Recognition Of Damage-associated Molecular Patterns Research Articles

Impact of chronic muscle use and disuse on innate immune signaling in skeletal muscle

Mitochondria exhibit high levels of adaptability to various stimuli such as chronic muscle use (i.e. exercise) or disuse, such as immobilization or denervation. These changes in the mitochondrial network ultimately affect the health and functioning of skeletal muscle, which contributes to whole-body metabolism, locomotion, and postural stability. It is now acknowledged that mitochondrial dysfunction can activate inflammatory pathways through the recognition of damage-associated molecular patterns (DAMPs). The objective of this study was to examine how changes in mitochondria brought about by either chronic muscle inactivity or chronic exercise training affect innate immune system activation. We hypothesized that an inverse relationship between mitochondrial content and innate immune signaling would be evident in skeletal muscle. To investigate this, skeletal muscle from the hindlimbs of mice was collected after 7 days of sciatic muscle denervation, or after 4.5 weeks of endurance swim training involving 240 minutes of daily exercise. We analyzed the expression of the NLRP3 inflammasome, innate immune system signaling proteins, mitochondrial markers, and mitochondrial DNA (mtDNA) content using western blotting, cytochrome C oxidase (COX) activity, ELISA and qPCR. Following 7 days of denervation, there was a significant decrease in both COX-IV protein and COX activity, indicating a reduction in mitochondrial content. This was accompanied by an increase (p<0.05) in NLRP3, procaspase-1, gasdermin-D (GSDMD) and its active N-terminal fragment, GSDMD-N, as well as a notable increase in IL-1β. In addition, other possible converging pathways were also upregulated including cGAS-STING, and gasdermin-E. In comparison, following exercise training, there was a significant increase in mitochondrial content, apparent through increases in COX-IV protein, COX activity and mitochondrial RNA content. This was associated with decreases in procaspase-1 and caspase-1 protein expression alongside reduced STING activation. These findings highlight an inverse relationship between mitochondrial content and the activation of several inflammatory pathways that possibly converge upon NLRP3 inflammasome activation and pyroptotic cell death, leading to detriments in skeletal muscle health. This work aims to further the understanding of innate immune signaling pathways within muscle which can potentially highlight therapeutic targets to regulate its activation under divergent metabolic conditions. This work was supported by funds from the Natural Science and Engineering Research Council (NSERC). Priyanka Khemraj is the holder of an Ontario Graduate Scholarship. David A. Hood is the holder of a Canadian Research Chair in Cell Physiology. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

The possible link between aluminum phosphide poisoning and NLRP3 inflammasome

Aluminum phosphide (AlP) is a fumigant used to control pests. However, human exposure to this substance can lead to poisoning. AlP reacts with gastric acid and water to release phosphine (PH3). This toxic gas affects the mitochondria and quickly enters the bloodstream. This gas impairs the mitochondria's ability to generate ATP, leading to oxidative stress, mitochondrial dysfunction, and damage to mitochondrial DNA (mt-DNA). Mitochondria release damage-associated molecular patterns (DAMPs) to shield cells from stress and stimulate the innate immune system.Nonetheless, if mitochondrial homeostasis is disrupted, an excessive immune response can occur, causing organ dysfunction. Mitochondrial reactive oxygen species (mt-ROS) and mt-DNA act as DAMPs. Upon recognition of DAMPs, the inflammasome is activated, causing inflammation. The nucleotide-binding domain, leucine-rich-containing family, and pyrin domain-containing-3 (NLRP3) gene on chromosome 1's extended arm encodes a protein that triggers the human inflammasome. NLRP3 is the most extensively researched inflammasome subfamily. It is essential to recognize that the pathophysiology of mitochondrial dysfunction and NLRP3 activation is complex and multifactorial, and a comprehensive approach may be needed to address both the underlying causes and downstream inflammatory responses effectively. The cGAS-STING pathway is essential for immune responses, and targeting specific nodes can be beneficial. Therapeutic approaches include small molecule drugs, biologics, vaccines, and combination therapies. Since there is a significant relationship between mitochondrial events and NLRP3 activation, targeting this inflammasome could be a promising strategy for developing antidotes for AlP poisoning.

