Dissecting molecular mechanisms of Parkinson's disease

Parkinson's disease is devastating neurodegenerative disorder, that remains incurable due to our lack of understanding about its cause at a molecular level. Understanding the molecular origins of human diseases requires accurate characterisation of the underlying processes. However, PD is complex and multifactorial, and it is therefore challenging to choose which molecular events to study, and indeed which molecular events are causative. Notably, 90% of Parkinson's disease cases are sporadic, whilst 5-10% are familial due to an identified mutation. Autosomal dominant and autosomal recessive forms of PD share many common pathological and clinical features with the sporadic PD, albeit with some variation. Importantly in this group of familial PD, the causative gene and protein is known and therefore provides a robust starting point for understanding potential molecular causative events in PD. Taken further, the large genome wide association studies in PD have highlighted that genetic risk to sporadic PD is caused by aberration in pathways that broadly map to those raised by the mendelian forms of PD: namely the abnormal aggregation of proteins, abnormal function of mitochondria, abnormal clearance mechanisms by lysosomes, and inflammation. Thus, the outcomes from both mendelian genetics and common variation converge, and therefore may be used to rationalise the basis for determining causation in both familial and sporadic PD.

I propose a framework within which selected human familial forms of PD (mitochondrial-PD, lysosomal-PD, and proteinopathy-PD) are used to in first to understand key molecular causative events at the onset of disease. Informed by the human genetics, this will focus first, in theme 1, on specific pathways to disease, in particular, how and why protein aggregation occurs inside cells, and then how the aggregation affects cellular function, and organellar function with mitochondria and lysosomes. In order to achieve this aim, we will apply sophisticated methods derived from physical chemistry and biophysics that allow us to visualize each protein aggregate as it is formed, and therefore understand the size and structure of the aggregates at unprecedented resolution. The application of novel biophysical methodology to track the intracellular aggregation process of alpha-synuclein in iPSC derived models of PD should reveal the structure of the toxic species of alpha-synuclein, and determine how it interacts with, and disrupts specific cellular processes such as mitochondrial function. In theme 2, we ask whether different cell types in the human brain play an important role in Parkinson's disease pathogenesis. Glial cells play crucial roles in neuronal function, and alterations in glial cells are known to occur in PD and induce inflammation in the brain. Utilising iPSC derived neurons and astrocytes, we will investigate how glial cells may be activated during PD, and how alterations in astrocyte function affect neurons. In theme 3, we will utilize the information from the mendelian forms of PD to generate a framework of data. This framework will then be used to interrogate the mechanisms that underlie a large group of cells derived from patients with sporadic PD. Specifically it will reveal whether the sporadic PD population is heterogeneous in its molecular aetiology, whether the genetic and molecular drivers of any individual with PD clusters closely to the mendelian forms. As a consequence, it will ultimately determine whether patients with sporadic disease can be subdivided according to their molecular causes. If the sporadic PD population in composed of forms of PD that are 'mitochondrial' or 'lysosomal' for example, then this would raise the possibility that therapies in fact need to be designed to address the molecular basis of an individual's form of PD, in this way laying the foundation for developing personalised medicine approaches in PD.

Parkinson's disease (PD) is a common neurodegenerative disease that remains defined by pathological hallmarks of end-stage disease, neuronal loss and protein aggregation. The aim of this research program is to understand the earliest molecular events that drive pathogenesis. Powerful clues to pathogenesis are provided by mendelian genes that cause familial PD, and genetic loci that confer risk to sporadic PD. Importantly, both approaches highlight selective convergent processes to be causal in PD, namely protein aggregation, mitochondrial homeostasis, lysosomal biology and inflammation. This provides the rationale for the overall approach of this program: monogenic forms of PD can be harnessed to delineate causative mechanisms in human neurons and astrocytes, and these mechanisms will be relevant in the sporadic PD population.
This proposal first addresses when and where protein oligomerization occurs in human neurons, and how oligomerisation is modulated by mitochondrial function, or lysosomal function. Second, we address what is the earliest mitochondrial defect in PD, and the underlying mitochondrial mechanisms that lead to neuronal loss. Single molecule and single cell methods in human iPSC derived monogenic models are used to characterize protein aggregation and mitochondrial function at high resolution, determine their intersection, and causality in monogenic PD. Third, we investigate whether PD specific astrogliopathy is due to reactive astrocytosis and inflammation, or intrinsic molecular changes in astrocytes causing loss of neuronal homeostasis. Co-culture paradigms of astrocytes and neurons are combined with imaging and transcriptomics to dissect the role of astrocytic biology and inflammation in PD. Fourth, the proposal defines a pipeline to harness information from monogenic PD to validate its relevance in sporadic PD, with the ultimate aim of critically refining our classification of the molecular origins of sporadic disease.

Parkinson's disease (PD) is the most common movement disorder caused by neurodegeneration, affecting 1-2% of people over the age of 65, with an estimated number of over 1.2 million people affected in Europe. This condition represents a very significant burden on our healthcare systems, as it is estimated that care for these patients costs 14 billion Euro per year in Europe. Treatment is currently purely symptomatic and there is an urgent need to develop disease-modifying therapies, as well as biomarkers capable of tracking its risk of onset and stage of progression. Perhaps the biggest challenge to addressing this need is the lack of understanding about the causes of PD. This program of work meets this need in the following ways: it utilizes familial forms of PD in which the initiating cause, or mutation is known, to identify key molecular events that can cause PD in human cells; it establishes the most important cell type that drives PD in the human brain; finally, it integrates this information to generate a network of molecular events that likely overlap or interact to cause PD in the sporadic (non-genetic) forms of disease. At this stage, it aims to classify sporadic PD cases on their molecular and cellular behavior in relation to the familial forms, allowing researchers to define different individuals with PD as having a different molecular subtype that drives their particular disease. If such stratification is possible then this opens the door to the possibility of designing specific treatments for specific individuals with PD.

This program of work therefore has a broad impact, and may bring about health, economic and societal benefits, that are outlined below.

(1) Discovery of new pathways in familial and sporadic PD will translate into new biomarkers and new druggable targets. This will have an important influence on biomarker development, drug discovery, drug development and ultimately to bringing drugs to market. Importantly as the discovery work, and the validation is performed in human models, this may overcome the current barriers to translational success. The impact goal is to drive rapid translation of molecular discoveries into realistic drug targets. Engagement with key pharmaceutical and biotech companies interested in drug development and commercialisation of diagnostic tests and biomarkers will be necessary to deliver this impact goal.

(2) Discovery of the molecular etiology of PD, and of new potential drug therapies will significantly impact the lives of patients with Parkinson's disease, patients with other alpha-synucleinopathies whose molecular pathogenesis is likely shared with Parkinson's disease (eg dementia with Lewy Body Disease, Multiple system atrophy), patients with other neurodegenerative diseases and their carers. The impact goal is to inform patients and their carers, to engage them in the research process, to recruit to trials, and to improve patient management and treatments. The target population for this impact is patients with PD and DLBD, patients with other neurodegenerative disorders, and patient charities, specifically Parkinson's UK and Cure Parkinson's Trust in the UK, and the Michael J Fox Foundation and the Safra Foundation globally.

(3) Scientific discovery will impact certain members of the public, and in particular, I am keen to see the impact of work reach, and inspire people of diverse backgrounds to recognize science as an equitable, accessible and exciting career, in particular school students and young people underrepresented in careers in STEM, and biomedical researchers who are underrepresented in senior roles. The impact goal is to enable, facilitate and inspire careers in biomedicine in underrepresented groups, through the promotion of equality and diversity in science.