Abstract: TH-PO0423
Multivalent FHR5 Oligomerisation Drives Complement Deregulation in CFHR5 Nephropathy and Resists Competitive Disruption
Session Information
- Glomerular Diseases: Autoimmune Diseases
October 22, 2026 | Location: Exhibit Hall A, Convention Center
Abstract Time: 10:00 AM - 12:00 PM
Category: Glomerular Diseases
- 1401 Glomerular Diseases: Mechanisms, including Podocyte Biology
Authors
- Liu, Long Yin Lavine, University College London, London, England, United Kingdom
- Carmichael, Joshua, University College London, London, England, United Kingdom
- Smith, Joanna K., University College London, London, England, United Kingdom
- Gale, Daniel P., University College London, London, England, United Kingdom
Background
CFHR5 nephropathy is an autosomal dominant C3 glomerulopathy caused by duplication of the Short Complement Regulator (SCR) 1/2 dimerisation domain of Complement Factor H Related protein 5 (FHR5). WT FHR5 is a complement activator that homodimerises via N-terminal SCR1/2 and binds glomerular C3d via its C-terminus, competing with Factor H-mediated alternative pathway regulation. How mutant FHR5 drives disease is unknown. Because SCR1/2 mediates dimerisation, we used isolated SCR1/2 to probe the oligomeric architecture of WT and mutant FHR5, and tested if disruption could affect glomerular C3 binding.
Methods
We developed a Grating-Coupled Interferometry (GCI) assay with oriented C3d immobilisation. WT FHR5, mutant FHR5, and 1:1 WT:mutant mixtures at physiological concentrations were analysed alone or with excess SCR1/2 across 12 C3d surface densities. SEC-MALS quantified oligomeric states of FHR5, SCR1/2 and a tandem SCR1/2-1/2 domain construct (mimicking the mutant FHR5 dimerisation domain) alone and in combination. In a nephrotoxic nephritis (NTN) mouse model, recombinant WT FHR5 was injected IV alone or with excess SCR1/2, with glomerular FHR5-C3 co-localisation assessed by IHC.
Results
WT FHR5 showed bivalent avidity-driven C3d binding, with affinity increasing with surface density. Excess SCR1/2 decreased WT dimerisation (on SEC-MALS) by ~70% at ratios >5:1 and accelerated dissociation rate. Supporting this, excess SCR1/2 reduced glomerular FHR5-C3 co-localisation in NTN. Mutant FHR5 showed multivalent avidity-driven C3d binding with faster association rate than WT and aggregated under SEC-MALS conditions. SEC-MALS resolved SCR1/2-1/2 oligomer composition as 45% dimers, 40% trimers, and 15% tetramers. SCR1/2 incorporated into the oligomers, generating larger species. In GCI, at heterozygous-mimicking 1:1 WT:mutant ratios mutant-like behaviour dominated. Excess SCR1/2 did not alter binding kinetics.
Conclusion
These results reveal multivalent FHR5 oligomerisation as the mechanism underlying CFHR5 nephropathy. WT and mutant SCR1/2 proteins preferentially self-oligomerise, with WT–mutant interactions predicted to enlarge rather than dissociate pathogenic oligomers, explaining the dominant mutant-like binding effects of full-length protein mixtures and supporting dominant inheritance. Effective therapeutic strategies will need to prevent or destabilise oligomerisation.
Funding
- Private Foundation Support