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

The peptidyl-prolyl isomerase Pin1 controls GM-CSF-induced priming of NADPH oxidase in human neutrophils and priming at inflammatory sites

The production of superoxide anions and other reactive oxygen species (ROS) by neutrophils is necessary for host defense against microbes. However, excessive ROS production can induce cell damage that participates in the inflammatory response. Superoxide anions are produced by the phagocyte NADPH oxidase, a multicomponent enzyme system consisting of two transmembrane proteins (gp91phox/NOX2 and p22phox) and four soluble cytosolic proteins (p40phox, p47phox, p67phox and the small G proteins Rac1/2). Stimulation of neutrophils by various agonists, such as the bacterial peptide formyl-Met-Leu-Phe (fMLF), induces NADPH oxidase activation and superoxide production, a process that is enhanced by the pro-inflammatory cytokines such as GM-CSF. The pathways involved in this GM-CSF-induced up-regulation or priming are not fully understood. Here we show that GM-CSF induces the activation of the prolyl cis/trans isomerase Pin1 in human neutrophils. Juglone and PiB, two selective Pin1 inhibitors, were able to block GM-CSF-induced priming of ROS production by human neutrophils. Interestingly, GM-CSF induced Pin1 binding to phosphorylated p47phox at Ser345. Neutrophils isolated from synovial fluid of patients with rheumatoid arthritis are known to be primed. Here we show that Pin1 activity was also increased in these neutrophils and that Pin1 inhibitors effectively inhibited ROS hyperproduction by the same cells. These results suggest that the prolyl cis/trans isomerase Pin1 may control GM-CSF-induced priming of ROS production by neutrophils and priming of neutrophils in synovial fluid of rheumatoid arthritis patients. Pharmacological targeting of Pin1 may be a valuable approach to the treatment of inflammation.

Diverse bacteria elicit distinct neutrophil responses in a physiologically relevant model of infection

An efficient neutrophil response is critical for fighting bacterial infections, which remain a significant global health concern; therefore, modulating neutrophil function could be an effective therapeutic approach. While we have a general understanding of how neutrophils respond to bacteria, how neutrophil function differs in response to diverse bacterial infections remains unclear. Here, we use a microfluidic infection-on-a-chip device to investigate the neutrophil response to four bacterial species: Pseudomonas aeruginosa, Salmonella enterica, Listeria monocytogenes, and Staphylococcus aureus. We find enhanced neutrophil extravasation to L. monocytogenes, a limited overall response to S. aureus, and identify IL-6 as universally important for neutrophil extravasation. Furthermore, we demonstrate a higher percentage of neutrophils generate reactive oxygen species (ROS) when combating gram-negative bacteria versus gram-positive bacteria. For all bacterial species, we found the percentage of neutrophils producing ROS increased following extravasation through an endothelium, underscoring the importance of studying neutrophil function in physiologically relevant models.

PVB exerts anti-inflammatory effects by inhibiting the activation of MAPK and NF-κB signaling pathways and ROS generation in neutrophils

Pinaverium bromide (PVB) has been shown to protect mice against sepsis, which is predominantly attributed to PVB-mediated anti-inflammatory effects by inhibiting primed neutrophils to produce proinflammatory cytokines. However, the underlying mechanism(s) by which PVB affects neutrophils remains unknown. In this study, we report that treatment with PVB either before or after LPS stimulation attenuated IL-1β and TNF-α expression at both mRNA and protein levels in LPS-activated murine neutrophils. Further experiments revealed that PVB inhibited the phosphorylation of ERK, JNK, and IκBα in LPS-stimulated murine neutrophils. Moreover, PVB reduced reactive oxygen species (ROS) levels via regulating NADPH oxidase 2 (NOX2) activity, as represented by inhibiting p47phox translocation from the cytoplasm to the cellular membrane. Importantly, PVB significantly attenuated IL-1β, TNF-α, IL-6, CXCL1 production in both LPS-stimulated low density neutrophils (LDNs) and normal density neutrophils (NDNs) isolated from septic patients. Collectively, we demonstrated that PVB exerts anti-inflammatory effect by attenuating ROS generation and suppressing the activation of MAPK and NF-κB signaling pathways, suggesting that PVB may act as a potential therapeutic agent for sepsis by inhibiting neutrophil priming and activation.

