Molecular pathology of age-related macular degeneration

“VEGF It is well established that the formation of blood vessels occurs by angiogenesis and that vascular endothelial growth factor (VEGF) is a key molecule in promoting angiogenesis (Ferrara et al., 2003).”

“A dual role for macrophages in AMD—Another plausible explanation for these seemingly contradictory findings is that macrophages comprise a heterogeneous group with a spectrum of phenotypes and activities (Mantovani et al., 2004).”

“…of the complement system generates a variety of pro-inflammatory responses, including the production of membrane-attack complexes (MAC) which lead to cell lysis, release of chemokines to mediate recruitment of inflammatory cells, and enhancement of capillary permeability (Walport, 2001a, b).”

“Currently, in the United States alone, 1.75 million people are affected by AMD and 7 million people are at risk of developing AMD (Friedman et al., 2004).”

“These SNPs have been reported to be major genetic factors for developing AMD in Caucasians (Edwards et al., 2005; Hageman et al., 2005; Haines et al., 2005; Klein et al., 2005; Tuo et al., 2006).”

“These SNPs have been reported to be major genetic factors for developing AMD in Caucasians (Edwards et al., 2005; Hageman et al., 2005; Haines et al., 2005; Klein et al., 2005; Tuo et al., 2006).”

“…Inhibition Study in Ocular Neovascularization, Clinical Trial and Minimally Classic/Occult Trial of the Anti-VEGF Antibody Ranibizumab in the Treatment of Neovascular Age-Related Macular Degeneration (MARINA) (AREDS, 2001; Bressler et al., 2003; Gragoudas et al., 2004; Rosenfeld et al., 2006).”

“The AA genotype has also been shown to induce angiogenesis in rat cornea (Koch et al., 1992).”

“Functionally, the D299G TLR4 variant has been linked to impaired LPS responsiveness in mice, which is reversible by TLR4 overexpression (Arbour et al., 2000).”

“These SNPs have been reported to be major genetic factors for developing AMD in Caucasians (Edwards et al., 2005; Hageman et al., 2005; Haines et al., 2005; Klein et al., 2005; Tuo et al., 2006).”

“…of the complement system generates a variety of pro-inflammatory responses, including the production of membrane-attack complexes (MAC) which lead to cell lysis, release of chemokines to mediate recruitment of inflammatory cells, and enhancement of capillary permeability (Walport, 2001a, b).”

“N IH -PA Author M anuscript N IH -PA Author M anuscript N IH -PA Author M anuscript one allele of the gene in 16% of the AMD patients (Allikmets, 1997; Allikmets et al., 1997).”

“…on the expression of 23,720 transcripts from trials on blood samples (n = 1002) or adipose tissue (n = 673), findings from over 50% of trials in adipose samples correlated to those from clinical trials related to obesity, compared to less than 10% in trials on blood samples (Emilsson et al., 2008).”

“The insertion introduces a 54-bp AU-rich element, known for its properties to control mRNA decay in many transcripts that encode a wide variety of proteins involved in transient biological processes (Barreau et al., 2005; Garneau et al., 2007; Khabar, 2005).”

“The molecular and cellular constituents of drusen have been analyzed extensively (Anderson et al., 2004; Crabb et al., 2002; Hageman et al., 2001; Johnson et al., 2000; Mullins et al., 2000; Russell et al., 2000).”

“…of studies have illustrated the presence of complement components and complement regulatory proteins in drusen and nearby RPE of AMD patients (Crabb et al., 2002; Hageman et al., 1999; Johnson et al., 2001; Johnson et al., 2000; Mullins et al., 2001; Nozaki et al., 2006), suggesting a role…”

“The larger the drusen, the greater the area they cover, and the larger the areas of hyperpigmentation and hypopigmentation of the RPE in the macula, the higher the risk of late age-related macular degeneration is (Klein et al., 2002).”

“BF is a complement activating factor, and studies have demonstrated that at least one of the two variants associated with AMD—R32Q BF—leads to an impairment in the complement activating function of BF (Gold et al., 2006).”

“CCL2 or CCR2 deficiency leads to impaired accumulation of macrophages at sites of inflammation (Kuziel et al., 1997; Lu et al., 1998).”

