Endocrine Abstracts (2009) 19 OC7

In vivo and ex vivo regulation of Visfatin production by leptin in human and murine adipose tissue: role of the PI3K and MAPK pathways

Bee Tan1, Jing Chen1, James Brown1, Raghu Adya1, Manjunath Ramanjaneya1, Cliff Bailey2, Hendrik Lehnert3 & Harpal Randeva1


1University of Warwick, Coventry, UK; 2Aston University, Birmingham, UK; 3University of Lübeck, Lübeck, Germany.


Apart from its role in energy storage, adipose tissue produces several hormones and cytokines termed ‘adipokines’ that have wide-ranging effects on carbohydrate and lipid metabolism; and thereby, play an important role in the pathogenesis of the metabolic syndrome. Visfatin is a novel adipokine, levels of which increase in obesity and is adipogenic; properties common to that of leptin. Thus, leptin may modulate visfatin production in adipose tissue. We investigated the effects of leptin on visfatin levels in 3T3-L1 adipocytes and human as well as murine adipose tissue, with or without a leptin antagonist. Furthermore, the potential signalling pathways and mechanisms regulating visfatin production in adipose tissue was studied. Real-time RT-PCR and western blotting were used to assess the relative mRNA and protein expression of visfatin. ELISA was performed to measure visfatin levels in conditioned media of adipose tissue explants. Small interfering RNA (siRNA) technology was employed to knockdown the leptin receptor. Leptin significantly (P<0.01) increased visfatin levels with a maximal response at leptin 10−9 M, returning to baseline at leptin 10−7 M in human and murine adipose tissue. Importantly, intra-peritoneal leptin injections administered to C57BL/6 ob/ob mice further supported leptin induced visfatin protein production in omental adipose tissue (P<0.05). Additionally, soluble leptin receptor levels rose dose-dependently with a maximal response at leptin 10−7 M (P<0.01). The use of a leptin antagonist negated the induction of visfatin and soluble leptin receptor. Furthermore, leptin induced visfatin production was significantly decreased in the presence of MAPK and PI3K inhibitors. Also, when leptin receptor (OB-R) gene was knocked down using siRNA, leptin induced visfatin expression was significantly decreased. Taken together, leptin increases visfatin production in adipose tissue in vivo and ex vivo via MAPK and PI3K signalling pathways. Leptin’s pleiotropic effects may be partially mediated by visfatin.

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