Changes in cytokeratin, vimentin and desmoplakin distribution during the repair of irradiation-induced lung injury in adult rats

Biological mechanisms of normal tissue damage: importance for the design of NTCP models

The normal tissue complication probability (NTCP) models that are currently being proposed for estimation of risk of harm following radiotherapy are mainly based on simplified empirical models, consisting of dose distribution parameters, possibly combined with clinical or other treatment-related factors. These are fitted to data from retrospective or prospective clinical studies. Although these models sometimes provide useful guidance for clinical practice, their predictive power on individuals seems to be limited. This paper examines the radiobiological mechanisms underlying the most important complications induced by radiotherapy, with the aim of identifying the essential parameters and functional relationships needed for effective predictive NTCP models. The clinical features of the complications are identified and reduced as much as possible into component parts. In a second step, experimental and clinical data are considered in order to identify the gross anatomical structures involved, and which dose distributions lead to these complications. Finally, the pathogenic pathways and cellular and more specific anatomical parameters that have to be considered in this pathway are determined. This analysis is carried out for some of the most critical organs and sites in radiotherapy, i.e. spinal cord, lung, rectum, oropharynx and heart. Signs and symptoms of severe late normal tissue complications present a very variable picture in the different organs at risk. Only in rare instances is the entire organ the critical target which elicits the particular complication. Moreover, the biological mechanisms that are involved in the pathogenesis differ between the different complications, even in the same organ. Different mechanisms are likely to be related to different shapes of dose effect relationships and different relationships between dose per fraction, dose rate, and overall treatment time and effects. There is good reason to conclude that each type of late complication after radiotherapy depends on its own specific mechanism which is triggered by the radiation exposure of particular structures or sub-volumes of (or related to) the respective organ at risk. Hence each complication will need the development of an NTCP model designed to accommodate this structure.

Growth hormone (GH) receptor knockout mice reveal actions of GH in lung development

The presence of growth hormone (GH) and GH receptors (GHRs) in the lung suggests it is an autocrine/paracrine target site for pulmonary GH action and/or an endocrine site of pituitary GH action. Roles for GH in lung growth or pulmonary function are, however, uncertain. The possibility that pituitary and/or pulmonary GH have physiological roles in lung development has therefore been investigated in GHR knockout (KO or -/-) mice, using a proteomics approach to determine if an absence of GH-signaling affects the proteome of the developing lung. More than 600 proteins were detected by 2-DE in the lungs of control [GHR (+/+)] and GHR (-/-) mice at the end of the alveolarization period (at day 14 postnatally). Of these, 39 differed significantly in protein content at the p>0.05 level [6 were of higher abundance in the GHR (-/-) group, 33 were of lower abundance] and 17 differed at the p>0.02 level [5 of higher abundance in the GHR (-/-) group, 12 of lower abundance] and 7 were definitively identified by MS. Vimentin, a protein involved in cellular proliferation, was reduced in content by approximately 75% in the lungs of the GHR (-/-) mice. Three proteins involved in oxidative protection [SH3 domain-binding glutamic acid-rich-like protein, peroxiredoxin 6 (Prdx6), and isocitrate dehydrogenase 1] were also of lower content in the GHR (-/-) lungs (by approximately 88%, 81% and 70%, respectively). Prdx6 is also involved in lipid and surfactant metabolism, as is apolipoprotein A-IV, the lung content of which was reduced by approximately 73% in these mice. Proteasome 26S ATPase subunit 4, a protein involved in the non-lysosomal degradation of intracellular proteins, and electron flavoprotein alpha subunit , involved in intracellular metabolism, were also reduced in content in the lungs of the GHR (-/-) mice (by approximately 70% and 49%, respectively). These results therefore suggest that these proteins are normally dependent upon GH signaling, and that GH is normally involved in early lung growth, oxidative protection, lipid and energy metabolism and in proteasomal activity. These roles may reflect endocrine actions of pituitary GH and/or local autocrine/paracrine actions of GH produced within the lung.

