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

Area of Science:

• Nephrology
• Immunology
• Genetics

Background:

• C3 glomerulopathies (C3G) are severe kidney diseases characterized by complement system dysregulation and C3 deposition in glomeruli.
• The complement system, particularly the alternative pathway, plays a critical role in immune responses but its dysregulation can lead to kidney damage.

Purpose of the Study:

• To identify the genetic basis of a familial C3 glomerulopathy (C3G).
• To investigate the functional consequences of a novel mutation in the complement factor H–related 1 (CFHR1) gene on FHR protein complex formation and complement regulation.

Main Methods:

• Genomic sequencing to identify mutations in the CFHR1 gene.
• Biochemical assays including surface plasmon resonance (SPR) and hemolytic assays to study FHR protein complex formation and function.
• Analysis of FHR1, FHR2, and FHR5 oligomerization and their interactions with complement components C3b, iC3b, and C3dg.

Main Results:

• A familial C3G-associated mutation in CFHR1 was identified, leading to duplication of N-terminal short consensus repeats (SCRs) in FHR1.
• Mutant FHR1 formed unusually large multimeric complexes due to N-terminal domain duplication.
• These large FHR complexes showed increased binding to C3b, iC3b, and C3dg and enhanced competition with complement factor H (FH), disrupting complement regulation.

Conclusions:

• The study identified a novel CFHR1 mutation linked to C3G, highlighting the role of FHR oligomerization in complement dysregulation.
• Changes in FHR oligomerization significantly impact the regulation of complement activation, providing insights into C3G pathogenesis.
• This research deepens the understanding of FHR biology and its contribution to severe renal diseases like C3G.