Role of the receptor for advanced glycation endproducts (RAGE) in retinal vasodegenerative pathology during diabetes in mice

Glycative stress as a cause of macular degeneration

People are living longer and rates of age-related diseases such as age-related macular degeneration (AMD) are accelerating, placing enormous burdens on patients and health care systems. The quality of carbohydrate foods consumed by an individual impacts health. The glycemic index (GI) is a kinetic measure of the rate at which glucose arrives in the blood stream after consuming various carbohydrates. Consuming diets that favor slowly digested carbohydrates releases sugar into the bloodstream gradually after consuming a meal (low glycemic index). This is associated with reduced risk for major age-related diseases including AMD, cardiovascular disease, and diabetes. In comparison, consuming the same amounts of different carbohydrates in higher GI diets, releases glucose into the blood rapidly, causing glycative stress as well as accumulation of advanced glycation end products (AGEs). Such AGEs are cytotoxic by virtue of their forming abnormal proteins and protein aggregates, as well as inhibiting proteolytic and other protective pathways that might otherwise selectively recognize and remove toxic species. Using in vitro and animal models of glycative stress, we observed that consuming higher GI diets perturbs metabolism and the microbiome, resulting in a shift to more lipid-rich metabolomic profiles. Interactions between aging, diet, eye phenotypes and physiology were observed. A large body of laboratory animal and human clinical epidemiologic data indicates that consuming lower GI diets, or lower glycemia diets, is protective against features of early AMD (AMDf) in mice and AMD prevalence or AMD progression in humans. Drugs may be optimized to diminish the ravages of higher glycemic diets. Human trials are indicated to determine if AMD progression can be retarded using lower GI diets. Here we summarized the current knowledge regarding the pathological role of glycative stress in retinal dysfunction and how dietary strategies might diminish retinal disease.

Exploring the Associated Genetic Causes of Diabetic Retinopathy as a Model of Inflammation in Retinal Diseases

To investigate potential biomarkers and biological processes associated with diabetic retinopathy (DR) using transcriptomic and proteomic data. The OmicsPred PheWAS application was interrogated to identify genes and proteins associated with DR and diabetes mellitus (DM) at a false discovery rate (FDR)-adjusted p-value of <0.05 and also <0.005. Gene Ontology PANTHER analysis and STRING database analysis were conducted to explore the biological processes and protein interactions related to the identified biomarkers. The interrogation identified 49 genes and 22 proteins associated with DR and/or DM; these were divided into those uniquely associated with diabetic retinopathy, uniquely associated with diabetes mellitus, and the ones seen in both conditions. The Gene Ontology PANTHER and STRING database analyses highlighted associations of several genes and proteins associated with diabetic retinopathy with adaptive immune response, valyl-TRNA aminoacylation, complement activation, and immune system processes. Our analyses highlight potential transcriptomic and proteomic biomarkers for DR and emphasize the association of known aspects of immune response, the complement system, advanced glycosylation end-product formation, and specific receptor and mitochondrial function with DR pathophysiology. These findings may suggest pathways for future research into novel diagnostic and therapeutic strategies for DR.

Mammalian Diaphanous1 signalling in neurovascular complications of diabetes

Over the past few decades, diabetes gradually has become one of the top non-communicable disorders, affecting 476.0 million in 2017 and is predicted to reach 570.9 million people in 2025. It is estimated that 70 to 100% of all diabetic patients will develop some if not all, diabetic complications over the course of the disease. Despite different symptoms, mechanisms underlying the development of diabetic complications are similar, likely stemming from deficits in both neuronal and vascular components supplying hyperglycaemia-susceptible tissues and organs. Diaph1, protein diaphanous homolog 1, although mainly known for its regulatory role in structural modification of actin and related cytoskeleton proteins, in recent years attracted research attention as a cytoplasmic partner of the receptor of advanced glycation end-products (RAGE) a signal transduction receptor, whose activation triggers an increase in proinflammatory molecules, oxidative stressors and cytokines in diabetes and its related complications. Both Diaph1 and RAGE are also a part of the RhoA signalling cascade, playing a significant role in the development of neurovascular disturbances underlying diabetes-related complications. In this review, based on the existing knowledge as well as compelling findings from our past and present studies, we address the role of Diaph1 signalling in metabolic stress and neurovascular degeneration in diabetic complications. In light of the most recent developments in biochemical, genomic and transcriptomic research, we describe current theories on the aetiology of diabetes complications, highlighting the function of the Diaph1 signalling system and its role in diabetes pathophysiology.

NOD1 deficiency ameliorates the progression of diabetic retinopathy by modulating bone marrow-retina crosstalk

BACKGROUND

Nucleotide-binding oligomerization domain-containing protein 1 (NOD1) plays a pivotal role in inducing metabolic inflammation in diabetes. Additionally, the NOD1 ligand disrupts the equilibrium of bone marrow-derived hematopoietic stem/progenitor cells, a process that has immense significance in the development of diabetic retinopathy (DR). We hypothesized that NOD1 depletion impedes the advancement of DR by resolving bone marrow dysfunction.

METHODS

We generated NOD1-/--Akita double-mutant mice and chimeric mice with hematopoietic-specific NOD1 depletion to study the role of NOD1 in the bone marrow-retina axis.

RESULTS

Elevated circulating NOD1 activators were observed in Akita mice after 6 months of diabetes. NOD1 depletion partially restored diabetes-induced structural changes and retinal electrical responses in NOD1-/--Akita mice. Loss of NOD1 significantly ameliorated the progression of diabetic retinal vascular degeneration, as determined by acellular capillary quantification. The preventive effect of NOD1 depletion on DR is linked to bone marrow phenotype alterations, including a restored HSC pool and a shift in hematopoiesis toward myelopoiesis. We also generated chimeric mice with hematopoietic-specific NOD1 ablation, and the results further indicated that NOD1 had a protective effect against DR. Mechanistically, loss of hematopoietic NOD1 resulted in reduced bone marrow-derived macrophage infiltration and decreased CXCL1 and CXCL2 secretion within the retina, subsequently leading to diminished neutrophil chemoattraction and NETosis.

CONCLUSIONS

The results of our study unveil, for the first time, the critical role of NOD1 as a trigger for a hematopoietic imbalance toward myelopoiesis and local retinal inflammation, culminating in DR progression. Targeting NOD1 in bone marrow may be a potential strategy for the prevention and treatment of DR.

Matrix viscoelasticity promotes liver cancer progression in the pre-cirrhotic liver

Type 2 diabetes mellitus is a major risk factor for hepatocellular carcinoma (HCC). Changes in extracellular matrix (ECM) mechanics contribute to cancer development1,2, and increased stiffness is known to promote HCC progression in cirrhotic conditions3,4. Type 2 diabetes mellitus is characterized by an accumulation of advanced glycation end-products (AGEs) in the ECM; however, how this affects HCC in non-cirrhotic conditions is unclear. Here we find that, in patients and animal models, AGEs promote changes in collagen architecture and enhance ECM viscoelasticity, with greater viscous dissipation and faster stress relaxation, but not changes in stiffness. High AGEs and viscoelasticity combined with oncogenic β-catenin signalling promote HCC induction, whereas inhibiting AGE production, reconstituting the AGE clearance receptor AGER1 or breaking AGE-mediated collagen cross-links reduces viscoelasticity and HCC growth. Matrix analysis and computational modelling demonstrate that lower interconnectivity of AGE-bundled collagen matrix, marked by shorter fibre length and greater heterogeneity, enhances viscoelasticity. Mechanistically, animal studies and 3D cell cultures show that enhanced viscoelasticity promotes HCC cell proliferation and invasion through an integrin-β1-tensin-1-YAP mechanotransductive pathway. These results reveal that AGE-mediated structural changes enhance ECM viscoelasticity, and that viscoelasticity can promote cancer progression in vivo, independent of stiffness.

Manifestation of Pathology in Animal Models of Diabetic Retinopathy Is Delayed from the Onset of Diabetes

Diabetic retinopathy (DR) is the most common complication that develops in patients with diabetes mellitus (DM) and is the leading cause of blindness worldwide. Fortunately, sight-threatening forms of DR develop only after several decades of DM. This well-documented resilience to DR suggests that the retina is capable of protecting itself from DM-related damage and also that accumulation of such damage occurs only after deterioration of this resilience. Despite the enormous translational significance of this phenomenon, very little is known regarding the nature of resilience to DR. Rodent models of DR have been used extensively to study the nature of the DM-induced damage, i.e., cardinal features of DR. Many of these same animal models can be used to investigate resilience because DR is delayed from the onset of DM by several weeks or months. The purpose of this review is to provide a comprehensive overview of the literature describing the use of rodent models of DR in type-1 and type-2 diabetic animals, which most clearly document the delay between the onset of DM and the appearance of DR. These readily available experimental settings can be used to advance our current understanding of resilience to DR and thereby identify biomarkers and targets for novel, prevention-based approaches to manage patients at risk for developing DR.

