Abstract 15469: Activation of Sting Pathway Promotes Epigenetic Induction of Smooth Muscle Cell Phenotypic Alterations in Aortic Wall

Abstract

Introduction: Smooth muscle cell phenotypic alteration is a prominent feature of aortic aneurysms and dissections (AAD) that causes the loss of functional, contractile, smooth muscle cells (SMCs) and subsequent aortic dysfunction. However, SMC phenotypic alteration in AAD and the underlying mechanism is poorly understood. Hypothesis: Stress on the aorta induces a phenotypic switch in SMCs from a contractile role to a pro-inflammatory role that promotes cell dysfunction and death. Methods: We performed single-cell RNA and ATAC sequencing (scRNA-seq, scATAC-seq) of ascending aortic tissues from patients with sporadic ascending AAD and organ donor controls, alongside murine aortic tissues from a sporadic AAD model and wild-type mice. The role of the STING pathway in SMC phenotypic alterations was studied in human aortic SMCs. Chromatin immunoprecipitation assays were used to study epigenetic regulation Results: Significant SMC transformation from a contractile phenotype to a pro-inflammatory, pro-fibroblast, and pro-death phenotype was seen in scRNA-seq of aortic tissues from AAD patients and a sporadic AAD murine tissue. Our sc-ATACseq indicated that SMC transformation was partially controlled by chromatin remodeling of these genes, and IRF3 was identified as a key transcriptional factor for the reduction of chromatin accessibility of contractile genes, but induction of chromatin accessibility of inflammatory genes. In cultured SMCs, cytosolic DNA, through STING-TBK1 signaling, activated IRF3, which directly bound cis-elements of contractile genes, and recruited EZH2 to induce repressive H3K27me3 modification, leading to SMC gene suppression. Activated IRF3 also induced inflammatory gene expression. SMC-Sting deficiency prevented proinflammatory phenotypic switch in the sporadic AAD mouse model and restored contractile phenotype. Conclusion: We highlight an epigenetic pathway responsible for SMC dysfunction that induced SMC gene suppression and SMC phenotype changes and identified STING-TBK-IRF3-EZH2 as key signaling that suppresses SMC genes. To the best of our knowledge, this is the first study reporting that the STING pathway contributes to AAD development by SMC transition from a contractile to an inflammatory phenotype.