Mechanisms of PEDF-mediated protection against reactive oxygen species damage in diabetic retinopathy and neuropathy

Effects and potential mechanisms of exercise and physical activity on eye health and ocular diseases

In the field of eye health, the profound impact of exercise and physical activity on various ocular diseases has become a focal point of attention. This review summarizes and elucidates the positive effects of exercise and physical activities on common ocular diseases, including dry eye disease (DED), cataracts, myopia, glaucoma, diabetic retinopathy (DR), and age-related macular degeneration (AMD). It also catalogues and offers exercise recommendations based on the varying impacts that different types and intensities of physical activities may have on specific eye conditions. Beyond correlations, this review also compiles potential mechanisms through which exercise and physical activity beneficially affect eye health. From mitigating ocular oxidative stress and inflammatory responses, reducing intraocular pressure, enhancing mitochondrial function, to promoting ocular blood circulation and the release of protective factors, the complex biological effects triggered by exercise and physical activities reveal their substantial potential in preventing and even assisting in the treatment of ocular diseases. This review aims not only to foster awareness and appreciation for how exercise and physical activity can improve eye health but also to serve as a catalyst for further exploration into the specific mechanisms and key targets through which exercise impacts ocular health. Such inquiries are crucial for advancing innovative strategies for the treatment of eye diseases, thereby holding significant implications for the development of new therapeutic approaches.

Molecular Mechanisms Linking Diabetes with Increased Risk of Thrombosis

This review will provide an overview of what is currently known about mechanisms linking poor glycaemic control with increased thrombotic risk. The leading causes of death in people with diabetes are strokes and cardiovascular disease. Significant morbidity is associated with an increased risk of thrombosis, resulting in myocardial infarction, ischaemic stroke, and peripheral vascular disease, along with the sequelae of these events, including loss of functional ability, heart failure, and amputations. While the increased platelet activity, pro-coagulability, and endothelial dysfunction directly impact this risk, the molecular mechanisms linking poor glycaemic control with increased thrombotic risk remain unclear. This review highlights the complex mechanisms underlying thrombosis prevalence in individuals with diabetes and hyperglycaemia. Post-translational modifications, such as O-GlcNAcylation, play a crucial role in controlling protein function in diabetes. However, the role of O-GlcNAcylation remains poorly understood due to its intricate regulation and the potential involvement of multiple variables. Further research is needed to determine the precise impact of O-GlcNAcylation on specific disease processes.

A systematic proteomic profiling and pathway analysis of protein biomarkers in diabetic retinopathy with subsequent validation of the IL-6 upstream regulator

Purpose

Diabetic retinopathy (DR) is a leading cause of irreversible blindness worldwide. Identifying risk factors associated with DR development and progression is crucial for improving treatment efficacy. Although proteomic changes in DR have been extensively studied, the results remain equivocal. Hence, this study aims to summarize and identify potential diagnostic or prognostic markers for DR. In addition, the upstream regulator responsible for protein deregulation of this disease was also validated.

Methods

We systematically analyzed the current literature on proteomic profile changes in DR, followed by pathway analysis identification. To validate the protein level changes, ELISA was performed from serum samples collected from 27 patients with DR and 25 healthy controls.

Results

Our analysis revealed that 1 candidate marker (afamin [AFM]) distinguished non-proliferative diabetic retinopathy (NPDR) from type 2 diabetic patients with no diabetic retinopathy/controls, 65 candidate markers distinguished proliferative diabetic retinopathy (PDR) from NPDR, 1 candidate marker (thyroid receptor-interacting protein 11 [TRIP11]) distinguished PDR from PDR-DME/DME, and 3 candidate markers for therapeutic evaluation of PDR. Our results pinpoint that inflammatory response, which IL-6 mainly modulated, is responsible for the changes of proteomic profiles identified in DR. This was also validated by ELISA analysis, indicating that IL-6 could be potentially useful for diagnosing DR.

Conclusion

We report a comprehensive patient-based proteomic approach to identify potential biomarkers for DR diagnosis, prognosis, and treatment evaluation.

Supplementary information

The online version contains supplementary material available at 10.1007/s40200-023-01204-6.

The molecular mechanism of Ang II induced-AAA models based on proteomics analysis in ApoE-/- and CD57BL/6J mice

Apolipoprotein knockout (ApoE^-/-) and CD57BL/6J mouse models of angiotensin II (Ang II)-induced abdominal aortic aneurysm (AAA) are commonly used in AAA research. However, the similarities and differences in the molecular mechanisms of AAA in these two genotypes have not been reported. In our study, we analyzed proteomics data from ApoE^-/- and CD57BL/6J mouse models of Ang II-induced AAA and control mice by LC-MS/MS. Gene set enrichment analysis (GSEA) of differentially abundance proteins (DAPs) in the ApoE^-/- or CD57BL/6J mouse groups was performed in R software, and infiltration of immune cells in groups was assessed. DAP that showed the same trend in abundance in ApoE^-/- and CD57BL/6J mice (S-DAP) were identified and subjected to GO enrichment, KEGG pathway, and connectivity map (CMap) analyses. The protein-protein interaction (PPI) network of the S-DAP was drawn, the key S-DAP were identified by MCODE, and the transcription factors (TFs) of crucial S-DAP were predicted by iRegulon in Cytoscape. Male ApoE^-/- and CD57BL/6J mouse models of Ang II-induced AAA are commonly used in AAA research, and extracellular matrix organization is associated with AAA in both of these models. However, there are some differences between the mechanisms underlying AAA in these two genotypes, and these differences need to be considered when studying AAA and selecting models. SIGNIFICANCE: Our research provided the first insight into the similarity and differential mechanisms of Ang II infused AAA models using ApoE^-/- and CD57BL/6J mice. This study might provide the some advises for the selection of Ang II infused AAA models for further AAA researches.

Bioengineering approaches for modelling retinal pathologies of the outer blood-retinal barrier

Alterations of the junctional complex of the outer blood-retinal barrier (oBRB), which is integrated by the close interaction of the retinal pigment epithelium, the Bruch's membrane, and the choriocapillaris, contribute to the loss of neuronal signalling and subsequent vision impairment in several retinal inflammatory disorders such as age-related macular degeneration and diabetic retinopathy. Reductionist approaches into the mechanisms that underlie such diseases have been hindered by the absence of adequate in vitro models using human cells to provide the 3D dynamic architecture that enables expression of the in vivo phenotype of the oBRB. Conventional in vitro cell models are based on 2D monolayer cellular cultures, unable to properly recapitulate the complexity of living systems. The main drawbacks of conventional oBRB models also emerge from the cell sourcing, the lack of an appropriate Bruch's membrane analogue, and the lack of choroidal microvasculature with flow. In the last years, the advent of organ-on-a-chip, bioengineering, and stem cell technologies is providing more advanced 3D models with flow, multicellularity, and external control over microenvironmental properties. By incorporating additional biological complexity, organ-on-a-chip devices can mirror physiologically relevant properties of the native tissue while offering additional set ups to model and study disease. In this review we first examine the current understanding of oBRB biology as a functional unit, highlighting the coordinated contribution of the different components to barrier function in health and disease. Then we describe recent advances in the use of pluripotent stem cells-derived retinal cells, Bruch's membrane analogues, and co-culture techniques to recapitulate the oBRB. We finally discuss current advances and challenges of oBRB-on-a-chip technologies for disease modelling.