The effect of GLP-1 receptor agonist lixisenatide on experimental diabetic retinopathy

AIMS

Glucagon-like peptide-1 receptor agonists are effective treatments for type 2 diabetes, effectively lowering glucose without weight gain and with low risk for hypoglycemia. However, their influence on the retinal neurovascular unit remains unclear. In this study, we analyzed the effects of the GLP-1 RA lixisenatide on diabetic retinopathy.

METHODS

Vasculo- and neuroprotective effects were assessed in experimental diabetic retinopathy and high glucose-cultivated C. elegans, respectively. In STZ-diabetic Wistar rats, acellular capillaries and pericytes (quantitative retinal morphometry), neuroretinal function (mfERG), macroglia (GFAP western blot) and microglia (immunohistochemistry) quantification, methylglyoxal (LC-MS/MS) and retinal gene expressions (RNA-sequencing) were determined. The antioxidant properties of lixisenatide were tested in C. elegans.

RESULTS

Lixisenatide had no effect on glucose metabolism. Lixisenatide preserved the retinal vasculature and neuroretinal function. The macro- and microglial activation was mitigated. Lixisenatide normalized some gene expression changes in diabetic animals to control levels. Ets2 was identified as a regulator of inflammatory genes. In C. elegans, lixisenatide showed the antioxidative property.

CONCLUSIONS

Our data suggest that lixisenatide has a protective effect on the diabetic retina, most likely due to a combination of neuroprotective, anti-inflammatory and antioxidative effects of lixisenatide on the neurovascular unit.

Subendothelial Matrix Stiffening by Lysyl Oxidase Enhances RAGE-Mediated Retinal Endothelial Activation in Diabetes

Endothelial cell (EC) activation is a crucial determinant of retinal vascular inflammation associated with diabetic retinopathy (DR), a major microvascular complication of diabetes. We previously showed that, similar to abnormal biochemical factors, aberrant mechanical cues in the form of lysyl oxidase (LOX)-dependent subendothelial matrix stiffening also contribute significantly to retinal EC activation in diabetes. Yet, how LOX is itself regulated and precisely how it mechanically controls retinal EC activation in diabetes is poorly understood. Here, we show that high-glucose-induced LOX upregulation in human retinal ECs (HRECs) is mediated by proinflammatory receptor for advanced glycation end products (RAGE). HRECs treated with methylglyoxal (MGO), an active precursor to the advanced glycation end product (AGE) MG-H1, exhibited LOX upregulation that was blocked by a RAGE inhibitor, thus confirming the ability of RAGE to promote LOX expression. Crucially, as a downstream effector of RAGE, LOX was found to mediate both the proinflammatory and matrix remodeling effects of AGE/RAGE, primarily through its ability to crosslink or stiffen matrix. Finally, using decellularized HREC-derived matrices and a mouse model of diabetes, we demonstrate that LOX-dependent matrix stiffening feeds back to enhance RAGE, thereby achieving its autoregulation and proinflammatory effects. Collectively, these findings provide fresh mechanistic insights into the regulation and proinflammatory role of LOX-dependent mechanical cues in diabetes while simultaneously implicating LOX as an alternative (downstream) target to block AGE/RAGE signaling in DR.

ARTICLE HIGHLIGHTS

We investigated the regulation and proinflammatory role of retinal endothelial lysyl oxidase (LOX) in diabetes. Findings reveal that LOX is upregulated by advanced glycation end products (AGE) and receptor for AGE (RAGE) and mediates AGE/RAGE-induced retinal endothelial cell activation and subendothelial matrix remodeling. We also show that LOX-dependent subendothelial matrix stiffening feeds back to enhance retinal endothelial RAGE. These findings implicate LOX as a key proinflammatory factor and an alternative (downstream) target to block AGE/RAGE signaling in diabetic retinopathy.

Effects of diabetes on microglial physiology: a systematic review of in vitro, preclinical and clinical studies

Diabetes mellitus is a heterogeneous chronic metabolic disorder characterized by the presence of hyperglycemia, commonly preceded by a prediabetic state. The excess of blood glucose can damage multiple organs, including the brain. In fact, cognitive decline and dementia are increasingly being recognized as important comorbidities of diabetes. Despite the largely consistent link between diabetes and dementia, the underlying causes of neurodegeneration in diabetic patients remain to be elucidated. A common factor for almost all neurological disorders is neuroinflammation, a complex inflammatory process in the central nervous system for the most part orchestrated by microglial cells, the main representatives of the immune system in the brain. In this context, our research question aimed to understand how diabetes affects brain and/or retinal microglia physiology. We conducted a systematic search in PubMed and Web of Science to identify research items addressing the effects of diabetes on microglial phenotypic modulation, including critical neuroinflammatory mediators and their pathways. The literature search yielded 1327 records, including 18 patents. Based on the title and abstracts, 830 papers were screened from which 250 primary research papers met the eligibility criteria (original research articles with patients or with a strict diabetes model without comorbidities, that included direct data about microglia in the brain or retina), and 17 additional research papers were included through forward and backward citations, resulting in a total of 267 primary research articles included in the scoping systematic review. We reviewed all primary publications investigating the effects of diabetes and/or its main pathophysiological traits on microglia, including in vitro studies, preclinical models of diabetes and clinical studies on diabetic patients. Although a strict classification of microglia remains elusive given their capacity to adapt to the environment and their morphological, ultrastructural and molecular dynamism, diabetes modulates microglial phenotypic states, triggering specific responses that include upregulation of activity markers (such as Iba1, CD11b, CD68, MHC-II and F4/80), morphological shift to amoeboid shape, secretion of a wide variety of cytokines and chemokines, metabolic reprogramming and generalized increase of oxidative stress. Pathways commonly activated by diabetes-related conditions include NF-κB, NLRP3 inflammasome, fractalkine/CX3CR1, MAPKs, AGEs/RAGE and Akt/mTOR. Altogether, the detailed portrait of complex interactions between diabetes and microglia physiology presented here can be regarded as an important starting point for future research focused on the microglia-metabolism interface.

The process of methylglyoxal-induced retinal capillary endothelial cell degeneration in rats

Methylglyoxal, a highly reactive dicarbonyl compound, is increased and accumulated in patients with diabetic mellitus. Methylglyoxal forms advanced glycation end products (AGE), contributing to the pathogenesis of diabetic complications, including diabetic retinopathy. Recent studies have shown that methylglyoxal induces diabetic retinopathy-like abnormalities in retinal vasculature. In this study, we investigated the processes and mechanisms of methylglyoxal-induced retinal capillary endothelial cell degeneration in rats. Morphological changes in vascular components (endothelial cells, pericytes, and basement membranes) were assessed in the retinas 2, 7, and 14 days after intravitreal injection of methylglyoxal. Intravitreal methylglyoxal injection induced retinal capillary endothelial cell degeneration in a dose- and time-dependent manner. Changes in the shape and distribution of pericytes occurred before the initiation of capillary regression in the retinas of methylglyoxal-injected eyes. The receptor for AGEs (RAGEs) antagonist FPS-ZM1, and the matrix metalloproteinase (MMP) inhibitor GM6001 significantly attenuated methylglyoxal-induced capillary endothelial cell degeneration. FPS-ZM1 failed to prevent pathological changes in pericytes in methylglyoxal-injected eyes. In situ zymography revealed that MMP activity was enhanced at sites of blood vessels with reduced pericyte coverage in methylglyoxal-injected eyes. These results suggest that intravitreal methylglyoxal injection induces pathological changes in pericytes before the initiation of capillary endothelial cell degeneration via an AGE-RAGE-independent pathway. The capillary endothelial cell degeneration is mediated by activating the AGE-RAGE pathway and increasing MMP activity in endothelial cells by impairing pericyte function in the retina.

