Oxidized LDL inhibits vascular endothelial growth factor-induced endothelial cell migration by an inhibitory effect on the Akt/endothelial nitric oxide synthase pathway

BACKGROUND: Oxidized LDL (oxLDL) inhibits endothelial cell (EC) migration. Stimulating ECs with vascular endothelial growth factor (VEGF) leads to the activation of Akt/protein kinase B, which in turn activates endothelial nitric oxide synthase (eNOS) by phosphorylation on serine 1177. VEGF-induced cell migration is dependent on the generation of nitric oxide (NO). Therefore, we investigated whether oxLDL affects EC migration by an inhibitory effect on the Akt/eNOS pathway. METHODS AND RESULTS: During an in vitro "scratched wound assay," oxLDL dose-dependently inhibited the VEGF-induced migration of human umbilical vein endothelial cells. Western blot analysis revealed that oxLDL dose- and time-dependently led to dephosphorylation and thus deactivation of Akt. Moreover, oxLDL inhibited the VEGF-induced generation of NO, as detected and quantified using a fluorescent NO indicator, 4,5-diaminofluorescein diacetate. Overexpression of a constitutively active Akt construct (Akt T308D/S473D) or a phosphomimetic eNOS construct (eNOS S1177D) almost completely reversed the inhibitory effect of oxLDL on VEGF-induced EC migration and NO generation. CONCLUSIONS: Our data indicate that oxLDL-induced dephosphorylation of Akt, followed by impaired eNOS activation, reduces the intracellular level of NO and thereby inhibits VEGF-induced EC migration.     

Anti-apoptotic signaling by hepatocyte growth factor/Met via the phosphatidylinositol 3-kinase/Akt and mitogen-activated protein kinase pathways

Hepatocyte growth factor (HGF) is a ligand of the receptor tyrosine kinase encoded by the c-Met protooncogene. HGF/Met signaling has multifunctional effects on various cell types. We sought to determine the role of HGF/Met in apoptosis and identify signal transducers involved in this process. In experiments with human SK-LMS-1 leiomyosarcoma cells, we show that the Akt kinase is activated by HGF in a time- and dose-dependent manner by phosphatidylinositol 3-kinase (PI3-kinase). Akt is also activated by active tumorigenic forms of Met, i.e., ligand-independent Tpr-Met, a truncated and constitutively dimerized form of Met, and a mutationally activated version of Met corresponding to that found in human hereditary papillary renal carcinoma. In NIH 3T3 cells transfected with wild-type Met, HGF inhibits apoptosis induced by serum starvation and UV irradiation. HGF-induced survival correlates with Akt activity and is inhibited by the specific PI3-kinase inhibitor LY294002, indicating that HGF inhibits cell death through the PI3-kinase/Akt signal transduction pathway. Furthermore, transiently transfected Tpr-Met activates Akt (both Akt1 and Akt2) and protects cells from apoptosis. Mitogen-activated protein kinase (MAPK) also is activated by HGF and rescues cells from apoptosis, although the cytoprotective effect is less marked than for PI3-kinase/Akt. Blocking MAPK with the specific MAPK kinase inhibitor PD098059 impairs the ability of HGF to promote cell survival. Similar results were obtained with NIH 3T3 cells expressing the fusion protein Trk-Met and stimulated with nerve growth factor, the Trk ligand. These results demonstrate that HGF/Met is capable of protecting cells from apoptosis by using both PI3-kinase/Akt and, to a lesser extent, MAPK pathways.     

Ligand-independent activation of vascular endothelial growth factor receptor 2 by fluid shear stress regulates activation of endothelial nitric oxide synthase

Fluid shear stress generated by blood flowing over the endothelium is a major determinant of arterial tone, vascular remodeling, and atherogenesis. Nitric oxide (NO) produced by endothelial NO synthase (eNOS) plays an essential role in regulation of vascular function and structure by blood flow, but the molecular mechanisms that transduce mechanical force to eNOS activation are not well understood. In this study, we found that laminar flow (shear stress=12 dyne/cm2) rapidly activates vascular endothelial growth factor receptor 2 (VEGFR2) in a ligand-independent manner and leads to eNOS activation in cultured endothelial cells. Flow-stimulated VEGFR2 recruits phosphoinositide 3-kinase and mediates activation of Akt and eNOS. Inhibiting VEGFR2 kinase with selective inhibitors blocks flow-induced activation of Akt and eNOS and production of NO. Decreasing VEGFR2 expression with antisense VEGFR2 oligonucleotides significantly attenuates activation of Akt and eNOS. Furthermore, Src kinases are involved in flow-stimulated VEGFR2 because inhibiting Src kinases by PP2, a selective inhibitor for Src kinases, abolishes flow-induced VEGFR2 tyrosine phosphorylation and downstream signaling. Finally, we show that inhibiting VEGFR2 kinase significantly reduces flow-mediated NO-dependent arteriolar dilation in vivo. These data identify VEGFR2 as a key mechanotransducer that activates eNOS in response to blood flow.     

