Role In Diabetic Retinopathy Research Articles

Upregulated VEGF and Robo4 correlate with the reduction of miR-15a in the development of diabetic retinopathy

PurposeVascular endothelial growth factor (VEGF) plays implicated roles in diabetic retinopathy (DR). The role of roundabout 4 (Robo 4) in angiogenesis and vasculogenesis is controversial; however, the interdependent relationship between these two factors has not been studied in DR. This study determined the colocalization of VEGF and Robo4 in fibrovascular membranes (FVM) from patients with proliferative diabetic retinopathy (PDR). MicroRNA (miRNA)-mediated modulation of VEGF and Robo4 was explored in diabetic rats and ARPE-19 tissue culture cells under hyperglycemia.MethodsVEGF and Robo4 co-expression in the FVM was analyzed using immunofluorescence. VEGF and Robo4 levels were determined in diabetic retinas and ARPE-19 tissue culture cells under high glucose using western blotting and RT-qPCR. MicroRNA agomir was intraocularly injected to increase miR-15a expression and downregulate VEGF and Robo4 levels in diabetic retinas.ResultsVEGF and Robo4 colocalization in FVM vessels was observed. Increased VEGF levels were consistent in diabetic retinas and ARPE-19 tissue culture cells cultured under hyperglycemia. Robo4 decreased in ARPE-19 tissue culture cells exposed to hyperglycemia for 72 h, whereas it increased in diabetic rat retinas. Several miRNAs were differentially expressed during DR progression. Furthermore, miR-15a agomir injection inhibited high levels of VEGF and Robo4 in diabetic retinas.ConclusionsVEGF and Robo4 were co-expressed in FVMs from PDR patients. In the early stages of DR, VEGF was upregulated and contributed to DR development, whereas, in the late stage of DR, VEGF and Robo4 worked together to aggravate DR progression. However, miR-15a could downregulate VEGF and Robo4 to ameliorate DR development.

Unraveling the role of genetics in the pathogenesis of diabetic retinopathy.

Diabetic retinopathy (DR) is a microvascular disease of the retina and the leading cause of visual disability in diabetic patients. Genetic factors have shown to play a pivotal role in DR onset, and several candidate genes have been associated with its progression. A literature search was performed to identify the genes known to be associated with DR through linkage analysis, candidate gene association, and genome-wide association studies (GWAS). A further literature search was performed to discover their potential connection with various biological pathways. A total of 65 genes were found and several of these genes belong to major signaling pathways known to play a significant role in DR, including systemic inflammation, angiogenesis, and neurogenesis. A comprehensive analysis presented in this review will be helpful in unraveling the role of genetics in the pathogenesis of DR.

Bioinformatics Analysis of Weighted Genes in Diabetic Retinopathy.

Intricate signaling networks and transcriptional regulators translate pathogen recognition into defense responses. The aim of this study was to identify the weighted genes involved in diabetic retinopathy (DR) in different rodent models of diabetes. We performed a gene coexpression analysis of publicly available microarray data, namely, the GSE19122 dataset from the Gene Expression Omnibus database. We conducted gene coexpression analysis on the microarray data to identify modules of functionally related coexpressed genes that are differentially expressed in different rodent models. We leveraged a richly curated expression dataset and used weighted gene coexpression network analysis to construct an undirected network. We screened 30 genes in the most closely related module. A protein-protein interaction network was constructed for the genes in the most related module using the Search Tool for the Retrieval of Interacting Genes. Gene Ontology enrichment analysis and Kyoto Encyclopedia of Genes and Genomes pathway enrichment analysis were performed for the 30 genes. Five visual perception-related genes (Pde6g, Guca1a, Rho, Sag, and Prph2) were significantly upregulated. Based on the competing endogenous RNA hypothesis, a link between the long noncoding RNA metastasis-associated lung adenocarcinoma transcript 1 (MALAT1) and visual perception-related mRNAs was constructed using bioinformatics tools. Six potential microRNAs (miR-155-5p, miR-1a-3p, miR-122-5p, miR-223-3p, miR-125b-5p, and miR-124-3p) were also screened. MALAT1 might play important roles in DR by regulating Sag and Guca1a through miR-124-3p and regulating Pde6g through miR-125b-5p.

