Up-regulation of MUC5AC mRNA expression in endotoxin-induced otitis media

We investigated the expression levels of MUC5AC in endotoxin-induced otitis media with effusion (OME) in thr rat using competitive polymerase chain re action (PCR) and the morphology of middle ear mucosa using transmission ele ctron microscopy (TEM). Experimental OME in the rat was induced after middl e ear instillation of Escherichia coli lipopolysaccharides (LPS). Middle ea r mucosa were obtained at 0 h, 12 h, Day 1, Day 3, Day 7 and Day 14 and rev erse transcriptase (RT)-PCRs were then performed for the identification of MUC1, MUC2, MUC5AC and submandibular mucin 1 expression. followed by compet itive PCRs for MUC5AC and beta (2)-microglobulin expression. Normal middle ear mucosa revealed no expression of mucin genes, whereas endotoxin upregul ated the expression of MUC5AC mRNA between 12 h and Day 7, with maximal exp ression at Days 1 and 3. Middle ears treated three times with LPS upregulat ed more MUC5AC mRNA expression, by a factor of approximate to 3.5, than tho se 1 day after one instillation. On TEM, dark, granulated cells were observ ed at Day 3 after endotoxin instillation, but mixed granulated cells were s een on the ears treated three times with LPS. These results suggest that MU C5AC could be one of the major mucin genes in the middle ear mucosa related to otitis media.