SAT070 The G Protein Coupled Receptor GPR31 Promotes Islet Inflammation And Diabetes
Authors: Checkcinco Christian , Tersey Sarah A , Mirmira Raghavendra G 
Published: October 2023

Abstract
Disclosure: C. Checkcinco: None. S.A. Tersey: None. R.G. Mirmira: None.
In type 1 diabetes a characteristic immune response targets insulin secreting beta cells in pancreatic islets, resulting in their destruction. This pathogenesis features inflammatory signaling cascades in both beta cells and infiltrating immune cell macrophages. 12-Lipoxygenase (12-LOX) contributes to inflammation in β cells and macrophages by producing the eicosanoid 12-HETE, which induces oxidative and ER stress resulting in cellular dysfunction. G-protein coupled receptor 31 (GPR31) was identified as a high affinity 12-HETE receptor and is increased in human islets after cytokine induced inflammation, but it remains unknown if GPR31 might mediate the downstream effects of 12-LOX. We found increased expression of GPR31 in C57Bl/6J islets, over 7 times higher relative to macrophages. To investigate the role of GPR31 during diabetic inflammation, whole body GPR31 knockout mice were generated on the C57Bl/6J background and studied for glucose homeostasis in the setting of diabetic inflammation. Islets and macrophages from these mice were studied following manipulations in vitro. Compared to wildtype (WT) littermates, Gpr31b-/- mice maintained similar body weight, beta-cell mass, and glucose homeostasis as mice aged. To mimic the setting of islet inflammation as seen in type 1 diabetes, WT and Gpr31b-/- mice were treated with the pro-diabetic toxin streptozotocin (which induces beta cell death and macrophage influx). Compared to WT, Gpr31b-/- mice showed protection from development of hyperglycemia and glucose tolerance tests showed &gt;30% protection reduction in area-under-the-curve, suggesting that GPR31 promotes islet dysfunction and hyperglycemia. To interrogate the role of GPR31 in the beta cell, we isolated islets from WT and Gpr31b-/- mice and treated them with proinflammatory cytokines followed by RNA sequencing to interrogate gene expression pathways. Differentially expressed genes in Gpr31b-/- islets included those pertaining to oxidative stress, MAPK signaling, and cellular homeostasis by Wnt/β-catenin, a finding reminiscent of pathways that are also altered following 12-LOX inhibition. To assess how GPR31 might impact macrophage function, we induced proinflammatory M1 polarization by lipopolysaccharide and interferon gamma in bone marrow-derived macrophages. We saw no significant difference in the extent of M1 polarization between GPR31b-/- and WT macrophages by flow cytometry, as assessed by the production of iNOS. We then asked if GPR31 was involved in the mobility of macrophages using a transwell assay with chemoattractant. We saw a ∼50% reduction in migrating bone marrow-derived macrophages in GPR31b-/- compared to WT. Taken together, these data are consistent with our previously published data on the 12-LOX knockout mice, suggesting that GPR31 may be involved in mediating the proinflammatory responses of 12-HETE in both β cells and macrophages.
Presentation: Saturday, June 17, 2023