALS [76] Reactivemicroglia and macrophages have been detected in spinalcord and motor cortex of ALS patients using conventionalimmunohistochemistry for activated monocyte-lineage-cellantigens (reviewed by [75]) MHC-I and MHC-II molecules1205732-integrins and leukocyte common antigen are upregu-lated indicating the presence of reactive microglia in thesetissues [75 77 78] Activated astrocytes and leukocytesare also observed as demonstrated by glial fibrillary acidicprotein (GFAP) and leukocyte functional antigen (LFA)-1staining respectively Furthermore the majority of LFA-1+leukocytes were CD8+ [79] suggesting a role for cytotoxic Tlymphocytes in disease progression This T cell presence isnot as prominent as that seen in T cell-mediated diseases likeMS In contrast it has been proposed that neuroinflammationin ALS and its animal models is driven mainly by reactivemacrophages and microglia and the resulting dysregulationin cytokine expression [76]

5 Role of Inflammation inStimulating CSPG Expression

Trauma-induced CNS injury and autoimmuneneurodegen-erative CNS disorders have several important similarities anddifferences in terms of the immuneinflammatory responseThis observation was noted by Popovich and colleagues[80] comparing MS and SCI and it could easily be furtherextended to include conditions like ALS AD and PDFor example one key feature observed in CNS diseasesis the disruption of the BBB which allows for an influxof inflammatory cells [81ndash84] In AD PD MS and ALSthe mechanisms for increased BBB permeability remainunknown Inflammatory mediators released from microgliaand T lymphocytes are related to this process but what trig-gers this release is still a matter of controversy On the otherhand in cases of traumatic CNS injuries BBB disruption isa direct consequence of traumatic insult Nonetheless thechronic endothelial permeability ismaintained and explainedby a perpetuated intraparenchymal inflammatory response

Both traumatic and autoimmuneneurodegenerativeCNS injuries show microglial activation and immune cellinfiltration Even the temporal sequence of events is similar inthese scenarios where microglia are recruited first releasinginflammatory cytokines and reactive oxygen species(ROS) as well as upregulating their antigen presentingcell capabilities Following increased BBB permeabilityhematogenous macrophages neutrophils and lymphocytesfollow mediating myelin vesiculation lipid peroxidation andfurther release of proinflammatory agents and free radicalsDemyelination ensues resulting from oligodendrocyteinjury and edema However in SCI this process is restrictedto CNS myelin whereas in conditions like MS myelindestruction and ROS are found in the CNS as well as in theperiphery [80]

Increases in pro- and anti-inflammatory cytokine levelsand ROS production are a common occurrence in traumaticand autoimmune or neurodegenerative CNS disorders Interms of therapeutic approaches this has been targetedrepeatedly using a variety of strategies that include antibodytreatments administration of cytokine receptor antagonistsor even proinflammatory cytokines themselves [85ndash90]Glucocorticoids like methylprednisolone have been usedextensively in light of their ability to suppress proinflamma-tory cytokine synthesis [91] Because activation of variousimmune cells during the inflammatory response is directlyassociated with secretion of ROS and tyrosine nitrationapproaches such as antioxidant administration inhibition ofinducible nitric oxide synthase iNOS and targeted depletionof hematogenous macrophages are all under investigation[92]

One of the main differences between SCI and autoim-muneneurodegenerative disorders is the induction time forcytokine expression Trauma-induced CNS injury is charac-terized by a transient increase in proinflammatory cytokinelevels that is followed by a relatively rapid restoration ofbaseline levels In this instance cytokines have a key role inthe acute-phase response Trauma related degeneration canbe attributed to the initial trauma itself since cell death and


tissue necrosis occur as early as one hour after injury Onthe other hand neurodegenerative conditions like MS andALS owe their prolonged progression to a slow and persistentincrease in proinflammatory cytokines Degenerative pro-cesses seen in these cases are more likely to be the result ofdirect effects of cytokines [80]

As previously noted following any type of insult to thecentral nervous system an immune response is elicited anda combination of vascular macrophages and active microgliainfiltrate the lesion site It is well documented that vascularmacrophages and activated microglia synthesize and secretemany different proinflammatory cytokine and chemokinemolecules [93ndash99] Activated microglial cells are known tosecrete a minimum of at least 20 different cytokine andchemokine molecules [100] Some of these molecules suchas Interleukin-1 (IL-1) IL-2 IL-6 IL-15 IL-18 Interferongamma (IFN-120574) and TNF-120572 are all known and documentedto be proinflammatory and found to be upregulated in casesof CNS tissue damage [98 100] Interestingly when theseproinflammatory cytokines and chemokines specifically IL-1 IL-2 IL-6 TNF-120572 IFN-120574 were injected into normalbrain tissue a significant amount of reactive astrogliosis wasobserved around the injection sites [93 94 96] Anotherstudy demonstrated that transforming growth factor alpha(TGF-120572 a cytokine expressed by macrophages) and trans-forming growth factor beta (TGF-120573 a cytokine expressed byboth microglia and macrophages) resulted in the upregula-tion and synthesis of chondroitin 6-sulphate proteoglycans inbrain tissue and in vitro cell culture experiments [99] Recentwork has identified a link between the activation of microgliaand the activation of astrocytes painting a picture of crosstalkand coregulation where astrocytes and microglia signal toeach othermodulating each otherrsquos activation and post-injuryactivities [95 97] Interestingly macrophages themselves cansynthesize and either degrade or secrete CSPGs and may bea potentially significant source of CSPGs in the post-injuryenvironment [101]

6 CSPG Deposition at CNS Lesions

CSPGs are upregulated rapidly in the tissue surroundinga lesion site due to the induction of reactive gliosis (seeFigure 3) There are many members of the CSPG family andindividual CSPGs are synthesized by different cell types andat different time points following injury Reactive astrocytessynthesize brevican neurocan and phosphacan while vascu-lar macrophages activated microglia and endogenous OPCsaccount for the increased expression of NG2 and versican[17 102 103]

In traumatic lesions CSPGs can be observed at the lesionvery quickly within the first 24 hours However the temporalpattern in which individual CSPG molecules are produced isdifferent Neurocan is the first to appear with brevican andversican following Their expression levels are maximal twoweeks after injury in a spinal cord injury model [103] Peakexpression of the NG2 proteoglycan occurs one week afterinjury because it is expressed by infiltrating macrophagesand OPCs Keratan sulfate proteoglycans which are alsoinhibitory to regeneration are also produced by infiltrating

Trauma

Disease

Proinflammatory

cytokinesCSPGs

Figure 3 Damage to the central nervous system either by traumaor disease processes initiates an increase in proinflammatorycytokines which stimulates the upregulation of CSPGs expression

macrophages microglia and OPCs as early as 3 days post-injury [103 104] Interestingly expression of phosphacan isinitially downregulated during the first 72 hours after lesionbut slowly increases over time reaching peak levels approx-imately eight weeks after injury [103] While all members ofthe CSPG family are expressed following a traumatic insult tothe CNS their location in the lesion area is also variable Neu-rocan is expressed close to the lesion center and around theimmediate border in a zone from 100 120583m to 500120583maround aspinal cord lesion Brevican lies close to the immediate injurysite as well deposited within 300 120583m of the lesion borderPhosphacan and versican are expressed in amore broad rangedeposition extending in a diffuse pattern as far as 600120583mfrom the impact site [103] Additionally while changes inCSPG expression in tissue adjacent to the damaged tissue arewell described alterations in CSPGs expression in areas distalto lesions are also observed In a study conducted byAndrewsand colleagues [105] following a spinal contusion at the T8level CSPG expression was detected in both the lumbar andcervical enlargements far away from the injury site Theydiscovered a strong upregulation of neurocan at the lesionepicenter and at both the lumbar and cervical enlargementsAggrecan and brevican were initially downregulated in thelesion and was unchanged in both spinal enlargements [105]While the total amount of NG2 protein did not change in thetissue around the lesion there was an accumulation of NG2in the lumbar enlargement but not the cervicalThe continualand differential expression of CSPGs changes over acute andchronic times following trauma and the changes that occurfar from the site of insult maintain a broad environmentinhibitory to regenerative response for many months post-injury

