Sleep Deprivation Modifies Noise-Induced Cochlear Injury Related to the Stress Hormone and Autophagy in Female Mice

Comparative transcriptome profiling reveals RNA splicing alterations and biological function in patients exposed to occupational noise

Genetic factors play an important role in susceptibility to noise-induced hearing loss (NIHL). Alternative splicing (AS) is an essential mechanism affecting gene expression associated with disease pathogenesis at the post-transcriptional level, but has rarely been studied in NIHL. To explore the role of AS in the development of NIHL, we performed a comprehensive analysis of RNA splicing alterations by comparing the RNA-seq data from blood samples from NIHL patients and subjects with normal hearing who were exposed to the same noise environment. A total of 356 differentially expressed genes, including 23 transcription factors, were identified between the two groups. Of particular note was the identification of 56 aberrant alternative splicing events generated by 41 differentially expressed genes between the two groups, with exon skipping events accounting for 54% of all the differentially alternative splicing (DAS) events. The results of functional enrichment analysis showed that these intersecting DAS genes and differentially expressed genes were significantly enriched in autophagy and mitochondria-related pathways. Together, our findings provide insights into the role of AS events in susceptibility and pathogenesis of NIHL.

The stress of losing sleep: Sex-specific neurobiological outcomes

Sleep is a vital and evolutionarily conserved process, critical to daily functioning and homeostatic balance. Losing sleep is inherently stressful and leads to numerous detrimental physiological outcomes. Despite sleep disturbances affecting everyone, women and female rodents are often excluded or underrepresented in clinical and pre-clinical studies. Advancing our understanding of the role of biological sex in the responses to sleep loss stands to greatly improve our ability to understand and treat health consequences of insufficient sleep. As such, this review discusses sex differences in response to sleep deprivation, with a focus on the sympathetic nervous system stress response and activation of the hypothalamic-pituitary-adrenal (HPA) axis. We review sex differences in several stress-related consequences of sleep loss, including inflammation, learning and memory deficits, and mood related changes. Focusing on women's health, we discuss the effects of sleep deprivation during the peripartum period. In closing, we present neurobiological mechanisms, including the contribution of sex hormones, orexins, circadian timing systems, and astrocytic neuromodulation, that may underlie potential sex differences in sleep deprivation responses.

Conditional Ablation of Glucocorticoid and Mineralocorticoid Receptors from Cochlear Supporting Cells Reveals Their Differential Roles for Hearing Sensitivity and Dynamics of Recovery from Noise-Induced Hearing Loss

Endogenous glucocorticoids (GC) are known to modulate basic elements of cochlear physiology. These include both noise-induced injury and circadian rhythms. While GC signaling in the cochlea can directly influence auditory transduction via actions on hair cells and spiral ganglion neurons, evidence also indicates that GC signaling exerts effects via tissue homeostatic processes that can include effects on cochlear immunomodulation. GCs act at both the glucocorticoid receptor (GR) and the mineralocorticoid receptor (MR). Most cell types in the cochlea express both receptors sensitive to GCs. The GR is associated with acquired sensorineural hearing loss (SNHL) through its effects on both gene expression and immunomodulatory programs. The MR has been associated with age-related hearing loss through dysfunction of ionic homeostatic balance. Cochlear supporting cells maintain local homeostatic requirements, are sensitive to perturbation, and participate in inflammatory signaling. Here, we have used conditional gene manipulation techniques to target Nr3c1 (GR) or Nr3c2 (MR) for tamoxifen-induced gene ablation in Sox9-expressing cochlear supporting cells of adult mice to investigate whether either of the receptors sensitive to GCs plays a role in protecting against (or exacerbating) noise-induced cochlear damage. We have selected mild intensity noise exposure to examine the role of these receptors related to more commonly experienced noise levels. Our results reveal distinct roles of these GC receptors for both basal auditory thresholds prior to noise exposure and during recovery from mild noise exposure. Prior to noise exposure, auditory brainstem responses (ABRs) were measured in mice carrying the floxed allele of interest and the Cre recombinase transgene, but not receiving tamoxifen injections (defined as control (no tamoxifen treatment), versus conditional knockout (cKO) mice, defined as mice having received tamoxifen injections. Results revealed hypersensitive thresholds to mid- to low-frequencies after tamoxifen-induced GR ablation from Sox9-expressing cochlear supporting cells compared to control (no tamoxifen) mice. GR ablation from Sox9-expressing cochlear supporting cells resulted in a permanent threshold shift in mid-basal cochlear frequency regions after mild noise exposure that produced only a temporary threshold shift in both control (no tamoxifen) f/fGR:Sox9iCre+ and heterozygous f/+GR:Sox9iCre+ tamoxifen-treated mice. A similar comparison of basal ABRs measured in control (no tamoxifen) and tamoxifen-treated, floxed MR mice prior to noise exposure indicated no difference in baseline thresholds. After mild noise exposure, MR ablation was initially associated with a complete threshold recovery at 22.6 kHz by 3 days post-noise. Threshold continued to shift to higher sensitivity over time such that by 30 days post-noise exposure the 22.6 kHz ABR threshold was 10 dB more sensitive than baseline. Further, MR ablation produced a temporary reduction in peak 1 neural amplitude one day post-noise. While supporting cell GR ablation trended towards reducing numbers of ribbon synapses, MR ablation reduced ribbon synapse counts but did not exacerbate noise-induced damage including synapse loss at the experimental endpoint. GR ablation from the targeted supporting cells increased the basal resting number of Iba1-positive (innate) immune cells (no noise exposure) and decreased the number of Iba1-positive cells seven days following noise exposure. MR ablation did not alter innate immune cell numbers at seven days post-noise exposure. Taken together, these findings support differential roles of cochlear supporting cell MR and GR expression at basal, resting conditions and especially during recovery from noise exposure.

