transforming-growth-factor-alpha and Bronchopulmonary-Dysplasia

Topics: Animals; Animals, Newborn; Bronchopulmonary Dysplasia; Disease Models, Animal; Epidermal Growth Factor; Fibroblast Growth Factors; Growth Substances; Humans; Infant, Newborn; Lung; Platelet-Derived Growth Factor; Respiratory Distress Syndrome, Newborn; Somatomedins; Transforming Growth Factor alpha; Transforming Growth Factor beta; Vascular Endothelial Growth Factor A

The epidermal growth factor receptor (EGF-R) is perhaps the best studied member of tyrosine kinase receptors. Its inactivation by homologous recombination results in three different phenotypes ranging from peri-implantation lethality to postnatal lethality. The mildest form of EGF-R inactivation leads to epithelial immaturity and postnatal death due to respiratory failure and necrotizing enterocolitis-like lesions in the intestine. The defects seen in this 'postnatal lethality phenotype' manifest in the classical EGF-responsive organs (skin, intestine) and organs undergoing branching morphogenesis during development (lung, kidney, mammary gland, pancreas and prostate), and thus accord with the concept of EGF family members being important epithelial mitogens. The respiratory failure of the EGF-R (-/-) mice results from impaired branching of the alveolar tree and leads to decreased surface for gas exchange. Overall, the lung phenotype bears similarity to respiratory distress syndrome and bronchopulmonary dysplasia--the most common complications of prematurity in humans. Intestinal changes seen in the EGF-R (-/-) mice vary in severity, the end-point being severe mucosal lesions and necroses. These findings resemble those seen in necrotizing enterocolitis of premature babies, a serious intestinal problem in the neonate. Although deficient EGF-R function is not the reason for these prematurity-associated diseases it may nevertheless exacerbate them. Potential usage of EGF transforming growth factor-alpha in clinical work is discussed.

Topics: Animals; Breast; Bronchopulmonary Dysplasia; Enterocolitis, Pseudomembranous; Epithelium; ErbB Receptors; Female; Humans; Infant, Newborn; Infant, Premature; Infant, Premature, Diseases; Intestines; Kidney; Lung; Male; Mammary Glands, Animal; Mice; Morphogenesis; Pancreas; Phenotype; Prostate; Pulmonary Alveoli; Pulmonary Gas Exchange; Recombination, Genetic; Respiratory Distress Syndrome, Newborn; Respiratory Insufficiency; Skin; Transforming Growth Factor alpha

Bronchopulmonary dysplasia (BPD) is characterized by alveolar simplification with decreased alveolar number and increased airspace. Previous studies suggested that transforming growth factor-α (TGF-α) may contribute to arrested alveolar development in BPD. Histone deacetylases (HDACs) control cellular signaling and gene expression. HDAC2 is crucial for suppression of inflammatory gene expression. Here we investigated whether HDAC2 was involved in the arrest of alveolarization, as well as the ability of HDAC2 to regulate TGF-α expression in a rat model of BPD induced by intra-amniotic injection of lipopolysaccharide (LPS). Results showed that LPS exposure led to a suppression of both HDAC1 and HDAC2 expression and activity, induced TGF-α expression, and disrupted alveolar morphology. Mechanistic studies showed that overexpression of HDAC2, but not HDAC1, suppressed LPS-induced TGF-α expression. Moreover, the HDAC inhibitor TSA or downregulation of HDAC2 by siRNA both significantly increased TGF-α expression in cultured myofibroblasts. Finally, preservation of HDAC activity by theophylline treatment improved alveolar development and attenuated TGF-α release. Together, these findings indicate that attenuation of TGF-α-mediated effects in the lung by enhancing HDAC2 may have a therapeutic effect on treating BPD.

Topics: Animals; Animals, Newborn; Bronchopulmonary Dysplasia; Cell Line; Down-Regulation; Female; Histone Deacetylase 1; Histone Deacetylase 2; Humans; Lipopolysaccharides; Lung; Rats; Transforming Growth Factor alpha; Up-Regulation

Bronchopulmonary dysplasia (BPD) is characterized by alveolar simplification with decreased alveolar number and increased airspace size. Formation of alveoli involves a process known as secondary septation triggered by myofibroblasts. This study investigated the underlying mechanisms of altered lung morphogenesis in a rat model of BPD induced by intra-amniotic injection of lipopolysaccharide (LPS). Results showed that LPS disrupted alveolar morphology and led to abnormal localization of myofibroblasts in the lung of newborn rats, mostly in primary septa with few in secondary septa. To identify potential mechanisms, in vitro experiments were carried out to observe the migration behavior of myofibroblasts. The migration speed of lung myofibroblasts increased with LPS treatment, whereas the directional persistence decreased. We found that LPS induced activation of EGFR and overexpression of its ligand, TGF-α in myofibroblasts. AG1478, an EGFR inhibitor, abrogated the enhanced locomotivity of myofibroblasts by LPS and also increased the directional persistence of myofibroblast migration. Myofibroblasts showed a high asymmetry of phospho-EGFR localization, which was absent after LPS treatment. Application of rhTGF-α to myofibroblasts decreased the directional persistence. Our findings indicated that asymmetry of phospho-EGFR localization in myofibroblasts was important for cell migration and its directional persistence. We speculate that LPS exposure disrupts the asymmetric localization of phospho-EGFR, leading to decreased stability of cell polarity and final abnormal location of myofibroblasts in vivo, which is critical to secondary septation and may contribute to the arrested alveolar development in BPD.

