The role of N-glycosylation in high glucose-induced upregulation of intercellular adhesion molecule-1 on bovine retinal endothelial cells

Purpose: The development of diabetic retinopathy has been implicated as a consequence of chronic inflammation. Given the role of the intercellular adhesion molecule-1 (ICAM-1) in inflammation, the potential effect of N-glycosylation on the upregulated expression of ICAM-1 at the surface of bovine retinal endothelial cells (BRECs) induced by high glucose concentrations was investigated.

Methods: Gene and protein expression of ICAM-1 in primary BRECs cultured in medium containing increasing concentrations of mannose or glucose in the presence or absence of tunicamycin were studied with reverse transcription-polymerase chain reaction and Western blot analysis, and the expression level of ICAM-1 at the surface of BRECs was examined with an immunofluorescence analysis. A lectin blot assay with PHA-L was performed to explore the level of N-glycans on cell total proteins or immunoprecipitated ICAM-1 from cells treated or untreated with high glucose.

Results: Both the mRNA and protein levels of ICAM-1, as well as the level of ICAM-1 on the cell surface, were significantly upregulated by increasing the concentration of glucose in the culture medium, with a peak concentration of 20 mm. Consistent with these results, a dramatic increase in the N-glycosylation of ICAM-1 in BRECs cultured with a high concentration of glucose was observed, which could be partially attenuated by tunicamycin treatment.

Conclusion: High glucose-induced upregulation of ICAM-1 on the surface of BRECs could be ascribed to the alterations in its N-glycosylation at least in part, indicating that interference with the glycosylation of ICAM-1 may contribute to improving the efficiency of current therapies with diabetic retinopathy.