The HtrA1 promoter polymorphism, smoking, and age-related macular degeneration in multiple case-control samples

Immunogenetic and Environmental Factors in Age-Related Macular Disease

Age-related macular degeneration (AMD) is a chronic disease, which often develops in older people, but this is not the rule. AMD pathogenesis changes include the anatomical and functional complex. As a result of damage, it occurs, in the retina and macula, among other areas. These changes may lead to partial or total loss of vision. This disease can occur in two clinical forms, i.e., dry (progression is slowly and gradually) and exudative (wet, progression is acute and severe), which usually started as dry form. A coexistence of both forms is possible. AMD etiology is not fully understood. Extensive genetic studies have shown that this disease is multifactorial and that genetic determinants, along with environmental and metabolic-functional factors, are important risk factors. This article reviews the impact of heavy metals, macro- and microelements, and genetic factors on the development of AMD. We present the current state of knowledge about the influence of environmental factors and genetic determinants on the progression of AMD in the confrontation with our own research conducted on the Polish population from Kuyavian-Pomeranian and Lubusz Regions. Our research is concentrated on showing how polluted environments of large agglomerations affects the development of AMD. In addition to confirming heavy metal accumulation, the growth of risk of acute phase factors and polymorphism in the genetic material in AMD development, it will also help in the detection of new markers of this disease. This will lead to a better understanding of the etiology of AMD and will help to establish prevention and early treatment.

Exploring the contribution of ARMS2 and HTRA1 genetic risk factors in age-related macular degeneration

Age-related macular degeneration (AMD) is the leading cause of severe irreversible central vision loss in individuals over 65 years old. Genome-wide association studies (GWASs) have shown that the region at chromosome 10q26, where the age-related maculopathy susceptibility (ARMS2/LOC387715) and HtrA serine peptidase 1 (HTRA1) genes are located, represents one of the strongest associated loci for AMD. However, the underlying biological mechanism of this genetic association has remained elusive. In this article, we extensively review the literature by us and others regarding the ARMS2/HTRA1 risk alleles and their functional significance. We also review the literature regarding the presumed function of the ARMS2 protein and the molecular processes of the HTRA1 protein in AMD pathogenesis in vitro and in vivo, including those of transgenic mice overexpressing HtrA1/HTRA1 which developed Bruch's membrane (BM) damage, choroidal neovascularization (CNV), and polypoidal choroidal vasculopathy (PCV), similar to human AMD patients. The elucidation of the molecular mechanisms of the ARMS2 and HTRA1 susceptibility loci has begun to untangle the complex biological pathways underlying AMD pathophysiology, pointing to new testable paradigms for treatment.

Lipopolysaccharide Activating NF-kB Signaling by Regulates HTRA1 Expression in Human Retinal Pigment Epithelial Cells

Inflammation and elevated expression of high temperature requirement A serine peptidase 1 (HTRA1) are known high risk factors for age-related macular degeneration (AMD). However, the specific mechanism that HTRA1 causes AMD and the relationship between HTRA1 and inflammation remains unclear. We found that lipopolysaccharide (LPS) induced inflammation enhanced the expression of HTRA1, NF-κB, and p-p65 in ARPE-19 cells. Overexpression of HTRA1 up-regulated NF-κB expression, and on the other hand knockdown of HTRA1 down-regulated the expression of NF-κB. Moreover, NF-κB siRNA has no significant effect on the expression of HTRA1, suggesting HTRA1 works upstream of NF-κB. These results demonstrated that HTRA1 plays a pivotal role in inflammation, explaining possible mechanism of overexpressed HTRA1-induced AMD. Celastrol, a very common anti-inflammatory and antioxidant drug, was found to suppress inflammation by inhibiting phosphorylation of p65 protein efficaciously in RPE cells, which may be applied to the therapy of age-related macular degeneration.

Elastin turnover in ocular diseases: A special focus on age-related macular degeneration

The extracellular matrix (ECM) and its turnover play a crucial role in the pathogenesis of several inflammatory diseases, including age-related macular degeneration (AMD). Elastin, a critical protein component of the ECM, not only provides structural and mechanical support to tissues, but also mediates several intracellular and extracellular molecular signaling pathways. Abnormal turnover of elastin has pathological implications. In the eye elastin is a major structural component of Bruch's membrane (BrM), a critical ECM structure separating the retinal pigment epithelium (RPE) from the choriocapillaris. Reduced integrity of macular BrM elastin, increased serum levels of elastin-derived peptides (EDPs), and elevated elastin antibodies have been reported in AMD. Existing reports suggest that elastases, the elastin-degrading enzymes secreted by RPE, infiltrating macrophages or neutrophils could be involved in BrM elastin degradation, thus contributing to AMD pathogenesis. EDPs derived from elastin degradation can increase inflammatory and angiogenic responses in tissues, and the elastin antibodies are shown to play roles in immune cell activity and complement activation. This review summarizes our current understanding on the elastases/elastin fragments-mediated mechanisms of AMD pathogenesis.

Polymorphism rs11200638 enhanced HtrA1 responsiveness and expression are associated with age-related macular degeneration

OBJECTIVES

To investigate the role of polymorphism rs11200638 of high-temperature requirement factor A-1 (HtrA1) gene in the pathogenesis of age-related macular degeneration (AMD).

METHODS

Cultured adult retinal pigment epithelial cells (ARPE-19) expressing HtrA1 gene were treated with H2O2 or lipopolysaccharides (LPS) and analysed using western blot and quantitative polymerase chain reaction to illustrate the effects of oxidative and inflammatory stress on HtrA1 gene expression. Luciferase reporter plasmid driven by HtrA1 promoter with either normal allele G or risk allele A at SNP rs11200638 was transfected to ARPE-19 cells to investigate the effect of the G/A variation on HtrA1 promoter activity. The effects of HtrA1 overexpression on ARPE-19 cells were analysed with respect to percentage of cell proliferation inhibition and cell apoptosis.

RESULTS

HtrA1 expression was significantly increased with LPS or H2O2 stimulations (p < 0.05). In ARPE-19 cells, HtrA1 promoters (-1 to -2175 bp from translation starting point) with risk allele A or normal G at rs11200638 did not show statistically significant differences in their luciferase reporter expression (p = 0.054425173), however, both promoters showed a persistent trend of higher luciferase expressions after 100 ng/ml LPS treatment. The luciferase expression level was significantly greater in the promoter with risk A when compared to that with normal G. Overexpression of HtrA1 resulted in apoptosis of ARPE-19 cells with 53.8 ± 1.6% of proliferation inhibition (p < 0.01).

