Regulation of mitochondrial uncoupling proteins in mouse inner ear ganglion cells in response to systemic kanamycin challenge

Noise Stress Abrogates Structure-Specific Endonucleases within the Mammalian Inner Ear

Nucleotide excision repair (NER) is a multistep biochemical process that maintains the integrity of the genome. Unlike other mechanisms that maintain genomic integrity, NER is distinguished by two irreversible nucleolytic events that are executed by the xeroderma pigmentosum group G (XPG) and xeroderma pigmentosum group F (XPF) structure-specific endonucleases. Beyond nucleolysis, XPG and XPF regulate the overall efficiency of NER through various protein-protein interactions. The current experiments evaluated whether an environmental stressor could negatively affect the expression of Xpg (Ercc5: excision repair cross-complementing 5) or Xpf (Ercc4: excision repair cross-complementing 4) in the mammalian cochlea. Ubiquitous background noise was used as an environmental stressor. Gene expression levels for Xpg and Xpf were quantified from the cochlear neurosensory epithelium after noise exposure. Further, nonlinear cochlear signal processing was investigated as a functional consequence of changes in endonuclease expression levels. Exposure to stressful background noise abrogated the expression of both Xpg and Xpf, and these effects were associated with pathological nonlinear signal processing from receptor cells within the mammalian inner ear. Given that exposure to environmental sounds (noise, music, etc.) is ubiquitous in daily life, sound-induced limitations to structure-specific endonucleases might represent an overlooked genomic threat.

Mitochondrial Uncoupling Proteins (UCPs) as Key Modulators of ROS Homeostasis: A Crosstalk between Diabesity and Male Infertility?

Uncoupling proteins (UCPs) are transmembrane proteins members of the mitochondrial anion transporter family present in the mitochondrial inner membrane. Currently, six homologs have been identified (UCP1-6) in mammals, with ubiquitous tissue distribution and multiple physiological functions. UCPs are regulators of key events for cellular bioenergetic metabolism, such as membrane potential, metabolic efficiency, and energy dissipation also functioning as pivotal modulators of ROS production and general cellular redox state. UCPs can act as proton channels, leading to proton re-entry the mitochondrial matrix from the intermembrane space and thus collapsing the proton gradient and decreasing the membrane potential. Each homolog exhibits its specific functions, from thermogenesis to regulation of ROS production. The expression and function of UCPs are intimately linked to diabesity, with their dysregulation/dysfunction not only associated to diabesity onset, but also by exacerbating oxidative stress-related damage. Male infertility is one of the most overlooked diabesity-related comorbidities, where high oxidative stress takes a major role. In this review, we discuss in detail the expression and function of the different UCP homologs. In addition, the role of UCPs as key regulators of ROS production and redox homeostasis, as well as their influence on the pathophysiology of diabesity and potential role on diabesity-induced male infertility is debated.

An Integrated LC-MS/MS Strategy for Quantifying the Oxidative-Redox Metabolome in Multiple Biological Samples

The cellular redox balance plays a significant role in cell fate decisions and in the regulation of responses to various kinds of stress. In this study, we defined a novel concept of the oxidative-redox metabolome, and established a method for the simultaneous quantification of 23 metabolites involved in the oxidative-redox metabolome, covering NAD⁺ pathway, FAD pathway, GSSG pathway, and ATP pathway by using the AB SCIEX 5500 QTRAP LC/MS/MS system. Corresponding oxidative-redox metabolomics analysis was performed in plasma of humans, hamsters and mice, and hamsters were demonstrated to display a stronger resemblance than mice to humans. The known reductant dithiothreitol (DTT) and oxidant hydrogen peroxide (H₂O₂) were selected to treat A549 and HeLa cells to validate the current method, showing that DTT moderately increased while H₂O₂ greatly decreased most analytes. Antibiotic treatment may disturb the oxidative-redox balance in vivo. By comparing the oxidative-redox metabolome in antibiotic-fed hamsters with that of control hamsters, we demonstrated a substantial metabolic disparity between the two, further verifying the applicability and reliability of our method.

The Novel Peptide Vaccine GV1001 Protects Hearing in a Kanamycin-induced Ototoxicity Mouse Model

HYPOTHESIS

We tested whether GV1001 has any ototoxic side effects at different doses and whether it protects hearing in an aminoglycoside-induced ototoxicity mouse model.

BACKGROUND

GV1001, a novel peptide vaccine currently being examined in a Phase 3 clinical trial to treat pancreatic cancer, also has anti-inflammatory and antioxidant effects.

