Biomedical subjects

T R Van De Water

Publications and source records attributed to T R Van De Water.

At least 19 recordsLinked to original sources

PubMed2004

Caspases, the enemy within, and their role in oxidative stress-induced apoptosis of inner ear sensory cells.

This review covers the general roles of members of the cysteine protease family of caspases in the process of apoptosis (programmed cell death) looking at their participation in both the "extrinsic" cell death receptor and the "intrinsic" mitochondrial cell death pathways. It defines the difference between initiator and effector caspases and shows the progression of caspase activations that ends up in the apoptotic cell death and elimination of a damaged cell. The review then presents what is currently know about the participation of caspases in the programmed cell death of inner ear sensory cells during the process of normal development and maturation of the inner ear and their importance in this process as illustrated by the results of caspase-3 gene knockout experiments. The participation of specific caspases and the sequence of their activation in the elimination (apoptosis) of damaged sensory cells from adult inner ears after an injury that generates oxidative stress are reviewed. Both the possibility and the potential efficacy of caspase inhibition with a broad-spectrum pancaspase inhibitor as an interventional therapy to treat and rescue oxidative stress-damaged inner ear sensory cells from apoptosis are presented and discussed.

Adult↗

PubMed2003

A peptide inhibitor of c-Jun N-terminal kinase protects against both aminoglycoside and acoustic trauma-induced auditory hair cell death and hearing loss.

Hearing loss can be caused by a variety of insults, including acoustic trauma and exposure to ototoxins, that principally effect the viability of sensory hair cells via the MAP kinase (MAPK) cell death signaling pathway that incorporates c-Jun N-terminal kinase (JNK). We evaluated the otoprotective efficacy of D-JNKI-1, a cell permeable peptide that blocks the MAPK-JNK signal pathway. The experimental studies included organ cultures of neonatal mouse cochlea exposed to an ototoxic drug and cochleae of adult guinea pigs that were exposed to either an ototoxic drug or acoustic trauma. Results obtained from the organ of Corti explants demonstrated that the MAPK-JNK signal pathway is associated with injury and that blocking of this signal pathway prevented apoptosis in areas of aminoglycoside damage. Treatment of the neomycin-exposed organ of Corti explants with D-JNKI-1 completely prevented hair cell death initiated by this ototoxin. Results from in vivo studies showed that direct application of D-JNKI-1 into the scala tympani of the guinea pig cochlea prevented nearly all hair cell death and permanent hearing loss induced by neomycin ototoxicity. Local delivery of D-JNKI-1 also prevented acoustic trauma-induced permanent hearing loss in a dose-dependent manner. These results indicate that the MAPK-JNK signal pathway is involved in both ototoxicity and acoustic trauma-induced hair cell loss and permanent hearing loss. Blocking this signal pathway with D-JNKI-1 is of potential therapeutic value for long-term protection of both the morphological integrity and physiological function of the organ of Corti during times of oxidative stress.

Acoustic Stimulation↗

PubMed2002

Epithelial supporting cells can differentiate into outer hair cells and Deiters' cells in the cultured organ of Corti.

The organ of Corti is a complex structure containing a single row of inner hair cells (IHCs) and three rows of outer hair cells (OHCs), supported respectively by one row of inner phalangeal cells and three rows of Deiters' cells. When fetal rat organ of Corti explants are cultured, supernumerary OHCs and supernumerary Deiters' cells are produced, without any additional cell proliferation. Analysis of semi- and ultrathin sections revealed that supernumerary OHCs are produced at the distal edge of the organ of Corti. Quantitative analysis of cell types present in the organ of Corti demonstrates that when the number of OHCs increases: (i) the total number of cells remains constant; (ii) the number of Deiters' cells increases; (iii) the number of tectal cells decreases and of Hensen's cells decreases. Using specific HC markers, i.e. jagged2 (Jag2) and Math1, we showed that in addition to existing OHCs, supernumerary OHCs, tectal cells and Hensen's cells expressed these markers in embryonic day 19 organ of Corti explants after 5 days in vitro. The results of this study suggest that Hensen's cells retain the capacity to differentiate into either tectal cells, which differentiate into OHCs, or into undertectal cells which differentiate into Deiters' cells.

