Chromosomal instability can favor macrophage-mediated immune response and induce a broad, vaccination-like anti-tumor IgG response

Chromosomal instability (CIN), a state in which cells undergo mitotic aberrations that generate chromosome copy number variations, generates aneuploidy and is thought to drive cancer evolution. Although associated with poor prognosis and reduced immune response, CIN generates aneuploidy-induced stresses that could be exploited for immunotherapies. In such contexts, macrophages and the CD47-SIRPα checkpoint are understudied. Here, CIN is induced pharmacologically induced in poorly immunogenic B16F10 mouse melanoma cells, generating persistent micronuclei and diverse aneuploidy while skewing macrophages towards an anti-cancer M1-like phenotype, based on RNA-sequencing profiling, surface marker expression and short-term antitumor studies. These results further translate to in vivo efficacy: Mice bearing CIN-afflicted tumors with wild-type CD47 levels survive only slightly longer relative to chromosomally stable controls, but long-term survival is maximized when combining macrophage-stimulating anti-tumor IgG opsonization and some form of disruption of the CD47-SIRPα checkpoint. Survivors make multi-epitope, de novo anti-cancer IgG that promote macrophage-mediated phagocytosis of CD47 knockout B16F10 cells and suppress tumoroids in vitro and growth of tumors in vivo . CIN does not greatly affect the level of the IgG response compared to previous studies but does significantly increase survival. These results highlight an unexpected therapeutic benefit from CIN when paired with maximal macrophage anti-cancer activity: an anti-cancer vaccination-like antibody response that can lead to more durable cures and further potentiate cell-mediated acquired immunity.

Differences in cell shape, motility, and growth reflect chromosomal number variations that can be visualized with live-cell ChReporters

Chromosome numbers often change dynamically in tumors and cultured cells, which complicates therapy as well as understanding genotype-mechanotype relationships. Here we use a live-cell "ChReporter" method to identify cells with a single chromosomal loss in efforts to better understand differences in cell shape, motility, and growth. We focus on a standard cancer line and first show clonal populations that retain the ChReporter exhibit large differences in cell and nuclear morphology as well as motility. Phenotype metrics follow simple rules, including migratory persistence scaling with speed, and cytoskeletal differences are evident from drug responses, imaging, and single-cell RNA sequencing. However, mechanotype-genotype relationships between fluorescent ChReporter-positive clones proved complex and motivated comparisons of clones that differ only in loss or retention of a Chromosome-5 ChReporter. When lost, fluorescence-null cells show low expression of Chromosome-5 genes, including a key tumor suppressor APC that regulates microtubules and proliferation. Colonies are compact, nuclei are rounded, and cells proliferate more, with drug results implicating APC, and patient survival data indicating an association in multiple tumor-types. Visual identification of genotype with ChReporters can thus help clarify mechanotype and mechano-evolution.

Recent advances in molecular targets and treatment of idiopathic pulmonary fibrosis: focus on TGFbeta signaling and the myofibroblast

Idiopathic Pulmonary Fibrosis (IPF) is characterized by injury and loss of lung epithelial cells, accumulation of fibroblasts/myofibroblasts and abnormal remodeling of the lung parenchyma. The prognosis for IPF patients is poor and current therapies are largely ineffective in preventing respiratory failure. Current therapeutic approaches target epithelial cell replacement, manipulation of fibroblasts/myofibroblasts, modulation of procoagulant/fibrinolytic activities, cytokine and growth factor production, angiogenesis, and reduction of oxidative stress. Myofibroblasts are the primary effector cells in fibrosis. These cells may be derived by the activation and proliferation of resident lung fibroblasts, from epithelial-mesenchymal transition (EMT), or through recruitment of circulating fibrocytes. Transforming growth factor beta (TGFbeta) is a profibrotic factor that increases fibroblast proliferation, stimulates the synthesis and deposition of connective tissue, and inhibits connective tissue breakdown. TGFbeta acts through the promoter of the type 1 collagen gene causing increased collagen synthesis. In addition, TGFbeta induces EMT in alveolar epithelial cells (AECs) in vitro and in vivo. AECs exhibit substantial plasticity and may serve as a source of fibroblasts and/or myofibroblasts in lung fibrosis. Therapeutic interventions interfering with the pathways that lead to myofibroblast expansion and AEC apoptosis should be of considerable benefit in the treatment of IPF. This review will focus on the critical role of TGFbeta on AECs EMT and myofibroblasts in the development of fibrosis.

Hypertrophic scar fibroblasts accelerate collagen gel contraction

Excessive contraction of hypertrophic scar and subsequent contracture formation are a formidable problem after thermal injury. A comparison between fibroblasts from hypertrophic scar and normal skin was made with the use of fibroblast-populated collagen lattices as a measure of cellular generated contractile forces. Hypertrophic scar and normal skin fibroblasts were mixed with soluble tendon collagen and Dulbecco's modified Eagle medium supplemented with 10% serum, and contraction was measured by serial area measurements. Parallel experiments in the presence of transforming growth factor-beta or anti-transforming growth factor-beta antibody examined the role of this cytokine on lattice contraction. Transforming growth factor-beta activity was measured in an additional set of 10 biopsy specimens. Hypertrophic scar fibroblasts contract lattices at a significantly faster rate than do normal skin fibroblasts. Exogenous transforming growth factor-beta increased lattice contraction by normal skin fibroblasts but had little effect on hypertrophic scar cell-populated lattices. The addition of anti-transforming growth factor-beta antibody decreased lattice contraction by both cell types. Transforming growth factor-beta activity was significantly increased in the hypertrophic scar biopsy specimens. Excessive scar contraction and post-burn scar contracture result from increased contraction forces generated by hypertrophic scar cells. This increased contractility appears to be mediated by increased endogenous presence of transforming growth factor-beta.

Antiapoptotic effect of found in inflammatory zone (FIZZ)1 on mouse lung fibroblasts

Myofibroblasts play an essential role in the abnormal deposition of extracellular matrix in pulmonary fibrosis. The presence or prolonged survival of these cells may be a key factor in the pathogenesis of progressive pulmonary fibrosis. Found in inflammatory zone (FIZZ)1 can induce myofibroblast differentiation and has an antiapoptotic effect on embryonic lung explant cultures. In this study, we investigated whether FIZZ1 also has an antiapoptotic effect on mouse lung fibroblasts (MLFs). Cells were treated with FIZZ1 for 24 h and then apoptosis was induced by TNFalpha in the presence of cycloheximide (CHX). FIZZ1 exhibited an antiapoptotic effect in MLFs, as assessed by flow cytometric analysis and TUNEL staining. Moreover, the cell number was higher in the FIZZ1-treated group relative to the non-treated control group after treatment with TNFalpha and CHX. FIZZ1 treatment also inhibited the apoptotic agent-induced activities of caspase-3 and caspase-8. Examination of potential signalling pathways revealed that FIZZ1 induced rapid phosphorylation of ERK-1/2, while PD98059, a MEK/ERK inhibitor, markedly induced activation of caspase-3. This anti-apoptotic effect of FIZZ1 was associated with induction of myofibroblast differentiation in response to FIZZ1 stimulation. Taken together, these findings suggest that FIZZ1 is involved in pulmonary fibrosis through both induction of myofibroblast differentiation and increased or prolonged survival of myofibroblasts. This effect of FIZZ1 was mediated by inhibition of caspase-3 and -8, with involvement of the ERK pathway.

An essential role for CCAAT/enhancer binding protein beta in bleomycin-induced pulmonary fibrosis

Pulmonary fibrosis is characterized by inflammation, genesis of myofibroblasts, and abnormal tissue repair. Despite extensive research, its pathogenesis remains incompletely understood. Previously, the transcription factor CCAAT/enhancer binding protein beta (C/EBPbeta) was found to be a key regulator of myofibroblast differentiation in vitro, and to be involved in the acute phase and inflammatory responses. In an attempt to test the role of C/EBPbeta in the development of pulmonary fibrosis, experiments using C/EBPbeta null mice and their wild-type littermates were conducted. Our findings indicated that, compared to wild-type mice, animals deficient in C/EBPbeta showed significantly reduced fibrotic lesions and collagen deposition in the lung upon endotracheal injection of bleomycin. Further studies on the mechanisms by which C/EBPbeta regulates fibrosis indicated that knockout of C/EBPbeta attenuates inflammatory cytokine expression in bleomycin-treated mice. The reduced alpha-smooth muscle actin gene expression in either isolated lung fibroblasts or lung tissue from bleomycin or saline-treated C/EBPbeta deficient mice suggests that C/EBPbeta regulates myofibroblast differentiation during fibrosis. Consistent with this finding, cells from C/EBPbeta deficient mice exhibited higher proliferative rates than those from wild-type mice. These data suggest that C/EBPbeta plays an essential role in pulmonary fibrosis and that this role appears to be multifactorial with respect to cytokine expression, cell differentiation, and proliferation.

