Haarzellen sind die empfindlichsten Elemente des Innenohres und ihre Schädigung ist der häufigste Grund für eine sensorineurale Schwerhörigkeit (SNSH). Das Verständnis der molekularen Vorgänge bei der Schädigung von Haarzellen bildet die Grundlage für neue prophylaktische und therapeutische Maßnahmen. Kürzlich konnte gezeigt werden, dass die Januskinase (JNK) Signaltransduktionskaskade in geschädigten Haarzellen aktiviert wird und das die Inhibition der JNK-Aktivation durch CEP-1347, Haarzellen vor Gentamicin-Toxizität und Lärmtrauma schützen kann [1]. In dieser Studie untersuchten wir, ob ein anderer Inhibitor der JNK-Signaltransduktionskaskade, CEP-11 004, Haarzellen vor Gentamicin-vermittelter Toxizität schützen kann. Explantate des Cortischen Organs von neonatalen Ratten wurden vor und während Gentamicin-Exposition mit CEP-11 004 behandelt. Es zeigte sich eine signifikante Abnahme des Haarzellverlustes in den mit CEP-11 004 behandelten Explantaten, verglichen mit den Explantaten, die nur Gentamicin-exponiert waren. CEP-11 004 alleine hatte keinen toxischen Effekt auf Haarzellen. Aufgrund der vorliegenden Ergebnisse folgern wir, dass die JNK-Signaltransduktionskaskade ein wichtige Rolle in der Gentamicin-vermittelten Ototoxizität spielt.
The hair cells are the most vulnerable elements in the cochlea, and damage to them is the most common cause of sensorineural hearing loss. Understanding the intracellular events that lead to the death of hair cells is a key to developing protective strategies. The Fas death receptor-mediated apoptotic pathway is well studied and plays an important role in the elimination of damaged cells in a number of different cellular systems. We have studied the role of the Fas receptor in aminoglycoside-mediated toxicity in vitro. We employed the MRL/MpJ-Fas mouse, which does not express a functional Fas receptor.Response of Fas-deficient hair cells to gentamicin was compared with the response of normal hair cells in vitro.Basal turn organ of Corti explants from p3-5 mice were maintained in tissue culture and treated with gentamicin for 72 hours. The explants were fixed and were stained with phalloidin, and counting was performed.There was no difference in hair cell loss between Fas mutant mice and control MRL/MpJ mice with a functional Fas receptor.The gentamicin-mediated hair cell death is not dependent on a functional Fas receptor.
We have previously demonstrated by FACS analysis and histochemistry that Fas ligand (FasL) increases on cochlear cell surfaces after immune response or stimulation with gamma-interferon (IFN-gamma). To determine whether the appearance of FasL on cochlear cell membranes is related to gene expression or to posttranslational events, cochlear cells were treated with IFN-gamma. They were evaluated for FasL gene expression by real-time PCR and for FasL protein localization by confocal microscopy of permeabilized and immunolabeled cells. Real-time PCR analysis of cDNAs generated from unstimulated or IFN-gamma-stimulated organ of Corti demonstrated no change in the transcription of the gene encoding FasL. In contrast, confocal microscopy revealed dramatic changes in the cellular distribution of FasL, consistent with movement from the endoplasmic reticulum to the cytoplasm and cell membrane. The results suggest that recruitment of preformed FasL from intracellular compartments, rather than its biosynthesis, is responsible for the increase in FasL on the cell surface following IFN-gamma stimulation. This is similar to the response of cytotoxic T lymphocytes in which gene expression is not involved in FasL surface appearance. Presumably, the use of preformed FasL increases the rapidity of this response. FasL localization to the membrane may be involved in protecting the inner ear from autoimmunity or inflammation. Alternatively it may be related to cochlear cell death in response to inflammatory stress.
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