Intravenous keratinocyte growth factor protects against experimental pulmonary injury

FOXO1 Couples KGF and PI-3K/AKT Signaling to NKX2.1-Regulated Differentiation of Alveolar Epithelial Cells

NKX2.1 is a master regulator of lung morphogenesis and cell specification; however, interactions of NKX2.1 with various transcription factors to regulate cell-specific gene expression and cell fate in the distal lung remain incompletely understood. FOXO1 is a key regulator of stem/progenitor cell maintenance/differentiation in several tissues but its role in the regulation of lung alveolar epithelial progenitor homeostasis has not been evaluated. We identified a novel role for FOXO1 in alveolar epithelial cell (AEC) differentiation that results in the removal of NKX2.1 from surfactant gene promoters and the subsequent loss of surfactant expression in alveolar epithelial type I-like (AT1-like) cells. We found that the FOXO1 forkhead domain potentiates a loss of surfactant gene expression through an interaction with the NKX2.1 homeodomain, disrupting NKX2.1 binding to the SFTPC promoter. In addition, blocking PI-3K/AKT signaling reduces phosphorylated FOXO-1 (p-FOXO1), allowing accumulated nuclear FOXO1 to interact with NKX2.1 in differentiating AEC. Inhibiting AEC differentiation in vitro with keratinocyte growth factor (KGF) maintained an AT2 cell phenotype through increased PI3K/AKT-mediated FOXO1 phosphorylation, resulting in higher levels of surfactant expression. Together these results indicate that FOXO1 plays a central role in AEC differentiation by directly binding NKX2.1 and suggests an essential role for FOXO1 in mediating AEC homeostasis.

Fibroblast growth factor 2 decreases bleomycin-induced pulmonary fibrosis and inhibits fibroblast collagen production and myofibroblast differentiation

Fibroblast growth factor (FGF) signaling has been implicated in the pathogenesis of pulmonary fibrosis. Mice lacking FGF2 have increased mortality and impaired epithelial recovery after bleomycin exposure, supporting a protective or reparative function following lung injury. To determine whether FGF2 overexpression reduces bleomycin-induced injury, we developed an inducible genetic system to express FGF2 in type II pneumocytes. Double-transgenic (DTG) mice with doxycycline-inducible overexpression of human FGF2 (SPC-rtTA;TRE-hFGF2) or single-transgenic controls were administered intratracheal bleomycin and fed doxycycline chow, starting at either day 0 or day 7. In addition, wild-type mice received intratracheal or intravenous recombinant FGF2, starting at the time of bleomycin treatment. Compared to controls, doxycycline-induced DTG mice had decreased pulmonary fibrosis 21 days after bleomycin, as assessed by gene expression and histology. This beneficial effect was seen when FGF2 overexpression was induced at day 0 or day 7 after bleomycin. FGF2 overexpression did not alter epithelial gene expression, bronchoalveolar lavage cellularity or total protein. In vitro studies using primary mouse and human lung fibroblasts showed that FGF2 strongly inhibited baseline and TGFβ1-induced expression of alpha smooth muscle actin (αSMA), collagen, and connective tissue growth factor. While FGF2 did not suppress phosphorylation of Smad2 or Smad-dependent gene expression, FGF2 inhibited TGFβ1-induced stress fiber formation and serum response factor-dependent gene expression. FGF2 inhibition of stress fiber formation and αSMA requires FGF receptor 1 (FGFR1) and downstream MEK/ERK, but not AKT signaling. In summary, overexpression of FGF2 protects against bleomycin-induced pulmonary fibrosis in vivo and reverses TGFβ1-induced collagen and αSMA expression and stress fiber formation in lung fibroblasts in vitro, without affecting either inflammation or epithelial gene expression. Our results suggest that in the lung, FGF2 is antifibrotic in part through decreased collagen expression and fibroblast to myofibroblast differentiation. Copyright © 2018 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

TGF beta inhibits HGF, FGF7, and FGF10 expression in normal and IPF lung fibroblasts

TGF beta is a multifunctional cytokine that is important in the pathogenesis of pulmonary fibrosis. The ability of TGF beta to stimulate smooth muscle actin and extracellular matrix gene expression in fibroblasts is well established. In this report, we evaluated the effect of TGF beta on the expression of HGF, FGF7 (KGF), and FGF10, important growth and survival factors for the alveolar epithelium. These growth factors are important for maintaining type II cells and for restoration of the epithelium after lung injury. Under conditions of normal serum supplementation or serum withdrawal TGF beta inhibited fibroblast expression of HGF, FGF7, and FGF10. We confirmed these observations with genome wide RNA sequencing of the response of control and IPF fibroblasts to TGF beta. In general, gene expression in IPF fibroblasts was similar to control fibroblasts. Reduced expression of HGF, FGF7, and FGF10 is another means whereby TGF beta impairs epithelial healing and promotes fibrosis after lung injury.

Mitogenic stimulation accelerates influenza-induced mortality by increasing susceptibility of alveolar type II cells to infection

Development of pneumonia is the most lethal consequence of influenza, increasing mortality more than 50-fold compared with uncomplicated infection. The spread of viral infection from conducting airways to the alveolar epithelium is therefore a pivotal event in influenza pathogenesis. We found that mitogenic stimulation with keratinocyte growth factor (KGF) markedly accelerated mortality after infectious challenge with influenza A virus (IAV). Coadministration of KGF with IAV markedly accelerated the spread of viral infection from the airways to alveoli compared with challenge with IAV alone, based on spatial and temporal analyses of viral nucleoprotein staining of lung tissue sections and dissociated lung cells. To better define the temporal relationship between KGF administration and susceptibility to IAV infection in vivo, we administered KGF 120, 48, 24, and 0 h before intrapulmonary IAV challenge and assessed the percentages of proliferating and IAV-infected, alveolar type II (AECII) cells in dispersed lung cell populations. Peak AECII infectivity coincided with the timing of KGF administration that also induced peak AECII proliferation. AECII from mice that were given intrapulmonary KGF before isolation and then infected with IAV ex vivo exhibited the same temporal pattern of proliferation and infectious susceptibility. KGF-induced increases in mortality, AECII proliferation, and enhanced IAV susceptibility were all reversed by pretreatment of the animals with the mTOR inhibitor rapamycin before mitogenic stimulation. Taken together, these data suggest mTOR signaling-dependent, mitogenic conditioning of AECII is a determinant of host susceptibility to infection with IAV.

