Abstract 2122: A Multiomic Timecourse Atlas Of Murine Vascular Disease Smooth Muscle Cell Transition Phenotypes And Their Perturbation With Tcf21 Knockout

Background: Vascular smooth muscle cells (SMC) contribute to heritable CAD risk and undergo cell changes to fibroblast-like (FMC) and osteochondrogenic (CMC) phenotypes. We perform molecular characterization of this transition process over the course of atherosclerosis development to better understand how causal SMC CAD genes such as TCF21 drive the phenotypic transition process to alter CAD risk. Methods/Results: Deep multiomic profiling of aortic roots from control atherosclerosis model ( Myh11Cre ERT2 , ROSA tdT/+ , ApoE -/- ) mice with SMC specific lineage tracing on high fat diet were harvested for 7 scRNA and 6 scATAC time points across 16 weeks. Similarly, aortic roots from Tcf21 knockout ( Myh11Cre ERT2 , Tcf21 ΔSMC/ΔSMC , ROSA tdT/+ , ApoE -/- ) were collected at 3 timepoints for paired scRNA/scATAC. Waddington-Optimal Transport (WOT) mapped transcriptional trajectories across SMC lineage clusters which terminate in FMC and CMC phenotype clusters. PANDO/CellOracle frameworks were used to create gene regulatory networks with the ability to model SMC transition perturbations in silico . These analyses generated a multiomic timecourse atlas demonstrating the lineage traced phenotypic progression of SMC to FMC and CMC. Upon knockout of Tcf21 , we discern notable shifts in the SMC to FMC transition characterized by differential scRNA transcriptional pathways and scATAC shifts in transcription factor (TF) motif accessibility which also overlap with WOT predicted TF enrichment for each cell state. These integrative analyses revealed Tcf21 regulation of Cebpb and the Tead1 -Hippo pathways as novel mechanisms for mediating its role in modulation of disease related processes such as inflammation, response to TGF- β signaling and cell proliferation. Further mechanistic validation is performed through a combination of TF binding site analysis with TEAD1 and CEBPB ChIP-Seq in human coronary artery SMCs, dual luciferase reporter assays and proximity ligation assays. Conclusion: We construct a single cell atherosclerosis timecourse to model mouse SMC cell states and perturb CAD gene Tcf21 to elucidate the interplay between epigenetic and transcriptional mechanisms which affect key SMC transition elements such as CEBPB and the TEAD1 -Hippo axis.