The Impact of Hyperglycemia on VEGF Secretion in Retinal Endothelial Cells

Aberrant expression of TRIM44, transcriptionally regulated by KLF9, contributes to the process of diabetic retinopathy

BACKGROUND

Diabetic retinopathy (DR) is the common cause of diabetic vascular complications and it causes blindness. Until now, there are still some patients with DR who lack effective treatment. Tripartite motif containing 44 (TRIM44) has been shown to play a significant role in endothelial cells. However, the role of TRIM44 in DR remains unknown.

METHODS

Diabetes was induced in rats through the administration of an intraperitoneal injection of 65 mg/kg of streptozotocin (STZ). Rat retinal microvascular endothelial cells (RMECs) were subjected to stimulation under high glucose (HG) conditions. A thorough proteomic investigation and bioinformatic analysis were performed to identify the differentially expressed proteins (DEPs) in rat RMECs after blocking TRIM44. A dual luciferase reporter assay was employed to assess the luciferase activity of TRIM44.

RESULTS

TRIM44 was highly expressed in the retinal tissues of rats with diabetes and HG-induced RMECs. In vivo assays suggested that TRIM44 silencing improved the pathological alterations of DR rats as demonstrated by the downregulated expression of isolectin-B4 and VEGFA, along with a decrease in acellular capillaries within the retinal tissues. Knockdown of TRIM44 markedly reduced cell viability, proliferation, migration, invasion, and angiogenesis in HG-evoked RMECs. Mechanistically, TRIM44 was demonstrated to be activated transcriptionally by KLF transcription factor 9 (KLF9), a known facilitator of angiogenesis in DR. In HG-induced cells, the loss of TRIM44 resulted in the reverse of the endothelial cell function caused by KLF9 overexpression. After the comprehensive analysis, 64 upregulated and 38 downregulated DEPs were screened out for a series of functional enrichment analyses.

CONCLUSIONS

Collectively, this study demonstrates that TRIM44 knockdown suppressed diabetes-induced retinal vascular dysfunction in DR.

MiR-185-5p is Involved in Regulating the Abnormal Proliferation of Retinal Microvascular Endothelial Cells via Targeting CXCR4

PURPOSE

This study aimed to explore the expression profile of miR-185-5p in proliferative DR (PDR), and further evaluate its diagnostic value and possible mechanism of miR-185-5p in PDR.

METHODS

The level of miR-185-5p was detected by qRT-PCR. The ROC curve was established to estimate the diagnostic ability of miR-185-5p. Transwell experiment and cell counting kit-8 (CCK-8) assays were conducted to assess the effect of miR-185-5p on the migration and proliferation of human retinal endothelial cells (HRECs) induced by high glucose. Enzyme linked immunosorbent assay (ELISA) was used to detect the concentrations of inflammatory factors. The luciferase reporter gene experiment was used to prove the interaction between miR-185-5p and CXCR4.

RESULTS

Compared to the control group, the expression of miR-185-5p was significantly up-regulated in both the type 2 diabetes mellitus (T2DM) group and the PDR groups, with higher levels in the PDR group than in the T2DM group. The ROC curve reveals that serum miR-185-5p can distinguish PDR patients from T2DM patients. MiR-185-5p levels in HRECs increased significantly after high glucose induction. High glucose induction also promoted the migration, proliferation and inflammation response of HRECs. However, when the intracellular miR-185-5p level was down-regulated by miR-185-5p inhibitor transfection, these effects were inhibited. The luciferase reporter gene assay showed that miR-185-5p directly targets CXCR4.

CONCLUSION

The expression of miR-185-5p is out of balance in PDR and it may be involved in regulating the migration and proliferation of HRECs by regulating CXCR4.

Autophagy-dependent ferroptosis may play a critical role in early stages of diabetic retinopathy

Diabetic retinopathy (DR), as one of the most common and significant microvascular complications of diabetes mellitus (DM), continues to elude effective targeted treatment for vision loss despite ongoing enrichment of the understanding of its pathogenic mechanisms from perspectives such as inflammation and oxidative stress. Recent studies have indicated that characteristic neuroglial degeneration induced by DM occurs before the onset of apparent microvascular lesions. In order to comprehensively grasp the early-stage pathological changes of DR, the retinal neurovascular unit (NVU) will become a crucial focal point for future research into the occurrence and progression of DR. Based on existing evidence, ferroptosis, a form of cell death regulated by processes like ferritinophagy and chaperone-mediated autophagy, mediates apoptosis in retinal NVU components, including pericytes and ganglion cells. Autophagy-dependent ferroptosis-related factors, including BECN1 and FABP4, may serve as both biomarkers for DR occurrence and development and potentially crucial targets for future effective DR treatments. The aforementioned findings present novel perspectives for comprehending the mechanisms underlying the early-stage pathological alterations in DR and open up innovative avenues for investigating supplementary therapeutic strategies.

