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The subcellular localization of the receptor for platelet-activating factor in neutrophils affects signaling and activation characteristics.

ABSTRACT: The localization in neutrophils, of the receptor for platelet-activating factor (PAFR), has been determined using subcellular fractionation and a receptor mobilization protocol. We show that the PAFR is expressed primarily in the plasma membrane. Although activation of neutrophils by PAF induces responses typical also of agonists that bind the formyl peptide receptors (FPR), known to be stored in mobilizable organelles, some quantitative as well as qualitative differences were observed when neutrophils were activated through these receptors. PAF is equipotent to fMLF (high affinity agonist for FPR1) to cleave off L-selectin and to induce granule/vesicle secretion but is more potent than fMLF to induce a rise in intracellular Ca(2+). Similar to fMLF, PAF induced also a robust release of reactive oxygen species, but with higher EC50 value and was less sensitive to a PI3K inhibitor compared to the fMLF response. Despite the lack of a granule localized storage pool of receptors, the PAF-induced superoxide production could be primed; receptor mobilization was, thus, not required for priming of the PAF response. The desensitized PAFR could not be reactivated, suggesting that distinct signaling pathways are utilized for termination of the responses triggered through FPR1 and PAFR.

SUBMITTER: Andreasson E

PROVIDER: S-EPMC3773398 | biostudies-literature | 2013

REPOSITORIES: biostudies-literature

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The subcellular localization of the receptor for platelet-activating factor in neutrophils affects signaling and activation characteristics.

Andréasson Emil E Önnheim Karin K Forsman Huamei H

Clinical & developmental immunology 20130829

The localization in neutrophils, of the receptor for platelet-activating factor (PAFR), has been determined using subcellular fractionation and a receptor mobilization protocol. We show that the PAFR is expressed primarily in the plasma membrane. Although activation of neutrophils by PAF induces responses typical also of agonists that bind the formyl peptide receptors (FPR), known to be stored in mobilizable organelles, some quantitative as well as qualitative differences were observed when neut ...[more]

PMID: 24069041

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Project description:Platelet-activating factor (PAF) desensitizes as well as stimulates its various target cells, We find that human polymorphonuclear neutrophils (PMN) exposed to PAF became maximally unresponsive to a second PAF challenge within 15-90 s in assays of Ca2+ mobilization and degranulation. The cells regained full PAF-sensitivity over the ensuing 20-40 min. These effects correlated with changes in PAF receptor availability. PMN treated with PAF, washed in regular buffer and assayed for PAF binding exhibited falls (maximal in 15 s), followed by rises (reaching control levels by 60 min), in the number of high-affinity PAF receptors. However, tracking studies showed that [3H]PAF accumulated on the cell surface for approximately 2 min before being internalized. Regular-buffer washes did not remove this superficial PAF, whereas a washing regimen using excess albumin to adsorb PAF removed 99% of the surface compound. PMN washed by the latter regimen after PAF exposure lost PAF receptors relatively slowly (maximal at approximately 5 min), but the ultimate extent of this loss and the rate at which receptor expression normalized were similar to those of cells washed in regular buffer. Neither cycloheximide nor actinomycin D influenced the course of the receptor changes, but two protein kinase C (PKC) blockers, staurosporine and 1-(5-isoquinolinesulphonyl)piperazine, inhibited the receptor-receptor-depleting actions of PAF. Indeed, a phorbol diester activator of PKC also caused PMN to decrease high-affinity PAF receptor numbers, and the two PKC blockers antagonized this action at concentrations that inhibited PAF-induced PAF receptor losses. We conclude that: (a) PAF induces PMN to down-regulate and then to re-express PAF receptors independently of protein synthesis; (b) these changes are likely to underlie the later stages and reversal of desensitization; (c) the onset (t < or = 2 min) of desensitization, however, precedes receptor down-regulation and must be due to receptor uncoupling from transductional elements; and (d) down-regulation of receptors for PAF appears to be mediated by PKC and/or elements inhibited by PKC blockers.

