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  • Title: Glucosamine modulates TNF-α-induced ICAM-1 expression and function through O-linked and N-linked glycosylation in human retinal pigment epithelial cells.
    Author: Chen CL, Liang CM, Chen YH, Tai MC, Lu DW, Chen JT.
    Journal: Invest Ophthalmol Vis Sci; 2012 Apr 24; 53(4):2281-91. PubMed ID: 22427561.
    Abstract:
    PURPOSE: The purpose of this article was to investigate the effects of glucosamine (GlcN) on the TNF-α-induced expression of intercellular adhesion molecule 1 (ICAM-1) and the function of ICAM-1 in ARPE-19 cells in vitro. METHODS: We quantified protein levels of TNF-α-induced ICAM-1 in ARPE-19 cells with Western blotting. The effects of GlcN on O-linked glycosylation, and therefore on ICAM-1 expression, were compared after the addition of alloxan, an inhibitor of O-linked N-acetylglucosamine transferase (OGT), or O-(2-acetamido-2-deoxy-d-glucopyranosylidene)amino-N-phenylcarbamate (PUGNAc), an inhibitor of N-acetylglucosaminidase (O-GlcNAcase [OGA]), or after OGT gene overexpression. The effect of GlcN on the N-linked glycosylation of ICAM-1 was evaluated by the change in its molecular mass on Western blotting. The effect of O-linked glycosylation on the nuclear factor κB (NF-κB) signaling pathway was examined using an NF-κB reporter gene assay. The effect of GlcN on ICAM-1 adhesion activity was examined using an ICAM-1 adhesion assay. RESULTS: GlcN, PUGNAc, and OGT overexpression inhibited TNF-α-induced ICAM-1 expression and NF-κB activity in ARPE-19 cells. Alloxan increased ICAM-1 expression and NF-κB activity in TNF-α-induced ARPE-19 cells. GlcN and tunicamycin reduced the molecular mass of TNF-α-induced ICAM-1 in ARPE-19 cells. The proteasome inhibitor MG-132 suppressed the GlcN-induced reduction in the molecular mass of TNF-α-induced ICAM-1. GlcN also attenuated the adhesion activity of TNF-α-induced ICAM-1. CONCLUSIONS: GlcN inhibits ICAM-1 expression and functions by modulating the O-linked glycosylation of factors involved in NF-κB signaling and by reducing the N-linked glycosylation of TNF-α-induced ICAM-1 in ARPE-19 cells. These effects may contribute to the GlcN-mediated anti-inflammatory effects in the eye.
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