Autophagy in Diabetic Retinopathy

Modified Citrus Pectin (MCP) Confers a Renoprotective Effect on Early-Stage Nephropathy in Type-2 Diabetic Mice

Diabetic nephropathy (DN) is a significant global health concern with a high morbidity rate. Accumulating evidence reveals that Galectin-3 (Gal-3), a β-galactoside-binding lectin, is a biomarker in kidney diseases. Our study aimed to assess the advantageous impacts of modified citrus pectin (MCP) as an alternative therapeutic strategy for the initial and ongoing progression of DN in mice with type 2 diabetes mellitus (T2DM). The animal model has been split into four groups: control group, T2DM group (mice received intraperitoneal injections of nicotinamide (NA) and streptozotocin (STZ), T2DM+MCP group (mice received 100 mg/kg/day MCP following T2DM induction), and MCP group (mice received 100 mg/kg/day). After 4 weeks, kidney weight, blood glucose level, serum kidney function tests, histopathological structure alterations, oxidative stress, inflammation, apoptosis, and fibrosis parameters were determined in renal tissues. Our findings demonstrated that MCP treatment reduced blood glucose levels, renal histological damage, and restored kidney weight and kidney function tests. Additionally, MCP reduced malondialdehyde level and restored glutathione level, and catalase activity. MCP demonstrated a notable reduction in inflammatory and apoptosis mediators TNF-α, iNOS, TGF-βRII and caspase-3. Overall, MCP could alleviate renal injury in an experimental model of DN by suppressing renal oxidative stress, inflammation, fibrosis, and apoptosis mediators.

Diabetes and high-glucose could upregulate the expression of receptor for activated C kinase 1 in retina

BACKGROUND

Diabetic retinopathy (DR) is a major ocular complication of diabetes mellitus, leading to visual impairment. Retinal pigment epithelium (RPE) injury is a key component of the outer blood retinal barrier, and its damage is an important indicator of DR. Receptor for activated C kinase 1 (RACK1) activates protein kinase C-ε (PKC-ε) to promote the generation of reactive oxygen species (ROS) in RPE cells, leading to apoptosis. Therefore, we hypothesize that the activation of RACK1 under hypoxic/high-glucose conditions may promote RPE cell apoptosis by modulating PKC-ε/ROS, thereby disrupting the barrier effect of the outer blood retinal barrier and contributing to the progression of DR.

AIM

To investigate the role and associated underlying mechanisms of RACK1 in the development of early DR.

METHODS

In this study, Sprague-Dawley rats and adult RPE cell line-19 (ARPE-19) cells were used as in vivo and in vitro models, respectively, to explore the role of RACK1 in mediating PKC-ε in early DR. Furthermore, the impact of RACK1 on apoptosis and barrier function of RPE cells was also investigated in the former model.

RESULTS

Streptozotocin-induced diabetic rats showed increased apoptosis and up-regulated expression of RACK1 and PKC-ε proteins in RPE cells following a prolonged modeling. Similarly, ARPE-19 cells exposed to high glucose and hypoxia displayed elevated mRNA and protein levels of RACK1 and PKC-ε, accompanied by an increases in ROS production, apoptosis rate, and monolayer permeability. However, silencing RACK1 significantly downregulated the expression of PKC-ε and ROS, reduced cell apoptosis and permeability, and protected barrier function.

CONCLUSION

RACK1 plays a significant role in the development of early DR and might serve as a potential therapeutic target for DR by regulating RPE apoptosis and barrier function.

Neuroprotective role of plumbagin on eye damage induced by high-sucrose diet in adult fruit fly Drosophila melanogaster

The natural compound plumbagin has a wide range of pharmacological and potential therapeutic activities, although its role in neuroretina degeneration is unknown. Here we evaluated the effects of plumbagin on retina homeostasis of the fruit fly Drosophila melanogaster fed with high glucose diet, a model of hyperglycemia-induced eye impairment to study the pathophysiology of diabetic retinopathy at the early stages. To this aim, the visual system of flies orally administered with plumbagin has been analyzed at structural, functional, and molecular/cellular level as for instance neuronal apoptosis/autophagy dysregulation and oxidative stress-related signals. Our results demonstrated that plumbagin ameliorates the visual performance of hyperglycemic flies. Drosophila eye-structure, clearly altered by hyperglycemia, i.e. defects of the pattern of ommatidia, irregular rhabdomeres, vacuoles, damaged mitochondria, and abnormal phototransduction units were rescued, at least in part, by plumbagin. In addition, it reactivated autophagy, decreased the presence of cell death/apoptotic features, and exerted antioxidant effects in the retina. In terms of mechanisms favoring death/survival ratio, Nrf2 signaling activation may be one of the strategies by which plumbagin reduced redox unbalance mainly increasing the levels of glutathione-S-transferase. Likewise, plumbagin may act additively and/or synergistically inhibiting the mitochondrial-endoplasmic reticulum stress and unfolded protein response pathways, which prevented neuronal impairment and eye damage induced by reactive oxygen species. These results provide an avenue for further studies, which may be helpful to develop novel therapeutic candidates and drug targets against eye neurotoxicity by high glucose, a key aspect in retinal complications of diabetes.

Prolonged Exposure to High Glucose Induces Premature Senescence Through Oxidative Stress and Autophagy in Retinal Pigment Epithelial Cells

Chronic hyperglycemia involves persistent high-glucose exposure and correlates with retinal degeneration. It causes various diseases, including diabetic retinopathy (DR), a major cause of adult vision loss. Most in vitro studies have investigated the damaging short-term effects of high glucose exposure on retinal pigment epithelial (RPE) cells. DR is also a severe complication of diabetes. In this study, we established a model with prolonged high-glucose exposure (15 and 75 mM exogenous glucose for two months) to mimic RPE tissue pathophysiology in patients with hyperglycemia. Prolonged high-glucose exposure attenuated glucose uptake and clonogenicity in ARPE-19 cells. It also significantly increased reactive oxygen species levels and decreased antioxidant protein (superoxide dismutase 2) levels in RPE cells, possibly causing oxidative stress and DNA damage and impairing proliferation. Western blotting showed that autophagic stress, endoplasmic reticulum stress, and genotoxic stress were induced by prolonged high-glucose exposure in RPE cells. Despite a moderate apoptotic cell population detected using the Annexin V-staining assay, the increases in the senescence-associated proteins p53 and p21 and SA-β-gal-positive cells suggest that prolonged high-glucose exposure dominantly sensitized RPE cells to premature senescence. Comprehensive next-generation sequencing suggested that upregulation of oxidative stress and DNA damage-associated pathways contributed to stress-induced premature senescence of ARPE-19 cells. Our findings elucidate the pathophysiology of hyperglycemia-associated retinal diseases and should benefit the future development of preventive drugs. Prolonged high-glucose exposure downregulates glucose uptake and oxidative stress by increasing reactive oxygen species (ROS) production through regulation of superoxide dismutase 2 (SOD2) expression. Autophagic stress, ER stress, and DNA damage stress (genotoxic stress) are also induced by prolonged high-glucose exposure in RPE cells. Consequently, multiple stresses induce the upregulation of the senescence-associated proteins p53 and p21. Although both apoptosis and premature senescence contribute to high glucose exposure-induced anti-proliferation of RPE cells, the present work shows that premature senescence rather than apoptosis is the dominant cause of RPE degeneration, eventually leading to the pathogenesis of DR.

Comprehensive analysis of ferritinophagy-related genes and immune infiltration landscape in diabetic retinopathy

Background

Diabetic retinopathy (DR) is deemed a microangiopathy and neurodegenerative disorder, which is a primary reason of visual impairment in the world. Ferritinophagy is a critical regulator of ferroptosis and has a vital part in the etiopathogenesis of DR. Nevertheless, its molecular mechanism in DR remains to be expounded.

Methods

The GSE146615 dataset was adopted to identify ferritinophagy-related differentially expressed genes (FRDEGs). The interactions and biological functions of the genes were described by means of functional enrichment analysis (FEA). The enriched gene sets were analyzed utilizing gene set enrichment analysis (GSEA) and gene set variation analysis (GSVA). Identification of hub genes was performed utilizing protein-protein interaction (PPI) analysis. mRNA-miRNA, mRNA-transcription factors (TF), mRNA-drugs, mRNA-RNA-binding proteins (RBP) interaction networks were constructed. In addition, datasets GSE60436 and GSE94019 were utilized for validation. The diagnostic performance of FRDEGs was assessed by means of receiver-operating characteristic curve monofactor analysis, followed by immune infiltration analysis. Lastly, quantitative real-time polymerase chain reaction (qRT-PCR) was implemented to analyze the validation of genes.

Results

In total, the identification of eight FRDEGs was completed utilizing differential expression analysis. FEA mainly implicated the autophagy of mitochondrion, mitochondrion disassembly, autophagosome assembly, and organization pathways. GSEA and GSVA mainly implicated the interferon alpha response, ultraviolet response up, interferon gamma response, apical junction, pical surface, and allograft rejection pathways. BECN1 and HERC2 displayed high diagnostic accuracies in validation sets. Immune infiltration analysis revealed that several immune cells related to ferritinophagy may be play potential roles in DR. Finally, qRT-PCR was utilized to validate the upregulated expression of BECN1 as well as the downregulated expression of BCAT2 and ATG7 in the DR model.

Conclusion

BECN1, HERC2, ATG7, and BCAT2 act as potential biomarkers for DR and might regulate ferritinophagy and the immune microenvironment to influence its development and progression. This research can provide new insights into pathogenesis of DR related to ferritinophagy.

