摘要目的:探讨微小RNA-21-5p（miR-21-5p）是否通过激活磷脂酰肌醇3激酶/丝氨酸-苏氨酸蛋白激酶（PI3K/Akt）信号通路调控Ⅱ型肺泡上皮细胞（AECⅡ）凋亡减轻高氧性急性肺损伤（HALI）。方法:将72只雄性SD大鼠按随机数字表法分为常氧对照组、HALI组、PI3K/Akt信号通路抑制剂LY294002+HALI组（LY+HALI组）、miR-21-5p过表达+LY294002+HALI组（miR-21-5p+LY+HALI组）、miR-21-5p过表达+HALI组（miR-21-5p+HALI组）及二甲基亚砜（DMSO）+ HALI组，每组12只。用95%氧气制备HALI动物模型；常氧对照组动物在常氧状态下正常饲养。制模前3周经气管导管滴入200 μL滴度（1×10 12 TU/mL）的miR-21-5p腺相关病毒载体AAV6-miR-21-5p转染肺组织；DMSO及LY294002均以0.3 mg/kg于制模前1 h经尾静脉给药。制模后48 h，取颈动脉血检测氧合指数（OI）及呼吸指数（RI），采用实时荧光定量反转录-聚合酶链反应（RT-PCR）检测miR-21-5p表达；取肺组织，采用酶联免疫吸附试验（ELISA）检测炎症因子〔肿瘤坏死因子-α（TNF-α）和白细胞介素（IL-6、IL-1β）〕水平，测定肺湿/干质量（W/D）比值，苏木素-伊红（HE）染色后光镜下观察肺组织病理学改变并进行病理学评分。每组取6只大鼠提纯AECⅡ细胞，应用流式细胞仪检测凋亡率，采用蛋白质免疫印迹试验（Western blotting）检测磷酸酶及张力蛋白同源基因（PTEN）和PI3K/Akt信号通路蛋白的表达水平。 结果:与常氧对照组比较，高氧暴露后可见肺泡间隔增厚，大量炎症细胞浸润，RI、炎症因子、肺W/D比值、病理学评分，以及AECⅡ细胞早期凋亡率、PTEN蛋白表达和Akt磷酸化水平均升高，而OI及miR-21-5p表达降低，说明模型制备成功。LY294002预处理后，可进一步加重HALI大鼠肺组织病理损伤，RI、炎症因子、肺W/D比值均较HALI组进一步升高，OI进一步降低，同时可促进AECⅡ细胞凋亡，进一步上调PTEN蛋白表达，并抑制Akt磷酸化；而miR-21-5p预处理可负向调控PTEN，激活PI3K/Akt信号通路，抑制AECⅡ细胞凋亡，减轻HALI，与LY+HALI组比较，炎症因子水平降低〔TNF-α（μg/L）：100.33±3.48比116.55±2.53，IL-6（ng/L）：141.06±3.70比161.31±3.59，IL-1β（μg/L）：90.82±3.69比112.23±2.87，均 P<0.05〕，RI、肺损伤病理学评分、肺W/D比值及AECⅡ细胞早期凋亡率明显降低〔RI：0.81±0.02比1.05±0.07，病理学评分（分）：0.304±0.008比0.359±0.007，肺W/D比值：5.29±0.03比5.52±0.08，细胞凋亡率：（27.20±2.34）%比（34.17±1.49）%，均 P<0.05〕，OI、miR-21-5p表达均明显升高〔OI（mmHg，1 mmHg≈0.133 kPa）：266.71±2.75比230.12±4.04，miR-21-5p（2 -ΔΔCt）：2.21±0.13比0.33±0.03，均 P<0.05〕，且AECⅡ细胞PTEN蛋白表达显著降低（PTEN/GAPDH：0.50±0.06比0.93±0.06， P<0.05），Akt磷酸化明显增加〔磷酸化Akt（p-Akt）蛋白（p-Akt/GAPDH）：0.86±0.05比0.56±0.06， P<0.05〕。 结论:miR-21-5p可能通过负向调控PTEN激活PI3K/Akt信号通路，从而抑制AECⅡ细胞凋亡，减轻HALI。

abstractsObjective:To investigate whether microRNA-21-5p (miR-21-5p) alleviates hyperoxia-induced acute lung injury (HALI) through activating the phosphatidylinositol 3 kinase/serine-threonine protein kinase (PI3K/Akt) signaling pathway by regulating apoptosis of type Ⅱ alveolar epithelial cell (AECⅡ).Methods:Seventy-two male Sprague-Dawley (SD) rats were divided into normozone-controlled group, HALI group, PI3K/Akt signaling pathway inhibitor LY294002+HALI group (LY+HALI group), miR-21-5p overexpression+LY294002+HALI group (miR-21-5p+LY+HALI group), miR-21-5p overexpression+HALI group (miR-21-5p+HALI group), and dimethyl sulfoxide (DMSO)+HALI group by random number table method with 12 rats in each group. Animal models of HALI were prepared using 95% concentrations of oxygen. The animals in the normozone-controlled group were fed normally under normoxia. Transfection of lung tissue by miR-21-5p adeno-associated viral vector AAV6-miR-21-5p was performed by instillation of 200 μL titer (1×10 12 TU/mL) through a tracheal catheter 3 weeks prior to modeling. DMSO and LY294002 were administered via the tail vein at 0.3 mg/kg 1 hour before modeling. After 48 hours of modeling, carotid artery blood was collected to detect oxygenation index (OI) and respiratory index (RI), and real-time fluorescence quantitative reverse transcription-polymerase chain reaction (RT-PCR) was used to detect miR-21-5p expression. Lung tissue was collected, and the levels of inflammatory factors including tumor necrosis factor-α (TNF-α) and interleukins (IL-6, IL-1β) were measured by enzyme-linked immunosorbent assay (ELISA), and the ratio of pulmonary wet/dry weight (W/D) was determined, and the pathological changes of lung histopathology were observed under the light microscopy after hematoxylin-eosin (HE) staining. Each group was purified AECⅡ cells from 6 rats, the apoptosis rate was detected by flow cytometry, and the expression levels of phosphatase and tensin homologous gene (PTEN), and proteins from the PI3K/Akt signaling pathway were detected by Western blotting. Results:Compared with the normozone-controlled group, alveolar septal thickening and massive inflammatory cell infiltration were found after hyperoxia exposure, RI, inflammatory factors, lung W/D ratio, pathological score, AECⅡ cells early apoptosis rate, PTEN protein expression and phosphorylation level of Akt were increased, while OI and miR-21-5p expression were decreased, indicating the successful preparation of the model. After pretreatment, LY294002 could aggravate the pathological injury of lung tissue in HALI rats, RI, inflammatory factors and lung W/D ratio were further increased, and OI was further reduced compared with HALI group. At the same time, it could promote the AECⅡ cell apoptosis, further up-regulate the expression of PTEN, and reduce the phosphorylation of Akt. However, miR-21-5p pretreatment could negatively regulate PTEN, activate PI3K/Akt signal pathway, inhibit AECⅡ cell apoptosis, and reduce HALI, which was shown by the decreased level of inflammatory factors in miR-21-5p+LY+HALI group compared with LY+HALI group [TNF-α (μg/L): 100.33±3.48 vs. 116.55±2.53, IL-6 (ng/L): 141.06±3.70 vs. 161.31±3.59, IL-1β (μg/L): 90.82±3.69 vs. 112.23±2.87, all P < 0.05], RI, lung injury pathology score, lung W/D ratio, and AECⅡ cell early apoptosis rate were significantly decreased [RI: 0.81±0.02 vs. 1.05±0.07, pathology score: 0.304±0.008 vs. 0.359±0.007, lung W/D ratio: 5.29±0.03 vs. 5.52±0.08, apoptosis rate: (27.20±2.34)% vs. (34.17±1.49)%, all P < 0.05], OI and expressions of miR-21-5p were significantly increased [OI (mmHg, 1 mmHg≈0.133 kPa): 266.71±2.75 vs. 230.12±4.04, miR-21-5p (2 -ΔΔCt): 2.21±0.13 vs. 0.33±0.03, both P < 0.05], and PTEN protein expression in AECⅡ cell was significantly reduced (PTEN/GAPDH: 0.50±0.06 vs. 0.93±0.06, P < 0.05), and phosphorylation level of Akt was significantly increased [phosphorylated Akt (p-Akt) protein (p-Akt/GAPDH): 0.86±0.05 vs. 0.56±0.06, P < 0.05]. Conclusion:miR-21-5p attenuates HALI by inhibiting AECⅡ cell apoptosis, possibly through negative regulation of PTEN to activate PI3K/Akt signaling pathway.