Riluzole inhibits VEGF-induced endothelial cell proliferation in vitro and hyperoxia-induced abnormal vessel formation in vivo

PURPOSE: The present study examined the effects of riluzole, a Food and Drug Administration-approved drug for amyotrophic lateral sclerosis, on VEGF-stimulated endothelial cell proliferation in culture, and on neovascularization in a rat model of retinopathy of prematurity (ROP). METHODS: Human umbilical vein endothelial cell and bovine retinal endothelial cell cultures were treated with VEGF to induce endothelial cell proliferation in the presence or absence of riluzole. Activation of PKC betaII was examined by quantifying its phosphorylated form on immunoblots. ROP was induced in 5-day-old rat pups by raising them in hyperoxic conditions for 7 days and in normoxic conditions for the next 5 days. Dextran fluorescence retinal angiography was used to quantitatively assess ROP. RESULTS: Riluzole inhibited VEGF-stimulated PKC betaII activation and cell proliferation in bovine retinal endothelial cell and human umbilical vein endothelial cell cultures. In addition, systemic administration of riluzole substantially ameliorated abnormal new vessel formation in the rat ROP model. CONCLUSIONS: The present results suggest that riluzole is a potent inhibitor of VEGF-induced endothelial cell proliferation both in vivo and in vitro. Since long-term use of riluzole has already been proven safe in humans, the present data indicate that clinical trials of riluzole for proliferative retinopathies should be implemented expeditiously.     

Effect of VEGF on retinal microvascular endothelial hydraulic conductivity: the role of NO

PURPOSE: Vascular endothelial growth factor (VEGF) increases microvascular permeability in vivo and has been hypothesized to play a role in plasma leakage in diabetic retinopathy. Few controlled studies have been conducted to determine the mechanism underlying the effect of VEGF on transport properties (e.g., hydraulic conductivity [Lp]). This study was conducted to determine the effect of VEGF on bovine retinal microvascular endothelial LP and the role of nitric oxide (NO) and the guanylate cyclase/guanosine 3', 5'-cyclic monophosphate/protein kinase G (GC/cGMP/PKG) pathway downstream of NO in mediating the VEGF response. METHODS: Bovine retinal microvascular endothelial cells (BRECs) were grown on porous polycarbonate filters, and water flux across BREC monolayers in response to a pressure differential was measured to determine endothelial LP RESULTS: VEGF (100 ng/ml) increased endothelial LP: within 30 minutes of addition and by 13.8-fold at the end of 3 hours of exposure. VEGF stimulated endothelial monolayers to release NO and incubation of the BRECs with the nitric oxide synthase inhibitor N(G)-monomethyl-L-arginine (L-NMMA; 100 microM) significantly attenuated the VEGF-induced LP increase. It was observed that incubation of the monolayers with the GC inhibitor LY-83583 (10 microM) did not alter the VEGF-mediated LP: response. Addition of the cGMP analogue 8-br-cGMP (1 mM) did not change the baseline LP over 4 hours. Also, the PKG inhibitor KT5823 (1 microM) did not inhibit the response of BREC LP to VEGF. CONCLUSIONS: These experiments indicate that VEGF elevates hydraulic conductivity in BRECs through a signaling mechanism that involves NO but not the GC/cGMP/PKG pathway.     

