• Xi-Wu Zhang, Bo-Yao Zhang, Shu-Wei Wang, De-Jun Gong, Lin Han, Zhi-Yun Xu, and Xiao-Hong Liu.
• Department of Cardiothoracic Surgery, Changhai Hospital, Second Military Medical University, Shanghai, China.
• J. Thorac. Cardiovasc. Surg.. 2014 Oct 1;148(4):1700-1708.e1.

ObjectiveValve calcification involves transdifferentiation of valve interstitial cells (VICs) into osteoblasts. Twist-related protein 1 (TWIST1) has been established as a negative regulator of osteoblast differentiation in both mouse and human mesenchymal stem cells, but its function in human aortic VICs is unknown. In our study, we determined the mechanism of TWIST1 action in regulating osteoblastic transdifferentiation of human aortic VICs.MethodsHuman calcified and noncalcified aortic valves were examined for TWIST1 expression. Human aortic VICs were isolated and cultured.ResultsThe data showed that calcified aortic valves express lower levels of TWIST1. In vitro experiments showed that TWIST1 overexpression inhibited the transdifferentiation of VICs into osteoblasts by decreasing the expression of runt-related transcription factor 2 (RUNX2) and its downstream osteoblastic markers. Through chromatin immunoprecipitation and dual luciferase assays, we found that TWIST1 repressed the expression of RUNX2 by directly binding to an E-box located at -820 bp of the RUNX2 P2 promoter region and inhibiting its activity.ConclusionsOur study results suggest that TWIST1 could play an important role in preventing human aortic valve calcification by negatively regulating osteoblastic transdifferentiation of human aortic VICs through direct inhibition of RUNX2.Copyright © 2014 The American Association for Thoracic Surgery. Published by Elsevier Inc. All rights reserved.

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