Fig. 4. Gpr91(Sucnr1) and its ligand, succinate, can inhibit lipolysis in adipocytes.

A) The “adipose” cluster (blue circle, lower part Fig. 3A) contained numerous regulators of adipocyte function. B) Adrb3, Hm74(Gpr109a) and Gpr91(Sucnr1) were expressed at similarly high levels in white adipose tissues (WAT) and isolated adipocytes. C) Isolated WAT was treated with isoproterenol (20nM) to stimulate lipolysis, as measured by glycerol release at 3 hours. Succinate added concurrently with isoproterenol inhibited lipolysis in a concentration-dependent manner with an apparent IC₅₀ of approximately 44μM. D) Isolated WAT was pretreated either with KRH/BSA or KRH/BSA containing pertussis toxin (PTX; 100 ng/mL) for 3 hours prior to exposure to the indicated conditions. Isoproterenol (20nM)-stimulated glycerol release was inhibited by the addition of 80μM succinate. Pretreatment of WAT with PTX abrogated this effect, suggesting succinate's inhibition of lipolysis occurred in a G_i/o-dependent manner, consistent with Gpr91 activation. E) Differentiated 3T3-L1 cells, which do not express Gpr91 mRNA, were transfected with mammalian expression vectors containing β2 adrenergic receptor (Adrb2) and control (green fluorescent protein; GFP) or Adrb2 and GPR91. Succinate (100μM) inhibited isoproterenol (10nM)-induced lipolysis in cells co-transfected with GPR91, but not GFP. The data shown are mean ± SD, n=3; p=0.025, unpaired student's t-test. This experiment was done three times with similar results.