Increase in acid sphingomyelinase level in human retinal endothelial cells and CD34+ circulating angiogenic cells isolated from diabetic individuals is associated with dysfunctional retinal vasculature and vascular repair process in diabetes

Diabetic retinopathy is a ceramidopathy reversible by anti-ceramide immunotherapy

Diabetic retinopathy is a microvascular disease that causes blindness. Using acid sphingomyelinase knockout mice, we reported that ceramide generation is critical for diabetic retinopathy development. Here, in patients with proliferative diabetic retinopathy, we identify vitreous ceramide imbalance with pathologic long-chain C16-ceramides increasing and protective very long-chain C26-ceramides decreasing. C16-ceramides generate pro-inflammatory/pro-apoptotic ceramide-rich platforms on endothelial surfaces. To geo-localize ceramide-rich platforms, we invented a three-dimensional confocal assay and showed that retinopathy-producing cytokines TNFα and IL-1β induce ceramide-rich platform formation on retinal endothelial cells within seconds, with volumes increasing 2-logs, yielding apoptotic death. Anti-ceramide antibodies abolish these events. Furthermore, intravitreal and systemic anti-ceramide antibodies protect from diabetic retinopathy in standardized rodent ischemia reperfusion and streptozotocin models. These data support (1) retinal endothelial ceramide as a diabetic retinopathy treatment target, (2) early-stage therapy of non-proliferative diabetic retinopathy to prevent progression, and (3) systemic diabetic retinopathy treatment; and they characterize diabetic retinopathy as a "ceramidopathy" reversible by anti-ceramide immunotherapy.

Cluster of differentiation molecules in the metabolic syndrome

Metabolic syndrome (MetS) represents a significant public health concern due to its association with an increased risk of cardiovascular disease, type 2 diabetes, and other serious health conditions. Despite extensive research, the underlying molecular mechanisms contributing to MetS pathogenesis remain elusive. This review aims to provide a comprehensive overview of the molecular mechanisms linking MetS and cluster of differentiation (CD) markers, which play critical roles in immune regulation and cellular signaling. Through an extensive literature review with a systematic approach, we examine the involvement of various CD markers in MetS development and progression, including their roles in adipose tissue inflammation, insulin resistance, dyslipidemia, and hypertension. Additionally, we discuss potential therapeutic strategies targeting CD markers for the management of MetS. By synthesizing current evidence, this review contributes to a deeper understanding of the complex interplay between immune dysregulation and metabolic dysfunction in MetS, paving the way for the development of novel therapeutic interventions.

Ocular pharmacological and biochemical profiles of 6-thioguanine: a drug repurposing study

Introduction

The purine analog 6-thioguanine (6TG), an old drug approved in the 60s to treat acute myeloid leukemia (AML), was tested in the diabetic retinopathy (DR) experimental in vivo setting along with a molecular modeling approach.

Methods

A computational analysis was performed to investigate the interaction of 6TG with MC1R and MC5R. This was confirmed in human umbilical vein endothelial cells (HUVECs) exposed to high glucose (25 mM) for 24 h. Cell viability in HUVECs exposed to high glucose and treated with 6TG (0.05-0.5-5 µM) was performed. To assess tube formation, HUVECs were treated for 24 h with 6TG 5 µM and AGRP (0.5-1-5 µM) or PG20N (0.5-1-5-10 µM), which are MC1R and MC5R antagonists, respectively. For the in vivo DR setting, diabetes was induced in C57BL/6J mice through a single streptozotocin (STZ) injection. After 2, 6, and 10 weeks, diabetic and control mice received 6TG intravitreally (0.5-1-2.5 mg/kg) alone or in combination with AGRP or PG20N. Fluorescein angiography (FA) was performed after 4 and 14 weeks after the onset of diabetes. After 14 weeks, mice were euthanized, and immunohistochemical analysis was performed to assess retinal levels of CD34, a marker of endothelial progenitor cell formation during neo-angiogenesis.