CONCLUSIONS

Risk haplotype A at rs11200638 significantly increased the responsiveness of HtrA1 promoter to inflammation and subsequently enhanced HtrA1 expression. HtrA1 overexpression induced ARPE-19 apoptosis and growth inhibition, relevant to pathogenesis of AMD.

HTRA1 rs11200638 variant and AMD risk from a comprehensive analysis about 15,316 subjects

BACKGROUND

The high-temperature requirement factor A1 (HTRA1) gene located at 10q26 locus has been associated with age-related macular degenerative (AMD), with the significantly related polymorphism being (rs11200638, -625G/A), however, above association is not consistent. We investigated a comprehensive analysis to evaluate the correlations between rs11200638 polymorphism and AMD susceptibility thoroughly addressing this issue.

METHODS

An identification was covered from the PubMed and Wanfang databases until 27th Jan, 2020. Odds ratios (OR) with 95% confidence intervals (CI) were applied to evaluate the associations. After a thorough and meticulous search, 35 different articles (33 case-control studies with HWE, 22 case-control studies about wet/dry AMD) were retrieved.

RESULTS

Individuals carrying A-allele or AA genotype may have an increased risk to be AMD disease. For example, there has a significantly increased relationship between rs11200638 polymorphism and AMD both for Asians (OR: 2.51, 95%CI: 2.22-2.83 for allelic contrast) and Caucasians [OR (95%CI) = 2.63(2.29-3.02) for allelic contrast]. Moreover, a similar trend in the source of control was detected. To classify the type of AMD, increased association was also observed in both wet (OR: 3.40, 95%CI: 2.90-3.99 for dominant model) and dry (OR: 2.08, 95%CI: 1.24-3.48 for dominant model) AMD. Finally, based on the different genotyping methods, increased relationships were identified by sequencing, TaqMan, PCR-RFLP and RT-PCR.

CONCLUSIONS

Our meta-analysis demonstrated that HTRA1 rs11200638 polymorphism may be related to the AMD development, especially about individuals carrying A-allele or AA genotype, who may be as identified targets to detect and intervene in advance. Further studies using Larger sample size studies, including information about gene-environment interactions will be necessary to carry out.

AMD-Associated HTRA1 Variants Do Not Influence TGF-β Signaling in Microglia

Genetic variants of high-temperature requirement A serine peptidase 1 (HTRA1) and age-related maculopathy susceptibility 2 (ARMS2) are associated with age-related macular degeneration (AMD). One HTRA1 single nucleotide polymorphism (SNP) is situated in the promotor region (rs11200638) resulting in increased expression, while two synonymous SNPs are located in exon 1 (rs1049331:C > T, rs2293870:G > T). HtrA1 is known to inhibit transforming growth factor-β (TGF-β) signaling, a pathway regulating quiescence of microglia, the resident immune cells of the brain and retina. Microglia-mediated immune responses contribute to AMD pathogenesis. It is currently unclear whether AMD-associated HTRA1 variants influence TGF-β signaling and microglia phenotypes. Here, we show that an HtrA1 isoform carrying AMD-associated SNPs in exon 1 exhibits increased proteolytic activity. However, when incubating TGF-β-treated reactive microglia with HtrA1 protein variants, neither the wildtype nor the SNP-associated isoforms changed microglia activation in vitro.

Association of HTRA1 rs11200638 with age-related macular degeneration (AMD) in Brazilian patients

Age-related macular degeneration is a multifactorial disease that can lead to vision impairment in older individuals. Although the etiology of age-related macular degeneration remains unknown, risk factors include age, ethnicity, smoking, hypertension, obesity, and genetic factors. Two main loci have been identified through genome-wide association studies, on chromosomes 1 and 10. Among the variants located at the 10q26 region, rs11200638, located at the HTRA1 gene promoter, has been associated with age-related macular degeneration in several populations and is considered the main polymorphism. We conducted a replication case-control study to analyze the frequency and participation of rs11200638 in the etiology of age-related macular degeneration in a sample of patients and controls from the State of São Paulo, Brazil, through polymerase chain reaction and enzymatic digestion. The frequency of the A allele was 57.60% in patients with age-related macular degeneration and 36.45% in controls (p value < 1e-07), representing a 2.369-fold higher risk factor for the disease. Both the AA and AG genotypes were observed more frequently in the age-related macular degeneration group compared to the control group (p = 1.21e-07 and 0.0357, respectively). No statistically significant results were observed after stratification in dry versus wet types or advanced versus non-advanced forms. To our knowledge, this is the first time the association between rs11200638 and overall age-related macular degeneration has been reported in South America.

HtrA1 Mediated Intracellular Effects on Tubulin Using a Polarized RPE Disease Model

Age-related macular degeneration (AMD) is the leading cause of irreversible vision loss. The protein HtrA1 is enriched in retinal pigment epithelial (RPE) cells isolated from AMD patients and in drusen deposits. However, it is poorly understood how increased levels of HtrA1 affect the physiological function of the RPE at the intracellular level. Here, we developed hfRPE (human fetal retinal pigment epithelial) cell culture model where cells fully differentiated into a polarized functional monolayer. In this model, we fine-tuned the cellular levels of HtrA1 by targeted overexpression. Our data show that HtrA1 enzymatic activity leads to intracellular degradation of tubulin with a corresponding reduction in the number of microtubules, and consequently to an altered mechanical cell phenotype. HtrA1 overexpression further leads to impaired apical processes and decreased phagocytosis, an essential function for photoreceptor survival. These cellular alterations correlate with the AMD phenotype and thus highlight HtrA1 as an intracellular target for therapeutic interventions towards AMD treatment.

Proteolytic Degradation and Inflammation Play Critical Roles in Polypoidal Choroidal Vasculopathy

Polypoidal choroidal vasculopathy (PCV) is a common subtype of wet age-related macular degeneration in Asian populations, whereas choroidal neovascularization is the typical subtype in Western populations. The cause of PCV is unknown. By comparing the phenotype of a PCV mouse model expressing protease high temperature requirement factor A1 (HTRA1) in retinal pigment epithelium with transgenic mice expressing the inactive HTRA1S328A, we showed that HTRA1-mediated degradation of elastin in choroidal vessels is critical for the development of PCV, which exhibited destructive extracellular matrix remodeling and vascular smooth muscle cell loss. Compared with weak PCV, severe PCV exhibited prominent immune complex deposition, complement activation, and infiltration of inflammatory cells, suggesting inflammation plays a key role in PCV progression. More important, we validated these findings in human PCV specimens. Intravitreal delivery of an HTRA1 inhibitor (DPMFKLboroV) was effective (36% lesion reduction; P = 0.009) in preventing PCV initiation but ineffective in treating existing lesions. Anti-inflammatory glucocorticoid was effective in preventing PCV progression but ineffective in preventing PCV initiation. These results suggest that PCV pathogenesis occurs through two stages. The initiation stage is mediated by proteolytic degradation of extracellular matrix proteins attributable to increased HTRA1 activity, whereas the progression stage is driven by inflammatory cascades. This study provides a basis for understanding the differences between PCV and choroidal neovascularization, and helps guide the design of effective therapies for PCV.

