Inhibition of ATP-induced inflammasome activation in blood monocytes

• Applicant: Professorin Dr. Veronika Grau
• Subject Area: General and Visceral Surgery ; Cardiac and Vascular Surgery
• Term: from 2016 to 2018
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 313857722

Interleukin-1beta (IL-1beta) is a cytokine of monocytes/macrophages that plays a central role in host defense. Excessive systemic IL-1beta levels, however, importantly contribute to systemic inflammatory response syndrome, a frequent and life-threatening complication of trauma and major surgery. Release of mature IL-1beta normally depends on two consecutive danger signals. Typical first signals are ligands of Toll-like receptors, which induce the expression of cytoplasmic pro-IL-1beta. ATP released from damaged cells is a trauma associated second stimulus, which is sensed by ATP receptor P2X7. P2X7 receptor activation induces formation of the inflammasome, leading to activation of the protease capase-1, which in turn cleaves pro-IL-1beta and enables release of mature IL-1beta. In response to inflammation, C-reactive protein (CRP) is produced in the liver and released to the circulation. Increased blood levels of CRP are a widely used as a clinical indicator for inflammation. CRP is an evolutionary highly conserved pentameric protein that binds one phosphocholine molecule per subunit. In experimental settings CRP interacts with bacterial surfaces and activates complement but its function in vivo is poorly understood.Recently, we discovered that stimulation of nicotinic acetylcholine receptors by canonical nicotinic agonists and by phosphocholine inhibits ATP-induced release of IL-1beta from human monocytes. Nicotinic stimulation impairs the ion channel function of receptor P2X7 but the signaling pathway between nicotinic receptors and P2X7 is unclear. Preliminary experiments revealed that also CRP efficiently suppresses ATP-induced release of IL-1beta. This effect seems to be sensitive to nicotinic antogonists. Interestingly, the half maximal inhibitory concentration (IC50) is about 4 mg/l, a concentration corresponding to blood values at the dividing line between healthy and sick. Regarding molar concentrations of phosphocholine bound to CRP, CRP isolated from human blood was at least an order of magnitude more efficient than free phosphocholine.The purpose of the project is 1) to decipher the molecular pathways by which nicotinic receptor activation translates into inhibition of inflammasome activation and to test the following hypotheses: 2) CRP functions as a potent anti-inflammatory molecule that inhibits ATP-induced release of IL-1beta from primed monocytes; 3) CRP acts synergistically with the attached phosphocholine molecules and presents them to nicotinic receptors. We will investigate a human monocytic cell line and primary monocytes isolated from the blood of healthy volunteers. The therapeutic potential of this novel anti-inflammatory pathway will be evaluated in preclinical experimental models for major trauma.

• DFG Programme: Research Grants