The Role of Cathepsin B and Cystatin C in Alzheimer's Disease

描述（由申请人提供）：淀粉样蛋白β (Abeta)是阿尔茨海默病（AD）的关键致病因子，由于生产过剩或清除效率低下，在大脑中积累并形成有毒的低聚物。因此，调节β降解和清除的途径是治疗干预的主要候选者。我们发现组织蛋白酶B (CatB)，一种半胱氨酸蛋白酶，在体内和体外都能降解β。在最近的研究中，我们发现CatB的β -降解活性被其内源性抑制剂胱氨酸抑制素C （cystatin C, CysC）抑制，减少CysC可增强CatB诱导的β -降解，并防止与β相关的突触和行为缺陷。然而，与其他一些Abeta降解酶不同，如neprilysin （NEP，一种在中性pH下具有最佳活性的内肽酶），CatB在c端截断Abeta，在酸性pH下具有最佳活性。在体内，CatB似乎比NEP更有效地减少高阶的β组装。这些观察结果表明，CatB和NEP可能在β降解中起互补作用。本提案的目的是确定CatB-CysC轴的细胞机制，以及它和NEP如何共同调节β降解。在特异性目标1中，我们将评估神经元CatB-CysC轴对体内β降解和神经元突触功能的影响。我们将比较小胶质细胞和神经元来源的CatB的作用。在特异性目标2中，我们将确定神经元CatB-CysC轴是否在内体-溶酶体途径中调节β降解。了解CatB-CysC轴的亚细胞机制是开发针对这一新发现的途径的治疗策略的先决条件。在Specific Aim 3中，我们将研究NEP在CatB诱导的β降解中的作用以及CatB在NEP诱导的β降解中的作用。通过定义CatB-CysC轴和NEP之间的相互作用，可能会出现对调节β -降解的分子机制的新见解。证实CatB-CysC轴作用与NEP互补，将为设计有效的Abeta清除策略奠定基础。

DESCRIPTION (provided by applicant): Amyloid beta (Abeta), a key pathogenic factor in Alzheimer's disease (AD), accumulates and forms toxic oligomers in the brain as a result of overproduction or inefficient clearance. Thus, pathways regulating Abeta degradation and clearance are prime candidates for therapeutic intervention. We discovered that cathepsin B (CatB), a cysteine protease, degrades Abeta in vitro and in vivo. In more recent studies, we showed that the Abeta -degrading activity of CatB is inhibited by its endogenous inhibitor, cystatin C (CysC), and that reducing CysC enhances CatB- induced Abeta degradation and protects against Abeta -associated synaptic and behavioral deficits. However, unlike some other Abeta degradation enzymes, such as neprilysin (NEP, an endopeptidase with optimal activity at a neutral pH), CatB truncates Abeta at the C-terminus with optimal activity at acidic pHs. CatB also appears to be more effective than NEP in reducing higher orders of Abeta assemblies in vivo. These observations suggest that CatB and NEP may play complementary roles in Abeta degradation. The objectives of this proposal are to determine the cellular mechanisms of the CatB-CysC axis and how it and NEP might work together to regulate Abeta degradation. In Specific Aim 1, we will assess the effects of the neuronal CatB-CysC axis on Abeta degradation and neuronal synaptic function in vivo. The effects of microglia- and neuron-derived CatB will be compared. In Specific Aim 2, we will determine if neuronal CatB-CysC axis acts in the endosomal-lysosomal pathway to regulate Abeta degradation. Understanding the subcellular mechanisms of CatB-CysC axis is a prerequisite for the development of therapeutic strategies that target this newly identified pathway. In Specific Aim 3, we will examine the role of NEP in CatB-induced Abeta degradation and the role of CatB in NEP-induced Abeta degradation. By defining the interplay between the CatB-CysC axis and NEP, new insights into molecular mechanisms regulating Abeta -degradation will likely emerge. Confirmation that the CatB-CysC axis action acts in a complementary manner with NEP would lay the foundation for designing effective Abeta clearance strategies.