Retinal fibrosis in diabetic retinopathy

In vivo monitoring of active subretinal fibrosis in mice using collagen hybridizing peptides

Subretinal fibrosis is associated with worse visual outcomes in patients with neovascular age-related macular degeneration. As there is a lack of optimal biomarkers and no method that directly detects collagen in the back of the eye, novel tools that monitor fibrosis-related changes in neovascular age-related macular degeneration are needed. Here, using two mouse models (the laser-induced choroidal neovascularization model, and the JR5558 mouse presenting with spontaneous subretinal neovascularization with fibrosis), we imaged active fibrotic lesions using fluorescently labeled collagen hybridizing peptides (CHPs), short peptides that bind to single α-chain collagen structures during collagen remodeling. JR5558 retinal pigment epithelium/choroid flat mounts showed CHP co-staining with fibrosis and epithelial mesenchymal transition-related markers; additionally, CHP histopathology staining correlated with in vivo CHP imaging. After laser-induced choroidal neovascularization, in vivo CHP binding correlated with laser intensity, histopathology CHP and fibronectin staining. Laser-induced choroidal neovascularization showed decreased CHP intensity over time in healing/regressing versus active scars in vivo, whereas increased CHP binding correlated with elevated fibrosis in JR5558 mouse eyes with age. In bispecific angiopoietin 2/vascular endothelial growth factor antibody-treated JR5558 mice, CHPs detected significantly decreased collagen remodeling versus immunoglobulin G control. These results demonstrate the first use of CHPs to directly image remodeling collagen in the eye and as a potential clinical optical biomarker of active subretinal fibrosis associated with ocular neovascularization.

Apigenin suppresses epithelial-mesenchymal transition in high glucose-induced retinal pigment epithelial cell by inhibiting CBP/p300-mediated histone acetylation

Epithelial mesenchymal transition (EMT) is a critical process implicated in the pathogenesis of retinal fibrosis and the exacerbation of diabetic retinopathy (DR) within retinal pigment epithelium (RPE) cells. Apigenin (AP), a potential dietary supplement for managing diabetes and its associated complications, has demonstrated inhibitory effects on EMT in various diseases. However, the specific impact and underlying mechanisms of AP on EMT in RPE cells remain poorly understood. In this study, we have successfully validated the inhibitory effects of AP on high glucose-induced EMT in ARPE-19 cells and diabetic db/db mice. Notably, our findings have identified CBP/p300 as a potential therapeutic target for EMT in RPE cells and have further substantiated that AP effectively downregulates the expression of EMT-related genes by attenuating the activity of CBP/p300, consequently reducing histone acetylation alterations within the promoter region of these genes. Taken together, our results provide novel evidence supporting the inhibitory effect of AP on EMT in RPE cells, and highlight the potential of specifically targeting CBP/p300 as a strategy for inhibiting retinal fibrosis in the context of DR.

TGF-β1 Mediates the EndoMt in High Glucose-Treated Human Retinal Microvascular Endothelial Cells

The purpose of our study was to investigate the role of TGF-β1 in the endothelial-to-mesenchymal transition (EndoMT) and fibrosis in high glucose (HG)-treated human retinal microvascular endothelial cells (HRMECs). HRMECs were cultured not only under normal glucose (NG) conditions with or without TGF-β1, but also under HG conditions with or without the TGF-β1 inhibitor SB431542. The expression of TGF-β1 was detected by real time-PCR and enzyme-linked immunosorbent assay. Morphological changes and migration of the HRMECs were observed using electron microscopy and scratch-wound assay. Endothelial markers, such as CD31 and vascular endothelial (VE)-cadherin, and the acquisition of fibrotic markers, such as alpha smooth muscle actin (α-SMA) and fibroblast-specific protein-1 (FSP-1), were determined by immunofluorescent staining and western blot. The level of TGF-β1 was significantly upregulated in HG-treated HRMECs. And HG stimulation promoted obvious morphological changes and the migration ability in HRMECs. Our results also demonstrated increased expression of α-SMA and FSP-1, and decreased expression of CD31 and VE-cadherin, in HG-treated HRMECs. These EndoMT-related changes were promoted by TGF-β1 and abrogated by SB431542. The results of this study demonstrated the important role of TGF-β1 in HG-induced vitreoretinal fibrosis. EndoMT is likely to be involved in the associated effects.

The effect of adjuvant Mitomycin C during vitrectomy on functional and anatomical outcomes in patients with severe diabetic tractional retinal detachment

PURPOSE

To evaluate the effect of adjuvant Mitomycin C (MMC) use on the anatomical and functional success of vitreoretinal surgery (VRS) in severe diabetic tractional retinal detachment (dTRD) patients.

METHODS

A retrospective analysis of consecutive patients undergoing VRS due to severe dTRD was conducted. Patients were categorized into those who received 20 µg/0.1 mL MMC via MMC sandwich method (Group 1) and those who did not (Group 2). Demographics, surgical characteristics, visual outcomes, and complications that may related to MMC were analyzed.

RESULTS

A total of 25 eyes were included, 13 in Group 1 and 12 in Group 2. No statistical difference was observed in baseline characteristics between the groups. The mean best-corrected visual acuity was 1.90 ± 0.43 logMAR and 1.93 ± 0.41 logMAR preoperatively and 1.60 ± 0.78 logMAR and 1.56 ± 0.78 logMAR postoperatively in Groups 1 and 2, respectively (p = 0.154). The postoperative mean intraocular pressure was 16.23 ± 2.55 mmHg and 13.08 ± 4.94 mmHg in Groups 1 and 2, respectively (p = 0.225). The rate of re-surgery was significantly lower in Group 1 (0% vs. 41.7% in Group 2, p = 0.015). Retina was attached in all patients at the last visit. No MMC-related complication was recorded.

CONCLUSION

Intraoperative adjuvant MMC application for severe dTRD significantly reduces re-surgery rates with good anatomical and functional outcomes safely.

Exploring the Potential of Wild Olive (Acebuche) Oil as a Pharm-Food to Prevent Ocular Hypertension and Fibrotic Events in the Retina of Hypertensive Mice

SCOPE

Our laboratory has previously described the antioxidant and anti-inflammatory potential of a wild olive (acebuche, ACE) oil against hypertension-associated vascular retinopathies. The current study aims to analyze the antifibrotic effect of ACE oil on the retina of hypertensive mice.

METHODS AND RESULTS

Mice are rendered hypertensive by administration of NG-nitro-L-arginine-methyl-ester (L-NAME) and simultaneously subjected to dietary supplementation with ACE oil or a reference extra virgin olive oil (EVOO). Intraocular pressure (IOP) is measured by rebound tonometry, and retinal vasculature/layers are analyzed by fundus fluorescein angiography and optical coherence tomography. Different fibrosis-related parameters are analyzed in the retina and choroid of normotensive and hypertensive mice with or without oil supplementation. Besides preventing the alterations found in hypertensive animals, including increased IOP, reduced fluorescein signal, and altered retinal layer thickness, the ACE oil-enriched diet improves collagen metabolism by regulating the expression of major fibrotic process modulators (matrix metalloproteinases, tissue inhibitors of metalloproteinases, connective tissue growth factor, and transforming growth factor beta family).

CONCLUSION

Regular consumption of EVOO and ACE oil (with better outcomes in the latter) might help reduce abnormally high IOP values in the context of hypertension-related retinal damage, with significant reduction in the surrounding fibrotic process.

Glial cell alterations in diabetes-induced neurodegeneration

Type 2 diabetes mellitus is a global epidemic that due to its increasing prevalence worldwide will likely become the most common debilitating health condition. Even if diabetes is primarily a metabolic disorder, it is now well established that key aspects of the pathogenesis of diabetes are associated with nervous system alterations, including deleterious chronic inflammation of neural tissues, referred here as neuroinflammation, along with different detrimental glial cell responses to stress conditions and neurodegenerative features. Moreover, diabetes resembles accelerated aging, further increasing the risk of developing age-linked neurodegenerative disorders. As such, the most common and disabling diabetic comorbidities, namely diabetic retinopathy, peripheral neuropathy, and cognitive decline, are intimately associated with neurodegeneration. As described in aging and other neurological disorders, glial cell alterations such as microglial, astrocyte, and Müller cell increased reactivity and dysfunctionality, myelin loss and Schwann cell alterations have been broadly described in diabetes in both human and animal models, where they are key contributors to chronic noxious inflammation of neural tissues within the PNS and CNS. In this review, we aim to describe in-depth the common and unique aspects underlying glial cell changes observed across the three main diabetic complications, with the goal of uncovering shared glial cells alterations and common pathological mechanisms that will enable the discovery of potential targets to limit neuroinflammation and prevent neurodegeneration in all three diabetic complications. Diabetes and its complications are already a public health concern due to its rapidly increasing incidence, and thus its health and economic impact. Hence, understanding the key role that glial cells play in the pathogenesis underlying peripheral neuropathy, retinopathy, and cognitive decline in diabetes will provide us with novel therapeutic approaches to tackle diabetic-associated neurodegeneration.

