Expression of epidermal growth factor, epidermal growth factor receptor and transforming growth factor-alpha in the human fetal inner ear

EGF Mediates Survival of Rat Cochlear Sensory Cells via an NF-κB Dependent Mechanism In Vitro

The survival of cochlear epithelial cells is of considerable importance, biologically. However, little is known about the growth factor(s) that are involved in the survival of cochlear sensory epithelial cells. In this study, we demonstrated that epidermal growth factor (EGF) plays a role in the survival of cochlear epithelial cells. Firstly, the presence of the EGF signaling pathway was demonstrated in the developing cochlear tissues of rats and a sensory epithelial cell line (OC1): -- epidermal growth factor receptor (EGFR), mitogen-activated protein kinase kinase (MAPKK), I kappa B alpha (IκBα), nuclear factor kappa B (NF-κB), and B cell lymphoma 2 (Bcl-2). Secondly, the addition of EGF to OC1 increased the promoter activity of NF-κB and cell viability but not cell cycle progression and cell number increase -- which suggests that EGF is for cellular survival rather than cell proliferation of OC1. Finally, pyrrolidine dithiocarbamate (PDTC, an inhibitor of NF-κB) and inhibitor kappa B alpha (IκBα) mutant (IκBαM, a specific inhibitor of NF-κB) abrogated the EGF-induced NF-κB activity and cell survival. These data suggest that EGF plays a role in the survival of cochlear sensory epithelial cells through the EGFR/MAPKK/IκBα/NF-κB/Bcl-2 pathway.

Stem cell therapy for hearing loss: Math1 overexpression in VOT-E36 cells

HYPOTHESIS

VOT-E36 cells acquire mechanosensitivity after mammalian atonal homolog 1 (Math1) overexpression.

BACKGROUND

VOT-E36 cells are derived from a population of epithelial cells in the ventral region of the otocyst at embryonic Day 10.5, before hair cell differentiation. These cells express a number of specific molecular markers for hair cells under both proliferation and differentiation states. Overexpression of Math1 can convert nonsensory epithelial cells into hair cells in the cochlea. Based on this information, we tested whether VOT-E36 cells can be converted into hair cells by Math1 overexpression.

METHODS

Using reverse transcriptase-polymerase chain reaction-based analysis, we first compared the expression patterns of various molecular markers for hair cell development in VOT-E36 cells between proliferation and differentiation states, and also before and after overexpression of Math1. Subsequently, with a standard calcium imaging method, we examined whether VOT-E36 cells overexpressing Math1 could detect mechanical vibrations and activate spiral ganglion neurons in a coculture model. In addition, using confocal and scanning electron microscopes, we examined morphologic changes of VOT-E36 cells after Math1 overexpression.

RESULTS

Consistent with previous reports, this study has shown that VOT-E36 cells express a number of specific molecular markers for hair cells in both proliferation and differentiation states. Under appropriate culture conditions, Math1 is transiently expressed in this cell line during conditional differentiation. In VOT-E36 cells overexpressing Math1, the normal expression pattern of certain molecular markers for mature hair cells is partially restored. Interestingly, after coculture with spiral ganglion neurons, VOT-E36 cells overexpressing Math1 are able to respond to mechanical vibrations and activate spiral ganglion neurons. Possible molecular mechanisms underlying this novel finding have been explored.

CONCLUSION

Math1 overexpression can partially restore presumably downstream signaling cascades for normal hair cell differentiation in VOT-E36 cells, which are able to detect mechanical vibrations after being cocultured with spiral ganglion neurons.

Expression of heregulin and ErbB/Her receptors in adult chinchilla cochlear and vestibular sensory epithelium

Immunolabeling of heregulin, a growth factor that enhances cell proliferation in damaged utricles, and one of its binding receptors, ErbB-2, has been briefly described in the P3 rat cochlea and utricle [Zheng et al. (1999) J. Neurocytol. 28, 901-912]. However, little is known about the distribution of heregulin and its three binding receptors in adult animals. Here we describe the immunolabeling patterns for heregulin, ErbB-2, ErbB-3 and ErB-4 in the cochlea, spiral ganglion, utricle and saccule of the adult chinchilla using confocal microscopy. Heregulin immunolabeling was intense along the apical pole of Deiters cells and Hensen cells and along the membrane of supporting cells of the utricle and saccule; light immunolabeling was present in the outer layer of the spiral prominence and cytoplasm of spiral ganglion neurons. In the cochlea, intense to moderate ErbB-2 immunolabeling was evident in the cytoplasm of pillar cells, outer hair cells (OHCs), border cells, stria vascularis and spiral ligament; moderate ErbB-2 immunolabeling was present in the cytoplasm of the hair cell and supporting cell layers of the utricle and saccule. In the cochlea, light ErbB-3 immunolabeling was present in the inner hair cells, OHCs, marginal and intermediate cell layers of the stria vascularis and spiral ganglion neurons; moderate ErbB-3 immunolabeling was present in the cytoplasm of hair cells and supporting cells of the utricle and saccule. In the cochlea, utricle and saccule, ErbB-4 immunolabeling was intense in the nuclei and light to moderate in the cytoplasm and membrane of sensory cells and supporting cells. These results suggest that heregulin acting through ErbB receptors and various receptor complexes may play an important role in cell proliferation and survival in the cochlea and vestibular system.