Project description:Caspase-8 is a protease with both pro-death and pro-survival functions: it is required for apoptosis induced by death receptors such as TNFR1 (tumor necrosis factor receptor 1) 1, and it has a critical role in suppressing necroptosis mediated by the kinase RIPK3 (receptor interacting protein kinase 3) and the pseudokinase MLKL (mixed lineage kinase-like) 2-4. Mice lacking caspase-8 display MLKL-dependent embryonic lethality 4, as do mice expressing catalytically inactive caspase-8 mutant C362A. However, Casp8C362A/C362A Mlkl-/- mice die in the perinatal period, whereas Casp8-/- Mlkl-/- mice are viable 4, indicating that inactive caspase-8 also has a pro-death scaffolding function. Here we show that inactive caspase-8 activates pyroptosis in MLKL-deficient intestinal epithelial cells around embryonic day 18, triggering the formation of ASC specks. Accordingly, intestinal atrophy and perinatal lethality in Casp8C362A/C362A Mlkl-/- mice was prevented by loss of caspase-1. In transfection studies, inactive caspase-8 mutants C362A or C362S were found in both the triton X-100 insoluble and soluble fractions, whereas wild-type caspase-8 existed only in the soluble fraction. Moreover, inactive caspase-8 shifted co-transfected ASC into the insoluble fraction, whereas wild-type caspase-8 did not. Thus, a defense mechanism is revealed that would allow intestinal epithelial cell death in the face of pathogens expressing virulence factors to inhibit caspase-8-dependent apoptosis and necroptosis.
Project description:Caspase-8 is a protease with both pro-death and pro-survival functions: it is required for apoptosis induced by death receptors such as TNFR1 (tumour necrosis factor receptor 1), and it has a critical role in suppressing necroptosis mediated by the kinase RIPK3 (receptor interacting protein kinase 3) and the pseudokinase MLKL (mixed lineage kinase-like). Mice lacking caspase-8 display MLKL-dependent embryonic lethality, as do mice expressing catalytically inactive caspase-8 mutant C362A. However, Casp8C362A/C362A Mlkl-/- mice die in the perinatal period, whereas Casp8-/- Mlkl-/- mice are viable, indicating that inactive caspase-8 also has a pro-death scaffolding function. Here we show that caspase-8 C362A triggers ASC speck formation and caspase-1-dependent pyroptosis in MLKL-deficient intestinal epithelial cells (IECs) around embryonic day 18. Pyroptosis contributed to the perinatal lethal phenotype because a number of Casp8 C362A/C362A Mlkl-/- Casp1-/- mice survived beyond weaning. Transfection studies suggested inactive caspase-8 adopts a distinct conformation to wild-type caspase-8, enabling it to engage the caspase-1 adaptor ASC. Wild-type caspase-8 was found in the Triton X-100 soluble fraction, whereas wild-type caspase-8 inhibited with the pan-caspase inhibitor emricasan, or inactive caspase-8 mutant C362A, were detected in the insoluble fraction. Moreover, inhibited or inactive caspase-8 shifted ASC into the insoluble fraction. Perinatal lethality was recapitulated when expression of caspase-8 C362A was restricted to IECs, but intriguingly, only in the absence of MLKL. Hence, unanticipated plasticity in death pathways is revealed such that IECs can undergo caspase-1-dependent death when caspase-8-dependent apoptosis and MLKL-dependent necroptosis are inhibited.
Project description:FADD-IEC KO and CASP8 IEC-KO mice spontaneously develop chronic colitis charcterized by inflammatory gene expression. We characterized the role of MLKL, RIPK3, ZBP1, in the upregulation of inlflammatory genes in these mice. We used microarray to study the effect of MLKL, RIPK3 and ZBP1 on the gene expression profile in FADD IEC-KO and/or CASP8 IEC-KO mice and detect effects on specific inflammatory genes.
Project description:FADD-IEC KO and CASP8 IEC-KO mice spontaneously develop chronic ileitis charcterized by inflammatory gene expression. We characterized the role of MLKL, RIPK3, ZBP1, in the upregulation of inlflammatory genes in these mice. We used microarray to study the effect of MLKL, RIPK3 and ZBP1 on the gene expression profile in FADD IEC-KO and/or CASP8 IEC-KO mice and detect effects on specific inflammatory genes.
