| Epilepsy is caused by multiple etiopathogenisis and characterized by the high degree synchronization of neurons in brain accompanied with an abnormal over-firing-induced self-limited dysfunction of CNS. Epilepsy is a group of common chronic diseases of neurology, typically combined with the alteration of local structure, metabolism and local cerebral blood flow. Idiopathic epilepsy displays the electrophysiological change of the brain during the seizure of onset or/and interphase, which is not secondarily affected from nervous system or other system disorders. Given the regular antiepileptic treatment, seizure in most patients may become under control. However, the seizure of 20%-30% of patients is difficult to be controlled and develops ultimately into intractable epilepsy, 60%-70% of which is temporal lobe epilepsy (TLE). By now, the pathogenesis of TLE is not clear. The long time repeated seizure and drug side-effects pose severe threat to the daily life of TLE patients. Therefore, it is of much consequence to investigate the pathogenesis of TLE.Hippocampus is the main epileptogenic focus of TLE, and is also the relay station and amplifier of the firing diffusion of other types of epilepsy. Meanwhile, both the dentate gyrus (DG) and subventricular zone (SVZ) are the main neurogenesis sites in the adult mammalian brain. The main pathological change of TLE is hippocampus sclerosis, which includes neuron loss, gliosis and synapse reorganization. The main type of TLE synapse reorganization is the mossy fiber sprouting (MFS) in the DG granule cells, entorhinal and CA3 areas. Studies in TLE patients'specimens and animal models have demostrated that the seizure-induced brain injury including MFS in DG granule cells, increased hippocampus neurogenesis and hilar-ectopic granule cells generation. Followed by the seizure-induced injury of the pyramidal cells in the CA1, CA3 and the neurons in the hilus of hippocampus, the inner molecular layer lost the fiber afference and mossy fibers disconnected from the target cells. Consequently, mossy fibers are triggered to sprout into the inner molecular layer and, establish the synaptic connection with granule cells. There is a mount of evidences indicated that the mossy fiber sprouting contributed to the spontaneous repeated seizure of the chronic epilepsy, meanwhile, reinforced the repeated seizures. However, the mechanisms of adult hippocampus neurogenesis under seizure, as well as the function of MFS, are still unclear.Evidences have showed that adult hippocampus DG neurogenesis increased by kainic acid (KA) induced hippocampus injury, and accompanied with increased abnormal neuron migration and synapse plasticity. Recently, both the foreign researchers and our group found that abnormal hippocampus neurogenensis observed in process of TLE onset, which mainly occurred following statural epilepticus and before the spontaneous repeated seizures. Hippocampus DG granule cells proliferation was significantly increased, most of newly born cells differentiated into neuron (granule cells), migrated into granule layer and became the mature granule cells as well as generated new axon to form the MFS. In addition, it has been reported that varies types of animal epilepsy model were accompanied by the seizure generation, the neurogenesis of DG granule cells increased and ectopia granule cells formatted MFS. However, the extent and time curve of increased hippocampus DG neurogenesis are different among all kinds of epilepsy models. After the status epilepticus and spontaneous repeated seizure, the reason why the increased DG granule cells in the hippocampus does not automatically migrate into the neuron-loss zone and supplement or substitute for the lost cells, the route by which proliferative DG stem cells in hippocampus migrated, and the position where those newly born cells located are still under investigation.Noggin and the bone morphogenetic protein 4 (BMP4) are the key regulatory molecules in the embryonic neurogenesis, and contribute to the development of the neural plate and neural tube. BMP4 inhibited the ectoderm cells differentiated into neurons, but facilitated these cells differentiated into epithelial cells. As an antergic binding protein of BMP4, noggin has more affinity with BMP4 and can prevent BMP4 from binding with its receptors. Accordingly, noggin inhibited the signal transduction of BMP receptor, and promoted these cells differentiated into neurons. In the adult CNS, noggin plays an important role in the neural stem cells proliferation and differentiation and maintaining the normal function of neurons. We also demonstreated that KA-induced status epilepticus caused tonic proliferation of hippocampus neural stem cells was related to the hippocampus BMP4 over-expression, and accompanied with mount of neurons in the CA3 and CA4 areas lost. There are still no reports about the function of noggin in the proliferation of the increased DG granule cells followed the KA-induced hippocampus injury.Therefore, to approach the relationship between the epilepsy pathogenesis and proliferation, migration and distribution of the neural stem cells, hippocampus injury animal model induced by KA intracerebroventricular (I.C.V.) injection was used in this study. We observed the expression of nestin and BMP4 in DG of hippocampus by a series of techniques, such as in-situ hybridization, immunohistochemistry and cell culture, etc. Meanwhile, in order to elucidate the effect of noggin on the proliferation of DG granule cells in hippocampus and the gliosis, we detected the neuron loss in the hippocampus of adult rats within 1 day to 30 days after KA I.C.V. injection and disclosed the relationship between the number of BrdU labeled cells in DG of hippocampus and the expression of noggin. Furthermore, we tried to confirm the effect of BMP4/noggin on the proliferation and differentiation of c17.2 neural stem cells in vitro culture of immortalization neural stem cell line. The main results are listed as following:1. Adult rats given KA I.C.V injection induced SE, the neuron loss in the hippocampal CA3 and CA4 areas of the injection side was notable throughout the whole experimental observation phase. There were no detectable cells to recover from injury; otherwise, few cells lost in the opposite side.2. Adult rats given KA I.C.V injection, the nestin positive cells in the DG sub-granular zone were abnormally proliferated and migrated, and those newly born neurons mainly located in the dentate hilus. At the same time, we observed that BMP4 mRNA positive cells increased significantly in this area, which indicated that the abnormal proliferation and migration of the adult DG granule cells may relate to the over-expression of BMP4 mRNA.3. Adult rats given KA I.C.V injection, the DG granule cells in the hippocampus were abnormally proliferated, and those newly born neurons mainly located in the DG sub-granular zone. Meanwhile, we observed that noggin mRNA positive cells distributed in the hippocampal DG hilus, sub-granule layer, CA3, and CA1 areas. The noggin mRNA positive cells in the hippocampus increased 3 days post lesion, while decreased 7 days post-lesion. It suggested that the abnormal proliferation of the DG granule cells in the KA-lesioned hippocampus may be related to the fluctuation of the noggin expression in the hippocampus.4. In vitro study, we demonstrated that the ability of proliferation and differentiation into neurons in the c17.2 neural stem cells was inhibited by BMP4, while noggin facilitated these processes.In conclusion, here we have showed the expression pattern of BMP4/noggin and its potential role in the proliferation and differentiation of hippocampal neural stem cells during the formation process of TLE. Furthermore, in vitro study, we observed the effect of BMP4/noggin on the ability of proliferation and differentiation in the c17.2 neural stem cells. All of these results indicate that KA-lesioned hippocampus promote the DG granule cells abnormally to proliferate and migrate, and those newly born neurons mainly locate in the hippocampus DG hilus area. This may be related to over-expression of BMP4 and the fluctuation of the noggin expression in the hippocampus. |
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