Apolipoprotein E mRNA is transported to dendrites and may have a role in synaptic structural plasticity

Although the dendritic localization and translation of a subset of mRNAs plays a pivotal role in synaptic plasticity, the dendritic mRNAs and their functions have been only minimally characterized thus far. In this study, we isolated mRNAs from Staufen2-containing ribonucleoprotein complexes, which function as modules for the transport of mRNA to the dendrites, and then constructed a cDNA library. Apolipoprotein E gene (APOE) mRNA was isolated from the dendritic mRNA-specific cDNA library. The specific localization of APOE mRNA was evaluated via in situ hybridization. The specific regions involved in the dendritic transport of APOE mRNA were determined using a visualization system employing green fluorescent protein-tagged bacteriophage MS2 RNA-binding protein. As a result, the proximal N-terminal or C-terminal regions of the ApoE-coding sequences were determined to be sufficient for dendritic transport. The level of dendritic APOE mRNA was significantly increased by depolarization-induced neuronal activity, but was reduced in the cell body regions. We assessed the functions of neuronal ApoE. The reduction of ganglioside GM1 by cholesterol depletion was completely blocked by ApoE over-expression. In addition, ApoE over-expression increased the immunoreactivity of the post-synaptic density 95 kDa antibody in the dendrites. These findings indicate that neuronal ApoE may be relevant to lipid rafts or synaptic structural plasticity.