Peptidyl arginine deiminase-4 activation exacerbates kidney ischemia-reperfusion injury

Peptidylarginine deiminase (PAD): A promising target for chronic diseases treatment

In 1958, the presence of citrulline in the structure of the proteins was discovered for the first time. Several years later they found that Arginine converted to citrulline during a post-translational modification process by PAD enzyme. Each PAD is expressed in a certain tissue developing a series of diseases such as inflammation and cancers. Among these, PAD2 and PAD4 play a role in the development of rheumatoid arthritis (RA) by producing citrullinated autoantigens and increasing the production of inflammatory cytokines. PAD4 is also associated with the formation of NET structures and thrombosis. In the crystallographic structure, PAD has several calcium binding sites, and the active site of the enzyme consists of different amino acids. Various PAD inhibitors have been developed divided into pan-PAD and selective PAD inhibitors. F-amidine, Cl-amidine, and BB-Cl-amidine are some of pan-PAD inhibitors. AFM-30a and JBI589 are selective for PAD2 and PAD4, respectively. There is a need to evaluate the effectiveness of existing inhibitors more accurately in the coming years, as well as design and production of novel inhibitors targeting highly specific isoforms.

Emerging therapeutic strategies targeting extracellular histones for critical and inflammatory diseases: an updated narrative review

Extracellular histones are crucial damage-associated molecular patterns involved in the development and progression of multiple critical and inflammatory diseases, such as sepsis, pancreatitis, trauma, acute liver failure, acute respiratory distress syndrome, vasculitis and arthritis. During the past decade, the physiopathologic mechanisms of histone-mediated hyperinflammation, endothelial dysfunction, coagulation activation, neuroimmune injury and organ dysfunction in diseases have been systematically elucidated. Emerging preclinical evidence further shows that anti-histone strategies with either their neutralizers (heparin, heparinoids, nature plasma proteins, small anion molecules and nanomedicines, etc.) or extracorporeal blood purification techniques can significantly alleviate histone-induced deleterious effects, and thus improve the outcomes of histone-related critical and inflammatory animal models. However, a systemic evaluation of the efficacy and safety of these histone-targeting therapeutic strategies is currently lacking. In this review, we first update our latest understanding of the underlying molecular mechanisms of histone-induced hyperinflammation, endothelial dysfunction, coagulopathy, and organ dysfunction. Then, we summarize the latest advances in histone-targeting therapy strategies with heparin, anti-histone antibodies, histone-binding proteins or molecules, and histone-affinity hemoadsorption in pre-clinical studies. Finally, challenges and future perspectives for improving the clinical translation of histone-targeting therapeutic strategies are also discussed to promote better management of patients with histone-related diseases.

Neutrophil extracellular traps (NETs) and fibrotic diseases

Fibrosis, a common cause and serious outcome of organ failure that can affect any organ, is responsible for up to 45% of all deaths in various clinical settings. Both preclinical models and clinical trials investigating various organ systems have shown that fibrosis is a highly dynamic process. Although many studies have sought to gain understanding of the mechanism of fibrosis progression, their findings have been mixed. In recent years, increasing evidence indicates that neutrophil extracellular traps (NETs) are involved in many inflammatory and autoimmune disorders and participate in the regulation of fibrotic processes in various organs and systems. In this review, we summarize the current understanding of the role of NETs in fibrosis development and progression and their possibility as therapeutic targets.

Innate immunity in diabetic nephropathy: Pathogenic mechanisms and therapeutic targets

Diabetic nephropathy (DN) represents a prevalent chronic microvascular complication of diabetes mellitus (DM) and is a major cause of end‐stage renal disease. The anfractuous surrounding of DN pathogenesis and the intricate nature of this metabolic disorder often pose challenges in both the diagnosis and treatment of DN compared to other kidney diseases. Hyperglycaemia in DM predispose vulnerable renal cells into microenvironmental disequilibrium and thereby results in innate immunocytes infiltration including neutrophils, macrophages, myeloid‐derived suppressor cells, dendritic cells, and so forth. These immune cells play dual roles in kidney injury and closely correlated with the degree of proteinuria in DN patients. Additionally, innate immune signaling cascades, initiated by altered metabolic and hemodynamic in diabetic context, are crucial in instigating and perpetuating renal inflammation, which detrimentally contribute to DN pathogenesis. As such, anti‐inflammatory therapies, particularly those targeting innate immunity, hold renoprotective promise in DN. In this article, we reviewed the origin and feature of the above four prominent kidney innate immune cells, analyze their pathogenic role in DN, and discuss potential targeted‐therapeutic strategies, aiming to enhance the current understanding of renal innate immunity and hence help to discover promising therapeutic approaches for DN.

Selective inhibition of peptidyl-arginine deiminase (PAD): can it control multiple inflammatory disorders as a promising therapeutic strategy?

Peptidyl arginine deiminases (PADs) are a family of post-translational modification enzymes that irreversibly citrullinate (deiminate) arginine residues of protein and convert them to a non-classical amino acid citrulline in the presence of calcium ions. It has five isotypes, such as PAD1, PAD2, PAD3, PAD4, and PAD6, found in mammalian species. It has been suggested that increased PAD expression in various tissues contributes to the development of multiple inflammatory diseases, including rheumatoid arthritis (RA), cancer, diabetes, and neurological disorders. Elevation of PAD enzyme expression depends on several factors like rising intracellular Ca²⁺ levels, oxidative stress, and proinflammatory cytokines. PAD inhibitors originating from natural or synthetic sources can be used as a novel therapeutic approach concerning inflammatory disorders. Here, we review the pathological role of PAD in several inflammatory disorders, factors that trigger PAD expression, epigenetic role and finally, decipher the therapeutic approach of PAD inhibitors in multiple inflammatory disorders.

ROLE OF PEPTIDYLARGININE DEIMINASE AND NEUTROPHIL EXTRACELLULAR TRAPS IN INJURIES: FUTURE NOVEL DIAGNOSTICS AND THERAPEUTIC TARGETS

ABSTRACT

Injuries lead to an early systemic inflammatory state with innate immune system activation. Neutrophil extracellular traps (NETs) are a complex of chromatin and proteins released from the activated neutrophils. Although initially described as a response to bacterial infections, NETs have also been identified in the sterile postinjury inflammatory state. Peptidylarginine deiminases (PADs) are a group of isoenzymes that catalyze the conversion of arginine to citrulline, termed citrullination or deimination. PAD2 and PAD4 have been demonstrated to play a role in NET formation through citrullinated histone 3. PAD2 and PAD4 have a variety of substrates with variable organ distribution. Preclinical and clinical studies have evaluated the role of PADs and NETs in major trauma, hemorrhage, burns, and traumatic brain injury. Neutrophil extracellular trap formation and PAD activation have been shown to contribute to the postinjury inflammatory state leading to a detrimental effect on organ systems. This review describes our current understanding of the role of PAD and NET formation following injury and burn. This is a new field of study, and the emerging data appear promising for the future development of targeted biomarkers and therapies in trauma.

