Mast Cell Proteases

Therapeutic strategies targeting the endothelial glycocalyx: acute deficits, but great potential

Damage of the endothelial glycocalyx, which ranges from 200 to 2000 nm in thickness, decreases vascular barrier function and leads to protein extravasation and tissue oedema, loss of nutritional blood flow, and an increase in platelet and leucocyte adhesion. Thus, its protection or the restoration of an already damaged glycocalyx seems to be a promising therapeutic target both in an acute critical care setting and in the treatment of chronic vascular disease. Drugs that can specifically increase the synthesis of glycocalyx components, refurbish it, or selectively prevent its enzymatic degradation do not seem to be available. Pharmacological blockers of radical production may be useful to diminish the oxygen radical stress on the glycocalyx. Tenable options are the application of hydrocortisone (inhibiting mast-cell degranulation), use of antithrombin III (lowering susceptibility to enzymatic attack), direct inhibition of the cytokine tumour necrosis factor-alpha, and avoidance of the liberation of natriuretic peptides (as in volume loading and heart surgery). Infusion of human plasma albumin (to maintain mechanical and chemical stability of the endothelial surface layer) seems the easiest treatment to implement.

Abnormal overexpression of mastocytes in skin biopsies of fibromyalgia patients

Formalin-fixed, paraffin-embedded skin tissue sections were collected from a matched cohort of 63 fibromyalgia syndrome (FMS) patients and 49 volunteers from the general population with both alpha1-antitrypsin (AAT) normal and deficiency variants. These tissues were examined for the expression of the broad-spectrum inhibitor AAT, the serine proteinases elastase and tryptase, the proinflammatory cytokines MCP-1 and TNFα, the endothelium biomarker VEGF, and the inflammation/nociception-related receptor PAR(2). The most relevant finding of the study was a significantly increased number of mast cells (MCs) in the papillary dermis of all FMS patients (greater than or equal to five to 14 per microscopic high power field) compared to zero to one in controls (p < 0.001). MCs strongly stained with tryptase, AAT and PAR(2) antibodies, exhibited a spindle-like shape and were uniformly distributed around blood vessels and appendages. MCP-1 and VEGF expressed weak/moderate positivity in most samples, with a higher expression in controls than in FMS patients (p < 0.001 and 0.051, respectively). No differences in elastase and TNFα were found between both groups. Moreover, no histological differences were found between samples from AAT deficiency and normal AAT phenotypes. Our results indicate that FMS is a MC-associated condition. MCs are present in skin and mucosal surfaces throughout the human body, and are easily stimulated by a number of physical, psychological, and chemical triggers to degranulate, releasing several proinflammatory products which are able to generate nervous peripheral stimuli causing CNS hypersensitivity, local, and systemic symptoms. Our findings open new avenues of research on FMS mechanisms and will benefit the diagnosis of patients and the development of therapeutics.

Characterization of the substrate specificity of human carboxypeptidase A4 and implications for a role in extracellular peptide processing

CPA4 (carboxypeptidase A4) is a member of the metallocarboxypeptidase family. CPA4 was originally found in a screen of mRNAs up-regulated by sodium butyrate-induced differentiation of cancer cells. Further studies suggested a relation between CPA4 and prostate cancer aggressiveness. In the present study, we determined that CPA4 is secreted from cells as a soluble proenzyme (pro-CPA4) that can be activated by endoproteases, such as trypsin. Three complementary approaches were used to study the substrate specificity of CPA4; kinetic analysis was performed using a new series of chromogenic substrates and some biologically relevant peptides, the cleavage of synthetic peptides was tested individually, and the cleavage of a mixture of >100 mouse brain peptides was examined using a quantitative peptidomics mass spectrometry-based approach. CPA4 was able to cleave hydrophobic C-terminal residues with a preference for Phe, Leu, Ile, Met, Tyr, and Val. However, not all peptides with C-terminal hydrophobic residues were cleaved, indicating the importance of additional residues within the peptide. Aliphatic, aromatic, and basic residues in the P1 position have a positive influence on the cleavage specificity. In contrast, acidic residues, Pro, and Gly have a negative influence in the P1 position. Some of the peptides identified as CPA4 substrates (such as neurotensin, granins, and opioid peptides) have been previously shown to function in cell proliferation and differentiation, potentially explaining the link between CPA4 and cancer aggressiveness. Taken together, these studies suggest that CPA4 functions in neuropeptide processing and regulation in the extracellular environment.

Mast cell proteases: multifaceted regulators of inflammatory disease

Mast cells (MCs) are currently receiving increased attention among the scientific community, largely because of the recent identification of crucial functions for MCs in a variety of disorders. However, it is in many cases not clear exactly how MCs contribute in the respective settings. MCs express extraordinarily high levels of a number of proteases of chymase, tryptase, and carboxypeptidase A type, and these are stored in high amounts as active enzymes in the MC secretory granules. Hence, MC degranulation leads to the massive release of fully active MC proteases, which probably have a major impact on any condition in which MC degranulation occurs. Indeed, the recent generation and evaluation of mouse strains lacking individual MC proteases have indicated crucial contributions of these to a number of different disorders. MC proteases may thus account for many of the effects ascribed to MCs and are currently emerging as promising candidates for treatment of MC-driven disease. In this review, we discuss these findings.

