Extra domain A of fibronectin primes leukotriene biosynthesis and stimulates neutrophil migration through activation of Toll-like receptor 4

TLR4 Antagonism Reduces Movement-Induced Nociception and ATF-3 Expression in Experimental Osteoarthritis

Introduction

Toll-like receptor 4 (TLR4) is a pattern recognition receptor involved in the detection of pathogen-associated molecular patterns (PAMPs), but also a "danger-sensing" receptor that recognizes host-derived endogenous molecules called damage-associated molecular patterns (DAMPs). The involvement of TLR4 in rheumatic diseases is becoming evident, as well as its potential role as a target for therapeutic intervention. Moreover, increasing evidence also suggests that TLR4 is implicated in chronic pain states. Thus, in this study, we evaluated whether a systemic administration of a synthetic antagonist of TLR4 (TLR4-A1) could decrease nociception and cartilage degradation in experimental osteoarthritis (OA). Furthermore, as the activation transcription factor (ATF)-3 serves as a negative regulator for TLR4-stimulated inflammatory response, we also evaluated the effect of TLR4 inhibition on ATF-3 expression in primary afferent neurons at the dorsal root ganglia (DRG).

Methods

OA was induced in adult male Wistar rats through an intra-articular injection of 2 mg of sodium mono-iodoacetate (MIA) into the left knee. From days 14 to 28 after OA induction, animals received an intraperitoneal injection of either TLR4-A1 (10 mg/kg) or vehicle. Movement- and loading-induced nociception was evaluated in all animals, by the Knee-Bend and CatWalk tests, before and at several time-points after TLR4-A1/vehicle administration. Immunofluorescence for TLR4 and ATF-3 was performed in L3-L5 DRG. Knee joints were processed for histopathological evaluation.

Results

Administration of TLR4-A1 markedly reduced movement-induced nociception in OA animals, particularly in the Knee-Bend test. Moreover, the increase of ATF-3 expression observed in DRG of OA animals was significantly reduced by TLR4-A1. However, no effect was observed in cartilage loss nor in the neuronal cytoplasmic expression of TLR4 upon antagonist administration.

Conclusion

The TLR4 antagonist administration possibly interrupts the TLR4 signalling cascade, thus decreasing the neurotoxic environment at the joint, which leads to a reduction in ATF-3 expression and in nociception associated with experimental OA.

The Dynamic Interplay Between Cardiac Inflammation and Fibrosis

Heart failure is a leading cause of death worldwide. While there are multiple etiologies contributing to the development of heart failure, all cause result in impairments in cardiac function that is characterized by changes in cardiac remodeling and compliance. Fibrosis is associated with nearly all forms of heart failure and is an important contributor to disease pathogenesis. Inflammation also plays a critical role in the heart and there is a large degree of interconnectedness between the inflammatory and fibrotic response. This review discusses the cellular and molecular mechanisms contributing to inflammation and fibrosis and the interplay between the two.

Toll-like Receptors as a Novel Therapeutic Target for Natural Products Against Chronic Diseases

Toll-like receptors (TLR) are one among the initial responders of the immune system which participate in the activation inflammatory processes. Several different types of TLR such as TLR2, TLR4, TLR7 and TLR9 have been identified in various cell types, each having distinct ligands like lipids, lipoproteins, nucleic acids and proteins. Though its prime concern is xenobiotic defences, TLR signalling has also recognized as an activator of inflammation and associated development of chronic degenerative disorders (CDDs) including obesity, type 2 diabetes mellitus (T2DM), fatty liver disease, cardiovascular and neurodegenerative disorders as well as various types of cancers. Numerous drugs are in use to prevent these disorders, which specifically inhibit different pathways associated with the development of CDDs. Compared to these drug targets, inhibition of TLR, which specifically responsible for the inflammatory insults has proven to be a better drug target. Several natural products have emerged as inhibitors of CDDs, which specifically targets TLR signalling, among these, many are in the clinical trials. This review is intended to summarize the recent progress on TLR association with CDDs and to list possible use of natural products, their combinations and their synthetic derivative in the prevention of TLR-driven CDD development.

Toll-like receptor 4: A promising crossroads in the diagnosis and treatment of several pathologies

Toll-like receptor 4 (TLR4) is expressed in a wide variety of cells and is the central component of the mammalian innate immune system. Since its discovery in 1997, TLR4 has been assigned an ever-increasing number of functions that extend from pathogen recognition to tissue damage identification and promotion of the intrinsic "damage repair response" in pain, intestinal, respiratory and vascular disorders. Precisely, the finding of conserved sequence homology among species along with the molecular and functional characterisation of the TLR4 gene enabled researchers to envisage a common operating system in the activation of innate immunity and the initiation of plastic changes at the onset of chronic pain. Malfunctioning in other conditions was conceived in parallel. In this respect, "pivot" proteins and pathway redundancy are not just evolutionary leftovers but essential for normal functioning or cell survival. Indeed, at present, TLR4 single nucleotide polymorphisms (SNP) and their association with certain dysfunctions and diseases are being confirmed in different pools of patients. However, despite its ability to trigger pathogen infection or alternatively tissue injury communications to immune system, TLR4 targeting might not be considered a panacea. This review article represents a compilation of what we know about TLR4 from clinics and basic research on the 20th anniversary of its discovery. Understanding how to fine-tune the interaction between TLR4 and its specific ligands may lead in the next decades to the development of promising new treatments, reducing polypharmacy and probably having an impact on drug use in numerous pathologies.

PEGylated pUR4/FUD peptide inhibitor of fibronectin fibrillogenesis decreases fibrosis in murine Unilateral Ureteral Obstruction model of kidney disease