Hydroquinone predisposes for retinal pigment epithelial (RPE) cell degeneration in inflammatory conditions

In addition to hypoxia, inflammation is capable of inducing vascular endothelial growth factor (VEGF) expression in human retinal pigment epithelial (RPE) cells. Excessive levels of VEGF promote choroidal neovascularization and thereby contribute to the pathogenesis of wet age-related macular degeneration (AMD). Intravitreal anti-VEGF injections ameliorate pathological vessel neoformation in wet AMD but excessive dampening of VEGF can result in a degeneration of the RPE. In the present study, we induced VEGF production by exposing human ARPE-19 cells to the pro-inflammatory IL-1α and subsequently to hydroquinone, a component of tobacco smoke that is a major environmental risk factor for AMD. Effects were monitored by measuring the levels of VEGF and anti-angiogenic pigment epithelium-derived factor (PEDF) using an enzyme-linked immunosorbent assay (ELISA) technique. In addition, we measured the production of reactive oxygen species (ROS) using the 2′,7′-dichlorofluorescin diacetate (H2DCFDA) probe and studied the effects of two anti-oxidants, ammonium pyrrolidinedithiocarbamate (APDC) and N-acetyl-cysteine (NAC), on VEGF production. Cellular and secreted VEGF as well as secreted PEDF levels were reduced at all tested hydroquinone concentrations (10, 50, or 200 µM); these effects were evident prior to any reduction of cell viability evoked by hydroquinone. Cell viability was carefully explored in our previous study and verified by microscoping in the present study. APDC further reduced the VEGF levels, whereas NAC increased them. The 50 μM concentration of hydroquinone increased ROS production in ARPE-19 cells primed with IL-1α. Hydroquinone disturbs the regulatory balance of VEGF and PEDF in inflammatory conditions. These data support the idea that hydroquinone mediates RPE degeneration by reducing VEGF levels and may predispose to dry AMD since VEGF is as well important for retinal integrity.

Diagnostic circulating biomarkers to detect vision-threatening diabetic retinopathy: Potential screening tool of the future?

With the increasing prevalence of diabetes in developing and developed countries, the socio-economic burden of diabetic retinopathy (DR), the leading complication of diabetes, is growing. Diabetic retinopathy (DR) is currently one of the leading causes of blindness in working-age adults worldwide. Robust methodologies exist to detect and monitor DR; however, these rely on specialist imaging techniques and qualified practitioners. This makes detecting and monitoring DR expensive and time-consuming, which is particularly problematic in developing countries where many patients will be remote and have little contact with specialist medical centres. Diabetic retinopathy (DR) is largely asymptomatic until late in the pathology. Therefore, early identification and stratification of vision-threatening DR (VTDR) is highly desirable and will ameliorate the global impact of this disease. A simple, reliable and more cost-effective test would greatly assist in decreasing the burden of DR around the world. Here, we evaluate and review data on circulating protein biomarkers, which have been verified in the context of DR. We also discuss the challenges and developments necessary to translate these promising data into clinically useful assays, to detect VTDR, and their potential integration into simple point-of-care testing devices.

Beyond the Liver: Liver-Eye Communication in Clinical and Experimental Aspects

The communication between organs participates in the regulation of body homeostasis under physiological conditions and the progression and adaptation of diseases under pathological conditions. The communication between the liver and the eyes has been received more and more attention. In this review, we summarized some molecular mediators that can reflect the relationship between the liver and the eye, and then extended the metabolic relationship between the liver and the eye. We also summarized some typical diseases and phenotypes that have been able to reflect the liver-eye connection in the clinic, especially non-alcoholic fatty liver disease (NAFLD) and diabetic retinopathy (DR). The close connection between the liver and the eye is reflected through multiple pathways such as metabolism, oxidative stress, and inflammation. In addition, we presented the connection between the liver and the eye in traditional Chinese medicine, and introduced the fact that artificial intelligence may use the close connection between the liver and the eye to help us solve some practical clinical problems. Paying attention to liver-eye communication will help us have a deeper and more comprehensive understanding of certain communication between liver diseases and eyes, and provide new ideas for their potential therapeutic strategy.

Pigment Epithelium-Derived Factor-Loaded PEGylated Nanoparticles as a New Antiangiogenic Therapy for Neovascularization

BACKGROUND

Pathological neovascularization, which involves a disruption in the balance between angiogenic and antiangiogenic factors under pathological conditions, is the basis of many intraocular diseases. Pigment epithelium-derived factor (PEDF) is a potent natural, endogenous inhibitor of neovascularization because of its antiangiogenic and neuroprotective benefits. However, its application is restricted by its instability and short half-life. The present study is aimed at investigating the cytotoxicity and antiangiogenic effects of PEDF-loaded PEGylated nanoparticles (NP-PEG-PEDF) on high glucose-stimulated human umbilical vein endothelial cells (HUVECs).

METHODS

In this study, NP-PEG-PEDF were fabricated using the multiple emulsion method for the first time. HUVECs were cultured in a high concentration of glucose (30 mmol/L D-glucose), simulating diabetic conditions. The antiangiogenic effects of vascular endothelial growth factor (VEGF), pure PEDF, and NP-PEG-PEDF on proliferation, migration, and tube formation were evaluated. VEGF secretion in high glucose-stimulated HUVECs was further tested in vitro.

RESULTS

NP-PEG-PEDF exhibited low cytotoxicity in HUVECs. Our results indicated that in vitro, NP-PEG-PEDF attenuated diabetes-induced HUVEC proliferation, migration, and tube formation and suppressed VEGF secretion. The apoptosis of diabetes-induced HUVECs occurred in a dose-dependent manner, which showed a statistically significant difference compared with the PEDF treatment group.

CONCLUSION

Our study is the first to demonstrate that NP-PEG-PEDF exert antiangiogenic effects on high glucose-stimulated HUVECs and have the potential to alleviate microvascular dysfunction. These data suggest that the NP-PEG-PEDF delivery system may offer an innovative therapeutic strategy for preventing neovascularization of the fundus.

Neurovascular Unit: A New Target for Treating Early Stages of Diabetic Retinopathy

The concept of diabetic retinopathy as a microvascular disease has evolved and is now considered a more complex diabetic complication in which neurovascular unit impairment plays an essential role and, therefore, can be considered as a main therapeutic target in the early stages of the disease. However, neurodegeneration is not always the apparent primary event in the natural story of diabetic retinopathy, and a phenotyping characterization is recommendable to identify those patients in whom neuroprotective treatment might be of benefit. In recent years, a myriad of treatments based on neuroprotection have been tested in experimental models, but more interestingly, there are drugs with a dual activity (neuroprotective and vasculotropic). In this review, the recent evidence concerning the therapeutic approaches targeting neurovascular unit impairment will be presented, along with a critical review of the scientific gaps and problems which remain to be overcome before our knowledge can be transferred to clinical practice.

