Emerging mechanisms contributing to mast cell-mediated pathophysiology with therapeutic implications

Mitochondrial activity related genes of mast cells identify poor prognosis and metastasis of ovarian cancer

The pro-tumorigenic or anti-tumorigenic role of tumor infiltrating mast cells (TIMs) in tumors depends not only on the type of cancer and the degree of tumor progression, but also on their location in the tumor bulk. In our investigation, we employed immunohistochemistry to reveal that the mast cells (MCs) in the tumor stroma are positively correlated with metastasis of ovarian cancer (OC), but not in the tumor parenchyma. To delve deeper into the influence of different culture matrix stiffness on MCs' biological functions within the tumor parenchymal and stromal regions, we conducted a transcriptome analysis of the mouse MC line (P815) cultured in two-dimensional (2D) or three-dimensional (3D) culture system. Further research has found that the softer 3D extracellular matrix stiffness could improve the mitochondrial activity of MCs to promote proliferation by increasing the expression levels of mitochondrial activity-related genes, namely Pet100, atp5md, and Cox7a2. Furthermore, employing LASSO regression analysis, we identified that Pet100 and Cox7a2 were closely associated with the prognosis of OC patients. These two genes were subsequently employed to construct a risk score model, which revealed that the high-risk group model as one of the prognostic factors for OC patients. Additionally, the XCell algorithm analysis showed that the high-risk group displayed a broader spectrum of immune cell infiltrations. Our research revealed that TIMs in the tumor stroma could promote the metastasis of OC, and mitochondrial activity-related proteins Pet100/Cox7a2 can serve as biomarkers for prognostic evaluation of OC.

Inhibition of pseudo-allergic reactions by vitamin K3 directly targeting GAB1 in mast cells

BACKGROUND

Vitamin K3 (VK3), a fat-soluble synthetic analog of the vitamin K family, has coagulant, anti-inflammatory, antibacterial, and anticancer properties. Pseudo allergy is a IgE-independent immune response associated with mast cells. This study investigated the role of VK3 in IgE-independent mast cell activation.

METHODS

Substance P (SP) was used to induce LAD2-cell activation in order to analyze the effects of VK3 in vitro. Cutaneous allergy and systemic allergy mouse models were used to analyze the anti-pseudo-allergic effects of VK3. Proteome microarray assays were used to analyze VK3-binding protein. Biolayer interferometry and immunoprecipitation were used to verify interaction between VK3 and its key targets. RNA interference was used to determine the role of GAB1 in LAD2cell activation.

RESULTS

VK3 inhibited SP-induced LAD2-cell activation, and resulted in the release of β-hexosaminidase, histamine and cytokines; VK3 inhibited SP-induced pseudo allergic reactions in mice, and serum histamine and TNF-α levels decreased. Degranulation of skin mast cells was reduced; GAB1 in mast cells was stably bound to VK3. GAB1 participated in SP-induced LAD2-cell activation. GAB1 knockdown in LAD2 cells prevented SP-induced β-hexosaminidase release, calcium mobilization and cell skeletal remodeling. VK3 directly binds to GAB1 and reduces its expression to inhibited SP-induced LAD2 cell activation.

CONCLUSION

The anti-pseudo-allergic activity of VK3 was confirmed in vitro and in vivo. VK3 can inhibit SP-induced mast cell activation by directly targeting GAB1. This study provides new insights on the activity of VK3 and the mechanism of pseudoallergic reaction.

3D bio-printing-based vascular-microtissue electrochemical biosensor for fish parvalbumin detection

A novel 3D bio-printing vascular microtissue biosensor was developed to detect fish parvalbumin quickly. The graphite rod electrode was modified with gold and copper organic framework (Cu-MOF) to improve the sensor properties. Polydopamine-modified multi-wall carbon nanotubes (PDA-MWCNT) were mixed with gelatin methacryloyl (GelMA) to prepare a conductive hydrogel. The conductive hydrogel was mixed with mast cells and endothelial cells to produce a bio-ink for 3D bioprinting. High throughput and standardized preparation of vascular microtissue was performed by stereolithography 3D bioprinting. The vascular microtissue was immobilized on the modified electrode to construct the microtissue sensor. The biosensor's peak current was positively correlated with the fish parvalbumin concentration, and the detection linear concentration range was 0.1 ∼ 2.5 μg/mL. The standard curve equation was IDPV(μA) = 31.30 + 5.46 CPV(μg/mL), the correlation coefficient R2 was 0.990 (n = 5), and the detection limit was 0.065 μg/mL. These indicated a biomimetic microtissue sensor detecting fish parvalbumin has been successfully constructed.

Mast cells in the autonomic nervous system and potential role in disorders with dysautonomia and neuroinflammation

Mast cells (MC) are ubiquitous in the body, and they are critical for not only in allergic diseases but also in immunity and inflammation, including having potential involvement in the pathophysiology of dysautonomias and neuroinflammatory disorders. MC are located perivascularly close to nerve endings and sites such as the carotid bodies, heart, hypothalamus, the pineal gland, and the adrenal gland that would allow them not only to regulate but also to be affected by the autonomic nervous system (ANS). MC are stimulated not only by allergens but also many other triggers including some from the ANS that can affect MC release of neurosensitizing, proinflammatory, and vasoactive mediators. Hence, MC may be able to regulate homeostatic functions that seem to be dysfunctional in many conditions, such as postural orthostatic tachycardia syndrome, autism spectrum disorder, myalgic encephalomyelitis/chronic fatigue syndrome, and Long-COVID syndrome. The evidence indicates that there is a possible association between these conditions and diseases associated with MC activation. There is no effective treatment for any form of these conditions other than minimizing symptoms. Given the many ways MC could be activated and the numerous mediators released, it would be important to develop ways to inhibit stimulation of MC and the release of ANS-relevant mediators.

