Immunopathological aspects of age-related macular degeneration

Age-related macular degeneration (AMD) represents a leading cause of blindness worldwide. While the clinical and histopathological aspects of AMD are well characterized, its etiology and pathogenesis remain unclear. Recent findings suggest a role for immunologic processes in AMD pathogenesis, including the age-related generation of extracellular deposits inside the Brusch membrane and beneath the retinal pigment epithelium, recruitment of macrophages for clearance of these deposits, complement activation, recruitment of tissue-destructive macrophages, microglial activation and accumulation, and proinflammatory effects of chronic inflammation by Chlamydia pneumoniae. This review discusses the evidence for the role of inflammation in human AMD and in animal models of AMD.     

Choriocapillaris breakdown precedes retinal degeneration in age-related macular degeneration

This work presents a combined light and electron microscopical approach to investigate the initial breakdown of the retinal pigment epithelium (RPE) and choriocapillaris (CC) in age-related macular degeneration (AMD). Perimacular sections of 12 dry and wet AMD eyes (82 ± 15 years) and 7 age-matched controls (75 ± 10 years) without retinal pathology were investigated. Disease progression was classified into 5 stages of retinal degeneration to investigate the concurrent CC breakdown. Special emphasis was laid on transitions where intact CC–RPE–retina complexes went over into highly atrophied areas. AMD sections showed elevated loss of photoreceptors, RPE and CC (p < 0.01), and thickened Bruch's membrane with increased basal laminar and linear deposits compared with controls. Up to 27% of the CC was lost in controls although RPE and retina were still intact. This primary loss of CC further increased with AMD (up to 100%). The data implicate that CC breakdown already occurs during normal aging and precedes degeneration of the RPE and retina with AMD, defining AMD as a vascular disease. Particular attention should be given to the investigation of early AMD stages and transitional stages to the late stage that reveal a possible sequence of degenerative steps with aging and AMD.     

Cerebral microbleeds and age-related macular degeneration: the AGES-Reykjavik Study

We test the hypothesis that cerebral microbleeds (CMB) and age-related macular degeneration (AMD), both linked to amyloid-β deposition, are correlated. This study includes 4205 participants (mean age 76.2; 57.8% women) in the Age, Gene/Environment Susceptibility (AGES)-Reykjavik Study (2002-2006). CMB were assessed from magnetic resonance images, and AMD was assessed using digital retinal images. Data were analyzed with multinomial logistic models controlling for major confounders. Evidence of CMB was detected in 476 persons (272 with strict lobar CMB and 204 with nonlobar CMB). AMD was detected in 1098 persons (869 with early AMD, 140 with exudative AMD, and 89 with pure geographic atrophy). Early and exudative AMD were not associated with CMB. The adjusted odds ratio of pure geographic atrophy was 1.62 (95% confidence interval 0.93-2.82, p = 0.089) for having any CMB, 1.43 (0.66-3.06, p = 0.363) for strict lobar CMB, and 1.85 (0.89-3.87, p = 0.100) for nonlobar CMB. This study provides no evidence that amyloid deposits in the brain and AMD are correlated. However, the suggestive association of geographic atrophy with CMB warrants further investigation.     

Segmentation of the optic disk in color eye fundus images using an adaptive morphological approach

The identification of some important retinal anatomical regions is a prerequisite for the computer aided diagnosis of several retinal diseases. In this paper, we propose a new adaptive method for the automatic segmentation of the optic disk in digital color fundus images, using mathematical morphology. The proposed method has been designed to be robust under varying illumination and image acquisition conditions, common in eye fundus imaging. Our experimental results based on two publicly available eye fundus image databases are encouraging, and indicate that our approach potentially can achieve a better performance than other known methods proposed in the literature. Using the DRIVE database (which consists of 40 retinal images), our method achieves a success rate of 100% in the correct location of the optic disk, with 41.47% of mean overlap. In the DIARETDB1 database (which consists of 89 retinal images), the optic disk is correctly located in 97.75% of the images, with a mean overlap of 43.65%.     