Effects of angiogenic growth factor combinations on retinal endothelial cells

The aim of this paper was to determine if growth factors, known to be upregulated in proliferative diabetic retinopathy, exerted combined effects on retinal endothelial cells. The authors explored the individual and collective actions of insulin-like growth factor I (IGF-I), vascular endothelial growth factor (VEGF), platelet-derived growth factor-BB (PDGF-BB), fibroblast growth factor-2 (FGF-2) and placenta growth factor (PlGF) on several parameters that reflect the angiogenic potential of endothelial cells. The effect of growth factors on cell migration and survival/proliferation was examined using primary cultures of bovine retinal endothelial cells (BREC). The authors also determined the growth factor action on capillary-like tube formation on a reconstituted basement membrane matrix and on the newly described phenomenon of secondary sprouting, in which endothelial cell colonies spontaneously survive, proliferate, migrate and invade the matrix after the original capillary-like tubes have collapsed. Sprouting cells were positive for von Willebrand factor and could aggregate into larger tubes with lumens. Incubation with VEGF+IGF-I or PlGF+FGF-2 enhanced tube stability by 40-50%, more than each growth factor alone or other combinations (5-20%). The concurrent addition of four growth factors did not improve the response seen with growth factor pairs. Surprisingly, PDGF-BB induced tube collapse. IGF-I and FGF-2 mildly enhanced BREC proliferation/survival (5-15%). However, VEGF+IGF-I or PlGF+FGF-2 increased BREC proliferation/survival by 25% under low serum conditions, whereas combinations of all four growth factors exerted a clearly synergistic effect (250% increase). PDGF-BB or FGF-2 stimulated secondary sprouting and were the only factors capable of exerting this effect alone. Even though VEGF, IGF-I or PlGF were not effective, if administered in pairs, they demonstrated increased responses. PDGF-BB was also able to enhance the effect of FGF-2+IGF-I+VEGF on BREC secondary sprouting, but not of any of them individually. No other growth factor tested was able to significantly improve the action of combinations of three other growth factors. VEGF increased cell migration in a wounded monolayer assay two-fold and PDGF-BB, 2.5 times, but other individual growth factors were ineffective. PlGF+FGF-2 enhanced cell migration more than each factor alone. VEGF+IGF-I+PlGF+FGF-2, however, increased cell migration four-fold. In summary, this study indicates that growth factors, overexpressed in diabetic retinopathy eyes, enhance the angiogenic characteristics of cultured cells (tube formation, proliferation, secondary sprouting and migration). Their effects, however, can be greatly augmented by other growth factors that alone exert little or no action. Therefore, diabetic retinal neovascularization may result from the additive or synergistic action of several growth factors.     

Hexose transport in microvascular endothelial cells cultured from bovine retina

The nature of glucose transport at the microvascular blood-retinal barrier was studied using primary cultures of microvascular endothelial cells from bovine retina. Uptake of 3-O-methyl-D-glucose (3MG), a non-metabolizable glucose analogue, was rapid and equilibrative. 3MG uptake could be inhibited by traditional glucose transport inhibitors such as phloretin, phlorizin and cytochalasin B but not by agents that deplete intracellular ATP (2,4-dinitrophenol) or that abolish the sodium gradient (ouabain). Uptake of 3MG by the cells could be stimulated by preloading with 50 mM-glucose, a phenomenon known as counter-transport. Insulin had no effect on 3MG uptake in the cells even after prolonged insulin deprivation. These results demonstrate the existence of a facilitative-diffusion type of glucose transport system in endothelial cells of the retinal microvasculature. Studies with 2-deoxy-D-glucose demonstrated that transport was not rate limiting for metabolism and that the endothelial cells contain free sugar when exposed to an extracellular sugar concentration in the physiologic range. The presence of this free sugar within the cell is necessary for efficient transendothelial transfer of glucose from blood to retina but it could also provide the basis for capillary damage in diabetes mellitus.     

胰岛素对正常糖和高糖浓度下牛视网膜微血管内皮细胞血管内皮生长因子表达的影响

目的 探讨胰岛素、糖浓度及其两者的联合作用对牛视网膜微血管内皮(BRE)细胞血管内皮生长因子(VEGF)表达的影响.方法 对照实验研究.采用选择性培养方法,培养BRE细胞,传代后分别在正常糖(5 mmol/L)或高糖(30 mmol/L)浓度下培养3 d,甘露醇平衡渗透压,血清饥饿12 h,给予或不给予100 nmol/L胰岛素作用24 h.实时荧光定量检测VEGF mRNA表达水平;人脐静脉血管内皮细胞增殖法、免疫荧光检测法、免疫印迹法检测VEGF蛋白表达水平.采用SPSS 12.0统计学软件对数据进行分析,胰岛素、糖浓度及其交互作用对BRE细胞的VEGF mRNA和VEGF蛋白表达水平的影响,采用2×2析因设计定量资料方差分析,以P<0.05作为差异有统计学意义.结果 胰岛素或高糖浓度可以显著提高BRE细胞的VEGFmRNA(F=5.67,9.04;均P<0.05)和VEGF蛋白(F=5.50,5.57;均P<0.05)表达水平,但胰岛素联合高糖浓度的作用较其单独作用减弱.结论 高糖浓度下可以降低胰岛素诱导的VEGF表达水平,因此,VEGF可能不是胰岛素治疗导致的糖尿病视网膜病变短期恶化的主要因素.     

