Strong immunoreactivity of beta-amyloid precursor protein, including the beta-amyloid protein sequence, at human neuromuscular junctions.

At the postsynaptic domain of the human neuromuscular junction (NMJ), we have demonstrated strong concentrations of the N-terminus 45-62, C-terminus 676-695 and beta-amyloid protein sequences of beta-amyloid precursor protein (beta APP). We used well-characterized monoclonal and polyclonal antibodies for co-localization with three other postsynaptic proteins, applying double and triple fluorescence labeling. Strong immunoreactivity of all three beta APP sequences was found at all NMJs identified by bound alpha-bungarotoxin (alpha BT), where they co-localized with alpha BT and with immunoreactive desmin and dystrophin, which are postsynaptic proteins of human NMJs. This appears to be the first demonstration of beta APP sequences concentrated postsynaptically at human NMJs. beta APP may have a role in normal junction biology and possibly in some diseases affecting NMJs.