ICOSLG acts as an oncogene to promote glycolysis, proliferation, migration, and invasion in gastric cancer cells.

Gastric cancer (GC) has emerged as one of the most common malignancies in gastrointestinal system. Inducible T-cell costimulator ligand (ICOSLG) was found to be highly expressed in various cancers, which contributes to disease progression. This study aims to investigate the role of ICOSLG and its potential mechanism of action in dictating the aggressiveness of GC cell. ICOSLG and miR-331-3p expression patterns in cancerous and para-cancerous tissues from GC patients were examined by quantitative reverse transcription-polymerase chain reaction (qRT-PCR). The miRNAs targeting ICOSLG were predicted by "miRDB", "starBase," and "TargetScan" databases. The interplay of ICOSLG and miR-331-3p in dictating the aggressiveness and glycolysis of GC cells was investigated by CCK-8 proliferation assay and Transwell migration/invasion assays, as well as the detection of glucose uptake, lactate production and ATP levels. The tumorigenesis of GC cells after ICOSLG silencing was examined in the nude mice. ICOSLG was highly expressed in GC tissues, and GC patients with high ICOSLG expression showed a poorer prognosis than the low-expression group. Further, high ICOSLG level was correlated with more advanced TNM stages, more lymph-node metastases, and poorer tumor differentiation. ICOSLG knockdown inhibited the proliferation, migration, invasion and tumor formation of GC cells, which was concomitant with reduced glucose consumption, lactate production, and ATP levels. In contrast, ICOSLG overexpression enhanced the aggressiveness of GC cells, and this effect was abrogated after the treatment with glycolysis inhibitor. We further found that miR-331-3p was a negative regulator of ICOSLG4, and miR-331-3p overexpression reduced ICOSLG4 expression and suppressed the aggressive phenotype induced by ICOSLG4 in GC cells. Together, these findings indicate that ICOSLG4, as an oncogene, is upregulated to promote glycolysis and the malignant phenotype in GC cells. miR-331-3p, which is downregulated in GC tissues, functions as a negative regulator of ICOSLG4. Targeting miR-331-3p/ICOSLG4 axis could potentially suppress GC progression.

Gentamicin administration leads to synaptic dysfunction in inner hair cells.

Ototoxicity is a major side effect of aminoglycosides, which can cause irreversible hearing loss. Previous studies on aminoglycoside-induced ototoxicity have primarily focused on the loss of sensory hair cells. Recent investigations have revealed that aminoglycosides can also lead to the loss of ribbon synapses in inner hair cells (IHCs). However, the functional implications of ribbon synapse loss and the underlying mechanisms remain unclear. In this study, we intraperitoneally injected C57BL/6 J mice with 300 mg/kg gentamicin once daily for 3, 10, and 20 days. Then, we performed immunofluorescence staining, patch-clamp recording, proteomics analysis and western blotting to characterize the changes in ribbon synapses in IHCs and the associated mechanisms. After gentamicin treatment, the auditory brainstem response (ABR) threshold was elevated, and the ABR wave I amplitude was decreased. We also observed loss of ribbon synapses in IHCs. Interestingly, ribbon synapse loss occurred on both the modiolar and pillar sides of IHCs. Whole-cell patch-clamp recordings in IHCs revealed a reduction in the calcium current amplitude, along with a shifted half-activation voltage and altered calcium voltage dependency. Moreover, exocytosis of IHCs was reduced, consistent with the reduction in the ABR wave I amplitude. Through proteomic analysis, western blotting, and immunofluorescence staining, we found that gentamicin treatment resulted in downregulation of myosin VI, a protein crucial for synaptic vesicle recycling and replenishment in IHCs. Furthermore, we evaluated the kinetics of endocytosis and found a significant reduction in IHC exocytosis, possibly reflecting the impact of myosin VI downregulation on synaptic vesicle recycling. In summary, our findings demonstrate that gentamicin treatment leads to synaptic dysfunction in IHCs, highlighting the important role of myosin VI downregulation in gentamicin-induced synaptic damage.

