Diabetes primes neutrophils to undergo NETosis, which impairs wound healing

Neutrophil extracellular traps coincide with a pro-coagulant status of microcirculatory endothelium in burn wounds

Burn-induced tissue loss is partly related to secondary expansion of necrosis into vital dermis neighboring the initial burn injury. An important factor herein is the severe loss of perfusion of the burn wound, probably caused by microvascular damage induced by the intense local inflammatory responses as well as burn-induced hypercoagulation. We hypothesize that the formation of neutrophilic extracellular traps (NETs) play an important role in this. The purpose of this study was to investigate postburn intravascular thrombosis, NETs formation and the coagulant state in the microvasculature of burns in both animal models and patients. We used two in vivo burn wound models: rats and pigs. In rats, the entire wound was excised at day 14 postburn and in pigs burn wound biopsies were collected at different time points up to 60 days postburn. To confirm the data in patients, eschar from the burn wound was obtained from burn wound patients at different time points after wounding. The number of intravascular thrombi, the presence of intravascular NETs and the number of tissue factor (TF) positive blood vessels in the burn wound was determined. In rats, a significant increase in intravascular thrombi and TF expression was observed 14 days postburn, that in majority coincided with NETs. In pigs, a significant increase in intravascular thrombi and TF expression was found over time up to 60 days postburn, that in majority coincided with NETs too. Also in eschar of burn wound patients, a significant increase in intravascular thrombi was noted, that in majority coincided with NETs, already 0.5 days postburn and remained elevated up to 46 days postburn. This study shows the presence of NETosis in microcirculatory thrombosis of burn wounds and a switch in the microcirculatory endothelium toward a procoagulant phenotype.

Lipoxin A4 encapsulated in PLGA microparticles accelerates wound healing of skin ulcers

Lipoxin A₄ (LXA₄) is involved in the resolution of inflammation and wound healing; however, it is extremely unstable. Thus, to preserve its biological activities and confer stability, we encapsulated LXA₄ in poly-lactic-co-glycolic acid (PLGA) microparticles (LXA₄-MS) and assessed its application in treating dorsal rat skin lesions. Ulcers were sealed with fibrin adhesive and treated with either LXA₄-MS, unloaded microparticles (Un-MS), soluble LXA₄, or PBS/glue (vehicle). All groups were compared at 0, 2, 7, and 14 days post-lesions. Our results revealed that LXA₄-MS accelerated wound healing from day 7 and reduced initial ulcer diameters by 80%. Soluble LXA₄, Un-MS, or PBS closed wounds by 60%, 45%, and 39%, respectively. LXA₄-MS reduced IL-1β and TNF-α, but increased TGF-β, collagen deposition, and the number of blood vessels. Compared to other treatments, LXA₄-MS reduced inflammatory cell numbers, myeloperoxidase (MPO) concentration, and metalloproteinase-8 (MMP8) mRNA in scar tissue, indicating decreased neutrophil chemotaxis. In addition, LXA₄-MS treatment increased macrophages and IL-4, suggesting a positive impact on wound healing. Finally, we demonstrated that WRW4, a selective LXA₄ receptor (ALX) antagonist, reversed healing by 50%, indicating that LXA₄ must interact with ALX to induce wound healing. Our results show that LXA₄-MS could be used as a pharmaceutical formulation for the treatment of skin ulcers.

Patterns and functional implications of platelets upon tumor "education"

While platelets are traditionally recognized to play a predominant role in hemostasis and thrombosis, increasing evidence verifies its involvement in malignancies. As a component of the tumor microenvironment, platelets influence carcinogenesis, tumor metastasis and chemotherapy efficiency. Platelets status is thus predictable as a hematological biomarker of cancer prognosis and a hot target for therapeutic intervention. On the other hand, the role of circulating tumor cells (CTCs) as an inducer of platelet activation and aggregation has been well acknowledged. The cross-talk between platelets and CTCs is reciprocal on that the CTCs activate platelets while platelets contribute to CTCs' survival and dissemination. This review covers some of the current issues related to the loop between platelets and tumor aggression, including the manners of tumor cells in "educating" platelets and biofunctional alterations of platelets upon tumor "education". We also highlight the potential clinical applications on the interplay between tumors and platelets. Further studies with well-designed prospective multicenter trials may contribute to clinical "liquid biopsy" diagnosis by evaluating the global changes of platelets.

Myeloid Cells in Cutaneous Wound Repair

Cutaneous wound repair is a complex, dynamic process with the goal of rapidly sealing any breach in the skin's protective barrier. Myeloid cells compose a significant proportion of the inflammatory cells recruited to a wound site and play important roles in decontaminating the injured tissue of any invading microorganisms. Subsequently, myeloid cells are able to influence many aspects of the healing response, in part through their capacity to release a large array of signaling molecules that allow them to communicate with and regulate the behavior of other wound cells and in turn, be themselves exquisitely regulated by the wound microenvironment. Macrophages, for example, appear to play important, temporally changing roles in the initiation of scarring and subsequently in matrix remodeling to resolve fibrosis. In this way, myeloid cells seem to play both positive (e.g., pathogen killing and matrix remodeling) and negative (e.g., scarring) roles in wound repair. Further research is of course needed to elucidate the precise temporal and spatial myeloid cell phenotypes and behaviors and ultimately to design effective strategies to optimize the beneficial functions of these cells while minimizing their detrimental contributions to improve wound healing in the clinic.

Cytochrome P450 (CYP) epoxygenases as potential targets in the management of impaired diabetic wound healing

Epoxyeicosatrienoic acids (EETs) are the epoxidation products of arachidonic acid catalyzed by cytochrome P450 (CYP) epoxygenases, which possess multiple biological activities. In the present study, we aimed to explore the role and effects of CYP epoxygenases/EETs in wound healing in ob/ob mice. Full-thickness skin dorsal wounds were made on ob/ob mice and C57BL/6 control mice. The mRNA and protein expression of CYP epoxygenases were determined in granulation tissues of wounds. Effects of EETs on wound healing were evaluated. Inflammation and angiogenesis in wounds were also observed. Compared with C57BL/6 mice, the mRNA and protein expression of CYP2C65 and CYP2J6 in the granulation tissues in ob/ob mice were significantly reduced. 11,12-EET treatment significantly improved wound healing in ob/ob mice, whereas 14,15-EEZE, an EET antagonist, showed the opposite effect. 11,12-EET treatment decreased neutrophil and macrophage infiltration to the wound sites, resulting in reduced production of inflammatory cytokines, decreased MMP-9 expression, and increased collagen accumulation in the granulation tissues of ob/ob mice. In addition, 11,12-EET increased angiogenesis in the granulation tissues of wounds in ob/ob mice. These findings indicate that reduced expression of CYP epoxygenases may contribute to impaired diabetic wound healing, and exogenous EETs may improve diabetic wound healing by modulating inflammation and angiogenesis.

Gestational Diabetes Mellitus Is Associated with Altered Neutrophil Activity

Gestational diabetes mellitus (GDM) is a unique form of glucose intolerance, in that it is transient and solely occurs in pregnancy. Pregnancies with GDM are at high risk of developing preeclampsia (PE), a leading cause of fetal and maternal morbidity or mortality. Since PE is associated with excessive activation of circulatory neutrophils and occurrence of neutrophil extracellular traps (NETs) in affected placentae, we examined these features in cases with GDM, as this could be a feature linking the two conditions. Our data indicate that neutrophil activity is indeed altered in GDM, exhibiting pronounced activation and spontaneous generation of NETs by isolated neutrophils in in vitro culture. In this manner, GDM may similarly affect neutrophil behavior and NET formation as witnessed in other forms of diabetes, with the addition of the physiological changes mediated by pregnancy. Since circulatory TNF-α levels are elevated in cases with GDM, a feature also observed in this study, we examined whether this pro-inflammatory cytokine contributed to neutrophil activation. By using infliximab, a clinically utilized TNF-α antagonist, we observed that the pro-NETotic effect of GDM sera was significantly reduced. We also detected pronounced neutrophil infiltrates in placentae from GDM cases. The occurrence of NETs in these tissues is suggested by the extracellular co-localization of citrullinated histones and myeloperoxidase. In addition, elevated neutrophil elastase (NE) mRNA and active enzymatic protein were also detected in such placentae. This latter finding could be important in the context of previous studies in cancer or diabetes model systems, which indicated that NE liberated from infiltrating neutrophils enters surrounding cells, altering cell signaling by the degradation of IRS1. These findings could potentiate the underlying inflammatory response process in GDM and possibly open an avenue for the therapeutic interventions in gestational hyperglycemia.

