Connective tissue of rat lung. II: Ultrastructural localization of collagen types III, IV, and VI

Morpho-Functional Study of Vascular Fluorochrome Delivery to Lung and Liver Metastases of Lewis Lung Carcinoma (3Ll)

The growth of 3LL liver and lung metastases related to Its vascular organization was studied by morphological and functional methods, using the Hoechst 33342 fluorescent DNA staining technique. Experimental liver and lung metastases were produced in syngeneic C57BL/6 mice by injection of 3LL tumor cells into a lateral tail vein or into the spleen, respectively. The resulting neoplasms were composed of large cells arranged in sheets with a thin irregularly distributed stroma. Scattered blood vessels with an open or closed lumen were observed within the tumor. Functional study of H33342 diffusion showed a single and reticular fluorescent pattern in liver metastases. In contrast, in lung metastases the fluorochrome diffusion revealed two different fluorescent patterns related to the location of the metastasis. Thus, parenchymal and subpleural metastasis presented a fluorescent pattern similar to that observed in the liver whereas metastases located around blood vessels and conducting airways never displayed fluorescence. In summary, our results suggest that the target metastatic organ and/or intra-organ location modulates the characteristics of metabolic exchange of the tumor cells In relation to the vascular organization of the metastatic focus.

Mechanisms of Lung Fibrosis Resolution

Fibrogenesis involves a dynamic interplay between factors that promote the biosynthesis and deposition of extracellular matrix along with pathways that degrade the extracellular matrix and eliminate the primary effector cells. Opposing the often held perception that fibrotic tissue is permanent, animal studies and clinical data now demonstrate the highly plastic nature of organ fibrosis that can, under certain circumstances, regress. This review describes the current understanding of the mechanisms whereby the lung is known to resolve fibrosis focusing on degradation of the extracellular matrix, removal of myofibroblasts, and the role of inflammatory cells. Although there are significant gaps in understanding lung fibrosis resolution, accelerated improvements in biotechnology and bioinformatics are expected to improve the understanding of these mechanisms and have high potential to lead to novel and effective restorative therapies in the treatment not only of pulmonary fibrosis, but also of a wide-ranging spectrum of chronic disorders.

Decreased expression of 14-3-3 in Paracoccidioides brasiliensis confirms its involvement in fungal pathogenesis

The interaction between the fungal pathogen Paracoccidioides brasiliensis and host cells is usually mediated by specific binding events between adhesins on the fungal surface and receptors on the host extracellular matrix or cell surface. One molecule implicated in the P. brasiliensis-host interaction is the 14-3-3 protein. The 14-3-3 protein belongs to a family of conserved regulatory molecules that are expressed in all eukaryotic cells and are involved in diverse cellular functions. Here, we investigated the relevance of the 14-3-3 protein to the virulence of P. brasiliensis. Using antisense RNA technology and Agrobacterium tumefaciens-mediated transformation, we generated a 14-3-3-silenced strain (expression reduced by ˜55%). This strain allowed us to investigate the interaction between 14-3-3 and the host and to correlate the functions of P. brasiliensis 14-3-3 with cellular features, such as morphological characteristics and virulence, that are important for pathogenesis.

Absence of fibromodulin affects matrix composition, collagen deposition and cell turnover in healthy and fibrotic lung parenchyma

The ECM exerts great effects on cells, and changed composition may therefore have profound impact. Small leucine-rich proteoglycans, e.g. fibromodulin, are essential in collagen assembly. Our aim was to investigate the role of fibromodulin in healthy and fibrotic lung parenchyma, theorizing that fibromodulin-deficient animals would be protected against fibrosis. Repeated subcutaneous bleomycin-injections were given to wild type and fibromodulin-deficient mice, inducing pulmonary fibrosis. Development of fibrosis, ECM composition, cell turnover and inflammatory responses were investigated. Fibromodulin-deficient animals were not protected from fibrosis, but the composition of the matrix was affected, with decreased Collagen I in fibromodulin-deficient animals, both in controls (0.07 ± 0.04% vs. 0.18 ± 0.07% tissue area) and after bleomycin (0.37 ± 0.16% vs. 0.61 ± 0.21% tissue area). Biglycan was increased in fibromodulin-deficient animals, whereas decorin was decreased. Furthermore, bleomycin increased cell turnover in wild type, but only proliferation in fibromodulin-deficient animals, resulting in hyperplasia. In addition, the bleomycin-induced immune response was affected in fibromodulin-deficient animals. We thus conclude that fibromodulin has a profound effect on ECM, both in healthy and fibrotic lung parenchyma, and may be providing a permissive microenvironment affecting cell turnover. Furthermore, this study highlights the need to acknowledge specific ECM components, when assessing tissue properties and ultimately cell behaviour.

Structural changes in the bronchial mucosa of young children at risk of developing asthma

BACKGROUND

Bronchial asthma often starts in early childhood. Clinical manifestation of the disease is likely due to inflammatory processes in the airways initiated by various stimuli. Developed remodelling is regularly observed in the bronchial mucosa of adult asthmatics but we still lack information about its onset and latter development with the natural course of the disease. In this study, we analysed histological findings in bronchial biopsies obtained from very young children (under 4 yr of age). We hypothesized that initial undetectable changes in the airway epithelium of children predisposed to asthma may be one of the first mechanisms leading to morphological changes in the bronchial mucosa.

METHODS

We measured the thickness of the basement membrane using a light microscope and analysed the presence of its three basic structural glycoproteins: laminin, tenascin and collagen IV, using immunohistochemical techniques. We compared these findings in children predisposed to asthma according to the selected clinical criteria of the Asthma Predictive Index and in a control group of children.

RESULTS

We found a significant difference in the thickness of the basement membrane between the two groups. We also found a difference in the subepithelial deposition of laminin and collagen IV in the basement membrane but no difference in the deposition of tenascin.

CONCLUSIONS

We conclude that initial changes leading to further remodelling may start at a very early age even before clinical manifestation of the disease.

