Impaired Binding of the Amd-Associated Complement Factor H 402h Allotype to Bruch’s Membrane in Human Retina

Abstract

Purpose: : Genetic association studies have demonstrated a strong association between the Y402H polymorphism in complement factor H (CFH) and AMD. The purpose of this study was to investigate the effect of this amino acid change on the localization of CFH in human macula tissue.

Methods: : Differentially labeled 402H and 402Y variants of CFH (either in the context of full-length protein (flCFH), purified from genotyped donors, or recombinant proteins comprising CCPs6-8) were simultaneously applied to human macula tissue sections and their binding determined by fluorescent microscopy. Sections were pretreated with specific glycosaminoglycan (GAG)-degrading enzymes to assess the role of these sulfated polysaccharides in CFH binding. Endogenous CFH was localized in the macula using anti-CFH antibodies.

Results: : The AMD-associated 402H variant bound less well to the Bruch’s membrane than the 402Y protein, whereas both variants bound equally well to the RPE. The GAGs heparan sulfate and dermatan sulfate were shown to play a major role in mediating these interactions and were also implicated in the localization of endogenous CFH. Competition experiments with specific heparin oligosaccharides indicate that the two variants of CFH recognize distinct structural features of heparan sulfates in the macula.

Conclusions: : We propose that the impaired binding of the 402H CFH variant to Bruch’s membrane results in complement over activation leading to inflammation, thus contributing directly to the development/progression of AMD. Our results suggest a disease mechanism and add weight to the genetic association studies implicating the 402H allele as an important risk factor in AMD.

Keywords: age-related macular degeneration • immunomodulation/immunoregulation • immunohistochemistry