Quantifying Caspase-1 Activity in Murine Macrophages

Live Imaging of Pyroptosis in Primary Murine Macrophages

Inflammasomes are the ultimate weapon of the macrophage immune arsenal. Inflammasome signalling in macrophages triggers pyroptosis, a lytic cell death pathway that facilitates inflammation-driven pathogen clearance. Imaging-based approaches to investigating cell death have proven useful, revealing cellular remodelling events such as the generation of extracellular vesicles, and continuing to uncover important structural changes in cells involved in inflammatory signalling. Pyroptosis has proved extremely challenging to image, because its lytic nature is incompatible with many well-established imaging approaches employed for other, non-lytic pathways. The complexities of ectopically expressing fluorescent constructs in primary macrophages and the sensitivity of such proteins to drug-based probes compound this difficulty. We and others have demonstrated key differences in pyroptosis induced by canonical versus noncanonical inflammasomes that delineate functional differences between these signalling pathways. Here, we describe a live imaging approach to study and compare canonical versus noncanonical inflammasome signalling and pyroptotic architecture in primary murine macrophages.

An Overview: The Toxicity of Ageratina adenophora on Animals and Its Possible Interventions

Ageratina adenophora is one of the major invasive weeds that causes instability of the ecosystem. Research has reported that A. adenophora produces allelochemicals that inhibit the growth and development of food crops, and also contain some toxic compounds that cause toxicity to animals that consume it. Over the past decades, studies on the identification of major toxic compounds of A. adenophora and their toxic molecular mechanisms have been reported. In addition, weed control interventions, such as herbicides application, was employed to reduce the spread of A. adenophora. However, the development of therapeutic and prophylactic measures to treat the various A. adenophora-induced toxicities, such as hepatotoxicity, splenotoxicity and other related disorders, have not been established to date. The main toxic pathogenesis of A. adenophora is oxidative stress and inflammation. However, numerous studies have verified that some extracts and secondary metabolites isolated from A. adenophora possess anti-oxidation and anti-inflammation activities, which implies that these extracts can relieve toxicity and aid in the development of drug or feed supplements to treat poisoning-related disorders caused by A. adenophora. Furthermore, beneficial bacteria isolated from rumen microbes and A. adenophora can degrade major toxic compounds in A. adenophora so as to be developed into microbial feed additives to help ameliorate toxicity mediated by A. adenophora. This review presents an overview of the toxic mechanisms of A. adenophora, provides possible therapeutic strategies that are available to mitigate the toxicity of A. adenophora and introduces relevant information on identifying novel prophylactic and therapeutic measures against A. adenophora-induced toxicity.

Vitamin D decreases expression of NLRP1 and NLRP3 ninflammasomes in placental explants from women with preeclampsia cultured with hydrogen peroxide

This study aimed to evaluate the immunomodulatory effect of vitamin D (VD) on the NLRP1 and NLRP3 inflammasomes in placental explants from preeclamptic (PE) and normotensive (NT) pregnant women. Placental explants from eight PE and eight NT pregnant women were cultured with or without hydrogen peroxide (H₂O₂)_, VD or H₂O₂ + VD. Gene and protein expression of NLRP1, NLRP3, HMGB1, caspase-1, IL-1β, TNF-α and IL-18 were determined by qPCR and Western blotting/ELISA. Compared to NT pregnant women, the endogenous gene expression of NLRP1, NLRP3, HMGB1, IL-1β, TNF-α and IL-18 was significantly higher in explants from PE and became decreased after VD treatment. Similarly, VD decreased the protein expression of NLRP1, NLRP3, caspase-1, HMGB1, IL-1β, TNF-α and IL-18 in PE. Placental explants from NT cultured with H₂O₂ showed increased gene and protein expression of NLRP1, NLRP3, caspase-1, IL-1β, TNF-α and HMGB1, while H₂O₂ was also able to increase TNF-α and caspase-1 gene expression in PE. Treatment with H₂O₂ + VD decreased gene/protein expression of NLRP1, NLRP3, caspase-1, HMGB1, IL-1β, TNF-α and IL-18 in PE and NT explants with H₂O₂. NLRP1 and NLRP3 are upregulated in the PE. VD may play an immunomodulatory role in the placental inflammation and downregulates oxidative stress induced in vitro by H₂O_2.

Activation of the NLRP3 Inflammasome Increases the IL-1β Level and Decreases GLUT4 Translocation in Skeletal Muscle during Insulin Resistance

