Figure 7.

Increase in AICD by alkalizing agent NH₄Cl and by Fe65 overexpression have different effects on neprilysin and Aβ. (A) Treatment of H4-APPwt cells with 5 mM NH₄Cl led to a strong increase in APP C-terminal fragments, including AICD. Concomitantly, neprilysin protein levels were increased and Aβ levels were decreased. Densitometric analysis of relative neprilysin expression and relative amount of secreted Aβ is shown in B. Neprilysin was 2.8-fold up-regulated, and Aβ secretion was decreased to 43% of control (n = 3, error bars represent SD; *p < 0.01, **p < 0.001, unpaired t test). (C) H4-Fe65i cells, expressing Fe65 under control of the tet-off system, were maintained with doxycycline for 3 d (Co), or Fe65 overexpression was induced by cultivating cells without doxycycline for 3 d (+Fe65). Fe65-expression, neprilysin, APP C-terminal fragments, and Aβ from these cells are shown. Although Fe65 overexpression led to an increase in AICD, larger APP C-terminal fragments were decreased. Concomitantly, Aβ levels increased. Neprilysin expression was not significantly affected by Fe65-mediated AICD induction. Densitometric quantification is shown in D.