Mitochondrial Oxidative Stress Promotes Atherosclerosis and Neutrophil Extracellular Traps in Aged Mice

RATIONALE

Mitochondrial oxidative stress (mitoOS) has been shown to be increased in various cell types in human atherosclerosis and with aging. However, the role of cell type-specific mitoOS in atherosclerosis in the setting of advanced age and the molecular mechanisms remains to be determined in vivo.

OBJECTIVE

The aim of this study was to examine the role of myeloid cell mitoOS in atherosclerosis in aged mice.

APPROACH AND RESULTS

Lethally irradiated low-density lipoprotein receptor-deficient mice (Ldlr^-/-) were reconstituted with bone marrow from either wild-type or mitochondrial catalase (mCAT) mice. mCAT transgenic mice contain ectopically expressed human catalase gene in mitochondria, which reduces mitoOS. Starting at the age of 36 weeks, mice were fed the Western-type diet for 16 weeks. We found that mitoOS in lesional myeloid cells was suppressed in aged mCAT→Ldlr^-/- chimeric mice compared with aged controls, and this led to a significant reduction in aortic root atherosclerotic lesion area despite higher plasma cholesterol levels. Neutrophil extracellular traps (NETs), a proinflammatory extracellular structure that contributes to atherosclerosis progression, were significantly increased in the lesions of aged mice compared with lesions of younger mice. Aged mCAT→Ldlr^-/- mice had less lesional neutrophils and decreased NETs compared with age-matched wild-type→Ldlr^-/- mice, whereas young mCAT→ and wild-type→Ldlr^-/- mice had comparable numbers of neutrophils and similar low levels of lesional NETs. Using cultured neutrophils, we showed that suppression of mitoOS reduced 7-ketocholesterol-induced NET release from neutrophils of aged but not younger mice.

CONCLUSIONS

MitoOS in lesional myeloid cells enhanced atherosclerosis development in aged mice, and this enhancement was associated with increased lesional NETs. Thus, mitoOS-induced NET formation is a potentially new therapeutic target to prevent atherosclerosis progression during aging.

Association of Body Mass Index With Infectious Complications in Free Tissue Transfer for Head and Neck Reconstructive Surgery

Importance

Elevated body mass index (BMI) has been proposed as a risk factor for morbidity and mortality among patients undergoing surgery. Conversely, an elevated BMI may confer a protective effect on perioperative morbidity.

Objective

To examine whether an elevated BMI is an independent risk factor for perioperative and postoperative infectious complications after free tissue transfer in head and neck reconstructive surgery.

Design, Setting, and Participants

This cohort study included patients undergoing major head and neck surgery requiring free tissue transfer at a tertiary care center. Data were collected for 415 patients treated from January 1, 2007, through December 31, 2014.

Main Outcomes and Measures

The outcome of interest was postoperative infection and complications after head and neck surgery using free flaps. Covariates considered for adjustment in the statistical model included alcohol consumption (defined as >5 drinks per day [eg, 360 mL of beer, 150 mL of wine, or 45 mL of 80-proof spirits]), type 2 diabetes, prior radiotherapy, anesthesia time, hypothyroidism, smoking, American Society of Anesthesiologists classification, antibiotic regimen received (defined as a standard regimen of a first- or second-generation cephalosporin with or without metronidazole hydrochloride vs an alternative antibiotic regimen for patients allergic to penicillin), and primary surgeon. A multiple logistic regression model was developed for the incidence of the infection end point as a function of elevated BMI (>30.0).

Results

Among the 415 patients included in this study (277 men [66.7%] and 138 women [33.2%]; mean [SD] age, 61.5 [13.9] years), type 2 diabetes and use of an alternative antibiotic regimen were found to be independently associated with increased infectious complications after free flap surgery of the head and neck, with estimated odds ratios of 2.78 (95% CI, 1.27-6.09) and 2.67 (95% CI, 1.14-6.25), respectively, in the multiple logistic regression model. However, a high BMI was not found to be statistically significant as an independent risk factor for postoperative infectious complication (estimated odds ratio, 1.19; 95% CI, 0.48-2.92).

Conclusions and Relevance

Elevated BMI does not seem to play a role as an independent risk factor in postoperative complications in free tissue transfer in head and neck surgery.

Host DNA released by NETosis promotes rhinovirus-induced type-2 allergic asthma exacerbation

Respiratory viral infections represent the most common cause of allergic asthma exacerbations. Amplification of the type-2 immune response is strongly implicated in asthma exacerbation, but how virus infection boosts type-2 responses is poorly understood. We report a significant correlation between the release of host double-stranded DNA (dsDNA) following rhinovirus infection and the exacerbation of type-2 allergic inflammation in humans. In a mouse model of allergic airway hypersensitivity, we show that rhinovirus infection triggers dsDNA release associated with the formation of neutrophil extracellular traps (NETs), known as NETosis. We further demonstrate that inhibiting NETosis by blocking neutrophil elastase or by degrading NETs with DNase protects mice from type-2 immunopathology. Furthermore, the injection of mouse genomic DNA alone is sufficient to recapitulate many features of rhinovirus-induced type-2 immune responses and asthma pathology. Thus, NETosis and its associated extracellular dsDNA contribute to the pathogenesis and may represent potential therapeutic targets of rhinovirus-induced asthma exacerbations.

Low concentrations of neutrophil extracellular traps induce proliferation in human keratinocytes via NF-kB activation

INTRODUCTION

Granulocytes play a pivotal role in innate immune response, as pathogen invasion activates neutrophils, a subclass of granulocytes, inducing the production of neutrophil extracellular traps (NETs). In this study, it has been evaluated how NETs could affect human keratinocytes (HaCaT cells) behaviour.

MATERIALS AND METHODS

HaCaT cells were treated with increasing NETs concentrations (0.01-200ng/ml) and the effect on cell proliferation was evaluated by MTT assay. Inhibition studies were performed by pre-treating cells with dexamethasone, chloropromazine or amiloride. NF-kB pathway activation was evaluated by western blot.

RESULTS

HaCaT cells stimulation with increasing concentrations of NETs (0.01-50ng/ml) for 48h resulted in a modulation of cell proliferation with a maximum increase corresponding to 0.5-1ng/ml stimulation. NETs low concentrations not only increased cell proliferation, but were also able to induce a faster wound closure in an in vitro scratch assay. NETs scaffold, composed by histone proteins and DNA, is recognized by Toll Like Receptor 9 (TLR 9) that, in turn, activates the NF-kB pathway. In fact, NETs induced proliferation was inhibited by chloropromazine (1nM), that blocks chlatrin vesicles formation, and by amiloride (50nM) that inhibits macropinocytosis. Moreover, dexamethasone, an inhibitor of NF-kB, was able to abolish the NETs effect.

DISCUSSION

This study thus demonstrates that low NETs concentrations undergo internalization finally resulting in a quick NF-kB pathway activation and HaCaT cells proliferation increase, suggesting a close relationship between first immune response and wound healing onset.

Short single-stranded DNA degradation products augment the activation of Toll-like receptor 9

Toll-like receptors encounter a diversity of degradation products in endosomes. TLR7 and TLR8 have been shown to be activated by RNA degradation products. Here we show that although TLR9 requires single-stranded DNA longer than 20 nucleotides for a robust response, TLR9 activation is augmented by CpG-containing oligodeoxyribonucleotides (sODNs) as short as 2 nucleotides, which, by themselves, do not induce activation in cell cultures, as well as in mice. sODNs also activate human TLR9 in combination with ODNs containing a single CpG motif that by themselves do not activate human TLR9. The specific sequence motif of sODN and colocalization of ODN and sODN suggest that the mechanism of activation involves binding of both ODN and sODN to TLR9. sODNs augment TLR9 activation by mammalian genomic DNA indicating the role of short DNA degradation products in the endosomes in response to infection or in autoimmune disease, particularly at limiting concentrations of ODNs.

