Mechanistic insights into the C-type lectin receptor CLEC12A-mediated immune recognition of monosodium urate crystal.

CLEC12A, a member of the C-type lectin receptor family involved in immune homeostasis, recognizes MSU crystals released from dying cells. However, the molecular mechanism underlying the CLEC12A-mediated recognition of MSU crystals remains unclear. Herein, we reported the crystal structure of the human CLEC12A-C-type lectin-like domain (CTLD) and identified a unique "basic patch" site on CLEC12A-CTLD that is necessary for the binding of MSU crystals. Meanwhile, we determined the interaction strength between CLEC12A-CTLD and MSU crystals using single-molecule force spectroscopy. Furthermore, we found that CLEC12A clusters at the cell membrane and seems to serve as an internalizing receptor of MSU crystals. Altogether, these findings provide mechanistic insights for understanding the molecular mechanisms underlying the interplay between CLEC12A and MSU crystals.

Caspases Connect Cell-Death Signaling to Organismal Homeostasis.

Some forms of regulated cell death, such as apoptosis, are precipitated by the activation of cysteine proteases of the caspase family, including caspase 8, 9, and 3. Other caspases, such as caspase 1 and 4, are well known for their pro-inflammatory functions but regulate cell death in a limited number of pathophysiological settings. Accumulating evidence suggests that the most conserved function of mammalian caspases is not to control cell death sensu stricto, but to regulate inflammatory and immune reactions to dying cells and infectious challenges. Here, we review the molecular and cellular mechanisms though which mammalian caspases connect cell-death signaling to the maintenance of organismal homeostasis.

Damage-associated molecular patterns in viral infection: potential therapeutic targets.

Frequent viral infections leading to infectious disease outbreaks have become a significant global health concern. Fully elucidating the molecular mechanisms of the immune response against viral infections is crucial for epidemic prevention and control. The innate immune response, the host's primary defense against viral infection, plays a pivotal role and has become a breakthrough in research mechanisms. A component of the innate immune system, damage-associated molecular patterns (DAMPs) are involved in inducing inflammatory responses to viral infections. Numerous DAMPs are released from virally infected cells, activating downstream signaling pathways via internal and external receptors on immune cells. This activation triggers immune responses and helps regulate viral host invasion. This review examines the immune regulatory mechanisms of various DAMPs, such as the S100 protein family, high mobility group box 1 (HMGB1), and heat shock proteins, in various viral infections to provide a theoretical basis for designing novel antiviral drugs.

Redox signaling and oxidative stress in systemic acquired resistance.

Plants fully depend on their immune systems to defend against pathogens. Upon pathogen attack, plants not only activate immune responses at the infection site but also trigger a defense mechanism known as systemic acquired resistance (SAR) in distal systemic tissues to prevent subsequent infections by a broad-spectrum of pathogens. SAR is induced by mobile signals produced at the infection site. Accumulating evidence suggests that reactive oxygen species (ROS) play a central role in SAR signaling. ROS burst at the infection site is one of the earliest cellular responses following pathogen infection and can spread to systemic tissues through membrane-associated NADPH oxidase-dependent relay production of ROS. It is well known that ROS ignite redox signaling and, when in excess, cause oxidative stress, damaging cellular components. In this review, we summarize current knowledge on redox regulation of several SAR signaling components. We discuss the ROS amplification loop in systemic tissues involving multiple SAR mobile signals. Moreover, we highlight the essential role of oxidative stress in generating SAR signals including azelaic acid and extracellular NAD(P) [eNAD(P)]. Finally, we propose that eNAD(P) is a damage-associated molecular pattern serving as a converging point of SAR mobile signals in systemic tissues.

Oxidative stress, malaria, sickle cell disease, and innate immunity.

Plasmodium falciparum shields from adaptive immunity in erythrocytes, but how might the innate immune system recognize infected cells? Replication by the parasite results in oxidative stress, causing surface expression of high-mannose glycans. These can act as pathogen-associated molecular patterns to stimulate phagocytosis in the spleen and the sickle cell allele enhances these responses.

Involvement of eNAMPT/TLR4 inflammatory signaling in progression of non-alcoholic fatty liver disease, steatohepatitis, and fibrosis.

