Hyperoxia causes angiopoietin 2-mediated acute lung injury and necrotic cell death

Prevention of LPS-induced acute lung injury in mice by mesenchymal stem cells overexpressing angiopoietin 1

BACKGROUND

The acute respiratory distress syndrome (ARDS), a clinical complication of severe acute lung injury (ALI) in humans, is a leading cause of morbidity and mortality in critically ill patients. ALI is characterized by disruption of the lung alveolar-capillary membrane barrier and resultant pulmonary edema associated with a proteinaceous alveolar exudate. Current specific treatment strategies for ALI/ARDS are lacking. We hypothesized that mesenchymal stem cells (MSCs), with or without transfection with the vasculoprotective gene angiopoietin 1 (ANGPT1) would have beneficial effects in experimental ALI in mice.

METHODS AND FINDINGS

Syngeneic MSCs with or without transfection with plasmid containing the human ANGPT1 gene (pANGPT1) were delivered through the right jugular vein of mice 30 min after intratracheal instillation of lipopolysaccharide (LPS) to induce lung injury. Administration of MSCs significantly reduced LPS-induced pulmonary inflammation, as reflected by reductions in total cell and neutrophil counts in bronchoalveolar lavage (BAL) fluid (53%, 95% confidence interval [CI] 7%-101%; and 60%, CI 4%-116%, respectively) as well as reducing levels of proinflammatory cytokines in both BAL fluid and lung parenchymal homogenates. Furthermore, administration of MSCs transfected with pANGPT1 resulted in nearly complete reversal of LPS-induced increases in lung permeability as assessed by reductions in IgM and albumin levels in BAL (96%, CI 6%-185%; and 74%, CI 23%-126%, respectively). Fluorescently tagged MSCs were detected in the lung tissues by confocal microscopy and flow cytometry in both naïve and LPS-injured animals up to 3 d.

CONCLUSIONS

Treatment with MSCs alone significantly reduced LPS-induced acute pulmonary inflammation in mice, while administration of pANGPT1-transfected MSCs resulted in a further improvement in both alveolar inflammation and permeability. These results suggest a potential role for cell-based ANGPT1 gene therapy to treat clinical ALI/ARDS.

Interfering with disease: a progress report on siRNA-based therapeutics

RNA interference (RNAi) has rapidly advanced since its initial discovery to form the basis of a new class of therapeutics. De Fougerolles and colleagues discuss the challenges in the development of RNAi-based therapeutics, focusing on lead identification/optimization and effective delivery, and review the latest clinical results.

RNA interference (RNAi) quietly crept into biological research in the 1990s when unexpected gene-silencing phenomena in plants and flatworms first perplexed scientists. Following the demonstration of RNAi in mammalian cells in 2001, it was quickly realized that this highly specific mechanism of sequence-specific gene silencing might be harnessed to develop a new class of drugs that interfere with disease-causing or disease-promoting genes. Here we discuss the considerations that go into developing RNAi-based therapeutics starting from in vitro lead design and identification, to in vivo pre-clinical drug delivery and testing. We conclude by reviewing the latest clinical experience with RNAi therapeutics.

Angiopoietin-1 Requires p190 RhoGAP to Protect against Vascular Leakage in Vivo

Angiopoietin-1 (Ang-1), a ligand of the endothelium-specific receptor Tie-2, inhibits permeability in the mature vasculature, but the mechanism remains unknown. Here we show that Ang-1 signals Rho family GTPases to organize the cytoskeleton into a junction-fortifying arrangement that enhances the permeability barrier function of the endothelium. Ang-1 phosphorylates Tie-2 and its downstream effector phosphatidylinositol 3-kinase. This induces activation of one endogenous GTPase, Rac1, and inhibition of another, RhoA. Loss of either part of this dual effect abrogates the cytoskeletal and anti-permeability actions of Ang-1, suggesting that coordinated GTPase regulation is necessary for the vessel-sealing effects of Ang-1. p190 RhoGAP, a GTPase regulatory protein, provides this coordinating function as it is phosphorylated by Ang-1 treatment, requires Rac1 activation, and is necessary for RhoA inhibition. Ang-1 prevents the cytoskeletal and pro-permeability effects of endotoxin but requires p190 RhoGAP to do so. Treatment with p190 RhoGAP small interfering RNA completely abolishes the ability of Ang-1 to rescue endotoxemia-induced pulmonary vascular leak and inflammation in mice. We conclude that Ang-1 prevents vascular permeability by regulating the endothelial cytoskeleton through coordinated and opposite effects on the Rho GTPases Rac1 and RhoA. By linking Rac1 activation and RhoA inhibition, p190 RhoGAP is critical to the protective effects of Ang-1 against endotoxin. These results provide mechanistic evidence that targeting the endothelium through Tie-2 may offer specific therapeutic strategies in life-threatening endotoxemic conditions such as sepsis and acute respiratory distress syndrome.

