Delayed Up-regulation of Vascular Endothelial Growth Factor and flk-1 after Global Cerebral Ischemia in Mongolian Gerbil -Possible roles in neuroangiogenesis?

Background : Vascular endothelial growth factor (VEGF) is an endothelial cell-specific mitogen and a potent mediator of vascular permeability. Flk-1, one of the receptors for VEGF, is important in vascular development. Increased expression of VEGF is related with reactive astrogliosis, which stimulates the proliferation of neural progenitor cells. VEGF expression increases in the acute phase of cerebral ischemia, however the expression of VEGF together with flk-1 in subacute stage is still unknown. This study is done to demonstrate the spatial/cellular patterns of expression for VEGF/flk-1 up to subacute stages and to find out the role of VEGF in ischemia. Methods : Transient global ischemia was induced by a 10 min-occlusion/reperfusion of the bilateral carotid arteries in the Mongolian gerbil. Immunohistochemistry and western blot were performed to ensure the expression of VEGF and flk-1 on the day1, 3, 7, 14, and 28. Results : Both VEGF and flk-1 initially increased at day1, and decreased at day3. Thereafter, VEGF gradually increased again to the initial level at day7 and to the peak level after day14. Flk-1 showed a peak expression at day14, and then decreased at day28. Immunohistochemical staining for VEGF showed immunoreactivity mainly on the cytoplasm of neurons and endothelium in cortex and hippocampus at day1, and neuron, endothelium, and glial cell from day14 to 28. The distribution and chronological patterns of flk-1 expression were similar to that of VEGF expression. Conclusions : We suggest that global cerebral ischemia can induce a delayed up-regulation of VEGF and flk-1, which may be associated with neuroangiogenesis and repair process.