Carboxypeptidase A3—A Key Component of the Protease Phenotype of Mast Cells

Deep skin fibroblast-mediated macrophage recruitment supports acute wound healing

Epithelial and immune cells have long been appreciated for their contribution to the early immune response after injury; however, much less is known about the role of mesenchymal cells. Using single nuclei RNA-sequencing, we defined changes in gene expression associated with inflammation at 1-day post-wounding (dpw) in mouse skin. Compared to keratinocytes and myeloid cells, we detected enriched expression of pro-inflammatory genes in fibroblasts associated with deeper layers of the skin. In particular, SCA1+ fibroblasts were enriched for numerous chemokines, including CCL2, CCL7, and IL33 compared to SCA1-fibroblasts. Genetic deletion of Ccl2 in fibroblasts resulted in fewer wound bed macrophages and monocytes during injury-induced inflammation with reduced revascularization and re-epithelialization during the proliferation phase of healing. These findings highlight the important contribution of deep skin fibroblast-derived factors to injury-induced inflammation and the impact of immune cell dysregulation on subsequent tissue repair.

Amphibian mast cells serve as barriers to chytrid fungus infections

Global amphibian declines are compounded by deadly disease outbreaks caused by the chytrid fungus, Batrachochytrium dendrobatidis (Bd). Much has been learned about the roles of amphibian skin-produced antimicrobial components and microbiomes in controlling Bd, yet almost nothing is known about the roles of skin-resident immune cells in anti-Bd defenses. Mammalian mast cells reside within and serve as key immune sentinels in barrier tissues like skin. Accordingly, we investigated the roles of Xenopus laevis frog mast cells during Bd infections. Our findings indicate that enrichment of X. laevis skin mast cells confers anti-Bd protection and ameliorates the inflammation-associated skin damage caused by Bd infection. This includes a significant reduction in infiltration of Bd-infected skin by neutrophils, promoting mucin content within cutaneous mucus glands, and preventing Bd-mediated changes to skin microbiomes. Mammalian mast cells are known for their production of the pleiotropic interleukin-4 (IL4) cytokine and our findings suggest that the X. laevis IL4 plays a key role in manifesting the effects seen following cutaneous mast cell enrichment. Together, this work underscores the importance of amphibian skin-resident immune cells in anti-Bd defenses and illuminates a novel avenue for investigating amphibian host-chytrid pathogen interactions.

CCAAT/enhancer-binding protein α-dependent regulation of granule formation in mast cells by intestinal bacteria

The antiallergic effects of gut microbiota have been attracting attention in recent years, but the underlying cellular and molecular mechanisms have not yet been fully understood. In this study, we aimed to investigate these mechanisms specifically focusing on mast cells. Mast cells retain intracellular granules containing various inflammatory mediators such as histamine, which are released outside the cells upon IgE and allergen stimulation. We previously reported that increased expression of the transcription factor, CCAAT/enhancer-binding protein α (C/EBPα), suppresses granule formation in mast cells and that Lacticaseibacillus casei JCM1134T (LC) upregulates C/EBPα levels. Here, granule formation in mouse bone marrow-derived mast cells was suppressed in a MyD88-dependent manner after LC treatment due to C/EBPα-dependent downregulation of the genes encoding serglycin (SRGN) and mast cell protease 4 (Mcpt4). Furthermore, C/EBPα expression was regulated by DNA methylation in the 5' region far upstream of the transcription start site. LC suppressed DNA methylation of specific CpG motifs in the 5' region of the C/EBPα gene. These results conclude that specific gut microbial components, such as those from LC, suppress granule formation in mast cells by inhibiting SRGN and Mcpt4 expression via reduced C/EBPα gene methylation.

Single cell RNA-sequencing of feline peripheral immune cells with V(D)J repertoire and cross species analysis of T lymphocytes

Introduction

The domestic cat (Felis catus) is a valued companion animal and a model for virally induced cancers and immunodeficiencies. However, species-specific limitations such as a scarcity of immune cell markers constrain our ability to resolve immune cell subsets at sufficient detail. The goal of this study was to characterize circulating feline T cells and other leukocytes based on their transcriptomic landscape and T-cell receptor repertoire using single cell RNA-sequencing.