Tumor necrosis factor-alpha protects synovial cells from nitric oxide induced apoptosis through phosphoinositide 3-kinase Akt signal transduction

OBJECTIVE: To investigate the anti-apoptotic role of tumor necrosis factor-a (TNF-a) and its signaling pathways in cultured human fibroblast-like synoviocytes (FLS) from patients with rheumatoid arthritis. METHODS: FLS were cultured in Dulbecco's modified Eagle's medium. Apoptotic cells were identified by TUNEL assay and Hoechst staining. Cell viability was determined by the MTT method. Expression of phospho-Akt and phospho-BAD was measured by Western blotting. RESULTS: A 24-h TNF-a treatment prevented FLS apoptosis induced by nitric oxide (NO) donor sodium nitroprusside dihydrate (SNP), achieving 70% protection. At 1-10 ng x ml-1 concentrations, TNF-a induced phosphorylation of Akt and BAD in a time and concentration-dependent manner. This effect was blocked by treatment with both LY294002 and nuclear factor-kB inhibitor pyrrolidine-dithiocarbamate. CONCLUSION: TNF-a has an anti-apoptotic effect in human FLS. Activation of Akt and BAD may have an important role in this process.     

胰岛素通过激活P13K／mTOR通路诱导人肾小球系膜细胞血管内皮细胞生长因子转录

目的探讨胰岛素诱导人肾小球系膜细胞（HMC）血管内皮细胞生长因子（VEGF）基因转录机制。方法（1）用VEGF报告质粒或低氧诱导因子1（HIF-1）结合位点畸变的VEGF mut报告质粒转染HMC,荧光素酶分析法检测其转录活性;（2）应用Real—time PCR、Western blot法分别检测HIF-1α mRNA和蛋白表达。结果（1）胰岛素呈剂量依赖性增加VEGF基因转录,在100nmol／L时达高峰,为未刺激组的2．14±0．17倍（P〈0．01）,但对转染VEGF mut报告质粒的HMC VEGF基因转录无影响;（2）Ly294002和雷帕霉素均可抑制胰岛素诱导的VEGF基因转录（P〈0．01）;（3）胰岛素呈时间依赖性上凋HIF-1α蛋白表达,4h达高峰,为对照组的2．35±0．35倍（P〈0．01）,但对其mRNA表达无影响。结论胰岛素通过激活P13K／mTOR通路和上调HIF-1α蛋白表达诱导HMC VEGF基因转录。     

Transforming growth factor-beta stimulates vascular endothelial growth factor production by folliculostellate pituitary cells

TGF-beta isoforms are expressed in the anterior pituitary and modulate the growth and function of endocrine pituitary cells. Recently, TGF-beta has been shown to stimulate growth and basic fibroblast growth factor secretion in nonendocrine folliculostellate (FS) pituitary cells. We therefore studied whether the production of FS cell-derived vascular endothelial growth factor (VEGF), the most important regulator of vascular permeability and angiogenesis, is affected by TGF-beta. We observed by RT-PCR that TtT/GF cells, which are FS mouse pituitary tumor cells, synthesize TGF-beta1, -beta2, and -beta3. They also express TGF-beta receptors types 1 and 2, as well as Smad2, Smad3, and Smad4 proteins, which are essential for TGF-betabinding and signaling. Stimulation of TtT/GF cells with either TGF-beta1 or TGF-beta3 induced a rapid translocation of Smad2 into the cell nuclei. Both TGF-beta isoforms dose dependently stimulated VEGF production in TtT/GF cells, but not in lactosomatotroph GH3 cells. Time-course studies and suppression of TGF-beta-induced VEGF production by cycloheximide suggest that TGF-beta induces de novo synthesis of VEGF in folliculostellate cells, which is completely blocked by dexamethasone. In primary rat pituitary cell cultures, TGF-beta1 and -beta3 stimulated VEGF production. TGF-beta stimulation of VEGF production by folliculostellate cells could modulate intrapituitary vascular permeability and integrity as well as angiogenesis in an auto-/paracrine manner.     

