Exosomes in postshock mesenteric lymph are key mediators of acute lung injury triggering the macrophage activation via Toll‐like receptor 4

Abstract

Acute lung injury (ALI) is a common cause of morbidity in patients after severe injury due to dysregulated inflammation, which is believed to be driven by gut-derived inflammatory mediators carried mesenteric lymph (ML). We have previously demonstrated that nano-sized extracellular vesicles, called exosomes, secreted into ML after trauma/hemorrhagic shock (T/HS) have the potential to activate immune cells Here, we assess the function of ML exosomes in the development of T/HS-induced ALI and the role of TLR4 in the ML exosome-mediated inflammatory response. ML exosomes isolated from rats subjected to T/HS stimulated NF-κB activation and caused proinflammatory cytokine production in alveolar macrophages. experiments revealed that intravenous injection of exosomes harvested after T/HS, but not before shock, caused recruitment of inflammatory cells in the lung, increased vascular permeability, and induced histologic ALI in naive mice. The exosome-depleted supernatant of ML had no effect on and inflammatory responses. We also demonstrated that both pharmacologic inhibition and genetic knockout of TLR4 completely abolished ML exosome-induced cytokine production in macrophages. Thus, our findings define the critical role of exosomes secreted into ML as a critical mediator of T/HS-induced ALI through macrophage TLR4 activation.-Kojima, M., Gimenes-Junior, J. A., Chan, T. W., Eliceiri, B. P., Baird, A., Costantini, T. W., Coimbra, R. Exosomes in postshock mesenteric lymph are key mediators of acute lung injury triggering the macrophage activation Toll-like receptor 4.

M1 But Not M0 Extracellular Vesicles Induce Polarization of RAW264.7 Macrophages Via the TLR4-NFκB Pathway In Vitro

“…In addition to the morphological changes observed herein, polarization of naive macrophages by M1-EVs into M1 macrophages in our study was also indicated by activation of the TLR4-NFκB signaling pathway and an associated increase in iNOS and CD86 expression. Previous research reported that alveolar macrophages were activated (e.g., release of pro-inflammatory cytokines) via the TLR4-NFκB signal pathway when subjected to mesenteric lymph exosomes from hemorrhagic shock rats [26]. In addition, the TLR4-NFκB pathway of human monocytes and monocytederived macrophages was induced when stimulated by EVs derived from calcium ionophore A23187-stimulated monocytes [19].…”

Innate immune responses to trauma

“…Input from the periphery also modulates the innate pulmonary immune response. In rats, exosomes in mesentery lymph after extra-pulmonary trauma and/or hemorrhagic shock activate alveolar macrophages via TLR4, which mounts a full ALI response 95 . Modulating the mesenteric lymph after traumatic shock in vivo with a pharmacologic vagal agonist results in a reduction in the activity of phosphorylated transcription factor STAT3 in circulating monocytes and attenuates the development of secondary ALI, as well as the systemic inflammatory response 96 .…”

Extracellular Vesicles in ARDS: New Insights into Pathogenesis with Novel Clinical Applications

“…Following trauma and hemorrhagic shock, gutderived extracellular vesicles were released into the mesenteric lymphatic system. Intravenous administration of these extracellular vesicles to naïve mice caused lung injury via macrophage TLR4 activation, including increased alveolar vascular permeability and inflammatory cell infiltration [17]. These findings indicate that similar mechanisms may be present in patients who develop ARDS following similar distant (indirect) insults.…”

“…Remarkably, mouse models have indicated that release of extracellular vesicles following distant injury, e.g., traumatic brain injury [16] or trauma and hemorrhagic shock [17], can mediate lung injury. Following trauma and hemorrhagic shock, gutderived extracellular vesicles were released into the mesenteric lymphatic system.…”