The relationship between blood vitamin A levels and diabetic retinopathy: a population-based study

We assessed the relationship between blood vitamin A levels and the risk of diabetic retinopathy. The study was population-based epidemiological study for 11,727 participants aged 40 or older who participated in the Korean National Health and Nutrition Examination Survey. Vitamin A in the blood was classified into quartiles. Diabetic retinopathy was diagnosed by the Early Treatment for Diabetic Retinopathy Study. After adjusting confounding variables such as age, sex, smoking, cholesterol, diabetes prevalence period, glycated hemoglobin levels, and high blood pressure, the odd ratio (OR) of vitamin A at quartile level 4 for diabetic retinopathy was 0.32 (95% confidence interval [CI], 0.14-0.72, P for trend < 0.001). In male, the OR of quartile 3 level vitamin A for diabetic retinopathy was 0.11 (95% CI, 0.01-0.69, P for trend = 0.010). In adults under the age of 60, the OR of vitamin A at quartile level 3 for diabetic retinopathy was 0.10. (95% CI, 0.03-0.29, P for trend < 0.001). Serum vitamin A high levels are associated with low risk of diabetic retinopathy. Particularly, there is a more effective relationship in male and adults under the age of 60.

Emerging role of m6A modification in fibrotic diseases and its potential therapeutic effect

Fibrosis can occur in a variety of organs such as the heart, lung, liver and kidney, and its pathological changes are mainly manifested by an increase in fibrous connective tissue and a decrease in parenchymal cells in organ tissues, and continuous progression can lead to structural damage and organ hypofunction, or even failure, seriously threatening human health and life. N6-methyladenosine (m6A) modification, as one of the most common types of internal modifications of RNA in eukaryotes, exerts a multifunctional role in physiological and pathological processes by regulating the metabolism of RNA. With the in-depth understanding and research of fibrosis, we found that m6A modification plays an important role in fibrosis, and m6A regulators can further participate in the pathophysiological process of fibrosis by regulating the function of specific cells. In our review, we summarized the latest research advances in m6A modification in fibrosis, as well as the specific functions of different m6A regulators. In addition, we focused on the mechanisms and roles of m6A modification in cardiac fibrosis, liver fibrosis, pulmonary fibrosis, renal fibrosis, retinal fibrosis and oral submucosal fibrosis, with the aim of providing new insights and references for finding potential therapeutic targets for fibrosis. Finally, we discussed the prospects and challenges of targeted m6A modification in the treatment of fibrotic diseases.

Effects of Apelin on the fibrosis of retinal tissues and Müller cells in diabetes retinopathy through the JAK2/STAT3 signalling pathway

Retinal fibrosis was a key characteristic of diabetes retinopathy (DR). Apelin was found to be a candidate for tissue fibrosis. Nevertheless, the role of Apelin in the Müller cells in DR remains unclear. This study identified the function and mechanism of Apelin in Müller cells and the fibrosis of retinal tissue. Western blot was carried out to detect the Apelin, GFAP, Collagen I, α-SMA, JAK2 and STAT3 protein levels. Masson staining was performed to display the histopathological changes in retinal tissue of diabetic mellitus (DM) rats. The immunofluorescence staining was conducted to evaluate the Apelin levels in the retinal tissue. The levels of GFAP, Collagen I and α-SMA in the retinal tissue of DM rats was visualised by the immunohistochemistry staining. The results showed that Apelin, GFAP, Collagen I andα-SMA expression was prominently elevated in the retinal tissue of DM rats and high glucose (HG)-exposed Müller cells. The results of Masson staining showed that the epiretinal fibrotic membrane was observed in DM rats. Apelin knockdown declined the GFAP, Collagen I andα-SMA levels. Besides, the protein levels of p-JAK2 and p-STAT3 were elevated in the HG-treated Müller cells, while Apelin knockdown declined them. FLLL32 treatment neutralised the role of Apelin. In conclusion, Apelin facilitated the fibrogenic activity of Müller cells through activating the JAK2/STAT3 signalling pathway, and thus inducing the retinal fibrosis in DR.

Fullerol rescues the light-induced retinal damage by modulating Müller glia cell fate

Excessive light exposure can damage photoreceptors and lead to blindness. Oxidative stress serves a key role in photo-induced retinal damage. Free radical scavengers have been proven to protect against photo-damaged retinal degeneration. Fullerol, a potent antioxidant, has the potential to protect against ultraviolet-B (UVB)-induced cornea injury by activating the endogenous stem cells. However, its effects on cell fate determination of Müller glia (MG) between gliosis and de-differentiation remain unclear. Therefore, we established a MG lineage-tracing mouse model of light-induced retinal damage to examine the therapeutic effects of fullerol. Fullerol exhibited superior protection against light-induced retinal injury compared to glutathione (GSH) and reduced oxidative stress levels, inhibited gliosis by suppressing the TGF-β pathway, and enhanced the de-differentiation of MG cells. RNA sequencing revealed that transcription candidate pathways, including Nrf2 and Wnt10a pathways, were involved in fullerol-induced neuroprotection. Fullerol-mediated transcriptional changes were validated by qPCR, Western blotting, and immunostaining using mouse retinas and human-derived Müller cell lines MIO-M1 cells, confirming that fullerol possibly modulated the Nrf2, Wnt10a, and TGF-β pathways in MG, which suppressed gliosis and promoted the de-differentiation of MG in light-induced retinal degeneration, indicating its potential in treating retinal diseases.

Chemical Transdifferentiation of Somatic Cells: Unleashing the Power of Small Molecules

Chemical transdifferentiation is a technique that utilizes small molecules to directly convert one cell type into another without passing through an intermediate stem cell state. This technique offers several advantages over other methods of cell reprogramming, such as simplicity, standardization, versatility, no ethical and safety concern and patient-specific therapies. Chemical transdifferentiation has been successfully applied to various cell types across different tissues and organs, and its potential applications are rapidly expanding as scientists continue to explore new combinations of small molecules and refine the mechanisms driving cell fate conversion. These applications have opened up new possibilities for regenerative medicine, disease modeling, drug discovery and tissue engineering. However, there are still challenges and limitations that need to be overcome before chemical transdifferentiation can be translated into clinical practice. These include low efficiency and reproducibility, incomplete understanding of the molecular mechanisms, long-term stability and functionality of the transdifferentiated cells, cell-type specificity and scalability. In this review, we compared the commonly used methods for cell transdifferentiation in recent years and discussed the current progress and future perspective of the chemical transdifferentiation of somatic cells and its potential impact on biomedicine. We believe that with ongoing research and technological advancements, the future holds tremendous promise for harnessing the power of small molecules to shape the cellular landscape and revolutionize the field of biomedicine.

Effects of autophagy inhibitor 3-methyladenine on a diabetic mice model

AIM

To investigate the role of autophagy inhibitor 3-methyladenine (3-MA) on a diabetic mice model (DM) and the potential mechanism.

METHODS

Male C57BL/6J mice were randomly divided into a normal control group (NC group) and an DM group. DM were induced by multiple low-dose intraperitoneal injection of streptozotocin (STZ) 60 mg/kg·d for 5 consecutive days. DM mice were randomly subdivided into untreated group (DM group), 3-MA (10 mg/kg·d by gavage) treated group (DM+3-MA group) and chloroquine (CQ; 50 mg/kg by intraperitoneal injection) treated group (DM+CQ group). The fasting blood glucose (FBG) levels were recorded every week. At the end of experiment, retinal samples were collected. The expression levels of pro-apoptotic proteins cleaved caspase-3, cleaved poly ADP-ribose polymerase 1 (PARP1) and Bax, anti-apoptotic protein Bcl-2, fibrosis-associated proteins Fibronectin and type 1 collagen α1 chain (COL1A1), vascular endothelial growth factor (VEGF), inflammatory factors interleukin (IL)-1β and tumor necrosis factor (TNF)-α, as well as autophagy related proteins LC3, Beclin-1 and P62 were determined by Western blotting. The oxidative stress indicators 8-hydroxydeoxyguanosine (8-OHdG) and malondialdehyde (MDA) were detected by commercial kits.

