MMP9 and Stroke: Nicotinamide adenine dinucleotide phosphate oxidase (NOX)-4, 5.9 × upregulated by TGF-β, is highly upregulated in stroke-associated pericytes, and its overexpression in pericytes induces a breakdown of the BBB by upregulating matrix metalloproteinase (MMP)-9 [36], the latter also associated with capillary damage during ischemia [37].