Low-grade chronic inflammation plays a pivotal role in the pathogenesis of insulin resistance (IR), and skeletal muscle has a central role in this condition. NLRP3 inflammasome activation pathways promote low-grade chronic inflammation in several tissues. However, a direct link between IR and NLRP3 inflammasome activation in skeletal muscle has not been reported. Here, we evaluated the NLRP3 inflammasome components and their role in GLUT4 translocation impairment in skeletal muscle during IR. Male C57BL/6J mice were fed with a normal control diet (NCD) or high-fat diet (HFD) for 8 weeks. The protein levels of NLRP3, ASC, caspase-1, gasdermin-D (GSDMD), and interleukin (IL)-1β were measured in both homogenized and isolated fibers from the flexor digitorum brevis (FDB) or soleus muscle. GLUT4 translocation was determined through GLUT4myc-eGFP electroporation of the FBD muscle. Our results, obtained using immunofluorescence, showed that adult skeletal muscle expresses the inflammasome components. In the FDB and soleus muscles, homogenates from HFD-fed mice, we found increased protein levels of NLRP3 and ASC, higher activation of caspase-1, and elevated IL-1β in its mature form, compared to NCD-fed mice. Moreover, GSDMD, a protein that mediates IL-1β secretion, was found to be increased in HFD-fed-mice muscles. Interestingly, MCC950, a specific pharmacological NLRP3 inflammasome inhibitor, promoted GLUT4 translocation in fibers isolated from the FDB muscle of NCD- and HFD-fed mice. In conclusion, we found increased NLRP3 inflammasome components in adult skeletal muscle of obese insulin-resistant animals, which might contribute to the low-grade chronic metabolic inflammation of skeletal muscle and IR development.

A comprehensive guide to studying inflammasome activation and cell death

Inflammasomes are multimeric heterogeneous mega-Dalton protein complexes that play key roles in the host innate immune response to infection and sterile insults. Assembly of the inflammasome complex following infection or injury begins with the oligomerization of the upstream inflammasome-forming sensor and proceeds through a multistep process of well-coordinated events and downstream effector functions. Together, these steps enable elegant experimental readouts with which to reliably assess the successful activation of the inflammasome complex and cell death. Here, we describe a comprehensive protocol that details several in vitro (in bone marrow-derived macrophages) and in vivo (in mice) strategies for activating the inflammasome and explain how to subsequently assess multiple downstream effects in parallel to unequivocally establish the activation status of the inflammasome and cell death pathways. Our workflow assesses inflammasome activation via the formation of the apoptosis-associated speck-like protein containing a CARD (ASC) speck; cleavage of caspase-1 and gasdermin D; release of IL-1β, IL-18, caspase-1, and lactate dehydrogenase from the cell; and real-time analysis of cell death by imaging. Analyses take up to ~24 h to complete. Overall, our multifaceted approach provides a comprehensive and consistent protocol for assessing inflammasome activation and cell death.

Nanocomposite packaging regulates extracellular ATP and programed cell death in edible mushroom (Flammulina velutipes)

Our previous study indicated that nanocomposite packaging material (Nano-PM) containing nano-Ag, nano-TiO₂, nano-SiO₂ and nanoattapulgite alleviated postharvest senescence of Flammulina velutipes by regulating respiration and energy metabolism. In this study, extracellular ATP (eATP) and programmed cell death (PCD) were employed as critical factors to further investigate the senescence mechanism of postharvest F. velutipes. Results demonstrated that Nano-PM delayed apyrase activity decrease and stimulated critical oxidative phosphorylation-related gene expression to inhibit eATP content increase, which is a crucial signaling molecule related to delaying senescence. The regulation of eATP resulted in alleviating PCD including chromosomal concentration, DNA fragmentation, Ca²⁺ influx, high caspase-1 activity and cytochrome c content and leading to high cell viability. Overall, Nano-PM alleviated PCD and postharvest senescence of F. velutipes by regulating extracellular ATP.

Guidelines for evaluating myocardial cell death

Cell death is a fundamental process in cardiac pathologies. Recent studies have revealed multiple forms of cell death, and several of them have been demonstrated to underlie adverse cardiac remodeling and heart failure. With the expansion in the area of myocardial cell death and increasing concerns over rigor and reproducibility, it is important and timely to set a guideline for the best practices of evaluating myocardial cell death. There are six major forms of regulated cell death observed in cardiac pathologies, namely apoptosis, necroptosis, mitochondrial-mediated necrosis, pyroptosis, ferroptosis, and autophagic cell death. In this article, we describe the best methods to identify, measure, and evaluate these modes of myocardial cell death. In addition, we discuss the limitations of currently practiced myocardial cell death mechanisms.

Ageratina adenophora causes spleen toxicity by inducing oxidative stress and pyroptosis in mice

Ageratina adenophora is an invasive weed with potent toxicological effects on livestock. Oxidative stress and pyroptosis play a pivotal role in regulating animal or human health and disease. The object of this study was to determine the mechanism underlying splenic toxicity induced by A. adenophora in a mouse model. Ageratina adenophora significantly increased the levels of reactive oxygen species and malondialdehyde, but decreased the antioxidants like catalase, superoxide dismutase, glutathione and glutathione peroxidase. In addition, the activity of the antioxidant enzymes was also decreased upon A. adenophora treatment. The induction of the pyroptosis pathway was evaluated in terms of the expression levels of Nod-like receptor protein 3, nuclear factor-κB, caspase-1, gasdermin-D and interleukin-1β, all of which were significantly elevated by A. adenophora. These findings suggest that A. adenophora impairs spleen function in mice through oxidative stress damage and pyroptosis.