Focus on host/organ unregulated response: a common cause of critical illness.

Focus on host/organ unregulated response: a common cause of critical illness.

The simultaneous perception of self- and non-self-danger signals potentiates plant innate immunity responses

Main conclusionThe simultaneous perception of endogenous and exogenous danger signals potentiates PAMP-triggered immunity in tomato and other downstream defence responses depending on the origin of the signal. Plant cells perceive a pathogen invasion by recognising endogenous or exogenous extracellular signals such as Damage-Associated Molecular Patterns (DAMPs) or Pathogen-Associated Molecular Patterns (PAMPs). In particular, DAMPs are intracellular molecules or cell wall fragments passive or actively released to the apoplast, whose extracellular recognition by intact cells triggers specific immune signalling, the so-called DAMP-triggered immunity. The extracellular recognition of DAMPs and PAMPs leads to a very similar intracellular signalling, and this similarity has generated a biological need to know why plants perceive molecules with such different origins and with overlapped innate immunity responses. Here, we report that the simultaneous perception of DAMPs and a PAMP strengthens early and late plant defence responses. To this aim, we studied classical PTI responses such as the generation of ROS and MAPK phosphorylation, but we also monitored the biosynthesis of phytocytokines and performed a non-targeted metabolomic analysis. We demonstrate that co-application of the bacterial peptide flagellin with the DAMPs cyclic AMP or cellobiose amplifies PAMP-triggered immunity responses. Both co-applications enhanced the synthesis of phytocytokines, but only simultaneous treatments with cAMP strengthened the flagellin-dependent metabolomic responses. In addition, cAMP and cellobiose treatments induced resistance against the hemibiotrophic bacteria Pseudomonas syringae pv. tomato DC3000. Overall, these results indicate that the complex mixture of DAMPs and PAMPs carries specific information that potentiates plant defence responses. However, downstream responses seem more specific depending on the composition of the mixture.

Kill and Clearance in HCC: An Approach Based on NK Cells and Macrophages

In our previous perspective, we investigated the role of hypoxic lesions in the development of necrotic zone in solid tumors (1). We suggested the increased infiltration of macrophages/monocytes to the pre-necrotic zone and under the influence of chemoattractants (VEGF, CCL2, and CCL5), danger signals, and a trail of necrotic debris as a mechanism to maximize their opportunity to clear the lesion. They continuously sample and mediates recognition of damage-associated molecular patterns (DAMPs), including heat shock proteins, cytokines, DNA, RNA, metabolic ATP, HMGB1, histones, altered carbohydrate, and negatively exposed phosphatidylserine (PS) on the surface of necrotic corpses or apoptotic cells. We suggested gradual alteration of gene expression in macrophages eventually turns off their phagocytic machinery leaving uncleared cell corpses as a rich source of building blocks for cancer stem cells. Even subtle differences in the internalized ligands could have far-reaching consequences on cytokine production and antigen presentation to NK cells. Here, we propose a synergistic act of kill and clearance by NK cells and macrophages as a therapeutic strategy in HCC. We have provided a comprehensive mechanism underlying human NK cell and macrophage dysfunction in HCC, investigated the crosstalk between NK cells and a group of myeloid-derived suppressor cells (MDSCs) with a typical monocytic phenotype (CD14+ HLA-DR-/low), and the immunosuppressive role of hypoxia in HCC. We have also outlined the possible future research directions to target the crosstalk between NK cells and macrophage/MDSC to enhance kill and clearance by NK cells and macrophages in HCC and other solid tumors.