“…been linked to increased risk of AMD (Mares-Perlman et al., 1995; Seddon et al., 2003), and analyses have revealed protective effects from antioxidants, nuts, fish, and omega-3 polysaccharide unsaturated fatty acids (AREDS, 2001; Cho et al., 2001; Seddon et al., 1994, 2001; Smith et al., 2000).”

“Immunohistochemical analyses have shown various molecular constituents, such as apolipoproteins B and E, different immunoglobulins, factor X, amyloid P component, amyloid β, complement C5 and C5b-9 terminal complexes, fibrinogen, vitronectin, and others, to be present in all phenotypes of hard and soft drusen (Anderso…”

“The insertion introduces a 54-bp AU-rich element, known for its properties to control mRNA decay in many transcripts that encode a wide variety of proteins involved in transient biological processes (Barreau et al., 2005; Garneau et al., 2007; Khabar, 2005).”

“These processes might therefore contribute to impaired RPE function and subsequent RPE and photoreceptor degeneration (Weng et al., 1999).”

“Pegaptanib (macugen), an oligonucleotide aptamer that targets the VEGF165 isoform, and ranibizumab (Lucentis) and bevacizumab (Avastin), both monoclonal antibodies against VEGF-A, are currently employed in AMD therapy (Ferrara et al., 2006; Kaiser, 2006).”

“In contrast, the fast migrating allotype (C3F), has been reported to be strongly associated with AMD in a study from English and Scottish populations (Yates et al., 2007).”

“…M anuscript N IH -PA Author M anuscript N IH -PA Author M anuscript HtrA1 mRNA and/or protein in the drusen and CNV components in AMD patients carrying the AA risk genotype has been reported in several studies (Cameron et al., 2007; Chan et al., 2007; Tuo et al., 2008; Yang et al., 2006) (Fig.”

“Hyperpigmentary changes associated with compensatory RPE cell proliferation are frequently observed at the periphery of these hypopigmented areas (de Jong, 2006).”

“The earliest pathological changes are the appearance of basal laminar deposits (BlamD) and basal linear deposits (BlinL) (Green and Enger, 1993).”

“CCL2 or CCR2 deficiency leads to impaired accumulation of macrophages at sites of inflammation (Kuziel et al., 1997; Lu et al., 1998).”

“When bound by its ligand, CX3CL1 (also known as fractalkine), CX3CR1 mediates mobilization of leukocytes to inflamed tissues and subsequent activation of these inflammatory cells (Fong et al., 1998).”

“…mainly from the retinal circulation in a process that has been called retinal angiomatous proliferations (RAP), also called deep retinal vascular anomalous complex or retinochoroidal anastomosis (Brancato et al., 2002;Donati et al., 2006;Ghazi, 2002;Hunter et al., 2004;Yannuzzi et al., 2001).”

“It is also possible that ARMS2 and its pathway may be linked to mitochondrial oxidative stress, while HtrA1 and its pathway may be involved in the regulation of cell survival via chaperon/proteases (Clausen et al., 2002), and the inhibition of immune response via TGF-β (Launay et al.”

“Among the elderly, AMD is regarded as the leading cause of blindness in the world (Gehrs et al., 2006).”

“Indeed, a murine model of Ccl2 or Ccr2 deficiency leads to decreased accumulation of macrophages in the retina, as well as key features of AMD including drusen (Ambati et al., 2003).”

“…of complement components and complement regulatory proteins in drusen and nearby RPE of AMD patients (Crabb et al., 2002; Hageman et al., 1999; Johnson et al., 2001; Johnson et al., 2000; Mullins et al., 2001; Nozaki et al., 2006), suggesting a role for complement in AMD pathogenesis (Bora et…”

“…bloated microglial cells and drusen deposits, presence of organelles in drusen, and the fact that microglial cells can express some of the components commonly identified in drusen as evidence that drusen in AMD might involve, at least in part, accumulated microglial cells (Combadiere et al., 2007).”

“Indeed, histological analysis of AMD retinas has depicted the presence of many activated microglia in the macular lesions (Gupta et al., 2003).”

“Increased expression of VEGF-A in the RPE and in the outer nuclear layer is reported in post-mortem maculae obtained from individuals with AMD (Kliffen et al., 1997).”

