Epistatic effect of TLR-1, -6 and -10 polymorphisms on organic dust-mediated cytokine response.

Exposure to organic dust from agricultural environments is associated with inflammatory respiratory conditions. The putative causal agents in organic dust include viral, microbial and fungal components, which are recognized by the family of Toll-like receptors (TLRs) and drive host innate and adaptive responses. Our aim in this study was to determine whether responsiveness to organic dust among agricultural workers was dependent on polymorphisms in the TLR10-TLR1-TLR6 gene cluster. We stimulated whole blood from 509 agricultural workers with organic dust, triacyl lipopeptide N-palmitoyl-S-dipalmitoylglyceryl Cys-Ser-(Lys)4 (Pam3CSK4) and the diacyl-lipopeptide peptidoglycan. Several of the tagging polymorphisms and haplotypes conferred hyper-responsiveness to organic dust with an increase in interleukin-6 (IL-6; P<0.005), but not tumor necrosis factor-α (TNF-α), secretion. We conclude that genetic variation in the TLR10-TLR1-TLR6 gene cluster mediates responsiveness to organic dust, but indicates different signaling pathways for IL-6 and TNF-α. These studies provide new insight into the role of the TLR10-TLR1-TLR6 gene cluster and the innate immune response to organic dust.

CXCR1/CXCR2 antagonist CXCL8(3-74)K11R/G31P blocks lung inflammation in swine barn dust-instilled mice.

Inhalation of agricultural occupational dusts from swine confinement facilities can result in lung inflammation. The innate immune response to organic barn dusts results in production of a number of pro-inflammatory factors in the lungs of barn workers such as cytokines, chemokines, and an influx of neutrophils. Many of these inflammatory factors are influenced by the chemokine CXCL8/IL-8 (KC or MIP-2 in mice). Previously, we have demonstrated that an endotoxin-independent component of swine barn dust extract (SBE) elevates lung chemokines in a protein kinase C (PKC)-dependent manner resulting in the significant formation of lung inflammatory cell infiltrates in a mouse model of SBE injury. In this study we test the ability of a CXCR1/CXCR2 antagonist, CXCL8(3-74)K11R/G31P (G31P) to block many of the features of lung-inflammation in response to challenge with SBE in an established mouse exposure system. Injection of G31P concurrent with SBE nasal instillation over a course of 3 weeks significantly reduced neutrophil accumulation in the lungs of barn dust exposed animals compared to those given SBE alone. There was a similar reduction in pro-inflammatory cytokines and chemokines IL-6, KC, and MIP-2 in SBE plus G31P-treated mice. In addition to excreted products, the receptors ICAM-1, CXCR1, and CXCR2, which all were elevated with SBE exposure, were also decreased with G31P treatment. SBE activation of PKCα and PKCε was reduced as well with G31P treatment. Thus, G31P was found to be highly effective at reducing several features of lung inflammation in mice exposed to barn dust extracts.

Swine barn dust stimulates CCL9 expression in mouse monocytes through PKC-delta activation.

Exposure to organic barn dusts has been shown to cause numerous lung problems to chronically exposed animal barn workers. Bacterial components in these dusts trigger innate immunity in the lungs that we are still trying to fully characterize. CCL9/MIP-1γ is constitutively expressed in high quantities in the mouse circulation, but at much lower levels in the lungs where it is inducible under certain circumstances. We show here that extracts from hog barn dusts (HDE) are capable of inducing significant increases of CCL9 mRNA and protein in RAW267.4 monocytic cells as well as in mouse lungs. We further show that incubation of CCL9 with HDE results in cleavage of CCL9, which others have shown to increase chemotactic signaling potential. Endotoxin and proteoglycan were determined to be the likely causes of this increase. We additionally present evidence for a role of PKC-delta in this activation. Addition of purified CCL9 protein to HDE treated cell culture resulted in a small, but significant reduction in KC production, suggesting a possible regulatory role for the chemokine.

Organic dust-induced lung injury and repair: Bi-directional regulation by TNFα and IL-10.

