Defective regulation of CXCR2 facilitates neutrophil release from bone marrow causing spontaneous inflammation in severely NF-kappa B-deficient mice

Artificial intelligence-driven multiomics predictive model for abdominal aortic aneurysm subtypes to identify heterogeneous immune cell infiltration and predict disease progression

BACKGROUND

Abdominal aortic aneurysm (AAA) poses a significant health risk and is influenced by various compositional features. This study aimed to develop an artificial intelligence-driven multiomics predictive model for AAA subtypes to identify heterogeneous immune cell infiltration and predict disease progression. Additionally, we investigated neutrophil heterogeneity in patients with different AAA subtypes to elucidate the relationship between the immune microenvironment and AAA pathogenesis.

METHODS

This study enrolled 517 patients with AAA, who were clustered using k-means algorithm to identify AAA subtypes and stratify the risk. We utilized residual convolutional neural network 200 to annotate and extract contrast-enhanced computed tomography angiography images of AAA. A precise predictive model for AAA subtypes was established using clinical, imaging, and immunological data. We performed a comparative analysis of neutrophil levels in the different subgroups and immune cell infiltration analysis to explore the associations between neutrophil levels and AAA. Quantitative polymerase chain reaction, Western blotting, and enzyme-linked immunosorbent assay were performed to elucidate the interplay between CXCL1, neutrophil activation, and the nuclear factor (NF)-κB pathway in AAA pathogenesis. Furthermore, the effect of CXCL1 silencing with small interfering RNA was investigated.

RESULTS

Two distinct AAA subtypes were identified, one clinically more severe and more likely to require surgical intervention. The CNN effectively detected AAA-associated lesion regions on computed tomography angiography, and the predictive model demonstrated excellent ability to discriminate between patients with the two identified AAA subtypes (area under the curve, 0.927). Neutrophil activation, AAA pathology, CXCL1 expression, and the NF-κB pathway were significantly correlated. CXCL1, NF-κB, IL-1β, and IL-8 were upregulated in AAA. CXCL1 silencing downregulated NF-κB, interleukin-1β, and interleukin-8.

CONCLUSION

The predictive model for AAA subtypes demonstrated accurate and reliable risk stratification and clinical management. CXCL1 overexpression activated neutrophils through the NF-κB pathway, contributing to AAA development. This pathway may, therefore, be a therapeutic target in AAA.

Design, Synthesis, and Application of Fluorescent Ligands Targeting the Intracellular Allosteric Binding Site of the CXC Chemokine Receptor 2

The inhibition of CXC chemokine receptor 2 (CXCR2), a key inflammatory mediator, is a potential strategy in the treatment of several pulmonary diseases and cancers. The complexity of endogenous chemokine interaction with the orthosteric binding site has led to the development of CXCR2 negative allosteric modulators (NAMs) targeting an intracellular pocket near the G protein binding site. Our understanding of NAM binding and mode of action has been limited by the availability of suitable tracer ligands for competition studies, allowing direct ligand binding measurements. Here, we report the rational design, synthesis, and pharmacological evaluation of a series of fluorescent NAMs, based on navarixin (2), which display high affinity and preferential binding for CXCR2 over CXCR1. We demonstrate their application in fluorescence imaging and NanoBRET binding assays, in whole cells or membranes, capable of kinetic and equilibrium analysis of NAM binding, providing a platform to screen for alternative chemophores targeting these receptors.

Inflammation and Neutrophil Oxidative Burst in a Family with NFKB1 p.R157X LOF and Sterile Necrotizing Fasciitis

Loss-of-function (LOF) mutations in NFKB1, coding for p105, may cause common variable immunodeficiency due to dysregulation of nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κΒ) pathway. Monoallelic LOF variants of NFKB1 can predispose to uncontrolled inflammation including sterile necrotizing fasciitis or pyoderma gangrenosum. In this study, we explored the impact of a heterozygous NFKB1 c.C936T/p.R157X LOF variant on immunity in sterile fasciitis patients and their family members. The p50 or p105 protein levels were reduced in all variant carriers. Interleukin-1β (IL-1β) and interleukin-8 (IL-8) levels were elevated in vitro, potentially contributing to the very high neutrophil counts observed during fasciitis episodes. Phosphorylation of p65/RelA was reduced in p.R157X neutrophils suggesting defective activation of canonical NF-κB. Oxidative burst after NF-κB-independent phorbol 12-myristate 13-acetate (PMA) stimulation was similar in both p.R157X and control neutrophils. Comparable amounts of nicotinamide adenine dinucleotide phosphate (NADPH) oxidase complex subunits were found in p.R157X and control neutrophils. However, a compromised oxidative burst was observed in p.R157X neutrophils following activation of NF-κB-dependent mechanisms following stimulation of toll-like receptor 2 (TLR2) and Dectin-1. Neutrophil extracellular trap formation was not affected by p.R157X. In summary, the NFKB1 c.C936T/p.R157X LOF variant has an impact on inflammation and neutrophil function and may play a role in the pathogenesis of sterile necrotizing fasciitis.

