Moderate GSK-3β inhibition improves neovascular architecture, reduces vascular leakage, and reduces retinal hypoxia in a model of ischemic retinopathy

Selective Activation of the Wnt-Signaling Pathway as a Novel Therapy for the Treatment of Diabetic Retinopathy and Other Retinal Vascular Diseases

Retinal ischemia, often associated with various disorders such as diabetic retinopathy (DR), retinal vein occlusion, glaucoma, optic neuropathies, stroke, and other retinopathies, is a major cause of visual impairment and blindness worldwide. As proper blood supply to the retina is critical to maintain its high metabolic demand, any impediment to blood flow can lead to a decrease in oxygen supply, resulting in retinal ischemia. In the pathogenesis of DR, including diabetic macular edema (DME), elevated blood glucose leads to blood-retina barrier (BRB) disruptions, vascular leakage, and capillary occlusion and dropouts, causing insufficient delivery of oxygen to the retina, and ultimately resulting in visual impairment. Other potential causes of DR include neuronal dysfunction in the absence of vascular defect, genetic, and environmental factors. The exact disease progression remains unclear and varies from patient to patient. Vascular leakage leading to edema clearly links to visual impairment and remains an important target for therapy. Despite recent advances in the treatment of DME and DR with anti-VEGFs, effective therapies with new mechanisms of action to address current treatment limitations regarding vessel regeneration and reperfusion of ischemic retinal areas are still needed. The Wnt signaling pathway plays a critical role in proper vascular development and maintenance in the retina, and thus provides a novel therapeutic approach for the treatment of diabetic and other retinopathies. In this review, we summarize the potential of this pathway to address treatment gaps with current therapies, its promise as a novel and potentially disease modifying therapy for patients with DR and opportunities in other retinal vascular diseases.

TCF7L2 promotes ER stress signaling in diabetic retinopathy

Diabetic retinopathy (DR) is one of the most common blindness in working-age adults. Transcription factor 7 like 2 (TCF7L2) is a susceptibility gene of DR, however, its roles in the pathogenesis of DR are still largely unknown. In this study, we found that TCF7L2 was mainly located in the cell nucleus of retinal ganglion cell layer (GCL) and inner nuclear layer (INL), while it was not expressed in the cell nucleus of retinal outer nuclear layer (ONL). Expression of TCF7L2 was significantly elevated in the retinas of db/db diabetic mice and oxygen-induced retinopathy (OIR) mice. Also, in Ad-hTCF7L2 treated hiPSCs-derived retinal progenitor cells (RPCs), activating transcription factor 6 (ATF6)-related endoplasmic reticulum (ER) stress signaling was remarkably activated. Moreover, knockdown of TCF7L2 significantly inhibited ATF6-related ER stress signaling. Furthermore, the data of endothelial permeability assay showed that RPCs pretreated with Ad-hTCF7L2 lead to enhanced monolayer permeability of human umbilical vein endothelial cells (HUVECs), and knockdown of TCF7L2 or ATF6 in RPCs could alleviate the monolayer permeability of HUVECs. Thus, our results showed that TCF7L2 could trigger ATF6-related ER stress signaling and promote vein endothelial cell permeability, which will provide important insight into the role of TCF7L2 in the pathogenesis of DR and contribute to designing potential therapies.

Using methanol to preserve retinas for immunostaining

BACKGROUND

Experimental studies on retinal vasculature and retinal ganglion cells (RGCs) investigating the developmental and pathological conditions of the retina mainly rely on whole-mount retinal immunostaining. Methanol, an auxiliary fixed medium for retinal whole-mount preparations, has been used in some studies; however, its application in short- and long-term storage of retinas for further study has not been well described. We aimed to evaluate methanol use as a preservation treatment for further immunostaining of the retina.