Increased JNK phosphorylation and oxidative stress in response to increased glucose flux through increased GLUT1 expression in rat retinal endothelial cells

PURPOSE: To investigate whether increased glucose flux through increased glucose transporter1 (GLUT1) expression results in increased oxidative stress and increased c-jun N-terminal kinase (JNK) phosphorylation. METHODS: GLUT1-overexpressing cells were established using a rat retinal endothelial cell line. The intracellular reactive oxygen species was detected by the oxidation of 5- (and -6)-chloromethyl-2',7'-dichlorodihydrofluorescein diacetate, acetyl ester (CM-H2-DCFDA). Western blot was performed to determine JNK phosphorylation and lipid peroxidation. Differentially expressed genes were detected by cDNA microarray analysis and confirmed by Northern blot analysis. RESULTS: Clones overexpressing GLUT1 showed an approximate four- to eightfold increase in GLUT1 expression and a 44% increase in intracellular glucose concentrations. GLUT1-overexpressing cells had a 80% increase in DCF fluorescence and increased lipid peroxidation, as well as increased JNK phosphorylation. Analysis of differentially expressed genes in GLUT1-overexpressing cells showed increased expression of JNK interacting protein (JIP)-1, a scaffold protein necessary for JNK activation. Northern blot analysis confirmed upregulation of JIP-1. Immunoprecipitation showed that phosphorylated JNK, but not total JNK, coimmunoprecipitated with JIP-1 protein. At the cellular level, JIP-1 was predominantly localized in cytoplasm, especially in the perinuclear area in retinal endothelial cells. CONCLUSIONS: GLUT1 overexpression and increased glucose flux result in increased oxidative stress and JNK phosphorylation in immortalized rat retinal endothelial cells. Further studies are needed to understand molecular events after increased glucose flux in retinal endothelial cells and the relation between increased oxidative stress and JNK phosphorylation.     

17 Beta-estradiol increases VEGF receptor-2 and promotes DNA synthesis in retinal microvascular endothelial cells.

PURPOSE: Estrogen is known to promote angiogenesis in gonads. The presence of estrogen receptors in the vascular endothelium of organs other than gonads has been reported. The goal of this study was to determine whether estrogen promotes the proliferation of retinal microvascular endothelial cells and to explore the mechanism of it. METHODS: DNA was quantitated using primary cultures of bovine retinal endothelial cells that were incubated with different doses of 17 beta-estradiol (E2), VEGF, or both. The changes in expression level of VEGF and VEGF receptor-2 (VEGFR2) were measured using northern blot analysis after treatment with E2. The presence of estrogen receptors in the endothelial cells was studied by immunohistochemistry and western blot analysis. RESULTS: 17 Beta-estradiol (E2) increased the DNA level in bovine retinal capillary endothelial cells (BRECs) by 177% at 1 nM (P < 0.05) and 150% at 10 nM (P < 0.05) by comparison with unstimulated BREC. One hundred nanomole tamoxifen completely blocked the E2-induced DNA synthesis in BRECs. Ten nanomole E2 augmented vascular endothelial growth factor (VEGF)-induced DNA synthesis in BRECs significantly (160%, P < 0.01). Ten nanomole E2 also increased VEGF mRNA expression, which peaked after 24 hours (6.7 times, P < 0.05), and VEGF receptor-2 (VEGFR2) mRNA expression, which peaked after 9 hours (2.4 times, P < 0.05). The mRNA expression level of VEGFR2 peaked with 10 nM E2 (P < 0.05) and that of VEGF reached maximum with 1 nM E2 (15 times, P < 0.001). VEGFR2 and VEGF proteins increased in parallel with their mRNA levels. Immunocytochemistry showed estrogen receptor expression in BRECs, and western blot analysis indicated the presence of a 67-kDa protein that was compatible with the estrogen receptor. CONCLUSIONS: These findings suggest that E2 may stimulate BREC growth by the receptor-mediated pathway and that E2 may augment the VEGF-dependent angiogenesis partly through the upregulation of VEGFR2.     

