Chemotaxis and transendothelial migration of CD34(+) hematopoietic progenitor cells induced by the inflammatory mediator leukotriene D4 are mediated by the 7-transmembrane receptor CysLT1

Cellular and Molecular Mechanisms of Environmental Pollutants on Hematopoiesis

Hematopoiesis is a complex and intricate process that aims to replenish blood components in a constant fashion. It is orchestrated mostly by hematopoietic progenitor cells (hematopoietic stem cells (HSCs)) that are capable of self-renewal and differentiation. These cells can originate other cell subtypes that are responsible for maintaining vital functions, mediate innate and adaptive immune responses, provide tissues with oxygen, and control coagulation. Hematopoiesis in adults takes place in the bone marrow, which is endowed with an extensive vasculature conferring an intense flow of cells. A myriad of cell subtypes can be found in the bone marrow at different levels of activation, being also under constant action of an extensive amount of diverse chemical mediators and enzymatic systems. Bone marrow platelets, mature erythrocytes and leukocytes are delivered into the bloodstream readily available to meet body demands. Leukocytes circulate and reach different tissues, returning or not returning to the bloodstream. Senescent leukocytes, specially granulocytes, return to the bone marrow to be phagocytized by macrophages, restarting granulopoiesis. The constant high production and delivery of cells into the bloodstream, alongside the fact that blood cells can also circulate between tissues, makes the hematopoietic system a prime target for toxic agents to act upon, making the understanding of the bone marrow microenvironment vital for both toxicological sciences and risk assessment. Environmental and occupational pollutants, therapeutic molecules, drugs of abuse, and even nutritional status can directly affect progenitor cells at their differentiation and maturation stages, altering behavior and function of blood compounds and resulting in impaired immune responses, anemias, leukemias, and blood coagulation disturbances. This review aims to describe the most recently investigated molecular and cellular toxicity mechanisms of current major environmental pollutants on hematopoiesis in the bone marrow.

Leukotriene D4 role in allergic asthma pathogenesis from cellular and therapeutic perspectives

Asthma is a chronic inflammatory and allergic disease that is mainly characterized by reversible airway obstruction and bronchial hyperresponsiveness. The incidence of asthma is increasing with more than 350 million people worldwide are affected. Up to now, there is no therapeutic option for asthma and most of the prescribed drugs aim to ameliorate the symptoms of the disease especially during the acute exacerbations after trigger exposure. Asthma is a heterogonous disease that involves interactions between inflammatory mediators and cellular components within the disease microenvironment including inflammatory and structural cells. Cysteinyl leukotrienes (cys-LTs) are inflammatory lipid mediators that have potent roles in asthma pathogenesis. CysLTs consisting of LTC₄, LTD₄, and LTE₄ are mainly secreted by leukocytes and act through three main G-protein coupled receptors (CysLT₁R, CysLT₂R, and CysLT₃R). LTD₄ is the most potent bronchoconstrictor which gives it the priority to be discussed in detail in this review. LTD₄ binds with high affinity to CysLT₁R and many studies showed that using CysLT₁R antagonists such as montelukast has a beneficial effect for asthmatics especially in corticosteroid refractory cases. Since asthma is a heterogeneous inflammatory disease of many cell types involved in the disease pathogenies and LTD₄ has a special role in inflammation and bronchoconstriction, this review highlights the role of LTD₄ on each cellular component in asthma and the benefits of using CysLT₁R antagonists in ameliorating LTD₄-induced effects.

An Overview on G Protein-coupled Receptor-induced Signal Transduction in Acute Myeloid Leukemia

BACKGROUND

Acute Myeloid Leukemia (AML) is a genetically heterogeneous disease characterized by uncontrolled proliferation of precursor myeloid-lineage cells in the bone marrow. AML is also characterized by patients with poor long-term survival outcomes due to relapse. Many efforts have been made to understand the biological heterogeneity of AML and the challenges to develop new therapies are therefore enormous. G Protein-coupled Receptors (GPCRs) are a large attractive drug-targeted family of transmembrane proteins, and aberrant GPCR expression and GPCR-mediated signaling have been implicated in leukemogenesis of AML. This review aims to identify the molecular players of GPCR signaling, focusing on the hematopoietic system, which are involved in AML to help developing novel drug targets and therapeutic strategies.

METHODS

We undertook an exhaustive and structured search of bibliographic databases for research focusing on GPCR, GPCR signaling and expression in AML.

RESULTS AND CONCLUSION

Many scientific reports were found with compelling evidence for the involvement of aberrant GPCR expression and perturbed GPCR-mediated signaling in the development of AML. The comprehensive analysis of GPCR in AML provides potential clinical biomarkers for prognostication, disease monitoring and therapeutic guidance. It will also help to provide marker panels for monitoring in AML. We conclude that GPCR-mediated signaling is contributing to leukemogenesis of AML, and postulate that mass spectrometrybased protein profiling of primary AML cells will accelerate the discovery of potential GPCR related biomarkers for AML.

Characterization of cysteinyl leukotriene-related receptors and their interactions in a mouse model of asthma

Identification of the characterization of cysteinyl leukotrienes receptor (CysLTRs) could facilitate our understanding of these receptors' role in asthma. We aimed to investigate the localization and interactions of CysLTRs using a mouse model of asthma. BALB/c mice were administered ovalbumin (OVA) to induce allergic asthma. Some mice were administered the antagonists of CysLTR1, CysLTR2, and purinergic receptor P2Y12 (P2Y12R) (montelukast, HAMI 3379 and clopidogrel, respectively). The expression levels of CysLTR1, CysLTR2, and P2Y12R on lung tissues and inflammatory cells were evaluated by western blot, flow cytometry, and immunochemistry. CysLTR1 and P2Y12R were significantly up-regulated in lung tissues (P < 0.05 for each) from mouse after being sensitized and challenged with OVA (OVA/OVA). The ratio of CysLTR1: CysLTR2: P2Y12R in lungs of negative control (NC) mice was shifted from 1:0.43:0.35 to 1:0.65:1.34 in OVA/OVA mice. Montelukast significantly diminished the up-regulation of CysLTR1, CysLTR2, and P2Y12R (P < 0.05 for each), while the effects of HAMI 3379 and clopidogrel were predominant on the expression of CysLTR2 and P2Y12R, respectively. Montelukast predominantly diminished the cell count, while clopidogrel potently inhibited the release of interleukin (IL)-4, IL-5, and IL-13. Our study demonstrated the interactions between CysLTRs, thereby highlighting the potential synergistic effects of CysLTR antagonists in asthma treatment.

Enhanced lipoxygenase/LTD4 signaling accounts for the exaggerated hypertensive and nephrotoxic effects of cyclosporine plus indomethacin in rats

The combined use of cyclosporine (CSA) and nonsteroidal antiinflammatory drugs (NSAIDs) causes exaggerated rises in systolic blood pressure (SBP) and nephrotoxicity. We examined whether these influences relate to the arachidonate/5-lipoxygenase (LOX) pathway. Rats were treated with CSA (20 mg kg^-1 day^-1), indomethacin (5 mg kg^-1 day^-1), or their combination for 10 days. Changes in SBP and renal biochemical/histopathological characteristics along with leukotriene levels were determined in rats treated with or without LT receptor antagonists. CSA or indomethacin caused: (i) renal tubular atrophy and interstitial fibrosis, (ii) increases in serum creatinine, blood urea nitrogen (BUN), and renal LTD4, LTB4, TNF-α, TGF-β1, and caspase-3, and (iii) decreases in renal PGE2 and total antioxidant capacity (TAC). SBP measured by tail-cuff plethysmography was increased by CSA but not indomethacin. These effects were mostly intensified in rats treated with CSA plus indomethacin. The co-treatment with montelukast (cysteinyl LT receptor blocker), but not ONO-4057 (LTB4 receptor blocker), ameliorated CSA/indomethacin-evoked hypertension, renal structural/biochemical deterioration, and LTD4 levels. Moreover, montelukast exhibited a greater capacity in reversing inflammatory, oxidative, apoptotic, and fibrotic abnormalities induced by CSA/indomethacin. Overall, lipoxygenase/LTD4 upregulation contributes to the exaggerated hypertension and nephrotoxicity caused by CSA/indomethacin. The therapeutic potential of cysteinyl LT receptor antagonism in rectifying CSA/NSAIDs-evoked anomalies is warranted.

