Abstract
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.