FRI025 Succinate Receptor Activation Increases Respiration In Human But Not Murine Brown Adipocytes
Authors: McNeill Ben T , Kelman Alexandra , Ramage Lynne E , Suchacki Karla J , Wakelin Sonia J , Morton Nicholas M , Stimson Roland H 
Published: October 2023

Abstract
Disclosure: B.T. McNeill: None. A. Kelman: None. L.E. Ramage: None. K.J. Suchacki: None. S.J. Wakelin: None. N.M. Morton: None. R.H. Stimson: None.
Brown adipose tissue (BAT) is a thermogenic tissue that generates heat to maintain body temperature. BAT activation is a potential therapeutic target for treating obesity-related cardiometabolic disease. We performed RNA sequencing of human primary brown and white adipocytes and identified SUCNR1, which encodes the succinate receptor, as highly differentially expressed (20-fold) in brown versus white adipocytes. Succinate is known to increase BAT thermogenesis, while SUCNR1 activation inhibits lipolysis in white adipose tissue (WAT). We hypothesized that SUCNR1 activation increases BAT thermogenesis in humans and in mice. To test this, we investigated the effect of succinate and the selective SUCNR1 agonist cis-epoxysuccinic acid (C-ESA) in human and murine primary brown/ beige adipocytes. In addition, we determined the metabolic effects of disruption of Sucnr1 in mice either fed control or a high fat (HFD) for 12 weeks and measured energy expenditure when housed at standard room temperature (21°C) and during cold exposure (4°C). In human brown and white adipocytes, succinate increased basal and noradrenaline-stimulated respiration, while C-ESA increased basal respiration only in human brown adipocytes without altering UCP1 mRNA levels. SUCNR1 activation reduced glycerol release only in human white adipocytes. Male (but not female) Sucnr1-/- mice exhibited impaired glucose tolerance versus Sucnr1+/+ littermates after 2 weeks of HFD, and greater fat mass was also observed in the Sucnr1-/- mice following chronic HFD. However, energy expenditure, locomotor activity and tail vein temperature were unchanged in male Sucnr1-/- mice either at 21°C or 4°C. In addition, expression of Ucp1 and Pgc1α in BAT and inguinal WAT were similar between genotypes. Sucnr1 deletion had no effect on fat mass or glucose tolerance in mice fed a control diet. In vitro, differentiated brown adipocytes from Sucnr1-/- mice demonstrated comparable cellular respiration and Ucp1 mRNA levels both basally and during noradrenaline stimulation to Sucnr1+/+ adipocytes. Succinate and C-ESA did not stimulate respiration in murine brown or white adipocytes. These data reveal that SUCNR1 activation enhances brown adipocyte respiration in human but not murine brown adipocytes, highlighting a novel pathway regulating BAT function in addition to differences between species. These data also reveal novel sex-specific differences in the metabolic effects of SUCNR1, although the mechanisms through which female mice are protected from the adverse metabolic effects of Sucnr1 deletion are unclear. SUCNR1 activation may be a novel therapeutic target to treat obesity and associated metabolic disease, but requires further research in humans to determine the specific mechanisms through which SUCNR1 regulates BAT thermogenesis.
Presentation: Friday, June 16, 2023