17beta-hydroxysteroid dehydrogenase type 11 is a major peroxisome proliferator-activated receptor alpha-regulated gene in mouse intestine.

In order to study the role of peroxisome proliferator-activated receptor alpha in mouse intestine, its agonist-induced proteins were identified by peptide mass fingerprinting followed by Northern blot analysis using their cDNAs. One of the most remarkably induced proteins was identified as 17beta-hydroxysterol dehydrogenase type 11. Its very rapid induction by various agonists was most efficient in intestine and then in liver. These findings together with recently reported results showing the enzyme family's wide substrate spectrum, including not only glucocorticoids and sex steroids but also bile acids, fatty acids and branched chain amino acids, suggest new roles for both peroxisome proliferator-activated receptor alpha and 17beta-hydroxysterol dehydrogenase type 11 in lipid metabolism and/or detoxification in the intestine.     

The peroxisome proliferator-activated receptor gamma regulates expression of the perilipin gene in adipocytes

Recent studies have shown that lipid droplets are covered with a proteinaceous coat, although the functions and identities of the component proteins have not yet been well elucidated. The first identified lipid droplet-specific proteins are the perilipins, a family of proteins coating the surfaces of lipid droplets of adipocytes. The generation of perilipin-null mice has revealed that although they consume more food than control mice, they have normal body weight and are resistant to diet-induced obesity. In one study (Martinez-Botas, J., Anderson, J. B., Tessier, D., Lapillonne, A., Chang, B. H. J., Quast, M. J., Gorenstein, D., Chen, K. H., and Chan, L. (2000) Nat. Genet. 26, 474-479) it was reported that in an animal model obesity was reversible by breeding perilipin -/- alleles into Lepr db/db obese mice, ostensibly by increasing the metabolic rate of the mice. To understand the exact mechanisms that drive the exclusive expression of the perilipin gene in adipocytes, we analyzed the 5'-flanking region of the mouse gene. Treatment of differentiating 3T3-L1 adipocytes with an agonist of proliferator-activated receptor (PPAR) gamma, the putative "master regulator" of adipocyte differentiation, significantly augmented perilipin gene expression. Reporter assays using the -2.0-kb promoter revealed that this region contains a functional PPARgamma-responsive element. Gel mobility shift and chromatin immunoprecipitation assays showed that endogenous PPARgamma protein binds to the perilipin promoter. PPARgamma2, an isoform exclusively expressed in adipocytes, was found to be the most potent regulator from among the PPAR family members including PPARalpha and PPARgamma1. These results make evident the fact that perilipin gene expression in differentiating adipocytes is crucially regulated by PPARgamma2, providing new insights into the adipogenic action of PPARgamma2 and adipose-specific gene expression, as well as potential anti-obesity pharmaceutical agents targeted to a reduction of the perilipin gene product.     

Angiotensin-(1-7) Mas-receptor deficiency decreases peroxisome proliferator-activated receptor gamma expression in adipocytes

The renin-angiotensin system is an important link between metabolic syndrome and cardiovascular diseases. Besides angiotensin II, other angiotensin peptides such as angiotensin-(1-7), have important biological activities. It has been demonstrated that angiotensin-(1-7), acting through the G protein-coupled receptor encoded by the Mas protooncogene have important actions on the cardiovascular system. However, the role of angiotensin-(1-7)-Mas axis in lipidic profile is not well established. In the present study, the adipocyte metabolism was investigated in wild type and FVB/N Mas-deficient male mice. The gene expression of peroxisome proliferator-activated receptor gamma, acetyl-CoA carboxylase and the amount of fatty acid synthase protein were reduced in the Mas-knockout mice. Serum nonesterified fatty acids of Mas-knockout showed a 50% increase in relation to wild type group. Basal and isoproterenol-stimulated lipolysis was similar between the groups, however, a significant decrease of the glycerol release (lipolytic index) in response to insulin was observed in wild type animals, while no effect of the insulin action was observed in a Mas-knockout group. The data suggest that the lack of angiotensin-(1-7) action through Mas receptor alters the response of adipocytes to insulin action. These effects might be related to decreased expression of PPARγ.     

