Characterization of mast cell‐derived rRNA‐containing microvesicles and their inflammatory impact on endothelial cells

Abstract

Tissue‐resident mast cells (MCs) are well known for their role in inflammatory responses and allergic and anaphylactic reactions, but they also contribute to processes of arterial remodeling. Although ribosomes and cytosolic RNAs are located around secretory granules in mature MCs, their functional role in MC responses remains unexplored. Previous studies by our group characterized extracellular RNA (eRNA) as an inflammatory and pathogenetic factor in vitro and in vivo. In the present study, RNA‐containing MCs and eRNA were located in close proximity to growing collateral arteries in vivo. In vitro, various agonists were found to induce the degranulation of MCs and the concomitant release of eRNA in association with microvesicles (MVs). The liberation of eRNA from MCs was abolished by MC stabilizers or by preventing the increase of intracellular Ca2+ in MCs. eRNA was found to be mainly contained inside MVs, as demonstrated by electron microscopy and immunocytochemistry. The exposure to and the uptake of MC‐released MVs by cultured endothelial cells increased their expression of cytokines, such as monocyte chemo‐attractant protein or IL‐6, in a dose‐ and time‐dependent manner. These results indicate that RNA‐containing MC‐derived MVs are likely to be involved in inflammatory responses, relevant, for example, to processes of vascular remodeling.—Elsemüller, A.‐K., Tomalla, V., Gärtner, U., Troidl, K., Jeratsch, S., Graumann, J., Baal, N., Hackstein, H., Lasch, M., Deindl, E., Preissner, K. T., Fischer, S. Characterization of mast cell‐derived rRNA‐containing microvesicles and their inflammatory impact on endothelial cells. FASEB J. 33, 5457–5467 (2019). http://www.fasebj.org

The Extraordinary Role of Extracellular RNA in Arteriogenesis, the Growth of Collateral Arteries

“…This is supported by the fact that various leukocytes including neutrophils and monocytes, whose extravasation is critical in arteriogenesis, secrete VEGF and have been demonstrated to do so in arteriogenesis [22][23][24][25]. In addition, treatment of endothelial cells with MVs derived from mast cells potentiated the release of vWF from endothelial cells just as endothelial cell-derived eRNA did [44]. Besides acting as a positive feedback mechanism for endothelial activation, an important effect of mast cell-derived eRNA might also be the stimulation of the expression of adhesion molecules on endothelial cells as was shown for ICAM-1 in vitro [44]-potentially through VEGFR2 or NFκB signaling.…”

“…The stimulatory effect of eRNA on cell adhesion was abolished by pre-treatment with a VEGFR2 inhibitor (Semaxanib), again highlighting that eRNA enhances VEGFR2 activation, whereas the TNFα-mediated effect was not diminished by pre-treatment with Semaxanib [3], since the release of TNFα occurs at a later stage of arteriogenesis following VEGFR2 activation and signaling. The expression of MCP-1, on the other hand, was increased by MV-derived eRNA from mast cells in vitro [44]. eRNA released by mast cells might therefore activate TACE and thus stimulate TNFα and subsequent MCP-1 release in arteriogenesis, thereby enhancing the local inflammatory response and leukocyte transmigration.…”

“…Physiologically and in arteriogenesis, leukocyte transmigration is facilitated by the interaction between endothelial adhesion molecules such as intercellular adhesion molecule 1 (ICAM-1) and leukocyte ligands such as macrophage-1 antigen (Mac-1) [40,41]. The expression of ICAM-1 has independently been shown to be upregulated on the one hand by fluid shear stress in vitro and in vivo [42,43] and on the other hand by eRNA in vitro [14,44]. In an in vivo model of peripheral arteriogenesis, the effects of eRNA on endothelial cell signaling were also demonstrated to be relevant for subsequent leukocyte adhesion, as inhibition of eRNA through RNase administration reduced the perivascular macrophage count to a similar degree as seen in ICAM-1 deficient mice [3].…”

“…Arteriogenesis, on the contrary, is a chronic process. Mast cells, whose degranulation is stimulated by the downstream effects of endothelial cell-derived eRNA, also release eRNA in the form of microvesicles concomitantly with degranulation [44]. This release of eRNA has been shown to promote local inflammatory processes and leukocyte extravasation [44].…”

“…Mast cells, whose degranulation is stimulated by the downstream effects of endothelial cell-derived eRNA, also release eRNA in the form of microvesicles concomitantly with degranulation [44]. This release of eRNA has been shown to promote local inflammatory processes and leukocyte extravasation [44]. Microvesicles (MV) are a type of extracellular vesicles that have been described to be released from a variety of cell types including endothelial cells, leukocytes, platelets and mast cells [78][79][80][81], often upon cell stress [82], to be involved in cell communication and inflammation including during angiogenesis [82,83], and to be selectively enriched with different types of RNA [84].…”