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、退行性和致死性神经系统疾病，涉及由于上和/或下运动神经元丧失导致的骨骼肌功能下降。肌萎缩侧索硬化症的临床症状包括肌无力、肌肉痉挛和疲劳、言语不清和吞咽困难。ALS通常在生命后期出现。ALS中的细胞变性特别发生在神经系统中。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（Familial ALS）。其中一些似乎是由于超氧化物歧化酶-1（SOD1）中的一些已鉴定的遗传突变，该基因编码含Cu/Zn的SOD。ALS如何引起运动神经元变性尚不清楚，尽管有几种假设的机制被认为有助于ALS。一个主要的假设机制是谷氨酸介导的兴奋性毒性，可能是由于受损的星形胶质细胞摄取谷氨酸。兴奋性毒性后，细胞内[Ca]（[Ca] i）升高，随后发生线粒体损伤和活性氧的产生;所有这些都可能导致运动神经元变性。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明确相关。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Hg 2+、Pb 2+和Cd 2+。这项R21建议旨在检验运动神经元暴露于甲基汞（MeHg）-使其易于受到兴奋性毒性损伤的假设。在许多类型的神经元中，甲基汞增加[Ca] i，破坏线粒体功能，并导致神经末梢释放囊泡谷氨酸。这些行为中的任何一种都可能有助于增强运动神经元对随后的环境暴露损伤的敏感性，或者在运动神经元中具有尚未确定的ALS遗传易感性。将使用一种过表达人类突变SOD 1（G93A）的转基因小鼠品系，比较一种普遍接受的FALS动物模型中的甲基汞船队。拟议的研究将涉及荧光测量的变化[Ca] i谷氨酸释放和线粒体Ca2+在舌下神经运动神经元在脑片的SOD 1小鼠的脑干慢性甲基汞暴露出生后。将使用转棒试验检查甲基汞加剧ALS体征发作的能力，以确定甲基汞是否更快地出现ALS样表型。拟议的探索性研究的结果应提供证据支持或反对环境暴露于甲基汞作为一个可能的贡献者运动神经元变性在ALS，特别是在易感或遗传易感人群。

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.