Promoter polymorphism of the erythropoietin gene in severe diabetic eye and kidney complications

Novel Genetic Actors of Diabetes-Associated Microvascular Complications: Retinopathy, Kidney Disease and Neuropathy

Both type 1 and type 2 diabetes mellitus can lead to the common microvascular complications of diabetic retinopathy, kidney disease, and neuropathy. Diabetic patients do not universally develop these complications. Long duration of diabetes and poor glycemic control explain a lot of the variability in the development of microvascular complications, but not all. Genetic factors account for some of the remaining variability because of the heritability and familial clustering of these complications. There have been a large number of investigations, including linkage studies, candidate gene studies, and genome-wide association studies, all of which have sought to identify the specific variants that increase susceptibility. For retinopathy, several genome-wide association studies have been performed in small or midsize samples, but no reproducible loci across the studies have been identified. For diabetic kidney disease, genome-wide association studies in larger samples have been performed, and loci for this complication are beginning to emerge. However, validation of the existing discoveries, and further novel discoveries in larger samples is ongoing. The amount of genetic research into diabetic neuropathy has been very limited, and much is dedicated to the understanding of genetic risk factors only. Collaborations that pool samples and aim to detect phenotype classifications more precisely are promising avenues for a better explanation of the genetics of diabetic microvascular complications.

Regulatory SNPs Alter the Gene Expression of Diabetic Retinopathy Associated Secretary Factors

OBJECTIVES

Diabetic retinopathy (DR) is a common microvascular complication in both type I and type II diabetes. Several previous reports indicated the serum centration of some secretary factors were highly associated with DR. Therefore, we hypothesis regulatory SNPs (rSNPs) genotype in secretary factors may alter these gene expression and lead to DR.

METHODS

At first, pyrosequencing were applying to screen the SNPs which present allele frequency different in DR and DNR. Then individual genotyping was processed by Taqman assays in Taiwanese DR and DNR patients. To evaluate the effect of SNP allele on transcriptional activity, we measured promoter activity using luciferase reporter constructs.

RESULTS

We found the frequencies of the CC, CG, and GG genotype of the rs2010963 polymorphism were 15.09%, 47.14%, and 37.74% in DR and 12.90%, 19.35%, and 67.74% in DNR, respectively (p = 0.0205). The prevalence of DR was higher (p = 0.00793) in patients with the CC or CG genotype (62.26% and 32.26% for DR and DNR, respectively) compared with the patients with the GG genotype. To evaluate the effect of rs2010963-C allele on transcriptional activity, we measured promoter activity using luciferase reporter constructs. The rs2010963-C reporter showed 1.6 to 2-fold higher luciferase activity than rs2010963-G in 3 cell lines.

CONCLUSION

Our data proposed rs2010963-C altered the expression level of VEGFA in different tissues. We suggested small increase but long term exposure to VEGFA may lead to DR finally.

Diabetic Retinopathy and Diabetic Macular Edema

Diabetic retinopathy and diabetic macular edema result from chronic damage to the neurovascular structures of the retina. The pathophysiology of retinal damage remains uncertain but includes metabolic and neuroinflammatory insults. These mechanisms are addressed by intensive metabolic control of the systemic disease and by the use of ocular anti-inflammatory agents, including vascular endothelial growth factor inhibitors and corticosteroids. Improved understanding of the ocular and systemic mechanisms that underlie diabetic retinopathy will lead to improved means to diagnose and treat retinopathy and better maintain vision.

Association of chemokine ligand 5/chemokine receptor 5 gene promoter polymorphisms with diabetic microvascular complications: A meta-analysis

Aims/Introduction

Chemokine ligand 5 (CCL5) is a member of the CC‐chemokine family expressed in various organs. It contributes to the migration of monocytes/macrophages into injured vascular walls by binding with its receptor chemokine receptor 5 (CCR5). Many studies have accessed the association between CCL5/CCR5 gene promoter polymorphisms and diabetic microvascular complications (DMI). However, the results are conflicting and inconclusive. The aim of the present study was to evaluate the association more precisely.

Materials and Methods

Trials were retrieved through PubMed, Embase, Medline, China National Knowledge Infrastructure, Web of Science and Cochrane database without restrictions on language. The pooled odds ratio (OR) and 95% confidence interval (CI) were used to describe the strength of association with DMI.

Results

Data were obtained from 11 case–control studies that included 2,737 DMI patients and 2,435 diabetic control subjects. In the overall analysis, the CCL5‐403 G/A and CCL5‐28 C/G gene polymorphisms were not significantly associated with the risk of DMI. However, CCR5‐59029 G/A was an independent risk factor of DMI in a dominant model (OR 1.77, 95% CI 1.06–2.97). Subgroup analysis showed that the risk of the CCR5 59029A‐positive genotype was significant in Asians (OR 2.08, 95% CI 1.68–2.57). In addition, the CCR5 59029A‐positive genotype was associated with increased risk of albuminuria.

Conclusions

There were no associations of CCL5 gene promoter polymorphism with the risk of DMI. However, the 59029A polymorphism in CCR5 might affect individual susceptibility for DMI.

Diabetic Macular Edema: Pathophysiology and Novel Therapeutic Targets

Diabetic macular edema (DME) is the major cause of vision loss in diabetic persons. Alteration of the blood-retinal barrier is the hallmark of this disease, characterized by pericyte loss and endothelial cell-cell junction breakdown. Recent animal and clinical studies strongly indicate that DME is an inflammatory disease. Multiple cytokines and chemokines are involved in the pathogenesis of DME, with multiple cellular involvement affecting the neurovascular unit. With the introduction of anti-vascular endothelial growth factor (VEGF) agents, the treatment of DME has been revolutionized, and the indication for laser therapy has been limited. However, the response to anti-VEGF drugs in DME is not as robust as in proliferative diabetic retinopathy, and many patients with DME do not show complete resolution of fluid despite multiple intravitreal injections. Potential novel therapies targeting molecules other than VEGF and using new drug-delivery systems currently are being developed and evaluated in clinical trials.

Genetics of diabetic nephropathy: a long road of discovery

The global prevalence of diabetic nephropathy is rising in parallel with the increasing incidence of diabetes in most countries. Unfortunately, up to 40 % of persons diagnosed with diabetes may develop kidney complications. Diabetic nephropathy is associated with substantially increased risks of cardiovascular disease and premature mortality. An inherited susceptibility to diabetic nephropathy exists, and progress is being made unravelling the genetic basis for nephropathy thanks to international research collaborations, shared biological resources and new analytical approaches. Multiple epidemiological studies have highlighted the clinical heterogeneity of nephropathy and the need for better phenotyping to help define important subgroups for analysis and increase the power of genetic studies. Collaborative genome-wide association studies for nephropathy have reported unique genes, highlighted novel biological pathways and suggested new disease mechanisms, but progress towards clinically relevant risk prediction models for diabetic nephropathy has been slow. This review summarises the current status, recent developments and ongoing challenges elucidating the genetics of diabetic nephropathy.

Anthrax lethal toxin suppresses high glucose induced VEGF over secretion through a post-translational mechanism

AIM

To prove anthrax lethal toxin (LeTx) blocks the mitogen activated protein kinases (MAPKs) activation by degrading the MAPK/ERK kinases (MEKs) to suppress vascular endothelial growth factor (VEGF) secretion.