Differences in junction-associated gene expression changes in three rat models of diabetic retinopathy with similar neurovascular phenotype

Diabetic retinopathy, also defined as microvascular complication of diabetes mellitus, affects the entire neurovascular unit with specific aberrations in every compartment. Neurodegeneration, glial activation and vasoregression are observed consistently in models of diabetic retinopathy. However, the order and the severity of these aberrations varies in different models, which is also true in patients. In this study, we analysed rat models of diabetic retinopathy with similar phenotypes to identify key differences in the pathogenesis. For this, we focussed on intercellular junction-associated gene expression, which are important for the communication and homeostasis within the neurovascular unit. Streptozotocin-injected diabetic Wistar rats, methylglyoxal supplemented Wistar rats and polycystin-2 transgenic (PKD) rats were analysed for neuroretinal function, vasoregression and retinal expression of junction-associated proteins. In all three models, neuroretinal impairment and vasoregression were observed, but gene expression profiling of junction-associated proteins demonstrated nearly no overlap between the three models. However, the differently expressed genes were from the main classes of claudins, connexins and integrins in all models. Changes in Rcor1 expression in diabetic rats and Egr1 expression in PKD rats confirmed the differences in upstream transcription factor level between the models. In PKD rats, a possible role for miRNA regulation was observed, indicated by an upregulation of miR-26b-5p, miR-122-5p and miR-300-3p, which was not observed in the other models. In silico allocation of connexins revealed not only differences in regulated subtypes, but also in affected retinal cell types, as well as connexin specific upstream regulators Sox7 and miR-92a-3p. In this study, we demonstrate that, despite their similar phenotype, models for diabetic retinopathy exhibit significant differences in their pathogenic pathways and primarily affected cell types. These results underline the importance for more sensitive diagnostic tools to identify pathogenic clusters in patients as the next step towards a desperately needed personalized therapy.

Activation of oxytocin receptors in mouse GABAergic amacrine cells modulates retinal dopaminergic signaling

Background

Oxytocin, secreted by oxytocin neurons in the hypothalamus, is an endogenous neuropeptide involved in modulating multiple sensory information processing pathways, and its roles in the brain have been associated with prosocial, maternal, and feeding-related behaviors. Visual information is necessary for initiating these behaviors, with the retina consisting of the first stage in the visual system mediating external stimulus perception. Oxytocin has been detected in the mammalian retina; however, the expression and possible function of oxytocin receptors (OxtR) in the retina remain unknown. Here, we explore the role of oxytocin in regulating visual information processing in the retina.

Results

We observed that OxtR mRNA and protein are expressed in the mouse retina. With Oxtr-Cre transgenic mice, immunostaining, and fluorescence in situ hybridization, we found that OxtRs are mainly expressed in GABAergic amacrine cells (ACs) in both the inner nuclear layer (INL) and ganglion cell layer (GCL). Further immunoreactivity studies showed that GABAergic OxtR⁺ neurons are mainly cholinergic and dopaminergic neurons in the INL and are cholinergic and corticotrophin-releasing hormone neurons in the GCL. Surprisingly, a high level of Oxtr mRNAs was detected in retinal dopaminergic neurons, and exogenous oxytocin application activated dopaminergic neurons to elevate the retinal dopamine level. Relying on in vivo electroretinographic recording, we found that activating retinal OxtRs reduced the activity of bipolar cells via OxtRs and dopamine receptors.

Conclusions

These data indicate the functional expression of OxtRs in retinal GABAergic ACs, especially dopaminergic ACs, and expand the interactions between oxytocinergic and dopaminergic systems. This study suggests that visual perception, from the first stage of information processing in the retina, is modulated by hypothalamic oxytocin signaling.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12915-022-01405-0.

The RAGE/DIAPH1 Signaling Axis & Implications for the Pathogenesis of Diabetic Complications

Increasing evidence links the RAGE (receptor for advanced glycation end products)/DIAPH1 (Diaphanous 1) signaling axis to the pathogenesis of diabetic complications. RAGE is a multi-ligand receptor and through these ligand-receptor interactions, extensive maladaptive effects are exerted on cell types and tissues targeted for dysfunction in hyperglycemia observed in both type 1 and type 2 diabetes. Recent evidence indicates that RAGE ligands, acting as damage-associated molecular patterns molecules, or DAMPs, through RAGE may impact interferon signaling pathways, specifically through upregulation of IRF7 (interferon regulatory factor 7), thereby heralding and evoking pro-inflammatory effects on vulnerable tissues. Although successful targeting of RAGE in the clinical milieu has, to date, not been met with success, recent approaches to target RAGE intracellular signaling may hold promise to fill this critical gap. This review focuses on recent examples of highlights and updates to the pathobiology of RAGE and DIAPH1 in diabetic complications.

Common pathways in dementia and diabetic retinopathy: understanding the mechanisms of diabetes-related cognitive decline

Type 2 diabetes (T2D) is associated with multiple comorbidities, including diabetic retinopathy (DR) and cognitive decline, and T2D patients have a significantly higher risk of developing Alzheimer's disease (AD). Both DR and AD are characterized by a number of pathological mechanisms that coalesce around the neurovascular unit, including neuroinflammation and degeneration, vascular degeneration, and glial activation. Chronic hyperglycemia and insulin resistance also play a significant role, leading to activation of pathological mechanisms such as increased oxidative stress and the accumulation of advanced glycation end-products (AGEs). Understanding these common pathways and the degree to which they occur simultaneously in the brain and retina during diabetes will provide avenues to identify T2D patients at risk of cognitive decline.

Molecular Characteristics of RAGE and Advances in Small-Molecule Inhibitors

Receptor for advanced glycation end-products (RAGE) is a member of the immunoglobulin superfamily. RAGE binds and mediates cellular responses to a range of DAMPs (damage-associated molecular pattern molecules), such as AGEs, HMGB1, and S100/calgranulins, and as an innate immune sensor, can recognize microbial PAMPs (pathogen-associated molecular pattern molecules), including bacterial LPS, bacterial DNA, and viral and parasitic proteins. RAGE and its ligands stimulate the activations of diverse pathways, such as p38MAPK, ERK1/2, Cdc42/Rac, and JNK, and trigger cascades of diverse signaling events that are involved in a wide spectrum of diseases, including diabetes mellitus, inflammatory, vascular and neurodegenerative diseases, atherothrombosis, and cancer. Thus, the targeted inhibition of RAGE or its ligands is considered an important strategy for the treatment of cancer and chronic inflammatory diseases.

AGER1 downregulation associates with fibrosis in nonalcoholic steatohepatitis and type 2 diabetes

Type 2 diabetes is clinically associated with progressive necroinflammation and fibrosis in nonalcoholic steatohepatitis (NASH). Advanced glycation end-products (AGEs) accumulate during prolonged hyperglycemia, but the mechanistic pathways that lead to accelerated liver fibrosis have not been well defined. In this study, we show that the AGEs clearance receptor AGER1 was downregulated in patients with NASH and diabetes and in our NASH models, whereas the proinflammatory receptor RAGE was induced. These findings were associated with necroinflammatory, fibrogenic, and pro-oxidant activity via the NADPH oxidase 4. Inhibition of AGEs or RAGE deletion in hepatocytes in vivo reversed these effects. We demonstrate that dysregulation of NRF2 by neddylation of cullin 3 was linked to AGER1 downregulation and that induction of NRF2 using an adeno-associated virus-mediated approach in hepatocytes in vivo reversed AGER1 downregulation, lowered the level of AGEs, and improved proinflammatory and fibrogenic responses in mice on a high AGEs diet. In patients with NASH and diabetes or insulin resistance, low AGER1 levels were associated with hepatocyte ballooning degeneration and ductular reaction. Collectively, prolonged exposure to AGEs in the liver promotes an AGER1/RAGE imbalance and consequent redox, inflammatory, and fibrogenic activity in NASH.

Patrolling Monocytes Are Recruited and Activated by Diabetes to Protect Retinal Microvessels

In diabetes there is a long latency between the onset of hyperglycemia and the appearance of structural microangiopathy. Because Ly6C^low patrolling monocytes (PMo) behave as housekeepers of the vasculature, we tested whether PMo protect microvessels against diabetes. We found that in wild-type mice, diabetes reduced PMo in the general circulation but increased by fourfold the absolute number of PMo adherent to retinal vessels (leukostasis). Conversely, in diabetic NR4A1^-/- mice, a model of absence of PMo, there was no increase in leukostasis, and at 6 months of diabetes, the number of retinal acellular capillaries almost doubled compared with diabetic wild-type mice. Circulating PMo showed gene expression changes indicative of enhanced migratory, vasculoprotective, and housekeeping activities, as well as profound suppression of genes related to inflammation and apoptosis. Promigratory CXCR4 was no longer upregulated at longer duration when retinal acellular capillaries begin to increase. Thus, after a short diabetes duration, PMo are the cells preferentially recruited to the retinal vessels and protect vessels from diabetic damage. These observations support the need for reinterpretation of the functional meaning of leukostasis in diabetes and document within the natural history of diabetic retinopathy processes of protection and repair that can provide novel paradigms for prevention.

