Figure 3.
Astrocytes secrete Aβ-degrading activity in vitro producing characteristic Aβ fragments. Freshly prepared synthetic human Aβ1–40 or Aβ1–42 was added to SFM or to SFM that had been conditioned by incubation with astrocytes for 24 h (ACM). The mixture was then incubated for 24 h at 37°C, and residual Aβ was measured by ELISA (A) (expressed as mean ± SD) or analyzed by Tris-Tricine–Western blotting (B). Non-degraded Aβ and its proteolytic fragments in the incubation mixtures were also analyzed by MALDI-TOF MS (C). Incubation with ACM significantly decreased Aβ levels as measured by ELISA (A) and immunoblotting (B) and generated several Aβ fragments detected by MALDI-TOF MS relative to insulin (internal standard) (C) that have been shown previously to arise from Aβ digestion with MMP-2 or -9. No significant differences in detected fragments were seen in digestions with Aβ1–40 compared with Aβ1–42. *p < 0.05; significant difference between ACM and SFM.