Abstract 11422: Galactosyltransferase 1-Associating Protein Prevents Murine Vascular Runx2 Expression, Osteogenesis and Calcification

Abstract

Introduction and Hypothesis: The ubiquitin-conjugating enzyme, galactosyltransferase 1-associating protein (GTAP), is an E2 ubiquitin-conjugating enzyme (UBE2q1), involved in stem cell proliferation and differentiation. Increased vascular smooth muscle cell (SMC) calcification characterizes atherosclerotic heart disease. We tested here the hypothesis that GTAP plays a role in regulation of SMC calcification and expression of the osteogenic protein Runx2. Methods and Results: Echocardiography was conducted in sv129 (WT) (n=10) and GTAP-knockout (GTAP -/- ) (n=11) mice, displayed reduced contractility in GTAP -/- vs. WT mice. In histopathology patch myocardial fibrosis, arterial hyperplasia and calcification occurred in GTAP -/- but not WT mice. Significantly increased calcium contents/dry proteins were found in the aortic rings of GTAP -/- vs. WT mice when ex vivo exposed to inorganic phosphate media for 9 days (Fig. 1a, p<0.05). To less extents, heterozygous GTAP -/+ mice also had increased calcium contents. Total proteins were extracted from aortic SMC transduced with cDNA coding for WT GTAP and loss-functional mutant GTAP C351A for Western blot assays. As shown in Fig. 1b, compared with mock treated SMC, WT GTAP overexpressing SMC had increased band intensity of the contractile proteins, α-SM-actin and SM22α, but much lower band intensity of Runx2 protein. SMC with overexpression of the GTAP C351A mutant modestly reduction in Runx2 band density, and had little impact on band intensity of the contractile protein α-SM-actin and SM22α. Conclusions: GTAP exerts protective effects on vascular SMC by inhibiting expression of Runx2 and calcification, while promoting expression of the contractile proteins, α-SM-actin and SM22α.