METHODS

In the first experiment, C57/BL6 mice were injected with GV1001 preparations at concentrations of 0.1 to 100 mg/kg for 7 days to evaluate the toxicity of GV1001 on the inner ear and kidneys. In the second experiment, the protective effect of GV1001 was tested in an ototoxicity mouse model that was generated by injecting 800 mg/kg kanamycin (KM) for 2 weeks. The hearing threshold and hair cell loss were compared between the KM + GV1001 group (treated with 10 mg/kg GV1001 for 2 wk) and the KM + saline group. The hearing threshold was measured before, and 7, 14, and 21 days after the initial treatment. The blood urea nitrogen level was measured.

RESULTS

No ototoxicity or renal toxicity was found following treatment with different doses of GV1001 (0.1-100 mg/kg). The KM + saline group showed impaired auditory function and markedly disoriented and missing cochlear hair cells, while the KM + GV1001 group showed significant hearing and hair cell preservation in comparison (p < 0.05).

CONCLUSION

GV1001 itself did not have any detrimental effects on the inner ear or kidney. In the KM induced ototoxicity model, concomitant administration of GV1001 protected against cochlear hair cell damage and preserve hearing.

Association between Uncoupling Protein 2 Gene Ala55val Polymorphism and Sudden Sensorineural Hearing Loss

OBJECTIVES

The pathology of sudden sensorineural hearing loss, which is known as sudden deafness (SD), remains unknown. The purpose of this study was to investigate the association between mitochondrial uncoupling protein 2 (UCP2) polymorphism and SD risk.

MATERIALS AND METHODS

We compared 83 patients suffering from SD and 2048 controls who participated in the Longitudinal Study of Aging at the National Institute for Longevity Sciences. Multiple logistic regression was used to calculate the odds ratios (ORs) for SD with a polymorphism of the UCP2 (rs660339) gene.

RESULTS

Under the additive model of inheritance, UCP2 polymorphisms showed significant association with a SD risk. The OR was 1.468 (95% confidence interval, 1.056-2.040) with an adjustment for any past history, such as diabetes, dyslipidemia, or hypertension, and for age and sex.

CONCLUSION

Our results imply that the UCP2 (rs660339) polymorphism has a significant association with the risk of developing SD.

Deficit of mitogen-activated protein kinase phosphatase 1 (DUSP1) accelerates progressive hearing loss

Mitogen-activated protein kinases (MAPK) such as p38 and the c-Jun N-terminal kinases (JNKs) are activated during the cellular response to stress signals. Their activity is regulated by the MAPK-phosphatase 1 (DUSP1), a key component of the anti-inflammatory response. Stress kinases are well-described elements of the response to otic injury and the otoprotective potential of JNK inhibitors is being tested in clinical trials. By contrast, there are no studies exploring the role of DUSP1 in hearing and hearing loss. Here we show that Dusp1 expression is age-regulated in the mouse cochlea. Dusp1 gene knock-out caused premature progressive hearing loss, as confirmed by auditory evoked responses in Dusp1^-/- mice. Hearing loss correlated with cell death in hair cells, degeneration of spiral neurons and increased macrophage infiltration. Dusp1^-/- mouse cochleae showed imbalanced redox status and dysregulated expression of cytokines. These data suggest that DUSP1 is essential for cochlear homeostasis in the response to stress during ageing.

Novel Peptide Vaccine GV1001 Rescues Hearing in Kanamycin/Furosemide-Treated Mice

The cell-penetrating peptide GV1001 has been investigated as an anticancer agent and recently demonstrated anti-oxidant and anti-inflammatory effects. It has shown a protective effect on a kanamycin (KM)-induced ototoxicity mouse model. In the present study, we administered GV1001 at different time points after inducing hair cell damage, and examined if it rescues hair cell loss and restores hearing. A deaf mouse model was created by intraperitoneal injection of KM and furosemide. First, to test the early temporal change of hearing and extent of hair cell damage after KM and furosemide injection, hearing and outer hair cells (OHCs) morphology were evaluated on day 1, day 2 and day 3 after injection. In the second experiment, following KM and furosemide injection, GV1001, dexamethasone, or saline were given for three consecutive days at different time points: D0 group (days 0, 1, and 2), D1 group (days 1, 2, and 3), D3 group (days 3, 4, and 5) and D7 group (days 7, 8, and 9). The hearing thresholds were measured at 8, 16, and 32 kHz before ototoxic insult, and 7 days and 14 days after KM and furosemide injection. After 14 days, each turn of the cochlea was imaged to evaluate OHCs damage. GV1001-treated mice showed significantly less hearing loss and OHCs damage than the saline control group in the D0, D1 and D3 groups (p < 0.0167). However, there was no hearing restoration or intact hair cell in the D7 group. GV1001 protected against cochlear hair cell damage, and furthermore, delayed administration of GV1001 up to 3 days rescued hair cell damage and hearing loss in KM/furosemide-induced deaf mouse model.