Abstract 104: Deletion Of Myd88 In T-Cells Worsens Pathology In A Mouse Model Of Non-Ischemic Heart Failure Through Enhanced T-Cell Survival And Effector Function:

Background: Heart failure (HF) is a leading cause of death worldwide, associated with cardiac and systemic inflammation. However, no anti-inflammatory therapies have shown success thus far. Damage associated molecular patterns (DAMPs) released in the heart can activate myeloid cells to promote antigen presentation to T-cells, which infiltrate the heart and participate in adverse cardiac remodeling. DAMP signaling converges onto the adaptor protein “Myeloid differentiation primary response 88” (MyD88). DAMP receptors and MyD88 are also expressed in T-cells, but their role in T-cell activation is unclear, and is unknown in the context of HF. We hypothesized that T-cell recognition of DAMPs through MyD88 causes “bystander activation” of T-cells and contributes to cardiac pathology in HF. Methods and Results: We reconstituted Tcra -/- mice, normally protected from HF, with WT or Myd88 -/- Type 1 helper T-cells (Th1) in the onset of transaortic constriction (TAC), a well-established model of HF. Surprisingly, we found that mice given Myd88 -/- Th1 cells exhibited significantly higher levels of cardiac T-cell infiltration, more severe fibrosis, and lower fractional shortening than mice given WT Th1 cells. We found that WT and Myd88 -/- Th1 cells had similar levels of IFNγ and Tbx21 by intracellular staining and RT-qPCR, indicating that MyD88 does not alter Th1 differentiation. However, Myd88 -/- Th1 cells secreted higher levels of IL-2 and TNFα, suggesting enhanced proliferative and pro-inflammatory effector function. We performed viability studies using live cell microscopy and measuring propidium iodide incorporation in real time, as well as by flow cytometry, and found that Myd88 -/- Th1 cells have a survival advantage compared to WT Th1 cells. Moreover, we found that Myd88 -/- Th1 cells exhibited higher levels of adhesion to ICAM-1 and VCAM-1, protein ligands involved in T-cell recruitment, compared to WT Th1 cells when perfused under conditions of shear flow. Conclusion: Together, these data demonstrate that T-cell MyD88 limits T-cell mediated pathology in HF by modulating Th1 effector function, survival, and adhesion ability. We identify novel role for T-cell MyD88 in cardiac inflammation that may be modulated in HF.

DAMP-sensing receptors in sterile inflammation and inflammatory diseases.

The innate immune system has the capacity to detect 'non-self' molecules derived from pathogens, known as pathogen-associated molecular patterns, via pattern recognition receptors. In addition, an increasing number of endogenous host-derived molecules, termed damage-associated molecular patterns (DAMPs), have been found to be sensed by various innate immune receptors. The recognition of DAMPs, which are produced or released by damaged and dying cells, promotes sterile inflammation, which is important for tissue repair and regeneration, butcan also lead to the development of numerous inflammatory diseases, such as metabolic disorders, neurodegenerative diseases, autoimmune diseases and cancer. Here we examine recent discoveries concerning the roles of DAMP-sensing receptors in sterile inflammation and in diseases resulting from dysregulated sterile inflammation, and then discuss insights into the cross-regulation of these receptors and their ligands.

Plant Immune Responses to Parasitic Nematodes.

Plant-parasitic nematodes (PPNs), such as root-knot nematodes (RKNs) and cyst nematodes (CNs), are among the most devastating pests in agriculture. RKNs and CNs induce redifferentiation of root cells into feeding cells, which provide water and nutrients to these nematodes. Plants trigger immune responses to PPN infection by recognizing PPN invasion through several different but complementary systems. Plants recognize pathogen-associated molecular patterns (PAMPs) sderived from PPNs by cell surface–localized pattern recognition receptors (PRRs), leading to pattern-triggered immunity (PTI). Plants can also recognize tissue and cellular damage caused by invasion or migration of PPNs through PRR-based recognition of damage-associated molecular patterns (DAMPs). Resistant plants have the added ability to recognize PPN effectors via intracellular nucleotide-binding domain leucine-rich repeat (NLR)-type immune receptors, leading to NLR-triggered immunity. Some PRRs may also recognize apoplastic PPN effectors and induce PTI. Plant immune responses against PPNs include the secretion of anti-nematode enzymes, the production of anti-nematode compounds, cell wall reinforcement, production of reactive oxygen species and nitric oxide, and hypersensitive response–mediated cell death. In this review, we summarize the recognition mechanisms for PPN infection and what is known about PPN-induced immune responses in plants.

