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Published on: October 19, 2013
Hyperoxia and apoptosis in developing mouse lung mesenchyme
Heather I Dieperink1, Timothy S Blackwell, Lawrence S Prince
1Department of Pediatrics, University of Alabama at Birmingham, 35294, USA.
Insights
High oxygen exposure (hyperoxia) harms premature infant lung development by inhibiting airway branching and causing cell death in lung tissue. This study shows hyperoxia directly induces apoptosis in fetal mouse lung mesenchyme, impacting airway formation.
Area of Science:
- Developmental Biology
- Neonatal Physiology
- Pulmonary Medicine
Background:
- Bronchopulmonary dysplasia (BPD) is a significant complication in premature infants, often linked to hyperoxia exposure.
- Lung development, including distal airway branching and alveolar septation, continues postnatally in premature infants, making them vulnerable to environmental insults.
- Hyperoxia, or excessive oxygen, is a known risk factor for BPD, but its direct impact on fetal lung development mechanisms is not fully understood.
Purpose of the Study:
- To investigate the direct effects of hyperoxia on distal airway branching in developing fetal mouse lungs.
- To determine if hyperoxia induces apoptosis in the fetal lung mesenchyme.
- To explore the role of NF-kappaB signaling in hyperoxia-induced lung injury.
Main Methods:
- Culturing E16 fetal mouse lung explants in normoxia (20% O2) and hyperoxia (95% O2).
- Assessing distal airway branching using microscopy.
- Quantifying apoptosis via caspase 3/7 activity assays, caspase 3 expression, and annexin V binding.
- Analyzing NF-kappaB activation (p65 localization) and its role in caspase 3 activation.
Main Results:
- Hyperoxia significantly reduced the number and complexity of distal airways in cultured lung explants.
- Increased apoptosis was observed in mesenchymal cells of hyperoxic explants, confirmed by elevated caspase 3/7 activity and annexin V binding.
- NF-kappaB activation was detected in hyperoxic explants, and its inhibition protected against hyperoxia-induced caspase 3 activation.
Conclusions:
- Hyperoxia directly inhibits distal airway branching in the developing fetal mouse lung.
- Hyperoxia induces apoptosis in fetal lung mesenchymal cells, contributing to impaired lung development.
- NF-kappaB activation plays a role in mediating hyperoxia-induced apoptosis in the fetal lung mesenchyme.
Abstract:
Hyperoxia contributes to the development of bronchopulmonary dysplasia in former premature infants. Injurious environmental factors such as hyperoxia may disrupt distal airway branching and alveolar septation, as these critical stages in lung development occur following birth in extremely premature infants. To test if hyperoxia directly inhibited distal airway branching, we cultured E16 fetal mouse lung explants in either 20% (control) or 95% oxygen (hyperoxia). Hyperoxia reduced the number of distal airways to less than 50% of controls. Explants cultured in 95% oxygen also had fewer complex distal airways compared with controls. Mesenchymal cells adjacent to distal airways in hyperoxic explants appeared apoptotic by phase microscopy. Consistent with increased apoptosis, explants cultured in hyperoxia had increased caspase 3/7 activity compared with controls. Hyperoxia also increased mesenchymal caspase 3 expression and annexin V binding within cultured explants as visualized by fluorescence microscopy. We measured increased annexin V binding in isolated primary fetal lung mesenchymal cells cultured in 95% oxygen suggesting a direct effect on cells within the mesenchyme. Hyperoxia can lead to NF-kappaB activation, which mediates inflammatory cascades and may protect cells from apoptosis. We detected NF-kappaB activation and nuclear p65 localization in explants exposed to 48 h of hyperoxia. Inhibition of NF-kappaB prevented the hyperoxia-induced activation of caspase 3. NF-kappaB activation may therefore contribute to apoptosis in the developing fetal mouse lung following hyperoxia exposure. Our data suggest hyperoxia inhibits distal airway branching and directly induces apoptosis of the fetal mouse lung mesenchyme.