maternal protein restriction permanently programs adipocyte growth and development in adult male rat...
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Journal of Cellular Biochemistry 101:381388 (2007)
Maternal Protein Restriction Permanently ProgramsAdipocyte Growth and Developmentin Adult Male Rat Offspring
Ting Zhang,1,2 Haiyan Guan,1,2 Edith Arany,3 David J. Hill,2,3 and Kaiping Yang1,2*1Department of Obstetrics and Gynaecology, Childrens Health Research Institute and Lawson HealthResearch Institute, University of Western Ontario, 800 Commissioners Rd. E., London, Ontario,Canada N6A 4G52Department of Physiology and Pharmacology, Childrens Health Research Institute and Lawson HealthResearch Institute, University of Western Ontario, 800 Commissioners Rd. E., London, Ontario,Canada N6A 4G53Department of Medicine, Childrens Health Research Institute and Lawson Health Research Institute,University of Western Ontario, 800 Commissioners Rd. E., London, Ontario, Canada N6A 4G5
Abstract We previously demonstrated that maternal protein restriction (MPR) during pregnancy and lactation led tofetal growth restriction and development of increased visceral adiposity in adult male rat offspring. Here we studied therate of proliferation and differentiation of adipocyte precursors (preadipocytes) in vitro to investigate whether MPR maypermanently program adipocyte growth and development in adult male offspring. Preadipocytes were isolated fromvisceral adipose tissue of control and MPR offspring at 130 days of age, and cultured under standard conditions. The rateof proliferation was studied by [3H]-thymidine incorporation, and the rate of differentiation assessed with the use ofbiochemical and morphological markers. Although it did not affect the rate of differentiation, MPR increased the rateof preadipocyte proliferation by almost twofold. To ascertain if the increased proliferation was due to persisting in vivoinfluences or aberrations inherent in the precursor cells, we studied the rate of preadipocyte proliferation in subcultures.We found that the increased rate of proliferation of MPR preadipocytes persisted throughout the first two subcultures,indicative of an inherent abnormality. In addition, we examined the rate of preadipocyte proliferation under reducedserum conditions. We showed that MPR reduced the rate of preadipocyte proliferation to 56 and 35% of the control in thepresence of 5 and 2.5% serum, respectively. Taken together, these results demonstrate that MPR permanently programsadipocyte growth and development such that adipocyte precursors derived from MPR offspring replicate excessivelyunder standard culture conditions but exhibit markedly attenuated growth rate under reduced serum conditions. J. Cell.Biochem. 101: 381388, 2007. 2007 Wiley-Liss, Inc.
Key words: maternal nutrition; visceral adiposity; adipogenesis; preadipocytes; proliferation and differentiation
Obesity is a serious medical problem notonly because it substantially impairs quality oflife and but also because it increases the risk ofhypertension, type 2 diabetes, coronary heart
disease, sleeping disorders, and cancers [Mok-dad et al., 2003]. There is strong evidence for agenetic component to human obesity [Hofbauer,2002]. Multiple systems regulate energy home-ostasis [Montague et al., 1997; Krysiak et al.,2001] and a number of genes associated withhuman obesity have been identified [Frogueland Boutin, 2001], yet the genetic component ofthis condition cannot explain the dramaticincrease in the prevalence of obesity in recentyears.A large number of epidemiological studies
have revealed a strong statistical associationbetween poor fetal growth and the subsequentdevelopment of type 2 diabetes, hypertension,
2007 Wiley-Liss, Inc.
Grant sponsor: Canadian Institutes of Health Research.