DNA degradation products are frequently found in the endosome, but how they regulate the activation of Toll-like receptors is not known. Here the authors show that single-stranded DNA as short as two nucleotides can enhance the ability of longer DNA oligonucleotides to activate Toll-like receptors.

Exacerbation of Thromboinflammation by Hyperglycemia Precipitates Cerebral Infarct Growth and Hemorrhagic Transformation

BACKGROUND AND PURPOSE

Admission hyperglycemia is associated with a poor outcome in acute ischemic stroke. How hyperglycemia impacts the pathophysiology of acute ischemic stroke remains largely unknown. We investigated how preexisting hyperglycemia increases ischemia/reperfusion cerebral injury.

METHODS

Normoglycemic and streptozotocin-treated hyperglycemic rats were subjected to transient middle cerebral artery occlusion. Infarct growth and brain perfusion were assessed by magnetic resonance imaging. Markers of platelet, coagulation, and neutrophil activation were measured in brain homogenates and plasma. Downstream microvascular thromboinflammation (DMT) was investigated by intravital microscopy.

RESULTS

Hyperglycemic rats had an increased infarct volume with an increased blood-brain barrier disruption and hemorrhagic transformation rate compared with normoglycemic rats. Magnetic resonance imaging scans revealed that hyperglycemia enhanced and accelerated lesion growth and was associated with hemorrhagic transformation originating from territories that were still not completely reperfused at 1 hour after middle cerebral artery recanalization. Intravital microscopy and analysis of brain homogenates showed that DMT began immediately after middle cerebral artery occlusion and was exacerbated by hyperglycemia. Measurement of plasma serotonin and matrix metalloproteinase-9 indicated that platelets and neutrophils were preactivated in hyperglycemic rats. Neutrophils from hyperglycemic diabetic patients showed increased adhesion to endothelial cells as compared with neutrophils from normoglycemic donors in flow chamber experiments.

CONCLUSIONS

We show that hyperglycemia primes the thromboinflammatory cascade, thus, amplifying middle cerebral artery occlusion-induced DMT. DMT exacerbation in hyperglycemic rats impaired reperfusion and precipitated neurovascular damage, blood-brain barrier disruption, and hemorrhagic transformation. Our results designate DMT as a possible target for reduction of the deleterious impact of hyperglycemia in acute ischemic stroke.

In vitro induction of NETosis: Comprehensive live imaging comparison and systematic review

BACKGROUND

Multiple inducers of in vitro Neutrophil Extracellular Trap (NET) formation (NETosis) have been described. Since there is much variation in study design and results, our aim was to create a systematic review of NETosis inducers and perform a standardized in vitro study of NETosis inducers important in (cardiac) wound healing.

METHODS

In vitro NETosis was studied by incubating neutrophils with PMA, living and dead bacteria (S. aureus and E. coli), LPS, (activated) platelets (supernatant), glucose and calcium ionophore Ionomycin using 3-hour periods of time-lapse confocal imaging.

RESULTS

PMA is a consistent and potent inducer of NETosis. Ionomycin also consistently resulted in extrusion of DNA, albeit with a process that differs from the NETosis process induced by PMA. In our standardized experiments, living bacteria were also potent inducers of NETosis, but dead bacteria, LPS, (activated) platelets (supernatant) and glucose did not induce NETosis.

CONCLUSION

Our systematic review confirms that there is much variation in study design and results of NETosis induction. Our experimental results confirm that under standardized conditions, PMA, living bacteria and Ionomycin all strongly induce NETosis, but real-time confocal imaging reveal different courses of events.

The soluble protease ADAMDEC1 released from activated platelets hydrolyzes platelet membrane pro-epidermal growth factor (EGF) to active high-molecular-weight EGF

Platelets are the sole source of EGF in circulation, yet how EGF is stored or released from stimulated cells is undefined. In fact, we found platelets did not store EGF, synthesized as a single 6-kDa domain in pro-EGF, but rather expressed intact pro-EGF precursor on granular and plasma membranes. Activated platelets released high-molecular-weight (HMW)-EGF, produced by a single cleavage between the EGF and the transmembrane domains of pro-EGF. We synthesized a fluorogenic peptide encompassing residues surrounding the putative sessile arginyl residue and found stimulated platelets released soluble activity that cleaved this pro-EGF_1020-1027 peptide. High throughput screening identified chymostatins, bacterial peptides with a central cyclic arginyl structure, as inhibitors of this activity. In contrast, the matrix metalloproteinase/TACE (tumor necrosis factor-α-converting enzyme) inhibitor GM6001 was ineffective. Stimulated platelets released the soluble protease ADAMDEC1, recombinant ADAMDEC1 hydrolyzed pro-EGF_1020-1027, and this activity was inhibited by chymostatin and not GM6001. Biotinylating platelet surface proteins showed ADAMDEC1 hydrolyzed surface pro-EGF to HMW-EGF that stimulated HeLa EGF receptor (EGFR) reporter cells and EGFR-dependent tumor cell migration. This proteolysis was inhibited by chymostatin and not GM6001. Metabolizing pro-EGF Arg¹⁰²³ to citrulline with recombinant polypeptide arginine deiminase 4 (PAD4) abolished ADAMDEC1-catalyzed pro-EGF_1020-1027 peptidolysis, while pretreating intact platelets with PAD4 suppressed ADAMDEC1-, thrombin-, or collagen-induced release of HMW-EGF. We conclude that activated platelets release ADAMDEC1, which hydrolyzes pro-EGF to soluble HMW-EGF, that HMW-EGF is active, that proteolytic cleavage of pro-EGF first occurs at the C-terminal arginyl residue of the EGF domain, and that proteolysis is the regulated and rate-limiting step in generating soluble EGF bioactivity from activated platelets.

Molecular and Cellular Mechanisms of Cardiovascular Disorders in Diabetes

The clinical correlations linking diabetes mellitus with accelerated atherosclerosis, cardiomyopathy, and increased post-myocardial infarction fatality rates are increasingly understood in mechanistic terms. The multiple mechanisms discussed in this review seem to share a common element: prolonged increases in reactive oxygen species (ROS) production in diabetic cardiovascular cells. Intracellular hyperglycemia causes excessive ROS production. This activates nuclear poly(ADP-ribose) polymerase, which inhibits GAPDH, shunting early glycolytic intermediates into pathogenic signaling pathways. ROS and poly(ADP-ribose) polymerase also reduce sirtuin, PGC-1α, and AMP-activated protein kinase activity. These changes cause decreased mitochondrial biogenesis, increased ROS production, and disturbed circadian clock synchronization of glucose and lipid metabolism. Excessive ROS production also facilitates nuclear transport of proatherogenic transcription factors, increases transcription of the neutrophil enzyme initiating NETosis, peptidylarginine deiminase 4, and activates the NOD-like receptor family, pyrin domain-containing 3 inflammasome. Insulin resistance causes excessive cardiomyocyte ROS production by increasing fatty acid flux and oxidation. This stimulates overexpression of the nuclear receptor PPARα and nuclear translocation of forkhead box O 1, which cause cardiomyopathy. ROS also shift the balance between mitochondrial fusion and fission in favor of increased fission, reducing the metabolic capacity and efficiency of the mitochondrial electron transport chain and ATP synthesis. Mitochondrial oxidative stress also plays a central role in angiotensin II-induced gap junction remodeling and arrhythmogenesis. ROS contribute to sudden death in diabetics after myocardial infarction by increasing post-translational protein modifications, which cause increased ryanodine receptor phosphorylation and downregulation of sarco-endoplasmic reticulum Ca(++)-ATPase transcription. Increased ROS also depress autonomic ganglion synaptic transmission by oxidizing the nAch receptor α3 subunit, potentially contributing to the increased risk of fatal cardiac arrhythmias associated with diabetic cardiac autonomic neuropathy.

