Survival of fetal rat otocyst cells grafted into the damaged inner ear

Hair cell loss induced by aging, ototoxic drugs and noise leads to irreversible hearing loss and balance disorders in mammals due to the failure of hair cells to regenerate. To investigate the possibility of transplantation therapy to repair damaged inner ear, we have examined whether grafted fetal otocyst cells could survive and migrate into injured sensory organs. We obtained otocyst cells from green fluorescein protein (GFP)-transgenic rats on embryonic day 12.5, then transplanted these cells into the inner ears of young rats previously exposed to intense sound. One month after transplantation, the grafted inner ear sensory organs were examined immunohistochemically. Grafted otocyst cells had survived and demonstrated special morphological features in the host organs; cells that migrated into the organ of Corti were similar to supporting cells. These results indicate that injured sensory organs express some kind of scaffolding that plays important roles in the survival and differentiation of the grafted otocyst cells.     

Inner ear hair cell regeneration in a mammal: Identification of a triggering factor

Recent observations have shown that mammals possess a limited capacity for regeneration of inner ear sensory epithelia. It is clear, however, that a mitogenic growth factor will be necessary to up-regulate this capacity before clinical application becomes feasible. This study used in vitro cultures of adult mouse vestibular organs for assessing the mitogenic effect of transforming growth factor alpha (TGF-α). Sixty-one utricles and cristae were maintained in culture for 7 to 8 days. Neomycin was used to damage the hair cells. Autoradiography permitted identification of any cell which had undergone mitosis during the culture period. The proliferative response was compared in organs exposed to TGF-alpha and those maintained in the basic culture medium only. The results demonstrated that TGF-alpha significantly increased cell proliferation in the sensory epithelia and also in the marginal zones surrounding them. This finding provides a scientific basis for the concept that inner ear hair cell damage in humans may someday be reversible pharmacologically.     

Immunohistochemical localization of nonerythroid spectrin (fodrin) in the sensory cells of the vestibular end organs of the rat and guinea pig

Indirect immunofluorescence method was used to study presence and localization of nonerythroid spectrin (fodrin) in the vestibular sensory epithelia. Cryosections of the vestibular organs were treated by monoclonal antibody (mAb) reacting with mammalian fodrin. Strong mAb labelling was observed in the cuticular plate of the vestibular hair cells. The stereocilia were nonreactive and supporting cells showed only a weak reaction. Fodrin seems to have similar localization in the inner ear hair cells as actin (except stereocilia) and it appears to be the major component of the membrane skeleton in the inner ear hair cells. Fodrin-associated membrane skeleton may be involved in the hair cell function in several different ways.     

Transplantation of neural stem cells into explants of rat inner ear

Damage and loss of hair cells in the inner ear is the most frequent cause of hearing loss and balance disorders. Mammalian hair cells do not regenerate in the conventional ways. To regenerate the hair cell in the mammalian inner ear we transplanted neural stem cells into explants of rat inner ear. The stem cells integrated successfully into the sensory epithelium of the vestibular organs, but not into the organ of Corti. This method is useful to investigate efficient ways to transplant stem cells into the inner ear.     

Gentamicin ototoxicity induced apoptosis of the vestibular hair cells of guinea pigs

To clarify mechanisms of inner ear cell death induced by aminoglycosides, we used an in situ nick-end labelling method to examine guinea pig vestibular epithelia after chronic systemic treatments with gentamicin to produce apoptosis. Such changes occurred in damaged hair cells, suggesting that this process may be crucial for subsequent repair and cell regeneration.     

