TAT-SNAP-23 treatment inhibits the priming of neutrophil functions contributing to shock and/or sepsis-induced extra-pulmonary acute lung injury

Apremilast ameliorates acute respiratory distress syndrome by inhibiting neutrophil-induced oxidative stress

BACKGROUND

The pathogenesis of acute respiratory distress syndrome (ARDS) is attributed to the dysregulation of oxidative stress and neutrophil recruitment. We aimed to investigate the anti-inflammatory effects of apremilast on human neutrophils and assess its efficacy for treating ARDS.

METHODS

We analysed superoxide anion generation, integrin expression, and adhesion in activated human neutrophils using spectrophotometry, flow cytometry, and immunofluorescence microscopy. Phosphorylation of extracellular signal-regulated kinase (ERK) and c-Jun N-terminal kinase (JNK) was determined using immunoblotting. A murine lipopolysaccharide (LPS)-induced ARDS model was used to evaluate the therapeutic effects of apremilast.

RESULTS

Apremilast significantly decreased superoxide anion production, reactive oxygen species (ROS) generation, cluster of differentiation (CD)11 b expression, and neutrophil adhesion in formyl-l-methionyl-l-leucyl-l-phenylalanine activated human neutrophils. Apremilast elevated cyclic 3',5'-adenosine monophosphate (cAMP) and protein kinase A (PKA) activity in activated neutrophils. It reduced cellular cAMP-specific phosphodiesterase (PDE) activity and selectively inhibited enzymatic PDE4 activity. The activated cAMP/PKA pathway suppressed the phosphorylation of ERK and JNK as well as Ca2+ mobilization in activated neutrophils. All inhibitory effects of apremilast on activated neutrophils were reversed by a PKA inhibitor. In vivo examinations indicated that apremilast alleviated lung neutrophil infiltration, myeloperoxidase (MPO) activity, pulmonary oedema, and alveolar damage in LPS-induced ARDS.

CONCLUSION

Apremilast inhibits inflammatory responses after neutrophil activation via cAMP/PKA-dependent inhibition of ERK and JNK activation. Our study revealed apremilast suppresses oxidative stress and chemotaxis by selectively inhibiting PDE4 in neutrophils and thus protects against endotoxin-induced ARDS in mice. Apremilast can be used as an alternative off-label drug in treating acute lung damage.

Myeloperoxidase: Regulation of Neutrophil Function and Target for Therapy

Neutrophils, the most abundant white blood cells in humans, are critical for host defense against invading pathogens. Equipped with an array of antimicrobial molecules, neutrophils can eradicate bacteria and clear debris. Among the microbicide proteins is the heme protein myeloperoxidase (MPO), stored in the azurophilic granules, and catalyzes the formation of the chlorinating oxidant HOCl and other oxidants (HOSCN and HOBr). MPO is generally associated with killing trapped bacteria and inflicting collateral tissue damage to the host. However, the characterization of non-enzymatic functions of MPO suggests additional roles for this protein. Indeed, evolving evidence indicates that MPO can directly modulate the function and fate of neutrophils, thereby shaping immunity. These actions include MPO orchestration of neutrophil trafficking, activation, phagocytosis, lifespan, formation of extracellular traps, and MPO-triggered autoimmunity. This review scrutinizes the multifaceted roles of MPO in immunity, focusing on neutrophil-mediated host defense, tissue damage, repair, and autoimmunity. We also discuss novel therapeutic approaches to target MPO activity, expression, or MPO signaling for the treatment of inflammatory and autoimmune diseases.

Differential dysregulation of granule subsets in WASH-deficient neutrophil leukocytes resulting in inflammation

Dysregulated secretion in neutrophil leukocytes associates with human inflammatory disease. The exocytosis response to triggering stimuli is sequential; gelatinase granules modulate the initiation of the innate immune response, followed by the release of pro-inflammatory azurophilic granules, requiring stronger stimulation. Exocytosis requires actin depolymerization which is actively counteracted under non-stimulatory conditions. Here we show that the actin nucleator, WASH, is necessary to maintain azurophilic granules in their refractory state by granule actin entrapment and interference with the Rab27a-JFC1 exocytic machinery. On the contrary, gelatinase granules of WASH-deficient neutrophil leukocytes are characterized by decreased Rac1, shortened granule-associated actin comets and impaired exocytosis. Rac1 activation restores exocytosis of these granules. In vivo, WASH deficiency induces exacerbated azurophilic granule exocytosis, inflammation, and decreased survival. WASH deficiency thus differentially impacts neutrophil granule subtypes, impairing exocytosis of granules that mediate the initiation of the neutrophil innate response while exacerbating pro-inflammatory granule secretion.

Targeting Neutrophils for Promoting the Resolution of Inflammation

Acute inflammation is a localized and self-limited innate host-defense mechanism against invading pathogens and tissue injury. Neutrophils, the most abundant immune cells in humans, play pivotal roles in host defense by eradicating invading pathogens and debris. Ideally, elimination of the offending insult prompts repair and return to homeostasis. However, the neutrophils` powerful weaponry to combat microbes can also cause tissue damage and neutrophil-driven inflammation is a unifying mechanism for many diseases. For timely resolution of inflammation, in addition to stopping neutrophil recruitment, emigrated neutrophils need to be disarmed and removed from the affected site. Accumulating evidence documents the phenotypic and functional versatility of neutrophils far beyond their antimicrobial functions. Hence, understanding the receptors that integrate opposing cues and checkpoints that determine the fate of neutrophils in inflamed tissues provides insight into the mechanisms that distinguish protective and dysregulated, excessive inflammation and govern resolution. This review aims to provide a brief overview and update with key points from recent advances on neutrophil heterogeneity, functional versatility and signaling, and discusses challenges and emerging therapeutic approaches that target neutrophils to enhance the resolution of inflammation.