Roles of PADI4 in the expression of cytokines involved in inflammation and adhesion in differentiated NB4 cells treated with ATRA

Differentiation syndrome (DS) is a common complication in patients with acute promyelocytic leukemia (APL) treated with all-trans-retinoic acid (ATRA). However, the target of ATRA during DS in patients with APL remains to be elucidated. Therefore, the current study aimed to investigate the role of peptidylarginine deiminase 4 (PADI4) in the differentiation of ATRA-induced NB4 APL cells. The results showed that PADI4 was significantly upregulated in peripheral blood samples derived from patients with APL DS compared with patients with APL only. In addition, whether ATRA could enhance the expression levels of PADI4 in NB4 cells in vitro was subsequently investigated. The results also showed that PADI4 overexpression promoted the differentiation of NB4 cells treated with ATRA, which was reversed after PADI4 silencing. To uncover the potential mechanisms underlying the above process, PADI4 overexpression induced the secretion of inflammation-related cytokines, such as TNF-α, IL-1β, IL-8, C-C motif chemokine (CCL)2, CCL4, CCR1 and intercellular adhesion molecule-1 in ATRA-treated NB4 cells. However, PADI4 knockdown in the same cells had the opposite effect. The above findings indicated that PADI4 could be involved in the differentiation of ATRA-induced NB4 cells and upregulation of cytokines.

Chemistry, Biosynthesis and Pharmacology of Streptonigrin: An Old Molecule with Future Prospects for New Drug Design, Development and Therapy

Streptonigrin is an aminoquinone alkaloid isolated from Streptomyces flocculus and is gaining attention as a drug molecule owing to its potential antitumor and antibiotic effects. It was previously used as an anticancer drug but has been discontinued because of its toxic effects. However, according to the most recent studies, the toxicity of streptonigrin and its structurally modified derivatives has been reduced while maintaining their potential pharmacological action at lower concentrations. To date, many investigations have been conducted on this molecule and its derivatives to determine the most effective molecule with low toxicity to enable new drug discovery. Therefore, the main objective of this study is to provide a comprehensive review and to discuss the prospects for streptonigrin and its derived compounds, which may boost the molecule as a highly interesting target molecule for new drug design, development and therapy. To complete this review, relevant literature was collected from several scientific databases, including Google Scholar, PubMed, Scopus and ScienceDirect. Following a complete screening, the obtained information is summarized in the present review to provide a good reference and accelerate the development and utilization of streptonigrin and its derivatives as pharmaceuticals.

Role of the PADI family in inflammatory autoimmune diseases and cancers: A systematic review

The peptidyl arginine deiminase (PADI) family is a calcium ion-dependent group of isozymes with sequence similarity that catalyze the citrullination of proteins. Histones can serve as the target substrate of PADI family isozymes, and therefore, the PADI family is involved in NETosis and the secretion of inflammatory cytokines. Thus, the PADI family is associated with the development of inflammatory autoimmune diseases and cancer, reproductive development, and other related diseases. In this review, we systematically discuss the role of the PADI family in the pathogenesis of various diseases based on studies from the past decade to provide a reference for future research.

Histone Modifications in Acute Kidney Injury

Background

Acute kidney injury (AKI) is a serious clinical problem associated with high morbidity and mortality worldwide. The pathophysiology and pathogenesis of AKI is complex and multifactorial. In recent years, epigenetics has emerged as an important regulatory mechanism in AKI.

Summary

There are several types of histone modification, including methylation, acetylation, phosphorylation, crotonylation, citrullination, and sumoylation. Histone modifications are associated with the transcription of many genes and activation of multiple signaling pathways that contribute to the pathogenesis of AKI. Thus, targeting histone modification may offer novel strategies to protect kidneys from AKI and enhance kidney repair and recovery. In this review, we summarize recent advances on the modification, regulation, and implication of histone modifications in AKI.

Key Messages

Histone modifications contribute to the pathogenesis of AKI. Understanding of epigenetic regulation in AKI will aid in establishing the utility of pharmacologic targeting of histone modification as a potential novel therapy for AKI.

PAD4 and Its Inhibitors in Cancer Progression and Prognosis

The systemic spread of malignancies and the risk of cancer-associated thrombosis are major clinical challenges in cancer therapy worldwide. As an important post-translational modification enzyme, peptidyl arginine deiminase 4 (PAD4) could mediate the citrullination of protein in different components (including nucleus and cytoplasm, etc.) of a variety of cells (tumor cells, neutrophils, macrophages, etc.), thus participating in gene regulation, neutrophil extracellular trap (NET) and macrophage extracellular trap (MET). Thereby, PAD4 plays an important role in enhancing the growth of primary tumors and facilitating the distant metastasis of cancer cells. In addition, it is related to the formation of cancer-associated thrombosis. Therefore, the development of PAD4-specific inhibitors may be a promising strategy for treating cancer, and it may improve patient prognosis. In this review, we describe PAD4 involvement in gene regulation, protein citrullination, and NET formation. We also discuss its potential role in cancer and cancer-associated thrombosis, and we summarize the development and application of PAD4 inhibitors.

The Fatal Circle of NETs and NET-Associated DAMPs Contributing to Organ Dysfunction

The innate immune system is the first line of defense against invading pathogens or sterile injuries. Pattern recognition receptors (PRR) sense molecules released from inflamed or damaged cells, or foreign molecules resulting from invading pathogens. PRRs can in turn induce inflammatory responses, comprising the generation of cytokines or chemokines, which further induce immune cell recruitment. Neutrophils represent an essential factor in the early immune response and fulfill numerous tasks to fight infection or heal injuries. The release of neutrophil extracellular traps (NETs) is part of it and was originally attributed to the capture and elimination of pathogens. In the last decade studies revealed a detrimental role of NETs during several diseases, often correlated with an exaggerated immune response. Overwhelming inflammation in single organs can induce remote organ damage, thereby further perpetuating release of inflammatory molecules. Here, we review recent findings regarding damage-associated molecular patterns (DAMPs) which are able to induce NET formation, as well as NET components known to act as DAMPs, generating a putative fatal circle of inflammation contributing to organ damage and sequentially occurring remote organ injury.

Genetic effect of ischemia-reperfusion injury upon primary graft dysfunction and chronic lung allograft dysfunction in lung transplantation: evidence based on transcriptome data

The unclear mechanism that ischemia-reperfusion injury (IRI) contributes to the development of primary graft dysfunction (PGD) and chronic lung allograft dysfunction (CLAD) remains a major issue in lung transplantation. Differentially expressed PGD-related genes and CLAD-related genes during IRI (IRI-PGD common genes and IRI-CLAD common genes) were identified using GEO datasets (GSE127003, GSE8021, GSE9102) and GeneCards datasets. Enrichment analysis and four network analyses, namely, protein-protein interaction, microRNA (miRNA)-gene, transcription factor (TF)-gene, and drug-gene networks, were then performed. Moreover, GSE161520 was analyzed to identify the differentially expressed core miRNAs during IRI in rats. Finally, Pearson correlation analysis and ROC analysis were performed. Eight IRI-PGD common genes (IL6, TNF, IL1A, IL1B, CSF3, CXCL8, SERPINE1, and PADI4) and 10 IRI-CLAD common genes (IL1A, ICAM1, CCL20, CCL2, IL1B, TNF, PADI4, CXCL8, GZMB, and IL6) were identified. Enrichment analysis showed that both IRI-PGD and IRI-CLAD common genes were significantly enriched in "AGE-RAGE signaling pathway in diabetic complication" and "IL-17 signaling pathway". Among the core miRNAs, miR-1-3p and miR-335 were differentially expressed in IRI rats. Among core TFs, CEBPB expression had a significant negative correlation with P/F ratio (r = -0.33, P = 0.021). In the reperfused lung allografts, the strongest positive correlation was exhibited between PADI4 expression and neutrophil proportion (r = 0.76, P < 0.001), and the strongest negative correlation was between PADI4 expression and M2 macrophage proportion (r = -0.74, P < 0.001). In lung allografts of PGD recipients, IL6 expression correlated with activated dendritic cells proportion (r = 0.86, P < 0.01), and IL1B expression correlated with the neutrophils proportion(r = 0.84, P < 0.01). In whole blood of CLAD recipients, GZMB expression correlated with activated CD4+ memory T cells proportion (r = 0.76, P < 0.001).Our study provides the novel insights into the molecular mechanisms by which IRI contributes to PGD and CLAD and potential targets for therapeutic intervention.