Noise Stress Induces an Epidermal Growth Factor Receptor/Xeroderma Pigmentosum-A Response in the Auditory Nerve

In response to toxic stressors, cancer cells defend themselves by mobilizing one or more epidermal growth factor receptor (EGFR) cascades that employ xeroderma pigmentosum-A (XPA) to repair damaged genes. Recent experiments discovered that neurons within the auditory nerve exhibit basal levels of EGFR+XPA co-expression. This finding implied that auditory neurons in particular or neurons in general have the capacity to mobilize an EGFR+XPA defense. Therefore, the current study tested the hypothesis that noise stress would alter the expression pattern of EGFR/XPA within the auditory nerve. Design-based stereology was used to quantify the proportion of neurons that expressed EGFR, XPA, and EGFR+XPA with and without noise stress. The results revealed an intricate neuronal response that is suggestive of alterations to both co-expression and individual expression of EGFR and XPA. In both the apical and middle cochlear coils, the noise stress depleted EGFR+XPA expression. Furthermore, there was a reduction in the proportion of neurons that expressed XPA-alone in the middle coils. However, the noise stress caused a significant increase in the proportion of neurons that expressed EGFR-alone in the middle coils. The basal cochlear coils failed to mobilize a significant response to the noise stress. These results suggest that EGFR and XPA might be part of the molecular defense repertoire of the auditory nerve.

[Correction of pathological conditions associated with insulin-resistant hyperglycaemia]

High level of glucose in the blood in hypoxic-ischemic states is one of the main factors that complicates the degree of brain damage. An increased level of reactive oxygen species and impaired functioning of the endogenous antioxidant system are the consequences of the hyperglycemic-ischemic condition. Medical treatment is necessary to compensate for the development of cerebrovascular disorders in ischemia comorbid to diabetes mellitus. The use of antioxidants (2-ethyl-6-methyl-3-hydroxypyridine succinate) is the most therapeutically effective.

Neurotransmitters in the vestibular system

Neuronal networks that are linked to the peripheral vestibular system contribute to gravitoinertial sensation, balance control, eye movement control, and autonomic function. Ascending connections to the limbic system and cerebral cortex are also important for motion perception and threat recognition, and play a role in comorbid balance and anxiety disorders. The vestibular system also shows remarkable plasticity, termed vestibular compensation. Activity in these networks is regulated by an interaction between: (1) intrinsic neurotransmitters of the inner ear, vestibular nerve, and vestibular nuclei; (2) neurotransmitters associated with thalamocortical and limbic pathways that receive projections originating in the vestibular nuclei; and (3) locus coeruleus and raphe (serotonergic and nonserotonergic) projections that influence the latter components. Because the ascending vestibular interoceptive and thalamocortical pathways include networks that influence a broad range of stress responses (endocrine and autonomic), memory consolidation, and cognitive functions, common transmitter substrates provide a basis for understanding features of acute and chronic vestibular disorders.

Localization and distribution of neurons that co-express xeroderma pigmentosum-A and epidermal growth factor receptor within Rosenthal's canal

Xeroderma pigmentosum-A (XPA) is a C4-type zinc-finger scaffolding protein that regulates the removal of bulky-helix distorting DNA damage products from the genome. Phosphorylation of serine residues within the XPA protein is associated with improved protection of genomic DNA and cell death resistance. Therefore, kinase signaling is one important mechanism for regulating the protective function of XPA. Previous experiments have shown that spiral ganglion neurons (SGNs) may mobilize XPA as a general stress response to chemical and physical ototoxicants. Therapeutic optimization of XPA via kinase signaling could serve as a means to improve DNA repair capacity within neurons following injury. The kinase signaling activity of the epidermal growth factor receptor (EGFR) has been shown in tumor cell lines to increase the repair of DNA damage products that are primarily repaired by XPA. Such observations suggest that EGFR may regulate the protective function of XPA. However, it is not known whether SGNs in particular or neurons in general could co-express XPA and EGFR. In the current study gene and protein expression of XPA and EGFR were determined from cochlear homogenates. Immunofluorescence assays were then employed to localize neurons expressing both EGFR and XPA within the ganglion. This work was then confirmed with double-immunohistochemistry. Rosenthal's canal served as the reference space in these experiments and design-based stereology was employed in first-order stereology quantification of immunoreactive neurons. The results confirmed that a population of SGNs that constitutively express XPA may also express the EGFR. These results provide the basis for future experiments designed to therapeutically manipulate the EGFR in order to regulate XPA activity and restore gene function in neurons following DNA damage.

