Cell Survival and Cytokine Release after Inflammasome Activation Is Regulated by the Toll-IL-1R Protein SARM

Overview of pyroptosis mechanism and in-depth analysis of cardiomyocyte pyroptosis mediated by NF-κB pathway in heart failure

The pyroptosis of cardiomyocytes has become an essential topic in heart failure research. The abnormal accumulation of these biological factors, including angiotensin II, advanced glycation end products, and various growth factors (such as connective tissue growth factor, vascular endothelial growth factor, transforming growth factor beta, among others), activates the nuclear factor-κB (NF-κB) signaling pathway in cardiovascular diseases, ultimately leading to pyroptosis of cardiomyocytes. Therefore, exploring the underlying molecular biological mechanisms is essential for developing novel drugs and therapeutic strategies. However, our current understanding of the precise regulatory mechanism of this complex signaling pathway in cardiomyocyte pyroptosis is still limited. Given this, this study reviews the milestone discoveries in the field of pyroptosis research since 1986, analyzes in detail the similarities, differences, and interactions between pyroptosis and other cell death modes (such as apoptosis, necroptosis, autophagy, and ferroptosis), and explores the deep connection between pyroptosis and heart failure. At the same time, it depicts in detail the complete pathway of the activation, transmission, and eventual cardiomyocyte pyroptosis of the NF-κB signaling pathway in the process of heart failure. In addition, the study also systematically summarizes various therapeutic approaches that can inhibit NF-κB to reduce cardiomyocyte pyroptosis, including drugs, natural compounds, small molecule inhibitors, gene editing, and other cutting-edge technologies, aiming to provide solid scientific support and new research perspectives for the prevention and treatment of heart failure.

Pyroptosis in health and disease: mechanisms, regulation and clinical perspective

Pyroptosis is a type of programmed cell death characterized by cell swelling and osmotic lysis, resulting in cytomembrane rupture and release of immunostimulatory components, which play a role in several pathological processes. Significant cellular responses to various stimuli involve the formation of inflammasomes, maturation of inflammatory caspases, and caspase-mediated cleavage of gasdermin. The function of pyroptosis in disease is complex but not a simple angelic or demonic role. While inflammatory diseases such as sepsis are associated with uncontrollable pyroptosis, the potent immune response induced by pyroptosis can be exploited as a therapeutic target for anti-tumor therapy. Thus, a comprehensive review of the role of pyroptosis in disease is crucial for further research and clinical translation from bench to bedside. In this review, we summarize the recent advancements in understanding the role of pyroptosis in disease, covering the related development history, molecular mechanisms including canonical, non-canonical, caspase 3/8, and granzyme-mediated pathways, and its regulatory function in health and multiple diseases. Moreover, this review also provides updates on promising therapeutic strategies by applying novel small molecule inhibitors and traditional medicines to regulate pyroptosis. The present dilemmas and future directions in the landscape of pyroptosis are also discussed from a clinical perspective, providing clues for scientists to develop novel drugs targeting pyroptosis.

SARM1-Dependent Axon Degeneration: Nucleotide Signaling, Neurodegenerative Disorders, Toxicity, and Therapeutic Opportunities

Axons are an essential component of the nervous system, and axon degeneration is an early feature of many neurodegenerative disorders. The NAD+ metabolome plays an essential role in regulating axonal integrity. Axonal levels of NAD+ and its precursor NMN are controlled in large part by the NAD+ synthesizing survival factor NMNAT2 and the pro-neurodegenerative NADase SARM1, whose activation triggers axon destruction. SARM1 has emerged as a promising axon-specific target for therapeutic intervention, and its function, regulation, structure, and role in neurodegenerative diseases have been extensively characterized in recent years. In this review, we first introduce the key molecular players involved in the SARM1-dependent axon degeneration program. Next, we summarize recent major advances in our understanding of how SARM1 is kept inactive in healthy neurons and how it becomes activated in injured or diseased neurons, which has involved important insights from structural biology. Finally, we discuss the role of SARM1 in neurodegenerative disorders and environmental neurotoxicity and its potential as a therapeutic target.

Bile acids attenuate hepatic inflammation during ischemia/reperfusion injury

Background & Aims

Persistent cholestasis has been associated with poor prognosis after orthotopic liver transplantation. In this study, we aimed to investigate how the accumulation of tauro-beta-muricholic acid (TβMCA), resulting from the reprogramming of bile acid (BA) metabolism during liver ischemia/reperfusion (IR) stress, attenuates liver inflammation.

Methods

Ingenuity Pathway Analysis was performed using transcriptome data from a murine hepatic IR model. Three different models of hepatic IR (liver warm IR, bile duct separation-IR, common bile duct ligation-IR) were employed. We generated adeno-associated virus-transfected mice and CD11b-DTR mice to assess the role of BAs in regulating the myeloid S1PR2-GSDMD axis. Hepatic BA levels were analyzed using targeted metabolomics. Finally, the correlation between the reprogramming of BA metabolism and hepatic S1PR2 levels was validated through RNA-seq of human liver transplant biopsies.

Results

We found that BA metabolism underwent reprogramming in murine hepatocytes under IR stress, leading to increased synthesis of TβMCA, catalyzed by the enzyme CYP2C70. The levels of hepatic TβMCA were negatively correlated with the severity of hepatic inflammation, as indicated by the serum IL-1β levels. Inhibition of hepatic CYP2C70 resulted in reduced TβMCA production, which subsequently increased serum IL-1β levels and exacerbated IR injury. Moreover, our findings suggested that TβMCA could inhibit canonical inflammasome activation in macrophages and attenuate inflammatory responses in a myeloid-specific S1PR2-GSDMD-dependent manner. Additionally, Gly-βMCA, a derivative of TβMCA, could effectively attenuate inflammatory injury in vivo and inhibit human macrophage pyroptosis in vitro.

Conclusions

IR stress orchestrates hepatic BA metabolism to generate TβMCA, which attenuates hepatic inflammatory injury by inhibiting the myeloid S1PR2-GSDMD axis. Bile acids have immunomodulatory functions in liver reperfusion injury that may guide therapeutic strategies.

Impact and implications

Our research reveals that liver ischemia-reperfusion stress triggers reprogramming of bile acid metabolism. This functions as an adaptive mechanism to mitigate inflammatory injury by regulating the S1PR2-GSDMD axis, thereby controlling the release of IL-1β from macrophages. Our results highlight the crucial role of bile acids in regulating hepatocyte-immune cell crosstalk, which demonstrates an immunomodulatory function in liver reperfusion injury that may guide therapeutic strategies targeting bile acids and their receptors.

The Role of the Nrf2 Pathway in Airway Tissue Damage Due to Viral Respiratory Infections

Respiratory viruses constitute a significant cause of illness and death worldwide. Respiratory virus-associated injuries include oxidative stress, ferroptosis, inflammation, pyroptosis, apoptosis, fibrosis, autoimmunity, and vascular injury. Several studies have demonstrated the involvement of the nuclear factor erythroid 2-related factor 2 (Nrf2) in the pathophysiology of viral infection and associated complications. It has thus emerged as a pivotal player in cellular defense mechanisms against such damage. Here, we discuss the impact of Nrf2 activation on airway injuries induced by respiratory viruses, including viruses, coronaviruses, rhinoviruses, and respiratory syncytial viruses. The inhibition or deregulation of Nrf2 pathway activation induces airway tissue damage in the presence of viral respiratory infections. In contrast, Nrf2 pathway activation demonstrates protection against tissue and organ injuries. Clinical trials involving Nrf2 agonists are needed to define the effect of Nrf2 therapeutics on airway tissues and organs damaged by viral respiratory infections.

SARM1 regulates pro-inflammatory cytokine expression in human monocytes by NADase-dependent and -independent mechanisms

SARM1 is a Toll-IL-1 receptor (TIR) domain-containing protein with roles in innate immunity and neuronal death in diverse organisms. Unlike other innate immune TIR proteins that function as adaptors for Toll-like receptors (TLRs), SARM1 has NADase activity, and this activity regulates murine neuronal cell death. However, whether human SARM1, and its NADase activity, are involved in innate immune regulation remains unclear. Here, we show that human SARM1 regulates proinflammatory cytokine expression in both an NADase-dependent and -independent manner in monocytes. SARM1 negatively regulated TLR4-dependent TNF mRNA induction independently of its NADase activity. In contrast, SARM1 inhibited IL-1β secretion through both NADase-dependent inhibition of pro-IL-1β expression, and NADase-independent suppression of the NLRP3 inflammasome and hence processing of pro-IL-1β to mature IL-1β. Our study reveals multiple mechanisms whereby SARM1 regulates pro-inflammatory cytokines in human monocytes and shows, compared to other mammalian TIR proteins, a distinct NADase-dependent role for SARM1 in innate immunity.

