Fibronectin and fibronectin receptors in lung development

Differentiation of human induced pluripotent stem cells into functional lung alveolar epithelial cells in 3D dynamic culture

Introduction: Understanding lung epithelium cell development from human induced pluripotent stem cells (IPSCs) in vitro can lead to an individualized model for lung engineering, therapy, and drug testing. Method: We developed a protocol to produce lung mature type I pneumocytes using encapsulation of human IPSCs in 1.1% (w/v) alginate solution within a rotating wall bioreactor system in only 20 days without using feeder cells. The aim was to reduce exposure to animal products and laborious interventions in the future. Results: The three-dimensional (3D) bioprocess allowed cell derivation into endoderm, and subsequently into type II alveolar epithelial cells within a very short period. Cells successfully expressed surfactant proteins C and B associated with type II alveolar epithelial cells, and the key structure of lamellar bodies and microvilli was shown by transmission electron microscopy. The survival rate was the highest under dynamic conditions, which reveal the possibility of adapting this integration for large-scale cell production of alveolar epithelial cells from human IPSCs. Discussion: We were able to develop a strategy for the culture and differentiation of human IPSCs into alveolar type II cells using an in vitro system that mimics the in vivo environment. Hydrogel beads would offer a suitable matrix for 3D cultures and that the high-aspect-ratio vessel bioreactor can be used to increase the differentiation of human IPSCs relative to the results obtained with traditional monolayer cultures.

Defining the Versican Interactome in Lung Health and Disease

The extracellular matrix (ECM) imparts critical mechanical and biochemical information to cells in the lungs. Proteoglycans are essential constituents of the ECM and play a crucial role in controlling numerous biological processes, including regulating cellular phenotype and function. Versican, a chondroitin sulfate proteoglycan required for embryonic development, is almost absent from mature, healthy lungs and is re-expressed and accumulates in acute and chronic lung disease. Studies using genetically engineered mice show that the versican-enriched matrix can be pro- or anti-inflammatory depending on the cellular source or disease process studied. The mechanisms whereby versican develops a contextual ECM remain largely unknown. The primary goal of this review is to provide an overview of the interaction of versican with its many binding partners, the "versican interactome," and how through these interactions, versican is an integrator of complex extracellular information. Hopefully, the information provided in this review will be used to develop future studies to determine how versican and its binding partners can develop contextual ECMs that control select biological processes. While this review focuses on versican and the lungs, what is described can be extended to other proteoglycans, tissues, and organs.

IL-33-induced neutrophil extracellular traps degrade fibronectin in a murine model of bronchopulmonary dysplasia

Bronchopulmonary dysplasia (BPD) is the leading cause of chronic lung disease in preterm neonates. Extracellular matrix (ECM) abnormalities reshape lung development, contributing to BPD progression. In the present study, we first discovered that the ECM component fibronectin was reduced in the pulmonary tissues of model mice with BPD induced by lipopolysaccharide (LPS) and hyper-oxygen. Meanwhile, interleukin-33 (IL-33) and other inflammatory cytokines were elevated in BPD lung tissues. LPS stimulated the production of IL-33 in alveolar epithelial cells via myeloid differentiation factor 88 (MyD88), protein 38 (p38), and nuclear factor-kappa B (NF-κB) protein 65 (p65). Following the knockout of either IL-33 or its receptor suppression of tumorigenicity 2 (ST2) in mice, BPD disease severity was improved, accompanied by elevated fibronectin. ST2 neutralization antibody also relieved BPD progression and restored the expression of fibronectin. IL-33 induced the formation of neutrophil extracellular traps (NETs), which degraded fibronectin in alveolar epithelial cells. Moreover, DNase-mediated degradation of NETs was protective against BPD. Finally, a fibronectin inhibitor directly decreased fibronectin and caused BPD-like disease in the mouse model. Our findings may shed light on the roles of IL-33-induced NETs and reduced fibronectin in the pathogenesis of BPD.

Lung Microvascular Niche, Repair, and Engineering

Biomaterials have been used for a long time in the field of medicine. Since the success of "tissue engineering" pioneered by Langer and Vacanti in 1993, tissue engineering studies have advanced from simple tissue generation to whole organ generation with three-dimensional reconstruction. Decellularized scaffolds have been widely used in the field of reconstructive surgery because the tissues used to generate decellularized scaffolds can be easily harvested from animals or humans. When a patient's own cells can be seeded onto decellularized biomaterials, theoretically this will create immunocompatible organs generated from allo- or xeno-organs. The most important aspect of lung tissue engineering is that the delicate three-dimensional structure of the organ is maintained during the tissue engineering process. Therefore, organ decellularization has special advantages for lung tissue engineering where it is essential to maintain the extremely thin basement membrane in the alveoli. Since 2010, there have been many methodological developments in the decellularization and recellularization of lung scaffolds, which includes improvements in the decellularization protocols and the selection and preparation of seeding cells. However, early transplanted engineered lungs terminated in organ failure in a short period. Immature vasculature reconstruction is considered to be the main cause of engineered organ failure. Immature vasculature causes thrombus formation in the engineered lung. Successful reconstruction of a mature vasculature network would be a major breakthrough in achieving success in lung engineering. In order to regenerate the mature vasculature network, we need to remodel the vascular niche, especially the microvasculature, in the organ scaffold. This review highlights the reconstruction of the vascular niche in a decellularized lung scaffold. Because the vascular niche consists of endothelial cells (ECs), pericytes, extracellular matrix (ECM), and the epithelial-endothelial interface, all of which might affect the vascular tight junction (TJ), we discuss ECM composition and reconstruction, the contribution of ECs and perivascular cells, the air-blood barrier (ABB) function, and the effects of physiological factors during the lung microvasculature repair and engineering process. The goal of the present review is to confirm the possibility of success in lung microvascular engineering in whole organ engineering and explore the future direction of the current methodology.