Cancer stem cells: advances in the glucose, lipid and amino acid metabolism.

Cancer stem cells (CSCs) are a class of cells with self-renewal and multi-directional differentiation potential, which are present in most tumors, particularly in aggressive tumors, and perform a pivotal role in recurrence and metastasis and are expected to be one of the important targets for tumor therapy. Studies of tumor metabolism in recent years have found that the metabolic characteristics of CSCs are distinct from those of differentiated tumor cells, which are unique to CSCs and contribute to the maintenance of the stemness characteristics of CSCs. Moreover, these altered metabolic profiles can drive the transformation between CSCs and non-CSCs, implying that these metabolic alterations are important markers for CSCs to play their biological roles. The identification of metabolic changes in CSCs and their metabolic plasticity mechanisms may provide some new opportunities for tumor therapy. In this paper, we review the metabolism-related mechanisms of CSCs in order to provide a theoretical basis for their potential application in tumor therapy.

O­GlcNAcylation mediates endometrial cancer progression by regulating the Hippo­YAP pathway.

The incidence of endometrial cancer (EC) is rapidly increasing worldwide. The majority of endometrial cancers are diagnosed at an early stage and are associated with a good prognosis; however, patients with advanced­stage EC have a poor prognosis and present with invasive metastasis. The mechanisms responsible for the invasion and metastasis of endometrial cancer remain unknown. Here, the present study aimed to examine the effects of O­GlcNAcylation on the malignancy of EC and its association with Yes­associated protein (YAP). It was found that the expression of O­GlcNAc transferase (OGT) and O­GlcNAcylation were increased in EC tissues; the decrease in O­GlcNAcylation levels was found to lead to the decreased proliferation, migration and invasion of EC cells. Mass spectrometric analysis revealed that OGT knockdown reduced the O­GlcNAcylation of YAP. Furthermore, it was found that the reduction in the O­GlcNAcylation of YAP promoted its phosphorylation, which in turn inhibited the access of YAP to the nucleus and downstream target gene activation, demonstrating that the level of O­GlcNAcylation affects the development of EC. On the whole, the findings of the present study indicate that YAP is a key molecule linking the O­GlcNAcylation and Hippo pathways, which together regulate the progression of EC.

Early assessment of circulating exosomal lncRNA-GC1 for monitoring neoadjuvant chemotherapy response in gastric cancer.

BACKGROUND: The timing of surgery for patients with gastric cancer (GC) who undergo neoadjuvant chemotherapy (neoCT) was mainly guided by serial radiologic imaging. However, an earlier assessment was indispensable to avoid delayed treatment for nonresponders and excessive toxicity for responders. Our previous study has identified circulating extracellular vesicles-derived lncRNA-GC1 as a biomarker for early detection and monitoring progression of GC. However, the potential role of neoCT remains poorly understood. METHODS: In this explorative biomarker analysis, we conducted a multi-cohort study to examine longitudinal levels of circulating extracellular vesicles-derived lncRNA-GC1 in 798 patients enrolled in the RESONANCE study (NCT01583361). Both circulating extracellular vesicles-derived lncRNA-GC1 and traditional gastrointestinal biomarkers were assessed at defined time nodes. Computed tomography (CT) scans were performed before treatment and 8-10 weeks and assessed based on the RECIST criteria. RESULTS: Circulating extracellular vesicles-derived lncRNA-GC1 could be detected in 96.3% of patients at baseline, and significant reductions were observed before cycle 2 (P<0.0001). Levels of circulating extracellular vesicles-derived lncRNA-GC1 showed a stronger correlation with tumor burden and exhibited earlier dynamic changes than the traditional gastrointestinal biomarkers during the first cycle of neoCT. Strong agreement was observed between circulating extracellular vesicles-derived lncRNA-GC1 response (reduction >50%) and radiographic response (Cohen's κ, 0.704). Importantly, circulating extracellular vesicles-derived lncRNA-GC1 maintained predictive value in two external cohorts. Patients with circulating extracellular vesicles-derived lncRNA-GC1 response showed superior disease-free survival [hazard ratio (HR), 0.6238; 95% CI, 0.4095-0.9501; P=0.0118] and overall survival (HR, 0.6131; 95% CI, 0.4016-0.9358; P=0.0090). CONCLUSION: Circulating extracellular vesicles-derived lncRNA-GC1 is an early marker of neoCT efficacy and predicts superior survival in GC patients treated with neoCT.