Hypertensive rat lungs retain hallmarks of vascular disease upon decellularization but support the growth of mesenchymal stem cells

There are an insufficient number of donor organs available to meet the demand for lung transplantation. This issue could be addressed by regenerating functional tissue from diseased or damaged lungs that would otherwise be deemed unsuitable for transplant. Detergent-mediated whole-lung decellularization produces a three-dimensional natural scaffold that can be repopulated with various cell types. In this study, we investigated the decellularization and initial recellularization of diseased lungs using a rat model of monocrotaline-induced pulmonary hypertension (MCT-PHT). Decellularization of control and MCT-PHT Sprague-Dawley rat lungs was accomplished by treating the lungs with a combination of Triton X-100, sodium deoxycholate, NaCl, and DNase. The resulting acellular matrices were characterized by DNA quantification, Western blotting, immunohistochemistry, and proteomic analyses revealing that decellularization was able to remove cells while leaving the extracellular matrix (ECM) components and lung ultrastructure intact. Decellularization significantly reduced DNA content (∼30-fold in MCT-PHT lungs and ∼50-fold in the control lungs) and enriched ECM components (>60-fold in both the control and MCT-PHT lungs) while depleting cellular proteins. MicroCT visualization of MCT-PHT rat lungs indicated that the vasculature was narrowed as a result of MCT treatment, and this characteristic was unchanged by decellularization. Mean arterial vessel diameter of representative decellularized MCT-PHT and control scaffolds was estimated to be 0.152±0.134 mm and 0.247±0.160 mm, respectively. Decellularized MCT-PHT lung scaffolds supported attachment and survival of rat adipose-derived stem cells (rASCs), seeded into the airspace or the vasculature, for at least 2 weeks. The cells seeded in MCT-PHT lung scaffolds proliferated and underwent apoptosis similar to control scaffolds; however, the initial percentage of apoptotic cells was slightly higher in MCT-PHT lungs (2.79±2.03% vs. 1.05±1.02% of airway-seeded rASCs, and 4.47±1.21% vs. 2.66±0.10% of vascular seeded rASCs). The ECM of cell-seeded scaffolds showed no signs of degradation by the cells after 14 days in culture. These data suggest that diseased hypertensive lungs can be efficiently decellularized similar to control lungs and have the potential to be recellularized with mesenchymal stem cells with the ultimate goal of generating healthy, functional pulmonary tissue.

Proteoglycan and collagen expression during human air conducting system development

The lung is formed from a bud that grows and divides in a dichotomous way. A bud is a new growth center which is determined by epithelial-mesenchymal interactions where proteins of the extracellular matrix (ECM) might be involved. To understand this protein participation during human lung development, we examined the expression and distribution of proteoglycans in relation to the different types of collagens during the period in which the air conducting system is installed. Using light microscopy and immunohistochemistry we evaluate the expression of collagens (I, III and VI) and proteoglycans (decorin, biglycan and lumican) between 8 to 10 weeks post fertilization and 11 to 14 weeks of gestational age of human embryo and fetus lungs. We show that decorin, lumican and all the collagen types investigated were expressed at the epithelium-mesenchymal interface, forming a sleeve around the bronchiolar ducts. In addition, biglycan was expressed in both the endothelial cells and the smooth muscle of the blood vessels. Thus, the similar distribution pattern of collagen and proteoglycans in the early developmental stages of the human lung may be closely related to the process of dichotomous division of the bronchial tree. This study provides a new insight concerning the participation of collagens and proteoglycans in the epithelial-mesenchymal interface during the period in which the air conducting system is installed in the human fetal lung.

Human pathogens utilize host extracellular matrix proteins laminin and collagen for adhesion and invasion of the host

Laminin (Ln) and collagen are multifunctional glycoproteins that play an important role in cellular morphogenesis, cell signalling, tissue repair and cell migration. These proteins are ubiquitously present in tissues as a part of the basement membrane (BM), constitute a protective layer around blood capillaries and are included in the extracellular matrix (ECM). As a component of BMs, both Lns and collagen(s), thus function as major mechanical containment molecules that protect tissues from pathogens. Invasive pathogens breach the basal lamina and degrade ECM proteins of interstitial spaces and connective tissues using various ECM-degrading proteases or surface-bound plasminogen and matrix metalloproteinases recruited from the host. Most pathogens associated with the respiratory, gastrointestinal, or urogenital tracts, as well as with the central nervous system or the skin, have the capacity to bind and degrade Lns and collagen(s) in order to adhere to and invade host tissues. In this review, we focus on the adaptability of various pathogens to utilize these ECM proteins as enhancers for adhesion to host tissues or as a targets for degradation in order to breach the cellular barriers. The major pathogens discussed are Streptococcus, Staphylococcus, Pseudomonas, Salmonella, Yersinia, Treponema, Mycobacterium, Clostridium, Listeria, Porphyromonas and Haemophilus; Candida, Aspergillus, Pneumocystis, Cryptococcus and Coccidioides; Acanthamoeba, Trypanosoma and Trichomonas; retrovirus and papilloma virus.

The airway epithelium: more than just a structural barrier

The mammalian airway is lined by a variety of specialized epithelial cells that not only serve as a physical barrier but also respond to environment-induced damage through the release of biologically active factors and constant cellular renewal. The lung epithelium responds to environmental insults such as pathogens, cigarette smoke and pollution by secreting inflammatory mediators and antimicrobial peptides, and by recruiting immune cells to the site of infection or damage. When the epithelium is severely damaged, basal cells and Clara cells that have stem-cell-like properties are capable of self-renewal and proliferation in the affected area, to repair the damage. In order to effectively fight off infections, the epithelium requires the assistance of neutrophils recruited from the peripheral circulation through transendothelial followed by transepithelial migration events. Activated neutrophils migrate across the epithelium through a series of ligand-receptor interactions to the site of injury, where they secrete proteolytic enzymes and oxidative radicals for pathogen destruction. However, chronic activation and recruitment of neutrophils in airway diseases such as chronic obstructive pulmonary disease and asthma has been associated with tissue damage and disease severity. In this paper, we review the current understanding of the airway epithelial response to injury and its interaction with inflammatory cells, in particular the neutrophil.

