Interleukin 1 suppresses expression of cartilage-specific types II and IX collagens and increases types I and III collagens in human chondrocytes

Effects of interleukin-1 on syntheses of alkaline phosphatase, type X collagen, and 1,25-dihydroxyvitamin D3 receptor, and matrix calcification in rabbit chondrocyte cultures

The effect of IL-1 on expression of the mineralization-related phenotype by chondrocytes was examined. In cultures of rabbit growth plate chondrocytes, IL-1 beta at 0.1 ng/ml caused 95% decreases in alkaline phosphatase activity, alkaline phosphatase mRNA levels, the incorporation of 45Ca into insoluble material, and the calcium content during the hypertrophic stage. These effects of IL-1 beta were dose-dependent and were observed in 24-48 h. Furthermore, IL-1 beta suppressed increase in cell size and the syntheses of 1,25-dihydroxyvitamin D3 receptor and type X collagen, other markers of hypertrophy, but had little effect on the synthesis of total protein including type II collagen. The inhibition of calcification was observed only when chondrocytes were exposed to IL-1 before the onset of calcification: IL-1 treatment from the mineralization stage had a marginal effect on 45Ca incorporation into insoluble material. These results suggest that IL-1 inhibits chondrocyte hypertrophy and the onset of calcification in ossifying cartilage.

Interleukin-1 beta regulation of fibroblast proteoglycan synthesis involves a decrease in versican steady-state mRNA levels

This study investigates the effects of interleukin (IL)-1 beta on proteoglycan metabolism by fibroblasts surrounded by endogenous extracellular matrix. In both three-dimensional matrix cultures and long-term monolayer cultures IL-1 beta caused a significant decrease in synthesis and deposition of sulphated proteoglycans, but had no effect on release of deposited material. The decrease in synthesis became successively more pronounced, and corresponded to 40-60% of the control after 72 h incubation. The reduction was almost totally accounted for by an effect on the chondroitin ABC-lyase-sensitive proteoglycans. Gel electrophoresis showed a significant decrease in a high-molecular-mass chondroitin ABC-lyase-sensitive proteoglycan after incubation with IL-1 beta. Northern-blot analyses of total RNA revealed a pronounced decrease in the steady-state mRNA levels of versican, the large chondroitin sulphate, with levels corresponding to 10-30% of controls. In comparison, the steady-state mRNA level for decorin, the major sulphated proteoglycan synthesized by the cells, was only slightly affected. The prominent decrease in synthesis of sulphated proteoglycans induced in long-term fibroblast cultures, including the pronounced decrease in versican steady-state mRNA levels, is likely to have a significant effect on the structure of the extracellular matrix. Induction of this type of change may constitute a significant mechanism whereby IL-1 beta can affect the properties of connective tissue during inflammation and wound healing.

Expression of 92-kD type IV collagenase/gelatinase (gelatinase B) in osteoarthritic cartilage and its induction in normal human articular cartilage by interleukin 1

We report here that a 92-kD gelatinolytic metalloproteinase is expressed as protein and mRNA in human osteoarthritic cartilage, but not in normal adult articular cartilage. Western immunoblotting demonstrated that the 92-kD gelatinolytic activity corresponded to 92-kD type IV collagenase/gelatinase (gelatinase B); mRNA for gelatinase B was identified by Northern blotting. Chondrocytes from normal cartilage also exhibited mRNA for 72-kD type IV collagenase/gelatinase (gelatinase A), tissue collagenase, and stromelysin-1, and these mRNAs were increased in osteoarthritic cartilage. Regional analysis of osteoarthritic cartilage samples from four individuals revealed that gelatinase B mRNA was expressed in grossly fibrillated areas; two of four nonfibrillated cartilage samples failed to exhibit the mRNA, but did have increased levels of mRNA for other neutral metalloproteinases. IL-1 alpha treatment of normal human cartilage explants or isolated chondrocytes induced increased levels of gelatinase B and increased mRNA for tissue collagenase and stromelysin-1. Under identical conditions, mRNA levels for gelatinase A were not increased indicating that regulation of this enzyme in human articular chondrocytes is distinct from that of other metalloproteinases. Our data showing expression of gelatinase B in fibrillated cartilage suggest that it is a marker of progressive articular cartilage degradation in osteoarthritis.