Sestrin 2 Deficiency Exacerbates Noise-Induced Cochlear Injury Through Inhibiting ULK1/Parkin-Mediated Mitophagy

Aims: Noise damage to auditory hair cells is associated with oxidative stress and mitochondrial dysfunction. This study aimed to investigate the possible effect of sestrin 2 (SESN2), an endogenous antioxidant protein, on noise-induced hearing loss (NIHL) and the underlying mechanisms. Results: We identified SESN2 as a protective factor against oxidative stress in NIHL through activation of Parkin-mediated mitophagy. Consistently, SESN2 expression was increased and mitophagy was induced during the early stage after a temporary threshold shift due to noise exposure or hydrogen peroxide(H2O2) stimulation; conversely, SESN2 deficiency blocked mitophagy and exacerbated acoustic trauma. Mechanistically, SESN2 interacted with Unc-51-like protein kinase 1(ULK1), promoting ULK1 protein-level stabilization by interfering with its proteasomal degradation. This stabilization is essential for mitophagy initiation, since restoring ULK1 expression in SESN2-silenced cells rescued mitophagy defects. Innovation and Conclusion: Our results provide novel insights regarding SESN2 as a therapeutic target against noise-induced cochlear injury, possibly through improved mitophagy. Antioxid. Redox Signal. 38, 115-136.

Vigilant Attention, Cerebral Blood Flow and Grey Matter Volume Change after 36 h of Acute Sleep Deprivation in Healthy Male Adults: A Pilot Study

It is commonly believed that alertness and attention decrease after sleep deprivation (SD). However, there are not enough studies on the changes in psychomotor vigilance testing (PVT) during SD and the corresponding changes in brain function and brain structure after SD. Therefore, we recruited 30 healthy adult men to perform a 36 h acute SD experiment, including the measurement of five indicators of PVT every 2 h, and analysis of cerebral blood flow (CBF) and grey matter volume (GMV) changes, before and after SD by magnetic resonance imaging (MRI). The PVT measurement found that the mean reaction time (RT), fastest 10% RT, minor lapses, and false starts all increased progressively within 20 h of SD, except for major lapses. Subsequently, all indexes showed a significant lengthening or increasing trend, and the peak value was in the range of 24 h-32 h and decreased at 36 h, in which the number of major lapses returned to normal. MRI showed that CBF decreased in the left orbital part of the superior frontal gyrus, the left of the rolandic operculum, the left triangular part, and the right opercular part of the inferior frontal gyrus, and CBF increased in the left lingual gyrus and the right superior gyrus after 36 h SD. The left lingual gyrus was negatively correlated with the major lapses, and both the inferior frontal gyrus and the superior frontal gyrus were positively correlated with the false starts. Still, there was no significant change in GMV. Therefore, we believe that 36 h of acute SD causes alterations in brain function and reduces alert attention, whereas short-term acute SD does not cause changes in brain structure.

Evaluating Risk of Noise-Induced Hearing Loss in Otologic Surgery

OBJECTIVES

To evaluate risk for noise-induced hearing damage from otologic surgery-related noise exposure, given recent research indicating that noise levels previously believed to be safe and without long-term consequence may result in cochlear synaptopathy with subsequent degeneration of spiral ganglion neurons, degradation of neural transmission in response to suprathreshold acoustic stimuli, and difficulty understanding in background noise.

METHODS

A prospective observational study of surgeon noise exposure during otologic and neurotologic procedures was performed in a tertiary care center. Surgeon noise exposure was recorded in A- and C-weighted decibel scales (dBA, dBC), including average equivalent (LA_eq) and peak (LA_peak, LC_peak) levels and noise dose.

RESULTS

Sound measurements taken at the ear with continuous recording equipment during cadaveric otologic surgery demonstrated LA_eq 80-83 dBA, LA_peaks of 105 dBA, LC_peaks of 127 dBC, with noise doses of 0.9% to 6.7%. Sound level measurements during live surgery translabyrinthine approaches yielded lower LAeq of 72 to 74 dBA and lower noise doses compared with temporal bone lab measurements. Raw sound recordings during live surgery demonstrated narrow band, high frequency, high amplitude spikes between 4 and 12 kHz.

