Collagen synthesis by normal and fibrotic human lung fibroblasts and the effect of transforming growth factor-beta

Collagen accumulation is a major feature of pulmonary fibrosis and other fibrotic lesions. We have studied the synthesis of collagens in fibroblasts cultured from normal and fibrotic human lung specimens and evaluated how it is affected by transforming growth factor-beta (TGF-beta). Fibroblasts were obtained from normal and fibrotic adult human lungs (n = 11; normal = 6, idiopathic pulmonary fibrosis = 5). They were exposed to TGF-beta and pulse-labeled with [3H]proline and [3H]glycine. Collagen production was measured as bacterial collagenase-susceptible radioactivity, and collagen mRNA levels were determined by a solution hybridization assay using labeled procollagen alpha 1[I] cDNA clone HF677 as probe. Synthesis of collagen types I, III, and V were assessed after separating them by DEAE-cellulose chromatography and SDS-polyacrylamide gel electrophoresis. The results showed that both normal and fibrotic lung fibroblasts synthesized similar amounts of collagen. Type I was the major collagen species synthesized by both normal and fibrotic cell types, and the relative proportion of type I, III, and V collagens was similar in both cell types. TGF-beta caused a two to fourfold increase in stimulation of collagen production and collagen mRNA levels, and no differences were detected in the response of normal and fibrotic lung fibroblasts. All collagen types were stimulated by the TGF-beta. TGF-beta did not increase fibroblast proliferation and the majority of normal and fibrotic lung cells exposed to TGF-beta remained in G1 phase of the cell cycle. We conclude that fibroblasts of normal and fibrotic human synthesize similar amounts of collagens.(ABSTRACT TRUNCATED AT 250 WORDS)     

Connective tissue synthesis by cultured scleroderma fibroblasts. I. In vitro collagen synthesis by normal and scleroderma dermal fibroblasts

The authors have been unable to demonstrate an increase in collagen synthesis by fibroblasts isolated from sclerodermatous skin. In order to elucidate this problem further, scleroderma fibroblasts were biopsied from upper dermis, from lower (including subcutaneous) dermis, and from adjacent clinically noninvolved skin. All cell lines failed to show a significant increase in collagen synthesis when they were compared to control fibroblast lines. One difference among them was that fibroblasts from involved areas showed a rate of collagen synthesis equal to or less than cells isolated from adjacent clinically noninvolved sites.     

Differential proliferation of fibroblasts cultured from normal and fibrotic human lungs

We studied the behavior of the cell cycle of cultured, early-passage human diploid pulmonary fibroblastlike cells (HDPFC) when grown in the presence of several growth factors. The rates of growth and growth fractions were studied in cultures from different origins. As much as 85 +/- 5% (SE) of HDPFC cultured from specimens with early fibrosis were cycling when the cells were grown in basal media supplemented with 10% serum or growth factors. In contrast, 55% +/- 8% (SE) of HDPFC from normal lung and only 31% +/- 5% (SE) of HDPFC cultured from specimens with dense fibrosis were cycling in those culture conditions. Results obtained by removal of any of the five growth factors from the defined medium indicated that the altered growth patterns were not related to any single growth factor tested. These studies are consistent with the hypothesis that HDPFC cultured from specimens with early fibrosis have a greater proliferative potential than HDPFC from late fibrosis.     

Production of collagenase and tissue inhibitor of metalloproteinases by fibroblasts derived from normal and fibrotic human lungs.

Several experiments have demonstrated low collagenolytic activity during the development of pulmonary fibrosis. In order to determine if fibroblasts play a role in this alteration, procollagenase and tissue inhibitor of metalloproteinases (TIMP) were quantified in fibroblasts derived from 12 human lung specimens (normal = 6, idiopathic pulmonary fibrosis [IPF] = 6). Under basal conditions, three cell strains from normal and three from fibrotic lung specimens did not synthesize collagenase and a similar number of normal and IPF-derived fibroblast strains produced the enzyme. However, the rate of enzyme synthesis among normal and fibrotic collagenase producing fibroblasts exhibited significant differences. Thus, whereas normal fibroblasts produced more than 300 ng/ml, fibrotic lung fibroblasts secreted approximately half of this amount (115 +/- 67 ng/ml). Phorbol myristate acetate (PMA) enhanced collagenase production in all of the 12 lung fibroblast lines tested. In four IPF fibroblasts, PMA increased collagenase secretion close to those of normal stimulated lung fibroblasts; however, a lower induction was observed in cell strains from two fibrotic lung specimens. There was a wide variation in TIMP production both in normal and fibrotic lung fibroblasts, and no statistically significant difference was observed. Under basal conditions, TIMP levels ranged from 329 to 16,911 ng/ml in normal lung cells, and from 377 to 17,557 in fibrotic lung fibroblasts. PMA induced a severalfold increase in all cell lines. These results suggest that there are subpopulations of lung fibroblasts with different potential to produce collagenase and TIMP in vitro, and that the predominance of low collagenase-producing subsets may contribute to the development of fibrosis.     