Exposure to organic dust increases chronic airway inflammatory disorders. Effective treatment strategies are lacking. It has been reported that hog barn dust extracts (HDE) induce TNFα through protein kinase C (PKC) activation and that lung inflammation is enhanced in scavenger receptor A (SRA/CD204) knockout (KO) mice following HDE. Because interleukin (IL)-10 production can limit excessive inflammation, it was hypothesized here that HDE-induced IL-10 would require CD204 to effect inflammatory responses. C57BL/6 wild-type (WT), SRA KO, and IL-10 KO mice were intranasally challenged daily for 8 days with HDE and subsequently rested for 3 days with/without recombinant IL-10 (rIL-10) treatment. Primary peritoneal macrophages (PM) and murine alveolar macrophages (MH-S cells) were treated in vitro with HDE, SRA ligand (fucoidan), rIL-10, and/or PKC isoform inhibitors. HDE induced in vivo lung IL-10 in WT, but not SRA KO mice, and similar trends were demonstrated in isolated PM from same treated mice. Lung lymphocyte aggregates and neutrophils were elevated in in vivo HDE-treated SRA and IL-10 KO mice after a 3-d recovery, and treatment during recovery with rIL-10 abrogated these responses. In vitro rIL-10 treatment reduced HDE-stimulated TNFα release in MH-S and WT PM. In SRA KO macrophages, there was reduced IL-10 and PKC zeta (ζ) activity and increased TNFα following in vitro HDE stimulation. Similarly, blocking SRA (24 hr fucoidan pre-treatment) resulted in enhanced HDE-stimulated macrophage TNFα and decreased IL-10 and PKCζ activation. PKCζ inhibitors blocked HDE-stimulated IL-10, but not TNFα. Collectively, HDE stimulates IL-10 by an SRA- and PKCζ-dependent mechanism to regulate TNFα. Enhancing resolution of dust-mediated lung inflammation through targeting IL-10 and/or SRA may represent new approaches to therapeutic interventions.

Exposure to hog barn dust alters airway epithelial ciliary beating.

Swine confinement workers are at increased risk of airway diseases, including mucus membrane irritation syndrome, chronic rhinosinusitis and chronic bronchitis. Dust extracts from swine confinement facilities stimulate the production of pro-inflammatory cytokines in bronchial epithelial cells, including interleukin (IL)-8. As IL-8 is capable of blocking beta-agonist-stimulated increases in cilia beating, which impacts on mucociliary clearance, it was hypothesised that hog barn-dust exposure might alter cilia responses to stimulation. To test this hypothesis, ciliated bovine bronchial epithelial cell cultures were exposed to hog barn-dust extract (HDE) and ciliary beat frequency (CBF) was assayed. An elevation in baseline CBF was observed. This effect appeared to be independent of endotoxin but dependent upon nitric oxide. HDE also stimulated nitric oxide production in bronchial epithelial cells; however, stimulation of cilia beating by a beta-agonist did not occur in cells pre-exposed to HDE. These data demonstrate that hog barn dust can alter normal stimulation of cilia, suggesting a mechanism for the abrogation of stimulated increases in mucociliary clearance in response to inhaled dust exposure.

Effect of elevated carbon dioxide on bronchial epithelial innate immune receptor response to organic dust from swine confinement barns.

Hypercapnia is known to have immunoregulatory effects within the lung. Cell culture systems demonstrate this in both macrophages and alveolar cell lines, suggesting that the alveoli are affected by changes in CO2 levels. We hypothesized that hypercapnia would also modulate human bronchial epithelial cell immune responses. Innate immune responses to Pam3CSK4 (TLR2 ligand), LPS (TLR4 ligand) and a complex innate immune stimulus, an extract from the organic dust of swine confinement barns (barn dust extract or BDE), were tested in a human bronchial epithelial cell line, BEAS-2B. Both TLR ligands showed a decrease in IL-6 and IL-8 production, and an increase in MCP-1 in response to elevated CO2 indicating an enhancement in cytokine production to hypercapnia. This change was not reflected in expression levels of TLR receptor RNA which remained unchanged in response to elevated CO2. Interestingly, barn dust showed an increase in IL-6, IL-8 and MCP-1 response at 9% CO2, suggesting that elevated CO2 exerts different effects on different stimuli. Our results show that airway epithelial cell immune responses to barn dust respond differently to hypercapnic conditions than individual TLR ligands.