Glycosaminoglycan secretion in xyloside treated polarized human colon carcinoma Caco-2 cells

Polarized epithelial cells like Madin-Darby canine kidney (MDCK) and CaCo-2 cells synthesize and secrete proteoglycans (PGs), mostly of heparan sulphate (HS) type in direction of the basal extracellular matrix, but also some in the apical direction. MDCK cells possess the capacity to synthesize chondroitin sulphate (CS) PGs that are mainly secreted into the apical medium, a process that is enhanced in the presence of hexyl-beta-D: -xyloside. We have now tested the capacity of several xylosides to enhance glycosaminoglycan (GAG) chain secretion from the human colon carcinoma cell line CaCo-2 in the differentiated and non-differentiated state. In these cells, benzyl-beta-D: -xyloside was a potent initiator of CS chains, which for these cells were predominantly secreted into the basolateral medium. Xylosides with other aglycone groups mediated only minor changes in GAG secretion. Although benzyl-beta-D: -xyloside stimulated the basolateral CS-GAG secretion in both differentiated and undifferentiated CaCo-2 cells, basolateral secretion of trypsin-like activity was dramatically enhanced in undifferentiated cells, but not significantly altered in differentiated cells.

The anti-allergic compound tranilast attenuates inflammation and inhibits bone destruction in collagen-induced arthritis in mice

BACKGROUND AND PURPOSE

Recent findings suggest the importance of mast cells in the pathogenesis of rheumatoid arthritis and their potential as a therapeutic target. Tranilast is an anti-allergic compound with a potent membrane-stabilizing effect on mast cells and a wide range of anti-inflammatory effects, thus may be advantageous in the treatment of arthritis. Here, we have evaluated the effects of tranilast on the progression of collagen-induced arthritis in mice.

EXPERIMENTAL APPROACH

Tranilast (400 mg.kg(-1).day(-1)) was orally administered for 8 weeks to mice with established collagen-induced arthritis. Arthritis was assessed by clinical signs and X-ray scores. In paw tissue, the numbers of mast cells and osteoclasts were measured by histological analysis, and several inflammatory factors were assessed by RT-PCR and Western blot analysis.*

KEY RESULTS

TNF-alpha-positive mast cells were present extensively throughout the inflamed synovium of vehicle-treated arthritic mice, with some mast cells in close proximity to osteoclasts in areas of marked bone and cartilage destruction. Tranilast significantly reduced clinical and X-ray scores of arthritis and decreased numbers of TNF-alpha-positive mast cells and mRNA levels of TNF-alpha, chymase (mouse mast cell protease 4), tryptase (mouse mast cell protease 6), stem cell factor, interleukin-6, cathepsin-K, receptor activator of nuclear factor-kappaB, and of receptor activator of nuclear factor-kappaB-ligand, but increased interleukin-10 mRNA level in paws of arthritic mice. Osteoclast numbers were decreased by treatment with tranilast.

CONCLUSIONS AND IMPLICATIONS

Tranilast possesses significant anti-rheumatic efficacy and, probably, this therapeutic effect is partly mediated by inhibition of mast cell activation and osteoclastogenesis.

Serglycin proteoglycan deletion in mouse platelets: physiological effects and their implications for platelet contributions to thrombosis, inflammation, atherosclerosis, and metastasis

Serglycin is found in all nucleated hematopoietic cells and platelets, blood vessels, various reproductive and developmental tissues, and in chondrocytes. The serglycin knockout mouse has demonstrated that this proteoglycan is required for proper generation and function of secretory granules in several hematopoietic cells. The effects on platelets are profound, and include diminishing platelet aggregation responses and formation of platelet thrombi. This chapter will review cell-specific aspects of serglycin structure, its gene regulation, cell and tissue localization, and the effects of serglycin deletion on hematopoietic cell granule structure and function. The effects of serglycin knockout on platelets are described and discussed in detail. Rationales for further investigations into the contribution of serglycin to the known roles of platelets in thrombosis, inflammation, atherosclerosis, and tumor metastasis are presented.

Expression profiling the temperature-dependent amphibian response to infection by Batrachochytrium dendrobatidis

Amphibians are experiencing a panzootic of unprecedented proportions caused by the emergence of Batrachochytrium dendrobatidis (Bd). However, all species are not equally at risk of infection, and risk is further modified by environmental variables, specifically temperature. In order to understand how, and when, hosts mount a response to Bd we analysed infection dynamics and patterns of gene expression in the model amphibian species Silurana (Xenopus) tropicalis. Mathematical modelling of infection dynamics demonstrate the existence of a temperature-dependent protective response that is largely independent of the intrinsic growth-rate of Bd. Using temporal expression-profiling by microarrays and qRT-PCR, we characterise this response in the main amphibian lymphoid tissue, the spleen. We demonstrate that clearance of Bd at the host-optimal temperature is not clearly associated with an adaptive immune response, but rather is correlated with the induction of components of host innate immunity including the expression of genes that are associated with the production of the antimicrobial skin peptide preprocareulein (PPCP) as well as inflammatory responses. We find that adaptive immunity appears to be lacking at host-optimal temperatures. This suggests that either Bd does not stimulate, or suppresses, adaptive immunity, or that trade-offs exist between innate and adaptive limbs of the amphibian immune system. At cold temperatures, S. tropicalis loses the ability to mount a PPCP-based innate response, and instead manifests a more pronounced inflammatory reaction that is characterised by the production of proteases and higher pathogen burdens. This study demonstrates the temperature-dependency of the amphibian response to infection by Bd and indicates the influence that changing climates may exert on the ectothermic host response to pathogens.

