Marrow-derived cells regulate the development of early diabetic retinopathy and tactile allodynia in mice

Intestinal neutrophil extracellular traps promote gut barrier damage exacerbating endotoxaemia, systemic inflammation and progression of diabetic retinopathy in type 2 diabetes

AIMS/HYPOTHESIS

Within the small intestine, neutrophils play an integral role in preventing bacterial infection. Upon interaction with bacteria or bacteria-derived antigens, neutrophils initiate a multi-staged response of which the terminal stage is NETosis, formation of protease-decorated nuclear DNA into extracellular traps. NETosis has a great propensity to elicit ocular damage and has been associated with diabetic retinopathy and diabetic macular oedema (DME) progression. Here, we interrogate the relationship between gut barrier dysfunction, endotoxaemia and systemic and intestinal neutrophilia in diabetic retinopathy.

METHODS

In a cohort of individuals with type 2 diabetes (n=58) with varying severity of diabetic retinopathy and DME, we characterised the abundance of circulating neutrophils by flow cytometry and markers of gut permeability and endotoxaemia by plasma ELISA. In a mouse model of type 2 diabetes, we examined the effects of diabetes on abundance and function of intestinal, blood and bone marrow neutrophils, gut barrier integrity, endotoxaemia and diabetic retinopathy severity. Pharmacological inhibition of NETosis was achieved by i.p. injection of the peptidyl arginine deiminase 4 inhibitor (PAD4i) GSK484 daily for 4 weeks between 6 and 7 months of type 2 diabetes.

RESULTS

In human participants, neutrophilia was unique to individuals with type 2 diabetes with diabetic retinopathy and DME and was accompanied by heightened circulating markers of gut permeability. At late-stage diabetes, neutrophilia and gut barrier dysfunction were seen in db/db mice. The db/db mice exhibited an increase in stem-like pre-neutrophils in the intestine and bone marrow and a decrease in haematopoietic vascular reparative cells. In the db/db mouse intestine, enhanced loss of gut barrier integrity was associated with elevated intestinal NETosis. Inhibition of NETosis by the PAD4i GSK484 resulted in decreased abundance of premature neutrophils in the intestine and blood and resulted in neutrophil retention in the bone marrow compared with vehicle-treated db/db mice. Additionally, the PAD4i decreased senescence within the gut epithelium and yielded a slowing of diabetic retinopathy progression.

CONCLUSIONS/INTERPRETATION

Severity of diabetic retinopathy and DME were associated with peripheral neutrophilia, gut barrier dysfunction and endotoxaemia in the human participants. db/db mice exhibited intestinal neutrophilia, specifically stem-like pre-neutrophils, which was associated with elevated NETosis and decreased levels of vascular reparative cells. Chronic inhibition of NETosis in db/db mice reduced intestinal senescence and NETs in the retina. These changes were associated with reduced endotoxaemia and an anti-inflammatory bone marrow milieu with retention of pre-neutrophils in the bone marrow and increased gut infiltration of myeloid angiogenic cells. Collectively, PAD-4i treatment decreased gut barrier dysfunction, restoring physiological haematopoiesis and levels of haematopoietic vascular reparative cells.

Neutrophil Extracellular Traps (NETs) as a Potential Target for Anti-Aging: Role of Therapeutic Apheresis

Neutrophil extracellular traps (NETs) are large structures composed of chromatin, histones and granule-derived proteins released extracellularly by neutrophils. They are generally considered to be a part of the antimicrobial defense strategy, preventing the dissemination of pathogens. However, overproduction of NETs or their ineffective clearance can drive various pathologies, many of which are associated with advanced age and involve uncontrolled inflammation, oxidative, cardiovascular and neurodegenerative stress as underlying mechanisms. Targeting NETs in the elderly as an anti-aging therapy seems to be a very attractive therapeutic approach. Therapeutic apheresis with a specific filter to remove NETs could be a promising strategy worth considering.

Identification of PDGFA as a Neutrophil-related Biomarker Linked to the Advancement of Diabetic Retinopathy through Integrated Bioinformatics Analysis

BACKGROUND

The dysregulation of the innate immune system plays a crucial role in the development of Diabetic Retinopathy (DR). To gain an insight into the underlying mechanism of DR, it is essential to identify specific biomarkers associated with immune cell infiltration.

METHODS

In this study, we retrieved the GSE94019 and GSE60436 datasets from the Gene Expression Omnibus (GEO) database. By utilizing CIBERSORT, MCPcounter, and xCell algorithms, we conducted a comprehensive analysis of the immune cell infiltration landscape in DR. The limma package was employed to identify Differentially Expressed Necroptosis-related Genes (DENRGs). Subsequently, enrichment analysis was performed to investigate the potential functions of the DENRGs. To identify the core DENRGs, the CytoHubba plug-in in Cytoscape software was utilized. The expression levels of these core DENRGs were verified in an independent dataset.

RESULTS

Our analysis identified 213 DENRGs, and among them, Platelet-derived Growth Factor subunit A (PDGFA) was identified as a core DENRG. Notably, the expression of PDGFA was found to be upregulated in DR, and this finding was further validated in the GSE102485 dataset. Additionally, the results of GSVA and GSEA revealed that in the high PDGFA group, there was activation of pathways related to inflammation and the immune system. Moreover, analysis of immune infiltration demonstrated a significant association between PDGFA gene expression and the infiltration levels of specific immune cells, including basophils, macrophages M1, macrophages, neutrophils, monocytes, NK cells, and B cells.

CONCLUSION

The involvement of neutrophils in the development and progression of DR is suggested. PDGFA has emerged as a potential marker and is linked to the infiltration of immune cells in DR. These findings shed new light on the underlying mechanisms of DR.

Unveiling the role of lipopolysaccharide-related genes in diabetic retinopathy: identification of key biomarkers and immune infiltration analysis

BACKGROUND

Growing evidence suggests a link between systemic lipopolysaccharide (LPS) exposure and worsening diabetic retinopathy (DR). This study aims to investigate DR's pathogenesis by analyzing LPS-related genes (LRGs) through bioinformatics.

METHODS

The CTD database was utilized to identify LRGs. The datasets associated with DR were acquired from the GEO database. The Venn diagram was used to identify the differentially expressed LRGs (DLRGs), and the putative molecular mechanism of these DLRGs was investigated through functional enrichment analysis. We used WGCNA, Lasso regression, and RF to identify hub DLRGs. The expression levels of these hub DLRGs were validated in an independent dataset (GSE102485) and cell experiments. Employing the CIBERSORT algorithm, we examined the infiltration of 22 distinct immune cell types in DR and assessed the association between key DLRGs and immune infiltrates through correlation analysis.

RESULTS

A total of 71 DLRGs were detected. These genes exhibited significant enrichment in pathways associated with inflammation. In addition, the in-depth analysis uncovered that five hub DLRGs (STK33 and EPHX2) linked to bacterial LPS displayed noteworthy diagnostic potential for individuals diagnosed with DR. The hub DLRGs expression in the high glucose-induced DR model was confirmed by qRT-PCR analysis. Furthermore, examination of immune infiltration indicated a significant association between these five genes and the extent of immune cell infiltration.

CONCLUSION

STK33 and EPHX2 serve as biomarkers related to bacterial LPS. Exploring these genes in-depth could provide innovative ideas and a foundation for comprehending the progression of the disease and developing targeted treatments for DR.

Mechanism and therapeutic targets of circulating immune cells in diabetic retinopathy

Diabetic retinopathy (DR) continues to be the leading cause of preventable vision loss among working-aged adults, marked by immune dysregulation within the retinal microenvironment. Typically, the retina is considered as an immune-privileged organ, where circulating immune cells are restricted from entry under normal conditions. However, during the progression of DR, this immune privilege is compromised as circulating immune cells breach the barrier and infiltrate the retina. Increasing evidence suggests that vascular and neuronal degeneration in DR is largely driven by the infiltration of immune cells, particularly neutrophils, monocyte-derived macrophages, and lymphocytes. This review delves into the mechanisms and therapeutic targets associated with these immune cell populations in DR, offering a promising and innovative approach to managing the disease.

Mechanical Regulation of Retinal Vascular Inflammation and Degeneration in Diabetes

Vascular inflammation is known to cause degeneration of retinal capillaries in early diabetic retinopathy (DR), a major microvascular complication of diabetes. Past studies investigating these diabetes-induced retinal vascular abnormalities have focused primarily on the role of molecular or biochemical cues. Here we show that retinal vascular inflammation and degeneration in diabetes are also mechanically regulated by the increase in retinal vascular stiffness caused by overexpression of the collagen-cross-linking enzyme lysyl oxidase (LOX). Treatment of diabetic mice with LOX inhibitor β-aminopropionitrile (BAPN) prevented the increase in retinal capillary stiffness, vascular intracellular adhesion molecule-1 overexpression, and leukostasis. Consistent with these anti-inflammatory effects, BAPN treatment of diabetic mice blocked the upregulation of proapoptotic caspase-3 in retinal vessels, which concomitantly reduced retinal capillary degeneration, pericyte ghost formation, and the diabetes-induced loss of contrast sensitivity in these mice. Finally, our in vitro studies indicate that retinal capillary stiffening is sufficient to increase the adhesiveness and neutrophil elastase-induced death of retinal endothelial cells. By uncovering a link between LOX-dependent capillary stiffening and the development of retinal vascular and functional defects in diabetes, these findings offer a new insight into DR pathogenesis that has important translational potential.