Fibronectin is a blood and extracellular matrix glycoprotein that plays important roles in wound healing and fibrosis since it controls the deposition of collagen and other extracellular matrix molecules and is a substrate for infiltrating lymphocytes. Using a high-affinity fibronectin-binding peptide (FUD/pUR4) that inhibits fibronectin deposition into extracellular matrix (ECM), we tested the ability of a PEGylated FUD/pUR4 (PEG-FUD) to inhibit fibrosis in the Unilateral Ureteral Obstruction (UUO) kidney disease model. Fibronectin fibrillogenesis assays, using human fibroblasts and human proximal tubular epithelial cultures, showed that PEG-FUD can inhibit fibronectin fibrillogenesis in vitro with an IC50 similar to unconjugated FUD, in the order of 20–35 nM. In contrast, a mutated FUD (mFUD) conjugated to PEG that lacked activity did not inhibit fibronectin assembly, even at 20 μM. The in vivo activity of PEG-FUD was tested in the murine UUO model by daily subcutaneous injection of 12.5 mg/kg for 7 days until harvest at day 10. Control treatments included saline, PEG, unconjugated FUD, and PEG-mFUD. Immunoblotting studies showed that fibronectin was enriched in the extracellular matrix fractions of extracted UUO kidneys, compared to contralateral untreated kidneys. In vivo, PEG-FUD significantly decreased fibronectin by ~70% in UUO kidneys as determined by both IHC and immunoblotting, respectively. In contrast, neither PEG-mFUD, PEG, nor saline had any significant effect. PEG-FUD also decreased collagens I and III and CD45-expressing cells (leukocytes) by ~60% and ~50%, as ascertained by picrosirius red staining and IHC, respectively. Immunoblotting studies also showed that the fibronectin remaining after PEG-FUD treatment was intact. Utilizing a custom-made polyclonal antibody generated against pUR4/FUD, intact PEG-FUD was detected by immunoblotting in both the ECM and lysate fractions of UUO kidneys. No adverse reaction or event was noted with any treatment. In summary, these studies suggest that PEG-FUD reached the kidneys without degradation, and decreased fibronectin incorporation into interstitial tissue. Decreased fibronectin was accompanied by a decrease in collagen and leukocyte infiltration. We propose that PEG-FUD, a specific inhibitor of fibronectin assembly, may be a candidate therapeutic for the treatment of fibrosis in kidney diseases.

Danger-Associated Molecular Patterns Derived From the Extracellular Matrix Provide Temporal Control of Innate Immunity

It is evident that components of the extracellular matrix (ECM) act as danger-associated molecular patterns (DAMPs) through direct interactions with pattern recognition receptors (PRRs) including Toll-like receptors (TLRs) and inflammasomes. Through these interactions, ECM-derived DAMPs autonomously trigger sterile inflammation or prolong pathogen-induced responses through the production of proinflammatory mediators and the recruitment of leukocytes to sites of injury and infection. Recent research, however, suggests that ECM-derived DAMPs are additionally involved in the resolution and fine-tuning of inflammation by orchestrating the production of anti-inflammatory mediators that are required for the resolution of tissue inflammation and the transition to acquired immunity. Thus, in this review, we discuss the current knowledge of the interplay between ECM-derived DAMPs and the innate immune signaling pathways that are activated to provide temporal control of innate immunity.

Lipidomics in translational research and the clinical significance of lipid-based biomarkers

Lipidomics is a rapidly developing field of study that focuses on the identification and quantitation of various lipid species in the lipidome. Lipidomics has now emerged in the forefront of scientific research due to the importance of lipids in metabolism, cancer, and disease. Using both targeted and untargeted mass spectrometry as a tool for analysis, progress in the field has rapidly progressed in the last decade. Having the ability to assess these small molecules in vivo has led to better understanding of several lipid-driven mechanisms and the identification of lipid-based biomarkers in neurodegenerative disease, cancer, sepsis, wound healing, and pre-eclampsia. Biomarker identification and mechanistic understanding of specific lipid pathways linked to a disease's pathologies can form the foundation in the development of novel therapeutics in hopes of curing human disease.

Toll-Like Receptor-4 Signaling Drives Persistent Fibroblast Activation and Prevents Fibrosis Resolution in Scleroderma

Significance: This review provides current overview of the emerging role of innate immunity in driving fibrosis, and preventing its resolution, in scleroderma (systemic sclerosis, SSc). Understanding the mechanisms of dysregulated innate immunity in fibrosis and SSc will provide opportunities for therapeutic interventions using novel agents and repurposed existing drugs. Recent Advances: New insights from genomic and genetic studies implicate components of innate immune signaling such as pattern recognition receptors (PRRs), downstream signaling intermediates, and endogenous inhibitors, in fibrosis in SSc. Recent studies distinguish innate immune signaling in tissue-resident myofibroblasts and bone marrow-derived immune cells and define their roles in the development and persistence of tissue fibrosis. Critical Issues: Activation of toll-like receptors (TLRs) and other PRR mechanisms occurs in resident nonimmune cells within injured tissue microenvironments. These cells respond to damage-associated molecular patterns (DAMPs), such as tenascin-C that are recognized as danger signals, and elicit matrix production, cytokine secretion, and myofibroblast transformation and survival. When these responses persist due to constitutive TLR activation or impaired termination by endogenous inhibitors, they interfere with fibrosis resolution. The genetic basis and molecular mechanisms of these phenomena in the context of fibrosis are under current investigation. Future Directions: Precise delineation of the pathogenic DAMPs, their interaction with TLRs and other PRRs, the downstream signaling pathways and transcriptional events, and the fibroblast-specific regulation and function of endogenous inhibitors of innate immunity, will form the foundation for innovative targeted therapies to block fibrosis by reestablishing balanced innate immune signaling in fibroblasts.

Endogenous ligands of TLR4 promote unresolving tissue fibrosis: Implications for systemic sclerosis and its targeted therapy

Fibrosis, the hallmark of scleroderma or systemic sclerosis (SSc), is a complex, dynamic and generally irreversible pathophysiological process that leads to tissue disruption, and lacks effective therapy. While early-stage fibrosis resembles normal wound healing, in SSc fibrosis fails to resolve. Innate immune signaling via toll-like receptors (TLRs) has recently emerged as a key driver of persistent fibrotic response in SSc. Recurrent injury in genetically predisposed individual causes generation of "damage-associated molecular patterns" (DAMPs) such as fibronectin-EDA and tenascin-C. Sensing of these danger signals by TLR4 on resident cells elicits potent stimulatory effects on fibrotic gene expression and myofibroblast differentiation, and appears to sensitize fibroblasts to the profibrotic stimulatory effect of TGF-β. Thus, DAMPs induce TLR4-mediated innate immune signaling on resident mesenchymal cells which drives the emergence and persistence of fibrotic cells in tissues, and underlies the switch from a self-limited repair response to non-resolving pathological fibrosis characteristic of SSc. In this review, we present current views of the DAMP-TLR4 axis in driving sustained fibroblasts activation and its pathogenic roles in fibrosis progression in SSc, and potential anti-fibrotic approaches for selective therapeutic targeting of TLR4 signaling.

