Fasting- and ghrelin-induced food intake is regulated by NAMPT in the hypothalamus.

AIM: Neurons in the arcuate nucleus of the hypothalamus are involved in regulation of food intake and energy expenditure, and dysregulation of signalling in these neurons promotes development of obesity. The role of the rate-limiting enzyme in the NAD+ salvage pathway, nicotinamide phosphoribosyltransferase (NAMPT), for regulation energy homeostasis by the hypothalamus has not been extensively studied. METHODS: We determined whether Nampt mRNA or protein levels in the hypothalamus of mice were affected by diet-induced obesity, by fasting and re-feeding, and by leptin and ghrelin treatment. Primary hypothalamic neurons were treated with FK866, a selective inhibitor of NAMPT, or rAAV carrying shRNA directed against Nampt, and levels of reactive oxygen species (ROS) and mitochondrial respiration were assessed. Fasting and ghrelin-induced food intake was measured in mice in metabolic cages after intracerebroventricular (ICV)-mediated FK866 administration. RESULTS: NAMPT levels in the hypothalamus were elevated by administration of ghrelin and leptin. In diet-induced obese mice, both protein and mRNA levels of NAMPT decreased in the hypothalamus. NAMPT inhibition in primary hypothalamic neurons significantly reduced levels of NAD+ , increased levels of ROS, and affected the expression of Agrp, Pomc and genes related to mitochondrial function. Finally, ICV-induced NAMPT inhibition by FK866 did not cause malaise or anhedonia, but completely ablated fasting- and ghrelin-induced increases in food intake. CONCLUSION: Our findings indicate that regulation of NAMPT levels in hypothalamic neurons is important for the control of fasting- and ghrelin-induced food intake.

Endothelin-1 induces CXCL1 and CXCL8 secretion in human melanoma cells.

The endothelin pathway plays a critical role in melanoma tumor progression by a variety of mechanisms that enhance tumor cell growth, invasion, and metastasis. Here, we investigate the effect of this pathway on CXC chemokine expression in human melanoma cells and melanocytes. As determined by ELISA, endothelin-1 (ET-1) induces CXCL1 and CXCL8 secretion in three human melanoma cell lines in a concentration-dependent fashion. These responses are mediated by the endothelin-B receptor and are sustained over a 40 h time course. ET-1 does not induce CXCL1 secretion in primary human melanocytes but ET-3, an endothelin isoform, induces a low level of CXCL1 secretion in certain cultures. Neither ET-1 nor ET-3 induces secretion of CXCL8 in primary human melanocytes; thus, this response may be specific for melanocytic cells that have undergone malignant transformation. We have previously demonstrated that ET-1 induces changes in the expression of adhesion molecules in melanoma cells such that invasion and metastasis are favored. This study demonstrates that ET-1 additionally induces secretion of CXC chemokines critical for melanoma metastasis and tumor progression.

Endothelin-1 upregulates MCAM in melanocytes.

Melanoma cell adhesion molecule (MCAM) is a cell-surface adhesion molecule expressed on over 70% of metastatic melanoma cells but not expressed in normal melanocytes invivo. Protein levels of MCAM correlate with aggressive invasive behavior of melanoma cells in vitro and invivo. Here we demonstrate that endothelin-1 (ET-1) upregulates MCAM protein in primary human melanocytes. MCAM upregulation by ET-1 occurs irrespective of degree of melanocyte pigmentation and is dose-responsive. The drug BQ788 is an endothelin-B (ET(B)) receptor antagonist and inhibits upregulation of MCAM by ET-1. In addition, endothelin-3 (ET-3) and N-succinyl-[Glu9, Ala11, 15]-ET-1-1620, both selective ET(B) agonists, are potent upregulators of MCAM. These demonstrate a critical role for the ET(B) receptor in the upregulation of MCAM by ET-1 and related isoforms. MCAM mRNA abundance is also increased by ET-1 stimulation, thus the mechanism of MCAM protein upregulation may occur at the level of transcription. Our previous studies have demonstrated that ET-1 downregulates E-cadherin in melanocytes and melanoma cells. Since E-cadherin is a melanoma invasion suppressor, and MCAM is a melanoma invasion promoter, ET-1 may promote melanoma invasion and metastasis through the regulation of adhesion molecule expression.