Reactivation of peroxisome proliferator-activated receptor alpha is associated with contractile dysfunction in hypertrophied rat heart

In pressure overload-induced hypertrophy, the heart increases its reliance on glucose as a fuel while decreasing fatty acid oxidation. A key regulator of this substrate switching in the hypertrophied heart is peroxisome proliferator-activated receptor alpha (PPARalpha). We tested the hypothesis that down-regulation of PPARalpha is an essential component of cardiac hypertrophy at the levels of increased mass, gene expression, and metabolism by pharmacologically reactivating PPARalpha. Pressure overload (induced by constriction of the ascending aorta for 7 days in rats) resulted in cardiac hypertrophy, increased expression of fetal genes (atrial natriuretic factor and skeletal alpha-actin), decreased expression of PPARalpha and PPARalpha-regulated genes (medium chain acyl-CoA dehydrogenase and pyruvate dehydrogenase kinase 4), and caused substrate switching (measured ex vivo in the isolated working heart preparation). Treatment of rats with the specific PPARalpha agonist WY-14,643 (8 days) did not affect the trophic response or atrial natriuretic factor induction to pressure overload. However, PPARalpha activation blocked skeletal alpha-actin induction, reversed the down-regulation of measured PPARalpha-regulated genes in the hypertrophied heart, and prevented substrate switching. This PPARalpha reactivation concomitantly resulted in severe depression of cardiac power and efficiency in the hypertrophied heart (measured ex vivo). Thus, PPARalpha down-regulation is essential for the maintenance of contractile function of the hypertrophied heart.     

Enhancement of the aquaporin adipose gene expression by a peroxisome proliferator-activated receptor gamma.

The current study demonstrates that aquaporin adipose (AQPap), an adipose-specific glycerol channel (Kishida, K., Kuriyama, H., Funahashi, T., Shimomura, I., Kihara, S., Ouchi, N., Nishida, M., Nishizawa, H., Matsuda, M., Takahashi, M., Hotta, K., Nakamura, T., Yamashita, S., Tochino, Y., and Matsuzawa, Y. (2000) J. Biol. Chem. 275, 20896-20902), is a target gene of peroxisome proliferator-activated receptor (PPAR) gamma. The AQPap mRNA amounts increased following the induction of PPARgamma in the differentiation of 3T3-L1 adipocytes. The AQPap mRNA in the adipose tissue increased when mice were treated with pioglitazone (PGZ), a synthetic PPARgamma ligand, and decreased in PPARgamma(+/-) heterozygous knockout mice. In 3T3-L1 adipocytes, PGZ augmented the AQPap mRNA expression and its promoter activity. Serial deletion of the promoter revealed the putative peroxisome proliferator-activated receptor response element (PPRE) at -93/-77. In 3T3-L1 preadipocytes, the expression of PPARgamma by transfection and PGZ activated the luciferase activity of the promoter containing the PPRE, whereas the PPRE-deleted mutant was not affected. The gel mobility shift assay showed the direct binding of PPARgamma-retinoid X receptor alpha complex to the PPRE. DeltaPPARgamma, which we generated as the dominant negative PPARgamma lacking the activation function-2 domain, suppressed the promoter activity in 3T3-L1 cells, dose-dependently. We conclude that AQPap is a novel adipose-specific target gene of PPARgamma through the binding of PPARgamma-retinoid X receptor complex to the PPRE region in its promoter.     

Down-regulation of peroxisome proliferator-activated receptor-gamma gene expression by sphingomyelins

We recently demonstrated that the sphingomyelin (SM) content of adipocyte membranes was negatively correlated with the expression of peroxisome proliferator-activated receptor-gamma (PPARgamma) in the subcutaneous adipose tissue of obese women with variable degrees of insulin resistance. We have now investigated whether SM really does have an impact on the expression of PPARgamma in 3T3-F442A adipocytes. Adding SM to the culture medium for 24 h caused a significant increase in SM content of adipocyte membranes and an acyl chain length-dependent decrease in the levels of PPARgamma mRNA and protein. The longer the acyl chain of the fatty acid of SM, the greater was the decrease in PPARgamma. These data suggest that the nature of the fatty acid is important in the regulation of PPARgamma by the SM pathway.     

