Unexpected concentric cardiac remodeling induced by selective in vivo cleavage of titin springs in a genetic mouse model

Abstract Background Titin is subject to proteolytic cleavage within its elastic I-band region under various cardiac conditions, including ischemic injury and chemotherapy. However, the acute consequences of titin spring cleavage on cardiac function in vivo remain poorly understood. Purpose To investigate the functional consequences of selective cleavage of cardiac titin springs in vivo using a genetic titin cleavage (TC) mouse model. Methods The TC mouse harbors a tobacco etch virus protease (TEVp) recognition cassette within the elastic titin springs. In vivo cleavage was induced by AAV9-mediated, cardiac-specific TEVp overexpression, with AAV9-eGFP serving as control. At day (D)6 and D13 post-injection, left ventricular (LV) structure and function were assessed by cardiac magnetic resonance imaging (cMRI) and transthoracic echocardiography (TTE). Mechanical properties were examined in isolated cardiomyocytes and myocardial fiber bundles. Transcriptomic and proteomic analyses were performed at both time points to compare TEVp- and GFP-expressing hearts. Results In homozygous TC mice, ~40% and ~55% of titin molecules were cleaved on D6 and D13 post-TEVp injection, respectively. cMRI and TTE revealed significant reductions in LV diameter and volume during both systole and diastole, beginning at D6, in TEVp versus GFP controls. Despite thickening of the interventricular septum and LV posterior wall, LV mass remained unchanged. Cardiac output declined markedly, whereas LVEF was preserved. Doppler imaging demonstrated reduced E and A wave velocities and a decreased e’/a’ ratio; the e/e’ ratio was transiently reduced at D6. Aortic valve Doppler further showed significantly decreased pressure gradients and blood flow velocities (mean and peak). This phenotype of impaired diastolic filling emerged while myocardial passive stiffness was lowered at D6 but markedly elevated by D13 relative to controls. The diastolic dysfunction could be explained by the loss of cardiomyocyte elastic recoil (restoring forces) and impaired mechanical connectivity. Omics analyses corroborated these mechanistic insights, revealing rapid upregulation of cell-matrix adhesion and ECM-remodeling pathways, cytoskeletal reorganization, absence of hypertrophic signaling, and failed rescue through apoptosis and protein quality control. Conclusion Selective in vivo cleavage of titin springs does not cause ventricular dilation but instead induces diastolic dysfunction with impaired ventricular filling and concentric remodeling—independent of myocardial stiffening. Loss of cardiomyocyte elastic recoil disrupts mechanical homeostasis, rapidly activating fibroblasts and promoting fibrotic stiffening. This maladaptive cascade culminates in pathological remodeling and heart failure.