c-Ret-mediated hearing loss in mice with Hirschsprung disease

Beneficial and adverse effects of dam construction in canal tannery wastewater effluent with a high content of chromium in Hazaribagh, Bangladesh

BACKGROUND

Blockage to divide downstream canals into upstream canals, into which tannery wastewater including a high concentration of trivalent chromium [Cr(III)] is directly discharged, has been constructed in Hazaribagh, a tannery built-up area in Bangladesh. However, there has been no study to verify the environmental significance of blockage construction for water pollution of Cr in nature.

METHODS

Consecutive fixed area monitoring for a total of 164 water samples collected outside and inside Hazaribagh from 2014 to 2023 was carried out to clarify the effects of stagnant and flowable canal water in the presence or absence of blockage on Cr(III) and hexavalent Cr [Cr(VI)] concentrations.

RESULTS

Since pollution of Cr(III) and Cr(VI) in Buriganga River (outside Hazaribagh) was not serious, this study then focused on their pollution in canal water (inside Hazaribagh) in the nonblockage period, blockage construction period and blockage destruction period. As expected, the mean Cr(III) concentration in downstream canal water samples in the blockage construction period was more than 98% lower than that in the upstream canal water samples in the same period, while the concentrations were comparable in downstream and upstream canal water samples in the nonblockage period and blockage destruction period. Unexpectedly, the mean concentration of Cr(VI) in the upstream canal water samples in the blockage construction period was 38.6-fold and 3.3-fold higher than that in the downstream canal water samples and the Cr(VI) guideline value by the US-EPA, respectively.

CONCLUSION

This study demonstrated for the first time not only a merit of decreased Cr(III) pollution but also a demerit of increased Cr(VI) pollution in stagnant water derived from blockage construction in natural environments. This bitter lesson obtained by the enclosure of Cr(III)-polluted water is globally applicable for water pollution of Cr(III), which is used in various industries including the leather industry.

Candidate Key Proteins in Tinnitus: A Bioinformatic Study of Synaptic Transmission in Spiral Ganglion Neurons

To study key proteins associated with changes in synaptic transmission in the spiral ganglion in tinnitus, we build three gene lists from the GeneCard database: 1. Perception of sound (PoS), 2. Acoustic stimulation (AcouStim), and 3. Tinnitus (Tin). Enrichment analysis by the DAVID database resulted in similar Gene Ontology (GO) terms for cellular components in all gene lists, reflecting synaptic structures known to be involved in auditory processing. The STRING protein-protein interaction (PPI) network and the Cytoscape data analyzer were used to identify the top two high-degree proteins (HDPs) and their high-score interaction proteins (HSIPs) identified by the combined score (CS) of the corresponding edges. The top two protein pairs (key proteins) for the PoS are BDNF-GDNF and OTOF-CACNA1D and for the AcouStim process BDNF-NTRK2 and TH-CALB1. The Tin process showed BDNF and NGF as HDPs, with high-score interactions with NTRK1 and NGFR at a comparable level. Compared to the PoS and AcouStim process, the number of HSIPs of key proteins (CS > 90. percentile) increases strongly in Tin. In the PoS and AcouStim networks, BDNF receptor signaling is the dominant pathway, and in the Tin network, the NGF-signaling pathway is of similar importance. Key proteins and their HSIPs are good indicators of biological processes and of signaling pathways characteristic for the normal hearing on the one hand and tinnitus on the other.

A review of the auditory-gut-brain axis

Hearing loss places a substantial burden on medical resources across the world and impacts quality of life for those affected. Further, it can occur peripherally and/or centrally. With many possible causes of hearing loss, there is scope for investigating the underlying mechanisms involved. Various signaling pathways connecting gut microbes and the brain (the gut-brain axis) have been identified and well established in a variety of diseases and disorders. However, the role of these pathways in providing links to other parts of the body has not been explored in much depth. Therefore, the aim of this review is to explore potential underlying mechanisms that connect the auditory system to the gut-brain axis. Using select keywords in PubMed, and additional hand-searching in google scholar, relevant studies were identified. In this review we summarize the key players in the auditory-gut-brain axis under four subheadings: anatomical, extracellular, immune and dietary. Firstly, we identify important anatomical structures in the auditory-gut-brain axis, particularly highlighting a direct connection provided by the vagus nerve. Leading on from this we discuss several extracellular signaling pathways which might connect the ear, gut and brain. A link is established between inflammatory responses in the ear and gut microbiome-altering interventions, highlighting a contribution of the immune system. Finally, we discuss the contribution of diet to the auditory-gut-brain axis. Based on the reviewed literature, we propose numerous possible key players connecting the auditory system to the gut-brain axis. In the future, a more thorough investigation of these key players in animal models and human research may provide insight and assist in developing effective interventions for treating hearing loss.

Decreased hearing levels at frequencies for understanding speech in tannery workers exposed to a high level of trivalent chromium in Bangladesh

Hexavalent chromium [Cr(VI)], which has a strong corrosive effect, has been reported to cause perforation of the eardrum. Trivalent chromium [Cr(III)] also has a weak corrosive effect. However, there has been no study on the effects of exposure to Cr, either Cr(VI) or Cr(III), on hearing levels in animals or humans. In this study, the effect of Cr(III) exposure on hearing levels was determined in a human study. Then the reproducibility of the results obtained in the human study and the etiology were investigated in an animal study. The mean levels of total chromium (t-Cr) in hair and toenails from 100 Bangladeshi tannery workers were >20-fold and >360-fold higher, respectively, than those in hair and toenails from 49 Bangladeshi non-tannery workers (office workers). Multivariate analysis revealed decreases of hearing levels (DHLs) at 1 k and 4 k Hz, frequencies that are crucial for understanding language, but not at 8 k and 12 k Hz, in the tannery workers. Since >99.99% of t-Cr in the wastewater that the workers were in direct contact with in the tanneries was Cr(III), the epidemiological results suggest Cr(III)-mediated DHLs in the tannery workers. The results of animal experiments in this study further showed that treatment with eardrops but not intraperitoneal injection with the same amount of Cr(III) that tannery workers might be exposed to resulted in DHL with a damaged eardrum in mice. Previous studies suggested that Cr(III) can directly reach the eardrums of tannery workers via droplets in the air. Cr(III) could also reach the eardrum via picking an ear canal with a finger contaminated with tannery wastewater including Cr(III). Taken together, the results of both human and animal studies suggest the risk of DHLs caused by damage of the eardrum through external exposure to Cr(III) via the ear canal.

