Modeling UBQLN2-mediated neurodegenerative disease in mice: Shared and divergent properties of wild type and mutant UBQLN2 in phase separation, subcellular localization, altered proteostasis pathways, and selective cytotoxicity.

Abstract

The ubiquitin-binding proteasomal shuttle protein UBQLN2 is implicated in common neurodegenerative disorders due to its accumulation in disease-specific aggregates and, when mutated, directly causes familial frontotemporal dementia/amyotrophic lateral sclerosis (FTD/ALS). Like other proteins linked to FTD/ALS, UBQLN2 undergoes phase separation to form condensates. The relationship of UBQLN2 phase separation and accumulation to neurodegeneration, however, remains uncertain. Employing biochemical, neuropathological and behavioral assays, we studied the impact of overexpressing WT or mutant UBQLN2 in the CNS of transgenic mice. Expression of UBQLN2 harboring a pathogenic mutation (P506T) elicited profound and widespread intraneuronal inclusion formation and aggregation without prominent neurodegenerative or behavioral changes. Both WT and mutant UBQLN2 formed ubiquitin- and P62-positive inclusions in neurons, supporting the view that UBQLN2 is intrinsically prone to phase separate, with the size, shape and frequency of inclusions depending on expression level and the presence or absence of a pathogenic mutation. Overexpression of WT or mutant UBQLN2 resulted in a dose-dependent decrease in levels of a key interacting chaperone, HSP70, as well as dose-dependent profound degeneration of the retina. We conclude that, at least in mice, robust aggregation of a pathogenic form of UBQLN2 is insufficient to cause neuronal loss recapitulating that of human FTD/ALS. Our results nevertheless support the view that altering the normal cellular balance of UBQLN2, whether wild type or mutant protein, has deleterious effects on cells of the CNS and retina that likely reflect perturbations in ubiquitin-dependent protein homeostasis.

• Authors: Lisa M Sharkey, Stephanie S Sandoval-Pistorius, Shannon J Moore, Julia E Gerson, Robert Komlo, Svetlana Fischer, Keyshla Y Negron-Rios, Emily V Crowley, Francisco Padron, Ronak Patel, Geoffrey G Murphy, Henry L Paulson
• Journal: Neurobiology of disease (Neurobiol Dis) Vol. 143 Pg. 105016 (09 2020) ISSN: 1095-953X [Electronic] United States
• PMID: 32653673 (Publication Type: Journal Article, Research Support, N.I.H., Extramural, Research Support, Non-U.S. Gov't)
• Copyright: Copyright © 2020 The Authors. Published by Elsevier Inc. All rights reserved.

Chemical References

• Adaptor Proteins, Signal Transducing
• Autophagy-Related Proteins
• UBQLN2 protein, mouse

Topics

• Adaptor Proteins, Signal Transducing (genetics, metabolism)
• Amyotrophic Lateral Sclerosis (metabolism, pathology)
• Animals
• Autophagy-Related Proteins (genetics, metabolism)
• Disease Models, Animal
• Frontotemporal Dementia (metabolism, pathology)
• Mice
• Mice, Inbred C57BL
• Mutation
• Nerve Degeneration (metabolism, pathology)
• Neurodegenerative Diseases (genetics, metabolism, pathology)
• Neurons (metabolism, pathology)
• Proteostasis (physiology)