SAT066 Leukotriene B4 Receptor 2 Mediates Macrophage Migration To Injured β Cells

Type 1 diabetes (T1D) is an autoimmune disease, characterized in part by islet inflammation and macrophage infiltration leading to β-cell injury and loss. The inflammatory mediator 12/15-lipoxygenase (12/15-LOX) and its lipid product 12-hydroxyeicosatetraenoic acid (12-HETE) have both been implicated in T1D. 12-HETE activates the low affinity receptor leukotriene B4 receptor 2 (LTB4R2, or simply BLT2), which was reported as a low-affinity receptor for 12-HETE, suggesting that BLT2 may play a proinflammatory role. Here, we used both mouse and zebrafish models to probe the roles of BLT2 in macrophage activation and/or recruitment to pancreatic islets during T1D progression. First, we analyzed Blt2 gene expression in a variety of C57BL/6J mouse tissues. We found Blt2 gene expression in bone marrow derived macrophages and peritoneal macrophages, however we found little to no expression in pancreatic islets. Although Blt2-/- mice showed a significantly reduced expression of Blt2, they exhibited overall normal growth and glucose tolerance. To uncover roles for BLT2 in macrophage function, we first interrogated its involvement in the in vitro polarization of proinflammatory macrophages to the M1-like state using LPS and IFN-γ and the M2-like state using IL-4. Under these conditions, we found no differences between Blt2-/- and wildtype macrophages, as assessed by flow cytometry analysis, suggesting that BLT2 does not play a substantial role in macrophage polarization. Next, to query roles for BLT2 in macrophage migration, we employed the transgenic zebrafish line Tg(mpeg:EGFP) in which macrophages are labeled with green fluorescent protein (GFP). Following zebrafish tailfin injury, we quantified macrophage accumulation at the injury at 6 hours post amputation. Inhibitory treatments of zebrafish larvae with either a chemical BLT2 inhibitor (LY255283) or by knockdown of the blt2a gene using an antisense morpholino, both decreased the number of GFP+ macrophages found at the injury site. Moreover, in the latter approach ectopic expression of blt2a mRNA effectively restored the wild-type phenotype. To determine if BLT2 mediates macrophage migration to injured islets, we employed a transgenic zebrafish model of β-cell injury, Tg(ins:NTR), in which metronidazole treatment rapidly induces β-cell injury. We treated the Tg(mpeg: GFP); Tg(ins: NTR) zebrafish with metronidazole and monitored macrophage migration into injured islets. We observed a significant decrease in macrophage migration towards injured β-cells in blt2a-knockdown zebrafish. Collectively, these results show that BLT2 plays a role in macrophage migration associated with tissue injury, including the islet β cell as seen in T1D.