The overarching goal of this study is to use complementary Drosophila, and human iPS-induced neurons to understand how mutations in the Ubiquilin 2 (UBQLN2) gene cause amyotrophic lateral sclerosis/frontotemporal dementia (ALS/FTD). UBQLN2 and closely related UBQLN1 belong to a family of eukaryotic ubiquitin (Ub)-binding proteins that function, in part, as chaperone factors for proteins that are destined for degradation by the proteasome. UBQLN1 and UBQLN2 share 74% amino acid identity, with the most striking difference being a proline-rich-repeat (PRR) domain that is unique to UBQLN2. Missense mutations within the UBQLN2 PRR cause familial, X-linked, forms of ALS/FTD, whereas ubiquilin histopathology, comprised of dense aggregates of UBQLN2 and UBQLN1, are observed in most instances of ALS/FTD regardless of UBQLN2 mutation status. To address pathomechanisms of UBQLN2-associated ALS/FTD we exploited the upstream activating sequence (UAS)/GAL4 system to generate isogenic Drosophila strains expressing wild-type (WT) and ALS mutant forms of UBQLN2 in different tissues and cell types. We found that UBQLN2ALS mutants elicited neurodegeneration phenotypes?including eye degeneration, motor defects, and lifespan shortening?that were more severe than phenotypes caused by equivalent expression of UBQLN2WT. A second chromosome deficiency screen identified 36 genetic intervals that either enhanced or reduced UBQLN2ALS toxicity and subsequent mapping has implicated endolysosomal transport and axonal guidance genes as key disease pathways. In this exploratory R21 grant proposal we will leverage the Drosophila UBQLN2-ALS model to answer the following questions concerning the mechanisms of UBQLN2 toxicity: (i) What genes and pathways contribute to UBQLN2-mediated neurodegeneration? (ii) What are the impacts of UBQLN2ALS mutants on endolysosomal dynamics? (iii) Can Drosophila genetic screens be leveraged to understand UBQLN2-mediated neurodegeneration in human iPS derived neurons? The proposed experiments will identify genetic determinants of UBQLN2-associated neurodegeneration with broader implications for understanding ALS/dementia and other neurodegenerative diseases involving pathologic protein accumulation.
The goal of this work is to better understand pathomechanisms of UBQLN2 associated neurodegeneration in Amyotrophic lateral sclerosis/frontotemporal dementia (ALS/FTD). The production of misfolded, aggregation- prone, proteins in neurons, either through disease-associated mutation or as a consequence of reduced protein clearance capacity, is causally linked to the development of a host of devastating neurodegenerative diseases, including ALS/FTD. In this project we are using the fruit fly, Drosophila melanogaster, and iPS derived neurons to understand how mutations in UBQLN2 which is involved in protein clearance trigger neurodegeneration. We have identified genetic modifiers for UBQLN2 associated neurodegeneration through Drosophila deficiency screen. We will validate genetic modifiers from Drosophila results in human iPS derived neurons. We hope to identify pathways whose perturbation either rescue or worsen UBQLN2-mediated neurodegeneration. In the future, this information may be leveraged to develop chemicals that attenuate ALS/FTD.
