Prostacyclin signaling boosts NADPH oxidase 4 in the endothelium promoting cytoprotection and angiogenesis

Aims: Prostacyclin (PGI₂) that is released from the vascular endothelium plays an important role in vasodilatation and thrombo-resistance, and it has long been suspected to protect cell survival. How it does so has never been clear. Recently, it has been shown that the NADPH oxidase 4 (Nox4) improves endothelial cell functions and promotes angiogenesis in vivo, but it was not known how to boost Nox4 therapeutically to exploit its protective functions in the vasculature. Here, we identified such a stimulus.

Results: The selective and stable prostacyclin receptor (IP-R) agonist cicaprost increases the expression of Nox4 in human endothelial cells of several types, including endothelial progenitor cells. The elevation of cellular cyclic-AMP increased Nox4 expression and H₂O₂ production and prevented endothelial cell apoptosis. We delineate the intracellular signaling that promotes cytoprotection: Cicaprost acts via the IP-R/protein kinase A (PKA)/cyclic adenosine monophosphate (cAMP) response element binding (CREB) protein pathway. Importantly, the up-regulation of Nox4 by cicaprost also enhanced endothelial cell proliferation, migration, and angiogenesis, with all effects being substantially decreased by Nox4 gene silencing. Finally, cicaprost enhanced the growth of blood vessels into subcutaneous sponges implanted in mice, an effect that was also blocked by Nox4 gene silencing.

Innovation: The prostacyclin analogue cicaprost induces Nox4 via IP receptor-cAMP/PKA/CREB pathway. The activation of this pathway protects endothelial cells and enhances pro-angiogenic activity both in vitro and in vivo.

Conclusion: Prostacyclin promotes the up-regulation of Nox4 in endothelial cells, which opens up a novel strategy that protects and enhances endothelial cell functions in cardiovascular disease, such as repair after myocardial infarction or other ischemic conditions.