RESULTS

Both 3-MA and CQ had short-term hypoglycemic effect on FBG and reduced the expression of VEGF and inflammatory factors IL-1β and TNF-α in DM mice. 3-MA also significantly alleviated oxidative stress indicators 8-OHdG and MDA, decreased the expression of fibrosis-related proteins Fibronectin and COL1A1, pro-apoptotic proteins cleaved caspase-3, cleaved PARP1, as well as the ratio of Bax/Bcl-2. CQ had no significant impact on the oxidative stress indicators, fibrosis, and apoptosis related proteins. The results of Western blotting for autophagy related proteins showed that the ratio of LC3 II/LC3 I and the expression of Beclin-1 in the retina of DM mice were decreased by 3-MA treatment, and the expression of P62 was further increased by CQ treatment.

CONCLUSION

3-MA has anti-apoptotic and anti-fibrotic effects on the retina of DM mice, and can attenuate retinal oxidative stress, VEGF expression and the production of inflammatory factors in the retina of DM mice. The underlying mechanism of the above effects of 3-MA may be related to its inhibition of early autophagy and hypoglycemic effect.

Activation of aryl hydrocarbon receptor by azatyrosine-phenylbutyric hydroxamide inhibits progression of diabetic retinopathy mice

Diabetic retinopathy (DR) is a severe consequence of long-term diabetes mellitus and may lead to vision loss. Retinal pigment epithelial (RPE) cells are a diverse group of retinal cells with varied metabolic and functional roles. In hypoxic conditions, RPE cells have been shown to produce angiogenic factors, such as vascular endothelial growth factor (VEGF), which is regulated by hypoxia-inducible factor 1-alpha (HIF1A). VEGF plays a crucial role in angiogenesis in DR. In the present study, we investigated whether azatyrosine-phenylbutyric hydroxamide (AZP) has therapeutic effect on DR therapy. In this study, we treated high glucose-activated human retinal pigment epithelial cells (ARPE-19) with and without AZP. The effector proteins were evaluated using western blotting. In the in vivo study, AZP was administered to the db/db mice as a DR animal model. Moreover, invasive imaging techniques such as optical coherence tomography (OCT), fundus photography, and fundus fluorescein angiography (FFA) were performed on the mice to assess DR progression. We found that treatment of AZP for 12 weeks reversed increasing DR retinal alterations in db/db mice, decreasing vascular density, retinal blood perfusion, retinal thickness, decreasing DR lesion, lipofuscin accumulation, HIF1A, VEGF, and inflammation factor expression. In addition, AZP treatment could activate the aryl hydrocarbon receptor AHR and reverse the high-glucose-induced HIF1A and VEGF in ARPE-19 cells and db/db mice. In conclusion, AZP activated AHR while inhibiting HIF1A and VEGF. This study indicates that AZP may be a promising therapeutic agent for treating DR.

Aberrant Akt2 signaling in the RPE may contribute to retinal fibrosis process in diabetic retinopathy

Diabetic Retinopathy (DR) is a complication of diabetes that causes blindness in adults. Retinal fibrosis is closely associated with developing proliferative diabetic retinopathy (PDR). Clinical studies have shown that fibrotic membranes exhibit uncontrolled growth in PDR and contribute to retinal detachment from RPE cells, ultimately leading to vision loss. While anti-VEGF agents and invasive laser treatments are the primary treatments for PDR, retinal fibrosis has received minimal attention as a potential target for therapeutic intervention. Therefore, to investigate the potential role of Akt2 in the diabetes-induced retinal fibrosis process, we generated RPE-specific Akt2 conditional knockout (cKO) mice and induced diabetes in these mice and Akt2^fl/fl control mice by intraperitoneal injection of streptozotocin. After an 8-month duration of diabetes (10 months of age), the mice were euthanized and expression of tight junction proteins, epithelial-mesenchymal transition (EMT), and fibrosis markers were examined in the RPE. Diabetes induction in the floxed control mice decreased levels of the RPE tight junction protein ZO-1 and adherens junction proteins occludin and E-cadherin; these decreases were rescued in Akt2 cKO diabetic mice. Loss of Akt2 also inhibited diabetes-induced elevation of RNA and protein levels of the EMT markers Snail/Slug and Twist1 in the RPE as compared to Akt2^fl/fl diabetic mice. We also found that in Akt2 cKO mice diabetes-induced increase of fibrosis markers, including collagen IV, Connective tissue growth factor (CTGF), fibronectin, and alpha-SMA was attenuated. Furthermore, we observed that high glucose-induced alterations in EMT and fibrosis markers in wild-type (WT) RPE explants were rescued in the presence of PI3K and ERK inhibitors, indicating diabetes-induced retinal fibrosis may be mediated via the PI3K/Akt2/ERK signaling, which could provide a novel target for DR therapy.

Elevated retinal fibrosis in experimental myopia is involved in the activation of the PI3K/AKT/ERK signaling pathway

OBJECTIVE

This study aimed to investigate the regulatory role of the PI3K/AKT/ERK signaling pathway in retinal fibrosis in -6.0 diopter (D) lens-induced myopic (LIM) guinea pigs.

METHODS

Biological measurements of eye tissues were performed on guinea pigs to obtain their refraction, axial length, retinal thickness, physiological function, and fundus retinal status. In addition, Masson staining and immunohistochemical (IHC) assay were further done to explore the changes in retinal morphology after myopic induction. Meanwhile, hydroxyproline (HYP) content was measured to evaluate the degree of retinal fibrosis. Moreover, the levels of the PI3K/AKT/ERK signaling pathway and fibrosis-related molecules in retinal tissues including matrix metalloproteinase 2(MMP2), collagen type I (Collagen I), and α-smooth muscle actin (α-SMA) were detected by real-time quantitative PCR (qPCR) and Western blot.

RESULTS

The LIM guinea pigs showed a significant myopic shift in refractive error and an increase in axial length compared with those of the normal control (NC) group. Masson staining, hydroxyproline content determination, and IHC showed an increase in retinal fibrosis. After myopic induction, qPCR and western blot analyses showed that phosphatidylinositol-3-kinase catalytic subunit α (PIK3CA), protein kinase B (AKT), extracellular regulated protein kinase 1/2 (ERK1/2), MMP2, Collagen I, and α-SMA were consistently elevated in the LIM group than those in the NC group.

CONCLUSION

The PI3K/AKT/ERK signaling pathway was activated in the retinal tissues of myopic guinea pigs, which exaggerated fibrotic lesions and reduced retinal thickness, ultimately leading to retinal physiological dysfunctions in myopic guinea pigs.

Hyperreflective Vasculature: A Negative Prognostic Sign for Retinal Vein Occlusion on Near-Infrared Reflectance Imaging

BACKGROUND AND OBJECTIVE

To investigate the clinical significance of hyperreflective vasculature visualized on near-infrared reflectance (NIR) in patients with retinal vein occlusion (RVO).

METHODS

In this retrospective study, RVO patients with NIR imaging and at least 1-year follow-up, and without confounding disease, were included. Two blinded independent graders identified vascular hyperreflectivity (HR) by detection of whiter signals in vessels. Visual acuity (VA), macular thickness (MT), and number of administered anti-vascular endothelial growth factor (anti-VEGF) injections were assessed.

RESULTS

RVO patients with HR (n = 20) and without HR (n = 31) demonstrated similarity in age, sex, and class of RVO. At presentation, the HR group had higher MT (P = 0.002) but no difference in VA (P = 0.1018). At 1 year, patients with HR had worse VA (P = 0.001), decreased MT (P = 0.011), and received more anti-VEGF injections (P < 0.001).

CONCLUSION

RVO patients with HR on NIR had significantly worse visual outcomes. Vascular HR on NIR imaging may be a biomarker, portending worse visual prognoses in RVO. [Ophthalmic Surg Lasers Imaging Retina 2023;54:266-270.].

The cGAS-STING pathway in diabetic retinopathy and age-related macular degeneration

Diabetic retinopathy and age-related macular degeneration are common retinal diseases with shared pathophysiology, including oxidative stress-induced inflammation. Cellular mechanisms responsible for converting oxidative stress into retinal damage are ill-defined but have begun to clarify. One common outcome of retinal oxidative stress is mitochondrial damage and subsequent release of mitochondrial DNA into the cytosol. This leads to activation of the cGAS-STING pathway, resulting in interferon release and disease-amplifying inflammation. This review summarizes the evolving link between aberrant cGAS-STING signaling and inflammation in common retinal diseases and provides prospective for targeting this system in diabetic retinopathy and age-related macular degeneration. Further defining the roles of this system in the retina is expected to reveal new disease pathology and novel therapeutic approaches.

Diet as a Source of Acrolein: Molecular Basis of Aldehyde Biological Activity in Diabetes and Digestive System Diseases

Acrolein, a highly reactive α,β-unsaturated aldehyde, is a compound involved in the pathogenesis of many diseases, including neurodegenerative diseases, cardiovascular and respiratory diseases, diabetes mellitus, and the development of cancers of various origins. In addition to environmental pollution (e.g., from car exhaust fumes) and tobacco smoke, a serious source of acrolein is our daily diet and improper thermal processing of animal and vegetable fats, carbohydrates, and amino acids. Dietary intake is one of the main routes of human exposure to acrolein, which is a major public health concern. This review focuses on the molecular mechanisms of acrolein activity in the context of its involvement in the pathogenesis of diseases related to the digestive system, including diabetes, alcoholic liver disease, and intestinal cancer.