Potential application of a hydrotalcite-like compound for reduction of toxicity to aquatic organisms via rapid and efficient removal of hydrogen sulfide

Hydrogen sulfide (H₂S) is known to have wide ranging toxicities not only as a gas but also as dissolved forms in aquatic environments. The diversity of aquatic organisms can be severely affected by hydrogen sulfide at very low concentrations, indicating the urgent necessity to develop an efficient method for removal of hydrogen sulfide in water. In this study, the removal capacity for hydrogen sulfide of our originally developed hydrotalcite-like compound composed of magnesium and iron (MF-HT) was investigated and its potential application for reduction of toxicity to aquatic organisms was evaluated. The MF-HT experimentally showed a high adsorption capacity of 146.5 mg/g with a fast adsorption equilibrium time of 45 min, both of which are top-class compared with those of other adsorbents previously reported. In fact, removal of hydrogen sulfide (1.2-152.5 mg/L) at an average rate of >97.6% was achieved in groundwater samples (n = 16) by the MF-HT within 60 min. The toxicities of groundwater, indicated by inhibition rate for microalgae (primary producers) and immobilization rate for crustaceans (secondary consumers), were reduced by 96.1% and 82.5% in 2-fold and 4-fold diluted groundwater, respectively, after treatment with the MF-HT for 60 min. These results indicate that MF-HT has an excellent safety record for aquatic organisms. After clarifying the adsorption mechanism, excellent reusability of MF-HT was also confirmed after regeneration using 1 M Na₂CO₃ solution. Considering the efficacy, speed, safety and cost of MF-HT, it could be a novel promising material for solving the problem of hydrogen sulfide pollution in the hydrosphere.

Redistribution of potentially toxic elements in the hydrosphere after the relocation of a group of tanneries

Simultaneous relocation of a group of pollutant sources in a heavily polluted area is a rare event. Such a relocation has been implemented in Hazaribagh, a tannery built-up area with heavy pollution, in Bangladesh. This provides a valuable opportunity to compare the changes in environmental conditions associated with the relocation of multiple putative sources. Our environmental monitoring for a period of 6 years at the stationary areas centered on Hazaribagh geographically revealed trivalent [Cr(III)], hexavalent [Cr(VI)] chromium, lead, iron, and manganese as tannery-related elements after the legal deadline for tannery relocation. The median Cr(III) level in canal water, into which wastewater from tanneries was directly discharged, after the relocation was 97% lower of that before the relocation, indicating a beneficial effect of the relocation. In contrast, the median Cr(VI) level in water samples just after the relocation and 2 years after the relocation were approximately 5-fold and 30-fold higher, respectively, than those before the relocation. These results indicate not only a harmful effect of the relocation but also the possibility of conversion from Cr(III) to Cr(VI) in nature. Although the health hazard indexes considering all of the tannery-related elements in all of the canal water samples before the relocation exceeded the safety thresholds, the percentages of samples in which the indexes exceeded their safety thresholds after the relocation decreased by 32.5%-45.0%. Treatment with our patented hydrotalcite-like compound consisting of magnesium and iron (MF-HT) resulted in decreases in the health hazard indexes in all of the water samples in which the indexes exceeded their safety thresholds to levels lower than their thresholds. Thus, this study shows the double-edged effects associated with the relocation and a potential solution.

Predictive molecular pathology in metastatic thyroid cancer: the role of RET fusions

BACKGROUND

Rearranged during transfection (RET) gene fusions are detected in 10-20% of thyroid cancer patients. Recently, RET fusion-positive metastatic thyroid cancers have attracted much attention owing to the FDA approval of two highly selective anti-RET tyrosine kinase inhibitors, namely, selpercatinib, and pralsetinib.

AREAS COVERED

This review summarizes the available evidence on the biological and predictive role of RET gene fusions in thyroid carcinoma patients and the latest screening assays currently used to detect these genomic alterations in histological and cytological specimens.

EXPERT OPINION

Management of advanced thyroid carcinoma has significantly evolved over the last decade thanks to the approval of three multikinase inhibitors, i.e. sorafenib, lenvatinib, cabozantinib, and of two selective RET-tyrosine inhibitors, i.e. selpercatinib and pralsetinib. In this setting, the detection of RET-fusions in advanced thyroid cancer specimens through the use of next-generation sequencing has become a commonly used strategy in clinical practice to select the best treatment options.

Development of an efficient remediation system with a low cost after identification of water pollutants including phenolic compounds in a tannery built-up area in Bangladesh

Water pollution caused by tannery wastewater is an important issue in developing countries. Most studies have focused on inorganic chemicals represented by chromium as a tannery-related main pollutant. This is the first study in which pollution of water by tannery-related organic chemicals was assessed by a combination of qualitative and quantitative analyses. Our quantitative analysis showed that the maximum concentration of total phenolic compounds (phenols), consisting of phenol, bisphenol F, p-cresol and chlorocresol, in canal water in a tannery built-up area in Bangladesh was >67-fold higher than the Environmental, Health and Safety (EHS) guideline value. Mapping of our results indicated tanneries as the sources of phenols pollution. Our original depurative, a hydrotalcite-like compound consisting of magnesium and iron (MF-HT), could adsorb all kinds of phenols and exhibited the highest phenol adsorption ability (115.8 mg/g) among reported hydrotalcite-like compounds. The levels of phenols in canal water samples were reduced to levels below the guideline value by using MF-HT with assistance of a photocatalytic reaction. Moreover, the mean level of chromium (112.2 mg/L) in canal water samples was decreased by 99.7% by using the depurative. Thus, the depurative has the potential for solving the problem of tannery-related water pollution by phenols and chromium.

Genetic interplay between transcription factor Pou4f1/Brn3a and neurotrophin receptor Ret in retinal ganglion cell type specification

Background

While the transcriptional code governing retinal ganglion cell (RGC) type specification begins to be understood, its interplay with neurotrophic signaling is largely unexplored. In mice, the transcription factor Brn3a/Pou4f1 is expressed in most RGCs, and is required for the specification of RGCs with small dendritic arbors. The Glial Derived Neurotrophic Factor (GDNF) receptor Ret is expressed in a subset of RGCs, including some expressing Brn3a, but its role in RGC development is not defined.

Methods

Here we use combinatorial genetic experiments using conditional knock-in reporter alleles at the Brn3a and Ret loci, in combination with retina- or Ret specific Cre drivers, to generate complete or mosaic genetic ablations of either Brn3a or Ret in RGCs. We then use sparse labelling to investigate Brn3a and Ret gene dosage effects on RGC dendritic arbor morphology. In addition, we use immunostaining and/or gene expression profiling by RNASeq to identify transcriptional targets relevant for the potential Brn3a-Ret interaction in RGC development.

Results

We find that mosaic gene dosage manipulation of the transcription factor Brn3a/Pou4f1 in neurotrophic receptor Ret heterozygote RGCs results in altered cell fate decisions and/or morphological dendritic defects. Specific RGC types are lost if Brn3a is ablated during embryogenesis and only mildly affected by postnatal Brn3a ablation. Sparse but not complete Brn3a heterozygosity combined with complete Ret heterozygosity has striking effects on RGC type distribution. Brn3a only mildly modulates Ret transcription, while Ret knockouts exhibit slightly skewed Brn3a and Brn3b expression during development that is corrected by adult age. Brn3a loss of function modestly but significantly affects distribution of Ret co-receptors GFRα1-3, and neurotrophin receptors TrkA and TrkC in RGCs.

