Notch pathway inhibitor DAPT enhances Atoh1 activity to generate new hair cells in situ in rat cochleae

Atoh1 overexpression in cochlear epithelium induces new hair cell formation. Use of adenovirus-mediated Atoh1 overexpression has mainly focused on the rat lesser epithelial ridge and induces ectopic hair cell regeneration. The sensory region of rat cochlea is difficult to transfect, thus new hair cells are rarely produced in situ in rat cochlear explants. After culturing rat cochleae in medium containing 10% fetal bovine serum, adenovirus successfully infected the sensory region as the width of the supporting cell area was significantly increased. Adenovirus encoding Atoh1 infected the sensory region and induced hair cell formation in situ. Combined application of the Notch inhibitor DAPT and Atoh1 increased the Atoh1 expression level and decreased hes1 and hes5 levels, further promoting hair cell generation. Our results demonstrate that DAPT enhances Atoh1 activity to promote hair cell regeneration in rat cochlear sensory epithelium in vitro.

EXPERIMENTAL STUDY OF COCHLEAR HAIR CELL LOSS IN THE GUINEA PIG

The damage to spiral organs related to age and sex in guinea pigs was studied by the surface preparation technique. Hair cell loss of spiral organs of the following four age groups: 8month, 1, 2, and 2.5-year old pigs, was assessed. Each group was divided Into two subgroups according to different sexes. The decrease of hair cell population was linearly related to age, but not related to sex. The damage rate was greater in outer hair cells than in inner hair calls. In all of animals of different ages and both sexes, outer hair cell loss was prominent at the apex of cochlea. Less damage to outer hair cell was found at the base of cochlea. Damage to inner hair cell was also increased with age, but to a lesser extent.

Distribution of Prestin on Outer Hair Cell Basolateral Surface

Prestin has been identified as a motor protein responsible for outer hair cell (OHC) electromotility and is expressed on the OHC surface. Previous studies revealed that OHC electromotility and its associated nonlinear capacitance were mainly located at the OHC lateral wall and absent at the apical cuticular plate and the basal nucleus region. Immunofluorescent staining for prestin also failed to demonstrate prestin expression at the OHC basal ends in whole-mount preparation of the organ of Corti. However, there lacks a definitive demonstration of the pattern of prestin distribution. The OHC lateral wall has a trilaminate organization and is composed of the plasma membrane, cortical lattice, and subsurface cisternae. In this study, the location of prestin proteins in dissociated OHCs was examined using immunofluorescent staining and confocal microscopy. We found that prestin was uniformly expressed on the basolateral surface, including the basal pole. No staining was seen on the cuticular plate and stereocilia. When co-stained with a membrane marker di-8-ANEPPS, prestin-labeling was found to be in the outer layer of the OHC lateral wall. After separating the plasma membrane from the underlying subsurface cisternae using a hypotonic extracellular solution, prestin-labeling was found to be in the plasma membrane, not the subsurface cisternae. The data show that prestin is expressed in the plasma membrane on the entire OHC basolateral surface.

HAIR CELL-LIKE CELL GENERATION INDUCED BY NATURE CULTURE OF ADULT RAT AUDITORY EPITHELIUM

Objective To establish adult rat auditory epithelial cell culture and try to find precursor cells of auditory hair cells in vitro. Methods With refinement of culture media and techniques, cochlear sensory epithelial cells of adult rat were cultured. Immunocytochemistry and Bromodeoxyuridine (BrdU)labeling were used to detect properties and mitotic status of cultured cells. Results The cultured auditory epithelial cells showed a large, flat epithelial morphotype and expressed F-actin and cytokeratin, a subset of cells generated from auditory epithelium were labeled by calretinin, a specific marker of early hair cell. Conclusion Adult rat auditory epithelium can be induced to generate hair cell-like cells by nature culture, this phenomenon suggests that progenitor cells may exist in rat cochlea and they may give birth to new hair cells. Whether these progenitor cells are tissue specific stem cells is still need more study.

Inner ear hair cell regeneration A look from the past to the future

Most recent studies on regeneration of inner ear hair cells focus on use of stem cells, gene therapy and neurotrophic factors. Cochlear gene therapy has been successfully used in the treatment of neu- rosensory hearing loss. This suggests that cochlear hair cell regeneration is possible. The objective of this paper is to review research and clinical application of inner near hair cell regeneration.

