Abstract
Purpose: :
Doynes Honeycomb Retinal Dystrophy/Malattia Leventinese (DHRD /ML), an inherited macular degeneration, is caused by a mutation in codon 345 of EFEMP1. Knockin mice with the Efemp1-R345W mutation develop basal deposits between the retinal pigment epithelia (RPE) and Bruch’s membrane and large vacuoles in the RPE. These Efemp1-R345W mutant mice provide a model to study the early stages in the pathogenesis of macular degeneration. In this study we address the role of complement and the underlying mechanisms in the development of the deposits and the RPE pathology.
Methods: :
Deposit formation and RPE pathology were analyzed in Efemp1-R345W knockin mice and Efemp1-R345W knockin mice that were null for C3 using electron microscopy. Quantitative analyses of these features were done using ImageJ software. A global analysis of the complement components in the basal deposits was done using a proteomics approach with high resolution mass spectrometry.
Results: :
The formation of deposits was essentially abolished in the Efemp1-R345W mutant mice that were null for C3 and the formation of the large vacuoles in the RPE was prevented. Complement components C3 and C4 were elevated in Bruch’s membrane of Efemp1-R345W mutant mice relative to control mice. The level of CFH was not increased in mutant relative to control mice. Low levels of subunits A, B and C of C1q were observed and were elevated in the mutant mice. Proteins required to initiate the lectin pathway were not detected.
Conclusions: :
These results implicate the classical complement pathway in generating the deposits and the RPE pathology, since C1q binding initiates the classical pathway. The demonstration that complement has an essential role in the formation of drusen-like basal deposits in Efemp1-R345W knockin mice suggests that complement is essential in an early step in the pathogenesis of macular degeneration.
Keywords: age-related macular degeneration • Bruch's membrane • proteomics