Project Summary/Abstract
The putative nucleotide sensor ZBP1 can trigger necroptotic cell death or transcriptional responses,
and genetic studies indicate that this pathway is required for host defense against an array of viral pathogens.
Furthermore, recent studies show that in some circumstances ZBP1 can become activated under sterile
conditions, implicating endogenous cellular products as potential ZBP1 ligands. However, despite long study,
the ligand responsible for activating ZBP1 and its interplay with other components of the nucleotide sensing
machinery remain controversial, with double-stranded RNA, ribonucleoprotein, and viral Z-form nucleic acid
species all suggested as ligand. ZBP1 shares its key nucleotide sensing domain with only one other
mammalian protein, ADAR1. ADAR1 inactivates endogenous dsRNA species to limit autoinflammatory
pathology, and mutations in ADAR1 in human patients lead to the severe autoimmune disease Acardi-
Goutieres syndrome (AGS). We hypothesize that ADAR1 and ZBP1 compete for a common endogenous
ligand, whose inactivation by ADAR1 is required to limit ZBP1 activation. In support of this idea, the pathology
observed in a newly-developed mouse model of human ADAR1 mutation was fully rescued by ablation of
ZBP1. This finding supports our hypothesis, and also implies that autoimmune pathology associated with loss
of ADAR1 function is caused by activation of ZBP1-dependent inflammation and cell death. Using these
observations as a starting point, the work proposed here will investigate ZBP1 activation and function by
pursuing three Aims: First, we will use ADAR1 mutation and additional new mouse models to facilitate
isolation and identification of an endogenous ZBP1 ligand. Second, we will assess the contribution of
necroptosis as well as ZBP1-mediated inflammatory signaling to the pathology of an animal model of human
AGS triggered by ADAR1 mutation, and test the ability of necroptosis inhibitors to ameliorate this pathology.
Third, we will investigate the role of other dsRNA sensors, including MDA5 and PKR, to ZBP1 ligand formation
and necroptotic pathway activation. Together this work will both reveal key aspects of ZBP1 function, and
identify ZBP1-dependent necroptosis as a potentially treatable target to ameliorate AGS.