title: Proteins in aggregates functionally impact multiple neurodegenerative disease models by forming proteasome-blocking complexes.
abstract: Age-dependent neurodegenerative diseases progressively form aggregates containing both shared components (e.g., TDP-43, phosphorylated tau) and proteins specific to each disease. We investigated whether diverse neuropathies might have additional aggregation-prone proteins in common, discoverable by proteomics. Caenorhabditis elegans expressing unc-54p/Q40::YFP, a model of polyglutamine array diseases such as Huntington's, accrues aggregates in muscle 2-6 days posthatch. These foci, isolated on antibody-coupled magnetic beads, were characterized by high-resolution mass spectrometry. Three Q40::YFP-associated proteins were inferred to promote aggregation and cytotoxicity, traits reduced or delayed by their RNA interference knockdown. These RNAi treatments also retarded aggregation/cytotoxicity in Alzheimer's disease models, nematodes with muscle or pan-neuronal Aβ₁₋₄₂ expression and behavioral phenotypes. The most abundant aggregated proteins are glutamine/asparagine-rich, favoring hydrophobic interactions with other random-coil domains. A particularly potent modulator of aggregation, CRAM-1/HYPK, contributed < 1% of protein aggregate peptides, yet its knockdown reduced Q40::YFP aggregates 72-86% (P < 10(-6) ). In worms expressing Aβ₁₋₄₂, knockdown of cram-1 reduced β-amyloid 60% (P < 0.002) and slowed age-dependent paralysis > 30% (P < 10(-6)). In wild-type worms, cram-1 knockdown reduced aggregation and extended lifespan, but impaired early reproduction. Protection against seeded aggregates requires proteasome function, implying that normal CRAM-1 levels promote aggregation by interfering with proteasomal degradation of misfolded proteins. Molecular dynamic modeling predicts spontaneous and stable interactions of CRAM-1 (or human orthologs) with ubiquitin, and we verified that CRAM-1 reduces degradation of a tagged-ubiquitin reporter. We propose that CRAM-1 exemplifies a class of primitive chaperones that are initially protective and highly beneficial for early reproduction, but ultimately impair aggregate clearance and limit longevity.
authors.affiliation: McClellan Veterans Medical Center, Central Arkansas Veterans Healthcare Service, Little Rock, AR, 72205, USA; Department of Geriatrics, University of Arkansas for Medical Sciences, Little Rock, AR 72205, USA.
authors.forename: Srinivas
authors.initials: S
authors.lastname: Ayyadevara
authors.forename: Meenakshisundaram
authors.initials: M
authors.lastname: Balasubramaniam
authors.forename: Yuan
authors.initials: Y
authors.lastname: Gao
authors.forename: Li-Rong
authors.initials: LR
authors.lastname: Yu
authors.forename: Ramani
authors.initials: R
authors.lastname: Alla
authors.forename: Robert
authors.initials: R
authors.lastname: Shmookler Reis
mesh_terms: D016229:Amyloid beta-Peptides / Q000378:metabolism; D000818:Animals; D015153:Blotting, Western; D017173:Caenorhabditis elegans / Q000378:metabolism*; D029742:Caenorhabditis elegans Proteins / Q000302:isolation & purification / Q000378:metabolism; D016923:Cell Death / Q000187:drug effects; D004195:Disease Models, Animal; D005298:Fertility / Q000187:drug effects; D005455:Fluorescent Antibody Technique; D055785:Gene Knockdown Techniques; D056004:Molecular Dynamics Simulation; D019636:Neurodegenerative Diseases / Q000378:metabolism* / Q000473:pathology*; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism*; D061988:Proteasome Inhibitors / Q000494:pharmacology*; D066329:Protein Aggregates; D055503:Protein Multimerization / Q000187:drug effects; D034622:RNA Interference / Q000187:drug effects; D025801:Ubiquitin / Q000378:metabolism
chemical_list: D016229:Amyloid beta-Peptides; D029742:Caenorhabditis elegans Proteins; D061988:Proteasome Inhibitors; D066329:Protein Aggregates; D025801:Ubiquitin; D046988:Proteasome Endopeptidase Complex
keywords: (protein) aggregation; Alzheimer (disease); C. elegans; Huntington (disease); neurodegeneration; proteasome