PAD Inhibitors as a Potential Treatment for SARS-CoV-2 Immunothrombosis

Since the discovery of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in December 2019, the virus's dynamicity has resulted in the evolution of various variants, including the delta variant and the more novel mu variant. With a multitude of mutant strains posing as challenges to vaccine efficacy, it is critical that researchers embrace the development of pharmacotherapeutics specific to SARS-CoV-2 pathophysiology. Neutrophil extracellular traps and their constituents, including citrullinated histones, display a linear connection with thrombotic manifestations in COVID-19 patients. Peptidylarginine deiminases (PADs) are a group of enzymes involved in the modification of histone arginine residues by citrullination, allowing for the formation of NETs. PAD inhibitors, specifically PAD-4 inhibitors, offer extensive pharmacotherapeutic potential across a broad range of inflammatory diseases such as COVID-19, through mediating NETs formation. Although numerous PAD-4 inhibitors exist, current literature has not explored the depth of utilizing these inhibitors clinically to treat thrombotic complications in COVID-19 patients. This review article offers the clinical significance of PAD-4 inhibitors in reducing thrombotic complications across various inflammatory disorders like COVID-19 and suggests that these inhibitors may be valuable in treating the origin of SARS-CoV-2 immunothrombosis.

Peptidylarginine Deiminase 2 Knockout Improves Survival in hemorrhagic shock

BACKGROUND

The peptidylarginine deiminase (PAD) family converts arginine into citrulline through protein citrullination. PAD2 and PAD4 inhibitors can improve survival in hemorrhagic shock (HS). However, the impact of isoform-specific PAD inhibition in improving survival has not been studied. In this study, we utilize selective Pad2 knockout mice to elucidate loss of function of PAD2 leads to pro-survival effect in HS.

METHODS

HS: Pad2 and wild-type (WT) mice (n = 5/group) were subjected to lethal HS (55% volume hemorrhage). Survival was monitored over 7 days. Myocardial infarction (MI): Pad2 and WT mice (n = 9/group) were subjected to MI by permanent LAD ligation to examine the effect of ischemia on the heart. After 24 h cardiac function and infarct size were measured.

RESULTS

HS: Pad2 mice demonstrated 100% survival compared with 0% for WT mice (P = 0.002). In a sub-lethal HS model, cardiac β-catenin levels were higher in Pad2 compared with WT after 24 h. MI: WT mice demonstrated larger MI (75%) compared with Pad2 (60%) (P < 0.05). Pad2 had significantly higher ejection fraction and fractional shortening compared with WT (P < 0.05).

CONCLUSIONS

Pad2 improves survival in lethal HS. Possible mechanisms by which loss of PAD2 function improves survival include the activation of cell survival pathways, improved tolerance of cardiac ischemia, and improved cardiac function during ischemia. PAD2 is promising as a future therapeutic target for the treatment of HS and cardiac ischemia.

Impact of transplantation on neutrophil extracellular trap formation in patients with end-stage renal disease: A single-center, prospective cohort study

ABSTRACT

Increased neutrophil extracellular trap (NET) formation associates with high cardiovascular risk and mortality in patients with end-stage renal disease (ESRD). However, the effect of transplantation on NETs and its associated markers remains unclear. This study aimed to characterize circulating citrullinated Histone H3 (H3cit) and Peptidyl Arginase Deiminase 4 (PAD4) in ESRD patients undergoing transplantation and evaluate the ability of their neutrophils to release NETs.This prospective cohort study included 80 healthy donors and 105 ESRD patients, out of which 95 received a transplant. H3cit and PAD4 circulating concentration was determined by enzyme-linked immunosorbent assay in healthy donors and ESRD patients at the time of enrollment. An additional measurement was carried out within the first 6 months after transplant surgery. In vitro NET formation assays were performed in neutrophils isolated from healthy donors, ESRD patients, and transplant recipients.H3cit and PAD4 levels were significantly higher in ESRD patients (H3cit, 14.38 ng/mL [5.78-27.13]; PAD4, 3.22 ng/mL [1.21-6.82]) than healthy donors (H3cit, 6.45 ng/mL [3.30-11.65], P < .0001; PAD4, 2.0 ng/mL [0.90-3.18], P = .0076). H3cit, but not PAD4, increased after transplantation, with 44.2% of post-transplant patients exhibiting high levels (≥ 27.1 ng/mL). In contrast, NET release triggered by phorbol 12-myristate 13-acetate was higher in neutrophils from ESRD patients (70.0% [52.7-94.6]) than healthy donors (32.2% [24.9-54.9], P < .001) and transplant recipients (19.5% [3.5-65.7], P < .05).The restoration of renal function due to transplantation could not reduce circulating levels of H3cit and PAD4 in ESRD patients. Furthermore, circulating H3cit levels were significantly increased after transplantation. Neutrophils from transplant recipients exhibit a reduced ability to form NETs.

Evaluation of peptidylarginine deiminase 4 and PADI4 polymorphisms in sepsis-induced acute kidney injury

BACKGROUND

The aim of this study is to evaluate the peptidylarginine deiminase 4 (PAD 4) concentration and PADI4 polymorphisms as predictors of acute kidney injury (AKI) development, the need for renal replacement therapy (RRT), and mortality in patients with septic shock.

METHODS

We included all individuals aged ≥ 18 years, with a diagnosis of septic shock at ICU admission. Blood samples were taken within the first 24 hours of the patient's admission to determine serum PAD4 concentration and its PADI4 polymorphism (rs11203367) and (rs874881). Patients were monitored during their ICU stay and the development of SAKI was evaluated. Among the patients in whom SAKI developed, mortality and the need for RRT were also evaluated.

RESULTS

There were 99 patients, 51.5% of whom developed SAKI and of these, 21.5% needed RRT and 80% died in the ICU. There was no difference between PAD4 concentration (p = 0.116) and its polymorphisms rs11203367 (p = 0.910) and rs874881 (p = 0.769) in patients in whom SAKI did or did not develop. However, PAD4 had a positive correlation with plasma urea concentration (r = 0.269 and p = 0.007) and creatinine (r = 0.284 and p = 0.004). The PAD4 concentration and PADI4 polymorphisms were also not associated with RRT and with mortality in patients with SAKI.

