The rareC9P167S risk variant for age-related macular degeneration increases polymerization of the terminal component of the complement cascade

Abstract

Age-related macular degeneration (AMD) is a complex neurodegenerative eye disease with behavioral and genetic etiology, and is the leading cause of irreversible vision loss among elderly Caucasians. Functionally significant genetic variants in the alternative pathway of complement have been strongly linked to disease. More recently, a rare variant in the terminal pathway of complement has been associated with increased risk, Complement component 9 (C9) P167S. To assess the functional consequence of this variant, C9 levels were measured in two independent cohorts of AMD patients. In both cohorts it was demonstrated that the P167S variant was associated with low C9 plasma levels. Further analysis showed that patients with advanced AMD had elevated sC5b-9 compared to those with non-advanced AMD, although this was not associated with the P167S polymorphism. Electron microscopy of membrane attack complexes (MAC) generated using recombinantly produced wild type or P167S C9 demonstrated identical MAC ring structures. In functional assays, the P167S variant displayed a higher propensity to polymerise and a small increase in its ability to induce haemolysis of sheep erythrocytes when added to C9-depleted serum. The demonstration that this C9 P167S AMD risk polymorphism displays increased polymerisation and functional activity provides a rationale for the gene therapy trials of sCD59 to inhibit the terminal pathway of complement in AMD that are underway.

Semi-Quantitative Multiplex Profiling of the Complement System Identifies Associations of Complement Proteins with Genetic Variants and Metabolites in Age-Related Macular Degeneration

“…Our study confirmed previously described associations of FHR-2 levels with genetic variants at the CFH locus [31], and reduced FB levels with the p.Leu9His (rs4151667) variant in the CFB gene [25,26]. The AMD-risk variant p.Pro167Ser (rs34882957) in the C9 gene was initially associated with elevated C9 levels [28], but a more recent study rather reported decreased C9 levels in carriers of the p.Pro167Ser variant [29]. The current study identified decreased C9 levels in carriers of the p.Pro167Ser variant in the C9 gene and gave consistent results for three independent peptides from C9, supporting the latter study that the C9 variant levels are genuinely lower.…”

“…Two clinical trials supplementing FH (GEM103, Gemini Therapeutics) and CFI (GT005, Gyroscope Therapeutics) are the first to be selecting patients based on genotype (carrying risk variants in CFH and CFI, respectively) before inclusion in the trials. Our current study and previous work by others [17,25,26,29,30,44] suggest that genetic variants at the CFH, CFI, C2/CFB, C9 and VTN loci can also be used to design personalised medicine approaches for AMD. Furthermore, the strong associations between circulating metabolites and complement components suggest that multiple disease pathways may need to be targeted for successful treatment of AMD.…”

“…The multiplex complement assay contains three peptides originated from C9; however, association analyses that were performed for C9 peptide levels with the C9 rs62358361 variant showed no significant results (Supplementary Table S17). The coding variant p.Pro167Ser (rs34882957) was previously associated with altered C9 levels [28,29]. The Mann-Whitney U test comparing carriers versus non-carriers identified significant differences in levels of all three C9 peptides with C9 genotype (p-value = 1.91 × 10 −10 for peptide #34; Supplementary Table S11).…”

“…The AMD-protective p.Leu9His (rs4151667) variant in the CFB gene is associated with reduced factor B (FB) levels [25,26], while the AMD-risk variant p.Gly119Arg (rs141853578) in the CFI gene is associated with reduced factor I (FI) levels [27]. The AMD-risk variant p.Pro167Ser (rs34882957) in the C9 gene was initially associated with elevated C9 levels [28], but a more recent study rather reported decreased C9 levels in carriers of the p.Pro167Ser variant [29]. Common variants at the CFH locus were recently shown to be strongly associated with levels of the factor H-related proteins FHR-1, FHR-2, FHR-3 and FHR-4, which are encoded by the CFHR genes located at the CFH locus downstream of the CFH gene.…”

Structural basis of soluble membrane attack complex packaging for clearance

“…Substitution of proline at this position may impact the ability of this loop to serve as a checkpoint for polymerization. Our structural model is further supported by mutational studies showing that mutation of Pro 146 increases C9 polymerization 35 . Taken together, our sMAC model provides a structural timeline in which the sequential extension of transmembrane β-hairpins may be regulated by the preceding monomer and a proline latch on the polymerizing MACPF interface (Fig.…”