Caspase-9b drives cellular transformation, lung inflammation, and lung tumorigenesis

Caspase 9 undergoes alternative splicing to produce two opposing isoforms: pro-apoptotic Caspase-9a (C9a) and pro-survival Caspase-9b (C9b). Previously, our laboratory reported that C9b is expressed in majority of non-small cell lung cancer tumors and directly activates the NF-κB pathway. In this study, the role of C9b in activation of the NF-κB pathway in vivo, lung inflammation and immune responses, and lung tumorigenesis were examined. Specifically, a transgenic mouse model expressing human C9b in the lung pneumocytes developed inflammatory lung lesions, which correlated with enhanced activation of the NF-κB pathway and increased influx of immunosuppressive MDSCs in contrast to wild-type mice. C9b mice presented with facial dermatitis, a thickened and disorganized dermis, enhanced collagen depth, and increased serum levels of IL-6. C9b mice also developed spontaneous lung tumors, and C9b cooperated with oncogenic KRAS in lung tumorigenesis. C9b expression also cooperated with oncogenic KRAS and p53 downregulation to drive the full cell transformation of human bronchial epithelial cells (e.g., tumor formation). Implications: Our findings show that C9b can directly activate NF-κB pathway in vivo to modulate lung inflammation, immune cell influx, and peripheral immune responses, which demonstrates that C9b is key factor in driving cell transformation and lung tumorigenesis.

Rapid postmortem ventilation improves donor lung viability by extending the tolerable warm ischemic time after cardiac death in mice

Uncontrolled donation after cardiac death (uDCD) contributes little to ameliorating donor lung shortage due to rapidly progressive warm ischemia after circulatory arrest. Here, we demonstrated non-hypoxia improves donor lung viability in a novel uDCD lung transplant model undergoing rapid ventilation after cardiac death and compared the evolution of ischemia-reperfusion injury in mice that underwent pulmonary artery ligation (PAL). The tolerable warm ischemia time at 37ºC was initially determined in mice using a modified PAL model. The donor lung following PAL was also transplanted into syngeneic mice and compared to those that underwent rapid ventilation or no ventilation at 37ºC prior to transplantation. Twenty-four hours following reperfusion, lung histology, PaO2/FIO2 ratio, and inflammatory mediators were measured. Four hours of PAL had little impact on PaO2/FIO2 ratio and acute lung injury score in contrast to significant injury induced by 5 hours of PAL. Four-hour PAL lungs showed an early myeloid-dominant inflammatory signature when compared to naïve lungs and substantially injured five-hour PAL lungs. In the context of transplantation, unventilated donor lungs showed severe injury after reperfusion, whereas ventilated donor lungs showed minimal changes in PaO2/FIO2 ratio, histologic score, and expression of inflammatory markers. Taken together, the tolerable warm ischemia time of murine lungs at 37^oC can be extended by maintaining alveolar ventilation for up to 4 hours. Non-hypoxic lung warm ischemia-reperfusion injury shows an early transcriptional signature of myeloid cell recruitment and extracellular matrix proteolysis prior to blood-gas barrier dysfunction and significant tissue damage.

PRMT4 inhibitor TP-064 inhibits the pro-inflammatory macrophage lipopolysaccharide response in vitro and ex vivo and induces peritonitis-associated neutrophilia in vivo

Previous in vitro studies have shown that protein arginine N-methyltransferase 4 (PRMT4) is a co-activator for an array of cellular activities, including NF-κB-regulated pro-inflammatory responses. Here we investigated the effect of PRMT4 inhibitor TP-064 treatment on macrophage inflammation in vitro and in vivo. Exposure of RAW 264.7 monocyte/macrophages to TP-064 was associated with a significant decrease in the production of pro-inflammatory cytokines upon a lipopolysaccharide challenge. Similarly, thioglycollate-elicited peritoneal cells isolated from wildtype mice treated with TP-064 showed lowered mRNA expression levels and cytokine production of pro-inflammatory mediators interleukin (IL)-1β, IL-6, IL-12p40, and tumor necrosis factor-α in response to lipopolysaccharide exposure. However, TP-064-treated mice exhibited an ongoing pro-inflammatory peritonitis after 5 days of thioglycollate exposure, as evident from a shift in the peritoneal macrophage polarization state from an anti-inflammatory LY6C^lowCD206^hi to a pro-inflammatory LY6C^hiCD206^low phenotype. In addition, TP-064-treated mice accumulated (activated) neutrophils within the peritoneum as well as in the blood (7-fold higher; P < 0.001) and major organs such as kidney and liver, without apparent tissue toxicity. TP-064 treatment downregulated hepatic mRNA expression levels of the PRMT4 target genes glucose-6-phosphatase catalytic subunit (-50%, P < 0.05) and the cyclin-dependent kinases 2 (-50%, P < 0.05) and 4 (-30%, P < 0.05), suggesting a direct transcriptional effect of PRMT4 also in hepatocytes. In conclusion, we have shown that the PRMT4 inhibitor TP-064 induces peritonitis-associated neutrophilia in vivo and inhibits the pro-inflammatory macrophage lipopolysaccharide response in vitro and ex vivo. Our findings suggest that TP-064 can possibly be applied as therapy in NF-κB-based inflammatory diseases.

