Early exercise intervention promotes myelin repair in the brains of ischemic rats by inhibiting the MEK/ERK pathway

Abstract

Our previous studies have shown that early exercise intervention after stroke increases neural activity and synaptic plasticity and promotes the recovery of nerve fiber bundle integrity in the brain. However, the effect of exercise on the repair of myelin in the brain and the related mechanism are still unclear. In this study, we randomly divided the rats into three groups. Before and after 28 days of intervention, body weight, nerve function, the infarct size, white matter fiber bundle integrity, and nerve myelin structure and function were observed by measuring body weight, analysis of modified neurological severity score, CatWalk gait analysis, MRI, luxol fast blue staining, immunofluorescence, and transmission electron microscopy. Changes in the expression of proteins in the MEK/ERK pathway were assessed. The results showed that early exercise intervention resulted in neurological recovery, decreased the infarct volume and increased nerve fiber integrity, the myelin coverage area, myelin basic protein (MBP) fluorescence intensity expression, and myelin thickness. Furthermore, the expression level of MBP was significantly increased after early exercise intervention, while the expression levels of p-MEK1/2 and p-ERK1/2 were significantly reduced. In the cell study, MBP expression levels were significantly higher in the oxygen and glucose deprivation and administration group.In summary, early exercise intervention after stroke can promote myelin repair by inhibiting the MEK/ERK signaling pathway.

Keywords: early exercise intervention; middle cerebral artery occlusion; myelin.

Figure 1

MNSS scores and status of the MCAO rats. (a) and (b) Representative T2WI images of each group and cerebral infarction volume ratio of rats in each group at 24 h after MCAO. N = 6/group. (c) Changes in the body weight of rats 28 days after MCAO. N = 12/group. (d) Changes in the mNSS scores of rats 28 days after MCAO. N = 12/group. (e) and (f) Representative paw step images and limbs’ supporting timing view of CatWalk gait analysis. (g) Quantitative analysis of catwalk at Day 28. N = 6/group. Compared with the sham group: *P < 0.05, **P < 0.01, and ***P < 0.001; compared with the MCAO-SED group: #P < 0.05, ##P < 0.01, and ###P < 0.001. Mean ± SEM.

Figure 2

MRI images of rats. (a) and (b) Representative T2WI images of each group and cerebral infarction volume ratio of rats in each group on the 7th day of intervention. (c) and (d) Representative T2WI images of each group and cerebral infarction volume ratio of rats in each group on the 28th day of intervention. (e) rFA values after intervention. (f) rADC values after intervention. *P < 0.05, **P < 0.01, and ***P < 0.001: the MCAO-EX group compared with the MCAO-SED group. #P < 0.05, ##P < 0.01, and ###P < 0.001: self-comparison of the MCAO-SED group and the MCAO-EX group on Day 28. ANOVA. Mean ± SEM. N = 6/group.

Figure 3

Myelin integrity assessment. (a) and (b) LFB staining of the ischemic penumbra striatum 28 days after MCAO. Scale bar = 1,000 μm. (c) and (d) Immunohistochemical staining of MBP and quantification of MBP expression in rats 28 days after MCAO (red rectangle in the figure). Scale bar = 100 μm. One-way ANOVA and the LSD-t post hoc test. Mean ± SEM. N = 6/group. (e) and (f) TEM analysis of myelin integrity in the external capsule (EC) on Day 28 after MCAO. Scale bar = 2 μm. *P < 0.05, **P < 0.01, and ***P < 0.001: the MCAO-EX group compared with the MCAO-SED group. Independent sample Kruskal‒Wallis test. Mean ± SEM. N = 300/group. MBP, myelin basic protein.

Figure 4

Protein expression in the ischemic penumbra. (a)–(h) At 28 days after MCAO, the expression levels of MEK1/2, p-MEK1/2, ERK1/2, p-ERK1/2, and MBP in penumbra tissues were analyzed by western blotting. #P < 0.05, ##P < 0.01, and ###P < 0.001: the MCAO-SED group compared with the sham group. *P < 0.05, **P < 0.01, and ***P < 0.001: the MCAO-EX group compared with the MCAO-SED group. One-way ANOVA and the LSD-t post hoc test. Mean ± SEM. The experiment was repeated three times.

Figure 5

Analysis of morphology and protein expression. (a) Cells from each group were observed under an optical microscope after 4 h of OGD and 4 days of reperfusion. Scale bar = 1,000 μm. (b–g) The expression of MEK1/2, p-MEK1/2, ERK1/2, p-ERK1/2, and MBP in MO3.13 cells was analyzed by western blotting after 4 h of OGD and 4 days of reperfusion. #P < 0.05, ##P < 0.01, and ###P < 0.001: the OGD group compared with the control group. *P < 0.05, **P < 0.01, and ***P < 0.001: the OGD + PD group compared with the OGD group. One-way ANOVA and the LSD-t post hoc test. Mean ± SEM. The experiment was repeated three times.