Expression of the proinflammatory cytokines in cochlear explant cultures: influence of normoxia and hypoxia

Hearing loss can be induced by a variety of factors including hypoxia and inflammation. Here, we investigated in vitro the effect of hypoxia on the expression of proinflammatory cytokines in the explanted cochlear tissues. Using RT-PCR, we determined the expression of genes encoding IL-1beta, IL-6 and TNF in the organ of Corti (OC), modiolus (MOD) and stria vascularis together with spiral ligament (SV+SL). In addition, using ELISA, we determined the concentration of IL-1beta and IL-6 in the supernatants of explant cultures. We found that the dissection, explanting and consecutive 24-h normoxic culture results in highly increased expression of IL-1beta and IL-6, as compared to the freshly isolated tissues. TNFalpha was upregulated only in the MOD. Interestingly, 24h of hypoxia decreased the number of mRNA encoding IL-1beta and IL-6 and increased the number of mRNA encoding TNFalpha in the SV+SL as compared to normoxia. The concentration of IL-6 measured in the explant tissue culture supernatants was significantly lower in hypoxic than in the normoxic cultures. Our results show that tissue dissection and explanting as well as hypoxia can influence the expression and secretion of proinflammatory cytokines. This implies the presence of tissue-specific regulatory pathways between hypoxia and inflammation in the inner ear.