Type VI collagen promotes lung epithelial cell spreading and wound-closure

Basement membrane (BM) is an essential part of the extracellular matrix (ECM) that plays a crucial role in mechanical support and signaling to epithelial cells during lung development, homeostasis and repair. Abnormal composition and remodeling of the lung ECM have been associated with developmental abnormalities observed in multiple pediatric and adult respiratory diseases. Collagen VI (COL6) is a well-studied muscle BM component, but its role in the lung and its effect on pulmonary epithelium is largely undetermined. We report the presence of COLVI immediately subjacent to human airway and alveolar epithelium in the pediatric lung, in a location where it is likely to interact with epithelial cells. In vitro, both primary human lung epithelial cells and human lung epithelial cell lines displayed an increased rate of “wound healing” in response to a scratch injury when plated on COL6 as compared to other matrices. For the 16HBE cell line, wounds remained >5-fold larger for cells on COL1 (p<0.001) and >6-fold larger on matrigel (p<0.001), a prototypical basement membrane, when compared to COL6 (>96% closure at 10 hr). The effect of COL6 upon lung epithelial cell phenotype was associated with an increase in cell spreading. Three hours after initial plating, 16HBE cells showed >7-fold less spreading on matrigel (p<0.01), and >4-fold less spreading on COL1 (p<0.01) when compared to COL6. Importantly, the addition of COL6 to other matrices also enhanced cell spreading. Similar responses were observed for primary cells. Inhibitor studies indicated both integrin β1 activity and activation of multiple signaling pathways was required for enhanced spreading on all matrices, with the PI3K/AKT pathway (PI3K, CDC42, RAC1) showing both significant and specific effects for spreading on COL6. Genetic gain-of-function experiments demonstrated enhanced PI3K/AKT pathway activity was sufficient to confer equivalent cell spreading on other matrices as compared to COL6. We conclude that COL6 has significant and specific effects upon human lung epithelial cell-autonomous functions.

Identification and characterisation of elongation factor Tu, a novel protein involved in Paracoccidioides brasiliensis-host interaction

Paracoccidioides spp., which are temperature-dependent dimorphic fungi, are responsible for the most prevalent human systemic mycosis in Latin America, the paracoccidioidomycosis. The aim of this study was to characterise the involvement of elongation factor Tu (EF-Tu) in Paracoccidioides brasiliensis-host interaction. Adhesive properties were examined using recombinant PbEF-Tu proteins and the respective polyclonal anti-rPbEF-Tu antibody. Immunogold analysis demonstrated the surface location of EF-Tu in P. brasiliensis. Moreover, PbEF-Tu was found to bind to fibronectin and plasminogen by enzyme-linked immunosorbent assay, and it was determined that the binding to plasminogen is at least partly dependent on lysine residues and ionic interactions. To verify the participation of EF-Tu in the interaction of P. brasiliensis with pneumocytes, we blocked the respective protein with an anti-rPbEF-Tu antibody and evaluated the consequences on the interaction index by flow cytometry. During the interaction, we observed a decrease of 2- and 3-fold at 8 and 24 h, respectively, suggesting the contribution of EF-Tu in fungal adhesion/invasion.

Laminin and Matrix metalloproteinase 11 regulate Fibronectin levels in the zebrafish myotendinous junction

BACKGROUND

Remodeling of the extracellular matrix (ECM) regulates cell adhesion as well as signaling between cells and their microenvironment. Despite the importance of tightly regulated ECM remodeling for normal muscle development and function, mechanisms underlying ECM remodeling in vivo remain elusive. One excellent paradigm in which to study ECM remodeling in vivo is morphogenesis of the myotendinous junction (MTJ) during zebrafish skeletal muscle development. During MTJ development, there are dramatic shifts in the primary components comprising the MTJ matrix. One such shift involves the replacement of Fibronectin (Fn)-rich matrix, which is essential for both somite and early muscle development, with laminin-rich matrix essential for normal function of the myotome. Here, we investigate the mechanism underlying this transition.

RESULTS

We show that laminin polymerization indirectly promotes Fn downregulation at the MTJ, via a matrix metalloproteinase 11 (Mmp11)-dependent mechanism. Laminin deposition and organization is required for localization of Mmp11 to the MTJ, where Mmp11 is both necessary and sufficient for Fn downregulation in vivo. Furthermore, reduction of residual Mmp11 in laminin mutants promotes a Fn-rich MTJ that partially rescues skeletal muscle architecture.

CONCLUSIONS

These results identify a mechanism for Fn downregulation at the MTJ, highlight crosstalk between laminin and Fn, and identify a new in vivo function for Mmp11. Taken together, our data demonstrate a novel signaling pathway mediating Fn downregulation. Our data revealing new regulatory mechanisms that guide ECM remodeling during morphogenesis in vivo may inform pathological conditions in which Fn is dysregulated.

Extracellular matrix bioscaffolds in tissue remodeling and morphogenesis

During normal morphogenesis the extracellular matrix (ECM) influences cell motility, proliferation, apoptosis, and differentiation. Tissue engineers have attempted to harness the cell signaling potential of ECM to promote the functional reconstruction, if not regeneration, of injured or missing adult tissues that otherwise heal by the formation of scar tissue. ECM bioscaffolds, derived from decellularized tissues, have been used to promote the formation of site appropriate, functional tissues in many clinical applications including skeletal muscle, fibrocartilage, lower urinary tract, and esophageal reconstruction, among others. These scaffolds function by the release or exposure of growth factors and cryptic peptides, modulation of the immune response, and recruitment of progenitor cells. Herein, we describe this process of ECM induced constructive remodeling and examine similarities to normal tissue morphogenesis.

