Functional Cooperation between Vitamin D Receptor and Runx2 in Vitamin D-Induced Vascular Calcification

<div><p>The transdifferentiation of vascular smooth muscle cells (VSMCs) into osteoblast-like cells has been implicated in the context of vascular calcification. We investigated the roles of vitamin D receptor (Vdr) and <i>runt-related transcription</i> factor <i>2</i> (<i>Runx2</i>) in the osteoblastic differentiation of VSMCs in response to vitamin D₃ using <i>in vitro</i> VSMCs cultures and <i>in vivo</i> in <i>Vdr</i> knockout (<i>Vdr</i>^<i>-/-</i>) and <i>Runx2 carboxy-terminus</i> truncated heterozygous (<i>Runx2</i>^<i>+/ΔC</i>) mice. Treatment of VSMCs with active vitamin D₃ promoted matrix mineral deposition, and increased the expressions of Vdr, Runx2, and of osteoblastic genes but decreased the expression of smooth muscle myosin heavy chain in primary VSMCs cultures. Immunoprecipitation experiments suggested an interaction between Vdr and Runx2. Furthermore, silencing <i>Vdr</i> or <i>Runx2</i> attenuated the procalcific effects of vitamin D₃. Functional cooperation between Vdr and Runx2 in vascular calcification was also confirmed in <i>in vivo</i> mouse models. Vascular calcification induced by high-dose vitamin D₃ was completely inhibited in <i>Vdr</i>^<i>-/-</i> or <i>Runx2</i>^<i>+/ΔC</i> mice, despite elevated levels of serum calcium or alkaline phosphatase. Collectively, these findings suggest that functional cooperation between Vdr and Runx2 is necessary for vascular calcification in response to vitamin D₃.</p>