“Espinosa-Heidmann et al. (2003) and Sakurai et al. (2003) and their colleagues showed that when administered to mice, these liposomes markedly impaired macrophage recruitment to areas of laser retinal injury.”

“Based upon this fact, Klaver et al. have speculated that an active biosynthesis of ApoE is required to support the high rate of photoreceptor renewal in the macular region (Klaver et al., 1998).”

“Microglia Microglia are the resident immune cells in the retina required for neuronal homeostasis and innate immune defense (Langmann, 2007).”

“Our data, including a population-based study (Wang et al., 2008), and data by Jakobsdottir and colleagues (Jakobsdottir et al., 2005) have both shown that the frequency of the ARMS2 risk allele is higher in patients with advanced AMD than in those with early or intermediate AMD.”

“Complement components, other inflammatory molecules, lipids, lipoproteins B and E, and glycoproteins are common constituents of ocular drusen (Johnson et al., 2002).”

“Blue light irradiation and treatment with hydrogen peroxide cause long-lasting mtDNA but not nuclear DNA mutations in cultured RPE cells (Ballinger et al., 1999; Godley et al., 2005).”

“ARMS2 SNP and AMD—The association of ARMS2 gene with AMD, especially advanced AMD, susceptibility has now been replicated in numbers of independent studies (Conley et al., 2006; Rivera et al., 2005; Ross et al., 2007; Schmidt et al., 2006; Seddon et al., 2007; Kanda et al., 2007).”

“…been linked to increased risk of AMD (Mares-Perlman et al., 1995; Seddon et al., 2003), and analyses have revealed protective effects from antioxidants, nuts, fish, and omega-3 polysaccharide unsaturated fatty acids (AREDS, 2001; Cho et al., 2001; Seddon et al., 1994, 2001; Smith et al., 2000).”

“Espinosa-Heidmann et al. (2003) and Sakurai et al. (2003) and their colleagues showed that when administered to mice, these liposomes markedly impaired macrophage recruitment to areas of laser retinal injury.”

“correlated the ARMS2 SNPs to ARMS2 expression level (Fritsche et al., 2008).”

“Similar to findings by Feher and colleagues (Feher et al., 2006), we have also found a drastic decrease in normal mitochondria in the photoreceptors and RPE cells of the AMD eyes as compared to that of the normal age-control eyes (Fig.”

“BlinL consist of vesicular material located in the inner collagenous zone of Bruch’s membrane and represent a specific marker for AMD (Curcio and Millican, 1999).”

“Both fat intake and obesity have been linked to increased risk of AMD (Mares-Perlman et al., 1995; Seddon et al., 2003), and analyses have revealed protective effects from antioxidants, nuts, fish, and omega-3 polysaccharide unsaturated fatty acids (AREDS, 2001; Cho et al.”

“A recent population-based cohort study in Australia (Tan et al., 2008) demonstrated that high dietary lutein and zeaxanthin intake reduced the risk of long-term incident AMD and that high beta-carotene intake was associated with an increased risk of AMD.”

“The larger the drusen, the greater the area they cover, and the larger the areas of hyperpigmentation and hypopigmentation of the RPE in the macula, the higher the risk of late age-related macular degeneration is (Klein et al., 2002).”

“Variation near the FI gene on chromosome 4q25 is associated with risk of advanced AMD, although no obvious functional variation has been discovered (Fagerness et al., 2008).”

“…components and complement regulatory proteins in drusen and nearby RPE of AMD patients (Crabb et al., 2002; Hageman et al., 1999; Johnson et al., 2001; Johnson et al., 2000; Mullins et al., 2001; Nozaki et al., 2006), suggesting a role for complement in AMD pathogenesis (Bora et al., 2008).”

“…been linked to increased risk of AMD (Mares-Perlman et al., 1995; Seddon et al., 2003), and analyses have revealed protective effects from antioxidants, nuts, fish, and omega-3 polysaccharide unsaturated fatty acids (AREDS, 2001; Cho et al., 2001; Seddon et al., 1994, 2001; Smith et al., 2000).”

“HtrA1 is also a secretory protein and an inhibitor of TGFβ family member (Oka et al., 2004).”