Inhibiting the SARM1-NAD+ axis reduces oxidative stress-induced damage to retinal and nerve cells

Retinal neurodegenerative diseases are a category of refractory blinding eye conditions closely associated with oxidative stress induced by mitochondrial dysfunction in retinal cells. SARM1, a core driver molecule leading to axonal degeneration, possesses NAD+ enzyme (NADase) activity. However, the role of the SARM1-NAD+ axis in oxidative stress-induced retinal cell death remains unclear. Here, we employed the SARM1 NADase inhibitor DSRM-3716 and established a glucose oxidase (GOx)-induced oxidative stress cell model. We found that compared to the GOx group, the DSRM-3716 pre-treated group reduced the hydrolysis of NAD+, inhibited the elevation of oxidative stress markers induced by GOx, decreased mitochondrial dysfunction, lowered the phosphorylation level of JNK, and attenuated the occurrence of pyroptosis in retinal and nerve cells, thereby providing protection for neurite growth. Further utilization of the JNK activator Anisomycin activated JNK, revealed that the JNK/c-Jun pathway down-regulated NMNAT2 expression. Consequently, it reduced cellular NAD+ synthesis, exacerbated mitochondrial dysfunction and cell pyroptosis, and reversed the protective effect of DSRM-3716 on cells. In summary, the inhibition of SARM1 NADase activity substantially mitigates oxidative damage to retinal cells and mitochondrial damage. Additionally, JNK simultaneously serves as both an upstream and downstream regulator in the SARM1-NAD+ axis, regulating retinal cell pyroptosis and neurite injury. Thus, this study provides new insights into the pathological processes of retinal cell oxidative stress and identifies potential therapeutic targets for retinal neurodegenerative diseases.

Hyperactivation of succinate dehydrogenase promotes pyroptosis of macrophage via ROS-induced GSDMD oligomerization in acute liver failure

Acute liver failure (ALF) is a life-threatening disease with high mortality. Given excessive inflammation is one of the major pathogenesis of ALF, candidates targeting inflammation could be beneficial in the condition. Now the effect of hyperactivated succinate dehydrogenase (SDH) on promoting inflammation in lipopolysaccharide (LPS)-treated macrophages has been studied. However, its role and mechanism in ALF is not well understood. Here intraperitoneal injection of D-galactosamine and LPS was conducted in male C57BL/6 J mice to induce the ALF model. Dimethyl malonate (DMM), which inhibited SDH activity, was injected intraperitoneally 30 min before ALF induction. Macrophage pyroptosis was induced by LPS plus adenosine triphosphate (ATP). Pyroptosis-related molecules and proteins including GSDMD oligomer were examined by ELISA and western blot techniques, respectively. ROS production was assessed by fluorescence staining. The study demonstrated SDH activity was increased in liver macrophages from ALF mice. Importantly, DMM administration inhibited ROS, IL-1β, and pyroptosis-associated proteins levels (NLRP3, cleaved caspase-1, GSDMD-N, and GSDMD oligomers) both in the ALF model and in macrophages stimulated with LPS plus ATP. In vitro, ROS promoted pyroptosis by facilitating GSDMD oligomerization. Additionally, when ROS levels were increased through the addition of H2O2 to the DMM group, the levels of GSDMD oligomers were reverted. In conclusion, SDH hyperactivation promotes macrophage pyroptosis by ROS-mediated GSDMD oligomerization, suggesting that targeting this pathway holds promise as a strategy for treating ALF and other inflammatory diseases.

NLRP inflammasomes in health and disease

NLRP inflammasomes are a group of cytosolic multiprotein oligomer pattern recognition receptors (PRRs) involved in the recognition of pathogen-associated molecular patterns (PAMPs) and danger-associated molecular patterns (DAMPs) produced by infected cells. They regulate innate immunity by triggering a protective inflammatory response. However, despite their protective role, aberrant NLPR inflammasome activation and gain-of-function mutations in NLRP sensor proteins are involved in occurrence and enhancement of non-communicating autoimmune, auto-inflammatory, and neurodegenerative diseases. In the last few years, significant advances have been achieved in the understanding of the NLRP inflammasome physiological functions and their molecular mechanisms of activation, as well as therapeutics that target NLRP inflammasome activity in inflammatory diseases. Here, we provide the latest research progress on NLRP inflammasomes, including NLRP1, CARD8, NLRP3, NLRP6, NLRP7, NLRP2, NLRP9, NLRP10, and NLRP12 regarding their structural and assembling features, signaling transduction and molecular activation mechanisms. Importantly, we highlight the mechanisms associated with NLRP inflammasome dysregulation involved in numerous human auto-inflammatory, autoimmune, and neurodegenerative diseases. Overall, we summarize the latest discoveries in NLRP biology, their forming inflammasomes, and their role in health and diseases, and provide therapeutic strategies and perspectives for future studies about NLRP inflammasomes.

The non-pathogenic protozoon Leishmania tarentolae interferes with the activation of NLRP3 inflammasome in human cells: new perspectives in the control of inflammation

Background

Innate immune responses against infectious agents can act as triggers of inflammatory diseases. On the other hand, various pathogens have developed mechanisms for the evasion of the immune response, based on an inhibition of innate immunity and inflammatory responses. Inflammatory diseases could thus be controlled through the administration of pathogens or pathogen-derived molecules, capable of interfering with the mechanisms at the basis of inflammation. In this framework, the NLRP3 inflammasome is an important component in innate antimicrobial responses and a major player in the inflammatory disease. Parasites of the genus Leishmania are master manipulators of innate immune mechanisms, and different species have been shown to inhibit inflammasome formation. However, the exploitation of pathogenic Leishmania species as blockers of NLRP3-based inflammatory diseases poses safety concerns.

Methods

To circumvent safety issues associated with pathogenic parasites, we focused on Leishmania tarentolae, a species of Leishmania that is not infectious to humans. Because NLRP3 typically develops in macrophages, in response to the detection and engulfment microorganisms, we performed our experiments on a monocyte-macrophage cell line (THP-1), either wild type or knockout for ASC, a key component of NLRP3 formation, with determination of cytokines and other markers of inflammation.

Results

L. tarentolae was shown to possess the capability of dampening the formation of NLRP3 inflammasome and the consequent expression of pro-inflammatory molecules, with minor differences compared to effects of pathogenic Leishmania species.

Conclusion

The non-pathogenic L. tarentolae appears a promising pro-biotic microbe with anti-inflammatory properties or a source of immune modulating cellular fractions or molecules, capable of interfering with the formation of the NLRP3 inflammasome.

Inhibition of CD38 enzymatic activity enhances CAR-T cell immune-therapeutic efficacy by repressing glycolytic metabolism

Chimeric antigen receptor (CAR)-T therapy has shown superior efficacy against hematopoietic malignancies. However, many patients failed to achieve sustainable tumor control partially due to CAR-T cell exhaustion and limited persistence. In this study, by performing single-cell multi-omics data analysis on patient-derived CAR-T cells, we identify CD38 as a potential hallmark of exhausted CAR-T cells, which is positively correlated with exhaustion-related transcription factors and further confirmed with in vitro exhaustion models. Moreover, inhibiting CD38 activity reverses tonic signaling- or tumor antigen-induced exhaustion independent of single-chain variable fragment design or costimulatory domain, resulting in improved CAR-T cell cytotoxicity and antitumor response. Mechanistically, CD38 inhibition synergizes the downregulation of CD38-cADPR -Ca2+ signaling and activation of the CD38-NAD+-SIRT1 axis to suppress glycolysis. Collectively, our findings shed light on the role of CD38 in CAR-T cell exhaustion and suggest potential clinical applications of CD38 inhibition in enhancing the efficacy and persistence of CAR-T cell therapy.

SARM1 regulates NAD+-linked metabolism and select immune genes in macrophages

Sterile alpha and HEAT/armadillo motif-containing protein (SARM1) was recently described as a NAD+-consuming enzyme and has previously been shown to regulate immune responses in macrophages. Neuronal SARM1 is known to contribute to axon degeneration due to its NADase activity. However, how SARM1 affects macrophage metabolism has not been explored. Here, we show that macrophages from Sarm1-/- mice display elevated NAD+ concentrations and lower cyclic ADP-ribose, a known product of SARM1-dependent NAD+ catabolism. Further, SARM1-deficient macrophages showed an increase in the reserve capacity of oxidative phosphorylation and glycolysis compared to WT cells. Stimulation of macrophages to a proinflammatory state by lipopolysaccharide (LPS) revealed that SARM1 restricts the ability of macrophages to upregulate glycolysis and limits the expression of the proinflammatory gene interleukin (Il) 1b, but boosts expression of anti-inflammatory Il10. In contrast, we show macrophages lacking SARM1 induced to an anti-inflammatory state by IL-4 stimulation display increased oxidative phosphorylation and glycolysis, and reduced expression of the anti-inflammatory gene, Fizz1. Overall, these data show that SARM1 fine-tunes immune gene transcription in macrophages via consumption of NAD+ and altered macrophage metabolism.