Stem cells and diabetic retinopathy: From models to treatment

Diabetic retinopathy is a common yet complex microvascular disease, caused as a complication of diabetes mellitus. Associated with hyperglycemia and subsequent metabolic abnormalities, advanced stages of the disease lead to fibrosis, subsequent visual impairment and blindness. Though clinical postmortems, animal and cell models provide information about the progression and prognosis of diabetic retinopathy, its underlying pathophysiology still needs a better understanding. In addition to it, the loss of pericytes, immature retinal angiogenesis and neuronal apoptosis portray the disease treatment to be challenging. Indulged with cell loss of both vascular and neuronal type cells, novel therapies like cell replacement strategies by various types of stem cells have been sightseen as a possible treatment of the disease. This review provides insight into the pathophysiology of diabetic retinopathy, current models used in modelling the disease, as well as the varied aspects of stem cells in generating three-dimensional retinal models. Further outlook on stem cell therapy and the future directions of stem cell treatment in diabetic retinopathy have also been contemplated.

Both live and heat-killed Bifidobacterium animalis J-12 alleviated oral ulcers in LVG golden Syrian hamsters by gavage by directly intervening in the intestinal flora structure

Live and heat-killed Bifidobacterium has been proven to have anti-inflammatory and antioxidant effects. In this study, we evaluated the effects of live and heat-killed Bifidobacterium animalis J-12 (J-12) on the oral ulceration of LVG golden Syrian hamsters after buccal membrane injection with methyl viologen dichloride. Results showed that interleukin-1β, glutathione, and malondialdehyde in serum were downregulated by the gavage of live and heat-killed J-12 bacteria. The J-12 live and heat-killed bacteria can reduce the expression of matrix metalloproteinase-9 by reducing the expression of nuclear factor kappa-B, thus reducing the expression of anti-inflammatory factors lipoxin A4 and prostaglandin E2. Reducing the expression of caspase-3 and adenosine diphosphate ribose polymerase resulted in a reduction of ulcer tissue DNA damage. In addition, regulating the structure of the intestinal flora prevented the process of oral ulcer formation. This study shows that J-12 can reduce the risk of oral ulcer formation while also having a positive effect on inhibiting existing oral ulcer growth.

Sphingosine 1-phosphate, a potential target in neovascular retinal disease

Neovascular ocular diseases (such as age-related macular degeneration, diabetic retinopathy and retinal vein occlusion) are characterised by common pathological processes that contribute to disease progression. These include angiogenesis, oedema, inflammation, cell death and fibrosis. Currently available therapies target the effects of vascular endothelial growth factor (VEGF), the main mediator of pathological angiogenesis. Unfortunately, VEGF blockers are expensive biological therapeutics that necessitate frequent intravitreal administration and are associated with multiple adverse effects. Thus, alternative treatment options associated with fewer side effects are required for disease management. This review introduces sphingosine 1-phosphate (S1P) as a potential pharmacological target for the treatment of neovascular ocular pathologies. S1P is a sphingolipid mediator that controls cellular growth, differentiation, survival and death. S1P actions are mediated by five G protein-coupled receptors (S1P_1-5 receptors) which are abundantly expressed in all retinal and subretinal structures. The action of S1P on S1P₁ receptors can reduce angiogenesis, increase endothelium integrity, reduce photoreceptor apoptosis and protect the retina against neurodegeneration. Conversely, S1P₂ receptor signalling can increase neovascularisation, disrupt endothelial junctions, stimulate VEGF release, and induce retinal cell apoptosis and degeneration of neural retina. The aim of this review is to thoroughly discuss the role of S1P and its different receptor subtypes in angiogenesis, inflammation, apoptosis and fibrosis in order to determine which of these S1P-mediated processes may be targeted therapeutically.

Role of Autotaxin in High Glucose-Induced Human ARPE-19 Cells

Autotaxin (ATX) is an enzymatic with lysophospholipase D (lysoPLD) activity. We investigated the role of ATX in high glucose (HG)-induced human retinal pigment epithelial (ARPE-19) cells to explore the pathogenesis of diabetic retinopathy (DR). We performed a quantitative real-time polymerase chain reaction, Western blotting, immunocytochemistry, enzyme-linked immunosorbent assay, cell permeability assay, and transepithelial electrical resistance measurement in HG-induced ARPE-19 cells and compared their results with those of normal glucose and osmotic pressure controls. ATX expression and its lysoPLD activity, barrier function, and expression of vascular endothelial growth factor receptors VEGFR-1 and VEGFR-2 were downregulated, while fibrotic responses, cytoskeletal reorganization, and transforming growth factor-β expression were upregulated, in the HG group. Our results suggest that HG induces intracellular ATX downregulation, barrier dysfunction, and fibrosis, which are involved in early DR and can be targeted for DR treatment.

Effects of the Calix[4]arene Derivative Compound OTX008 on High Glucose-Stimulated ARPE-19 Cells: Focus on Galectin-1/TGF-β/EMT Pathway

Diabetic retinopathy (DR) is a neurovascular disease characterized by the reduction of retina integrity and functionality, as a consequence of retinal pigment epithelial cell fibrosis. Although galectin-1 (a glycan-binding protein) has been associated with dysregulated retinal angiogenesis, no evidence has been reported about galectin-1 roles in DR-induced fibrosis. ARPE-19 cells were cultured in normal (5 mM) or high glucose (35 mM) for 3 days, then exposed to the selective galectin-1 inhibitor OTX008 (2.5–5–10 μM) for 6 days. The determination of cell viability and ROS content along with the analysis of specific proteins (by immunocytochemistry, Western blotting, and ELISA) or mRNAs (by real time-PCR) were performed. OTX008 5 μM and 10 μM improved cell viability and markedly reduced galectin-1 protein expression in cells exposed to high glucose. This was paralleled by a down-regulation of the TGF-β/, NF-kB p65 levels, and ROS content. Moreover, epithelial–mesenchymal transition markers were reduced by OTX008 5 μM and 10 μM. The inhibition of galectin-1 by OTX008 in DR may preserve retinal pigment epithelial cell integrity and functionality by reducing their pro-fibrotic phenotype and epithelial–mesenchymal transition phenomenon induced by diabetes.

mTOR inhibition as a novel gene therapeutic strategy for diabetic retinopathy

In addition to laser photocoagulation, therapeutic interventions for diabetic retinopathy (DR) have heretofore consisted of anti-VEGF drugs, which, besides drawbacks inherent to the treatments themselves, are limited in scope and may not fully address the condition’s complex pathophysiology. This is because DR is a multifactorial condition, meaning a gene therapy focused on a target with broader effects, such as the mechanistic target of rapamycin (mTOR), may prove to be the solution in overcoming these concerns. Having previously demonstrated the potential of a mTOR-inhibiting shRNA packaged in a recombinant adeno-associated virus to address a variety of angiogenic retinal diseases, here we explore the effects of rAAV2-shmTOR-SD in a streptozotocin-induced diabetic mouse model. Delivered via intravitreal injection, the therapeutic efficacy of the virus vector upon early DR processes was examined. rAAV2-shmTOR-SD effectively transduced mouse retinas and therein downregulated mTOR expression, which was elevated in sham-treated and control shRNA-injected (rAAV2-shCon-SD) control groups. mTOR inhibition additionally led to marked reductions in pericyte loss, acellular capillary formation, vascular permeability, and retinal cell layer thinning, processes that contribute to DR progression. Immunohistochemistry showed that rAAV2-shmTOR-SD decreased ganglion cell loss and pathogenic Müller cell activation and proliferation, while also having anti-apoptotic activity, with these effects suggesting the therapeutic virus vector may be neuroprotective. Taken together, these results build upon our previous work to demonstrate the broad ability of rAAV2-shmTOR-SD to address aspects of DR pathophysiology further evidencing its potential as a human gene therapeutic strategy for DR.

Immune Cells in Subretinal Wound Healing and Fibrosis

The subretinal space is devoid of any immune cells under normal conditions and is an immune privileged site. When photoreceptors and/or retinal pigment epithelial cells suffer from an injury, a wound healing process will be initiated. Retinal microglia and the complement system, as the first line of retinal defense, are activated to participate in the wound healing process. If the injury is severe or persists for a prolonged period, they may fail to heal the damage and circulating immune cells will be summoned leading to chronic inflammation and abnormal wound healing, i.e., subretinal or intraretinal fibrosis, a sight-threatening condition frequently observed in rhematogenous retinal detachment, age-related macular degeneration and recurrent uveoretinitis. Here, we discussed the principles of subretinal wound healing with a strong focus on the conditions whereby the damage is beyond the healing capacity of the retinal defense system and highlighted the roles of circulating immune cells in subretinal wound healing and fibrosis.