Dehydroleucodine and xanthatin, two natural anti-inflammatory lactones, inhibit mast cell degranulation by affecting the actin cytoskeleton

Actin remodeling is a critical regulator of mast cell secretion. In previous work, we have shown that dehydroleucodine and xanthatin, two natural α,β-unsaturated lactones, exhibit anti-inflammatory and mast cell stabilizing properties. Based on this background, this study aimed to determine whether the mast cell stabilizing action of these lactones is associated with changes in the actin cytoskeleton. Rat peritoneal mast cells were preincubated in the presence of dehydroleucodine or xanthatin before incubation with compound 48/80. Comparative studies with sodium cromoglycate and latrunculin B were also made. After treatments, different assays were performed on mast cell samples: β-hexosaminidase release, cell viability studies, quantification of mast cells and their state of degranulation by light microscopy, transmission electron microscopy, and actin staining for microscopy observation. Results showed that dehydroleucodine and xanthatin inhibited mast cell degranulation, evidenced by the inhibition of β-hexosaminidase release and decreased degranulated mast cell percentage. At the same time, both lactones altered the F-actin cytoskeleton in mast cells resulting, similarly to Latrunculin B, in a higher concentration of nuclear F-actin when activated by compound 48/80. For the first time, this study describes the biological properties of dehydroleucodine and xanthatin concerning to the rearrangement of actin filaments during stimulated exocytosis in mast cells. These data have important implications for developing new anti-inflammatory and mast cell stabilizing drugs and for designing new small molecules that may interact with the actin cytoskeleton.

Comparative analyses of various IgE-mediated and non-IgE-mediated inducers of mast cell degranulation for in vitro study

In vitro investigations of mast cell (MC) degranulation are essential for studying many diseases, particularly allergy and urticaria. Many MC-degranulation inducers are currently available. However, there is no previous systematic comparative analysis of these available inducers in term of their efficacies to induce MC degranulation. Herein, we performed systematic comparisons of efficacies of five well-known and commonly used MC-degranulation inducers. RBL-2H3 cells were sensitized with 50 ng/ml anti-DNP IgE or biotinylated IgE followed by stimulation with 100 ng/ml DNP-BSA or streptavidin, respectively. For non-IgE-mediated inducers, the cells were treated with 5 µg/ml substance P, compound 48/80, or A23187. At 15-, 30-, 45- and 60-min post-induction, several common MC-degranulation markers (including intracellular [Ca2+], β-hexosaminidase release, tryptase expression by immunofluorescence staining, cellular tryptase level by immunoblotting, secretory tryptase level by immunoblotting, CD63 expression by immunofluorescence staining, and CD63 expression by flow cytometry) were evaluated. The data showed that all these markers significantly increased after activation by all inducers. Among them, A23187 provided the greatest degrees of increases in intracellular [Ca2+] and β-hexosaminidase release at all time-points and upregulation of CD63 at one time-point. These data indicate that all these IgE-mediated (anti-DNP IgE/DNP-BSA and biotinylated IgE/streptavidin) and non-IgE-mediated (substance P, compound 48/80, and A23187) inducers effectively induce MC degranulation, while A23187 seems to be the most effective inducer for MC degranulation.

Communication between Mast Cells and Group 2 Innate Lymphoid Cells in the Skin

The skin is a dynamic organ with a complex immune network critical for maintaining balance and defending against various pathogens. Different types of cells in the skin, such as mast cells (MCs) and group 2 innate lymphoid cells (ILC2s), contribute to immune regulation and play essential roles in the early immune response to various triggers, including allergens. It is beneficial to dissect cell-to-cell interactions in the skin to elucidate the mechanisms underlying skin immunity. The current manuscript concentrates explicitly on the communication pathways between MCs and ILC2s in the skin, highlighting their ability to regulate immune responses, inflammation, and tissue repair. Furthermore, it discusses how the interactions between MCs and ILC2s play a crucial role in various skin conditions, such as autoimmune diseases, dermatological disorders, and allergic reactions. Understanding the complex interactions between MCs and ILC2s in different skin conditions is crucial to developing targeted treatments for related disorders. The discovery of shared pathways could pave the way for novel therapeutic interventions to restore immunological balance in diseased skin tissues.

Hereditary Alpha Tryptasemia: Validation of a Single-Well Multiplex Digital Droplet PCR Assay in a Cohort of Symptomatic Patients

BACKGROUND

Hereditary alpha tryptasemia (HαT) has significant prevalence and potential morbidity in the general population. However, it remains largely undiagnosed in routine clinical diagnostics due to low availability of efficient assessment methods. To address this issue, we developed a reliable and efficient single-well multiplex digital droplet PCR assay.

METHODS

The assay was based on the reconstruction of the TPSAB1 gene through quantification of the ratio of α- and β-tryptase copy number variants (CNV) in a single-well measurement. We performed analytical validation by determining CNV measurement clustering around the expected copy numbers in 281 cases and determined the diagnostic accuracy of basal serum tryptase (BST) to predict HαT and HαT subtypes in 141 symptomatic patients.

RESULTS

The assay determined α- and β-tryptase CNVs with an overall accuracy, expressed as a 99% prediction interval, of 0.03 ± 0.27 copy numbers. The optimal BST cutoff level to predict HαT in symptomatic patients, who had no other explanation for relatively high tryptase levels (i.e., no diagnosis of systemic mastocytosis, myeloid neoplasm, or end-stage renal failure), was 9.2 ng/mL (sensitivity: 98.1%; specificity: 96.6%). HαT showed a linear gene-dose effect, with an average gene-dose increase of 7.5 ng/mL per extra α-tryptase gene.

