Abstract P367: ‘Youthful’ Phenotype Of C-kit+ Cardiac Fibroblasts

Introduction: Fibroblasts are critical contributors to myocardial development, tissue homeostasis and remodeling. Cardiac fibroblast population heterogeneity and plasticity present a challenge for categorization of biological and functional properties. Distinct molecular markers and associated signaling pathways provide valuable insight for cardiac fibroblast biology and interventional strategies to influence injury response and remodeling. Receptor tyrosine kinase c-Kit mediates cell survival, proliferation, migration, and is activated by pathological injury. However, the biological significance of c-Kit within cardiac fibroblast population has not been addressed. Approach: An inducible c-Kit reporter mouse detects promoter activation with Green Fluorescent Protein (GFP) expression in cardiac interstitial cells (CICs). Coincidence of GFP and c-Kit with the DDR2 fibroblast marker was confirmed at protein level using flow cytometry and immunohistochemistry. Subsequently, cardiac fibroblasts expressing DDR2 with or without c-Kit were isolated and characterized in vitro . Results: A subset of DDR2 + cardiac fibroblasts also express c-Kit with coincidence in ~8% of total CICs. Pathological injury induces coincidence as well as expression of c-Kit and DDR2. Cultured cardiac DDR2+ fibroblasts that are c-Kit+ exhibit youthful morphological and functional phenotypes compared to c-Kit- cells including 1) significantly smaller size, 2) higher cellular motility, 3) enhanced proliferation, 4) less multinucleation, 5) decreased senescence-associated β-galactosidase staining, and 6) down-regulation of p53 senescence marker. Mechanistically, c-Kit expression correlates with signaling implicated in proliferation and cell migration including phospho-ERK and pro-Caspase 3. Conclusion: The phenotype of c-kit+ on DDR2+ cardiac fibroblasts correlates with multiple characteristics of ‘youthful’ cells. To our knowledge, this represents the first evaluation of c-Kit biology within DDR2+ cardiac fibroblast population and provides a fundamental basis for future studies to influence myocardial biology, cardiac remodeling, and response to pathological injury.