LMNB1 deletion in ovarian cancer inhibits the proliferation and metastasis of tumor cells through PI3K/Akt pathway.

Ovarian cancer (OC) is a common malignant tumor in gynecology. LMNB1 is an important component of the nuclear skeleton. The expression of LMNB1 in ovarian cancer is significantly higher than that in normal tissues, but its role in tumor still needs comprehensive investigation. In this study, we overexpressed and knocked down LMNB1 in ovarian cancer cells and explore the effect of LMNB1 on the cell proliferation, migration and the underlying mechanism. We analyzed the expression levels of LMNB1 in ovarian cancer and their clinical relevance by using bioinformatics methods, qRT-PCR, Western blot and immunohistochemistry. To state the effect and mechanism of LMNB1 on OC in vitro and in vivo, we performed mouse xenograft studies, CCK8, cloning formation, Edu incorporation, wound healing, transwell and flow cytometry assay in stable LMNB1 knockdown OC cells, following by RNA-seq. Overexpression of LMNB1 indicates the progression of OC. LMNB1 knockdown inhibited the proliferation and migration of OC cells by suppressing the FGF1-mediated PI3K-Akt signaling pathway. Our study shows LMNB1 as a novel prognostic factor and therapeutic target in OC.

The relationship between round window and ear canal Cochlear microphonic.

Hypothesis: Cochlear microphonic recorded at ear canal (CM-EC) can be a substitute for the one recorded at round window (CM-RW). Background: Almost all clinics do not measure tone-burst evoked CM due to technical difficulty although it can provide more information than click evoked CM. Moreover, clinicians like the CM-EC more than that measured at CM-RW because CM-EC is non-invasive. There is difference between CM-RW and CM-EC, for example, CM-EC is less prominent than CM-RW, therefore, studying tone-burst evoked CM-EC and its relationship with CM-RW are highly significant and can promote the clinical application of CM-EC. Method: Nine guinea pigs were randomly allocated into three groups, group 1 was not exposed to noise, called normal control. group 2 and group 3 were exposed to the low- (0.5-2 kHz) and high-frequency band-noise (6-8 kHz) at 120 dB SPL for 1 h, respectively. It was difficulty to record low-frequency CM due to severe environmental interruption, in current study the recording technology of tone-burst evoked CM was optimized so that tone-burst evoked CM was measured across full speech frequency (0.5-8 kHz) in the presence of normal hearing and noise induced hearing loss (NIHL). Results: CM-RW and CM-EC were successfully recorded across speech frequency. Significant reduction in CM amplitude was observed at 0.5 and 2 kHz in group 2, at 6 and 8 kHz in group 3 as compared to group 1, p < .05, indicating that CM amplitude was sensitive to band-noise exposure. Significant correlation between CM-RW and CM-EC was also verified, p < .05. Conclusion: CM-EC is a useful objective test for evaluation of hearing function; the result of current study supports the clinical application of non-invasive CM-EC.

Biallelic p.V37I variant in GJB2 is associated with increasing incidence of hearing loss with age.

