Abstract
BACKGROUND: Myocardial fibrosis is prevalent in cardiomyopathies that result in heart failure with reduced ejection fraction. Heart failure with reduced ejection fraction treated with a left ventricular assist device (LVAD) yields hemodynamic unloading and may provide partial cardiomyocyte recovery, but contemporary studies reveal no consistent reductions in fibrosis. This study tested the hypothesis that, despite normalization of hemodynamic overload by LVAD, fibrosis and fibroblast activation persist resulting in sustained increases in myocardial stiffness. METHODS AND RESULTS: Tissues from subjects with heart failure with reduced ejection fraction undergoing LVAD implantation (pre-LVAD), from transplanted hearts with LVAD (post-LVAD) or without cardiac pathology (control) were collected. Quantification of myocardial stiffness and collagen content revealed significant increases in pre-LVAD versus control that remained elevated in post-LVAD. Myocardial fibroblast populations increased in pre- and post-LVAD hearts versus control. Control, pre-LVAD, and post-LVAD fibroblasts were isolated and plated on substrates with mechanical stiffnesses reflective of normal (≈2 kPa) or fibrotic (≈8 kPa) myocardium. Quantification of collagen I and α-smooth muscle actin production demonstrated that control fibroblasts were responsive to substrate stiffness, whereas pre- and post-LVAD fibroblasts were unresponsive and exhibited no significant differences on either substrate. Bulk-RNA sequence analysis revealed changes in gene expression in pre-LVAD versus control fibroblasts including mechano-sensitive pathways that appear to be uncoupled, resulting in increased expression of genes implicated in proliferation, whereas mechano-sensing genes were decreased. CONCLUSIONS: These data support that sustained cardiac hemodynamic overload leads to a phenotypic conversion in fibroblasts in which the capacity to detect changes in mechanical input is muted, thus contributing to retention of collagen content and stiffness in both pre- and post-LVAD hearts.