A crosstalk between TGF-β/Smad3 and Wnt/β-catenin pathways promotes vascular smooth muscle cell proliferation

Rationale: Endovascular interventions performed for atherosclerotic lesions trigger excessive vascular smooth muscle cell (SMC) proliferation leading to intimal hyperplasia. Our previous studies show that following endovascular injury, elevated TGF-beta/Smad3 promotes SMC proliferation and intimal hyperplasia. Furthermore in cultured SMCs, elevated TGF-beta/Smad3 increases the expression of several Wnt genes. Here we investigate a crosstalk between TGF-beta/Smad3 and Wnt/beta-catenin signaling and its role in SMC proliferation. Methods and results: To mimic TGF-beta/Smad3 up-regulation in vivo, rat aortic SMCs were treated with Smad3-expressing adenovirus (AdSmad3) or AdGFP control followed by stimulation with TGF-beta 1 (or solvent). AdSmad3/TGF-beta treatment up-regulated Wnt2b, Wnt4, Wnt5a, Wnt9a, and Wnt11 (confirmed by qRT-PCR and ELISA), and also increased beta-catenin protein as detected by Western blotting. Blocking Wnt signaling using a Frizzled receptor inhibitor (Niclosamide) abolished TGF-beta/Smad3-induced beta-catenin stabilization. Increasing beta-catenin through degradation inhibition (using SKL2001) or by adenoviral expression enhanced SMC proliferation. Furthermore, application of recombinant Wnt2b, Wnt4, Wnt5a, or Wnt9a, but not Wnt11, stabilized beta-catenin and stimulated SMC proliferation as well. In addition, increased beta-catenin was found in the neointima of injured rat carotid artery where TGF-beta and Smad3 are known to be up-regulated. Conclusions: These results suggest a novel mechanism whereby elevated TGF-beta/Smad3 stimulates the secretion of canonical Wnts which in turn enhances SMC proliferation through beta-catenin stabilization. This crosstalk between TGF-beta/Smad3 and Wnt/beta-catenin canonical pathways provides new insights into the pathophysiology of vascular SMCs linked to intimal hyperplasia. (C) 2016 Elsevier Inc. All rights reserved.