Palliative Role of Zamzam Water against Cyclosporine-Induced Nephrotoxicity through Modulating Autophagy and Apoptosis Crosstalk

Cyclosporine (CsA) is considered one of the main components of treatment protocols for organ transplantation owing to its immunosuppressive effect. However, its use is very restricted due to its nephrotoxic effect. ZW is an alkaline fluid rich in various trace elements and has a great ability to stimulate antioxidant processes. This study aimed to investigate the possible mitigating effect of ZW on CsA-induced nephrotoxicity and its underlying mechanisms. Forty rats were allocated into four groups (n = 10): a control group, ZW group, cyclosporine A group (injected subcutaneously (SC) with CsA (20 mg/kg/day)), and cyclosporine A+ Zamzam water group (administered CsA (SC) and ZW as their only drinking water (100 mL/cage/day) for 21 days). Exposure to CsA significantly (p < 0.001) increased the serum creatinine level, lipid peroxidation marker level (malondialdehyde; MDA), and the expression of apoptotic markers procaspase-8, caspase-8, caspase- 9, calpain, cytochrome c, caspas-3, P62, and mTOR in renal tissues. Meanwhile, it markedly decreased (p< 0.001) the autophagic markers (AMPK, ULK-I, ATag5, LC3, and Beclin-1), antiapoptotic Bcl-2, and antioxidant enzymes. Moreover, the administration of CsA caused histological alterations in renal tissues. ZW significantly (p < 0.001) reversed all the changes caused by CsA and conclusively achieved a positive outcome in restraining CsA-induced nephrotoxicity, as indicated by the restoration of the histological architecture, improvement of renal function, inhibition of apoptosis, and enhancement of autophagy via the AMPK/mTOR pathway.

Identification of critical autophagy-related proteins in diabetic retinopathy: A multi-dimensional computational study

Diabetic retinopathy (DR) is a common consequence of diabetes mellitus and a primary cause of visual impairment in middle-aged and elderly individuals. DR is susceptible to cellular degradation facilitated by autophagy. In this study, we have employed a multi-layer relatedness (MLR) approach to uncover novel autophagy-related proteins involved in DR. The objective of MLR is to determine the relatedness of autophagic and DR proteins by incorporating both expression and prior-knowledge-based similarities. We constructed a prior knowledge-based network and identified the topologically significant novel disease-related candidate autophagic proteins (CAPs). Then, we evaluated their significance in a gene co-expression and a differentially-expressed gene (DEG) network. Finally, we investigated the proximity of CAPs to the known disease-related proteins. Leveraging this methodology, we identified three crucial autophagy-related proteins, TP53, HSAP90AA1, and PIK3R1, which can influence the DR interactome in various layers of heterogeneity of clinical manifestations. They are strongly related to multiple detrimental characteristics of DR, such as pericyte loss, angiogenesis, apoptosis, and endothelial cell migration, and hence may be used to prevent or delay the progression and development of DR. We evaluated one of the identified targets, TP53, in a cell-based model and found that its inhibition resulted in reduced angiogenesis in high glucose condition required to control DR.

Autophagy and senescence of rat retinal precursor cells under high glucose

Backgrounds

Diabetic retinopathy (DR) is a common diabetic ocular disease characterized by retinal ganglion cell (RGC) changes. An abnormal environment, hyperglycemia, may progressively alter the structure and function of RGCs, which is a primary pathological feature of retinal neurodegeneration in DR. Accumulated studies confirmed autophagy and senescence play a vital role in DR; however, the underlying mechanisms need to be clarified.

Methods

This study included the microarray expression profiling dataset GSE60436 from Gene Expression Omnibus (GEO) to conduct the bioinformatics analysis. The R software was used to identify autophagy-related genes (ARGs) that were differentially expressed in fibrovascular membranes (FVMs) and normal retinas. Co-expression and tissue-specific expression were elicited for the filtered genes. The genes were then analyzed by ontology (GO) enrichment analysis, Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis and Gene Set Enrichment Analysis (GSEA). R28 cells were cultured with high glucose, detected by reverse transcription-quantitative (RT-qPCR) and stained by apoptosis kit.

Results

In the retina, 31 differentially expressed ARGs (24 up-regulated genes) were discovered and enriched. The enrichment results revealed that differentially expressed ARGs were significantly enriched in autophagy, apoptosis, aging, and neural function. Four hub genes (i.e., TP53, CASP1, CCL2, and CASP1) were significantly up-regulated. Upregulation of cellular autophagy and apoptosis level was detected in the hyperglycemia model in vitro.

Conclusions

Our results provide evidence for the autophagy and cellular senescence mechanisms involved in retinal hyperglycemia injury, and the protective function of autophagy is limited. Further study may favour understanding the disease progression and neuroprotection of DR.

Autophagy-nutrient sensing pathways in diabetic complications

The incidence of diabetes has been increasing in recent decades which is affecting the population of both, developed and developing countries. Diabetes is associated with micro and macrovascular complications which predominantly result from hyperglycemia and disrupted metabolic pathways. Persistent hyperglycemia leads to increased reactive oxygen species (ROS) generation, formation of misfolded and abnormal proteins, and disruption of normal cellular functioning. The inability to maintain metabolic homeostasis under excessive energy and nutrient input, which induces insulin resistance, is a crucial feature during the transition from obesity to diabetes. According to various study reports, redox alterations, intracellular stress and chronic inflammation responses have all been linked to dysregulated energy metabolism and insulin resistance. Autophagy has been considered a cleansing mechanism to prevent these anomalies and restore cellular homeostasis. However, disrupted autophagy has been linked to the pathogenesis of metabolic disorders such as obesity and diabetes. Recent studies have reported that the regulation of autophagy has a beneficial role against these conditions. When there is plenty of food, nutrient-sensing pathways activate anabolism and storage, but the shortage of food activates homeostatic mechanisms like autophagy, which mobilises internal stockpiles. These nutrient-sensing pathways are well conserved in eukaryotes and are involved in the regulation of autophagy which includes SIRT1, mTOR and AMPK. The current review focuses on the role of SIRT1, mTOR and AMPK in regulating autophagy and suggests autophagy along with these nutrient-sensing pathways as potential therapeutic targets in reducing the progression of various diabetic complications.

Thioredoxin-interacting protein in diabetic retinal neurodegeneration: A novel potential therapeutic target for diabetic retinopathy

Diabetic retinopathy (DR) is a common complication of diabetes mellitus and has been considered a microvascular disease for a long time. However, recent evidence suggests that diabetic retinal neurodegeneration (DRN), which manifests as neuronal apoptosis, a decrease in optic nerve axons, and reactive gliosis, occurs prior to retinal microvascular alterations. Thioredoxin-interacting protein (TXNIP) is an endogenous inhibitor of thioredoxin (Trx), and it acts by inhibiting its reducing capacity, thereby promoting cellular oxidative stress. In addition, it participates in regulating multiple signaling pathways as a member of the α-arrestin family of proteins. Accumulating evidence suggests that TXNIP is upregulated in diabetes and plays a pivotal role in the pathophysiological process of DR. In this review, we summarized the role of TXNIP in DRN, aiming to provide evidence for DR treatment in the future.

Research progress on the relationship between autophagy and chronic complications of diabetes

Diabetes is a common metabolic disease whose hyperglycemic state can induce diverse complications and even threaten human health and life security. Currently, the treatment of diabetes is restricted to drugs that regulate blood glucose and have certain accompanying side effects. Autophagy, a research hotspot, has been proven to be involved in the occurrence and progression of the chronic complications of diabetes. Autophagy, as an essential organismal defense mechanism, refers to the wrapping of cytoplasmic proteins, broken organelles or pathogens by vesicles, which are then degraded by lysosomes to maintain the stability of the intracellular environment. Here, we review the relevant aspects of autophagy and the molecular mechanisms of autophagy in diabetic chronic complications, and further analyze the impact of improving autophagy on diabetic chronic complications, which will contribute to a new direction for further prevention and treatment of diabetic chronic complications.

MitoTEMPOL Inhibits ROS-Induced Retinal Vascularization Pattern by Modulating Autophagy and Apoptosis in Rat-Injected Streptozotocin Model

Diabetic retinopathy leads to retinal malfunction, blindness, and reduced quality of life in adult diabetes patients. The involvement of reactive oxygen species (ROS) regulation stimulated by high blood glucose levels opens the opportunity for ROS modulator agents such as MitoTEMPOL. This study aims to explore the effect of MitoTEMPOL on ROS balance that may be correlated with retinal vascularization pattern, autophagy, and apoptosis in a streptozotocin-induced rat model. Four groups of male Wistar rats (i.e., control, TEMPOL (100 mg/kg body weight [BW]), diabetic (streptozotocin, 50 mg/kg BW single dose), and diabetic + TEMPOL; n = 5 for each group) were used in the study. MitoTEMPOL was given for 5 weeks, followed by funduscopy, and gene and protein expression were explored from the rat’s retina. Streptozotocin injection decreased bodyweight and increased food and water intake, as well as fasting blood glucose. The results showed that MitoTEMPOL reduced retinal vascularization pattern and decreased superoxide dismutase gene expression and protein carbonyl, caspase 3, and caspase 9 protein levels. A modulation of autophagy in diabetes that was reversed in the diabetic + TEMPOL group was found. In conclusion, MitoTEMPOL modulation on autophagy and apoptosis contributes to its role as a potent antioxidant to prevent diabetic retinopathy by inhibiting ROS-induced retinal vascularization patterns.

