Cross talk between NADPH oxidase and autophagy in pulmonary artery endothelial cells with intrauterine persistent pulmonary hypertension

Div. of Neonatology, Dept. of Pediatrics, Medical College of Wisconsin, Wauwatosa, WI 53226, USA.
AJP Lung Cellular and Molecular Physiology (Impact Factor: 4.08). 01/2012; 302(7):L651-63. DOI: 10.1152/ajplung.00177.2011
Source: PubMed


Autophagy is a process for cells to degrade proteins or entire organelles to maintain a balance in the synthesis, degradation, and subsequent recycling of cellular products. Increased reactive oxygen species formation is known to induce autophagy. We previously reported that increased NADPH oxidase (NOX) activity in pulmonary artery endothelial cells (PAEC) from fetal lambs with persistent pulmonary hypertension (PPHN) contributes to impaired angiogenesis in PPHN-PAEC compared with normal PAEC. We hypothesized that increased NOX activity in PPHN-PAEC is associated with increased autophagy, which, in turn, contributes to impaired angiogenesis in PPHN-PAEC. In the present study, we detected increased autophagy in PPHN-PAEC as shown by increased ratio of the microtubule-associated protein 1 light chain (LC3)-II to LC3-I and increased percentage of green fluorescent protein-LC3 punctate positive cells. Inhibiting autophagy by 3-methyladenine, chloroquine, and beclin-1 knockdown in PPHN-PAEC has led to decreased autophagy and increased in vitro angiogenesis. Inhibition of autophagy also decreased the association between gp91(phox) and p47(phox), NOX activity, and superoxide generation. A nonspecific antioxidant N-acetylcysteine and a NOX inhibitor apocynin decreased autophagy in PPHN-PAEC. In conclusion, autophagy may contribute to impaired angiogenesis in PPHN-PAEC through increasing NOX activity. Our results suggest that, in PPHN-PAEC, a positive feedback relationship between autophagy and NOX activity may regulate angiogenesis.

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    • "In this study, we sought to characterize the effect of chloroquine on BMPR-II levels in the endothelium. Recent research using PAECs from a persistent pulmonary hypertension model in fetal lambs described impaired angiogenesis which could be rescued by chloroquine inhibition of autophagy (38). However, as yet there is no literature describing the regulation of BMPR-II by chloroquine in endothelial cells. "
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    • "Excessive oxidative stress, on the other hand, promotes cell apoptosis by activating the death-related pathway, known as type II programmed cell death (PCD). In persistent pulmonary hypertension (PPHN), autophagy of the pulmonary artery endothelial cells (PAECs) is proapoptotic and forms a positive feedback loop with Nox-derived ROS [76]. "
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    ABSTRACT: Pulmonary artery endothelial cells (PAEC) isolated from fetal lambs with in utero pulmonary hypertension (IPH) have phenotypical changes that lead to increased reactive oxygen species (ROS) formation and impaired angiogenesis. AMP-activated protein kinase (AMPK) is known to be activated by ROS, which is expected to help angiogenesis in IPH-PAEC. The objectives of this study were to investigate AMPK responses in IPH and its role in angiogenesis. We observed that when compared to control PAEC, IPH-PAEC have decreased phosphorylation of AMPKα catalytic subunit and AMPK downstream enzymes, indicating a decrease in AMPK activity. In addition, the expression of AMPK kinases is decreased and protein phosphatase 2 is increased in IPH-PAEC, potentially contributing to the decreased AMPK activation. Metformin, an AMPK activator, improved IPH-PAEC angiogenesis, while increasing endothelial NO synthase (eNOS) serine(1179) phosphorylation and decreasing the eNOS-caveolin-1 association. Metformin also increased MnSOD activity and the expression of both eNOS and MnSOD. The increase in angiogenesis by Metformin is abolished by pretreatment with AMPK inhibitor, Compound C. Expression of vascular endothelial growth factor (VEGF) and platelet-derived growth factor β (PDGFβ) are decreased in IPH-PAEC compared to control PAEC and were not altered by Metformin. These data indicate that Metformin improves angiogenesis through mechanisms independent of these angiogenic factors. In conclusion, activation of AMPK restores angiogenesis and increases the bio-availability of NO in IPH. Whether Metformin is beneficial in the management of pulmonary hypertension requires further investigation.
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