Methods

Peripheral blood from 4 healthy cats was enriched for T cells by flow cytometry cell sorting using a mouse anti-feline CD5 monoclonal antibody. Libraries for whole transcriptome, alpha/beta T cell receptor transcripts and gamma/delta T cell receptor transcripts were constructed using the 10x Genomics Chromium Next GEM Single Cell 5' reagent kit and the Chromium Single Cell V(D)J Enrichment Kit with custom reverse primers for the feline orthologs.

Results

Unsupervised clustering of whole transcriptome data revealed 7 major cell populations - T cells, neutrophils, monocytic cells, B cells, plasmacytoid dendritic cells, mast cells and platelets. Sub cluster analysis of T cells resolved naive (CD4+ and CD8+), CD4+ effector T cells, CD8+ cytotoxic T cells and gamma/delta T cells. Cross species analysis revealed a high conservation of T cell subsets along an effector gradient with equitable representation of veterinary species (horse, dog, pig) and humans with the cat. Our V(D)J repertoire analysis demonstrated a skewed T-cell receptor alpha gene usage and a restricted T-cell receptor gamma junctional length in CD8+ cytotoxic T cells compared to other alpha/beta T cell subsets. Among myeloid cells, we resolved three clusters of classical monocytes with polarization into pro- and anti-inflammatory phenotypes in addition to a cluster of conventional dendritic cells. Lastly, our neutrophil sub clustering revealed a larger mature neutrophil cluster and a smaller exhausted/activated cluster.

Discussion

Our study is the first to characterize subsets of circulating T cells utilizing an integrative approach of single cell RNA-sequencing, V(D)J repertoire analysis and cross species analysis. In addition, we characterize the transcriptome of several myeloid cell subsets and demonstrate immune cell relatedness across different species.

RNA sequencing provides novel insights into the pathogenesis of naturally occurring myxomatous mitral valve disease stage B1 in beagle dogs

Myxomatous mitral valve disease (MMVD) is the most common cardiovascular disorder in dogs with a high prevalence, accounting for approximately 75% of all canine heart disease cases. MMVD is a complex disease and shows variable progression from mild valve leakage to severe regurgitation, potentially leading to heart failure. However, the molecular mechanisms and age-related changes that govern disease progression, especially at the early stage (B1) before the development of discernable clinical signs, remain poorly understood. In this prospective study, we aimed to compare gene expression differences between blood samples of aged beagle dogs with stage B1 MMVD and those of healthy controls using RNA sequencing. Clinical evaluation was also conducted, which revealed minimal differences in radiographic and echocardiographic measurements despite distinct biomarker variations between the two groups. Comparative transcriptomics revealed differentially expressed genes associated with extracellular matrix remodeling, prostaglandin metabolism, immune modulation, and interferon-related pathways, which bear functional relevance for MMVD. In particular, the top 10 over- and under-expressed genes represent promising candidates for influencing pathogenic changes in MMVD stage B1. Our research findings, which include identified variations in clinical markers and gene expression, enhance our understanding of MMVD. Furthermore, they underscore the need for further research into early diagnosis and treatment strategies, as, to the best of our knowledge, no prior studies have explored the precise molecular mechanisms of stage B1 in MMVD through total RNA sequencing.