Circulating vitamin D concentration and age-related macular degeneration: Systematic review and meta-analysis

Vitamin D may be involved in ocular function in older adults, but there is no current consensus on a possible association between circulating concentrations of 25-hydroxyvitamin D (25OHD) and the occurrence of age-related macular degeneration (AMD). Our objective was to systematically review and quantitatively assess the association of circulating 25OHD concentration with AMD. A Medline search was conducted in November 2015, with no date limit, using the MeSH terms “Vitamin D” OR “Vitamin D deficiency” OR “Ergocalciferols” OR ‘Cholecalciferol’ combined with “Age-related macular degeneration” OR “Macular degeneration” OR “Retinal degeneration” OR “Macula lutea” OR “Retina”. Fixed and random-effects meta-analyses were performed to compute (i) standard mean difference in 25OHD concentration between AMD and non-AMD patients; (ii) AMD risk according to circulating 25OHD concentration. Of the 243 retrieved studies, 11 observational studies—10 cross-sectional studies and 1 cohort study—met the selection criteria. The number of participants ranged from 65 to 17,045 (52–100% women), and the number with AMD ranged from 31 to 1440. Circulating 25OHD concentration was 15% lower in AMD compared with non-AMD on average. AMD was inversely associated with the highest 25OHD quintile compared with the lowest (summary odds ratio (OR) = 0.83 [95%CI:0.71–0.97]), notably late AMD (summary OR = 0.47 [95%CI:0.28–0.79]). Circulating 25OHD < 50 nmol/L was also associated with late-stage AMD (summary OR = 2.18 [95%CI:1.34–3.56]), an association that did not persist when all categories of AMD were considered (summary OR = 1.26 [95%CI:0.90–1.76]). In conclusion, this meta-analysis provides evidence that high 25OHD concentrations may be protective against AMD, and that 25OHD concentrations below 50 nmol/L are associated with late AMD.     

Multilocus analysis of age-related macular degeneration

Age-related macular degeneration (AMD) is a late onset vision disorder. Recent studies demonstrate that alterations in complement cascade genes are associated with AMD. Of the three identified complement loci, variants in complement factor H (CFH) have the highest impact as does an independent locus at 10q26. Our matched case–control study using the Age-Related Eye Disease Study (AREDS) cohort confirms and extends the associations in these loci. Subjects were genotyped for single nucleotide polymorphisms (SNPs) from CFH, complement component 2 (C2), complement component 3 (C3), complement factor B (CFB), age-related maculopathy susceptibility (ARMS2), HtrA serine peptidase 1 (HTRA1), and apolipoprotein E (APOE). Individual SNPs, and haplotypes showed risk trends consistent with those seen in other population studies for CFH, C3, C2, and CFB. SNP rs10490924 on chromosome 10 in exon 1 of the ARMS2 gene showed a highly significant association with an odds ratio (OR) of 3.2 (95% CI 2.4–4.2) for the risk allele and rs11200638 located in the proximal promoter region of HTRA1 showed a higher significant association with an OR of 3.4 (95% CI 2.5–4.6) with our AMD cases. We found that APOE haplotypes were not significantly associated with disease status. Adjustments for other risk factors did not significantly alter the observed associations. This study validates the complement pathway''s involvement in AMD and suggests that allelic variants in complement genes have a direct role in disease. These results also support previous findings that variants in the region of 10q26 exert an independent risk for AMD.     

Association between vascular endothelial growth factor gene polymorphisms and age-related macular degeneration in a Polish population