Although the progression of non-alcoholic fatty liver disease (NAFLD) from steatosis to steatohepatitis (NASH) and cirrhosis remains poorly understood, a critical role for dysregulated innate immunity has emerged. We examined the utility of ALT-100, a monoclonal antibody (mAb), in reducing NAFLD severity and progression to NASH/hepatic fibrosis. ALT-100 neutralizes eNAMPT (extracellular nicotinamide phosphoribosyltransferase), a novel damage-associated molecular pattern protein (DAMP) and Toll-like receptor 4 (TLR4) ligand. Histologic and biochemical markers were measured in liver tissues and plasma from human NAFLD subjects and NAFLD mice (streptozotocin/high-fat diet-STZ/HFD, 12 weeks). Human NAFLD subjects (n = 5) exhibited significantly increased NAMPT hepatic expression and significantly elevated plasma levels of eNAMPT, IL-6, Ang-2, and IL-1RA compared to healthy controls, with IL-6 and Ang-2 levels significantly increased in NASH non-survivors. Untreated STZ/HFD-exposed mice displayed significant increases in NAFLD activity scores, liver triglycerides, NAMPT hepatic expression, plasma cytokine levels (eNAMPT, IL-6, and TNFα), and histologic evidence of hepatocyte ballooning and hepatic fibrosis. Mice receiving the eNAMPT-neutralizing ALT-100 mAb (0.4 mg/kg/week, IP, weeks 9 to 12) exhibited marked attenuation of each index of NASH progression/severity. Thus, activation of the eNAMPT/TLR4 inflammatory pathway contributes to NAFLD severity and NASH/hepatic fibrosis. ALT-100 is potentially an effective therapeutic approach to address this unmet NAFLD need.

Largemouth bass galectin, MsGal-9: Mediating various functions as a pattern recognition receptor and a potential damage-associated molecular pattern.

Galectins are lectins that bind to ß-galactose and are widely expressed in immune system tissues, playing pivotal roles in innate immunity through their conserved carbohydrate-recognition domains (CRDs). In this present investigation, a tandem-repeat galectin was discovered in the largemouth bass, Micropterus salmoides (designated as MsGal-9). The open reading frame of MsGal-9 encodes two CRDs, each containing two consensus motifs that are essential for ligand binding. MsGal-9 is expressed in various tissues of the largemouth bass, with particularly high expression levels in the liver and spleen. The full-length form of MsGal-9, as well as the N-terminal (MsGal-9-N) and C-terminal (MsGal-9-C) CRDs, were individually recombined. Their ability for nonself recognition was studied. The three recombinant proteins were able to bind to glucan (GLU), peptidoglycan (PGN), and lipopolysaccharide (LPS), with MsGal-9 displaying the highest binding activity. Furthermore, rMsGal-9-N exhibited higher binding activity towards GLU in comparison to rMsGal-9-C. Further investigations revealed that the full-length rMsGal-9 could significantly bind to Gram-positive bacteria, Gram-negative bacteria, and fungi, while rMsGal-9-C specifically bound to Escherichia coli. However, rMsGal-9-N did not exhibit significant binding activity towards any microbes. These findings indicate that MsGal-9 requires both CRDs to cooperate in order to fulfill its nonself recognition function. All three recombinant proteins demonstrated agglutination activity towards various microbes, with MsGal-9 and MsGal-9-N displaying a similar broad binding spectrum, while MsGal-9-C agglutinated three types of bacteria. Moreover, both MsGal-9 and MsGal-9-N were capable of coagulating largemouth bass red blood cells, whereas MsGal-9-C lacked this ability. However, MsGal-9-C played a significant role in enhancing the encapsulation of leukocytes in comparison to MsGal-9-N. All three proteins acted as potential damage-associated molecular patterns (DAMPs), inducing apoptosis in leukocytes.

Cationic ribosomal proteins can inhibit pro-inflammatory action stimulated by LPS+HMGB1 and are hindered by advanced glycation end products.