Blockade of c-Jun N-terminal kinase pathway attenuates gentamicin-induced cochlear and vestibular hair cell death

The ototoxic action of aminoglycoside antibiotics leading to the loss of hair cells of the inner ear is well documented. However, the molecular mechanisms are poorly defined. We have previously shown that in neomycin-exposed organotypic cultures of the cochlea, the c-Jun N-terminal kinase (JNK) pathway--associated with stress, injury and apoptosis--is activated in hair cells and leads to their death. We have also shown that hair cell death can be attenuated by CEP-1347, an inhibitor of JNK signalling [Pirvola et al., J. Neurosci. 20 (2000) 43-50]. In the present study, we demonstrate that gentamicin-induced ototoxicity leads to JNK activation and apoptosis in the inner ear hair cells in vivo. We also show that systemic administration of CEP-1347 attenuates gentamicin-induced decrease of auditory sensitivity and cochlear hair cell damage. In addition, CEP-1347 treatment reduces the extent of hair cell loss in the ampullary cristae after gentamicin intoxication. Particularly, the inner hair cells of the cochlea and type I hair cells of the vestibular organs are protected. We have previously shown that also acoustic overstimulation leads to apoptosis of cochlear hair cells and that CEP-1347 can attenuate noise-induced sensory cell loss. These results suggest that activation of the JNK cascade may be a common molecular outcome of cellular stress in the inner ear sensory epithelia, and that attenuation of the lesion can be provided by inhibiting JNK activation.     

听觉损伤后毛细胞再生与聋病基因治疗策略

听觉损伤可引起耳蜗毛细胞和听觉神经元的不可逆性损伤,从而导致永久性的感音神经性耳聋。虽然内耳所独具的结构是基因治疗非常独特和重要的靶器官,但能否实现损伤后毛细胞的再生是其前提条件。国内外研究者们做了大量的探索并取得重要突破,从非哺乳动物到哺乳动物毛细胞再生,从前庭毛细胞到耳蜗毛细胞再生,从未成熟期到成年期毛细胞再生,从离体培养毛细胞再生到在体毛细胞再生,整整经历了近半个世纪。但是毛细胞的再生并不等同于听力完全恢复。针对内耳基因治疗时间窗问题,我们根据听觉损伤后不同的病理状态,提出听觉损伤后毛细胞再生和基因治疗的基本策略：（1）毛细胞纤毛损伤阶段,是基因治疗的最好时机,通过完全修复或纤毛再生达到功能的完全或部分恢复;（2）内耳毛细胞虽有损伤但没有坏死,支持细胞和神经纤维基本正常,所以有恢复形态和功能的机会,这个阶段导入Math1基因应该有效,是基因治疗的最关键时机;（3）毛细胞严重损伤但支持细胞尚存,是毛细胞再生的抢救阶段,而且还可以争取在Corti器细胞构架没有塌陷之前进行干细胞导入,所以这个阶段内细胞移植可能有效地实现听力恢复;（4）Corti器完全失去构架,仅仅残留上皮层或瘢痕化,基因导入完全无效,即使干细胞导入也会面临困难,如何重塑Corti器构架是巨大挑战。为了实现耳聋基因治疗临床应用的可能性。我们还探索了最有效简便的外源基因内耳导入方式以及高效安全可靠的基因载体比如纳米载体的研发。毛细胞再生研究已经取得突破性进展,但还面临诸多挑战。通过不懈的努力,聋病基因治疗的最终临床应用一定会实现。     

Pattern of hair cell loss and delayed peripheral neuron degeneration in inner ear by a high-dose intratympanic gentamicin

To gain insights into the ototoxic effects of aminoglycoside antibiotics (AmAn) and delayed peripheral ganglion neuron death in the inner ear, experimental animal models were widely used with several different approaches including AmAn systemic injections, combination treatment of AmAn and diuretics, or local application of AmAn. In these approaches, systemic AmAn treatment alone usually causes incomplete damage to hair cells in the inner ear. Co-administration of diuretic and AmAn can completely destroy the cochlear hair cells, but it is impossible to damage the vestibular system. Only the approach of AmAn local application can selectively eliminate most sensory hair cells in the inner ear. Therefore, AmAn local application is more suitable for studies for complete hair cell destructions in cochlear and vestibular system and the following delayed peripheral ganglion neuron death. In current studies, guinea pigs were unilaterally treated with a high concentration of gentamicin (GM, 40 mg/ml) through the tympanic membrane into the middle ear cavity. Auditory functions and vestibular functions were measured before and after GM treatment. The loss of hair cells and delayed degeneration of ganglion neurons in both cochlear and vestibular system were quantified 30 days or 60 days after treatment. The results showed that both auditory and vestibular functions were completely abolished after GM treatment. The sensory hair cells were totally missing in the cochlea, and severely destroyed in vestibular end-organs. The delayed spiral ganglion neuron death 60 days after the deafening procedure was over 50%. However, no obvious pathological changes were observed in vestibular ganglion neurons 60 days post-treatment. These results indicated that a high concentration of gentamycin delivered to the middle ear cavity can destroy most sensory hair cells in the inner ear that subsequently causes the delayed spiral ganglion neuron degeneration. This model might be useful for studies of hair cell regenerations, delayed degeneration of peripheral auditory neurons, and/or vestibular compensation. In addition, a potential problem of ABR recording for unilateral deafness and issues about vestibular compensation are also discussed.     