Grape seed extracts attenuate retinal Müller cell gliosis in streptozotocin-diabetic rats

Müller cell gliosis, with a characterization of increase in glial fibrillary acidic protein (GFAP), plays a key role in diabetic retinopathy (DR), a leading cause of blindness in people of working age. Recent studies have shown that in diabetes Müller cells produced high levels of vascular endothelial growth factor (VEGF) and pro-inflammatory cytokines. In the present study, we investigated whether GSEs protect against hyperglycemia-induced injury to Müller cells in retinal tissues and cell culture. The results showed that GSEs attenuated diabetes-induced increase in GFAP, VEGF, and inflammatory factors in the retina of streptozotocin-diabetic rats. Studies in primary Müller cells supported these findings by detecting a reduction in angiogenic and inflammatory mediators upon treatment with GSEs. We believe that GSEs may alleviate oxidative stress by increasing the expression of Nrf2-responsive antioxidant genes including HO-1 and GCLC. These data demonstrated that GSEs protect the retina against injury during DR.

Association of Plasma Pentraxin-3 Levels with Retinopathy and Systemic Factors in Diabetic Patients.

Diabetic retinopathy (DR) is mainly caused by metabolic factors, vascular inflammation, and endothelial dysfunction. We aimed to evaluate the relationship of DR with inflammatory and biochemical alterations in type 2 diabetics. A total of 89 diabetic patients with retinopathy [(DR (+) (n = 30)], without retinopathy [(DR (-) (n = 32)], and 27 control subjects were involved in the study. Demographic properties, biochemical values, ophtalmologic evaluation, C-reactive protein (CRP), and pentraxin-3 (PTX-3) levels were recorded. There was significant difference between controls, DR (-) and DR (+) groups with regard to serum PTX-3 levels. Control group had the lowest and DR (+) group revealed the highest PTX-3 levels. Severity of retinopathy was not related with CRP or PTX-3 levels. Duration of diabetes was longer, systolic blood pressure (SBP) and urinary albumin-creatinine ratio (UACR) were significantly higher in DR (+) subjects than DR (-) subjects. Multivariate analysis revealed that PTX-3 level and SBP were the variables that had a significant effect on DR (P = 0.002, OR = 1.61, and P = 0.021, OR = 1.06, respectively). Plasma PTX-3 levels may be a valuable predictor of DR-like factors such as duration of diabetes, hypertension, and UACR. Although inflammation has an important role in DR, we think that biomarkers reflecting inflammation is not sufficient to predict development and progression of DR; but follow up with PTX-3 levels along with ophthalmological evaluation may be useful. A single determination may not reflect the variations over time, so repeat measures may provide knowledge if PTX-3 is just a biomarker or has a causal role.

Involvement of ciliary neurotrophic factor in early diabetic retinal neuropathy in streptozotocin-induced diabetic rats

ObjectiveCiliary neurotrophic factor (CNTF) has been evaluated as a candidate therapeutic agent for diabetes and its neural complications. However, its role in diabetic retinopathy has not been fully elucidated.MethodsThis is a randomized unblinded animal experiment. Wistar rats with streptozocin (STZ)-induced diabetes were regularly injected with CNTF or vehicle control in their vitreous bodies beginning at 2 weeks after STZ injection. A total of five injections were used. In diabetic rats, the levels of CNTF and neurotrophin-3 (NT-3) were evaluated by enzyme-linked immunosorbent assays (ELISA) and real-time PCR. The abundance of tyrosine hydroxylase (TH) and β-III tubulin was detected by western blot. Transferase-mediated dUTP nick-end labeling staining (TUNEL) was used to detect cell apoptosis in the retinal tissue. The activation of caspase-3 was also measured.ResultsThe protein and mRNA levels of CNTF in diabetic rat retinas were reduced compared to control rats. In addition, retinal ganglion cells (RGCs) and dopaminergic amacrine cells appeared to undergo degeneration in diabetic rat retinas, as revealed by transferase-mediated dUTP nick-end labeling staining (TUNEL). Tyrosine hydroxylase (TH) and β-III tubulin protein levels also decreased significantly. Intraocular administration of CNTF rescued RGCs and dopaminergic amacrine cells from neurodegeneration and counteracted the downregulation of β-III tubulin and TH expression, thus demonstrating its therapeutic potential.ConclusionOur study suggests that early diabetic retinal neuropathy involves the reduced expression of CNTF and can be ameliorated by an exogenous supply of this neurotrophin.

