Neuronal regulation of myelination

描述(申请人提供)：在包括人类在内的脊椎动物中，外周(PNS)和中枢神经系统(CNS)的快速神经元通讯依赖于适当的髓鞘形成。PNS的髓鞘形成细胞为雪旺细胞(SC)，中枢神经系统的髓鞘形成细胞为少突胶质细胞(OL)。这些特殊的细胞包裹神经元突起，从而促进电脉冲的快速传播。PNS髓鞘在几种类型的Charcot-Marie-Tooth(CMT)病中存在缺陷，这是最常见的遗传性神经疾病之一。中枢神经系统髓鞘的异常发育会导致称为脑白质营养不良的疾病。我们之前描述了一种严重的周围神经病CMT4J，它是由人类FIG4/SAC3基因突变引起的，该基因编码一种进化保守的脂磷酸酶，调节细胞内溶酶体途径的囊泡运输。我们研究的主要目的是了解FIG4缺乏扰乱髓鞘形成的分子机制，并在临床前模型中开发CMT4J的治疗策略。Fig4表达整体缺失的突变小鼠(图4-/-)表现出中枢和三叉神经节髓鞘显著减少，严重震颤和幼年死亡。电生理记录显示，坐骨神经和视神经的电脉冲传导速度减慢。令人惊讶的是，图4-/-小鼠的髓鞘缺陷可以通过野生型Fig4的神经元特异性表达来“拯救”。基于这些观察，我们假设图4的缺失扰乱了髓鞘形成所需的神经元特异性信号机制。在特定的目标1和目标2中，我们使用小鼠遗传学和蛋白质组学的组合来识别图4突变小鼠中被破坏的神经元髓鞘信号，并确定在体内对图4的时间需求。这些实验将为指导髓鞘发生的神经元信号提供新的机械性见解。为了建立人类CMT4J的模型，我们开发了在图4-/-背景(CMT4J小鼠)上普遍表达低水平人类疾病等位基因Fig4-I41T的转基因小鼠。这些小鼠表现出与图4-/-小鼠类似的髓鞘过少，但存活到成年，具有许多人类疾病的神经学特征。由于我们已经证明Fig4在神经元中的转基因表达足以驱动髓鞘形成，我们提出了一项针对特定目的的基因治疗研究3。将病毒载体转导CMT4J小鼠的背根节神经元(PNS)和视网膜神经节细胞(CNS)表达野生型Fig4。将监测坐骨神经或视神经的髓鞘形成、结节结构和神经传导速度，作为疗效的指标。通过图4基因疗法恢复小鼠的髓鞘形成，将为髓鞘形成障碍患者提供一种新的治疗途径。

DESCRIPTION (provided by applicant): In vertebrates, including humans, rapid neuronal communication in the peripheral (PNS) and central nervous system (CNS) is dependent on proper myelination. The myelin-forming cell in the PNS is the Schwann cell (SC) and in the CNS the oligodendrocyte (OL). These specialized cells ensheath neuronal processes and thereby facilitate rapid propagation of electrical impulses. PNS myelin is defective in several types of Charcot-Marie-Tooth (CMT) disease, one of the most common inherited neurological disorders. Abnormal development of myelin in the CNS results in disorders known as leukodystrophies. We previously described the severe peripheral neuropathy CMT4J, caused by mutation of the human FIG4/SAC3 gene encoding an evolutionarily conserved lipid phosphatase that regulates intracellular vesicle trafficking along the endo-lysosomal pathway. The main objectives of our research are to understand the molecular mechanisms by which FIG4 deficiency disrupts myelin formation, and to develop treatment strategies for CMT4J in a preclinical model. Mutant mice with global loss of Fig4 expression (Fig4-/-) exhibit dramatic reduction of myelin in the CNS and PNS, severe tremor, and juvenile lethality. Electrophysiological recordings revealed slowed conduction of electrical impulses in sciatic and optic nerves. Surprisingly, the myelin defects in Fig4-/- mice can be "rescued" by neuron-specific expression of wildtype Fig4. Based on these observations, we hypothesize that loss of Fig4 disrupts neuron-specific signaling mechanisms required for myelination. In Specific Aim 1 and Aim 2 we use a combination of mouse genetics and proteomics to identify the neuronal myelination signals that are disrupted in Fig4 mutant mice and to determine the temporal requirement for Fig4 in vivo. These experiments will provide new mechanistic insights into the neuronal signals that direct myelinogenesis. To model human CMT4J, we developed transgenic mice that ubiquitously express low levels of the human disease allele Fig4-I41T on a Fig4-/- background (CMT4J mice). These mice exhibit hypomyelination comparable to that of Fig4-/- mice, but survive to adulthood with many neurologic features of the human disease. Since we have shown that transgenic expression of Fig4 in neurons is sufficient to drive myelination, we propose a gene therapy study in Specific Aim 3. Dorsal root ganglion neurons (PNS) and retinal ganglion cells (CNS) of CMT4J mice will be transduced with viral vectors to express wildtype Fig4. Myelination, nodal structure, and nerve conduction velocity in sciatic or optic nerve will be monitored as indicators of efficacy. Restoration of myelination by Fig4 gene therapy in mice would demonstrate a new therapeutic avenue for patients suffering from myelination disorders.