MOLECULAR MECHANISMS OF HEXACARBON-INDUCED AXON ATROPHY

2，5-己二酮（HD）是工业溶剂甲基正丁基酮和正己烷的神经毒性γ-二酮代谢物，可引起远端轴突病。 巨大的神经纤维轴突索被认为是其形态学特征，因此，一直是机制研究的焦点。 然而，已发表的证据表明，轴突萎缩，这也发生在响应γ-二酮中毒，可能是一个重要的致病事件。 在当前资助期间，PI实验室进行的定量形态测定研究表明，HD中毒大鼠外周神经中的纤维萎缩是一种特定的普遍效应，与神经传导异常在时间上相关，并先于行为缺陷。这些发现表明萎缩是γ-二酮诱导的神经毒性的重要病理生理学组成部分。 平行分子测定表明，神经丝（NF）基因表达和神经含量的减少是HD暴露大鼠轴突口径减少的直接原因。 相反，我们的研究表明，巨轴突solding是一种附带现象，与低剂量HD暴露。 本研究项目的长期目标是评估轴突萎缩的神经毒理学相关性，并确定相应的分子机制。 HD如何诱导NF合成的选择性减少是未知的。 过去十年的研究表明，成熟的轴突口径是通过靶源性神经营养因子对NF表达的影响来维持的。因此，我们假设γ-二酮诱导的轴突萎缩是由神经元营养因子信号传导的破坏产生的。本研究拟从以下几个方面对这一假说进行验证：（1）在γ-二酮中毒大鼠的外周神经轴上，检测神经营养因子（BDNF，NGF）信号复合物的形成、激活和逆行转运。(2)将测定γ-二酮对神经营养素-trk受体结合和神经元内化的影响。(3)评估γ-二酮中毒对Ras信号转导通路的神经营养素-受体复合物刺激和MAP激酶活化以及随后的核转位的影响。 拟议的研究代表了一个新的研究领域的毒性轴突病的机制，并具有广泛的影响，获得性或遗传性人类神经病变与纤维萎缩。 此外，我们的研究可能会提出新的药物治疗的基础上神经营养因子的干预或替代。

2,5-Hexanedione (HD), the neurotoxic gamma-diketone metabolite of industrial solvents methyl n-butyl ketone and n-hexane, causes distal axonopathy. Giant neurofilamentous axonal swellings have been considered the morphologic hallmark and, accordingly, have been the focus of mechanistic research. However, published evidence suggests that axon atrophy, which also occurs in response to gamma-diketone intoxication, might be a significant pathogenic event. Quantitative morphometric studies conducted in the PI's laboratory during the current funding period showed that fiber atrophy in peripheral nerve of HD-intoxicated rats was a specific, prevalent effect that was temporally correlated to nerve conduction abnormalities and preceded behavioral defects. These findings implied atrophy was an essential pathophysiologic component of gamma-diketone-induced neurotoxicity. Parallel molecular determinations suggested that a reduction in neurofilament (NF) genetic expression and nerve content were the immediate cause of decreased axon caliber in HD exposed rats. In contrast, our research indicated giant axonal swellings were an epiphenomenon related to low dose HD exposure. The long-term objectives of this research project are to evaluate the neurotoxicological relevance of axonal atrophy and determine the corresponding molecular mechanism. How HD induces a selective reduction in NF synthesis is unknown. Research over the past decade has shown that mature axon caliber is maintained by target-derived neurotrophic factor influence on NF expression. Therefore, we hypothesize gamma-diketone-induced axon atrophy is produced by disruption of neuronal trophic factor signaling. This hypothesis will be tested according to the following specific aims: (1) The formation, activation and retrograde transport of neurotrophin (BDNF, NGF) signal complexes will be measured in peripheral nerve axis of gamma-diketone intoxicated rats. (2) gamma-Diketone influences on neurotrophin-trk receptor binding and neuronal internalization will be determined. (3) Assess the effects of gamma-diketone intoxication on neurotrophin-receptor complex stimulation of the Ras signal transduction pathway and activation of MAP kinase and subsequent nuclear translocation. The proposed research represents a new area of investigation into mechanisms of toxic axonopathies and has broad-based implications for acquired or inherited human neuropathies associated with fiber atrophy. In addition, our studies might suggest novel pharmacotherapies based on neurotrophin intervention or replacement.