Results

The computational analysis evidenced a more stable binding of 6TG binding at MC5R than MC1R. This was confirmed by the tube formation assay in HUVECs exposed to high glucose. Indeed, the anti-angiogenic activity of 6TG was eradicated by a higher dose of the MC5R antagonist PG20N (10 µM) compared to the MC1R antagonist AGRP (5 µM). The retinal anti-angiogenic effect of 6TG was evident also in diabetic mice, showing a reduction in retinal vascular alterations by FA analysis. This effect was not observed in diabetic mice receiving 6TG in combination with AGRP or PG20N. Accordingly, retinal CD34 staining was reduced in diabetic mice treated with 6TG. Conversely, it was not decreased in diabetic mice receiving 6TG combined with AGRP or PG20N.

Conclusion

6TG evidenced a marked anti-angiogenic activity in HUVECs exposed to high glucose and in mice with DR. This seems to be mediated by MC1R and MC5R retinal receptors.

Common mechanisms underlying diabetic vascular complications: focus on the interaction of metabolic disorders, immuno-inflammation, and endothelial dysfunction

Diabetic vascular complications (DVCs), including macro- and micro- angiopathy, account for a high percentage of mortality in patients with diabetes mellitus (DM). Endothelial dysfunction is the initial and role step for the pathogenesis of DVCs. Hyperglycemia and lipid metabolism disorders contribute to endothelial dysfunction via direct injury of metabolism products, crosstalk between immunity and inflammation, as well as related interaction network. Although physiological and phenotypic differences support their specified changes in different targeted organs, there are still several common mechanisms underlying DVCs. Also, inhibitors of these common mechanisms may decrease the incidence of DVCs effectively. Thus, this review may provide new insights into the possible measures for the secondary prevention of DM. And we discussed the current limitations of those present preventive measures in DVCs research. Video Abstract.

A Comprehensive Profiling of Cellular Sphingolipids in Mammalian Endothelial and Microglial Cells Cultured in Normal and High-Glucose Conditions

Sphingolipids (SPLs) play a diverse role in maintaining cellular homeostasis. Dysregulated SPL metabolism is associated with pathological changes in stressed and diseased cells. This study investigates differences in SPL metabolism between cultured human primary retinal endothelial (HREC) and murine microglial cells (BV2) in normal conditions (normal glucose, NG, 5 mM) and under high-glucose (HG, 25 mM)-induced stress by sphingolipidomics, immunohistochemistry, biochemical, and molecular assays. Measurable differences were observed in SPL profiles between HREC and BV2 cells. High-glucose treatment caused a >2.5-fold increase in the levels of Lactosyl-ceramide (LacCer) in HREC, but in BV2 cells, it induced Hexosyl-Ceramides (HexCer) by threefold and a significant increase in Sphingosine-1-phosphate (S1P) compared to NG. Altered SPL profiles coincided with changes in transcript levels of inflammatory and vascular permeability mediators in HREC and inflammatory mediators in BV2 cells. Differences in SPL profiles and differential responses to HG stress between endothelial and microglial cells suggest that SPL metabolism and signaling differ in mammalian cell types and, therefore, their pathological association with those cell types.

Effects of Lycium barbarum L. Polysaccharides on Vascular Retinopathy: An Insight Review

Vascular retinopathy is a pathological change in the retina caused by ocular or systemic vascular diseases that can lead to blurred vision and the risk of blindness. Lycium barbarum polysaccharides (LBPs) are extracted from the fruit of traditional Chinese medicine, L. barbarum. They have strong biological activities, including immune regulation, antioxidation, and neuroprotection, and have been shown to improve vision in numerous studies. At present, there is no systematic literature review of LBPs on vascular retinal prevention and treatment. We review the structural characterization and extraction methods of LBPs, focus on the mechanism and pharmacokinetics of LBPs in improving vascular retinopathy, and discuss the future clinical application and lack of work. LBPs are involved in the regulation of VEGF, Rho/ROCK, PI3K/Akt/mTOR, Nrf2/HO-1, AGEs/RAGE signaling pathways, which can alleviate the occurrence and development of vascular retinal diseases in an inflammatory response, oxidative stress, apoptosis, autophagy, and neuroprotection. LBPs are mainly absorbed by the small intestine and stomach and excreted through urine and feces. Their low bioavailability in vivo has led to the development of novel dosage forms, including multicompartment delivery systems and scaffolds. Data from the literature confirm the medicinal potential of LBPs as a new direction for the prevention and complementary treatment of vascular retinopathy.

