PPAR-gamma Pro12Ala genotype and risk of cognitive decline in elders

G Allele of the rs1801282 Polymorphism in PPARγ Gene Confers an Increased Risk of Obesity and Hypercholesterolemia, While T Allele of the rs3856806 Polymorphism Displays a Protective Role Against Dyslipidemia: A Systematic Review and Meta-Analysis

BACKGROUND

The relationships between the rs1801282 and rs3856806 polymorphisms in nuclear receptor peroxisome proliferator-activated receptor gamma (PPARγ) gene and obesity indexes as well as serum lipid levels have been extensively investigated in various studies, but the results were inconsistent and even contradictory.

METHODS

PubMed, Google Scholar, Embase, Cochrane Library, Web of Science, Wanfang, CNKI and VIP databases were searched for eligible studies. The random-effTPDEects model was used, and standardized mean difference (SMD) with 95% confidence interval (CI) was calculated to estimate the differences in obesity indexes and serum lipid levels between the subjects with different genotypes in a dominant model. Heterogeneity among studies was assessed by Cochran's x²-based Q-statistic test. Publication bias was identified by using Begg's test.

RESULTS

One hundred and twenty studies (70,317 subjects) and 33 studies (18,353 subjects) were identified in the analyses for the rs1801282 and rs3856806 polymorphisms, respectively. The G allele carriers of the rs1801282 polymorphism had higher levels of body mass index (SMD = 0.08 kg/m², 95% CI = 0.04 to 0.12 kg/m², p < 0.001), waist circumference (SMD = 0.12 cm, 95% CI = 0.06 to 0.18 cm, p < 0.001) and total cholesterol (SMD = 0.07 mmol/L, 95% CI = 0.02 to 0.11 mmol/L, p < 0.01) than the CC homozygotes. The T allele carriers of the rs3856806 polymorphism had lower levels of low-density lipoprotein cholesterol (SMD = -0.09 mmol/L, 95% CI = -0.15 to -0.03 mmol/L, p < 0.01) and higher levels of high-density lipoprotein cholesterol (SMD = 0.06 mmol/L, 95% CI = 0.02 to 0.10 mmol/L, p < 0.01) than the CC homozygotes.

CONCLUSIONS

The meta-analysis suggests that the G allele of the rs1801282 polymorphism confers an increased risk of obesity and hypercholesterolemia, while the T allele of the rs3856806 polymorphism displays a protective role against dyslipidemia, which can partly explain the associations between these polymorphisms and cardiovascular disease.

SYSTEMATIC REVIEW REGISTRATION

https://www.crd.york.ac.uk/prospero/, identifier [CRD42022319347].

Obesity and aging: Molecular mechanisms and therapeutic approaches

The epidemic of obesity is a major challenge for health policymakers due to its far-reaching effects on population health and potentially overwhelming financial burden on healthcare systems. Obesity is associated with an increased risk of developing acute and chronic diseases, including hypertension, stroke, myocardial infarction, cardiovascular disease, diabetes, and cancer. Interestingly, the metabolic dysregulation associated with obesity is similar to that observed in normal aging, and substantial evidence suggests the potential of obesity to accelerate aging. Therefore, understanding the mechanism of fat tissue dysfunction in obesity could provide insights into the processes that contribute to the metabolic dysfunction associated with the aging process. Here, we review the molecular and cellular mechanisms underlying both obesity and aging, and how obesity and aging can predispose individuals to chronic health complications. The potential of lifestyle and pharmacological interventions to counter obesity and obesity-related pathologies, as well as aging, is also addressed.

Investigating Predictors of Cognitive Decline Using Machine Learning

OBJECTIVES

Genetic risks for cognitive decline are not modifiable; however their relative importance compared to modifiable factors is unclear. We used machine learning to evaluate modifiable and genetic risk factors for Alzheimer's disease (AD), to predict cognitive decline.