Inhibition of TXNDC5 attenuates lipopolysaccharide-induced septic shock by altering inflammatory responses

Sepsis and its severe form, septic shock, represent the leading cause of death among hospitalized patients. Thioredoxin is a ubiquitous protein essential for cellular redox balance and its aberrant expression is associated with a wide spectrum of inflammation-related pathological conditions. The current study aimed to compare the expression of thioredoxin domain containing 5 (TXNDC5) in septic patients with or without septic shock and to explore the potential regulatory effects of TXNDC5 in sepsis. We analyzed the RNA expression data downloaded from the Gene Expression Omnibus database and measured the plasma level of TXNDC5 in septic patients. The results showed that TXNDC5 was upregulated in patients with septic shock compared to septic patients without shock or healthy controls. We further treated wild-type mice and cultured macrophages with lipopolysaccharide (LPS) and found that TXNDC5 was highly expressed in mice with LPS-induced sepsis and macrophages subjected to LPS stimulation compared to corresponding controls. Then a mouse strain with targeted depletion of Txndc5 was generated. Txndc5 depletion reduced inflammatory cytokine production and affected the recruitment of macrophages and neutrophils into the blood and peritoneum of mice challenged with LPS. Further analysis revealed that TXNDC5 inhibition alleviated LPS-induced sepsis by inhibiting the NF-κB signaling pathway. In summary, these findings suggested that the inhibition of TXNDC5 may be a potential approach to treat sepsis and related syndromes.

Patho-Mechanisms for Hemorrhage/Sepsis-Induced Indirect Acute Respiratory Distress Syndrome: A Role for Lung TIE1 and Its Regulation by Neutrophils

INTRODUCTION

Severe hemorrhage (Hem) has been shown to be causal for the development of extra-pulmonary/indirect acute respiratory distress syndrome (iARDS) and is associated with severe endothelial cell (EC) injury. EC growth factors, Angiopoietin (Ang)-1 and -2, maintain vascular homeostasis via tightly regulated competitive interaction with the tyrosine kinase receptor, Tie2, expressed on ECs.

OBJECTIVE

Since it has been reported that the orphan receptor, Tie1, may be able to play a role in Ang:Tie2 signaling; we chose to examine Tie1's capacity to alter the lung Ang:Tie2 interaction in response to the sequential insults of shock/sepsis (cecal ligation and puncture [CLP]), culminating in iARDS.

METHODS

Male mice were subjected to Hem alone or sequential Hem followed 24 hours later by CLP that induces iARDS. Changes in lung and/or plasma levels of Tie1, Tie2, Ang-1, Ang-2, various systemic cytokine/chemokines and indices of lung injury/inflammation were then determined. The role of Tie1 was established by intravenous administration of Tie1 specific or control siRNA at 1 h post-Hem. Alternatively, the contribution of neutrophils was assessed by pre-treating mice with anti-neutrophil antibody depletion 48 h prior to Hem.

RESULTS

Lung tissue levels of Tie1 expression elevated over the first 6 to 24 h post-Hem alone. Subsequently, we found that treatment of Hem/CLP mice with Tie1-specific siRNA not only decreased Tie1 expression in lung tissue compared to control siRNA, but, suppressed the rise in lung inflammatory cytokines, lung MPO and the rise in lung protein leak. Finally, much as we have previously shown that neutrophil interaction with resident pulmonary vascular ECs contribute significantly to Ang-2 release and EC dysfunction, central to the development of iARDS. Here, we report that depletion of neutrophils also decreased lung tissue Tie1 expression and increased Tie2 activation in Hem/CLP mice.

CONCLUSION

Together, these data imply that shock-induced increased expression of Tie1 can contribute to EC activation by inhibiting Ang:Tie2 interaction, culminating in EC dysfunction and the development of iARDS.

Endothelial Transcytosis in Acute Lung Injury: Emerging Mechanisms and Therapeutic Approaches

Acute Lung Injury (ALI) is characterized by widespread inflammation which in its severe form, Acute Respiratory Distress Syndrome (ARDS), leads to compromise in respiration causing hypoxemia and death in a substantial number of affected individuals. Loss of endothelial barrier integrity, pneumocyte necrosis, and circulating leukocyte recruitment into the injured lung are recognized mechanisms that contribute to the progression of ALI/ARDS. Additionally, damage to the pulmonary microvasculature by Gram-negative and positive bacteria or viruses (e.g., Escherichia coli, SARS-Cov-2) leads to increased protein and fluid permeability and interstitial edema, further impairing lung function. While most of the vascular leakage is attributed to loss of inter-endothelial junctional integrity, studies in animal models suggest that transendothelial transport of protein through caveolar vesicles, known as transcytosis, occurs in the early phase of ALI/ARDS. Here, we discuss the role of transcytosis in healthy and injured endothelium and highlight recent studies that have contributed to our understanding of the process during ALI/ARDS. We also cover potential approaches that utilize caveolar transport to deliver therapeutics to the lungs which may prevent further injury or improve recovery.