PURPOSE: This study aimed to quantitatively assess the incidence of hearing loss in relation to age in individuals with biallelic p.V37I variant in GJB2. METHODS: Population screening of the biallelic p.V37I variant was performed in 30,122 individuals aged between 0 and 97 years in Shanghai. Hearing thresholds of the biallelic p.V37I individuals and the controls were determined by click auditory brainstem response or pure tone audiometry. RESULTS: Biallelic p.V37I was detected in 0.528% (159/30,122) of the subjects. Of the biallelic p.V37I newborns, 43.91% (18/41) passed their distortion-product otoacoustic emissions-based newborn hearing screening or had hearing thresholds lower than 20 decible above normal hearing level. The older newborns had elevated hearing thresholds, with increasing incidence of 9.52%, 23.08%, 59.38%, and 80.00% for moderate or higher grade of hearing loss in age groups of 7 to 15 years, 20 to 40 years, 40 to 60 years, and 60 to 85 years, respectively. Their hearing deteriorated at a rate of 0.40 dB hearing level per year on average; males were more susceptible, and deterioration occurred preferentially at higher sound frequencies. CONCLUSION: The biallelic p.V37I variant is associated with steadily progressive hearing loss with increasing incidence over the course of life. Most of the biallelic p.V37I individuals may develop significant hearing loss in adulthood and, can benefit from early diagnosis and intervention through wide-spread genetic screening.

Reduced O-GlcNAcylation of SNAP-23 promotes cisplatin resistance by inducing exosome secretion in ovarian cancer.

Exosomes have been associated with chemoresistance in various cancers, but such a role in ovarian cancer is not yet clear. Here, using in vitro cell-based and in vivo mouse model experiments, we show that downregulation of O-GlcNAcylation, a key post-translational protein modification, promotes exosome secretion. This increases exosome-mediated efflux of cisplatin from cancer cells resulting in chemoresistance. Mechanistically, our data indicate that downregulation of O-GlcNAclation transferase (OGT) reduces O-GlcNAclation of SNAP-23. Notably, O-GlcNAcylation of SNAP-23 is vital for regulating exosome release in ovarian cancer cells. Reduced O-GlcNAclation of SNAP-23 subsequently promotes the formation of soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) complex consisting of SNAP-23, VAMP8, and Stx4 proteins. This enhances exosome release causing chemoresistance by increasing the efflux of intracellular cisplatin.

Screening and Identification of a Specific Binding Peptide to Ovarian Cancer Cells from a Phage-Displayed Peptide Library.

To select specific binding peptides for imaging and detection of human ovarian cancer. The phage 12-mer peptide library was used to select specific phage clones to ovarian cancer cells. After four rounds of biopanning, the binding specificity of randomly selected phage clones to ovarian cancer cells was determined by enzyme-linked immunosorbent assay (ELISA). DNA sequencing and homology analysis were performed on specifically bound phages. The binding ability of the selected peptides to SKOV3 cells was confirmed by fluorescence microscopy and flow cytometry. After four rounds of optimized biological panning, phage recovery was 34-fold higher than that of the first round, and the specific phage clones bound to SKOV3 cells were significantly enriched. A total of 32 positive phage clones were preliminarily identified by ELISA from 54 randomly selected clones, and the positive rate was 59.3%. S36 was identified as the clone with best affinity to SKOV3 cells via fluorescence microscopy and flow cytometry. A representative clone of OSP2, S36 is expected to be an effective probe for diagnosis and treatment of ovarian cancer.

Growth differentiation factor-15 promotes immune escape of ovarian cancer via targeting CD44 in dendritic cells.