Ultracytochemical localization of the erythrocyte/HepG2-type glucose transporter (GLUT1) in cells of the blood-retinal barrier in the rat.

The blood-retinal barrier is part of the blood-ocular barrier. Retinal pigment epithelial cells connected by tight junctions serve as an outer blood-retinal barrier, and the nonfenestrated endothelial cells of blood vessels sealed by tight junctions serve as an inner blood-retinal barrier. Using antibodies specific for the erythrocyte/HepG2-type glucose transporter (GLUT1), one isoform of facilitated-diffusion glucose transporters, it was found, by ultrastructural cytochemical examination, that GLUT1 in the rat was localized at both the apical and basolateral plasma membranes of retinal pigment epithelial cells. The fenestrated endothelial cells of the underlying choriocapillaries were negative for GLUT1. In the inner retina, GLUT1 was found at both the luminal and contraluminal plasma membranes of endothelial cells. These observations show that GLUT1 is concentrated at the critical plasma membranes of the blood-retinal barrier and may serve as the machinery for glucose transport across the barrier.     

VEGF activation of protein kinase C stimulates occludin phosphorylation and contributes to endothelial permeability

PURPOSE: VEGF is a potent permeabilizing factor that contributes to the pathogenesis of diabetic retinopathy and brain tumors. VEGF-induced vascular permeability in vivo and in cell culture requires PKC activity, but the mechanism by which PKC regulates barrier properties remains unknown. This study was conducted to examine how VEGF and diabetes alter occludin phosphorylation and endothelial cell permeability. METHODS: Chemical PKC inhibitors and activators were used to treat primary retinal endothelial cells in culture. In vitro kinase assays and Western blot analysis of two-dimensional (2D) and one-dimensional (1D) gel retardation assays were used to analyze occludin phosphorylation. Endothelial cell permeability was determined by measuring the flux of 70-kDa dextran through a cell monolayer in culture. Exogenous expression of a dominant negative PKCbetaII mutant (S217A) was used to assess the PKC dependence of VEGF-induced occludin phosphorylation and endothelial permeability. Occludin phosphorylation was also determined in retinas of streptozotocin-induced diabetic rats. RESULTS: VEGF stimulated the phosphorylation of occludin in primary retinal endothelial cells. Chemical inhibitors of PKC activity blocked the VEGF-induced increase in occludin phosphorylation, as assessed by 2D gel and gel retardation in Western blot analysis, and blocked part of the VEGF-induced monolayer permeability to 70-kDa dextran. Expression of a dominant negative PKCbetaII mutant blocked VEGF-induced occludin phosphorylation and endothelial permeability. Finally, elevated occludin phosphorylation was observed in the retina of diabetic animals. CONCLUSIONS: These results strongly suggest that VEGF-induced endothelial permeability requires PKC-dependent phosphorylation of occludin. Regulation of PKC activity and tight junction protein modifications may have therapeutic implications for treatment of diabetic retinopathy and brain tumors.     

Vascular endothelial growth factor expression and secretion by retinal pigment epithelial cells in high glucose and hypoxia is protein kinase C-dependent

Retinal pigment epithelial (RPE) cells express vascular endothelial growth factor (VEGF) in response to high glucose or hypoxia. We hypothesised that VEGF expression and secretion by RPE cells in high glucose and hypoxia are regulated by protein kinase C (PKC). Primary cultured RPE cells from Sprague-Dawley rats were growth-arrested for 48 hr in 0.5% FBS in 5.6 or 30 mm D-glucose. Cells were exposed to hypoxic conditions (<1% O(2), 5% CO(2)) for the last 15-18 hr of growth-arrest. PKC -alpha, -beta(1), -delta, -epsilon, and -zeta were expressed by RPE cells and exposure to high glucose for 48 hr had no effect on expression as demonstrated by Western immunoblotting. High glucose, hypoxia or VEGF stimulated translocation of a number of the PKC isozymes to the membrane or particulate fractions implying activation. In response to high glucose or acute phorbol myristate acetate (PMA) stimulation, VEGF mRNA analysed by RT-PCR was increased. Intracellular VEGF protein identified by immunoblotting and confocal immunofluorescence imaging was significantly increased by high glucose, hypoxia or acute PMA stimulation. Calphostin C or a specific inhibitor of PKC-zeta prevented high glucose-stimulated VEGF expression in high glucose. VEGF secretion, as measured by ELISA in the culture medium, was enhanced in hypoxia but not in high glucose. Following exposure of RPE cells to PMA for 24 hr, PKC-delta was significantly down regulated, whereas PKC-alpha, -beta, -epsilon and -zeta remained unchanged. Secretion of VEGF in normal or high glucose, or hypoxia was significantly reduced following treatment with PMA for 24 hr but not with the PKC-zeta inhibitor. We conclude that in high glucose and hypoxia PKC isozymes are activated and are necessary for VEGF expression. Secretion of VEGF is enhanced in hypoxia and appears to be regulated by PKC-delta. RPE cells may contribute to the pathogenesis of retinopathy caused by high glucose and hypoxia through the expression and secretion of VEGF that are regulated by PKC isozymes.     