CRP, IL-1α, IL-1β, and IL-6 levels and the risk of breast cancer: a two-sample Mendelian randomization study

Epidemiological studies have reported a positive association between chronic inflammation and cancer risk. However, the causal association between chronic inflammation and breast cancer (BC) risk remains unclear. Here, we performed a Mendelian randomization study to investigate the etiological role of chronic inflammation in BC risk. We acquired data regarding C-reactive protein (CRP), interleukin (IL)-1a, IL-1b, and IL-6 expression and BC related to single nucleotide polymorphisms (SNPs) from two larger consortia (the genome-wide association studies and the Breast Cancer Association Consortium). Next, we conducted the two-sample Mendelian randomization study to investigate the relationship of the abovementioned inflammatory factors with the incidence of BC. We found that genetically predicted CRP, IL-6, and IL-1a levels did not increase BC incidence (odds ratio (OR)CRP 1.06, 95% confidence interval (CI) 0.98-1.12, P = 0.2059, ORIL-6 1.05, 95% CI 0.95-1.16, P = 0.3297 and ORIL-1a 1.01, 95% CI 0.99-1.03, P = 0.2167). However, in subgroup analysis, genetically predicted IL-1b levels increased ER + BC incidence (OR 1.15, 95% CI 1.03-1.27, P = 0.0088). Our study suggested that genetically predicted IL-1b levels were found to increase ER + BC susceptibility. However, due to the support of only one SNP, heterogeneity and pleiotropy tests cannot be performed, which deserves further research.

The Role of NMNAT2/SARM1 in Neuropathy Development

Chemotherapy-induced peripheral neuropathy (CIPN) commonly arises as a side effect of diverse cancer chemotherapy treatments. This condition presents symptoms such as numbness, tingling, and altered sensation in patients, often accompanied by neuropathic pain. Pathologically, CIPN is characterized by an intensive "dying-back" axonopathy, starting at the intra-epidermal sensory innervations and advancing retrogradely. The lack of comprehensive understanding regarding its underlying mechanisms explains the absence of effective treatments for CIPN. Recent investigations into axon degeneration mechanisms have pinpointed nicotinamide mononucleotide adenylyltransferase 2 (NMNAT2) and sterile alpha and TIR motif-containing 1 protein (SARM1) as pivotal mediators of injury-induced axonal degeneration. In this review, we aim to explore various studies shedding light on the interplay between NMNAT2 and SARM1 proteins and their roles in the progression of CIPN.

Nanomaterial-induced pyroptosis: a cell type-specific perspective

This review presents the advancements in nanomaterial (NM)-induced pyroptosis in specific types of cells. We elucidate the relevance of pyroptosis and delineate its mechanisms and classifications. We also retrospectively analyze pyroptosis induced by various NMs in a broad spectrum of non-tumorous cellular environments to highlight the multifunctionality of NMs in modulating cell death pathways. We identify key knowledge gaps in current research and propose potential areas for future exploration. This review emphasizes the need to focus on less-studied areas, including the pathways and mechanisms of NM-triggered pyroptosis in non-tumor-specific cell types, the interplay between biological and environmental factors, and the interactions between NMs and cells. This review aims to encourage further investigations into the complex interplay between NMs and pyroptosis, thereby providing a basis for developing safer and more effective nanomedical therapeutic applications.

Gasdermin E dictates inflammatory responses by controlling the mode of neutrophil death

Both lytic and apoptotic cell death remove senescent and damaged cells in living organisms. However, they elicit contrasting pro- and anti-inflammatory responses, respectively. The precise cellular mechanism that governs the choice between these two modes of death remains incompletely understood. Here we identify Gasdermin E (GSDME) as a master switch for neutrophil lytic pyroptotic death. The tightly regulated GSDME cleavage and activation in aging neutrophils are mediated by proteinase-3 and caspase-3, leading to pyroptosis. GSDME deficiency does not alter neutrophil overall survival rate; instead, it specifically precludes pyroptosis and skews neutrophil death towards apoptosis, thereby attenuating inflammatory responses due to augmented efferocytosis of apoptotic neutrophils by macrophages. In a clinically relevant acid-aspiration-induced lung injury model, neutrophil-specific deletion of GSDME reduces pulmonary inflammation, facilitates inflammation resolution, and alleviates lung injury. Thus, by controlling the mode of neutrophil death, GSDME dictates host inflammatory outcomes, providing a potential therapeutic target for infectious and inflammatory diseases.

Sarm1 knockout prevents type 1 diabetic bone disease in females independent of neuropathy

Patients with diabetes have a high risk of developing skeletal diseases accompanied by diabetic peripheral neuropathy (DPN). In this study, we isolated the role of DPN in skeletal disease with global and conditional knockout models of sterile-α and TIR-motif-containing protein-1 (Sarm1). SARM1, an NADase highly expressed in the nervous system, regulates axon degeneration upon a range of insults, including DPN. Global knockout of Sarm1 prevented DPN, but not skeletal disease, in male mice with type 1 diabetes (T1D). Female wild-type mice also developed diabetic bone disease but without DPN. Unexpectedly, global Sarm1 knockout completely protected female mice from T1D-associated bone suppression and skeletal fragility despite comparable muscle atrophy and hyperglycemia. Global Sarm1 knockout rescued bone health through sustained osteoblast function with abrogation of local oxidative stress responses. This was independent of the neural actions of SARM1, as beneficial effects on bone were lost with neural conditional Sarm1 knockout. This study demonstrates that the onset of skeletal disease occurs rapidly in both male and female mice with T1D completely independently of DPN. In addition, this reveals that clinical SARM1 inhibitors, currently being developed for treatment of neuropathy, may also have benefits for diabetic bone through actions outside of the nervous system.

The pathogenesis and potential therapeutic targets in sepsis

Sepsis is defined as "a life-threatening organ dysfunction caused by dysregulated host systemic inflammatory and immune response to infection." At present, sepsis continues to pose a grave healthcare concern worldwide. Despite the use of supportive measures in treating traditional sepsis, such as intravenous fluids, vasoactive substances, and oxygen plus antibiotics to eradicate harmful pathogens, there is an ongoing increase in both the morbidity and mortality associated with sepsis during clinical interventions. Therefore, it is urgent to design specific pharmacologic agents for the treatment of sepsis and convert them into a novel targeted treatment strategy. Herein, we provide an overview of the molecular mechanisms that may be involved in sepsis, such as the inflammatory response, immune dysfunction, complement deactivation, mitochondrial damage, and endoplasmic reticulum stress. Additionally, we highlight important targets involved in sepsis-related regulatory mechanisms, including GSDMD, HMGB1, STING, and SQSTM1, among others. We summarize the latest advancements in potential therapeutic drugs that specifically target these signaling pathways and paramount targets, covering both preclinical studies and clinical trials. In addition, this review provides a detailed description of the crosstalk and function between signaling pathways and vital targets, which provides more opportunities for the clinical development of new treatments for sepsis.

Phosphorylated SARM1 is involved in the pathological process of rotenone-induced neurodegeneration

Sterile alpha and Toll/interleukin receptor motif-containing protein 1 (SARM1) is a NAD+ hydrolase that plays a key role in axonal degeneration and neuronal cell death. We reported that c-Jun N-terminal kinase (JNK) activates SARM1 through phosphorylation at Ser-548. The importance of SARM1 phosphorylation in the pathological process of Parkinson's disease (PD) has not been determined. We thus conducted the present study by using rotenone (an inducer of PD-like pathology) and neurons derived from induced pluripotent stem cells (iPSCs) from healthy donors and a patient with familial PD PARK2 (FPD2). The results showed that compared to the healthy neurons, FPD2 neurons were more vulnerable to rotenone-induced stress and had higher levels of SARM1 phosphorylation. Similar cellular events were obtained when we used PARK2-knockdown neurons derived from healthy donor iPSCs. These events in both types of PD-model neurons were suppressed in neurons treated with JNK inhibitors, Ca2+-signal inhibitors, or by a SARM1-knockdown procedure. The degenerative events were enhanced in neurons overexpressing wild-type SARM1 and conversely suppressed in neurons overexpressing the SARM1-S548A mutant. We also detected elevated SARM1 phosphorylation in the midbrain of PD-model mice. The results indicate that phosphorylated SARM1 plays an important role in the pathological process of rotenone-induced neurodegeneration.

