Aspirin-Triggered Lipoxins Override the Apoptosis-Delaying Action of Serum Amyloid A in Human Neutrophils: A Novel Mechanism for Resolution of Inflammation

Abstract

Myeloperoxidase (MPO), a heme protein abundantly expressed in the azurophilic granules in neutrophils generates cytotoxic oxidants and signals through the adhesion molecule CD11b/CD18 (Mac‐1) to activate and rescue neutrophils from apoptosis. Since aspirin‐triggered 15‐epi‐lipoxin A4 (15‐epi‐LXA4) inhibits Mac‐1‐mediated neutrophil adhesion, we studied its impact on MPO suppression of neutrophil apoptosis. Pretreatment of neutrophils with 15‐epi‐LXA4 or its metabolically stable analog 15‐epi‐16‐p‐fluorophenoxy‐LXA4 through downregulation of surface expression of Mac‐1 and inhibition of MPO release overcame the powerful anti‐apoptosis signal from MPO. 15‐epi‐LXA4 promoted apoptosis by attenuating MPO‐induced concurrent activation of ERK and phosphatidylinositol 3‐kinase/Akt‐mediated phosphorylation of Bad and reducing the expression of the anti‐apoptotic protein Mcl‐1. These led to collapse of mitochondrial transmembrane potential, cytochrome c release, resulting in increased caspase‐3 activity. The pro‐apoptotic action of 15‐epi‐LXA4 was predominant over MPO‐mediated effects even when 15‐epi‐LXA4 was added at 4‐hour post‐MPO. 15‐epi‐LXA4 did not inhibit the catalytic activity of MPO. Our results indicate that through overriding the MPO survival signal, aspirin‐triggered lipoxins may prevent neutrophil‐mediated tissue injury. (Grant support: CIHR MOP‐64283).

Ligand-specific conformational change of the G-protein–coupled receptor ALX/FPR2 determines proresolving functional responses

“…Of note, this leukocyte type expresses FPR1 and ALX, but not FPR3 (2), making it ideal to explore heterodimerization in primary cells. We conducted functional experiments using protocols validated for LXA 4 : this ALX agonist abolishes the delay in apoptosis of SAA-treated neutrophils (7). In line with these studies, addition of SAA augmented neutrophil lifespan with a significant effect at >6 h (Fig.…”

“…The results obtained with the transfected HEK293 cell model were therefore validated with primary neutrophils. Filép and coworkers have described the ability of LXA 4 to override the effects of SAA, a prosurvival factor for human neutrophils (7). Fine tuning of neutrophil lifespan is fundamental for an appropriate inflammatory reaction, avoiding the risk for chronicity (31,32).…”

Proresolving and Tissue-Protective Actions of Annexin A1–Based Cleavage-Resistant Peptides Are Mediated by Formyl Peptide Receptor 2/Lipoxin A4 Receptor

“…Annexin A1 (AnxA1), a 37-kDa glucocorticoid regulated protein, possesses anti-inflammatory and proresolving actions reducing human (4) and murine (5) neutrophil-endothelial interactions, accelerating neutrophil apoptosis (6), stimulating macrophage efferocytosis (7) and neuroprotection (8). Consistent with this notion, AnxA1-deficient mice display inappropriate inflammatory responses in a number of disease models including experimental autoimmune encephalomyelitis (9), cerebral ischemia reperfusion (10), and nociception (11).…”

“…Indeed, elevated local levels of proinflammatory mediators in inflammatory exudates can lead to aberrant neutrophil activation and reduce programmed death, favoring perpetuation of tissue damage with the downstream risk for chronic inflammation (3). Serum amyloid A, an acute-phase protein that is used as a marker of disease activity and severity in a number of chronic diseases, is one of the mediators able to promote neutrophil recruitment (6,30) together with extending their persistence at the site of inflammation (6). AnxA1 2-50 and CR-AnxA1 2-50 potently reversed the antiapoptotic actions of SAA.…”

Biasing the lipoxin A 4 /formyl peptide receptor 2 pushes inflammatory resolution

“…ALX binds an unusually large number of structurally diverse ligands and conveys contrasting biological signals. For example, ALX mediates the proinflammatory actions, including leukocyte trafficking, activation, and delaying neutrophil apoptosis of the acute-phase protein serum amyloid A (SAA) and the antimicrobial peptide LL-37 (7,8). Annexin A1 (AnxA1), AnxA1-derived peptide Ac2-26, and lipoxin A 4 (LXA 4 ) also signal through ALX to inhibit leukocyte recruitment, enhance neutrophil apoptosis, and macrophage efferocytosis (2, 7, 9-11), key events in inflammatory resolution.…”