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 downregulation. 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 decreased under these conditions. αSMA N-cadherin, and β-catenin proteins were significantly decreased with or without normoxic recovery. 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.

KEYWORDS:

• bronchopulmonary dysplasia
• chronic lung disease
• fetal lung fibroblasts
• hyperoxia
• hypoxia

Acknowledgments

Portions of the work conducted by H.N. were conducted in partial fulfillment of the requirements for the degree Doctor of Philosophy from Michigan State University.

Declaration of interest

The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper. This manuscript has not been published elsewhere and it has not been submitted simultaneously for publication elsewhere.

Funding

This work was supported by American Academy of Pediatrics Marshal Klaus award to T.M., NHLBI grant to B.D.U. (HL-45136), and by a grant from the Sparrow Hospital Fellowship Research Fund to T.M.