Extracellular Vesicles Contribute to the Pathophysiology and Progression of Pleural Fibrosis by Promoting MesoMT and Neo-Angiogenesis.

Abstract

Severe pleural space inflammation associated with exudative pleural effusions leads to the development of pleural fibrosis (PF). Pathological tissue remodeling in PF is associated with profibrotic changes in the pleural mesothelium and neo-angiogenesis within the fibrotic region. However, the factors that promote these processes remain poorly understood. This study investigates the role of extracellular vesicles (EVs) in the development and progression of PF, focusing on mesothelial to mesenchymal transition (MesoMT) and neo-angiogenesis. Human pleural mesothelial cells (HPMCs) were treated with coagulation proteases factor Xa (FXa) and thrombin and EV production was quantified using nanoparticle tracking analysis. The functional relevance of these EVs was assessed by evaluating their ability to promote profibrotic phenotype in HPMCs and induce tube formation in endothelial cells. FXa and thrombin treatments significantly increased EV generation from HPMCs via protease-activated receptor (PAR)-mediated cell signaling. Our studies showed that these EVs primed HPMCs towards a profibrotic phenotype and enhanced tube formation in endothelial cells. Further investigations in preclinical mouse models of PF revealed elevated EV levels in pleural fluids from injury-induced mice, compared to saline controls. In clinical specimens, exudative pleural effusions from patients with empyema and parapneumonic effusions exhibited significantly elevated EV numbers compared to transudative effusions from congestive heart failure patients. More importantly, EVs isolated from exudative effusions promoted a profibrotic phenotype in naïve HPMCs and enhanced tube formation similar to the effects observed with FXa- and thrombin-generated EVs. These findings offer new insights into PF pathogenesis by identifying EVs as previously unknown contributors that modulate mesothelial to mesenchymal transition (MesoMT) and neo-angiogenesis.