Mesenchymal cells isolated after acute lung injury manifest an enhanced proliferative phenotype

Hypoxia enhances IPF mesenchymal progenitor cell fibrogenicity via the lactate/GPR81/HIF1α pathway

Hypoxia is a sentinel feature of idiopathic pulmonary fibrosis (IPF). The IPF microenvironment contains high lactate levels, and hypoxia enhances cellular lactate production. Lactate, acting through the GPR81 lactate receptor, serves as a signal molecule regulating cellular processes. We previously identified intrinsically fibrogenic mesenchymal progenitor cells (MPCs) that drive fibrosis in the lungs of patients with IPF. However, whether hypoxia enhances IPF MPC fibrogenicity is unclear. We hypothesized that hypoxia increases IPF MPC fibrogenicity via lactate and its cognate receptor GPR81. Here we show that hypoxia promotes IPF MPC self-renewal. The mechanism involves hypoxia-mediated enhancement of LDHA function and lactate production and release. Hypoxia also increases HIF1α levels, and this increase in turn augments the expression of GPR81. Exogenous lactate operating through GPR81 promotes IPF MPC self-renewal. IHC analysis of IPF lung tissue demonstrates IPF MPCs expressing GPR81 and hypoxic markers on the periphery of the fibroblastic focus. We show that hypoxia enhances IPF MPC fibrogenicity in vivo. We demonstrate that knockdown of GPR81 inhibits hypoxia-induced IPF MPC self-renewal in vitro and attenuates hypoxia-induced IPF MPC fibrogenicity in vivo. Our data demonstrate that hypoxia creates a feed-forward loop that augments IPF MPC fibrogenicity via the lactate/GPR81/HIF1α pathway.

Tackling MARCKS-PIP3 circuit attenuates fibroblast activation and fibrosis progression

Targeting activated fibroblasts, including myofibroblast differentiation, has emerged as a key therapeutic strategy in patients with idiopathic pulmonary fibrosis (IPF). However, there is no available therapy capable of selectively eradicating myofibroblasts or limiting their genesis. Through an integrative analysis of the regulator genes that are responsible for the activation of IPF fibroblasts, we noticed the phosphatidylinositol 4,5-bisphosphate (PIP2)-binding protein, myristoylated alanine-rich C-kinase substrate (MARCKS), as a potential target molecule for IPF. Herein, we have employed a 25-mer novel peptide, MARCKS phosphorylation site domain sequence (MPS), to determine if MARCKS inhibition reduces pulmonary fibrosis through the inactivation of PI3K/protein kinase B (AKT) signaling in fibroblast cells. We first observed that higher levels of MARCKS phosphorylation and the myofibroblast marker α-smooth muscle actin (α-SMA) were notably overexpressed in all tested IPF lung tissues and fibroblast cells. Treatment with the MPS peptide suppressed levels of MARCKS phosphorylation in primary IPF fibroblasts. A kinetic assay confirmed that this peptide binds to phospholipids, particularly PIP2, with a dissociation constant of 17.64 nM. As expected, a decrease of phosphatidylinositol (3,4,5)-trisphosphate pools and AKT activity occurred in MPS-treated IPF fibroblast cells. MPS peptide was demonstrated to impair cell proliferation, invasion, and migration in multiple IPF fibroblast cells in vitro as well as to reduce pulmonary fibrosis in bleomycin-treated mice in vivo. Surprisingly, we found that MPS peptide decreases α-SMA expression and synergistically interacts with nintedanib treatment in IPF fibroblasts. Our data suggest MARCKS as a druggable target in pulmonary fibrosis and also provide a promising antifibrotic agent that may lead to effective IPF treatments.-Yang, D. C., Li, J.-M., Xu, J., Oldham, J., Phan, S. H., Last, J. A., Wu, R., Chen, C.-H. Tackling MARCKS-PIP3 circuit attenuates fibroblast activation and fibrosis progression.

FoxO3 an important player in fibrogenesis and therapeutic target for idiopathic pulmonary fibrosis

Idiopathic pulmonary fibrosis (IPF) is a progressive and fatal parenchymal lung disease with limited therapeutic options, with fibroblast-to-myofibroblast transdifferentiation and hyperproliferation playing a major role. Investigating ex vivo-cultured (myo)fibroblasts from human IPF lungs as well as fibroblasts isolated from bleomycin-challenged mice, Forkhead box O3 (FoxO3) transcription factor was found to be less expressed, hyperphosphorylated, and nuclear-excluded relative to non-diseased controls. Downregulation and/or hyperphosphorylation of FoxO3 was reproduced by exposure of normal human lung fibroblasts to various pro-fibrotic growth factors and cytokines (FCS, PDGF, IGF1, TGF-β1). Moreover, selective knockdown of FoxO3 in the normal human lung fibroblasts reproduced the transdifferentiation and hyperproliferation phenotype. Importantly, mice with global- (Foxo3-/-) or fibroblast-specific (Foxo3f.b-/-) FoxO3 knockout displayed enhanced susceptibility to bleomycin challenge, with augmented fibrosis, loss of lung function, and increased mortality. Activation of FoxO3 with UCN-01, a staurosporine derivative currently investigated in clinical cancer trials, reverted the IPF myofibroblast phenotype in vitro and blocked the bleomycin-induced lung fibrosis in vivo These studies implicate FoxO3 as a critical integrator of pro-fibrotic signaling in lung fibrosis and pharmacological reconstitution of FoxO3 as a novel treatment strategy.

The Role of TGF-β in the Association Between Primary Graft Dysfunction and Bronchiolitis Obliterans Syndrome

Primary graft dysfunction (PGD) is a possible risk factor for bronchiolitis obliterans syndrome (BOS) following lung transplantation; however, the mechanism for any such association is poorly understood. Based on the association of TGF-β with acute and chronic inflammatory disorders, we hypothesized that it might play a role in the continuum between PGD and BOS. Thus, the association between PGD and BOS was assessed in a single-center cohort of lung transplant recipients. Bronchoalveolar lavage fluid concentrations of TGF-β and procollagen collected within 24 h of transplantation were compared across the spectrum of PGD, and incorporated into Cox models of BOS. Immunohistochemistry localized expression of TGF-β and its receptor in early lung biopsies posttransplant. We found an association between PGD and BOS in both bilateral and single lung recipients with a hazard ratio of 3.07 (95% CI 1.76-5.38) for the most severe form of PGD. TGF-β and procollagen concentrations were elevated during PGD (p < 0.01), and associated with increased rates of BOS. Expression of TGF-β and its receptor localized to allograft infiltrating mononuclear and stromal cells, and the airway epithelium. These findings validate the association between PGD and the subsequent development of BOS, and suggest that this association may be mediated by receptor/TGF-β biology.

miR-210 promotes IPF fibroblast proliferation in response to hypoxia

Idiopathic pulmonary fibrosis (IPF) is characterized by the relentless spread of fibroblasts from scarred alveoli into adjacent alveolar units, resulting in progressive hypoxia and death by asphyxiation. Although hypoxia is a prominent clinical feature of IPF, the role of hypoxia as a driver of the progressive fibrotic nature of the disease has not been explored. Here, we demonstrate that hypoxia robustly stimulates the proliferation of IPF fibroblasts. We found that miR-210 expression markedly increases in IPF fibroblasts in response to hypoxia and that knockdown of miR-210 decreases hypoxia-induced IPF fibroblast proliferation. Silencing hypoxia-inducible factor (HIF)-2α inhibits the hypoxia-mediated increase in miR-210 expression and blocks IPF fibroblast proliferation, indicating that HIF-2α is upstream of miR-210. We demonstrate that the miR-210 downstream target MNT is repressed in hypoxic IPF fibroblasts and that knockdown of miR-210 increases MNT expression. Overexpression of MNT inhibits hypoxia-induced IPF fibroblast proliferation. Together, these data indicate that hypoxia potently stimulates miR-210 expression via HIF-2α, and high miR-210 expression drives fibroblast proliferation by repressing the c-myc inhibitor, MNT. In situ analysis of IPF lung tissue demonstrates miR-210 expression in a similar distribution with HIF-2α and the hypoxic marker carbonic anhydrase-IX in cells within the IPF fibrotic reticulum. Our results raise the possibility that a pathological feed-forward loop exists in the IPF lung, in which hypoxia promotes IPF fibroblast proliferation via stimulation of miR-210 expression, which in turn worsens hypoxia.