Molecular Mechanisms of and Possible Treatment Strategies for Idiopathic Pulmonary Fibrosis

Pulmonary fibrosis is characterized by lung inflammation and abnormal tissue repair, resulting in the replacement of normal functional tissue with an abnormal accumulation of fibroblasts and deposition of collagen in the lung. This process involves cellular interactions via a complex cytokine-signaling mechanism and heightened collagen gene expression, ultimately resulting in its abnormal collagen deposition in the lung. Our current understanding of the pathogenesis of pulmonary fibrosis suggests that in addition to inflammatory cells, the fibroblast and signaling events that mediate fibroblast proliferation and myofibroblasts, play important roles in the diverse processes that constitute fibrosis. Increasing knowledge of cytokine biology, cytokine-signaling and cell matrix interactions have shed some light on the genesis of pulmonary fibrosis; however, the importance of inflammation in pulmonary fibrosis remains controversial. This remains true because the inflammatory component is variable at the time of diagnosis, and the most potent anti-inflammatory drugs that have been widely used in the treatment of pulmonary fibrosis do not seem to interfere with the fibrotic disease progression. Pulmonary fibrosis is a highly lethal disorder, which continues to pose major clinical challenges because an effective therapeutic regimen is yet to be determined. This review summarizes recent progress in understanding the molecular mechanisms of pulmonary fibrosis, and includes a more detailed discussion of the potential points of therapeutic attack in pulmonary fibrosis. In addition, a detailed discussion is presented regarding each of the potential therapies which have emerged from the animal models of pulmonary fibrosis, and which have been developed through advances in cellular and molecular biology.

Role of Smad3 in the regulation of rat telomerase reverse transcriptase by TGFβ

Telomerase is induced in certain pathological conditions such as cancer and tissue injury and repair. This induction in fibroblasts from injured lung is repressed by transforming growth factor beta (TGFbeta) via yet unknown mechanisms. In this study, the role of Smad3 in the inhibition of telomerase reverse transcriptase (TERT) gene transcription by TGFbeta was investigated. The rat TERT (rTERT) gene promoter was cloned by PCR amplification and fused with a luciferase reporter gene. This construct was used to analyse regulation of promoter activity in fibroblasts isolated from bleomycin-injured lung with induced telomerase activity. The results showed that TGFbeta inhibited rTERT transcription while stimulating Smad3 expression. Interestingly, TGFbeta also inhibited the expression of c-myc. Cotransfection with a Smad3 expressing plasmid further repressed rTERT transcription and c-myc expression, while cotransfection with the corresponding antisense Smad3 construct had the opposite effect. Mutation of an E-box in the rTERT promoter suppressed its activity, which could be further reduced by TGFbeta treatment. In contrast, mutation at a Smad binding element enhanced promoter activity whose inhibition was impaired by TGFbeta treatment. Thus TGFbeta inhibition of rTERT gene expression was directly mediated by Smad3 via the Smad binding element, while c-myc appears to primarily regulate its constitutive or induced expression.

Lung interleukin-4 gene expression in a murine model of bleomycin-induced pulmonary fibrosis

Interleukin-4 (IL-4) is known to activate mononuclear cells as well as fibroblasts, all of which are important in the pathogenesis of pulmonary fibrosis. To investigate the potential role of this cytokine, lung IL-4 expression was examined in a murine model of bleomycin-induced pulmonary fibrosis. Lung fibrosis was induced in CBA/J mice by endotracheal injection of bleomycin on day 0. On selected days after treatment, lungs were harvested for reverse transcriptase polymerase chain reaction (RT-PCR), Northern, in-situ hybridization and immunohistochemical analyses. RT-PCR and Northern analyses revealed significant increases in lung IL-4 mRNA content between days 3 and 14 after induction of lung injury, which decreased toward control level after day 21. Both in-situ hybridization and immunohistochemistry showed low or undetectable IL-4 expression in control lungs and in injured lungs before day 3 after bleomycin injection. There was however elevated expression in mononuclear cells and macrophages between days 3 and 14, localized to areas of active fibrosis. These results demonstrate that IL-4 is upregulated significantly in this model. They suggest a potential role for this cytokine in pulmonary fibrosis, perhaps via its ability to stimulate and amplify the inflammatory response, stimulate collagen synthesis in fibroblasts, and thus promote the progression to fibrosis and end stage lung disease.

Role of cytokines and cytokine therapy in wound healing and fibrotic diseases

Cytokines are critical to a myriad of fundamental homeostatic and pathophysiological processes such as fever, wound healing, inflammation, tissue repair and fibrosis. They play important roles in regulating cell function such as proliferation, migration, and matrix synthesis. It is the balance or the net effect of the complex interplay between these mediators, which appears to play a major role in regulating the initiation, progression and resolution of wounds. Wound healing involves a complex process including induction of acute inflammation by the initial injury, followed by parenchymal and mesenchymal cell proliferation, migration, and activation with production and deposition of extracellular matrix. Failure to resolve or abnormal wound healing results in fibrosis. The latter process involves similar cellular interactions via complex cytokine networks, which result in extensive remodeling with heightened extracellular matrix production and their abnormal deposition in the tissue. Various cytokines, both promoting and inhibiting fibrogenesis, have been implicated in the pathogenesis of fibrosis and wound healing. Recent progress in understanding the mechanisms underlying the pathogenesis of fibrosis leads us to expect that inhibitors of pro-fibrogenic cytokines and growth factors may be useful as novel therapeutic agents in controlling undesirable fibrosis. In this review, the role of cytokines in wound healing and fibrosis will be summarized and highlighted with more detailed discussion reserved for the possible points of therapeutic attack in pulmonary fibrosis. In this review, the major cytokines that are in current clinical use will be also discussed. In addition, advances in the application of novel cytokines and anti-cytokines for accelerating wound healing and attenuating fibrosis both at the experimental and the clinical trial levels will be discussed.

Regulation of alpha-smooth muscle actin gene expression in myofibroblast differentiation from rat lung fibroblasts

Myofibroblasts express alpha-smooth muscle actin and have a phenotype intermediate between fibroblasts and smooth muscle cells. Their emergence can be induced by cytokines such as transforming growth factor beta; but the regulatory mechanism for induction of alpha-smooth muscle actin gene expression in myofibroblast differentiation has not been determined. To examine this mechanism at the level of the alpha-smooth muscle actin promoter, rat lung fibroblasts were transfected with varying lengths of the alpha-smooth muscle actin promoter linked to the chloramphenicol acetyl transferase reporter gene and treated with transforming growth factor beta1. The results show that the shortest inducible promoter was 150 base pairs long, suggesting the presence in this region of cis-elements of potential importance in transforming growth factor beta1 induced myofibroblast differentiation. Transfection of "decoy" oligonucleotides corresponding to sequences for four suspected regulatory factors demonstrated that only the transforming growth factor beta control element is involved in the regulation of transforming growth factor beta1-induced alpha-smooth muscle actin expression in myofibroblast differentiation. Consistent with this conclusion is the finding that a mutation in the transforming growth factor beta control element caused a significant reduction in promoter activity. These observations taken together show that alpha-smooth muscle actin promoter regulation during myofibroblast differentiation is uniquely different from that in smooth muscle cells and other cell lines. Since myofibroblasts play a key role in wound contraction and synthesis of extracellular matrix, clarification of this differentiation mechanism should provide new insight into fibrogenesis and suggest future novel strategies for modulation of wound healing and controlling fibrosis.