METHODS

We generated oxygen-induced retinopathy (OIR) and optic nerve crush (ONC) mouse models and used their retinas for analysis. We pipetted cold methanol (-20°C) on the surface of the retina to help fix the tissues while promoting permeability, after which the retinas were stored in cold methanol (-20°C) for 1, 6, or 12 months before being evaluated using various optical techniques. Thereafter, retinal whole-mount immunostaining was performed to analyse retinal neovascularisation and retinal hypoxia in OIR model, and retinal ganglion cell survival rate in ONC model.

RESULTS

Quantitative analysis revealed no significant differences in the fixed retinas after long-term storage in terms of retinal vasculature or retinal hypoxia in the OIR model. Similarly, no significant difference was found in RGC survival rate after long-term storage in methanol. These results suggest that methanol can be used as a storage medium when preserving retinal whole-mount samples.

CONCLUSIONS

Cold (-20°C) methanol can serve as an effective medium for long-term storage of fixed retinas, which is useful for further research.

The tumour neovasculature-homing dimeric peptide GX1 demonstrates antiangiogenic activity in the retinal neovasculature

Identification of molecules specific to the retinal neovasculature will promote antiangiogenic therapy with enhanced targeting ability. The specificity of phage-displayed peptide GX1 (a cyclic 7-mer peptide motif CGNSNPKSC) to gastric cancer neovasculature has been extensively confirmed both in vitro and in vivo. To investigate the potential application of GX1 in antiangiogenic therapy targeting retinal angiogenesis-related diseases, we performed immunohistochemistry and immunofluorescence analyses. GX1 demonstrated positive staining in the retinal neovasculature in an oxygen-induced mouse model of retinopathy (OIR) as well as in rat retinal microvasculature endothelial cells (RMECs), confirming the major role of the GX1 receptor during retinal angiogenesis. Dimeric GX1 was synthesized to increase the binding affinity to the GX1 receptor, and the antiangiogenic effects were examined in RMECs in vitro and the retinal neovasculature in the OIR in vivo. Cell proliferation was evaluated using a Cell Counting Kit-8 (CCK-8) assay, revealing that compared with the GX1 monomer, dimeric GX1 significantly inhibited RMEC proliferation (P < 0.05). This finding may be attributed to the enhanced (P < 0.05) apoptosis induced by dimeric GX1 in RMECs based on results obtained from TUNEL, flow cytometric and cell cycle analyses. In RMECs, in vitro cell migration and tube formation were significantly inhibited following exposure to dimeric GX1. Intravitreal administration of dimeric GX1 resulted in a greater reduction in the retinal neovascularization in vivo than administration of the GX1 monomer (P < 0.05). In conclusion, dimeric GX1 showed greater inhibition of angiogenesis than monomeric GX1 and could be a promising agent for antiangiogenic therapy in retinal angiogenesis-related diseases.

CM082, a novel VEGF receptor tyrosine kinase inhibitor, can inhibit angiogenesis in vitro and in vivo

The goal of this study was to evaluate the effects of CM082, a novel vascular endothelial growth factor (VEGF) receptor-2 tyrosine kinase inhibitor, on human umbilical vein endothelial cells (HUVECs), and oxygen-induced retinopathy (OIR) mice. HUVECs were stimulated with rHuVEGF165 and then treated with CM082 to assess the antiangiogenic effects of CM082; subsequently, proliferation, wound-healing migration, Transwell invasion, tube formation assays, and Western blotting were performed in vitro. Retinal neovascularization tufts, avascular area, and TUNEL assays were estimated for OIR mice after intraperitoneal injection with CM082. CM082 significantly inhibited proliferation, migration, invasion, and tube formation induced by stimulation of HUVECs with rHuVEGF165; this inhibitory effect was mediated by blocking VEGFR2 activation. CM082 significantly inhibited retinal neovascularization and avascular area and did not increase apoptosis in the retina of OIR mice. The findings demonstrated that CM082 exhibits highly antiangiogenic effects in HUVECs and OIR mice. Thus, it may serve as an alternative treatment for neovascular eye disease in the future.

