Extracellular vesicles from ALI models induce endothelial dysfunction.

One distinguishing characteristic of acute respiratory distress syndrome (ARDS) or its lesser form, acute lung injury (ALI), is dysfunction of the lung endothelium. This dysfunction leads to increased permeability and eventual pulmonary edema. Despite the globally climbing rates of ARDS, the mechanisms of endothelial dysfunction are poorly understood. Recently, extracellular vesicles (EVs) have been shown to induce various microvascular disease states, as they contain various endothelial-targeting cargo in the form of mRNA, proteins, lipids, and miRNAs. Therefore, we hypothesized that EVs play a role in the endothelial dysfunction observed in ARDS/ALI. EVs were isolated from the plasma of male Sprague Dawley rats which were given saline or P. aeruginosa (PA103) via intratracheal (IT) injection for 48h. ALI was confirmed by determining the wet to dry weights of the rodent lungs. We then tested the effect of the EVs isolated from saline- and ALI treated animals (sEVs and ALI-EVs, respectively) on endothelial barrier function and modifications in gene expression. We found that treatment with ALI-EVs, but not sEVs, increased rat lung microvascular endothelial cell (RLMVEC) permeability in the presence of lipopolysaccharide (LPS). Interestingly, ALI-EVs did not induce endothelial dysfunction on their own, rather exacerbated the damage induced by LPS. We further noted ALI-EVs, but not sEVs, increased gene expression of toll-like receptor 4 (TLR4), which is the main pattern recognition receptor (PRR) for LPS and its downstream signaling molecule, MyD88 in the presence of LPS in RLMVEC. Further, we found that ALI-EVs, together with LPS, increased gene expression of intracellular adhesion molecule 1 (ICAM-1), vascular adhesion molecule 1 (VCAM-1), and interleukin 6 (IL-6), which are all involved in inflammatory signaling. Thus, it is likely that through the modulation of inflammatory signaling mediators, ALI-EVs contain select cargo that worsen the endothelial barrier in settings where LPS is present, such as bacterial-ARDS