Differential modulation of degradative and repair responses of interleukin-1-treated chondrocytes by platelet-derived growth factor

Interleukin 1 (IL-1) plays a dual role in cartilage matrix degeneration by promoting extracellular proteinase action such as the matrix metalloproteinases (increased degradation) and by suppressing the synthesis of extracellular matrix molecules (inhibition of repair). Platelet-derived growth factor (PDGF) is a wound-healing hormone which is released along with IL-1 during the inflammatory response. Since previous studies have shown that PDGF enhances IL-1 alpha effects on metalloproteinase activity, in this report, we have examined whether PDGF modifies IL-1 beta effects on cartilage proteoglycan synthesis. Initially, we confirmed that rabbit articular chondrocytes treated with IL-1 beta + PDGF induced higher proteinase activity, in comparison with IL-1-treated cells. We further observed that the increased proteinase activity correlated with an increase in the synthesis of collagenase/stromelysin proteins and a corresponding increase in the steady-state mRNA levels for both the enzymes. Studies on IL-1 receptor expression suggested that PDGF caused an increase in IL-1 receptor expression which, by augmenting the IL-1 response, may have led to the increase in proteinase induction. Analysis of proteoglycan synthesis confirmed that IL-1 reduced the incorporation of sulphated proteoglycan, aggrecan, into the extracellular matrix of chondrocytes, whereas PDGF stimulated it. However, cells treated with IL-1 + PDGF synthesized normal levels of aggrecan. This is in contrast with cells treated with IL-1 + fibroblast growth factor, in which case only proteinase activity was potentiated. The results allow us to conclude that (a) the two effector functions that play a role in matrix remodelling, namely matrix lysis (proteinase induction) and matrix repair (proteoglycan synthesis), occur via distinct pathways and (b) PDGF may play a crucial role in cartilage repair by initially causing matrix degradation followed by promoting new matrix synthesis.

Interferon-gamma stimulates the secretion of IL-1, but not of IL-6, by glomerular mesangial cells

IL-1 activity in culture supernatant and cell lysate from rat mesangial cells stimulated with interferon-gamma (IFN-gamma) was measured by a thymocyte proliferation assay. While IFN-gamma alone had no effect on the secretion or the intracellular pool of IL-1, the enhancement by IFN-gamma of IL-1 secretion in response to lipopolysaccharide (LPS) was observed. The stimulatory effect of culture supernatant on thymocyte proliferation was abrogated by preincubation with the anti-IL-1 antibody. At least 4-h incubation with IFN-gamma and LPS was required to detect enhancing effect of IFN-gamma. The addition of as little as 1 U/ml IFN-gamma significantly increased IL-1 secretion in the presence of 10 micrograms/ml LPS. The IL-6 activity in culture supernatants was determined by measurement of thymidine uptake in mouse IL-6-dependent cell line (MH60.BSF2). Mesangial cells secreted IL-6 in culture supernatant without additional stimuli and LPS distinctly increased it as described previously. However, in contrast to IL-1 production, no effect of IFN-gamma on IL-6 secretion was observed in the presence or absence of LPS. Moreover, we determined whether enhanced IL-1 release is associated with Ia expression on mesangial cells. IFN-gamma alone and the combination with LPS induced marked expression of Ia antigen, whereas LPS alone did not. We conclude that IFN-gamma stimulates the production of IL-1, but not IL-6, by mesangial cells and suggest an important role of IFN-gamma in the pathogenesis of glomerulonephritis by regulating the mesangial production of IL-1 and the accessory cell function of mesangial cells.

