Fenofibrate triggers apoptosis of glioblastoma cells in vitro

Comment on: Wilk A, et al. Cell Cycle 2012; 11:2660-71.     

Involvement of PPARα and PPARγ in apoptosis and proliferation of human hepatocarcinoma HepG2 cells

Peroxisome proliferator‐activated receptors (PPARs) mediate the effects of various ligands, known as peroxisome proliferators, a heterogeneous class of compounds including industrial chemicals, pharmaceuticals, and biomolecules such as fatty acids and eicosanoids. Among peroxisome proliferators, fibrate derivatives are considered specific ligands for PPARα, whereas eicosanoids, such as PGJ2, for PPARγ. The study aimed to clarify the relation between PPARs and apoptosis or proliferation on the same type of cells, using clofibrate as specific ligand of PPARα and PGJ2 as specific ligand of PPARγ. The cells used were human hepatocarcinoma HepG2 cells. The results showed that PPARα protein content increased in HepG2 cells treated with clofibrate, causing apoptosis in a time‐ and concentration‐dependent way, as evidenced by the citofluorimetric assay and determination of BAD, myc and protein phosphatase 2A protein content. It also emerged that PPARγ increased in the same cells when treated with a specific ligand of this PPAR; in this case the increase of PPARγ did not cause an increase of apoptosis, but a time‐ and concentration‐dependent inhibition of cell proliferation, evidenced by decreased cell numbers and increased number of cells in the G0/G1 phase of the cycle. It may be concluded that PPARα is chiefly related to apoptosis and PPARγ to cell proliferation. Copyright © 2010 John Wiley & Sons, Ltd.     

The orphan nuclear receptor small heterodimer partner is required for thiazolidinedione effects in leptin-deficient mice

Background

Small heterodimer partner (SHP, NR0B2) is involved in diverse metabolic pathways, including hepatic bile acid, lipid and glucose homeostasis, and has been implicated in effects on the peroxisome proliferator-activated receptor γ (PPARγ), a master regulator of adipogenesis and the receptor for antidiabetic drugs thiazolidinediones (TZDs). In this study, we aim to investigate the role of SHP in TZD response by comparing TZD-treated leptin-deficient (ob/ob) and leptin-, SHP-deficient (ob/ob;Shp^−/−) double mutant mice.

Results

Both ob/ob and double mutant ob/ob;Shp^−/− mice developed hyperglycemia, insulin resistance, and hyperlipidemia, but hepatic fat accumulation was decreased in the double mutant ob/ob;Shp^−/− mice. PPARγ2 mRNA levels were markedly lower in ob/ob;Shp^−/− liver and decreased to a lesser extent in adipose tissue. The TZD troglitazone did not reduce glucose or circulating triglyceride levels in ob/ob;Shp^−/− mice. Expression of the adipocytokines, such as adiponectin and resistin, was not stimulated by troglitazone treatment. Expression of hepatic lipogenic genes was also reduced in ob/ob;Shp^−/− mice. Moreover, overexpression of SHP by adenovirus infection increased PPARγ2 mRNA levels in mouse primary hepatocytes.

Conclusions

Our results suggest that SHP is required for both antidiabetic and hypolipidemic effects of TZDs in ob/ob mice through regulation of PPARγ expression.     

FoxO3A promotes metabolic adaptation to hypoxia by antagonizing Myc function

Exposure of metazoan organisms to hypoxia engages a metabolic switch orchestrated by the hypoxia-inducible factor 1 (HIF-1). HIF-1 mediates induction of glycolysis and active repression of mitochondrial respiration that reduces oxygen consumption and inhibits the production of potentially harmful reactive oxygen species (ROS). Here, we show that FoxO3A is activated in hypoxia downstream of HIF-1 and mediates the hypoxic repression of a set of nuclear-encoded mitochondrial genes. FoxO3A is required for hypoxic suppression of mitochondrial mass, oxygen consumption, and ROS production and promotes cell survival in hypoxia. FoxO3A is recruited to the promoters of nuclear-encoded mitochondrial genes where it directly antagonizes c-Myc function via a mechanism that does not require binding to the consensus FoxO recognition element. Furthermore, we show that FoxO3A is activated in human hypoxic tumour tissue in vivo and that FoxO3A short-hairpin RNA (shRNA)-expressing xenograft tumours are decreased in size and metabolically changed. Our findings define a novel mechanism by which FoxO3A promotes metabolic adaptation and stress resistance in hypoxia.     

