The mast cell response to substance P: effects of neuraminidase, limulin, and some novel synthetic peptide antagonists

MrgX2‑mediated internalization of LL‑37 and degranulation of human LAD2 mast cells

LL‑37 is the sole antimicrobial peptide of human cathelicidin comprising 37 amino acids, which is expressed mainly in epithelial cells and neutrophils, and activates mast cells. In the present study, in order to elucidate the mechanism of mast cell activation by LL‑37, the associations between the internalization of LL‑37 and Mas‑related gene X2 (MrgX2)‑mediated mast cell activation (degranulation) was investigated using the human mast cell line, LAD2. LL‑37 was rapidly internalized into the cells, and induced degranulation, as assessed by the extracellular release of β‑hexosaminidase. Pertussis toxin, a G‑protein inhibitor, significantly suppressed the internalization of LL‑37 and the degranulation of LAD2 cells. Furthermore, small interfering (si)‑RNA‑mediated knockdown of MrgX2, a putative G protein‑coupled receptor for LL‑37, inhibited the internalization of LL‑37 and degranulation of LAD2 cells. Notably, LL‑37 internalization was enhanced by the stable expression of MrgX2 in HMC‑1 and 293 cells. In addition, the internalized LL‑37 mainly colocalized with MrgX2 in the perinuclear region of LAD2 cells. Furthermore, neuraminidase treatment, which removes negatively charged sialic acid from the cell surface, markedly reduced the internalization of LL‑37 and degranulation of LAD2 cells, and clathrin‑mediated endocytosis inhibitors (dynasore and chlorpromazine) inhibited the internalization and degranulation of LAD2 cells. Taken together, these observations indicated that LL‑37 may bind the negatively charged cell surface molecules, rapidly internalize into the cells via clathrin‑mediated endocytosis and interact with MrgX2 to activate mast cells (LAD2 cells).

Aging-associated shifts in functional status of mast cells located by adult and aged mesenteric lymphatic vessels

We had previously proposed the presence of permanent stimulatory influences in the tissue microenvironment surrounding the aged mesenteric lymphatic vessels (MLV), which influence aged lymphatic function. In this study, we performed immunohistochemical labeling of proteins known to be present in mast cells (mast cell tryptase, c-kit, prostaglandin D(2) synthase, histidine decarboxylase, histamine, transmembrane protein 16A, and TNF-α) with double verification of mast cells in the same segment of rat mesentery containing MLV by labeling with Alexa Fluor 488-conjugated avidin followed by toluidine blue staining. Additionally, we evaluated the aging-associated changes in the number of mast cells located by MLV and in their functional status by inducing mast cell activation by various activators (substance P; anti-rat DNP Immunoglobulin E; peptidoglycan from Staphyloccus aureus and compound 48/80) in the presence of ruthenium red followed by subsequent staining by toluidine blue. We found that there was a 27% aging-associated increase in the total number of mast cells, with an ∼400% increase in the number of activated mast cells in aged mesenteric tissue in resting conditions with diminished ability of mast cells to be newly activated in the presence of inflammatory or chemical stimuli. We conclude that higher degree of preactivation of mast cells in aged mesenteric tissue is important for development of aging-associated impairment of function of mesenteric lymphatic vessels. The limited number of intact aged mast cells located close to the mesenteric lymphatic compartments to react to the presence of acute stimuli may be considered contributory to the aging-associated deteriorations in immune response.

Trichinella spiralis: histamine secretion induced by TSL-1 antigens from unsensitized mast cells

Mast cells' hyperplasia and activation are prominent features in Trichinella spiralis infection. Recently, it was shown that TSL-1 antigens from T. spiralis muscle larvae induce IL-4 and TNF release by unsensitized, normal mast cells (MC) involving an Ig-independent mechanism. In this study, we characterized histamine secretion induced by TSL-1 antigens from normal, unsensitized rat peritoneal MC. Maximum histamine secretion (30+/-5.3% SEM, n=13) was achieved with 30 ng/mL TSL-1 antigens. However, TSL-1 did not induce an increase in beta-hexosaminidase release or NADPH oxidase activity by MC. Interestingly, histamine secretion by TSL-1 was completed at 10s, and was inhibited by both Bordetella pertussis toxin and neuraminidase V, characteristics similar to those involved in substance P-induced histamine secretion. However, in contrast to substance P, TSL-1 induced histamine secretion in the absence of detectable changes in intracellular Ca(2+). We are investigating the molecular pathways involved in MC activation by TSL-1.