Innate Neutrophil Memory Dynamics in Disease Pathogenesis

Neutrophils, the most abundant leukocytes in circulation and the first responders to infection and inflammation, closely modulate both acute and chronic inflammatory processes. Resting neutrophils constantly patrol vasculature and migrate to tissues when challenges occur. When infection and/or inflammation recede, tissue neutrophils will be subsequently cleaned up by macrophages which collectively contribute to the resolution of inflammation. While most studies focus on the anti-microbial function of neutrophils including phagocytosis, degranulation, and neutrophil extracellular traps (NETs) formation, recent research highlighted additional contributions of neutrophils beyond simply controlling infectious agents. Neutrophils with resolving characteristics may alter the activities of neighboring cells and facilitate inflammation resolution, modulate long-term macrophage and adaptive immune responses, therefore having important impacts on host pathophysiology. The focus of this chapter is to provide an updated assessment of recent progress in the emerging field of neutrophil programming and memory in the context of both acute and chronic diseases.

The Controversy About the Effects of Different Doses of Corticosteroid Treatment on Clinical Outcomes for Acute Respiratory Distress Syndrome Patients: An Observational Study

Background: Corticosteroid usage in acute respiratory distress syndrome (ARDS) remains controversial. We aim to explore the correlation between the different doses of corticosteroid administration and the prognosis of ARDS.

Methods: All patients were diagnosed with ARDS on initial hospital admission and received systemic corticosteroid treatment for ARDS. The main outcomes were the effects of corticosteroid treatment on clinical parameters and the mortality of ARDS patients. Secondary outcomes were factors associated with the mortality of ARDS patients.

Results: 105 ARDS patients were included in this study. Corticosteroid treatment markedly decreased serum interleukin-18 (IL-18) level (424.0 ± 32.19 vs. 290.2 ± 17.14; p = 0.0003) and improved arterial partial pressure of oxygen/fraction of inspired oxygen (PaO₂/FiO₂) (174.10 ± 65.28 vs. 255.42 ± 92.49; p < 0.0001). The acute physiology and chronic health evaluation (APACHE II) score (16.15 ± 4.41 vs. 14.88 ± 4.57, p = 0.042) decreased significantly on the seventh day after systemic corticosteroid treatment. Interestingly, the serum IL-18 decreased significantly (304.52 ± 286.00 vs. 85.85 ± 97.22, p < 0.0001), whereas the improvement of PaO₂/FiO₂ (24.78 ± 35.03 vs. 97.17 ± 44.82, p < 0.001) was inconspicuous after systemic corticosteroid treatment for non-survival patients, compared with survival patients. Furthermore, the receiver operating characteristic (ROC) model revealed, when equivalent methylprednisolone usage was 146.5 mg/d, it had the best sensitivity and specificity to predict the death of ARDS. Survival analysis by Kaplan–Meier curves presented the higher 45-day mortality in high-dose corticosteroid treatment group (logrank test p < 0.0001). Multivariate Cox regression analyses demonstrated that serum IL-18 level, APACHE II score, D-dimer, and high-dose corticosteroid treatment were associated with the death of ARDS.

Conclusion: Appropriate dose of corticosteroids may be beneficial for ARDS patients through improving the oxygenation and moderately inhibiting inflammatory response. The benefits and risks should be carefully weighed when using high-dose corticosteroid for ARDS.

Trial registration: This work was registered in ClinicalTrials.gov. Name of the registry: Corticosteroid Treatment for Acute Respiratory Distress Syndrome. Trial registration number: NCT02819453. URL of trial registry record: https://register.clinicaltrials.gov.

Roles of neutrophil granule proteins in orchestrating inflammation and immunity

Neutrophil granulocytes form the first line of host defense against invading pathogens and tissue injury. They are rapidly recruited from the blood to the affected sites, where they deploy an impressive arsenal of effectors to eliminate invading microbes and damaged cells. This capacity is endowed in part by readily mobilizable proteins acquired during granulopoiesis and stored in multiple types of cytosolic granules with each granule type containing a unique cargo. Once released, granule proteins contribute to killing bacteria within the phagosome or the extracellular milieu, but are also capable of inflicting collateral tissue damage. Neutrophil-driven inflammation underlies many common diseases. Research over the last decade has documented neutrophil heterogeneity and functional versatility far beyond their antimicrobial function. Emerging evidence indicates that neutrophils utilize granule proteins to interact with innate and adaptive immune cells and orchestrate the inflammatory response. Granule proteins have been identified as important modulators of neutrophil trafficking, reverse transendothelial migration, phagocytosis, neutrophil life span, neutrophil extracellular trap formation, efferocytosis, cytokine activity, and autoimmunity. Hence, defining their roles within the inflammatory locus is critical for minimizing damage to the neighboring tissue and return to homeostasis. Here, we provide an overview of recent advances in the regulation of degranulation, granule protein functions, and signaling in modulating neutrophil-mediated immunity. We also discuss how targeting granule proteins and/or signaling could be harnessed for therapeutic benefits.

