15‐Epi‐lipoxin A ₄ inhibits human neutrophil superoxide anion generation by regulating polyisoprenyl diphosphate phosphatase 1

Abstract

Regulation of leukocyte activation is critical to limit unintended tissue injury during acute inflammation. On neutrophil activation, polyisoprenyl diphosphate phosphatase 1 (PDP1) rapidly converts presqualene diphosphate to presqualene monophosphate to facilitate cell activation. Lipoxins are potent anti-inflammatory mediators for neutrophils, yet their counterregulatory signaling mechanisms remain to be determined. 15-Epi-lipoxin A4 (15-epi-LXA4) blocked agonist-initiated association of the nicotinamide adenine dinucleotide phosphate oxidase components p47(PHOX) and p22(PHOX) in human neutrophils. 15-Epi-LXA4 (0.1-100 nM) inhibited neutrophil superoxide anion (O2(-)) generation in a concentration- and ALX/FPR2 receptor-dependent manner that was disrupted by PDP1-specific antibodies. In differentiated HL60 cells, a myeloid cell line, agonist-initiated O2(-) generation was inhibited by PDP1 siRNA. Recombinant human PDP1 was directly phosphorylated in vitro by select protein kinase C (PKC) isoforms, including PKCβII. When neutrophils were exposed to formyl-methionyl-leucyl-phenylalanine (fMLP), PKCβII was rapidly phosphorylated and physically associated with PDP1. Agonist-initiated conversion of neutrophil presqualene diphosphate to presqualene monophosphate was blocked by PKCβII inhibition. Neutrophil exposure to 15-epi-LXA4 attenuated fMLP triggered PKCβII phosphorylation and its interactions with PDP1. Together, these findings indicate that PDP1 serves an integral signaling role in neutrophil proinflammatory responses and as a target for counter-regulatory mediators.

Effects of Lipoxin A4 on antimicrobial actions of neutrophils in sepsis

“…In ex vivo studies, LXA 4 had no effect on PMA stimulated neutrophil free radical generation in CLP cells. The variability in free radical production between different studies may be related to the number of platelets in the preparation as LXA 4 reduction in free radical production is dependent on neutrophil-platelet interaction [49]. Taken together with in vivo data, the results support the notion that LXA 4 did not cause excessive neutrophil free radical formation in sepsis.…”

“…On the other hand, excessive neutrophil derived free radical production has been implicated in tissue injury in several inflammatory conditions [4,5]. The effects of LXA 4 on neutrophil respiratory burst is highly variable, where there are studies which report no change in free radical production in human neutrophils after fMLP stimulation [6,29], and also a decrease [48,49]. Our results showed that CLP only rats had lower blood neutrophil free radical production compared to sham controls while in vivo LXA 4 administration did not significantly affect PMA stimulated free radical production compared to CLP.…”

Attenuation of Lipopolysaccharide-Induced Lung Vascular Stiffening by Lipoxin Reduces Lung Inflammation

“…A recent study by Carlo and colleagues demonstrates inhibition of agonist-induced assembly of NADPH oxidase complex by eLXA 4 and inhibition of superoxide anion generation by human neutrophils (14).…”

Resolution of Acute Inflammation in the Lung

“…One intracellular signaling mechanism for SPM regulation of cellular responses in human neutrophils is via receptor-mediated inhibition of protein kinase C – βII (PKCβII) phosphorylation and activation of polyisoprenyl diphosphate phosphatase 1 (PDP1), a pivotal phosphatase for polyisoprenyl diphosphate remodeling (131). Polyisoprenyl phosphates are present in resting cell membranes.…”

“…The phosphatase responsible for the rapid conversion of PSDP to PSMP was recently identified as PDP1 (135, 136). Both PSDP and PDP1 are present in human neutrophils (132, 136), and when neutrophils are activated by soluble pro-inflammatory stimuli, there is an increase in phospho-PKCβII (131) that can phosphorylate PDP1 and lead to PSDP conversion to PSMP, facilitating NADPH oxidase assembly and other functional responses (131). In contrast, the SPM 15-epi-LXA 4 interacts with ALX/FPR2 receptors to block agonist-triggered PKCβII phosphorylation and subsequent PDP1 activation, leading to increased availability of PSDP that restrains cellular pro-inflammatory responses (131).…”