Mast cells regulate homeostatic intestinal epithelial migration and barrier function by a chymase/Mcpt4-dependent mechanism

Altered intestinal barrier function is postulated to be a central predisposing factor to intestinal diseases, including inflammatory bowel diseases and food allergies. However, the mechanisms involved in maintaining homeostatic intestinal barrier integrity remain undefined. In this study, we demonstrate that mice deficient in mast cells (Kit(W-sh/W-sh) [Wsh]) or mast cell chymase (Mcpt4(-/-)) have significantly decreased basal small intestinal permeability compared with wild-type (WT) mice. Altered intestinal barrier function was linked to decreased intestinal epithelial cell migration along the villus/crypt axis, altered intestinal morphology, and dysregulated claudin-3 crypt expression. Remarkably, engraftment of Wsh mice with WT but not Mcpt4(-/-) mast cells restored intestinal epithelial cell migration, morphology, and intestinal epithelial barrier function. Collectively, these findings identify a mechanism by which mast cells regulate homeostatic intestinal epithelial migration and barrier function.

Increased differentiation of dermal mast cells in mice lacking the Mpl gene

Thrombopoietin interactions with its receptor, Mpl, play an important role in the regulation of hematopoietic stem/progenitor cell proliferation and differentiation. In this study, we report that the mast cell restricted progenitor cells (MCP) and the mast cell precursors in the bone marrow of wild-type mice express Mpl on their surface. Furthermore, targeted deletion of the Mpl gene in mice decreases the number of MCP while increasing the number of mast cell precursors present in the marrow and spleen. It also increases the number of mast cells present in the dermis, in the peritoneal cavity, and in the gut of the mice. In addition, serosal mast cells from Mpl(null) mice have a distinctive differentiation profile similar to that expressed by wild-type dermal mast cells. These results suggest that not only does ligation of thrombopoietin with the Mpl receptor exert an effect at the mast cell restricted progenitor cell level, but also plays an unexpected yet important role in mast cell maturation.

The impact of the glycocalyx on microcirculatory oxygen distribution in critical illness

PURPOSE OF REVIEW

Main problems of critical illness and sepsis are an altered oxygen distribution and microvascular dysfunction linked to tissue oedema. This review seeks to analyse the role of the endothelial glycocalyx in this context.

RECENT FINDINGS

The presence of vascular leakage is typically associated with interstitial oedema, arterial hypotension, hypovolaemia and often a bad outcome in patients with systemic inflammation. Early goal-directed therapy provides significant benefits in severe sepsis and septic shock, but is mostly aimed at improving macrohaemodynamics. Recent data suggest that microcirculation also contributes significantly to the pathophysiology of critical illness. In fact, the endothelial glycocalyx plays a major role in vascular barrier competence. According to experimental evidence, it can easily be degraded in the presence of inflammation, but, theoretically also protected by several measures. Clinical studies revealed a positive correlation of the severity of sepsis and ischaemia with mortality, but also with a deterioration of the endothelial glycocalyx. Future investigation should focus on the preservation of this structure and assess microcirculatory variables to judge the success of cardiocirculatory therapy.

SUMMARY

Deterioration of the endothelial glycocalyx initiates a breakdown of the vascular barrier in systemic inflammatory response syndrome and sepsis. Preserving this structure in critical illness might be a future therapeutical goal to improve microcirculatory oxygen distribution.

Infection of mast cells with live streptococci causes a toll-like receptor 2- and cell-cell contact-dependent cytokine and chemokine response

Mast cells (MCs) are strongly implicated in immunity toward bacterial infection, but the molecular mechanisms by which MCs contribute to the host response are only partially understood. We addressed this issue by examining the direct effects of a Gram-positive pathogen, Streptococcus equi, on bone marrow-derived MCs (BMMCs). Ultrastructural analysis revealed extensive formation of dilated rough endoplasmic reticulum in response to bacterial infection, indicating strong induction of protein synthesis. However, the BMMCs did not show signs of extensive degranulation, and this was supported by only slow release of histamine in response to infection. Coculture of live bacteria with BMMCs caused a profound secretion of CCL2/MCP-1, CCL7/MCP-3, CXCL2/MIP-2, CCL5/RANTES, interleukin-4 (IL-4), IL-6, IL-12, IL-13, and tumor necrosis factor alpha, as shown by antibody-based cytokine/chemokine arrays and/or enzyme-linked immunosorbent assay. In contrast, heat-inactivated bacteria caused only minimal cytokine/chemokine release. The cytokine/chemokine responses were substantially attenuated in Toll-like receptor 2-deficient BMMCs and were strongly dependent on cell-cell contacts between bacteria and BMMCs. Gene chip microarray analysis confirmed a massively upregulated expression of the genes coding for the secreted cytokines and chemokines and also identified a pronounced upregulation of numerous additional genes, including transcription factors, signaling molecules, and proteases. Together, the present study outlines MC-dependent molecular events associated with Gram-positive infection and thus provides an advancement in our understanding of how MCs may contribute to host defense toward bacterial insults.