Herpes Virus Entry Mediator (HVEM) Expression Promotes Inflammation/ Organ Injury in Response to Experimental Indirect-Acute Lung Injury

Therapeutic interventions to treat acute lung injury (ALI) remain largely limited to lung-protective strategies, as a real molecular pathophysiologically driven therapeutic intervention has yet to become available. While we have previously documented the expression of herpes virus entry mediator (HVEM) on leukocytes of septic mice and critically ill patients, its functional role in shock/sepsis-induced ALI has not yet been studied. Inasmuch, a murine model of indirect ALI (iALI) was induced by hemorrhagic shock (HEM) followed by cecal ligation and puncture (CLP), septic challenge and HVEM-siRNA or phosphate buffered saline was administrated by intratracheal instillation 2 h after hemorrhage to determine the role of HVEM in the development of experimental iALI. Indices of lung injury were measured. HVEM expression was significantly elevated in iALI mice. Compared with phosphate buffered saline treated iALI mice, HVEM knock-down by siRNA caused a reduction of cytokine/chemokine levels, myeloperoxidase activity, broncho-alveolar lavage fluid (BALF) cell count and protein concentration. HVEM-siRNA treatment reduced inflammation and attenuated pulmonary architecture destruction as well as provided an early (60 h post HEM-CLP) survival benefit in iALI mice. This ability of anti-HVEM treatment to prevent the development of iALI and provide a transient survival benefit implies that mitigating signaling through HVEM may be a novel target worth further investigation.

Therapeutic targeting of neutrophil exocytosis

Dysregulation of neutrophil activation causes disease in humans. Neither global inhibition of neutrophil functions nor neutrophil depletion provides safe and/or effective therapeutic approaches. The role of neutrophil granule exocytosis in multiple steps leading to recruitment and cell injury led each of our laboratories to develop molecular inhibitors that interfere with specific molecular regulators of secretion. This review summarizes neutrophil granule formation and contents, the role granule cargo plays in neutrophil functional responses and neutrophil-mediated diseases, and the mechanisms of granule release that provide the rationale for development of our exocytosis inhibitors. We present evidence for the inhibition of granule exocytosis in vitro and in vivo by those inhibitors and summarize animal data indicating that inhibition of neutrophil exocytosis is a viable therapeutic strategy.

The clinical consequences of neutrophil priming

PURPOSE OF REVIEW

Neutrophils priming has been long studied in vitro. Recent studies describe it in vivo. In pathophysiological conditions, complex, heterogeneous characteristics of priming are described in the last few years.

RECENT FINDINGS

Priming can occur systemically when insults such as sepsis or trauma result in an array of circulating mediators and circulating primed neutrophils seem to exert detrimental effects either directly, or indirectly by interacting with other cells, thereby contributing to the development of organ dysfunction. Local priming of neutrophils augments their ability to clear infection, but may also lead to local bystander tissue injury, for example, in the inflamed joint. The complexity, heterogeneity and dynamic nature of inflammatory responses and the accessibility of cells from local sites make neutrophil priming challenging to study in human disease; however, recent advances have made significant progress to this field.

SUMMARY

Herein, we summarize the literature regarding neutrophil priming in selected conditions. In some diseases and in the setting of specific genetic influences, the priming repertoire seems to be restricted, with only some neutrophil functions upregulated. A greater understanding of the nature of neutrophil priming and its role in human disease is required before this process becomes tractable to therapeutic intervention.

The Prolyl Isomerase Pin1 Controls Lipopolysaccharide-Induced Priming of NADPH Oxidase in Human Neutrophils

Production of superoxide anion and other reactive oxygen species (ROS) by neutrophils has a vital role in host defense against microbes. However, over-production can induce cell injury participating to inflammation. Superoxide anion is produced by the phagocyte NADPH oxidase/NOX2, a multicomponent enzyme system consisting of six proteins: two trans-membrane proteins (gp91 ^phox and p22 ^phox ) and four soluble cytosolic proteins (p40 ^phox , p67 ^phox , p47 ^phox , and the small G-proteins, Rac1/2). Phosphorylation of p47 ^phox on several serines regulates NADPH oxidase activation. LPS released by gram negative bacteria can enhance or prime neutrophil superoxide production in combination with other agonists such as the bacterial peptide formyl-Met-Leu-Phe (fMLP). Since the pathways involved in LPS-induced priming are not completely understood, we investigated the role of the prolyl cis/trans isomerase Pin1 in this process. Two different Pin1 inhibitors, PiB, and Juglone are able to block LPS-induced priming of ROS production by human neutrophils in a concentration dependent manner. PiB and Juglone did not inhibit LPS-induced CD11b translocation neither CD62L shedding. LPS induced an increase of Pin1 activity in neutrophils similar to TNFα and fMLP. Since the phosphorylation of p47 ^phox on Ser345 is critical for NADPH oxidase up-regulation, we investigated the effect of LPS on this process. Results show that LPS induced the phosphorylation of p47 ^phox mainly on serine 345 and induced the activation of p38MAPKinase and ERK1/2. These results suggest that the prolyl cis/trans isomerase Pin1 may control LPS-induced priming of superoxide production in human neutrophils. Pharmacological targeting of Pin1 could be a valuable approach in sepsis.

Tim-3 Regulates Tregs' Ability to Resolve the Inflammation and Proliferation of Acute Lung Injury by Modulating Macrophages Polarization

We recently reported that CD4CD25 regulatory T cells (Tregs) contributed to the recovery of patients with acute lung injury (ALI) by upregulating T cell immunoglobulin and mucin-domain containing-3 (Tim-3). However, the molecular mechanism by which Tim-3 regulates Tregs' function in the resolution and fibroproliferation after ALI remains unknown. In this study, we adoptively transferred Tim-3Tregs or Tim-3Tregs into lipopolysaccharide -induced ALI mice model. Data demonstrated that Tim-3Tregs not only decreased indices of lung inflammation and injury but also mitigated lung fibrosis after ALI. Furthermore, we observed that the transfer of Tim-3Tregs led to M2-like macrophage differentiation as demonstrated by significantly upregulated levels of M2-associated phenotypic markers as well as downregulated expressions of M1-related markers in both the profibrotic lung tissue and sorted pulmonary monocytes after ALI. In addition, cytokines such as interleukin (IL)-10 and IL-4 were also upregulated in lung tissues after Tim-3Tregs transferring. In vitro experiments further demonstrated that cell-contact cocultures with Tregs lacking Tim-3 presented decreased polarization of M2-like macrophages partially mediated by a decreased expression and function of STAT-3. Therefore, these data demonstrate a previously unrecognized function of Tim-3 on Tregs in their ability to repress the fibroproliferation of ALI by inducing alternative macrophages polarization. Moreover, the data highlight that Tim-3Tregs-mediated induction of M2-like macrophages may be a novel treatment modality with transitional potential.