Liver fluke (Fasciola hepatica)-derived peptides activate rat peritoneal mast cells

Short peptides with sequences derived from those found in the tegumental antigen of Fasciola hepatica have been synthesised. Incubation of some of these peptides with rat peritoneal mast cells resulted in the degranulation of the cells as measured by a histamine release assay. This activity was shown to be associated with the proline-lysine-proline motif, which is responsible for the induction of mast cell degranulation by the mammalian bioactive peptide substance P. Studies on the mode of action of the fluke-derived peptide indicated that it was operating through the same biochemical pathways as substance P. The implications of these findings for the development of immune responses during parasite infections are discussed.

Amperometric characterization of exocytotic events from single mast cells: dependence on external and internal Ca++ sources

Mast cells exocytotically release histamine/serotonin in response to different secretagogues. We have used substance P and compound 48/80 to study the Ca++ dependency of serotonin exocytosis from peritoneal mast cells using carbon fiber amperometric techniques. The exocytotic release pattern consists of a burst of events superimposed on a slow, transient, amperometric current baseline increase. Cellular re lease parameters (number, frequency and total charge of amperometric events) and individual event characteristics (charge integral, half width and peak amplitude) were similar for the two secretagogues used. Zero Ca++ conditions greatly reduced, without completely abolishing,cellular release parameters. Cyclopiazonic acid, an inhibitor of the endoplasmatic Ca++ ATPase, reduced the cellular exocytotic capacity and diminished the amplitude of individual exocytotic events more effectively than the 0 Ca++ condition. The cyclopiazonic acid effects occurred in the presence of external Ca++, indicating that this condition is not sufficient for maintaining full exocytotic capacity. The results confirm the importance of intracellular Ca++ for exocytotic activation. For the first time evidence is presented that the integrity of intracellular Ca++ pools determines the amplitude and frequency of individual exocytotic events. Saponin, a non-specific detergent, also induced quantal release similar to that obtained with substance P and compound 48/80. This release was not dependent on extracellular Ca++, but cyclopiazonic acid significantly reduced individual exocytotic release.

Mechanism of histamine release induced by levofloxacin, a fluoroquinolone antibacterial agent

The present study was designed to clarify the mechanism of histamine release caused by levofloxacin, a fluoroquinolone antibacterial agent, using rat peritoneal mast cells. Levofloxacin induced a concentration-dependent histamine secretion from 300 microg/ml without lactate dehydrogenase leakage, and the release was rapidly completed within 30 s. This action was dependent on temperature, energy, pH and intracellular Ca(2+), similarly to the effect of compound 48/80, a basic compound. Unlike that with the calcium ionophore A23187, histamine secretion due to levofloxacin or compound 48/80 was prevented by pretreatment with either pertussis toxin or benzalkonium chloride, a selective inhibitor of G proteins of G(i) subtypes. Moreover, the histamine release elicited by levofloxacin or compound 48/80 was suppressed by hydrolysis of sialic acid residues on the cell surface brought about by neuraminidase. These results demonstrate that the mechanism by which levofloxacin exerts histamine release may be closely linked to activation of pertussis toxin-sensitive G proteins.