CysLT1 receptor antagonist alleviates pathogenesis of collagen-induced arthritis mouse model

Cysteinyl leukotrienes (CysLTs) play a key role in inflammatory diseases such as asthma and their receptors’ antagonists are currently used as anti-asthmatic drugs. CysLTs have also been found to participate in other inflammatory reactions. Here, we reported that in rheumatoid arthritis (RA) animals model, collagen-induced arthritis, (CIA), CysLT1, a receptor for CysLTs, was up-regulated in hind paw and lymph node, while CysLTs levels in the blood were also higher than normal mice. Montelukast, a drug targeting CysLT1, has been shown to effectively reduce the CIA incidence, peak severity, and cumulative disease scores. Further study indicated that CysLT1 signaling did not affect the differentiation of pathogenic T helper cells. We conclude that montelukast may play important roles in the pathogenesis of CIA, mainly by inducing infiltration of pathogenic T cells, increasing IL-17A secretion and expression of IL-17A, while these effects can be blocked by CysLT1 antagonists. Our findings indicate that antagonist of CysLT1 receptor may be used to treat rheumatoid arthritis.

Leukotriene signaling via ALOX5 and cysteinyl leukotriene receptor 1 is dispensable for in vitro growth of CD34+CD38- stem and progenitor cells in chronic myeloid leukemia

Tyrosine kinase inhibitors targeting the BCR-ABL oncoprotein in chronic myeloid leukemia (CML) are remarkably effective inducing deep molecular remission in most patients. However, they are less effective to eradicate the leukemic stem cells (LSC), resulting in disease persistence. Therefore, there is great need to develop novel therapeutic strategies to specifically target the LSC. In an experimental mouse CML model system, the leukotriene pathway, and specifically, the expression ALOX5, encoding 5-lipoxygenase (5-LO), has been reported as a critical regulator of the LSC. Based on these results, the 5-LO inhibitor zileuton has been introduced in clinical trials as a therapeutic option to target the LSC although its effect on primary human CML LSC has not been studied. We have here by using multiplex single cell PCR analyzed the expression of the mediators of the leukotriene pathway in bone marrow (BM) BCR-ABL⁺CD34⁺CD38^- cells at diagnosis, and found low or undetectable expression of ALOX5. In line with this, zileuton did not exert significant overall growth inhibition in the long-term culture-initiating cell (LTC-IC) and colony (CFU-C) assays of BM CD34⁺CD38^- cells from 7 CML patients. The majority of the single leukemic BCR-ABL⁺CD34⁺CD38^- cells expressed cysteinyl leukotriene receptors CYSLT1 and CYSLT2. However, montelukast, an inhibitor of CYSLT1, also failed to significantly suppress CFU-C and LTC-IC growth. These findings indicate that targeting ALOX5 or CYSLT1 signaling with leukotriene antagonists, introduced into the clinical practice primarily as prophylaxis and treatment for asthma, may not be a promising pharmacological strategy to eradicate persisting LSC in CML patients.

Expression of CysLTR1 and 2 in Maturating Lymphocytes of Hyperplasic Tonsils Compared to Peripheral Cells in Children

Cysteinyl-leukotriene receptors 1 and 2 (CysLTR1 and 2) are related to allergic inflammatory responses. Recent studies demonstrated their role in lymphocyte division and maturation in the bone marrow. Few data are available about CysLTRs function in lymphocyte maturation in tonsils. The objectives of this study are to compare CysLTRs expression in peripheral blood lymphocytes with expression in maturating lymphocytes of hyperplasic tonsil and to check the influence of respiratory allergies in this process. Leukocytes of peripheral blood (PL) and hyperplasic tonsils of children were immunostained for CysLTR1, CysLTR2, CD3 (T cells), and CD19 (B cells) and read in flow cytometer. Lymphocyte of tonsils were divided in differentiating small cells (SC) and mitotic large cells (LC); percentage of B and T cells expressing CysLTRs was determined, and comparison was done using ANOVA and Tukey's tests. Data were analyzed as a whole and categorizing patients according the presence of allergies. Sixty children were enrolled in this study. There was a large expression of CysLTR1 and 2 in CD3+ LC, and such expression decreased progressively in SC and PL. In B cells, the highest expression of CysLTR1 and 2 was found in PL while SC showed the lowest and LC showed the intermediate expression. This pattern kept unchanged in groups of allergic and non-allergic individuals. CysLTRs seem to be involved in lymphocyte maturation that occurs in tonsils, without influence of allergies. New studies aiming the clinic treatment of tonsil hyperplasia must be targeted to the development of drugs capable of blocking both CysLTR1 and 2.

Odd couple: The unexpected partnership of glucocorticoid hormones and cysteinyl-leukotrienes in the extrinsic regulation of murine bone-marrow eosinopoiesis

Granulopoiesis in murine bone-marrow is regulated by both intrinsic and extrinsic factors (including hormones, drugs, inflammatory mediators and cytokines). Eosinophils, a minor subpopulation of circulating leukocytes, which remains better understood in its contributions to tissue injury in allergic disease than in its presumably beneficial actions in host defense, provide a striking example of joint regulation of granulopoiesis within murine bone-marrow by all of these classes of extrinsic factors. We first described the upregulation of eosinopoiesis in bone-marrow of allergen-sensitized mice following airway allergen challenge. Over the last decade, we were able to show a critical role for endogenous glucocorticoid hormones and cytokines in mediating this phenomenon through modification of cytokine effects, thereby supporting a positive association between stress hormones and allergic reactions. We have further shown that cysteinyl-leukotrienes (CysLT), a major proinflammatory class of lipid mediators, generated through the 5-lipoxygenase pathway, upregulate bone-marrow eosinopoiesis in vivo and in vitro. CysLT mediate the positive effects of drugs (indomethacin and aspirin) and of proallergic cytokines (eotaxin/CCL11 and interleukin-13) on in vitro eosinopoiesis. While these actions of endogenous GC and CysLT might seem unrelated and even antagonistic, we demonstrated a critical partnership of these mediators in vivo, shedding light on mechanisms linking stress to allergy: GC are required for CysLT-mediated upregulation of bone-marrow eosinopoiesis in vivo, but also attenuate subsequent ex vivo responses to CysLT. GC and CysLT therefore work together to induce eosinophilia, but through subtle regulatory mechanisms also limit the magnitude of subsequent bone-marrow responses to allergen.

Cysteinyl leukotriene E4 activates human group 2 innate lymphoid cells and enhances the effect of prostaglandin D2 and epithelial cytokines

Background

Group 2 innate lymphoid cells (ILC2s) are a potential innate source of type 2 cytokines in the pathogenesis of allergic conditions. Epithelial cytokines (IL-33, IL-25, and thymic stromal lymphopoietin [TSLP]) and mast cell mediators (prostaglandin D₂ [PGD₂]) are critical activators of ILC2s. Cysteinyl leukotrienes (cysLTs), including leukotriene (LT) C₄, LTD₄, and LTE₄, are metabolites of arachidonic acid and mediate inflammatory responses. Their role in human ILC2s is still poorly understood.

Objectives

We sought to determine the role of cysLTs and their relationship with other ILC2 stimulators in the activation of human ILC2s.

Methods

For ex vivo studies, fresh blood from patients with atopic dermatitis and healthy control subjects was analyzed with flow cytometry. For in vitro studies, ILC2s were isolated and cultured. The effects of cysLTs, PGD₂, IL-33, IL-25, TSLP, and IL-2 alone or in combination on ILC2s were defined by using chemotaxis, apoptosis, ELISA, Luminex, quantitative RT-PCR, and flow cytometric assays. The effect of endogenous cysLTs was assessed by using human mast cell supernatants.

Results

Human ILC2s expressed the LT receptor CysLT₁, levels of which were increased in atopic subjects. CysLTs, particularly LTE₄, induced migration, reduced apoptosis, and promoted cytokine production in human ILC2s in vitro. LTE₄ enhanced the effect of PGD₂, IL-25, IL-33, and TSLP, resulting in increased production of type 2 and other proinflammatory cytokines. The effect of LTE₄ was inhibited by montelukast, a CysLT₁ antagonist. Interestingly, addition of IL-2 to LTE₄ and epithelial cytokines significantly amplified ILC2 activation and upregulated expression of the receptors for IL-33 and IL-25.

Conclusion

CysLTs, particularly LTE₄, are important contributors to the triggering of human ILC2s in inflammatory responses, particularly when combined with other ILC2 activators.