Glyoxalase System as a Therapeutic Target against Diabetic Retinopathy

Hyperglycemia, a defining characteristic of diabetes, combined with oxidative stress, results in the formation of advanced glycation end products (AGEs). AGEs are toxic compounds that have adverse effects on many tissues including the retina and lens. AGEs promote the formation of reactive oxygen species (ROS), which, in turn, boost the production of AGEs, resulting in positive feedback loops, a vicious cycle that compromises tissue fitness. Oxidative stress and the accumulation of AGEs are etiologically associated with the pathogenesis of multiple diseases including diabetic retinopathy (DR). DR is a devastating microvascular complication of diabetes mellitus and the leading cause of blindness in working-age adults. The onset and development of DR is multifactorial. Lowering AGEs accumulation may represent a potential therapeutic approach to slow this sight-threatening diabetic complication. To set DR in a physiological context, in this review we first describe relations between oxidative stress, formation of AGEs, and aging in several tissues of the eye, each of which is associated with a major age-related eye pathology. We summarize mechanisms of AGEs generation and anti-AGEs detoxifying systems. We specifically feature the potential of the glyoxalase system in the retina in the prevention of AGEs-associated damage linked to DR. We provide a comparative analysis of glyoxalase activity in different tissues from wild-type mice, supporting a major role for the glyoxalase system in the detoxification of AGEs in the retina, and present the manipulation of this system as a therapeutic strategy to prevent the onset of DR.

Distribution of Highly Prevalent Musculoskeletal Disorders and Their Association With Diabetes Complications in a Population of 140 Individuals With Type 1 Diabetes: A Retrospective Study in a French Diabetes Center

Although they are usually not considered to be diabetes complications, musculoskeletal disorders (MSKDs) are common in individuals with type 1 or type 2 diabetes and can strongly interfere with daily diabetes care, especially in people using diabetes technologies. The authors of this retrospective study in a population of 140 patients with type 1 diabetes report the distribution of subtypes of MSKDs and speculate about the mechanisms involved. The authors emphasize the need for multidisciplinary care involving not only the diabetes care team but also orthopedic surgeons. This report should lead to large, prospective studies to increase knowledge about these under-studied complications.

Association of candidate gene polymorphisms with diabetic retinopathy in Chinese patients with type 2 diabetes

AIM

To investigate the association between a set of six candidate genes and the risk of diabetic retinopathy (DR) in an urban community cohort of Chinese patients with type 2 diabetes mellitus (T2DM).

METHODS

A population-based cross-sectional study. The diabetic subjects were recruited from an urban community in Beijing and categorized into groups of proliferative diabetic retinopathy (PDR), non-proliferative diabetic retinopathy (NPDR), or diabetic without any retinopathy (DWR) based on the fundus photography and duration of diabetes. Six candidate genes, including advanced glycation end product specific receptor (AGER), aldose reductase (AKR1B1), inducible nitric oxide synthase (iNOS), pigment epithelium derived factor (PEDF), tumor necrosis factor-alpha (TNF-α), and paraoxonase 1 (PON1), were chosen based on Meta-analysis of genetic association studies for DR and biochemical pathways implicated in DR progression. The allele and genotype distribution of 21 functional single-nucleotide polymorphisms (SNPs) in those 6 candidate genes were investigated using MassARRAY genotyping system.

RESULTS

Among 1461 diabetic patients recruited from community, 569 were selected in following genotyping analysis, including 97 patients with PDR, 217 with NPDR, and 255 with DWR. For the promoter variant rs1051993 in AGER gene, the distribution of allele and genotype in PDR group differed from that in DWR group (allele: P=0.011; genotype: P=0.01). Compared with DWR, patients with PDR had lower frequencies of heterozygous genotype GT (9.8% for DWR, 1% for PDR, OR: 0.10, 95%CI: 0.01-0.72) and minor allele T (4.9% for DWR, 0.5% for PDR, OR: 0.10, 95%CI: 0.01-0.75). In multivariate model, the distribution of genotype for rs1051993 in PDR group was significantly different from that in DWR group (GT vs GG: OR: 0.07, 95%CI: 0.01-0.61, P<0.001). No association with DR was observed in other genotyped SNPs.

CONCLUSION

The data suggest a significant association of the promoter variant rs1051993 in AGER gene with PDR in Chinese cohort with T2DM.

Advanced glycation end products induce immature angiogenesis in in vivo and ex vivo mouse models

Proliferative diabetic retinopathy (PDR) is a progressive disease predominantly involving pathological angiogenesis and is characterized by the development of immature, fragile, and easily hemorrhagic new vessels. Advanced glycation end products (AGEs) and the receptor for AGEs (RAGE) play important roles in the progression of diabetic retinopathy. Our previous studies demonstrated that AGEs promoted HUVEC angiogenesis by inducing moesin phosphorylation via RhoA/Rho-associated protein kinase (ROCK) pathway. The aim of this study was to further confirm AGE-induced angiogenesis in vivo and the involvement of RAGE, ROCK, and moesin phosphorylation in this process. We performed the study in an AGE-treated mouse model with various angiogenesis assays in multiple in vivo and ex vivo models. The results demonstrated that AGEs promoted significant neovascularization in whole mount retina and mouse aortic ring of adult and postnatal mice and in Matrigel plug as well, which were consistently accompanied by increased moesin phosphorylation. The increase of AGE-evoked neovascularization and moesin phosphorylation were both attenuated by RAGE knockout or ROCK inhibitor Y27632 administration in mice. We also revealed the pathological characteristics of AGE-promoted angiogenesis by demonstrating the decrease of pericyte coverage and the disarranged endothelial alignment in microvessels. In conclusion, this study provides in vivo evidences that AGEs induce immature angiogenesis by binding to RAGE, activating the RhoA/ROCK signal pathway and inducing moesin phosphorylation.NEW & NOTEWORTHY Advanced glycation end product (AGE)-induced formation of neovessels and phosphorylation of moesin in retina and aortic ring required AGE receptors. AGEs increased neovessels and the phosphorylation of moesin in retina and aortic ring via RhoA/ROCK pathway. AGE-induced immature angiogenesis in AGE-treated mouse retina and aortic ring. The AGE-RAGE axis and moesin could be candidate targets for overcoming relative diseases.

Methylglyoxal, a Highly Reactive Dicarbonyl Compound, in Diabetes, Its Vascular Complications, and Other Age-Related Diseases

The formation and accumulation of methylglyoxal (MGO), a highly reactive dicarbonyl compound, has been implicated in the pathogenesis of type 2 diabetes, vascular complications of diabetes, and several other age-related chronic inflammatory diseases such as cardiovascular disease, cancer, and disorders of the central nervous system. MGO is mainly formed as a byproduct of glycolysis and, under physiological circumstances, detoxified by the glyoxalase system. MGO is the major precursor of nonenzymatic glycation of proteins and DNA, subsequently leading to the formation of advanced glycation end products (AGEs). MGO and MGO-derived AGEs can impact on organs and tissues affecting their functions and structure. In this review we summarize the formation of MGO, the detoxification of MGO by the glyoxalase system, and the biochemical pathways through which MGO is linked to the development of diabetes, vascular complications of diabetes, and other age-related diseases. Although interventions to treat MGO-associated complications are not yet available in the clinical setting, several strategies to lower MGO have been developed over the years. We will summarize several new directions to target MGO stress including glyoxalase inducers and MGO scavengers. Targeting MGO burden may provide new therapeutic applications to mitigate diseases in which MGO plays a crucial role.

Vascular Inflammation Risk Factors in Retinal Disease

Inflammation of the blood vessels that serve the central nervous system has been increasingly identified as an early and possibly initiating event among neurodegenerative conditions such as Alzheimer's disease and related dementias. However, the causal relevance of vascular inflammation to major retinal degenerative diseases is unresolved. Here, we describe how genetics, aging-associated changes, and environmental factors contribute to vascular inflammation in age-related macular degeneration, diabetic retinopathy, and glaucoma. We highlight the importance of mouse models in studying the underlying mechanisms and possible treatments for these diseases. We conclude that data support vascular inflammation playing a central if not primary role in retinal degenerative diseases, and this association should be a focus of future research.

Imaging and Biomarkers in Diabetic Macular Edema and Diabetic Retinopathy

PURPOSE OF REVIEW

Diabetic retinopathy (DR) is the leading cause of acquired vision loss in adults across the globe. Early identification and treatment of patients with DR is paramount for vision preservation. The aim of this review paper is to outline current and new imaging techniques and biomarkers that are valuable for clinical diagnosis and management of DR.

RECENT FINDINGS

Ultrawide field imaging and automated deep learning algorithms are recent advancements on traditional fundus photography and fluorescein angiography. Optical coherence tomography (OCT) and OCT angiography are techniques that image retinal anatomy and vasculature and OCT is routinely used to monitor response to treatment. Many circulating, vitreous, and genetic biomarkers have been studied to facilitate disease detection and development of new treatments. Recent advancements in retinal imaging and identification of promising new biomarkers for DR have the potential to increase detection, risk stratification, and treatment for patients with DR.

