During the past ten years, dramatic advances have been made in unraveling the biological bases of age-related macular degeneration (AMD), the most common cause of irreversible blindness in western populations. In that timeframe, two distinct lines of evidence emerged which implicated chronic local inflammation and activation of the complement cascade in AMD pathogenesis. First, a number of complement system proteins, complement activators, and complement regulatory proteins were identified as molecular constituents of drusen, the hallmark extracellular deposits associated with early AMD. Subsequently, genetic studies revealed highly significant statistical associations between AMD and variants of several complement pathway-associated genes including: Complement factor H (CFH), complement factor H-related 1 and 3 (CFHR1 and CFHR3), complement factor B (CFB), complement component 2 (C2), and complement component 3 (C3). In this article, we revisit our original hypothesis that chronic local inflammatory and immune-mediated events at the level of Bruch’s membrane play critical roles in drusen biogenesis and, by extension, in the pathobiology of AMD. Secondly, we report the results of a new screening for additional AMD-associated polymorphisms in a battery of 63 complement-related genes. Third, we identify and characterize the local complement system in the RPE-choroid complex -- thus adding a new dimension of biological complexity to the role of the complement system in ocular aging and AMD. Finally, we evaluate the most salient, recent evidence that bears directly on the role of complement in AMD pathogenesis and progression. Collectively, these recent findings strongly re-affirm the importance of the complement system in AMD. They lay the groundwork for further studies that may lead to the identification of a transcriptional disease signature of AMD, and hasten the development of new therapeutic approaches that will restore the complement-modulating activity that appears to be compromised in genetically susceptible individuals.

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Lipids accumulate in Bruch's membrane (BrM), a specialized vascular intima of the eye, and in extracellular lesions associated with aging and age-related maculopathy (ARM). We tested the hypothesis that ARM and atherosclerotic cardiovascular disease share molecules and mechanisms pertaining to extracellular lipid accumulation by localizing cholesterol and apolipoprotein B (apo B) in BrM, basal deposits, and drusen. Human donor eyes were preserved <4 hours postmortem and cryosectioned. Sections were stained with traditional lipid stains and filipin for esterified and unesterified cholesterol or probed with antibodies to apo B, apo E, and apo C-III. Normal adult retinal pigment epithelium (RPE) was subjected to RT-PCR and Western blot analysis for apolipoprotein mRNA and protein. Esterified and unesterified cholesterol was present in all drusen and basal deposits of ARM and normal eyes. Both apo B and apo E but not apo C-III were found in BrM, drusen, and basal deposits. Age-related maculopathy (ARM) is the leading cause of new, untreatable vision loss in the elderly in Western societies. [1][2][3] As shown in Figure 1A, ARM involves the retinal pigment epithelium (RPE, cells dedicated to sustaining photoreceptor health), the choriocapillaris (the blood supply to photoreceptors and the RPE), and Bruch's membrane (BrM, a thin vascular intima between the RPE and choriocapillaris). 4,5 Early ARM is characterized by moderate vision loss associated with characteristic extracellular lesions. Lesions between the RPE basal lamina and BrM can be focal (drusen) or diffuse (basal linear deposits). A diffuse lesion between the RPE and its basal lamina is basal laminar deposit. The term "sub-RPE deposits" is used for the combination of drusen and basal deposits and "basal deposits" for the combination of basal laminar deposit and basal linear deposit. Late ARM is characterized by severe vision loss associated with extensive RPE atrophy with or without the sequelae of choroidal neovascularization, ie, in-growth of choriocapillaries through BrM and under the RPE in the plane of drusen and basal linear deposits. Because the causes of ARM are obscure, recent studies have sought molecules present in the affected tissues and characteristic lesions to identify biochemical pathways perturbed by disease. 6 An important but incompletely characterized component of BrM and sub-RPE deposits is lipids. Normal BrM accumulates lipids with age, and the accumulation of esterified and unesterified cholesterol (EC and UC)-containing particles is especially prominent in the macula. 7-10 Drusen and basal deposits in aged eyes without ARM contain lipids, including cholesterol, 9 -13 and current evidence suggests that individual sub-RPE deposits are preferentially enriched in either neutral lipids or polar lipids. 13 The source of lipids and mechanisms of deposition are unknown. Analyses of BrM/ choroid lipid composition have implicated both local cells and plasma. 8,9 Atherosclerotic cardiovascular disease (CVD), the leading cause of death in Wester...

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We demonstrate histologically sub-retinal drusenoid debris in three aged human eyes, two of them affected by age-related maculopathy. By postmortem fundus examination, the lesions appeared drusen-like, i.e., they were pale spots apparently at the level of the retinal pigment epithelium (RPE). Light and electron microscopy revealed aggregations of membranous debris, the principal constituent of soft drusen, in the sub-retinal space. Immunohistochemistry and confocal microscopy confirmed the presence of molecules typically associated with drusen (positive for unesterified cholesterol, apoE, complement factor H, and vitronectin) without evidence for molecules associated with photoreceptors (lectins and opsins), Müller cells (glial fibrillary acid protein and cellular retinal binding protein, CRALPB), or RPE (CRALPB). The fact that a drusenoid material, sharing some markers with conventional drusen, can occur on opposite faces of the RPE, suggests deranged polarity of normally highly vectorial processes for basolateral secretion from RPE, and that overproduction of secreted materials and direction of secretion are independently specified processes. In the future, drusenoid sub-retinal debris might be more frequently revealed by emerging high-resolution imaging techniques.