Comparative gene expression study of the vestibular organ of the Igf1 deficient mouse using whole-transcript arrays

The auditory and vestibular organs form the inner ear and have a common developmental origin. Insulin like growth factor 1 (IGF-1) has a central role in the development of the cochlea and maintenance of hearing. Its deficiency causes sensorineural hearing loss in man and mice. During chicken early development, IGF-1 modulates neurogenesis of the cochleovestibular ganglion but no further studies have been conducted to explore the potential role of IGF-1 in the vestibular system. In this study we have compared the whole transcriptome of the vestibular organ from wild type and Igf1(-/-) mice at different developmental and postnatal times. RNA was prepared from E18.5, P15 and P90 vestibular organs of Igf1(-/-) and Igf1(+/+) mice and the transcriptome analysed in triplicates using Affymetrix(®) Mouse Gene 1.1 ST Array Plates. These plates are whole-transcript arrays that include probes to measure both messenger (mRNA) and long intergenic non-coding RNA transcripts (lincRNA), with a coverage of over 28 thousand coding transcripts and over 7 thousands non-coding transcripts. Given the complexity of the data we used two different methods VSN-RMA and mmBGX to analyse and compare the data. This is to better evaluate the number of false positives and to quantify uncertainty of low signals. We identified a number of differentially expressed genes that we described using functional analysis and validated using RT-qPCR. The morphology of the vestibular organ did not show differences between genotypes and no evident alterations were observed in the vestibular sensory areas of the null mice. However, well-defined cellular alterations were found in the vestibular neurons with respect their number and size. Although these mice did not show a dramatic vestibular phenotype, we conducted a functional analysis on differentially expressed genes between genotypes and across time. This was with the aim to identify new pathways that are involved in the development of the vestibular organ as well as pathways that maybe affected by the lack of IGF-1 and be associated to the morphological changes of the vestibular neurons that we observed in the Igf1(-/-) mice.

D‑galactose‑induced mitochondrial DNA oxidative damage in the auditory cortex of rats

Chronic administration of D-galactose (D-gal) is a useful method for establishing a model of natural aging in the auditory system. Previous studies have demonstrated that NADPH oxidases (NOXs) may be an important source of reactive oxygen species (ROS) in the peripheral auditory system (PAS) and cause an increase in mitochondrial DNA (mtDNA) common deletion (CD) levels in the PAS and central auditory system (CAS) of rats with D-gal-induced aging. However, the source of the ROS in the CAS and the mechanisms of age-related hearing loss (ARHL) have yet to be elucidated. In the present study, male Sprague Dawley rats were administered a daily injection of D-gal (150, 300 and 500 mg/kg, respectively) for eight weeks. All three doses of D-gal caused a significant increase in the expression of NOX2, 8-hydroxy-2-deoxyguanosine, a biomarker of DNA oxidative damage, and uncoupling protein 2, together with a decrease in the mitochondrial total antioxidant capabilities in the auditory cortex, as compared with the control rats (injected daily with the same volume of 0.9% saline for eight weeks). The levels of the mtDNA CD were also increased in the auditory cortex of the D-gal-induced aging rats. These findings suggest that both NOX- and mitochondria-associated ROS generation may contribute to mtDNA oxidative damage in the auditory cortex of the CAS of D-gal-induced aging rats. This study may provide novel insight into the development of ARHL.

Vestibular damage in chronic ototoxicity: a mini-review

Ototoxicity is a major cause of the loss of hearing and balance in humans. Ototoxic compounds include pharmaceuticals such as aminoglycoside antibiotics, anti-malarial drugs, loop diuretics and chemotherapeutic platinum agents, and industrial chemicals including several solvents and nitriles. Human and rodent data indicate that the main target of toxicity is hair cells (HCs), which are the mechanosensory cells responsible for sensory transduction in both the auditory and the vestibular system. Nevertheless, the compounds may also affect the auditory and vestibular ganglion neurons. Exposure to ototoxic compounds has been found to cause HC apoptosis, HC necrosis, and damage to the afferent terminals, of differing severity depending on the ototoxicity model. One major pathway frequently involved in HC apoptosis is the c-jun N-terminal kinase (JNK) signaling pathway activated by reactive oxygen species, but other apoptotic pathways can also play a role in ototoxicity. Moreover, little is known about the effects of chronic low-dose exposure. In rodent vestibular epithelia, extrusion of live HCs from the sensory epithelium may be the predominant form of cell demise during chronic ototoxicity. In addition, greater involvement of the afferent terminals may occur, particularly the calyx units contacting type I vestibular HCs. As glutamate is the neurotransmitter in this synapse, excitotoxic phenomena may participate in afferent and ganglion neuron damage. Better knowledge of the events that take place in chronic ototoxicity is of great interest, as it will increase understanding of the sensory loss associated with chronic exposure and aging.

