Clonal colony formation from spiral ganglion stem cells

Cochlear Sox2+ Glial Cells Are Potent Progenitors for Spiral Ganglion Neuron Reprogramming Induced by Small Molecules

In the mammalian cochlea, spiral ganglion neurons (SGNs) relay the acoustic information to the central auditory circuits. Degeneration of SGNs is a major cause of sensorineural hearing loss and severely affects the effectiveness of cochlear implant therapy. Cochlear glial cells are able to form spheres and differentiate into neurons in vitro. However, the identity of these progenitor cells is elusive, and it is unclear how to differentiate these cells toward functional SGNs. In this study, we found that Sox2⁺ subpopulation of cochlear glial cells preserves high potency of neuronal differentiation. Interestingly, Sox2 expression was downregulated during neuronal differentiation and Sox2 overexpression paradoxically inhibited neuronal differentiation. Our data suggest that Sox2⁺ glial cells are potent SGN progenitor cells, a phenotype independent of Sox2 expression. Furthermore, we identified a combination of small molecules that not only promoted neuronal differentiation of Sox2^– glial cells, but also removed glial cell identity and promoted the maturation of the induced neurons (iNs) toward SGN fate. In summary, we identified Sox2⁺ glial subpopulation with high neuronal potency and small molecules inducing neuronal differentiation toward SGNs.

The biological strategies for hearing re-establishment based on the stem/progenitor cells

The cochlea is the essential organ for hearing and includes both auditory sensory hair cells and spiral ganglion neurons. The discovery of inner ear stem cell brings hope to the regeneration of hair cell and spiral ganglion neuron as well as the followed hearing re-establishment. Thus the investigation on characteristics of inner ear stem/progenitor cells and related regulating clue is important to make such regeneration a reality. In addition, attempts have also been made to transplant exogenous stem cells into the inner ear to restore hearing function. In this review, we describe recent advances in the characterization of mammalian inner ear progenitor/stem cells and the mechanisms of regulating their proliferation and differentiation, and summarize studies that have used exogenous stem cells to repair damaged hair cells and neurons in the inner ear.

[Strategies for a regenerative therapy of hearing loss. German version]

Despite impressive technical progress in the field of conventional hearing aids and implantable hearing systems, the hopes for the treatment of inner ear diseases such as hearing loss and tinnitus have become increasingly directed toward regenerative therapeutic approaches. This review discusses the currently most promising strategies for hair cell regeneration in the inner ear to treat hearing loss, including stem cell-based, gene transfer-based, and pharmacological interventions. Furthermore, previous milestones and ground-breaking work in this scientific field are identified. After many years of basic research, the first clinical trials with a regenerative therapeutic approach for hearing-impaired patients were recently initiated. Although there is still a long and bumpy road ahead until a true breakthrough is achieved, it seems more realistic than ever that regenerative therapies for the inner ear will find their way into clinical practice.

The Presence of Neural Stem Cells and Changes in Stem Cell-Like Activity With Age in Mouse Spiral Ganglion Cells In Vivo and In Vitro

Objectives

Spiral ganglion neurons (SGNs) include potential endogenous progenitor populations for the regeneration of the peripheral auditory system. However, whether these populations are present in adult mice is largely unknown. We examined the presence and characteristics of SGN-neural stem cells (NSCs) in mice as a function of age.

Methods

The expression of Nestin and Ki67 was examined in sequentially dissected cochlear modiolar tissues from mice of different ages (from postnatal day to 24 weeks) and the sphere-forming populations from the SGNs were isolated and differentiated into different cell types.

Results

There were significant decreases in Nestin and Ki67 double-positive mitotic progenitor cells in vivo with increasing mouse age. The SGNs formed spheres exhibiting self-renewing activity and multipotent capacity, which were seen in NSCs and were capable of differentiating into neuron and glial cell types. The SGN spheres derived from mice at an early age (postnatal day or 2 weeks) contained more mitotic stem cells than those from mice at a late age.

Conclusion.

Our findings showed the presence of self-renewing and proliferative subtypes of SGN-NSCs which might serve as a promising source for the regeneration of auditory neurons even in adult mice.