Conditional inactivation of the ectodomain shedding of pro-TNFα in monocytes prevents lethality from LPS-induced septic shock

Abstract

Background: TNFalpha is synthesized as a membrane-bound precursor and proteolytically released from cells. Soluble TNFalpha is the primary mediator of pathologies such as rheumatoid arthritis, Crohn's disease, and endotoxin shock. Although several different enzymes have been implicated in this proteolytic activity, recent studies lean toward the TNFalpha converting enzyme (TACE/ADAM17) as the most relevant TNFalphasheddasein vivo.In the present study, we asked whether the inactivation TACE could yield a protection from lipopolysaccharide(LPS)-induced septic shockin mice. Material(s) and Method(s): To abrogate TNFalpha shedding activity in vivo, we generated conditional TACE-deficient mice using Cre-loxP system [1]. We mated these mice with Mx1-Cretg mice and LysM-Cretg mice to inactivate TACE in BM cells and macrophage/monocyte lineage cells, respectively. Endotoxin shock was induced by i.p. injection of 5 mug of LPS and 20 mg of D-galactosamine. All injected mice were closely monitored every hour for the first 16 h and every 3-6 h thereafter. Results/conclusions: We found that temporal disruption of TACE under the control of Mx1 transgene prevented lethality from endotoxin shock. Furthermore, inactivation of TACE in macrophage/monocyte lineage cells also rendered significant protection against LPS-induced septic shock. Consistent with these findings, serum TNFalpha levels in the TACE mutant mice were much lower than those in control mice. The present study thus shows that 1) TACE is indeed a principal enzyme responsible for the release of soluble TNFalpha in vivo, and that 2) inactivation of TACE in macrophage/monocyte lineage cells is sufficient to yield strong protection against LPS-induced endotoxin shock. Taken together, the present data indicate inhibition of TACE activity as a potential therapeutic target for TNFalpha-related disorders.