Two different patterns of airway branching regulated by different components of the extracellular matrix in vitro

The IGF-I/IGF-R1 pathway regulates postnatal lung growth and is a nonspecific regulator of alveologenesis in the neonatal rat

IGF-I, IGF-II, and the IGF-I receptor are widely distributed throughout the neonatal rat lung on days 4, 7, 10, and 14 of life, with a similar abundance at each of these time points. Injection of 20 μg/g of a truncated soluble IGF-I receptor on days 2 and 5 of life, to decoy ligand away from the endogenous IGF-I receptor, reduced lung weight and lung-to-body weight ratio, reduced lung tissue fraction, and impaired alveolar formation, as assessed by secondary crest formation and mean linear intercepts on day 7 of life. Lung procollagen I content and elastin fiber density were also reduced. Injection of 100 μg/day of neutralizing anti-IGF-I, to prevent IGF-I from binding to the IGF-I receptor, on days 3, 4, and 5 of life reduced tissue fraction and elastin fiber density and impaired alveolar formation on day 6 of life. Both interventions reduced total lung cell and secondary crest cell DNA synthesis and small vessel counts per unit area, but these effects were lost after normalization to the reduced tissue fraction. These findings are consistent with a role for IGF-I binding to the IGF-I receptor in postnatal lung growth and on alveologenesis through a nonspecific positive effect on DNA synthesis. Injection of 100 μg/day of neutralizing anti-IGF-II, to prevent IGF-II from binding to the IGF-I receptor, on days 3, 4, and 5 of life had no effect on total lung cell DNA synthesis per unit area on day 6 of life, and a role for IGF-II in postnatal alveologenesis was not further pursued.

Toxicological Screening for the Effects of Short-Term Exposure of Sidestream Cigarette Smoke on Angiogenesis

Angiogenesis is a fundamental process that ensures adequate metabolic supply to tissues in numerous biological and pathological states, including tumorigenesis. Cigarette smoking causes numerous adverse effects, some of which are associated with disruption of the normal process of angiogenesis. It is believed that sidestream cigarette smoke severely affects different components that help in the normal process of angiogenesis. Sidestream cigarette smoke is composed primarily of smoke that emanates from the burning end of a cigarette, and contaminants that diffuse through the cigarette paper. The aim of the current study was to ascertain the toxicological effects of different sidestream cigarette smoke solutions (SSCSS) on angiogenesis by using chicken chorioallantoic membrane (CAM) assay. Decrease in total vascular area, diameter of secondary and tertiary blood vessels, cell proliferation, migration of blood vessels toward ectoderm, and number of capillary plexuses formation was observed by application of SSCSS. Scanning microscopy also revealed deviation in pattern formed by the major capillary plexuses and the fibrillar elements of the mesoderm SSCSS in treated CAMs. It is concluded that SSCSS may hinder the normal process of angiogenesis resulting in abnormal blood supply to tissues and decreased repair and remodeling, which are common problems among smoke-exposed individuals. Further study is required to delineate the effects of different chemicals in SSCSS on angiogenesis.

Impaired wound healing by exposure of different mainstream whole smoke solutions of commercial cigarettes

Cigarette smoke has been shown to potentiate wound damage and delayed ulcer healing. The chicken dorsum excisional wound assay was used to elucidate the deleterious effects of different mainstream whole smoke solutions (MSWSS) on the fundamental processes of wound healing. Gross, histopathology, SEM and computer based 3D image probing techniques were utilized to quantify different toxic effects of MSWSS on wound healing. A total of 160 chicks, aged 1 week, divided in eight groups were exposed to MSWSS with different nicotine concentration; 0.2mg (group A), 0.3mg (group B), 0.5mg (group C), 0.6mg (group D), 0.7mg (group E) and 1mg (group F). A very highly significant reduction (P<0.001) in wound closure was observed among all MSWSS treated groups at day 8 post-wounding. Histological investigations revealed a significant impede outcome in the re-epithelialization of all MSWSS exposed wounds. Delayed dermal matrix regeneration and maturation of collagen bundles were observed among all MSWSS treated wounds. Similar results were achieved through SEM of treated wounds. Histological and image probing analysis unveiled the scanty neovascularization among MSWSS treated wounds. Abbot curve, angular spectrum and different other parameters of 3D surface topographies of wounds revealed a very highly significant reduction (P<0.001) in angiogenesis among all MSWSS treated groups. These annotations validate the damaging effects of MSWSS on the healing of wounds.