Assessment of circulating fibrotic proteins (periostin and tenascin -C) In Type 2 diabetes mellitus patients with and without retinopathy

PURPOSE

Diabetic retinopathy is a leading cause of vision impairment. Surging diabetic population and poor visual care raises the need for better diagnostic tools. Hence, it is worthwhile to look for biomarkers associated with the disease pathogenesis. Periostin and tenascin-C are matricellular proteins mediating fibrillogenesis in retinopathy. Their serum levels and association with the presence and severity of retinopathy in diabetics is of importance to be explored.

METHODS

The study involved two groups of type 2 diabetes patients, 38 controls without retinopathy and 38 cases with retinopathy. We obtained serum sample and performed biochemical autoanalysis for routine parameters. Special parameters periostin, tenascin-C, and C-peptide were estimated by ELISA.

RESULTS

Periostin and tenascin-C were significantly elevated in the retinopathy group. Periostin progressively increased among subgroups. C-peptide decreased significantly in retinopathy group and had a negative correlation with duration of DM, duration of retinopathy, HbA1c and tenascin-C. We observed a positive correlation for periostin and tenascin-C with duration of diabetes. The AUC for C-peptide was the highest (0.750) amongst our parameters. HOMA 2 (%B) index was significantly lower in retinopathy group.

CONCLUSIONS

Serum Levels of PO and TnC increased in retinopathy. As the disease advances, periostin level increases, indicating continuing fibrosis and fibrovascular membrane formation. Periostin and tenascin-C increase with duration of retinopathy whereas levels of C-peptide decrease. C-peptide has a better differentiating potential for DR from DM. Reduced insulin production as indicated by declined HOMA 2-%BETA in retinopathy favors hyperglycemia and chronic inflammatory state for the disease progression.

Harnessing the Neuroprotective Behaviors of Müller Glia for Retinal Repair

Progressive and irreversible vision loss in mature and aging adults creates a health and economic burden, worldwide. Despite the advancements of many contemporary therapies to restore vision, few approaches have considered the innate benefits of gliosis, the endogenous processes of retinal repair that precede vision loss. Retinal gliosis is fundamentally driven by Müller glia (MG) and is characterized by three primary cellular mechanisms: hypertrophy, proliferation, and migration. In early stages of gliosis, these processes have neuroprotective potential to halt the progression of disease and encourage synaptic activity among neurons. Later stages, however, can lead to glial scarring, which is a hallmark of disease progression and blindness. As a result, the neuroprotective abilities of MG have remained incompletely explored and poorly integrated into current treatment regimens. Bioengineering studies of the intrinsic behaviors of MG hold promise to exploit glial reparative ability, while repressing neuro-disruptive MG responses. In particular, recent in vitro systems have become primary models to analyze individual gliotic processes and provide a stepping stone for in vivo strategies. This review highlights recent studies of MG gliosis seeking to harness MG neuroprotective ability for regeneration using contemporary biotechnologies. We emphasize the importance of studying gliosis as a reparative mechanism, rather than disregarding it as an unfortunate clinical prognosis in diseased retina.

Dopamine Receptor Signaling Regulates Fibrotic Activation of Retinal Pigmented Epithelial Cells

Retinal pigmented epithelial (RPE) cells play an important role in retinal fibrotic diseases such as proliferative vitreoretinopathy (PVR). The purpose of this study was to elucidate the involvement of dopamine receptor signaling in regulating the fibrotic activation of RPE cells. Dopamine receptor expression, the effect of dopamine on fibrotic activity, and dopamine production were measured in the human RPE cell line ARPE-19. The fibrotic activation of RPE cells was evaluated in response to treatments with selective dopamine receptor agonists and antagonists by measuring gene expression, migration, proliferation, and fibronectin deposition. DRD2 and DRD5 are the dominant dopaminergic receptors expressed in ARPE-19 cells and TGFβ stimulates enhances autocrine release of dopamine which we show further exasperates fibrotic activation. Finally, treatment with D2 dopamine receptor antagonists or D5 dopamine receptor agonists inhibits profibrotic gene expression, migration, proliferation, and fibronectin deposition and thus may serve as effective mechanisms for treating retinal fibrosis including PVR.

Regulations of Retinal Inflammation: Focusing on Müller Glia

Retinal inflammation underlies multiple prevalent retinal diseases. While microglia are one of the most studied cell types regarding retinal inflammation, growing evidence shows that Müller glia play critical roles in the regulation of retinal inflammation. Müller glia express various receptors for cytokines and release cytokines to regulate inflammation. Müller glia are part of the blood-retinal barrier and interact with microglia in the inflammatory responses. The unique metabolic features of Müller glia in the retina makes them vital for retinal homeostasis maintenance, regulating retinal inflammation by lipid metabolism, purine metabolism, iron metabolism, trophic factors, and antioxidants. miRNAs in Müller glia regulate inflammatory responses via different mechanisms and potentially regulate retinal regeneration. Novel therapies are explored targeting Müller glia for inflammatory retinal diseases treatment. Here we review new findings regarding the roles of Müller glia in retinal inflammation and discuss the related novel therapies for retinal diseases.

Resolution of Inflammation in Retinal Disorders: Briefly the State

The most frequent retinal diseases, such as diabetic retinopathy, age-related macular degeneration and posterior uveitis, are underlined by oxidative stress or aging-induced retinal inflammation, which contributes to vision impairing or loss. Resolution of inflammation is emerging as a critical phase able to counteract the inflammatory process leading to the progression of retinal damage. Particularly, pro-resolving mediators (PMs) play a key role in the modulation of inflammatory exudates and could be considered a new target to be investigated in different inflammatory-autoimmune pathologies. Here, we highlight the most recent studies concerning the role of the main PMs (lipoxins, resolvins, prtectins, maresins and annexins) in retinal inflammation, in order to collect the best evidence in the field of inflammatory retinal damage resolution and to propose novel pharmacological approaches in the management of the most common retinal diseases.

MicroRNAs and their delivery in diabetic fibrosis

The global prevalence of diabetes mellitus was estimated to be 463 million people in 2019 and is predicted to rise to 700 million by 2045. The associated financial and societal costs of this burgeoning epidemic demand an understanding of the pathology of this disease, and its complications, that will inform treatment to enable improved patient outcomes. Nearly two decades after the sequencing of the human genome, the significance of noncoding RNA expression is still being assessed. The family of functional noncoding RNAs known as microRNAs regulates the expression of most genes encoded by the human genome. Altered microRNA expression profiles have been observed both in diabetes and in diabetic complications. These transcripts therefore have significant potential and novelty as targets for therapy, therapeutic agents and biomarkers.

Decorin Concentrations in Aqueous Humor of Patients with Diabetic Retinopathy

Diabetic retinopathy (DR) is a microvascular complication of diabetes in the retina. Chronic hyperglycemia damages retinal microvasculature embedded into the extracellular matrix (ECM), causing fluid leakage and ischemic retinal neovascularization. Current treatment strategies include intravitreal anti-vascular endothelial growth factor (VEGF) or steroidal injections, laser photocoagulation, or vitrectomy in severe cases. However, treatment may require multiple modalities or repeat treatments due to variable response. Though DR management has achieved great success, improved, long-lasting, and predictable treatments are needed, including new biomarkers and therapeutic approaches. Small-leucine rich proteoglycans, such as decorin, constitute an integral component of retinal endothelial ECM. Therefore, any damage to microvasculature can trigger its antifibrotic and antiangiogenic response against retinal vascular pathologies, including DR. We conducted a cross-sectional study to examine the association between aqueous humor (AH) decorin levels, if any, and severity of DR. A total of 82 subjects (26 control, 56 DR) were recruited. AH was collected and decorin concentrations were measured using an enzyme-linked immunosorbent assay (ELISA). Decorin was significantly increased in the AH of DR subjects compared to controls (p = 0.0034). AH decorin levels were increased in severe DR groups in ETDRS and Gloucestershire classifications. Decorin concentrations also displayed a significant association with visual acuity (LogMAR) measurements. In conclusion, aqueous humor decorin concentrations were found elevated in DR subjects, possibly due to a compensatory response to the retinal microvascular changes during hyperglycemia.

Ocular expression of cyclin-dependent kinase 5 in patients with proliferative diabetic retinopathy

Aims/Introduction

Inhibition of peroxisome proliferator‐activated receptor gamma (PPARγ) phosphorylation mediated by cyclin‐dependent kinase 5 (Cdk5) is one of the main mechanisms of action of antidiabetic drugs. In this study, we analyzed the ocular expression and activation of Cdk5 in patients with proliferative diabetic retinopathy (PDR).