Association between polymorphism rs11200638 in the HTRA1 gene and the response to anti-VEGF treatment of exudative AMD: a meta-analysis

BACKGROUND

Anti-angiogenesis treatments are the most commonly used treatments for the vision loss caused by exudative age-related macular degeneration (AMD), in which the anti-vascular endothelial growth factor (VEGF) drugs with ranibizumab and bevacizumab are current standard treatments. However, the outcome of anti-VEGF therapeutics is not uniform in all patients.

METHODS

We performed a literature-based meta-analysis including, five published studies relevant to HTRA1 and response to anti-VEGF treatment (bevacizumab or ranibizumab). Summary odds ratios (ORs) and 95% confidence intervals (CIs) were estimated using fixed- and random-effects models. Sensitivity analysis and meta-regression were also performed. Q-statistic test and Egger's test was used to evaluate heterogeneity and publication bias respectively.

RESULTS

Overall, no association between the rs11200638 polymorphism in HTRA1 gene and the anti-VEGF treatment response was found in the genotype GG versus AA (OR = 1.06; 95% CI: 0.77 to 1.48; P = 0.98), genotype GA versus AA (OR = 1.11; 95% CI: 0.83 to 1.47; P = 0.93), genotype GG + GA versus AA (OR = 1.22; 95% CI: 0.94 to 1.57; P = 0.09), and allele G versus A (OR = 0.92; 95% CI: 0.78 to 1.08; P = 0.14). In the subgroup analysis by ethnicity Caucasian population, and a significant association was still not observed in all genetic models. Sensitivity analysis indicated the robustness of our findings, and no publication bias was observed in our meta-analysis.

CONCLUSIONS

This study shows that there was no association between the polymorphism rs11200638 in HTRA1 gene and response to anti-VEGF treatment of exudative AMD. However, more studies are needed to further prove the conclusion of present study, especially well-designed and high quality randomised controlled trials or intervention studies.

Specific correlation between the major chromosome 10q26 haplotype conferring risk for age-related macular degeneration and the expression of HTRA1

PURPOSE

A region within chromosome 10q26 has a set of single nucleotide polymorphisms (SNPs) that define a haplotype that confers high risk for age-related macular degeneration (AMD). We used a bioinformatics approach to search for genes in this region that may be responsible for risk for AMD by assessing levels of gene expression in individuals carrying different haplotypes and by searching for open chromatin regions in the retinal pigment epithelium (RPE) that might include one or more of the SNPs.

METHODS

We surveyed the PubMed and the 1000 Genomes databases to find all common (minor allele frequency > 0.01) SNPs in 10q26 strongly associated with AMD. We used the HaploReg and LDlink databases to find sets of SNPs with alleles in linkage disequilibrium and used the Genotype-Tissue Expression (GTEx) database to search for correlations between genotypes at individual SNPs and the relative level of expression of the genes. We also accessed Encyclopedia of DNA Elements (ENCODE) to find segments of open chromatin in the region with the AMD-associated SNPs. Predicted transcription factor binding motifs were identified using HOMER, PROMO, and RegulomeDB software programs.

RESULTS

There are 34 polymorphisms within a 30-kb region that are in strong linkage disequilibrium (r2>0.8) with the reference SNP rs10490924 previously associated with risk for AMD. The expression of three genes in this region, PLEKHA1, ARMS2, and HTRA1 varies between people who have the low-AMD-risk haplotype compared with those with the high-AMD-risk haplotype. For PLEKHA1, 44 tissues have an expression pattern with the high-AMD-risk haplotype associated with low expression (rs10490924 effect size -0.43, p = 3.8 x 10-5 in ovary). With regard to ARMS2, the variation is most pronounced in testes: homozygotes with the high-AMD-risk haplotype express ARMS2 at lower levels than homozygotes with the low-AMD-risk haplotype; expression in heterozygotes falls in between (rs10490924 effect size -0.79, p = 7.5 x 10-24). For HTRA1, the expression pattern is the opposite; the high-AMD-risk haplotype has higher levels of expression in 27 tissues (rs10490924 effect size 0.40, p = 1.5 × 10-7 in testes). None of the other 22 genes within one megabase of rs10490924, or any gene in the entire genome, have mRNA expression levels that correlate with the high-AMD-risk haplotype. More than 100 other SNPs in the 10q26 region affect the expression of PLEKHA1 and ARMS2 but not that of HTRA1; none of these SNPs affects the risk for AMD according to published genome-wide association studies (GWASs). Two of the AMD-risk SNPs (rs36212732 and rs36212733) affect transcription factor binding sites in proximity to a DNase I hypersensitive region (i.e., a region of open chromatin) in RPE cells.

CONCLUSIONS

SNPs in chromosome 10q26 that influence the expression of only PLEKHA1 or ARMS2 are not associated with risk for AMD, while most SNPs that influence the expression of HTRA1 are associated with risk for AMD. Two of the AMD-risk SNPs affect transcription factor binding sites that may control expression of one of the linked genes in the RPE. These findings suggest that the variation in the risk for AMD associated with chromosome 10q26 is likely due to variation in HTRA1 expression. Modulating HTRA1 activity might be a potential therapy for AMD.

Inhibition of cell proliferation, migration and apoptosis in blue-light illuminated human retinal pigment epithelium cells by down-regulation of HtrA1

AIM

To investigate the effect of HtrA1 on the proliferation, migration and apoptosis of human retinal pigment epithelium (RPE) cells in the light injured model, as well as the expression of the apoptosis related molecules.

METHODS

The human RPE cell line ARPE-19 was exposed to blue light to establish the light injured model. The cells were transfected with HtrA1 siRNA to knockdown HtrA1 expression. Subsequent expression of HtrA1 was determined by real-time polymerase chain reaction (RT-PCR) and Western blot, respectively. Changes in cell proliferation, migration and apoptosis were assessed by cell counting kit-8 (CCK-8), Transwell assay and flow cytometry respectively, as well as changes in the mRNA and protein levels of Bax, Caspase-3 and Bcl-2 expression.

RESULTS

HtrA1 was highly expressed in ARPE-19 cells after blue light irradiation. Knockdown of HtrA1 expression inhibited the proliferation, migration and apoptosis of the blue-light-irradiated ARPE-19 cells (P<0.05). Bax and Caspase-3 expression were significantly reduced both at mRNA and protein levels (P<0.05) after siRNA treatment. Bcl-2 expression significantly increased in blue-light-irradiated ARPE-19 cells after siRNA interference (P<0.05).