In neurodegenerative lesions the timeline of CSPGexpression is not well understood as all histopathology inhumans occurs post-mortem However several studies havedocumented the presence of CSPGs in human tissue andupregulation in animal models of disease In Alzheimerrsquos


disease when the formation of the 120573-amyloid plaques andneurofibrillary tangles was examined it was found thatthese lesions were surrounded in a shell of GFAP positivereactive astrocytes which indicate that reactive gliosis hadoccurred [106] Further examination of AD brains revealedthe expression of CSPGs heparan sulfate proteoglycans(HSPGs) and dermatan sulfate proteoglycans (DSPGs) Theupregulation of CSPG expression has also been discoveredin other neurodegenerative diseases such as Huntingtonrsquosdisease MS around the inclusions of Parkinsonrsquos disease inPickrsquos disease and progressive supranuclear palsy [106 107]The edges of active MS demyelinating lesions are rich in theCSPGs aggrecan neurocan and versican [108] Further anincrease in the levels of bone morphogenic protein (BMP)has been detected in areas of demyelination Activation ofBMP stimulates increased synthesis of CSPGs fromastrocytessurrounding the lesion [109] In other forms of nontraumaticCNS injuries such as stroke and amyotrophic lateral sclerosisreactive astrogliosis occurs with CSPG deposition as a resultof the pathology [110 111]

Regardless of the etiology most CNS lesions involvean immune response including the recruitment of vascularmacrophages and activated microglial cells [10 29 100 112113] The cytokine and chemokine molecules expressed bythese immune cell infiltrates elicit a process of reactiveastrogliosis which in turn is responsible for the upregulationof CSPG expression While the overexpression of proteogly-cans that occurs following injury is highly inhibitory to theregenerative response it is also important to note that thisprocess is also necessary The upregulation of CSPGs occursquickly to contain the tissue damage By interfering with orpreventing the formation of the glial scar not only tissuedegeneration is significantly worse but the spread of damageinto areas not initially damaged can be up to 60 greater[12ndash15] This poses an interesting challenge to researchershow to bypass or neutralize the well-known and documentedinhibitory effects of CSPGs on regeneration while not totallyor permanently ablating or eliminating the formation andfunction of the glial scar

7 Inhibitory Effect of CSPGs on Neuronal andOligodendroglial Cells

At themolecular level in vitro studies have demonstrated thatCSPGs can interact with adhesion molecules expressed onvarious cell types [114]When axonal growth cones come intocontact with CSPGs they collapse and retract This is likelythe reason for the abortive regenerative sprouting observedin spinal cord lesions [10 33] The interaction of CSPGs andneurons activates the Rho-ROCK andor protein kinase C(PKC) intracellular signaling cascades which inhibit processextension It was also noted that by blocking activation oftheRho-Rock andor PKC signalling pathways the inhibitoryeffects of CSPGs could be reversed [26] It has also beendemonstrated in vitro that CSPGs can influence the activity ofthe axonal growth cone In dorsal root ganglion cultures thepresence of CSPGs induced changes in local protein synthesisin the growth cone with an increase in RhoA transcripts

(a cytoskeletal regulator) being found locally within thegrowth cone after CSPG contact [115]

While CSPGs are widely accepted to be inhibitory toaxonal regeneration the inhibitory nature of individualCSPG molecules varies among the proteoglycans In vitropurified brevican has been shown to be inhibitory to bothaxonal attachment and growth [29 116] while both neurocanand phosphacan have been shown to interact with neuralcell adhesionmolecules (N-CAM) similarly inhibiting axonalgrowth [29 116] Conversely versican is not thought to beinhibitory to either axonal regrowth or adhesion Axons areable to grow through deposits of versican in vitro and arenot inhibited by the presence of purified versican [117 118]Certain in vitro studies have demonstrated that NG2 can beinhibitory to the process of axonal outgrowth while otherstudies have demonstrated that NG2 is not only permissiveto axonal growth but can stabilize the axon post-injury [103119ndash122] A novel brain-derived proteoglycan Te38 is highlyinhibitory to axon outgrowth [123] and it is present withinthe lesion site of a spinal cord injury [123 124] The Te38proteoglycan could be detected for up to 4 weeks post-injuryhowever the exact expression pattern for Te38 has yet to bedetermined

While the inhibitory effects of CSPGs on axons havebeen known for some time the effects they exert on othercell populations such as oligodendrocytes have only beenrecently considered CSPGs exert a highly inhibitory influ-ence on oligodendrocytes [125ndash127] Studies utilizing an invitro model of the glial scar with isolated OPCs revealed asignificant inhibition of process outgrowth and differentia-tion [125] When the OPCs processes came into contact withCSPGs the cellular process retracted and avoided contactwith theCSPG rich surface similar towhatwas observedwithneurons Additional studies by other laboratories have con-firmed these findings suggesting CSPGs exert an inhibitoryeffect on oligodendrocytes [126 127]

In vivo CSPG expression can modulate the migrationand differentiation of endogenous OPCs that are attracted toCNS lesions Accumulation of OPCs at the edge of a lesioncan be observed after spinal cord injury in the regions distalto the lesion site [128ndash130] There is somewhat conflictingevidence as to whether they can differentiate intomyelinatingoligodendrocytes in the area around the lesion They maydifferentiate into mature cells but may not survive for longertimes after injury [131 132] In addition to the CS-GAGsthe presence of other glycosaminoglycans like hyaluronanneeds to be taken into consideration as hyaluronan is knownto modulate the behavior of oligodendrocytes The presenceof hyaluronan in active demyelinating lesions in MS andother white matter diseases can inhibit the differentiation ofendogenous OPCs located near the lesions [133 134] Thusthe expression of glycosaminoglycans at a lesion site haseffects not only on neuronal regeneration but possibly onremyelination as well

The cellular receptors which interact with proteoglycanshave only recently been identified Potential surface receptorsfor proteoglycans on neurons and glial cells include theprotein tyrosine phosphatase sigma (PTP120590) Loss of thePTP120590 receptor by gene knockdown or inhibition of receptor


activation renders neuronal process outgrowth insensitiveto CSPG deposits [134] Studies have also recently shownthat the PTP120590 receptor may also be involved with theobserved inhibitory effects CSPGs exert on oligodendrocytes[127 135] While PTP120590 has been observed in both neuronsand oligodendrocytes other receptors for CSPGs have beenidentified in neurons only including Nogo 66 Receptor 1(NgR1) Nogo 66 Receptor 3 (NgR3) and leukocyte commonantigen receptor (LAR) [136 137] To date there are nodefinitive reports that NgR1 NgR3 or LAR function as CSPGreceptors in oligodendrocytes