Astragaloside IV targets PRDX6, inhibits the activation of RAC subunit in NADPH oxidase 2 for oxidative damage

BACKGROUND

Radix Astragali Mongolici, as a traditional Chinese medicine, is widely used in the treatment of qi deficiency, viral or bacterial infection, inflammation and cancer. Astragaloside IV (AST), a key active compound in Radix Astragali Mongolici, has been shown to reduce disease progression by inhibiting oxidative stress and inflammation. However, the specific target and mechanism of action of AST in improving oxidative stress are still unclear.

PURPOSE

This study aims to explore the target and mechanism of AST to improve oxidative stress, and to explain the biological process of oxidative stress.

METHODS

AST functional probes were designed to capture target proteins and combined with protein spectrum to analyze target proteins. Small molecule and protein interaction technologies were used to verify the mode of action, while computer dynamics simulation technology was used to analyze the site of interaction with the target protein. The pharmacological activity of AST in improving oxidative stress was evaluated in a mouse model of acute lung injury induced by LPS. Additionally, pharmacological and serial molecular biological approaches were used to explore the underlying mechanism of action.

RESULTS

AST inhibits PLA2 activity in PRDX6 by targeting the PLA2 catalytic triad pocket. This binding alters the conformation and structural stability of PRDX6 and interferes with the interaction between PRDX6 and RAC, hindering the activation of the RAC-GDI heterodimer. Inactivation of RAC prevents NOX2 maturation, attenuates superoxide anion production, and improves oxidative stress damage.

CONCLUSION

The findings of this research indicate that AST impedes PLA2 activity by acting on the catalytic triad of PRDX6. This, in turn, disrupts the interaction between PRDX6 and RAC, thereby hindering the maturation of NOX2 and diminishing the oxidative stress damage.

Human neutrophils ≠ murine neutrophils: Does it matter?

Human and murine neutrophils differ with respect to representation in blood, receptors, nuclear morphology, signaling pathways, granule proteins, NADPH oxidase regulation, magnitude of oxidant and hypochlorous acid production, and their repertoire of secreted molecules. These differences often matter and can undermine extrapolations from murine studies to clinical care, as illustrated by several failed therapeutic interventions based on mouse models. Likewise, coevolution of host and pathogen undercuts fidelity of murine models of neutrophil-predominant human infections. However, murine systems that accurately model the human condition can yield insights into human biology difficult to obtain otherwise. The challenge for investigators who employ murine systems is to distinguish models from pretenders and to know when the mouse provides biologically accurate insights. Testing with human neutrophils observations made in murine systems would provide a safeguard but is not always possible. At a minimum, studies that use exclusively murine neutrophils should have accurate titles supported by data and restrict conclusions to murine neutrophils and not encompass all neutrophils. For now, the integration of evidence from studies of neutrophil biology performed using valid murine models coupled with testing in vitro of human neutrophils combines the best of both approaches to elucidate the mysteries of human neutrophil biology.

The regulatory role of Pin1 in neuronal death

Regulated cell death predominantly involves apoptosis, autophagy, and regulated necrosis. It is vital that we understand how key regulatory signals can control the process of cell death. Pin1 is a cis-trans isomerase that catalyzes the isomerization of phosphorylated serine or threonine-proline motifs of a protein, thereby acting as a crucial molecular switch and regulating the protein functionality and the signaling pathways involved. However, we know very little about how Pin1-associated pathways might play a role in regulated cell death. In this paper, we review the role of Pin1 in regulated cell death and related research progress and summarize Pin1-related pathways in regulated cell death. Aside from the involvement of Pin1 in the apoptosis that accompanies neurodegenerative diseases, accumulating evidence suggests that Pin1 also plays a role in regulated necrosis and autophagy, thereby exhibiting distinct effects, including both neurotoxic and neuroprotective effects. Gaining an enhanced understanding of Pin1 in neuronal death may provide us with new options for the development of therapeutic target for neurodegenerative disorders.

