Figure 2.

Loss of axonal sAPP is not involved in axonal degeneration induced by mechanical or toxin damage. A–C, Immunofluorescent microscopic analysis using an antibody to the APP N terminus to examine the “patchy” loss of surface APP (sAPP) on axons of neurons deprived of NGF (A), following axotomy (B), or treated with vincristine (C). Note the loss of sAPP following NGF withdrawal but not after mechanical or toxic insults, and that the loss of sAPP after NGF withdrawal persists despite the expression of cytNmnat1 or Bcl-xl. Quantification of the percentage of axons with decreased sAPP is displayed for each condition (see Materials and Methods). D, Conditioned medium was subjected to Western blot analysis for cleaved N-terminal APP fragment using anti-N-APP antibody. The presence of shed N-terminal APP fragments was detected after NGF deprivation even under conditions where the axons were protected due to overexpression of Bcl-xl or cytNmnat1. Significantly different (*p < 0.001, Student's t test) from neurons grown in the presence of NGF.