Effect of intravenously administered adeno-associated virus encoding TrkB gene on hippocampal neurogenesis

Hippocampal neurogenesis mediated by activation of tropomyosin receptor kinases B (TrkB) is thought to play important roles in repair of brain function injury caused by neurodegenerative disorders. Therefore, stimulation of TrkB-mediated neurogenesis would be a possible therapeutic target. In the present study, we examined effect of overexpression of TrkB gene in the brain on hippocampal neurogenesis and any behavior change invivo after systemic gene transduction with an aim to clarify possible treatment strategy. For such purpose blood-brain barrier permeable adeno-associated virus serotype PHP.eB (AAV-PHP.eB) was used to transduce TrkB gene in the brain. Flag-tagged mouse TrkB gene was first inserted to pAAV-CMV vector, followed by co-transfection with AAV-PHP. eB vector to construct the final AAV construct (AAV-PHP.eB-mTrkB-flag). Transfection with the transgene plasmid in neuroblastoma cell line Neuro2a increased expression of TrkB gene product, the phosphorylation of which was increased in the presence of a TrkB agonist 7,8-dihydroxyflavone, confirming activation of exogenously transfected TrkB. Intravenous administration of AAV-PHP.eB-mTrkB-flag not only increased expression of TrkB, but also tended to increase area of new-born neuron marker Dcx-positive cells in hippocampus compared to control AAV-treated mice, implying possible promotion of neurogenesis. Thus, AAV-mediated TrkB gene transduction would be the possible treatment of neurodegenerative disorders by performing further analyses of its pharmacological actions.