Lung Regeneration: Endogenous and Exogenous Stem Cell Mediated Therapeutic Approaches

The tissue turnover of unperturbed adult lung is remarkably slow. However, after injury or insult, a specialised group of facultative lung progenitors become activated to replenish damaged tissue through a reparative process called regeneration. Disruption in this process results in healing by fibrosis causing aberrant lung remodelling and organ dysfunction. Post-insult failure of regeneration leads to various incurable lung diseases including chronic obstructive pulmonary disease (COPD) and idiopathic pulmonary fibrosis. Therefore, identification of true endogenous lung progenitors/stem cells, and their regenerative pathway are crucial for next-generation therapeutic development. Recent studies provide exciting and novel insights into postnatal lung development and post-injury lung regeneration by native lung progenitors. Furthermore, exogenous application of bone marrow stem cells, embryonic stem cells and inducible pluripotent stem cells (iPSC) show evidences of their regenerative capacity in the repair of injured and diseased lungs. With the advent of modern tissue engineering techniques, whole lung regeneration in the lab using de-cellularised tissue scaffold and stem cells is now becoming reality. In this review, we will highlight the advancement of our understanding in lung regeneration and development of stem cell mediated therapeutic strategies in combating incurable lung diseases.

Attenuating endogenous Fgfr2b ligands during bleomycin-induced lung fibrosis does not compromise murine lung repair

Fibroblast growth factors (Fgfs) mediate organ repair. Lung epithelial cell overexpression of Fgf10 postbleomycin injury is both protective and therapeutic, characterized by increased survival and attenuated fibrosis. Exogenous administration of FGF7 (palifermin) also showed prophylactic survival benefits in mice. The role of endogenous Fgfr2b ligands on bleomycin-induced lung fibrosis is still elusive. This study reports the expression of endogenous Fgfr2b ligands, receptors, and signaling targets in wild-type mice following bleomycin lung injury. In addition, the impact of attenuating endogenous Fgfr2b-ligands following bleomycin-induced fibrosis was tested by using a doxycycline (dox)-based inducible, soluble, dominant-negative form of the Fgfr2b receptor. Double-transgenic (DTG) Rosa26(rtTA/+);tet(O)solFgfr2b mice were validated for the expression and activity of soluble Fgfr2b (failure to regenerate maxillary incisors, attenuated recombinant FGF7 signal in the lung). As previously reported, no defects in lung morphometry were detected in DTG (+dox) mice exposed from postnatal days (PN) 1 through PN105. Female single-transgenic (STG) and DTG mice were subjected to various levels of bleomycin injury (1.0, 2.0, and 3.0 U/kg). Fgfr2b ligands were attenuated either throughout injury (days 0-11; days 0-28) or during later stages (days 6-28 and 14-28). No significant changes in survival, weight, lung function, confluent areas of fibrosis, or hydroxyproline deposition were detected in DTG mice. These results indicate that endogenous Fgfr2b ligands do not significantly protect against bleomycin injury, nor do they expedite the resolution of bleomycin-induced lung injury in mice.

Palifermin for the protection and regeneration of epithelial tissues following injury: new findings in basic research and pre-clinical models

Keratinocyte growth factor (KGF) is a paracrine-acting epithelial mitogen produced by cells of mesenchymal origin, that plays an important role in protecting and repairing epithelial tissues. Pre-clinical data initially demonstrated that a recombinant truncated KGF (palifermin) could reduce gastrointestinal injury and mortality resulting from a variety of toxic exposures. Furthermore, the use of palifermin in patients with hematological malignancies reduced the incidence and duration of severe oral mucositis experienced after intensive chemoradiotherapy. Based upon these findings, as well as the observation that KGF receptors are expressed in many, if not all, epithelial tissues, pre-clinical studies have been conducted to determine the efficacy of palifermin in protecting different epithelial tissues from toxic injury in an attempt to model various clinical situations in which it might prove to be of benefit in limiting tissue damage. In this article, we review these studies to provide the pre-clinical background for clinical trials that are described in the accompanying article and the rationale for additional clinical applications of palifermin.

Potential clinical application of KGF-2 (FGF-10) for acute lung injury/acute respiratory distress syndrome

Acute lung injury (ALI)/acute respiratory distress syndrome (ARDS) is an acute life-threatening form of hypoxemic respiratory failure with a high mortality rate, and there is still a great need for more effective therapies for such a severe and lethal disease. Dysfunction of endothelial and epithelial barriers is one of the most important mechanisms in hypoxia-associated ALI/ARDS. The acceleration of the epithelial repair process in the injured lung may provide an effective therapeutic target. KGF-2, a potent alveolar epithelial cell mitogen, plays an important role in organ morphogenesis and epithelial differentiation, and modulates a variety of mechanisms recognized to be important in alveolar repair and resolution in ALI/ARDS. Preclinical and clinical studies have suggested that KGF-2 may be the candidate of novel therapies for alveolar epithelial damage during ALI/ARDS.

Effects of recombinant human keratinocyte growth factor on surfactant, plasma, and liver phospholipid homeostasis in hyperoxic neonatal rats

Respiratory distress and bronchopulmonary dysplasia (BPD) are major problems in preterm infants that are often addressed by glucocorticoid treatment and increased oxygen supply, causing catabolic and injurious side effects. Recombinant human keratinocyte growth factor (rhKGF) is noncatabolic and antiapoptotic and increases surfactant pools in immature lungs. Despite its usefulness in injured neonatal lungs, the mechanisms of improved surfactant homeostasis in vivo and systemic effects on lipid homeostasis are unknown. We therefore exposed newborn rats to 85% vs. 21% oxygen and treated them systemically with rhKGF for 48 h before death at 7 days. We determined type II pneumocyte (PN-II) proliferation, surfactant protein (SP) mRNA expression, and the pulmonary metabolism of individual phosphatidylcholine (PC) species using [D(9)-methyl]choline and tandem mass spectrometry. In addition, we assessed liver and plasma lipid metabolism, addressing PC synthesis de novo, the liver-specific phosphatidylethanolamine methyl transferase (PEMT) pathway, and triglyceride concentrations. rhKGF was found to maintain PN-II proliferation and increased SP-B/C expression and surfactant PC in both normoxic and hyperoxic lungs. We found increased total PC together with decreased [D(9)-methyl]choline enrichment, suggesting decreased turnover rather than increased secretion and synthesis as the underlying mechanism. In the liver, rhKGF increased PC synthesis, both de novo and via PEMT, underlining the organotypic differences of rhKGF actions on lipid metabolism. rhKGF increased the hepatic secretion of newly synthesized polyunsaturated PC, indicating improved systemic supply with choline and essential fatty acids. We suggest that rhKGF has potential as a therapeutic agent in neonates by improving pulmonary and systemic PC homeostasis.