Novel pharmacological inhibition of EZH2 attenuates septic shock by altering innate inflammatory responses to sepsis

The function of histone methyltransferase enhancer of zeste homolog 2 (EZH2) in sepsis remains unknown. We reported here that the expression of EZH2 and H3K27me3 was significantly upregulated in the circulation of septic patients, whereas patients who survived presented downregulated the expression of EZH2 on CD14+ monocytes. We further identified increased expression of EZH2 in the circulation, peritoneal fluid, and septic lungs from CLP mice. 3-DZNeP treated CLP mice improved mortality and protected from organ injury. EZH2 inhibition not only suppressed the activation of inflammatory cells and release of cytokines in the circulation and infectious sites, but also promoted bacteria clearance and replenished the circulating monocyte and neutrophil pool from bone marrow. Blockage of EZH2 also suppressed the progression of lung injury and alleviated inflammation by decreasing the pulmonary cell apoptosis, reducing inflammatory cells infiltration and cytokines release through inhibition of the STAT3 signaling pathway and recovery of PPARγ activation. In addition, EZH2 inhibitor blunted macrophage M1 polarization by SOCS3/STAT1 pathway. Overall, these data suggest that EZH2 could be a potential biomarker predicting clinical outcome and a new target for therapeutic interference in sepsis.

Priming and de-priming of neutrophil responses in vitro and in vivo

The activation status of neutrophils can cycle from basal through primed to fully activated ("green-amber-red"), and at least in vitro, primed cells can spontaneously revert to a near basal phenotype. This broad range of neutrophil responsiveness confers extensive functional flexibility, allowing neutrophils to respond rapidly and appropriately to varied and evolving threats throughout the body. Primed and activated cells display dramatically enhanced bactericidal capacity (including augmented respiratory burst activity, degranulation and longevity), but this enhancement also confers the capacity for significant unintended tissue injury. Neutrophil priming and its consequences have been associated with adverse outcomes in a range of disease states, hence understanding the signalling processes that regulate the transition between basal and primed states (and back again) may offer new opportunities for therapeutic intervention in pathological settings. A wide array of host- and pathogen-derived molecules is able to modulate the functional status of these versatile cells. Reflecting this extensive repertoire of potential mediators, priming can be established by a range of signalling pathways (including mitogen-activated protein kinases, phosphoinositide 3-kinases, phospholipase D and calcium transients) and intracellular processes (including endocytosis, vesicle trafficking and the engagement of adhesion molecules). The signalling pathways engaged, and the exact cellular phenotype that results, vary according to the priming agent(s) to which the neutrophil is exposed and the precise environmental context. Herein we describe the signals that establish priming (in particular for enhanced respiratory burst, degranulation and prolonged lifespan) and describe the recently recognised process of de-priming, correlating in vitro observations with in vivo significance.

Downregulation of Paralemmin-3 Ameliorates Lipopolysaccharide-Induced Acute Lung Injury in Rats by Regulating Inflammatory Response and Inhibiting Formation of TLR4/MyD88 and TLR4/TRIF Complexes

Previous studies have demonstrated paralemmin-3 (PALM3) participates in Toll-like receptor (TLR) signaling. This study investigated the effect of PALM3 knockdown on lipopolysaccharide (LPS)-induced acute lung injury (ALI) and its underlying mechanisms. We constructed a recombinant adenoviral vector containing short hairpin RNA for PALM3 to knockdown PALM3 expression. A transgene-free adenoviral vector was used as a negative control. The ALI rat model was established by LPS peritoneal injection at 48-h post-transfection. Results showed that downregulation of PALM3 improved the survival rate, attenuated lung pathological changes, alleviated pulmonary edema, lung vascular leakage and neutrophil infiltration, inhibited the production of proinflammatory cytokines and activation of nuclear factor κB and interferon β regulatory factor 3, and promoted the secretion of anti-inflammatory cytokine interleukin-10 and expression of suppressor of cytokine signaling-3 in the ALI rat model. However, PALM3 knockdown had no effect on TLR4, myeloid differentiation factor 88 (MyD88), and Toll-interleukin-1 receptor domain-containing adaptor inducing interferon β (TRIF) expression. Moreover, PALM3 knockdown reduced the interaction of TLR4 with MyD88 or TRIF induced by LPS in rat lungs. Therefore, the downregulation of PALM3 protected rats from LPS-induced ALI and its mechanisms were partially associated with the modulation of inflammatory responses and inhibition of TLR4/MyD88 and TLR4/TRIF complex formation.

