ADAM17 inhibition effects on Mer shedding

Background: Mer belongs to TAM, a tyrosine kinase receptor family with essential roles in the homeostasis of the immune response. Among TA M members, Mer is the less characterized regarding its biological role. Mer is activated by its ligand Gas6, while it is inactivated through proteolytic shedding by the metalloproteinase ADAM17 in response to inflammatory stimuli such as lipopolysaccharides (LPS). Since Mer is involved in pathophysiological conditions as infection, we investigated the ADAM17 inhibitor GW280264X (GW) in order to evaluate both its toxicity and efficacy. Methods: GW cytotoxic effect was evaluated in vitro by MTT assay and morphological analysis using MS1, Raw264.7 and primary murine macrophages as endothelial cells and macrophage models. Mer expression was evaluated by flow cytometry both in vitro and in vivo. Results: Through morphological analysis and MTT assay we found 10 μM as optimal GW concentration without toxic effects in vitro and this concentration was able to avoid Mer shedding in presence of LPS in vitro. Shedding was prevented also in vivo in a mouse model of peritonitis and Mer was mainly expressed in F4/80+ CD11b+ cells compared to single CD11b+ cells. Additionally, the efficacy of GW was shorter in vitro (∼6 hours) than in vivo, where GW was still effective 24 hours after a single intraperitoneal injection. Conclusions: Our studies indicate that GW is effective in inhibiting ADAM17 and in preventing Mer shedding both in vitro and in vivo.