Abstract
Hypertrophic cardiomyopathy (HCM), the most common inherited cardiomyopathy, is driven by mutations in sarcomeric proteins and characterized by interstitial fibrosis. Cardiac fibroblasts (CFs), as key mediators of fibrosis, respond to extracellular matrix (ECM) stiffening, which may further drive disease progression. While the relationship between CF stiffness and ECM elasticity is well established, how CFs viscoelasticity adapts to mechanical cues remains unclear. Here, we investigated the viscoelasticity of cell spheroids (CSs) derived from primary human CFs (healthy, healthy treated with TGF-β, HCM, and HCM treated with TGF-β). CSs were subjected to parallel plate compression at different displacement rates (0.5, 1, 2, 5 µm/s) up to 30% strain followed by stress relaxation at 30% strain. Viscosity and elasticity were quantified using the standard linear solid (SLS) model. Our results showed that the apparent compression modulus increased with displacement rate, confirming the viscoelastic nature of CSs. Stress relaxation tests revealed that HCM spheroids exhibited significantly higher elasticity and viscosity compared to healthy controls, likely due to their fibrotic phenotype and increased α-smooth muscle actin (α-SMA) expression, as confirmed by gene analysis. TGF-β further increased elasticity by two-fold in both groups, consistent with enhanced ECM deposition observed via confocal microscopy, but had no significant effect on viscosity, suggesting that ECM accumulation alone may not directly influence viscous behavior. These findings highlight a distinct viscoelastic signature in HCM-derived CSs, enhancing our understanding of the biomechanical aspect of fibrosis in disease progression. This study provides a foundation for further understanding of the mechanobiology in cardiac fibrosis.