Analysis of the peroxisome proliferator activated receptor gamma (PPARgamma) gene in HAIRAN syndrome with obesity

PPAR-γ signalling as a key mediator of human hair follicle physiology and pathology

Peroxisome proliferator-activated receptors (PPARs) are abundantly expressed in human skin, with PPAR-γ being the most intensively investigated isoform. In various ex vivo and in vivo models, PPAR-γ-mediated signalling has recently surfaced as an essential element of hair follicle (HF) development, growth and stem cell biology. Moreover, the availability of novel, topically applicable PPAR-γ modulators with a favourable toxicological profile has extended the range of potential applications in clinical dermatology. In this review, we synthesize where this field currently stands and sketch promising future research avenues, focussing on the role of PPAR-γ-mediated signalling in the biology and pathology of human scalp HFs, with special emphasis on scarring alopecias such as lichen planopilaris and frontal fibrosing alopecia as model human epithelial stem cell diseases. In particular, we discuss whether and how pharmacological modulation of PPAR-γ signalling may be employed for the management of hair growth disorders, for example, in scarring alopecia (by reducing HF inflammation as well as by promoting the survival and suppressing pathological epithelial-mesenchymal transition of keratin 15 + epithelial stem cells in the bulge) and in hirsutism/hypertrichosis (by promoting catagen development). Moreover, we explore the potential role of PPAR-γ in androgenetic alopecia, HF energy metabolism and HF ageing, and consider clinical perspectives that emanate from the limited data available on this so far. As this field of translational human hair research is still in its infancy, many open questions exist, for which we briefly delineate selected experimental approaches that promise to generate instructive answers in the near future.

Peroxisome proliferator activating receptor alpha and gamma polymorphisms and metabolic abnormalities in HIV-infected patients receiving highly active antiretroviral therapy: the ANRS CO8 APROCO-COPILOTE study

Highly active antiretroviral therapy (HAART) is associated with fat redistribution and metabolic disorders. The present study was undertaken to evaluate the association between peroxisome proliferator activated receptor (PPAR)α and PPARγ polymorphisms, two genes involved in lipid metabolism and adipocyte differentiation, and elements of the metabolic syndrome, lipodystrophy, or carbohydrate metabolism abnormalities in patients receiving HAART. The frequency distribution of rare alleles for PPARα (L162V) and PPARγ (P12A and H449H) was compared using the chi square test in 363 HIV-1-infected patients classified according to the presence or absence of the metabolic syndrome after 48 months of follow-up on their first PI-containing regimen. The P12A rare g allele was present in 12% patients with normal glucose metabolism, 11% patients with impaired glucose tolerance or impaired fasting glucose, and 35% patients with diabetes (p=0.014). The rare g allele for L162V was present in 14% of patients free of hypertriglyceridemia and in 7% patients with hypertriglyceridemia (p=0.04). The rare g allele for L162V was found in 15% of patients free of any sign of lipodystrophy and 8% with at least one sign of lipodystrophy (p=0.04) and the rare t allele for H449H was found in 14% of patients free of any sign of lipodystrophy and 23% of patients with at least one sign of lipodystrophy (p=0.05). There was no convincing association between any polymorphism of PPARα and PPARγ and each individual component of the metabolic syndrome, except for the relationship of the P12A polymorphism with diabetes. Confirmatory studies on a larger number of individuals are needed.

Acanthosis nigricans and truncal fat in overweight and obese children

BACKGROUND

Screening for acanthosis nigricans (AcN) in overweight children is repeatedly recommended. The significance of AcN, and its relation to central obesity in children, is unclear.

OBJECTIVE

To compare clinical and anthropometric parameters associated with adiposity, between overweight and obese children with and without AcN.

METHODS

One hundred and forty-nine overweight and obese children were screened for AcN. Height, weight, waist and hip circumferences, triceps skinfold thickness and segmental body fat amounts were measured.

RESULTS

Twenty-two (14.8%) children had AcN. Children with AcN had greater height, weight, BMI, waist circumference, waist-to-height-ratio, triceps skinfold thickness, and total and truncal body fat percentage, compared to those without AcN. After adjustment for age and BMI, no adiposity measure was increased in children with AcN.

CONCLUSION

Overweight and obese children with AcN basically have greater overall and central adiposity, than those without it. Adjusting for BMI, there is no evidence for increased abdominal fat in these children.

