Increased Nuclear Susceptibility to Mechanical Stress in Phospholamban R14del Cardiomyopathy: A New Perspective on Disease Heterogeneity

Background: Clinical presentation of phospholamban (PLN) R14del cardiomyopathy is highly variable, from asymptomatic carriers to rapidly progressing heart failure. which cannot be fully explained by its known disturbance of sarcoplasmic reticulum calcium handling. Nuclear calcium signalling, shaped by sarcoplasmic reticulum calcium release, plays a key role in regulating gene expression and the cellular response to mechanical stress. However, how the R14del variant affects nuclear signalling under mechanical loading remains unclear. Objective: To uncover the impact of the PLN R14del variation on mechanosensing, nuclear calcium handling and its link to the variable clinical representation of this cardiomyopathy. Methods: Human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) carrying the PLN R14del variant, an isogenic control, and wildtype control were subjected to mechanical stimulation by cyclic stretch or cultured on substrates with physiological (10-20 kPa) and pathological (65-85 kPa) stiffness. Nuclear morphology, cytoskeletal organisation and nuclear body formation were assessed via immunofluorescence. Traction force microscopy was used to assess mechanical stress and force generation. Cardiac tissues from PLN R14del cardiomyopathy patients, dilated cardiomyopathy patients, and healthy controls were analysed under mechanical loading (at left ventricular assist device implantation) and unloading (at heart transplantation). Living myocardial slices from a PLN R14del patient were maintained under overloading or physiological loading conditions. Results: PLN R14del hiPSC-CMs showed impaired nuclear calcium handling and, under mechanical stress, exhibited impaired mechanotransduction and elevated nuclear bodies. A strain-avoidance response was triggered but failed to prevent apoptosis. Nuclear abnormalities were confirmed in patient myocardial slices and cardiac biopsies which normalized upon relative mechanical unloading. Conclusion: PLN R14del increases nuclear susceptibility to mechanical stress, linking nuclear dysfunction to new disease insights and highlighting potential for mechanobiology-based therapeutic interventions.