Targeted pharmacotherapy against neurodegeneration and neuroinflammation in early diabetic retinopathy

Diabetic retinopathy (DR), the most frequent complication of diabetes, is one of the leading causes of irreversible blindness in working-age adults and has traditionally been regarded as a microvascular disease. However, increasing evidence has revealed that synaptic neurodegeneration of retinal ganglion cells (RGCs) and activation of glial cells may represent some of the earliest events in the pathogenesis of DR. Upon diabetes-induced metabolic stress, abnormal glycogen synthase kinase-3β (GSK-3β) activation drives tau hyperphosphorylation and β-catenin downregulation, leading to mitochondrial impairment and synaptic neurodegeneration prior to RGC apoptosis. Moreover, glial cell activation triggers enhanced inflammation and oxidative stress, which may accelerate the deterioration of diabetic RGCs neurodegeneration. These findings have opened up opportunities for therapies, such as inhibition of GSK-3β, glial cell activation, glutamate excitotoxicity and the use of neuroprotective drugs targeting early neurodegenerative processes in the retina and halting the progression of DR before the manifestation of microvascular abnormalities. Such interventions could potentially remedy early neurodegeneration and help prevent vision loss in people suffering from DR.

Retinitis Pigmentosa and Retinal Degenerations: Deciphering Pathways and Targets for Drug Discovery and Development

Inherited retinal diseases (IRDs) are a group of retinopathies generally caused by genetic mutations. Retinitis pigmentosa (RP) represents one of the most studied IRDs. RP leads to intense vision loss or blindness resulting from the degeneration of photoreceptor cells. To date, RP is mainly treated with palliative supplementation of vitamin A and retinoids, gene therapies, or surgical interventions. Therefore, a pharmacologically based therapy is an urgent need requiring a medicinal chemistry approach, to validate molecular targets able to deal with retinal degeneration. This Review aims at outlining the recent research efforts in identifying new drug targets for RP, especially focusing on the neuroprotective role of the Wnt/β-catenin/GSK3β pathway and apoptosis modulators (in particular PARP-1) but also on growth factors such as VEGF and BDNF. Furthermore, the role of spatiotemporally expressed G protein-coupled receptors (GPR124) in the retina and the emerging function of histone deacetylase inhibitors in promoting retinal neuroprotection will be discussed.

GSK-3 Inhibitors: From the Brain to the Retina and Back Again

Enzyme glycogen synthase kinase-3 (GSK-3) is a candidate pharmacological target for the treatment of neurodegenerative diseases of the brain. Given the many molecular, cellular, and functional features shared by the brain and the retina in both physiological and pathological processes, drugs originally designed to treat neurodegenerative diseases of the brain could be useful candidates for the treatment of retinal degenerative pathologies. Moreover, the accessibility of the eye to noninvasive, quantitative diagnostic techniques allows for easier evaluation of the efficacy of candidate therapies in clinical trials. In this chapter, we discuss the potential of GSK-3 inhibitors in the treatment of retinal degeneration.

Glycogen synthase kinase 3β inhibition reduces mitochondrial oxidative stress in chronic myocardial ischemia

OBJECTIVES

Glycogen synthase kinase 3β (GSK-3β) inhibition has been reported to increase microvascular density and improve myocardial blood flow in a porcine model of chronic myocardial ischemia and metabolic syndrome. Inhibition of GSK-3β can also be cardioprotective by modulating fibrosis signaling and mitochondrial-induced apoptosis. We hypothesized GSK-3β inhibition would have a beneficial effect on myocardial fibrosis and oxidative stress in a porcine model of chronic myocardial ischemia and metabolic syndrome.

METHODS

Pigs were fed a high fat diet for 4 weeks followed by placement of an ameroid constrictor to the left circumflex coronary artery. Three weeks later animals received either no drug or a GSK-3β inhibitor. The diets and placebo/GSK-3β inhibition were continued for an additional 5 weeks, the pigs were then euthanized, and the myocardial tissue was harvested. Collagen expression was analyzed via Picrosirius staining. Oxidative stress was analyzed via Oxyblot analysis. Protein expression was analyzed via Western blot.

