The Molecular and Cellular Basis of Parkinson’s Disease

Parkinson’s disease (PD) affects >1% of the population over the age of 65. Currently, there are over 100,000 people affected in Canada alone and the numbers will only grow as the population ages. PD involves the death of dopamine (DA) neurons in the midbrain, which leads to devastating motor and functional impairment. Moreover, it is becoming clear that PD pathology is not limited to DA neurons but is much more widespread, involving cells both inside and outside the brain. These non-DA lesions often precede DA involvement and help explain the many early non-motor symptoms in PD patients, which until recently have been largely ignored. Although treatment for PD is available, its effectiveness diminishes over the long term. Hope for a more definitive treatment lies in basic biomedical research. Over the last decades, the discovery of genes responsible for familial forms of PD have transformed what had been considered until the late 1990s as a prototypic “environmental disease” into one of the most complex multi-genetic diseases of the brain. More recently, genome-wide association studies (GWAS) have uncovered over a hundred genetic risk loci associated with PD. This offers a tremendous opportunity to generate new hypotheses about PD biology and identify new therapeutic targets. 

Our lab has had a longstanding interest in investigating the molecular and cellular roles of PD genes, as deciphering how their dysfunction perturbs core molecular and cellular mechanisms is likely to provide key insights into the disease’s pathogenesis. Recent years have seen the emergence of powerful research tools, including human induced pluripotent stem cell (iPSC)–derived 2D and 3D models, machine learning–based computational analytical frameworks, and high-throughput screening platforms. As a team, we are leveraging these approaches to more effectively elucidate the mechanisms underlying PD.

Ongoing projects in the lab

Modeling Parkinson’s disease – iPSC models and targeted assays

In collaboration with Dr. Durcan’s Early Drug Discovery Unit, the Neuro-EDDU , our team is developing models of PD using human iPSCs. Through the Neuro C-BIG Repository, we have access to numerous lines derived from healthy individuals as well as PD patients bearing different genetic mutations associated with the disease. We are also putting a lot of effort into genetically engineering iPSCs lines in order to generate isogenic pairs for our studies. 

We are able to grow and differentiate iPSCs into dopaminergic, cortical or motor neurons as well as astrocytes and microglial cells, to investigate PD pathogenesis in 2D cultures. We also work towards co-culturing different iPSC derived cell types in 2D. Finally, we are producing iPSC-derived organoids with these various cell types, which allows us to study PD pathological pathways and mechanisms in 3D environments. 

Over recent years, we have developed a comprehensive set of targeted phenotypic assays in immortalized cells and iPSC lines, that capture key pathogenic mechanisms in PD, including misfolded α-synuclein uptake and seeding, mitochondrial dysfunction, and lysosomal abnormalities. These optimized assays are well suited for robust, high-throughput microscopy-based screening, and we continue to expand this platform by developing additional disease-relevant assays.

Investigating PD-associated genes – high-throughput genetic screens

High throughput genetic screens represent a powerful, unbiased approach to uncover novel therapeutic targets and unravel molecular mechanisms and pathways underlying disease. Such screens can be designed to be broadly exploratory or tailored to address specific biological questions, and leveraging their potential has been a major focus of our work in recent years.

In an effort to understand how α-synuclein fibrils are accumulating into cells, as well as the potential associated pathological effects, we produce α-synuclein pre-formed fibrils (PFF) in vitro, in collaboration with the Neuro-EDDU, and developed a robust cell-based α-synuclein uptake assay. Using these tools, we performed a genome-wide CRISPR screen and have already identified several candidate genes that may regulate cellular uptake of α-synuclein.

In parallel, we are deeply interested in what we term the “PD GWASome”. Over the past decade, GWAS have uncovered over a hundred genetic risk loci associated with PD, offering an unprecedented opportunity to generate new hypotheses about PD biology and uncover novel therapeutic targets. Unfortunately, this has not panned out, as much of the field still focuses on the first 6-8 PD genes, some discovered over 25 years ago. Cumulatively, highly studied PD genes such as SNCA, PRKN, PINK1, LRRK2 and GBA1 have >20,000 citations in PubMed. In contrast, the majority of the ~300 genes encompassed within the 134 PD GWAS risk loci remain largely unexplored, with little to no PD-related literature. Understanding how these lesser-studied genes converge onto shared cellular pathways is essential, as it may reveal central disease mechanisms that are currently overlooked and inform the development of more effective disease-modifying therapies. Accordingly, our current objective is to functionally characterize a large subset of PD GWAS genes using PD-relevant, cell-based phenotypic assays through systematic high-throughput screening.

Understanding mitochondrial biology – Parkin/PINK1 and the TOM complex

The study of Parkin/PINK1 function in mitochondrial biology, and the role of mitochondrial dysfunction in PD pathology, is one of our long-standing interests in the lab. Throughout the years, we developed an expertise in monitoring mitochondrial dysfunction in vitro, we helped unravel new mitochondrial quality control mechanisms such as mitochondrial derived vesicles, and we contributed to elucidating Parkin structure and function. Our recent work revealed the complexity of the TOM–TIM supercomplex and the contribution of PINK1 to its organization. 

Building on these findings, our current research focuses on PINK1 biology at the mitochondrial surface and its precise role within the TOM–TIM complex.