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.     

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.     

Birth Weight,Adulthood BMI,and Subsequent Weight Gain in Relation to Leptin Levels in Swedish Women

LISSNER, LAUREN, CECILIA KARLSSON, ANNA KARIN LINDROOS, LARS SJOSTROM, BJORN CARLSSON, LENA CARLSSON, AND CALLE BENGTSSON. Birth weight, adulthood BMI, and subsequent weight gain in relation to leptin levels in Swedish women. Obes Res. Objective Leptin seems to be involved in the regulation of energy balance, although little is known about the epidemiology of leptin with respect to prediction of weight gain and incidence of obesity-related diseases. The dual aim of this study is to document characteristics of leptin after long-term storage, and to describe its relation to body weight, from birth to old age, in an ongoing prospective study. Research Methods and Procedures A population-based sample of Swedish women was first examined at the ages of 38 to 60 and re-examined 24 years later. This study used 1358 frozen serum samples that had been stored 29 years for analysis of leptin concentrations and their relation to body weight history. Results Leptin values obtained from stored samples showed the same correlation with relative weight as that seen in a contemporary sample with similar demographic characteristics. Lower self-reported birth weight was associated with higher leptin levels in adulthood (p = 0.01), controlling for age and adult BMI. Prospective analyses revealed that high leptin in 38 to 46-year-olds predicted subsequent long-term weight gain (p = 0.003), although no significant associations were seen in women initially aged 50 or older. Discussion: It is feasible to use frozen serum for studying leptin in relation to obesity and related developments many years later. High leptin level was a risk factor for subsequent weight gain in 38- and 46-year-old women. Retrospective analyses involving birth weight suggest that leptin resistance in adulthood might have fetal origins.     

PPARδ activation inhibits angiotensin II induced cardiomyocyte hypertrophy by suppressing intracellular Ca2+ signaling pathway

Peroxisome proliferator‐activated receptors δ (PPARδ) is known to be expressed ubiquitously, and the predominant PPAR subtype of cardiac cells. However, relatively less is known regarding the role of PPARδ in cardiac cells except that PPARδ ligand treatment protects cardiac hypertrophy by inhibiting NF‐κB activation. Thus, in the present study, we examined the effect of selective PPARδ ligand L‐165041 on angiotensin II (AngII) induced cardiac hypertrophy and its underlying mechanism using cardiomyocyte. According to our data, L‐165041 (10 µM) inhibited AngII‐induced [³H] leucine incorporation, induction of the fetal gene atrial natriuretic factor (ANF) and increase of cardiomyocyte size. Previous studies have implicated the activation of focal adhesion kinase (FAK) in the progress of cardiomyocyte hypertrophy. L‐165041 pretreatment significantly inhibited AngII‐induced intracellular Ca²⁺ increase and subsequent phosphorylation of FAK. Further experiment using Ca²⁺ ionophore A23187 confirmed that Ca²⁺ induced FAK phosphorylation, and this was also blocked by L‐165041 pretreatment. In addition, overexpression of PPARδ using adenovirus significantly inhibited AngII‐induced intracellular Ca²⁺ increase and FAK expression, while PPARδ siRNA treatment abolished the effect of L‐165041. These data indicate that PPARδ ligand L‐165041 inhibits AngII induced cardiac hypertrophy by suppressing intracellular Ca²⁺/FAK/ERK signaling pathway in a PPARδ dependent mechanism. J. Cell. Biochem. 106: 823–834, 2009. © 2009 Wiley‐Liss, Inc.