No abstract

High-mobility group box 1 (HMGB1), a nuclear protein that has endogenous cytokine-like activity, is involved in several neurological diseases by mediating inflammatory response. In this study, a lateral head rotation device was used to establish a rat diffuse axonal injury (DAI) model. The dynamic expression of HMGB1, apoptosis-associated proteins, and proinflammatory cytokines were detected by Western blot, and neuronal apoptosis was observed by TUNEL staining. The extracellular release of HMGB1 and the accumulation of β-APP were observed by immunofluorescence and immunohistochemistry, respectively. The brain injury was indicated by modified neurological severity score (mNSS), brain water content (BWC), and the extravasation of Evans blue. We showed that HMGB1 level obviously decreased within 48 h after DAI, accompanied by neuronal apoptosis, the activation of caspases 3 and 9, and the phosphorylation of BCL-2. Inhibiting HMGB1 with glycyrrhizic acid (GL) can suppress the activation of apoptosis-associated proteins and inhibit the expression of proinflammatory cytokines, which ameliorated motor and cognitive deficits, reduced neuronal apoptosis, and protected the integrity of blood brain barrier (BBB) and axonal injury after experimental DAI in rats. Thus, HMGB1 may be involved in the inflammatory response after DAI, and inhibition of HMGB1 release with GL can notably alleviate the brain injury after DAI.

Increasing evidence suggests that secondary injury after diffuse axonal injury (DAI) damages more axons than the initial insult, but the underlying mechanisms of this phenomenon are not fully understood. Recent studies show that toll-like receptor 4 (TLR4) plays a critical role in promoting adaptive immune responses and have been shown to be associated with brain damage. The purpose of this study was to investigate the role of the TLR4 signalling pathway in secondary axonal injury in the cortices of DAI rats. TLR4 was mainly localized in microglial cells and neurons, and the levels of TLR4 downstream signalling molecules, including TLR4, myeloid differentiation primary response gene 88, toll/IR-1-(TIR-) domain-containing adaptor protein inducing interferon-beta, interferon regulatory factor 3, interferon β, nuclear factor κB (NF-κB) p65, and phospho-NF-κB p65, significantly increased and peaked at 1 d after DAI. Inhibition of TLR4 by TAK-242 attenuated apoptosis, neuronal and axonal injury, and glial responses. The neuroprotective effects of TLR4 inhibition were associated with decreases in the levels of TLR4 downstream signalling molecules and inflammatory factors, including interleukin-1β, interleukin-6, and tumour necrosis factor-α. These results suggest that the TLR4 signalling pathway plays an important role in secondary injury and may be an important therapeutic target following DAI.

No abstract

Ca²⁺ overload is considered to be the most important ion imbalance in the neuronal injury. Store-operated Ca²⁺ entry has been suggested to be a significant mechanism of excessive Ca²⁺ influx in many cells. The role of store-operated Ca²⁺ entry in neuronal ischemic injury has yet to be elucidated. The aim of this study was to assess the role of store-operated calcium channel (SOCC) proteins involved with calcium overload in the induction of delayed neuronal death after global ischemia in rats. A transient RNA interference model of global ischemia in rats was established to determine the role of SOCC-induced Ca²⁺ overload in delayed neuronal death. We found that STIM1 and ORAI1 expression in the hippocampus increased continuously after global ischemia and peaked on day 4. These data were consistent with an increase in the intracellular calcium concentration. Using Stim1 siRNA to suppress SOCC activity in the early stage of ischemia significantly inhibited STIM1 and ORAI1 expression and decreased the intracellular calcium concentration in neurons. In addition, the neurological function of rats improved after the Stim1 siRNA injection. High expression of STIM1 and ORAI may be the source of excessive calcium influx after ischemic damage. Blocking of this SOCC-induced calcium influx could lead to an improved neuronal survival. These data suggest that calcium influx through SOCC is another nonexcitotoxicity mechanism of ischemic neuronal death.