Identification of a cell-of-origin for fibroblasts comprising the fibrotic reticulum in idiopathic pulmonary fibrosis

Idiopathic pulmonary fibrosis (IPF) is a progressive disease of the middle aged and elderly with a prevalence of one million persons worldwide. The fibrosis spreads from affected alveoli into contiguous alveoli, creating a reticular network that leads to death by asphyxiation. Lung fibroblasts from patients with IPF have phenotypic hallmarks, distinguishing them from their normal counterparts: pathologically activated Akt signaling axis, increased collagen and α-smooth muscle actin expression, distinct gene expression profile, and ability to form fibrotic lesions in model organisms. Despite the centrality of these fibroblasts in disease pathogenesis, their origin remains uncertain. Here, we report the identification of cells in the lungs of patients with IPF with the properties of mesenchymal progenitors. In contrast to progenitors isolated from nonfibrotic lungs, IPF mesenchymal progenitor cells produce daughter cells manifesting the full spectrum of IPF hallmarks, including the ability to form fibrotic lesions in zebrafish embryos and mouse lungs, and a transcriptional profile reflecting these properties. Morphological analysis of IPF lung tissue revealed that mesenchymal progenitor cells and cells with the characteristics of their progeny comprised the fibrotic reticulum. These data establish that the lungs of patients with IPF contain pathological mesenchymal progenitor cells that are cells of origin for fibrosis-mediating fibroblasts. These fibrogenic mesenchymal progenitors and their progeny represent an unexplored target for novel therapies to interdict fibrosis.

Epigenetic regulation of Thy-1 gene expression by histone modification is involved in lipopolysaccharide-induced lung fibroblast proliferation

Lipopolysaccharide (LPS)-induced pulmonary fibrosis is characterized by aberrant proliferation and activation of lung fibroblasts. Epigenetic regulation of thymocyte differentiation antigen 1 (Thy-1) is associated with lung fibroblast phenotype transformation that results in aberrant cell proliferation. However, it is not clear whether the epigenetic regulation of Thy-1 expression is required for LPS-induced lung fibroblast proliferation. To address this issue and better understand the relative underlying mechanisms, we used mouse lung fibroblasts as model to observe the changes of Thy-1 expression and histone deacetylation after LPS challenge. The results showed that cellular DNA synthesis, measured by BrdU incorporation, was impacted less in the early stage (24 hrs) after the challenge of LPS, but significantly increased at 48 or 72 hrs after the challenge of LPS. Meanwhile, Thy-1 expression, which was detected by real-time PCR and Western blot, in lung fibroblasts decreased with increased time after LPS challenge and diminished at 72 hrs. We also found that the acetylation of either histone H3 or H4 decreased in the LPS-challenged lung fibroblasts. ChIP assay revealed that the acetylation of histone H4 (Ace-H4) decreased in the Thy-1 promoter region in response to LPS. In addition, all the above changes could be attenuated by depletion of TLR4 gene. Our studies indicate that epigenetic regulation of Thy-1 gene expression by histone modification is involved in LPS-induced lung fibroblast proliferation.

Low α(2)β(1) integrin function enhances the proliferation of fibroblasts from patients with idiopathic pulmonary fibrosis by activation of the β-catenin pathway

Idiopathic pulmonary fibrosis (IPF) is a progressive and incurable fibroproliferative disorder characterized by unrelenting proliferation of fibroblasts and their deposition of collagen within alveoli, resulting in permanently scarred, nonfunctional airspaces. Normally, polymerized collagen suppresses fibroblast proliferation and serves as a physiological restraint to limit fibroproliferation after tissue injury. The IPF fibroblast, however, is a pathologically altered cell that has acquired the capacity to elude the proliferation-suppressive effects of polymerized collagen. The mechanism for this phenomenon remains incompletely understood. Here, we demonstrate that expression of α(2)β(1) integrin, a major collagen receptor, is pathologically low in IPF fibroblasts interacting with polymerized collagen. Low integrin expression in IPF fibroblasts is associated with a failure to induce PP2A phosphatase activity, resulting in abnormally high levels of phosphorylated (inactive) GSK-3β and high levels of active β-catenin in the nucleus. Knockdown of β-catenin in IPF fibroblasts inhibits their ability to proliferate on collagen. Interdiction of α(2)β(1) integrin in control fibroblasts reproduces the IPF phenotype and leads to the inability of these cells to activate PP2A, resulting in high levels of phosphorylated GSK-3β and active β-catenin and in enhanced proliferation on collagen. Our findings indicate that the IPF fibroblast phenotype is characterized by low α(2)β(1) integrin expression, resulting in a failure of integrin to activate PP2A phosphatase, which permits inappropriate activation of the β-catenin pathway.

Lipopolysaccharide induces lung fibroblast proliferation through Toll-like receptor 4 signaling and the phosphoinositide3-kinase-Akt pathway

Pulmonary fibrosis is characterized by lung fibroblast proliferation and collagen secretion. In lipopolysaccharide (LPS)-induced acute lung injury (ALI), aberrant proliferation of lung fibroblasts is initiated in early disease stages, but the underlying mechanism remains unknown. In this study, we knocked down Toll-like receptor 4 (TLR4) expression in cultured mouse lung fibroblasts using TLR4-siRNA-lentivirus in order to investigate the effects of LPS challenge on lung fibroblast proliferation, phosphoinositide3-kinase (PI3K)-Akt pathway activation, and phosphatase and tensin homolog (PTEN) expression. Lung fibroblast proliferation, detected by BrdU assay, was unaffected by 1 mug/mL LPS challenge up to 24 hours, but at 72 hours, cell proliferation increased significantly. This proliferation was inhibited by siRNA-mediated TLR4 knockdown or treatment with the PI3K inhibitor, Ly294002. In addition, siRNA-mediated knockdown of TLR4 inhibited the LPS-induced up-regulation of TLR4, down-regulation of PTEN, and activation of the PI3K-Akt pathway (overexpression of phospho-Akt) at 72 hours, as detected by real-time PCR and Western blot analysis. Treatment with the PTEN inhibitor, bpV(phen), led to activation of the PI3K-Akt pathway. Neither the baseline expression nor LPS-induced down-regulation of PTEN in lung fibroblasts was influenced by PI3K activation state. PTEN inhibition was sufficient to exert the LPS effect on lung fibroblast proliferation, and PI3K-Akt pathway inhibition could reverse this process. Collectively, these results indicate that LPS can promote lung fibroblast proliferation via a TLR4 signaling mechanism that involves PTEN expression down-regulation and PI3K-Akt pathway activation. Moreover, PI3K-Akt pathway activation is a downstream effect of PTEN inhibition and plays a critical role in lung fibroblast proliferation. This mechanism could contribute to, and possibly accelerate, pulmonary fibrosis in the early stages of ALI/ARDS.