Topics: Animals; Bronchopulmonary Dysplasia; Cell Movement; Cell Polarity; Cells, Cultured; ErbB Receptors; Female; Humans; Infant, Newborn; Lipopolysaccharides; Myofibroblasts; Phosphorylation; Pulmonary Alveoli; Rats; Rats, Sprague-Dawley; Transforming Growth Factor alpha

Preterm infants exposed to oxygen and mechanical ventilation are at risk for bronchopulmonary dysplasia (BPD), a multifactorial chronic lung disorder characterized by arrested alveolar development and nonsprouting, dysmorphic microvascular angiogenesis. The molecular regulation of this BPD-associated pathological angiogenesis remains incompletely understood. In this study, the authors used focused microarray technology to characterize the angiogenic gene expression profile in postmortem lung samples from short-term ventilated preterm infants (born at 24 to 27 weeks' gestation) and age-matched control infants. Microarray analysis identified differential expression of 13 of 112 angiogenesis-related genes. Genes significantly up-regulated in ventilated lungs included the antiangiogenic genes thrombospondin-1, collagen XVIII alpha-1, and tissue inhibitor of metalloproteinase-1 (TIMP1), as well as endoglin, transforming growth factor-alpha, and monocyte chemoattractant protein-1 (CCL2). Increased expression of thrombospondin-1 in ventilated lungs was verified by real-time polymerase chain reaction (PCR) and immunolocalized primarily to intravascular platelets and fibrin aggregates. Down-regulated genes included proangiogenic angiogenin and midkine, as well as vascular endothelial growth factor (VEGF)-B, VEGF receptor-2, and the angiopoietin receptor TEK/Tie-2. In conclusion, short-term ventilated lungs show a shift from traditional angiogenic growth factors to alternative, often antisprouting regulators. This angiogenic shift may be implicated in the regulation of dysmorphic angiogenesis and, consequently, deficient alveolarization characteristic of infants with BPD.

Topics: Antigens, CD; Blood Platelets; Bronchopulmonary Dysplasia; Chemokine CCL2; Chronic Disease; Collagen Type XVIII; Down-Regulation; Endoglin; Female; Fibrin; Gene Expression Profiling; Humans; Infant, Newborn; Infant, Premature; Lung; Male; Neovascularization, Physiologic; Receptor, TIE-2; Receptors, Cell Surface; Respiration, Artificial; Retrospective Studies; Thrombospondin 1; Tissue Inhibitor of Metalloproteinase-1; Transforming Growth Factor alpha; Up-Regulation; Vascular Endothelial Growth Factor B

Transforming growth factor-alpha (TGF-alpha) and its receptor, the epithelial growth factor receptor (EGFR), have been associated with lung remodeling in premature infants with bronchopulmonary dysplasia (BPD). The goal of this study was to target TGF-alpha overexpression to the saccular phase of lung morphogenesis and determine early alterations in gene expression. Conditional lung-specific TGF-alpha bitransgenic mice and single-transgene control mice were generated. TGF-alpha overexpression was induced by doxycycline (Dox) treatment from embryonic day 16.5 (E16.5) to E18.5. After birth, all bitransgenic pups died by postnatal day 7 (P7). Lung histology at E18.5 and P1 showed abnormal lung morphogenesis in bitransgenic mice, characterized by mesenchymal thickening, vascular remodeling, and poor apposition of capillaries to distal air spaces. Surfactant levels (saturated phosphatidylcholine) were not reduced in bitransgenic mice. Microarray analysis was performed after 1 or 2 days of Dox treatment during the saccular (E17.5, E18.5) and alveolar phases (P4, P5) to identify genes induced by EGFR signaling that were shared or unique to each phase. We found 196 genes to be altered (>1.5-fold change; P < 0.01 for at least 2 time points), with only 32% similarly altered in both saccular and alveolar phases. Western blot analysis and immunostaining showed that five genes selected from the microarrays (egr-1, SP-B, SP-D, S100A4, and pleiotrophin) were also increased at the protein level. Pathological changes in TGF-alpha-overexpressing mice bore similarities to premature infants born in the saccular phase who develop BPD, including remodeling of the distal lung septae and arteries.

Topics: Animals; Body Weight; Bronchopulmonary Dysplasia; Cell Differentiation; ErbB Receptors; Gene Expression Profiling; Gene Expression Regulation, Developmental; Humans; Infant, Newborn; Mice; Mice, Transgenic; Microscopy, Electron, Transmission; Myocardium; Oligonucleotide Array Sequence Analysis; Organ Size; Pulmonary Alveoli; Rats; Respiratory Mucosa; Transcription, Genetic; Transforming Growth Factor alpha