Project description:Necroptosis is a lytic form of cell death that is mediated by the kinase RIPK3 and the pseudokinase MLKL when caspase-8 is inhibited downstream of death receptors, toll-like receptor 3 (TLR3), TLR4, and the intracellular Z-form nucleic acid sensor ZBP1. Oligomerization and activation of RIPK3 is driven by interactions with the kinase RIPK1, the TLR adaptor TRIF, or ZBP1. In this study, we use immunohistochemistry (IHC) and in situ hybridization (ISH) assays to generate a tissue atlas characterizing RIPK1, RIPK3, Mlkl, and ZBP1 expression in mouse tissues. RIPK1, RIPK3, and Mlkl were co-expressed in most immune cell populations, endothelial cells, and many mucosal epithelia. ZBP1 was expressed in many immune populations, but had more variable expression in epithelia compared to RIPK1, RIPK3, and Mlkl. Intriguingly, expression of ZBP1 was elevated in Casp8-/- Tnfr1-/- embryos prior to their succumbing to aberrant necroptosis around embryonic day 15. ZBP1 contributed to this embryonic lethality because rare Casp8-/- Tnfr1-/- Zbp1-/- mice survived until after birth. Necroptosis mediated by TRIF contributed to the demise of Casp8-/- Tnfr1-/- Zbp1-/- pups in the perinatal period. Of note, Casp8-/- Tnfr1-/- Trif-/- Zbp1-/- mice exhibited autoinflammation and morbidity, typically within 5-7 weeks of being born, which is not seen in Casp8-/- Ripk1-/- Trif-/- Zbp1-/-, Casp8-/- Ripk3-/-, or Casp8-/- Mlkl-/- mice. Therefore, after birth, loss of caspase-8 probably unleashes RIPK1-dependent necroptosis driven by death receptors other than TNFR1.
Project description:Purpose: Necroptosis as been implicated in various deseases. The goal of this study is to invastigate the impact of RIPK3 and MLKL in the lipid metabolism of adipocytes. Methods: 3T3-L1 preadipocytes invalidated or not for RIPK3 or MLKL were exposed differenciated into mature adipocytes and the mRNA profiles of wild type (WT), RIPK3-/- knockout (RIPK3-KO) or MLKL-/- knockout 3T3-L1 cells control (J0) or differenciated into mature adipocytes (J7) were generated by deep sequencing, in 3 copies, using Illumina NOVAseq 6000 plateform. Differential expression analysis between two conditions/groups (five biological replicates per condition) was performed using DESeq2 R package. Genes with an adjusted P value < 0.05 found by DESeq2 were assigned as differentially expressed. qRT–PCR validation was performed using SYBR Green assays Results: The DEGs were clustered using a hierarchical clustering algorithm, and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis unveiled a clear reduction in the expression of genes involved in the early or late stages of adipogenesis in MLKL-KO cells Conclusions: Taken together, these data suggest that Mlkl but not Ripk3 deficiency impaired adipogenesis of 3T3-L1 cells by reducing the expression of pro-adipogenic factors and genes involved in fatty acid metabolism.
Project description:ATAC-seq on embryonic e16.5 mouse intestine For data usage terms and conditions, please refer to http://www.genome.gov/27528022 and http://www.genome.gov/Pages/Research/ENCODE/ENCODE_Data_Use_Policy_for_External_Users_03-07-14.pdf
Project description:Neuroinflammatory processes are a prominent contributor to the pathology of Parkinson’s disease (PD), characterized by the progressive loss of dopaminergic neurons in the substantia nigra (SN) and deposits of α-synuclein aggregates. MLKL-mediated cell necroptosis might occur in the onset of PD and lead to neuronal dopaminergic degeneration. However, the link between α-synuclein, neuroinflammatory processes, and neurodegeneration in PD remains unclear. Here, our in vitro study indicated that inhibition of MLKL exerted a protective effect against 6-OHDA- and TNF-α-induced neuronal cell death. Furthermore, we created a mouse model (Tg-Mlkl-/-) with typical progressive Parkinson traits by crossbreeding SNCA A53T transgenic mice with MLKL knockout mice. Tg-Mlkl-/ mice displayed dramatically improved motor symptoms and reduced hyperphosphorylated α-synuclein expression. More data suggested that MLKL deficiency protected dopaminergic neurons, blocked neuronal cell death, and attenuated neuroinflammation by inhibiting the activation of the microglia and astrocytes. Single-cell RNA-seq analysis revealed reduced microglial cells and damped neuron death in the SN of the Tg-Mlkl-/- mice. Subcluster analysis identified a unique cell type-specific transcriptome profiling in the MLKL deficiency mice. Thus, MLKL represents a critical therapeutic target for reducing neuroinflammation and preventing dopaminergic neuron degeneration.