Impairment of Ceramide-Mediated Endothelial Instant Membrane Resealing During Diabetes Mellitus

Recent studies have indicated that instant cell membrane resealing (ICMR) controls the activation of NOD-like receptor pyrin domain containing 3 (Nlrp3) inflammasomes in endothelial cells, thereby initiating and promoting vascular inflammation. It remains unknown whether this impaired ICMR occurs under diabetic condition or hyperglycemia contributing to endothelial dysfunction leading to vascular inflammation, a hallmark of diabetic vascular injury. The present study aims to examine whether ICMR occurs during in control and diabetic mice and to explore related molecular mechanisms associated with acid sphingomyelinase (ASM)-mediated ceramide production. Using confocal microscopy, we demonstrated that mouse aortic endothelial cells (MAECs) exposed to high glucose levels exhibited much more retarded ICMR after laser-induced membrane injury, compared to that in control cells. The high glucose-induced impairment of membrane resealing in MAECs was prevented when these cells were pretreated with sphingomyelin or C24-ceramide. Mechanistically, high glucose treatment decreased association of membrane ceramide with annexin A5, an essential element of membrane repair machinery. Consistently, the association of ceramide with annexin A5 was significantly reduced in the coronary arterial endothelium of mice with streptozotocin-induced diabetes mellitus compared to that in non-diabetic control mice. Moreover, a marked reduction of the association of ceramide with annexin A5 was observed in coronary arterial endothelium of ASM knockout mice regardless of their diabetic status. Lastly, high glucose treatment or ASM gene deletion substantially impaired ICMR in coronary arterial endothelium of mice receiving membrane puncturing agents. Collectively, our data suggest that ceramide-mediated ICMR in vascular endothelial cells is impaired during diabetes mellitus due to dissociation of ceramide with annexin A5 and ASM play a critical role in this ICMR.

Relationships between ocular surface sphingomyelinases, Meibum and Tear Sphingolipids, and clinical parameters of meibomian gland dysfunction

PURPOSE

Sphingolipids (SPL) are a class of lipid molecules that play important functional and structural roles in our body and are a component of meibum. Sphingomyelinases (SMases) are key enzymes in sphingolipid metabolism that hydrolyze sphingomyelin (SM) and generate ceramide (Cer). The purpose of this study was to examine relationships between ocular surface SMases, SPL composition, and parameters of Meibomian gland dysfunction (MGD).

METHODS

Individuals were grouped by meibum quality (n = 25 with poor-quality, MGD, and n = 25 with good-quality, control). Meibum and tears were analyzed with LC-MS to quantify SPL classes: Cer, Hexosyl-Ceramide (Hex-Cer), SM, Sphingosine (Sph), and sphingosine 1-phosphate (S1P). SMase activity in tears were quantified using a commercially available 'SMase assay'. Statistical analysis included multiple linear regression analyses to assess the impact of SMase activity on lipid composition, as well as ocular surface symptoms and signs of MGD.

RESULTS

Demographic characteristics were similar between the two groups. nSMase and aSMase levels were lower in the poor vs good quality group. aSMase activity in tears negatively correlated with SM in meibum and tears and positively with Sph in meibum and S1P in tears. Lower SMase activity were associated with signs of MGD, most notably Meibomian gland dropout.

CONCLUSION

This study suggests that individuals with MGD have reduced enzymatic activity of SMases in tears. Specifically, individuals with poor vs good meibum quality were noted to have alterations in SMase activity and SPL composition of meibum and tears which may reflect deviations from normal lipid metabolism in individuals with MGD.