*Correspondence to: Dr. Kaiping Yang, Childrens HealthResearch Institute, Room A5-132, Victoria ResearchLaboratories- Westminster Campus, 800 CommissionersRoad East, London, Ont., Canada N6A 4G5.E-mail: email@example.com
Received 16 August 2006; Accepted 30 September 2006
and obesity, visceral obesity in particular[Osmond and Barker, 2000]. These observa-tions were made initially by Barker and collea-gues in England, but have now been reproducedin a large number of populations worldwide[Byrne and Phillips, 2000]. These findings haveled to the fetal origins hypothesis, whichstates that an adverse intrauterine environ-ment programs or imprints the development offetal tissues, permanently determining physio-logical responses, and ultimately producingdysfunction and disease [Purdy and Metzger,1996]. However, the molecular mechanismsthat underpin this relationship remain elusive.Since the world-wide maternal malnutrition
is themost common cause for poor early growth,and amino acids play a critical role in fetalgrowth [Petry et al., 2001], thematernal proteinrestriction (MPR) rat model has become one ofthe most extensively studied models of fetalgrowth restriction [Ozanne, 2001]. In thismodel, rat dams are subjected to a low proteindiet (8% protein) instead of control diet (20%protein) throughout pregnancy and lactation.As a consequence, the resulting offspringexhibit low-birth weight and become diabetic,insulin resistant, and hypertensive [Haleset al., 1996; Petry et al., 1997]. It has beenreported thatMPRhad a long-term influence onthe structure and function of certain organs,such as pancreas [Snoeck et al., 1990; Dahriet al., 1991; Petrick et al., 1999; Holness et al.,2000; Joanette et al., 2004], liver [Ozanne et al.,1996a; Burns et al., 1997] and muscle [Ozanneet al., 1996b].Recently we have demonstrated that protein
restriction during pregnancy and lactationleads to fetal growth restriction and develop-ment of increased visceral adiposity in adultmale rat offspring [Guan et al., 2005]. Further-more, we have also obtained evidence suggest-ing that visceral adiposity in our rat model ischaracterized by adipocyte hyperplasia becausethere were no apparent differences in the sizeof adipocytes between control and MPR off-spring. This contention is consistent with theDNAmicroarray results showing that levels of anumber of genes involved in cellular prolifera-tion and differentiation were up-regulated inMPR adipose tissue while the expression ofgenes involved in apoptosis did not change[Guan et al., 2005]. Since adipocyte hyperplasiaresults from the recruitment of new adipocytesfrom precursor cells in adipose tissue and
involves the proliferation and differentiationof preadipocytes, the present study wasdesigned to test the hypothesis that preadipo-cytes from MPR offspring possess a greaterpotential for proliferation and differentiation.
MATERIALS AND METHODS
Experimental Animals and Dietary Manipulations
The MPR rat model was established asdescribed previously [Guan et al., 2005]. Inbrief, virgin female Wistar rats (Charles RiverLaboratories,Wilmington,MA)weighting 240260 g were housed individually andmaintainedat 228C on a 12:12-h light-dark cycle. They weremated, and day 0 of gestation was set as theday on which vaginal plugs were expelled.The pregnant dams were fed either a diet con-taining 20% protein (control diet) or an isoca-loric diet containing 8% protein (low-proteindiet) throughout pregnancy and lactation. At3 days of age, litters were randomly reduced to8 pups, thus ensuring a standard litter size permother. At 21 days of age, all offspring wereweaned onto a 20% protein diet. At 130 days ofage, male offspring were sacrificed and theirvisceral fat pads (composed of mesenteric,omental, and retroperitoneal fat masses) wereisolated. For simplicity, the two groups ofoffspring will be termed control and MPR rats.
Isolation and Culture of Preadipocytes
Preadipocytes were isolated from control andMPR rats as described previously [Aoki et al.,2004]. Briefly, the visceral fat pads weredissected from visible blood vessels and con-nective tissue, weighed, finely minced anddigested in digestion buffer (3 ml/g tissue)consisting of Dulbeccos modified Eagles med-ium (DMEM) (Invitrogen Life Technologies,Burlington, Ontario, Canada), 0.5 mg/ml col-lagenase class IV (Sigma, Oakville, Ontario,Canada) and 1.5% bovine serum albumin (BSA)(Sigma) for 45 min at 378C, under mildcontrolled agitation. The resultant digest mate-rial was filtered through 250 mm nylon meshand centrifuged at 600g for 5 min to separatethe floating adipocytes. The cell pellet wasresuspended, washed with dulbeccos phos-phate-buffered saline (DPBS) containing 10%newborn calf serum (NCS) (Invitrogen LifeTechnologies), filtered through 25 mm nylonmesh and then centrifuged. The pelletedpreadipocytes were resuspended in standard
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culturemedium (DMEM/F-12medium (Invitro-gen Life Technologies) supplemented with 10%fetal bovine serum (FBS) (Sigma), 50 U/mlpenicillin and 50 mg/ml streptomycin (Invitro-gen Life Technologies)). The cell number wasdetermined with a hemocytometer. Preadipo-cytes were seeded in 24-well plates and 100-mmdishes and cultured in ahumidified incubator at378C, in the presence of 5% CO2. For simplicity,preadipocytes derived from control and MPRrats will be termed control and MPR preadipo-cytes.For subculture, primary preadipocytes were
seeded in 100-mm dishes and cultured instandard culture medium for 34 days untilthey reached 6070% confluence. Cells werethen washed, detached by incubation withTrypsin-EDTA and centrifuged at 600g for5 min. The resulting pellets were used forsubculture. The first two subcultures were usedfor proliferation study.
Proliferation capacity of preadipocytes wasassessed by measuring the rate of [3H]-thymi-dine incorporation. Primary preadipocyteswereseeded in 24-well plates at a density of 1 104cells/cm2 (day 0) and incubated in standardculture medium for 24 h. Subsequently, themedium was changed to DMEM/F-12 contain-ing with 10, 5, or 2.5% FBS. [3H]-thymidine(