Induction of telomerase activity in fibroblasts from bleomycin-injured lungs

Bleomycin-induced lung injury causes increased fibroblast numbers in the lung and pulmonary fibrosis. Studies of fibroblasts isolated from such injured lungs have revealed evidence of increased intrinsic proliferative capacity, but the mechanism is unknown. Telomerase catalyzes the addition of telomeric DNA repeats onto chromosomal ends, which is associated with increased cellular life span or immortality. To examine whether telomerase might play a role in regulating fibroblast proliferative capacity in pulmonary fibrosis, lung fibroblasts were isolated from rats treated with endotracheal injections of phosphate-buffered saline or bleomycin. At selected time points, the rats were killed and lung fibroblasts isolated. The isolated cells and lung tissue were then used in experiments for measurement of telomerase activity. The results show undetectable telomerase activity in fibroblasts isolated from control uninjured lungs, or in the control lung tissue extracts. Similar results were obtained in cells and lung tissue from Days 1, 3, and 28 bleomycin-injured lungs. However, significant telomerase activity was detected in fibroblasts and tissue extracts isolated from Days 7, 14, and 21 bleomycin-treated rat lungs, with maximal activity observed in the Day 14 samples. Analysis of the isolated cells for telomerase messenger RNA or reverse transcriptase expression, combined with alpha-smooth-muscle actin expression by immunohistochemistry, revealed that telomerase expression localized primarily to nonmyofibroblasts. These findings suggest that in addition to elevated growth factor expression, the injured lung fibroblast population may contain cells with increased life span, which could contribute to the observed overall increase in lung fibroblast numbers.

Vitamin A antagonizes decreased cell growth and elevated collagen-degrading matrix metalloproteinases and stimulates collagen accumulation in naturally aged human skin

Damage to human skin due to ultraviolet light from the sun (photoaging) and damage occurring as a consequence of the passage of time (chronologic or natural aging) are considered to be distinct entities. Photoaging is caused in part by damage to skin connective tissue by increased elaboration of collagen-degrading matrix metalloproteinases, and by reduced collagen synthesis. As matrix metalloproteinase levels are known to rise in fibroblasts as a function of age, and as oxidant stress is believed to underlie changes associated with both photoaging and natural aging, we determined whether natural skin aging, like photoaging, gives rise to increased matrix metalloproteinases and reduced collagen synthesis. In addition, we determined whether topical vitamin A (retinol) could stimulate new collagen deposition in sun-protected aged skin, as it does in photoaged skin. Sun-protected skin samples were obtained from 72 individuals in four age groups: 18-29 y, 30-59 y, 60-79 y, and 80+ y. Histologic and cellular markers of connective tissue abnormalities were significantly elevated in the 60-79 y and 80+ y groups, compared with the two younger age groups. Increased matrix metalloproteinase levels and decreased collagen synthesis/expression were associated with this connective tissue damage. In a separate group of 53 individuals (80+ y of age), topical application of 1% vitamin A for 7 d increased fibroblast growth and collagen synthesis, and concomitantly reduced the levels of matrix-degrading matrix metalloproteinases. Our findings indicate that naturally aged, sun-protected skin and photoaged skin share important molecular features including connective tissue damage, elevated matrix metalloproteinase levels, and reduced collagen production. In addition, vitamin A treatment reduces matrix metalloproteinase expression and stimulates collagen synthesis in naturally aged, sun-protected skin, as it does in photoaged skin.

Inhibition of myofibroblast apoptosis by transforming growth factor beta(1)

Fibroblast differentiation to the myofibroblast phenotype is associated with alpha-smooth-muscle actin (alpha-SMA) expression and regulated by cytokines. Among these, transforming growth factor (TGF)-beta(1) and interleukin (IL)-1beta can stimulate and inhibit myofibroblast differentiation, respectively. IL-1beta inhibits alpha-SMA expression by inducing apoptosis selectively in myofibroblasts via induction of nitric oxide synthase (inducible nitric oxide synthase [iNOS]). Because TGF-beta is known to inhibit iNOS expression, this study was undertaken to see if this cytokine can protect against IL-1beta-induced myofibroblast apoptosis. Rat lung fibroblasts were treated with IL-1beta and/or TGF-beta(1) and examined for expression of alpha-SMA, iNOS, and the apoptotic regulatory proteins bax and bcl-2. The results show that TGF-beta(1) caused a virtually complete suppression of IL-1beta-induced iNOS expression while preventing the decline in alpha-SMA expression or the myofibroblast subpopulation. TGF-beta(1) treatment also completely suppressed the IL-1beta-induced apoptosis in myofibroblasts. IL-1beta-induced apoptosis was associated with a significant decline in expression of the antiapoptotic protein bcl-2, which was prevented by concomitant TGF-beta(1) treatment. The level of the proapoptotic protein bax, however, was not significantly altered by either cytokine. These data suggest that TGF-beta(1) inhibits IL-1beta-induced apoptosis in myofibroblasts by at least two mechanisms, namely, the suppression of iNOS expression and the prevention of a decline in bcl-2 expression. Thus, TGF-beta(1) may be additionally important in fibrosis by virtue of this novel ability to promote myofibroblast survival by preventing the myofibroblast from undergoing apoptosis.

The role of eosinophils in pulmonary fibrosis (Review)

Pulmonary fibrosis is commonly characterized by inflammation of the alveolar wall, leading to derangement of normal alveolar architecture, and interstitial as well as intra-alveolar fibrosis. The process involves cellular interactions via a complex cytokine network and heightened collagen gene expression with abnormal deposition in the lung. Recent studies have identified a myriad of cytokines with potential roles in pulmonary fibrosis. Based on in vivo antibody neutralization studies, important roles for tumor necrosis á (TNFá), macrophage inflammatory protein 1á (MIP-1á) and transforming growth factor (TGF), have been established. The recent demonstration that the eosinophil is a major source for several of these key pro-fibrogenic cytokines during the early stages of fibrosis, strongly suggest a role for the eosinophil in pulmonary fibrosis. In vitro, eosinophils can elaborate factors capable of stimulating fibroblast proliferation, and their presence in lungs undergoing many forms of pulmonary fibrosis has been well documented. Further support for a role for eosinophils in pulmonary fibrosis are suggested by clinical data showing a correlation between lung eosinophil count and a poor prognosis and decreased responsiveness to therapy. This review will focus on the recent findings, which suggest novel potential roles for the eosinophil in the pathogenesis of pulmonary fibrosis.

The role of IL-5 in bleomycin-induced pulmonary fibrosis

Eosinophils are known to express cytokines capable of promoting fibrosis. Interleukin-5 (IL-5) is important in regulating eosinophilopoiesis, eosinophil recruitment and activation. Lung IL-5 expression is elevated in pulmonary fibrosis, wherein the eosinophil is a primary source of fibrogenic cytokines. To determine the role of IL-5 in pulmonary fibrosis, the effects of anti-IL-5 antibody were investigated in a model of bleomycin-induced pulmonary fibrosis. Fibrosis was induced in mice by endotracheal bleomycin treatment. Animals were also treated with either anti-IL-5 antibody or control IgG. Lungs were then analyzed for fibrosis, eosinophil influx, chemotactic activity, and cytokine expression. The results show that a primary chemotactic activity at the height of eosinophil recruitment is IL-5. Furthermore, anti-IL-5 antibody caused significant reduction in lung eosinophilia, cytokine expression, and fibrosis. These findings taken together suggest an important role for IL-5 in pulmonary fibrosis via its ability to regulate eosinophilic inflammation, and thus eosinophil-dependent fibrogenic cytokine production.

TNF and IL-6 mediate MIP-1alpha expression in bleomycin-induced lung injury

Previously, macrophage inflammatory protein-1alpha (MIP-1alpha), a member of the C-C chemokine family, has been implicated in bleomycin-induced pulmonary fibrosis, a model of the human disease idiopathic pulmonary fibrosis. Neutralization of MIP-1alpha protein with anti-MIP-1alpha antibodies significantly attenuated both mononuclear phagocyte recruitment and pulmonary fibrosis in bleomycin-challenged CBA/J mice. However, the specific stimuli for MIP-1alpha expression in the bleomycin-induced lesion have not been characterized. In this report, two mediators of the inflammatory response to bleomycin, tumor necrosis factor (TNF) and interleukin-6 (IL-6), were evaluated as putative stimuli for MIP-1alpha expression after bleomycin challenge in CBA/J mice. Elevated levels of bioactive TNF and IL-6 were detected in bronchoalveolar lavage (BAL) fluid and lung homogenates from bleomycin-treated CBA/J mice at time points post-bleomycin challenge, which precede MIP-1alpha protein expression. Treatment of bleomycin-challenged mice with soluble TNF receptor (sTNFr) or anti-IL-6 antibodies significantly decreased MIP-1alpha protein expression in the lungs. Furthermore, normal alveolar macrophages secreted elevated levels of MIP-1alpha protein in response to treatment with TNF plus IL-6 or bleomycin plus IL-6, but not TNF, bleomycin, or IL-6 alone. Finally, leukocytes recovered from the BAL fluid of bleomycin-challenged mice secreted higher levels of MIP-1alpha protein, compared to controls, when treated with TNF alone. Based on the data presented here, we propose that TNF and IL-6 are part of a cytokine network that modulates MIP-1alpha protein expression in the profibrotic inflammatory lesion during the response to intratracheal bleomycin challenge.

