A transcriptional enhancer regulates cardiac maturation [scRNA-seq]

Cardiomyocyte maturation is crucial for generating adult cardiomyocytes and the application of human pluripotent stem cell derived-cardiomyocytes (hPSC-CMs). However, regulation at the cis-regulatory element level, and its role in heart disease remain unclear. Alpha-actinin 2 (ACTN2) levels increase during CM maturation. Here, we investigate a clinically relevant, conserved ACTN2 enhancer's effects on CM maturation using hPSC and mouse models. Heterozygous ACTN2 enhancer deletion led to abnormal CM morphology, reduced function, and mitochondrial respiration. Transcriptomic analyses in vitro and in vivo showed disrupted CM maturation and upregulated anabolic mammalian target for rapamycin (mTOR) signaling promoting senescence and hindering maturation. As confirmation, ACTN2 enhancer deletion induced heat shock protein 90A expression, a chaperone mediating mTOR activation. Conversely, targeting the ACTN2 enhancer via enhancer CRISPR activation (enCRISPRa) promoted hPSC-CM maturation. Our studies reveal the transcriptional enhancer's role in cardiac maturation and disease, offering insights into potentially fine-tuning gene expression to modulate cardiomyocyte physiology. Overall design: To investigate the role of a conserved ACTN2 enhancer in vitro, we used CRISPR/Cas9 and deleted this enhancer genomic region in human pluripotent stem cells (hPSCs) (H9). We then differentiated the cells to cardiomyoaytes (hPSC-CMs) and perfomed single cell RNA-Seq at differentiated day 20 CMs.