ARTICLE HIGHLIGHTS

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.

Early Depletion of Neutrophils Reduces Retinal Inflammation and Neovascularization in Mice with Oxygen-Induced Retinopathy

Retinal inflammation is a central feature of ocular neovascular diseases such as diabetic retinopathy and retinopathy of prematurity, but the contribution of neutrophils to this process is not fully understood. We studied oxygen-induced retinopathy (OIR) which develops in two phases, featuring hyperoxia-induced retinal vaso-obliteration in phase I, followed by retinal neovascularization in phase II. As neutrophils are acute responders to tissue damage, we evaluated whether neutrophil depletion with an anti-Ly6G mAb administered in phase I OIR influenced retinal inflammation and vascular injury. Neutrophils were measured in blood and spleen via flow cytometry, and myeloperoxidase, an indicator of neutrophil activity, was evaluated in the retina using Western blotting. Retinal vasculopathy was assessed by quantitating vaso-obliteration, neovascularization, vascular leakage, and VEGF levels. The inflammatory factors, TNF, MCP-1, and ICAM-1 were measured in retina. In the OIR controls, neutrophils were increased in the blood and spleen in phase I but not phase II OIR. In OIR, the anti-Ly6G mAb reduced neutrophils in the blood and spleen, and myeloperoxidase, inflammation, and vasculopathy in the retina. Our findings revealed that the early rise in neutrophils in OIR primes the retina for an inflammatory and angiogenic response that promotes severe damage to the retinal vasculature.

Perilipin 2-positive mononuclear phagocytes accumulate in the diabetic retina and promote PPARγ-dependent vasodegeneration

Type 2 diabetes mellitus (T2DM), characterized by hyperglycemia and dyslipidemia, leads to nonproliferative diabetic retinopathy (NPDR). NPDR is associated with blood-retina barrier disruption, plasma exudates, microvascular degeneration, elevated inflammatory cytokine levels, and monocyte (Mo) infiltration. Whether and how the diabetes-associated changes in plasma lipid and carbohydrate levels modify Mo differentiation remains unknown. Here, we show that mononuclear phagocytes (MPs) in areas of vascular leakage in DR donor retinas expressed perilipin 2 (PLIN2), a marker of intracellular lipid load. Strong upregulation of PLIN2 was also observed when healthy donor Mos were treated with plasma from patients with T2DM or with palmitate concentrations typical of those found in T2DM plasma, but not under high-glucose conditions. PLIN2 expression correlated with the expression of other key genes involved in lipid metabolism (ACADVL, PDK4) and the DR biomarkers ANGPTL4 and CXCL8. Mechanistically, we show that lipid-exposed MPs induced capillary degeneration in ex vivo explants that was inhibited by pharmaceutical inhibition of PPARγ signaling. Our study reveals a mechanism linking dyslipidemia-induced MP polarization to the increased inflammatory cytokine levels and microvascular degeneration that characterize NPDR. This study provides comprehensive insights into the glycemia-independent activation of Mos in T2DM and identifies MP PPARγ as a target for inhibition of lipid-activated MPs in DR.

Activated cGAS/STING signaling elicits endothelial cell senescence in early diabetic retinopathy

Diabetic retinopathy (DR) is a leading cause of blindness in working-age adults and remains an important public health issue worldwide. Here we demonstrate that the expression of stimulator of interferon genes (STING) is increased in patients with DR and animal models of diabetic eye disease. STING has been previously shown to regulate cell senescence and inflammation, key contributors to the development and progression of DR. To investigate the mechanism whereby STING contributes to the pathogenesis of DR, diabetes was induced in STING-KO mice and STINGGT (loss-of-function mutation) mice, and molecular alterations and pathological changes in the retina were characterized. We report that retinal endothelial cell senescence, inflammation, and capillary degeneration were all inhibited in STING-KO diabetic mice; these observations were independently corroborated in STINGGT mice. These protective effects resulted from the reduction in TBK1, IRF3, and NF-κB phosphorylation in the absence of STING. Collectively, our results suggest that targeting STING may be an effective therapy for the early prevention and treatment of DR.

CCR2-positive monocytes contribute to the pathogenesis of early diabetic retinopathy in mice

AIMS/HYPOTHESIS

Accumulating evidence suggests that leucocytes play a critical role in diabetes-induced vascular lesions and other abnormalities that characterise the early stages of diabetic retinopathy. However, the role of monocytes has yet to be fully investigated; therefore, we used Ccr2^-/- mice to study the role of CCR2⁺ inflammatory monocytes in the pathogenesis of diabetes-induced degeneration of retinal capillaries.

METHODS

Experimental diabetes was induced in wild-type and Ccr2^-/- mice using streptozotocin. After 2 months, superoxide levels, expression of inflammatory genes, leucostasis, leucocyte- and monocyte-mediated cytotoxicity against retinal endothelial cell death, retinal thickness and visual function were evaluated. Retinal capillary degeneration was determined after 8 months of diabetes. Flow cytometry of peripheral blood for differential expression of CCR2 in monocytes was assessed.

RESULTS

In nondiabetic mice, CCR2 was highly expressed on monocytes, and Ccr2^-/- mice lack CCR2⁺ monocytes in the peripheral blood. Diabetes-induced retinal superoxide, expression of proinflammatory genes Inos and Icam1, leucostasis and leucocyte-mediated cytotoxicity against retinal endothelial cells were inhibited in diabetic Ccr2-deficient mice and in chimeric mice lacking Ccr2 only from myeloid cells. In order to focus on monocytes, these cells were immuno-isolated after 2 months of diabetes, and they significantly increased monocyte-mediated endothelial cell cytotoxicity ex vivo. Monocytes from Ccr2-deficient mice caused significantly less endothelial cell death. The diabetes-induced retinal capillary degeneration was inhibited in Ccr2^-/- mice and in chimeric mice lacking Ccr2 only from myeloid cells.

CONCLUSIONS/INTERPRETATION

CCR2⁺ inflammatory monocytes contribute to the pathogenesis of early lesions of diabetic retinopathy.

Identifying Hyperreflective Foci in Diabetic Retinopathy via VEGF-Induced Local Self-Renewal of CX3CR1+ Vitreous Resident Macrophages

Intraretinal hyperreflective foci (HRF) are significant biomarkers for diabetic macular edema. However, HRF at the vitreoretinal interface (VRI) have not been examined in diabetic retinopathy (DR). A prospective observational clinical study with 162 consecutive eyes using OCT imaging showed significantly increased HRF at the VRI during DR progression (P < 0.01), which was reversed by anti-vascular endothelial growth factor (VEGF) therapy. F4/80+ macrophages increased significantly at the VRI in Kimba (vegfa+/+) or Akimba (Akita × Kimba) mice (both P < 0.01), but not in diabetic Akita (Ins2+/-) mice, indicating macrophage activation was modulated by elevated VEGF rather than the diabetic milieu. Macrophage depletion significantly reduced HRF at the VRI (P < 0.01). Furthermore, BrdU administration in Ccr2rfp/+Cx3cr1gfp/+vegfa+/- mice identified a significant contribution of M2-like tissue-resident macrophages (TRMs) at the VRI. Ki-67+ and CD11b+ cells were observed in preretinal tissues of DR patients, while exposure of vitreal macrophages to vitreous derived from PDR patients induced a significant proliferation response in vitro (P < 0.01). Taken together, the evidence suggests that VEGF drives a local proliferation of vitreous resident macrophages (VRMs) at the VRI during DR. This phenomenon helps to explain the derivation and disease-relevance of the HRF lesions observed through OCT imaging in patients.

