Prior hypoxia prevents downregulation of ACE-2 by hyperoxia in fetal human lung fibroblasts

Abstract

Purpose/Aim of Study The renin angiotensin system is involved in experimentally induced lung fibrosis. Angiotensin (ANG)-II is profibrotic. Angiotensin converting enzyme-2 (ACE-2) cleaves ANG-II and is thus protective. ACE-2 has recently been reported to be significantly decreased under hyperoxic conditions. Hyperoxia is linked to Bronchopulmonary Dysplasia and lung fibrosis. Fetal lung cells normally do not undergo fibrotic changes with physiologic hypoxemia. We hypothesized that hypoxia prior to hyperoxic exposure in fetal lung fibroblasts (IMR-90 cell line) might be protective by preventing ACE-2 down-regulation. Materials and Methods IMR-90 cells were exposed to hypoxia (1%O2/99%N2) followed by hyperoxia (95%O2/5%CO2) or normoxia (21%O2) in vitro. Cells and culture media were recovered separately for assays of ACE-2, TNF-α Converting Enzyme (TACE), αSmooth muscle actin “αSMA” -myofibroblast marker-, N-Cadherin and β-catenin immunoreactive protein. Results ACE-2 significantly increased when IMR-90 were hypoxic prior to hyperoxic exposure with no recovery. In contrast to hyperoxia alone, ACE-2 did not decrease when IMR-90 were hypoxic prior to hyperoxic exposure with recovery. TACE/ADAM17 protein and mRNA were significantly increased in cells allowed to recover in 21% O2. αSMA N-Cadherin and β-Catenin proteins were significantly decreased in both groups. Conclusions Hypoxia prior to hyperoxic exposure of fetal lung fibroblasts prevented ACE-2 downregulation and decreased ADAM17/TACE protein and mRNA. αSMA, N-Cadherin and β-catenin were also significantly decreased under these conditions.

Degradation of Lung Protective Angiotensin Converting Enzyme-2 by Meconium in Human Alveolar Epithelial Cells: A Potential Pathogenic Mechanism in Meconium Aspiration Syndrome

“…Our study is limited by small sample size, and the fact that it used adult human lung AECs. However, our laboratory has demonstrated the presence of ACE-2 in neonatal mouse lung as well as in fetal lung fibroblasts [36,37]. Therefore, it is plausible that a similar effect of meconium on fetal and neonatal lungs would be observed.…”

“…Also, we have not examined the direct effect of downregulation of ACE-2 and meconium-induced apoptosis in this study. Nevertheless, our laboratory has previously shown that ACE-2 downregulation leads to apoptosis of human A549 cells, MLE12 cells and fetal fibroblast IMR 90 cells in response to various noxious stimuli, e.g., bleomycin [18], hyperoxia [36] and hypoxia [37]. Therefore, it is safe to assume that meconium-induced human A549 cells apoptosis is due to downregulation of ACE-2.…”

The renin angiotensin system in liver and lung: impact and therapeutic potential in organ fibrosis

“…Similar to liver disease, ACE-2 has been shown to play an established protective role in lung disease through effects mediated by Mas oncogene, the ACE-2 peptide product ANG1-7 receptor. 54,73─75 Previous studies from our lab and other groups suggest that ACE-2 is down-regulated in fibrotic conditions of the adult and neonatal human lung 54,73,74 via Mas receptor mechanisms. 70 Data from our lab was first to discover the significant decrease of ACE-2 in the human IPF lung and identify the protective effects of ACE-2 in the IPF disease.…”

“…27 Supplemental oxygen, which is frequently used in the treatment of pulmonary insufficiency in premature infants, has been implicated in the development of BPD. 73,74 In adult animal models of acute lung injury, 79,80 ACE-2 was shown to inhibit lung edema formation and inflammation as well as fibrogenesis. However, little is known about the role of ACE-2 in neonatal models of BPD.…”

“…Our research group showed that ACE-2 is expressed in fetal human lung fibroblasts but is significantly decreased by hyperoxic gas lung injury, 74 an effect reversed when hyperoxia preceded by hypoxia. 73 Furthermore, Wagenaar et al 75 showed that Mas receptor agonists reduce inflammation of the oxygen-induced lung injury in rats. 75 Chorioamnionitis and mechanical ventilation are also associated with bronchopulmonary dysplasia (BPD) in preterm infants.…”