Animals↗

PubMed2001

Growth factor treatment enhances vestibular hair cell renewal and results in improved vestibular function.

The vestibules of adult guinea pigs were lesioned with gentamicin and then treated with perilymphatic infusion of either of two growth factor mixtures (i.e., GF I or GF II). GF I contained transforming growth factor alpha (TGFalpha), insulin-like growth factor type one (IGF-1), and retinoic acid (RA), whereas GF II contained those three factors and brain-derived neurotrophic factor. Treatment with GF I significantly enhanced vestibular hair cell renewal in ototoxin-damaged utricles and the maturation of stereociliary bundle morphology. The addition of brain-derived neurotrophic factor to the GF II infusion mixture resulted in the return of type 1 vestibular hair cells in ototoxin-damaged cristae, and improved vestibular function. These results suggest that growth factor therapy may be an effective treatment for balance disorders that are the result of hair cell dysfunction and/or loss.

Animals↗

PubMed2001

Round window membrane delivery of L-methionine provides protection from cisplatin ototoxicity without compromising chemotherapeutic efficacy.

Cisplatin (cis-diamminedichloroplatinum(II) (CDDP)) is a widely used, highly effective, oncolytic agent that has serious ototoxic side-effects. To test the effectiveness of local delivery, of L-methionine (L-Met) as an otoprotective agent against CDDP ototoxicity, we used a rat model of a highly metastatic breast cancer tumor, i.e. Fisher 344 rats implanted with MTLn3 breast cancer cells. Four experimental groups were evaluated--I: untreated; II: CDDP-treated (three dosages); III: systemically-delivered L-Met + CDDP-treated; IV: locally delivered L-Met + CDDP-treated. The integrity of the outer hair cells (OHCs) was determined using scanning electron microscopy (SEM); hearing was assessed by recording auditory brainstem responses (ABRs) at multiple frequencies. The chemotherapeutic effectiveness of CDDP was quantified by measuring changes in tumor mass and the presence of tumor metastasis. L-Met provided otoprotection of the OHCs against CDDP toxicity in the cochleae of rats following either systemic (III) or local (IV) administration. The ABRs were unchanged in each of the L-Met protection Groups (III and IV) and in the untreated animals of Group I. Treatment with CDDP only (II) induced significant hearing losses at both 16 and 18 kHz when compared to ABRs of untreated rats(I). CDDP was effective in controlling the MTLn3 initiated breast cancer tumors in the CDDP-treated (II) and the local L-Met protection, CDDP-treated (IV) Groups. In contrast, the tumors in the systemic L-Met protection, CDDP-treated Group (III) were not controlled by the CDDP treatment regime. This study demonstrates that local delivery of L-Met to the scala tympani of the cochlea via the round window membrane (IV) provides effective protection against CDDP ototoxicity without compromising its ability to control a highly metastatic form of cancer.

Adenocarcinoma↗

PubMed2001

Gene expression in the mammalian cochlea: a study of multiple vector systems.

Successful delivery of genes to the inner ear has been demonstrated using a variety of vectors and animal models. As our understanding of the molecular pathophysiology of hearing and balance disorders increases, the delivery of genes is becoming central to our ability to manipulate the function of the inner ear. This study evaluates the efficacy of gene transfer and the distribution of three different vector types within the inner ear. Adenovirus vectors, herpes virus vectors and liposomes carrying a plasmid with the green fluorescent protein or beta galactosidase marker genes and a CMV promoter were introduced into the inner ear of 3-month-old mice. The temporal bones and brain were then removed from the animals and examined for transgene expression. Distribution of staining in the treated ear was compared with distribution of staining in the contralateral inner ear. Staining for T cell markers was also carried out to determine inner ear immune response to gene transfer. Herpes virus vectors appear to target neurons most efficiently. Liposome vectors were least efficient in terms of gene transfer. Adenovirus vectors accomplished gene transfer to the widest variety of inner ear cells including auditory and vestibular hair cells. Newer generation adenovirus vectors promise less immune reaction and toxicity than traditional vectors and will be useful for both research and future clinical applications.

