VEGF-B inhibits hyperglycemia- and Macugen-induced retinal apoptosis

Mechanistic insights into the alterations and regulation of the AKT signaling pathway in diabetic retinopathy

In the early stages of diabetic retinopathy (DR), diabetes-related hyperglycemia directly inhibits the AKT signaling pathway by increasing oxidative stress or inhibiting growth factor expression, which leads to retinal cell apoptosis, nerve proliferation and fundus microvascular disease. However, due to compensatory vascular hyperplasia in the late stage of DR, the vascular endothelial growth factor (VEGF)/phosphatidylinositol 3 kinase (PI3K)/AKT cascade is activated, resulting in opposite levels of AKT regulation compared with the early stage. Studies have shown that many factors, including insulin, insulin-like growth factor-1 (IGF-1), VEGF and others, can regulate the AKT pathway. Disruption of the insulin pathway decreases AKT activation. IGF-1 downregulation decreases the activation of AKT in DR, which abrogates the neuroprotective effect, upregulates VEGF expression and thus induces neovascularization. Although inhibiting VEGF is the main treatment for neovascularization in DR, excessive inhibition may lead to apoptosis in inner retinal neurons. AKT pathway substrates, including mammalian target of rapamycin (mTOR), forkhead box O (FOXO), glycogen synthase kinase-3 (GSK-3)/nuclear factor erythroid 2-related factor 2 (Nrf2), and nuclear factor kappa-B (NF-κB), are a research focus. mTOR inhibitors can delay or prevent retinal microangiopathy, whereas low mTOR activity can decrease retinal protein synthesis. Inactivated AKT fails to inhibit FOXO and thus causes apoptosis. The GSK-3/Nrf2 cascade regulates oxidation and inflammation in DR. NF-κB is activated in diabetic retinas and is involved in inflammation and apoptosis. Many pathways or vital activities, such as the Janus kinase (JAK)/signal transducer and activator of transcription (STAT) and mitogen-activated protein kinase (MAPK) signaling pathways, interact with the AKT pathway to influence DR development. Numerous regulatory methods can simultaneously impact the AKT pathway and other pathways, and it is essential to consider both the connections and interactions between these pathways. In this review, we summarize changes in the AKT signaling pathway in DR and targeted drugs based on these potential sites.

Vitamin D3 preserves blood retinal barrier integrity in an in vitro model of diabetic retinopathy

The impairment of the blood retinal barrier (BRB) represents one of the main features of diabetic retinopathy, a secondary microvascular complication of diabetes. Hyperglycemia is a triggering factor of vascular cells damage in diabetic retinopathy. The aim of this study was to assess the effects of vitamin D₃ on BRB protection, and to investigate its regulatory role on inflammatory pathways. We challenged human retinal endothelial cells with high glucose (HG) levels. We found that vitamin D₃ attenuates cell damage elicited by HG, maintaining cell viability and reducing the expression of inflammatory cytokines such as IL-1β and ICAM-1. Furthermore, we showed that vitamin D₃ preserved the BRB integrity as demonstrated by trans-endothelial electrical resistance, permeability assay, and cell junction morphology and quantification (ZO-1 and VE-cadherin). In conclusion this in vitro study provided new insights on the retinal protective role of vitamin D₃, particularly as regard as the early phase of diabetic retinopathy, characterized by BRB breakdown and inflammation.

Dioscin Reduces Vascular Damage in the Retina of db/db Mice by Inhibiting the VEGFA Signaling Pathway

Diabetic retinopathy (DR) is a complication of diabetes that has a serious impact on the quality of life of patients. VEGFA is necessary in the physiological state to maintain endothelial activity and physical properties of blood vessels. VEGFA plays an important role in the promotion of neovascularization; therefore, inhibition of VEGFA can degrade the structure of blood vessels and reduce neovascularization. In the present study, HERB, a high-throughput experimental and reference-oriented database of herbal medicines, was used for compound mining targeting VEGFA. The compounds most likely to interact with VEGFA were screened by molecular docking. Next, the compounds were used to verify whether it could inhibit the activity of the VEGF signaling pathway in vitro and neovascularization in vivo. In vitro, we found that dioscin could inhibit the activation of the VEGFA–VEGFR2 signaling pathway and cell proliferation of human retinal microvascular endothelial cells in a high-glucose (HG) environment. A more important dioscin intervention inhibits the expression of pro-angiogenic factors in the retinas of db/db mice. In conclusion, our study indicates that dioscin reduces the vascular damage and the expression of pro-angiogenic factors in the retina of db/db mice and implies an important and potential application of dioscin for treatment of DR in clinics.

