摘要目的 探讨自噬对脓毒症小鼠中性粒细胞程序性死亡配体-1(PD-L1)表达的影响及其作用机制.方法 ① 体内实验:将6～8周龄雄性C57BL/6小鼠按随机数字表法分为假手术组(Sham组)、盲肠结扎穿孔术(CLP)组和雷帕霉素(RAP)+CLP组,每组10只.采用CLP模拟脓毒症模型;Sham组不结扎盲肠及穿孔,其他操作同CLP组.RAP+CLP组小鼠于制模前7 d腹腔注射自噬激动剂RAP 4 mg·kg-1·d-1 ;Sham组和CLP组不予任何处理.各组于术后4 d留取肺脏、肝脏、脾脏和胰腺组织进行免疫组化染色,光镜下观察各器官中性粒细胞的浸润情况;通过免疫荧光染色检测术后1 d、4 d小鼠肺脏中性粒细胞免疫抑制分子PD-L1和自噬标志蛋白微管相关蛋白1轻链3 (LC3)的表达.② 体外实验:提取和重悬小鼠骨髓中性粒细胞至1×1010/L,分为空白对照组(不给予任何处理)、RAP对照组(RAP 100 μmol/L)、自噬抑制剂Bafilomycin A1(Baf)对照组(Baf 10 μmol/L)、脂多糖(LPS)刺激组(LPS 1 mg/L)、RAP+LPS组、Baf+LPS组,后两组分别于LPS刺激前30 min给予100 μmol/L RAP或10 μmol/L Baf预处理.于LPS刺激0、4、12 h用反转录-聚合酶链反应(RT-PCR)检测中性粒细胞PD-L1 mRNA表达;采用蛋白质免疫印迹试验(Western Blot)检测PD-L1、LC3和自噬相关蛋白p62的蛋白表达.结果 ① 体内实验:免疫组化显示CLP术后4 d小鼠肺脏、肝脏、脾脏和胰腺组织中均有大量中性粒细胞浸润;免疫荧光显示,随CLP术后时间延长,小鼠肺脏中性粒细胞LC3阳性表达呈降低趋势,而PD-L1的表达大幅度升高;给予RAP预处理可以促进CLP小鼠LC3的表达,同时抑制PD-L1的表达.② 体外实验:在mRNA水平上,随LPS刺激时间延长,小鼠中性粒细胞PD-L1 mRNA表达均呈持续升高趋势,12 h达峰值,且明显高于空白对照组(2-ΔΔCT :72.2±10.0比13.0±0.8,P＜0.01);给予自噬抑制剂RAP预处理后,PD-L1的mRNA表达较LPS刺激组明显降低(2-ΔΔCT :12 h为47.4±7.3比72.2±10.0,P＜0.01);而给予自噬激动剂Baf预处理后,PD-L1的mRNA表达则较LPS刺激组明显升高(2-ΔΔCT :12 h为109.1±7.4比72.2±10.0,P＜0.01).在蛋白水平上,LPS刺激中性粒细胞后4 h,PD-L1、LC3及p62阳性表达较空白对照组显著增加,且PD-L1和p62随时间延长呈持续增加趋势;当使用RAP预处理后,PD-L1和p62阳性表达明显减少,而LC3表达进一步增加,说明自噬水平增加,自噬流通畅;与此相反,当使用Baf预处理后,PD-L1、LC3及p62表达均显著增加,说明自噬体与溶酶体的结合受阻,自噬流不畅.结论 脓毒症时中性粒细胞在各个器官的浸润增加,肺脏中性粒细胞PD-L1表达明显增加,而自噬水平有所下降;LPS刺激下的中性粒细胞PD-L1表达可以被自噬激动剂所抑制,被自噬抑制剂所促进;PD-L1对脓毒症具有负向调控作用,可以通过靶向促进自噬来抑制脓毒症时PD-L1的表达,从而改善脓毒症.