Fibronectin.

Fibronectin is a glycoprotein consisting of repeating units of amino acids, which form domains that enable the molecule to interact with a variety of cells through both integrin and non-integrin receptors. It is encoded by a single gene, but alternative splicing of pre-mRNA allows formation of multiple isoforms that have critical roles in cell adhesion, migration and proliferation. The essential nature of fibronectin in development has clearly been demonstrated in a "knock-out" mouse model in which early lethality occurs. Fibronectin influences diverse processes including inflammation, wound repair, malignant metastasis, microorganism attachment and thrombosis. Researchers are currently developing tools, including synthetic peptides based on specific fibronectin regions. These molecules have been shown to alter processes such as lymphocyte binding in synovial tissue of rheumatoid arthritis, coronary arteriopathy in animal models of cardiac transplantation, and platelet aggregation in patients, and are thus providing important new therapeutic possibilities.

Th2-type cytokines modulate IL-6 release by human bronchial epithelial cells.

The multifunctional cytokine IL-6, which can be locally produced by human bronchial epithelial cells (HBECs), has been found to play a role in IL-4 dependent IgE synthesis. Since the allergic reaction in bronchial asthma is associated with the upregulation of IL-4 and Th2 type of immune response, the purpose of our study was to assess whether IL-4 and related cytokines IL-10 and IL-13 regulate IL-6 release by HBEC s. HBECs were obtained by bronchial brushing, cultured in LHC-9/RPMI 1640. At the third passage the cells were stimulated with cytokines (0.1-20 ng/ml) diluted in unsupplemented media for 24 h. The supernatants were tested for IL-6 content by sandwich ELISA. Unstimulated HBECs produced detectable amounts of IL-6 (368+/-25 pg/ml). Exposure to IL-10 (368+/-22 pg/ml) and IL-13 (395+/-6 pg/ml) resulted in little changes. IL-4 caused a slight but significant increase in IL-6 release (530+/-45 pg/ml), P<0.05, TNFalpha (1657+/-85 pg/ml) and IFNgamma (1953+/-37 pg/ml) showed strong induction of IL-6 release in HBECs (P<0.005 and P<0.001, respectively). Both IL-4 and IL-13 significantly inhibited TNF induced IL-6 release (P<0.01 for both) while augmenting the effect of IFNgamma (P<0.005 and P<0.01, respectively.). IL-10 was without a significant effect. We conclude that Th2-type cytokines IL-4 and IL-13 affect the release of IL-6 by HBECs in response to TNFalpha (inhibition) and IFgamma (augmentation). IL-10 had no effect on the regulation of IL-6 release. Modulation of IL-6 levels by Th2-type cytokines may play a role in allergic reactions through the IL-6 promoting effect on IL-4 mediated IgE production.

Clinical efficacy and cost benefit of pulse flow oxygen in hospitalized patients.

Pulse flow oxygen administered during early inspiration is a promising approach to oxygen conservation. Previous short-term studies show equivalent arterial PO2, 55 to 60 percent oxygen savings, and no reduction of nasal humidity when compared with continuous flow nasal cannula oxygen. This study compares the clinical efficacy of pulse flow and continuous flow oxygen in 100 patients recently hospitalized for diseases requiring O2 therapy. In an unblinded crossover design, pulse and continuous O2 were administered alternately during four 51/2-hour periods. Oxygen saturation was monitored continuously during the 23-hour study. Mean SaO2 on pulse flow (95.6 +/- 2.7 percent) was clinically the same as continuous flow (95.3 +/- 2.6 percent). Mean SaO2 on pulse flow during the 30 minutes before or after each crossover (95.5 +/- 3.3 percent) was similar to continuous flow during the 30 minutes near crossover (95.3 +/- 3.1 percent). It is concluded that the two delivery systems produce similar levels of SaO2 over the course of a day and night. Analysis of potential cost savings achieved by use of the device for a 350-bed hospital suggests a savings of about $50,000 yearly when accompanied by termination of oxygen humidification.

Nutritionally associated increased carbon dioxide production. Excess total calories vs high proportion of carbohydrate calories.

