Pneumologie 2016; 70 - SOP7
DOI: 10.1055/s-0036-1584659

A soluble factor mediates alpha-1 antitrypsin-induced inhibition of ATP-induced IL-1β release by monocytic cells

R Siebers 1, B Fink 1, K Richter 1, S Wilker 1, M Küllmar 1, S Zukunft 2, N Aggarwal 3, A Zakrzewicz 1, W Padberg 1, S Janciauskiene 3, V Grau 1
  • 1Laboratory of Experimental Surgery, Department of General and Thoracic Surgery, Justus-Liebig-University Gießen, Gießen
  • 2Institute for Vascular Signalling, Goethe University Frankfurt, Frankfurt
  • 3Department of Pulmonology, Hannover Medical School, Hannover

Introduction: Alpha-1 antitrypsin (AAT), a major antiprotease of the lung, exerts anti-inflammatory functions via poorly defined pathways. At previous DZL meetings, we provided evidence that AAT is a potent inhibitor of ATP-induced release of IL-1β from human monocytes, and that CD36, calcium-independent phospholipase A2 (iPLA2) and nicotinic acetylcholine receptor (nAChR) subunit α9 participate in this mechanism. Here we test the hypothesis that AAT induces the release of a soluble factor X from U937 cells, which then inhibits ATP-dependent inflammasome activation via nAChR. As glycerophosphocholine (GPC) is a metabolite of membrane phospholipids cleaved by iPLA2, we tested whether GPC functionally resembles factor X.

Methods: A low molecular weight fraction of conditioned medium from AAT-treated U937 cells was produced by ultrafiltration (cut-off 10 kDa). LPS-primed U937 cells were stimulated with the P2X7 agonist 2'(3')-O-(4-Benzoylbenzoyl)adenosine-5'-triphosphate (BzATP) and IL-1β was measured in cell culture supernatants by ELISA. The low molecular weight fraction of conditioned medium or GPC was added together with BzATP in the presence or absence of nicotinic antagonists.

Results: Conditioned medium from AAT-treated U937 cells contained a low molecular weight factor that significantly reduced the release of IL-1β in response to BzATP. GPC also significantly inhibited BzATP-induced IL-1β release in a dose-dependent manner. General nicotinic antagonists and specific antagonists of nAChR containing subunit α9 completely reverted the inhibitory effect of conditioned medium and GPC.

Discussion: Our results confirm the hypothesis that AAT stimulates the release of a soluble factor X from U937 cells. This factor seems to be a potent agonist of nAChR containing subunit α9, which efficiently inhibits P2X7 receptors. Hence, we suggest a triple-membrane-passing signaling pathway triggered by AAT that inhibits inflammasome activation and release of IL-1β in human monocytes. Understanding this novel signaling pathway might lead to the development of efficient therapies for the treatment of systemic inflammation.