An official American Thoracic Society research statement: noninfectious lung injury after hematopoietic stem cell transplantation: idiopathic pneumonia syndrome

RATIONALE

Acute lung dysfunction of noninfectious etiology, known as idiopathic pneumonia syndrome (IPS), is a severe complication following hematopoietic stem cell transplantation (HSCT). Several mouse models have been recently developed to determine the underlying causes of IPS. A cohesive interpretation of experimental data and their relationship to the findings of clinical research studies in humans is needed to better understand the basis for current and future clinical trials for the prevention/treatment of IPS.

OBJECTIVES

Our goal was to perform a comprehensive review of the preclinical (i.e., murine models) and clinical research on IPS.

METHODS

An ATS committee performed PubMed and OVID searches for published, peer-reviewed articles using the keywords "idiopathic pneumonia syndrome" or "lung injury" or "pulmonary complications" AND "bone marrow transplant" or "hematopoietic stem cell transplant." No specific inclusion or exclusion criteria were determined a priori for this review.

MEASUREMENTS AND MAIN RESULTS

Experimental models that reproduce the various patterns of lung injury observed after HSCT have identified that both soluble and cellular inflammatory mediators contribute to the inflammation engendered during the development of IPS. To date, 10 preclinical murine models of the IPS spectrum have been established using various donor and host strain combinations used to study graft-versus-host disease (GVHD). This, as well as the demonstrated T cell dependency of IPS development in these models, supports the concept that the lung is a target of immune-mediated attack after HSCT. The most developed therapeutic strategy for IPS involves blocking TNF signaling with etanercept, which is currently being evaluated in clinical trials.

CONCLUSIONS

IPS remains a frequently fatal complication that limits the broader use of allogeneic HSCT as a successful treatment modality. Faced with the clinical syndrome of IPS, one can categorize the disease entity with the appropriate tools, although cases of unclassifiable IPS will remain. Significant research efforts have resulted in a paradigm shift away from identifying noninfectious lung injury after HSCT solely as an idiopathic clinical syndrome and toward understanding IPS as a process involving aspects of both the adaptive and the innate immune response. Importantly, new laboratory insights are currently being translated to the clinic and will likely prove important to the development of future strategies to prevent or treat this serious disorder.

Palifermin induces alveolar maintenance programs in emphysematous mice

RATIONALE

Emphysema is characterized by destruction of alveoli with ensuing airspace enlargement and loss of alveoli. Induction of alveolar regeneration is still a major challenge in emphysema therapy.

OBJECTIVES

To investigate whether therapeutic application of palifermin (DeltaN23-KGF) is able to induce a regenerative response in distal lung parenchyma after induction of pulmonary emphysema.

METHODS

Mice were therapeutically treated at three occasions by oropharyngeal aspiration of 10 mg DeltaN23-KGF per kg body weight after induction of emphysema by porcine pancreatic elastase.

MEASUREMENTS AND MAIN RESULTS

Airflow limitation associated with emphysema was largely reversed as assessed by noninvasive head-out body plethysmography. Porcine pancreatic elastase-induced airspace enlargement and loss of alveoli were partially reversed as assessed by design-based stereology. DeltaN23-KGF induced proliferation of epithelium, endothelium, and fibroblasts being associated with enhanced differentiation as well as increased expression of vascular endothelial growth factor, vascular endothelial growth factor receptors, transforming growth factor (TGF)-beta1, TGF-beta2, (phospho-) Smad2, plasminogen activator inhibitor-1, and elastin as assessed by quantitative reverse transcriptase-polymerase chain reaction, Western blotting, and immunohistochemistry. DeltaN23-KGF induced the expression of TGF-beta1 in and release of active TGF-beta1 from primary mouse alveolar epithelial type 2 (AE2) cells, murine AE2-like cells LA-4, and cocultures of LA-4 and murine lung fibroblasts (MLF), but not in MLF cultured alone. Recombinant TGF-beta1 but not DeltaN23-KGF induced elastin gene expression in MLF. Blockade of TGF-signaling by neutralizing antibody abolished these effects of DeltaN23-KGF in LA-4/MLF cocultures.

CONCLUSIONS

Our data demonstrate that therapeutic application of DeltaN23-KGF has the potential to induce alveolar maintenance programs in emphysematous lungs and suggest that the regenerative effect on interstitial tissue is linked to AE2 cell-derived TGF-beta1.

Bone marrow stem cells expressing keratinocyte growth factor via an inducible lentivirus protects against bleomycin-induced pulmonary fibrosis

Many common diseases of the gas exchange surface of the lung have no specific treatment but cause serious morbidity and mortality. Idiopathic Pulmonary Fibrosis (IPF) is characterized by alveolar epithelial cell injury, interstitial inflammation, fibroblast proliferation and collagen accumulation within the lung parenchyma. Keratinocyte Growth Factor (KGF, also known as FGF-7) is a critical mediator of pulmonary epithelial repair through stimulation of epithelial cell proliferation. During repair, the lung not only uses resident cells after injury but also recruits circulating bone marrow-derived cells (BMDC). Several groups have used Mesenchymal Stromal Cells (MSCs) as therapeutic vectors, but little is known about the potential of Hematopoietic Stem cells (HSCs). Using an inducible lentiviral vector (Tet-On) expressing KGF, we were able to efficiently transduce both MSCs and HSCs, and demonstrated that KGF expression is induced in a regulated manner both in vitro and in vivo. We used the in vivo bleomycin-induced lung fibrosis model to assess the potential therapeutic effect of MSCs and HSCs. While both populations reduced the collagen accumulation associated with bleomycin-induced lung fibrosis, only transplantation of transduced HSCs greatly attenuated the histological damage. Using double immunohistochemistry, we show that the reduced lung damage likely occurs through endogenous type II pneumocyte proliferation induced by KGF. Taken together, our data indicates that bone marrow transplantation of lentivirus-transduced HSCs can attenuate lung damage, and shows for the first time the potential of using an inducible Tet-On system for cell based gene therapy in the lung.

