Mutations that prevent caspase cleavage of RIPK1 cause autoinflammatory disease

RIPK1 is a key regulator of innate immune signalling pathways. To ensure an optimal inflammatory response, RIPK1 is regulated post-translationally by well-characterized ubiquitylation and phosphorylation events, as well as by caspase-8-mediated cleavage 1 – 7 . The physiological relevance of this cleavage event remains unclear, although it is thought to inhibit activation of RIPK3 and necroptosis 8 . Here we show that the heterozygous missense mutations D324N, D324H and D324Y prevent caspase cleavage of RIPK1 in humans and result in an early-onset periodic fever syndrome and severe intermittent lymphadenopathy—a condition we term ‘cleavage-resistant RIPK1-induced autoinflammatory syndrome’. To define the mechanism for this disease, we generated a cleavage-resistant Ripk1 D325A mutant mouse strain. Whereas Ripk1 −/− mice died postnatally from systemic inflammation, Ripk1 D325A/D325A mice died during embryogenesis. Embryonic lethality was completely prevented by the combined loss of Casp8 and Ripk3 , but not by loss of Ripk3 or Mlkl alone. Loss of RIPK1 kinase activity also prevented Ripk1 D325A/D325A embryonic lethality, although the mice died before weaning from multi-organ inflammation in a RIPK3-dependent manner. Consistently, Ripk1 D325A/D325A and Ripk1 D325A /+ cells were hypersensitive to RIPK3-dependent TNF-induced apoptosis and necroptosis. Heterozygous Ripk1 D325A /+ mice were viable and grossly normal, but were hyper-responsive to inflammatory stimuli in vivo. Our results demonstrate the importance of caspase-mediated RIPK1 cleavage during embryonic development and show that caspase cleavage of RIPK1 not only inhibits necroptosis but also maintains inflammatory homeostasis throughout life. Heterozygous mutateons in the caspase-8 cleavage site of RIPK1 cause a range of autoinflammatory symptoms in humans, and caspase-8 cleavage of RIPK1 in a mouse model limits TNF-induced cell death and inflammation.