AAV-mediated transgene delivery targeting spiral ganglion nonsensory cells

In-situ neuronal reprogramming in the cochlea through gene therapy offers an avenue to restore hearing loss caused by neuronal damage. One possible source of neuronal conversion is the nonspiral ganglion cells (NSGCs), which include satellite cells, Schwann cells, and otic mesenchyme cells. A major obstacle for this approach is the vector-mediated transgene delivery toward NSGCs. Herein, we sought to assess the transduction profile of adeno-associated virus (AAV) serotypes with peripheral glial cell tropism in the murine inner ear. AAV-1, AAV-DJ, and AAV-PHP.eB with a cytomegalovirus promoter-driven enhanced green flourescent protein (eGFP) reporter were injected into CBA/CaJ neonatal mice via the posterior semicircular canal. One week postinjection, the cochlear tissue was collected for immunohistochemistry in whole-mount and mid-modiolar sections to assess the colocalization of eGFP within the NSGCs in the osseous spiral lamina and Rosenthal's canal. The contralateral ear served as an internal control. Auditory brain responses (ABRs) were recorded 30 days postinjection to assess for hearing loss. AAV-1 and AAV-DJ demonstrated 30-32% transduction efficacy of Pou3f4 immunopositive otic mesenchyme cells, whereas transduction efficacy of Sox2 or Sox10 positive Schwann cells and satellite cells was 0.8-1.82% for all serotypes. At 30 days postinjection, ABR thresholds in the injected mice were comparable to those of the noninjected control. We were able to transduce otic mesenchyme cells among SGNCs in the spiral ganglion region, whereas transduction of Schwann cells and satellite cells continues to pose challenges with AAV-1, AAV-DJ, and AAV-PHP.eB serotypes.