Analysis of otospiralin down-regulation and acoustic damage to organ of Corti in guinea pig.

Noise over-stimulation induces or influences molecular pathways in the cochlea. One approach to the identification of the components of these pathways is to examine genes and proteins that change after the different types and levels of stress. Quantitative RT-PCR was used to understand if there were changes in the expression of proteins not directly involved in perception of sound consequently to white noise administration. We found a downregulation of mRNA level of otospiralin, a protein expressed by fibrocytes in the cochlea of guinea pigs, after white noise over-stimulation at 108 dB SPL. This level of noise caused a temporary threshold shift (TTS) after 2h and a permanent threshold shift (PTS) after 5h. This could indicate that otospiralin is directly involved in ion homeostasis in endolimph. On the other hand one cannot exclude that the down-regulation of otospiralin could alter the fibrocytes themselves and indirectly perturb hair cells metabolism. By using in situ hybridization we have showed that there was not relevant change in cell types expressing otospiralin after noise stress. In order to determine whether there was damage together with TTS, we have examined, by SEM analysis, the hair cells fate in the organ of Corti after exposure to white noise. After 2 h of treatment the damage is mainly evident to the 2nd and 3rd rows of outer hair cells whereas inner hair cells are no compromised. Apical turn outer hair cells are more vulnerable to damage than basal ones. After 1 month from over-stimulation, in agreement with the measure of the TTS, there is a recovery only in the specimens treated for 2 h. We can conclude that, consequently to the administration of white noise for 2 h, the sensorial epithelium is able to recover the damage because the cells are only weakly damaged. On the contrary white noise over-stimulation for 5h, lead to the death of sensorial cells, probably for ROS induced apoptosis, and the epithelium is no more able to recover the damage

Genetica della funzione uditiva normale e patologica

Incidenza delle ipoacusie genetiche e metodologia diagnostica audiologica negli isolati genetic

Coding region intron/exon organization, alternative splicing, and X-chromosome inactivation of the KRAB/FPB-domain-containing human zinc finger gene ZNF41

ZNF41 belongs to a cluster of human zinc finger genes residing within a gene-rich region at Xp11.23. ZNF41 encodes a KRAB/FPB (Kruppel-associated/finger preceding box) domain, a potent transcription repression motif present in hundreds of vertebrate zinc finger protein genes, composed of two protein modules, A and B. Three introns, placed at identical positions in paralogous genes, interrupt four exons encoding the ZNF41 N-terminal amino acids, the KRAB/FPB-A and KRAB/FPB-B modules, and the remaining coding region adjoined to the C-terminal zinc finger domain. Since the KRAB/FPB-A and KRAB/FPB-B modules are encoded by dedicated exons in ZNF41 and paralogous genes, exon skipping may lead to differential usage of these modules in alternative gene products. RT-PCR analysis of ZNF41 mRNAs showed that, while skipping of the KRAB/FPB-A and/or KRAB/FPB-B exons was not detected, the use of alternative donor/acceptor sites upstream of the KRAB/FPB-A exon generates multiple ZNF41 transcripts potentially encoding polypeptides differing in the N-terminal region and expressed in different tissues. The expression pattern in cell hybrids containing either active or inactive X chromosomes indicates that ZNF41, which resides within a region of the X chromosome that includes genes that are both subject to and escape X-inactivation, is susceptible to X-chromosome inactivation

Effect over time of allopurinol on noise-induced hearing loss in guinea pigs.

Temporary threshold shift (TTS) and permanent threshold shift (PTS) may follow prolonged noise exposure. Several reports suggest that noise-induced damage to the cochlea may be related to the activity of reactive oxygen species (ROS). Drugs that scavenge or block ROS formation also protect the cochlea. Guinea pigs, treated with allopurinol, were exposed to white noise (120 dB SPL) or impulse noise (114 dB SPL) for 2 and 5 h. The protective effect of allopurinol was confirmed, but, at these levels of sound, it was present only after noise exposure up to 2 h. This study also offers evidence suggesting that allopurinol does not influence the establishment of PTS

Down-regulation of otospiralin mRNA in response to acoustic stress in guinea pig

Noise over-stimulation will induce or influence molecular pathways in the cochlea; one approach to the identification of the components of these pathways in the cochlea is to examine genes and proteins that change following different types and levels of stress. Quantitative reverse transcription polymerase chain reaction provides a method to look at differential expression of genes in the acoustic stress response. By using this technique we have revealed a down-regulation of the level of otospiralin mRNA in the cochlea of guinea pigs after white noise over-stimulation for 2 h at 108 dB SPL. Otospiralin represents an inner ear specific protein found in fibrocytes of spiral limbus and spiral ligament in the cochlea, and some regions of the vestibule as the stroma underlying the utricle and crista sensory epithelia and the subepithelial layer of the walls of semicircular canals and maculae. It has been recently reported that transient down-regulation of otospiralin in guinea pigs causes vestibular syndrome and deafness. Our results suggest a possible role of this gene in response to acoustical stress, although the exact mechanism remains to be resolved