MMP9 and ischemia: In line with this, previous studies showed that during ischemia pericytes secrete TGFβ1 and matrix metalloproteinases-9 (MMP9), possibly as a fast angiogenic response to hypoxia.63 In addition, inflammatory conditions, such as in ischemic stroke, could induce the pericytes to produce proinflammatory cytokines, chemokines and other pro-inflammatory factors,29,64, , –67 which could further impair the cellular microenvironment and disrupt the BBB.