Similarities and differences between the responses induced in human phagocytes through activation of the medium chain fatty acid receptor GPR84 and the short chain fatty acid receptor FFA2R

Abstract

GPR84 is a recently de-orphanized member of the G-protein coupled receptor (GPCR) family recognizing medium chain fatty acids, and has been suggested to play important roles in inflammation. Due to the lack of potent and selective GPR84 ligands, the basic knowledge related to GPR84 functions is very limited. In this study, we have characterized the GPR84 activation profile and regulation mechanism in human phagocytes, using two recently developed small molecules that specifically target GPR84 agonistically (ZQ16) and antagonistically (GLPG1205), respectively. Compared to our earlier characterization of the short chain fatty acid receptor FFA2R which is functionally expressed in neutrophils but not in monocytes, GPR84 is expressed in both cell types and in monocyte-derived macrophages. In neutrophils, the GPR84 agonist had an activation profile very similar to that of FFA2R. The GPR84-mediated superoxide release was low in naïve cells, but the response could be significantly primed by TNFα and by the actin cytoskeleton disrupting agent Latrunculin A. Similar to that of FFA2R, a desensitization mechanism bypassing the actin cytoskeleton was utilized by GPR84. All ZQ16-mediated cellular responses were sensitive to GLPG1205, confirming the GPR84-dependency. Finally, our data of in vivo transmigrated tissue neutrophils indicate that both GPR84 and FFA2R are involved in neutrophil recruitment processes in vivo. In summary, we show functional similarities but also some important differences between GPR84 and FFA2R in human phagocytes, thus providing some mechanistic insights into GPR84 regulation in blood neutrophils and cells recruited to an aseptic inflammatory site in vivo.

Functional selective ATP receptor signaling controlled by the free fatty acid receptor 2 through a novel allosteric modulation mechanism

“…No transient rise in [Ca 2+ ] i was induced in these cells by propionate in the presence or absence of Cmp58 (Fig. 7C), confirming the earlier finding that monocytes lack functional FFA2Rs (14,34). However, monocytes express functional P2Y 2 Rs, as shown by the ability of ATP to induce a transient rise in [Ca 2+ ] i in these cells (Fig.…”

“…This gains support from the fact that the specific FFA2R antagonists (CATPB and GLPG0974) inhibit the response as well as from the fact that ATP was unable to activate the oxidase in monocytes that lack functional FFA2Rs (this study and refs. 14,34). In addition, as the receptor crosstalk activation is clearly reliant on Gaq, this implies that the signals that initiate the crosstalkregulated activation of FFA2R are downstream of this G-protein subunit.…”

Barbadin selectively modulates FPR2-mediated neutrophil functions independent of receptor endocytosis

“…A significantly lower degree of priming effect was observed in cells that were exposed to a reduced concentration (from 10 µM to 0.1 µM) than cells incubated constantly to an effective priming concentration (10 µM) of Barbadin (Fig 4 B and C). This suggests that the neutrophil priming induced by Barbadin is a process that is reversible, unlike many other priming processes that involve an irreversible process of neutrophil granule secretion [17,29,30]. The effect of Barbadin on FPR2-mediated ROS production resembled the effect induced by the F-actin-disrupting agent latrunculin A. Barbadin and latrunculin A both prolonged and increased the magnitude of FPR2-mediated neutrophil ROS production as compared to the corresponding ROS production in non-treated control cells ( Fig 4D).…”

“…Our data reveal that Barbadin is able to prime neutrophils for enhanced FPR2-mediated ROS production. Neutrophil priming is a well-known process both in vitro and in vivo [17,29,30,34,35], and an increased exposure of intracellular granule-localized receptors to the plasma membrane as a result of granule secretion has been suggested to be one of the main mechanisms that augments neutrophil NADPH-oxidase activity [17,29,30]. We next determined whether the receptor mobilizing effect with increased surface FPR2 expression could account for the Barbadin-induced priming effect.…”

“…The precise role of -arrestin in regulating FPR2 signaling and function is not known, but it is clear that some FPR2 agonists, but not all, are capable of promoting recruitment of -arrestin [5]. We have previously proposed that the dynamic transfer of agonist-occupied FPR2 from an active signaling state to a non-signaling state (i.e., receptor desensitization) is not directly associated with the ability of the receptoragonist complex to recruit -arrestin [9], but appears to involve receptor coupling to the actin 5 cytoskeleton [11,[15][16][17][18]. Nevertheless, the ability to recruit -arrestin is of functional importance also in neutrophils as demonstrated by the finding that FPR2 agonists that are biased away from -arrestin recruitment induce ROS production without concomitant induction of chemotactic migration [9][10][11].In the present study, we investigated the role of β-arrestin in regulating FPR2 endocytosis and the NADPH-oxidase activation in neutrophils by using Barbadin as a tool compound.…”