METHODS

Human adult retinal pigmented epithelium (ARPE) cells were cultured and treated with normal glucose, high glucose or high glucose with LeTx for additional 24, 48 or 72h for viable cell count. Total RNA from the ARPE was isolated for reverse transcription polymerase chain reaction (RT-PCR). The conditioned medium of ARPE cells treated in different group for 48h was filtered and diluted to detect the concentration of VEGF by enzyme-linked immunosorbant assays. Evaluate the role of MEK/MAPK pathway in the secretion of VEGF by immunoblotting.

RESULTS

In this study, we proved high glucose induced activation of the MAPK extracellular signal-regulated kinase (ERK1/2) and p38 in the ARPE cell line was blocked by anthrax LeTx. LeTx also inhibited high glucose induced ARPE cell over proliferation.

CONCLUSION

LeTx suppressed high glucose induced VEGF over secretion in the ARPE cells, mainly through a post-translational mechanism.

Genetic Studies on Diabetic Microvascular Complications: Focusing on Genome-Wide Association Studies

Diabetes is a common metabolic disorder with a worldwide prevalence of 8.3% and is the leading cause of visual loss, end-stage renal disease and amputation. Recently, genome-wide association studies (GWASs) have identified genetic risk factors for diabetic microvascular complications of retinopathy, nephropathy, and neuropathy. We summarized the recent findings of GWASs on diabetic microvascular complications and highlighted the challenges and our opinion on future directives. Five GWASs were conducted on diabetic retinopathy, nine on nephropathy, and one on neuropathic pain. The majority of recent GWASs were underpowered and heterogeneous in terms of study design, inclusion criteria and phenotype definition. Therefore, few reached the genome-wide significance threshold and the findings were inconsistent across the studies. Recent GWASs provided novel information on genetic risk factors and the possible pathophysiology of diabetic microvascular complications. However, further collaborative efforts to standardize phenotype definition and increase sample size are necessary for successful genetic studies on diabetic microvascular complications.

Genetic disposition and modifiable factors independently associated with anemia in patients with type 2 diabetes mellitus

AIMS

Anemia is prevalent but under-recognized in patients with diabetes mellitus (DM). Genetic variants in angiotensin-converting enzyme (ACE), tumor necrosis factor-alpha (TNF-α) and erythropoietin (EPO) have been associated with diabetic nephropathy. In the present study, we investigated the associations between anemia and polymorphisms in EPO promoter (rs1617640), TNF-α G-308A and ACE Insertion/Deletion in Chinese patients with type 2 diabetes.

METHODS

Polymorphisms in ACE, TNF-α and EPO were genotyped in 1142 patients. Anemia was defined as hemoglobin (Hb) levels below 12 g/dL for women and 13 g/dL for men.

RESULTS

286 (25%) patients had anemia. Patients with anemia were older, had longer duration of diabetes, worse renal function and more albuminuria. ACE Insertion/Deletion and TNF-a G-308A were not associated with anemia. The frequencies of EPO polymorphism (rs1617640) were significantly different between anemic and nonanemic patients. Patients with TT genotype had higher prevalence of anemia than those with TG and GG. Regression analysis identified EPO SNP, duration of DM, serum albumin, albuminuria and renal function independently associated with anemia. After adjusting for multiple variables, TT and TG genotypes were associated with 3-5-fold increased risk for anemia compared to GG.

CONCLUSIONS

The EPO genotype in Chinese patients with type 2 diabetes is associated with anemia and may help to identify those at risk. Further evaluation of its effect on clinical outcomes in prospective studies may be useful to predict the outcomes of erythropoiesis stimulating therapy, and to individualize anemia management.

The genetics of diabetic complications

The rising global prevalence of diabetes mellitus is accompanied by an increasing burden of morbidity and mortality that is attributable to the complications of chronic hyperglycaemia. These complications include blindness, renal failure and cardiovascular disease. Current therapeutic options for chronic hyperglycaemia reduce, but do not eradicate, the risk of these complications. Success in defining new preventative and therapeutic strategies hinges on an improved understanding of the molecular processes involved in the development of these complications. This Review explores the role of human genetics in delivering such insights, and describes progress in characterizing the sequence variants that influence individual predisposition to diabetic kidney disease, retinopathy, neuropathy and accelerated cardiovascular disease. Numerous risk variants for microvascular complications of diabetes have been reported, but very few have shown robust replication. Furthermore, only limited evidence exists of a difference in the repertoire of risk variants influencing macrovascular disease between those with and those without diabetes. Here, we outline the challenges associated with the genetic analysis of diabetic complications and highlight ongoing efforts to deliver biological insights that can drive translational benefits.

An analysis of the association between a polymorphism of KCNJ11 and diabetic retinopathy in a Chinese Han population

Background

Genome-wide association studies (GWAS) have reported that the polymorphism rs5219 of the potassium inwardly rectifying channel, subfamily J, member 11 (KCNJ11) is associated with type 2 diabetes mellitus (T2DM). Given that diabetic retinopathy (DR) is one of the most common microvascular complications of T2DM, GWAS have identified a number of potential susceptibility genes for DR. However, only a fraction of them have been replicated in different studies and show consistent genetic associations with the occurrence of DR. The aim of the present study was to investigate whether common variants of KCNJ11 confer DR in a cohort of the Chinese Han population.

Methods

A case–control study of 580 T2DM patients, including 105 T2DM with DR and 475 T2DM without DR was performed. A single nucleotide polymorphism (SNP) of KCNJ11 (rs5219) was genotyped, and its association with DR was explored using a dominant genetic model. Genotyping was performed by iPLEX technology. Univariate and multivariate logistic regression (MLR) analysis controlling for confounders was conducted to evaluate the association between rs5219 and DR.

Results

The A allele frequency of rs5219 was significantly higher in DR patients than that in the patients without DR (49.01% versus 38.68%, P <0.05). We found the minor A allele could increase the risk to develop DR (ORint = 1.58, 95% CI: 1.139 to 2.192 for allele and P = 0.006, ORint = 1.607, 95% CI: 1.267 to 2.038 for genotype and P <0.001) in the Chinese Han population.

Conclusions

Our findings provided evidence that KCNJ11 was associated with DR in Chinese Han patients with T2DM.

Diabetic retinopathy: variations in patient therapeutic outcomes and pharmacogenomics

Diabetes and its microvascular complications in patients poses a significant challenge and constitutes a major health problem. When it comes to manifestations in the eye, each case of diabetic retinopathy (DR) is unique, in terms of the phenotype, genotype, and, more importantly, the therapeutic response. It is therefore important to identify factors that distinguish one patient from another. Personalized therapy in DR is a new trend aimed at achieving maximum therapeutic response in patients by identifying genotypic and phenotypic factors that may result in less than optimal response to conventional therapy, and consequently, lead to poorer outcome. With advances in the identification of these genetic markers, such as gene polymorphisms and human leucocyte antigen associations, as well as development of drugs that can target their effects, the future of personalized medicine in DR is promising. In this comprehensive review, data from various studies have been analyzed to present what has been achieved in the field of pharmacogenomics thus far. An insight into future research is also provided.

