TNF-α Impairs Pericyte-Mediated Cerebral Microcirculation via the NF-κB/iNOS Axis After Experimental Traumatic Brain Injury

Background Secondary structural and functional abnormalities of the neurovascular unit are important pathological mechanisms following traumatic brain injury (TBI). The tumor necrosis factor α (TNF-α)/nuclear factor-κB (NF-κB) pathway regulates neuroinflammation and oxidative damage, which may act as triggers for pathological processes after TBI. However, the role of TNF-α/NF-κB in pericyte-mediated cerebral microcirculation are currently unknown. Methods We assessed the activity and mechanisms of the TNF-α/NF-κB signaling axis on pericyte-mediated microcirculation using the mouse controlled cortical impact model and BV2 cells. Immunofluorescent staining and western blot analysis were used to detect activation of the TNF-α/NF-κB signaling pathway and the expression of inducible nitric oxide synthase (iNOS) to evaluate the effects of the TNF-α specific inhibitor infliximab (IFX). Modified neurological severity scores, Garcia test, Nissl staining, and TUNEL staining were employed to determine the neuroprotective effects of IFX supplementation. The relative blood flow values in the capillary areas surrounding the impinging lesion were observed by Laser speckle contrast imaging. The impact of IFX on pericyte markers was assessed to evaluate whether pericyte damage was dependent on the TNF-α/NF-κB/iNOS axis to gain further insight into the mechanisms underlying the development of the microcirculation disturbance after TBI. Results Microglia were activated after TBI, and the expression of NF-κB, iNOS, a disintegrin and metalloproteinase 17, inflammatory factors, and free radicals increased around the injury areas. After lipopolysaccharide treatment, the expression of TNF-α and downstream NF-κB/iNOS in BV2 cells was significantly upregulated. Pharmacological inhibition of TNF-α via IFX significantly reduced NF-κB p65 phosphorylation and nuclear translocation and downregulated iNOS expression. Meanwhile, we found that specific inhibition of TNF-α reversed pericyte marker loss, and improved pericyte function and cerebral microcirculation perfusion after TBI, which could attenuate inflammation and oxidative damage, reduce neuronal cell damage and apoptosis, and play a neuroprotective role. Conclusion The results of this study suggested that microglia activated and released TNF-α after TBI, which promoted neuroinflammation and oxidative stress by activating downstream NF-κB/iNOS signals, and this led to pericyte-mediated disturbance of the cerebral microcirculation, which may be one of the vital mechanisms of secondary injury in TBI.