Potential Contribution of Environmental Metals to ALS

描述（由申请人提供）：肌萎缩性侧索硬化症（ALS）是一种进行性、退行性和致命的神经系统疾病，由于上部和/或下部运动神经元的丧失而导致骨骼肌功能下降。ALS的临床症状包括骨骼肌无力、肌肉痉挛和疲劳、言语不清和吞咽困难。ALS通常出现在生命的后期。肌萎缩侧索硬化症的细胞退化主要发生在神经系统。已经确定了两种形式的ALS。绝大多数ALS病例被称为散发性（SALS），其中疾病的病因不明，但没有ALS家族史。5-12%的ALS病例被称为家族性ALS。其中一些似乎是由于超氧化物歧化酶-1 （SOD1）基因的一些已确定的遗传突变，SOD1基因编码含SOD的Cu/Zn。肌萎缩侧索硬化症是如何引起运动神经元退化的尚不清楚，尽管有几种假设的机制被认为是导致肌萎缩侧索硬化症的原因。一个主要的假设机制是谷氨酸介导的兴奋性毒性，可能是由于星形细胞对谷氨酸的摄取受损。兴奋性毒性发生后，细胞内[Ca] （[Ca]i）升高，随后线粒体损伤并产生活性氧；所有这些都可能导致运动神经元退化。环境暴露因素对ALS病因的贡献已被反复假设，但没有特定的环境暴露因素与ALS有明确的联系。被认为可能导致ALS病因的环境毒物包括神经毒性重金属，特别是Hg2+、Pb2+和Cd2+。这项R21提案旨在验证运动神经元暴露于甲基汞（MeHg）的假设，甲基汞使运动神经元容易受到兴奋性毒性损伤。在许多类型的神经元中，MeHg增加[Ca]，破坏线粒体功能，并导致神经末梢释放水泡状谷氨酸。这些行为中的任何一种都可能导致运动神经元对随后的环境暴露损伤的敏感性增强，或者运动神经元对ALS的遗传易感性尚未确定。一种过表达人类突变体SOD1 （G93A）的转基因小鼠系将被用于比较FALS动物模型中MeHg的船队。拟议的研究将包括荧光测量出生后慢性甲基汞暴露后SOD1小鼠脑干切片中[Ca]i谷氨酸释放和线粒体Ca2+的变化。MeHg加重als症状发作的能力将通过旋转杆试验进行检查，以确定MeHg是否更快地发作als样表型。提出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因素，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 vast 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]i) 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, but 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]i 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]i 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.