Hyperoxia downregulates angiotensin-converting enzyme-2 in human fetal lung fibroblasts

Abstract

BACKGROUND Angiotensin (ANG) II is involved in experimental hyperoxia-induced lung fibrosis. Angiotensin-converting enzyme-2 (ACE-2) degrades ANG II and is thus protective, but is downregulated in adult human and experimental lung fibrosis. Hyperoxia is a known cause of chronic fibrotic lung disease in neonates, but the role of ACE-2 in neonatal lung fibrosis is unknown. We hypothesized that ACE-2 in human fetal lung cells might be downregulated by hyperoxic gas. METHODS Fetal human lung fibroblast IMR90 cells were exposed to hyperoxic (95% O2/5% CO2) or normoxic (21% O2/5% CO2) gas in vitro. Cells and culture media were recovered separately for assays of ACE-2 enzymatic activity, mRNA, and immunoreactive protein. RESULTS Hyperoxia decreased ACE-2 immunoreactive protein and enzyme activity in IMR90 cells (both P < 0.01), but did not change ACE-2 mRNA. ACE-2 protein was increased in the cell supernatant, suggesting protease-mediated ectodomain shedding. TAPI-2, an inhibitor of TNF-α–converting enzyme (TACE/ADAM17), prevented both the decrease in cellular ACE-2 and the increase in soluble ACE-2 (both P < 0.05). CONCLUSION These data show that ACE-2 is expressed in fetal human lung fibroblasts but is significantly decreased by hyperoxic gas. They also suggest that hyperoxia decreases ACE-2 through a shedding mechanism mediated by ADAM17/TACE.

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

“…If a 24h period of normoxic recovery follows the hyperoxic exposure, ACE-2 immunoreactive protein is unchanged relative to unexposed cells; this further clarifies the work of Oarhe et al (16) which showed a reduction of ACE-2 following hyperoxic exposure alone.…”

“…By densitometry (Panel B), the decrease was statistically significant (p<0.05) In Panel C, TACE/ADAM17 mRNA was also reduced by when exposure to hypoxia preceded exposure to hyperoxia, in contrast to the increase in TACE mRNA caused by hyperoxic gas alone (16). …”

“…Recent data from our lab (16) showed that ACE-2 is expressed but down-regulated in IMR-90 cells exposed to hyperoxia followed by normoxic recovery. Normally, in spite of hypoxemia in-utero, fetal lung cells do not undergo fibrotic changes and/or develop changes of chronic lung disease.…”

“…Oarhe et al (16) recently reported that hyperoxia followed by normoxic recovery worsens plasma membrane integrity compared to controls. With hypoxia preceding hyperoxic exposure, we noted a significant decrease in mean number of dead cells in the treated group followed by normoxic recovery, when compared to corresponding controls (in 21% the whole time).…”

“…In previous work from this laboratory, Oarhe et al (16) recently showed that ACE-2 is expressed in fetal human lung fibroblasts and is significantly down-regulated by exposure to hyperoxic gas followed by normoxic recovery through a shedding mechanism mediated by Tumor Necrosis Factor-Alpha Converting Enzyme (ADAM17/TACE). We therefore hypothesized that hypoxia prior to hyperoxia in fetal lung fibroblasts may be protective (prevent ACE-2 from decreasing), simulating the physiologic fetal hypoxemia prior to be exposed to the normoxia/relative hyperoxia after birth.…”