Activated protein C ameliorates diabetes-induced atherosclerosis by sustaining macrophage efferocytosis

Macrophage efferocytosis, essential for the resolution of inflammation and plaque stability in atherosclerosis, is impaired in diabetes. Thrombomodulin (TM) and endothelial protein C receptor (EPCR), key mediators of protein C activation (PC), have vasculoprotective and anti-inflammatory roles, yet their involvement in macrophage efferocytosis in diabetes-induced atherosclerosis remains unclear. Here, we demonstrate that expression of EPCR was reduced in atherosclerotic lesions of diabetic patients compared to non-diabetic controls. In parallel, efferocytosis was impaired in atherosclerotic lesions and in monocytes derived macrophages of diabetic patients. In vitro, treatment with activated PC (aPC) or its cytoprotective selective variant (3K3A-aPC) restored high glucose-impaired macrophage efferocytosis. Mechanistic studies revealed that aPC restored efferocytosis through Arginase-1 and modulation of Rac1-ATF6 signaling. Additionally, macrophage protease-activated receptor 1 (PAR1) was identified as the key receptor mediating aPC's effects on efferocytosis. Mimicking biased PAR-1 signaling via parmodulin-2 reverses glucose impaired efferocytosis. In vivo, aPC treatment of diabetic ApoE^-/- mice increased MerTK expression in atherosclerotic lesions. aPC's vasculoprotective effects, including the reduction of plaque size, were abrogated upon MerTK inhibition using morpholinos, underscoring the pivotal role of MerTK in mediating aPC's atheroprotective actions. These findings suggest that impaired TM-PAR1-aPC signaling contributes to defective macrophage efferocytosis in diabetes-associated atherosclerosis and that aPC-based therapies may offer a novel strategy to enhance macrophage function and prevent diabetes induced atherosclerosis.