Self-extracellular RNA acts in synergy with exogenous danger signals to promote inflammation

• Published in: PloS one 2017-12, Vol.12 (12), p.e0190002-e0190002
• Main Authors: Noll, Frederik, Behnke, Jonas, Leiting, Silke, Troidl, Kerstin, Alves, Gustavo Teixeira, Müller-Redetzky, Holger, Preissner, Klaus T, Fischer, Silvia
• Format: Article
• Language: English
• Subjects: Animals; Antibodies; Biochemistry; Biology and Life Sciences; Bone marrow; Cell activation; Cell culture; Colony-stimulating factor; Cytokines; Cytokines - metabolism; Deoxyribonucleic acid; Development and progression; Diglycerides - pharmacology; DNA; Extracellular signal-regulated kinase; Extracellular Space - metabolism; Fibroblasts; Genetic aspects; Hazards; Heart; Immune response; Immune system; Infectious diseases; Inflammation; Inflammation - metabolism; Innate immunity; Interleukin 6; Ischemia; Kinases; Ligands; Lipopeptides - pharmacology; Lipopolysaccharides; Macrophages; Macrophages - drug effects; Macrophages - metabolism; Medical schools; Medicine and Health Sciences; Mice, Inbred C57BL; NF-κB protein; Oligopeptides - pharmacology; Pathogen-Associated Molecular Pattern Molecules - metabolism; Physiological aspects; Proteins; Reperfusion; Research and analysis methods; Ribonucleic acid; RNA; RNA - metabolism; Rodents; Signal transduction; Signal Transduction - drug effects; Signaling; Stem cell transplantation; Stem cells; Synergistic effect; Time Factors; TLR2 protein; TLR3 protein; TLR4 protein; TLR7 protein; Toll-like receptors; Toll-Like Receptors - antagonists & inhibitors; Toll-Like Receptors - metabolism; Tumor necrosis factor-α; Viral infections
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0190002

Self-extracellular RNA (eRNA), released from stressed or injured cells upon various pathological situations such as ischemia-reperfusion-injury, has been shown to act as an alarmin by inducing procoagulatory and proinflammatory responses. In particular, M1-polarization of macrophages by eRNA resulted in the expression and release of a variety of cytokines, including tumor necrosis factor (TNF)-α or interleukin-6 (IL-6). The present study now investigates in which way self-eRNA may influence the response of macrophages towards various Toll-like receptor (TLR)-agonists. Isolated agonists of TLR2 (Pam2CSK4), TLR3 (PolyIC), TLR4 (LPS), or TLR7 (R848) induced the release of TNF-α in a concentration-dependent manner in murine macrophages, differentiated from bone marrow-derived stem cells by mouse colony stimulating factor. Here, the presence of eRNA shifted the dose-response curve for Pam2CSK4 (Pam) considerably to the left, indicating that eRNA synergistically enhanced the cytokine liberation from macrophages even at very low Pam-levels. The synergistic activation of TLR2 by eRNA/Pam was duplicated by other TLR2-agonists such as FSL-1 or Pam3CSK4. In contrast, for TLR4-agonists such as LPS a synergistic effect of eRNA was much weaker, and was not existent for TLR3-, or TLR7-agonists. The synergistic eRNA/Pam action was dependent on the NFκB-signaling pathway as well as on p38MAP- and MEK1/ERK-kinases and was prevented by predigestion of eRNA with RNase1 or by antibodies against TLR2. Thus, the presence of self-eRNA as alarming molecule sensitizes innate immune responses towards pathogen-associated molecular patterns (PAMPs) in a synergistic way and may thereby contribute to the differentiated outcome of inflammatory responses.