Increased cardiac mast cell density and mediator release in patients with dilated cardiomyopathy

Histamine receptors in heart failure

The biogenic amine, histamine, is found predominantly in mast cells, as well as specific histaminergic neurons. Histamine exerts its many and varied actions via four G-protein-coupled receptors numbered one through four. Histamine has multiple effects on cardiac physiology, mainly via the histamine 1 and 2 receptors, which on a simplified level have opposing effects on heart rate, force of contraction, and coronary vasculature function. In heart failure, the actions of the histamine receptors are complex, the histamine 1 receptor appears to have detrimental actions predominantly in the coronary vasculature, while the histamine 2 receptor mediates adverse effects on cardiac remodeling via actions on cardiomyocytes, fibroblasts, and even endothelial cells. Conversely, there is growing evidence that the histamine 3 receptor exerts protective actions when activated. Little is known about the histamine 4 receptor in heart failure. Targeting histamine receptors as a therapeutic approach for heart failure is an important area of investigation given the over-the-counter access to many compounds targeting these receptors, and thus the relatively straight forward possibility of drug repurposing. In this review, we briefly describe histamine receptor signaling and the actions of each histamine receptor in normal cardiac physiology, before describing in more detail the known role of each histamine receptor in adverse cardiac remodeling and heart failure. This includes information from both clinical studies and experimental animal models. It is the goal of this review article to bring more focus to the possibility of targeting histamine receptors as therapy for heart failure.

Mast Cells in Diabetes and Diabetic Wound Healing

Mast cells (MCs) are granulated, immune cells of the myeloid lineage that are present in connective tissues. Apart from their classical role in allergies, MCs also mediate various inflammatory responses due to the nature of their secretory products. They are involved in important physiological and pathophysiological responses related to inflammation, chronic wounds, and autoimmune diseases. There are also indications that MCs are associated with diabetes and its complications. MCs and MC-derived mediators participate in all wound healing stages and are involved in the pathogenesis of non-healing, chronic diabetic foot ulcers (DFUs). More specifically, recent work has shown increased degranulation of skin MCs in human diabetes and diabetic mice, which is associated with impaired wound healing. Furthermore, MC stabilization, either systemic or local at the skin level, improves wound healing in diabetic mice. Understanding the precise role of MCs in wound progression and healing processes can be of critical importance as it can lead to the development of new targeted therapies for diabetic foot ulceration, one of the most devastating complications of diabetes.

Leukocyte-Dependent Regulation of Cardiac Fibrosis

Cardiac fibrosis begins as an intrinsic response to injury or ageing that functions to preserve the tissue from further damage. Fibrosis results from activated cardiac myofibroblasts, which secrete extracellular matrix (ECM) proteins in an effort to replace damaged tissue; however, excessive ECM deposition leads to pathological fibrotic remodeling. At this extent, fibrosis gravely disturbs myocardial compliance, and ultimately leads to adverse outcomes like heart failure with heightened mortality. As such, understanding the complexity behind fibrotic remodeling has been a focal point of cardiac research in recent years. Resident cardiac fibroblasts and activated myofibroblasts have been proven integral to the fibrotic response; however, several findings point to additional cell types that may contribute to the development of pathological fibrosis. For one, leukocytes expand in number after injury and exhibit high plasticity, thus their distinct role(s) in cardiac fibrosis is an ongoing and controversial field of study. This review summarizes current findings, focusing on both direct and indirect leukocyte-mediated mechanisms of fibrosis, which may provide novel targeted strategies against fibrotic remodeling.

Mast cell-deficiency protects mice from streptozotocin-induced diabetic cardiomyopathy