Target cells in radiation pneumopathy

Radiation pneumopathy is the reaction of the organ lung to radiation effects in various target cells. It starts as an exudative inflammation, with the clinical picture of interstitial pneumonia 6-12 weeks after irradiation, and proceeds to a productive chronic inflammation lasting several months and terminating, as other chronic inflammations do, in scar formation, called lung fibrosis. Lung fibrosis is the common end point after lung damage from a wide range of damaging agents. The pathogenetic process leading to the signs and symptoms of radiation pneumopathy is an integrated response of the complex organization of lung tissue. Clinical and pathologic data in patients do not support the hypothesis that the early inflammatory phase of radiation "pneumonitis" and late "radiation fibrosis" are independent pathogenetic processes in the same way as acute radiodermatitis and subcutaneous fibrosis are separate pathologic entities. The target cell population that initiates the pathogenetic process in the lung is not known, and it has been suggested that no single identifiable target exists. The entire process is the result of complex functional alterations in endothelial cells, pneumocytes, macrophages, and other resident and transient cells. No evidence has been found for a role of stem cell sterilization, for impaired transit cell proliferation, or for hypoplasia, which is the hallmark of other acute inflammatory normal tissue damage (i.e., in the mucosa). The radiobiologic concepts developed in cellular radiobiology are not adequate for the quantitative analysis of radiation pneumopathy. A new analytical framework based on structurally defined intercellular interaction by signaling molecules and their activation needs to be developed. This would not be only an abstract radiobiologic paradigm but would be the key to the development of potential therapeutic interventions in irradiated patients.

Radiation response of cell organelles

The cellular responses to various form of radiation, including ionizing- and UV-irradiation or exposure to electromagnetic fields is manifested as irreversible and reversible structural and functional changes to cells and cell organelles. Moreover, beside the morphological signs related to cell death, there are several reversible alterations in the structure of different cell organelles. The radiation-induced changes in the supramolecular organization of the membranes, including plasma membrane, and different cell organelle membranes, play a significant role in the development of acute radiation injury. These signs of radiation-induced reversible perturbation biological membranes reflect changes in the organization and/or composition of the glycocalix, modified activity and/or distribution of different membrane domains, including enzymes and binding sites. The observed changes of the cell surface micromorphology and the alteration of intercellular connections are closely related to the reorganization of the cytoskeletal elements in the irradiated cells. The mitochondria, endoplasmic reticulum, Golgi-complex, the lysosomal system have long been considered to be direct intracellular targets of irradiation. The listed morphological alterations of nuclear chromatin (e.g. changes of fine structure, altered number of nucleolar organizing regions and micronuclei, development of chromosome aberrations) may originate from the radiation-induced damage to the supramolecular organization of DNA and/or nucleus specific proteins. These endpoints of radiation effects resulted as direct consequence(s) of absorbed radiation energy, and indirectly altered intra-, intercellular communication or modified signal transduction. Some complementary data suggest that all these effects are not strictly specific to radiation and may be best considered as general stress responses, similar to those observed after application of various injurious agents and treatments to cells. Moreover, they may be equally responsible for direct degradation of supramolecular component of cells, altered signal transduction, or changes in the amount or ratio of any extracellular mediators upon irradiation. Nevertheless, qualitative and/or quantitative evaluation of any changes of chromosomes by different techniques (morphological analysis of metaphase chromosomes, fluorescent in situ hybridization, development of micronuclei etc.) are useful biological indicators as well as "biological dosimeters" of radiation injury. It is suggested, that some modern methods such as immunohistochemical detection of different proteins, specific markers of cell organelles and cytoskeleton, inspection of distribution of cell surface charged sites and different membrane domains and application of tracer substances may all be included into protocols for evaluation of cell alterations induced by different types and intensities of radiation.

Cytokeratin expression patterns in the rat respiratory tract as markers of epithelial differentiation in inhalation toxicology. II. Changes in cytokeratin expression patterns following 8-day exposure to room-aged cigarette sidestream smoke

The expression of specific cytokeratin (CK) polypeptide patterns is a sensitive marker of the cytoskeletal differentiation of epithelial cells. We developed an immunohistochemical method to assess CK expression patterns in the rat respiratory tract using serial paraffin-embedded sections from the nasal cavity, trachea, and lung. In the present study, this method was used to detect exposure-related differences in CK expression patterns in adult Wistar rats following inhalation of room-aged sidestream smoke (11 mg total particulate matter/m3 air, 8 days, 12 hr/day, whole body). In the anterior nasal cavity level 1 (NL1), changes in CK expression patterns were observed in the respiratory epithelium of the lateral wall and the maxilloturbinate (CK14, CK15, and CK18) and in the squamous epithelium of the ventral meatus (CK13). At nasal cavity level 2 (NL2), immediately behind NL1, changes were observed in the olfactory epithelium (CK13, CK14, and CK18) and in the respiratory epithelium of the septum (CK7 and CK19), the lateral wall (CK7 and CK13), and the lateral aspect of the maxilloturbinate (CK14). Changes were also observed in the submucosal glands, nasolacrimal duct, and vomeronasal organ. In the trachea only CK7 expression changed, and in the lung expression of CK7 (bronchioli) and CK8 (bronchus) changed; the expression of other CK polypeptides did not change. The observed changes in CK expression at NL1 correlated with the histomorphological changes, whereas CK expression changes were also seen in the olfactory and respiratory epithelia at NL2 and in the trachea and lung, where no histomorphological changes were seen. These findings indicate that changes in CK expression in respiratory tract epithelial cells are a sensitive marker for cellular stress response.