Independent expression of fibril-forming collagens I, II, and III in chondrocytes of human osteoarthritic cartilage

Normal and osteoarthritic human articular cartilage was investigated by in situ hybridization for expression patterns of the fibrillar collagens type I, II, and III to evaluate phenotypic changes of articular chondrocytes related to the disease. In 11 out of 20 samples, a defined subset of chondrocytes in the superficial and upper middle zone of osteoarthritic cartilage showed significant levels of cytoplasmic alpha 1 (III) mRNA, whereas strong signals of alpha 1 (II) mRNA were found in the upper and lower middle zone, partially overlapping with the zone of alpha 1 (III) mRNA-expressing cells. The extent of type II and III collagen expression depended on the integrity of the extracellular matrix surrounding the chondrocytes, and the location within the articular cartilage. No alpha 1 (I) mRNA was detectable in osteoarthritic original articular cartilage. The alpha 1 (I) probe did, however, reveal signals in pannus-like tissue, osteophytes, and bone cells. In normal articular cartilage, no detectable levels of cytoplasmic mRNA for alpha 1(I), alpha 2 (I), or alpha 1 (III) were seen. Using specific mono- and polyclonal antibodies, we found deposition of type III collagen but hardly any of type I collagen in the superficial zone of osteoarthritic cartilage that is consistent with the in situ hybridization results. These results indicate a phenotypic alteration in a defined subset of chondrocytes in conditions of diseased cartilage, expressing and synthesizing collagen type III independently from type I collagen, but in part simultaneously with type II collagen.

Direct evidence for active metalloproteinases mediating matrix degradation in interleukin 1-stimulated human articular cartilage

When adult human articular cartilage was maintained in organ culture in the presence of interleukin 1 beta, increased destruction of the extracellular matrix was observed, as judged by increased type II collagen degradation in situ determined immunohistochemically and the increased release of proteoglycan into the culture medium. Concomitant with these changes was the increased release of latent metalloproteinases into the culture medium. Culture of cartilage in the presence of a peptidylhydroxamate metalloproteinase inhibitor indicated a key role for the active forms of these enzymes in situ, since it produced a marked reduction in both proteoglycan release and collagen degradation. This compound had no detectable cytotoxic effects in organ culture and did not reduce the secretion of the metalloproteinases. The results of this study provide direct evidence that the latent metalloproteinase precursors, whose release is greatly stimulated by interleukin 1, are indeed activated to some degree and participate in cartilage matrix degradation.

Regulation of expression of the type I collagen genes

The identification and functional analysis of DNA-protein interactions in the intronic and 5' flanking regions of the type I collagen genes has begun to define a series of cis-elements and trans-acting factors which regulate transcription of these genes. Studies such as these will eventually be expected to elucidate the mechanisms responsible for coordinate transcription of the alpha 1 and alpha 2 genes, a question which remains central to the field of collagen research. Although it is relatively straightforward to define sites of DNA-protein binding, interpretation of the functional importance of such interactions can be extremely complex. Furthermore, while mutation or deletion of a particular binding site may alter the functional activity of a construct transfected into cultured cells, there is no guarantee that a similar change will have the same effect in vivo, where the entire gene locus is present in its native chromosomal context. Nevertheless, these kinds of in vitro studies offer the best current approach to defining and isolating transcription factors that control expression of the alpha 1 and alpha 2 genes. Ultimately, it will be necessary to test the activity of such factors (and their respective cis-elements) in defined systems in vivo.

Cellular responses to human chondrocytes: absence of allogeneic responses in the presence of HLA-DR and ICAM-1

To assess the accessory cell function of human articular chondrocytes, we assessed the ability of human chondrocytes to stimulate allogeneic peripheral blood mononuclear cells (PBMC) and to support phytohaemagglutinin (PHA)-induced proliferation of highly purified T cells. We also examined the surface expression of HLA-DR and ICAM-1 on the chondrocytes both unstimulated and stimulated with cytokines in vitro. Chondrocytes failed to stimulate allogeneic PBMC despite the constitutive expression of MHC class I molecules and the cytokine-induced expression of class II molecules but were able to support T cell proliferation to PHA, IFN-gamma and to a limited extent, IL-1 beta, induced class II expression on chondrocytes. ICAM-1 was present on 94-99% of freshly isolated cells; this declined with culture (17-59%; P < 0.005) but was readily induced by IFN-gamma, IL-1 beta, and tumour necrosis factor-alpha. Alloreactivity and, presumably, autoreactivity to chondrocytes requires factors in addition to the surface expression of DR and ICAM-1. However the presence of these molecules suggests a capacity for cell-cell interactions in inflammatory sites such as the cartilage pannus junction.