Neutrophil subtypes shape HIV-specific CD8 T-cell responses after vaccinia virus infection

Neutrophils are innate immune cells involved in the elimination of pathogens and can also induce adaptive immune responses. Nα and Nβ neutrophils have been described with distinct in vitro capacity to generate antigen-specific CD8 T-cell responses. However, how these cell types exert their role in vivo and how manipulation of Nβ/Nα ratio influences vaccine-mediated immune responses are not known. In this study, we find that these neutrophil subtypes show distinct migratory and motility patterns and different ability to interact with CD8 T cells in the spleen following vaccinia virus (VACV) infection. Moreover, after analysis of adhesion, inflammatory, and migration markers, we observe that Nβ neutrophils overexpress the α4β1 integrin compared to Nα. Finally, by inhibiting α4β1 integrin, we increase the Nβ/Nα ratio and enhance CD8 T-cell responses to HIV VACV-delivered antigens. These findings provide significant advancements in the comprehension of neutrophil-based control of adaptive immune system and their relevance in vaccine design.

The pathophysiology of SARS-CoV-2: A suggested model and therapeutic approach

In this paper, a model is proposed of the pathophysiological processes of COVID-19 starting from the infection of human type II alveolar epithelial cells (pneumocytes) by SARS-CoV-2 and culminating in the development of ARDS. The innate immune response to infection of type II alveolar epithelial cells leads both to their death by apoptosis and pyroptosis and to alveolar macrophage activation. Activated macrophages secrete proinflammatory cytokines and chemokines and tend to polarise into the inflammatory M1 phenotype. These changes are associated with activation of vascular endothelial cells and thence the recruitment of highly toxic neutrophils and inflammatory activated platelets into the alveolar space. Activated vascular endothelial cells become a source of proinflammatory cytokines and reactive oxygen species (ROS) and contribute to the development of coagulopathy, systemic sepsis, a cytokine storm and ARDS. Pulmonary activated platelets are also an important source of proinflammatory cytokines and ROS, as well as exacerbating pulmonary neutrophil-mediated inflammatory responses and contributing to systemic sepsis by binding to neutrophils to form platelet-neutrophil complexes (PNCs). PNC formation increases neutrophil recruitment, activation priming and extraversion of these immune cells into inflamed pulmonary tissue, thereby contributing to ARDS. Sequestered PNCs cause the development of a procoagulant and proinflammatory environment. The contribution to ARDS of increased extracellular histone levels, circulating mitochondrial DNA, the chromatin protein HMGB1, decreased neutrophil apoptosis, impaired macrophage efferocytosis, the cytokine storm, the toll-like receptor radical cycle, pyroptosis, necroinflammation, lymphopenia and a high Th17 to regulatory T lymphocyte ratio are detailed.

Cell Type-Specific Roles of NF-κB Linking Inflammation and Thrombosis

The transcription factor NF-κB is a central mediator of inflammation with multiple links to thrombotic processes. In this review, we focus on the role of NF-κB signaling in cell types within the vasculature and the circulation that are involved in thrombo-inflammatory processes. All these cells express NF-κB, which mediates important functions in cellular interactions, cell survival and differentiation, as well as expression of cytokines, chemokines, and coagulation factors. Even platelets, as anucleated cells, contain NF-κB family members and their corresponding signaling molecules, which are involved in platelet activation, as well as secondary feedback circuits. The response of endothelial cells to inflammation and NF-κB activation is characterized by the induction of adhesion molecules promoting binding and transmigration of leukocytes, while simultaneously increasing their thrombogenic potential. Paracrine signaling from endothelial cells activates NF-κB in vascular smooth muscle cells and causes a phenotypic switch to a “synthetic” state associated with a decrease in contractile proteins. Monocytes react to inflammatory situations with enforced expression of tissue factor and after differentiation to macrophages with altered polarization. Neutrophils respond with an extension of their life span—and upon full activation they can expel their DNA thereby forming so-called neutrophil extracellular traps (NETs), which exert antibacterial functions, but also induce a strong coagulatory response. This may cause formation of microthrombi that are important for the immobilization of pathogens, a process designated as immunothrombosis. However, deregulation of the complex cellular links between inflammation and thrombosis by unrestrained NET formation or the loss of the endothelial layer due to mechanical rupture or erosion can result in rapid activation and aggregation of platelets and the manifestation of thrombo-inflammatory diseases. Sepsis is an important example of such a disorder caused by a dysregulated host response to infection finally leading to severe coagulopathies. NF-κB is critically involved in these pathophysiological processes as it induces both inflammatory and thrombotic responses.