NETosis in Cancer - Platelet-Neutrophil Crosstalk Promotes Tumor-Associated Pathology

It has become increasingly clear that circulating immune cells in the body have a major impact on cancer development, progression, and outcome. The role of both platelets and neutrophils as independent regulators of various processes in cancer has been known for long, but it has quite recently emerged that the platelet-neutrophil interplay is yet a critical component to take into account during malignant disease. It was reported a few years ago that neutrophils in mice with cancer have increased propensity to form neutrophil extracellular traps (NETs) - web-like structures formed by externalized chromatin and secreted proteases. The initial finding describing this as a cell death-associated process has been followed by reports of additional mechanisms for NET formation (NETosis), and it has been shown that similar structures can be formed also without lysis and neutrophil cell death as a consequence. Furthermore, presence of NETs in humans with cancer has been verified in a few recent studies, indicating that tumor-induced NETosis is clinically relevant. Several reports have also described that NETs contribute to cancer-associated pathology, by promoting processes responsible for cancer-related death such as thrombosis, systemic inflammation, and relapse of the disease. This review summarizes current knowledge about NETosis in cancer, including the role of platelets as regulators of tumor-induced NETosis. It has been shown that platelets can serve as inducers of NETosis, and the platelet-neutrophil interface can therefore be an important issue to consider when designing therapies targeting cancer-associated pathology in the future.

Sickle red cells as danger signals on proinflammatory gene expression, leukotriene B4 and interleukin-1 beta production in peripheral blood mononuclear cell

This study tested the hypothesis that sickle red blood cell (SS-RBC) induce Toll-like receptors (TLR) and Nod-like receptor family, pyrin domain containing 3 (NLRP3)- inflammasome expression in peripheral blood mononuclear cells (PBMC). TLR and NLRP3 inflammasome could contribute to the maintenance of the inflammatory status in sickle cell anemia (SCA) patients, since SS-RBC act as danger signals activating these pathways. In this study, first, we evaluated TLR (2, 4, 5 and 9), NLRP3, Caspase-1, interleukin (IL)-1β and IL-18 expression in PBMC freshly isolated from SCA patients (SS-PBMC) in comparison with PBMC from healthy individuals (AA-PBMC). In the second moment, we investigated whether SS-RBC could interfere with the expression of these molecules in PBMC from healthy donor, in the absence or presence of hydroxyurea (HU) in vitro. TLRs and NLRP3 inflammasome expression were investigated by qPCR. IL-1β, Leukotriene-B4 (LTB4) and nitrite production were measured in PBMC (from healthy donor) culture supernatants. TLR2, TLR4, TLR5, NLRP3 and IL-1β were highly expressed in SS-PBMC when compared to AA-PBMC. Additionally, SS-RBC induced TLR9, NLRP3, Caspase-1, IL-1β and IL-18 expression and induced IL-1β, LTB4 and nitrite production in PBMC cultures. HU did not prevent TLR and NLRP3 inflammasome expression, but increased TLR2 and IL-18 expression and reduced nitrite production. In conclusion, our data suggest that TLR and inflammasome complexes may be key inducers of inflammation in SCA patients, probably through SS-RBC; also, HU does not prevent NLRP3 inflammasome- and TLR-dependent inflammation, indicating the need to develop new therapeutic strategies to SCA patients that act with different mechanisms of those observed for HU.

Keloids: The paradigm of skin fibrosis - Pathomechanisms and treatment

Keloids, fibroproliferative dermal tumors with effusive accumulation of extracellular matrix (ECM) components, particularly collagen, result from excessive expression of growth factors and cytokines. The etiology of keloids is unknown but they occur after dermal injury in genetically susceptible individuals, and they cause both physical and psychological distress for the affected individuals. Several treatment methods for keloids exist, including the combination therapy of surgical excision followed by intralesional steroid therapy, however, they have high recurrence rate regardless of the current treatment method. Improved understanding of the pathomechanisms leading to keloid formation will hopefully identify pathways that serve as specific targets to improve therapy for this devastating, currently intractable, disorder.

WISP1 mediates hepatic warm ischemia reperfusion injury via TLR4 signaling in mice

Wnt-induced secreted protein-1 (WISP1) is an extracellular matrix protein that has been reported in cancer researches. Our previous studies on WISP1 implied it could be a harmful mediator in septic mice. However, its role in liver ischemia reperfusion (I/R) injury is unknown. This study investigated the effects of WISP1 on liver I/R damage. Male C57BL/6 wild-type mice were used to undergo 60 min segmental (70%) ischemia. WISP1 expression was measured after indicated time points of reperfusion. Anti-WISP1 antibody was injected intraperitoneally to mice. Toll-like receptor 4 (TLR4) knockout mice and TIR-domain-containing adaptor inducing interferon-β (TRIF) knockout mice were adopted in this study. WISP1 was significantly enhanced after 6 h of reperfusion when compared with sham treated mice and significantly decreased either by TLR4 knockout mice or TRIF knockout mice. Anti-WISP1 antibody significantly decreased serum alanine aminotransferase (ALT), aspartate aminotransferase (AST), pathological changes and pro-inflammatory cytokine levels in the mice following I/R. Furthermore, significantly increased serum transaminase levels were found in C57 wild-type mice treated with recombinant WISP1 protein, but not found in TLR4 knockout or TRIF knockout mice subjected to liver I/R. Taken together, WISP1 might contribute to hepatic ischemia reperfusion injury in mice and possibly depends on TLR4/TRIF signaling.

Altered Innate Immune Responses in Neutrophils from Patients with Well- and Suboptimally Controlled Asthma

BACKGROUND

Respiratory infections are a major cause of asthma exacerbations where neutrophilic inflammation dominates and is associated with steroid refractory asthma. Structural airway cells in asthma differ from nonasthmatics; however it is unknown if neutrophils differ. We investigated neutrophil immune responses in patients who have good (AGood) and suboptimal (ASubopt) asthma symptom control.

METHODS

Peripheral blood neutrophils from AGood (ACQ < 0.75, n = 11), ASubopt (ACQ > 0.75, n = 7), and healthy controls (HC) (n = 9) were stimulated with bacterial (LPS (1 μg/mL), fMLF (100 nM)), and viral (imiquimod (3 μg/mL), R848 (1.5 μg/mL), and poly I:C (10 μg/mL)) surrogates or live rhinovirus (RV) 16 (MOI1). Cell-free supernatant was collected after 1 h for neutrophil elastase (NE) and matrix metalloproteinase- (MMP-) 9 measurements or after 24 h for CXCL8 release. Results. Constitutive NE was enhanced in AGood neutrophils compared to HC. fMLF stimulated neutrophils from ASubopt but not AGood produced 50% of HC levels. fMLF induced MMP-9 was impaired in ASubopt and AGood compared to HC. fMLF stimulated CXCL8 but not MMP-9 was positively correlated with FEV1 and FEV1/FVC. ASubopt and AGood responded similarly to other stimuli.