The Extracellular Matrix in Bronchopulmonary Dysplasia: Target and Source

Bronchopulmonary dysplasia (BPD) is a common complication of preterm birth that contributes significantly to morbidity and mortality in neonatal intensive care units. BPD results from life-saving interventions, such as mechanical ventilation and oxygen supplementation used to manage preterm infants with acute respiratory failure, which may be complicated by pulmonary infection. The pathogenic pathways driving BPD are not well-delineated but include disturbances to the coordinated action of gene expression, cell-cell communication, physical forces, and cell interactions with the extracellular matrix (ECM), which together guide normal lung development. Efforts to further delineate these pathways have been assisted by the use of animal models of BPD, which rely on infection, injurious mechanical ventilation, or oxygen supplementation, where histopathological features of BPD can be mimicked. Notable among these are perturbations to ECM structures, namely, the organization of the elastin and collagen networks in the developing lung. Dysregulated collagen deposition and disturbed elastin fiber organization are pathological hallmarks of clinical and experimental BPD. Strides have been made in understanding the disturbances to ECM production in the developing lung, but much still remains to be discovered about how ECM maturation and turnover are dysregulated in aberrantly developing lungs. This review aims to inform the reader about the state-of-the-art concerning the ECM in BPD, to highlight the gaps in our knowledge and current controversies, and to suggest directions for future work in this exciting and complex area of lung development (patho)biology.

Revascularization of decellularized lung scaffolds: principles and progress

There is a clear unmet clinical need for novel biotechnology-based therapeutic approaches to lung repair and/or replacement, such as tissue engineering of whole bioengineered lungs. Recent studies have demonstrated the feasibility of decellularizing the whole organ by removal of all its cellular components, thus leaving behind the extracellular matrix as a complex three-dimensional (3D) biomimetic scaffold. Implantation of decellularized lung scaffolds (DLS), which were recellularized with patient-specific lung (progenitor) cells, is deemed the ultimate alternative to lung transplantation. Preclinical studies demonstrated that, upon implantation in rodent models, bioengineered lungs that were recellularized with airway and vascular cells were capable of gas exchange for up to 14 days. However, the long-term applicability of this concept is thwarted in part by the failure of current approaches to reconstruct a physiologically functional, quiescent endothelium lining the entire vascular tree of reseeded lung scaffolds, as inferred from the occurrence of hemorrhage into the airway compartment and thrombosis in the vasculature in vivo. In this review, we explore the idea that successful whole lung bioengineering will critically depend on 1) preserving and/or reestablishing the integrity of the subendothelial basement membrane, especially of the ultrathin respiratory membrane separating airways and capillaries, during and following decellularization and 2) restoring vascular physiological functionality including the barrier function and quiescence of the endothelial lining following reseeding of the vascular compartment. We posit that physiological reconstitution of the pulmonary vascular tree in its entirety will significantly promote the clinical translation of the next generation of bioengineered whole lungs.

Hanging on for the ride: adhesion to the extracellular matrix mediates cellular responses in skeletal muscle morphogenesis and disease

Skeletal muscle specification and morphogenesis during early development are critical for normal physiology. In addition to mediating locomotion, skeletal muscle is a secretory organ that contributes to metabolic homeostasis. Muscle is a highly adaptable tissue, as evidenced by the ability to increase muscle cell size and/or number in response to weight bearing exercise. Conversely, muscle wasting can occur during aging (sarcopenia), cancer (cancer cachexia), extended hospital stays (disuse atrophy), and in many genetic diseases collectively known as the muscular dystrophies and myopathies. It is therefore of great interest to understand the cellular and molecular mechanisms that mediate skeletal muscle development and adaptation. Muscle morphogenesis transforms short muscle precursor cells into long, multinucleate myotubes that anchor to tendons via the myotendinous junction. This process requires carefully orchestrated interactions between cells and their extracellular matrix microenvironment. These interactions are dynamic, allowing muscle cells to sense biophysical, structural, organizational, and/or signaling changes within their microenvironment and respond appropriately. In many musculoskeletal diseases, these cell adhesion interactions are disrupted to such a degree that normal cellular adaptive responses are not sufficient to compensate for accumulating damage. Thus, one major focus of current research is to identify the cell adhesion mechanisms that drive muscle morphogenesis, with the hope that understanding how muscle cell adhesion promotes the intrinsic adaptability of muscle tissue during development may provide insight into potential therapeutic approaches for muscle diseases. Our objectives in this review are to highlight recent studies suggesting conserved roles for cell-extracellular matrix adhesion in vertebrate muscle morphogenesis and cellular adaptive responses in animal models of muscle diseases.

Cellular and physical mechanisms of branching morphogenesis

Branching morphogenesis is the developmental program that builds the ramified epithelial trees of various organs, including the airways of the lung, the collecting ducts of the kidney, and the ducts of the mammary and salivary glands. Even though the final geometries of epithelial trees are distinct, the molecular signaling pathways that control branching morphogenesis appear to be conserved across organs and species. However, despite this molecular homology, recent advances in cell lineage analysis and real-time imaging have uncovered surprising differences in the mechanisms that build these diverse tissues. Here, we review these studies and discuss the cellular and physical mechanisms that can contribute to branching morphogenesis.

miRNA regulated pathways in late stage murine lung development

Background

MicroRNAs play important roles in regulating biological processes, including organ morphogenesis and maturation. However, little is known about specific pathways regulated by miRNA during lung development. Between the canalicular and saccular stages of the developing lung several important cellular events occur, including the onset of surfactant synthesis, microvascular remodeling and structural preparation for subsequent alveolarization. The miRNAs that are actively regulated, and the identity of their targets during this important developmental interval in the lung remain elusive.

