Non-Hematopoietic MLKL Protects Against Salmonella Mucosal Infection by Enhancing Inflammasome Activation

Abstract

The intestinal mucosal barrier is critical for host defense against pathogens infection. Here, we demonstrate that the mixed lineage kinase-like protein (MLKL), a necroptosis effector, promotes intestinal epithelial barrier function by enhancing inflammasome activation. MLKL−/− mice were more susceptible to Salmonella infection compared with wild-type counterparts, with higher mortality rates, increased body weight loss, exacerbated intestinal inflammation, more bacterial colonization, and severe epithelial barrier disruption. MLKL deficiency promoted early epithelial colonization of Salmonella prior to developing apparent intestinal pathology. Active MLKL was predominantly expressed in crypt epithelial cells, and experiments using bone marrow chimeras found that the protective effects of MLKL were dependent on its expression in non-hematopoietic cells. Intestinal mucosa of MLKL−/− mice had impaired caspase-1 and gasdermin D cleavages and decreased interleukin (IL)-18 release. Moreover, administration of exogenous recombinant IL-18 rescued the phenotype of increased bacterial colonization in MLKL−/− mice. Thus, our results uncover the role of MLKL in enhancing inflammasome activation in intestinal epithelial cells to inhibit early bacterial colonization.

Interferons Transcriptionally Up-Regulate MLKL Expression in Cancer Cells

“…In line with this notion, constitutive IFN signaling has recently been reported to maintain a critical threshold of MLKL expression to license necroptosis [34]. Besides its function in necroptosis, MLKL has been shown to regulate endosomal trafficking and the generation of extracellular vesicles and to contribute to inflammasome activation [35], [36], [37], [38], [39], [40].

Figure 6IRF1 and STAT1 regulate MLKL expression.IFNs like IFNγ bind to their IFN receptor and induce the activation and phosphorylation of STAT1. The transcription factor STAT1 induces the expression of ISGs such as IRF1.

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Pyroptosis versus necroptosis: similarities, differences, and crosstalk

“…This study is important because it demonstrates that necroptoticinduced disease may, in some circumstances, be inhibited by targeting a single downstream inflammatory mediator. More recently, it was reported that MLKL activation in the intestinal mucosa was required for inflammasome-mediated protection against Salmonella infection [104], while Staphylococcus toxin-induced MLKLtriggered NLRP3 activation to promote damaging inflammation [105]. It will be interesting to define which other necroptotic disease models may also respond to NLRP3 inflammasome inhibition, or whether there are other specific DAMPS, such as HMGB1, whose targeting may be useful to limit damaging, necroptoticinduced, inflammation.…”

Necroptosis in Intestinal Inflammation and Cancer: New Concepts and Therapeutic Perspectives

“…Moreover, MLKL protects from Salmonella infection promoting intestinal epithelial barrier function by inducing inflammasome activation in IECs. Besides, mice with MLKL ablation are more susceptible to Salmonella infection and present impaired caspase-1 and GSDMD cleavage with consequently decreased interleukin IL-18 release [ 70 ].…”

“…It is unclear whether MLKL is involved in this process [ 87 ]. However, a recent paper showed that MLKL promoted intestinal epithelial barrier function by enhancing inflammasome activation [ 70 ].…”

“…Clostridium perfringens uses its large arsenal of protein toxins to produce histotoxic, neurologic and intestinal infections in humans and animals, resulting in the activation of intracellular pathways with a variety of effects, commonly including cell death, such as apoptosis, necrosis and/or necroptosis [ 117 ]. MLKL -/- mice are more susceptible to Salmonella infection compared to their wild-type counterparts, with higher mortality rates, increased body weight loss, exacerbated intestinal inflammation, more bacterial colonization, and severe epithelial barrier disruption [ 70 ].…”