Formyl peptide receptor 1 is functionally expressed on human lens epithelial cells and promotes lens homeostasis (149.19)

Abstract

Abstract Formyl peptide receptor 1 (FPR1) is a chemoattractant receptor specific for phagocytes, without clearly defined function for non-hematopoietic cells. We found that the lens of Fpr1-/- mice degenerates by 6 months of age without infection or inflammation. Thus, we hypothesized functional expression of FPR1 on lens epithelial cells, the only cell type present in lens. Flow cytometry, qPCR and PTX sensitive fMLF-induced calcium flux assays showed functional FPR1 expression in fetal human lens (FHL-124) cells and in the human lens epithelial cell line SRA 01/04. Despite strong anti-FPR1 binding to lens cells by FACS, similar to that observed for human neutrophils or hFPR1-transfected HEK 293 cells, fluorescent FPR1 ligand fNLFNYK-Fl only poorly bound to FHL-124 cells, with > 80% non-specific binding; by contrast, human neutrophils and hFPR1-transfected HEK-293 cells exhibited >70% specific binding. The KD of fNLFNYK-Fl at neutrophil FPR1 and hFPR1-transfected HEK-293 cells was 2-3 nM, but ~ 0.2 nM in FHL-124 cells. fMLF internalized ~80% of neutrophil FPR1, but only ~25% of FHL-124 FPR1. FPR1 protein in FHL-124 cells resisted siRNA-mediated knockdown, despite strongly reduced mRNA levels, and could only be detected by Western blot using alkali-stripped membranes, suggesting high-molecular complexes of FPR1 and peripheral membrane proteins. The data suggest different conformations of FPR1 in neutrophils versus lens epithelial cells and a key function in lens maintenance.