The common PPAR-gamma2 Pro12Ala variant is associated with greater insulin sensitivity

Several genetic variants of peroxisome proliferator-activated receptor-gamma2 (PPAR-gamma2) have been identified, among which Pro12Ala, a missense mutation in exon 2, is highly prevalent in Caucasian populations. Up to now, conflicting results with regard to the association between this mutation and complex traits, such as obesity, insulin sensitivity and Type 2 diabetes, have been reported. We investigated the influence of the Pro12Ala polymorphism of PPAR-gamma2 on insulin sensitivity in a large Italian population sample, n=1215, in whom extensive clinical and biochemical analyses were performed. To estimate the insulin sensitivity status, the homeostasis model assessment of insulin resistance (HOMA-IR) was calculated; in the obese/overweight subjects an oral glucose tolerance test (OGTT) was also performed and the Matsuda insulin sensitivity index (ISI) calculated. The insulin secretion index (homeostasis model assessment of percent beta-cell function, HOMA-beta%) was utilized to evaluate beta-cell function. The effect of the Pro12Ala polymorphism on quantitative variables was tested using multiple linear regression analysis. X12Ala (either Pro12Ala or Ala12Ala) genotype was associated with significantly lower fasting insulin levels compared to Pro/Pro (P=0.01 after correction for multiple comparisons) in all subjects. Consistent with this finding, significantly lower HOMA-IR was observed in X12Ala carriers (P=0.013 after correction for multiple comparisons) in all cohort. Moreover, no significant interaction effect was observed between body mass index and X12Ala polymorphism and between gender and X12Ala polymorphism in modulating insulin sensitivity. Our observations substantially extend previous findings and demonstrated that X12Ala variant is significantly associated with greater insulin sensitivity.

The Pro12Ala PPARgamma2 gene missense mutation is associated with obesity and insulin resistance in Swedish middle-aged men

BACKGROUND

A missense mutation in exon B of the adipocyte-specific isoform peroxisome proliferator-activated receptor-gamma2 (PPARgamma2) has recently been described, leading to the substitution of proline to alanine at codon 12, which causes a reduction in the transcriptional activity of PPARgamma2. The Pro12Ala PPARgamma2 polymorphism has been variably associated with obesity, insulin sensitivity, and dyslipidemia.

AIMS AND METHODS

In the present study, we addressed the hypothesis that the Pro12Ala variant is associated with obesity and estimates of insulin, glucose, and lipid metabolism as well as circulating hormones including salivary cortisol in 284 unrelated Swedish men born in 1944. The subjects were genotyped by using PCR amplification of exon B of the PPARgamma2 gene followed by digestion with the restriction enzyme BstUI.

RESULTS

Tests for differences between the PPARgamma2 genotypes revealed that the PPARgamma2 Ala homozygotes (n = 6) had higher body mass index (P = 0.022), abdominal sagittal diameter (P = 0.038), and nearly 3 times higher fasting insulin levels (P < 0.001) as well as higher HOMA insulin-resistance index (P = 0.011) compared to the PPARgamma2 Pro homozygotes (n = 186). This association was independent of body mass and fat distribution. In addition, subjects with the Ala/Ala genotype had lower total cholesterol (P = 0.012) as well as a trend toward lower high- and low-density lipoprotein cholesterol (P = 0.071 and P = 0.095) compared to the other PPARgamma2 genotypes.

CONCLUSION

In summary, these findings both confirm and expand the current notion that the PPARgamma2 gene might play a role in the etiology of obesity and that genetic variability in PPARgamma2 is associated with variations in body fat mass and insulin sensitivity.

Haplotype analysis of the PPARgamma Pro12Ala and C1431T variants reveals opposing associations with body weight

BACKGROUND

Variation at the PPARG locus may influence susceptibility to type 2 diabetes and related traits. The Pro12Ala polymorphism may modulate receptor activity and is associated with protection from type 2 diabetes. However, there have been inconsistent reports of its association with obesity. The silent C1431T polymorphism has not been as extensively studied, but the rare T allele has also been inconsistently linked to increases in weight. Both rare alleles are in linkage disequilibrium and the independent associations of these two polymorphisms have not been addressed.

RESULTS

We have genotyped a large population with type 2 diabetes (n = 1107), two populations of non-diabetics from Glasgow (n = 186) and Dundee (n = 254) and also a healthy group undergoing physical training (n = 148) and investigated the association of genotype with body mass index. This analysis has demonstrated that the Ala12 and T1431 alleles are present together in approximately 70% of the carriers. By considering the other 30% of individuals with haplotypes that only carry one of these polymorphisms, we have demonstrated that the Ala12 allele is consistently associated with a lower BMI, whilst the T1431 allele is consistently associated with higher BMI.

CONCLUSION

This study has therefore revealed an opposing interaction of these polymorphisms, which may help to explain previous inconsistencies in the association of PPARG polymorphisms and body weight.

