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Ching-Long Chen, Chang-Min Liang, Yi-Hao Chen, Ming-Cheng Tai, Da-Wen Lu, Jiann-Torng Chen; Glucosamine Modulates TNF-α–Induced ICAM-1 Expression and Function Through O-Linked and N-Linked Glycosylation in Human Retinal Pigment Epithelial Cells. Invest. Ophthalmol. Vis. Sci. 2012;53(4):2281-2291. doi: 10.1167/iovs.11-9291.
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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.
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.
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.
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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