8 Therapeutic Modulation of CSPGsChondroitinase ABC

Given that CSPGs are a major barrier to repair and regen-eration a key experimental strategy for enhancing axonalregeneration and plasticity has been to modify the inhibitoryextracellular environment The bacterial enzyme chondroiti-nase ABC (cABC) can neutralize the inhibitory nature of theCSPG molecules and thus was tested in many injury modelscABC is an enzyme produced by the bacteria Proteus vulgariswhich catalyzes the removal of the glycosaminoglycan sidechains from the central core protein [138] Numerous in vivostudies have shown that by treating a CNS lesion site with theenzyme cABC axonal sprouting growth and plasticity aresignificantly increased [139ndash147] This is often accompaniedby a significant increase in recovery of motor function whichsuggests that cABC is an attractive candidate for therapeuticapplications However to date there is little anatomicalevidence to suggest that administration of cABC has allowedfor axonal regrowth over long distances While substantialaxonal growth can be observed into and even through a SCIlesion there are no studies that demonstrate axonal regrowthto its original targetThis is likely due to the slow growth ratesof regenerating axons and the short time points examinedin the reported experiments It could also be due to thefact that measured improvements in motor function resultfrom other mechanisms such as formation of alternativeneuronal circuits improved survival of motor neurons aswell as remyelination The underlying explanation for themotor improvements observed after cABC administrationare currently not well understood

One critical issue with the use of cABC as a therapeuticagent is the thermal instability of the enzyme The biologicalactivity of cABC decreases quickly when in solution andis sensitive to temperature A study by Tester et al [148]demonstrated that if cABC in solution was incubated at 37∘Cits enzymatic activity was significantly reduced after 3 daysand totally lost by 5 days These findings reveal that whilethe therapeutic ability of cABC is promising experimentalstabilization of the enzyme is likely to be needed for itto be a more effective therapeutic agent [148] Currentlymethods for administering cABC range from a constantinfusion soaking a piece of gelfoam in cABC and applyingit directly to the injury site [142] to directly infusing theenzyme into the ventricles of the brain [149] There havebeen several experimental approaches to stabilize the enzymeor to provide a continual supply of active enzyme at a

lesion Modification of the protein structure by amino acidsubstitutions has generated forms of cABC that show morestable enzymatic activity [150] Alternatively the gene forcABC can be inserted into a viral vector which can be eitherdirectly introduced into a CNS lesion or introduced into cellswhich can then be transplanted into a lesion [151ndash155] Bothmethods can produce sustained levels of enzyme in vivowith digestion of CSPGs To avoid the use of viral vectorswe have incorporated cABC into biodegradable nanosphereswhich protects the enzymatic activity for manymonths [156]When tested in an in vivo model of spinal cord injury theslow release of active cABC from nanospheres resulted in asignificant increase in the level of CSPG digestion at 2 weeksand 1 month after injury when compared to direct injectionsas well as a significant increase in the level of axonal sproutingthroughout the lesion site [157]

While cABC treatment digests CSPGs there is evidencethat following deglycanation intact CSPGs are eventuallyreconstituted in the tissue This turnover occurs approxi-mately two-weeks following deglycanation and was demon-strated in a study by Crespo et al [138] In this study aCNS lesion was inflicted to the nigrostriatal tract followed bycABC treatment Prepared lesion site extracts were analyzedwith the 1B5 antibody to identify digested CSPGs At 1 4and 7 days after lesion 1B5 labeling was clearly visible butby 14 days after lesion 1B5 immunoreactivity was no longerpresent [138] This suggests that by 2 weeks postlesion thedigested CSPGs have been either reformed or cleared fromthe lesion site Therefore a continual supply of cABC withinthe lesion site is presumably needed until axonal outgrowthand repair of neural connections is complete Should CSPGturnover occur before axonal outgrowth or remyelinationis complete the newly deposited CSPGs would once againcreate a highly inhibitory influence and halt the regenerationHowever there is clearly a need for a balance of CSPGdegradation and reconstitutionWhile cABC treatment offersa temporary breakdown of CSPGs within the glial scar tofoster axonal outgrowth total ablation of the glial scar resultsin more severe tissue damage [12] Therefore at least the coreproteins of CSPGs and perhaps the intact CSPG moleculemay be needed to stabilize the spinal cord environment afterCNS injury

9 Postulated Mechanisms for cABCImprovements in CNS Function after Injury

While many studies claim functional recovery is a result ofaxonal regeneration they fail to rule out other adaptivemech-anisms that may account for the recovery of function Suchmechanisms include possible spontaneous remyelination ofspared axons or the formation of alternative neural circuits[158ndash160] It is essential in the field of neural regenerationresearch especially when agents like cABC are tested thatthe motor behavior data be correlated with neuroanatomicdata to determine the cellular mechanisms underlying motorrecovery Introducing cABC into a post-injury environmentrich in CSPGs which have well-known inhibitory effects onneurons OPCs and possibly other cells will change theirbehavior in the dynamic lesion environment Therefore the


observed recovery of function could be the collective resultsof multiple events not related to axonal regeneration

Most studies using cABC have focused on the effectson neurons documenting significant axonal sprouting andgrowth around a lesion after cABC treatment [139ndash144]However the extent of axonal regeneration is widely vari-able between studies and no long distance regeneration isobserved While experimental treatment with cABC is fre-quent in the field of spinal cord injury it has also been testedas a potential therapeutic agent in stroke and TBI researchStudies demonstrate that while the functionalbehavioralrecovery is mixed in all cases of cABC administrationfollowing TBI or stroke there are signs of anatomical reorga-nization with degradation of the CSPGmatrix perineuronalnets and evidence of axonal sprouting and growth [145ndash147]

It is also possible that what is sometimes characterized asaxonal regeneration may actually be the sprouting of sparedaxons [161] When the total percentage of CNS axons foundto regenerate is compared to the results found after PNSinjury the results are striking Under optimal conditions onaverage 90 of axons are found to regenerate within thePNS [161] However in regeneration studies examining CSTaxons only 2ndash10 of CST axons are reported to regenerateand for relatively short distances [161] Likewise sim7 ofrubrospinal axons regenerate at best following experimentalintervention [161] And finally the distance CNS axonsactually grow is rather meager As summarized by Bradburyand McMahon [161] the proportion of axons (CST axons)induced to grow longer than two spinal segments is less than10

CSPGs have a strong inhibitory influence onOPCprocessoutgrowth and differentiation both in vitro and in vivoand this may affect remyelination near a CNS lesion Thereis significant OPC infiltration to a SCI lesion site aftercABC treatment which occurs quickly after injury [121 124130 162] The inhibitory effects of individual CSPGs wereidentified using an in vitro assay the strongest inhibition wasobserved with the mixes of CSPGs containing high levels ofboth neurocan and phosphacan This is highly homologousto the CSPGs composition of the glial scar [124] Cellulareffects included stunting of cytoplasmic process outgrowthand myelin sheet formation and impeding the migratoryability of the OPCs It is well known that following an injuryto the CNS OPCs begin to migrate towards the site ofoligodendrocyte loss and some spontaneous remyelinationdoes occur however sustained remyelination of spared axonshas never been well documented [22 128]

Using a spinal cord injury model treatment with cABCshowed a significant increase in the number of OPCs foundinside and around the lesion site [130] This occurs quitequickly after injury and is independent of axonal sproutingIn the absence of cABC OPCs migrate towards the distaledge of the lesion over the two week period This findingmirrors that of previous studies which show an accumulationof OPCs in the regions distal to the lesion site [128 129]Moreover this also correlates to the timewhen the expressionof CSPGs and establishment of the glial scar in the proximalarea immediately adjacent to the lesion becomes maximal[10 29 103] The administration of cABC immediately after

injury allowed for a significant increase in overall numberof OPCs as well as access into areas proximal and withinthe lesion Interestingly a large increase in OPC numberwas observed deep inside the lesion site [130] The signalattracting OPCs into the lesion cavity is unknown Howeverthere is speculation that demyelination and myelin break-down may be the cue One element common to cuprizoneand SCI models is the microglial activation and clearance ofmyelin debris [10 29 163] Thus demyelination followed bymicroglial activation may be recruitment signals for OPCs