Neutrophil exocytosis induces podocyte cytoskeletal reorganization and proteinuria in experimental glomerulonephritis

Acute glomerulonephritis is characterized by rapid glomerular neutrophil recruitment, proteinuria, and glomerular hypercellularity. The current study tested the hypothesis that the release of neutrophil granule contents plays a role in both the loss of filtration barrier leading to proteinuria and the increase in glomerular cells. Inhibition of neutrophil exocytosis with a peptide inhibitor prevented proteinuria and attenuated podocyte and endothelial cell injury but had no effect on glomerular hypercellularity in an experimental acute glomerulonephritis model in mice. Cultivation of podocytes with neutrophil granule contents disrupted cytoskeletal organization, an in vitro model for podocyte effacement and loss of filtration barrier. Activated, cultured podocytes released cytokines that stimulated neutrophil chemotaxis, primed respiratory burst activity, and stimulated neutrophil exocytosis. We conclude that crosstalk between podocytes and neutrophils contributes to disruption of the glomerular filtration barrier in acute glomerulonephritis. Neutrophil granule products induce podocyte injury but do not participate in the proliferative response of intrinsic glomerular cells.

M2A and M2C Macrophage Subsets Ameliorate Inflammation and Fibroproliferation in Acute Lung Injury Through Interleukin 10 Pathway

The role of M2 macrophages in the resolution and fibroproliferation of acute lung injury (ALI) is poorly understood. In this study, we investigated the effects of two M2 macrophage subtypes, M2a induced by interleukin (IL)-4/IL-13 and M2c induced by IL-10/transforming growth factor -β, on the pathogenesis of ALI. M2a and M2c were adoptively transferred into lipopolysaccharide-induced ALI mice model. Data showed that Vybrant-labeled macrophages appeared in the lungs of ALI mice. Subsequently, we observed that both subsets significantly reduced lung inflammation and injury including a reduction of neutrophil influx into the lung and an augmentation of apoptosis. Interestingly, M2c macrophages more effectively suppressed indices of lung injury than M2a macrophages. M2c macrophages were also more effective than M2a in reduction of lung fibrosis. In addition, we found that M2c but not M2a macrophages increased IL-10 level in lung tissues of the recipient ALI mice partially mediated by activating the JAK1/STAT3/suppressor of cytokine signaling 3 signaling pathway. After blocking IL-10, these superior effects of M2c over M2a were abolished. These data imply that M2c are more potent than M2a macrophages in protecting against lung injury and subsequent fibrosis due to their ability to produce IL-10. Therefore, reprogramming macrophages to M2c subset may be a novel treatment modality with transitional potential.

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.

ABIN1 Determines Severity of Glomerulonephritis via Activation of Intrinsic Glomerular Inflammation

Transcription factor NF-κB regulates expression of numerous genes that control inflammation and is activated in glomerular cells in glomerulonephritis (GN). We previously identified genetic variants for a NF-κB regulatory, ubiquitin-binding protein ABIN1 as risk factors for GN in systemic autoimmunity. The goal was to define glomerular inflammatory events controlled by ABIN1 function in GN. Nephrotoxic serum nephritis was induced in wild-type (WT) and ubiquitin-binding deficient ABIN1[D485N] mice, and renal pathophysiology and glomerular inflammatory phenotypes were assessed. Proteinuria was also measured in ABIN1[D485N] mice transplanted with WT mouse bone marrow. Inflammatory activation of ABIN1[D472N] (D485N homolog) cultured human-derived podocytes, and interaction with primary human neutrophils were also assessed. Disruption of ABIN1 function exacerbated proteinuria, podocyte injury, glomerular NF-κB activity, glomerular expression of inflammatory mediators, and glomerular recruitment and retention of neutrophils in antibody-mediated nephritis. Transplantation of WT bone marrow did not prevent the increased proteinuria in ABIN1[D845N] mice. Tumor necrosis factor-stimulated enhanced expression and secretion of NF-κB-targeted proinflammatory mediators in ABIN1[D472N] cultured podocytes compared with WT cells. Supernatants from ABIN1[D472N] podocytes accelerated chemotaxis of human neutrophils, and ABIN1[D472N] podocytes displayed a greater susceptibility to injurious morphologic findings induced by neutrophil granule contents. These studies define a novel role for ABIN1 dysfunction and NF-κB in mediating GN through proinflammatory activation of podocytes.

Neutrophil programming dynamics and its disease relevance

Neutrophils are traditionally considered as first responders to infection and provide antimicrobial host defense. However, recent advances indicate that neutrophils are also critically involved in the modulation of host immune environments by dynamically adopting distinct functional states. Functionally diverse neutrophil subsets are increasingly recognized as critical components mediating host pathophysiology. Despite its emerging significance, molecular mechanisms as well as functional relevance of dynamically programmed neutrophils remain to be better defined. The increasing complexity of neutrophil functions may require integrative studies that address programming dynamics of neutrophils and their pathophysiological relevance. This review aims to provide an update on the emerging topics of neutrophil programming dynamics as well as their functional relevance in diseases.

Priming of the neutrophil respiratory burst: role in host defense and inflammation

Neutrophils are the major circulating white blood cells in humans. They play an essential role in host defense against pathogens. In healthy individuals, circulating neutrophils are in a dormant state with very low efficiency of capture and arrest on the quiescent endothelium. Upon infection and subsequent release of pro-inflammatory mediators, the vascular endothelium signals to circulating neutrophils to roll, adhere, and cross the endothelial barrier. Neutrophils migrate toward the infection site along a gradient of chemo-attractants, then recognize and engulf the pathogen. To kill this pathogen entrapped inside the vacuole, neutrophils produce and release high quantities of antibacterial peptides, proteases, and reactive oxygen species (ROS). The robust ROS production is also called 'the respiratory burst', and the NADPH oxidase or NOX2 is the enzyme responsible for the production of superoxide anion, leading to other ROS. In vitro, several soluble and particulate agonists induce neutrophil ROS production. This process can be enhanced by prior neutrophil treatment with 'priming' agents, which alone do not induce a respiratory burst. In this review, we will describe the priming process and discuss the beneficial role of controlled neutrophil priming in host defense and the detrimental effect of excessive neutrophil priming in inflammatory diseases.