Endothelial colony-forming cells and mesenchymal stem cells from ECMO circuits of term infants

OBJECTIVE

Endothelial progenitor cells (EPCs) have been examined in numerous adult diseases and have been suggested as a cellular-based therapy. However, there are no reports describing EPCs being isolated from newborn peripheral blood.

STUDY DESIGN

Endothelial colony-forming cells (ECFCs), a subtype of EPCs, were isolated from blood collected from 12 neonatal extracorporeal membrane oxygenation (ECMO) circuits.

RESULT

ECFCs were isolated in all samples. We unexpectedly isolated a distinctly different colony of mesenchymal stem cells (MSCs) in seven samples. Both cell types expressed the expected endothelial or mesenchymal cell surface antigens.

CONCLUSION

To our knowledge, this is the first report of ECFCs and MSCs isolated from peripheral blood of critically ill term newborns. Both cells types may be mobilized in response to critical illness or to the ECMO circuit. Further studies evaluating the role of stem cells in various newborn conditions are warranted.

Pathologic caveolin-1 regulation of PTEN in idiopathic pulmonary fibrosis

Idiopathic pulmonary fibrosis (IPF) is a progressive fibroproliferative disorder refractory to current pharmacological therapies. Fibroblasts isolated from IPF patients display pathological activation of PI3K/Akt caused by low PTEN phosphatase activity. This enables these cells to escape the negative proliferative properties of polymerized collagen. The mechanism underlying low PTEN activity in IPF fibroblasts is unclear, but our prior studies indicate that membrane-associated PTEN expression is decreased in these cells. Caveolin-1 is an integral membrane protein whose expression is decreased in IPF lung tissue, but how low caveolin-1 contributes to pathological fibrosis is incompletely understood. The objective of this study was to examine the hypothesis that caveolin-1 regulates PTEN function in IPF fibroblasts. Here we demonstrate that caveolin-1 expression is a determinant of membrane PTEN levels and show that PTEN interacts with caveolin-1 via its caveolin-1-binding sequence. We demonstrate that caveolin-1 expression is low in IPF fibroblasts and that this correlates with low membrane PTEN levels, whereas overexpression of caveolin-1 restores membrane PTEN levels, inhibits Akt phosphorylation, and suppresses proliferation. We demonstrate that caveolin-1 and PTEN expression are low in myofibroblasts within IPF fibroblastic foci. These data indicate that IPF fibroblasts display low caveolin-1 expression, which results in low membrane-associated PTEN expression. This creates a membrane microenvironment depleted of inhibitory phosphatase activity, facilitating the aberrant activation PI3K/Akt and pathological proliferation.

Pathological integrin signaling enhances proliferation of primary lung fibroblasts from patients with idiopathic pulmonary fibrosis

Idiopathic pulmonary fibrosis (IPF) is a relentlessly progressive lung disease in which fibroblasts accumulate in the alveolar wall within a type I collagen–rich matrix. Although lung fibroblasts derived from patients with IPF display durable pathological alterations in proliferative function, the molecular mechanisms differentiating IPF fibroblasts from their normal counterparts remain unknown. Polymerized type I collagen normally inhibits fibroblast proliferation, providing a physiological mechanism to limit fibroproliferation after tissue injury. We demonstrate that β1 integrin interaction with polymerized collagen inhibits normal fibroblast proliferation by suppression of the phosphoinositide 3-kinase (PI3K)–Akt–S6K1 signal pathway due to maintenance of high phosphatase activity of the tumor suppressor phosphatase and tensin homologue (PTEN). In contrast, IPF fibroblasts eluded this restraint, displaying a pathological pattern of β1 integrin signaling in response to polymerized collagen that leads to aberrant activation of the PI3K–Akt–S6K1 signal pathway caused by inappropriately low PTEN activity. Mice deficient in PTEN showed a prolonged fibroproliferative response after tissue injury, and immunohistochemical analysis of IPF lung tissue demonstrates activation of Akt in cells within fibrotic foci. These results provide direct evidence for defective negative regulation of the proliferative pathway in IPF fibroblasts and support the theory that the pathogenesis of IPF involves an intrinsic fibroblast defect.

Prostaglandin E2 mediates IL-1beta-related fibroblast mitogenic effects in acute lung injury through differential utilization of prostanoid receptors

The fibroproliferative response to acute lung injury (ALI) results in severe, persistent respiratory dysfunction. We have reported that IL-1beta is elevated in pulmonary edema fluid in those with ALI and mediates an autocrine-acting, fibroblast mitogenic pathway. In this study, we examine the role of IL-1beta-mediated induction of cyclooxygenase-2 and PGE2, and evaluate the significance of individual E prostanoid (EP) receptors in mediating the fibroproliferative effects of IL-1beta in ALI. Blocking studies on human lung fibroblasts indicate that IL-1beta is the major cyclooxygenase-2 mRNA and PGE2-inducing factor in pulmonary edema fluid and accounts for the differential PGE2 induction noted in samples from ALI patients. Surprisingly, we found that PGE2 produced by IL-1beta-stimulated fibroblasts enhances fibroblast proliferation. Further studies revealed that the effect of fibroblast proliferation is biphasic, with the promitogenic effect of PGE2 noted at concentrations close to that detected in pulmonary edema fluid from ALI patients. The suppressive effects of PGE2 were mimicked by the EP2-selective receptor agonist, butaprost, by cAMP activation, and were lost in murine lung fibroblasts that lack EP2. Conversely, the promitogenic effects of mid-range concentrations of PGE2 were mimicked by the EP3-selective agent, sulprostone, by cAMP reduction, and lost upon inhibition of Gi-mediated signaling with pertussis toxin. Taken together, these data demonstrate that PGE2 can stimulate or inhibit fibroblast proliferation at clinically relevant concentrations, via preferential signaling through EP3 or EP2 receptors, respectively. Such mechanisms may drive the fibroproliferative response to ALI.

Constitutive activation of prosurvival signaling in alveolar mesenchymal cells isolated from patients with nonresolving acute respiratory distress syndrome

Acute respiratory distress syndrome (ARDS) is a clinical syndrome characterized by stereotypic host inflammatory and repair cellular responses; however, mechanisms regulating the resolution of ARDS are poorly understood. Here, we report the isolation and characterization of a novel population of mesenchymal cells from the alveolar space of ARDS patients via fiber-optic bronchoscopy with bronchoalveolar lavage (BAL). BAL was performed on 17 patients during the course of ARDS. Immunofluorescence staining and multiparameter flow cytometric analysis defined a population of alveolar mesenchymal cells (AMCs) that are CD45-/prolyl-4-hydroxylase+/alpha-smooth muscle actin+/-. AMCs proliferated in ex vivo cell culture for multiple passages; early passage (3-5) cells were subsequently analyzed in 13 patients. AMCs isolated from patients with persistent or nonresolving ARDS (ARDS-NR, n = 4) demonstrate enhanced constitutive activation of prosurvival signaling pathways involving PKB/Akt, FKHR, and BCL-2 family proteins compared with AMCs from patients with resolving ARDS (ARDS-R, n = 9). Exogenous transforming growth factor-beta1 markedly induces PKB/Akt activation in AMCs from ARDS-R. ARDS-NR cells are more resistant to serum deprivation-induced apoptosis compared with ARDS-R. This study identifies a novel population of mesenchymal cells that can be isolated from the alveolar spaces of ARDS patients. AMCs in patients with ARDS-NR acquire an activational profile characterized by enhanced prosurvival signaling and an antiapoptotic phenotype. These findings support the concept that apoptosis of mesenchymal cells may be an essential component of normal repair and resolution of ARDS and suggest that dysregulation of this process may contribute to persistent ARDS.

