Abstract 169: Smad3 Drives Cross-Talk Between TGFß and Wnt/ß-Catenin Signaling Pathways in Smooth Muscle Cells

Abstract

Restenosis (neo-intimal hyperplasia) occurs in approximately 25-50% of patients undergoing arterial interventions, primarily due to the proliferation and migration of arterial smooth muscle cells (SMCs) into the peri-luminal area. Recently, Wnt/β-catenin signaling has been shown to promote SMC proliferation and enhance neo-intimal hyperplasia but its mechanism of activation is unclear. Interestingly, Wnt/β-catenin has been shown to be activated by TGFβ in mesenchymal stem cells and fibroblasts. We have shown that TGFβ and its downstream signaling protein, Smad3, are upregulated following vascular injury and that Smad3 overexpressing SMCs display enhanced proliferation, migration, and neo-intimal hyperplasia. These results led us to hypothesize that TGFβ, through Smad3, activates Wnt/β-catenin to regulate SMC behavior following arterial injury . In primary rat SMCs, TGFβ (5ng/mL) led to β-catenin activation and relocalization from the plasma membrane to the cytoplasm / nucleus within 24 hours. Furthermore, qRT-PCR results demonstrated that expression of Wnt11 (22 fold) and Wnt9a (3.9 fold) were significantly upregulated after 24 hours of TGFβ stimulation (p<0.05, n=3). In addition, 24 hours of TGFβ stimulation in SMCs overexpressing Smad3 (TGFβ/Smad3) further enhanced the gene expression of Wnt11 (>300 fold) and Wnt9a (14 fold) and also stimulated significant increases in Wnt2b (41 fold), Wnt5a (2.9 fold), and Wnt4 (3.2 fold) (p<0.05, n=3) as measured by qRT-PCR. Western blot results demonstrated that the combined TGFβ/Smad3 stimulation increased β-catenin protein levels, suggesting that TGFβ activates canonical Wnt signaling leading to stabilization of β-catenin protein. In normal rat carotid arteries, β-catenin protein was undetectable via immunohistochemistry but could be seen in SMCs of the vessel media at 3 days post-balloon angioplasty and in neo-intimal cells at 7 and 14 days. Smad3 was also expressed in neo-intimal cells at 7 and 14 days post-angioplasty suggesting that TGFβ, through Smad3, is responsible for Wnt/β-Catenin activation during vascular injury. In conclusion, this work describes a novel cross-talk in SMCs between TGFβ and Wnt signaling which may provide a viable target for future anti-restenotic treatments.