PPARγ activation induces autophagy in breast cancer cells

It has been previously shown that PPARγ ligands induce apoptotic cell death in a variety of cancer cells. Given the evidence that these ligands have a receptor-independent function, we further examined the specific role of PPARγ activation in this biological process. Surprisingly, we failed to demonstrate that MDA-MB-231 breast cancer cells undergo apoptosis when treated with sub-saturation doses of troglitazone and rosiglitazone, which are synthetic PPARγ ligands. Acridine orange (AO) staining showed acidic vesicular formation within ligand-treated cells, indicative of autophagic activity. This was confirmed by autophagosome formation as indicated by redistribution of LC3, an autophagy-specific protein, and the appearance of double-membrane autophagic vacuoles by electron microscopy following exposure to ligand. To determine the mechanism by which PPARγ induces autophagy, we transduced primary mammary epithelial cells with a constitutively active mutant of PPARγ and screened gene expression associated with PPARγ activation by genome-wide array analysis. HIF1α and BNIP3 were among 42 genes up-regulated by active PPARγ. Activation of PPARγ induced HIF1α and BNIP3 protein and mRNA abundance. HIF1α knockdown by shRNA abolished the autophagosome formation induced by PPARγ activation. In summary, our data shows a specific induction of autophagy by PPARγ activation in breast cancer cells providing an understanding of distinct roles of PPARγ in tumorigenesis.     

Impact of dietary protein content on uncoupling protein mRNA abundance in swine

The present study was designed to determine if dietary protein can alter uncoupling protein (UCP) expression in swine, as has been shown in rats, and attempt to identify the mechanism. Eight pigs (~ 50 kg body mass) were fed an 18% crude protein (CP) diet while another eight pigs were switched to a diet containing 12% crude protein (CP) and fed these diets until 110 kg body mass. The outer (OSQ) and middle (MSQ) subcutaneous adipose tissues, liver, leaf fat, longissimus (LM), red portion of the semitendinosus (STR) and the white portion of the ST (STW) were analyzed for gene expression by real-time PCR. Feeding of 12% CP did not alter growth or carcass composition, relative to 18% CP (P > 0.05). Serum growth hormone, non-esterified fatty acids, triglycerides and urea nitrogen were reduced with the feeding of 12% CP (P < 0.05). The UCP2 mRNA abundance was reduced in LM, STR, MSQ and OSQ with feeding of 12% CP (P < 0.05), as was UCP3 mRNA abundance in MSQ and STW (P < 0.01). Peroxisome proliferation activated receptor α (PPARα) and PPARγ were reduced in MSQ and STR (P < 0.05) with feeding 12% CP as was the PPARα regulated protein, acyl CoA oxidase (ACOX, P < 0.05). These data suggest that feeding 12% CP relative to 18% CP reduces serum NEFA, which reduces PPARα and PPARγ expression and consequently reduces UCP2 lipoperoxidation in OSQ and STR and also reduced UCP3 associated fatty acid transport in MSQ and STW.     

Cellular and molecular effects of thiazolidinediones on bone cells: a review

Thiazolidinediones represent a class of molecules used in the treatment of type 2 diabetes mellitus. Despite interesting effects in lowering blood glucose and HbA1c levels durably, an augmentation of the fracture risk in women has emerged in the past years. This review is providing the readers with information about the cellular and molecular mechanisms involved in bone and bone cells in response to these drugs.     

Berberine modulates deacetylation of PPARγ to promote adipose tissue remodeling and thermogenesis via AMPK/SIRT1 pathway

Pharmacological stimulation of adipose tissue remodeling and thermogenesis to increase energy expenditure is expected to be a viable therapeutic strategy for obesity. Berberine has been reported to have pharmacological activity in adipose tissue to anti-obesity, while the mechanism remains unclear. Here, we observed that berberine significantly reduced the body weight and insulin resistance of high-fat diet mice by promoting the distribution of brown adipose tissue and thermogenesis. We have further demonstrated that berberine activated energy metabolic sensing pathway AMPK/SIRT1 axis to increase the level of PPARγ deacetylation, which leads to promoting adipose tissue remodeling and increasing the expression of the thermogenic protein UCP-1. These findings suggest that berberine that enhances the AMPK/SIRT1 pathway can act as a selective PPARγ activator to promote adipose tissue remodeling and thermogenesis. This study proposes a new mechanism for the regulation of berberine in adipose tissue and offers a great prospect for berberine in obesity treatment