Matrix metalloproteinase-3 promotes early blood-spinal cord barrier disruption and hemorrhage and impairs long-term neurological recovery after spinal cord injury.

After spinal cord injury (SCI), blood-spinal cord barrier (BSCB) disruption by matrix metalloproteinases (MMPs) leads to BSCB permeability and blood cell infiltration, contributing to permanent neurological disability. Herein, we report that MMP-3 plays a critical role in BSCB disruption after SCI in mice. MMP-3 was induced in infiltrated neutrophils and blood vessels after SCI, and NF-κB as a transcription factor was involved in MMP-3 expression. BSCB permeability and blood cell infiltration after injury were more reduced in Mmp3 knockout (KO) mice than in wild-type (WT) mice, which was significantly inhibited by Mmp3 siRNA or a general inhibitor of MMPs, N-isobutyl-N-(4-methoxyphenylsulfonyl)glycyl hydroxamic acid. The level of tight junction proteins, such as occludin and zonula occludens-1, which decreased after SCI, was also higher in Mmp3 KO than in WT mice. Exogenously, MMP-3 injection into the normal spinal cord also induced BSCB permeability. Furthermore, MMP-9 activation after injury was mediated by MMP-3 activation. Finally, improved functional recovery was observed in Mmp3 KO mice compared with WT mice after injury. These results demonstrated the role of MMP-3 in BSCB disruption after SCI for the first time and suggest that the regulation of MMP-3 can be considered a therapeutic target to inhibit BSCB disruption and hemorrhage, and thereby enhance functional recovery after acute SCI.