This study compared carbon dioxide production (VCO2) from isocaloric nutritional regimens with varying concentration of carbohydrates with VCO2 from low and high caloric nutritional regimens with constant concentrations of carbohydrates (CHO) in 20 stable mechanically ventilated patients. Ten patients (group A) received total parental nutrition in the form of three isocaloric nutritional regimens; 40 percent CHO/40 percent fat/20 percent protein, 60 percent CHO/20 percent fat/20 percent protein, and 75 percent CHO/5 percent fat/20 percent protein. The VCO2 did not change with increasing CHO proportion; 205 +/- 35 ml/min, 203 +/- 25 ml/min, and 211 +/- 35 ml/min, respectively. Ten additional patients (group B) received three nutritional regimens at 1.0, 1.5, and 2.0 times the estimated resting expenditure with a 60 percent CHO/20 percent fat/20 percent protein proportion. The VCO2 increased with increasing total calories, 181 +/- 23 ml/min, 211 +/- 38 ml/min, and 244 +/- 40 ml/min (p less than 0.05). High caloric feeding increases VCO2 in contrast to high percentage carbohydrate formulation. Thus, moderate caloric intake appears to be more important in avoiding nutritionally related increases in VCO2 in stable mechanically ventilated patients.

General vs local anesthesia. Effect on bronchoalveolar lavage findings.

Bronchoalveolar lavage (BAL) can be performed with the patient undergoing either local or general anesthesia (GA). This study investigates whether the type of anesthesia affects BAL fluid and cell recovery. Eighty patients, were selected for study. Fluid recoveries were significantly less in the GA group for both the bronchial and alveolar lavages. The differences were confirmed for BAL fluid recovery in a subsequent group of 120 unselected patients. Bronchoscope size did not appear to affect recovery, nor did anesthesia time; BAL fluid recovery from patients with respiratory failure who were intubated and mechanically ventilated was similar to that in the GA group, suggesting that lower recovery rates may be due to mechanical ventilation. The BAL fluid cell counts were related to fluid recovery, but airway neutrophils represented a higher percentage of BAL lavage fluid cells in the GA lavages, independent of differences in the volume of lavage fluid recovered.

The bronchitis index. A semiquantitative visual scale for the assessment of airways inflammation.

Flexible fiberoptic bronchoscopy has been proven to be an effective tool for the assessment and characterization of airway inflammation. Visual inspection of airways affected by chronic bronchitis discloses an abnormal appearance characterized by erythema, edema, secretions, and friability. It was hypothesized that the visual appearance of airway inflammation could be assessed in a semiquantitative manner. A bronchitis index (BI) was developed that scores the visual appearance of airways according to the presence or absence of abnormal edema, erythema, secretions, and friability (0 = normal, 3 = remarkably abnormal). The BI was determined in three study groups: 86 subjects with chronic bronchitis, 15 subjects who smoked cigarettes, but did not have chronic bronchitis, and 25 normal, nonsmoking control subjects. The reproducibility of the BI was determined by comparing the results from pairs of two independent observers assessing 249 subjects undergoing fiberoptic bronchoscopy under various investigative protocols. In total, nine investigators scored the airways. For the three observer pairs with more than six observations, there were no differences noted in the BI (p = 0.43, 0.67, 0.82). To control for the effect of cough upon the BI, lidocaine usage was recorded. No correlation was found between lidocaine usage and BI. As previously noted for a smaller group of subjects, the BI was found to be elevated in those with chronic bronchitis (13.2 +/- 0.53) compared with both asymptomatic smokers (8.5 +/- 0.89, p < 0.0005) and normal volunteers (2.3 +/- 0.55, p < 0.0001); the latter two groups also differed significantly (p < 0.0001). The BI was also found to correlate significantly with bronchial sample lavage fluid neutrophil content in lavage fluid obtained after determination of the BI and with cigarette smoking as quantitated by pack years. Conversely, the BI correlated negatively with the spirometric measures of airway obstruction, FEV1, FEV1/FVC, FEV25-75, and FEFmax. Thus, the BI appears to be a reproducible, semiquantitative assessment of the visual appearance of airway inflammation. It may be a useful bronchoscopic adjunct for the assessment of airway inflammation in clinical investigations.