Pulmonary edema fluid from patients with early lung injury stimulates fibroblast proliferation through IL-1 beta-induced IL-6 expression

Although the fibroproliferative response to lung injury occurs with a high frequency in patients with clinical acute lung injury, the mechanisms that initiate this response are largely unknown. This study was undertaken first to identify fibroblast mitogenic factors in pulmonary edema fluid, and second to examine the human lung fibroblast's gene expression profile in response to pulmonary edema fluid. The edema fluid obtained from patients with early lung injury has an eightfold higher concentration of IL-1beta and a twofold greater IL-1beta-dependent mitogenic effect than does fluid obtained from control patients with hydrostatic pulmonary edema. Furthermore, fibroblasts responded to acute lung injury patient-derived edema fluid through production of soluble mediators that possess an autocrine mitogenic effect. Gene array analysis reveals that acute lung injury edema fluid induces several inflammation-modulating and proliferation-related genes in fibroblasts, whose inductions are similarly dependent on bioactive IL-1beta. Most notably, the 20-fold induction of IL-6 mRNA and protein was completely blocked by IL-1 receptor antagonist. The combined addition of IL-1beta and IL-6 was mitogenic, and the proliferative response to conditioned medium from IL-1beta-exposed cells was blocked by antagonistically acting Abs to IL-6 or to gp130. These novel findings indicate that soluble IL-1beta bioactivity and autocrine IL-1beta-dependent IL-6 up-regulation are critical initiators of fibroblast activation and proliferation and that they likely play a role in the fibroproliferative response seen in human acute lung injury.

An HSV-TK transgenic mouse model to evaluate elimination of fibroblasts for fibrosis therapy

Pathological fibroproliferation after tissue injury is harmful and may lead to organ dysfunction. Unfortunately, fibroproliferative diseases remain intractable to current therapeutic strategies. Thus, new therapeutic approaches are needed. One possible approach is to promote resolution of physiological fibroproliferation that follows injury before it becomes pathological by activating apoptosis selectively in fibrotic lesions. However, it is not known whether selective elimination of fibroblasts will prevent fibrosis or impede repair or worsen injury by eliminating topographic signals essential to organ reconstitution. To address this question, a tractable in vivo model system is needed in which fibroblasts can be targeted to undergo apoptosis at a chosen time and place. We developed transgenic mice expressing HSV-TK from the type I collagen promoter to determine whether selective elimination of fibroblasts actively forming fibrotic lesions is an effective therapeutic strategy for fibroproliferative disorders. The transgene renders fibroblasts actively forming fibrotic tissue susceptible to ganciclovir. To validate the transgenic model we examined whether administration of ganciclovir prevents the development of fibrosis in sponges implanted subcutaneously in the backs of the transgenic mice. We demonstrate that fibroblasts/myofibroblasts isolated from sponges express HSV-TK protein and are selectively ablated by ganciclovir in vitro. In adult transgenic mice, ganciclovir treatment attenuated the development of fibrotic tissue in the sponges both biochemically and histologically. We conclude that this transgenic model system is an ideal approach to determine whether targeted ablation of fibroblasts is an effective therapeutic strategy for fibrotic diseases.

Transforming growth factor-beta: a mediator of cell regulation in acute respiratory distress syndrome

OBJECTIVE

To review recent advances in the use of transforming growth factor (TGF)-beta in acute lung injury and to apply this knowledge to understanding the pathophysiology of this syndrome.

DATA SOURCES AND STUDY SELECTION

Published research and review articles in the English language related to the role of TGF-beta in acute lung injury.

DATA EXTRACTION AND SYNTHESIS

The cytokine TGF-beta plays a critical role in the resolution of tissue injury in multiple organs, including the lung. Following injury, TGF-beta has been most thoroughly evaluated during the late phases of tissue repair, where it plays a critical role in the development of pulmonary fibrosis. In contrast, recent animal studies showed that expression levels of several TGF-beta-inducible genes were dramatically increased as early as 2 days after the induction of injury. The integrin alpha(v)beta(6) activates latent TGF-beta in the lungs. Mice lacking this integrin were completely protected from pulmonary edema in a model of bleomycin-induced acute lung injury. Pharmacologic inhibition of TGF-beta also protected wild-type mice from pulmonary edema induced by bleomycin or Escherichia coli endotoxin. Similar findings also have been reported in patients in a clinical study evaluating TGF-beta in the bronchoalveolar lavage fluid during the course of acute respiratory distress syndrome (ARDS). Indeed, the bronchoalveolar lavage concentrations were dramatically increased as early as 1 day after the initiation of ARDS criteria and were correlated with decreases in the Pao(2)/Fio(2) ratio, suggesting an important role for TGF-b1 in the development of ARDS in humans.

CONCLUSIONS

These studies suggest that TGF-beta not only participates in the late phase of acute lung injury, but also might be active early in acute lung injury and potentially could contribute to the development of pulmonary edema. Integrin-mediated local activation of TGF-beta is critical to the development of pulmonary edema in ARDS, and blocking TGF-beta or its activation could be an effective treatment for this disorder.

Obliterative airway disease progresses in heterotopic airway allografts without persistent alloimmune stimulus

BACKGROUND

Up to 50% of human lung allografts develop chronic rejection manifested as obliterative bronchiolitis (OB). This complication frequently progresses despite maximal immunosuppression, suggesting that, once initiated, factors other than alloimmunity play a role in its progression. In animals, heterotopically transplanted allograft airways develop obliterative airway disease (OAD), an immunologically mediated lesion that is used as a preclinical model of OB. We sought to determine whether OAD would progress even after removal from the alloimmune environment.

METHODS

Tracheas from Lewis rats were transplanted subcutaneously into Brown Norway recipients to create allografts. After 7 or 14 days of alloimmune stimulus, these allografts were removed and retransplanted into an isogeneic environment for an additional 21 days. Histology was assessed at each time point, with quantitation of the airway epithelium and intraluminal fibroproliferation.

RESULTS

Allografts exposed to 14 days of alloimmune stimulus had a significant loss of airway epithelium compared with grafts exposed to only 7 days ( <0.001). There was little fibroproliferation seen in either of these groups. After retransplantation, the grafts initially exposed to 7 days of alloimmune stimulus had few abnormalities. In contrast, the group exposed initially to 14 days of alloimmunity and retransplanted had near complete obliteration of the lumen with fibroproliferation (96.9% occlusion, =0.001) and absent airway epithelium.

CONCLUSIONS

OAD progresses despite removal of alloimmunity if the initial period of alloimmune injury is sufficient. Airway epithelial loss correlated with progression to fibroproliferation, suggesting that the epithelium plays a significant role in the pathogenesis of OB.

c-Jun regulates vascular smooth muscle cell growth and neointima formation after arterial injury. Inhibition by a novel DNA enzyme targeting c-Jun

Neointima formation is a characteristic feature of common vascular pathologies, such as atherosclerosis and post-angioplasty restenosis, and involves smooth muscle cell proliferation. Determination of whether the bZIP transcription factor c-Jun plays a direct regulatory role in arterial lesion formation, or indeed in other disease, has been hampered by the lack of a potent and specific pharmacological inhibitor. c-Jun is poorly expressed in the uninjured artery wall and transiently induced following arterial injury in animal models. Here we generated a gene-specific DNAzyme-targeting c-Jun. We show that c-Jun protein is expressed in human atherosclerotic lesions. Dz13, a catalytically active c-Jun DNAzyme, cleaved c-Jun RNA and inhibited inducible c-Jun protein expression in vascular smooth muscle cells. Dz13 blocked vascular smooth muscle cell proliferation with potency exceeding its exact non-catalytic antisense oligodeoxynucleotide equivalent. Moreover, Dz13 abrogated smooth muscle cell repair following scraping injury in vitro and intimal thickening in injured rat carotid arteries in vivo. These studies demonstrate the positive influence on neointima formation by c-Jun and the therapeutic potential of a DNAzyme controlling its expression.