Results

Using TLDA low density real-time PCR arrays, the expression of 376 miRNAs in male and female fetal mouse lungs of gestational days E15 – E18 were profiled. Statistical analyses identified 25 and 37 miRNAs that changed significantly between sexes and with gestation, respectively. In silico analysis using Ingenuity Pathway Analysis (IPA) identified specific pathways and networks known to be targets of these miRNAs which are important to lung development. Pathways that are targeted by sex regulated miRNAs include retinoin, IGFR1, Tp53 and Akt. Pathways targeted by gestation-regulated miRNAs include VEGFA and mediators of glucose metabolism.

Conclusion

MiRNAs are differentially regulated across time and between sexes during the canalicular and saccular stages of lung development. Sex-associated differential miRNA expression may regulate the differences in structural and functional male and female lung development, as shown by networks generated using in silico analysis. These data provide a valuable resource to further enhance the understanding of miRNA control of lung development and maturation.

Neisseria gonorrhoeae induced disruption of cell junction complexes in epithelial cells of the human genital tract

Pathogenic microorganisms, such as Neisseria gonorrhoeae, have developed mechanisms to alter epithelial barriers in order to reach subepithelial tissues for host colonization. The aim of this study was to examine the effects of gonococci on cell junction complexes of genital epithelial cells of women. Polarized Ishikawa cells, a cell line derived from endometrial epithelium, were used for experimental infection. Infected cells displayed a spindle-like shape with an irregular distribution, indicating potential alteration of cell-cell contacts. Accordingly, analysis by confocal microscopy and cellular fractionation revealed that gonococci induced redistribution of the adherens junction proteins E-cadherin and its adapter protein β-catenin from the membrane to a cytoplasmic pool, with no significant differences in protein levels. In contrast, gonococcal infection did not induce modification of either expression or distribution of the tight junction proteins Occludin and ZO-1. Similar results were observed for Fallopian tube epithelia. Interestingly, infected Ishikawa cells also showed an altered pattern of actin cytoskeleton, observed in the form of stress fibers across the cytoplasm, which in turn matched a strong alteration on the expression of fibronectin, an adhesive glycoprotein component of extracellular matrix. Interestingly, using western blotting, activation of the ERK pathway was detected after gonococcal infection while p38 pathway was not activated. All effects were pili and Opa independent. Altogether, results indicated that gonococcus, as a mechanism of pathogenesis, induced disruption of junction complexes with early detaching of E-cadherin and β-catenin from the adherens junction complex, followed by a redistribution and reorganization of actin cytoskeleton and fibronectin within the extracellular matrix.

Mesenchymal nuclear factor I B regulates cell proliferation and epithelial differentiation during lung maturation

The Nuclear factor I (NFI) transcription factor family consists of four genes (Nfia, Nfib, Nfic and Nfix) that regulate the development of multiple organ systems in mice and humans. Nfib is expressed in both lung mesenchyme and epithelium and mice lacking Nfib have severe lung maturation defects and die at birth. Here we continue our analysis of the phenotype of Nfib⁻/⁻ lungs and show that Nfib specifically in lung mesenchyme controls late epithelial and mesenchymal cell proliferation and differentiation. There are more PCNA, BrdU, PHH3 and Ki67 positive cells in Nfib⁻/⁻ lungs than in wild type lungs at E18.5 and this increase in proliferation marker expression is seen in both epithelial and mesenchymal cells. The loss of Nfib in all lung cells decreases the expression of markers for alveolar epithelial cells (Aqp5 and Sftpc), Clara cells (Scgb1a1) and ciliated cells (Foxj1) in E18.5 lungs. To test for a specific role of Nfib in lung mesenchyme we generated and analyzed Nfib(flox/flox), Dermo1-Cre mice. Loss of Nfib only in mesenchyme results in decreased Aqp5, Sftpc and Foxj1 expression, increased cell proliferation, and a defect in sacculation similar to that seen in Nfib⁻/⁻ mice. In contrast, mesenchyme specific loss of Nfib had no effect on the expression of Scgb1a1 in the airway. Microarray and QPCR analyses indicate that the loss of Nfib in lung mesenchyme affects the expression of genes associated with extracellular matrix, cell adhesion and FGF signaling which could affect distal lung maturation. Our data indicate that mesenchymal Nfib regulates both mesenchymal and epithelial cell proliferation through multiple pathways and that mesenchymal NFI-B-mediated signals are essential for the maturation of distal lung epithelium.

Btbd7 regulates epithelial cell dynamics and branching morphogenesis

During embryonic development, many organs form by extensive branching of epithelia through the formation of clefts and buds. In cleft formation, buds are delineated by the conversion of epithelial cell-cell adhesions to cell-matrix adhesions, but the mechanisms of cleft formation are not clear. We have identified Btbd7 as a dynamic regulator of branching morphogenesis. Btbd7 provides a mechanistic link between the extracellular matrix and cleft propagation through its highly focal expression leading to local regulation of Snail2 (Slug), E-cadherin, and epithelial cell motility. Inhibition experiments show that Btbd7 is required for branching of embryonic mammalian salivary glands and lungs. Hence, Btbd7 is a regulatory gene that promotes epithelial tissue remodeling and formation of branched organs.

Development, repair and fibrosis: what is common and why it matters

The complex structure of the lung is developed sequentially, initially by epithelial tube branching and later by septation of terminal air sacs with accompanying coordinated growth of a variety of lung epithelial and mesenchymal cells. Groups of transcriptional factors, peptide growth factors and their intracellular signaling regulators, as well as extracellular matrix proteins are programmed to be expressed at appropriate levels in the right place at the right time to control normal lung formation. Studies of lung development and lung repair/fibrosis to date have discovered that many of the same factors that control normal development are also key players in lung injury repair and fibrosis. Transforming growth factor-beta (TGF-beta) family peptide signaling is a prime example. Lack of TGF-beta signaling results in abnormal lung branching morphogenesis and alveolarization during development, whereas excessive amounts of TGF-beta signaling cause severe hypoplasia in the immature lung and fibrosis in mature lung. This leads us to propose the 'Goldilocks' hypothesis of regulatory signaling in lung development and injury repair that everything must be done just right!

