Abstract 16843: Diastolic Dysfunction Due to Structual Changes in Mutant Troponin I May Cause Restrictive Cardiomyopathy; Cryo-Electron Microscopic Analysis Using Induced Pluripotent Stem Cell Derived Cardiomyocytes

Abstract

Introduction: Restrictive cardiomyopathy (RCM) is characterized by ventricular diastolic dysfunction with preserved contraction. Since there is no effective treatment other than heart transplantation, the development of novel treatment strategy by elucidating pathophysiology of RCM is an important issue under the serious donor shortage.Various troponin I mutations have been reported in patients with RCM and given that troponin I regulates the inhibition of cardiac contraction, it is possible that structural changes in mutant troponin I cause diastolic dysfunction in RCM. Recently, cryo-electron microscopy (cryo-EM) has made it possible to analyze the structure of thin filaments of muscle fibers. In this study, we applied the technology of induced pluripotent stem cell (iPSC) to cryo-EM structural analysis of thin filaments in cardiomyocytes from RCM patients with troponin I mutations. Methods: We established an iPSC line from a pediatric RCM patient with heterozygous TNNI3 mutation (R170W). Then the iPSCs were differentiated to cardiomyocytes to compare the cellular physiological, structural features. Normal adult iPS cell derived cardiomyocytes (Ctrl-iPSC-CM) were used as control. We also extracted thin filaments from iPSC-CMs and analyzed their structure with cryo-EM. Results: PCR analysis revealed the percentage of mutant alleles in TNNI3 mRNA was about 80% in the differentiated RCM-iPSC-CM, which was similar to the results in the myocardium of the same patient. The RCM-iPSC-CM demonstrated slower diastolic rate and longer diastolic time by cell motion analyses than Ctrl-iPSC-CM. Immunostaining showed a disarrayed sarcomeres in the RCM-iPSC-CM. Tthe structure of the thin filaments extracted from the RCM-iPSC-CMs observed with cryo-EM was close to that in the presence of calcium (contractile myocardium), even though the filaments were purified in the absence of calcium. Conclusions: The iPSC-derived cardiomyocytes could effectively represent the diastolic dysfunction of RCM. The structures of thin filaments were possibly explained for the phenotype of restrictive cardiomyopathy.