Extracellular RNA (eRNA), released from cells under conditions of injury or vascular disease, acts as potent prothrombotic factor and promotes vascular hyperpermeability related to oedema formation in vivo. In this study, we aimed to investigate the mechanism by which eRNA triggers inflammatory processes, particularly associated with different steps of leukocyte recruitment. Using intravital microscopy of murine cremaster muscle venules, eRNA (but not DNA) significantly induced leukocyte adhesion and transmigration in vivo, which was comparable in its effects to the function of tumour-necrosis-factor-α (TNF-α). In vitro, eRNA promoted adhesion and transmigration of monocytic cells on and across endothelial cell monolayers. eRNA-induced monocyte adhesion in vitro was mediated by activation of the vascular endothelial growth factor (VEGF)/VEGF-receptor-2 system and was abolished by neutralising antibodies against intercellular adhesion molecule-1 or the p2-inte-grin Mac-1. Additionally, eRNA induced the release of TNF-α from monocytic cells in a time- and concentration-dependent manner, which involved activation of TNF- α -converting enzyme (TACE) as well as the nuclear factor kB signalling machinery. In vivo, inhibiton of TACE significantly reduced eRNA-induced leukocyte adhesion. Our findings present evidence that eRNA in connection with tissue/vascular damage provokes a potent inflammatory response by inducing leukocyte recruitment and by mobilising proinflammatory cytokines from monocytes.

Extracellular RNA (eRNA) released from injured cells promotes tissue permeability, thrombosis, and inflammation in vitro and in vivo, and RNase1 pretreatment can reduce all these effects. In this study, we investigated the role of the eRNA/RNase1 system in tumor progression and metastasis. Under quiescent and stimulatory conditions, tumor cells released much higher levels of endogenous extracellular RNA (eRNA) than nontumor cells. In glioblastomas, eRNA was detected at higher levels in tumors than nontumor tissue. eRNA induced tumor cells to adhere to and migrate through human cerebral microvascular endothelial cells (HCMEC/D3), in a manner requiring activation of VEGF signaling. In addition, eRNA liberated TNF-α from macrophages in a manner requiring activation of the TNF-α–converting enzyme TACE. Accordingly, supernatants derived from eRNA-treated macrophages enhanced tumor cell adhesion to HCMEC/D3. TNF-α release evoked by eRNA relied upon signaling activation of mitogen-activated protein kinases and the NF-κB pathway. In subcutaneous xenograft models of human cancer, administration of RNase1 but not DNase decreased tumor volume and weight. Taken together, these results suggest that eRNA released from tumor cells has the capacity to promote tumor cell invasion through endothelial barriers by both direct and indirect mechanisms, including through a mechanism involving TNF-α release from tumor-infiltrating monocytes/macrophages. Our findings establish a crucial role for eRNA in driving tumor progression, and they suggest applications for extracellular RNase1 as an antiinvasive regimen for cancer treatment. Cancer Res; 73(16); 5080–9. ©2013 AACR.

Neurological disorders such as stroke, multiple sclerosis, as well as the neurodegenerative diseases Parkinson's or Alzheimer's disease are accompanied or even powered by danger associated molecular patterns (DAMPs), defined as endogenous molecules released from stressed or damaged tissue. Besides protein-related DAMPs or “alarmins”, numerous nucleic acid DAMPs exist in body fluids, such as cell-free nuclear and mitochondrial DNA as well as different species of extracellular RNA, collectively termed as self-extracellular nucleic acids (SENAs). Among these, microRNA, long non-coding RNAs, circular RNAs and extracellular ribosomal RNA constitute the majority of RNA-based DAMPs. Upon tissue injury, necrosis or apoptosis, such SENAs are released from neuronal, immune and other cells predominantly in association with extracellular vesicles and may be translocated to target cells where they can induce intracellular regulatory pathways in gene transcription and translation. The majority of SENA-induced signaling reactions in the brain appear to be related to neuroinflammatory processes, often causally associated with the onset or progression of the respective disease. In this review, the impact of the diverse types of SENAs on neuroinflammatory and neurodegenerative diseases will be discussed. Based on the accumulating knowledge in this field, several specific antagonistic approaches are presented that could serve as therapeutic interventions to lower the pathological outcome of the indicated brain disorders.

Extracellular RNA (eRNA) released under injury or pathological conditions has been identified as a yet unrecognized vascular alarm signal to induce procoagulant, permeability‐promoting, and proinflammatory activities. eRNA‐induced functions were largely prevented by administration of RNase1 as a natural blood vessel‐protective antagonist of eRNA. The aim of this study was to investigate the inflammatory regulation of endothelial cell RNase1, which is partly stored in Weibel‐Palade bodies of these cells. Long‐term treatment of human umbilical vein endothelial cells (HUVECs) with inflammatory agents like tumor necrosis factor α (TNF‐α) or interleukin 1β (IL‐1β), but not with eRNA, significantly decreased the release (34±5%; 34±7% of control) as well as the cellular expression (19.5±5%; 33±8% of control) of RNase1. Down‐regulation of RNase1 by TNF‐α stimulation or RNase1 siRNA knockdown increased the permeability of HUVEC monolayers, demonstrated by dearrangement of VE‐cadherins at cell‐cell borders. Mechanistically, cytokine‐induced decrease of RNase1 expression did not involve the nuclear factor κ B (NFκB) signaling pathway but epigenic modifications. Since inhibition of histone deacetylases resulted in recovery of RNase1 expression and secretion after cytokine treatment, an acetylation‐dependent process of RNase1 regulation is proposed. These results indicate that cytokine‐mediated down‐regulation of RNase1 in endothelial cells may aggravate eRNA‐induced inflammatory activities and thereby disturbs the vascular homeostasis of the extracellular RNA/RNase system.—Gansler, J., Preissner, K. T., Fischer, S. Influence of proinflammatory stimuli on the expression of vascular ribonuclease 1 in endothelial cells. FASEB J. 28, 752–760 (2014). www.fasebj.org