CONCLUSION

Our single-well multiplex digital droplet PCR assay accurately determined HαT and could be implemented as a state-of-the-art routine diagnostic test. The assay demonstrated a strong correlation with BST and the optimal threshold for identifying HαT in symptomatic patients with unexplained high tryptase concentrations was at a BST level of 9.2 ng/mL.

Topical drug delivery strategies for enhancing drug effectiveness by skin barriers, drug delivery systems and individualized dosing

Topical drug delivery is widely used in various diseases because of the advantages of not passing through the gastrointestinal tract, avoiding gastrointestinal irritation and hepatic first-pass effect, and reaching the lesion directly to reduce unnecessary adverse reactions. The skin helps the organism to defend itself against a huge majority of external aggressions and is one of the most important lines of defense of the body. However, the skin's strong barrier ability is also a huge obstacle to the effectiveness of topical medications. Allowing the bioactive, composition in a drug to pass through the stratum corneum barrier as needed to reach the target site is the most essential need for the bioactive, composition to exert its therapeutic effect. The state of the skin barrier, the choice of delivery system for the bioactive, composition, and individualized disease detection and dosing planning influence the effectiveness of topical medications. Nowadays, enhancing transdermal absorption of topically applied drugs is the hottest research area. However, enhancing transdermal absorption of drugs is not the first choice to improve the effectiveness of all drugs. Excessive transdermal absorption enhances topical drug accumulation at non-target sites and the occurrence of adverse reactions. This paper introduces topical drug delivery strategies to improve drug effectiveness from three perspectives: skin barrier, drug delivery system and individualized drug delivery, describes the current status and shortcomings of topical drug research, and provides new directions and ideas for topical drug research.

A one-pot and eco-friendly synthesis of novel β-substituted-α-halomethyl acrylates and the bioactivity of these compounds in an in vitro model of mast cell degranulation induced by pro-inflammatory stimuli

The goal of the present work was to develop novel β-substituted-α-halomethyl acrylates from a methodology in an aqueous phase and to evaluate their bioactivity as potential inhibitors of mast cell activation. Eleven β-substituted-α-halomethyl acrylates were synthesized through a modified Horner-Wadsworth-Emmons reaction. Compound 48/80 and the calcium ionophore A23187 stimulated the release of β-hexosaminidase from mast cells. The effect induced by compound 48/80 was inhibited by compound 5 (320 µM) and compound 9 (160 and 320 µM) without causing cytotoxic effects. The effect induced by A23187 was inhibited by compound 5 (40, 80, 160, and 320 µM) without affecting cell viability. The inhibitory effects exhibited by compounds 5 and 9 were more potent than those of the reference compound sodium cromoglycate at the same concentrations. The biochemical results were consistent with the morphological findings obtained by light and transmission electron microscopy. This study reports, for the first time, that the new synthetic compounds methyl (Z)- 2-bromo-3-(furan-3-yl)acrylate (compound 5) and methyl (E)- 2-bromo-3-(3-bromophenyl)acrylate (compound 9) strongly inhibit mast cell degranulation, without affecting cell viability. The implications of these results are relevant as a basis for developing new anti-inflammatory and mast cell stabilizing drugs.

Activation of the receptor KIT induces the secretion of exosome-like small extracellular vesicles

The receptor tyrosine kinase (RTK) KIT and its ligand stem cell factor (SCF) are essential for human mast cell (huMC) survival and proliferation. HuMCs expressing oncogenic KIT variants secrete large numbers of extracellular vesicles (EVs). The role KIT plays in regulating EV secretion has not been examined. Here, we investigated the effects of stimulation or inhibition of KIT activity on the secretion of small EVs (sEVs). In huMCs expressing constitutively active KIT, the quantity and quality of secreted sEVs positively correlated with the activity status of KIT. SCF-mediated stimulation of KIT in huMCs or murine MCs, or of transiently expressed KIT in HeLa cells, enhanced the release of sEVs expressing exosome markers. In contrast, ligand-mediated stimulation of the RTK EGFR in HeLa cells did not affect sEV secretion. The release of sEVs induced by either constitutively active or ligand-activated KIT was remarkably decreased when cells were treated with KIT inhibitors, concomitant with reduced exosome markers in sEVs. Similarly, inhibition of oncogenic KIT signalling kinases like PI3K, and MAPK significantly reduced the secretion of sEVs. Thus, activation of KIT and its early signalling cascades stimulate the secretion of exosome-like sEVs in a regulated fashion, which may have implications for KIT-driven functions.

CREB Is Indispensable to KIT Function in Human Skin Mast Cells-A Positive Feedback Loop between CREB and KIT Orchestrates Skin Mast Cell Fate

