Association of Apolipoprotein E Polymorphisms With Normal Tension Glaucoma in a Chinese Population

Serum lipid and lipoprotein profiles and their association with intraocular pressure in primary open-angle glaucoma: an observational cross-sectional study in the Chinese population

BACKGROUND

Glaucoma is a leading cause of vision impairment and permanent blindness. Primary open-angle glaucoma (POAG) is a prominent type of primary glaucoma; however, its cause is difficult to determine. This study aimed to analyze the serum lipid profile of Chinese POAG patients and assess its correlation with intraocular pressure (IOP).

METHODS

The study included 1,139, 1,248, and 356 Chinese individuals with POAG, primary angle closure glaucoma (PACG), and controls, respectively. Peripheral whole blood samples were collected at the time of diagnosis. Enzymatic colorimetry was used to determine serum levels of different lipids: high-density lipoproteins (HDL), low-density lipoproteins (LDL), triglycerides, cholesterol, and very low-density lipoproteins (VLDL). Additionally, immunoturbidimetry was used to quantify serum levels of apolipoproteins A (APOA), B (APOB), E (APOE), and lipoprotein A [Lp(a)], while intraocular pressure (IOP) was measured in all patients with POAG.

RESULTS

After adjusting for age and sex, patients with POAG exhibited elevated serum levels of VLDL, APOA, and APOE but mitigated cholesterol levels compared with the control participants. Significantly lower serum triglyceride, VLDL, and Lp(a) levels were found in patients with PACG than in control participants. Serum cholesterol (P = 0.019; β = -0.75, 95% confidence interval [CI]: -1.38 - -0.12) and HDL levels (P < 0.001; β = -2.91, 95% CI: -4.58 - -1.25) were inversely linked to IOP in patients with POAG, after adjusting for age, sex, and ocular metrics. In addition, serum Lp(a) levels were correlated with the average IOP (P = 0.023; β = -0.0039, 95% CI: -0.0073 - -0.006) and night peak (P = 0.027; β = -0.0061, 95% CI: -0.0113 - -0.0008) in patients with POAG.

CONCLUSIONS

Significantly different serum lipid and lipoprotein profiles were observed in POAG and PACG patients. This study highlighted the differences in serum lipid and lipoprotein levels among Chinese POAG patients and their relationship with IOP and IOP fluctuation. Serum lipid and lipoprotein profiles should be considered while evaluating glaucoma risk.

Female-Specific Association between the Apolipoprotein E E4 Allele and Age at Diagnosis of Glaucoma in UK Biobank

OBJECTIVE

To explore the impact of the apolipoprotein E (APOE) E4 allele in the gender-specific aging process in glaucoma by illustrating the interaction between risk factors, including the APOE E4 allele, gender, and intraocular pressure (IOP), for age at diagnosis (AAD) of glaucoma.

DESIGN

A cross-sectional study included UK Biobank participants with complete data (2006-2010) for analysis. Data were analyzed in December 2023.

PARTICIPANTS

Two thousand two hundred thirty-six glaucoma patients and 103 232 controls.

METHODS

We evaluated multivariable-adjusted associations of AAD of glaucoma, APOE E4 allele (0: absence; 1: presence), and IOP using linear mixed model (LMM) analyses across groups stratified by AAD of mean age of menopause (50 years) and gender.

MAIN OUTCOMES MEASURES

Age at diagnosis of glaucoma, APOE E4 allele, and IOP.

RESULTS

Patients with glaucoma were older and had a higher percentage of males and a higher mean IOP compared to controls (all P < 0.001). Further stratifying the patients with glaucoma by AAD of 50 and gender, lower IOP (model 1 adjusted by age, βIOP = -0.096 ± 0.041, P = 0.019), and positive APOE E4 allele (model 2 adjusted by age and IOP, βe4 = 1.093 ± 0.488, P = 0.026) were associated with an older AAD in females with an AAD <50 years under univariate LMM. In multivariate LMM adjusted by age (model 3), the effect size of both factors increased in the multivariate model as the beta-value increased (βIOP = -0.111 ± 0.040, P = 0.007; βe4 = 1.235 ± 0.485, P = 0.012) (model 1 vs. model 3: P = 0.011). In females with an AAD ≥50 years, only positive APOE E4 allele (adjusted by age and IOP, βe4 = -1.121 ± 0.412, P = 0.007) was associated with a younger AAD. In males, only higher IOP was associated with an older AAD in those with an AAD ≥50 years (βIOP = 0.088 ± 0.032, P = 0.006).

CONCLUSIONS

Apolipoprotein E E4 allele may initially delay and later accelerate the development of glaucoma in females around the transition period of 50 years, which is the mean age of menopause, and importantly, this is independent of IOP. Understanding the specific transition states and modifiable factors within each age phase is crucial for developing interventions or strategies that promote healthy aging.

FINANCIAL DISCLOSURES

Proprietary or commercial disclosure may be found in the Footnotes and Disclosures at the end of this article.

APOE ε2-Carriers Are Associated with an Increased Risk of Primary Angle-Closure Glaucoma in Patients of Saudi Origin

This study investigated the association between apolipoprotein E (APOE) gene polymorphisms (rs429358 and rs7412) and primary angle-closure glaucoma (PACG) and pseudoexfoliation glaucoma (PXG) in a Saudi cohort. Genotyping of 437 DNA samples (251 controls, 92 PACG, 94 PXG) was conducted using PCR-based Sanger sequencing. The results showed no significant differences in the allele and genotype frequencies of rs429358 and rs7412 between the PACG/PXG cases and controls. Haplotype analysis revealed ε3 as predominant, followed by ε4 and ε2 alleles, with no significant variance in PACG/PXG. However, APOE genotype analysis indicated a significant association between ε2-carriers and PACG (odds ratio = 4.82, 95% CI 1.52-15.26, p = 0.007), whereas no notable association was observed with PXG. Logistic regression confirmed ε2-carriers as a significant predictor for PACG (p = 0.008), while age emerged as significant for PXG (p < 0.001). These findings suggest a potential role of ε2-carriers in PACG risk within the Saudi cohort. Further validation and larger-scale investigations are essential to elucidate the precise role of APOE in PACG pathogenesis and progression.