Increased Serum VEGF-B Level Is Associated With Renal Function Impairment in Patients With Type 2 Diabetes

AIMS/INTRODUCTION

Renal function impairment related to type 2 diabetes (T2DM) presents serious threat to public health. Previous studies suggest that vascular endothelial growth factor-B (VEGF-B) might contribute to renal injury. Therefore, this study investigated the association of serum VEGF-B level with the risk of renal function impairment in T2DM patients.

MATERIALS AND METHODS

Serum VEGF-B levels were measured in 213 patients with type 2 diabetes and 31 healthy participants. Participants with type 2 diabetes were further divided into a group of 112 participants with eGFR<90 mL/min/1.73m² and 101 participants with eGFR≥ 90 mL/min/1.73m². Clinical data were collected, and a binary logistic regression model was employed to test the association between potential predictors and eGFR.

RESULTS

Serum VEGF-B levels evaluated in type 2 diabetes patients compared with healthy controls. In patients with type 2 diabetes, serum VEGF-B level was positively correlated with triglyceride, serum creatinine and cystatin C while negatively correlated with HDL-C and eGFR. Binary logistic regression showed that serum VEGF-B level was an independent risk factor of eGFR<90 mL/min/1.73m².

CONCLUSIONS

Serum VEGF-B level is associated with renal function impairment in patients with type 2 diabetes and may be a potential drug target for diabetic kidney disease.

Vascular endothelial growth factor B inhibits insulin secretion in MIN6 cells and reduces Ca2+ and cyclic adenosine monophosphate levels through PI3K/AKT pathway

BACKGROUND

Type 2 diabetes (T2D) is characterized by insufficient insulin secretion caused by defective pancreatic β-cell function or insulin resistance, resulting in an increase in blood glucose. However, the mechanism involved in this lack of insulin secretion is unclear. The level of vascular endothelial growth factor B (VEGF-B) is significantly increased in T2D patients. The inactivation of VEGF-B could restore insulin sensitivity in db/db mice by reducing fatty acid accumulation. It is speculated that VEGF-B is related to pancreatic β-cell dysfunction and is an important factor affecting β-cell secretion of insulin. As an in vitro model of normal pancreatic β-cells, the MIN6 cell line can be used to analyze the mechanism of insulin secretion and related biological effects.

AIM

To study the role of VEGF-B in the insulin secretion signaling pathway in MIN6 cells and explore the effect of VEGF-B on blood glucose regulation.

METHODS

The MIN6 mouse pancreatic islet β-cell line was used as the model system. By administering exogenous VEGF-B protein or knocking down VEGF-B expression in MIN6 cells, we examined the effects of VEGF-B on insulin secretion, Ca²⁺ and cyclic adenosine monophosphate (cAMP) levels, and the insulin secretion signaling pathway.

RESULTS

Exogenous VEGF-B inhibited the secretion of insulin and simultaneously reduced the levels of Ca²⁺ and cAMP in MIN6 cells. Exogenous VEGF-B also reduced the expression of phospholipase C gamma 1 (PLCγ1), phosphatidylinositol 3-kinase (PI3K), serine/threonine kinase (AKT), and other proteins in the insulin secretion pathway. Upon knockdown of VEGF-B, MIN6 cells exhibited increased insulin secretion and Ca²⁺ and cAMP levels and upregulated expression of PLCγ1, PI3K, AKT, and other proteins.

CONCLUSION

VEGF-B can regulate insulin secretion by modulating the levels of Ca²⁺ and cAMP. VEGF-B involvement in insulin secretion is related to the expression of PLCγ1, PI3K, AKT, and other signaling proteins. These results provide theoretical support and an experimental basis for the study of VEGF-B in the pathogenesis of T2D.

VEGF-B Is an Autocrine Gliotrophic Factor for Müller Cells under Pathologic Conditions

Purpose

Müller glia are important in retinal health and disease and are a major source of retinal VEGF-A. Of the different VEGF family members, the role of VEGF-A in retinal health and disease has been studied extensively. The potential contribution of other VEGF family members to retinal pathophysiology, however, remains poorly defined. This study aimed to understand the role of VEGF-B in Müller cell pathophysiology.

Methods

The expression of different VEGFs and their receptors in human MIO-M1 and mouse QMMuC-1 Müller cell lines and primary murine Müller cells was examined by RT-PCR, ELISA, and Western blot. The effect of recombinant VEGF-B or VEGF-B neutralization on Müller cell viability and survival under normal, hypoxic, and oxidative (4-hydroxynonenal [4-HNE]) conditions was evaluated by Alamar Blue, Yo-Pro uptake, and immunocytochemistry. The expression of glial fibrillary acidic protein, aquaporin-4, inward rectifying K⁺ channel subtype 4.1, glutamine synthetase, and transient receptor potential vanilloid 4 under different treatment conditions was examined by RT-PCR, immunocytochemistry, and Western blot. Transient receptor potential vanilloid 4 channel activity was assessed using a Fura-2–based calcium assay.

