AMPA Receptor Expression and Selective Neuronal Death

描述(申请人提供)：肌萎缩侧索硬化症(ALS)，一种致命的进行性神经退行性疾病，运动神经元选择性死亡，原因尚不完全清楚。这种显著的选择性脆弱性为了解这种毁灭性疾病的机制提供了重要线索。有证据表明，ALS涉及AMPA受体介导的谷氨酸兴奋毒性，我们的工作已经开始阐明这一机制对运动神经元的选择性基础。我们发现，培养的脊髓运动神经元对兴奋性毒性的易感性与其对钙具有特别高的通透性或特别弱的脱敏程度的AMPA受体的表达无关，而是与AMPA受体在非常高的表面密度下的表达有关。这种高密度表达功能性AMPA受体的特性，似乎足以解释脊髓运动神经元在体外的选择性脆弱性。更广泛地说，作为整个项目的一个主题的假设是，ALS中运动神经元的选择性脆弱性可能在很大程度上可以通过其谷氨酸受体表达的独特特征来解释。 本提案将延长最初供资期间的工作，以解决与这一假设有关的三个重要问题。具体目的1利用膜片钳技术和分子生物学技术对成年大鼠急性脊髓切片上的运动神经元进行研究，明确脊髓组织环境中成熟运动神经元表达AMPA受体的生理和分子特征。特定目标2将研究与疾病相关的AMPA受体表达获得性改变是否会影响兴奋性毒性的易感性。特别是，将研究慢性暴露于亚致死浓度的NO对G1uR2 mRNA编辑的影响。具体目标3将确定构成皮质脊髓束的上运动神经元是否也表现出解释其选择性易损性的AMPA受体表达模式。 这些实验将有助于确定ALS运动神经元退化的非常明确的机制，使治疗的分子靶点成为焦点。

DESCRIPTION (provided by applicant): Amyotrophic lateral sclerosis (ALS), a fatal progressive neurodegenerative disorder, motor neurons selectively die, for reasons that are incompletely understood. This remarkable selective vulnerability provides an important clue to the mechanism of this devastating disease. Evidence suggests that ALS involves glutamate excitotoxicity mediated by AMPA receptors, and our work has begun to elucidate the basis for the selectivity for motor neurons of this mechanism. We showed that vulnerability to excitotoxicity of cultured spinal motor neurons correlates not with their expression of AMPA receptors having a particularly high permeability to Ca2 or a particularly weak degree of desensitization, but rather with expression of AMPA receptors at a very high surface density. This property, expression of a high density of functional AMPA receptors, appears to be sufficient to explain the in vitro selective vulnerability of spinal motor neurons. More generally, the hypothesis serving as a theme of the entire project is that motor neuron selective vulnerability in ALS may be largely explained by the unique features of their glutamate receptor expression. The present proposal will extend the work of the initial funding period to address three important issues relating to this hypothesis. Specific aim 1 will define the physiological and molecular characteristics of AMPA receptors expressed by mature motor neurons in the tissue environment of the spinal cord, using patch-clamp and molecular techniques applied to motor neurons in acute spinal cord slices from mature rats. Specific aim 2 will examine whether disease-related acquired alterations in AMPA receptor expression might affect vulnerability to excitotoxicity. In particular, the effects of chronic exposure to sub-lethal concentrations of NO on the editing of mRNA for G1uR2 will be examined. Specific aim 3 will determine whether upper motor neurons, which form the corticospinal tract, also exhibit a pattern of AMPA receptor expression that explains their selective vulnerability. These experiments will help to define a very clear mechanism for motor neuron degeneration in ALS putting molecular targets for therapy into sharp focus.