NEUTROPHIL HETEROGENEITY IN SEPSIS: THE ROLE OF DAMAGE-ASSOCIATED MOLECULAR PATTERNS

ABSTRACT

Sepsis is a severe inflammatory disease syndrome caused by the dysregulated host response to infection. Neutrophils act as the first line of defense against pathogens by releasing effector molecules such as reactive oxygen species, myeloperoxidase, and neutrophil extracellular traps. However, uncontrolled activation of neutrophils and extensive release of effector molecules often cause a "friendly fire" to damage organ systems. Although neutrophils are considered a short-lived, terminally differentiated homogeneous population, recent studies have revealed its heterogeneity comprising different subsets or states implicated in sepsis pathophysiology. Besides the well-known N1 and N2 subsets of neutrophils, several new subsets including aged, antigen-presenting, reverse-migrated, intercellular adhesion molecule-1 + , low-density, olfactomedin 4 + , and Siglec-F + neutrophils have been reported. These neutrophils potentially contribute to the pathogenesis of sepsis based on their proinflammatory and immunosuppressive functions. Damage-associated molecular patterns (DAMPs) are endogenous molecules to induce inflammation by stimulating pattern recognition receptors on immune cells. Different kinds of DAMPs have been shown to contribute to sepsis pathophysiology, including extracellular cold-inducible RNA-binding protein, high-mobility group box 1, extracellular histones, and heat shock proteins. In this review, we summarize the different subsets of neutrophils and their association with sepsis and discuss the novel roles of DAMPs on neutrophil heterogeneity.

Extracellular vesicle mediated feto-maternal HMGB1 signaling induces preterm birth

Preterm birth (PTB; <37 weeks of gestation) impacts ∼11% of all pregnancies and contributes to 1 million neonatal deaths worldwide annually. An understanding of the feto-maternal (F-M) signals that initiate birthing (parturition) at term is critical to design strategies to prevent their premature activation, resulting in PTB. Although endocrine and immune cell signaling are well-reported, fetal-derived paracrine signals capable of transitioning quiescent uterus to an active state of labor are poorly studied. Recent reports have suggested that senescence of the fetal amnion membrane coinciding with fetal growth and maturation generates inflammatory signals capable of triggering parturition. This is by increasing the inflammatory load at the feto-maternal interface (FMi) tissues (i.e., amniochorion-decidua). High mobility group box 1 protein (HMGB1), an alarmin, is one of the inflammatory signals released by senescent amnion cells via extracellular vesicles (exosomes; 40-160 nm). Increased levels of HMGB1 in the amniotic fluid, cord and maternal blood are associated with term and PTB. This study tested the hypothesis that senescent amnion cells release HMGB1, which is fetal signaling capable of increasing FMi inflammation, predisposing them to parturition. To test this hypothesis, exosomes from amnion epithelial cells (AECs) grown under normal conditions were engineered to contain HMGB1 by electroporation (eHMGB1). eHMGB1 was characterized (quantity, size, shape, markers and loading efficiency), and its propagation through FMi was tested using a four-chamber microfluidic organ-on-a-chip device (FMi-OOC) that contained four distinct cell types (amnion and chorion mesenchymal, chorion trophoblast and decidual cells) connected through microchannels. eHMGB1 propagated through the fetal cells and matrix to the maternal decidua and increased inflammation (receptor expression [RAGE and TLR4] and cytokines). Furthermore, intra-amniotic injection of eHMGB1 (containing 10 ng) into pregnant CD-1 mice on embryonic day 17 led to PTB. Injecting carboxyfluorescein succinimidyl ester (CFSE)-labeled eHMGB1, we determined in vivo kinetics and report that eHMGB1 trafficking resulting in PTB was associated with increased FMi inflammation. This study determined that fetal exosome mediated paracrine signaling can generate inflammation and induce parturition. Besides, in vivo functional validation of FMi-OOC experiments strengthens the reliability of such devices to test physiologic and pathologic systems.