Results

VEGF-B was expressed in Müller cells at the highest levels compared with other members of the VEGF family. VEGF-B neutralization did not affect Müller cell viability or functionality under normal conditions, but enhanced hypoxia– or 4-HNE–induced Müller cell death and decreased inward rectifying K⁺ channel subtype 4.1 and aquaporin-4 expression. Recombinant VEGF-B restored Müller cell glutamine synthetase expression under hypoxic conditions and protected Müller cells from 4-HNE–induced damage by normalizing transient receptor potential vanilloid 4 channel expression and activity.

Conclusions

Autocrine production of VEGF-B protects Müller cells under pathologic conditions.

Neurotrophic Effects of Vascular Endothelial Growth Factor B and Novel Mimetic Peptides on Neurons from the Central Nervous System

Vascular endothelial growth factor B (VEGFB) is a pleiotropic trophic factor, which in contrast to the closely related VEGFA is known to have a limited effect on angiogenesis. VEGFB improves survival in various tissues including the nervous system, where the effect was observed mainly for peripheral neurons. The neurotrophic effect of VEGFB on central nervous system neurons has been less investigated. Here we demonstrated that VEGFB promotes neurite outgrowth from primary cerebellar granule, hippocampal, and retinal neurons in vitro. VEGFB protected hippocampal and retinal neurons from both oxidative stress and glutamate-induced neuronal death. The VEGF receptor 1 (VEGFR1) is required for VEGFB-induced neurotrophic and neuroprotective effects. Using a structure-based approach, we designed short peptides, termed Vefin1-7, mimicking the binding interface of VEGFB to VEGFR1. Vefins were analyzed for their secondary structure and binding to VEGF receptors and compared with previously described peptides derived from VEGFA, another ligand of VEGFR1. We show that Vefins have neurotrophic and neuroprotective effects on primary hippocampal, cerebellar granule, and retinal neurons in vitro with potencies comparable to VEGFB. Similar to VEGFB, Vefins were not mitogenic for MCF-7 cancer cells. Furthermore, one of the peptides, Vefin7, even dose-dependently inhibited the proliferation of MCF-7 cells in vitro. Unraveling the neurotrophic and neuroprotective potentials of VEGFB, the only nonangiogenic factor of the VEGF family, is promising for the development of neuroprotective peptide-based therapies.

Novel function of VEGF-B as an antioxidant and therapeutic implications

Oxidative stress, due to insufficiency of antioxidants or over-production of oxidants, can lead to severe cell and tissue damage. Oxidative stress occurs constantly and has been shown to be involved in innumerable diseases, such as degenerative, cardiovascular, neurological, and metabolic disorders, cancer, and aging, thus highlighting the vital need of antioxidant defense mechanisms. Vascular endothelial growth factor B (VEGF-B) was discovered a long time ago, and is abundantly expressed in most types of cells and tissues. VEGF-B remained functionally mysterious for many years and later on has been shown to be minimally angiogenic. Recently, VEGF-B is reported to be a potent antioxidant by boosting the expression of key antioxidant enzymes. Thus, one major role of VEGF-B lies in safeguarding tissues and cells from oxidative stress-induced damage. VEGF-B may therefore have promising therapeutic utilities in treating oxidative stress-related diseases. In this review, we discuss the current knowledge on the newly discovered antioxidant function of VEGF-B and the related molecular mechanisms, particularly, in relationship to some oxidative stress-related diseases, such as retinitis pigmentosa, age-related macular degeneration, diabetic retinopathy, glaucoma, amyotrophic lateral sclerosis, Alzheimer's disease, and Parkinson's disease.

Curcumin prevents high glucose damage in retinal pigment epithelial cells through ERK1/2-mediated activation of the Nrf2/HO-1 pathway

To study the effects of curcumin on human retinal pigment epithelial (RPE) cells exposed to high glucose (HG) insult, we performed in vitro studies on RPE cells cultured both in normal and HG conditions to assess the effects of curcumin on the cell viability, nuclear factor erythroid 2-related factor 2 (Nrf2) expression, HO-1 activity, and ERK1/2 expression. RPE cells exposed to HG insult were treated with curcumin. The cell viability, apoptosis, HO-1 activity, ERK, and Nrf2 expression were evaluated. The data indicated that treatment with curcumin caused a significant decrease in terms of apoptosis. Further, curcumin was able to induce HO-1 expression via Nrf2 activation and counteracts the damage elicited by HG. The present study demonstrated that curcumin provides protection against HG-induced damage in RPE cells through the activation of Nrf2/HO-1 signaling that involves the ERK pathway, suggesting that curcumin may have therapeutic value in the treatment of diabetic retinopathy.