Conclusions

Based on these observations, we propose that Brn3a and Ret converge onto developmental pathways that control RGC type specification, potentially through a competitive mechanism requiring signaling from the surrounding tissue.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13064-021-00155-z.

The importance of the RET gene in thyroid cancer and therapeutic implications

Since the discovery of the RET receptor tyrosine kinase in 1985, alterations of this protein have been found in diverse thyroid cancer subtypes. RET gene rearrangements are observed in papillary thyroid carcinoma, which result in RET fusion products. By contrast, single amino acid substitutions and small insertions and/or deletions are typical of hereditary and sporadic medullary thyroid carcinoma. RET rearrangements and mutations of extracellular cysteines facilitate dimerization and kinase activation, whereas mutations in the RET kinase coding domain drive dimerization-independent kinase activation. Thus, RET kinase inhibition is an attractive therapeutic target in patients with RET alterations. This approach was initially achieved using multikinase inhibitors, which affect multiple deregulated pathways that include RET kinase. In clinical practice, use of multikinase inhibitors in patients with advanced thyroid cancer resulted in therapeutic efficacy, which was associated with frequent and sometimes severe adverse effects. However, remarkable progress has been achieved with the identification of novel potent and selective RET kinase inhibitors for the treatment of advanced thyroid cancer. Although expanded clinical validation in future trials is needed, the sustained antitumoural activity and the improved safety profile of these novel compounds is opening a new exciting era in precision oncology for RET-driven cancers.

Loss-of-function mutation of c-Ret causes cerebellar hypoplasia in mice with Hirschsprung disease and Down's syndrome

The c-RET proto-oncogene encodes a receptor-tyrosine kinase. Loss-of-function mutations of RET have been shown to be associated with Hirschsprung disease and Down's syndrome (HSCR-DS) in humans. DS is known to involve cerebellar hypoplasia, which is characterized by reduced cerebellar size. Despite the fact that c-Ret has been shown to be associated with HSCR-DS in humans and to be expressed in Purkinje cells (PCs) in experimental animals, there is limited information about the role of activity of c-Ret/c-RET kinase in cerebellar hypoplasia. We found that a loss-of-function mutation of c-Ret Y1062 in PCs causes cerebellar hypoplasia in c-Ret mutant mice. Wild-type mice had increased phosphorylation of c-Ret in PCs during postnatal development, while c-Ret mutant mice had postnatal hypoplasia of the cerebellum with immature neurite outgrowth in PCs and granule cells (GCs). c-Ret mutant mice also showed decreased numbers of glial fibers and mitogenic sonic hedgehog (Shh)-positive vesicles in the external germinal layer of PCs. c-Ret-mediated cerebellar hypoplasia was rescued by subcutaneous injection of a smoothened agonist (SAG) as well as by reduced expression of Patched1, a negative regulator for Shh. Our results suggest that the loss-of-function mutation of c-Ret Y1062 results in the development of cerebellar hypoplasia via impairment of the Shh-mediated development of GCs and glial fibers in mice with HSCR-DS.

Hair graying with aging in mice carrying oncogenic RET

Hair graying is a representative sign of aging in animals and humans. However, the mechanism for hair graying with aging remains largely unknown. In this study, we found that the microscopic appearance of hair follicles without melanocyte stem cells (MSCs) and descendant melanocytes as well as macroscopic appearances of hair graying in RET‐transgenic mice carrying RET oncogene (RET‐mice) are in accordance with previously reported results for hair graying in humans. Therefore, RET‐mice could be a novel model mouse line for age‐related hair graying. We further showed hair graying with aging in RET‐mice associated with RET‐mediated acceleration of hair cycles, increase of senescent follicular keratinocyte stem cells (KSCs), and decreased expression levels of endothelin‐1 (ET‐1) in bulges, decreased endothelin receptor B (Ednrb) expression in MSCs, resulting in a decreased number of follicular MSCs. We then showed that hair graying in RET‐mice was accelerated by congenitally decreased Ednrb expression in MSCs in heterozygously Ednrb‐deleted RET‐mice [Ednrb(+/−);RET‐mice]. We finally partially confirmed common mechanisms of hair graying with aging in mice and humans. Taken together, our results suggest that age‐related dysfunction between ET‐1 in follicular KSCs and endothelin receptor B (Ednrb) in follicular MSCs via cumulative hair cycles is correlated with hair graying with aging.

Multidisciplinary approach to assess the toxicities of arsenic and barium in drinking water

Well water could be a stable source of drinking water. Recently, the use of well water as drinking water has been encouraged in developing countries. However, many kinds of disorders caused by toxic elements in well drinking water have been reported. It is our urgent task to resolve the global issue of element-originating diseases. In this review article, our multidisciplinary approaches focusing on oncogenic toxicities and disturbances of sensory organs (skin and ear) induced by arsenic and barium are introduced. First, our environmental monitoring in developing countries in Asia showed elevated concentrations of arsenic and barium in well drinking water. Then our experimental studies in mice and our epidemiological studies in humans showed arsenic-mediated increased risks of hyperpigmented skin and hearing loss with partial elucidation of their mechanisms. Our experimental studies using cultured cells with focus on the expression and activity levels of intracellular signal transduction molecules such as c-SRC, c-RET, and oncogenic RET showed risks for malignant transformation and/or progression arose from arsenic and barium. Finally, our original hydrotalcite-like compound was proposed as a novel remediation system to effectively remove arsenic and barium from well drinking water. Hopefully, comprehensive studies consisting of (1) environmental monitoring, (2) health risk assessments, and (3) remediation will be expanded in the field of environmental health to prevent various disorders caused by environmental factors including toxic elements in drinking water.

A unique system that can sensitively assess the risk of chemical leukoderma by using murine tail skin

Chemical leukoderma is a patchy hypopigmentation in the skin. Phenol derivatives such as raspberry ketone have been reported to cause the development of occupationally induced leukoderma. Recently, 2% (w/w) rhododenol, a reduced form of raspberry ketone used in a skin-lightning agent, also caused the development of leukoderma in >16,000 users, about 2% of all users, in Asian countries including Japan. However, a method for assessing the risk of leukoderma caused by 2% rhododenol has not been established despite the fact that the development of leukoderma caused by 30% rhododenol was previously shown in animal experiments. Establishment of a novel technique for risk assessment of leukoderma in humans caused by external treatment with chemicals is needed to prevent a possible future chemical disaster. This study demonstrated that external treatment with 2% rhododenol and the same concentration of raspberry ketone caused the development of leukoderma in murine tail skin without exception with significant decreases in the amount of melanin and number of melanocytes in the epidermis. Thus, a novel in vivo technique that can assess the risk of leukoderma caused by 2% rhododenol was developed. The unique technique using tail skin has the potential to prevent chemical leukoderma in the future.