Cyto- and Histopographic Assessment of CPA3-Positive Testicular Mast Cells in Obstructive and Non-Obstructive Azoospermia

Infertility is an important personal and society disease, of which the male factor represents half of all causes. One of the aspects less studied in male infertility is the immunological testicular microenvironment. Mast cells (MCs), having high potential for regulating spermatogenesis due to fine-tuning the state of the integrative buffer metabolic environment, are one of the most crucial cellular subpopulations of the testicular interstitium. One important component of the MC secretome is proteases that can act as proinflammatory agents and in extracellular matrix (ECM) remodeling. In the testis, MCs are an important cell component of the testicular interstitial tissue (TIT). However, there are still no studies addressing the analysis of a specific MC protease-carboxypeptidase A3 (CPA3)-in cases with altered spermatogenesis. The cytological and histotopographic features of testicular CPA3+ MCs were examined in a study involving 34 men with azoospermia. As revealed, in cases with non-obstructive azoospermia, a higher content of CPA3+ MCs in the TIT and migration to the microvasculature and peritubular tissue of seminiferous tubules were observed when compared with cases with obstructive azoospermia. Additionally, a high frequency of CPA3+ MCs colocalization with fibroblasts, Leydig cells, and elastic fibers was detected in cases with NOA. Thus, CPA3 seems to be of crucial pathogenetic significance in the formation of a profibrogenic background of the tissue microenvironment, which may have direct and indirect effects on spermatogenesis.

Space-Flight- and Microgravity-Dependent Alteration of Mast Cell Population and Protease Expression in Digestive Organs of Mongolian Gerbils

Mast cell (MC)-specific proteases are of particular interest for space biology and medicine due to their biological activity in regulating targets of a specific tissue microenvironment. MC tryptase and chymase obtain the ability to remodel connective tissue through direct and indirect mechanisms. Yet, MC-specific protease expression under space flight conditions has not been adequately investigated. Using immunohistochemical stainings, we analyzed in this study the protease profile of the jejunal, gastric, and hepatic MC populations in three groups of Mongolian gerbils-vivarium control, synchronous experiment, and 12-day orbital flight on the Foton-M3 spacecraft-and in two groups-vivarium control and anti-orthostatic suspension-included in the experiment simulating effects of weightlessness in the ground-based conditions. After a space flight, there was a decreased number of MCs in the studied organs combined with an increased proportion of chymase-positive MCs and MCs with a simultaneous content of tryptase and chymase; the secretion of specific proteases into the extracellular matrix increased. These changes in the expression of proteases were observed both in the mucosal and connective tissue MC subpopulations of the stomach and jejunum. Notably, the relative content of tryptase-positive MCs in the studied organs of the digestive system decreased. Space flight conditions simulated in the synchronous experiment caused no similar significant changes in the protease profile of MC populations. The space flight conditions resulted in an increased chymase expression combined with a decreased total number of protease-positive MCs, apparently due to participating in the processes of extracellular matrix remodeling and regulating the state of the cardiovascular system.

TGFβ Inhibitor A83-01 Enhances Murine HSPC Expansion for Gene Therapy

Murine hematopoietic stem and progenitor cells (HSPCs) are commonly used as model systems during gene therapeutic retroviral vector development and preclinical biosafety assessment. Here, we developed cell culture conditions to maintain stemness and prevent differentiation during HSPC culture. We used the small compounds A83-01, pomalidomide, and UM171 (APU). Highly purified LSK SLAM cells expanded in medium containing SCF, IL-3, FLT3-L, and IL-11 but rapidly differentiated to myeloid progenitors and mast cells. The supplementation of APU attenuated the differentiation and preserved the stemness of HSPCs. The TGFβ inhibitor A83-01 was identified as the major effector. It significantly inhibited the mast-cell-associated expression of FcεR1α and the transcription of genes regulating the formation of granules and promoted a 3800-fold expansion of LSK cells. As a functional readout, we used expanded HSPCs in state-of-the-art genotoxicity assays. Like fresh cells, APU-expanded HSPCs transduced with a mutagenic retroviral vector developed a myeloid differentiation block with clonal restriction and dysregulated oncogenic transcriptomic signatures due to vector integration near the high-risk locus Mecom. Thus, expanded HSPCs might serve as a novel cell source for retroviral vector testing and genotoxicity studies.