Exploring the role of apolipoprotein E gene promoter polymorphisms in susceptibility to normal-tension glaucoma in a Korean population

Glaucoma, particularly primary open-angle glaucoma (POAG), poses a significant global health concern. Distinguished by intraocular pressure (IOP), POAG encompasses high-tension glaucoma (HTG) and normal-tension glaucoma (NTG). Apolipoprotein E (APOE) is a multifaceted protein with roles in lipid metabolism, neurobiology, and neurodegenerative diseases. However, controversies persist regarding the impact of APOE single-nucleotide polymorphisms (SNPs) on open-angle glaucoma and NTG. This study aimed to identify APOE-specific SNPs influencing NTG risk. A cohort of 178 patients with NTG recruited from Uijeongbu St. Mary's Hospital and 32,858 individuals from the Korean Genome and Epidemiology Study (KoGES) cohort were included in the analysis. Genotype and haplotype analyses were performed on three promoter SNPs (rs449647, rs769446, and rs405509) and two exonic SNPs (rs429358 and rs7412) located on chromosome 19. Among the five SNPs, rs769446 genotypes exhibited significant differences between cases and controls. The minor allele C of rs769446 emerged as a protective factor against NTG. Furthermore, haplotype analysis of the five SNPs revealed that the A-T-G-T-T haplotype was a statistically significant risk factor for NTG. This study indicated an association between APOE promoter SNPs and NTG in the Korean population. Further studies are required to understand how APOE promoter SNPs contribute to NTG pathogenesis.

Association of Gene Polymorphisms with Normal Tension Glaucoma: A Systematic Review and Meta-Analysis

BACKGROUND

Normal tension glaucoma (NTG) is becoming a more and more serious problem, especially in Asia. But the pathological mechanisms are still not illustrated clearly. We carried out this research to uncover the gene polymorphisms with NTG.

METHODS

We searched in Web of Science, Embase, Pubmed and Cochrane databases for qualified case-control studies investigating the association between single nucleotide polymorphisms (SNPs) and NTG risk. Odds ratios (ORs) and 95% confidence intervals (CIs) for each SNP were estimated by fixed- or random-effect models. Sensitivity analysis was also performed to strengthen the reliability of the results.

RESULTS

Fifty-six studies involving 33 candidate SNPs in 14 genetic loci were verified to be eligible for our meta-analysis. Significant associations were found between 16 SNPs (rs166850 of OPA1; rs10451941 of OPA1; rs735860 of ELOVL5; rs678350 of HK2; c.603T>A/Met98Lys of OPTN; c.412G>A/Thr34Thr of OPTN; rs10759930 of TLR4; rs1927914 of TLR4; rs1927911 of TLR4; c.*70C>G of EDNRA; rs1042522/-Arg72Pro of P53; rs10483727 of SIX1-SIX6; rs33912345 of SIX1-SIX6; rs2033008 of NCK2; rs3213787 of SRBD1 and c.231G>A of EDNRA) with increased or decreased risk of NTG.

CONCLUSIONS

In this study, we confirmed 16 genetic polymorphisms in 10 genes (OPA1, ELOVL5, HK2, OPTN, TLR4, EDNRA, P53, NCK2, SRBD1 and SIX1-SIX6) were associated with NTG.

Role of APOE in glaucoma

Glaucoma is a chronic blinding eye disease caused by the progressive loss of retinal ganglion cells (RGCs). Currently, no clinically approved treatment can directly improve the survival rate of RGCs. The Apolipoprotein E (APOE) gene is closely related to the genetic risk of numerous neurodegenerative diseases and has become a hot topic in the field of neurodegenerative disease research in recent years. The optic nerve and retina are extensions of the brain's nervous system. The pathogenesis of retinal degenerative diseases is closely related to the degenerative diseases of the nerves in the brain. APOE consists of three alleles, ε4, ε3, and ε2, in a single locus. They have varying degrees of risk for glaucoma. APOE4 and the APOE gene deletion (APOE-/-) can reduce RGC loss. By contrast, APOE3 and the overall presence of APOE genes (APOE+/+) result in significant loss of RGC bodies and axons, increasing the risk of glaucoma RGCs death. Currently, there is no clear literature indicating that APOE2 is beneficial or harmful to glaucoma. This study summarises the mechanism of different APOE genes in glaucoma and speculates that APOE targeted intervention may be a promising method for protecting against RGCs loss in glaucoma.

Association of APOE Haplotypes With Common Age-Related Ocular Diseases in 412,171 Individuals

Purpose

Apolipoprotein E4 (APOE4), a known risk factor for Alzheimer's disease, has controversially been associated with reduced risk of primary open-angle glaucoma (POAG) and age-related macular degeneration (AMD). Here, we sought to systematically quantify the associations of APOE haplotypes with age-related ocular diseases and to assess their scope and age-dependency.

Methods

We included genetic and registry data from 412,171 Finnish individuals in the FinnGen study. Disease endpoints were defined using nationwide registries. APOE genotypes were directly genotyped using Illumina and Affymetrix arrays or imputed using a custom Finnish reference panel. We evaluated the disease associations of APOE genotypes containing ε2 (without ε4) and ε4 (without ε2) compared with the ε3ε3 genotype using logistic regressions stratified by age.

Results

APOE ε4 enriched haplotypes were inversely associated with overall glaucoma (odds ratio [OR] = 0.95, 95% confidence interval [CI] = 0.92-0.99, P = 0.0047), and its subtypes POAG (OR = 0.95, P = 0.027), normal-tension glaucoma (OR = 0.87, P = 0.0058), and suspected glaucoma (OR = 0.95, P = 0.014). Individuals with the ε4 allele also had lower odds for AMD (OR = 0.80, 95% CI = 0.76-0.84, P < 0.001), seen both in dry and neovascular subgroups. A slight negative association was also detected in senile cataract, but this was not reproducible in age-group analyses.

Conclusions

Our results support prior evidence of the inverse association of APOE ε4 with glaucoma, but the association was weaker than for AMD. We could not show an association with exfoliation glaucoma, supporting the hypothesis that APOE may be involved in regulating retinal ganglion cell degeneration rather than intraocular pressure.