Highly-Expressed MiR-221-3p Distinctly Increases the Incidence of Diabetic Retinopathy in Patients With Type 2 Diabetes Mellitus

Objective

Diabetic retinopathy (DR) is the leading cause of blindness in patients with diabetes mellitus (DM). MiR-221-3p is implicated in microvascular dysfunction in DR, and we explored their relationship.

Methods

Patients with type 2 diabetes mellitus (T2DM) were allocated to the non-DR (NDR)/nonproliferative DR (NPDR)/proliferative DR (PDR) groups, with their clinical baseline and pathological data collected. The miR-221-3p and VEGF levels were determined by reverse transcription quantitative polymerase chain reaction (RT-qPCR) and ELISA, respectively. Peripheral blood endothelial progenitor cell (EPC) and endothelial cell (EC) ratios were ascertained by flow cytometry. The correlations between miR-221-3p levels and VEGF/EPCs/ECs, the predictive value of serum miR-221-3p levels in DR, and the independent risk factors for DR occurrence in T2DM were analyzed by Pearson's correlation analysis, receiver operating characteristic (ROC) curve, and multifactorial logistic regression analysis.

Results

Serum miR-221-3p was highly expressed in DR. Clinical severity of DR was positively correlated with miR-221-3p levels. Endothelial function was impaired in DR. Serum miR-221-3p levels in DR were favorably correlated with VEGF and ECs and negatively associated with EPCs. The area under the curve of serum miR-221-3p in evaluating DR occurrence in patients with T2DM was 0.8178 (1.235 cutoff value, 69.62% sensitivity, and 82.35% specificity). High expression of miR-221-3p increased DR incidence in patients with T2DM. Diabetes course, VEGF, EPCs, ECs, and miR-221-3p levels were independent risk factors for DR development in patients with T2DM.

Conclusions

Serum miR-221-3p levels in patients with DR were positively correlated with VEGF and ECs and negatively linked with EPCs. Highly expressed miR-221-3p distinctly increased DR incidence in patients with T2DM and was an independent risk factor for DR development in patients with T2DM.

Translational Relevance

This study assessed serum miR-221-3p level and endothelial function indicators (VEGF, EPCs, and ECs) in patients with DR and analyzed the correlation between each indicator. We found that high serum miR-221-3p expression prominently increased the incidence of DR in patients with T2DM and was an independent risk factor for the development of DR in patients with T2DM. This study provided a scientific basis for further clarification of the pathogenesis of DR, and also provided new ideas for clinical prediction and management of DR.

Serine-arginine-rich protein kinase-1 inhibition for the treatment of diabetic retinopathy

Angiogenic VEGF isoforms are upregulated in diabetic retinopathy (DR), driving pathological growth and fluid leakage. Serine-arginine-rich protein kinase-1 (SRPK1) regulates VEGF splicing, and its inhibition blocks angiogenesis. We tested the hypothesis that SRPK1 is activated in diabetes, and an SRPK1 inhibitor (SPHINX31) switches VEGF splicing in DR and prevents increased vascular permeability into the retina. SRPK1 was activated by high glucose (HG), in a PKC-dependent manner, and was blocked by SPHINX31. HG induced release of SRSF1 from the nuclear speckles, which was also SRPK1 dependent, and increased retinal pigment epithelial (RPE) monolayer admittance, which was reversed by SRPK1 inhibition (P < 0.05). Diabetes increased retinal permeability and thickness after 14 days which was blocked by treatment with SPHINX31 eye drops (P < 0.0001). These results show that SRPK1 inhibition, administered as an eye drop, protected the retinal barrier from hyperglycemia-associated loss of integrity in RPE cells in vitro and in diabetic rats in vivo. A clinical trial of another SRPK1 inhibitor has now been initiated in patients with diabetic macular edema.NEW & NOTEWORTHY VEGF-A₁₆₅b splicing is induced by hyperglycemia through PKC-mediated activation of SRPK1 in RPE cells, increasing their permeability and angiogenic capability. SRPK1 inhibitors can be given as eye drops to reduce retinal permeability and edema in diabetic retinopathy.