Effect of transforming growth factor beta on synthesis of glycosaminoglycans by human lung fibroblasts

The processes of lung growth, injury, and repair are characterized by alterations in fibroblast synthesis and interstitial distribution of extracellular matrix components. Transforming growth factor beta (TGF-beta), which is postulated to play a role in modulating lung repair, alters the distribution of several matrix components such as collagen and fibronectin. We studied the effect of TGF-beta on the synthesis and distribution of the various glycosaminoglycans (GAGs) and whether these effects may explain its role in lung repair. Human diploid lung fibroblasts (IMR-90) were exposed to various concentrations of TGF-beta (0-5 nM) for variable periods of time (0-18 h). Newly synthesized GAGs were labeled with either [3H]glucosamine or [35S]sulfate. Individual GAGs were separated by size exclusion chromatography after serial enzymatic and chemical digestions and quantitated using scintillation counting. There was a dose-dependent increase in total GAG synthesis with maximal levels detected after 6 h of exposure. This increase was noted in all individual GAG types measured and was observed in both the cell associated GAGs (cell-matrix fraction) as well as the GAGs released into the medium (medium fraction). In the cell-matrix fraction, TGF-beta increased the proportion of heparan sulfate that was membrane bound as well as the proportion of dermatan sulfate in the intracellular compartment. In the medium fraction, TGF-beta increased the proportion of hyaluronic acid, chondroitin sulfate and dermatan sulfate released. We conclude that the role of TGF-beta in lung growth and repair may be related to increased synthesis of GAGs by human lung fibroblasts as well as alterations in the distribution of individual GAGs.     

Effect of hyperlipidemic rat serum on the synthesis of collagen by chick embryo fibroblasts.

The effect of hyperlipidemic rat serum and its fractions on the synthetic functions of embryonic fibroblasts was studied. Moderately hypercholesterolemic sera (100-140 mg/100 ml) stimulated the synthesis of collagen, but not the synthesis of non-collagenous proteins nor the incorporation of glucosamine or cytidine. The stimulating principle was nondialyzable. It was not associated with the isolated total lipoproteins but was found in the infranatant fraction of sera centrifuged at a density of 1.220.     

Effects of various cytokines on collagen synthesis by normal rat hepatocytes in primary cultures and fibroblasts

Collagen formation is an important function of liver parenchymal and nonparenchymal cells that may be relevant to the pathogenesis of hepatic fibrosis. In the present study, the effect of various kinds of cytokines and prednisolone on collagen synthesis by hepatocytes obtained from perfused rat livers and confluent human skin fibroblasts were investigated. The cells were cultured in serum-free medium for 24 h with [3H]proline and various additives. The amounts of collagen and noncollagen protein synthesis were calculated from the incorporation of [3H]proline into collagen-sensitive and collagen-resistant proteins. The additions of interleukin 1 alpha, interleukin 1 beta and transforming growth factor alpha enhanced both collagen and noncollagen protein synthesis by hepatocytes as well as by fibroblasts. Transforming growth factor beta also increased both collagen and noncollagen protein synthesis by fibroblasts while it selectively inhibited collagen synthesis by hepatocytes. Interferon preparations and prednisolone showed a selective suppression of collagen synthesis by both cells, indicating that these additives did not affect either cell viability or proliferation during the observed period. These results suggest that collagen synthesis by liver parenchymal cells is either positively or negatively modulated by various kinds of cytokines and hormone.     

1 alpha,25-Dihydroxyvitamin D3 inhibits gamma-interferon synthesis by normal human peripheral blood lymphocytes.