Mast cells in asthma--state of the art

Mast cells (MCs) play a central role in tissue homoeostasis, sensing the local environment through numerous innate cell surface receptors. This enables them to respond rapidly to perceived tissue insults with a view to initiating a co-ordinated programme of inflammation and repair. However, when the tissue insult is chronic, the ongoing release of multiple pro-inflammatory mediators, proteases, cytokines and chemokines leads to tissue damage and remodelling. In asthma, there is strong evidence of ongoing MC activation, and their mediators and cell-cell signals are capable of regulating many facets of asthma pathophysiology. This article reviews the evidence behind this.

Cysteinyl Leukotrienes and Their Receptors: Emerging Therapeutic Targets in Central Nervous System Disorders

Cysteinyl leukotrienes are a group of the inflammatory lipid molecules well known as mediators of inflammatory signaling in the allergic diseases. Although they are traditionally known for their role in allergic asthma, allergic rhinitis, and others, recent advances in the field of biomedical research highlighted the role of these inflammatory mediators in a broader range of diseases such as in the inflammation associated with the central nervous system (CNS) disorders, vascular inflammation (atherosclerotic), and in cancer. Among the CNS diseases, they, along with their synthesis precursor enzyme 5-lipoxygenase and their receptors, have been shown to be associated with brain injury, Multiple sclerosis, Alzheimer's disease, Parkinson's disease, brain ischemia, epilepsy, and others. However, a lot more remains elusive as the research in these areas is emerging and only a little has been discovered. Herein, through this review, we first provided a general up-to-date information on the synthesis pathway and the receptors for the molecules. Next, we summarized the current findings on their role in the brain disorders, with an insight given to the future perspectives.

Leukemia and ABC transporters

Acute myeloid leukemia (AML) is a heterogeneous disease caused by aberrant proliferation and/or differentiation of myeloid progenitors. However, only ~65% of AML patients respond to induction chemotherapy and the overall survival rate for AML remains low (~24% for 5-year survival). The conventional view suggests that ATP-binding cassette (ABC) transporters contribute to treatment failure due to their drug-effluxing capabilities. This might be overly simplistic. Some ABC transporters export endogenous substrates that have defined roles in normal hematopoietic progenitors. It is conceivable that these substances also provide an advantage to leukemic progenitors. This review will highlight how certain endogenous substrates impact normal hematopoietic cells and suggest that ABC transporters facilitate export of these substances to affect both normal hematopoietic and leukemic progenitors. For example, the ability to export certain endogenous ligands may facilitate leukemogenesis by modifying leukemic progenitor cell proliferation or survival. If so, the addition of ABC transporter inhibitors to traditional chemotherapy might improve therapeutic efficacy by not just increasing intracellular drug accumulation but also blocking the beneficial effects ABC transporter ligands have on cell survival.

Roles of 5-lipoxygenase and cysteinyl-leukotriene type 1 receptors in the hematological response to allergen challenge and its prevention by diethylcarbamazine in a murine model of asthma

Diethylcarbamazine (DEC), which blocks leukotriene production, abolishes the challenge-induced increase in eosinopoiesis in bone-marrow from ovalbumin- (OVA-) sensitized mice, suggesting that 5-lipoxygenase (5-LO) products contribute to the hematological responses in experimental asthma models. We explored the relationship between 5-LO, central and peripheral eosinophilia, and effectiveness of DEC, using PAS or BALB/c mice and 5-LO-deficient mutants. We quantified eosinophil numbers in freshly harvested or cultured bone-marrow, peritoneal lavage fluid, and spleen, with or without administration of leukotriene generation inhibitors (DEC and MK886) and cisteinyl-leukotriene type I receptor antagonist (montelukast). The increase in eosinophil numbers in bone-marrow, observed in sensitized/challenged wild-type mice, was abolished by MK886 and DEC pretreatment. In ALOX mutants, by contrast, there was no increase in bone-marrow eosinophil counts, nor in eosinophil production in culture, in response to sensitization/challenge. In sensitized/challenged ALOX mice, challenge-induced migration of eosinophils to the peritoneal cavity was significantly reduced relative to the wild-type PAS controls. DEC was ineffective in ALOX mice, as expected from a mechanism of action dependent on 5-LO. In BALB/c mice, challenge significantly increased spleen eosinophil numbers and DEC treatment prevented this increase. Overall, 5-LO appears as indispensable to the systemic hematological response to allergen challenge, as well as to the effectiveness of DEC.

5-Lipoxygenase and cysteinyl leukotriene receptor 1 regulate epidermal growth factor-induced cell migration through Tiam1 upregulation and Rac1 activation

Cell migration is an essential step for tumor metastasis. The small GTPase Rac1 plays an important role in cell migration. Previously, we reported that epidermal growth factor (EGF) induced two waves of Rac1 activation; namely, at 5 min and 12 h after stimulation. A second wave of EGF-induced Rac1 activation was required for EGF-induced cell migration, however, the spatiotemporal regulation of the second wave of EGF-induced Rac1 activation remains largely unclear. In this study, we found that 5-lipoxygenase (5-LOX) is activated in the process of EGF-induced cell migration, and that leukotriene C₄ (LTC₄) produced by 5-LOX mediated the second wave of Rac1 activation, as well as cell migration. Furthermore, these effects caused by LTC₄ were found to be blocked in the presence of the antagonist of cysteinyl leukotriene receptor 1 (CysLT1). This blockage indicates that LTC₄-mediated CysLT1 signaling regulates the second EGF-induced wave of Rac1 activation. We also found that 5-LOX inhibitors, CysLT1 antagonists and the knockdown of CysLT1 inhibited EGF-induced T cell lymphoma invasion and metastasis-inducing protein 1 (Tiam1) expression. Tiam1 expression is required for the second wave of EGF-induced Rac1 activation in A431 cells. Therefore, our results indicate that the 5-LOX/LTC₄/CysLT1 signaling pathway regulates EGF-induced cell migration by increasing Tiam1 expression, leading to a second wave of Rac1 activation. Thus, CysLT1 may serve as a new molecular target for antimetastatic therapy. In addition, the CysLT1 antagonist, montelukast, which is used clinically for allergy treatment, might have great potential as a novel type of antimetastatic agent.

Lung type 2 innate lymphoid cells express cysteinyl leukotriene receptor 1, which regulates TH2 cytokine production

BACKGROUND

Cysteinyl leukotrienes (CysLTs) contribute to asthma pathogenesis, in part through cysteinyl leukotriene receptor 1 (CysLT1R). Recently discovered lineage-negative type 2 innate lymphoid cells (ILC2s) potently produce IL-5 and IL-13.

OBJECTIVES

We hypothesized that lung ILC2s might be activated by leukotrienes through CysLT1R.

METHODS

ILC2s (Thy1.2(+) lineage-negative lymphocytes) and CysLT1R were detected in the lungs of wild-type, signal transducer and activator of transcription 6-deficient (STAT6(-/-)), and recombination-activating gene 2-deficient (RAG2(-/-)) mice by means of flow cytometry. T(H)2 cytokine levels were measured in purified lung ILC2s stimulated with leukotriene D₄ (LTD₄) in the presence or absence of the CysLT1R antagonist montelukast. Calcium influx was measured by using Fluo-4 intensity. Intranasal leukotriene C₄, D₄, and E₄ were administered to naive mice, and levels of ILC2 IL-5 production were determined. Finally, LTD₄ was coadministered with Alternaria species repetitively to RAG2(-/-) mice (with ILC2s) and IL-7 receptor-deficient mice (lack ILC2s), and total ILC2 numbers, proliferation (Ki-67(+)), and bronchoalveolar lavage fluid eosinophil numbers were measured.

RESULTS

CysLT1R was expressed on lung ILC2s from wild-type, RAG2(-/-), and STAT6(-/-) naive and Alternaria species-challenged mice. In vitro LTD₄ induced ILC2s to rapidly generate high levels of IL-5 and IL-13 within 6 hours of stimulation. Interestingly, LTD4, but not IL-33, induced high levels of IL-4 by ILC2s. LTD₄ administered in vivo rapidly induced ILC2 IL-5 production that was significantly reduced by montelukast before treatment. Finally, LTD₄ potentiated Alternaria species-induced eosinophilia, as well as ILC2 accumulation and proliferation.

CONCLUSIONS

We present novel data that CysLT1R is expressed on ILC2s and LTD₄ potently induces CysLT1R-dependent ILC2 production of IL-4, IL-5, and IL-13. Additionally, LTD₄ potentiates Alternaria species-induced eosinophilia and ILC2 proliferation and accumulation.