Investigation of the Renal Protective Effect of Combined Dietary Polyphenols in Streptozotocin-Induced Diabetic Aged Rats

Natural polyphenols are widely reported to have a large range of pharmacological properties, especially antioxidant activities and free radical scavenging capacities. In this study, we investigate the effects of naringin, chlorogenic acid, and quercetin mixtures (NCQ) on renal fibrosis in streptozotocin (STZ)-induced diabetic aged rats and its underlying mechanisms for ten consecutive weeks. The oxidative defense system in the kidneys of treated rats was found to be improved. Several biomarkers were investigated including the blood urea nitrogen, creatinine, and uric acid. Moreover, antioxidant parameters were evaluated and we found that superoxide dismutase, catalase, glutathione peroxidase, Na⁺-K⁺-ATPase activities, the nitric oxide production, the protein carbonyl, the advanced oxidation protein products, lipid peroxidation, and reduced glutathione levels were all significantly balanced and close to control values. In addition, NCQ restored renal injuries and fibrosis as assessed by histological method and molecular biology investigation of the matrix metalloproteinase, the transforming growth factor-beta TGF-β, the tumor necrosis factor TNFα, and p53 expression. Our study proposes the NCQ combination as potential plant-derived bioactive compounds to prevent diabetic nephropathy.

The impact of zinc on the molecular signaling pathways in the diabetes disease

Since there's been an upsurge in people with diabetes or pre-diabetes conditions, many studies have been conducted to evaluate approaches for reducing the complications of diabetes. One of the most common therapeutic elements suggested for this purpose is zinc (Zn). Zn has long been shown to positively improve complications of both type 1 and type 2 diabetes. This review aims to provide comprehensive information about the influence of Zn on the various signaling pathways in multiple tissues with diabetic conditions, with great attention to the treatment period and effective dose of Zn.

CircFAT1 regulates retinal pigment epithelial cell pyroptosis and autophagy via mediating m6A reader protein YTHDF2 expression in diabetic retinopathy

Diabetic retinopathy (DR) is a serious blinding complication of diabetes. At present, the therapeutic intervention effect is limited. We aimed to investigate the circRNA expression profiles in retinal proliferative fibrovascular membranes of patients with DR and explore the effect of circFAT1 on pyroptosis and autophagy of high glucose (HG)-induced retinal pigment epithelial (RPE) cells and its molecualr mechanism. In this study, circRNA sequencing was performed to determine the expression profiles of circRNAs in DR patients. The expression of circFAT1 was measured by qRT-PCR. Cell counting kit-8, transmission electron microscope, western blot, immunofluorescence and enzyme-linked immunosorbent assay were conducted to explore the roles of HG and circFAT1 in RPE cell pyroptosis and autophagy. RNA pull down was used to determine the binding protein of circFAT1. Our data showed that HG significantly reduced the viability of RPE cells, inhibited cell autophagy and contributed to cell pyroptosis. In addition, a total of 189 differentially expressed circRNAs (DEcircRNAs) were identified between DR patients and non-DR patients, including 93 upregulated and 96 downregulated DEcircRNAs in the retinal proliferative fibrovascular membranes of DR patients. Pathway analysis showed that DEcircRNAs were mainly involved in MAPK signaling pathway, TGF-beta signaling pathway and adherens junction. Moreover, circFAT1 was significantly downregulated in retinal proliferative fibrovascular membranes of DR patients and HG-induced RPE cells. CircFAT1 overexpression remarkably enhanced the expression of LC3B, while reduced the expression of GSDMD in HG-induced RPE cells. RNA pull down combined with western blot analysis indicated that circFAT1 bound to m6A reader YTHDF2. YTHDF2 overexpression significantly increased the protein expression of LC3B in HG-induced RPE cells. In summary, circFAT1 promoted autophagy and inhibited pyroptosis of RPE cells induced by HG, and could combine with YTHDF2. This study provides new ideas for DR prevention and treatment.

TFEB-Mediated Lysosomal Restoration Alleviates High Glucose-Induced Cataracts Via Attenuating Oxidative Stress

Purpose

Diabetic cataract (DC) is a visual disorder arising from diabetes mellitus (DM). Autophagy, a prosurvival intracellular process through lysosomal fusion and degradation, has been implicated in multiple diabetic complications. Herein, we performed in vivo and in vitro assays to explore the specific roles of the autophagy-lysosome pathway in DC.

Methods

Streptozotocin-induced DM and incubation in high glucose (HG) led to rat lens opacification. Protein Simple Wes, Western blot, and immunoassay were utilized to investigate autophagic changes in lens epithelial cells (LECs) and lens fiber cells (LFCs). RNA-sequencing (RNA-seq) was performed to explore genetic changes in the lenses of diabetic rats. Moreover, autophagy-lysosomal functions were examined using lysotracker, Western blot, and immunofluorescence analyses in HG-cultured primary rabbit LECs.

Results

First, DM and HG culture led to fibrotic LECs, swelling LFCs, and eventually cataracts. Further analysis showed aberrant autophagic degradation in LECs and LFCs during cataract formation. RNA-seq data revealed that the differentially expressed genes (DEGs) were enriched in the lysosome pathway. In primary LECs, HG treatment resulted in decreased transcription factor EB (TFEB) and cathepsin B (CTSB) activity, and increased lysosomal size and pH values. Moreover, TFEB-mediated dysfunctional lysosomes resulted from excessive oxidative stress in LECs under HG conditions. Furthermore, TFEB activation by curcumin analog C1 alleviated HG-induced cataracts through enhancing lysosome biogenesis and activating protective autophagy, thereby attenuating HG-mediated oxidative damage.

Conclusions

In summary, we first identified that ROS-TFEB-dependent lysosomal dysfunction contributed to autophagy blockage in HG-induced cataracts. Additionally, TFEB-mediated lysosomal restoration might be a promising therapeutic method for preventing and treating DC through mitigating oxidative stress.

Shabyar Ameliorates High Glucose Induced Retinal Pigment Epithelium Injury Through Suppressing Aldose Reductase and AMPK/mTOR/ULK1 Autophagy Pathway

Shabyar (SBA) is a traditional medicine formula for relieving vision loss caused by factors including diabetic retinopathy (DR) in clinics. However, the mechanism of it on retina protective effect still unclear. The present study aimed to investigate whether its protective effect was related to aldose reductase (AR) inhibition and retinal pigment epithelial cell injury mediated by autophagy or not. Human retinal pigment epithelial cells (ARPE-19) induced by high glucose was used as a model in vitro, with Epalrestat (EPL, AR inhibitor) and Difrarel (DFR, DR therapeutic drug) as positive controls. Western blotting and Polyol pathway products assay showed that SBA reduced the expression of AR protein and the content of ROS, and sorbitol, increased the level of Na⁺-K⁺-ATPase and alleviated cell edema. Western blotting and DCFH-DA probe assay showed that SBA decreased pAMPK/AMPK and pULK1/ULK1 which associated with autophagy initiation, down-regulated Beclin-1, Atg3, Atg5, Atg7, LC3 II and Bax/Bcl2 ratio, and up-regulated pmTOR/mTOR, SQSTM1/p62 and mitochondrial membrane potential (MMP), reduces intracellular autophagosomes. Real-Time PCR assay showed that SBA had no significant effect on mRNA expression of AR and mTOR. These data demonstrated that SBA treatment inhibits the autophagy of ARPE-19 through the AMPK/mTOR/ULK1 signaling pathway, and reduced early-stage apoptosis occurred by high glucose. These findings reveal the protective role and mechanism of SBA on retinal pigment epithelium, and provide experimental basis for the clinical application of SBA in the treatment of DR.

Quercetin: an effective polyphenol in alleviating diabetes and diabetic complications

Various studies, especially in recent years, have shown that quercetin has beneficial therapeutic effects in various human diseases, including diabetes. Quercetin has significant anti-diabetic effects and may be helpful in lowering blood sugar and increasing insulin sensitivity. Quercetin appears to affect many factors and signaling pathways involved in insulin resistance and the pathogenesis of type 2 of diabetes. TNFα, NFKB, AMPK, AKT, and NRF2 are among the factors that are affected by quercetin. In addition, quercetin can be effective in preventing and ameliorating the diabetic complications, including diabetic nephropathy, cardiovascular complications, neuropathy, delayed wound healing, and retinopathy, and affects the key mechanisms involved in the pathogenesis of these complications. These positive effects of quercetin may be related to its anti-inflammatory and anti-oxidant properties. In this article, after a brief review of the pathogenesis of insulin resistance and type 2 diabetes, we will review the latest findings on the anti-diabetic effects of quercetin with a molecular perspective. Then we will review the effects of quercetin on the key mechanisms of pathogenesis of diabetes complications including nephropathy, cardiovascular complications, neuropathy, delayed wound healing, and retinopathy. Finally, clinical trials investigating the effect of quercetin on diabetes and diabetes complications will be reviewed.

