Wnt1from Cochlear Schwann Cells Enhances Neuronal Differentiation Of Transplanted Neural Stem Cells (NSCs) In A Rat Spiral Ganglion Neuron (SGN) Degeneration Model

1ObjectiveWhile neural stem cell (NSC) transplantation is widely expected to become atherapy for nervous system degenerative diseases and injuries, the low neuronaldifferentiation of NSCs which were transplanted into the inner ear is a majorobstacle for the successful treatment of spiral ganglion neuron (SGN)degeneration. In this study, we validated whether the local microenvironmentinfluences the neuronal differentiation of transplanted NSCs in the inner ear.2MethodsOuabain was locally administered to the round window niche to establish theSGN degeneration animal model. NSCs were isolated, cultured and transplantedinto the scala tympani of control or SGN-degenerative cochleae.Immunofluorescence staining and real-time RT-PCR were used to identify theeffect of the inner ear local microenvironment on the neuronal differentiation oftransplanted NSCs. Lentiviral vector infection and transwell co-culture systemwas used in vitro. 3ResultsUsing a rat SGN degeneration model, we demonstrated that transplantedNSCs were more likely to differentiate into MAP2+neurons in SGN-degenerative cochleae than in control cochleae. Using real-time quantitativePCR and an immunofluorescence assay, we also proved that the expression ofWnt1(a ligand of Wnt signaling) increases significantly in Schwann cells in theSGN-degenerative cochlea. We further verified that NSC cultures expressreceptors and signaling components for Wnts. Based on these expressionpatterns, we hypothesized that Schwann cell-derived Wnt1and Wnt signalingmight be involved in the regulation of the neuronal differentiation oftransplanted NSCs. We verified our hypothesis in vitro using a co-culture system.We transduced a lentiviral vector expressing Wnt1into cochlear Schwann cellcultures and co-cultured them with NSC cultures. Co-culture with Wnt1-expressing Schwann cells resulted in a significant increase in the percentage ofNSCs that differentiated into MAP2+neurons, whereas this differentiationenhancing effect was prevented by Dkk1(an inhibitor of the Wnt signalingpathway).4ConclusionThese results suggested that Wnt1derived from cochlear Schwann cellsenhanced the neuronal differentiation of transplanted NSCs through Wntsignaling pathway activation. Alterations of the microenvironment deservedetailed investigation because they may help us to conceive effective strategiesto overcome the barrier of the low differentiation rate of transplanted NSCs.