Transplantation of directly converted HDF-iNSC to the scala tympani of the cochlea increases neural structure and central auditory connection in an auditory neuropathy animal model

Cochlear implants (CIs) provide effective rehabilitation for severe-to-profound hearing loss, yet their success is limited by secondary degeneration of auditory neurons. Direct transdifferentiation, which enables lineage conversion of somatic cells into neural stem cells without a pluripotent stage, offers advantages over induced pluripotent stem cells by reducing tumorigenic risk, shortening reprogramming time, and producing expandable, patient-specific cells for autologous therapy. Oct4 is a critical factor for establishing pluripotency, but it is not required for direct reprogramming. Inclusion of Oct4 can enhance reprogramming efficiency and induce a more ‘plastic’ cellular state, which may facilitate improved integration and functional adaptation following transplantation into the target organ. Induced neural stem cells (iNSCs) were generated from human dermal fibroblasts. We generated iNSCs by transducing the exogenous Oct4 protein in combination with Sox2, Klf4, and c-Myc. The properties of these iNSCs were characterized, and their therapeutic potential was evaluated following transplantation in an animal model of auditory neuropathy. Histologic and functional assessment were performed. Immunostaining and flow cytometry results showed that human iNSCs express Nestin, Sox2, and Pax6. Constitutive expression of SKM and transient Oct4 priming induced iNSCs from HDFs under NSC-permissive culture conditions. Isolated iNSCs had similar morphological features and expression markers as control human NSCs. Transplanted human iNSCs improved cochlear cellular integrity, particularly by enhancing neural structures including neurons and nerve fibers. Although peripheral synaptic connections were not restored, synaptic marker toward the central auditory pathway was significantly increased. eABR responses showed statistically higher response in iNSC transplanted animals. Direct transdifferentiation provides an efficient strategy to generate autologous iNSCs capable of preserving and repairing auditory neural structures. By improving neural health, this approach has the potential to enhance CI performance, expand candidacy to patients with long-term hearing loss, and establish a novel regenerative avenue for functional hearing restoration.