Acinetobacter baumannii capsular promotes autophagy and apoptosis of murine macrophages by inhibiting PI3K/Akt/mTOR signaling pathway
HAN Chang-ming1,2, DAI Xiao-yue1, DUAN Qian-mei2, QIU Sheng-gang2, SHI Li-xin2,XIA Wen1, ZOU Zhi-qing1, Dinsh Kumar K1, WU Liang1, YIN Qing3, XU Hua-xi 1
(1. School of Medicine, Jiangsu University, Zhenjiang Jiangsu 212013; 2. Department of Neurology, Jiangdu People′s Hospital of Yangzhou, Yangzhou Jiangsu 225200; 3. Department of Clinical Laboratory, Affiliated Hospital of Jiangsu University, Zhenjiang Jiangsu 212001, China)
Abstract：[Abstract\]Objective: To study the capability of Acinetobacter baumannii with different thickness capsules induce Raw 264.7 cell autophagy and apoptosis, and its potential mechanisms. Methods: A baumannii was isolated from the sputum of patients with pneumonia. The bacterial capsule was stained by Congo red staining, and the bacterial strains with significantly different capsule thickness were selected for subsequent study. Raw 264.7 cells were infected with thick capsular strain (AbH strain) or thin capsular strain (AbB strain), and the cells were harvested at 1 h, 3 h and 6 h after infection. The expression of autophagyrelated proteins LC3 and Beclin1, as well as the phosphorylation levels of PI3K, Akt and mTOR were determined by Western blotting. Flow cytometry was used to determine the reactive oxygen species(ROS) production and apoptosis rate. Results: After A. baumannii was stained with Congo red, the cells were shown purpleblack, the background was red, and the capsule was not stained. The bacterial capsule thickness was clearly judged. Two strains with significant differences in capsular thickness were grouped, namely thick capsular strain (AbH strain) and thin capsular strain (AbB strain). The expression of autophagyrelated protein Beclin1 of Raw 264.7 cells induced by AbH strain were significantly higher than that of AbB strain (P<0.05), and the apoptosis rate of Raw 264.7 cells induced by AbH strain was also significantly higher than that of AbB strain (P<0.05). Two strains of A. baumannii could induce a significant increase in the production of ROS in Raw 264.7 cells (P<0.05), and the ability of AbH strain to induce ROS production was significantly higher than that of AbB strains (P<0.05). After Raw 264.7 cells were infected with two strains respectively, the phosphorylation levels of PI3K, Akt and mTOR were significantly inhibited, and the inhibition increased when the time prolonged (P<0.05). Conclusion: A. baumannii could induce autophagy and apoptosis of Raw 264.7 cells, and the induction ability is positively correlated with bacterial capsule thickness. A. baumannii with thick capsule has a stronger ability to induce ROS production in Raw 264.7 cells and inhibit the activation of PI3K/Akt/mTOR signaling pathway, which ultimately enhances autophagy and apoptosis of Raw 264.7 cells.