CONCLUSION

Noise exposure to surgeons, staff, and patients in the operating room is acceptable per NIOSH recommendations. Temporal bone lab noise exposures are greater, possibly due to poorly maintained drill systems and lack of noise shielding from microscope bulk, yet are also within NIOSH recommended levels.

New Target of Oxidative Stress Regulation in Cochleae: Alternative Splicing of the p62/Sqstm1 Gene

We investigated oxidative stress and antioxidant response in the p62/Sqstm1-Keap1-Nrf2 pathway in C57BL/6 mice cochleae during age-related hearing loss (ARHL) and noise-induced hearing loss (NIHL), and the function of full-length and variant p62 in the regulation of Nrf2 activation. Groups of young (2 months), old (13-14 months), control, and acoustic trauma (AT) mice were examined cochlear damage and oxidative stress as follows: auditory brainstem response and hair cell counts; malondialdehyde (MDA) levels measured by assay kit and 7,8-dihydro-8-oxoguanine (8-oxoG) detected by immunohistochemistry. Full-length and variant p62 were examined for expression in cochleae, hippocampus (HIP), and auditory cortex (AC) using immunoblotting. Keap1-Nrf2 pathway activation was based on immunoblotting of nuclear Nrf2 and quantitative real-time PCR of Nrf2 target genes HO-1/NQO-1. The oxidative function of full-length and variant p62 was examined in HEI-OC-1 cells by flow cytometry. The results showed hearing loss, and cochlear hair cell loss was associated with MDA accumulation and 8-oxoG expression during ARHL and NIHL. Nrf2 showed no obvious changes in nuclear protein. Expression levels mRNA for HO-1 and NQO1 were lower in old mice and mildly greater in AT Mice. The expression of p62 splicing variant lacking the Keap1-interacting region was greater than full-length p62 in cochleae. However, the expression of p62 splicing variant was lesser than full-length p62 in HIP and AC. For HEI-OC-1 cells, overexpression of full-length p62 decreased ROS levels induced by H₂O₂. Oxidative stress is closely related to ARHL and NIHL. Changing the ratio of full-length to variant p62 protein expression may be a new target to reduce the level of oxidative stress in cochleae.

Reporting Data on Auditory Brainstem Responses (ABR) in Rats: Recommendations Based on Review of Experimental Protocols and Literature

Research in hearing science is accelerating, and a wealth of data concerning auditory brainstem responses (ABR) in various animal models is published in peer-reviewed journals every year. Recently, we reviewed studies using ABR measurements in tinnitus rat models. We found significant discrepancies in the outcomes of these studies, some due to different research approaches and others due to different methodologies. Thus, the present work aimed to collect comprehensive information on all factors influencing ABR recordings in rats and compile recommendations on ABR data reporting. A questionnaire with queries about animal husbandry, transfer, handling, and the exact test conditions before, during, and after ABR recordings was sent to 125 researchers who published the relevant studies between 2015 and 2021. Eighteen researchers provided detailed answers on factors related to ABR measurements. Based on the analysis of the returned questionnaires, we identified three domains reflecting animal-, equipment-, and experiment-dependent factors that might influence the ABR outcome, thus requiring reporting in published research. The analysis of survey results led to the compilation of recommendations for reporting ABR outcomes supported by a literature review. Following these recommendations should facilitate comparative and meta-analyses of ABR results provided by various research groups.

Noise-Induced Hearing Loss: Updates on Molecular Targets and Potential Interventions

Noise overexposure leads to hair cell loss, synaptic ribbon reduction, and auditory nerve deterioration, resulting in transient or permanent hearing loss depending on the exposure severity. Oxidative stress, inflammation, calcium overload, glutamate excitotoxicity, and energy metabolism disturbance are the main contributors to noise-induced hearing loss (NIHL) up to now. Gene variations are also identified as NIHL related. Glucocorticoid is the only approved medication for NIHL treatment. New pharmaceuticals targeting oxidative stress, inflammation, or noise-induced neuropathy are emerging, highlighted by the nanoparticle-based drug delivery system. Given the complexity of the pathogenesis behind NIHL, deeper and more comprehensive studies still need to be fulfilled.

Autophagy: A Novel Horizon for Hair Cell Protection

As a general sensory disorder, hearing loss was a major concern worldwide. Autophagy is a common cellular reaction to stress that degrades cytoplasmic waste through the lysosome pathway. Autophagy not only plays major roles in maintaining intracellular homeostasis but is also involved in the development and pathogenesis of many diseases. In the auditory system, several studies revealed the link between autophagy and hearing protection. In this review, we aimed to establish the correlation between autophagy and hair cells (HCs) from the aspects of ototoxic drugs, aging, and acoustic trauma and discussed whether autophagy could serve as a potential measure in the protection of HCs.