“[PubMed: 17909628] Conley YP, Jakobsdottir J, Mah T, Weeks DE, Klein R, Kuller L, Ferrell RE, Gorin MB. CFH, ELOVL4, PLEKHA1 and LOC387715 genes and susceptibility to age-related maculopathy: AREDS and CHS cohorts and meta-analyses.”

“ARMS2 SNP and AMD—The association of ARMS2 gene with AMD, especially advanced AMD, susceptibility has now been replicated in numbers of independent studies (Conley et al., 2006; Rivera et al., 2005; Ross et al., 2007; Schmidt et al., 2006; Seddon et al., 2007; Kanda et al., 2007).”

“Moreover, elevated serum level of CRP has been shown to be associated with AMD (Mold et al., 1999; Seddon et al., 2004).”

“Immunohistochemical analyses have shown various molecular constituents, such as apolipoproteins B and E, different immunoglobulins, factor X, amyloid P component, amyloid b, complement C5 and C5b-9 terminal complexes, fibrinogen, vitronectin, and others, to be present in all phenotypes of hard and soft drusen (Anderso…”

“Both fat intake and obesity have been linked to increased risk of AMD (Mares-Perlman et al., 1995; Seddon et al., 2003), and analyses have revealed protective effects from antioxidants, nuts, fish, and omega-3 polysaccharide unsaturated fatty acids (AREDS, 2001; Cho et al.”

“Several studies later confirmed a role for ApoE SNP in AMD (Baird et al., 2006; Jun et al., 2005; Kovacs et al., 2007; Schmidt et al., 2002; Souied et al., 1998; Zareparsi et al., 2004), while others found no effect (Kaur et al.”

“…may favor neovascularization by enhancing degradation of extracellular matrix components through increased expression of matrix metalloproteinases (Grau et al., 2006), or by binding to transforming growth factor (TGF)-β, an angiogenic factor whose expression has been geographically and temporally…”

“The notion that microglia contribute to drusen-like deposits is further strengthened by another study demonstrating that increasing fundus autofluorescence seen in aging wild-type mice consists of perivascular and subretinal microglia, which might also contain lipofuscin granules (Xu et al., 2008).”

“demonstrating that decreased macrophage influx after laser injury to Ccl2−/− mice is associated with reduced laserinduced CNV (Tsutsumi et al., 2003).”

“In the earliest stage, they may be visible ophthalmoscopically, when their diameter exceeds 25 µm (Sarks et al., 1999), as semitranslucent punctate dots in retro-illumination.”

“Association with a microbial component triggers upregulation of pro-inflammatory genes such as tissue necrosis factor, interleukin-1b, and interleukin-6, through the NFkB pathway (Misch and Hawn, 2008).”

“might therefore be secondary to the direct injury to CNV endothelium, rather than the depletion of macrophages (Apte et al., 2006).”

“This suggests that reduced binding of CRP by CFH might lead to impaired targeting of CFH to cellular debris (Laine et al., 2007; Skerka et al., 2007).”

“Many linkage and association studies have indicated that the most replicated signals reside on chromosome 1q25–31 and 10q26 (Fisher et al., 2005; Jakobsdottir et al., 2005; Klein et al., 1998; Majewski et al., 2003).”

“…components and complement regulatory proteins in drusen and nearby RPE of AMD patients (Crabb et al., 2002; Hageman et al., 1999; Johnson et al., 2001; Johnson et al., 2000; Mullins et al., 2001; Nozaki et al., 2006), suggesting a role for complement in AMD pathogenesis (Bora et al., 2008).”

“At age 2 years, cfh−/− mice exhibited significantly reduced visual acuity and rod response amplitudes on electroretinography as compared with age-matched control mice (Coffey et al., 2007).”

“CFH dysfunction may lead to excessive inflammation and tissue damage involved in the pathogenesis of AMD (Johnson et al., 2006).”

“The L412F variant of the TLR3 gene (i.e. a leucine to phenylalanine change at amino acid 412), encoded by the T allele at rs3775291 of the TLR3 gene, has been reported in three case-control cohorts to be protective against dry AMD, possibly through suppression of RPE apoptosis (Yang et al., 2008).”

“As described above, the CX3CR1 chemokine receptor found on microglia has been shown to harbor SNPs (T280M and V249I) that have been associated with increased risk of AMD in some reports (Chan et al., 2005; Tuo et al., 2004).”