The pathogenesis of age-related macular degeneration (AMD) is thought to be determined by an array of environmental and genetic factors. The association of increased expression of vascular endothelial growth factor (VEGF) with AMD, especially the wet form of AMD, was reported in several studies. The VEGF gene is highly polymorphic and some of its polymorphisms may affect its expression. In our work, we searched for an association between the −460C> (rs833061) and −634G>C (rs2010963) polymorphisms of the VEGF gene and the occurrence of AMD and its dry and wet forms. We have chosen these polymorphisms because they were shown to be significant in other studies and we previously showed their association with diabetic retinopathy. A total of 401 individuals were enrolled in this study: 136 controls, and 88 patients with dry and 177 with wet AMD. The polymorphisms were determined with DNA from peripheral blood lymphocytes by allele-specific and restriction fragment length polymorphism polymerase chain reaction. The significance of the polymorphisms was assessed by multiple logistic regression, producing odds ratios (ORs) and 95% confidence intervals (CIs). We observed a weak association (OR 2.90) between AMD occurrence and the C/T genotype of the −460C>T polymorphism. An association (OR 3.77) between the C/T genotype of the −460C>T polymorphism and the occurrence of dry AMD was observed. The T/T genotype considerably lowered the risk of dry AMD (OR 0.19). Dry AMD was associated with the C/C genotype of the −634G>C polymorphism (OR 3.68). Another weak association (OR 2.63) was found between the C/T genotype of the −460C>T polymorphism and the occurrence of wet AMD. The occurrence of AMD was correlated with the presence of the combined C/T–G/G genotype of both polymorphisms (OR 2.41), whereas the T/T–G/G and T/T–G/C genotypes exerted a protective effect against the disease (OR 0.22 and 0.48, respectively). The presence of the C/T–G/G and C/T–C/C combined genotypes increased the risk of dry AMD (OR 2.08 and 3.77, respectively), whereas the presence of the T/T–G/G and T/T–G/C genotypes decreased the risk (OR 0.15 and 0.28, respectively). In the wet form of AMD, the combined genotype C/T–G/G slightly favored the disease (OR 2.61) and the T/T–G/G genotype had a protective effect (OR 0.25). Analysis of haplotypes of both polymorphisms yielded similar results for AMD in general as well as for the dry and wet forms of the disease: the CG haplotype favored both forms of AMD, whereas the TG haplotype protected against both forms of AMD. The results obtained indicate that the −460C>T and −634G>C polymorphisms of the VEGF gene may be associated with the dry and wet forms of AMD in a Polish population.     

CFH基因R1210C突变与中国人老年黄斑变性的相关性研究

目的 补体因子H(complement factor H,CFH)基因R1210C突变与高加索人老年黄斑变性(age-related macular degeneration,AMD)显著相关.我们通过对中国大陆汉族人群进行病例-对照研究,评估CFH基因R1210C突变与中国人老年黄斑变性的相关性.方法 收集258例中国汉族人湿性AMD患者作为病例组,同时收集来自同一地区426名正常中国汉族人作为对照,应用直接测序法检测CFH基因中R1210C的突变情况,并比较病例组和对照组的差异.结果 258例中国人AMD患者和426名正常中国人的CFH基因中未发现R1210C突变.结论 中国人老年黄斑变性与CFH基因R1210C突变可能无关.     

Correlation of complement factor H gene polymorphisms with exudative age-related macular degeneration in a Chinese cohort

To evaluate the association between complement factor H (CFH) gene polymorphism and the risk of exudative age-related macular degeneration (AMD) in a case-control study in a Chinese cohort. One hundred and thirty-six exudative AMD patients and 140 age- and sex-matched control subjects were recruited. We genotyped 3 common single nucleotide polymorphisms (SNPs), namely, -257C>T (rs3753394), Y402H (rs1061170) and IVS15 (rs1329428), genetic analyses were performed on all available genotype data. All the possible haplotypes of these 3 SNPs were detected. Polymerase chain reaction (PCR) and allele-specific restriction endonuclease digestion were performed, some PCR products of these 3 SNPs were sequenced. The risk alleles (T, C or G) of the 3 SNPs conferred 1.72-fold, 3.14-fold, and 1.79-fold of increased likelihood of the disease, respectively (P<0.05). The heterozygous genotype in rs1061170 (TC) revealed significant association, meanwhile rs3753394 and rs1329428 had a slight association with the disease, respectively. Significant differences were shown in the risk alleles in the 3 SNPs among different Chinese cohort. Low linkage disequilibrium was found among the 3 SNPs. The haplotypes TCG and CTG revealed as risk factors, whereas the protective haplotype CTA was over-represented in controls. We found significant association between risk alleles (T, C or G) of the 3 SNPs and the disease. The genetic divergence across multiple populations within Chinese existed. Risk haplotypes and protective haplotype were found in this study.     

