C3 glomerulopathy–associated CFHR1 mutation alters FHR oligomerization and complement regulation

Abstract

C3 glomerulopathies (C3G) are a group of severe renal diseases with distinct patterns of glomerular inflammation and C3 deposition caused by complement dysregulation. Here we report the identification of a familial C3G-associated genomic mutation in the gene complement factor H-related 1 (CFHR1), which encodes FHR1. The mutation resulted in the duplication of the N-terminal short consensus repeats (SCRs) that are conserved in FHR2 and FHR5. We determined that native FHR1, FHR2, and FHR5 circulate in plasma as homo-and hetero-oligomeric complexes, the formation of which is likely mediated by the conserved N-terminal domain. In mutant FHR1, duplication of the N-terminal domain resulted in the formation of unusually large multimeric FHR complexes that exhibited increased avidity for the FHR1 ligands C3b, iC3b, and C3dg and enhanced competition with complement factor H (FH) in surface plasmon resonance (SPR) studies and hemolytic assays. These data revealed that FHR1, FHR2, and FHR5 organize a combinatorial repertoire of oligomeric complexes and demonstrated that changes in FHR oligomerization influence the regulation of complement activation. In summary, our identification and characterization of a unique CFHR1 mutation provides insights into the biology of the FHRs and contributes to our understanding of the pathogenic mechanisms underlying C3G.

A Novel Atypical Hemolytic Uremic Syndrome–Associated Hybrid CFHR1/CFH Gene Encoding a Fusion Protein That Antagonizes Factor H–Dependent Complement Regulation

“…They are present as a complex mix of heterooligomeric proteins (dimers and tetramers), in which the oligomers containing FHR1 are mostly the major components. 17 We, therefore, refer to the purified mix of FHR1 (including the hybrid FHR1/FH), FHR2, and FHR5 heterooligomers here as purified FHR1 ( Figure 6C). Addition of purified FHR1 from heterozygous CFHR1/CFH hybrid carriers to two different control sera resulted in dose-dependent sheep erythrocyte hemolysis, whereas equal amounts of purified FHR1 from normal serum had no effect ( Figure 6D).…”

The role of the alternative pathway of complement activation in glomerular diseases

“…Single SLE cases associated with different C3 mutations have been reported in the Japanese population [73,74]. Further, first described in patients of Cypriot origin, familial cases of C3G, associated with mutant CFHR proteins, have also been found in patients of other ethnicities [39,40,[75][76][77][78].…”

“…For instance, the novel mutant multimeric CFHR1 protein that showed enhanced competition with CFH was a result of an intragenic duplication in N-terminal SCRs of CFHR1 gene. The dysregulation of complement was present only on the certain surfaces, but (according to the authors) probably did not occur on the endothelium, explaining the C3G and not aHUS onset [39]. Malik et al [76] reported a unique hybrid CFHR3-1 gene, which caused a familial C3G.…”

“…First, CFHRs may compete with CFH for the same binding site on C3b, but because of lack of the regulatory domains, they do not exhibit both cofactor and decay acceleration activity. This process was called complement deregulation, and so far, CFHR1, CFHR2, and CFHR5 have been described to be a competitive antagonist of CFH [37][38][39][40]. Secondly, CFHR5 may deregulate complement indirectly by competing with CFH in binding to other than C3b physiological ligands, including pentraxin PTX3, CRP and extracellular matrix [36].…”

“…1), the 3D model of C3 places the MG1 (C3S/F; rs2230199) and C3d region (CFH binding site) in a close proximity [14,47]. This implicates the possibility that the presence of many different risks variants of C3 and CFH [50] + (DDD) --c.C1775T/p.R592Q (rs121909583) [101] + --V619 M (rs146613648) [64] + --R1303H [64] + --R13200Q [64] + --C1518R [64] + --D1625H [64] + --ΔDG3923 [64] + (DDD) + -c.131_146del; p.Leu44Argfs*19 [73] - [12,34,62,65,68] + (DDD, C3GN) + (SLE) -V62I (rs800292) [34,[63][64][65] + (DDD) [75] + − − Duplication in CFHR1 gene [39] + − − CFHR3-1 hybrid gene [76] + --CFHR2-CFHR5 hybrid gene [40] + --CFHR5-CFHR2 hybrid gene [77] + − − CFHR1-5 hybrid gene [80] + − − rs16840639 [69] - [34] + (DDD) --−20T/C (rs9427662) [34] + (DDD) --IVS1 + 75T/A [34] + (DDD) --IVS2 + 58C/T [34] + (DDD) --in a single individual may have a more potent effect on AP regulation and may increase the risk of GN development.…”