Abstract 10850: Investigating the Role of a Cardiac Enhancer in the Development of Heart Failure

Abstract

Introduction: Alpha actinin-2 (ACTN2) is a major cytoskeletal protein that plays a critical role in maintaining the structural and functional integrity of the sarcomere. ACTN2 mutations, although rare, have been shown to be associated with various types of cardiomyopathy. Using genome-wide association and multi-omic approaches, we recently identified non-coding variants that showed a strong association with heart failure (HF). Two of the variants are within an evolutionary conserved transcriptional enhancer region that regulates the ACTN2 gene in human stem cell derived cardiomyocytes (hPSC-CMs). However, the role of cardiac enhancers in the development of HF remains unknown, therefore we used engineered heart tissues (EHT) from hPSC-CMs to investigate the effects of the ACTN2 enhancer. Methods: We used hPSC-CMs and performed morphologic and functional analyses by immunostaining, calcium transient measurements and quantitative assays such as western blotting, proteomics, qPCR and single cell transcriptomics. Next, we utilized CRISPR interference (CRISPRi) and chromatin immunoprecipitation (ChIP) to analyze the transcriptional regulation of the ACTN2 enhancer. Finally, we measured force generation using EHTs. Results: We first engineered hPSC-CMs carrying an ACTN2 enhancer deletion. This resulted in decreased ACTN2 gene and protein expression, and cardiomyocytes developed myofibrillar disarray, hypertrophy, lower beating rates and suppressed calcium transients. Moreover, EHTs demonstrated reduced mechanical force. Using CRISPRi and ChIP we found that the transcription factor MEF2c binds a short DNA sequence containing an enhancer variant to regulate ACTN2 expression. Single cell RNA-Seq analysis of hPSC-CMs treated with isoproterenol to model the hyperadrenergic state observed in HF, revealed the induction of pathways involved in protein quality control, actin fragmentation and apoptosis. We have also recently developed a mouse model to address the effect of the enhancer in vivo . Conclusions: Our study confirms that a conserved and clinically relevant enhancer region can effectively regulate ACTN2 , and variants within that region can have detrimental consequences on CMs which can contribute to HF.