Abstract 422: Protease-Activated Receptor 2 is Critical for the Formation and Progression of Atherosclerosis

Abstract

Objective: Protease-activated receptor 2 (PAR-2)-dependent signaling results in augmented inflammation and has been implicated in the pathogenesis of several autoimmune conditions. While PAR-2 protein is present in coronary atherosclerotic lesions, the relevance of this finding has not been investigated in experimental models. The objective of this study was to determine the effects of PAR-2 on the development of atherosclerosis. Methods and Results: Relative expression of PAR-2 is increased in human coronary artery (21 fold) and mouse aortic arch (16 fold) atheromas versus control coronary and aortic arch arteries, respectively (P = 0.001). To determine the effect of PAR-2 deficiency on atherosclerosis, male low density lipoprotein receptor deficient ( Ldlr -/- ) mice (8-12 weeks old) that were Par-2 +/+ or Par-2 -/- were fed a fat and cholesterol-enriched diet for 12 (n = 10 each group) or 24 weeks (n = 5 each group). PAR-2 deficiency attenuated atherosclerosis in the aortic sinus and aortic root with no effects on total plasma cholesterol concentrations or lipoprotein distributions after 12 (P = 0.000433) and 24 (P = 0.037) weeks. These reductions were attributable to both hematopoietic and non-hematopoietic-derived PAR-2 from analysis of bone marrow experiments (n = 15 for each of 4 chimeric groups; P < 0.05). Mechanistic studies using ex vivo macrophages show that activation of PAR-2 results in augmented foam cell formation and apoptosis with treatment of oxidized low-density lipoprotein in conjunction with decreased expression of the nuclear receptor LXR-alpha and several cholesterol transporters. In addition, PAR-2 activation of ex-vivo cultured vascular smooth muscle cells (VSMCs) augments their transition to a macrophage-like state (after cholesterol treatment) via upregulation of human antigen R (HuR) and resultant stabilization of the transcription factor Krüppel-like factor 4 (KLF4). Conclusion: Our results indicate PAR-2 deficiency significantly attenuates the initiation (12 weeks) and reduces the progression (24 weeks) of atherosclerosis potentially via regulation of both lipid efflux from macrophages and the phenotypic modulation of VSMCs.