NG2细胞在未成熟脑惊厥性脑损伤神经环路形成中的作用

Epidemiological studies indicated that seizures and epilepsy occurs more frequently in children than in adults with more severe cognitive function impairment. But the reasons are still poorly understood. Earlier studies suggested that seizure-induced acute and sub-acute cellular and molecular alterations in the immature brain compared with the adult brain are different and epileptogenesis after seizures may due to the fact that seizures interfere with the highly regulated developmental processes in the immature brain. While developmental process of myelination is one of the characters of brain development in the postnatal brain and it plays an important role in electric network and inhibition of axon sprouting. We investigate whether seizure can alter hippocampal circuitry through impairing the formation of myelination in the developing brain. Surprisingly, a significant demyelination in the hippocampus was found in immature brain compared to the mature brain not only in the acute but also the long-lasting stage after seizure. The reasons for remyelination failure after seizure are poorly understood. However,the identification of increasing NG2 glial cells ( oligodendrocytes precursors ) in the hippocampus after seizure suggests a critical regulatory mechanism in the inhibition of NG2 cells differentiation preventing their maturation to myelinating oligodendrocytes. In addition to myelination , recent reports have showed that NG2 cells can form synapses with neurons. This type of synapses can functionally integrated into their local network and undergo activity-dependent modifications analogous to long-term potentiation (LTP) at excitatory synapses, a hallmark of neuronal plasticity. We hypothesis that the increasing NG2 cells may play a role in the aberrant network formation after seizure in the developing brain through myelination and synapses with neuron. Inducing the differentiation of NG2 cells may help promote the remyelination,prevent axon sprouting and reduce the synapotgenesis to repair the seizure-related brain injury. This study is designed to concern about the role of increasing NG2 cells in aberrant network formation in hippocampus of immature brain after seizure in vivo and in vitro.

小儿惊厥发生率远高于成人，且容易出现惊厥持续状态，可导致以海马神经元死亡和异常神经环路形成为特征的惊厥性脑损伤，继发癫痫、认知障碍等后遗症。本课题组前期研究发现，未成熟脑内海马神经元对惊厥性损伤具有相对耐受性，髓鞘却存在比成熟脑更严重的持续性损伤，而形成髓鞘的少突胶质前体细胞（NG2细胞）呈明显增生，提示惊厥后发育期脑内存在显著的髓鞘化障碍，可能形成异常神经环路，增加继发惊厥的易感性，NG2细胞具有重要作用。本课题拟在前期基础上，以NG2细胞为中心，结合在体和体外实验，研究惊厥后不同发育期脑内NG2细胞结构和功能的变化，从髓鞘化障碍、突触形成异常两个方面，对比观察NG2细胞分化异常在惊厥后异常神经环路形成中的作用及其年龄差异；进而探索针对性调控NG2细胞分化，能否促进髓鞘修复，减少轴突芽生及异常突触的形成，降低惊厥易感性，减少继发癫痫和认知障碍，为临床有效防治小儿惊厥性脑损伤提供理论依据。

惊厥是小儿时期最常见的神经系统急症，小儿惊厥不仅发生率高，且容易出现严重惊厥和惊厥持续状态。临床及实验研究证明，长时程惊厥或惊厥持续状态发作后，易导致以选择性海马神经元死亡、异常神经环路形成为特征的惊厥性脑损伤，遗留癫痫、智力低下等后遗症。因此，从神经元、神经环路形成等不同途径阐明未成熟脑惊厥性脑损伤的病理生理机制，将为有效修复惊厥性脑损伤提供理论依据。 本研究以NG2细胞为中心，从髓鞘化异常及突触形成异常两个方面，对比研究NG2细胞分化障碍在惊厥后形成异常环路中的作用以及年龄差异；进而探索针对性调控NG2细胞分化，能否促进髓鞘修复，减少轴突芽生及异常突触的形成，为阐明未成熟脑惊厥性脑损伤的病理生理机制，有效修复惊厥性脑损伤提供理论依据。结果发现，在SC后癫痫发生过程中，NG2细胞虽增殖却分化成熟障碍，且伴有髓鞘损伤、轴突病变、苔藓纤维芽生及突触形成数量和结构异常等现象。通过设计Lingo-1逆转录病毒，可有效调控NG2细胞的增殖分化。抑制Lingo-1的表达，可促进NG2细胞增殖分化成熟，且能有效改善惊厥后髓鞘、轴突损害及异常突触的形成，明显降低未成熟脑的惊厥易感性，对认知功能也有改善。本研究结果提示，通过Lingo-1慢病毒表达载体调控NG2细胞的分化，使其在SC后有效增殖并分化为成熟的少突胶质细胞，可提高未成熟脑对惊厥的耐受力，降低惊厥阈值，从而达到修复惊厥性脑损伤的目的，这将是内源性修复惊厥性脑损伤的有效途径。