Effect of Obesity on the Expression of Genes Associated with Severe Asthma-A Pilot Study

Asthma is a complex condition resulting from the interaction of genes and environment. Obesity is a risk factor to develop asthma and contributes to poor response to asthma therapy and severity. The aim of the study was to evaluate the effect of obesity on the expression levels of genes previously associated with severe asthma. Three groups of subjects were studied: non-obese asthmatics (NOA), obese asthma patients (OA), and non-asthmatic obese subjects (O). Previously reported overexpressed (IL-10, MSR1, PHLDA1, SERPINB2, and CD86) and underexpressed genes (CHI3L1, CPA3, IL-8, and PI3) in severe asthma were analyzed by RT-qPCR in peripheral blood mononuclear cells (PBMCs). In the overexpressed genes, obesity significantly decreased the expression of MSR1 and PHLDA1 and had no effects on CD86, IL-10, and SERPINB2. In underexpressed genes, obesity did not affect PI3, CHI3L1, and IL-8 and significantly reduced CPA3 expression. The results of this study show that obesity should be included among the known factors that can contribute toward modifying the expression of genes associated with asthma and, in particular, severe asthma.

Mast Cells as a Potential Target of Molecular Hydrogen in Regulating the Local Tissue Microenvironment

Knowledge of the biological effects of molecular hydrogen (H₂), hydrogen gas, is constantly advancing, giving a reason for the optimism in several healthcare practitioners regarding the management of multiple diseases, including socially significant ones (malignant neoplasms, diabetes mellitus, viral hepatitis, mental and behavioral disorders). However, mechanisms underlying the biological effects of H₂ are still being actively debated. In this review, we focus on mast cells as a potential target for H₂ at the specific tissue microenvironment level. H₂ regulates the processing of pro-inflammatory components of the mast cell secretome and their entry into the extracellular matrix; this can significantly affect the capacity of the integrated-buffer metabolism and the structure of the immune landscape of the local tissue microenvironment. The analysis performed highlights several potential mechanisms for developing the biological effects of H₂ and offers great opportunities for translating the obtained findings into clinical practice.

Mast Cell Tryptase and Carboxypeptidase A3 in the Formation of Ovarian Endometrioid Cysts

The mechanisms of ovarian endometrioid cyst formation, or cystic ovarian endometriosis, still remain to be elucidated. To address this issue, we analyzed the involvement of mast cell (MC) tryptase and carboxypeptidase A3 (CPA3) in the development of endometriomas. It was found that the formation of endometrioid cysts was accompanied by an increased MC population in the ovarian medulla, as well as by an MC appearance in the cortical substance. The formation of MC subpopulations was associated with endometrioma wall structures. An active, targeted secretion of tryptase and CPA3 to the epithelium of endometrioid cysts, immunocompetent cells, and the cells of the cytogenic ovarian stroma was detected. The identification of specific proteases in the cell nuclei of the ovarian local tissue microenvironment suggests new mechanisms for the regulatory effects of MCs. The cytoplasmic outgrowths of MCs propagate in the structures of the stroma over a considerable distance; they offer new potentials for MC effects on the structures of the ovarian-specific tissue microenvironment under pathological conditions. Our findings indicate the potential roles of MC tryptase and CPA3 in the development of ovarian endometriomas and infer new perspectives on their uses as pharmacological targets in personalized medicine.

Human C1q Tumor Necrosis Factor 8 (CTRP8) defines a novel tryptase+ mast cell subpopulation in the prostate cancer microenvironment