Disruption of normal embryonic angiogenesis by direct exposure of mainstream whole smoke solutions of commercial cigarettes

Angiogenesis is activated in the female reproductive system during embryogenesis and embryo implantation. Smoking during pregnancy has been linked to interfere with normal process of angiogenesis resulting an increased incidence of ectopic pregnancy, spontaneous abortion, preterm delivery and sudden infant death syndrome. Chorioallantoic membrane (CAM) assay was used as an alternative in vivo approach to evaluate the toxicological effects of different mainstream whole smoke solutions (MSWSS) of commercial cigarettes on embryonic angiogenesis. Seventy 5-day-old CAMs, divided in seven groups were exposed to MSWSS with different nicotine concentration: 0.2mg (group B), 0.3mg (group C), 0.5mg (group D), 0.6mg (group E), 0.7mg (group F) and 1mg (group G). All smoke solutions caused varying levels of disruption on the normal process of angiogenesis and have shown to adversely affect the diameters of blood vessels, capillary plexus formation and organization of the fibrillar materials of CAMs. Abbot curve, angular spectrum and 3D surface roughness of CAMs were also measured for precise quantification of angiogenesis. Moderate to dramatic changes were observed in all treated groups with a very highly significant (P<0.001) disruption observed on CAMs of group G. No significant change was observed in different groups treated with pure nicotine. Current observations demonstrated that MSWSS of different commercial cigarettes have toxic effects on the process of angiogenesis and smoking during pregnancy may lead to an increased risk of spontaneous abortion and preterm delivery.

Do different branching epithelia use a conserved developmental mechanism?

Formation of branching epithelial trees from unbranched precursors is a common process in animal organogenesis. In humans, for example, this process gives rise to the airways of the lungs, the urine-collecting ducts of the kidneys and the excretory epithelia of the mammary, prostate and salivary glands. Branching in these different organs, and in different animal classes and phyla, is morphologically similar enough to suggest that they might use a conserved developmental programme, while being dissimilar enough not to make it obviously certain that they do. In this article, I review recent discoveries about the molecular regulation of branching morphogenesis in the best-studied systems, and present evidence for and against the idea of there being a highly conserved mechanism. Overall, I come to the tentative conclusion that key mechanisms are highly conserved, at least within vertebrates, but acknowledge that more work needs to be done before the case is proved beyond reasonable doubt.

Signaling through the EGF receptor controls lung morphogenesis in part by regulating MT1-MMP-mediated activation of gelatinase A/MMP2

Epithelial-mesenchymal interactions during lung development require extracellular signaling factors that facilitate branching morphogenesis. We show here that matrix metalloproteinases (MMPs) originating in the mesenchyme are necessary for epithelial branching and alveolization. We found that the delayed lung maturation characterized by abnormal branching and poor alveolization seen in mice deficient in epidermal growth factor receptor(Egfr-/-) is accompanied by aberrant expression of MMPs. By in situ zymography, the lungs from newborn Egfr-/- mice had low gelatinolytic activity compared with wildtype. Inhibition of MMPs in developing lungs in vivo or in vitro severely retarded morphogenesis. Egfr-/- mice had low expression of MT1-MMP/MMP14, which is a potent activator of gelatinase A/MMP2, in their lungs. Egf ligand increased MT1-MMP mRNA by tenfold in lung fibroblasts from wild type, but not from Egfr-/- mice. Extracts from lungs of Egfr-/- mice showed a tenfold reduction in active MMP-2, but only a slight decrease in proMMP-2 by zymography. At birth, MMP-2-/- mice had a lung phenotype characterized by abnormal lung alveolization which phenocopied that of Egfr-/- mice, albeit somewhat less severe. We conclude that proteolysis mediates epithelial/mesenchymal interactions during lung morphogenesis. From the phenotypes of the Egfr-/- mice, we identify MT1-MMP as a major downstream target of Egfr signaling in lung in vivo and in vitro. MT1-MMP is, in turn, necessary for activation of MMP-2, a mesenchymal enzyme that is required for normal lung morphogenesis.