The association of previously reported polymorphisms for microvascular complications in a meta-analysis of diabetic retinopathy

We investigated the association of signals from previous GWAS and candidate gene meta-analyses for diabetic retinopathy (DR) or nephropathy (DN), as well as an EPO variant in meta-analyses of severe (SDR) and mild diabetic retinopathy (MDR). Meta-analyses of SDR (≥severe non-proliferative diabetic retinopathy (NPDR) or history of panretinal photocoagulation) and MDR (≥mild NPDR), defined based on seven-field stereoscopic fundus photographs, were performed in two well-characterized type 1 diabetes (T1D) cohorts: the Diabetes Control and Complications Trial/Epidemiology of Diabetes Interventions and Complications (DCCT/EDIC, n = 1,304) and Wisconsin Epidemiologic Study of Diabetic Retinopathy (WESDR, n = 603). Among 34 previous signals for DR, after controlling for multiple testing, no association was replicated in our meta-analyses. rs1571942 and rs12219125 at PLXDC2 locus showed nominally significant (<0.05) association with SDR in the same direction as previous report, as did rs1801282 in PPARG gene with MDR. Among 55 loci previously associated with DN, three showed suggestive associations with SDR in our study without maintaining significance after correction for multiple testing. Of particular interest, rs1617640 (EPO) was not significantly associated with DR status, combined SDR–DN phenotype, time to SDR or time to DN (all P > 0.05). Lack of replication of previous DR hits and EPO despite reasonable statistical power implies that many of these may be false positives. Consistent with pleiotropy, we provide suggestive collective evidence for association between DR and variants previously associated with DN without reaching statistical significance at any single locus.

Meta-analysis of diabetic nephropathy associated genetic variants in inflammation and angiogenesis involved in different biochemical pathways

Background

Diabetes mellitus is the most common chronic endocrine disorder, affecting an estimated population of 382 million people worldwide. It is associated with microvascular and macrovascular complications, including diabetic nephropathy (DN); primary cause of end-stage renal disease. Different inflammatory and angiogenic molecules in various pathways are important modulators in the pathogenesis and progression of diabetic nephropathy. Differential disease risk in DN may be partly attributable to genetic susceptibility. In this meta-analysis, we aimed to determine which of the previously investigated genetic variants in these pathways are significantly associated with the development of DN and to examine the functional role of these genes.

Methods

A systematic search was conducted to collect and analyze all studies published till June 2013; that investigated the association between genetic variants involved in inflammatory cytokines and angiogenesis and diabetic nephropathy. Genetic variants associated with DN were selected and analyzed by using Comprehensive Meta Analysis software. Pathway analysis of the genes with variants showing significant positive association with DN was performed using Genomatix Genome Analyzer (Genomatix, Munich, Germany).

Results

After the inclusion and exclusion criteria for this analysis, 34 studies were included in this meta-analysis. 11 genetic variants showed significant positive association with DN in a random-effects meta-analysis. These included genetic variants within or near VEGFA, CCR5, CCL2, IL-1, MMP9, EPO, IL-8, ADIPOQ and IL-10. rs1800871 (T) genetic variant in IL-10 showed protective effect for DN. Most of these eleven genetic variants were involved in GPCR signaling and receptor binding pathways whereas four were involved in chronic kidney failure. rs833061 [OR 2.08 (95% CI 1.63-2.66)] in the VEGFA gene and rs3917887 [OR 2.04 (95% CI 1.64-2.54)] in the CCL2 gene showed the most significant association with the risk of diabetic nephropathy.

Conclusions

Our results indicate that 11 genetic variants within or near VEGFA, CCR5, CCL2, IL-1, MMP9, EPO, IL-8, ADIPOQ and IL-10 showed significant positive association with diabetic nephropathy. Gene Ontology or pathway analysis showed that these genes may contribute to the pathophysiology of DN. The functional relevance of the variants and their pathways can lead to increased biological insights and development of new therapeutic targets.

Electronic supplementary material

The online version of this article (doi:10.1186/s12881-014-0103-8) contains supplementary material, which is available to authorized users.

Functional genomic annotation of genetic risk loci highlights inflammation and epithelial biology networks in CKD

Genome-wide association studies (GWASs) have identified multiple loci associated with the risk of CKD. Almost all risk variants are localized to the noncoding region of the genome; therefore, the role of these variants in CKD development is largely unknown. We hypothesized that polymorphisms alter transcription factor binding, thereby influencing the expression of nearby genes. Here, we examined the regulation of transcripts in the vicinity of CKD-associated polymorphisms in control and diseased human kidney samples and used systems biology approaches to identify potentially causal genes for prioritization. We interrogated the expression and regulation of 226 transcripts in the vicinity of 44 single nucleotide polymorphisms using RNA sequencing and gene expression arrays from 95 microdissected control and diseased tubule samples and 51 glomerular samples. Gene expression analysis from 41 tubule samples served for external validation. 92 transcripts in the tubule compartment and 34 transcripts in glomeruli showed statistically significant correlation with eGFR. Many novel genes, including ACSM2A/2B, FAM47E, and PLXDC1, were identified. We observed that the expression of multiple genes in the vicinity of any single CKD risk allele correlated with renal function, potentially indicating that genetic variants influence multiple transcripts. Network analysis of GFR-correlating transcripts highlighted two major clusters; a positive correlation with epithelial and vascular functions and an inverse correlation with inflammatory gene cluster. In summary, our functional genomics analysis highlighted novel genes and critical pathways associated with kidney function for future analysis.

Erythropoietin rs1617640 G allele associates with an attenuated rise of serum erythropoietin and a marked decline of hemoglobin in hepatitis C patients undergoing antiviral therapy

BACKGROUND

A decline in hemoglobin (Hb) concentration during antiviral therapy in chronic hepatitis C (CHC) is a serious side effect. It may compel to dose reduction or even termination of antiviral treatment. The activation of erythropoietin (EPO) synthesis as a physiological response to anemia and its relation to a genetic variation within the EPO gene has not been evaluated yet.

METHODS

Data of 348 CHC patients were reviewed retrospectively. Samples were genotyped for EPO rs1617640 and inosine triphosphatase (ITPA) rs1127354. Serum EPO concentrations were determined before and during therapy. Primary endpoints were set as Hb decline >3 g/dl at weeks 4 and 12.

RESULTS

EPO rs1617640 G homozygotes showed a significantly lower rise of serum EPO level over time than T allele carriers (p < 0.001). The cumulative frequency of a significant Hb reduction added up to 40%. Multivariate analysis revealed that besides age, ribavirin starting dose and baseline Hb also EPO rs1617640 G homozygosity associates with Hb reduction at week 4 (p = 0.025) and 12 (p = 0.029), while ITPA C homozygotes are at risk for Hb decline particularly early during treatment. Furthermore, EPO rs1617640 G homozygotes were more frequently in need for blood transfusion, epoetin-α supplementation, or ribavirin dose reduction (p < 0.001).

CONCLUSIONS

Our data suggest that EPO rs1617640 genotype, the rise of serum EPO concentration as well as ITPA rs1127354 genotype are promising parameters to evaluate the Hb decline during antiviral therapy. A rational adjustment of therapy with epoetin-α supplementation might prevent serious adverse events or the need to terminate treatment.