Epigenetic modifications in hyperhomocysteinemia: potential role in diabetic retinopathy and age-related macular degeneration.

To study Hyperhomocysteinemia (HHcy)-induced epigenetic modifications as potential mechanisms of blood retinal barrier (BRB) dysfunction, retinas isolated from three- week-old mice with elevated level of Homocysteine (Hcy) due to lack of the enzyme cystathionine β-synthase (cbs–/–, cbs+/– and cbs+/+), human retinal endothelial cells (HRECs), and human retinal pigmented epithelial cells (ARPE-19) treated with or without Hcy were evaluated for (1) histone deacetylases (HDAC), (2) DNA methylation (DNMT), and (3) miRNA analysis. Differentially expressed miRNAs in mice with HHcy were further compared with miRNA analysis of diabetic mice retinas (STZ) and miRNAs within the exosomes released from Hcy-treated RPEs. Differentially expressed miRNAs were further evaluated for predicted target genes and associated pathways using Ingenuity Pathway Analysis. HHcy significantly increased HDAC and DNMT activity in HRECs, ARPE-19, and cbs mice retinas, whereas inhibition of HDAC and DNMT decreased Hcy-induced BRB dysfunction. MiRNA profiling detected 127 miRNAs in cbs+/– and 39 miRNAs in cbs–/– mice retinas, which were significantly differentially expressed compared to cbs+/+. MiRNA pathway analysis showed their involvement in HDAC and DNMT activation, endoplasmic reticulum (ER), and oxidative stresses, inflammation, hypoxia, and angiogenesis pathways. Hcy-induced epigenetic modifications may be involved in retinopathies associated with HHcy, such as age-related macular degeneration and diabetic retinopathy.

An effective image processing method for detection of diabetic retinopathy diseases from retinal fundus images

Diabetic retinopathy (i.e., DR), is an eye disorder caused by diabetes, diabetic retinopathy detection is an important task in retinal fundus images due the early detection and treatment can potentially reduce the risk of blindness. Retinal fundus images play an important role in diabetic retinopathy through disease diagnosis, disease recognition (i.e., by ophthalmologists), and treatment. The current state-of-the-art techniques are not satisfied with sensitivity and specificity. In fact, there are still other issues to be resolved in state-of-the-art techniques such as performances, accuracy, and easily identify the DR disease effectively. Therefore, this paper proposes an effective image processing method for detection of diabetic retinopathy diseases from retinal fundus images that will satisfy the performance metrics (i.e., sensitivity, specificity, accuracy). The proposed automatic screening system for diabetic retinopathy was conducted in several steps: Pre-processing, optic disc detection and removal, blood vessel segmentation and removal, elimination of fovea, feature extraction (i.e., Micro-aneurysm, retinal hemorrhage, and exudates), feature selection and classification. Finally, a software-based simulation using MATLAB was performed using DIARETDB1 dataset and the obtained results are validated by comparing with expert ophthalmologists. The results of the conducted experiments showed an efficient and effective in sensitivity, specificity and accuracy.

Identification of Protein Biomarkers for Diabetic Retinopathy using Sequence Mining Techniques

Bioinformatics and sequence mining are the application and development of data mining techniques to solve problems by comprehending biological data. Sequence analysis is the most primitive operation in sequence mining techniques. Modern sequence mining research is specialized in analyzing sequential patterns which are relevant and distinct from one another and utilizing retrieved sequences similarity and distance between different protein sequences can be analyzed. Diabetic retinopathy is the major cause of blindness in individuals mostly adults with diabetes and is it is the common problem of diabetes mellitus across the world. Various research analyses stated that there are many proteins which are found to take part in diabetic retinopathy. In this paper, we have evaluated certain proteins which are closely related with diabetic retinopathy with the help of multiple alignment tool viz. Clustal Omega and obtained a phylogenetic tree of 28 protein sequences gathered from National Center for Biotechnology Information (NCBI). In this work data mining technique called sequence mining plays a significant role in providing phylogram obtained with Neighbor-Joining algorithm. From the phylogenetic tree it was recognized that cortistatin, vitamin-D receptor and somatostatin proteins has close connection with diabetic retinopathy. Molecular docking studies have also been performed which is the most extensively used method for the calculation of protein-ligand interactions. In silico docking studies indicated that four inhibitory compounds i.e. Quercetin, Kaempferol, Naringenin and Melicitrin interact with aldose reductase which also found to have role in diabetic retinopathy. Outcomes infer that techniques intended to standardize cortistatin, vitamin-D receptor and somatostatin activities be of huge advantage and provide benefit in inhibiting diabetic retinopathy.