Mast cell production of TNF-alpha induced by substance P evidence for a modulatory role of substance P-antagonists

Unregulated increasing of Tumor necrosis factor-alpha (TNF-alpha) could be pathogenic in inflammatory diseases. The aim of this study was to investigate the anti-inflammatory role of the Substance P-antagonists (SPAs) through the inhibition of histamine release (HR) and TNF-alpha production from mast cell. Rat peritoneal mast cells (PMC) stimulated with Substance P (SP), in the presence of SPAs or not, were analyzed for HR and TNF-alpha protein production. Competitive Polymerase Chain Reaction, with an internal standard competing with target cDNA for the same primers, was used to determine the TNF-alpha mRNA expression. We show that the increase of either HR and TNF-alpha levels in peritoneal (PMC) after induction with SP was inhibited by pre-incubation with SPA or with the Peptide 101 (P101), while the [D-Pro2, D-Phe7, D-Trp9]-SP (dSP) had no effect. Neuraminidase treatment suggests that dSP, as well as SP, interacts with sialic acid residues on the cell surface. Moreover, SPA and P101 also inhibit the release of histamine and TNF-alpha induced by dSP suggesting that a receptor-independent mechanism is involved. These data could be useful to better understand the mechanisms involved in the mast cell activation and TNF-alpha production in the inflammatory diseases where SP is involved.

Neutrophil Defensins Induce Histamine Secretion from Mast Cells: Mechanisms of Action

Defensins are endogenous antimicrobial peptides stored in neutrophil granules. Here we report that a panel of defensins from human, rat, guinea pig, and rabbit neutrophils all have histamine-releasing activity, degranulating rat peritoneal mast cells with EC50 ranging from 70 to 2500 nM, and between 45 and 60% of the total histamine released. The EC50 for defensin-induced histamine secretion correlates with their net basic charge at neutral pH. There is no correlation between histamine release and antimicrobial potency. Degranulation induced by defensins has characteristics similar to those of activation by substance P. The maximum percent histamine release is achieved in <10 s, and it can be markedly inhibited by pertussis toxin (100 ng/ml) and by pretreatment of mast cells with neuraminidase. These properties differ from those for degranulation induced by IgE-dependent Ag stimulation and by the calcium ionophore A23187. GTPase activity, a measure of G protein activation, was induced in a membrane fraction from mast cells following treatment with defensin. Thus, neutrophil defensins are potent mast cell secretagogues that act in a manner similar to substance P and 48/80, through a rapid G protein-dependent response that is mechanistically distinct from Ag/IgE-dependent mast cell activation. Defensins may provide important pathways for communication between neutrophils and mast cells in defenses against microbial agents and in acute inflammatory responses.

Substance P-related inhibitors of mast cell exocytosis act on G-proteins or on the cell surface

[p-Glu5,D-Trp(7,9,10)]substance P-(5-11) inhibited mastoparan-stimulated GTPase activity in homogenized rat peritoneal mast cells and decreased histamine secretion induced by mastoparan from streptolysin O-permeabilized mast cells (IC50 of about 30 microM), but not from intact cells. In contrast, [D-Pro4,D-Trp(7,9,10)]substance P-(4-11) inhibited the secretion from intact cells (IC50 of about 10 microM) but had no effect on histamine secretion from permeabilized cells, suggesting that this peptide exerts its inhibitory effect on the plasma membrane, whereas [p-Glu5,D-Trp(7,9,10)]substance P-(5-11) interacts with G proteins. Pretreatment of mast cells with neuraminidase led to an inhibition of the secretory response to mastoparan and related triggers. This response was restored following cell permeabilization, demonstrating the role of the cell surface on the entry of mastoparan and related triggers and on their ability to reach G proteins sensitive to pertussis toxin and [p-Glu5,D-Trp(7,9,10)]substance P-(5-11).

Inhibitory effect of neuraminidase on SP-induced histamine release and TNF-alpha mRNA in rat mast cells: evidence of a receptor-independent mechanism

The neuropeptide substance P (SP) is a mediator of neuro-inflammation and can play a role by induction of histamine release (HR) and TNF-alpha. However, its effect on the heterogeneous response of mast cells (MC) has not been completely studied. We have established that the SR can induce 25% of HR in highly purified rat uterine MC at diestrous but not at proestrous phases of the reproductive cycle and 88% of HR in peritoneal mast cells (PMC). We also found 2.2 fold increase in TNF-alpha mRNA at diestrous, in SP stimulated uterine MC versus control and 2.7 fold increase in PMC; RT and competitive PCR were used to amplify the TNF-alpha mRNA. We have thereafter investigated the mechanism whereby the binding of SP to sialic acid on the MC membrane, could trigger secretion of histamine and induction of TNF-alpha mRNA. The neuraminidase pretreatment (0.1 U/ml) inhibited SP-stimulated HR from either uterine MC and PMC (98% and 50%, respectively) and totally inhibited SP-stimulated TNF-alpha mRNA levels. The neuraminidase effect was not toxic, since it was not observed in IgE mediated HR and TNF-alpha mRNA levels. In conclusion, the inhibitory effect of the neuraminidase on the SP-mediated increase of histamine and TNF-alpha mRNA, suggests that the SP-sialic acid interaction could have a role in the MC heterogeneous response.

