Abstract 500: Vitamin D Supplementation Attenuates ADAM-12-mediated Proliferation of Carotid Artery Smooth Muscle Cells of Hypercholesterolemic Swine

Abstract

Introduction: Risk of hypertension, peripheral artery disease, myocardial infarction and development of human atherosclerosis has been linked to vitamin D deficiency. Atheromatous cytokines, including IL-6, TNF-α and epidermal growth factor receptor (EGFR) family growth factors are released at the site of atherosclerosis and boost the activity of proteolytic enzymes such as ADAMs (a disintegrin and metalloproteinases). ADAM-12 cleaves proHB-EGF (Heparin-binding EGF-like growth factor) activating EGFR, resulting in increased proliferation of smooth muscle cells (SMCs). The aim of this study was to examine the effect of vitamin D on IL-6 and TNF-α-induced ADAM-12, pEGFR expression, HB-EGF release and SMC proliferation. Methods: Micro-swine were fed with vitamin D-deficient high cholesterol diet, high cholesterol diet containing 900 IU of vitamin D, and high cholesterol diet containing 3000 IU of vitamin D for total of 12 months. After six months, serum cholesterol levels of 500-600 mg/dL were achieved in all the three groups. The protein expression of ADAM-12 & pEGFR, and HB-EGF release, in presence or absence of IL-6, TNF-α and Calcitriol, in SMCs was quantified by western Blot. HB-EGF release was measured by ELISA. The proliferation was assayed by [3H]-Thymidine incorporation and cell counting method. Results: The protein expression of ADAM-12 & pEGFR, HB-EGF release were significantly reduced in carotid artery SMCs isolated from Vitamin D-supplemented swine. IL-6 and TNF-α treatment increased the protein expression of ADAM-12 & pEGFR and HB-EGF release in carotid artery SMCs. Proliferation capacity was higher in SMCs isolated from Vitamin D-deficient swine carotid artery, potentiated by IL-6 and TNF-α. Calcitriol inhibited the ADAM-12, pEGFR expression and HB-EGF released in SMCs of hypercholesterolemic swine. Calcitriol also inhibited the proliferation of carotid artery SMCs isolated from Vit D-deficient, D-sufficient and D-supplemented swine. Conclusion: Together, these results suggest that vitamin D deficiency enhances proliferation of SMCs, which is potentiated by atheromatous cytokines. Whereas, vitamin D supplementation regulates ADAM-12-mediated cleavage of proHB-EGF and activation of EGFR inhibiting SMC proliferation.