The role of cytokines and their inhibitors in arthritis

The role of cytokines in inflammatory joint diseases is well documented, especially with regard to tissue destruction and remodelling. In these processes, IL-1 and TNF alpha play a prominent part by stimulating protease production. The regulation of their production, their release and their effects on target cells (e.g. synovial cells, chondrocytes and bone-derived cells) has therefore been the subject of intensive investigations. In this context a new dimension has emerged recently due to the observation of the existence of natural specific cytokine inhibitors. IL-1-ra and the soluble fragments of both TNF receptors--inhibitory by binding to TNF alpha--are natural products. These appear to be the molecules best suited for controlling the imbalance between pro- and anti-inflammatory processes. The use of the recombinant forms of these inhibitors may open new perspectives for therapeutic intervention. The fact that the respective mechanisms of action of receptor antagonists and inhibitory binding proteins differ does not rule out their complementarity. Preliminary experiments with animal models have yielded promising results which should be followed up by clinical trials.

Inhibition of proteoglycan synthesis by transforming growth factor beta in anatomically intact articular cartilage of murine patellae

The effect of transforming growth factor beta (TGF beta) on proteoglycan synthesis and degradation in anatomically intact articular cartilage of murine patellae was studied. Exogenously added TGF beta up to a concentration of 200 pmol/l had no effect on proteoglycan synthesis in intact articular cartilage. Neutralisation of endogenously produced TGF beta with a specific monoclonal antibody to TGF beta, however, led to stimulation of proteoglycan synthesis, indicating that TGF beta itself inhibits proteoglycan synthesis in anatomically intact cartilage. Transforming growth factor beta decreased the degradation of proteoglycans in intact cartilage in the absence of fetal calf serum or insulin-like growth factor 1. In the presence of fetal calf serum or insulin-like growth factor 1, TGF beta had no additional effect on proteoglycan breakdown.

Discordant regulation of human type I collagen genes by prostaglandin E2

We examined the expression of type I collagen genes in prostaglandin E2 (PGE2)-treated human lung fibroblast cultures. Addition of PGE2 to fibroblast cultures inhibited alpha 1(I) mRNA levels by approx. 25% after 6 h and 60% after 24 h. Further studies showed that dibutyryl cAMP did not inhibit alpha 1(I) mRNA levels and that cycloheximide blocked the inhibitory effect of PGE2. In contrast, PGE2 treatment with or without cycloheximide did not affect alpha 2(I) mRNA levels. Moreover, in vitro translation of RNA derived from untreated and PGE2-treated cells yielded similar amounts of alpha 2(I) collagen peptides. Taken together, these results suggest that PGE2 induces a protein which inhibits alpha 1(I) transcription through distinct regulatory elements not under the control of cAMP and provide further evidence that the type I collagen genes can be discordantly regulated.

Preferential mRNA expression of prostromelysin relative to procollagenase and in situ localization in human articular cartilage

An imbalance between extracellular proteinases and their inhibitors is thought to underlie cartilage degradation. In cultures of adult cartilage, prostromelysin mRNA levels were much higher than those for procollagenase and this differential was increased in cultures stimulated with IL-1 beta. Analysis of mRNA prepared from freshly isolated chondrocytes showed abundant amounts of prostromelysin mRNA in normal adult cartilage but low levels in the neonate. Not all adult cartilage may possess such high levels of prostromelysin mRNA, as the message levels in the cartilage remaining on late-stage osteoarthritic joints were lower than those in normal adult cartilage. Relative to prostromelysin mRNA, little procollagenase and TIMP mRNA were found in the adult cartilage. In situ hybridization revealed that metalloproteinase mRNAs were localized in chondrocytes of the superficial zone in adult cartilage. However, upon IL-1 beta treatment, chondrocytes in all cartilage zones were observed to express prostromelysin mRNA. Relative to the neonate, the normal adult cartilage appears to have a high degradative potential, if one accepts that steady-state mRNA levels reflect prostromelysin production. As the adult cartilage is not apparently undergoing rapid turnover, it would appear that control of prostromelysin activation may be the major regulatory step in stromelysin-induced cartilage degradation.