Mitochondria of trained skeletal muscle are protected from deleterious effects of statins

INTRODUCTION

Statins are associated with adverse skeletal muscle effects. Our objective was to determine if muscular adaptations following exercise training prevented deleterious effects of atorvastatin in glycolytic skeletal muscle.

METHODS

Twenty rats were divided into 2 groups: a control group (n = 10; Cont) and a 10 days of training group (n = 10; Training). Using the permeabilized fibers technique, we explored mitochondrial function.

RESULTS

Exercise training increased V(max) and H(2)O(2) production without altering the free radical leak, and mRNA expression of SOD2 and Cox1 were higher in trained muscle. In the Cont group, atorvastatin exposure increased H(2)O(2) production and decreased skeletal muscle V(max). The decreased V(max) effect of atorvastatin was dose dependent. Interestingly, the half-maximal inhibitory concentration (IC(50)) was higher in the Training group. H(2)O(2) production increased in trained muscle after atorvastatin exposure.

CONCLUSIONS

These results suggest that improvements in mitochondrial respiratory and antioxidant capacities following endurance training protected mitochondria against statin exposure.

Molecular genetic epidemiology of age-related hearing impairment

Genetic epidemiology focuses on the genetic determinants in the etiology of disease among populations and seeks to elucidate the role of genetic factors and their interaction with environmental factors in disease occurrence. In recent years, genetic epidemiological research has become more focused on complex diseases, and human genome analysis technology has made remarkable advances. Age-related hearing impairment (ARHI) is a complex trait, which results from a multitude of confounding intrinsic and extrinsic factors. Although the number of genetic investigations of ARHI is increasing at a surprising rate, the etiology of ARHI is not firmly established. In this article, we review (1) the methodological strategies used to analyze genetic factors that contribute to human ARHI, (2) several representative investigations, and (3) specific genetic risk factors for human ARHI identified in previous work.

Role of mitochondrial uncoupling protein 4 in rat inner ear

The uncoupling protein 4 (UCP4) belongs to the mitochondrial anion transporter family. Protein tissue distribution and functions are still a matter of debate. Using an antibody we have previously shown that UCP4 appears in neurons and to a lesser extent in astrocytes of murine neuronal tissue as early as days 12-14 of embryonic development (Smorodchenko et al., 2009). Here we demonstrated for the first time that neurosensory cells such as hair cells of the inner ear and mechanosensitive Merkel cells in skin also express a significant amount of UCP4. We tested the hypothesis about whether UCP4 contributes to the regulation of oxidative stress using the model of oxygen deprivation. For this we compared the protein expression level in freshly isolated explants of organ of Corti, modiolus and stria vascularis from neonatal rats with explants cultured under hypoxia. Western blot analysis revealed that the UCP4 level was not increased under hypoxic conditions, when compared to the mitochondrial outer membrane protein VDAC or to the anti-oxidative enzyme SOD2. We moreover demonstrated that UCP4 expression is differently regulated during postnatal stages and is region-specific. We hypothesized that UCP4 may play an important role in functional maturation of the rat inner ear.

The association between gene polymorphisms in uncoupling proteins and hearing impairment in Japanese elderly

CONCLUSION

This study illustrates that UCP2 Ala55Val polymorphisms exhibit a significant association with age-related hearing loss in the Japanese population.

OBJECTIVES

Mitochondrial uncoupling proteins (UCPs) have been suggested to play a protective role against neuron oxidative damage and a thermal signaling role in neuron modulation in the inner ear. In the current study, we examined the relationship between gene polymorphisms in UCP1 and UCP2 and hearing impairment (HI) in Japanese elderly.

METHODS

A total of 1547 subjects aged 40-79 years and living in Aichi prefecture, Japan, were entered into this study. Subjects were followed up every 2 years, and the cumulative number of subjects for 3 sequential examinations in 6 years was 4942 persons. Detailed questionnaires, pure-tone audiometry measurements, and UCP1 A-3826G and UCP2 Ala55Val polymorphisms were examined. Using generalized estimating equations, associations between HI and gene polymorphisms in UCP1 and UCP2 with age, sex, history of occupational noise exposure, and body mass index were analyzed under dominant, recessive, and additive models.

