Dystrophin, a central component of the dystrophin-glycoprotein complex (DGC), links the cytoskeleton to the extracellular matrix (ECM), ensuring mechanical stability and serving as a signaling hub. Loss of full-length dystrophin disrupts sarcolemma stability, force transmission, and signaling, causing Duchenne muscular dystrophy (DMD) and its cardiomyopathy. While membrane fragility has long been proposed as a pathogenic mechanism, the underlying processes remain unclear. We generated cardiomyocytes and engineered heart tissues (EHTs) from hiPSCs derived from three DMD patients with early-onset systolic dysfunction carrying deletions in exons 46–48, 50, and 51, resulting in complete dystrophin loss. DMD-EHTs were compared with control-EHTs from two healthy donors. By day 50 post-cardiac induction, EHTs were mounted on a force-length recording apparatus to assess twitch contractions under isometric conditions across varying pacing frequencies and extracellular calcium levels. DMD-EHTs exhibited reduced isometric tension compared with controls, without changes in twitch duration. Calcium titration revealed increased buffering capacity in DMD-EHTs. We used two methods to probe membrane stability against external mechanical perturbations: (1) single cells were loaded with calcein-AM and subjected to hypo-osmotic shock (30 mOsm Tyrode’s with propidium iodide). Epifluorescence imaging showed increased permeability in DMD cardiomyocytes, indicating higher susceptibility to hypotonic stress; (2) dual laser optical tweezers mechanics was employed to apply local deformations to the membrane with ramp-and-hold pushes and pulls resulting in membrane indentation and tether, respectively. Compared to controls, DMD-hiPSC-CMs displayed about 40% lower apparent cell elastic moduli during indentation and 50% lower force for membrane/cortex detachment underlying tether formation, showing an increase in membrane plasticity and in the fragility of the membrane-cortex system. Together, these findings support a model in which impaired membrane-cortex coupling reduces the threshold for stress-induced membrane damage, contributing to cardiomyopathy in DMD. 20223L2C9N.
Pertici et al. (Sun,) studied this question.