Pharmacological targeting of peptidylarginine deiminase 4 prevents cancer-associated kidney injury in mice

Renal insufficiency is a frequent cancer-associated problem affecting more than half of all cancer patients at the time of diagnosis. To minimize nephrotoxic effects the dosage of anticancer drugs are reduced in these patients, leading to sub-optimal treatment efficacy. Despite the severity of this cancer-associated pathology, the molecular mechanisms, as well as therapeutic options, are still largely lacking. We here show that formation of intravascular tumor-induced neutrophil extracellular traps (NETs) is a cause of kidney injury in tumor-bearing mice. Analysis of clinical biomarkers for kidney function revealed impaired creatinine clearance and elevated total protein levels in urine from tumor-bearing mice. Electron microscopy analysis of the kidneys from mice with cancer showed reversible pathological signs such as mesangial hypercellularity, while permanent damage such as fibrosis or necrosis was not observed. Removal of NETs by treatment with DNase I, or pharmacological inhibition of the enzyme peptidylarginine deiminase 4 (PAD4), was sufficient to restore renal function in mice with cancer. Tumor-induced systemic inflammation and impaired perfusion of peripheral vessels could be reverted by the PAD4 inhibitor. In conclusion, the current study identifies NETosis as a previously unknown cause of cancer-associated renal dysfunction and describes a novel promising approach to prevent renal failure in individuals with cancer.

Promoting tissue regeneration by modulating the immune system

The immune system plays a central role in tissue repair and regeneration. Indeed, the immune response to tissue injury is crucial in determining the speed and the outcome of the healing process, including the extent of scarring and the restoration of organ function. Therefore, controlling immune components via biomaterials and drug delivery systems is becoming an attractive approach in regenerative medicine, since therapies based on stem cells and growth factors have not yet proven to be broadly effective in the clinic. To integrate the immune system into regenerative strategies, one of the first challenges is to understand the precise functions of the different immune components during the tissue healing process. While remarkable progress has been made, the immune mechanisms involved are still elusive, and there is indication for both negative and positive roles depending on the tissue type or organ and life stage. It is well recognized that the innate immune response comprising danger signals, neutrophils and macrophages modulates tissue healing. In addition, it is becoming evident that the adaptive immune response, in particular T cell subset activities, plays a critical role. In this review, we first present an overview of the basic immune mechanisms involved in tissue repair and regeneration. Then, we highlight various approaches based on biomaterials and drug delivery systems that aim at modulating these mechanisms to limit fibrosis and promote regeneration. We propose that the next generation of regenerative therapies may evolve from typical biomaterial-, stem cell-, or growth factor-centric approaches to an immune-centric approach.

STATEMENT OF SIGNIFICANCE

Most regenerative strategies have not yet proven to be safe or reasonably efficient in the clinic. In addition to stem cells and growth factors, the immune system plays a crucial role in the tissue healing process. Here, we propose that controlling the immune-mediated mechanisms of tissue repair and regeneration may support existing regenerative strategies or could be an alternative to using stem cells and growth factors. The first part of this review we highlight key immune mechanisms involved in the tissue healing process and marks them as potential target for designing regenerative strategies. In the second part, we discuss various approaches using biomaterials and drug delivery systems that aim at modulating the components of the immune system to promote tissue regeneration.

Aspirin-Triggered Resolvin D1-modified materials promote the accumulation of pro-regenerative immune cell subsets and enhance vascular remodeling

Many goals in tissue engineering rely on modulating cellular localization and polarization of cell signaling, including the inhibition of inflammatory infiltrate, facilitation of inflammatory cell egress, and clearance of apoptotic cells. Omega-3 polyunsaturated fatty acid-derived resolvins are gaining increasing recognition for their essential roles in inhibition of neutrophil invasion into inflamed tissue and promotion of macrophage phagocytosis of cellular debris as well as their egress to the lymphatics. Biomaterial-based release of lipid mediators is a largely under-explored approach that provides a method to manipulate local lipid signaling gradients in vivo and direct the recruitment and/or polarization of anti-inflammatory cell subsets to suppress inflammatory signaling and enhance angiogenesis and tissue regeneration. The goal of this study was to encapsulate Aspirin-Triggered Resolvin D1 (AT-RvD1) into a degradable biomaterial in order to elucidate the effects of sustained, localized delivery in a model of sterile inflammation. Flow cytometric and imaging analysis at both 1 and 3days after injury showed that localized AT-RvD1 delivery was able significantly increase the accumulation of anti-inflammatory monocytes and M2 macrophages while limiting the infiltration of neutrophils. Additionally, cytokine profiling and longitudinal vascular analysis revealed a shift towards a pro-angiogenic profile with increased concentrations of VEGF and SDF-1α, and increased arteriolar diameter and tortuosity. These results demonstrate the ability of locally-delivered AT-RvD1 to increase pro-regenerative immune subpopulations and promote vascular remodeling.

STATEMENT OF SIGNIFICANCE

This work is motivated by our efforts to explore the underlying mechanisms of inflammation resolution after injury and to develop biomaterial-based approaches to amplify endogenous mechanisms of resolution and repair. Though specific lipid mediators have been identified that actively promote the resolution of inflammation, biomaterial-based localized delivery of these mediators has been largely unexplored. We loaded Aspirin-Triggered Resolvin D1 into a PLGA scaffold and examined the effects of sustained, localized delivery on the innate immune response. We found that biomaterial delivery of resolvin was able to enhance the accumulation of pro-regenerative populations of immune cells, including anti-inflammatory monocytes, population that has never before been shown to respond to resolvin treatment, and also enhance vascular remodeling in response to tissue injury.

Neutrophils as protagonists and targets in chronic inflammation

Traditionally, neutrophils have been acknowledged to be the first immune cells that are recruited to an inflamed tissue and have mainly been considered in the context of acute inflammation. By contrast, their importance during chronic inflammation has been studied in less depth. This Review aims to summarize our current understanding of the roles of neutrophils in chronic inflammation, with a focus on how they communicate with other immune and non-immune cells within tissues. We also scrutinize the roles of neutrophils in wound healing and the resolution of inflammation, and finally, we outline emerging therapeutic strategies that target neutrophils.

Interactions between Neutrophils and Pseudomonas aeruginosa in Cystic Fibrosis

Cystic fibrosis (CF) affects 70,000 patients worldwide. Morbidity and mortality in CF is largely caused by lung complications due to the triad of impaired mucociliary clearance, microbial infections and chronic inflammation. Cystic fibrosis airway inflammation is mediated by robust infiltration of polymorphonuclear neutrophil granulocytes (PMNs, neutrophils). Neutrophils are not capable of clearing lung infections and contribute to tissue damage by releasing their dangerous cargo. Pseudomonas aeruginosa is an opportunistic pathogen causing infections in immunocompromised individuals. P. aeruginosa is a main respiratory pathogen in CF infecting most patients. Although PMNs are key to attack and clear P. aeruginosa in immunocompetent individuals, PMNs fail to do so in CF. Understanding why neutrophils cannot clear P. aeruginosa in CF is essential to design novel therapies. This review provides an overview of the antimicrobial mechanisms by which PMNs attack and eliminate P. aeruginosa. It also summarizes current advances in our understanding of why PMNs are incapable of clearing P. aeruginosa and how this bacterium adapts to and resists PMN-mediated killing in the airways of CF patients chronically infected with P. aeruginosa.

The potential effect of biological sealants on colorectal anastomosis healing in experimental research involving severe diabetes

Colorectal anastomoses continuous to pose a significant challenge in current surgical practice. Anastomotic leakage remains one of the most frequent and dramatic complications of colorectal surgery, even in centres of high specialisation. Diabetes is a well-established independent factor which results in higher anastomotic leakage rates. Fibrin sealants have been applied in experimental and clinical studies for the prevention of anastomotic dehiscence. However, little is known regarding their impact on diabetic patients. Several fibrin sealants have been proposed as adjunct to standard surgical techniques to prevent leakage from colonic anastomoses following the reversal of temporary colostomies, approved for general haemostasis. This review summarises current advances in colorectal anastomoses and provides evidence that may strengthen the need for tissue sealants in colorectal anastomoses of diabetic patients. We searched Medline (1966-2016) and Scopus (2004-2016) for current evidence in the field. To date, there is no evidence to support the use of fibrin sealants as an adjunct in diabetic patients who undergo colorectal surgery. Experimental animal models with extreme diabetes could be of significant use in the present field and further research is needed prior to application of fibrin sealants in a clinical setting.