Mast cell differentiation and activation is closely linked to expression of genes coding for the serglycin proteoglycan core protein and a distinct set of chondroitin sulfate and heparin sulfotransferases

Serglycin (SG) proteoglycan consists of a small core protein to which glycosaminoglycans of chondroitin sulfate or heparin type are attached. SG is crucial for maintaining mast cell (MC) granule homeostasis through promoting the storage of various basic granule constituents, where the degree of chondroitin sulfate/heparin sulfation is essential for optimal SG functionality. However, the regulation of the SG core protein expression and of the various chondroitin sulfate/heparin sulfotransferases during MC differentiation and activation are poorly understood. Here we addressed these issues and show that expression of the SG core protein, chondroitin 4-sulfotransferase (C4ST)-1, and GalNAc(4S)-6-O-sulfotransferase (GalNAc4S6ST) are closely linked to MC maturation. In contrast, the expression of chondroitin 6-sulfotransferase correlated negatively with MC maturation. The expression of N-deacetylase/N-sulfotransferase (NDST)-2, a key enzyme in heparin synthesis, also correlated strongly with MC maturation, whereas the expression of the NDST-1 isoform was approximately equal at all stages of maturation. MC activation by either calcium ionophore or IgE ligation caused an up-regulated expression of the SG core protein, C4ST-1, and GalNAc4S6ST, accompanied by increased secretion of chondroitin sulfate as shown by biosynthetic labeling experiments. In contrast, NDST-2 was down-regulated after MC activation, suggesting that MC activation modulates the nature of the glycosaminoglycan chains attached to the SG core protein. Taken together, these data show that MC maturation is associated with the expression of a distinct signature of genes involved in SG proteoglycan synthesis, and that MC activation modulates their expression.

Engineered cystine knot miniproteins as potent inhibitors of human mast cell tryptase beta

Here we report the design, chemical and recombinant synthesis, and functional properties of a series of novel inhibitors of human mast cell tryptase beta, a protease of considerable interest as a therapeutic target for the treatment of allergic asthma and inflammatory disorders. These inhibitors are derived from a linear variant of the cyclic cystine knot miniprotein MCoTI-II, originally isolated from the seeds of Momordica cochinchinensis. A synthetic cyclic miniprotein that bears additional positive charge in the loop connecting the N- and C-termini inhibits all monomers of the tryptase beta tetramer with an overall equilibrium dissociation constant K(i) of 1 nM and thus is one of the most potent proteinaceous inhibitors of tryptase beta described to date. These cystine knot miniproteins may therefore become valuable scaffolds for the design of a new generation of tryptase inhibitors.

Mouse mast cell protease 4 is the major chymase in murine airways and has a protective role in allergic airway inflammation

It is widely established that mast cells (MCs) have a harmful role in asthma, for example by secreting various proinflammatory substances stored within their secretory granule. However, in this study, we show that one of the substances stored within MC granule, chymase, in fact has a protective role in allergic airway inflammation, indicating that MCs may possess both harmful and protective activities in connection with this type of disease. Wild-type (WT) mice and mice lacking mouse MC protease 4 (mMCP-4), a chymase that is functionally homologous to human chymase, were sensitized and challenged with OVA, followed by the assessment of airway physiology and inflammatory parameters. Our results show that the airway hyperresponsiveness was significantly higher in mMCP-4(-/-) as compared with WT mice. Moreover, the degree of lung tissue inflammation was markedly higher in mice lacking mMCP-4 than in WT controls. Histological analysis revealed that OVA sensitization/challenge resulted in a marked increased in the thickness of the smooth muscle cell (SMC) layer and, notably, that the degree of SMC layer thickening was more pronounced in mMCP-4(-/-) animals than in WT controls, thus indicating that chymase may have an effect on airway SMCs. In support of this, mMCP-4-positive MCs were located in the close vicinity of the SMC layer, mainly in the upper airways, and mMCP-4 was shown to be the major chymase expressed in these MCs. Taken together, our results indicate that chymase present in the upper airways protects against allergic airway responses, possibly by regulating SMCs.

Transcriptional regulation of mouse mast cell protease-2 by interleukin-15

Mast cells (MCs) play a critical role in innate and adaptive immunity through the release of cytokines, chemokines, lipid mediators, biogenic amines, and proteases. We recently showed that the activities of MC proteases are transcriptionally regulated by intracellularly retained interleukin-15 (IL-15), and we provided evidence that this cytokine acts as a specific regulator of mouse mast cell protease-2 (mMCP-2). Here, we show that in wild-type bone marrow-derived mast cells (BMMCs) IL-15 inhibits mMCP-2 transcription indirectly by inducing differential expression and mMCP-2 promoter binding of the bifunctional transcription factors C/EBPbeta and YY1. In wild-type BMMCs, C/EBPbeta expression predominates over YY1 expression, and thus C/EBPbeta preferentially binds to the mMCP-2 promoter. In IL-15-deficient BMMCs, the opposite is found: YY1 expression predominates and binds to the mMCP-2 promoter at the expense of C/EBPbeta. Hypertranscription of the mMCP-2 gene in IL-15-deficient BMMCs is associated with histone acetylation and, intriguingly, with methylation of non-CpG dinucleotides within the MCP-2 promoter. This suggests a novel model of cytokine-controlled protease transcription: non-CpG methylation maintains a chromosomal domain in an "open" configuration that is permissive for gene expression.