METHODS

Health and Retirement Study participants, aged 65-90 years, with DNA and >2 cognitive evaluations, were included (n = 7,142). Predictors included age, body mass index, gender, education, APOE ε4, cardiovascular, hypertension, diabetes, stroke, neighborhood socioeconomic status (NSES), and AD risk genes. Latent class trajectory analyses of cognitive scores determined the form and number of classes. Random Forests (RF) classification investigated predictors of cognitive trajectories. Performance metrics (accuracy, sensitivity, and specificity) were reported.

RESULTS

Three classes were identified. Discriminating highest from lowest classes produced the best RF performance: accuracy = 78% (1.0%), sensitivity = 75% (1.0%), and specificity = 81% (1.0%). Top ranked predictors were education, age, gender, stroke, NSES, and diabetes, APOE ε4 carrier status, and body mass index (BMI). When discriminating high from medium classes, top predictors were education, age, gender, stroke, diabetes, NSES, and BMI. When discriminating medium from the low classes, education, NSES, age, diabetes, and stroke were top predictors.

DISCUSSION

The combination of latent trajectories and RF classification techniques suggested that nongenetic factors contribute more to cognitive decline than genetic factors. Education was the most relevant predictor for discrimination.

Aqueous extract of pomegranate enriched in ellagitannins prevents anxiety-like behavior and metabolic changes induced by cafeteria diet in an animal model of menopause

Women around menopause are vulnerable to present psychiatric and metabolic disorders; thus, therapies that contribute to treat both pathologies are required. Previous reports showed that an aqueous extract of pomegranate (Punica granatum), enriched in ellagitannins, exerts an antidepressant-like effect in ovariectomized rats. We analyze whether this aqueous extract of P. granatum (AE-PG) prevents the anxiety-like behavior induced by a cafeteria diet (CAF) in middle-aged ovariectomized rats at the same time that it prevents an increase in body weight, glucose, lipids, and the changes on mRNA expression of the peroxisome proliferator-activated receptor-gamma (PPAR-γ) in the liver. Also, the effects of AE-PG on the protein levels of PPAR-γphospho-PPAR-γ, extracellular signal-regulated protein kinase (ERK1/2) and phospho-ERK1/2 were measured in the hippocampus and amygdala. CAF induced anxiety-like behavior, augmented lipids and glucose blood levels, body weight, visceral fat, insulin resistance, and decreased mRNA expression of PPAR-γ in the liver. In rats fed with the CAF, AE-PG prevented the anxiety-like behavior, reduced body weight, lowered lipid levels, reduced insulin resistance, and increased PPAR-γ mRNA expression in the liver. In the hippocampus, ERK1/2 but not PPAR-γ protein levels were decreased by CAF, while AE-PG prevented these effects. In the amygdala, CAF increased the phosphorylation of PPARγ, and AE-PG prevented it. In contrast, AE-PG rescued the decreased ERK1/2 protein level in the hippocampus caused by CAF. In conclusion, AE-PG treatment prevented anxiogenic and metabolic effects induced by CAF, and its effects appear to be mediated by ERK1/2 and PPARγ depending on the brain area studied.

The PPARG Pro12Ala Polymorphism and 20-year Cognitive Decline: Race and Sex Heterogeneity

Previous reports suggest race/ethnic and sex heterogeneity in the association between the Pro12Ala polymorphism of the peroxisome proliferator-activated receptor gamma (PPARG) gene and cognitive decline. Tests of verbal memory, processing speed, and verbal fluency and a composite global Z-score were used to assess cognitive performance longitudinally in a large (n=11,620) biracial cohort of older adults in the Atherosclerosis Risk in Communities Neurocognitive Study from midlife to older age. Linear mixed models were used to estimate associations between the Ala12 allele and cognitive performance over 20 years of follow-up. Heterogeneity was present for rate of cognitive decline as measured by the global Z-score by race, sex, and Ala12 allele status (P=0.01 for 4-way interaction term: race×sex×time×Ala12 carrier status). Stratified analysis showed a significantly increased rate of global cognitive decline over the 20-year follow-up for carriers of the Ala12 allele compared with noncarriers among black male individuals (-0.92 SD decline vs. -0.57 SD; P=0.02) but not among black female, white male, or white female individuals. Decline in global cognitive function among black male Ala12 carriers was primarily driven by decline in verbal memory. Our data underscore the context-dependent association between the Pro12Ala polymorphism and cognitive decline, specifically race/ethnic background and sex.

