Combination of Factor H Mutation and Properdin Deficiency Causes Subretinal and Sub-RPE Deposition

Abstract

Purpose : Both factor H (fH) and properdin (fP) regulate complement. fH is a complement inhibitor, while fP activates the alternative pathway (AP). Mutations in fH are associated with several human kidney diseases and macular degeneration. Surprisingly, knocking out fP converted the mild C3 glomerulonephritis of a fH-mutant mouse to a lethal C3 glomerulonephritis with features of human dense deposit disease (DDD)¹. Here we characterized its retinal phenotype.

Methods : Mice with a fH C-terminal mutation leading to SCR 19-20 truncation (fH^m/m) were crossed with fP knockout mice (fP^-/-) to generate fH^m/m/fP^−/− mice. Electroretinography (ERG) and fundus imaging were performed to assess retinal function and appearance in fH^m/m/fP^−/−, fH^m/m, fP^−/− mice and wild-type (WT) mice. After euthanasia, at age 2-3 months, eyes were used for electron microscopy (EM), histology, immunolabeling with C3 antibody and rhodamine-conjugated peanut agglutinin lectin (PNA).

Results : ERG showed decreased rod a-waves in fH^m/m/fP^−/− mice, but not in fH^m/m, fP^−/− mice and WT mice. Similarly, fundus images showed more hypopigmented lesions in fH^m/m/fP^−/− mice than other genotypes. Thinning of the ONL was observed in fH^m/m/fP^−/− mice. EM showed subretinal and sub-RPE deposits in fH^m/m/fP^−/− mice, combined with thickening of Bruch’s membrane and RPE hypertrophy. Increased C3 staining in Bruch’s membrane and fewer PNA staining cones were found in fH^m/m/fP^−/− mice compared with other genotypes.

Conclusions : Our results indicate that the combination of a fH mutation in the C terminus of the mouse fH gene with properdin knockout leads to subretinal and sub-RPE complement-containing deposits, as well as photoreceptor and RPE degeneration. The co-occurrence of C3 glomerulopathy and AMD-like retinal degeneration in this mouse model recapitulates the clinical observations of retinopathy in human C3 glomerulopathy patients. The fH^m/m/fP^−/− mouse represents a new mouse model of complement-mediated rapid onset dense deposit disease with retinal manifestations related to AMD, and could be useful in exploring the pathogenic mechanism and therapy of AMD and AMD-like retinopathies.

This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.

 

Electron microscopy shows lipid droplets in RPE cell, sub-RPE depostion and thickening of Bruch's membrane in fH^m/mfP^-/-

 

Immunostaining of C3 and RPE65 in RPE cell and Bruch's membrane