Attenuation of extracellular acidic pH-induced cyclooxygenase-2 expression by nitric oxid

초록

Corneal endothelial cells play an important role in maintaining transparency and ionic balance. Inflammation causesmany changes both in the intracellular and extracellular environments including acidosis. The purpose of this study was to demonstrate the relationship between changes in extracellular pH and expression of cyclooxygenase-2 in cultured bovine corneal endothelial cells. When extracellular pH ([pH]o) was changed to acidic (6.4), the expression of COX-2 was increased in a time-dependent manner. The peak increment of COX-2 mRNA expression was observed at 2 h incubation in acidic pH condition. This [pH]o-induced COX-2 mRNA expression was decreased to the control ([pH]o = 7.4) level when cells were pretreated with actinomycin D. In the acidic condition, the [pH]o-induced expressions of COX-2 mRNA or protein were diminished to the control level by treatment with spermine NONOate (SPER/NO, a nitric oxide donor). In order to demonstrate the effect of H+ ion, cells were treated with carbonyl cyanide m-chlorophenylhydrazone (CCCP, a H+ionophore). The CCCP treatment induced COX-2 mRNA in a concentration- and time-dependent manner as with the acidic pH. This CCCP-induced COX-2 mRNA expression was diminished also by co-treatment with SPER/NO. The immuno-cytochemical results supported the results of COX-2 mRNA. This study demonstrates that COX-2 expression is increased by acidic changes of extracellular pH that could result from bacterial infection and this may be countered by the over-produced nitric oxide, which could also result from bacterial infection. Thus, over production of NO may regulate COX-2 gene expression during inflammation in corneal endothelial cells for self-cytoprotection