Consequences of PDGFRα+ fibroblast reduction in adult murine hearts

Fibroblasts produce the majority of collagen in the heart and are thought to regulate extracellular matrix (ECM) turnover. Although fibrosis accompanies many cardiac pathologies and is generally deleterious, the role of fibroblasts in maintaining the basal ECM network and in fibrosis in vivo is poorly understood. We genetically ablated fibroblasts in mice to evaluate the impact on homeostasis of adult ECM and cardiac function after injury. Fibroblast-ablated mice demonstrated a 60-80% reduction in cardiac fibroblasts, which did not overtly alter fibrillar collagen or the ECM proteome evaluated by quantitative mass spectrometry and N-terminomics. However, the distribution and quantity of collagen VI, a microfibrillar collagen that forms an open network with the basement membrane, was altered. In fibroblast-ablated mice, cardiac function was better preserved following angiotensin II/phenylephrine (AngII/PE)-induced fibrosis and myocardial infarction. Analysis of cardiomyocyte function demonstrated weaker contractions and slowed calcium decline in both uninjured and AngII/PE infused fibroblast-ablated mice. Moreover, fibroblast-ablated hearts had a similar gene expression profile to hearts with physiological hypertrophy after AngII/PE infusion. Our results indicate that the adult mouse heart tolerated a significant degree of fibroblast loss with potential beneficial impacts on cardiac function. Controlled fibroblast reduction may have therapeutic value in heart disease by providing cardioprotective effects.