Establishment of an induced pluripotent stem cells model of hereditary transthyretin amyloid cardiomyopathy for drug testing

Abstract

Introduction: Hereditary transthyretin-associated amyloidosis (ATTR) cardiomyopathy (CM) is an autosomal dominant cause of restrictive CM. The unstable mutant transthyretin (TTR) protein secreted from the liver would aggregate to form cytotoxic oligomers and fibrils affecting the heart. Epigallocatechin gallate (EGCG) was proposed to help prevent TTR deposition in the heart by preventing aggregates formation; however, its indirect effects on the cardiomyocytes under ATTR-CM remained largely unknown. Objective: This study aimed to create an induced pluripotent stem cells (iPSC)-derived model for ATTR-CM to investigate the effects of EGCG on ATTR-CM. The model consisted of two cell types: iPSC-hepatocytes (iHep) and iPSC-cardiomyocytes (iCM). Method: Two iPSC cell lines with TTR Gly67Glu and Ala117Ser mutation were reprogrammed from the ATTR-CM patients’ peripheral blood mononuclear cells. The iPSC cell lines were differentiated into iHep and iCM, and the conditioned medium from the iHep was transferred for 14 days. 1M EGCG was added to the conditioned medium in the treatment group. The iCM subsequently undergo phenotypic, electromechanical, and molecular characterisation. Results: The mutant TTR secreted with the two iHep with TTR gene mutations caused increased surface area and size of TTR depositions in the iCM. Besides, the iCM exposed to mutant TTR demonstrated contraction impairment (decreased rate of contraction, relaxation, and tau) and abnormal calcium transient (increased peak height, total calcium released, deflection velocity and recovery velocity). The abnormal electromechanical coupling phenotype in ATTR-CM was not observed in the 1M EGCG treatment group. The iCM exposed to mutant TTR were subjected to increased cell apoptosis and cytotoxicity compared to the control. The diseased group was associated with increased oxidative stress, autophagy impairment, and unfolded protein response (increased CHOP, XBP1-u, ATF4 and IRE1). However, the activation of the aforementioned pathways was not identified in the group treated with 1M EGCG. Conclusion: The iPSC-derived dual-cell model with iHep and iCM could reproduce the disease phenotype and molecular pathways of ATTR-CM. 1M EGCG could prevent the amyloid deposition, abnormal electromechanical coupling, and abnormal cellular response. This suggested the potential of modulating the autophagy and unfolded protein response in the treatment of ATTR-CM.