Potential Contribution of Environmental Metals to ALS

描述(申请人提供)：肌萎缩侧索硬化症(ALS)是一种进行性、退行性和致命性神经系统疾病，涉及骨骼肌功能下降，原因是上端和/或下端运动神经元丧失。肌萎缩侧索硬化症的临床症状包括骨骼肌无力、肌肉抽筋和疲劳、说话含糊和吞咽困难。肌萎缩侧索硬化症通常出现在IFE的较晚阶段。肌萎缩侧索硬化症的细胞退化专门发生在神经系统。目前已鉴定出两种形式的肌萎缩侧索硬化症。大多数ALS病例被称为散发性(SALS)，其病因不明，但没有ALS家族史。5-12%的ALS病例被称为家族性ALS(FALS)。其中一些似乎是由于超氧化物歧化酶-1(SOD1)基因的一些已识别的、遗传的突变所致，超氧化物歧化酶-1基因编码含有SOD的铜/锌。肌萎缩侧索硬化症是如何导致运动神经元退化的尚不清楚，尽管有几种假定的机制被认为与肌萎缩侧索硬化症有关。一个主要的假设机制是谷氨酸介导的兴奋性毒性，可能是由于：O损害星形胶质细胞对谷氨酸的摄取。兴奋性毒性后，细胞内[Ca]([Ca]|)升高，随后线粒体损伤，产生活性氧，所有这些都可能导致运动神经元变性。环境暴露因素对肌萎缩侧索硬化症的病因的贡献已被反复假设，但没有特定的环境暴露因素与肌萎缩侧索硬化症有明确的联系。在环境毒物中)被认为是ALS病因学的可能贡献者包括神经毒性重金属，特别是Hg2+、Pb2*和CD2*这一R21建议旨在测试这样一种假设，即运动神经元暴露于甲基汞(MeHg)-使其容易受到兴奋性毒性损伤。在许多类型的神经元中，甲基汞增加[Ca]；，破坏线粒体功能，并导致囊泡谷氨酸从神经末梢释放。这些行为中的任何一种都可能有助于提高运动神经元对随后的环境暴露损伤的敏感性，或者有助于具有尚未确定的ALS遗传易感性的运动神经元。一种过度表达人类突变体SOD1(G93A)的转基因小鼠将被用来比较普遍接受的FALS动物模型中的甲基汞车队。拟议的研究将涉及荧光测量出生后慢性甲基汞暴露后SOD1小鼠脑干脑片中舌下运动神经元[Ca]h谷氨酸释放和线粒体钙离子的变化。甲基汞加剧肌萎缩侧索硬化症症状发作的能力将通过旋转棒试验进行检查，以确定甲汞是否更快地出现肌萎缩侧索硬化症样表型。拟议的探索性研究结果应提供证据，支持或反对环境暴露于甲基汞，作为ALS期间运动神经元退化的可能贡献者-特别是在易感或遗传易感人群中。

DESCRIPTION (provided by applicant): Amyotrophic Lateral Sclerosis (ALS) is a progressive, degenerative and fatal neurological disorder which involves decreased skeletal muscle function as a result of loss of upper and/or lower motor neurons. Clinical signs of ALS include skeleta muscle weakness, muscle cramping and fatiguing, slurred speech and difficulty swallowing. ALS typically presents later in ife. Cellular degeneration in ALS occurs specifically in the nervous system. Two forms of ALS have been identified. The vasi majority of cases of ALS are referred to as sporadic (SALS), in which the etiology of the disease is unknown, but there is no family history of ALS. Between 5-12% of ALS cases are referred to as Familial ALS (FALS). Some of these appear to be due to a number of identified, inherited mutations in superoxide dismutase-1 (SOD1) the gene which encodes Cu/Zn containing SOD. How ALS causes motor neuron degeneration is as yet unknown, although several postulated mechanisms are thought to contribute to ALS. One major hypothesized mechanism is glutamate mediated excitotoxicity, perhaps due :o impaired astrocytic uptake of glutamate. Following excitotoxicity, elevations of intracellular [Ca] ([Ca]|) with subsequent mitochondrial damage and generation of reactive oxygen species occur; all of these could contribute to motor neuron degeneration. Contribution of environmental exposure factors to the etiology of ALS has been repeatedly hypothesized, bul no specific environmental exposure factors have definitively been linked with ALS. Among the environmental toxicants )roposed as possible contributors to the etiology of ALS include neurotoxic heavy-metals, particularly Hg2+, Pb2* and Cd2* This R21 proposal is designed to test the hypothesis that exposure of motor neurons to methylmercury (MeHg)-predisposes them to excitotoxic damage. In a number of types of neurons, MeHg increases [Ca];, disrupts mitochondrial function,, and causes release of vesicular glutamate from nerve endings. Any of these actions could contribute to enhanced sensitivity of motor neurons to subsequent environmental exposure damage, or in motor neurons having as yet undetermined genetic predisposition to ALS. A transgenic mouse line overexpressing the human mutant SOD1 (G93A) will be used to compare fleets of MeHg in a commonly accepted animal model of FALS. Proposed studies will involve fluorescent measurements of changes in [Ca]h glutamate release and mitochondrial Ca2+ in hypoglossal motor neurons in slices of brainstem of SOD1 mice following chronic MeHg exposure postnatally. The ability of MeHg to exacerbate the onset of ALS-signs will be examined using a rotarod test to determine if the onset of ALS-like phenotype is faster with MeHg. Results of the proposed exploratory study should provide evidence for or against environmental exposure to MeHg as a. possible contributor to motor neuron degeneration during ALS-particularly in susceptible or genetically predisposed populations.