ProteostaSys: a systems view of proteostasis

The progression of neurodegenerative diseases such as Alzheimer’s disease (AD) or Parkinson’s disease (PD), is linked to the spreading of protein aggregation across interconnected brain regions. Fibrillar seeds are transferred between cells, inducing misfolding and aggregation of its native monomeric counterpart. A critical rate-limiting step in this process is the rupture of endolysosomal vesicles, which releases transferred aggregates into the cytosol, where they promote further aggregation of endogenous proteins. While the pathways underlying endolysosomal damage and repair have been increasingly studied, many aspects remain unclear. We conducted a genome-wide RNAi screen in a novel C. elegans model of tau spreading and identified sphingolipid metabolism genes as critical for endolysosomal integrity. Using C. elegans and cell culture models, we investigated how disruption of sphingolipid homeostasis affects endolysosomal membrane integrity and contributes to tau aggregation and toxicity. Fluorescence recovery after photobleaching and C-Laurdan dye imaging revealed that silencing sphingolipid metabolism genes decreases endolysosomal vesicle membrane fluidity, increasing endolysosomal rupture. The accumulation of aggregated tau in endolysosomal vesicles further aggravated endomembrane rigidification and damage and promoted seeded tau aggregation, potentially by facilitating the escape of tau seeds from the endolysosomal system. Supplementation with unsaturated fatty acids improved membrane fluidity, suppressing endolysosomal rupture and seeded tau aggregation in cell models, and alleviating tau-associated neurotoxicity in C. elegans. Conversely, supplementation with the saturated fatty acid palmitic acid worsened these effects. These findings provide insights into how impaired sphingolipid homeostasis drives tau pathology, suggesting membrane fluidity restoration as a potential therapeutic strategy for AD.

Professor Carmen Nussbaum

Ludwig Maximilians University Munich, Germany

Professor Carmen Nussbaum

Ludwig Maximilians University Munich, Germany

Carmen Nussbaum studied Biology and pursued her doctoral research at the Technical University of Munich, earning her PhD in December 2008. She then joined Northwestern University in Evanston, IL, USA, as a postdoctoral fellow. From 2014 to 2022, she led a research group at Heidelberg University and the German Cancer Research Center. Since 2022, she holds a W2 Professorship in the Department of Neuroanatomy at Ludwig-Maximilians-University of Munich. Her research utilises C. elegans and cell culture models to study the molecular mechanisms underlying neurodegenerative diseases. She focused on the dual role of the Hsp70 disaggregation machinery in the prion-like propagation of α-synuclein and tau, demonstrating that while chaperone-mediated disaggregation solubilises protein aggregates, it also generates small, seeding-competent toxic species. More recently, her work has focused on the role of endolysosomal integrity in prion-like aggregate propagation.

Protein disulfide formation contributes to protein folding and function, as evidenced by numerous oxidoreductases that maintain disulfide status within various cell compartments.  Many of these oxidoreductases, including thioredoxins (Trxs) and protein disulfide isomerases (PDIs), arose from a common evolutionary precursor and employ transient thiol-disulfide exchange mechanisms when interacting with their redox partners.  Because disulfide bonds that form between Trx superfamily members and their redox partners are often short-lived, we developed a chemical cross-linking strategy that irreversibly captures these proteins when interacting with potential redox partners.  Using the thiol-reactive cross-linker divinyl sulfone (DVSF), Trx2, a cytosolic Trx in baker’s yeast, undergoes cross-linking with its most prominent redox partners via modification of its active site cysteines. Likewise, upon DVSF treatment, PDIs that promote oxidative protein folding in the ER form cross-linked complexes with known redox partners, including many chaperones and protein clearance factors. More recently, we have turned our attention to less studied redox networks, seeking to identify the interaction partners of disulfide maintenance systems in mitochondria.  Particularly, we have characterised the putative redox partners of yeast Trx3, a disulfide reductase that resides in the mitochondrial matrix. We have found that Trx3 interacts with numerous metabolic enzymes, including members of the branched chain amino acid biosynthesis pathway, as well as proteins in the proteostasis network.  Our current work suggests disulfide bond homeostasis and flux through specific metabolic pathways may be linked in previously undescribed ways.

Professor James West

The College of Wooster, USA

Professor James West

The College of Wooster, USA

James West received his PhD in Biochemistry from Vanderbilt University in 2005, working in Larry Marnett’s laboratory on apoptotic cell death mechanisms and cellular responses to protein-damaging lipid peroxidation byproducts. Subsequently, he performed postdoctoral research in the Department of Molecular Biosciences at Northwestern University in the laboratory of Rick Morimoto, studying small molecule activators of the heat shock response and parallel stress responses. He began a faculty position at The College of Wooster in 2008, where his research program has focused on interrogating protein disulfide formation and reduction networks, primarily in a baker’s yeast model system.