Project description:This data series contains spotted oligo microarray data from 10 different experiments using Agilent Rat v2 microarrays. This data is being made public in support of Fillon S et al. Journal of Immunology, (2006). Proinflammatory bacterial components are at least partially responsible for causing the clinical features of sepsis, a syndrome that causes >100,000 deaths each year in the US (1). In the case of Gram positive infection, a key bacterial element recognized by the innate immune system is the cell wall, a complex network of peptidoglycan covalently linked to teichoic acids, proteins and lipoproteins. The current model of innate immune recognition of Gram positive bacteria suggests bacterial cell wall interacts with host recognition proteins, such as toll-like receptors (TLR) and Nod proteins. We describe an additional recognition system mediated by the platelet activating factor receptor (PAFr) and directed to the pathogen associated molecular pattern (PAMP) phosphorylcholine that results in uptake of bacterial components into host cells. Intravascular choline-containing cell walls bound to endothelial cells and caused rapid lethality in wild type, Tlr2-/- and Nod2-/- mice, but not in Pafr-/- mice. Cell wall exited the vasculature into the heart and brain, accumulating within endothelial cells, cardiomyocytes and neurons in a PAFr-dependent way. Physiological consequences of the cell wall/PAFr interaction were cell specific, being noninflammatory in endothelial cells and neurons, but causing rapid loss of cardiomyocyte contractility that contributed to death. Thus, PAFr shepherds phosphorylcholine-containing bacterial components such as cell wall into host cells from where the response ranges from quiescence to severe pathophysiology. Keywords: Competitive hybridizations The ten experiments in this series comprise of four distinct experiments, two of which were performed as biological triplicates and two as biological duplicates. The table below describes the overall design in detail: File Name Experiment 16011868017643v41_GEO_format.txt RBCEC Replicate 1 16011868017644v41_GEO_format.txt RBCEC Replicate 2 251186821865v41_GEO_format.txt Neuron Replicate 1 16011868021377v41_GEO_format.txt Neuron Replicate 2 251186821690v41_GEO_format.txt CW/Lyt44 Replicate 1 251186821691v41_GEO_format.txt CW/Lyt44 Replicate 2 251186821692v41_GEO_format.txt CW/Lyt44 Replicate 1 251186821693v41_GEO_format.txt CW+TNF/Lyt44+TNF Replicate 1 251186821694v41_GEO_format.txt CW+TNF/Lyt44+TNF Replicate 2 251186829677v41_GEO_format.txt CW+TNF/Lyt44+TNF Replicate 3

Project description:Platelet-activating factor (PAF) is an important mediator of the systemic inflammatory response. In the case of sepsis, proper activation and function of neutrophils as the first line of cellular defense are based on a well-balanced physiological response. However, little is known about the role of PAF in cellular changes of neutrophils during sepsis. Therefore, this study investigates the reaction patterns of neutrophils induced by PAF with a focus on membrane potential (MP), intracellular pH, and cellular swelling under physiological and pathophysiological conditions and hypothesizes that the PAF-mediated response of granulocytes is altered during sepsis. The cellular response of granulocytes including MP, intracellular pH, cellular swelling, and other activation markers were analyzed by multiparametric flow cytometry. In addition, the chemotactic activity and the formation of platelet-neutrophil complexes after exposure to PAF were investigated. The changes of the (electro-)physiological response features were translationally verified in a human ex vivo whole blood model of endotoxemia as well as during polymicrobial porcine sepsis. In neutrophils from healthy human donors, PAF elicited a rapid depolarization, an intracellular alkalization, and an increase in cell size in a time- and dose-dependent manner. Mechanistically, the alkalization was dependent on sodium-proton exchanger 1 (NHE1) activity, while the change in cellular shape was sodium flux- but only partially NHE1-dependent. In a pathophysiological altered environment, the PAF-induced response of neutrophils was modulated. Acidifying the extracellular pH in vitro enhanced PAF-mediated depolarization, whereas the increases in cell size and intracellular pH were largely unaffected. Ex vivo exposure of human whole blood to lipopolysaccharide diminished the PAF-induced intracellular alkalization and the change in neutrophil size. During experimental porcine sepsis, depolarization of the MP was significantly impaired. Additionally, there was a trend for increased cellular swelling, whereas intracellular alkalization remained stable. Overall, an impaired (electro-)physiological response of neutrophils to PAF stimulation represents a cellular hallmark of those cells challenged during systemic inflammation. Furthermore, this altered response may be indicative of and causative for the development of neutrophil dysfunction during sepsis.

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The subcellular localization of the receptor for platelet-activating factor in neutrophils affects signaling and activation characteristics.

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The subcellular localization of the receptor for platelet-activating factor in neutrophils affects signaling and activation characteristics.

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