CONCLUSION

PAD4 concentration and its polymorphisms were not associated with SAKI development, the need for RRT, or mortality in patients with septic shock. However, PAD4 concentrations were associated with creatinine and urea levels in these patients.

Role of Epigenetics in the Regulation of Immune Functions of the Skin

This review is intended to illuminate the emerging understanding of epigenetic modifications that regulate both adaptive and innate immunity in the skin. Host defense of the epidermis and dermis involves the interplay of many cell types to enable homeostasis; tolerance to the external environment; and appropriate response to transient microbial, chemical, and physical insults. To understand this process, the study of cutaneous immunology has focused on immune responses that reflect both adaptive learned and genetically programmed innate defense systems. However, recent advances have begun to reveal that epigenetic modifications of chromatin structure also have a major influence on the skin immune system. This deeper understanding of how enzymatic changes in chromatin structure can modify the skin immune system and may explain how environmental exposures during life, and the microbiome, lead to both short-term and long-term changes in cutaneous allergic and other inflammatory processes. Understanding the mechanisms responsible for alterations in gene and chromatin structure within skin immunocytes could provide key insights into the pathogenesis of inflammatory skin diseases that have thus far evaded understanding by dermatologists.

Renal proximal tubular NEMO plays a critical role in ischemic acute kidney injury

We determined that renal proximal tubular (PT) NF-κB essential modulator (NEMO) plays a direct and critical role in ischemic acute kidney injury (AKI) using mice lacking renal PT NEMO and by targeted renal PT NEMO inhibition with mesoscale nanoparticle-encapsulated NEMO binding peptide (NBP MNP). We subjected renal PT NEMO-deficient mice, WT mice, and C57BL/6 mice to sham surgery or 30 minutes of renal ischemia and reperfusion (IR). C57BL/6 mice received NBP MNP or empty MNP before renal IR injury. Mice treated with NBP MNP and mice deficient in renal PT NEMO were protected against ischemic AKI, having decreased renal tubular necrosis, inflammation, and apoptosis compared with control MNP-treated or WT mice, respectively. Recombinant peptidylarginine deiminase type 4 (rPAD4) targeted kidney PT NEMO to exacerbate ischemic AKI in that exogenous rPAD4 exacerbated renal IR injury in WT mice but not in renal PT NEMO-deficient mice. Furthermore, rPAD4 upregulated proinflammatory cytokine mRNA and NF-κB activation in freshly isolated renal proximal tubules from WT mice but not from PT NEMO-deficient mice. Taken together, our studies suggest that renal PT NEMO plays a critical role in ischemic AKI by promoting renal tubular inflammation, apoptosis, and necrosis.

Casting A Wide Net On Surgery: The Central Role of Neutrophil Extracellular Traps

: Since their discovery, neutrophil extracellular traps (NETs) have been implicated in a broad array of functions, both beneficial and detrimental to the host. Indeed, NETs have roles in infection, sepsis, wound healing, thrombotic disease, and cancer propagation, all of which are directly implicated in the care of surgical patients. Here we provide an updated review on the role of NETs in the perioperative period with specific emphasis on perioperative infections, wound healing, vascular complications, cancer propagation, as well as discussing ongoing, and future therapeutic targets. Surgeons will benefit from understanding the latest discoveries in neutrophil biology and how these novel functions affect the care of surgical patients. Furthermore, novel anti-NET therapies are being developed which may have profound effects on the care of surgical patients.

Mechanisms and therapeutic targets of ischemic acute kidney injury

Acute kidney injury (AKI) due to renal ischemia reperfusion (IR) is a major clinical problem without effective therapy and is a significant and frequent cause of morbidity and mortality during the perioperative period. Although the pathophysiology of ischemic AKI is not completely understood, several important mechanisms of renal IR-induced AKI have been studied. Renal ischemia and subsequent reperfusion injury initiates signaling cascades mediating renal cell necrosis, apoptosis, and inflammation, leading to AKI. Better understanding of the molecular and cellular pathophysiological mechanisms underlying ischemic AKI will provide more targeted approach to prevent and treat renal IR injury. In this review, we summarize important mechanisms of ischemic AKI, including renal cell death pathways and the contribution of endothelial cells, epithelial cells, and leukocytes to the inflammatory response during ischemic AKI. Additionally, we provide some updated potential therapeutic targets for the prevention or treatment of ischemic AKI, including Toll-like receptors, adenosine receptors, and peptidylarginine deiminase 4. Finally, we propose mechanisms of ischemic AKI-induced liver, intestine, and kidney dysfunction and systemic inflammation mainly mediated by Paneth cell degranulation as a potential explanation for the high mortality observed with AKI.

Inhibition of peptidyl arginine deiminase-4 protects against myocardial infarction induced cardiac dysfunction

Peptidyl arginine deiminase-4 (PAD4), a PAD enzyme family member, catalyzes the posttranslational conversion of arginine residues to citrulline in target proteins. Although PAD4 is believed to play a crucial role in various pathological conditions such as infectious diseases, autoimmune diseases, and ischemic conditions, the effect of PAD4 in myocardial infarction (MI)-induced cardiac injury remains to be examined. Here, we hypothesize that PAD4 contributes to cardiac ischemic injury by exacerbating the inflammatory response and promoting neutrophil extracellular trap (NET) formation after MI. Permanent left coronary artery ligation, a condition that mimics MI, was performed on male C57BL/6 mice. [(3S,4R)-3-amino-4-hydroxy-1-piperidinyl] [2-[1-(cyclopropylmethyl)-1H-indol-2-yl]-7-methoxy-1-methyl-1H-benzimidazol-5-yl]-methanone (GSK484), an inhibitor of PAD4, was delivered via intraperitoneal injection to inhibit PAD4 activity. Cardiac PAD4 expression, tissue injury scoring, neutrophil infiltration, cit-H3 expression, NET formation, inflammatory cytokine secretion, apoptosis, and cardiac function were analyzed. In the current study, we discovered the protective effect of PAD4 inhibition using the PAD4-specific inhibitor GSK484 in cardiomyocytes challenged by MI. GSK484-mediated PAD4 inhibition can moderately preserve ventricle histological structure and myocardium integrity after MI, thereby reducing the infarct size and decreasing myocardial enzyme levels in serum. PAD4 inhibition also effectively protects cardiomyocytes from MI-induced NET formation and inflammatory cytokine secretion, in turn alleviating cardiac ischemia-induced apoptosis of cardiomyocytes. Collectively, these findings demonstrate the efficacy of specific PAD4 inhibition in reducing MI-induced neutrophil infiltration, NET formation, inflammatory reaction, and cardiomyocyte apoptosis, thereby increasing overall cardiac function improvement. These results provide novel insights for the development of new strategies to treat cardiovascular dysfunction in MI patients.

Neutrophil Extracellular Traps in the Establishment and Progression of Renal Diseases

Uncontrolled inflammatory and immune responses are often involved in the development of acute and chronic forms of renal injury. Neutrophils are innate immune cells recruited early to sites of inflammation, where they produce pro-inflammatory cytokines and release mesh-like structures comprised of DNA and granular proteins known as neutrophil extracellular traps (NETs). NETs are potentially toxic, contribute to glomerular injury, activate autoimmune processes, induce vascular damage, and promote kidney fibrosis. Evidence from multiple studies suggests that an imbalance between production and clearance of NETs is detrimental for renal health. Hence strategies aimed at modulating NET-associated processes could have a therapeutic impact on a myriad of inflammatory diseases that target the kidney. Here, we summarize the role of NETs in the pathogenesis of renal diseases and their mechanisms of tissue damage.