Heat shock protein 70 is a key molecule to rescue imbalance caused by low-frequency noise

A previous study showed that people living in urban areas are generally exposed to low-frequency noise (LFN) with frequencies below 100 Hz and sound levels of 60-110 dB in daily and occupational environments. Exposure to LFN has been shown to affect balance in humans and mice. However, there is no information about prevention of LFN-mediated imbalance because of a lack of information about the target region based on health risk assessment of LFN exposure. Here, we show that acute exposure to LFN at 100 Hz, 95 dB, but not at 85 dB or 90 dB, for only 1 h caused imbalance in mice. The exposed mice also had decreased cervical vestibular-evoked myogenic potential (cVEMP) with impaired activity of vestibular hair cells. Since imbalance in the exposed mice was irreversible, morphological damage in the vestibules of the exposed mice was further examined. The exposed mice had breakage of the otoconial membrane in the vestibule. LFN-mediated imbalance and breakage of the otoconial membrane in mice were rescued by overexpression of a stress-reactive molecular chaperone, heat shock protein 70 (Hsp70), which has been shown to be induced by exposure of mice to 12 h per day of LFN at 95 dB for 5 days. Taken together, the results of this study demonstrate that acute exposure to LFN at 100 Hz, 95 dB for only 1 h caused irreversible imbalance in mice with structural damage of the otoconial membrane as the target region for LFN-mediated imbalance, which can be rescued by Hsp70.

Characterization of retinal ganglion cell, horizontal cell, and amacrine cell types expressing the neurotrophic receptor tyrosine kinase Ret

We report the retinal expression pattern of Ret, a receptor tyrosine kinase for the glial derived neurotrophic factor (GDNF) family ligands (GFLs), during development and in the adult mouse. Ret is initially expressed in retinal ganglion cells (RGCs), followed by horizontal cells (HCs) and amacrine cells (ACs), beginning with the early stages of postmitotic development. Ret expression persists in all three classes of neurons in the adult. Using RNA sequencing, immunostaining and random sparse recombination, we show that Ret is expressed in at least three distinct types of ACs, and ten types of RGCs. Using intersectional genetics, we describe the dendritic arbor morphologies of RGC types expressing Ret in combination with each of the three members of the POU4f/Brn3 family of transcription factors. Ret expression overlaps with Brn3a in 4 RGC types, with Brn3b in 5 RGC types, and with Brn3c in one RGC type, respectively. Ret⁺ RGCs project to the lateral geniculate nucleus (LGN), pretectal area (PTA) and superior colliculus (SC), and avoid the suprachiasmatic nucleus and accessory optic system. Brn3a⁺ Ret⁺ and Brn3c⁺ Ret⁺ RGCs project preferentially to contralateral retinorecipient areas, while Brn3b⁺ Ret⁺ RGCs shows minor ipsilateral projections to the olivary pretectal nucleus and the LGN. Our findings establish intersectional genetic approaches for the anatomic and developmental characterization of individual Ret⁺ RGC types. In addition, they provide necessary information for addressing the potential interplay between GDNF neurotrophic signaling and transcriptional regulation in RGC type specification.

Oral exposure to arsenic causes hearing loss in young people aged 12-29 years and in young mice

There is no information on the association between oral exposure to arsenic (As) and hearing loss in humans or mice. In this combined epidemiological study and experimental study, the association of oral exposure to As with hearing loss in people aged 12–29 years and young mice was examined. Subjects in the exposure group (n = 48), who were drinking tube well water contaminated with As, showed significantly higher risks of hearing loss at 4 kHz [odds ratio (OR) = 7.60; 95% confidence interval (CI): 1.56, 57.88], 8 kHz (OR = 5.00; 95% CI: 1.48, 18.90) and 12 kHz (OR = 8.72; 95% CI: 2.09, 47.77) than did subjects in the control group (n = 29). We next performed an experiment in which young mice were exposed to As via drinking water at 22.5 mg/L, which is a much greater concentration than that in human studies. The exposure group showed hearing loss and accumulation of As in inner ears. Ex vivo exposure of the organ of Corti from mice exposed to As significantly decreased the number of auditory neurons and fibers. Thus, our combined study showed that oral exposure to As caused hearing loss in young people and young mice.

Manganese-Mediated Decrease in Levels of c-RET and Tyrosine Hydroxylase Expression In Vitro

Previous studies showed that overexposure to manganese causes parkinsonism, a disorder of dopaminergic neurons. Previous studies also showed that activity of c-RET kinase controls dopamine production through regulation of tyrosine hydroxylase (TH) expression, suggesting the involvement of c-RET in the development of parkinsonism. To our knowledge, however, there is no report showing a correlation between manganese-mediated parkinsonism and c-RET. In this study, we examined the effect of manganese on the expression and/or activation levels of c-RET and TH in human TH-expressing cells (TGW cells). We first found that treatment with 30 and 100 μM manganese resulted in reduction of c-RET transcript level and degradation of c-RET protein through promotion of ubiquitination. We then examined the biological significance of manganese-mediated decrease of c-RET protein expression. Decreased TH expression with decreased c-RET kinase activity was observed in c-RET protein-depleted TGW cells by treatment with manganese (30 μM) as well as by c-RET siRNA transfection. Since TH protein has been shown to be involved in the dopamine-producing pathway in previous studies, our results indicate the possibility that manganese-mediated reduction of TH expression and phosphorylation via decreased expression of c-RET protein in neural cells is involved in parkinsonism induced by manganese.

Exposure to diphtheria toxin during the juvenile period impairs both inner and outer hair cells in C57BL/6 mice

Diphtheria toxin (DT) administration into transgenic mice that express the DT receptor (DTR) under control of specific promoters is often used for cell ablation studies in vivo. Because DTR is not expressed in mice, DT injection has been assumed to be nontoxic to cells in vivo. In this study, we demonstrated that DT application during the juvenile stage leads to hearing loss in wild-type mice. Auditory brainstem response measurement showed severe hearing loss in C57BL/6 mice administered DT during the juvenile period, and the hearing loss persisted into adulthood. However, ototoxicity did not occur when DT was applied on postnatal day 28 or later. Histological studies demonstrated that hearing loss was accompanied by significant degeneration of inner and outer hair cells (HCs), as well as spiral ganglion neurons. Scanning electron microscopy showed quick degeneration of inner HCs within 3days and gradual degeneration of outer HCs within 1week. These results demonstrated that DT has ototoxic action on C57BL/6 mice during the juvenile period, but not thereafter, and the hearing loss was due to degeneration of inner and outer HCs by unknown DT-related mechanisms.