Implicit mechanistic role of the collagen, smooth muscle, and elastic tissue components in strengthening the air and blood capillaries of the avian lung

To identify the forces that may exist in the parabronchus of the avian lung and that which may explain the reported strengths of the terminal respiratory units, the air capillaries and the blood capillaries, the arrangement of the parabronchial collagen fibers (CF) of the lung of the domestic fowl, Gallus gallus variant domesticus was investigated by discriminatory staining, selective alkali digestion, and vascular casting followed by alkali digestion. On the luminal circumference, the atrial and the infundibular CF are directly connected to the smooth muscle fibers and the elastic tissue fibers. The CF in this part of the parabronchus form the internal column (the axial scaffold), whereas the CF in the interparabronchial septa and those associated with the walls of the interparabronchial blood vessels form the external, i.e. the peripheral, parabronchial CF scaffold. Thin CF penetrate the exchange tissue directly from the interparabronchial septa and indirectly by accompanying the intraparabronchial blood vessels. Forming a dense network that supports the air and blood capillaries, the CF weave through the exchange tissue. The exchange tissue, specifically the air and blood capillaries, is effectively suspended between CF pillars by an intricate system of thin CF, elastic and smooth muscle fibers. The CF course through the basement membranes of the walls of the blood and air capillaries. Based on the architecture of the smooth muscle fibers, the CF, the elastic muscle fibers, and structures like the interparabronchial septa and their associated blood vessels, it is envisaged that dynamic tensional, resistive, and compressive forces exist in the parabronchus, forming a tensegrity (tension integrity) system that gives the lung rigidity while strengthening the air and blood capillaries.

Characterization of gels composed of blends of collagen I, collagen III, and chondroitin sulfate

Type I collagen is explored heavily for use in biomaterials, but the role of other extracellular matrix components in regulating collagen organization is gaining attention. We show that as the ratio of type III to type I collagen increases, fibril diameter decreases. A mixture of the two collagen types results in a more open structural network, corresponding to a more compliant material, as compared to a material composed of only one collagen type. Glycosaminoglycans also affect collagen organization and tissue properties. We show that chondroitin sulfate decreases the collagen fibril diameter. Additionally, chondroitin sulfate (CS) increases the void space of a collagen I or collagen III gel, resulting in a more compliant material, but the interactions between types I and III collagen negate the effects of CS. The simple combination of these components results in materials with unique structural, mechanical, and biological cues that can be useful in tailoring biomaterials for tissue engineering.

Expression of FACIT collagens XII and XIV during bleomycin-induced pulmonary fibrosis in mice

Collagens XII and XIV are members of a subfamily of fibril-associated collagens with interrupted triple-helices (FACITs) that facilitate the interactions of adjacent collagen fibrils. Using immunohistochemistry and in situ hybridization, we analyzed the spatial and temporal expression pattern of collagens XII and XIV during bleomycin-induced pulmonary fibrosis. C57Bl mice were treated with bleomycin (1 U, i.p., every other day for 8 days) or saline (control), and lung tissue samples were analyzed 2-12 weeks later. Collagen I protein expression was increased in the lung 2 weeks post bleomycin treatment and persisted for at least 12 weeks. In contrast, collagen XII and XIV expression was low until 4 weeks after bleomycin treatment. Whereas collagen XII expression was greatest between 4 weeks and 8 weeks, expression of collagen XIV persisted from 4 to 12 weeks, which suggests that these two proteins may play distinct roles in the fibrotic process. The mRNA for lysyl oxidase (LOX), an enzyme for cross-linking of collagens, had a delayed increase in the lung after bleomycin administration. It reached a maximum after 8 weeks, and persisted throughout the 12 weeks of the study. These data support the hypothesis that fibrosis is a multistep process that involves both collagen accumulation and changes in the molecules that modulate the biomechanical properties of fibrils.

Pseudoxanthoma elasticum: a clinical, histopathological, and molecular update

Pseudoxanthoma elasticum is an autosomally inherited disorder that is associated with the accumulation of mineralized and fragmented elastic fibers in the skin, Bruch's membrane in the retina, and vessel walls. The ophthalmic and dermatologic expression of pseudoxanthoma elasticum and its vascular complications are heterogeneous, with considerable variation in phenotype, progression, and mode of inheritance. Using linkage analysis and mutation detection techniques, mutations in the ABCC6 gene were recently implicated in the etiology of pseudoxanthoma elasticum. ABCC6 encodes the sixth member of the ATP-binding cassette transporter and multidrug resistance protein family (MRP6). In humans, this transmembrane protein is highly expressed in the liver and kidney. Lower expression was found in tissues affected by pseudoxanthoma elasticum, including skin, retina, and vessel walls. So far, the substrates transported by the ABCC6 protein and its physiological role in the etiology of pseudoxanthoma elasticum are not known. A functional transport study of rat MRP6 suggests that small peptides such as the endothelin receptor antagonist BQ123 are transported by MRP6. Similar molecules transported by ABCC6 in humans may be essential for extracellular matrix deposition or turnover of connective tissue at specific sites in the body. One of these sites is Bruch's membrane. This review is an update on etiology of pseudoxanthoma elasticum, including its clinical and genetic features, pathogenesis, and biomolecular basis.

Unique structural features that influence neutrophil emigration into the lung

Neutrophil emigration in the lung differs substantially from that in systemic vascular beds where extravasation occurs primarily through postcapillary venules. Migration into the alveolus occurs directly from alveolar capillaries and appears to progress through a sequence of steps uniquely influenced by the cellular anatomy and organization of the alveolar wall. The cascade of adhesive and stimulatory events so critical to the extravasation of neutrophils from postcapillary venules in many tissues is not evident in this setting. Compelling evidence exists for unique cascades of biophysical, adhesive, stimulatory, and guidance factors that arrest neutrophils in the alveolar capillary bed and direct their movement through the endothelium, interstitial space, and alveolar epithelium. A prominent path accessible to the neutrophil appears to be determined by the structural interactions of endothelial cells, interstitial fibroblasts, as well as type I and type II alveolar epithelial cells.

