An evaluation of the complement-regulating activities of human complement factor H (FH) variants associated with age-related macular degeneration

Robyn M. Biggs, Elisavet Makou, Scott Lauder, Andrew P. Herbert, Paul N. Barlow, Suresh K. Katti*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

Abstract / Description of output

Purpose. Factor H (FH, encoded by CFH) prevents activation of the complement system’s alternative pathway (AP) on host tissues. FH impedes C3 convertase (C3bBb) formation, accelerates C3bBb decay, and is a cofactor for factor I (FI)–catalyzed C3b cleavage. Numerous CFH variants are associated with age-related macular degeneration (AMD), but their functional consequences frequently remain undetermined. Here, we conduct functional comparisons between a control version of FH (not AMD linked) and 21 AMD-linked FH variants. 

Methods. Recombinantly produced, untagged, full-length FH versions were assayed for binding to C3b and decay acceleration of C3bBb using surface-plasmon resonance, FIcofactor activity using a fluorescent probe of C3b integrity, suppression of C5b-9 assembly on an AP-activating surface, and inhibition of human AP-mediated lysis of sheep erythrocytes. 

Results. All versions were successfully purified despite below-average yields for Arg2Thr, Arg53Cys, Arg175Pro, Arg175Gln, Ile221Val, Tyr402His, Pro503Ala, Arg567Gly, Gly1194Asp, and Arg1210Cys. Compared to control FH, Arg2Thr, Leu3Val, Ser58Ala, Asp90Gly, Asp130Asn, Gln400Lys, Tyr402His, Gly650Val, Ser890Ile, and Thr965Met showed minimal functional differences. Arg1210C, Arg53His, Arg175Gln, Gly1194Asp, Pro503Ala, Arg53Cys, Arg576Gly, and Arg175Pro (in order of decreasing efficacy) underperformed, while Ile221Val, Arg303Gln, and Arg303Trp were “marginal.” We newly identified variants toward the center of the molecule, Pro503Ala and Arg567Gly, as potentially pathogenic. 

Conclusions. Our approach could be extended to other variants of uncertain significance and to assays for noncanonical FH activities, aiming to facilitate selection of cohorts most likely to benefit from therapeutic FH. This is timely as recombinant therapeutic FH is in development for intravitreal treatment of AMD in patients with reduced FH functionality.

Original languageEnglish
Article number30
Number of pages12
JournalInvestigative Ophthalmology & Visual Science (IOVS)
Volume63
Issue number12
DOIs
Publication statusPublished - 29 Nov 2022

Keywords / Materials (for Non-textual outputs)

  • age-related macular degeneration
  • alternative pathway
  • complement
  • factor H
  • factor H missense variants
  • therapy

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