Protective effects of piperine on the retina of mice with streptozotocin-induced diabetes by suppressing HIF-1/VEGFA pathway and promoting PEDF expression

AIM

To evaluate the protective mechanisms of piperine in the retina of mice with streptozotocin-induced diabetes.

METHODS

In experiments in vitro, stimulation by chemical hypoxia was established in ARPE-19 cells. Then, the expression of hypoxia-inducible factor-1α (HIF-1α), vascular endothelial growth factor A (VEGFA), and pigment epithelium-derived factor (PEDF) was assessed at the mRNA and protein levels. In experiments in vivo, diabetes mellitus was established by intraperitoneally injecting 150 mg/kg streptozotocin once. After 3wk of the onset of diabetes, 15 mg/kg piperine was intraperitoneally injected once daily for 1 or 3wk. Then, the retinal morphology and mRNA and protein expression were assessed.

RESULTS

In hypoxia, 1-100 µmol/L piperine significantly decreased the expression of VEGFA mRNA and increased the expression of PEDF mRNA without affecting HIF-1α mRNA. Meanwhile, 100 µmol/L piperine substantially decreased the protein level of VEGFA and increased the protein level of PEDF. The HIF-1α protein level was also hampered by piperine. In the diabetic retina of mice, the morphological damage was alleviated by piperine. Likewise, the retinal vascular leakage was substantially decreased by piperine. Further, the protein levels of HIF-1α and VEGFA were significantly reduced by piperine. Moreover, the level of the antiangiogenic factor of PEDF dramatically increased by piperine.

CONCLUSION

Piperine may exert protective effects on the retina of mice with diabetes via regulating the pro-antiangiogenic homeostasis composed of HIF-1/VEGFA and PEDF.

Pigment epithelium-derived factor, a novel decidual natural killer cells-derived factor, protects decidual stromal cells via anti-inflammation and anti-apoptosis in early pregnancy

STUDY QUESTION

What is the role of pigment epithelium-derived factor (PEDF) from decidual natural killer (dNK) cells during early pregnancy?

SUMMARY ANSWER

PEDF from dNK cells limits the lipopolysaccharide (LPS)-induced apoptosis and inflammation of decidual stromal cells (DSCs) to maintain DSCs homoeostasis and immune balance at the maternal-foetal interface during early pregnancy.

WHAT IS KNOWN ALREADY

dNK cells, which secrete PEDF, play critical roles during pregnancy via a series of key regulators. PEDF, a multifunctional endogenous glycoprotein, exhibits a wide range of biological actions upon angiogenesis, inflammation, metabolic homoeostasis, immunomodulation etc., providing potential clinical applications.

STUDY DESIGN, SIZE, DURATION

Natural killer (NK) cells from decidua and peripheral blood as well as DSCs isolated from normal pregnancy (NP) during the first trimester (6-10 weeks) and the matched patients suffering recurrent miscarriage (RM) were studied. RNA-sequencing analysis of dNK cells was performed to screen for potential key genes involved in RM. The expression of PEDF in dNK cells in NP and RM was examined. A coculture system with LPS-stimulated DSCs and NK cell supernatants derived from NP or RM was established to explore the regulatory mechanisms of PEDF at the maternal-foetal interface.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Peripheral blood and decidual tissues were obtained from women with NP (n = 61) and RM (n = 21). The expression levels of PEDF in NK cells and its receptor (PEDFR) on DSCs were analysed using flow cytometry, western blot and immunohistochemistry. Purified peripheral natural killer (pNK) cells were cocultured with DSCs or trophoblast cells or a combination of both cell types, and PEDF expression in pNK cells was then examined by flow cytometry. DSCs were treated with LPS, an outer-membrane component of Gram-negative bacteria, thereby mimicking an enhanced inflammatory status within decidua, and were cocultured with dNK cell supernatants from NP or RM. In the coculture system, plasmids expressing short hairpin RNA were used to silence PEDFR on DSCs and block the PEDF/PEDFR interaction. Inflammatory cytokines and apoptosis of DSCs treated as described above were assessed by flow cytometry. Western blotting was performed, and the specific signal pathway inhibitors were used to determine downstream PEDF/PEDFR signalling in early decidua.

MAIN RESULTS AND THE ROLE OF CHANCE

Markedly higher RNA (P < 0.001) and protein expression of PEDF (P < 0.01) was detected in normal dNK cells when compared with pNK cells. Compared with pNK cells cultured alone, PEDF expression in pNK cells was elevated after coculture with DSCs (P < 0.01) or trophoblast cells (P < 0.001). The increased pro-inflammatory cytokine, tumour necrosis factor-α and apoptosis of DSCs following LPS stimulation were suppressed by recombinant human PEDF (P < 0.001) or the supernatant of dNK cells derived from NP (P < 0.001). However, these effects were somewhat abrogated when the PEDF/PEDFR interaction was blocked with PEDFR short hairpin sRNA (P < 0.01). Furthermore, dNK cell-derived PEDF protected DSCs from LPS-induced inflammation via inhibition of nuclear factor kappa-B activation, while also protecting DSCs from LPS-induced apoptosis via promotion of extracellular signal-regulated kinase expression. Compared with NP, both significantly decreased PEDF RNA (P < 0.001) and protein expression (P < 0.001) in dNK cells, but not in pNK cells (P > 0.05), were detected in women with RM. PEDFR on DSCs was also decreased within RM compared with that within NP (P < 0.001). As a result, dNK cell-mediated anti-inflammation (P < 0.01) and anti-apoptosis (P < 0.05) for protection of LPS-treated DSCs was attenuated in patients suffering from RM.

LARGE SCALE DATA

N/A.

LIMITATIONS, REASONS FOR CAUTION

We cannot exclude the possibility that the differences in amounts of PEDF and its receptor in tissue from NP versus RM women could be caused by the miscarriage event in women with RM. Our experiments only involved human samples investigated in vitro. Experiments in animal models and human study cohorts are still needed to confirm these findings and further clarify the role of PEDF-PEDFR in NP and/or RM.

WIDER IMPLICATIONS OF THE FINDINGS

To the best of our knowledge, this is the first study to demonstrate PEDF expression and function at the maternal-foetal interface in the first trimester, providing further evidence that PEDF exhibits functional diversity and has great potential for clinical application(s). The findings of selectively high expression of PEDF in normal dNK cells and the PEDF-mediated role of dNK cells during NP and RM help to further elucidate the immune mechanisms behind RM.

STUDY FUNDING/COMPETING INTEREST(S)

This work was supported by the National Basic Research Programme of China (2017YFC1001403 and 2015CB943300), Nature Science Foundation from National Nature Science Foundation of China (NSFC; 31970859, 81630036, 81501334, 91542116, 31570920, 81490744 and 31171437), the Innovation-oriented Science and Technology Grant from NHC Key Laboratory of Reproduction Regulation (CX2017-2), the Programme of Shanghai Academic/Technology Research Leader (17XD1400900) and the Key Project of Shanghai Basic Research from Shanghai Municipal Science and Technology Commission (STCSM; 12JC1401600). None of the authors has any conflict of interest to declare.