Candesartan, angiotensin II type 1 receptor blocker is able to relieve age-related cognitive impairment

BACKGROUND

Candesartan is one of the standard antihypertensive drug belonging to AT1R angiotensin receptor blockers (ARBs) group. Beneficial effects of this drug in the treatment of hypertension are well recognized. In this study we tested a hypothesis that candesartan could alleviate age-related memory decline.

METHODS

Aged and young rats have been treated with candesartan (0.1mg kg^-1) for 21days and then underwent a battery of behavioral tests: for assessment of long-term memory (Passive avoidance test - PA), recognition memory (Object recognition test - OR), locomotor functions (Open field - OF) and anxiety behavior (Elevated plus maze - EPM).

RESULTS

Aged rats (2-years-old) displayed clear declining tendency in the retrieval of passive avoidance behavior showing thus increased forgetting. Prolonged administration of candesartan significantly (p<0.01) reversed this phenomenon causing recall measured as the avoidance latency, and surprisingly also showed the tendency to recall deterioration observed in the young rats. More optimistic results were achieved in the OR, where candesartan significantly improved recognition memory (p<0.001) of aged rats who performed even better than the young ones (p<0.05).

CONCLUSIONS

It appears that candesartan potently abolishes some kinds of aging-induced memory impairments and cognitive declines in aged rats, but in some circumstances it may even could increase the damage of memory. It seems that the use of sartans in the treatment of hypertension for patients with associated cognitive impairment, or for people in risk groups for such disorders can be an interesting alternative.

Cognitive decline and the PPAR-γ Pro12Ala genotype: variation by sex and ethnicity

Objective

We investigated the association between the peroxisome proliferator-activated receptor (PPAR)-gamma Pro12Ala polymorphism and cognitive decline in older adults.

Methods

Participants from a population-based cohort of older Hispanic and non-Hispanic white adults (n = 492) were administered the Mini Mental State Examination (MMSE), a multi-domain cognitive screening tool, and the Behavioral Dyscontrol Scale (BDS), a measure of executive cognitive function, at baseline and at follow-up, an average of 22 months later. Multiple linear regression was used to investigate the association between the two cognitive test scores and the Pro12Ala polymorphism.

Results

At baseline, presence of the Ala12 allele was not significantly associated with MMSE score (P = 0.62) nor with BDS score (P = 0.85). Heterogeneity was present for cognitive decline as measured by the MMSE among ethnic, sex and Ala12 allele status (P = 0.04 for three-way interaction term). Stratification by the cross-classification of sex and ethnicity revealed significantly greater declines in MMSE score among male Hispanic carriers of the Ala12 allele compared to male Hispanic non-carriers (decline = 4.0 versus 1.6 points; P = 0.02). A significant difference in decline between Ala12 carriers and non-carriers was not present among the other sex/ethnic groups.

Conclusions

Carriers of the PPAR-γ Ala12 allele showed greater cognitive decline compared to non-carriers as detected by the MMSE but the risk varied across sex and ethnic groups. Male Ala12 carriers of Hispanic origin may be a high-risk group for cognitive decline.

