Molecular basis of age-related synaptic alterations

描述(申请人提供)：与年龄相关的精神功能变化与中枢和外周神经系统的形态和分子变化有关，并可能是由于这种变化。大多数神经生物学家一致认为，其中一些变化涉及突触，但衰老与突触变化的关系知之甚少。神经肌肉接头(NMJ)是研究与年龄相关的突触结构和功能改变以及阐明其分子基础的理想系统。令人兴奋的初步结果表明，衰老导致NMJ突触前和突触后成分发生重大的形态和分子变化。 在突触前，轴突较少，曲张轴突较多，轴突出芽较多。突触后部位通常是支离破碎的，部分神经支配。伴随着这些形态变化，三种突触黏附分子--层粘连蛋白α4、层粘连蛋白β2和集聚蛋白在老年NMJ中显著降低。支持层粘连蛋白α4在衰老中的作用，它的缺失导致小鼠突触过早老化。令人惊讶的是，衰老和层粘连蛋白α4的缺失并没有改变眼外NMJ的形态，NMJ是一种在神经肌肉疾病--肌萎缩侧索硬化症(ALS)中幸免于难的肌肉。这些新的发现表明，层粘连蛋白α4、层粘连蛋白α2、集聚蛋白及其同源受体可能在突触老化和神经功能障碍中发挥关键作用。为了开始揭示这些分子在老化突触中的作用，我将首先使用免疫组织化学和原位杂交来评估这些分子何时以及如何减少。我还将在它们的受体中寻找与年龄相关的变化，如麝香、整合素和P/Q型钙通道。为了测试层粘连蛋白Beta2和集聚蛋白在衰老中的因果作用，我将使用条件性和杂合子小鼠来评估它们的缺失或大量减少是否会导致年轻成年NMJ的缺陷。最后，为了探讨衰老与ALS的关系，我将评估突触黏附分子在ALS小鼠模型中的表达。总而言之，这些研究可能会让我识别出可以减弱甚至逆转年龄对突触的有害影响的分子。因此，这些实验可以提供工具来改善认知和脊肌疾病背后的一些突触缺陷。

DESCRIPTION (provided by applicant): Age-related changes in mental function are associated with, and are presumably due to, morphological and molecular alterations in the central and peripheral nervous systems. Most neurobiologists agree that some of these changes involve synapses, but relationships of aging to synaptic alteration are poorly understood. The neuromuscular junction (NMJ) is an ideal system to examine age-associated structural and functional alterations in synapses, and to elucidate their molecular bases. Exciting preliminary results show that aging causes major morphological and molecular changes to the pre- and post-synaptic components of the NMJ. Presynaptically, there are fewer axons, more varicose axons and more axonal sprouting. The postsynaptic sites are often fragmented and partially innervated. Concomitant with these morphological changes, three synaptic adhesion molecules, laminin alpha4, laminin beta2 and agrin, are significantly decreased in aged NMJs. Supporting a role for laminin alpha4 in aging, its deletion causes premature synaptic aging in mice. Surprisingly, old age and the absence of laminin alpha4 do not alter the morphology of extraocular NMJs, a muscle also spared in the neuromuscular disease, amyotrophic lateral sclerosis (ALS). These novel findings suggest that laminin alpha4, laminin aeta2, agrin and their cognate receptors may play a critical role in synaptic aging and neurological disorders. To begin uncovering the role of these molecules in aging synapses, I will first assess when and how these molecules decrease using immunohistochemistry and in situ hybridization. I will also seek age-related alternations in their receptors, such as MuSK, Integrins and P/Q-type calcium channels. To test for a causal role for laminin beta2 and agrin in aging, I will use conditional and heterozygous mice to assess if their absence or substantial decrease causes defects in young adult NMJs. Finally, to probe the relationship of aging to ALS, I will assess the expression of synaptic adhesion molecules in a mouse model of ALS. Together, these studies may allow me to identify molecules that can attenuate or even reverse age-induced deleterious effects on synapses. Consequently, these experiments could provide tools to ameliorate a number of synaptic defects underlying cognitive and spinalmuscular diseases.