Endosomal-Lysosomal Function in Neuronal Storage Disease

说明书(申请人提供)：最初设想的储存障碍被认为是由于在酸性环境中具有大量降解酶的末端细胞器(溶酶体)内缺乏水解酶活性所致。需要用于降解的缺失酶的底物积累在第三级溶酶体中，随着时间的推移，细胞质拥挤被认为会导致细胞功能受损，继而导致细胞死亡。糖鞘糖脂(GSLS)、粘多糖和糖蛋白是典型的需要溶酶体降解的底物，并且根据它们的积累建立了许多种类的贮藏疾病(糖鞘糖脂、粘多糖和糖蛋白等)。其中许多储存化合物在大脑中显著表达，有限的神经发生和长期神经元存活的需要被认为放大了细胞内储存的细胞毒性效应。重要的是，近年来的研究显著改变了这种对溶酶体储存障碍的看法。首先，参与许多非溶酶体和/或非酶功能的蛋白质现在被认为是细胞内溶酶体储存的原因。这些蛋白质中的一些对溶酶体酶的加工或靶向是必不可少的，但另一些是可溶性的非酶溶酶体蛋白或参与细胞器或底物运输的跨膜蛋白。其次，溶酶体本身已经不再简单地被视为一个独立的末端细胞器，而是被视为动态连续体中的一个细胞组件。内体-溶酶体系统本身被认为不仅对分子的降解和再循环至关重要，而且在信号转导事件和内环境平衡控制机制中也是如此。许多通过内体-溶酶体系统的分子(GSLS、胆固醇等)已被确定为专业微域(“筏”)的组成部分，据信在质膜中充当信号平台。因此，溶酶体储藏疾病可能代表着筏功能紊乱的状态，其储存由内体和溶酶体内的筏“原木堵塞”组成。这种异常与大脑中的存储特别相关，在大脑中，神经元不仅退化，而且会经历奇怪和独特的变化，从某些类型的神经元上长出新的、突触覆盖的异位树突，到另一些类型的神经元上形成不寻常的轴突异常。目前的提议将使用体内和体外分析以及神经元储存疾病的小鼠模型相结合的方法来测试专注于储存疾病的分子/细胞发病机制的特定假设。我们相信，在理解方面的这些进展将为潜在的治疗策略提供新的见解，并进一步阐明内体-溶酶体系统在健康和疾病中所发挥的关键作用。

DESCRIPTION (provided by applicant): Storage disorders as originally conceived were believed caused by an absence of hydrolytic enzyme activity within end-organelles (lysosomes) possessing numerous degradative enzymes in an acid milieu. Substrates requiring the missing enzyme for degradation accumulated within tertiary lysosomes and over time cytoplasmic crowding was believed to lead to compromise in cell function followed by cell death. Glycosphingolipids (GSLs), mucopolysaccharides and glycoproteins were documented as typical substrates requiring the lysosome for degradation and numerous classes of storage diseases were established on the basis of their accumulation (glycosphingolipidoses, mucopolysaccharidoses, glycoproteinoses, etc.). Many of these storage compounds were prominently expressed in brain where limited neurogenesis and the need for long-term neuronal survival were believed to amplify the cytotoxic effects of intracellular storage. Importantly, studies of recent years have significantly altered this view of lysosomal storage disorders. Firstly, proteins involved in a host of non-lysosomal and/or non-enzymatic functions have now been documented as causes of intracellular lysosomal storage. Some of these proteins are essential for processing or targeting of lysosomal enzymes but others are soluble non-enzyme lysosomal proteins or are transmembrane proteins involved in organelle or substrate trafficking. Secondly, the lysosome itself has come to be viewed not simply as an independent end-organelle, but rather as a cell component in dynamic continuum with endosomes. The endosomal-lysosomal system has itself been established as critical not only for the degradation and recycling of molecules but also in signal transduction events and homeostatic control mechanisms. Many of the molecules transiting through the endosomal-lysosomal system (GSLs, cholesterol, etc.) have been identified as constituent parts of specialized microdomains ("rafts") believed to act as signaling platforms in the plasmalemma. Consequently, lysosomal storage diseases may represent states of disordered raft function with storage consisting of "log jams" of rafts within endosomes and lysosomes. Such abnormalities are particularly relevant to storage in brain where neurons do not simply degenerate but undergo bizarre and unique alterations ranging from sprouting of new, synapse-covered ectopic dendrites on some classes of neurons to formation of unusual axonal abnormalities on others. The current proposal will use a combination of in vivo and in vitro analyses and murine models of neuronal storage diseases to test specific hypotheses focused on the molecular/cellular pathogenesis of storage diseases. Such advances in understanding we believe will provide new insights into potential treatment strategies and further elucidate the critical role played by the endosomal-lysosomal system in both health and disease.