The biological relevance of pigment epithelium-derived factor on the path from aging to age-related disease

Pigment epithelium-derived factor (PEDF) is an endogenously produced protein that contributes to cell growth arrest, and reduced levels of PEDF are associated with the progression of cellular senescence and the aging process. However, the mechanisms underlying PEDF regulation of these events are not completely clear. Increased PEDF activity may induce anti-aging processes, suggesting the potential therapeutic value of PEDF as an anti-aging and age-related disease. In this review, we recapitulate the molecular and cellular mechanisms of aging following the characteristics and specific roles of the PEDF in cell cycle arrest and its relevance to cellular senescence and aging pathways. In this context, the discovery and fluctuations of PEDF in age-related diseases are summarised. In light of the importance of PEDF in cellular senescence and aging processes, better comprehension of the mechanism(s) of PEDF in the regulation of cell cycle and the aging process can conceivably facilitate the development of therapeutic strategies for diseases that occur with aging.

PEDF promotes the repair of bone marrow endothelial cell injury and accelerates hematopoietic reconstruction after bone marrow transplantation

Background

Preconditioning before bone marrow transplantation such as irradiation causes vascular endothelial cells damage and promoting the repair of damaged endothelial cells is beneficial for hematopoietic reconstitution. Pigment epithelium-derived factor (PEDF) regulates vascular permeability. However, PEDF’s role in the repair of damaged endothelial cells during preconditioning remains unclear. The purpose of our study is to investigate PEDF’s effect on preconditioning-induced damage of endothelial cells and hematopoietic reconstitution.

Methods

Damaged endothelial cells induced by irradiation was co-cultured with hematopoietic stem cells (HSC) in the absence or presence of PEDF followed by analysis of HSC number, cell cycle, colony formation and differentiation. In addition, PEDF was injected into mice model of bone marrow transplantation followed by analysis of bone marrow injury, HSC number and peripheral hematopoietic reconstitution as well as the secretion of cytokines (SCF, TGF-β, IL-6 and TNF-α). Comparisons between two groups were performed by student t-test and multiple groups by one-way or two-way ANOVA.

Results

Damaged endothelial cells reduced HSC expansion and colony formation, induced HSC cell cycle arrest and apoptosis and promoted HSC differentiation as well as decreased PEDF expression. Addition of PEDF increased CD144 expression in damaged endothelial cells and inhibited the increase of endothelial permeability, which were abolished after addition of PEDF receptor inhibitor Atglistatin. Additionally, PEDF ameliorated the inhibitory effect of damaged endothelial cells on HSC expansion in vitro. Finally, PEDF accelerated hematopoietic reconstitution after bone marrow transplantation in mice and promoted the secretion of SCF, TGF-β and IL-6.

Conclusions

PEDF inhibits the increased endothelial permeability induced by irradiation and reverse the inhibitory effect of injured endothelial cells on hematopoietic stem cells and promote hematopoietic reconstruction.

PEDF Attenuates Ocular Surface Damage in Diabetic Mice Model Through Its Antioxidant Properties

PURPOSE

To investigate the antioxidative effect and mechanism of pigment epithelium-derived factor (PEDF) on the ocular surface damage in diabetic mice.

METHODS

C57BL/6 mice were injected intraperitoneally with streptozocin to generate diabetic models and then 50 nM PEDF or artificial tears were used to treat the diabetic mice. Treatment was given three times a day for eight weeks. Corneal epithelial damage, corneal sensitivity, and tear volume were quantified by fluorescein staining, esthesiometer, and phenol red cotton thread, respectively. Animals were sacrificed at 16 weeks after diabetes and the whole globe specimens were subjected to histochemical staining. Reactive oxygen species (ROS) generation was detected by 2',7-dichlorodihydrofluorescein probe. The levels of receptor for advanced glycation end products (RAGE) and superoxide dismutase 1 (SOD1) were examined by quantitative real-time PCR and western blotting.

RESULTS

Topical application of PEDF improved corneal epithelial damage, increased corneal sensitivity, and tear volume in diabetic mice. ROS levels in the cornea were significantly higher in the diabetic mice than in the normal mice. Moreover, PEDF attenuated the accumulation of ROS, decreased the expression of RAGE, and elevated SOD1 expression in the cornea.

CONCLUSIONS

Topical application of PEDF can alleviate diabetes-related ocular surface damage and increase tear volume, along with the improvement of oxidative stress status.

The role of pigment epithelium-derived factor in protecting against cellular stress

Since its discovery as a neurotrophic factor in retinal pigmented epithelium cells in the late 1980s, there has been an increase in understanding of the role that pigment epithelium-derived factor (PEDF) plays in cellular functions. PEDF plays an important role in mediating cellular protection during exposure to oxidative stress and inflammation by preventing stress-induced angiogenesis and apoptosis. PEDF acts to reduce oxidative stress by promoting mitochondrial stability and by regulating the expression of enzymes involved in ROS accumulation and clearance. PEDF protects against the negative effects of oxidative stress by regulating cell survival pathways and the expression of inflammatory and proangiogenic mediators. PEDF-mediated cellular protection may be of clinical importance in diseases characterised by oxidative stress, chronic inflammation and pathological neovascularization, indicating that targeting PEDF may be a potential focus for therapeutic interventions in chronic diseases. In this review, we provide a historical perspective on the discoveries of PEDF interactions and functions, and discuss recent in vitro, in vivo and clinical findings to provide a current summary of the important protective effects following cellular exposure to stress stimuli and future clinical potential of PEDF.

Schizandrin A Protects Human Retinal Pigment Epithelial Cell Line ARPE-19 against HG-Induced Cell Injury by Regulation of miR-145

Diabetic retinopathy (DR) is a serious complication of diabetes, which is the main cause of blindness among adults. Traditional Chinese medicines (TCMs) have been proven to delay the development of DR. Nonetheless, the effect of Schizandrin A (SchA) on DR remains uninvestigated. The present study aimed to probe the protective effect of SchA on high-glucose (HG)-induced injury in ARPE-19 cells. We observed that SchA accelerated cell proliferation, prohibited apoptosis, and restrained pro-inflammatory cytokines (monocyte chemoattractant protein-1 [MCP-1], interleukin-6 [IL-6], and tumor necrosis factor alpha [TNF-α]) and reactive oxygen species (ROS) level in HG-stimulated cells. Additionally, miR-145 expression was upregulated in HG and SchA co-treated cells, and miR-145 inhibition reversed the protective effect of SchA on HG-managed ARPE-19 cells. Interestingly, downregulated myeloid differentiation factor 88 (MyD88) was found in HG and SchA co-treated cells, and upregulation of MyD88 was observed in miR-145 inhibitor-transfected cells. Additionally, SchA hindered nuclear factor κB (NF-κB) and p38 mitogen-activated protein kinase (p38MAPK) signaling pathways in HG-treated ARPE-19 cells. The findings validated that SchA could protect ARPE-19 cells from HG-induced cell injury by regulation of miR-145.