We previously found that ribosomal protein L9 (RPL9) is a novel advanced glycation end product (AGE)-binding protein that can decrease pro-inflammatory TNF-α expression stimulated by lipopolysaccharide (LPS) plus high-mobility group box 1 (HMGB1), suggesting that RPL9 has a role in regulating LPS+HMGB1-stimulated inflammatory reactions. Among the various ribosomal proteins, it was found that RPS5 reproduced the regulatory activity of RPL9 on LPS+HMGB1-stimulated TNF-α expression in macrophage-like RAW264.7 cells. RPL9 and RPS5 share a common feature as cationic proteins. Polylysine, a cationic polypeptide, and a synthetic peptide of the cationic region from RPL9 also exhibited reducing activity on LPS+HMGB1-induced TNF-α expression. By pull-down assay, RPL9 and RPS5 were confirmed to interact with AGEs. When AGEs coexisted with LPS, HMGB1, plus RPL9 or RPS5, the reducing effect of TNF-α expression by these cationic ribosomal proteins was shown to be abrogated. The results suggest that cationic ribosomal proteins have a regulatory role in the pro-inflammatory response induced by LPS+HMGB1, and in the pathophysiological condition of accumulating AGEs, this regulatory effect is abolished, which exacerbates inflammation.

Damage-Associated Molecular Patterns and Systemic Signaling.

Cellular damage inflicted by wounding, pathogen infection, and herbivory releases a variety of host-derived metabolites, degraded structural components, and peptides into the extracellular space that act as alarm signals when perceived by adjacent cells. These so-called damage-associated molecular patterns (DAMPs) function through plasma membrane localized pattern recognition receptors to regulate wound and immune responses. In plants, DAMPs act as elicitors themselves, often inducing immune outputs such as calcium influx, reactive oxygen species generation, defense gene expression, and phytohormone signaling. Consequently, DAMP perception results in a priming effect that enhances resistance against subsequent pathogen infections. Alongside their established function in local tissues, recent evidence supports a critical role of DAMP signaling in generation and/or amplification of mobile signals that induce systemic immune priming. Here, we summarize the identity, signaling, and synergy of proposed and established plant DAMPs, with a focus on those with published roles in systemic signaling.

A comprehensive overview of radiation therapy impacts of various cancer treatments and pivotal role in the immune system.

The cancer treatment landscape is significantly evolving, focusing on advanced radiation therapy methods to maximize effectiveness and minimize the adverse effects. Recognized as a pivotal component in cancer and disease treatment, radiation therapy (RT) has drawn attention in recent research that delves into its intricate interplay with inflammation and the immune response. This exploration unveils the underlying processes that significantly influence treatment outcomes. In this context, the potential advantages of combining bronchoscopy with RT across diverse clinical scenarios, alongside the targeted impact of brachytherapy, are explored. Concurrently, radiation treatments serve multifaceted roles such as DNA repair, cell elimination, and generating immune stress signaling molecules known as damage-associated molecular patterns, elucidating their effectiveness in treating various diseases. External beam RT introduces versatility by utilizing particles such as photons, electrons, protons, or carbon ions, each offering distinct advantages. Advanced RT techniques contribute to the evolving landscape, with emerging technologies like FLASH, spatially fractionated RT, and others poised to revolutionize the field. The comprehension of RT, striving for improved treatment outcomes, reduced side effects, and facilitating personalized and innovative treatments for cancer and noncancer patients. After navigating these advancements, the goal is fixed to usher in a new era in which RT is a cornerstone of precision and effectiveness in medical interventions. In summarizing the myriad findings, the review underscores the significance of understanding the differential impacts of radiation approaches on inflammation and immune modulation, offering valuable insights for developing innovative therapeutic interventions that harness the immune system in conjunction with RT.

Peroxiredoxin 1 aggravates acute kidney injury by promoting inflammation through Mincle/Syk/NF-κB signaling.

