Mast cells and inflammation.

Mast cells are well known for their role in allergic and anaphylactic reactions, as well as their involvement in acquired and innate immunity. Increasing evidence now implicates mast cells in inflammatory diseases where they are activated by non-allergic triggers, such as neuropeptides and cytokines, often exerting synergistic effects as in the case of IL-33 and neurotensin. Mast cells can also release pro-inflammatory mediators selectively without degranulation. In particular, IL-1 induces selective release of IL-6, while corticotropin-releasing hormone secreted under stress induces the release of vascular endothelial growth factor. Many inflammatory diseases involve mast cells in cross-talk with T cells, such as atopic dermatitis, psoriasis and multiple sclerosis, which all worsen by stress. How mast cell differential responses are regulated is still unresolved. Preliminary evidence suggests that mitochondrial function and dynamics control mast cell degranulation, but not selective release. Recent findings also indicate that mast cells have immunomodulatory properties. Understanding selective release of mediators could explain how mast cells participate in numerous diverse biologic processes, and how they exert both immunostimulatory and immunosuppressive actions. Unraveling selective mast cell secretion could also help develop unique mast cell inhibitors with novel therapeutic applications. This article is part of a Special Issue entitled: Mast cells in inflammation.

Rupatadine inhibits inflammatory mediator release from human laboratory of allergic diseases 2 cultured mast cells stimulated by platelet-activating factor.

BACKGROUND: Mast cells are involved in allergy and inflammation by the secretion of multiple mediators, including histamine, cytokines, and platelet-activating factor (PAF), in response to different triggers, including emotional stress. PAF has been associated with allergic inflammation, but there are no clinically available PAF inhibitors. OBJECTIVE: To investigate whether PAF could stimulate human mast cell mediator release and whether rupatadine (RUP), a dual histamine-1 and PAF receptor antagonist, could inhibit the effect of PAF on human mast cells. METHODS: Laboratory of allergic diseases 2 cultured mast cells were stimulated with PAF (0.001, 0.01, and 0.1 µmol/L) and substance P (1 µmol/L) with or without pretreatment with RUP (2.5 and 25 µmol/L), which was added 10 minutes before stimulation. Release of ß-hexosaminidase was measured in supernatant fluid by spectrophotoscopy, and histamine, interleukin-8, and tumor necrosis factor were measured by enzyme-linked immunosorbent assay. RESULTS: PAF stimulated a statistically significant release of histamine, interleukin-8, and tumor necrosis factor (0.001-0.1 µmol/L) that was comparable to that stimulated by substance P. Pretreatment with RUP (25 µmol/L) for 10 minutes inhibited this effect. In contrast, pretreatment of laboratory of allergic diseases 2 cells with diphenhydramine (25 µmol/L) did not inhibit mediator release, suggesting that the effect of RUP was not due to its antihistaminic effect. CONCLUSION: PAF stimulates human mast cell release of proinflammatory mediators that is inhibited by RUP. This action endows RUP with additional properties in treating allergic inflammation.

Mitochondria distinguish granule-stored from de novo synthesized tumor necrosis factor secretion in human mast cells.

BACKGROUND: Mast cells are immune cells derived from hematopoietic precursors that mature in the tissue microenvironment. Mast cells are critical for allergic, immune and inflammatory processes, many of which involve tumor necrosis factor (TNF). These cells uniquely store TNF in their secretory granules. Upon stimulation, mast cells rapidly (30 min) secrete ß-hexosaminidase and granule-stored TNF through degranulation, but also increase TNF mRNA and release de novo synthesized TNF 24 h later. The regulation of these two distinct pathways is poorly understood. METHODS: Human LAD2 leukemic mast cells are stimulated by substance P. TNF secretion and gene expression were measured by ELISA and real-time PCR, and mitochondrial dynamics was observed in live cells under confocal microscopy. Cell energy consumption was measured in terms of oxygen consumption rate. RESULTS: Here, we show that granule-stored TNF is preformed, and its secretion from LAD2 mast cells stimulated by substance P (1) exhibits higher energy consumption and is inhibited by the mitochondrial ATP pump blocker oligomycin, (2) shows rapid increase in intracellular calcium levels, and (3) exhibits reversible mitochondrial translocation, from a perinuclear distribution to the cell surface, as compared to de novo synthesized TNF release induced by lipopolysaccharide. This mitochondrial translocation is confirmed using primary human umbilical cord blood-derived mast cells stimulated by an allergic trigger (IgE/streptavidin). CONCLUSION: Our findings indicate that unique mitochondrial functions distinguish granule-stored from newly synthesized TNF release from human mast cells, thus permitting the versatile involvement of mast cells in different biological processes.

