Screening in human cardiac organoids identifies a requirement for the mevalonate pathway in cardiomyocyte proliferation

Hudson JE

QIMR Berghofer Medical Research Institute.

Rationale: Induction of endogenous cardiomyocyte proliferation is a promising strategy for cardiac regeneration. Recent studies suggest that dual inhibition of glycogen synthase kinase 3 (GSK3) and serine/threonine protein kinase 4 (STK4 aka MST1) potently drives cardiomyocyte proliferation but the mechanisms of action are not defined. Objective: Decipher the effects of GSK3 and MST1 inhibition on cardiomyocyte proliferation and identify small molecules that can drive proliferation without detrimental effects on contractile force. Methods and Results: We coupled high throughput proteomics and functional screening of small molecules in single miniaturised human cardiac organoids (hCOs) to identify key pathways driving cardiomyocyte proliferation. We report that GSK3 inhibition activates a cell cycle network whereas MST1 inhibition drives the mevalonate pathway, with synergistic effects on proliferation. However, all GSK3 inhibitors tested also reduced contractile force in hCO. This was overcome by screening of 105 compounds, identifying a p38 inhibitor, which activated a cell cycle network without reducing force. The screen also identified a TGFBR inhibitor that induced the mevalonate pathway, increased protein prenylation and synergised with cell cycle activators to promote proliferation. Inhibition of the mevalonate pathway abolished the myocyte proliferative response and also reduced cell cycle activity in immature cardiomyocytes, consistent with downregulation of the mevalonate pathway during cardiac maturation in vivo. Conclusions: These findings implicate the mevalonate pathway in cardiomyocyte cell cycle control, which could have important ramifications for congenital heart disease and the development of regenerative therapeutic strategies for heart failure.