Abstract P169: β-catenin C-terminal Domain/Sphingosine-1-Phosphate Receptor 1 Axis Drives Neointima Formation After Carotid Injury

Abstract

Introduction: The β-catenin C-terminal domain (CTD) is required for artery formation during embryogenesis, but its role in vascular remodeling in adulthood is unknown. Inhibitors targeting specifically the CTD of β-catenin have been developed, but their use in obstructive vascular disease is not yet justified because of this gap of knowledge. Loss of β-catenin in mouse aortic smooth muscle cells (MASMCs) decreases the transcript levels of sphingosine-1-phosphate receptor 1 (S1PR1). However, no studies have evaluated the crosstalk between these proteins in vascular remodeling. Hypothesis: We hypothesized that the CTD of β-catenin promotes neointima formation after vascular injury, and that it acts by inducing S1PR1 expression. Methods: We studied mice bearing a knockin mutant β-catenin allele (ΔC) that lacks β-catenin CTD transcriptional activity. Mice expressing the SMC-specific SMA-CreERT2 and bearing one floxed and one mutant β-catenin allele were treated with tamoxifen to inactivate the floxed allele, leaving the mutant allele as the only source of β-catenin in SMC (SMβCΔC mice). Carotid artery ligation was performed to induce vascular injury. MASMCs were isolated from SMβCΔC mice (βCΔC cells). Results: We found reduced neointima formation after injury in SMβCΔC male (SMβCWT/-: 0.52±0.09 vs SMβCΔC: 0.16±0.05; n=10; P<0.05) and female (SMβCWT/-: 0.56±0.11 vs SMβCΔC: 0.17±0.04; n=10; P<0.05) mice. These findings were associated with reduced SMC proliferation, increased SMC apoptosis, and prevention of loss of SMC markers. In vitro, βCΔC MASMCs showed reduced growth compared to control cells (n=6; P<0.05). βCΔC MASMCs also showed reduced S1PR1 expression and decreased S1pr1 promoter activity, which were both rescued by the transfection of a constitutively active form of β-catenin. Interestingly, overexpression of S1PR1 restored βCΔC MASMC growth towards control levels (n=6; P<0.05). In vivo, we found reduced S1PR1 expression in SMCs of injured arteries from SMβCΔC mice. Conclusion: Our results define an essential SMC β-catenin CTD-S1PR1 axis that drives neointima formation after arterial injury, and point to multiple points for potential therapeutic intervention to control vascular remodeling in disease.