Immunohistochemical characterization of clathrin assembly protein AP180 and synaptophysin in human brain

Neurons rely on clathrin-mediated endocytosis for retrieving synaptic vesicles (SVs) at the presynaptic compartment after the release of neurotransmitters. The clathrin assembly protein AP180 is shown to be a regulator for this clathrin-dependent SV recycling pathway. AP180 is efficient in facilitating the formation of clathrin-coated vesicles and regulating their size, but its exact location in synapse is not clear. In this study, we compared the expression of AP180 with synaptophysin in the aged human brain using confocal immunofluorescence microscopy. Synaptophysin is well characterized for its association with SVs and therefore a commonly used presynaptic marker. We achieved satisfactory immunofluorescent labeling by using an autofluorescence blocker Sudan Black B and more photostable Alexa Fluor dyes. Although we found that AP180 had an overall expression similar to synaptophysin, the immunoreactivity for the two proteins did not always co-localize.