10 Xyloside and Other Agents

In the field of MS research it has been demonstrated thatinhibiting the synthesis of CSPGs improves the outcomeof the pathology [126] Xyloside blocks the attachment ofthe GAGs to the CSPGrsquos central core protein which is theprimary inhibitory element of CSPGs Thus the depositionof CSPGs without GAG side chains does not create anenvironment that retards tissue repair When xyloside wasadministered in a lysolecithin-induced model of demyeli-nation it not only resulted in a greatly reduced area ofdemyelination but there was also a significant increase inthe number of mature oligodendrocytes found within theMSplaque [126] Due to potential side effects xylosides may notbe useful to treat SCI in humans However the results furthersupport the observation that CSPGs are inhibitory to repair ofthe injured CNS due to the presence of GAG side chains andthat neutralizing CSPGs allows for regenerativereparativeresponse to progress

Alternatively in vitro experiments have successfully tar-geted the enzymes responsible for the polymerization ofthe GAG side chains [164] When siRNA directed againstchondroitin polymerizing factor (ChPF) was introduced intoastrocytes CSPG core proteins were produced but they werenot decorated with the GAG side chain and did not pose asignificant barrier to axonal growth from cerebellar granuleneurons [164] In another study it was demonstrated that theadministration of xylosyltransferase-1 (XT-1) a DNA enzymeagainst the GAG chain initiating enzyme greatly reducedthe presence of GAG chains which subsequently allowed forthe regeneration of microtransplanted adult sensory axonspast the central core of a spinal cord stab lesion [165]DisruptingCSPGs synthesis could provide a potentially noveltherapeutic treatment paradigm targeting assembly of theGAG chains in newly synthesized proteoglycans rather thandigestion of existing GAG chains with cABC

11 Summary and Future Directions

Significant progress has been made in understanding thepost-injury tissue response after CNS injury especially theidentification and characterization of molecules at the lesionsite that inhibit axonal regeneration and identifying agentsthat can enhance the capacity for repair There is over-whelming evidence that following any insult to the CNStraumatic or degenerative an inflammatory reaction occursand the activation of microglia astrocytes and invasion ofvascular macrophages result in an upregulation and synthesis


of CSPGs (Figure 3)There is also strong evidence that CSPGsform an important protective barrier preventing furthersecondary tissue damage [12ndash15]However it is also a primaryreason axonal regeneration and remyelination fails followingany type of injury to the CNS

Modification of CS-GAG expression on CSPGs whilenot completely ablating the CSPG molecule is a reasonableapproach to facilitating repair One promising avenue isthe administration of cABC at the site of a CNS lesionto remove the inhibitory GAG chains and neutralize theinhibitory nature of CSPGs cABC has been tested in manyinjury studies and often results in an improvement in motorfunction However long distance axonal regeneration israrely observed In the SCI field it is widely accepted thatcABC will need to be used in conjunction with agents suchas neurotrophins that can directly promote neuronal survivaland stimulate axonal growth An alternative strategy targetsthe new synthesis of CSPGs after injury by blocking theaddition of GAG side chains These agents also reduce thepresence to the inhibitory GAG chains but they have notbeen as well documented in injury models Like cABC it isprobable that they need to be utilized in conjunction withfactors that directly stimulate axonal sprouting and regrowthto maximize repair and recovery of function

While modification of CSPG expression is an attractivetherapeutic approach there are still many questions whichneed to be answered How long would an agent such ascABC be needed Axonal growth is a slow process whichcan take months in animals and longer in humans howevercABC may only be needed at specific times to allow theregeneration process to initiate Delivery methods are veryimportant as well cABC is a labile enzyme losing activityquickly in solution There are several choices for long termdelivery including viral expression and biomaterial packag-ing However how would this be silenced once regenerationis accomplished and cABC is no longer needed Excess cABCwould destabilize perineuronal nets in uninjured tissuewhich could potentially result in aberrant axonal sproutingand circuit formation as well as synaptic instability Althoughthere are no reports of adverse effects in animal studies thereis also the possibility that the long term presence of cABCcould trigger an immune response in humans

The most important consideration for repair of thedamaged CNS is that controlling CSPG expression is onlyone aspect of the solution Neurotrophic agents that directlypromote neuronal survival and axonal growth are just asimportant particularly for regeneration of specific neuronalpopulations as are methods to direct these regeneratingaxons to their targets CSPG regulation is but one importantstep in restoring CNS function after injury or disease

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

References

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nervous system ldquobridgesrdquo after central nervous system injury inadult ratsrdquo Science vol 214 no 4523 pp 931ndash933 1981

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[4] K J L Fernandes D P Fan B J Tsui S L Cassar and WTetzlaff ldquoInfluence of the axotomy to cell body distance in ratrubrospinal and spinal motor neurons differential regulation ofGAP-43 Tubulins and Neurofilament-Mrdquo Journal of Compar-ative Neurology vol 414 pp 494ndash510 1999

[5] M K Hossain-Ibrahim K Rezajooi J K MacNally M RJ Mason A R Lieberman and P N Anderson ldquoEffectsof lipopolysaccharide-induced inflammation on expression ofgrowth-associated genes by corticospinal neuronsrdquo BMC Neu-roscience vol 7 article 8 2006

[6] M R J Mason A R Lieberman and P N Anderson ldquoCor-ticospinal neurons up-regulate a range of growth-associatedgenes following intracortical but not spinal axotomyrdquo Euro-pean Journal of Neuroscience vol 18 no 4 pp 789ndash802 2003

[7] Injury Prevention amp Control Traumatic Brain Injury ldquoCentersfor Disease Control and Preventionrdquo httpwwwcdcgovTrau-maticBrainInjury

[8] SCI Information Network University of Alabama at Birming-ham 2013 httpswwwnsciscuabedu

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[77] H Akiyama and P L McGeer ldquoBrain microglia constitutivelyexpress 120573-2 integrinsrdquo Journal of Neuroimmunology vol 30 no1 pp 81ndash93 1990

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[82] NWeiss FMiller S Cazaubon and PO Couraud ldquoThe blood-brain barrier in brain homeostasis and neurological diseasesrdquoBiochimica et BiophysicaActa vol 1788 no 4 pp 842ndash857 2009

[83] B Obermeier R Daneman and R M Ransohoff ldquoDevelop-ment maintenance and disruption of the blood-brain barrierrdquoNature Medicine vol 19 no 12 pp 1584ndash1596 2013

[84] B O Popescu E C Toescu L M Popescu et al ldquoBlood-brain barrier alterations in ageing and dementiardquo Journal of theNeurological Sciences vol 283 no 1-2 pp 99ndash106 2009

[85] R M Friedlander and J Yuan ldquoICE neuronal apoptosis andneurodegenerationrdquo Cell Death and Differentiation vol 5 no10 pp 823ndash831 1998


[86] G Kim J Xu S Song et al ldquoTumor necrosis factor receptordeletion reduces nuclear factor-120581B activation cellular inhibitorof apoptosis protein 2 expression and functional recovery aftertraumatic spinal cord injuryrdquo Journal of Neuroscience vol 21 no17 pp 6617ndash6625 2001