豚鼠前庭感觉上皮损伤中细胞凋亡的观察

细胞凋亡对细胞增殖、器官发生和功能维持起着重要作用。一定剂量的庆大霉素连续注射，造成豚鼠前庭器官损伤。采用半薄切片，透射电镜（TEM）和TUNEL（TdT－modidedbiotin-dUTPNick-endlabeling，末端脱氧核苷酸转移酶介导的生物素标记）原位杂交技术，特异标记DNA片段3′－OH末端，原位显示凋亡细胞。在半薄切片和TEM观察中发现两种类型的细胞损伤方式：①毛细胞肿胀，胞浆空泡化，细胞体从顶端表面挤出；②毛细胞在上皮内变性，显示出细胞凋亡的形态特征，包括细胞核凝缩，核膜消失，成碎块状，并由支持细胞吞噬。原位杂交显示：细胞凋亡标记阳性细胞主要分布在上皮表层，较高水平标记主要发生于给药后第3到7天。提示细胞凋亡是内耳前庭感觉细胞损伤的一种重要方式，凋亡的主动发生可能是一种潜在的介入方式来减少氨基甙类抗生素对毛细胞造成的急性损伤，并与感觉上皮损伤后的修复过程有关。     

Application of cell therapy to inner ear diseases

Most inner ear disorders involve irreversible loss of hair cells and their associated neurons. Recent advances in genetics and cell biology have raised hopes for the regeneration or protection of these cells. Cell therapy is a rapidly growing research area, and is potentially applicable to the treatment of inner ear disorders. Recent studies on cell transplantation into the inner ear have suggested that such cell therapy may be progressing towards the clinical application. This review highlights recent advances in cell transplantation studies focusing on the inner ear.     

Quantitative study of human Scarpa's ganglion and vestibular sensory epithelia

Methods for counting vestibular ganglion cells and determining the densities of hair cells and intraepithelial basophilic inclusions (IBI) in samples of cross-sectioned vestibular sensory epithelia are described. Data obtained by means of these methods in vestibular sensory epithelia and Scarpa's ganglia in individual temporal bones from subjects at different ages are presented. Both vestibular hair cells and nerve cells in Scarpa's ganglia are found numerically reduced in ears of aged individuals. Changes in the vestibular sensory epithelia appear to precede those seen in Scarpa's ganglion. The incidence of intraepithelial basophilic inclusions correlates with degeneration in the respective vestibular sensory epithelia. There are no striking differences in hair cells densities of the different vestibular sense organs of the same ear and from subjects at about the same age.     

ErbB Expression: The Mouse Inner Ear and Maturation of the Mitogenic Response to Heregulin

In humans, hair cell loss often leads to hearing and balance impairments. Hair cell replacement is vigorous and spontaneous in avians and nonmammalian vertebrates. In mammals, in contrast, it occurs at a very low rate, or not at all, presumably because of a very low level of supporting cell proliferation following injury. Heregulin (HRG), a member of the epidermal growth factor (EGF) family of growth factors, is reported to be a potent mitogen for neonatal rat vestibular sensory epithelium, but its effects in adults are unknown. We report here that HRG- stimulates cell proliferation in organotypic cultures of neonatal, but not adult, mouse utricular sensory epithelia. Our findings support the idea that the proliferative capabilities of the adult mammalian vestibular sensory epithelia differ significantly from that seen in neonatal animals. Immunohistochemistry reveals that HRG-binding receptors (erbBs 2–4) and erbB1 are widely expressed in vestibular and auditory sensory epithelia in neonatal and adult mouse inner ear. The distribution of erbBs in the neonatal and adult mouse ear is consistent with the EGF receptor/ligand family regulating diverse cellular processes in the inner ear, including cell proliferation and differentiation. Present address (Mette Kirkegaard): Department of Zoophysiology, Bld. 131, Universitetsparken, University of Aarhus, Denmark     

