Proteins in aggregates functionally impact multiple neurodegenerative disease models by forming proteasome-blocking complexes.
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 A????? 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 A?????, knockdown of cram-1 reduced ?-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.
Mesh Terms:
Amyloid beta-Peptides, Animals, Blotting, Western, Caenorhabditis elegans, Caenorhabditis elegans Proteins, Cell Death, Disease Models, Animal, Fertility, Fluorescent Antibody Technique, Gene Knockdown Techniques, Molecular Dynamics Simulation, Neurodegenerative Diseases, Proteasome Endopeptidase Complex, Proteasome Inhibitors, Protein Aggregates, Protein Multimerization, RNA Interference, Ubiquitin
Amyloid beta-Peptides, Animals, Blotting, Western, Caenorhabditis elegans, Caenorhabditis elegans Proteins, Cell Death, Disease Models, Animal, Fertility, Fluorescent Antibody Technique, Gene Knockdown Techniques, Molecular Dynamics Simulation, Neurodegenerative Diseases, Proteasome Endopeptidase Complex, Proteasome Inhibitors, Protein Aggregates, Protein Multimerization, RNA Interference, Ubiquitin
Aging Cell
Date: Feb. 01, 2015
PubMed ID: 25510159
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