Defective complement control of factor H (Y402H) and FHL-1 in age-related macular degeneration

Area of Science:

• Ophthalmology
• Immunology
• Genetics

Background:

• Age-related macular degeneration (AMD) is a leading cause of irreversible blindness in the elderly.
• A common variant (Tyr402His) in the complement Factor H gene (CFH) is strongly associated with AMD risk.
• The precise mechanism by which this CFH variant contributes to AMD pathogenesis remains incompletely understood.

Purpose of the Study:

• To investigate the functional consequences of the CFH Tyr402His risk variant.
• To determine the binding properties and cellular regulatory functions of the CFH 402His variant.
• To identify and characterize the role of Factor H-like protein 1 (FHL-1) in AMD pathogenesis.

Main Methods:

• Binding assays were performed to assess the interaction of CFH variants with C reactive protein (CRP), heparin, and retinal pigment epithelial cells.
• Complement regulatory activity of CFH and FHL-1 variants was evaluated at the cell surface.
• Expression and function of FHL-1, an alternative splice product of CFH, were examined in ocular tissues.

Main Results:

• The CFH 402His risk variant exhibited significantly reduced binding to CRP, heparin, and retinal pigment epithelial cells compared to the wild-type.
• This reduced binding correlated with impaired complement regulation on the cell surface, especially in the presence of CRP.
• The FHL-1 protein, including the 402His residue, was identified in the eye, and its risk variant displayed similar defects in cell binding and complement regulation.

Conclusions:

• The CFH Tyr402His variant and the corresponding FHL-1 variant impair complement regulation in the eye due to reduced cell surface binding.
• Dysregulated local complement activation, potentially exacerbated by CRP, contributes to inflammation and cell damage, driving AMD pathogenesis.
• CFH and FHL-1 may function synergistically in the eye, and their compromised regulatory function represents a key mechanism in the development of age-related macular degeneration.