Epigallocatechin gallate targeting of membrane type 1 matrix metalloproteinase-mediated Src and Janus kinase/signal transducers and activators of transcription 3 signaling inhibits transcription of colony-stimulating factors 2 and 3 in mesenchymal stromal cells

BACKGROUND

CSF-2 and CSF-3 confer proangiogenic and immunomodulatory properties to mesenchymal stromal cells (MSCs).

RESULTS

Transcriptional regulation of CSF-2 and CSF-3 in concanavalin A-activated MSCs requires MT1-MMP signaling and is inhibited by EGCG.

CONCLUSION

The chemopreventive properties of diet-derived EGCG alter MT1-MMP-mediated intracellular signaling.

SIGNIFICANCE

Pharmacological targeting of MSCs proangiogenic functions may prevent their contribution to tumor development. Epigallocatechin gallate (EGCG), a major form of tea catechins, possesses immunomodulatory and antiangiogenic effects, both of which contribute to its chemopreventive properties. In this study, we evaluated the impact of EGCG treatment on the expression of colony-stimulating factors (CSF) secreted from human bone marrow-derived mesenchymal stromal cells (MSCs), all of which also contribute to the immunomodulatory and angiogenic properties of these cells. MSCs were activated with concanavalin A (ConA), a Toll-like receptor (TLR)-2 and TLR-6 agonist as well as a membrane type 1 matrix metalloproteinase (MT1-MMP) inducer, which increased granulocyte macrophage-CSF (GM-CSF, CSF-2), granulocyte CSF (G-CSF, CSF-3), and MT1-MMP gene expression. EGCG antagonized the ConA-induced CSF-2 and CSF-3 gene expression, and this process required an MT1-MMP-mediated sequential activation of the Src and JAK/STAT pathways. Gene silencing of MT1-MMP expression further demonstrated its requirement in the phosphorylation of Src and STAT3, whereas overexpression of a nonphosphorylatable MT1-MMP mutant (Y573F) abrogated CSF-2 and CSF-3 transcriptional increases. Given that MSCs are recruited within vascularizing tumors and are believed to contribute to tumor angiogenesis, possibly through secretion of CSF-2 and CSF-3, our study suggests that diet-derived polyphenols such as EGCG may exert chemopreventive action through pharmacological targeting of the MT1-MMP intracellular signaling.

GPCRs in stem cell function

Many tissues of the body cannot only repair themselves, but also self-renew, a property mainly due to stem cells and the various mechanisms that regulate their behavior. Stem cell biology is a relatively new field. While advances are slowly being realized, stem cells possess huge potential to ameliorate disease and counteract the aging process, causing its speculation as the next panacea. Amidst public pressure to advance rapidly to clinical trials, there is a need to understand the biology of stem cells and to support basic research programs. Without a proper comprehension of how cells and tissues are maintained during the adult life span, clinical trials are bound to fail. This review will cover the basic biology of stem cells, the various types of stem cells, their potential function, and the advantages and disadvantages to their use in medicine. We will next cover the role of G protein-coupled receptors in the regulation of stem cells and their potential in future clinical applications.

G protein-coupled receptor crosstalk and signaling in hematopoietic stem and progenitor cells

A variety of G protein-coupled receptors (GPCRs) is expressed in hematopoietic stem and progenitor cells (HPCs), including the chemokine receptor CXCR4, the leukotriene receptor CysLT1, the sphingosine 1-phosphate receptor S1P1, the cannabinoid receptor CB2, and the complement receptor C3aR. While the role of CXCR4 in stem cell homing is largely established, the function of the other GPCRs expressed in HPCs is only partially understood. CXCR4 and CysLT1 inhibit their own activation after ligand binding (homologous desensitization). Stimulation of S1P1 or C3aR has been shown to activate CXCR4 in HPCs that may sensitize CXCR4-dependent stem cell homing. In contrast, activation of CXCR4 results in a loss of CysLT1 function, which is most likely mediated by protein kinase C (PKC) signaling (heterologous desensitization) and could explain the ineffectiveness of CysLT1 antagonists to mobilize HPCs in vivo. Further characterization of GPCR crosstalk will allow a better understanding of HPC trafficking.

Molecular mechanisms underlying adhesion and migration of hematopoietic stem cells

Hematopoietic stem cell transplantation is the most powerful treatment modality for a large number of hematopoietic malignancies, including leukemia. Successful hematopoietic recovery after transplantation depends on homing of hematopoietic stem cells to the bone marrow and subsequent lodging of those cells in specific niches in the bone marrow. Migration of hematopoietic stem cells to the bone marrow is a highly regulated process that requires correct regulation of the expression and activity of various molecules including chemoattractants, selectins and integrins. This review will discuss recent studies that have extended our understanding of the molecular mechanisms underlying adhesion, migration and bone marrow homing of hematopoietic stem cells.

The G protein-coupled receptor CysLT1 mediates chemokine-like effects and prolongs survival in chronic lymphocytic leukemia

The G protein-coupled receptor (GPCR) CXCR4 is involved in bone marrow tropism and survival of chronic lymphocytic leukemia (CLL) cells. The function of the GPCRs cysteinyl leukotriene receptor 1 (CysLT1) and CysLT2 remains elusive. Here we demonstrate that in CLL and normal B lymphocytes, CysLT1 mRNA is consistently expressed, in contrast to low CysLT2 levels. Similar to the CXCR4 ligand CXCL12, the cysteinyl leukotriene (cysLT) LTD(4) induces calcium fluxes, actin polymerization, and chemotaxis. These effects are blocked by specific CysLT1 antagonists. Their inhibition by pertussis toxin suggests Giα/o protein involvement. Furthermore, CysLT1 mediates MAP-kinase phosphorylation, which implicates contribution of cysLT to survival. Indeed, CysLT1 antagonists induce apoptosis and reduce viability independent of Gαi/o protein signaling. Considering the production of cysLTs in the bone marrow, our data suggest that CysLT1 induces chemokine-like effects, supports accumulation and survival of CLL cells in the bone marrow and thus represents a potential treatment target.

Mast cell chemotaxis - chemoattractants and signaling pathways

Migration of mast cells is essential for their recruitment within target tissues where they play an important role in innate and adaptive immune responses. These processes rely on the ability of mast cells to recognize appropriate chemotactic stimuli and react to them by a chemotactic response. Another level of intercellular communication is attained by production of chemoattractants by activated mast cells, which results in accumulation of mast cells and other hematopoietic cells at the sites of inflammation. Mast cells express numerous surface receptors for various ligands with properties of potent chemoattractants. They include the stem cell factor (SCF) recognized by c-Kit, antigen, which binds to immunoglobulin E (IgE) anchored to the high affinity IgE receptor (FcεRI), highly cytokinergic (HC) IgE recognized by FcεRI, lipid mediator sphingosine-1-phosphate (S1P), which binds to G protein-coupled receptors (GPCRs). Other large groups of chemoattractants are eicosanoids [prostaglandin E₂ and D₂, leukotriene (LT) B₄, LTD₄, and LTC₄, and others] and chemokines (CC, CXC, C, and CX3C), which also bind to various GPCRs. Further noteworthy chemoattractants are isoforms of transforming growth factor (TGF) β1–3, which are sensitively recognized by TGF-β serine/threonine type I and II β receptors, adenosine, C1q, C3a, and C5a components of the complement, 5-hydroxytryptamine, neuroendocrine peptide catestatin, tumor necrosis factor-α, and others. Here we discuss the major types of chemoattractants recognized by mast cells, their target receptors, as well as signaling pathways they utilize. We also briefly deal with methods used for studies of mast cell chemotaxis and with ways of how these studies profited from the results obtained in other cellular systems.

Human T(H)2 cells respond to cysteinyl leukotrienes through selective expression of cysteinyl leukotriene receptor 1

BACKGROUND

Allergic asthma is characterized by reversible airway obstruction and bronchial hyperresponsiveness associated with T(H)2 cell-mediated inflammation. Cysteinyl leukotrienes (CysLTs) are potent lipid mediators involved in bronchoconstriction, mucus secretion, and cell trafficking in asthmatic patients. Recent data have implicated CysLTs in the establishment and amplification of T(H)2 responses in murine models, although the precise mechanisms are unresolved.

OBJECTIVES

Preliminary microarray studies suggested that human T(H)2 cells might selectively express cysteinyl leukotriene receptor 1 (CYSLTR1) mRNA. We sought to establish whether human T(H)2 cells are indeed a CysLT target cell type.

