Up-regulation of hypoxia-inducible factor-1 alpha by cobalt chloride prevents hearing loss in noise-exposed mice

Expression of placental glycans and its role in regulating peripheral blood NK cells during preeclampsia: a perspective

Preeclampsia is a pregnancy-related multisystem disorder characterized by altered trophoblast invasion, oxidative stress, exacerbation of systemic inflammatory response, and endothelial damage. The pathogenesis includes hypertension and mild-to-severe microangiopathy in the kidney, liver, placenta, and brain. The main mechanisms involved in its pathogenesis have been proposed to limit trophoblast invasion and increase the release of extracellular vesicles from the syncytiotrophoblast into the maternal circulation, exacerbating the systemic inflammatory response. The placenta expresses glycans as part of its development and maternal immune tolerance during gestation. The expression profile of glycans at the maternal-fetal interface may play a fundamental role in physiological pregnancy changes and disorders such as preeclampsia. It is unclear whether glycans and their lectin-like receptors are involved in the mechanisms of maternal-fetal recognition by immune cells during pregnancy homeostasis. The expression profile of glycans appears to be altered in hypertensive disorders of pregnancy, which could lead to alterations in the placental microenvironment and vascular endothelium in pregnancy conditions such as preeclampsia. Glycans with immunomodulatory properties at the maternal-fetal interface are altered in early-onset severe preeclampsia, implying that innate immune system components, such as NK cells, exacerbate the systemic inflammatory response observed in preeclampsia. In this article, we discuss the evidence for the role of glycans in gestational physiology and the perspective of glycobiology on the pathophysiology of hypertensive disorders in gestation.

Accumulated ROS Activates HIF-1α-Induced Glycolysis and Exerts a Protective Effect on Sensory Hair Cells Against Noise-Induced Damage

Noise exposure causes noise-induced hearing loss (NIHL). NIHL exhibits loss of inner ear sensory hair cells and is often irreparable. Although oxidative stress is involved in hearing loss, the complex mechanisms involved in NIHL are unclear. Hypoxia-inducible factor 1α (HIF-1α) has been suggested to be essential for protecting sensory hair cells. Additionally, it has been shown that ROS is involved in modulating the stability of HIF-1α. To investigate the NIHL pathogenesis, we established a tert-butyl hydroperoxide (t-BHP)-induced oxidative stress damage model in hair-like HEI-OC1 cells and an NIHL model in C57BL/6 mice. Protein and mRNA expression were determined, and biochemical parameters including reactive oxygen species (ROS) accumulation, glucose uptake, adenosine triphosphat (ATP) production, and mitochondrial content were evaluated. In HEI-OC1 cells, t-BHP induced ROS accumulation and reduced mitochondrial content and oxygen consumption, but the ATP level was unaffected. Additionally, there was increased glucose uptake and lactate release along with elevated expression of HIF-1α, glucose transporter 1, and several glycolytic enzymes. Consistently, noise trauma induced oxidative stress and the expression of HIF-1α and glycolytic enzymes in mice. Thus, we concluded that ROS induced HIF-1α expression, which promoted glycolysis, suggesting a metabolic shift maintained the ATP level to attenuate hair cell damage in NIHL.

Evaluation of Oxidative-Stress Pathway and Recovery of Sudden Sensorineural Hearing Loss

Introduction  Although the pathogenesis of sudden sensorineural hearing loss (SSNHL) has been discussed in the literature, many unclear points remain. Several authors have hypothesized that oxidative stress plays a role in the pathogenesis of noise-related hearing loss, as well as in drug- and aging-related hearing loss. Reactive oxygen species (ROS) may contribute to the pathogenesis of SSNHL in a similar way as in cases of ototoxicity, noise-induced hearing loss and presbyacusis. Objective  The aim of the present study was to find potential peripheral biomarkers to show the levels of oxidative stress in samples of peripheral blood collected from SSNHL patients with and withouth metabolic disease. Methods  In total, 80 consecutive patients with SSNHL were evaluated in the otolaryngology emergency room and outpatient clinic of a tertiary hospital between May 2017 and May 2019. All patients underwent detailed anamnesis, physical examination, audiometry, magnetic resonance imaging (MRI) of the inner ears, and blood tests for serum lipids and plasma activity of thiobarbituric acid reactive species (TBARS). Results  No significant effect of malondialdehyde (MDA) activity was observed regarding the hearing recovery of patients who developed SSNHL. Conclusion  We did not observe a significant correlation between the concentration of TBARs in the peripheral blood or the presence of arterial hypertension and the severity of the initial hearing loss or the prognosis of hearing recovery in patients with SSNHL. The concentration of TBARs in the peripheral blood may not adequately represent the abnormalities that occur in the intracoclear environment.