Primaquine Diphosphate, a Known Antimalarial Drug, Blocks Vascular Leakage Acting Through Junction Stabilization

Endothelial barrier integrity is important for vascular homeostasis, and hyperpermeability participates in the progression of many pathological states, such as diabetic retinopathy, ischemic stroke, chronic bowel disease, and inflammatory disease. Here, using drug repositioning, we discovered that primaquine diphosphate (PD), previously known as an antimalarial drug, was a potential blocker of vascular leakage. PD inhibited the linear pattern of vascular endothelial growth factors (VEGF)-induced disruption at the cell boundaries, blocked the formation of VEGF-induced actin stress fibers, and stabilized the cortactin actin rings in endothelial cells. PD significantly reduced leakage in the Miles assay and mouse model of streptozotocin (STZ)-induced diabetic retinopathy. Targeted prediction programs and deubiquitinating enzyme activity assays identified a potential mechanism of action for PD and demonstrated that this operates via ubiquitin specific protease 1 (USP1). USP1 inhibition demonstrated a conserved barrier function by inhibiting VEGF-induced leakage in endothelial permeability assays. Taken together, these findings suggest that PD could be used as a novel drug for vascular leakage by maintaining endothelial integrity.

Retinal Vascular Endothelial Cell Dysfunction and Neuroretinal Degeneration in Diabetic Patients

Diabetes mellitus (DM) has become a vital societal problem as epidemiological studies demonstrate the increasing incidence of type 1 and type 2 diabetes. Lesions observed in the retina in the course of diabetes, referred to as diabetic retinopathy (DR), are caused by vascular abnormalities and are ischemic in nature. Vascular lesions in diabetes pertain to small vessels (microangiopathy) and involve precapillary arterioles, capillaries and small veins. Pericyte loss, thickening of the basement membrane, and damage and proliferation of endothelial cells are observed. Endothelial cells (monolayer squamous epithelium) form the smooth internal vascular lining indispensable for normal blood flow. Breaking its continuity initiates blood coagulation at that site. The endothelium controls the process of exchange of chemical substances (nutritional, regulatory, waste products) between blood and the retina, and blood cell passing through the vascular wall. Endothelial cells produce biologically active substances involved in blood coagulation, regulating vascular wall tension and stimulating neoangiogenesis. On the other hand, recent studies have demonstrated that diabetic retinopathy may be not only a microvascular disease, but is a result of neuroretinal degeneration. Neuroretinal degeneration appears structurally, as neural apoptosis of amacrine and Muller cells, reactive gliosis, ganglion cell layer/inner plexiform (GCL) thickness, retinal thickness, and retinal nerve fiber layer thickness, and a reduction of the neuroretinal rim in minimum rim width (MRW) and functionally as an abnormal electroretinogram (ERG), dark adaptation, contrast sensitivity, color vision, and microperimetric test. The findings in early stages of diabetic retinopathy may precede microvascular changes of this disease. Furthermore, the article's objective is to characterize the factors and mechanisms conducive to microvascular changes and neuroretinal apoptosis in diabetic retinopathy. Only when all the measures preventing vascular dysfunction are determined will the risk of complications in the course of diabetes be minimized.

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.

Tissue Plasminogen Activator Promotes TXNIP-NLRP3 Inflammasome Activation after Hyperglycemic Stroke in Mice

