Collagen synthesis by human fibroblasts. Regulation by transforming growth factor-beta in the presence of other inflammatory mediators

Expression of TIMP-1, TIMP-2 and collagenase mRNA in periodontitis-affected human gingival tissue

Collagenolysis in periodontitis is thought to be modulated by the expression of three genes, collagenase, tissue inhibitors of metalloproteinases-1 and -2 (TIMP-1 and -2). We assessed the possible difference in TIMP-1, TIMP-2 and collagenase mRNA levels between gingival samples from patients with periodontitis and those from healthy subjects by reverse transcription-polymerase chain reaction (RT-PCR). This technique allows detection of transcripts from a very small sample quantity. The experiments showed that levels of TIMP-1 and collagenase transcripts relative to beta-actin are significantly higher in the diseased group than in healthy controls (8.11 +/- 0.83 versus 1.38 +/- 0.28% for TIMP-1 and 0.50 +/- 0.10 versus 0.0075 +/- 0.0024% for collagenase, respectively). The difference in TIMP-2 between the two groups (2.91 +/- 0.46 versus 1.84 +/- 0.87%) did not differ. Therefore, the host would have responded to the increase in collagenase level by preferentially producing TIMP-1 against tissue destruction. The differential gene expression of TIMP-1 and TIMP-2 in our study may account for a distinct genetic regulation of TIMP-1 and -2 in vivo.

Dexamethasone treatment suppresses collagen synthesis in infants with bronchopulmonary dysplasia

Collagen is an essential component of connective tissue and is present in the pulmonary interstitium. Collagen deposition is known to increase in many acquired chronic diseases, including bronchopulmonary dysplasia (BPD). Urinary excretion of hydroxyproline has been used as a specific index of collagen synthesis. Many studies have demonstrated that dexamethasone therapy is associated with respiratory improvement in infants with BDP but the mechanism of this effect is not well understood. We postulated that in infants with BDP who receive dexamethasone, suppression of collagen synthesis may cause respiratory improvement. Therefore, we studied the effect of dexamethasone on respiratory status and urinary excretion of hydroxyproline in 14 ventilator-dependent infants with BDP. Infants received 0.5 mg/kg/day dexamethasone, tapered by half every 3 days to complete a 12 day course. Eleven of the 14 infants were extubated at a mean +/- SD of 8.7 +/- 4.9 days after starting dexamethasone. Mean urinary hydroxyproline/creatinine ratios at 3, 6, 9, and 12 days of dexamethasone therapy were significantly lower than the mean pretreatment value, but after discontinuation rapidly rose toward baseline values. Decreased urinary excretion of hydroxyproline indicates that dexamethasone suppressed collagen synthesis in these infants. We speculate that suppression of collagen synthesis reduced pulmonary inflammation and fibrosis, resulting in respiratory improvement.

Expression and function of gingival fibroblast C1q receptors are upregulated by interleukin-1 beta and transforming growth factor-beta

In injury and inflammation, complement (C) component C1q, in addition to its central role in initiation of classical pathway of complement activation, modulates diverse cellular functions by binding to specific cell surface receptors. Interaction of substrate-bound C1q with receptors for the collagen-like domain of C1q (C1qRC) of human gingival fibroblasts (HGF) promotes cell attachment. We investigated modulation of the adhesive function and expression of C1qRC by interleukin-1 beta (IL-1 beta) and transforming growth factor-beta (TGF-beta). Confluent fibroblast monolayers were incubated under standard culture conditions with or without cytokines. C1qRC function was measured by attachment assays. IL-1 beta and TGF-beta increased fibroblast adhesion to C1q to 146% and 131% of controls, respectively. Cytokine enhancement of HGF adhesion was concentration-dependent, saturable (20 ng/ml IL-1 beta; 1 ng/ml TGF-beta) and time-dependent (IL-1 beta 12-hr peak; TGF-beta 24-hr peak). Effect of IL-1 beta and TGF-beta on C1qRC expression was assessed by flow cytometry measurements of fluorescence intensity of cells stained with C1q and FITC anti-C1q antibody, and by binding studies with 125I-C1q. Cells treated with cytokines displayed a two- to four-fold increased fluorescence of cell-bound C1q compared to controls. Binding studies indicated the increased fluorescence correlated with increase in number of C1qRC in both IL-1 beta (4.7 x 10(6)/cell) and TGF-beta (3.9 x 10(6)/cell)-treated cells, compared to control (3.0 x 10(6)/cell), but had no effect on binding affinity. Rates of internalization of receptor-bound C1q were similar in cytokine-treated cells and controls. We propose from these data that IL-1 beta and TGF-beta have the ability to upregulate C1qRC expression, and this effect contributes to increased adhesion of HGF to substrate-bound C1q.

