Physical activity promotes angio- and vasculogenesis in the post-ischemic brain

Abstract

Clinical and experimental evidence supports the notion that regular physical activity up regulates endothelial nitric oxide synthase, improves endothelium-dependent vasorelaxation, and protects from vascular disease. Here, we demonstrate that continuous voluntary training on running wheels via up regulation of endothelial nitric oxide synthase improves neo-vascularization and long-term recovery following mild brain ischemia induced by 30 min filamentous occlusion of the left middle cerebral artery followed by reperfusion in the mouse. Experiments were performed under isofluorane anesthesia in 129/SV wild-type mice or chimeric mice that were transplanted with bone marrow from transgenic mice that express the lacZ gene under control of the endothelial promotor Tie2. In ischemic animals, physical activity conferred up regulation of endothelial nitric oxide synthase in the vasculature and of endothelial progenitor cells in the spleen and bone marrow as measured by FACS analysis and cell culture techniques. This was associated with higher numbers of circulating endothelial progenitor cells in the blood, enhanced neo-vascularization in a disc angiogenesis model, and increased engraftment of Tie2/lacZ positive bone marrow-derived cells in the ischemic brain. Six weeks after the insult, trained animals had higher numbers of newborn endothelial cells in the brain (as determined by bromodesoxyuridine/von Willebrand factor double immunostaining and confocal microscopy) and increased density of perfused vessels with apparent normal morphology (as determined by tiled-field mapping of Evans Blue perfused brains). This conferred sustained augmentation of absolute regional cerebral blood flow in the ischemic lesion in trained vs. sedentary mice at 6 weeks after the insult (as determined by 14-C iodoantipyrine autoradiography). In fact, exercised mice had smaller ischemic lesion sizes (determined on NeuN-immunostained coronal brain sections by computer assisted volumetry), improved functional scores (Bederson test, wire hanging) and better performance in the Morris water maze when compared to sedentary animals. Co-administration of the nitric oxide synthase inhibitor L-NAME in the drinking water not only inhibited up regulation of endothelial progenitor cells by physical activity but also completely abrogated the stroke-protective effects of exercise. In conclusion, voluntary physical activity enhances regeneration in the ischemic brain by endothelial nitric oxide-dependent mechanisms leading to improved neo-vascularization and increased cerebral blood flow.