The peroxisome proliferator-activated receptor-gamma2 Pro12Ala polymorphism

Peroxisome proliferator-activated receptor (PPAR)-gamma is a transcription factor with a key role in adipocyte differentiation. The Ala allele of the common Pro12Ala polymorphism in the isoform PPAR-gamma2 is associated with reduced risk for type 2 diabetes. The effect on the individual is weak, but because of a prevalence of >75% of the high-risk Pro allele, the population-attributable risk is enormous. The in vivo effects of the polymorphism are secondary to alterations in adipose tissue, where PPAR-gamma2 is predominantly expressed. Moderate reduction in transcriptional activity of PPAR-gamma as a result of the polymorphism modulates production and release of adipose-derived factors. Both decreased release of insulin-desensitizing free fatty acids, tumor necrosis factor-alpha, and resistin and increased release of the insulin-sensitizing hormone adiponectin result in secondary improvement of insulin sensitivity of glucose uptake and suppression of glucose production. The population effect of this polymorphism may be modulated by environmental or genetic factors such as obesity, ethnicity, ratio of unsaturated to saturated fatty acids, and genetic background. Once diabetes has developed, the protective effect of the Ala allele may be lost, since increased vascular complications and more pronounced beta-cell dysfunction have been reported. These observations, however, are currently unexplained. In conclusion, the Pro12Ala polymorphism in PPAR-gamma2 represents the first genetic variant with a broad impact on the risk of common type 2 diabetes. The precise understanding of its mechanism may lead to novel diagnostic, preventive, and therapeutic approaches for improving the management of type 2 diabetes.

Genetic analysis of four novel peroxisome proliferator activated receptor-gamma splice variants in monkey macrophages

Peroxisome proliferator activated receptor-gamma (PPAR-gamma) is abundantly expressed in atherosclerotic lesions and is implicated in atherogenesis. The existence of three splice variants, PPAR-gamma 1, PPAR-gamma 2, and PPAR-gamma 3 has been established. Using monocyte-derived macrophages from cynomolgus monkeys, we demonstrate here the identification of two new PPAR-gamma exons, exon C and exon D, which splice together with already established exons A1, A2, and B in the 5(') terminal region to generate four novel PPAR-gamma subtypes, PPAR-gamma 4, -gamma 5, -gamma 6, and -gamma 7. PPAR-gamma 4 and gamma 5 were detected only in macrophages whereas gamma 6 and gamma 7 were expressed both in macrophages and adipose tissues. None of these novel isoforms were detected in muscle, kidney, and spleen from monkeys. We found sequences identical to exons C and D in the human genome database. These and all PPAR-gamma exons known to date are encoded by a single gene, located from region 10498 K to 10384 K on human chromosome 3. We cloned and expressed PPAR-gamma 1, PPAR-gamma 4, and PPAR-gamma 5 proteins in yeast using the expression vector pPICZB. As expected, all recombinant proteins showed a molecular weight of approximately 50 kDa. We also investigated the effect of a high-fat diet on the level of macrophage PPAR-gamma expression in monkeys. RT-PCR showed a significant increase in total PPAR-gamma and ABCA1 mRNA levels in macrophages of fat-fed monkeys (n=7) compared to those maintained on a normal diet (n=2). However, none of the novel isoforms seemed to be induced by fat-feeding. We used tetracycline-responsive expression vectors to obtain moderate expression of PPAR-gamma 4 and -gamma 5 in CHO cells. In these cells, expression of PPAR-gamma 5 but not -gamma 4 repressed the expression of ABCA1. Neither isoform modulated the expression of lipoprotein lipase. Our results suggest that individual PPAR-gamma isoforms may be responsible for unique tissue-specific biological effects and that PPAR-gamma 4 and -gamma 5 may modulate macrophage function and atherogenesis.

The human obesity gene map: the 2000 update

This report constitutes the seventh update of the human obesity gene map incorporating published results up to the end of October 2000. Evidence from the rodent and human obesity cases caused by single-gene mutations, Mendelian disorders exhibiting obesity as a clinical feature, quantitative trait loci uncovered in human genome-wide scans and in cross-breeding experiments in various animal models, and association and linkage studies with candidate genes and other markers are reviewed. Forty-seven human cases of obesity caused by single-gene mutations in six different genes have been reported in the literature to date. Twenty-four Mendelian disorders exhibiting obesity as one of their clinical manifestations have now been mapped. The number of different quantitative trait loci reported from animal models currently reaches 115. Attempts to relate DNA sequence variation in specific genes to obesity phenotypes continue to grow, with 130 studies reporting positive associations with 48 candidate genes. Finally, 59 loci have been linked to obesity indicators in genomic scans and other linkage study designs. The obesity gene map reveals that putative loci affecting obesity-related phenotypes can be found on all chromosomes except chromosome Y. A total of 54 new loci have been added to the map in the past 12 months and the number of genes, markers, and chromosomal regions that have been associated or linked with human obesity phenotypes is now above 250. Likewise, the number of negative studies, which are only partially reviewed here, is also on the rise.