Extracellular DNA traps in inflammation, injury and healing

Following strong activation signals, several types of immune cells reportedly release chromatin and granular proteins into the extracellular space, forming DNA traps. This process is especially prominent in neutrophils but also occurs in other innate immune cells such as macrophages, eosinophils, basophils and mast cells. Initial reports demonstrated that extracellular traps belong to the bactericidal and anti-fungal armamentarium of leukocytes, but subsequent studies also linked trap formation to a variety of human diseases. These pathological roles of extracellular DNA traps are now the focus of intensive biomedical research. The type of pathology associated with the release of extracellular DNA traps is mainly determined by the site of trap formation and the way in which these traps are further processed. Targeting the formation of aberrant extracellular DNA traps or promoting their efficient clearance are attractive goals for future therapeutic interventions, but the manifold actions of extracellular DNA traps complicate these approaches.

Neutrophil Extracellular Traps Sustain Inflammatory Signals in Ulcerative Colitis

BACKGROUND AND AIMS

In ulcerative colitis [UC], mucosal damage occurs in areas that are infiltrated with neutrophils. The antimicrobial function of neutrophils relies in part on the formation of extracellular web-like structures, named neutrophil extracellular traps [NETs]. The formation and/or clearance of aberrant NETs have been associated with several immune diseases. Here we investigated the role of NETs in UC-related inflammation.

METHODS

The expression of NET-associated proteins was evaluated in colonic biopsies of patients with Crohn's disease [CD], UC and in normal controls [NC] by Western blotting, immunofluorescence and immunohistochemistry. Colonic biopsies of UC patients were analysed before and after anti-tumour necrosis factor α [anti-TNF-α] treatment. The capacity of neutrophils to produce NETs upon activation was tested in vitro. UC lamina propria mononuclear cells [LPMCs] were cultured with NETs in the presence or absence of an extracellular signal-regulated kinase-1/2 [ERK1/2] inhibitor and inflammatory cytokine induction was assessed by real-time polymerase chain reaction and enzyme-linked immunosorbent assay. We also characterized the contribution of NETs in dextran sodium sulfate [DSS]-induced colitis.

RESULTS

NET-associated proteins were over-expressed in inflamed colon of UC patients as compared to CD patients and NC. Circulating neutrophils of UC patients produced NETs in response to TNF-α stimulation, and reduced expression of NET-related proteins and diminished NET formation were seen in patients receiving successful treatment with anti-TNF-α. Treatment of UC LPMCs with NETs activated ERK1/2, thus enhancing TNF-α and interleukin-1β [IL-1β] production. NETs were induced in mice with DSS-colitis and in vivo inhibition of NET release attenuated colitis.

CONCLUSIONS

Our data show that NET release occurs in UC and suggest a role for NETs in sustaining mucosal inflammation in this disorder.

Peptidyl arginine deiminase-4 exacerbates ischemic AKI by finding NEMO

Peptidyl arginine deiminase-4 (PAD4) catalyzes the conversion of peptidylarginine residues to peptidylcitrulline. We have previously shown that kidney ischemia-reperfusion (I/R) injury increases renal proximal tubular PAD4 expression and activity. Furthermore, kidney PAD4 plays a critical role in ischemic acute kidney injury (AKI) by promoting renal tubular inflammation, neutrophil infiltration, and NF-κB activation. However, the mechanisms of PAD4-mediated renal tubular inflammation and NF-κB activation after I/R remain unclear. Here, we show that recombinant PAD4 preferentially citrullinates recombinant IKKγ [also called NF-κB essential modulator (NEMO)] over recombinant IKKα or IKKβ. Consistent with this finding, PAD4 citrullinated renal proximal tubular cell IKKγ and promoted NF-κB activation via IκBα phosphorylation in vitro. NEMO inhibition with a selective NEMO-binding peptide attenuated PAD4-mediated proinflammatory cytokine mRNA induction in HK-2 cells. Moreover, NEMO inhibition did not affect proximal tubular cell survival, proliferation, or apoptosis, unlike global NF-κB inhibition. In vivo, NEMO-binding peptide treatment protected against ischemic AKI. Finally, NEMO-binding peptide attenuated recombinant PAD4-mediated exacerbation of ischemic AKI, renal tubular inflammation, and apoptosis. Taken together, our results show that PAD4 exacerbates ischemic AKI and inflammation by promoting renal tubular NF-κB activity and inflammation via NEMO citrullination. Targeting NEMO activation may serve as a potential therapy for this devastating clinical problem.

Neutrophil extracellular traps in ischemic AKI: new way to kill

Neutrophil extracellular traps, originally discovered as a mechanism to combat microbial infection, have recently been implicated in tissue damage including acute kidney injury. Raup-Konsavage et al. now present further insights to demonstrate a critical role of neutrophil peptidyl arginine deiminase-4 in the formation of neutrophil extracellular trap, inflammation, and tissue damage in ischemic acute kidney infection. Targeting peptidyl arginine deiminase-4 and/or neutrophil extracellular trap may offer a new therapeutic strategy for acute kidney infection.

Divergent roles for kidney proximal tubule and granulocyte PAD4 in ischemic AKI

We previously demonstrated that kidney peptidylarginine deiminase-4 (PAD4) plays a critical role in ischemic acute kidney injury (AKI) in mice by promoting renal tubular inflammation and neutrophil infiltration (Ham A, Rabadi M, Kim M, Brown KM, Ma Z, D'Agati V, Lee HT. Am J Physiol Renal Physiol 307: F1052-F1062, 2014). Although the role of PAD4 in granulocytes including neutrophils is well known, we surprisingly observed profound renal proximal tubular PAD4 induction after renal ischemia-reperfusion (I/R) injury. Here we tested the hypothesis that renal proximal tubular PAD4 rather than myeloid-cell lineage PAD4 plays a critical role in exacerbating ischemic AKI by utilizing mice lacking PAD4 in renal proximal tubules (PAD4ff PEPCK Cre mice) or in granulocytes (PAD4ff LysM Cre mice). Mice lacking renal proximal tubular PAD4 were significantly protected against ischemic AKI compared with wild-type (PAD4ff) mice. Surprisingly, mice lacking PAD4 in myeloid cells were also protected against renal I/R injury although this protection was less compared with renal proximal tubular PAD4-deficient mice. Renal proximal tubular PAD4-deficient mice had profoundly reduced renal tubular apoptosis, whereas myeloid-cell PAD4-deficient mice showed markedly reduced renal neutrophil infiltration. Taken together, our studies suggest that both renal proximal tubular PAD4 as well as myeloid-cell lineage PAD4 play a critical role in exacerbating ischemic AKI. Renal proximal tubular PAD4 appears to contribute to ischemic AKI by promoting renal tubular apoptosis, whereas myeloid-cell PAD4 is preferentially involved in promoting neutrophil infiltration to the kidney and inflammation after renal I/R.

