The novel E3 ligase of PPAR?? TRIM25 regulates adipocyte differentiation

Department of Biological SciencesPeroxisome proliferator-activated receptor ?? (PPAR??) is a ligand-dependent transcription factor which regulates glucose homeostasis and adipocyte differentiation. Its transcriptional activity is regulated by not only ligands but also post-translational modifications (PTMs). In this study, we demonstrate a novel E3 ligase of PPAR??, TRIM25 directly induces ubiquitination of PPAR?? followed by proteasome-dependent degradation. During the adipocyte differentiation, both mRNA and protein expression of TRIM25 significantly decreased and negatively correlated with the expression of PPAR??. Stable expression of TRIM25 reduces PPAR?? protein levels, but not mRNA expression, and suppressed adipocyte differentiation in 3T3-L1 cells. In contrast, specific knock-down of TRIM25 increases PPAR?? protein levels and stimulates adipocyte differentiation. Furthermore, TRIM25 knock-out mouse embryonic fibroblast (MEFs) shows an increased ability for adipocyte differentiation compared with wild-type MEFs. Taken together, these data indicate that TRIM25 is a novel E3 ubiquitin ligase of PPAR??, and depict TRIM25 as a novel target for PPAR??-involved metabolic diseases.ope

Peroxisome proliferator-activated receptor delta limits the expansion of pathogenic Th cells during central nervous system autoimmunity.

Peroxisome proliferator-activated receptors (PPARs; PPAR-alpha, PPAR-delta, and PPAR-gamma) comprise a family of nuclear receptors that sense fatty acid levels and translate this information into altered gene transcription. Previously, it was reported that treatment of mice with a synthetic ligand activator of PPAR-delta, GW0742, ameliorates experimental autoimmune encephalomyelitis (EAE), indicating a possible role for this nuclear receptor in the control of central nervous system (CNS) autoimmune inflammation. We show that mice deficient in PPAR-delta (PPAR-delta(-/-)) develop a severe inflammatory response during EAE characterized by a striking accumulation of IFN-gamma(+)IL-17A(-) and IFN-gamma(+)IL-17A(+) CD4(+) cells in the spinal cord. The preferential expansion of these T helper subsets in the CNS of PPAR-delta(-/-) mice occurred as a result of a constellation of immune system aberrations that included higher CD4(+) cell proliferation, cytokine production, and T-bet expression and enhanced expression of IL-12 family cytokines by myeloid cells. We also show that the effect of PPAR-delta in inhibiting the production of IFN-gamma and IL-12 family cytokines is ligand dependent and is observed in both mouse and human immune cells. Collectively, these findings suggest that PPAR-delta serves as an important molecular brake for the control of autoimmune inflammation

PPAR? Downregulation by TGF in Fibroblast and Impaired Expression and Function in Systemic Sclerosis: A Novel Mechanism for Progressive Fibrogenesis

The nuclear orphan receptor peroxisome proliferator-activated receptor-gamma (PPAR-γ) is expressed in multiple cell types in addition to adipocytes. Upon its activation by natural ligands such as fatty acids and eicosanoids, or by synthetic agonists such as rosiglitazone, PPAR-γ regulates adipogenesis, glucose uptake and inflammatory responses. Recent studies establish a novel role for PPAR-γ signaling as an endogenous mechanism for regulating transforming growth factor-ß (TGF-ß)- dependent fibrogenesis. Here, we sought to characterize PPAR-γ function in the prototypic fibrosing disorder systemic sclerosis (SSc), and delineate the factors governing PPAR-γ expression. We report that PPAR-γ levels were markedly diminished in skin and lung biopsies from patients with SSc, and in fibroblasts explanted from the lesional skin. In normal fibroblasts, treatment with TGF-ß resulted in a time- and dose-dependent down-regulation of PPAR-γ expression. Inhibition occurred at the transcriptional level and was mediated via canonical Smad signal transduction. Genome-wide expression profiling of SSc skin biopsies revealed a marked attenuation of PPAR-γ levels and transcriptional activity in a subset of patients with diffuse cutaneous SSc, which was correlated with the presence of a ''TGF-ß responsive gene signature'' in these biopsies. Together, these results demonstrate that the expression and function of PPAR-γ are impaired in SSc, and reveal the existence of a reciprocal inhibitory cross-talk between TGF-ß activation and PPAR-γ signaling in the context of fibrogenesis. In light of the potent anti-fibrotic effects attributed to PPAR-γ, these observations lead us to propose that excessive TGF-ß activity in SSc accounts for impaired PPAR-γ function, which in turn contributes to unchecked fibroblast activation and progressive fibrosis. © 2010 Wei et al

In silico design of potent agonists for human PPAR γ

Peroxisome proliferator-activated receptor (PPAR γ) acts as a key regulator on adipocyte differentiation and glucose homeostasis. PPAR γ has been implicated in the pathology of type 2 diabetes. As human PPAR γ activity is considered important in improving insulin sensitivity, in silico screening was carried out to find potent agonists for human PPAR γ protein. The co-crystal structure of PPAR γ, solved through X-Ray diffraction method was retrieved from the protein data bank. Four PPAR γ agonists selected from literature were submitted to subsequent 2D searching protocol using Ligand.Info, which yielded 1699 structural analogs. The PPAR γ co-crystal structure and ligand dataset were preprocessed using protein preparation wizard and LigPrep, respectively. Further, docking was performed by using three phased docking protocol of Maestro v9.2 that implements Glide v5.7. The obtained thirteen leads through docking were compared with the existing inhibitors and seven leads with good binding affinity with PPAR γ were proposed. The binding orientations of the seven leads were coinciding well with the native co-crystal structure of human PPAR γ. Thus, the proposed seven leads can be suggested as potential agonists for improving insulin sensitivity in the treatment of type 2 diabetes mellitus if synthesized and validated in animal model