Immune escape is the main cause of the low response rate to immunotherapy for cancer, including ovarian cancer. Growth differentiation factor-15 (GDF-15) inhibits immune cell function. However, only few reports described the mechanism. Therefore, the aim of this study was to investigate the mechanism of immune escape regulated by GDF-15 in ovarian cancer. Ovarian cancer patients and healthy women were enrolled in this study. Immunohistochemistry and ELISA were performed to measure GDF-15 expression. Immunoprecipitation combined with mass spectrometry, surface plasmon resonance, and co-immunoprecipitation assay were used to evaluate the interaction between GDF-15 and the surface molecules of DCs. Immunofluorescence analysis, flow cytometry and transwell assay were used to evaluate additional effects of GDF-15 on DCs. The results showed that GDF-15 expression was higher in the ovarian cancer patients compared to that in the healthy women. The TIMER algorithm revealed that highly GDF-15 expression is associated with immune DC infiltration in immunoreactive high-grade serous carcinoma. A further study showed that GDF-15 suppressed DCs maturation, as well as IL-12p40 and TNF-α secretion, the length and number of protrusions and the migration. More importantly, CD44 in the surface of DCs interacted with GDF-15. The overexpression of CD44 in DCs resulted in the suppression of the inhibitory effect of GDF-15 on the length and number of DC synapses. In DCs overexpressing CD44 the inhibition of GDF-15 on the expression of CD11c, CD83 and CD86 was decreased, while in DCs with a knockdown of CD44 the inhibition was further enhanced. Knockdown of CD44 in DCs enhanced the inhibitory effect of GDF-15 on DC migration, while the overexpression of CD44 inhibited the inhibitory effect of GDF-15 on DC migration. In conclusion, the present study suggested that GDF-15 might facilitate ovarian cancer immune escape by interacting with CD44 in DCs to inhibit their function.

Electron Microscopic Reconstruction of Neural Circuitry in the Cochlea.

Recent studies reveal great diversity in the structure, function, and efferent innervation of afferent synaptic connections between the cochlear inner hair cells (IHCs) and spiral ganglion neurons (SGNs), which likely enables audition to process a wide range of sound pressures. By performing an extensive electron microscopic (EM) reconstruction of the neural circuitry in the mature mouse organ of Corti, we demonstrate that afferent SGN dendrites differ in abundance and composition of efferent innervation in a manner dependent on their afferent synaptic connectivity with IHCs. SGNs that sample glutamate release from several presynaptic ribbons receive more efferent innervation from lateral olivocochlear projections than those driven by a single ribbon. Next to the prevailing unbranched SGN dendrites, we found branched SGN dendrites that can contact several ribbons of 1-2 IHCs. Unexpectedly, medial olivocochlear neurons provide efferent innervation of SGN dendrites, preferring those forming single-ribbon, pillar-side synapses. We propose a fine-tuning of afferent and efferent SGN innervation.

AFSBN: A Method of Artificial Fish Swarm Optimizing Bayesian Network for Epistasis Detection.

How to mine the interaction between SNPs (namely epistasis) efficiently and accurately must be considered when to tackle the complexity of underlying biological mechanisms. In order to overcome the defect of low learning efficiency and local optimal, this work proposes an epistasis mining method using artificial fish swarm optimizing Bayesian network (AFSBN). This method uses the characteristics of global optimization, good robustness and fast convergence about the artificial fish swarm algorithm, and uses the algorithm into the heuristic search strategy of Bayesian network. The initial network structure can be evolved through the manipulations of foraging behavior, clustering behavior, tail-chasing behavior and random behavior. This algorithm chooses different behaviors to modify the network state according to the changing of surrounding environment and the states of partners. It realizes the interaction between each artificial fish and its neighboring environment, and finally finds the optimal network in the population. We compared AFSBN with other existing algorithms on both simulated and real datasets. The experimental results demonstrate that our method outperforms others in epistasis detection accuracy in the case of not affecting the efficiency basically for different datasets.

Lung adenocarcinoma harboring rare epidermal growth factor receptor L858R and V834L mutations treated with icotinib: A case report.

BACKGROUND: Epidermal growth factor receptor (EGFR) tyrosine-kinase inhibitors are widely used for the treatment of non-small-cell lung cancer with EGFR mutations. However, patients with rare, even compound EGFR mutations have different responses to EGFR-tyrosine-kinase inhibitors, which bring uncertainty to clinical treatment. CASE SUMMARY: A 45-year-old female patient presented with a 3-mo history of cough and white sputum without chest pain. Chest computed tomography revealed lung space-occupying lesions and multiple lymphadenectasis. Bronchoscopy and pathology suggested lung adenocarcinoma. Compound variation of EGFR gene (exon 21 L858R/V834L) was detected in both tissue and circulating tumor deoxyribonucleic acid samples. As a result of next-generation sequencing and her family's wishes, the patient was given oral treatment with icotinib hydrochloride (125 mg/d, tid) from March 21, 2019 and has achieved stable disease for the last 1 year. CONCLUSION: Non-small cell lung adenocarcinoma with EGFR L858R/V834L was treated successfully with icotinib, and it may be a new medication treatment option.