A group of three fibroblast secreted polypeptides suppressed by cellular ageing and interferon-gamma

The structural and quantitative characteristics of many fibroblast-secreted proteins are modified during the in vitro cellular ageing. Here we report that three polypeptides (80, 84 and 87 kDa) absent from late passage fibroblast cultures, are constitutively secreted from young (early passage) cultures of various fibroblast strains whereas they are suppressed by the action of interferon-gamma. The three polypeptides were isolated and monoclonal antibodies were produced against the 84 kDa polypeptide. Immunoprecipitation experiments showed that the three polypeptides share common epitopes. The 80 and 84 kDa polypeptides were studied further and proved to be glycosylated polypeptides exhibiting analogous CNBr digestion peptide maps and identity in their sequenced N-terminal segments.

Collagen synthesis in fibroblasts from human colon: regulatory aspects and differences with skin fibroblasts

The purpose of this study was to examine regulation of collagen synthesis in human colon fibroblasts and compare the results from colon fibroblasts with those obtained in fibroblasts from human skin. The effects of interleukin-1 beta, tumour necrosis factor alpha, interferon gamma, transforming growth factor-beta, dexamethasone, and the calcium ionophore A23187 were investigated. All compounds were tested both in the absence and in the presence of fetal calf serum in the culture medium. The process of collagen synthesis in fibroblasts from colon and skin appears to be affected differently by these regulatory compounds. The most pronounced differences were that the relative collagen synthesis increased in dermal fibroblasts and decreased in colon fibroblasts upon addition of serum. In the presence of serum, interleukin-1 beta inhibited collagen synthesis in skin fibroblasts but not in colon fibroblasts. Dexamethasone suppressed the relative collagen synthesis in skin fibroblasts but not in colon fibroblasts. Transforming growth factor-beta stimulated the collagen synthesis in dermal fibroblasts in the presence of serum, but inhibited the process in colon fibroblasts. Because fibroblasts are the primary sources of collagen needed during wound repair, these results may offer (part of) the explanation why wounds in skin and intestine appear to behave differently under certain conditions.

Characterization of fibroblast clones from periodontal granulation tissue in vitro

Connective tissues are known to be composed of heterogeneous fibroblast subpopulations. The significance of this heterogeneity in different physiological and pathological conditions is poorly understood. Granulation tissue is formed in connective tissue during wound healing, chronic inflammation, and certain pathological conditions. In this study, heterogeneity of fibroblasts from granulation tissue was investigated by cell-cloning techniques. Granulation-tissue fibroblasts (GTFs) from both chronically inflamed periodontal lesions and healing wound granulation tissue behaved similarly. GTFs showed a more pronounced decrease in proliferative capacity with increasing cumulative population doubling levels (CPDLs) and 30-40% lower cloning efficiency compared with normal gingival fibroblasts (HGFs). Morphologically, cells in GTF cultures were mainly large, whereas HGFs were mainly small in size. Both cell-line types showed heterogeneity in cell morphology. Clones composed of large stellate-like cells predominated in GTF cultures, whereas clones composed of small spindle-shaped or epithelioid cells predominated in HGF cultures. In both cell-line type the proportion of clones composed of large cells increased without increasing CPDL. These findings show that the properties of the fibroblasts changed during their in vitro life spans. The finding that normal connective tissue and granulation tissues contain morphologically distinct fibroblast clones in different proportions suggests that local factors could stimulate local fibroblasts to differentiate into GTFs. Alternatively, local factors could select some fibroblast subpopulations to overgrow the others to form granulation tissue.