Animals↗

PubMed2001

Supernumerary outer hair cells arise external to the last row of sensory cells in the organ of corti.

During the development of the mammalian inner ear, the number of hair cells produced is highly regulated and remains constant throughout life. The mechanism underlying this regulation is beginning to be understood although many aspects still remain obscure. When late embryonic or early postnatal rat organs of Corti were cultured, the production of supernumerary hair cells was observed. This overproduction of sensory cells could be modulated by the addition of several growth factors. In this study, we examined explants of rat organs of Corti that produced supernumerary hair cells. In the supernumerary hair cell region, up to two rows of inner hair cells and five rows of outer hair cells were observed. Morphological evaluation of these specimens revealed that less mature hair cells were located in the most external rows of these sensory cells. When a supernumerary hair cell was produced, a supporting cell (i.e. Deiters' cell) was also produced, strongly suggesting that the conversion of a Deiters' cell into a hair cell was not the mechanism that produced these extra hair cells. Based on these results, we propose that prosensory cells located at the external edge of the organ of Corti retain a capacity to form hair cells and that it is these prosensory cells that differentiate into supernumerary hair cells and Deiters' cells.

Animals↗

PubMed2001

Oxidative stress in aging in the C57B16/J mouse cochlea.

Presbycusis is a complex of high frequency hearing loss and disproportionate loss of speech discrimination that is seen concomitantly with physical signs of aging. Among the most extensively characterized strains of mice that show an early hearing loss is the C57B16/J strain, a strain that shows early onset of high frequency hearing loss at age 6 months and complete hearing loss by 1 year of age. The histopathology of this strain consists of loss of hair cells and spiral ganglion neurons in the basal turn, with a progression of loss of hair cells and ganglion neurons towards the apical portion of the cochlea as the animal ages. The process of aging has been extensively studied and although details differ in various organisms the consensus today is that oxidative stress, i.e. free radical-mediated tissue damage, is one of the core mechanisms of aging. Aerobic metabolism results in the creation of hydrogen peroxide and reactive oxygen species. These are normally detoxified by a variety of enzymes and free radical scavengers, including superoxide dismutase (SOD), catalase and glutathione. To determine whether oxidative stress plays a role in the pathophysiology of hearing loss in this mouse model of presbycusis we determined the relative change in mRNA production for selected free radical detoxifying enzymes in the C57B16/J mouse cochlea. Using semi-quantitative RT-PCR with tubulin mRNA as a control, relative levels of antioxidant enzyme mRNAs were determined. There was an overall increase in SOD1 mRNA levels when comparing 1 and 9 month time points, and a transient increase in the expression level of catalase mRNA. B6.CAST+ Ahl mice, which carry the C57B16/J genome but receive their Ahl gene from CAST mice, do not show these alteractions in antioxidant enzyme production. Our results suggest that at an age of 9 months, at which point significant hearing loss has developed, the C57B16/J mouse cochlea is exposed to increased levels of free radicals and that the Ahl gene of the C57B16/J mouse mediates this decrease in protective enzymes and therefore increase in levels of oxidative stress.

Aging↗

PubMed2001

L-n-acetyl-cysteine protection against cisplatin-induced auditory neuronal and hair cell toxicity.