Normal patterns of angiogenesis and extracellular matrix deposition in chick chorioallantoic membranes are disrupted by mainstream and sidestream cigarette smoke

The adverse effects of cigarette smoke on mature blood vessels are well established, whereas little is known about the influence of smoke on blood vessel development. To determine if cigarette smoke alters angiogenesis, chick chorioallantoic membranes (CAMs) were exposed for 4 days to culture medium (control) or to mainstream (MS) or sidestream (SS) smoke solution, and then blood vessel patterns were compared in blind tests. In contrast to the normal tree-like branching of control blood vessels, smoke-treated CAMs often had vessels that ran parallel to each other without much branching. A significant increase in the number of fibroblasts was observed in histological sections of treated CAMs, and this increase correlated with alterations in extracellular matrix components. Many more matrix fibrils were observed in treated CAMs than in controls using scanning electron microscopy. Immunohistochemistry showed that type III collagen was distributed in a tight band adjacent to the endoderm in controls but was distributed throughout the mesoderm in both treatment groups. Western blots confirmed that both type I and type III collagen were more abundant in treated CAMs than in controls. Fibronectin, which was localized immunohistochemically in the basal laminae and mesodermal matrix of controls, increased in abundance in CAMs treated with SS smoke solutions. Hyaluronic acid, which was present in a dense band subjacent to the capillary plexus of control CAMs, was greatly reduced in MS-treated CAMs and was absent in SS-treated CAMs. These observations demonstrate that both MS and SS cigarette smoke solutions caused abnormal pattern formation of CAM blood vessels and altered the composition of the extracellular matrix in the CAM mesoderm.

Inhibition of distal lung morphogenesis in Nkx2.1(-/-) embryos

In vitro and in vivo results are consistent with a critical role for NKX2.1, an epithelial homeodomain transcription factor in lung morphogenesis. Nkx2.1 null mutant embryos die at birth due to respiratory insufficiency caused by profoundly abnormal lungs. However, the precise role of NKX2.1 in the multistep process of lung structural morphogenesis and differentiation of various pulmonary cell types remains unknown. In the current study, we tested the hypothesis that the mutant lungs do not undergo branching morphogenesis beyond the formation of the mainstem bronchi and therefore consist solely of dilated tracheobronchial structures. To test this hypothesis, we determined the spatial and temporal expression pattern of a number of extracellular matrix (ECM) proteins and their cellular receptors, including alpha-integrins, laminin, and collagen type IV. Although laminin is expressed in the mutant Nkx2.1(-/-) lungs, expression of alpha-integrins and collagen type IV is significantly reduced or absent. In addition, examination of regionally specific expression of differentially spliced Vegf (vascular endothelial growth factor) transcripts, clearly indicates that the epithelial phenotype of the Nkx2.1(-/-) lungs is similar to the tracheobronchial epithelium. In contrast to wild-type lungs in which both Vegf1 and Vegf3 are developmentally expressed, Nkx2.1(-/-) lungs are characterized by predominant expression of Vegf1 and reduced or absent Vegf3. A similar pattern of Vegf expression is also observed in isolated tracheo-bronchial tissue. The sum of these findings suggest that at least two separate pathways may exist in embryonic lung morphogenesis: proximal lung morphogenesis is Nkx2.1 independent, while distal lung morphogenesis appears to be strictly dependent on the wild-type activity of Nkx2.1.