Noncanonical pyroptosis is triggered by Caspase 4/5/11, which cleaves Gasdermin D (GSDMD), leading to cell lysis. While GSDMD has been studied previously in systemic lupus erythematosus (SLE), the role of pyroptosis in SLE pathogenesis remains unclear and contentious, with limited understanding of Caspase 11-mediated pyroptosis in this condition. In this study, we explored the level of Caspase 11-mediated pyroptosis in SLE, identifying both the upstream pathways and the interaction between pyroptosis and adaptive immune responses. We observed increased Caspase 5/11 and GSDMD-dependent pyroptosis in the macrophages/monocytes of both lupus patients and mice. We identified serum lipopolysaccharide (LPS), released from the gut due to a compromised gut barrier, as the signal that triggers Caspase 11 activation in MRL/lpr mice. We further discovered that pyroptotic macrophages promote the differentiation of mature B cells independently of T cells. Additionally, inhibiting Caspase 11 and preventing LPS leakage proved effective in improving lupus symptoms in MRL/lpr mice. These findings suggest that elevated serum LPS, resulting from a damaged gut barrier, induces Caspase 11/GSDMD-mediated pyroptosis, which in turn promotes B cell differentiation and enhances autoimmune responses in SLE. Thus, targeting Caspase 11 could be a viable therapeutic strategy for SLE.

The subgingival biofilm attached to tooth surfaces triggers and maintains periodontitis. Previously, late-onset periodontitis has been considered a consequence of dysbiosis and a resultant polymicrobial disruption of host homeostasis. However, a multitude of studies did not show \"healthy\" oral microbiota pattern, but a high diversity depending on culture, diets, regional differences, age, social state etc. These findings relativise the aetiological role of the dysbiosis in periodontitis. Furthermore, many late-onset periodontitis traits cannot be explained by dysbiosis; e.g. age-relatedness, attenuation by anti-ageing therapy, neutrophil hyper-responsiveness, and microbiota shifting by dysregulated immunity, yet point to the crucial role of dysregulated immunity and neutrophils in particular. Furthermore, patients with neutropenia and neutrophil defects inevitably develop early-onset periodontitis. Intra-gingivally injecting lipopolysaccharide (LPS) alone causes an exaggerated neutrophil response sufficient to precipitate experimental periodontitis. Vice versa to the surplus of LPS, the increased neutrophil responsiveness characteristic for late-onset periodontitis can effectuate gingiva damage likewise. The exaggerated neutrophil extracellular trap (NET) response in late-onset periodontitis is blameable for damage of gingival barrier, its penetration by bacteria and pathogen-associated molecular patterns (PAMPs) as well as stimulation of Th17 cells, resulting in further neutrophil activation. This identifies the dysregulated immunity as the main contributor to periodontal disease.

Zoonotic pathogens, such as COVID-19, reside in animal hosts before jumping species to infect humans. The Carnivora, like mink, carry many zoonoses, yet how diversity in host immune genes across species affect pathogen carriage is poorly understood. Here, we describe a progressive evolutionary downregulation of pathogen-sensing inflammasome pathways in Carnivora. This includes the loss of nucleotide-oligomerization domain leucine-rich repeat receptors (NLRs), acquisition of a unique caspase-1/-4 effector fusion protein that processes gasdermin D pore formation without inducing rapid lytic cell death, and the formation of a caspase-8 containing inflammasome that inefficiently processes interleukin-1β. Inflammasomes regulate gut immunity, but the carnivorous diet has antimicrobial properties that could compensate for the loss of these immune pathways. We speculate that the consequences of systemic inflammasome downregulation, however, can impair host sensing of specific pathogens such that they can reside undetected in the Carnivora.

The innate immune system is the body\'s first line of defense against pathogens and its protection against infectious diseases. On the surface of host myeloid cells, Toll-like receptor 4 (TLR4) senses lipopolysaccharide (LPS), the major outer membrane component of Gram-negative bacteria. Intracellularly, LPS is recognized by caspase 11 through the noncanonical inflammasome to induce pyroptosis-an inflammatory form of lytic cell death. While TLR4-mediated signaling perturbations result in secretion of cytokines and chemokines that help clear infection and facilitate adaptive immunity, caspase 11-mediated pyroptosis leads to the release of damage-associated molecular patterns and inflammatory mediators. Although the core signaling events and many associated proteins in the TLR4 signaling pathway are known, the complex signaling events and protein networks within the noncanonical inflammasome pathway remain obscure. Moreover, there is mounting evidence for pathogen-specific innate immune tuning. We characterized the major LPS structures from two different pathogens, modeled their binding to the surface receptors, systematically examined macrophage inflammatory responses to these LPS molecules, and surveyed the temporal differences in global protein secretion resulting from TLR4 and caspase 11 activation in macrophages using mass spectrometry (MS)-based quantitative proteomics. This integrated strategy, spanning functional activity assays, top-down structural elucidation of endotoxins, and secretome analysis of stimulated macrophages, allowed us to identify crucial differences in TLR4- and caspase 11-mediated protein secretion in response to two Gram-negative bacterial endotoxins. IMPORTANCE Macrophages and monocytes are innate immune cells playing an important role in orchestrating the initial innate immune response to bacterial infection and the tissue damage. This response is facilitated by specific receptors on the cell surface and intracellularly. One of the bacterial molecules recognized is a Gram-negative bacteria cell wall component, lipopolysaccharide (LPS). The structure of LPS differs between different species. We have characterized the innate immune responses to the LPS molecules from two bacteria, Escherichia coli and Bordetella pertussis, administered either extracellularly or intracellularly, whose structures we first determined. We observed marked differences in the temporal dynamics and amounts of proteins secreted by the innate immune cells stimulated by any of these molecules and routes. This suggests that there is specificity in the first line of response to different Gram-negative bacteria that can be explored to tailor specific therapeutic interventions.

