Transport and binding of tumor necrosis factor-α in articular cartilage depend on its quaternary structure

Abstract

The effect of tumor necrosis factor-α (TNFα) on cartilage matrix degradation is mediated by its transport and binding within the extracellular matrix (ECM) of the tissue, which mediates availability to cell receptors. Since the bioactive form of TNFα is a homotrimer of monomeric subunits, conversion between trimeric and monomeric forms during intratissue transport may affect binding to ECM and, thereby, bioactivity within cartilage. We studied the transport and binding of TNFα in cartilage, considering the quaternary structure of this cytokine. Competitive binding assays showed significant binding of TNFα in cartilage tissue, leading to an enhanced uptake. However, studies in which TNFα was cross-linked to remain in the trimeric form revealed that the binding of trimeric TNFα was negligible. Thus, binding of TNFα to ECM was associated with the monomeric form. Binding of TNFα was not disrupted by pre-treating cartilage tissue with trypsin, which removes proteoglycans and glycoproteins but leaves the collagen network intact. Therefore, proteoglycan loss during osteoarthritis should only alter the passive diffusion of TNFα but not its binding interaction with the remaining matrix. Our results suggest that matrix binding and trimer-monomer conversion of TNFα both play crucial roles in regulating the accessibility of bioactive TNFα within cartilage.

Natural Conformational Sampling of Human TNFα Visualized by Double Electron-Electron Resonance

“…Protomer loss can lead to multimerization, with the higher oligomers acting as a reservoir of TNF α protomers. This mechanism could tightly regulate the biological activity of TNF α at physiological concentrations ( 59 ). However, large differences in TNF α half-life occur between volunteers and patients with an activated immune system.…”

The particle in the spider's web: transport through biological hydrogels

“…12,93 For example, sialic acid-terminated O-linked oligosaccharide chains on secreted mucin molecules, particularly Muc5AC, act as decoy receptors for sialic acid targeting bacteria and viruses, including the influenza virus. 94 This interaction slows penetration of sialic acid targeting bacteria and viruses through the mucus layer to the vulnerable epithelium 95,96 and competitively inhibits binding to cell-associated sialic acid.…”

Extracellular matrix turnover and inflammation in chemically-induced TMJ arthritis mouse models

“…First, we show that the TMJ synovial fluid from diseased patients undergoing therapeutic arthroscopy or arthrocentesis has elevated levels of CTXII, a type II collagen degradative product that has been established as a marker for TMJ arthritis [37], and that TMJ synovial fluid from patients with inflammatory pathology has elevated levels of TNF-alpha. Given these findings, we speculated that direct delivery of TNF-alpha, which is involved in the pathogenesis of rheumatoid arthritis (RA) and known to stimulate fibroblast activity and fibrosis and a known chemical irritant, CFA, could replicate this phenotype in a mouse model [38] [39].…”