Pathologic amyloid beta-protein cell surface fibril assembly on cultured human cerebrovascular smooth muscle cells

Cerebrovascular amyloid beta-protein (A beta) deposition is a key pathological feature of Alzheimer's disease and hereditary cerebral hemorrhage with amyloidosis-Dutch type (HCHWA-D). A beta(1-40) containing the E22Q HCHWA-D mutation, but not wild-type A beta(1-40), potently induces several pathologic responses in cultured human cerebrovascular smooth muscle cells, including cellular degeneration and a robust increase in the levels of cellular A beta precursor. In the present study, we show by several quantitative criteria, including thioflavin T fluorescence binding, circular dichroism spectroscopy, and transmission electron microscopic analysis, that at a concentration of 25 microM neither HCHWA-D A beta(1-40) nor wild-type A beta(1-40) appreciably assembles into beta-pleated sheet-containing fibrils in solution over a 6-day incubation period. In contrast, at the same concentrations, HCHWA-D A beta(1-40), but not wild-type A beta(1-40), selectively binds and assembles into abundant fibrils on the surfaces of cultured human cerebrovascular smooth muscle cells. The simultaneous addition of an equimolar concentration of the dye Congo red prevents the cell surface fibril assembly of HCHWA-D A beta(1-40). Moreover, Congo red effectively blocks the key pathologic responses induced by HCHWA-D A beta(1-40) in these cells. The present findings suggest that the surface of human cerebrovascular smooth muscle cells may selectively orchestrate the assembly of pathogenic A beta fibrils and that cell surface A beta fibril formation plays an important role in causing the pathologic responses in these cells.