NAD+ metabolism in peripheral neuropathic pain

Nicotinamide adenine dinucleotide (NAD⁺) is an omnipresent metabolite that participates in redox reactions. Multiple NAD⁺-consuming enzymes are implicated in numerous biological processes, including transcription, signaling, and cell survival. Multiple pieces of evidence have demonstrated that NAD⁺-consuming enzymes, including poly(ADP-ribose) polymerases (PARPs), sirtuins (SIRTs), and sterile alpha and TIR motif-containing 1 (SARM1), play major roles in peripheral neuropathic pain of various etiologies. These NAD⁺ consumers primarily participate in peripheral neuropathic pain via mechanisms such as mitochondrial dysfunction, oxidative stress, and inflammation. Furthermore, NAD⁺ synthase and nicotinamide phosphoribosyltransferase (NAMPT) have recently been found to contribute to the regulation of pain. Here, we review the evidence indicating the involvement of NAD⁺ metabolism in the pathological mechanisms of peripheral neuropathic pain. Advanced understanding of the molecular and cellular mechanisms associated with NAD⁺ in peripheral neuropathic pain will facilitate the development of novel treatment options for diverse types of peripheral neuropathic pain.

Reducing Akt2 in retinal pigment epithelial cells causes a compensatory increase in Akt1 and attenuates diabetic retinopathy

The retinal pigment epithelium (RPE) plays an important role in the development of diabetic retinopathy (DR), a leading cause of blindness worldwide. Here we set out to explore the role of Akt2 signaling-integral to both RPE homeostasis and glucose metabolism-to DR. Using human tissue and genetically manipulated mice (including RPE-specific conditional knockout (cKO) and knock-in (KI) mice), we investigate whether Akts in the RPE influences DR in models of diabetic eye disease. We found that Akt1 and Akt2 activities were reciprocally regulated in the RPE of DR donor tissue and diabetic mice. Akt2 cKO attenuated diabetes-induced retinal abnormalities through a compensatory upregulation of phospho-Akt1 leading to an inhibition of vascular injury, inflammatory cytokine release, and infiltration of immune cells mediated by the GSK3β/NF-κB signaling pathway; overexpression of Akt2 has no effect. We propose that targeting Akt1 activity in the RPE may be a novel therapy for treating DR.

Nomogram for Prediction of Diabetic Retinopathy Among Type 2 Diabetes Population in Xinjiang, China

PURPOSE

To establish an accurate risk prediction model of diabetic retinopathy (DR) using cost effective and easily available patients' characteristics and clinical biomarkers.

PATIENTS AND METHODS

Totally 18,904 cases diagnosed type 2 diabetes mellitus (T2DM) were collected, among which 13,980 cases were selected after quality screening. The least absolute shrinkage and selection operator (LASSO) regression models were used for univariate analysis and factors selection, and the multi-factor logistic regression analysis was used to establish the prediction model. Discrimination, calibration, and clinical usefulness of the prediction model were assessed using AUC/ Harrell's C statistic, calibration plot, and decision curve analysis. Both the development group and validation group were assessed.

RESULTS

Candidate variables were selected by Lasso regression and multivariate logistic regression analysis. Finally, the candidate predictive variables were included diabetic peripheral neuropathy (DPN), age, neutrophilic granulocyte (NE), high-density lipoprotein (HDL), hemoglobin A1c (HbA1C), duration of T2DM, and glycosylated serum protein (GSP) were used to establish a nomogram model for predicting the risk of DR. In the development group, the area under the receiver operating characteristic curve (AUC) was 0.882 (95% CI, 0.875-0.888). In the validation group, the AUC was 0.870 (95% CI, 0.856-0.881). Meanwhile, the optimism-corrected Harrell's C statistic were 0.878 and 0.867 in the development group and the validation group, respectively. Decision curve analysis demonstrated that the nomogram was clinically useful.

CONCLUSION

We constructed and verified nomograms that could accurately predict the risk of DR in T2DM patients, which could be used to predict the personalized risk of DR patients in Xinjiang, China.

Regulation of Adrenergic, Serotonin, and Dopamine Receptors to Inhibit Diabetic Retinopathy: Monotherapies versus Combination Therapies

We compared monotherapies and combinations of therapies that regulate G-protein-coupled receptors (GPCRs) with respect to their abilities to inhibit early stages of diabetic retinopathy (DR) in streptozotocin-diabetic mice. Metoprolol (MTP; 0.04-1.0 mg/kg b.wt./day), bromocriptine (BRM; 0.01-0.1 mg/kg b.wt./day), doxazosin (DOX; 0.01-1.0 mg/kg b.wt./day), or tamsulosin (TAM; 0.05-0.25 mg/kg b.wt./day) were injected individually daily for 2 months in dose-response studies to assess their effects on the diabetes-induced increases in retinal superoxide and leukocyte-mediated cytotoxicity against vascular endothelial cells, both of which abnormalities have been implicated in the development of DR. Each of the individual drugs inhibited the diabetes-induced increase in retinal superoxide at the higher concentrations tested, but the inhibition was lost at lower doses. To determine whether combination therapies had superior effects over individual drugs, we intentionally selected for each drug a low dose that had little or no effect on the diabetes-induced retinal superoxide for use separately or in combinations in 8-month studies of retinal function, vascular permeability, and capillary degeneration in diabetes. At the low doses used, combinations of the drugs generally were more effective than individual drugs, but the low-dose MTP alone totally inhibited diabetes-induced reduction in a vision task, BRM or DOX alone totally inhibited the vascular permeability defect, and DOX alone totally inhibited diabetes-induced degeneration of retinal capillaries. Although low-dose MTP, BRM, DOX, or TAM individually had beneficial effects on some endpoints, combination of the therapies better inhibited the spectrum of DR lesions evaluated. SIGNIFICANCE STATEMENT: The pathogenesis of early stages of diabetic retinopathy remains incompletely understood, but multiple different cell types are believed to be involved in the pathogenic process. We have compared the effects of monotherapies to those of combinations of drugs that regulate GPCR signaling pathways with respect to their relative abilities to inhibit the development of early diabetic retinopathy.

Neutrophil-Derived Proteases Contribute to the Pathogenesis of Early Diabetic Retinopathy

Purpose

Previous studies indicate that leukocytes, notably neutrophils, play a causal role in the capillary degeneration observed in diabetic retinopathy (DR), however, the mechanism by which they cause such degeneration is unknown. Neutrophil elastase (NE) is a protease released by neutrophils which participates in a variety of inflammatory diseases. In the present work, we investigated the potential involvement of NE in the development of early DR.

Methods

Experimental diabetes was induced in NE-deficient mice (Elane-/-), in mice treated daily with the NE inhibitor, sivelestat, and in mice overexpressing human alpha-1 antitrypsin (hAAT+). Mice were assessed for diabetes-induced retinal superoxide generation, inflammation, leukostasis, and capillary degeneration.

Results

In mice diabetic for 2 months, deletion of NE or selective inhibition of NE inhibited diabetes-induced retinal superoxide levels and inflammation, and inhibited leukocyte-mediated cytotoxicity of retinal endothelial cells. In mice diabetic for 8 months, genetic deletion of NE significantly inhibited diabetes-induced retinal capillary degeneration.

Conclusions

These results suggest that a protease released from neutrophils contributes to the development of DR, and that blocking NE activity could be a novel therapy to inhibit DR.

Updates on sphingolipids: Spotlight on retinopathy

The sphingolipids ceramide (Cer), ceramide-1-phosphate (C1P), sphingosine (Sph), and sphingosine-1-phosphate (S1P)) are key signaling molecules that regulate many patho-biological processes. During the last decade, they have gained increasing attention since they may participate in important and numerous retinal processes, such as neuronal survival and death, proliferation and migration of neuronal and vascular cells, inflammation, and neovascularization. Cer for instance has emerged as a key mediator of inflammation and death of neuronal and retinal pigment epithelium cells in experimental models of retinopathies such as glaucoma, age-related macular degeneration (AMD), and retinitis pigmentosa. S1P may have opposite biological actions, preventing photoreceptor and ganglion cell degeneration but also promoting inflammation, fibrosis, and neovascularization in AMD, glaucoma, and pro-fibrotic disorders. Alterations in Cer, S1P, and ceramide 1- phosphate may also contribute to uveitis. Furthermore, use of inhibitors that either prevent Cer increase or modulate S1P signaling, such as Myriocin, desipramine, and Fingolimod (FTY720), have been shown to preserve neuronal viability and retinal function. Collectively, the expanding role for these sphingolipids in the modulation of vital processes in retina cell types and in their dysregulation in retinal degenerations makes them attractive therapeutic targets.

CD40 Expressed in Endothelial Cells Promotes Upregulation of ICAM-1 But Not Pro-Inflammatory Cytokines, NOS2 and P2X7 in the Diabetic Retina

Purpose

CD40 is an upstream inducer of inflammation in the diabetic retina. CD40 is upregulated in retinal endothelial cells in diabetes. The purpose of this study was to determine whether expression of CD40 in endothelial cells is sufficient to promote inflammatory responses in the retina of diabetic mice.

Methods

Transgenic mice with CD40 expression restricted to endothelial cells (Trg-CD40 EC), transgenic control mice (Trg-Ctr), B6, and CD40^−/− mice were made diabetic using streptozotocin. Leukostasis was assessed using FITC-conjugated ConA. Pro-inflammatory molecule expression was examined by real-time PCR, immunohistochemistry, ELISA, or flow cytometry. Release of ATP was assessed by ATP bioluminescence.

