Interleukin-1 alpha modulates collagen gene expression in cultured synovial cells

Effect of cyclic tensile load on the regulation of the expression of matrix metalloproteases (MMPs -1, -3) and structural components in synovial cells

Synovial cells are reported to colonize synthetic ligament scaffolds following anterior cruciate ligament (ACL) reconstruction but the process leading to ligamentization is poorly understood. The present study investigated the effect of cyclic tensile strain on the expression of genes involved in matrix remodelling in bovine synovial cells seeded onto an artificial ligament scaffold. Synovial cells were seeded and cultured on polyester scaffolds for 3 weeks and subsequently subjected to cyclic tensile strain of 4.5% for 1 hr at frequency of 1 Hz. Changes in the levels of expression of genes for major ligament components (type I and type III collagen) and also metalloproteinases (MMP-1 and MMP-3), and TIMP-1 were examined using RT-PCR. Additionally, metalloproteinase activity was measured using both zymography and collagenase assays. The gene expression of MMP-3 transcripts in the loaded group was almost 3-fold that observed in control group but no differences were observed in other transcripts. Consistent with these findings, MMP-3 activity increased by 85% under mechanical stimulus, and MMP-1 activity showed no changes. Over expression of MMP-3 under cyclic tensile load may mediate the proteolysis of certain substrates surrounding the ligament scaffold. This will play a critical role in facilitating cell migration, proliferation and tissue remodelling by breaking down the provisional tissue formed by the synovium, and by generating factors that induce angiogenesis and chemotactic cell migration.

Costimulation of fibroblast collagen and transforming growth factor beta1 gene expression by monocyte chemoattractant protein-1 via specific receptors

Recent studies indicate potential roles of monocyte chemotactic protein-1 (MCP-1) in recruitment of monocytes to sites of inflammation. However, their increased expression does not always correlate with monocyte influx, suggesting other possible biological activities for this member of the C-C chemokine family. In view of its potential role in regulating extracellular matrix expression in fibrotic disorders, the effects of MCP-1 on lung fibroblast collagen expression were evaluated. Isolated rat lung fibroblasts were treated with increasing doses of MCP-1 for variable periods of time and examined for effects on collagen synthesis and expression of procollagen alpha1(I) mRNA expression. The results show that MCP-1 was able to stimulate collagen expression in these cells in a dose-dependent manner but required over 24 h for significant elevation to occur. In view of this delayed time course, the possibility of mediation via endogenous transforming growth factor beta (TGFbeta) was tested by the ability of anti-TGFbeta antibody to inhibit this MCP-1 stimulation of collagen expression. Significant but incomplete inhibition by this antibody was observed. Pretreatment of the cells with antisense but not by sense or missense TGFbeta1 oligodeoxyribonucleotides caused essentially complete inhibition of this MCP-1 stimulatory effect. Furthermore, MCP-1 treatment was found to also stimulate TGFbeta secretion and mRNA expression, which was also abolished by pretreatment with antisense TGFbeta1 oligodeoxyribonucleotides. The kinetics of TGFbeta expression indicates that significant increase preceded that for collagen expression. Binding studies using 125I-labeled MCP-1 indicated the presence of specific and saturable binding sites with a dissociation constant consistent with the dose response curves for stimulation of fibroblast collagen synthesis and TGFbeta activity by MCP-1. These results taken together suggest that MCP-1 stimulates fibroblast collagen expression via specific receptors and endogenous up-regulation of TGFbeta expression. The latter then results in autocrine and/or juxtacrine stimulation of collagen gene expression.