Lung organogenesis

Developmental lung biology is a field that has the potential for significant human impact: lung disease at the extremes of age continues to cause major morbidity and mortality worldwide. Understanding how the lung develops holds the promise that investigators can use this knowledge to aid lung repair and regeneration. In the decade since the "molecular embryology" of the lung was first comprehensively reviewed, new challenges have emerged-and it is on these that we focus the current review. Firstly, there is a critical need to understand the progenitor cell biology of the lung in order to exploit the potential of stem cells for the treatment of lung disease. Secondly, the current familiar descriptions of lung morphogenesis governed by growth and transcription factors need to be elaborated upon with the reinclusion and reconsideration of other factors, such as mechanics, in lung growth. Thirdly, efforts to parse the finer detail of lung bud signaling may need to be combined with broader consideration of overarching mechanisms that may be therapeutically easier to target: in this arena, we advance the proposal that looking at the lung in general (and branching in particular) in terms of clocks may yield unexpected benefits.

The role of integrin alpha8beta1 in fetal lung morphogenesis and injury

Prenatal inflammation prevents normal lung morphogenesis and leads to bronchopulmonary dysplasia (BPD), a common complication of preterm birth. We previously demonstrated in a bacterial endotoxin mouse model of BPD that disrupting fibronectin localization in the fetal lung mesenchyme causes arrested saccular airway branching. In this study we show that expression of the fibronectin receptor, integrin alpha8beta1 is decreased in the lung mesenchyme in the same inflammation model suggesting it is required for normal lung development. We verified a role for integrin alpha8beta1 in lung development using integrin alpha8-null mice, which develop fusion of the medial and caudal lobes as well as abnormalities in airway division. We further show in vivo and in vitro that alpha8-null fetal lung mesenchymal cells fail to form stable adhesions and have increased migration. Thus we propose that integrin alpha8beta1 plays a critical role in lung morphogenesis by regulating mesenchymal cell adhesion and migration. Furthermore, our data suggest that disruption of the interactions between extracellular matrix and integrin alpha8beta1 may contribute to the pathogenesis of BPD.

Stimulation of lung carcinoma cell growth by fibronectin-integrin signalling

Throughout many countries, lung cancer will kill more people this year than malignancies related to breast, prostate, colon, liver, kidney and melanoma combined. Despite recent advances in understanding the molecular biology of lung carcinoma and the introduction of multiple new chemotherapeutic agents for its treatment, its dismal five-year survival rate (<15%) has not changed substantially. The lack of advancement in this area reflects the limited knowledge available concerning the factors that promote oncogenic transformation and proliferation of carcinoma cells in the lung. Malignant transformation plays a key role in tumor growth and invasion; however, other factors such as the surrounding stroma, local growth factors, vascularity, and systemic hormones are important contributors as well. We believe that the composition of the lung extracellular matrix is also important due to its ability to affect malignant cell behavior in vitro. The matrix glycoprotein fibronectin, for example, is highly expressed in chronic lung disorders where most lung carcinomas are identified. This document reviews information that implicates fibronectin in the stimulation of lung carcinoma cell growth. Data available to date indicate that by binding to specific integrin receptors expressed on the surface of tumor cells, fibronectin stimulates intracellular signals implicated in the pathobiology of lung carcinogenesis and lung tumor chemoresistance including mitogen-activated protein kinases, GTPases, and the PI3-kinase/Akt/mTOR pathway. Thus, integrin-mediated signals triggered by fibronectin in tumor cells represent promising targets for the development of novel anti-cancer strategies.

Transforming growth factor-beta signaling mediates hypoxia-induced pulmonary arterial remodeling and inhibition of alveolar development in newborn mouse lung

Hypoxia causes abnormal neonatal pulmonary artery remodeling (PAR) and inhibition of alveolar development (IAD). Transforming growth factor (TGF)-beta is an important regulator of lung development and repair from injury. We tested the hypothesis that inhibition of TGF-beta signaling attenuates hypoxia-induced PAR and IAD. Mice with an inducible dominant-negative mutation of the TGF-beta type II receptor (DNTGFbetaRII) and nontransgenic wild-type (WT) mice were exposed to hypoxia (12% O(2)) or air from birth to 14 days of age. Expression of DNTGFbetaRII was induced by 20 microg/g ZnSO(4) given intraperitoneally daily from birth. PAR, IAD, cell proliferation, and expression of extracellular matrix (ECM) proteins were assessed. In WT mice, hypoxia led to thicker, more muscularized resistance pulmonary arteries and impaired alveolarization, accompanied by increases in active TGF-beta and phosphorylated Smad2. Hypoxia-induced PAR and IAD were greatly attenuated in DNTGFbetaRII mice given ZnSO(4) compared with WT control mice and DNTGFbetaRII mice not given ZnSO(4). The stimulatory effects of hypoxic exposure on pulmonary arterial cell proliferation and lung ECM proteins were abrogated in DNTGFbetaRII mice given ZnSO(4). These data support the conclusion that TGF-beta plays an important role in hypoxia-induced pulmonary vascular adaptation and IAD in the newborn animal model.