APOE4 impairs the microglial response in Alzheimer's disease by inducing TGFβ-mediated checkpoints

The APOE4 allele is the strongest genetic risk factor for late-onset Alzheimer's disease (AD). The contribution of microglial APOE4 to AD pathogenesis is unknown, although APOE has the most enriched gene expression in neurodegenerative microglia (MGnD). Here, we show in mice and humans a negative role of microglial APOE4 in the induction of the MGnD response to neurodegeneration. Deletion of microglial APOE4 restores the MGnD phenotype associated with neuroprotection in P301S tau transgenic mice and decreases pathology in APP/PS1 mice. MGnD-astrocyte cross-talk associated with β-amyloid (Aβ) plaque encapsulation and clearance are mediated via LGALS3 signaling following microglial APOE4 deletion. In the brains of AD donors carrying the APOE4 allele, we found a sex-dependent reciprocal induction of AD risk factors associated with suppression of MGnD genes in females, including LGALS3, compared to individuals homozygous for the APOE3 allele. Mechanistically, APOE4-mediated induction of ITGB8-transforming growth factor-β (TGFβ) signaling impairs the MGnD response via upregulation of microglial homeostatic checkpoints, including Inpp5d, in mice. Deletion of Inpp5d in microglia restores MGnD-astrocyte cross-talk and facilitates plaque clearance in APP/PS1 mice. We identify the microglial APOE4-ITGB8-TGFβ pathway as a negative regulator of microglial response to AD pathology, and restoring the MGnD phenotype via blocking ITGB8-TGFβ signaling provides a promising therapeutic intervention for AD.

No Strong Association Between the Apolipoprotein E E4 Allele and Glaucoma: a Multicohort Study

Purpose

To elucidate a potential association between the apolipoprotein E (APOE) E4 allele and glaucoma prevalence in large cohorts.

Design

A cross-sectional analysis of baseline and prospectively collected cohort data.

Participants

UK Biobank (UKBB) participants of genetically determined European ancestry (n = 438 711). Replication analyses were performed using clinical and genotyping data collected from European participants recruited to the Canadian Longitudinal Study of Aging (CLSA; n = 18 199), the Australian and New Zealand Registry of Advanced Glaucoma (ANZRAG; n = 1970), and the Blue Mountains Eye Study (BMES; n = 2440).

Methods

Apolipoprotein E alleles and genotypes were determined, and their distributions were compared on the basis of glaucoma status. Similar analyses were performed using positive control outcomes associated with the APOE E4 allele (death, dementia, age-related macular degeneration) and negative control outcomes not associated with the APOE E4 allele (cataract, diabetic eye disease). Outcome phenotypes were also correlated with Alzheimer's dementia (AD), a clinical outcome highly associated with the APOE E4 allele.

Main Outcome Measures

Results of APOE E4 genotype-phenotype comparisons were reported as odds ratios (ORs) with 95% confidence intervals (CIs). Replication analyses investigated APOE E4 associations in 2 replication cohorts (CLSA and ANZRAG/BMES).

Results

The APOE E4 allele was inversely associated with glaucoma (OR, 0.96; 95% CI, 0.93-0.99; P = 0.016) and both negative controls (cataract: OR, 0.98; 95% CI, 0.96-0.99; P = 0.015; diabetic eye disease: OR, 0.92; 95% CI, 0.87-0.97; P = 0.003) in the UKBB cohort. A paradoxical positive association was observed between AD and both glaucoma (OR, 1.30; 95% CI, 1.08-1.54; P < 0.01) and cataract (OR, 1.15; 1.04-1.28; P = 0.018). No association between the APOE E4 allele and glaucoma was observed in either replication cohort (CLSA: OR, 1.03; 95% CI, 0.89-1.19; P = 0.66; ANZRAG/BMES: OR, 0.97; 95% CI, 0.84-1.12; P = 0.65).

Conclusions

A small negative association observed between APOE E4 and glaucoma within the UKBB was not evident in either replication cohort and may represent an artifact of glaucoma underdiagnosis in APOE E4 carriers.

Financial Disclosures

The author(s) have no proprietary or commercial interest in any materials discussed in this article.

Myeloid masquerade: Microglial transcriptional signatures in retinal development and disease

Microglia are dynamic guardians of neural tissue and the resident immune cells of the central nervous system (CNS). The disease-associated microglial signature (DAM), also known as the microglial neurodegenerative phenotype (MGnD), has gained significant attention in recent years as a fundamental microglial response common to various neurodegenerative disease pathologies. Interestingly, this signature shares many features in common with developmental microglia, suggesting the existence of recycled gene programs which play a role both in early neural circuit formation as well as in response to aging and disease. In addition, recent advances in single cell RNA sequencing have revealed significant heterogeneity within the original DAM signature, with contributions from both yolk sac-derived microglia as well as bone marrow-derived macrophages. In this review, we examine the role of the DAM signature in retinal development and disease, highlighting crosstalk between resident microglia and infiltrating monocytes which may critically contribute to the underlying mechanisms of age-related neurodegeneration.

Inverse Association of APOE ε4 and Glaucoma Modified by Systemic Hypertension: The Canadian Longitudinal Study on Aging

Purpose

Studies examining the apolipoprotein E (APOE) ε4 allele and glaucoma are inconsistent, which could be due to interactions with other factors. We examined the relationship between the APOE ε4 allele and glaucoma and intraocular pressure in a large, population-based random sample and explored whether the APOE ε4 allele interacted with systemic hypertension.

Methods

Data came from the Canadian Longitudinal Study on Aging, a population-based study that included 24,655 adults ages 45 to 85 years old in the European ancestry cohort. APOE genotypes were derived from single-nucleotide polymorphisms rs429358 and rs7412. Participants were asked about a prior diagnosis of glaucoma from a doctor. Corneal compensated intraocular pressure (IOP) was measured using the Reichart Ocular Response Analyzer.

Results

Having an APOE ε4 allele was associated with a lower odds of glaucoma after adjusting for age, sex, IOP, and the top 10 population structure principal components (odds ratio [OR] = 0.83; 95% confidence interval [CI], 0.69-0.98; P = 0.033). A novel statistically significant interaction was found in that having an APOE ε4 allele was only associated with glaucoma in those without systemic hypertension (OR = 0.62; 95% CI, 0.46-0.85) although it was not associated in those with it (OR = 0.97; 95% CI, 0.79-1.21) (interaction term P value = 0.017). APOE ε4 was not associated with IOP (β = -0.01; 95% CI, -0.13 to 0.10).