Mast cells (MCs) have been implicated in the pathogenesis of cardiometabolic diseases by releasing pro-inflammatory mediators. Patients and animals with diabetic cardiomyopathy (DCM) also show inflammatory cell accumulation in the heart. Here, we detected MCs in mouse heart after streptozotocin (STZ)-induced DCM. DCM production caused significant systole and diastole interventricular septum and left ventricular (LV) posterior wall thinning, and systolic LV internal dilation in wild-type (WT) mice. DCM production also led to significant reductions of fractional shortening percentage, heart rate, body weight, heart weight, and significant increases of kidney, pancreas, and lung weight to body weight ratios, and blood hemoglobin HbA1c and glucose levels in WT mice. All these changes were improved or disappeared in MC-deficient Kit^W-sh/W-sh mice. In the myocardium from WT DCM mice, we detected significant decrease of cardiac cell proliferation and increases of cardiac cell death, chemokine expression, macrophage infiltration, inflammatory cytokine expression, and collagen deposition. These changes were also improved or disappeared in Kit^W-sh/W-sh DCM mice. Adoptive transfer of bone marrow-derived MCs (BMMCs) from WT mice fully or partially reversed these cardiac functional and morphologic changes in Kit^W-sh/W-sh DCM recipient mice. Yet, adoptive transfer of BMMCs from Il6^-/- and Tnf^-/- mice failed to make these corrections or at much less extent than the WT BMMCs. Mechanistic studies demonstrated a role of MC and MC-derived IL6 and TNF-α in promoting cardiomyocyte death and cardiac fibroblast TGF-β signaling, and collagen synthesis and deposition. Therefore, MC inhibition may have therapeutic potential in attenuating DCM progression.

Identification of Potential Gene Interactions in Heart Failure Caused by Idiopathic Dilated Cardiomyopathy

Background

Many heart failure (HF) cases are caused by idiopathic dilated cardiomyopathy (iDCM). This study explored the mechanisms of the development and progression of HF caused by iDCM.

Material/Methods

The gene expression profiles of 102 samples were downloaded from the GEO database (GSE5406). Differentially expressed genes (DEGs) were identified through GO analysis and a KEGG pathway analysis, respectively. A protein–protein interaction (PPI) network was constructed and analyzed to screen potential regulatory proteins. In addition, MCODE and a cytoHubba plugin were used to identify the module and hub genes of DEGs. Finally, transcription factors (TFs) were predicted using PASTAA. We did not perform whole-exome sequencing (WES) for detecting mitochondrial DNA (mtDNA).

Results

A total of 197 DEGs were screened, and 3 modules, and 4 upregulated and 11 downregulated hub genes were screened. The GO analysis focused on the terms and 12 KEGG pathways were enriched. The FOS, TIMP1, and SERPINE1 hub genes, as well as some key TFs, demonstrated important roles in the progression of HF caused by iDCM. CEBPD, CEBOB, CDC37L1, and SRGN may be new targets for HF in iDCM patients.

Conclusions

The identified DEGs and their enriched pathways provide references for exploring the mechanisms of the development and progression of HF patients with iDCM. Moreover, modules, hub genes, and TFs may be useful in the treatment and diagnosis of HF patients with iDCM. However, mtDNA was not investigated.

Chymase inhibitors for the treatment of cardiac diseases: a patent review (2010-2018)

INTRODUCTION

Chymase is primarily found in mast cells (MCs), fibroblasts, and vascular endothelial cells. MC chymase is released into the extracellular interstitium in response to inflammatory signals, tissue injury, and cellular stress. Among many functions, chymase is a major extravascular source for angiotensin II (Ang II) generation. Several recent pre-clinical and a few clinical studies point to the relatively unrecognized fact that chymase inhibition may have significant therapeutic advantages over other treatments in halting progression of cardiac and vascular disease.

AREAS COVERED

The present review covers patent literature on chymase inhibitors for the treatment of cardiac diseases registered between 2010 and 2018.

EXPERT OPINION

Increase in cardiac MC number in various cardiac diseases has been found in pathological tissues of human and experimental animals. Meta-analysis data from large clinical trials employing angiotensin-converting enzyme (ACE) inhibitors show a relatively small risk reduction of clinical cardiovascular endpoints. The disconnect between the expected benefit associated with Ang II blockade of synthesis or activity underscores a greater participation of chymase compared to ACE in forming Ang II in humans. Emerging literature and a reconsideration of previous studies provide lucid arguments to reconsider chymase as a primary Ang II forming enzyme in human heart and vasculature.