Safety and effectiveness of apatinib in patients with previously treated metastatic gastric cancer: a sub-analysis from the real-world study of apatinib for gastric cancer treatment (AHEAD-G202).

Apatinib, a VEGFR2 receptor tyrosine kinase inhibitor, showed survival benefits in Asian patients with heavily pretreated advanced gastric cancer. However, the adverse event (AEs) profile of apatinib has limited its use. Dosing schedules are used to alleviate toxicities despite no supportive evidence. This study aimed to analyze the toxicity and effectiveness of apatinib alone, especially with different dosing strategies in advanced gastric cancer patients under a real-world setting. Data from the subpopulation of patients who failed ≥2 chemotherapy regimens enrolled in the AHEAD-G202 trial were analyzed. The primary endpoint was safety. The secondary endpoints were overall survival (OS) and progression-free survival (PFS). Totally 120 patients were included into three groups by the initial daily doses: 43 (35.8%) patients in the low-dose (250 mg) group, 67 (55.8%) patients in the mid-dose (425 mg to 500 mg) group, and 10 (8.3%) patients in the high-dose (675 to 850 mg) group. Grade 3/4 treatment-emergent AEs were infrequent (<5%), with the most commonly reported grade 3/4 AEs being hand-foot syndrome (4.2%), hypertension (4.2%,), fatigue (4.2%), and difficulty in swallowing (4.2%) which gradually decreased among the high-, mid-, and low-dose groups. The median OS and PFS were 6.33 months (95% CI, 4.57-7.73) and 3.83 months (95% CI: 1.40-4.20), respectively and were comparable among the three doses groups. We found heavily pretreated advanced gastric cancer patients can tolerate and benefit from lower-doses of apatinib therapy. The lower initial daily dosing strategy represents an alternative approach for optimizing apatinib dosing in clinical practice.

Down-regulation of AMPK signaling pathway rescues hearing loss in TFB1 transgenic mice and delays age-related hearing loss.

AMP-activated protein kinase (AMPK) integrates the regulation of cell growth and metabolism. AMPK activation occurs in response to cellular energy decline and mitochondrial dysfunction triggered by reactive oxygen species (ROS). In aged Tg-mtTFB1 mice, a mitochondrial deafness mouse model, hearing loss is accompanied with cochlear pathology including reduced endocochlear potential (EP) and loss of spiral ganglion neurons (SGN), inner hair cell (IHC) synapses and outer hair cells (OHC). Accumulated ROS and increased apoptosis signaling were also detected in cochlear tissues, accompanied by activation of AMPK. To further explore the role of AMPK signaling in the auditory phenotype, we used genetically knocked out AMPKα1 as a rescue to Tg-mtTFB1 mice and observed: improved ABR wave I, EP and IHC function, normal SGNs, IHC synapses morphology and OHC survivals, with decreased ROS, reduced pro-apoptotic signaling (Bax) and increased anti-apoptotic signaling (Bcl-2) in the cochlear tissues, indicating that reduced AMPK attenuated apoptosis via ROS-AMPK-Bcl2 pathway in the cochlea. To conclude, AMPK hyperactivation causes accelerated presbycusis in Tg-mtTFB1 mice by redox imbalance and dysregulation of the apoptosis pathway. The effects of AMPK downregulation on pro-survival function and reduction of oxidative stress indicate AMPK serves as a target to rescue or relieve mitochondrial hearing loss.

An open label, multicenter, noninterventional study of apatinib in advanced gastric cancer patients (AHEAD-G202).