Diet and risk of diabetic retinopathy: a systematic review.

Diabetic retinopathy is a microvascular complication of diabetes that threatens all individuals with diabetes, leading to vision loss or blindness if left untreated. It is frequently associated with diabetic macular edema, which can occur at any point during the development of diabetic retinopathy. The key factors known to lead to its development include hyperglycemia, hypertension, and the duration of diabetes. Though the diet is important in the development of diabetes, its role in diabetic retinopathy has not been clearly identified. In this systematic review, we aimed to identify, summarize and interpret the literature on the association between the diet and dietary intakes of specific foods, nutrients, and food groups, and the risk of diabetic retinopathy. We searched PubMed and Web of Science for English-language studies evaluating the association between the dietary intake of individual foods, macro or micronutrients, dietary supplements, and dietary patterns and their association with retinopathy or macular edema. After reviewing potentially relevant abstracts and, when necessary, full texts, we identified 27 relevant studies. Identified studies investigated intakes of fruit, vegetables, fish, milk, carbohydrates, fibre, fat, protein, salt, potassium, vitamins C, D, and E, carotenoids, dietary supplements, green tea and alcohol. Studies suggest that adherence to the Mediterranean diet and high fruit, vegetable and fish intake may protect against the development of diabetic retinopathy, although the evidence is limited. Studies concerning other aspects of the diet are not in agreement. The role of the diet in the development of diabetic retinopathy is an area that warrants more attention.

The Role of Glycemic Control and Variability in Diabetic Retinopathy.

Diabetic retinopathy (DR) is a common microvascular complication of diabetes mellitus (DM) and is considered the leading cause of visual impairment in working-aged adults worldwide. The duration of DM and hyperglycemia have been associated with DR, although the exact role in the pathogenesis of DR and diabetic macular edema remains controversial. As a result, a reasonable question arising is whether control of blood glucose levels may alter the course of DR. Studies have shown that glycemic control remains an important factor for the presence and progression of DR. HbA1c seems to be an indicator which cannot demonstrate exactly the degree of glycemic control, while sudden variations of blood glucose may play an important role in DR; therefore, glycemic variability may be useful to predict DM complications, such as DR.

The Relationships between SORD -888G>C Gene Polymorphism and Diabetic Retinopathy in a South Sumatran Malay Population

The sorbitol dehydrogenase (SORD) enzyme has 2 promoter regions with polymorphisms at -1214 C>G (rs2055858) and -888 G>C (rs3759890), which have a complete imbalance, related to gene expression in retinal cells of diabetic patients, and more likely to have a role in diabetic retinopathy (DR) pathogenesis. The SORD -888G>C genotype occurs more often in Japanese DR patients than in patients without complications. A relationship between DR and the G allele in -888G>C polymorphism is observed in Diabetes Mellitus (DM) type-2 patients. This study aims to elucidate the relationship between the SORD -888 G>C gene polymorphism to the occurrence of DR cases in Malay population in South Sumatra. This is a case-control study. Malay DM type-2 patients who undergo direct ophthalmoscopy and fundus imaging in the Dr. Mohammad Husein Central General Hospital eye clinic in Palembang, South Sumatra, Indonesia were the subjects of this study. Patient DNA was isolated from blood samples, PCR analyzed and sequenced in order to determine the polymorphism frequencies of the SORD -888 G>C gene. The results showed that every subject had GG genotype in SORD -888 G>C gene promoter. There was no observable polymorphism in SORD -888G>C gene in the authentic Malay population in South Sumatra.