Mechanisms of Cardiac Repair and Regeneration

Cardiovascular regenerative therapies are pursued on both basic and translational levels. Although efficacy and value of cell therapy for myocardial regeneration can be debated, there is a consensus that profound deficits in mechanistic understanding limit advances, optimization, and implementation. In collaboration with the TACTICS (Transnational Alliance for Regenerative Therapies in Cardiovascular Syndromes), this review overviews several pivotal aspects of biological processes impinging on cardiac maintenance, repair, and regeneration. The goal of summarizing current mechanistic understanding is to prompt innovative directions for fundamental studies delineating cellular reparative and regenerative processes. Empowering myocardial regenerative interventions, whether dependent on endogenous processes or exogenously delivered repair agents, ultimately depends on mastering mechanisms and novel strategies that take advantage of rather than being limited by inherent myocardial biology.

The role of neuropeptides in adverse myocardial remodeling and heart failure

In addition to traditional neurotransmitters of the sympathetic and parasympathetic nervous systems, the heart also contains numerous neuropeptides. These neuropeptides not only modulate the effects of neurotransmitters, but also have independent effects on cardiac function. While in most cases the physiological actions of these neuropeptides are well defined, their contributions to cardiac pathology are less appreciated. Some neuropeptides are cardioprotective, some promote adverse cardiac remodeling and heart failure, and in the case of others their functions are unclear. Some have both cardioprotective and adverse effects depending on the specific cardiac pathology and progression of that pathology. In this review, we briefly describe the actions of several neuropeptides on normal cardiac physiology, before describing in more detail their role in adverse cardiac remodeling and heart failure. It is our goal to bring more focus toward understanding the contribution of neuropeptides to the pathogenesis of heart failure, and to consider them as potential therapeutic targets.

The Innate Immune Response in Myocardial Infarction, Repair, and Regeneration

Following myocardial infarction (MI), resident innate immune cells such as macrophages, innate lymphoid cells, and mast cells rapidly coordinate their function to contain inflammation by removing dying cells and promoting cardiomyocyte replenishment. To sustain local tissue repair functions, hematopoietic progenitors are mobilized from the bone marrow to the spleen to generate subsequent myeloid cells such as monocytes and neutrophils, which are rapidly recruited at the site of MI. A finely tuned balance between local adaptation and recruitment controls the overall outcome of the cardiac tissue regeneration versus repair and scar formation.In this chapter, the (potential) roles of the innate immune system residing in the heart are discussed in the context of recent findings about macrophage ontogeny and their homeostasis with circulating monocytes during cardiac tissue growth and after myocardial infarction. Their interactions with other members of the innate immune system are also discussed with a particular emphasis on the potential involvement of mast cells and innate lymphoid cells during MI, largely underestimated until recently. Understanding the development and the functions of the different protagonists responding to MI as well as their potential cross talk could help design new strategies for regenerative medicine intervention.

The emerging prominence of the cardiac mast cell as a potent mediator of adverse myocardial remodeling

Cardiac mast cells store and release a variety of biologically active mediators, several of which have been implicated in the activation of matrix metalloproteinases in the volume-overloaded heart, while others are involved in the fibrotic process in pressure-overloaded hearts. Increased numbers of mast cells have been reported in explanted human hearts with dilated cardiomyopathy and in animal models of experimentally induced hypertension, myocardial infarction, and chronic cardiac volume overload. Also, there is evolving evidence implicating the cardiac mast cell as having a major role in the adverse remodeling underlying these cardiovascular disorders. Thus, the cardiac mast cell is the focus of this chapter that begins with a historical background, followed by sections on methods for their isolation and characterization, endogenous secretagogues, phenotype, and ability of estrogen to alter their phenotype so as to provide cardioprotection. Finally the role of mast cells in myocardial remodeling secondary to a sustained cardiac volume overload, hypertension, and ischemic injury and future research directions are discussed.

Mast cells in human health and disease

Mast cells are primarily known for their role in defense against pathogens, particularly bacteria; neutralization of venom toxins; and for triggering allergic responses and anaphylaxis. In addition to these direct effector functions, activated mast cells rapidly recruit other innate and adaptive immune cells and can participate in "tuning" the immune response. In this review we touch briefly on these important functions and then focus on some of the less-appreciated roles of mast cells in human disease including cancer, autoimmune inflammation, organ transplant, and fibrosis. Although it is difficult to formally assign causal roles to mast cells in human disease, we offer a general review of data that correlate the presence and activation of mast cells with exacerbated inflammation and disease progression. Conversely, in some restricted contexts, mast cells may offer protective roles. For example, the presence of mast cells in some malignant or cardiovascular diseases is associated with favorable prognosis. In these cases, specific localization of mast cells within the tissue and whether they express chymase or tryptase (or both) are diagnostically important considerations. Finally, we review experimental animal models that imply a causal role for mast cells in disease and discuss important caveats and controversies of these findings.