PAD4 Deficiency Leads to Decreased Organ Dysfunction and Improved Survival in a Dual Insult Model of Hemorrhagic Shock and Sepsis

Indirect acute respiratory distress syndrome (iARDS) is caused by a nonpulmonary inflammatory process resulting from insults such as nonpulmonary sepsis. Neutrophils are thought to play a significant role in mediating ARDS, with the development of iARDS being characterized by dysregulation and recruitment of activated neutrophils into the lung. Recently, a novel mechanism of microbial killing by neutrophils was identified through the formation of neutrophil extracellular traps (NETs). NETs are composed of large webs of decondensed chromatin released from activated neutrophils into the extracellular space; they are regulated by the enzyme peptidylarginine deiminase 4 (PAD4) through mediation of chromatin decondensation via citrullination of target histones. Components of NETs have been implicated in ARDS. However, it is unknown whether there is any pathological significance of NET formation in ARDS caused indirectly by nonpulmonary insult. We subjected PAD4-/- mice and wild-type mice to a "two-hit" model of hypovolemic shock (fixed-pressure hemorrhage [Hem]) followed by septic cecal ligation and puncture (CLP) insult (Hem/CLP). Mice were hemorrhaged and resuscitated; 24 h after Hem, mice were then subjected to CLP. Overall, PAD4 deletion led to an improved survival as compared with wild-type mice. PAD4-/- mice displayed a marked decrease in neutrophil influx into the lung, as well decreased presence of proinflammatory mediators. PAD4-/- mice were also able to maintain baseline kidney function after Hem/CLP. These data taken together suggest PAD4-mediated NET formation contributes to the mortality associated with shock/sepsis and may play a role in the pathobiology of end organ injury in response to combined hemorrhage plus sepsis.

The Peptidylarginine Deiminase Inhibitor Cl-Amidine Suppresses Inducible Nitric Oxide Synthase Expression in Dendritic Cells

The conversion of peptidylarginine into peptidylcitrulline by calcium-dependent peptidylarginine deiminases (PADs) has been implicated in the pathogenesis of a number of diseases, identifying PADs as therapeutic targets for various diseases. The PAD inhibitor Cl-amidine ameliorates the disease course, severity, and clinical manifestation in multiple disease models, and it also modulates dendritic cell (DC) functions such as cytokine production, antigen presentation, and T cell proliferation. The beneficial effects of Cl-amidine make it an attractive compound for PAD-targeting therapeutic strategies in inflammatory diseases. Here, we found that Cl-amidine inhibited nitric oxide (NO) generation in a time- and dose-dependent manner in maturing DCs activated by lipopolysaccharide (LPS). This suppression of NO generation was independent of changes in NO synthase (NOS) enzyme activity levels but was instead dependent on changes in inducible NO synthase (iNOS) transcription and expression levels. Several upstream signaling pathways for iNOS expression, including the mitogen-activated protein kinase, nuclear factor-κB p65 (NF-κB p65), and hypoxia-inducible factor 1 pathways, were not affected by Cl-amidine. By contrast, the LPS-induced signal transducer and the activator of transcription (STAT) phosphorylation and activator protein-1 (AP-1) transcriptional activities (c-Fos, JunD, and phosphorylated c-Jun) were decreased in Cl-amidine-treated DCs. Inhibition of Janus kinase/STAT signaling dramatically suppressed iNOS expression and NO production, whereas AP-1 inhibition had no effect. These results indicate that Cl-amidine-inhibited STAT activation may suppress iNOS expression. Additionally, we found mildly reduced cyclooxygenase-2 expression and prostaglandin E2 production in Cl-amidine-treated DCs. Our findings indicate that Cl-amidine acts as a novel suppressor of iNOS expression, suggesting that Cl-amidine has the potential to ameliorate the effects of excessive iNOS/NO-linked immune responses.

Neutrophil peptidyl arginine deiminase-4 has a pivotal role in ischemia/reperfusion-induced acute kidney injury

Ischemia/reperfusion is a common cause of acute kidney injury (AKI). However, mechanisms underlying the sudden loss in kidney function and tissue injury remain to be fully elucidated. Here, we investigated the role of peptidyl arginine deiminase-4 (PAD4), which converts arginine to citrulline and plays a role in epigenetic regulation and inflammation, in renal ischemia/reperfusion injury. PAD4 expression was highly induced in infiltrating leukocytes 24 hours following renal ischemia and reperfusion. This induction was accompanied by citrullination of histone H3 and formation of neutrophil extracellular traps in kidneys of wild-type mice. By contrast, PAD4-deficient mice did not form neutrophil extracellular traps, expressed lower levels of pro-inflammatory cytokines and were partially protected from renal ischemia/reperfusion-induced AKI. Furthermore, PAD4-deficient mice recovered kidney function 48 hours after ischemia/reperfusion, whereas kidney function in the wild-type mice progressively worsened. Administration of DNase I, which degrades neutrophil extracellular traps or the PAD-specific inhibitor YW3-56 before ischemia, partially prevented renal ischemia/reperfusion-induced AKI. Notably, transfer of neutrophils from wild-type, but not from PAD4-deficient mice, was sufficient to restore renal neutrophil extracellular trap formation and impair kidney function following renal ischemia/reperfusion. Thus, neutrophil PAD4 plays a pivotal role in renal ischemia/reperfusion-induced AKI.

ATP induces PAD4 in renal proximal tubule cells via P2X7 receptor activation to exacerbate ischemic AKI

We previously demonstrated that renal tubular peptidylarginine deiminase-4 (PAD4) is induced after ischemia-reperfusion (IR) injury and this induction of PAD4 exacerbates ischemic acute kidney injury (AKI) by promoting renal tubular inflammation and neutrophil infiltration. However, the mechanisms of renal tubular PAD4 induction after IR remain unknown. Here, we tested the hypothesis that ATP, a proinflammatory danger-associated molecular pattern (DAMP) ligand released from necrotic cells after IR injury, induces renal tubular PAD4 and exacerbates ischemic AKI via P2 purinergic receptor activation. ATP as well as ATPγS (a nonmetabolizable ATP analog) induced PAD4 mRNA, protein, and activity in human and mouse renal proximal tubule cells. Supporting the hypothesis that ATP induces renal tubular PAD4 via P2X7 receptor activation, A804598 (a selective P2X7 receptor antagonist) blocked the ATP-mediated induction of renal tubular PAD4 whereas BzATP (a selective P2X7 receptor agonist) mimicked the effects of ATP by inducing renal tubular PAD4 expression and activity. Moreover, ATP-mediated calcium influx in renal proximal tubule cells was blocked by A804598 and was mimicked by BzATP. P2X7 activation by BzATP also induced PAD4 expression and activity in mouse kidney in vivo. Finally, supporting a critical role for PAD4 in P2X7-mediated exacerbation of renal injury, BzATP exacerbated ischemic AKI in PAD4 wild-type mice but not in PAD4-deficient mice. Taken together, our studies show that ATP induces renal tubular PAD4 via P2X7 receptor activation to exacerbate renal tubular inflammation and injury after IR.