Longitudinal In Vivo Characterization of the Streptozotocin-Induced Diabetic Mouse Model: Focus on Early Inner Retinal Responses

Purpose

The goal of this study was to perform an extensive temporal characterization of the early pathologic processes in the streptozotocin (STZ)-induced diabetic retinopathy (DR) mouse model, beyond the vascular phenotype, and to investigate the potential of clinically relevant compounds in attenuating these processes.

Methods

Visual acuity and contrast sensitivity (CS) were studied in the mouse STZ model until 24 weeks postdiabetes onset. ERG, spectral domain optical coherence tomography (SD-OCT), leukostasis, and immunohistochemistry were applied to investigate neurodegeneration, inflammation, and gliosis during early-, mid- and late-phase diabetes. Aflibercept or triamcinolone acetonide (TAAC) was administered to investigate their efficacy on the aforementioned processes.

Results

Visual acuity and CS loss started at 4 and 18 weeks postdiabetes onset, respectively, and progressively declined over time. ERG amplitudes were diminished and OP latencies increased after 6 weeks, whereas SD-OCT revealed retinal thinning from 4 weeks postdiabetes. Immunohistochemical analyses linked these findings to retinal ganglion and cholinergic amacrine cell loss at 4 and 8 weeks postdiabetes onset, respectively, which was further decreased after aflibercept administration. The number of adherent leukocytes was augmented after 2 weeks, whereas increased micro- and macroglia reactivity was present from 4 weeks postdiabetes. Aflibercept or TAAC showed improved efficacy on inflammation and gliosis.

Conclusions

STZ-induced diabetic mice developed early pathologic DR hallmarks, from which inflammation seemed the initial trigger, leading to further development of functional and morphologic retinal changes. These findings indicate that the mouse STZ model is suitable to study novel integrative non-vascular therapies to treat early DR.

STAT3 activation in circulating myeloid-derived cells contributes to retinal microvascular dysfunction in diabetes

Background

Leukostasis is a key patho-physiological event responsible for capillary occlusion in diabetic retinopathy. Circulating monocytes are the main cell type entrapped in retinal vessels in diabetes. In this study, we investigated the role of the signal transducer and activator of transcription 3 (STAT3) pathway in diabetes-induced immune cell activation and its contribution to retinal microvascular degeneration.

Methods

Forty-one patients with type 1 diabetes (T1D) [mild non-proliferative diabetic retinopathy (mNPDR) (n = 13), active proliferative DR (aPDR) (n = 14), inactive PDR (iPDR) (n = 14)] and 13 age- and gender-matched healthy controls were recruited to the study. C57BL/6 J WT mice, SOCS3^fl/fl and LysM^Cre/+SOCS3^fl/fl mice were rendered diabetic by Streptozotocin injection. The expression of the phosphorylated human and mouse STAT3 (pSTAT3), mouse LFA-1, CD62L, CD11b and MHC-II in circulating immune cells was evaluated by flow cytometry. The expression of suppressor of cytokine signalling 3 (SOCS3) was examined by real-time RT-PCR. Mouse plasma levels of cytokines were measured by Cytometric Beads Array assay. Retinal leukostasis was examined following FITC-Concanavalin A perfusion and acellular capillary was examined following Isolectin B4 and Collagen IV staining.

Results

Compared to healthy controls, the expression of pSTAT3 in circulating leukocytes was statistically significantly higher in mNPDR but not aPDR and was negatively correlated with diabetes duration. The expression of pSTAT3 and its inhibitor SOCS3 was also significantly increased in leukocytes from diabetic mice. Diabetic mice had higher plasma levels of IL6 and CCL2 compared with control mice. LysM^Cre/+SOCS3^fl/fl mice and SOCS3^fl/fl mice developed comparative levels of diabetes, but leukocyte activation, retinal leukostasis and number of acellular capillaries were statistically significantly increased in LysM^Cre/+SOCS3^fl/fl diabetic mice.

Conclusion

STAT3 activation in circulating immune cells appears to contribute to retinal microvascular degeneration and may be involved in DR initiation in T1D.

Electronic supplementary material

The online version of this article (10.1186/s12974-019-1533-1) contains supplementary material, which is available to authorized users.

Tanshinone IIa protects retinal endothelial cells against mitochondrial fission induced by methylglyoxal through glyoxalase 1

Advanced glycation end products (AGEs) play an important role in the onset of diabetic retinopathy. Therefore, in the current study, we investigate whether and how Tanshinone IIa (Tan IIa) from Salvia miltiorrhiza protects bovine retinal endothelial cells (BRECs) against methylglyoxal (MGO) mediated cell dysfunction. The results showed that MGO reduced cell viability in dose dependent manner. The treatment of Tan IIa (50 μM) significantly improved cell viability induced by MGO in BRECs. MGO increased cellular reactive oxygen species formation and cellular nitric oxide (NO) level; enhanced nox1 and iNOS mRNA levels; inhibited prdx1 mRNA level. The treatment of Tan IIa effectually ameliorated cellular oxidative stress. Exposure of MGO resulted in mitochondrial fission and decrease of opa1 and mfn1. No significant difference in mRNA levels of mfn2 and drp1 was detected between MGO and medium. Tan IIa reduced mitochondrial fragmentation, enhanced the mRNA levels of mfn1 and opa1 in MGO cultured BRECs. The short time exposure of cellular antioxidatants, dimethylthiourea (10 mM) and tiron (10 mM) had no effect on mitochondrial fission although they ameliorated cellular reactive oxygen species level. Moreover, overexpression of glyoxalase 1 (GLO1) increased key proteins of mitochondrial fusion, including opa1 and mfn1 in BRECs cultured with MGO. However, inhibition of GLO1 by siRNA abolished the effect of Tan IIa on induction of mitochondrial fusion in MGO cultured BRECs. In conclusion, MGO caused the injury of retinal endothelial cells through induction of mitochondrial dysfunction and mitochondrial fission, the treatment of Tan IIa ameliorated mitochondrial dysfunction and fission induced by AGEs through enhancing GLO1.

Neuroinflammation in Retinitis Pigmentosa, Diabetic Retinopathy, and Age-Related Macular Degeneration: A Minireview

The eye is an immuno-privileged organ. However, certain diseases such as uveitis are intrinsically linked to inflammation. In several retinal degenerative diseases, there is a unique damage at the onset of the disease, but evidence suggests that chronic and low-grade inflammatory processes play an important role in their progression. Studies have identified similar signaling pathways and changes in resident immune cells within the retina among these diseases. Herein, we will discuss some of these studies and propose how understanding this inflammatory response could aid in the development of therapies.

Human vitreous in proliferative diabetic retinopathy: Characterization and translational implications

Diabetic retinopathy (DR) is one of the leading causes of visual impairment in the working-age population. DR is a progressive eye disease caused by long-term accumulation of hyperglycaemia-mediated pathological alterations in the retina of diabetic patients. DR begins with asymptomatic retinal abnormalities and may progress to advanced-stage proliferative diabetic retinopathy (PDR), characterized by neovascularization or preretinal/vitreous haemorrhages. The vitreous, a transparent gel that fills the posterior cavity of the eye, plays a vital role in maintaining ocular function. Structural and molecular alterations of the vitreous, observed during DR progression, are consequences of metabolic and functional modifications of the retinal tissue. Thus, vitreal alterations reflect the pathological events occurring at the vitreoretinal interface. These events are caused by hypoxic, oxidative, inflammatory, neurodegenerative, and leukostatic conditions that occur during diabetes. Conversely, PDR vitreous can exert pathological effects on the diabetic retina, resulting in activation of a vicious cycle that contributes to disease progression. In this review, we recapitulate the major pathological features of DR/PDR, and focus on the structural and molecular changes that characterize the vitreal structure and composition during DR and progression to PDR. In PDR, vitreous represents a reservoir of pathological signalling molecules. Therefore, in this review we discuss how studying the biological activity of the vitreous in different in vitro, ex vivo, and in vivo experimental models can provide insights into the pathogenesis of PDR. In addition, the vitreous from PDR patients can represent a novel tool to obtain preclinical experimental evidences for the development and characterization of new therapeutic drug candidates for PDR therapy.

Methods to label, image, and analyze the complex structural architectures of microvascular networks

Microvascular networks play key roles in oxygen transport and nutrient delivery to meet the varied and dynamic metabolic needs of different tissues throughout the body, and their spatial architectures of interconnected blood vessel segments are highly complex. Moreover, functional adaptations of the microcirculation enabled by structural adaptations in microvascular network architecture are required for development, wound healing, and often invoked in disease conditions, including the top eight causes of death in the Unites States. Effective characterization of microvascular network architectures is not only limited by the available techniques to visualize microvessels but also reliant on the available quantitative metrics that accurately delineate between spatial patterns in altered networks. In this review, we survey models used for studying the microvasculature, methods to label and image microvessels, and the metrics and software packages used to quantify microvascular networks. These programs have provided researchers with invaluable tools, yet we estimate that they have collectively attained low adoption rates, possibly due to limitations with basic validation, segmentation performance, and nonstandard sets of quantification metrics. To address these existing constraints, we discuss opportunities to improve effectiveness, rigor, and reproducibility of microvascular network quantification to better serve the current and future needs of microvascular research.