Myocardial remodeling in diabetic cardiomyopathy associated with cardiac mast cell activation

Diabetic cardiomyopathy is a specific disease process distinct from coronary artery disease and hypertension. The disease features cardiac remodeling stimulated by hyperglycemia of the left ventricle wall and disrupts contractile functions. Cardiac mast cells may be activated by metabolic byproducts resulted from hyperglycermia and then participate in the remodeling process by releasing a multitude of cytokines and bioactive enzymes. Nedocromil, a pharmacologic stabilizer of mast cells, has been shown to normalize cytokine levels and attenuate cardiac remodeling. In this study, we describe the activation of cardiac mast cells by inducing diabetes in normal mice using streptozotocin (STZ). Next, we treated the diabetic mice with nedocromil for 12 weeks and then examined their hearts for signs of cardiac remodeling and quantified contractile function. We observed significantly impaired heart function in diabetic mice, as well as increased cardiac mast cell density and elevated mast cell secretions that correlated with gene expression and aberrant cytokine levels associated with cardiac remodeling. Nedocromil treatment halted contractile dysfunction in diabetic mice and reduced cardiac mast cell density, which correlated with reduced bioactive enzyme secretions, reduced expression of extracellular matrix remodeling factors and collagen synthesis, and normalized cytokine levels. However, the results showed nedocromil treatments did not return diabetic mice to a normal state. We concluded that manipulation of cardiac mast cell function is sufficient to attenuate cardiomyopathy stimulated by diabetes, but other cellular pathways also contribute to the disease process.

Mast cell inhibition attenuates myocardial damage, adverse remodeling, and dysfunction during fulminant myocarditis in the rat

BACKGROUND

Myocarditis is a life-threatening heart disease characterized by myocardial inflammation, necrosis, and chronic fibrosis. While mast cell inhibition has been suggested to prevent fibrosis in rat myocarditis, little is known about its effectiveness in attenuating cardiac remodeling and dysfunction in myocarditis. Thus, we sought to test the hypothesis that mast cell inhibition will attenuate the inflammatory reaction and associated left ventricular (LV) remodeling and dysfunction after fulminant autoimmune myocarditis. Methods and

RESULTS

To induce experimental autoimmune myocarditis, we immunized 30 rats with porcine cardiac myosin (PCM) twice at a 7-day interval. On day 8 animals were randomized into treatment with either an intraperitoneal (IP) injection of 25mg/kg of cromolyn sodium (n = 13) or an equivalent volume (∼0.5 mL IP) of normal saline (n = 11). All animals were scanned by serial echocardiography studies before treatment (baseline echocardiogram) and after 20 days of cromolyn sodium (28 days after immunization). Furthermore, serial cardiac magnetic resonance was performed in a subgroup of 12 animals. After 20 days of treatment (28 days from first immunization), hearts were harvested for histopathological analysis. By echocardiography, cromolyn sodium prevented LV dilatation and attenuated LV dysfunction, compared with controls. Postmortem analysis of hearts showed that cromolyn sodium reduced myocardial fibrosis, as well as the number and size of cardiac mast cells in the inflamed myocardium, compared with controls.

CONCLUSIONS

Our study suggests that mast cell inhibition with cromolyn sodium attenuates adverse LV remodeling and dysfunction in myocarditis. This mechanism-based therapy is clinically relevant and could improve the outcome of patients at risk for inflammatory cardiomyopathy and heart failure.

