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Multifaceted roles of cysteinyl leukotrienes in eliciting eosinophil granule protein secretion.

Baptista-dos-Reis R, Muniz VS, Neves JS - Biomed Res Int (2015)

Bottom Line: Cysteinyl leukotrienes (cysLTs) are cell membrane-impermeant lipid mediators that play major roles in the pathogenesis of eosinophilic inflammation and are recognized to act via at least 2 receptors, namely, cysLT1 receptor (cysLT1R) and cysLT2 receptor (cysLT2R).Eosinophils, which are granulocytes classically associated with host defense against parasitic helminthes and allergic conditions, are distinguished from leukocytes by their dominant population of cytoplasmic crystalloid (also termed secretory, specific, or secondary) granules that contain robust stores of diverse preformed proteins.We also discuss the importance of this finding in eosinophil immunobiology and speculate on its potential role(s) in eosinophilic diseases.

View Article: PubMed Central - PubMed

Affiliation: Institute of Biomedical Sciences, Federal University of Rio de Janeiro, Centro de Ciências da Saúde (CCS), 373 Carlos Chagas Filho Avenue, Room F 14, 1st Floor, Ilha do Fundão, 21941-590 Rio de Janeiro, RJ, Brazil.

ABSTRACT
Cysteinyl leukotrienes (cysLTs) are cell membrane-impermeant lipid mediators that play major roles in the pathogenesis of eosinophilic inflammation and are recognized to act via at least 2 receptors, namely, cysLT1 receptor (cysLT1R) and cysLT2 receptor (cysLT2R). Eosinophils, which are granulocytes classically associated with host defense against parasitic helminthes and allergic conditions, are distinguished from leukocytes by their dominant population of cytoplasmic crystalloid (also termed secretory, specific, or secondary) granules that contain robust stores of diverse preformed proteins. Human eosinophils are the main source of cysLTs and are recognized to express both cysLTs receptors (cysLTRs) on their surface, at the plasma membrane. More recently, we identified the expression of cysLTRs in eosinophil granule membranes and demonstrated that cysLTs, acting via their granule membrane-expressed receptors, elicit secretion from cell-free human eosinophil granules. Herein, we review the multifaceted roles of cysLTs in eliciting eosinophil granule protein secretion. We discuss the intracrine and autocrine/paracrine secretory responses evoked by cysLTs in eosinophils and in cell-free extracellular eosinophil crystalloid granules. We also discuss the importance of this finding in eosinophil immunobiology and speculate on its potential role(s) in eosinophilic diseases.

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Stimulating cell-free eosinophil granules with the agonists LTC4, LTD4, and LTE4 elicited the secretion of eosinophil cationic protein (ECP) but not eosinophil-derived cytokines or chemokines from the granules. Cysteinyl leukotriene receptor (cysLTR) or P2Y12 receptor (P2Y12R) blockers inhibited ECP secretion after LTC4/LTD4/LTE4 stimulation of cell-free eosinophil granules.
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fig2: Stimulating cell-free eosinophil granules with the agonists LTC4, LTD4, and LTE4 elicited the secretion of eosinophil cationic protein (ECP) but not eosinophil-derived cytokines or chemokines from the granules. Cysteinyl leukotriene receptor (cysLTR) or P2Y12 receptor (P2Y12R) blockers inhibited ECP secretion after LTC4/LTD4/LTE4 stimulation of cell-free eosinophil granules.

