After spinal cord injury, the disruption of blood-spinal cord barrier by activation of matrix metalloprotease is a critical event leading to infiltration of blood cells, inflammatory responses and neuronal cell death, contributing to permanent neurological disability. Recent evidence indicates that fluoxetine, an anti-depressant drug, is shown to have neuroprotective effects in ischaemic brain injury, but the precise mechanism underlying its protective effects is largely unknown. Here, we show that fluoxetine prevented blood-spinal cord barrier disruption via inhibition of matrix metalloprotease activation after spinal cord injury. After a moderate contusion injury at the T9 level of spinal cord with an infinite horizon impactor in the mouse, fluoxetine (10 mg/kg) was injected intraperitoneally and further administered once a day for indicated time points. Fluoxetine treatment significantly inhibited messenger RNA expression of matrix metalloprotease 2, 9 and 12 after spinal cord injury. By zymography and fluorimetric enzyme activity assay, fluoxetine also significantly reduced matrix metalloprotease 2 and matrix metalloprotease 9 activities after injury. In addition, fluoxetine inhibited nuclear factor kappa B-dependent matrix metalloprotease 9 expression in bEnd.3, a brain endothelial cell line, after oxygen-glucose deprivation/reoxygenation. Fluoxetine also attenuated the loss of tight junction molecules such as zona occludens 1 and occludin after injury in vivo as well as in bEnd.3 cultures. By immunofluorescence staining, fluoxetine prevented the breakdown of the tight junction integrity in endothelial cells of blood vessel after injury. Furthermore, fluoxetine inhibited the messenger RNA expression of chemokines such as Groα, MIP1α and 1β, and prevented the infiltration of neutrophils and macrophages, and reduced the expression of inflammatory mediators after injury. Finally, fluoxetine attenuated apoptotic cell death and improved locomotor function after injury. Thus, our results indicate that fluoxetine improved functional recovery in part by inhibiting matrix metalloprotease activation and preventing blood-spinal cord barrier disruption after spinal cord injury. Furthermore, our study suggests that fluoxetine may represent a potential therapeutic agent for preserving blood-brain barrier integrity following ischaemic brain injury and spinal cord injury in humans.

The blood-brain barrier (BBB) including blood-spinal cord barrier (BSCB) is a highly specialized brain endothelial structure of the fully differentiated neurovascular system. When damaged by various insults including traumatic spinal cord injury (SCI), the BBB or BSCB disruption elicits blood infiltration and inflammation, thereby generating neurotoxic products that can compromise synaptic and neuronal functions (Hawkins and Davis 2005;Zlokovic 2005;Abbott et al. 2006) and induces the ''programmed death'' of neurons and glia, leading to permanent neurological deficits (Xu et al. 2001;Noble et al. 2002;Gerzanich et al. 2009 Seoul, KoreaAbstract The disruption of blood-spinal cord barrier (BSCB) after spinal cord injury (SCI) elicits an intensive local inflammation by the infiltration of blood cells such as neutrophils and macrophages, leading to cell death and permanent neurological disability. SCI activates matrix metalloprotease-9 (MMP-9), which is known to induce BSCB disruption. Here, we examined whether valproic acid (VPA), a histone deacetylase inhibitor, would attenuate BSCB disruption by inhibiting MMP-9 activity, leading to improvement of functional outcome after SCI. After moderate spinal cord contusion injury at T9, VPA (300 mg/kg) were immediately injected subcutaneously and further injected every 12 h for 5 days. Our data show that VPA inhibited MMP-9 activity after injury, and attenuated BSCB permeability and degradation of tight junction molecules such as occludin and ZO-1. In addition, VPA reduced the expression of inflammatory mediators including tumor necrosis factor-a. Furthermore, VPA increased the levels of acetylated histone 3, pAkt, and heat-shock protein 27 and 70, which have antiapoptotic functions after SCI. Finally, VPA inhibited apoptotic cell death and caspase 3 activation, reduced the lesion volume and improved functional recovery after injury. Thus, our results demonstrated that VPA improves functional recovery by attenuating BSCB disruption via inhibition of MMP-9 activity after SCI.