Skin mast cells (MCs) are critical effector cells in acute allergic reactions, and they contribute to chronic dermatoses like urticaria and atopic and contact dermatitis. KIT represents the cells' crucial receptor tyrosine kinase, which orchestrates proliferation, survival, and functional programs throughout the lifespan. cAMP response element binding protein (CREB), an evolutionarily well-conserved transcription factor (TF), regulates multiple cellular programs, but its function in MCs is poorly understood. We recently reported that CREB is an effector of the SCF (Stem Cell Factor)/KIT axis. Here, we ask whether CREB may also act upstream of KIT to orchestrate its functioning. Primary human MCs were isolated from skin and cultured in SCF+IL-4 (Interleukin-4). Pharmacological inhibition (666-15) and RNA interference served to manipulate CREB function. We studied KIT expression using flow cytometry and RT-qPCR, KIT-mediated signaling using immunoblotting, and cell survival using scatterplot and caspase-3 activity. The proliferation and cycle phases were quantified following BrdU incorporation. Transient CREB perturbation resulted in reduced KIT expression. Conversely, microphthalmia transcription factor (MITF) was unnecessary for KIT maintenance. KIT attenuation secondary to CREB was associated with heavily impaired KIT functional outputs, like anti-apoptosis and cell cycle progression. Likewise, KIT-elicited phosphorylation of ERK1/2 (Extracellular Signal-Regulated Kinase 1/2), AKT, and STAT5 (Signal Transducer and Activator of Transcription) was substantially diminished upon CREB inhibition. Surprisingly, the longer-term interference of CREB led to complete cell elimination, in a way surpassing KIT inhibition. Collectively, we reveal CREB as non-redundant in MCs, with its absence being incompatible with skin MCs' existence. Since SCF/KIT regulates CREB activity and, vice versa, CREB is required for KIT function, a positive feedforward loop between these elements dictates skin MCs' fate.

Degranulation of human mast cells: modulation by P2 receptors' agonists

Since the late 1970s, there has been an alarming increase in the incidence of asthma and its morbidity and mortality. Acute obstruction and inflammation of allergic asthmatic airways are frequently caused by inhalation of exogenous substances such as allergens cross-linking IgE receptors expressed on the surface of the human lung mast cells (HLMC). The degree of constriction of human airways produced by identical amounts of inhaled allergens may vary from day to day and even hour to hour. Endogenous factors in the human mast cell (HMC)'s microenvironment during allergen exposure may markedly modulate the degranulation response. An increase in allergic responsiveness may significantly enhance bronchoconstriction and breathlessness. This review focuses on the role that the ubiquitous endogenous purine nucleotide, extracellular adenosine 5'-triphosphate (ATP), which is a component of the damage-associated molecular patterns, plays in mast cells' physiology. ATP activates P2 purinergic cell-surface receptors (P2R) to trigger signaling cascades resulting in heightened inflammatory responses. ATP is the most potent enhancer of IgE-mediated HLMC degranulation described to date. Current knowledge of ATP as it relates to targeted receptor(s) on HMC along with most recent studies exploring HMC post-receptor activation pathways are discussed. In addition, the reviewed studies may explain why brief, minimal exposures to allergens (e.g., dust, cat, mouse, and grass) can unpredictably lead to intense clinical reactions. Furthermore, potential therapeutic approaches targeting ATP-related enhancement of allergic reactions are presented.

Potential Role of Moesin in Regulating Mast Cell Secretion

Mast cells have existed for millions of years in species that never suffer from allergic reactions. Hence, in addition to allergies, mast cells can play a critical role in homeostasis and inflammation via secretion of numerous vasoactive, pro-inflammatory and neuro-sensitizing mediators. Secretion may utilize different modes that involve the cytoskeleton, but our understanding of the molecular mechanisms regulating secretion is still not well understood. The Ezrin/Radixin/Moesin (ERM) family of proteins is involved in linking cell surface-initiated signaling to the actin cytoskeleton. However, how ERMs may regulate secretion from mast cells is still poorly understood. ERMs contain two functional domains connected through a long α-helix region, the N-terminal FERM (band 4.1 protein-ERM) domain and the C-terminal ERM association domain (C-ERMAD). The FERM domain and the C-ERMAD can bind to each other in a head-to-tail manner, leading to a closed/inactive conformation. Typically, phosphorylation on the C-terminus Thr has been associated with the activation of ERMs, including secretion from macrophages and platelets. It has previously been shown that the ability of the so-called mast cell "stabilizer" disodium cromoglycate (cromolyn) to inhibit secretion from rat mast cells closely paralleled the phosphorylation of a 78 kDa protein, which was subsequently shown to be moesin, a member of ERMs. Interestingly, the phosphorylation of moesin during the inhibition of mast cell secretion was on the N-terminal Ser56/74 and Thr66 residues. This phosphorylation pattern could lock moesin in its inactive state and render it inaccessible to binding to the Soluble NSF attachment protein receptors (SNAREs) and synaptosomal-associated proteins (SNAPs) critical for exocytosis. Using confocal microscopic imaging, we showed moesin was found to colocalize with actin and cluster around secretory granules during inhibition of secretion. In conclusion, the phosphorylation pattern and localization of moesin may be important in the regulation of mast cell secretion and could be targeted for the development of effective inhibitors of secretion of allergic and inflammatory mediators from mast cells.

Research Advances in Mast Cell Biology and Their Translation Into Novel Therapies for Anaphylaxis

Anaphylaxis is an acute, potentially life-threatening systemic allergic reaction for which there are no known reliable preventative therapies. Its primary cell mediator, the mast cell, has several pathophysiologic roles and functions in IgE-mediated reactions that continue to be poorly understood. Recent advances in the understanding of allergic mechanisms have identified novel targets for inhibiting mast cell function and activation. The prevention of anaphylaxis is within reach with new drugs that could modulate immune tolerance, mast cell proliferation and differentiation, and IgE regulation and production. Several US Food and Drug Administration-approved drugs for chronic urticaria, mastocytosis, and cancer are also being repurposed to prevent anaphylaxis. New therapeutics have not only shown promise in potential efficacy for preventing IgE-mediated reactions, but in some cases, they are able to inform us about mast cell mechanisms in vivo. This review summarizes the most recent advances in the treatment of anaphylaxis that have arisen from new pharmacologic tools and our current understanding of mast cell biology.

