Preischemic induction of TNF-alpha by physical exercise reduces blood-brain barrier dysfunction in stroke

The effect of treadmill training pre-exercise on glutamate receptor expression in rats after cerebral ischemia

Physical exercise has been demonstrated to be neuroprotective in both clinical and laboratory settings. However, the exact mechanism underlying this effect is unclear. Our study aimed to investigate whether pre-ischemic treadmill training could serve as a form of ischemic preconditioning in a rat model undergoing middle cerebral artery occlusion (MCAO). Thirty-six rats were divided into three groups: a sham control group, a non-exercise with operation group and an exercise with operation group. After treadmill training, ischemia was induced by occluding the MCA for 2 h, followed by reperfusion. Half of the rats in each group were sacrificed for mRNA detection of mGluR5 and NR2B 80 min after occlusion. The remaining animals were evaluated for neurological deficits by behavioral scoring and then decapitated to assess the infarct volume. The mRNA expression of mGluR5 and NR2B was detected by real-time PCR. The results suggest that pre-ischemic treadmill training may induce brain ischemic tolerance by reducing the mRNA levels of mGluR5 and NR2B, and thus, the results indicate that physical exercise might be an effective method to establish ischemic preconditioning.

Matrix metalloproteinase-9 (MMP-9) expression and extracellular signal-regulated kinase 1 and 2 (ERK1/2) activation in exercise-reduced neuronal apoptosis after stroke

Exercise preconditioning has been shown to reduce neuronal damage in ischemic/reperfusion (I/R) injury. ERK1/2 signaling in injury has been thought to modulate neuroprotection. In this study, we investigated the effects of ERK1/2 activation on the expression and activity of MMP-9 and downstream neuronal apoptosis. Adult male Sprague-Dawley rats were subjected to 30min of exercise on a treadmill for 3 weeks. Stroke was induced by a 2-h middle cerebral artery (MCA) occlusion using an intraluminal filament. Apoptotic protein caspase-3 and neuronal apoptosis in cortex and striatum was determined by Western blot at 24h reperfusion and TUNEL staining at 48h reperfusion in 5 I/R injury groups: no treatment, MMP-9 inhibitor (doxycycline), pre-ischemic exercise, exercised animals undergone ERK1/2 inhibition (U0126), and dual inhibition of ERK1/2 and MMP-9 in exercised ischemic rats. Cerebral MMP-9 expression in ischemic rats with different treatment was determined at 6, 12 and 24h reperfusion by real-time PCR for mRNA, Western blot for protein and zymography for enzyme activity. Exercise preconditioning significantly (p<0.05) reduced apoptosis determined by caspase-3 and TUNEL. In non-exercised rats, doxycycline treatment had significant (p<0.05) reductions in apoptosis after I/R injury. The dual ERK1/2-MMP-9 inhibited exercised animals had significantly (p<0.05) reduced neuronal apoptosis that was similar to that seen in exercised ischemic rats. MMP-9 expression in I/R injury was significantly (p<0.05) reduced in the exercised animals as compared to non-exercised controls. When ERK1/2 was inhibited, the reduced MMP-9 expression was reversed to the level seen in the non-exercised controls. This study has suggested that exercise-induced neuroprotection in I/R injury may be mediated by MMP-9 and ERK1/2 expression, leading to a reduction in neuronal apoptosis.

Exercise preconditioning reduces neuronal apoptosis in stroke by up-regulating heat shock protein-70 (heat shock protein-72) and extracellular-signal-regulated-kinase 1/2

Exercise preconditioning induces neuroprotection after stroke. We investigated the beneficial role of heat shock protein-70 (HSP-70) and phosphorylated extracellular-signal-regulated-kinase 1/2 (pERK 1/2), as they pertain to reducing apoptosis and their influence on Bcl-x(L), Bax, and apoptosis-inducing factor (AIF) in rats subjected to ischemia and reperfusion. Adult male Sprague-Dawley rats were subjected to 30 min of exercise on a treadmill for 1, 2, or 3 weeks. Stroke was induced by a 2-h middle cerebral artery (MCA) occlusion using an intraluminal filament. Protein levels of HSP-70, pERK 1/2, Bcl-x(L), Bax, and AIF were analyzed using Western blot. Neuroprotection was based on levels of apoptosis (TUNEL) and infarct volume (Nissl staining). Immunocytochemistry was used for cellular expression of HSP-70 and pERK 1/2. Significant (P<0.05) up-regulation of HSP-70 and pERK 1/2 after 3 weeks of exercise coincided with significant (P<0.05) reduction in neuronal apoptosis and brain infarct volume. Inhibition of either one of these two factors showed a significant (P<0.05) reversal in the neuroprotection. Bax and AIF were down-regulated, while levels of Bcl-x(L) were up-regulated in response to stroke after exercise. Inhibiting HSP-70 or pERK 1/2 reversed this resultant increase or decrease. Our results indicate that exercise diminishes neuronal injury in stroke by up-regulating HSP-70 and ERK 1/2.

Toll-like receptor-4 and cytokine cascade in stroke after exercise

OBJECTIVES

As part of the innate immune system, activation of Toll-like receptor-4 by inflammatory mediators causes the release of inflammatory cytokines, leading to cellular damage. Exercise for 3 weeks has been shown to provide neuroprotection against ischemia/reperfusion insults by decreasing inflammation. This study explores the expression of Toll-like receptor-4 in brain parenchyma during an ischemic stroke after exercise, in association with brain injury.

METHODS

Adult male Sprague-Dawley rats were studied in four groups (control, exercise, stroke and stroke after exercise). Exercise consisted of 30 minutes of treadmill running daily for 3 weeks. Using an intraluminal filament, a stroke was induced by 2 hour middle cerebral artery occlusion. Nissl staining was used to determine brain infarct volume. Brain Toll-like receptor-4 messenger RNA expression and protein levels were determined by real time reverse transcriptase polymerase chain reaction and Western blot, respectively.

RESULTS

Exercise significantly (p<0.05) decreased Toll-like receptor-4 messenger RNA and protein expression, in association with significantly (p<0.05) reduced brain infarct volume. The stroke group had significantly (p<0.05) increased levels of Toll-like receptor-4 expression compared to the control, whereas the exercise/stroke group was significantly (p<0.05) attenuated.

CONCLUSION

Exercise reduced Toll-like receptor-4 expression within brain tissue in response to ischemia/reperfusion insult. This is the first paper, to our knowledge, indicating the correlation between exercise, Toll-like receptor-4 expression and reduced brain infarct volume.

Exercise and the brain: something to chew on

Evidence is accumulating that exercise has profound benefits for brain function. Physical activity improves learning and memory in humans and animals. Moreover, an active lifestyle might prevent or delay loss of cognitive function with aging or neurodegenerative disease. Recent research indicates that the effects of exercise on the brain can be enhanced by concurrent consumption of natural products such as omega fatty acids or plant polyphenols. The potential synergy between diet and exercise could involve common cellular pathways important for neurogenesis, cell survival, synaptic plasticity and vascular function. Optimal maintenance of brain health might depend on exercise and intake of natural products.