In the mammalian eye type VI collagen tetramers form three morphologically different aggregates

The organization of the aggregates occurring in the stroma: (1) of the murine and human cornea after incubation in an ATP acidic solution; (2) of surgically excised epiretinal membranes (ERM); and (3) of the trabecular meshwork of monkey eyes was investigated morphologically and immunocytochemically on thin section electron microscopy. Morphology. The aggregates in the cornea appeared as cross-banded fibrils. The bands were uniformly electron dense (single banded form); they were separated from each other by interbands consisting of a bundle of filaments emerging in cross section as small areas of randomly assembled dot-like structures. In the ERM, most of the aggregates stood out as heteromorphic cross-banded bodies showing dense bands with electron denser borders (double banded form) and interbands composed of longitudinally oriented, parallel sheets or laminae of amorphous material enclosing thin, similarly oriented filaments. These extended, thinner and double in number (since interlacing with similar components of the opposite sheet), into the pale central zone of the dense band. The aggregates of the trabecular meshwork were heteromorphic, had uniformly dense bands (single banded form as in the cornea), but their interbands displayed longitudinal sheets (as the ERM aggregates). Immunocytochemistry revealed type VI collagen in the three eye aggregates with gold particles preferentially localized at the interbands. The specificity of the antibodies used was tested by Western blot analysis of type VI collagen samples extracted from human placenta and on homogenates of human cornea. In conclusion, the results indicate that the tetramers of type VI collagen may aggregate differently into structures with distinct supramolecular arrangements. These are illustrated in schematic drawings.

Composition of the pulmonary interstitium during normal development of the human fetus

Normal lung development is dependent on epithelial-mesenchymal interactions. This study was undertaken to examine the structure of the interstitium of the developing human fetal lung, concentrating particularly on the first and second trimesters. Lung tissue was obtained at autopsy from nonmalformed, nonmacerated cases of spontaneous abortion (n = 15), stillbirth (n = 9), and very early neonatal death (n = 5) (range of gestations, 10-42 weeks). Paraffin-embedded tissue sections were examined using immunohistochemical methods to determine expression of collagens I, III, IV, V, and VI; the glycoproteins fibronectin and laminin; and the intermediate filaments vimentin, alpha-smooth muscle actin (alphaSMA), and desmin. Collagens III and VI and cells expressing alphaSMA were present consistently at points of airway branching and secondary crest formation, indicating a role for these components in the initiation and stabilization of airway branches in the developing lung. Desmin expression by stromal cells succeeded alphaSMA temporally, and may represent a marker of terminal smooth muscle differentiation within the airway; it was not detected in the vascular tree. Other components were widely expressed throughout the extracellular matrix, including basement membranes, at all gestations. The spatial and temporal patterns of expression of components of the lung interstitium provide clues to the mechanisms underlying normal human lung development and possible insights into the pathogenesis of fetal and neonatal lung disease.

Sulfation of extracellular matrices modifies growth factor effects on type II cells on laminin substrata

The alveolar basement membrane contains a variety of extracellular matrix (ECM) molecules, including laminin and sulfated glycosaminoglycans of proteoglycans. These mixtures exist within microdomains of differing levels of sulfate, which may specifically interact to be key determinants of the known capacity of the type II cell to respond to certain growth factors. Isolated type II cells were exposed to either acidic fibroblast growth factor (FGF-1), basic fibroblast growth factor (FGF-2), or keratinocyte growth factor (KGF; FGF-7) on culture wells precoated with laminin alone or in combination with chondroitin sulfate (CS), high-molecular-weight heparin, or their desulfated forms. Desulfated heparin significantly elevated FGF-1- and FGF-2-stimulated DNA synthesis, whereas desulfated CS and N-desulfated heparin elevated FGF-7-stimulated DNA synthesis by type II cells on laminin substrata. When FGF-1 was mixed into the various test matrix substrata, DNA synthesis was significantly increased in all cases. These results demonstrated that decreased levels of sulfate in ECM substrata act to upregulate responses to heparin-binding growth factors by alveolar epithelial cells on laminin substrata.

Immunohistochemical and ultrastructural localization of MP78/70 (betaig-h3) in extracellular matrix of developing and mature bovine tissues

MP78/70 is a matrix protein, with 78-kD and 70-kD isoforms, which was initially identified in bovine tissue extracts designed to solubilize elastin-associated microfibrils. Peptide analysis has shown that MP78/70 is closely related to the human protein, betaig-h3. In the present study an antibody raised to a synthetic betaig-h3 peptide was shown specifically to identify MP78/70 in purified form and in bovine tissue extracts. This is consistent with MP78/70 and betaig-h3 being the bovine and human forms, respectively, of the same protein. The antibody was further affinity-purified on MP78/70 bound to Sepharose and used to localize the protein in a range of bovine tissues. Immunofluorescence showed that MP78/70 was localized to collagen fibers in tissues such as developing nuchal ligament, aorta and lung, and mature cornea; to reticular fibers in fetal spleen; and to capsule and tubule basement membranes in developing kidney. No general localization to elastic fibers was observed. The staining pattern in most tissues more closely resembled that of Type VI collagen, which occurs as collagen fiber-associated microfibrils, than that of fibrillin-1, a component of elastin-associated microfibrils. However, MP78/70 appeared to be less widely distributed than Type VI collagen. Immunoelectron microscopy showed that MP78/70 was predominantly found in loose association with collagen fibers in most tissues examined and was also located on the surface of the capsule basement membrane in developing kidney. Double labeling experiments indicated that MP78/70 is co-distributed with Type VI collagen microfibrils located in these regions. In some elastic tissues significant immunolabel was detected in regions of interface between collagen fibers and fibrillin-containing microfibrils of adjacent elastic fibers, and at the outer margins of the latter structures. Overall, the evidence points to MP78/70 having a bridging function, perhaps in association with Type VI collagen microfibrils, linking or stabilizing the interaction between interstitial collagen fibrils and other matrix structures, including some basement membranes and elastin-associated microfibrils.