The role of eosinophils in pulmonary fibrosis (Review)

Pulmonary fibrosis is commonly characterized by inflammation of the alveolar wall, leading to derangement of normal alveolar architecture, and interstitial as well as intra-alveolar fibrosis. The process involves cellular interactions via a complex cytokine network and heightened collagen gene expression with abnormal deposition in the lung. Recent studies have identified a myriad of cytokines with potential roles in pulmonary fibrosis. Based on in vivo antibody neutralization studies, important roles for tumor necrosis á (TNFá), macrophage inflammatory protein 1á (MIP-1á) and transforming growth factor (TGF), have been established. The recent demonstration that the eosinophil is a major source for several of these key pro-fibrogenic cytokines during the early stages of fibrosis, strongly suggest a role for the eosinophil in pulmonary fibrosis. In vitro, eosinophils can elaborate factors capable of stimulating fibroblast proliferation, and their presence in lungs undergoing many forms of pulmonary fibrosis has been well documented. Further support for a role for eosinophils in pulmonary fibrosis are suggested by clinical data showing a correlation between lung eosinophil count and a poor prognosis and decreased responsiveness to therapy. This review will focus on the recent findings, which suggest novel potential roles for the eosinophil in the pathogenesis of pulmonary fibrosis.

Lung interleukin-5 expression in murine bleomycin-induced pulmonary fibrosis

Eosinophils are primary sources of fibrogenic cytokines in lung fibrosis, and interleukin (IL)-5 is important in their differentiation, proliferation, recruitment and activation. To investigate the potential role of this cytokine, lung IL-5 expression was examined in a murine model of bleomycin-induced pulmonary fibrosis. Analysis of lung RNA showed significant increases in lung IL-5 mRNA content between days 3 and 14 after induction of lung injury, which decreased toward control levels after day 21. In situ hybridization revealed essentially no detectable IL-5 mRNA expression before day 3, but showed elevated expression in mononuclear cells and eosinophils between days 3 and 14, localized within areas of active fibrosis. After 21 days, the intensity and number of IL-5-expressing cells significantly declined. Immunostaining with anti-IL-5 antibodies confirmed the predominant IL-5 expression by mononuclear cells and eosinophils in areas of active fibrosis. The kinetics of increase in the number of cells expressing significant IL-5 mRNA in lung sections paralleled that for IL-5 mRNA expression in whole-lung homogenates. These results demonstrate for the first time that IL-5 is upregulated in this murine model and suggest a novel role for this cytokine in pulmonary fibrosis via its ability to recruit and activate eosinophils.

Transforming growth factor-beta 1 increases lysyl oxidase enzyme activity and mRNA in rat aortic smooth muscle cells

PURPOSE

This investigation was designed to test the hypothesis that transforming growth factor-beta 1 (TGF-beta 1) regulates lysyl oxidase secretion from vascular smooth muscle cells. Lysyl oxidase is an enzyme that catalyzes an essential step in collagen and elastin cross-linking in the extracellular matrix, and TGF-beta 1 has been implicated in the pathogenesis of restenosis after vascular injury. The effect of TGF-beta 1 on lysyl oxidase in vascular smooth muscle cells has not been previously defined.

METHODS

Rat aortic smooth muscle cells were grown in culture to confluence. Cells in passage 2 to 6 were incubated for 24 hours in media containing 0.1, 0.5, 1.0, or 10.0 ng/ml of TGF-beta 1. Lysyl oxidase activity in the media was quantitated with a tritium-release bioassay against an insoluble 3H-labeled aortic clastin substrate. Northern blot analyses were performed to determine steady-state levels of lysyl oxidase mRNA in the smooth muscle cells.

RESULTS

Lysyl oxidase activity in the media increased 1.5-fold above control levels after exposure to 10 ng/ml of TGF-beta 1 (p < 0.01). This increase in lysyl oxidase activity was associated with a concentration-dependent increase in steady-state levels of lysyl oxidase mRNA, being 4.3- and 6.2-fold above control levels after exposure to 1 and 10 ng/ml TGF-beta 1, respectively (p < 0.01). The observed increase in steady-state lysyl oxidase mRNA after exposure to TGF-beta 1 was also time-dependent over the 24-hour experimental period.

CONCLUSIONS

TGF-beta 1 appears to regulate lysyl oxidase in cultured rat aortic smooth muscle cells. Increases in lysyl oxidase activity may be one of the mechanisms by which TGF-beta 1 contributes to arterial restenosis after vascular injury.

Regulation of lung fibroblast alpha-smooth muscle actin expression, contractile phenotype, and apoptosis by IL-1beta

IL-1 is important in regulating lung inflammation and potentially fibrosis as well. To clarify the role of this cytokine vis-à-vis changes in lung fibroblast phenotype in pulmonary fibrosis, the effects of IL-1beta on isolated lung fibroblasts were examined. Rat lung fibroblasts were treated with increasing doses of IL-1beta and examined for effects on cell number, alpha-smooth muscle actin expression, apoptosis, nitric oxide (NO) production, and contractility in collagen gels. The results show that IL-1beta caused dose-dependent down-regulation of alpha-smooth muscle actin protein and mRNA expression. The kinetics of mRNA inhibition was rapid and preceded the effects on protein expression. This IL-1beta-induced decrease in actin expression was associated with inhibition of contractility evaluated using fibroblast-populated collagen gels. Since IL-1beta inhibition of actin expression was accompanied by reduction in cell number, the effect on apoptosis was examined. Significant increase in the number of apoptotic nuclei and DNA fragmentation was observed upon IL-1beta treatment, with a dose-response curve that mirrored that for the decline in actin-positive cells. More than one-half of the apoptotic cells were actin positive at high IL-1beta doses, suggesting that the actin-expressing cells may be more susceptible to IL-1beta-induced apoptosis. IL-1beta also induced NO production in these cells, which was inhibited by NG-monomethyl-L-arginine. Similarly, IL-1beta-induced apoptosis and inhibition of actin expression were inhibited by this arginine analogue. Hence, induction of apoptosis by IL-1beta via NO production may be an important mechanism for regulating lung fibroblast alpha-smooth muscle actin expression, and consequently its contractile phenotype as well.

Regulation of lung fibroblast alpha-smooth muscle actin expression, contractile phenotype, and apoptosis by IL-1beta

IL-1 is important in regulating lung inflammation and potentially fibrosis as well. To clarify the role of this cytokine vis-à-vis changes in lung fibroblast phenotype in pulmonary fibrosis, the effects of IL-1beta on isolated lung fibroblasts were examined. Rat lung fibroblasts were treated with increasing doses of IL-1beta and examined for effects on cell number, alpha-smooth muscle actin expression, apoptosis, nitric oxide (NO) production, and contractility in collagen gels. The results show that IL-1beta caused dose-dependent down-regulation of alpha-smooth muscle actin protein and mRNA expression. The kinetics of mRNA inhibition was rapid and preceded the effects on protein expression. This IL-1beta-induced decrease in actin expression was associated with inhibition of contractility evaluated using fibroblast-populated collagen gels. Since IL-1beta inhibition of actin expression was accompanied by reduction in cell number, the effect on apoptosis was examined. Significant increase in the number of apoptotic nuclei and DNA fragmentation was observed upon IL-1beta treatment, with a dose-response curve that mirrored that for the decline in actin-positive cells. More than one-half of the apoptotic cells were actin positive at high IL-1beta doses, suggesting that the actin-expressing cells may be more susceptible to IL-1beta-induced apoptosis. IL-1beta also induced NO production in these cells, which was inhibited by NG-monomethyl-L-arginine. Similarly, IL-1beta-induced apoptosis and inhibition of actin expression were inhibited by this arginine analogue. Hence, induction of apoptosis by IL-1beta via NO production may be an important mechanism for regulating lung fibroblast alpha-smooth muscle actin expression, and consequently its contractile phenotype as well.