Genetics of diabetes complications

Chronic hyperglycemia and duration of diabetes are the major risk factors associated with development of micro- and macrovascular complications of diabetes. Although it is believed that hyperglycemia induces damage to the particular cell subtypes, e.g., mesangial cells in the renal glomerulus, capillary endothelial cells in the retina, and neurons and Schwann cells in peripheral nerves, the exact mechanisms underlying these damaging defects are not yet well understood. Clustering of micro- and macrovascular complications in families of patients with diabetes suggests a strong genetic susceptibility. However, until now only a handful number of genetic variants were reported to be associated with either nephropathy (ACE, ELMO1, FRMD3, and AKR1B1) or retinopathy (VEGF, AKR1B1, and EPO), and only a few studies were carried out for genetic susceptibility to cardiovascular diseases (ADIPOQ, GLUL) in patients with diabetes. It is, therefore, obvious that the accumulation of more data from larger studies and better phenotypically characterized cohorts is needed to facilitate genetic discoveries and unravel novel insights into the pathogenesis of diabetic complications.

Mitochondrial haplogroups are associated with severity of diabetic retinopathy

PURPOSE

To determine if specific mitochondrial haplogroups associate with nonproliferative diabetic retinopathy (NPDR) and proliferative diabetic retinopathy (PDR).

METHODS

Deidentified medical records for Caucasian patients with diabetic retinopathy (DR; 153 NPDR and 138 PDR) were obtained from BioVU, Vanderbilt University's electronic, deidentified DNA databank. An independent cohort of Caucasian patients with DR (44 NPDR and 57 PDR) from the Vanderbilt Eye Institute (VEI) was used for validation. We tested for an association between mitochondrial haplogroups and PDR among patients with DR.

RESULTS

In the BioVU cohort, PDR frequency among Caucasian DR patients differed significantly by mitochondrial haplogroup (P = 0.027). Replication in the VEI cohort confirmed this association (P = 0.0064). In the combined cohort, patients from the common haplogroup H were more likely to have PDR (odds ratio [OR] = 2.0 [95% confidence interval (CI) = 1.3-3.0], P = 0.0012), while patients from haplogroup Uk were less likely to have PDR (OR = 0.5 [95% CI = 0.3-0.8], P = 0.0049). In logistic regression analyses, the addition of diabetes duration, hemoglobin A1c (HgbA1c) levels, and hypertension had no effect on the associations of haplogroups H and Uk with PDR.

CONCLUSIONS

In this study, DR patients from mitochondrial haplogroup H were more likely to have PDR, while DR patients from haplogroup Uk were less likely to have PDR. The association was independent of the major clinical variables affecting PDR. The mitochondrial haplogroups were as strong a risk factor for PDR as were elevated HgbA1c levels.

Role of FAM18B in diabetic retinopathy

PURPOSE

Genome-wide association studies have suggested an association between a previously uncharacterized gene, FAM18B, and diabetic retinopathy. This study explores the role of FAM18B in diabetic retinopathy. An improved understanding of FAM18B could yield important insights into the pathogenesis of this sight-threatening complication of diabetes mellitus.

METHODS

Postmortem human eyes were examined with immunohistochemistry and immunofluorescence for the presence of FAM18B. Expression of FAM18B in primary human retinal microvascular endothelial cells (HRMECs) exposed to hyperglycemia, vascular endothelial growth factor (VEGF), or advanced glycation end products (AGEs) was determined with quantitative reverse-transcription PCR (qRT-PCR) and/or western blot. The role of FAM18B in regulating human retinal microvascular endothelial cell viability, migration, and endothelial tube formation was determined following RNAi-mediated knockdown of FAM18B. The presence of FAM18B was determined with qRT-PCR in CD34+/VEGFR2+ mononuclear cells isolated from a cohort of 17 diabetic subjects with and without diabetic retinopathy.

RESULTS

Immunohistochemistry and immunofluorescence demonstrated the presence of FAM18B in the human retina with prominent vascular staining. Hyperglycemia, VEGF, and AGEs downregulated the expression of FAM18B in HRMECs. RNAi-mediated knockdown of FAM18B in HRMECs contributed to enhanced migration and tube formation as well as exacerbating the hyperglycemia-induced decrease in HRMEC viability. The enhanced migration, tube formation, and decrease in the viability of HRMECs as a result of FAM18B downregulation was reversed with pyrrolidine dithiocarbamate (PDTC), a specific nuclear factor-kappa B (NF-κB) inhibitor. CD34+/VEGFR2+ mononuclear cells from subjects with proliferative diabetic retinopathy demonstrated significantly reduced mRNA expression of FAM18B compared to diabetic subjects without retinopathy.

CONCLUSIONS

FAM18B is expressed in the retina. Diabetic culture conditions decrease the expression of FAM18B in HRMECs. The downregulation of FAM18B by siRNA in HRMECs results in enhanced migration and tube formation, but also exacerbates the hyperglycemia-induced decrease in HRMEC viability. The pathogenic changes observed in HRMECs as a result of FAM18B downregulation were reversed with PDTC, a specific NF-κB inhibitor. This study is the first to demonstrate a potential role for FAM18B in the pathogenesis of diabetic retinopathy.

Genetics of diabetic retinopathy

Diabetic retinopathy (DR) is a polygenic disorder. Twin studies and familial aggregation studies have documented clear familial clustering. Heritability has been estimated to be as high as 27 % for any DR and 52 % for proliferative diabetic retinopathy (PDR), an advanced form of the disease. Linkage analyses, candidate gene association studies and genome-wide association studies (GWAS) performed to date have not identified any widely reproducible risk loci for DR. Combined analysis of the data from multiple GWAS is emerging as an important next step to explain the unaccounted heritability. Key factors to future discovery of the genetic underpinnings of DR are precise DR ascertainment, a focus on the more heritable disease forms such as PDR, stringent selection of control participants with regards to duration of diabetes, and methods that allow combination of existing datasets from different ethnicities to achieve sufficient sample sizes to detect variants with modest effect sizes.

Genetics of diabetic retinopathy

Multiple studies have shown that genetic factors may play an important role in determining an individual's risk for the development of diabetic retinopathy (DR) and progression to proliferative DR. However, consistent and definitive genetic associations with DR across broad populations have been not been established. Numerous genes have been studied for their association with DR and the results of these investigations have most specifically pointed to three specific genes that are likely involved in DR development and progression. The gene coding for vascular endothelial growth factor, aldose reductase, and the receptor for advanced glycation end products have been extensively evaluated, and specific polymorphisms of these genes have been suggested to potentially increase the risk of DR development. In this paper, we have reviewed the published literature on the genetics of DR and the potential implications for DR development and progression.

Berberine attenuates high glucose-induced proliferation and extracellular matrix accumulation in mesangial cells: involvement of suppression of cell cycle progression and NF-κB/AP-1 pathways

Berberine has been shown to have renoprotective effects on diabetes through attenuating TGF-β1 and fibronectin (FN) expression. However, how berberine regulates TGF-β1 and FN is not fully clear. Here we investigated whether berberine inhibited TGF-β1 and FN expression in high glucose-cultured mesangial cells. Berberine significantly inhibited mesangial cell proliferation and hypertrophy by increasing the cell population in G1-phase and reducing that in S-phase. In addition, berberine reversed high glucose-induced down-regulation of cyclin-dependent kinase inhibitor p21(Waf1)/(Cip1) and p27(Kip1). Berberine inhibited p65 translocation to the nucleus and c-jun phosphorylation induced by high glucose. Furthermore, berberine attenuated high glucose-induced expression of TGF-β1 and FN. Using a luciferase reporter assay, we found that high glucose-induced transcription activity of NF-κB and AP-1 was blocked by berberine. Electrophoretic mobility shift assay showed that high glucose increased that NF-κB and AP-1 DNA binding activity. These data indicate that berberine inhibited mesangial cell proliferation and hypertrophy by modulating cell cycle progress. In addition, berberine suppressed high glucose-induced TGF-β1 and FN expression by blocking NF-κB/AP-1 pathways.