Influence of continuous infusion of interleukin-1 alpha on the core protein and the core protein fragments of the small proteoglycan decorin in cartilage

Decorin, a collagen-binding small proteoglycan, is considered to have a specific function in the organization or stability of the collagen network. Therefore, alteration of its molecular properties may be of pathophysiological relevance during the development of cartilage damage. It is shown here that normal cartilage from rabbit knee-joint contains glycosaminoglycan chain-bearing core protein fragments of 39, 23, and 18 kDa, each one amounting to approximately 5-6% of the intact decorin core protein. Continuous infusion of human recombinant interleukin-1 alpha for 14 days (200 ng/day) into a knee-joint led in condylar cartilage to a reduction in the amount of intact core protein from 2 micrograms/mg wet tissue to about 1.1 micrograms/mg. The increase in its quantity found after infusion of heat-inactivated interleukin-1 was not statistically significant. The concentration of all three core protein fragments became reduced to a similar extent as the intact core protein under the influence of the cytokine, and additional fragments were not found. Surprisingly, there was a much smaller response to interleukin-1-treatment in patellar cartilage.

Cellular localization of procollagen gene transcripts in inflammatory bowel diseases

The cellular localization of procollagen types I, III, IV, and V gene transcripts was determined in tissues from 12 patients with either Crohn's disease (CD) or ulcerative colitis (UC) and nine controls by in situ hybridization with 35S-labeled RNA probes. In CD, the signal intensity and number of labeled cells were significantly increased, particularly in deeper intestinal layers. In contrast, the labeled cells in UC were concentrated in the subepithelial intestinal layers, with an overexpression of procollagen III RNA transcripts. Immunohistological stainings for procollagen types I, III, and IV showed a weaker staining in UC than in CD, indicating that increased transcript levels in UC are unrelated to the enhanced collagen protein deposition, although the increase of procollagen messenger RNA levels correlated with the density of the inflammatory infiltrate. It was concluded that both CD and UC show highly increased procollagen RNA transcript levels but differ in collagen deposition. Thus, different posttranscriptional or posttranslational regulatory mechanisms, such as collagen degradation, may account for the observed differences.

Influence of interleukin-1 on the morphology and proteoglycan metabolism of cultured bovine articular chondrocytes

Bovine articular chondrocytes cultured in agarose gel in the presence of serum elaborated a highly organized extracellular matrix rich in proteoglycans and collagens. The cultures were evaluated quantitatively by radiosulfate labeling of proteoglycans, and by densitometry following staining with alcian blue. In addition, immunohistochemical methods were used to demonstrate the presence of several components of cartilage proteoglycan molecules. Treatment with Interleukin-1 (Il-1) or retinol resulted in diminished synthesis and enhanced catabolism of matrix proteoglycans, but the chondrocytes were more sensitive to human recombinant Il-1 alpha than to Il-1 beta. Treatment with Il-1 alpha or retinol resulted in a profound disorganization of the residual matrix around the majority of the chondrocytes, while Il-1 beta caused much less severe changes. Some variation in cellular response to Il-1 alpha may result from the heterogeneity previously reported among articular chondrocytes.

Proteinase-mediated cartilage degradation in osteoarthritis

Osteoarthritis (OA) is a disease of complex etiology that results in articular cartilage breakdown. Current experimental evidence strongly suggests that proteinases may be involved in this loss of cartilage matrix. The present review summarizes the evidence for implicating proteinases in the etiopathogenesis of OA and suggests that blockade of proteinase activity may provide a rational basis for new therapeutic agents.

Are cytokines involved in osteoarthritic pathophysiology?

