Pharmacological or genetic inhibition of LTCC promotes cardiomyocyte proliferation through inhibition of calcineurin activity

Cardiomyocytes (CMs) lost during ischemic cardiac injury cannot be replaced due to their limited proliferative capacity. Ca2+ is an important signal transducer that regulates key cellular processes, but its role in regulating CM proliferation is incompletely understood. A drug screen targeting proteins involved in CM Ca2+ cycling in human embryonic stem cell-derived cardiac organoids (hCOs) revealed that only the inhibition of L-Type Calcium Channel (LTCC) using nifedipine induced the CM cell cycle. Overexpression of Ras-related associated with Diabetes (RRAD), an endogenous inhibitor of LTCC, induced CM cell cycle activity in vitro, in human cardiac slices, and in vivo. Mechanistically, LTCC inhibition by RRAD or nifedipine induced CM cell cycle by modulating calcineurin activity and Hoxb13 nuclear translocation. Moreover, ectopic expression of RRAD/CDK4/CCND in combination induced CM proliferation in vitro and in vivo, improved cardiac function and reduced scar size post-myocardial infarction. Together, these findings represent a robust pathway for new Ca2+ signaling-based cardiac regenerative strategies. Overall design: To gain insights into the mechanism of action of LTCC-induced cardiac proliferation in hCOs, bulk RNA sequencing was performed after 8 h of treatment with nifedipine or DMSO control