Tissue inhibitor of metalloproteinases 3 regulates extracellular matrix--cell signaling during bronchiole branching morphogenesis

Tissue inhibitors of metalloproteinases (TIMPs) regulate extracellular matrix (ECM) degradation by matrix metalloproteinases (MMPs) throughout embryogenesis. We examined lungs from TIMP3 null mice and found decreased bronchiole branching, enhanced activity of MMPs and enhanced fibronectin degradation throughout lung development compared to controls. Activation of focal adhesion kinase (FAK) was also reduced from embryonic days 12.5 through 14.5 in TIMP3 null lungs. Treatment with a synthetic MMP inhibitor, GM6001, in utero enhanced the branching pattern in both wild type and null lungs accompanied by a restoration of fibronectin localization, signaling through FAK and epithelial cell proliferation in null lungs. Direct down-regulation of FAK abundance in WT lung organ culture by siRNA targeting resulted in reduced bronchiole branching, phenocopying the TIMP3 defect. We propose that enhanced MMP activity in the absence of TIMP3 interferes with focal ECM proteolysis, perturbing the intracellular signaling necessary for correct pattern formation of the bronchiole tree during bronchiole branching morphogenesis. Thus, TIMP3 can indirectly regulate epithelial cell proliferation via MMP inhibitory activity. While others have demonstrated this function for MMPs, and there is in vitro evidence that TIMP3 controls proliferation, to our knowledge this is the first evidence of TIMP3 regulating proliferation in vivo.

Tenascin-C induced signaling in cancer

Tenascin-C is an adhesion modulatory extracellular matrix molecule that is highly expressed in the microenvironment of most solid tumors. High tenascin-C expression reduces the prognosis of disease-free survival in patients with some cancers. The possible role of tenascin-C in tumor initiation and progression is addressed with emphasis on underlying signaling mechanisms. How tenascin-C affects malignant transformation, uncontrolled proliferation, angiogenesis, metastasis and escape from tumor immunosurveillance is summarized. Finally, we discuss how the phenotypes of tenascin-C knock-out mice may help define the roles of tenascin-C in tumorigenesis and how this knowledge could be applied to cancer therapy.

β1 integrins modulate p66ShcA expression and EGF-induced MAP kinase activation in fetal lung cells

ShcA proteins mediate Erk1/Erk2 activation by integrins and epidermal growth factor (EGF), and are expressed as p46ShcA, p52ShcA, and p66ShcA. Although p52ShcA and p46ShcA mediate Erk1/Erk2 activation, p66ShcA antagonizes Erk activation. p66ShcA is spatially regulated during lung development, leading us to hypothesize that integrin signaling regulates p66ShcA expression and, consequently, EGF signaling. Fetal lung mesenchymal cells were isolated from E16 Swiss-Webster mice, stimulated with oligopeptide extracellular matrix analogs or anti-integrin antibodies, and subjected to ShcA Western analyses and EGF-stimulated Erk1/Erk2 kinase assays. p66ShcA expression was decreased by anti-alpha1 integrin antibody and DGEA collagen analog, and increased by anti-beta1, anti-alpha4, and anti-alpha5 integrin antibodies and RGDS fibronectin analog. Paradoxically, beta1 integrin stimulation increased EGF-induced Erk activation while increasing expression of the inhibitory p66ShcA isoform. This paradox was resolved by demonstrating that Erk inhibition attenuates integrin-mediated p66ShcA induction. These results suggest that p66ShcA is up-regulated as inhibitory feedback on integrin-mediated Erk activation.

Lgl1, a mesenchymal modulator of early lung branching morphogenesis, is a secreted glycoprotein imported by late gestation lung epithelial cells

Secreted glycoproteins serve a variety of functions related to cell-cell communication in developmental systems. We cloned LGL1, a novel glucocorticoid-inducible gene in foetal lung, and described its temporal and spatial localization in the rat. Disruption of foetal mesenchyme-specific LGL1 expression using antisense oligodeoxynucleotides, which was associated with a 50% decrease in lgl1 protein levels, inhibited airway epithelial branching in foetal rat gestational day 13 lung buds in explant culture. These findings suggested that lgl1 functions as a secreted signalling molecule. We now provide evidence supporting a role for lgl1 in mesenchymal-epithelial interactions that govern lung organogenesis. Lgl1 is a secreted glycoprotein with a conserved N-terminal secretory signal peptide. Using dual immunofluorescence, intracellular lgl1 was found to co-localize with markers of the Golgi apparatus and endoplasmic reticulum, consistent with its association with secretory vesicles. Using pulse-chase studies, we show that lgl1 is a stable protein with a half-life of 11.5 h. Furthermore, at gestational days 20 and 21 (term=22), foetal distal lung epithelial cells import lgl1 protein. Taken together, our findings support distinct roles for lgl1 as a mediator of glucocorticoid-induced mesenchymal-epithelial interactions in early and late foetal lung organogenesis.

Expression of the integrin subunit alpha8 in murine lung development

The complex interplay between cells and extracellular matrix (ECM) proteins is critical for lung development. Integrins are key modulators of this interaction. The integrin subunit alpha 8 associates with the beta(1)-subunit to form an RGD-binding integrin. We previously showed that, in adult lung, alpha 8 is expressed in contractile interstitial cells and smooth muscle cells and is upregulated in lung injury. To gain insight into the function of alpha 8 during lung development, we examined the spatiotemporal expression of alpha 8 throughout murine lung development. We compared the distribution of alpha 8 with alpha-smooth muscle actin (alpha SMA), fibronectin (alpha 8 ligand), and cytokeratin. alpha 8 co-localized with alpha SMA and fibronectin in the peribronchial and perivascular regions. In all stages, alpha 8 immunoreactivity was detected diffusely in the mesenchyme except for cells surrounding distal, newly forming airways. alpha 8, alpha SMA, and fibronectin co-localized at tips of secondary septae in the alveolar stage. We conclude that alpha 8 is marker for lung mesenchymal cells starting early in development. alpha 8 is also a marker for smooth muscle cells, expressed as early as alpha SMA. Co-localization of alpha 8 with fibronectin suggests a role in branching morphogenesis. Furthermore, alpha 8 may participate in secondary septation by modulating signals from the extracellular matrix to alveolar myofibroblasts.