The putative role and mechanism of action of cytokines in the progression of arthritic diseases such as osteoarthritis (OA) has received particular attention because of the important interaction between articular cartilage and synovium in the pathophysiology of the diseased state. Maintaining matrix homeostasis in the normal adult cartilage phenotype requires normal turnover of matrix components, principally collagen and proteoglycan. Chondrocytes and synovial fibroblasts are targeted, via specific cell-surface receptors, by cytokines like interleukin 1 (IL-1) and tumor necrosis factor alpha (TNF-alpha) to produce matrix proteases and to suppress the synthesis of collagen and proteoglycan. Thus, cytokines not only favor tissue destruction, but also inhibit tissue repair. A structurally heterogeneous group of factors capable of directly antagonizing cytokine action is described, which acts either by blocking cytokine-receptor binding, inhibiting local cytokine synthesis, or complexing the cytokine into an inactive form. Furthermore, many growth factors, such as transforming growth factor-beta (TGF-beta), can counteract the net effect of cytokines by stimulating the synthesis of matrix components or natural inhibitors of cartilage degrading enzymes.

Relationship between procollagen III peptide serum levels, synovitis of weight bearing joints and disability in rheumatoid arthritis

We studied P-III-P levels along with several acute phase reactants, Beta-2-microglobulin and autoantibody synthesis in 52 rheumatoid patients. No relationship arose between P-III-P levels and immunological parameters nor with acute phase reactants. We observed a highly significant difference between P-III-P levels in patients with knee and/or hip involvement with respect to those with only polyarthritis of small joints (86.1 +/- 21.5 vs 61.2 +/- 19.1 ng/ml; p less than 0.001). In 24 consecutive patients we also observed a significant correlation (p less than 0.02) between P-III-P levels and AIMS score. We conclude that P-III-P levels are mainly related to the synovial inflammation of major joints and as such P-III-P might represent the biochemical marker of the synovial mass in rheumatoid arthritis.

Interleukin-1-induced suppression of type II collagen gene transcription involves DNA regulatory elements

Interleukin-1 is a proinflammatory polypeptide that influences cartilage macromolecular degradation and synthesis. Since previous studies have suggested that interleukin-1 may inhibit type II collagen synthesis, we have studied the mechanism of inhibition of type II collagen synthesis by interleukin-1. When rabbit articular chondrocytes were treated with purified recombinant interleukin-1 beta or macrophage-conditioned medium, the synthesis and assembly of type II collagen into the extracellular matrix were greatly reduced. The inhibition was concentration-dependent and occurred within 10 h of treatment with interleukin-1, with greater inhibition occurring at 30 h. The reduced level of collagen synthesis correlated with a reduction in the steady-state mRNA levels coding for type II collagen, as measured by a Northern blot analysis. This further correlated with a reduction in the transcription of type II collagen gene, as determined by nuclear run-on experiments. Finally, transfection studies using plasmid constructs containing DNA regulatory sequences from the type II gene, coupled to a reporter gene (CAT), revealed that in comparison to control chondrocytes, interleukin-1 treated cells showed a reduced level of CAT activity. These studies demonstrate that the inhibition of collagen type II synthesis by interleukin-1 is due to a reduction in the transcription of the type II collagen gene and that the reduction in gene transcription involves DNA regulatory sequences that determine type II collagen gene expression.

Modulation of extracellular matrix metabolism in rabbit articular chondrocytes and human rheumatoid synovial cells by the non-steroidal anti-inflammatory drug etodolac. I: Collagen synthesis

Cultures of human rheumatoid synovial cells and rabbit articular chondrocytes were exposed to various concentrations of Etodolac (from 0.01 to 10 micrograms/ml) in presence or absence of 500 pg/ml (5 U/ml) human recombinant Interleukin-1 beta (IL-1 beta). Incubation of chondrocytes with Etodolac for 24 h did not alter collagen biosynthesis. In contrast, 1 micrograms/ml Etodolac caused a 20% increase of collagen production in synoviocytes. Addition of Etodolac in combination with IL-1 could partially suppress the inhibitory effect exerted by the cytokine on both cell types. Four-day exposure of chondrocytes to 0.1 and 1 micrograms/ml Etodolac led to an increased accumulation of collagen in the cell layer compartment. However, this treatment could not prevent the inhibitory effect of IL-1 on this collagen fraction. Treatment of synoviocytes for eight days with the same concentrations of Etodolac did not modify their collagen production but suppressed totally the inhibitory effect of IL-1. These data show that Etodolac is able to augment chondrocyte metabolism during a long term treatment. Moreover, under certain conditions, this drug can reduce or even suppress the IL-1-induced inhibition of collagen biosynthesis, a process that may take a part in the connective tissue alterations associated with osteoarticular diseases such as rheumatoid arthritis and osteoarthritis.