Type I pig collagen enhances the efficacy of PEDF 34-mer peptide in a mouse model of laser-induced choroidal neovascularization

BACKGROUND

Pigment epithelium-derived factor (PEDF)-derived 34-mer peptide (PEDF34, Asp⁴⁴-Asn⁷⁷) has anti-angiogenic activity but has limitations in clinical application because of an inverted bell-shaped dose-effect relationship and a short half-life. In this study, we attempted to mitigate these problems by mixing PEDF34 with type I collagen.

METHODS

The anti-angiogenic activity of the PEDF34/atelocollagen mixture was evaluated by HUVEC tube formation assay and in a laser-induced choroidal neovascular (CNV) mouse model. PEDF34 and/or collagen were administrated using intravitreal injections or eye drops. CNV lesion size was quantified using FITC-dextran-perfused retinal whole mounts. Western blot analysis and inhibitor assays were used to define the action mechanisms of PEDF34 and the mixture.

RESULTS

Collagen broadened the effective dose range of PEDF34 in the tube formation assay by > 250 times (from 0.2 to 50 nM). In the CNV model, five intravitreal injections of PEDF34 were required for therapeutic effect, whereas the mixture had a significant therapeutic effect following a single injection. Eye drops of the mixture showed significantly stronger CNV-suppressive effects than drops of PEDF34 alone. The anti-angiogenic activity of PEDF34 might be mediated by inhibition of ERK and JNK activation by VEGF, and collagen potentiated these effects.

CONCLUSIONS

Collagen can serve as a carrier and reservoir of PEDF34. PEDF peptide/collagen mixture is easy to prepare than conventional methods for maintaining the therapeutic effect of PEDF peptide.

p53 mediates PEDF‑induced autophagy in human umbilical vein endothelial cells through sestrin2 signaling

Autophagy is a conserved catabolic process by which cytoplasmic components are delivered into lysosomes for degradation. Pigment epithelium‑derived factor (PEDF) has been reported to be associated with autophagy and can induce p53 expression; however, the mechanism relating PEDF with autophagy in endothelial cells remains poorly understood. The present study aimed to investigate the association between the PEDF‑p53‑sestrin pathway and autophagy in human umbilical vein endothelial cells (HUVECs). PEDF‑induced autophagy was examined by fluorescence microscopy and western blot analysis. p53 small interfering (si)RNA and sestrin2 siRNA were constructed and transfected into HUVECs prior to PEDF treatment. The protein expression levels of microtubule‑associated protein light chain 3 (LC3) I, LC3 II and p62 were evaluated by western blot analysis, and the mRNA expression levels of p53 and sestrin2 were determined using reverse transcription‑quantitative polymerase chain reaction analysis. The regulation of mechanistic target of rapamycin (mTOR) was reflected by p70S6 kinase (p70S6K) and eukaryotic translation initiation factor 4E‑binding protein 1 (4E‑BP1) protein expression levels, as determined by western blot analysis. PEDF could induce HUVEC autophagy by sequentially inducing p53 and sestrin2 expression, as observed by fluorescence microscopy and western blot analysis. Conversely, the induction of sestrin2 by PEDF was eliminated by p53 siRNA. In addition, p53 siRNA and sestrin2 siRNA could attenuate PEDF‑induced HUVEC autophagy. Inhibition of mTOR may be the mechanism responsible for PEDF‑induced autophagy; as p70S6K and 4E‑BP1 phosphorylation levels were significantly upregulated in p53 siRNA‑treated and sestrin2 siRNA‑treated groups. The findings of the present study indicated that PEDF may trigger autophagy in HUVECs by inducing p53 and sestrin2 expression, and inhibiting mTOR expression; these findings may contribute to the improved understanding of diseases, including cancer and atherosclerosis.

Autophagy: a new mechanism for regulating VEGF and PEDF expression in retinal pigment epithelium cells

AIM

To investigate the regulation of vascular endothelial growth factors (VEGF) and pigment epithelium-derived factor (PEDF) expression by autophagy in retinal pigment epithelium (RPE) cells on exposure to hypoxia.

METHODS

ARPE-19, an RPE cell line, was treated as following: the control group was kept in a normoxic incubator; the hypoxia group was incubated in a hypoxic incubator with 1% O₂/5% CO₂/94% N₂ for 24h; the hypoxia + 3-methyladenine (3-MA) group was pretreated with 10 mmol/L 3-MA for 1h and then in the hypoxic incubator for 24h; and the hypoxia + chloroquine (CQ) group was pretreated with 50 µmol/L CQ for 1h and then in the hypoxic incubator for 24h. The morphology and ultrastructure of the cells was observed by an inverted microscope or a transmission electronic microscope (TEM). Western blot was performed to assay the expression of autophagy-associated markers, including microtubule associated protein 1 light chain 3 B (LC3B), Beclin-1, Atg5 and p62. The concentration of VEGF and PEDF in the culture supernatant was determined by ELISA, and the ratio of VEGF/PEDF was calculated.

RESULTS

There were no obvious differences in cell morphology among different groups and autolysosomes could be observed in the cytoplasm in all groups. Compared to the control cells, the LC3B-II/I ratio and levels of Beclin-1 and Atg5 were significantly increased and p62 level was significantly decreased in the hypoxia group. With the increase of VEGF and decrease of PEDF concentration, the VEGF/PEDF ratio was significantly increased in the hypoxia group compared to the control cells. The LC3B-II/I ratio was significantly reduced by 3-MA treatment and increased by CQ treatment. The expressions of Beclin-1 and Atg5 were significantly reduced by 3-MA or CQ treatment, while expression of p62 was increased in the 3-MA or CQ treated cells. The concentration of VEGF was significantly decreased and PEDF increased, thereby the VEGF/PEDF ratio was decreased in the hypoxia + 3-MA group and hypoxia + CQ group compared with that in the hypoxia group.

CONCLUSION

Hypoxia leads to elevated autophagy in RPE cells, and expression of VEGF and PEDF might be regulated by autophagy on exposure to hypoxia to further participate in regulating the formation of retinal neovascularization.

