SUCNR1-mediated chemotaxis of macrophages aggravates obesity-induced inflammation and diabetes

Aims/hypothesis Obesity induces macrophages to drive inflammation in adipose tissue, a crucial step towards the development of type 2 diabetes. The tricarboxylic acid (TCA) cycle intermediate succinate is released from cells under metabolic stress and has recently emerged as a metabolic signal induced by proinflammatory stimuli. We therefore investigated whether succinate receptor 1 (SUCNR1) could play a role in the development of adipose tissue inflammation and type 2 diabetes. Methods Succinate levels were determined in human plasma samples from individuals with type 2 diabetes and nondiabetic participants. Succinate release from adipose tissue explants was studied. Sucnr1(-/-) and wild-type (WT) litter-mate mice were fed a high-fat diet (HFD) or low-fat diet (LFD) for 16 weeks. Serum metabolic variables, adipose tissue inflammation, macrophage migration and glucose tolerance were determined. Results We show that hypoxia and hyperglycaemia independently drive the release of succinate from mouse adipose tissue (17-fold and up to 18-fold, respectively) and that plasma levels of succinate were higher in participants with type 2 diabetes compared with non-diabetic individuals (+53%; p < 0.01). Sucnr1(-/-) mice had significantly reduced numbers of macrophages (0.56 +/- 0.07 vs 0.92 +/- 0.15 F4/80 cells/adipocytes, p < 0.05) and crown-like structures (0.06 +/- 0.02 vs 0.14 +/- 0.02, CLS/adipocytes p < 0.01) in adipose tissue and significantly improved glucose tolerance (p < 0.001) compared with WT mice fed an HFD, despite similarly increased body weights. Consistently, macrophages from Sucnr1(-/-) mice showed reduced chemotaxis towards medium collected from apoptotic and hypoxic adipocytes (-59%; p < 0.05). Conclusions/interpretation Our results reveal that activation of SUCNR1 in macrophages is important for both infiltration and inflammation of adipose tissue in obesity, and suggest that SUCNR1 is a promising therapeutic target in obesity-induced type 2 diabetes. Data availability The dataset generated and analysed during the current study is available in GEO with the accession number GSE64104, www.ncbi.nlm.nih.gov/geo/query/acc.cgi? acc=GSE64104.