Autophagy-mediated neuroprotection induced by octreotide in an ex vivo model of early diabetic retinopathy

Neuronal injury plays a major role in diabetic retinopathy (DR). Our hypothesis was that the balance between neuronal death and survival may depend on a similar equilibrium between apoptosis and autophagy and that a neuroprotectant may act by influencing this equilibrium. Ex vivo mouse retinal explants were treated with high glucose (HG) for 10days and the somatostatin analog octreotide (OCT) was used as a neuroprotectant. Chloroquine (CQ) was used as an autophagy inhibitor. Apoptotic and autophagic markers were evaluated using western blot and immunohistochemistry. HG-treated explants displayed a significant increase of apoptosis paralleled by a significant decrease of the autophagic flux, which was likely to be due to increased activity of the autophagy regulator mTOR (mammalian target of rapamycin). Treatment with OCT rescued HG-treated retinal explants from apoptosis and determined an increase of autophagic activity with concomitant mTOR inhibition. Blocking the autophagic flux with CQ completely abolished the anti-apoptotic effect of OCT. Immunohistochemical observations showed that OCT-induced autophagy is localized to populations of bipolar and amacrine cells and to ganglion cells. These observations revealed the antithetic role of apoptosis and autophagy, highlighting their equilibrium from which neuronal survival is likely to depend. These data suggest the crucial role covered by autophagy, which could be considered as a molecular target for DR neuroprotective treatment strategies.

Neural degeneration mechanisms in diabetic retinopathy: The role of apoptosis and autophagy

PurposeThat neuronal injury plays a major role in diabetic retinopathy (DR) is gaining increasing recognition. In particular, we have recently shown, using an ex vivo model of early DR, that neuroprotection may also reduce the expression of proangiogenic factors. Given the importance of neuronal health in DR, we chose to better analyze the mechanisms of cell death involved in this disease. Our hypothesis was that the balance between neuronal death and survival may depend on a similar equilibrium between apoptosis and autophagy: in this context, a neuroprotective treatment would act by influencing this equilibrium.MethodsEx vivo mouse retinal explants were treated with high glucose (HG, 75 mM) for 10 days and the somatostatin analog octreotide (OCT, 1µM) was used as a neuroprotectant. Chloroquine (CQ, 10µM) was used as an autophagy inhibitor. Apoptotic and autophagic markers were evaluated using Western blot and immunohistochemistry.ResultsConsistent with our previous observations, HG‐treated retinal explants displayed a significant increase of apoptosis. Concurrently, HG treatment caused a significant decrease of the autophagic flux, which was likely to be due to increased activity of the autophagy regulator mTOR. Treatment with OCT rescued HG‐treated retinal explants from apoptosis and determined an increase of autophagic activity with concomitant mTOR inhibition. Blocking the autophagic flux with CQ completely abolished the anti‐apoptotic effect of OCT.ConclusionsApoptosis and autophagy seem to play opposite roles and a delicate balance between apoptotic and autophagic fluxes is responsible for the death or survival of retinal neurons in stressing conditions like HG. Consistently, the data obtained with CQ suggest that the anti‐apoptotic effect of OCT in HG‐treated retinas is mediated by an increase of the autophagic flux.

Circular Noncoding RNA HIPK3 Mediates Retinal Vascular Dysfunction in Diabetes Mellitus.

The vascular complications of diabetes mellitus are the major causes of morbidity and mortality among people with diabetes. Circular RNAs are a class of endogenous noncoding RNAs that regulate gene expression in eukaryotes. In this study, we investigated the role of circular RNA in retinal vascular dysfunction induced by diabetes mellitus. Quantitative polymerase chain reactions, Sanger sequencing, and Northern blots were conducted to detect circular HIPK3 (circHIPK3) expression pattern on diabetes mellitus-related stresses. MTT (3-[4,5-dimethythiazol-2-yl]-2,5-diphenyl tetrazolium bromide) assays, EdU (5-ethynyl-2'-deoxyuridine) incorporation assays, Transwell migration assays, and Matrigel assays were conducted to detect the role of circHIPK3 in retinal endothelial cell function in vitro. Retinal trypsin digestion, vascular permeability assays, and ELISA assays were conducted to detect the role of circHIPK3 in retinal vascular dysfunction in vivo. Bioinformatics analysis, luciferase activity assays, RNA pull-down assays, and in vitro studies were conducted to reveal the mechanism of circHIPK3-mediated retinal vascular dysfunction. circHIPK3 expression was significantly upregulated in diabetic retinas and retinal endothelial cells following stressors related to diabetes mellitus. circHIPK3 silencing or overexpressing circHIPK3 changed retinal endothelial cell viability, proliferation, migration, and tube formation in vitro. circHIPK3 silencing in vivo alleviated retinal vascular dysfunction, as shown by decreased retinal acellular capillaries, vascular leakage, and inflammation. circHIPK3 acted as an endogenous miR-30a-3p sponge to sequester and inhibit miR-30a-3p activity, which led to increased vascular endothelial growth factor-C, FZD4, and WNT2 expression. Ectopic expression of miR-30a-3p mimicked the effect of circHIPK3 silencing on vascular endothelial phenotypes in vivo and in vitro. The circular RNA circHIPK3 plays a role in diabetic retinopathy by blocking miR-30a function, leading to increased endothelial proliferation and vascular dysfunction. These data suggest that circular RNA is a potential target to control diabetic proliferative retinopathy.