TNF-alpha-mediated lung cytokine networking and eosinophil recruitment in pulmonary fibrosis

Despite abundant evidence documenting the importance of TNF-alpha in the pathogenesis of pulmonary fibrosis, its actual role has not been fully elucidated. Recent observations also indicate that eosinophils found in fibrotic lung express elevated levels of cytokines known to be important in lung fibrosis. These findings suggest a possible role for TNF-alpha in eosinophil recruitment and cytokine expression in this disease. To examine this hypothesis, pulmonary fibrosis was induced in mice by endotracheal bleomycin treatment, and separate groups of animals were also treated with either anti-TNF-alpha Ab or control serum. On days 7 and 14 post-bleomycin treatment, lungs were harvested and analyzed for fibrosis, cytokine expression, and eosinophil influx. Anti-TNF-alpha caused a significant reduction in lung fibrosis, as indicated by a reduction in hydroxyproline content, which was accompanied by suppression of lung TGF-beta1, IL-5, and JE mRNA expression. Examination of tissue sections revealed a significant reduction in lung eosinophils and overall cellularity by anti-TNF-alpha treatment without a significant effect on the number of lung macrophages. The number of IL-5-expressing cells was also significantly reduced by anti-TNF-alpha treatment. Since IL-5 is important in eosinophil differentiation, activation, and recruitment, these findings suggest a novel mechanism by which TNF-alpha could mediate pulmonary fibrosis via induction of IL-5-mediated eosinophil recruitment and fibrogenic cytokine production. Since these eosinophil-derived cytokines include JE/monocyte chemotactic factor-1 and TGF-beta1, this cytokine networking orchestrated by TNF-alpha could, in turn, amplify the inflammatory response and drive the progression to fibrosis and end-stage lung disease.

TNF-alpha-mediated lung cytokine networking and eosinophil recruitment in pulmonary fibrosis

Despite abundant evidence documenting the importance of TNF-alpha in the pathogenesis of pulmonary fibrosis, its actual role has not been fully elucidated. Recent observations also indicate that eosinophils found in fibrotic lung express elevated levels of cytokines known to be important in lung fibrosis. These findings suggest a possible role for TNF-alpha in eosinophil recruitment and cytokine expression in this disease. To examine this hypothesis, pulmonary fibrosis was induced in mice by endotracheal bleomycin treatment, and separate groups of animals were also treated with either anti-TNF-alpha Ab or control serum. On days 7 and 14 post-bleomycin treatment, lungs were harvested and analyzed for fibrosis, cytokine expression, and eosinophil influx. Anti-TNF-alpha caused a significant reduction in lung fibrosis, as indicated by a reduction in hydroxyproline content, which was accompanied by suppression of lung TGF-beta1, IL-5, and JE mRNA expression. Examination of tissue sections revealed a significant reduction in lung eosinophils and overall cellularity by anti-TNF-alpha treatment without a significant effect on the number of lung macrophages. The number of IL-5-expressing cells was also significantly reduced by anti-TNF-alpha treatment. Since IL-5 is important in eosinophil differentiation, activation, and recruitment, these findings suggest a novel mechanism by which TNF-alpha could mediate pulmonary fibrosis via induction of IL-5-mediated eosinophil recruitment and fibrogenic cytokine production. Since these eosinophil-derived cytokines include JE/monocyte chemotactic factor-1 and TGF-beta1, this cytokine networking orchestrated by TNF-alpha could, in turn, amplify the inflammatory response and drive the progression to fibrosis and end-stage lung disease.

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.

Cytokines and pulmonary fibrosis

In the past several years, significant progress in many aspects of pulmonary fibrosis research has been made. Among them, the finding that a variety of cytokines play important roles in the complex process appears most intriguing. These cytokines include at least transforming growth factor-beta (TGF-beta), tumor necrosis factor-alpha (TNF-alpha), platelet-derived growth factor, fibroblast growth factors, (TGF-alpha), interleukin-1, monocyte chemoattractant protein-1 and macrophage inflammatory protein-1 alpha. These cytokines have been demonstrated to be produced at the sites of active fibrosis where they appear to be expressed by activated inflammatory cells, such as macrophages and eosinophils. More interestingly, other noninflammatory lung cells including mesenchymal cells, such as myofibroblasts, and epithelial cells, have been found to be significant sources as well, albeit in most instances at somewhat different time points than those by inflammatory cells. Study of the individual cytokines in vitro has revealed a variety of potential roles for these cytokines in the regulation of the fibrotic process in vivo, including chemoattractant, mitogenic activities for fibroblasts, stimulation of extracellular matrix and alpha-smooth muscle actin gene expression, alteration of the contractile phenotype of fibroblasts and regulation of diverse functions of lung inflammatory and epithelial cells which can further impact on the fibrotic process by autocrine and paracrine mechanisms. Of these cytokines, it appears that TGF-beta is probably the most important cytokine in terms of the direct stimulation of lung matrix expression which typifies fibrosis. Recently however, there is accumulating evidence to indicate that the situation is much more complex than any one single cytokine being solely responsible for the fibrotic response. The concept of complex lung cytokine networks, orchestrated by a few key cytokines, such as TNF-alpha, being responsible for this response has received strong support from recent studies. This means that it is the balance of positive (profibrogenic) and negative (antifibrogenic) forces generated from interaction among the various cytokines constituting these networks, which may finally determine the outcome of lung injury and inflammation. The importance of these cytokines also suggests new potential targets for designing new therapies for progressive pulmonary fibrosis, and perhaps their utility in prognostication as well.

Fibronectin is the major fibroblast chemoattractant in rabbit anti-glomerular basement membrane disease

The mechanism for fibroblast recruitment in renal fibrosis due to anti-glomerular basement membrane (anti-GBM) disease is unknown. Since fibroblast recruitment can occur via chemotaxis, assessment of the possible production of fibroblast chemotactic activity by affected renal tissue and its identification could provide important clues. Anti-GBM disease was induced by injection of guinea pig anti-rabbit GBM immunoglobulin G into rabbits previously sensitized to guinea pig immunoglobulin G. On days 4, 7, and 14 after induction, renal tissue was harvested and glomeruli isolated. Overnight serum-free conditioned media from whole cortex and glomeruli were prepared and assayed for fibroblast chemotactic activity. The results show low level activity in both conditioned media from control animals. In contrast, conditioned media from anti-GBM-treated animals at all time points showed significantly elevated fibroblast chemotactic activity peaking on day 4 with subsequent reduction thereafter. The magnitude of increase in cortical conditioned media was significantly higher than that for glomerular conditioned media, suggesting that most of the activity was derived from extraglomerular sources. Gel filtration analysis revealed the activity to be heterogeneous, consisting of at least four major species with estimated molecular weights ranging from 10 to > 100 kd. Acidification of conditioned media failed to increase chemotactic activity significantly, whereas protease digestion abolished it. Treatment of conditioned media with antifibronectin inhibited > 85% of the chemotactic activity, whereas antibodies to platelet-derived growth factor and transforming growth factor-beta did not have a significant effect. These findings taken together suggest that fibronectin-derived peptides represent the predominant fibroblast chemoattractant produced by renal cortex in anti-GBM disease.

Lung fibroblast alpha-smooth muscle actin expression and contractile phenotype in bleomycin-induced pulmonary fibrosis

The emergence of the myofibroblast phenotype (characterized by alpha-smooth muscle actin expression) in wound healing and in tissues undergoing fibrosis is thought to be responsible for the increased contractility of the affected tissues. In bleomycin-induced pulmonary fibrosis, the myofibroblast is also responsible for the observed increase in collagen gene expression. To evaluate further these phenotypic changes in lung fibroblasts, contractile and other phenotypic properties of fibroblasts isolated from lungs of rats with bleomycin-induced fibrosis were compared with those of normal rats using in vitro models. Pulmonary fibrosis was induced in rats by endotracheal injection on day 0, and 7 and 14 days later the animals were sacrificed and lung fibroblasts isolated. Using immunofluorescence, < 10% of fibroblasts from control animals express alpha-smooth muscle actin when cultured as a monolayer. In contrast, 19% and 21% of cells from day 7 and day 14 bleomycin-treated animals, respectively, expressed this actin and with greater intensity than in control lung cells. This increase in actin expression was associated with enhanced contractility when evaluated using a three-dimensional cell culture model consisting of fibroblast-populated collagen gels. This enhanced contractility was abolished by treatment with antibody to transforming growth factor-beta (TGF-beta), whereas exogenous TGF-beta 1 and serum-stimulated contraction of control lung fibroblasts. TGF-beta 1 gene expression was greater in cells from bleomycin-treated animals than those from control lungs. These results show that cells with the myofibroblast phenotype are more abundant in fibrotic lung, and that these cells possess greater contractile capacity in vitro at least partly by virtue of their enhanced endogenous TGF-beta 1 gene expression.