Disturbance of inorganic phosphate metabolism in diabetes mellitus: its relevance to the pathogenesis of diabetic retinopathy

Early in the progression of diabetes, a paradoxical metabolic imbalance in inorganic phosphate (Pi) occurs that may lead to reduced high energy phosphate and tissue hypoxia. These changes take place in the cells and tissues in which the entry of glucose is not controlled by insulin, particularly in poorly regulated diabetes patients in whom long-term vascular complications are more likely. Various conditions are involved in this disturbance in Pi. First, the homeostatic function of the kidneys is suboptimal in diabetes, because elevated blood glucose concentrations depolarize the brush border membrane for Pi reabsorption and lead to lack of intracellular phosphate and hyperphosphaturia. Second, during hyperglycemic-hyperinsulinemic intervals, high amounts of glucose enter muscle and fat tissues, which are insulin sensitive. Intracellular glucose is metabolized by phosphorylation, which leads to a reduction in plasma Pi, and subsequent deleterious effects on glucose metabolism in insulin insensitive tissues. Hypophosphatemia is closely related to a decrease in adenosine triphosphate (ATP) in the aging process and in uremia. Any interruption of optimal ATP production might lead to cell injury and possible cell death, and evidence will be provided herein that such cell death does occur in diabetic retinopathy. Based on this information, the mechanism of capillary microaneurysms formation in diabetic retinopathy and the pathogenesis of diabetic retinopathy must be reevaluated.

VEGFA activates erythropoietin receptor and enhances VEGFR2-mediated pathological angiogenesis

Clinical and animal studies implicate erythropoietin (EPO) and EPO receptor (EPOR) signaling in angiogenesis. In the eye, EPO is involved in both physiological and pathological angiogenesis in the retina. We hypothesized that EPOR signaling is important in pathological angiogenesis and tested this hypothesis using a rat model of oxygen-induced retinopathy that is representative of human retinopathy of prematurity. We first determined that EPOR expression and activation were increased and that activated EPOR was localized to retinal vascular endothelial cells (ECs) in retinas at postnatal day 18 (p18), when pathological angiogenesis in the form of intravitreal neovascularization occurred. In human retinal microvascular ECs, EPOR was up-regulated and activated by VEGF. Lentiviral-delivered shRNAs that knocked down Müller cell-expressed VEGF in the retinopathy of prematurity model also reduced phosphorylated EPOR (p-EPOR) and VEGFR2 (p-VEGFR2) in retinal ECs. In human retinal microvascular ECs, VEGFR2-activated EPOR caused an interaction between p-EPOR and p-VEGFR2; knockdown of EPOR by siRNA transfection reduced VEGF-induced EC proliferation in association with reduced p-VEGFR2 and p-STAT3; however, inhibition of VEGFR2 activation by siRNA transfection or semaxanib (SU5416) abolished VEGFA-induced proliferation of ECs and phosphorylation of VEGFR2, EPOR, and STAT3. Our results show that VEGFA-induced p-VEGFR2 activates EPOR and causes an interaction between p-EPOR and p-VEGFR2 to enhance VEGFA-induced EC proliferation by exacerbating STAT3 activation, leading to pathological angiogenesis.

Candidate gene association study for diabetic retinopathy in Chinese patients with type 2 diabetes

PURPOSE

To investigate whether variants in a set of eight candidate genes are associated with diabetic retinopathy (DR) in a cohort of Chinese patients with type 2 diabetes mellitus (T2DM).

METHODS

Case-control study. Patients with T2DM were recruited from the Desheng community in urban Beijing and assigned into a DR group or diabetic without retinopathy (DWR) group, based on the duration of diabetes and grading of fundus images. Twenty-six single-nucleotide polymorphisms (SNPs) within eight candidate genes, including PPARγ, vascular endothelial growth factor (VEGF) and its receptor kinase insert domain receptor (KDR), erythropoietin, aldose reductase, protein kinase C-β, angiotensin-converting enzyme, and intercellular adhesion molecule 1, were analyzed using the MassARRAY genotyping system.

RESULTS

A total of 500 patients with T2DM (216 with DR and 284 with DWR) were enrolled in the study. Significant associations of DR were noted with genotypes of four SNPs-rs699947 (p<0.001), rs833061 (p = 0.001), rs13207351 (p<0.001), and rs2146323 (p=0.006)--in the VEGF gene and one variant, rs2071559, in the KDR gene (p=0.034). After adjustment for covariates, significant association of DR remained with the homozygous genotype of the minor allele for the SNPs rs699947 (odds ratio [OR] = 3.54, 95% confidence interval [CI]: 1.12-11.19), rs833061 (OR = 3.72, 95% CI: 1.17-11.85), rs13207351 (OR = 3.76, 95% CI: 1.21-11.71), and rs2146323 (OR = 2.8, 95% CI: 1.46-5.37) in the VEGF gene as well as the SNP rs2071559 (OR = 1.62, 95% CI: 1.08-2.41) in the KDR gene. However, only rs699947 and rs13207351 in the VEGF gene remained statistically significant after Bonferroni correction. No associations were found in other genes tested.

CONCLUSIONS

These data expanded previous observations on the association of DR with variants in the VEGF gene in Chinese patients with T2DM. Moreover, a possible association between DR and KDR polymorphisms is suggested.

Interleukin 8 promoter polymorphism predicts the initial response to bevacizumab treatment for exudative age-related macular degeneration

PURPOSE

To study the association of single-nucleotide polymorphisms of interleukin 8, vascular endothelial growth factor, erythropoietin, complement factor H, complement component C3, and LOC387715 genes with the response to bevacizumab treatment in exudative age-related macular degeneration.

METHODS

Clinical records, smoking history, optical coherence tomography, and angiographies of 96 bevacizumab-treated exudative age-related macular degeneration patients were analyzed retrospectively. Blood DNA was collected. Based on the disappearance of intra- or subretinal fluid in optical coherence tomography, patients were graded as responders, partial responders, or nonresponders after 3 initial treatment visits and a median time of 3.5 months.

RESULTS

Interleukin 8 promoter polymorphism -251A/T was significantly associated with persisting fluid in optical coherence tomography. The A allele was more frequent in nonresponders than in responders (P = 0.033). In multivariate modeling, the AA genotype of -251A/T (P = 0.043) and occult (P = 0.042) or predominantly classic (P = 0.040) lesions predicted poorer outcome. Visual acuity change was better in responders than in nonresponders (P = 0.006). Baseline lesion size (P = 0.006) and retinal cysts after the treatment (P < 0.001) correlated with less visual acuity gain.

CONCLUSION

The A allele and the homozygous AA genotype of interleukin 8 -251A/T were associated with anatomical nonresponse to bevacizumab treatment.