A null mutation for tissue inhibitor of metalloproteinases-3 (Timp-3) impairs murine bronchiole branching morphogenesis

Tissue inhibitors of metalloproteinases (TIMPs) regulate extracellular matrix (ECM) degradation by matrix metalloproteinases (MMPs). We have examined the role of TIMP-3 on ECM homeostasis and bronchiole branching morphogenesis during murine embryogenesis. Employing an in vitro organ culture system, we found decreased bronchiolar branching in null lungs when compared with wild type (WT) counterparts after 2 days in culture. When a synthetic inhibitor of MMPs at low dose was added to the culture system, branching was augmented regardless of genotype. Gelatin and in situ zymography revealed that null lungs exhibited enhanced activation of MMPs throughout lung development. We analysed the impact of increased MMP activity on a number of ECM molecules by Western blot analysis, but found that only fibronectin abundance was consistently reduced in the null lungs throughout development. To confirm that our observed defect in culture was not simply a developmental delay in the null lung, we examined null and WT lungs from newborn pups. Here, we found not only a reduced number of bronchioles in the null, but also that the bronchiole tubes were dilated compared with controls and that alveologenesis was attenuated. We propose that the deletion of TIMP-3 disrupts the exquisite TIMP/MMP balance required for proper focal ECM proteolysis, which leads to correct bronchiole branching morphogenesis in the developing mouse lung.

Fibronectin blocks p38 and jnk activation by cyclic strain in Caco-2 cells

Diverse repetitive forces deform the intestinal epithelium and basement membrane. Such repetitive deformation induces intestinal epithelial proliferation, differentiation, and intracellular signaling. Although at least some deformation-induced signals probably involve integrins, the matrix-dependence of these signals is poorly understood. We compared rapid strain activation of p38 and jnk in human Caco-2 intestinal epithelial cells cultured on collagen I, collagen IV, laminin, and tissue fibronectin. These signals were inhibited in cells on a fibronectin substrate, but activated by strain on collagens and laminin. Furthermore, adding 300 microg/ml plasma fibronectin (approximately the concentration found in plasma) to the culture medium inhibited strain activation of p38 and jnk in cells cultured on collagen. Since tissue and plasma fibronectin levels vary in acute or chronic inflammatory or infectious conditions, these results suggest that tissue or plasma fibronectin may modulate the intestinal epithelial response to repetitive deformation.

Fibronectin requirement in branching morphogenesis

Many organs, including salivary glands, lung and kidney, are formed during embryonic development by epithelial branching. In branching morphogenesis, repetitive epithelial cleft and bud formation create the complex three-dimensional branching structures characteristic of many organs. Although the mechanisms are poorly understood, one might involve the site-specific accumulation of some regulatory protein. Here we show that the extracellular matrix protein fibronectin is essential for cleft formation during the initiation of epithelial branching. Fibronectin messenger RNA and fibrils appeared transiently and focally in forming cleft regions of submandibular salivary-gland epithelia, accompanied by an adjacent loss of cadherin localization. Decreasing the fibronectin concentration by using small interfering RNA and inhibition by anti-fibronectin or anti-integrin antibodies blocked cleft formation and branching. Exogenous fibronectin accelerated cleft formation and branching. Similar effects of fibronectin suppression and augmentation were observed in developing lung and kidney. Mechanistic studies revealed that fibrillar fibronectin can induce cell-matrix adhesions on cultured human salivary epithelial cells with a local loss of cadherins at cell-cell junctions. Thus, fibronectin expression is required for cleft formation in branching morphogenesis associated with the conversion of cell-cell adhesions to cell-matrix adhesions.

Extracellular matrix components in nasal polyposis

OBJECTIVE

Macroscopically, tissue hydration in nasal polyps seems to be a phenomenon of unknown etiology. As the macromolecular composition of extracellular matrix (ECM) determines to a large extent tissue hydration, which in turn determines tissue volume, we investigated ECM components in nasal polyps (NP) in comparison to nasal mucosa of the inferior turbinate (TM) and sinus mucosa from patients with chronic sinusitis without polyps (CS).

MATERIAL AND METHODS

The following parameters were determined: (i) the dry weight of freeze-dried NP, TM and CS; (ii) the total protein content (Bio-Rad Protein Assay) of the tissue; (iii) the quality of proteins, using sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE); (iv) the amount of albumin, using nephelometry; and (v) the amount of hyaluronic acid, using a chemical method: deaminative hydrolysis with carbazole.

RESULTS

In 20 NP we found a significantly elevated total protein content compared to TM (n = 20) and CS (n = 15), referred to 0.1 g dry of tissue. In SDS-PAGE of NP (n = 20) a protein band at approximately 70 kDa, representing albumin, dominated, in comparison to TM. The amount of albumin was significantly increased in NP compared to CS and TM. In contrast, the amount of the glycosaminoglycan, hyaluronic acid, was not elevated in NP or CS.

CONCLUSION

Albumin was significantly increased in NP and CS, possibly as a result of inflammatory plasma exudation mechanisms. Hyaluronic acid seems to play no role in the tissue hydration of NP.

