Extracellular adenosine enhances pulmonary artery vasa vasorum endothelium cell barrier function via the Gi/ELMO1/Rac1/PKA-dependent signaling mechanisms.

: The vasa vasorum (VV), the microvascular network around large vessels, has been recognized as an important contributor to the pathological vascular remodeling in cardiovascular diseases. In animal models of pulmonary hypertension, we previously shown that chronic hypoxia profoundly increased pulmonary artery (PA) VV permeability, associated with infiltration of inflammatory and progenitor cells in the arterial wall, perivascular inflammation, and structural vascular remodeling. Extracellular adenosine was shown to exhibit a barrier-protective effect on VV endothelial cells (VVEC) via cAMP-independent mechanism, which involved adenosine A1 receptor-mediated activation of Gi-PI3K-Akt pathway and actin cytoskeleton remodeling. In this study we investigated in more detail the mechanisms linking Gi activation to downstream barrier protection pathways. Using a small interference RNA (siRNA) technique and Transendothelial Electrical Resistance (TER) assay, we found that the adaptor protein, ELMO1, the tyrosine phosphatase Shp2, and atypical Gi- and Rac-mediated PKA activation are implicated in VVEC barrier enhancement. In contrast, the actin-interacting GTP-binding protein, girdin and the PAK1 downstream target, LIM kinase, are not involved in this response. In addition, adenosine-dependent cytoskeletal rearrangement involves activation of cofilin and inactivation of ERM regulatory cytoskeletal proteins, consistent with a barrier-protective mechanism. Collectively, our data indicate that targeting adenosine receptors and downstream barrier protective pathways in VVEC may represent novel pharmacologic approach for hypoxia-induced VV hyper permeability in PH and possibly other cardiovascular diseases associated with impaired vascular barrier function.