Effect of neurotropic factors on survival of transplanted embryonic inner ear tissues

This paper addresses cochlear transplantation and presents a study on the effect of brain derived neurotrophic factor (BDNF) and Neurotrophin-3 (NT-3) on the survival of transplanted embryonic inner ear tissues.

Injection of adult mouse mesenchymal stem cells into the developing chick inner ear

This series of experiments attempted to characterize the abilities of stem cells derived from bone marrow and adipose tissue to integrate into the sensory epithelium of the inner ear and to differentiate into hair cells or neural cell types.

Extraintestinal Crohn's disease mimicking autoimmune inner ear disease: a histopathological approach

Patients with autoimmune inner ear disease develop rapidly progressive sensorineural hearing loss over a period of several weeks or months, often accompanied by vestibular loss. This disease can occur as a distinct clinical entity or in association with an underlying autoimmune disorder. Treatment comprises immunosuppression by corticosteroids, cytostatic drugs or tumor necrosis factor- antagonists. We report histopathological and immunohistochemical findings of the inner ear of a patient with a granulomatous inner ear disease suffering from Crohn's disease that was nonresponsive to treatment and who underwent surgery for bilateral cochlear implants.

Differential distribution of stem cells in the auditory and vestibular organs of the inner ear

The adult mammalian cochlea lacks regenerative capacity, which is the main reason for the permanence of hearing loss. Vestibular organs, in contrast, replace a small number of lost hair cells. The reason for this difference is unknown. In this work we show isolation of sphere-forming stem cells from the early postnatal organ of Corti, vestibular sensory epithelia, the spiral ganglion, and the stria vascularis. Organ of Corti and vestibular sensory epithelial stem cells give rise to cells that express multiple hair cell markers and express functional ion channels reminiscent of nascent hair cells. Spiral ganglion stem cells display features of neural stem cells and can give rise to neurons and glial cell types. We found that the ability for sphere formation in the mouse cochlea decreases about 100-fold during the second and third postnatal weeks; this decrease is substantially faster than the reduction of stem cells in vestibular organs, which maintain their stem cell population also at older ages. Coincidentally, the relative expression of developmental and progenitor cell markers in the cochlea decreases during the first 3 postnatal weeks, which is in sharp contrast to the vestibular system, where expression of progenitor cell markers remains constant or even increases during this period. Our findings indicate that the lack of regenerative capacity in the adult mammalian cochlea is either a result of an early postnatal loss of stem cells or diminishment of stem cell features of maturing cochlear cells.

[Stem-cell-based approaches for treating inner ear diseases]

The capacity of stem cells to regenerate lost tissue cells has gained recognition among physicians. Despite the successful use of blood stem cells for treating blood cancers, other stem cell types have not yet been widely introduced into clinical practice. Therapy options involving stem cells for inner ear diseases consequently have not been implemented. Nonetheless, several reports have recently been published describing the generation of morphologically and immunologically distinctive inner ear cell types-such as hair cells, supporting cells, and spiral ganglion neurons-from stem cells. Although promising, all of these studies still lack functional results regarding hearing restoration or vestibular function.

Isolation of sphere-forming stem cells from the mouse inner ear

The mammalian inner ear has very limited ability to regenerate lost sensory hair cells. This deficiency becomes apparent when hair cell loss leads to hearing loss as a result of either ototoxic insult or the aging process. Coincidently, with this inability to regenerate lost hair cells, the adult cochlea does not appear to harbor cells with a proliferative capacity that could serve as progenitor cells for lost cells. In contrast, adult mammalian vestibular sensory epithelia display a limited ability for hair cell regeneration, and sphere-forming cells with stem cell features can be isolated from the adult murine vestibular system. The neonatal inner ear, however, does harbor sphere-forming stem cells residing in cochlear and vestibular tissues. Here, we provide protocols to isolate sphere-forming stem cells from neonatal vestibular and cochlear sensory epithelia as well as from the spiral ganglion. We further describe procedures for sphere propagation, cell differentiation, and characterization of inner ear cell types derived from spheres. Sphere-forming stem cells from the mouse inner ear are an important tool for the development of cellular replacement strategies of damaged inner ears and are a bona fide progenitor cell source for transplantation studies.

Creatine supports propagation and promotes neuronal differentiation of inner ear progenitor cells

Long-term propagation of inner ear-derived progenitor/stem cells beyond the third generation and differentiation into inner ear cell types has been shown to be feasible, but challenging. We investigated whether the known neuroprotective guanidine compound creatine (Cr) promotes propagation of inner ear progenitor/stem cells as mitogen-expanded neurosphere cultures judged from the formation of spheres over passages. In addition, we studied whether Cr alone or in combination with brain-derived neurotrophic factor (BDNF) promotes neuronal differentiation of inner ear progenitors. For this purpose, early postnatal rat spiral ganglia, utricle, and organ of Corti-derived progenitors were grown as floating spheres in the absence (controls) or presence of Cr (5 mM) from passage 3 onward. Similarly, dissociated sphere-derived cultures were differentiated for 14 days in the presence or absence of Cr (5 mM) and spiral ganglia sphere-derived cultures in a combination of Cr with the neurotrophin BDNF (50 ng/ml). We found that the cumulative total number of spheres over all passages was significantly higher after Cr supplementation as compared with controls in all the three inner ear cultures. In contrast, sphere sizes were not affected by the administration of Cr. Administration of Cr during differentiation of spiral ganglia cells resulted in a significantly higher density of β-III-tubulin-positive cells compared with controls, whereas densities of myosin VIIa-positive cells in cultures of utricle and organ of Corti were not affected by the treatment. Importantly, a combination of Cr with the neurotrophin BDNF resulted in further significantly increased densities of β-III-tubulin-positive cells in cultures of spiral ganglia cells as compared with single treatments. In sum, Cr promoted continuing propagation of rat inner ear-derived progenitor cells and supported specifically in combination with BDNF the differentiation of neuronal cell types from spiral ganglion-derived spheres.

NOX3-Targeted Therapies for Inner Ear Pathologies

Inner ear pathologies are associated with major morbidity and loss of life quality in affected patients. In many of these conditions, production of reactive oxygen-species (ROS) is thought to be a key pathological mechanism. While the sources of ROS are complex (including for example mitochondria), there is increasing evidence that activation of NOX enzymes, in particular NOX3, plays a key role. NOX3 is a multi-subunit NADPH oxidase, functionally and structurally closely related to NOX1 and NOX2. In both the vestibular and the cochlear compartments of the inner ear, high levels of NOX3 mRNA are expressed. In NOX3 mutant mice, the vestibular function is perturbed due to a lack of otoconia, while only minor alterations of hearing have been documented. However, there is increasing evidence that activation of NOX3 through drugs, noise and probably also aging, leads to hearing loss. Thus, NOX3 is an interesting target to treat and prevent inner ear pathologies and a few first animal models based on drug - or molecular therapy have been reported. So far however, there are no specific NOX3 inhibitors with a documented penetration into the inner ear. Nevertheless, certain antioxidants and non-specific NOX inhibitors diminish hearing loss in animal models. Development of small molecules inhibitors or molecular strategies against NOX3 could improve specificity and efficiency of redox-targeted treatments. In this review, we will discuss arguments for the involvement of NOX3 in inner ear pathologies and therapeutic approaches to target NOX3 activity.