Induction of lung fibroblast apoptosis by soluble fibronectin peptides

Despite the importance of fibroproliferative lung disorders, no safe and effective therapies exist for reducing the size of the fibroblast population in existing fibrotic lesions. Recent work suggests that therapies that promote fibroblast apoptosis during the repair phase following lung injury may facilitate lung repair by eliminating excess fibrotic tissue. We report here our finding that three soluble fibronectin peptides (RGD, CS-1, and FN-C/H-V) induce apoptosis in lung fibroblasts. Fibroblast susceptibility to these peptides was dose and time dependent, with a maximal effect observed at 96 h (87 +/- 16% [mean +/- SEM] apoptosis). The peptides were able to induce fibroblast apoptosis in fibrin gels, an in vitro model of early fibroproliferative lesions. Fibroblasts were difficult to kill. All three peptides were required for maximal apoptosis of anchored cells. Apoptosis occurred by disruption of adhesion (anoikis). Treatment of fibroblasts with peptides caused proteolysis of pp125FAK, a tyrosine kinase involved in integrin-mediated signaling related to cell survival. These data show that soluble fibronectin peptides trigger nontransformed fibroblast apoptosis in routine culture and in fibrin gels by a mechanism that includes disruption of an integrin-mediated survival signaling pathway. The use of small fibronectin peptides to promote fibroblast apoptosis warrants further study as possible antifibrotic therapy.

Mechanisms of repair and remodeling following acute lung injury

At present, we largely lack the ability to correlate the clinical course of ARDS patients with potential factors involved in the biochemical and cellular basis of lung repair. This requires very large patient databases with measurement of many biochemical parameters. Important mechanistic determinants during the repair phase can be sought by correlation with late outcomes, but a large-scale cooperative effort among multiple centers with sharing of follow-up data and patient specimens is essential. We also lack detailed human histologic material from many phases of ARDS and, particularly, know little of the long-term morphologic impact of ARDS in survivors. Establishment of a national registry that follows ARDS survivors and that would seek their cooperation in advance in obtaining autopsy specimens when they die of other causes would be very valuable. Correlating the pathology with their pulmonary function during recovery would give important insights into the reasons for the different patterns of abnormal pulmonary functions. The factors that determine the success of repair are of critical importance in testing new ARDS treatment strategies. Would accelerating the resolution of alveolar edema alter the course of subsequent fibrosis and inflammation? Does surfactant replacement therapy--a costly proposition in adults with ARDS--lead to better long-term outcomes in survivors? How much should we worry about the use of high levels of oxygen for support of arterial partial pressure of oxygen? Is it better to accept hyperoxia to avoid pressure or volume trauma induced by mechanical ventilation with higher minute ventilations? These major management issues all may affect the success of the late repair and recovery process. Intervention trials need to examine the long-term physiologic and functional outcomes.

Interstitial fibrosis and growth factors

Interstitial pulmonary fibrosis (IPF) is scarring of the lung caused by a variety of inhaled agents including mineral particles, organic dusts, and oxidant gases. The disease afflicts millions of individuals worldwide, and there are no effective therapeutic approaches. A major reason for this lack of useful treatments is that few of the molecular mechanisms of disease have been defined sufficiently to design appropriate targets for therapy. Our laboratory has focused on the molecular mechanisms through which three selected peptide growth factors could play a role in the development of IPF. Hundreds of growth factors and cytokines could be involved in the complex disease process. We are studying platelet-derived growth factor because it is the most potent mesenchymal cell mitogen yet described, transforming growth factor beta because it is a powerful inducer of extracellular matrix (scar tissue) components by mesenchymal cells, and tumor necrosis factor alpha because it is a pleiotropic cytokine that we and others have shown is essential for the development of IPF in animal models. This review describes some of the evidence from studies in humans, in animal models, and in vitro, that supports the growth factor hypothesis. The use of modern molecular and transgenic technologies could elucidate those targets that will allow effective therapeutic approaches.

Chronic hypoxia induces exaggerated growth responses in pulmonary artery adventitial fibroblasts: potential contribution of specific protein kinase c isozymes

Enhanced proliferation of adventitial fibroblasts is a major contributor to the structural remodeling of the pulmonary artery (PA) that occurs during hypoxia-induced pulmonary hypertension. The mechanisms responsible for the exuberant growth of fibroblasts are unknown; however, protein kinase C (PKC) isozymes have previously been shown to be important in the enhanced growth properties of immature PA fibroblasts. We tested the hypotheses that PA adventitial fibroblasts from neonatal calves exposed chronically to hypoxia after birth would express augmented growth responses compared with fibroblasts from the control adventitia and that these properties would be associated with selective changes in expression of PKC isozymes. We studied the effects of serum, purified mitogens, and hypoxia on the growth of aggregate populations of fibroblasts isolated from the PA of neonatal control calves (Neo-C) and calves chronically exposed to hypoxia for 2 wk beginning on Day 1 of life (Neo-Hyp). Neo-Hyp fibroblasts demonstrated higher proliferative capabilities than did Neo-C cells in response to all the stimuli tested. Importantly, hypoxia was found to act synergistically with peptide mitogens (platelet-derived growth factor, basic fibroblast growth factor, insulin-like growth factor-I) to stimulate growth in Neo-Hyp but not in Neo-C cells. Using PKC-isozyme nonselective and selective inhibitors and immunoblot analysis, we found differences in utilization of PKC isozymes in Neo-Hyp and Neo-C fibroblasts and have identified PKC-betaI and -zeta as key contributors to the augmented growth of Neo-Hyp fibroblasts. Although the activity of PKC-betaI and -zeta isozymes was increased by hypoxia in serum-deprived Neo-C and Neo-Hyp fibroblasts, under normoxia, quiescent Neo-Hyp fibroblasts had higher PKC-zeta-specific activity than did Neo-C cells. These results suggest that neonatal PA adventitial fibroblasts acquire new growth properties in the setting of hypoxia- induced pulmonary hypertension and that the augmented proliferative characteristics of the Neo-Hyp fibroblasts might be associated with changes in specifc PKC isozyme expression and activation patterns.

Subendothelial cells from normal bovine arteries exhibit autonomous growth and constitutively activated intracellular signaling

The arterial media is comprised of heterogeneous smooth muscle cell (SMC) subpopulations with markedly different growth responses to pathophysiological stimuli. Little information exists regarding the intracellular signaling pathways that contribute to these differences. Therefore, we investigated the growth-related signaling pathways in a unique subset of subendothelial SMCs (L1 cells) from normal, mature, bovine arteries and compared them with those in "traditional" SMCs derived from the middle media (L2 SMCs). Subendothelial L1 cells exhibited serum-independent autonomous growth, not observed in L2 SMCs. Autonomous growth of L1 cells was driven largely by the constitutively activated extracellular signal-regulated kinase (ERK-1/2) cascade. Inhibition of upstream activators of ERKs (MAP kinase kinase-1, p21(ras), receptor tyrosine kinases, and Gi protein-coupled receptors) led to suppression of autonomous growth in these cells. L1 cells also exhibited constitutive activation of important downstream targets of ERKs (cytosolic phospholipase A(2), cyclooxygenase-2) and secreted large amounts of prostaglandins. Importantly, L1 cells secreted potent mitogenic factor(s), which could potentially contribute in an autocrine fashion to the constitutive activation of these cells. Our data suggest that unique arterial cells with autonomous growth potential and constitutively activated signaling pathways exist in normal arteries and may contribute selectively to the pathogenesis of vascular diseases.