The adipokine C1q Tumor Necrosis Factor 8 (CTRP8) is the least known member of the 15 CTRP proteins and a ligand of the relaxin receptor RXFP1. We previously demonstrated the ability of the CTRP8-RXFP1 interaction to promote motility, matrix invasion, and drug resistance. The lack of specific tools to detect CTRP8 protein severely limits our knowledge on CTRP8 biological functions in normal and tumor tissues. Here, we have generated and characterized the first specific antiserum to human CTRP8 which identified CTRP8 as a novel marker of tryptase+ mast cells (MC_T) in normal human tissues and in the prostate cancer (PC) microenvironment. Using human PC tissue microarrays composed of neoplastic and corresponding tumor-adjacent prostate tissues, we have identified a significantly higher number of CTRP8+ MC_T in the peritumor versus intratumor compartment of PC tissues of Gleason scores 6 and 7. Higher numbers of CTRP8+ MC_T correlated with the clinical parameter of biochemical recurrence. We showed that the human MC line ROSA^{KIT WT} expressed RXFP1 transcripts and responded to CTRP8 treatment with a small but significant increase in cell proliferation. Like the cognate RXFP1 ligand RLN-2 and the small molecule RXFP1 agonist ML-290, CTRP8 reduced degranulation of ROSA^{KIT WT} MC stimulated by the Ca²⁺-ionophore A14187. In conclusion, this is the first report to identify the RXFP1 agonist CTRP8 as a novel marker of MC_T and autocrine/paracrine oncogenic factor within the PC microenvironment.

Mast Cells in Regeneration of the Skin in Burn Wound with Special Emphasis on Molecular Hydrogen Effect

The mechanisms of regeneration for the fibrous component of the connective tissue of the dermis are still insufficiently studied. The aim of this study was to evaluate the effectiveness of the use of molecular hydrogen on the local therapy of a II degree burn wound with the intensification of collagen fibrillogenesis in the skin. We analyzed the involvement of mast cells (MCs) in the regeneration of the collagen fibers of the connective tissue using water with a high content of molecular hydrogen and in a therapeutic ointment for the cell wounds. Thermal burns led to an increase in the skin MC population, accompanied by a systemic rearrangement of the extracellular matrix. The use of molecular hydrogen for the treatment of burn wounds stimulated the regeneration processes by activating the formation of the fibrous component of the dermis, accelerating wound healing. Thus, the intensification of collagen fibrillogenesis was comparable to the effects of a therapeutic ointment. The remodeling of the extracellular matrix correlated with a decrease in the area of damaged skin. Skin regeneration induced by the activation of the secretory activity of MCs may be one of the possible points of implementation of the biological effects of molecular hydrogen in the treatment of burn wounds. Thus, the positive effects of molecular hydrogen on skin repair can be used in clinical practice to increase the effectiveness of therapy after thermal exposure.

Chloroacetate esterase reaction combined with immunohistochemical characterization of the specific tissue microenvironment of mast cells

This study provides a combined histochemical method for detecting enzyme activity of chloroacetate esterase simultaneously with immunolabeling of the components of a specific tissue microenvironment on formalin-fixed, paraffin-embedded specimens. Chromogenic detection of the molecular targets within and outside the mast cells provides novel options in determining the histoarchitectonics of organ-specific mast cell populations, studying the functional significance of chloroacetate esterase and specifying the immune landscape of the tissue microenvironment.

Protease Profile of Tumor-Associated Mast Cells in Melanoma

Mast cells (MCs) produce a variety of mediators, including proteases—tryptase, chymase, and carboxypeptidases—which are important for the immune response. However, a detailed assessment of the mechanisms of biogenesis and excretion of proteases in melanoma has yet to be carried out. In this study, we present data on phenotype and secretory pathways of proteases in MCs in the course of melanoma. The development of melanoma was found to be accompanied by the appearance in the tumor-associated MC population of several pools with a predominant content of one or two specific proteases with a low content or complete absence of others. Elucidation of the molecular and morphological features of the expression of MC proteases in melanoma allows us a fresh perspective of the pathogenesis of the disease, and can be used to clarify MCs classification, the disease prognosis, and evaluate the effectiveness of ongoing antitumor therapy.

Dynamically upregulated mast cell CPA3 patterns in chronic obstructive pulmonary disease and idiopathic pulmonary fibrosis

Background

The mast cell-specific metalloprotease CPA3 has been given important roles in lung tissue homeostasis and disease pathogenesis. However, the dynamics and spatial distribution of mast cell CPA3 expression in lung diseases remain unknown.

