Abstract
Purpose :
In genome wide association studies, mutations in complement proteins were found to be highly associated with age-related macular degeneration (AMD). While this association has been well studied, little progress has been made in understanding or pharmacologically intervening in AMD progression from a complement perspective. Rodent AMD model systems don’t fully mimic the pathophysiological progression of AMD. We sought to better understand complement expression, localization, and activity within animals used as AMD models in comparison to their role in humans.
Methods :
Mouse, rat, and human donor eyes were used in this study. C3, C5, and CFH gene expression was assessed through RNA in situ hybridization, quantitative RT-PCR, and single-cell RNA-sequencing. Complement protein localization was studied via immunohistochemistry.
Results :
C3 transcripts and protein are localized in the choroid of rat, mice, and human eyes. The rodent species also contain C3 protein in the RPE layer. C5 was minimally expressed/detected in all three species; however, it did show species-dependent localization. C5 was localized to the RPE or retina in mice and rats, respectively, while human C5 was found in drusen, choriocapillaris, and the choroid. Interstingly, species differences were found when examining CFH. Both mice and rats expressed CFH mainly in the RPE, with little to no expression from the choroid. In contrast, expression from human donor eyes was confined to the choroid. This localization pattern was seen at the protein level with rodent CFH protein being found in both the RPE and choroid and human protein being found solely in the choroid and sclera.
Conclusions :
Unsuccessful attempts to treat AMD by inhibition of complement in the eye are based off work done in rodent model systems. We found that complement components C3, C5, and CFH vary among species in localization. This key finding may shed light on why rodent model systems fail to recapitulate AMD fully. The species-specific complement variation gains more importance upon realization that the differing regions between rodents and humans are separated by the Bruch’s membrane – a non-permeable barrier within the eye. Through our unbiased characterization of core complement proteins C3, C5 and CFH in mice, rats, and human eyes we have uncovered species-specific expression and localization patterns that are informative to future therapeutic design.
This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.