Recombinant SARS-CoV-2 Spike Protein Stimulates Secretion of Chymase, Tryptase, and IL-1β from Human Mast Cells, Augmented by IL-33

SARS-CoV-2 infects cells via its spike (S) protein binding to its surface receptor angiotensin-converting enzyme 2 (ACE2) and results in the production of multiple proinflammatory cytokines, especially in the lungs, leading to what is known as COVID-19. However, the cell source and the mechanism of secretion of such cytokines have not been adequately characterized. In this study, we used human cultured mast cells that are plentiful in the lungs and showed that recombinant SARS-CoV-2 full-length S protein (1-10 ng/mL), but not its receptor-binding domain (RBD), stimulates the secretion of the proinflammatory cytokine interleukin-1β (IL-1β) as well as the proteolytic enzymes chymase and tryptase. The secretion of IL-1β, chymase, and tryptase is augmented by the co-administration of interleukin-33 (IL-33) (30 ng/mL). This effect is mediated via toll-like receptor 4 (TLR4) for IL-1β and via ACE2 for chymase and tryptase. These results provide evidence that the SARS-CoV-2 S protein contributes to inflammation by stimulating mast cells through different receptors and could lead to new targeted treatment approaches.

Targeting active sites of inflammation using inherent properties of tissue-resident mast cells

Mast cells play a pivotal role in initiating and directing host's immune response. They reside in tissues that primarily interface with the external environment. Activated mast cells respond to environmental cues throughout acute and chronic inflammation through releasing immune mediators via rapid degranulation, or long-term de novo expression. Mast cell activation results in the rapid release of a variety of unique enzymes and reactive oxygen species. Furthermore, the increased density of mast cell unique receptors like mas related G protein-coupled receptor X2 also characterizes the inflamed tissues. The presence of these molecules (either released mediators or surface receptors) are particular to the sites of active inflammation, and are a result of mast cell activation. Herein, the molecular design principles for capitalizing on these novel mast cell properties is discussed with the goal of manipulating localized inflammation. STATEMENT OF SIGNIFICANCE: Mast cells are immune regulating cells that play a crucial role in both innate and adaptive immune responses. The activation of mast cells causes the release of multiple unique profiles of biomolecules, which are specific to both tissue and disease. These unique characteristics are tightly regulated and afford a localized stimulus for targeting inflammatory diseases. Herein, these important mast cell attributes are discussed in the frame of highlighting strategies for the design of bioresponsive functional materials to target regions of inflammations.

Role of SARS-CoV-2 Spike-Protein-Induced Activation of Microglia and Mast Cells in the Pathogenesis of Neuro-COVID

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) causes coronavirus disease 2019 (COVID-19). About 45% of COVID-19 patients experience several symptoms a few months after the initial infection and develop post-acute sequelae of SARS-CoV-2 (PASC), referred to as "Long-COVID," characterized by persistent physical and mental fatigue. However, the exact pathogenetic mechanisms affecting the brain are still not well-understood. There is increasing evidence of neurovascular inflammation in the brain. However, the precise role of the neuroinflammatory response that contributes to the disease severity of COVID-19 and long COVID pathogenesis is not clearly understood. Here, we review the reports that the SARS-CoV-2 spike protein can cause blood-brain barrier (BBB) dysfunction and damage neurons either directly, or via activation of brain mast cells and microglia and the release of various neuroinflammatory molecules. Moreover, we provide recent evidence that the novel flavanol eriodictyol is particularly suited for development as an effective treatment alone or together with oleuropein and sulforaphane (ViralProtek®), all of which have potent anti-viral and anti-inflammatory actions.

Chymase Inhibition Resolves and Prevents Deep Vein Thrombosis Without Increasing Bleeding Time in the Mouse Model

Background Deep vein thrombosis (DVT) is the primary cause of pulmonary embolism and the third most life-threatening cardiovascular disease in North America. Post-DVT anticoagulants, such as warfarin, heparin, and direct oral anticoagulants, reduce the incidence of subsequent venous thrombi. However, all currently used anticoagulants affect bleeding time at various degrees, and there is therefore a need for improved therapeutic regimens in DVT. It has recently been shown that mast cells play a crucial role in a DVT murine model. The underlying mechanism involved in the prothrombotic properties of mast cells, however, has yet to be identified. Methods and Results C57BL/6 mice and mouse mast cell protease-4 (mMCP-4) genetically depleted mice (mMCP-4 knockout) were used in 2 mouse models of DVT, partial ligation (stenosis) and ferric chloride-endothelial injury model of the inferior vena cava. Thrombus formation and impact of genetically repressed or pharmacologically (specific inhibitor TY-51469) inhibited mMCP-4 were evaluated by morphometric measurements of thrombi immunochemistry (mouse and human DVT), color Doppler ultrasound, bleeding times, and enzymatic activity assays ex vivo. Recombinant chymases, mMCP-4 (mouse) and CMA-1 (human), were used to characterize the interaction with murine and human plasmin, respectively, by mass spectrometry and enzymatic activity assays. Inhibiting mast cell-generated mMCP-4, genetically or pharmacologically, resolves and prevents venous thrombus formation in both DVT models. Inferior vena cava blood flow obstruction was observed in the stenosis model after 6 hours of ligation, in control- but not in TY-51469-treated mice. In addition, chymase inhibition had no impact on bleeding times of healthy or DVT mice. Furthermore, endogenous chymase limits plasmin activity in thrombi ex vivo. Recombinant mouse or human chymase degrades/inactivates purified plasmin in vitro. Finally, mast cell-containing immunoreactive chymase was identified in human DVT. Conclusions This study identified a major role for mMCP-4, a granule-localized protease of chymase type, in DVT formation. These findings support a novel pharmacological strategy to resolve or prevent DVT without affecting the coagulation cascade through the inhibition of chymase activity.