Exploring Endothelial Colony-Forming Cells to Better Understand the Pathophysiology of Disease: An Updated Review

Endothelial cell (EC) dysfunction has been implicated in a variety of pathological conditions. The collection of ECs from patients is typically conducted postmortem or through invasive procedures, such as surgery and interventional procedures, hampering efforts to clarify the role of ECs in disease onset and progression. In contrast, endothelial colony-forming cells (ECFCs), also termed late endothelial progenitor cells, late outgrowth endothelial cells, blood outgrowth endothelial cells, or endothelial outgrowth cells, are obtained in a minimally invasive manner, namely, by the culture of human peripheral blood mononuclear cells in endothelial growth medium. ECFCs resemble mature ECs phenotypically, genetically, and functionally, making them excellent surrogates for ECs. Numerous studies have been performed that examined ECFC function in conditions such as coronary artery disease, diabetes mellitus, hereditary hemorrhagic telangiectasia, congenital bicuspid aortic valve disease, pulmonary arterial hypertension, venous thromboembolic disease, and von Willebrand disease. Here, we provide an updated review of studies using ECFCs that were performed to better understand the pathophysiology of disease. We also discuss the potential of ECFCs as disease biomarkers and the standardized methods to culture, quantify, and evaluate ECFCs and suggest the future direction of research in this field.

Lycium barbarum polysaccharides attenuates high glucose-induced diabetic retinal angiogenesis by rescuing the expression of miR-15a-5p in RF/6A cells

ETHNOPHARMACOLOGICAL RELEVANCE

Lycium barbarum L., a classical traditional Chinese Medicine, has long been used to treat ocular diseases. Lycium barbarum polysaccharides (LBP) is an effective component of Lycium barbarum L. with a wide range of pharmacological activities. This research aims to investigate the inhibition of high glucose-induced angiogenesis by LBP in RF/6A cells.

MATERIALS AND METHODS

A high-glucose-induced angiogenesis model was established using monkey retinal vascular endothelial (RF/6A) cells. Different dosages administration times of LBP and glucose concentrations were tested. Under the optimized conditions, RF/6A cells were treated with LBP for 48 h, followed by another 48-h culture in high glucose (25 mmol/L) medium. The effect and mechanism of LBP were investigated following the treatment.

RESULTS

The expression of miR-15a-5p and miR-15a-3p in RF/6A cells decreased significantly after 48 h of 25 or 50 mmol/L high glucose treatment. The expression of miR-15a-5p was higher than that of miR-15a-3p. Mimic-miR-15a-5p or 600 mg/L LBP could increase the apoptosis of cells and the total length of vascular branches. The expression of VEGFA, VEGFR2, and ANG2 proteins was reduced, while the expression of ANG1 protein was elevated. Expression of ASM mRNA and protein was also inhibited.

CONCLUSIONS

LBP attenuates diabetic retinal angiogenesis by rescuing the expression of miR-15a-5p in RF/6A cells.

Integrated lipids biomarker of the prediabetes and type 2 diabetes mellitus Chinese patients

INTRODUCTION

Dyslipidemia is a hallmark of T2DM, and as such, analyses of lipid metabolic profiles in affected patients have the potential to permit the development of an integrated lipid metabolite-based biomarker model that can facilitate early patient diagnosis and treatment.

METHODS

Untargeted and targeted lipidomics approaches were used to analyze serum samples from newly diagnosed 93 Chinese participants in discovery cohort and 440 in validation cohort via UHPLC-MS and UHPLC-MS/MS first. The acid sphingomyelinase protein expression was analyzed by Western blot.