[87] K Selmaj A Walczak M Mycko T Berkowicz T Kohnoand C S Raine ldquoSuppression of experimental autoimmuneencephalomyelitis with a TNF binding protein (TNFbp) cor-relates with down-regulation of VCAM-1VLA-4rdquo EuropeanJournal of Immunology vol 28 pp 2035ndash2044 1998

[88] K W Selmaj ldquoTumour necrosis factor and anti-tumour necro-sis factor approach to inflammatory demyelinating diseases ofthe central nervous systemrdquo Annals of the Rheumatic Diseasesvol 59 supplement 1 pp i94ndashi102 2000

[89] W J Streit S AWalter and N A Pennell ldquoReactive microglio-sisrdquo Progress in Neurobiology vol 57 no 6 pp 563ndash581 1999

[90] M Tuna S Polat T Erman et al ldquoEffect of anti-rat interleukin-6 antibody after spinal cord injury in the rat inducible nitricoxide synthase expression sodium- and potassium-activatedmagnesium-dependent adenosine-51015840-triphosphatase andsuperoxide dismutase activation and ultrastructural changesrdquoJournal of Neurosurgery vol 95 no 1 pp 64ndash73 2001

[91] K G Kahl N Kruse K V Toyka and P Rieckmann ldquoSerialanalysis of cytokine mRNA profiles in whole blood samplesfrom patients with early multiple sclerosisrdquo Journal of theNeurological Sciences vol 200 no 1-2 pp 53ndash55 2002

[92] P G Popovich Z Guan PWei I Huitinga N VanRooijen andB T Stokes ldquoDepletion of hematogenous macrophages pro-motes partial hindlimb recovery and neuroanatomical repairafter experimental spinal cord injuryrdquo Experimental Neurologyvol 158 no 2 pp 351ndash365 1999

[93] V Balasingam T Tejada-Berges E Wright R Bouckova andV W Yong ldquoReactive astrogliosis in the neonatal mouse brainand its modulation by cytokinesrdquo Journal of Neuroscience vol14 no 2 pp 846ndash856 1994

[94] D Giulian J Woodward D G Young J F Krebs and LB Lachman ldquoInterleukin-1 injected into mammalian brainstimulates astrogliosis and neovascularizationrdquo Journal of Neu-roscience vol 8 no 7 pp 2485ndash2490 1988

[95] R Shechter C Raposo A London I Sagi and M SchwartzldquoThe glial scar-monocyte interplay a pivotal resolution phase inspinal cord repairrdquo PLoS ONE vol 6 no 12 Article ID e279692011

[96] V W Yong R Moumdjian F P Young et al ldquo120574-Interferonpromotes proliferation of adult human astrocytes in vitro andreactive gliosis in the adult mouse brain in vivordquo Proceedings ofthe National Academy of Sciences of the United States of Americavol 88 no 16 pp 7016ndash7020 1991

[97] W Liu Y Tang and J Feng ldquoCross talk between activationof microglia and astrocytes in pathological conditions in thecentral nervous systemrdquo Life Sciences vol 89 no 5-6 pp 141ndash146 2011

[98] J A Smith A Das S K Ray and N L Banik ldquoRole of pro-inflammatory cytokines released from microglia in neurode-generative diseasesrdquo Brain Research Bulletin vol 87 no 1 pp10ndash20 2012

[99] F Properzi D Carulli R A Asher et al ldquoChondroitin 6-sulphate synthesis is up-regulated in injured CNS inducedby injury-related cytokines and enhanced in axon-growthinhibitory gliardquo European Journal of Neuroscience vol 21 no2 pp 378ndash390 2005

[100] U Hanisch ldquoMicroglia as a source and target of cytokinesrdquoGLIA vol 40 no 2 pp 140ndash155 2002

[101] L Uhlin-Hansen T Wik L Kjellen E Berg F Forsdahland S O Kolset ldquoProteoglycan metabolism in normal andinflammatory human macrophagesrdquo Blood vol 82 no 9 pp2880ndash2889 1993

[102] R A Asher D A Morgenstern M C Shearer K H AdcockP Pesheva and J W Fawcett ldquoVersican is upregulated in CNSinjury and is a product of oligodendrocyte lineage cellsrdquo Journalof Neuroscience vol 22 no 6 pp 2225ndash2236 2002

[103] L L Jones R U Margolis and M H Tuszynski ldquoThe chon-droitin sulfate proteoglycans neurocan brevican phosphacanand versican are differentially regulated following spinal cordinjuryrdquo Experimental Neurology vol 182 no 2 pp 399ndash4112003

[104] S Imagama K Sakamoto R Tauchi et al ldquoKeratan sulfaterestricts neural plasticity after spinal cord injuryrdquo Journal ofNeuroscience vol 31 no 47 pp 17091ndash17102 2011

[105] E M Andrews R J Richards F Q Yin M S Viapiano andL B Jakeman ldquoAlterations in chondroitin sulfate proteoglycanexpression occur both at and far from the site of spinalcontusion injuryrdquo Experimental Neurology vol 235 no 1 pp174ndash187 2012

[106] P L McGeer and E G McGeer ldquoThe inflammatory responsesystemof brain implications for therapy ofAlzheimer and otherneurodegenerative diseasesrdquoBrain Research Reviews vol 21 no2 pp 195ndash218 1995

[107] D Bonneh-Barkay and C A Wiley ldquoBrain extracellular matrixin neurodegenerationrdquo Brain Pathology vol 19 no 4 pp 573ndash585 2009

[108] R A Sobel and A S Ahmed ldquoWhite matter extracellularmatrix chondroitin sulfatedermatan sulfate proteoglycans inmultiple sclerosisrdquo Journal of Neuropathology and ExperimentalNeurology vol 60 no 12 pp 1198ndash1207 2001

[109] M L Fuller A K DeChant B Rothstein et al ldquoBone morpho-genetic proteins promote gliosis in demyelinating spinal cordlesionsrdquo Annals of Neurology vol 62 no 3 pp 288ndash300 2007

[110] G Barreto R E White Y Ouyang L Xu and R G GiffardldquoAstrocytes Targets for neuroprotection in strokerdquo CentralNervous System Agents in Medicinal Chemistry vol 11 no 2 pp164ndash173 2011

[111] H Mizuno HWarita M Aoki and Y Itoyama ldquoAccumulationof chondroitin sulfate proteoglycans in the microenvironmentof spinal motor neurons in amyotrophic lateral sclerosis trans-genic ratsrdquo Journal of Neuroscience Research vol 86 no 11 pp2515ndash2523 2008

[112] MGTanseyMKMcCoy andTC Frank-Cannon ldquoNeuroin-flammatory mechanisms in Parkinsonrsquos disease potential envi-ronmental triggers pathways and targets for early therapeuticinterventionrdquo Experimental Neurology vol 208 no 1 pp 1ndash252007

[113] T Town V Nikolic and J Tan ldquoThe microglial ldquoactivationrdquocontinuum From innate to adaptive responsesrdquo Journal ofNeuroinflammation vol 2 article 24 2005

[114] D R Friedlander P Milev L Karthikeyan R K MargolisR U Margolis and M Grumet ldquoThe neuronal chondroitinsulfate proteoglycan neurocan binds to the neural cell adhesionmolecules Ng-CAML1NILE and N-CAM and inhibits neu-ronal adhesion and neurite outgrowthrdquo Journal of Cell Biologyvol 125 no 3 pp 669ndash680 1994


[115] B A Walker S Ji and S R Jaffrey ldquoIntra-axonal translation ofRhoA promotes axon growth inhibition by CSPGrdquo Journal ofNeuroscience vol 32 no 41 pp 14442ndash14447 2012