Isolation and partial characterization of a growth factor from human cementum

Cementum is the mineralized interface through which collagen fibers of periodontal connective tissues are anchored onto the tooth surface. We have isolated and partially characterized a mitogenic factor from human cementum which has properties different from other growth factors. Cementum was harvested from healthy human teeth, extracted in 1.0 M CH3COOH and mitogenic activities were fractionated by heparin-affinity chromatography. Proteins eluted by 0.4-0.6 M NaCl, which contained most of the cementum mitogenic activity, were precipitated by trichloroacetic acid and resolved by HPLC through ion-exchange and reverse-phase columns. NaDodSO4-polyacrylamide gel electrophoresis revealed that the purified preparation contained a M(r) 23,000 protein and this protein was associated with mitogenic activity. The purified cementum-derived growth factor (CGF) was active alone, but at suboptimal concentrations its activity was potentiated by small quantities of plasma-derived serum and epidermal growth factor (EGF). The activity was resistant to heat, but it was destroyed by trypsin digestion. Reduction and alkylation destroyed the mitogenic activity, however electrophoretic mobility was not affected. Binding of EGF to fibroblast membranes was not affected by the CGF and assays to detect platelet-derived growth factor were negative. These characteristics indicated that CGF is a distinct molecular species. Our data show that cementum contains several mitogenic factors and that CGF is the major cementum mitogen.

Alpha-smooth muscle actin is expressed in a subpopulation of cultured and cloned fibroblasts and is modulated by gamma-interferon

Clinical and experimental investigations have shown that, during wound healing and fibrocontractive diseases, fibroblasts acquire, more or less permanently according to the situation, morphological and biochemical features of smooth muscle (SM) cells including the expression of alpha-SM actin. Primary and passaged cultures of rat and human fibroblasts contain a subpopulation of cells expressing alpha-SM actin. These cells could derive from SM cells and/or pericytes present in the tissue from which cultures have been produced or represent bona fide fibroblasts. We have investigated the presence of alpha-SM actin in fibroblast cultures, clones, and subclones. In all cases the fibroblastic populations studied showed a proportion of alpha-SM actin expressing cells. Even after cloning, we never obtained populations negative for alpha-SM actin. We conclude that alpha-SM actin expression in fibroblastic cultures is not due to contaminant cells but is a feature of fibroblasts themselves. Our results support the view that fibroblastic cells are a heterogeneous population. It has been previously shown that gamma-interferon (gamma-IFN) decreases alpha-SM actin expression in SM cells. In rat and human fibroblasts, gamma-IFN decreases alpha-SM actin protein and mRNA expression as well as proliferation. The properties of this cytokine make it a good candidate for exerting an anti-fibrotic activity in vivo.

Effect of gamma-interferon on collagen synthesis by normal and fibrotic human lung fibroblasts

Increased lung collagen and increased collagen synthesis by lung fibroblasts is well recognized in pulmonary fibrosis. gamma-Interferon has been shown to inhibit collagen synthesis by fibroblasts. To understand its effect on lung fibroblasts we compared how this lymphokine affects the growth and collagen synthesis of normal and fibrotic human lung fibroblasts. The results showed that gamma-IFN inhibited DNA synthesis in all fibroblast strains examined. Both collagen production and type 1 mRNA levels were reduced in three normal and two fibrotic cell strains exposed to gamma-IFN, while they were not affected in one strain from fibrotic lung. Even though an occasional cell was unaffected by the gamma-IFN, collagen mRNA level was reduced in most cells and it remained reduced for 48 h after removing the gamma-IFN. These results show that gamma-IFN inhibits the growth of fibroblast cultures derived from normal and fibrotic human lungs and suppresses collagen synthesis in most of these cells.