The complement system in age-related macular degeneration: A review of rare genetic variants and implications for personalized treatment

Age-related macular degeneration (AMD) is a progressive retinal disease and the major cause of irreversible vision loss in the elderly. Numerous studies have found both common and rare genetic variants in the complement pathway to play a role in the pathogenesis of AMD. In this review we provide an overview of rare variants identified in AMD patients, and summarize the functional consequences of rare genetic variation in complement genes on the complement system. Finally, we discuss the relevance of this work in light of ongoing clinical trials that study the effectiveness of complement inhibitors against AMD.     

Genetic deficiency of complement factor H in a patient with age-related macular degeneration and membranoproliferative glomerulonephritis

Age-related macular degeneration (AMD) and membranoproliferative glomerulonephritis type II (MPGN2) are dense deposit diseases that share a genetic association with complement genes and have complement proteins as important components of the dense deposits. Here, we present the case of a 64-year-old smoker male who developed both AMD and MPGN2 in his late 50s. The patient presented persistent low plasma levels of C3, factor H levels in the lower part of the normal range and C3NeF traces. Genetic analyses of the CFH, CFB, C3, CFHR1-CFHR3 and LOC387715/HTRA1 genes revealed that the patient was heterozygote for a novel missense mutation in exon 9 of CFH (c.1292 G > A) that results in a Cys431Tyr substitution in SCR7 of the factor H protein. In addition, he was homozygote for the His402 CFH allele, heterozygote for the Ser69 LOC387715 allele, homozygote for the Arg32 (BFS) CFB allele, heterozygote for the Gly102 (C3F) C3 allele and carried no deletion of the CFHR1/CFHR3 genes. Proteomic and functional analyses indicate absence in plasma of the factor H allele carrying the Cys431Tyr mutation. As a whole, these data recapitulate a prototypical complement genetic profile, including a partial factor H deficiency and the presence of major risk factors for AMD and MPGN2, which support the hypothesis that these dense deposit diseases have a common pathogenic mechanism involving dysregulation of the alternative pathway of complement activation.     

CX3CR1 polymorphisms and the risk of age-related macular degeneration

Background: Age-related macular degeneration (AMD), a most common eye disease, can lead to irreversible visual impairment. Age, genetic and environmental factors have been implicated in AMD. Chemokine (C-X3-C motif) receptor 1 (CX3CR1) gene polymorphisms could influence the susceptibility of AMD. Methods: We tested the association between AMD and single nocleotide polymorphisms (SNPs) of CX3CR1 gene (rs3732378 and rs3732379) in 102 cases and 115 controls from China. Genotypes were determined by MassArray genotyping assay method. Association between CX3CR1 gene polymorphisms and AMD were examined by χ² test and logistic regression. Results: Genotype distribution of CX3CR1 gene polymorphisms were in accordance with HWE examination. No obvious differences were observed in the genotypes of rs3732378 polymorphism between case and control groups (P>0.05), but A allele of it could increase the risk of AMD (P=0.025, OR=2.391, 95% CI=1.092-5.237). Both TT genotype and T allele of rs3732379 were significantly associated with the susceptibility of AMD (P=8.663, OR=8.663, 95% CI=1.044-71.874; P=0.021, OR=2.076, 95% CI=1.104-3.903). Age, gender and smoking status were used as common confounders to adjust the association between CX3CR1 gene polymorphism and AMD risk. Then we found that rs3732378 had no obvious association with AMD susceptibility. TT genotype of rs3732379 related to the occurrence of AMD, but the association was not significant (P=0.050, OR=8.274, 95% CI=1.002-69.963). T allele of rs3732379 might increase the susceptibility of AMD (P=0.029, OR=2.033, 95% CI=1.077-3.838). Conclusion: T allele of rs3732379 might have a positive association with the susceptibility of AMD.     

A polymorphism of LOC387715 gene is associated with age-related macular degeneration in the Japanese population

Age-related macular degeneration (AMD) is one of the leading causes of blindness among older adults in developed countries and also in Japan. Previous research suggests that AMD is etiologically a complex disease, caused by multiple genes and environmental factors. Association studies have identified that a complement factor H gene (CFH) variant is a major risk factor for AMD in Caucasians. However, we and two other groups have reported no association between CFH and AMD in the Japanese population. Recent studies have suggested that LOC387715 on chromosome 10q26 may be the second major risk loci for AMD in Caucasians. In this study, we examined the association between LOC387715 and AMD in Japanese, and our results show that polymorphism of the LOC387715 gene is associated with AMD in Japanese as well as in Caucasians. Our data show a disease odds ratio of 6.20 (95% CI: 2.87-13.40) conferred by homozygosity for risk alleles at LOC387715 compared with the non-risk genotype. A polymorphism of LOC387715 gene is associated with AMD in the Japanese population.     