Vitamin D Impacts on Skeletal Muscle Dysfunction in Patients with COPD Promoting Mitochondrial Health

Skeletal muscle dysfunction is frequently associated with chronic obstructive pulmonary disease (COPD), which is characterized by a permanent airflow limitation, with a worsening respiratory disorder during disease evolution. In COPD, the pathophysiological changes related to the chronic inflammatory state affect oxidant–antioxidant balance, which is one of the main mechanisms accompanying extra-pulmonary comorbidity such as muscle wasting. Muscle impairment is characterized by alterations on muscle fiber architecture, contractile protein integrity, and mitochondrial dysfunction. Exogenous and endogenous sources of reactive oxygen species (ROS) are present in COPD pathology. One of the endogenous sources of ROS is represented by mitochondria. Evidence demonstrated that vitamin D plays a crucial role for the maintenance of skeletal muscle health. Vitamin D deficiency affects oxidative stress and mitochondrial function influencing disease course through an effect on muscle function in COPD patients. This review will focus on vitamin-D-linked mechanisms that could modulate and ameliorate the damage response to free radicals in muscle fibers, evaluating vitamin D supplementation with enough potent effect to contrast mitochondrial impairment, but which avoids potential severe side effects.

Sirt5-mediated desuccinylation of OPTN protects retinal ganglion cells from autophagic flux blockade in diabetic retinopathy

Retinal neurodegeneration develops early in the course of diabetic retinopathy (DR), and our previous research showed that succinate accumulation results in retinal ganglion cells (RGCs) dysfunction in the retinas of rats with DR. Succinate can enhance lysine succinylation, but the succinylation of DR is not well understood. In this study, we investigated the role of the succinylome in DR and identified the key factor in this process. TMT labeling and LC–MS/MS analysis were combined to quantify the differentially succinylated proteins between vitreous humor (VH) samples from DR and non-DR patients. A total of 74 sites in 35 proteins were differentially succinylated between DR and non-DR vitreous humor samples, among which succinylation of the K108 site of optineurin (OPTN K108^su) in the defense response was enriched by GO analysis based on the biological process category. Then, using a streptozotocin (STZ)-induced diabetic rat model, R28 cells and primary rat RGCs (rRGCs), we demonstrated that OPTN underwent lysine succinylation in the retinas of rats with DR and that OPTN K108^su mediated autophagic flux blockade under high-glucose (HG) conditions. Sirt5 can desuccinylate OPTN K108^su, thus protecting RGCs function from high glucose-induced RGCs autophagic flux blockade in the diabetic retina. Overall, desuccinylation of OPTN is an essential adaptive mechanism for ameliorating autophagic flux blockade in RGCs under DR conditions, and targeting the Sirt5-desuccK108-OPTN axis may thus open an avenue for therapeutic intervention in RCGs dysfunction.

Arjunolic acid from Cyclocarya paliurus ameliorates diabetic retinopathy through AMPK/mTOR/HO-1 regulated autophagy pathway

ETHNOPHARMACOLOGICAL RELEVANCE

Cyclocarya paliurus (CP) is a traditional Chinese herb and possesses a variety of biological activities including anti-hyperglycemia, anti-hyperlipidemia, antioxidant and anti-inflammation. Arjunolic acid (AA) is an abundant and bioactive ingredient in CP that shows significant protection against many metabolic diseases such as diabetic complication. Diabetic retinopathy (DR) is a serious complication of diabetes and may lead to vision loss. However, the protective effects and underlying mechanisms of AA against DR is not still understood.

AIM OF THE STUDY

We aimed to investigate whether AA activates AMPK/mTOR/HO-1 regulated autophagy pathway to alleviate DR.

MATERIALS AND METHODS

In the study, the STZ-induced diabetic model of rats was established, and AA with 10 and 30 mg/kg dosages was given orally for ten weeks to investigate their effect on retinal injury of DR. H₂O₂-induced ARPE-19 cells were applied to evaluate anti-apoptosis and anti-oxidant effect of AA.

RESULTS

The results revealed that AA could prevent STZ-induced weight loss and increase the retinal thickness and nuclei counts. The level of HO-1 protein was upregulated both in vivo and in vitro. In addition, AA prevented retinal damage and cell apoptosis through the AMPK-mTOR-regulated autophagy pathway. Furthermore, anti-apoptosis capacity, as well as the expression of HO-1 and LC3 protein, were effectively locked by AMPK inhibitor dorsomorphin dihydrochloride (compound C).

CONCLUSIONS

This finding implies that AA may be a promising candidate drug by protecting retinal cells from STZ-induced oxidative stress and inflammation through the AMPK/mTOR/HO-1 regulated autophagy pathway.

Procyanidin protects human retinal pigment epithelial cells from high glucose by inhibiting autophagy

PURPOSE

The damage of hyperglycemia to the retinal pigment epithelial (RPE) cells is a critical event in diabetic retinopathy (DR). Procyanidin (PC), a kind of polyphenol compounds, has shown to be effective in preventing and treating diabetes as well as its complications, in which autophagy disorder is involved in the pathological mechanism. However, it remains unclear whether PC can play a protective role in DR by regulating the autophagy of RPE. Here, the effect of PC on RPE under high glucose conditions and the role of autophagy were investigated.

MATERIALS AND METHODS

The cell viability of ARPE-19, a human RPE cell line, was detected by cell counting kit-8 (CCK-8) and the apoptosis rate was measured by flow cytometry. The protein expressions of apoptosis markers, including Bax, Bcl-2, and Caspase-3, as well as autophagy markers including LC3, p62, p53, and mTOR were detected by Western blotting. Autophagic flux in ARPE-19 cells was detected by transfection with Ad-mCherry-GFP-LC3B.

RESULTS

Under high glucose conditions, the viability of ARPE-19 was decreased and the apoptosis rate increased, the protein expressions of Bax, Caspase-3, LC3-II/LC3-I, and p-p53 were all increased and the expressions of Bcl-2, p62, and p-mTOR decreased, and autophagic flux was increased compared with that of the controls. Treatment with PC weakened all these changes caused by high glucose. When rapamycin (RPM), an autophagy agonist was added, the cell viability of ARPE-19 by PC treatment was decreased while the apoptosis was increased.

CONCLUSIONS

Our findings indicate that through the p53/mTOR autophagy pathway, PC may protect RPE cells from high glucose-induced injury.

The interplay of autophagy and oxidative stress in the pathogenesis and therapy of retinal degenerative diseases

Oxidative stress is mainly caused by intracellular reactive oxygen species (ROS) production, which is highly associated with normal physiological homeostasis and the pathogenesis of diseases, particularly ocular diseases. Autophagy is a self-clearance pathway that removes oxidized cellular components and regulates cellular ROS levels. ROS can modulate autophagy activity through transcriptional and posttranslational mechanisms. Autophagy further triggers transcription factor activation and degrades impaired organelles and proteins to eliminate excessive ROS in cells. Thus, autophagy may play an antioxidant role in protecting ocular cells from oxidative stress. Nevertheless, excessive autophagy may cause autophagic cell death. In this review, we summarize the mechanisms of interaction between ROS and autophagy and their roles in the pathogenesis of several ocular diseases, including glaucoma, age-related macular degeneration (AMD), diabetic retinopathy (DR), and optic nerve atrophy, which are major causes of blindness. The autophagy modulators used to treat ocular diseases are further discussed. The findings of the studies reviewed here might shed light on the development and use of autophagy modulators for the future treatment of ocular diseases.

Identification and Validation of Autophagy-Related Genes in Diabetic Retinopathy

BACKGROUND

Diabetic retinopathy (DR) is one of the most common microvascular complications of diabetes, which is associated with damage of blood-retinal barrier and ischemia of retinal vasculature. It devastates visual acuity due to leakage of retinal vessels and aberrant pathological angiogenesis in diabetic patients. The etiology of DR is complex, accumulated studies have shown that autophagy plays an important role in the pathogenesis of DR, but its specific mechanism needs to be further studied.

METHODS

This study chose the online Gene Expression Omnibus (GEO) microarray expression profiling dataset GSE146615 to carry on the research. Autophagy-related genes that were potentially differentially expressed in DR were screened by R software. Then, the differentially expressed autophagy-related genes were analyzed by correlation analysis, tissue-specific gene expression, gene-ontology (GO) enrichment analysis, Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis and protein-protein interaction (PPI) network analysis. Finally, retinal pigment epithelial cell line (ARPE-19) incubated with high glucose (HG) was used to mimic the DR model, and the mRNA level of key genes was verified by quantitative real-time polymerase chain reaction (qRT-PCR) in vitro.

RESULTS

A total of 23 differentially expressed autophagy-related genes (9 up-regulated genes and 14 down-regulated genes) were identified by differential expression analysis. The analysis of tissue-specific gene expression showed that these differentially expressed autophagy-related genes were enriched in the retina. GO and KEGG enrichment analysis showed that differentially expressed autophagy-related genes were significantly enriched in autophagy-related pathways such as regulation of autophagy and macroautophagy. Then 10 hub genes were identified by PPI network analysis and construction of key modules. Finally, qRT-PCR confirmed that the expression of MAPK3 in the DR model was consistent with the results of bioinformatics analysis of mRNA chip.

CONCLUSION

Through bioinformatics analysis, we identified 23 potential DR autophagy-related genes, among which the down-regulated expression of MAPK3 may affect the occurrence and development of DR by regulating autophagy. It provides a novel insight into the pathogenesis of DR.

