Effect of activating cannabinoid receptor 2 on sepsis-induced acute lung injury in mice: the role of autophagy

Objective To evaluate the effect of activating cannabinoid receptor 2(CB2R) on sepsis-induced acute lung injury and the role of autophagy in mice. Methods Twenty-four SPF male C57BL/6 mice, aged 8-10 weeks, weighing 20-25 g, were divided into 4 groups(n=6 each) using a random number table method: sham operation group(group Sham), sepsis group(group Sep), sepsis plus CB2R agonist HU308 group(group Sep+ HU308) and sepsis plus HU308 plus autophagy inhibitor 3-methyladenine group(group Sep+ HU308+ 3-MA). Sepsis was induced by cecal ligation and puncture in anesthetized mice. HU308 2.5 mg/kg was intraperitoneally injected at 15 min after surgery in Sep+ HU308 and Sep+ HU308+ 3-MA groups, and 15 min later 3-MA 10 mg/kg was intraperitoneally injected in group Sep+ HU308+ 3-MA. Lung tissues were obtained at 12 h after surgery and stained with haematoxylin and eosin for examination of the pathological changes which were scored and for determination of the expression of tumor-necrosis factor-alpha(TNF-α), interleukin-18(IL-18) and IL-1β mRNA(by real-time polymerase chain reaction), expression of autophagy-related protein 5(Atg5)(by immuno-histochemistry), and expression of microtubule-associated protein 1 light chain 3(LC3), Beclin-1 and p62(by Western blot). The ratio of LC3Ⅱ to LC3Ⅰ(LC3Ⅱ/LC3Ⅰ ratio) was calculated. Results Compared with group Sham, the expression of TNF-α, IL-18 and IL-1β mRNA was significantly up-regulated, and LC3Ⅱ/LC3Ⅰratio and lung injury score were increased in the other three groups, the expression of Beclin-1 was up-regulated, and the expression of p62 was down-regulated in group Sep and group Sep+ HU308, and the expression of p62 was significantly up-regulated in group Sep+ HU308+ 3-MA(P<0.05). Compared with group Sep, the expression of TNF-α, IL-18 and IL-1β mRNA was significantly down-regulated, the expression of Atg5 was up-regulated, and lung injury score was decreased in group Sep+ HU308 and group Sep+ HU308+ 3-MA, LC3Ⅱ/LC3Ⅰratio was increased, the expression of Beclin-1 was up-regulated, and the expression of p62 was down-regulated in group Sep+ HU308, and the expression of Beclin-1 was down-regulated, and the expression of p62 was up-regulated in group Sep+ HU308+ 3-MA(P<0.05). Compared with group Sep+ HU308, the expression of TNF-α, IL-18 and IL-1β mRNA was significantly up-regulated, the expression of Atg5 and Beclin-1 was down-regulated, LC3Ⅱ/LC3Ⅰratio was decreased, the expression of p62 was up-regulated, and lung injury scores were increased in group Sep+ HU308+ 3-MA(P<0.05). Conclusion Activating CB2R can alleviate acute lung injury in septic mice, and the mechanism may be partially related to enhancing autophagy and reducing inflammatory responses. Key words: Receptor, cannabinoid, CB2; Autophagy; Sepsis; Respiratory distress syndrome, adult