Damage-associated molecular patterns (DAMPs) are a cause of acute kidney injury (AKI). Our knowledge of these DAMPs remains incomplete. Here, we report serum peroxiredoxin 1 (Prdx1) as a novel DAMP for AKI. Lipopolysaccharide (LPS) and kidney ischemia/reperfusion injury instigated AKI with concurrent increases in serum Prdx1 and reductions of Prdx1 expression in kidney tubular epithelial cells. Genetic knockout of Prdx1 or use of a Prdx1-neutralizing antibody protected mice from AKI and this protection was impaired by introduction of recombinant Prdx1 (rPrdx1). Mechanistically, lipopolysaccharide increased serum and kidney proinflammatory cytokines, macrophage infiltration, and the content of M1 macrophages. All these events were suppressed in Prdx1-/- mice and renewed upon introduction of rPrdx1. In primary peritoneal macrophages, rPrdx1 induced M1 polarization, activated macrophage-inducible C-type lectin (Mincle) signaling, and enhanced proinflammatory cytokine production. Prdx1 interacted with Mincle to initiate acute kidney inflammation. Of note, rPrdx1 upregulated Mincle and the spleen tyrosine kinase Syk system in the primary peritoneal macrophages, while knockdown of Mincle abolished the increase in activated Syk. Additionally, rPrdx1 treatment enhanced the downstream events of Syk, including transcription factor NF-κB signaling pathways. Furthermore, serum Prdx1 was found to be increased in patients with AKI; the increase of which was associated with kidney function decline and inflammatory biomarkers in patient serum. Thus, kidney-derived serum Prdx1 contributes to AKI at least in part by activating Mincle signaling and downstream pathways.

Glycolaldehyde-derived advanced glycation end products promote macrophage proliferation via the JAK-STAT signaling pathway.

BACKGROUND: Advanced glycation end products (AGEs) are heterogeneous proinflammatory molecules produced by a non-enzymatic glycation reaction between reducing sugars (and their metabolites) and biomolecules with amino groups, such as proteins. Although increases in and the accumulation of AGEs have been implicated in the onset and exacerbation of lifestyle- or age-related diseases, including diabetes, their physiological functions have not yet been elucidated in detail. METHODS AND RESULTS: The present study investigated the cellular responses of the macrophage cell line RAW264.7 stimulated by glycolaldehyde-derived AGEs (Glycol-AGEs) known as representative toxic AGEs. The results obtained showed that Glycol-AGEs significantly promoted the proliferation of RAW264.7 cells at a low concentration range (1-10 µg/mL) in a concentration-dependent manner. On the other hand, neither TNF-α production nor cytotoxicity were induced by the same concentrations of Glycol-AGEs. The increases observed in cell proliferation by low concentrations of Glycol-AGEs were also detected in receptor triple knockout (RAGE-TLR4-TLR2 KO) cells as well as in wild-type cells. Increases in cell proliferation were not affected by various kinase inhibitors, including MAP kinase inhibitors, but were significantly suppressed by JAK2 and STAT5 inhibitors. In addition, the expression of some cell cycle-related genes was up-regulated by the stimulation with Glycol-AGEs. CONCLUSIONS: These results suggest a novel physiological role for AGEs in the promotion of cell proliferation via the JAK-STAT pathway.

BSR1, a Rice Receptor-like Cytoplasmic Kinase, Positively Regulates Defense Responses to Herbivory.

Crops experience herbivory by arthropods and microbial infections. In the interaction between plants and chewing herbivores, lepidopteran larval oral secretions (OS) and plant-derived damage-associated molecular patterns (DAMPs) trigger plant defense responses. However, the mechanisms underlying anti-herbivore defense, especially in monocots, have not been elucidated. The receptor-like cytoplasmic kinase Broad-Spectrum Resistance 1 (BSR1) of Oryza sativa L. (rice) mediates cytoplasmic defense signaling in response to microbial pathogens and enhances disease resistance when overexpressed. Here, we investigated whether BSR1 contributes to anti-herbivore defense responses. BSR1 knockout suppressed rice responses triggered by OS from the chewing herbivore Mythimna loreyi Duponchel (Lepidoptera: Noctuidae) and peptidic DAMPs OsPeps, including the activation of genes required for biosynthesis of diterpenoid phytoalexins (DPs). BSR1-overexpressing rice plants exhibited hyperactivation of DP accumulation and ethylene signaling after treatment with simulated herbivory and acquired enhanced resistance to larval feeding. As the biological significance of herbivory-induced accumulation of rice DPs remains unexplained, their physiological activities in M. loreyi were analyzed. The addition of momilactone B, a rice DP, to the artificial diet suppressed the growth of M. loreyi larvae. Altogether, this study revealed that BSR1 and herbivory-induced rice DPs are involved in the defense against chewing insects, in addition to pathogens.

The danger signal interferon-induced protein 35 (IFP35) mediates acetaminophen-induced liver injury.