Transcriptional regulation of decorin gene expression. Induction by quiescence and repression by tumor necrosis factor-alpha

Decorin, a leucine-rich proteoglycan with ubiquitous tissue distribution, may play essential biological roles during inflammation and cancer growth through its ability to bind extracellular matrix constituents and growth factors. In this study, we demonstrate that decorin gene expression is greatly enhanced after normal diploid fibroblasts reach confluency and cease to proliferate. Elevation of decorin mRNA steady state levels was maintained for up to 16 days postconfluency. In vitro transcription analyses indicated enhanced transcriptional activity in quiescent fibroblasts when compared to cells harvested in their logarithmic phase of growth. This phenotypic trait was reversed by the exogenous addition of tumor necrosis factor-alpha (TNF-alpha). Furthermore, transforming growth factor-beta (TGF-beta) down-regulated decorin gene expression in an additive manner with TNF-alpha. Transient cell transfection assays using plasmid constructs harboring the decorin promoter linked to the chloramphenicol acetyltransferase reporter gene demonstrated a dose-dependent transcriptional repression by TNF-alpha. These findings were further corroborated by in vitro transcription experiments using nuclear extracts from control and TNF-alpha-treated quiescent fibroblasts. In contrast, the decorin promoter constructs failed to respond to TGF-beta, thus suggesting either post-transcriptional regulation by this growth factor or lack of TGF-beta-responsive elements. Further experiments with 5' deletion constructs showed two TNF-alpha response elements, one residing within the 5'-untranslated region (exon Ib), the other one between residues -188 and -140 of the decorin promoter. Collectively, our results indicate that TNF-alpha, through its ability to transcriptionally inhibit decorin gene expression in growth-arrested cells, may be a key modulator of the biological functions of this proteoglycan.

Uncoordinate regulation of collagenase, stromelysin, and tissue inhibitor of metalloproteinases genes by prostaglandin E2: selective enhancement of collagenase gene expression in human dermal fibroblasts in culture

The degradative effects of interleukin-1 (IL-1) on the extracellular matrix of connective tissue are mediated primarily by metalloproteinases and prostaglandins. Clinical observations suggest that these effects can be prevented, to some extent, by the use of non-steroidal anti-inflammatory drugs. We have examined the role of prostaglandin E2 (PGE2) in IL-1-induced gene expression by human skin fibroblasts in culture. Incubation of confluent fibroblast cultures with varying concentrations (0.01-1.0 microgram/ml) of PGE2 led to a dose-dependent elevation of collagenase mRNA steady-state levels, the promoter activity, and the secretion of the protein, whereas relatively little effect was observed on stromelysin and TIMP gene expression. Exogenous PGE2 had no additive or synergistic effect with IL-1 on collagenase gene expression. Furthermore, commonly used non-steroidal anti-inflammatory drugs (indomethacin, acetyl salicylic acid and ibuprofen), at doses which block prostaglandin synthesis in cultured fibroblasts, failed to counteract IL-1-induced collagenase and stromelysin gene expression, nor did they affect TIMP expression. Although the effects of PGE2 did not potentiate those of IL-1 on collagenase gene expression in vitro, one could speculate that massive production of PGE2 by connective tissue cells in vivo in response to inflammatory mediators such as IL-1 or tumor necrosis factor-alpha, could lead to sustained expression of collagenase in connective tissue cells after clearance of the growth factors.

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.

Interleukin-6 does not regulate interstitial collagenase, stromelysin and tissue inhibitor of metalloproteinases synthesis by cultured human fibroblasts

We have examined the effect of interleukin-6 (IL-6) on the synthesis of matrix metalloproteinases (MMPs) and tissue inhibitor of metalloproteinases (TIMP) by human skin fibroblasts, both at protein and messenger RNA levels. IL-6 did not modulate the production of MMPs and TIMP. Furthermore IL-6 did not modify the stimulatory effect exerted by interleukin-1 (IL-1) on the expression of MMPs and TIMP. These results strongly suggest that IL-6 is not involved in the extracellular matrix breakdown, either directly by acting on cell production of MMPs or TIMP, or indirectly by modulating the effect of IL-1 on the synthesis of MMPs and TIMP.

