THOC6 deficiency leads to cardiomyopathy by reducing myocardial contractile proteins in cardiomyocytes.

The THOC6 protein is an essential part of the THO complex. Biallelic loss-of-function variants in the THOC6 gene are linked to Beaulieu-Boycott-Innes syndrome (BBIS; OMIM #613680). Although research predominantly focuses on THOC6's involvement in neurodevelopmental disorders, approximately 80% of BBIS patients present with cardiac anomalies, including structural heart disease, cardiomyopathy, and arrhythmia. Despite this, the connection between THOC6 expression and cardiac development remains underexplored. This study firstly investigates THOC6's role in heart development. This study we firstly utilized CRISPR/Cas9 to knock out THOC6 in H9C2 cardiomyocytes, revealing a reduction in cell proliferation and an increase in apoptosis. With RNA sequencing (RNA-seq) analysis we found abundant gene changes after THOC6 knockout (KO) in H9C2, which associated with hypertrophic cardiomyopathy, arrhythmogenic right ventricular cardiomyopathy, and dilated cardiomyopathy. Protein-protein interaction analysis and experimental validation indicated that THOC6 regulates the expression of type I collagen (COL1A1, COL1A2) and cytoskeletal protein (Cardiac α actin 1) in cardiomyocytes. Subsequently, we generated a THOC6 knockout cell lines in human induced pluripotent stem cells (hiPSCs) derived from a healthy individual using CRISPR/Cas9 technology. THOC6 knockout (KO) in hiPSCs-derived cardiomyocytes (hiPSC-CMs) led to the early manifestation of hypertrophic cardiomyopathy and dilated cardiomyopathy phenotypic characteristics, including disrupted sarcomeric organization. Notably, THOC6 KO hiPSC-CMs demonstrated a significant decreased in COL1A2 and β-tubulin expression levels. THOC6 may influence cardiac development by regulating myocardial contractile proteins, primarily type I collagen, cardiac α actin 1 and β-tubulin.