Abstract
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.