Antioxidant Therapy against Oxidative Damage of the Inner Ear: Protection and Preconditioning

Oxidative stress is an important mechanism underlying cellular damage of the inner ear, resulting in hearing loss. In order to prevent hearing loss, several types of antioxidants have been investigated; several experiments have shown their ability to effectively prevent noise-induced hearing loss, age-related hearing loss, and ototoxicity in animal models. Exogenous antioxidants has been used as single therapeutic agents or in combination. Antioxidant therapy is generally administered before the production of reactive oxygen species. However, post-exposure treatment could also be effective. Preconditioning refers to the phenomenon of pre-inducing a preventative pathway by subtle stimuli that do not cause permanent damage in the inner ear. This renders the inner ear more resistant to actual stimuli that cause permanent hearing damage. The preconditioning mechanism is also related to the induction of antioxidant enzymes. In this review, we discuss the mechanisms underlying antioxidant-associated therapeutic effects and preconditioning in the inner ear.

Increased Risk of Sensorineural Hearing Loss as a Result of Exposure to Air Pollution

Whether exposure to air pollution is associated with developing sensorineural hearing loss (SHL) remains controversial. Using data from the National Health Insurance Research Database, we recruited a total of 75,767 subjects aged older than 20 years with no history of SHL from 1998 to 2010, and they were followed up until SHL was observed, they withdrew from the National Health Insurance program, or the study ended. The subjects were evenly exposed to low-level, mid-level, and high-level carbon monoxide (CO) and nitrogen dioxide (NO₂). The incidence rate ratio of SHL for patients exposed to high-level CO was 1.24 (95% confidence interval (CI) = 1.14–1.36). The NO₂ pollutants increased the incidence rate ratios of SHL in mid-level NO₂ and high-level NO₂ exposures by 1.10 (95% CI = 1.10–1.32) and 1.36 (95% CI = 1.24–1.49) times, respectively. The adjusted hazard ratio (adj. HR) of SHL in patients exposed to high-level CO was 1.45 (95% CI = 1.31–1.59), relative to that of patients exposed to low-level CO. Compared to patients exposed to low-level NO₂, patients exposed to mid-level NO₂ (adj. HR = 1.40, 95% CI = 1.27–1.54) and high-level NO₂ (adj. HR = 1.63, 95% CI = 1.48–1.81) had a higher risk of developing SHL. The increased risk of SHL following the increased concentrations of air pollutants (CO and NO₂) was statistically significant in this study. In conclusion, the subjects’ exposure to air pollution exhibited a significantly higher risk of developing SHL in Taiwan.

Induction of Redox-Active Gene Expression by CoCl2 Ameliorates Oxidative Stress-Mediated Injury of Murine Auditory Cells

