Expression Changes Of Neuroglobin In Traumatic Brain Injury

As we all known that oxygen is the source of life. The metabolism and ultilization of oxygen are two important subjects in life science. It is well known that brain is the most sensitive organ to hypoxia. However, for a long time, people didn't know whether there exists a specific gene for oxygen utilization in brain. Till 2000, Burmester reported a newly identified protein—neuroglobin (NGB), mainly expressed in nervous systems and retina of vertebrate, which is a monomer with high oxygen affinity. The oxygen-binding properties of neuroglobin are comparable to another oxygen-binding protein, myoglobin, suggesting a similar function of neuroglobin in the brain. Studies revealed NGB binds oxygen reversibly and plays an important role in oxygen homeostasis of neural tissues. Other studies demonstrated that expression of NGB could be upregulated under hypoxic conditions and had neuro-protective function both in vitro and in vivo. Adil reported that neuroglobin over-expressing transgenic mice were resistant to cerebral and myocardial ischemia. The discovery of NGB and the results of recent studies provide new opportunities to further the understanding of neuroprotection and may ultimately lead to novel therapeutic strategies for the treatment of cerebral vescular accidents and other neurodegenerated diseases.However, relatively little is known about the changes of NGB expression in the brain after traumatic brain injury (TBI). The major content of our study included four parts as follows:1. We chose Marmarou's model to induce the TBI in adult rats, and then evaluated the severity of injury through ethological observation and pathological examination. The results showed that the mortality of this TBI model was 37.04% and all the changes of experimental animals, including ethology and pathology, were consistent with the changes of severe TBI.2. We cloned the cDNA coding sequence of NGB in rattus norvegicus, furthermore constructed the plasmid containing this sequence. Sequence similarity analysis showed that the cloned cDNA sequence of rat NGB is 98% to rat NGB (RnNGB, NM033359). The consentration of the plasmid was 260μg/ml. It could be used in following experiment as a standard preparation of NGB-positive plasmid.3. Using Real-time quantitative PCR and western blotting technique, we found the 'bimodal' expression changes of NGB in rat brain after TBI. The transcription of NGB-mRNA significantly increased and reached a peak at 30 minutes after TBI in rat brain. Accordingly, the NGB protein significantly increased at 1-hour post-injury and reached a peak at 2-hour after TBI in rat brain. After that, the expression of NGB increased again in both transcription and translation levels. The transcription of NGB-mRNA significantly increased at 12-hour and reached a peak at 48-hour post-injury, meanwhile the NGB protein significantly increased at 24-hour and reached a peak at 72-hour post-injury. Based on above, we conclude that NGB could be rapidly up-regulated by acute stress of traumatic injury and sondary ischemia insult both in mRNA level and protein level. It suggested us that NGB might play an important role in sensing and responding to traumatic stress and sondary ischemic-hypoxic insult.4. We observed the dynamic changes of NGB expression after TBI in rat. Interestingly, our results also revealed that changes of NGB expression were companied with the ratio changes of Bax to Bcl-2. NGB protein was up-regulated in two periods, which were 30min to 1h and 48h to 72h. The ratio of Bax to Bcl-2 also decreased during these two periods. It suggested that NGB might be resistant to apoptosis induced by TBI and its sondary insults.In conclusion, NGB may have important function in the adaptive protection process of TBI and its sondary insults. The present study may be useful for furthering the understanding of neuroprotection and may ultimately lead to novel therapeutic strategies for the treatment of TBI.