Sensitisation of articular afferents in normal and inflamed knee joints by substance P in the rat

To examine whether substance P (SP) influences the response properties of fine articular afferents in normal and acutely inflamed joints, single units were recorded from the rat knee during normal and noxious joint rotations. Only three of 39 units were activated by a single bolus injection of 0.1 mM SP. However, 35% (7/20) of the nerve fibres from the normal joint and 21% (4/19) of the units from the inflamed joint significantly increased their responses to movements after the SP injection. This was most prominent during noxious movements in normal joints, whereas in inflamed joints increase of responses occurred mainly during normal movements. These data indicate that SP may also be involved in the process of sensitisation of primary afferents during an inflammation.

Fine sensory innervation of the knee joint capsule by group III and group IV nerve fibers in the cat

Afferent group III and IV nerve fibers of the knee joint markedly differ in their responsiveness to mechanical stimulation, which may be reflected in the structure and location of their terminals. Therefore, in sympathectomized cats, the fine afferent innervation of the knee joint capsule was studied via ultrastructural three-dimensional reconstructions over distances of up to 300 microns. Small peripheral nerves and "free" (noncorpuscular) sensory nerve endings were found in a superficial layer of the outer fibrous part of the capsule, in the patellar retinaculum, and in the outer and inner surface layers of the medial collateral and patellar ligaments. Group III nerve fibers showed a proximal myelinated portion inside the nerve, an intermediate portion that lacks a myelin sheath and is only surrounded by perineurium, and a distal portion outside of the perineurium that forms the sensory ending proper. Group IV fibers showed only two distinct portions, an intraperineurial (proximal) and an extraperineurial (distal) portion without any further morphological differences. Outside of the perineurium, a network formed by Schwann cells ("Schwann cell reticulum") provides a pathway for the distal portion of the sensory axons. No distinct subgroups of the sensory terminal fibers could be defined according to the configuration of the Schwann cells and the nerve fiber terminals. Sensory terminals were located adjacent to different structures such as venous and lymphatic vessels, fat cells, and collagenous fibers. Distinct parts of the same terminal nerve fiber were found in close contact to a vessel wall; others were surrounded by dense collagenous tissue. Close to sensory endings, mast cells and mast cell-like cells were frequently found, indicating a functional relationship.

Human and rat cutaneous mast cells: involvement of a G protein in the response to peptidergic stimuli

Recent evidence suggests that peptides induce the release of mediators from rat peritoneal mast cell by means of a receptor-independent mechanism, possibly involving an interaction with sialic acid residues at the cell surface followed by the activation of a guanine nucleotide binding protein (G protein). We have now examined the potential involvement of sialic acid residues and of G protein stimulation in the activation of both human and rat cutaneous mast cells by neuropeptide Y, its C-terminal fragments and the wasp venom peptide, mastoparan. Neuropeptide Y-(18-36) was the most effective histamine releaser of the fragments tested, the order of potency being neuropeptide Y-(18-36) > neuropeptide Y-(22-36) > neuropeptide Y-(1-36). This order of potency suggests that the effects of the peptides are not mediated through classical NPY receptors. The hydrolysis of sialic acid residues by neuraminidase and the inhibition of G proteins by benzalkonium chloride or pertussis toxin significantly inhibited the secretory response of cutaneous mast cells to neuropeptide Y-(18-36) and mastoparan. These results demonstrate that the peptidergic pathway described for the activation of peritoneal rat mast cells is also involved in the response of cutaneous human and rat mast cells to peptides.