Resveratrol alleviates sepsis-induced acute lung injury by suppressing inflammation and apoptosis of alveolar macrophage cells

Sepsis is a major cause of death in intensive care units. The purpose of this study was to investigate the effect of resveratrol (RSV) on sepsis-induced acute lung injury (ALI). The underlying molecular mechanisms were deciphered by both in vitro and in vivo experiments. Polymicrobial sepsis was induced in C57BL/6 mice by cecal ligation and puncture (CLP). RSV pretreatment significantly attenuated CLP-induced acute lung injury, which was associated with enhanced expression of VEGF-B. The protective properties of RSV were assayed in lipopolysaccharide (LPS)-stimulated MH-S cells. We determine that RSV administration inhibited the increased production of TNF-α, IL-6, and IL-1β in LPS-stimulated MH-S cells, which was associated with inhibition of the nuclear factor-κB, P38, and ERK signaling pathways. We also provide evidence that RSV administration reduced LPS-induced apoptosis of MH-S cells by altering the unbalance of Bax/Bcl-2 and inhibiting LPS-induced autophagy. The inhibitory effects of RSV on cytokine levels and apoptosis of alveolar macrophages were both blocked by VEGF-B siRNA. Furthermore, RSV administration regulated LPS-induced C5aR and C5L2 expression, revealing an additional mechanism underlying RSV's anti-inflammatory and anti-apoptosis effects. Collectively, these results demonstrated that RSV was able to protect against sepsis-induced acute lung injury by activating the VEGF-B signaling pathway.

Retinal Protection and Distribution of Curcumin in Vitro and in Vivo

Diabetic retinopathy (DR), a secondary complication of diabetes, is a leading cause of irreversible blindness accounting for 5% of world blindness cases in working age. Oxidative stress and inflammation are considered causes of DR. Curcumin, a product with anti-oxidant and anti-inflammatory properties, is currently proposed as oral supplementation therapy for retinal degenerative diseases, including DR. In this study we predicted the pharmacodynamic profile of curcumin through an in silico approach. Furthermore, we tested the anti-oxidant and anti-inflammatory activity of curcumin on human retinal pigmented epithelial cells exposed to oxidative stress, human retinal endothelial and human retinal pericytes (HRPCs) cultured with high glucose. Because currently marketed curcumin nutraceutical products have not been so far evaluated for their ocular bioavailability; we assessed retinal distribution of curcumin, following oral administration, in rabbit eye. Curcumin (10 μM) decreased significantly (p < 0.01) ROS concentration and TNF-α release in retinal pigmented epithelial cells and retinal endothelial cells, respectively. The same curcumin concentration significantly (p < 0.01) protected retinal pericytes from high glucose damage as assessed by cell viability and LDH release. Among the tested formulations, only that containing a hydrophilic carrier provided therapeutic levels of curcumin in rabbit retina. In conclusion, our data suggest that curcumin, when properly formulated, may be of value in clinical practice to manage retinal diseases.

Vascular Endothelial Growth Factor B and Its Signaling

In diabetes, compromised glucose utilization leads the heart to use FA almost exclusively for ATP generation. Chronically, this adaptation unfortunately leads to the conversion of FA to potentially toxic FA metabolites. Paired with increased formation of reactive oxygen species related to excessive mitochondrial oxidation of FA, can provoke cardiac cell death. To protect against this cell demise, intrinsic mechanisms must be available to the heart. Vascular endothelial growth factor B (VEGFB) may be one growth factor that plays an important role in protecting against heart failure. As a member of the VEGF family, initial studies with VEGFB focused on its role in angiogenesis. Surprisingly, VEGFB does not appear to play a direct role in angiogenesis under normal conditions or even when overexpressed, but has been implicated in influencing vascular growth indirectly by affecting VEGFA action. Intriguingly, VEGFB has also been shown to alter gene expression of proteins involved in cardiac metabolism and promote cell survival. Conversely, multiple models of heart failure, including diabetic cardiomyopathy, have indicated a significant drop in VEGFB. In this review, we will discuss the biology of VEGFB, and its relationship to diabetic cardiomyopathy.

