Cochlear nucleus whole mount explants promote the differentiation of neuronal stem cells from the cochlear nucleus in co-culture experiments

Spontaneous Calcium Oscillations through Differentiation: A Calcium Imaging Analysis of Rat Cochlear Nucleus Neural Stem Cells

Causal therapies for the auditory-pathway and inner-ear diseases are still not yet available for clinical application. Regenerative medicine approaches are discussed and examined as possible therapy options. Neural stem cells could play a role in the regeneration of the auditory pathway. In recent years, neural stem and progenitor cells have been identified in the cochlear nucleus, the second nucleus of the auditory pathway. The current investigation aimed to analyze cell maturation concerning cellular calcium activity. Cochlear nuclei from PND9 CD rats were microscopically dissected and propagated as neurospheres in free-floating cultures in stem-cell medium (Neurobasal, B27, GlutaMAX, EGF, bFGF). After 30 days, the dissociation and plating of these cells took place under withdrawal of the growth factors and the addition of retinoic acid, which induces neural cell differentiation. Calcium imaging analysis with BAPTA-1/Oregon Green was carried out at different times during the differentiation phase. In addition, the influence of different voltage-dependent calcium channels was analyzed through the targeted application of inhibitors of the L-, N-, R- and T-type calcium channels. For this purpose, comparative examinations were performed on CN NSCs, and primary CN neurons. As the cells differentiated, a significant increase in spontaneous neuronal calcium activity was demonstrated. In the differentiation stage, specific frequencies of the spontaneous calcium oscillations were measured in different regions of the individual cells. Initially, the highest frequency of spontaneous calcium oscillations was ascertainable in the maturing somata. Over time, these were overtaken by calcium oscillations in the axons and dendrites. Additionally, in the area of the growth cones, an increasing activity was determined. By inhibiting voltage-dependent calcium channels, their expression and function in the differentiation process were confirmed. A comparable pattern of maturation of these channels was found in CN NSCs and primary CN neurons. The present results show that neural stem cells of the rat cochlear nucleus differentiated not only morphologically but also functionally. Spontaneous calcium activities are of great relevance in terms of neurogenesis and integration into existing neuronal structures. These functional aspects of neurogenesis within the auditory pathway could serve as future targets for the exogenous control of neuronal regeneration.

Different Neurogenic Potential in the Subnuclei of the Postnatal Rat Cochlear Nucleus

In patients suffering from hearing loss, the reduced or absent neural input induces morphological changes in the cochlear nucleus (CN). Neural stem cells have recently been identified in this first auditory relay. Afferent nerve signals and their impact on the immanent neural stem and progenitor cells already impinge upon the survival of early postnatal cells within the CN. This auditory brainstem nucleus consists of three different subnuclei: the anteroventral cochlear nucleus (AVCN), the posteroventral cochlear nucleus (PVCN), and the dorsal cochlear nucleus (DCN). Since these subdivisions differ ontogenetically and physiologically, the question arose whether regional differences exist in the neurogenic niche. CN from postnatal day nine Sprague-Dawley rats were microscopically dissected into their subnuclei and cultivated in vitro as free-floating cell cultures and as whole-mount organ cultures. In addition to cell quantifications, immunocytological and immunohistological studies of the propagated cells and organ preparations were performed. The PVCN part showed the highest mitotic potential, while the AVCN and DCN had comparable activity. Specific stem cell markers and the ability to differentiate into cells of the neural lineage were detected in all three compartments. The present study shows that in all subnuclei of rat CN, there is a postnatal neural stem cell niche, which, however, differs significantly in its potential. The results can be explained by the origin from different regions in the rhombic lip, the species, and the various analysis techniques applied. In conclusion, the presented results provide further insight into the neurogenic potential of the CN, which may prove beneficial for the development of new regenerative strategies for hearing loss.

Neuronal differentiation of dental pulp stem cells from human permanent and deciduous teeth following coculture with rat auditory brainstem slices

Sensorineural hearing loss is a common disability found worldwide which is associated with a degeneration of spiral ganglion neurons (SGN). It is a challenge to restore SGN due to the permanent degeneration and viability of SGN is requisite for patients to receive an advantage from hearing aid devices. Human dental pulp stem cells (DPSC) and stem cells from human exfoliated deciduous teeth (SHED) are self-renewing stem cells that originate from the neural crest during development. These stem cells have a high potential for neuronal differentiation. This is primarily due to their multilineage differentiation potential and their relative ease of access. Previously, we have shown the ability of these stem cell types to differentiate into spiral ganglion neuron-like cells. In this study, we induced the cells into neural precursor cells (NPC) and cocultured with auditory brainstem slice (ABS) encompassing cochlear nucleus by the Stoppini method. We also investigated their ability to differentiate after 2 weeks and 4 weeks in coculture. Neuronal differentiation of DPSC-NPC and SHED-NPC was higher expression of specific markers to SGN, TrkB, and Gata3, compared to monoculture. The cells also highly expressed synaptic vesicle protein (SV2A) and exhibited intracellular calcium oscillations. Our findings demonstrated the possibility of using DPSCs and SHEDs as an autologous stem cell-based therapy for sensorineural hearing loss patients.