BACKGROUND: Apatinib has been proved to be effective and well tolerated among patients in phase II and III studies. Here, we evaluated the safety and effectiveness of apatinib in advanced gastric cancer patients in a real-world setting. METHODS: This study enrolled advanced gastric cancer patients who had progressed or relapsed despite systemic chemotherapy. The primary outcome was safety and the secondary outcomes included overall survival (OS) and progression-free survival (PFS). RESULTS: A total of 337 patients were included. In total, 62 (18.4%), 102 (30.3%), and 173 (51.3%) patients received first, second, and third or higher line apatinib therapy, respectively. Grade 3/4 treatment-emergent adverse events (AEs) were infrequent (<5%), with hypertension (6.8%) being the only grade 3/4 AE occurring in more than 5% of the patients and across the low-dose (250 mg, 7.3%), mid-dose (425-500 mg, 6.1%), and high-dose group (675-850 mg, 2/15, 13.3%). The median OS and PFS were 7.13 months (95% CI, 6.17-7.93) and 4.20 months (95% CI, 4.60-4.77), respectively, and were comparable among the low-, mid-, and high-dose groups. CONCLUSION: Lower daily doses of apatinib achieved comparable OS and PFS versus higher daily doses of apatinib while maintaining a more benign safety profile in advanced gastric cancer patients. CLINICAL TRIAL REGISTRATION: ClinicalTrials.gov identifier: NCT02668380.

Hearing consequences in Gjb2 knock-in mice: implications for human p.V37I mutation.

Human p.V37I mutation of GJB2 gene was strongly correlated with late-onset progressive hearing loss, especially among East Asia populations. We generated a knock-in mouse model based on human p.V37I variant (c.109G>A) that recapitulated the human phenotype. Cochlear pathology revealed no significant hair cell loss, stria vascularis atrophy or spiral ganglion neuron loss, but a significant change in the length of gap junction plaques, which may have contributed to the observed mild endocochlear potential (EP) drop in homozygous mice lasting lifetime. The cochlear amplification in homozygous mice was compromised, but outer hair cells' function remained unchanged, indicating that the reduced amplification was EP- rather than prestin-generated. In addition to ABR threshold elevation, ABR wave I latencies were also prolonged in aged homozygous animals. We found in homozygous IHCs a significant increase in ICa but no change in Ca2+ efficiency in triggering exocytosis. Environmental insults such as noise exposure, middle ear injection of KCl solution and systemic application of furosemide all exacerbated the pathological phenotype in homozygous mice. We conclude that this Gjb2 mutation-induced hearing loss results from 1) reduced cochlear amplifier caused by lowered EP, 2) IHCs excitotoxicity associated with potassium accumulation around hair cells, and 3) progression induced by environmental insults.

Cellular Differences in the Cochlea of CBA and B6 Mice May Underlie Their Difference in Susceptibility to Hearing Loss.

Hearing is an extremely delicate sense that is particularly vulnerable to insults from environment, including drugs and noise. Unsurprisingly, mice of different genetic backgrounds show different susceptibility to hearing loss. In particular, CBA/CaJ (CBA) mice maintain relatively stable hearing over age while C57BL/6J (B6) mice show a steady decline of hearing, making them a popular model for early onset hearing loss. To reveal possible underlying mechanisms, we examined cellular differences in the cochlea of these two mouse strains. Although the ABR threshold and Wave I latency are comparable between them, B6 mice have a smaller Wave I amplitude. This difference is probably due to fewer spiral ganglion neurons found in B6 mice, as the number of ribbon synapses per inner hair cell (IHC) is comparable between the two mouse strains. Next, we compared the outer hair cell (OHC) function and we found OHCs from B6 mice are larger in size but the prestin density is similar among them, consistent with the finding that they share similar hearing thresholds. Lastly, we examined the IHC function and we found IHCs from B6 mice have a larger Ca2+ current, release more synaptic vesicles and recycle synaptic vesicles more quickly. Taken together, our results suggest that excessive exocytosis from IHCs in B6 mice may raise the probability of glutamate toxicity in ribbon synapses, which could accumulate over time and eventually lead to early onset hearing loss.