Objective— Proliferation of vascular smooth muscle cells (VSMCs) is a crucial event in the pathogenesis of intimal hyperplasia, the main cause of restenosis following vascular reconstruction. Here, the impact of sonic hedgehog (Shh)/Gli family zinc finger 2 (Gli2) signaling on VSMC proliferation was assessed.

Methods and Results— Increased Shh signaling was detected in VSMCs in the neointima of vein grafts obtained from mice undergoing restenosis. Comparable results were found in primary cultured human VSMCs (hVSMCs) obtained from patients undergoing coronary bypass surgery, which were used to further assess the impacts of Shh signaling on VSMC proliferation. Inhibition of Shh signaling in hVSMCs through treatment with cyclopamine or knockdown of Gli2 results in G₁ arrest and reduced cyclin D1, cyclin E, and phosphorylated retinoblastoma (pRB) levels. In contrast, activation of Shh/Gli2 signaling in hVSMCs results in increased levels of G₁ cyclins and promotes G₁-S transition. Stimulation of hVSMC proliferation by Shh is abolished by cyclin D1 knockdown.

Conclusion— Combined, these results demonstrate that Shh/Gli2 signaling stimulates VSMC proliferation via regulation of the G₁ cyclin-retinoblastoma axis and suggest that antagonists that target the Shh pathway may be therapeutically beneficial in the prevention of intimal hyperplasia.