Results

Diabetic B6 and Trg-CD40 EC mice exhibited increased retinal mRNA levels of ICAM-1, higher ICAM-1 expression in endothelial cells, and increased leukostasis. These responses were not detected in diabetic mice that lacked CD40 (CD40^−/− and Trg-Ctr). Diabetic B6 but not Trg-CD40 EC mice upregulated TNF-α, IL-1β, and NOS2 mRNA levels. CD40 stimulation in retinal endothelial cells upregulated ICAM-1 but not TNF-α, IL-1β, or NOS2. CD40 ligation did not trigger ATP release by retinal endothelial cells or pro-inflammatory cytokine production in bystander myeloid cells. In contrast to diabetic B6 mice, diabetic Trg-CD40 EC mice did not upregulate P2X₇ mRNA levels in the retina.

Conclusions

Endothelial cell CD40 promotes ICAM-1 upregulation and leukostasis. In contrast, endothelial cell CD40 does not lead to pro-inflammatory cytokine and NOS2 upregulation likely because it does not activate purinergic-mediated pro-inflammatory molecule expression by myeloid cells or induce expression of these pro-inflammatory molecules in endothelial cells.

Photoreceptor cells and RPE contribute to the development of diabetic retinopathy

Diabetic retinopathy (DR) is a leading cause of blindness. It has long been regarded as vascular disease, but work in the past years has shown abnormalities also in the neural retina. Unfortunately, research on the vascular and neural abnormalities have remained largely separate, instead of being integrated into a comprehensive view of DR that includes both the neural and vascular components. Recent evidence suggests that the most predominant neural cell in the retina (photoreceptors) and the adjacent retinal pigment epithelium (RPE) play an important role in the development of vascular lesions characteristic of DR. This review summarizes evidence that the outer retina is altered in diabetes, and that photoreceptors and RPE contribute to retinal vascular alterations in the early stages of the retinopathy. The possible molecular mechanisms by which cells of the outer retina might contribute to retinal vascular damage in diabetes also are discussed. Diabetes-induced alterations in the outer retina represent a novel therapeutic target to inhibit DR.

Aryl Hydrocarbon Receptor Agonist VAF347 Impedes Retinal Pathogenesis in Diabetic Mice

Diabetic retinopathy is the leading cause of blindness in the working-age population worldwide. Although the cause of diabetic retinopathy is multifactorial, IL-17A is a prevalent inflammatory cytokine involved in the promotion of diabetes-mediated retinal inflammation and the progression of diabetic retinopathy. The primary source of IL-17A is Th17 cells, which are T helper cells that have been differentiated by dendritic cells in a proinflammatory cytokine environment. Aryl hydrocarbon receptor (AhR) is a ligand-dependent transcription factor that can manipulate dendritic cell maturation, halt the production of IL-6 (a proinflammatory cytokine), and suppress Th17 cell differentiation. In the current study, we examined the efficacy of an AhR agonist, VAF347, as a potential therapeutic for the onset of non-proliferative diabetic retinopathy in streptozotocin (STZ)-induced diabetic C57BL/6 mice. We determined that diabetes-mediated leukostasis, oxidative stress, and inflammation in the retina of STZ-diabetic mice were all significantly lower when treated with the AhR agonist VAF347. Furthermore, when VAF347 was subcutaneously injected into STZ-diabetic mice, retinal capillary degeneration was ameliorated, which is the hallmark of non-proliferative diabetic retinopathy in this diabetes murine model. Collectively, these findings provide evidence that the AhR agonist VAF347 could be a potentially novel therapeutic for non-proliferative diabetic retinopathy.

Sphingolipids as critical players in retinal physiology and pathology

Sphingolipids have emerged as bioactive lipids involved in the regulation of many physiological and pathological processes. In the retina, they have been established to participate in numerous processes, such as neuronal survival and death, proliferation and migration of neuronal and vascular cells, inflammation, and neovascularization. Dysregulation of sphingolipids is therefore crucial in the onset and progression of retinal diseases. This review examines the involvement of sphingolipids in retinal physiology and diseases. Ceramide (Cer) has emerged as a common mediator of inflammation and death of neuronal and retinal pigment epithelium cells in animal models of retinopathies such as glaucoma, age-related macular degeneration (AMD), and retinitis pigmentosa. Sphingosine-1-phosphate (S1P) has opposite roles, preventing photoreceptor and ganglion cell degeneration but also promoting inflammation, fibrosis, and neovascularization in AMD, glaucoma, and pro-fibrotic disorders. Alterations in Cer, S1P, and ceramide 1-phosphate may also contribute to uveitis. Notably, use of inhibitors that either prevent Cer increase or modulate S1P signaling, such as Myriocin, desipramine, and Fingolimod (FTY720), preserves neuronal viability and retinal function. These findings underscore the relevance of alterations in the sphingolipid metabolic network in the etiology of multiple retinopathies and highlight the potential of modulating their metabolism for the design of novel therapeutic approaches.

A study of therapeutic effects of 670 nm irradiation in different types of diabetic macular edema

The purpose of this study was to investigate the therapeutic effects of 670 nm irradiation in patients with diabetic macular edema. In several studies, positive effects of red/near-infrared irradiation showed in a range of ocular diseases such as macular degeneration, macular edema, and retinitis pigmentosa. This study was conducted on forty five eyes of 26 diabetic patients with macular edema between the ages of 51 and 80.

Measurement of visual acuity and slit lamp examination, funduscopy, and optical coherence tomography were performed in all subjects. None of the patients had proliferative retinopathy. We used a portable LED device (Warp 10, Quantum Devices) for treatment. Patients held this device at a distance of 3 cm from their eyes for 240 seconds for three months. Full ophthalmic examinations were repeated 1, 2, and 3 months after treatment.

After 3 months, the mean visual acuity improved from 0.44 ± 0.38 log MAR to 0.27 ± 0.24 log MAR and vision increased by 1.52 ± 1.16 lines post treatment (р<0.001). The mean central macula thickness decreased from 381.49 ± 144.40 μm to 359.72 ± 128.84 μm (р=0.050). In patients with mild and moderate nonproliferative diabetic retinopathy, the mean central retinal thickness decreased 52.06 ± 67.78 μm and 39.27 ± 44.69 μm, respectively, but patients with severe type showed an increase of 34.93 ± 65.65 μm in the mean central retinal thickness (р<0.001). Also, the severity of macular edema had no effect on final outcomes (р>0.05). Photobiomodulation can positively affect diabetic macular edema, especially in patients with mild to moderate diabetic retinopathy.

Neutrophil extracellular traps target senescent vasculature for tissue remodeling in retinopathy

In developed countries, the leading causes of blindness such as diabetic retinopathy are characterized by disorganized vasculature that can become fibrotic. Although many such pathological vessels often naturally regress and spare sight-threatening complications, the underlying mechanisms remain unknown. Here, we used orthogonal approaches in human patients with proliferative diabetic retinopathy and a mouse model of ischemic retinopathies to identify an unconventional role for neutrophils in vascular remodeling during late-stage sterile inflammation. Senescent vasculature released a secretome that attracted neutrophils and triggered the production of neutrophil extracellular traps (NETs). NETs ultimately cleared diseased endothelial cells and remodeled unhealthy vessels. Genetic or pharmacological inhibition of NETosis prevented the regression of senescent vessels and prolonged disease. Thus, clearance of senescent retinal blood vessels leads to reparative vascular remodeling.

Successful induction of diabetes in mice demonstrates no gender difference in development of early diabetic retinopathy

Purpose

Female mice have been found to be resistant to streptozotocin (STZ)-induced diabetes, and pre-clinical research related to diabetic complications commonly omits females. The purpose of this study was to develop a method to induce diabetes in female mice, and to determine if retinas of diabetic female mice develop molecular changes and histopathological abnormalities comparable to those which develop in male diabetic mice.

Methods

To induce diabetes, animals of both sexes received daily intraperitoneal (i.p.) injection of STZ for 5 consecutive days at 55 mg/kg BW (a dose that is known to induce diabetes in male mice) or for females, 75 mg/kg BW of STZ. Retinal abnormalities that have been implicated in the development of the retinopathy (superoxide generation and expression of inflammatory proteins, iNOS and ICAM-1) were evaluated at 2 months of diabetes, and retinal capillary degeneration was evaluated at 8 months of diabetes.