Absence of NUCKS augments paracrine effects of mesenchymal stem cells-mediated cardiac protection

Bone marrow-derived mesenchymal stem cells (BM-MSCs) contribute to myocardial repair after myocardial infarction (MI) by secreting a panel of growth factors and cytokines. This study was to investigate the potential mechanisms of the nuclear casein kinase and cyclin-dependent kinase substrate 1 (NUCKS) in regulation of the profiles of BM-MSCs secretion and compare the therapeutic efficacy of NUCKS^-/-- and wide type-BM-MSCs (WT-BM-MSCs) on MI. The secretion profiles between NUCKS^-/-- and WT-BM-MSCs under hypoxia (1%O₂) were analyzed. Gene function analysis showed that compared with WT-BM-MSCs-conditioned medium (CdM), some genes over-presented in NUCKS^-/--BM-MSCs-CdM were closely associated with inflammatory response, regulation of cell proliferation, death, migration and secretion. Notably, VEGFa in NUCKS^-/--BM-MSCs-CdM was higher than that of WT-BM-MSCs-CdM. WT-BM-MSCs and NUCKS^-/--BM-MSCs were transplanted into the peri-infarct region in mice of MI. At 4 weeks after cell transplantation, NUCKS^-/-- or WT-BM-MSCs group significantly improved heart function and vessels density and reduced infarction size and apoptosis of cardiomyocytes. Furthermore, NUCKS^-/--BM-MSCs provided better cardioprotective effects than WT-BM-MSCs against MI. Our study demonstrates that depletion of NUCKS enhances the therapeutic efficacy of BM-MSCs for MI via regulating the secretion.

Melatonin ameliorates myocardial ischemia/reperfusion injury in type 1 diabetic rats by preserving mitochondrial function: role of AMPK-PGC-1α-SIRT3 signaling

Enhancing mitochondrial biogenesis and reducing mitochondrial oxidative stress have emerged as crucial therapeutic strategies to ameliorate diabetic myocardial ischemia/reperfusion (MI/R) injury. Melatonin has been reported to be a safe and potent cardioprotective agent. However, its role on mitochondrial biogenesis or reactive oxygen species (ROS) production in type 1 diabetic myocardium and the underlying mechanisms remain unknown. We hypothesize that melatonin ameliorates MI/R injury in type 1 diabetic rats by preserving mitochondrial function via AMPK-PGC-1α-SIRT3 signaling pathway. Both our in vivo and in vitro data showed that melatonin reduced MI/R injury by improving cardiac function, enhancing mitochondrial SOD activity, ATP production and oxidative phosphorylation complex (II, III and IV), reducing myocardial apoptosis and mitochondrial MDA, H₂O₂ generation. Importantly, melatonin also activated AMPK-PGC-1α-SIRT3 signaling and increased SOD2, NRF1 and TFAM expressions. However, these effects were abolished by Compound C (a specific AMPK signaling blocker) administration. Additionally, our cellular experiment showed that SIRT3 siRNA inhibited the cytoprotective effect of melatonin without affecting p-AMPK/AMPK ratio and PGC-1α expression. Taken together, we concluded that melatonin preserves mitochondrial function by reducing mitochondrial oxidative stress and enhancing its biogenesis, thus ameliorating MI/R injury in type 1 diabetic state. AMPK-PGC1α-SIRT3 axis plays an essential role in this process.

Effects of blueberry anthocyanins on retinal oxidative stress and inflammation in diabetes through Nrf2/HO-1 signaling

Anthocyanins, which are abundant in blueberries, provide significant protection against many chronic diseases. We investigated the effects of blueberry anthocyanins (BA) on diabetes-induced oxidative stress and inflammation in rat retinas. Male rats were divided randomly into five groups. Intraperitoneal injection of streptozotocin (STZ, 60mg/kg) was used to induce a rat diabetes model. BA at 20, 40, and 80mg/kg were given orally for about 12weeks. The results showed that BA could prevent diabetes-induced weight loss and increased blood glucose. BA also upregulated the antioxidant capacity of the retina, increased the content of glutathione (GSH) and glutathione peroxidase (GPx) activity, and decreased malondialdehyde (MDA) and reactive oxygen species (ROS) levels. Vascular endothelial growth factor (VEGF) and interleukin-1β (IL-1β) in the serum of diabetes model rats were upregulated, and BA reversed these changes significantly. Furthermore, BA increased the mRNA levels of Nrf2 and HO-1, as well as the nuclear location of Nrf2 and protein levels of HO-1. These results suggested that BA can protect retinal cells from diabetes-induced oxidative stress and inflammation, and this may be regulated through Nrf2/HO-1 signaling.