Tryptophan residues in TDP-43 and SOD1 modulate the cross-seeding and toxicity of SOD1

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease of motor neurons. Neuronal superoxide dismutase-1 (SOD1) inclusion bodies are characteristic of familial ALS with SOD1 mutations, while a hallmark of sporadic ALS is inclusions containing aggregated WT TAR DNA-binding protein 43 (TDP-43). We show here that co-expression of mutant or WT TDP-43 with SOD1 leads to misfolding of endogenous SOD1 and aggregation of SOD1 reporter protein SOD1G85R-GFP in human cell cultures and promotes synergistic axonopathy in zebrafish. Intriguingly, this pathological interaction is modulated by natively solvent-exposed tryptophans in SOD1 (tryptophan-32) and TDP-43 RNA-recognition motif RRM1 (tryptophan-172), in concert with natively sequestered TDP-43 N-terminal domain tryptophan-68. TDP-43 RRM1 intrabodies reduce WT SOD1 misfolding in human cell cultures, via blocking tryptophan-172. Tryptophan-68 becomes antibody-accessible in aggregated TDP-43 in sporadic ALS motor neurons and cell culture. 5-fluorouridine inhibits TDP-43-induced G85R-GFP SOD1 aggregation in human cell cultures and ameliorates axonopathy in zebrafish, via its interaction with SOD1 tryptophan-32. Collectively, our results establish a novel and potentially druggable tryptophan-mediated mechanism whereby two principal ALS disease effector proteins might directly interact in disease.

A Month in Neurodegenerative Disease Research (AMiNDR): The evolution of an open-access podcast series for Alzheimer's researchers

BACKGROUND

With the increasing strain on researchers' time and the constant flow of new publications, staying up to date with the latest findings in the field of Alzheimer's disease research is more challenging than ever. To address this problem, we launched a podcast series in June 2020 which covers primary peer-reviewed articles. Each episode comes with a bibliography citing the abstracts covered, and a description by theme. Since then, we have focused on program evaluation and quality improvement with the following aims: 1) Implement a systematic and consistent approach within the team and across episodes, 2) Increase our global reach, and 3) Provide a valuable service to researchers.

METHODS

Areas for improvement were identified by the core founders of the podcast, 25 new team members, and listener feedback. 1) A systematic approach to sorting papers into defined themes was developed based on thematic coding of abstracts to identify major themes and sub-themes. We also implemented quality control measures and standardized hosting procedures. 2) To evaluate our reach, we used analytics from the Simplecast podcast platform to track the number of downloads over time and the geographical location of our listeners. 3) Formal and informal feedback was collected through a survey and social media platforms, respectively. We also plan to assess additional analytics to track the use of our bibliographies to evaluate their value and whether our podcast prompted listeners to consult the original article.

RESULTS

From our original four broad-strokes themes in early 2020, we have expanded to 25 themes to curate focused episodes on topics relevant to researchers. We also developed a semi-automated quality control regimen to ensure that we cover all papers that appear on PubMed each month, without duplicates. To standardize summarizing and hosting procedures, we created guidelines to train new members of our team. We have received significantly more positive feedback for our recent series that implemented the improvements, and observed a gradual increase in our weekly downloads from a global listener base.

CONCLUSION

With the feedback received and data collected on listener trends, it seems that researchers worldwide are benefiting from our podcast platform and its improvements.

A Rational Structured Epitope Defines a Distinct Subclass of Toxic Amyloid-beta Oligomers

Oligomers of amyloid-β (AβO) are deemed key in synaptotoxicity and amyloid seeding of Alzheimer's disease (AD). However, the heterogeneous and dynamic nature of AβO and inadequate markers for AβO subtypes have stymied effective AβO identification and therapeutic targeting in vivo. We identified an AβO-subclass epitope defined by differential solvent orientation of the lysine 28 side chain in a constrained loop of serine-asparagine-lysine (cSNK), rarely displayed in molecular dynamics simulations of monomer and fibril ensembles. A mouse monoclonal antibody targeting AβO^cSNK recognizes ∼50-60 kDa SDS-resistant soluble Aβ assemblages in AD brain and prolongs the lag phase of Aβ aggregation in vitro. Acute peripheral infusion of a murine IgG1 anti-AβO^cSNK in two AD mouse models reduced soluble brain Aβ aggregates by 20-30%. Chronic cSNK peptide immunization of APP/PS1 mice engendered an anti-AβO^cSNK IgG1 response without epitope spreading to Aβ monomers or fibrils and was accompanied by preservation of global PSD95 expression and improved cued fear memory. Our data indicate that the oligomer subtype AβO^cSNK participates in synaptotoxicity and propagation of Aβ aggregation in vitro and in vivo.