Failure to detect active virus replication in mast cells at various tissue sites of HIV patients by immunohistochemistry

A recent report postulated that the mast cell population is a significant reservoir for persistent HIV infection. Our study attempted to validate this hypothesis by quantitatively comparing the distribution of mast cells and cells expressing the HIV protein p24 in HIV infected patients. Consecutive sections of paraffin-embedded human tissues from various tissue sites were subjected to immunohistochemistry with monoclonal antibodies to mast cell tryptase, viral protein p24, and other molecules. The sub-cellular distribution of these molecules was examined, to determine whether immunoreactivities to these molecules would be co-localized within the same cells. Our study revealed that, in two immediate adjacent sections immunostained for mast cell tryptase and p24, respectively, all or nearly all tryptase and p24 expressing cells were distributed at different areas. In the single section double immunostained for mast cell tryptase and p24, 5 (1.1%) of 460 large p24 expressing cell clusters encountered showed a single or few mast cells within or adjacent to p24 expressing cell clusters, but no distinct co-localization of these two proteins was observed. Similarly, no distinct co-localization was observed in any of over 500 isolated individual mast cells and p24 expressing cells. In contrast, macrophages were consistently intermixed with or adjacent to p24 expressing cells, and p24 immunostaining were seen in the cytoplasm of a subset of macrophages. These findings suggest that tissue mast cells do not show evidence for active virus replication by the techniques employed.

Critical role of mast cell chymase in mouse abdominal aortic aneurysm formation

BACKGROUND

Mast cell chymase may participate in the pathogenesis of human abdominal aortic aneurysm (AAA), yet a direct contribution of this serine protease to AAA formation remains unknown.

METHODS AND RESULTS

Human AAA lesions had high numbers of chymase-immunoreactive mast cells. Serum chymase level correlated with AAA growth rate (P=0.009) in a prospective clinical study. In experimental AAA produced by aortic elastase perfusion in wild-type (WT) mice or those deficient in the chymase ortholog mouse mast cell protease-4 (mMCP-4) or deficient in mMCP-5 (Mcpt4(-/-), Mcpt5(-/-)), Mcpt4(-/-) but not Mcpt5(-/-) had reduced AAA formation 14 days after elastase perfusion. Even 8 weeks after perfusion, aortic expansion in Mcpt4(-/-) mice fell by 50% compared with that of the WT mice (P=0.0003). AAA lesions in Mcpt4(-/-) mice had fewer inflammatory cells and less apoptosis, angiogenesis, and elastin fragmentation than those of WT mice. Although Kit(W-sh/W-sh) mice had protection from AAA formation, reconstitution with mast cells from WT mice, but not those from Mcpt4(-/-) mice, partially restored the AAA phenotype. Mechanistic studies suggested that mMCP-4 regulates expression and activation of cysteine protease cathepsins, elastin degradation, angiogenesis, and vascular cell apoptosis.

CONCLUSIONS

High chymase-positive mast cell content in human AAA lesions, greatly reduced AAA formation in Mcpt4(-/-) mice, and significant correlation of serum chymase levels with human AAA expansion rate suggests participation of mast cell chymase in the progression of human and mouse AAA.

Mast cell-dependent proteolytic modification of HDL particles during anaphylactic shock in the mouse reduces their ability to induce cholesterol efflux from macrophage foam cells ex vivo

OBJECTIVE

We have found previously that proteolytic modification of HDL by mast cell chymase in vitro reduces cholesterol efflux from cultured macrophage foam cells. Here, we evaluated whether mast cell-dependent proteolysis of HDL particles may occur in vivo, and whether such modification would impair their function in inducing cellular cholesterol efflux ex vivo.

METHODS

Systemic activation of mast cells in the mouse was achieved by intraperitoneal injection of a high dose of the mast cell-specific noncytotoxic degranulating agent, compound 48/80. Serum and intraperitoneal fluid were then evaluated for degradation of HDL apolipoproteins and for their potential to act as cholesterol acceptors from cultured mouse macrophage foam cells.

RESULTS

Lysates of isolated mouse peritoneal mast cells containing active chymase partially proteolyzed apoA-I in alpha- and prebeta-HDL particles in mouse serum in vitro, and, when injected into the mouse peritoneal cavity, the lysates also degraded endogenous apoA-I in peritoneal fluid in vivo. Systemic activation of mast cells in mast cell-competent mice, but not in mast cell-deficient (W-sash c-kit mutant) mice, reduced the ability of serum and intraperitoneal fluid derived from these animals to promote efflux of cellular cholesterol. This inhibitory effect was related to mast cell-dependent proteolytic degradation of apoA-I, apoA-IV, and apoE, i.e., the HDL-associated apolipoproteins that are efficient inducers of cholesterol efflux.

CONCLUSION

The present results document a role for extracellular mast cell-dependent proteolysis in the generation of dysfunctional HDL, and suggest an inhibitory role for mast cells in the initial step of reverse cholesterol transport in vivo.

The cathelicidin LL-37 activates human mast cells and is degraded by mast cell tryptase: counter-regulation by CXCL4

The cathelicidin LL-37 represents a potent antimicrobial and cell-stimulating agent, most abundantly expressed in peripheral organs such as lung and skin during inflammation. Because mast cells (MC) overtake prominent immunomodulatory roles in these organs, we wondered whether interactions exist between MC and LL-37. In this study, we show for the first time to our knowledge that physiological concentrations of LL-37 induce degranulation in purified human lung MC. Intriguingly, as a consequence LL-37 rapidly undergoes limited cleavage by a released protease. The enzyme was identified as beta-tryptase by inhibitor studies and by comparison to the recombinant protease. Examining the resulting LL-37 fragments for their functional activity, we found that none of the typical capacities of intact LL-37, i.e., MC degranulation, bactericidal activity, and neutralization of LPS, were retained. Conversely, we found that another inflammatory protein, the platelet-derived chemokine CXCL4, protects LL-37 from cleavage by beta-tryptase. Interestingly, CXCL4 did not act as a direct enzyme inhibitor, but destabilized active tetrameric beta-tryptase by antagonizing the heparin component required for the integrity of the tetramer. Altogether our results suggest that interaction of LL-37 and MC initiates an effective feedback loop to limit cathelicidin activity during inflammation, whereas CXCL4 may represent a physiological counter-regulator of beta-tryptase activity.

