Mechanism of miR-26b up-regulated expression and neuron apoptosis in the hippocampus induced by intermittent hypoxia

Abstract

Objective To study the cognitive impairment in SD rats after intermittent hypoxia (IH), and explore the relation of miR-26b up-regulated expression and neuron apoptosis in the hippocampus of SD rats after IH. Methods Eight-week-old male SD rats (n=20, each weighing approximately 300±10 g) were randomly divided into normal oxygen control group, IH 1-week group, IH 2-weeks group and IH 4-weeks group (n=5). Rats in the later three groups were given IH for different times, and rats in the normal oxygen control group were given normal oxygen. The spatial learning and memory abilities were detected by Morris Water Maze (MWM) in the normal oxygen control group and IH 4-weeks group. The levels of apoptosis proteins Caspase3 and Bax and anti-apoptosis protein Bcl-2 in the hippocampus of 4 groups were detected by Western blotting. The miR-26b expression level in the 4 groups was detected by real time-PCR. Results (1) The results of MWM revealed that the mean escape latency in the IH 4-weeks group was significantly prolonged as compared with that in the normal oxygen control group (P<0.05); the time entering into the target quadrant in the IH 4-weeks group ([22.0±6.7] s) was significantly shorter than that in the normal oxygen control group ([39.8±8.8] s, P<0.05). (2) Western blotting indicated that up-regulated expressions of apoptosis proteins Bax and Casepase3 and down-regulated expression of anti-apoptosis protein Bcl-2 in the IH 1-week group, IH 2-weeks group and IH 4-weeks group were noted as compared with those in the control group, with significant differences (P<0.05); significantly higher apoptosis protein Bax and Casepase3 expressions in the IH 1-week group were noted as compared with those in the IH 2-weeks group and IH 4-weeks group (P<0.05), while significantly decreased Bcl-2 expression in the IH 1-week group was noted as compared with that in the IH 2-weeks group and IH 4-weeks group (P<0.05). (3) The results of real time-PCR revealed that the miR-26b expression level in the hippocampus was up-regulated in the IH 1-week group, IH 2-weeks group and IH 4-weeks group as compared with that in the control group, with significant differences (P<0.05); miR-26b expression level in the IH 1-week group was significantly higher as compared with that in the IH 2-weeks group and IH 4-weeks group (P<0.05). Conclusion The miR-26b up-regulated expression in the hippocampus might refer to Bax/Bcl-2-related mitochondrial apoptotic signaling pathway after IH brain injury; miR-26b could be a potential mean of gene therapy after IH brain injury. Key words: Intermittent hypoxia; Cognitive impairment; Neuron; Apoptosis; MiR-26b