Results

Daily i.p. injection of STZ for 5 consecutive days at a concentration of 55 mg/kg BW was sufficient to induce diabetes in 100% of male mice, but only 33% of female mice. However, females did become hyperglycemic when the dose of STZ administered was increased to 75 mg/kg BW. The resulting STZ-induced hyperglycemia in female and male mice was sustained for at least 8 months. After induction of the diabetes, both sexes responded similarly with respect to the oxidative stress, expression of iNOS, and degeneration of retinal capillaries, but differed in the limited population evaluated with respect to expression of ICAM-1.

Conclusions

The resistance of female mice to STZ-induced diabetes can be overcome by increasing the dose of STZ used. Female mice can, and should, be included in pre-clinical studies of diabetes and its complications.

RORγt Inhibitor-SR1001 Halts Retinal Inflammation, Capillary Degeneration, and the Progression of Diabetic Retinopathy

Diabetic retinopathy is a diabetes-mediated retinal microvascular disease that is the leading cause of blindness in the working-age population worldwide. Interleukin (IL)-17A is an inflammatory cytokine that has been previously shown to play a pivotal role in the promotion and progression of diabetic retinopathy. Retinoic acid-related orphan receptor gammaT (RORγt) is a ligand-dependent transcription factor that mediates IL-17A production. However, the role of RORγt in diabetes-mediated retinal inflammation and capillary degeneration, as well as its potential therapeutic attributes for diabetic retinopathy has not yet been determined. In the current study, we examined retinal inflammation and vascular pathology in streptozotocin-induced diabetic mice. We found RORγt expressing cells in the retinal vasculature of diabetic mice. Further, diabetes-mediated retinal inflammation, oxidative stress, and retinal endothelial cell death were all significantly lower in RORγt-/- mice. Finally, when a RORγt small molecule inhibitor (SR1001) was subcutaneously injected into diabetic mice, retinal inflammation and capillary degeneration were ameliorated. These findings establish a pathologic role for RORγt in the onset of diabetic retinopathy and identify a potentially novel therapeutic for this blinding disease.

The CD40-ATP-P2X 7 Receptor Pathway: Cell to Cell Cross-Talk to Promote Inflammation and Programmed Cell Death of Endothelial Cells

Extracellular adenosine 5′-triphosphate (ATP) functions not only as a neurotransmitter but is also released by non-excitable cells and mediates cell–cell communication involving glia. In pathological conditions, extracellular ATP released by astrocytes may act as a “danger” signal that activates microglia and promotes neuroinflammation. This review summarizes in vitro and in vivo studies that identified CD40 as a novel trigger of ATP release and purinergic-induced inflammation. The use of transgenic mice with expression of CD40 restricted to retinal Müller glia and a model of diabetic retinopathy (a disease where the CD40 pathway is activated) established that CD40 induces release of ATP in Müller glia and triggers in microglia/macrophages purinergic receptor-dependent inflammatory responses that drive the development of retinopathy. The CD40-ATP-P2X₇ pathway not only amplifies inflammation but also induces death of retinal endothelial cells, an event key to the development of capillary degeneration and retinal ischemia. Taken together, CD40 expressed in non-hematopoietic cells is sufficient to mediate inflammation and tissue pathology as well as cause death of retinal endothelial cells. This process likely contributes to development of degenerate capillaries, a hallmark of diabetic and ischemic retinopathies. Blockade of signaling pathways downstream of CD40 operative in non-hematopoietic cells may offer a novel means of treating diabetic and ischemic retinopathies.

Neutrophil elastase contributes to the pathological vascular permeability characteristic of diabetic retinopathy

AIMS/HYPOTHESIS

Levels of neutrophil elastase, a serine protease secreted by neutrophils, are elevated in diabetes. The purpose of this study was to determine whether neutrophil elastase (NE) contributes to the diabetes-induced increase in retinal vascular permeability in mice with streptozotocin-induced diabetes, and, if so, to investigate the potential role of IL-17 in this process.

METHODS

In vivo, diabetes was induced in neutrophil elastase-deficient (Elane^-/-), Il-17a^-/- and wild-type mice. After 8 months of diabetes, Elane^-/- mice and wild-type age-matched control mice were injected with FITC-BSA. Fluorescence microscopy was used to assess leakage of FITC-BSA from the retinal vasculature into the neural retina. The level of NE in Il-17a^-/- diabetic retina and sera were determined by ELISA. In vitro, the effect of NE on the permeability and viability of human retinal endothelial cells and the expression of junction proteins and adhesion molecules were studied.

RESULTS

Eight months of diabetes resulted in increased retinal vascular permeability and levels of NE in retina and plasma of wild-type animals. All of these abnormalities were significantly inhibited in mice lacking the elastase. The diabetes-induced increase in NE was inhibited in mice lacking IL-17. In vitro, NE increased retinal endothelial cell permeability, which was partially inhibited by a myeloid differentiation primary response 88 (MyD88) inhibitor, NF-κB inhibitor, and protease-activated receptor (PAR)2 inhibitor. NE degraded vascular endothelial-cadherin (VE-cadherin) in a concentration-dependent manner.

CONCLUSIONS/INTERPRETATION

IL-17 regulates NE expression in diabetes. NE contributes to vascular leakage in diabetic retinopathy, partially through activation of MyD88, NF-κB and PAR2 and degradation of VE-cadherin.

Montelukast Prevents Early Diabetic Retinopathy in Mice

Chronic inflammation and oxidative stress are critical components in the pathogenic cascade of early diabetic retinopathy, characterized by neuronal and vascular degeneration. We investigated pharmacologic inhibition of the proinflammatory leukotriene cascade for therapeutic benefit in early diabetic retinopathy. Using the streptozotocin-induced diabetes mouse model, we administered montelukast, a leukotriene receptor antagonist, and diabetes-related retinal pathology was assessed. Early biochemical and cellular function measures were evaluated at 3 months' diabetes duration and included vascular permeability, superoxide production, leukotriene generation, leukocyte-induced microvascular endothelial cell death, and retinal function by electroretinography. Histopathology assessments at 9 months' diabetes duration included capillary degeneration and retinal ganglion cell loss. Leukotriene receptor antagonism resulted in a significant reduction of early, diabetes-induced retinal capillary leakage, superoxide generation, leukocyte adherence, and leukotriene generation. After 9 months of diabetes, the retinal microvasculature from untreated diabetic mice demonstrated a nearly threefold increase in capillary degeneration compared with nondiabetic mice. Montelukast inhibited the diabetes-induced capillary and neuronal degeneration, whether administered as a prevention strategy, immediately after induction of diabetes, or as an intervention strategy starting at 4.5 months after confirmation of diabetes. Pharmacologic blockade of the leukotriene pathway holds potential as a novel therapy to prevent or slow the development of diabetic retinopathy.

Diabetes induces IL-17A-Act1-FADD-dependent retinal endothelial cell death and capillary degeneration

PURPOSE

Diabetes leads to progressive complications such as diabetic retinopathy, which is the leading cause of blindness within the working-age population worldwide. Interleukin (IL)-17A is a cytokine that promotes and progresses diabetes. The objective of this study was to determine the role of IL-17A in retinal capillary degeneration, and to identify the mechanism that induces retinal endothelial cell death. These are clinically meaningful abnormalities that characterize early-stage non-proliferative diabetic retinopathy.

METHODS

Retinal capillary degeneration was examined in vivo using the streptozotocin (STZ) diabetes murine model. Diabetic-hyperglycemia was sustained for an 8-month period in wild type (C57BL/6) and IL-17A^-/- mice to elucidate the role of IL-17A in retinal capillary degeneration. Further, ex vivo studies were performed in retinal endothelial cells to identify the IL-17A-dependent mechanism that induces cell death.

RESULTS

It was determined that diabetes-induced retinal capillary degeneration was significantly lower in IL-17A^-/- mice. Further, retinal endothelial cell death occurred through an IL-17A/IL-17R ➔ Act1/FADD signaling cascade, which caused caspase-mediated apoptosis.

CONCLUSION

These are the first findings that establish a pathologic role for IL-17A in retinal capillary degeneration. Further, a novel IL-17A-dependent apoptotic mechanism was discovered, which identifies potential therapeutic targets for the early onset of diabetic retinopathy.

Pathophysiology of Diabetic Retinopathy: Contribution and Limitations of Laboratory Research

Preclinical models of diabetic retinopathy are indispensable in the drug discovery and development of new therapies. They are, however, imperfect facsimiles of diabetic retinopathy in humans. This chapter discusses the advantages, limitations, and physiological and pathological relevance of preclinical models of diabetic retinopathy. The judicious interpretation and extrapolation of data derived from these models to humans and a correspondingly greater emphasis placed on translational medical research in early-stage clinical trials are essential to more successfully inhibit the development and progression of diabetic retinopathy in the future.