Materials and Methods

The concentrations of PPARγ, Cdk5 and its activating subunit (p35) were determined in the vitreous body of 24 PDR and 63 control eyes by enzyme‐linked immunosorbent assay. In addition, the messenger ribonucleic acid and protein expression levels of PPARγ, Cdk5 and p35 were measured in proliferative neovascular membranes from seven PDR eyes and non‐neovascular epiretinal membranes from five control eyes by quantitative real‐time polymerase chain reaction and immunohistochemical analysis.

Results

PPARγ, Cdk5 and p35 concentrations in the vitreous body were significantly higher in the PDR group compared with the control group. There was also a positive significant correlation of Cdk5 with PPARγ and p35 in the PDR group. Furthermore, the messenger ribonucleic acid expression levels of PPARγ, Cdk5 and p35 in proliferative neovascular membranes were significantly higher in the PDR group compared with the control group. Immunostaining showed increased protein expression levels of PPARγ, Cdk5 and p35 in proliferative neovascular membranes in the PDR group compared with the control group.

Conclusions

Cdk5 activation is involved in PDR pathogenesis through PPARγ expression, and inhibition of Cdk5‐mediated PPARγ phosphorylation might be a new therapeutic target for treatment of PDR.

Updates on the Current Treatments for Diabetic Retinopathy and Possibility of Future Oral Therapy

Diabetic retinopathy (DR) is a complication of diabetes and one of the leading causes of vision loss worldwide. Despite extensive efforts to reduce visual impairment, the prevalence of DR is still increasing. The initial pathophysiology of DR includes damage to vascular endothelial cells and loss of pericytes. Ensuing hypoxic responses trigger the expression of vascular endothelial growth factor (VEGF) and other pro-angiogenic factors. At present, the most effective treatment for DR and diabetic macular edema (DME) is the control of blood glucose levels. More advanced cases require laser, anti-VEGF therapy, steroid, and vitrectomy. Pan-retinal photocoagulation for non-proliferative diabetic retinopathy (NPDR) is well established and has demonstrated promising outcomes for preventing the progressive stage of DR. Furthermore, the efficacy of laser therapies such as grid and subthreshold diode laser micropulse photocoagulation (SDM) for DME has been reported. Vitrectomy has been performed for vitreous hemorrhage and tractional retinal detachment for patients with PDR. In addition, anti-VEGF treatment has been widely used for DME, and recently its potential to prevent the progression of PDR has been remarked. Even with these treatments, many patients with DR lose their vision and suffer from potential side effects. Thus, we need alternative treatments to address these limitations. In recent years, the relationship between DR, lipid metabolism, and inflammation has been featured. Research in diabetic animal models points to peroxisome proliferator-activated receptor alpha (PPARα) activation in cellular metabolism and inflammation by oral fenofibrate and/or pemafibrate as a promising target for DR. In this paper, we review the status of existing therapies, summarize PPARα activation therapies for DR, and discuss their potentials as promising DR treatments.

Yes-associated protein is essential for proliferative vitreoretinopathy development via the epithelial-mesenchymal transition in retinal pigment epithelial fibrosis

This study was aim to investigate whether the progression of proliferative vitreoretinopathy (PVR) depended on the activation of Yes‐associated protein (YAP) and the subsequent epithelial‐mesenchymal transition (EMT) of retinal pigment epithelial (RPE) cell. The effect of YAP activation on retinal fibrosis in a PVR mouse model and in human ARPE‐19 cells in vitro was studied. After treated with transforming growth factor‐β2(TGF‐β2), the expressions of fibrogenic molecules, YAP activation and the TGF‐β2‐Smad signalling pathway in ARPE‐19 cells were detected by Western blot and immunocytochemical analyses. The effect of YAP on change in fibrosis and EMT was tested by knockdown experiment using verteporfin (YAP inhibitor). YAP was upregulated in the PVR mouse model and during TGF‐β2–induced RPE cell EMT. In an in vivo study, verteporfin attenuated PVR progression in a mouse model. Additionally, YAP knockdown retained phenotype of RPE cells and ameliorated TGF‐β2–induced migration, gel contraction and EMT in vitro. YAP knockdown inhibited the TGF‐β2–induced upregulation of connective tissue growth factor (CTGF), smooth muscle actin (SMA‐α) and fibronectin. YAP was essential for the TGF‐β2–induced nuclear translocation and phosphorylation of Smad2/3. Our work provides direct evidence that YAP is an essential regulator of EMT and profibrotic responses in PVR and indicates that YAP inhibition could be a potential target in PVR therapeutic intervention.

CircRNAs: Decrypting the novel targets of fibrosis and aging

Fibrosis is a typical aging-related pathological process involving almost all organs. It is usually initiated by organic injury and leads to the gradual decline of organ function or even loss. Circular RNAs (circRNAs) are being hailed as a newly rediscovered class of covalently closed transcripts without a 5' cap or 3' tail which draw increasing attention. In particular, circRNAs have been identified to be involved in the multifaceted processes of fibrosis in various organs, including the heart, liver, lung, and kidney. As more and more circRNAs are functionally characterized, they have become novel therapies for fibrosis. In this review, we systematically summarized current studies regarding the roles of circRNAs in fibrosis and shed light on the basis of circRNAs as a potential treatment for fibrosis.

Targeting RGD-binding integrins as an integrative therapy for diabetic retinopathy and neovascular age-related macular degeneration

Integrins are a class of transmembrane receptors that are involved in a wide range of biological functions. Dysregulation of integrins has been implicated in many pathological processes and consequently, they are attractive therapeutic targets. In the ophthalmology arena, there is extensive evidence suggesting that integrins play an important role in diabetic retinopathy (DR), age-related macular degeneration (AMD), glaucoma, dry eye disease and retinal vein occlusion. For example, there is extensive evidence that arginyl-glycyl-aspartic acid (Arg-Gly-Asp; RGD)-binding integrins are involved in key disease hallmarks of DR and neovascular AMD (nvAMD), specifically inflammation, vascular leakage, angiogenesis and fibrosis. Based on such evidence, drugs that engage integrin-linked pathways have received attention for their potential to block all these vision-threatening pathways. This review focuses on the pathophysiological role that RGD-binding integrins can have in complex multifactorial retinal disorders like DR, diabetic macular edema (DME) and nvAMD, which are leading causes of blindness in developed countries. Special emphasis will be given on how RGD-binding integrins can modulate the intricate molecular pathways and regulate the underlying pathological mechanisms. For instance, the interplay between integrins and key molecular players such as growth factors, cytokines and enzymes will be summarized. In addition, recent clinical advances linked to targeting RGD-binding integrins in the context of DME and nvAMD will be discussed alongside future potential for limiting progression of these diseases.

VEGF-Independent Activation of Müller Cells by the Vitreous from Proliferative Diabetic Retinopathy Patients

Proliferative diabetic retinopathy (PDR), a major complication of diabetes mellitus, results from an inflammation-sustained interplay among endothelial cells, neurons, and glia. Even though anti-vascular endothelial growth factor (VEGF) interventions represent the therapeutic option for PDR, they are only partially efficacious. In PDR, Müller cells undergo reactive gliosis, produce inflammatory cytokines/chemokines, and contribute to scar formation and retinal neovascularization. However, the impact of anti-VEGF interventions on Müller cell activation has not been fully elucidated. Here, we show that treatment of MIO-M1 Müller cells with vitreous obtained from PDR patients stimulates cell proliferation and motility, and activates various intracellular signaling pathways. This leads to cytokine/chemokine upregulation, a response that was not mimicked by treatment with recombinant VEGF nor inhibited by the anti-VEGF drug ranibizumab. In contrast, fibroblast growth factor-2 (FGF2) induced a significant overexpression of various cytokines/chemokines in MIO-M1 cells. In addition, the FGF receptor tyrosine kinase inhibitor BGJ398, the pan-FGF trap NSC12, the heparin-binding protein antagonist N-tert-butyloxycarbonyl-Phe-Leu-Phe-Leu-Phe Boc2, and the anti-inflammatory hydrocortisone all inhibited Müller cell activation mediated by PDR vitreous. These findings point to a role for various modulators beside VEGF in Müller cell activation and pave the way to the search for novel therapeutic strategies in PDR.