Methylglyoxal induces retinopathy-type lesions in the absence of hyperglycemia: studies in a rat model

The aim of this study was to evaluate whether damage to the neurovascular unit in diabetes depends on reactive metabolites such as methylglyoxal (MG), and to assess its impact on retinal gene expression. Male Wistar rats were supplied with MG (50 mM) by drinking water and compared with age-matched streptozotocin-diabetic animals and untreated controls. Retinal damage was evaluated for the accumulation of MG-derived advanced glycation end products, changes in hexosamine and PKC pathway activation, microglial activation, vascular alterations (pericyte loss and vasoregression), neuroretinal function assessed by electroretinogram, and neurodegeneration. Retinal gene regulation was studied by microarray analysis, and transcription factor involvement was identified by upstream regulator analysis. Systemic application of MG by drinking water increased retinal MG to levels comparable with diabetic animals. Elevated retinal MG resulted in MG-derived hydroimidazolone modifications in the ganglion cell layer, inner nuclear layer, and outer nuclear layer, a moderate activation of the hexosamine pathway, a pan-retinal activation of microglia, loss of pericytes, increased formation of acellular capillaries, decreased function of bipolar cells, and increased expression of the crystallin gene family. MG mimics important aspects of diabetic retinopathy and plays a pathogenic role in microglial activation, vascular damage, and neuroretinal dysfunction. In response to MG, the retina induces expression of neuroprotective crystallins.-Schlotterer, A., Kolibabka, M., Lin, J., Acunman, K., Dietrich, N., Sticht, C., Fleming, T., Nawroth, P., Hammes, H.-P. Methylglyoxal induces retinopathy-type lesions in the absence of hyperglycemia: studies in a rat model.

miR-30a-5p inhibition promotes interaction of Fas+ endothelial cells and FasL+ microglia to decrease pathological neovascularization and promote physiological angiogenesis

Ischemia-induced angiogenesis contributes to various neuronal and retinal diseases, and often results in neurodegeneration and visual impairment. Current treatments involve the use of anti-VEGF agents but are not successful in all cases. In this study we determined that miR-30a-5p is another important mediator of retinal angiogenesis. Using a rodent model of ischemic retinopathy, we show that inhibiting miR-30a-5p reduces neovascularization and promotes tissue repair, through modulation of microglial and endothelial cell cross-talk. miR-30a-5p inhibition results in increased expression of the death receptor Fas and CCL2, to decrease endothelial cell survival and promote microglial migration and phagocytic function in focal regions of ischemic injury. Our data suggest that miR-30a-5p inhibition accelerates tissue repair by enhancing FasL-Fas crosstalk between microglia and endothelial cells, to promote endothelial cell apoptosis and removal of dead endothelial cells. Finally, we found that miR-30a levels were increased in the vitreous of patients with proliferative diabetic retinopathy. Our study identifies a role for miR-30a in the pathogenesis of neovascular retinal disease by modulating microglial and endothelial cell function, and suggests it may be a therapeutic target to treat ischemia-mediated conditions.

Mechanistic targeting of advanced glycation end-products in age-related diseases

Glycative stress, caused by the accumulation of cytotoxic and irreversibly-formed sugar-derived advanced glycation end-products (AGEs), contributes to morbidity associated with aging, age-related diseases, and metabolic diseases. In this review, we summarize pathways leading to formation of AGEs, largely from sugars and glycolytic intermediates, and discuss detoxification of AGE precursors, including the glyoxalase system and DJ-1/Park7 deglycase. Disease pathogenesis downstream of AGE accumulation can be cell autonomous due to aggregation of glycated proteins and impaired protein function, which occurs in ocular cataracts. Extracellular AGEs also activate RAGE signaling, leading to oxidative stress, inflammation, and leukostasis in diabetic complications such as diabetic retinopathy. Pharmaceutical agents have been tested in animal models and clinically to diminish glycative burden. We summarize existing strategies and point out several new directions to diminish glycative stress including: plant-derived polyphenols as AGE inhibitors and glyoxalase inducers; improved dietary patterns, particularly Mediterranean and low glycemic diets; and enhancing proteolytic capacities of the ubiquitin-proteasome and autophagy pathways that are involved in cellular clearing of AGEs.

Increased serum periostin concentrations are associated with the presence of diabetic retinopathy in patients with type 2 diabetes mellitus

PURPOSE

To determine the association between serum periostin and the presence of diabetic retinopathy (DR).

METHODS

Serum periostin was detected in 114 healthy subjects, 122 patients with type 2 diabetes mellitus (T2DM) and 159 patients with DR and compared among groups. Clinical data and other laboratory measurements such as glycated hemoglobin (HbA1c), lipid profiles, serum creatinine (Cr) and high-sensitivity CRP (hsCRP) were also collected and compared among groups. For subgroup analysis, patients with DR were divided into a non-proliferated diabetic retinopathy (NPDR) group and a proliferated diabetic retinopathy (PDR) group. Multivariate analysis was performed using logistic regression models.

RESULTS

The serum periostin level was significantly higher in patients with diabetic retinopathy compared with healthy subjects and patients with T2DM (both P < 0.001, respectively). Also, the periostin level was significantly higher in the PDR group compared to the NPDR group (P = 0.044). Multivariate logistic regression revealed that serum periostin was independently associated with the presence of DR in patients with T2DM (P < 0.001). The receiver operating characteristic (ROC) curves for DR development using serum periostin showed that the area under the receiver operating characteristic curves (AUC) was 0.838 (P < 0.001).

CONCLUSIONS

The current study demonstrated that serum periostin is significantly associated with the presence of DR in patients with T2DM and is an independent risk factor of DR.

Sustained high glucose exposure sensitizes macrophage responses to cytokine stimuli but reduces their phagocytic activity

Background

Macrophages are tissue resident immune cells important for host defence and homeostasis. During diabetes, macrophages and other innate immune cells are known to have a pro-inflammatory phenotype, which is believed to contribute to the pathogenesis of various diabetic complications. However, diabetic patients are highly susceptible to bacterial infections, and often have impaired wound healing. The molecular mechanism underlying the paradox of macrophage function in diabetes is not fully understood. Recent evidence suggests that macrophage functions are governed by metabolic reprograming. Diabetes is a disorder that affects glucose metabolism; dysregulated macrophage function in diabetes may be related to alterations in their metabolic pathways. In this study, we seek to understand the effect of high glucose exposure on macrophage phenotype and functions.

Results

Bone marrow cells were cultured in short or long term high glucose and normal glucose medium; the number and phenotype of bone marrow derived macrophages were not affected by long-term high glucose treatment. Short-term high glucose increased the expression of IL-1β. Long-term high glucose increased the expression of IL-1β and TNFα but reduced the expression of IL-12p40 and nitric oxide production in M1 macrophage. The treatment also increased Arg-1 and IL-10 expression in M2 macrophages. Phagocytosis and bactericidal activity was reduced in long-term high glucose treated macrophages and peritoneal macrophages from diabetic mice. Long-term high glucose treatment reduced macrophage glycolytic capacity and glycolytic reserve without affecting mitochondrial ATP production and oxidative respiration.

Conclusion

Long-term high glucose sensitizes macrophages to cytokine stimulation and reduces phagocytosis and nitric oxide production, which may be related to impaired glycolytic capacity.

Electronic supplementary material

The online version of this article (10.1186/s12865-018-0261-0) contains supplementary material, which is available to authorized users.

TRPC proteins contribute to development of diabetic retinopathy and regulate glyoxalase 1 activity and methylglyoxal accumulation

OBJECTIVE

Diabetic retinopathy (DR) is induced by an accumulation of reactive metabolites such as ROS, RNS, and RCS species, which were reported to modulate the activity of cation channels of the TRPC family. In this study, we use Trpc1/4/5/6^-/- compound knockout mice to analyze the contribution of these TRPC proteins to diabetic retinopathy.

METHODS

We used Nanostring- and qPCR-based analysis to determine mRNA levels of TRPC channels in control and diabetic retinae and retinal cell types. Chronic hyperglycemia was induced by Streptozotocin (STZ) treatment. To assess the development of diabetic retinopathy, vasoregression, pericyte loss, and thickness of individual retinal layers were analyzed. Plasma and cellular methylglyoxal (MG) levels, as well as Glyoxalase 1 (GLO1) enzyme activity and protein expression, were measured in WT and Trpc1/4/5/6^-/- cells or tissues. MG-evoked toxicity in cells of both genotypes was compared by MTT assay.

