Role of the TLR4 pathway in blood-spinal cord barrier dysfunction during the bimodal stage after ischemia/reperfusion injury in rats

Background: spinal cord ischemia-reperfusion (i/r) involves two-phase injury,including an initial acute ischemic insult and subsequent inflammatory reperfusion injury,resulting in blood-spinal cord barrier (bscb) dysfunction involving the tlr4 pathway. however,the correlation between tlr4/myd88-dependent and tlr4/trif-dependent pathways in bscb dysfunction is not fully understood. the aim of this study is to characterize inflammatory responses in spinal cord i/r and the events that define its clinical progression with delayed neurological deficits,supporting a bimodal mechanism of injury.methods: rats were intrathecally pretreated with tak-242,myd88 inhibitory peptide,or resveratrol at a 12 h interval for 3 days before undergoing 14-minute occlusion of aortic arch. evan's blue (eb) extravasation and water content were detected at 6,12,18,24,36,48,and 72 h after reperfusion. eb extravasation,water content,and nf-κb activation were increased with time after reperfusion,suggesting a bimodal distribution,as maximal increasing were detected at both 12 and 48 h after reperfusion. the changes were directly proportional to tlr4 levels determined by western blot. double-labeled immunohistochemical analysis was also used to detect the relationship between different cell types of bscb with tlr4. furthermore,nf-κb and il-1β were analyzed at 12 and 48 h to identify the correlation between myd88-dependent and trif-dependent pathways.results: rats without functional tlr4 and myd88 attenuated bscb leakage and inflammatory responses at 12 h,suggesting the ischemic event was largely mediated by myd88-dependent pathway. similar protective effects observed in rats with depleted tlr4,myd88,and trif receptor at 48 h infer that the ongoing inflammation which occurred in late phase was mainly initiated by trif-dependent pathway and such inflammatory response could be further amplified by myd88-dependent pathway. additionally,microglia appeared to play a major role in early phase of inflammation after i/r injury,while in late responding phase both microglia and astrocytes were necessary.conclusions: these findings indicate the relevance of tlr4/myd88-dependent and tlr4/trif-dependent pathways in bimodal phases of inflammatory responses after i/r injury,corresponding with the clinical progression of injury and delayed onset of symptoms. the clinical usage of tlr4 signaling inhibitors at different phases may be a therapeutic option for the prevention of delayed injury. © 2014 li et al.; licensee biomed central ltd.