Reciprocal interactions between gut microbiota and autophagy

A symbiotic relationship has set up between the gut microbiota and its host in the course of evolution, forming an interkingdom consortium. The gut offers a favorable ecological niche for microbial communities, with the whole body and external factors (e.g., diet or medications) contributing to modulating this microenvironment. Reciprocally, the gut microbiota is important for maintaining health by acting not only on the gut mucosa but also on other organs. However, failure in one or another of these two partners can lead to the breakdown in their symbiotic equilibrium and contribute to disease onset and/or progression. Several microbial and host processes are devoted to facing up the stress that could alter the symbiosis, ensuring the resilience of the ecosystem. Among these processes, autophagy is a host catabolic process integrating a wide range of stress in order to maintain cell survival and homeostasis. This cytoprotective mechanism, which is ubiquitous and operates at basal level in all tissues, can be rapidly down- or up-regulated at the transcriptional, post-transcriptional, or post-translational levels, to respond to various stress conditions. Because of its sensitivity to all, metabolic-, immune-, and microbial-derived stimuli, autophagy is at the crossroad of the dialogue between changes occurring in the gut microbiota and the host responses. In this review, we first delineate the modulation of host autophagy by the gut microbiota locally in the gut and in peripheral organs. Then, we describe the autophagy-related mechanisms affecting the gut microbiota. We conclude this review with the current challenges and an outlook toward the future interventions aiming at modulating host autophagy by targeting the gut microbiota.

Curcumin is a Potential Adjuvant to Alleviates Diabetic Retinal Injury via Reducing Oxidative Stress and Maintaining Nrf2 Pathway Homeostasis

Curcumin is a natural polyphenol compound with anti-diabetic, anti-oxidative, and anti-inflammatory effects. Although many studies have reported the protective effect of curcumin in diabetes mellitus or diabetic nephropathy, there is a lack of research on curcumin in diabetic retinopathy. The purpose of this study was to investigate the therapeutic effects of curcumin on the diabetic retinal injury. Streptozotocin (STZ)-induced diabetic rats (60, n = 12 each) were respectively given curcumin orally (200 mg/kg/day), insulin subcutaneously (4–6 IU/day), and combined therapy with curcumin and insulin for 4 weeks. Retinal histopathological changes, oxidative stress markers, and transcriptome profiles from each group were observed. Curcumin, insulin, or combination therapy significantly reduced blood glucose, alleviated oxidative stress, and improved pathological damage in diabetic rats. Curcumin not only significantly reduced retinal edema but also had a better anti-photoreceptor apoptosis effect than insulin. In the early stage of diabetes, the enhancement of oxidative stress in the retina induced the adaptive activation of the nuclear factor E2-associated factor 2 (Nrf2) pathway. Treatment of curcumin alleviated the compensatory activation of the Nrf2 pathway induced by oxidative stress, by virtue of its antioxidant ability to transfer hydrogen atoms to free radicals. When curcumin combined with insulin, the effect of maintaining Nrf2 pathway homeostasis in diabetic rats was better than that of insulin alone. Transcriptomic analyses revealed that curcumin either alone, or combined with insulin, inhibited the AGE-RAGE signaling pathway and the extracellular matrix (ECM)-receptor interaction in the diabetic retina. Thus, at the early stage of diabetes, curcumin can be used to alleviate diabetic retinal injury through its anti-oxidative effect. If taking curcumin as a potential complementary therapeutic option in combination with antihyperglycemic agents, which would lead to more effective therapeutic outcomes against diabetic complications.

LncRNA ATP2B1-AS1 modulates endothelial permeability via regulating miR-4729/IQGAP2 axis in diabetic retinopathy

Aims/Introduction

Mounting evidence shows that long non‐coding RNAs (lncRNAs) are important to modulate the biological process of diabetic retinopathy (DR). We aimed to investigate the role of lncRNAs in DR and elucidate the exact mechanism.

Materials and Methods

Real‐time quantitative polymerase chain reaction was carried out to distinguish the lncRNA ATPase plasma membrane Ca²⁺ transporting 1 antisense RNA 1 (ATP2B1‐AS1) expression in DR patients and HG‐treated human retinal endothelial cells (HRECs). Dual‐luciferase reporter system was used to verify that ATP2B1‐AS1 could act as a microRNA (miR)‐4729 sponge, and miR‐4729 could bind to 3′UTR of IQ motif‐containing GTPase‐activating protein 2 (IQGAP2). Cell proliferation assay, wound healing migration assay, transwell assay, tube formation assay and immunofluorescence were used to investigate cell proliferation, migration and angiogenesis in HRECs.

Results

The present results showed that ATP2B1‐AS1 was downregulated in DR patients and high‐glucose‐induced HRECs. In gain‐ and loss‐of‐function assays, ATP2B1‐AS1 overexpression could significantly reduce cell proliferation, migration, angiogenesis and permeability induced by high glucose in vitro. Additionally, we carried out dual‐luciferase reporter experiments to determine that ATP2B1‐AS1 could act as a miR‐4729 sponge. ATP2B1‐AS1 overexpression could rescue miR‐4729 mimics and short hairpin RNA‐IQGAP2 induced cell proliferation, migration and angiogenesis in HRECs.

Conclusions

The present study showed that ATP2B1‐AS1 acted as a miR‐4729 sponge to regulate IQGAP2 reducing high‐glucose‐induced endothelial dysfunction in DR.

Downregulation of AMPK dependent FOXO3 and TFEB involves in the inhibition of autophagy in diabetic cataract

PURPOSE

Autophagy plays a crucial role in intracellular quality control of crystalline lens and AMPK has regulatory effect on autophagy. However, whether AMPK regulated autophagy is involved in diabetic cataract (DC) progression remains unknown. This study aims to investigate the AMPK-FOXO3 and AMPK-TFEB induced autophagy activity in DC patients.

MATERIALS AND METHODS

First, anterior capsule specimens from DC and age-related cataract (ARC) patients were obtained to compare the expression difference of autophagy-related genes. The phosphorylation levels of AMPK, AKT, and mTOR and the expression of FOXO3 and TFEB were measured. Then, human lens epithelial cells (LECs, SRA 01/04) were cultured with 30 mM or 5.5 mM glucose, and AMPK activator (AICAR) and inhibitor (Compound C) were applied to further investigate the regulatory role of AMPK on autophagy.

RESULTS

Compared with ARC patients, the expression of autophagy-related genes ATG5, FYCO1, ATG8, ATG12, Beclin1, and ULK1 in anterior capsules LECs of DC patients were significantly down-regulated. Meanwhile, AMPK and AMPK-dependent transcription factors, FOXO3 and TFEB were also inhibited. Similar results were found in high glucose (HG) treated SRA 01/04 model. Notably, this down-regulation of autophagy activity was rescued by AICAR in vitro, which was manifested by inhibition of AKT and mTOR phosphorylation and up-regulation of FOXO3, TFEB, Beclin1 and LC3B-II expression.

CONCLUSIONS

Down-regulation of AMPK-FOXO3 and AMPK-TFEB induced autophagy activity was found in both LECs of anterior capsule from DC patients and SRA 01/04 cells under HG condition, which may be the underlying mechanism of DC formation. Thus, targeting AMPK-induced autophagy may be a potential therapeutic approach for diabetic cataract.

Antioxidant, Anti-Inflammatory, and Immunomodulatory Properties of Tea-The Positive Impact of Tea Consumption on Patients with Autoimmune Diabetes

The physiological markers of autoimmune diabetes include functional disorders of the antioxidative system as well as progressing inflammation and the presence of autoantibodies. Even though people with type 1 diabetes show genetic predispositions facilitating the onset of the disease, it is believed that dietary factors can stimulate the initiation and progression of the disease. This paper analyses the possibility of using tea as an element of diet therapy in the treatment of type 1 diabetes. Based on information available in literature covering the last 10 years, the impact of regular tea consumption or diet supplements containing tea polyphenols on the oxidative status as well as inflammatory and autoimmune response of the organism was analyzed. Studies conducted on laboratory animals, human patients, and in vitro revealed positive effects of the consumption of tea or polyphenols isolated therefrom on the diabetic body. Few reports available in the literature pertain to the impact of tea on organisms affected by type 1 diabetes as most (over 85%) have focused on cases of type 2 diabetes. It has been concluded that by introducing tea into the diet, it is possible to alleviate some of the consequences of oxidative stress and inflammation, thus limiting their destructive impact on the patients' organisms, consequently improving their quality of life, regardless of the type of diabetes. Furthermore, elimination of inflammation should reduce the incidence of immune response. One should consider more widespread promotion of tea consumption by individuals genetically predisposed to diabetes, especially considering the drink's low price, easy availability, overall benefits to human health, and above all, the fact that it can be safely used over extended periods of time, regardless of the patient's age.

Protective role of vitamin D against oxidative stress in diabetic retinopathy

Diabetic retinopathy (DR) is a microvascular complication of diabetes mellitus. There is much evidence showing that a high level of mitochondrial overproduction of reactive oxygen species in the diabetic retina contributes in modifying cellular signalling and leads to retinal cell damage and finally to the development of DR pathogenesis. In the last few decades, it has been reported that vitamin D is involved in DR pathogenesis. Vitamin D, traditionally known as an essential nutrient crucial in bone metabolism, has also been proven to be a very effective antioxidant. It has been demonstrated that it modulates the production of advanced glycosylated end products, as well as several pathways including protein kinase C, the polyol pathway leading to the reduction of free radical formation. It prevents the translocation of nuclear factor kappa B, preventing the inflammatory response, acting as an immunomodulator, and modulates autophagy and apoptosis. In this review, we explore the molecular mechanisms by which vitamin D protects the eye from oxidative stress, in order to evaluate whether vitamin D supplementation may be useful to mitigate the deleterious effects of free radicals in DR.