Mentions: Intracrine roles for cysLTs are described in the literature, but the mechanisms involved that can explain cysLTs' intracellular actions remain unknown [32, 44, 45]. A description of intracellular cysLTRs expression in human eosinophils was recently provided by our group [34]. In 2010, we reported, for the first time, that the receptors for cysLTs, cysLT1R and cysLT2R, and the purinergic P2Y12R are expressed on eosinophil granule membranes [34]. We showed that eosinophil granules express amino-terminal, ligand-binding domains for cysLT1R and cysLT2R and the P2Y12R on their membranes. We previously observed that certain cytokine and chemokine receptors are richly present on eosinophil granules [22, 33, 49]. These granules, upon extrusion from eosinophils, responded to a stimulating cytokine, interferon-γ, and a chemokine, eotaxin-1 (CCL11), via cognate granule membrane-expressed receptors to activate intragranular signaling pathways that elicit granule protein secretion [33, 50]. Stimulating cell-free eosinophil granules with the agonists LTC4, LTD4, and LTE4 elicited the secretion of ECP, but not eosinophil-derived cytokines or chemokines, from the granules (as detected by cytokine multiplex assays). Montelukast, a recognized inhibitor that principally inhibits cysLT1R, as well as the P2Y12R antagonist MRS 2395, inhibited eosinophil granule ECP secretion after LTC4/LTD4/LTE4 stimulation of cell-free eosinophil granules [34] (Figure 2). The capacity of a cysLT1R inhibitor or a P2Y12R antagonist, such as montelukast and MRS 2395, respectively, to similarly inhibit the secretion elicited by ligands (e.g., LTE4) not active for cysLT1R or not classically selective for the receptor (e.g., P2Y12R), suggests functional heterodimerization of cysLT1R and other receptors (e.g., functional heterodimerization between cysLT1R, cysLT2R, and P2Y12R) expressed on eosinophil granule membranes; whether this is the case remains to be ascertained. In addition, montelukast's potential off-target effects could not be discounted. Notably, the dose response to the three cysLTs varied. LTC4 and LTE4 elicited ECP secretion only at lower (subnanomolar) concentrations, which was fully consistent with the high-dose inhibition characteristic of the GPCRs. Intriguingly, LTD4 elicited ECP secretion at low and high, but not intermediate, concentrations. This dose response suggests the engagement of two receptors sensitive to LTD4, with the first responding to low LTD4 levels and then exhibiting higher dose inhibition and the second receptor putatively mediating secretion at higher concentrations of LTD4. As previously mentioned, oligomerization of leukotriene and purinergic receptors has been widely suggested [15, 16]. However, whether dimerization of receptors is involved in this response remains to be elucidated. These findings highlight the capacity of cysLTRs to stimulate cell-free granule secretory responses. Furthermore, for granules serving as intracellular organelles these data identify novel mechanisms whereby LTC4 and extracellularly generated LTD4 and LTE4 (if these mediators could be, by any chance, internalized by the cell) may serve as intracrine mediators of eosinophil granule-derived secretion. However, there is no evidence that the cysLT1R, cysLT2R, or P2Y12R expressed on granule membranes is involved in the intracrine actions of cysLTs described previously [32]. This phenomenon is not likely, considering that LTC4- and LTD4-elicited IL-4 release in permeabilized eosinophils is not blocked by inhibitors of cysLT1R and cysLT2R [32].


Multifaceted roles of cysteinyl leukotrienes in eliciting eosinophil granule protein secretion.

Baptista-dos-Reis R, Muniz VS, Neves JS - Biomed Res Int (2015)

Stimulating cell-free eosinophil granules with the agonists LTC4, LTD4, and LTE4 elicited the secretion of eosinophil cationic protein (ECP) but not eosinophil-derived cytokines or chemokines from the granules. Cysteinyl leukotriene receptor (cysLTR) or P2Y12 receptor (P2Y12R) blockers inhibited ECP secretion after LTC4/LTD4/LTE4 stimulation of cell-free eosinophil granules.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4383494&req=5