Chymotrypsin-like protease (chymase) mediates endothelial activation by factors derived from preeclamptic placentas

Endothelial cells (EC) activation is an important inflammatory phenotypic change in the vascular system in women with preeclampsia (PE). In PE, maternal vessel chymotrypsin-like protease (CLP)/chymase expression was increased. Chymase is an inflammatory protease. In this study, we specifically examined whether placental-derived CLP could induce EC activation and whether EC activation is associated with increased cellular protease expression. Human uterine microvascular endothelial cells (UtMVECs) were used. Endothelial activation was determined by endothelial adhesion molecule P-selectin, E-selectin, inter-cellular adhesion molecule (ICAM), and vascular cell adhesion molecule (VCAM) expressions and by extracellular regulated kinase (ERK) activity. Activation of endogenous CLP/chymase associated with ERK phosphorylation was further examined by CLP/chymase short interfering RNA (siRNA). Our results showed that cells treated with PE placental conditioned medium revealed increased P-selectin, E-selectin, and VCAM-1 expressions and increased ERK phosphorylation. Increased endothelial adhesion molecule expression and phosphorylated ERK (pERK) induction could be attenuated or abolished by depletion of CLP in the conditioned medium or by transfecting ECs with CLP/chymase siRNA. These observations suggest that placental-derived CLP/chymase is responsible for inducing endothelial inflammatory phenotypic changes possibly by upregulation of cell adhesion molecule expressions, activation of cellular protease, and induction of ERK phosphorylation. We speculate that activation of endothelial CLP/chymase may directly relate to the increased inflammatory phenotypic changes in the vascular system in women with PE.

Lipid-rich enteral nutrition reduces postoperative ileus in rats via activation of cholecystokinin-receptors

OBJECTIVE

This study investigates the effect of lipid-rich nutrition on the local inflammatory response and gastrointestinal hypomotility in a rat model of postoperative ileus.

BACKGROUND

Postoperative ileus is a major clinical problem, in which inflammation of the intestinal muscularis plays a key pathogenic event. Previously, administration of lipid-rich nutrition has been shown to reduce inflammation by activation of the autonomic nervous system via cholecystokinin-receptors.

METHODS

Postoperative ileus was induced by manipulation of the small intestine in rats. Peritoneal lavage fluid, plasma, and jejunal segments were collected at several time points to determine inflammatory mediators in fasted rats and rats fed a lipid-rich or control nutrition. Gastrointestinal transit was measured 24 hours after surgery.

RESULTS

Administration of lipid-rich nutrition markedly reduced the manipulation-induced local inflammatory response compared to rats treated with control nutrition. The intervention with lipid-rich nutrition significantly reduced plasma levels of rat mast cell protease-II (P < 0.05) and peritoneal levels of tumor necrosis factor-alpha (P < 0.01) and interleukin-6 (P < 0.05). Furthermore, the influx of neutrophils, expressed as tissue level myeloperoxidase was significantly prevented by lipid-rich nutrition (P < 0.05). Above all administration of lipid-rich enteral nutrition resulted in a significant improvement of gastrointestinal transit compared to control nutrition (P < 0.05). Blocking of cholecystokinin-receptors prevented the anti-inflammatory and motility promoting effect of lipid-rich feeding.

CONCLUSION

Our data demonstrate that nutritional stimulation of the autonomic nervous system with enteral lipids reduces postoperative ileus by inhibition of inflammation. Clinically, lipid-rich enteral nutrition may be a new therapeutic option in the treatment of postoperative ileus.

Human basophils express the glycosylphosphatidylinositol-anchored low-affinity IgG receptor FcgammaRIIIB (CD16B)

Basophils express not only high-affinity IgE receptors, but also low-affinity IgG receptors. Which, among these receptors, are expressed by human basophils is poorly known. Low-affinity IgG receptors comprise CD32 (FcgammaRIIA, FcgammaRIIB, and FcgammaRIIC) and CD16 (FcgammaRIIIA and FcgammaRIIIB). FcgammaRIIA, FcgammaRIIC, and FcgammaRIIIA are activating receptors, FcgammaRIIB are inhibitory receptors, FcgammaRIIIB are GPI-anchored receptors whose function is poorly understood. Basophils were reported to express FcgammaRII, but not FcgammaRIII. We aimed at further identifying basophil IgG receptors. Basophils from normal donors and from patients suffering from an allergic skin disease (atopic dermatitis), allergic respiratory diseases (allergic rhinitis and asthma), or a nonallergic skin disease (chronic urticaria) were examined. We found that normal basophils contain FcgammaRIII transcripts and express FcgammaRIIIB, but not FcgammaRIIIA, which were detected on 24-81% basophils from normal donors and on 12-100% basophils from patients. Noticeably, the proportion of FcgammaRIIIB(+) basophils was significantly lower in atopic dermatitis patients than in other subjects. This decreased FcgammaRIII expression was not correlated with an activated phenotype of basophils in atopic dermatitis patients, although FcgammaRIIIB expression was down-regulated upon basophil activation by anti-IgE. Our results challenge the two dogmas 1) that basophils do not express FcgammaRIII and 2) that FcgammaRIIIB is exclusively expressed by neutrophils. They suggest that a proportion of basophils may be lost during enrichment procedures in which FcgammaRIII(+) cells are discarded by negative sorting using anti-CD16 Abs. They unravel an unexpected complexity of IgG receptors susceptible to modulate basophil activation. They identify a novel systemic alteration in atopic dermatitis.