Conclusions

Evidence increasingly points to the APOE ε4 allele having protective benefits against glaucoma, but this association was limited to those without systemic hypertension. Further research is needed to understand the biological mechanisms for these findings and the treatment potential they hold.

Apolipoprotein E4 impairs the response of neurodegenerative retinal microglia and prevents neuronal loss in glaucoma

The apolipoprotein E4 (APOE4) allele is associated with an increased risk of Alzheimer disease and a decreased risk of glaucoma, but the underlying mechanisms remain poorly understood. Here, we found that in two mouse glaucoma models, microglia transitioned to a neurodegenerative phenotype characterized by upregulation of Apoe and Lgals3 (Galectin-3), which were also upregulated in human glaucomatous retinas. Mice with targeted deletion of Apoe in microglia or carrying the human APOE4 allele were protected from retinal ganglion cell (RGC) loss, despite elevated intraocular pressure (IOP). Similarly to Apoe-/- retinal microglia, APOE4-expressing microglia did not upregulate neurodegeneration-associated genes, including Lgals3, following IOP elevation. Genetic and pharmacologic targeting of Galectin-3 ameliorated RGC degeneration, and Galectin-3 expression was attenuated in human APOE4 glaucoma samples. These results demonstrate that impaired activation of APOE4 microglia is protective in glaucoma and that the APOE-Galectin-3 signaling can be targeted to treat this blinding disease.

The APOE E4 Allele Is Associated with Faster Rates of Neuroretinal Thinning in a Prospective Cohort Study of Suspect and Early Glaucoma

Purpose

Design

Participants

Methods

Main Outcome Measures

Results

Conclusions

Asian Race and Primary Open-Angle Glaucoma: Where Do We Stand?

Primary open-angle glaucoma (POAG) is an optic neuropathy characterized by irreversible retinal ganglion cell damage and visual field loss. The global POAG prevalence is estimated to be 3.05%, and near term is expected to significantly rise, especially within aging Asian populations. Primary angle-closure glaucoma disproportionately affects Asians, with up to four times greater prevalence of normal-tension glaucoma reported compared with high-tension glaucoma. Estimates for overall POAG prevalence in Asian populations vary, with Chinese and Indian populations representing the majority of future cases. Structural characteristics associated with glaucoma progression including the optic nerve head, retina, and cornea are distinct in Asians, serving as intermediates between African and European descent populations. Patterns in IOP suggest some similarities between races, with a significant inverse relationship between age and IOP only in Asian populations. Genetic differences have been suggested to play a role in these differences, however, a clear genetic pattern is yet to be established. POAG pathogenesis differs between Asians and other ethnicities, and it may differ within the broad classification of the Asian race. Greater awareness and further research are needed to improve treatment plans and outcomes for the increasingly high prevalence of normal tension glaucoma within aging Asian populations.

Association of APOE With Primary Open-Angle Glaucoma Suggests a Protective Effect for APOE ε4

Purpose

Prior studies have demonstrated that microglial activation is involved in the pathogenesis of primary open-angle glaucoma (POAG). Here we sought to identify genetic associations between POAG and variants in APOE and TREM2, genes associated with Alzheimer disease (AD) that critically regulate microglial neurodegeneration-associated molecular signature.

Methods

APOE genotypes were called using imputed data from the NEIGHBOR consortium (2120 POAG cases, 2262 controls) and a second cohort from the Massachusetts Eye and Ear Infirmary (MEEI; 486 cases, 344 controls). TREM2 coding variants were genotyped by means of the Illumina HumanExome BeadArray. The data set was analyzed for association with POAG overall, as well as the high-tension glaucoma (HTG) and normal-tension glaucoma (NTG) subgroups, using logistic regression adjusting for age and sex.

Results

In the combined NEIGHBOR-MEEI data set, significant association was observed for APOE ε4 in POAG overall (odds ratio [OR], 0.83; 95% confidence interval [CI], 0.74–0.94; P = 0.0022) and in both the HTG subgroup (OR, 0.81; 95% CI, 0.70–0.94; P = 0.0052) and NTG subgroup (OR, 0.71; 95% CI, 0.58–0.87; P = 0.0014). A rare TREM2 variant (A105V) was found only in HTG cases (3 of 2863 cases) and in none of the controls (P = 0.03). Three TREM2 rare variants associated with AD were not significantly associated with POAG (P > 0.05).

Conclusions

We have found that the APOE ε4 allele is associated with a reduced risk of POAG. Interestingly, the same allele is adversely associated with AD, suggesting a mechanistic difference between neurodegenerative diseases of the eye and the brain. TREM2 variants associated with AD did not significantly contribute to POAG risk.

"Association of APOE gene polymorphisms with primary open angle glaucoma in Brazilian patients"

Background: Primary open-angle glaucoma (POAG) is a multifactorial disease that affects 65.5 million people worldwide. In addition to the genetic variants already established as indicators of greater risk for POAG, the apolipoprotein (APOE) gene has been studied in some populations, with controversial results. The aim of this study is to investigate the frequency of the genetic variants of APOE in the Brazilian population, and to evaluate the association between these polymorphisms and the risk of POAG. Methods: APOE variants (rs429358; rs7412) were genotyped in 402 POAG patients and 401 controls. We evaluated the association between APOE genetic variants and the risk for POAG, as well as the correlation between the requirement of glaucoma surgery and the APOE polymorphisms. Results: Among the three APOE gene isoforms, we found a low frequency of APOE alleles ε2 (7.34%) and ε4 (11.76%), but a high frequency of ε3 (80.88%) in our population. When compared to ε3ε3 reference genotype, ε2 allele-carriers (OR = 1.516; p-value = 0.04) and ε2ε3 genotype (OR = 1.655; p-value = 0.02) were associated with a greater risk for POAG. An additive genetic model confirmed the influence of the ε2 allele in the risk of POAG in this sample of the Brazilian population (OR = 1.502; p-value = 0.04). There was no significant association between the analyzed genotypes and the requirement or number of glaucoma surgeries (p > .05). Conclusion: Brazilian individuals carrying the APOEε2 allele may be at an increased risk for the development of POAG.

