Glucocorticoid-Induced Leucine Zipper Suppresses ICAM-1 and MCP-1 Expression by Dephosphorylation of NF-κB p65 in Retinal Endothelial Cells.

PURPOSE

Glucocorticoid-induced leucine zipper (GILZ) is involved in anti-inflammatory activities in several animal models and in various cell types. In this study, we explored the role of GILZ in rat retinal vascular endothelial cells.

METHODS

Glucocorticoid-induced leucine zipper overexpression or silencing was established using GILZ overexpressing recombinant lentivirus (OE-GILZ-rLV) or short-hairpin RNA targeting GILZ recombinant lentivirus (shRNA-GILZ-rLV), respectively, in rat primary retinal microvascular endothelial cells (RMECs) and intact retina. Seventy-two hours after transfection, RMECs were stimulated with 1000 ng/mL lipopolysaccharide (LPS), 20 μM isoliensinine (an alkaloid derived from the embryos of Nelumbo nucifera, could enhance the dephosphorylation of p65 at Ser536), or PBS for another 24 hours. Western blotting and immunofluorescence were performed to measure protein expression. The concentrations of intercellular adhesion molecule (ICAM)-1 and monocyte chemoattractant protein (MCP)-1 in the RMEC culture media were measured by ELISA.

RESULTS

Lipopolysaccharide downregulated GILZ expression in RMECs in a time- and dose-dependent manner, and the decrease in GILZ expression was accompanied by increased ICAM-1 and MCP-1 expression. Glucocorticoid-induced leucine zipper overexpression decreased LPS-induced ICAM-1 and MCP-1 expression, whereas GILZ silencing significantly attenuated the production of both cytokines. Glucocorticoid-induced leucine zipper overexpression also inhibited LPS-induced nuclear factor-κB p65 nuclear translocation in RMECs that was mediated by enhanced p65 dephosphorylation. The dephosphorylation of NF-κB p65 further downregulated ICAM-1 and MCP-1 expression in RMECs.

CONCLUSIONS

Glucocorticoid-induced leucine zipper overexpression inhibited NF-κB p65 nuclear translocation by enhancing p65 dephosphorylation. Exogenous GILZ regulated ICAM-1 and MCP-1 expression, which was probably mediated by enhanced p65 dephosphorylation.