Collagen type VI is a component of the extracellular matrix microfibril network of the prostatic stroma

Stroma-epithelium relationships are of great relevance in prostatic morphogenesis and physiology. However, little knowledge exists about either stromal cells or extracellular matrix composition and arrangement in this system. Ultrastructural analysis revealed the existence of a microfibrillar system which occupies large areas of the rat prostatic stroma. In this work, we have applied immunocytochemistry and an ATP treatment for the ultrastructural identification of collagen type VI microfibrils, aiming at examining its participation in the prostatic microfibrillar network. Immunocytochemistry was also extended to a human case of prostatic nodular hyperplasia. Both methods succeeded in identifying collagen type VI in the rat ventral prostate. Collagen type VI is evenly distributed throughout the stroma but mainly associated with the basal lamina, collagen fibrils, and around the stromal cells. The use of ATP treatment allowed for the discrimination between collagen type VI and elastin-associated microfibrils, and demonstrated that these two classes of microfibrils establish an extended, mixed, and open network. The same aspects of association with the basal lamina, with stromal cells (particularly with smooth muscle cells), and with fibrillar components of the stroma were observed in the human tissue. We suggest that the collagen type VI and elastin-associated microfibril system may be involved in the control of some aspects of cellular behavior and may also play a structural role, maintaining the organ integrity after the deformations occurring under smooth muscle contraction.

The pathogenesis of pulmonary fibrosis: is there a fibrosis gene?

Interstitial fibrosis is seen in the lung in response to a variety of insults, and often appears stereotypical in terms of its clinical and pathological features. However, exposure to a known aetiological factor does not always lead to fibrosis. For example in bleomycin-induced pulmonary fibrosis, a wide variation in response is seen both in humans and in animal models, which is not completely accounted for by known risk factors. These observations and the existence of a number of familial forms of lung fibrosis suggest a genetic predisposition. Current hypotheses concerning the pathogenesis of pulmonary fibrosis propose an initial stage involving the influx of inflammatory cells into the interstitium. These cells, together with activated resident cells are then thought to release polypeptide mediators that stimulate the fibroblast proliferation and matrix protein synthesis typical of these disorders. Genetic influences could have an important role in regulating a number of these events, altering the immunological response to injury or modulating collagen metabolism in the lung. However, despite recent advances in molecular genetic techniques, there have been few human studies to date. Most have concentrated on genetic loci with a high degree of polymorphism such as the human leucocyte antigen (HLA) system and yield conflicting results. Others offer tantalising but as yet, incomplete insights into the mechanisms involved. Defining the genetic abnormalities underlying both the familial forms of pulmonary fibrosis and the variations seen in response to lung injury should enhance our understanding of the pathogenic processes and help to focus research in this area.

Immunohistochemical distribution of type VI collagen in developing human kidney

The distribution of type VI collagen was investigated immunohistochemically in the developing human kidney from 15 to 32 weeks gestational age and it was compared with that observed in the normal infantile and adult human kidney. In fetal kidney, type VI collagen was widely distributed as a fibrillar network in the subcapsularly undifferentiated mesenchyme and intertubular interstitium, and as a basement membrane-like structure around the ureteral bud branches, tubules, and collecting ducts. During nephrogenesis, type VI collagen disappeared from the induced mesenchyme close to the tips of ureteral branches, while it formed a distinct basement membrane-like structure around the early stages of nephron differentiation (comma-shaped and S-shaped bodies) and later along Bowman's capsule of capillary loop and maturing glomeruli A strong immureactivity for type VI collagen was also found in the glomerular basement membrane and mesangial areas of capillary loop and maturing glomeruli. In infantile kidney, type VI collagen showed a distribution pattern similar to that observed during the fetal period. In adult human kidney, glomerular basement membrane showed a weak positivity for type VI collagen and the basement membrane-like staining around Bowman's capsule, tubules, and collecting ducts was less evident than in fetal and infantile kidney. Our immunohistochemical findings suggest that type VI collagen is a normal component of the glomerular and extraglomerular extracellular matrix of developing human kidney and that it undergoes changes in the expression during maturation.

Immunohistochemical expression of type VI collagen in superficial fibromatoses

The expression of type VI collagen was studied immunohistochemically in 26 cases of superficial fibromatoses (palmar, plantar and penile) using an immunoperoxidase method for light microscopic visualization. The polyclonal antibody against type VI collagen used in this study was isolated from human placenta and its specifity was tested by immunoblotting assay. All cases consisted of multiple nodules showing a variable degree of cellularity and fibrosis. Depending on the predominant histological appearance of these nodules, each case was assigned to the three following phases: proliferative, involutional and residual. Morphologically normal palmar and plantar aponeuroses were included as controls. Immunohistochemical findings showed that type VI collagen was present as longitudinal thin fibers in normal palmar and plantar aponeuroses. A differential expression of this collagen was found in the different stages of superficial fibromatoses. Type VI collagen was markedly expressed as a distinct fibrillar network in the extracellular matrix (ECM) surrounding proliferating stromal cells in proliferative and involutional phases. Its expression completely disappeared from the connective tissue undergoing fibrotic transformation during involutional and residual phases. The results of the present study suggest that type VI collagen is an extracellular marker of stromal tissue proliferation and is involved in the early phases of tissue remodelling occurring in the superficial fibromatoses.