Overexpression of fibroblast growth factor-10 during both inflammatory and fibrotic phases attenuates bleomycin-induced pulmonary fibrosis in mice

RATIONALE

Fibroblast growth factor-10 (FGF10) controls survival, proliferation, and differentiation of distal-alveolar epithelial progenitor cells during lung development.

OBJECTIVES

To test for the protective and regenerative effect of Fgf10 overexpression in a bleomycin-induced mouse model of pulmonary inflammation and fibrosis.

METHODS

In SP-C-rtTA; tet(O)Fgf10 double-transgenic mice, lung fibrosis was induced in 2-month-old transgenic mice by subcutaneous delivery of bleomycin (BLM), using an osmotic minipump for 1 week. Exogenous Fgf10 expression in the alveolar epithelium was induced for 7 days with doxycycline during the first, second, and third weeks after bleomycin pump implantation, and lungs were examined at 28 days.

MEASUREMENTS AND MAIN RESULTS

Fgf10 overexpression during Week 1 (inflammatory phase) resulted in increased survival and attenuated lung fibrosis score and collagen deposition. In these Fgf10-overexpressing mice, an increase in regulatory T cells and a reduction in both transforming growth factor-beta(1) and matrix metalloproteinase-2 activity were observed in bronchoalveolar lavage fluids whereas the number of surfactant protein C (SP-C)-positive, alveolar epithelial type II cells (AEC2) was markedly elevated. Analysis of SP-C and TUNEL (terminal deoxynucleotidyltransferase dUTP nick end labeling) double-positive cells and isolation of AEC2 from lungs overexpressing Fgf10 demonstrated increased AEC2 survival. Expression of Fgf10 during Weeks 2 and 3 (fibrotic phase) showed significant attenuation of the lung fibrosis score and collagen deposition.

CONCLUSIONS

In the bleomycin model of lung inflammation and fibrosis, Fgf10 overexpression during both the inflammatory and fibrotic phases results in a greatly reduced extent of lung fibrosis, suggesting that FGF10 may be useful as a novel approach to the treatment of pulmonary fibrosis.

High tidal volume mechanical ventilation with hyperoxia alters alveolar type II cell adhesion

Patients with acute respiratory distress syndrome undergoing mechanical ventilation may be exposed to both high levels of stretch and high levels of oxygen. We hypothesized that the combination of high stretch and hyperoxia promotes loss of epithelial adhesion and impairs epithelial repair mechanisms necessary for restoration of barrier function. We utilized a model of high tidal volume mechanical ventilation (25 ml/kg) with hyperoxia (50% O(2)) in rats to investigate alveolar type II (AT2) cell adhesion and focal adhesion signaling. AT2 cells isolated from rats exposed to hyperoxia and high tidal volume mechanical ventilation (MVHO) exhibited significantly decreased cell adhesion and reduction in phosphotyrosyl levels of focal adhesion kinase (FAK) and paxillin compared with control rats, rats exposed to hyperoxia without ventilation (HO), or rats ventilated with normoxia (MV). MV alone increased phosphorylation of p130(Cas). RhoA activation was increased by MV, HO, and the combination of MV and HO. Treatment of MVHO cells with keratinocyte growth factor (KGF) for 1 h upon isolation reduced RhoA activity and restored attachment to control levels. Attachment and migration of control AT2 cells was significantly decreased by constitutively active RhoA or a kinase inactive form of FAK (FRNK), whereas expression of dominant negative RhoA in cells from MVHO-treated rats restored cell adhesion. Mechanical ventilation with hyperoxia promotes changes in focal adhesion proteins and RhoA in AT2 cells that may be deleterious for cell adhesion and migration.

KGF promotes integrin alpha5 expression through CCAAT/enhancer-binding protein-beta

Keratinocyte growth factor (KGF) and alpha(5)beta(1)-integrin are not expressed in normal skin but they are both highly upregulated in the migrating epidermis during wound healing. Here we report that KGF increased alpha(5) mRNA and protein levels in epidermoid carcinoma cells and stratified bioengineered epidermis. Interestingly, KGF increased integrin alpha(5) in the basal as well as suprabasal cell epidermal layers. Promoter studies indicated that KGF-induced integrin alpha(5) promoter activation was dependent on the C/EBP transcription factor binding site. Accordingly, KGF induced sustained phosphorylation of C/EBP-beta that was dependent on activation of ERK1/2. In addition, a dominant negative form of C/EBP-beta inhibited alpha(5) promoter activity and blocking C/EBP-beta with siRNA diminished integrin alpha(5) expression. Taken together, our data indicate that KGF increased integrin alpha(5) expression by phosphorylating C/EBP-beta. Interestingly, KGF-induced upregulation of integrin alpha(5) was more pronounced in three-dimensional tissue analogues than in conventional two-dimensional culture suggesting that stratified epidermis may be useful in understanding the effects of growth factors in the local tissue microenvironment.

Keratinocyte growth factor improves repair in the injured tracheal epithelium

Keratinocyte growth factor (KGF) is a critical growth factor in lung development and is a protective agent after lung injury, although the exact mechanisms of this protective effect have not yet been elucidated. Our laboratory has shown that circulating epithelial progenitor cells can traffic to the airway and that they appear to be derived from the bone marrow. On this basis, we hypothesized that KGF and its putative receptor (KGFR) would be important to these cells. We showed that the KGFR, which is found almost exclusively on epithelial cells, was present on cells in the bone marrow and circulation of mice that identified a subpopulation of cytokeratin 5+ circulating epithelial progenitor cells (CEPC). In addition, the KGFR co-localized with a population of cytokeratin 5+ basal cells in the repairing proximal airway. Systemic administration of KGF resulted in a significant increase in mobilization of cytokeratin 5+ CEPC at 6 h after injection. Administration of KGF to mouse recipients of heterotopic syngeneic tracheal transplants resulted in protection and more rapid repair of the tracheal epithelium, with an increase in the number of CEPC in the epithelium of the airway, and this effect was abrogated by blocking CEPC with anti-CXCL12 antibodies. KGF therefore appears to be an important growth factor for local resident progenitor epithelial cell repair and for mobilization and enhanced engraftment of CEPC to the injured proximal airway epithelium.

