Abstract
Objective: Medial artery calcification is associated with increased cardiovascular morbidity and mortality. It occurs with diabetes and chronic kidney disease. We have previously demonstrated that the matrix metallopeptidase 3 (MMP-3) is strongly induced in arterial calcification. We also showed that MMP-3 inhibition decreases calcium accumulation in vascular SMCs and that MMP-3 deficient mice develop less medial calcification than wildtype controls. In this series of continuing experiments, we evaluate the effects of MMP-3 on SMCs phenotypic transformation in vitro and in vivo. Methods and Results: Confluent rat aortic smooth muscle cells (RASMCs) cultured in calcification medium containing elevated calcium and phosphate levels for 7 days showed increased MMP-3 activity, decreased expression of the SMC markers SM-actin and SM-MHC, and increased expression of the bone markers alkaline phosphatase (ALP) and osterix (Osx). Cells were next exposed a selective MMP-3 inhibitor 2(EMD Millipore). In the presence of inhibitor, MMP-3 activity (MMP-3 activity assay kit, Abcam) was significantly decreased. Additionally, SMC osteogenic transformation was prevented as demonstrated by maintenance of SM22α and SM-MHC expression with reduction of ALP and Osx expression. In confirmatory experiments, MMP-3 reduction with siRNA inhibited the calcification of SMC that were exposed to calcification medium. We next evaluated phenotypic marker expression in MMP-3 knockout and wild-type mice injected with vitamin D 3 , a model of medial artery calcification. At 7 days after injection, expression of the SMC marker gene SM-MHC was significantly greater in MMP-3 KO mice than controls, while bone cell marker genes (Runx2, ALP, Osx) were decreased as measured by qPCR. Deletion of MMP-3 thus inhibited the osteogenic transformation of medial SMCs in vitamin D 3 -treated mice suggesting that it may control calcification via local effects within the arterial wall. Conclusion: Together these findings suggest that MMP-3 promotes medial artery calcification through local effects on the phenotypic state of vascular SMCs, and further, that it may serve as a therapeutic target to reduce calcification and improve outcomes in our PAD patient population.
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