CONCLUSION

Silence of HtrA1 may inhibit the proliferation, migration and apoptosis of ARPE-19 cells in light injured model. Moreover, HtrA1 suppression in blue-light-irradiated ARPE-19 cells may ameliorate cell apoptosis through down-regulation of Bax and Caspase-3, and up-regulation of Bcl-2 expression.

No Sex Differences in the Frequencies of Common Single Nucleotide Polymorphisms Associated with Age-Related Macular Degeneration

PURPOSE

Since some studies have reported differences in the association of age-related macular degeneration (AMD) with biological sex, we set out to determine whether the difference in the disease susceptibility is afforded by common single nucleotide polymorphisms (SNPs) associated with AMD.

METHODS

We genotyped 2067 Caucasian subjects from the Age-Related Eye Disease Study cohort for commonly associated AMD SNPs, including those in CFH (rs1061170, rs1410996, and rs3766404), ARMS2 (rs10490924), and C3 (rs2230199) using either a Sequenom MassARRAY MALDI-TOF mass spectrometer or using Taqman genotyping reagents. A Cox proportional hazards model was used to determine the effect of genotype, age, sex, and smoking status on the development of AMD.

RESULTS

All tested SNPs genotyped are associated strongly with AMD (p < 0.0001), in concordance with previous studies. However, we found no observable differences in any of the SNPs studied when categorized by sex. Interactions between SNPs and sex were found to be not statistically significant (p = 0.38-0.79).

CONCLUSIONS

The difference between male and female incidence of AMD is not explained by the most commonly AMD-associated SNPs, though it does not exclude the possibility that other, less common SNPs contribute to this difference.

Functional single nucleotide polymorphism in IL-17A 3' untranslated region is targeted by miR-4480 in vitro and may be associated with age-related macular degeneration

Age-related macular degeneration (AMD) is a leading cause of irreversible central vision loss in the elderly. Genetic factors contributing to AMD include single nucleotide polymorphisms (SNPs) in immune-related genes including CFH, C2, CFI, C9, and C3, thus implicating these pathways in AMD pathogenesis. MicroRNAs (miRNAs) are powerful regulators of gene expression and execute this function by binding to the 3' untranslated region (3'UTR) of target mRNAs, leading to mRNA degradation. In this study, we searched for the possible association of SNPs in the 3'UTR region of IL-17A, a gene implicated in AMD pathogenesis without any previous SNP association with AMD. Using two independent sample cohorts of Caucasian subjects, six SNPs in the IL-17A 3'-UTR were selected for genotyping based on bioinformatic predictions of the SNP effect on microRNA binding. The SNP rs7747909 was found to be associated with AMD (P < 0.05) in the NEI cohort, using a dominant model logistic regression. Luciferase reporter gene assays and RNA electrophoretic mobility shift assays were performed using ARPE-19 cells to confirm the preferential binding of microRNAs to the major allele of the SNP. Our findings support the hypothesis that microRNA-mediated gene dysregulation may play a role in the pathogenesis of AMD.

Association of Htra1 gene polymorphisms with the risk of developing AMD in Iranian population

BACKGROUND

Half of the cases of vision loss in people under 60 years of age have been attributed to age-related macular degeneration (AMD). This is a multifactorial disease with late onset. It has been demonstrated that many different genetic loci are implicated in the risk of developing AMD in different populations. In the current study, we investigated the association of high-temperature ‎requirement A-1 (HTRA1) gene polymorphisms with the risk of developing AMD in the Iranian population.

METHODS

Genomic DNA samples were extracted from 120 patients with AMD and 120 healthy age- and sex-matched controls. A 385 base-pair fragment of the HTRA1 gene promoter region was amplified using the polymerase chain reaction (PCR) technique and sequenced. The frequencies of the alleles were calculated and statistical analysis was performed using SPSS software.

RESULTS

Our study demonstrated that the rate of polymorphisms rs11200638 -625 G>A and rs2672598 -487T>C were significantly greater in AMD patients than in healthy controls from the Iranian population.

CONCLUSIONS

The results of our study indicate that HTRA1 gene promoter region polymorphisms are associated with the risk of developing AMD in the Iranian population.

The Age-Related Macular Degeneration Complex: Linking Epidemiology and Histopathology Using the Minnesota Grading System (The Inaugural Frederick C. Blodi Lecture)

PURPOSE

To describe the histopathologic findings of the four stages of age-related macular degeneration (AMD) as defined by the Age-Related Eye Disease Study (AREDS) using the Minnesota grading system (MGS).

CLINICAL RELEVANCE

There are no animal models for AMD. Eye banks enable access to human tissue with AMD. The level of AMD (grades 1 through 4) as defined by AREDS is determined ex vivo using the MGS. The AREDS has the largest collection to date of prospectively gathered data on the natural history of AMD. Since the MGS uses the same clinical criteria as AREDS, the addition of histopathologic findings of graded tissue confirms important pathophysiology at each stage of AMD.

METHODS

Four eye bank eyes were graded according to the MGS. Only the right eyes were dissected for phenotype grading. The fellow (left) eyes were fixed for histopathologic study. The eyes were serially sectioned (7 μm) through the macula. Individual slides were examined, and a two-dimensional reconstruction of the topography of the macula was created for each donor. Selected, unstained slides were used for immunohistochemical staining. In one donor, portions of tissue were obtained for transmission electron microscopic (TEM) processing.

RESULTS

Donor 1 had a rare hard, nodular druse (MGS1). Donor 2 had intermediate confluent drusen (MGS2). Donor 3 had numerous intermediate drusen (MGS3) in the right eye. Histopathology of the fellow left showed basal laminar deposits (BLamD), soft drusen, and an area of occult choroidal neovascularization underlying the retinal pigment epithelium (RPE) with endothelial cells (CD31-positive). Donor 4 also had MGS 3 along with reticular pseudodrusen (RPD). Histologic and TEM examination demonstrated diffuse BLamD, thickening of Bruch's membrane, hard drusen, and focal nodules underlying the RPE that corresponded to the RPD. EM examination demonstrated both BLamD and electron-dense material located just external to the elastic layer of Bruch's membrane.

CONCLUSION

Eye bank eyes graded using the MGS serve as an important link to the phenotypic and epidemiologic data from the AREDS. Thus, the MGS serves as a system to study the histopathology at each stage of AMD to better understand the relevant pathophysiologic changes in disease progression.