Keratinocyte growth factor expression and activity in cancer: implications for use in patients with solid tumors

Keratinocyte growth factor (KGF) is a locally acting epithelial mitogen that is produced by cells of mesenchymal origin and has an important role in protecting and repairing epithelial tissues. Use of recombinant human KGF (palifermin) in patients with hematologic malignancies reduces the incidence and duration of severe oral mucositis experienced after intensive chemoradiotherapy. These results suggest that KGF may be useful in the treatment of patients with other kinds of tumors, including those of epithelial origin. However, its application in this context raises issues that were not pertinent to its use in hematologic cancer because epithelial tumor cells, unlike blood cells, often express the KGF receptor (FGFR2b). Thus, it is important to examine whether KGF could promote the growth of epithelial tumors or protect such tumor cells from the effects of chemotherapy agents. Analyses of KGF and FGFR2b expression in tumor specimens and of KGF activity on transformed cells in vitro and in vivo do not indicate a definitive role for KGF in tumorigenesis. On the contrary, restoring FGFR2b expression to certain malignant cells can induce cell differentiation or apoptosis. However, other observations suggest that, in specific situations, KGF may contribute to epithelial tumorigenesis. Thus, further studies are warranted to examine the nature and extent of KGF involvement in these settings. In addition, clinical trials in patients with solid tumors are underway to assess the potential benefits of using KGF to protect normal tissue from the adverse effects of chemoradiotherapy and its possible impact on clinical outcome.

Biomimetic delivery of keratinocyte growth factor upon cellular demand for accelerated wound healing in vitro and in vivo

Exogenous keratinocyte growth factor (KGF) significantly enhances wound healing, but its use is hampered by a short biological half-life and lack of tissue selectivity. We used a biomimetic approach to achieve cell-controlled delivery of KGF by covalently attaching a fluorescent matrix-binding peptide that contained two domains: one recognized by factor XIII and the other by plasmin. Modified KGF was incorporated into the fibrin matrix at high concentration in a factor XIII-dependent manner. Cell-mediated activation of plasminogen to plasmin degraded the fibrin matrix and cleaved the peptides, releasing active KGF to the local microenvironment and enhancing epithelial cell proliferation and migration. To demonstrate in vivo effectiveness, we used a hybrid model of wound healing that involved transplanting human bioengineered skin onto athymic mice. At 6 weeks after grafting, the transplanted tissues underwent full thickness wounding and treatment with fibrin gels containing bound KGF. In contrast to topical KGF, fibrin-bound KGF persisted in the wounds for several days and was released gradually, resulting in significantly enhanced wound closure. A fibrinolytic inhibitor prevented this healing, indicating the requirement for cell-mediated fibrin degradation to release KGF. In conclusion, this biomimetic approach of localized, cell-controlled delivery of growth factors may accelerate healing of large full-thickness wounds and chronic wounds that are notoriously difficult to heal.

Protection of epithelial cells by keratinocyte growth factor signaling

Oxidative injury to the lung is associated with widespread injury to the alveolar epithelium, which can be fatal unless the process is controlled and repaired. Keratinocyte growth factor (KGF), a member of the fibroblast growth factor family, has been shown to protect the lung from a variety of oxidative insults. The mechanism(s) underlying the protective effects of KGF in lung injury is being investigated in many laboratories. Although KGF has potent mitogenic effects on epithelial cells, the proliferative effect of KGF was shown to be abolished in oxygen-breathing animals, but KGF was still able to inhibit alveolar damage. This demonstrates that the protective effect of KGF cannot simply be explained by the ability of KGF to stimulate type II cell proliferation. To identify the mechanisms involved in the protective effects of KGF, we used an inducible lung-specific transgenic approach to overexpress KGF in murine lungs, since constitutive overexpression of KGF in the mouse affects lung development. The transgenic system allowed us to identify the pro-survival Akt pathway as an important mediator of the protective effects of KGF both in vivo and in vitro. In addition, use of a yeast two-hybrid system led to the identification two proteins p90RSK and PAK4 that associate with the KGF receptor and are important for the protective functions of KGF. Experiments are underway to determine whether the different pathways triggered by KGF all converge on the Akt pathway, or whether they independently induce protective mechanisms that along with Akt are crucial for cell survival.

Keratinocyte growth factor therapy in murine oleic acid-induced acute lung injury

Alveolar type II (ATII) cell proliferation and differentiation are important mechanisms in repair following injury to the alveolar epithelium. KGF is a potent ATII cell mitogen, which has been demonstrated to be protective in a number of animal models of lung injury. We have assessed the effect of recombinant human KGF (rhKGF) and liposome-mediated KGF gene delivery in vivo and evaluated the potential of KGF as a therapy for acute lung injury in mice. rhKGF was administered intratracheally in male BALB/c mice to assess dose response and time course of proliferation. SP-B immunohistochemistry demonstrated significant increases in ATII cell numbers at all rhKGF doses compared with control animals and peaked 2 days following administration of 10 mg/kg rhKGF. Protein therapy in general is very expensive, and gene therapy has been suggested as a cheaper alternative for many protein replacement therapies. We evaluated the effect of topical and systemic liposome-mediated KGF-gene delivery on ATII cell proliferation. SP-B immunohistochemistry showed only modest increases in ATII cell numbers following gene delivery, and these approaches were therefore not believed to be capable of reaching therapeutic levels. The effect of rhKGF was evaluated in a murine model of OA-induced lung injury. This model was found to be associated with significant alveolar damage leading to severe impairment of gas exchange and lung compliance. Pretreatment with rhKGF 2 days before intravenous OA challenge resulted in significant improvements in PO2, PCO2, and lung compliance. This study suggests the feasibility of KGF as a therapy for acute lung injury.

Bench-to-bedside review: the role of the alveolar epithelium in the resolution of pulmonary edema in acute lung injury

Clearance of pulmonary edema fluid is accomplished by active ion transport, predominantly by the alveolar epithelium. Various ion pumps and channels on the surface of the alveolar epithelial cell generate an osmotic gradient across the epithelium, which in turn drives the movement of water out of the airspaces. Here, the mechanisms of alveolar ion and fluid clearance are reviewed. In addition, many factors that regulate the rate of edema clearance, such as catecholamines, steroids, cytokines, and growth factors, are discussed. Finally, we address the changes to the alveolar epithelium and its transport processes during acute lung injury (ALI). Since relevant clinical outcomes correlate with rates of edema clearance in ALI, therapies based on our understanding of the mechanisms and regulation of fluid transport may be developed.