Rhizoma coptidis as a Potential Treatment Agent for Type 2 Diabetes Mellitus and the Underlying Mechanisms: A Review

Diabetes mellitus, especially type 2 diabetes mellitus (T2DM), has become a significant public health burden. Rhizoma coptidis (RC), known as Huang Lian, is widely used for treating diabetes in China. The bioactive compounds of RC, especially alkaloids, have the potential to suppress T2DM-induced lesions, including diabetic vascular dysfunction, diabetic heart disease, diabetic hyperlipidemia, diabetic nephropathy, diabetic encephalopathy, diabetic osteopathy, diabetic enteropathy, and diabetic retinopathy. This review summarizes the effects of RC and its bioactive compounds on T2DM and T2DM complications. Less research has been conducted on non-alkaloid fractions of RC, which may exert synergistic action with alkaloids. Moreover, we summarized the pharmacokinetic properties and structure-activity relationships of RC on T2DM with reference to extant literature and showed clearly that RC has potential therapeutic effect on T2DM.

The alliance between nerve fibers and stem cell populations in bone marrow: life partners in sickness and health

The bone marrow (BM) is the central hematopoietic organ in adult mammals, with great potential to be used as a tool to improve the efficacy of the body's response to a number of malignancies and stressful conditions. The nervous system emerges as a critical regulatory player of the BM both under homeostatic and pathologic settings, with essential roles in cellular anchorage and egress, stem cell differentiation, and endothelial cell permeability. This review collects the current knowledge on the interplay between the nervous system and the BM cell populations, with a focus on how the nervous system modulates hematopoietic stem and progenitor cell, mesenchymal stromal cell, and endothelial progenitor cell activity in BM. We have also highlighted the pathologies that have been associated with disturbances in the neuronal signaling in BM and discussed if targeting the nervous system, either by modulating the activity of specific neuronal circuits or by pharmacologically leveling the activity of sympathetic and sensorial signaling-responsive cells in BM, is a promising therapeutic approach to tackling pathologies from BM origin.-Leitão, L., Alves, C. J., Sousa, D. M., Neto, E., Conceição, F., Lamghari, M. The alliance between nerve fibers and stem cell populations in bone marrow: life partners in sickness and health.

Transducin1, Phototransduction and the Development of Early Diabetic Retinopathy

Purpose

Recent evidence suggests that retinal photoreceptor cells have an important role in the pathogenesis of retinal microvascular lesions in diabetes. We investigated the role of rod cell phototransduction on the pathogenesis of early diabetic retinopathy (DR) using Gnat1-/- mice (which causes permanent inhibition of phototransduction in rod cells without degeneration).

Methods

Retinal thickness, oxidative stress, expression of inflammatory proteins, electroretinograms (ERG) and optokinetic responses, and capillary permeability and degeneration were evaluated at up to 8 months of diabetes.

Results

The diabetes-induced degeneration of retinal capillaries was significantly inhibited in the Gnat1-/- diabetics. The effect of the Gnat1 deletion on the diabetes-induced increase in permeability showed a nonuniform accumulation of albumin in the neural retina; the defect was inhibited in diabetic Gnat1-/- mice in the inner plexiform layer (IPL), but neither in the outer plexiform (OPL) nor inner nuclear (INL) layers. In Gnat1-deficient animals, the diabetes-induced increase in expression of inflammatory associated proteins (iNOS and ICAM-1, and phosphorylation of IĸB) in the retina, and the leukocyte mediated killing of retinal endothelial cells were inhibited, however the diabetes-mediated induction of oxidative stress was not inhibited.

Conclusions

In conclusion, deletion of transducin1 (and the resulting inhibition of phototransduction in rod cells) inhibits the development of retinal vascular pathology in early DR.

Role of Bioactive Sphingolipids in Inflammation and Eye Diseases

Inflammation is a common underlying factor in a diversity of ocular diseases, ranging from macular degeneration, autoimmune uveitis, glaucoma, diabetic retinopathy and microbial infection. In addition to the variety of known cellular mediators of inflammation, such as cytokines, chemokines and lipid mediators, there is now considerable evidence that sphingolipid metabolites also play a central role in the regulation of inflammatory pathways. Various sphingolipid metabolites, such as ceramide (Cer), ceramide-1-phosphate (C1P), sphingosine-1-phosphate (S1P), and lactosylceramide (LacCer) can contribute to ocular inflammatory diseases through multiple pathways. For example, inflammation generates Cer from sphingomyelins (SM) in the plasma membrane, which induces death receptor ligand formation and leads to apoptosis of retinal pigment epithelial (RPE) and photoreceptor cells. Inflammatory stress by reactive oxygen species leads to LacCer accumulation and S1P secretion and induces proliferation of retinal endothelial cells and eventual formation of new vessels. In sphingolipid/lysosomal storage disorders, sphingolipid metabolites accumulate in lysosomes and can cause ocular disorders that have an inflammatory etiology. Sphingolipid metabolites activate complement factors in the immune-response mediated pathogenesis of macular degeneration. These examples highlight the integral association between sphingolipids and inflammation in ocular diseases.

A role for bone marrow-derived cells in diabetic nephropathy

Diabetes mellitus causes systemic disorders. We previously demonstrated that diabetic condition forced bone marrow-derived cells (BMDCs) to express TNF-α, leading to the development of diabetic neuropathy in mice. Here, we hypothesized that these abnormal BMDCs are also involved in diabetic nephropathy. To test our hypothesis, mice were irradiated to receive total bone marrow (BM) from the transgenic mice expressing green fluorescent protein before diabetes was induced by streptozotocin. Confocal microscopy showed that the diabetic glomerulus had more BMDCs compared with the nondiabetic glomerulus. Most of these cells exhibited endothelial phenotypes, being negative for several markers, including podocin (a maker of podocyte), α8 integrin (mesangial cell), CD68, and F4/80 (macrophage). Next, the total BM of diabetic mice was transplanted into nondiabetic mice to examine if diabetic BM per se could cause glomerular injury. The recipient mice exhibiting normal glycemia developed albuminuria and mesangial expansion with an increase in capillary area. The number of BMDCs increased in the glomerulus of the recipient mice. These cells were found to exhibit the endothelial phenotype and to express TNF-α. These data suggest that diabetic BMDCs per se could initiate glomerular disease. Finally, eNOS knockout mice were used to examine if residential endothelial injury could attract BMDCs into the glomerulus. However, endothelial dysfunction due to eNOS deficiency failed to attract BMDCs into the glomerulus. In summary, BMDCs may be involved in the development of diabetic nephropathy.-Nobuta, H., Katagi, M., Kume, S., Terashima, T., Araki, S., Maegawa, H., Kojima, H., Nakagawa, T. A role for bone marrow-derived cells in diabetic nephropathy.

Dual Inhibitors of PARPs and ROCKs

Recent network and system biology analyses suggest that most complex diseases are regulated by robust and highly interconnected pathways that could be better modulated by small molecules binding to multiple biological targets. These pieces of evidence recently led to devote efforts on identifying single chemical entities that bind to two different disease-relevant targets. Here, we first predicted in silico and later confirmed in vitro that UPF 1069, a known bioactive poly(ADP-ribose) polymerase-1/2 (PARP1/2) molecule, and hydroxyfasudil, a known bioactive Rho-associated protein kinase-1/2 (ROCK1/2) molecule, have low-micromolar cross-affinity for ROCK1/2 and PARP1/2, respectively. These molecules can now be regarded as chemical seeds from which pharmacological tools could be generated to study the impact of dual inhibition of PARPs and ROCKs in preclinical models of a variety of complex diseases where both targets are involved.

Sweet Stress: Coping With Vascular Dysfunction in Diabetic Retinopathy

Oxidative stress plays key roles in the pathogenesis of retinal diseases, such as diabetic retinopathy. Reactive oxygen species (ROS) are increased in the retina in diabetes and the antioxidant defense system is also compromised. Increased ROS stimulate the release of pro-inflammatory cytokines, promoting a chronic low-grade inflammation involving various signaling pathways. An excessive production of ROS can lead to retinal endothelial cell injury, increased microvascular permeability, and recruitment of inflammatory cells at the site of inflammation. Recent studies have started unraveling the complex crosstalk between retinal endothelial cells and neuroglial cells or leukocytes, via both cell-to-cell contact and secretion of cytokines. This crosstalk is essential for the maintenance of the integrity of retinal vascular structure. Under diabetic conditions, an aberrant interaction between endothelial cells and other resident cells of the retina or invading inflammatory cells takes place in the retina. Impairment in the secretion and flow of molecular signals between different cells can compromise the retinal vascular architecture and trigger angiogenesis. In this review, the synergistic contributions of redox-inflammatory processes for endothelial dysfunction in diabetic retinopathy will be examined, with particular attention paid to endothelial cell communication with other retinal cells.