Effects of rumenic acid rich conjugated linoleic acid supplementation on cognitive function and handgrip performance in older men and women

The purpose of this study was to investigate the effects of 8weeks at 6g per day of RAR CLA versus placebo on cognitive function and handgrip performance in older men and women. Sixty-five (43 women, 22 men) participants (mean±SD; age=72.4±5.9yrs; BMI=26.6±4.2kg·m^-2) were randomly assigned to a RAR CLA (n=30: 10 men, 20 women) or placebo (PLA; high oleic sunflower oil; n=35: 12 men, 23 women) group in double-blind fashion and consumed 6g·d^-1 of their allocated supplement for 8weeks. Before (Visit 1) and after supplementation (Visit 2), subjects completed the Serial Sevens Subtraction Test (S₇), Trail Making Test Part A (TM_A) and Part B (TM_B), and Rey's Auditory Verbal Learning Test (RAVLT) to measure cognitive function. The RAVLT included 5, 15-item auditory word recalls (R_1-5), an interference word recall (R_B), a 6th word recall (R₆), and a 15-item visual word recognition trial (R_R). For handgrip performance, subjects completed maximal voluntary isometric handgrip strength (MVIC) testing before (MVIC_PRE) and after (MVIC_POST) a handgrip fatigue test at 50% MVIC_PRE. Hand joint discomfort was measured during MVIC_PRE, MVIC_POST, and the handgrip fatigue test. There were no treatment differences (p>0.05) for handgrip strength, handgrip fatigue, or cognitive function as measured by the Trail Making Test and Serial Seven's Subtraction Test in men or women. However, RAR CLA supplementation improved cognitive function as indicated by the RAVLT R₅ in men. A qualitative examination of the mean change scores suggested that, compared to PLA, RAR CLA supplementation was associated with a small improvement in joint discomfort in both men and women. Longer-term studies are needed to more fully understand the potential impact of RAR CLA on cognitive function and hand joint discomfort in older adults, particularly in those with lower cognitive function.

Seipin knockout in mice impairs stem cell proliferation and progenitor cell differentiation in the adult hippocampal dentate gyrus via reduced levels of PPARγ

The seipin gene (BSCL2) was originally identified in humans as a loss-of-function gene associated with congenital generalized lipodystrophy type 2 (CGL2). Neuronal seipin-knockout (seipin-nKO) mice display a depression-like phenotype with a reduced level of hippocampal peroxisome proliferator-activated receptor gamma (PPARγ). The present study investigated the influence of seipin deficiency on adult neurogenesis in the hippocampal dentate gyrus (DG) and the underlying mechanisms of the effects. We show that the proliferative capability of stem cells in seipin-nKO mice was substantially reduced compared to in wild-type (WT) mice, and that this could be rescued by the PPARγ agonist rosiglitazone (rosi). In seipin-nKO mice, neuronal differentiation of progenitor cells was inhibited, with the enhancement of astrogliogenesis; both of these effects were recovered by rosi treatment during early stages of progenitor cell differentiation. In addition, rosi treatment could correct the decline in hippocampal ERK2 phosphorylation and cyclin A mRNA level in seipin-nKO mice. The MEK inhibitor U0126 abolished the rosi-rescued cell proliferation and cyclin A expression in seipin-nKO mice. In seipin-nKO mice, the hippocampal Wnt3 protein level was less than that in WT mice, and there was a reduction of neurogenin 1 (Neurog1) and neurogenic differentiation 1 (NeuroD1) mRNA, levels of which were corrected by rosi treatment. STAT3 phosphorylation (Tyr705) was enhanced in seipin-nKO mice, and was further elevated by rosi treatment. Finally, rosi treatment for 10 days could alleviate the depression-like phenotype in seipin-nKO mice, and this alleviation was blocked by the MEK inhibitor U0126. The results indicate that, by reducing PPARγ, seipin deficiency impairs proliferation and differentiation of neural stem and progenitor cells, respectively, in the adult DG, which might be responsible for the production of the depression-like phenotype in seipin-nKO mice.

Obesity and Pro12Ala Polymorphism of Peroxisome Proliferator-Activated Receptor-Gamma Gene in Healthy Adults: A Systematic Review and Meta-Analysis

BACKGROUND

The aim of this systematic review was to evaluate the relationship between obesity and peroxisome proliferator-activated receptor-gamma (PPARx03B3;) Pro12Ala polymorphism in healthy adults.