Keratinocyte growth factor transiently alters pulmonary function in rats

Keratinocyte growth factor (KGF) is a mitogen for pulmonary epithelial cells. Intratracheal administration of KGF to adult rats results in alveolar epithelial type II and bronchiolar epithelial cell proliferation. While cellular responses to KGF have been intensively studied, functional consequences regarding lung function are unknown. Therefore, in this study, we sought to investigate whether KGF alters pulmonary function variables. Rats received either recombinant human KGF (rHuKGF) (5 mg/kg) or vehicle intratracheally. Before and on days 3 and 7 after treatment, pulmonary function was determined by body plethysmography. Subsequently, lung histological changes were quantified. rHuKGF induced a transient proliferation of alveolar and bronchiolar epithelial cells. The extent of type II cell hyperplasia was significantly correlated with a transient reduction in tidal volume and an increase in breathing frequency. In addition, quasi-static compliance, total lung capacity, and vital capacity were reduced after rHuKGF instillation, suggesting the development of a transitory restrictive lung disorder. Moreover, reduced expiratory flow rates and forced expiratory volumes, as well as increased functional residual capacity after rHuKGF but not vehicle, suggest obstructive lung function changes. In conclusion, the induction of alveolar and bronchiolar epithelial cell proliferation by KGF is paralleled by moderate functional consequences that should be taken into account when the therapeutic potential of KGF is tested.

Surfactant protein A is a required mediator of keratinocyte growth factor after experimental marrow transplantation

We reported an association between the ability of recombinant human keratinocyte growth factor (rHuKGF) to upregulate the expression of surfactant protein A (SP-A) and to downregulate pulmonary inflammation that occurs after allogeneic bone marrow transplantation (BMT). To establish a causal relationship, rHuKGF (5 mg/kg) was administered subcutaneously for three consecutive days before irradiation to SP-A-sufficient and -deficient [SP-A(+/+) and SP-A(-/-), respectively] mice given inflammation-inducing allogeneic spleen T cells at the time of BMT. In contrast with SP-A(+/+) mice, rHuKGF failed to suppress the high levels of TNF-alpha, IFN-gamma, and nitric oxide contained in bronchoalveolar lavage fluids collected on day 7 after BMT from SP-A(-/-) mice. Early post-BMT weight loss was attenuated by rHuKGF in both SP-A(+/+) and SP-A(-/-) recipients. In the absence of supportive respiratory care, however, SP-A deficiency eventually abolished the ability of rHuKGF to prevent weight loss and to improve survival monitored for 1 mo after allogeneic BMT. In further experiments, the addition of cyclophosphamide (which is known to cause severe injury to the alveolar epithelium in donor T cell-recipient mice) to the conditioning regimen prevented rHuKGF-induced upregulation of SP-A and suppression of lung inflammation in both SP-A(+/+) and SP-A(-/-) mice. We conclude that endogenous baseline SP-A levels and optimal upregulation of SP-A are required for the anti-inflammatory protective effects of KGF after allogeneic transplantation.

Keratinocyte growth factor and beta-cell differentiation in human fetal pancreatic endocrine precursor cells

AIMS AND HYPOTHESIS

Keratinocyte growth factor (KGF) is a member of the heparin-binding fibroblast growth factor family with a high degree of specificity for epithelial cells in vitro and in vivo. Our aim was to study the effect of KGF on beta-cell growth and differentiation on islet-like cell clusters derived from human fetal pancreas.

METHODS

We investigated the effects of KGF, in vitro, on beta-cell differentiation from undifferentiated pancreatic precursor cells and in vivo after transplantating human fetal pancreatic cells into athymic rats treated with KGF.

RESULTS

Treatment of islet-like cell clusters with KGF in vitro did not change the number of insulin producing cells, as measured by the measurement of insulin content or DNA. The in vivo treatment of recipient rats with KGF increased the number of beta cells within the grafts 8 weeks after transplantation. At this time, glucose-stimulated insulin secretion was evaluated by glucose stimulation tests in rats bearing the transplants. Measurements of human C-peptide concentrations after glucose challenge showed that the newly differentiated beta cells in the KGF-treated group were functionally competent as opposed to the control group, where the graft failed to release insulin appropriately.

CONCLUSION/INTERPRETATION

These findings suggest that in vivo, KGF is capable of inducing human fetal beta-cell expansion. The growth promoting effect of KGF on beta cells occurred mainly through the activation of ductal cell proliferation and their subsequent differentiation into beta cells.

Inducible expression of keratinocyte growth factor (KGF) in mice inhibits lung epithelial cell death induced by hyperoxia

Oxidant-induced injury to the lung is associated with extensive damage to the lung epithelium. Instillation of keratinocyte growth factor (KGF) in the lungs of animals protects animals from oxidant-induced injury but the mechanism of protection is not well understood. An inherent problem in studying KGF function in vivo has been that constitutive overexpression of KGF in the lung causes embryonic lethality with extensive pulmonary malformation. Here we report the development of a stringently regulated, tetracycline-inducible, lung-specific transgenic system that allows regulated expression of KGF in the lung without causing developmental abnormalities from leaky KGF expression. By using this system, we show that exposure of KGF-expressing mice to hyperoxia protects the lung epithelium but not the endothelium from cell death in accordance with the selective expression of KGF receptor on epithelial and not on endothelial cells. Investigations of KGF-induced cell survival pathways revealed KGF-induced activation of the multifunctional pro-survival Akt signaling axis both in vitro and in vivo. Inhibition of KGF-induced Akt activation by a dominant-negative mutant of Akt blocked the KGF-mediated protection of epithelial cells exposed to hyperoxia. KGF-induced Akt activation may play an important role in inhibiting lung alveolar cell death thereby preserving the lung architecture and function during oxidative stress.