OBJECTIVES: The aim of this study is to determine the efficacy of L-N-acetyl-cysteine (L-NAC) as a protectant for inner ear auditory sensory cells against the toxic effects of cisplatin. STUDY DESIGN: Prospective laboratory study of the otoprotective effect of L-NAC on auditory neurons and hair cells in vitro. METHODS: The study has two arms. The first arm evaluated the neuroprotective effect of L-NAC on early postpartum auditory ganglion cell cultures. Two culture media were used. The two media differed in that one of them was enhanced by the addition of neurotrophins (neurotrophin type 3 and brain-derived neurotrophic factor) and a growth factor (transforming growth factor-beta1). Then the survival of cisplatin-treated auditory neurons was studied before and after pretreatment with protective levels of L-NAC. The second arm of the study evaluated the effect of L-NAC on cisplatin damage initiated to auditory hair cells. Early-postpartum organ of Corti explants were grown in culture. Their rate of survival was studied after exposure to toxic levels of cisplatin. Then, survival of cisplatin-damaged hair cells was studied after they were pretreated with L-NAC. RESULTS: Pretreatment of cultures with L-NAC protected both auditory neurons and hair cells from the effects of exposure to toxic levels of cisplatin. This observed otoprotective effect was dose dependent. CONCLUSIONS: Our in vitro studies have demonstrated that L-NAC protected both auditory neurons and hair cells from the toxic effects of cisplatin. Because it protects both of these inner ear structures, L-NAC may be potentially useful in protecting hearing, in general, from cisplatin-induced damage. In addition, L-NAC has low systemic and mucosal toxicity. It also has a low molecular weight that may allow it to readily cross the round window membrane. All these characteristics make it potentially suitable for transtympanic application for the prevention of the ototoxicity of cisplatin in vivo.

Acetylcysteine↗

PubMed2000

Connexins, hearing and deafness: clinical aspects of mutations in the connexin 26 gene.

Congenital deafness is a very frequent disorder occurring in approximately I in 1000 live births. Mutations in GJB2 encoding for gap junction protein connexin-26 (Cx26) have been established as the basis of autosomal recessive non-syndromic hearing loss and proposed in some rare cases of autosomal dominant form of deafness. Connexin are gap-junction proteins which constitute a major system of intercellular communication important in the exchange of electrolytes, second messengers and metabolites. In the inner ear, connexin 26 expression was demonstrated in the stria vascularis, basement membrane, limbus and the spiral prominence of the human cochlea. The loss of connexin 26 in the gap junction complex would expect to disrupt the recycling of potassium from the synapses at the base of hair cells through the supporting cells and fibroblasts of potassium ions back to the high potassium containing endolymph of the cochlear duct and therefore would result in a local intoxication of the Corti s organ by potassium, leading to the hearing loss. The discovery of the genes responsible of hearing loss in particular the identification of mutations in the gene coding for connexin 26 allows to hope some tremendous help in genetic counseling. The possible implication of the mutation of the connexin gene in the pathophysiology of some progressive adult deafness opens new prospects in the fine diagnostic of the ear diseases and eventually may lead to new therapeutic strategies applied to the cochlea.

Adult↗

PubMed2000

Immunolocalization of connexin 26 in the developing mouse cochlea.

Gap junctions play a pivotal role in embryonic development by forming specialized regions of cell-cell communication. In this study, we demonstrate the temporal-spatial distribution of connexin 26 in the embryonic and early postnatal mouse cochlea. Our results show localization of this gap junction protein to specific cochlear structures, including the inner and outer sulcus cells, the supporting cells of the inner hair cells, the mesenchyme derived portion of the stria vascularis, and the cells of the spiral ligament that interface with the basal cells of the stria vascularis. This suggests that this gap junction protein of served patterns of connexin 26 distribution is important for the differentiation and development of these structures (e.g., the role of the inner sulcus cells in producing the tectorial membrane).

Animals↗

PubMed2000

Epidermal growth factor upregulates production of supernumerary hair cells in neonatal rat organ of corti explants.