Proteomic Analysis of Plasma sEVs Reveals That TNFAIP8 Is a New Biomarker of Cell Proliferation in Diabetic Retinopathy

Small extracellular vesicles (sEVs) derived from the plasma have been increasingly recognized as important vehicles of intercellular communication and potential sources of new biomarkers for multiple diseases. In this study, proteomic profiles of plasma sEVs from normal subjects and diabetic patients with or without diabetic retinopathy (DR) were systematically compared using iTRAQ-based quantitative proteomics. Among a total of 901 identified proteins in plasma sEVs (false discovery rate (FDR) < 1%), 90 proteins were found to have significantly changed levels in DR. Based on the findings from the proteomic analysis, the role of tumor necrosis factor-α-induced protein 8 (TNFAIP8) in promoting human retinal microvascular endothelial cell (HRMEC) proliferation was investigated. The enzyme-linked immunosorbent assay (ELISA) showed that TNFAIP8 levels in plasma sEVs and vitreous are elevated in DR, whereas not statistically different in large EVs (lEVs) and plasma. In addition, in vitro experiments demonstrated that 4-hydroxynonenal (4-HNE) increased the expression of TNFAIP8 in HRMECs. TNFAIP8 significantly increased HRMECs cell viability and promote cell migration and tube formation, and the depletion of TNFAIP8 impaired HRMEC proliferation. We demonstrated that TNFAIP8 in plasma sEVs could be used as a potential biomarker of DR. Functional studies suggested that TNFAIP8 might be an important mediator of angiogenesis in DR.

Intravitreal autologous mesenchymal stem cell transplantation: a non-randomized phase I clinical trial in patients with retinitis pigmentosa

Background

Retinitis pigmentosa (RP) is a progressive inherited retinal disease with great interest for finding effective treatment modalities. Stem cell-based therapy is one of the promising candidates. We aimed to investigate the safety, feasibility, and short-term efficacy of intravitreal injection of bone marrow-derived mesenchymal stem cells (BM-MSCs) in participants with advanced stage RP.

Methods

This non-randomized phase I clinical trial enrolled 14 participants, categorized into three groups based on a single dose intravitreal BM-MSC injection of 1 × 10⁶, 5 × 10⁶, or 1 × 10⁷ cells. We evaluated signs of inflammation and other adverse events (AEs). We also assessed the best corrected visual acuity (BCVA), visual field (VF), central subfield thickness (CST), and subjective experiences.

Results

During the 12-month period, we noticed several mild and transient AEs. Interestingly, we found statistically significant improvements in the BCVA compared to baseline, although they returned to the baseline at 12 months. The VF and CST were stable, indicating no remarkable disease progression. We followed 12 participants beyond the study period, ranging from 1.5 to 7 years, and observed one severe but manageable AE at year 3.

Conclusion

Intravitreal injection of BM-MSCs appears to be safe and potentially effective. All adverse events during the 12-month period required observation without any intervention. For the long-term follow-up, only one participant needed surgical treatment for a serious adverse event and the vision was restored. An enrollment of larger number of participants with less advanced RP and long-term follow-up is required to evaluate the safety and efficacy of this intervention.

Trial registration

ClinicalTrials.gov, NCT01531348. Registered on February 10, 2012

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-020-02122-7.

Proteomic analysis of anti-angiogenic effects by conbercept in the mice with oxygen induced retinopathy

AIM

To analyze the retinal proteomes with and without conbercept treatments in mice with oxygen-induced retinopathy (OIR) and identify proteins involved in the molecular mechanisms mediated by conbercept.

METHODS

OIR was induced in fifty-six C57BL/6J mouse pups and randomly divided into four groups. Group 1: Normal17 (n=7), mice without OIR and treated with normal air. Group 2: OIR12/EXP1 (n=14), mice received 75% oxygen from postnatal day (P) 7 to 12. Group 3: OIR17/Control (n=14), mice received 75% oxygen from P7 to P12 and then normal air to P17. Group 4: Lang17/EXP2 (n=21), mice received 75% oxygen from P7 to P12 with intravitreal injection of 1 µL conbercept at the concentration of 10 mg/mL at P12, and then normal air from P12 to P17. Liquid Chromatography-Mass Spectrometry (LC-MS)/MS data were reviewed to find proteins that were up-regulated after the conbercept treatment. Gene ontology (GO) analysis was performed of conbercept-mediated changes in proteins involved in single-organism processes, biological regulation, cellular processes, immune responses, metabolic processes, locomotion and multiple-organism processes.

RESULTS

Conbercept induced a reversal of hypoxia-inducible factor 1 signaling pathway as revealed by the Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis and also induced down-regulation of proteins involved in blood coagulation and fibrin clot formation as demonstrated by the Database for Annotation, Visualization and Integrated Discovery (DAVID) and the stimulation of interferon genes studies. These appear to be risk factors of retinal fibrosis. Additional conbercept-specific fibrosis risk factors were also identified and may serve as therapeutic targets for fibrosis.

CONCLUSION

Our studies reveal that many novel proteins are differentially regulated by conbercept. The new insights may warrant a valuable resource for conbercept treatment.

Molecular mechanisms and the vital roles of resistin, TLR 4, and NF-κB in treating type 2 diabetic complications

Background

Type 2 diabetes in obese (≥ 25 and ≥ 30 kg/m2) patients is the foremost cause of cardiovascular complications like stroke, osteoarthritis, cancers (endometrial, breast, ovarian, liver, kidney, colon, and prostate), and vascular complications like diabetic neuropathy, diabetic and retinopathy, and diabetic nephropathy. It is recognized as a global burden disorder with high prevalence in middle-income nations which might lead to a double burden on health care professionals. Hence, this review emphasizes on understanding the complexity and vital signaling tracts involved in diabetic complications for effective treatment.

Main body

Type 2 diabetes in overweight patients induces the creation of specific ROS that further leads to changes in cellular proliferation, hypothalamus, and fringe. The resistin, TLR4, and NF-κB signalings are mainly involved in the progression of central and fringe changes such as insulin resistance and inflammation in diabetic patients. The overexpression of these signals might lead to the rapid progression of diabetic vascular complications induced by the release of proinflammatory cytokines, chemokines, interleukins, and cyclooxygenase-mediated chemicals. Until now, there has been no curative treatment for diabetes. Therefore, to effectively treat complications of type 2 diabetes, the researchers need to concentrate on the molecular mechanisms and important signaling tracts involved.

Conclusion

In this review, we suggested the molecular mechanism of STZ-HFD induced type 2 diabetes and the vital roles of resistin, TLR4, and NF-κB signalings in central, fringe changes, and development diabetic complications for its effective treatment.

Graphical abstract

Near-infrared reflectance imaging of neovascularization in proliferative diabetic retinopathy

Background

Blood is one of the main absorbers in the near-infrared spectrum and thus retinal vessels appear dark in near-infrared reflectance (NIR) images. Proliferative diabetic retinopathy (PDR) is characterized by abnormal neovascularization which also absorbs light and appears dark against a lighter fundus background. We analyzed neovascularization in PDR using NIR imaging, by observing changes in the neovascular complexes (NVCs) contrast and reflectivity over time.

Methods

Retrospective case series of 20 eyes of 17 patients with PDR who underwent NIR imaging with optical coherence tomography (OCT) using the Spectralis System. NVCs presence and activity was determined using clinical, tomographic and angiographic criteria. At baseline, all NVCs were qualitatively graded in the NIR image into 3 groups (absent, present and inactive and present and active) and their evolution over time was registered as progression, regression or same status.

Results

Twenty-seven NVCs were imaged, of which, 52% were neovascularization of the disc (NVD) and 48% were elsewhere (NVE). Consecutive NIR images were obtained from baseline to up to 5 time-points with a mean follow-up of 3.2 ± 1.7 years. All eyes underwent laser treatment and 30% had additional intravitreal therapy. Using NIR imaging, NVCs were classified at baseline as absent, present and inactive and present and active, respectively in 11, 4 and 85% of cases. NIR identified active neovascularization as hyporeflective irregular dark vessels originating from the retinal venules in NVE or from the disc in NVD. In all groups during follow-up, progression was identified as the development of new vascular hyporeflective dark fronds while regression was shown by reduced dark perfusion. Five eyes developed a wolf’s jaw configuration with vascular hyporeflective new vessels and hyperreflective tissue from extensive fibrosis. Fibrosis was more apparent in later images, reaching 86%. In 3 cases (11%), the NVC was no longer seen in NIR, although was still identifiable on OCT over the NVC area.

Conclusions

NIR is a non-invasive imaging modality commonly performed alongside OCT and frequently overlooked which can be useful to evaluate NVCs in PDR. Changes in NVC contrast and reflectivity due to blood perfusion can help in the detection and monitoring of diabetic proliferative disease and aid clinicians in daily practice.