Stem cell factor is responsible for the rapid response in mature mast cell density in the acutely stressed heart

In the abdominal aortocaval (AV) fistula model of heart failure, we have shown that the acute doubling of cardiac mature mast cell (MC) density involved the maturation, but not proliferation, of a resident population of immature cardiac MCs. An increase in stem cell factor (SCF) may be responsible for this MC maturation process. Thus, the purpose of this study was to determine if: 1) myocardial SCF levels are increased following the initiation of cardiac volume overload; 2) the incubation of left ventricular (LV) tissue slices with SCF results in an increase in mature MC density; and 3) chemical degranulation of mature cardiac MCs in LV tissue slices results in an increase in SCF and mature MC density via MC chymase. Male rats with either sham or AV fistula surgery were studied at 6h and 1 and 3 days post-surgery. LV slices from normal male rat hearts were incubated for 16h with media alone or media containing one of the following: 1) recombinant rat SCF (20 ng/ml) to determine the effects of SCF on MC maturation; 2) the MC secretagogue compound 48/80 (20 μg/ml) to determine the effects of MC degranulation on SCF levels and mature MC density; 3) media containing compound 48/80 and anti-SCF (5 μg/ml) to block the effects of SCF; 4) chymase (100 nM) to determine the effects of chymase on SCF; and 5) compound 48/80 and chymostatin (chymase inhibitor, 10 μM) to block the effects of MC chymase. In AV fistula animals, myocardial SCF was significantly elevated above that in the sham group at 6h and 1 day post fistula by 2 and 1.8 fold, respectively, and then returned to normal by 3 days; this increase slightly preceded significant increases in MC density. Incubation of LV slices with SCF resulted in a doubling of mature MC density and this was concomitant with a significant decrease in the number of immature mast cells. Incubation of LV slices with compound 48/80 increased media SCF levels and mature MC density and with anti-SCF and chymostatin prevented these compound 48/80-induced increases. Incubation with chymase increased media SCF levels and mature MC density. These findings indicate that activated mature cardiac mast cells are responsible, in a paracrine fashion, for the increase in mature MC density post AV fistula by rapidly increasing SCF levels via the release of chymase.

Increased expression of stem cell factor and its receptor after left ventricular assist device support: a potential novel target for therapeutic interventions in heart failure

BACKGROUND

Left ventricular assist devices (LVADs) cause an influx of mast cells into the failing heart, but the underlying mechanism is unknown. This study investigates the potential role of stem cell factor (SCF) and its receptor (c-Kit) in promoting the recruitment of mast cells during heart failure and after LVAD support.

METHODS

Myocardial samples were collected from 10 end-stage heart failure patients undergoing LVAD implantation (pre-LVAD) and paired with samples taken at the time of orthotopic heart transplantation (post-LVAD). Biopsies of normal hearts served as controls. We assessed gene expression of SCF and c-Kit. In addition, we stained for SCF, c-Kit, tryptase and chymase, and utilized in situ hybridization to determine the origin of SCF.

RESULTS

SCF mRNA and overall mast cell numbers were significantly increased (p < 0.01/p < 0.001) after LVAD support as compared with paired heart failure tissues. c-Kit mRNA was significantly increased post-LVAD compared with normal tissues (p < 0.05). The c-Kit protein was expressed only in cardiac mast cells. SCF mRNA was found in endothelial cells, myocytes and interstitial cells, as confirmed by antibody staining.

CONCLUSIONS

LVADs cause an increase of SCF and c-Kit gene expression, which coincides with a surge of mast cells after ventricular unloading. This suggests that SCF functions as an important mediator for the recruitment of mast cells to the mechanically unloaded human heart.

Protection from adverse myocardial remodeling secondary to chronic volume overload in mast cell deficient rats

Mast cells have diverse roles throughout the body as evidenced by their heterogeneous nature. In the heart, cardiac mast cells have been implicated in left ventricular (LV) remodeling in response to elevated myocardial stress. Accordingly, the purpose of this study was to use mast cell deficient rats (Ws/Ws) to delineate the interaction between cardiac mast cell activation and LV remodeling. LV matrix metalloproteinase (MMP) activity, fibrillar collagen, TNF-alpha levels, and LV diameter were compared in Ws/Ws and wild type (WT) rats subjected to 5 d (n=3/group) and 8 weeks (n=4/group) of aortocaval fistula-induced volume overload. In contrast to attenuation of myocardial remodeling in the Ws/Ws group: 1) MMP-2 activity was significantly increased in the WT group at 5 days; 2) there was marked degradation of the extracellular collagen matrix in WT at 5 days and 8 weeks; 3) the percent increase in LV diameter from baseline was significantly greater in WT at 2, 4, 6, and 8 weeks post-fistula; and 4) myocardial TNF-alpha levels were markedly elevated in the WT group at 5 days post-fistula. These results underscore the importance of cardiac mast cells in mediating MMP activation, collagen degradation and LV dilatation and suggest that mast cell-derived TNF-alpha plays a role in early myocardial remodeling.

