Mitochondria Are a Subset of Extracellular Vesicles Released by Activated Monocytes and Induce Type I IFN and TNF Responses in Endothelial Cells

Abstract

Rationale: Extracellular vesicles, including microvesicles, are increasingly recognized as important mediators in cardiovascular disease. The cargo and surface proteins they carry are considered to define their biological activity, including their inflammatory properties. Monocyte to endothelial cell signaling is a prerequisite for the propagation of inflammatory responses. However, the contribution of microvesicles in this process is poorly understood. Objective: To elucidate the mechanisms by which microvesicles derived from activated monocytic cells exert inflammatory effects on endothelial cells. Methods and Results: LPS (lipopolysaccharide)-stimulated monocytic cells release free mitochondria and microvesicles with mitochondrial content as demonstrated by flow cytometry, quantitative polymerase chain reaction, Western Blot, and transmission electron microscopy. Using RNAseq analysis and quantitative reverse transcription-polymerase chain reaction, we demonstrated that both mitochondria directly isolated from and microvesicles released by LPS-activated monocytic cells, as well as circulating microvesicles isolated from volunteers receiving low-dose LPS-injections, induce type I IFN (interferon), and TNF (tumor necrosis factor) responses in endothelial cells. Depletion of free mitochondria significantly reduced the ability of these microvesicles to induce type I IFN and TNF-dependent genes. We identified mitochondria-associated TNFα and RNA from stressed mitochondria as major inducers of these responses. Finally, we demonstrated that the proinflammatory potential of microvesicles and directly isolated mitochondria were drastically reduced when they were derived from monocytic cells with nonrespiring mitochondria or monocytic cells cultured in the presence of pyruvate or the mitochondrial reactive oxygen species scavenger MitoTEMPO. Conclusions: Mitochondria and mitochondria embedded in microvesicles constitute a major subset of extracellular vesicles released by activated monocytes, and their proinflammatory activity on endothelial cells is determined by the activation status of their parental cells. Thus, mitochondria may represent critical intercellular mediators in cardiovascular disease and other inflammatory settings associated with type I IFN and TNF signaling.

Extracellular Vesicles as Signaling Mediators and Disease Biomarkers across Biological Barriers

“…For example, regarding innate immunity, amplification of the chemotactic recruitment of neutrophils during the inflammatory response is mediated by an autocrine/paracrine cascade driven by leukotriene B4 vehiculated within EVs released by chemotactic neutrophils [175]. Additionally, it has been demonstrated recently that the secretion of EV-embedded mitochondrial components and even whole mitochondria by activated monocytes induces systemic proinflammatory type I IFN and TNF responses in endothelia [176]. This response may contribute to cardiovascular disease and to other autoinflammatory diseases associated with type I IFN and TNF signaling.…”

Extracellular Mitochondria in Traumatic Brain Injury Induced Coagulopathy

“…These findings add to a growing body of evidence that mitochondria can be released into the extracellular space and transferred between cells. [23][24][25] The question remains as to whether mitochondria are released exclusively from apoptotic or injured cells or from cells undergoing normal renewal as well. In a phospholipidomic study, high levels of the brain-specific mitochondrial anionic phospholipid cardiolipin (1,3-bis(sn-3′-phosphatidyl)-sn-glycerol) were detected in peripheral blood samples collected from neonatal rats subjected to TBI, in parallel with the reduction of cardiolipin in injured brain tissue.…”

T‐cell–derived extracellular vesicles regulate B‐cell IgG production via pyruvate kinase muscle isozyme 2

“…Different contents of EVs can result from differences in their parental cells (43), thus indicating that the different ceramide contents in EV‐produced T cells may affect EV ceramides. For ceramide production, 3 main metabolic pathways have been described: de novo pathway, sphingomyelinase pathway, and salvage pathway (44, 45).…”