Acute liver injury caused by overdose usage of acetaminophen (APAP) is an intractable clinical problem. Necrotic hepatocytes release large amounts of intracellular components including damage-associated molecular patterns (DAMPs) which contribute to liver failure and may serve as therapeutic targets. However, the pathogenic mechanisms of DAMPs in APAP-induced liver injury (AILI) are remain largely uncovered. Here, we found that a recently identified DAMP, interferon-induced protein 35 (IFP35), is involved in the early phase of AILI. Our data demonstrated that although the expression level of IFP35 is not significantly increased in either patients or mice with AILI, it is released from necrotic hepatocytes. Within 24 h post APAP injection, mice lacking Ifp35 are resistant to APAP-induced toxicity, and induce less inflammatory response than that of wild-type mice, including reduced AST/ALT level, pro-inflammatory cytokines production and neutrophils infiltration. More importantly, antibody of IFP35 reduces the expression level of inflammatory factors and chemokines. This study brings new knowledge into the pathogenic mechanism of AILI.

Fungal oxysterol-binding protein-related proteins promote pathogen virulence and activate plant immunity.

Oxysterol-binding protein-related proteins (ORPs) are a conserved class of lipid transfer proteins that are closely involved in multiple cellular processes in eukaryotes, but their roles in plant-pathogen interactions are mostly unknown. We show that transient expression of ORPs of Magnaporthe oryzae (MoORPs) in Nicotiana benthamina plants triggered oxidative bursts and cell death; treatment of tobacco Bright Yellow-2 suspension cells with recombinant MoORPs elicited the production of reactive oxygen species. Despite ORPs being normally described as intracellular proteins, we detected MoORPs in fungal culture filtrates and intercellular fluids from barley plants infected with the fungus. More importantly, infiltration of Arabidopsis plants with recombinant Arabidopsis or fungal ORPs activated oxidative bursts, callose deposition, and PR1 gene expression, and enhanced plant disease resistance, implying that ORPs may function as endogenous and exogenous danger signals triggering plant innate immunity. Extracellular application of fungal ORPs exerted an opposite impact on salicylic acid and jasmonic acid/ethylene signaling pathways. Brassinosteroid Insensitive 1-associated Kinase 1 was dispensable for the ORP-activated defense. Besides, simultaneous knockout of MoORP1 and MoORP3 abolished fungal colony radial growth and conidiation, whereas double knockout of MoORP1 and MoORP2 compromised fungal virulence on barley and rice plants. These observations collectively highlight the multifaceted role of MoORPs in the modulation of plant innate immunity and promotion of fungal development and virulence in M. oryzae.

Identification of ribosomal protein L9 as a novel regulator of proinflammatory damage-associated molecular pattern molecules.

BACKGROUND: We previously reported that advanced glycation endproducts (AGEs) increase the proinflammatory activity of high mobility group box-1 (HMGB1), a representative damage-associated molecular pattern molecule (DAMP), through their direct interaction. This suggested that AGEs activate other DAMPs and led us to search for novel DAMPs capable of interacting with AGEs. METHODS AND RESULTS: The chromatographic analysis using AGE-immobilized gel revealed the ribosomal protein family to be a factor with binding activity to AGEs. Ribosomal protein L9 (RPL9), a member of the ribosomal protein family, was found in the centrifugal supernatant of ruptured cells and in the serum of lipopolysaccharide (LPS)-stimulated sepsis model mice, exhibiting similar characteristic properties to HMGB1. Although HMGB1 potentiated LPS-stimulated TNF-α expression in macrophage-like RAW264.7 cells, RPL9 hardly exhibited this activity. Of note, RPL9 significantly suppressed the potentiated mRNA expression and protein production of TNF-α by HMGB1 plus LPS stimulation, suggesting its regulatory roles in DAMP-induced proinflammatory activity. Based on the differential scanning fluorimetric analysis, the direct interaction between RPL9 and HMGB1 may play a role in the suppressive effects of RPL9. CONCLUSIONS: This study suggested that RPL9 is a novel type of DAMP with a regulatory role in the proinflammatory response and provided insight into the pathophysiology of inflammatory diseases.

Mitochondrial-derived damage-associated molecular patterns amplify neuroinflammation in neurodegenerative diseases.

