Characteristics and parameters of hearing loss in guinea pigs caused by impulse noise exposure
Chen Zhiting  found that more than 50 times of 145dB SPL impulse noise exposure can increase the hearing threshold by more than 70dB SPL on average. In this study, the average hearing threshold increased by 20dB SPL after 165dB SPL impulse noise exposure for 40 times. This difference indicates that the increase in impulse noise stimulation Sound intensity, reduce the number of exposures, and less damage to the auditory system. They also found that hearing recovery was the fastest within one week after exposure, which is consistent with the change trend of hearing thresholds in animals after acute noise damage in this study.
Impulse noise damage affects the proteomics of guinea pig inner ear
In recent years, proteomics related research on NIHL has gradually become a research hotspot. In the past, Samson  used antibody microarray technology to quantify the exposure of chinchillas to 112dB SPL noise for 2 hours, and then 1st day after noise exposure and 7th days after noise exposure. 28th days after noise exposure, the changes in protein expression in different regions of the chinchilla cochlea were detected, indicating that the p38/MAPK signal transduction activated by the focal adhesion signaling pathway plays a key role in the mechanism of NIHL.
Yukihide  used iTRAQ proteomics method to divide 24 mice exposed to 120dB SPL noise for 2 hours into 4 groups to identify different regulatory proteins of dexamethasone in the mouse cochlea, and the results show that myelin protein and heat shock protein 70 are closely related to noise-induced hearing loss, and dexamethasone significantly regulates the expression level of these proteins in the mouse cochlea.
In this study, the TMT proteomics method was used to identify the difference in protein expression in the cochlea under the influence of noise and screened out 6 kinds of hearing related proteins that were significantly down-regulated, TNC; COL11A2; COL2A1; THBS2; COL11A1; RPL38. Except RPL38, all belong to the ECM family.
There are 3 types of collagen in the 6 different proteins: COL11A2, COL11A1, COL2A1, all of which were down-regulation on the seventh day after noise exposure. Collagen in the ECM protein family is a fibrous structural protein, mainly involved in the construction of cartilage . Previous studies have found that mutations in the COL11A2 gene can cause autosomal recessive non-syndromic sensorineural hearing loss (DFNB53) and autosomal dominant non-syndromic sensorineural hearing loss (DFNA13). The loss of collagen fibers in the mouse tectorial membrane will affect the function of outer hair cells ; the COL11A1 gene is expressed in the mouse auditory vesicles , Booth  used splicing variants in the study it was found that COL11A2 gene mutations can cause DFNA37; Cao  found that COL2A1 knockout mice have hearing loss and vestibular function reduction, and its mutations cause sensorineural hearing loss in patients with Type 1 Stickler syndrome . In the inner ear, type II collagen and type XI collagen are located in the tectorial membrane. It is a colloidal structure composed of extracellular material, located on the reticulum plate of the spiral organ, rich in actin, Type II collagen and type XI collagen. The tectorial membrane plays a vital role in the sensory transmission of sound . Normally, the tips of the three-dimensional cilia on the outer hair cells are embedded in the tectorial membrane, while the tips of the cilia on the inner hair cells are adjacent to this structure. The shearing movement between the apex of the hair cell cilia and the tectorial membrane causes the mechanical displacement of the top cilia of the inner hair cell, thereby opening the mechanically sensitive conduction channel. On the first day after impulse noise stimulation, the expression of COL11A2 and COL11A1 were up-regulated by about 15%, and the expression of COL2A1 was up-regulated by about 6%, that is, the expression of ECM protein increased, which in turn changed the arrangement of collagen fibers on the tectorial membrane to make it from an orderly parallel arrangement to a random arrangement, which changes the mechanical properties of the tectorial membrane and destroys the shearing movement of the cilia and the tectorial membrane at the top of the outer hair cells, resulting in the destruction of hearing . After the recovery period, the hearing threshold is increased compared with before. The down-regulated of COL11A2 and COL11A1 is within 10%, and the down-regulated of COL2A1 is more than 20%, and the expression of ECM protein decreases rapidly. It is speculated that the arrangement of collagen fibers on the tectorial membrane has some recovery. It shows that ECM protein plays a vital role in hearing loss and repair during noise exposure.
Impulse noise activates multiple signal transduction pathways in the inner ear of guinea pigs
Pathway significant enrichment method is the same as GO functional enrichment analysis. Through Pathway significant enrichment, the most important biochemical metabolic pathways and signal transduction pathways involved in differentially expressed proteins can be determined. In the data analysis, we screened significant pathways and found that down-regulated differential proteins (ECM proteins) are enriched in protein digestion and absorption pathways, and ECM-receptor interaction pathway, focal adhesion signal pathway (Figure 4). Focal adhesion is a special structure formed by the contact point between cells and extracellular matrix. It is mainly involved in the structural connection between membrane receptors and the actin cytoskeleton. Signal molecules initiate downstream signal transduction events, which ultimately lead to the actin cytoskeleton. The recombination, cell shape and motility, and gene expression changes, the down-regulated expression of this pathway can attenuate the activation of the p38/MAPK signaling pathway . first day after noise exposure, the animal’s hearing threshold dropped rapidly, and the expression of ECM protein was up-regulation. At the same time, oxidative stress in the inner ear up-regulated Fas ligand, which combined with the corresponding receptor would lead to the formation of a death-inducing signal complex , so noise-induced up-regulation of Fas signals may be an important upstream event in NIHL, because these receptors mediate the signal cascade, and finally lead to apoptosis through p38/MAPK signaling ; after a seven day recovery period, ECM protein expression is down-regulated, the corresponding oxidative stress is weakened, and the apoptosis of inner ear cells is reduced. Currently, p38/MAPK inhibitors have been shown to protect the inner ear from noise damage . Interestingly, TNC protein is related to hearing loss . Studies have found that it is a new pathogenic gene of DFNA13 , but it also has repair effect. It was found that its down-regulated expression was detected on the seventh day of the study, but it’s increased by about 3% compared to first day.It is very likely that during the acute injury period on the first day after noise exposure, the oxidative stress pathway was activated, which stimulated the repair of TNC protein. The increase in TNC protein exceeded 20%. In the repair period, the corresponding oxidative stress attenuation, reducing the apoptosis of inner ear cells, the repairing effect of TNC protein is weakened, and the expression of TNC protein is gradually weakened during the repairing period, but it is still higher than normal.
It is worth noting that the RPL38 protein is located in the cytoplasmic ribosome and is involved in ribosome assembly, middle ear morphogenesis, sensory perception of sound and other functions. It does not belong to the ECM family, and information related to deafness is not yet known. it was found that its expression was down-regulation in the seventh days after noise exposure group compared with the first day after noise exposure group in this study. In order to explore whether it is a potential biomarker of NIHL, in the next study, the RPL38 protein will be selected. Through qualitative and quantitative verification of the upstream and downstream expression of the protein in the cochlea, it is also necessary to explore the location of the protein in the cochlea.