Suppression of in vivo β-amyloid peptide toxicity by overexpression of the HSP-16.2 small chaperone protein

Expression of the human beta-amyloid peptide (A beta) in a transgenic Caenorhabditis elegans Alzheimer disease model leads to the induction of HSP-16 proteins, a family of small heat shock-inducible proteins homologous to vertebrate alpha B crystallin. These proteins also co-localize and co-immunoprecipitate with A beta in this model (Fonte, V., Kapulkin, V., Taft, A., Fluet, A., Friedman, D., and Link, C. D. (2002) Proc. Natl. Acad. Sci. U. S. A. 99, 9439-9444). To investigate the molecular basis and biological function of this interaction between HSP-16 and A beta, we generated transgenic C. elegans animals with high level, constitutive expression of HSP-16.2. We find that constitutive expression of wild type, but not mutant, HSP-16.2 partially suppresses A beta toxicity. Wild type A beta-(1-42), but not A beta single chain dimer, was observed to become sequestered in HSP-16.2-containing inclusions, indicating a conformation-dependent interaction between HSP-16.2 and A beta in vivo. Constitutive expression of HSP-16.2 could reduce amyloid fibril formation, but it did not reduce the overall accumulation of A beta peptide or alter the pattern of the predominant oligomeric species. Studies with recombinant HSP-16.2 demonstrated that HSP-16.2 can bind directly to A beta in vitro, with a preferential affinity for oligomeric A beta species. This interaction between A beta and HSP-16.2 also influences the formation of A beta oligomers in in vitro assays. These studies are consistent with a model in which small chaperone proteins reduce A beta toxicity by interacting directly with the A beta peptide and altering its oligomerization pathways, thereby reducing the formation of a minor toxic species.