Laminin-modified gellan gum hydrogels loaded with the nerve growth factor to enhance the proliferation and differentiation of neuronal stem cells

The reconstruction of peripheral nerves has lately received great attention as many patients suffer from peripheral nerve injury every year around the world. However, the damage to human nerve cells has different degrees of irreversibility due to a slow growth speed and low adhesion with the surrounding tissues. In an effort to overcome this challenge, we applied novel laminin (LN)-modified thiolated gellan gum (TGG) and loaded the nerve growth factor (NGF) as a tissue engineering scaffold for facilitating neuronal stem cell proliferation via a synergy effect for the ERK–MAPK pathway. TGG was characterized by ¹H NMR spectroscopy and scanning electron microscopy, and its rheological behavior was also studied. The NGF release curve fitted the Korsmeyer–Peppas model and belonged to a Fickian diffusion-controlled release mechanism. The neuronal stem cells from newborn SD rats could adhere tightly and proliferate at a relatively rapid speed, showing excellent biocompatibility and the ability to promote growth in the modified TGG. LN and NGF could decrease the apoptosis effects of neuronal stem cells, as shown via the flow cytometry results. In a three-dimensional culture environment, LN and NGF could facilitate neuronal stem cells to differentiate into neurons, as proved by immunofluorescence, q-PCR, and western blot analyses. Therefore, the rational design of the TGG gel loaded with NGF has promising applications in the reconstruction of peripheral nerves.

Laminin-modified thiolated gellan gum and loaded with the nerve growth factor in facilitateding neuronal stem cell proliferation and differentiation.

Isolation and Characterization of Neural Stem Cells from the Rat Inferior Colliculus

The inferior colliculus (IC) is a nucleus of the auditory pathway and its fourth relay station. It integrates afferent information from the superior olivary complex and the cochlear nucleus. To date, no causal therapeutic options are known for damaged neuronal structures in this area. Regenerative medicine offers a potential approach to causally treating hearing impairment. After neural stem cells had been identified in certain areas of the auditory pathway, the question arouses, whether the IC also has a neurogenic potential. Cells from the IC of postnatal day 6 rats were extracted and cultured as neurospheres. Cells in the neurospheres showed mitotic activity and positive stain of neural stem cell markers (Nestin, DCX, Atoh1, and Sox-2). In addition, single cells were differentiated into neuronal and glial cells shown by the markers β-III-tubulin, GFAP, and MBP. In summary, basic stem cell criteria could be detected and characterized in cells isolated from the IC of the rat. These findings will lead to a better understanding of the development of the auditory pathway and may also be relevant for identifying causal therapeutic approaches in the future.

Impact of siRNA targeting of β-catenin on differentiation of rat neural stem cells and gene expression of Ngn1 and BMP4 following in vitro hypoxic-ischemic brain damage

The aim of the present study was to investigate the possible damage-repair mechanisms of neural stem cells (NSCs) following hypoxic-ischemic brain damage (HIBD). NSCs obtained from Sprague Dawley rats were treated with tissue homogenate from normal or HIBD tissue, and β-catenin expression was silenced using siRNA. The differentiation of NSCs was observed by immunofluorescence, and semiquantitative reverse transcription-polymerase chain reaction and western blot analysis were applied to detect the mRNA and protein expression levels of Ngn1 and BMP4 in the NSCs. Compared with control NSCs, culture with brain tissue homogenate significantly increased the differentiation of NSCs into neurons and oligodendrocytes (P<0.05), whereas differentiation into astrocytes was significantly reduced (P<0.05). Compared with negative control-transfected cells, knockdown of β-catenin expression significantly decreased the differentiation of NSCs into neurons and oligodendrocytes (P<0.01), whereas the percentage of NSCs differentiated into astrocytes was significantly increased (P<0.01). Compared with control NSCs, the mRNA and protein expression levels of Ngn1 were significantly increased (P<0.01) and BMP4 levels were significantly reduced (P<0.01) by exposure of the cells to brain tissue homogenate. Compared with the negative control plasmid-transfected NSCs, the levels of Ngn1 mRNA and protein were significantly reduced by β-catenin siRNA (P<0.01), whereas BMP4 levels were significantly increased (P<0.01). In summary, the damaged brain tissues in HIBD may promote NSCs to differentiate into neurons for self-repair processes. β-Catenin, BMP4 and Ngn1 may be important for the coordination of NSC proliferation and differentiation following HIBD.