Objective       To determine the role of neuronal precursor cell expressed developmentally down-regulated 4 (NEDD4) in myocardial adaptation to chronic hypoxia and investigate the underlying mechanisms. Methods ①A total of 32 children wit

h congenital heart diseases [cyanotic (n=18) or acyanotic cardiac defects (n=14)

]

admitted in our institute were recruited in this study. Their tissue samples of the right ventricular myocardium taken immediately after aortic clamping were employed to detect the distribution and protein expression of NEDD4 by immunohistochemical assay and Western blotting respectively. ② Cardiomyocytes were cultured under normoxic or hypoxic condition. The hypoxic cells were transfected with NEDD4 siRNA by Lipofectamine® RNAiMAX Reagent to knockdown the expression of NEDD4. The cells without transfection or transfected with non-targeting control siRNA served as control cells. Then the cells were cultured under normoxia (74% N

2

5% CO

2

and 21% O

2

) for 48 h followed by hypoxia (94% N

2

5% CO

2

and 1% O

2

) for 72 h

Western blotting and flow cytometry were used to detect the protein expression of NEDD4 and phospho-AMPK and the proportion of damaged myocardial cells respectively.       Results       ① Cyanotic children had significantly lower oxygen saturation than non-cyanotic group before surgery (P0.05). NEDD4 protein was mainly located in the cytoplasm. And its protein level was obviously lower in the cyanotic children than the acyanotic ones (0.42±0.06 vs 0.72±0.07

P0.05). ② The proportion of dead cardiomyocytes was larger in the cells under hypoxia than those under normoxic culture (P0.05). But NEDD4 siRNA transfection inhibited the cell death induced by hypoxia (P0.05). Western blotting showed that the level of p-AMPK was significantly higher in the transfected cells than in the blank cells (0.88±0.04 vs 0.21±0.01

P0.05).       Conclusion       NEDD4 may participate in myocardial adaptation to chronic hypoxia by regulating the activation of AMPK.