Role of the PI3K‑mTOR autophagy pathway in nerve damage in rats with intermittent hypoxia‑aggravated whole brain ischemia

Abstract

The present study aimed to compare the expression of phosphatidylinositol 3-kinase (PI3-K), mammalian target of rapamycin (mTOR) and Beclin-1 between the hippocampi of normal rats and intermittent ischemic rats following whole brain ischemia/reperfusion (I/R), and investigate the role of the PI3K-mTOR autophagy pathway in rat nerve damage following intermittent hypoxia (IH)-aggravated whole brain ischemia. A total of 80 male Wistar rats were divided by random number table into a sham operation group (SO group; 20 rats), pure cerebral ischemia/reperfusion group (I/R group; 20 rats), intermittent hypoxia for 7 days-I/R group (IH7+I/R group; 20 rats) and intermittent hypoxia for 21 days-IR group (IH21+I/R group; 20 rats). Prior to model establishment, the rats in the IH7+I/R group and IH21+I/R group underwent intermittent hypoxia for 7 and 21 days, respectively. The optimized Pulsinelli 4-vessel occlusion method was used to prepare the I/R model. H&E staining and transmission electron microscopy were performed to observe the morphological changes of nerve cells in the hippocampus. Immunohistochemical and reverse transcription-quantitative polymerase chain reaction (RT-qPCR) analyses were performed to detect the expression levels of PI3-K, mTOR and Beclin-1 in the hippocampal brain tissues of the rats. A Morris water maze test was used to assess rat learning and memory. The results showed that, compared with the SO group, the rats in the I/R group exhibited structural damage in neurons (shown by H&E staining), a reduced number of viable nerve cells, and decreased learning and memory ability at each time point. The results of the immunohistochemical analysis showed that the numbers of PI3-K, mTOR and Beclin-1 immunopositive cells were increased (P<0.05). The RT-qPCR analysis showed increased expression levels of PI3-K, mTOR and Beclin-1 (P<0.05). Compared with the I/R group, the rats in the IH-I/R groups exhibited aggravated structural damage in neurons, shown by H&E staining and electron microscopy. The number of viable nerve cells was decreased, and the rats exhibited decreased learning ability and memory. The immunohistochemical analysis revealed that the numbers of PI3-K, mTOR and Beclin-1 immunopositive cells were increased (P<0.05). The RT-qPCR analysis showed increased expression levels of PI3-K, mTOR and Beclin-1 (P<0.05). The above changes were more marked in the IH21+I/R group (P<0.05). Taken together, IH was shown to aggravate nerve damage following whole brain I/R. The underlying mechanism was associated with activation of the PI3K-mTOR-autophagy pathway and increased loss of nerve cells.