Update on Neutrophil Function in Severe Inflammation

Neutrophils are main players in the effector phase of the host defense against micro-organisms and have a major role in the innate immune response. Neutrophils show phenotypic heterogeneity and functional flexibility, which highlight their importance in regulation of immune function. However, neutrophils can play a dual role and besides their antimicrobial function, deregulation of neutrophils and their hyperactivity can lead to tissue damage in severe inflammation or trauma. Neutrophils also have an important role in the modulation of the immune system in response to severe injury and trauma. In this review we will provide an overview of the current understanding of neutrophil subpopulations and their function during and post-infection and discuss the possible mechanisms of immune modulation by neutrophils in severe inflammation.

Cxcl8b and Cxcr2 Regulate Neutrophil Migration through Bloodstream in Zebrafish

Neutrophils play an essential role during an inflammatory response, which is dependent on their rapid recruitment from the bone marrow to the vasculature. However, there is no information about the molecular signals that regulate neutrophil entry to circulation during an inflammatory process in humans. This is mainly due to the lack of a suitable model of study that contains similar set of molecules and that allows in vivo analyses. In this study, we used the zebrafish to assess the role of Cxcl8a, Cxcl8b, and Cxcr2 in neutrophil migration to blood circulation after injury. Using Tg(BACmpx:GFP)ⁱ¹¹⁴ transgenic embryos and two damage models (severe and mild), we developed in vivo lack of function assays. We found that the transcription levels of cxcl8a, cxcl8b, and cxcr2 were upregulated in the severe damage model. In contrast, only cxcr2 and cxcl8a mRNA levels were increased during mild damage. After knocking down Cxcl8a, neutrophil quantity decreased at the injury site, while Cxcl8b decreased neutrophils in circulation. When inhibiting Cxcr2, we observed a decrease in neutrophil entry to the bloodstream. In conclusion, we identified different functions for both Cxcl8 paralogues, being the Cxcl8b/Cxcr2 axis that regulates neutrophil entry to the bloodstream, while Cxcl8a/Cxcr2 regulates the migration to the affected area.

Genetic Ablation of CXCR2 Protects against Cigarette Smoke-Induced Lung Inflammation and Injury

Antagonism of CXCR2 receptors, predominately located on neutrophils and critical for their immunomodulatory activity, is an attractive pharmacological therapeutic approach aimed at reducing the potentially damaging effects of heightened neutrophil influx into the lung. The role CXCR2 in lung inflammation in response to cigarette smoke (CS) inhalation using the mutant mouse approach is not known. We hypothesized that genetic ablation of CXCR2 would protect mice against CS-induced inflammation and DNA damage response. We used CXCR2^−/− deficient/mutant (knock-out, KO) mice, and assessed the changes in critical lung inflammatory NF-κB-driven chemokines released from the parenchyma of CS-exposed mice. The extent of tissue damage was assessed by the number of DNA damaging γH2AX positive cells. CXCR2 KO mice exhibited protection from heightened levels of neutrophils measured in BALF taken from mice exposed to CS. IL-8 (KC mouse) levels in the BALF from CS-exposed CXCR2 KO were elevated compared to WT. IL-6 levels in BALF were refractory to increase by CS in CXCR2 KO mice. There were no significant changes to MIP-2, MCP-1, or IL-1β. Total levels of NF-κB were maintained at lower levels in CS-exposed CXCR2 KO mice compared to WT mice exposed to CS. Finally, CXCR2 KO mice were protected from lung cells positive for DNA damage response and senescence marker γH2AX. CXCR2 KO mice are protected from heightened inflammatory response mediated by increased neutrophil response as a result of acute 3 day CS exposure. This is also associated with changes in pro-inflammatory chemokines and reduced incursion of γH2AX indicating CXCR2 deficient mice are protected from lung injury. Thus, CXCR2 may be a pharmacological target in setting of inflammation and DNA damage in the pathogenesis of COPD.

NK cells regulate CXCR2+ neutrophil recruitment during acute lung injury

A critical step in the pathogenesis of acute lung injury (ALI) is excessive recruitment of polymorphonuclear neutrophils (PMNs) into the lungs, causing significant collateral tissue damage. Defining the molecular and cellular steps that control neutrophil infiltration and activation during ALI is therefore of important therapeutic relevance. Based on previous findings implicating the transcription factor Tbet in mucosal Th1-inflammation, we hypothesized a detrimental role for Tbet during ALI. In line with our hypothesis, initial studies of endotoxin-induced lung injury revealed a marked protection of Tbet^-/- mice, including attenuated neutrophilia compared to WT counterparts. Surprisingly, subsequent studies identified natural killer (NK) cells as the major source of pulmonary Tbet during ALI. In addition, a chemokine screen suggested that mature Tbet⁺ NK-cells are critical for the production of pulmonary CXCL1 and -2, thereby contributing to pulmonary PMN recruitment. Indeed, both NK-cell Ab depletion and adoptive transfer studies provide evidence for NK cells in the orchestration of neutrophil recruitment during endotoxin-induced ALI. Taken together, these findings identify a novel role for Tbet⁺ NK-cells in initiating the early events of noninfectious pulmonary inflammation.