Both mitochondrial dysfunction and neuroinflammation are implicated in neurodegeneration and neurodegenerative diseases. Accumulating evidence shows multiple links between mitochondrial dysfunction and neuroinflammation. Mitochondrial-derived damage-associated molecular patterns (DAMPs) are recognized by immune receptors of microglia and aggravate neuroinflammation. On the other hand, inflammatory factors released by activated glial cells trigger an intracellular cascade, which regulates mitochondrial metabolism and function. The crosstalk between mitochondrial dysfunction and neuroinflammatory activation is a complex and dynamic process. There is strong evidence that mitochondrial dysfunction precedes neuroinflammation during the progression of diseases. Thus, an in-depth understanding of the specific molecular mechanisms associated with mitochondrial dysfunction and the progression of neuroinflammation in neurodegenerative diseases may contribute to the identification of new targets for the treatment of diseases. In this review, we describe in detail the DAMPs that induce or aggravate neuroinflammation in neurodegenerative diseases including mtDNA, mitochondrial unfolded protein response (mtUPR), mitochondrial reactive oxygen species (mtROS), adenosine triphosphate (ATP), transcription factor A mitochondria (TFAM), cardiolipin, cytochrome c, mitochondrial Ca2+ and iron.

The Involvement of Alarmins in the Pathogenesis of Sjögren's Syndrome.

Sjögren's syndrome (SS) is a chronic autoimmune disease that affects exocrine glands, primarily the salivary and lachrymal glands. It is characterized by lymphoplasmacytic infiltration of the glandular tissues, ultimately leading to their dysfunction and destruction. Besides classic dry eyes and dry mouth defined as sicca syndrome, patients affected by the disease also typically display symptoms such as fatigue, pain and in more than 50% of cases, systemic manifestations such as arthritis, interstitial lung involvement, neurological involvement and an increased risk of lymphoma. The pathophysiological mechanisms underlying SS still remain elusive. The crucial role of innate immunity has been advocated in recent years regarding the pathogenesis of pSS, especially in the initiation and progression toward autoimmunity. Alarmins are endogenous molecules that belong to the large family of damage associated molecular pattern (DAMP). Alarmins are rapidly released, ensuing cell injury and interacting with pattern recognition receptors (PRR) such as toll-like receptors (TLR) to recruit and activate cells of the innate immune system and to promote adaptive immunity responses. This review highlights the current knowledge of various alarmins and their role in the pathogenesis of pSS.

Necroptosis in pathogenesis of osteoarthritis and its therapeutic implications.

Osteoarthritis is a progressive degenerative joint disease induced by many causes, for which there is no radical cure currently. Necroptosis is a newly reported programmed cell death, and its related factors are also inseparable from the progress of osteoarthritis. For examples, damage-associated molecular pattern promotes the release of various inflammatory factors, so as to recruit macrophages and promote local inflammation of the joint; inhibition of receptor-interacting protein kinase can reduce the death of cell and the expression of inflammatory factors, so as to reduce cartilage damage. Therefore, in-depth study of the regulatory mechanism of necroptosis in osteoarthritis will help to further reveal the pathogenesis of osteoarthritis, so as to provide potential targets for the treatment of osteoarthritis.

Inducing immunogenic cell death in immuno-oncological therapies.

Immunotherapy has revolutionized cancer treatment and substantially improved patient outcomes with respect to multiple types of tumors. However, most patients cannot benefit from such therapies, mainly due to the intrinsic low immunogenicity of cancer cells (CCs) that allows them to escape recognition by immune cells of the body. Immunogenic cell death (ICD), which is a form of regulated cell death, engages in a complex dialogue between dying CCs and immune cells in the tumor microenvironment (TME), ultimately evoking the damage-associated molecular pattern (DAMP) signals to activate tumor-specific immunity. The ICD inducers mediate the death of CCs and improve both antigenicity and adjuvanticity. At the same time, they reprogram TME with a "cold-warm-hot" immune status, ultimately amplifying and sustaining dendritic cell- and T cell-dependent innate sensing as well as the antitumor immune responses. In this review, we discuss how to stimulate ICD based upon the biological properties of CCs that have evolved under diverse stress conditions. Additionally, we highlight how this dynamic interaction contributes to priming tumor immunogenicity, thereby boosting anticancer immune responses. We believe that a deep understanding of these ICD processes will provide a framework for evaluating its vital role in cancer immunotherapy.