Complement activation and choriocapillaris loss in early AMD: implications for pathophysiology and therapy

Age-related macular degeneration (AMD) is a common and devastating disease that can result in severe visual dysfunction. Over the last decade, great progress has been made in identifying genetic variants that contribute to AMD, many of which lie in genes involved in the complement cascade. In this review we discuss the significance of complement activation in AMD, particularly with respect to the formation of the membrane attack complex in the aging choriocapillaris. We review the clinical, histological and biochemical data that indicate that vascular loss in the choroid occurs very early in the pathogenesis of AMD, and discuss the potential impact of vascular dropout on the retinal pigment epithelium, Bruch's membrane and the photoreceptor cells. Finally, we present a hypothesis for the pathogenesis of early AMD and consider the implications of this model on the development of new therapies.

The role of proteases and inflammatory molecules in triggering neovascular age-related macular degeneration: basic science to clinical relevance

Age-related macular degeneration (AMD) causes severe vision impairment in aged individuals. The health impact and cost of the disease will dramatically increase over the years, with the increase in the aging population. Currently, antivascular endothelial growth factor agents are routinely used for managing late-stage AMD, and recent data have shown that up to 15%-33% of patients do not respond to this treatment. Henceforth, there is a need to develop better treatment options. One avenue is to investigate the role proteases and inflammatory molecules might have in regulating and being regulated by vascular endothelial growth factor. Moreover, emerging data indicate that proteases and inflammatory molecules might be critical in the development and progression of AMD. This article reviews recent literature that investigates proteases and inflammatory molecules involved in the development of AMD. Gaining insights into the proteolytic and inflammatory pathways associated with the pathophysiology of AMD could enable the development of additional or alternative drug strategies for the treatment of AMD.

In-depth analyses unveil the association and possible functional involvement of novel RAD51B polymorphisms in age-related macular degeneration

The contribution of DNA damage to the pathogenesis of age-related macular degeneration (AMD) has been reported. Recently, a genomewide association study detected the association of a single-nucleotide polymorphism (SNP) in RAD51B (rs8017304 A>G) with AMD. RAD51B is involved in recombinational repair of DNA double-strand breaks. We analyzed RAD51B influence on AMD using two cohorts from Caucasian and Han Chinese populations. The Caucasian set replicated the rs8017304 A>G association and revealed two novel AMD-associated SNPs in RAD51B, rs17105278 T>C and rs4902566 C>T. Under the dominant model, these two SNPs exhibit highly significant disease risk. SNP-SNP interaction analysis on rs17105278 T>C and rs4902566 C>T homozygous demonstrated a synergistic effect on AMD risk, reaching an odds ratio multifold higher than well-established AMD susceptibility loci in genes such as CFH, HTRA1, and ARMS2. Functional study revealed lower RAD51B mRNA expression in cultured primary human fetal retinal pigment epithelium (hfRPE) carrying rs17105278 T>C variants than in hfRPE carrying rs17105278 wild type. We concluded that the risk of developing AMD exhibits dose dependency as well as an epistatic combined effect in rs17105278 T>C and rs4902566 C>T carriers and that the elevated risk for rs17105278 T>C carriers may be due to decreased transcription of RAD51B. This study further confirms the role of DNA damage/DNA repair in AMD pathogenesis.

Chromosome 10q26 locus and age-related macular degeneration: a progress update

Age-related macular degeneration (AMD) is the leading cause of late-onset central vision loss in developed countries. Both genetic and environmental factors contribute to the onset of AMD. Variation at a locus on chromosome 10q26 has been consistently associated with this disease and represents one of the two strongest genetic effects being identified in AMD. At least three genes are located within the bounds of the locus: pleckstrin homology domain containing family A member 1 (PLEKHA1), age-related maculopathy susceptibility 2 (ARMS2) and high-temperature requirement A serine peptidase 1 (HTRA1), all of which are associated with AMD. Due to the strong linkage disequilibrium (LD) across this region, statistical genetic analysis alone is incapable of distinguishing the effect of an individual gene in the locus. Uncertainty remains, however, in regards to which gene is responsible for the linkage and association of the locus with AMD. Investigating functional consequences of the associated variants and related genes tends to be essential to identifying the biologically responsible gene(s) underlying AMD. This review examines the recent progress and current uncertainty on the genetic and functional analyses of the 10q26 locus in AMD with a focus on ARMS2 and HTRA1. A discussion, which entails the possible multi-faceted approaches for pinpointing the gene(s) in the locus underlying the pathogenesis of AMD, is also included.

Variants at chromosome 10q26 locus and the expression of HTRA1 in the retina

Variations in a locus at chromosome 10q26 are strongly associated with the risk of age-related macular degeneration (AMD). The most significantly associated haplotype includes a nonsynonymous SNP rs10490924 in the exon 1 of ARMS2 and rs11200638 in the promoter region of HTRA1. It is under debate which gene(s), ARMS2, HTRA1 or some other genes are functionally responsible for the genetic association. To verify whether the associated variants correlate with a higher HTRA1 expression level as previously reported, HTRA1 mRNA and protein were measured in a larger human retina-RPE-choroid samples (n = 82). Results show there is no significant change of HTRA1 mRNA level among genotypes at rs11200638, rs10490924 or an indel variant of ARMS2. Furthermore, two AMD-associated synonymous SNPs rs1049331 and rs2293870 in HTRA1 exon 1 do not change its protein level either. These results suggest that the AMD-associated variants in the chromosome 10q26 locus do not significantly affect the expression of HTRA1.

HtrA1 is induced by oxidative stress and enhances cell senescence through p38 MAPK pathway

Genetic predisposition and senescence of retinal pigment epithelium induced by oxidative stress are major contributors to age-related macular degeneration (AMD). Single-nucleotide polymorphisms in HTRA1 are strongly linked to the onset of AMD. In this study, we examine the role of HtrA1 in premature senescence and cell death induced by oxidative stress. HtrA1 mRNA and protein were up-regulated during premature senescence induced by H2O2 in both mouse embryonic fibroblasts (MEFs) and ARPE-19 cells. Expression of the senescence markers p21(CIP1/WAF1) and p16(INK4a), and SA-β-galactosidase activity, were higher in HtrA1+/- MEFs than in HtrA1-/- MEFs. HtrA1+/+ and HtrA1+/- MEFs were more resistant than HtrA1-/- MEFs to H2O2-induced cell death. Activation of p38 MAPK by oxidative stress was quicker in HtrA1+/- MEFs than in HtrA1-/- MEFs. The effects of excess HtrA1 were examined by transient transfection of cells with HtrA1 expression vectors or by addition of recombinant proteins. Excess wild type HtrA1 accelerated premature senescence of MEFs and ARPE-19 cells, while the protease-inactive HtrA1 S328A did not. HtrA1-induced senescence was abrogated by inhibition of p38 MAPK. We conclude that HtrA1 is induced by oxidative stress and promotes premature cell senescence through p38 MAPK in a protease activity-dependent manner.

