Differential expression of complement proteins in mammalian eyes

Abstract

Purpose : Age related macular degeneration (AMD) results from complex interactions of environmental and genetic risk factors. Genetic studies have shown strong association between complement genes and AMD. Rodent models based on expression of human genetic risk variants in complement genes have exhibited limited phenotypic similarity to human disease. We have shown that complement factor H (CFH) and complement 3 (C3) mRNA expression patterns are different between human and rodent eyes (Hua Yang etc, 2022 ARVO). In the present study, we further investigated CFH and C3 protein expression across different species.

Methods : Flat mount, cryo-and paraffin sections of normal mouse, rat and human donor eyes were immunostained to determine the CFH and C3 protein expression. Donor eyes from patients diagnosed with AMD (aged from 39 to 96 years old) and from rats after light damage were also examined. Second antibody only, CFH or C3 knockout rat eyes were used as negative controls.

Results : In rodent eyes (both mouse and rat), CFH protein was broadly expressed in the retinal pigment epithelium (RPE), choroid and sclera, with some expression found in inner nuclear layer (INL), inner segment and retinal ganglion cell (RGC) layers of the retina. C3 protein was expressed mainly in RGC, INL, RPE, choroid and sclera. However, in human eye, CFH and C3 proteins were strongly expressed in the choroid capillaries and surrounding tissues. Some expression is also found in sclera. C3 or CFH proteins were absent in human RPE cells with or without AMD.

Conclusions : Our results show that CFH and C3 protein expression patterns are different between human and rodent eyes. Rodent animal models based on manipulating CFH or C3 expression might not represent human AMD. These data suggest that choroid, but not RPE is the main site of complement action in the pathogeneses of AMD.

This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.