Dynamic changes of FasL protein expression in retinal tissue with aging in retinal degeneration mice

Abstract

Background Retinal transplantation is a new approach to the treatment of retinal degeneration diseases, and how to avoid or reduce the immune rejection after transplantation is a problem.In experimental studies on retinal transplantation, C57BL/6 mice are often used as donors and rd mice serve as recipients.Studies showed that Fas ligand (FasL) protein induces the apoptosis of Fas+ inflammatory cells by FasL/Fas signal pathway, speculating that FasL protein is associated with immune rejection after transplantation. Objective The aim of this study was to investigate FasL protein expression change in retinas of C57BL/6 mice and rd mice with aging and reveal the immune characteristics of the mouse retinas. Methods The frozen sections of eyeball from C57BL/6 mice and rd mice at the age of postnatal (PN)-0 week, PN-1 week, PN-2 week, PN-3 week and PN-4 week were prepared.The expression of FasL protein in the mouse retinas was examined by immnofluorescense technique.Images were acquired by fluorescence microscope and analyzed semi-quantitively by software from laser scanning confocal microscope as the fluorescence intensity (FI). The results were compared among different strains of mice. Results The retina developed imperfectly in PN-1 week C57BL/6 mice and FasL protein was positively expressed in the whole retina.In PN-2, 3 and 4 week C57BL/6 mice, retinas finished the development with 10 layers, and retinal pigment epithelium (RPE), inner segment (IS), outer limiting membrane (OLM), outer plexiform layer (OPL), inner nuclear layer (INL), inner plexiform layer (IPL) and ganglion cell layer (GCL). Retinal structure and expression of FasL protein in the whole retina of rd mice in the PN-1 week were similar with C57BL/6 mice, however, ONL cells of rd mice were evidently decreased with aging.The RPE, OPL, INL, IPL and GCL expressed the FasL protein in PN-2, PN-3 and PN-4 week rd mice.The mean FI of FasL protein in the RPE layer was 184.199±16.747, 186.797±7.904 and 184.319±18.795 in rd mice of PN-2 week, PN-3 week and PN-4 week, which were significantly higher than 160.402±22.851, 160.995±22.799 and 105.787±17.676 in C57BL/6 mice (t=-3.360, P=0.002; t'=-4.277, P=0.000; t=-12.175, P=0.000). There were not significant differences in the mean FI of FasL protein in IPL between C57BL/6 mice and rd mice at ages of PN-2 week, PN-3 week and PN-4 week (all at P>0.05). Conclusions The cells of retinal ONL are gradually decreased with the development of rd mice, and FasL protein expression intensity in RPE is evidently enhanced in rd mice compared with C57BL/6 mice. Key words: Fas ligand protein; Retina/immunology; Pigment epithelium of eye/immunology; Apoptosis; Immune privilege; Retinitis pigmentosa; Mice, inbred, C57BL; rd mice