BACKGROUND - In mammalian, regenerative therapy after myocardial infarction (MI) is hampered by the limited regenerative capacity of adult heart, while a transient regenerative capacity is maintained in the neonatal heart. Systemic phosphorylation signaling analysis on ischemic neonatal myocardium might be helpful to identify key pathways involved in heart regeneration. We aimed to define kinase-substrate network in ischemic neonatal myocardium and identify key pathways involved in heart regeneration post ischemic insult.

METHODS - Quantitative phosphoproteomics profiling was performed on infarct border zone of neonatal myocardium, and kinase-substrate network analysis revealed 11 kinases with enriched substrates and upregulated phosphorylation levels including CHK1 kinase. The effect of CHK1 on cardiac regeneration was tested on ICR-CD1 neonatal and adult mice underwent apical resection or MI.

RESULTS - In vitro, CHK1 overexpression promoted, while CHK1 knockdown blunted cardiomyocyte (CM) proliferation. In vivo, inhibition of CHK1 hindered myocardial regeneration on resection border zone in neonatal mice. In adult MI mice, CHK1 overexpression on infarct border zone upregulated mTORC1/P70S6K pathway, promoted CM proliferation and improved cardiac function. Inhibiting mTOR activity by rapamycin blunted the neonatal CM proliferation induced by CHK1 overexpression in vitro.

CONCLUSIONS - Our study indicates that phosphoproteome of neonatal regenerative myocardium could help identify important signaling pathways involved in myocardial regeneration. CHK1 is found to be a key signaling responsible for neonatal regeneration. Myocardial overexpression of CHK1 could improve cardiac regeneration in adult hearts through activating mTORC1/P70S6K pathway, CHK1 might thus serve as a potential novel target in myocardial repair post MI.