Functional Characterization of the Disease-Associated N-Terminal Complement Factor H Mutation W198R

Area of Science:

• Immunology
• Nephrology
• Molecular Biology

Background:

• Complement alternative pathway dysregulation is implicated in kidney diseases such as atypical hemolytic uremic syndrome (aHUS) and C3 glomerulopathy (C3G).
• A patient with a history of chronic glomerulonephritis and later aHUS was found to have a heterozygous missense mutation (W198R) in the factor H (FH) CCP3 domain.

Purpose of the Study:

• To investigate the functional significance of the FH W198R mutation.
• To elucidate the role of this mutation in complement alternative pathway regulation and its potential link to observed kidney diseases.

Main Methods:

• Recombinant expression of wild-type (FH1-4WT) and mutant (FH1-4W198R) factor H complement control protein (CCP) domains 1-4.
• Biochemical assays measuring C3b binding, cofactor activity, and decay accelerating activity.
• Hemolysis assays using rabbit and sheep erythrocytes to assess complement-mediated lysis protection.

Main Results:

• The FH1-4W198R mutant exhibited reduced C3b binding compared to FH1-4WT.
• Impaired cofactor and decay accelerating activities were observed for FH1-4W198R.
• Hemolysis assays showed that FH1-4W198R was less effective in protecting erythrocytes from complement-mediated lysis.

Conclusions:

• The W198R exchange in factor H leads to impaired regulation of the complement alternative pathway.
• The heterozygous nature of this mutation may contribute to the manifestation of multiple complement-mediated kidney diseases in patients.
• This study highlights the critical role of factor H in maintaining complement homeostasis and preventing renal pathology.