Diosmetin protects against ischemia/reperfusion-induced acute kidney injury in mice

BACKGROUND

Renal ischemia/reperfusion (I/R)-induced acute kidney injury remains to be a troublesome condition in clinical practice. Although the exact molecular mechanisms underlying renal I/R injury are incompletely understood, the deleterious progress of renal I/R injury involves inflammation, apoptosis, and oxidative stress. Diosmetin is a member of the flavonoid glycosides family, which suppresses the inflammatory response and cellular apoptosis and enhances antioxidant activity. The purpose of this study was to investigate the protective effect of diosmetin on I/R-induced renal injury in mice.

METHODS

Thirty BALB/c mice were randomly divided into five groups. Four groups of mice received diosmetin (0.25, 0.5, and 1 mg/kg) or vehicle (I/R group) before ischemia. Another group received vehicle without ischemia to serve as a negative control (sham-operated group). Twenty-four hours after reperfusion, serum and renal tissues were harvested to evaluate renal function and histopathologic features. In addition, the expression of inflammation-related proteins, apoptotic molecules, and antioxidant enzymes was analyzed.

RESULTS

Compared with sham mice, the I/R group significantly exacerbated renal function and renal tube architecture and increased the inflammatory response and renal tubule apoptosis. Nevertheless, pretreatment with diosmetin reversed these changes. In addition, diosmetin treatment resulted in a marked increase in antioxidant protein expression compared with I/R mice.

CONCLUSIONS

The renoprotective effects of diosmetin involved suppression of the nuclear factor-κB and mitochondrial apoptosis pathways, as well as activation of the nuclear factor erythroid 2-related factor 2/heme oxygenase-1 pathway. Diosmetin has significant potential as a therapeutic intervention to ameliorate renal injury after renal I/R.

Targeting Inflammation in So-Called Acute Kidney Injury

The clinical category of acute kidney injury includes a wide range of completely different disorders, many with their own pathomechanisms and treatment targets. In this review we focus on the role of inflammation in the pathogenesis of acute tubular necrosis (ATN). We approach this topic by first discussing the role of the immune system in the different phases of ATN (ie, early and late injury phase, recovery phase, and the long-term outcome phase of an ATN episode). A more detailed discussion focuses on putative therapeutic targets among the following mechanisms and mediators: oxidative stress and reactive oxygen species-related necroinflammation, regulated cell death-related necroinflammation, immunoregulatory lipid mediators, cytokines and cytokine signaling, chemokines and chemokine signaling, neutrophils and neutrophils extracellular traps (NETs) associated neutrophil cell death, called NETosis, extracellular histones, proinflammatory mononuclear phagocytes, humoral mediators such as complement, pentraxins, and natural antibodies. Any prioritization of these targets has to take into account the intrinsic differences between rodent models and human ATN, the current acute kidney injury definitions, and the timing of clinical decision making. Several conceptual problems need to be solved before anti-inflammatory drugs that are efficacious in rodent ATN may become useful therapeutics for human ATN.

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.

Association of anti-peptidyl arginine deiminase antibodies with radiographic severity of rheumatoid arthritis in African Americans

Background

Evidence suggests that the presence of peptidyl arginine deiminase type 4 (PAD4) antibodies is associated with radiographic-severity rheumatoid arthritis (RA) among Caucasian patients. The presence of anti-PAD4 antibodies that were cross-reactivity against PAD3 was associated with more aggressive erosive disease (compared with the presence of anti-PAD4 antibodies without anti-PAD3 crossreactivity) in Caucasian RA patients. The objectives of this study were to determine the prevalence of serum anti-PAD4 and anti-PAD4/PAD3 cross-reactive autoantibodies in African Americans with RA and whether these antibodies associate with radiographic severity and radiographic progression.

Methods

Serum anti-PAD4 and anti-PAD4/PAD3 antibodies were measured by immunoprecipitation, and the temporal trends in titers were analyzed. We compared total radiographic scores among anti-PAD4-positive, anti-PAD4/PAD3-positive, and anti-PAD4-negative patients and used a zero-inflated negative binomial model to determine associations between radiographic severity and antibody status. Logistic regression was used to analyze radiographic progression.

Results

Of 192 African-American patients with RA, 73 % were anti-citrullinated peptide/protein antibody (ACPA)-positive, 46 out of 192 (24 %) of whom had serum anti-PAD4 antibodies. Median (interquartile range) total Sharp van der Heijde radiographic scores were 2 (1–97.5) in ACPA-positive patients and 0 (0–3) in ACPA-negative patients (P < 0.001). Of the 46 anti-PAD4-positive patients, 20 had anti-PAD4 antibodies that cross-reacted with PAD3. In patients with early RA, anti-PAD4 and anti-PAD4/PAD3 antibody titers increased over time (P = 0.006, P = 0.001, respectively). Median (interquartile range) total radiographic scores were higher for anti-PAD4-positive than for anti-PAD4-negative patients (3 (1–115) versus 2 (0–11), respectively; P = 0.005). Median (interquartile range) total radiographic score for anti-PAD4/PAD3-positive patients was 76 (3–117) (P < 0.001) versus anti-PAD4-negative patients. Only anti-PAD4/PAD3 antibodies associated with radiographic severity (incidence rate ratio = 2.81; 95 % confidence interval 1.23, 6.43).

Conclusion

This analysis suggests that autoantibodies against PAD4 and PAD3 proteins may serve as biomarkers for identifying African-American patients with RA and higher radiographic severity.

Electronic supplementary material

The online version of this article (doi:10.1186/s13075-016-1126-7) contains supplementary material, which is available to authorized users.

Nucleic Acid-Targeting Pathways Promote Inflammation in Obesity-Related Insulin Resistance

Obesity-related inflammation of metabolic tissues, including visceral adipose tissue (VAT) and liver, are key factors in the development of insulin resistance (IR), though many of the contributing mechanisms remain unclear. We show that nucleic-acid-targeting pathways downstream of extracellular trap (ET) formation, unmethylated CpG DNA, or ribonucleic acids drive inflammation in IR. High-fat diet (HFD)-fed mice show increased release of ETs in VAT, decreased systemic clearance of ETs, and increased autoantibodies against conserved nuclear antigens. In HFD-fed mice, this excess of nucleic acids and related protein antigens worsens metabolic parameters through a number of mechanisms, including activation of VAT macrophages and expansion of plasmacytoid dendritic cells (pDCs) in the liver. Consistently, HFD-fed mice lacking critical responders of nucleic acid pathways, Toll-like receptors (TLR)7 and TLR9, show reduced metabolic inflammation and improved glucose homeostasis. Treatment of HFD-fed mice with inhibitors of ET formation or a TLR7/9 antagonist improves metabolic disease. These findings reveal a pathogenic role for nucleic acid targeting as a driver of metabolic inflammation in IR.