CONCLUSIONS

Circulating neutrophils are different in asthma; however, this is likely to be related to airflow limitation rather than asthma control.

Genetic Ablation of Extra Domain A of Fibronectin in Hypercholesterolemic Mice Improves Stroke Outcome by Reducing Thrombo-Inflammation

BACKGROUND

The fibronectin-splicing variant containing extra domain A (Fn-EDA) is present in negligible amounts in the plasma of healthy humans but markedly elevated in patients with comorbid conditions, including diabetes mellitus and hypercholesterolemia, which are risk factors for stroke. It remains unknown, however, whether Fn-EDA worsens stroke outcomes in such conditions. We determined the role of Fn-EDA in stroke outcome in a model of hypercholesterolemia, the apolipoprotein E-deficient (Apoe(-/-)) mouse.

METHODS AND RESULTS

In a transient cerebral ischemia/reperfusion injury model, Apoe(-/-) mice expressing fibronectin deficient in EDA (Fn-EDA(-/-)Apoe(-/-) mice) exhibited smaller infarcts and improved neurological outcomes at days 1 and 8 (P<0.05 versus Apoe(-/-) mice). Concomitantly, intracerebral thrombosis [assessed by fibrin(ogen) deposition] and postischemic inflammation (phospho-nuclear factor-κB p65, phospho-IκB kinase α/β, interleukin 1β, and tumor necrosis factor-α) within lesions of Fn-EDA(-/-)Apoe(-/-) mice were markedly decreased (P<0.05 versus Apoe(-/-) mice). In an FeCl3 injury-induced carotid artery thrombosis model, thrombus growth rate and the time to occlusion were prolonged in Fn-EDA(-/-)Apoe(-/-) mice (P<0.05 versus Apoe(-/-) mice). Genetic ablation of TLR4 improved stroke outcome in Apoe(-/-) mice (P<0.05) but had no effect on stroke outcome in Fn-EDA(-/-)Apoe(-/-) mice. Bone marrow transplantation experiments revealed that nonhematopoietic cell-derived Fn-EDA exacerbates stroke through Toll-like receptor-4 expressed on hematopoietic cells. Infusion of a specific inhibitor of Fn-EDA into Apoe(-/-) mouse 15 minutes after reperfusion significantly improved stroke outcome.

CONCLUSIONS

Hypercholesterolemic mice deficient in Fn-EDA exhibit reduced cerebral thrombosis and less inflammatory response after ischemia/reperfusion injury. These findings suggest that targeting Fn-EDA could be an effective therapeutic strategy in stroke associated with hypercholesterolemia.

Differential neutrophil activation in viral infections: Enhanced TLR-7/8-mediated CXCL8 release in asthma

Background and objective

Respiratory viral infections are a major cause of asthma exacerbations. Neutrophils accumulate in the airways and the mechanisms that link neutrophilic inflammation, viral infections and exacerbations are unclear. This study aims to investigate anti‐viral responses in neutrophils from patients with and without asthma and to investigate if neutrophils can be directly activated by respiratory viruses.

Methods

Neutrophils from peripheral blood from asthmatic and non‐asthmatic individuals were isolated and stimulated with lipopolysaccharide (LPS) (1 μg/mL), f‐met‐leu‐phe (fMLP) (100 nM), imiquimod (3 μg/mL), R848 (1.5 μg/mL), poly I:C (10 μg/mL), RV16 (multiplicity of infection (MOI)1), respiratory syncytial virus (RSV) (MOI1) or influenza virus (MOI1). Cell‐free supernatants were collected after 1 h of neutrophil elastase (NE) and matrix metalloproteinase (MMP)‐9 release, or after 24 h for CXCL8 release.

Results

LPS, fMLP, imiquimod and R848 stimulated the release of CXCL8, NE and MMP‐9 whereas poly I:C selectively induced CXCL8 release only. R848‐induced CXCL8 release was enhanced in neutrophils from asthmatics compared with non‐asthmatic cells (P < 0.01). RSV triggered the release of CXCL8 and NE from neutrophils, whereas RV16 or influenza had no effect.

Conclusion

Neutrophils release CXCL8, NE and MMP‐9 in response to viral surrogates with R848‐induced CXCL8 release being specifically enhanced in asthmatic neutrophils. Toll‐like receptor (TLR7/8) dysregulation may play a role in neutrophilic inflammation in viral‐induced exacerbations.

We aimed to investigate and compare neutrophil responses to bacterial compounds and viral mimetics as well as compare responses between people with and without asthma. We also investigated neutrophil responses to live respiratory viruses. Here we provide a novel comprehensive comparison showing differential and specific activation in innate immune cells.

See Editorial, page 10

Cellular fibronectin containing extra domain A promotes arterial thrombosis in mice through platelet Toll-like receptor 4

Cellular fibronectin containing extra domain A (Fn-EDA+), which is produced in response to tissue injury in several disease states, has prothrombotic activity and is known to interact with Toll-like-receptor 4 (TLR4). The underlying mechanism and cell types involved in mediating the prothrombotic effect of Fn-EDA+ still remain unknown. Using intravital microscopy, we evaluated susceptibility to carotid artery thrombosis after FeCl3-induced injury in mice expressing Fn lacking EDA (Fn-EDA(-/-) mice) or Fn containing EDA (Fn-EDA(+/+) mice). Fn-EDA(-/-) mice exhibited prolonged times to first thrombus formation and complete occlusion and a significant decrease in the rate of thrombus growth (P < .05 vs Fn-EDA(+/+) mice). Genetic deletion of TLR4 reversed the accelerated thrombosis in Fn-EDA(+/+) mice (P < .05) but had no effect in Fn-EDA(-/-) mice. Bone marrow transplantation experiments revealed that TLR4 expressed on hematopoietic cells contributes to accelerated thrombosis in Fn-EDA(+/+) mice. In vitro studies showed that cellular Fn-EDA+ interacts with platelet TLR4 and promotes agonist-induced platelet aggregation. Finally, Fn-EDA(+/+) mice specifically lacking platelet TLR4 exhibited prolonged times to first thrombus formation and complete occlusion (P < .05 vs Fn-EDA(+/+) mice containing platelet TLR4). We conclude that platelet TLR4 contributes to the prothrombotic effect of cellular Fn-EDA+, suggesting another link between thrombosis and innate immunity.