Leukoregulin down-regulates type I collagen mRNA levels and promoter activity in human dermal fibroblasts, and counteracts the up-regulation elicited by transforming growth factor-beta

Leukoregulin (LR), a T-cell-derived growth factor, modulates fibroblast functions in vitro [Mauviel, Rédini, Hartmann, Loyau & Pujol (1991) J. Cell Biol. 113, 1455-1462]. In the present study, incubation of human dermal fibroblasts with LR (0.1-2 units/ml) resulted in decreases in the mRNA steady-state levels for alpha 1(I), alpha 2(I) and alpha 1(III), but not alpha 2(V), collagen genes. LR also down-regulated alpha 2(I) collagen promoter activity in transient cell transfections of control cells as well as those incubated with transforming growth factor-beta, a potent up-regulator of collagen type I gene expression. Thus LR is a strong inhibitor of type I collagen gene expression, acting at the level of transcription.

Transforming growth factor-beta 1 (TGF-beta 1) expression and regulation in rat cortical astrocytes

Transforming growth factor-beta 1 (TGF-beta 1) is a potent modulator of immune and glial cells' functions and thus, could play an important role in neuro-immune interaction. However, published reports disagree on whether or not TGF-beta 1 is expressed in normal brain. We demonstrate here the constitutive expression of TGF-beta 1 mRNA but not protein in both cerebral cortex and primary rat cortical astrocytes. Steady-state TGF-beta 1 mRNA level increased 2-fold in adult compared to neonatal cortex and during proliferation and differentiation of astrocytes in primary culture. This response was not accompanied by the appearance of detectable TGF-beta protein either in vivo or in vitro. However, both intracellular immunoreactive TGF-beta and extracellular TGF-beta 1 activity were detected upon in vitro stimulation of astrocytes with interleukin-1 (IL-1). The extracellular TGF-beta 1 increased with time of exposure to and concentration of IL-1. In contrast, the amount of TGF-beta 1 mRNA remained unchanged during stimulation of astrocytes with IL-1. These results suggest that the production of TGF-beta 1 in astrocytes is regulated at both mRNA and protein levels. The former may occur during astrocytic development, and the latter during astrocytic response to injury in association with elevation of IL-1.

Lung cytokine production in bleomycin-induced pulmonary fibrosis

In bleomycin-induced pulmonary fibrosis, lung injury is accompanied with inflammation and subsequent fibrosis. In this study, lung mRNA for several cytokines was measured in bleomycin-treated mice to evaluate their roles in lung fibrosis. Significant increases in tumor necrosis factor-alpha (TNF-alpha) and transforming growth factor-beta (TGF-beta) mRNA were found in lungs of bleomycin-treated responder CBA mice but not in nonresponder BALB/c mice. Increases in responder animals peaked on day 7 after bleomycin administration, and subsequently returned toward control levels. This time course paralleled that for the increase in beta-actin mRNA, but preceded the peak increase in mRNA for collagens I and III. When lung macrophages were analyzed for cytokine secretion, differences were observed between alveolar macrophages and interstitial cells, and between cells from bleomycin-responsive CBA and nonresponsive BALB/c mice. Only alveolar macrophages from CBA mice secreted increased amounts of IL-1. TNF-alpha activity was increased in conditioned media of alveolar and interstitial cells of CBA mice, while only alveolar macrophages of nonresponder BALB/c mice secreted any activity. The kinetics of the increased secretion of TNF-alpha was dissimilar for these different cells. These results are consistent with the conclusion that increased production of TNF-alpha and TGF-beta is an important component of the fibrotic process.

