Microglia, the primary immune effector cells in the CNS, are polarized to anti-inflammatory type after brain injury, and secretes a range of neurotrophic elements such as transforming growth factor-β (TGF-β), brain-derived neurotrophic factor (BDNF) for promoting neural regeneration, and vascular endothelial growth factor (VEGF) to contact with endothelial cells to stimulate angiogenesis, enhancing cerebral blood flow, thus facilitating neural function recovery [[20], [21], [22]]. Here, BDNF is linked to injury.