Hippocampal protein aggregation signatures fully distinguish pathogenic and wildtype UBQLN2 in amyotrophic lateral sclerosis

Mutations in the UBQLN2 gene cause X-linked dominant amyotrophic lateral sclerosis (ALS) and/or frontotemporal dementia (FTD) characterised by ubiquilin 2 aggregates in neurons of the motor cortex, hippocampus, cerebellum, and spinal cord. However, ubiquilin 2 neuropathology is also seen in sporadic and familial ALS or FTD cases not caused by UBQLN2 mutations, particularly C9ORF72-linked cases. This makes the mechanistic role of ubiquilin 2 mutations and the value of ubiquilin 2 pathology for predicting genotype unclear. Here we examine a cohort of 31 genotypically diverse ALS cases with or without FTD, including four cases with UBQLN2 mutations (resulting in p.P497H, p.P506S, and two cases with p.T487I). Using double-, triple-, and six-label fluorescent immunohistochemistry, we mapped the co-localisation of ubiquilin 2 with phosphorylated TDP-43 (pTDP-43), dipeptide repeat aggregates, and p62, in the hippocampus of controls (n=5), or ALS with or without FTD in sporadic (n=19), unknown familial (n=3), SOD1-linked (n=1), C9ORF72-linked (n=4), and UBQLN2-linked (n=4) cases. We differentiate between i) ubiquilin 2 aggregation together with, or driven by, pTDP-43 or dipeptide repeat proteins, and ii) ubiquilin 2 self-aggregation driven by UBQLN2 gene mutations. Together we describe a hippocampal protein aggregation signature that fully distinguishes mutant from wildtype ubiquilin 2 in ALS with or without FTD, whereby mutant ubiquilin 2 is more prone than wildtype to aggregate independently of driving factors. This neuropathological signature can be used to assess the pathogenicity of UBQLN2 gene mutations and to understand the mechanisms of UBQLN2-linked disease.

Probing Protein Aggregation at Buried Interfaces: Distinguishing Adsorbed Protein Monomer, Dimer, and Monomer-Dimer Mixture in Situ

Protein adsorption on surfaces greatly impacts many applications such as biomedical materials, anti-biofouling coatings, bio-separation membranes, biosensors, and antibody protein drugs etc. For example, protein drug adsorption on widely used...

Phosphorylated resveratrol as a protein aggregation suppressor in-vitro and in-vivo

The stability of proteins in solution poses a great challenge for both, technical applications and molecular biology including neurodegenerative diseases. In this work, a phosphorylated resveratrol material was examined for...

Inhibition of the formation of lysozyme fibrillar assemblies by the isoquinoline alkaloid coralyne

Protein aggregation into oligomeric and fibrillar species are the hallmark of many degenerative diseases like Alzheimer’s and prion diseases, as well as type II diabetes. Compounds that can modulate protein...

Preserving protein homeostasis prevents motor impairment in DNA Damage Response-compromised C. elegans

To maintain genome integrity, cells rely on a complex system of DNA repair pathways and cell cycle checkpoints, together referred to as the DNA damage response (DDR). Impairments in DDR pathways are linked to cancer, but also to a wide range of degenerative processes, frequently including progressive neuropathy and accelerated aging. How defects in mechanistically distinct DDR pathways can drive similar degenerative phenotypes is not understood. Here we show that defects in various DDR components are linked to a loss of protein homeostasis in Caenorhabditis elegans. Prolonged silencing of atm-1, brc-1 or ung-1, central components in respectively checkpoint signaling, double strand break repair and base excision repair enhances the global aggregation of proteins occurring in adult animals, and accelerates polyglutamine protein aggregation in a model for neurodegenerative diseases. Overexpression of the molecular chaperone HSP-16.2 prevents enhanced protein aggregation in atm-1, brc-1 or ung-1-compromised animals. Strikingly, rebalancing protein homeostasis with HSP-16.2 almost completely rescues age-associated impaired motor function in these animals as well. This reveals that the consequences of a loss of atm-1, brc-1 or ung-1 converge on an impaired protein homeostasis to cause degeneration. These findings indicate that a loss of protein homeostasis is a crucial downstream consequence of DNA repair defects, and thereby provide an attractive novel framework for understanding the broad link between DDR defects and degenerative processes.

Amyloid-like aggregating proteins cause lysosomal defects in neurons via gain-of-function toxicity

The autophagy-lysosomal pathway is impaired in many neurodegenerative diseases characterized by protein aggregation, but the link between aggregation and lysosomal dysfunction remains poorly understood. Here, we combine cryo-electron tomography, proteomics, and cell biology studies to investigate the effects of protein aggregates in primary neurons. We use artificial amyloid-like β-sheet proteins (β proteins) to focus on the gain-of-function aspect of aggregation. These proteins form fibrillar aggregates and cause neurotoxicity. We show that late stages of autophagy are impaired by the aggregates, resulting in lysosomal alterations reminiscent of lysosomal storage disorders. Mechanistically, β proteins interact with and sequester AP-3 μ1, a subunit of the AP-3 adaptor complex involved in protein trafficking to lysosomal organelles. This leads to destabilization of the AP-3 complex, missorting of AP-3 cargo, and lysosomal defects. Restoring AP-3μ1 expression ameliorates neurotoxicity caused by β proteins. Altogether, our results highlight the link between protein aggregation, lysosomal impairments, and neurotoxicity.