Modulation of human dermal fibroblast extracellular matrix metabolism by the lymphokine leukoregulin

The effect of leukoregulin, a 50-kD lymphokine with unique antitumor properties, was studied in vitro on several fibroblast functions. Leukoregulin did not inhibit fibroblast proliferation, as measured by cell enumeration and [3H]thymidine incorporation, and had no cytotoxic effect in terms of increased membrane permeability detected by trypan blue exclusion, two of the major leukoregulin actions on tumor cells. Leukoregulin induced a dose-dependent decrease in collagen synthesis, demonstrated by decreased [3H]proline incorporation into collagenase-digestible protein, as early as 6 h after the addition of the lymphokine to human fibroblasts. Leukoregulin inhibited the synthesis of both type I and type III collagen, as measured by SDS-PAGE and by specific radioimmunoassay. Neutralizing antibodies to interleukin-1 alpha, interleukin-1 beta, tumor necrosis factor-alpha, and interferon-gamma failed to alter the effect of leukoregulin on collagen synthesis, attesting that leukoregulin action was not due to contamination by these cytokines. Inhibition of collagen synthesis occurred concomitantly with increased secretion of prostaglandin E2 and a transient rise in intracellular cyclic AMP content, peaking at 6 h. However, blocking prostaglandin synthesis with indomethacin did not counteract inhibition of collagen synthesis by leukoregulin, demonstrating independence of this action of leukoregulin from cyclooxygenase metabolites. Leukoregulin also stimulated glycosaminoglycan production in a dose-dependent manner, affecting the synthesis of hyaluronic acid as the major fibroblast-derived extracellular glycosaminoglycan. In addition, secretion of neutral proteases (collagenase, elastase, caseinase) was increased. These observations indicate that leukoregulin is able to regulate synthesis of molecules critical to the deposition of the extracellular matrix by nontransformed nonmalignant fibroblasts.

Interleukin-1 beta-induced changes in the kinetic constants of L-proline uptake in human skin fibroblasts

The effects of interleukin-1 beta (IL-1) on L-proline uptake in human skin fibroblasts were investigated. Exposure of the fibroblasts to IL-1 (5, 10 or 50 pg/ml) for 2 h did not change L-proline uptake. In contrast, inhibition was observed after 6 h of IL-1 treatment, and only 60% of the control uptake remained after incubation for 24 h with 10 pg of IL-1/ml. IL-1 depressed the activity of both transfer systems; the low-affinity system inhibited by alpha-(methylamino)isobutyric acid (Me-AIB), corresponding to system A, and a high-affinity transfer system which is unaffected by Me-AIB. The inhibitory effect increased as the L-proline concentration decreased. To determine whether IL-1-induced prostaglandin release influences proline uptake, indomethacin (14 microM) was added as a cyclo-oxygenase inhibitor. Indomethacin itself decreased L-proline uptake but to a lesser extent than did IL-1. When IL-1 was tested in the presence of indomethacin, the inhibition of L-proline uptake was still observed, with values between those obtained with each substance in isolation. This suggests that the inhibitory effect of IL-1 on proline uptake by skin fibroblast does not only involve the prostaglandins that accumulate in the medium, but no firm conclusion can be drawn, due to the fact that the inhibition by the two agents was not statistically independent. Kinetic analyses for 1 min combined with inhibition experiments showed that IL-1 induced a decrease in the Km and Vmax, values of the high-affinity transport system, whereas it increased the Km of system A. Therefore the two systems of proline uptake in skin fibroblasts are probably inhibited by IL-1 via different mechanisms.

Comparative effects of interleukin-1 and tumor necrosis factor-alpha on collagen production and corresponding procollagen mRNA levels in human dermal fibroblasts