Immunoquantification of type I, III, IV and V collagen in small samples of human lung parenchyma

The involvement of collagen in pathological conditions underscores the need for sensitive, collagen type-specific assays. A method for the quantification of different types of collagen in lung has been developed. Human lung parenchyma is digested with cyanogen bromide which results in almost complete solubilization of collagen to type-specific collagen peptides. The peptides are quantified using inhibition enzyme immunoassays with type-specific antibodies. The 50% inhibition value for the type I collagen assay is 1 microgram type I collagen peptides, for the type III collagen assay 350 ng type III collagen peptides, for the type IV collagen 200 ng type IV collagen peptides, and for the type V collagen assay 50 ng type V collagen peptides. Using less than 1 mg lyophilized human parenchymal lung tissue it was established that the amount of collagen/mg dry tissue (+/- SD, n = 10) is 84.6 +/- 16.1 micrograms for type I collagen, 26.6 +/- 10.3 micrograms for type III collagen, 9.6 +/- 2.0 micrograms for type IV collagen and 1.8 +/- 0.3 micrograms for type V collagen. The procedure is useful for the quantification of different types of collagen, including minor collagens, and requires only minimal sample preparation.

Distribution of extracellular matrix glycoproteins in the human mesonephros

We analyzed the expression and distribution of collagen types IV and VI, laminin and fibronectin during the development and regression of the mesonephros in human embryos and fetuses ranging from 6 to 12 weeks of gestation by indirect immunoperoxidase methods. Type IV collagen, laminin and fibronectin were detected along the glomerular, tubular and capsular basement membranes of developing and mature nephrons. Only type IV collagen and fibronectin were found in the mesangium. Type VI collagen formed a delicate interstitial fibrillar network and a continuous basement membrane-like structure along the mesonephric nephrons. Basement membranes (GBM) of developing and mature glomeruli showed a distinct continuous staining for this collagen. The mesangial matrix was rich in type VI collagen. Mesonephric involution started during the 8th week of gestation and coincided with a moderate expansion of mesangial matrix and progressive collapse of the capillary walls, while the tubules became thinner and shorter. Staining for all extracellular matrix glycoproteins studied showed GBM wrinkling, gradual disintegration of some capillary loops and glomerulosclerosis. The sclerotic glomeruli were strongly positive for type IV collagen and less positive for type VI collagen and fibronectin. Laminin was absent. Our results indicate that collagen types IV, VI, laminin and fibronectin may be involved in the development and regression of the human mesonephros.

Expression and distribution of type VI collagen in gynecomastia

We investigated the distribution of type VI collagen in 36 cases of routinely fixed and paraffin-embedded gynecomastia using an immunoperoxidase method for light microscopic visualization. Four samples of normal male mammary gland tissue were also included as controls. A protease predigestion was essential for the visualization of this extracellular matrix (ECM) glycoprotein. In normal male breast, no immunoreaction for type VI collagen was detected in the stroma surrounding the ducts. Gynecomastia was classified into three histological types: florid (type I), fibrous (type II), and intermediate (type III). Type VI collagen was differentially expressed in the periductal stroma of all types. This collagen was markedly expressed at the early disease stage (type I) when the periductal stroma is highly cellular and vascular. Its expression decreased when periductal stroma undergoing fibrotic transformation (type III) and completely disappeared from the dense periductal stroma of fibrous stage (type II). These findings suggest that type VI collagen is involved in the ECM remodelling occurring in gynecomastia.

Patterns of type VI collagen compared to types I, III and V collagen in human embryonic and fetal skin and in fetal skin-derived cell cultures

The distribution of type VI collagen was examined in human embryonic and fetal skin and in cultured cells and matrix from this tissue. Frozen sections were immunolabeled with primary antibodies against type VI collagen and types I, III or V collagen, and processed further for fluorescence microscopy and immunoelectron microscopy. At 6 weeks estimated gestational age (EGA), type VI collagen was identified by positive fluorescence and by immunogold staining of filaments and fibers beneath the dermal-epidermal junction (DEJ), weaker fluorescence in the fine matrix of the dermis, and stronger fluorescence in the subcutis. At progressive stages of gestation, immunolabeling for type VI collagen increased in the dermis in parallel with increased deposition of types I and III collagen. By 15 weeks EGA, type VI collagen stained intensely throughout the dermis. At 13 weeks EGA, type VI collagen appeared diminished from the growing tips of invaginating hair buds, but as the hair peg developed, type VI collagen accumulated in adnexal sheaths. Cell cultures were derived from fetal skin at 7.5 to 12 weeks EGA. In primary explant cultures containing both keratinocytes and fibroblasts, mats of type V collagen were present beneath keratinocytes and associated with dense spots that co-labeled for both type VI and type V collagen. In passaged cultures of fibroblasts, individual cells with or without pretreatment with monensin were positive for type VI and/or types I, III or V collagen. Fibrous matrix that was labeled for type VI collagen was also immunopositive for type I or III collagen, while filamentous matrix that was type VI collagen positive tended to exclude types I and III collagen but in some areas to overlap with type V collagen. These findings support the hypothesis that type VI collagen present in both filamentous and fibrous matrix and networks of type VI collagen may serve as a fine scaffolding that facilitates the integration of types I and III collagen into developing fibrous matrix.

Localization of collagen type VI in articular cartilage of young and adult mice

Collagen type VI was demonstrated immunomorphologically in articular cartilage (distal femur) of young (2-8 weeks) and adult mice by fluorescence and electron microscopy (gold-labelled second antibody--sandwich method) using pre- and post-embedding techniques. This collagen type was mainly seen in the vicinity of chondrocytes, and in larger amounts in adult cartilage. Electron-microscopic inspection (pre-embedding technique) revealed labelling above plaques that were 40-160 nm in size, and from which up to 7 fine filaments (< or = 10 nm) per unit sectional plane radiated. Using the post-embedding technique, only labelled plaques could be demonstrated; fine filaments were not perceptible. This was partly a result of the low contrast. It is assumed that the globular ends of up to 20 of the fine type VI filaments are anchored in one plaque and that the antibodies bind to the non-collagenous globular domains. Filaments radiated from the plaques and formed a three-dimensional network that stabilized the structures of the cartilaginous matrix. Antibodies against fibronectin also labelled similar plaques. The ends of the type VI filaments are possibly linked into the plaques by fibronectin.