SUMMARY

Weighted mean differences (WMDs) of body mass index (BMI) were calculated for different inheritance models and subgroups. Fifty-six studies were eligible for inclusion in the meta-analysis. The result shows that the Ala allele of this polymorphism was associated with increased WMD in mean BMI (WMD = 0.29, 95% CI 0.10-0.48, p = 0.003). The Ala carriers were associated with increased WMD in mean BMI values in both genders and in the Caucasian subgroup. The associations were seen among people with higher levels of BMI (BMI ≥35).

MESSAGE

The Ala allele of the PPARx03B3; Pro12Ala polymorphism in healthy adults was associated with increased BMI under a dominant model of inheritance.

Association of the variants in the PPARG gene and serum lipid levels: a meta-analysis of 74 studies

Considerable studies have been carried out to investigate the relationship between the polymorphisms of PPARG (Pro12Ala, C161T and C1431T) and serum lipid levels, but the results were inconclusive. Hence, we conducted a meta-analysis to clarify the association. MEDLINE, EMBASE and the Cochrane Library databases were searched systematically. The subgroup analysis was performed based on ethnicity. Seventy-four studies with 54,953 subjects were included in this meta-analysis. In Pro12Ala, the group with the ‘PP’ (C/C genotype) genotype group had lower levels of total cholesterol (TC) (mean difference, MD: −0.02, P < 0.00001; I² = 28%), low-density lipoprotein cholesterol (LDL-C) (MD: −0.02, P < 0.00001; I² = 30%) and higher levels of triglyceride (TG) (MD: 0.06, P < 0.00001; I² = 30%) than the combined ‘PA+AA’ (PA = C/G genotype, AA = G/G genotype) genotype group in Asian population, and the group with the ‘PP’ genotype had higher levels of TG (MD: 0.07, P < 0.02; I² = 67%) than the combined ‘PA+AA’ genotype group in non-Asian population. No statistically significant differences in the levels of TC, TG, high-density lipoprotein cholesterol, LDL-C were detected between different genotypes in C161T(Asian or non-Asian) and C1431T(Asian) polymorphisms. This meta-analysis was a renewed and confirmed study to assess the association between PPARG polymorphisms and serum lipid levels in Asian and non-Asian populations. There is a prominent association between Pro12Ala polymorphism and the levels of TC, LDL-C and TG in Asian population. No statistically significant differences in serum lipid levels were detected between different genotypes in C161T and C1431T polymorphisms.

Adverse oral health and cognitive decline: the health, aging and body composition study

OBJECTIVES

To investigate the relationship between periodontal disease and cognitive decline.

DESIGN

Analysis of a prospective cohort study.

SETTING

The Health, Aging and Body Composition (Health ABC) Study.

PARTICIPANTS

One thousand fifty-three participants who were administered the Modified Mini-Mental State Examination (3MS) at Year 1 (baseline) and Year 3 and had participated in a comprehensive periodontal examination at Year 2.

MEASUREMENTS

The prospective association between a range of oral health parameters and cognitive function was examined. Decline in 3MS score from Year 3 to 5 was investigated in 947 (89.9%) participants. Covariates included age, sex, education, race, cardiovascular disease and risk, and depressive symptoms.

RESULTS

Most indicators of adverse oral health at Year 2 were associated with cognitive impairment based on averaged 3MS scores less than 80 for Years 1 and 3, but education and race substantially confounded these associations. Higher gingival index, a measure of gingival inflammation, at Year 2 remained independently associated with this definition of cognitive impairment and, in fully adjusted analyses, was also an independent predictor of a more-than-5-point cognitive decline from Year 3 to 5.

CONCLUSION

Periodontitis may be a risk factor for cognitive decline. Gingivitis is reversible, and periodontitis to some degree is preventable and controllable when manifest. Therefore, further research is needed to clarify potential underlying mechanisms and oral health interventions that might ameliorate cognitive decline.

NMDA receptor involvement in antidepressant-like effect of pioglitazone in the forced swimming test in mice

RATIONALE

Previously, we showed that pioglitazone exerts its antidepressant-like effect through peroxisome proliferator-activated receptor gamma receptors and demonstrated the possible involvement of calcium-dependent nitric oxide synthase inhibitors. Based upon the in vitro results, pioglitazone reduces N-methyl-D-aspartate (NMDA)-mediated calcium currents in hippocampal neurons.

