Up-regulation of placental leptin by human chorionic gonadotropin.

Leptin, the 16,000 molecular weight protein product of the obese gene, was originally considered as an adipocyte-derived signaling molecule for the central control of metabolism. However, leptin has been suggested to be involved in other functions during pregnancy, particularly in placenta, in which it was found to be expressed. In the present work, we have found that recombinant human chorionic gonadotropin (hCG) added to BeWo choriocarcinoma cell line showed a stimulatory effect on endogenous leptin expression, when analyzed by Western blot. This effect was time and dose dependent. Maximal effect was achieved at hCG 100 IU/ml. Moreover, hCG treatment enhanced leptin promoter activity up to 12.9 times, evaluated by transient transfection with a plasmid construction containing different promoter regions and the reporter gene luciferase. This effect was dose dependent and evidenced with all the promoter regions analyzed, regardless of length. Similar results were obtained with placental explants, thus indicating physiological relevance. Because hCG signal transduction usually involves cAMP signaling, this pathway was analyzed. Contrarily, we found that dibutyryl cAMP counteracted hCG effect on leptin expression. Furthermore, cotransfection with the catalytic subunit of PKA and/or the transcription factor cAMP response element binding protein repressed leptin expression. Thereafter we determined that hCG effect could be partially blocked by pharmacologic inhibition of MAPK pathway with 50 microM PD98059 but not by the inhibition of the phosphatidylinositol 3-kinase pathway with 0.1 microm wortmannin. Moreover, hCG treatment promoted MAPK kinase and ERK1/ERK2 phosphorylation in placental cells. Finally, cotransfection with a dominant-negative mutant of MAPK blocked the hCG-mediated activation of leptin expression. In conclusion, we provide some evidence suggesting that hCG induces leptin expression in trophoblastic cells probably involving the MAPK signal transduction pathway.

Cancer genes hypermethylated in human embryonic stem cells.

Developmental genes are silenced in embryonic stem cells by a bivalent histone-based chromatin mark. It has been proposed that this mark also confers a predisposition to aberrant DNA promoter hypermethylation of tumor suppressor genes (TSGs) in cancer. We report here that silencing of a significant proportion of these TSGs in human embryonic and adult stem cells is associated with promoter DNA hypermethylation. Our results indicate a role for DNA methylation in the control of gene expression in human stem cells and suggest that, for genes repressed by promoter hypermethylation in stem cells in vivo, the aberrant process in cancer could be understood as a defect in establishing an unmethylated promoter during differentiation, rather than as an anomalous process of de novo hypermethylation.

The L162V polymorphism of the PPARA gene is associated with stage C of heart failure.

In human heart failure (HF) peroxisome proliferator-activated receptor alpha (PPAR alpha) is downregulated and consequently, the expression of genes involved in fatty acid oxidation repressed. The L162V (rs1800206) is a functional polymorphism of the human PPAR alpha gene (PPARA). In the present study we have investigated whether this polymorphism is associated with the development of stage C of HF.

CB1 blockade potentiates down-regulation of lipogenic gene expression in perirenal adipose tissue in high carbohydrate diet-induced obesity.

De novo lipogenesis and hypercaloric diets are thought to contribute to increased fat mass, particularly in abdominal fat depots. CB1 is highly expressed in adipose tissue, and CB1-mediated signalling is associated with stimulation of lipogenesis and diet-induced obesity, though its contribution to increasing fat deposition in adipose tissue is controversial. Lipogenesis is regulated by transcription factors such as liver X receptor (LXR), sterol-response element binding protein (SREBP) and carbohydrate-responsive-element-binding protein (ChREBP). We evaluated the role of CB1 in the gene expression of these factors and their target genes in relation to lipogenesis in the perirenal adipose tissue (PrAT) of rats fed a high-carbohydrate diet (HCHD) or a high-fat diet (HFD). Both obesity models showed an up-regulated gene expression of CB1 and Lxrα in this adipose pad. The Srebf-1 and ChREBP gene expressions were down-regulated in HFD but not in HCHD. The expression of their target genes encoding for lipogenic enzymes showed a decrease in diet-induced obesity and was particularly dramatic in HFD. In HCHD, CB1 blockade by AM251 reduced the Srebf-1 and ChREBP expression and totally abrogated the remnant gene expression of their target lipogenic enzymes. The phosphorylated form of the extracellular signal-regulated kinase (ERK-p), which participates in the CB1-mediated signalling pathway, was markedly present in the PrAT of obese rats. ERK-p was drastically repressed by AM251 indicating that CB1 is actually functional in PrAT of obese animals, though its activation loses the ability to stimulate lipogenesis in PrAT of obese rats. Even so, the remnant expression levels of lipogenic transcription factors found in HCHD-fed rats are still dependent on CB1 activity. Hence, in HCHD-induced obesity, CB1 blockade may help to further potentiate the reduction of lipogenesis in PrAT by means of inducing down-regulation of the ChREBP and Srebf-1 gene expression, and consequently in the expression of lipogenic enzymes.