Association of Pigment Epithelium Derived Factor With von Willebrand Factor and Plasminogen Activator Inhibitor 1 in Patients With Type 2 Diabetes

To compare circulating pigment epithelium derived factor (PEDF) levels in type 2 diabetes patients (T2D) with and without metabolic syndrome (MetS+/-) to healthy controls and assess PEDF association with plasminogen activator inhibitor-1 (PAI-1) and von Willebrand factor (vWF) as markers of endothelial dysfunction. Fifty T2D individuals and forty healthy controls were included. PEDF, PAI-1, vWF, anthropological parameters, lipids, and markers of insulin resistance were investigated in all subjects. Compared to controls only MetS+ diabetics had higher PEDF levels [14.2 (10.2-16.0) mg/l vs. 11.1 (8.6-14.4) mg/l; p<0.05]. PEDF significantly correlated: positively with body mass index (ρ=0.25), smoking (ρ=0.21), C-reactive protein (ρ=0.22), triglycerides (ρ=0.38), non-HDL-cholesterol (ρ=0.39), apolipoprotein B (ρ=0.38), fasting glucose (ρ=0.22), glycated hemoglobin (ρ=0.24), C-peptide (ρ=0.28), insulin (ρ=0.26); and negatively with HDL-cholesterol (ρ=-0.42) and apolipoprotein A1 (ρ=-0.27). Independent association of PEDF with vWF in T2DMetS- subjects was found. Significantly elevated PEDF in T2DMet+ patients and its association with adverse metabolic profile confirmed PEDF as a marker of insulin resistance. Negative independent association of PEDF with vWF in T2DMetS- patients may reveal its angio-protective role.

Nanoparticle-Mediated Delivery of Neuroprotective Substances for the Treatment of Diabetic Retinopathy

BACKGROUND

Diabetic retinopathy (DR) is a major complication of diabetes, characterized by extensive vascular pathology leading to vision loss. Neuronal suffering and death are also present in the diabetic retina as a result of different molecular mechanisms that are compromised or modified in response to high glucose. The aim of this paper is to highlight recent data indicating that neurodegeneration is likely to play a primary role in the development of DR and that strategies based on nanomedicine may be exploited to deliver neuroprotection to the retina.

METHODS

An extensive analysis of the publications dealing with the role of neuroprotection in DR and with nanoparticle-mediated drug delivery to the retina has been conducted using PubMed, with particular attention to the most recent papers.

RESULTS

There are important limitations related to possible systemic side effects of neuroprotective substances and to drug bioavailability in the retina such as, for instance, the amount of drug reaching the retina, the need of keeping to a minimum the number of administrations (especially, for example, in the case of intraocular injections) and the need of assuring a long-lasting, graded intraocular drug delivery. In recent years, a variety of investigations have been aimed at the exploitation of approaches of nanomedicine to enhance the pharmacokinetics and pharmacodynamic activity of intraocularly delivered drugs. In particular, we provide some preliminary results that we have obtained about the feasibility of delivering magnetic nanoparticles functionalized with a neuroprotectant to mouse eyes through intraocular injections.

CONCLUSION

We propose that nanoparticles functionalized with neuroprotective substances may be used to protect the diabetic retina, thus causing an impact in the design of future pharmacologic treatments for DR.

Long-term photoreceptor rescue in two rodent models of retinitis pigmentosa by adeno-associated virus delivery of Stanniocalcin-1

Retinal degenerations, including age-related macular degeneration and the retinitis pigmentosa family of diseases, are among the leading causes of legal blindness in the United States. We previously found that Stanniocalcin-1 (STC-1) reduced photoreceptor loss in the S334ter-3 and Royal College of Surgeons rat models of retinal degeneration. The results were attributed in part to a reduction in oxidative stress. Herein, we tested the hypothesis that long-term delivery of STC-1 would provide therapeutic rescue in more chronic models of retinal degeneration. To achieve sustained delivery, we produced an adeno-associated virus (AAV) construct to express STC-1 (AAV-STC-1) under the control of a retinal ganglion cell targeting promoter human synapsin 1 (hSYN1). AAV-STC-1 was injected intravitreally into the P23H-1 and S334ter-4 rhodopsin transgenic rats at postnatal day 10. Tissues were collected at postnatal day 120 for confirmation of STC-1 overexpression and histologic and molecular analysis. Electroretinography (ERG) was performed in a cohort of animals at that time. Overexpression of STC-1 resulted in a significant preservation of photoreceptors as assessed by outer nuclear thickness in the P23H-1 (P < 0.05) and the S334ter-4 (P < 0.005) models compared to controls. Additionally, retinal function was significantly improved in the P23H-1 model with overexpressed STC-1 as assessed by ERG analysis (scotopic b-wave P < 0.005 and photopic b-wave P < 0.05). Microarray analysis identified common downstream gene expression changes that occurred in both models. Genes of interest based on their function were selected for validation by quantitative real-time PCR and were significantly increased in the S334ter-4 model.

Recovery of Corneal Sensitivity and Increase in Nerve Density and Wound Healing in Diabetic Mice After PEDF Plus DHA Treatment

Diabetic keratopathy decreases corneal sensation and tear secretion and delays wound healing after injury. In the current study, we tested the effect of treatment with pigment epithelium-derived factor (PEDF) in combination with docosahexaenoic acid (DHA) on corneal nerve regeneration in a mouse model of diabetes with or without corneal injury. The study was performed in streptozotocin-induced diabetic mice (C57BL/6). Ten weeks after streptozotocin injection, diabetic mice showed significant decreases of corneal sensitivity, tear production, and epithelial subbasal nerve density when compared with age-matched normal mice. After diabetic mice were wounded in the right eye and treated in both eyes with PEDF+DHA for 2 weeks, there was a significant increase in corneal epithelial nerve regeneration and substance P-positive nerve density in both wounded and unwounded eyes compared with vehicle-treated corneas. There also was elevated corneal sensitivity and tear production in the treated corneas compared with vehicle. In addition, PEDF+DHA accelerated corneal wound healing, selectively recruited type 2 macrophages, and prevented neutrophil infiltration in diabetic wounded corneas. These results suggest that topical treatment with PEDF+DHA promotes corneal nerve regeneration and wound healing in diabetic mice and could potentially be exploited as a therapeutic option for the treatment of diabetic keratopathy.

Molecular mechanisms of ROS production and oxidative stress in diabetes

Oxidative stress and chronic inflammation are known to be associated with the development of metabolic diseases, including diabetes. Oxidative stress, an imbalance between oxidative and antioxidative systems of cells and tissues, is a result of over production of oxidative-free radicals and associated reactive oxygen species (ROS). One outcome of excessive levels of ROS is the modification of the structure and function of cellular proteins and lipids, leading to cellular dysfunction including impaired energy metabolism, altered cell signalling and cell cycle control, impaired cell transport mechanisms and overall dysfunctional biological activity, immune activation and inflammation. Nutritional stress, such as that caused by excess high-fat and/or carbohydrate diets, promotes oxidative stress as evident by increased lipid peroxidation products, protein carbonylation and decreased antioxidant status. In obesity, chronic oxidative stress and associated inflammation are the underlying factors that lead to the development of pathologies such as insulin resistance, dysregulated pathways of metabolism, diabetes and cardiovascular disease through impaired signalling and metabolism resulting in dysfunction to insulin secretion, insulin action and immune responses. However, exercise may counter excessive levels of oxidative stress and thus improve metabolic and inflammatory outcomes. In the present article, we review the cellular and molecular origins and significance of ROS production, the molecular targets and responses describing how oxidative stress affects cell function including mechanisms of insulin secretion and action, from the point of view of possible application of novel diabetic therapies based on redox regulation.