1 alpha,25-Dihydroxyvitamin D3 [1,25-(OH)2D3], the biologically active metabolite of vitamin D3, inhibited synthesis of gamma-interferon (IFN-gamma) by phytohemagglutinin-activated peripheral blood lymphocytes (PBLs). A significant reduction of IFN-gamma protein levels in PBL culture medium was achieved with a physiologic 1,25-(OH)2D3 concentration (0.1 nM). 1,25-(OH)2D3 also inhibited accumulation of IFN-gamma mRNA in activated PBLs in a dose-dependent fashion. The ability of 1,25-(OH)2D3 to modulate IFN-gamma protein synthesis was unaltered in the presence of high concentrations of recombinant human interleukin 2. The suppression of IFN-gamma synthesis by PBLs was specific for 1,25-(OH)2D3; the potencies of other vitamin D3 metabolites were correlated with their affinities for the cellular 1,25-(OH)2D3 receptor. The time course of 1,25-(OH)2D3 receptor expression in phytohemagglutinin-activated PBLs was correlated with the time course of 1,25-(OH)2D3-mediated inhibition of IFN-gamma synthesis. In selected experiments, T-lymphocyte-enriched cell preparations were utilized. In these experiments, 1,25-(OH)2D3 was equally active as in PBL preparations. Finally, we examined the effects of 1,25-(OH)2D3 on the constitutive IFN-gamma production by two human T-lymphocyte lines transformed by human T-lymphotropic virus type I. The cell lines were established from a normal donor (cell line S-LB1) and from a patient with vitamin D-dependent rickets type 2 (cell line Ab-VDR). IFN-gamma synthesis by S-LB1 cells was inhibited in a dose-dependent fashion by 1,25-(OH)2D3, whereas IFN-gamma synthesis by Ab-VDR cells was not altered by 1,25-(OH)2D3. The data presented in this study provide further evidence for a role of 1,25-(OH)2D3 in immunoregulation.     

Cell types involved in collagen and fibronectin production in normal and fibrotic human liver

Three collagen types (I, III and IV) and fibronectin were localized in normal and alcoholic human liver by light and electron microscopy using the indirect immunoperoxidase technique. In normal liver, most of the bundles of collagen fibers stained for type pro-III collagen while only a few reacted for type I. Basement membranes stained for type IV collagen which formed discontinuous discrete deposits in sinusoids. Only fibronectin appeared as an almost continuous layer in the space of Disse. At the intracellular level, hepatocytes were found to contain little type I collagen and large amounts of fibronectin. Fat-storing cells strongly stained for type IV collagen and expressed low amounts of types I and III collagen and fibronectin. Endothelial cells contained low amounts of all the components. Alcoholic livers were studied at three stages: steatosis, fibrosis and cirrhosis. Qualitative and quantitative differences were observed in extracellular and intracellular distributions of matrix proteins. Increased amounts of all components were usually found in fibrotic and cirrhotic livers compared to normal liver. In two fibrotic livers which contained numerous bundles of collagen in the sinusoids, fat-storing cells stained more intensely for type III collagen. In a cryptogenic fibrotic liver, abundant type IV collagen was observed in hepatocytes. These results suggest that hepatocytes, fat-storing cells and endothelial cells are engaged in production of extracellular matrix components in normal human liver. In fibrosis, hepatocytes which normally did not synthesize types III and IV collagen may produce these collagens.     

Effect of N-acetyl-seryl-aspartyl-lysyl-proline on DNA and collagen synthesis in rat cardiac fibroblasts

N:-Acetyl-seryl-aspartyl-lysyl-proline (Ac-SDKP) is a natural inhibitor of pluripotent hematopoietic stem cell entry into the S phase of the cell cycle and is normally present in human plasma. Ac-SDKP is exclusively hydrolyzed by ACE, and its plasma concentration is increased 5-fold after ACE inhibition in humans. We examined the effect of 0.05 to 100 nmol/L Ac-SDKP on 24-hour (3)H-thymidine incorporation (DNA synthesis) by cardiac fibroblasts both in the absence and presence of 5% FCS. Captopril (1 micromol/L) was added in all cases to prevent the degradation of Ac-SDKP. Treatment of cardiac fibroblasts with 5% FCS increased thymidine incorporation from a control value of 12 469+/-594 to 24 598+/-1051 cpm (P:<0.001). Cotreatment with 1 nmol/L Ac-SDKP reduced stimulation to control levels (10 373+/-200 cpm, P:<0.001). We measured hydroxyproline content and incorporation of (3)H-proline into collagenous fibroblast proteins and found that Ac-SDKP blocked endothelin-1 (10(-8) mol/L)-induced collagen synthesis in a biphasic and dose-dependent manner, causing inhibition at low doses, whereas high doses had little or no effect. It also blunted the activity of p44/p42 mitogen-activated protein kinase in a biphasic and dose-dependent manner in serum-stimulated fibroblasts, suggesting that the inhibitory effect of DNA and collagen synthesis may depend in part on blocking mitogen-activated protein kinase activity. Participation of p44/p42 in collagen synthesis was confirmed, because a specific inhibitor for p44/p42 activation (PD 98059, 25 micromol/L) was able to block endothelin-1-induced collagen synthesis, similar to the effect of Ac-SDKP. The fact that Ac-SDKP inhibits DNA and collagen synthesis in cardiac fibroblasts suggests that it may be an important endogenous regulator of fibroblast proliferation and collagen synthesis in the heart. Ac-SDKP may participate in the cardioprotective effect of ACE inhibitors by limiting fibroblast proliferation (and hence collagen production), and therefore it would reduce fibrosis in patients with hypertension.     

