Wnt16 attenuates TGFβ-induced chondrogenic transformation in vascular smooth muscle.

OBJECTIVE: Phenotypic plasticity of vascular smooth muscle cells (VSMCs) contributes to cardiovascular disease. Chondrocyte-like transformation of VSMCs associates with vascular calcification and underlies the formation of aortic cartilaginous metaplasia induced in mice by genetic loss of matrix Gla protein (MGP). Previous microarray analysis identified a dramatic downregulation of Wnt16 in calcified MGP-null aortae, suggesting an antagonistic role for Wnt16 in the chondrogenic transformation of VSMCs.

APPROACH AND RESULTS: Wnt16 is significantly downregulated in MGP-null aortae, before the histological appearance of cartilaginous metaplasia, and in primary MGP-null VSMCs. In contrast, intrinsic TGFβ is activated in MGP-null VSMCs and is necessary for spontaneous chondrogenesis of these cells in high-density micromass cultures. TGFβ3-induced chondrogenic transformation in wild-type VSMCs associates with Smad2/3-dependent Wnt16 downregulation, but Wnt16 does not suppress TGFβ3-induced Smad activation. In addition, TGFβ3 inhibits Notch signaling in wild-type VSMCs, and this pathway is downregulated in MGP-null aortae. Exogenous Wnt16 stimulates Notch activity and attenuates TGFβ3-induced downregulation of Notch in wild-type VSMCs, prevents chondrogenesis in MGP-null and TGFβ3-treated wild-type VSMCs, and stabilizes expression of contractile markers of differentiated VSMCs.

CONCLUSIONS: We describe a novel TGFβ-Wnt16-Notch signaling conduit in the chondrocyte-like transformation of VSMCs and identify endogenous TGFβ activity in MGP-null VSMCs as a critical mediator of chondrogenesis. Our proposed model suggests that the activated TGFβ pathway inhibits expression of Wnt16, which is a positive regulator of Notch signaling and a stabilizer of VSMC phenotype. These data advance the comprehensive mechanistic understanding of VSMC transformation and may identify a novel potential therapeutic target in vascular calcification.