The ARMS2 A69S variant and bilateral advanced age-related macular degeneration

PURPOSE

To identify genetic associations between specific risk genes and bilateral advanced age-related macular degeneration (AMD) in a retrospective, observational case series of 1,003 patients: 173 patients with geographic atrophy in at least 1 eye and 830 patients with choroidal neovascularization in at least 1 eye.

METHODS

Patients underwent clinical examination and fundus photography. The images were subsequently graded using a modified grading system adapted from the Age-Related Eye Disease Study. Genetic analysis was performed to identify genotypes at 4 AMD-associated variants (ARMS2 A69S, CFH Y402H, C3 R102G, and CFB R32Q) in these patients.

RESULTS

There were no statistically significant relationships between clinical findings and genotypes at CFH, C3, and CFB. The genotype at ARMS2 correlated with bilateral advanced AMD using a variety of comparisons: unilateral geographic atrophy versus bilateral geographic atrophy (P = 0.08), unilateral choroidal neovascularization versus bilateral choroidal neovascularization (P = 9.0 × 10(-8)), and unilateral late AMD versus bilateral late AMD (P = 5.9 × 10(-8)).

CONCLUSION

In this series, in patients with geographic atrophy or choroidal neovascularization in at least 1 eye, the ARMS2 A69S substitution strongly associated with geographic atrophy or choroidal neovascularization in the fellow eye. The ARMS2 A69S substitution may serve as a marker for bilateral advanced AMD.

Genetics of immunological and inflammatory components in age-related macular degeneration

Age-related macular degeneration (AMD), affecting 30 to 50 million elder individuals worldwide, is a disease affecting the macular retina and choroid that can lead to irreversible central vision loss and blindness. Recent findings support a role for immunologic processes in AMD pathogenesis, including generation of inflammatory related molecules in the Bruch's membrane, recruitment of macrophages, complement activation, microglial activation and accumulation in the macular lesions. Pro-inflammatory effects of chronic inflammation and oxidative stress can result in abnormal retinal pigment epithelium, photoreceptor atrophy and choroidal neovascularization. The associations of immunological and inflammatory genes, in particular the genes related to innate immunity with AMD support the involvement of various immunological pathways in the AMD pathogenesis. We review the literature on the involvements of inflammatory genes in AMD, highlight recent genetic discoveries, and discuss the potential application of such knowledge in the management of patients with AMD.

Association of genetic polymorphisms with response to bevacizumab for neovascular age-related macular degeneration in the Chinese population

AIMS

To determine whether there is an association between CFH, ARMS2, HTRA1, VEGF, SERPING1 or C3 genotypes and patient response to treatment with intravitreal bevacizumab for neovascular age-related macular degeneration (AMD).

MATERIALS & METHODS

This was a multicenter prospective study. One hundred and forty four patients with neovascular AMD treated with bevacizumab were recruited from 13 centers. Twelve SNPs were genotyped using Sequenom. Visual acuity score (VAS), central retinal thickness and maximum thickness of lesion were measured at each visit.

RESULTS

For the CFH rs800292 polymorphism, mean VAS changes were 4.4, 8.7 and 15.5 letters in the CC, CT and TT genotype carriers (p = 0.009). For ARMS2 rs10490924, mean VAS changes were 3.6, 12.1 and 9.6 letters for the TT, TG and GG genotypes (p = 0.001). For HTRA1 rs11200638, mean VAS changes were 3.6, 12.3 and 9.6 letters for the AA, AG and GG genotypes (p < 0.001).

CONCLUSION

CFH, ARMS2 and HTRA1 genotypes may influence patient response to treatment with intravitreal bevacizumab for neovascular AMD.

HTRA1 in Age-Related Macular Degeneration

Age-related macular degeneration (AMD) is a leading cause of severe visual impairment and irreversible blindness in most developed countries, affecting more than 50 million of elderly people worldwide. Current treatments, such as intravitreal injection of antiangiogenic agents, mitigate the effect of advanced AMD but cannot completely cure the disease. Comprehensive understanding of the AMD pathological mechanisms is important for the development of new therapies. Previously, we identified a single-nucleotide polymorphism (rs11200638) in the promoter region of the high temperature requirement factor A1 (HTRA1) gene on chromosome 10q26 to be associated with exudative AMD. In further biological studies, we have provided evidence that HTRA1 could be a potential disease-causing gene within the 10q26 locus. In this review, we summarize the pathology of AMD and the molecular function of the HtrA1 protein. Also evaluated are the genetic effects of HTRA1 polymorphism on AMD in different populations and interactions with other AMD-associated genes, especially with the complement factor H (CFH) gene, which was identified for nonexudative AMD. The biological roles of HtrA1 are exhaustively examined on its contribution to the multifactorial pathogenic mechanism of AMD. Although HtrA1 should play a part in AMD pathogenesis, a host of other genetic and environmental factors, known and unknown, is involved and warrants intensive future research.

Pharmacogenetics and age-related macular degeneration

Pharmacogenetics seeks to explain interpatient variability in response to medications by investigating genotype-phenotype correlations. There is a small but growing body of data regarding the pharmacogenetics of both nonexudative and exudative age-related macular degeneration. Most reported data concern polymorphisms in the complement factor H and age-related maculopathy susceptibility 2 genes. At this time, the data are not consistent and no definite conclusions may be drawn. As clinical trials data continue to accumulate, these relationships may become more apparent.

Increased expression of multifunctional serine protease, HTRA1, in retinal pigment epithelium induces polypoidal choroidal vasculopathy in mice

Age-related macular degeneration (AMD) is the leading cause of irreversible blindness in the elderly. Wet AMD includes typical choroidal neovascularization (CNV) and polypoidal choroidal vasculopathy (PCV). The etiology and pathogenesis of CNV and PCV are not well understood. Genome-wide association studies have linked a multifunctional serine protease, HTRA1, to AMD. However, the precise role of HTRA1 in AMD remains elusive. By transgenically expressing human HTRA1 in mouse retinal pigment epithelium, we showed that increased HTRA1 induced cardinal features of PCV, including branching networks of choroidal vessels, polypoidal lesions, severe degeneration of the elastic laminae, and tunica media of choroidal vessels. In addition, HTRA1 mice displayed retinal pigment epithelium atrophy and photoreceptor degeneration. Senescent HTRA1 mice developed occult CNV, which likely resulted from the degradation of the elastic lamina of Bruch's membrane and up-regulation of VEGF. Our results indicate that increased HTRA1 is sufficient to cause PCV and is a significant risk factor for CNV.