OBJECTIVE

In this study, we evaluated the involvement of the NMDA receptor (NMDAR) on the antidepressant-like effect of pioglitazone in the forced swimming test (FST) in mice.

METHOD

After the assessment of locomotor activity in the open-field test, mice were forced to swim individually and the immobility time of the last 4 min was evaluated. Pioglitazone was administered orally with doses of 5, 10, and 20 mg/kg 4 h before FST. To assess the involvement of NMDARs in the possible antidepressant-like effect of pioglitazone, a selective glutamate receptor agonist, NMDA (75 mg/kg, intraperitoneally [i.p.] or 20 ng/mouse, intracerebroventricularly [i.c.v.]), was administered before pioglitazone (20 mg/kg). To further determine a possible role of NMDARs in this effect, a noncompetitive antagonist of the NMDA, MK-801 (0.05 mg/kg, i.p. or 100 ng/mouse, i.c.v.), was coadministered with pioglitazone (10 mg/kg) 4 h prior to FST.

RESULTS

Pioglitazone (20 mg/kg) administered 4 h prior to FST significantly reduced the immobility time. Coadministration of the noneffective doses of pioglitazone and MK-801 revealed an antidepressant-like effect in FST. Moreover, NMDA significantly reversed the antidepressant-like effect of pioglitazone administered 4 h prior to FST.

CONCLUSION

The antidepressant-like effect of pioglitazone in the FST is mediated partly through NMDAR signaling. This study provides a new approach for the treatment of depression.

PPARγ and stress: implications for aging

Complex interactions link psychological stress and aging - stress generally promotes aging processes, and conversely, aging can contribute to stress dysregulation. Stress and aging have remarkably similar effects on brain. Both induce neuroinflammation and alter neuronal metabolism and activity, which to varying extents are causally-linked to the development of stress and aging pathology. As such, induction of one or more of these brain disturbances by either stress or aging could predispose for the development of dysfunction in the other. Notably, peroxisome proliferator-activated receptor γ (PPARγ) is expressed in brain regions that regulate both stress and aging (e.g., hippocampus) and can act to prevent the consequences of aging and stress on the brain. In addition, PPARγ agonists reduce the physiological stress response itself. Thus, PPARγ may represent a critical mechanistic link between brain aging and stress that could hold therapeutic potential for the prevention and treatment of age-related cognitive and mood disorders.

Evidence of the involvement of K+ channels and PPARgamma receptors in the antidepressant-like activity of diphenyl diselenide in mice

OBJECTIVES

This study investigated the involvement of different types of K(+) channels and PPARgamma receptors in the antidepressant-like effect of diphenyl diselenide in mice.

METHODS

Mice were pretreated with subeffective doses of K(+) channel inhibitors (tetraethylammonium, glibenclamide, charybdotoxin and apamin), openers (cromakalim, minoxidil), GW 9662 (a PPARgamma antagonist) or vehicle. Thirty minutes later the mice received diphenyl diselenide in either an effective or a subeffective dose, 30 min before a tail-suspension test.

KEY FINDINGS

Pre-treatment with tetraethylammonium, charybdotoxin or apamin combined with a subeffective dose of diphenyl diselenide was effective in decreasing the immobility time in the mouse tail-suspension test. The reduction in the immobility time elicited by an effective dose of diphenyl diselenide in this test was prevented by the pretreatment of mice with minoxidil and GW 9662.

CONCLUSIONS

Diphenyl diselenide elicited an antidepressant-like effect and this action was mediated, at least in part, by modulation of K(+) channels and PPARgamma receptors.