Cytokeratin expression patterns in the rat respiratory tract as markers of epithelial differentiation in inhalation toxicology. I. Determination of normal cytokeratin expression patterns in nose, larynx, trachea, and lung

Cytokeratin (CK) polypeptides constitute the intermediate filament cytoskeleton of epithelial cells. The patterns of CK expression can be regarded as specific markers for the epithelial differentiation status. Our objective was to map the cell type-specific CK expression patterns at all representative sites of the respiratory tract of untreated rats to use as a base for the detection of inhalation exposure-related differentiation changes. Using routine paraffin-embedded sections and a panel of well-characterized monoclonal antibodies for immunohistochemistry, we obtained CK staining patterns as follows. Nasal cavity: respiratory epithelium CK18, CK19 (basal, ciliated, nonciliated cells), CK14, and/or CK15 (basal and nonciliated cells); olfactory epithelium CK18 (basal, mid, apical zones and Bowman's glands), CK14, and CK15 (basal zone); squamous epithelium of ventral meatus CK14, CK15 (basal and suprabasal cells), CK1, 10/11, and CK13 (suprabasal cells); glands and columnar epithelia of vomeronasal organ and nasolacrimal duct CK7 and CK13 in addition to respiratory epithelial CK pattern. Trachea: similar to nasal respiratory epithelium with pronounced CK15 and additional CK7. Larynx: CK14, CK15 (basal, ciliated, nonciliated cells), CK8, CK18, CK19 (not in basal cells), CK4, and CK13 (cuboidal and squamoid cells of ventral half). Lung: bronchial epithelium CK14 and CK15 (basal cells only); bronchial and alveolar epithelium CK7, CK8, CK18, and CK19; bronchiolar epithelium similar but less CK8 and no CK7; pleural mesothelium CK7, CK8, and CK19. This inventory of complex CK expression patterns provides the basis for investigating test substance-related effects in inhalation toxicology, e.g., cigarette smoke-induced changes.

Upregulation of gap junction protein connexin43 in alveolar epithelial cells of rats with radiation-induced pulmonary fibrosis

The degree of immunoreactive connexin43 (C x 43) in rat lung was evaluated during the development of radiation-induced pulmonary fibrosis in rat by a double immunofluorescence technique using polyclonal antisera to Cx43 and monoclonal antibodies to cytokeratins on cryostat sections. In normal rat lungs, Cx43 was detected in pneumocytes type II and I, in large blood vessel endothelia, in peribronchial smooth muscle cells, and in some peribronchial and perivascular interstitial cells. As early as 1 week after irradiation, enhanced immunoreactivity for Cx43 in the epithelial cells was detected. In severely injured lungs (about 3 months after irradiation), Cx43 was found also in the cytoplasm of type II pneumocytes. These findings were confirmed by western blot data. Western blot analysis also revealed increased phosphorylation of Cx43. It remains to be investigated whether the increased content of Cx43 in irradiated rat lung may be due to an enhanced number of gap junctions between type I and II alveolar epithelial cells.

Distribution of von Willebrand factor in capillary endothelial cells of rat lungs with pulmonary fibrosis

To determine the value of von Willebrand factor (vWF) antigen as a marker of endothelial injury in radiation-induced fibrosis of rat lungs, we studied endothelial immunoreactivity to antibodies against vWF using the indirect immunoperoxidase technique combined with morphometric analysis. Using immunoelectron microscopy of LR White embedded lung samples to detect vWF, immunogold-labelled Weibel Palade bodies were found in endothelial cells of capillary endothelium. The irradiated lungs showed a statistically significant elevation of vWF expression, ie, vWF positive endothelia per unit area, and a significant increase of vWF expression per unit of parenchyma as well. The results suggest that vWF antigen expression and the number of vWF positive structures is modulated under condition of injury in radiation-induced fibrosis.

Expression of CD44 isoforms during bleomycin-or radiation-induced pulmonary fibrosis in rats and mini-pigs

The distribution of CD44s and CD44v molecules in normal and injured lung tissue of rats and mini-pigs was studied by examining the immunohistochemical binding of monoclonal antibodies against CD44 isoforms. We showed that the expression of CD44v and CD44s varies greatly among different pulmonary fibrosis samples and that some tissues express either enhanced expression of CD44s, particularly in the interstitium and on alveolar macrophages, or very low levels of CD44v in the alveolar epithelium. Normal type II pneumocytes expressed the CD44s and CD44v molecules at the basolateral aspect of the cell. Such localisation favours a role for CD44 in epithelial cell-fibroblast interaction during lung development and repair.