The effects of recombinant human Interleukin-1 alpha (IL-1 alpha), Interleukin-1 beta (IL-1 beta), and Tumor Necrosis Factor-alpha (TNF-alpha) on collagen biosynthesis were studied in vitro using dermal fibroblast cultures. Both forms of IL-1 and TNF-alpha induced a dose-dependent inhibition of both types I and III collagen synthesis, as measured by radioimmunoassay, gel electrophoresis, or collagenase-sensitive material. This effect was accompanied by a significant release of prostaglandin E2 into the culture medium. However, indomethacin, a potent inhibitor of prostaglandin synthesis, could not prevent the inhibitory effect of the three cytokines on collagen synthesis. Measurement of type I and type III procollagen mRNA levels in IL-1 treated cells revealed that both IL-1 alpha and IL-1 beta were potent enhancers of procollagen gene expression at pretranslational level. On the other hand, TNF-alpha was found to reduce the steady-state levels of type I and III procollagen mRNA in a dose-dependent manner. Quantitation of IL-1 beta and TNF-alpha transcripts following TNF-alpha treatment of fibroblasts indicated that this cytokine can induce IL-1 beta gene expression in these cells. By contrast, TNF-alpha mRNA remained at a constant level after TNF-alpha exposure. These data suggest that IL-1 and TNF-alpha, two cytokines that share several biologic activities, modulate collagen deposition in dermal fibroblasts by mechanisms that are clearly different: TNF-alpha appears to act at a transcriptional level to inhibit collagen synthesis, whereas IL-1 inhibitory action involves important translational regulation, still unknown, that counterbalances its stimulatory effect on procollagen mRNA levels. Moreover, our data suggest the existence of local fibroblastic cytokine production that may be involved in the modulation of extracellular matrix deposition.

Joint occurrence of collagen mRNA containing cells and macrophages in human atherosclerotic vessels

Cells with enhanced levels of collagen type I and III mRNA were identified and localized in frozen tissue sections from samples of human atherosclerotic renal and common iliac arteries by in situ hybridization using complementary 35S-labeled RNA probes. Serial sections were immunohistochemically stained for smooth muscle cells, monocytes, and differentiated macrophages. In the fibromuscular intima and in the fibrous plaques, cells with enhanced transcriptional activity were located mainly in the vicinity of differentiated macrophages. In three patients, lack of enhanced transcriptional activity in a proliferated intima was connected with complete absence of macrophages, thus indicating a quiescent stage of atherosclerosis. Immunohistochemical staining of serial sections for smooth muscle cells (SMC) revealed the presence of this cell type throughout the proliferated intima in atherosclerotic arteries including those areas in which enhanced collagen mRNAs were detected. The present results support the idea that macrophages play an important role in the activation of collagen synthesis in SMC of atherosclerotic vessel walls.

Interleukin-1 beta prevents the stimulatory effect of transforming growth factor-beta on collagen gene expression in human skin fibroblasts

Transforming growth factors beta 1 and beta 2 (TGF-beta 1 and TGF-beta 2) are well-characterized strong inducers of collagen gene expression. A 100 pM concentration of TGF-beta 1 or TGF-beta 2 increases pro alpha 1(I) collagen mRNA levels in human skin fibroblasts 6.6-fold and 7.0-fold respectively, and also increases the accumulation of procollagens in the cell culture medium. Interleukin-1 beta (IL-1 beta) is an inflammatory mediator which also regulates connective tissue metabolism. A small concentration of IL-1 beta (0.01-1.0 unit/ml) slightly increases pro alpha 1(I) collagen mRNA levels (2.2-fold). Here we provide evidence that IL-1 beta prevents the stimulatory effect of TGFs-beta on collagen synthesis in human skin fibroblasts. An IL-1 beta concentration of 1 unit/ml is enough to keep pro alpha 1(I) collagen mRNA levels at control values in cells stimulated by 100 pM-TGF-beta 1. Thus the results indicate that IL-1 beta inhibits collagen synthesis in cells activated by TGFs-beta, whereas it does not significantly change or might even stimulate collagen gene expression in non-activated cells.

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.