Mast cells: multifaceted immune cells with diverse roles in health and disease

Mast cells were discovered more than 100 years ago and until recently, have been considered renegades of the host with the sole purpose of perpetuating allergy. The discovery of mast cell-deficient mice that could be reconstituted with mast cells (the so called "mast cell knock-in" mice) has allowed the study of the in vivo functions of mast cells and revealed several new facets of these cells. It is now evident that mast cells have a much broader impact on many physiological and pathologic processes. Mast cells, particularly through their dynamic interaction with the nervous system, have been implicated in wound healing, tissue remodeling, and homeostasis. Perhaps the most progress has been made in our understanding of the role of mast cells in immunity outside the realm of allergy, and host defense. Mast cells play critical roles in both innate and adaptive immunity, including immune tolerance. Greater insight into mast cell biology has prompted studies probing the additional consequences of mast cell dysfunction, which reveal a central role for mast cells in the pathogenesis of autoimmune disorders, cardiovascular disorders, and cancer. Here, we review recent developments in the study of mast cells, which present a complex picture of mast cell functions.

Increased mast cell density during the infection with velogenic Newcastle disease virus in chickens

In addition to their well-characterized role in allergic inflammation, recent data confirm that mast cells play a more extensive role in a variety of viral infections. The contribution of mast cells to Newcastle disease pathogenesis has not been investigated. We evaluated mast cell activity after Newcastle disease virus (NDV) infection in specific pathogen free chickens using cytochemical and immunocytochemical analyses. The results were as follows. Severe tissue damage was observed in the proventriculus, duodenum, jejunum and caecal tonsil, and NDV antigens were detected and presented extensively in these tissues. Second, in the NDV-infected group, the mast cell population was increased markedly in the proventriculus, duodenum, jejunum and caecal tonsil at 24, 48, 72 and 96 h after infection (P<0.01). However, very few mast cells were observed in those same tissues in the control. More intriguingly, the greatest number of mast cells was found in the proventriculus, which also showed the greatest level of NDV antigens. Third, the content of tryptase was significantly higher (P<0.01) in the NDV-infected group compared with the control from 24 to 96 h post infection). Furthermore, as an important protease released by mast cells, tryptase had a positive correlation with mast cell distribution. These data indicated that mast cells were involved in the response to NDV. Our results also suggested that the broad range of mast cell mediators might have a role in the pathology of Newcastle disease.

Our perception of the mast cell from Paul Ehrlich to now

Just over a century ago Paul Ehrlich received the Nobel Prize for his studies of immunity. This review describes one of his legacies, the histochemical description of the mast cell, and the research that has ensued since then. After a long period of largely descriptive studies, which revealed little about the biological role of the mast cell, the field was galvanized in the 1950s by the recognition that the mast cell was the main repository of histamine and a key participant in anaphylactic reactions. Although the mast cell was long-viewed in these terms, recent research has now shown that the mast cell also plays a key role in innate and adaptive immune responses, autoimmune disease, and possibly tissue homeostasis by virtue of its expression of a diverse array of receptors and biologically active products. In addition, the responsiveness of mast cells to immunological and pathological stimulants is highly modulated by the tissue cytokine environment and by synergistic, or inhibitory, interactions among the various mast cell receptor systems. This once enigmatic cell of Paul Ehrlich has proved to be both adaptable and multifunctional.

Serglycin proteoglycan: regulating the storage and activities of hematopoietic proteases

Serglycin (SG), like all other proteoglycans, consists of a protein "core" to which sulfated and thereby negatively charged polysaccharide chains of glycosaminoglycan type are attached. The recent generation of mice lacking a functional SG gene has revealed a number of biological functions of SG. In particular, it has been shown that SG has a key role in promoting the storage and in regulating the activities of a number of proteases expressed in hematopoietic cell types, most notably various mast cell proteases. In this review, we summarize the recent development in our understanding of the biological function of SG, in particular by focusing on the novel insight provided through analysis of the SG-deficient mouse strain.

Mast cell chymase contributes to the antibody response and the severity of autoimmune arthritis

Mast cells are implicated in rheumatoid arthritis, but the mechanism by which they contribute to disease progression is not clarified. Here we investigated whether mouse mast cell protease-4 (mMCP-4), a chymase present in the mast cell secretory granule, contributes to experimental arthritis. Two models of arthritis were investigated in mMCP-4(+/+) and mMCP-4(-/-) DBA/1 mice: collagen-induced arthritis (CIA) was induced by immunization with collagen II (CII) in Freund's complete adjuvant, and a passive model of arthritis was induced by administration of anti-CII antibodies. The clinical scores were significantly reduced in the mMCP-4(-/-) animals as compared to mMCP-4(+/+) controls in both arthritis models. In CIA, the number of affected paws was lower in the CII-immunized mMCP-4(-/-) mice, with less cartilage destruction, pannus formation, and mononuclear cell and mast cell influx in the mMCP-4(-/-) joints. Interestingly, the lower clinical scores in the CII-immunized mMCP-4(-/-) mice coincided with lower serum levels of immunoglobulin G anti-CII antibodies. Our findings identify a pathogenic role of mMCP-4 in autoimmune arthritis.