Hyperglycemia has been shown to counterbalance the beneficial effects of tissue plasminogen activator (tPA) and increase the risk of intracerebral hemorrhage in ischemic stroke. Thioredoxin interacting protein (TXNIP) mediates hyperglycemia-induced oxidative damage and inflammation in the brain and reduces cerebral glucose uptake/utilization. We have recently reported that TXNIP-induced NLRP3 (NOD-like receptor pyrin domain-containing-3) inflammasome activation contributes to neuronal damage after ischemic stroke. Here, we tested the hypothesis that tPA induces TXNIP-NLRP3 inflammasome activation after ischemic stroke, in hyperglycemic mice. Acute hyperglycemia was induced in mice by intraperitoneal (IP) administration of a 20% glucose solution. This was followed by transient middle cerebral artery occlusion (t-MCAO), with or without intravenous (IV) tPA administered at reperfusion. The IV-tPA exacerbated hyperglycemia-induced neurological deficits, ipsilateral edema and hemorrhagic transformation, and accentuated peroxisome proliferator activated receptor-γ (PPAR-γ) upregulation and TXNIP/NLRP3 inflammasome activation after ischemic stroke. Higher expression of TXNIP in hyperglycemic t-MCAO animals augmented glucose transporter 1 (GLUT-1) downregulation and increased vascular endothelial growth factor-A (VEGF-A) expression/matrix metallopeptidase 9 (MMP-9) signaling, all of which result in blood brain barrier (BBB) disruption and increased permeability to endogenous immunoglobulin G (IgG). It was also associated with a discernible buildup of nitrotyrosine and accumulation of dysfunctional tight junction proteins: zonula occludens-1 (ZO-1), occludin and claudin-5. Moreover, tPA administration triggered activation of high mobility group box protein 1 (HMGB-1), nuclear factor kappa B (NF-κB), and tumor necrosis factor-α (TNF-α) expression in the ischemic penumbra of hyperglycemic animals. All of these observations suggest a powerful role for TXNIP-NLRP3 inflammasome activation in the tPA-induced toxicity seen with hyperglycemic stroke.

Knockdown of MALAT1 attenuates high-glucose-induced angiogenesis and inflammation via endoplasmic reticulum stress in human retinal vascular endothelial cells

Diabetic retinopathy (DR) is one of the most severe complications of diabetes mellitus, and retinal endoplasmic reticulum stress (ERS) plays an important role in the pathogenesis of DR. However, the exact mechanisms by which ERS mediates DR remain unclear. In this study, human retinal vascular endothelial cells (RVECs) were cultured in high-glucose (HG) medium to mimic the environment of DR. The expression of long non-coding RNA (lncRNA)-metastasis-associated lung adenocarcinoma transcript 1 (MALAT1) was determined by quantitative real time PCR. ERS markers (glucose-regulated protein 78 [GRP78] and C/EBP homologous protein [CHOP]) were measured by immunofluorescence and western blotting. Cell viability was analyzed by the CCK-8 assay. The angiogenesis of RVECs was evaluated by tube formation assays. The levels of pro-inflammation cytokines TNF-α and IL-6 in RVECs were determined by ELISA assays. We found that exposure to HG levels upregulated MALAT1 and GRP78 expression in RVECs. While, GRP78 overexpression strengthened CHOP expression, cell proliferation suppression, capillary morphogenesis and inflammation in HG-treated RVECs. Importantly, knockdown of MALAT1 reversed HG-induced cell proliferation suppression, inhibited capillary morphogenesis, and inflammation in RVECs, and those effects were reversed by GRP78 overexpression. These results suggest that MALAT1 promotes HG-induced angiogenesis and inflammation in RVECs by upregulating ER stress, and might be target for treating DR.

Impact of Metabolic Syndrome on Neuroinflammation and the Blood-Brain Barrier

Metabolic syndrome, which includes diabetes and obesity, is one of the most widespread medical conditions. It induces systemic inflammation, causing far reaching effects on the body that are still being uncovered. Neuropathologies triggered by metabolic syndrome often result from increased permeability of the blood-brain-barrier (BBB). The BBB, a system designed to restrict entry of toxins, immune cells, and pathogens to the brain, is vital for proper neuronal function. Local and systemic inflammation induced by obesity or type 2 diabetes mellitus can cause BBB breakdown, decreased removal of waste, and increased infiltration of immune cells. This leads to disruption of glial and neuronal cells, causing hormonal dysregulation, increased immune sensitivity, or cognitive impairment depending on the affected brain region. Inflammatory effects of metabolic syndrome have been linked to neurodegenerative diseases. In this review, we discuss the effects of obesity and diabetes-induced inflammation on the BBB, the roles played by leptin and insulin resistance, as well as BBB changes occurring at the molecular level. We explore signaling pathways including VEGF, HIFs, PKC, Rho/ROCK, eNOS, and miRNAs. Finally, we discuss the broader implications of neural inflammation, including its connection to Alzheimer's disease, multiple sclerosis, and the gut microbiome.

Models of retinal diseases and their applicability in drug discovery

INTRODUCTION

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