Autophagy positively regulates Wnt signaling in mice with diabetic retinopathy

Diabetic retinopathy (DR) is a microvascular complication of diabetes. Aberrant Wnt signaling activation plays a pathological role in DR. However, the underlying mechanisms of aberrant Wnt signaling in DR remain unknown. Autophagy has been reported to be involved in the pathophysiology of DR. The present study aimed therefore to investigate the regulatory effects of autophagy on Wnt signaling in DR. Wnt signaling was activated in the retina of db/db mice combined with an increase in the expression of the autophagic proteins microtubule-associated protein 1A/1B-light chain 3 and beclin-1 and a decrease in the expression of the autophagic protein P62. Inhibition of autophagy by 3-methyladenin decreased Wnt signaling in diabetic retinas, indicating a potential association between Wnt signaling and autophagy. Rapamycin, an autophagy inducer, upregulated Wnt signaling in the retina of normal C57BL/6J mice. In cultured Müller cells, rapamycin induced autophagy and activated Wnt signaling, while chloroquine, an autophagy inhibitor, inhibited autophagy and downregulated Wnt signaling, suggesting that autophagy could regulate Wnt signaling in mice retina and retinal cells. In summary, this study demonstrated that autophagy may positively regulate Wnt signaling in diabetic retinas, indicating a potential mechanism of Wnt signaling upregulation in DR and a possible novel therapeutic target of DR.

Relationship of Hydroxychloroquine and Ophthalmic Complications in Patients with Type 2 Diabetes in Taiwan

The purpose of this study is to evaluate the relationship between hydroxychloroquine (HCQ) and diabetic retinopathy (DR) via the national health insurance research database (NHIRD) of Taiwan. All patients with newly diagnosed type 2 diabetes (n = 47,353) in the NHIRD (2000–2012) were enrolled in the study. The case group consists of participants with diabetic ophthalmic complications; 1:1 matching by age (±1 year old), sex, and diagnosis year of diabetes was used to provide an index date for the control group that corresponded to the case group (n = 5550). Chi-square test for categorical variables and Student’s t-test for continuous variables were used. Conditional logistic regression was performed to estimate the adjusted odds ratio (aOR) of DR. The total number of HCQ user was 99 patients (1.8%) in the case group and 93 patients (1.7%) in the control group. Patients with hypertension (aOR = 1.21, 95% CI = 1.11–1.31) and hyperlipidemia (aOR = 1.65, 95% CI = 1.52–1.79) significantly increased the risk of diabetic ophthalmic complications (p < 0.001). Conversely, the use of HCQ and the presence of rheumatoid diseases did not show any significance in increased risk of DR. HCQ prescription can improve systemic glycemic profile, but it does not decrease the risk of diabetic ophthalmic complications.

Relative Contribution of Different Mitochondrial Oxidative Phosphorylation Components to the Retinal Pigment Epithelium Barrier Function: Implications for RPE-Related Retinal Diseases

Disruption of retinal pigment epithelial (RPE) barrier integrity is involved in the pathology of several blinding retinal diseases including age-related macular degeneration (AMD) and diabetic retinopathy (DR), but the underlying causes and pathophysiology are not completely well-defined. Mitochondria dysfunction has often been considered as a potential candidate implicated in such a process. In this study, we aimed to dissect the role of different mitochondrial components; specifically, those of oxidative phosphorylation (OxPhos), in maintaining the barrier functionality of RPE. Electric cell-substrate impedance sensing (ECIS) technology was used to collect multi-frequency electrical impedance data to assess in real-time the barrier formation of the RPE cells. For this purpose, the human retinal pigment epithelial cell line-ARPE-19-was used and treated with varying concentrations of specific mitochondrial inhibitors that target different steps in OxPhos: Rotenone for complex I (the largest protein complex in the electron transport chain (ETC)); oligomycin for ATP synthase; and carbonyl cyanide-p-trifluoromethoxyphenyl hydrazone (FCCP) for uncoupling ATP synthesis from the accompanying ETC. Furthermore, data were modeled using the ECIS-Zθ software to investigate in depth the effects of these inhibitors on three separate barrier parameters: cell-cell interactions (Rb), cell-matrix interactions (α), and the cell membrane capacitance (Cm). The viability of ARPE-19 cells was determined by lactate dehydrogenase (LDH) Cytotoxicity Assay. The ECIS program's modeling demonstrated that FCCP and thus OxPhos uncoupling disrupt the barrier function in the ARPE-19 cells across all three components of the total resistance (Rb, α, and Cm) in a dose-dependent manner. On the other hand, oligomycin and thus ATP synthase inhibition mostly affects the ARPE-19 cells' attachment to their substrate evident by a significant decrease in α resistance in a dose-dependent manner, both at the end and throughout the duration of the experiment. On the contrary, rotenone and complex I inhibition mostly affect the ARPE-19 paracellular resistance Rb in a dose-dependent manner compared to basolateral resistance α or Cm. Our results clearly demonstrate differential roles for different mitochondrial components in maintaining RPE cell functionality in which uncoupling of OxPhos is a major contributing factor to the disruption barrier function. Such differences can be used in investigating gene expression as well as for screening of selective agents that improve the OxPhos coupling efficiency to be used in the therapeutic approach for treating RPE-related retinal diseases.

Nutraceutical Strategy to Counteract Eye Neurodegeneration and Oxidative Stress in Drosophila melanogaster Fed with High-Sugar Diet

Aberrant production of reactive oxygen species (ROS) is a common feature of damaged retinal neurons in diabetic retinopathy, and antioxidants may exert both preventive and therapeutic action. To evaluate the beneficial and antioxidant properties of food supplementation with Lisosan G, a powder of bran and germ of grain (Triticum aestivum) obtained by fermentation with selected lactobacillus and natural yeast strains, we used an in vivo model of hyperglycemia-induced retinal damage, the fruit fly Drosophila melanogaster fed with high-sucrose diet. Lisosan G positively affected the visual system of hyperglycemic flies at structural/functional level, decreased apoptosis, and reactivated protective autophagy at the retina internal network. Also, in high sucrose-fed Drosophila, Lisosan G reduced the levels of brain ROS and retina peroxynitrite. The analysis of oxidative stress-related metabolites suggested 7,8-dihydrofolate, uric acid, dihydroorotate, γ-L-glutamyl-L-cysteine, allantoin, cysteinyl-glycine, and quinolate as key mediators of Lisosan G-induced inhibition of neuronal ROS, along with the upregulation of glutathione system. Of note, Lisosan G may impact oxidative stress and the ensuing retinal cell death, also independently from autophagy, although the autophagy-ROS cross-talk is critical. This study demonstrated that the continuous supplementation with the alimentary integrator Lisosan G exerts a robust and multifaceted antioxidant effect on retinal neurons, thus providing efficacious neuroprotection of hyperglycemic eye.

Autophagy: A Novel Pharmacological Target in Diabetic Retinopathy

Autophagy is the major catabolic pathway involved in removing and recycling damaged macromolecules and organelles and several evidences suggest that dysfunctions of this pathway contribute to the onset and progression of central and peripheral neurodegenerative diseases. Diabetic retinopathy (DR) is a serious complication of diabetes mellitus representing the main preventable cause of acquired blindness worldwide. DR has traditionally been considered as a microvascular disease, however this concept has evolved and neurodegeneration and neuroinflammation have emerged as important determinants in the pathogenesis and evolution of the retinal pathology. Here we review the role of autophagy in experimental models of DR and explore the potential of this pathway as a target for alternative therapeutic approaches.

Autophagy dysregulation mediates the damage of high glucose to retinal pigment epithelium cells

AIM

To observe the role and mechanism of autophagy in retinal pigment epithelial cell (RPE) damaged by high glucose, so as to offer a new idea for the treatment of diabetic retinopathy (DR).

METHODS

ARPE-19, a human RPE cell line cultured in vitro was divided into the normal control (NC), autophagy inhibitor 3-methyladenine (3-MA), high-glucose (HG), and HG+3-MA groups. Cell viability was detected by CCK-8 assay and the apoptosis rate was measured by flow cytometry. The protein expressions of apoptosis markers, including Bax, Bcl-2, and Caspase-3, as well as autophagy marker including microtubule-related protein 1 light chain 3 (LC3), p62, and mechanistic target of rapamycin (mTOR) were detected by Western blotting. Autophagic flux was detected by transfection with Ad-mCherry-GFP-LC3B.

RESULTS

Under high glucose conditions, the viability of ARPE-19 was decreased, and the apoptosis rate increased, the protein expressions of Bax, Caspase-3, and LC3-II/LC3-I were all increased and the expressions of Bcl-2, p62 and p-mTOR decreased, and autophagic flux was increased compared with that of the controls. Treatment with 3-MA reversed all these changes caused by high glucose.

CONCLUSION

The current study demonstrates the mechanisms of cell damage of ARPE-19 through high glucose/mTOR/autophagy/apoptosis pathway, and new strategies for DR may be developed based on autophagy regulation to manage cell death of RPE cells.

Expression of autophagy and apoptosis-related factors in the periodontal tissue of experimental diabetic rats: a histomorphometric, microtomographic and immunohistochemical study

Objective

This study aimed to investigate the expression of autophagy-related factors microtubule-associated protein l light chain 3 (LC3) and the apoptosis-related factors BCL2-associated X protein (Bax) and B cell lymphoma-2 (Bcl-2) in the periodontal tissue of experimental diabetic rats. These data were used to explore the potential mechanism in diabetes-induced periodontal tissue lesions.

