The interleukin‐1 receptor in normal and osteoarthritic human articular chondrocytes. Identification as the type I receptor and analysis of binding kinetics and biologic function

Abstract

Objective. To identify and investigate the kinetic binding properties of interleukin-1 receptors (IL-lR), and examine the abilities of the-2 IL-1 isoforms to stimulate metalloprotease synthesis, in normal and osteoarthritic (OA) chondrocytes.Methods. Receptor affinity and density were determined using radioligand binding experiments and flow cytometry. Immunocytochemical analysis and affinity cross-linking studies were performed for characterization of IL-1R.Results. While no difference in receptor affinity Factors such as IL-2, interferon-y, tumor necrosis factor a, and bovine insulin did not compete with IL-1p. By covalent ligand cross-linking and electrophoretic analysis, only type I IL-lR, a protein of 80 kd, was detected on chondrocytes. By immunocytochemical analysis, IL-1R was identified at the cell membrane level, in both normal and OA chondrocytes. The presence of nuclear staining was also observed, but only in OA chondrocytes. Recombinant human IL-1 (a and p) induced the secretion of stromelysin and collagenase in a dose-dependent manner. The IL-1 concentration required for half-maximal metalloprotease stimulation was 3-4 times lower in OA chondrocytes than in normal cells. _____Conclusion. These results indicate that OA chondrocytes have a higher sensitivity to the stimulation of metalloprotease synthesis by IL-1 than do normal cells. This could be related to the increased levels of IL-1R expressed in the OA cells. The implications of these findings with regard to the possible roles of IL-1 and IL-1R in the pathogenesis of OA are discussed.Erosion of articular cartilage in osteoarthritis (OA) is probably mediated by proteolytic degradation of extracellular matrix macromolecules. Metalloproteases are believed to be the primary enzyme systems

Intracellular Interleukin-1α Functionally Interacts with Histone Acetyltransferase Complexes

“…The original vector contains Myc and His tags downstream of the cloned cDNA, therefore, all the IL-1␣ proteins were expressed as double tagged chimeras with N-terminal FLAG and C-terminal Myc and His tags. Fragments encoding human deletion mutants IL-1NTP-VVATN (internal deletion aa 78 -87), IL-1NTP-EDSSS (terminal deletion aa [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19], and IL-1NTP-ITDDD (terminal deletion aa 96 -111) were amplified and cloned into BamHI and XhoI sites of modified pcDNA4/TO/MycHis (see above) vector.…”

“…The nuclear localization signal (NLS), present in the IL-1NTP molecule, was shown to be essential for the biological activity of intracellular IL-1␣ (7,8). Indeed, overexpressed intracellular IL-1␣ precursor (pre-IL-1␣), but not IL-1MAT, was able to inhibit cell growth and to induce the expression of the plasminogen activator inhibitor-1 and collagenase genes (9,10). Pre-IL-1␣ was shown to stimulate proliferation of smooth muscle cells (11) and to regulate the migration and the lifespan of endothelial cells (12,13).…”

Evidence for a key role of leptin in osteoarthritis

“…OA changes are not limited to cartilage, because remodeling of the underlying bone and development of osteophytes are also observed in osteoarthritic joints. Several inflammatory components such as tumor necrosis factor ␣ and IL-1 have been detected in the synovial fluid (SF) of patients with OA and have been implicated in the degenerative process by inhibiting extracellular matrix synthesis and increasing catabolic activities of metalloproteinases (26)(27)(28)(29). In response to cartilage damage, various growth factors, including insulin-like growth factor 1 (IGF-1) or transforming growth factor ␤ (TGF␤), are activated and stimulate chondrocytes to repair the damaged extracellular matrix by forming cell clusters and increasing their anabolic activity (30)(31)(32)(33).…”

Extended haplotypes and linkage disequilibrium in the IL1R1–IL1A–IL1B–IL1RN gene cluster: association with knee osteoarthritis

“…10,11 It is also known that OA cartilage explants are more susceptible to the effects of IL-1 than similar explants from nonarthritic cartilage 12 and that this susceptibility is related to the expression of IL-1 receptor types 1 and 2 on chondrocytes. 13 A further line of evidence comes from genetic studies. First-degree relatives of patients with generalised radiologic OA are twice as likely to develop the disease as people in the general population, 14 and monozygotic twins are significantly more concordant for hand and knee osteoarthritis than dizygotic twins.…”