Heat shock proteins 70 and 90 inhibit early stages of amyloid β-(1-42) aggregation in vitro

Alzheimer disease is a neurological disorder that is characterized by the presence of fibrils and oligomers composed of the amyloid beta(A beta) peptide. In models of Alzheimer disease, overexpression of molecular chaperones, specifically heat shock protein 70 (Hsp70), suppresses phenotypes related to A beta aggregation. These observations led to the hypothesis that chaperones might interact with A beta and block self-association. However, although biochemical evidence to support this model has been collected in other neurodegenerative systems, the interaction between chaperones and A beta has not been similarly explored. Here, we examine the effects of Hsp70/40 and Hsp90 on A beta aggregation in vitro. We found that recombinant Hsp70/40 and Hsp90 block A beta self-assembly and that these chaperones are effective at substoichiometric concentrations (similar to 1: 50). The antiaggregation activity of Hsp70 can be inhibited by a nonhydrolyzable nucleotide analog and encouraged by pharmacological stimulation of its ATPase activity. Finally, we were interested in discerning what type of amyloid structures can be acted upon by these chaperones. To address this question, we added Hsp70/ 40 and Hsp90 to pre-formed oligomers and fibrils. Based on thioflavin T reactivity, the combination of Hsp70/40 and Hsp90 caused structural changes in oligomers but had little effect on fibrils. These results suggest that if these chaperones are present in the same cellular compartment in which A beta is produced, Hsp70/40 and Hsp90 may suppress the early stages of self-assembly. Thus, these results are consistent with a model in which pharmacological activation of chaperones might have a favorable therapeutic effect on Alzheimer disease.