Cardiac hypertrophy is an abnormal enlargement of heart muscle. It frequently results in congestive heart failure, which is a leading cause of human death. Previous studies demonstrated that the nitric oxide (NO), cyclic GMP (cGMP), and protein kinase G (PKG) signaling pathway can inhibit cardiac hypertrophy and thus improve cardiac function. However, the underlying mechanisms are not fully understood. Here, based on the human embryonic stem cell-derived cardiomyocyte (hESC-CM) model system, we showed that Orai1, the pore-forming subunit of store-operated Ca 21 entry (SOCE), is the downstream effector of PKG. Treatment of hESC-CMs with an a-adrenoceptor agonist phenylephrine (PE) caused a marked hypertrophy, which was accompanied by an upregulation of Orai1. Moreover, suppression of Orai1 expression/activity using Orai1-siRNAs or a dominant-negative construct Orai1 G98A inhibited the hypertrophy, suggesting that Orai1-mediated SOCE is indispensable for the PE-induced hypertrophy of hESC-CMs. In addition, the hypertrophy was inhibited by NO and cGMP via activating PKG. Importantly, substitution of Ala for Ser 34 in Orai1 abolished the antihypertrophic effects of NO, cGMP, and PKG. Furthermore, PKG could directly phosphorylate Orai1 at Ser 34 and thus prevent Orai1-mediated SOCE. Together, we conclude that NO, cGMP, and PKG inhibit the hypertrophy of hESC-CMs via PKG-mediated phosphorylation on Orai1-Ser-34. These results provide novel mechanistic insights into the action of cGMP-PKG-related antihypertrophic agents, such as NO donors and sildenafil. STEM CELLS 2015;33:2973-2984
SIGNIFICANCE STATEMENTCardiac hypertrophy is an abnormal enlargement of cardiomyocytes. It contributes to congestive heart failure. Nitric oxide donors and cGMP-phosphodiesterase inhibitors have been used in clinical trials to treat cardiac hypertrophy. However, the underlying mechanisms of these agents are not fully understood. Here, with the use of human embryonic stem cell-derived cardiomyocytes as the model, we uncovered a novel mechanism underlying the inhibitory effect of these agents on cardiac hypertrophy. We found that nitric oxide and cGMP, via protein kinase G-mediated phosphorylation on Orai1 proteins, inhibit the cardiomyocyte hypertrophy. This study provides novel mechanistic insights into the action of nitric oxide-related anti-hypertrophic agents.