成年外周神经系统中神经发生的一种新模式—背根节感觉神经元前体的来源、特征及proBDNF对其分化成熟的研究

Neuronal addition in the postnatal DRG in rats, and other species, has been defined but the mechanism underlying this phenomenon is not understood. So far there have been only a few studies focusing on the neurogenesis in the adult PNS possibly due to the difficulty in identification of the new-born cells. In human, chronic pain is the most common medical condition which causes disability and loss of working force. There is no effective treatment for some types of pain such as neuropathic pain because the underlying mechanisms are not fully understood.Our study indicates that the number of sensory neurons in the dorsal root and trigeminal ganglia is increased with ageing. The sensory neuron addition with ageing and with peripheral nerve injury may underlie the pathogenesis of chronic pain in aged people.This study will lead to the identification of sensory neuron precursors in postnatal DRG and the understanding of how the proBDNF regulate the maturation of these committed precursors. This study will also shed light on how the number of sensory neurons matches dramatically increasing innervating territories during the postnatal somatic growth and links the outside environment to the brain. The elucidation of the identity of the postnatal sensory neuron addition will pave the way to a further understanding of periphery sensory neuropathy during chronic afflictions for example, diabetes, and cancer-chemotherapy regime, and regeneration after peripheral nerve injury.

已知成年CNS的神经发生在大脑可塑性、学习记忆和损伤修复中起关键作用。成年PNS的神经发生也同样具有重要意义，但却重视不够，原因之一就是很难确定新生神经元的来源。神经病理性疼痛是一种难以治愈的慢性痛状态，产生机制不完全清楚，再生过程中新老神经元错误环路的形成是原因之一。前期研究发现背根节（DRG）成年时感觉神经元明显多于新生时；外周神经损伤后DRG中神经元先减后增；DRG某些卫星细胞（SGC）在proBDNF抗体作用下表达DCX、Tuj1等早期神经元标记物，具有神经元前体细胞的特征，提示这些细胞可能来源于SGC的某个休眠期亚群；这可能是一种不同于CNS的新的神经发生方式。本项目拟采用外周神经损伤模型、体内示踪、免疫荧光、抗体封闭、分子生物学等技术和方法，确定这些细胞的来源及特性，以及proBDNF在其成熟过程中的作用及机制。为进一步阐明外周神经发生和神经病理性疼痛机制提供一种新的理论依据。

中枢神经系统中脑源性神经营养因子前体(proBDNF)和脑源性神经营养因子（BDNF）发挥不同的作用，他们的受体和信号通路也不同。与BDNF促进神经元生长的作用相反，proBDNF诱导细胞凋亡，抑制神经元存活。目前对于proBDNF的研究多集中于中枢神经系统，例如小脑，大脑皮质，海马等，然而在外周神经系统proBDNF发挥怎样作用？其在神经元分化成熟过程中的调控机制目前仍没有清楚的研究。本研究结合体内和体外实验成功分离培养和鉴定出背根节卫星胶质细胞（DRG- SGCs），推测神经元前体细胞可能是在大鼠妊娠的19天左右从细胞周期进入到休眠期；且进入休眠期的细胞属于卫星细胞的特殊亚群，可能是感觉神经元前体细胞的来源；proBDNF可能参与了正常和外周神经损伤大鼠神经元前体细胞的分化成熟过程。体外成功分离和鉴定出生后感觉神经元前体细胞群，并结合体内及体外实验初步确定了休眠期感觉神经元前体细胞的起源和特征，推测DRG中存在一类休眠期SGCs，一定条件下能向神经元样细胞分化；发现抗proBDNF血清诱导SGCs可转化为神经元前体细胞，进一步诱导可分化为成熟神经元。本项目发现一种不同于中枢神经系统 的新的神经发生方式，为进一步阐明外周神经发生和神经病理性疼痛机制提供一种新的理论依据。