Increased autophagy sustains the survival and pro-tumourigenic effects of neutrophils in human hepatocellular carcinoma

BACKGROUND & AIMS

Neutrophils are common cells of the inflammatory infiltrate and are predominantly enriched in many cancers. We recently found that neutrophils are accumulated in human hepatocellular carcinoma (HCC), where they promote disease progression by releasing matrix metalloproteinase-9 (MMP9). The underlying mechanisms, however, that allow tumour microenvironments to educate neutrophils are largely unknown.

METHODS

Neutrophils were purified from HCC patients and healthy donors. Immunohistochemistry and immunoblotting were used for the evaluation of autophagy in neutrophils. The regulation and function of increased neutrophil autophagy were assessed by both in vitro and ex vivo studies.

RESULTS

Most neutrophils in HCC intratumoural regions, in contrast to those located in the paired non-tumoural areas and within tumour vessels, substantially expressed autophagy-specific protein LC3. Soluble factors derived from hepatoma, including hyaluronan fragments, triggered a considerable increase of functional LC3 and autophagosomes in neutrophils, but this was unrelated to the deactivation of mTOR signalling. Inhibiting the activation of Erk1/2, p38, and NF-κB signals could significantly attenuate such tumour-elicited autophagy. These neutrophils, undergoing autophagy, exhibited long-lived phenotypes with retained Mcl-1 and significantly more intact mitochondria as well as low cleaved caspase-3, which could be abolished by inhibiting the initiation of autophagy. Moreover, increased neutrophil autophagy also correlated with sustained production of pro-metastatic oncostatin M and MMP9 and advanced migration of cancer cells.

CONCLUSIONS

Increased autophagy in neutrophils may represent a novel mechanism that links the innate response to neoplastic progression in humans. Studying the mechanisms that selectively modulate neutrophil autophagy will provide a novel strategy for anti-cancer therapy.

Sputum ADAM8 expression is increased in severe asthma and COPD

BACKGROUND

Severe asthma and chronic obstructive pulmonary disease (COPD) are chronic inflammatory airway diseases in which the mechanisms are not fully understood. A disintegrin and metalloproteinase domain 8 (ADAM8) is an enzyme expressed on most leucocytes and may be important for facilitating leucocyte migration in respiratory disease.

OBJECTIVE

To investigate ADAM8 mRNA and protein expression in asthma and COPD and its relationship between asthma severity and inflammatory phenotypes.

METHODS

Induced sputum was collected from 113 subjects with asthma (severe n = 31, uncontrolled n = 39 and controlled n = 35), 20 subjects with COPD and 21 healthy controls. Sputum ADAM8 mRNA expression was measured by qPCR, and soluble ADAM8 (sADAM8) protein was measured in the sputum supernatant by validated ELISA.

RESULTS

ADAM8 mRNA correlated with ADAM8 protein levels (r = 0.27, P < 0.01). ADAM8 mRNA (P = 0.004) and sADAM8 protein (P = 0.014) levels were significantly higher in both asthma and COPD compared with healthy controls. ADAM8 mRNA (P = 0.035) and sADAM8 protein (P = 0.002) levels were significantly higher in severe asthma compared with controlled asthma. Total inflammatory cell count (P < 0.01) and neutrophils (P < 0.01) were also elevated in severe asthmatic sputum. Although ADAM8 mRNA was significantly higher in eosinophilic and neutrophilic asthma (P < 0.001), sADAM8 did not differ between asthma inflammatory phenotypes. ADAM8 expression positively correlated with sputum total cell count and sputum neutrophils.

CONCLUSIONS AND CLINICAL RELEVANCE

ADAM8 expression is increased in both severe asthma and COPD and associated with sputum total cell count and neutrophils. ADAM8 may facilitate neutrophil migration to the airways in severe asthma and COPD.

The role of oxidative stress during inflammatory processes

Abstract The production of various reactive oxidant species in excess of endogenous antioxidant defense mechanisms promotes the development of a state of oxidative stress, with significant biological consequences. In recent years, evidence has emerged that oxidative stress plays a crucial role in the development and perpetuation of inflammation, and thus contributes to the pathophysiology of a number of debilitating illnesses, such as cardiovascular diseases, diabetes, cancer, or neurodegenerative processes. Oxidants affect all stages of the inflammatory response, including the release by damaged tissues of molecules acting as endogenous danger signals, their sensing by innate immune receptors from the Toll-like (TLRs) and the NOD-like (NLRs) families, and the activation of signaling pathways initiating the adaptive cellular response to such signals. In this article, after summarizing the basic aspects of redox biology and inflammation, we review in detail the current knowledge on the fundamental connections between oxidative stress and inflammatory processes, with a special emphasis on the danger molecule high-mobility group box-1, the TLRs, the NLRP-3 receptor, and the inflammasome, as well as the transcription factor nuclear factor-κB.

FibronectinEDA promotes chronic cutaneous fibrosis through Toll-like receptor signaling

Scleroderma is a progressive autoimmune disease affecting multiple organs. Fibrosis, the hallmark of scleroderma, represents transformation of self-limited wound healing into a deregulated self-sustaining process. The factors responsible for maintaining persistent fibroblast activation in scleroderma and other conditions with chronic fibrosis are not well understood. Toll-like receptor 4 (TLR4) and its damage-associated endogenous ligands are implicated in immune and fibrotic responses. We now show that fibronectin extra domain A (Fn(EDA)) is an endogenous TLR4 ligand markedly elevated in the circulation and lesional skin biopsies from patients with scleroderma, as well as in mice with experimentally induced cutaneous fibrosis. Synthesis of Fn(EDA) was preferentially stimulated by transforming growth factor-β in normal fibroblasts and was constitutively up-regulated in scleroderma fibroblasts. Exogenous Fn(EDA) was a potent stimulus for collagen production, myofibroblast differentiation, and wound healing in vitro and increased the mechanical stiffness of human organotypic skin equivalents. Each of these profibrotic Fn(EDA) responses was abrogated by genetic, RNA interference, or pharmacological disruption of TLR4 signaling. Moreover, either genetic loss of Fn(EDA) or TLR4 blockade using a small molecule mitigated experimentally induced cutaneous fibrosis in mice. These observations implicate the Fn(EDA)-TLR4 axis in cutaneous fibrosis and suggest a paradigm in which aberrant Fn(EDA) accumulation in the fibrotic milieu drives sustained fibroblast activation via TLR4. This model explains how a damage-associated endogenous TLR4 ligand might contribute to converting self-limited tissue repair responses into intractable fibrogenesis in chronic conditions such as scleroderma. Disrupting sustained TLR4 signaling therefore represents a potential strategy for the treatment of fibrosis in scleroderma.

