Global Proteotoxicity Caused by Human ß2 Microglobulin Variants Impairs the Unfolded Protein Response in C. elegans.

Aggregation of ß2 microglobulin (ß2m) into amyloid fibrils is associated with systemic amyloidosis, caused by the deposition of amyloid fibrils containing the wild-type protein and its truncated variant, ΔN6 ß2m, in haemo-dialysed patients. A second form of familial systemic amyloidosis caused by the ß2m variant, D76N, results in amyloid deposits in the viscera, without renal dysfunction. Although the folding and misfolding mechanisms of ß2 microglobulin have been widely studied in vitro and in vivo, we lack a comparable understanding of the molecular mechanisms underlying toxicity in a cellular and organismal environment. Here, we established transgenic C. elegans lines expressing wild-type (WT) human ß2m, or the two highly amyloidogenic naturally occurring variants, D76N ß2m and ΔN6 ß2m, in the C. elegans bodywall muscle. Nematodes expressing the D76N ß2m and ΔN6 ß2m variants exhibit increased age-dependent and cell nonautonomous proteotoxicity associated with reduced motility, delayed development and shortened lifespan. Both ß2m variants cause widespread endogenous protein aggregation contributing to the increased toxicity in aged animals. We show that expression of ß2m reduces the capacity of C. elegans to cope with heat and endoplasmic reticulum (ER) stress, correlating with a deficiency to upregulate BiP/hsp-4 transcripts in response to ER stress in young adult animals. Interestingly, protein secretion in all ß2m variants is reduced, despite the presence of the natural signal sequence, suggesting a possible link between organismal ß2m toxicity and a disrupted ER secretory metabolism.

A short motif in the N-terminal region of α-synuclein is critical for both aggregation and function.

Aggregation of human α-synuclein (αSyn) is linked to Parkinson's disease (PD) pathology. The central region of the αSyn sequence contains the non-amyloid ß-component (NAC) crucial for aggregation. However, how NAC flanking regions modulate αSyn aggregation remains unclear. Using bioinformatics, mutation and NMR, we identify a 7-residue sequence, named P1 (residues 36-42), that controls αSyn aggregation. Deletion or substitution of this 'master controller' prevents aggregation at pH 7.5 in vitro. At lower pH, P1 synergises with a sequence containing the preNAC region (P2, residues 45-57) to prevent aggregation. Deleting P1 (ΔP1) or both P1 and P2 (ΔΔ) also prevents age-dependent αSyn aggregation and toxicity in C. elegans models and prevents αSyn-mediated vesicle fusion by altering the conformational properties of the protein when lipid bound. The results highlight the importance of a master-controller sequence motif that controls both αSyn aggregation and function-a region that could be targeted to prevent aggregation in disease.