Abstract
BACKGROUND: The global aging population is increasingly inflicted with Alzheimer's disease (AD), but a cure is still unavailable. Neurotrophic factor-α1/carboxypeptidase E (NF-α1/CPE) gene therapy has been shown to prevent and reverse memory loss and pathology in AD mouse models. However, the mechanisms of action of NF-α1/CPE are not fully understood. We investigated if a non-enzymatic form of NF-α1/CPE-E342Q is efficient in reversing AD pathology and carried out a proteomic study to uncover the mechanisms of action of NF-α1/CPE in AD mice. METHODS: AAV-human NF-α1/CPE or a non-enzymatic form, NF-α1/CPE-E342Q, was delivered into the hippocampus of 3 × Tg-AD male mice. The effects on cognitive function, neurodegeneration, synaptogenesis and autophagy were investigated. A quantitative proteomic analysis of the hippocampus was carried out. RESULTS: Hippocampal delivery of AAV-NF-α1/CPE-E342Q prevented memory loss, neurodegeneration and microglial activation in 3 × Tg-AD mice, indicating that the action is independent of its enzymatic activity. Quantitative proteomic analysis of the hippocampus of 3 × Tg-AD mice revealed differential expression of > 2000 proteins involving many metabolic pathways after NF-α1/CPE gene therapy. Of these, two new proteins, Snx4 and Trim28, which increase Aβ production and tau levels, respectively, were down-regulated by NF-α1/CPE. Western blot analysis verified their reduction in AAV-NF-α1/CPE-treated 3 × Tg-AD mice compared to untreated mice. Our proteomic analysis indicated synaptic organization as the top signaling pathway altered in response to CPE expression. Synaptic markers PSD95 and Synapsin1 were decreased in 3 × Tg-AD mice and were restored with AAV-NF-α1/CPE treatment. Proteomic analysis hypothesized involvement of autophagic signaling pathway. Indeed, multiple protein markers of autophagy were down-regulated in 3 × Tg-AD mice, accounting for impaired autophagy. NF-α1/CPE gene therapy upregulated the levels of these proteins in 3 × Tg-AD mice, thereby reversing autophagic impairment. CONCLUSIONS: This study uncovered vast actions of NF-α1/CPE in restoring expression of networks of critical proteins including those necessary for maintaining neuronal survival, synaptogenesis and autophagy, while down-regulating many proteins that promote tau and Aβ accumulation to reverse memory loss and AD pathology in 3 × Tg-AD mice. AAV-NF-α1/CPE gene therapy uniquely targets many metabolic levels, offering a promising holistic approach for AD treatment (Graphical Abstract).