The action of TNFα and TGFβ include specific alterations of the glycosylation of bovine and human chondrocytes

Abstract

Joint destruction in arthritis is often associated with high levels of inflammatory cytokines. Previous work has shown that inflammatory conditions can alter the activities of glycosyltransferases that synthesize the glycan chains of glycoproteins, and that these changes in turn can influence the functions of glycoproteins. We therefore examined glycosyltransferases involved in glycoprotein biosynthesis in primary cultures of bovine articular chondrocytes and human chondrocytes isolated from knee cartilage of osteoarthritis patients. Bovine chondrocytes exhibited enzyme activities involved in the synthesis of bi-antennary complex Asn-linked N-glycans, as well as the enzymes involved in the synthesis of GalNAc-Ser/Thr-linked O-glycans with the core 1 structure. Human chondrocytes, in addition, were able to synthesize more complex O-glycans with core 2 structures. TNFalpha was found to induce apoptosis in chondrocytes, and this process was associated with significant changes in lectin binding to chondrocyte cell surface glycans. TGFbeta increased cell proliferation, and had significant effects on cell surface glycosylation in bovine but not in human cells. These cytokine-specific effects were partially correlated with changes in glycosyltransferase activities. Thus, chondrocytes have many of the enzymes necessary for the synthesis of N- and O-glycan chains of glycoproteins. The O-glycosylation pathways and the effects of TNFalpha and TGFbeta on glycosylation differed between bovine and human chondrocytes. These alterations are of potential importance for the regulation of the functions of cell surface receptors on chondrocytes, and for an understanding of the pathophysiology of arthritis.

Lectin binding patterns reflect the phenotypic status of in vitro chondrocyte models

“…In the O-glycosylation pathways of most cell types, the primary GalNAc− epitope is converted to the core 1 structure Galβ1-3GalNAc−. These carbohydrate structures may provide binding sites for D. biflorus agglutinin and PNA, respectively (Yang et al 2007). Subsequently, the core 1 structure can be further extended in different ways, e.g., by fucosylation reactions forming the Fucα1-2Galβ1-4GlcNAc− residue which can be specifically detected by U. europaeus isoagglutinin I (Baldus et al 1996).…”

“…To account for N-linked oligosaccharide chains, the binding of L. culinaris agglutinin and S. nigra agglutinin was assessed identifying the expression of high-mannose type oligosaccharides and sialylα2-6Gal termini capping some complex-type N-glycans, respectively (Akama et al 2006;Yang et al 2007). No differences in the expression of these N-glycan structures were found between C-28/I2 and T/C-28a2 cells.…”

“…A panel of lectins was selected to probe for a range of oligosaccharide sequences determining specific products of the O-glycosylation and N-glycosylation pathways (Liener et al 1986;Baldus et al 1996;Yang et al 2004Yang et al , 2007. In the O-glycosylation pathways of most cell types, the primary GalNAc− epitope is converted to the core 1 structure Galβ1-3GalNAc−.…”

“…The attachment of oligosaccharide chains to asparagine (N-linked) or serine/ threonine (O-linked) residues represents a common posttranslational modification of proteins potentially influencing biological processes such as apoptosis, inflammation, cell signaling, protection against proteolytic degradation, and protein folding (Knudson and Knudson 2001;Yang et al 2007). Furthermore, the protein backbone of major cartilage proteoglycans is often associated with carbohydrate chains such as chondroitin sulfate, heparan sulfate, and keratan sulfate.…”

Inflammation and arthritis: perspectives of the glycobiologist

“…IL-1 and IL-7 induce cartilage breakdown, and IL-1 suppresses collagen and proteoglycan synthesis in chondrocytes while inhibiting the proliferative and anabolic effect of TGF-β [2,3]. TGF-β also stimulates specific glycosyltransferase activities in bone and cartilage cells [4][5][6].…”