KLF4 in Smooth Muscle Cell-Derived Progenitor Cells Is Essential for Angiotensin II-Induced Cardiac Inflammation and Fibrosis.

BACKGROUND: Cardiac fibrosis is defined by the excessive accumulation of ECM (extracellular matrix) material resulting in cardiac tissue scarring and dysfunction. Although it is commonly accepted that myofibroblasts are the major contributors to ECM deposition in cardiac fibrosis, their origin remains controversial. Our group discovered that a subpopulation of resident vascular stem cells residing within the artery adventitia (termed adventitial Sca1+ smooth muscle-derived [AdvSca1-SM] cells) originates from mature vascular smooth muscle cells through a KLF4 (Kruppel-like factor 4)-dependent in situ reprogramming process. However, the molecular mechanism(s) whereby KLF4 regulates the AdvSca1-SM phenotype remain unclear. METHODS: We leveraged a highly specific AdvSca1-SM cell reporter system, single-cell RNA-sequencing, and spatial transcriptomic approaches to examine the spatiotemporal differentiation trajectory of AdvSca1-SM cells in AngII (angiotensin II) challenged cardiac tissues. To examine the function of KLF4, we compared the cardiac inflammation and fibrotic response of wild-type and AdvSca1-SM-specific Klf4 knockout mice. RESULTS: We demonstrate the profibrotic differentiation trajectory of coronary artery-associated AdvSca1-SM cells in cardiac fibrosis, characterized by loss of stemness-related genes, including Klf4, but gain of expression of a profibrotic phenotype. Importantly, these changes were recapitulated in human cardiac hypertrophic tissue, supporting the translational significance of a profibrotic transition of AdvSca1-SM-like cells in human cardiomyopathy. Spatially, AdvSca1-SM cells expand from the adventitia to the cardiac interstitium while exhibiting close association with T cells. AdvSca1-SM cell-specific knockout of Klf4 before AngII treatment paradoxically protected against cardiac T-cell inflammation, fibrosis, and systolic dysfunction. CONCLUSIONS: Overall, our data reveal the contribution of AdvSca1-SM cells to myofibroblasts in the setting of AngII-induced cardiac fibrosis. KLF4 not only maintains the stemness of AdvSca1-SM cells but also orchestrates their response to profibrotic stimuli and interactions with T cells. KLF4 may serve as a therapeutic target in cardiac fibrosis.