NLRP3 and cancer: Pathogenesis and therapeutic opportunities

More than a decade ago IL-1 blockade was suggested as an add-on therapy for the treatment of cancer. This proposal was based on the overall safety record of anti-IL-1 biologics and the anti-tumor properties of IL-1 blockade in animal models of cancer. Today, a new frontier in IL-1 activity regulation has developed with several orally active NLRP3 inhibitors currently in clinical trials, including cancer. Despite an increasing body of evidence suggesting a role of NLRP3 and IL-1-mediated inflammation driving cancer initiation, immunosuppression, growth, and metastasis, NLRP3 activation in cancer remains controversial. In this review, we discuss the recent advances in the understanding of NLRP3 activation in cancer. Further, we discuss the current opportunities for NLRP3 inhibition in cancer intervention with novel small molecules.

Pyroptosis: the potential eye of the storm in adult-onset Still's disease

Pyroptosis, a form of programmed cell death with a high pro-inflammatory effect, causes cell lysis and leads to the secretion of countless interleukin-1β (IL-1β) and IL-18 cytokines, resulting in a subsequent extreme inflammatory response through the caspase-1-dependent pathway or caspase-1-independent pathway. Adult-onset Still's disease (AOSD) is a systemic inflammatory disease with extensive disease manifestations and severe complications such as macrophage activation syndrome, which is characterized by high-grade inflammation and cytokine storms regulated by IL-1β and IL-18. To date, the pathogenesis of AOSD is unclear, and the available therapy is unsatisfactory. As such, AOSD is still a challenging disease. In addition, the high inflammatory states and the increased expression of multiple pyroptosis markers in AOSD indicate that pyroptosis plays an important role in the pathogenesis of AOSD. Accordingly, this review summarizes the molecular mechanisms of pyroptosis and describes the potential role of pyroptosis in AOSD, the therapeutic practicalities of pyroptosis target drugs in AOSD, and the therapeutic blueprint of other pyroptosis target drugs.

Circumventing pyroptosis via hyperactivation shapes superior immune responses of human type 2 dendritic cells compared to type 3 dendritic cells

Exploiting inflammasome activation in dendritic cells (DCs) is a promising approach to fight cancer and to augment adjuvant-induced immune responses. As inflammasome formation is typically accompanied by pyroptosis, hyperactivation-defined as inflammasome activation in the absence of pyroptosis-represents a mechanism of circumventing cell death of DCs while simultaneously benefitting from inflammasome signaling. We previously demonstrated a unique specialization for inflammasome responses and hyperactivation of human cDC2 among all human DC subsets. As recent investigations revealed heterogeneity among the human cDC2 population, we aimed to analyze whether the two recently identified cDC2 subpopulations DC2 and DC3 harbor similar or different inflammasome characteristics. Here, we report that both DC2 and DC3 are inflammasome competent. We show that DC3 generally induce stronger inflammasome responses, which are associated with higher levels of cell death. Although DC2 release lower levels of inflammasome-dependent IL-1β, they induce stronger CD4+ T cell responses than DC3, which are predominantly skewed toward a TH 1/TH 17 phenotype. Thus, mainly DC2 seem to be able to enter a state of hyperactivation, resulting in enhanced T cell stimulatory capacity.

Pyroptosis modulation by bacterial effector proteins

Pyroptosis is a proinflammatory form of programmed cell death featured with membrane pore formation that causes cellular swelling and allows the release of intracellular inflammatory mediators. This cell death process is elicited by the activation of the pore-forming proteins named gasdermins, and is intricately orchestrated by diverse regulatory factors in mammalian hosts to exert a prompt immune response against infections. However, growing evidence suggests that bacterial pathogens have evolved to regulate host pyroptosis for evading immune clearance and establishing progressive infection. In this review, we highlight current understandings of the functional role and regulatory network of pyroptosis in host antibacterial immunity. Thereafter, we further discuss the latest advances elucidating the mechanisms by which bacterial pathogens modulate pyroptosis through adopting their effector proteins to drive infections. A better understanding of regulatory mechanisms underlying pyroptosis at the interface of host-bacterial interactions will shed new light on the pathogenesis of infectious diseases and contribute to the development of promising therapeutic strategies against bacterial pathogens.

Gasdermin-E mediates mitochondrial damage in axons and neurodegeneration

Mitochondrial dysfunction and axon loss are hallmarks of neurologic diseases. Gasdermin (GSDM) proteins are executioner pore-forming molecules that mediate cell death, yet their roles in the central nervous system (CNS) are not well understood. Here, we find that one GSDM family member, GSDME, is expressed by both mouse and human neurons. GSDME plays a role in mitochondrial damage and axon loss. Mitochondrial neurotoxins induced caspase-dependent GSDME cleavage and rapid localization to mitochondria in axons, where GSDME promoted mitochondrial depolarization, trafficking defects, and neurite retraction. Frontotemporal dementia (FTD)/amyotrophic lateral sclerosis (ALS)-associated proteins TDP-43 and PR-50 induced GSDME-mediated damage to mitochondria and neurite loss. GSDME knockdown protected against neurite loss in ALS patient iPSC-derived motor neurons. Knockout of GSDME in SOD1G93A ALS mice prolonged survival, ameliorated motor dysfunction, rescued motor neuron loss, and reduced neuroinflammation. We identify GSDME as an executioner of neuronal mitochondrial dysfunction that may contribute to neurodegeneration.

Capsaicin receptor TRPV1 maintains quiescence of hepatic stellate cells in the liver via recruitment of SARM1

BACKGROUND & AIMS

Capsaicin receptor, also known as transient receptor potential vanilloid 1 (TRPV1), is involved in pain physiology and neurogenic inflammation. Herein, we discovered the presence of TRPV1 in hepatic stellate cells (HSCs) and aimed to delineate its function in this cell type and liver fibrosis.

METHODS

TRPV1 expression was examined in liver biopsies from patients with liver fibrosis using quantitative real-time PCR and immunostaining. Its contribution to liver fibrosis was examined in Trpv1^-/- mice, upon lentiviral delivery of the TRPV1 gene, and in human and mouse primary HSCs, using patch clamp, intracellular Ca²⁺ mobilization determination, FACS analyses and gain/loss of function experiments. Binding of sterile alpha and Toll/interleukin-1 receptor motif-containing protein 1 (SARM1) to TRPV1 was determined using mass spectrometry, co-immunoprecipitation, surface plasmon resonance, bioluminescence resonance energy transfer, and NanoBiT.

RESULTS

TRPV1 mRNA levels are significantly downregulated in patients with liver fibrosis and mouse models, showing a negative correlation with F stage and α-smooth muscle actin expression, a marker of HSC activation. TRPV1 expression and function decrease during HSC activation in fibrotic livers in vivo or during culture. Genetic and pharmacological inhibition of TRPV1 in quiescent HSCs leads to NF-κB activation and pro-inflammatory cytokine production. TRPV1 requires binding of its N-terminal ankyrin repeat domain to the TIR-His583 (Toll/interleukin-1 receptor) domain of SARM1 to prevent HSCs from pro-inflammatory activation. Trpv1^-/- mice display increased HSC activation and more severe liver fibrosis, whereas TRPV1 overexpression is antifibrotic in various disease models.

CONCLUSION

The antifibrotic properties of TRPV1 are attributed to the prevention of HSC activation via the recruitment of SARM1, which could be an attractive therapeutic strategy against liver fibrosis.

IMPACT AND IMPLICATIONS

We identified the neuronal channel protein TRPV1 as a gatekeeper of quiescence in hepatic stellate cells, a key driver of liver fibrogenesis and chronic liver disease. Physiologically expressed in healthy liver and consistently downregulated during liver fibrosis development, its therapeutic re-expression is expected to have few side effects, making it an attractive target diagnostic tool and drug candidate for industry and clinicians.

Benchmarking omics-based prediction of asthma development in children

BACKGROUND

Asthma is a heterogeneous disease with high morbidity. Advancement in high-throughput multi-omics approaches has enabled the collection of molecular assessments at different layers, providing a complementary perspective of complex diseases. Numerous computational methods have been developed for the omics-based patient classification or disease outcome prediction. Yet, a systematic benchmarking of those methods using various combinations of omics data for the prediction of asthma development is still lacking.