Age-related macular degeneration and the complement system

Age-related macular degeneration (AMD) is the leading cause of blindness in the developed world. It is a complex multifactorial disease, and despite new advances in treatment, many patients still succumb to visual impairment. The complement pathway has been implicated in the pathogenesis of many diseases, and recently variants in several genes encoding complement pathway proteins have been associated with AMD. Complement proteins have been found in histological specimens of eyes with AMD. Altered levels of both intrinsic complement proteins and activated products have been found in the circulation of patients with AMD. Complement activation may be triggered by oxidative stress, resulting from retinal exposure to incoming light; indeed an inter-play between these two pathological processes seems to exist. Finally, complement inhibitors are currently being evaluated in clinical trials. This article reviews the role of the complement system in AMD, and the potential of complement inhibition in preventing the devastating blindness resulting from this disease.

Apolipoprotein E gene and age-related macular degeneration in a Chinese population

PURPOSE

To examine the association between apolipoprotein E (APOE) polymorphisms and age-related macular degeneration (AMD) in a Chinese population.

METHODS

The study consisted of 712 subjects, including 201 controls, 363 cases with early AMD, and 148 cases with exudative AMD. Genomic DNA was extracted from venous blood leukocytes. Common allelic variants of APOE (ε2, ε3, and ε4) were analyzed by PCR and direct sequencing.

RESULTS

APOE ε3ε3 was the most frequent genotype, with a frequency of 72.6% in controls, 72.5% in early AMD, and 70.3% in exudative AMD. Frequency of the ε2 allele was 6.7% in controls, 7.4% in early AMD, and 8.8% in exudative AMD. Frequency of the ε4 allele was 8.7% in controls, 7.7% in early AMD, and 7.8% in exudative AMD. No statistically significant difference in APOE genotype and allele frequency distribution was observed among controls, cases with early AMD, and cases with exudative AMD. For ε2 allele carriers, the odds ratio was 1.12 (95% confidence interval [CI], 0.65-1.93) for early AMD and 1.06 (95% CI, 0.53-2.10) for exudative AMD. For ε4 allele carriers, the odds ratio was 1.04 (95% CI, 0.61-1.75) for early AMD and 0.83 (95% CI, 0.42-1.62) for exudative AMD.

CONCLUSIONS

Our data provide no evidence to support an association of APOE polymorphisms with early or exudative AMD, suggesting that APOE is less likely to be a major AMD susceptibility gene in the Chinese population.

LOC387715/HTRA1 polymorphisms, smoking and combined effects on exudative age-related macular degeneration in a Korean population

BACKGROUND

This study was to investigate the association of two single nucleotide polymorphisms (SNPs) in LOC387715 and HTRA1 with exudative age-related macular degeneration (AMD) in a Korean population and the gene-gene and gene-environment interactions in the development of AMD.

METHODS

We genotyped two SNPs that are located in the LOC387715 locus (rs10490924) and HTRA1 (rs11200638) in 137 cases of exudative AMD and 187 controls.

RESULTS

Both two SNPs were significantly associated with AMD (P = 0.0001). Homozygotes for the risk allele at LOC387715 and HTRA1 had a 3.80-fold and a 4.03-fold increased risk of exudative AMD, respectively, compared with homozygotes for the wild-type allele (P = 0.0001). The joint effects for complement factor H (CFH) Y402H and 10q26 variants indicated an increased risk of exudative AMD. The odds ratios (ORs) of AMD for individuals carrying one-, two- and three-copy risk alleles of CFH Y402H and LOC387715 were 1.08, 3.49 and 3.64, respectively. Also, the combination effect of the CFH Y402H risk alleles with HTRA1 risk alleles was dose-dependent. The interaction analysis between gene and environmental factors showed that among several factors, smoking synergistically increased the susceptibility of AMD for variants of LOC387715 and HTRA1, with OR 8.33 (3.05-22.74) and OR 8.50 (3.07-23.51), respectively.

CONCLUSION

This study demonstrated the significant association of the 10q26 SNPs (HTRA1 and LOC387715) in an AMD cohort from Korea and was consistent with previous studies from other populations. Also, a statistically significant interaction between genetic and environmental factors was found.

Analysis of the indel at the ARMS2 3'UTR in age-related macular degeneration

Controversy remains as to which gene at the chromosome 10q26 locus confers risk for age-related macular degeneration (AMD) and statistical genetic analysis is confounded by the strong linkage disequilibrium (LD) across the region. Functional analysis of related genetic variations could solve this puzzle. Recently, Fritsche et al. reported that AMD is associated with unstable ARMS2 transcripts possibly caused by a complex insertion/deletion (indel; consisting of a 443 bp deletion and an adjacent 54 bp insertion) in its 3'UTR (untranslated region). To validate this indel, we sequenced our samples. We found that this indel is even more complex and is composed of two side-by-side indels separated by 17 bp: (1) 9 bp deletion with 10 bp insertion; (2) 417 bp deletion with 27 bp insertion. The indel is significantly associated with the risk of AMD, but is also in strong LD with the non-synonymous single nucleotide polymorphism rs10490924 (A69S). We also found that ARMS2 is expressed not only in placenta and retina but also in multiple human tissues. Using quantitative PCR, we found no correlation between the indel and ARMS2 mRNA level in human retina and blood samples. The lack of functional effects of the 3'UTR indel, the amino acid substitution of rs10490924 (A69S), and strong LD between them suggest that A69S, not the indel, is the variant that confers risk of AMD. To our knowledge, it is the first time it has been shown that ARMS2 is widely expressed in human tissues. Conclusively, the indel at 3'UTR of ARMS2 actually contains two side-by-side indels. The indels are associated with risk of AMD, but not correlated with ARMS2 mRNA level.

HTRA1 promoter polymorphism and risk of age-related macular degeneration: a meta-analysis

PURPOSE

To clarify the role of human high-temperature requirement A-1 (HTRA1) gene promoter polymorphism (-512G>A) in age-related macular degeneration (AMD).

METHODS

Relevant studies were identified by searching PubMed and EMBASE database. A logistic regression analysis proposed for molecular association studies was carried out to estimate the genetic effect and the possible genetic model of action.

RESULTS

Fourteen case-control studies were included in this meta-analysis. There was strong evidence for an association between HTRA1 -512G>A polymorphism and AMD (p < 0.001). The genetic model test indicated that the genetic model was most likely to be co-dominant. Overall, our meta-analysis showed that AA and GA genotypes were associated with increased risk of AMD (AA vs. GG: odds ratio(1) [OR(1)] = 7.46; 95% confidence interval [CI] = 6.16-9.04; GA vs. GG: OR(2) = 2.27, 95% CI = 2.02-2.55). In stratified analysis by ethnicity and age, the genetic effect seemed to be stronger in Caucasians and subjects > or =73 years of age than in Asians and subjects <73 years of age. When subgroup analysis was conducted by AMD type, significant association was noted for wet AMD but not for dry AMD.