CREB Is Activated by the SCF/KIT Axis in a Partially ERK-Dependent Manner and Orchestrates Survival and the Induction of Immediate Early Genes in Human Skin Mast Cells

cAMP response element binding protein (CREB) functions as a prototypical stimulus-inducible transcription factor (TF) that initiates multiple cellular changes in response to activation. Despite pronounced expression in mast cells (MCs), CREB function is surprisingly ill-defined in the lineage. Skin MCs (skMCs) are critical effector cells in acute allergic and pseudo-allergic settings, and they contribute to various chronic dermatoses such as urticaria, atopic dermatitis, allergic contact dermatitis, psoriasis, prurigo, rosacea and others. Using MCs of skin origin, we demonstrate herein that CREB is rapidly phosphorylated on serine-133 upon SCF-mediated KIT dimerization. Phosphorylation initiated by the SCF/KIT axis required intrinsic KIT kinase activity and partially depended on ERK1/2, but not on other kinases such as p38, JNK, PI3K or PKA. CREB was constitutively nuclear, where phosphorylation occurred. Interestingly, ERK did not translocate to the nucleus upon SCF activation of skMCs, but a fraction was present in the nucleus at baseline, and phosphorylation was prompted in the cytoplasm and nucleus in situ. CREB was required for SCF-facilitated survival, as demonstrated with the CREB-selective inhibitor 666-15. Knock-down of CREB by RNA interference duplicated CREB's anti-apoptotic function. On comparison with other modules (PI3K, p38 and MEK/ERK), CREB was equal or more potent at survival promotion. SCF efficiently induces immediate early genes (IEGs) in skMCs (FOS, JUNB and NR4A2). We now demonstrate that CREB is an essential partaker in this induction. Collectively, the ancient TF CREB is a crucial component of skMCs, where it operates as an effector of the SCF/KIT axis, orchestrating IEG induction and lifespan.

DNA methylation regulatory patterns and underlying pathways behind the co-pathogenesis of allergic rhinitis and chronic spontaneous urticaria

Background

Allergic rhinitis (AR) and chronic spontaneous urticaria (CSU) are often concurrent in patients. Changes in DNA methylation affect T cell biological processes, which may explain the occurrence and progression of comorbidity. However, downstream regulatory pathways of DNA methylation in two diseases and the underlying mechanisms have not been fully elucidated.

Methods

The GSE50101, GSE72541, GSE50222 and OEP002482 were mined for the identification of differentially expressed genes (DEGs) or co-expressed genes and differentially methylated genes (DMGs) in AR and CSU patients. We applied GO analysis and consensus clustering to study the potential functions and signal pathways of selected genes in two diseases. GSVA and logistic regression analysis were used to find the regulatory pathway between DNA methylation and activation patterns of CD4+ T cells. Besides, we used the Illumina 850k chip to detect DNA methylation expression profiles and recognize the differentially methylated CpG positions (DMPs) on corresponding genes. Finally, we annotated the biological process of these genes using GO and KEGG pathway analysis.

Result

The AR-related DEGs were found closely related to the differentiation and activation of CD4+ T cells. The DEGs or co-expressed genes of CD4+ T cells in AR and CSU patients were also clustered using GO and KEGG analysis and we got 57 co-regulatory pathways. Furthermore, logistic regression analysis showed that the regulation of cellular component size was closely related to the activation of CD4+ T cells regulated by DNA methylation. We got self-tested data using the Illumina 850k chip and identified 98 CpGs that were differentially methylated in patients. Finally, we mapped the DMPs to 15 genes and found that they were mainly enriched in the same CD4+T cell regulating pathway.

Conclusion

Our study indicated that DNA methylation affected by pollen participated in the activation patterns of CD4 + T cells, providing a novel direction for the symptomatic treatment of the co-occurrence of AR and CSU.

CRISPR/Cas9-engineering of HMC-1.2 cells renders a human mast cell line with a single D816V-KIT mutation: An improved preclinical model for research on mastocytosis

The HMC-1.2 human mast cell (huMC) line is often employed in the study of attributes of neoplastic huMCs as found in patients with mastocytosis and their sensitivity to interventional drugs in vitro and in vivo. HMC-1.2 cells express constitutively active KIT, an essential growth factor receptor for huMC survival and function, due to the presence of two oncogenic mutations (D816V and V560G). However, systemic mastocytosis is commonly associated with a single D816V-KIT mutation. The functional consequences of the coexisting KIT mutations in HMC-1.2 cells are unknown. We used CRISPR/Cas9-engineering to reverse the V560G mutation in HMC-1.2 cells, resulting in a subline (HMC-1.3) with a single mono-allelic D816V-KIT variant. Transcriptome analyses predicted reduced activity in pathways involved in survival, cell-to-cell adhesion, and neoplasia in HMC-1.3 compared to HMC-1.2 cells, with differences in expression of molecular components and cell surface markers. Consistently, subcutaneous inoculation of HMC-1.3 into mice produced significantly smaller tumors than HMC-1.2 cells, and in colony assays, HMC-1.3 formed less numerous and smaller colonies than HMC-1.2 cells. However, in liquid culture conditions, the growth of HMC-1.2 and HMC-1.3 cells was comparable. Phosphorylation levels of ERK1/2, AKT and STAT5, representing pathways associated with constitutive oncogenic KIT signaling, were also similar between HMC-1.2 and HMC-1.3 cells. Despite these similarities in liquid culture, survival of HMC-1.3 cells was diminished in response to various pharmacological inhibitors, including tyrosine kinase inhibitors used clinically for treatment of advanced systemic mastocytosis, and JAK2 and BCL2 inhibitors, making HMC-1.3 more susceptible to these drugs than HMC-1.2 cells. Our study thus reveals that the additional V560G-KIT oncogenic variant in HMC-1.2 cells modifies transcriptional programs induced by D816V-KIT, confers a survival advantage, alters sensitivity to interventional drugs, and increases the tumorigenicity, suggesting that engineered huMCs with a single D816V-KIT variant may represent an improved preclinical model for mastocytosis.

