Charge alterations of E22 enhance the pathogenic properties of the amyloid β-protein

Cerebral amyloid angiopathy (CAA) due to amyloid beta-protein (A beta) is a key pathological feature of patients with Alzheimer's disease and hereditary cerebral hemorrhage with amyloidosis, Dutch-type (HCHWA-D). The CAA in these disorders is characterized by deposition of A beta in the smooth muscle 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 associated with CAA and hemorrhagic stroke. These two similar disorders, stemming from amino acid substitutions at position 22 of A beta, implicate the importance of this site in the pathology of HCHWA. Previously we showed that HCHWA-D A beta(1-40) containing the E22Q substitution induces robust pathologic responses in cultured human cerebrovascular smooth muscle cells (HCSM cells), including highly elevated levels of cell-associated A beta precursor (A beta PP) and cell death. In the present study, a series of E22 mutant A beta(1-40) peptides were synthesized, and their pathogenic properties toward cultured HCSM cells were evaluated. Quantitative fluorescence analyses showed that mutant A beta(1-40) peptides either containing a loss of charge (E22Q and E22A) or a change of charge (E22K) bind to the surface of HCSM cells and form amyloid fibrils. Similarly, this same group of E22 mutant A beta(1-40) peptides caused enhanced pathologic responses in HCSM cells. In contrast, wild-type E22 or the charge-preserving E22D A beta(1-40) peptides were devoid of any of these pathogenic properties. These data suggest that a change or loss of charge at position 22 of A beta enhances the pathogenic effects of the peptide toward HCSM cells and may contribute to the pathogenesis of the phenotypically related HCHWA disorders.