American journal of physiology. Lung cellular and molecular physiology
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Am. J. Physiol. Lung Cell Mol. Physiol. · Jan 2012
Altered expression of tight junction molecules in alveolar septa in lung injury and fibrosis.
The dysfunction of alveolar barriers is a critical factor in the development of lung injury and subsequent fibrosis, but the underlying molecular mechanisms remain poorly understood. To clarify the pathogenic roles of tight junctions in lung injury and fibrosis, we examined the altered expression of claudins, the major components of tight junctions, in the lungs of disease models with pulmonary fibrosis. Among the 24 known claudins, claudin-1, claudin-3, claudin-4, claudin-7, and claudin-10 were identified as components of airway tight junctions. ⋯ In addition, we analyzed the influence of transforming growth factor-β (TGF-β), a critical mediator of pulmonary fibrosis that is upregulated after bleomycin-induced lung injury, on tight junctions in vitro. The addition of TGF-β decreased the expression of claudin-5 in human umbilical vein endothelial cells and disrupted the tight junctions of epithelial cells (A549). These results suggest that bleomycin-induced lung injury causes pathogenic alterations in tight junctions and that such alterations seem to be induced by TGF-β.
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Am. J. Physiol. Lung Cell Mol. Physiol. · Jan 2012
Dopamine inhibits pulmonary edema through the VEGF-VEGFR2 axis in a murine model of acute lung injury.
The neurotransmitter dopamine and its dopamine receptor D2 (D2DR) agonists are known to inhibit vascular permeability factor/vascular endothelial growth factor (VEGF)-mediated angiogenesis and vascular permeability. Lung injury is a clinical syndrome associated with increased microvascular permeability. However, the effects of dopamine on pulmonary edema, a phenomenon critical to the pathophysiology of both acute and chronic lung injuries, have yet to be established. ⋯ We used D2DR knockout mice to confirm that dopamine acts through D2DR to block vascular permeability in our lung injury model. As expected, a D2DR agonist failed to reduce pulmonary edema in D2DR(-/-) mice. Taken together, our results suggest that dopamine acts through D2DR to inhibit pulmonary edema-associated vascular permeability, which is mediated through VEGF-VEGFR2 signaling and conveys protective effects in an ALI model.
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Am. J. Physiol. Lung Cell Mol. Physiol. · Jan 2012
Comparative StudyNF-κB activation and polyubiquitin conjugation are required for pulmonary inflammation-induced diaphragm atrophy.
Loss of diaphragm muscle strength in inflammatory lung disease contributes to mortality and is associated with diaphragm fiber atrophy. Ubiquitin (Ub) 26S-proteasome system (UPS)-dependent protein breakdown, which mediates muscle atrophy in a number of physiological and pathological conditions, is elevated in diaphragm muscle of patients with chronic obstructive pulmonary disease. Nuclear factor kappa B (NF-κB), an essential regulator of many inflammatory processes, has been implicated in the regulation of poly-Ub conjugation of muscle proteins targeted for proteolysis by the UPS. ⋯ Poly-Ub conjugation was increased in diaphragm, as was the expression of muscle-specific E3 Ub ligases. Genetic suppression of poly-Ub conjugation prevented inflammation-induced diaphragm muscle atrophy, as did muscle-specific inhibition of NF-κB signaling. In conclusion, the present study is the first to demonstrate that diaphragm muscle atrophy, resulting from acute pulmonary inflammation, requires NF-κB activation and UPS-mediated protein degradation.
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Am. J. Physiol. Lung Cell Mol. Physiol. · Jan 2012
Regulation and function of the two-pore-domain (K2P) potassium channel Trek-1 in alveolar epithelial cells.
Hyperoxia can lead to a myriad of deleterious effects in the lung including epithelial damage and diffuse inflammation. The specific mechanisms by which hyperoxia promotes these pathological changes are not completely understood. Activation of ion channels has been proposed as one of the mechanisms required for cell activation and mediator secretion. ⋯ Release of KC/IL-8 was not affected by Trek-1 deficiency. Overall, deficiency of Trek-1 had a more pronounced effect on mediator secretion than exposure to hyperoxia. This is the first report suggesting that the K(+) channel Trek-1 could be involved in regulation of alveolar epithelial cell proliferation and cytokine secretion, but a direct association with hyperoxia-induced changes in Trek-1 levels remains elusive.
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Am. J. Physiol. Lung Cell Mol. Physiol. · Jan 2012
Excess soluble vascular endothelial growth factor receptor-1 in amniotic fluid impairs lung growth in rats: linking preeclampsia with bronchopulmonary dysplasia.
Epidemiological studies have shown that maternal preeclampsia (PE) increases the risk of bronchopulmonary dysplasia (BPD), but the underlying mechanism is unknown. Soluble vascular endothelial growth factor receptor-1 (soluble VEGFR1, known as soluble fms-like tyrosine kinase 1, or sFlt-1), an endogenous antagonist of vascular endothelial growth factor (VEGF), is markedly elevated in amniotic fluid and maternal blood in PE. Therefore, we hypothesized that antenatal exposure to excess sFlt-1 disrupts lung development through impaired VEGF signaling in utero, providing a mechanistic link between PE and BPD. ⋯ In addition, intra-amniotic sFlt-1 treatment suppressed activation of lung VEGF receptor-2 and increased apoptosis in endothelial and mesenchymal cells in the newborn lung. We conclude that exposure to excess sFlt-1 in amniotic fluid during late gestation causes sustained reductions in alveolarization and pulmonary vascular growth during infancy, accompanied by biventricular hypertrophy suggesting pulmonary and systemic hypertension. We speculate that impaired VEGF signaling in utero due to exposure of high amniotic fluid levels of sFlt-1 in PE disrupts lung growth and contributes to the increased risk of BPD in infants born to mothers with PE.