METHODS

We examined the expression of CYSLTR1 using real-time PCR in human T(H)1 and T(H)2 cells. We functionally assessed cysteinyl leukotriene receptor 1 protein (CysLT(1)) expression using calcium flux, cyclic AMP, and chemotaxis assays.

RESULTS

We show that human T(H)2 cells selectively express CYSLTR1 mRNA at high levels compared with T(H)1 cells after in vitro differentiation from naive precursors. Human T(H)2 cells are selectively responsive to CysLTs in a calcium flux assay when compared with T(H)1 cells with a rank order of potency similar to that described for CysLT(1) (leukotriene [LT] D(4) > LTC(4) > LTE(4)). We also show that LTD(4)-induced signaling in T(H)2 cells is mediated through CysLT(1) coupled to G(α)q and G(α)i proteins, and both pathways can be completely inhibited by selective CysLT(1) antagonists. LTD(4) is also found to possess potent chemotactic activity for T(H)2 cells at low nanomolar concentrations.

CONCLUSIONS

These findings suggest a novel mechanism of action for CysLTs in the pathogenesis of asthma and provide a potential explanation for the anti-inflammatory effects of CysLT(1) antagonists.

Monitoring the glioma tropism of bone marrow-derived progenitor cells by 2-photon laser scanning microscopy and positron emission tomography

Intracerebral experimental gliomas attract intravenously injected murine or human bone marrow-derived hematopoietic progenitor and stem cells (HPC) in vitro, ex vivo, and in vivo, indicating that these progenitor cells might be suitable vehicles for a cell-based delivery of therapeutic molecules to malignant gliomas. With regard to therapeutic application, it is important to investigate cell fates in vivo (i.e., the time-dependent intratumoral and systemic distribution after intravenously injection). Conventional histological analysis has limitations in this regard because longitudinal monitoring is precluded. Here, we used 2-photon laser scanning microscopy (2PLSM), positron emission tomography (PET), and MRI to study the fate of intravenously injected HPC carrying fluorescence, bioluminescence, and PET reporter genes in glioma-bearing mice. Our 2PLSM-based monitoring studies revealed that HPC homing to intracerebral experimental gliomas occurred already within the first 6 h and was most efficient within the first 24 h after intravenous injection. The highest PET signals were detected in intracerebral gliomas, whereas the tracer uptake in other organs, notably spleen, lung, liver, and muscle, remained at background levels. The results have important implications for designing schedules for therapeutic cell-based anti-glioma approaches. Moreover, the PET reporter-based imaging technique will allow noninvasive monitoring of cell fate in future cell-based therapeutic antiglioma approaches.

Antiasthmatic drugs targeting the cysteinyl leukotriene receptor 1 alleviate central nervous system inflammatory cell infiltration and pathogenesis of experimental autoimmune encephalomyelitis

Cysteinyl leukotrienes (CysLTs) are potent proinflammatory mediators and are considered to play a key role in inflammatory diseases such as asthma. Antagonists targeting the receptor of CysLTs (CysLT1) are currently used as antiasthmatic drugs. CysLTs have also been implicated in other inflammatory reactions. In this study, we report that in experimental autoimmune encephalomyelitis animals, CysLT1 is upregulated in immune tissue and the spinal cord, and CysLT levels in the blood and cerebrospinal fluid are also higher than in normal mice. Two clinically used antiasthma drugs, montelukast and zafirlukast, both targeting CysLT1, effectively block the CNS infiltration of inflammatory cells and thus reduce the incidence, peak severity, and cumulative clinical scores. Further study indicated that CysLT1 signaling does not affect the differentiation of pathogenic T helper cells. It might affect the pathogenesis of experimental autoimmune encephalomyelitis by increasing the secretion of IL-17 from myelin oligodendrocyte glycoprotein-specific T cells, increasing the permeability of the blood-brain barrier and inducing chemotaxis of T cells. These effects can be blocked by CysLT1 antagonists. Our findings indicate that the antiasthmatic drugs against CysLT1 can also be used to treat multiple sclerosis.

Pleiotropic effects of prostaglandin E2 in hematopoiesis; prostaglandin E2 and other eicosanoids regulate hematopoietic stem and progenitor cell function

Eicosanoids have been implicated in the physiological regulation of hematopoiesis with pleiotropic effects on hematopoietic stem cells and various classes of lineage restricted progenitor cells. Herein we review the effects of eicosanoids on hematopoiesis, focusing on new findings implicating prostaglandin E(2) in enhancing hematopoietic stem cell engraftment by enhancing stem cell homing, survival and self-renewal. We also describe a role for cannabinoids in hematopoiesis. Lastly, we discuss the yin and yang of various eicosanoids in modulating hematopoietic stem and progenitor cell functions and summarize potential strategies to take advantage of these effects for therapeutic benefit for hematopoietic stem cell transplantation.

Leukotrienes and airway inflammation

BACKGROUND

Asthma is a common chronic inflammatory disease of the airways characterized by airway obstruction and hyperresponsiveness. Leukotrienes (LTs) are lipid mediators that contribute to many aspects of asthma pathogenesis. As the LT pathway is relatively steroid-resistant, its blockade by alternative strategies is a desirable component of asthma management. Cysteinyl LT (cysLT) receptor 1 antagonists (LTRAs) have been utilized worldwide for more than 10years, and while their efficacy in asthma is well accepted, their limitations are also evident.

SCOPE OF REVIEW

In this review, we summarize the biological effects of LTs in asthma, review recent advances in LT receptors, and consider possible new therapeutic targets in the LT pathway that offer the potential to achieve better control of asthma in the future.

MAJOR CONCLUSIONS

CysLTs play pathogenetic roles in many aspects of asthma, and blockade of cysLT receptor 1 by currently available LTRAs is certainly beneficial in disease management. On the other hand, the limitations of LTRAs are also apparent. Recent studies have revealed new receptors for cysLTs other than classical cysLT receptors 1 and 2, as well as the potential importance of LTB(4) in asthma.

GENERAL SIGNIFICANCE

Recent findings provide clues to new approaches for targeting the LT pathway that may overcome the current limitations of LTRAs and achieve superior control of asthma. This article is part of a Special Issue entitled: Biochemistry of Asthma.

G-protein coupled receptors in stem cell self-renewal and differentiation

Stem cells have great potential for understanding early development, treating human disease, tissue trauma and early phase drug discovery. The factors that control the regulation of stem cell survival, proliferation, migration and differentiation are still emerging. Some evidence now exists demonstrating the potent effects of various G-protein coupled receptor (GPCR) ligands on the biology of stem cells. This review aims to give an overview of the current knowledge of the regulation of embryonic and somatic stem cell maintenance and differentiation by GPCR ligands.

Eicosanoid regulation of hematopoiesis and hematopoietic stem and progenitor trafficking

Hematopoietic stem cell (HSC) transplantation is a potentially curative treatment for numerous hematological malignancies. The transplant procedure as performed today takes advantage of HSC trafficking; either egress of HSC from the bone marrow to the peripheral blood, that is, mobilization, for acquisition of the hematopoietic graft, and/or trafficking of HSC from the peripheral blood to bone marrow niches in the recipient patient, that is HSC homing. Numerous studies, many of which are reviewed herein, have defined hematopoietic regulatory mechanisms mediated by the 20-carbon lipid family of eicosanoids, and recent evidence strongly supports a role for eicosanoids in regulation of hematopoietic trafficking, adding a new role whereby eicosanoids regulate hematopoiesis. Short-term exposure of HSC to the eicosanoid prostaglandin E(2) increases CXCR4 receptor expression, migration and in vivo homing of HSC. In contrast, cannabinoids reduce hematopoietic progenitor cell (HPC) CXCR4 expression and induce HPC mobilization when administered in vivo. Leukotrienes have been shown to alter CD34(+) cell adhesion, migration and regulate HSC proliferation, suggesting that eicosanoids have both opposing and complimentary roles in the regulation of hematopoiesis. As numerous FDA approved compounds regulate eicosanoid signaling or biosynthesis, the utility of eicosanoid-based therapeutic strategies to improve hematopoietic transplantation can be rapidly evaluated.

