Adherence-dependent shifts in the patterns of beta-amyloid peptides secreted by human mononuclear phagocytes

Cells of the mononuclear phagocyte system are closely associated with vascular and neuritic beta-amyloid deposits in Alzheimer's disease. Using one-dimensional and newly developed two-dimensional Abeta-SDS-PAGE Western immunoblot techniques (1D/2D-Abeta-WIB) we investigated the patterns of Abeta peptides released by primary non-adherent and adherence-activated human mononuclear phagocytes in vitro. An overall increase of total released Abeta peptides (Abeta(total)) was observed in adherence-activated mononuclear phagocyte cultures. 2D-Abeta-WIB revealed that the proportion of Abeta(1-40) decreased significantly to 50.2+/-5.4% (n=10) of Abeta(total) compared to 65.9+/-5.6% (n=7) in non-adherent cultures (p<0.0001, t=5.82). Abeta(1-42) accounted for only 3.0+/-2.1% of Abeta(total) and its proportion did not change significantly upon adherence (2.8+/-0.5% of Abeta(total)). In adherence-activated cultures we detected pronounced shifts in the fractional pattern of released Abeta peptides in favour of N-truncated species. The second most prominent Abeta peptide accounted for as much as 12.7+/-3.0% of Abeta(total) (2.0+/-1.2% in non-adherent cultures; p<0.0001, t=9.00) and was identified as Abeta(2-40) by comigration with a synthetic peptide and by N-terminal-specific antibodies. A strong increase of a further Abeta immunoreactive spot migrating at pI 5.45 was observed. It accounted for 9.2+/-1.7% of Abeta(total) as compared to 1.0+/-0.9% in non-adherent cultures (p<0.0001, t=11.61) and presumably represented a variant of Abeta(2-40) as determined by C-terminal Abeta(40)-specific immunoprecipitation and N-terminal-specific immunodetection. Thus, mononuclear phagocytes might be one source of the N-truncated Abeta peptides regularly found in human plasma and are less likely to contribute substantially to plasma Abeta(1-42).