Eosinophils in chronically inflamed human upper airway tissues express transforming growth factor beta 1 gene (TGF beta 1)

Transforming growth factor beta (TGF beta) is a multifunctional protein which has been suggested to play a central role in the pathogenesis of chronic inflammation and fibrosis. Nasal polyposis is a condition affecting the upper airways characterized by the presence of chronic inflammation and varying degrees of fibrosis. To examine the potential role of TGF beta in the pathogenesis of this condition, we investigated gene expression and cytokine production in nasal polyp tissues as well as in the normal nasal mucosa. By Northern blot analysis using a porcine TGF beta 1 cDNA probe, we detected TGF beta 1-specific mRNA in nasal polyp tissues, as well as in the tissue from a patient with allergic rhinitis, but not in the normal nasal mucosa. By the combination of tissue section staining with chromotrope 2R with in situ hybridization using the same TGF beta 1 probe, we found that approximately 50% of the eosinophils infiltrating the polyp tissue express the TGF beta 1 gene. In addition, immunohistochemical localization of TGF beta 1 was detected associated with extracellular matrix as well as in cells in the stroma. These results suggest that in nasal polyposis where eosinophils are the most prevalent inflammatory cell, TGF beta 1 synthesized by these cells may contribute to the structural abnormalities such as stromal fibrosis and basement membrane thickening which characterize this disease.

Human lung fibroblast subpopulations with different C1q binding and functional properties

Human lung fibroblasts differing in C1q binding, steady-state levels of collagen synthesis, and other functional properties were isolated. Explants of normal human lung specimens were cultured in medium containing complement-inactivated plasma-derived human serum or complete human serum. Cells obtained were treated with C1q and fluorescein isothiocyanate-anti-C1q antibody and separated based on fluorescence intensity in a fluorescence-activated cell sorter (FACS). FACS profiles showed that fibroblasts obtained in the presence of plasma-derived serum (HF cells) displayed higher fluorescence intensity than those obtained in complete serum (LF cells). The unsorted and sorted HF and LF fibroblasts retained their respective fluorescence phenotypes after subculture. The LF fibroblasts proliferated faster than HF cells and contained more cycling cells. However, whereas the sorted HF cells grew normally, sorted LF cells grew poorly. Collagen production and pro alpha l[I] mRNA levels in HF cells were 2.6 +/- 0.7 and 2.1 +/- 0.6 times as high as LF cells (n = 4). Collagen synthesis in both HF and LF cells was stimulated by transforming growth factor-beta and inhibited by interferon-gamma, but the stimulation was greater and inhibition less in LF cells. Our results indicate that C1q binding and the type of C1q receptors can serve as markers for fibroblast subpopulations differing in collagen synthesis, and that selection of subpopulations and their differential sensitivity to regulatory molecules can contribute to collagen alterations associated with inflammation, fibrosis, and other acquired diseases.

Transforming growth factor beta 1 stimulates type II collagen expression in cultured periosteum-derived cells

Chondrogenesis can occur during a bone repair process, which is related to several growth factors. Transforming growth factor beta 1 (TGF-beta 1) downregulates the expression of type II collagen by chondrocytes in vitro, but injection of TGF-beta 1 into the periosteum in vivo increases type II collagen mRNA levels and initiates chondrogenesis. We examined the effect of TGF-beta 1 on collagen gene expression in a bovine periosteum-derived cell culture system to evaluate its direct effect on the periosteum. Cultured cells expressed alkaline phosphatase and collagen pro alpha 1(I) and pro alpha 1(II) mRNAs. A low level of type II collagen synthesis was demonstrated by immunoprecipitation. TGF-beta 1 had no effect on periosteal cell proliferation. Expression of collagen pro alpha 1(I) mRNA did not change with TGF-beta 1 treatment, but alkaline phosphatase mRNA showed a dose-dependent decrease. Expression of collagen pro alpha 1(II) mRNA was stimulated 2.7-fold by TGF-beta 1. TGF-beta 1 also caused a 2.6-fold increase in type II collagen synthesis by immunoprecipitation. These findings indicate that TGF-beta 1 is an enhancer of the expression of the chondrocyte phenotype of the periosteal cells and suggest that TGF-beta 1 is important in initiating and promoting cartilage formation in vivo.

