Substitutions at codon 22 of Alzheimer's A beta peptide induce diverse conformational changes and apoptotic effects in human cerebral endothelial cells

Cerebral amyloid angiopathy is commonly associated with normal aging and Al zheimer's disease and it is also the principal feature of hereditary cerebr al hemorrhage with amyloidosis Dutch type, a familial condition associated to a point mutation G to C at codon 693 of the amyloid beta (AP) precursor protein gene resulting in a Glu to Gin substitution at position 22 of the A beta (E22Q). The patients carrying the A beta E22Q variant usually present with lobar cerebral hemorrhages before 50 years of age. A different mutati on described in several members of three Italian kindred who presented with recurrent hemorrhagic strokes late in life, between 60 and 70 years of age , also associated with extensive cerebrovascular amyloid deposition has bee n found at the same position 22, this time resulting in a Glu to Lye substi tution (E22K). We have compared the secondary structure, aggregation, and f ibrillization properties of the two A beta 40 variants and the wild type pe ptide. Using flow cytometry analysis after staining with propidium iodide a nd annexin V, we also evaluated the cytotoxic effects of the peptides on hu man cerebral endothelial cells in culture. Under the conditions tested, the E22Q peptide exhibited the highest content of P-sheet conformation and the fastest aggregation/fibrillization properties. The Dutch variant also indu ced apoptosis of cerebral endothelial cells at a concentration of 25 mu M, whereas the wild type AP and the E22K mutant had no effect. The data sugges t that different amino acids at position 22 confer distinct structural prop erties to the peptides that appear to influence the onset and aggressivenes s of the disease rather than the phenotype.