Cellular localization of transforming growth factor-beta expression in bleomycin-induced pulmonary fibrosis

Bleomycin-induced pulmonary fibrosis is associated with increased lung transforming growth factor-beta (TGF-beta) gene expression, but cellular localization of the source of this expression has not been unequivocally established. In this study, lung fibrosis was induced in rats by endotracheal bleomycin injection on day 0 and, on selected days afterwards, lungs were harvested for in situ hybridization, immunohistochemical and histochemical analyses for TGF-beta 1 mRNA and protein expression, and cell identification. The results show that control lungs express essentially no detectable TGF-beta 1 mRNA or protein in the parenchyma. Before day 3 after bleomycin treatment, scattered bronchiolar epithelial cells, mononuclear cells, and eosinophils expressed elevated levels of TGF-beta 1. Between days 3 and 14, there was a major increase in the number of eosinophils, myofibroblasts, and fibroblasts strongly expressing TGF-beta 1 mRNA and protein. TGF-beta 1-producing cells were predominantly localized within areas of injury and active fibrosis. After day 14, the intensity and number of TGF-beta 1-expressing cells significantly declined and were predominantly found in fibroblasts in fibrotic areas. The expression of TGF-beta 1 protein was generally coincident with that for mRNA with the exception of bronchiolar epithelial cells in which strong protein expression was unaccompanied by a commensurate increase in mRNA. The study demonstrates that myofibroblasts, fibroblasts, and eosinophils represent the major sources of increased lung TGF-beta 1 expression in this model of pulmonary fibrosis.

A role for C-C chemokines in fibrotic lung disease

Pulmonary fibrosis is the end point of a chronic inflammatory process characterized by leukocyte recruitment and activation, fibroblast proliferation, and increased extracellular matrix production. Previous studies of models of pulmonary fibrosis have investigated the role of cytokines in the evolution of the fibrotic response. The involvement of tumor necrosis factor and interleukin-1 in bleomycin-induced lung injury, a model of idiopathic pulmonary fibrosis, has been well established, suggesting that cytokines mediate the initiation and maintenance of chronic inflammatory lesions. However, the aforementioned cytokines alone cannot account for the recruitment and activation of specific leukocyte populations found in the bleomycin model. Recently, a family of novel proinflammatory cytokines (chemokines) was cloned and characterized, yielding many putative mediators of leukocyte functions. Macrophage inflammatory protein-1 alpha (MIP-1 alpha) and monocyte chemoattractant protein-1 (MCP-1) belong to the C-C chemotactic cytokine family, a group of low-molecular-weight peptides. These molecules modulate chemotaxis, proliferation, and cytokine expression in leukocyte subsets. Our group has investigated the roles of MCP-1 and MIP-1 alpha in the bleomycin model. Both MCP-1 and MIP-1 alpha are expressed in a time-dependent manner after bleomycin challenge, and passive immunization of these animals with either anti-MIP-1 alpha or anti-MCP-1 antibodies attenuated leukocyte accumulation. In addition, we have identified specific cell types expressing MCP-1 or MIP-1 alpha by in situ hybridization and immunohistochemical localization, respectively. Furthermore, our results indicate that MIP-1 alpha expression is mediated by alveolar macrophage-derived tumor necrosis factor, identifying an important cytokine pathway in the initiation of pulmonary fibrosis. Finally, anti-MIP-1 alpha therapy attenuated fibrosis, providing direct evidence for its involvement in fibrotic pathology. Our work has clearly established that the C-C chemokines MCP-1 and MIP-1 alpha are expressed and contribute to the initiation and maintenance of the bleomycin-induced pulmonary lesion.

Lung monocyte chemoattractant protein-1 gene expression in bleomycin-induced pulmonary fibrosis

Recent studies indicate that monocyte chemoattractant protein-1 (MCP-1) may play an important role in pulmonary inflammation. In vitro studies show that a number of cell types are capable of producing MCP-1. In this study, MCP-1 expression in lungs of rats with bleomycin (BLM)-induced pulmonary fibrosis is examined to evaluate its cellular origin and potential role in pathogenesis. Lung fibrosis was induced in male Fisher 344 rats by endotracheal injection on day 0. On selected days after injection, lungs were harvested for in situ and Northern hybridization analyses for MCP-1 mRNA expression, immunochemical and histochemical analyses for MCP-1 protein expression, and identification of cell type. Northern analysis revealed significant elevation in lung MCP-1 mRNA expression beginning on day 3 post-BLM treatment, increasing to a peak on day 7, and then decreasing toward control levels after day 21. In situ hybridization combined with histochemical staining with chromotrope 2R indicate that most of the cells expressing MCP-1 mRNA at these time points are primarily eosinophils. A few scattered reactive fibroblasts, some mononuclear cells, epithelial cells, and cells of certain blood vessel walls also express this mRNA. Increased MCP-1 protein expression also was found to be predominantly within and adjacent to eosinophils. The eosinophils expressing this mRNA were found predominantly within areas of active fibrosis. The kinetics of increase in the number of cells expressing significant MCP-1 mRNA in lung sections paralleled that for MCP-1 mRNA expression, as assessed by Northern analysis. These results, for the first time, demonstrate that MCP-1 is up-regulated significantly in this rat animal model, and that infiltrating eosinophils represent the major cellular source for this increased MCP-1 expression.

Production and function of murine macrophage inflammatory protein-1 alpha in bleomycin-induced lung injury

We investigated the role of macrophage inflammatory protein-1 alpha (MIP-1 alpha) in bleomycin-induced lung injury, a model of interstitial lung disease. Bleomycin stimulates a T cell-dependent pulmonary inflammatory response characterized by an increase in leukocyte infiltration, fibroblast proliferation, and collagen synthesis. Intratracheal challenge of CBA/J mice with bleomycin resulted in a significant time-dependent increase in MIP-1 alpha protein levels both in whole-lung homogenates and bronchoalveolar lavage fluid. The kinetics of MIP-1 alpha expression were biphasic, with the first peak occurring at 2 days postinstillation and the second peak at 16 days. These levels of Ag expression temporally correlated with the accumulation of granulocytes, lymphocytes, and mononuclear phagocytes in the lung. In addition, immunohistochemical staining identified alveolar macrophages and bronchial epithelial cells as the primary cellular sources of MIP-1 alpha production. Interestingly, passive immunization of bleomycin-challenged mice with anti-MIP-1 alpha Abs significantly reduced pulmonary mononuclear phagocyte accumulation and fibrosis. These experiments establish that MIP-1 alpha protein is expressed in the lungs of bleomycin-treated mice and provide evidence that MIP-1 alpha promotes leukocyte accumulation and activation. Furthermore, these findings support the notion that leukocyte accumulation and activation are linked to fibrosis.

Lung monocyte chemoattractant protein-1 gene expression in bleomycin-induced pulmonary fibrosis

Recent studies indicate that monocyte chemoattractant protein-1 (MCP-1) may play an important role in pulmonary inflammation. In vitro studies show that a number of cell types are capable of producing MCP-1. In this study, MCP-1 expression in lungs of rats with bleomycin (BLM)-induced pulmonary fibrosis is examined to evaluate its cellular origin and potential role in pathogenesis. Lung fibrosis was induced in male Fisher 344 rats by endotracheal injection on day 0. On selected days after injection, lungs were harvested for in situ and Northern hybridization analyses for MCP-1 mRNA expression, immunochemical and histochemical analyses for MCP-1 protein expression, and identification of cell type. Northern analysis revealed significant elevation in lung MCP-1 mRNA expression beginning on day 3 post-BLM treatment, increasing to a peak on day 7, and then decreasing toward control levels after day 21. In situ hybridization combined with histochemical staining with chromotrope 2R indicate that most of the cells expressing MCP-1 mRNA at these time points are primarily eosinophils. A few scattered reactive fibroblasts, some mononuclear cells, epithelial cells, and cells of certain blood vessel walls also express this mRNA. Increased MCP-1 protein expression also was found to be predominantly within and adjacent to eosinophils. The eosinophils expressing this mRNA were found predominantly within areas of active fibrosis. The kinetics of increase in the number of cells expressing significant MCP-1 mRNA in lung sections paralleled that for MCP-1 mRNA expression, as assessed by Northern analysis. These results, for the first time, demonstrate that MCP-1 is up-regulated significantly in this rat animal model, and that infiltrating eosinophils represent the major cellular source for this increased MCP-1 expression.

