Direct Reprogramming of Spiral Ganglion Non-neuronal Cells into Neurons: Toward Ameliorating Sensorineural Hearing Loss by Gene Therapy

Abstract

Primary auditory neurons (PANs) play a critical role in hearing by transmitting sound information from the inner ear to the brain. Their progressive degeneration is associated with excessive noise, disease and aging. The loss of PANs leads to permanent hearing impairment since they are incapable of regenerating. Spiral ganglion non-neuronal cells (SGNNCs), comprised mainly of glia, are resident within the modiolus and continue to survive after PAN loss. These attributes make SGNNCs an excellent target for replacing damaged PANs through cellular reprogramming. We used the neurogenic pioneer transcription factor Ascl1 and the auditory neuron differentiation factor NeuroD1 to reprogram SGNNCs into induced neurons (iNs). The overexpression of both Ascl1 and NeuroD1 in vitro generated iNs at high efficiency. Transcriptome analyses revealed that iNs displayed a transcriptome profile resembling that of endogenous PANs, including expression of several key markers of neuronal identity: Tubb3, Map2, Prph, Snap25, and Prox1. Pathway analyses indicated that essential pathways in neuronal growth and maturation were activated in cells upon neuronal induction. Furthermore, iNs extended projections toward cochlear hair cells and cochlear nucleus neurons when cultured with each respective tissue. Taken together, our study demonstrates that PAN-like neurons can be generated from endogenous SGNNCs. This work suggests that gene therapy can be a viable strategy to treat sensorineural hearing loss caused by degeneration of PANs.

In vivo ectopic Ngn1 and Neurod1 convert neonatal cochlear glial cells into spiral ganglion neurons

“…Previous studies showed that cochlear glia cells were plastic and could be converted into SGNs in vitro. 15 Our current study further demonstrated plasticity of neonatal glial cells in vivo. Our data supported that neonatal glial cells distributed in middle and apical cochlear turns were more plastic than those in basal turn (data not shown).…”

“…Neurog1 (also known as Ngn1 ) and Neurod1 are b‐HLH transcription factors that are necessary for SGN development . In addition, Neurod1 is known to reprogram chromatin, induce neuronal gene expression, and is sufficient to successfully reprogram in vitro cochlear glial cells into SGNs which express neuronal markers, Tuj1, Map2, and Prox1 . We set out to induce ectopic Ngn1 and Neurod1 expression in neonatal cochlear glial cells in vivo via the Cre/Loxp‐mediated genetic approach …”

“…26,27 In addition, Neurod1 is known to reprogram chromatin, induce neuronal gene expression, and is sufficient to successfully reprogram in vitro cochlear glial cells into SGNs which express neuronal markers, Tuj1, Map2, and Prox1. 15,28 We set out to induce ectopic Ngn1 and Neurod1 expression in neonatal cochlear glial cells in vivo via the Cre/ Loxp-mediated genetic approach. 29 We firstly constructed a new Cre-mediated conditional knock-in mouse strain, Rosa26-CAG-Loxp-stop-Loxp-Neurog1*3xHA-P2A-Neurod1*3xFlag-T2A-EGFP, which for short we called Rosa26-LSL-Ngn1-Neurod1 ( Figure 1A-C).…”

“…A similar approach has been successful in regenerating neurons from glial cells in the mouse cortex . Recently, isolated cochlear glial cells were converted in vitro into SGNs via the induction of Ascl1 and/or Neurod1 . Nonetheless, it remains unknown whether this is possible in vivo.…”

Identification of Methylated Gene Biomarkers in Patients with Alzheimer’s Disease Based on Machine Learning

“…CORO2B, a central nervous system gene, is involved in brain cellular cytoskeleton rearrangement and motility and molecular trafficking [34,35]. The up-regulated expression of CORO2B has been detected in induced neurons [36]. It is pointed out that CORO2B is associated with the neurological disease such as neuroblastoma [37].…”