The influence of erythropoietin (EPO T → G) and α-actinin-3 (ACTN3 R577X) polymorphisms on runners' responses to the dietary ingestion of antioxidant supplementation based on pequi oil ( Caryocar brasiliense Camb.): a before-after study

BACKGROUND/AIMS

As diet can affect an individual's genes and these can affect response to supplementation, we aimed to investigate the influence of erythropoietin (EPO T→G) and α-actinin-3 (ACTN3 R577X) polymorphisms on plasma lipid peroxidation, hemogram and biochemical dosages of creatine kinase, aspartate aminotransferase, alanine aminotransferase and C-reactive protein (including high-sensitivity C-reactive protein) of runners (n = 123) before and after 14 days of 400 mg pequi oil supplementation, a natural carotenoid-rich oil, after races under closely comparable conditions.

METHODS/RESULTS

Blood samples were taken immediately after racing to perform the tests. Before pequi oil supplementation, EPO polymorphism influenced erythrogram and plateletgram results, suggesting an aerobic advantage for the TG genotype and a disadvantage for the GG genotype as regards possible microvascular complications, while no association was found for ACTN3 polymorphism with endurance performance. Both polymorphisms influenced the runners' response to pequi oil: significant responses were observed for the EPO TT genotype in erythrocyte, hematocrit, mean corpuscular hemoglobin and mean corpuscular hemoglobin concentration values, and for the TT and TG genotypes in red blood cell distribution width values. Significant differences were also observed in the plateletgram for the TT and TG genotypes. ACTN3 mainly influenced aspartate aminotransferase and creatine kinase values: heterozygotes had a significant reduction in aspartate aminotransferase values and homozygous individuals (XX) in creatine kinase values after pequi oil supplementation.

CONCLUSION

These results emphasize the importance of studying nutrigenomic effects on athletes' performance.

Genetics in diabetic retinopathy: current concepts and new insights

There is emerging evidence which indicates the essential role of genetic factors in the development of diabetic retinopathy (DR). In this regard it should be highlighted that genetic factors account for 25-50% of the risk of developing DR. Therefore, the use of genetic analysis to identify those diabetic patients most prone to developing DR might be useful in designing a more individualized treatment. In this regard, there are three main research strategies: candidate gene studies, linkage studies and Genome-Wide Association Studies (GWAS). In the candidate gene approach, several genes encoding proteins closely related to DR development have been analyzed. The linkage studies analyze shared alleles among family members with DR under the assumption that these predispose to a more aggressive development of DR. Finally, Genome-Wide Association Studies (GWAS) are a new tool involving a massive evaluation of single nucleotide polymorphisms (SNP) in large samples. In this review the available information using these three methodologies is critically analyzed. A genetic approach in order to identify new candidates in the pathogenesis of DR would permit us to design more targeted therapeutic strategies in order to decrease this devastating complication of diabetes. Basic researchers, ophthalmologists, diabetologists and geneticists should work together in order to gain new insights into this issue.

Chromosome 2q31.1 associates with ESRD in women with type 1 diabetes

Sex and genetic variation influence the risk of developing diabetic nephropathy and ESRD in patients with type 1 diabetes. We performed a genome-wide association study in a cohort of 3652 patients from the Finnish Diabetic Nephropathy (FinnDiane) Study with type 1 diabetes to determine whether sex-specific genetic risk factors for ESRD exist. A common variant, rs4972593 on chromosome 2q31.1, was associated with ESRD in women (P<5×10(-8)) but not in men (P=0.77). This association was replicated in the meta-analysis of three independent type 1 diabetes cohorts (P=0.02) and remained significant for women (P<5×10(-8); odds ratio, 1.81 [95% confidence interval, 1.47 to 2.24]) upon combined meta-analysis of the discovery and replication cohorts. rs4972593 is located between the genes that code for the Sp3 transcription factor, which interacts directly with estrogen receptor α and regulates the expression of genes linked to glomerular function and the pathogenesis of nephropathy, and the CDCA7 transcription factor, which regulates cell proliferation. Further examination revealed potential transcription factor-binding sites within rs4972593 and predicted eight estrogen-responsive elements within 5 kb of this locus. Moreover, we found sex-specific differences in the glomerular expression levels of SP3 (P=0.004). Overall, these results suggest that rs4972593 is a sex-specific genetic variant associated with ESRD in patients with type 1 diabetes and may underlie the sex-specific protection against ESRD.

Candidate genes for proliferative diabetic retinopathy

Several candidate genes have been so far implicated in the pathogenesis of proliferative diabetic retinopathy (PDR) in subjects with type 2 diabetes. Since the principal pathogenetic mechanisms for diabetic retinopathy (DR) and PDR are different, the main pathogenetic mechanism in DR is increased vascular permeability, whereas in PDR the crucial pathogenetic mechanisms are fibrosis and neoangiogenesis. Due to that fact, different candidate genes are expected to be involved in the development of either DR or PDR. None of the candidate genes, however, can be fully and solely responsible for the development of PDR and for DR progression into PDR. Epigenetic mechanisms are expected to be involved in the pathogenesis of PDR as well. Gene polymorphisms responsible for PDR and epigenetic mechanisms responsible for PDR are reviewed in this paper.

Advances in the genomics of common eye diseases

Genome-wide association studies (GWAS) and other genomic technologies have accelerated the discovery of genes and genomic regions contributing to common human ocular disorders with complex inheritance. Age-related macular degeneration (AMD), diabetic retinopathy (DR), glaucoma and myopia account for the majority of visual impairment worldwide. Over 19 genes and/or genomic regions have been associated with AMD. Current investigations are assessing the clinical utility of risk score panels and therapies targeting disease-specific pathways. DR is the leading cause of blindness in the United States and globally is a major cause of vision loss. Genomic investigations have identified molecular pathways associated with DR in animal models which could suggest novel therapeutic targets. Three types of glaucoma, primary-open-angle glaucoma (POAG), angle-closure glaucoma and exfoliation syndrome (XFS) glaucoma, are common age-related conditions. Five genomic regions have been associated with POAG, three with angle-closure glaucoma and one with XFS. Myopia causes substantial ocular morbidity throughout the world. Recent large GWAS have identified >20 associated loci for this condition. In this report, we present a comprehensive overview of the genes and genomic regions contributing to disease susceptibility for these common blinding ocular disorders and discuss the next steps toward translation to effective gene-based screening tests and novel therapies targeting the molecular events contributing to disease.

Antiangiogenic therapy for ischemic retinopathies

Neovascularization is a common pathological process in various retinal vascular disorders including diabetic retinopathy (DR), age-related macular degeneration (AMD) and retinal vein occlusion (RVO). The development of neovascular vessels may lead to complications such as vitreous hemorrhage, fibrovascular tissue formation, and traction retinal detachments. Ultimately, irreversible vision loss may result. Various proangiogenic factors are involved in these complex processes. Different antiangiogenic drugs have been formulated in an attempt treat these vascular disorders. One factor that plays a major role in the development of retinal neovascularization is vascular endothelial growth factor (VEGF). Anti-VEGF agents are currently FDA approved for the treatment of AMD and RVO. They are also extensively used as an off-label treatment for diabetic macular edema (DME), proliferative DR, and neovascular glaucoma. However, at this time, the long-term safety of chronic VEGF inhibition has not been extensively evaluated. A large and rapidly expanding body of research on angiogenesis is being conducted at multiple centers across the globe to determine the exact contributions and interactions among a variety of angiogenic factors in an effort to determine the therapeutic potential of antiangiogenic agent in the treatment of a variety of retinal diseases.