Collagen cross-linking in adult patients with acute and chronic fibrotic lung disease. Molecular markers for fibrotic collagen

Lung tissue from patients with interstitial lung disease (ILD), adult respiratory distress syndrome (ARDS), and control subjects with no obvious fibrotic lung disease was analyzed for its content of the collagen cross-links hydroxylysinonorleucine (HLNL), dihydroxylysinonorleucine (DHLNL), and hydroxypyridinium (OHP). We observed significant elevations of the DHLNL:HLNL ratio in patients with ARDS, and significant increases in the content of OHP in lungs of patients with ILD. These results are consistent with data from animal models of fibrotic lung disease, suggesting that increases in the DHLNL:HLNL ratio of lung collagen may serve as a marker of an acute fibrotic episode, whereas increased lung collagen OHP content serves as a marker of chronic lung fibrosis. We suggest that the underlying mechanism for the changes in DHLNL content in (pre)fibrotic acutely injured lung tissue and in OHP content in long-term fibrosis may be an increase in the activity of lysyl hydroxylase, a key intracellular enzyme responsible for a specific post-translational modification of collagen.     

Simultaneous synthesis of types I and III collagen by fibroblasts in culture.

Specific antibodies against types I and III collagens and procollagens were used to localize these proteins in cultured human cells. These studies indicate that the same cell makes both proteins. No type III procollagen synthesis was observed in cells from two patients with two patients with the Ehlers-Danlos type IV syndrome.     

Heterogeneity of collagen synthesis in normal and systemic sclerosis skin fibroblasts. Increased proportion of high collagen-producing cells in systemic sclerosis fibroblasts

Objective. The goal of this study was to quantitatively analyze the distribution of collagen synthesis in normal and systemic sclerosis (SSc) fibroblast populations in order to determine the extent of activation in SSc populations. Methods. We used quantitative in situ hybridization to assess the population distribution of type I collagen synthesis. Fibroblast cultures were derived from both clinically involved and uninvolved skin regions of patients with SSc, and from healthy adults, and assessed for levels of α1(I) procollagen messenger RNA (mRNA). Results. Dermal fibroblasts from both patients with SSc and normal adults were heterogeneous for distribution of α1(I) procollagen mRNA when assessed by in situ hybridization, with a wide range of grains per cell. In contrast, clones of neonatal fibroblasts showed a relatively homogeneous distribution of grain counts. Involved SSc skin fibroblasts had a larger proportion of cells in the high collagen-producing mRNA subpopulation (mean ± SEM 28.4 ± 6.85%), compared with normal fibroblasts (1.75 ± 1.44%) and uninvolved fibroblasts (9.6 ± 6.73%). Conversely, within the low collagen-producing mRNA subpopulation, involved fibroblasts had a smaller proportion of cells (mean ± SEM 14.0 ± 5.63%) than did uninvolved fibroblasts (37.8 ± 13.69%), while normal fibroblasts had a majority of the cells in this subpopulation (53.5 ± 8.68%). Conclusion. These results suggest that only a specific subset of fibroblasts are activated in SSc, as evidenced by an increased proportion of cells with high levels of α1(I) procollagen mRNA. Differences between the SSc and normal fibroblast populations appeared to be quantitative rather than qualitative. This may be a result of either clonal selection or selective activation in the pathogenesis of SSc.     

Distribution of basement membrane proteins in normal and fibrotic human liver: collagen type IV, laminin, and fibronectin.