Oxidative Stress and Vascular Dysfunction in the Retina: Therapeutic Strategies

Many retinal diseases, such as diabetic retinopathy, glaucoma, and age-related macular (AMD) degeneration, are associated with elevated reactive oxygen species (ROS) levels. ROS are important intracellular signaling molecules that regulate numerous physiological actions, including vascular reactivity and neuron function. However, excessive ROS formation has been linked to vascular endothelial dysfunction, neuron degeneration, and inflammation in the retina. ROS can directly modify cellular molecules and impair their function. Moreover, ROS can stimulate the production of inflammatory cytokines, such as tumor necrosis factor-alpha (TNF-α) and interleukin-6 (IL-6) causing inflammation and cell death. However, there are various compounds with direct or indirect antioxidant activity that have been used to reduce ROS accumulation in animal models and humans. In this review, we report on the physiological and pathophysiological role of ROS in the retina with a special focus on the vascular system. Moreover, we present therapeutic approaches for individual retinal diseases targeting retinal signaling pathways involving ROS.

A technique for shotgun proteomic analysis of the precorneal tear film in dogs with naturally occurring primary glaucoma

OBJECTIVE

To introduce a protocol for the characterization of protein patterns in tears of dogs with primary angle closure glaucoma (PACG) and primary open-angle glaucoma (POAG).

ANIMALS

Nineteen dogs (25 eyes).

METHODS

Tear samples were collected using a Schirmer tear strip, from dogs with PACG (PACG-affected eyes, n = 8; unaffected eyes predisposed to PACG, n = 7), POAG (n = 4), and healthy controls (n = 6). Protein precipitation and trypsin digestion were performed for analyses via liquid chromatography-tandem mass spectrometry. Proteins were identified using the SwissProt protein sequence database. Relative protein expression in 17 eyes (15 dogs) was evaluated using Proteome Discoverer 2.0. Pathway analyses were performed to investigate molecular mechanisms associated with primary glaucoma.

RESULTS

Unique peptides were identified in 505 proteins, with Major allergen Can f 1 and albumin identified with high confidence. Proteins unique to tears from diseased eyes (PACG: n = 7; POAG: n = 14) were identified. Nucleoside diphosphate was unique to tears in PACG eyes naïve to therapy, while retinal binding protein and NSFL1 cofactor p47 were unique to medicated PACG eyes. Relative expression of 34 proteins differed between disease states. Pathway analyses identified that the 'inflammatory response' was among the top disease/disorders in dogs with primary glaucoma (PACG and POAG) but not in healthy controls.

CONCLUSION

Tear samples suitable for mass spectrometry were readily obtained from pet dogs without needing specialized equipment. Further studies to validate the findings and explore potential candidate biomarkers for early disease detection and potential therapeutic targets are indicated.

Apolipoprotein E Deficiency Causes Endothelial Dysfunction in the Mouse Retina

Objective

Atherogenic lipoproteins may impair vascular reactivity consecutively causing tissue damage in multiple organs via abnormal perfusion and excessive reactive oxygen species generation. We tested the hypothesis that chronic hypercholesterolemia causes endothelial dysfunction and cell loss in the retina.

Methods

Twelve-month-old apolipoprotein E-deficient (ApoE-/-) mice and age-matched wild-type controls were used in this study (n = 8 per genotype for each experiment). Intraocular pressure, blood pressure, and ocular perfusion pressure were determined. Retinal arteriole responses were studied in vitro, and reactive oxygen and nitrogen species were quantified in the retinal and optic nerve cryosections. The expression of the lectin-like oxidized low-density lipoprotein receptor-1 (LOX-1) and the NADPH oxidase isoforms, NOX1, NOX2, and NOX4, were determined in retinal cryosections by immunofluorescence microscopy. Pro- and antioxidant redox genes were quantified in retinal explants by PCR. Moreover, cell number in the retinal ganglion cell layer and axon number in the optic nerve was calculated.

Results

Responses to the endothelium-dependent vasodilator, acetylcholine, were markedly impaired in retinal arterioles of ApoE-/- mice (P < 0.01). LOX-1 (P = 0.0007) and NOX2 (P = 0.0027) expressions as well as levels of reactive oxygen species (P = 0.0022) were increased in blood vessels but not in other retinal structures. In contrast, reactive nitrogen species were barely detectable in both mouse genotypes. Messenger RNA for HIF-1α, VEGF-A, NOX1, and NOX2, but also for various antioxidant redox genes was elevated in the retina of ApoE-/- mice. Total cell number in the retinal ganglion cell layer did not differ between ApoE-/- and wild-type mice (P = 0.2171). Also, axon number in the optic nerve did not differ between ApoE-/- and wild-type mice (P = 0.6435).

Conclusion

Apolipoprotein E deficiency induces oxidative stress and endothelial dysfunction in retinal arterioles, which may trigger hypoxia in the retinal tissue. Oxidative stress in nonvascular retinal tissue appears to be prevented by the upregulation of antioxidant redox enzymes, resulting in neuron preservation.

Latest Developments in Normal-Pressure Glaucoma: Diagnosis, Epidemiology, Genetics, Etiology, Causes and Mechanisms to Management

Normal-pressure glaucoma (NPG) is part of the spectrum of the open-angle glaucomas and morphologically characterized, as any glaucoma, by a loss of neuroretinal rim parallel to an enlargement and deepening of the optic cup, and development or enlargement of parapapillary beta zone. These morphological characteristics, in addition to the therapeutic benefit of lowering the intraocular pressure (IOP), make NPG differ from vascular-induced optic neuropathy. Based on the anatomy of the optic nerve as a cerebral fascicle, the physiological counter-pressure against the IOP is the orbital cerebrospinal fluid pressure (CSFP), with both pressures forming the trans-lamina cribrosa pressure difference (TLCPD). In contrast to the IOP, the TLCPD is the true pressure exerting force on the optic nerve fibers when passing through the lamina cribrosa. As a theoretical notion, an abnormally high TLCPD due to a low CSFP, in association with a low arterial blood pressure, could therefore be involved in the pathogenesis of NPG. It fits with the finding that the reduction of the IOP (and thus indirectly of the TLCPD) is (the only proven) procedure for NPG therapy. This review additionally highlights the genetic background, diagnostic methods, and therapeutic modalities of NPG.

