Abstract 11817: Induced Pluripotent Stem Cell-Derived Cardiac Disease Modeling for Studying Mitogenic Cardiomyopathy in Alström Syndrome

Introduction: Cardiomyopathies are a prominent cause of heart failure and affect millions of people worldwide. We reported two case studies describing siblings with a mutation in the Alström 1 (ALMS1) gene causing Alström syndrome (ALMS), who developed mitogenic cardiomyopathy, characterized by delayed postnatal cardiomyocyte (CM) cell cycle arrest resulting in neonatal heart failure and death in early infancy. OBJECTIVES : To generate induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs) from ALMS patients and investigate molecular mechanisms of persistent CM proliferation in co-culture with ALMS1 fibroblasts. METHODS : We reprogrammed somatic cells from ALMS patients with mitogenic cardiomyopathy into iPSCs using Sendai virus technology and generated ALMS-specific iPSC-CMs using established in vitro differentiation protocols. We analyzed cell cycle progression by determining CM percentages in the G0/G1, S and G2/M phase using flow cytometry, and measured expression and secretion of periostin (POSTN) and collagens from ALMS1 fibroblasts in the extracellular matrix (ECM) using RT-QPCR and western blot. Finally, we investigated Hippo signaling by measuring expression and nuclear translocation of its downstream effectors YAP/TAZ using western blot and immunostaining. RESULTS : iPSC-CMs were successfully generated from ALMS patients and controls. ALMS1-deficient iPSC-CMs exhibited impaired ability to undergo cell cycle arrest, evidenced by a higher cell percentage in the G2/M phase. Furthermore, increased ECM levels of POSTN, a potent regulator of CM proliferation, were observed in co-cultures of ALMS1-deficient iPSC-CMs and ALMS1 fibroblasts. Finally, we found preliminary evidence of dysregulation of the Hippo pathway with altered cellular localization of YAP, and dysregulated total YAP and phosphorylated YAP. CONCLUSION : ALMS1-deficient iPSC-CMs recapitulate persistent postnatal proliferation observed in ALMS patients with mitogenic cardiomyopathy. Increased POSTN in the ECM and altered downstream Hippo signaling contribute to the mitogenic phenotype and suggest critical cues for future therapies aiming at stimulating CM turnover, a much-sought objective in cardiac repair to improve contractile function.