230: Unraveling the role of Adam17 in IL-6 trans-signaling

IL-6 is a key regulator of immune responses after bacterial infection. IL-6 signaling is mediated via the receptor subunits IL-6R and gp130. The signal transducing subunit gp130 is ubiquitously expressed whereas IL-6R expression is restricted to hepatocytes and some leukocytes. The IL-6R can be cleaved from the cell surface by ADAM proteases. The soluble form of the IL-6R (sIL-6R) has the same IL-6 binding affinity as the membrane-bound receptor. The resulting IL-6/sIL-6R complex activates cells, which only express gp130 on their cell surface, a process called trans-signaling. Thus, IL-6-transsignaling following IL-6R proteolysis essentially renders all cells of the body responsive to IL-6. The proteolytic web controlling IL-6R shedding in vivo under pathophysiological conditions is poorly characterized. Recently, it was demonstrated that human IL-6R is a substrate for the protease ADAM17 in contrast to the murine ADAM17, which is mainly cleaved by ADAM10. However, these data were raised in cell culture systems. We analyzed IL-6R shedding in vivo on leukocytes after infection with Listeria monocytogenes or LPS-challenge of ADAM17 and ADAM10-deficient mice. ADAM17 and ADAM10 knockout mice are not viable. For this reason we generated a hypomorphic ADAM17 mouse model which expresses only 5% of the normal ADAM17 levels. Additionally we use conditional ADAM10 mice with ADAM10 deleted either in monocytes or Tcells. Listeria infection led to massive shedding of the IL-6R on Tcells and inflammatory monocytes. Further we could demonstrate that Listeria -induced IL-6R cleavage is abrogated in hypomorphic ADAM17 ex/ex mice. Additionally we can show that serum levels of sIL-6R are elevated after LPS challenge of wildtype but not ADAM17 ex/ex mice. These results strongly suggest that ADAM17 is the main IL-6R sheddase under pathophysiological conditions. In future experiments we will evaluate the contribution of the protease ADAM10 in mediating IL-6R shedding to uncover the proteolytic steps involved in IL-6 trans-signaling.