Regenerative Medizin in der Therapie der Innenohrschwerhörigkeit

Regenerative medicine offers the prospect of causal treatment of sensorineural hearing loss. In humans, the loss of sensory hair cells is irreversible and results in chronic hearing loss. Other vertebrates, particularly birds, have the capability to spontaneously regenerate lost sensory hair cells and restore hearing. In the bird model, regeneration of hair cells is based on the proliferation of supporting cells. In mammals, supporting cells have lost their proliferative capacity and are terminally differentiated. To gain an understanding about regeneration of hair cells in mammals, cell division of supporting cells has to be controlled. Gene disruption of the cell cycle inhibitor p27(Kip1) allows supporting cell proliferation in the organ of Corti in vivo. Furthermore, in vitro studies indicate that newly generated cells may differentiate into hair cells after p27(Kip1) disruption. Other current methods to induce hair cell regeneration include the gene transfer of Math1 and transplantation of stem cells to the inner ear.     

Transient receptor potential channels in the inner ear: presence of transient receptor potential channel subfamily 1 and 4 in the guinea pig inner ear

CONCLUSION: The results of this study indicate that transient receptor potential subfamily 1 (TRPV1) may play a functional role in sensory cell physiology and that TRPV4 may be important for fluid homeostasis in the inner ear. OBJECTIVE: To analyze the expression of TRPV1 and -4 in the normal guinea pig inner ear. MATERIAL AND METHODS: Albino guinea pigs were used. The location of TRPV1 and -4 in the inner ear, i.e. cochlea, vestibular end organs and endolymphatic sac, was investigated by means of immunohistochemistry. RESULTS: Immunohistochemistry revealed the presence of TRPV1 in the hair cells and supporting cells of the organ of Corti, in spiral ganglion cells, sensory cells of the vestibular end organs and vestibular ganglion cells. TRPV4 was found in the hair cells and supporting cells of the organ of Corti, in marginal cells of the stria vascularis, spiral ganglion cells, sensory cells, transitional cells, dark cells in the vestibular end organs, vestibular ganglion cells and epithelial cells of the endolymphatic sac.     

From gene identification to gene therapy

Inner ear disease due to hair cell loss is common, and no restorative treatments for the balance and hearing impairment are currently available. To develop clinical means for enhancing protection and regeneration in the inner ear, it is necessary to understand the molecular basis for hereditary and acquired deafness and vestibular disorders. One approach is to identify and characterize genes that regulate protection or repair in other systems. For that purpose, we have used the differential display assay and compared gene expression between normal and acoustically traumatized inner ears of chicks. Several chick cDNAs that were identified are considered as candidates for roles in the reparative process that follows trauma in the basilar papilla. The mammalian vestibular epithelium has a limited regenerative capability. To identify genes that may participate in the regenerative response, we have used gene arrays profiling, comparing normal to drug-traumatized vestibular epithelia. We identified several genes that are differentially expressed in traumatized vestibular epithelium, including several insulin-like growth factor-I binding proteins. To use this molecular knowledge for enhancing protection and repair in the organ of Corti, it is necessary to overexpress the genes of choice in the inner ear. Using viral-mediated gene transfer, we overexpressed transgenic glial cell line-derived neurotrophic factor and demonstrated a robust protective effect against acoustic and ototoxic inner ear trauma. Future identification of the genes that are important for protection and regeneration, along with improved gene transfer technology, will allow the use of gene therapy for treating hereditary and environmental inner ear disease.     