ANRIL polymorphism rs1333049, a novel genetic predictor for diabetic retinopathy complication

The 9p21 ANRIL (antisense non-coding RNA in INK4 locus) polymorphisms had reported association with type 2 diabetes mellitus (T2DM) and its induced macro/microvascular complications. However, the ANRIL single nucleotide polymorphism (SNP) rs1333049 has never been studied for its role in diabetic retinopathy; we therefore assessed its role in Pakistani population suffering from diabetes-induced retinopathy. The rs1333049 was genotyped in 806 individuals including 504 T2DM cases [206 patients without retinopathy (DNR) and 298 with retinopathy (DR) (non-proliferative DR (NPDR):147; proliferative DR (PDR): 151)] and 302 unaffected controls using allele-refractory mutation system (ARMS) polymerase chain reaction (PCR). The statistical analysis including genetic power estimation, χ2 test and Fisher's exact test were performed for the studied panel. Genetic power estimation showed that 504 T2DM cases and 302 controls had >80% power to detect the association between ANRIL rs1333049 variant and diabetes patients with retinopathy in Pakistani population. An association was found between rs1333049 CC genotype and T2DM [χ2=13.9 (p=0.0015); recessive model (RM): odds ratio (OR)=2.36, 95% confidence interval (95%CI)=1.42–3.95, p=0.001], DNR [χ2=14.2 (p=0.00081); RM: p=0.001, OR=2.66, 95%CI=1.48–4.79, dominant model (DM): p=0.02 OR=1.68, 95%CI=1.07–2.63], DR: (χ2=6.5, p=0.0381; OR=2.16, 95%CI=1.23–3.79, p=0.006), NPDR (χ2=4.25, p=0.03; OR=2.02, 95%CI=1.03–3.96, p=0.03) and PDR (χ2=8.11, p=0.02; OR=2.29, 95%CI=1.19–4.39, p=0.01) when compared with the healthy control subjects. The minor allele C was found to be associated with T2DM (OR=1.32, 95%CI=1.07–1.63, p=0.009) and DNR (OR=1.49, 95%CI=1.15–1.94, p=0.002). The ANRIL rs1333049 CC genotype is found to have a pathogenic role in the onset of T2DM and its induced retinopathy complication.

Serum and aqueous humor concentrations of interleukin-27 in diabetic retinopathy patients.

Interleukin (IL)-27 has been reported to possess anti- and proinflammatory properties in several immune related-disorders, but its role in diabetic retinopathy is still elusive. Here, we aimed to (i) evaluate IL-27 concentrations in serum and aqueous humor of diabetic patients with or without retinopathy and (ii) test whether IL-27 is correlated with some risk factors of diabetic retinopathy. The study comprised 60 diabetic patients with and without retinopathy along with 20 healthy controls. Serum and aqueous humor concentrations of IL-27 were assessed by ELISA. The mean of IL-27 concentration in aqueous humor in patients with diabetic retinopathy (6.7±2.7ng/L) was significantly elevated in comparison with either diabetic patients without retinopathy (4.6±0.5ng/L) or healthy control group (4.1±0.8ng/L). Besides, IL-27 concentration in aqueous humor was positively correlated with serum glucose, lipid profile and glycated hemoglobin (HbA1c). Based on this study, IL-27 is implicated in the pathogenesis of diabetic retinopathy and positively correlates with the disorder progression.

Connexin channel and its role in diabetic retinopathy.