“Blue light irradiation and treatment with hydrogen peroxide cause long-lasting mtDNA but not nuclear DNA mutations in cultured RPE cells (Ballinger et al., 1999; Godley et al., 2005).”

“A number of studies have illustrated the presence of complement components and complement regulatory proteins in drusen and nearby RPE of AMD patients (Crabb et al., 2002; Hageman et al., 1999; Johnson et al., 2001; Johnson et al., 2000; Mullins et al., 2001; Nozaki et al., 2006), suggesting a role for complement in A…”

“These mice also exhibited ultrastructural signs of AMD such as accumulation of lipofuscin granules, as well as increased the N-retinylidene–N-retinylethanolamine (A2E) accumulation on biochemical analysis (Chan et al., 2008; Tuo et al., 2007).”

“A genome-wide scan and genetic linkage analysis of 70 families with AMD suggests that chromosome 10q26 may contain a common AMD gene (Majewski et al., 2003).”

“Moreover, multiple subsequent studies showed little or no relation of ABCA4 mutations with AMD (Bojanowski et al., 2005; De La Paz et al., 1999; Souied et al., 2000; Stone et al., 1998).”

“This suggests that reduced binding of CRP by CFH might lead to impaired targeting of CFH to cellular debris (Laine et al., 2007; Skerka et al., 2007).”

“wide linkage studies (Weeks et al., 2004) and supported by a genome-scan meta-analysis (Fisher et al.”

“Recently, several studies offered direct evidence of mitochondrial alterations in AMD (Feher et al., 2006; Nordgaard et al., 2006, 2008).”

“Another study, which involved 45 patients with neovascular disease, identified a haplotypic association in both the promoter and an intronic region of the VEGF gene (Churchill et al., 2006).”

“A study by Zareparsi et al reported that the D299G (aspartate to glycine at amino acid 299) TLR4 (encoded in chromosome 9q32–33) polymorphism leads to increased AMD risk (OR = 2.65) (Zareparsi et al., 2005).”

“Neovascular AMD was found to be associated with the rs2010963 (G634C) VEGF-A SNP in a case-control cohort, and in a family cohort with two intronic VEGF-A SNPs (rs833070 and rs3025030) (Haines et al., 2006).”

“The insertion introduces a 54-bp AU-rich element, known for its properties to control mRNA decay in many transcripts that encode a wide variety of proteins involved in transient biological processes (Barreau et al., 2005; Garneau et al., 2007; Khabar, 2005).”

“TGFβ also is a potent inhibitor for immune response (Lehner, 2008; Wahl, 2007).”

“Complement system While AMD is a highly complex disease with numerous intersecting etiological factors, recent studies have generated significant interest in the inflammatory underpinnings of AMD pathogenesis (Klein et al., 2008b).”

“Moreover, the SNP variant rs2511989 located in the SERPING1 gene encoding the complement component 1 (C1) inhibitor was recently reported to occur less frequently in AMD cases than in control subjects (Ennis et al., 2008).”

“The molecular and cellular constituents of drusen have been analyzed extensively (Anderson et al., 2004; Crabb et al., 2002; Hageman et al., 2001; Johnson et al., 2000; Mullins et al., 2000; Russell et al., 2000).”

“Moreover, several studies have demonstrated that animal models with complement knockdown, either genetically or with pharmacological agents such as anti-complement antibodies, exhibit decreased CNV after laser injury, a commonly employed model for AMD-associated CNV in humans (Patel and Chan, 2008).”

“…the macrophages, have been histologically demonstrated near AMD lesions, including in areas of Bruch membrane breakdown, RPE atrophy, and choroidal neovascularization (Coleman et al., 2008; Dastgheib and Green, 1994; Green, 1999; Grossniklaus et al., 2002; Lopez et al., 1993; Penfold et al., 2001).”

“, 2004) and higher levels of antioxidant enzymes (Decanini et al., 2007; Frank et al., 1999) compared with non-AMD eyes, which indicate that oxidative stress plays an important role in AMD.”

“Both CX3CR1 and CX3CL1 are rich in the retina and brain (Combadiere et al., 1998; Foxman et al., 2002).”