RESULTS

UCP1 A-3826G polymorphism did not exhibit any significant association with HI. However, UCP2 Ala55Val polymorphism did exhibit a significant association with HI under all the dominant (p = 0.0167), recessive (p = 0.0411), and additive (p = 0.0061) models.

Comparison of different aminoglycoside antibiotic treatments to refine ototoxicity studies in adult mice

Hearing and balance receptors in the inner ear are highly susceptible to damage caused by a wide variety of toxic substances, including aminoglycosides. This class of antibiotics is commonly used in medicine, even though they may produce irreversible bilateral neurosensorial deafness. To identify potential ototoxic agents and novel therapeutic targets, it is necessary to generate standardized animal models of aminoglycoside ototoxicity, which will also serve to explore otic cell repair and regeneration. Although the mouse is the species most often used in biomedical research, due to the genetic information and genetically-modified strains available, there are few standard models of aminoglycoside ototoxicity in adult mice. Most protocols to produce ototoxicity in adult mice employ high doses of aminoglycosides for long periods of time, which causes systemic toxicity, side-effects and high mortality rates. Here, we compare the effects of systemic treatment with four different, yet common, aminoglycoside antibiotics in two mouse strains, evaluating their effects on mortality, cochlear morphology and auditory brainstem responses. Our data indicate that gentamicin and neomycin caused high mortality in the adult mouse without significantly changing the auditory threshold. Amikacin produced a tolerable rate of mortality but at doses that did not exhibit ototoxicity. Finally, intramuscular injection of kanamycin in C57BL/6JOlaHsd mice induced significant dose-dependent bilateral hearing loss with a moderate rate of mortality and less discomfort than following subcutaneous administration.

A protein interaction network for the large conductance Ca(2+)-activated K(+) channel in the mouse cochlea

The large conductance Ca(2+)-activated K(+) or BK channel has a role in sensory/neuronal excitation, intracellular signaling, and metabolism. In the non-mammalian cochlea, the onset of BK during development correlates with increased hearing sensitivity and underlies frequency tuning in non-mammals, whereas its role is less clear in mammalian hearing. To gain insights into BK function in mammals, coimmunoprecipitation and two-dimensional PAGE, combined with mass spectrometry, were used to reveal 174 putative BKAPs from cytoplasmic and membrane/cytoskeletal fractions of mouse cochlea. Eleven BKAPs were verified using reciprocal coimmunoprecipitation, including annexin, apolipoprotein, calmodulin, hippocalcin, and myelin P0, among others. These proteins were immunocolocalized with BK in sensory and neuronal cells. A bioinformatics approach was used to mine databases to reveal binary partners and the resultant protein network, as well as to determine previous ion channel affiliations, subcellular localization, and cellular processes. The search for binary partners using the IntAct molecular interaction database produced a putative global network of 160 nodes connected with 188 edges that contained 12 major hubs. Additional mining of databases revealed that more than 50% of primary BKAPs had prior affiliations with K(+) and Ca(2+) channels. Although a majority of BKAPs are found in either the cytoplasm or membrane and contribute to cellular processes that primarily involve metabolism (30.5%) and trafficking/scaffolding (23.6%), at least 20% are mitochondrial-related. Among the BKAPs are chaperonins such as calreticulin, GRP78, and HSP60 that, when reduced with siRNAs, alter BKalpha expression in CHO cells. Studies of BKalpha in mitochondria revealed compartmentalization in sensory cells, whereas heterologous expression of a BK-DEC splice variant cloned from cochlea revealed a BK mitochondrial candidate. The studies described herein provide insights into BK-related functions that include not only cell excitation, but also cell signaling and apoptosis, and involve proteins concerned with Ca(2+) regulation, structure, and hearing loss.

Comparative analysis of uncoupling protein 4 distribution in various tissues under physiological conditions and during development

UCP4 is a member of the mitochondrial uncoupling protein subfamily and one of the three UCPs (UCP2, UCP4, UCP5), associated with the nervous system. Its putative functions include thermogenesis, attenuation of reactive oxidative species (ROS), regulation of mitochondrial calcium concentration and involvement in cell differentiation and apoptosis. Here we investigate UCP4's subcellular, cellular and tissue distribution, using an antibody designed specially for this study, and discuss the findings in terms of the protein's possible functions. Western blot and immunohistochemistry data confirmed that UCP4 is expressed predominantly in the central nervous system (CNS), as previously shown at mRNA level. No protein was found in heart, spleen, stomach, intestine, lung, thymus, muscles, adrenal gland, testis and liver. The reports revealing UCP4 mRNA in kidney and white adipose tissue were not confirmed at protein level. The amount of UCP4 varies in the mitochondria of different brain regions, with the highest protein content found in cortex. We show that UCP4 is present in fetal murine brain tissue as early as embryonic days 12-14 (E12-E14), which coincides with the beginning of neuronal differentiation. The UCP4 content in mitochondria decreases as the age of mice increases. UCP4 preferential expression in neurons and its developmental expression pattern under physiological conditions may indicate a specific protein function, e.g. in neuronal cell differentiation.

