Hsp104 Targets Multiple Intermediates on the Amyloid Pathway and Suppresses the Seeding Capacity of Aβ Fibrils and Protofibrils

Abstract

The heat shock protein Hsp104 has been reported to possess the ability to modulate protein aggregation and toxicity and to "catalyze" the disaggregation and recovery of protein aggregates, including amyloid fibrils, in yeast, Escherichia coli, mammalian cell cultures, and animal models of Huntington's disease and Parkinson's disease. To provide mechanistic insight into the molecular mechanisms by which Hsp104 modulates aggregation and fibrillogenesis, the effect of Hsp104 on the fibrillogenesis of amyloid beta (Aβ) was investigated by characterizing its ability to interfere with oligomerization and fibrillogenesis of different species along the amyloid-formation pathway of Aβ. To probe the disaggregation activity of Hsp104, its ability to dissociate preformed protofibrillar and fibrillar aggregates of Aβ was assessed in the presence and in the absence of ATP. Our results show that Hsp104 inhibits the fibrillization of monomeric and protofibrillar forms of Aβ in a concentration-dependent but ATP-independent manner. Inhibition of Aβ fibrillization by Hsp104 is observable up to Hsp104/Aβ stoichiometric ratios of 1:1000, suggesting a preferential interaction of Hsp104 with aggregation intermediates (e.g., oligomers, protofibrils, small fibrils) on the pathway of Aβ amyloid formation. This hypothesis is consistent with our observations that Hsp104 (i) interacts with Aβ protofibrils, (ii) inhibits conversion of protofibrils into amyloid fibrils, (iii) arrests fibril elongation and reassembly, and (iv) abolishes the capacity of protofibrils and sonicated fibrils to seed the fibrillization of monomeric Aβ. Together, these findings suggest that the strong inhibition of Aβ fibrillization by Hsp104 is mediated by its ability to act at different stages and target multiple intermediates on the pathway to amyloid formation.

BRICHOS Domains Efficiently Delay Fibrillation of Amyloid β-Peptide

“…Because no binding of A␤ monomer to BRICHOS was detected, it is likely that BRICHOS instead binds to assemblies formed early in the aggregation processes. The chaperones Hsp104, Hsp70, and Hsp40 are active at substoichiometric amounts and preferentially interact with intermediates formed in the fibril formation process (13,14). In overexpressing cell lines, Hsp70 protects against A␤ 42 -induced neuronal death (60), whereas ␣B-crystallin, Hsp27, Hsp20, and HspB2/B3 reduce A␤ cell toxicity (61).…”

“…Molecular chaperones have evolved to counteract misfolding in the cell. Examples are the heat-shock proteins (Hsp) 70, Hsp90, and Hsp104 (13)(14)(15)(16) and * This work was supported by the Swedish Research Council.…”

Molecular Chaperone Hsp104 Can Promote Yeast Prion Generation

“…Surprisingly, no metazoan homolog or analog of Hsp104p has been identified; such unique disaggregation activity is restricted to bacteria, fungi, and plants. Several attempts were made to introduce the wellcharacterized yeast HSP104 gene in rodent models of neurodegenerative disorders (Vacher et al 2005;Perrin et al 2007;Arimon et al 2008;Lo Bianco et al 2008). These reports showed that Hsp104 was able to reduce aggregation rates for various amyloids and even prolong the lifespan of a Huntington disease mouse model by 20% (Vacher et al 2005).…”

Disaggregases, molecular chaperones that resolubilize protein aggregates

“…For example, Hsp104 has been shown to convert an aggregated and protease resistant mammalian prion-like protein fragment of PrP Sc into a random coiled structure (Schirmer andLindquist 1997, Liu et al 2011). Additionally, Hsp104 inhibits the seeding properties of Abeta fibrils (Arimon et al 2008), and is effective against protein aggregation (Mosser et al 2004). Furthermore, the overexpression of Hsp104 in transgenic mice expressing the first 171 residues of mutant huntingtin, used as a model for Huntington's disease, reduced the formation of aggregates and prolonged the lifespan of the animals (Vacher et al 2005).…”