Abstract 16650: Role of Copper Transport Proteins in VSMC Phenotypic Modulation and Vascular Remodeling

Abstract

Vascular smooth muscle cell (VSMC) phenotypic modulation plays a critical role in vascular repair and vascular remodeling after injury. This involves transition from quiescent contractile (C) to de-differentiated phenotype (S)(C to S) induced by PDGF, followed by re-differentiation to contractile phenotype (S to C). Copper (Cu), an essential micronutrient, is involved in vascular remodeling, and its bioavailability is controlled by Cu transport proteins (importer CTR1 and exporter ATP7A) and Cu chaperone (antioxidant-1, Atox1), which activates Cu enzymes such as amine oxidase, SSAO. However, role of Cu transport proteins in VSMC phenotypic modulation is entirely unknown. Here we show that PDGF stimulation in primary VSMC induced de-differentiation (C to S) by downregulating contractile SMC protein, which was accompanied by a robust increase in Cu uptake and CTR1, ATP7A and SSAO levels, and inhibited by Cu chelators. Knockdown of CTR1, ATP7A, SSAO, but not siAtox1, suppressed PDGF-induced VSMC de-differentiation (69%, 72% and 92%, respectively). Of note, ATP7A depletion inhibited PDGF-induced SSAO while SSAO siRNA suppressed ATP7A induction, suggesting that there is a positive feedback loop whereby ATP7A-SSAO pathway promotes de-differentiation. Mechanistically, PDGF-induced expression of KLF4, a repressor of SMC protein expression, was blocked by depletion of CTR1, ATP7A and SSAO. We reported that Atox1 also functions as a Cu-dependent transcription factor independent of ATP7A. Consistently, Atox1 siRNA suppressed serum starvation-induced VSMC re-differentiation, and overexpression of Atox1 increased SMC contractile gene expression. In vivo vascular injury model showed that SSAO and Atox1 were increased in neointimal SMCs at early de-differentiation phase and at later re-differentiation phase, respectively, in response to injury. Summary and Conclusion: CTR1-ATP7A-SSAO pathway is involved in PDGF-induced VSMC de-differentiation via regulating KLF4 while Cu dependent transcription factor function of Atox1 promotes VSMC re-differentiation via regulating SMC contractile gene transcription. Cu transport proteins and SSAO are potential therapeutic targets for modulating VSMC phenotype switching and vascular remodeling.