BDNF-TrkB信号在前庭代偿过程中的表达调控及机制研究

It remains unclear about the etiology and pathogenesis of vertigo, and the treatment of vertigo is very difficult in clinics. The mechanisms of vestibular compensation, which bases on the plasticity of the central nervous system, have not been elucidated. Brain-derived neurotrophic factor (BDNF) is a member of the neurotrophin family, BDNF-tyrosine receptor kinase B (TrkB) signaling can modulate synaptic plasticity on both excitatory and inhibitory synapses in the developed nervous system. It is reported that BDNF can promote the process of vestibular compensation, we found that BDNF and its receptor TrkB were expressed in both the Purkinje cells in the flocculus and Purkinje cell terminals in the medial vestibular nucleus(MVN) in the rat, furthermore, unilateral labyrinthectomy (UL) can downregulate the KCC2 (a switch in BDNF signaling) in the flocculus and MVN. These results suggest that BDNF-TrkB signaling may play important roles in the process of vestibular compensation. In this study, we use a variety of experimental techniques and methods to explore the roles and mechanisms of BDNF-TrkB signaling in rat cerebello-vestibular pathway after UL, in order to further reveal the mechanisms of vestibular compensation, and provide some neuropharmacology bases for the individualized comprehensive treatment of vertigo.

眩晕疾病的病因和发病机制迄今未明，临床上治疗较为困难。基于中枢可塑性的前庭代偿，目前机制尚未阐明。BDNF是神经营养因子家族的一员，在发达的神经系统内能调节兴奋性和抑制性突触的突触传递可塑性。动物实验发现BDNF能促进前庭代偿的恢复，我们新近实验发现大鼠绒球浦肯野细胞和MVN浦肯野终末有BDNF及其受体TrkB的表达, 单侧迷路切除术能下调MVN和绒球中BDNF信号通路中的关键因子KCC2。上述实验结果提示BDNF-TrkB信号在前庭代偿的发展过程中可能具有重要的意义和作用。本研究用多种实验技术和方法探讨大鼠小脑前庭通路中BDNF-TrkB信号在单侧迷路切除术后的作用及机制，旨在进一步揭示前庭代偿的机制，为眩晕疾病的临床药物治疗及个体化综合治疗奠定神经药理学基础。

所有的啮齿类动物动物单侧毁损迷路后都会引起一系列失代偿症状。这些症状逐渐减轻至消失的过程称为前庭代偿。单侧迷路切除术(UL)引起术侧前庭外周器官失传入，所以前庭代偿归因于中枢神经系统（CNS）可塑性。前庭代偿的机制很复杂且未完全阐明， 目前认为前庭代偿与前庭内侧核（MVN）神经元的自发性静息电位的恢复有关，而CNS内神经递质及调质的变化也在这个过程中起了重要的作用。脑源性神经营养因子（BDNF）是神经营养因子家族的一员，在发展过程中对神经元的存活和分化发挥作用，例如BDNF与与前庭系统的发展有关，BDNF基因的敲除引起小鼠严重的前庭神经元损失，在发达的神经系统内的BDNF可以调节兴奋性和抑制性突触的突触传递可塑性为探讨BDNF信号通路在前庭代偿过程中的作用机制，本研究用免疫组化，Western blot及实时定量PCR三种方法对大鼠MVN中BDNF, TrkB.FL, TrkB.T1和K+/ CL-协同转运蛋白亚型2 (KCC2)在UL后不同时程的变化进行研究，旨在进一步揭示前庭代偿的机制，为眩晕疾病临床药物治疗及个体化综合治疗奠定药理学基础。 .我们结果表明大鼠MVN内中存在BDNF，TrkB.FL, TrkB.T1及KCC2，大鼠术侧MVN内BDNF和TrkB.FL在UL后8小时升高,1天和7天时恢复到正常水平。大鼠术侧MVN内KCC2在UL后8小时降低,1天和7天时恢复到正常水平。TrkB.T1在UL后没有变化。UL可诱导大鼠术侧绒球内BDNF和TrkB.FL在UL后4小时升高， 8小时以后这种变化消失。大鼠术侧绒球内TrkB.T1在UL后4小时降低，8小时后恢复到正常水平；KCC2在UL后8小时和1天降低，3天和7天是恢复到正常水平。BDNF及其受体TrkB亚型都在绒球浦肯野细胞上有表达，并且与KCC2共表达于浦肯野细胞上。我们推测在UL后术侧MVN内BDNF升高通过其TrkB.FL受体下调了KCC2在术侧MVN内的表达，引起术侧MVN神经元去抑制作用，达到UL后双侧MVN神经元电活动平衡的恢复。UL后术侧绒球内BDNF升高通过其TrkB.FL及TrkB.T1受体下调了术侧绒球内KCC2的表达来调节绒球内抑制信号，从而减少对术侧MVN的单突触抑制作用，进一步引起术侧MVN神经元去抑制作用，达到UL后双侧MVN神经元静息活动的平衡。