Functional consequences of inducible genetic elements from the p53 SOS response in a mammalian organ system

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

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

Emerging and established therapies for chemotherapy-induced ototoxicity

PURPOSE

Ototoxicity is considered a dose-limiting side effect of some chemotherapies. Hearing loss, in particular, can have significant implications for the quality of life for cancer survivors. Here, we review therapeutic approaches to mitigating ototoxicity related to chemotherapy.

METHODS

Literature review.

CONCLUSIONS

Numerous otoprotection strategies are undergoing active investigation. However, numerous challenges exist to confer adequate protection while retaining the anti-cancer efficacy of the chemotherapy.

IMPLICATIONS FOR CANCER SURVIVORS

Ototoxicity can have significant implications for cancer survivors, notably those receiving cisplatin. Clinical translation of multiple otoprotection approaches will aid in limiting these consequences.

Abnormal neural adaptation consequent to combined exposure to jet fuel and noise

A fundamental property of first-order sensory neurons is the ability to alter their response properties as a function of change in the statistical parameters of an input signal. Such neural adaptation shapes the performance features of contiguous neural circuits that ultimately drive sensory discrimination. The current study focused on whether combined exposure to jet fuel and noise might alter the capacity of the auditory nerve to adapt to stimulus presentation speed. Young hooded Long-Evans 4-5 weeks old male rats were grouped and used in the current experiment. One group was exposed via inhalation to 1000 mg/m³ of jet propulsion fuel for 6 hr per day, 5 days per week for 4 weeks. Another group was exposed to a 5.5-11.3 kHz band-pass noise at 85 dB SPL for 6 hr per day, 5 days per week for 4 weeks. An additional group was simultaneously exposed to both jet fuel and noise. An age-matched group served as control and was not exposed to either jet fuel or noise. After experimental exposures, animals were given 4 weeks to recover and then assessed for neural adaptation. Both slow and fast rectangular voltage pulses were employed to elicit neuroelectric activity from the animals. Data demonstrated significant neural adaptation (1.46 μV shift) among controls, where neural activity decreased as the stimulus presentation speed rose from 10 to 100 per sec. This effect might also be observed in animals in the jet fuel treated and rats in the noise-exposed group. However, animals who were simultaneously exposed to both jet fuel and noise failed to exhibit neural adaptation. This abnormality appeared to be masked because independent slow and fast stimuli produced similar neural activity between controls and rats exposed to both jet fuel and noise. Therefore, neural adaptation assays may further be developed to unmask silent neurotoxicity consequent to physiochemical exposures.

Age-related and noise-induced hearing loss alters grasshopper mouse (Onychomys) vocalizations

Age-related and noise-induced hearing loss disorders are among the most common pathologies affecting Americans across their lifespans. Loss of auditory feedback due to hearing disorders is correlated with changes in voice and speech-motor control in humans. Although rodents are increasingly used to model human age- and noise-induced hearing loss, few studies have assessed vocal changes after acoustic trauma. Northern grasshopper mice (Onychomys leucogaster) represent a candidate model because their hearing sensitivity is matched to the frequencies of long-distance vocalizations that are produced using vocal fold vibrations similar to human speech. In this study, we quantified changes in auditory brainstem responses (ABRs) and vocalizations related to aging and noise-induced acoustic trauma. Mice showed a progressive decrease in hearing sensitivity across 4-32 kHz, with males losing hearing more rapidly than females. In addition, noise-exposed mice had a 61.55 dB SPL decrease in ABR sensitivity following a noise exposure, with some individuals exhibiting a 21.25 dB recovery 300-330 days after noise exposure. We also found that older grasshopper mice produced calls with lower fundamental frequency. Sex differences were measured in duration of calls with females producing longer calls with age. Our findings indicate that grasshopper mice experience age- and noise- induced hearing loss and concomitant changes in vocal output, making them a promising model for hearing and communication disorders.

Effects of acute noise exposure on DNA damage response genes in the cochlea, cortex, heart and liver

Noise as a systemic stressor induces various organ dysfunctions and the underlying molecular pathology is unknown. Previous studies have shown that noise exposure results in the accumulation of DNA damage in auditory and non-auditory organs. The DNA damage response (DDR) is a global protective mechanism that plays a critical role in maintaining DNA integrity. However, the role of DDR genes in noise induced systemic (non-auditory) pathology has not been investigated. The current pilot study was designed to test the hypothesis that an acute noise exposure would alter the normal expression of DDR genes (e.g., ATM, p53 & XPC) in auditory (cochlea) and non-auditory organs, such as the cortex, heart and liver. Mice were used as subjects in this study and consisted of a baseline group, a one-hour noise exposure (@105 dB) group, and a four-hour noise exposure (@105 dB) group. ATM, p53 and XPC expression levels were quantified through end-point polymerize chain reactions. The current study demonstrated that noise exposure failed to elicit statistically significant changes in DDR genes (relative to baseline) across the various organs. The failure of the cochlea, heart, cortex and liver to upregulate protective DDR genes during acute noise exposure might help to explain their susceptibility to noise-induced DNA damage. This suggests that, biomedical interventions to upregulate DDR genes may need to be implemented before noise exposure or during the early stages of noise exposure.