Endothelial Caspase-8 prevents fatal necroptotic hemorrhage caused by commensal bacteria

Abstract

Caspase-8 transduces signals from death receptor ligands, such as tumor necrosis factor, to drive potent responses including inflammation, cell proliferation or cell death. This is a developmentally essential function because in utero deletion of endothelial Caspase-8 causes systemic circulatory collapse during embryogenesis. Whether endothelial Caspase-8 is also required for cardiovascular patency during adulthood was unknown. To address this question, we used an inducible Cre recombinase system to delete endothelial Casp8 in 6-week-old conditionally gene-targeted mice. Extensive whole body vascular gene targeting was confirmed, yet the dominant phenotype was fatal hemorrhagic lesions exclusively within the small intestine. The emergence of these intestinal lesions was not a maladaptive immune response to endothelial Caspase-8-deficiency, but instead relied upon aberrant Toll-like receptor sensing of microbial commensals and tumor necrosis factor receptor signaling. This lethal phenotype was prevented in compound mutant mice that lacked the necroptotic cell death effector, MLKL. Thus, distinct from its systemic role during embryogenesis, our data show that dysregulated microbial- and death receptor-signaling uniquely culminate in the adult mouse small intestine to unleash MLKL-dependent necroptotic hemorrhage after loss of endothelial Caspase-8. These data support a critical role for Caspase-8 in preserving gut vascular integrity in the face of microbial commensals.

Death by TNF: a road to inflammation

“…Inducible deletion of Casp8 in the endothelium of 6-week-old mice causes fatal haemorrhagic lesions exclusively within the small intestine driven by microbial commensals and TNF. This phenotype is prevented in mice that lack MLKL, confirming that the haemorrhage is caused by unrestrained necroptosis in the small intestine 97 . Deficiency of FADD or caspase 8 in keratinocytes causes keratinocyte necroptosis and severe skin inflammation in mice, which is prevented by RIPK3 loss and is partly dependent on TNF 94 , 98 , 99 .…”

An immunohistochemical atlas of necroptotic pathway expression

“…TNF) or genetic deficiency (e.g. deletion of Casp8 or Fadd ) (Bader et al , 2023; Schwarzer et al , 2020; Tisch et al , 2022; Zelic et al , 2018). In liver, Kupffer cells expressed Caspase-8, RIPK1 and RIPK3 (arrowheads Fig.…”

“…Next, we addressed whether microbiota-depletion affects necroptotic pathway expression. This question was prompted by studies showing that antibiotics offer protection in various models of intestinal necroptosis (Bader et al ., 2023; Gunther et al , 2015; Li et al , 2020; Xie et al , 2020). As shown in Fig.…”

“…Co-housed littermates were split across two cages. The drinking water for one cage was supplemented with 1g/L ampicillin, 1g/L neomycin, 1g/L metronidazole, 0.5g/L enrofloxacin, 2.5g/L meropenem as in (Bader et al ., 2023). Antibiotic-supplemented water was replaced after 3 days.…”

“…TNF) or genetic deficiency (e.g. deletion of Casp8 or Fadd) (42)(43)(44)(45). In liver, Kupffer cells expressed Caspase-8, RIPK1 and RIPK3 (Fig.…”