Hog barn dust extract augments lymphocyte adhesion to human airway epithelial cells.

The dust of hog confinement facilities induces airway inflammation. Mechanisms by which this dust modulates inflammation are not completely defined, although it is clear that exposure to dust can modulate both epithelial cell and inflammatory cell function. In this work, we demonstrate that airway epithelial cell (BEAS-2B) treatment with hog barn dust extract (HDE) results in augmentation of peripheral blood lymphocyte adhesion to epithelial cell cultures in vitro. The augmentation of lymphocyte adhesion to epithelial cells is dependent on the concentration of HDE and time of HDE exposure, with twofold increases observed by 3 h and maintained at 24 h. Similar results are seen with primary human bronchial epithelial cells in culture. Lymphocyte adhesion to epithelial cells is inhibited in a concentration-dependent fashion by the treatment of epithelial cells with antibody to intercellular adhesion molecule-1 (ICAM-1). In addition, HDE exposure of epithelial cells results in an approximate twofold increase in ICAM-1 expression as determined by flow cytometry analysis. Pretreatment of epithelial cells with a protein kinase C-alpha (PKC-alpha) inhibitor, Gö-6976, also inhibited subsequent lymphocyte adhesion to HDE-exposed epithelial cells. These data suggest that airway epithelial cell HDE exposure enhances subsequent lymphocyte adhesion to epithelial cells that is mediated in part by HDE modulation of ICAM-1 expression and PKC-alpha.

Hog barn dust extract stimulates IL-8 and IL-6 release in human bronchial epithelial cells via PKC activation.

Hog barn workers have an increased incidence of respiratory tract symptoms and demonstrate an increase in lung inflammatory mediators, including interleukin (IL)-8 and IL-6. Utilizing direct kinase assays for protein kinase C (PKC) activation, we demonstrated that dust from hog confinement facilities, or hog dust extract (HDE), augments PKC activity of human airway epithelial cells in vitro. A 5% dilution of HDE typically stimulates an approximately twofold increase in human bronchial epithelial cell (HBEC) PKC activity compared with control medium-treated cells. This increase in PKC is observed with 15 min of HDE treatment, and kinase activity reaches peak activity by 1-2 h of HDE treatment before returning to baseline PKC levels between 6 and 24 h. The classic PKC inhibitor, calphostin C, blocks HDE-stimulated PKC activity and associated IL-8 and IL-6 release. Desensitization to HDE stimulation of PKC activation does not appear to occur because subsequent exposures to HDE after an initial exposure result in further augmentation of PKC. Detoxification of HDE with polymyxin B to remove endotoxin did not change PKC activation or IL-8 release, suggesting that endotoxin is not solely responsible for HDE augmentation of PKC. These data support the hypothesis that HDE exposure augments HBEC IL-8 and IL-6 release via a PKC-dependent pathway.

IL-4 and IL-13 stimulate human bronchial epithelial cells to release IL-8.

Cytokine networks are important in regulating the traffic of inflammatory cells in the airways. Interleukin-8 (IL-8) released by human bronchial epithelial cells (HBECs) is thought to be of particular importance in attracting neutrophils and monocytes to sites of inflammation. Increased release of IL-8 by HBECs in response to Th-1 cytokines such as TNF alpha and IL-1 beta may be an important pathophysiologic pathway. The present study was designed to explore the role of the Th2 cytokine IL-4 and the functionally related interleukins IL-10, and IL-13 on the regulation of IL-8 release by HBECs. HBECs (passage 4-6) were cultured in LHC9/RPMI and when confluent cells were stimulated in unsupplemented medium LHCD/RPMI by IL-4, IL-10, and IL-13 at 10 ng/ml concentration for all cytokines. TNF alpha stimulation was used as a positive control. After 24 hours supernatants were collected and tested for IL-8 by a sandwich ELISA. Unstimulated HBECs spontaneously released limited amounts of IL-8 (11 +/-1 pM) and significantly increased cytokine production in response to IL-4 (42 +/- 1 pM), IL-13 (30 +/- 1 pM) and TNF (128 +/- 11 pM). Stimulation with IL-10 (11 +/- pM) did not change basal production of IL-8. When HBECs were co-stimulated with IL-4 plus TNF, the production of IL-8 was further increased (204 +/- 5 pM). In contrast, IL-10 attenuated the effect of TNF during co-stimulation (82 +/- 5 pM). IL-13 did not affect the release of IL-8 induced by TNF (111 +/- 9 pM). Northern blot analysis of IL-8 mRNA levels showed the highest induction of IL-8 mRNA in HBECs co-stimulated with TNF and IL-4. We conclude from our study that IL-4 directly induces IL-8 release from HBECs and amplifies the release of IL-8 in response to TNF alpha. IL-13 is less active and IL-10 has an inhibitory effect. Airway epithelial cells are able to interact, therefore, with products of both Th1 and Th2 cells with respect to modulating release of IL-8.