Regulation of genes involved in carnitine homeostasis by PPARa across different species (rat, mouse, pig, cattle, chicken, and human)

Recent studies in rodents convincingly demonstrated that PPAR-alpha is a key regulator of genes involved in carnitine homeostasis, which serves as a reasonable explanation for the phenomenon that energy deprivation and fibrate treatment, both of which cause activation of hepatic PPAR-alpha, causes a strong increase of hepatic carnitine concentration in rats. The present paper aimed to comprehensively analyse available data from genetic and animal studies with mice, rats, pigs, cows, and laying hens and from human studies in order to compare the regulation of genes involved in carnitine homeostasis by PPAR-alpha across different species. Overall, our comparative analysis indicates that the role of PPAR-alpha as a regulator of carnitine homeostasis is well conserved across different species. However, despite demonstrating a well-conserved role of PPAR-alpha as a key regulator of carnitine homeostasis in general, our comprehensive analysis shows that this assumption particularly applies to the regulation by PPAR-alpha of carnitine uptake which is obviously highly conserved across species, whereas regulation by PPAR-alpha of carnitine biosynthesis appears less well conserved across species

The PPARy ligand rosiglitazone influences triacylglycerol metabolism in non-obese males, without increasing the transcriptional activity of PPARy in the subcutaneous adipose tissue

PPAR¿ is obligatory for fat mass generation and is thought to determine the amount of TAG stored per fat cell. We investigated whether ligand availability for PPAR¿ is rate limiting in fat mass generation and substrate metabolism. Twenty healthy men (20¿29 years) were randomly assigned to receive the PPAR¿ ligand rosiglitazone (RSG) (8 mg/d) (n 10) or a placebo (n 10) during a stay of 7 d in a respiration chamber. Food intake was ad libitum, resulting in positive energy balances of 32·2 MJ (placebo) and 44·7 MJ (RSG). Fat cell size and expression of PPAR¿, adipocyte fatty acid-binding protein (aP2), adipsin, adiponectin and fasting-induced adipose factor (FIAF) were determined in subcutaneous abdominal fat biopsies. The total amount of fat stored and the amount of TAG per fat cell were not different between groups. For the entire group, fat cell size was decreased after overeating (P = 0·02). FIAF mRNA levels were decreased after overeating in the RSG group (P = 0·01), with a trend towards a decrease in the placebo group. Unexpectedly, RSG treatment did not influence the expression levels of PPAR¿ and of the PPAR¿ responsive genes aP2, adiponectin and adipsin. In addition, RSG resulted in a larger increase in plasma TAG during overeating than placebo treatment. These results suggest that in healthy, non-obese males the PPAR¿ ligand RSG influences TAG metabolism, independent of its PPAR¿ transcriptional activity in the subcutaneous adipose tissue

PPM1A Controls Diabetic Gene Programming through Directly Dephosphorylating PPAR?? at Ser273

Peroxisome proliferator-activated receptor gamma (PPAR gamma) is a master regulator of adipose tissue biology. In obesity, phosphorylation of PPAR gamma at Ser273 (pSer273) by cyclin-dependent kinase 5 (CDK5)/extracellular signal-regulated kinase (ERK) orchestrates diabetic gene reprogramming via dysregulation of specific gene expression. Although many recent studies have focused on the development of non-classical agonist drugs that inhibit the phosphorylation of PPAR gamma at Ser273, the molecular mechanism of PPAR gamma dephosphorylation at Ser273 is not well characterized. Here, we report that protein phosphatase Mg2+/Mn2+-dependent 1A (PPM1A) is a novel PPAR gamma phosphatase that directly dephosphorylates Ser273 and restores diabetic gene expression which is dysregulated by pSer273. The expression of PPM1A significantly decreases in two models of insulin resistance: diet-induced obese (DIO) mice and db/db mice, in which it negatively correlates with pSer273. Transcriptomic analysis using microarray and genotype-tissue expression (GTEx) data in humans shows positive correlations between PPM1A and most of the genes that are dysregulated by pSer273. These findings suggest that PPM1A dephosphorylates PPAR gamma at Ser273 and represents a potential target for the treatment of obesity-linked metabolic disorders

Peroxisome Proliferator-activated receptor alpha gene variation influences age of onset and progression of type 2 diabetes

Dysregulation of fatty acid metabolism is important in the pathogenesis of type 2 diabetes. Peroxisome proliferator-activated receptor (PPAR) is a master regulator of fatty acid catabolism, and PPAR activators delay the onset of type 2 diabetes. We examined association between three PPAR gene polymorphisms (an AC variant in intron 1, the L162V variant, and the intron 7 GC variant) and age at diagnosis of type 2 diabetes in 912 Caucasian type 2 diabetic subjects. Individually, PPAR gene variants did not influence age at diagnosis, but in combination, the rare alleles of both the intron 1 AC (P < 0.001) and intron 7 GC (P = 0.025) variants synergistically lowered age at diagnosis (interaction P < 0.001). Overall, the PPAR haplotype signficantly influenced age at diagnosis (P = 0.027), with the C-L-C and C-V-C haplotypes (intron 1-L162V-intron 7) accelerating onset of diabetes by 5.9 (P = 0.02) and 10 (P = 0.03) years, respectively, as compared with the common A-L-G haplotype, and was associated with an odds ratio for early-onset diabetes (age at diagnosis 45 years) of 3.75 (95% CI 1.65–8.56, P = 0.002). Intron 1 C-allele carriers also progressed more rapidly to insulin monotherapy (AA 9.4 ± 1.5 and AC + CC 5.3 ± 1.1 years, P = 0.002). These data indicate that PPAR gene variation influences the onset and progression of type 2 diabetes