Peptidergic pathway in human skin and rat peritoneal mast cell activation

The common pathway of heterogenous mast cell activation as mediated by antigens is through the cross-linking of IgE bound to Fc epsilon RI receptors. The peptidergic pathway of mast cell activation, achieved by cationic secretagogues, is restricted to "serosal" mast cells, the experimental models being rat peritoneal and human skin mast cells. Cationic secretagogues include positively charged peptides but also various amines such as compound 48/80 and natural polyamines. An early intracellular event of this pathway is the activation of pertussis toxin-sensitive G proteins. The correlation observed between the ability of basic compounds to trigger mast cell exocytosis and their potency to activate purified G proteins strongly suggests that cationic compounds activate mast cell G proteins via a receptor-independent but membrane-assisted process. In this paper, alternative mechanisms are discussed. The consequence of G protein stimulation is the activation of phospholipase C with an increase in inositol triphosphates. Natural polyamines are relatively poor triggers of mast cells (10(-4) to 10(-2) M). Neuropeptides such as substance P, neuropeptide Y or vasoactive intestinal peptide, peptidic hormones such as kinins, and venoms such as mastoparan and mast cell degranulating peptide, are all active in a concentration range from 10(-7) to 10(-4) M. The cationic anaphylatoxin C3a also stimulates mast cells at concentrations below precursor complement C3 blood levels. The component C3 of the complement system is one of only a few plasma proteins having activation fragments (i.e. C3a) that can be generated at micromolar levels. The effects of basic secretagogues defines a peptidergic pathway of mast cell activation, which represents a potentially toxic process considering the tissue effects caused by exogenous basic compounds such as venom peptides and certain amine containing drugs. Peptidergic activation of mast cells may also be a pathophysiological process having an important role in neurogenic inflammation and in diseases involving extensive activation of the blood complement cascade.

Ultrastructural evidence for neurogenically mediated changes in blood vessels of the rat dura mater and tongue following antidromic trigeminal stimulation

We investigated the effects of unilateral electrical trigeminal ganglion stimulation (0.1 or 1.0 mA, 5 Hz, 5 ms, 5 min) on the morphology of blood vessels within the rat dura mater and tongue using light and transmission electron microscopy. Stimulation at both intensities caused changes which were confined to the ipsilateral post-capillary venules except in the tongue where arterioles were affected as well. Changes were more marked after 1.0 mA. Dramatic increases in the numbers of endothelial pinocytotic vesicles were found along the luminal and abluminal surfaces ipsilateral to the stimulation. Tight junctions remained largely intact, except that injected ferritin particles were occasionally trapped inside these junctions. Cytoplasmic microvilli and endothelial blebs were sometimes present as well. Approximately 80% of the examined dural post-capillary venules showed one or more of these endothelial changes. Horseradish peroxidase injected intravenously 5 min prior to stimulation was detected in the extracellular space surrounding dural blood vessels and within pinocytotic vesicles. Ferritin injected similarly, was also localized in post-capillary venule walls, interstitial spaces, intraendothelial vesicles and in vacuoles. Platelet accumulation and aggregation were present in approximately 10% of post-capillary venules in dura and tongue. These changes were associated with mast cell secretion, but neither vascular nor mast cell activation was observed in adult rats in whom C-fibers were destroyed during the neonatal period with capsaicin. The present observations provide morphological evidence which supports findings from previously reported albumin tracer studies suggesting enhanced transport and endothelial activation following electrical stimulation of small caliber afferent fibers.