Inhibition of Methylglyoxal-Induced AGEs/RAGE Expression Contributes to Dermal Protection by N-Acetyl-L-Cysteine

BACKGROUND/AIM

Accumulation of advanced glycation end products (AGEs) is a major cause of diabetes mellitus (DM) skin complications. Methylglyoxal (MGO), a reactive dicarbonyl compound, is a crucial intermediate of AGEs generation. N-acetyl-L-cysteine (NAC), an active ingredient of some medicines, can induce endogenous GSH and hydrogen sulfide generation, and set off a condensation reaction with MGO. However, there is rare evidence to show NAC can alleviate DM-induced skin injury through inhibition of AGEs generation or toxicity. The present study aimed to observe the effects of NAC on MGO-induced inflammatory injury and investigate the roles of AGEs and its receptor (RAGE) in NAC's dermal protection in human HaCaT keratinocytes.

METHODS

The cells were exposed to MGO to simulate a high MGO status in diabetic blood or tissues. The content of AGEs in serum or cell medium was measured with ELISA. The protective effects of NAC against MGO-induce injury were evaluated by administration before MGO one hour, in virtue of cell viability, mitochondrial membrane potential, inflammation reaction, nuclear factor (NF)-κB activation, matrix metalloproteinase (MMP)-9 expression, as well as cellular behavioral function.

RESULTS

We found the AGEs levels of patients with DM were elevated comparing with healthy volunteers. The in vitro AGEs generation was also able to be enhanced by the exposure of HaCaT cells to MGO, which reduced dose-dependently cellular viability, damaged mitochondrial function, triggered secretion of interleukin (IL)-6 and IL-8, activated NF-κB and upregulated MMP-9 expression. Furthermore, the exposure caused cellular adhesion and migration dysfunction, as well as collagen type I inhibition. Importantly, before the exposure to MGO, the preconditioning with NAC significantly attenuated MGO-induced AGEs generation, improved cellular viability and mitochondrial function, partially reversed the overexpression of proinflammatory factors and MMP-9, as well as the activation of NF-κB. Lastly, NAC blocked MGO-induced RAGE upregulation, and inhibition of RAGE with its neutralizing antibody significantly alleviated MGO-induced NF-κB activation, MMP-9 upregulation and inflammatory injury in HaCaT cells.

CONCLUSION

The present work indicates the administration of NAC can prevent MGO-induced dermal inflammatory injury through inhibition of AGEs/RAGE signal, which may provide a basal support for the treatment of diabetic skin complications with NAC-containing medicines in the future.

Insulin treatment prevents wounding associated changes in tissue and circulating neutrophil MMP-9 and NGAL in diabetic rats

Neutrophils are important for wound repair, but their persistence can impair the healing process. Neutrophils express matrix metalloproteinases including MMP-9 and its regulator neutrophil gelatinase associated lipocalin (NGAL). Whether wounding affects neutrophil MMP-9 and NGAL in diabetic animals is not known. Skin wound tissue MMP-9 and NGAL was examined by qRT-PCR and immunohistochemistry in control, diabetic and insulin treated diabetic rats. The temporal expression of MMP-9 and NGAL mRNA, MMP-9 activity and the NGAL/MMP-9 complex was also investigated in an implant model and their circulating neutrophils. The cellular localisation of MMP-9 and NGAL was confirmed by immunofluorescence and the ability of glucose to regulate these factors was examined in isolated neutrophils. In skin wound tissue compared with control, diabetes increased neutrophil infiltration, NGAL mRNA and MMP-9 protein (P<0.05). Diabetes significantly increased implant neutrophil NGAL and MMP-9 protein as well as NGAL mRNA, wound fluid NGAL/MMP-9 complex and MMP-9 activity (all <0.05). Circulating neutrophil MMP-9 and NGAL was also increased in these diabetic animals (P<0.05). These changes were prevented by insulin treatment. Ex vivo, high glucose (25mM) increased neutrophil NGAL and MMP-9 (both by 2 fold, P<0.05). NGAL and MMP-9 are increased in wound and circulating neutrophils in diabetic rodents. These changes and the association between higher NGAL and increased wound fluid MMP-9 activity suggest that increased neutrophil NGAL may contribute to increased MMP-9 in poorly healing diabetic wounds. Whether targeting neutrophil NGAL or MMP-9 can improve diabetic wound healing remains to be investigated.

Electrospun Template Architecture and Composition Regulate Neutrophil NETosis In Vitro and In Vivo<sup/>

Mounting evidence indicates that neutrophils, first responders to an implanted biomaterial, prime the microenvironment for recruited immune cells by secreting factors and releasing neutrophil extracellular traps (NETs) through NETosis. In this study, we investigated the role of electrospun template architecture and composition in regulating NETosis. Electrospun polydioxanone (PDO), collagen type I (COL), and blended PDO-COL templates (PC) were fabricated with small-diameter (0.25-0.35 μm) and large-diameter (1.0-2.00 μm) fibers. Neutrophil-template interactions were evaluated in vitro for 3 and 24 h with human neutrophils, and the PDO templates were studied in vivo (rat subcutaneous model) for 1 and 7 days. Template-bound NETs were quantified by fluorescent microscopy and an On-cell Western assay. The in vitro results indicate that larger fiber diameters reduced NETosis on PDO templates, whereas the incorporation of COL attenuated NETosis independent of fiber diameter. The in vivo results similarly revealed a lower degree of NETs on large-diameter PDO templates at 1 day, resulting in marginal tissue integration of the templates at 7 days. In contrast, the small-diameter PDO templates, which were coated in a large amount of NETs at 24 h in vivo, were surrounded by capsule-like tissue at 7 days. These preliminary in vivo results validate the in vitro model and signify NETosis as a potentially significant physiological response and a critical preconditioning event for the innate immune response to templates. In conclusion, these results demonstrate the importance of characterizing the neutrophil's acute confrontation with biomaterials to engineer templates capable of promoting in situ regeneration.

Neutrophil Extracellular Traps and Its Implications in Inflammation: An Overview

In addition to physical barriers, neutrophils are considered a part of the first line of immune defense. They can be found in the bloodstream, with a lifespan of 6–8 h, and in tissue, where they can last up to 7 days. The mechanisms that neutrophils utilize for host defense are phagocytosis, degranulation, cytokine production, and, the most recently described, neutrophil extracellular trap (NET) production. NETs are DNA structures released due to chromatin decondensation and spreading, and they thus occupy three to five times the volume of condensed chromatin. Several proteins adhere to NETs, including histones and over 30 components of primary and secondary granules, among them components with bactericidal activity such as elastase, myeloperoxidase, cathepsin G, lactoferrin, pentraxin 3, gelatinase, proteinase 3, LL37, peptidoglycan-binding proteins, and others with bactericidal activity able to destroy virulence factors. Three models for NETosis are known to date. (a) Suicidal NETosis, with a duration of 2–4 h, is the best described model. (b) In vital NETosis with nuclear DNA release, neutrophils release NETs without exhibiting loss of nuclear or plasma membrane within 5–60 min, and it is independent of reactive oxygen species (ROS) and the Raf/MERK/ERK pathway. (c) The final type is vital NETosis with release of mitochondrial DNA that is dependent on ROS and produced after stimuli with GM-CSF and lipopolysaccharide. Recent research has revealed neutrophils as more sophisticated immune cells that are able to precisely regulate their granular enzymes release by ion fluxes and can release immunomodulatory cytokines and chemokines that interact with various components of the immune system. Therefore, they can play a key role in autoimmunity and in autoinflammatory and metabolic diseases. In this review, we intend to show the two roles played by neutrophils: as a first line of defense against microorganisms and as a contributor to the pathogenesis of various illnesses, such as autoimmune, autoinflammatory, and metabolic diseases.

