Summary
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.
Keywords
Extracellular RNA - inflammation - leukocyte recruitment - TNF-α - endothelial cells
- vasculature