MMP9 and stroke disorder: At intercellular junctions, MMP-9 directly compromises tight-junction complexes (e.g., claudin-5, occludin, ZO-1), increasing paracellular permeability and promoting blood–tissue barrier disruption; in the cerebral endothelium, VEGF-MMP-9 signaling compromises tight junctions and disrupts transport systems, and selective MMP-9 blockade attenuates blood–brain barrier breakdown in stroke models [50].