[116] K E Dow and W Wang ldquoCell biology of astrocyte proteogly-cansrdquo Cellular and Molecular Life Sciences vol 54 no 6 pp567ndash581 1998

[117] K-H Braunewell P Pesheva J B McCarthy L T FurchtB Schmitz and M Schachner ldquoFunctional involvement ofsciatic nerve-derived versican and decorin-like molecules andother chondroitin sulphate proteoglycans in ECM-mediatedcell adhesion and neurite outgrowthrdquo European Journal ofNeuroscience vol 7 no 4 pp 805ndash814 1995

[118] P S Fidler K Schuette R AAsher et al ldquoComparing astrocyticcell lines that are inhibitory or permissive for axon growththe major axon-inhibitory proteoglycan is NG2rdquo Journal ofNeuroscience vol 19 no 20 pp 8778ndash8788 1999

[119] A M Tan W Zhang and J M Levine ldquoNG2 a component ofthe glial scar that inhibits axon growthrdquo Journal of Anatomy vol207 no 6 pp 717ndash725 2005

[120] D M McTigue R Tripathi and P Wei ldquoNG2 colocalizes withaxons and is expressed by amixed cell population in spinal cordlesionsrdquo Journal ofNeuropathology andExperimentalNeurologyvol 65 no 4 pp 406ndash420 2006

[121] Z Yang R Suzuki S B Daniels C B Brunquell C J Salaand A Nishiyama ldquoNG2 glial cells provide a favorable substratefor growing axonsrdquo Journal of Neuroscience vol 26 no 14 pp3829ndash3839 2006

[122] S A Busch K P Horn F X Cuascut et al ldquoAdult NG2+cellsare permissive to neurite outgrowth and stabilize sensory axonsduring macrophage-induced axonal dieback after spinal cordinjuryrdquo Journal of Neuroscience vol 30 no 1 pp 255ndash265 2010

[123] S Henke-Fahle K Wild A Sierra and P P Monnier ldquoChar-acterization of a new brain-derived proteoglycan inhibitingretinal ganglion cell axon outgrowthrdquo Molecular and CellularNeuroscience vol 18 no 5 pp 541ndash556 2001

[124] P P Monnier A Sierra J M Schwab S Henke-Fahle andB K Mueller ldquoThe RhoROCK pathway mediates neuritegrowth-inhibitory activity associated with the chondroitin sul-fate proteoglycans of the CNS glial scarrdquoMolecular and CellularNeuroscience vol 22 no 3 pp 319ndash330 2003

[125] J R Siebert and D J Osterhout ldquoThe inhibitory effects ofchondroitin sulfate proteoglycans on oligodendrocytesrdquo Journalof Neurochemistry vol 119 no 1 pp 176ndash188 2011

[126] L W Lau M B Keough S Haylock-Jacobs et al ldquoChondroitinsulfate proteoglycans in demyelinated lesions impair remyelina-tionrdquo Annals of Neurology vol 72 no 3 pp 419ndash432 2012

[127] J C Pendleton M J Shamblott D S Gary et al ldquoChon-droitin sulfate proteoglycans inhibit oligodendrocyte myelina-tion through PTP120590rdquo Experimental Neurology vol 247 pp 113ndash121 2013

[128] J M Levine R Reynolds and J W Fawcett ldquoThe oligo-dendrocyte precursor cell in health and diseaserdquo Trends inNeurosciences vol 24 no 1 pp 39ndash47 2001

[129] R B Tripathi andDMMcTigue ldquoChronically increased ciliaryneurotrophic factor and fibroblast growth factor-2 expressionafter spinal contusion in ratsrdquo Journal of Comparative Neurol-ogy vol 510 no 2 pp 129ndash144 2008

[130] J R Siebert D J Stelzner and D J Osterhout ldquoChondroitinasetreatment following spinal contusion injury increasesmigrationof oligodendrocyte progenitor cellsrdquo Experimental Neurologyvol 231 no 1 pp 19ndash29 2011

[131] M J Crowe J C Bresnahan Sl Shuman J N Masters and MS Beattie ldquoApoptosis and delayed degeneration after spinal cordinjury in rats and monkeysrdquo Nature Medicine vol 3 no 1 pp73ndash76 1997

[132] H M Bramlett and W D Dietrich ldquoProgressive damage afterbrain and spinal cord injury pathomechanisms and treatmentstrategiesrdquo Progress in Brain Research vol 161 pp 125ndash141 2007

[133] S A Back T M F Tuohy H Chen et al ldquoHyaluronan accu-mulates in demyelinated lesions and inhibits oligodendrocyteprogenitor maturationrdquoNature Medicine vol 11 no 9 pp 966ndash972 2005

[134] M Bugiani N Postma E Polder et al ldquoHyaluronan accumu-lation and arrested oligodendrocyte progenitor maturation invanishing white matter diseaserdquo Brain vol 136 no 1 pp 209ndash222 2013

[135] D E Harlow and W B Macklin ldquoInhibitors of remyelinationECM changes SPGs and PTPsrdquo Experimental Neurology vol251 pp 39ndash46 2014

[136] D Fisher B Xing J Dill et al ldquoLeukocyte common antigen-related phosphatase is a functional receptor for chondroitinsulfate proteoglycan axon growth inhibitorsrdquo Journal of Neuro-science vol 31 no 40 pp 14051ndash14066 2011

[137] T L Dickendesher K T Baldwin Y A Mironova et al ldquoNgR1and NgR3 are receptors for chondroitin sulfate proteoglycansrdquoNature Neuroscience vol 15 no 5 pp 703ndash712 2012

[138] D Crespo R A Asher R Lin K E Rhodes and J W FawcettldquoHow does chondroitinase promote functional recovery in thedamaged CNSrdquo Experimental Neurology vol 206 no 2 pp159ndash171 2007

[139] J Zuo D Neubauer K Dyess T A Ferguson and D MuirldquoDegradation of chondroitin sulfate proteoglycan enhances theneurite- promoting potential of spinal cord tissuerdquo Experimen-tal Neurology vol 154 no 2 pp 654ndash662 1998

[140] L Yick W Wu K So H K Yip and D K Shum ldquoChondroiti-nase ABC promotes axonal regeneration of Clarkersquos neuronsafter spinal cord injuryrdquo NeuroReport vol 11 no 5 pp 1063ndash1067 2000

[141] E J Bradbury L D F Moon R J Popat et al ldquoChondroitinaseABC promotes functional recovery after spinal cord injuryrdquoNature vol 416 no 6881 pp 636ndash640 2002

[142] L Yick P Cheung K So and W Wu ldquoAxonal regenerationof Clarkersquos neurons beyond the spinal cord injury scar aftertreatment with chondroitinase ABCrdquo Experimental Neurologyvol 182 no 1 pp 160ndash168 2003

[143] A W Barritt M Davies F Marchand et al ldquoChondroitinaseABC promotes sprouting of intact and injured spinal systemsafter spinal cord injuryrdquo Journal of Neuroscience vol 26 no 42pp 10856ndash10867 2006

[144] V J Tom R Kadakia L Santi and J D Houle ldquoAdministrationof chondroitinase ABC rostral or caudal to a spinal cord injurysite promotes anatomical but not functional plasticityrdquo Journalof Neurotrauma vol 26 no 12 pp 2323ndash2333 2009