Mast cell-derived cathepsin g: a possible role in the adverse remodeling of the failing human heart

BACKGROUND

The role of cardiac mast cells (MCs) in the progression to heart failure has recently become increasingly evident. Cathepsin g is a neutrophil- and mast cell-derived protease, which can convert angiotensin I to angiotensin II and thereby activate the TGF-beta pathway, resulting in myocyte necrosis, hypertrophy, and increased fibrosis. This study focuses on mast cell-derived cathepsin g in the human heart during heart failure and following mechanical unloading by means of heart-assist devices (LVADs).

MATERIALS AND METHODS

Myocardial tissue was obtained from 10 patients with end-stage cardiomyopathy at the time of LVAD implantation (pre-LVAD) and following orthotopic heart transplantation (post-LAVD). In addition, biopsies of four normal hearts served as a control group. Paraffin-embedded sections were dual stained for cathepsin g and tryptase, a known marker for mast cells, using standard immunohistochemistry protocols. Total cathepsin g positive mast cells were counted.

RESULTS

No cathepsin g positive MCs were found in normal hearts. However, we found evidence for cathepsin g in cardiac MCs in heart failure tissues (pre-LVAD). During heart failure, 46% of total MCs were cathepsin g positive as compared to after mechanical unloading, where only 11% of total MCs were cathepsin g positive (P<0.001).

CONCLUSION

Heart failure causes an increase of myocardial MCs. We have provided evidence that cathepsin g positive MCs accumulate during heart failure and their total percentage decreases after ventricular unloading. This coincides with the decrease in myocyte necrosis, hypertrophy, and fibrosis. Thus, cathepsin g may play a role in the progression to heart failure by activating angiotensin II, leading to detrimental effects on the heart.

Arachidonic Acid Metabolism as a Potential Mediator of Cardiac Fibrosis Associated with Inflammation

An increase in left ventricular collagen (cardiac fibrosis) is a detrimental process that adversely affects heart function. Strong evidence implicates the infiltration of inflammatory cells as a critical part of the process resulting in cardiac fibrosis. Inflammatory cells are capable of releasing arachidonic acid, which may be further metabolized by cyclooxygenase, lipoxygenase, and cytochrome P450 monooxygenase enzymes to biologically active products, including PGs, leukotrienes, epoxyeicosatrienoic acids, and hydroxyeicosatetraenoic acids. Some of these products have profibrotic properties and may represent a pathway by which inflammatory cells initiate and mediate the development of cardiac fibrosis. In this study, we critically review the current literature on the potential link between this pathway and cardiac fibrosis.

Pharmacologic inhibition of mast cell degranulation prevents left ventricular remodeling induced by chronic volume overload in rats

BACKGROUND

Left ventricular (LV) hypertrophy and dilation are important compensatory responses to chronic volume overload; however, the mechanisms responsible for this LV remodeling have not been well characterized. Previous observations that the number of myocardial mast cells are increased in congestive heart failure (CHF) suggested the hypothesis that mast cells might be involved in the ventricular remodeling induced by a chronic volume overload.

METHODS AND RESULTS

Accordingly, the intent of this study was to determine the contribution of mast cells to LV remodeling, dysfunction, and morbidity/mortality secondary to CHF in the infrarenal aortocaval fistula model of sustained volume overload. To this end, LV end-diastolic pressure, size, and function (ie, isovolumetric pressure-volume relations in the blood-perfused isolated heart) were assessed in both nedocromil sodium treated and untreated rats at 8 weeks after fistula and compared with age-matched controls. Nedocromil, a mast cell-stabilizing drug, effectively prevented the LV dilation and decreased contractility seen in the untreated fistula group in a dose-dependent fashion, resulting in a significant reduction in the incidence of morbidity/mortality from CHF.

CONCLUSION

The ability of mast cell stabilization to prevent ventricular dilation induced by chronic volume overload identifies a key role for mast cells in the regulation of myocardial remodeling.