Circulating LTD4 in patients with hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is a type of inflammation-related cancer that usually follows chronic inflammations. Leukotriene D4 (LTD4) is a potent biologically active arachidonic acid-derived lipid mediator that is intimately involved in inflammations and cancers. Although previous researches found overexpression of LTD4 in several other cancers, the circulating LTD4 level in HCC remains unknown. The aim of this study was to examine concentrations of LTD4 and analyze its roles in HCC. The results showed that remarkably high circulating LTD4 in HCC versus healthy subjects (p < 0.001). The levels of LTD4 were neither associated with parameters expressing tumor burden, such as AFP, nor with inflammation factors AST and γ-GT. In addition, the significant increase of circulating LTD4 levels was obtained in patients with HCC accompanied by chronic hepatitis B (CHB), compared with those patients suffering HCC alone(P < 0.05). Furthermore, although the slightly lower levels of LTD4 were detected in HCC patients with non-metastasis and therapy compared with metastasis and non-therapy, no significant differences were detected. Taken together, the levels of circulating LTD4 are elevated in HCC and it may participate in the pathogenesis of HCC as an inflammatory factor from CHB disease to HCC.

Hemopoietic progenitors: the role of eosinophil/basophil progenitors in allergic airway inflammation

Progenitor cells play important roles in the physiology and homeostasis of the overall hemopoietic system. The majority of hemopoietic activity takes place in the bone marrow, under the influence of resident marrow stromal cells, accessory cells, and/or their products. This constitutes the complex network of the hemopoietic inductive microenvironment, which is crucial for providing signals necessary for the maintenance of populations of progenitors at varying stages of lineage commitment. Accumulation of eosinophils and basophils in tissues is characteristic of allergic inflammation. A large body of evidence now exists which confirms that these tissue inflammatory events are coincident with relevant changes in progenitors; it has thus been hypothesized that the observed changes in mature cell numbers occur directly or indirectly as a result of differentiation of lineage-committed eosinophil/basophil, and perhaps other, progenitor cells. Differentiation and maturation of hemopoietic cells have traditionally been thought to be restricted to the bone marrow microenvironment. More recently, evidence has accumulated to suggest that some hemopoietic cells present in allergic tissue may be recruited from the bone marrow, traffic through the peripheral circulation and into tissues to participate in the ongoing inflammatory process at these distal sites. The clinical administration of monotherapy with topical corticosteroids, oral cysteinyl leukotriene antagonists and cytokine antagonists such as antibodies to interleukin-5, suggest that suppression of hemopoietic contributions to allergic inflammation may be necessary for full control of allergic inflammation and disease manifestations. In addition to progenitors being targets of therapy, they may well determine how and whether allergic inflammation is generated in early life, thus serving as biomarkers of disease.

Haemopoietic processes in allergic disease: eosinophil/basophil development

Haemopoietic myeloid progenitors contribute to the ongoing recruitment of pro-inflammatory cells, such as eosinophils and basophils (Eo/B), to target tissue sites in allergic diseases. It is apparent that the development of allergic inflammation is critically dependent on the ability of the bone marrow to support the proliferation, differentiation and mobilization of haemopoietic progenitors. The haemopoietic inductive microenvironment in the bone marrow is crucial for providing signals necessary for maintenance of progenitor populations at varying stages of lineage commitment and permitting these cells to circulate in the bloodstream. Progenitors demonstrate responsiveness to specific cytokines, which varies with stage of differentiation. Pro-inflammatory signals, Th2 cytokines in particular, generated following allergen challenge, can impact on haemopoietic progenitor differentiation and mobilization, leading to accelerated Eo/B production. Allergen inhalation by allergic asthmatics induces a time-dependent change in cytokine levels within the bone marrow compartment, influencing differentiation of Eo/B progenitors, as evidenced by the relationship between increased bone marrow IL-5 levels and Eo/B production. It is proposed that inhaled allergen induces trafficking of IL-5-producing T lymphocytes to the bone marrow, further promoting eosinophilopoiesis through IL-5R signalling. In this manner, Th2 lymphocyte trafficking from the airway may regulate events occurring in the bone marrow. Negative regulators of Eo/B differentiation, including Th1 cytokines, may prove to be important for restoring homeostasis. Eo/B progenitors are also altered in cord blood of infants at risk of atopy and asthma, offering a potential biomarker for, and raising the possibility that Eo/B progenitors are directly involved in the development of allergic disease. For example, changes in the expression of haemopoietic cytokine receptors on cord blood progenitor cells are associated with maternal allergic sensitization, atopic risk and its development, suggesting that haemopoietic processes underlying the allergic phenotype may begin to evolve in the perinatal period.

The CysLT1 ligand leukotriene D4 supports alpha4beta1- and alpha5beta1-mediated adhesion and proliferation of CD34+ hematopoietic progenitor cells

Cytokines and chemokines control hematopoietic stem and progenitor cell (HPC) proliferation and trafficking. However, the role of nonpeptide mediators in the bone marrow microenvironment has remained elusive. Particularly CysLT(1), a G protein-coupled receptor recognizing inflammatory mediators of the cysteinyl leukotriene family, is highly expressed in HPCs. We therefore analyzed the effects of its ligands on human CD34(+) HPCs. The most potent CysLT(1) ligand, LTD(4), rapidly and significantly up-regulated alpha(4)beta(1) and alpha(5)beta(1) integrin-dependent adhesion of both primitive and committed HPC. LTD(4)-triggered adhesion was inhibited by specific CysLT(1) antagonists. The effects of other CysLT(1) ligands were weak (LTC(4)) or absent (LTE(4)). In serum-free liquid cultures supplemented with various hematopoietic cytokines including IL-3, only LTD(4) significantly augmented the expansion of HPCs in a dose-dependent manner comparable to that of peptide growth factors. LTC(4) and LTE(4) were less effective. In CD34(+) cell lines and primary HPCs, LTD(4) induced phosphorylation of p44/42 ERK/MAPK and focal adhesion kinase-related tyrosine kinase Pyk2, which is linked to integrin activation. Bone marrow stromal cells produced biologically significant amounts of cysteinyl leukotrienes only when hematopoietic cells were absent, suggesting a regulatory feedback mechanism in the hematopoietic microenvironment. In contrast to antagonists of the homing-related G protein-coupled receptor CXCR4, administration of a CysLT(1) antagonist failed to induce human CD34(+) HPC mobilization in vivo. Our results suggest that cysteinyl leukotriene may contribute to HPC retention and proliferation only when cysteinyl leukotriene levels are increased either systemically during inflammation or locally during marrow aplasia.

Eosinophil progenitors in allergy and asthma - do they matter?

Allergic inflammation is associated with marked infiltration of eosinophils in affected tissues. The eosinophil is believed to be a key effector cells in allergen induced asthma pathogenesis. However, the role of eosinophils in the clinical manifestation of asthma has recently been questioned, since therapies directed against eosinophil infiltration (i.e. anti-interleukin-5) failed to improve clinical symptoms such as airways hyper-responsiveness (AHR) in patients with asthma. Although eosinophils in peripheral blood and the airways were largely depleted after anti-IL-5 treatment, residual eosinophilia in lung tissue persisted, which permits speculation that the remaining eosinophils may be sufficient to drive the asthma symptomatology. Furthermore, recent findings suggest that primitive eosinophil progenitor cells traffic from the bone marrow to sites of inflammation in response to allergen exposure. These progenitors may then differentiate in situ and thus provide an ongoing supply of mature pro-inflammatory cells and secretory mediators that augment the inflammatory response. In the present article, we will review the evidence for these findings, and discuss the rationale for targeting hematopoiesis and their migration pathways in the treatment of allergic diseases. Furthermore, this review will highlight the hypothesis that both IL-5- and CCR3-mediated signaling pathways may need to be targeted in order to control the inflammation and AHR associated with asthma.

Endothelial progenitor cell homing: prominent role of the IGF2-IGF2R-PLCbeta2 axis

Homing of endothelial progenitor cells (EPCs) to the neovascular zone is now considered to be an essential step in the formation of vascular networks during embryonic development and also for neovascularization in postnatal life. We report here the prominent role of the insulin-like growth factor 2 (IGF2)/IGF2 receptor (IGF2R) system in promoting EPC homing. With high-level expression of IGF2R in EPCs, IGF2-induced hypoxic conditions stimulated multiple steps of EPC homing in vitro and promoted both EPC recruitment and incorporation into the neovascular area, resulting in enhanced angiogenesis in vivo. Remarkably, all IGF2 actions were exerted predominantly through IGF2R-linked G(i) protein signaling and required intracellular Ca(2+) mobilization induced by the beta2 isoform of phospholipase C. Together, these findings indicate that locally generated IGF2 at either ischemic or tumor sites may contribute to postnatal vasculogenesis by augmenting the recruitment of EPCs. The utilization of the IGF2/IGF2R system may therefore be useful for the development of novel means to treat angiogenesis-dependent diseases.

