Abstract
BackgroundThe receptor for advanced glycation end-products (RAGE) is involved in neuroinflammation. This study investigated the changes in RAGE expression following noise-induced hearing loss.MethodsThree-week-old female Sprague–Dawley rats were exposed to 115 dB SPL white noise for 4 h daily for 3 d (noise group, n = 16). In parallel, age and sex-matched control rats were raised under standard conditions without noise exposure (control group, n = 16). After 2 h (noise immediate, n = 8) and 4 wk (noise 4-week, n = 8) of noise exposure, the auditory cortex was harvested and cytoplasmic and nuclear fractions were isolated. The gene expression levels of tumor necrosis factor alpha (TNF-α), interleukin 6 (IL6), interleukin 1 beta (IL1β), nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB), and RAGE were evaluated using real-time reverse transcription polymerase chain reaction. The protein expression levels of nuclear RAGE and cytosolic RAGE were evaluated using western blotting. Additionally, matrix metalloproteinase 9 (MMP9) was pharmacologically inhibited in the noise immediate group, and then nuclear and cytosolic RAGE expression levels were evaluated.ResultsThe noise immediate and noise 4-week groups exhibited increased auditory thresholds at 4, 8, 16, and 32 kHz frequencies. The genes encoding the pro-inflammatory cytokines TNF-α, IL6, IL1β, and NF- κB were increased 3.74, 1.63, 6.42, and 6.23-fold in the noise immediate group, respectively (P = 0.047, 0.043, 0.044, and 0.041). RAGE mRNA expression was elevated 1.42-fold in the noise 4-week group (P = 0.032). Cytosolic RAGE expression was increased 1.76 and 6.99-fold in the noise immediate and noise 4-week groups, respectively (P = 0.04 and 0.03). Nuclear RAGE expression was comparable between the noise and control groups. matrix metalloproteinase 9 (MMP9) inhibition reduced cytosolic RAGE expression in the noise immediate group (P = 0.004).ConclusionsNoise exposure increased the expression of cytosolic RAGE in the auditory cortex and upregulated pro-inflammatory genes, but this response could be alleviated by MMP9 inhibition.
Highlights
The receptor for advanced glycation end-products (RAGE) is involved in neuroinflammation
We investigated the changes in expression of proinflammatory genes and RAGE in the auditory cortex of rats with noise-induced hearing loss after immediate and 4 wk noise exposure
Spatial activity changes after noise exposure In the Y-maze tests, the number of total arm entry was decreased in the noise 4-week group, compared to control group (7.17 vs. 13.83, P = 0.036) (Fig. 3)
Summary
The receptor for advanced glycation end-products (RAGE) is involved in neuroinflammation. This study investigated the changes in RAGE expression following noise-induced hearing loss. Studies show that noise-induced hearing loss is involved in neuroinflammatory changes in the central auditory pathways [11, 29]. A previous study reported an increase in RAGE expression in rat hippocampus following a 4 wk noise exposure [6]. The authors described increased expression of pro-inflammatory genes including TNF-α and amyloid precursor protein and its cleavage enzymes, β- and γ-secretases [6] This finding implied that noise exposure induced neuroinflammatory and neurodegenerative changes which might be initiated in the early phase exposure. High glucose-induced hearing loss showed increased expression of RAGE, AGE, and NF-κB in rat cochlear hair cells [31]. The increased RAGE, AGE, and NF-κB levels were attenuated following antioxidant treatment [31], implicating oxidative stress responses in inflammation and RAGE pathways
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