Free radicals formed in the inner ear in response to high-intensity noise, are regarded as detrimental factors for noise-induced hearing loss (NIHL). We reported previously that intraperitoneal injection of cobalt chloride attenuated the loss of sensory hair cells and NIHL in mice. The present study was designed to understand the preconditioning effect of CoCl₂ on oxidative stress-mediated cytotoxicity. Treatment of auditory cells with CoCl₂ promoted cell proliferation, with increases in the expressions of two redox-active transcription factors (hypoxia-inducible factor 1α, HIF-1α, nuclear factor erythroid 2-related factor 2; Nrf-2) and an antioxidant enzyme (peroxiredoxin 6, Prdx6). Hydrogen peroxide treatment resulted in the induction of cell death and reduction of these protein expressions, reversed by pretreatment with CoCl₂. Knockdown of HIF-1α or Nrf-2 attenuated the preconditioning effect of CoCl₂. Luciferase reporter analysis with a Prdx6 promoter revealed transactivation of Prdx6 expression by HIF-1α and Nrf-2. The intense immunoreactivities of HIF-1α, Nrf-2, and Prdx6 in the organ of Corti (OC), spiral ganglion cells (SGC), and stria vascularis (SV) of the cochlea in CoCl₂-injected mice suggested CoCl₂-induced activation of HIF-1α, Nrf-2, and Prdx6 in vivo. Therefore, we revealed that the protective effect of CoCl₂ is achieved through distinctive signaling mechanisms involving HIF-1α, Nrf-2, and Prdx6.

DNA methylation dynamics during embryonic development and postnatal maturation of the mouse auditory sensory epithelium

The inner ear is a complex structure responsible for hearing and balance, and organ pathology is associated with deafness and balance disorders. To evaluate the role of epigenomic dynamics, we performed whole genome bisulfite sequencing at key time points during the development and maturation of the mouse inner ear sensory epithelium (SE). Our single-nucleotide resolution maps revealed variations in both general characteristics and dynamics of DNA methylation over time. This allowed us to predict the location of non-coding regulatory regions and to identify several novel candidate regulatory factors, such as Bach2, that connect stage-specific regulatory elements to molecular features that drive the development and maturation of the SE. Constructing in silico regulatory networks around sites of differential methylation enabled us to link key inner ear regulators, such as Atoh1 and Stat3, to pathways responsible for cell lineage determination and maturation, such as the Notch pathway. We also discovered that a putative enhancer, defined as a low methylated region (LMR), can upregulate the GJB6 gene and a neighboring non-coding RNA. The study of inner ear SE methylomes revealed novel regulatory regions in the hearing organ, which may improve diagnostic capabilities, and has the potential to guide the development of therapeutics for hearing loss by providing multiple intervention points for manipulation of the auditory system.

MiR-34a contributes to diabetes-related cochlear hair cell apoptosis via SIRT1/HIF-1α signaling

Type 2 diabetes (T2DM) has been considered to be associated with a higher likelihood of hearing impairment (HI). However, the molecular mechanisms underlying the association between diabetes and HI are poorly understood. MicroRNAs have recently been demonstrated to be closely associated with hearing loss and considered as promising therapeutic targets. Herein, we investigated whether miR-34a contributes to diabetes-related cochlear hair cell apoptosis and sought to identify the underlying mechanism. The results showed that miR-34a was up-regulated in the cochleas of db/db mice, accompanied by significant hearing threshold elevation and hair cell loss. However, the expression of SIRT1 was significantly down-regulated, while hypoxia-inducible factor-1alpha (HIF-1α) levels were dramatically increased in the cochleas of db/db mice. In addition, in the high-glucose cultured House Ear Institute-Organ of Corti 1 (HEI-OC1) cell line, miR-34a overexpression inhibited sirtuin1 (SIRT1) expression, increased HIF-1α levels and promoted apoptosis. MiR-34a knockdown exerted effects that were diametrically opposed to those observed with overexpression. Interestingly, HIF-1α knockdown almost eliminated the cell apoptosis induced by high glucose levels. We also examined the modulation of HIF-1α expression by SIRT1. The results showed that SIRT1 knockdown further promoted high-glucose-induced HIF-1α expression, while SIRT1 overexpression significantly inhibited HIF-1α level induced by high glucose. These findings point to a new mechanism by which miR-34a exerts its detrimental effects by negatively regulating SIRT1/HIF-1α signaling and provide new therapeutic targets for treating hearing impairment during diabetes.