The organ of Corti is highly ordered, with a single row of inner hair cells and three rows of outer hair cells. The number of hair cells produced was thought to be limited by the time of their terminal mitosis (i.e. E14 in the mouse). However, exogenous application of retinoic acid has been shown to stimulate the formation of supernumerary hair cells in organ of Corti explants from E13 to E16 mouse embryos. Using late embryonic and neonatal rat organ of Corti explants, we investigated the potential for production of supernumerary hair cells in more mature auditory sensory epithelia. When newborn rat organ of Corti explants were cultured under control conditions, an area of supernumerary hair cells was observed in a segment of organ of Corti that was at the junction between the basal and middle turns. In these areas of supernumerary hair cells the number of hair cells increased per unit of length, but remained constant per surface unit, further demonstrating the supernumerary character of this phenomenon. Organ of Corti explants treated with epidermal growth factor (EGF) showed a 50% increase in the length of the organ of Corti segment containing supernumerary hair cells. Upregulation of supernumerary hair cell formation by EGF was found to start and be maximal at birth (P0) and to disappear by 2 days after birth (P2). Treatment of EGF stimulated P0 explants with an antimitotic drug, cytosine arabinoside (ARAc), demonstrated that the production of supernumerary hair cells occurred independently of cell division.

Animals↗

PubMed2000

Genetic patterning of embryonic inner ear development.

The commitment of the otocyst to form balance (pars superior) and hearing (pars inferior) receptors is under the control of patterning genes. Intersecting patterns of gene expression has been proposed to explain the regionalization of inner ear sensory receptor development. Insights into the roles of patterning genes is being acquired from the analysis of inner ear development of null mutation mice. An example of the consequences of the loss of expression of a single patterning gene is the effect of a null mutation of paired-box gene 2 (Pax2) on formation of the cochlea. Pax2 transcripts are expressed in the pars inferior of the otocyst and null mutant inner ears show agenesis of the cochlea. This is an example of the profound effect that loss of a single patterning gene can have on inner ear development. However, more typically there is redundancy of gene action during inner ear development as exemplified by the overlapping pattern of expression of two closely related homeobox-containing genes (i.e. Hmx2 and Hmx3) in the pars superior of the otocyst. Hmx2 and Hmx3 genes are both expressed early in otic development with Hmx3 transcripts present in the placode. However, null mutation of the Hmx3 patterning gene produced only a limited vestibular defect, and did not result in the agenesis of the vestibule. This result suggests that there is redundancy in genes that have similar patterns of regional expression in the otic anlagen.

Animals↗

PubMed2000

Notch signaling regulates the pattern of auditory hair cell differentiation in mammals.

The development of the mammalian cochlea is an example of patterning in the peripheral nervous system. Sensory hair cells and supporting cells in the cochlea differentiate via regional and cell fate specification. The Notch signaling components shows both distinct and overlapping expression patterns of Notch1 receptor and its ligands Jagged1 (Jag1) and Jagged2 (Jag2) in the developing auditory epithelium of the rat. On embryonic day 16 (E16), many precursor cells within the Kölliker's organ immunostained for the presence of both Notch1 and Jag1, while the area of hair cell precursors did not express either Notch1 and Jag1. During initial events of hair cell differentiation between E18 and birth, Notch1 and Jag1 expression predominated in supporting cells and Jag2 in nascent hair cells. Early after birth, Jag2 expression decreased in hair cells while the pattern of Notch1 expression now included both supporting cells and hair cells. We show that the normal pattern of hair cell differentiation is disrupted by alteration of Notch signaling. A decrease of either Notch1 or Jag1 expression by antisense oligonucleotides in cultures of the developing sensory epithelium resulted in an increase in the number of hair cells. Our data suggest that the Notch1 signaling pathway is involved in a complex interplay between the consequences of different ligand-Notch1 combinations during cochlear morphogenesis and the phases of hair cell differentiation.

Animals↗

PubMed1998

Caspase inhibitors prevent cisplatin-induced apoptosis of auditory sensory cells.