6-Hydroxy-5,7-dimethoxy-flavone suppresses the neutrophil respiratory burst via selective PDE4 inhibition to ameliorate acute lung injury

Over-activated neutrophils produce enormous oxidative stress and play a key role in the development of acute and chronic inflammatory diseases. 6-Hydroxy-5,7-dimethoxy-flavone (UFM24), a flavone isolated from the Annonaceae Uvaria flexuosa, showed inhibitory effects on human neutrophil activation and salutary effects on lipopolysaccharide (LPS)-induced acute lung injury (ALI) in mice. UFM24 potently inhibited superoxide anion (O₂^•-) generation, reactive oxidants, and CD11b expression, but not elastase release, in N-formyl-l-methionyl-l-leucyl-l-phenylalanine (fMLF)-activated human neutrophils. However, UFM24 failed to scavenge O₂^•- and inhibit the activity of subcellular NADPH oxidase. fMLF-induced phosphorylation of protein kinase B (Akt) was inhibited by UFM24. Noticeably, UFM24 increased cyclic adenosine monophosphate (cAMP) concentration and protein kinase (PK) A activity in activated human neutrophils. PKA inhibitors significantly reversed the inhibitory effects of UFM24, suggesting that the effects of UFM24 were through cAMP/PKA-dependent inhibition of Akt activation. Additionally, activity of cAMP-related phosphodiesterase (PDE)4, but not PDE3 or PDE7, was significantly reduced by UFM24. Furthermore, UFM24 attenuated neutrophil infiltration, myeloperoxidase activity, and pulmonary edema in LPS-induced ALI in mice. In conclusion, our data demonstrated that UFM24 inhibits oxidative burst in human neutrophils through inhibition of PDE4 activity. UFM24 also exhibited significant protection against endotoxin-induced ALI in mice. UFM24 has potential as an anti-inflammatory agent for treating neutrophilic lung damage.

Enhanced Innate Inflammation Induced by Anti-BTLA Antibody in Dual Insult Model of Hemorrhagic Shock/Sepsis

Sepsis following hemorrhagic shock is a common clinical condition, in which innate immune system suffers from severe suppression. B and T lymphocyte attenuator (BTLA) is an immune-regulatory coinhibitory receptor expressed not only on adaptive, but also on innate immune cells. Our previous data showed that BTLA gene deficient mice were protected from septic mortality when compared with wild-type control C57BL/6 mice. Here, we extended our study by treating C57BL/6 mice with an anti-BTLA monoclonal antibody (clone 6A6; reported to have the ability to neutralize or agonize/potentiate BTLA signaling) in a mouse model of hemorrhagic shock (Hem) followed by sepsis induced by cecal ligation and puncture (CLP); positing initially that if BTLA engagement was neutralized, like gene deficiency, an anti-BTLA mAb would have the similar effects on the inflammatory response/morbidity in these mice after such insults. Here, we report that BTLA expression is elevated on innate immune cells after Hem/CLP. However, anti-BTLA antibody treatment increased cytokine (TNF-α, IL-12, IL-10)/chemokine (KC, MIP-2, MCP-1) levels and inflammatory cells (neutrophils, macrophages, dendritic cells) recruitment in the peritoneal cavity, which in turn aggravated organ injury and elevated these animals' mortality in Hem/CLP. When compared with the protective effects of our previous study using BTLA gene deficient mice in a model of lethal septic challenge, we further confirmed BTLA's contribution to enhanced innate cell recruitment, elevated IL-10 levels, and reduced survival, and that engagement of antibody with BTLA potentiates/exacerbates the pathophysiology in Hem/sepsis.

Cl-Amidine Prevents Histone 3 Citrullination and Neutrophil Extracellular Trap Formation, and Improves Survival in a Murine Sepsis Model

Sepsis refers to the presence of a serious infection that correlates with systemic and uncontrolled immune activation. Posttranslational histone modification plays an important role in chromatin decondensation, which is regulated by citrullination. Citrullinated histone H3 (H3cit) has been identified as a component of neutrophil extracellular traps (NETs), which are released into the extracellular space as part of the neutrophil response to infection. The conversion of arginine to citrulline residues on histones is catalyzed by peptidylarginine deiminase 4 (PAD4). This study's goals were to characterize the presence of PAD4-catalyzed H3cit and NET formation during the onset of sepsis and elucidate the effects on the immune response when this mechanism of action is blocked. Adult C57BL/6 male mice were treated with Cl-amidine, an inhibitor of PAD4, 1 h prior to sepsis induced by cecal ligation and puncture (CLP). Twenty-four hours after CLP, cytokine levels, H3cit protein expression, neutrophil counts, and NET production were evaluated in the peritoneal cavity. Survival studies were also performed. Here we demonstrate that Cl-amidine treatment prior to CLP improves overall survival in sepsis and the abrogation of PAD4 has minimal effects on the proinflammatory immune response to sepsis, while it has no effect on overall neutrophil migration to the peritoneum.

