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Generation of Amyloidogenic C-terminal Fragments during Rapid Axonal Transport in Vivo of -Amyloid Precursor Protein in the Optic Nerve (*)

The amyloid β-protein (Aβ) is a major component of extracellular deposits that are characteristic features of Alzheimer's disease. Aβ is derived from the large transmembrane β-amyloid precursor protein (βAPP). In the rabbit optic nerve/optic tract (ON), βAPP is synthesized in vivo in retinal ganglion cell perikarya, rapidly transported into the ON axons in small transport vesicles and is subsequently transferred to the axonal plasma membrane as well as to the presynaptic nerve terminals (Morin, P. J., Abraham, C. R., Amaratunga, A., Johnson, R. J., Huber, G., Sandell, J. H., and Fine, R. E.(1993) J. Neurochem. 61, 464-473). Present results indicate that there is rapid processing of βAPP in the ON to generate a 14-kDa C-terminal membrane-associated fragment that contains the Aβ sequence. By using equilibrium sucrose density gradient fractionation, this fragment, as well as non-amyloidogenic C-terminal fragments and intact βAPP, are detected in at least two classes of transport vesicles destined for the plasma membrane and the presynaptic nerve terminal. The two classes of transported vesicles are distinguished by labeling kinetics as well as by density. In contrast to the ON, only non-amyloidogenic C-terminal fragments are generated in the retina, which contains the perikarya of retinal ganglion cells and glial (Muller) cells which also produce βAPP.