ABSTRACT
Objective:To evaluate the role of phosphatidylinositol 3-kinase/protein kinase B (PI3K/Akt) signaling pathway in reduction of acute lung injury (ALI) by bone marrow mesenchymal stem cells (MSCs)-conditioned medium in rats.Methods:Thirty-two healthy male Sprague-Dawley rats, aged 6-8 weeks, weighing 200-250 g, were divided into 4 groups ( n=8 each) according to the random number table method: control group (group C), group ALI, ALI + bone marrow MSCs-conditioned medium group (group M), and ALI + bone marrow MSCs-conditioned medium + LY294002 group (group L). A rat model of ALI was developed by endotracheal inhalation of aerosolized lipopolysaccharide (LPS) 5 mg/kg in anesthetized animals in group ALI, group M and group L. At 1 h after LPS administration, serum-free DMEM medium 1 ml was intravenously injected in group C and group ALI, bone marrow MSCs-conditioned medium 1 ml was intravenously injected in group M, PI3K inhibitor LY294002 30 mg/kg was intraperitoneally injected at 2 h before the model was developed, and bone marrow MSCs-conditioned medium 1 ml was intravenously injected at 1 h after the model was developed in group L. The blood samples were taken from the heart at 24 h after LPS administration, and serum was isolated for determination of the serum levels of tumor necrosis factor-alpha (TNF-α) and interleukin-6 (IL-6) (by enzyme-linked immunosorbent assay). Then the rats were sacrificed and lung tissues were obtained for determination of the lung wet/dry weight ratio (W/D ratio), expression of Akt and phosphorylated Akt (p-Akt) (by Western blot) and for microscopic examination of the pathological changes which were scored.The p-Akt/Akt ratio was calculated. Results:Compared with group C, the W/D ratio, lung injury score and serum levels of TNF-α and IL-6 were significantly increased, the expression of p-Akt in lung tissues was down-regulated, the ratio of p-Akt/Akt was decreased ( P<0.05), and pathological changes were found in lung tissues in group ALI.Compared with group ALI, the W/D ratio, lung injury score and serum levels of TNF-α and IL-6 were significantly decreased, the expression of p-Akt in lung tissues was up-regulated, the ratio of p-Akt/Akt was increased ( P<0.05), and pathological changes were significantly attenuated in group M, and no significant change was found in the parameters mentioned above in group L ( P>0.05). Compared with group M, the W/D ratio, lung injury score and serum levels of TNF-α and IL-6 were significantly increased, the expression of p-Akt in lung tissues was down-regulated, the ratio of p-Akt/Akt was decreased ( P<0.05), and pathological changes were accentuated in group L. There were no significant differences in the expression of Akt in lung tissues between the four groups ( P>0.05). Conclusions:PI3K/Akt signaling pathway is involved in reduction of ALI by bone marrow MSCs-conditioned medium in rats.