RESULTS

GSK-3β inhibition was associated with decreased collagen expression and oxidative stress in the ischemic and nonischemic myocardial tissue compared with control. There was a decrease in profibrotic proteins transforming growth factor-β, p-SMAD2/3, and matrix metalloproteinase-9, and in proapoptotic and oxidative stress proteins, apoptosis inducing factor, the cleaved caspase 3/caspase 3 protein ratio and phosphorylated myeloid cell leukemia sequence-1 in the GSK-3β inhibited group compared with the control.

CONCLUSIONS

In the setting of metabolic syndrome and chronic myocardial ischemia, inhibition of GSK-3β decreases collagen formation and oxidative stress in myocardial tissue. GSK-3β inhibition might be having this beneficial effect by downregulating transforming growth factor-β/SMAD2/3 signaling and decreasing mitochondrial induced cellular stress.

A Critical Analysis of the Available In Vitro and Ex Vivo Methods to Study Retinal Angiogenesis

Angiogenesis is a biological process with a central role in retinal diseases. The choice of the ideal method to study angiogenesis, particularly in the retina, remains a problem. Angiogenesis can be assessed through in vitro and in vivo studies. In spite of inherent limitations, in vitro studies are faster, easier to perform and quantify, and typically less expensive and allow the study of isolated angiogenesis steps. We performed a systematic review of PubMed searching for original articles that applied in vitro or ex vivo angiogenic retinal assays until May 2017, presenting the available assays and discussing their applicability, advantages, and disadvantages. Most of the studies evaluated migration, proliferation, and tube formation of endothelial cells in response to inhibitory or stimulatory compounds. Other aspects of angiogenesis were studied by assessing cell permeability, adhesion, or apoptosis, as well as by implementing organotypic models of the retina. Emphasis is placed on how the methods are applied and how they can contribute to retinal angiogenesis comprehension. We also discuss how to choose the best cell culture to implement these methods. When applied together, in vitro and ex vivo studies constitute a powerful tool to improve retinal angiogenesis knowledge. This review provides support for researchers to better select the most suitable protocols in this field.

Suppression of Retinal Neovascularization by Inhibition of Galectin-1 in a Murine Model of Oxygen-Induced Retinopathy

Galectin-1 (Gal-1) has been proved to be an important factor in the process of tumor angiogenesis recently. As a small molecule, OTX008 serves as a selective inhibitor of Gal-1. In this study, the role of Gal-1 and the antiangiogenic effect of OTX008 on retinal neovascularization (RNV) were investigated using a mouse model of oxygen-induced retinopathy. The outcome indicated that Gal-1 was overexpressed and closely related to retinal neovessels in OIR. After intravitreal injection of OTX008 at P12, the RNV was significantly reduced at P17, measuring by cross-sectional H&E staining and whole-mount fluorescence. Our results demonstrate the inhibitory function of OTX008 on RNV, which provides a promising strategy of treating retinal angiogenic diseases such as retinopathy of prematurity and proliferative diabetic retinopathy.

Calpain inhibition modulates glycogen synthase kinase 3β pathways in ischemic myocardium: A proteomic and mechanistic analysis

BACKGROUND

Calpain inhibition has an enhancing effect on myocardial perfusion and improves myocardial density by inhibiting glycogen synthase kinase 3β (GSK-3β) and up-regulating downstream signaling pathways, including the insulin/PI3K and WNT/β-catenin pathways, in a pig model of chronic myocardial ischemia in the setting of metabolic syndrome.

METHODS

Pigs were fed a high-fat diet for 4 weeks, then underwent placement of an ameroid constrictor to the left circumflex artery. Three weeks later, the animals received no drug (high-cholesterol controls [HCC]), a high-dose calpain inhibitor (HCI), a low-dose calpain inhibitor (LCI), or a GSK-3β inhibitor (GSK-3βI). The diets and drug regimens were continued for 5 weeks and the myocardial tissue was harvested.

