Defining the Role of TCF21 in Adventitial Fibroblasts in Atherosclerosis - PROJECT SUMMARY Coronary artery disease (CAD) remains a rising cause of morbidity and mortality in the United States. Human genetics suggest that a significant portion of the inheritable risk of CAD is related to fibroblast-specific regions of the genome. Using single cell transcriptomics, our group has identified a transcriptionally distinct adventitial fibroblast (AdvFib) population, which undergoes early phenotypic modulation during atherosclerosis development. Specific ablation of AdvFib significantly reduces plaque burden, suggesting their ability to influence atherosclerosis. To identify regulators of AdvFib, we characterized regions of altered chromatin accessibility upon AdvFib activation, revealing the transcription factor Tcf21. Tcf21 is predominantly expressed in AdvFib, and its expression declines upon AdvFib phenotypic activation. Tcf21 knockout in murine AdvFib increases vascular calcifications and upregulation of pro-atherogenic inflammatory cytokines. Given the restricted expression of Tcf21 to AdvFib and phenotypic activation of AdvFib upon Tcf21 knockdown, the central hypothesis underlying this proposal is that overexpression of Tcf21 locks AdvFib in a quiescent state, which then prevents the downstream activation of non-cell-autonomous signals that trigger plaque formation. Using an AdvFib-specific Tcf21 overexpression mouse model, I will characterize histological changes in plaque and alterations in non-AdvFib plaque cells, such as smooth muscle cells and inflammatory cells. I will then use single-cell RNA sequencing to characterize transcriptional changes of AdvFib upon Tcf21 overexpression and downstream transcriptional changes in non-AdvFib plaque cells. Given the putative effect of Tcf21 on the activation/recruitment of inflammatory cells, my goal is to characterize the precise epigenetic regions of Tcf21 binding to understand how Tcf21 regulates inflammatory cytokine production. Overall, this study will elucidate the role of AdvFib in atherosclerosis and characterize how Tcf21 regulates AdvFib.