Photobiomodulation Inhibits Long-term Structural and Functional Lesions of Diabetic Retinopathy

Previous studies demonstrated that brief (3 to 4 min) daily application of light at 670 nm to diabetic rodents inhibited molecular and pathophysiologic processes implicated in the pathogenesis of diabetic retinopathy (DR) and reversed diabetic macular edema in small numbers of patients studied. Whether or not this therapy would inhibit the neural and vascular lesions that characterize the early stages of the retinopathy was unknown. We administered photobiomodulation (PBM) therapy daily for 8 months to streptozotocin-diabetic mice and assessed effects of PBM on visual function, retinal capillary permeability, and capillary degeneration using published methods. Vitamin D receptor and Cyp24a1 transcripts were quantified by quantitative real-time PCR, and the abundance of c-Kit⁺ stem cells in blood and retina were assessed. Long-term daily administration of PBM significantly inhibited the diabetes-induced leakage and degeneration of retinal capillaries and also significantly inhibited the diabetes-induced reduction in visual function. PBM also inhibited diabetes-induced reductions in retinal Cyp24a1 mRNA levels and numbers of circulating stem cells (CD45^-/c-Kit⁺), but these effects may not account for the beneficial effects of PBM on the retinopathy. PBM significantly inhibits the functional and histopathologic features of early DR, and these effects likely are mediated via multiple mechanisms.

Mechanisms of macular edema: Beyond the surface

Macular edema consists of intra- or subretinal fluid accumulation in the macular region. It occurs during the course of numerous retinal disorders and can cause severe impairment of central vision. Major causes of macular edema include diabetes, branch and central retinal vein occlusion, choroidal neovascularization, posterior uveitis, postoperative inflammation and central serous chorioretinopathy. The healthy retina is maintained in a relatively dehydrated, transparent state compatible with optimal light transmission by multiple active and passive systems. Fluid accumulation results from an imbalance between processes governing fluid entry and exit, and is driven by Starling equation when inner or outer blood-retinal barriers are disrupted. The multiple and intricate mechanisms involved in retinal hydro-ionic homeostasis, their molecular and cellular basis, and how their deregulation lead to retinal edema, are addressed in this review. Analyzing the distribution of junction proteins and water channels in the human macula, several hypotheses are raised to explain why edema forms specifically in the macular region. "Pure" clinical phenotypes of macular edema, that result presumably from a single causative mechanism, are detailed. Finally, diabetic macular edema is investigated, as a complex multifactorial pathogenic example. This comprehensive review on the current understanding of macular edema and its mechanisms opens perspectives to identify new preventive and therapeutic strategies for this sight-threatening condition.

Photoreceptor cells produce inflammatory products that contribute to retinal vascular permeability in a mouse model of diabetes

AIMS/HYPOTHESIS

Recent studies suggest that photoreceptor cells produce mediators or products that contribute to retinal capillary damage in diabetes. The purpose of this study was to determine if photoreceptor cells release soluble factors that contribute to retinal vascular permeability in diabetes.

METHODS

To assess retinal vascular leakage, a streptozotocin-induced mouse model of diabetes, with hyperglycaemia for 8 months, and age-matched control mice, were injected with FITC-BSA. Fluorescence microscopy was used to detect leakage of FITC-BSA from the retinal vasculature into the neural retina. Ex vivo and in vitro experiments were performed to determine if photoreceptor cells released products that directly increased retinal endothelial cell permeability or cell death. Effects of products released by photoreceptors on tight junction and cell adhesion proteins were assessed by quantitative reverse transcription PCR (qRT-PCR). Inflammatory products released by photoreceptors into media were measured using protein arrays.

RESULTS

Eight months duration of diabetes increased retinal vascular permeability in wild-type mice, but this defect was inhibited in opsin-deficient diabetic mice in which photoreceptor cells had degenerated earlier. Photoreceptor cells from diabetic wild-type mice released inflammatory products (e.g. IL-1α, IL-1β, IL-6, IL-12, chemokine C-X-C motif ligand 1 [CXCL1], monocyte chemoattractant protein 1 [MCP-1], CXCL12a, I-309, chemokine ligand 25 [CCL25] and TNF-α), which directly contributed to increased retinal endothelial cell permeability, at least in part via changes in claudin (tight junction) mRNA. Products released from photoreceptor cells from diabetic mice or under diabetes-like conditions did not directly kill retinal endothelial cells in vitro.

CONCLUSIONS/INTERPRETATION

Photoreceptor cells can produce inflammatory products that contribute to retinal vascular permeability in mouse models of diabetes.

Photoreceptor Cells Influence Retinal Vascular Degeneration in Mouse Models of Retinal Degeneration and Diabetes

Purpose

Loss of photoreceptor cells is associated with retinal vascular degeneration in retinitis pigmentosa, whereas the presence of photoreceptor cells is implicated in vascular degeneration in diabetic retinopathy. To investigate how both the absence and presence of photoreceptors could damage the retinal vasculature, we compared two mouse models of photoreceptor degeneration (opsin^−/− and Rho^P23H/P23H ) and control C57Bl/5J mice, each with and without diabetes.

Methods

Retinal thickness, superoxide, expression of inflammatory proteins, ERG and optokinetic responses, leukocyte cytotoxicity, and capillary degeneration were evaluated at 1 to 10 months of age using published methods.

Results

Retinal photoreceptor cells degenerated completely in the opsin mutants by 2 to 4 months of age, and visual function subsided correspondingly. Retinal capillary degeneration was substantial while photoreceptors were still present, but slowed after the photoreceptors degenerated. Diabetes did not further exacerbate capillary degeneration in these models of photoreceptor degeneration, but did cause capillary degeneration in wild-type animals. Photoreceptor cells, however, did not degenerate in wild-type diabetic mice, presumably because the stress responses in these cells were less than in the opsin mutants. Retinal superoxide and leukocyte damage to retinal endothelium contributed to the degeneration of retinal capillaries in diabetes, and leukocyte-mediated damage was increased in both opsin mutants during photoreceptor cell degeneration.

Conclusions

Photoreceptor cells affect the integrity of the retinal microvasculature. Deterioration of retinal capillaries in opsin mutants was appreciable while photoreceptor cells were present and stressed, but was less after photoreceptors degenerated. This finding proves relevant to diabetes, where persistent stress in photoreceptors likewise contributes to capillary degeneration.

Photoreceptor Cells Produce Inflammatory Mediators That Contribute to Endothelial Cell Death in Diabetes

PURPOSE

Recent studies suggest that photoreceptor cells regulate local inflammation in the retina in diabetes. The purpose of this study was to determine if photoreceptor cells themselves produce inflammatory proteins in diabetes and if soluble factors released by photoreceptors in elevated glucose induce inflammatory changes in nearby cells.

METHODS

Laser capture microdissection was used to isolate the outer retina (photoreceptors) from the inner retina in nondiabetic and diabetic mice. Diabetes-induced changes in the expression of inflammatory targets were assessed by reverse transcription polymerase chain reaction and immunohistochemistry. Cell culture experiments were carried out to determine if photoreceptors in vitro and ex vivo release soluble mediators that can stimulate nearby cells. Photoreceptor contribution to leukocyte-mediated endothelial cell death was tested using coculture models.

RESULTS

Messenger ribonucleic acid and protein expression levels for inflammatory proteins intercellular adhesion molecule 1 (ICAM1), inducible nitric oxide synthase (iNOS), and cyclooxygenase 2 (COX2) were increased in photoreceptors cells in diabetes. In vitro and ex vivo studies show that photoreceptor cells in elevated glucose release mediators that can induce tumor necrosis factor-α in leukocytes and endothelial cells, but not in glia. The soluble mediators released by photoreceptor cells in elevated glucose are regulated by transforming growth factor β-activated kinase 1 and nicotinamide adenine dinucleotide phosphate oxidase (NADPH oxidase) signaling. In contrast to enhanced leukocyte-mediated killing of endothelial cells by leukocytes from wild-type diabetic mice, leukocytes from diabetic mice lacking photoreceptor cells (opsin-/-) did not kill endothelial cells.

CONCLUSIONS

These data indicate that photoreceptor cells are a source of inflammatory proteins in diabetes, and their release of soluble mediators can contribute to the death of retinal capillaries in diabetes.

Do photoreceptor cells cause the development of retinal vascular disease?

The retinal vasculature is affected in a number of clinically important retinopathies, including diabetic retinopathy. There has been a considerable amount of research into the pathogenesis of retinal microvascular diseases, but the potential contribution of the most abundant cell population in the retina, photoreceptor cells, has been largely overlooked. This review summarizes ongoing research suggesting that photoreceptor cells play a critical role in the development of retinal vascular disease in diabetic retinopathy and other retinopathies.