Contribution of stress to asthma worsening through mast cell activation.

OBJECTIVE: To review the available evidence linking stress to asthma and to investigate whether mast cells contribute to the effect of stress through activation by corticotropin-releasing hormone (CRH). DATA SOURCE: The PubMed database was searched for articles (1998-2011) using the keywords anxiety, asthma, exacerbation, inflammation, mast cells, socioeconomic status, stress, violence, and worsening. STUDY SELECTION: Articles were selected based on their relevance to the topic, with emphasis on clinical or epidemiologic data linking stress to asthma and studies that offered possible explanations for how stress may affect asthma. RESULTS: Many articles point to an association between stress (socioeconomic status, interpersonal conflicts, emotional distress, terrorism) and asthma exacerbations but without any distinct pathogenetic mechanism. A few articles have reported reduced circulating cortisol and/or sensitivity to corticosteroids. We propose that mast cells, known to be involved in the pathophysiology of asthma, can be activated by CRH, which is secreted under stress in the lungs, leading to selective release of proinflammatory mediators. This effect may be augmented by neuropeptides or cytokines. CRH also reduces T-regulatory cell production of interleukin 10, which in known to inhibit allergic mast cell activation. CONCLUSION: More studies are required to investigate lung levels of CRH and selective mast cell mediators. Reducing stress and using CRH receptor antagonists and/or mast cell blockers may serve as possible new therapeutic approaches for asthma.

Human mast cell degranulation and preformed TNF secretion require mitochondrial translocation to exocytosis sites: relevance to atopic dermatitis.

BACKGROUND: Mast cells derive from hematopoietic cell precursors and participate in tissue allergic, immune, and inflammatory processes. They secrete many mediators, including preformed TNF, in response to allergic, neuropeptide, and environmental triggers. However, regulation of mast cell degranulation is not well understood. OBJECTIVE: We investigated the role of mitochondrial dynamics in degranulation of human cultured mast cells. METHODS: Human umbilical cord blood-derived mast cells (hCBMCs) and Laboratory of Allergic Diseases 2 (LAD2) mast cells were examined by confocal and differential interference contrast microscopy during activation by IgE/antigen and substance P (SP). Mast cells in control and atopic dermatitis (AD) skin were evaluated by transmission electron microscopy. LAD2 cells were pretreated with mitochondrial division inhibitor, a dynamin-related protein 1 (Drp1) inhibitor, and small interfering RNA for Drp1, which is necessary for mitochondrial fission and translocation. Calcineurin and Drp1 gene expression was analyzed in stimulated LAD2 cells and AD skin biopsies. RESULTS: Stimulation of hCBMCs with IgE/antigen or LAD2 cells with SP leads to rapid (30 minutes) secretion of preformed TNF. Degranulation is accompanied by mitochondrial translocation from a perinuclear location to exocytosis sites. Extracellular calcium depletion prevents these effects, indicating calcium requirement. The calcium-dependent calcineurin and Drp1 are activated 30 minutes after SP stimulation. Reduction of Drp1 activity by mitochondrial division inhibitor and decrease of Drp1 expression using small interfering RNA inhibit mitochondrial translocation, degranulation, and TNF secretion. Mitochondrial translocation is also evident by transmission electron microscopy in skin mast cells from AD biopsies, in which gene expression of calcineurin, Drp1, and SP is higher than in normal skin. CONCLUSION: Human mast cell degranulation requires mitochondrial dynamics, also implicated in AD.

Stimulated human mast cells secrete mitochondrial components that have autocrine and paracrine inflammatory actions.

