Abstract 279: Vitamin D3 Attenuates ADAM-12--Mediated Shedding of EGFR in Carotid Artery Smooth Muscle Cells of Hypercholesterolemic Swine

Deficiency of Vitamin D is linked to an increased risk of hypertension, peripheral artery disease, and myocardial infarction and is a major risk factor for the development of human atherosclerosis. Atheromatous cytokines, including TNF-α, IL-6 and IFN-γ, and EGF receptor family growth factors are released at the site of atherosclerosis and act on proteolytic enzymes, MMPs (matrix metalloproteinases), ADAMs (a disintegrin and metalloproteinases), and ADAMTS (a disintegrin and metalloproteinase with thrombospondin motifs). ADAM-12 activates EGFR resulting in increased migration and proliferation of smooth muscle cells (SMCs). The aim of this study was to examine the effect of vitamin D on IL-6-induced ADAM-12 expression and SMC migration and proliferation. Micro-swine were fed with either vitamin D-deficient high cholesterol diet or high cholesterol diet containing 900 IU of vitamin D for 6 months. After six months when serum cholesterol levels ranged from 500-600 mg/dL, vitamin D-deficient group continued on the same deficient diet, whereas the other group received supplementation of vitamin D (1,000 IU/d) for 6 months. The mRNA expression of ADAM-12 and EGFR in whole carotid artery and in IL-6-treated SMCs was quantified by qPCR. The proliferation was assayed by CyQuant NF cell proliferation assay. The mRNA transcripts of ADAM-12 and EGFR were significantly increased in carotid arteries from Vitamin D-deficient than in vitamin D- supplemented swine. Treatment of SMCs with IL-6 also increased the mRNA transcripts of ADAM-12 and EGFR in vitamin D-deficient swine SMCs compared to vitamin D-supplemented swine SMCs. The cell proliferation was higher in SMCs isolated from Vitamin D-deficient swine carotid artery compared to vitamin D- supplemented swine carotid artery. Together, these results suggest that Vitamin D regulates ADAM-12-mediated activation of EGFR and vitamin D deficiency further enhances proliferation of SMCs, which is potentiated by atheromatous cytokines.