Characterizing Human Cardiac Fibroblast Responsiveness to Hemodynamic Unloading in Heart Failure with Reduced Ejection Fraction

Background: Myocardial interstitial fibrosis is a common pathology in cardiomyopathies leading to ventricular dilation and increased hemodynamic load that result in heart failure with reduced ejection fraction (HFrEF). Previous research has shown that HFrEF patients treated with a left ventricular assist device (LVAD) undergo hemodynamic unloading resulting in at least partial cardiomyocyte recovery. However, evidence supports that these patients do not experience a regression of fibrosis and demonstrate, in some cases, a worsening of fibrosis after LVAD treatment. Purpose: We hypothesize that human cardiac fibroblasts (HCFs) are constitutively activated in HFrEF myocardium but remain unresponsive to hemodynamic unloading with LVAD placement. Methods and Results: Forty human subjects with HFrEF undergoing LVAD implantation were enrolled to provide a portion of myocardium routinely removed during LVAD placement. In addition, 7 biopsies previously collected from transplanted hearts with extended LVAD treatment were also evaluated (LVEX). Quantification of PSR stained sections revealed a significant increase in collagen content in the HFrEF tissue (Collagen volume fraction % (CVF) = 2.8±0.2) in comparison to control tissues (CVF = 0.9±0.2) that remained elevated in LVEX hearts (CVF = 3.1±0.3). HCFs derived from biopsies received at LVAD placement were isolated and grown to confluence. HCFs from HFrEF patients and control HCFs from healthy donors were then plated on substrates with mechanical stiffnesses reflective of either normal myocardium (2kPa) or failing myocardium (8kPa). Cells were collected at 4- and 7-day timepoints and levels of collagen I (Col I) and alpha-smooth muscle actin (α-SMA) were quantified through western blot analysis with β-actin as a loading control. Whereas control HCFs were responsive to changes in substrate stiffness producing more Col I and α-SMA on 8kPa versus 2kPa, HCFs from HFrEF patients were unresponsive to changes in stiffness exhibiting no significant difference in production on 2 vs. 8kPa. Conclusion: These data suggest that HCFs isolated from the failing myocardium do not respond to changes in mechanical load and hence, might contribute to persistent increases in fibrosis in failing and unloaded hearts.