Impaired p47phox phosphorylation in neutrophils from patients with p67phox-deficient chronic granulomatous disease

Superoxide production by the phagocyte reduced NAD phosphate (NADPH) oxidase is essential for innate immunity as shown in chronic granulomatous disease (CGD), an immunodeficiency disease resulting from mutations in 1 of its genes. The NADPH oxidase is composed of 2 membrane proteins (gp91phox/NOX2 and p22phox) and 4 cytosolic proteins (p47phox, p67phox, p40phox, and Rac1/2). The phosphorylation of p47phox is required for NADPH oxidase activation in cells. As p47phox and p67phox can form a tight complex in cells, we hypothesized that p67phox could regulate p47phox phosphorylation. To investigate this hypothesis, we used phospho-specific antibodies against 5 major p47phox-phosphorylated sites (Ser304, Ser315, Ser320, Ser328, and Ser345) and neutrophils from healthy donors and from p67phox-/- CGD patients. Results showed that formyl-methionyl-leucyl-phenylalanine and phorbol myristate acetate induced a time- and a concentration-dependent phosphorylation of p47phox on Ser304, Ser315, Ser320, and Ser328 in healthy human neutrophils. Interestingly, in neutrophils and Epstein-Barr virus-transformed B lymphocytes from p67phox-/- CGD patients, phosphorylation of p47phox on serine residues was dramatically reduced. In COSphox cells, the presence of p67phox led to increased phosphorylation of p47phox. In vitro studies showed that recombinant p47phox was phosphorylated on Ser304, Ser315, Ser320, and Ser328 by different PKC isoforms and the addition of recombinant p67phox alone or in combination with p40phox potentiated this process. Thus, p67phox and p40phox are required for optimal p47phox phosphorylation on Ser304, Ser315, Ser320, and Ser328 in intact cells. Therefore, p67phox and p40phox are novel regulators of p47phox-phosphorylation.

Pin1 as Molecular Switch in Vascular Endothelium: Notes on Its Putative Role in Age-Associated Vascular Diseases

By controlling the change of the backbones of several cellular substrates, the peptidyl-prolyl cis-trans isomerase Pin1 acts as key fine-tuner and amplifier of multiple signaling pathways, thereby inducing several biological consequences, both in physiological and pathological conditions. Data from the literature indicate a prominent role of Pin1 in the regulating of vascular homeostasis. In this review, we will critically dissect Pin1’s role as conformational switch regulating the homeostasis of vascular endothelium, by specifically modulating nitric oxide (NO) bioavailability. In this regard, Pin1 has been reported to directly control NO production by interacting with bovine endothelial nitric oxide synthase (eNOS) at Ser¹¹⁶-Pro¹¹⁷ (human equivalent is Ser¹¹⁴-Pro¹¹⁵) in a phosphorylation-dependent manner, regulating its catalytic activity, as well as by regulating other intracellular players, such as VEGF and TGF-β, thereby impinging upon NO release. Furthermore, since Pin1 has been found to act as a critical driver of vascular cell proliferation, apoptosis, and inflammation, with implication in many vascular diseases (e.g., diabetes, atherosclerosis, hypertension, and cardiac hypertrophy), evidence indicating that Pin1 may serve a pivotal role in vascular endothelium will be discussed. Understanding the role of Pin1 in vascular homeostasis is crucial in terms of finding a new possible therapeutic player and target in vascular pathologies, including those affecting the elderly (such as small and large vessel diseases and vascular dementia) or those promoting the full expression of neurodegenerative dementing diseases.

Neutrophil-derived extracellular vesicles modulate the phenotype of naïve human neutrophils

Neutrophils (PMN) regulate inflammation in many ways, including communication with other immune cells via extracellular vesicles (EVs). EVs released by human neutrophils activated with N-formylmethionyl-leucyl-phenylalanine (fMLF) (PMN-fMLF EVs) had an outside-out orientation and contained functionally important neutrophil plasma membrane proteins, including flavocytochrome b558, and enzymatically active granule proteins, elastase, and myeloperoxidase. Treatment of naïve PMN with PMN-fMLF EVs primed fMLF-stimulated NADPH oxidase activity, increased surface expression of the complement receptors CD11b/CD18 and CD35, the specific granule membrane protein CD66, and flavocytochrome b558 , and promoted phagocytosis of serum-opsonized Staphylococcus aureus. The primed oxidase activity reflected increased surface expression of flavocytochrome b558 and phosphorylation of SER345 in p47phox , two recognized mechanisms for oxidase priming. Taken together, these data demonstrate that stimulated PMN released EVs that altered the phenotype of naïve phagocytes by priming of the NADPH oxidase activity and augmenting phagocytosis, two responses that are integral to optimal PMN host defense.