Apoptosis-related genes change their expression with age and hearing loss in the mouse cochlea

To understand possible causative roles of apoptosis gene regulation in age-related hearing loss (presbycusis), apoptotic gene expression patterns in the CBA mouse cochlea of four different age and hearing loss groups were compared, using GeneChip and real-time (qPCR) microarrays. GeneChip transcriptional expression patterns of 318 apoptosis-related genes were analyzed. Thirty eight probes (35 genes) showed significant differences in expression. The significant gene families include Caspases, B-cell leukemia/lymphoma2 family, P53, Calpains, Mitogen activated protein kinase family, Jun oncogene, Nuclear factor of kappa light chain gene enhancer in B-cells inhibitor-related and tumor necrosis factor-related genes. The GeneChip results of 31 genes were validated using the new TaqMan Low Density Array (TLDA). Eight genes showed highly correlated results with the GeneChip data. These genes are: activating transcription factor3, B-cell leukemia/lymphoma2, Bcl2-like1, caspase4 apoptosis-related cysteine protease 4, Calpain2, dual specificity phosphatase9, tumor necrosis factor receptor superfamily member12a, and Tumor necrosis factor superfamily member13b, suggesting they may play critical roles in inner ear aging.

Rapid identification of PAX2/5/8 direct downstream targets in the otic vesicle by combinatorial use of bioinformatics tools

A novel bioinformatics pipeline is used to discover PAX2/5/8 direct downstream targets involved in inner ear development.

Background

The pax2/5/8 genes belonging to the PAX family of transcription factors are key developmental regulators that are involved in the patterning of various embryonic tissues. More particularly, their function in inner ear specification has been widely described. However, little is known about the direct downstream targets and, so far, no global approaches have been performed to identify these target genes in this particular tissue.

Results

Here we present an original bioinformatics pipeline composed of comparative genomics, database querying and text mining tools, which is designed to rapidly and specifically discover PAX2/5/8 direct downstream targets involved in inner ear development. We provide evidence supported by experimental validation in medaka fish that brain 2 (POU domain, class 3, transcription factor 2), claudin-7, secretory pathway component sec31-like and meteorin-like precursor are novel direct downstream targets of PAX2/5/8.

Conclusions

This study illustrates the power of extensive mining of public data repositories using bioinformatics methods to provide answers for a specific biological question. It furthermore demonstrates how the usage of such a combinatorial approach is advantageous for the biologist in terms of experimentation time and costs.

Ototoxicity and noise trauma: electron transfer, reactive oxygen species, cell signaling, electrical effects, and protection by antioxidants: practical medical aspects

Ototoxins are substances of various structures and classes. This review provides extensive evidence for involvement of electron transfer (ET), reactive oxygen species (ROS) and oxidative stress (OS) as a unifying theme. Successful application is made to the large majority of ototoxins, as well as noise trauma. We believe it is not coincidental that these toxins generally incorporate ET functionalities (quinone, metal complex, ArNO(2), or conjugated iminium) either per se or in metabolites, potentially giving rise to ROS by redox cycling. Some categories, e.g., peroxides and noise, appear to operate via non-ET routes in generating OS. These highly reactive entities can then inflict injury via OS upon various constituents of the ear apparatus. The theoretical framework is supported by the extensive literature on beneficial effects of antioxidants, both for toxins and noise. Involvement of cell signaling and electrical effects are discussed. This review is the first comprehensive one based on a unified mechanistic approach. Various practical medical aspects are also addressed. There is extensive documentation for beneficial effects of antioxidants whose use might be recommended clinically for prevention of ototoxicity and noise trauma. Recent research indicates that catalytic antioxidants may be more effective. In addition to ototoxicity, a widespread problem consists of ear infections by bacteria which are demonstrating increasing resistance to conventional therapies. A recent, novel approach to improved drugs involves use of agents which inhibit quorum sensors that play important roles in bacterial functioning. Prevention of ear injury by noise trauma is also discussed, along with ear therapeutics.

