Abstract 478: Role Of FXR1 And Senescence In Intimal Hyperplasia And Vascular Biology

Introduction: Despite the advent of stents, intimal hyperplasia subsequent to vascular interventional procedures remains a major obstacle. Vascular smooth muscle cells (VSMC) play a critical role in the pathogenesis of intimal hyperplasia; therefore regulation of VSMC gene expression is a logical intervention point. FXR1 is a muscle-enhanced RNA binding protein and expression is increased in injured arteries. We have shown that modulation of FXR1 levels affects stability and abundance of inflammatory transcripts in VSMC, suggesting that FXR1 is a negative regulator of inflammation. This drives our hypothesis that FXR1 is involved in mitigating vascular disease and regulating inflammatory and proliferative mRNA in VSMC. Approach/Results: We developed a novel VSMC-specific conditional knockout mouse (FXR1 VSMC/VSMC ). In a carotid artery ligation model of intimal hyperplasia FXR1 VSMC/VSMC mice, have significantly reduced neointima formation (p<0.001) post-ligation compared to controls. To determine the mechanism of these effects, we knocked down FXR1 in human VSMC and observed decreased proliferation (p<0.05) as well as increased beta galactosidase (p<0.05) and gamma H2AX (p<0.01) staining, indicative of senescence. Senescent cells exhibit a senescence associated secretory phenotype (SASP) with characteristic gene expression leading to increased inflammation in the tissue microenvironment. RIP-sequencing demonstrated that FXR1 interacts with transcripts involved in cell cycle control, and stability of these transcripts is decreased with FXR1 KO. qPCR analysis from FXR1 KO mouse VSMC show increased transcripts associated with senescence (p21, p16, p53) as well as increased SASP-associated mRNA. Furthermore, wild-type human VSMC cultured in conditioned media from cells transfected with FXR1 siRNA show increased SASP mRNA and increased proliferation compared with cells cultured in conditioned media from scrambled control cells. Summary & Conclusions: Our results are the first to suggest that in addition to destabilization of inflammatory transcripts, FXR1 may stabilize cell cycle related genes in VSMC, and absence of FXR1 leads to induction of a senescent phenotype, an increase in SASP genes, and reduction of intimal hyperplasia.