RESULTS

Calpain and GSK-3β inhibition caused an increase in myocardial perfusion ratios at rest and during pacing compared with controls. Pigs in the LCI and HCI groups had increased vessel density in the ischemic myocardium, and pigs in the GSK-3βI group had increased vessel density in the ischemic and nonischemic myocardium compared with the HCC group. Calpain inhibition modulates proteins involved in the insulin/PI3K and WNT/β-catenin pathways. Quantitative proteomics revealed that calpain and GSK-3β inhibition significantly modulated the expression of proteins enriched in cytoskeletal regulation, metabolism, respiration, and calcium-binding pathways.

CONCLUSIONS

In the setting of metabolic syndrome, calpain or GSK-3β inhibition increases vessel density in both ischemic and nonischemic myocardial tissue. Calpain inhibition may exert these effects through the inhibition of GSK-3β and up-regulation of downstream signaling pathways, including the insulin/PI3K and WNT/β-catenin pathways.

A first-in-human phase I dose-escalation, pharmacokinetic, and pharmacodynamic evaluation of intravenous LY2090314, a glycogen synthase kinase 3 inhibitor, administered in combination with pemetrexed and carboplatin

PURPOSE

LY2090314 (LY) is a glycogen synthase kinase 3 inhibitor with preclinical efficacy in xenograft models when combined with platinum regimens. A first-in-human phase 1 dose-escalation study evaluated the combination of LY with pemetrexed/carboplatin.

PATIENTS AND METHODS

Forty-one patients with advanced solid tumors received single-dose LY monotherapy lead-in and 37 patients received LY (10-120 mg) plus pemetrexed/carboplatin (500 mg/m(2) and 5-6 AUC, respectively) across 8 dose levels every 21 days. Primary objective was maximum tolerated dose (MTD) determination; secondary endpoints included safety, antitumor activity, pharmacokinetics, and beta-catenin pharmacodynamics.

RESULTS

MTD of LY with pemetrexed/carboplatin was 40 mg. Eleven dose-limiting toxicities (DLTs) occurred in ten patients. DLTs during LY monotherapy occurred at ≥ 40 mg: grade 2 visual disturbance (n = 1) and grade 3/4 peri-infusional thoracic pain during or shortly post infusion (n = 4; chest, upper abdominal, and back pain). Ranitidine was added after de-escalation to 80 mg LY to minimize peri-infusional thoracic pain. Following LY with pemetrexed/carboplatin therapy, DLTs included grade 3/4 thrombocytopenia (n = 4) and grade 4 neutropenia (n = 1). Best overall response by RECIST included 5 confirmed partial responses (non-small cell lung cancer [n = 3], mesothelioma, and breast cancer) and 19 patients having stable disease. Systemic LY exposure was approximately linear over dose range studied. Transient upregulation of beta-catenin measured in peripheral blood mononuclear cells (PBMCs) occurred at 40 mg LY.

CONCLUSIONS

The initial safety profile of LY2090314 was established. MTD LY dose with pemetrexed/carboplatin is 40 mg IV every 3 weeks plus ranitidine. Efficacy of LY plus pemetrexed/carboplatin requires confirmation in randomized trials.

Molecular control of capillary morphogenesis and maturation by recognition and remodeling of the extracellular matrix: functional roles of endothelial cells and pericytes in health and disease