Identification and expression of a new type II transmembrane protein in human mast cells

A cDNA encoding a new type II transmembrane protein has been isolated from human mast cells by subtraction cloning. This cDNA contains an open reading frame of 186 amino acids. RT-PCR analysis showed that this gene is differentially expressed in mast cells. Therefore, the peptide encoded by this gene was termed mast cell-expressed membrane protein 1 (MCEMP1). The MCEMP1 gene contains seven exons and was mapped to human chromosome 19p13.3. The epitope-tagged MCEMP1 has been expressed in mammalian cells and found to be localized to the cellular membrane with its C-terminus extending to the outside of the membrane and N-terminus into the cytoplasmic compartment. Monoclonal antibodies against MCEMP1 were generated and characterized by immunoprecipitation and FACS. The results showed that the native MCEMP1 is expressed in cord blood-derived mast cells and HMC-1 and THP-1 cell lines, but not in other cell types that we have tested. Immunochemical staining of human lung sections showed that MCEMP1 staining is specifically associated with lung mast cells.

Key role of mast cells and their major secretory products in inflammatory bowel disease

Historically, mast cells were known as a key cell type involved in type I hypersensitivity. Until last two decades, this cell type was recognized to be widely involved in a number of non-allergic diseases including inflammatory bowel disease (IBD). Markedly increased numbers of mast cells were observed in the mucosa of the ileum and colon of patients with IBD, which was accompanied by great changes of the content in mast cells such as dramatically increased expression of TNF-α, IL-16 and substance P. The evidence of mast cell degranulation was found in the wall of intestine from patients with IBD with immunohistochemistry technique. The highly elevated histamine and tryptase levels were detected in mucosa of patients with IBD, strongly suggesting that mast cell degranulation is involved in the pathogenesis of IBD. However, little is known of the actions of histamine, tryptase, chymase and carboxypeptidase in IBD. Over the last decade, heparin has been used to treat IBD in clinical practice. The low molecular weight heparin (LMWH) was effective as adjuvant therapy, and the patients showed good clinical and laboratory response with no serious adverse effects. The roles of PGD2, LTC4, PAF and mast cell cytokines in IBD were also discussed. Recently, a series of experiments with dispersed colon mast cells suggested there should be at least two pathways in man for mast cells to amplify their own activation-degranulation signals in an autocrine or paracrine manner. The hypothesis is that mast cell secretogogues induce mast cell degranulation, release histamine, then stimulate the adjacent mast cells or positively feedback to further stimulate its host mast cells through H₁ receptor. Whereas released tryptase acts similarly to histamine, but activates mast cells through its receptor PAR-2. The connections between current anti-IBD therapies or potential therapies for IBD with mast cells were discussed, implicating further that mast cell is a key cell type that is involved in the pathogenesis of IBD. In conclusion, while pathogenesis of IBD remains unclear, the key role of mast cells in this group of diseases demonstrated in the current review implicates strongly that IBD is a mast cell associated disease. Therefore, close attentions should be paid to the role of mast cells in IBD.

Hyperhomocysteinemia leads to pathological ventricular hypertrophy in normotensive rats

A recent report indicated that hyperhomocysteinemia (Hhe), in addition to its atherothrombotic effects, exacerbates the adverse cardiac remodeling seen in response to hypertension, a powerful stimulus for pathological ventricular hypertrophy. The present study was undertaken to determine whether Hhe has a direct effect on ventricular remodeling and function in the absence of other hypertrophic stimuli. Male Wistar-Kyoto rats were fed either an amino acid-defined control diet or an intermediate Hhe-inducing diet. After 10 wk of dietary treatment, rats were subjected to echocardiographic assessment of left ventricular (LV) dimensions and systolic function. Subsequently, blood was collected for plasma homocysteine measurements, and the rats were killed for histomorphometric and biochemical assessment of cardiac remodeling and for in vitro cardiac function studies. Significant LV hypertrophy was detected by echocardiographic measurements, and in vitro results showed hypertrophy with significantly increased myocyte size in the LV and right ventricle (RV). LV and RV remodeling was characterized by a disproportionate increase in perivascular and interstitial collagen, coronary arteriolar wall thickening, and myocardial mast cell infiltration. In vitro study of LV function demonstrated abnormal diastolic function secondary to decreased compliance because the rate of relaxation did not differ between groups. LV systolic function did not vary between groups in vitro. In summary, in the absence of other hypertrophic stimuli short-term intermediate Hhe caused pathological hypertrophy and remodeling of both ventricles with diastolic dysfunction of the LV. These results demonstrate that Hhe has direct adverse effects on cardiac structure and function, which may represent a novel direct link between Hhe and cardiovascular morbidity and mortality, independent of other risk factors.

