MMP9 and brain ischemia: Animals and patient studies have discovered that cerebral ischemia can induce expression of MMPs, particularly, the increased activity of MMP-2 and MMP-9, which is closely related to increased cerebral microvascular permeability, BBB destruction, inflammatory cell invasion, and brain edema (Rosell and Lo, 2008; Kurzepa et al., 2014; Yang and Rosenberg, 2015).