ABSTRACT
@#BACKGROUND. Prostaglandin E2 (PGE2) is the most abundant prostanoid and a very potent lipid mediator, and is produced predominantly from arachidonic acid by it’s tightly regulated cyclooxygenases (COXs) and prostaglandin E synthases. PGE2 is involved in regulating many different fundamental biological functions, including immune responses. Recently, we have demonstrated that bacterial LPS induces NO production in auditory cells via an inducible NO synthase expression. The LPS-induced production of an excessive NO amount is suggested to cause injury of auditory cells, followed by ototoxicity. Auditory cells injured by such an inflammatory response must be accompanied by tissue repair and remodeling. In order to clarify the production of PGE2 in auditory cells for regulation of inflammatory response or tissue repair AIM: We aimed to examine an effect of LPS on the production of prostaglandin E2 in auditory cells. MATERIALS AND METHODS: The murine auditory cell line HEI-OC1 was established from long-term cultures of immortomouse cochlea and used as conditionally-immortalized auditory cells. HEI-OC1 cells were stimulated with or without LPS. The concentration of PGE2, TNF-α, IL-1β in the culture supernatant was determined with ELISA. COX-2 protein expression and mRNA were measured by immunoblotting and reverse transcription PCR, respectively. The bands were quantified by densitometric analysis using ImageJ software. Statistical analysis was performed using Student’s t-test and P values < 0.05 were considered significant. All experiments were performed independently at least three times. Data represent the mean value of triplicates SD. RESULT: HEI-OC1 auditory cells constitutively produce a small amount of PGE2. LPS augmented the PGE2 production via enhanced cyclooxygenase 2 (COX2) expression. LPS-induced augmentation of COX2 expression was dependent on up-regulation of COX2 mRNA expression. LPS induced the production of TNF-a, but not IL-1b An anti-TNF-α neutralizing Ab significantly inhibited PGE2 production and COX2 mRNA expression in response to LPS. LPS-induced PGE2 production was prevented by a series of pharmacological signaling inhibitors to NF- κB and MAPKs. Pam3CSK4 as a TLR2 ligand, as well as LPS as a TLR4 ligand, augmented the PGE2 production. However, poly I:C as a TLR3 ligand, imiquimod as a TLR7 ligand and CpG DNA as a TLR9 ligand did not augment it. HEI-OC1 cells expressed TLR2, TLR4 and TLR9, but not TLR3 or TLR7. CONCLUSION: The auditory cells produce PGE2 in response to LPS via COX2 expression. The PGE2 production may be involved in tissue repair and remodeling in the organ of Corti. Auditory cells might be important effector cells in host response to infection and inflammation in the organ of Corti and cochleae.