Axonal transport of Frizzled5 by Alcadein -containing vesicles is associated with kinesin-1

Alcadein alpha (Alc alpha) and amyloid-beta protein precursor (APP) are cargo receptors that associate vesicles with kinesin-1. These vesicles, which contain either Alc alpha or APP, transport various proteins/cargo molecules into axon nerve terminals. Here, we analyzed immune-iso-lated Alc alpha- and APP-containing vesicles of adult mouse brains with LC-MS/MS and identified proteins present in vesicles that contained either Alc alpha or APP. Among these proteins, Friz-zled-5 (Fzd5), a Wnt receptor, was detected mainly in Alc alpha vesicles. Although colocalization ratios of Fzd5 with Alc alpha are low in the neurites of differentiating neurons by a low expression of Fzd5 in embryonic brains, the suppression of Alc alpha expression decreased the localization of Fzd5 in neurites of primary cultured neurons. Furthermore, Fzd5-EGFP expressed in primary cultured neurons was preferentially transported in axons with the transport velocities of Alc alpha vesicles. In synaptosomal fractions of adult-mice brains that express higher levels of Fzd5, the amount of Fzd5 and the phosphorylation level of calcium/calmodulin-dependent protein ki-nase-II were reduced in the Alc alpha-deficient mice. These results suggest that reduced transport of Fzd5 by Alc alpha-containing vesicles associated with kinesin-1 in axon terminals may impair the response to Wnt ligands in the noncanonical Ca2+-dependent signal transduction pathway at nerve terminals of mature neurons.