Charge alterations of E22 enhance the pathogenic properties of the amyloidbeta-protein

Cerebral amyloid angiopathy (CAA) due to amyloid beta-protein (A beta) is a key pathological feature of patients with Alzheimer's disease and heredita ry cerebral hemorrhage with amyloidosis, Dutch-type (HCHWA-D). The CAA in t hese disorders is characterized by deposition of A beta in the smooth muscl e cells within the cerebral vessel wall. Recently, a new mutation in A beta , E22K, was identified in several Italian families that, like HCHWA-D, is a ssociated with CAA and hemorrhagic stroke. These two similar disorders, ste mming from amino acid substitutions at position 22 of A beta, implicate the importance of this site in the pathology of HCHWA. Previously we showed th at HCHWA-D A beta(1-40) containing the E22Q substitution induces robust pat hologic responses in cultured human cerebrovascular smooth muscle cells (HC SM cells), including highly elevated levels of cell-associated A beta precu rsor (A beta PP) and cell death. In the present study, a series of E22 muta nt A beta(1-40) peptides were synthesized, and their pathogenic properties toward cultured HCSM cells were evaluated. Quantitative fluorescence analys es showed that mutant A beta(1-40) peptides either containing a loss of cha rge (E22Q and E22A) or a change of charge (E22K) bind to the surface of HCS M cells and form amyloid fibrils. Similarly, this same group of E22 mutant A beta(1-40) peptides caused enhanced pathologic responses in HCSM cells. I n contrast, wild-type E22 or the charge-preserving E22D A beta(1-40) peptid es were devoid of any of these pathogenic properties. These data suggest th at a change or loss of charge at position 22 of A beta enhances the pathoge nic effects of the peptide toward HCSM cells and may contribute to the path ogenesis of the phenotypically related HCHWA disorders.