A novel co-culture model of the blood-retinal barrier based on primary retinal endothelial cells, pericytes and astrocytes

Loss of blood-retinal barrier (BRB) properties is an important feature in the pathology of diabetic macular edema (DME), but cellular mechanisms underlying BRB dysfunction are poorly understood. Therefore, we developed and characterized a novel in?vitro BRB model, based on primary bovine retinal endothelial cells (BRECs). These cells were shown to maintain specific in?vivo BRB properties by expressing high levels of the endothelial junction proteins occludin, claudin-5, VE-cadherin and ZO-1 at cell borders, and the specific pumps glucose transporter-1 (GLUT1) and efflux transporter P-glycoprotein (MDR1). To investigate the influence of pericytes and astrocytes on BRB maintenance in?vitro, we compared five different co-culture BRB models, based on BRECs, bovine retinal pericytes (BRPCs) and rat glial cells. Co-cultures of BRECs with BRPCs and glial cells showed the highest trans-endothelial resistance (TEER) as well as decreased permeability of tracers after vascular endothelial growth factor (VEGF) stimulation, suggesting a major role for these cell types in maintaining barrier properties. To mimic the in?vivo situation of DME, we stimulated BRECs with VEGF, which downregulated MDR1 and GLUT1 mRNA levels, transiently reduced expression levels of endothelial junctional proteins and altered their organization, increased the number of intercellular gaps in BRECs monolayers and influence the permeability of the model to differently-sized molecular tracers. Moreover, as has been shown in?vivo, expression of plasmalemma vesicle-associated protein (PLVAP) was increased in endothelial cells in the presence of VEGF. This in?vitro model is the first co-culture model of the BRB that mimicks in?vivo VEGF-dependent changes occurring in DME.     

Ibrolipim对糖尿病小型猪视网膜血管内皮生长因子表达的影响

目的　观察血管内皮生长因子(VEGF)在早期糖尿病视网膜病变中的表达以及Ibrolipim (NO 1886)对 2型糖尿病小型猪血糖的影响;探讨药物Ibrolipim对视网膜VEGF的作用。 方法　采用高脂高蔗糖饲料喂养贵州小香猪,创建 2型糖尿病动物模型,并用Ibrolipim进行干预,用RT PCR、免疫组织化学和Westernblot技术检测VEGF转录和蛋白表达。 结果　正常组视网膜VEGFmRNA表达量少,免疫组织化学反应阳性较弱,VEGF蛋白表达较低;实验组视网膜VEGFmRNA表达上调,免疫组织化学反应呈强阳性 (P<0 01 ),VEGF蛋白表达增高;治疗组视网膜VEGFmRNA及VEGF蛋白表达介于其他两组之间。 结论　早期糖尿病视网膜中VEGF表达增高;Ibrolipim可通过降低血糖,改善视网膜组织缺氧,来抑制VEGFmRNA及蛋白的表达。     

Effect of curcumin on proliferation of human retinal endothelial cells under in vitro conditions

