Abstract 317: Resident Vascular Adventitial Progenitor Cells Of Smooth Muscle Cell-lineage Adopt Profibrotic Phenotype And Contribute To Cardiac Fibrosis

Activated cardiac myofibroblasts are the major contributors to ECM deposition in pathological cardiovascular fibrosis, which is the characteristic feature of cardiovascular diseases. However, due to potential heterogeneity of myofibroblasts, the origin of these cells remains controversial. Using highly specific smooth muscle cell lineage-tracing mouse models, we discovered the smooth muscle cell origin of a subpopulation of resident vascular adventitial progenitor cells, defined by the expression of the stem cell marker Sca1 (AdvSca1-SM cells), which rapidly proliferate and adopt a myofibroblast phenotype in response to acute vascular injury. Further, we identified a specific gene signature of active hedgehog/Wnt/β-catenin/ Klf4 signaling in AdvSca1-SM cells and validated a Gli1 -CreERT2-ROSA26-YFP (Gli1) reporter mouse model to be a faithful lineage tracing system for AdvSca1-SM cells. However, the function of AdvSca1-SM cells in cardiac fibrosis is unknown. Using immunofluorescent staining and label-free second harmonic generation (SHG) imaging, we observed the expansion and migration of AdvSca1-SM cells in close association with perivascular and interstitial cardiac fibrosis in pressure overload-induced cardiac fibrosis in Gli1 reporter mice. We performed single cell RNA sequencing (scRNA-seq) to examine the phenotype of AdvSca1-SM cells in Angiotensin II (AngII) model. Our data showed that, upon AngII challenge, AdvSca1-SM cells differentiate along a profibrotic trajectory, which is characterized by loss of expression of Klf4 , the lncRNA, Meg3 , and stemness genes and up-regulation of myofibroblast genes. Importantly, AngII-induced profibrotic transcriptomic changes of AdvSca1-SM cells were recapitulated in human ventricular tissues exhibiting a gene signature of cardiac hypertrophy, emphasizing the translational significance of this phenotypic transition. Connectivity map analysis of the scRNA-seq data identified statins as potential candidates for inhibition of the profibrotic transition of AdvSca1-SM cells. In agreement, simvastatin induced the expression of stemness genes and inhibited TGFβ-induced up-regulation of αSMA and down-regulation of Klf4 in cultured AdvSca1-SM cells.