Cause and effect relationship between myocardial mast cell number and matrix metalloproteinase activity

The objectives of this study were to investigate the temporal response of left ventricular (LV) matrix metalloproteinase (MMP) activity and collagen volume fraction (CVF) induced by an aortocaval fistula and the role of cardiac mast cells in regulating MMP activity. LV tissue was analyzed for MMP activity, CVF, and mast cell number in rats euthanized at 0.5, 1, 2, 3, 5, 14, 21, 35, and 56 days. Additional rats treated with the mast cell membrane-stabilizing drug cromolyn sodium were euthanized 1, 2, and 3 days postfistula. Marked increases in MMP activity occurred rapidly and remained significantly elevated for 5 days before returning toward normal. A significant decrease in CVF occurred by day 5, but thereafter CVF rebounded to normal or above normal values. The number of myocardial mast cells also significantly increased postfistula, and there was a close association between mast cell density and MMP activity. Cromolyn treatment prevented the increase in mast cell number and MMP activity. Thus it is concluded that cardiac mast cells play a major role in the regulation of MMP activity.

Cardiac mast cell-mediated activation of gelatinase and alteration of ventricular diastolic function

Mast cells contain proteases capable of activating matrix metalloproteinases (MMPs). However, given the relatively low density of mast cells in the myocardium (i.e., 1.5-5.3 cells/mm(2)), it is unknown whether these enzymes are present in sufficient quantities in the normal heart to mediate MMP activation. Accordingly, this study sought to determine whether chemically induced degranulation of cardiac mast cells (with compound 48/80) would have an effect in isolated, blood-perfused, functioning rat hearts. Mast cell degranulation produced a 15% increase in histamine levels present in the coronary efflux, a significant increase in myocardial water (i.e., edema) relative to normal values (80.1 +/- 3.4% vs. 77.4 +/- 1.08%, P < or = 0.03), a substantial activation of MMP-2 (126% increase relative to controls, P < or = 0.02), and a marked decrease in myocardial collagen volume fraction (0.46 +/- 0.10% vs. 0.97 +/- 0.33%, P < or = 0.001). Furthermore, although an increase in ventricular stiffness was expected due to the extent of edema resulting from mast cell degranulation, modest ventricular dilatation was observed. These findings clearly demonstrate that the number of mast cells present in normal hearts is sufficient to mediate activation of MMPs and produce extracellular matrix degradation, thereby potentially causing subsequent ventricular dilatation.

Effects of mast cells on the behavior of isolated heart fibroblasts: modulation of collagen remodeling and gene expression

The extracellular matrix plays a critical role in the development and maintenance of the vertebrate heart. Changes in the accumulation, composition, or organization of the extracellular matrix are known to deleteriously affect heart function. Mast cells are thought to stimulate collagen expression and fibroblast proliferation accompanying fibrosis in some organs; however, the effects of mast cells on the heart interstitium are largely unexplored. The present studies were carried out to determine the effects of mast cells on isolated heart fibroblasts. Several in vitro assays were used including collagen gel contraction to examine the effects of mast cells on the function of isolated fibroblasts. Neonatal heart fibroblasts were cultured either with mast cells, mast cell-conditioned medium, or mast cell extracts, and their ability to contract collagen gels measured. Results from these experiments indicated that mast cells inhibit heart fibroblast migration and contraction of 3-dimensional collagen gels. Further experiments indicated that incubation of neonatal heart fibroblasts with extracts of mast cells altered the expression of collagen, matrix metalloproteases, and matrix receptors of the integrin family. These studies suggest that mast cells play an important role in the regulation of the cardiac interstitial matrix. Further studies are warranted to determine the mechanisms whereby mast cells modulate fibroblast activity.