PURPOSE: To investigate the effect of high glucose on the proliferation of human retinal endothelial cells (HRECs) and to elucidate the possible mechanisms of antiangiogenic activity of curcumin, a diferuloylmethane. METHODS: Human retinal endothelial cells were isolated from the retinal tissue obtained from human donors and the culture system was established. The effect of curcumin on the proliferation of primary HRECs in the presence of low and high glucose was measured by MTT and thymidine uptake assays. Apoptosis was assessed by TUNEL assay and other adjuvant tools. Effect of curcumin on phorbol ester stimulated intracellular reactive oxygen species (ROS) generation in high glucose conditions was assessed by fluorescence assay. Finally, semiquantitative RT-PCR and Western blot analysis was performed to measure VEGF mRNA production and VEGF induced PKC-betaII translocation, respectively in the presence and absence of curcumin. RESULTS: HREC culture was established successfully at passages 3 and 4 at 80% confluence. Curcumin effectively inhibited endothelial cell proliferation in a dose-dependent manner. At a concentration of 10 microM, curcumin significantly inhibited HREC proliferation in high-glucose-treated cells, as verified by both MTT and thymidine uptake assay. Curcumin also showed a significant (P = 0.03) reduction of intracellular ROS generation in HRECs. RNA expression studies showed that curcumin had an inhibitory effect on the glucose-induced VEGF mRNA expression. In addition, VEGF-mediated, membrane-associated changes in the PKC-betaII translocation in HRECs was inhibited by 31% on treatment with 10 microM curcumin. CONCLUSIONS: These data suggest an underlying mechanism whereby curcumin induces the apoptosis in HRECs by the regulation of intracellular ROS generation, VEGF expression and release, and VEGF-mediated PKC-betaII translocation.     

Glucose-induced activation of glucose uptake in cells from the inner and outer blood-retinal barrier

PURPOSE: The purpose of this study was to elucidate in vitro the effect of elevated glucose on glucose uptake in the cells comprising the inner and outer blood-retinal barriers: human retinal pigment epithelial (hRPE) and human retinal vascular endothelial (hRVE) cells. METHODS: Primary cultures of hRPE and hRVE cells grown in 5.5 or 22 mM glucose or in 22 mM mannitol were used to measure the rates of glucose uptake with [(3)H]-3-O-methyl glucose as a tracer. GLUT1 expression was measured by Northern and western blot analyses. Cellular fractionation was performed by differential centrifugation. GLUT1 overexpression was accomplished by adenoviral transduction. RESULTS: Increasing media glucose from 5.5 to 22 mM for 30 minutes caused a 1.9-fold increase in the V(max) of glucose uptake in hRPE cells and a 2.5-fold increase in hRVE cells. These increases were nonosmotic and glucose specific, in that the exposure to 22 mM mannitol did not affect the V(max) of glucose uptake. mRNA, total protein expression, and translocation of GLUT1, the glucose transporter predominantly expressed in hRPE and hRVE cells, were not affected by 22 mM glucose for up to 48 hours. High-glucose effects on V(max) were abolished with 10 microg/mL of the microtubule assembly inhibitor nocodazole. hRPE cells transduced to overexpress GLUT1 showed a 1.5-fold increase in the V(max) for glucose uptake versus control-transduced cells. However, the magnitude of glucose-induced increase in glucose uptake was the same in GLUT1- and control-transduced cells. CONCLUSIONS: High glucose induced 1.9- and 2.5-fold increases in the V(max) of glucose uptake in hRPE and hRVE cells, respectively. These increases were not due to an increase in GLUT1 expression. The increases were dependent on microtubule integrity, but not on GLUT1 translocation. The mechanism of the increases is unknown. GLUT1 regulating protein(s) and/or novel glucose transporter(s) may be involved in the regulation of glucose uptake by glucose in the cells that comprise the blood-retinal barrier.     