This review addresses fundamental mechanisms underlying how capillaries form in three-dimensional extracellular matrices and how endothelial cells (ECs) and pericytes co-assemble to form capillary networks. In addition to playing a critical role in supplying oxygen and nutrients to tissues, recent work suggests that blood vessels supply important signals to facilitate tissue development. Here, we hypothesize that another major function of capillaries is to supply signals to suppress major disease mechanisms including inflammation, infection, thrombosis, hemorrhage, edema, ischemic injury, fibrosis, autoimmune disease and tumor growth/progression. Capillary dysfunction plays a key pathogenic role in many human diseases, and thus, this suppressing function may be attenuated and central toward the initiation and progression of disease. We describe how capillaries form through creation of EC-lined tube networks and vascular guidance tunnels in 3D extracellular matrices. Pericytes recruit to the abluminal EC tube surface within these tunnel spaces, and work together to assemble the vascular basement membrane matrix. These processes occur under serum-free conditions in 3D collagen or fibrin matrices and in response to five key growth factors which are stem cell factor, interleukin-3, stromal-derived factor-1α, fibroblast growth factor-2 and insulin. In addition, we identified a key role for EC-derived platelet-derived growth factor-BB and heparin-binding epidermal growth factor in pericyte recruitment and proliferation to promote EC-pericyte tube co-assembly and vascular basement membrane matrix deposition. A molecular understanding of capillary morphogenesis and maturation should lead to novel therapeutic strategies to repair capillary dysfunction in major human disease contexts including cancer and diabetes.

The alternative complement pathway regulates pathological angiogenesis in the retina

A defining feature in proliferative retinopathies is the formation of pathological neovessels. In these diseases, the balance between neovessel formation and regression determines blindness, making the modulation of neovessel growth highly desirable. The role of the immune system in these retinopathies is of increasing interest, but it is not completely understood. We investigated the role of the alternative complement pathway during the formation and resolution of aberrant neovascularization. We used alternative complement pathway-deficient (Fb(-/-)) mice and age- and strain-matched control mice to assess neovessel development and regression in an oxygen-induced retinopathy (OIR) mouse model. In the control mice, we found increased transcription of Fb after OIR treatment. In the Fb(-/-) mice, we prepared retinal flatmounts and identified an increased number of neovessels, peaking at postnatal day 17 (P17; P=0.001). Subjecting human umbilical vein endothelial cells (HUVECs) to low oxygen, mimicking a characteristic of neovessels, decreased the expression of the complement inhibitor Cd55. Finally, using laser capture microdissection (LCM) to isolate the neovessels after OIR, we found decreased expression of Cd55 (P=0.005). Together, our data implicate the alternative complement pathway in facilitating neovessel clearance by down-regulating the complement inhibitor Cd55 specifically on neovessels, allowing for their targeted removal while leaving the established vasculature intact.-Sweigard, J. H., Yanai, R., Gaissert, P., Saint-Geniez, M., Kataoka, K., Thanos, A., Stahl, G. L., Lambris, J. D., Connor, K. M. The alternative complement pathway regulates pathological angiogenesis in the retina.

Knockdown of β-catenin controls both apoptotic and autophagic cell death through LKB1/AMPK signaling in head and neck squamous cell carcinoma cell lines

The Wnt/β-catenin pathway regulates the viability and radiosensitivity of head and neck squamous cancer cells (HNSCC). Increased β-catenin predisposes HNSCC patients to poor prognosis and survival. This study was conducted to determine the mechanism by which β-catenin regulates the viability of HNSCC. AMC-HN-3, -HN-8, UM-SCC-38, and -SCC-47 cells, which were established from human head and neck cancer specimens, and underwent cell death following β-catenin silencing. β-Catenin silencing significantly induced G1 arrest and increased the expression of Bax and active caspase-3, which demonstrates the sequential activation of apoptotic cascades following treatment of HNSCC with targeted siRNA. Intriguingly, β-catenin silencing also induced autophagy. Here, we confirm that the number of autophagic vacuoles and the expression of type II light chain 3 were increased in cells that were treated with β-catenin siRNA. These cell death modes are most likely due to the activation of LKB1-dependent AMPK following β-catenin silencing. The activated LKB1/AMPK pathway in AMC-HN-3 cells caused G1 arrest by phosphorylating p53 and suppressing mTOR signaling. In addition, treating AMC-HN-3 cells with LKB1 siRNA preserved cell viability against β-catenin silencing-induced cytotoxicity. Taken together, these results imply that following β-catenin silencing, HNSCC undergo both apoptotic and autophagic cell death that are under the control of LKB1/AMPK. To the best of our knowledge, these results suggest for the first time that novel crosstalk between β-catenin and the LKB1/AMPK pathway regulates the viability of HNSCC. This study thus presents new insights into our understanding of the cellular and molecular mechanisms involved in β-catenin silencing-induced cell death.