OBJECTIVE

We aimed to investigate the computational methods in disease status prediction using multi-omics data.

METHOD

We systematically benchmarked 18 computational methods using all the 63 combinations of six omics data (GWAS, miRNA, mRNA, microbiome, metabolome, DNA methylation) collected in The Vitamin D Antenatal Asthma Reduction Trial (VDAART) cohort. We evaluated each method using standard performance metrics for each of the 63 omics combinations.

RESULTS

Our results indicate that overall Logistic Regression, Multi-Layer Perceptron, and MOGONET display superior performance, and the combination of transcriptional, genomic and microbiome data achieves the best prediction. Moreover, we find that including the clinical data can further improve the prediction performance for some but not all the omics combinations.

CONCLUSIONS

Specific omics combinations can reach the optimal prediction of asthma development in children. And certain computational methods showed superior performance than other methods.

NAD+-Consuming Enzymes in Stem Cell Homeostasis

Nicotinamide adenine dinucleotide (NAD⁺) is a coenzyme used in redox reactions, energy metabolism, and mitochondrial biogenesis. NAD⁺ is also required as a cofactor by nonredox NAD⁺-dependent enzymes. Hundreds of enzymes that consume NAD⁺ have been identified. The NAD⁺-consuming enzymes are involved in a variety of cellular processes such as signal transduction, DNA repair, cellular senescence, and stem cell (SC) homeostasis. In this review, we discussed how different types of NAD⁺-consuming enzymes regulate SC functions and summarized current research on the roles of the NAD⁺ consumers in SC homeostasis. We hope to provide a more global and integrative insight to the mechanism and intervention of SC homeostasis via the regulation of the NAD⁺-consuming enzymes.

Pyroptosis in bone loss

Pyroptosis could be responsible for the bone loss from bone metabolic diseases, leading to the negative impact on people's health and life. It has been shown that osteoclasts, osteoblasts, macrophages, chondrocytes, periodontal and gingival cells may be involved in bone loss linked with pyroptosis. So far, the involved mechanisms have not been fully elucidated. In this review, we introduced the related cells involved in the pyroptosis associated with bone loss and summarized the role of these cells in the bone metabolism during the process of pyroptosis. We also discuss the clinical potential of targeting mechanisms in the osteoclasts, osteoblasts, macrophages, chondrocytes, periodontal and gingival cells touched upon pyroptosis to treat bone loss from bone metabolic diseases as well as the challenges of avoiding potential side effects and producing efficient treatment methods.

Uncoupled pyroptosis and IL-1β secretion downstream of inflammasome signaling

Inflammasomes are supramolecular platforms that organize in response to various damage-associated molecular patterns and pathogen-associated molecular patterns. Upon activation, inflammasome sensors (with or without the help of ASC) activate caspase-1 and other inflammatory caspases that cleave gasdermin D and pro-IL-1β/pro-IL-18, leading to pyroptosis and mature cytokine secretion. Pyroptosis enables intracellular pathogen niche disruption and intracellular content release at the cost of cell death, inducing pro-inflammatory responses in the neighboring cells. IL-1β is a potent pro-inflammatory regulator for neutrophil recruitment, macrophage activation, and T-cell expansion. Thus, pyroptosis and cytokine secretion are the two main mechanisms that occur downstream of inflammasome signaling; they maintain homeostasis, drive the innate immune response, and shape adaptive immunity. This review aims to discuss the possible mechanisms, timing, consequences, and significance of the two uncoupling preferences downstream of inflammasome signaling. While pyroptosis and cytokine secretion may be usually coupled, pyroptosis-predominant and cytokine-predominant uncoupling are also observed in a stimulus-, cell type-, or context-dependent manner, contributing to the pathogenesis and development of numerous pathological conditions such as cryopyrin-associated periodic syndromes, LPS-induced sepsis, and Salmonella enterica serovar Typhimurium infection. Hyperactive cells consistently release IL-1β without LDH leakage and pyroptotic death, thereby leading to prolonged inflammation, expanding the lifespans of pyroptosis-resistant neutrophils, and hyperactivating stimuli-challenged macrophages, dendritic cells, monocytes, and specific nonimmune cells. Death inflammasome activation also induces GSDMD-mediated pyroptosis with no IL-1β secretion, which may increase lethality in vivo. The sublytic GSDMD pore formation associated with lower expressions of pyroptotic components, GSDMD-mediated extracellular vesicles, or other GSDMD-independent pathways that involve unconventional secretion could contribute to the cytokine-predominant uncoupling; the regulation of caspase-1 dynamics, which may generate various active species with different activities in terms of GSDMD or pro-IL-1β, could lead to pyroptosis-predominant uncoupling. These uncoupling preferences enable precise reactions to different stimuli of different intensities under specific conditions at the single-cell level, promoting cooperative cell and host fate decisions and participating in the pathogen "game". Appropriate decisions in terms of coupling and uncoupling are required to heal tissues and eliminate threats, and further studies exploring the inflammasome tilt toward pyroptosis or cytokine secretion may be helpful.

Deciphering the Role of Pyroptosis Impact on Cardiovascular Diseases

Pyroptosis has become a noteworthy area of focus in recent years due to its association with inflammatory diseases. Pyroptosis is a type of programmed cell death accompanied by an inflammatory response, and the discovery of the gasdermin family has expanded the study of pyroptosis. The primary characteristics of pyroptosis include cell expansion, membrane penetration, and the ejection of cell contents. In healthy physiology, pyroptosis is an essential part of the host's defence against pathogen infection. Excessive Pyroptosis, however, can lead to unchecked and persistent inflammatory responses, including the emergence of inflammatory diseases. More precisely, gasdermin family members have a role in the creation of membrane holes during pyroptosis, which leads to cell lysis. It is also related to how pro-inflammatory intracellular substances, including IL-1, IL-18, and High mobility group box 1 (HMGB1), are used. Two different signalling pathways, one of which is regulated by caspase-1 and the other by caspase-4/5/11, are the primary causes of pyroptosis. Cardiovascular diseases are often associated with cell death and acute or chronic inflammation, making this area of research particularly relevant. In this review, we first systematically summarize recent findings related to Pyroptosis, exploring its characteristics and the signalling pathway mechanisms, as well as various treatment strategies based on its modulation that has emerged from the studies. Some of these strategies are currently undergoing clinical trials. Additionally, the article elaborates on the scientific evidence indicating the role of Pyroptosis in various cardiovascular diseases. As a whole, this should shed insight into future paths and present innovative ideas for employing Pyroptosis as a strong disease-fighting weapon.

The curious case of SARM1: Dr. Jekyll and Mr. Hyde in cell death and immunity?

Sterile alpha and toll/interleukin-1 receptor motif-containing protein 1 (SARM1) was first identified as a novel ortholog of Drosophila protein CG7915 and was subsequently placed as the fifth member of the human TIR-containing adaptor protein. SARM1 holds a unique position in this family where, unlike other members, it downregulates NFκB activity in response to immunogenic stimulation, interacts with another member of the family, TRIF, to negatively regulate its function, and it also mediates cell death responses. Over the past decade, SARM1 has emerged as one of the primary mediators of programmed axonal degeneration and this robust regulation of axonal degeneration-especially in models of peripheral neuropathy and traumatic injury-makes it an attractive target for therapeutic intervention. The TIR domain of SARM1 possesses an intrinsic NADase activity resulting in cellular energy deficits within the axons, a striking deviation from its other family members of human TLR adaptors. Interestingly, the TIR NADase activity, as seen in SARM1, is also observed in several prokaryotic TIR-containing proteins where they are involved in immune evasion once within the host. Although the immune function of SARM1 is yet to be conclusively discerned, this closeness in function with the prokaryotic TIR-domain containing proteins, places it at an interesting juncture of evolution raising questions about its origin and function in cell death and immunity. In this review, we discuss how a conserved immune adaptor protein like SARM1 switches to a pro-neurodegenerative function and the evolutionarily significance of the process.