Collagen synthesis in cultured aortic smooth muscle cells. Modulation by collagen lattice culture, transforming growth factor-beta 1, and epidermal growth factor

We investigated the effects of transforming growth factor-beta 1 (TGF-beta 1) and epidermal growth factor (EGF) on the protein synthesis and production of collagen in cultured smooth muscle cells (SMCs) from the aortic media of pigs. SMCs were cultured as monolayers on plastic as well as in three-dimensional collagen lattices to gain some information about the influence of a preexisting collagenous matrix on the growth factor-induced effects. A 48-hour exposure of SMCs to TGF-beta 1 at concentrations of 5 ng/ml in the presence of 1% serum caused a marked enhancement of the production of collagen and noncollagen proteins. The rate of net collagen production by SMCs exposed to TGF-beta 1 was approximately threefold higher than that of control cells. Moreover, TGF-beta 1 specifically stimulated collagen synthesis, resulting in a greater proportion of collagen in total proteins synthesized compared with controls. The preexisting matrix of collagen lattices affects the response of SMCs to TGF-beta 1 and EGF. In monolayer cultures the collagen proportion increased twofold under the influence of TGF-beta 1, whereas in collagen lattices the specific stimulation of collagen synthesis was lower. We found that EGF enhanced TGF-beta 1-induced protein production in collagen lattices but not in monolayer cultures. In addition, the protein production by SMCs was influenced differently by EGF in these culture systems. Taken together, these data show a mutual influence of growth factors and extracellular matrix components on collagen production in SMCs, thus indicating that TGF-beta 1 may be an important pathophysiological regulator of collagen metabolism in the vessel wall.

Peptide growth factors and wound healing

Growth factors and cytokines are important signal transducers in wound microenvironments. Experimental data are accumulating rapidly which demonstrate their ability to influence populations of polymorphs and macrophages to migrate to the wound, subsequently to be replaced by synthetic cells which produce collagen and matrix; these events are controlled sequentially at cell receptor level by a variety of locally delivered (paracrine and autocrine) peptides. Preliminary results from clinical trials using recombinant human growth factors to improve cutaneous healing are encouraging. Current research aims to produce growth preparations which can be applied to a wound to accelerate healing.

Cytokines, fibrosis and the failure of glaucoma filtration surgery

Current therapies for the prevention of fibrosis after glaucoma filtering surgery can be effective but often produce unwanted side effects. An understanding of the cellular basis of the fibrotic reaction may lead to better treatments. Wound repair revolves around angiogenesis and the activation of fibroblasts by cytokines. These peptides, a number of which have been described, act together in intricately complicated networks to encourage fibroblast chemotaxis, proliferation and contractility, as well as to stimulate the production of glycosaminoglycans and collagen. Since interferons seem to inhibit many of these responses, they deserve further evaluation in the treatment of ocular fibrosis.

Role of fibroblast subpopulations in periodontal physiology and pathology

Fibroblasts are the principal cell type in the soft connective tissues of the periodontium; they perform important functions in development, physiology, and disease. A growing number of reports have indicated site-specific phenotypic variation of fibroblasts. Heterogeneity of metabolic traits has been demonstrated in cells from healthy and diseased tissues. The tissue distribution and relative proportions of fibroblast subpopulations have a significant impact on the regulation of connective tissue function in health and disease.

Cellular ageing related proteins secreted by human fibroblasts

Fibroblast secreted proteins participate in the formation of extracellular matrix. Extracellular matrix affects growth factor action, mediates cell adhesion and supports cell growth. Structural and quantitative characteristics of secreted proteins are modified in a similar manner, during both in vivo and in vitro cellular ageing. Such ageing related modifications may either be directly controlled by primary ageing causes, or evolve from a reformation of the extracellular matrix induced by a few ageing defects in key proteins such as fibronectin. They may result in the further inhibition of cell adhesion, cell stimulation by growth factors and, eventually, of cell proliferative ability.

Interferon-gamma reverses the stimulation of collagen but not fibronectin gene expression by transforming growth factor-beta in normal human fibroblasts