Mast cells are hematopoietically-derived tissue immune cells that participate in acquired and innate immunity, as well as in inflammation through release of many chemokines and cytokines, especially in response to the pro-inflammatory peptide substance P (SP). Inflammation is critical in the pathogenesis of many diseases, but the trigger(s) is often unknown. We investigated if mast cell stimulation leads to secretion of mitochondrial components and whether these could elicit autocrine and/or paracrine inflammatory effects. Here we show that human LAD2 mast cells stimulated by IgE/anti-IgE or by the SP led to secretion of mitochondrial particles, mitochondrial (mt) mtDNA and ATP without cell death. Mitochondria purified from LAD2 cells and, when mitochondria added to mast cells trigger degranulation and release of histamine, PGD(2), IL-8, TNF, and IL-1ß. This stimulatory effect is partially inhibited by an ATP receptor antagonist and by DNAse. These results suggest that the mitochondrial protein fraction may also contribute. Purified mitochondria also stimulate IL-8 and vascular endothelial growth factor (VEGF) release from cultured human keratinocytes, and VEGF release from primary human microvascular endothelial cells. In order to investigate if mitochondrial components could be secreted in vivo, we injected rats intraperiotoneally (ip) with compound 48/80, which mimicks the action of SP. Peritoneal mast cells degranulated and mitochondrial particles were documented by transimission electron microscopy outside the cells. We also wished to investigate if mitochondrial components secreted locally could reach the systemic circulation. Administration ip of mtDNA isolated from LAD2 cells in rats was detected in their serum within 4 hr, indicating that extravascular mtDNA could enter the systemic circulation. Secretion of mitochondrial components from stimulated live mast cells may act as "autopathogens" contributing to the pathogenesis of inflammatory diseases and may be used as targets for novel treatments.

Neurotensin and CRH interactions augment human mast cell activation.

Stress affects immunity, but the mechanism is not known. Neurotensin (NT) and corticotropin-releasing hormone (CRH) are secreted under stress in various tissues, and have immunomodulatory actions. We had previously shown that NT augments the ability of CRH to increase mast cell-dependent skin vascular permeability in rodents. Here we show that NT triggered human mast cell degranulation and significantly augmented CRH-induced vascular endothelial growth factor (VEGF) release. Investigation of various signaling molecules indicated that only NF-κB activation was involved. These effects were blocked by pretreatment with the NTR antagonist SR48692. NT induced expression of CRH receptor-1 (CRHR-1), as shown by Western blot and FACS analysis. Interestingly, CRH also induced NTR gene and protein expression. These results indicate unique interactions among NT, CRH, and mast cells that may contribute to auto-immune and inflammatory diseases that worsen with stress.

IL-9 induces VEGF secretion from human mast cells and IL-9/IL-9 receptor genes are overexpressed in atopic dermatitis.

Interleukin 9 (IL-9) has been implicated in mast cell-related inflammatory diseases, such as asthma, where vascular endothelial growth factor (VEGF) is involved. Here we report that IL-9 (10-20 ng/ml) induces gene expression and secretion of VEGF from human LAD2. IL-9 does not induce mast cell degranulation or the release of other mediators (IL-1, IL-8, or TNF). VEGF production in response to IL-9 involves STAT-3 activation. The effect is inhibited (about 80%) by the STAT-3 inhibitor, Stattic. Gene-expression of IL-9 and IL-9 receptor is significantly increased in lesional skin areas of atopic dermatitis (AD) patients as compared to normal control skin, while serum IL-9 is not different from controls. These results imply that functional interactions between IL-9 and mast cells leading to VEGF release contribute to the initiation/propagation of the pathogenesis of AD, a skin inflammatory disease.

Mast cells in allergic and inflammatory diseases.

Mast cells are important in the development of allergic and anaphylactic reactions, but also in acquired and innate immunity. There is also increasing evidence that mast cells participate in inflammatory diseases, where they can be activated by non-allergic triggers, such as neuropeptides and cytokines, often having synergistic effects as in the case of substance P (SP) and IL-33. Secretion of vasoactive mediators, cytokines and proteinases contribute to the development of coronary artery disease (CAD), as well as to diet-induced obesity and the metabolic syndrome. Mast cells may be able to orchestrate such different biological processes through their ability to release pro-inflammatory mediators selectively without the degranulation typical of allergic reactions. Recent evidence suggests that mitochondrial uncoupling protein 2 (UCP2) and mitochondrial translocation regulate mast cell degranulation, but not selective mediator release. Better understanding of these two processes and how mast cells exert both immunostimulatory and immunosuppressive actions could lead to the development of inhibitors of release of specific mediators with novel therapeutic applications.