Pigment epithelial-derived factor in human fetal membranes

OBJECTIVE

Our main objective was to document, pigment epithelial-derived factor (PEDF), a secreted serine protease inhibitor with anti-angiogenic, anti-inflammatory, and anti-oxidant properties, expression in human fetal membranes from preterm prelabor rupture of the membranes (pPROM) and in in vitro cultures stimulated with cigarette smoke extract (CSE) or lipopolysaccharides (LPS), two major risk factors for pPROM (behavioral and bacterial, respectively).

METHOD

We documented PEDF mRNA expression in clinical samples of fetal membranes from patients with pPROM using quantitative RT-PCR. Also, mRNA and protein levels were documented in fetal membranes (from normal term cesarean sections [not in labor]) in an organ explant system stimulated with CSE or lipopolysaccharide (LPS). Immunohistochemistry (IHC) was used to localize PEDF in fetal membranes.

RESULTS

We report no changes in PEDF mRNA expression in pPROM compared to term births (p = .59) or after treatment with CSE or LPS. However, by adding sulforaphane the PEDF mRNA expression increased significantly p < .000032. PEDF was localized to both amnion and chorion layers, but no difference was seen in staining intensities after CSE or LPS treatment compared to control.

CONCLUSIONS

PEDF, a product of fetal membrane cells, is unaltered in pPROM or after exposure to risk factors of pPROM. The antioxidant stimulating substance sulforaphane contribute to an increase in PEDF mRNA in fetal membranes.

Retinal Neurodegeneration in the Course of Diabetes-Pathogenesis and Clinical Perspective

Diabetic retinopathy is generally considered as a microvascular disease which develops as a result of chronic hyperglycaemia. However, the neuronal apoptosis and reactive gliosis are recently postulated as early changes in diabetic retinopathy. This phenomenon is described as a neurodegeneration and suggests that diabetic retinopathy should be recognized as a neurovascular complication. In this review, we discuss the mechanisms leading to the neurodegeneration of the retina in diabetic patients including: low-grade inflammatory process, oxidative stress, activation of polymorphonuclear neutrophils, glutamate excitotoxicity and imbalance in the neuroprotective factors. Secondly, we point out the clinical significance of measuring the retinal neurodegeneration.

Pigment Epithelium-Derived Factor Declines in Response to an Oral Glucose Load and Is Correlated with Vitamin D and BMI but Not Diabetes Status in Children and Young Adults

BACKGROUND

Pigment epithelium-derived factor (PEDF) is associated with obesity and diabetes complications in adults, yet little is known about PEDF in younger individuals. We investigated the relationship between PEDF and various metabolic biomarkers in young healthy volunteers (HV) and similar-aged patients with diabetes (type 1 and type 2).

METHODS

A fasting blood sample was collected in 48 HV, 11 patients with type 1 diabetes (T1D), and 11 patients with type 2 diabetes (T2D) 12-25 years of age. In 9 healthy subjects, PEDF was also serially measured during a frequently sampled oral glucose tolerance test (OGTT).

RESULTS

PEDF was positively correlated with BMI and systolic blood pressure and negatively correlated with vitamin D. Upon multivariable analysis, BMI and vitamin D were independent predictors of PEDF. Prior to adjustment, PEDF was highest in T2D patients (7,168.9 ± 4417.4 ng/mL) and lowest in individuals with T1D (2,967.7 ± 947.1 ng/mL) but did not differ by diagnosis when adjusted for BMI and vitamin D. Among volunteers who underwent an OGTT, PEDF declined by ∼20% in response to an oral glucose load.

CONCLUSION

PEDF was acutely regulated by a glucose load and was correlated with BMI but not with diabetes. The negative correlation with vitamin D, independent of BMI, raises the question whether PEDF plays a compensatory role in bone matrix mineralization.

Pigment epithelium-derived factor (PEDF) regulates metabolism and insulin secretion from a clonal rat pancreatic beta cell line BRIN-BD11 and mouse islets

Pigment epithelium-derived factor (PEDF) is a multifunctional glycoprotein, associated with lipid catabolism and insulin resistance. In the present study, PEDF increased chronic and acute insulin secretion in a clonal rat β-cell line BRIN-BD11, without alteration of glucose consumption. PEDF also stimulated insulin secretion from primary mouse islets. Seahorse flux analysis demonstrated that PEDF did not change mitochondrial respiration and glycolytic function. The cytosolic presence of the putative PEDF receptor - adipose triglyceride lipase (ATGL) - was identified, and ATGL associated stimulation of glycerol release was robustly enhanced by PEDF, while intracellular ATP levels increased. Addition of palmitate or ex vivo stimulation with inflammatory mediators induced β-cell dysfunction, effects not altered by the addition of PEDF. In conclusion, PEDF increased insulin secretion in BRIN-BD11 and islet cells, but had no impact on glucose metabolism. Thus elevated lipolysis and enhanced fatty acid availability may impact insulin secretion following PEDF receptor (ATGL) stimulation.

Neuroprotection as a Therapeutic Target for Diabetic Retinopathy

Diabetic retinopathy (DR) is a multifactorial progressive disease of the retina and a leading cause of vision loss. DR has long been regarded as a vascular disorder, although neuronal death and visual impairment appear before vascular lesions, suggesting an important role played by neurodegeneration in DR and the appropriateness of neuroprotective strategies. Upregulation of vascular endothelial growth factor (VEGF), the main target of current therapies, is likely to be one of the first responses to retinal hyperglycemic stress and VEGF may represent an important survival factor in early phases of DR. Of central importance for clinical trials is the detection of retinal neurodegeneration in the clinical setting, and spectral domain optical coherence tomography seems the most indicated technique. Many substances have been tested in animal studies for their neuroprotective properties and for possible use in humans. Perhaps, the most intriguing perspective is the use of endogenous neuroprotective substances or nutraceuticals. Together, the data point to the central role of neurodegeneration in the pathogenesis of DR and indicate neuroprotection as an effective strategy for treating this disease. However, clinical trials to determine not only the effectiveness and safety but also the compliance of a noninvasive route of drug administration are needed.

Priorities and trends in the study of proteins in eye research, 1924-2014

PURPOSE

To identify the proteins that are relevant to eye research and develop assays for the study of a set of these proteins.

EXPERIMENTAL DESIGN

We conducted a bibliometric analysis by merging gene lists for human and mouse from the National Center for Biotechnology Information FTP site and combining them with PubMed references that were retrieved with the search terms "eye" [MeSH Terms] OR "eye" [All Fields] OR "eyes" [All Fields].

RESULTS

For human and mouse eye studies, respectively, the total number of publications was 13,525 and 23,895 and the total number of proteins was 4050 and 4717. For proteins in human and mouse eye studies, respectively, 88.7 and 81.7% had five or fewer citations. The top 50 most intensively studied proteins for human and mouse eye studies were generally in the areas of photoreceptors and phototransduction, inflammation, and angiogenesis, neurodevelopment, lens transparency, and cell-cycle and cellular processes. We proposed selected reaction monitoring assays that were developed in silico for the top fifty most intensively studied proteins in human and mouse eye research.

