Inflammation in macrophages and pancreatic islets is a hallmark of both type 1 diabetes (T1D) and type 2 diabetes (T2D). The enzyme 12-lipoxygenase (12-LOX) is expressed in macrophages and β cells, produces the eicosanoid 12(S)-HETE and promotes inflammation. GPR31 has recently been identified as the 12(S)-HETE receptor. To clarify the role of GPR31 in diabetic inflammation, we generated Gpr31b-/- mice on the C57BL/6J background. Gpr31-/- mice are viable, with normal body weight, glucose tolerance, and β-cell mass, similar to 12-LOX knockout mice. Upon low dose streptozotocin treatment to induce β-cell inflammation, Gpr31b-/- mice remained normoglycemic unlike wildtype littermates, and exhibited no reductions in β-cell mass. Isolated islets treated with the insulin receptor antagonist S961 to mimic insulin resistance showed the expected decrease in Ins1, Pdx1, and Gpx1 mRNA levels. By contrast, in Gpr31b-/- islets, these genes remained unaltered. Additionally, Gpr31b-/- islets showed a trend towards a decrease in ER stress markers Ddit3 and spliced-Xbp1 expression. To examine GPR31 in macrophage inflammation, we first interrogated its role in the generation of proinflammatory macrophages upon polarization in vitro to the M1 state; under these conditions, we found no differences between Gpr31b-/- and wildtype macrophages, suggesting that GPR31 does not play a role in macrophage polarization. To test a role for GPR31 in proinflammatory macrophage function, we leveraged a zebrafish tailfin injury model, in which macrophages migrate to the site of tailfin injury. Compared to control fish, fish harboring knockdown of GPR31 showed reduced numbers of macrophages at the site of injury. Taken together, our data support the notion that the effects of 12-LOX are mediated through GPR31, and that GPR31 appears to promote proinflammatory responses in both macrophages and pancreatic islets.
S. A. Tersey: None. M. Walsh: None. M. Hernandez-perez: None. J. Dowgielewicz: None. A. Kulkarni: None. R. Anderson: None. R. G. Mirmira: Advisory Panel; Self; Hibercell Inc., Sigilon Therapeutics, Inc., Veralox Therapeutics, Employee; Spouse/Partner; Beta Bionics, Inc.
National Center for Advancing Translational Sciences (R03TR003381)