Production and function of murine macrophage inflammatory protein-1 alpha in bleomycin-induced lung injury

We investigated the role of macrophage inflammatory protein-1 alpha (MIP-1 alpha) in bleomycin-induced lung injury, a model of interstitial lung disease. Bleomycin stimulates a T cell-dependent pulmonary inflammatory response characterized by an increase in leukocyte infiltration, fibroblast proliferation, and collagen synthesis. Intratracheal challenge of CBA/J mice with bleomycin resulted in a significant time-dependent increase in MIP-1 alpha protein levels both in whole-lung homogenates and bronchoalveolar lavage fluid. The kinetics of MIP-1 alpha expression were biphasic, with the first peak occurring at 2 days postinstillation and the second peak at 16 days. These levels of Ag expression temporally correlated with the accumulation of granulocytes, lymphocytes, and mononuclear phagocytes in the lung. In addition, immunohistochemical staining identified alveolar macrophages and bronchial epithelial cells as the primary cellular sources of MIP-1 alpha production. Interestingly, passive immunization of bleomycin-challenged mice with anti-MIP-1 alpha Abs significantly reduced pulmonary mononuclear phagocyte accumulation and fibrosis. These experiments establish that MIP-1 alpha protein is expressed in the lungs of bleomycin-treated mice and provide evidence that MIP-1 alpha promotes leukocyte accumulation and activation. Furthermore, these findings support the notion that leukocyte accumulation and activation are linked to fibrosis.

Myofibroblasts and their role in lung collagen gene expression during pulmonary fibrosis. A combined immunohistochemical and in situ hybridization study

Appearance of contractile filament-laden stromal cells or myofibroblasts is a characteristic of lung fibrotic lesions. The role of these cells in fibrosis and their cytoskeletal phenotype are not fully delineated. This study was undertaken to further investigate these issues using a model of lung fibrosis. Rats were treated endotracheally with bleomycin on day 0, and their lungs examined at various time points by in situ hybridization for alpha 1(I) procollagen mRNA expression and by immunohistochemistry for desmin and alpha-smooth muscle actin expression. The results show an increase in the number of cells resembling fibroblasts and strongly positive for alpha-smooth muscle actin, desmin and procollagen mRNA expression in lungs of animals treated with bleomycin, with the increase being maximal between days 7 and 14 after bleomycin treatment. Two types of newly positive cells could be discerned. The first expressing alpha-smooth muscle actin, desmin, and procollagen mRNA was localized in active fibrotic lesions. The second expressing only alpha-smooth muscle actin and procollagen mRNA was localized in fibrotic submesothelial areas. Almost all of the newly reactive alpha-smooth muscle actin-positive cells strongly express procollagen mRNA, and they constituted most of the cells actively expressing procollagen. These findings suggest that the newly appearing myofibroblast characterized by alpha-smooth muscle actin and/or desmin expression may be responsible for most if not all of the increased lung collagen gene expression in pulmonary fibrosis.

Evaluation of quantitative magnetic resonance imaging as a noninvasive technique for measuring renal scarring in a rabbit model of antiglomerular basement membrane disease

Renal function tests are an insensitive means of detecting progressive scarring of the kidney such as occurs in chronic allograft rejection and lupus nephritis. Alternative approaches for the measurement of small progressive changes in renal structure on a repetitive basis are needed. Quantitative magnetic resonance imaging (proton T1 relaxation time) was assessed for this purpose. A rabbit model of antiglomerular basement membrane disease that develops glomerular and interstitial inflammation followed by scarring of the renal cortex was used. Longitudinal studies of cortical T1 showed a marked prolongation of T1 during the initial inflammation and edema associated with glomerular crescent formation (Day 7). The T1 remained prolonged up to Day 120 in animals with significant fibrosis and crescent formation when the wet/dry weight ratio (a measure of edema) had returned to baseline. T1 was a more sensitive index of renal injury than was serum creatinine for all of the end points measured (cortical hydroxyproline per dry weight, percent crescent formation, or histologic fibrosis score). It was concluded from these studies that measurement of renal cortical T1 is quite a sensitive index of renal injury, probably more sensitive than the measurement of serum creatinine, but that this method does not discriminate between edema and scarring.

In situ hybridization analysis of rat lung alpha 1(I) and alpha 2(I) collagen gene expression in pulmonary fibrosis induced by endotracheal bleomycin injection

BACKGROUND

Endotracheal bleomycin administration in rats and other animal species causes rapid development of pulmonary fibrosis, characterized by a transiently increased number of contractile, filament-laden parenchymal cells and increased lung collagen synthesis and deposition. However, the identity and source of the cells that actively synthesize collagen and other extracellular matrix and their relationship to the altered lung structure and function remain uncertain.

EXPERIMENTAL DESIGN

In this study, the cells expressing alpha 1(I) and alpha 2(I) procollagen genes were identified and their localization analyzed in control and bleomycin-treated rat lungs at different time points, by in situ and Northern hybridization analyses.

RESULTS

In control lungs, only a few scattered fibroblasts with weak expression of the alpha 1(I) procollagen gene were localized exclusively in the adventitia of the primary and tertiary bronchi, as well as major blood vessels. At day 3 after bleomycin treatment, scattered interstitial cells with significantly increased alpha 1(I) and alpha 2(I) procollagen gene expression were observed in the adventitia of bronchioles, terminal bronchioles, and adjacent small blood vessels. At days 7 and 14, there was a dramatic increase in the number of interstitial cells expressing large amounts of alpha 1(I) procollagen messenger RNA in these areas and extending to the lung parenchyma. This was followed on days 21 and 28 by significant decreases in procollagen gene expression and the number of cells with increased collagen gene expression. Most of the cells with enhanced collagen gene expression were arrayed in a disorganized fashion and were localized mainly around bronchioles, terminal bronchioles, and adjacent small blood vessels as well as in the irregularly distributed fibrotic foci, some submesothelial areas, and injured parenchyma. Northern blot analysis was consistent with the above in situ hybridization observation of the kinetics of collagen gene expression.

CONCLUSIONS

The results indicate that in this rat fibrosis model, increased numbers of the interstitial cells with high expression of type I procollagen genes are derived primarily from the fibroblasts in the adventitia of bronchioles, terminal bronchioles, and adjacent blood vessels, as well as the submesothelial region. This then can result in further expansion to adjacent parenchyma and alveolar areas.

Phenotypic differences in cytokine responsiveness of hypertrophic scar versus normal dermal fibroblasts

The alteration of normal dermal fibroblast function that leads to the development of hypertrophic scar after thermal injury is unknown. To determine functional differences that might explain this process, fibroblasts were cultured from biopsies of post-thermal injury mature hypertrophic scars and patient-matched normal skin. The mitogenic responses of scar cells to fetal bovine serum, epidermal growth factor (EGF), platelet-derived growth factor (PDGF), and tumor necrosis factor alpha (TNF alpha) were determined and compared to normal skin cells. Collagen synthetic rate was also compared in the presence and absence of transforming growth factor beta 1 (TGF beta 1). Whereas both scar and normal cells responded with increased thymidine uptake to serum and cytokines, the stimulation to EGF and serum was significantly lower in scar cells. In contrast, synthesis of collagen, but not of non-collagenous proteins, was increased in scar relative to normal cells, both basally and when stimulated with low doses of TGF beta 1. Additionally, the fraction of protein synthesized as collagen was significantly higher in scar fibroblasts. These results suggest that fibroblasts from hypertrophic scars demonstrate stable phenotypic differences in cytokine responsiveness in comparison to cells from unaffected skin. The increased rate of collagen synthesis and decreased responsiveness to mitogens are consistent with the increased extracellular matrix content and decreased cellularity of hypertrophic scars.

