Lysophospholipids of Different Classes Mobilize Neutrophil Secretory Vesicles and Induce Redundant Signaling through G2A

Abstract

Lysophosphatidylcholine has been shown to enhance neutrophil functions through a mechanism involving the G protein-coupled receptor G2A. Recent data support an indirect effect of lysophosphatidylcholine on G2A rather than direct ligand binding. These observations prompted the hypothesis that other lysophospholipids (lyso-PLs) may also signal for human neutrophil activation through G2A. To this end, 1-oleoyl-2-hydroxy-sn-glycero-3-[phospho-l-choline], but also C18:1/OH lyso-PLs bearing the phosphoserine and phosphoethanolamine head groups, presented on albumin, were shown to signal for calcium flux in a self- and cross-desensitizing manner, implicating a single receptor. Blocking Abs to G2A inhibited calcium signaling by all three lyso-PLs. Furthermore, inhibition by both pertussis toxin and U-73122 established signaling via the Gαi/phospholipase C pathway for calcium mobilization. Altered plasma membrane localization of G2A has been hypothesized to facilitate signaling. Accordingly, an increase in detectable G2A was demonstrated by 1 min after lyso-PL stimulation and was followed by visible patching of the receptor. Western blotting showed that G2A resides in the plasma membrane/secretory vesicle fraction and not in neutrophil primary, secondary, or tertiary granules. Enhanced detection of G2A induced by lyso-PLs was paralleled by enhanced detection of CD45, confirming mobilization of the labile secretory vesicle pool. Together, these data show that lyso-PLs bearing various head groups redundantly mobilize G2A latent within secretory vesicles and result in G2A receptor/Gαi/phospholipase C signaling for calcium flux in neutrophils.

NADPH Oxidase-dependent Generation of Lysophosphatidylserine Enhances Clearance of Activated and Dying Neutrophils via G2A

“…Lyso-PS Are Abundant Modified PS Species Generated in Neutrophils Stimulated to Activate the NADPH Oxidase-The signaling potential of lyso-PS was first recognized in its description as a potent mast cell secretagogue, and it has subsequently been given signaling roles in other settings (20,21,39,55,56). Here, we have shown that lyso-PS species were generated in vitro and in vivo as major modified PS species in neutrophils stimulated to activate the NADPH oxidase.…”

“…Macrophage G2A Signaling-We have recently reported that lyso-PS can signal through the G proteincoupled receptor, G2A, for calcium flux (20), and G2A has been recently described as a receptor on macrophages responsible for mediating macrophage chemotactic responses (50,51). Accordingly, G2A appeared to be a reasonable candidate for lyso-PS-dependent enhancement of apoptotic cell engulfment.…”

“…Lyso-PS species have been shown to be biologically active, signaling via G protein-coupled receptors (e.g. GPR34 on mast cells and via G2A on neutrophils (20,21)). …”

Functional metagenomic discovery of bacterial effectors in the human microbiome and isolation of commendamide, a GPCR G2A/132 agonist

“…G2A-knockout mice have increased susceptibility to atherosclerosis and develop late-onset autoimmunity (31). These phenotypes are thought to arise from disruption of G2A-dependent modulation of immune cell function including differentiation and chemotaxis (62,(64)(65)(66)(67)(68)(69)(70)(71). This suggests that Bacteroides spp.…”

Immunomodulatory Actions of Lysophosphatidylcholine

“…Synergistically enhances PMA-induced superoxide anion generation (Englberger et al, 1987) Generation from stored blood (Silliman et al, 1994;Silliman et al, 1996) Superoxide anion generation is inhibited with PI3K inhibitors (Nishioka et al, 1998) H 2 O 2 generation/bactericidal activity in a G2A-dependent manner (Yan et al, 2004) Priming of NADPH oxidase is dependent on [Ca 2+ ] i increase Apoptosis↓ (Biffl et al, 2003) [Ca 2+ ] i ↑ via G2A/mobilization of G2A along with secretory vesicles (Frasch et al, 2007) [Ca 2+ ] i ↑ via PLC in HL60 cells (Okajima et al, 1998) macrophages, chemotaxis of these cells to LPC is mediated by G2A (Peter et al, 2008).…”