Fractalkine Signaling Attenuates Perivascular Clustering of Microglia and Fibrinogen Leakage during Systemic Inflammation in Mouse Models of Diabetic Retinopathy

Fractalkine (FKN) is a chemokine expressed constitutively by healthy neurons and signals to microglia upon interaction with the FKN receptor, CX3CR1. Signaling between FKN and CX3CR1 transduces inhibitory signals that ameliorate microglial activation and proinflammatory cytokine release in neuroinflammatory conditions. The aim of this study is to determine the mechanisms associated with microglial activation and vascular leakage during diabetic retinopathy (DR) and under conditions of low-level endotoxemia, common in diabetic patients. Utilizing the Ins2^Akita strain (Akita), a mouse model of type 1 diabetes, our results show that leakage of the blood-protein fibrin(ogen) into the retina occurs as a result of chronic (4 months) but not acute (1.5 months) hyperglycemia. Conversely, inducing endotoxin-mediated systemic inflammation during acute diabetes resulted in fibrinogen deposition in the retina, a phenotype that was exacerbated in mice lacking CX3CR1 signaling. Systemic inflammation in Cx3cr1^-/- mice led to robust perivascular clustering of proliferating microglia in areas of fibrinogen extravasation, and induced IL-1β expression in microglia and astrocytes. Lastly, we determined a protective effect of modulating FKN/CX3CR1 signaling in the diabetic retina. We show that intravitreal (iv) administration of recombinant FKN into diabetic FKN-KO mice, reduced fibrinogen deposition and perivascular clustering of microglia in the retina during systemic inflammation. These data suggest that dysregulated microglial activation via loss of FKN/CX3CR1 signaling disrupts the vascular integrity in retina during systemic inflammation.

Critical Role of the CXCL10/C-X-C Chemokine Receptor 3 Axis in Promoting Leukocyte Recruitment and Neuronal Injury during Traumatic Optic Neuropathy Induced by Optic Nerve Crush

Traumatic optic neuropathy (TON) is an acute injury of the optic nerve secondary to trauma. Loss of retinal ganglion cells (RGCs) is a key pathological process in TON, yet mechanisms responsible for RGC death remain unclear. In a mouse model of TON, real-time noninvasive imaging revealed a dramatic increase in leukocyte rolling and adhesion in veins near the optic nerve (ON) head at 9 hours after ON injury. Although RGC dysfunction and loss were not detected at 24 hours after injury, massive leukocyte infiltration was observed in the superficial retina. These cells were identified as T cells, microglia/monocytes, and neutrophils but not B cells. CXCL10 is a chemokine that recruits leukocytes after binding to its receptor C-X-C chemokine receptor (CXCR) 3. The levels of CXCL10 and CXCR3 were markedly elevated in TON, and up-regulation of CXCL10 was mediated by STAT1/3. Deleting CXCR3 in leukocytes significantly reduced leukocyte recruitment, and prevented RGC death at 7 days after ON injury. Treatment with CXCR3 antagonist attenuated TON-induced RGC dysfunction and cell loss. In vitro co-culture of primary RGCs with leukocytes resulted in increased RGC apoptosis, which was exaggerated in the presence of CXCL10. These results indicate that leukocyte recruitment in retinal vessels near the ON head is an early event in TON and the CXCL10/CXCR3 axis has a critical role in recruiting leukocytes and inducing RGC death.

Lymphoblastoid Cell Lines as a Tool to Study Inter-Individual Differences in the Response to Glucose

Background

White blood cells have been shown in animal studies to play a central role in the pathogenesis of diabetic retinopathy. Lymphoblastoid cells are immortalized EBV-transformed primary B-cell leukocytes that have been extensively used as a model for conditions in which white blood cells play a primary role. The purpose of this study was to investigate whether lymphoblastoid cell lines, by retaining many of the key features of primary leukocytes, can be induced with glucose to demonstrate relevant biological responses to those found in diabetic retinopathy.

Methods

Lymphoblastoid cell lines were obtained from twenty-three human subjects. Differences between high and standard glucose conditions were assessed for expression, endothelial adhesion, and reactive oxygen species.

Results

Collectively, stimulation of the lymphoblastoid cell lines with high glucose demonstrated corresponding changes on molecular, cellular and functional levels. Lymphoblastoid cell lines up-regulated expression of a panel of genes associated with the leukocyte-mediated inflammation found in diabetic retinopathy that include: a cytokine (IL-1B fold change = 2.11, p-value = 0.02), an enzyme (PKCB fold change = 2.30, p-value = 0.01), transcription factors (NFKB-p50 fold change = 2.05, p-value = 0.01), (NFKB-p65 fold change = 2.82, p-value = 0.003), and an adhesion molecule (CD18 fold change = 2.59, 0.02). Protein expression of CD18 was also increased (p-value = 2.14x10^-5). The lymphoblastoid cell lines demonstrated increased adhesiveness to endothelial cells (p = 1.28x10^-5). Reactive oxygen species were increased (p = 2.56x10^-6). Significant inter-individual variation among the lymphoblastoid cell lines in these responses was evident (F = 18.70, p < 0.0001).

Conclusions

Exposure of lymphoblastoid cell lines derived from different human subjects to high glucose demonstrated differential and heterogeneous gene expression, adhesion, and cellular effects that recapitulated features found in the diabetic state. Lymphoblastoid cells may represent a useful tool to guide an individualized understanding of the development and potential treatment of diabetic complications like retinopathy.

Angiogenesis and Inflammation Crosstalk in Diabetic Retinopathy

Diabetic retinopathy (DR) is one of the most prevalent microvascular complications of diabetes and one of the most frequent causes of blindness in active age. Etiopathogenesis behind this important complication is related to several biochemical, hemodynamic and endocrine mechanisms with a preponderant initial role assumed by polyol pathways, increment of growth factors, accumulation of advanced glycation end products (AGE), activation of protein kinase C (PKC), activation of the renin-angiotensin-aldosterone system (RAAS), and leukostasis. Chronic and sustained hyperglycemia works as a trigger to the early alterations that culminate in vascular dysfunction. Hypoxia also plays an essential role in disease progression with promotion of neovascularization and vascular dystrophies with vitreous hemorrhages induction. Thus, the accumulation of fluids and protein exudates in ocular cavities leads to an opacity augmentation of the cornea that associated to neurodegeneration results in vision loss, being this a devastating characteristic of the disease final stage. During disease progression, inflammatory molecules are produced and angiogenesis occur. Furthermore, VEGF is overexpressed by the maintained hyperglycemic environment and up-regulated by tissue hypoxia. Also pro-inflammatory mediators regulated by cytokines, such as tumor necrosis factor (TNF-α) and interleukin-1 beta (IL-1β), and growth factors leads to the progression of these processes, culminating in vasopermeability (diabetes macular edema) and/or pathological angiogenesis (proliferative diabetic retinopathy). It was found a mutual contribution between inflammation and angiogenesis along the process. J. Cell. Biochem. 117: 2443-2453, 2016. © 2016 Wiley Periodicals, Inc.

Bone Marrow-Derived Stem Cells: a Mixed Blessing in the Multifaceted World of Diabetic Complications

Diabetes is one of the main economic burdens in health care, which threatens to worsen dramatically if prevalence forecasts are correct. What makes diabetes harmful is the multi-organ distribution of its microvascular and macrovascular complications. Regenerative medicine with cellular therapy could be the dam against life-threatening or life-altering complications. Bone marrow-derived stem cells are putative candidates to achieve this goal. Unfortunately, the bone marrow itself is affected by diabetes, as it can develop a microangiopathy and neuropathy similar to other body tissues. Neuropathy leads to impaired stem cell mobilization from marrow, the so-called mobilopathy. Here, we review the role of bone marrow-derived stem cells in diabetes: how they are affected by compromised bone marrow integrity, how they contribute to other diabetic complications, and how they can be used as a treatment for these. Eventually, we suggest new tactics to optimize stem cell therapy.

Presence of retinal pericyte-reactive autoantibodies in diabetic retinopathy patients

The loss of retinal pericytes (RPCs) is a hallmark of early stage diabetic retinopathy (DR), but the mechanism underlying RPC death is unclear. Although it was postulated in previous studies using bovine RPCs that autoantibodies against RPCs might develop and induce RPC death, it is unknown whether autoantibodies against cell-surface antigens on human RPCs exist in DR patients, whether such autoantibodies contribute to RPC damage/loss, and if they do, through which mechanism. We screened serum samples from DR patients and controls using primary human RPCs and found that that levels of IgGs reactive to RPCs were significantly higher in the DR group than the control group. Serum samples with higher RPC-reactive IgG levels induced more severe complement-mediated RPC damage than those with lower RPC-reactive IgG levels. We also assessed levels of the complement-activation products C3a, C4a and C5a in these serum samples, and found that serum levels of C3a and C5a, but not C4a, were higher in the DR group than control group. These data provide evidence the first time showing that autoantibodies against RPCs can develop in DR patients, and that these autoantibodies could contribute to pericyte damage through complement activation.