Basic flbroblast growth factor protects auditory neurons and hair cells from noise exposure and glutamate neurotoxicity

The purpose of the present study was to determine protectivie effects of basic fibroblast growth factor (bFGF) on cochlear neurons and hair cells in vitro and in vivo. In experiment I, cultured spiral ganglion neurons (SGNs) prepared from P3 mice were exposed to 20mM glutamate for 2 hours before the culture medium was replaced with fresh medium containing 0, 25, 50, and 100 ng/ml bFGF, respectively. Fourteen days later, all cultures were fixed with 4% paraformaldehyde, and stained with 1% toluidine blue. The number of surviving SGNs were counted and the length of SGNs neurites were measured. Exposure to 20 mM glutamate for 24 hours resulted in an inhibition on neurite outgrowth of SGNs and elevated cell death. Treatment of the cultures with bFGF led to promotion of neurite outgrowth and elevated number of surviving SGNs. Effects of bFGF were dose dependent with the highest potency at 100 ng/ml. In experiment Ⅱ, in vivo studies were carried out with guinea pigs in which bFGF or artificial perilymph was perfused into the cochlea to assess possible protective effects of bFGF on cochlear hair cells and compound action potentials(CAP). The CAPs were measured before, immediatly and 48 hours after exposure to noise. Significant differences in CAP were observed (p＜0. 05 ) among the bFGF perfused group, control group(t =3. 896 ) and artificial perilymph perfused group (t =2. 520) at 48 hours after noise exposure, Cochleae were removed and hair cell Loss was analyzed in surface preparations prepared from all experimental animals. Acoustic trauma caused loss of 651 and 687 inner hair cells in the control and artificial perilymph perfused group, respectively. In sharp contrast, only 31 inner hair cells were lost in the bFGF perfused ears. Similarly, more outer hair cells died in the control and perilymph perfuesed group (41830 and 41968, respectively) than in the group treated with bFGF (34258). Our results demonstrate that bFGF protected SGNs against glutmate neurotoxicity in vitro. In addition, treatment with bFGF also protected hair cells from acoustic trauma.

Quantitative Relations between Outer Hair Cell Electromotility and Nonlinear Capacitance

The electrically evoked somatic motility of outer hair cells （OHC）, briefly termed OHC electromotility, plays a crucial role in cochlear amplification that underlies the remarkably high sensitivity and frequency selectivity of the mammalian hearing. Accompanying OHC electromotility is a voltage-dependent gating charge movement within the cell lateral membrane, manifested as a measurable nonlinear capacitance （NLC） in OHCs. The electromotility and NLC of OHCs are highly correlated by sharing a common molecular substrate, the motor protein prestin. In this study, we systematically characterized the quantitative relationship between OHC electromotility and NLC in their voltage dependences for the purpose of further understanding the electromechanical transduction in OHCs. The results demonstrated that the two possess differing voltage dependences with the V^2 of electromotility consistently being -20 mV depolarized in comparison with that of NLC although their slope factors a are statistically identical. Further investigations showed that the initial state of OHCs influences the voltage dependence of electromotility but not that of NLC, indicating that some biophysical factors other than the motor protein per se are involved in the process of OHC length changes. We proposed that the cytoskeletal spectrin-actin framework underneath the OHC plasma membrane and the cell＇ s turgor are the two most probable factors that cause the voltage-dependence discrepancy between OHC electromotility and NLC.

