Abstract Body: Background
Myocardial stiffening is a hallmark of heart failure and is typically attributed to extracellular matrix remodeling and fibrosis. However, pediatric dilated cardiomyopathy (DCM) develops with minimal fibrosis, suggesting that cardiomyocyte-intrinsic mechanisms contribute to early disease pathogenesis. We hypothesized that persistent activation of WNT signaling led to early cytoskeletal remodeling, increasing cardiomyocyte stiffness prior to overt myocardial dysfunction in pediatric DCM.
Methods
We examined cardiomyocyte mechanical and cytoskeletal remodeling in neonatal rat ventricular myocytes and a neonatal rat model treated with isoproterenol and secreted frizzled-related protein-1 (ISO+sFRP1) (Due to increased levels of catecholamines and sFRP1 in pediatric DCM sera). Molecular mechanisms were investigated through echocardiography and next-generation-sequencing. Myocardial stiffness was quantified using atomic force microscopy. Cytoskeletal organization was assessed by phalloidin staining, F/G-actin quantification, and analysis of detyrosinated tubulin. Findings were compared with explanted pediatric and adult human myocardium.
Results
ISO+sFRP1 treatment resulted in an increase in myocardial stiffness that recapitulated the increase in stiffness in pediatric DCM (Figure 1), in the absence of overt fibrosis (not shown). We identified activation of WNT signaling in both ISO+sFRP1-treated rats and uniquely in pediatric DCM hearts (Figure 2). Early cytoskeletal remodeling was observed after only 3 hours of treatment with ISO+sFRP1, characterized by increased phalloidin intensity, a shift toward filamentous actin (F-actin), and elevated detyrosinated tubulin levels (Figure 3). These changes indicate reinforcement of both actin and microtubule cytoskeletal networks. Importantly, these structural changes are an acute response to treatment, suggesting that cytoskeletal remodeling is an early driver of mechanical dysfunction.
Conclusions
Our findings suggest that cytoskeletal remodeling is an acute response to the ISO+sFRP1 insult and likely precedes overt cardiac dysfunction. These results highlight cytoskeletal stiffness as a potential therapeutic target for preventing progression to pediatric DCM.