RESULTS AND DISCUSSION

Through these analyses, we developed a novel integrated biomarker signature composed of LPC 22:6, PC(16:0/20:4), PE(22:6/16:0), Cer(d18:1/24:0)/SM(d18:1/19:0), Cer(d18:1/24:0)/SM(d18:0/16:0), TG(18:1/18:2/18:2), TG(16:0/16:0/20:3), and TG(18:0/16:0/18:2). The area under the curve (AUC) values for this integrated biomarker signature for prediabetes and T2DM patients were 0.841 (cutoff: 0.565) and 0.894 (cutoff: 0.633), respectively. Furthermore, theresults of western blot analysis of frozen adipose tissue from 3 week (prediabetes) and 12 week (T2DM) Goto-Kakizaki (GK) rats also confirmed that acid sphingomyelinase is responsible for significant disruptions in ceramide and sphingomyelin homeostasis. Network analyses of the biomarkers associated with this biosignature suggested that the most profoundly affected lipid metabolism pathways in the context of diabetes include de novo ceramide synthesis, sphingomyelin metabolism, and additional pathways associated with phosphatidylcholine synthesis. Together, these results offer new biological insights regarding the role of serum lipids in the context of insidious T2DM development, and may offer new avenues for future diagnostic and/or therapeutic research.

Ceramide-mediation of diffusion in supported lipid bilayers

The fluidity and compositional heterogeneity of the mammalian plasma membrane play deterministic roles in a variety of membrane functions. Designing model bilayer systems allows for compositional control over these properties. Ceramide is a phospholipid capable of extensive headgroup-region hydrogen bonding, and we report here on the role of ceramide in planar model bilayers. We use fluorescence recovery after photobleaching (FRAP) to obtain translational diffusion constants of two chromophores in supported model bilayers composed of cholesterol, 1,2-dioleoyl-sn-phosphatidylcholine (DOPC), sphingomyelin, and ceramide. FRAP data for perylene report on the acyl chain region of the model bilayer and FRAP data for 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine-N-(lissamine rhodamine B sulfonyl) sense diffusional dynamics in the bilayer headgroup region. Dynamics in the headgroup region exhibit anomalous diffusion behavior that is characteristic of spatially heterogeneous media.

Alpha-mangostin improves endothelial dysfunction in db/db mice through inhibition of aSMase/ceramide pathway

Diabetic vascular complications are the leading causes of death and disability in patients with diabetes. Alpha-mangostin has been reported to have anti-diabetic capacity in recent years. Here, we investigated the protective function of alpha-mangostin on endothelium in vitro and in vivo experiments. We also observed that alpha-mangostin improved impaired endothelium-dependent vasodilation (EDV) of diabetic animals while it limited the aSMase/ceramide pathway and up-regulated eNOS/NO pathway in aortas from diabetic mice. Meanwhile, alpha-mangostin inhibited elevated aSMase/ceramide pathway and reversed impaired EDV induced by high glucose in isolated mouse aortas. In addition, alpha-mangostin increased phosphorylation of eNOS and NO production in high glucose-treated aortas. Alpha-mangostin normalized high glucose-induced activation of aSMase/ceramide pathway and improved eNOS/NO pathway in endothelial cells with high glucose. In conclusion, alpha-mangostin regulates eNOS/NO pathway and improves EDV in aortas of diabetic mice through inhibiting aSMase activity and endogenous ceramide accumulation.

Lipid metabolism dysregulation in diabetic retinopathy

Lipid metabolic abnormalities have emerged as potential risk factors for the development and progression of diabetic complications, including diabetic retinopathy (DR). This review article provides an overview of the results of clinical trials evaluating the potential benefits of lipid-lowering drugs, such as fibrates, omega-3 fatty acids, and statins, for the prevention and treatment of DR. Although several clinical trials demonstrated that treatment with fibrates leads to improvement of DR, there is a dissociation between the protective effects of fibrates in the retina, and the intended blood lipid classes, including plasma triglycerides, total cholesterol, or HDL:LDL cholesterol ratio. Guided by these findings, plasma lipid and lipoprotein-independent mechanisms are addressed based on clinical, cell culture, and animal model studies. Potential retinal-specific effects of fatty acid oxidation products, cholesterol, and ceramide, as well as lipid-independent effects of PPAR alpha activation, are summarized based on the current literature. Overall, this review highlights promising potential of lipid-based treatment strategies further enhanced by the new knowledge of intraretinal lipids and lipoproteins in DR.

