ABSTRACT
Objective To evaluate the role of 1-phosphatidylinositol 3-kinase/serine threonine kinase (PI3K/Akt) signaling pathway in carbon monoxide (CO)-induced up-regulation of mitochondrial fusion proteins in endotoxin-challenged alveolar epithelial cells of rats.Methods The rat alveolar epithelial cells were cultured in a 5％ CO2 cell culture incubator at 37 ℃ with F12K complete medium containing 10％ fetal bovine serum and 1％ green chain double antibody,and divided into 10 groups (n=5 each) according to the random number table method:control group (C group),endotoxin group (L group),lipopolysaccharide (LPS) plus exogenous CO-releasing agent CO-releasing-molecule-2 (CORM-2) group (L+CO group),LPS plus PI3K inhibitor LY294002 group (L+LY group),LPS plus CORM-2 plus LY294002 group (L+ CO+LY group),LPS plus inactive CO releasing agent iCORM-2 group (L+iCO group),LPS plus dimethyl sulfoxide (DMSO) group (L+D group),CORM-2 group (CO group),LY294002 group (LY group) and CORM-2 plus LY294002 group (CO+LY group).LPS 10 μg/ml was added to the culture medium in group L.CORM-2 100 μmol/L was added to the culture medium and 1 h later 10 μg/ml LPS was added in L+CO group.LY294002 25 μmol/L was added to the medium,and 1 h later LPS 10 μg/ml was added in L+LY group.In L+CO+LY group,25 μmol/L LY294002 was added to the culture medium,CORM-2 100 μmol/L was added 1 h later,and then LPS 10 μg/ml was added 1 h later.iCORM 100 μmol/L was added to the culture medium and 1 h later LPS 10 μg/ml was added in L+iCO group.In L+D group,the equal concentration of DMSO was added to the culture medium and 1 h later LPS 1 μg/ml was added.CORM-2 100 μmol/L was added to the culture medium in CO group.LY294002 25 μmol/L was added to culture medium in LY group.LY294002 25 μmol/L was added to the culture medium,and 1 h later CORM-2 100 μmol/L was added in CO+LY group.Cells were harvested after 24 h of incubation for measurement of the malondialdehyde (MDA) content,superoxide dismutase (SOD) activity and expression of heme oxygenase-1 (HO-1),phosphorylated Akt (p-Akt),mitochondrial fusion proteins mitofusion 1 (Mfn1),Mfn2 and optic atrophy 1 (OPA1) by Western blot.Results Compared with group C,the MDA content was significantly increased and SOD activity was decreased in L,L+CO,L+LY,L+CO+LY,L+iCO,L+D groups,and the expression of HO-1,Mfn1,Mfn2,OPA1 protein and p-Akt was significantly up-regulated in group L (P＜0.05).Compared with group L,MDA content was significantly decreased and SOD activity was increased in group L+CO,MDA content was significantly increased and SOD activity was decreased in group L+LY,the expression of HO-1,Mfn1,Mfn2,OPA1 protein and p-Akt was significantly up-regulated in group L+ CO,and the expression of HO-1,Mfn1,Mfn2,OPA1 protein and p-Akt was significantly down-regulated in group L+LY (P＜0.05).Compared with group L+CO,the MDA content was significantly increased,SOD activity was decreased,and the expression of HO-1,Mfn1,Mfn2,OPA1 and p-Akt was down-regulated in group L+CO+LY (P＜0.05).Conclusion The mechanism by which CO up-regulates the expression of mitochondrial fusion proteins in endotoxin-challenged alveolar epithelial cells is related to activating PI3K/Akt signaling pathway in rats.