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

Cells of the mononuclear phagocyte system are closely associated with vascular and neuritic β-amyloid deposits in Alzheimer’s disease. Using one-dimensional and newly developed two-dimensional Aβ-SDS–PAGE Western immunoblot techniques (1D/2D-Aβ-WIB) we investigated the patterns of Aβ peptides released by primary non-adherent and adherence-activated human mononuclear phagocytes in vitro. An overall increase of total released Aβ peptides (Aβtotal) was observed in adherence-activated mononuclear phagocyte cultures. 2D-Aβ-WIB revealed that the proportion of Aβ1–40 decreased significantly to 50.2 ± 5.4% (n = 10) of Aβtotal compared to 65.9 ± 5.6% (n = 7) in non-adherent cultures (p < 0.0001, t = 5.82). Aβ1–42 accounted for only 3.0 ± 2.1% of Aβtotal and its proportion did not change significantly upon adherence (2.8 ± 0.5% of Aβtotal). In adherence-activated cultures we detected pronounced shifts in the fractional pattern of released Aβ peptides in favour of N-truncated species. The second most prominent Aβ peptide accounted for as much as 12.7 ± 3.0% of Aβtotal (2.0 ± 1.2% in non-adherent cultures; p < 0.0001, t = 9.00) and was identified as Aβ2–40 by comigration with a synthetic peptide and by N-terminal-specific antibodies. A strong increase of a further Aβ immunoreactive spot migrating at pI 5.45 was observed. It accounted for 9.2 ± 1.7% of Aβtotal as compared to 1.0 ± 0.9% in non-adherent cultures (p < 0.0001, t = 11.61) and presumably represented a variant of Aβ2–40 as determined by C-terminal Aβ40-specific immunoprecipitation and N-terminal-specific immunodetection. Thus, mononuclear phagocytes might be one source of the N-truncated Aβ peptides regularly found in human plasma and are less likely to contribute substantially to plasma Aβ1-42.