Gutting it Out: Developing Effective Immunotherapies for Patients With Colorectal Cancer

Risk factors for colorectal cancer (CRC) include proinflammatory diets, sedentary habits, and obesity, in addition to genetic syndromes that predispose individuals to this disease. Current treatment relies on surgical excision and cytotoxic chemotherapies. There has been a renewed interest in immunotherapy as a treatment option for CRC given the success in melanoma and microsatellite instable (MSI) CRC. Immunotherapy with checkpoint inhibitors only plays a role in the 4%-6% of patients with MSIhigh tumors and even within this subpopulation, response rates can vary from 30% to 50%. Most patients with CRC do not respond to this modality of treatment, even though colorectal tumors are frequently infiltrated with T cells. Tumor cells limit apoptosis and survive following intensive chemotherapy leading to drug resistance and induction of autophagy. Pharmacological or molecular inhibition of autophagy improves the efficacy of cytotoxic chemotherapy in murine models. The microbiome clearly plays an etiologic role, in some or most colon tumors, realized by elegant findings in murine models and now investigated in human clinical trials. Recent results have suggested that cancer vaccines may be beneficial, perhaps best as preventive strategies. The search for therapies that can be combined with current approaches to increase their efficacy, and new knowledge of the biology of CRC are pivotal to improve the care of patients suffering from this disease. Here, we review the basic immunobiology of CRC, current "state-of-the-art" immunotherapies and define those areas with greatest therapeutic promise for the future.

Mitochondrial DNA Is a Pro-Inflammatory Damage-Associated Molecular Pattern Released During Active IBD

Background

Due to common evolutionary origins, mitochondrial DNA (mtDNA) shares many similarities with immunogenic bacterial DNA. MtDNA is recognized as a pro-inflammatory damage-associated molecular pattern (DAMP) with a pathogenic role in several inflammatory diseases. We hypothesised that mtDNA is released during active disease, serving as a key pro-inflammatory factor in inflammatory bowel disease (IBD).

Methods

Between 2014 and 2015, we collected plasma separated within 2 hours of sampling from 97 prospectively recruited IBD patients (67 ulcerative colitis [UC] and 30 Crohn's disease [CD]) and 40 non-IBD controls. We measured circulating mtDNA using quantitative polymerase chain reaction (amplifying mitochondria COXIII/ND2 genes) and also in mouse colitis induced by dextran sulfate-sodium (DSS). We used a mass spectometry approach to detect free plasma mitochondrial formylated peptides. Furthermore, we examined for mitochondrial damage using electron microscopy (EM) and TLR9 expression, the target for mtDNA, in human intestinal IBD mucosa.

Results

Plasma mtDNA levels were increased in UC and CD (both P < 0.0001) compared with non-IBD controls. These levels were significantly correlated to blood (C-reactive protein, albumin, white cell count), clinical and endoscopic markers of severity, and disease activity. In active UC, we identified 5 mitochondrial formylated peptides (the most abundant being fMMYALF with known chemoattractant function) in plasma. We observed mitochondrial damage in inflamed UC mucosa and significantly higher fecal MtDNA levels (vs non-IBD controls [P < 0.0001]), which supports gut mucosal mitochondrial DAMP release as the primary source. In parallel, plasma mtDNA levels increased during induction of acute DSS colitis and were associated with more severe colitis (P < 0.05). In active IBD, TLR9+ lamina propria inflammatory cells were significantly higher in UC and CD compared with controls (P < 0.05).

Conclusions

We present the first evidence to show that mtDNA is released during active IBD. MtDNA is a potential mechanistic biomarker, and our data point to mtDNA-TLR9 as a therapeutic target in IBD. 10.1093/ibd/izy095_videoizy095.video5776747659001.

Hepatic inflammation and fibrosis: functional links and key pathways

Inflammation is one of the most characteristic features of chronic liver disease of viral, alcoholic, fatty, and autoimmune origin. Inflammation is typically present in all disease stages and associated with the development of fibrosis, cirrhosis, and hepatocellular carcinoma. In the past decade, numerous studies have contributed to improved understanding of the links between hepatic inflammation and fibrosis. Here, we review mechanisms that link inflammation with the development of liver fibrosis, focusing on the role of inflammatory mediators in hepatic stellate cell (HSC) activation and HSC survival during fibrogenesis and fibrosis regression. We will summarize the contributions of different inflammatory cells, including hepatic macrophages, T and B lymphocytes, natural killer cells and platelets, as well as key effectors, such as cytokines, chemokines, and damage-associated molecular patterns. Furthermore, we will discuss the relevance of inflammatory signaling pathways for clinical liver disease and for the development of antifibrogenic strategies.