Regulation of endothelial cell morphogenesis by the protein kinase D (PKD)/glycogen synthase kinase 3 (GSK3)β pathway

Vascular morphogenesis is a key process for development, reproduction, and pathogenesis. Thus understanding the mechanisms of this process is of pathophysiological importance. Despite the fact that collagen I is the most abundant and potent promorphogenic molecule known, the molecular mechanisms by which this protein regulates endothelial cell tube morphogenesis are still unclear. Here we provide strong evidence that collagen I induces tube morphogenesis by inhibiting glycogen synthase kinase 3β (GSK3β). Further mechanistic studies revealed that GSK3β activity is regulated by protein kinase D (PKD). PKD inhibited GSK3β activity, which was required for collagen I-induced endothelial tube morphogenesis. We also found that GSK3β regulated trafficking of integrin α(2)β(1) in a Rab11-dependent manner. Taken together, our studies highlight the important role of PKD in the regulation of collagen I-induced vascular morphogenesis and show that it is mediated by the modulation of GSK3β activity and integrin α(2)β(1) trafficking.

TMP prevents retinal neovascularization and imparts neuroprotection in an oxygen-induced retinopathy model

PURPOSE

To evaluate the effects of tetramethylpyrazine (TMP) on retinal neovascularization (NV) and neuroprotection in an oxygen-induced retinopathy (OIR) model.

METHODS

Neonatal C57BL/6J mice were subjected to 75% oxygen from postnatal day 7 (P7) to P12 and then returned to room air. TMP (200 mg/kg) or normal saline was given daily from P12 to P17. Immunostaining, HE staining, TUNEL assay, and RT-PCR were used to assess the effects of TMP on retinal neurovascular repair.

RESULTS

TMP effectively prevented pathologic NV and accelerated physiologic revascularization by enhancing the formation of endothelial tip cells at the edges of the repairing capillary networks and preserving the astrocytic template in the avascular retina. TMP also prevented morphologic changes and significantly decreased TUNEL-positive cells in the avascular retina by rescuing neurons such as amacrine, rod bipolar, horizontal, and Müller cells. In TMP-treated mice retinas, there was a less obvious loss of amacrine cell bodies and their distinct bands; the number of both rod bipolar and horizontal cell bodies, as well as the density of their dendrites in the outer plexiform layer, was greater than that in OIR control mice. TMP not only decreased the loss of alignment of Müller cell bodies and distortion of processes but reduced the reactive expression of GFAP in Müller cells. Furthermore, HIF-1α and VEGF mRNA expression were downregulated in TMP-treated mice retinas.

CONCLUSIONS

TMP improved neurovascular recovery by preventing NV and protecting retinal astroglia cells and neurons from ischemia-induced cell death partially due to its downregulation of HIF-1α and VEGF mRNA expression.

Hypoxia-induced β-catenin downregulation involves p53-dependent activation of Siah-1

Solid tumors contain extensive hypoxic areas and it is of considerable importance to decipher the potential role of hypoxia in signaling pathway regulation. In the present study, we examined the impact of hypoxia on β-catenin status and the mechanisms involved. Hypoxia significantly decreased β-catenin protein, but had no effect on glycogen synthase kinase (GSK)-3β or adenomatous polyposis coli (APC) levels. However, hypoxia-induced β-catenin downregulation seemed to require APC but not GSK-3β. Further investigation revealed that hypoxia significantly upregulated Siah-1, the human homolog of Drosophila seven in absentia. In addition, hypoxia augmented the interaction between β-catenin and SIP and Skp1. Silencing of Siah-1, as well as the use of a dominant negative Siah-1 mutant, attenuated these responses to hypoxia and rescued β-catenin transactivation. The Siah-1-mediated degradation of β-catenin during hypoxia may involve p53, but not hypoxia-inducible factor-1, activation. Together, the results suggest that hypoxia downregulates β-catenin by increasing Siah-1 expression in a p53-dependent manner.

