Caspase-8 controls the gut response to microbial challenges by Tnf-α-dependent and independent pathways

Abstract

ObjectivesIntestinal epithelial cells (IEC) express toll-like receptors (TLR) that facilitate microbial recognition. Stimulation of TLR ligands induces a transient increase in epithelial cell shedding, a mechanism that serves the antibacterial and antiviral host defence of the epithelium and promotes elimination of intracellular pathogens. Although activation of the extrinsic apoptosis pathway has been described during inflammatory shedding, its functional involvement is currently unclear.DesignWe investigated the functional involvement of caspase-8 signalling in microbial-induced intestinal cell shedding by injecting Lipopolysaccharide (LPS) to mimic bacterial pathogens and poly(I:C) as a probe for RNA viruses in vivo.ResultsTLR stimulation of IEC was associated with a rapid activation of caspase-8 and increased epithelial cell shedding. In mice with an epithelial cell-specific deletion of caspase-8 TLR stimulation caused Rip3-dependent epithelial necroptosis instead of apoptosis. Mortality and tissue damage were more severe in mice in which IECs died by necroptosis than apoptosis. Inhibition of receptor-interacting protein (Rip) kinases rescued the epithelium from TLR-induced gut damage. TLR3-induced necroptosis was directly mediated via TRIF-dependent pathways, independent of Tnf-α and type III interferons, whereas TLR4-induced tissue damage was critically dependent on Tnf-α.ConclusionsTogether, our data demonstrate an essential role for caspase-8 in maintaining the gut barrier in response to mucosal pathogens by permitting inflammatory shedding and preventing necroptosis of infected cells. These data suggest that therapeutic strategies targeting the cell death machinery represent a promising new option for the treatment of inflammatory and infective enteropathies.

Intracellular nicotinamide adenine dinucleotide promotes TNF-induced necroptosis in a sirtuin-dependent manner

“…51,52 (ii) In addition to masking the potential role of the NAD + -sirtuin axis, recent observations indicate that these inhibitors can promote the production of soluble factors, including a number of cytokines (IL-6, IL-1β, IL-8, GM-CSF and CXCL2), chemokines (CCL2, RANTES and CXCL1) 53 and type I interferons (in response to mitochondrial damage) 54,55 that could interfere with the necroptotic signaling pathway. [56][57][58] Although the present study confirms previously reported observations suggesting a role for SIRT2 in promoting necroptosis, 33 they are at apparent odds with the observation that SIRT2-KO mice remain sensitive to the in vivo toxicity of exogenously administered TNF. 50 Possible explanations for this apparent discrepancy include the possible functional redundancy between sirtuin members as this multigene family often share substrate specificity 49 and the uncertainty concerning the mechanism underlying TNF toxicity in SIRT2-KO mice.…”

BATF-dependent IL-7RhiGM-CSF+ T cells control intestinal graft-versus-host disease

“…Immunohistochemical analysis was performed on formalin-fixed and deparaffinized tissue sections from the distal mouse colon using the tyramide signal amplification (TSA) Cy3 System (PerkinElmer), as recommended by the manufacturer and as described previously (56). In brief, for antigen retrieval, sections were treated for 20 minutes with heated citrate buffer (10 mM, pH 6).…”

The toll-like receptor 3 pathway in homeostasis, responses to injury and wound repair

“…Levels of inducible nitric oxide synthase, cyclooxygenase-2, serum CXCL1/KC (derived from keratinocytes) and amyloid A were also reduced in poly(IC)-treated mice [69]. However, other studies actually implicate TLR3 signalling in inducing acute injury in gut epithelia [70][71][72]. Intraperitoneal injection of rotavirus dsRNA resulted in severe injury in the small intestine as characterized by thinning of the intestinal wall, erosion of villi and the mucus membrane, and weight loss; Tlr3 -/-mice were protected from such effects [70][71][72].…”

“…However, other studies actually implicate TLR3 signalling in inducing acute injury in gut epithelia [70][71][72]. Intraperitoneal injection of rotavirus dsRNA resulted in severe injury in the small intestine as characterized by thinning of the intestinal wall, erosion of villi and the mucus membrane, and weight loss; Tlr3 -/-mice were protected from such effects [70][71][72]. Poly(IC) administration also upregulated serum levels of several cytokines including IL-15 and IFN- [70].…”

“…Poly(IC), acting via TLR3, TRIF and caspase-8, also induced epithelial cell apoptosis and altered the structure and function of the intestine [71], which may relate to host-protective functions against viral infections. Indeed, a subsequent study showed that epithelial-specific deletion of caspase-8 resulted in TRIFdependent TLR3-mediated necroptosis and a more severe inflammatory phenotype [72].…”