[Ultraviolet B irradiation induces NF-kappaB activation and tumor necrosis factor-alpha production in mouse cornea]

To evaluate the activation of nuclear factor-kappaB (NF-kappaB) and expression of tumor necrosis factor (TNF)-alpha in mouse cornea following different doses of ultraviolet-B (UVB) irradiation and to demonstrate the potential role of NF-kappaB in the corneal damage.

ICR mice were randomly divided into control group, mice irradiated by low dose (300 mJ/cm2) and high dose (1200 mJ/cm2) of UVB group. The mouse corneas were observed under a slit lamp microscope, and corneal opacity was graded to evaluate corneal damage. Then the mice were sacrificed at time points varying from 6 hours to 72 hours after treatment and then corneas were excised. Translocation of NF-kappaB was examined by electrophoretic mobility shift assay (EMSA). TNF-alpha production was measured by enzyme-linked immunosorbant assay (ELISA). Moreover, eyes were harvested for routine histological analysis and electron microscopy.

Mild corneal edema was observed after low-dose of UVB irradiation, and resolved after 72 hours.However, significant and persistent corneal edema was observed after high dose of UVB irradiation. EMSA results showed that the marked increased activation of NF-kappaB after UVB irradiation, compared with the control group. The level of activity of NF-kappaB was enhanced as the radiant exposure increased. The significance was statistically different at each time point between groups. ELISA showed rapid production of high levels of TNF-alpha concomitant with the up-regulation of NF-kappaB. Histological findings by electron microscopy demonstrated only damage of corneal epithelial cell and superficial keratocytes in low-dose group. Ultrastructural morphology in high-dose group showed deeper damage including keratocytes throughout the whole stroma and endothelial cells.

These results suggest that acute ultraviolet exposure induces the activation of NF-kappaB which results in the production of proinflammatory cytokines such as TNF-alpha. Moreover, the up-regulated NF-KB activation was concomitant with the enhanced corneal damage. These findings imply that NF-kappaB may play an important role in the pathogenesis of UV-induced damage of cornea.