Risk Assessment of Neonatal Exposure to Low Frequency Noise Based on Balance in Mice

General electric devices and ventilation systems are known to generate low frequency noise (LFN) with frequencies of <100 Hz. Previous studies showed that exposure to LFN caused impairments of balance in humans and mice during adulthood. On the other hand, a previous study showed that noise levels in the neonatal intensive care unit (NICU) were greater than those in general home or office environments. Therefore, it is possible that neonates have a potential risk to be exposed to LFN in the NICU. However, the risk of neonatal exposure to LFN remains unclear in humans and mice. In this study, male ICR mice were exposed to LFN at 100 Hz for 4 weeks after birth and then subjected to rotarod and beam crossing tests in order to assess LFN-mediated risk of imbalance during the neonatal period. Exposure to LFN at 70 dB, but not exposure to LFN up to 60 dB, during the neonatal period significantly decreased performance scores for rotarod and beam crossing tests compared to the scores of the control group. The number of calbindin-positive hair cells in the saccule and utricle was decreased in mice exposed to LFN at 70 dB for 4 weeks in the neonatal phase. Cessation of exposure for 10 weeks did not result in recovery of the decreased performance in rotarod and beam crossing tests. Thus, our results suggest that 70 dB is a possible threshold for exposure to LFN for 4 weeks during the neonatal period causing unrecoverable imbalance in mice.

Impairments of Inner Ears Caused by Physical Environmental Stresses

The inner ears contain the organ of Corti, vestibule and semicircular canal. The organ of Corti is crucial for hearing, while the vestibule and semicircular canal play important roles in maintaining balance. Exposure to noise at excessive levels is known to cause damages of the inner ears, resulting in noise-induced hearing loss. On the other hand, noise levels (dB) are used for the evaluation of health risks by exposure to noise, although noise consists of sound with broad frequencies (Hz). Thus, information about the frequency-dependent effect of noise on health is largely unknown. In this review, we first introduce noise-induced hearing loss caused by exposure to audible noise. We then describe the imbalance in mice exposed to low-frequency noise (100 Hz).

Transcription factor LSF (TFCP2) inhibits melanoma growth

Late SV40 factor 3 (LSF), a transcription factor, contributes to human hepatocellular carcinoma (HCC). However, decreased expression level of LSF in skin melanoma compared to that in benign melanocytic tumors and nevi in mice and humans was found in this study. Anchorage-dependent and -independent growth of melanoma cells was suppressed by LSF overexpression through an increased percentage of G1 phase cells and an increased p21^CIP1 expression level in vitro and in vivo. Anchorage-dependent growth in LSF-overexpressed melanoma cells was promoted by depletion of LSF in the LSF-overexpressed cells. Integrated results of our EMSA and chromatin immunoprecipitation assays showed binding of LSF within a 150-bp upstream region of the transcription start site of p21CIP1 in melanoma cells. Taken together, our results suggest potential roles of LSF as a growth regulator through control of the transcription of p21^CIP1 in melanocytes and melanoma cells as well as a biomarker for nevus.

Manganese-mediated acceleration of age-related hearing loss in mice

Despite the fact that manganese (Mn) is known to be a neurotoxic element relevant to age-related disorders, the risk of oral exposure to Mn for age-related hearing loss remains unclear. In this study, we orally exposed wild-type young adult mice to Mn (Mn-exposed WT-mice) at 1.65 and 16.50 mg/L for 4 weeks. Mn-exposed WT-mice showed acceleration of age-related hearing loss. Mn-exposed WT-mice had neurodegeneration of spiral ganglion neurons (SGNs) with increased number of lipofuscin granules. Mn-exposed WT-mice also had increased hypoxia-inducible factor-1 alpha (Hif-1α) protein with less hydroxylation at proline 564 and decreased c-Ret protein in SGNs. Mn-mediated acceleration of age-related hearing loss involving neurodegeneration of SGNs was rescued in RET-transgenic mice carrying constitutively activated RET. Thus, oral exposure to Mn accelerates age-related hearing loss in mice with Ret-mediated neurodegeneration of SGNs.

Deltex-3-like (DTX3L) stimulates metastasis of melanoma through FAK/PI3K/AKT but not MEK/ERK pathway

Deltex-3-like (DTX3L), an E3 ligase, is a member of the Deltex (DTX) family and is also called B-lymphoma and BAL-associated protein (BBAP). Previously, we established RFP/RET-transgenic mice, in which systemic hyperpigmented skin, benign melanocytic tumor(s) and melanoma(s) develop stepwise. Here we showed that levels of Dtx3l/DTX3L in spontaneous melanoma in RFP/RET-transgenic mice and human melanoma cell lines were significantly higher than those in benign melanocytic cells and primarily cultured normal human epithelial melanocytes, respectively. Immunohistochemical analysis of human tissues showed that more than 80% of the melanomas highly expressed DTX3L. Activity of FAK/PI3K/AKT signaling, but not that of MEK/ERK signaling, was decreased in Dtx3l/DTX3L-depleted murine and human melanoma cells. In summary, we demonstrated not only increased DTX3L level in melanoma cells but also DTX3L-mediated regulation of invasion and metastasis in melanoma through FAK/PI3K/AKT but not MEK/ERK signaling. Our analysis in human BRAFV600E inhibitor-resistant melanoma cells showed about 80% decreased invasion in the DTX3L-depleted cells compared to that in the DTX3L-intact cells. Thus, DTX3L is clinically a potential therapeutic target as well as a potential biomarker for melanoma.

Commentary to Gorelenkova Miller and Mieyal (2015): sulfhydryl-mediated redox signaling in inflammation: role in neurodegenerative diseases

Gorelenkova Miller and Mieyal (Arch Toxicol 89(9): 1439-1467, 2015) recently published a review paper suggesting that reversible cysteine plays a key role in redox-linked signal transduction via alteration of protein function, resulting in an association with many diseases including neurodegenerative disorders. Following their suggestions, we considered the correlation between sulfhydryl-mediated redox signaling and neurodegenerative diseases by focusing on RET proteins, a protein tyrosine kinases (PTKs) potentially sited upstream of the signal transduction cascade. c-RET is the receptor for glial cell line-derived neurotrophic factor family ligands. c-RET has been reported to be involved in not only Hirschsprung disease via development of the enteric nervous system but also neurodegenerative diseases including Parkinson's disease and amyotrophic lateral sclerosis. We also showed that c-RET might be associated with hearing loss via neurodegeneration of spiral ganglion neurons in the inner ear after birth in mice and humans. Moreover, we have reported that three kinds of oxidative stress, ultraviolet light-induced stress, osmotic stress and arsenic-induced stress, modulate kinase activity of RET-PTC1 without an extracellular domain as well as c-RET by conformational change of RET protein (dimerization) via disulfide bond formation. The oxidative stresses also modulate kinase activity of RET-PTC1 with cysteine 365 (C365) replaced by alanine with promotion of dimer formation, but not with cysteine 376 (C376) replaced by alanine. Since C376 of Ret-PTC-1 or its equivalent is most highly conserved and crucial for activity in PTKs, the cysteine could be one of major targets for oxidative stresses.