Danger signalling during cancer cell death: origins, plasticity and regulation

Accumulating data indicates that following anti-cancer treatments, cancer cell death can be perceived as immunogenic or tolerogenic by the immune system. The former is made possible due to the ability of certain anti-cancer modalities to induce immunogenic cell death (ICD) that is associated with the emission of damage-associated molecular patterns (DAMPs), which assist in unlocking a sequence of events leading to the development of anti-tumour immunity. In response to ICD inducers, activation of endoplasmic reticulum (ER) stress has been identified to be indispensable to confer the immunogenic character of cancer cell death, due to its ability to coordinate the danger signalling pathways responsible for the trafficking of vital DAMPs and subsequent anti-cancer immune responses. However, in recent times, certain processes apart from ER stress have emerged (e.g., autophagy and possibly viral response-like signature), which have the ability to influence danger signalling. In this review, we discuss the molecular nature, emerging plasticity in the danger signalling mechanisms and immunological impact of known DAMPs in the context of immunogenic cancer cell death. We also discuss key effector mechanisms modulating the interface between dying cancer cells and the immune cells, which we believe are crucial for the therapeutic relevance of ICD in the context of human cancers, and also discuss the influence of experimental conditions and animal models on these.

Achieving CNS axon regeneration by manipulating convergent neuro-immune signaling

After central nervous system (CNS) trauma, axons have a low capacity for regeneration. Regeneration failure is associated with a muted regenerative response of the neuron itself, combined with a growth-inhibitory and cytotoxic post-injury environment. After spinal cord injury (SCI), resident and infiltrating immune cells (especially microglia/macrophages) contribute significantly to the growth-refractory milieu near the lesion. By targeting both the regenerative potential of the axon and the cytotoxic phenotype of microglia/macrophages, we may be able to improve CNS repair after SCI. In this review, we discuss molecules shown to impact CNS repair by affecting both immune cells and neurons. Specifically, we provide examples of pattern recognition receptors, integrins, cytokines/chemokines, nuclear receptors and galectins that could improve CNS repair. In many cases, signaling by these molecules is complex and may have contradictory effects on recovery depending on the cell types involved or the model studied. Despite this caveat, deciphering convergent signaling pathways on immune cells (which affect axon growth indirectly) and neurons (direct effects on axon growth) could improve repair and recovery after SCI. Future studies must continue to consider how regenerative therapies targeting neurons impact other cells in the pathological CNS. By identifying molecules that simultaneously improve axon regenerative capacity and drive the protective, growth-promoting phenotype of immune cells, we may discover SCI therapies that act synergistically to improve CNS repair and functional recovery.

Damaged-self recognition as a general strategy for injury detection

Plants perceive endogenous molecules or their fragments as signals of danger when these appear at increased concentrations in the extracellular space, and they respond with increased endogenous levels of jasmonic acid. The wound hormone jasmonic acid represents a central player in the induced resistance of plants to herbivore feeding and infection by necrotrophic pathogens. This 'damaged self recognition' mechanism of plants exhibits astonishing similarities to the perception of 'damage-associated molecular patterns' (DAMPs) by the human immune system: endogenous cell constituents, or their fragments, that can be released into the extracellular milieu during states of cellular stress or damage function as 'stress signals' and trigger inflammatory and other immunity-related responses. Multicellular organisms use endogenous molecules as danger signals to mount adequate healing and resistance-related responses without depending on exogenous signals and to place exogenous, enemy-derived molecular signals into the adequate functional context.

A novel pathway combining calreticulin exposure and ATP secretion in immunogenic cancer cell death