Methods

Using a histology-based approach for quantitative spatial decoding of mRNA and protein single cell, this study investigates the dynamics of CPA3 expression across mast cells residing in lungs from control subjects and patients with severe chronic obstructive pulmonary disease (COPD) or idiopathic lung fibrosis (IPF).

Results

Mast cells in COPD lungs had an anatomically widespread increase of CPA3 mRNA (bronchioles p < 0.001, pulmonary vessels p < 0.01, and alveolar parenchyma p < 0.01) compared to controls, while granule-stored CPA3 protein was unaltered. IPF lungs had a significant upregulation of both mast cell density, CPA3 mRNA (p < 0.001) and protein (p < 0.05), in the fibrotic alveolar tissue. Spatial expression maps revealed altered mast cell mRNA/protein quotients in lung areas subjected to disease-relevant histopathological alterations. Elevated CPA3 mRNA also correlated to lung tissue eosinophils, CD3 T cells, and declined lung function. Single-cell RNA sequencing of bronchial mast cells confirmed CPA3 as a top expressed gene with potential links to both inflammatory and protective markers.

Conclusion

This study shows that lung tissue mast cell populations in COPD and IPF lungs have spatially complex and markedly upregulated CPA3 expression profiles that correlate with immunopathological alterations and lung function. Given the proposed roles of CPA3 in tissue homeostasis, remodeling, and inflammation, these alterations are likely to have clinical consequences.

Mast Cell and Basophil Granule Proteases - In Vivo Targets and Function

Proteases are stored in very large amounts within abundant cytoplasmic granules of mast cells (MCs), and in lower amounts in basophils. These proteases are stored in their active form in complex with negatively charged proteoglycans, such as heparin and chondroitin sulfate, ready for rapid release upon MC and basophil activation. The absolute majority of these proteases belong to the large family of chymotrypsin related serine proteases. Three such enzymes are found in human MCs, a chymotryptic enzyme, the chymase, a tryptic enzyme, the tryptase and cathepsin G. Cathepsin G has in primates both chymase and tryptase activity. MCs also express a MC specific exopeptidase, carboxypeptidase A3 (CPA3). The targets and thereby the functions of these enzymes have for many years been the major question of the field. However, the fact that some of these enzymes have a relatively broad specificity has made it difficult to obtain reliable information about the biologically most important targets for these enzymes. Under optimal conditions they may cleave a relatively large number of potential targets. Three of these enzymes, the chymase, the tryptase and CPA3, have been shown to inactivate several venoms from snakes, scorpions, bees and Gila monster. The chymase has also been shown to cleave several connective tissue components and thereby to be an important player in connective tissue homeostasis. This enzyme can also generate angiotensin II (Ang II) by cleavage of Ang I and have thereby a role in blood pressure regulation. It also display anticoagulant activity by cleaving fibrinogen and thrombin. A regulatory function on excessive TH2 immunity has also been observed for both the chymase and the tryptase by cleavage of a highly selective set of cytokines and chemokines. The chymase also appear to have a protective role against ectoparasites such as ticks, mosquitos and leeches by the cleavage of their anticoagulant proteins. We here review the data that has accumulated concerning the potential in vivo functions of these enzymes and we discuss how this information sheds new light on the role of MCs and basophils in health and disease.

New Biomarkers in Anaphylaxis (Beyond Tryptase)

Purpose of Review

The purpose of this review is to provide a better understanding of anaphylaxis pathophysiology and describe the underlying mechanisms, effector cells, and the potential biomarkers involved depending on the anaphylaxis endotypes.

Recent Findings

New insight into the potential relevance of pathways others than IgE-dependent anaphylaxis has been unraveled, as well as other biomarkers than tryptase, such as the role of platelet activation factor, basogranulin, dipeptidyl peptidase I, CCL-2, and other cytokines.

Summary

Gaining knowledge of all the mediators and cellular activation/communication pathways involved in each endotype of anaphylaxis will allow the application of precision medicine in patients with anaphylactic reactions, providing insights to the most appropriate approach in each case and helping to stratify severity and risk prediction.