Keratinocyte growth factor (KGF) decreases ICAM-1 and VCAM-1 cell expression on bronchial epithelial cells

Activation of leucocytes during airway inflammatory reaction involves adhesion to bronchial epithelial cells (BEC), a process implicating specific interactions between glycoproteins with epithelial cell surface proteins, mainly intercellular adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1). In this study, the effect of keratinocyte growth factor (KGF), a growth factor involved in pulmonary epithelium repair, was evaluated on adhesion molecule expression with BEAS-2B cells and BEC and granulocyte adherence to BEAS-2B. The modulation by KGF of membrane and mRNA expression of ICAM-1 and VCAM-1 was studied on confluent cells stimulated or not with tumour necrosis factor-alpha (TNF) (200 UI/ml) or TNF and interleukin (IL)-4 (50 UI/ml and 10 ng/ml). Levels of soluble-(s)ICAM-1 and sVCAM-1 were measured by ELISA. Although moderately, KGF significantly decreased membrane ICAM-1 expression in unstimulated BEAS-2B cells (24% inhibition at 100 ng/ml) or in TNF- or TNF + IL-4-stimulated cells (22.5 and 18.7% inhibition, respectively). Treatment with KGF tended to decrease VCAM-1 expression in TNF- and TNF + IL-4-stimulated BEAS-2B (P = n.s. and P < 0.05, 14 and 15% inhibition, respectively). In primary culture of BEC, adhesion molecule expression was also reduced. ICAM-1 and VCAM-1 mRNA expression were also inhibited by KGF. Levels of sICAM-1 and sVCAM-1 were not significantly increased in supernatants from KGF-treated cells (30% and 24% increase at 100 ng/ml, respectively) compared to controls. Moreover, KGF decreased by 31% the adherence of neutrophils to TNF-activated BEAS-2B. In conclusion, KGF decreases ICAM-1 and VCAM-1 expression and neutrophil adherence in BEC. These suggest its involvement in the resolution of the inflammatory reaction.

Sharing signals: connecting lung epithelial cells with gap junction channels

Gap junction channels enable the direct flow of signaling molecules and metabolites between cells. Alveolar epithelial cells show great variability in the expression of gap junction proteins (connexins) as a function of cell phenotype and cell state. Differential connexin expression and control by alveolar epithelial cells have the potential to enable these cells to regulate the extent of intercellular coupling in response to cell stress and to regulate surfactant secretion. However, defining the precise signals transmitted through gap junction channels and the cross talk between gap junctions and other signaling pathways has proven difficult. Insights from what is known about roles for gap junctions in other systems in the context of the connexin expression pattern by lung cells can be used to predict potential roles for gap junctional communication between alveolar epithelial cells.

Invited review: Active fluid clearance from the distal air spaces of the lung

Active ion transport drives iso-osmolar alveolar fluid clearance, a hypothesis originally suggested by in vivo studies in sheep 20 yr ago. Over the last two decades, remarkable progress has been made in establishing a critical role for active sodium transport as a primary mechanism that drives fluid clearance from the distal air spaces of the lung. The rate of fluid transport can be increased in most species, including the human lung, by cAMP stimulation. Catecholamine-independent mechanisms, including hormones, growth factors, and cytokines, can also upregulate epithelial fluid clearance in the lung. The new insights into the role of the distal lung epithelium in actively regulating lung fluid balance has important implications for the resolution of clinical pulmonary edema.

Lung epithelial fluid transport and the resolution of pulmonary edema

The discovery of mechanisms that regulate salt and water transport by the alveolar and distal airway epithelium of the lung has generated new insights into the regulation of lung fluid balance under both normal and pathological conditions. There is convincing evidence that active sodium and chloride transporters are expressed in the distal lung epithelium and are responsible for the ability of the lung to remove alveolar fluid at the time of birth as well as in the mature lung when pathological conditions lead to the development of pulmonary edema. Currently, the best described molecular transporters are the epithelial sodium channel, the cystic fibrosis transmembrane conductance regulator, Na+-K+-ATPase, and several aquaporin water channels. Both catecholamine-dependent and -independent mechanisms can upregulate isosmolar fluid transport across the distal lung epithelium. Experimental and clinical studies have made it possible to examine the role of these transporters in the resolution of pulmonary edema.

Keratinocyte growth factor can enhance alveolar epithelial repair by nonmitogenic mechanisms

Pretreatment with keratinocyte growth factor (KGF) ameliorates experimentally induced acute lung injury in rats. Although alveolar epithelial type II cell hyperplasia probably contributes, the mechanisms underlying KGF's protective effect remain incompletely described. Therefore, we tested the hypothesis that KGF given to rats in vivo would enhance alveolar epithelial repair in vitro by nonproliferative mechanisms. After intratracheal instillation (48 h) of KGF (5 mg/kg), alveolar epithelial type II cells were isolated for in vitro alveolar epithelial repair studies. KGF-treated cells had markedly increased epithelial repair (96 +/- 22%) compared with control cells (P < 0.001). KGF-treated cells had increased cell spreading and migration at the wound edge but no increase in in vitro proliferation compared with control cells. KGF-treated cells were more adherent to extracellular matrix proteins and polystyrene. Inhibition of the epidermal growth factor (EGF) receptor with tyrosine kinase inhibitors abolished the KGF effect on epithelial repair. In conclusion, in vivo administration of KGF augments the epithelial repair rate of alveolar epithelial cells by altering cell adherence, spreading, and migration and through stimulation of the EGF receptor.

Keratinocyte and hepatocyte growth factors in the lung: roles in lung development, inflammation, and repair

A growing body of evidence indicates that the epithelial-specific growth factors keratinocyte growth factor (KGF), fibroblast growth factor (FGF)-10, and hepatocyte growth factor (HGF) play important roles in lung development, lung inflammation, and repair. The therapeutic potential of these growth factors in lung disease has yet to be fully explored. KGF has been best studied and has impressive protective effects against a wide variety of injurious stimuli when given as a pretreatment in animal models. Whether this protective effect could translate to a treatment effect in humans with acute lung injury needs to be investigated. FGF-10 and HGF may also have therapeutic potential, but more extensive studies in animal models are needed. Because HGF lacks true epithelial specificity, it may have less potential than KGF and FGF-10 as a targeted therapy to facilitate lung epithelial repair. Regardless of their therapeutic potential, studies of the unique roles played by these growth factors in the pathogenesis and the resolution of acute lung injury and other lung diseases will continue to enhance our understanding of the complex pathophysiology of inflammation and repair in the lung.