Surface-exposed calreticulin (ecto-CRT) and secreted ATP are crucial damage-associated molecular patterns (DAMPs) for immunogenic apoptosis. Inducers of immunogenic apoptosis rely on an endoplasmic reticulum (ER)-based (reactive oxygen species (ROS)-regulated) pathway for ecto-CRT induction, but the ATP secretion pathway is unknown. We found that after photodynamic therapy (PDT), which generates ROS-mediated ER stress, dying cancer cells undergo immunogenic apoptosis characterized by phenotypic maturation (CD80(high), CD83(high), CD86(high), MHC-II(high)) and functional stimulation (NO(high), IL-10(absent), IL-1β(high)) of dendritic cells as well as induction of a protective antitumour immune response. Intriguingly, early after PDT the cancer cells displayed ecto-CRT and secreted ATP before exhibiting biochemical signatures of apoptosis, through overlapping PERK-orchestrated pathways that require a functional secretory pathway and phosphoinositide 3-kinase (PI3K)-mediated plasma membrane/extracellular trafficking. Interestingly, eIF2α phosphorylation and caspase-8 signalling are dispensable for this ecto-CRT exposure. We also identified LRP1/CD91 as the surface docking site for ecto-CRT and found that depletion of PERK, PI3K p110α and LRP1 but not caspase-8 reduced the immunogenicity of the cancer cells. These results unravel a novel PERK-dependent subroutine for the early and simultaneous emission of two critical DAMPs following ROS-mediated ER stress.

Hypericin-based photodynamic therapy induces surface exposure of damage-associated molecular patterns like HSP70 and calreticulin

Surface-exposed HSP70 and calreticulin are damage-associated molecular patterns (DAMPs) crucially involved in modulating the success of cancer therapy. Photodynamic therapy (PDT) involves the administration of a photosensitising (PTS) agent followed by visible light-irradiation. The reactive oxygen species that are thus generated directly kill tumours by damaging their microvasculature and inducing a local inflammatory reaction. PDT with the PTS photofrin is associated with DAMPs exposure, but the same is not true for other PTSs. Here, we show that when cancer cells are treated with hypericin-based PDT (Hyp-PDT), they surface-expose both HSP70 and calreticulin (CRT). Induction of CRT exposure was not accompanied by co-exposure of ERp57, but this did not compromise the ability of the exposed CRT to regulate the phagocytosis of Hyp-PDT-treated cancer cells by dendritic cells. Interestingly, we found that Hyp-PDT-induced CRT exposure (in contrast to anthracycline-induced CRT exposure) was independent of the presence of ERp57. Our results indicate that Hyp-PDT is a potential anti-cancer immunogenic modality.

Involvement of damage-associated molecular patterns in tumor response to photodynamic therapy: surface expression of calreticulin and high-mobility group box-1 release

Damage-associated molecular patterns (DAMPs), danger signal molecules expressed after injury or infection, have become recognized as prerequisite for orchestrating effective anti-tumor host response. The expression of two prototypical DAMPs, calreticulin and high-mobility group box-1 (HMGB1) protein, was examined following Photofrin-photodynamic therapy (PDT) of Lewis lung carcinoma (LLC) cells in vitro and LLC tumors growing in syngeneic mice. Cell surface expression of calreticulin was found to be highly increased at 1 h after PDT treatment both in vitro and in vivo. Increased exposure of calreticulin was also detected on the surface of macrophages from PDT-treated LLC tumors. At the same time interval, a rise in serum HMGB1 was detected in host mice. Intracellular staining of macrophages co-incubated for 16 h with PDT-treated LLC cells revealed elevated levels of HMGB1 in these cells. The knowledge of the involvement of these DAMPs uncovers important mechanistic insights into the development of host response induced by PDT.

Toll like receptors in diseases of the lung

The lung is in continuous contact with a diverse array of infectious agents, foreign antigens, and host-derived danger signals. To sample this expansive internal and external milieu, both resident myeloid and stromal/structure cells of the lung express a full complement of toll like receptors (TLRs) which recognize pathogen-associated molecular patterns (PAMPs) and endogenous danger-associated molecular patterns (DAMPs). TLRs play a vital role in immune host defense against bacterial, mycobacterial, fungal, and viral pathogens of the lung. Additionally, TLRs contribute to disease pathogenesis in non-infectious pulmonary disorders, including airway disease, acute lung injury, and interstitial lung disease. In this review, TLR biology in the context of experimental infectious and non-infectious lung disease is discussed, and correlates to human lung disease, including therapeutic implications of these findings, are defined.