Cellular and Molecular Mechanisms of Autoimmunity and Lupus Nephritis

Autoimmunity involves immune responses directed against self, which are a result of defective self/foreign distinction of the immune system, leading to proliferation of self-reactive lymphocytes, and is characterized by systemic, as well as tissue-specific, inflammation. Numerous mechanisms operate to ensure the immune tolerance to self-antigens. However, monogenetic defects or genetic variants that weaken immune tolerance render susceptibility to the loss of immune tolerance, which is further triggered by environmental factors. In this review, we discuss the phenomenon of immune tolerance, genetic and environmental factors that influence the immune tolerance, factors that induce autoimmunity such as epigenetic and transcription factors, neutrophil extracellular trap formation, extracellular vesicles, ion channels, and lipid mediators, as well as costimulatory or coinhibitory molecules that contribute to an autoimmune response. Further, we discuss the cellular and molecular mechanisms of autoimmune tissue injury and inflammation during systemic lupus erythematosus and lupus nephritis.

An exploratory look at NETosis in atherosclerosis

Current evidence suggests the likelihood of a link between venous thromboembolism (VTE) and atherosclerosis, although they have been traditionally considered as different pathological entities. The contribution of neutrophils to human atherogenesis has been underestimated, if compared to their contribution established in VTE. This is due to the major importance attributed to macrophages in plaque destabilization. Nevertheless, the role of neutrophils in atherogenesis deserves increasing attention. In particular, neutrophil extracellular traps (NETs) are net-like chromatin fibres that are released from dying neutrophils. The death of neutrophils with NETs formation is called NETosis. During activation, neutrophils produce reactive oxygen species (ROS), through the activation of nicotinamide adenine dinucleotide phosphate (NADPH) oxidase. The main function of NETs is trapping and killing pathogens. Nevertheless, NETs formation has been observed in various chronic inflammatory diseases, autoimmune diseases, vasculitis, lung diseases, cancer and VTE. Recent studies suggest that NETs formation might contribute also to atherosclerosis progression. New data report the presence of NETs in the luminal portion of human atherosclerotic vessels and coronary specimens obtained from patients after acute myocardial infarction. Programmed death mechanisms in atherosclerosis such as apoptosis, efferocytosis and also NETosis, share common features and triggers. If defective, they can lead the cells to a switch from programmed death to necrosis, resulting in the release of pro-atherogenic factors, accumulation of cell debris and progression of the disease. This review provides evidence on the emerging role of neutrophils focusing on NETosis and oxidative stress burden in orchestrating common mechanisms in atherosclerosis and thrombosis.

Myeloperoxidase amplified high glucose-induced endothelial dysfunction in vasculature: Role of NADPH oxidase and hypochlorous acid

Nicotinamide adenine dinucleotide phosphate (NADPH) oxidase-derived reactive oxygen species (ROS) such as superoxide and hydrogen peroxide (H₂O₂), have emerged as important molecules in the pathogenesis of diabetic endothelial dysfunction. Additionally, neutrophils-derived myeloperoxidase (MPO) and MPO-catalyzed hypochlorous acid (HOCl) play important roles in the vascular injury. However, it is unknown whether MPO can use vascular-derived ROS to induce diabetic endothelial dysfunction. In the present study, we demonstrated that NADPH oxidase was the main source of ROS formation in high glucose-cultured human umbilical vein endothelial cells (HUVECs), and played a critical role in high glucose-induced endothelial dysfunction such as cell apoptosis, loss of cell viability and reduction of nitric oxide (NO). However, the addition of MPO could amplify the high glucose-induced endothelial dysfunction which was inhibited by the presence of apocynin (NADPH oxidase inhibitor), catalase (H₂O₂ scavenger), or methionine (HOCl scavenger), demonstrating the contribution of NADPH oxidase-H₂O₂-MPO-HOCl pathway in the MPO/high glucose-induced vascular injury. In high glucose-incubated rat aortas, MPO also exacerbated the NADPH oxidase-induced impairment of endothelium-dependent relaxation. Consistent with these in vitro data, in diabetic rat aortas, both MPO expresion and NADPH oxidase activity were increased while the endothelial function was simultaneously impaired. The results suggested that vascular-bound MPO could amplify high glucose-induced vascular injury in diabetes. MPO-NADPH oxidase-HOCl may represent an important pathogenic pathway in diabetic vascular diseases.

NETopathies? Unraveling the Dark Side of Old Diseases through Neutrophils

Neutrophil extracellular traps (NETs) were initially described as an antimicrobial mechanism of neutrophils. Over the last decade, several lines of evidence support the involvement of NETs in a plethora of pathological conditions. Clinical and experimental data indicate that NET release constitutes a shared mechanism, which is involved in a different degree in various manifestations of non-infectious diseases. Even though the backbone of NETs is similar, there are differences in their protein load in different diseases, which represent alterations in neutrophil protein expression in distinct disorder-specific microenvironments. The characterization of NET protein load in different NET-driven disorders could be of significant diagnostic and/or therapeutic value. Additionally, it will provide further evidence for the role of NETs in disease pathogenesis, and it will enable the characterization of disorders in which neutrophils and NET-dependent inflammation are of critical importance.

Histones and Neutrophil Extracellular Traps Enhance Tubular Necrosis and Remote Organ Injury in Ischemic AKI

Severe AKI is often associated with multiorgan dysfunction, but the mechanisms of this remote tissue injury are unknown. We hypothesized that renal necroinflammation releases cytotoxic molecules that may cause remote organ damage. In hypoxia-induced tubular epithelial cell necrosis in vitro, histone secretion from ischemic tubular cells primed neutrophils to form neutrophil extracellular traps. These traps induced tubular epithelial cell death and stimulated neutrophil extracellular trap formation in fresh neutrophils. In vivo, ischemia-reperfusion injury in the mouse kidney induced tubular necrosis, which preceded the expansion of localized and circulating neutrophil extracellular traps and the increased expression of inflammatory and injury-related genes. Pretreatment with inhibitors of neutrophil extracellular trap formation reduced kidney injury. Dual inhibition of neutrophil trap formation and tubular cell necrosis had an additive protective effect. Moreover, pretreatment with antihistone IgG suppressed ischemia-induced neutrophil extracellular trap formation and renal injury. Renal ischemic injury also increased the levels of circulating histones, and we detected neutrophil infiltration and TUNEL-positive cells in the lungs, liver, brain, and heart along with neutrophil extracellular trap accumulation in the lungs. Inhibition of neutrophil extracellular trap formation or of circulating histones reduced these effects as well. These data suggest that tubular necrosis and neutrophil extracellular trap formation accelerate kidney damage and remote organ dysfunction through cytokine and histone release and identify novel molecular targets to limit renal necroinflammation and multiorgan failure.

Umbilical cord-derived mesenchymal stromal cell-conditioned medium exerts in vitro antiaging effects in human fibroblasts

BACKGROUND AIMS

Chronic wounds are a common complication of diabetes. Fibroblast-myofibroblast differentiation is important for wound repair, which is commonly impaired in non-healing wounds, and the underlying mechanisms need to be further elucidated.

METHODS

We used high glucose (HG) to simulated the diabetes microenvironment and explored its effects on the biological features of fibroblasts in vitro.

RESULTS

The results showed that prolonged HG induced senescence in fibroblasts through activation of p21 and p16 in a reactive oxygen species (ROS)-dependent manner, further delayed the viability and migration in fibroblasts and also depressed fibroblast differentiation through the TGF-β/Smad signaling pathway. However, mesenchymal stromal cell-conditioned medium (MSC-CM) counteracts the effects of HG. Treatment of fibroblasts with MSC-CM decreased HG-induced ROS overproduction, ameliorated HG-induced senescence in fibroblasts and reversed the defects in myofibroblast formation. Our results may provide clues for the pathogenesis of chronic wounds and a theoretical basis to develop MSC-CM as an alternative therapeutic method to treatment of chronic wounds.