Osthol attenuates neutrophilic oxidative stress and hemorrhagic shock-induced lung injury via inhibition of phosphodiesterase 4

Oxidative stress caused by neutrophils is an important pathogenic factor in trauma/hemorrhagic (T/H)-induced acute lung injury (ALI). Osthol, a natural coumarin found in traditional medicinal plants, has therapeutic potential in various diseases. However, the pharmacological effects of osthol in human neutrophils and its molecular mechanism of action remain elusive. In this study, our data showed that osthol potently inhibited the production of superoxide anion (O2(•-)) and reactive oxidants derived therefrom as well as expression of CD11b in N-formylmethionylleucylphenylalanine (FMLP)-activated human neutrophils. However, osthol inhibited neutrophil degranulation only slightly and it failed to inhibit the activity of subcellular NADPH oxidase. FMLP-induced phosphorylation of extracellular signal-regulated kinase (ERK) and protein kinase B (Akt) was inhibited by osthol. Notably, osthol increased the cAMP concentration and protein kinase A (PKA) activity in activated neutrophils. PKA inhibitors reversed the inhibitory effects of osthol, suggesting that these are mediated through cAMP/PKA-dependent inhibition of ERK and Akt activation. Furthermore, the activity of cAMP-specific phosphodiesterase (PDE) 4, but not PDE3 or PDE7, was significantly reduced by osthol. In addition, osthol reduced myeloperoxidase activity and pulmonary edema in rats subjected to T/H shock. In conclusion, our data suggest that osthol has effective anti-inflammatory activity in human neutrophils through the suppression of PDE4 and protects significantly against T/H shock-induced ALI in rats. Osthol may have potential for future clinical application as a novel adjunct therapy to treat lung inflammation caused by adverse circulatory conditions.

Programmed cell death receptor ligand 1 modulates the regulatory T cells' capacity to repress shock/sepsis-induced indirect acute lung injury by recruiting phosphatase SRC homology region 2 domain-containing phosphatase 1

We recently reported that adoptively transferred (AT) exogenous CD4+ CD25+ regulatory T cells (Tregs) to wild-type (WT) mice can directly act to repress shock/sepsis-induced experimental indirect acute lung injury (iALI), and this is mediated in part by programmed cell death receptor 1 (PD-1). In this study, we further determine whether recipient mouse lacking PD-L1, one of the primary ligands for PD-1, contributes to the manipulation of the Tregs' capacity to repress lung injury. To do this, Tregs isolated from the spleen of WT mice were AT into PD-L1 mice subjected to hemorrhagic shock and subsequent to cecal ligation and puncture to induce iALI. Samples were collected for analyses 24 h after cecal ligation and puncture. We found that in PD-L1-recipient mice, AT WT-Tregs lost the ability to reverse the development of iALI seen in WT recipient mice (i.e., no reduction of lung injury indices assessed by histology and vascular leakage, failure to decrease the lung neutrophil influx [myeloperoxidase activity], or the rise in lung apoptosis [caspase 3 activity]). Also, a significant increase in interleukin 1β (IL-1β) and keratinocyte-derived chemokine, but no changes in IL-6, IL-10, and IL-17A levels in lung tissues were seen in these mice compared with iALI mice without AT of Tregs. Furthermore, we noted that the lung tissue tyrosine phosphatase Src homology region 2 domain-containing phosphatase 1 (SHP-1), but not SHP-2, was activated with the AT of Tregs in PD-L1(-/-) iALI mice. Finally, through local depletion of CD4+ T cells or CD25+ (Tregs) in the lung, prior to inducing iALI, we found that SHP-1 activation was associated with the loss of Tregs' protective effects in vivo. Collectively, our data reveal that PD-L1 is a critical modulator of Tregs' ability to suppress iALI, and this appears to involve SHP-1 activation.

Biodistribution and Efficacy of Targeted Pulmonary Delivery of a Protein Kinase C-δ Inhibitory Peptide: Impact on Indirect Lung Injury

Sepsis and sepsis-induced lung injury remain a leading cause of death in intensive care units. We identified protein kinase C-δ (PKCδ) as a critical regulator of the acute inflammatory response and demonstrated that PKCδ inhibition was lung-protective in a rodent sepsis model, suggesting that targeting PKCδ is a potential strategy for preserving pulmonary function in the setting of indirect lung injury. In this study, whole-body organ biodistribution and pulmonary cellular distribution of a transactivator of transcription (TAT)-conjugated PKCδ inhibitory peptide (PKCδ-TAT) was determined following intratracheal (IT) delivery in control and septic [cecal ligation and puncture (CLP)] rats to ascertain the impact of disease pathology on biodistribution and efficacy. There was negligible lung uptake of radiolabeled peptide upon intravenous delivery [<1% initial dose (ID)], whereas IT administration resulted in lung retention of >65% ID with minimal uptake in liver or kidney (<2% ID). IT delivery of a fluorescent-tagged (tetramethylrhodamine-PKCδ-TAT) peptide demonstrated uniform spatial distribution and cellular uptake throughout the peripheral lung. IT delivery of PKCδ-TAT at the time of CLP surgery significantly reduced PKCδ activation (tyrosine phosphorylation, nuclear translocation and cleavage) and acute lung inflammation, resulting in improved lung function and gas exchange. Importantly, peptide efficacy was similar when delivered at 4 hours post-CLP, demonstrating therapeutic relevance. Conversely, spatial lung distribution and efficacy were significantly impaired at 8 hours post-CLP, which corresponded to marked histopathological progression of lung injury. These studies establish a functional connection between peptide spatial distribution, inflammatory histopathology in the lung, and efficacy of this anti-inflammatory peptide.