Characterization of the Transcriptomes of Lgr5+ Hair Cell Progenitors and Lgr5- Supporting Cells in the Mouse Cochlea

Cochlear supporting cells (SCs) have been shown to be a promising resource for hair cell (HC) regeneration in the neonatal mouse cochlea. Previous studies have reported that Lgr5+ SCs can regenerate HCs both in vitro and in vivo and thus are considered to be inner ear progenitor cells. Lgr5+ progenitors are able to regenerate more HCs than Lgr5- SCs, and it is important to understand the mechanism behind the proliferation and HC regeneration of these progenitors. Here, we isolated Lgr5+ progenitors and Lgr5- SCs from Lgr5-EGFP-CreERT2/Sox2-CreERT2/Rosa26-tdTomato mice via flow cytometry. As expected, we found that Lgr5+ progenitors had significantly higher proliferation and HC regeneration ability than Lgr5- SCs. Next, we performed RNA-Seq to determine the gene expression profiles of Lgr5+ progenitors and Lgr5- SCs. We analyzed the genes that were enriched and differentially expressed in Lgr5+ progenitors and Lgr5- SCs, and we found 8 cell cycle genes, 9 transcription factors, and 24 cell signaling pathway genes that were uniquely expressed in one population but not the other. Last, we made a protein–protein interaction network to further analyze the role of these differentially expressed genes. In conclusion, we present a set of genes that might regulate the proliferation and HC regeneration ability of Lgr5+ progenitors, and these might serve as potential new therapeutic targets for HC regeneration.

Macrophage Migration Inhibitory Factor Deficiency Causes Prolonged Hearing Loss After Acoustic Overstimulation

HYPOTHESIS

Macrophage migration inhibitory factor plays an important role in noise-induced hearing loss.

BACKGROUND

Macrophage migration inhibitory factor is an essential factor in axis formation and neural development. Macrophage migration inhibitory factor is expressed in the inner ear, but its function remains to be elucidated.

METHODS

Macrophage migration inhibitory factor-deficient mice (MIF(-/-) mice) were used in this study. Wild-type and MIF(-/-) mice received noise exposure composed of octave band noise. Auditory brainstem response thresholds were examined before (control) and at 0, 12, and 24 hours and 2 weeks after the intense noise exposure. Morphological findings of cochlear hair cells were investigated using scanning electron microscopy. Histopathological examination with hematoxylin and eosin staining and TUNEL assay were also performed.

RESULTS

In both the wild-type and MIF(-/-) mice, acoustic overstimulation induced significant hearing loss compared with the control level. Two weeks after the intense noise exposure, the MIF(-/-) mice had an increased hearing threshold compared with the wild-type mice. Scanning electron microscopy demonstrated that the outer hair cells in the MIF(-/-) mice were affected 2 weeks after noise exposure compared with the wild-type mice. TUNEL-positive cells were identified in the organ of Corti of the MIF(-/-) mice.

CONCLUSION

The MIF(-/-) mice had prolonged hearing loss and significant loss of cochlear hair cells after intense noise exposure. Macrophage migration inhibitory factor may play an important role in recovery from acoustic trauma. Management of macrophage migration inhibitory factor may be a novel therapeutic option for noise-induced hearing loss.

The effects of CoCl2 on HIF-1α protein under experimental conditions of autoprogressive hypoxia using mouse models

It is well known that cobalt chloride (CoCl2) can enhance the stability of hypoxia-inducible factor (HIF)-1α. The aim of this study is to detect the effect of CoCl2 on the hypoxia tolerance of mice which were repeatedly exposed to autoprogressive hypoxia. Balb/c mice were randomly divided into groups of chemical pretreatment and normal saline (NS), respectively injected with CoCl2 and NS 3 h before exposure to hypoxia for 0 run (H0), 1 run (H1), and 4 runs (H4). Western Blot, electrophoretic mobility shift assay (EMSA), extracellular recordings population spikes in area cornus ammonis I (CA 1) of mouse hippocampal slices and real-time were used in this study. Our results demonstrated that the tolerance of mice to hypoxia, the changes of HIF-1α protein level and HIF-1 DNA binding activity in mice hippocampus, the mRNA level of erythropoietin (EPO) and vascular endothelial growth factor (VEGF), and the disappearance time of population spikes of hippocampal slices were substantially different between the control group and the CoCl2 group. Over-induction of HIF-1α by pretreatment with CoCl2 before hypoxia did not increase the hypoxia tolerance.