A steatotic liver is increasingly vulnerable to ischemia reperfusion injury (IRI), and the underlying mechanisms are incompletely defined. Caspases are endo-proteases, which provide critical regulatory connections between cell death and inflammation. Caspase 1 is driven by inflammasomes which are key signaling platforms, that detect sterile stressors (DAMPs), releasing the highly pro-inflammatory cytokine interleukin IL-8 and IL-1β. To delineate the involvement of Caspase 1 and 11 in hepatocellular injury in steatotic liver undergoing IRI. Male C57BL6/Wild Type and Caspase 1Null, Caspase 11-/- and Caspase 1-/-/11-/- mice were fed a high fat diet (HFD) for 12 weeks. These mice were subjected to 40 min of ischemia followed by 2-24 h of reperfusion. Hepatocellular injury was assessed by histopathologic injury scoring, serum ALT and propidium iodide (PI) uptake, mRNA levels of Caspase 1, IL-1β by RT PCR, Caspase 1 activity assay and Caspase 1. Specific Caspase 1, inhibitor experiments were carried out. All groups gained similar body weight after a 12-week HFD. Cleaved Caspase 1 protein levels, Caspase 1 mRNA levels were significantly higher in steatotic liver undergoing IRI. Executor of pyroptosis cleaved GSDMD levels were higher in HFD fed mouse compared to lean. In addition, genetic deletion of Caspase 1, Casp1Null mouse expressing Caspase-11 and Caspase 1/11 double knock out demonstrated significant reduction in serum ALT (p < 0.01), Injury Score, (p < 0.0002) but not in Caspase 11 alone. Caspase 1 is the driver of hepatocellular injury in a steatotic liver undergoing IRI, inhibition of which leads to hepatoprotection, thus providing a therapeutic target for clinical use.

Ischemia reperfusion injury (IRI) during liver transplantation increases morbidity and contributes to allograft dysfunction. There are no therapeutic strategies to mitigate IRI. We examined a novel hypothesis: caspase 1 and caspase 11 serve as danger-associated molecular pattern (DAMPs) sensors in IRI. By performing microarray analysis and using caspase 1/caspase 11 double-knockout (Casp DKO) mice, we show that the canonical and non-canonical inflammasome regulators are upregulated in mouse liver IRI. Ischemic pre (IPC)- and post-conditioning (IPO) induce upregulation of the canonical and non-canonical inflammasome regulators. Trained immunity (TI) regulators are upregulated in IPC and IPO. Furthermore, caspase 1 is activated during liver IRI, and Casp DKO attenuates liver IRI. Casp DKO maintained normal liver histology via decreased DNA damage. Finally, the decreased TUNEL assay-detected DNA damage is the underlying histopathological and molecular mechanisms of attenuated liver pyroptosis and IRI. In summary, liver IRI induces the upregulation of canonical and non-canonical inflammasomes and TI enzyme pathways. Casp DKO attenuate liver IRI. Development of novel therapeutics targeting caspase 1/caspase 11 and TI may help mitigate injury secondary to IRI. Our findings have provided novel insights on the roles of caspase 1, caspase 11, and inflammasome in sensing IRI derived DAMPs and TI-promoted IRI-induced liver injury.

Enteric-associated neurons (EANs) are closely associated with immune cells and continuously monitor and modulate homeostatic intestinal functions, including motility and nutrient sensing. Bidirectional interactions between neuronal and immune cells are altered during disease processes such as neurodegeneration or irritable bowel syndrome. We investigated the effects of infection-induced inflammation on intrinsic EANs (iEANs) and the role of intestinal muscularis macrophages (MMs) in this context. Using murine models of enteric infections, we observed long-term gastrointestinal symptoms, including reduced motility and loss of excitatory iEANs, which was mediated by a Nlrp6- and Casp11-dependent mechanism, depended on infection history, and could be reversed by manipulation of the microbiota. MMs responded to luminal infection by upregulating a neuroprotective program via β2-adrenergic receptor (β2-AR) signaling and mediated neuronal protection through an arginase 1-polyamine axis. Our results identify a mechanism of neuronal death post-infection and point to a role for tissue-resident MMs in limiting neuronal damage.

In this study, we demonstrate the upregulation in the expression of caspases 1 and 11 by SJL/J mouse brain astrocytes infected with the BeAn strain of Theiler\'s murine encephalomyelitis virus (TMEV). The upregulation of both proteases hints at protection of astrocytic cells from apoptotic death. We therefore looked for the reason of the demonstrated absence of programmed cell death in BeAn-infected SJL/J astrocytes. Complementary RNA (cRNA) from mock- and TMEV-infected cells was hybridized to the whole murine genome U74v2 DNA microarray from Affymetrix. Those experiments demonstrated the upregulation of gene expression for caspases 1 and 11 in infected cells. We further confirmed and validated their messenger RNA (mRNA) increase by reverse transcriptase quantitative real-time PCR (qPCR). The presence of both enzymatically active caspases 1 and 11 was demonstrated in cell lysates using a colorimetric and fluorymetric assay, respectively. We also show that overexpressed caspase 11 activated caspase 1 after preincubation of cytosol in vitro following a time-dependent process. This induction was neutralized by an anti-caspase 11 polyclonal antibody. These results demonstrate the activation of the caspase 1 precursor by caspase 11 and suggest a new mechanism of protection of BeAn-infected astrocytes from apoptosis. The direct experimental evidence that the protection effect demonstrated in this article was mediated by caspase 1, is provided by the fact that its specific inhibitor Z-WEHD-FMK induced de novo apoptotic death.