Carcinogenic risk of chromium, copper and arsenic in CCA-treated wood

We showed that 2.1% of 233 pieces of lumber debris after the Great East Japan Earthquake was chromated copper arsenate (CCA)-treated wood. Since hexavalent chromium (Cr), copper (Cu) and pentavalent arsenic (As) in the debris may be diffused in the air via incineration, we exposed human lung normal (BEAS-2B) and carcinoma (A549) cells to Cr, Cu and As at the molar ratio in a representative CCA-treated wood. Co-exposure to 0.10 μM Cr and 0.06 μM As, which solely had no effect on colony formation, synergistically promoted colony formation in BEAS-2B cells, but not A549 cells, with activation of the PI3K/AKT pathway. Sole exposure and co-exposure to Cu showed limited effects. Since previous reports showed Cr and As concentrations to which human lungs might be exposed, our results suggest the importance to avoid diffusion of Cr and As in the air via incineration of debris including CCA-treated wood after the disaster.

[Analysis of Environmental-Stress-Related Impairments of Inner Ear]

Noise stress generated in industry is one of the environmental factors that physically affects the functions of the inner ear. Exposure to noise can cause hearing loss, resulting in serious problems in occupational and daily life. At present, however, there are very limited ways to prevent hearing impairments. The inner ear consists of the organ of Corti, vestibule and semicircular canal. Functional or morphological damage of these tissues in the inner ear caused by genetic factors, aging or environmental factors can result in hearing or balance impairments. In this review, we first introduce a deafness-related molecule found by our clinical research. Our experimental research using genetically engineered mice further demonstrated that impaired activity of the target molecule caused congenital and age-related hearing loss with neurodegeneration of spiral ganglion neurons in the inner ears. We also describe impaired balance in mice caused by exposure to low-frequency noise under experimental conditions with indoor environmental monitoring. We believe that our approaches to pursue both experimental research and fieldwork research complementarily are crucial for the development of a method for prevention of impairments of the inner ear.

Correlated expression levels of endothelin receptor B and Plexin C1 in melanoma

Discussion concerning the effect of endothelin receptor B (Ednrb) on melanoma continues because Ednrb has been reported to have both tumor promoting and suppressive effects for melanoma. In order to examine Ednrb-related signaling in melanomagenesis, DNA microarray analysis for a melanoma from a RFP/RET-transgenic mouse (RET-mouse) and a melanoma from an Ednrb-heterozygously deleted RET-mouse [Ednrb(+/-);RET-mouse], in both of which melanoma spontaneously develops, was performed in this study. We found that the expression level of Plexin C1 (PlxnC1), a suppressor for melanoma, in a melanoma from an Ednrb(+/-);RET-mouse was drastically decreased compared to that in a melanoma from a RET-mouse. Therefore, we further examined the correlation between Ednrb and PlxnC1 expression levels in melanomas. PlxnC1 transcript expression levels in melanomas from Ednrb(+/-);RET-mice were lower than those in melanomas from RET-mice. A strong correlation between Ednrb and PlxnC1 transcript expression levels (R = 0.78, p < 0.01) was also found in melanomas from both RET-mice and Ednrb(+/-);RET-mice. Correspondingly, there was a significant correlation between transcript (R = 0.80; p < 0.01) and protein (R = 0.60; p < 0.01) expression levels of EDNRB and PLXNC1 in human primary melanomas. Together with our results showing that the expression level of PLXNC1 transcript was reduced in EDNRB-depleted human melanoma cells, our results showing positively correlated expression levels of Ednrb/EDNRB and PlxnC1/PLXNC1 in melanoma suggest that PlxnC1/PLXNC1 is involved in the Ednrb/EDNRB-mediated suppressive effect on melanoma.

GNG2 inhibits invasion of human malignant melanoma cells with decreased FAK activity

It is well known that heterotrimeric G protein is composed of a Gα-subunit and a Gβγ-dimer and promotes cancer characteristics. Our recent study showed reduced G protein γ2 subunit (Gng2/GNG2) expression levels in malignant melanoma cells compared with those in benign melanocytic cells in both mice and humans. Our recent study also showed that reduced GNG2 alone augmented proliferation of malignant melanoma cells. To our knowledge, however, there is no evidence showing an effect of Gng2/GNG2 alone on metastasis of any cancers including malignant melanoma. In his study, we first prepared GNG2-overexpressed SK-Mel28 human malignant melanoma cells, in which GNG2 protein expression level was undetectably low. Migration and invasion activities of the GNG2-overexpressed malignant melanoma cells were suppressed up to 1/10th, with decreased activity of focal adhesion kinase (FAK). We then found that the expression level of GNG2 in A375M, a highly metastatic cell line, was significantly lower than that in A375P, the parental cell line of A375M. We finally showed that knockdown of GNG2 alone in A375P cells enhanced migration and invasion with increased FAK activity. Taken together, our results suggest that overexpression of GNG2 alone inhibits metastasis in human malignant melanoma cells with decreased FAK activity. Thus, GNG2 might be a candidate of molecular targets of prevention and therapy for metastasis of malignant melanoma.

Glial cell line-derived neurotrophic factor (GDNF) induces neuritogenesis in the cochlear spiral ganglion via neural cell adhesion molecule (NCAM)

Glial cell line-derived neurotrophic factor (GDNF) increases survival and neurite extension of spiral ganglion neurons (SGNs), the primary neurons of the auditory system, via yet unknown signaling mechanisms. In other cell types, signaling is achieved by the GPI-linked GDNF family receptor α1 (GFRα1) via recruitment of transmembrane receptors: Ret (re-arranged during transformation) and/or NCAM (neural cell adhesion molecule). Here we show that GDNF enhances neuritogenesis in organotypic cultures of spiral ganglia from 5-day-old rats and mice. Addition of GFRα1-Fc increases this effect. GDNF/GFRα1-Fc stimulation activates intracellular PI3K/Akt and MEK/Erk signaling cascades as detected by Western blot analysis of cultures prepared from rats at postnatal days 5 (P5, before the onset of hearing) and 20 (P20, after the onset of hearing). Both cascades mediate GDNF stimulation of neuritogenesis, since application of the Akt inhibitor Wortmannin or the Erk inhibitor U0126 abolished GDNF/GFRα1-Fc stimulated neuritogenesis in P5 rats. Since cultures of P5 NCAM-deficient mice failed to respond by neuritogenesis to GDNF/GFRα1-Fc, we conclude that NCAM serves as a receptor for GDNF signaling responsible for neuritogenesis in early postnatal spiral ganglion.

Functional analysis of GNG2 in human malignant melanoma cells

BACKGROUND

Previous studies have revealed that heterotrimeric G protein is composed of a Gα-subunit and a Gβγ-dimer and is correlated with c-Src and AKT activities. Our recent study showed reduced G protein γ2 subunit (Gng2/GNG2) expression levels in malignant melanoma cells compared with those in benign melanocytic cells in both mice and humans. At present, however, there is no evidence showing an effect of Gng2/GNG2 alone on cancer biology.