Caspase-1 and the inflammasome promote polycystic kidney disease progression

We and others have previously shown that the presence of renal innate immune cells can promote polycystic kidney disease (PKD) progression. In this study, we examined the influence of the inflammasome, a key part of the innate immune system, on PKD. The inflammasome is a system of molecular sensors, receptors, and scaffolds that responds to stimuli like cellular damage or microbes by activating Caspase-1, and generating critical mediators of the inflammatory milieu, including IL-1β and IL-18. We provide evidence that the inflammasome is primed in PKD, as multiple inflammasome sensors were upregulated in cystic kidneys from human ADPKD patients, as well as in kidneys from both orthologous (PKD1 RC/RC or RC/RC) and non-orthologous (jck) mouse models of PKD. Further, we demonstrate that the inflammasome is activated in female RC/RC mice kidneys, and this activation occurs in renal leukocytes, primarily in CD11c+ cells. Knock-out of Casp1, the gene encoding Caspase-1, in the RC/RC mice significantly restrained cystic disease progression in female mice, implying sex-specific differences in the renal immune environment. RNAseq analysis implicated the promotion of MYC/YAP pathways as a mechanism underlying the pro-cystic effects of the Caspase-1/inflammasome in females. Finally, treatment of RC/RC mice with hydroxychloroquine, a widely used immunomodulatory drug that has been shown to inhibit the inflammasome, protected renal function specifically in females and restrained cyst enlargement in both male and female RC/RC mice. Collectively, these results provide evidence for the first time that the activated Caspase-1/inflammasome promotes cyst expansion and disease progression in PKD, particularly in females. Moreover, the data suggest that this innate immune pathway may be a relevant target for therapy in PKD.

Pyroptosis in development, inflammation and disease

In the early 2000s, caspase-1, an important molecule that has been shown to be involved in the regulation of inflammation, cell survival and diseases, was given a new function: regulating a new mode of cell death that was later defined as pyroptosis. Since then, the inflammasome, the inflammatory caspases (caspase-4/5/11) and their substrate gasdermins (gasdermin A, B, C, D, E and DFNB59) has also been reported to be involved in the pyroptotic pathway, and this pathway is closely related to the development of various diseases. In addition, important apoptotic effectors caspase-3/8 and granzymes have also been reported to b involved in the induction of pyroptosis. In our article, we summarize findings that help define the roles of inflammasomes, inflammatory caspases, gasdermins, and other mediators of pyroptosis, and how they determine cell fate and regulate disease progression.

Astrocytic SARM1 promotes neuroinflammation and axonal demyelination in experimental autoimmune encephalomyelitis through inhibiting GDNF signaling

Astrocytes are important components of the innate immune response in the central nervous system (CNS), involving in the inflammatory and neurotoxic responses that occur in CNS diseases, such as multiple sclerosis (MS). Recent studies have shown that SARM1 plays a critical role in axonal degeneration and inflammation. However, the detailed role of astrocytic SARM1 in MS remains unclear. Here, we established the MS model of mice - experimental autoimmune encephalomyelitis (EAE) and found that SARM1 was upregulated in astrocytes of the spinal cords of EAE mice. Moreover, conditional knockout of astrocytic SARM1 (SARM1GFAP-CKO mice, SARM1Aldh1L1-CKO mice) delayed EAE with later onset, alleviated the inflammatory infiltration, and inhibited the demyelination and neuronal death. Mechanically, RNA-seq revealed that the expression of glial-derived neurotrophic factor (GDNF) was upregulated in SARM1-/- astrocytes. Western blot and immunostaining further confirmed the upregulation of GDNF in spinal cord astrocytes of SARM1GFAP-CKO EAE mice. Interestingly, the downregulation of GDNF by streptozotocin (STZ, a drug used to downregulate GDNF) treatment worsened the deficits of SARM1GFAP-CKO EAE mice. These findings identify that astrocytic SARM1 promotes neuroinflammation and axonal demyelination in EAE by inhibiting the expression of GDNF, reveal the novel role of SARM1/GDNF signaling in EAE, and provide new therapeutic ideas for the treatment of MS.

Klebsiella pneumoniae hijacks the Toll-IL-1R protein SARM1 in a type I IFN-dependent manner to antagonize host immunity

Many bacterial pathogens antagonize host defense responses by translocating effector proteins into cells. It remains an open question how those pathogens not encoding effectors counteract anti-bacterial immunity. Here, we show that Klebsiella pneumoniae exploits the evolutionary conserved innate protein SARM1 to regulate negatively MyD88- and TRIF-governed inflammation, and the activation of the MAP kinases ERK and JNK. SARM1 is required for Klebsiella induction of interleukin-10 (IL-10) by fine-tuning the p38-type I interferon (IFN) axis. SARM1 inhibits the activation of Klebsiella-induced absent in melanoma 2 inflammasome to limit IL-1β production, suppressing further inflammation. Klebsiella exploits type I IFNs to induce SARM1 in a capsule and lipopolysaccharide O-polysaccharide-dependent manner via the TLR4-TRAM-TRIF-IRF3-IFNAR1 pathway. Absence of SARM1 reduces the intracellular survival of K. pneumoniae in macrophages, whereas sarm1-deficient mice control the infection. Altogether, our results illustrate an anti-immunology strategy deployed by a human pathogen. SARM1 inhibition will show a beneficial effect to treat Klebsiella infections.

Toll-Like Receptor 3 in Cardiovascular Diseases

Toll-like receptor 3 (TLR3) is an important member of the innate immune response receptor toll-like receptors (TLRs) family, which plays a vital role in regulating immune response, promoting the maturation and differentiation of immune cells, and participating in the response of pro-inflammatory factors. TLR3 is activated by pathogen-associated molecular patterns and damage-associated molecular patterns, which support the pathophysiology of many diseases related to inflammation. An increasing number of studies have confirmed that TLR3, as a crucial medium of innate immunity, participates in the occurrence and development of cardiovascular diseases (CVDs) by regulating the transcription and translation of various cytokines, thus affecting the structure and physiological function of resident cells in the cardiovascular system, including vascular endothelial cells, vascular smooth muscle cells, cardiomyocytes, fibroblasts and macrophages. The dysfunction and structural damage of vascular endothelial cells and proliferation of vascular smooth muscle cells are the key factors in the occurrence of vascular diseases such as pulmonary arterial hypertension, atherosclerosis, myocardial hypertrophy, myocardial infarction, ischaemia/reperfusion injury, and heart failure. Meanwhile, cardiomyocytes, fibroblasts, and macrophages are involved in the development of CVDs. Therefore, the purpose of this review was to explore the latest research published on TLR3 in CVDs and discuss current understanding of potential mechanisms by which TLR3 contributes to CVDs. Even though TLR3 is a developing area, it has strong treatment potential as an immunomodulator and deserves further study for clinical translation.

Ainsliadimer C, a disesquiterpenoid isolated from Ainsliaea macrocephala, ameliorates inflammatory responses in adipose tissue via Sirtuin 1-NLRP3 inflammasome axis

Interleukin-1β (IL-1β), a key pro-inflammatory cytokine, is majorly produced by macrophages through NOD-, LRR-, and pyrin domain-containing protein 3 (NLRP3) inflammasome, which has been identified as the culprit to deteriorate the inflammatory crosstalk between macrophages and adipocytes. Ainsliadimer C (AC) is a disesquiterpenoid isolated from Ainsliaea macrocephala. In the current study, we investigated the effects of AC on adipose tissue inflammation in co-culture of macrophages and adipocytes in vitro as well as in LPS-treated mice in vivo. We showed that AC (20-80 µM) dose-dependently inhibited the secretion of IL-1β from LPS plus ATP-stimulated THP-1 macrophages by inhibiting the activation of NLRP3 inflammasome. Furthermore, we found that AC treatment activated NAD⁺-dependent deacetylase Sirtuin 1 (SIRT1), resulting in reduced acetylation level of NLRP3. Molecular modeling analysis revealed that binding of AC to sirtuin-activating compound-binding domain increased the affinity of the substrate to the catalytic domain of SIRT1. Moreover, AC (80 µM) significantly attenuated macrophage-conditioned medium-induced inflammatory responses in 3T3-L1 adipocytes. In LPS-induced acute inflammatory mice, administration of AC (20, 60 mg·kg^-1·d^-1, ip) for 5 days significantly suppressed the pro-inflammatory cytokine levels in serum and epididymal white adipose tissue (eWAT), attenuated macrophage infiltration into eWAT, and mitigated adipose tissue inflammation. The beneficial effects of AC were blocked by co-administration of a selective SIRT1 inhibitor EX-527 (10 mg·kg^-1·d^-1). Taken together, AC suppresses NLRP3-mediated IL-1β secretion through activating SIRT1, leading to attenuated inflammation in macrophages and adipose tissue, which might be a candidate to treat obesity-associated metabolic diseases.