Prolyl-Isomerase Pin1 Controls Key fMLP-Induced Neutrophil Functions

Neutrophils are key cells of the innate immune and inflammatory responses. They are the first blood cells to migrate to the infection site where they release high amounts of reactive oxygen species (ROS) and several peptides and enzymes required for microbial killing. However, excessive neutrophil activation can induce tissue injury participating in inflammation, thus the characterization of the enzymes involved in neutrophil activation could help to identify new pharmacological targets to treat inflammation. The prolyl-isomerase Pin1 is a ubiquitous enzyme involved in several functions, however, its role in neutrophil functions is less known. In this study, we show that the bacterial peptide N-formyl-methionyl-leucyl-phenylalanine (fMLP or fMLF), a G-protein coupled receptor (GPCR) agonist-induced Pin1 activation in human neutrophils. PiB and juglone, two Pin1 inhibitors inhibited Pin1 activity in neutrophils and consequently inhibited fMLP-induced chemotaxis and -degranulation of azurophil and specific granules as measured by myeloperoxidase and neutrophil gelatinase-associated lipocalin (NGAL) release respectively. We also showed that PiB inhibited TNFα + fMLP-induced superoxide production, confirming the effect of juglone. These data show that inhibitors of Pin1 impaired key pro-inflammatory neutrophil functions elicited by GPCR activation and suggest that Pin1 could control neutrophil inflammatory functions.

Effects of Juglone on Neutrophil Degranulation and Myeloperoxidase Activity Related to Equine Laminitis

Experimental laminitis, characterized by a failure of the dermal-epidermal interface of the foot, can be induced in horses by the oral administration of a black walnut extract (BWE). In the early phase of this severe and painful disease, an activation of neutrophil occurs, with the release of myeloperoxidase (MPO), a pro-oxidant enzyme of neutrophils, in plasma, skin, and laminar tissue. Juglone, a naphthoquinone derivative endowed with redox properties, is found in walnuts and has been incriminated in this neutrophil activation. We report for the first time the inhibitory activity of juglone on the degranulation of neutrophils induced by cytochalasin B and formyl-methionyl-leucyl-phenylalanine as monitored by the MPO release (>90% inhibition for 25 and 50 μM). Moreover, it also acts on the peroxidase activity of MPO by interacting with the intermediate "π cation radical," as evidenced by the classical and specific immunological extraction followed by enzymatic detection (SIEFED) assays. These results are confirmed by a docking study showing the perfect positioning of juglone in the MPO enzyme active site and its interaction with one of the amino acids (Arg-239) of MPO apoprotein. By chemiluminescence and electron paramagnetic resonance techniques, we demonstrated that juglone inhibited reactive oxygen species (ROS) and superoxide anion free radical produced from phorbol myristate acetate (PMA)-activated polymorphonuclear neutrophils (PMNs). These results indicate that juglone is not the trigger for equine laminitis, at least if we focus on the modulation of neutrophil activation.