Activation of peroxisome proliferator-activated receptor gamma inhibits osteoprotegerin gene expression in human aortic smooth muscle cells

Increasing evidence indicates an important role of PPAR gamma activation in modulating the development and progression of atherosclerosis, however, the mechanisms involved in these effects are not well understood since the PPAR gamma-regulated genes in vascular smooth muscle cells (VSMC) are poorly defined. Here we reported that PPAR gamma ligands, GW7845, ciglitazone and troglitazone had the effect of inhibiting osteoprotegerin (OPG) expression in human aortic smooth muscle cells (HASMC). The effect of GW7845 and ciglitazone on OPG expression was completely abolished by GW9662, a PPAR gamma antagonist. Overexpression of PPAR gamma in HASMC by the infection of a PPAR gamma adenovirus dramatically decreased OPG expression. In addition, PPAR gamma activation inhibited OPG promoter activity. Taken together, our data suggest that OPG expression is a novel PPAR gamma target gene in VSMC and downregulation of OPG expression by PPAR gamma activation provides a new insight into the understanding of the role of PPAR gamma in atheroscelrosis and hypertension.     

Retinoid X receptor and peroxisome proliferator-activated receptor-gamma agonists cooperate to inhibit matrix metalloproteinase gene expression

Introduction  

We recently described the ability of retinoid X receptor (RXR) ligand LG100268 (LG268) to inhibit interleukin-1-beta (IL-1-β)-driven matrix metalloproteinase-1 (MMP-1) and MMP-13 gene expression in SW-1353 chondrosarcoma cells. Other investigators have demonstrated similar effects in chondrocytes treated with rosiglitazone, a ligand for peroxisome proliferator-activated receptor-gamma (PPARγ), for which RXR is an obligate dimerization partner. The goals of this study were to evaluate the inhibition of IL-1-β-induced expression of MMP-1 and MMP-13 by combinatorial treatment with RXR and PPARγ ligands and to investigate the molecular mechanisms of this inhibition.     

Up-regulation of peroxisome proliferator-activated receptor gamma in radiation-induced heart injury in rats

To explore the expression level and the role of peroxisome proliferator-activated receptor gamma (PPAR-γ) in radiation-induced heart injury in a rat model, thirty-two Sprague–Dawley rats were divided into three groups (the control group, the 15-Gy irradiation group and the 18-Gy irradiation group). Experimental animals were exposed to radiation generated by a linear accelerator at the chest and killed after 3 months. Heart tissues from these animals were removed for Masson staining, PPAR-γ immunohistochemical staining, Western blot analysis and real-time polymerase chain reaction assay (RT-PCR). In addition, the protein expression of matrix metalloprotein-1 (MMP-1), tissue inhibitor of metalloproteinase-1 (TIMP-1) and transforming growth factor type beta1 (TGF-β1), all of which are associated with fibrosis, was measured. Masson staining revealed significant myocardial fibrosis, degeneration and necrosis in rats exposed to radiation. The results of immunohistochemical staining and Western blot analysis showed that PPAR-γ protein expression in hearts of the irradiation groups was significantly higher than in the control group, especially in myocardium and vascular endothelial (p < 0.05). RT-PCR results also showed a parallel increase in PPAR-γ mRNA expression in the heart of the irradiation groups compared with the control group (p < 0.05). The expression of MMP-1 protein was not significantly different in three groups (p > 0.05). The expression of TIMP-1 and TGF-β1 proteins was, however, higher in two irradiation groups than in the control group (p < 0.05). These data demonstrate that PPAR-γ expression is up-regulated on both mRNA and protein levels in heart injured by radiation. PPAR-γ may play an important role in radiation-induced heart injury.     

Peroxisome proliferator-activated receptor alpha-independent peroxisome proliferation

Hepatic peroxisome proliferation, increases in the numerical and volume density of peroxisomes, is believed to be closely related to peroxisome proliferator-activated receptor alpha (PPARalpha) activation; however, it remains unknown whether peroxisome proliferation depends absolutely on this activation. To verify occurrence of PPARalpha-independent peroxisome proliferation, fenofibrate treatment was used, which was expected to significantly enhance PPARalpha dependence in the assay system. Surprisingly, a novel type of PPARalpha-independent peroxisome proliferation and enlargement was uncovered in PPARalpha-null mice. The increased expression of dynamin-like protein 1, but not peroxisome biogenesis factor 11alpha, might be associated with the PPARalpha-independent peroxisome proliferation at least in part.