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

Abstract

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 Efemp1R345W/R345W knock-in mice (Efemp1ki/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 Efemp1ki/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 Efemp1ki/ki eyes with an approximately two-fold elevation of complement breakdown products iC3b and Ba (p < 0.05). Deletion of the Cfb gene in female Efemp1ki/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 Efemp1ki/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 Efemp1ki/ki mice supports systemic inhibition of the alternative complement pathway as a potential treatment of dry AMD and DHRD/ML.

The extracellular microenvironment in immune dysregulation and inflammation in retinal disorders

“…Animal models have greatly fostered our knowledge about the molecular pathomechanism of DHRD/ML disease. Efemp1 R345W/R345W knock-in mice mimic the phenotype seen in human patients and show formation of sub-RPE deposits which do not form in wildtype littermates or Efemp1 -/knock-out mice of the same age (177). In fact, Efemp1-deficientmice intriguingly appear to be protected from drusen formation, suggesting a role of murine Efemp1 in generating the drusen-like deposits (178).…”

“…Extending these initial studies, additional data were presented recently demonstrating that complement factor B is critical for sub-RPE deposit formation in the Efemp1 R345W/R345W mouse model (177). Quantitative RNA sequencing and subsequent proteomics demonstrated that expression of inflammatory pathway genes was increased in neural retina and posterior eyecups in 17-month-old Efemp1 R345W/R345W mice compared to wildtype mice.…”

“…This was further supported by applying a small molecule inhibitor of Cfb reducing sub-RPE deposition by 65%. This reduction, however, was only observed in female mice, but not in male animals (177). Interestingly, loss-of-function alleles in the CFB gene in humans are associated with a decreased risk of developing AMD (181,182).…”

Bruch’s Membrane: A Key Consideration with Complement-Based Therapies for Age-Related Macular Degeneration

“…This is supported by the presence of multiple complement components and regulators in drusen [67,114,[116][117][118]. In fact, complement proteins C3 and Factor B (FB) have been found to be essential for drusen formation in mouse models of inherited retinal degeneration [119][120][121]. This model is triggered by inducing the missense p.R345W variant in the EFEMP1 (EGF-containing fibulin-like extracellular matrix protein 1) gene, which encodes fibulin-3 involved in extracellular matrix development.…”

EFEMP1 contributes to light-dependent ocular growth in zebrafish

“…In relation to human visual diseases, an autosomal dominant gain-of-function mutation in the EFEMP1 gene (c.1033C>T, p.Arg345Trp) is known to be associated with Malattia Leventinese and Doyne honeycomb retinal dystrophy (Stone et al, 1999), leading to accumulation of drusen (yellow-white deposits) beneath the basal retinal pigment epithelium (RPE), a pathologic sign that overlaps with age-related macular degeneration (AMD) (Marmorstein et al, 2002). A number of studies suggest that sub-RPE deposits may result from abnormal interactions between EFEMP1 and complement system proteins, for example, complement component 3 (C3), complement factor B (FB) and complement factor H (CFH) (Crowley et al, 2022; Garland et al, 2013).…”