The splicing factor hnRNPL demonstrates conserved myocardial regulation across species and is altered in heart failure

Heart failure (HF) is highly prevalent. Mechanisms underlying HF remain incompletely understood. Splicing factors (SF), which control pre‐mRNA alternative splicing, regulate cardiac structure and function. This study investigated regulation of the splicing factor heterogeneous nuclear ribonucleoprotein‐L (hnRNPL) in the failing heart. hnRNPL protein increased in left ventricular tissue from mice with transaortic constriction‐induced HF and from HF patients. In left ventricular tissue, hnRNPL was detected predominantly in nuclei. Knockdown of the hnRNPL homolog Smooth in Drosophila induced cardiomyopathy. Computational analysis of predicted mouse and human hnRNPL binding sites suggested hnRNPL‐mediated alternative splicing of tropomyosin, which was confirmed in C2C12 myoblasts. These findings identify hnRNPL as a sensor of cardiac dysfunction and suggest that disturbances of hnRNPL affect alternative splicing in HF. Expression of the splicing factor heterogeneous nuclear ribonucleoprotein L (hnRNPL) increases in the failing left ventricle across mammalian species. Deletion of hnRNPL homolog smooth causes cardiac dysfunction in Drosophila. hnRNPL knockdown disrupts normal splicing of tropomyosin, a sequence known to be important in cardiac function. Thus, hnRNPL is altered in the failing heart and hnRNPL‐mediated RNA splicing opposes cardiac dysfunction.