Detection of apoptosis by RT-PCR array in mefloquine-induced cochlear damage

Objective To investigate the occurrence and possible mechanisms of apoptosis in cochlear epithelium and spiral ganglion neurons after mefloquine treatment. Methods We used quantitative RT-PCR apoptosis-focused gene arrays （96-well, 84 apoptosis related genes） to assess changes of gene expression in the cochlear basilar membrane （hair cells-supporting cells） and spiral ganglion neurons of rat cochlear organotypic cultures treated with 100 IxM mefloquine for 3 h. Results Significant up-or down-regulation in gene expression was detected in 23 genes in the cochlear basilar membrane, and in 32 genes in the spiral ganglion neurons compared with time-matched controls. The responding genes could be classified as pro-or anti-apoptotic, and were mainly implicated in the Bcl-2, Caspase, Card, IAP, TNF ligand / TNF receptor, Death domain / Death effector domain, DNA damage / p53, and NF-kappa B families. Synthetic analysis suggested that these families could be revised to two major pathways mainly involved in t]he death receptor-mediated signaling pathway and apoptotic mitochondrial pathway. In addition, it was found that numerous anti-apoptotic genes such as Bcl2al, Birclb, Birc3, Birc4, Bnipl, Cflar, II10, Lhx4, Mcll, Nfkbl, Prlr, Prok2, and TNF were greatly up-regulated in the cochlear tissue, which might imply the co-existence of protective response in the ceils at the early stage of mefloquine-induced damage.

EFFECTS OF DIABETES ON HEARING AND COCHLEAR STRUCTURES

Diabetes mellitus (DM) is a chronic systemic disease characterized by hyperglycemia, with various patho-genic mechanisms. From absolute or relative insulin deficiency, patients with DM often demonstrate vari-ous levels of metabolic disorders. Major clinical manifestations of DM include metabolic disorders, vascu-lar lesions, circulatory disturbances and neurologic complications. Along with advances in DM research, re-ports of DM related tinnitus and hearing impairment have increased continuously. Research on DM related auditory system dysfunction has focused on cochlear microcirculation, cellular homeostasis, genetics and ag-ing. Cochlear microcirculation plays an important role in cochlear physiology and its disorders are associat-ed with many inner ear diseases. Ischemia and subsequent reperfusion seen in cochlear microcirculation dis-orders are important factors in hearing damage. Understanding cochlear microcirculation and structural as well as functional changes in DM patients with hearing loss and their causal factors will help reveal patho-genic mechanisms in diabetic hearing loss and provide new ideas in developing interventions and preventing damages caused by diabetes.

Lead neurotoxicity in rat cochlear organotypic cultures

Lead is a major environmental toxicant throughout the world.Lead can induce severe neurotoxicity including irreversible hearing impairment.Many in vivo studies have shown that lead damages the auditory nervous system,but has little or no effect on cochlear sensory hair cells.To gain insights on lead ototoxic and neurotoxic effects in vitro,lead acetate (LA) was applied to postnatal day 3-4 rat cochlear organotypic cultures for 24 or 72 h with doses of 0.1,0.5,1,2 or 4 mM.After 24 or 72 h treatment with lead acetate,nearly all of cochlear sensory hair cells were intact.However,after 72 h treatment,the peripheral auditory nerve fibers projecting to the hair cells and the spiral ganglion neurons (SGN) were damaged when lead concentration exceeded 2 mM.Our results indicated that 72 h treatment with only the high doses (> 2 mM) of lead actate damaged SGNs and peripheral nerve fibers;hair cells remained structurally intact even after 4 mM treatment.These results show that lead primarily damages cochlear nerve fibers andSGNratherthanhaircells.

Lentivirus carrying the Atoh1 gene infects normal rat cochlea

Lentivirus carrying the Atohl gene can infect Corti＇s organ and express a hair-like cell surface marker in the supporting cell area. However, expression of the gene carried by adenovirus is instantaneous, which undoubtedly limits its clinical application. Lentivirus acts as a carrier that can stably and continuously express genes. In this study, the cochlear structure and hearing level were not affected, and Atohl gene carried by lentivirus promoted the production of hair-like cells in the cochlear supporting cell area. This led to expression of the hair-like cell surface marker myosin 7a 30 days after lentivirus carrying Atohl was microinjected into the cochlear round window of rats.

An Overview of Electrically Evoked Otoacoustic Emissions in the Mammalian Cochlea

Alternating currents injected into the cochlea are able to evoke outer hair cell-mediated basilar membrane motion, thus give rise to production of otoacoustic emissions. This electrically evoked otoacoustic emission(EEOAE) provides a useful tool for the research of out hair cell electromotility in vivo. This article reviews the research work on EEOAEs in mammals. Features of the EEOAEs and theories of their generation are introduced. Methods of EEOAE measurement are also described.

