Molecular mechanisms of the endothelial barrier protection by PDE4 inhibition and purinoceptor A2A stimulation

Stimulation of endothelial Gs-protein-coupled P1 and P2Y receptors (purinoceptors) by extracellular purines leads to an enhancement of pulmonary endothelial barrier and protection against edemagenic factors Purinoceptor agonists have a potential as therapeutic tools for a number of vascular pathologies, including acute lung injury (ALI) and acute respiratory distress syndrome (ARDS). Pivotal role in the enhancement/protection belongs to the cAMP-dependent activation of PKA and Epac1 followed by endothelial cell (EC) cytoskeleton remodeling. However, the activated PKA may also stimulate cAMP-specific phosphodiesterases (PDEs), providing an efficient down-regulation of the signaling. Our preliminary data show, for the first time, that PDE4 inhibition greatly potentiate an enhancement of the EC barrier function of human pulmonary EC caused by extracellular adenosine (Ado) and A2A receptor agonist. Dramatic increases in amplitude (up to 30%) and duration (about two times) of agonist-mediated barrier enhancement were registered in the EC pretreated with PDE4 inhibitor. Moreover, our data suggest that an inhibition of PDE4 in purine-stimulated EC may critically change cAMP-dependent signaling network and mobilize the mechanisms which may not be involved in the barrier enhancement stimulated by purinoceptor agonists alone. Inhibitors of cAMP-specific PDEs are currently under development for the treatment of asthma and chronic obstructive pulmonary disease. Our proposal is aimed, for the first time, to demonstrate that selective PDE4 inhibitors may be successfully used for acute pulmonary pathologies, such as ALI/ARDS, if combined with purinoceptor agonists. Our project will be focused on the detailed characterization of PDE4 functions in the deterioration of the EC barrier-enhancing signaling mediated by A2A receptor agonists. We will also explore the barrier-protective effect of the PDE4 inhibitors on the agonist-stimulated EC challenged with edemagenic agents and will address its molecular mechanisms. We anticipate an efficient endothelial barrier protection by combined PDE4-inhibitor/A2A-agonist treatment in murine model of ALI. We expect that the results obtained in proposed experiments may help to develop novel therapeutic approaches to cure acute lung disorders. (AHA Program: Scientist Development Grant)