Regulation of rat pulmonary endothelial cell interleukin-6 production by bleomycin: effects of cellular fatty acid composition

Previous studies have shown upregulation of lung cell interleukin-6 (IL-6) production in bleomycin-induced pulmonary fibrosis. To further elucidate the regulatory mechanisms governing this disease, the effects of bleomycin on the production of the pleiotropic cytokine, IL-6, were investigated in lung endothelial cells. Rat pulmonary artery endothelial cells were treated with bleomycin at doses previously shown to be effective in upregulating cytokine production in these cells, and the conditioned media was collected and assayed for IL-6 activity. The results show that these endothelial cells constitutively produced IL-6 and that bleomycin increased the production in a time- and dose-dependent manner. Feeding rats diets deficient in n-6 fatty acids is known to ameliorate bleomycin-induced lung fibrosis. In order to examine if fatty acids could modulate IL-6 production in vitro, cells were lipid depleted and then supplemented with 18:1n-9, 18:2n-6, or 18:3n-3 fatty acids, and the effects of bleomycin on IL-6 production reexamined. This regimen resulted in significant depletion of arachidonate in the 18:1n-9 and 18:3n-3 supplemented cells, which was associated with significantly reduced IL-6 production relative to the 18:2n-6-supplemented cells, both constitutively and when stimulated with bleomycin. Preincubation with indomethacin did not significantly inhibit the production of IL-6 by all three groups of cells, nor did supplementation with a stable prostacyclin analog increase IL-6 production. These results suggest that endothelial cell IL-6 production is not directly dependent on prostacyclin or other cyclooxygenase metabolites but may require or be upregulated by 18:2n-6 and/or metabolites derived from it.(ABSTRACT TRUNCATED AT 250 WORDS)

Expression of monocyte chemoattractant protein-1 (MCP-1) by rat alveolar macrophages during chronic lung injury

Using a well-characterized model of bleomycin-induced pulmonary fibrosis in the rat, we determined that there was a time-dependent elaboration of monocyte chemotactic activity in bronchoalveolar lavage fluid. Northern hybridization analysis revealed markedly increased expression of rat monocyte chemoattractant protein-1 (MCP-1) mRNA in alveolar macrophages (AMs) from rats following induction of pulmonary fibrosis. Monocyte chemotactic activity was also significantly increased in conditioned media from AMs retrieved from injured rat lungs. These data suggest that one important role of AMs in the pathogenesis of chronic inflammatory lung injury and pulmonary fibrosis is the regulation of monocyte recruitment and activation within the lung secondary to secretion of monocyte chemoattractants including MCP-1.

Urine transforming growth factor-beta activity is related to the degree of scarring in crescentic nephritis in the rabbit

Crescentic nephritis was induced in rabbits by injection of antirabbit glomerular basement membrane (GBM) antibodies. Urine samples were obtained by catheterization and assayed for transforming growth factor-beta (TGF-beta) activity. On day 31, all animals were sacrificed for evaluation of renal cortical histopathology and collagen content. The results show that control rabbit urine contains measurable amounts of TGF-beta. Urine TGF-beta activity was expressed in relation to urine creatinine concentration to correct for variation in urine concentration. When expressed in this manner, urine TGF-beta activity increased from day 2 onwards, peaked on day 7 and returned to normal levels after day 14. This time course is identical to that previously seen for the cortical and glomerular production of TGF-beta in the same model. Furthermore, when the normalized TGF-beta values for each animal were compared to their respective fibrosis parameters on day 31, significant correlations were observed for the values of urine TGF-beta activities on day 7 and all indices of fibrosis. These results suggest that measurements of urine TGF-beta activity at certain critical stages of disease could be useful in predicting the progression to end-stage renal disease with fibrosis and might serve as a helpful noninvasive adjunct in monitoring response to therapy.

Expression and regulation of human pulmonary fibroblast-derived monocyte chemotactic peptide-1

Monocyte recruitment is essential for maintenance of normal pulmonary macrophage populations. In addition, acute and chronic inflammatory pulmonary diseases are associated with sequestration of mononuclear phagocytes in the lung. Although alveolar macrophages (AM phi) can secrete a number of potent inflammatory and chemoattractment mediators, these immune cells do not produce monocyte chemotactic peptide (MCP-1) in response to lipopolysaccharide (LPS), tumor necrosis factor (TNF), or interleukin-1 beta (IL-1 beta). The pulmonary fibroblast (PF) may play a pivotal role in monocyte recruitment. In these studies, we demonstrate a time- and dose-dependent production of PF-derived steady-state MCP-1 mRNA, MCP-1 antigen, and monocyte chemotactic bioactivity attributable to MCP-1. In cellular models examining cytokine networks between AM phi and PF, LSP-stimulated AM phi (conditioned media) induced PF-derived steady-state MCP-1 mRNA expression that was markedly attenuated by the presence of neutralizing TNF and IL-1 beta antibodies. Furthermore, we showed the dose- and time-dependent suppression of IL-1 beta-stimulated PF-derived MCP-1 by dexamethasone and prostaglandin E2. These findings demonstrated that PF are an important cellular source of MCP-1 and this production of MCP-1 may be influenced by immunomodulators.

Regulation of rat pulmonary artery endothelial cell transforming growth factor-beta production by IL-1 beta and tumor necrosis factor-alpha

Recent studies suggest that transforming growth factor-beta (TGF-beta) production is up-regulated at sites of tissue injury, inflammation and repair, or fibrosis. Endothelial cells represent a potentially important in vivo source of TGF-beta; however, the identity of endogenous modulators of TGF-beta production by these cells remains unclear. To address this issue, the effects of the cytokines, IL-1 beta, and TNF-alpha on TGF-beta production by rat pulmonary artery endothelial cells were examined. Conditioned media from cells treated with 0 to 20 ng/ml IL-1 beta and/or TNF-alpha were assayed for TGF-beta activity using a mink lung epithelial cell line. The results show that rat pulmonary artery endothelial cells secreted undetectable amounts of active TGF-beta in the absence of cytokines. However, upon acidification of the conditioned media before assay, a time-dependent increase in TGF-beta activity was noted in media from both untreated and cytokine-treated cells. However, both IL-1 beta and TNF-alpha treatment caused the secretion of significantly greater amounts of TGF-beta activity than control cells, in a dose-dependent manner, with maximal response obtained at cytokine doses of greater than 10 ng/ml. At equivalent doses of cytokine tested, the magnitude of the response was significantly greater with IL-1 beta. These responses were paralleled by increases in steady state mRNA levels for TGF-beta 1. Addition of both cytokines resulted in a synergistic response. Synergism with IL-1 beta was also noted with the fibrogenic agent bleomycin. Kinetic studies indicated that a minimum of 4 h of treatment with either IL-1 beta or TNF-alpha was required for detection of significant increases in either secreted TGF-beta activity or steady state TGF-beta 1 mRNA levels. Thus, endothelial cells could play a role in various TGF-beta-dependent processes in vivo, in situations wherein IL-1 beta and/or TNF-alpha may be present at comparable concentrations.

Regulation of rat pulmonary artery endothelial cell transforming growth factor-beta production by IL-1 beta and tumor necrosis factor-alpha

Recent studies suggest that transforming growth factor-beta (TGF-beta) production is up-regulated at sites of tissue injury, inflammation and repair, or fibrosis. Endothelial cells represent a potentially important in vivo source of TGF-beta; however, the identity of endogenous modulators of TGF-beta production by these cells remains unclear. To address this issue, the effects of the cytokines, IL-1 beta, and TNF-alpha on TGF-beta production by rat pulmonary artery endothelial cells were examined. Conditioned media from cells treated with 0 to 20 ng/ml IL-1 beta and/or TNF-alpha were assayed for TGF-beta activity using a mink lung epithelial cell line. The results show that rat pulmonary artery endothelial cells secreted undetectable amounts of active TGF-beta in the absence of cytokines. However, upon acidification of the conditioned media before assay, a time-dependent increase in TGF-beta activity was noted in media from both untreated and cytokine-treated cells. However, both IL-1 beta and TNF-alpha treatment caused the secretion of significantly greater amounts of TGF-beta activity than control cells, in a dose-dependent manner, with maximal response obtained at cytokine doses of greater than 10 ng/ml. At equivalent doses of cytokine tested, the magnitude of the response was significantly greater with IL-1 beta. These responses were paralleled by increases in steady state mRNA levels for TGF-beta 1. Addition of both cytokines resulted in a synergistic response. Synergism with IL-1 beta was also noted with the fibrogenic agent bleomycin. Kinetic studies indicated that a minimum of 4 h of treatment with either IL-1 beta or TNF-alpha was required for detection of significant increases in either secreted TGF-beta activity or steady state TGF-beta 1 mRNA levels. Thus, endothelial cells could play a role in various TGF-beta-dependent processes in vivo, in situations wherein IL-1 beta and/or TNF-alpha may be present at comparable concentrations.