Effects of exogenous nitric oxide and hyperoxia on lung fibroblast viability and DNA fragmentation

Effective lung repair after acute injury requires elimination of proliferating mesenchymal and inflammatory cells without inducing an acute inflammatory response or disturbing concomitant repair of lung microvasculature. Previous studies have shown that endogenous NO regulates programmed cell death in fibroblasts and can modulate wound fibroblast synthetic function. We hypothesized that exposure of human lung fibroblasts to NO gas would decrease viability and induce apoptotic cell death. Primary cultures of normal human lung fibroblasts were exposed for 4 h to room air (RA), 80% oxygen, NO (at either 20 or 50 ppm) blended with RA, or NO blended with 80% O(2), then incubated for 24 to 72 h. Cell viability was determined by fluorescence viability/cytotoxicity assay and DNA fragmentation by TUNEL assay. Peroxynitrite formation was assessed using immunoblotting for S-nitrosotyrosine. NO plus O(2) induced significant cell death at 20 and 50 ppm NO when compared to either RA or O(2) alone at both 24 and 72 h (p < 0.05). Incubation with superoxide dismutase (SOD), catalase (CAT) or SOD + CAT significantly decreased cell death in fibroblasts treated with NO(20)/O(2) and NO(50)/O(2) compared with controls (p < 0.05). NO(20)/O(2) and NO(50)/O(2) exposure significantly increased TUNEL mean fluorescence intensity (MFI), consistent with increased DNA fragmentation, compared to RA at 24 and 72 h (p < 0.05). Antioxidants decreased MFI in cells exposed to NO(20)/O(2) (CAT and SOD + CAT) compared to controls at 24 h (p < 0.05). Western blot analysis for S-nitrosotyrosine showed increased signal intensity in fibroblasts exposed to NO at 20 and 50 ppm plus O(2) compared to RA or O(2) alone. Incubation with SOD + CAT reduced signal intensity for peroxynitrite in cells exposed to NO(20)/O(2). We conclude that NO in hyperoxic conditions induces fibroblast cell death and DNA fragmentation, which could be partially mediated by peroxynitrite synthesis.

Proliferation, C-myc, and cyclin D1 expression in diffuse alveolar damage: potential roles in pathogenesis and implications for prognosis

In this study we compared expression of DNA topoisomerase IIalpha, a marker of cellular proliferation, c-myc, and cyclin D1 in lung biopsy specimens showing diffuse alveolar damage (DAD) with control lung tissues. We subsequently correlated DNA topoisomerase IIalpha, c-myc, and cyclin D1 expression with survival. We hypothesized that poor outcome may correlate with a higher proliferation index, and that c-myc and cyclin D1 activation are potentially important regulators of both proliferation and apoptosis in DAD. Immnuohistochemical stains for c-myc, cyclin D1, and DNA topoisomerase IIalpha were performed on 10 cases of DAD (15 cases for DNA topoisomerase IIalpha) and 10 control lungs. A proliferation index for each case was calculated by dividing the number of nuclei expressing DNA topoisomerase IIalpha by the total number of nuclei counted. The percentages of alveolar pneumocytes and interstitial cells staining positively for c-myc and cyclin D1 were estimated. The average proliferation index (DNA topoisomerase IIalpha index) in DAD (0.16 +/- 0.06, n = 15) was significantly greater than in control lungs (0.00 +/- 0.01, n = 10) (P < .0001). The average proliferation index of patients with DAD who died of respiratory failure (0.18 +/- 0.05, n = 9) was significantly greater than the average proliferation index of patients whose respiratory disease resolved or stabilized (0.11 +/- 0.05, n = 5) (P < .03). Expression of c-myc in alveolar pneumocytes and interstitial cells was more intense and slightly more widespread in cases of DAD compared with control lungs. In 9 of 10 cases of DAD, cyclin D1 expression was present in up to 30% of alveolar pneumocytes and up to 10% of interstitial cells. No staining for cyclin D1 was present in control lungs. These results show that the proliferation index in DAD potentially correlates with patient survival. Furthermore, enhanced expression of c-myc and cyclin D1 may contribute to dysregulation of cellular proliferation and apoptosis observed in DAD.

Differential expression of platelet-derived growth factor-alpha receptor by Thy-1(-) and Thy-1(+) lung fibroblasts

Fibroblasts are heterogeneous with respect to surface markers, morphology, and participation in fibrotic responses. This study was undertaken to determine whether Thy-1(-) and Thy-1(+) rat lung fibroblasts, which have distinct and relevant phenotypes, differ in their proliferative responses to platelet-derived growth factor (PDGF) isoforms. Homogeneous populations of Thy-1(-) and Thy-1(+) fibroblasts were found to proliferate equally in the presence of PDGF-BB, but PDGF-AA-mediated proliferation occurred only in Thy-1(-) cells. This differential activity correlated with significantly higher expression of PDGF-alpha receptor in Thy-1(-) fibroblasts as shown by immunoblotting, immunofluorescence, and Northern blotting. There was a rapid increase in c-myc mRNA in Thy-1(-) but not in Thy-1(+) fibroblasts on stimulation with PDGF-AA and PDGF-BB. The PDGF-alpha receptor, which mediates signaling by all PDGF isoforms, has been implicated in numerous clinical and experimental forms of fibrosis and regulates lung morphogenesis. Differential expression of the PDGF-alpha receptor supports distinct roles for Thy-1(-) and Thy-1(+) fibroblast populations in developmental and fibrotic processes in the lung.

Lovastatin induces fibroblast apoptosis in vitro and in vivo. A possible therapy for fibroproliferative disorders

Diseases associated with pathological fibroproliferation represent a major cause of morbidity and mortality. Despite the importance of this class of disorders, current therapy is of limited value, and no therapy is available to reduce the fibroblast population size within existing fibrotic lesions. In this regard, constitutive expression of growth-promoting genes can sensitize cells to undergo apoptosis. Studies in our laboratory have demonstrated that lovastatin potently induces apoptosis in fibroblasts constitutively expressing Myc, and that lung fibroblasts isolated from fibrotic lesions constitutively express growth-promoting genes. In this study, we sought to determine if nontransformed lung fibroblasts would manifest susceptibility to lovastatin-induced apoptosis similar to that observed in fibroblasts ectopically expressing Myc. Here we show that clinically achievable concentrations of lovastatin induce apoptosis in normal and fibrotic lung fibroblasts in vitro, as evidenced by acridine orange staining, terminal transferase nick end translation (TUNEL), and DNA laddering. Apoptosis of human lung fibroblasts was dose- and time-dependent, and blocked by exogenous mevalonic acid. Furthermore, apoptosis was associated with decreased levels of mature Ras, a molecule directly implicated in fibroblast rescue from apoptosis. The ability of lovastatin to induce fibroblast apoptosis in vivo was examined using a guinea pig wound chamber model. Lovastatin (5 microM, 8 d) reduced granulation tissue formation in the wound chambers by 64.7%, with associated ultrastructural evidence of fibroblast apoptosis. These findings support further study of 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase inhibitors as potential therapy for patients with fibroproliferative disorders.

