Project Summary Dilated Cardiomyopathy (DCM) is the leading cause of heart failure. Characterized by left ventricular dilation and impaired contractility, DCM results in pump failure and arrhythmogenesis leading directly to heart failure and sudden cardiac death. There are more than 50 genes implicated in DCM development that each produce a common DCM pathology. Induced pluripotent stem cell derived cardiomyocytes (iPSC-CMs) carrying DCM mutations display phenotypic aspects of genetic DCM, providing a powerful in vitro tool to study the cellular and molecular mechanisms of the disease. Our previous work utilized a specific patient-derived DCM mutation in iPSC-CMs and found that these cells, with a known phenotype of protein aggregation, exhibited increased Endoplasmic Reticulum (ER) stress which resulted in an activation of the Unfolded Protein Response (UPR), a compensatory and adaptive reaction to cell stress and aberrant protein folding. Further activating the UPR pharmacologically reduced ER stress in these cells and rescued cardiomyocyte contractility, indicating a direct link between the ER stress identified in this cell line and the impaired cardiac function seen in DCM. Our preliminary findings identified that Activating Transcription Factor 4 (ATF4), a stress response transcription factor, is a key mediator of the UPR upregulation that relieves the cardiomyocyte of ER stress. Endogenous ATF4 expression is upregulated during UPR activation, however its efficacy as a transcription factor remains inhibited in DCM. We have found that pharmacological bolstering of the UPR response increases ATF4 transcription factor activity and rescues cardiac contractility. The proposed research plan will investigate the UPR across several DCM gene mutations to identify how impaired proteostasis results in cardiac dysfunction, uncovering a novel phenotype in DCM which we believe will be broadly applicable to other cardiac diseases. Further, we will investigate the mechanism of ATF4 rescue of ER stress induced contractility deficits in iPSC- CMs and in mouse models of genetic DCM to reveal an new mechanism and therapeutic target for DCM.

Project Narrative Adding to the growing evidence of impaired proteostasis as a cellular hallmark of cardiac disease, Endoplasmic Reticulum stress, protein aggregation, and activation of the Unfolded Protein Response (UPR) have been identified in a genetically inherited form of Dilated Cardiomyopathy (DCM). Pharmacological activation of the UPR alleviates ER stress and rescues impaired contractility in DCM cardiomyocytes. Understanding the mechanism of how UPR bolstering improves DCM phenotypes will identify new therapeutic targets to treat the cell stress in the cardiomyocyte that underlies DCM.