Monocytes of patients with unstable angina express high levels of chemokine and pattern-recognition receptors

Background and aimsMacrophages derived from monocytes play an important role in atherosclerosis progression. Subpopulations of circulating classical, intermediate, and non-classical monocytes possess distinct functions and phenotypes, and participate in the pathogenesis of disease. The aim of this study was to compare the quantity and phenotypes of circulating monocyte subpopulations in patients with established atherosclerosis and healthy control individuals. Additionally, the study aimed to provide insight into the functional activity of monocytes against a heat shock protein (HSP60). MethodsChemokine and pattern recognition receptors in monocyte subsets obtained from peripheral blood of acute and chronic coronary artery disease patients and controls were quantified by flow cytometry. Furthermore, monocytes from healthy controls were stimulated in vitro with HSP60, and the cytokines produced by them were evaluated by flow cytometry. ResultsEighteen controls (C), 34 individuals with risk factors for cardiovascular disease (RF), 32 patients with stable angina (SA), and 16 patients with unstable angina (UA) were enrolled in the study. The absolute count of intermediate monocytes was found to be increased in patients of the UA group; high frequencies of the chemokine receptors CCR2, CCR5, and CX3CR1 were also observed in this subpopulation. Moreover, the pattern recognition receptors TLR2 and TLR4 were more frequent in intermediate monocytes from the UA group. Furthermore, the intermediate monocytes from healthy individuals produced IL-12p70 after stimulation with HSP60. ConclusionsOur results show that intermediate monocytes of UA patients exhibited an enhanced expression of the receptors involved in the recognition of damage-associated molecular patterns (DAMPs) and enhancement of the migratory function. Hence, they might contribute to the propagation and progression of inflammation observed in atherosclerosis, especially in the acute setting.

Damage-associated molecular pattern recognition is required for induction of retinal neuroprotective pathways in a sex-dependent manner

Retinal degeneration is a common cause of irreversible blindness and is caused by the death of retinal light-sensitive neurons called photoreceptors. At the onset of degeneration, stressed photoreceptors cause retinal glial cells to secrete neuroprotective factors that slow the pace of degeneration. Leukemia inhibitory factor (LIF) is one such factor that is required for endogenous neuroprotection. Photoreceptors are known to release signals of cellular stress, called damage-associated molecular patterns (DAMPs) early in degeneration, and we hypothesized that receptors for DAMPs or pattern recognition receptors (PRRs) play a key role in the induction of LIF and neuroprotective stress responses in retinal glial cells. Toll-like receptor 2 (TLR2) is a well-established DAMP receptor. In our experiments, activation of TLR2 protected both male and female mice from light damage, while the loss of TLR2 in female mice did not impact photoreceptor survival. In contrast, induction of protective stress responses, microglial phenotype and photoreceptor survival were strongly impacted in male TLR2−/− mice. Lastly, using publicly available gene expression data, we show that TLR2 is expressed highly in resting microglia prior to injury, but is also induced in Müller cells in inherited retinal degeneration.

