Complement factor B is critical for sub-RPE deposit accumulation in a model of Doyne honeycomb retinal dystrophy with features of age-related macular degeneration

EFEMP1 R345W is a dominant mutation causing Doyne honeycomb retinal dystrophy/malattia leventinese (DHRD/ML), a rare blinding disease with clinical pathology similar to age-related macular degeneration (AMD). Aged Efemp1 (R345W/R345W) knock-in mice (Efemp1(ki/ki)) develop microscopic deposits on the basal side of retinal pigment epithelial cells (RPE), an early feature in DHRD/ML and AMD. Here, we assessed the role of alternative complement pathway component factor B (FB) in the formation of these deposits. RNA-seq analysis of the posterior eyecups revealed increased unfolded protein response, decreased mitochondrial function in the neural retina (by 3 months of age) and increased inflammatory pathways in both neural retina and posterior eyecups (at 17 months of age) of Efemp1(ki/ki) mice compared with wild-type littermate controls. Proteomics analysis of eye lysates confirmed similar dysregulated pathways as detected by RNA-seq. Complement activation was increased in aged Efemp1(ki/ki) eyes with an approximately 2-fold elevation of complement breakdown products iC3b and Ba (P < 0.05). Deletion of the Cfb gene in female Efemp1(ki/ki) mice partially normalized the above dysregulated biological pathway changes and oral dosing of a small molecule FB inhibitor from 10 to 12 months of age reduced sub-RPE deposits by 65% (P = 0.029). In contrast, male Efemp1(ki/ki) mice had fewer sub-RPE deposits than age-matched females, no elevation of ocular complement activation and no effect of FB inhibition on sub-RPE deposits. The effects of FB deletion or inhibition on Efemp1(ki/ki) mice supports systemic inhibition of the alternative complement pathway as a potential treatment of dry AMD and DHRD/ML.