Alterations of 5-hydroxymethylcytosines in circulating cell-free DNA reflect retinopathy in type 2 diabetes

Diabetic retinopathy (DR) is a common microvascular complication that may cause severe visual impairment and blindness in patients with type 2 diabetes mellitus (T2DM). Early detection of DR will expand the range of potential treatment options and enable better control of disease progression. Epigenetic dysregulation has been implicated in the pathogenesis of microvascular complications in patients with T2DM. We sought to explore the diagnostic value of 5-hydroxymethylcytosines (5hmC) in circulating cell-free DNA (cfDNA) for DR, taking advantage of a highly sensitive technique, the 5hmC-Seal. The genome-wide 5hmC profiles in cfDNA samples from 35 patients diagnosed with DR and 35 age-, gender-, diabetic duration-matched T2DM controls were obtained using the 5hmC-Seal, followed by a case-control analysis and external validation. The genomic distribution of 5hmC in cfDNA from patients with DR reflected potential gene regulatory relevance, showing co-localization with histone modification marks for active expression (e.g., H3K4me1). A three-gene signature (MESP1, LY6G6D, LINC01556) associated with DR was detected using the elastic net regularization on the multivariable logistic regression model, showing high accuracy to distinguish patients with DR from T2DM controls (AUC [area under curve] = 91.4%; 95% CI [confidence interval], 84.3- 98.5%), achieving a sensitivity of 88.6% and a specificity of 91.4%. In an external testing set, the 5hmC model detected 5 out of 6 DR patients and predicted 7 out of 8 non-DR patients with other microvascular complications. Circulating cfDNA from patients with DR contained 5hmC information that could be exploited for DR detection. As a novel non-invasive approach, the 5hmC-Seal holds the promise to be an integrated part of patient care and surveillance tool for T2DM patients.

Optical Coherence Tomography Angiography Features of Neovascularization in Proliferative Diabetic Retinopathy

Purpose

To describe features of neovascularization in proliferative diabetic retinopathy (PDR) using optical coherence tomography angiography (OCTA).

Methods

A retrospective case series was performed in 23 eyes from 21 patients who underwent OCTA of neovascular complexes (NVCs) due to PDR. Eyes were imaged with the DRI Triton swept-source OCTA, Avanti RTVue XR or Cirrus HD-OCT 5000 as part of routine clinical examination. Segmentation was adjusted to include vasculature between the vitreous cavity and the internal limiting membrane (ILM). The presence of NVCs was confirmed by clinical examination and multimodal imaging such as color or red-free fundus photography, fluorescein angiography, multicolor imaging or near-infrared reflectance.

Results

Thirty-five NVCs were imaged, of which, 34% were neovascularization of the disc (NVD) and 66% were neovascularization elsewhere (NVE). On structural OCT B-scans, NVE appeared as medium to highly reflective tissue that breached the ILM, while NVD showed highly reflective tissue protruding from the disc in a sea fan configuration. Flow signal was seen on OCTA in all cases of NVE and in 67% of NVD lesions. Areas with minimal or absent retinal flow signal identified retinal nonperfusion areas and were found adjacent to 87% of NVE. Intraretinal microvascular abnormalities (IRMAs) were noted next to 70% of NVE. Absent flow signal was seen in 4 NVD cases showing posterior shadowing and were considered inactive.

Conclusion

OCTA appears useful for imaging NVCs, IRMAs, and retinal nonperfusion areas in eyes with diabetic retinopathy. This imaging modality enables noninvasive screening and monitoring of PDR and can obviate the need for additional testing in certain clinical settings.

The cells involved in the pathological process of diabetic retinopathy

Diabetic retinopathy(DR) is an expanding global health problem, the exact mechanism of which has not yet been clarified clearly, new insights into retinal physiology indicate that diabetes-induced retinal dysfunction may be viewed as an impairment of the retinal neurovascular unit, including retinal ganglion cells, glial cells, endothelial cells, pericytes, and retinal pigment epithelium. Different retinal cells have unique structure and functions, while the interactions among which are less known. Cells are the basic unit of organism structure and function, their impairment could lead to abnormal physiological functions and even organ disorder. Considering the body is multi-dimension and the complexity of DR, one point or a single type of cell can't be used to illustrate the mechanism of occurrence and development of DR. In this review, we provided a systematic and comprehensive elaboration of the cells that are involved in the process of DR. We underlined the importance of considering the neurovascular unit, not just retinal vascular and neural cells, in understanding the pathophysiology of DR. Our studies provided a better understanding of the pathological process in DR and provide a theoretical basis for further research.

YAP is essential for TGF-β-induced retinal fibrosis in diabetic rats via promoting the fibrogenic activity of Müller cells

The purpose of this study was to investigate whether Yes-associated protein (YAP) activation and proliferation of retinal Müller cells play a role in the development of TGF-β-induced retinal fibrosis. We studied the effects of YAP activation on retinal fibrosis in diabetic rats and human retinal Müller cells (hMCs) in vitro. The retinal expression of YAP and fibrogenic molecules in rats was detected using Western blotting and immunohistochemistry. After treatment with transforming growth factor-β1 (TGF-β1), the levels of fibrogenic molecules, and the activation of YAP and PI3K/Akt signalling pathway in hMCs were detected with Western blotting. The effect of YAP on retinal fibrotic changes was evaluated using YAP knockdown experiments and YAP inhibitors. Results showed that YAP expression was increased in the retina of diabetic rats along with increased retinal fibrosis. In cultured hMCs, YAP inhibition suppressed TGF-β1-stimulated hMC differentiation to myofibroblasts and extracellular matrix (ECM) production, while YAP activation promoted hMC differentiation and ECM production independent of TGF-β1. Furthermore, hMCs cultured on a gel with greater stiffness differentiated into myofibroblasts in a YAP-dependent manner. In diabetic rats, treatment with the YAP inhibitor verteporfin suppressed retinal fibrogenesis. In addition, the TGF-β1-induced PI3K/Akt signalling pathway mediated YAP activation as well as expression of fibrogenic molecules. The interaction between ECM stiffness and YAP forms a feed-forward process leading to retinal fibrosis. Our work highlights YAP as an essential regulator of pro-fibrotic responses in TGF-β-induced retinal fibrosis.

PPARα-Dependent Effects of Palmitoylethanolamide Against Retinal Neovascularization and Fibrosis

Purpose

Pathological neovascularization and fibrosis are common pathological changes of many retinal diseases, such as proliferative retinopathy (PR) and age-related macular degeneration (AMD). Treatment modalities for these pathological changes are limited. The purpose of the present study was to test the effects of palmitoylethanolamide (PEA), an endocannabinoid mimetic amide, on retinal neovascularization and fibrosis and to determine its molecular mechanism of action.

Methods

A rat Müller cell line (rMC-1), a mouse model of oxygen-induced retinopathy (OIR), and the very-low-density lipoprotein receptor (VLDLR) knockout mouse model were used. PEA was intraperitoneally injected or orally administrated in animal models. Inflammation and profibrotic changes were evaluated by western blot analysis. Glial fibrillary acidic protein (GFAP) and peroxisome proliferator-activated receptor alpha (PPARα) were measured by RT-PCR and western blot analysis.

Results

Profibrotic changes were present in OIR and Vldlr-/- retinas. PEA significantly alleviated inflammation and inhibited neovascularization in OIR and Vldlr-/- retinas and suppressed profibrotic changes in OIR and Vldlr-/- retinas. Moreover, PEA potently suppressed Müller gliosis in these retinas. In rMC-1 cells, PEA suppressed Müller gliosis, reduced inflammatory cytokines, and attenuated profibrotic changes. Further, both mRNA and protein levels of PPARα were elevated in the retina under PEA treatment, and the effects of PEA were abolished in Pparα-/- OIR mice.

Conclusions

PEA reduced retinal neovascularization and fibrotic changes and suppressed Müller gliosis in experimental PR and neovascular AMD by activating PPARα. PEA may be a potential treatment for retinopathies with pathological neovascularization and fibrosis.

Retinal Physiology and Circulation: Effect of Diabetes

In this article, we present a discussion of diabetes and its complications, including the macrovascular and microvascular effects, with the latter of consequence to the retina. We will discuss the anatomy and physiology of the retina, including aspects of metabolism and mechanisms of oxygenation, with the latter accomplished via a combination of the retinal and choroidal blood circulations. Both of these vasculatures are altered in diabetes, with the retinal circulation intimately involved in the pathology of diabetic retinopathy. The later stages of diabetic retinopathy involve poorly controlled angiogenesis that is of great concern, but in our discussion, we will focus more on several alterations in the retinal circulation occurring earlier in the progression of disease, including reductions in blood flow and a possible redistribution of perfusion that may leave some areas of the retina ischemic and hypoxic. Finally, we include in this article a more recent area of investigation regarding the diabetic retinal vasculature, that is, the alterations to the endothelial surface layer that normally plays a vital role in maintaining physiological functions. © 2020 American Physiological Society. Compr Physiol 10:933-974, 2020.