CONCLUSIONS AND CLINICAL RELEVANCE

We conclude that scientists engaged in eye research tend to focus on the same proteins. Newer resources and tools in proteomics can expand the investigations to lesser-known proteins of the eye.

In Vivo Imaging of Retinal Oxidative Stress Using a Reactive Oxygen Species-Activated Fluorescent Probe

PURPOSE

In vivo methods for detecting oxidative stress in the eye would improve screening and monitoring of the leading causes of blindness: diabetic retinopathy, glaucoma, and age-related macular degeneration.

METHODS

To develop an in vivo biomarker for oxidative stress in the eye, we tested the efficacy of a reactive oxygen species (ROS)-activated, near-infrared hydrocyanine-800CW (H-800CW) fluorescent probe in light-induced retinal degeneration (LIRD) mouse models. After intravitreal delivery in LIRD rats, fluorescent microscopy was used to confirm that the oxidized H-800CW appeared in the same retinal layers as an established ROS marker (dichlorofluorescein).

RESULTS

Dose-response curves of increasing concentrations of intravenously injected H-800CW demonstrated linear increases in both intensity and total area of fundus hyperfluorescence in LIRD mice, as detected by scanning laser ophthalmoscopy. Fundus hyperfluorescence also correlated with the duration of light damage and functional deficits in vision after LIRD. In LIRD rats with intravitreal injections of H-800CW, fluorescent labeling was localized to photoreceptor inner segments, similar to dichlorofluorescein.

CONCLUSIONS

Hydrocyanine-800CW detects retinal ROS in vivo and shows potential as a novel biomarker for ROS levels in ophthalmic diseases.

Biomarkers in Diabetic Retinopathy

There is a global diabetes epidemic correlating with an increase in obesity. This coincidence may lead to a rise in the prevalence of type 2 diabetes. There is also an as yet unexplained increase in the incidence of type 1 diabetes, which is not related to adiposity. Whilst improved diabetes care has substantially improved diabetes outcomes, the disease remains a common cause of working age adult-onset blindness. Diabetic retinopathy is the most frequently occurring complication of diabetes; it is greatly feared by many diabetes patients. There are multiple risk factors and markers for the onset and progression of diabetic retinopathy, yet residual risk remains. Screening for diabetic retinopathy is recommended to facilitate early detection and treatment. Common biomarkers of diabetic retinopathy and its risk in clinical practice today relate to the visualization of the retinal vasculature and measures of glycemia, lipids, blood pressure, body weight, smoking, and pregnancy status. Greater knowledge of novel biomarkers and mediators of diabetic retinopathy, such as those related to inflammation and angiogenesis, has contributed to the development of additional therapeutics, in particular for late-stage retinopathy, including intra-ocular corticosteroids and intravitreal vascular endothelial growth factor inhibitors ('anti-VEGFs') agents. Unfortunately, in spite of a range of treatments (including laser photocoagulation, intraocular steroids, and anti-VEGF agents, and more recently oral fenofibrate, a PPAR-alpha agonist lipid-lowering drug), many patients with diabetic retinopathy do not respond well to current therapeutics. Therefore, more effective treatments for diabetic retinopathy are necessary. New analytical techniques, in particular those related to molecular markers, are accelerating progress in diabetic retinopathy research. Given the increasing incidence and prevalence of diabetes, and the limited capacity of healthcare systems to screen and treat diabetic retinopathy, there is need to reliably identify and triage people with diabetes. Biomarkers may facilitate a better understanding of diabetic retinopathy, and contribute to the development of novel treatments and new clinical strategies to prevent vision loss in people with diabetes. This article reviews key aspects related to biomarker research, and focuses on some specific biomarkers relevant to diabetic retinopathy.

Effect of shRNA-mediated knockdown of vascular endothelial growth factor on the proliferation of choroid-retinal endothelial cells under hypoxic conditions

The aim of the present study was to investigate the role of vascular endothelial growth factor (VEGF) in cell proliferation under hypoxic conditions. Gene knockdown of VEGF was conducted in the choroid-retinal endothelial RF/6A cell line by transfection with short hairpin RNA (shRNA), in which a shRNA fragment against VEGF was synthesized and cloned into the vector, pSilencer 2.1-U6 neo. Subsequently, a model of hypoxia was established in the RF/6A cell line via treatment with CoCl₂, into which the recombinant plasmids, containing the VEGF-targeting shRNA (p-shRNA), were transfected. The study included four treatment groups, namely a control group (normal group), a hypoxia group treated with CoCl₂ (CoCl₂ group), a control plasmid group that were subjected to CoCl₂ treatment and transfection with a pSilencer 2.1-U6 neo plasmid without the shRNA (CoCl₂ + p-NC group), and a group treated with CoCl₂ and transfected with a pSilencer 2.1-U6 neo plasmid containing the VEGF-targeting shRNA (CoCl₂ + p-shRNA group). Subsequent to treatment, the mRNA and protein expression levels of VEGF were evaluated using quantitative polymerase chain reaction and western blot analysis, respectively, In addition, cell proliferation was assessed. RF/6A cells treated with CoCl₂ reduced cell connectivity, irregular morphology and reduced thickness compared with the cells in the normal group. However, cells in the CoCl₂ + p-shRNA group exhibited an improved morphology compared with the CoCl₂ and CoCl₂ + p-NC groups. Cell proliferation in the CoCl₂ group was enhanced in a time-dependent manner. However, the hypoxia-induced increase in cell proliferation was significantly inhibited in the CoCl₂ + p-shRNA group, with inhibition rates of 16, 32 and 38% at 24, 48 and 72 h, respectively. The mRNA and protein expression levels of VEGF were increased in the CoCl₂ group when compared with the normal group, and these hypoxia-induced increases in VEGF expression were reduced in the CoCl₂ + p-shRNA group. Therefore, the results indicated that the targeted knockdown of VEGF in vascular endothelial cells may be effective for the treatment of retinal neovascularization diseases.

Increased serum pigment epithelium-derived factor in women with gestational diabetes is associated with type 2 diabetes

Background. Pigment epithelium-derived factor (PEDF) is demonstrated to be elevated in diabetes patients. However, no reports have emerged in pregnant women with gestational diabetes mellitus (GDM). This study was undertaken to investigate serum PEDF levels in GDM women and to evaluate PEDF as a biomarker to predict diabetes postpartum. Methods. Serum PEDF concentration and clinical characteristics were detected in the pregnant women with GDM (n = 120) and without GDM (control group, n = 120). Results. PEDF levels were elevated in subjects with GDM versus controls. Univariate correlations showed that serum PEDF levels were positively correlated with fasting glucose and fasting insulin levels, respectively, and negatively correlated with adiponectin. Receiver operating characteristic (ROC) analysis demonstrated that the AUC of serum PEDF for diabetes mellitus in women postpartum was 0.893. Conclusion. Serum PEDF was elevated in pregnant women with GDM, which is probably an early detection marker for predicting development of GDM to diabetes mellitus.