RESULTS

We find that Trpc1/4/5/6^-/- mice are protected from hyperglycemia-evoked vasoregression determined by the formation of acellular capillaries and pericyte drop-out. In addition, Trpc1/4/5/6^-/- mice are resistant to the STZ-induced reduction in retinal layer thickness. The RCS metabolite methylglyoxal, which represents a key mediator for the development of diabetic retinopathy, was significantly reduced in plasma and red blood cells (RBCs) of STZ-treated Trpc1/4/5/6^-/- mice compared to controls. GLO1 is the major MG detoxifying enzyme, and its activity and protein expression were significantly elevated in Trpc1/4/5/6-deficient cells, which led to significantly increased resistance to MG toxicity. GLO1 activity was also increased in retinal extracts from Trpc1/4/5/6^-/- mice. The TRPCs investigated here are expressed at different levels in endothelial and glial cells of the retina.

CONCLUSION

The protective phenotype in diabetic retinopathy observed in Trpc1/4/5/6^-/- mice is suggestive of a predominant action of TRPCs in Müller cells and microglia because of their central position in the retention of a proper homoeostasis of the neurovascular unit.

Diabetic retinopathy: hyperglycaemia, oxidative stress and beyond

Diabetic retinopathy remains a relevant clinical problem. In parallel with diagnostic and therapeutic improvements, the role of glycaemia and reactive metabolites causing cell stress and biochemical abnormalities as treatment targets needs continuous re-evaluation. Furthermore, the basic mechanisms of physiological angiogenesis, remodelling and pruning give important clues about the origins of vasoregression during the very early stages of diabetic retinopathy and can be modelled in animals. This review summarises evidence supporting a role for the neurovascular unit-composed of neuronal, glial and vascular cells-as a responder to the biochemical changes imposed by reactive metabolites and high glucose. Normoglycaemic animal models developing retinal degeneration, provide valuable information about common pathways downstream of progressive neuronal damage that induce vasoregression, as in diabetic models. These models can serve to assess novel treatments addressing the entire neurovascular unit for the benefit of early diabetic retinopathy.

Advanced glycation endproducts link inflammatory cues to upregulation of galectin-1 in diabetic retinopathy

Diabetic retinopathy (DR) is an inflammatory and progressive vaso-occlusive disease resulting in angiogenesis. Galectin-1 is a hypoxia-induced angiogenic factor associated with cancer and proliferative DR. Here we reveal a significant upregulation of galectin-1 in eyes of DR patients along with progression of clinical stages beginning from the pre-ischemic, inflammatory stage with diabetic macular edema, but not in eyes with non-diabetic retinal vascular occlusions. As for its regulatory mechanism unrelated to hypoxia but selective to DR, in vitro galectin-1/LGALS1 expression was shown to increase after application to Müller glial cells with interleukin (IL)-1β, which was induced in monocyte-derived macrophages and microglial cells via toll-like receptor (TLR) 4 signaling stimulated by advanced glycation endproducts (AGE). In vivo inhibition of AGE generation with aminoguanidine, macrophage depletion with clodronate liposomes, and antibody-based blockade of Il-1β and Tlr4 attenuated diabetes-induced retinal Lgals1 expression in mice. Fibrovascular tissues from proliferative DR eyes were immunoreactive for AGE, TRL4 and IL-1β in macrophages, and IL-1β receptor-positive glial cells expressed galectin-1. Therefore, diabetes-induced retinal AGE accumulation was suggested to activate IL-1β-related inflammatory cues in macrophages followed by Müller cells, linking to galectin-1 upregulation in human DR with time. Our data highlight AGE-triggered inflammation as the DR-selective inducer of galectin-1.

Glycation & the RAGE axis: targeting signal transduction through DIAPH1

INTRODUCTION

The consequences of chronic disease are vast and unremitting; hence, understanding the pathogenic mechanisms mediating such disorders holds promise to identify therapeutics and diminish the consequences. The ligands of the receptor for advanced glycation end products (RAGE) accumulate in chronic diseases, particularly those characterized by inflammation and metabolic dysfunction. Although first discovered and reported as a receptor for advanced glycation end products (AGEs), the expansion of the repertoire of RAGE ligands implicates the receptor in diverse milieus, such as autoimmunity, chronic inflammation, obesity, diabetes, and neurodegeneration. Areas covered: This review summarizes current knowledge regarding the ligand families of RAGE and data from human subjects and animal models on the role of the RAGE axis in chronic diseases. The recent discovery that the cytoplasmic domain of RAGE binds to the formin homology 1 (FH1) domain, DIAPH1, and that this interaction is essential for RAGE ligand-stimulated signal transduction, is discussed. Finally, we review therapeutic opportunities targeting the RAGE axis as a means to mitigate chronic diseases. Expert commentary: With the aging of the population and the epidemic of cardiometabolic disease, therapeutic strategies to target molecular pathways that contribute to the sequelae of these chronic diseases are urgently needed. In this review, we propose that the ligand/RAGE axis and its signaling nexus is a key factor in the pathogenesis of chronic disease and that therapeutic interruption of this pathway may improve quality and duration of life.

Pericytes, an overlooked player in vascular pathobiology

Pericytes are a heterogeneous population of cells located in the blood vessel wall. They were first identified in the 19th century by Rouget, however their biological role and potential for drug targeting have taken time to be recognised. Isolation of pericytes from several different tissues has allowed a better phenotypic and functional characterization. These findings revealed a tissue-specific, multi-functional group of cells with multilineage potential. Given this emerging evidence, pericytes have acquired specific roles in pathobiological events in vascular diseases. In this review article, we will provide a compelling overview of the main diseases in which pericytes are involved, from well-established mechanisms to the latest findings. Pericyte involvement in diabetes and cancer will be discussed extensively. In the last part of the article we will review therapeutic approaches for these diseases in light of the recently acquired knowledge. To unravel pericyte-related vascular pathobiological events is pivotal not only for more tailored treatments of disease but also to establish pericytes as a therapeutic tool.

Receptor for Advanced Glycation End Products-Mediated Signaling Impairs the Maintenance of Bone Marrow Mesenchymal Stromal Cells in Diabetic Model Mice

Bone marrow mesenchymal stromal cells (BM-MSCs) have been demonstrated to contribute to tissue regeneration. However, chronic pathological conditions, such as diabetes and aging, can result in a decreased number and/or quality of BM-MSCs. We therefore investigated the maintenance mechanism of BM-MSCs by studying signaling through the receptor for advanced glycation end products (RAGE), which is thought to be activated under various pathological conditions. The abundance of endogenous BM-MSCs decreased in a type 2 diabetes mellitus (DM2) model, as determined by performing colony-forming unit (CFU) assays. Flow cytometric analysis revealed that the prevalence of the Lin^-/ckit^-/CD106⁺/CD44^- BM population, which was previously identified as a slow-cycling BM-MSC population, also decreased. Furthermore, in a streptozotocin-induced type 1 DM model (DM1), the CFUs of fibroblasts and the prevalence of the Lin^-/ckit^-/CD106⁺/CD44^- BM population also significantly decreased. BM-MSCs in RAGE knockout (KO) mice were resistant to such reduction induced by streptozotocin treatment, suggesting that chronic RAGE signaling worsened the maintenance mechanism of BM-MSCs. Using an in vitro culture condition, BM-MSCs from RAGE-KO mice showed less proliferation and expressed significantly more Nanog and Oct-4, which are key factors in multipotency, than did wild-type BM-MSCs. Furthermore, RAGE-KO BM-MSCs showed a greater capacity for differentiation into mesenchymal lineages, such as adipocytes and osteocytes. These data suggested that RAGE signaling inhibition is useful for maintaining BM-MSCs in vitro. Together, our findings indicated that perturbation of BM-MSCs in DM could be partially explained by chronic RAGE signaling and that targeting the RAGE signaling pathway is a viable approach for maintaining BM-MSCs under chronic pathological conditions.

Association of genetic variants in the receptor for advanced glycation end products gene with diabetic retinopathy: A meta-analysis

BACKGROUND

Diabetic retinopathy (DR) is a major sight-threatening diabetic complication. Previous studies have examined the association of DR with multiple genetic variants in the receptor for advanced glycation end products (RAGE) gene, with inconsistent results.

OBJECTIVE

To perform a systematic literature search and conduct meta-analyses to examine the association of genetic variants in RAGE with DR.

DATA SOURCES

PubMed, Cochrane Library, Embase, Google Scholar, and HuGE.

STUDY ELIGIBILITY CRITERIA AND PARTICIPANTS

Studies were on human subjects; the studies were case-control ones and included subjects who had DR and those who did not have DR; and the studies provided genotype data for genetic variants in RAGE, separately for subjects who had and did not have DR, or provided odds ratios (ORs) and the 95% confidence intervals (CIs), or provided sufficient data for the calculation of OR and the 95% CI.