Quercetin is more effective than cromolyn in blocking human mast cell cytokine release and inhibits contact dermatitis and photosensitivity in humans.

Mast cells are immune cells critical in the pathogenesis of allergic, but also inflammatory and autoimmune diseases through release of many pro-inflammatory cytokines such as IL-8 and TNF. Contact dermatitis and photosensitivity are skin conditions that involve non-immune triggers such as substance P (SP), and do not respond to conventional treatment. Inhibition of mast cell cytokine release could be effective therapy for such diseases. Unfortunately, disodium cromoglycate (cromolyn), the only compound marketed as a mast cell "stabilizer", is not particularly effective in blocking human mast cells. Instead, flavonoids are potent anti-oxidant and anti-inflammatory compounds with mast cell inhibitory actions. Here, we first compared the flavonoid quercetin (Que) and cromolyn on cultured human mast cells. Que and cromolyn (100 µM) can effectively inhibit secretion of histamine and PGD(2). Que and cromolyn also inhibit histamine, leukotrienes and PGD(2) from primary human cord blood-derived cultured mast cells (hCBMCs) stimulated by IgE/Anti-IgE. However, Que is more effective than cromolyn in inhibiting IL-8 and TNF release from LAD2 mast cells stimulated by SP. Moreover, Que reduces IL-6 release from hCBMCs in a dose-dependent manner. Que inhibits cytosolic calcium level increase and NF-kappa B activation. Interestingly, Que is effective prophylactically, while cromolyn must be added together with the trigger or it rapidly loses its effect. In two pilot, open-label, clinical trials, Que significantly decreased contact dermatitis and photosensitivity, skin conditions that do not respond to conventional treatment. In summary, Que is a promising candidate as an effective mast cell inhibitor for allergic and inflammatory diseases, especially in formulations that permit more sufficient oral absorption.

Substance P (SP) induces expression of functional corticotropin-releasing hormone receptor-1 (CRHR-1) in human mast cells.

Corticotropin-releasing hormone (CRH) is secreted under stress and regulates the hypothalamic-pituitary-adrenal axis. However, CRH is also secreted outside the brain where it exerts proinflammatory effects through activation of mast cells, which are increasingly implicated in immunity and inflammation. Substance P (SP) is also involved in inflammatory diseases. Human LAD2 leukemic mast cells express only CRHR-1 mRNA weakly. Treatment of LAD2 cells with SP (0.5-2 µM) for 6 hours significantly increases corticotropin-releasing hormone receptor-1 (CRHR-1) mRNA and protein expression. Addition of CRH (1 µM) to LAD2 cells, which are "primed" with SP for 48 hours and then washed, induces synthesis and release of IL-8, tumor necrosis factor (TNF), and vascular endothelial growth factor (VEGF) 24 hours later. These effects are blocked by pretreatment with an NK-1 receptor antagonist. Treatment of LAD2 cells with CRH (1 µM) for 6 hours induces gene expression of NK-1 as compared with controls. However, repeated stimulation of mast cells with CRH (1 µM) leads to downregulation of CRHR-1 and upregulation in NK-1 gene expression. These results indicate that SP can stimulate mast cells and also increase expression of functional CRHR-1, whereas CRH induces NK-1 gene expression. These results may explain CRHR-1 and NK-1 expression in lesional skin of psoriatic patients.

Mast cells squeeze the heart and stretch the gird: their role in atherosclerosis and obesity.

Mast cells are crucial for the development of allergic and anaphylactic reactions, but they are also involved in acquired and innate immunity. Increasing evidence now implicates mast cells in inflammatory diseases through activation by non-allergic triggers such as neuropeptides and cytokines. This review discusses how mast cells contribute to the inflammatory processes associated with coronary artery disease and obesity. Animal models indicate that mast cells, through the secretion of various vasoactive mediators, cytokines and proteinases, contribute to coronary plaque progression and destabilization, as well as to diet-induced obesity and diabetes. Understanding how mast cells participate in these inflammatory processes could help in the development of unique inhibitors with novel therapeutic applications for these diseases, which constitute the greatest current threat to global human health and welfare.