Gene expression profiling in the remnant kidney model of wild type and kinin B1 and B2 receptor knockout mice

Angiotensin-converting enzyme inhibitors are the most efficient pharmacologic agents to delay the development of end-stage renal disease (ESRD). This is a multipharmacologic approach that inhibits angiotensin II formation while increasing kinin concentrations. Considerable attention has been focused on the role of decreased angiotensin II levels; however, the role of increased kinin levels is gaining in interest. Kinins affect cellular physiology by interacting with one of two receptors being the more inducible B1 and the more constitutive B2 receptors. This study utilizes the mouse remnant kidney of 20 weeks duration as a model of ESRD. Whole mouse genome microarrays were used to evaluate gene expression in the remnant kidneys of wild type, B1 and B2 receptor knockout animals. The microarray data indicate that gene families involved in vascular damage, inflammation, fibrosis, and proteinuria were upregulated, whereas gene families involved in cell growth, metabolism, lipid, and protein biosynthesis were downregulated in the remnant kidneys. Interestingly, the microarray analyses coupled to histological evaluations are suggestive of a possible protective role of kinins operating through the B2 receptor subtype in this model of renal disease. The results highlight the potential of microarray technology for unraveling complex mechanisms contributing to chronic renal failure.

Changes in mitochondrial uncoupling protein expression in the rat vestibular nerve after labyrinthectomy

In the present study, to elucidate the role of mitochondrial uncoupling proteins (UCPs) in inner ear, we examined quantitative changes in the mRNA expression in vestibular ganglion (VG) after unilateral labyrinthectomy (UL) in rats. Using real-time PCR methods, UCP2, 3 and 4 mRNA expressions in the ipsilateral VG were significantly up-regulated with the maximum increase at the post-operative 1 day and all but UCP2 returned to the control level 1 week after UL. UCP2 mRNA expression was significantly up-regulated even 4 weeks after UL. Only UCP2 mRNA expression in the contralateral VG was gradually up-regulated between 1 and 4 weeks after UL. According to previous reports, UCP2 and 3 as well as UCP1 were thermogenic in yeast and brain UCP2 was suggested to modulate pre- and post-synaptic events by axonal thermogenesis. It was also reported that UCP1, 2 and 3 responses to superoxide application were an antioxidant protective mechanism. These findings suggest that mitochondrial UCPs could play both a neuro-protective role against oxidative damage and a thermal signaling role for neuro-modulation in vestibular nerve.

Gentamicin uptake in the chinchilla inner ear

Studies of transtympanic gentamicin have focused on clinical use and outcomes. This study presents evidence of bilateral uptake and retention of gentamicin in certain inner ear cells and structures following transtympanic gentamicin application. Middle ear application of gentamicin was performed by either minipump (Alza model, 2002) or transtympanic injection in a chinchilla model. Histological sections of decalcified temporal bones were stained to identify the distribution of gentamicin. Using both anti-gentamicin immunohistochemistry and autoradiography of tracer amounts of tritiated gentamicin, Scarpa's and spiral ganglion cells, stria vascularis, and vestibular dark cells of the injected ear were found to have higher levels of gentamicin and retain it within cell bodies while staining levels fell to background levels in the rest of the injected ear over the course of 14 days. There was no evidence of an apical to basal gradient of anti-gentamicin staining within the spiral ganglion. Contralateral inner ear cells showed light anti-gentamicin staining. Cell bodies in the ipsilateral dorsal cochlear nucleus bordering the cochlear aqueduct (CA) showed a lateral to medial gradient of gentamicin staining, suggesting the CA as a potential site of transfer of gentamicin to the contralateral ear. Direct effects of aminoglycosides on ganglion cells may have implications on both the success of cochlear implantation in patients deafened following systemic aminoglycoside therapy and on the advisability of clinical practices of transtympanic gentamicin therapy and ototopic aminoglycoside treatment.

Effect of intracochlear perfusion of vanilloids on cochlear neural activity in the guinea pig

Recent findings show that the vanilloid receptor subtype 1 (TRPV1) is expressed by cochlear outer hair cells and spiral ganglion cells, and that its expression is up-regulated in ganglion cells after aminoglycoside treatment. This study tested the hypothesis that agents that act on TRPV1 receptors affect the spectrum of ensemble background activity (EBA). Consecutive intracochlear perfusions of the TRPV1 agonist, capsaicin (CAP 0.1, 1, and 10 parts per million), as well as its antagonist capsazepine (CZP), were used to test effects of TRPV1 activation on EBA recorded from the cochlear base. Perfusion with CAP alone produced a dose-dependent increase of the 900-Hz peak ratio (power normalized re the overall spectrum) of the EBA. The CAP effect was attenuated during concurrent perfusion with CZP. These findings are consistent with the hypothesis that TRPV1 activation increases background activity of spiral ganglion cells and support a role of TRPV1 in gating spontaneous and evoked auditory nerve excitability.