abstractsObjective To investigate the effect and mechanism of autophagy on the expression of neutrophil programmed death ligand-1 (PD-L1) in mice with sepsis. Methods ① In vivo experiment: male C57BL/6 mice aged 6-8 weeks were divided into sham operation group (Sham group), cecum ligation and perforation (CLP) group, and rapamycin (RAP)+CLP group by random number table with 10 mice in each group. The sepsis model was reproduced by CLP, and the cecum and perforation were not ligated in Sham group, and other operations were the same as CLP group. The mice in RAP+CLP group were intraperitoneally injected with autophagy agonist RAP 4 mg·kg-1·d-1 7 days before modeling, while the mice in Sham group and CLP group were not treated. Lung, liver, spleen and pancreas tissues were harvested for immunohistochemical staining 4 days after the operation, and the infiltration of neutrophils in various organs was observed under light microscope. Meanwhile, the expressions of immunosuppressive molecule PD-L1 and autophagy marker microtubule-associated protein 1 light chain 3 (LC3) in lung neutrophils were determined by immunofluorescence staining. ② In vitro experiment: mouse bone marrow neutrophils were extracted and re-suspended to 1×1010/L, and they were divided into blank control group (without any treatment), RAP control group (RAP 100 μmol/L), autophagy inhibitor Bafilomycin A1 (Baf) control group (Baf 10 μmol/L), lipopolysaccharide (LPS) stimulation group (LPS 1 mg /L), RAP+LPS group, and Baf+LPS group. The latter two groups were pretreated with 100 μmol/L RAP or 10 μmol/L Baf 30 minutes before LPS stimulation, respectively. The expression of PD-L1 mRNA of neutrophils was determined by reverse transcription-polymerase chain reaction (RT-PCR) at 0, 4, 12 hours after LPS stimulation. At the same time, the expressions of PD-L1, LC3 and p62 at the protein level were determined by Western Blot. Results① In vivo experiment: according to immunohistochemical experiments, a large amount of infiltration of neutrophils in lung, liver, spleen and pancreas was found at 4 hours after CLP. In the immunofluorescence, with the time extension after CLP, the positive expression of LC3 in the lung tissue showed a decreased tendency, and PD-L1 expression was significantly increased. RAP pretreatment could promote the expression of LC3 and reduce the expression of PD-L1 in CLP mice.② In vitro experiment: in terms of mRNA levels, with the extension of LPS stimulation time, the expression of PD-L1 mRNA in mouse neutrophils was increased continuously, and peaked at 12 hours, it was significantly higher than that in the blank control group (2-ΔΔCT: 72.2±10.0 vs. 13.0±0.8, P < 0.01). Compared with LPS stimulation group, the expression of PD-L1 mRNA in RAP+LPS group was significantly down-regulated [12-hour PD-L1 mRNA (2-ΔΔCT): 47.4±7.3 vs. 72.2±10.0, P < 0.01]. In Baf+LPS group, PD-L1 mRNA expression was significantly up-regulated as compared with that in LPS stimulation group [12-hour PD-L1 mRNA (2-ΔΔCT): 109.1±7.4 vs. 72.2±10.0, P < 0.01]. At the protein levels, at 4 hours after LPS stimulation, the positive expressions of PD-L1, LC3 and p62 were increased significantly as compared with those in the blank control group, and PD-L1 and p62 were increased continuously with time. Compared with the LPS stimulation group, the expressions of PD-L1 and p62 in the RAP+LPS group were significantly down-regulated, while the expression of LC3 was continually increased, indicating that the level of autophagy was increased, and autophagy was circulated smoothly. On the contrary, the expressions of PD-L1, LC3 and p62 in the Baf+LPS group were significantly up-regulated, indicating that the binding of autophagy and lysosome was blocked, and autophagy was not smooth. Conclusions In sepsis, the infiltration of neutrophils in all organs increased, and the expression of PD-L1 of neutrophils in lungs was increased significantly, while the expression level of autophagy was decreased. The expression of PD-L1 stimulated by LPS can be inhibited by autophagy agonists, and promoted by autophagy inhibitors. PD-L1 has a negative regulatory effect on sepsis. It can reduce the expression of PD-L1 molecule in sepsis by targeting autophagy, so as to improve sepsis.