Red blood cells stimulate human lung fibroblasts to secrete interleukin-8.

Following lung injury, red blood cells (RBC) may interact with extracellular matrix (ECM). Fibroblasts, the resident cell in the ECM, have the capacity to produce and secrete a variety of mediators including interleukin-8 (IL-8). In the present study we hypothesized that RBC, or soluble factors released from them, may stimulate IL-8 production by fibroblasts. Fibroblasts were cultured in a three-dimensional collagen gel culture system in the presence or absence of RBC or conditioned medium from RBC (RBC-CM). IL-8 release from fibroblasts was significantly increased when cultured with RBC or RBC-CM and both tumor necrosis factor-alpha (TNF-alpha) and interleukin-1beta (IL-1beta) further stimulated this IL-8 secretion. The enhanced production of IL-8 within fibroblasts was accompanied by increased IL-8 mRNA expression. To evaluate whether RBC-fibroblast interaction may lead to recruitment of neutrophils, a functional migration assay was performed. RBC and RBC-CM, in the presence of IL-1beta and TNF-alpha, increased the transmigration of neutrophils. Our results indicate that RBC, when interacting with ECM, may participate in the recruitment of inflammatory cells by stimulating fibroblasts to secrete IL-8. This might be an important mechanism regulating tissue repair after injury.

Regulation of fibroblast proliferation in three-dimensional collagen gel matrix.

Fibroblasts in vivo reside in a three-dimensional (3-D) matrix. The 3-D culture method using collagen gels provides valuable information, but it also has some practical difficulties. In particular, the changes caused by the contraction of gels and the occasional abrupt detachment from the underlying surface have made extended culture difficult. In this study, the 3-D culture method was modified in order to observe the cells with minimal change of substrata for longer periods. The proliferation characteristics of fibroblasts cultured in gels in response to fetal calf serum (FCS), to two defined growth factors, insulin and platelet-derived growth factor (PDGF), and to a growth inhibitory factor, prostaglandin E2 (PGE2), were evaluated with this system in comparison with monolayer cultured fibroblasts. The DNA content of fibroblasts cultured both in gels and on dishes increased in response to FCS in a concentration-dependent manner. The proliferation of gel-cultured fibroblasts, however, was lower than that of dish-cultured cells, and higher concentrations of serum were necessary for proliferation. The response of gel-cultured cells to PDGF was also less than that of dish-cultured cells. In addition, fibroblasts cultured in gel culture did not respond to insulin, while the fibroblasts on dishes responded to insulin in a concentration-dependent manner. In contrast to the reduced response to growth stimulators, PGE2 inhibited proliferation in gel culture and in monolayer culture similarly. The reduced responsiveness to growth stimulation but equivalent response to growth inhibition may account for reduced proliferation of fibroblasts in 3-D culture.

Fibronectin production by cultured human lung fibroblasts in three-dimensional collagen gel culture.

