Defining a Molecular Link between Parkinson and Gaucher Diseases

GBA1基因突变是帕金森病(PD)最常见的已知危险因素。虽然临床研究证明了GBA1突变与帕金森病的发生之间存在联系的有力证据，但一直缺乏机械性的见解。GBA1编码葡萄糖脑苷酶(GCase)，是一种将葡萄糖神经酰胺(GluCer)分解为葡萄糖和神经酰胺的溶酶体酶，在高谢病(GD)中缺乏。最近的研究表明，GCase与帕金森病相关的淀粉样蛋白-α-突触核蛋白(α-SYN)之间存在关系；然而，导致这种联系的具体分子机制仍然不清楚。 在我们的工作中，我们重点研究了溶酶体中α-syn和GCase相互作用的结构-功能关系。我们评估了酶的活性，用中子反射法表征了膜结合蛋白复合体，并评价了GCase激活剂皂苷C对复合体形成和GCase活性的影响。在定义分子相互作用，驱动在体内的GCase和α-SYN水平之间的相互关系，我们已经转向研究如何在溶酶体中降解α-SYN。随着溶酶体移除易聚集的物种或过量水平的α-syn，发生在溶酶体内的分子相互作用，如与GCase的相互作用将是相关的。这种相互作用可以通过改变α-syn裂解位点的可用性来调节蛋白分解效率，并决定了蛋白酶的特异性和有效性。 我们正在测试关于溶酶体如何在健康和疾病相关的条件下促进α-syn蛋白稳定的假设。具体地说，我们正在研究α-syn和溶酶体酶、半胱氨酸组织蛋白和GCase之间的关系。我们的工作指出了半胱氨酸组织蛋白在溶酶体清除α-syn中的直接作用。我们感兴趣的是如何将这些酶作为帕金森病进展的干预策略。对于半胱氨酸组织蛋白酶，我们的数据尤其令人信服，组织蛋白酶L(CTSL)具有降解α-突触蛋白纤维的潜力。对于GCase来说，在基于细胞和动物的PD模型中，其水平或活性的增强似乎可以改善α-syn毒性；然而，这种情况发生的分子基础还不是很清楚。我们的研究正在努力解决这两个方面：评估CTSL是否可以作为一种可行的治疗药物来清除α-SYN的细胞，并阐明观察到的PD风险与GCase浓度之间的相关性的机制(S)。

Mutations in the GBA1 gene are the most common of the known risk factors for Parkinson disease (PD). While clinical studies argue a strong case towards a link between GBA1 mutations and the development of PD, mechanistic insights have been lacking. GBA1 encodes glucocerebrosidase (GCase), a lysosomal enzyme which hydrolyzes glucosylceramide (GluCer) into glucose and ceramide and is deficient in Gaucher disease (GD). Recent research suggests a relationship between GCase and the PD-related amyloid-forming protein, alpha-synuclein (alpha-syn); however, the specific molecular mechanisms responsible for association remain elusive. In our work, we focused on the structure-function relationship of alpha-syn and GCase interaction in the lysosome. We have evaluated enzymatic activity, characterized the membrane-bound protein complex by neutron reflectometry, and assessed the effect of Saposin C, an activator for GCase, on complex formation and GCase activity. In defining the molecular interactions that drive the reciprocal relationship between GCase and alpha-syn levels in vivo, we have turned to investigate how alpha-syn is degraded in the lysosome. As the lysosome removes aggregation-prone species or excess levels of alpha-syn, molecular interactions that occur within the lysosome such as with GCase would be pertinent. Such interactions could modulate proteolysis efficiency by altering availability of alpha-syn cleavage sites and dictate protease specificity and efficacy. We are testing hypotheses on how lysosomes contribute to alpha-syn proteostasis under healthy and disease-related conditions. Specifically, we are investigating the relationship between alpha-syn and lysosomal enzymes, cysteine cathepsins and GCase. Our work points to a direct role of cysteine cathepsins in the lysosomal clearance of alpha-syn. We are interested in how these enzymes could be targeted as an intervention strategy in PD progression. With cysteine cathepsins, our data are especially compelling for the potential for cathepsin L (CtsL) to degrade alpha-syn fibrils. For GCase, the enhancement of its levels or activity appears to ameliorate alpha-syn toxicity in cell-based and animal PD models; however, the molecular basis for why this occurs is not well understood. Our research efforts are addressing both these fronts: to evaluate whether CtsL could be a viable therapeutic agent towards cellular clearance of alpha-syn and to elucidate the mechanism(s) responsible for the observed correlation between risk for PD and GCase concentration.