Adenovirus-mediated siRNA targeting CXCR2 attenuates titanium particle-induced osteolysis by suppressing osteoclast formation

Background

Wear particle-induced peri-implant loosening is the most common complication affecting long-term outcomes in patients who undergo total joint arthroplasty. Wear particles and by-products from joint replacements may cause chronic local inflammation and foreign body reactions, which can in turn lead to osteolysis. Thus, inhibiting the formation and activity of osteoclasts may improve the functionality and long-term success of total joint arthroplasty. The aim of this study was to interfere with CXC chemokine receptor type 2 (CXCR2) to explore its role in wear particle-induced osteolysis.

Material/Methods

Morphological and biochemical assays were used to assess osteoclastogenesis in vivo and in vitro. CXCR2 was upregulated in osteoclast formation.

Results

Local injection with adenovirus-mediated siRNA targeting CXCR2 inhibited titanium-induced osteolysis in a mouse calvarial model in vivo. Furthermore, siCXCR2 suppressed osteoclast formation both directly by acting on osteoclasts themselves and indirectly by altering RANKL and OPG expression in osteoblasts in vitro.

Conclusions

CXCR2 plays a critical role in particle-induced osteolysis, and siCXCR2 may be a novel treatment for aseptic loosening.

G-CSF is a key modulator of MDSC and could be a potential therapeutic target in colitis-associated colorectal cancers

Granulocyte colony-stimulating factor (G-CSF) is an essential regulator of neutrophil trafficking and is highly expressed in multiple tumors. Myeloid derived suppressor cells (MDSCs) promote neoplastic progression through multiple mechanisms by immune suppression. Despite the findings of G-CSF function in colon cancer progression, the precise mechanism of G-CSF on MDSCs regulation and its blockade effects on tumor growth remains a worthy area of investigation. In this study we observed an overexpression of G-CSF in a mouse colitis-associated cancer (CAC) model, which was consistent with the accumulation of MDSCs in mouse colon tissues. Further in vitro studies demonstrated that G-CSF could promote MDSCs survival and activation through signal transducer and activator of transcription 3 (STAT3) signaling pathway. Moreover, compared with isotype control, anti-G-CSF mAb treatment demonstrated reduced MDSC accumulation, which led to a marked decrease in neoplasm size and number in mice. Our results indicated that G-CSF is a critical regulating molecule in the migration, proliferation and function maintenance of MDSCs, which could be a potential therapeutic target for colitis-associated cancer.

Activation of the nuclear factor-κB pathway during postnatal lung inflammation preserves alveolarization by suppressing macrophage inflammatory protein-2

A significant portion of lung development is completed postnatally during alveolarization, rendering the immature lung vulnerable to inflammatory stimuli that can disrupt lung structure and function. Although the NF-κB pathway has well-recognized pro-inflammatory functions, novel anti-inflammatory and developmental roles for NF-κB have recently been described. Thus, to determine how NF-κB modulates alveolarization during inflammation, we exposed postnatal day 6 mice to vehicle (PBS), systemic lipopolysaccharide (LPS), or the combination of LPS and the global NF-κB pathway inhibitor BAY 11-7082 (LPS + BAY). LPS impaired alveolarization, decreased lung cell proliferation, and reduced epithelial growth factor expression. BAY exaggerated these detrimental effects of LPS, further suppressing proliferation and disrupting pulmonary angiogenesis, an essential component of alveolarization. The more severe pathology induced by LPS + BAY was associated with marked increases in lung and plasma levels of macrophage inflammatory protein-2 (MIP-2). Experiments using primary neonatal pulmonary endothelial cells (PEC) demonstrated that MIP-2 directly impaired neonatal PEC migration in vitro; and neutralization of MIP-2 in vivo preserved lung cell proliferation and pulmonary angiogenesis and prevented the more severe alveolar disruption induced by the combined treatment of LPS + BAY. Taken together, these studies demonstrate a key anti-inflammatory function of the NF-κB pathway in the early alveolar lung that functions to mitigate the detrimental effects of inflammation on pulmonary angiogenesis and alveolarization. Furthermore, these data suggest that neutralization of MIP-2 may represent a novel therapeutic target that could be beneficial in preserving lung growth in premature infants exposed to inflammatory stress.

Chemokine CXCL1-Mediated Neutrophil Trafficking in the Lung: Role of CXCR2 Activation

The chemokine CXCL1 and its receptor CXCR2 play a crucial role in host immune response by recruiting and activating neutrophils for microbial killing at the tissue site. Dysregulation in this process has been implicated in collateral tissue damage causing disease. CXCL1 reversibly exists as monomers and dimers, and it has been proposed that distinct monomer and dimer activities and the monomer-dimer equilibrium regulate the neutrophil function. However, the molecular mechanisms linking the CXCL1/CXCR2 axis and the neutrophil 'beneficial' and 'destructive' phenotypes are not known. In this study, we characterized neutrophil trafficking and its consequence in the mouse lung by the CXCL1 wild type (WT), which exists as monomers and dimers, and by a nondissociating dimer. Whereas the WT, compared to the dimer, was more active at low doses, both the WT and the dimer elicited a large neutrophil efflux at high doses. Importantly, robust neutrophil recruitment elicited by the WT or dimer was not detrimental to lung tissue integrity and, further, could not be correlated to surface CXCR2 levels. We conclude that the CXCL1 monomer-dimer distribution and receptor interactions are highly coupled and regulate neutrophil trafficking and that injury in the context of disease is a consequence of inappropriate CXCR2 activation at the target tissue and not due to mechanical forces exerted by neutrophils during recruitment.