The Regulation and Modification of GSDMD Signaling in Diseases

Gasdermin D (GSDMD) serves as a key executor to trigger pyroptosis and is emerging as an attractive checkpoint in host defense, inflammatory, autoimmune diseases, and many other systemic diseases. Although canonical and non-canonical inflammasome-mediated classic GSDMD cleavage, GSDMD-NT migration to cell membrane, GSDMD-NT oligomerization, and pore forming have been well recognized, a few unique features of GSDMD in specific condition beyond its classic function, including non-lytic function of GSDMD, the modification and regulating mechanism of GSDMD signaling have also come to great attention and played a crucial role in biological processes and diseases. In the current review, we emphasized the GSDMD protein expression, stabilization, modification, activation, pore formation, and repair during pyroptosis, especially the regulation and modification of GSDMD signaling, such as GSDMD complex in polyubiquitination and non-pyroptosis release of IL-1β, ADP-riboxanation, NINJ1 in pore forming, GSDMD binding protein TRIM21, GSDMD succination, and Regulator-Rag-mTOR-ROS regulation of GSDMD. We also discussed the novel therapeutic strategies of targeting GSDMD and summarized recently identified inhibitors with great prospect.

Insights into inflammasome regulation: cellular, molecular, and pathogenic control of inflammasome activation

Maintenance of immune homeostasis is an intricate process wherein inflammasomes play a pivotal role by contributing to innate and adaptive immune responses. Inflammasomes are ensembles of adaptor proteins that can trigger a signal following innate sensing of pathogens or non-pathogens eventuating in the inductions of IL-1β and IL-18. These inflammatory cytokines substantially influence the antigen-presenting cell's costimulatory functions and T helper cell differentiation, contributing to adaptive immunity. As acute and chronic disease conditions may accompany parallel tissue damage, we analyze the critical role of extracellular factors such as cytokines, amyloids, cholesterol crystals, etc., intracellular metabolites, and signaling molecules regulating inflammasome activation/inhibition. We develop an operative framework for inflammasome function and regulation by host cell factors and pathogens. While inflammasomes influence the innate and adaptive immune components' interplay modulating the anti-pathogen adaptive immune response, pathogens may target inflammasome inhibition as a survival strategy. As trapped between health and diseases, inflammasomes serve as promising therapeutic targets and their modus operandi serves as a scientific rationale for devising better therapeutic strategies.

The central inflammasome adaptor protein ASC activates the inflammasome after transition from a soluble to an insoluble state

Apoptosis-associated speck-like protein containing a caspase recruitment domain (CARD) (ASC) is a 22 kDa protein that functions as the central adaptor for inflammasome assembly. ASC forms insoluble specks in monocytes undergoing pyroptosis, and the polymerization of ASC provides a template of CARDs that leads to proximity-mediated autoactivation of caspase-1 in canonical inflammasomes. However, specks are insoluble protein complexes, and solubility is typically important for protein function. Therefore, we sought to define whether ASC specks comprise active inflammasome complexes or are simply the end stage of exhausted ASC polymers. Using a THP-1 cell–lysing model of caspase-1 activation that is ASC dependent, we compared caspase-1 activation induced by preassembled insoluble ASC specks and soluble monomeric forms of ASC. Unexpectedly, after controlling for the concentration dependence of ASC oligomerization, we found that only insoluble forms of ASC promoted caspase-1 autocatalysis. This link to insolubility was recapitulated with recombinant ASC. We show that purified recombinant ASC spontaneously precipitated and was functional, whereas the maltose-binding protein–ASC fusion to ASC (promoting enhanced solubility) was inactive until induced to insolubility by binding to amylose beads. This functional link to insolubility also held true for the Y146A mutation of the CARD of ASC, which avoids insolubility and caspase-1 activation. Thus, we conclude that the role of ASC insolubility in inflammasome function is inextricably linked to its pyrin domain–mediated and CARD-mediated polymerizations. These findings will support future studies into the molecular mechanisms controlling ASC solubility.

Specific NLRP3 Inflammasome Assembling and Regulation in Neutrophils: Relevance in Inflammatory and Infectious Diseases

The NLRP3 inflammasome is a cytosolic multimeric protein platform that leads to the activation of the protease zymogen, caspase-1 (CASP1). Inflammasome activation mediates the proteolytic activation of pro-inflammatory cytokines (IL-1β and IL-18) and program cell death called pyroptosis. The pyroptosis is mediated by the protein executioner Gasdermin D (GSDMD), which forms pores at the plasma membrane to facilitate IL-1β/IL-18 secretion and causes pyroptosis. The NLRP3 inflammasome is activated in response to a large number of pathogenic and sterile insults. However, an uncontrolled inflammasome activation may drive inflammation-associated diseases. Initially, inflammasome-competent cells were believed to be limited to macrophages, dendritic cells (DC), and monocytes. However, emerging evidence indicates that neutrophils can assemble inflammasomes in response to various stimuli with functional relevance. Interestingly, the regulation of inflammasome in neutrophils appears to be unconventional. This review provides a broad overview of the role and regulation of inflammasomes—and more specifically NLRP3—in neutrophils.

SARM1 Promotes Photoreceptor Degeneration in an Oxidative Stress Model of Retinal Degeneration

SARM1 (sterile alpha and armadillo motif-containing protein) is a highly conserved Toll/IL-1 Receptor (TIR) adaptor with important roles in mediating immune responses. Studies in the brain have shown that SARM1 plays a role in induction of neuronal axon degeneration in response to a variety of injuries. We recently demonstrated that SARM1 is pro-degenerative in a genetic model of inherited retinopathy. This current study aimed to characterise the effect of SARM1 deletion in an alternative model of retinal degeneration (RD) in which the retinal pigment epithelium (RPE) fragments following administration of oxidising agent, sodium iodate (NaIO3), leading to subsequent photoreceptor cell death. Following administration of NaIO3, we observed no apparent difference in rate of loss of RPE integrity in SARM1 deficient mice compared to WT counterparts. However, despite no differences in RPE degeneration, photoreceptor cell number and retinal thickness were increased in Sarm1–/– mice compared to WT counterparts. This apparent protection of the photoreceptors in SARM1 deficient mice is supported by an observed decrease in pro-apoptotic caspase-3 in the photoreceptor layer of Sarm1–/– mice compared to WT. Together these data indicate a pro-degenerative role for SARM1 in the photoreceptors, but not in the RPE, in an oxidative stress induced model of retinal degeneration consistent with its known degenerative role in neurons in a range of neurodegenerative settings.

Neuroinflammation, Sleep, and Circadian Rhythms

Molecules involved in innate immunity affect sleep and circadian oscillators and vice versa. Sleep-inducing inflammatory molecules are activated by increased waking activity and pathogens. Pathologies that alter inflammatory molecules, such as traumatic brain injury, cancer, cardiovascular disease, and stroke often are associated with disturbed sleep and electroencephalogram power spectra. Moreover, sleep disorders, such as insomnia and sleep disordered breathing, are associated with increased dysregulation of inflammatory processes. Inflammatory molecules in both the central nervous system and periphery can alter sleep. Inflammation can also modulate cerebral vascular hemodynamics which is associated with alterations in electroencephalogram power spectra. However, further research is needed to determine the interactions of sleep regulatory inflammatory molecules and circadian clocks. The purpose of this review is to: 1) describe the role of the inflammatory cytokines interleukin-1 beta and tumor necrosis factor-alpha and nucleotide-binding domain and leucine-rich repeat protein-3 inflammasomes in sleep regulation, 2) to discuss the relationship between the vagus nerve in translating inflammatory signals between the periphery and central nervous system to alter sleep, and 3) to present information about the relationship between cerebral vascular hemodynamics and the electroencephalogram during sleep.

BAFF Blockade Attenuates DSS-Induced Chronic Colitis via Inhibiting NLRP3 Inflammasome and NF-κB Activation

Background

BAFF production is increased in IBD patients. However, the specific role of BAFF in IBD is still uncovered. This study aimed to investigate the expression and function of BAFF in experimental colitis and the potential mechanisms.

Methods

BAFF levels in the serum and colon tissues were measured by ELISA in DSS-induced colitis mice. Mouse-derived BAFF antibody was administered in DSS mice. The changes of body weight, disease activity index (DAI) scores, colon length, spleen weight, histopathological damage, inflammatory indicators, NF-κB signaling, and NLRP3 inflammasome were assayed in DSS mice and control. LPS-primed RAW264.7 cells and bone marrow derived macrophages (BMDMs) were treated with BAFF blockage and recombinant mouse BAFF. Inflammatory associated cytokines, NLRP3 inflammasomes and NF-κB signaling were detected among groups.