Understanding the mechanisms controlling Leishmania amazonensis infection in vitro: the role of LTB4 derived from human neutrophils

Neutrophils are rapidly recruited to the site of Leishmania infection and play an active role in capturing and killing parasites. They are the main source of leukotriene B₄ (LTB₄), a potent proinflammatory lipid mediator. However, the role of LTB₄ in neutrophil infection by Leishmania amazonensis is not clear. In this study, we show that L. amazonensis or its lipophosphoglycan can induce neutrophil activation, degranulation, and LTB₄ production. Using pharmacological inhibitors of leukotriene synthesis, our findings reveal an LTB₄-driven autocrine/paracrine regulatory effect. In particular, neutrophil-derived LTB₄ controls L. amazonensis killing, degranulation, and reactive oxygen species production. In addition, L. amazonensis infection induces an early increase in Toll-like receptor 2 expression, which facilitates parasite internalization. Nuclear factor kappa B (NFkB) pathway activation represents a required upstream event for L. amazonensis–induced LTB₄ synthesis. These leishmanicidal mechanisms mediated by neutrophil-derived LTB₄ act through activation of its receptor, B leukotriene receptor 1 (BLT1).

Evolving Bacterial Envelopes and Plasticity of TLR2-Dependent Responses: Basic Research and Translational Opportunities

Innate immune mechanisms that follow early recognition of microbes influence the nature and magnitude of subsequent adaptive immune responses. Early detection of microbes depends on pattern recognition receptors that sense pathogen-associated molecular patterns or microbial-associated molecular patterns (PAMPS or MAMPs, respectively). The bacterial envelope contains MAMPs that include membrane proteins, lipopeptides, glycopolymers, and other pro-inflammatory molecules. Bacteria are selected by environmental pressures resulting in quantitative or qualitative changes in their envelope structures that often promote evasion of host immune responses and therefore, infection. However, recent studies have shown that slight, adaptive changes in MAMPs on the bacterial cell wall may result in their ability to induce the secretion not only of pro-inflammatory cytokines but also of anti-inflammatory cytokines. This effect can fine-tune the subsequent response to microbes expressing these MAMPs and lead to the establishment of a commensal state within the host rather than infectious disease. In this review, we will examine the plasticity of Toll-like receptor (TLR) 2 signaling as evidence of evolving MAMPs, using the better-characterized TLR4 as a template. We will review the role of differential dimerization of TLR2 and the arrangement of signaling complexes and co-receptors in determining the capacity of the host to recognize an array of TLR2 ligands and generate different immune responses to these ligands. Last, we will assess briefly how this plasticity may expand the array of interactions between microbes and immune systems beyond the traditional disease-causing paradigm.

The role of leukotrienes in immunopathogenesis of rheumatoid arthritis

Rheumatoid arthritis (RA) is a chronic inflammatory disorder of joints for which there is no strict cure. However, conventional medications can reduce inflammation, relieve pain, and slow joint damage. Leukotrienes are a family of paracrine agents derived from oxidative metabolism of arachidonic acid. Synthesis of lipid mediators and subsequent induction of receptor activity are tightly regulated under normal physiological conditions, so that enzyme and/or receptor dysfunction can lead to a variety of clinical signs and symptoms of disease, such as local pain and tissue edema. In these tissues, immunocompetent cells accumulate at the site of injury, contributing to tissue damage and perpetuation of the disease process. Leukotrienes (often leukotriene B4) as potent chemotactic agents can provoke most signs and symptoms in rheumatoid arthritis by initiating, coordinating, sustaining, and amplifying the inflammatory response, through recruitment of leukocytes. A number of studies have reported that pharmacological modulation in this field can significantly attenuate clinical manifestations associated with different inflammatory pathologies.

Role of the Toll Like receptor (TLR) radical cycle in chronic inflammation: possible treatments targeting the TLR4 pathway

Activation of the Toll-like receptor 4 (TLR4) complex, a receptor of the innate immune system, may underpin the pathophysiology of many human diseases, including asthma, cardiovascular disorder, diabetes, obesity, metabolic syndrome, autoimmune disorders, neuroinflammatory disorders, schizophrenia, bipolar disorder, autism, clinical depression, chronic fatigue syndrome, alcohol abuse, and toluene inhalation. TLRs are pattern recognition receptors that recognize damage-associated molecular patterns and pathogen-associated molecular patterns, including lipopolysaccharide (LPS) from gram-negative bacteria. Here we focus on the environmental factors, which are known to trigger TLR4, e.g., ozone, atmosphere particulate matter, long-lived reactive oxygen intermediate, pentachlorophenol, ionizing radiation, and toluene. Activation of the TLR4 pathways may cause chronic inflammation and increased production of reactive oxygen and nitrogen species (ROS/RNS) and oxidative and nitrosative stress and therefore TLR-related diseases. This implies that drugs or substances that modify these pathways may prevent or improve the abovementioned diseases. Here we review some of the most promising drugs and agents that have the potential to attenuate TLR-mediated inflammation, e.g., anti-LPS strategies that aim to neutralize LPS (synthetic anti-LPS peptides and recombinant factor C) and TLR4/MyD88 antagonists, including eritoran, CyP, EM-163, epigallocatechin-3-gallate, 6-shogaol, cinnamon extract, N-acetylcysteine, melatonin, and molecular hydrogen. The authors posit that activation of the TLR radical (ROS/RNS) cycle is a common pathway underpinning many "civilization" disorders and that targeting the TLR radical cycle may be an effective method to treat many inflammatory disorders.

Danger-associated molecular patterns (DAMPs) in acute lung injury

Danger-associated molecular patterns (DAMPs) are host-derived molecules that can function to regulate the activation of pathogen recognition receptors (PRRs). These molecules play a critical role in modulating the lung injury response. DAMPs originate from multiple sources, including injured and dying cells, the extracellular matrix, or exist as immunomodulatory proteins within the airspace and interstitium. DAMPs can function as either toll-like receptor (TLR) agonists or antagonists, and can modulate both TLR and nod-like receptor (NLR) signalling cascades. Collectively, this diverse group of molecules may represent important therapeutic targets in the prevention and/or treatment of acute lung injury (ALI) and its more severe form, acute respiratory distress syndrome (ARDS).