Nitric oxide induces HepG2 cell death via extracellular signal-regulated protein kinase activation by regulating acid sphingomyelinase

Nitric oxide (NO) plays a vital role in the occurrence and development of tumours. Acid sphingomyelinase (ASM) participates in cell apoptosis, cell proliferation, metabolism and other biological processes. However, whether ASM has an effect on NO-treated HepG2 cells remains unknown, and the role of the extracellular signal-regulated protein kinase (ERK) pathway is also unclear. In the present study, the effects of NO on cell viability and apoptosis were assayed, followed by investigating the mRNA and protein levels of ASM and ERK phosphorylation in NO-treated HepG2 cells. The results showed that diethylenetriamine/NO (DETA-NO), an NO donor, promoted HepG2 cell death and apoptosis in a concentration-dependent manner and that the mRNA and protein expression levels of ASM were significantly decreased in DETA-NO-treated HepG2 cells. Moreover, ERK phosphorylation was significantly increased in DETA-NO-treated HepG2 cells. The inhibition of ERK phosphorylation increased DETA-NO-induced cell apoptosis. In summary, DETA-NO can promote HepG2 cell death in a concentration-dependent manner by activating ERK and NO might activate ERK by regulating ASM and then inducing HepG2 cell death.

Accumulation of advanced glycation end products potentiate human retinal capillary endothelial cells mediated diabetic retinopathy

The major ophthalmic complication in patients with diabetes is diabetic retinopathy (DR), which is one of the major eye diseases that causes blindness. It is well established that the occurrence and duration of DR is positively correlated with duration of diabetes. Advanced glycation end product (AGE) accumulation in patients with diabetes is one factor that leads to the development of DR. However, the underlying mechanisms remain unclear. In the present study, the role of phosphoinositide 3‑kinase/protein kinase B (Akt) signaling in AGE‑induced DR development was investigated. An in vitro experimental system was used to study the effects of AGEs on human retinal capillary endothelial cells (HRCECs) and Müller cells. Flow cytometry, MTT, western blotting and BrdU incorporation assays were performed. Reverse transcription‑quantitative polymerase chain reaction was used to measure the expression of angiogenesis‑associated genes. Functional assays of angiogenesis, including HRCEC invasion and tube formation assays. It was demonstrated that the expression of receptor for AGEs was upregulated in HRCECs and Müller cells following treatment with AGEs. AGE treatment did not affect Müller cell viability, but enhanced HRCEC viability. Akt inhibition increased cell apoptosis and death in HRCECs. AGE treatment upregulated the expression of pro‑angiogenic genes, which was suppressed by Akt inhibitor treatment. In addition, Akt inhibitor treatment suppressed HRCEC invasion and tube formation ability. The present study suggested that Akt‑mediated signaling may serve critical roles in the development of DR due to the accumulation of AGEs. Akt may be a potential therapeutic target in DR.

Inhibition of acid sphingomyelinase activity ameliorates endothelial dysfunction in db/db mice

Acid sphingomyelinase (aSMase) plays an important role in endothelial dysfunction. Here, we show that elevated aSMase activity and ceramide content were reduced by desipramine treatment in diabetic animals. The inhibitor of aSMase, desipramine, improved vascular dysfunction in db/db mice. High glucose (HG)-induced up-regulation of aSMase activity and ceramide levels were restored by treatment with aSMase siRNA or desipramine in endothelial cells. In addition, aSMase siRNA or desipramine treatment increased the release of nitric oxide (NO) and the phosphorylation of endothelial NO synthase (eNOS) in diabetic mouse aortas and aortic endothelial cells with HG.

These results indicate that inhibition of aSMase/ceramide pathway improves endothelium-dependent vascular relaxation (EDR) largely through regulating the eNOS/NO pathway in diabetic animals.

