MicroRNA-21-5p regulates autophagy and apoptosis via the activation of the PI3K/AKT/mTOR signaling pathway and reducing H2O2-induced damage in primary AEC-II.

Objective: We examined whether miR-21-5p activates the PI3K/AKT/mTOR signaling pathway, thereby inhibiting autophagy and apoptosis induced by H2O2 in AEC II cells.

Background: MicroRNA and autophagy play crucial roles in important biological processes during hyperoxia-induced acute lung injury. Located on chromosome 17q23.1, miR-21-5p, as a critical component of the miRNAs family, significantly contributes to the regulation of cell growth, apoptosis, and autophagy. However, the underlying mechanism through which miR-21-5p suppresses H2O2-induced autophagy and apoptosis of primary AEC-II in vitro remains to be fully elucidated.

Methods: To investigate the regulatory role of miR-21-5p in autophagy, primary type II alveolar epithelial cells (AEC-II) were isolated from rat lung tissue and subjected to 0.5 mmol/L H2O2 in a cell culture environment to simulate hyperoxia-induced acute lung injury. Cell viability was detected by cell counting Kit 8. Reactive oxygen species and apoptosis were detected by flow cytometry. Autophagy levels in AEC-II were evaluated by autophagic double marker method. The expressions of apoptosis and autophagy related proteins were detected by Western blotting.

Results: We found that in the process of H2O2 injury of AEC-II, the level of autophagy flow was up-regulated and the expression of miR-21-5p was down-regulated. Overexpression of miR-21-5p can significantly reduce the level of autophagy flow, inhibit apoptosis, and activate the AKT/mTOR signaling pathway.We pretreated with rapamycin, an mTOR inhibitor, to block the biological effects of miR-21-5p. In addition, pretreatment with MHY1485, an mTOR activator, inhibited AEC-II autophagy flow levels and increased apoptosis.

Conclusions: In summary, miR-21-5p can inhibit H2O2-induced AEC-II apoptosis and autophagy flow, which is partially mediated by the AKT/mTOR signaling pathway.MiR-21-5p could be used as both a clinical biomarker and a promising molecular target in patients with HALI.