Title: Mechanisms of lung endothelial barrier protection in acute lung injury: role of extracellular purines

Abstract:

The endothelial cells (EC) lining the vessels are in close contact with each other forming a tight barrier. Any breach in the EC barrier is a cardinal feature of acute lung injury (ALI) and its more severe form, Acute Respiratory Distress Syndrome (ARDS), and results in pulmonary edema, and impaired gas exchange and may cause respiratory failure. Despite the obvious importance of the EC barrier, a paucity of information exists concerning the mechanisms involved in the preservation of barrier integrity. We have demonstrated that extracellular purines, ATP (stable analog, ATPγS) and adenosine can preserve EC barrier integrity in vitro and reduce ALI in mice. However, while in both cases EC barrier-protective mechanisms involved cytoskeletal reorganization culminating in an increase in cortical F-actin, the upstream signaling events for extracellular purines differ significantly and include activation of P1 A2 receptors coupled to Gs for adenosine and P2Y receptors coupled to Gi for ATP. Further, we demonstrated that adenosine-induced EC barrier enhancement involves activations of cAMP-dependent protein kinase A (PKA) and myosin light chain (MLC) phosphatase (MLCP), followed by decrease in MLC phosphorylation, thus reducing EC contractility. In parallel, adenosine strengthens EC barrier through activation of small GTPase, Rac1. Unlike adenosine, ATP-mediated EC barrier-enhancement involves unconventional Gi-mediated cAMP-independent PKA, MLCP and Rac1 activations, which may be coordinated through the actions of adapter protein GAB1, Shp2 (a non-receptor Tyr phosphatase), and AKAP2 (PKA anchoring protein 2)-mediated signaling. AKAP2 was found in immune complexes with PKA and Gi and directly interacts with MLCP suggesting that the AKAP2/MLCP axis is a novel regulator of P2Y/Gi-mediated EC barrier enhancement. Further, our data demonstrate the involvement of a regulatory molecule ELMO1 (Engulfment and cell motility protein 1) in P2Y/Gi-mediated EC barrier strengthening, which together with the adapter protein Dock180 formed a bipartite GEF (Guanine nucleotide exchange factor) for Rac1, suggesting the involvement of ELMO1/Dock180 axis in Gi-mediated Rac1 activation. Collectively, our data suggested that while adenosine-induced EC barrier enhancement involves activation of Gs/cAMP-mediated signaling, ATPγS-induced P2Y-mediated EC barrier strengthening requires Gi-mediated, coordinated activation of GAB1/Shp2 and Dock180/ELMO1 leading to activation of PKA and Rac1 pathways, respectively.

Biography:

Verin completed his Ph.D. at the age of 29 years from Moscow State University, Moscow, USSR, and postdoctoral studies at the University of Indiana. During his scientific carrier, he was a faculty member at Johns Hopkins and the University of Chicago. Currently, he is a Professor at the Vascular Biology Center and Pulmonary Division, School of Medicine, Medical College of Georgia, at Augusta University, Augusta, GA.   He has published more than 170 papers in reputed journals primarily in the field of pulmonary vascular endothelial barrier regulation.  He served as an Editorial board member of the American Journal of Physiology (Lung) from 2006-2011 and Editor-in-chief of the academic journal, Vessel Plus, in 2016-2022. He is currently serving as an academic editor of the British Journal of Medicine and Medical Research and Cardiology and Angiology, and an editorial board member in several other journals in the field of pulmonary/cardiovascular research such as Biomolecules, Cardiovascular Pharmacology, Journal of Multidisciplinary Pathology, Tissue Barriers, World Journal of Respirology.