Exercise preconditioning reduces brain damage and inhibits TNF-alpha receptor expression after hypoxia/reoxygenation: an in vivo and in vitro study.

Exercise reduces ischemia and reperfusion injury in rat stroke models. We investigated whether gradual increases in tumor necrosis factor-alpha (TNF-alpha) reported during exercise down-regulates expression of TNF-alpha receptors I and II (TNFRI and II) in stroke, leading to reduced brain damage. Adult male Sprague Dawley rats were subjected to 30 minutes of exercise on a treadmill each day for 3 weeks. Then, stroke was induced by a 2-hour middle cerebral artery (MCA) occlusion using an intra-luminal filament. Expressions of TNFRI and II mRNA in the brain were detected using a real-time reverse transcriptase-polymerase chain reaction (RT-PCR). Protein expressions of TNFRI and II were determined by enzyme-linked immunoabsorbant assay (ELISA) in serum and brain homogenates. Spatial distribution of TNF-alpha receptors in brain regions was determined with immunocytochemistry. In human umbilical vein endothelial cells (HUVEC), we addressed the causal effect of TNF-alpha pretreatment on TNF I and II expression using ELISA and real-time PCR. In exercised rats after stroke, brain infarct was significantly (p<0.01) reduced in the entire MCA supplied regions, associated with a mild expression of TNFRI and II mRNA and protein. The TNF-alpha receptors were restricted to the ischemic core. In contrast, a robust expression of TNFRI and II molecules was found in non-exercised rats subjected to similar ischemia/reperfusion insults. An in vitro study revealed a causal link between TNF-alpha pretreatment and reduced cellular expression of TNF-alpha receptors under hypoxic/reoxygenated conditions. Our results suggest that reduced-brain damage in ischemic rats after exercise preconditioning may be attributable to the reduced expression of TNF-alpha receptors. Chronically increased TNF-alpha expression was also found to reduce TNFI and II responding to acute ischemia/reperfusion insult.

Exercise preconditioning ameliorates inflammatory injury in ischemic rats during reperfusion.

There is evidence that physical activity is associated with decreased brain injury resulting from transient middle cerebral artery (MCA) occlusion. We investigated whether exercise could reduce stroke-induced brain inflammatory injury and its associated mediators. Sprague Dawley rats (3 months old) were subjected to 30 min exercise on a treadmill each day for 1-3 weeks. Stroke, in exercised and non-exercised animals, was then induced by a 2-h MCA occlusion followed by 48 h of reperfusion using an intraluminal filament. Endothelial expression of the intercellular adhesion molecule 1 (ICAM-1) and leukocyte infiltration were determined by immunocytochemistry. Expressions of tumor necrosis factor-alpha (TNF-alpha) and ICAM-1 mRNA were detected using a real-time reverse transcriptase-polymerase chain reaction in ischemic rats with or without exercise, and in non-ischemic control rats following exercise. Expression of TNF-alpha increased after exercise for 2 and 3 weeks. The overexpression of TNF-alpha was not further elevated in 3-week exercised rats subjected to a transient MCA occlusion and 6 or 12 h of reperfusion, as compared to that in non-exercised rats. Furthermore, ICAM-1 mRNA expression remained at significantly (P<0.01) low levels in exercised animals during ischemia/reperfusion. Pre-ischemic exercise significantly (P<0.01) reduced numbers of ICAM-1-positive vessels and infiltrating leukocytes in the frontoparietal cortex and dorsolateral striatum in ischemic rats after 48 h of reperfusion. Exercised ischemic rats demonstrated an 11+/-7% infarct volume of contralateral hemisphere as compared to a 52+/-3% volume in non-exercised ischemic rats. The data suggests that exercise inhibits inflammatory injury (i.e., decreased expression of inflammatory mediators and reduced accumulation of leukocytes) during reperfusion, leading to reduced brain damage. Chronically increased expression of TNF-alpha during exercise prevent the same downstream inflammatory events as does acutely elevated TNF-alpha after ischemia/reperfusion.

Exercise-induced overexpression of angiogenic factors and reduction of ischemia/reperfusion injury in stroke.

The purpose of this study was to determine if exercise could induce expression of vascular endothelial growth factor (VEGF) and angiopoietin 1 and 2, in association with angiogenesis; and if angiogenic changes correlated with reduced brain injury in stroke. Adult male Sprague Dawley rats (3 month old, n=44) were exercised on a treadmill 30 minutes each day for 1, 3 or 6 weeks, or housed as non-exercised controls for 3 weeks. Some 3 week-exercised rats were then housed for an additional 3 weeks. Exercise significantly (p<0.01) increased mRNA (determined by real-time reverse transcriptase-polymerase chain reaction) expression of angiopoietin 1 and 2 as early as 1 week, with further increases occurring at 3 weeks. A mild increase after 1 week and a robust increase after 3 weeks of exercise in four isoforms (120, 144, 164, 188) of VEGF mRNA levels were significantly (p<0.01) observed, with VEGF(144) being more markedly up-regulated. Overexpression of the mRNAs decreased upon withdrawal of exercise. A significant increase (p<0.01) in the density of microvessels (determined by laminin-immunocytochemistry) was found at 3 weeks of exercise and this continued after exercise was withdrawn. In exercising rats subjected to 2-h MCA occlusion followed by 48-h reperfusion, neurological deficits and infarct volume were significantly reduced. Neuroprotection continued after 3 weeks of rest. This study indicates that pre-ischemic exercise reduces brain injury in stroke. The reduced damage is associated with angiogenesis, possibly induced by angiogenic factors following exercise. Physical exercise up-regulates mRNA levels of the angiopoietin family and VEGF.