CXCR2 is essential for cerebral endothelial activation and leukocyte recruitment during neuroinflammation

Background

Chemokines and chemokine receptors cooperate to promote immune cell recruitment to the central nervous system (CNS). In this study, we investigated the roles of CXCR2 and CXCL1 in leukocyte recruitment to the CNS using a murine model of neuroinflammation.

Methods

Wild-type (WT), CXCL1^−/−, and CXCR2^−/− mice each received an intracerebroventricular (i.c.v.) injection of lipopolysaccharide (LPS). Esterase staining and intravital microscopy were performed to examine neutrophil recruitment to the brain. To assess endothelial activation in these mice, the expression of adhesion molecules was measured via quantitative real-time polymerase chain reaction (PCR) and Western blotting. To identify the cellular source of functional CXCR2, chimeric mice were generated by transferring bone marrow cells between the WT and CXCR2^−/− mice.

Results

Expression levels of the chemokines CXCL1, CXCL2, and CXCL5 were significantly increased in the brain following the i.c.v. injection of LPS. CXCR2 or CXCL1 deficiency blocked neutrophil infiltration and leukocyte recruitment in the cerebral microvessels. In the CXCR2^−/− and CXCL1^−/− mice, the cerebral endothelial expression of adhesion molecules such as P-selectin and VCAM-1 was dramatically reduced. Furthermore, the bone marrow transfer experiments demonstrated that CXCR2 expression on CNS-residing cells is essential for cerebral endothelial activation and leukocyte recruitment. Compared with microglia, cultured astrocytes secreted a much higher level of CXCL1 in vitro. Astrocyte culture conditioned medium significantly increased the expression of VCAM-1 and ICAM-1 in cerebral endothelial cells in a CXCR2-dependent manner. Additionally, CXCR2 messenger RNA (mRNA) expression in cerebral endothelial cells but not in microglia or astrocytes was increased following tumor necrosis factor-α (TNF-α) stimulation. The intravenous injection of the CXCR2 antagonist SB225002 significantly inhibited endothelial activation and leukocyte recruitment to cerebral microvessels.

Conclusions

CXCL1 secreted by astrocytes and endothelial CXCR2 play essential roles in cerebral endothelial activation and subsequent leukocyte recruitment during neuroinflammation.

No major role for the transcription factor NF-κB in bone marrow function during peritonitis in the mouse

Nuclear factor-kappa B (NF-κB) is a multipotent transcription factor that plays a pivotal role in immune reactions, inflammation, and possibly hematopoiesis as well. Mobilization of neutrophilic granulocytes during inflammation is a highly regulated process, but one that is incompletely understood. We studied the in vivo activity of NF-κB in mouse organs and cells, with a focus on bone marrow, during acute inflammation. NF-κB activity was studied in transgenic mice expressing a luciferase reporter expressed in a NF-κB activation-dependent fashion. Acute peritoneal inflammation was induced by lipopolysaccharide (LPS), the casein digest bacto-tryptone, or the insoluble polysaccharide zymosan. Organs were removed and blood, bone marrow, and peritoneal cells were separated using density gradient centrifugation. NF-κB activity in organ homogenates and cell lysates was quantified. These three inflammatory agents increased NF-κB activity to a variable extent within the inflamed peritoneal cavity, liver, and spleen, with LPS being the strongest stimulus. LPS, but not bacto-tryptone or zymosan, activated NF-κB in lung and bone marrow, the latter activity mainly observed in density fractions rich in immature bone marrow cells. NF-κB activation was prominent at 6 h after induction of peritonitis, fading at 24 h, as expected for an acute phase phenomenon. From this proof-of-principle study with luciferase reporter mice dependent on NF-κB activation, we suggest that, in steady-state mice, mobilization of bone marrow granulocytes to an inflammatory site can occur without discernible activation of NF-κB in bone marrow.

Nuclear factor-kappa-B signaling in lung development and disease: one pathway, numerous functions

In contrast to other organs, the lung completes a significant portion of its development after term birth. During this stage of alveolarization, division of the alveolar ducts into alveolar sacs by secondary septation, and expansion of the pulmonary vasculature by means of angiogenesis markedly increase the gas exchange surface area of the lung. However, postnatal completion of growth renders the lung highly susceptible to environmental insults such as inflammation that disrupt this developmental program. This is particularly evident in the setting of preterm birth, where impairment of alveolarization causes bronchopulmonary dysplasia, a chronic lung disease associated with significant morbidity. The nuclear factor κ-B (NFκB) family of transcription factors are ubiquitously expressed, and function to regulate diverse cellular processes including proliferation, survival, and immunity. Extensive evidence suggests that activation of NFκB is important in the regulation of inflammation and in the control of angiogenesis. Therefore, NFκB-mediated downstream effects likely influence the lung response to injury and may also mediate normal alveolar development. This review summarizes the main biologic functions of NFκB, and highlights the regulatory mechanisms that allow for diversity and specificity in downstream gene activation. This is followed by a description of the pro and anti-inflammatory functions of NFκB in the lung, and of NFκB-mediated angiogenic effects. Finally, this review summarizes the clinical and experimental data that support a role for NFκB in mediating postnatal angiogenesis and alveolarization, and discusses the challenges that remain in developing therapies that can selectively block the detrimental functions of NFκB yet preserve the beneficial effects.