The human type II procollagen gene: identification of an additional protein-coding domain and location of potential regulatory sequences in the promoter and first intron

The complete DNA sequence (6 kb) of the 5' portion of the human type II procollagen gene (COL2A1) was determined from the promoter through the third exon including intron sequences and 690 bp of 5' flanking sequence. Three regions between -501 and -649 in the human promoter share high sequence homology to the rat type II procollagen gene and suggest that the functional sequences within the promoter may extend to at least 649 bp upstream from the start site of transcription. The first intron of the human gene contains elements known to play a role in transcription of other genes: three GC boxes, an inverted repeat with homology to a serum responsive element, a viral core enhancer motif, a high-affinity recognition sequence for nuclear factor-1, and an alternating purine/pyrimidine stretch composed of GT repeats. Both the promoter and a portion of the first intron have a high percentage of G + C residues and a high frequency of CpG dinucleotides. In addition, a protein domain that has been identified in the human COL2A1 gene is present in pro-alpha 1(I) and pro-alpha 1(III) collagen but was not previously described for pro-alpha 1(II) collagen. On the basis of this new information we present a modified gene structure for the exons encoding the pro-alpha 1(II) collagen NH2-propeptide.

Modulation by interleukin 1 and tumor necrosis factor alpha of production of collagenase, tissue inhibitor of metalloproteinases and collagen types in differentiated and dedifferentiated articular chondrocytes

The actions of interleukin 1 (IL1) and tumor necrosis factor alpha (TNF alpha) on several parameters of the collagen metabolism of rabbit articular chondrocytes were studied by comparing the responses of either differentiated chondrocytes in primoculture or dedifferentiated cells in late passage culture to human recombinant (hr) IL1 alpha, hr-TNF alpha and cytokine-enriched fractions of rabbit macrophage-conditioned media. In response to IL1 or TNF alpha, differentiated chondrocytes (i.e., producing the cartilage-specific collagens, types II and XI, but no type I), sharply reduced their synthesis of collagen, a reduction which involved both types II and XI collagens, without consistently changing their production of non-collagenous proteins; they also incorporated a smaller proportion of collagen into the matrix. Similar levels of response were obtained for hr-IL1 alpha at picomolar and for hr-TNF alpha at nanomolar concentrations. However, the action of TNF alpha, but not of IL1, was manifested only in the presence of serum. Simultaneously, IL1, but not TNF alpha, induced the chondrocyte production of procollagenase (a difference which contrasted with the similar levels of procollagenase induced by both cytokines in synovial and skin fibroblasts) but neither cytokine influenced the accumulation of the collagenase inhibitor TIMP. These effects were not affected by indomethacin and are thus unlikely to be prostaglandin-mediated. During their dedifferentiation in monolayer subcultures, chondrocytes became more sensitive to the procollagenase-inducing ability of IL1 and TNF alpha, but their response to TNF alpha was lower than to IL1. They also increased their production of TIMP, which remained unaffected by the cytokines. Simultaneously, they decreased their production of collagen and substituted progressively the synthesis of fibroblast-specific collagens, types I, III and V, for types II and XI. Acting on dedifferentiated cells, even in the presence of indomethacin, IL1 and TNF alpha further decreased the synthesis of collagen, reducing the production of both typical type I (i.e. [alpha 1(I)]2 x alpha 2(I) molecules) and type V collagens as well as their incorporation into the matrix, but increasing the synthesis of type III collagen. Therefore not only IL1, but also TNF alpha can exert profound influences on the collagen degradation and repair processes occurring in the pathology of articular cartilage.

