Complement as driver of neuroinflammation and -degeneration in Parkinson‘s disease

β-葡萄糖脑苷酶基因杂合突变被认为是帕金森病的最大危险因素之一，帕金森病是一种以多巴胺能神经元变性为病理特征的运动障碍。GBA纯合子突变是高谢病最常见的溶酶体储存障碍，其特征是编码的溶酶体酶葡萄糖脑苷酶活性降低，随后其底物葡萄糖神经酰胺(GC)在包括大脑在内的多个器官中积聚。最近，高谢病患者产生了抗GC的自身抗体，形成了GC特异性免疫复合体。这些复合体激活了补体系统，导致C5a的产生，从而触发了其同源C5a受体1(C5aR1)在高雪病倾向小鼠和患者的免疫细胞上的激活。一些观察也指出，免疫系统在帕金森病的病因中有重要贡献，然而，驱动免疫细胞激活的机制尚不清楚。支持这一应用的总体假设是，葡萄糖脑苷酶活性降低会导致GBA相关性帕金森患者大脑中补体激活和随后的补体驱动的小胶质细胞激活。为了解决这一假设，我们将检测携带GBA突变的患者死后脑和脑脊液样本中补体因子C3、C5及其切割片段C3a和C5a的水平。此外，我们将从患者来源的诱导多能干细胞(IPSC)中建立神经元-小胶质细胞共培养疾病模型(目标1)。我们将评估小胶质细胞的激活和补体因子C3和C5的自主产生，并在这些细胞中裂解成C3a和C5a，以确定与患者和对照细胞相比的补体激活水平(目标2)。此外，在这个模型中，我们将确定C5aR1的基因敲除或药物抑制的直接神经保护作用。为了从机制上深入了解GBA相关的神经炎症过程，我们将进行神经元-小胶质细胞共培养的单细胞表达谱分析(目标3)。该项目建立在申请者在IPSC技术和神经科学以及补体和炎症研究方面的广泛专业知识的基础上。阐明帕金森综合征导致神经炎症的机制可能在未来的治疗中具有重要的意义。

Heterozygous mutations in the β-glucocerebrosidase (GBA) gene have been identified as one of the strongest risk factors for Parkinson’s disease, a movement disorder that is pathologically characterized by the degeneration of dopaminergic neurons. Homozygous mutations of GBA are responsible for Gaucher’s disease, which is the most prevalent lysosomal storage disorder, characterized by decreased activity of the encoded lysosomal enzyme glucocerebrosidase and subsequent accumulation of its substrate glucosylceramide (GC) in several organs including the brain. Recently, autoantibody generation against GC was shown in Gaucher’s disease patients that form GC-specific immune complexes. Such complexes activated the complement system resulting in C5a generation, which triggered the activation of its cognate C5a receptor 1 (C5aR1) on immune cells in Gaucher-prone mice and patients. Several observations point also to a significant contribution of the immune system in the etiology of Parkinson’s disease, however, the mechanisms driving the activation of immune cells remains unclear. The overall hypothesis underlying this application is that reduced glucocerebrosidase activity leads to complement activation and subsequent complement-driven microglia activation in the brain of patients with GBA-associated parkinsonism. To address this hypothesis, we will determine levels of complement factors C3, C5 and their cleavage fragments, C3a and C5a, in postmortem brain and cerebrospinal fluid samples from patients carrying GBA mutations. Further, we will generate a neuron-microglia co-culture disease model from patient-derived induced pluripotent stem cells (iPSC) (Objective 1). We will assess the activation of microglia and the autonomous production of complement factors C3 and C5, and cleavage into C3a and C5a in such cells to define the level of complement activation comparing patient vs. control cells (Objective 2). Moreover, we will determine the direct neuroprotective effect of a genetic knockout or pharmacological inhibition of C5aR1 in this model. To gain mechanistic insight into GBA-linked neuroinflammatory processes we will perform single-cell expression profiling of neuron-microglia co-cultures (Objective 3). The project builds on the extensive expertise of the applicants in iPSC technology and neuroscience as well as complement and inflammation research. Elucidating the mechanisms leading to neuroinflammation in parkinsonism might be of great therapeutic relevance in the future.