自噬在感音神经性耳聋中的研究进展

自噬能够清除细胞内损伤的细胞器及错误折叠的蛋白质,是细胞应对损伤、维持稳态的一种方式。自噬在各种疾病的发生发展中都发挥重要作用,在药物性耳聋、老年性耳聋以及噪声性耳聋中能够减少毛细胞死亡,从而保护听力。本综述总结了自噬在感音神经性耳聋中的研究进展,以期为自噬在毛细胞损伤中的作用及机制研究提供参考。

Role of Wnt and Notch signaling in regulating hair cell regeneration in the cochlea

Sensory hair cells in the inner ear are responsible for sound recognition. Damage to hair cells in adult mammals causes permanent hearing impairment because these cells cannot regenerate. By contrast, newborn mammals possess limited regenerative capacity because of the active participation of various signaling pathways, including Wnt and Notch signaling. The Wnt and Notch pathways are highly sophisticated and conserved signaling pathways that control multiple cellular events necessary for the formation of sensory hair cells. Both signaling pathways allow resident supporting cells to regenerate hair cells in the neonatal cochlea. In this regard, Wnt and Notch signaling has gained increased research attention in hair cell regeneration. This review presents the current understanding of the Wnt and Notch signaling pathways in the auditory portion of the inner ear and discusses the possibilities of controlling these pathways with the hair cell fate determiner Atohl to regulate hair cell regeneration in the mammalian cochlea.

脉冲噪声暴露后早期大鼠耳蜗外毛细胞死亡时程观察

目的观察强脉冲噪声暴露后早期大鼠耳蜗毛细胞损伤发展的规律。方法将大鼠暴露于平均压力峰值级为154dBSPL的脉冲噪声100发,分别于噪声暴露后10min、30min、3h、6h解剖取耳蜗,应用碘化丙锭(PI)标记耳蜗基底膜,荧光显微镜下观察脉冲噪声暴露后耳蜗毛细胞凋亡和坏死的时程特点。结果强脉冲噪声暴露后10min出现外毛细胞核染色质移位及凋亡小体,30min可见到少量肿胀的外毛细胞核,3h观察到少量外毛细胞核的缺失。6h耳蜗基底膜损伤区出现大片外毛细胞核缺失和部分微小球形固缩的外毛细胞核。结论耳蜗外毛细胞死亡发生于强脉冲噪声暴露后即刻,外毛细胞凋亡先于坏死。细胞凋亡过程迅速,强脉冲噪声暴露后6h耳蜗基底膜损伤区大部分死亡细胞已被清除。

脉冲与脉冲稳态复合型强噪声对豚鼠听觉器官的影响

目的研究不同强度脉冲噪声与脉冲稳态复合型高强噪声对豚鼠听觉器官的影响。方法 48只豚鼠随机分为对照组 (C)、5次 1 5 1dB (Ps,TB=2 0ms)脉冲组 (P1 )、9次 1 5 1dB脉冲组 (P2 )、9次 1 5 5dB脉冲组 (P3)、9次 1 5 5dB脉冲加 1 1 0dB稳态噪声复合组 (Com1 )、5次 1 5 5dB脉冲加 1 1 8dB稳态噪声复合组 (Com2 ) ,每组 8只。检测噪声暴露前后中耳损伤、ABR听阈及 1周后的毛细胞变化。结果中耳无明显损伤 ;暴露后即刻、2 4h各暴露组均有明显的暂时性听力损失 (P <0 .0 1 ) ,1周后 ,复合噪声组听力仍未完全恢复 (P <0 .0 5 ) ;各暴露组的毛细胞均有不同程度缺损 ,并伴有基底膜变薄内陷。结论脉冲噪声可引起豚鼠暂时性听力损失 ,并造成毛细胞部分缺损 ,复合高强度的稳态噪声时 ,可造成豚鼠永久性听力损失。

强噪声引起的耳蜗毛细胞核形态学变化

为定量观察噪声引起的耳蜗毛细胞核形态学变化 ,将豚鼠暴露于 115dBSPL的 4kHz窄带噪声 4h。 14天后解剖取耳蜗 ,应用细胞核DNA染料Hoechst 3334 2标记毛细胞核 ,荧光显微镜下观察毛细胞核形态和数量的变化。结果发现 ,毛细胞核同时出现的 3种形态学改变 :核肿胀、核固缩和核消失 ,其中核肿胀细胞数目多于核消失 ,核固缩较为少见。爆震后毛细胞的损伤是一个复杂的、长期的、非同步的病理变化过程 ,存在较多核肿胀的毛细胞。提示 ,此期耳蜗可能仍存在大量可逆变化的受损毛细胞。

