MMP9 and stroke disorder: When stroke events occur, blood neutrophils could be rapidly recruited to areas of ischemic brain, release matrix metalloproteinases-9 (MMP-9), which could degrade tight junction proteins and basal lamina type IV collagen, increasing the blood-brain barrier (BBB) permeability, thereby resulting in BBB disruption and tissue damage, which is accompanied by edema and hemorrhage (32–35).