Small heat shock protein HspB8:: its distribution in Alzheimer's disease brains and its inhibition of amyloid-β protein aggregation and cerebrovascular amyloid-β toxicity

Alzheimer's disease (AD) is characterized by pathological lesions, such as senile plaques (SPs) and cerebral amyloid angiopathy (CAA), both predominantly consisting of a proteolytic cleavage product of the amyloid-beta precursor protein (APP), the amyloid-beta peptide (A beta). CAA is also the major pathological lesion in hereditary cerebral hemorrhage with amyloidosis of the Dutch type (HCHWA-D), caused by a mutation in the gene coding for the A beta peptide. Several members of the small heat shock protein (sHsp) family, such as alpha B-crystallin, Hsp27, Hsp20 and HspB2, are associated with the pathological lesions of AD, and the direct interaction between sHsps and A beta has been demonstrated in vitro. HspB8, also named Hsp22 of H11, is a recently discovered member of the sHsp family, which has chaperone activity and is observed in neuronal tissue. Furthermore, HspB8 affects protein aggregation, which has been shown by its ability to prevent formation of mutant huntingtin aggregates. The aim of this study was to investigate whether HspB8 is associated with the pathological lesions of AD and HCHWA-D and whether there are effects of HspB8 on A beta aggregation and A beta-mediated cytotoxicity. We observed the expression of HspB8 in classic SPs in AD brains. In addition, HspB8 was found in CAA in HCHWA-D brains, but not in AD brains. Direct interaction of HspB8 with A beta(1-42), A beta(1-40) and A beta(1-40) with the Dutch mutation was demonstrated by surface plasmon resonance. Furthermore, co-incubation of HspB8 with D-A beta(1-40) resulted in the complete inhibition of D-A beta(1-40)-mediated death of cerebrovascular cells, likely mediated by a reduction in both the beta-sheet formation of D-A beta(1-40) and its accumulation at the cell surface. In contrast, however, with A beta(1-42), HspB8 neither affected beta-sheet formation nor A beta-mediated cell death. We conclude that HspB8 might play an important role in regulating A beta aggregation and, therefore, the development of classic SPs in AD and CAA in HCHWA-D.