Pro12Ala polymorphism in PPAR-gamma2 and dementia in Chinese nonagenarians/centenarians

We examined the existence of a relationship between polymorphism and dementia in subjects aged 90 years and above. The sample included 732 unrelated Chinese nonagenarians/centenarians (aged 90-108 years, mean age 93.68 years; 67.5% women). The Pro12Ala variant was examined using polymerase chain reaction restriction fragment length polymorphism. Cognitive function was measured with 30-item mini-mental state examination. The genotype frequencies of the Pro12Ala polymorphism were 0% Ala12Ala, 9.1% Pro12Ala, and 90.9% Pro12Pro. The prevalence rates of dementia were 64.9% in the whole sample (45.0% for men and 74.5% for women). In both men and women, between subjects with and without 12Ala carriers, there was no significant difference in cognitive function scores and also no significant difference in prevalence of dementia; there was no significant difference in frequency of 12Ala carriers between subjects with and without dementia. Multiple logistic regression was performed by adjusting clinical factors that are thought to be associated with cognitive function or with 12Ala carriers. We found that 12Ala is not a risk factor for dementia. We found that Pro12Ala polymorphism in PPAR-gamma2 was not directly correlated with dementia among Chinese nonagenarians and centenarians.

APOE dependent-association of PPAR-γ genetic variants with Alzheimer's disease risk

The peroxisome proliferator-activated receptor-γ (PPAR-γ) is a ligand-inducible transcription factor that suppresses microglial inflammatory responses and inhibits amyloid beta (Aβ) production through promoting cholesterol efflux from glial cells. PPAR-γ agonists have been advanced as a new disease altering approach to Alzheimer's disease (AD), with rosiglitazone therapy having improved cognition in those AD patients that did not possess an Apolipoprotein E (APOE) ε4 allele. The current study was designed to explore the effect of interactions between PPAR-γ and APOE gene polymorphisms on the AD risk. We examined genetic variations of PPAR-γ by genotyping 7 haplotype tagging SNPs (htSNPs) (rs10510412, rs17793951, rs1801282, rs4135263, rs1151999, rs709149, and rs709154) in a group of 352 Spanish late-onset AD cases and 438 controls. The PPAR-γ TCCA haplotype derived from SNPs in introns 4 (rs4135263), 5 (rs1151999), and 6 (rs709149 and rs709154) showed a strong protective effect against AD in APOE ε4 allele noncarriers (p=0.001, permutation p=0.006, Bonferroni corrected p=0.021), with a frequency of 39% in cases and 50% in controls. Our data suggest that PPAR-γ genetic variants may modify the risk of AD in an APOE ε4 allele-dependent fashion.

The PPAR-gamma Pro12Ala polymorphism and risk of cognitive impairment in a longitudinal study

The Pro12Ala polymorphism in the PPAR-gamma gene has been associated with reduced incidence of type 2 diabetes. Although diabetes has been implicated as a risk factor for dementia, the association of Pro12Ala with cognitive impairment is unclear. Dementia and cognitive impairment without dementia (CIND) were determined during six annual follow-up evaluations in a cohort of 929 older Latinos. Among those with diabetes at baseline, there was an increased rate of dementia/CIND for Ala carriers compared to non-carriers (adjusted hazard ratio (HR)=2.5, 95% confidence interval (CI): 1.3-4.9) but not among non-diabetic participants (adjusted HR=0.94; 95% CI: 0.49-1.8). Among males, there was also an increased rate for Ala carriers (adjusted HR=2.7, 95% CI: 1.4-5.2) but not among female carriers (adjusted HR=0.88; 95% CI: 0.47-1.6). The rate of dementia/CIND was highest in diabetic male Ala carriers (adjusted HR=4.2; 95% CI: 1.5-11) compared to non-diabetic male carriers (adjusted HR=2.9; 95% CI: 1.1-7.4), diabetic female carriers (HR=1.6; 95% CI: 0.66-4.1), and non-diabetic female carriers (HR=0.52; 95% CI: 0.21-1.3). These data suggest that although the Ala variant is associated with a reduced risk of type 2 diabetes, it may increase the risk of cognitive impairment in individuals once diabetes has developed. Male Ala carriers may also have a greater risk of dementia/CIND.