GSK-3β: a signaling pathway node modulating neural stem cell and endothelial cell interactions

The neurogenic areas of the brain are highly organized structures in which there is dynamic reciprocal modulation of neural stem cells (NSC) and microvascular endothelial cells (BEC) resulting in control of neural stem cell and vascular proliferation, survival and differentiation throughout the life of the individual. Select molecules such as GSK-3β, functioning as signaling nodes, and their downstream signaling components including HIF-1α, HIF-2α and β-catenin participate in regulating and orchestrating the diverse responses involved in this complex process. In this report we demonstrate GSK-3β's role as a signaling node in two mouse strains (C57BL/6, which have been found to respond to and recover from a hypoxic insult from P3 to P11 poorly and CD-1, which have been found to respond to and recover from a hypoxic insult from P3 to P11 well both in vivo and in vitro) which mimic the wide range of responsiveness to hypoxic insult observed in the very low birth weight premature infant population. Differences in levels of neural stem cell and microvascular endothelial cell GSK-3β activation, β-catenin serine phosphorylation, HIF-1α and 2α, BDNF, SDF-1 and VEGF, β-III-tubulin and cleaved notch-1 expression in C57BL/6 and CD-1 subventricular zone tissues, and cultured NSC and BEC were noted. Specifically, CD1 pups, SVZ tissues and isolated NSC and BEC exhibit less GSK-3β and β-catenin serine phoslphorylation and greater HIF-1α and 2α, BDNF, SDF-1 and VEGF, β-III-tubulin and cleaved notch-1 expression compared to C57BL/6. Correlating with these changes were differences of several neural stem cell and microvascular endothelial cell behaviors including proliferation, apoptosis, migration and differentiation with CD1 NSC exhibiting greater proliferation and migration and decreased apoptosis and differentiation and CD1 BEC exhibiting greater angiogenesis. Further, upon treatment with nanomolar concentrations of a GSK-3β inhibitor (SB412682), C57 NSC and BEC behaviors could be brought to CD1 levels, consistent with the concept of GSK-3β functioning as a multifunctional signaling pathway node, modulating several behaviors in these cells. Lastly, the therapeutic potential of targeting GSK-3β is discussed.

Molecular basis for endothelial lumen formation and tubulogenesis during vasculogenesis and angiogenic sprouting

Many studies reveal a fundamental role for extracellular matrix-mediated signaling through integrins and Rho GTPases as well as matrix metalloproteinases (MMPs) in the molecular control of vascular tube morphogenesis in three-dimensional (3D) tissue environments. Recent work has defined an endothelial cell (EC) lumen signaling complex of proteins that controls these vascular morphogenic events. These findings reveal a signaling interdependence between Cdc42 and MT1-MMP to control the 3D matrix-specific process of EC tubulogenesis. The EC tube formation process results in the creation of a network of proteolytically generated vascular guidance tunnels in 3D matrices that are utilized to remodel EC-lined tubes through EC motility and could facilitate processes such as flow-induced remodeling and arteriovenous EC sorting and differentiation. Within vascular guidance tunnels, key dynamic interactions occur between ECs and pericytes to affect vessel remodeling, diameter, and vascular basement membrane matrix assembly, a fundamental process necessary for endothelial tube maturation and stabilization. Thus, the EC lumen and tube formation mechanism coordinates the concomitant establishment of a network of vascular tubes within tunnel spaces to allow for flow responsiveness, EC-mural cell interactions, and vascular extracellular matrix assembly to control the development of the functional microcirculation.