In vitro studies tested the efficacy of three caspase inhibitors, Ac-VAD-cmk (caspase-1 inhibitor), z-DEVD-fmk (caspase-3 inhibitor) and B-D-fmk (BOCDFK, a general inhibitor), for protecting auditory sensory cells from cisplatin-damage induced loss. Treatment of 3-day-old rat organ of Corti explants with these caspase inhibitors protected > 80% of the auditory hair cells from cisplatin-damage initiated apoptosis. Dissociated cell cultures of 3-day-old rat spinal ganglia treated with any of these three caspase inhibitors in addition to exogenous neurotrophin have highly significant increases in neuronal survival following cisplatin exposure. These results indicate that loss of auditory sensory cells as a result of cisplatin-induced damage involves apoptosis and that blocking of this cell death pathway at the caspase level effectively rescues both hair cells and neurons.

Animals↗

PubMed1998

Brain-derived neurotrophic factor gene therapy prevents spiral ganglion degeneration after hair cell loss.

Destruction of auditory hair cells results in the secondary degeneration of auditory neurons. This is because of the loss of neurotrophic factor support from the auditory hair cells, namely neurotrophin 3, which is normally produced by the inner hair cells. Both in vitro and in vivo studies have shown that delivery of either neurotrophin 3 or brain-derived neurotrophic factor to these neurons can replace the trophic support supplied by the hair cells and prevent their degeneration. To prevent the degeneration of auditory neurons that occurs after neomycin destruction of the auditory hair cells we used a replication defective herpes simplex-1 vector (HSVbdnflac) to transfect the gene for brain-derived neurotrophic factor into the damaged spiral ganglion. Four weeks after the HSVbdnflac therapy we were able to detect stable functional production of brain-derived neurotrophic factor that supported the survival of auditory neurons and prevented the loss of these neurons because of trophic factor deprivation-induced apoptosis.

Animals↗

PubMed1998

Changes in cochlear antioxidant enzyme activity after sound conditioning and noise exposure in the chinchilla.

Exposure to low level noise prior to a high level exposure reduces noise-induced hearing loss in mammals. This phenomenon is known as sound conditioning or 'toughening'. Reactive oxygen intermediates have been implicated in noise-induced cochlear damage. To evaluate if in situ antioxidant processes may play a role in the toughening phenomenon initiated by low level noise exposure we analyzed glutathione reductase, gamma-glutamyl cysteine synthetase, and catalase in stria vascularis and organ of Corti fractions from cochleae of chinchillas exposed to a sound conditioning paradigm. Chinchillas were either (A) kept in quiet cages (control), (B) exposed to conditioning noise of a 0.5 kHz octave band (90 dB for 6 h/day for 10 days), (C) exposed to high level noise (105 dB for 4 h) or (D) exposed to conditioning noise (B) followed by exposure to the higher level noise (C). Each of the noise exposure conditions (B, C, D) induced changes in the levels of these three antioxidant enzymes. The enzyme-specific activity data for the four subject groups support the following two hypotheses. (1) Changes in glutathione reductase, gamma-glutamyl cysteine synthetase, and catalase play a role in attenuating hearing loss associated with sound conditioning followed by high level noise. (2) Hair cells in the organ of Corti are protected from noise-induced damage by increasing stria vascularis levels of catalase, a hydrogen peroxide scavenging enzyme, and of enzymes involved in maintaining glutathione in the reduced state. The model formulated by these hypotheses suggests that agents that protect or augment the glutathione system in the cochlea may be protective against noise-induced hearing loss.

Acoustic Stimulation↗

PubMed1998

Factors controlling hair-cell regeneration/repair in the inner ear.

Damaged hair cells in the avian basilar papilla are replaced by regenerative proliferation of supporting cells and transdifferentiation of supporting cells into hair cells. In the mammalian vestibular system, transdifferentiation and, possibly, the repair of damaged hair cells appear to play significant roles. Several growth factors have been found to be associated with the regeneration/repair process: insulin, insulin-like growth factor 1 (IGF-1), and fibroblast growth factors are important for avian inner ear regeneration/repair, whereas epidermal growth factor, transforming growth factor alpha, insulin, IGF-1, and IGF-2 are important for regeneration/repair in the mammalian labyrinth. Increasing evidence suggests that regeneration/repair of mammalian auditory hair cells is possible during the early neonatal period and may exist to a very limited degree at later times.

Animals↗