Diabetic retinopathy is the leading cause of blindness in the working age population. Unfortunately, there is no cure for this devastating ocular complication. The early stage of diabetic retinopathy is characterized by the loss of various cell types in the retina, namely endothelial cells and pericytes. As the disease progresses, vascular leakage, a clinical hallmark of diabetic retinopathy, becomes evident and may eventually lead to diabetic macular edema, the most common cause of vision loss in diabetic retinopathy. Substantial evidence indicates that the disruption of connexin-mediated cellular communication plays a critical role in the pathogenesis of diabetic retinopathy. Yet, it is unclear how altered communication via connexin channel mediated cell-to-cell and cell-to-extracellular microenvironment is linked to the development of diabetic retinopathy. Recent observations suggest the possibility that connexin hemichannels may play a role in the pathogenesis of diabetic retinopathy by allowing communication between cells and the microenvironment. Interestingly, recent studies suggest that connexin channels may be involved in regulating retinal vascular permeability. These cellular events are coordinated at least in part via connexin-mediated intercellular communication and the maintenance of retinal vascular homeostasis. This review highlights the effect of high glucose and diabetic condition on connexin channels and their impact on the development of diabetic retinopathy.

Intraocular Delivery of miR-146 Inhibits Diabetes-Induced Retinal Functional Defects in Diabetic Rat Model.

Previously, we showed that microRNA-146 (miR-146) is a pivotal negative feedback regulator of multiple nuclear factor kappa-B (NF-κB) activation pathways in retinal endothelial cells (RECs). We hypothesized that miR-146 plays an important role in diabetic retinopathy (DR) by inhibiting diabetes-induced inflammatory response in the retina. The purpose of the current study is to test this hypothesis in vivo. Lentiviruses expressing rno-miR-146a, lenti-miR-146a, and negative control oligonucleotide with scrambled sequence, lenti-miR-neg ctl, were produced. Young male Sprague-Dawley rats were injected with a single dose of streptozotocin ([STZ] 65 mg/kg) to induce diabetes. One week after diabetes, animals were injected with lentivirus intravitreally (4 μl, ∼106 CFU/mL). Three months after diabetes, retinal microvascular leakage was tested by Evans blue assay; retinal function by electroretinogram (ERG). Total RNA and protein lysate were isolated from the retina for quantitative (q)RT-PCR and Western blot analyses. Lenti-miR-146a robustly transduced human retinal endothelial cells (HRECs) and increased the expression of miR-146a in vitro. In vivo, intravitreal injection of lenti-miR-146a increased the expression of miR-146a in the retina, while its key downstream target genes, including CARD10, IRAK1, and TRAF6, were downregulated. Intravitreal delivery of miR-146 inhibited diabetes-induced upregulation of NF-κB downstream gene, Intercellular Adhesion Molecule 1 (ICAM1), as well as microvascular leakage and retinal functional defects. Intravitreal delivery of miR-146 inhibited diabetes-induced NF-κB activation and retinal microvascular and neuronal functional defects in a diabetic rat model.

Elevated Glucose and Interleukin-1β Differentially Affect Retinal Microglial Cell Proliferation.

Diabetic retinopathy is considered a neurovascular disorder, hyperglycemia being considered the main risk factor for this pathology. Diabetic retinopathy also presents features of a low-grade chronic inflammatory disease, including increased levels of cytokines in the retina, such as interleukin-1 beta (IL-1β). However, how high glucose and IL-1β affect the different retinal cell types remains to be clarified. In retinal neural cell cultures, we found that IL-1β and IL-1RI are present in microglia, macroglia, and neurons. Exposure of retinal neural cell cultures to high glucose upregulated both mRNA and protein levels of IL-1β. High glucose decreased microglial and macroglial cell proliferation, whereas IL-1β increased their proliferation. Interestingly, under high glucose condition, although the number of microglial cells decreased, they showed a less ramified morphology, suggesting a more activated state, as supported by the upregulation of the levels of ED-1, a marker of microglia activation. In conclusion, IL-1β might play a key role in diabetic retinopathy, affecting microglial and macroglial cells and ultimately contributing to neural changes observed in diabetic patients. Particularly, since IL-1β has an important role in retinal microglia activation and proliferation under diabetes, limiting IL-1β-triggered inflammatory processes may provide a new therapeutic strategy to prevent the progression of diabetic retinopathy.