Prevalence of Normal-Tension Glaucoma in the Chinese Population: A Systematic Review and Meta-Analysis

PURPOSE

To investigate the prevalence of normal-tension glaucoma (NTG) in the Chinese population through systematic review and meta-analysis.

DESIGN

Systematic review and meta-analysis.

METHODS

All Chinese population-based studies that reported the prevalence of NTG were identified. We searched PubMed and Chinese databases including Wanfang, China National Knowledge Infrastructure, and VIP for studies published before December 31, 2017. Random effects meta-analysis was conducted to estimate the pooled prevalence of NTG.

RESULTS

Twelve studies were included in this review and meta-analysis, including 9 population-based studies and 3 studies from glaucoma clinics and managed care networks. The 9 population-based studies included a total of 30,892 subjects with 498 patients with primary open-angle glaucoma (POAG) and 354 patients with NTG. The prevalence of estimated NTG ranged from 0.36% to 1.98% and the percentage of NTG among POAG ranged from 51.43% to 83.58%. In the glaucoma clinic and managed care network studies, NTG prevalence was much lower. The overall pooled proportion of NTG among POAG in the Chinese population was 70.0% (95% confidence interval [CI] 62.0-77.0%). The overall pooled prevalence of POAG and NTG was 2.0% (95% CI 1.0-2.0%) and 1.0% (95% CI 1.0-1.0%), respectively. For the meta-regression of the NTG/POAG proportion, we found that age, gender, intraocular pressure, and China versus not China were not significantly associated with NTG/POAG prevalence, although the proportional prevalence decreased with increasing age category.

CONCLUSIONS

In this systematic review, we found that NTG is common among patients with POAG in the Chinese population. Our findings can help guide future glaucoma studies and public health guidelines in the Chinese population.

An Updated Review on the Genetics of Primary Open Angle Glaucoma

Epidemiological studies suggest that by 2020 the prevalence of primary open angle glaucoma (POAG) is estimated to increase to 76.0 million, and to 111.8 million by 2040 globally due to the population aging. The prevalence of POAG is the highest among those of African descent, followed by Asians, and the lowest in Europeans. POAG is a genetically complex trait with a substantial fraction exhibiting a significant heritability. Less than 10% of POAG cases in the general population are caused by specific gene mutations and the remaining cases are polygenic. Quantitative traits related to POAG pathogenesis such as intra-ocular pressure (IOP), vertical cup/disc ratio (VCDR), optic disc area, and central corneal thickness (CCT) are highly heritable, and likely to be influenced at least in part by genes and show substantial variation in human populations. Recent genome-wide association studies (GWAS) have identified several single nucleotide polymorphisms (SNPs) at different loci including CAV1/CAV2, TMCO1, CDKN2B-AS1, CDC7-TGFBR3, SIX1/SIX6, GAS7 and ATOH7 to be associated with POAG and its related quantitative traits (endophenotypes). The chapter provides a brief overview on the different GWAS and SNP association studies and their correlation with various clinical parameters important for POAG in the population worldwide, including the Middle East.

Neuroprotective effect against axonal damage-induced retinal ganglion cell death in apolipoprotein E-deficient mice through the suppression of kainate receptor signaling

Apolipoprotein E (ApoE) plays important roles in the body, including a carrier of cholesterols, an anti-oxidant, and a ligand for the low-density lipoprotein receptors. In the nervous system, the presence of ApoE4 isoforms is associated with Alzheimer's disease. ApoE gene polymorphisms are also associated with glaucoma, but the function of ApoE in the retina remains unclear. In this study, we investigated the role of ApoE in axonal damage-induced RGC death. ApoE was detected in the astrocytes and Müller cells in the wild-type (WT) retina. RGC damage was induced in adult ApoE-deficient mice (male, 10-12 weeks old) through ocular hypertension (OH), optic nerve crush (NC), or by administering kainic acid (KA) intravitreally. The WT mice were treated with a glutamate receptor antagonist (MK801 or CNQX) 30 min before performing NC or left untreated. Seven days later, the retinas were flat mounted and Fluorogold-labeled RGCs were counted. We found that the RGCs in the ApoE-deficient mice were resistant to OH-induced RGC death and optic nerve degeneration 4 weeks after induction. In WT mice, NC effectively induced RGC death (control: 4085±331 cells/mm(2), NC: 1728±170 cells/mm(2)). CNQX, an inhibitor of KA receptors, suppressed this RGC death (3031±246 cells/mm(2)), but MK801, an inhibitor of NMDA receptors, did not (1769±212 cells/mm(2)). This indicated the involvement of KA receptor signaling in NC-induced RGC death. We found that NC- or KA-induced RGC death was significantly less in the ApoE-deficient mice than in the WT mice. These data suggest that the ApoE deficiency had a neuroprotective effect against axonal damage-induced RGC death by suppressing the KA receptor signaling.

Genome-wide association studies: applications and insights gained in Ophthalmology

Genome-wide association studies (GWAS) use high-throughput genotyping technologies to genotype thousands of single-nucleotide polymorphisms (SNPs) and relate them to the development of clinical and quantitative traits. Their use has been highly successful in the field of ophthalmology, and since the advent of GWAS in 2005, many genes not previously suspected of having a role in disease have been identified and the findings replicated. We conducted an extensive literature review and describe the concept, design, advantages, and limitations of GWAS and provide a detailed description of the applications and discoveries of GWAS in the field of eye disease to date. There have been many novel findings revealing previously unknown biological insights in a diverse range of common ocular conditions. GWAS have been a highly successful modality for investigating the pathogenesis of a wide variety of ophthalmic conditions. The insights gained into the pathogenesis of disease provide not only a better understanding of underlying disease mechanism but also offer a rationale for targeted treatment and preventative strategies. Expansive international collaboration and standardised phenotyping will permit the continued success of this investigative technique.

Apolipoprotein E gene ε4ε4 is associated with elevated risk of primary open angle glaucoma in Asians: a meta-analysis

Background

Epidemiological studies have evaluated the association between Apolipoprotein E (APOE) gene ε2/ε3/ε4 polymorphism and glaucoma susceptibility. However, the published data are still inconclusive. The aim of the present study is to evaluate the impact of APOE gene ε2/ε3/ε4 polymorphism on glaucoma risk by using meta-analysis.

