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Thomas W Carion, Matthew Greenwood, Karsten Gronert, Elizabeth A Berger; The role of FPR2 signaling in the pathogenesis of bacterial keratitis. Invest. Ophthalmol. Vis. Sci. 2016;57(12):No Pagination Specified.
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The formyl peptide receptor 2 (FPR2) is a promiscuous transmembrane protein belonging to the GPCR family. Ligands for FPR2 include pro-resolving lipids (LXA4, RvD1) and annexin 1. Pro-inflammatory serum amyloid A (SAA) and cathelicidin LL-37 also bind to FPR2. Depending on the ligand, different downstream signal transduction pathways can be activated. The role of FPR2 in disease pathogenesis of bacterial keratitis is the focus of the study described herein.
Bacterial keratitis was induced in resistant BALB/c and susceptible B6 mice using P. aeruginosa (PA) ATCC 19660 for in vivo studies. Peritoneal-derived PMN and macrophages were isolated from B6 and BALB/c mice, and then stimulated with PA for in vitro studies. Lipidomic analysis, real-time RT-PCR, Western Blot, and functional PMN and macrophage assays were used to assess differential FPR2 pathway activation between the two strains. Additionally, to further assess the role of FPR2 in vivo, WRW4 (FPR2 antagonist) was utilized to confirm the observed effects.
mRNA transcript levels of FPR2 were increased in B6 vs BALB/c corneas and B6-derived PMNs and macrophages stimulated with PA. Significant increases in the pro-resolving intermediates for LXA4 and RvD1 (15-HETE and 17-HDHA) were observed in BALB/c vs B6 infected corneas. In contrast, pro-inflammatory SAA and LL-37 were upregulated in B6 vs BALB/c corneas, PMNs and macrophages. Downstream signaling molecules ERK1/2, associated with pro-inflammatory SAA/LL-37 interaction were upregulated in corneas, PMNs and macrophages in B6 vs. BALB/c. While anti-inflammatory signaling molecule p38α/β/γ/δ subunits were upregulated in corneas, PMNs and macrophages in BALB/c vs B6.
As the first study to explore the role of FPR2 in the pathogenesis of bacterial keratitis, our results suggest differential activation of the FPR2 pathway in BALB/c vs B6 mice. Thus, it appears a pro-inflammatory FPR2 interaction contributes to susceptibility observed in B6 mice; while pro-resolving molecule:FPR2 interaction in BALB/c, allows for proper PA clearance and a return to homeostasis. In addition, preliminary studies indicate the neuropeptide, VIP, not only increases mRNA levels of pro-resolving 12-/15-LOX but also anti-inflammatory p38 molecules, which could offer a therapeutic point of intervention for enhancing upstream and downstream pro-resolving FPR2 signal transduction.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.
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