CXCR2-driven ovarian cancer progression involves upregulation of proinflammatory chemokines by potentiating NF-κB activation via EGFR-transactivated Akt signaling

Ovarian cancer is an inflammation-associated malignancy with a high mortality rate. CXCR2 expressing ovarian cancers are aggressive with poorer outcomes. We therefore investigated molecular mechanisms involved in CXCR2-driven cancer progression by comparing CXCR2 positive and negative ovarian cancer cell lines. Stably CXCR2 transfected SKOV-3 cells had a faster growth rate as compared to control cells transfected with empty vector. Particularly, tumor necrosis factor (TNF), abundantly expressed in ovarian cancer, enhanced cell proliferation by decreasing the G0-G1 phase in CXCR2 transfected cells. TNF increased nuclear factor-κB (NF-κB) activity to a greater degree in CXCR2 transfected cells than control cells as well as provided a greater activation of IκB. CXCR2 transfected cells expressed higher levels of its proinflammatory ligands, CXCL1/2 and enhanced more proliferation, migration, invasion and colony formation. CXCR2 positive cells also activated more EGFR, which led to higher Akt activation. Enhanced NF-κB activity in CXCR2 positive cells was reduced by a PI3K/Akt inhibitor rather than an Erk inhibitor. CXCL1 added to CXCR2 positive cells led to an increased activation of IκB. CXCL1 also led to a significantly greater number of invasive cells in CXCR2 transfected cells, which was blocked by the NF-κB inhibitor, Bay 11-7082. In addition, enhanced cell proliferation in CXCR2 positive cells was more sensitive to CXCL1 antibody or an NF-κB inhibitor. Finally, CXCR2 transfection of parental cells increased CXCL1 promoter activity via an NF-κB site. Thus augmentation of proinflammatory chemokines CXCL1/2, by potentiating NF-κB activation through EGFR-transactivated Akt, contributes to CXCR2-driven ovarian cancer progression.

Increased atherosclerotic lesion formation and vascular leukocyte accumulation in renal impairment are mediated by interleukin-17A

RATIONALE

Atherosclerosis is a major cause of death in patients with chronic kidney disease. Chronic inflammation of the arterial wall including invasion, proliferation, and differentiation of leukocytes is important in atherosclerotic lesion development. How atherosclerotic inflammation is altered in renal impairment is incompletely understood.

OBJECTIVE

This study analyzed leukocytes of the atherosclerotic aorta in mice with impaired and normal renal function and studied a mechanism for the alteration in aortic myeloid leukocytes.

METHODS AND RESULTS

Unilateral nephrectomy significantly decreased glomerular filtration rate and increased atherosclerotic lesion size and aortic leukocyte numbers in 2 murine atherosclerosis models, apolipoprotein E (Apoe(-/-)) and low-density lipoprotein (LDL) receptor-deficient (LDLr(-/-)) mice. The number of aortic myeloid cells increased significantly. They took-up less oxidized LDL, whereas CD11c expression, interaction with T cells, and aortic T cell proliferation were significantly enhanced in renal impairment. In human peripheral blood mononuclear cell cultures, chronic kidney disease serum decreased lipid uptake and increased human leukocyte antigen II (HLA II) expression. Supplementation with interleukin-17A similarly increased HLA II and CD11c expression and impaired oxidized LDL uptake. Interleukin-17A expression was increased in atherosclerotic mice with renal impairment. Ablation of interleukin-17A in LDLr(-/-) mice by lethal irradiation and reconstitution with Il17a(-/-) bone marrow abolished the effect of renal impairment on aortic CD11b(+) myeloid cell accumulation, CD11c expression, and cell proliferation. Atherosclerotic lesion size was decreased to levels observed in normal kidney function.

CONCLUSIONS

Kidney function modifies arterial myeloid cell accumulation and phenotype in atherosclerosis. Our results suggest a central role for interleukin-17A in aggravation of vascular inflammation and atherosclerosis in renal impairment.

CXCR2: a target for pancreatic cancer treatment?

INTRODUCTION

Pancreatic cancer, a leading cause of cancer deaths worldwide, is very aggressive and has minimally effective treatment options. For those who have no surgical options, medical treatments are limited. The chemokine receptor CXCR2 has become the subject of much interest recently because of multiple studies indicating its involvement in cancer and inflammatory conditions. Research now indicates that CXCR2 and its ligands are intimately involved in tumor regulation and growth and that inhibition of its function shows promising results in multiple cancer types, including pancreatic cancer.