Leukotriene D(4) induces gene expression in human monocytes through cysteinyl leukotriene type I receptor

BACKGROUND

Cysteinyl leukotrienes (CysLTs) are important mediators of innate immune responsiveness and chronic inflammatory diseases. CysLTs acting through CysLT receptors can influence the migration and activity of cells, such as eosinophils, monocytes, and dendritic cells.

OBJECTIVE

We sought to determine the gene expression signature of human monocytes in response to CysLTs and to elucidate the signaling pathways involved in monocyte activation.

METHODS

Gene expression was analyzed by using oligonucleotide microarrays. Responsiveness to CysLTs was assessed by using real-time PCR, calcium flux, kinase activation, and chemotaxis assays.

RESULTS

CysLT type 1 receptor (CysLTR(1)) transcript 1 is predominantly expressed in human monocytes, and CysLTs signal through CysLTR(1) in these cells. Several immediate-early genes, including early growth response 2 and 3, FBJ murine osteosarcoma viral oncogene homolog B, activating transcription factor 3, and nuclear receptor subfamily 4 were significantly induced by leukotriene (LT) D(4). This effect was mediated by CysLTR(1) coupled to the G protein alpha inhibitory subunit, activation of phospholipase C, and inositol-1,4,5-triphosphate and store-operated calcium channels. LTD(4) induced p38 mitogen-activated protein kinase phosphorylation, a pathway also involved in the regulation of immediate-early gene expression in monocytes. LTD(4) stimulated monocyte chemotactic activity that was fully blocked by a selective CysLTR(1) inhibitor, MK571, and pertussis toxin, suggesting that CysLTR(1) coupled to the G protein alpha inhibitory subunit is a dominant functional pathway in human monocytes.

CONCLUSION

Our data show that CysLTs acting through CysLTR(1) can significantly influence the activation and migration of human monocytes and that these effects can be fully inhibited by CysLTR(1) antagonists.

Blockade of avidity and focal clustering of beta 2-integrin by cysteinyl leukotriene antagonism attenuates eosinophil adhesion

BACKGROUND

Cysteinyl leukotriene (cysLT) antagonism attenuates migration of eosinophils into airways during immune challenge in human subjects and animal models. The intracellular signaling mechanism by which this occurs has not been elucidated.

OBJECTIVE

We sought to determine the relative efficacy and mechanism by which 5-lipoxygenase (5-LO) inhibition and cysLT(1) receptor (cysLT(1)R) antagonism block beta(2)-integrin adhesion in isolated human eosinophils in vitro.

METHODS

Human blood eosinophils were isolated by means of immunomagnetic separation. Upregulation of CD11b expression, active conformation of CD11b, and focal clustering of beta(2)-integrin caused by IL-5, eotaxin-1 or leukotriene (LT) B(4) was assessed by means of flow cytometry and confocal microscopy. The effect and mechanism of cysLT(1)R or 5-LO blockade on these components of beta(2)-integrin adhesion were determined.

RESULTS

Montelukast, a cysLT(1)R antagonist, and AA861, a 5-LO enzyme inhibitor, blocked (1) avidity of beta(2)-integrin, (2) beta(2)-integrin-mediated adhesion to intercellular adhesion molecule 1, and (3) focal clustering of CD11b elicited by LTB(4). However, adhesion caused by either IL-5 or eotaxin-1 was not attenuated for eosinophils pretreated with either montelukast or AA861.

CONCLUSION

Our data demonstrate that (1) LTB(4) causes autocrine upregulation of adhesion through secretion of cysLTs, and (2) blockade of cysLT(1)R blocks the avidity and focal clustering of CD11b/CD18 for eosinophils activated by LTB(4) but not by IL-5 or eotaxin-1.

CLINICAL IMPLICATIONS

Unlike cysLT-induced adhesion, adhesion caused by IL-5 or eotaxin-1 is not regulated through the cysLT(1)R, suggesting that cysLTs have specific but limited potential to upregulate eosinophil adhesion.

Monocyte derived dendritic cells generated by IFN-alpha acquire mature dendritic and natural killer cell properties as shown by gene expression analysis

BACKGROUND

Dendritic cell (DC) vaccines can induce antitumor immune responses in patients with malignant diseases, while the most suitable DC culture conditions have not been established yet. In this study we compared monocyte derived human DC from conventional cultures containing GM-CSF and IL-4/TNF-alpha (IL-4/TNF-DC) with DC generated by the novel protocol using GM-CSF and IFN-alpha (IFN-DC).

METHODS

To characterise the molecular differences of both DC preparations, gene expression profiling was performed using Affymetrix microarrays. The data were conformed on a protein level by immunophenotyping, and functional tests for T cell stimulation, migration and cytolytic activity were performed.

RESULTS

Both methods resulted in CD11c+ CD86+ HLA-DR+ cells with a typical DC morphology that could efficiently stimulate T cells. But gene expression profiling revealed two distinct DC populations. Whereas IL-4/TNF-DC showed a higher expression of genes envolved in phagocytosis IFN-DC had higher RNA levels for markers of DC maturity and migration to the lymph nodes like DCLAMP, CCR7 and CD49d. This different orientation of both DC populations was confined by a 2.3 fold greater migration in transwell experiments (p = 0.01). Most interestingly, IFN-DC also showed higher RNA levels for markers of NK cells such as TRAIL, granzymes, KLRs and other NK cell receptors. On a protein level, intracytoplasmatic TRAIL and granzyme B were observed in 90% of IFN-DC. This translated into a cytolytic activity against K562 cells with a median specific lysis of 26% at high effector cell numbers as determined by propidium iodide uptake, whereas IL-4/TNF-DC did not induce any tumor cell lysis (p = 0.006). Thus, IFN-DC combined characteristics of mature DC and natural killer cells.

CONCLUSION

Our results suggest that IFN-DC not only stimulate adaptive but also mediate innate antitumor immune responses. Therefore, IFN-DC should be evaluated in clinical vaccination trials. In particular, this could be relevant for patients with diseases responsive to a treatment with IFN-alpha such as Non-Hodgkin lymphoma or chronic myeloid leukemia.

Cysteinyl-leukotrienes and their receptors in asthma and other inflammatory diseases: critical update and emerging trends

Cysteinyl-leukotrienes (cysteinyl-LTs), that is, LTC4, LTD4, and LTE4, trigger contractile and inflammatory responses through the specific interaction with G protein-coupled receptors (GPCRs) belonging to the purine receptor cluster of the rhodopsin family, and identified as CysLT receptors (CysLTRs). Cysteinyl-LTs have a clear role in pathophysiological conditions such as asthma and allergic rhinitis (AR), and have been implicated in other inflammatory conditions including cardiovascular diseases, cancer, atopic dermatitis, and urticaria. Molecular cloning of human CysLT1R and CysLT2R subtypes has confirmed most of the previous pharmacological characterization and identified distinct expression patterns only partially overlapping. Interestingly, recent data provide evidence for the immunomodulation of CysLTR expression, the existence of additional receptor subtypes, and of an intracellular pool of CysLTRs that may have roles different from those of plasma membrane receptors. Furthermore, genetic variants have been identified for the CysLTRs that may interact to confer risk for atopy. Finally, a crosstalk between the cysteinyl-LT and the purine systems is being delineated. This review will summarize and attempt to integrate recent data derived from studies on the molecular pharmacology and pharmacogenetics of CysLTRs, and will consider the therapeutic opportunities arising from the new roles suggested for cysteinyl-LTs and their receptors.

Mast cells and eicosanoid mediators: a system of reciprocal paracrine and autocrine regulation

When activated by specific antigen, complement, or other transmembrane stimuli, mast cells (MCs) generate three eicosanoids: prostaglandin (PG)D(2), leukotriene (LT)B(4), and LTC(4), the parent molecule of the cysteinyl leukotrienes (cysLTs). These diverse lipid mediators, which are generated from a single cell membrane-associated precursor, arachidonic acid, can initiate, amplify, or dampen inflammatory responses and influence the magnitude, duration, and nature of subsequent immune responses. PGD(2) and cysLTs, which were originally recognized for their bronchoconstricting and vasoactive properties, also serve diverse and pivotal functions in effector cell trafficking, antigen presentation, leukocyte activation, matrix deposition, and fibrosis. LTB(4) is a powerful chemoattractant for neutrophils and certain lymphocyte subsets. Thus, MCs can contribute to each of these processes through eicosanoid generation. Additionally, MCs express G-protein-coupled receptors specific for cysLTs, LTB(4), and another eicosanoid, PGE(2). Each of these receptors can regulate MC functions in vivo by autocrine and paracrine mechanisms. This review focuses on the biologic functions for MC-associated eicosanoids, the regulation of their production, and the mechanisms by which eicosanoids may regulate MC function in host defense and disease.