166 TLR-4-Regulated Cerebrospinal Fluid Hypersecretion in Post-Hemorrhagic Hydrocephalus

Abstract INTRODUCTION Intraventricular hemorrhage (IVH) frequently causes post-hemorrhagic hydrocephalus (PHH) as a result of impaired cerebrospinal fluid (CSF) homeostasis. The most common treatment for PHH is surgical CSF shunting, a procedure fraught with complications. Historically, it is thought that PHH results from impaired reabsorption of CSF, however, little consideration has been given to the role of CSF hypersecretion. Recently, toll-like receptor-4 (TLR-4) has been implicated in the CNS by detecting “alarmins”, including IVH-derived metabolites, via recognition of damage-associated molecular patterns. We speculate that IVH triggers TLR-4-dependent inflammation at the choroid plexus epithelia (CPE), leading to CSF hypersecretion contributing to the development of PHH. METHODS In an established rat model of IVH, we assessed the rate of CSF secretion, CPE inflammation and the effect of genetic and pharmacological intervention on the development of PHH. We developed and implemented a novel surgical method in rats to measure the rate of CSF secretion. TLR-4 knockout rats, antisense oligodeoxynucleotide-mediated gene knockdown, and intracerebroventricular delivery of FDA-approved drugs were used to assess the role of specific inflammatory and ion transport targets on CSF secretion rate and ventriculomegaly following IVH. Immunoblot and immunohistochemistry were used to detect and quantify inflammatory markers. RESULTS >We show IVH triggers TLR4-NFkB-mediated inflammation at the CPE that is associated with a striking ∼3-fold increase in CSF secretion sufficient to cause PHH. CSF hypersecretion is dependent on the NFkB-regulated kinase SPAK, which interacts with and phosphorylates the bumetanide-sensitive NKCC1 at the CPE apical membrane. Genetic ablation of TLR-4 or SPAK, and pharmacology antagonizing TLR-4-NFkB signaling or the SPAK-NKCC1 complex normalizes CSF secretion rates and ventriculomegaly after IVH. CONCLUSION These data uncover a previously unrecognized role for CSF hypersecretion in the pathogenesis of PHH, and reveal a novel TLR-4-dependent regulatory pathway of CSF secretion that can be targeted with repurposed, FDA-approved drugs for the non-surgical treatment of PHH.

Toll-like receptor 2 and type 2 diabetes.

Innate immunity plays a crucial role in the pathogenesis of type 2 diabetes and related complications. Since the toll-like receptors (TLRs) are central to innate immunity, it appears that they are important participants in the development and pathogenesis of the disease. Previous investigations demonstrated that TLR2 homodimers and TLR2 heterodimers with TLR1 or TLR6 activate innate immunity upon recognition of damage-associated molecular patterns (DAMPs). Several DAMPs are released during type 2 diabetes, so it may be hypothesized that TLR2 is significantly involved in its progression. Here, we review recent data on the important roles and status of TLR2 in type 2 diabetes and related complications.

Abstract 562: Dinaciclib induces immunogenic cell death and enhances anti-PD-1 mediated tumor suppression

Abstract Blockade of the checkpoint inhibitor PD-1 has demonstrated remarkable success in the clinic for the treatment of a growing list of different cancers. However, several tumor types are resistant to anti-PD-1 monotherapy. This observation has spurred numerous combination studies to reveal what additional therapeutic interventions may complement anti-PD1 blockade. Recently it has been shown that immunogenic cell death (ICD), induced by radiation and/or chemotherapy, improves T cell responses against different tumor types. ICD is characterized by damage-associated molecular patterns (DAMPs) including surface expression of calreticulin, and release of ATP and HMGB1. Recognition of DAMPs triggers dendritic cell maturation and functions that are critical for tumor antigen-specific T cell activation. Thus therapies that evoke ICD may further augment anti-tumor immunity elicited by anti-PD-1. In mouse syngeneic tumor models, we observed combinatorial anti-tumor activity of anti-PD1 and the cyclin-dependent kinase inhibitor, dinaciclib. We hypothesized that dinaciclib potentiates the effects of anti-PD-1 by eliciting ICD. Indeed, tumor cells treated with dinaciclib express the hallmarks of ICD including HMGB1 and ATP release and surface expression of calreticulin. Dinaciclib treatment also increases tumor cell phagocytosis and induces dendritic cell maturation. Furthermore, mice immunized with dinaciclib-treated tumor cells are resistant to subsequent tumor challenge. Tumors from mice receiving anti-PD1 and dinaciclib have increased T cell infiltration and dendritic cell activation, indicating the overall quality of the immune response generated may be improved with the combo. Taken together, these findings suggest a potential mechanism for the observed synergy between dinaciclib and anti-PD1. Dinaciclib induces immunogenic cell death, converting the tumor cell into an endogenous vaccine and thereby boosting the effects of anti-PD-1. Citation Format: Dewan Mohammed Sakib Hossain, Fernando Ugarte, Anandi Sawant, Mingmei Cai, Venkataraman Sriram, Elaine Pinheiro, Svetlana Sadekova, Alissa Chackerian. Dinaciclib induces immunogenic cell death and enhances anti-PD-1 mediated tumor suppression. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 562.