Neutrophils from chronic lymphocytic leukemia patients exhibit an increased capacity to release extracellular traps (NETs)

Chronic lymphocytic leukemia (CLL) is characterized by immune defects that contribute to a high rate of infections and autoimmune cytopenias. Neutrophils are the first line of innate immunity and respond to pathogens through multiple mechanisms, including the release of neutrophil extracellular traps (NETs). These web-like structures composed of DNA, histones, and granular proteins are also produced under sterile conditions and play important roles in thrombosis and autoimmune disorders. Here we show that neutrophils from CLL patients are more prone to release NETs compared to those from age-matched healthy donors (HD). Increased generation of NETs was not due to higher levels of elastase, myeloperoxidase, or reactive oxygen species production. Instead, we found that plasma from CLL patients was able to prime neutrophils from HD to generate higher amounts of NETs upon activation. Plasmatic IL-8 was involved in the priming effect since its depletion reduced plasma capacity to enhance NETs release. Finally, we found that culture with NETs delayed spontaneous apoptosis and increased the expression of activation markers on leukemic B cells. Our study provides new insights into the immune dysregulation in CLL and suggests that the chronic inflammatory environment typical of CLL probably underlies this inappropriate neutrophil priming.

Peptidylarginine deiminase 4 promotes age-related organ fibrosis

Peptidylarginine deiminase 4 (PAD4) citrullinates proteins. In neutrophils, it causes chromatin decondensation and release of NETs, which are injurious. Martinod et al. show in this study that NETs promote fibrosis in a cardiac model and that PAD4-deficient mice have reduced age-related organ fibrosis.

Aging promotes inflammation, a process contributing to fibrosis and decline in organ function. The release of neutrophil extracellular traps (NETs [NETosis]), orchestrated by peptidylarginine deiminase 4 (PAD4), damages organs in acute inflammatory models. We determined that NETosis is more prevalent in aged mice and investigated the role of PAD4/NETs in age-related organ fibrosis. Reduction in fibrosis was seen in the hearts and lungs of aged PAD4^−/− mice compared with wild-type (WT) mice. An increase in left ventricular interstitial collagen deposition and a decline in systolic and diastolic function were present only in WT mice, and not in PAD4^−/− mice. In an experimental model of cardiac fibrosis, cardiac pressure overload induced NETosis and significant platelet recruitment in WT but not PAD4^−/− myocardium. DNase 1 was given to assess the effects of extracellular chromatin. PAD4 deficiency or DNase 1 similarly protected hearts from fibrosis. We propose a role for NETs in cardiac fibrosis and conclude that PAD4 regulates age-related organ fibrosis and dysfunction.

NETosis before and after Hyperglycemic Control in Type 2 Diabetes Mellitus Patients

Introduction and Objective

Diabetes is characterized by chronic inflammation, endothelial dysfunction, increased risk of infections and early cardiovascular disease. By releasing neutrophil extracellular traps (NETs), neutrophils kill bacteria and exert pro-inflammatory and pro-thrombotic activities. Increased NETosis has been found in cross-sectional studies including treated type 2 diabetes mellitus (T2DM) patients. In this study, we determined whether the ability of neutrophils to form NETs differs in diabetic patients pre- and post-hyperglycemic control versus healthy donors (HD), and the relationship between NETosis with pro-thrombotic, pro-inflammatory biomarkers and thrombotic clinical events.

Methods

Diabetic patients recently diagnosed and after 6 and 12 months of treatment (N = 25) and HD (N = 25) were included. NET formation was studied by microscopy and fluorometry. Nucleosomes, HNE-DNA complexes, von Willebrand factor (vWF), IL6 and TNFα plasma levels were measured by ELISA and P-selectin on the platelet surface was assessed by cytometry.

Results

Basal levels of NETs in recently diagnosed T2DM patients were higher compared to HD. While TNFα stimulation of control neutrophils resulted in DNA release, patient neutrophils were not responsive. Although glycemia decreased after 6 months of metformin treatment, basal and TNFα and PMA-stimulated NETs reached normal values after 12 months. Compared to controls, nucleosomes, HNE-DNA complexes, IL-6 and TNFα levels were increased in recently diagnosed patients and decreased after 12 months of treatment. P-selectin and vWF levels were similar in both populations.

Conclusion

Our data suggest that NETs could represent a biomarker for T2DM. Increased NETosis in T2DM patients does not appear to be the consequence of impaired glycemic control but rather due to pro-inflammatory cytokines and is not related to thrombotic events.

Neutrophil extracellular trap formation and circulating nucleosomes in patients with chronic myeloproliferative neoplasms

The mechanisms underlying increased thrombotic risk in chronic myeloproliferative neoplasms (MPN) are incompletely understood. We assessed whether neutrophil extracellular traps (NETs), which promote thrombosis, contribute to the procoagulant state in essential thrombocythemia, polycythemia vera and myelofibrosis (MF) patients. Although MPN neutrophils showed increased basal reactive oxygen species (ROS), enhanced NETosis by unstimulated neutrophils was an infrequent finding, whereas PMA-triggered NETosis was impaired, particularly in MF, due to decreased PMA-triggered ROS production. Elevated circulating nucleosomes were a prominent finding and were higher in patients with advanced disease, which may have potential prognostic implication. Histone-MPO complexes, proposed as specific NET biomarker, were seldomly detected, suggesting NETs may not be the main source of nucleosomes in most patients, whereas their correlation with high LDH points to increased cell turn-over as a plausible origin. Lack of association of nucleosomes or NETs with thrombosis or activation markers does not support their use as predictors of thrombosis although prospective studies in a larger cohort may help define their potential contribution to MPN thrombosis. These results do not provide evidence for relevant in vivo NETosis in MPN patients under steady state conditions, although availability of standardized NET biomarkers may contribute to further research in this field.

Neutrophil extracellular traps: protagonists of cancer progression?

Neutrophil extracellular traps (NETs) are a defense mechanism first described to trap and kill bacteria and other pathogens. Increasingly, however, their involvement in the pathogenesis of inflammatory and malignant diseases is being recognized. Several recent studies have suggested important roles of NETs in tumor progression, metastasis and tumor-associated thrombosis. Although systematic studies to address the role of NETs in tumor development are still scarce, we will explore the emerging evidence for NETs as potential protagonists in malignant disease and highlight the mechanisms through which these effects may be exerted. Future questions arising from our current knowledge of direct and indirect interactions between NETs and cancer cells will be outlined and we will explore NETs as candidate pharmaceutical targets in cancer patients.

Understanding the molecular mechanisms of NETs and their role in antiviral innate immunity

Polymorphonuclear neutrophils (PMNs) are the most abundant cells in the context of innate immunity; they are one of the first cells to arrive at the site of viral infection constituting the first line of defense in response to invading pathogens. Indeed, neutrophils are provided with several defense mechanisms including release of cytokines, cytotoxic granules and the last recently described neutrophil extracellular traps (NETs). The main components of NETs are DNA, granular antimicrobial peptides, and nuclear and cytoplasmic proteins, that together play an important role in the innate immune response. While NETs were first described as a mechanism against bacteria and fungi, recently, several studies are beginning to elucidate how NETs are involved in the host antiviral response and the prominent characteristics of this new mechanism are discussed in the present review.

Current Challenges and Limitations in Antibody-Based Detection of Citrullinated Histones

Studies on NETosis demand reliable and convenient markers to monitor the progress of this form of cell death. Because a determining step in the release of nuclear chromatin NETs requires the conversion of arginine residues to citrulline residues in histones by peptidylarginine deiminase, citrullinated histones can provide such a marker. Here, we evaluate antibody reagents for the detection of citrulline residues in histones and observe alarming differences between commercial antisera and mouse and rabbit monoclonal antibodies in their ability to detect their nominal target residues. Differences between antibodies that are currently used to detect citrulline residues in histones could jeopardize efforts to reach a scientific consensus and instead lead to inconsistent and even conflicting conclusions regarding the regulation of histone deimination. Our results will assist others in planning their initial or ongoing studies on peptidylarginine deiminase activity with the use of currently available antibodies. Furthermore, we argue that, along with the careful attention to experimental conditions and calcium concentrations, validated antibody reagents are urgently needed to avoid possible setbacks in the research on NETosis.

