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。巨大的神经丝状轴突肿胀被认为是形态学上的标志，因此一直是机制研究的焦点。然而，已发表的证据表明，轴突萎缩也发生在对γ -二酮中毒的反应中，可能是一个重要的致病事件。PI实验室在当前资助期内进行的定量形态学研究表明，hd中毒大鼠周围神经纤维萎缩是一种特定的、普遍的效应，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暴露大鼠轴突直径减少的直接原因。相反，我们的研究表明，巨大的轴突肿胀是与低剂量HD暴露相关的附带现象。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合成选择性减少尚不清楚。过去十年的研究表明，成熟的轴突直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-二酮诱导的轴突萎缩是由神经元营养因子信号的破坏引起的。我们将根据以下具体目的对这一假设进行验证：(1)测量γ -二酮中毒大鼠周围神经轴神经营养因子（BDNF、NGF）信号复合物的形成、激活和逆行运输。(2) γ -二酮对神经营养因子-trk受体结合和神经元内化的影响将被确定。(3)评估γ -二酮中毒对神经营养因子受体复合物刺激Ras信号转导通路和MAP激酶激活及随后核易位的影响。提出的研究代表了毒性轴突病机制研究的新领域，并对与纤维萎缩相关的获得性或遗传性人类神经病变具有广泛的意义。此外，我们的研究可能建议基于神经营养因子干预或替代的新型药物治疗。

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.