Heterogeneity in hormone responses and patterns of collagen synthesis in cloned dermal fibroblasts

Fibroblasts cultured from normal human dermis are heterogeneous with respect to growth kinetics, synthetic function, and morphologic features. There are many examples of clonal heterogeneity in apparently homogeneous connective tissue cell populations, and it has been suggested that selection of cell populations with particular phenotypic features is the basis for the development of pathologic connective tissue changes in inflammatory disorders. In these studies we report characterization of the pattern of matrix biosynthesis and responses to hormones in cells cloned from normal human dermis. The results indicate that cloned dermal fibroblasts are heterogeneous with respect to synthesis of collagens as well as their responses to prostaglandin E2 and parathyroid hormone. Selective expansion of clonal populations with unique patterns of matrix synthesis and cell surface receptors could provide the basis for abnormal connective tissue remodeling in certain pathologic states.

Cytokines and cytokine inhibitors or antagonists in rheumatoid arthritis

This review has summarized some of the evidence suggesting that cytokines may play an important role in mediating pathophysiologic events in RA. However, these proteins are capable of mediating both stimulatory (agonist) and inhibitory (antagonist) effects in the rheumatoid synovium. GM-CSF, IL-1, TNF alpha, and PDGF are all produced in the rheumatoid synovium and may function to induce inflammation, enzyme release, fibroblast proliferation, and tissue destruction. Local release of IL-6 may alter the effects of IL-1 and TNF alpha, as well as induce Ig production and hepatic synthesis of acute-phase proteins. However, specific inhibitors of IL-1 and TNF alpha exist, which, if also released into the synovium, may antagonize the proinflammatory effects of these cytokines. In addition, IL-1 may have antiinflammatory effects, such as the induction of the synthesis of collagen and enzyme inhibitors by chondrocytes and synovial fibroblasts. Stimulation of these latter cells by TGF beta also may result in decreased matrix degradation and increased formation of scar tissue. The developing scenario is one of cell-cell interactions that are influenced in positive and negative manners by the local release of various mediators. A further understanding of cytokines and cytokine inhibitors in the rheumatoid synovium may lead to the development of more specific and effective therapeutic agents.

The accumulation of type I collagen mRNAs in human embryonic lung fibroblasts stimulated by transforming growth factor-beta

We examined the expression of type I collagen mRNAs (alpha 1(I) and alpha 2 (I)) by embryonic lung fibroblasts in cultures treated with transforming growth factor-beta (TGF-beta). TGF-beta caused a concentration dependent increase in the expression of alpha 1(I) mRNA for type I collagen. TGF-beta at low concentration (0.1 ng/ml) slightly increased the level of alpha 1(I) mRNA. Higher concentrations of TGF-beta (1.0 and 5.0 ng/ml) further increased the amount of alpha 1(I) mRNA. The increase in alpha 1(I) mRNA was associated with a marked increase in production of intact type I collagen molecules. TGF-beta did not increase expression of alpha 2(I) mRNA. The alpha 2(I) mRNA levels in human lung fibroblast cultures were not affected by varying the duration of exposure to TGF-beta nor the concentration of TGF-beta. In contrast, TGF-beta increased the amount of both alpha 1(I) and alpha 2(I) mRNA in NIH3T3 cells. These data suggest that the amount of alpha 2(I) mRNA is not rate limiting with respect to type I collagen production during TGF-beta stimulation in human lung fibroblast cultures.

Interleukin 1: the first interleukin

The name 'interleukin' and the designation of interleukin 1 (IL-1) derived from the Second International Lymphokine Workshop held in Switzerland in 1979. Since then interest in the original interleukin (IL-1) has increased exponentially as measured by the numbers of publications and meetings. The main reasons for this can be seen in the accompanying centrefold. The perception of IL-1 as a biological mediator in every organ system has attracted scientists from widely different backgrounds into this area and a steady succession of important and often surprising insights into IL-1 biology has ensured that interest has been sustained at a high level. This overview of the biology of IL-1 on the tenth anniversary of its turbulent life has been compiled by Franco di Giovine and Gordon Duff. It is of necessity selective and biased towards human IL-1 and begins with some general points (mainly cautionary) as a backdrop to the centrefold.