Decorin GAG Synthesis and TGF- Signaling Mediate Ox-LDL–Induced Mineralization of Human Vascular Smooth Muscle Cells

Objective—Decorin and oxidized low-density lipoprotein (Ox-LDL) independently induce osteogenic differentiation of vascular smooth muscle cells (VSMCs). We aimed to determine whether decorin glycosaminoglycan (GAG) chain synthesis contributes to Ox-LDL–induced differentiation and calcification of human VSMCs in vitro. Methods and Results—Human VSMCs treated with Ox-LDL to induce oxidative stress showed increased alkaline phosphatase (ALP) activity, accelerated mineralization, and a difference in both decorin GAG chain biosynthesis and CS/DS structure compared with untreated controls. Ox-LDL increased mRNA abundance of both xylosyltransferase (XT)-I, the key enzyme responsible for GAG chain biosynthesis and Msx2, a marker of osteogenic differentiation. Furthermore, downregulation of XT-I expression using small interfering RNA blocked Ox-LDL–induced VSMC mineralization. Adenoviral-mediated overexpression of decorin, but not a mutated unglycanated form, accelerated mineralization of VSMCs, suggesting GAG chain addition on decorin is crucial for the process of differentiation. The decorin-induced VSMC osteogenic differentiation involved activation of the transforming growth factor (TGF)- pathway, because it was attenuated by blocking of TGF- receptor signaling and because decorin overexpression potentiated phosphorylation of the downstream signaling molecule smad2. Conclusion—These studies provide direct evidence that oxidative stress–mediated decorin GAG chain synthesis triggers TGF- signaling and mineralization of VSMCs in vitro. (Arterioscler Thromb Vasc Biol. 2011;31:608-615.