Brain-targeting liposome-based APOE2 gene delivery exacerbates soluble amyloid-ß accumulation in AppNL-G-F mice

Alzheimer's disease (AD) is the most common cause of late-life dementia characterized by progressive neurodegeneration and brain deposition of amyloid-ß (Aß) and phosphorylated tau. The APOE e2 encoding apolipoprotein E (APOE2) is a protective allele against AD among the three genotypes (APOE e2, e3, e4), while APOE4 is the strongest genetic factor substantially increasing AD risk. APOE regulates brain lipid homeostasis and maintaining synaptic plasticity and neuronal function, where APOE2 has a superior function compared to APOE3 and APOE4. Gene therapy that increases APOE2 levels in the brain is, therefore, a promising therapeutic strategy for AD treatment. We previously reported that PEGylated liposomes conjugated with transferrin and a cell-penetrating peptide Penetratin sufficiently deliver chitosan-APOE2 cDNA plasmid complex into the brain of wild-type mice. Here, we investigated how brain-targeting liposome-based APOE2 gene delivery influences Aß)-related pathologies in amyloid model AppNL-G-F knockin mice at 12-month-old. We found a trend of reductions of insoluble Aß levels in the mouse cortices 1 month after APOE2 gene therapy. Furthermore, in the AppNL-G-F knockin mice that received the APOE2 gene therapy, brain transcriptome analysis through RNA-sequencing identified the upregulation of genes/pathways related to neuronal development. This was supported by increases of Dlg4 and Syp mRNAs coding synaptic proteins in the experimental group. On the other hand, we found that APOE2 gene delivery increased soluble Aß levels, including oligomers, as well as exacerbated neurite dystrophy and decreased synaptophysin. Together, our results suggest that brain-targeting liposome-based APOE2 gene therapy is potentially beneficial for synaptic formation at the transcriptional level. Forced APOE2 expressions, however, may exacerbate Aß toxicity by increasing the dissociation of Aß oligomers from aggregates in the presence of considerable amyloid burden. Overall design: We performed bulk RNA sequencing of amyloid model AppNL-G-F knockin mice and investigated changes in gene expression and pathway alternations.