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

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-β/Smad3 promotes SMC proliferation and intimal hyperplasia. Furthermore in cultured SMCs, elevated TGF-β/Smad3 increases the expression of several Wnt genes. Here we investigate a crosstalk between TGF-β/Smad3 and Wnt/β-catenin signaling and its role in SMC proliferation.

To mimic TGF-β/Smad3 up-regulation in vivo, rat aortic SMCs were treated with Smad3-expressing adenovirus (AdSmad3) or AdGFP control followed by stimulation with TGF-β1 (or solvent). AdSmad3/TGF-β treatment up-regulated Wnt2b, Wnt4, Wnt5a, Wnt9a, and Wnt11 (confirmed by qRT-PCR and ELISA), and also increased β-catenin protein as detected by Western blotting. Blocking Wnt signaling using a Frizzled receptor inhibitor (Niclosamide) abolished TGF-β/Smad3-induced β-catenin stabilization. Increasing β-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 β-catenin and stimulated SMC proliferation as well. In addition, increased β-catenin was found in the neointima of injured rat carotid artery where TGF-β and Smad3 are known to be up-regulated.

These results suggest a novel mechanism whereby elevated TGF-β/Smad3 stimulates the secretion of canonical Wnts which in turn enhances SMC proliferation through β-catenin stabilization. This crosstalk between TGF-β/Smad3 and Wnt/β-catenin canonical pathways provides new insights into the pathophysiology of vascular SMCs linked to intimal hyperplasia.