fig2: Stimulating cell-free eosinophil granules with the agonists LTC4, LTD4, and LTE4 elicited the secretion of eosinophil cationic protein (ECP) but not eosinophil-derived cytokines or chemokines from the granules. Cysteinyl leukotriene receptor (cysLTR) or P2Y12 receptor (P2Y12R) blockers inhibited ECP secretion after LTC4/LTD4/LTE4 stimulation of cell-free eosinophil granules.
Mentions: Intracrine roles for cysLTs are described in the literature, but the mechanisms involved that can explain cysLTs' intracellular actions remain unknown [32, 44, 45]. A description of intracellular cysLTRs expression in human eosinophils was recently provided by our group [34]. In 2010, we reported, for the first time, that the receptors for cysLTs, cysLT1R and cysLT2R, and the purinergic P2Y12R are expressed on eosinophil granule membranes [34]. We showed that eosinophil granules express amino-terminal, ligand-binding domains for cysLT1R and cysLT2R and the P2Y12R on their membranes. We previously observed that certain cytokine and chemokine receptors are richly present on eosinophil granules [22, 33, 49]. These granules, upon extrusion from eosinophils, responded to a stimulating cytokine, interferon-γ, and a chemokine, eotaxin-1 (CCL11), via cognate granule membrane-expressed receptors to activate intragranular signaling pathways that elicit granule protein secretion [33, 50]. Stimulating cell-free eosinophil granules with the agonists LTC4, LTD4, and LTE4 elicited the secretion of ECP, but not eosinophil-derived cytokines or chemokines, from the granules (as detected by cytokine multiplex assays). Montelukast, a recognized inhibitor that principally inhibits cysLT1R, as well as the P2Y12R antagonist MRS 2395, inhibited eosinophil granule ECP secretion after LTC4/LTD4/LTE4 stimulation of cell-free eosinophil granules [34] (Figure 2). The capacity of a cysLT1R inhibitor or a P2Y12R antagonist, such as montelukast and MRS 2395, respectively, to similarly inhibit the secretion elicited by ligands (e.g., LTE4) not active for cysLT1R or not classically selective for the receptor (e.g., P2Y12R), suggests functional heterodimerization of cysLT1R and other receptors (e.g., functional heterodimerization between cysLT1R, cysLT2R, and P2Y12R) expressed on eosinophil granule membranes; whether this is the case remains to be ascertained. In addition, montelukast's potential off-target effects could not be discounted. Notably, the dose response to the three cysLTs varied. LTC4 and LTE4 elicited ECP secretion only at lower (subnanomolar) concentrations, which was fully consistent with the high-dose inhibition characteristic of the GPCRs. Intriguingly, LTD4 elicited ECP secretion at low and high, but not intermediate, concentrations. This dose response suggests the engagement of two receptors sensitive to LTD4, with the first responding to low LTD4 levels and then exhibiting higher dose inhibition and the second receptor putatively mediating secretion at higher concentrations of LTD4. As previously mentioned, oligomerization of leukotriene and purinergic receptors has been widely suggested [15, 16]. However, whether dimerization of receptors is involved in this response remains to be elucidated. These findings highlight the capacity of cysLTRs to stimulate cell-free granule secretory responses. Furthermore, for granules serving as intracellular organelles these data identify novel mechanisms whereby LTC4 and extracellularly generated LTD4 and LTE4 (if these mediators could be, by any chance, internalized by the cell) may serve as intracrine mediators of eosinophil granule-derived secretion. However, there is no evidence that the cysLT1R, cysLT2R, or P2Y12R expressed on granule membranes is involved in the intracrine actions of cysLTs described previously [32]. This phenomenon is not likely, considering that LTC4- and LTD4-elicited IL-4 release in permeabilized eosinophils is not blocked by inhibitors of cysLT1R and cysLT2R [32].

Bottom Line: Cysteinyl leukotrienes (cysLTs) are cell membrane-impermeant lipid mediators that play major roles in the pathogenesis of eosinophilic inflammation and are recognized to act via at least 2 receptors, namely, cysLT1 receptor (cysLT1R) and cysLT2 receptor (cysLT2R).Eosinophils, which are granulocytes classically associated with host defense against parasitic helminthes and allergic conditions, are distinguished from leukocytes by their dominant population of cytoplasmic crystalloid (also termed secretory, specific, or secondary) granules that contain robust stores of diverse preformed proteins.We also discuss the importance of this finding in eosinophil immunobiology and speculate on its potential role(s) in eosinophilic diseases.

View Article: PubMed Central - PubMed

Affiliation: Institute of Biomedical Sciences, Federal University of Rio de Janeiro, Centro de Ciências da Saúde (CCS), 373 Carlos Chagas Filho Avenue, Room F 14, 1st Floor, Ilha do Fundão, 21941-590 Rio de Janeiro, RJ, Brazil.

ABSTRACT
Cysteinyl leukotrienes (cysLTs) are cell membrane-impermeant lipid mediators that play major roles in the pathogenesis of eosinophilic inflammation and are recognized to act via at least 2 receptors, namely, cysLT1 receptor (cysLT1R) and cysLT2 receptor (cysLT2R). Eosinophils, which are granulocytes classically associated with host defense against parasitic helminthes and allergic conditions, are distinguished from leukocytes by their dominant population of cytoplasmic crystalloid (also termed secretory, specific, or secondary) granules that contain robust stores of diverse preformed proteins. Human eosinophils are the main source of cysLTs and are recognized to express both cysLTs receptors (cysLTRs) on their surface, at the plasma membrane. More recently, we identified the expression of cysLTRs in eosinophil granule membranes and demonstrated that cysLTs, acting via their granule membrane-expressed receptors, elicit secretion from cell-free human eosinophil granules. Herein, we review the multifaceted roles of cysLTs in eliciting eosinophil granule protein secretion. We discuss the intracrine and autocrine/paracrine secretory responses evoked by cysLTs in eosinophils and in cell-free extracellular eosinophil crystalloid granules. We also discuss the importance of this finding in eosinophil immunobiology and speculate on its potential role(s) in eosinophilic diseases.

Show MeSH
Related in: MedlinePlus