Effects of venoms on neutrophil respiratory burst: a major inflammatory function

Neutrophils play a pivotal role in innate immunity and in the inflammatory response. Neutrophils are very motile cells that are rapidly recruited to the inflammatory site as the body first line of defense. Their bactericidal activity is due to the release into the phagocytic vacuole, called phagosome, of several toxic molecules directed against microbes. Neutrophil stimulation induces release of this arsenal into the phagosome and induces the assembly at the membrane of subunits of the NAPDH oxidase, the enzyme responsible for the production of superoxide anion that gives rise to other reactive oxygen species (ROS), a process called respiratory burst. Altogether, they are responsible for the bactericidal activity of the neutrophils. Excessive activation of neutrophils can lead to extensive release of these toxic agents, inducing tissue injury and the inflammatory reaction. Envenomation, caused by different animal species (bees, wasps, scorpions, snakes etc.), is well known to induce a local and acute inflammatory reaction, characterized by recruitment and activation of leukocytes and the release of several inflammatory mediators, including prostaglandins and cytokines. Venoms contain several molecules such as enzymes (phospholipase A2, L-amino acid oxidase and proteases, among others) and peptides (disintegrins, mastoporan, parabutoporin etc.). These molecules are able to stimulate or inhibit ROS production by neutrophils. The present review article gives a general overview of the main neutrophil functions focusing on ROS production and summarizes how venoms and venom molecules can affect this function.

NADPH Oxidases (NOX): An Overview from Discovery, Molecular Mechanisms to Physiology and Pathology

The reactive oxygen species (ROS)-producing enzyme NADPH oxidase (NOX) was first identified in the membrane of phagocytic cells. For many years, its only known role was in immune defense, where its ROS production leads to the destruction of pathogens by the immune cells. NOX from phagocytes catalyzes, via one-electron trans-membrane transfer to molecular oxygen, the production of the superoxide anion. Over the years, six human homologs of the catalytic subunit of the phagocyte NADPH oxidase were found: NOX1, NOX3, NOX4, NOX5, DUOX1, and DUOX2. Together with the NOX2/gp91phox component present in the phagocyte NADPH oxidase assembly itself, the homologs are now referred to as the NOX family of NADPH oxidases. NOX are complex multidomain proteins with varying requirements for assembly with combinations of other proteins for activity. The recent structural insights acquired on both prokaryotic and eukaryotic NOX open new perspectives for the understanding of the molecular mechanisms inherent to NOX regulation and ROS production (superoxide or hydrogen peroxide). This new structural information will certainly inform new investigations of human disease. As specialized ROS producers, NOX enzymes participate in numerous crucial physiological processes, including host defense, the post-translational processing of proteins, cellular signaling, regulation of gene expression, and cell differentiation. These diversities of physiological context will be discussed in this review. We also discuss NOX misregulation, which can contribute to a wide range of severe pathologies, such as atherosclerosis, hypertension, diabetic nephropathy, lung fibrosis, cancer, or neurodegenerative diseases, giving this family of membrane proteins a strong therapeutic interest.

The TLR4-MyD88 Signaling Axis Regulates Lung Monocyte Differentiation Pathways in Response to Streptococcus pneumoniae

Streptococcus pneumoniae is the main cause of bacterial pneumonia, a condition that currently produces significant global morbidity and mortality. The initial immune response to this bacterium occurs when the innate system recognizes common motifs expressed by many pathogens, events driven by pattern recognition receptors like the Toll-like family receptors (TLRs). In this study, lung myeloid-cell populations responsible for the innate immune response (IIR) against S. pneumoniae, and their dependence on the TLR4-signaling axis, were analyzed in TLR4-/- and Myeloid-Differentiation factor-88 deficient (MyD88-/-) mice. Neutrophils and monocyte-derived cells were recruited in infected mice 3-days post-infection. Compared to wild-type mice, there was an increased bacterial load in both these deficient mouse strains and an altered IIR, although TLR4-/- mice were more susceptible to bacterial infection. These mice also developed fewer alveolar macrophages, weaker neutrophil infiltration, less Ly6Chigh monocyte differentiation and a disrupted classical and non-classical monocyte profile. The pro-inflammatory cytokine profile (CXCL1, TNF-α, IL-6, and IL-1β) was also severely affected by the lack of TLR4 and no induction of Th1 was observed in these mice. The respiratory burst (ROS production) after infection was profoundly dampened in TLR4-/- and MyD88-/- mice. These data demonstrate the complex dynamics of myeloid populations and a key role of the TLR4-signaling axis in the IIR to S. pneumoniae, which involves both the MyD88 and TRIF (Toll/IL-1R domain-containing adaptor-inducing IFN-β) dependent pathways.