Pattern Recognition Receptors in Cancer Progression and Metastasis.

The innate immune system is an integral component of the inflammatory response to pathophysiological stimuli. Toll-like receptors (TLRs) and inflammasomes are the major sensors and pattern recognition receptors (PRRs) of the innate immune system that activate stimulus (signal)-specific pro-inflammatory responses. Chronic activation of PRRs has been found to be associated with the aggressiveness of various cancers and poor prognosis. Involvement of PRRs was earlier considered to be limited to infection- and injury-driven carcinogenesis, where they are activated by pathogenic ligands. With the recognition of damage-associated molecular patterns (DAMPs) as ligands of PRRs, the role of PRRs in carcinogenesis has also been implicated in other non-pathogen-driven neoplasms. Dying (apoptotic or necrotic) cells shed a plethora of DAMPs causing persistent activation of PRRs, leading to chronic inflammation and carcinogenesis. Such chronic activation of TLRs promotes tumor cell proliferation and enhances tumor cell invasion and metastasis by regulating pro-inflammatory cytokines, metalloproteinases, and integrins. Due to the decisive role of PRRs in carcinogenesis, targeting PRRs appears to be an effective cancer-preventive strategy. This review provides a brief account on the association of PRRs with various cancers and their role in carcinogenesis.

Clec12a: Quieting the Dead

Immune activation as a result of the recognition of damage-associated molecular patterns needs to be controlled. In this issue of Immunity, Neumann etal. (2014) demonstrates that Clec12a is a receptor for dead cells through the recognition of uric acid crystals and contributes to the dampening of the responses.

A1.70 Sterile inflammation occurs in a TLR9-independent manner in experimental arthritis and rheumatoid arthritis

Background and ObjectivesRheumatoid arthritis (RA) is an inflammatory disease of unknown etiology. Toll-like receptor (TLR) 9 recognizes pathogen-derived DNA and even self DNA under certain circumstances. Interestingly, environmental factors and...

The Yin and Yang of innate immunity in stroke.

Immune system plays an elementary role in the pathophysiological progress of ischemic stroke. It consists of innate and adaptive immune system. Activated within minutes after ischemic onset, innate immunity is responsible for the elimination of necrotic cells and tissue repair, while it is critically involved in the initiation and amplification of poststroke inflammation that amplifies ischemic damage to the brain tissue. Innate immune response requires days to be fully developed, providing a considerable time window for therapeutic intervention, suggesting prospect of novel immunomodulatory therapies against poststroke inflammation-induced brain injury. However, obstacles still exist and a comprehensive understanding of ischemic stroke and innate immune reaction is essential. In this review, we highlighted the current experimental and clinical data depicting the innate immune response following ischemic stroke, mainly focusing on the recognition of damage-associated molecular patterns, activation and recruitment of innate immune cells, and involvement of various cytokines. In addition, clinical trials targeting innate immunity were also documented regardless of the outcome, stressing the requirements for further investigation.

The Yin and Yang of Toll-like receptors in cancer

Recognition of non-self molecular patterns by pattern recognition receptors is a cornerstone of innate immunity. Toll-like receptors (TLRs) exert a key role in recognizing pathogen-associated molecular patterns (PAMPs) but have also been implicated in the recognition of damage-associated molecular patterns (DAMPs). As such, TLRs regulate a wide range of biological responses including inflammatory and immune responses during carcinogenesis. The high expression of TLRs by antigen-presenting cells, including dendritic cells, and their ability to induce antitumor mediators such as type I interferon has led to efforts to utilize TLR agonists in tumor therapy in order to convert the often tolerant immune response toward antitumor responses. However, TLRs are also increasingly recognized as regulators of tumor-promoting inflammation and promoters of tumor survival signals. Here, we will review in detail the dichotomous role of TLRs in tumor biology, focusing on relevant TLR-dependent pro- and antitumor pathways, and discuss clinical applications of TLR-targeted therapies for tumor prevention and treatment.