Antibodies to the C-terminus of the beta-amyloid precursor protein (APP): a site specific marker for the detection of traumatic axonal injury.

Antibodies to the amyloid precursor protein (APP) are commonly used to detect traumatic axonal injury (TAI). Carried by fast anterograde axoplasmic transport, APP will pool at regions of impaired transport associated with TAI. Based primarily upon commercial antibody availability, previous studies have targeted the N-terminus of APP, which, with respect to antigen detection, is suboptimally located within anterogradely transported vesicles. Recently, antibodies to the APP C-terminus, located on the external surface of anterogradely transported vesicles, have become available, allowing for the exploration of their utility in detecting TAI. To this end, rats were subjected to an impact acceleration injury, surviving 30 min to 24 h post-injury. They were then perfused, their brains sectioned and prepared for dual label immunofluorescent microscopy, single label bright field microscopy, and electron microscopy (EM). Antibodies to the APP C-terminus yielded the ready detection of intensely labeled TAI with significantly reduced diffuse background staining in comparison to antibodies to the APP N-terminus in both dual label immunofluorescent and single label bright-field approaches. EM examination of antibodies to the APP C-terminus in TAI revealed intense labeling of pooled intra-axonal vesicular profiles, confirming the anterogradely transported vesicular source of the APP seen in TAI. Interestingly, in addition to providing a technically superior approach and new detailed information on the subcellular localization of APP, antibodies to the APP C-terminus also proved more cost effective. Immunofluorescent studies of APP C-terminus immunoreactivity involved 1/3 the cost of targeting the N-terminus, while bright field APP C-terminus studies were performed for 1/20 the cost.