Specific antibodies to collagen type IV, laminin, and fibronectin were used to localise these proteins by indirect immunofluorescence in frozen sections of normal and fibrotic liver. In normal livers distinct staining was found in basement membranes of blood and lymph vessels, of bile ducts and ductules and around nerve axons. Positive reactions for type IV collagen and fibronectin were also observed in the perisinusoidal space, while hepatocytes and most of the interstitial matrix of portal fields remained unstained. Liver specimens obtained from patients with alcoholic liver disease (fatty liver, hepatitis or cirrhosis) and chronic active hepatitis showed a more intense reaction with the antibodies in the perisnusoidal space including now distinct staining for laminin. These patterns were particularly prominent at borders between fibrotic septa and remnants of parenchyma or pseudolobules. Strong reactions were also found for type IV collagen and fibronectin in the periportal interstitium and in large fibrotic areas. The findings support previous electron-microscopical and chemical evidence for increased basement membrane production in human liver fibrosis and demonstrate that this may involve different proteins and occur at different anatomical sites.     

Modulation of mucin synthesis by gamma-interferon in human colon adenocarcinoma cells

OBJECTIVES: Recombinant human interferon has been shown to enhance the expression of histocompatibility antigens and certain tumor-associated antigens in a variety of carcinoma cell lines. Since many tumor-associated antigens are mucins, we investigated the effect of recombinant human gamma-interferon on mucin production and secretion by colon cancer cell lines. METHODS: Control and gamma-interferon-treated cells were labeled with [(3)H]glucosamine in DMEM-H16 medium with 5% FCS for 24 h. Analysis was performed by gel filtration on Sepharose CL-4B columns, and the high-molecular-weight glycoprotein eluted at the void volume from the cytosol and medium was counted (expressed as dpm/4 x 10(6) cells). In another experiment the void volume was compared to concentration curves of standard mucins (expressed as mg/10(7) cells). RESULTS: gamma-Interferon increased mucin synthesis in HT-29 and LIM-6 cells, but not in LS174T and CACO2 cells. In HT-29 and LIM-6 cells, mucin synthesis was induced by gamma-interferon in a dose-dependent manner. The percentage of mucin secreted into the medium was also increased. CONCLUSION: The heterogeneity of response of human colon cancer cell lines to gamma-interferon by mucin production may limit the specific role of gamma-interferon as a modulator of mucin-type tumor-associated antigens.     

Extracellular matrix in normal and fibrotic human lungs

Polyclonal affinity-purified antibodies to human collagen types I, III, and IV, and laminin were used to compare the extracellular matrix (ECM) in 10 normal and 32 abnormal lungs by indirect immunofluorescence. In normal lungs, type IV collagen and laminin codistributed in a uniform linear pattern along the epithelial and endothelial basement membranes. Type III collagen was found within the alveolar septa and interstitium in an interrupted ribbonlike pattern and was aggregated at the entrance rings of the alveoli. Type I collagen was distributed irregularly within the alveolar wall and was less prominent than type III collagen. In patients with pulmonary disease not characterized by interstitial fibrosis (n = 15), the distribution of ECM components studied was essentially normal. In pulmonary disease in which interstitial fibrosis was the characteristic feature, such as idiopathic pulmonary fibrosis (IPF) and adult respiratory distress syndrome (ARDS) (n = 17), collagen types I and III accumulated in the expanded interstitium. Type III collagen was initially predominant in the thickened alveolar septa and interstitium, whereas type I collagen appeared to be the principal collagen at later stages in the disease course. The basement membrane was disrupted early in the disease course with invasion of the alveolar spaces by interstitial collagens similar in type to those present in the adjacent interstitium.     

Stimulation of collagen formation by insulin and insulin-like growth factor I in cultures of human lung fibroblasts

We examined the effects of insulin and insulin-like growth factor I (IGF-I) on the production of collagen by cultures of human embryonic lung fibroblasts. Insulin at 20 ng/ml increased collagen accumulation by 58% and total protein formation by 18%. At 2 micrograms/ml, insulin increased collagen production by 2- to 3-fold and total protein production by 2-fold. The mRNA levels for alpha 1(I) and alpha 1(III) collagen chains were elevated by insulin compared with untreated control values. IGF-I at 10 ng/ml increased collagen production 2-fold. IGF-I at 100 ng/ml maximally increased collagen production 3-fold. A specific antibody to the IGF-I receptor (alpha IR-3) caused a concentration-related decline in insulin-induced collagen formation. The addition of antibody at 1 micrograms/ml, resulted in 80% inhibition of insulin-induced collagen accumulation. Higher levels of antibody were required to inhibit IGF-I mediated collagen formation. The presence of antibody (alpha IR-3) also blocked fibroblast proliferation stimulated by epidermal growth factor plus insulin. These data show that insulin-induced collagen formation is mediated primarily through an interaction with the IGF-I receptor. The modulation of extracellular matrix production by insulin may influence the repair of tissue injury and the development of the accelerated atherosclerosis that accompanies the diabetic state in humans.