- Systematically address and revisit the issue of “reduced penetrance” using hereditary movement disorders as an example
- Discover mechanisms explaining reduced penetrance in a multimodal fashion
- Develop bioinformatics and statistical tools, new ethics standards, and a sustainable Knowledge Base for the members of the Research Unit and the scientific community
- Advancement of ethics methodology for enrolling clinically unaffected mutation carriers in studies aimed at understanding reduced penetrance
Long-Term Scientific Aims
- Employ additional ‘omics’ approaches and (animal) models to validate findings
- Identify and functionally characterize non-coding variants relevant for reduced penetrance or for delaying disease expression
- Focus on epigenetic mechanisms as a likely additional important modifier of penetrance
- Build on newly identified modifiers of reduced penetrance to gain mechanistic insight through functional studies
- Extend and further deepen phenotyping by including neuroimaging and electrophysiology techniques (endophenotyping), as well as data on environmental factors
- Translate findings into genetic counseling routines
- Explore newly identified genomic factors relevant for the reduction in penetrance as potential therapeutic targets
The figure below shows the interaction between the projects of the Research Unit. Projects P1-P8 all address different aspects of reduced penetrance in movement disorders with a focus on Parkinson’s disease (blue), monogenic dystonia (red), dystonia-parkinsonism (purple), dystonia in general (pink), or method development/analysis (gray). (A) Data from all projects are continuously provided by, and fed back to, the Central Cohort Project (Z2) and to the Central Knowledge Base (INF). Likewise, data from INF (both from the literature and own preliminary or newly generated) will inform additional queries to Z2; conversely, all available and newly collected data will further complement INF with similar feedback mechanisms to and from P1-P8. Z1 serves as central coordination project of the entire Research Unit. (B) In addition, there will be direct interactions between projects P1-P8.
Molecular mechanisms defining penetrance of LRRK2-associated Parkinson’s disease
Mutations in the Parkinson’s disease (PD) gene Leucine-rich repeat kinase 2 (LRRK2) are dominantly inherited with reduced penetrance. To date, little is known about the molecular mechanisms that trigger the onset of LRRK2-PD. To allow for better monitoring of progression and, ultimately, for the identification of penetrance-associated cellular pathways, in ProtectMove I, we investigated markers of LRRK2-PD manifestation. In fibroblasts from manifesting (LRRK2+/PD+; n=10) and non-manifesting carriers (LRRK2+/PD-; n=21) of the G2019S mutation, first, we confirmed a link between PD onset and LRRK2 phosphorylation. Second, inspired by a report connecting LRRK2 kinase activity with mitochondrial DNA (mtDNA) lesions, we assessed mtDNA integrity and mitochondrial function in LRRK2+/PD- and LRRK2+/PD+ fibroblasts and observed an accumulation of mtDNA deletions and decreased complex I activity in the latter. In light of a study showing reduced urate in LRRK2+/PD+ individuals, we explored urate-induced Nrf2-ARE antioxidant signaling. Interestingly, the Nrf2-ARE target TFAM, which acts as mtDNA transcription and packaging factor was reduced in LRRK2+/PD+ neurons, increasing mtDNA exposure to reactive oxygen species. We hypothesize that a vicious cycle between environment, mitochondrial function and LRRK2 kinase activity, where the mtDNA acts as central interface, defines LRRK2-PD penetrance. To assess environmental factors contributing to penetrance and to identify relevant toxins (Objective 1), we will collect environmental exposure, diet and medication information from the LIPAD cohort (LRRK2+/PD+, n=1,500; LRRK2+/PD-, n=500; controls, n=500). Moreover, in selected persons, we will perform untargeted toxicology. To investigate penetrance-associated (epi-)genetic mtDNA alterations (Objective 2), we will perform sequencing and quantitative mtDNA analyses in blood samples from LIPAD. To determine the contribution of rare variants in nuclear genes involved in antioxidant signaling and mitochondrial function to penetrance (Objective 3), whole genome sequencing and polygenic risk score analyses will be applied to individuals from LIPAD. Finally, to test the causal link between toxin exposure, mtDNA disintegration, mitochondrial dysfunction, LRRK2 kinase activity, and antioxidant signaling (Objective 4), we will conduct RNA-Seq and functional studies in LRRK2+/PD+ and LRRK2+/PD- neurons before and after exposure to oxidative stressors, kinase inhibitors and antioxidants. The results from our study will help to guide personalized medicine approaches, which aim at delaying the onset of LRRK2-PD. Project P1 is led by Principal Investigators well-versed in epidemiological, clinical, genetic and cellular studies. Furthermore, they benefit from (inter-)national collaborations allowing to expand P1 to epigenetic and toxicology analyses. P1 is embedded in a close network of interactions within ProtectMove II. This includes projects P2-P4, P8-P10, INF, Z2 and all Cores.