Resolvin D2 limits atherosclerosis progression via myeloid cell-GPR18.

Dysregulated inflammation-resolution programs are associated with atherosclerosis progression. Resolvins, in part, mediate inflammation-resolution programs. Indeed, Resolvin D2 (RvD2) activates GPR18, a G-protein-coupled receptor, and limits plaque progression, though the cellular targets of RvD2 remain unknown. Here, we developed a humanized GPR18 floxed ("fl/fl") and a myeloid (Lysozyme M Cre) GPR18 knockout (mKO) mouse. We functionally validated this model by assessing efferocytosis in bone marrow-derived macrophages (BMDMs) and found that RvD2 enhanced efferocytosis in the fl/fl, but not in the mKO BMDMs. To understand the functions of RvD2-GPR18 in atherosclerosis, we performed a bone marrow transfer of fl/fl or mKO bone marrow into Ldlr-/- recipients. For these experiments, we treated each genotype with either Vehicle/PBS or RvD2 (25 ng/mouse, 3 times/week for 3 weeks). Myeloid loss of GPR18 resulted in significantly more necrosis, increased cleaved caspase-3+ cells and decreased percentage of Arginase-1+ -Mac2+ cells without a change in overall Mac2+ plaque macrophages, compared with fl/fl➔Ldlr-/- transplanted mice. RvD2 treatment decreased plaque necrosis, the percent of cleaved caspase-3+ cells and increased the percent of Arginase-1+ -Mac2+ cells in fl/fl➔Ldlr-/- mice, but not in the mKO➔Ldlr-/- transplanted mice. These results suggest that GPR18 plays a causal role in limiting atherosclerosis progression and that RvD2's ability to limit plaque necrosis is in part dependent on myeloid GRP18.

Resolvin D2-GPR18 Signaling on Myeloid Cells Limits Plaque Necrosis.

Introduction/Objective: Dysregulated inflammation-resolution programs are associated with atherosclerosis progression. Inflammation-resolution is in part mediated by Resolvins, including Resolvin D2 (RvD2). RvD2, which activates a G-protein coupled receptor (GPCR) called GPR18, limits plaque progression. Cellular targets of RvD2 are not known. Approach and Results: Here we developed humanized GPR18 floxed ("fl/fl") and a myeloid (Lysozyme M Cre) GPR18 knockout (mKO) mouse. We functionally validated this model by assessing efferocytosis in bone marrow derived macrophages (BMDMs) and found that RvD2 enhanced efferocytosis in the fl/fl, but not in the mKO BMDMs. We employed two different models to evaluate the role of GPR18 in atherosclerosis. We first used the PCSK9-gain of function approach and found increased necrosis in the plaques of the mKO mice compared with fl/fl mice. Next, we performed a bone marrow transfer of fl/fl or mKO bone marrow into Ldlr -/- recipients. For these experiments, we treated each genotype with either Veh or RvD2 (25 ng/mouse, 3 times/week for 3 weeks). Myeloid loss of GPR18 resulted in significantly more necrosis and cleaved caspase-3 + cells compared with fl/fl transplanted mice. RvD2 treatment decreased plaques necrosis and cleaved caspase-3 + cells in fl/fl, but not in the mKO transplanted mice. Conclusions: These results are the first to suggest a causative role for endogenous RvD2 signaling on myeloid cells in limiting plaque necrosis. Moreover, these results provide a mechanistic basis for RvD2 as a therapy limiting plaque necrosis.