Is the Cx43-specific inhibitor 43Gap26 a relevant therapeutic target in BPD and BPD-PH induced by hyperoxia?

Introduction

Premature newborns exposed to oxygen are at risk for bronchopulmonary dysplasia (BPD), characterized by lung growth arrest and inflammation. Connexin 43-gap junction (Cx43-GJ) plays a central role in lung development and macrophages-induced inflammation, and is increased by hyperoxia. We thus explored the role of CX43-GJ in experimental BPD.

Methods

We used neonatal rats exposed to normoxia or hyperoxia (90% O₂) and daily treated or not with a specific Cx43 inhibitor (43Gap26) during 14 days. Some experiments were also performed in human fetal pulmonary artery smooth muscle cells (HfPA-SMC) exposed to normoxia or hyperoxia (60% O₂) and treated or not with 43Gap26 for 2 days.

Results

In vivo, we showed that 43Gap26 decreased hyperoxia-induced increased Cx43 expression in lung and improved hypo-alveolarization. However, 43Gap26 did not prevent 1) the hyperoxia-induced alteration of lung function (plethysmographie), 2) the decreased SP-B expression, 3) the disruption of extracellular matrix components (fibronectin and collagen I/III), 4) the increased macrophagic infiltration and M2 polarization, and 5) the increased secretion of pro-inflammatory cytokines (Tissue Inhibitor of Metalloproteinases-1). Furthermore, 43Gap26 blocked the hyperoxia-induced proliferation of type II alveolar epithelial cells, and did not prevent BPD-associated pulmonary hypertension (PH-BPD) or the increased mortality. In vitro, on HfPA-SMC, we confirmed that although an increased Cx43 expression was induced by hyperoxia, 43Gap26 had no effect on the hyperoxia-induced increase of pro-inflammatory cytokines such as IL-6 and Macrophage Inhibitory Factor (MIF). Finally, although we did not demonstrate an increase in oxidative stress in our 2 models, 43Gap26 decreased the hyperoxia-induced increase in heme oxygenase-1 expression in pulmonary arteries.

Conclusion

Despite an improved alveolarization in an animal model of hyperoxia-induced BPD, specific inhibition of Cx43 does not appear to be a new potential therapeutic strategy in BPD and PH-BPD as it did not prevent mortality as well as the main hallmarks of BPD and PH-BPD (altered lung function, pulmonary vascular growth arrest and remodeling, inflammation).