The potential role of BAX and BCL-2 expression in diffuse alveolar damage

Apoptosis of type II pneumocytes has been identified in diffuse alveolar damage (DAD), is associated with p53 and WAF1 expression, and may be of pathogenetic importance. BAX, a homologue of BCL-2, is induced by p53 and is a promoter of apoptosis. The proapoptotic effect of BAX is negatively regulated by its binding with BCL-2. In this study, we sought to investigate that role of BAX and BCL-2 in DAD. We hypothesized that alterations in BAX and BCL-2 expression may be important in determining the susceptibility of type II pneumocytes and interstitial cells to apoptosis. Twenty-eight cases of DAD and 16 control cases (i.e., lung tissues adjacent to resected tumors) were retrieved from the files of the University of Utah and the Armed Forces Institute of Pathology. Immunohistochemical stains were performed with antigen retrieval by microwave using antibodies recognizing BAX and BCL-2. The percentage of positively staining pneumocytes and interstitial cells was estimated in each case to the nearest 10%. BAX expression was markedly increased in pneumocytes and interstitial cells in DAD compared with control lung tissues. In DAD, BAX was identified on an average of 80% of alveolar pneumocytes (range 30 to 100%) and 70% of interstitial cells (range 20 to 90%). In control lungs, BAX was identified on an average of 10% of pneumocytes (range 0 to 20%) but not in interstitial cells. Focal BCL-2 staining was identified in interstitial myofibroblasts in 7 of 25 cases of DAD but was only identified in bronchiolar epithelium of control lungs. These results suggest that the induction of BAX in DAD may enhance the susceptibility of alveolar epithelial cells to apoptosis, whereas BCL-2 expression may contribute to the absence of apoptosis in interstitial myofibroblasts. Expression of BCL-2 in interstitial myofibroblasts may contribute to the development of pulmonary fibrosis in some patients.

The immunobiology of interferon-gamma inducible protein 10 kD (IP-10): a novel, pleiotropic member of the C-X-C chemokine superfamily

Interferon-gamma inducible protein 10 kD (IP-10) is a highly inducible, primary response gene that belongs to the C-X-C chemokine superfamily. Despite the original cloning of IP-10 in 1985, its biological functions are still unclear although accumulating reports indicate that it is a pleiotropic molecule capable of eliciting potent biological effects, including stimulation of monocytes, natural killer and T-cell migration, regulation of T-cell and bone marrow progenitor maturation, modulation of adhesion molecule expression as well as inhibition of angiogenesis. More interest is now likely to be focused on IP-10 due to the recent cloning of an IP-10 receptor. This paper aims to highlight our current knowledge of IP-10 and its homologues as well as defining its likely involvement in regulating fibroproliferation following inflammatory lung injury.

A novel mechanism of JNK1 activation. Nuclear translocation and activation of JNK1 during ischemia and reperfusion

Cytokines and various cellular stresses are known to activate c-Jun NH2-terminal kinase (JNK), which plays a role in conveying signals from the cytosol to the nucleus. Here we investigate the translocation and activation of JNK1 during ischemia and reperfusion in perfused rat heart. Ischemia induces the translocation of JNK1 from the cytosol fraction to the nuclear fraction in a time-dependent manner. Immunohistochemical observation also shows that JNK1 staining in the nucleus is enhanced after ischemia. During reperfusion after ischemia, further nuclear translocation of JNK1 is apparently inhibited. In contrast, JNK1 activity in the nuclear fraction does not increased during ischemia but increases significantly during reperfusion with a peak at 10 min of reperfusion. The activation of JNK1 is confirmed by the phosphorylation of endogenous c-Jun (Ser-73) with similar kinetics. The level of c-jun mRNA also increases during reperfusion but not during ischemia. Based on fractionation and immunohistochemical analyses, an upstream kinase for JNK1, SAPK/ERK kinase 1 (SEK1), is constantly present in both the nucleus and cytoplasm throughout ischemia and reperfusion, whereas an upstream kinase for mitogen-activated protein kinase, MAPK/ERK kinase 1, remains in the cytosol. Furthermore, phosphorylation at Thr-223 of SEK1, necessary for its activation, rapidly increases in the nuclear fraction during postischemic reperfusion. These findings demonstrate that JNK1 translocates to the nucleus during ischemia without activation and is then activated during reperfusion, probably by SEK1 in the nucleus.

Induction of fibroblast apoptosis by anti-CD44 antibody: implications for the treatment of fibroproliferative lung disease

Fibroblast migration and proliferation within the alveolar wall and airspace after lung injury can lead to the development of fibrosis. Fibroblast cell surface CD44 is an adhesion receptor for provisional matrix proteins and mediates fibroblast invasion into fibrin matrices. Here we show that incubation of cultured fibroblasts with an anti-CD44 monoclonal antibody induces fibroblast detachment from the substratum and morphological changes compatible with apoptosis. In addition, we show that anti-CD44 monoclonal antibody rapidly induces fibroblast apoptosis within fibrin matrices. The effect of anti-CD44 antibody on induction of fibroblast apoptosis occurred within 8 hours and was dose dependent. Anti-CD44 antibody also induced fibroblast apoptosis in suspension. Furthermore, fibroblasts plated on anti-CD44-antibody-coated surfaces initially attached and spread on the antibody; however, after an 8-hour incubation time, many of the cells developed characteristic morphological features of apoptosis. Collectively, these data indicate that apoptosis did not result solely due to detachment from the substratum. Our results identify a new function for fibroblast cell surface CD44 related to the control of cell viability. We suggest this function may be important in fibroblast population control and could potentially be exploited in designing anti-fibrotic therapies.

Acute lung injury fibroblast migration and invasion of a fibrin matrix is mediated by CD44

Fibrosis results when myofibroblasts invade the wound fibrin provisional matrix. Extracellular matrix receptors on the cell surface mediate cell adhesion, migration, and invasion. Recent work with transformed cells indicates that these cells use the cell surface matrix receptor CD44 for migration and invasion. In this study, we examine whether lung fibroblasts, isolated from patients dying with acute alveolar fibrosis, use CD44 to invade a fibrin matrix. Consistent with a role for CD44 in mediating fibroblast invasion and subsequent tissue fibrosis, immunohistochemical analysis of lung tissue from patients who died from acute alveolar fibrosis after lung injury reveals CD44-expressing mesenchymal cells throughout newly formed fibrotic tissue. PCR, Western, and immunoprecipitation analysis demonstrate that the 85-kD CD44 isoform is expressed by acute lung injury fibroblasts. Consistent with a role in mediating matrix adhesion and migration ultrastructurally, CD44 was found uniformly over the cell surface and was found densely labeling filopodia and lamellipodia, highly motile structures involved in cell migration. To determine if lung injury fibroblasts use CD44 to invade fibrin, a fibrin gel model of fibrosis was used. By blocking the function of CD44 with monoclonal antibodies, fibroblast invasion into a fibrin matrix was inhibited. To examine the mechanism by which CD44 mediates fibroblast invasion, the role of CD44 in fibroblast migration and adhesion was evaluated. Anti-CD44 antibody blocked fibroblast migration on the provisional matrix proteins fibronectin, fibrinogen, and hyaluronic acid. Additionally, fibroblast CD44 mediated adhesion to the provisional matrix proteins fibronectin, fibrin, and hyaluronic acid, but not to laminin, a component of the basement membrane. These findings support the hypothesis that fibroblast CD44 functions as an adhesion receptor for provisional matrix proteins and is capable of mediating fibroblast migration and invasion of the wound provisional matrix resulting in the formation of fibrotic tissue.