缺氧对体外培养大鼠耳蜗毛细胞的损伤作用

目的:建立耳蜗器官体外培养模型,观察缺氧对体外培养耳蜗内毛细胞(IHC)及外毛细胞(OHC)的影响。方法:分离生后3d Wistar大鼠耳蜗基底膜,平铺在含有DMEM培养液的培养基内(每盘6条基底膜),2盘为1组,随机分为8组,放置在37℃、5%CO2培养箱培养,其中7组作为实验组,按不同时间段进行缺氧(37℃、90%N2、5%CO2、5%O2)培养;1组作为对照组放置在37℃、5%CO2培养箱。采用Phalloidin荧光标记观察耳蜗中IHC及OHC形态变化并计数单位面积(24 mm×36 mm)细胞数即细胞密度。结果:在缺氧早期(0.5 h)IHC形态及密度无明显变化;1 h细胞轻度肿胀,体积增大,单位面积细胞数减少,细胞密度与对照组比较差异无显著性(P>0.05);2 h时IHC散在缺失,细胞密度与对照组比较差异有显著性(P<0.01);6 h时IHC缺失增多,并可见毛细胞坏死后遗留的“空神经杯”现象,细胞密度与对照组比差异有显著性(P<0.01);随缺氧时间延长,IHC缺失逐渐加重。OHC在缺氧早期(0.5 h、1 h)形态学改变不明显,2 h偶见细胞缺失,随缺氧时间延长,6 h后出现不同程度的排列拥挤、紊乱及缺失,单位面积细胞数目减少,细胞密度与对照组比较差异有显著性(P<0.01),以48 h最严重。结论:缺氧造成体外培养耳蜗毛细胞缺失,以IHC为重。

水杨酸钠急慢性注射致豚鼠耳蜗形态学的改变

目的 :研究水杨酸钠对豚鼠耳蜗形态学改变的急慢性作用。方法 :采用单次和长期注射水杨酸钠建模分别在光镜、电镜 (扫描、透射 )下观察 1次及多次注射水杨酸钠组和生理盐水对照组豚鼠耳蜗基底膜Corti器 ,特别是外毛细胞形态的改变。结果 :以相应的生理盐水组为对照 ,急性水杨酸钠注射 2h主要引起透射电镜下豚鼠外毛细胞侧壁表面下池发生扩张性空泡形成 ;慢性水杨酸钠注射 2周主要引起豚鼠外毛细胞在透射电镜下出现表面下池肿胀、扩张、空泡形成 ,以及透射和扫描电镜下均出现静纤毛柔软、弯曲。结论 :急慢性水杨酸钠注射引起豚鼠耳蜗形态学改变可能为耳蜗功能改变的原因 。

5-磷酸二酯酶抑制剂对噪声性聋影响的实验研究

目的探讨5-磷酸二酯酶(PDE5)抑制剂对豚鼠噪声性聋的影响。方法豚鼠随机数字表法分为对照组、噪声暴露组和西地那非给药组,每组15只。西地那非组及噪声组豚鼠在白噪声暴露1周后分别腹腔注射西地那非10mg/(kg.d)及生理盐水4 ml/(kg.d),连续给药4周。分别测试噪声暴露前1天、噪声暴露后1、2及4周听性脑干反应(ABR)阈值及80dB HL下ABRⅠ波潜伏期,并通过扫描电镜观察噪声暴露后4周豚鼠耳蜗毛细胞的形态变化。结果与噪声暴露前相比,西地那非组ABR阈值及Ⅰ波潜伏期均小于噪声组,差异具有统计学意义(P值均<0.01)。扫描电镜显示,噪声组豚鼠耳蜗内、外毛细胞均出现听毛紊乱、融合及缺失;而西地那非组耳蜗病变较轻,听毛仅有轻微倒伏、融合现象。结论西地那非能够减轻噪声对豚鼠耳蜗毛细胞的损害,降低噪声性听觉损伤引起的ABR阈值升高,缩短其引起的Ⅰ波潜伏期延长。