DHA attenuates Aβ peptide secretion and serves as the precursor for NPD1 biosynthesis; meanwhile, sAPPα activates NPD1 formation. (A) HN cells were grown for up to 8 weeks. (B and C) After 4 weeks of culture, aging HN cells displayed approximately equal populations of neurons and glia and stained positive with the (red fluorescent) neuron-specific marker βIII tubulin (6) (B) and the (green fluorescent) glia-specific marker GFAP (C). (D and E) HN cells in culture normally release Aβ40 and Aβ42 peptides over 8 weeks of aging. Secretion by HN cells of Aβ42 peptide was approximately one-tenth that of Aβ40 peptide; IL-1β (10 ng/ml in modified HNMM; see ref. 3) increased, and DHA decreased, the release of both Aβ40 and Aβ42 peptides into the cell culture medium. CON, control. (F) DHA (100 nM) induced NPD1 biosynthesis in HN cells, and this induction was age-dependent. (G–I) HN cells incubated in the presence of 10, 20, 50, and 100 ng/ml of sAPPα showed dose-dependent upregulation of NPD1 formation (G); HN cells incubated with sAPPα (at 20 and 100 ng/ml) and/or DHA (at 50 nM; even in the presence of Aβ42) also displayed upregulated production of NPD1 (H and I). *P < 0.05 (ANOVA).