Methods

A comprehensive literature search of PubMed, EMBASE, Cochrane, Elsevier Science Direct and CNKI databases was conducted to identify relevant articles, with the last report up to January 5, 2014. Pooled odds ratio (OR) and 95% confidence interval (CI) were used to assess the strength of association by using the fixed or random effect model.

Results

Fifteen separate studies including 2,700 cases and 2,365 controls were included in the meta-analysis. We did not detect a significant association between APOE gene ε2/ε3/ε4 polymorphism and glaucoma in overall population (P > 0.0083). In Asians, we detected an association of the ε4ε4 genotype with elevated risk for glaucoma (OR = 5.22, 95% CI = 1.85-14.68, P = 0.002), mainly for primary open angle glaucoma (OR = 4.98, 95% CI = 1.75-14.20, P = 0.003).

Conclusions

The meta-analysis suggests that APOE gene ε4ε4 may be associated with elevated risk for primary open angle glaucoma in Asians. However, more epidemiologic studies based on larger sample size, case–control design and stratified by ethnicity as well as types of glaucoma are suggested to further clarify the relationship between APOE gene ε2/ε3/ε4 polymorphism and genetic predisposition to glaucoma.

Role of the APOE ε2/ε3/ε4 polymorphism in the development of primary open-angle glaucoma: evidence from a comprehensive meta-analysis

Primary open-angle glaucoma (POAG) is one of the leading causes of blindness worldwide. The association between the APOE ε2/ε3/ε4 polymorphism and the risk of POAG has been widely reported, but the results of previous studies remain controversial. To comprehensively evaluate the APOE ɛ2/ɛ3/ε4 polymorphism on the genetic risk for POAG, we performed a systematic review and meta-analysis of previously published studies. The PubMed and Web of Science databases were systematically searched to identify relevant studies. Data were extracted from these studies and odds ratios with corresponding 95% confidence intervals were computed to estimate the strength of the association. Stratified analyses according to ethnicity and sensitivity analyses were also conducted for further confirmation. A total of nine studies were eligible for the meta-analysis, and these studies included data on 1928 POAG cases and 1793 unrelated match controls. The combined results showed that there were no associations between the APOE ε2/ε3/ε4 polymorphism and POAG risk in any of the 10 comparison models. The analysis that was stratified by ethnicity subgroups also failed to reveal a significant association. The sensitivity analysis confirmed the stability and reliability of the findings. There was no risk of publication bias. Our meta-analysis provides strong evidence that the APOE ε2/ε3/ε4 polymorphism is not associated with POAG susceptibility in any populations.

Neurodegenerative Genes Polymorphisms of the -491A/T APOE, the -877T/C APP and the Risk of Primary Open-angle Glaucoma in the Polish Population

BACKGROUND

Glaucoma is characterized by optic neuropathy of the retinal ganglion cell. It may be possible that β-amyloid (Aβ) and apolipoprotein E (APOE), the main proteins of the pathogenesis of AD, play a role in glaucoma development. The aim of this study was to evaluate a relationship between the APP and APOE gene polymorphisms and the risk of primary open-angle glaucoma (POAG) occurrence.

MATERIALS AND METHODS

The study consisted of 183 patients with POAG and 209 healthy subjects. Genomic DNA was extracted from peripheral blood. Analysis of the gene polymorphisms was performed using PCR-RFLP.

RESULTS

We found a statistically significant increase of the -491 T allele frequency (p=0.02; OR=1.48; 95% CI=1.06-2.08) of APOE in POAG compared to healthy controls. There were no differences in the genotype and allele distributions and odds ratios of the APP polymorphism between patients and controls group. We also found an association between APOE polymorphic variant and retinal nerve fiber layer (RNFL). There was a statistically significant difference in the APOE gene A/T genotype frequency in the early POAG stage and middle-advanced POAG stage in comparison to the advanced POAG stage (p=0.04; OR=3.38; 95% CI=1.04-10.97).

CONCLUSIONS

The -491 T allele of APOE polymorphism may be associated with a risk of POAG occurrence in the Polish population.

Lack of association of apolipoprotein E (Apo E) ε2/ε3/ε4 polymorphisms with primary open-angle glaucoma: a meta-analysis from 1916 cases and 1756 controls

Background

A number of case-control studies were conducted to investigate the association of apolipoprotein E (Apo E) polymorphisms with primary open angle glaucoma (POAG). But the results remain controversial. This meta-analysis aims to comprehensively evaluate the relationship between a common ε2/ε3/ε4 polymorphism in Apo E gene on the risk of POAG.

Method

A comprehensive literature search for studies published up to April 2013 was performed. Summary odds ratios (ORs) and 95% confidence intervals (CI) were calculated employing random-effects models irrespective of between-study heterogeneity. Publication bias of literatures was evaluated using funnel plots and Egger's test.

Results

A total of 12 studies including 1916 cases and 1756 controls meeting the predefined criteria were involved in this meta-analysis. Overall, the Apo E ε2 allele and ε4 allele were not associated with POAG, compared with those carrying ε3 allele, with ORs of 0.98 (95% CI, 0.79 to 1.23; P = 0.872) and 1.05 (95% CI, 0.78 to 1.41; P = 0.743), respectively. Genotypic analysis also found no significant association between the ε4 carriers (ε3/ε4+ε4/ε4), ε2 carriers (ε2/ε3+ε2/ε2) and POAG, compared with participants with Apo E ε3/3, with ORs of 0.91 (95% CI, 0.66 to 1.25; P = 0.543) and 1.08 (95% CI, 0.74 to 1.57; P = 0.694), respectively. In the subgroup analysis by ethnicity, source of controls, genotyping methods, Hardy-Weinberg equilibrium or not, or type of the POAG, still no obvious associations were found.

Conclusions

This meta-analysis suggests that Apo E ε2/ε3/ε4 polymorphisms may not be associated with the risk of POAG. However, well-designed studies with larger sample size and more ethnic groups are required to further validate the results.