OBJECTIVE

The purpose of this study was to examine the biological significance of GNG2 in human malignant melanoma cells.

METHODS

Levels of proliferation and activities of signal transduction molecules were examined in both GNG2-overexpressed and -depleted human malignant melanoma cells.

RESULTS

Proliferation of GNG2-overexpressed SK-Mel28 human malignant melanoma cells was suppressed with decreased c-SRC and AKT activities and increased p21(Cip/WAF1) expression level in vitro. In contrast, proliferation of GNG2-depleted A375P human malignant melanoma cells was enhanced with increased c-SRC and AKT activities and decreased p21(Cip/WAF1) expression level in vitro. In the in vivo experiment, the mean tumor size of GNG2-overexpressed SK-Mel28 cells was less than 1/45th of that of control SK-Mel28 cells in nude mice at 95 days after inoculation.

CONCLUSION

We demonstrated for the first time that increased protein expression level of GNG2 alone inhibits proliferation of malignant melanoma cells in vitro and in vivo, suggesting that GNG2 could be a novel molecular target for malignant melanoma therapy.

Hearing impairments caused by genetic and environmental factors

Impairments of hearing and balance are major problems in the field of occupational and environmental health. Such impairments have previously been reported to be caused by genetic and environmental factors. However, their mechanisms have not been fully clarified. On the other hand, the inner ear contains spiral ganglion neurons (SGNs) in the organ of Corti, which serve as the primary carriers of auditory information from sensory cells to the auditory cortex in the cerebrum. Inner ears also contain a vestibule in the vicinity of the organ of Corti—one of the organs responsible for balance. Thus, inner ears could be a good target to clarify the pathogeneses of sensorineural hearing losses and impaired balance. In our previous studies with c-Ret knock-in mice and Endothelin receptor B (Ednrb) knock-out mice, it was found that syndromic hearing losses involved postnatal neurodegeneration of SGNs caused by impairments of c-Ret and Ednrb, which play important roles in neuronal development and maintenance of the enteric nervous system. The organ of Corti and the vestibule in inner ears also suffer from degeneration caused by environmental stresses including noise and heavy metals, resulting in impairments of hearing and balance. In this review, we introduce impairments of hearing and balance caused by genetic and environmental factors and focus on impairments of SGNs and the vestibule in inner ears as the pathogeneses caused by these factors.

Exposure to low-dose barium by drinking water causes hearing loss in mice

PURPOSE

We continuously ingest barium as a general element by drinking water and foods in our daily life. Exposure to high-dose barium (>100mg/kg/day) has been shown to cause physiological impairments. Direct administration of barium to inner ears by vascular perfusion has been shown to cause physiological impairments in inner ears. However, the toxic influence of oral exposure to low-dose barium on hearing levels has not been clarified in vivo. We analyzed the toxic influence of oral exposure to low-dose barium on hearing levels and inner ears in mice.

EXPERIMENTAL DESIGN

We orally administered barium at low doses of 0.14 and 1.4 mg/kg/day to wild-type ICR mice by drinking water. The doses are equivalent to and 10-fold higher than the limit level (0.7 mg/l) of WHO health-based guidelines for drinking water, respectively. After 2-week exposure, hearing levels were measured by auditory brain stem responses and inner ears were morphologically analyzed. After 2-month exposure, tissue distribution of barium was measured by inductively coupled plasma mass spectrometry.

RESULTS

Low-dose barium in drinking water caused severe hearing loss in mice. Inner ears including inner and outer hair cells, stria vascularis and spiral ganglion neurons showed severe degeneration. The Barium-administered group showed significantly higher levels of barium in inner ears than those in the control group, while barium levels in bone did not show a significant difference between the two groups. Barium levels in other tissues including the cerebrum, cerebellum, heart, liver and kidney were undetectably low in both groups.

CONCLUSIONS

Our results demonstrate for the first time that low-dose barium administered by drinking water specifically distributes to inner ears resulting in severe ototoxicity with degeneration of inner ears in mice.

Chronic exposure to low frequency noise at moderate levels causes impaired balance in mice

We are routinely exposed to low frequency noise (LFN; below 0.5 kHz) at moderate levels of 60-70 dB sound pressure level (SPL) generated from various sources in occupational and daily environments. LFN has been reported to affect balance in humans. However, there is limited information about the influence of chronic exposure to LFN at moderate levels for balance. In this study, we investigated whether chronic exposure to LFN at a moderate level of 70 dB SPL affects the vestibule, which is one of the organs responsible for balance in mice. Wild-type ICR mice were exposed for 1 month to LFN (0.1 kHz) and high frequency noise (HFN; 16 kHz) at 70 dB SPL at a distance of approximately 10-20 cm. Behavior analyses including rotarod, beam-crossing and footprint analyses showed impairments of balance in LFN-exposed mice but not in non-exposed mice or HFN-exposed mice. Immunohistochemical analysis showed a decreased number of vestibular hair cells and increased levels of oxidative stress in LFN-exposed mice compared to those in non-exposed mice. Our results suggest that chronic exposure to LFN at moderate levels causes impaired balance involving morphological impairments of the vestibule with enhanced levels of oxidative stress. Thus, the results of this study indicate the importance of considering the risk of chronic exposure to LFN at a moderate level for imbalance.

Reduced GNG2 expression levels in mouse malignant melanomas and human melanoma cell lines

Heterotrimeric G protein is composed of a Gα-subunit and a Gβγ-dimer. Previous studies have revealed that Gβγ-dimers including the Gγ2 subunit (Gng2/GNG2) are associated with cell proliferation, differentiation, invasion and angiogenesis. At present, however, there is no information on the expression level of Gng2/GNG2 alone in any kind of tumor. In this study, we performed DNA microarray analysis in a benign melanocytic tumor and a malignant melanoma from RET-transgenic mice (RET-mice). Gng2 transcript expression levels in a malignant melanoma were less than 1/10 of the level in a benign tumor. The difference in Gng2 transcript expression levels between benign tumors and malignant melanomas was greatest among all of the G protein γ subunits examined in this study. Moreover, protein expression levels of Gng2 were decreased in malignant melanomas compared with those in benign melanocytic tumors in RET-mice. Analysis of human malignant melanomas also showed reduced GNG2 protein expression levels in five human malignant melanoma cell lines compared with the expression levels in normal human epithelial melanocytes (NHEM). Thus, we demonstrated for the first time that Gng2/GNG2 expression levels are reduced in malignant melanoma, suggesting that GNG2 could be a novel biomarker for malignant melanoma.

c-Ret-mediated hearing losses

About 120 million people worldwide suffer from congenital (early-onset) hearing loss. Thirty percent of them have syndromic hearing loss and the remaining 70% have non-syndromic hearing loss. In addition, a large number of elderly people worldwide suffer from age-related (late-onset) hearing loss. c-Ret and c-RET have been shown to be essential for the development and maintenance of neurons including the enteric nervous system (ENS) in mice and humans. Impairments of endothelin receptor B (EDNRB) and SOX10 have been shown to cause a significantly increased risk of dominant sensorineural deafness in Hirschsprung disease (HSCR) patients. We have recently shown that impairments of tyrosine 1062 (Y1062) phosphorylation in c-Ret causes syndromic congenital deafness in mice and humans and non-syndromic age-related hearing loss with neurodegeneration of spiral ganglion neurons (SGNs) in mice. This review focuses on the pathogenesis of hearing loss caused by impairments of c-Ret.