Roles of angiopoietin-1 and angiopoietin-2 on airway microvascular permeability in asthmatic patients

BACKGROUND

Vascular endothelial growth factor (VEGF) increases microvascular permeability. Recently, considerable attention has been devoted to the physiologic roles of angiopoietin-1 and angiopoietin-2 as regulatory factors of VEGF. This study was designed to examine the roles of angiopoietin-1 and angiopoietin-2 in controlling airway microvascular permeability in asthma.

METHODS

Levels of these angiogenic factors and airway vascular permeability index were examined in 30 asthmatics and 12 control subjects. After 2-week run-in period, all asthmatics were randomly assigned to receive fluticasone propionate (400 mug/d) or montelukast (10 mg) for 12 weeks.

RESULTS

VEGF, angiopoietin-1, and angiopoietin-2 levels in induced sputum were significantly higher in asthmatics than in control subjects. We found an inverse correlation between angiopoietin-1 level and vascular permeability index in asthmatics, while there was a positive correlation between angiopoietin-2 level and that index. VEGF and angiopoietin-1 levels were significantly decreased after fluticasone therapy, while VEGF and angiopoietin-2 levels were significantly decreased after montelukast therapy. Although VEGF levels after treatment were different between two groups, vascular permeability index in the montelukast group was the same level as that in the fluticasone group. Moreover, improvement in vascular permeability index after fluticasone therapy was inversely correlated with decrease in angiopoietin-1 level, while that after montelukast therapy was positively correlated with decrease in angiopoietin-2 level.

CONCLUSIONS

Angiopoietin-1 and angiopoietin-2 play complementary and coordinated roles in regulating microvascular permeability stimulated by VEGF in asthma. Combination of corticosteroids with leukotriene antagonists might effectively improve plasma leakage and provide a new strategy in treating bronchial asthma.

Developmental differences in the responses of IL-6 and IL-13 transgenic mice exposed to hyperoxia

Our previous work has shown that adult mice with overexpression of IL-6 and IL-13 in the lung have enhanced survival in hyperoxia associated with reduced hyperoxia-induced lung injury and cell death. We hypothesized that there are developmental differences in these responses in the adult vs. the newborn (NB) animal, and these responses have clinical relevance in the human NB. We compared the responses to 100% O(2) of NB IL-6 and IL-13 transgenic mice with wild-type littermate controls by evaluating mortality, lung tissue TUNEL staining, and mRNA expression using RT-PCR. We used ELISA to measure IL-6 levels in tracheal aspirates from human neonates. Our results show that, in contrast to the cytoprotective effects in mature mice, IL-6 caused significantly increased mortality, DNA injury, caspases, cell death regulator and angiogenic factor expression in hyperoxia in the NB. Furthermore, tracheal aspirate levels of IL-6 were significantly increased in premature neonates with respiratory distress syndrome who had an adverse outcome (bronchopulmonary dysplasia/death). In contrast to the protective effects in adults, there was no survival advantage to the NB IL-13 mice in hyperoxia. These findings imply that caution should be exercised in extrapolating results from the adult to the NB.

Angiogenesis in lung development, injury and repair: implications for chronic lung disease of prematurity

Since the initial description of bronchopulmonary dysplasia (BPD) 40 years ago, advances in perinatal care have allowed the survival of infants that are more immature. The disease has not disappeared, but it now affects infants with undeveloped distal airspaces, resulting in an arrest of alveolar development. The histological changes that occur during normal lung development are well described, but little is known about the signaling mechanisms that regulate saccular and alveolar development. Understanding how alveoli and the underlying capillary network develop and how these mechanisms are disrupted in preterm infants with BPD is critical to develop efficient and effective therapies for lung diseases characterized by alveolar damage. This brief review focuses on the recently recognized role of angiogenic growth factors during normal alveolar development, injury and repair with a particular emphasis on the vascular endothelial growth factor.