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

描述(申请人提供)：淀粉样β蛋白(Abeta)是阿尔茨海默病(AD)的关键致病因素，由于生产过剩或清除效率低下，会在大脑中积聚并形成有毒的寡聚体。因此，调节Abeta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)是一种半胱氨酸蛋白酶，在体外和体内都能降解Abeta。在最近的研究中，我们发现CatB的Abeta降解活性被其内源性抑制剂CysC(CysC)抑制，减少CysC可以增强CatB诱导的Abeta降解，并保护Abeta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下活性最高的内肽酶)，CatB在C末端截短Abeta，在酸性PHS时具有最佳活性。在体内，CatB似乎也比NEP更有效地减少更高顺序的Abeta组装。这些观察结果表明，CatB和NEP在Abeta降解过程中可能起互补作用。这项建议的目的是确定CatB-CysC轴的细胞机制，以及它和NEP如何共同调节Abeta的降解。在具体目标1中，我们将在体内评估神经元CatB-CysC轴对Abeta降解和神经元突触功能的影响。小胶质细胞和神经元来源的CatB的效果将进行比较。在特定的目标2中，我们将确定神经元CatB-CysC轴是否作用于内体-溶酶体途径来调节Abeta的降解。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。在具体目标3中，我们将研究NEP在CatB诱导的Abeta降解中的作用，以及CatB在NEP诱导的Abeta降解中的作用。通过定义CatB-CysC轴和NEP之间的相互作用，可能会出现对调控Aβ降解的分子机制的新见解。确认CatB-CysC轴的作用与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.