AREAS COVERED

In this study, the authors review basic molecular and structural details of CXCR2, as well as the known functions of CXCR2 and several of its ligands in inflammation and cancer biology with specific attention to pancreatic cancer. Then the future possibilities and questions remaining for pharmacological intervention against CXCR2 in pancreatic cancer are explored.

EXPERT OPINION

Many current inhibitory strategies already exist for targeting CXCR2 in vitro as well as in vivo. Clinically speaking, CXCR2 is an exciting potential target for pancreatic cancer; however, CXCR2 is functionally important for multiple processes and therapeutic options would benefit from further work toward understanding of these roles as well as structural and target specificity.

CXCR2: From Bench to Bedside

Leukocyte recruitment to sites of infection or tissue damage plays a crucial role for the innate immune response. Chemokine-dependent signaling in immune cells is a very important mechanism leading to integrin activation and leukocyte recruitment. CXC chemokine receptor 2 (CXCR2) is a prominent chemokine receptor on neutrophils. During the last years, several studies were performed investigating the role of CXCR2 in different diseases. Until now, many CXCR2 inhibitors are tested in animal models and clinical trials and promising results were obtained. This review gives an overview of the structure of CXCR2 and the signaling pathways that are activated following CXCR2 stimulation. We discuss in detail the role of this chemokine receptor in different disease models including acute lung injury, COPD, sepsis, and ischemia-reperfusion-injury. Furthermore, this review summarizes the results of clinical trials which used CXCR2 inhibitors.

Neutrophilic granulocytes modulate invariant NKT cell function in mice and humans

Invariant NKT (iNKT) cells are a conserved αβTCR(+) T cell population that can swiftly produce large amounts of cytokines, thereby activating other leukocytes, including neutrophilic granulocytes (neutrophils). In this study, we investigated the reverse relationship, showing that high neutrophil concentrations suppress the iNKT cell response in mice and humans. Peripheral Vα14 iNKT cells from spontaneously neutrophilic mice produced reduced cytokines in response to the model iNKT cell Ag α-galactosyl ceramide and expressed lower amounts of the T-box transcription factor 21 and GATA3 transcription factor than did wild-type controls. This influence was extrinsic, as iNKT cell transcription factor expression in mixed chimeric mice depended on neutrophil count, not iNKT cell genotype. Transcription factor expression was also decreased in primary iNKT cells from the neutrophil-rich bone marrow compared with spleen in wild-type mice. In vitro, the function of both mouse and human iNKT cells was inhibited by coincubation with neutrophils. This required cell-cell contact with live neutrophils. Neutrophilic inflammation in experimental peritonitis in mice decreased iNKT cell T-box transcription factor 21 and GATA3 expression and α-galactosyl ceramide-induced cytokine production in vivo. This was reverted by blockade of neutrophil mobilization. Similarly, iNKT cells from the human peritoneal cavity expressed lower transcription factor levels during neutrophilic peritonitis. Our data reveal a novel regulatory axis whereby neutrophils reduce iNKT cell responses, which may be important in shaping the extent of inflammation.

Experimental stroke-induced changes in the bone marrow reveal complex regulation of leukocyte responses

Stroke induces a systemic response that involves rapid activation of inflammatory cascades, followed later by immunodepression. Experimental stroke-induced responses in the bone marrow, which is the primary source of circulating monocytes and granulocytes, have not been investigated previously. We show that cerebral ischaemia induced early (4  hours) release of CXCR2-positive granulocytes from the bone marrow, which was associated with rapid systemic upregulation of CXCL1 (a ligand for CXCR2) and granulocyte-colony-stimulating factor, a key cytokine involved in the mobilisation of bone marrow leukocytes. This process involves rapid activation of nuclear factor-κB and p38 mitogen-activated protein kinase in bone marrow myeloid cells. T-cell numbers in the bone marrow increased after stroke, and bone marrow cells did not show suppressed cytokine response to bacterial endotoxin stimulation in vitro. Stroke-induced laterality observed in the brain stem and in the bone marrow indicates direct involvement of the autonomic nervous system in stroke-induced cell mobilisation. We also show that systemic inflammatory changes and leukocyte responses in the bone marrow are profoundly affected by both anaesthetic and surgical stress. We conclude that stroke influences leukocyte responses in the bone marrow through multiple mechanisms and suggest that preclinical studies should take into consideration the effect of surgical manipulation in experimental models of stroke.

NF-κB in immunobiology

NF-κB was first discovered and characterized 25 years ago as a key regulator of inducible gene expression in the immune system. Thus, it is not surprising that the clearest biological role of NF-κB is in the development and function of the immune system. Both innate and adaptive immune responses as well as the development and maintenance of the cells and tissues that comprise the immune system are, at multiple steps, under the control of the NF-κB family of transcription factors. Although this is a well-studied area of NF-κB research, new and significant findings continue to accumulate. This review will focus on these areas of recent progress while also providing a broad overview of the roles of NF-κB in mammalian immunobiology.