Selective immunocapture reveals neoplastic human mast cells secrete distinct microvesicle- and exosome-like populations of KIT-containing extracellular vesicles

Activating mutations in the receptor KIT promote the dysregulated proliferation of human mast cells (huMCs). The resulting neoplastic huMCs secrete extracellular vesicles (EVs) that can transfer oncogenic KIT among other cargo into recipient cells. Despite potential contributions to diseases, KIT-containing EVs have not been thoroughly investigated. Here, we isolated and characterized KIT-EV subpopulations released by neoplastic huMCs using an immunocapture approach that selectively isolates EVs containing KIT in its proper topology. Immunocapture of EVs on KIT antibody-coated electron microscopy (EM) affinity grids allowed to assess the morphology and size of KIT-EVs. Immunoblot analysis demonstrated KIT-EVs have a distinct protein profile from KIT-depleted EVs, contain exosome and microvesicle markers, and are separated into these subtypes by ultracentrifugation. Cell treatment with sphingomyelinase inhibitors shifted the protein content among KIT-EV subtypes, suggesting different biogenesis routes. Proteomic analysis revealed huMC KIT-EVs are enriched in proteins involved in signalling, immune responses, and cell migration, suggesting diverse biological functions, and indicated neoplastic huMCs disseminate KIT via shuttling in heterogeneous microvesicle- and exosome-like EVs. Further, selective KIT-immunocapture will enable the enrichment of specific huMC-derived EVs from complex human biosamples and facilitate an understanding of their in vivo functions and potential to serve as biomarkers of specific biological pathologies.

Targeting Mast Cells in Allergic Disease: Current Therapies and Drug Repurposing

The incidence of allergic disease has grown tremendously in the past three generations. While current treatments are effective for some, there is considerable unmet need. Mast cells are critical effectors of allergic inflammation. Their secreted mediators and the receptors for these mediators have long been the target of allergy therapy. Recent drugs have moved a step earlier in mast cell activation, blocking IgE, IL-4, and IL-13 interactions with their receptors. In this review, we summarize the latest therapies targeting mast cells as well as new drugs in clinical trials. In addition, we offer support for repurposing FDA-approved drugs to target mast cells in new ways. With a multitude of highly selective drugs available for cancer, autoimmunity, and metabolic disorders, drug repurposing offers optimism for the future of allergy therapy.

The Role of Crosstalk of Immune Cells in Pathogenesis of Chronic Spontaneous Urticaria

Chronic spontaneous urticaria (CSU) is defined as recurrent episodes of spontaneous wheal development and/or angioedema for more than six weeks and at least twice a week. The core link in the pathogenesis of CSU is the activation of mast cells, T cells, eosinophils, and other immune cells infiltrating around the small venules of the lesion. Increased vascular permeability, vasodilatation, and recruitment of inflammatory cells directly depend on mast cell mediators’ release. Complex regulatory systems tightly influence the critical roles of mast cells in the local microenvironment. The bias toward Th2 inflammation and autoantibodies derived from B cells, histamine expressed by basophils, and initiation of the extrinsic coagulation pathway by eosinophils or monocytes exerts powerful modulatory influences on mast cells. Cell-to-cell interactions between mast cells and eosinophils/T cells also are regulators of their function and may involve CSU’s pathomechanism. This review summarizes up-to-date knowledge regarding the crosstalk between mast cells and other immune cells, providing the impetus to develop new research concepts and treatment strategies for CSU.

A Critical Function for the Transcription Factors GLI1 and GLI2 in the Proliferation and Survival of Human Mast Cells

Mast cell hyperactivity and accumulation in tissues are associated with allergy and other mast cell-related disorders. However, the molecular pathways regulating mast cell survival in homeostasis and disease are not completely understood. As glioma-associated oncogene (GLI) proteins are involved in both tissue homeostasis and in the hematopoietic system by regulating cell fate decisions, we sought to investigate the role for GLI proteins in the control of proliferation and survival of human mast cells. GLI1 transcripts were present in primary human mast cells and mast cell lines harboring or not activating mutations in the tyrosine kinase receptor KIT (HMC-1.1 and HMC-1.2, and LAD2 cells, respectively), while GLI2 transcripts were only present in HMC-1.1 and HMC-1.2 cells, suggesting a role for oncogenic KIT signaling in the regulation of GLI2. Reduction in GLI activity by small molecule inhibitors, or by shRNA-mediated knockdown of GLI1 or GLI2, led to increases in apoptotic cell death in both cultured human and murine mast cells, and reduced the number of peritoneal mast cells in mice. Although GLI proteins are typically activated via the hedgehog pathway, steady-state activation of GLI in mast cells occurred primarily via non-canonical pathways. Apoptosis induced by GLI silencing was associated with a downregulation in the expression of KIT and of genes that influence p53 stability and function including USP48, which promotes p53 degradation; and iASPP, which inhibits p53-induced transcription, thus leading to the induction of p53-regulated apoptotic genes. Furthermore, we found that GLI silencing inhibited the proliferation of neoplastic mast cell lines, an effect that was more pronounced in rapidly growing cells. Our findings support the conclusion that GLI1/2 transcription factors are critical regulators of mast cell survival and that their inhibition leads to a significant reduction in the number of mast cells in vitro and in vivo, even in cells with constitutively active KIT variants. This knowledge can potentially be applicable to reducing mast cell burden in mast cell-related diseases.