KGF alters gene expression in human airway epithelia: potential regulation of the inflammatory response

Keratinocyte growth factor (KGF) regulates several functions in adult and developing lung epithelia; it causes proliferation, stimulates secretion of fluid and electrolytes, enhances repair, and may minimize injury. To gain insight into the molecular processes influenced by KGF, we applied KGF to primary cultures of well-differentiated human airway epithelia and used microarray hybridization to assess the abundance of gene transcripts. Of 7,069 genes tested, KGF changed expression levels of 910. Earlier studies showed that KGF causes epithelial proliferation, and as expected, treatment altered expression of numerous genes involved in cell proliferation. We found that KGF stimulated transepithelial Cl(-) transport, but the number of cystic fibrosis (CF) transmembrane conductance regulator (CFTR) transcripts fell. Although transcripts for ClC-1 and ClC-7 Cl(-) channels increased, KGF failed to augment transepithelial Cl(-) transport in CF epithelia, suggesting that KGF-stimulated Cl(-) transport in differentiated airway epithelia depends on the CFTR Cl(-) channel. Interestingly, KGF decreased transcripts for many interferon (IFN)-induced genes. IFN causes trafficking of Stat dimers to the nucleus, where they activate transcription of IFN-induced genes. We found that KGF prevented the IFN-stimulated trafficking of Stat1 from the cytosol to the nucleus, suggesting a molecular mechanism for KGF-mediated suppression of the IFN-signaling pathway. These results suggest that in addition to stimulating proliferation and repair of damaged airway epithelia, KGF stimulates Cl(-) transport and may dampen the response of epithelial cells to inflammatory mediators.

KGF regulates pulmonary epithelial proliferation and surfactant protein gene expression in adult rat lung

Keratinocyte growth factor (KGF, FGF-7) is a potent mitogen for epithelial cells. We instilled recombinant human KGF to determine the effects of KGF on alveolar epithelial cells. Left lungs of adult rats were instilled intrabronchially with KGF (5 mg/kg) or normal saline. KGF instillation resulted in epithelial cell hyperplasia, and the alveolar bromodeoxyuridine (BrdU) labeling index peaked at 35% on day 2 after instillation. The mRNA levels for the surfactant proteins (SPs) SP-A, SP-B, and SP-D were increased in whole lung tissue on days 1 and 2 after KGF treatment and then returned to control levels on days 3-7. SP-C mRNA levels were increased on days 2-5 after KGF instillation. However, all surfactant protein mRNAs were reduced in type II cells isolated from rats instilled with KGF 2 or 3 days before isolation. These observations were confirmed by in situ hybridization. Instillation of KGF also increased the amount of SP-A and SP-D in lavage fluid. Transcripts for CC10, the 10-kDa Clara cell protein, were decreased. KGF increases the mRNA for the surfactant proteins per lung because of type II cell hyperplasia, but the mRNA per cell is slightly diminished as measured in isolated cells or estimated by in situ hybridization.

Keratinocyte growth factor prevents ventilator-induced lung injury in an ex vivo rat model

Mechanical ventilation has been shown to produce lung injury characterized by noncardiogenic pulmonary edema. Keratinocyte growth factor (KGF) is a heparin-binding growth factor that causes alveolar type II pneumocyte hyperplasia. KGF pretreatment and the resultant pneumocyte hyperplasia reduce fluid flux in models of lung injury. We utilized the isolated perfused rat lung model to produce lung injury by varying tidal volume and the level of positive end-expiratory pressure during mechanical ventilation. Pretreatment with KGF attenuated ventilator-induced lung injury (VILI). This was demonstrated by lower wet-to-dry lung weight ratios and less lung water accumulation in the KGF group. Further, KGF prevented the decline in dynamic compliance and alveolar protein accumulation in VILI. KGF pretreatment reduced alveolar accumulation of intravascularly administered fluorescein isothiocyanate-labeled high-molecular-weight dextran. Thus, pretreatment with KFG attenuates injury in this ex vivo model of VILI via mechanisms that prevent increases in permeability.

KGF pretreatment decreases B7 and granzyme B expression and hastens repair in lungs of mice after allogeneic BMT

We investigated keratinocyte growth factor (KGF) as a pretreatment therapy for idiopathic pneumonia syndrome (IPS) generated as a result of lung damage and allogeneic T cell-dependent inflammatory events occurring in the early peri-bone marrow (BM) transplant (BMT) period. B10.BR (H2(k)) recipient mice were transplanted with C57BL/6 (H2(b)) BM with spleen cells after lethal irradiation with and without cyclophosphamide conditioning with and without subcutaneous KGF pretreatment. KGF-pretreated mice had fewer injured alveolar type II (ATII) cells at the time of BMT and exhibited ATII cell hyperplasia at day 3 post-BMT. The composition of infiltrating cells on day 7 post-BMT was not altered by KGF pretreatment, but the frequencies of cells expressing the T-cell costimulatory molecules B7.1 and B7.2 and mRNA for the cytolysin granzyme B (usually increased in IPS) were decreased by KGF. Sera from KGF-treated mice had increases in the Th2 cytokines interleukin (IL)-4, IL-6, and IL-13 4 days after cessation of KGF administration (i.e., at the time of BMT). These data suggest that KGF hinders IPS by two modes: 1) stimulation of alveolar epithelialization and 2) attenuation of immune-mediated injury as a consequence of failure to upregulate cytolytic molecules and B7 ligand expression and the induction of anti-inflammatory Th2 cytokines in situ.

Keratinocyte growth factor protects alveolar epithelium and endothelium from oxygen-induced injury in mice

Keratinocyte growth factor (KGF) has been used successfully to prevent alveolar damage induced by oxygen exposure in rodents. However, this treatment was used intratracheally and before oxygen exposure, which limited its clinical application. In the present study, mice were treated with the recombinant human KGF intravenously before (days -2 and -1) or during (days 0 and +1) oxygen exposure. In both cases, lung damage was attenuated. KGF increased the number of cells incorporating bromodeoxyuridine (BrdU) in the septa and in bronchial epithelium of air-breathing mice but not of oxygen-exposed mice, indicating that the protective effect of KGF is not necessarily associated with proliferation. Oxygen-induced damage of alveolar epithelium and, unexpectedly, of endothelium was prevented by KGF treatment as seen by electron microscopy. We investigated the effect of KGF on different mechanisms known to be involved in oxygen toxicity. The induction of p53, Bax, and Bcl-x mRNAs during hyperoxia was to a large extent prevented by KGF. Surfactant proteins A and B mRNAs were not markedly modified by KGF. The anti-fibrinolytic activity observed in the alveoli during hyperoxia was to a large extent prevented by KGF, most probably by suppressing the expression of plasminogen activator inhibitor-1 (PAI-1) mRNA and protein. As PAI-1 -/- mice are more resistant to hyperoxia, KGF might act, at least in part, by decreasing the expression of this protease inhibitor and by restoring the fibrinolytic activity into the lungs.