Results

BAFF production was elevated systemically and locally in colitis mice. BAFF blockade improved the body weight loss, DAI scores, colon length, spleen weight, and histopathological damage in colitis mice. Immunoflurescence analysis revealed that elevated macrophages in mucosal lamina propria were the primary source of BAFF in the colon. NLRP3 inflammasome and NF-κB signaling pathway activation were dramatically inhibited in DSS mice treated with BAFF blockage. In LPS-primed RAW264.7 cells/BMDMs, BAFF blockade decreased the activation of NLRP3 inflammasome (NLPR3, ASC, cleaved IL-1β, cleaved caspase 1) via inhibiting NF-κB signaling pathway. Moreover, LPS synergizes with BAFF to promote inflammatory factor secretion and expression of NF-κB signaling pathway in RAW264.7 cells.

Conclusions

These results suggested that BAFF blockade protected against colitis partially by relieving inflammation, inhibiting intestinal NLRP3 inflammasome and NF-κB signaling pathway from macrophages. BAFF plays an important role in inflammation regulation in IBD, thus providing a novel idea for further research on colitis and experimental evidences for novel potential therapeutic target in IBD.

Recent Advances in the Development of Toll-like Receptor Agonist-Based Vaccine Adjuvants for Infectious Diseases

Vaccines are powerful tools for controlling microbial infections and preventing epidemic diseases. Efficient inactive, subunit, or viral-like particle vaccines usually rely on a safe and potent adjuvant to boost the immune response to the antigen. After a slow start, over the last decade there has been increased developments on adjuvants for human vaccines. The development of adjuvants has paralleled our increased understanding of the molecular mechanisms for the pattern recognition receptor (PRR)-mediated activation of immune responses. Toll-like receptors (TLRs) are a group of PRRs that recognize microbial pathogens to initiate a host’s response to infection. Activation of TLRs triggers potent and immediate innate immune responses, which leads to subsequent adaptive immune responses. Therefore, these TLRs are ideal targets for the development of effective adjuvants. To date, TLR agonists such as monophosphoryl lipid A (MPL) and CpG-1018 have been formulated in licensed vaccines for their adjuvant activity, and other TLR agonists are being developed for this purpose. The COVID-19 pandemic has also accelerated clinical research of vaccines containing TLR agonist-based adjuvants. In this paper, we reviewed the agonists for TLR activation and the molecular mechanisms associated with the adjuvants’ effects on TLR activation, emphasizing recent advances in the development of TLR agonist-based vaccine adjuvants for infectious diseases.

Epithelial Gasdermin D shapes the host-microbial interface by driving mucus layer formation

Goblet cells and their main secretory product, mucus, play crucial roles in orchestrating the colonic host-microbe interactions that help maintain gut homeostasis. However, the precise intracellular machinery underlying this goblet cell-induced mucus secretion remains poorly understood. Gasdermin D (GSDMD) is a recently identified pore-forming effector protein that causes pyroptosis, a lytic proinflammatory type of cell death occurring during various pathophysiological conditions. Here, we reveal an unexpected function of GSDMD in goblet cell mucin secretion and mucus layer formation. Specific deletion of Gsdmd in intestinal epithelial cells (ΔIEC) led to abrogated mucus secretion with a concomitant loss of the mucus layer. This impaired colonic mucus layer in Gsdmd^ΔIEC mice featured a disturbed host-microbial interface and inefficient clearance of enteric pathogens from the mucosal surface. Mechanistically, stimulation of goblet cells activates caspases to process GSDMD via reactive oxygen species production; in turn, this activated GSDMD drives mucin secretion through calcium ion-dependent scinderin-mediated cortical F-actin disassembly, which is a key step in granule exocytosis. This study links epithelial GSDMD to the secretory granule exocytotic pathway and highlights its physiological nonpyroptotic role in shaping mucosal homeostasis in the gut.

Ubiquitination of NLRP3 by gp78/Insig-1 restrains NLRP3 inflammasome activation

The NLRP3 (NOD-, LRR- and pyrin domain-containing protein 3) inflammasome plays a pivotal role in defending the host against infection as well as sterile inflammation. Activation of the NLRP3 inflammasome is critically regulated by a de-ubiquitination mechanism, but little is known about how ubiquitination restrains NLRP3 activity. Here, we showed that the membrane-bound E3 ubiquitin ligase gp78 mediated mixed ubiquitination of NLRP3, which inhibited NLRP3 inflammasome activation by suppressing the oligomerization and subcellular translocation of NLRP3. In addition, the endoplasmic reticulum membrane protein insulin-induced gene 1 (Insig-1) was required for this gp78-NLRP3 interaction and gp78-mediated NLRP3 ubiquitination. gp78 or Insig-1 deficiency in myeloid cells led to exacerbated NLRP3 inflammasome-dependent inflammation in vivo, including lipopolysaccharide-induced systemic inflammation and alum-induced peritonitis. Taken together, our study identifies gp78-mediated NLRP3 ubiquitination as a regulatory mechanism that restrains inflammasome activation and highlights NLRP3 ubiquitination as a potential therapeutic target for inflammatory diseases.

SARM1 Ablation Is Protective and Preserves Spatial Vision in an In Vivo Mouse Model of Retinal Ganglion Cell Degeneration

The challenge of developing gene therapies for genetic forms of blindness is heightened by the heterogeneity of these conditions. However, mechanistic commonalities indicate key pathways that may be targeted in a gene-independent approach. Mitochondrial dysfunction and axon degeneration are common features of many neurodegenerative conditions including retinal degenerations. Here we explore the neuroprotective effect afforded by the absence of sterile alpha and Toll/interleukin-1 receptor motif-containing 1 (SARM1), a prodegenerative NADase, in a rotenone-induced mouse model of retinal ganglion cell loss and visual dysfunction. Sarm1 knockout mice retain visual function after rotenone insult, displaying preservation of photopic negative response following rotenone treatment in addition to significantly higher optokinetic response measurements than wild type mice following rotenone. Protection of spatial vision is sustained over time in both sexes and is accompanied by increased RGC survival and additionally preservation of axonal density in optic nerves of Sarm1^−/− mice insulted with rotenone. Primary fibroblasts extracted from Sarm1^−/− mice demonstrate an increased oxygen consumption rate relative to those from wild type mice, with significantly higher basal, maximal and spare respiratory capacity. Collectively, our data indicate that Sarm1 ablation increases mitochondrial bioenergetics and confers histological and functional protection in vivo in the mouse retina against mitochondrial dysfunction, a hallmark of many neurodegenerative conditions including a variety of ocular disorders.

Targeting Pyroptotic Cell Death Pathways in Retinal Disease

Pyroptosis is a gasdermin-mediated, pro-inflammatory form of cell death distinct from apoptosis. In recent years, increasing attention has shifted toward pyroptosis as more studies demonstrate its involvement in diverse inflammatory disease states, including retinal diseases. This review discusses how currently known pyroptotic cell death pathways have been implicated in models of age-related macular degeneration, diabetic retinopathy, and glaucoma. We also identify potential future therapeutic strategies for these retinopathies that target drivers of pyroptotic cell death. Presently, the drivers of pyroptosis that have been studied the most in retinal cells are the nucleotide-binding and oligomerization domain-like receptor family pyrin domain-containing 3 (NLRP3) inflammasome, caspase-1, and gasdermin D (GSDMD). Targeting these proteins may help us develop new drug therapies, or supplement existing therapies, in the treatment of retinal diseases. As novel mechanisms of pyroptosis come to light, including those involving other inflammatory caspases and members of the gasdermin protein family, more targets for pyroptosis-mediated therapies in retinal disease can be explored.

NAD+-consuming enzymes in immune defense against viral infection

The COVID-19 pandemic reminds us that in spite of the scientific progress in the past century, there is a lack of general antiviral strategies. In analogy to broad-spectrum antibiotics as antibacterial agents, developing broad spectrum antiviral agents would buy us time for the development of vaccines and treatments for future viral infections. In addition to targeting viral factors, a possible strategy is to understand host immune defense mechanisms and develop methods to boost the antiviral immune response. Here we summarize the role of NAD⁺-consuming enzymes in the immune defense against viral infections, with the hope that a better understanding of this process could help to develop better antiviral therapeutics targeting these enzymes. These NAD⁺-consuming enzymes include PARPs, sirtuins, CD38, and SARM1. Among these, the antiviral function of PARPs is particularly important and will be a focus of this review. Interestingly, NAD⁺ biosynthetic enzymes are also implicated in immune responses. In addition, many viruses, including SARS-CoV-2 contain a macrodomain-containing protein (NSP3 in SARS-CoV-2), which serves to counteract the antiviral function of host PARPs. Therefore, NAD⁺ and NAD⁺-consuming enzymes play crucial roles in immune responses against viral infections and detailed mechanistic understandings in the future will likely facilitate the development of general antiviral strategies.