Circulating angiogenic stem cells in type 2 diabetes are associated with glycemic control and endothelial dysfunction

Circulating angiogenic cells (CACs) of various described phenotypes participate in the regeneration of the damaged endothelium, but the abundance of these cells is highly influenced by external cues including diabetes. It is not entirely clear which CAC populations are most reflective of endothelial function nor which are impacted by diabetes. To answer these questions, we enrolled a human cohort with variable CVD risk and determined relationships between stratified levels of CACs and indices of diabetes and vascular function. We also determined associations between CAC functional markers and diabetes and identified pro-angiogenic molecules which are impacted by diabetes. We found that subjects with low levels of CD34+/AC133+/CD31+/CD45dim cells (CAC-3) had a significantly higher incidence of diabetes (p = 0.004), higher HbA1c levels (p = 0.049) and higher CVD risk scores. Furthermore, there was an association between low CAC-3 levels and impaired vascular function (p = 0.023). These cells from diabetics had reduced levels of CXCR4 and VEGFR2, while diabetics had higher levels of certain cytokines and pro-angiogenic molecules. These results suggest that quantitative and functional defects of CD34+/AC133+/CD31+/CD45dim cells are associated with diabetes and vascular impairment and that this cell type may be a prognostic indicator of CVD and vascular dysfunction.

Mitochondrial dysfunctions, endothelial progenitor cells and diabetic retinopathy

AIM

Diabetic retinopathy (DR) is the leading cause of vision loss in the working age population. Endothelial progenitor cells (EPC) play a vital role in vascular damage repair. This article will review recent progress regarding mitochondrial and EPC dysfunction associated with DR.

RESULTS

EPCs represent a limited population of adult stem cells possessing vasculogenic potential postnatally; their number and function are changed in DR. Among all the function changes, mitochondrial dysfunction plays an important role in the dysregulation of EPCs, as mitochondria regulate energy balance, and cell fate determination.

CONCLUSIONS

Although the mechanism for the role of mitochondria dysregulation in EPC function remains elusive, mitochondria of EPCs represent a promising target for the treatment of the vasculopathy presented within DR.

Models of retinal diseases and their applicability in drug discovery

INTRODUCTION

The impact of vision debilitating diseases is a global public health concern, which will continue until effective preventative and management protocols are developed. Two retinal diseases responsible for the majority of vision loss in the working age adults and elderly populations are diabetic retinopathy (DR) and age-related macular degeneration (AMD), respectively. Model systems, which recapitulate aspects of human pathology, are valid experimental modalities that have contributed to the identification of signaling pathways involved in disease development and consequently potential therapies. Areas covered: The pathology of DR and AMD, which serve as the basis for designing appropriate models of disease, is discussed. The authors also review in vitro and in vivo models of DR and AMD and evaluate the utility of these models in exploratory and pre-clinical studies. Expert opinion: The complex nature of non-Mendelian diseases such as DR and AMD has made identification of effective therapeutic treatments challenging. However, the authors believe that while in vivo models are often criticized for not being a 'perfect' recapitulation of disease, they have been valuable experimentally when used with consideration of the strengths and limitations of the experimental model selected and have a place in the drug discovery process.

The Role of Microglia in Diabetic Retinopathy: Inflammation, Microvasculature Defects and Neurodegeneration

Diabetic retinopathy is a common complication of diabetes mellitus, which appears in one third of all diabetic patients and is a prominent cause of vision loss. First discovered as a microvascular disease, intensive research in the field identified inflammation and neurodegeneration to be part of diabetic retinopathy. Microglia, the resident monocytes of the retina, are activated due to a complex interplay between the different cell types of the retina and diverse pathological pathways. The trigger for developing diabetic retinopathy is diabetes-induced hyperglycemia, accompanied by leukostasis and vascular leakages. Transcriptional changes in activated microglia, mediated via the nuclear factor kappa-light-chain-enhancer of activated B cells (NFκB) and extracellular signal–regulated kinase (ERK) signaling pathways, results in release of various pro-inflammatory mediators, including cytokines, chemokines, caspases and glutamate. Activated microglia additionally increased proliferation and migration. Among other consequences, these changes in microglia severely affected retinal neurons, causing increased apoptosis and subsequent thinning of the nerve fiber layer, resulting in visual loss. New potential therapeutics need to interfere with these diabetic complications even before changes in the retina are diagnosed, to prevent neuronal apoptosis and blindness in patients.