正常神经元细胞极易受放射损伤，促进受损后神经元再生十分重要。申请人在小脑外颗粒层（EGL）中发现一群正常在体内处于静息状态的前体细胞（NEPs），当放射线杀伤几乎所有皮质中的神经元细胞后，NEPs可以活化增殖，补充损失的神经元，参与小脑功能的恢复。进一步研究发现，放射线可使NEPs中HMGA表达上调，由于HMGA的表达水平对恢复神经细胞再生能力至关重要，我们推测NEPs中HMGA的表达上调诱导其活化，而HMGA自身受miRNA调控， miRNA的表达与NEPs表观遗传特征相关。本项目拟以这群细胞为研究对象，利用转基因小鼠体内实验结合原代神经细胞体外诱导培养，确证其在小脑放射损伤修复中的重要作用，阐明其放射抵抗及再生机制，明确表观遗传因素、miRNA、HMGA与NEPs活化的关系。本项目的实施将进一步加深对神经细胞再生激活机制的认识，为开发促进损伤后脑功能恢复的有效治疗措施奠定应用研究基础。

Radiation therapy is part of the first-line treatment for this tumor, and in combination with chemotherapy and surgery has resulted in a marked improvement in survival for brain tumor patients. Even though radiation is very effective at killing tumor cells, it also causes significant destruction to normal neuronal populations in the developing cerebellum. Children who undergo radiotherapy and survive often suffer severe side effects such as cognitive deficits and coordination problems. Currently there is no successful treatment for these long-term impairments. The goals of this study are to investigate how neuronal progenitors in cerebellum respond to radiation, and identify progenitors that are capable of regenerating cerebellum damaged by radiation. Granule neuron precursors (GNPs) generate the most abundant neurons in cerebellum, and are highly sensitive to radiation. It has been previously reported that moderate level of irradiation induces massive cell death among GNPs, but a subset of progenitors have the capacity to repopulate the cerebellum. Our preliminary data suggest that a subset of cerebellar progenitor that expresses Nestin (a cytoskeleton protein commonly used as a maker for neural stem cells) may represent such regenerative cells. These Nestin expressing progenitors (NEPs) are resistant to radiation and start propagation following radiation. The HMGA associated chromatin-remodeling may be involved in this process. It should be taken into consideration that HGMA genes are targeted by miR-15, miR-16, miR-26a, miR-196a2 and Let-7a, and some of these microRNAs (miR-16, miR-196a and Let-7a) have methylated promoters. Characterization of the radio-resistant and regenerative properties of NEPs is a critical first step towards developing novel approaches to mitigate the damage in the cerebellum after radiotherapy. Upon completion of this project, we will elucidate the important role of chromatin-remodeling in NEPs activation following radiotherapy, which will shed light on the molecular basis of neural cells regeneration. Our studies will demonstrate that regulation of NEPs chromatin state is important for neural cells regeneration, and could be used to design combined approaches for brain tumor radiotherapy.