NETosis provides the link between activation of neutrophils on hemodialysis membrane and comorbidities in dialyzed patients

INTRODUCTION

Neutrophil extracellular traps (NETs) are formed by activated neutrophils during the process of NETosis in which the nuclear material is released into extracellular space, including DNA molecules, citrullinated histones, and neutrophil granule enzymes, such as elastase. This material forms networks that are able not only to physically entrap bacteria but also to provide elevated concentration of bactericidal components. Over the last years, it has become clear that NETs can also be formed under numerous sterile inflammatory conditions, i.e., thrombosis, cancer, SLE, atherosclerosis, and diabetes.

METHOD

We reviewed studies published until July 2016 to find possible associations between elevated cell-free DNA levels in dialyzed patients and the process of NETosis and its consequences.

RESULTS

The process of NETosis, its elevated activation, or impaired clearance provides the link between clinical conditions and elevated levels of cell-free DNA found in plasma after the hemodialytic procedure which itself is able to activate neutrophils via platelets and ROS formation. NETs stimulate thrombosis and endothelial damage, and their formation may contribute to the development of spectrum of comorbidities described in dialyzed patients.

CONCLUSION

The study of plasma cell-free DNA levels together with markers of NETosis could contribute to the evaluation of the influence of hemodialysis on the immune system of patients.

NETosis as Source of Autoantigens in Rheumatoid Arthritis

In neutrophils (but also in eosinophils and in mast cells), different inflammatory stimuli induce histone deimination, chromatin decondensation, and NET formation. These web-like structures that trap and kill microbes contain DNA, cationic granule proteins, and antimicrobial peptides, but the most abundant proteins are core histones. Histones contained in NETs have been deiminated, and arginines are converted in citrullines. While deimination is a physiological process amplified in inflammatory conditions, only individuals carrying genetic predisposition to develop rheumatoid arthritis (RA) make antibodies to deiminated proteins. These antibodies, collectively identified as anti-citrullinated proteins/peptides antibodies (ACPA), react with different deiminated proteins and display partially overlapping specificities. In this paper, we will summarize current evidence supporting the role of NETosis as critical mechanism in the breach of tolerance to self-antigens and in supporting expansion and differentiation of autoreactive cells. In fact, several lines of evidence connect NETosis with RA: RA unstimulated synovial fluid neutrophils display enhanced NETosis; sera from RA patients with Felty's syndrome bind deiminated H3 and NETs; a high number of RA sera bind deiminated H4 contained in NETs; human monoclonal antibodies generated from RA synovial B cells decorate NETs and bind deiminated histones. In RA, NETs represent on one side an important source of autoantigens bearing posttranslational modifications and fueling the production of ACPA. On the other side, NETs deliver signals that maintain an inflammatory milieu and contribute to the expansion and differentiation of ACPA-producing B cells.

A motive for killing: effector functions of regulated lytic cell death

Immunological responses activated by pathogen recognition come in many guises. The proliferation, differentiation and recruitment of immune cells, and the production of inflammatory cytokines and chemokines are central to lifelong immunity. Cell death serves as a key function in the resolution of innate and adaptive immune responses. It also coordinates cell-intrinsic effector functions to restrict infection. Necrosis was formally considered a passive form of cell death or a consequence of pathogen virulence factor expression, and necrotic tissue is frequently associated with infection. However, there is now emerging evidence that points to a role for regulated forms of necrosis, such as pyroptosis and necroptosis, driving inflammation and shaping the immune response.

Elevated homocysteine levels in type 2 diabetes induce constitutive neutrophil extracellular traps

Constitutively active neutrophil extracellular traps (NETs) and elevated plasma homocysteine are independent risk factors for Type 2 Diabetes (T2D) associated vascular diseases. Here, we show robust NETosis due to elevated plasma homocysteine levels in T2D subjects and increased components of NETs such as neutrophil elastase and cell free DNA. Cooperative NETs formation was observed in neutrophils exposed to homocysteine, IL-6 and high glucose suggesting acute temporal changes tightly regulate constitutive NETosis. Homocysteine induced NETs by NADPH oxidase dependent and independent mechanisms. Constitutively higher levels of calcium and mitochondrial superoxides under hyperglycemic conditions were further elevated in response to homocysteine leading to accelerated NETosis. Homocysteine showed robust interaction between neutrophils and platelets by inducing platelet aggregation and NETosis in an interdependent manner. Our data demonstrates that homocysteine can alter innate immune function by promoting NETs formation and disturbs homeostasis between platelets and neutrophils which may lead to T2D associated vascular diseases.

Extracellular HSP60 triggers tissue regeneration and wound healing by regulating inflammation and cell proliferation

After injury, zebrafish can restore many tissues that do not regenerate well in mammals, making it a useful vertebrate model for studying regenerative biology. We performed a systematic screen to identify genes essential for hair cell regeneration in zebrafish, and found that the heat shock protein Hspd1 (Hsp60) has a critical role in the regeneration of hair cells and amputated caudal fins. We showed HSP60-injected extracellularly promoted cell proliferation and regeneration in both hair cells and caudal fins. We showed that hspd1 mutant was deficient in leukocyte infiltration at the site of injury. Topical application of HSP60 in a diabetic mouse skin wound model dramatically accelerated wound healing compared with controls. Stimulation of human peripheral blood mononuclear cells with HSP60 triggered a specific induction of M2 phase CD163-positive monocytes. Our results demonstrate that the normally intracellular chaperonin HSP60 has an extracellular signalling function in injury inflammation and tissue regeneration, likely through promoting the M2 phase for macrophages.

Neutrophil extracellular traps exacerbate Th1-mediated autoimmune responses in rheumatoid arthritis by promoting DC maturation

Aberrant formation of neutrophil extracellular traps (NETs) is a key feature in rheumatoid arthritis (RA) and plays a pivotal role in disease pathogenesis. However, the mechanism through which NETs shape the autoimmune response in RA remains elusive. In this study, we demonstrate that inhibition of peptidylarginine deiminases activity in collagen-induced arthritis (CIA) mouse model significantly reduces NET formation, attenuates clinical disease activity, and prevents joint destruction. Importantly, peptidylarginine deiminase 4 blocking markedly reduces the frequency of collagen-specific IFN-γ-producing T helper 1 (Th1) cells in the draining lymph nodes of immunized mice. Exposure of dendritic cells (DCs) to CIA-derived NETs induces DC maturation characterized by significant upregulation of costimulatory molecules, as well as elevated secretion of IL-6. Moreover, CIA-NET-treated DCs promote the induction of antigen-specific Th1 cells in vitro. Finally, NETs from RA patients show an increased potential to induce the maturation of DCs from healthy individuals, corroborating the findings obtained in CIA mouse model. Collectively, our findings delineate an important role of NETs in the induction and expansion of Th1 pathogenic cells in CIA through maturation of DCs and reveal a novel role of NETs in shaping the RA-autoimmune response that could be exploited therapeutically.

Inhibition of NET Release Fails to Reduce Adipose Tissue Inflammation in Mice

Obesity-associated diseases such as Type 2 diabetes, liver disease and cardiovascular diseases are profoundly mediated by low-grade chronic inflammation of the adipose tissue. Recently, the importance of neutrophils and neutrophil-derived myeloperoxidase and neutrophil elastase on the induction of insulin resistance has been established. Since neutrophil elastase and myeloperoxidase are critically involved in the release of neutrophil extracellular traps (NETs), we here hypothesized that NETs may be relevant to early adipose tissue inflammation. Thus, we tested the effect of the Peptidyl Arginine Deiminase 4 inhibitor Cl-amidine, a compound preventing histone citrullination and subsequent NET release, in a mouse model of adipose tissue inflammation. C57BL6 mice received a 60% high fat diet for 10 weeks and were treated with either Cl-amidine or vehicle. Flow cytometry of adipose tissue and liver, immunohistological analysis and glucose and insulin tolerance tests were performed to determine the effect of the treatment and diet. Although high fat diet feeding induced insulin resistance no significant effect was observed between the treatment groups. In addition no effect was found in leukocyte infiltration and activation in the adipose tissue and liver. Therefore we concluded that inhibition of neutrophil extracellular trap formation may have no clinical relevance for early obesity-mediated pathogenesis of the adipose tissue and liver.

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.