Immunocytochemical distribution of E-cadherin in normal and injured lung tissue of the rat

Affinity purified rabbit anti-mouse E-cadherin antibodies, reacting with diverse rat epithelia, were used to characterize epithelial changes in a radiation-induced fibrosis model of rat lung by immunoblotting techniques, immunoperoxidase and immunofluorescence microscopy. Immunostaining of normal rat lung tissues revealed a predominant staining of type II pneumocytes. Immunoelectron microscopy confirmed the immunohistochemical data of normal lung tissue obtained at the light microscopic level. In severely injured rat lung, we found enhanced immunoreactivity for E-cadherin at the surface of type I alveolar epithelial cells. The results suggest that E-cadherin is an adhesion molecule that is modulated after pathological alteration of the alveolar epithelium and that the antiserum may be useful for the characterization of normal and diseased rat epithelia.

Monoclonal antibodies to surfactant protein D: evaluation of immunoreactivity in normal rat lung and in a radiation-induced fibrosis model

This report describes the development of a new panel of monoclonal antibodies established after immunization of mice with purified surfactant protein D of the rat. To enhance the detection of SP-D in formalin- or Schaffer-fixed samples, immunohistochemistry was performed by using microwave pretreatment of paraffin sections. Using these new antibodies that bind to type II epithelial cells, Clara cells, and alveolar macrophages, the responses of lung parenchymal cells were examined in a radiation-induced fibrosis model. Increased accumulation of extracellular SP-D in the alveolar space was found. Double staining with anti-surfactant protein A antibodies revealed different Clara cell populations containing one or both types of surfactant proteins.

Bauhinia purpurea lectin (BPA) binding of rat type I pneumocytes: alveolar epithelial alterations after radiation-induced lung injury

In the rat lung, we found that the Bauhinia purpurea lectin (BPA) specifically binds to the type I alveolar epithelial cells and to the alveolar macrophages. Double label fluorescence employing FITC-coupled Maclura pomifera lectin (MPA) and bBPA-avidin-Texas Red showed that BPA binding was confined to type I cells. In addition, a minor staining of the luminal border of the terminal bronchiolar epithelium was found. The sequence of tissue injury following X-radiation was examined in rats. BPA is a suitable marker which indicates epithelial changes during the early stage of pneumonitis and the subsequent development of fibrosis.

Immunohistochemical localization of the beta subunit of prolyl 4-hydroxylase in human alveolar epithelial cells

The beta subunit of prolyl 4-hydroxylase, the protein-disulfide isomerase (PDJ), catalyzes the hydroxylation of proline residues of collagens and proteins with collagen-like structure, a step essential for the folding of the procollagen chains to form triple-helices. In the present study, we report the selective immunohistological localization of PDI in type II alveolar and bronchial epithelial cells. The detection of the hidden antigen with the monoclonal antibody 5B5 is usually not successful in paraffin sections but was possible after microwave pretreatment of tissue sections. In cases of severe lung injury (fibrosing alveolitis) enhanced immunoreactivity was found for this enzyme in epithelial, endothelial as well as interstitial cells and in alveolar macrophages. The results indicate a possible involvement of the pulmonary epithelial cells in the upregulation of collagen production during the process of fibrosis.

Immuno- and lectin histochemistry of epithelial subtypes and their changes in a radiation-induced lung fibrosis model of the mini pig

Cell types of lung epithelia of mini pigs have been studied using a panel of monoclonal and polyclonal antibodies against cytokeratins (CKs) and vimentin and three lectins before and after radiation-induced fibrosis. In normal tissues, CK18 specific antibodies reacted above all with type II alveolar epithelial cells, while CK7 and pan CK-specific antibodies stained the whole alveolar epithelium. In bronchial epithelial cells, CKs 7, 8, 18 and focally CKs 4 and 13 as well as vimentin were found. Cell specificity of the CK pattern was confirmed by double label immunofluorescence using type II cell-specific Maclura pomifera (MPA) lectin, type I cell specific Lycopersicon esculentum (LEA) lectin and capillary endothelium-binding Dolichos biflorus (DBA) lectin. In experimental pulmonary fibrosis, enhanced coexpression of CK and vimentin was observed in bronchial epithelium. Subtypes of alveolar epithelial cells were no longer easily distinguishable. CK18 was found to be expressed in the entire alveolar epithelium. The gradual loss of the normal alveolar epithelial marker, as seen by the binding of MPA to type I-like cells, of LEA to type II-like cells and the partial loss of MPA-binding to type II cells, was paralleled by the appearance of CK4, typical for squamous epithelia, and the occurrence of DBA-binding in epithelial cells. Implications of these results for general concepts of intermediate filament protein expression and lectin binding in the fibrotic process are discussed.