Peptidyl arginine deiminase-4-deficient mice are protected against kidney and liver injury after renal ischemia and reperfusion

We previously demonstrated that renal peptidyl arginine deiminase-4 (PAD4) is induced after renal ischemia and reperfusion (I/R) injury and exacerbates acute kidney injury (AKI) by increasing the renal tubular inflammatory response. Here, we tested whether genetic ablation of PAD4 attenuates renal injury and inflammation after I/R in mice. After renal I/R, PAD4 wild-type mice develop severe AKI with large increases in plasma creatinine, neutrophil infiltration, as well as significant renal tubular necrosis, apoptosis, and proinflammatory cytokine generation. In contrast, PAD4-deficient mice are protected against ischemic AKI with reduced real tubular neutrophil infiltration, renal tubular necrosis, and apoptosis. In addition, hepatic injury and inflammation observed in PAD4 wild-type mice after renal I/R are significantly attenuated in PAD4-deficient mice. We also show that increased renal tubular PAD4 expression after renal I/R is associated with translocation of PAD4 from the nucleus to the cytosol. Consistent with PAD4 cytosolic translocation, we show increased renal tubular cytosolic peptidyl-citrullination after ischemic AKI. Mechanistically, recombinant PAD4 treatment increased nuclear translocation of NF-κB in cultured human as well as murine proximal tubule cells that is inhibited by a PAD4 inhibitor (2-chloroamidine). Taken together, our studies further support the hypothesis that renal tubular PAD4 plays a critical role in renal I/R injury by increasing the renal tubular inflammatory response and neutrophil infiltration after renal I/R perhaps by interacting with the proinflammatory transcription factor NF-κB in the cytosol and promoting its nuclear translocation.

Overexpression of PAD4 suppresses drug resistance of NSCLC cell lines to gefitinib through inhibiting Elk1-mediated epithelial-mesenchymal transition

It is reported that epithelial-to-mesenchymal transition (EMT) could induce resistance in tumor cells, and knockdown of peptidylarginine deiminase IV (PAD4) induces the activity of EMT. However, the role of PAD4 in gefitinib‑acquired resistance in non-small cell lung cancer (NSCLC) remains unclear. In this study, we aimed to investigate the role of PAD4 in the resistance of NSCLC to gefitinib. The cells resistant to gefitinib were established in accordance with the literature, and were derived from NSCLC cell lines HCC827 and H1650. Real-time quantitative PCR and western blot results showed that PAD4 was obviously downregulated in the cells resistant to gefitinib. Overexpression of PAD4 distinctly inhibited gefitinib resistance, whereas PAD4 downregulation had the opposite effect. Further data indicated that PAD4 upregulation could restrain EMT activity via controlling the expression of ETS-domain containing protein (Elk1). Conversely, inhibition of PAD4 showed the reverse function compared with PAD4 upregulation. Above all, our study showed that overexpression of PAD4 constrains the activity of EMT via suppressing Elk1 expression, and inhibits resistance of NSCLC to gefitinib.

Organ distribution of histones after intravenous infusion of FITC histones or after sepsis

Histones appear in plasma during infectious or non-infectious sepsis and are associated with multiorgan injury. In the current studies, intravenous infusion of histones resulted in their localization in major organs. In vitro exposure of mouse macrophages to histones caused a buildup of histones on cell membranes followed by localization into cytosol and into the nucleus. After polymicrobial sepsis (cecal ligation and puncture), histones appeared in plasma as well as in a multiorgan pattern, peaking at 8 h followed by decline. In lungs, histones and neutrophils appeared together, with evidence for formation of neutrophil extracellular traps (NETs), which represent an innate immune response to trap and kill bacteria and other infectious agents. In liver, there was intense NET formation, featuring linear patterns containing histones and strands of DNA. When neutrophils were activated in vitro with C5a or phorbol myristate acetate, NET formation ensued. While formation of NETs represents entrapment and killing of infectious agents, the simultaneous release from neutrophils of histones often results in tissue/organ damage.

Inhibition of peptidylarginine deiminase attenuates inflammation and improves survival in a rat model of hemorrhagic shock

BACKGROUND

We have recently shown that inhibition of peptidylarginine deiminase (PAD) improves survival in a rodent model of lethal cecal ligation and puncture. The roles of PAD inhibitors in hemorrhagic shock (HS), however, are largely unknown. The goal of this study was to investigate the effects of YW3-56, a novel PAD inhibitor, on survival after severe HS.

METHODS

Mouse macrophages were exposed to hypoxic conditions followed by reoxygenation in the presence or absence of YW3-56. Enzyme-linked immunosorbent assay (ELISA) was performed to measure levels of secreted tumor necrosis factor α and interleukin-6 in the culture medium. Cell viability was determined by methyl thiazolyl tetrazolium assay. In the survival experiment, anesthetized male Wistar-Kyoto rats (n = 10/group) were subjected to 55% blood loss, and treated with or without YW3-56 (10 mg/kg, intraperitoneally). Survival was monitored for 12 h. In the nonsurvival experiment, morphologic changes of the lungs were examined. Levels of circulating cytokine-induced neutrophil chemoattractant 1 (CINC-1) and myeloperoxidase (MPO) in the lungs were measured by ELISA. Expression of lung intercellular adhesion molecules-1 (ICAM-1) was also determined by Western blotting.

RESULTS

Hypoxia/reoxygenation (H/R) insult induced tumor necrosis factor α and interleukin-6 secretion from macrophages, which was significantly attenuated by YW3-56 treatment. YW3-56 treatment also increased cell viability when macrophages were exposed to H/R up to 6/15 h and improved survival rate from 20% to 60% in lethal HS rat model. Compared to the sham groups, pulmonary MPO activity and ICAM-1 expression in the HS group were significantly increased, and acute lung injury was associated with a higher degree of CINC-1 levels in serum. Intraperitoneal delivery of YW3-56 significantly reduced pulmonary MPO and ICAM-1 expression and attenuated acute lung injury.

CONCLUSIONS

Our results demonstrate for the first time that administration of YW3-56, a novel PAD inhibitor, can improve survival in a rat model of HS and in a cell culture model of H/R. The survival advantage is associated with an attenuation of local and systemic pro-inflammatory cytokines and the protection against acute lung injury after hemorrhage. Thus, PAD inhibition may represent a novel and promising therapeutic strategy for severe HS.

Biliary tract external drainage alleviates kidney injury in shock

BACKGROUND

Kidney injury is common in hemorrhagic shock (HS). Kidney injury leads to a systemic increase in serum chemokines and cytokines and causes injuries to other vital organs. Our previous studies showed that vitamin C led to organ protection and inflammation inhibitory effects in rat models of HS via induction heme oxygenase-1 (HO-1). We also found that biliary tract external drainage (BTED) increased the expression levels of HO-1 in rat livers. We investigated roles of BTED in kidney injury and its relationship with the HO-1 pathway in HS in this research.

METHODS

Rat models of HS were induced by drawing blood from the femoral artery. BTED was performed by inserting a catheter into the bile duct. Thirty-six Sprague-Dawley rats were randomized to sham group; HS group; zinc protoporphyrin IX (Znpp) group; BTED group; BTED + Znpp group, and BTED + bile infusion group. The expression levels of HO-1 in the kidney were analyzed by Western blotting. The expression levels of occludin messenger RNA in the kidney were analyzed by real-time reverse transcription-polymerase chain reaction. The expression levels of occludin in the kidney were analyzed by immunohistochemistry. Histology of renal was performed by hematoxylin and eosin staining.

RESULTS

Occludin messenger RNA and protein levels in the kidney increased markedly after BTED under HS conditions. Renal histopathologic scores decreased significantly after BTED under HS conditions. Znpp significantly inhibited all mentioned effects.

CONCLUSIONS

BTED alleviates kidney injury in rats of HS via the HO-1 pathway.