Common variants on chromosome 9p21 are associated with normal tension glaucoma

Although intraocular pressure (IOP) is the most definitive cause of glaucoma, a subtype of open angle glaucoma (OAG) termed normal tension glaucoma (NTG), which occurs in spite of normal IOP, accounts for a large part of glaucoma cases, especially in Japan. To find common genetic variants contributing to NTG in Japanese patients, we conducted a genome-wide association study (GWAS). We performed the first screening for 531,009 autosomal SNPs with a discovery cohort of 286 cases and 557 controls, and then a second screening for the top 30 suggestive loci in an independent cohort of 183 cases and 514 controls. Our findings identified a significantly associated SNP; rs523096 [combined p-value = 7.40× 10⁻⁸, odds ratio (OR)  = 2.00 with 95% confidence interval (CI) 1.55–2.58] located 10 kbp upstream of CDKN2B on chromosome 9p21. Moreover, analysis of another independent case-control set successfully replicated the results of the screening studies (combined values of all 3 stages p = 4.96 × 10⁻¹¹, OR  = 2.13 with 95% CI 1.69–2.68). The SNPs near rs523096 were recently reported to be associated with OAG associated with elevated IOP in primary open-angle glaucoma (POAG), the predominant subtype of glaucoma in Caucasian populations. Our results revealed that the 9p21 locus is also associated with NTG in Japanese. In addition, we identified SNPs more strongly associated with NTG.

Glaucoma and Alzheimer’s disease in the elderly

Primary open angle glaucoma and Alzheimer’s disease have long been established as two separate pathological entities, primarily affecting the elderly. The progressive, irreversible course of both diseases has significant implications on an aging population. As the complex pathophysiology of the two diseases has progressively unraveled over the past two decades, common pathophysiological changes have also been elucidated. Some of these mechanisms have established a strong grounding, whilst others remain principally speculative. The mutual neuropathological changes in primary open angle glaucoma and Alzheimer’s disease have facilitated the development of neuroprotective strategies. While most of these strategies are still in the preclinical phase, they have shown great promise in experimental animal studies. Further understanding of the common pathophysiology of primary open angle glaucoma and Alzheimer’s disease and their timeline may have great implications on early diagnosis and effective therapeutic targeting.

Alzheimer's disease and primary open-angle glaucoma: is there a connection?

AIM

To present, through a thorough literature research, current and older scientific efforts to investigate the putative association between Alzheimer's disease (AD) and glaucoma, especially primary open-angle glaucoma (POAG).

METHODS

We included in our review article epidemiological, experimental and clinical laboratory studies.

RESULTS

While many authors support the existence of a strong correlation between the AD and POAG, based on epidemiological, genetic and immunohistochemical data, others present contradictory results, leaving the issue unresolved.

CONCLUSION

Further research, probably targeted towards genetic parameters and based on large, multicenter studies has yet to be conducted. It is the authors' opinion however, that the existing data already justify the need for at least some degree of elevated clinical alertness for the occurrence of AD in patients with glaucoma and of glaucoma in patients with AD.

Glaucoma: genes, phenotypes, and new directions for therapy

Glaucoma, a leading cause of blindness worldwide, is characterized by progressive optic nerve damage, usually associated with intraocular pressure. Although the clinical progression of the disease is well defined, the molecular events responsible for glaucoma are currently poorly understood and current therapeutic strategies are not curative. This review summarizes the human genetics and genomic approaches that have shed light on the complex inheritance of glaucoma genes and the potential for gene-based and cellular therapies that this research makes possible.

Investigation of the association between the GLC3A locus and normal tension glaucoma in Japanese patients by microsatellite analysis

Purpose:

To investigate whether the GLC3A locus harboring the CYP1B1 gene is associated with normal tension glaucoma (NTG) in Japanese patients.

Materials and Methods:

One hundred forty-two Japanese patients with NTG and 101 Japanese healthy controls were recruited. Patients exhibiting a comparatively early onset were selected as this suggests that genetic factors may show stronger involvement. Genotyping and assessment of allelic diversity was performed on 13 highly polymorphic microsatellite markers in and around the GLC3A locus.

Results:

There were decreased frequencies of the 444 allele of D2S0416i and the 258 allele of D2S0425i in cases compared to controls (P = 0.022 and P = 0.034, respectively). However, this statistical significance disappeared when corrected (Pc > 0.05). We did not find any significant association between the remaining 11 microsatellite markers, including D2S177, which may be associated with CYP1B1, and NTG (P > 0.05).

Conclusions:

Our study showed no association between the GLCA3 locus and NTG, suggesting that the CYP1B1 gene, which is reportedly involved in a range of glaucoma phenotypes, may not be an associated factor in the pathogenesis of NTG.

The genetics of primary open-angle glaucoma: a review

Glaucoma is the major cause of irreversible blindness worldwide. Primary open-angle glaucoma (POAG), as the most prevalent form of glaucoma, is a complex inherited disorder and affects more than 2 million individuals in the United States. It has become increasingly clear that a host of genetic as well as environmental factors are likely to contribute to the phenotype. A number of chromosomal and genetic associations have been reported for POAG. This review examines what is currently known about the underlying genetic structure, what remains to be learned, and how this may affect our medical management of this major blinding disease.

Glaucoma of the brain: a disease model for the study of transsynaptic neural degeneration

The identification of mechanisms precipitating neuronal death and injury is an intense area of investigation requiring reliable models to assess the effects of neuroprotective agents. Most are suboptimal since the effects of initial damage are diffuse and may not be reproducible or easily quantifiable. The ideal laboratory model should have the ability to (a) clearly detect evidence of neuronal injury and recovery, (b) accurately measure morphologically the extent of these changes, and (c) provide functional evidence for damage and recovery. Glaucoma is a disease of visual neurons in the eye and brain. In the visual system, neuroanatomical pathways and retinotopic organization are exquisitely defined, functional modalities are highly characterized and can be dissected physiologically, visual input parameters can be modified, visual functional output can be readily tested and measured, changes in the eye and the visual brain can be directly visualized and imaged, and pathological and compensatory changes in brain centers of vision can be examined and measured specifically. For these reasons, the glaucoma disease model is ideal for the study of response and recovery to injury in the central nervous system due to anterograde and retrograde degeneration from the eye to the brain and the brain to the eye, respectively. The study of this glaucoma model of transsynaptic brain injury may be relevant to understanding more complex pathways and point to new strategies to prevent disease progression in other neurodegenerative diseases.