Reconstituted high-density lipoprotein inhibits thrombin-induced endothelial tissue factor expression through inhibition of RhoA and stimulation of phosphatidylinositol 3-kinase but not Akt/endothelial nitric oxide synthase

Endothelial cells express negligible amounts of tissue factor (TF) that can be induced by thrombin, which is important for acute coronary syndromes. Recent research suggests that endothelial TF expression is positively regulated by RhoA and p38mapk, but negatively by Akt/endothelial nitric oxide synthase (eNOS) pathway. High-density lipoprotein (HDL) is atheroprotective and exerts antiatherothrombotic effect. This study investigated the effect of a reconstituted HDL (rHDL) on endothelial TF expression induced by thrombin and the underlying mechanisms. In cultured human umbilical vein and aortic endothelial cells, thrombin (4 U/mL, 4 hours) increased TF protein level, which was reduced by rHDL (0.1 mg/mL, 43% inhibition, n=3 to 7, P<0.01). Activation of RhoA but not p38mapk by thrombin was prevented by rHDL. rHDL stimulated Akt/eNOS pathway. The phosphatidylinositol 3-kinase (PI3K) inhibitors wortmannin or LY294002 abolished the activation of Akt/eNOS and reversed the inhibitory effect of rHDL on TF expression. Adenoviral expression of the active PI3K mutant (p110) reduced TF expression stimulated by thrombin without inhibiting RhoA activation, whereas expression of the active Akt mutant (m/p) further facilitated TF upregulation by thrombin. Moreover, a dominant-negative Akt mutant (KA) reduced thrombin's effect and did not reverse the rHDL's inhibitory effect on TF expression. Inhibition of eNOS by N(omega)-nitro-L-arginine methyl ester (100 micromol/L) did not affect the rHDL's effect. In conclusion, rHDL inhibits thrombin-induced human endothelial TF expression through inhibition of RhoA and activation of PI3K but not Akt/eNOS. These findings implicate a novel mechanism of antiatherothrombotic effects of HDL.     

Activation of endothelial nitric oxide synthase by cilostazol via a cAMP/protein kinase A- and phosphatidylinositol 3-kinase/Akt-dependent mechanism

We investigated the effect of cilostazol on nitric oxide (NO) production in human aortic endothelial cells (HAEC). Cilostazol increased NO production in a concentration-dependent manner, and NO production was also increased by other cyclic-AMP (cAMP)-elevating agents (forskolin, cilostamide, and rolipram). Cilostazol increased intracellular cAMP level, and that effect was enhanced in the presence of forskolin. In Western blot analysis, cilostazol increased phosphorylation of endothelial nitric oxide synthase (eNOS) at Ser(1177) and of Akt at Ser(473) and dephosphorylation of eNOS at Thr(495). Cilostazol's regulation of eNOS phosphorylation was reversed by protein kinase A inhibitor peptide (PKAI) and by LY294002, a phosphatidylinositol 3-kinase (PI3K) inhibitor. Moreover, the cilostazol-induced increase in NO production was inhibited by PKAI, LY294002, and N(G)-nitro-l-arginine methyl ester hydrochloride (l-NAME), a NOS inhibitor. In an in vitro model of angiogenesis, cilostazol-enhanced endothelial tube formation, an effect that was completely attenuated by inhibitors of PKA, PI3K, and NOS. These results suggest that cilostazol induces NO production by eNOS activation via a cAMP/PKA- and PI3K/Akt-dependent mechanism and that this effect is involved in capillary-like tube formation in HAEC.     

Effect of aerobic exercise combined with resistive exercise on vascular endothelial function and its impact on phosphatidylinositol 3-kinase/protein kinase B/endothelial nitric oxide synthase pathway in diabetic rats

正Objective To investigate the effects of aerobic exercise combined with resistive exercise on vascular endothelial function and its impact on phosphatidylinosito13-kinase/protein kinase B/endothelial nitric oxide synthase(PI3K/Akt/e NOS)pathway in diabetic rats.MethodsSD rats were randomly divided into control group(NC),     

胰岛素通过激活P13K/mTOR通路诱导人肾小系膜细胞血管内皮细胞生长因子转录

目的 探讨胰岛素诱导人肾小球系膜细胞(HMC)血管内皮细胞生长因子(VEGF)基因转录机制. 方法 (1)用VEGF报告质粒或低氧诱导因子1(HIF-1)结合位点畸变的VEGF mut报告质粒转染HMC,荧光素酶分析法检测其转录活性;(2)应用Real-time PCR、Western blot法分别检测HIF-1α mRNA和蛋白表达. 结果 (1)胰岛素呈剂量依赖性增加VEGF基因转录,在100nmol/L时达高峰,为未刺激组的2.14±0.17倍(P<0.01),但对转染VEGF mut报告质粒的HMC VEGF基因转录无影响;(2)Ly294002和雷帕霉素均可抑制胰岛素诱导的VEGF基因转录(P<0.01);(3)胰岛素呈时间依赖性上调HIF-1α蛋白表达,4h达高峰,为对照组的2.35±0.35倍(P<0.01),但对其mRNA表达无影响. 结论 胰岛素通过激活P13K/mTOR通路和上调HIF-1α蛋白表达诱导HMC VEGF基因转录.