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Protective Role of Smad6 in Inflammation-Induced Valvular Cell Calcification

Xin Li1, Jina Lim2, Jinxiu Lu3

  • 1Department of Medicine, University of California, Los Angeles, California.

Journal of Cellular Biochemistry
|April 14, 2015
PubMed

Insights

Inhibitory Smad6, a key regulator in vascular calcification, is reduced by tumor necrosis factor alpha (TNF-α). This reduction promotes inflammation-induced calcific aortic and valvular disease (CAVD) by upregulating BMP-2 signaling.

Area of Science:

  • Cardiovascular Biology
  • Molecular Medicine
  • Biochemistry

Background:

  • Calcific aortic and valvular disease (CAVD) is linked to hyperlipidemia and chronic inflammation.
  • Inhibitory Smad proteins (I-Smads), specifically Smad6 and Smad7, are implicated in valve development and potentially CAVD.
  • The role of I-Smads in inflammation-driven calcific vasculopathy remains unclear.

Purpose of the Study:

  • To investigate the role of I-Smads in the pathogenesis of atherosclerotic calcification.
  • To determine if Smad6 and Smad7 expression is altered in hyperlipidemia-associated CAVD.
  • To elucidate the mechanism by which inflammatory cytokines influence valvular interstitial cells (VICs) and CAVD.

Main Methods:

  • Comparative analysis of Smad6 and Smad7 expression in hyperlipidemic versus normolipemic mouse models.
  • Culture and treatment of murine aortic valve interstitial cells (mVICs) with tumor necrosis factor alpha (TNF-α).
  • Assessment of alkaline phosphatase (ALP) activity, matrix mineralization, and gene expression (BMP-2, Wnt, redox-regulated genes) in mVICs.
  • Smad6 knockdown using lentiviral shRNA to evaluate its specific role in TNF-α-induced calcification.

Main Results:

  • Smad6 expression was significantly reduced in aortic and valve tissues of hyperlipidemic mice, correlating with increased TNF-α.
  • TNF-α treatment of mVICs upregulated ALP activity, matrix mineralization, and BMP-2 expression, while downregulating Smad6.
  • Smad6 knockdown exacerbated TNF-α-induced calcification and BMP-2 upregulation in mVICs, indicating a critical inhibitory role for Smad6.
  • Smad7 expression was not significantly affected by TNF-α or hyperlipidemia.

Conclusions:

  • TNF-α promotes valvular and vascular cell calcification, partly by specifically decreasing Smad6 expression.
  • Reduced Smad6 levels enhance BMP-2 signaling, contributing to the development of calcific aortic and valvular disease.
  • Smad6 acts as a crucial endogenous inhibitor of inflammation-induced calcification in the aortic valve.

Keywords:
BONE MORPHOGENETIC PROTEIN-2CALCIFICATIONTNF-αTUMOR NECROSIS FACTOR-αVALVULAR CELLS

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