Immunohistochemical localization of chondroitin sulfate, chondroitin sulfate proteoglycan, heparan sulfate proteoglycan, entactin, and laminin in basement membranes of postnatal developing and adult rat lungs

Histologic preparations of lungs from 1-, 5-, 10-, 18-, and 25-day-old postnatal and adult rats were examined immunohistochemically with antibodies specific against chondroitin sulfate (CS), basement membrane chondroitin sulfate proteoglycan (BM-CSPG), heparan sulfate proteoglycan (HSPG), entactin, and laminin. A monoclonal antibody specific for the glycosaminoglycan portion (CS) of CSPG and a monoclonal antibody against the core protein of CSPG were used in an immunoperoxidase sequence to stain extracellular matrix (ECM) components of pulmonary basement membranes (BMs). Anti-CS stained airway BM strongly and alveolar BM weakly in the adult rat lung, as well as in vascular and airway adventitia. In developing lungs, immunoreactivity was strong in all ECM sites, including BM, at day 1 postnatal, and progressively diminished thereafter except in vascular and airway adventitia. Anti-CSPG stained alveolar, airway, and vascular BMs, in addition to smooth muscle external laminae (EL), in the adult and developing rat. Immunostaining for CSPG required hyaluronidase digestion, whereas CS staining was lost with the same treatment. A polyclonal antibody to the core protein of HSPG was found to be similarly distributed to CSPG by immunoperoxidase staining in adult and developing rat lungs, with the notable exception that little immunoreactivity for HSPG was found in smooth muscle EL. Commercially obtained polyclonal antibodies to entactin and laminin gave immunostaining comparable to that seen with CSPG, except that entactin showed particular affinity for EL. These results offer a more detailed perspective on previous survey observations of CSPG, HSPG, and entactin in the rat lung, and describe the immunoreactivity of CS for the first time.(ABSTRACT TRUNCATED AT 250 WORDS)

The hepatic extracellular matrix. I. Components and distribution in normal liver

The unique nature of the hepatic extracellular matrix (ECM) is predicated by the special configuration of the space of Disse. Whereas other epithelial organs have two basement membranes (BM) and a substantial ECM interposed between endothelial and epithelial cells, the liver lobule has no BM and only an attenuated ECM, consisting mostly of fibronectin, some collagen type I, and minor quantities of types III, IV, V, and VI. This configuration, together with the abundant fenestrations and gaps of the sinusoidal endothelial cells, seems ideally suited to facilitate the rapid bidirectional exchange of macromolecules normally taking place between plasma and hepatocytes. During organogenesis, the liver anlage is vascularized by continuous capillaries with BM, but by day 13.5 of development (in the rat) the vessels in the immediate proximity of hepatocytes become fenestrated, lacking specialized junctions and BM, suggesting that the hepatocytes produce signals capable of modulating the endothelial phenotype. In regeneration, hepatocyte proliferation precedes vascular proliferation resulting in the formation of hepatocyte clusters that, temporarily, lack sinusoids. Eventually, vascular proliferation follows and the normal hepatocyte-vascular relationships are restored. During this period laminin synthesis by Ito cells is prominent. As soon as hepatocytes become stable, secretion of the sinusoid phenotype-maintaining factors resumes and laminin synthesis and secretion terminates. The interplay between extracellular matrix and liver cells is essential for normal homeostasis and its modification results in deranged hepatic function.

Age-related changes of sulfated proteoglycans in the normal human trabecular meshwork

Ultrastructural changes in sulfated proteoglycans were studied in 12 pairs of normal eye-bank eyes (aged 1 day to 92 years), using the cationic dye, cuprolinic blue, in a 'critical electrolyte concentration'. Pretreatment of trabecular meshwork sections with various glycosaminoglycanases and nitrous acid served to characterize these proteoglycans. Three sizes of proteoglycan-cuprolinic blue (PG-CB) complexes were found in association with different extracellular matrix components. Small, thin PG-CB complexes were closely associated with collagen fibrils. Large, thick PG-CB complexes, although located close to collagen fibrils in a variety of places, were most commonly seen between the boundaries of the collagen bundles, where they were associated with fine filaments. Both types of collagen-associated PG-CB complexes contained chondroitin sulfate and dermatan sulfate, with dermatan sulfate predominant. Basal lamina-associated PG-CB complexes contained heparan sulfate. An age-related, progressive coalescence of collagen was found in normal trabecular meshwork in a statistically significant fashion; the regions of collagen coalescence were associated with a decrease of small, collagen-associated PG-CB complexes and an increase of a previously unrecognized matrix material. The measurement of areas of coalescence of collagen was used as an indirect indicator of small, collagen-associated PG-CB complex loss with age. Large collagen-associated PG-CB complexes and basal lamina-associated PG-CB complexes decreased from infant to young adult; no additional loss with age was found. Further studies will be needed to determine whether loss of sulfated PGs plays a role in increased aqueous outflow resistance that characterizes glaucoma.

Isolation, characterization, and localization of cardiac collagen type VI. Associations with other extracellular matrix components

We have isolated and characterized collagen type VI from murine, canine, and nonhuman primate hearts. In the three species studied, collagen type I was the major collagenous component of the cardiac interstitium (80% of total collagen), whereas collagen type VI represented approximately 5% of total collagen. To define the exact distribution of collagen type VI and its possible interactions with other components of the cardiac extracellular matrix, collagen types I, III, IV, and VI, laminin, and fibronectin were localized in the rat myocardium by immunohistochemistry, using monospecific antibodies. In the rat myocardium, collagen type VI was prevalent in the media and adventitia of muscular arteries, in fine connective tissue septa, in the area surrounding capillaries, and in the delicate endomysium in proximity to myocardial cells. When compared with the immunohistochemical localization of collagen types I, III, and IV, laminin, and fibronectin, the continuity and hierarchical organization of the cardiac extracellular matrix became apparent. The matrix forms a continuous network extending from the pericardium to the endocardium. Furthermore, there is an arborescent hierarchy in the system such that collagen type I is more prevalent in the wider septa, collagen type III being more obvious in medium-sized branches, and fibronectin and collagen type VI prevailing in the terminal (pericellular) aspects of the network. In this pericellular location, fibronectin and collagen type VI, by means of specific interactions, may act as anchor components linking the myocardial cell basement membranes not only to the extracellular matrix but also to the cardiac interstitial cells. This continuity, organization, and coupling of the cardiac extracellular matrix appears well suited to integrate and distribute the physical stress generated by the continuous contraction and relaxation of the myocardium.