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

The effect of Etodolac on glycosaminoglycan (GAG) synthesis by human synovial cells and rabbit articular chondrocytes in culture was studied at doses ranging from 0.01 to 10 micrograms/ml. In chondrocyte cultures, short-term exposure to Etodolac decreased the total amount of GAGs (mainly chondroitin sulfate) affecting essentially the cell layer-associated fraction. When cells were incubated with Interleukin-1 (IL-1), Etodolac still exerted its inhibiting effect on GAG synthesis. Long-term exposure of chondrocytes to Etodolac caused a diminution of the total GAG synthesis for the highest concentration studied (1 micrograms/ml). IL-1 alone or in combination with Etodolac decreased the synthesis of GAGs suggesting that pretreatment with Etodolac cannot prevent the action of IL-1. In synoviocyte cultures, the drug caused an inhibition of the GAG biosynthesis (mainly hyaluronic acid). In presence of IL-1, Etodolac at the highest concentration partially diminished the stimulatory effect of IL-1. A 8-day exposure of the cells to Etodolac led to a decrease of GAG synthesis. In the same experiment, IL-1 alone caused a slight increase of GAG production that was not abolished by Etodolac treatment.

Resting chondrocytes in culture survive without growth factors, but are sensitive to toxic oxygen metabolites

Chondrocytes in dense suspension culture in agarose survive in serum-free DME because they secrete low molecular mass compounds supporting their own viability. This activity can be replaced by pyruvate, or sulfhydryl compounds, e.g., cysteine or dithioerythritol. Catalase, an enzyme decomposing H2O2, also protects the cells, whereas superoxide dismutase has no effect. Therefore, chondrocytes in culture are sensitive to toxic compounds derived from molecular oxygen, i.e., hydroxyl radicals or hydrogen peroxide spontaneously generated in DME containing ascorbate and ferrous ions. Poly-ADP-ribosylation is an important step in the cascade of events triggered by these compounds. To survive, chondrocytes do not require stimulation by growth factors. They remain resting cells in fully defined, serum-free culture also at low density. Proliferation and hypertrophy can be induced by serum, but not by low cell density alone.

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.

Continuous stressing of mouse interparietal suture fibroblasts in vitro

The morphological and biochemical response of sutural fibroblasts in vitro to continuous force was examined. Cells from mouse interparietal sutures were grown and subcultured on glass slides. Titanium disks coated with collagen were allowed to attach to the cellular multilayers. Four of the glass slides were then placed at an angle of 75 degrees for a period of three days so that continuous stress would be created, while four others were left flat. Also, four glass slides were left flat with no disk. Following the incubation period, the dishes were labeled with 14C-glycine for 15 h. The cells and medium were then collected for collagen extraction followed by SDS-polyacrylamide gel electrophoresis. Dried gels impregnated with fluor were exposed to x-ray films that were then scanned densitometrically for collagen types I and III. It was found that the proportion of newly-synthesized type III collagen increased significantly with the application of continuous stress. A second set of experimental and control glass slides was fixed in glutaraldehyde and post-fixed in osmium tetroxide. Following critical-point drying and coating, the glass slides were examined under a scanning electron microscope. The scanning images showed the formation of a ligament-like structure between the disk and the glass slide. Moreover, mitotic activity, as evidenced by spheroidal cells, was stimulated in the areas previously adjacent to the disc, which had since moved away. This system offers a standardized continuous force system that can stress cells in a ligament-like structure and thus provides an in vitro model analogous to clinical orthodontic and orthopedic stress.

Ito-cell gene expression and collagen regulation

Ito cells are perisinusoidal cells thought to be a major source of collagen in normal and fibrotic livers. These cells appear to have features similar to several cell types but when cultured assume a fibroblast-like morphology. In this study we evaluated the phenotype of both freshly isolated and cultured Ito cells by examining their gene expression. To better define the modulators of Ito-cell collagen synthesis, we also examined the effect of transforming growth factor-beta 1, tumor necrosis factor-alpha and dexamethasone on collagen synthesis by these cells. Northern hybridization analysis revealed that cultured Ito cells expressed different types of procollagen mRNAs than did freshly isolated cells. Cultured cells contained large amounts of type I procollagen mRNA and lesser amounts of types III and IV, whereas freshly isolated cells contained more type IV procollagen mRNA than types I and III. Treatment of cultured cells with either transforming growth factor-beta 1 or tumor necrosis factor-alpha resulted in a greater than three-fold increase in total collagen content, and the effects of these cytokines on Ito-cell collagen synthesis involved different levels of gene regulation. Transforming growth factor-beta 1-treated cells had an approximately threefold increase in their type I procollagen mRNA levels, whereas no increase in this mRNA level was found in tumor necrosis factor-alpha-treated cells. Transforming growth factor-beta 1 treatment induced a twofold increase in transforming growth factor-beta 1 mRNA content in cultured cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Receptor-mediated endocytosis and nuclear transport of human interleukin 1 alpha