骨形态发生蛋白4在内耳发育及在毛细胞与螺旋神经节细胞再生中的研究进展

听力损失是人类最常见的感觉缺陷,主要涉及到毛细胞(HCs)和螺旋神经节细胞(SGCs)的损失等。在内耳发育过程中,骨形态发生蛋白4(BMP4)的表达具有时序性和特异性,并且通过调控分泌蛋白Tsukushin(TSK)、性别决定相关基因簇2蛋白(SOX2)等细胞因子,与WNT和SHH等信号通路之间相互作用,参与耳泡的诱导、前庭和耳蜗等器官的形成、HCs和SGCs等细胞的分化过程。此外,近些年在哺乳动物与非哺乳动物的耳蜗外植体中,发现BMP4在HCs和SGCs的再生中起重要作用。综述BMP4调控内耳发育、诱导HCs和SGCs再生的作用,以及相关的研究进展,以期为HCs和SGCs再生相关机制的阐明奠定基础,为听力损失的治疗带来新的思路与策略。     

Mature middle and inner ears express Chd7 and exhibit distinctive pathologies in a mouse model of CHARGE syndrome

Heterozygous mutations in the gene encoding chromodomain-DNA-binding-protein 7 (CHD7) cause CHARGE syndrome, a multiple anomaly condition which includes vestibular dysfunction and hearing loss. Mice with heterozygous Chd7 mutations exhibit semicircular canal dysgenesis and abnormal inner ear neurogenesis, and are an excellent model of CHARGE syndrome. Here we characterized Chd7 expression in mature middle and inner ears, analyzed morphological features of mutant ears and tested whether Chd7 mutant mice have altered responses to noise exposure and correlated those responses to inner and middle ear structure. We found that Chd7 is highly expressed in mature inner and outer hair cells, spiral ganglion neurons, vestibular sensory epithelia and middle ear ossicles. There were no obvious defects in individual hair cell morphology by prestin immunostaining or scanning electron microscopy, and cochlear innervation appeared normal in Chd7(Gt)(/+) mice. Hearing thresholds by auditory brainstem response (ABR) testing were elevated at 4 and 16 kHz in Chd7(Gt)(/+) mice, and there were reduced distortion product otoacoustic emissions (DPOAE). Exposure of Chd7(Gt)(/+) mice to broadband noise resulted in variable degrees of hair cell loss which inversely correlated with severity of stapedial defects. The degrees of hair cell loss and threshold shifts after noise exposure were more severe in wild type mice than in mutants. Together, these data indicate that Chd7(Gt)(/+) mice have combined conductive and sensorineural hearing loss, correlating with changes in both middle and inner ears.     

Spontaneous hair cell regeneration in the mouse utricle following gentamicin ototoxicity

Whereas most epithelial tissues turn-over and regenerate after a traumatic lesion, this restorative ability is diminished in the sensory epithelia of the inner ear; it is absent in the cochlea and exists only in a limited capacity in the vestibular epithelium. The extent of regeneration in vestibular hair cells has been characterized for several mammalian species including guinea pig, rat, and chinchilla, but not yet in mouse. As the fundamental model species for investigating hereditary disease, the mouse can be studied using a wide variety of genetic and molecular tools. To design a mouse model for vestibular hair cell regeneration research, an aminoglycoside-induced method of complete hair cell elimination was developed in our lab and applied to the murine utricle. Loss of utricular hair cells was observed using scanning electron microscopy, and corroborated by a loss of fluorescent signal in utricles from transgenic mice with GFP-positive hair cells. Regenerative capability was characterized at several time points up to six months following insult. Using scanning electron microscopy, we observed that as early as two weeks after insult, a few immature hair cells, demonstrating the characteristic immature morphology indicative of regeneration, could be seen in the utricle. As time progressed, larger numbers of immature hair cells could be seen along with some mature cells resembling surface morphology of type II hair cells. By six months post-lesion, numerous regenerated hair cells were present in the utricle, however, neither their number nor their appearance was normal. A BrdU assay suggested that at least some of the regeneration of mouse vestibular hair cells involved mitosis. Our results demonstrate that the vestibular sensory epithelium in mice can spontaneously regenerate, elucidate the time course of this process, and identify involvement of mitosis in some cases. These data establish a road map of the murine vestibular regenerative process, which can be used for elucidating the molecular events that govern this process.