[145] S Soleman P K Yip D A Duricki and L D FMoon ldquoDelayedtreatment with chondroitinase ABC promotes sensorimotorrecovery and plasticity after stroke in aged ratsrdquo Brain vol 135no 4 pp 1210ndash1223 2012

[146] J J Hill K Jin X O Mao L Xie and D A GreenbergldquoIntracerebral chondroitinase ABC and heparan sulfate proteo-glycan glypican improve outcome from chronic stroke in ratsrdquoProceedings of the National Academy of Sciences of the UnitedStates of America vol 109 no 23 pp 9155ndash9160 2012


[147] N G Harris Y A Mironova D A Hovda and R L SuttonldquoChondroitinase ABC enhances pericontusion axonal sprout-ing but does not confer robust improvements in behavioralrecoveryrdquo Journal of Neurotrauma vol 27 no 11 pp 1971ndash19822010

[148] N J Tester A H Plaas andD RHowland ldquoEffect of body tem-perature on chondroitinase ABCrsquos ability to cleave chondroitinsulfate glycosaminoglycansrdquo Journal of Neuroscience Researchvol 85 no 5 pp 1110ndash1118 2007

[149] G Garcıa-Alıas R Lin S F Akrimi D Story E J Bradburyand JW Fawcett ldquoTherapeutic timewindow for the applicationof chondroitinase ABC after spinal cord injuryrdquo ExperimentalNeurology vol 210 no 2 pp 331ndash338 2008

[150] M Nazari-Robati K Khajeh M Aminian N Mollania andA Golestani ldquoEnhancement of thermal stability of chondroiti-nase ABC i by site-directed mutagenesis an insight fromRamachandran plotrdquo Biochimica et Biophysica Acta - Proteinsand Proteomics vol 1834 no 2 pp 479ndash486 2013

[151] G M Curinga D M Snow C Mashburn et al ldquoMammalian-produced chondroitinase AC mitigates axon inhibition bychondroitin sulfate proteoglycansrdquo Journal of Neurochemistryvol 102 no 1 pp 275ndash288 2007

[152] Y Jin A Ketschek Z Jiang G Smith and I Fischer ldquoChon-droitinase activity can be transduced by a lentiviral vector invitro and in vivordquo Journal of Neuroscience Methods vol 199 no2 pp 203ndash213 2011

[153] R Zhao E M Muir J N Alves et al ldquoLentiviral vectorsexpress chondroitinase ABC in cortical projections and pro-mote sprouting of injured corticospinal axonsrdquo Journal ofNeuroscience Methods vol 201 no 1 pp 228ndash238 2011

[154] H Kanno Y Pressman A Moody et al ldquoCombination ofengineered Schwann cell grafts to secrete neurotrophin andchondroitinase promotes axonal regeneration and locomotionafter spinal cord injuryrdquoThe Journal of Neuroscience vol 34 no5 pp 1838ndash1855 2014

[155] K Bartus N D James A Didangelos et al ldquoLarge-scale chon-droitin sulfate proteoglycan digestion with chondroitinase genetherapy leads to reduced pathology andmodulates macrophagephenotype following spinal cord contusion injuryrdquo Journal ofNeuroscience vol 34 no 14 pp 4822ndash4836 2014

[156] JD Lannu RChoi AAu et al ldquoChondroitinase activity is pro-tected for extended times when incorporated into nanospheresfor time release deliveryrdquo Neuroscience abstracts WashingtonDC USA Society for Neuroscience 2007

[157] D J Osterhout P D Garma A Au et al ldquoChondroitinaserelease from nanospheres induces axonal sprouting after spinalcord injuryrdquo Submitted

[158] F M Bareyre M Kerschensteiner O Raineteau T C Metten-leiterOWeinmann andME Schwab ldquoThe injured spinal cordspontaneously forms a new intraspinal circuit in adult ratsrdquoNature Neuroscience vol 7 no 3 pp 269ndash277 2004

[159] I C Maier and M E Schwab ldquoSprouting regeneration andcircuit formation in the injured spinal cord factors and activityrdquoNature Medicine vol 12 pp 790ndash792 2006

[160] G Courtine B Song R R Roy et al ldquoRecovery of supraspinalcontrol of stepping via indirect propriospinal relay connectionsafter spinal cord injuryrdquo Nature Medicine vol 14 no 1 pp 69ndash74 2008

[161] E J Bradbury and S B McMahon ldquoSpinal cord repair strate-gies why do they workrdquo Nature Reviews Neuroscience vol 7no 8 pp 644ndash653 2006

[162] S Karimi-Abdolrezaee D Schut J Wang and M G FehlingsldquoChondroitinase and growth factors enhance activation andoligodendrocyte differentiation of endogenous neural precur-sor cells after spinal cord injuryrdquo PLoS ONE vol 7 no 5 ArticleID e37589 2012

[163] G KMatsushima andPMorell ldquoTheneurotoxicant cuprizoneas a model to study demyelination and remyelination in thecentral nervous systemrdquo Brain Pathology vol 11 no 1 pp 107ndash116 2001

[164] T L Laabs HWang Y Katagiri T McCann J W Fawcett andH M Geller ldquoInhibiting glycosaminoglycan chain polymer-ization decreases the inhibitory activity of astrocyte-derivedchondroitin sulfate proteoglycansrdquo Journal of Neuroscience vol27 no 52 pp 14494ndash14501 2007

[165] B Grimpe and J Silver ldquoA novel DNA enzyme reduces gly-cosaminoglycan chains in the glial scar and allows microtrans-planted dorsal root ganglia axons to regenerate beyond lesionsin the spinal cordrdquo Journal of Neuroscience vol 24 no 6 pp1393ndash1397 2004

[166] M L Lemons J D Sandy D K Anderson and D R HowlandldquoIntact aggrecan and chondroitin sulfate-depleted aggrecancore glycoprotein inhibit axon growth in the adult rat spinalcordrdquoExperimental Neurology vol 184 no 2 pp 981ndash990 2003

[167] J Silver and J H Miller ldquoRegeneration beyond the glial scarrdquoNature Reviews Neuroscience vol 5 no 2 pp 146ndash156 2004

[168] M Grumet P Milev T Sakurai et al ldquoInteractions withtenascin and differential effects on cell adhesion of neurocanand phosphacan two major chondroitin sulfate proteoglycansof nervous tissuerdquoThe Journal of Biological Chemistry vol 269no 16 pp 12142ndash12146 1994

[169] R K Margolis U W E Rauch P Maurel and R U MargolisldquoNeurocan and phosphacan two major nervous tissue-specificchondroitin sulfate proteoglycansrdquo Perspectives onDevelopmen-tal Neurobiology vol 3 no 4 pp 273ndash290 1996

[170] L L Jones and M H Tuszynski ldquoSpinal cord injury elicitsexpression of keratan sulfate proteoglycans by macrophagesreactive microglia and oligodendrocyte progenitorsrdquoThe Jour-nal of Neuroscience vol 22 no 11 pp 4611ndash4624 2002

[171] L L Jones Y Yamaguchi W B Stallcup and M H TuszynskildquoNG2 is a major chondroitin sulfate proteoglycan producedafter spinal cord injury and is expressed by macrophages andoligodendrocyte progenitorsrdquo Journal of Neuroscience vol 22no 7 pp 2792ndash2803 2002

[172] L Zhu J Lu S S W Tay H Jiang and B P He ldquoInducedNG2 expressingmicroglia in the facialmotor nucleus after facialnerve axotomyrdquo Neuroscience vol 166 no 3 pp 842ndash851 2010