Structural and functional relationships between type II pneumocytes and components of extracellular matrices

Type II pneumocytes of the pulmonary alveolus are dynamic cells with multiple functional capabilities in vivo, including secretion of surface-active lipoproteins and cell renewal of the epithelial lining of the alveolus, involving its differentiation into another cell type (the type I pneumocyte). The factors that influence and control these processes, which are vital to the function of the alveolus, have begun to be more clearly understood in recent years, in large part because of the development of adequate in vitro systems, which permit the manipulation of relevant variables. These appear to be a complex interaction between insoluble components of extracellular matrices, principally of the basement membrane, and soluble factors that include hormones and growth factors. This review focuses particularly on those components of extracellular matrices that specifically and nonspecifically impact on type II cell function, and it attempts to bring together the diverse technical approaches used to define and examine these relationships cytochemically and functionally.

Collagen type I and III occur together in hybrid fibrils in the space of Disse of normal rat liver

Collagen type I and procollagen type III were localized at the ultrastructural level on ultrathin frozen sections of rat liver by the protein A-gold technique using affinity-purified primary antibodies. Both collagen type I and procollagen type III were localized on nearly all solitary and bundled fibrils in the space of Disse. Simultaneous localization of collagen type I and procollagen type III by a double-labeling procedure using protein A-gold probes of different sizes unequivocally demonstrated the presence of both collagens in the same fibrils. Measurement of the diameter of large numbers of collagen fibrils in the space of Disse of the rat liver showed a unimodal distribution of the fibril diameters around an average value of 62.4 nm (S.D. = 12.8 nm), and 91% of the collagen bundles contained less than 30 fibrils. Additional measurements on epoxy resin-embedded material of five biopsy specimens of normal human liver showed a comparable unimodal distribution of the fibril diameters around an average value of 57.2 nm (S.D. = 9.6 nm), and 74% of the bundles contained less than 60 fibrils. The latter observation demonstrates that human liver contains broader interstitial collagen bundles than rat liver. From these results, we conclude that the space of Disse of normal rat and human liver contains a uniform population of striated interstitial collagen fibrils. In the rat liver, these fibrils contain both collagen type I and procollagen type III. Therefore the concept that procollagen type III is predominantly localized in small diameter fibrils or bundles, whereas collagen type I is preferentially localized in thick ones, does not hold.

Localization of collagen in the rat lung: biochemical quantitation of types I and III collagen in small airways, vessels, and parenchyma

The marked insolubility of pulmonary collagen has limited its accurate biochemical quantitation in small samples of lung and other tissues. We have recently developed a microassay based on radioisotope dilution techniques that we have used for the accurate determination of types I and III collagen in extremely small tissue samples. By applying this method to carefully dissected small airways and vessels and samples of parenchymal tissue of rat lungs, we have localized and quantitated biochemically the type I and III structural collagens of the lung. Large pulmonary arteries are the units richest in these interstitial collagen types on the basis of dried tissue weight (50 micrograms/100 micrograms dried tissue). Amounts of both types I and III collagen are considerably lower in the alveolar domain than in vessels and airways of the rat lung. The proportion of tissue composed of these collagen types decreases centripetally in rat pulmonary arteries, but increases in the bronchial tree. The relative proportions of type I and type III remain constant in all the structures tested. The higher total amount of collagen in the nonalveolar domain has implications for biochemical studies based on whole lung samples.

Lung surfactant-associated proteins and type IV collagen share common epitopes. An immunocytochemical demonstration

Among the surfactant-associated proteins (SP-A) characterized so far, there is a group of glycoproteins 26 to 34 kDa that features collagenlike sequences near their N-terminal end. We herein report the cross-reactivity of a rabbit polyclonal antibody to EHS tumor-derived type IV collagen towards rat SP-A. Rat lung tissues were processed for the localization of both type IV collagen and SP-A by high-resolution immunocytochemistry, applying the protein A-gold technique with specific antibodies. In addition to the various basal laminae of the pulmonary tissue, the antitype IV collagen antibody labeled the surfactant material found in alveolar spaces and macrophages, as well as in type II pneumocytes. The surfactant nature of the alveolar material labeled by the antiserum to type IV collagen was confirmed by the positive labeling obtained using an antibody to SP-A. This antibody labeled specifically the alveolar surfactant material, without binding any basal laminae. Several control experiments demonstrated the specificity of each labeling. These results were further supported by immunoblot experiments on nitrocellulose membrane. These findings thus provide further support to the existence of collagenlike sequences on SP-A, and further demonstrate that this structural similarity with collagens can lead to some cross-antigenicity.

Cellular events in alveolitis and the evolution of pulmonary fibrosis

"Alveolitis", as opposed to "pneumonia" sensu strictiori, is a term used to denote diffuse inflammatory changes of the pulmonary parenchyma, excluding those that result from local bacterial, fungal or other extracellular microbial growth. The various types of alveolitis are classified according to their histological characteristics and range from "luminal phagocytic" or "mural lymphoplasmacellular" and "exudative" to "fibrosing" alveolitis. In this overview, various exogenous and endogenous causes of different types of alveolitis, and the cellular events in their pathogenesis are briefly discussed to illustrate the complex mechanisms involved. Particular emphasis is placed on the possible transition from diffuse exudative to fibrosing alveolitis. It appears that pulmonary fibrosis, which is usually patchy rather than truly diffuse, does not have a uniform pathogenesis. Besides the possibility of a certain degree of a diffuse fibrosis three major pathways are evident: (1) granulation tissue budding into alveolar lumina (luminal fibrosis) (2) exudate incorporation into alveolar walls (mural fibrosis) and--at least equally important--(3) so-called collapse (atelectatic) induration (obliterative-interseptal fibrosis), a process that has largely been neglected so far.