A novel hairless mouse model for malignant melanoma

BACKGROUND

An appropriate animal model for malignant melanoma could be a strong tool to develop biomarkers through analysis of melanomagenesis.

OBJECTIVE

Development of a novel animal model that spontaneously develops malignant melanoma with a high percentage.

METHODS

We crossed oncogenic RET (RFP-RET)-carrying transgenic mice of line 304/B6 (RET-mice) with hairless mice (hr/hr) and newly established hairless RFP-RET-transgenic mice of line 304-hr/hr (HL-RET-mice).

RESULTS

The HL-RET-mice developed hyperpigmented skin and benign melanocytic tumors without exception. More importantly, 63.8% (46/72) of the benign tumors were transformed to malignant melanoma in the HL-RET-mice. Mean time until the development of benign melanocytic tumors (2.4 months; n = 102) in the HL-RET-mice was about half of that in the original RET-mice (4.6 months; n = 20). Mean life span in the HL-RET-mice (9.7 months; n = 38) was also significantly (p < 0.01) shorter than that in the original RET-mice (10.8 months; n = 20). Since early development of tumors could contribute to shortening of the research period, HL-RET-mice could be a useful model for analysis of melanomagenesis. We then found that the expression level of Mps one binder kinase activator-like-2B (Mobkl2b) in benign tumors was higher than that in malignant melanoma in HL-RET-mice. Expression level of MOBKL2B in malignant melanoma cell lines was also lower than that in non-malignant melanocytic cells in mice and humans, suggesting that MOBKL2B could be a novel marker for malignant melanoma.

CONCLUSION

We established a novel hairless RET-transgenic mouse line spontaneously developing cutaneous malignant melanomas from benign melanocytic tumors. This mouse model may be useful to find new candidates of melanoma-related molecule.

Molecular Network Associated with MITF in Skin Melanoma Development and Progression

Various environmental and genetic factors affect the development and progression of skin cancers including melanoma. Melanoma development is initially triggered by environmental factors including ultraviolet (UV) light, and then genetic/epigenetic alterations occur in skin melanocytes. These first triggers alter the conditions of numerous genes and proteins, and they induce and/or reduce gene expression and activate and/or repress protein stability and activity, resulting in melanoma progression. Microphthalmia-associated transcription factor (MITF) is a master regulator gene of melanocyte development and differentiation and is also associated with melanoma development and progression. To find better approaches to molecular-based therapies for patients, understanding MITF function in skin melanoma development and progression is important. Here, we review the molecular networks associated with MITF in skin melanoma development and progression.

RAS/RAF/MEK/ERK and PI3K/PTEN/AKT Signaling in Malignant Melanoma Progression and Therapy

Cutaneous malignant melanoma is one of the most serious skin cancers and is highly invasive and markedly resistant to conventional therapy. Melanomagenesis is initially triggered by environmental agents including ultraviolet (UV), which induces genetic/epigenetic alterations in the chromosomes of melanocytes. In human melanomas, the RAS/RAF/MEK/ERK (MAPK) and the PI3K/PTEN/AKT (AKT) signaling pathways are two major signaling pathways and are constitutively activated through genetic alterations. Mutations of RAF, RAS, and PTEN contribute to antiapoptosis, abnormal proliferation, angiogenesis, and invasion for melanoma development and progression. To find better approaches to therapies for patients, understanding these MAPK and AKT signaling mechanisms of melanoma development and progression is important. Here, we review MAPK and AKT signaling networks associated with melanoma development and progression.

Genetic background strongly modifies the severity of symptoms of Hirschsprung disease, but not hearing loss in rats carrying Ednrb(sl) mutations

Hirschsprung disease (HSCR) is thought to result as a consequence of multiple gene interactions that modulate the ability of enteric neural crest cells to populate the developing gut. However, it remains unknown whether the single complete deletion of important HSCR-associated genes is sufficient to result in HSCR disease. In this study, we found that the null mutation of the Ednrb gene, thought indispensable for enteric neuron development, is insufficient to result in HSCR disease when bred onto a different genetic background in rats carrying Ednrb^sl mutations. Moreover, we found that this mutation results in serious congenital sensorineural deafness, and these strains may be used as ideal models of Waardenburg Syndrome Type 4 (WS4). Furthermore, we evaluated how the same changed genetic background modifies three features of WS4 syndrome, aganglionosis, hearing loss, and pigment disorder in these congenic strains. We found that the same genetic background markedly changed the aganglionosis, but resulted in only slight changes to hearing loss and pigment disorder. This provided the important evidence, in support of previous studies, that different lineages of neural crest-derived cells migrating along with various pathways are regulated by different signal molecules. This study will help us to better understand complicated diseases such as HSCR and WS4 syndrome.

Partial requirement of endothelin receptor B in spiral ganglion neurons for postnatal development of hearing

Impairments of endothelin receptor B (Ednrb/EDNRB) cause the development of Waardenburg-Shah syndrome with congenital hearing loss, hypopigmentation, and megacolon disease in mice and humans. Hearing loss in Waardenburg-Shah syndrome has been thought to be caused by an Ednrb-mediated congenital defect of melanocytes in the stria vascularis (SV) of inner ears. Here we show that Ednrb expressed in spiral ganglion neurons (SGNs) in inner ears is required for postnatal development of hearing in mice. Ednrb protein was expressed in SGNs from WT mice on postnatal day 19 (P19), whereas it was undetectable in SGNs from WT mice on P3. Correspondingly, Ednrb homozygously deleted mice (Ednrb(-/-) mice) with congenital hearing loss showed degeneration of SGNs on P19 but not on P3. The congenital hearing loss involving neurodegeneration of SGNs as well as megacolon disease in Ednrb(-/-) mice were markedly improved by introducing an Ednrb transgene under control of the dopamine β-hydroxylase promoter (Ednrb(-/-);DBH-Ednrb mice) on P19. Neither defects of melanocytes nor hypopigmentation in the SV and skin in Ednrb(-/-) mice was rescued in the Ednrb(-/-);DBH-Ednrb mice. Thus, the results of this study indicate a novel role of Ednrb expressed in SGNs distinct from that in melanocytes in the SV contributing partially to postnatal hearing development.