Fibronectin-α4β1 interactions in hepatic cold ischemia and reperfusion injury: regulation of MMP-9 and MT1-MMP via the p38 MAPK pathway

Liver ischemia-reperfusion injury (IRI) remains a challenging problem in clinical settings. The expression of fibronectin (FN) by endothelial cells is a prominent feature of the hepatic response to injury. Here we investigate the effects of the connecting segment-1 (CS-1) peptide therapy, which blocks FN-α4β1 integrin leukocyte interactions, in a well-established model of 24-h cold liver IRI. CS-1 peptides significantly inhibited leukocyte recruitment and local release of proinflammatory mediators (COX-2, iNOS and TNF-α), ameliorating liver IRI and improving recipient survival rate. CS1 therapy inhibited the phosphorylation of p38 MAPK, a kinase linked to inflammatory processes. Moreover, in addition to downregulating the expression of matrix metalloproteinase-9 (MMP-9) in hepatic IRI, CS-1 peptide therapy depressed the expression of membrane type 1-matrix metalloproteinase (MT1-MMP/MMP-14) by macrophages, a membrane-tethered MMP important for focal matrix proteolysis. Inhibition of p38 MAPK activity, with its pharmacological antagonist SB203580, downregulated MMP-9 and MT1-MMP/MMP-14 expressions by FN-stimulated macrophages, suggesting that p38 MAPK kinase pathway controls FN-mediated inductions of MMP-9 and MT1-MMP/MMP-14. Hence, this study provides new insights on the role of FN in liver injury, which can potentially be applied to the development of new pharmacological strategies for the successful protection against hepatic IRI.

Alternatively-spliced extra domain A of fibronectin promotes acute inflammation and brain injury after cerebral ischemia in mice

BACKGROUND AND PURPOSE

The fibronectin isoform containing the alternatively spliced extra domain A (EDA(+)-FN) is normally absent from the circulation, but plasma levels of EDA(+)-FN can become markedly elevated in several human pathological conditions associated with inflammation including ischemic stroke. It remains unknown whether EDA(+)-FN contributes to stroke pathogenesis or is simply an associative marker. Several in vitro studies suggest that EDA(+)-FN can activate Toll-like receptor 4, an innate immune receptor that triggers proinflammatory responses. We undertook a genetic approach in mice to investigate the ability of EDA(+)-FN to mediate inflammatory brain damage in a focal cerebral ischemia/reperfusion injury model.

METHODS

We used genetically modified EDA(+/+) mice, which constitutively express EDA(+)-FN. Extent of injury, neurological outcome, and inflammatory mechanisms were assessed after 1-hour cerebral ischemia/23-hour reperfusion injury and compared with wild-type mice.

RESULTS

We found that EDA(+/+) mice developed significantly larger infarcts and severe neurological deficits that were associated with significant increased neutrophil and macrophage infiltration as quantitated by immunohistochemistry. Additionally, we found upregulation of nuclear factor-κB, cyclo-oxygenase-2, and inflammatory cytokines tumor necrosis factor-α, interleukin-1β, and interleukin-6 in the EDA(+/+) mice compared with wild-type mice. Interestingly, increased brain injury and neurological deficits were largely abrogated in EDA(+/+) mice by treatment with a specific Toll-like receptor 4 inhibitor.

CONCLUSIONS

These findings provide the first evidence that EDA(+)-FN promotes inflammatory brain injury after ischemic stroke and suggest that the elevated levels of plasma EDA(+)-FN observed in chronic inflammatory conditions could worsen injury and outcome in patients after acute stroke.

Anti-citrullinated fibronectin antibodies in rheumatoid arthritis are associated with human leukocyte antigen-DRB1 shared epitope alleles

Introduction

Fibronectin is one of the most abundant proteins present in the inflamed joint. Here, we characterized the citrullination of fibronectin in the joints of rheumatoid arthritis (RA) patients and studied the prevalence, epitope specificity and human leukocyte antigen (HLA) association of autoantibodies against citrullinated fibronectin in RA.

Methods

Citrullinated residues in fibronectin isolated from RA patient synovial fluid were identified by mass spectrometry. The corresponding citrullinated and non-citrullinated peptides were synthesized and used to analyze the presence of autoantibodies to these peptides in RA sera and sera from other diseases and healthy controls by ELISA. The data were compared with risk factors like shared epitope HLA alleles and smoking, and with clinical features.

Results

Five citrullinated residues were identified in fibronectin from RA synovial fluid. RA sera reacted in a citrulline-dependent manner with two out of four citrullinated fibronectin peptides, one of which contains two adjacent citrulline residues, in contrast to non-RA sera, which were not reactive. The most frequently recognized peptide (FN-Cit_1035,1036, LTVGLTXXGQPRQY, in which × represents citrulline) was primarily targeted by anti-CCP (cyclic citrullinated peptide) 2-positive RA patients. Anti-FN-Cit_1035,1036 autoantibodies were detected in 50% of established anti-CCP2-positive RA patients and in 45% of such patients from a early arthritis clinic. These antibodies appeared to be predominantly of the immunoglobulin G (IgG) isotype and to be associated with HLA shared epitope alleles (odds ratio = 2.11).

Conclusions

Fibronectin in the inflamed synovia of RA patients can be citrullinated at least at five positions. Together with the flanking amino acids, three of these citrullinated residues comprise two epitopes recognized by RA autoantibodies. Anti-citrullinated fibronectin peptide antibodies are associated with HLA shared epitope alleles.

Extracellular matrix dynamics and fetal membrane rupture

The extracellular matrix (ECM) plays an important role in determining cell and organ function: (1) it is an organizing substrate that provides tissue tensile strength; (2) it anchors cells and influences cell morphology and function via interaction with cell surface receptors; and (3) it is a reservoir for growth factors. Alterations in the content and the composition of the ECM determine its physical and biological properties, including strength and susceptibility to degradation. The ECM components themselves also harbor cryptic matrikines, which when exposed by conformational change or proteolysis have potent effects on cell function, including stimulating the production of cytokines and matrix metalloproteinases (MMPs). Collectively, these properties of the ECM reflect a dynamic tissue component that influences both tissue form and function. This review illustrates how defects in ECM synthesis and metabolism and the physiological process of ECM turnover contribute to changes in the fetal membranes that precede normal parturition and contribute to the pathological events leading to preterm premature rupture of membranes (PPROM).