CONCLUSIONS

This meta-analysis summarizes the strong evidence for an association between HTRA1 -512G>A polymorphism and AMD and indicates a co-dominant model of action.

Toll-like receptor polymorphisms and age-related macular degeneration: replication in three case-control samples

PURPOSE

Innate immunity appears to play a key role in age-related macular degeneration (AMD). Although two previous studies reported that gene variations in Toll-like receptor (TLR)-3 and -4 are associated with AMD, other studies have not confirmed these associations. In this study, three independent samples (two U.S. clinic-based case-control study samples and one Australian population-based study sample) were used to further assess the association of the polymorphisms rs3775291 in TLR3 and rs4986790 in TLR4 with AMD.

METHODS

AMD cases and unrelated controls were collected from the National Eye Institute Clinical Center (NEI, n = 320), the Age-Related Eye Disease Study (AREDS, n = 483), and the Blue Mountains Eye Study (BMES, n = 852). DNA extracted from subjects was genotyped for rs3775291 and rs4986790, and the associations with AMD were investigated.

RESULTS

Neither of the two polymorphisms rs3775291 and rs4986790 had a statistically significant association with AMD in any of the three sample sets or in combinations of the sets. Analysis of the combined geographic atrophy or neovascular AMD cases in the NEI, AREDS, and BMES sample sets also failed to demonstrate statistically significant associations of those two single nucleotide polymorphisms with advanced AMD.

CONCLUSIONS

Even with previously verified samples sets and adequate study powers, the results did not confirm the reported associations of TLR3 rs3775291 and TLR4 rs4986790 with AMD in the three independent samples, individually or combined.

Enhanced HtrA2/Omi expression in oxidative injury to retinal pigment epithelial cells and murine models of neurodegeneration

PURPOSE

To investigate the role of HtrA2/Omi, a nuclear-encoded mitochondrial serine protease with a proapoptosis function, under H(2)O(2)-induced oxidative stress in human RPE, in the Ccl2(-)(/)(-)Cx3cr1(-)(/)(-) double-knockout (DKO) mouse retina, and the HtrA2/Omi-deficient mice.

METHODS

Oxidative stress was induced in ARPE-19 cells by 1 mM H(2)O(2) for 2 hours. HtrA2/Omi and caspase-3 expression was evaluated using RQ-PCR, immunohistochemistry, or Western blot. Cell viability was detected by MTT assay. HtrA2/Omi expression in the subcellular components and activated caspase-3 were measured. These processes were also evaluated in cells treated with UCF-101, an HtrA2/Omi inhibitor or in cells subjected to RNAi against HtrA2/Omi. Oxidative stress was assayed and compared in retinas of DKO and wild-type (WT) mice by determining serum NADPH oxidase subunits and nitrite levels. Transmission electron microscopy was used to view the retinal ultrastructure of the HtrA2/Omi-deficient mice.

RESULTS

H(2)O(2)-induced oxidative damage resulted in HtrA2/Omi translocation from mitochondria to cytosol, leading to RPE cell apoptosis via a caspase-mediated pathway. Treatment of RPE cells with UCF-101 reduced the cytosolic translocation of HtrA2/Omi, attenuated caspase-3 activation, and decreased apoptosis. After specific HtrA2 downregulation, increased cell viability was measured in H(2)O(2)-treated ARPE-19 cells. Retina of DKO mice exhibit increased oxidative stress and upregulation of HtrA2/Omi. Fewer and abnormal mitochondria were found in HtrA2/Omi(-)(/)(-) photoreceptors and RPE.

CONCLUSIONS

These findings suggest that HtrA2/Omi is related to RPE apoptosis due to oxidative stress, which may play an important role in the integrity of mitochondria and the pathogenesis of AMD.

Multifactor effects and evidence of potential interaction between complement factor H Y402H and LOC387715 A69S in age-related macular degeneration

Background

Variants in the complement cascade genes and the LOC387715/HTRA1, have been widely reported to associate with age-related macular degeneration (AMD), the most common cause of visual impairment in industrialized countries.

Methods/Principal Findings

We investigated the association between the LOC387715 A69S and complement component C3 R102G risk alleles in the Finnish case-control material and found a significant association with both variants (OR 2.98, p = 3.75×10⁻⁹; non-AMD controls and OR 2.79, p = 2.78×10⁻¹⁹, blood donor controls and OR 1.83, p = 0.008; non-AMD controls and OR 1.39, p = 0.039; blood donor controls), respectively. Previously, we have shown a strong association between complement factor H (CFH) Y402H and AMD in the Finnish population. A carrier of at least one risk allele in each of the three susceptibility loci (LOC387715, C3, CFH) had an 18-fold risk of AMD when compared to a non-carrier homozygote in all three loci. A tentative gene-gene interaction between the two major AMD-associated loci, LOC387715 and CFH, was found in this study using a multiplicative (logistic regression) model, a synergy index (departure-from-additivity model) and the mutual information method (MI), suggesting that a common causative pathway may exist for these genes. Smoking (ever vs. never) exerted an extra risk for AMD, but somewhat surprisingly, only in connection with other factors such as sex and the C3 genotype. Population attributable risks (PAR) for the CFH, LOC387715 and C3 variants were 58.2%, 51.4% and 5.8%, respectively, the summary PAR for the three variants being 65.4%.

Conclusions/Significance

Evidence for gene-gene interaction between two major AMD associated loci CFH and LOC387715 was obtained using three methods, logistic regression, a synergy index and the mutual information (MI) index.

Molecular pathology of age-related macular degeneration

Age-related macular degeneration (AMD) is a leading cause of irreversible blindness in the world. Although the etiology and pathogenesis of AMD remain largely unclear, a complex interaction of genetic and environmental factors is thought to exist. AMD pathology is characterized by degeneration involving the retinal photoreceptors, retinal pigment epithelium, and Bruch's membrane, as well as, in some cases, alterations in choroidal capillaries. Recent research on the genetic and molecular underpinnings of AMD brings to light several basic molecular pathways and pathophysiological processes that might mediate AMD risk, progression, and/or response to therapy. This review summarizes, in detail, the molecular pathological findings in both humans and animal models, including genetic variations in CFH, CX3CR1, and ARMS2/HtrA1, as well as the role of numerous molecules implicated in inflammation, apoptosis, cholesterol trafficking, angiogenesis, and oxidative stress.