Alzheimer's disease and age-related macular degeneration have different genetic models for complement gene variation

Alzheimer's disease (AD) and age-related macular degeneration (AMD) are both neurodegenerative disorders which share common pathological and biochemical features of the complement pathway. The aim of this study was to investigate whether there is an association between well replicated AMD genetic risk factors and AD. A large cohort of AD (n = 3898) patients and controls were genotyped for single nucleotide polymorphisms (SNPs) in the complement factor H (CFH), the Age-related maculopathy susceptibility protein 2 (ARMS2) the complement component 2 (C2), the complement factor B (CFB), and the complement component 3 (C3) genes. While significant but modest associations were identified between the complement factor H, the age-related maculopathy susceptibility protein 2, and the complement component 3 single nucleotide polymorphisms and AD, these were different in direction or genetic model to that observed in AMD. In addition the multilocus genetic model that predicts around a half of the sibling risk for AMD does not predict risk for AD. Our study provides further support to the hypothesis that while activation of the alternative complement pathway is central to AMD pathogenesis, it is less involved in AD.     

Haplotypes of RHO polymorphisms and susceptibility to age-related macular degeneration

Objective: To investigate whether haplotypes of rhodopsin (RHO) polymorphisms including rs7984, rs2855552, rs2855557 and rs2410 were associated with age-related macular degeneration (AMD) risk in Chinese Han population. Methods: Genotypes of rs7984, rs2855552, rs2855557 and rs2410 were detected with polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) in 186 cases and 196 healthy controls. Then, the haplotypes were established with Haploview 4.2 software. And the effects of clinical charactersitics on the frequency of GTTG haplotype were also analyzed. Odds ratios (ORs) with 95% confidence interval (95% CI) were utilized to assess the relationship of haplotypes and genotypes of RHO polymorphisms with susceptibility to AMD. Results: Genotype distribution of all polymorphisms in control group were all in agreement with Hardy-Weinberg equilibrium (HWE) (P>0.05). In the analysis, we found that mutant alleles of rs7984 and rs2855557 were both associated with increased risk of AMD. For genotype analysis, rs7984 AA and rs2855557AA, rs2410GG genotypes all could increase the risk for AMD (OR=1.905, 95% CI=1.143-3.174; OR=2.226, 95% CI=1.261-3.932; OR=2.073, 95% CI=1.105-3.888). However, rs2855552 showed no effects on the onset of AMD. Compared with GTTA, the haplotypes of GGTG, ATAA and GTTG were all related with AMD susceptibility. Further analysis suggested that age, hypertension and hyperlipidemia history play important roles in the frequency alteration of GTTG haplotype. Conclusion: RHO polymorphisms (rs7984, rs2855557 and rs2410) and haplotypes may confer remarkable susceptibility to AMD. Further investigation showed that gene and environmental factors may work together in the pathogenesis of AMD.     

年龄相关性黄斑变性的分子遗传流行病学研究进展

年龄相关性黄斑变性是发达国家老年人致盲的主要原因,它是一种具有高度遗传异质性的疾病.随着分子生物学和分子遗传学的发展,已经发现多个潜在的致病基因.现就年龄相关性黄斑变性的易感基因和遗传流行病学的研究进展进行综述.     