Sparing effect by montelukast treatment for chronic graft versus host disease: a pilot study

BACKGROUND

Chronic graft versus host disease (GvHD) is a major complication after allogeneic stem cell transplantation (SCT), which is usually progression from acute GvHD. Chronic GvHD is the main cause of severe morbidity and mortality in long-term survivors after SCT. The cysteinyl leukotrienes (cysLTs) and eosinophils play an important role in the pathogenesis of GvHD, which is the rationale for the combined use of montelukast (Mk) in the treatment of this illness.

METHODS

Mk was administrated to 19 eligible patients with refractory chronic GvHD, in addition to their standard immunosuppressive regimens. Mk was given orally (10 mg once daily) for a mean period of 10 months (range, 2-21 months). Organ-specific response was determined by the new scoring criteria established by the National Institutes of Health consensus project.

RESULTS

Based on organ involvements endpoints, overall response to the combined therapy with Mk was observed in 15 of 19 (79%) patients. Significant improvement of skin liver and gastrointestinal was observed in 53%, 62%, and 46%, respectively. Generally, Mk was notably beneficial in milder stages of GvHD, which lead to earlier withdrawal of other immunosuppressive agents. Side effects of Mk administration were not documented, nor were cases of relapse of the basic disease.

CONCLUSIONS

Our preliminary prospective investigation supports the potential efficacy of Mk as a safe and toxicity-sparing supplement to standard therapy for patients with chronic GvHD. Future clinical studies are necessary to establish the optimal dose of Mk and its role in the symptomatic and prophylactic treatment of acute and chronic GvHD.

Differential effects of G protein coupled receptors on hematopoietic progenitor cell growth depend on their signaling capacities

We have shown that CD34(+) hematopoietic progenitor and stem cells (HPCs) consistently express several G protein-coupled receptors (GPCRs): the chemokine receptor CXCR4, the cysteinyl-leukotriene receptor cysLT1, and receptors for sphingosine 1-phosphate (S1P), particularly S1P1. These GPCRs differentially mediate chemotactic, adhesive, and proliferative responses in HPCs. To elucidate the diversity of the responses observed, we compared their signaling capacities in CD34(+) cells. In primary CD34(+) progenitors, the strongest effects on calcium signaling (intracellular calcium fluxes) were mediated by cysLT1. Analyses in CD34(+) cell lines revealed that calcium signaling induced by cysLT1 was only partially inhibited by pertussis toxin (PTX), while responses induced by CXCR4 and S1P receptors were completely blocked. These findings indicate that cysLT1 signals via Gi and Gq proteins, while CXCR4 and also S1P receptors (e.g., S1P1) only induce Gi protein-mediated effects. By analysis of downstream signaling, we could provide further evidence that combined activation of PTX-insensitive (Gq-mediated) and PTX-sensitive (Gi-mediated) pathways by cysLT1 may explain the strong and broad effects of cysteinyl-leukotrienes in early hematopoietic cells, while signaling of CXCR4 and S1P1 solely depends on Gi proteins, resulting in effects mainly restricted to migration and adhesion.

G-protein-coupled receptors and asthma endophenotypes: the cysteinyl leukotriene system in perspective

Genetic variation in specific G-protein coupled receptors (GPCRs) is associated with a spectrum of respiratory disease predispositions and drug response phenotypes. Although certain GPCR gene variants can be disease-causing through the expression of inactive, overactive, or constitutively active receptor proteins, many more GPCR gene variants confer risk for potentially deleterious endophenotypes. Endophenotypes are traits, such as bronchiole hyperactivity, atopy, and aspirin intolerant asthma, which have a strong genetic component and are risk factors for a variety of more complex outcomes that may include disease states. GPCR genes implicated in asthma endophenotypes include variants of the cysteinyl leukotriene receptors (CYSLTR1 and CYSLTR2), and prostaglandin D2 receptors (PTGDR and CRTH2), thromboxane A2 receptor (TBXA2R), beta2-adrenergic receptor (ADRB2), chemokine receptor 5 (CCR5), and the G protein-coupled receptor associated with asthma (GPRA). This review of the contribution of variability in these genes places the contribution of the cysteinyl leukotriene system to respiratory endophenotypes in perspective. The genetic variant(s) of receptors that are associated with endophenotypes are discussed in the context of the extent to which they contribute to a disease phenotype or altered drug efficacy.

The role of sphingosine 1-phosphate receptors in the trafficking of hematopoietic progenitor cells

Sphingosine 1-phosphate (S1P) is an ubiquitously present extracellular lipid mediator that is released by several cell types, particularly by activated platelets. The effects of S1P are mediated by a specific family of G protein-coupled sphingosine 1-phosphate receptors (S1P1-S1P5). We demonstrate that S1P acts on hematopoietic progenitor cells as a chemotactic factor, attracting peripheral blood CD34(+) cells in vitro. Furthermore, constant activation of S1P receptors augments CXCR4-mediated signal transduction induced by stromal cell-derived factor 1 (SDF-1). These effects are most likely mediated by the S1P1 receptor consistently expressed in both primitive and committed CD34(+) hematopoietic progenitor cells (HPCs). In vivo, sustained activation of S1P1 by a receptor agonist during the homing process resulted in increased engraftment. Given the fact that activated platelets represent a major source of extracellular S1P, SDF-1-mediated stem cell homing may occur at sites of tissue injury in addition to the bone marrow. This could explain the previously observed contribution of primary hematopoietic stem cells to tissue repair in myocardial infarction and other diseases.

Cysteinyl leukotrienes: multi-functional mediators in allergic rhinitis

Cysteinyl leukotrienes (CysLTs) are a family of inflammatory lipid mediators synthesized from arachidonic acid by a variety of cells, including mast cells, eosinophils, basophils, and macrophages. This article reviews the data for the role of CysLTs as multi-functional mediators in allergic rhinitis (AR). We review the evidence that: (1) CysLTs are released from inflammatory cells that participate in AR, (2) receptors for CysLTs are located in nasal tissue, (3) CysLTs are increased in patients with AR and are released following allergen exposure, (4) administration of CysLTs reproduces the symptoms of AR, (5) CysLTs play roles in the maturation, as well as tissue recruitment, of inflammatory cells, and (6) a complex inter-regulation between CysLTs and a variety of other inflammatory mediators exists.

The extracellular nucleotide UTP is a potent inducer of hematopoietic stem cell migration

Homing and engraftment of hematopoietic stem cells (HSCs) to the bone marrow (BM) involve a complex interplay between chemokines, cytokines, and nonpeptide molecules. Extracellular nucleotides and their cognate P2 receptors are emerging as key factors of inflammation and related chemotactic responses. In this study, we investigated the activity of extracellular adenosine triphosphate (ATP) and uridine triphosphate (UTP) on CXCL12-stimulated CD34+ HSC chemotaxis. In vitro, UTP significantly improved HSC migration, inhibited cell membrane CXCR4 down-regulation by migrating CD34+ cells, and increased cell adhesion to fibronectin. In vivo, preincubation with UTP significantly enhanced the BM homing efficiency of human CD34+ cells in immunodeficient mice. Pertussis toxin blocked CXCL12- and UTP-dependent chemotactic responses, suggesting that G-protein alpha-subunits (Galphai) may provide a converging signal for CXCR4- and P2Y-activated transduction pathways. In addition, gene expression profiling of UTP- and CXCL12-treated CD34+ cells and in vitro inhibition assays demonstrated that Rho guanosine 5'-triphosphatase (GTPase) Rac2 and downstream effectors Rho GTPase-activated kinases 1 and 2 (ROCK1/2) are involved in UTP-promoted/CXCL12-dependent HSC migration. Our data suggest that UTP may physiologically modulate the homing of HSCs to the BM, in concert with CXCL12, via the activation of converging signaling pathways between CXCR4 and P2Y receptors, involving Galphai proteins and RhoGTPases.