MMP9 and ischemia: Matrix metalloproteinases (MMPs) are a family of over 20 extracellular endopeptidases that cleave a wide range of protein substrates in diverse signaling pathways.1 In particular, the subfamily of gelatinases, MMP-2 (gelatinase A) and MMP-9 (gelatinase B), have been implicated as key mediators of proteolytic blood–brain barrier (BBB) disruption associated with traumatic injury,2 ischemia,3 and neuroinflammatory disorders.4