Toll-like receptor 3 signaling enables human esophageal epithelial cells to sense endogenous danger signals released by necrotic cells

The mechanisms by which gastroesophageal reflux disease esophagitis develops are controversial. Although many support the notion that caustic injury leads to reflux esophagitis, others have proposed that reflux esophagitis is caused by esophageal epithelial cytokine-mediated inflammation. We previously demonstrated that Toll-like receptor 3 (TLR3) is highly expressed and functional in the nontransformed human esophageal epithelial cell line EPC2-hTERT. In addition to activation by viral double-stranded RNA, TLR3 can be activated by endogenous mRNA released by necrotic cells. In the present study, we investigated the role of esophageal epithelial TLR3 to sense danger signals released by necrotic esophageal epithelial cells in vitro. Following induction of freeze-thaw necrosis, necrotic EPC2-hTERT cell supernatants (NCS) were used to stimulate EPC2-hTERT monolayers, leading to NF-κB-dependent induction of IL-8 mRNA expression. Responses to self-derived NCS were not observed in transformed gastrointestinal epithelial cell lines, including TE-1 and Caco-2 cells, suggesting that the ability to sense endogenous danger signals is unique to nontransformed esophageal epithelial cells. To determine the immunostimulatory role of epithelial RNA, EPC2-hTERT cells were stimulated with self-derived mRNA, which significantly induced IL-8 mRNA expression. Finally, suppression of TLR3 signaling in a DN-TLR3 cell line, hTERT-ΔTIR-TLR3, led to reduced NCS-induced IL-8 induction by both NCS and mRNA stimulation. Our results demonstrate that human esophageal epithelial cells can sense endogenous danger signals, in part through TLR3 signaling. This supports the concept that epithelial injury plays an inciting role in the pathogenesis of reflux-induced esophagitis, providing important insights into the mechanisms by which epithelial injury leads to inflammation.

The role of proteomics in the diagnosis of chorioamnionitis and early-onset neonatal sepsis

Intrauterine infection is a unique pathologic process that raises the risk for early-onset neonatal sepsis (EONS). By acting synergistically with prematurity, EONS increases the risk for adverse neonatal outcomes, including intraventricular hemorrhage and cerebral palsy. Although several pathways for the pathogenesis of fetal damage have been proposed, the basic molecular mechanisms that modulate these events remain incompletely understood. Discovery of clinically and biologically relevant biomarkers able to reveal key pathogenic pathways and predict pregnancies at risk for antenatal fetal damage is a priority. Proteomics provides a unique opportunity to fill this gap.

Cancer Cells Expressing Toll-like Receptors and the Tumor Microenvironment

Toll-like receptors (TLRs) play a crucial role in the innate immune response and the subsequent induction of adaptive immune responses against microbial infection or tissue injury. Recent findings show that functional TLRs are expressed not only on immune cells but also on cancer cells. TLRs play an active role in carcinogenesis and tumor progression during chronic inflammation that involves the tumor microenvironment. Damage-associated molecular patterns (DAMPs) derived from injured normal epithelial cells and necrotic cancer cells appear to be present at significant levels in the tumor microenvironment, and their stimulation of specific TLRs can foster chronic inflammation. This review discusses how carcinogenesis, cancer progression, and site-specific metastasis are related to interactions between cancer cells, immune cells, and DAMPs through TLR activation in the tumor microenvironment.

Receptor-mediated signalling in plants: molecular patterns and programmes

A highly evolved surveillance system in plants is able to detect a broad range of signals originating from pathogens, damaged tissues, or altered developmental processes, initiating sophisticated molecular mechanisms that result in defence, wound healing, and development. Microbe-associated molecular pattern molecules (MAMPs), damage-associated molecular pattern molecules (DAMPs), virulence factors, secreted proteins, and processed peptides can be recognized directly or indirectly by this surveillance system. Nucleotide binding-leucine rich repeat proteins (NB-LRR) are intracellular receptors and have been targeted by breeders for decades to elicit resistance to crop pathogens in the field. Receptor-like kinases (RLKs) or receptor like proteins (RLPs) are membrane bound signalling molecules with an extracellular receptor domain. They provide an early warning system for the presence of potential pathogens and activate protective immune signalling in plants. In addition, they act as a signal amplifier in the case of tissue damage, establishing symbiotic relationships and effecting developmental processes. The identification of several important ligands for the RLK-type receptors provided an opportunity to understand how plants differentiate, how they distinguish beneficial and detrimental stimuli, and how they co-ordinate the role of various types of receptors under varying environmental conditions. The diverse roles of extra-and intracellular plant receptors are examined here and the recent findings on how they promote defence and development is reviewed.