Several studies have suggested that MMP2 and MMP9 may contribute to BBB breakdown [13, 17]—for example, MMP9 appears to mediate the loss of TJ stability observed in mice with 1,2-dichloroethane-induced brain edema [46]—and our observation that MMP3 mRNA levels were much higher in BMVECs than in MVECs from other organs (e.g., the heart, lungs, spleen, and kidney) suggests that it may have a unique and essential role in BMVECs, particularly since many of the ECM proteins that form the basal lamina of cerebral blood vessels can be proteolysed by MMP3 [19]. This evidence concerns the gene MMP9 and brain edema.