Serum amyloid A and pairing formyl peptide receptor 2 are expressed in corneas and involved in inflammation-mediated neovascularization

AIM To solidify the involvement of Saa-related pathway in corneal neovascularization (CorNV). The pathogenesis of inflammatory CorNV is not fully understood yet, and our previous study implicated that serum amyloid A (Saa) l {Saal) and Saa.3 were among the genes up-regulated upon CorNV induction in mice. METHODS Microarray data obtained during our profiling project on CorNV were analyzed for the genes encoding the four SAA family members (Saai-4), six reported SAA receptors (formyl peptide receptor 2, Tlr2, Tlr4, Cd.36, Scarbi, P2rxy) and seven matrix metallopeptidases {Mrap) la, lb, 2, 3, 9, 10, 13 reportedly to be expressed upon SAA pathway activation. The baseline expression or changes of interested genes were further confirmed in animals with CorNV using molecular or histological methods. CorNV was induced in Balb/c and C5 7BL/6 mice by placing either three interrupted 1 0-0 sutures or a 2 mm filter paper soaked with sodium hydroxide in the central area of the cornea. At desired time points, the corneas were harvested for histology examination or for extraction of mRNA and protein. The mRNA levels of Saal, Saa.3, Fpr2, Mmp2 and Mmpg in corneas were detected using quantitative reverse transcription-PCR, and SAA3 protein in tissues detected using immunohistochemistry or western blotting. RESULTS Microarray data analysis revealed that Saal, Saag, Fpr2, Mmp2, Mmpg messengers were readily detected in normal corneas and significantly up-regulated upon CorNV induction. The changes of these five genes were confirmed with real-time PCR assay. On the contrary, other SAA members (Saa2, Saa4), other SAA receptors {Tlr2, Tlr4, Cd6, P2rxy, etc), or other Mmps {Mmpia, Mmpib, Mrapg, Mrapio, Mmpig) did not show consistent changes. Immunohistochemistry study and western blotting further confirmed the expression of SAA3 products in normal corneas as well as their up-regulation in corneas with CorNV. CONCLUSION SAA-FPR2 pathway composing genes were expressed in normal murine corneas and, upon inflammatory stimuli challenge to the corneas, their expressions were up-regulated, suggesting their roles in pathogenesis of CorNV. The potential usefulness of SAA-FPR2 targets in future management of CorNV-related diseases deserves investigation.