Human neutrophil formyl peptide receptor phosphorylation and the mucosal inflammatory response

Area of Science:

• Immunology
• Cell Biology
• Gastroenterology

Background:

• Bacterial/mitochondrial formyl peptide receptor 1 (fMLF) analogs activate neutrophils (PMN) at infection sites, aiding inflammation and wound healing.
• FPR1 signaling is crucial in neutrophil function during infection and tissue repair.
• Understanding FPR1 regulation is key to modulating inflammatory responses.

Purpose of the Study:

• To quantify unphosphorylated (UFPR1) and total (TFPR1) FPR1 levels in isolated PMN.
• To investigate the mechanisms regulating UFPR1 levels in response to fMLF and other stimuli.
• To assess FPR1 expression in PMN from patients with active ulcerative colitis (UC).

Main Methods:

• Quantification of UFPR1 and TFPR1 using phosphosensitive and phosphorylation-independent antibodies.
• Stimulation of isolated PMN with fMLF, its antagonists, metabolic inhibitors, and other signaling molecules.
• Assessment of PMN FPR1 levels after transmigration through cultured intestinal epithelial cells.
• Analysis of PMN and mucosal samples from patients with active UC.

Main Results:

• fMLF stimulation caused a rapid and significant decrease in UFPR1 levels (70% reduction) in isolated PMN, while TFPR1 remained largely unchanged.
• Antagonists and metabolic inhibitors prevented the fMLF-induced UFPR1 decrease, suggesting a G protein-insensitive phosphorylation event.
• PMN from UC patients showed decreased UFPR1 in inflamed mucosal samples, correlating with active inflammation.
• UFPR1 loss is attributed to C-terminal S/T phosphorylation, distinct from G-protein mediated signaling.

Conclusions:

• fMLF-dependent phosphorylation leads to a rapid loss of UFPR1 from the neutrophil surface.
• This phosphorylation event is G protein-insensitive and occurs in isolated PMN and in vivo during active inflammation.
• The observed UFPR1 decrease in PMN from UC patients suggests a role in inflammatory bowel disease pathogenesis.