Lack of genetic association between PPARG gene polymorphisms and Finnish late-onset Alzheimer's disease

Single nucleotide polymorphisms (SNPs) in diabetes related peroxisome proliferator-activated receptor gamma (PPARG) gene were investigated with a case-control approach. To examine the genetic association of this gene with Alzheimer's disease (AD) risk, we used the TaqMan technique to genotype eight SNP sites for PPARG gene, in 538 Finnish AD cases and 672 controls and conducted a single allele and genotypic distribution comparison as well as estimated haplotype frequencies between cases and controls. No significant differences in AD risk were found in single SNP and haplotype analyses for PPARG gene between the study groups. We conclude that PPARG gene does not play a major role in the genetic predisposition to AD in the Finnish population.

RAR/RXR and PPAR/RXR signaling in neurological and psychiatric diseases

Retinoids are important signals in brain development. They regulate gene transcription by binding to retinoic acid receptors (RAR) and, as was discovered recently, a peroxisome proliferator-activated receptor (PPAR). Traditional ligands of PPAR are best known for their functions in lipid metabolism and inflammation. RAR and PPAR are ligand-activated transcription factors, which share members of the retinoid X receptor (RXR) family as heterodimeric partners. Both signal transduction pathways have recently been implicated in the progression of neurodegenerative and psychiatric diseases. Since inflammatory processes contribute to various neurodegenerative diseases, the anti-inflammatory activity of retinoids and PPARgamma agonists recommends them as potential therapeutic targets. In addition, genetic linkage studies, transgenic mouse models and experiments with vitamin A deprivation provide evidence that retinoic acid signaling is directly involved in physiology and pathology of motoneurons, of the basal ganglia and of cognitive functions. The activation of PPAR/RXR and RAR/RXR transcription factors has therefore been proposed as a therapeutic strategy in disorders of the central nervous system.

PPARG Pro12Ala genotype and risk of cognitive decline in elders? Maybe with diabetes

The Pro12Ala polymorphism of peroxisome proliferator-activated receptor-gamma (PPARG; NCBI dbSNP rs1801282) has been associated with preservation of cognitive function, decreased risk of diabetes, and increased risk of obesity. We attempted to replicate these associations, testing cognitive function and lifetime cognitive change in 519 participants who took the same cognitive test at ages 11 and 79 years. Scores were also available for other cognitive tests at age 79 years, along with history of diabetes, current Body Mass Index (BMI), and other disease and demographic variables. Pro12Ala carrier status was not directly associated with diabetes history or BMI. In carriers who contracted diabetes despite carrying the protective allele, cognitive decline as measured by one test was significantly greater than in other groups. Only six individuals fell into this group; the other cognitive tests did not show this effect. This sample did not replicate the direct association of the PPARG Pro12Ala allele with diabetes status or preserved cognitive function. The data did suggest that risk of cognitive decline is greater when Pro12Ala carriers contract diabetes.

PPARgamma in human and mouse physiology

The peroxisome proliferator activated receptor gamma (PPARgamma) is a member in the nuclear receptor superfamily which mediates part of the regulatory effects of dietary fatty acids on gene expression. As PPARgamma also coordinates adipocyte differentiation, it is an important component in storing the excess nutritional energy as fat. Our genes have evolved into maximizing energy storage, and PPARgamma has a central role in the mismatch between our genes and our affluent western society which results in a broad range of metabolic disturbances, collectively known as the metabolic syndrome. A flurry of human and mouse studies has shed new light on the mechanisms how the commonly used insulin sensitizer drugs and PPARgamma activators, thiazolidinediones, act, and which of their physiological effects are dependent of PPARgamma. It is now evident that the full activation of PPARgamma is less advantageous than targeted modulation of its activity. Furthermore, new roles for PPARgamma signaling have been discovered in inflammation, bone morphogenesis, endothelial function, cancer, longevity, and atherosclerosis, to mention a few. Here we draw together and discuss these recent advances in the research into PPARgamma biology.