TCF7L2 variation and proliferative diabetic retinopathy

Proliferative diabetic retinopathy (PDR) is the most severe vision-threatening complication of diabetes. For investigation of genetic association between TCF7L2 and PDR in Caucasian type 2 diabetes mellitus (T2DM) and its functional consequences, 383 T2DM patients with PDR (T2DM-PDR) and 756 T2DM patients without diabetic retinopathy (T2DM-no DR) were genotyped with rs7903146 in TCF7L2. We found that risk allele (T) frequency of rs7903146 was significantly higher in T2DM-PDR patients (allelic P = 2.52E-04). In lymphoblastoid cells induced to undergo endoplasmic reticulum (ER) stress by treatment of tunicamycin, higher fold change of TCF7L2 and VEGFA mRNA levels were observed in rs7903146-TT cells than in rs7903146-CC cells (P = 0.02 for TCF7L2; P = 0.004 for VEGFA), suggesting that ER stress plays a role in PDR pathogenesis. Silencing TCF7L2 resulted in decreased mRNA levels of both TCF7L2 and VEGFA (P < 0.001). Retinas of oxygen-induced retinopathy mice (a model for PDR) had higher TCF7L2 and VEGFA mRNA levels than those of controls (P = 2.9E-04 for TCF7L2; P = 1.9E-07 for VEGFA). Together, data from our study show that TCF7L2-rs7903146 is associated with PDR in Caucasian T2DM and suggest that TCF7L2 promotes pathological retinal neovascularization via ER stress-dependent upregulation of VEGFA.

Optimal treatment of diabetic retinopathy

Diabetic retinopathy (DRP) is a common complication caused by multiple biochemical abnormalities of the underlying metabolic disease. While the incidence of DRP appears to decline due to evidence-based changes in diabetes management, the predicted increase in patients affected in particular by type 2 diabetes may outweigh the positive trend. The diagnosis is based on the alterations of the vessels, usually indicating abnormalities of the blood-retinal barrier and increased vasoregression, but the neuroglial elements appear equally vulnerable to the diabetic condition. Control of blood glucose, blood pressure and timely identification of coincident nephropathy are important to prevent progression to vision-threatening stages. Guidelines give specific indications for laser photocoagulation, in particular when euglycemia is no longer effective in preventing progression to advanced stages. Intravitreal administration of antibodies directed against the single best characterized propagator of clinically significant macular edema, vascular endothelial growth factor (VEGF), has become popular despite uncertainty about the patient subgroups which benefit best and the optimum administration schedule. Multifactorial intervention beyond glycemic control includes antihypertensive, lipid-lowering and antiaggregatory and is effective in type 2 diabetic patients with high-risk profiles, in particular coincident nephropathy.

Pigment epithelium-derived factor (PEDF) peptide eye drops reduce inflammation, cell death and vascular leakage in diabetic retinopathy in Ins2(Akita) mice

Inflammation, neurodegeneration and microvascular irregularities are included in the spectrum of defects associated with diabetic retinopathy. Here, we evaluated intraocular deliverability features of two pigment epithelium-derived factor (PEDF) derivatives given as eye drops and their efficacy in modulating diabetes-induced retinal complications. The antiangiogenic PEDF60-77 (P60) and neuroprotective PEDF78-121 (P78) derivatives were applied to Ins2(Akita) mouse eyes once a week for 15 wks at the onset of hyperglycemia. Peptides, labeled with Alexa Fluor 488, were observed penetrating the cornea by 1-4 h and gained access to the ciliary body, retinal pigment epithelium (RPE)-choroid complex, retina microvasculature and vitreous. Peak vitreous levels were 0.2 μg/mL for P60 and 0.9 μg/mL for P78 after 0.5 and 4 h, respectively. Both peptides reduced vascular leakage by ~60% and increased zona occludens 1 (ZO1) and occludin expression in the microvasculature to nondiabetic levels. P60 induced pERK1/2 and P78 promoted pAKT in Muller glia, two signals that were dampened in diabetic conditions. Pharmacologically inhibiting AKT signaling in the retina blocked effects of the peptides on ZO1 and occludin expression. P78 reduced levels of 9/20 cytokines in diabetic vitreous including interferon (IFN)-γ, interleukin (IL)-6, IL-3 and tumor necrosis factor (TNF)-α. P60 lowered levels of 6/20 cytokines but was less effective than P78. Neuroprotective P78 prevented diabetes-induced microglia activation by ~60%, retinal ganglion cell (RGC) death by ~22% and inner plexiform layer thinning by ~13%. In summary, we provide evidence that PEDF bioactive derivatives gained access to the retina by topical delivery and validated their efficacy in reducing diabetic retinopathy complications. Our findings argue for glia regulation of microvascular leakage and an early root cause for RGC degeneration embedded in microglia activation.

Association between polymorphisms in erythropoietin gene and upper limit haematocrit levels among regular blood donors

PURPOSE OF THE STUDY

Erythropoietin (EPO) is a glycoprotein hormone that functions primarily on the stimulation and control of erythropoiesis in bone marrow. In this study, polymorphisms in EPO gene; C3434T, G3544T (rs551238) and rs1617640 were evaluated to determine their frequencies and genotype distribution patterns among blood donors with upper-limit haematocrit level.

SUBJECTS AND METHODS

A total of 298 subjects, 181 blood donors with haematocrit level greater or equal to 48% and 117 donors with haematocrit between 42-47.5% as control were recruited. All subjects were genotyped for C3434T, rs551238 polymorphisms and for rs1617640 using restriction fragment length polymorphism method (PCR-RFLP) and sequencing techniques.

RESULTS

A significant difference was found in rs1617640 and rs551238 genotype frequencies in blood donors with upper-haematocrit compared to the control group (P<0.05). In accordance with genotype frequencies, G allele in these two polymorphisms were found at higher frequency among upper-haematocrit group compared to the control (P<0.05). On the other hand, C3434T polymorphism was not significantly different between the two groups, neither for genotype frequencies nor for allele frequencies.

CONCLUSION

Results suggest a strong association between rs551238 and rs1617640 polymorphisms in the EPO gene and upper-limit haematocrit level among blood donors.

-374 T/A polymorphism in RAGE gene is associated with onset of diabetes mellitus, atherosclerosis, and renal dysfunction in patients with hypertension

Receptor of advanced glycation end products (RAGE) is reportedly linked with chronic inflammatory diseases due to aging or diabetes. The aim of this study was to show how -374 T/A RAGE has an impact on systemic vascular damage and renal function. The study subjects were a total of 468 essential hypertension patients from the Non-Invasive Atherosclerotic Evaluation in Hypertension (NOAH) study cohort. We prospectively examined the association of -374 T/A RAGE with their prognoses and investigated the correlation between -374 T/A RAGE and multiple clinical parameters. Kaplan-Meier analysis did not show a significant association of -374 T/A RAGE with total mortality or the prevalence of cardiovascular events. Carriers of the A allele showed a significantly higher prevalence of diabetes mellitus (DM) and lower estimated glomerular filtration rate (eGFR) than subjects without this allele. In subjects with DM, carriers of the A allele showed a significantly lower eGFR. These significant correlations were only seen in male subjects. Carriers of the A allele of -374 T/A RAGE show an independent risk of atherosclerosis and reduced renal function in male hypertensive patients with DM.