In this study we demonstrate that 125I-labelled interleukin (IL) 1 alpha binds specifically to its receptor on the surface of EL4 6.1 cells and is subsequently endocytosed and translocated from the cell membrane to the nucleus, where it progressively accumulates. Two-dimensional polyacrylamide-gel electrophoresis revealed that the internalized 125I-IL1 alpha associated with the nucleus was intact, with negligible breakdown products present. Specific and saturable binding of 125I-IL1 alpha was demonstrated on purified nuclei isolated from these cells. Binding of the radiolabelled ligand showed similar kinetics to that of the plasma-membrane receptor, and was inhibited by both unlabelled IL1 alpha and IL1 beta. Equilibrium binding studies on isolated nuclei revealed a single high-affinity binding site, with a Kd of 17 +/- 2 pM, and 79 +/- 12 binding sites per nucleus. These studies demonstrate that receptor-mediated endocytosis of IL1 results in its accumulation in the nucleus, and this mechanism may play an important role in mediating some of the actions of IL1.

Inhibition of collagen synthesis by interleukin-1 in three-dimensional collagen lattice cultures of fibroblasts

Interleukin-1 (Il-1) was added to collagen lattice cultures of human skin fibroblasts. No cell division was induced, the ability of fibroblasts to contract the lattices was decreased and a dose-related inhibition of collagen synthesis without effect on non-collagen proteins was found. Indomethacin had no influence on these effects.

Interleukin-1 alpha and beta induce interleukin-1 beta gene expression in human dermal fibroblasts

The ability of the two forms of interleukin-1, IL-1 alpha and IL-1 beta, to induce IL-1 beta gene expression in human skin fibroblasts was studied in vitro, using Northern blot hybridization. Both recombinant IL-1 alpha and IL-1 beta caused a dramatic increase in IL-1 beta mRNA levels, IL-1 alpha being more efficient than IL-1 beta. Blockage of the prostaglandin synthesis by indomethacin reduced the basal level of IL-1 beta mRNA in control cultures and decreased also the stimulatory effect exerted by both IL-1s on IL-1 beta gene expression. These data suggest that IL-1 and prostaglandin (mainly PGE2) may act synergistically to stimulate IL-1 gene expression in dermal fibroblasts, contributing as a local amplifier system to the alterations of connective tissue in inflammatory processes.

Tumor necrosis factor inhibits collagen and fibronectin synthesis in human dermal fibroblasts

Tumor necrosis factor (TNF) caused inhibition of collagen production by confluent cultures of human dermal fibroblasts in a dose-dependent manner. Concomitant increase of prostaglandin E2 release was observed as a result of TNF-induced cell activation. However, a blockade of the cyclooxygenase pathway of arachidonate metabolism by indomethacin did not abrogate the inhibitory effect of TNF on collagen synthesis, suggesting that this effect could be independent of prostaglandin metabolism. Gel electrophoresis of the newly synthesized macromolecules from the culture media showed that both type I and type III collagens as well as fibronectin were affected by the inhibition. Electrophoresis of cell layer-associated proteins demonstrated that the reduction in amounts of collagen and fibronectin in the medium did not result from an intracellular accumulation of these macromolecules. Production of procollagens was reduced in parallel to that of collagens, suggesting that the effect of TNF is exerted before the processing steps of procollagens. These results clearly show that TNF could play a role in modulation of matrix deposition by fibroblasts during inflammatory processes.