Changes in cytoskeletal organization and metabolism related to maturation and aging of the neuron.

为了了解细胞骨架组织和代谢的变化，这些变化是正常衰老和疾病期间观察到的神经退行性过程的基础，我们用轴突运输系统研究了培养神经元和活体内轴突细胞骨架的性质。轴突细胞骨架的主要特征之一是存在大量的微管蛋白，该微管蛋白在各种条件下都是不溶的，可使胞质微管脱溶（MT）。这种不溶性微管蛋白的比例在发育或再生过程中变化，表明其参与轴突中MT的稳定。在培养的背根神经节神经元中，我们发现在突起形成过程中出现了不溶性微管蛋白，并且数量增加。使用视频增强显微镜，不溶性微管蛋白被进一步鉴定为MT，其即使在通过去污剂脱膜暴露于细胞外介质后也是稳定的。β-亚氨基二丙腈，其破坏轴突细胞骨架的组织并抑制NF转运。相关的tau蛋白作为MT稳定化的另一个因素进行了研究。与脑MT相关的tau蛋白（由44- 66 kDa和宽pI范围的许多同种型组成）相比，从外周轴突分离的tau蛋白仅含有高度磷酸化的最酸性同种型。超过60%的轴突tau蛋白是不溶性的。坐骨神经轴突运输研究表明，不溶性tau蛋白与不溶性微管蛋白在SCa中以最慢的速率运输，这表明tau蛋白与稳定的MT之间存在密切联系。可溶性tau蛋白在SCb中的转运速度明显加快。

To understand the changes in cytoskeletal organization and metabolism which underly neurodegenerative processes observed during normal aging as well as disease, we studied the properties of the axonal cytoskeleton in cultured neurons and in vivo using the axonal transport system.One of the major characteristics of the axonal cytoskeleton is the presence of a large amount of tubulin which is insoluble under various conditions to depolymerize cytoplasmic microtubules (MTs). The proportion of such insoluble tubulin varies during development or regeneration, suggesting its involvement in MT stabilization in the axon. In dorsal root ganglion neurons in culture, we found that insoluble tubulin appeared and increased in amount during neurite formation. Using video-enhanced microscopy, insoluble tubulin was further identified with MTs which were stable even after exposure to extracellular medium by detergent demembranation.Phosphorylation state of neurofilaments (NFs) was found to be one of the factors regulating tubulin solubility through NF-MT interaction by the use of beta, beta'-iminodipropionitrile which disrupts the organization of the axonal cytoskeleton and inhibits NF transport.MT-associated proten tau was studied as another factor in MT stabilization. Compared with tau associated with brain MTs, which consists of many isoforms ranging between 44-66kDa and wide pI ranges, tau isolated from the peripheral axon contained only the most acidic isofoms that were highly phosphorylated. More than 60% of axonal tau was insoluble. Axonal transport studies in the sciatic nerve showed that insoluble tau was transported with insoluble tubulin at the slowest rate in SCa, suggesting the close association between tau and the stable MTs. Soluble tau was transported significantly faster in SCb.