17-β-estradiol inhibits hyperosmolarity-induced proinflammatory cytokine elevation via the p38 MAPK pathway in human corneal epithelial cells

PURPOSE: To evaluate the effects of 17-β-estradiol on hyperosmolar stress-induced proinflammatory cytokine production of interleukin (IL)-6, IL-1, and tumor necrosis factor-alpha (TNF-α) in SV40-immortalized human corneal epithelial cells (hCECs) and the regulatory effects of the mitogen-activated protein kinase (MAPK) signaling pathways in this process. METHODS: SV40 hCECs cultured in normal osmolar media were switched to a higher osmolarity (450 mOsM) by adding NaCl with or without pretreatment with 17-β-estradiol. Real-time polymerase chain reaction and ELISA were applied to characterize IL-6, IL-1, and TNF-α gene and protein expression. Cells were treated for 15−60 min, lysed in radioimmunoprecipitation assay (RIPA) buffer and subjected to a western blot with phospho (p)-specific antibodies against extracellular signal-regulated protein kinase 1/2 (ERK1/2), P38 kinase, and c-Jun N-terminal kinase 1/2 (JNK1/2). RESULTS: The expression and production of IL-6, IL-1, and TNF-α in SV40 hCECs increased when the media osmolarity was switched to 450 mOsM. Pretreatment with 10(−10) M 17-β-estradiol greatly inhibited the increased expression and production of IL-6, IL-1, and TNF-α induced by hyperosmolarity, whereas with the administration of SB203580 (10 μM), an inhibitor of the p38 pathway, the inhibiting effect of 17-β-estradiol disappeared. The western blot results showed that the increased phosphorylation level of p38 caused by hyperosmolarity was greatly inhibited by 17-β-estradiol. CONCLUSIONS: 17-β-estradiol greatly inhibited the expression and production of proinflammatory cytokines IL-6, IL-1, and TNF-α, which were stimulated by hyperosmolarity in SV40-immortalized hCECs. The results also suggested that the p38 MAPK signaling pathway was involved in the regulatory effects of estrogen on hCECs. These findings may contribute to an understanding of the etiologic roles and therapeutic implications of the hormone estrogen in dry eye disease.