Fibronectin splice variants: understanding their multiple roles in health and disease using engineered mouse models

The extracellular matrix (ECM) is a highly dynamic network of proteins, glycoproteins, and proteoglycans. Numerous diseases result from mutation in genes coding for ECM proteins, but only recently it has been reported that mutations in the fibronectin (FN) gene were associated with a human disorder. FN is one of the main components of the ECM. It generates protein diversity through alternative splicing of a single pre-mRNA, having at least 20 different isoforms in humans. The precise function of these protein isoforms has remained obscure in most cases. Only in the recent few years, it was possible to shed light on the multiple roles of the alternatively spliced FN isoforms. This substantial progress was achieved basically with the knowledge derived from engineered mouse models bearing subtle mutations in specific FN domains. These data, together with a recent report associating mutations in the FN gene to a form of glomerulopathy, clearly show that mutations in constitutive exons or misregulation of alternatively spliced domains of the FN gene may have nonlethal pathological consequences. In this review, we focus on the pathological consequences of mutations in the FN gene, by connecting the function of alternatively spliced isoforms of fibronectin to human diseases.

Toll-like receptor--a potent driving force behind rheumatoid arthritis

Toll like receptor (TLR), one of the key functions of innate immune system, can recognize not only exogenous pathogen-associated molecular patterns, namely PAMPs, but also endogenous molecules created upon tissue injury, sterile inflammation and degeneration. Endogenous TLR ligands are called as damage-associated molecular patters (DAMPs), including endogenous molecules released by activated and necrotic cells, and extracellular matrix molecules. DAMPs are also known as alarmins. TLR research has brought about new insights in the rheumatic diseases. Previous reports suggest that TLRs and the signal pathways intensively contribute to the pathogenesis of rheumatoid arthritis (RA) and other arthritic conditions with interaction of various TLR ligands. Accumulated knowledge of TLR system is summarized to overlook TLRs and the signaling pathway in arthritis conditions, with special reference to RA.

Tumor cell cross talk with tumor-associated leukocytes leads to induction of tumor exosomal fibronectin and promotes tumor progression

Exosomes participate in intercellular communication, but most data published are based on exosomes released from in vitro cultured cells that do not communicate with neighboring cells located in the same microenvironment as the exosomal-producing cells in vivo. In this study, our data show that co-culture of leukocytes isolated from breast tumor tissue leads to uptake of fibronectin (FN) on or in the tumor exosomes (Exo(fib+)). The induction of FN and exosomal uptake is tumor tissue derived and leukocyte specific, because leukocytes isolated from the peripheral blood of naïve mice failed to induce FN uptake by tumor exosomes. Furthermore, depletion of both CD25(+) cells and Gr-1(+) cells from tumor-associated leukocytes causes a reduction of Exo(fib+), suggesting that tumor-associated CD25(+) cells and Gr-1(+) cells participate in FN production and uptake by tumor exosomes, resulting in Exo(fib+). As a result of tumor cells absorbing Exo(fib+), two major events are induced: focal adhesion kinase/Src-dependent signaling pathways are activated, and the production of proinflammatory cytokines and metalloproteinase 9 is enhanced in response to absorbing exosomes. This, in turn, enhances tumor cell invasion in vitro and in vivo. Collectively, our findings provide evidence that exosomes released from freshly excised tumor tissue cells that have communicated/interacted with immune cells gain new immune evasion capacity.

Fibronectin III 13-14 domains induce joint damage via Toll-like receptor 4 activation and synergize with interleukin-1 and tumour necrosis factor

Cartilage loss is a feature of chronic arthritis. It results from degradation of the extracellular matrix which is composed predominantly of aggrecan and type II collagen. Extracellular matrix degradation is mediated by aggrecanases and matrix metalloproteinases (MMPs). Recently, a number of endogenous matrix molecules, including fibronectin (FN), have been implicated in mediating cartilage degradation. We were interested in studying the C-terminal heparin-binding region of FN since it mediates aggrecan and type II collagen breakdown in cartilage, but the specific FN domains responsible for proteolytic enzyme activity and their receptors in cartilage are unknown. In this study, the ability of recombinant FN domains to induce cartilage breakdown was tested. We found that the FN III 13-14 domains in the C-terminal heparin-binding region of FN are potent inducers of aggrecanase activity in articular cartilage. In murine studies, the FN III 13-14-induced aggrecanase activity was inhibited in Toll-like receptor 4 (TLR4) knockout mice but not wild-type mice. FN III 13-14 domains also synergized with the known catabolic cytokines interleukin-1α and tumour necrosis factor and induced secretion of MMP-1, MMP-3, gp38 and serum amyloid-like protein A in chondrocytes. Our studies provide a mechanistic link between the innate immune receptor TLR4 and sterile arthritis induced by the FN III 13-14 domains of the endogenous matrix molecule FN.

Neutrophils promote motility of cancer cells via a hyaluronan-mediated TLR4/PI3K activation loop

Inflammation is a component of tumour progression mechanisms. Neutrophils are a common inflammatory infiltrate in many tumours, but their regulation and functions in neoplasia are not understood. We recently demonstrated that pro-inflammatory IL-17-producing cells recruited blood neutrophils into the peritumoural stroma of hepatocellular carcinoma by epithelium-derived CXC chemokines. Here we show that a substantial population of neutrophils accumulates in the peritumoural stroma of hepatocellular, cervical, colorectal, and gastric carcinomas, and that this correlates with metastases in hepatocellular and gastric carcinomas. Exposure of neutrophils to culture supernatants from several types of solid tumour cells (TSN) resulted in sustained survival and pro-tumourigenic effects of cells. Kinetic experiments reveal that, shortly after exposure to TSN, neutrophils began to provoke activation and then produced significant inflammatory cytokines and expressed more anti-apoptotic Mcl-1 but less pro-apoptotic Bax. These long-lived neutrophils effectively enhanced the cancer cell motility via a contact-dependent mechanism; this effect, together with early activation and subsequent longevity of TSN-exposed neutrophils, could be reversed by blocking the activation of PI3K/Akt signalling in neutrophils. Moreover, we found that hyaluronan (HA) fragments constitute a common factor produced by various tumours that mimics the effect of TSN to induce long-lived neutrophils and subsequent malignant cell migration. The effects of TSN were inhibited by function blocking interactions between HA and its receptor TLR4 on neutrophils, suggesting that this is a key signalling pathway involved. These results indicate that HA derived from malignant cells educates neutrophils to adopt an activated phenotype, and in that way stimulates the metastasis of malignant cells, which represents a positive regulatory loop between tumours and their stroma during neoplastic progression.