Cytokines in human lung fibrosis

Fibrosis is a pathological process characterized by the replacement of normal tissue by mesenchymal cells and the extracellular matrix produced by these cells. The sequence of events leading to fibrosis of an organ involves the subsequent processes of injury with inflammation and disruption of the normal tissue architecture, followed by tissue repair with accumulation of mesenchymal cells in the area of derangement. The same sequence of events occurs in wound healing with normal granulation tissue and scar formation, but, while normal scar formation is very localized and transient, in contrast, in fibrosis, the repair process is exaggerated and usually widespread and can be chronic. Inflammatory cells (mainly mononuclear phagocytes), platelets, endothelial cells, and type II pneumocytes play a direct and indirect role in tissue injury and repair. The evaluation of three human fibrotic lung diseases, two diffuse [idiopathic pulmonary fibrosis (IPF), and the adult respiratory distress syndrome (ARDS)], and one focal (tumor stroma in lung cancer), has shown that several cytokines participate to the local injury and inflammatory reaction [interleukin-1 (IL-1), interleukin-8 (IL-8), monocyte chemotactic protein-1 (MCP-1), tumor necrosis factor-alpha (TNF-alpha)], while other cytokines are involved in tissue repair and fibrosis [platelet-derived growth factor (PDGF), insulin-like growth factor-1 (IGF-1), transforming growth factor-beta (TGF-beta), and basic-fibroblast growth factor (b-FGF)]. A better understanding of the cytokines and cytokine networks involved in lung fibrosis leads to the possibility of new therapeutic approaches.

Immunocytochemical detection of growth factors (PDGF and TGF beta) in equine chronic pneumonia

The roles played by platelet-derived growth factor (PDGF) and transforming growth factor beta (TGF beta) in the development of pulmonary fibrosis in equine chronic pneumonia varied greatly. Macrophages, epithelial cells and fibroblasts were identified as a source of PDGF, the principal role of which was related to its mitotic effect on epithelial cells, and particularly on fibroblasts in the final phase of the disease. TGF beta was detected in epithelial cells in all three phases of the disease and in fibroblasts in the last phase. However, the role of TGF beta in this pulmonary disease is not clear because its expression in the cytoplasm of fibroblasts in areas of strong collagenation during the last phase was weak. Nonetheless, it was responsible for the production and release of collagen during the stage of total fibrosis.

Sustained and distinctive patterns of gene activation in synovial fibroblasts and whole synovial tissue obtained from inflammatory synovitis

Fibroblastoid synovial lining cells isolated from rheumatoid and other chronic inflammatory synovial tissue exhibit distinctive and sustained alterations in serial culture not commonly found in similarly cultured cells from osteoarthritic synovium. These are demonstrable using a multi-gene dot blot assay by labelling reverse transcribed fibroblast cDNA which is hybridized to plasmids containing relevant target gene inserts. Cultured synovial fibroblastoid cells from patients with chronic inflammatory synovitis expressed significantly higher levels of stromelysin, vimentin and TIMP-1 mRNA and lower levels of c-myc compared to cells isolated from osteoarthritis synovium although with considerable variation. Early fetal synovial lining cells were similar to cells from osteoarthritis synovium but vimentin expression was higher. Marked differences in patterns of gene expression between cell lines persisted through 10 serial passages over 6-8 months. In whole synovia, the average level of mRNA for stromelysin, vimentin, IL-4, IL-6, TIMP-1, cathepsin D, gelatinase, TGF alpha, c-fms and DR beta were preferentially expressed in inflammatory tissue while c-myc expression was higher in osteoarthritis synovium. Inflammatory synovium also expressed TNF alpha, IL-1 alpha, IL-1 beta, IL-2, c-sis, tissue plasminogen activator, CSF-1, and GM-CSF. This pattern resembles, in part, that found in cultured inflammatory fibroblasts but, in addition, gene products apparently reflecting the presence of activated monocytes and lymphocytes were detected. These results provide evidence that profiles of certain gene activation in cells from patients with inflammatory synovitis differ from those with non-inflammatory disease and suggest that the fibroblastoid cells are responsible for a considerable proportion of the altered phenotypic expression pattern in whole tissue. Furthermore, this modulated pattern of gene activation appears to be an intrinsic pro-inflammatory characteristic of the fibroblastoid cells initiated in response to chronic inflammation and persists for a prolonged period in the absence of other inflammatory cells.

Bactericidal activity of synthetic peptides based on the structure of the 55-kilodalton bactericidal protein from human neutrophils

Short (10- to 11-mer) hydrophilic peptides based on the structure of the 55-kDa bactericidal protein (BP55, B/PI, and CAP57) from human neutrophil granules were identified from the hydropathy plot of the 456-amino-acid sequence predicted from the nucleotide sequences of cDNA clones for BP55 and B/PI. Peptides corresponding to amino acid residues 90 to 99 (peptide #90-99), 86 to 99, or 90 to 102 of BP55 were bactericidal toward 5 x 10(6) Pseudomonas aeruginosa cells at 0.6 x 10(-5) to 1.5 x 10(-5) M and killed an Escherichia coli rough strain at 3 x 10(-5) M. The #90-99 peptide with a cysteine added at the amino terminus (C#90-99) was approximately 10 times more active than #90-99, killing P. aeruginosa at 1.5 x 10(-6) M. Peptides representing amino acid residues 27 to 37, 118 to 127, and 160 to 170 and the first 10 amino acids of the signal sequence for BP55 were not bactericidal. When coupled to either keyhole limpet hemocyanin or ovalbumin protein carriers through the thiol group, the C#90-99 peptide was not diminished on a molar basis in its capacity for killing of P. aeruginosa. Two other relatively hydrophilic peptides with an added amino-terminal cysteine, peptides C#227-236 and C#418-427, were not bactericidal at 1.2 x 10(-4) M or at 100 times the effective bactericidal concentration of C#90-99. The C#90-99 peptide killed E. coli at 1.5 x 10(-5) M, or at 10 times the concentration required to kill an equal number of P. aeruginosa cells. Although Pseudomonas cepacia and Staphylococcus aureus were resistent to killing by the parent BP55 molecule, they were susceptible to the C#90-99 and #90-99 peptides in the same concentration range as was E. coli. When all peptides were compared for the ability to neutralize E. coli O55:B5 endotoxin in a Limulus amoebocyte lysate assay, the C#227-236, C#418-427, and #160-170 peptides completely inhibited gelation at a 10(-4) M concentration. All other synthetic peptides, including bactericidal peptide #90-99 and its congeners, lacked endotoxin-neutralizing activity at the highest concentration tested (4.5 x 10(-4) M). A hybrid of the C#227-236 and #90-99 peptides (CHybrid) was identical to the C#227-236 peptide component in effectiveness for carrying out endotoxin neutralization and was fivefold better than the #90-99 peptide in its capacity for killing P. aeruginosa.

Cytokines and pulmonary fibrosis

Chronically inflamed and fibrotic tissue of the respiratory tract can be shown to actively express the genes and products of a number of powerful growth and differentiating factors. The initial activation of lung inflammatory cells, including alveolar macrophages, is presumed to result in the release of early acting cytokines such as IL-1 and TNF. Subsequent activation and possible phenotype alteration of the structural cells results in release of other growth factors and accumulation of blood derived inflammatory cells. These cells, once they have entered the tissue and become further activated, may begin to release their own autocrine factors and "feed back" some of the similar signals to the tissue cells in a paracrine manner, further inducing differentiation and phenotype change. These internal tissue cell and cytokine cascades could account for the chronic nature of the inflammation. Therapeutic intervention must therefore take into account the inflammatory component as well as the nature of the cytokines and structural cells involved in the propagation of the disease.