Common variants of the genes encoding erythropoietin and its receptor modulate cognitive performance in schizophrenia

Erythropoietin (EPO) improves cognitive performance in clinical studies and rodent experiments. We hypothesized that an intrinsic role of EPO for cognition exists, with particular relevance in situations of cognitive decline, which is reflected by associations of EPO and EPO receptor (EPOR) genotypes with cognitive functions. To prove this hypothesis, schizophrenic patients (N > 1000) were genotyped for 5' upstream-located gene variants, EPO SNP rs1617640 (T/G) and EPORSTR(GA)(n). Associations of these variants were obtained for cognitive processing speed, fine motor skills and short-term memory readouts, with one particular combination of genotypes superior to all others (p < 0.0001). In an independent healthy control sample (N > 800), these associations were confirmed. A matching preclinical study with mice demonstrated cognitive processing speed and memory enhanced upon transgenic expression of constitutively active EPOR in pyramidal neurons of cortex and hippocampus. We thus predicted that the human genotypes associated with better cognition would reflect gain-of-function effects. Indeed, reporter gene assays and quantitative transcriptional analysis of peripheral blood mononuclear cells showed genotype-dependent EPO/EPOR expression differences. Together, these findings reveal a role of endogenous EPO/EPOR for cognition, at least in schizophrenic patients.

Imbalanced levels of angiogenic and angiostatic factors in vitreous, plasma and postmortem retinal tissue of patients with proliferative diabetic retinopathy

A role for vascular endothelial growth factor (VEGF) has been clearly implicated in the pathogenesis of proliferative diabetic retinopathy (PDR). However, other molecules and mechanisms may be operating independently, or in conjunction with VEGF in the pathogenesis of this disease. Therefore, we made an attempt to comparatively investigate the levels of angiogenic and angiostatic factors in vitreous, plasma and postmortem retinal tissue of subjects with Proliferative Diabetic Retinopathy (PDR) compared to control subjects. The vitreous and plasma concentrations of VEGF, EPO (Erythropoietin) and PEDF (Pigment Epithelium Derived Factor) were measured using Enzyme Linked Immunosorbent Assay (ELISA) and the postmortem retinal tissue was subjected to Western blot analysis. The mean vitreous and plasma levels of VEGF and EPO in patients with PDR were significantly (p<0.001) higher than those in subjects without diabetes. Conversely, the vitreous and plasma levels of PEDF were significantly (p<0.001) lower in the PDR patients compared to control subjects. Multivariate logistic-regression analyses indicated that EPO was more strongly associated with PDR than VEGF. The protein expression of the VEGF and EPO in the retinal tissue was significantly higher in PDR and diabetes without complication groups compared to controls. Compared to controls, the protein expression of PEDF was significantly lower in retinal tissues from diabetes patients without complications and in patients with PDR. The fact that the vitreous and plasma levels and the retinal tissue protein expression of EPO were strongly associated with PDR implies a definite role of 'hypererythropoietinemia' in neovascularization processes.

Insights into the genetic architecture of diabetic nephropathy

Diabetic nephropathy (DN) is a devastating complication of type 1 and type 2 diabetes and leads to increased morbidity and premature mortality. Susceptibility to DN has an inherent genetic basis as evidenced by familial aggregation and ethnic-specific prevalence rates. Progress in identifying the underlying genetic architecture has been arduous with the realization that a single locus of large effect does not exist, unlike in predisposition to non-diabetic nephropathy in individuals with African ancestry. Numerous risk variants have been identified, each with a nominal effect, and they collectively contribute to disease. These results have identified loci targeting novel pathways for disease susceptibility. With continued technological advances and development of new analytic methods, additional genetic variants and mechanisms (e.g., epigenetic variation) will be identified and help to elucidate the pathogenesis of DN. These advances will lead to early detection and development of novel therapeutic strategies to decrease the incidence of disease.

Association testing of previously reported variants in a large case-control meta-analysis of diabetic nephropathy

We formed the GEnetics of Nephropathy-an International Effort (GENIE) consortium to examine previously reported genetic associations with diabetic nephropathy (DN) in type 1 diabetes. GENIE consists of 6,366 similarly ascertained participants of European ancestry with type 1 diabetes, with and without DN, from the All Ireland-Warren 3-Genetics of Kidneys in Diabetes U.K. and Republic of Ireland (U.K.-R.O.I.) collection and the Finnish Diabetic Nephropathy Study (FinnDiane), combined with reanalyzed data from the Genetics of Kidneys in Diabetes U.S. Study (U.S. GoKinD). We found little evidence for the association of the EPO promoter polymorphism, rs161740, with the combined phenotype of proliferative retinopathy and end-stage renal disease in U.K.-R.O.I. (odds ratio [OR] 1.14, P = 0.19) or FinnDiane (OR 1.06, P = 0.60). However, a fixed-effects meta-analysis that included the previously reported cohorts retained a genome-wide significant association with that phenotype (OR 1.31, P = 2 × 10(-9)). An expanded investigation of the ELMO1 locus and genetic regions reported to be associated with DN in the U.S. GoKinD yielded only nominal statistical significance for these loci. Finally, top candidates identified in a recent meta-analysis failed to reach genome-wide significance. In conclusion, we were unable to replicate most of the previously reported genetic associations for DN, and significance for the EPO promoter association was attenuated.

Novel targets against retinal angiogenesis in diabetic retinopathy

Proliferative diabetic retinopathy (PDR), characterized by pathologic retinal angiogenesis, is a major cause of blindness in the USA and globally. Treatments targeting vascular endothelial growth factor (VEGF) have emerged as a beneficial part of the therapeutic armamentarium for this condition, highlighting the utility of identifying and targeting specific pathogenic molecules. There continues to be active research into the molecular players regulating retinal angiogenesis, including pro-angiogenic factors, anti-angiogenic factors, and integrins and matrix proteinases. New insights have been especially prominent regarding molecules which regulate specialized endothelial cells called tip cells, which play a lead role in endothelial sprouting. Together, these research efforts are uncovering new, important molecular regulators of retinal angiogenesis, which provide fertile areas for therapeutic exploration. This review discusses potential molecular targets, with an emphasis towards newer targets.

Ophthalmic drug discovery: novel targets and mechanisms for retinal diseases and glaucoma

Blindness affects 60 million people worldwide. The leading causes of irreversible blindness include age-related macular degeneration, retinal vascular diseases and glaucoma. The unique features of the eye provide both benefits and challenges for drug discovery and delivery. During the past decade, the landscape for ocular drug therapy has substantially changed and our knowledge of the pathogenesis of ophthalmic diseases has grown considerably. Anti-angiogenic drugs have emerged as the most effective form of therapy for age-related macular degeneration and retinal vascular diseases. Lowering intraocular pressure is still the mainstay for glaucoma treatment but neuroprotective drugs represent a promising next-generation therapy. This Review discusses the current state of ocular drug therapy and highlights future therapeutic opportunities.