Trigeminal sensory fiber stimulation induces morphological changes reflecting secretion in rat dura mater mast cells

Mast cells are involved in allergic reactions, but may also participate in neurogenic inflammation. The morphology of mast cells in rat dura mater and tongue was evaluated by histochemistry, as well as by scanning and transmission electron microscopy following unilateral trigeminal ganglion stimulation (5 min, 5 Hz, 5 ms, and 0.02, 0.1 or 1.0 mA). Mast cells in dura and tongue of normal animals were numerous, perivascular and often in close proximity to nerve fibers. After 5 min of electrical stimulation, mast cells contralateral to the stimulation showed histochemical characteristics of normal peripheral tissue mast cells (Safranin-positive), and by electron microscopy appeared homogeneous with numerous intact electron-dense granules. On the stimulated side, however, the staining characteristics of mast cells showed changes indicating progressive intracellular loss of their granular content. In addition, the total number of stainable mast cells decreased at all three stimulus intensities, but reached significance only at 0.1 and 0.02 mA. Ultrastructural evidence of granule changes consistent with secretion were observed although degranulation was not observed until 20 min after stimulation. There were no mast cell changes after electrical trigeminal stimulation in adult rats treated as neonates with capsaicin to destroy small caliber sensory afferent axons. These results suggest that mast cells may secrete in response to electrical stimulation of trigeminal axons, possibly mediated by antidromic release of neuropeptides, and may participate in the development of neurogenic inflammation.

Tachykinin receptors and the airways

The tachykinins, substance P, neurokinin A and neurokinin B, belong to a structural family of peptides. In mammalian airways, substance P and neurokinin A are colocalized to afferent C-fibres. Substance P-containing fibres are close to bronchial epithelium, smooth muscle, mucus glands and blood vessels. Sensory neuropeptides may be released locally, possibly as a result of a local reflex, and produce bronchial obstruction through activation of specific receptors on these various tissues. Three types of tachykinin receptors, namely NK-1, NK-2 and NK-3 receptors, have been characterized by preferential activation by substance P, neurokinin A and neurokinin B respectively. NK-1 and NK-2 receptors were recently cloned. The determination of receptor types involved in the effects of tachykinins in the airways has been done with synthetic agonists and antagonists binding specifically to NK-1, NK-2 and NK-3 receptors. Although the existence of species differences, the conclusion that bronchial smooth muscle contraction is mainly related to activation of NK-2 receptors on bronchial smooth muscle cell has been drawn. The hypothesis of a NK-2 receptor subclassification has been proposed with NK-2A receptor subtype in the guinea-pig airways. Other effects in the airways are related to stimulation of NK-1 receptors on mucus cells, vessels, epithelium and inflammatory cells. A non-receptor-mediated mechanism is also involved in the effect of substance P on inflammatory cells and mast cells.

G protein activation: a receptor-independent mode of action for cationic amphiphilic neuropeptides and venom peptides

The neuropeptide substance P, the venom peptide mastoparan and the synthetic polyamine compound 48/80 activate rat peritoneal mast cells, leading to rapid histamine release by exocytosis. Although these effects are inhibited by pertussis toxin and involve a transient increase in IP3, no selective membrane receptors have been identified. However, it has recently been shown that these compounds activate G proteins in vitro. Here Yves Landry and colleagues discuss the proposal that direct activation of G protein is the physiological mechanism of action of substance P on rat peritoneal mast cells, this mechanism being mimicked by mastoparan and 48/80, and possibly by other cationic amphiphilic peptides such as kinins. These compounds might be of help in defining the interaction between membrane receptors and G proteins.

The development of neurogenic plasma extravasation in the rat dura mater does not depend upon the degranulation of mast cells

Mast cells were visualized in stretch preparations of the rat dura mater and were found mostly in relation to small and large blood vessels. The overall number of dural mast cells was unaffected by electrical trigeminal or chemical deafferentation. As in other tissues, mast cell degranulation increased at sites of local injury (electrode penetration) or after systemic treatment with compound 48/80. However, mast cells did not degranulate following electrical trigeminal stimulation, or after injection of drugs (capsaicin or substance P) which promote plasma extravasation in the dura. Furthermore, pretreatment with a mast cell stabilizer (sodium dicromoglycate) or with large doses of H1 and H2 histamine receptor blockers (mepyramine and cimetidine), did not block electrically- or chemically-induced neurogenic plasma extravasation (NPE). Daily pretreatment with 48/80 however completely attenuated or abolished NPE. Taken together these data suggest that as assessed by the extrusion of metachromatic granules, mast cells are not essential to the development of neurogenic inflammation within the rat dura mater. However, these findings cannot exclude the possibility that mast cells may amplify or modulate this process.