It has recently become apparent that several cytokines and growth factors are capable of modulating fibroblast proliferation and biosynthetic activity. To understand the role of these factors in connective tissue regulation, we examined the effects of the simultaneous addition of interferon-gamma (IFN-gamma) and transforming growth factor-beta (TGF-beta) on normal human dermal fibroblast collagen and fibronectin production. In addition, in vitro transcription rates and steady-state mRNA levels for these molecules were determined by nuclear run-off assays and Northern and dot-blot hybridization using specific human cDNA probes. Treatment of cultures with TGF-beta caused stimulation of collagen and fibronectin production. Addition of IFN-gamma to the TGF-beta-treated cultures abrogated the stimulatory effects of TGF-beta on collagen production in a dose-dependent manner and resulted in a net inhibition of collagen production. In contrast, the increase in fibronectin synthesis induced by TGF-beta was augmented further by IFN-gamma. These changes in collagen and fibronectin production were accompanied by parallel changes in the steady-state mRNA levels for these proteins. The effects of TGF-beta plus IFN-gamma on fibronectin gene expression appeared to be mediated entirely by transcriptional mechanisms, whereas the effects on collagen gene expression resulted from a combination of transcriptional and post-transcriptional events.

Interferon-gamma reverses the stimulation of collagen but not fibronectin gene expression by transforming growth factor-beta in normal human fibroblasts

It has recently become apparent that several cytokines and growth factors are capable of modulating fibroblast proliferation and biosynthetic activity. To understand the role of these factors in connective tissue regulation, we examined the effects of the simultaneous addition of interferon-gamma (IFN-gamma) and transforming growth factor-beta (TGF-beta) on normal human dermal fibroblast collagen and fibronectin production. In addition, in vitro transcription rates and steady-state mRNA levels for these molecules were determined by nuclear run-off assays and Northern and dot-blot hybridization using specific human cDNA probes. Treatment of cultures with TGF-beta caused stimulation of collagen and fibronectin production. Addition of IFN-gamma to the TGF-beta-treated cultures abrogated the stimulatory effects of TGF-beta on collagen production in a dose-dependent manner and resulted in a net inhibition of collagen production. In contrast, the increase in fibronectin synthesis induced by TGF-beta was augmented further by IFN-gamma. These changes in collagen and fibronectin production were accompanied by parallel changes in the steady-state mRNA levels for these proteins. The effects of TGF-beta plus IFN-gamma on fibronectin gene expression appeared to be mediated entirely by transcriptional mechanisms, whereas the effects on collagen gene expression resulted from a combination of transcriptional and post-transcriptional events.

Tryptophan-induced eosinophilia-myalgia syndrome

Eight patients who became ill while taking tryptophan had myalgia, fatigue, rash, fever, edema, alopecia, arthralgias, diminished joint motion, skin tightening, muscle cramping, and distal paresthesias. Three had shortness of breath, and one had pulmonary hypertension. Laboratory abnormalities included peripheral eosinophilia, leukocytosis, thrombocytosis, raised erythrocyte sedimentation rate, and elevated serum levels of aldolase, lactate dehydrogenase, and liver enzymes. Of 4 chest radiographs, 3 were abnormal. Of 5 skin and muscle biopsies, 4 showed sclerosis or mixed inflammatory cell infiltration of the dermis, subcutis, and fascia. Eosinophils were often present, but vasculitis was absent. Muscle inflammation was minimal. We conclude that the "eosinophilia-myalgia syndrome" is related to the ingestion of tryptophan and that abnormalities in the secretion of lymphokines may be important in its pathogenesis.

Collagen synthesis in explants from rat intestine

Collagen is the major structural component of the intestinal wall and its metabolism is of special interest for intestinal strength. We describe collagen synthesis in short-term (3 h) incubations of rat intestinal tissue, as measured in terms of incorporation of [3H]proline in collagenase-digestible protein and percentage relative collagen synthesis. In this time span, incorporation of [3H]proline in collagen increases linearly with time and tissue weight. Addition of unlabeled proline during incubation, in excess of the 0.1 microM [3H]proline always present, strongly increases both total protein and collagen synthesis, suggesting that proline transport is rate limiting. Further experiments have been performed in the presence of labeled proline alone and with the addition of 0.35 mM unlabeled proline. Collagen synthesis is significantly higher in colon than in ileum, comprising 0.37 and 0.21%, respectively, of total protein synthesis. Also, collagen synthesis decreases considerably with age, both in ileum and colon. The results presented here demonstrate that rat intestinal explants synthesize measurable amounts of collagen in vitro and that the system used is able to detect changes in in vivo synthetic capability such as those induced by ageing.