Mitochondrial alterations of retinal pigment epithelium in age-related macular degeneration

Mitochondrial dysfunctions have been implicated in the pathophysiology of several age-related diseases including age-related macular degeneration (AMD), a progressive neurodegenerative disease affecting primarily the retinal pigment epithelium (RPE). The aims of our electron microscopic and morphometric studies were to reveal qualitative and quantitative alterations of mitochondria in human RPE from AMD and from age- and sex-matched controls. With increasing age a significant decrease in number and area of mitochondria, as well as loss of cristae and matrix density were found in both AMD and control specimens. These decreases were significantly greater in AMD than in normal aging. Alterations of mitochondria were accompanied by proliferation of peroxisomes and lipofuscin granules in both AMD and control specimens, although the difference between groups was significant only for peroxisomes. Unexpectedly, morphometric data showed that the RPE alterations seen in AMD may also develop in normal aging, 10-15 years after appearing in AMD patients. These findings suggest that (i) the severity of mitochondrial and peroxisomal alterations are different between AMD and normal aging, and (ii) the timing of damage to RPE may be critical for the development of AMD. We conclude that besides the well-documented age-related changes in mitochondrial DNA, alterations of mitochondrial membranes may also play a role in the pathogenesis of AMD. These membranes could be a new target for treatment of AMD and other age-related diseases.     

Loss of endothelial planar cell polarity and cellular clearance mechanisms in age-related macular degeneration

Apoptosis, autophagosomes, and lysosomes are lacking in the retinal pigment epithelium (RPE) of age-related macular degeneration (AMD) eyes. Necrosis, not apoptosis, appeared to be the prominent type of cell death in RPE, which led to the accumulation of cell debris within and on both sides of Bruch’s membrane. The endothelium of the choriocapillaris had an altered planar cell polarity which encompassed the disappearance of fenestrations, the thickening of cytoplasm, and anterior nuclear dislocation. There were no significant differences in RPE and choroidal aberrations between macular and temporal regions. Loss of endothelial polarity could be at the crux of AMD initiation and progression.     

Circulating anti-retinal antibodies as immune markers in age-related macular degeneration

Age-related macular maculopathy (ARM) and age-related macular degeneration (AMD) are the leading causes of blindness in the Western world. Despite the magnitude of this clinical problem, very little is known about the pathogenesis of the disease. In this study, we analysed the sera (using indirect immunohistochemistry and Western blot analysis) from a very large cohort of such patients and normal age-matched controls to detect circulating anti-retinal antibodies. Patients with bilateral drusen (n = 64) and with chorioretinal neovascularization (CNV) (n = 51) were recruited in addition to age-matched control subjects (n = 39). The sera were analysed for anti-retinal immunoglobulins on retinal sections. The data were then correlated with the clinical features graded according to the International Classification and Grading System of ARM and AMD. The sera of patients with drusen (93.75%) and CNV (82.27%) were found to have a significantly (P = 0.02) higher titre of autoantibodies to the retina in comparison with controls (8.69%), indicating significant evidence of involvement of the immune process in early stages of AMD. Subsequent statistical analysis of the drusen group showed significant progressive staining (P = 0.0009) in the nuclei layers from early to late stages of ARM. Western blotting confirmed the presence of anti-retinal immunoglobulins to retinal antigens. As anti-retinal immunoglobulins are present in patients with bilateral drusen and exudative AMD, these antibodies could play a significant role in the pathogenesis of AMD. Whilst we do not have evidence that these antibodies precede disease onset, the possibility that their presence might contribute to disease progression needs to be investigated. Finally, the eventual identification of the target antigens detected by these antibodies may permit the future development of new diagnostic methods for ARM and AMD.     

Auto-adjusted 3-D optic disk viewing from low-resolution stereo fundus image

Three-dimensional (3-D) visualization of the optic nerve head (optic disk) is very useful for clinical applications. It allows clinicians to measure the disk parameters more accurately and thus make the pathological diagnosis and progression monitoring easier. This paper describes an automatic, precise, 3-D optic nerve head reconstruction method from a pair of stereo images for which efficient steps including sparse-image registration and dense-depth recovery are used. A combination of two registration methods is used to detect the sub-pixel correspondences. The proposed method takes advantages of both the correlation methods which is robust to noise and the feature-based method on its accuracy. The searching range in image registration is auto-adjusted based on the previous iteration result. Only sparse matched points are computed to speed up the processing and the sub-pixel matching is used to overcome the problem of low resolution in the image. This is followed by the piecewise cubic interpolation to obtain the dense disparities and depths. Multiple windowing is applied here by first using the large window to obtain basic disparities followed by the small window and previous basic disparities to measure details. The result is then smoothed and displayed as the final 3-D shape.