[173] J Bu N Akhtar and A Nishiyama ldquoTransient expression of theNG2proteoglycan by a subpopulation of activatedmacrophagesin an excitotoxic hippocampal lesionrdquo GLIA vol 34 no 4 pp296ndash310 2001

[174] L Zhu P Xiang K Guo et al ldquoMicrogliamonocytes with NG2expression have no phagocytic function in the cortex after LPSfocal injection into the rat brainrdquo GLIA vol 60 no 9 pp 1417ndash1426 2012

Submit your manuscripts athttpwwwhindawicom

PainResearch and TreatmentHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom

Volume 2014

ToxinsJournal of

VaccinesJournal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

AntibioticsInternational Journal of

ToxicologyJournal of


StrokeResearch and TreatmentHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Drug DeliveryJournal of



Advances in Pharmacological Sciences

Tropical MedicineJournal of


Medicinal ChemistryInternational Journal of


AddictionJournal of



BioMed Research International

Emergency Medicine InternationalHindawi Publishing Corporationhttpwwwhindawicom Volume 2014


Autoimmune Diseases


Anesthesiology Research and Practice

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of


Pharmaceutics


MEDIATORSINFLAMMATION

of


G1

G1

G1

G1

G1

G1

Aggrecan

Brevican

Neurocan

Versican(V0)

G2 G3

G3

G3

Versican(V1)

Versican(V2)

G3

G3

G3

(a)

D2

D1

CAD

FN3D

CAD

FN3D

PhosphacanRPTP

(b)

ED1

ED2

Neuron-glial antigen 2

(c)

Figure 1 Schematic representation of individual proteoglycan molecules (a) Members of the lectican family aggrecan brevican neurocanand the three isotypes of versican all share a similar homology with a G1 domain at the N-terminus and a G3 domain at the C-terminusTheGAGside chain varies in number among the different lectican familymembers but is attached to the central core of the protein (b) Phosphacanis a splice variant of the RPTP molecule lacking the transmembrane and two intracellular domains found in the RPTP molecule (c) NG2is a transmembrane proteoglycan that lacks homology to any of the other CSPGs NG2 has two large extracellular domains separated by anextended region where the GAGs are attached a transmembrane domain and short cytoplasmic tail NG2 can be cleaved by enzymes at thecell surface and released into the extracellular matrix (adapted and modified from [16 18])

of CNS tissue damage It is important to understand thatupregulation of CSPG expression in response to an insult isthought to be a protective mechanism an attempt to walloff the area of damage and limit its spread [12ndash15] How-ever this creates a cellular microenvironment that inhibitsregeneration and repair It follows then that one therapeuticapproach to enhance CNS repair involves modulation ofCSPG expression which can change the cellular environmentto allow for neural regeneration

2 Chondroitin Sulfate Proteoglycans

Among the many CSPG molecules expressed in the CNS arethe lectican group which include aggrecan three forms ofversican (V0 V1 and V2) neurocan and brevican (Figure 1)All members of the lectican family consist of a central coreprotein that has an N-terminal G1 domain and a C-terminalG3 domainThe central domain binds the chondroitin sulfateglycosaminoglycan side chains (CS-GAG) [16ndash18]The aggre-can proteoglycan is the only member of the lectican groupthat has an additional globular (G2) near the G1 domainIndividual lectican molecules differ in the number of CS-GAG chains attached to their core proteins with over onehundred GAG side chains being found in aggrecan and aslittle as zero to five GAG chains being found in brevicanand neurocan [18] (Figure 1) The lectican family of CSPGsis largely produced by two major cell groups in the CNSneurons and astrocytes (Table 1)

Other proteoglycans that have major roles in the pathol-ogy of CNS injury are phosphacan and NG2 (Figure 1)

Phosphacan is a splice variant of receptor-type proteintyrosine phosphatase (RPTP) and lacks the two intracellulartyrosine phosphatase domains that are found in RPTP [18]This RPTP splice variant is secreted into the extracellularenvironment and contains attachment regions for CS-GAGchains Neuron-glial antigen 2 (NG2) is a unique CSPGthat lacks sequence homology to other known CSPGsNG2 proteoglycan is a transmembrane proteoglycan com-posed of a large extracellular domain (two large globulardomains separated by an extended region to which the GAGsattach) transmembrane domain and a short cytoplasmic tail(Figure 1) [18 19] Cells that express the NG2 proteoglycaninclude oligodendrocyte progenitor cells polydendrocytesactivated microglia and activated macrophages (Table 1)

The variations in the length of the core protein and thevarying number of GAG side chains attached to the centraldomain are major determinants of the biological activity ofan individual proteoglycan However the biological effects ofa proteoglycan are also affected by the sulfation patterns oftheN-acetylgalactosamine and glucuronate disaccharide thebasic unit that composes the CS-GAG [16 18] There are fourdifferent sulfation patterns that can occur based on eithermonosulfation or disulfation of the N-acetylgalactosamine(GalNAc) and glucuronate disaccharide (GlcA) of the GAGdisaccharide leading to the synthesis of the CS-A CS-C CS-D and CS-E CS-GAGs (Figure 2) [16ndash18 20] Sulfation ofthe chondroitin sulfate disaccharide can occur in the 4 and6 positions of the GalNAc and the 2 position of the GlcA[16 18 20] It has been demonstrated that a CSPG moleculecan be either inhibitory or permissive for axonal growth


Table 1


Neurons










GlcA GalNAc

OO

O O OO

O

OO

OO O

OO

O

OOO

OO

O

O

OO

O

n

nn

nn

HONH

H C CO



CS-A


CH OSO

OSO 3

CS-D


CS-CCH OSO


CS-E


CH OSOO SO

CO2H R1 R2

R3

H3

H2

minusminus minus

minus

O3

O SOminusO3

H2H2







3 Traumatic Lesions























Trauma

Disease

Proinflammatory

cytokinesCSPGs










































References



























































































































































































Volume 2014

ToxinsJournal of

VaccinesJournal of















AddictionJournal of






Autoimmune Diseases




Journal of


Pharmaceutics



of


Table 1


Neurons










GlcA GalNAc

OO

O O OO

O

OO

OO O

OO

O

OOO

OO

O

O

OO

O

n

nn

nn

HONH

H C CO



CS-A


CH OSO

OSO 3

CS-D


CS-CCH OSO


CS-E


CH OSOO SO

CO2H R1 R2

R3

H3

H2

minusminus minus

minus

O3

O SOminusO3

H2H2







3 Traumatic Lesions























Trauma

Disease

Proinflammatory

cytokinesCSPGs










































References



























































































































































































Volume 2014

ToxinsJournal of

VaccinesJournal of















AddictionJournal of






Autoimmune Diseases




Journal of


Pharmaceutics



of




3 Traumatic Lesions























Trauma

Disease

Proinflammatory

cytokinesCSPGs










































References



























































































































































































Volume 2014

ToxinsJournal of

VaccinesJournal of















AddictionJournal of






Autoimmune Diseases




Journal of


Pharmaceutics



of
















Trauma

Disease

Proinflammatory

cytokinesCSPGs










































References



























































































































































































Volume 2014

ToxinsJournal of

VaccinesJournal of















AddictionJournal of






Autoimmune Diseases




Journal of


Pharmaceutics



of







































References



























































































































































































Volume 2014

ToxinsJournal of

VaccinesJournal of















AddictionJournal of






Autoimmune Diseases




Journal of


Pharmaceutics



of








































































































































































Volume 2014

ToxinsJournal of

VaccinesJournal of















AddictionJournal of






Autoimmune Diseases




Journal of


Pharmaceutics



of

review article chondroitin sulfate proteoglycans in the...

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