Methods

A total of 32 Sprague Dawley (SD) rats were randomly assigned into diabetes (group D, n = 16) and control groups (group N, n = 16). The diabetic group was induced by intraperitoneal injection of 1% streptozotocin (STZ, 60 mg/kg) and the control group was injected with citrate buffer (0.1mol/L). Rats were sacrificed after 4 and 8 weeks of feeding and collected as D1, N1 groups and D2, N2 groups, and the maxilla were retained for analysis. The changes in periodontal tissue structure were observed by hematoxylin-eosin (HE) staining. The expression and distribution of LC3, Bax and Bcl-2 in the periodontium of the rats was detected by immunohistochemical (SP) staining.

Results

Diabetic rats showed several changes compared to control animals including sparse alveolar bone trabecular structure, loss of the lamina dura and absorption of the local alveolar bone. The positive expression level of LC3 in the gingival epithelial, periodontal ligament and alveolar bone of group D1 was significantly higher than in the N1, N2 and D2 groups (P < 0.05). The level of Bax expression in the group D2 rats was significantly higher than those in the N1, N2 and D1 groups (P < 0.05), while the positive degree of Bcl-2 was significantly lower than those of other groups (P < 0.001). LC3 was negatively correlated with Bax and was irrelevant with Bcl-2; Bcl-2 was not correlated with Bax.

Conclusions

The expression of LC3, Bax and Bcl-2 changes in the periodontal tissue of diabetic rats may indicate that autophagy and apoptotic are involved in the process of periodontal tissue damage in diabetic rats. These changes may be one of the mechanisms of periodontal tissue lesions.

In-depth transcriptomic analysis of human retina reveals molecular mechanisms underlying diabetic retinopathy

Diabetic Retinopathy (DR) is among the major global causes for vision loss. With the rise in diabetes prevalence, an increase in DR incidence is expected. Current understanding of both the molecular etiology and pathways involved in the initiation and progression of DR is limited. Via RNA-Sequencing, we analyzed mRNA and miRNA expression profiles of 80 human post-mortem retinal samples from 43 patients diagnosed with various stages of DR. We found differentially expressed transcripts to be predominantly associated with late stage DR and pathways such as hippo and gap junction signaling. A multivariate regression model identified transcripts with progressive changes throughout disease stages, which in turn displayed significant overlap with sphingolipid and cGMP-PKG signaling. Combined analysis of miRNA and mRNA expression further uncovered disease-relevant miRNA/mRNA associations as potential mechanisms of post-transcriptional regulation. Finally, integrating human retinal single cell RNA-Sequencing data revealed a continuous loss of retinal ganglion cells, and Müller cell mediated changes in histidine and β-alanine signaling. While previously considered primarily a vascular disease, attention in DR has shifted to additional mechanisms and cell-types. Our findings offer an unprecedented and unbiased insight into molecular pathways and cell-specific changes in the development of DR, and provide potential avenues for future therapeutic intervention.

Stimulation of AMPK Prevents Diabetes-Induced Photoreceptor Cell Degeneration

Diabetic retinopathy (DR) is a kind of severe retinal neurodegeneration. The advanced glycation end products (AGEs) affect autophagy, and mitochondrial function is involved in DR. Adenosine-activated protein kinase (AMPK) is an important metabolic sensor that can regulate energy homeostasis in cells. However, the effect of AMPK in DR is still not fully understood. In this study, we investigated the effect of AMPK on diabetes-induced photoreceptor cell degeneration. In vivo, a diabetic mouse model was established by streptozotocin (STZ) injection. Haematoxylin-eosin (HE) staining was used to observe retinal morphology and measure the thicknesses of different layers in the retina. Electroretinogram (ERG) was used to evaluate retinal function. In vitro, 661w cells were treated with AGEs with/without an AMPK agonist (metformin) or AMPK inhibitor (compound C). Flow cytometry and CCK-8 assays were used to analyse apoptosis. Mitochondrial membrane potential was analysed by JC-1. Western blotting and qRT-PCR were used to examine the expression of related proteins and genes, respectively. The wave amplitude and the thickness of the outer nuclear layer were decreased in diabetic mice. The expression of rhodopsin and opsin was also decreased in diabetic mice. In vitro, the percentage of apoptotic cells was increased, the expression of the apoptosis-related protein Bax was increased, and Bcl-2 was decreased after AGE treatment in 661w cells. The expression of the autophagy-related protein LC3 was decreased, and p62 was increased. The mitochondrial-related gene expression and membrane potential were decreased, and mitochondrial morphology was abnormal, as observed by TEM. However, AMPK stimulation ameliorated this effect. These results indicate that AMPK stimulation can delay diabetes-induced photoreceptor degeneration by regulating autophagy and mitochondrial function.

SIRT1: Mechanism and Protective Effect in Diabetic Nephropathy

Diabetic nephropathy (DN) is referred to as the microvascular complication of the kidneys induced by insufficient production of insulin or an ineffective cellular response to insulin, and is the main cause of end-stage renal disease. Currently, available therapies provide only symptomatic relief and fail to improve the outcome of diabetic nephropathy. Studies on diabetic animals had shown overexpression of SIRT1 in both podocytes and renal tubular cells attenuated proteinuria and kidney injury in the animal model of DN. Sirt1 exerts renoprotective effects in DKD in part through the deacetylation of transcription factors involved in the disease pathogenesis, such as NF-кB, Smad3, FOXO and p53. The purpose of this review is to highlight the protective mechanism of SIRT1 involved in the pathogenesis of diabetic nephropathy.

Melatonin prevents blood-retinal barrier breakdown and mitochondrial dysfunction in high glucose and hypoxia-induced in vitro diabetic macular edema model

Diabetic macular edema (DME) is a leading cause of blindness in diabetic retinopathy. Prolonged hyperglycemia plus hypoxia contributes to DME pathogenesis. Retinal pigmented epithelial cells comprise the outer blood-retinal barrier and are essential for maintaining physiological functioning of the retina. Melatonin acts as an antioxidant and regulator of mitochondrial bioenergetics and has a protective effect against ocular diseases. However, the role of mitochondrial dysfunction and the therapeutic potential of melatonin in DME remain largely unexplored. Here, we used an in vitro model of DME to investigate blood-retinal barrier integrity and permeability, angiogenesis, mitochondrial dynamics, and apoptosis signaling to evaluate the potential protective efficacy of melatonin in DME. We found that melatonin prevents cell hyper-permeability and outer barrier breakdown by reducing HIF-1α, HIF-1β and VEGF and VEGF receptor gene expression. In addition, melatonin reduced the expression of genes involved in mitochondrial fission (DRP1, hFis1, MIEF2, MFF), mitophagy (PINK, BNip3, NIX), and increased the expression of genes involved in mitochondrial biogenesis (PGC-1α, NRF2, PPAR-γ) to maintain mitochondrial homeostasis. Moreover, melatonin prevented apoptosis of retinal pigmented epithelial cells. Our results suggest that mitochondrial dysfunction may be involved in DME pathology, and melatonin may have therapeutic value in DME, by targeting signaling in mitochondria.

Evaluation of the neuronal and microvascular components of the macula in patients with diabetic retinopathy

PURPOSE

To investigate whether abnormal retinal microcirculation correlates with retinal neuronal changes in untreated diabetic eyes without macular edema.

METHODS

This study enrolled 29 diabetic patients without diabetic retinopathy (DR), 18 patients with mild non-proliferative diabetic retinopathy (NPDR), 15 patients with moderate NPDR, 14 patients with severe NPDR, 27 patients with proliferative diabetic retinopathy (PDR), and 25 healthy control subjects. Pattern electroretinography (PERG) and optical coherence tomography angiography (OCT-A) tests were performed.

RESULTS

Differences in the mean values for the area, acircularity index, and perimeter of foveal avascular zone were statistically significant between the healthy control group and the diabetic patients (P  < 0.05 for all). P50 and N95 amplitudes were statistically significantly lower in the PDR group compared to diabetic patients without DR, control, and moderate NPDR groups (P  < 0.05 for all). The whole retina vessel densities in superficial and deep capillary plexus were lower in the PDR group compared to the diabetic patients without DR and control group (P < 0.05 for all). There were statistically significant positive correlations between the amplitudes of the P50 and N95 waves with the vessel densities.

CONCLUSION

The existence of significant correlations between PERG and OCT-A parameters in diabetic patients has shown that vascular and neuronal changes in the macula affect each other in diabetic patients.

Mingmu Xiaomeng Tablets Restore Autophagy and Alleviate Diabetic Retinopathy by Inhibiting PI3K/Akt/mTOR Signaling

Objective: To investigate the effect of Mingmu Xiaomeng tablets (MMXM) on the expression of phosphoinositide 3-kinase (PI3K)/Akt/mammalian target of rapamycin (mTOR)-related proteins in a diabetic rat model.

Methods: Thirty-two male Sprague Dawley rats were randomly divided into four groups: normal control (NC), diabetic model (DM) control, MMXM, and calcium dobesilate (CD) Rats injected with streptozotocin (STZ) were used as an experimental diabetes model. After 14 weeks, autophagy and PI3K/Akt/mTOR signaling pathway proteins were detected by western blot. Glial fibrillary acidic protein (GFAP) expression in Müller cells was examined by immunohistochemistry. Retinal function was evaluated with electroretinography, and retinal ultrastructure was observed by transmission electron microscopy. Serum cytokine levels were detected with protein chip technology.

Results: MMXM restored autophagy by decreasing the protein expression of LC3-II and p62 and reducing the phosphorylation of PI3K, Akt, and mTOR, thus promoting autophagy. MMXM decreased GFAP expression in retinal Müller cells; restored electrophysiology indexes and retinal ultrastructures; and reduced serum levels of interleukin (IL)-1β, IL-4, IL-6, tumor necrosis factor-α, and vascular endothelial growth factor.

