Abstract P072: Adipocyte AT 2 Receptor Suppresses UCP1 Transcription and Thereby Resting Metabolic Rate

Abstract

The renin-angiotensin system (RAS) contributes to energy balance through opposing actions in the brain and periphery. We hypothesize that tissue- and receptor-specific RAS modulation may represent a novel therapeutic approach to obesity. Transgenic “sRA” mice exhibit brain-specific RAS hyperactivity through expression of human renin in neurons (synapsin promoter) and human angiotensinogen via its own promoter. Previously we documented that sRA mice exhibit a suppressed circulating RAS, and an elevated resting metabolic rate (RMR) that is sensitive to replacement of circulating angiotensin II or the AT 2 receptor (AT 2 R) agonist, CGP-42112a (CGP, 100 ng/kg/min, s.c.). sRA mice exhibit a robust and specific elevation in uncoupling protein-1 (UCP1) expression and glucose uptake in inguinal white adipose tissue (iWAT). Chronic infusion of the AT 2 R agonist, CGP-42112a (CGP) into sRA mice increased weight gain and normalized RMR and inguinal fat expression of UCP1, but had no effect on food intake or digestive efficiency. RMR suppression by CGP was not mediated through attenuation of adipose sympathetic nervous activity (SNA, measured via multifiber nerve recordings), leading to the hypothesis that AT 2 R action on the adipocyte suppresses adipose sensitivity to SNA. Cultured primary mouse adipocytes were isolated from the iWAT, and norepinephrine (NE, 1 nM) treatment induced UCP1 mRNA (597 -fold of vehicle, P<0.05), however this UCP1 induction was attenuated with CGP co-treatment (10 nM, 0.2 -fold of NE alone, P<0.05). In human adipocytes, activation of AT 2 R also prevented the NE-induced increase in UCP1 mRNA. NE additionally significantly increased lipolysis by adipocytes (measured via free glycerol in the media; P<0.05), but AT 2 R activation had no effect (vehicle= 15.9 ug/mL; NE= 70.8 ug/mL; NE + CGP=64.7 ug/mL). These data support a suppressive action of AT 2 R upon RMR that is mediated specifically through the suppression of UCP1 expression, but not its activation by lipolysis, within subcutaneous adipocytes. Ongoing studies are examining the transcriptional regulation of UCP1 by adipose AT 2 R activation.