Complement Component C3 Plays a Critical Role in Protecting the Aging Retina in a Murine Model of Age-Related Macular Degeneration

Complement component C3 is the central complement component and a key inflammatory protein activated in age-related macular degeneration (AMD). AMD is associated with genetic variation in complement proteins that results in enhanced activation of C3 through the complement alternative pathway. These include complement factor H (CFH), a negative regulator of C3 activation. Both C3 inhibition and/or CFH augmentation are potential therapeutic strategies in AMD. Herein, we examined retinal integrity in aged (12 months) mice deficient in both factors H and C3 (CFH-/-.C3(-/-)), CFH alone (CFH-/-), or C3 alone (C3(-/-)), and wild-type mice (C57BL/6). Retinal function was assessed by electroretinography, and retinal morphological features were analyzed at Light and electron microscope Levels. Retinas were also stained for amyloid beta (A beta) deposition, inflammation, and macrophage accumulation. Contrary to expectation, electroretinograms of CFH-/-.C3(-/-) mice displayed more severely reduced responses than those of other mice. All mutant strains showed significant photoreceptor loss and thickening of Bruch's membrane compared with wild-type C57BL/6, but these changes were greater in CFH-/-.C3(-/-) mice. CFH-/-.C3(-/-) mice had significantly more A beta on Bruch's membrane, fewer macrophages, and high levels of retinal inflammation than the other groups. Our data show that both uncontrolled C3 activation (CFH-/-) and complete absence of C3 (CFH-/-.C3(-/-) and C3(-/-)) negatively affect aged retinas. These findings suggest that strategies that inhibit C3 in AMD may be deleterious.