JPND GBA - personalised medicine for Parkinson disease: clinical and therapeutic stratification

Parkinson disease (PD) has a lifetime risk of 3-4%, and there are approximately 60,000 new cases annually in the EU. All PD-related costs in the EU are estimated at 13 billion euros per annum.
Recent advances in PD have identified that glucocerebrosidase 1 (GBA1) mutations are numerically the most important risk factor for PD. They are found in 10-15% of PD (25% in Ashkenazi Jews), and increase the risk for PD by 20-30x.
PD involves the loss of brain cells (neurons) and the accumulation of a protein called alpha-synuclein (a-syn). GBA1 mutations cause impaired activity of the glucocerebrosidase enzyme (GCase) that is involved in the normal breakdown of unwanted or redundant cell constituents, including proteins. It has been shown that GBA1 mutations and reduced GCasae activity result in an increase in a-syn concentrations. Intriguingly, accumulation of a-syn causes impaired GCase activity in the normal enzyme. Thus there is a strong reciprocal relationship between GCase activity and a-syn levels. On this basis, it is considered that the GBA1 mutations that lead to GCase inhibition, initiate a self-amplifying cycle of GCase deficiency and a-syn accumulation that causes PD. This is reflected in those that carry GBA1 mutations and develop PD by their earlier onset and more rapid progression than those without GBA1 mutations.
In this project we will investigate the evolution of clinical features prior to and during the development of PD in those that carry GBA1 mutations. The participants have access to cohorts of those with GBA1 mutations, with and without PD (>700 un the UK). We will integrate the web-based clinical assessments developed in the UK cohort with those in Italy and Spain to understand the pattern of prodromal features and how they evolve to clinical PD. We will also collect samples for biomarker analysis so that we can combine these with the clinical characteristics to identify those within the cohorts who are most at risk for the development of PD. Patients will be asked to provide skin scrapes so that we can culture these cells and convert them through an established protocol, into dopaminergic neurons - the type that degenerate first in PD. These stem cell derived models will be used to investigate specific aspects of the cellular biochemical effects of GBA1 mutations to understand the basis of the link with increased a-syn levels. as part of this we will develop an advnced model of the dopaminergic neurons in 3-dimensions, a so-called brain organoid. These models are valuable to understand the spatial spread of a-syn from one neuron to another. We hypothesise that GBA1 mutations will accelerate the spread of a-syn.
Our stem-cell derived models, including the organoids will also be used to test whether a compound (ambroxol) is capable of reversing the effects of GBA1 mutations. Ambroxol is a molecule that binds to mutatant GCase and delivers it to its correct location within the cell (the lysosome). It is an a repurposed drug, currently on sale as a cough linctus. In cell, stem cell, fly and animal models, amroxol has been able to increase GCase activity in GBA1 mutation models, and reduce a-syn levels. Therefore it represents a promising compound for future investigation as a potential drug to slow PD.

This grant will investigate the evolution of clinical features prior to and during the development of PD in those that carry GBA1 mutations, and the downstream molecular, biochemical and cellular consequences of the mutations in patient material, patient-derived cell and animal models. This will be translated into a personalised clinical and biochemical biomarker risk profile for GBA-PD. We will further test a small molecule GBA1 chaperone to slow or reverse the pathology of PD in cell and animal models as a means to develop personalised medical therapy for GBA1-PD.
We will develop clinic and web-based recruitment of GBA1 mutant carriers (currently >700) to provide integrated and harmonised clinical and biochemical biomarker assessment tools across 4 European countries.
We will investigate the molecular basis for the link between GBA1 mutations and PD pathology, specifically their relationship to the levels of alpha-synuclein (A-SYN) and its aggregation and spread. This will use patient-derived neuronal stem cells and 3-D mid-brain organoids of GBA1 mutations (L444P and N370S) with adeno-associated viral vector (AAV)-induced or endogenous overexpression of A-SYN or direct injection of A-SYN fibrils. We will also determine the mitochondrial and lysosomal functional consequences of GBA1 mutations, and their effects on glia and inflammatory activation. We will further investigate the ability of ambroxol, a GBA1 chaperone to reverse the abnormalities seen in our cell and organoid GBA1 models, to confirm this therapeutic approach as a rational intervention to slow or prevent PD development or progression.

We perceive that the following groups will benefit from our research and results, and we will seek to ensure that the impact is properly conveyed.

Patients: 3 diseases
Glucocerebrosidase gene (GBA) mutations are seen in three diseases: Gaucher disease (GD), Parkinson disease (PD) and dementia with Lewy bodies (DLB). Our data on increasing brain glucocerebrosidase enzyme (GCase) will be of direct relevance to the management of all three, and the evidence for reducing alpha-synuclein (A-SYN) levels of particular relevance to PD and DLB patients.
The GD patient community is already engaged with our work (https://www.gaucher.org.uk/research/rapsodi) and participates both in our research and recruitment. A brain penetrable GCase chaperone such as ambroxol could provide important therapeutic options for study in GD type 2 and 3 where CNS disease is present. Providing insight into the possible pathogenetic mechanisms that underlie the risk for PD amongst GD sufferers and their carrier relatives will be important to aid counseling and potential therapy.
The PD and DLB communities will benefit from an understanding of how GCase interacts with A-SYN and how the latter spreads through the brain. Investigating the GBA-GCase pathway as a potential therapeutic target is of relevance to the treatment and prevention of these diseases. The PD patient communities are already engaged with our work, participating in our public awareness meetings (https://www.eventbrite.co.uk/e/rapsodi-study-update-event-tickets-58802741583), supporting our work on their websites (https://www.cureparkinsons.org.uk/news/rapsodistudy and https://www.parkinsons.org.uk/research/rapsodi-identifying-early-features-parkinsons-and-gaucher as well as supporting our research with funding (see PUK and CPT grants in Schapira CV).
Therefore we believe that our research here will benefit important patient groups as well as their relatives and communities given the genetic nature of the basis for disease.
Scientific community
The recognition that GBA mutations significantly increase the risk for PD and DLB has generated considerable interest and research over the last few years. Research in this area is providing valuable insights into the pathophysiology of the synucleinopathies and the interactions between GBA mutations and A-SYN. The value of our studies will be to show how A-SYN spread can occur through a neuronal network and how this might be modulated by lysosomal or exosomal function. These studies will be performed in iPSCs and in midbrain organoids. Therefore the results will provide a proof of principle that these models are valuable as tools for investigation in other diseases. In particular, the mechanisms of protein spread and how this might be modified by genetics will be relevant to other neurodegenerative diseases.

Pharmaceutical and Biotech industries
A-SYN biology is an important target for therapeutic intervention in the synucleinopathies. Thus both passive and active antibody immune strategies are being tested in early clinical phase studies to reduce A-SYN levels. The results from our studies will demonstrate not only the underlying molecular and cellular mechanisms for increased A-SYN levels in GBA mutations, but also how A-SYN spread and how this might be retarded or prevented. Such a strategy if successful will be either an alternative to, or complementary with the immunotherapies. Indeed, the concept of multiple but related interventions is more likely to be successful in complex diseases involving neurodegeneration. We already have a well-funded program of research with Eisai Pharmaceuticals to develop novel modulators of GCase activity. Therefore, we anticipate substantial interest not only in the results of our studies, but in the models created and how they can be used to test potential drug action 'in a dish'.