Selected recent advances in understanding the role of human mast cells in health and disease

Mast cells are highly granular tissue-resident cells and key drivers of inflammation, particularly in allergies as well as in other inflammatory diseases. Most mast cell research was initially conducted in rodents but has increasingly shifted to the human system, with the advancement of research technologies and methodologies. Today we can analyze primary human cells including rare subpopulations, we can produce and maintain mast cells isolated from human tissues, and there are several human mast cell lines. These tools have substantially facilitated our understanding of their role and function in different organs in both health and disease. We can now define more clearly where human mast cells originate from, how they develop, which mediators they store, produce de novo, and release, how they are activated and by which receptors, and which neighbouring cells they interact with and by which mechanisms. Considerable progress has also been made regarding the potential contribution of mast cells to disease, which, in turn, has led to the development of novel approaches for preventing key pathogenic effects of mast cells, heralding the era of mast cell-targeted therapeutics. In this review, we present and discuss a selection of some of the most significant advancements and remaining gaps in our understanding of human mast cells during the last 25 years, with a focus on clinical relevance.

Mast Cells Mediate Inflammatory Injury and Aggravate Neurological Impairment in Experimental Subarachnoid Hemorrhage Through Microglial PAR-2 Pathway

Subarachnoid hemorrhage (SAH) is a devastating cerebrovascular disease with high mortality and disability. Aberrant neuroinflammation has been identified as a critical factor accounting for the poor prognosis of SAH patients. Mast cells (MCs), the sentinel cells of the immune system, play a critical in the early immune reactions and participate in multiple pathophysiological process. However, the exact role of MCs on the pathophysiological process after SAH has not been fully understood. The current study was conducted to determine the role of MCs and MC stabilization in the context of SAH. Mouse SAH model was established by endovascular perforation process. Mice received saline or cromolyn (MC stabilizer) or compound 48/80 (MCs degranulator). Post-SAH evaluation included neurobehavioral test, western blot, immunofluorescence, and toluidine blue staining. We demonstrated that SAH induced MCs activation/degranulation. Administration of MC stabilizer cromolyn conferred a better neurologic outcome and decreased brain edema when compared with SAH+vehicle group. Furthermore, cromolyn significantly inhibited neuroinflammatory response and alleviated neuronal damage after SAH. However, pharmacological activation of MCs with compound 48/80 dramatically aggravated SAH-induced brain injury and exacerbated neurologic outcomes. Notably, pharmacological inhibition of microglial PAR-2 significantly reversed MCs-induced inflammatory response and neurological impairment. Additionally, the effect of MCs-derived tryptase in mediating neuroinflammation was also abolished by the microglial PAR-2 blockage in vitro. Taken together, MCs yielded inflammatory injury through activating microglia-related neuroinflammation after SAH. These data shed light on the notion that MCs might be a novel and promising therapeutic target for SAH.

Licochalcone A inhibits MAS-related GPR family member X2-induced pseudo-allergic reaction by suppressing nuclear migration of nuclear factor-κB

Licochalcone A (Lico A) is a natural flavonoid belonging to the class of substituted chalcone that has various biological effects. Mast cells (MCs) are innate immune cells that mediate hypersensitivity and pseudo-allergic reactions. MAS-related GPR family member X2 (MRGPRX2) on MCs has been recognized as the main receptor for pseudo-allergic reactions. In this study, we investigated the anti-pseudo-allergy effect of Lico A and its underlying mechanism. Substance P (SP), as an MC activator, was used to establish an in vitro and in vivo model of pseudo-allergy. The in vivo effect of Lico A was investigated using passive cutaneous anaphylaxis (PCA) and active systemic allergy, along with degranulation, Ca²⁺ influx in vitro. SP-induced laboratory of allergic disease 2 (LAD2) cell mRNA expression was explored using RNA-seq, and Lico A inhibited LAD2 cell activation by reverse transcription polymerase chain reaction (RT-PCR), western blotting, and immunofluorescence staining. Lico A showed an inhibitory effect on SP-induced MC activation and pseudo-allergy both in vitro and in vivo. The nuclear factor (NF)-κB pathway is involved in MRGPRX2 induced MC activation, which is inhibited by Lico A. In conclusion, Lico A inhibited the pseudo-allergic reaction mediated by MRGPRX2 by blocking NF-κB nuclear migration.

Chrysin Inhibits Pseudo-allergic Reaction by Suppressing Mitochondrial STAT3 Activation via MAS-Related GPR Family Member X2

Chrysin, one of the most pharmacologically active natural flavonoids, has been extracted from various plants. Mast cells are an important part of innate immunity-mediating anaphylaxis. Pseudo-allergic reactions are currently believed to be associated with the MAS-related GPR family member X2 (MrgX2). In this study, the anti-pseudo allergy effect of chrysin and its underlying mechanisms were studied in vitro and in vivo. Chrysin inhibited passive cutaneous anaphylaxis and systemic pseudo-allergy in vivo. LAD2 cell degranulation, calcium ion (Ca²⁺) influx, and adenosine 5'-triphosphate (ATP) content were significantly suppressed in a dose-dependent manner. Chrysin suppressed pseudo-allergic reactions through the PLC/IP3/Ca²⁺ and ERK/STAT3 serine 727 pathways downstream of MrgX2. Therefore, mitochondrial ATP, but not glycolysis, is vital for pseudo-allergic reactions mediated by MrgX2. This study provides new insights for the treatment of pseudo-allergy.