土槿乙酸对高糖环境下人视网膜微血管内皮细胞表达血管内皮生长因子的影响

目的　观察土槿乙酸对高糖环境下人视网膜微血管内皮细胞（human retinal microvascular endothelial cells,HRMEC）表达血管内皮生长因子（vascular endothelial growth factor,VEGF）的影响。方法　体外培养HRMEC,根据不同的实验目的将其分为低糖空白对照（PL）组、土槿乙酸对照（P0）组、高糖对照（PH）组以及不同浓度土槿乙酸+高糖（P1、P2、P3）组。采用MTT法检测土槿乙酸作用后HRMEC的增殖情况,实时定量PCR和Western blot检测VEGF的mRNA和蛋白表达以及核转录因子FOXO3a的磷酸化,免疫荧光检测FOXO3a的核转位,染色质共沉淀检测FOXO3a和VEGF启动子的结合。结果　PH组HRMEC增殖率和VEGF表达水平明显高于PL组,并且随着时间的延长,HRMEC增殖率和VEGF表达均逐渐增高（均为P<0.05）;而经不同浓度土槿乙酸处理后的P1组、P2组和P3组中的HRMEC增殖率及VEGF表达水平与PH组相比,差异也均有统计学意义（均为P＜0.05）。Western blot结果显示,P0组HRMEC中FOXO3a磷酸化水平较低,PL组和PH组均有不同程度增高,而P1、P2、P3组随着土槿乙酸浓度的增加,FOXO3a磷酸化水平随之降低。免疫荧光和染色质共沉淀结果显示,P0组HRMEC中FOXO3a在细胞核内含量较多,和VEGF启动子的结合水平较高;而在PL组和PH组,细胞浆中FOXO3a明显增多,核内FOXO3a和VEGF的结合水平低于P0组;P1组、P2组及P3组中细胞核内FOXO3a以及FOXO3a-VEGF DNA复合体明显增多。结论　土槿乙酸能抑制高糖条件下HRMEC的增殖,最终激活核转录因子FOXO3a,从而下调HRMEC表达VEGF。     

A study of the effects of angiotensins 1, 2, 3 and bradykinin on the replication of bovine retinal capillary endothelial cells and pericytes.

The renin-angiotensin system of the human eye may play a role in the regulation of retinal blood flow and the development of new vessels. We have investigated whether angiotensins 1, 2 and 3 or bradykinin, in concentrations ranging between 1 x 10(-12) and 1 x 10(-6), have any mitogenic activity on cultured bovine retinal endothelial cells (BREC) and pericytes (BRP). Cell replication was assessed by 3H-thymidine incorporation and, in the case of BREC and AT-2, also by cell counts. AT-2 was also tested on bovine aortic EC (BAEC). None of the substances elicited any response on BREC, BRP or BAEC. Whether angiotensin(s) induce angiogenesis in retinal vessels in vivo remains to be established but this does not appear to occur through direct stimulation of cell replication.     

Selective relocalization and proteasomal downregulation of PKCalpha induced by platelet-activating factor in retinal pigment epithelium

PURPOSE: Protein kinases C (PKCs) are key cell-signaling mediators in retinal physiology and pathophysiology. The cellular localization of PKC isoforms is important in defining their activity and specificity; the present study investigated the modulatory potential of the proinflammatory mediator platelet-activating factor (PAF) on the subcellular distribution of PKCalpha, beta, and delta isotypes. METHODS: This study used real-time visualization of green fluorescent protein fused to PKCalpha, beta, or delta in the human retinal pigment epithelial (RPE) cell line ARPE-19. RESULTS: In PAF-stimulated ARPE-19 cells, PKCalpha translocated to the plasma membrane and then colocalized with Golgi markers p230 and GM130; PKCbeta translocated to the plasma membrane but not to the Golgi; and PKCdelta translocated to the Golgi. Pretreatment with PKC inhibitor calphostin C abolished the PAF-induced translocation of PKCalpha to the plasma membrane or to the Golgi, but the Golgi inhibitor Brefeldin A only prevented the accumulation of PKCalpha in Golgi, without affecting its membrane relocalization. PAF promoted depletion of PKCalpha and delta isoforms but not that of PKCbeta. Proteasome inhibitors lactacystin and MG-132 prevented the PAF-induced depletion of PKCalpha, but the inhibitor of lysosomal proteolysis E-64d was ineffective in rescuing PKCalpha. CONCLUSIONS: These results suggest that the PAF-induced downregulation of PKCalpha occurs principally through the proteasomal pathway. This remarkable PAF-mediated diversity in PKC translocation and downregulation highlights the significance of isotype-specific PKC activation in signaling pathways in ARPE-19 cells. These signaling events may be critical during RPE responses to oxidative stress, inflammation, and retinal degenerations, when PAF production is enhanced.