Promoting Autophagy Mitigates Stress-Induced Remodeling in Patient iPSC-CMs with the Phospholamban R9C Mutation

Phospholamban (PLN) is a key regulator of adrenergic signaling and calcium homeostasis in cardiomyocytes. The PLN R9C mutation causes early-onset dilated cardiomyopathy (DCM) and premature death, yet the mechanisms underlying its pathogenic remodeling remain unclear. In this study, patient-specific induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs) harboring the PLN R9C and their isogenic corrected controls are generated to investigate the molecular and functional consequences of the mutation. At baseline, PLN R9C iPSC-CMs exhibit near-normal calcium handling but blunt β-adrenergic signaling and slightly enhanced contractility. Under functional stress induced by a pro-maturation medium, mutant cells develop marked sarcomere disarray, impaired calcium handling, elevated diastolic calcium, and reduced contractile force, whereas corrected cells show adaptive improvement. Transcriptomic and biochemical analyses reveal activation of proteostasis pathways but accumulation of PLN pentamers and impaired autophagic flux, suggesting that autophagic overload contributes to functional remodeling. Treatment with the autophagy activator metformin mitigates sarcomere disorganization, restores calcium homeostasis, and improves contractility in patient-derived iPSC-CMs. These findings are further validated in wild-type and genome-engineered PLN R9C iPSC-CMs. Collectively, the study demonstrates that PLN R9C drives stress-induced pathological remodeling by disrupting proteostasis, and that enhancing autophagic flux offers a promising therapeutic strategy for DCM patients carrying PLN mutations.