Objective      To determine the changes of mitochondr

ial dynamics under hypoxia and the potential role of Sirt1 in this condition.        Methods      Twenty-nine children diagnosed with congenital heart diseases were recruited from the institute of cardiovascular surgery of Xinqiao hospital since 2014

and included 14 acyanotic cases and 15 cyanotic cases. The myocardial tissues of right ventricular outflow tract were taken for further analysis. Western blot analysis was employed to detect the expression levels of mitochondrial pro-fission proteins Drp1 and Fis1 in the myocardial tissues. H9c2 cells were cultured in a hypoxic incubator (94% N

2

5% CO

2

1% O

2

) for 0

2

4

8 and 12 h respectively

  and Drp1 and Fis1 expression levels were detected by Western blotting. Mitochondria-targeted red fluorescent protein (mt-RFP)-expressing plasmid together with blank vector

Sirt1 overexpression plasmid or Sh-Sirt1 interference plasmid co-transfected H9c2 cells

and then the cells were cultured in a normoxic or hypoxic incubator. Confocal microscopy was used to visualize mitochondrial morphology. Adenovirus-Sirt1 or lentivirus-Sh-Sirt1 was added to H9c2 cells to activate or inhibit Sirt1 expression

and Drp1 and Fis1 expressions were measured by Western blotting after 12 h hypoxia treatment. LDH assay was employed to assess cytotoxicity after the H9c2 cells were transfected with the empty vector

Sirt1 overexpression plasmid or Sh-Sirt1 interference plasmid.        Results      Compared with the acyanotic group

Drp1 and Fis1 expression levels were significantly increased in the cyanotic group (Drp1: 0.47±0.11 vs 0.76±0.12

Fis1: 0.53±0.02 vs 0.83±0.03

P0.05). In H9c2 cells

Drp1 and Fis1 were activated after hypoxia exposure in a time-dependent manner. Confocal images of H9c2 cells expressing mt-RFP showed that Sirt1 overexpression significantly suppressed hypoxia-induced mitochondrial fission whereas Sirt1 interference promoted mitochondrial fission (P0.05). Compared with the control group

the expression levels of Drp1 and Fis1 were de

creased after Sirt1 overexpression

and prominently increased after Sirt1 interference (Drp1: 0.47±0.02 vs 0.36±0.02 vs 0.78±0.04

Fis1: 0.64±0.02 vs 0.42±0.02 vs 0.80±0.04

P0.05). Sirt1 overexpression decreased the mortality rates of H9c2 cells challenged by hypoxia (P0.05).        Conclusion      Sirt1 may be involved in hypoxic adaptation through regulating the expression of Drp1 and Fis1 in the cardiac myocytes.