Altered γ-secretase activity in mild cognitive impairment and Alzheimer's disease.
Bottom Line: The ratios Aβ40/43 versus Aβ38/42 in CSF (each representing cleavage efficiency of Aβ43 or Aβ42) were largely proportional to each other but generally higher in MCI/AD patients compared to control subjects.These data suggest that γ-secretase activity in MCI/AD patients is enhanced at the conversion of Aβ43 and 42 to Aβ40 and 38, respectively.Consequently, we measured the in vitro activity of raft-associated γ-secretase isolated from control as well as MCI/AD brains and found the same, significant alterations in the γ-secretase activity in MCI/AD brains.
Affiliation: Immuno-Biological Laboratories Co., Fujioka, Japan.Show MeSH
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Mentions: To further test our hypothesis, we directly measured γ-secretase activities associated with lipid rafts isolated from AD, MCI and control cortices (Brodmann areas 9–11). For definite confirmation of the Aβ species, the reaction mixtures were subjected to quantitative Western blotting using specific antibodies rather than ELISA. At time 0, deposited Aβ42/43 species were detected in rafts from MCI/AD brains but not in control specimen (Supporting Information Fig S3). The amounts of ln(Aβ38 + Aβ42), which reflect the total capacity of the Aβ38/42-producing line, did not vary between AD, MCI and controls (Supporting Information Fig S4; p = 0.969, ANOVA). Thus, the gross activities of raft γ-secretase were comparable among the three groups. However, the plotted values for Aβ40/43 versus Aβ38/42 are divided into two groups: MCI/AD and controls (Fig 5; Aβ40/43 for control vs. MCI/AD, p < 0.001; Aβ38/42 for control vs. MCI/AD, p = 0.001; Welch's t-test) in the same way as those derived from CSF (Fig 4). It is notable that Figs. .4 and 5 are based on different methods, ELISA and Western blotting, respectively, but give similar results. There were no significant differences between MCI and AD specimen, although MCI patients (91 ± 4.9-year-old) were older than controls (77 ± 6.5-year-old) or AD patients (80 ± 5.0-year-old) (Aβ40/43 for MCI vs. AD, p = 0.342; Aβ38/42 for MCI vs. AD, p = 0.911). There were similar significant differences between control versus AD in the groups of which the ages were not significantly different (Aβ40/43 for control vs. AD, p < 0.001; Aβ38/42 for control vs. AD, p = 0.03).
Affiliation: Immuno-Biological Laboratories Co., Fujioka, Japan.