Osteitis fibrosa is mediated by Platelet-Derived Growth Factor-A via a phosphoinositide 3-kinase-dependent signaling pathway in a rat model for chronic hyperparathyroidism

Abnormal secretion of PTH by the parathyroid glands contributes to a variety of common skeletal disorders. Prior studies implicate platelet-derived growth factor-A (PDGF-A) as an important mediator of selective PTH actions on bone. The present studies used targeted gene profiling and small-molecule antagonists directed against candidate gene products to elucidate the roles of specific PTH-regulated genes and signaling pathways. A group of 29 genes in rats continuously infused with PTH and cotreated with the PDGF receptor antagonist trapidil were differentially expressed compared with PTH treatment alone. Several of the identified genes were functionally clustered as regulators of fibroblast differentiation and extracellular matrix modeling, including the matrix cross-linking enzyme lysyl oxidase (LOX). Treatment with beta-aminopropionitrile, an irreversible inhibitor of LOX activity, dramatically reduced diffuse mineralization but had no effect on PTH-induced fibrosis. In contrast, the receptor tyrosine kinase inhibitor Gleevec and the phosphoinositide 3-kinase inhibitor wortmannin each reduced bone marrow fibrosis. In summary, the present studies support the hypotheses that PTH-induced bone marrow fibrosis is mediated by PDGF-A via a phosphoinositide 3-kinase-dependent signaling pathway and that increased LOX gene expression plays a key role in abnormal mineralization, a hallmark of chronic hyperparathyroidism.

The development of allergic inflammation

Allergic disorders, such as anaphylaxis, hay fever, eczema and asthma, now afflict roughly 25% of people in the developed world. In allergic subjects, persistent or repetitive exposure to allergens, which typically are intrinsically innocuous substances common in the environment, results in chronic allergic inflammation. This in turn produces long-term changes in the structure of the affected organs and substantial abnormalities in their function. It is therefore important to understand the characteristics and consequences of acute and chronic allergic inflammation, and in particular to explore how mast cells can contribute to several features of this maladaptive pattern of immunological reactivity.

Pathophysiology of food-induced anaphylaxis

Food-induced anaphylaxis is a steadily increasing problem in westernized countries and now represents the leading cause of anaphylaxis in the outpatient setting, particularly in children. Much of our knowledge of the pathophysiology of food-induced anaphylaxis comes from animal studies. Food anaphylaxis in humans is thought to be entirely IgE mediated. Several features appear to be unique to these reactions; factors such as exercise can lower the "threshold" for anaphylaxis in certain susceptible individuals. Different methods of thermal processing can modify the allergenicity of food proteins. Alteration of stomach pH can allow for incomplete digestion of food proteins, leading to increased absorption of intact food allergens. Low serum platelet-activating factor acetylhydrolase may predispose to fatal food-induced anaphylaxis. With a greater understanding of the pathophysiology of food-induced anaphylaxis, novel approaches not only to identify those at risk, but to treat and ultimately prevent food-induced anaphylaxis, are on the horizon.

Immunomodulatory mast cells: negative, as well as positive, regulators of immunity

Mast cells can promote inflammation and other tissue changes in IgE-associated allergic disorders, as well as in certain innate and adaptive immune responses that are thought to be independent of IgE. However, mast cells can also have anti-inflammatory and immunosuppressive functions. Here, we review the evidence that mast cells can have negative, as well as positive, immunomodulatory roles in vivo, and we propose that mast cells can both enhance and later suppress certain features of an immune response.

Serotonin and histamine storage in mast cell secretory granules is dependent on serglycin proteoglycan

BACKGROUND

Serotonin and histamine are components of human and rodent mast cell secretory granules.

OBJECTIVE

Serotonin and histamine are stored in the same compartment as serglycin proteoglycan. Here we addressed the possibility that serglycin may be involved in their storage and/or release.

METHODS

The storage and release of histamine and serotonin was studied in bone marrow-derived mast cells (BMMCs) and in peritoneal mast cells from wild-type or serglycin-/- mice.

RESULTS

Both serotonin and histamine storage in BMMCs was positively correlated with the degree of mast cell differentiation, and the amount of stored amine was reduced in serglycin-/- BMMCs compared with wild-type controls. The amounts of histamine/serotonin stored were reflected by the expression levels of histidine decarboxylase and tryptophan hydroxylase 1, respectively. Calcium ionophore activation resulted in serotonin/histamine release both from wild-type and serglycin-/- BMMCs. Interestingly, serotonin release was induced in cells lacking intracellular stores of serotonin, suggesting de novo synthesis. The knockout of serglycin affected the levels of stored and released mast cell serotonin and histamine to an even larger extent in in vivo-derived mast cells than in BMMCs.

CONCLUSION

These results establish a previously assumed, but not proven, role of serglycin in storage of histamine and, further, establish for the first time that serotonin storage in mast cells is dependent on serglycin proteoglycan.