Resolvin D2/GPR18 signaling enhances monocytic myeloid-derived suppressor cell function to mitigate abdominal aortic aneurysm formation

Abdominal aortic aneurysm (AAA) formation is a chronic vascular pathology characterized by inflammation, leukocyte infiltration, and vascular remodeling. The aim of this study was to delineate the protective role of Resolvin D2 (RvD2), a bioactive isoform of specialized pro-resolving lipid mediators, via G-protein-coupled receptor 18 (GPR18) receptor signaling in attenuating AAAs. Importantly, RvD2 and GPR18 levels were significantly decreased in aortic tissue of AAA patients compared with controls. Furthermore, using an established murine model of AAA in C57BL/6 (WT) mice, we observed that treatment with RvD2 significantly attenuated aortic diameter, pro-inflammatory cytokine production, immune cell infiltration (neutrophils and macrophages), elastic fiber disruption, and increased smooth muscle cell α-actin expression as well as increased TGF-β2 and IL-10 expressions compared to untreated mice. Moreover, the RvD2-mediated protection from vascular remodeling and AAA formation was blocked when mice were previously treated with siRNA for GPR18 signifying the importance of RvD2/GPR18 signaling in vascular inflammation. Mechanistically, RvD2-mediated protection significantly enhanced infiltration and activation of monocytic myeloid-derived suppressor cells (M-MDSCs) by increasing TGF-β2 and IL-10 secretions in a GPR18-dependent manner to attenuate aortic inflammation and vascular remodeling. Collectively, this study demonstrates that RvD2 treatment induces an expansion of myeloid-lineage committed progenitors, such as M-MDSCs, activates GPR18-dependent signaling to enhance TGF-β2 and IL-10 secretion, and mitigates SMC activation that contributes to resolution of aortic inflammation and remodeling during AAA formation.