Hypoxia and lung branching morphogenesis

Morphogens, growth factors and extracellular matrix (ECM) components modulate early lung branching, and have been studied extensively both in vivo and in vitro. In vitro studies have been particularly useful, because tissue can be manipulated either chemically or mechanically. For the most part, such studies have been conducted at ambient oxygen tensions, despite the fact that the fetus develops in a low oxygen environment. Since oxygen tension regulates the expression of various growth factors, adhesion molecules and their receptors, we investigated whether the low oxygen environment of the fetus contributes towards lung branching morphogenesis by affecting one or more these mediators. Using an established fetal lung explant model, we demonstrated that in comparison to tissues cultured at ambient oxygen concentration (21% O2), fetal lung explants cultured at 3% O2 show increases in terminal branching and cellular proliferation, and they display appropriate proximal to distal differentiation. To investigate the factor(s) mediating the induction of lung branching morphogenesis and differentiation by fetal oxygen tension, we focused on matrix metalloproteinases (MMPs), a group of zinc-dependent enzymes that modify ECM structure and function. Our results reveal that hypoxia suppresses MMP activity, leading to the accumulation of specific ECM components, including tenascin-C (TN-C), that act to stimulate lung branching. These studies demonstrate that low oxygen in the setting of the developing lung positively regulates lung branching morphogenesis, and suggest that the pathologic responses to low oxygen in the adult lung reflect a dysregulation of this lung developmental program.

TGF-beta3-null mutation does not abrogate fetal lung maturation in vivo by glucocorticoids

Newborn transforming growth factor (TGF)-beta3-null mutant mice exhibit defects of palatogenesis and pulmonary development. Glucocorticoids, which play a central role in fetal lung maturation, have been postulated to mediate their stimulatory effects on tropoelastin mRNA expression through TGF-beta3 in cultured lung fibroblasts. In the present study, we analyzed the abnormally developed lungs in TGF-beta3-null mutant mice and compared the effects of glucocorticoids on gene expression and lung morphology between TGF-beta3 knockout and wild-type mice. Lungs of TGF-beta3-null mutant mice on embryonic day 18.5 did not form normal saccular structures and had a thick mesenchyme between terminal air spaces. Moreover, the number of surfactant protein C-positive cells was decreased in TGF-beta3-null mutant lungs. Interestingly, glucocorticoids were able to promote lung maturation and increased expression of both tropoelastin and fibronectin but decreased the relative number of surfactant protein C-positive cells in fetal lungs of both genotypes. This finding provides direct evidence that glucocorticoid signaling in the lung can use alternative pathways and can exert its effect without the presence of TGF-beta3.

Plasma fibronectin: three steps to purification and stability

Large amounts of soluble fibronectin were easily purified from cryoprecipitated or fresh citrated human blood plasma by a three-step combination of gelatin and heparin-cellufine affinity chromatography. The elution conditions were optimized to obtain a homogeneous fraction on SDS-PAGE and Western blot under reducing condition. No proteolytic activities were detected by zymography at acidic or neutral pH. Furthermore, the fibronectin preparation was stable over time up to 456 h at 37 degrees C in the presence of calcium, zinc, or mercury. This preparation of very stable fibronectin, called highly purified fibronectin (hpFN), gave a yield of 7.00 +/- 0.77 mg of fibronectin per gram of cryoprecipitated plasma and 0.16 mg of fibronectin per milliliter of fresh citrated, giving a yield of 32 to 53% (from presumed fibronectin concentration). This preparation may be useful for cellular tests and interaction analysis.

Cloning of rat fibrillin-2 cDNA and its role in branching morphogenesis of embryonic lung

Fibrillin-2 is an extracellular matrix protein. It is associated with elastic fibers in several tissues and is believed to serve as a ligand for alphavbeta3 integrin, the latter being a known morphogen. In this study, the role of fibrillin-2 in lung development was investigated. Also, rat fibrillin-2 cDNA was isolated and sequenced and its spatiotemporal expression determined. It had approximately 88% homology with human fibrillin-2 and had Ca(2+) binding epidermal growth factor-like domains, transforming growth factor-beta binding protein motifs, and two RGD binding sites. Northern blot analysis revealed an approximately 10-kb transcript, and fibrillin-2 expression was developmentally regulated, and it paralleled that of tropoelastin. At day 13 of gestation, fibrillin-2 was expressed in the mesenchyme and at the epithelial:mesenchymal interface. From day 13 to 19 of gestation, its expression intensified and was confined around the tracheobronchial airways, while it lessened during the postnatal period. Immunoprecipitation revealed an approximately 350-kDa band by SDS-PAGE. Treatment with fibrillin-2 antisense oligodeoxynucleotide induced dysmorphogenesis of the lung explants. They were smaller and had rudimentary lung bud branches, collapsed conducting airways, and loose expanded mesenchyme. Concomitantly, fibrillin-2 mRNA, antibody reactivity in the explants, and fibrillin-2-specific radioincorporation were reduced. Anti-alphav and -laminin antibody reactivity and their respective incorporated specific radioactivities were unaltered. These data indicate that fibrillin-2 modulates organogenesis of the lung in the context of epithelial:mesenchymal interactions. Conceivably, the collapse of the conducting airways may also be related to the perturbed biology of the fibrillin-2 interacting protein, i.e., elastin, the latter being critical for the normal biophysiology of the lungs.

Heparin inhibits lung branching morphogenesis: potential role of smooth muscle cells in cleft formation

Lung branching morphogenesis is the process by which the embryonic lung undergoes repetitive branching to form the bronchial tree. This process occurs during the pseudoglandular stage of lung development and requires epithelial-mesenchymal interactions. Coinciding with lung branching morphogenesis is the appearance of parabronchial smooth muscle cells (PSMCs) and the accumulation of extracellular matrices (ECMs) around the developing airways. The authors previously reported in preliminary form that heparin prevents the branching of murine lung explants (Roman et al., Am Rev Respir Dis. 1991; 143:A401); this article corroborates those early observations and expands them by demonstrating that heparin results in disruption of PSMC distribution and abnormal organization of ECMs around the developing airways. These changes were associated with inhibition of lung branching morphogenesis in the absence of effects on cell proliferation. The data provide further support for the role of ECMs in lung branching morphogenesis, and points to PSMCs as potential players in this process.