Alzheimer’s Disease: Genetics, Pathogenesis, Models, and Experimental Therapeutics

[Auguste Deter, Alois Alzheimer's patient in November 1901, first described patient with Alzheimer's Disease.]

[1864 - Dr. Alois Alzheimer, psychiatrist, pathologist, born in Marktbreit, Bavaria]

Causes of dementia

Definitions

Dementia – a general term for a group of disorders that cause irreversible cognitive decline as a result of biological damage to brain cells

Alzheimer’s disease (AD) –the most common dementia, accounting for 50-70 percent of cases

Other forms of dementia include

•Vascular dementia

•Parkinson’s disease

•Dementia with Lewy bodies

•Frontotemporal dementia

•Creutzfeldt-Jakob disease

•Normal pressure hydrocephalus

Alzheimer’s disease = Alzheimer’s disease and related dementias

Clinical features and Laboratory studies

• Alzheimer disease (AD) is the most common form of dementia and usually occurs in old age.

• It is invariably fatal, generally within ten years of the first signs.

• Normal aging involves forgetfulness but the early signs of AD include unusual memory loss.

(remembering recent events and the names of people and things)

• As the disease progresses the patient exhibits more serious problems. (subject to mood swings and unable to perform complex activities such as

driving.)

• In the latter stages they forget how to do simple things and then require full-time care.

Neuropathorogy and Biochemistry of AD• Neuropathology

– Alzheimer's disease is characterised by loss of neurons and synapses in the cerebral cortex and certain subcortical regions.

– This loss results in degeneration in the temporal lobe and parietal lobe, and parts of the frontal cortex.

– Reductions in the size of specific brain regions in patients as they progressed from mild cognitive impairment to Alzheimer's disease.

Both amyloid plaques and neurofibrillary tangles are clearly visible by microscopy in brains of those afflicted by AD.

– Plaques are dense, mostly insoluble deposits of amyloid-beta peptide and cellular material outside and around neurons.

– Tangles (neurofibrillary tangles) are aggregates of the microtubule-associated protein tau which has become hyperphosphorylated and accumulate inside the cells themselves.

• Biochemistry

– Enzymes act on the APP (amyloid precursor protein) and cut it into fragments. The beta-amyloid fragment is crucial in the formation of senile plaques in AD.

– AD has been identified as a protein misfolding disease, caused by accumulation of abnormally folded A-beta and tau proteins in the brain.

– Plaques are made up of small peptides, 39–43 amino acids, called beta-amyloid (also written as A-beta or Aβ).

• fragment from a larger protein called APP, a transmembrane protein that penetrates through the neuron's membrane.

• (APP: neuron growth, survival and post-injury repair)

Neuropathorogy and Biochemistry of AD

• Biochemistry

– In Alzheimer's disease, an abnormal aggregation of the tau protein lead to the disintegration of microtubules in brain cells.

• Tau protein(microtubule-associated protein) stabilizes the microtubules when phosphorylated.

• In AD, tau becoming hyperphosphorylated; creating neurofibrillary tangles and disintegrating the neuron's transport system.

Neuropathorogy and Biochemistry of AD

Genetic: Familial AD and risk factors

The majority of cases of Alzheimer's disease are sporadic– not genetically inherited although some genes may act as risk factors– around 0.1% of the cases are familial forms of autosomal-dominant

inheritance

Autosomal dominant familial AD can be attributed to mutations in one of three genes: amyloid precursor protein (APP) and presenilins 1 and 2. – Mutations in the APP and presenilin genes increase the production of a

Aβ42.

The best known genetic risk factor is the inheritance of the ε4 allele of the apolipoprotein E (APOE). – Between 40 and 80% of patients with AD possess at least one apoE4 allele. – Therefore the APOE4 allele increases the risk of the disease.

APP and PS families of proteins

Familial Alzheimer disease is caused by mutations in at least 3 genes:

• PSEN1 - Presenilin 1 (PSEN1 located on chromosome 14)– Mutations in this gene cause familial Alzheimer's type under 50 years

old. – This protein has been identified as part of the enzymatic complex that

cleaves amyloid beta peptide from APP.

• PSEN2 - Presenilin 2 (PSEN2 located on chromosome 1)– The presenilin 2 gene is very similar in structure and function to PSEN1.

• APP – Amyloid beta (A4) precursor protein

– Processing of the amyloid precursor protein– Mutations to the amyloid beta A4 precursor protein (APP) located on the

long arm of chromosome 21 causes familial Alzheimer disease.

• Secretase

– BACE1• β-amyloid cleaving enzyme1• This transmembrane aspartyl protease is directlly involved in

the cleavage of APP at the sites of Aβ in APP.

– γ-secretase• This multiprotein catalytic complex includes PS1 and PS2;

nicastrin (Nct), a type 1 transmembrane glycoprotein; and Aph-1 and Pen-2, two multipass transmembrane protein.

APP and PS families of proteins

Processing of APP by secretases

Genetic models of Aβ amyloidosis and AD-linked taupathies

• Aβ amyloidosis

– Amyloid beta is a peptide of 39-43 amino acids – Main constituent of amyloid plaques in the brains of Alzheimer’s

disease patients.– Aβ is proteolytically derived from a larger integral membrane

protein, the amyloid precursor protein (APP).

• AD-linked taupathies

– Taupathies are a class of neurodegenerative diseases resulting from the pathological aggregation of tau protein in so-called neurofibrillary tangles (NFT) in the human brain.

Targeting of genes encoding amyloidogenic secretases

To understand the function of some of the proteins thought to have roles in AD: targeted a variety of genes including BACE1, PS1, Nct, and Aph-1.

• BACE1-/- Mice

– BACE1 is a key enzyme in the generation of the Aβ peptide that plays a central role in the pathogenesis of Alzheimer's disease.

• PS1-/- Mice

– PS1 knock-in mice exhibited NFT-like tau pathology in the absence of Aβ deposition.

– PS1 mutations contribute to the onset of AD not only by enhancing Aβ1–42 production but by also processing that lead to neurodegeneration.

Clinical approaches to Alzheimer’s Disease

• Cholinesterase Inhibitor

– 약물로저하된시냅스간극의뇌의아세틸콜린분해를억제– 콜린농도를증가시켜뇌세포사이의의사소통을회복– Tacrine, Donepezil, Rivastigminne, Galantamine

• NMDA Antagonists

– 중등도및중증의알츠하이머병환자에서기억력을안정시키는효과– Glutamate 가작용하는 NMDA 수용체가활성화되는것방지– Memanitn

• β- and γ-secretase Inhibition and γ-secretase Modulation

– Toxic peptide Aβ42 의레벨을감소시켜주는 γ-secretase 의선택적조절– Flurizan

Conclusions

It is anticipated that discoveries during the next few year will lead to the design of new mechanism-based therapies that can be tested in animal models, and, eventually, these approaches will be introduced successfully into the clinic for the benefit of patients with this devastating illness.

Thank you

Referance

• http://www.youtube.com/watch?v=9Wv9jrk-gXc

• http://www.kmle.co.kr/search.php?Search=Alzheimer+disease&Page=3

• http://blog.naver.com/hanhosp?Redirect=Log&logNo=130095137523

• http://blog.naver.com/hanhosp?Redirect=Log&logNo=130095137523

• Alzheimer disease. (Castellani RJ et al., 2010)

• Alzheimer's disease neurofibrillary degeneration: pivotal and multifactorial. (qbal K et al., 2010)