STUDY APPRAISAL AND SYNTHESIS METHODS

We used OR as a measure of association, and used random-effects model in all the meta-analyses. Between-study heterogeneity was assessed using I, and publication bias was evaluated using Egger test.

RESULTS

A total of 13 studies met the eligibility criteria and were included in our analyses. We found that Gly82Ser was significantly associated with DR (OR = 2.40, 95% CI: 1.46-3.97; P = 0.001) using a recessive model. -374T/A also showed significant association with DR under a dominant model (OR = 1.21, 95% CI: 1.03-1.43; P = 0.023). We did not find a significant association of DR with other genetic variants in RAGE.

LIMITATIONS

The number of included studies is small for some genetic variants; duration of diabetes varied across studies; most studies were conducted in Asia; and it is not clear whether the observed association can be generalized to other ethnicities; and we could not control for other potential confounding factors.

CONCLUSIONS AND IMPLICATIONS OF KEY FINDINGS

We found that Gly82Ser in RAGE showed significant association with DR. More studies with larger sample sizes that control for important risk factors, such as duration of diabetes, are needed to validate our findings.

Adeno-Associated Virus Overexpression of Angiotensin-Converting Enzyme-2 Reverses Diabetic Retinopathy in Type 1 Diabetes in Mice

Angiotensin-converting enzyme (ACE)-2 is the primary enzyme of the vasoprotective axis of the renin angiotensin system that regulates the classic renin angiotensin system axis. We aimed to determine whether local retinal overexpression of adenoassociated virus (AAV)-ACE2 prevents or reverses diabetic retinopathy. Green fluorescent protein (GFP)-chimeric mice were generated to distinguish resident (retinal) from infiltrating bone marrow-derived inflammatory cells and were made diabetic using streptozotocin injections. Retinal digestion using trypsin was performed and acellular capillaries enumerated. Capillary occlusion by GFP(+) cells was used to measure leukostasis. Overexpression of ACE2 prevented (prevention cohort: untreated diabetic, 11.3 ± 1.4; ACE2 diabetic, 6.4 ± 0.9 per mm(2)) and partially reversed (reversal cohort: untreated diabetic, 15.7 ± 1.9; ACE2 diabetic, 6.5 ± 1.2 per mm(2)) the diabetes-associated increase of acellular capillaries and the increase of infiltrating inflammatory cells into the retina (F4/80(+)) (prevention cohort: untreated diabetic, 24.2 ± 6.7; ACE2 diabetic, 2.5 ± 1.6 per mm(2); reversal cohort: untreated diabetic, 56.8 ± 5.2; ACE2 diabetic, 5.6 ± 2.3 per mm(2)). In both study cohorts, intracapillary bone marrow-derived cells, indicative of leukostasis, were only observed in diabetic animals receiving control AAV injections. These results indicate that diabetic retinopathy, and possibly other diabetic microvascular complications, can be prevented and reversed by locally restoring the balance between the classic and vasoprotective renin angiotensin system.

Extract of Polygonum cuspidatum Attenuates Diabetic Retinopathy by Inhibiting the High-Mobility Group Box-1 (HMGB1) Signaling Pathway in Streptozotocin-Induced Diabetic Rats

High-mobility group box-1 (HMGB1) is a well-known pro-inflammatory cytokine. We aimed to investigate the effect of the ethanol extract of the root of P. cuspidatum (PCE) on retinal inflammation in diabetic retinopathy. PCE (100 or 350 mg/kg/day) was administered to diabetic rats for 16 weeks, and hyperglycemia and body weight loss developed in the diabetic rats. The retinal expression levels of HMGB1 and receptor for advanced glycation end products (RAGE) and the activity of nuclear factor-kappa B (NF-κB) in the retina were examined. Additionally, a chromatin immunoprecipitation assay was performed to analyze the binding of NF-κB binding to the RAGE promoter in the diabetic retinas. The levels of HMGB1 and RAGE expression, NF-κB activity, and NF-κB binding to the RAGE promoter were increased in the diabetic retinas. However, treatment with PCE ameliorated the increases in HMGB1 and RAGE expression, and NF-κB activity in the retina. In addition, in diabetic rats, retinal vascular permeability and the loosening of the tight junctions were inhibited by PCE. These findings suggest that PCE has a preventative effect against diabetes-induced vascular permeability by inhibiting HMGB1-RAGE-NF-κB activation in diabetic retinas. The oral administration of PCE may significantly help to suppress the development of diabetic retinopathy in patients with diabetes.

High Glucose Stimulates Tumorigenesis in Hepatocellular Carcinoma Cells Through AGER-Dependent O-GlcNAcylation of c-Jun

Epidemiologic studies suggest that hepatocellular carcinoma (HCC) has a strong relationship with diabetes. However, the underlying molecular mechanisms still remain unclear. Here, we demonstrated that high glucose (HG), one of the main characteristics of diabetes, was capable of accelerating tumorigenesis in HCC cells. Advanced glycosylation end product-specific receptor (AGER) was identified as a stimulator during this process. Mechanistically, AGER activated a hexosamine biosynthetic pathway, leading to enhanced O-GlcNAcylation of target proteins. Notably, AGER was capable of increasing activity and stability of proto-oncoprotein c-Jun via O-GlcNAcylation of this protein at Ser73. Interestingly, c-Jun can conversely enhance AGER transcription. Thereby, a positive autoregulatory feedback loop that stimulates diabetic HCC was established. Finally, we found that AG490, an inhibitor of Janus kinase, has the ability to impair AGER expression and its functions in HCC cells. In conclusion, AGER and its functions to stimulate O-GlcNAcylation are important during liver tumorigenesis, when high blood glucose levels are inadequately controlled.

Palmitoylethanolamide, a Natural Retinoprotectant: Its Putative Relevance for the Treatment of Glaucoma and Diabetic Retinopathy

Retinopathy is a threat to the eyesight, and glaucoma and diabetes are the main causes for the damage of retinal cells. Recent insights pointed out a common pathogenetic pathway for both disorders, based on chronic inflammation. Palmitoylethanolamide (PEA) is an endogenous cell protective lipid. Since its discovery in 1957 as a biologically active component in foods and in many living organisms, around 500 scientific papers have been published on PEA's anti-inflammatory and neuron-protective properties. PEA has been evaluated for glaucoma, diabetic retinopathy, and uveitis, pathological states based on chronic inflammation, respiratory disorders, and various pain syndromes in a number of clinical trials since the 70s of 20th century. PEA is available as a food supplement (PeaPure) and as diet food for medical purposes in Italy (Normast, PeaVera, and Visimast). These products are notified in Italy for the nutritional support in glaucoma and neuroinflammation. PEA has been tested in at least 9 double blind placebo controlled studies, among which two studies were in glaucoma, and found to be safe and effective up to 1.8 g/day, with excellent tolerability. PEA therefore holds a promise in the treatment of a number of retinopathies. We discuss PEA as a putative anti-inflammatory and retinoprotectant compound in the treatment of retinopathies, especially related to glaucoma and diabetes.

Advanced Glycation End Products Impair Voltage-Gated K+ Channels-Mediated Coronary Vasodilation in Diabetic Rats

Background

We have previously reported that high glucose impairs coronary vasodilation by reducing voltage-gated K⁺ (K_v) channel activity. However, the underlying mechanisms remain unknown. Advanced glycation end products (AGEs) are potent factors that contribute to the development of diabetic vasculopathy. The aim of this study was to investigate the role of AGEs in high glucose-induced impairment of K_v channels-mediated coronary vasodilation.

Methods

Patch-clamp recording and molecular biological techniques were used to assess the function and expression of K_v channels. Vasodilation of isolated rat small coronary arteries was measured using a pressurized myograph. Treatment of isolated coronary vascular smooth muscle cells (VSMCs) and streptozotocin-induced diabetic rats with aminoguanidine, the chemical inhibitor of AGEs formation, was performed to determine the contribution of AGEs.

Results

Incubation of VSMCs with high glucose reduced K_v current density by 60.4 ± 4.8%, and decreased expression of K_v1.2 and K_v1.5 both at the gene and protein level, whereas inhibiting AGEs formation or blocking AGEs interacting with their receptors prevented high glucose-induced impairment of K_v channels. In addition, diabetic rats manifested reduced K_v channels-mediated coronary dilation (9.3 ± 1.4% vs. 36.9 ± 1.4%, P < 0.05), which was partly corrected by the treatment with aminoguanidine (24.4 ± 2.2% vs. 9.3 ± 1.4%, P < 0.05).

Conclusions

Excessive formation of AGEs impairs K_v channels in VSMCs, then leading to attenuation of K_v channels-mediated coronary vasodilation.