In vivo, fibroblasts are distributed in a three-dimensional (3-D) connective tissue matrix. Fibronectin is a major product of fibroblasts in routine cell culture and is thought to regulate many aspects of fibroblast biology. In this context, we sought to determine if the interaction of fibroblasts with a 3-D matrix might affect fibronectin production. To examine this hypothesis, fibronectin production by fibroblasts cultured in a 3-D collagen gel or on plastic dishes was measured by ELISA. Fibroblasts in 3-D gel culture produced more fibronectin than those in monolayer culture. Fibroblasts in 3-D culture produced increasing amounts of fibronectin when the collagen concentration of the gel was increased. The 3-D nature of the matrix appeared to be crucial because plating the fibroblasts on the surface of a plastic dish underneath a collagen gel was not different from plating them on a plastic dish in the absence of collagen. In addition to increased fibronectin production, the distribution of the fibronectin produced in 3-D culture was different from that of monolayer culture. In monolayer culture, more than half of the fibronectin was released into the culture medium. In 3-D culture, however, approximately two-thirds remained in the collagen gel. In summary, the presence of a 3-D collagen matrix increases fibroblast fibronectin production and results in greater retention of fibronectin in the vicinity of the producing cells.

Contraction of fibroblast-containing collagen gels: initial collagen concentration regulates the degree of contraction and cell survival.

Remodeling of extracellular matrix involves a number of steps including the recruitment, accumulation, and eventual apoptosis of parenchymal cells as well as the production, organization, and rearrangement of extracellular matrix produced by these cells. The culture of fibroblasts in three-dimensional gels made of type I collagen has been used as a model of tissue contraction which characterizes both wound repair and fibrosis. The current study was designed to determine the effect of initial collagen concentration on the ability of fibroblasts to contract collagen gels and on cell survival. Native type I collagen was extracted from rat tail tendons and used to prepare collagen gels with varying collagen concentrations (0.75-2.0 mg/ml). Human lung fibroblasts (HFL-1) were cast into the gels and cultured in Dulbecco modified Eagle medium with 0.1% fetal calf serum for 2 wk. The gel size, collagen content, and deoxyribonucleic acid (DNA) content were determined. Gels prepared with an initial concentration of 0.75 mg/ml contracted more rapidly and to a smaller final size than gels prepared from 2 mg/ml initial collagen concentration (final size 7.1 versus 36.4% of initial size, P < 0.01). There was no significant degradation of the collagen in the gels under either condition. Hence, the dramatically increased contraction of the lower density gels resulted in a higher final density (P < 0.01). Cell density was estimated from DNA content. In low initial density gels, the final DNA content was significantly less than that in higher initial density gels (0.73 versus 1.88 microg/gel, P < 0.05). This was accompanied by an increased percentage of apoptotic cells at day 14 (43.3 versus 34.1%, P < 0.05). If the gels were maintained in the attached state which largely prevents contraction, apoptosis was significantly reduced, suggesting that contraction rather than matrix composition was a requirement for the increased apoptosis. In summary, these findings indicate that the initial matrix composition can lead to differing outcomes during fibroblast-mediated wound contraction.

Persistence of TGF-beta1 induction of increased fibroblast contractility.

Fibroblast contraction of collagen gels is regarded as a model of wound contraction. Transforming growth factor (TGF)-beta added to such gels can augment contraction consistent with its suggested role as a mediator of fibrotic repair. Since fibroblasts isolated from fibrotic tissues have been suggested to express a "fibrotic phenotype," we hypothesized that TGF-beta exposure may lead to a persistent increase in fibroblasts' contractility. To evaluate this question, confluent human fetal lung fibroblasts were treated with serum-free Dulbecco modified Eagle medium (DMEM), with or without 100 pM [corrected] TGF-beta1, TGF-beta2, or TGF-beta3 for 48 h. Fibroblasts were then trypsinized and cast into gels composed of native type I collagen isolated from rat tail tendons. After 20 min for gelation, the gels were released and maintained in serum-free DMEM. TGF-beta-pretreated fibroblasts caused significantly more rapid gel contraction (52.5+/-0.6, 50.9+/-0.2, and 50.3+/-0.5% by TGF-beta1, -beta2, and -beta3 pretreated fibroblasts, respectively) than control fibroblasts (74.0+/-0.3%, P < 0.01). This effect is concentration dependent (50-200 nM), and all three isoforms had equal activity. The effect of TGF-beta1, however, persisted for only a short period of time following the removal of TGF-beta, and was lost with sequential passage. These observations suggest that the persistent increase in collagen-gel contractility, mediated by fibroblasts from fibrotic tissues, would not appear to be solely due to previous exposure of these cells to TGF-beta.