Conclusion: MMXM may protect the diabetic retina by inhibiting PI3K/Akt/mTOR signaling and enhancing autophagy.

Mitophagy in Human Diseases

Mitophagy is a selective autophagic process, essential for cellular homeostasis, that eliminates dysfunctional mitochondria. Activated by inner membrane depolarization, it plays an important role during development and is fundamental in highly differentiated post-mitotic cells that are highly dependent on aerobic metabolism, such as neurons, muscle cells, and hepatocytes. Both defective and excessive mitophagy have been proposed to contribute to age-related neurodegenerative diseases, such as Parkinson’s and Alzheimer’s diseases, metabolic diseases, vascular complications of diabetes, myocardial injury, muscle dystrophy, and liver disease, among others. Pharmacological or dietary interventions that restore mitophagy homeostasis and facilitate the elimination of irreversibly damaged mitochondria, thus, could serve as potential therapies in several chronic diseases. However, despite extraordinary advances in this field, mainly derived from in vitro and preclinical animal models, human applications based on the regulation of mitochondrial quality in patients have not yet been approved. In this review, we summarize the key selective mitochondrial autophagy pathways and their role in prevalent chronic human diseases and highlight the potential use of specific interventions.

Combination of pathological and spectroscopic characterization to promote diagnosis of retinal pigment epithelium-Bruch's membrane complex in a diabetic rat model

Diabetic retinopathy (DR) is a common condition of diabetes, and approaches to detecting early DR using the unique characteristics of the retinal pigment epithelium-Bruch's membrane complex (RBC) have increasingly attracted attention. A diabetic model was established in Sprague-Dawley rats via streptozocin (STZ) injection for 1 (DM1) and 6 months (DM6), confirmed by weekly blood glucose measurement. Serum and retinal tissue-based advanced glycation endproducts (AGE) levels significantly elevated in diabetic rats, and RBC was evaluated by transmission electron microscopy and Raman spectroscopy. The results showed that whole Raman spectra and all marked band intensities could respectively achieve almost equal and accurate discrimination of all animal groups, along with the determination of important molecules from the band data. Further quantitative analyses indicated series of metabolic disturbance due to hyperglycemia were involved while the body self-regulation mechanism still played a role with different effects during the disease progression. Given this, Raman spectroscopy can reliably distinguish the early characterization of DR in addition to providing intrinsic key molecules that is sensitive to identify the early disease progression.

mTOR-dependent dysregulation of autophagy contributes to the retinal ganglion cell loss in streptozotocin-induced diabetic retinopathy

BACKGROUND

Neurodegeneration, an early event in the pathogenesis of diabetic retinopathy (DR), precedes clinically detectable microvascular damage. Autophagy dysregulation is considered a potential cause of neuronal cell loss, however underlying mechanisms remain unclear. The mechanistic target of rapamycin (mTOR) integrates diverse environmental signals to coordinate biological processes, including autophagy. Here, we investigated the role of mTOR signaling in neuronal cell death in DR.

METHODS

Diabetes was induced by a single intraperitoneal injection of streptozotocin and tissue samples were harvested at 1, 2, 3, 4, and 6 months of diabetes. Early-stage of DR was investigated in 1-month-diabetic mice treated with phlorizin (two daily subcutaneous injections at a dose of 200 mg/kg of body weight during the last 7 full days of the experiment and the morning of the 8th day, 3 h before sacrifice) or rapamycin (daily intraperitoneal injections, at a dose of 3 mg/kg for the same period as for phlorizin treatment). The effect of autophagy modulation on retinal ganglion cells was investigated in 3-months-diabetic mice treated with phlorizin (two daily subcutaneous injections during the last 10 full days of the experiment and the morning of the 11th day, 3 h before sacrifice) or MHY1485 (daily i.p. injections, at a dose of 10 mg/kg for the same period as for phlorizin treatment). Tissue samples obtained from treated/untreated diabetic mice and age-matched controls were used for Western blot and histologic analysis.

RESULTS

mTOR-related proteins and glucose transporter 1 (GLUT1) was upregulated at 1 month and downregulated in the following period up to 6 months. Diabetes-induced neurodegeneration was characterized by an increase of apoptotic marker-cleaved caspase 3, a decrease of the total number of cells, and NeuN immunoreactivity in the ganglion cell layer, as well as an increase of autophagic protein. Insulin-independent glycemic control restored the mTOR pathway activity and GLUT1 expression, along with a decrease of autophagic and apoptotic proteins in 3-months-diabetic mice neuroretina. However, blockade of autophagy using MHY1485 resulted in a more protective effect on ganglion cells compared with phlorizin treatment.

CONCLUSION

Collectively, our study describes the mechanisms of neurodegeneration through the hyperglycemia/ mTOR/ autophagy/ apoptosis pathway. Video Abstract.

Melatonin exerts protective effects on diabetic retinopathy via inhibition of Wnt/β-catenin pathway as revealed by quantitative proteomics

Diabetic retinopathy (DR), the most common ocular complication resulting from diabetes in working-age adults, causes vision impairment and even blindness because of microvascular damage to the retina. Melatonin is an endogenous neurohormone possessing various biological properties, including the regulation of oxidative stress, inflammation, autophagy, and angiogenesis functions. To evaluate the effects of melatonin on DR, we first investigated the role of melatonin in retinal angiogenesis and inner blood-retina barrier (iBRB) under high glucose conditions in vitro and in vivo. Melatonin administration ameliorated high glucose-induced iBRB disruption, cell proliferation, cell migration, invasion and tube formation, and decreased the expression levels of VEGF, MMP-2, and MMP-9. Furthermore, melatonin treatment increased the level of autophagy but decreased the expression levels of inflammation-related factors under high glucose conditions. To further explore the underlying mechanism, we evaluated human retinal microvascular endothelial cells (HRMECs) via tandem mass tags (TMT)-labeled quantitative proteomics under high-glucose conditions with or without melatonin. Bioinformatics analysis results revealed that the main enrichment pathway of differentially expressed proteins (DEPs) was the Wnt pathway. We found that melatonin inhibited the activation of Wnt/β-catenin pathway following DR. These abovementioned protective effects of melatonin under hyperglycemia were blocked by lithium chloride (LiCl; activator of the Wnt/β-catenin signaling pathway). In summary, melatonin exerts protective effects on experimental DR via inhibiting Wnt/β-catenin pathway by, at least partially, alleviating autophagic dysfunction and inflammatory activation.

Retinal damage in a new model of hyperglycemia induced by high-sucrose diets

Loss of retinal neurons may precede clinical signs of diabetic retinopathy (DR). We studied for the first time the effects of hyperglycemia on the visual system of the fruit fly Drosophila melanogaster to characterize a model for glucose-induced retinal neurodegeneration, thus complementing more traditional vertebrate systems. Adult flies were fed with increased high-sucrose regimens which did not modify the locomotion ability, muscle phenotype and mobility after 10 days. The increased availability of dietary sucrose induced hyperglycemia and phosphorylation of Akt in fat tissue, without significant effects on adult growth and viability, consistent with the early phase of insulin signaling and a low impact on the overall metabolic profile of flies at short term. Noteworthy, high-sucrose diets significantly decreased Drosophila responsiveness to the light as a consequence of vision defects. Hyperglycemia did not alter the gross anatomical architecture of the external eye phenotype although a progressive damage of photosensitive units was observed. Appreciable levels of cleaved caspase 3 and nitrotyrosine were detected in the internal retina network as well as punctate staining of Light-Chain 3 and p62, and accumulated autophagosomes, indicating apoptotic features, peroxynitrite formation and autophagy turnover defects. In summary, our results in Drosophila support the view that hyperglycemia induced by high-sucrose diets lead to eye defects, apoptosis/autophagy dysregulation, oxidative stress, and visual dysfunctions which are evolutionarily conserved, thus offering a meaningful opportunity of using a simple in vivo model to study the pathophysiology of neuroretinal alterations that develop in patients at the early stages of DR.

Casein Kinase 2-Interacting Protein-1 Alleviates High Glucose-Reduced Autophagy, Oxidative Stress, and Apoptosis in Retinal Pigment Epithelial Cells via Activating the p62/KEAP1/NRF2 Signaling Pathway

Background

Casein kinase 2-interacting protein-1 (CKIP-1) has been proved to be associated with complications of diabetes. Diabetic retinopathy is a main diabetic complication which usually leads to blindness. The current study aims to investigate the role of CKIP-1 in high glucose-treated retinal pigment epithelial (RPE) cells which is a component of blood-retinal barriers.

Methods

The RPE cells, ARPE-19, are treated with high glucose to mimic the diabetic stimulation. CKIP-1 was overexpressed in ARPE-19 cells to evaluate its effects on autophagy, oxidative stress, and apoptosis induced by high glucose treatment, using Western blot, immunofluorescence, and flow cytometry assays, respectively.

Results

CKIP-1 was expressed at a lower level in high glucose-treated cells than in normal glucose cells. Overexpression of CKIP-1 enhanced the Nrf2 translocation to the nucleus. Furthermore, high glucose-induced autophagy, oxidative stress, and apoptosis were inhibited after overexpression of CKIP-1. Also, CKIP-1 regulates the p62/Keap1/Nrf2 signaling, which might be the potential mechanism in this model.

Conclusion

In conclusion, CKIP-1 may be a potential therapeutic target that protects RPE cells from injury and subsequent diabetic retinopathy induced by high glucose.