Acute laminar shear stress reversibly increases human glomerular endothelial cell permeability via activation of endothelial nitric oxide synthase

Laminar shear stress is a key determinant of systemic vascular behavior, including through activation of endothelial nitric oxide synthase (eNOS), but little is known of its role in the glomerulus. We confirmed eNOS expression by glomerular endothelial cells (GEnC) in tissue sections and examined effects of acute exposure (up to 24 h) to physiologically relevant levels of laminar shear stress (10-20 dyn/cm(2)) in conditionally immortalized human GEnC. Laminar shear stress caused an orientation of GEnC and stress fibers parallel to the direction of flow and induced Akt and eNOS phosphorylation along with NO production. Inhibition of the phophatidylinositol (PI)3-kinase/Akt pathway attenuated laminar shear stress-induced eNOS phosphorylation and NO production. Laminar shear stress of 10 dyn/cm(2) had a dramatic effect on GEnC permeability, reversibly decreasing the electrical resistance across GEnC monolayers. Finally, the laminar shear stress-induced reduction in electrical resistance was attenuated by the NOS inhibitors l-N(G)-monomethyl arginine (l-NMMA) and l-N(G)-nitroarginine methyl ester (l-NAME) and also by inhibition of the PI3-kinase/Akt pathway. Hence we have shown for GEnC in vitro that acute permeability responses to laminar shear stress are dependent on NO, produced via activation of the PI3-kinase/Akt pathway and increased eNOS phosphorylation. These results suggest the importance of laminar shear stress and NO in regulating the contribution of GEnC to the permeability properties of the glomerular capillary wall.     

KLF2-dependent, shear stress-induced expression of CD59: a novel cytoprotective mechanism against complement-mediated injury in the vasculature

Complement activation may predispose to vascular injury and atherogenesis. The atheroprotective actions of unidirectional laminar shear stress led us to explore its influence on endothelial cell expression of complement inhibitory proteins CD59 and decay-accelerating factor. Human umbilical vein and aortic endothelial cells were exposed to laminar shear stress (12 dynes/cm(2)) or disturbed flow (+/- 5 dynes/cm(2) at 1Hz) in a parallel plate flow chamber. Laminar shear induced a flow rate-dependent increase in steady-state CD59 mRNA, reaching 4-fold at 12 dynes/cm(2). Following 24-48 h of laminar shear stress, cell surface expression of CD59 was up-regulated by 100%, whereas decay-accelerating factor expression was unchanged. The increase in CD59 following laminar shear was functionally significant, reducing C9 deposition and complement-mediated lysis of flow-conditioned endothelial cells by 50%. Although CD59 induction was independent of PI3-K, ERK1/2 and nitric oxide, an RNA interference approach demonstrated dependence upon an ERK5/KLF2 signaling pathway. In contrast to laminar shear stress, disturbed flow failed to induce endothelial cell CD59 protein expression. Likewise, CD59 expression on vascular endothelium was significantly higher in atheroresistant regions of the murine aorta exposed to unidirectional laminar shear stress, when compared with atheroprone areas exposed to disturbed flow. We propose that up-regulation of CD59 via ERK5/KLF2 activation leads to endothelial resistance to complement-mediated injury and protects from atherogenesis in regions of laminar shear stress.     

IP(3)-dependent intracellular Ca(2+) release is required for cAMP-induced c-fos expression in hippocampal neurons

Endothelial argininosuccinate synthetase 1 (ASS1) regulates the provision of l-arginine to nitric oxide synthase 3 (NOS3). Previous studies demonstrated that endothelial ASS1 expression was induced by laminar shear stress (LSS) and that this enzyme plays a role in maintaining anti-inflammatory microenvironments through enhancing NO production. However, differently from the case of NOS3, the regulatory mechanism for the endothelial ASS1 expression in response to LSS is not well understood. This study addressed a specific issue whether endothelial ASS1 expression is regulated by Kruppel-like factors (KLFs) that are presumed to coordinate endothelial gene expressions in response to LSS. The cDNA microarray data indicated that LSS stimulated the expression of numerous KLFs in human umbilical vein endothelial cells. KLF4 showed the highest fold increase and LSS-dependent increases of KLF4 and most other KLFs were similar in young versus senescent endothelial cells. LSS-induced KLF4 expression was verified by RT-PCR and Western blotting. LSS-induced ASS1 expression and NO production were suppressed by a small interfering RNA for KLF4. The ectopic expression of KLF4 led to the increase of ASS1 expression and NO production. The present study demonstrated a key regulatory role of KLF4 in the endothelial ASS1 expression and NO production in response to LSS.     

Recruitment of endothelial caveolae into mechanotransduction pathways by flow conditioning in vitro

The luminal surface of rat lung microvascular endothelial cells in situ is sensitive to changing hemodynamic parameters. Acute mechanosignaling events initiated in response to flow changes in perfused lung microvessels are localized within specialized invaginated microdomains called caveolae. Here we report that chronic exposure to shear stress alters caveolin expression and distribution, increases caveolae density, and leads to enhanced mechanosensitivity to subsequent changes in hemodynamic forces within cultured endothelial cells. Flow-preconditioned cells expressed a fivefold increase in caveolin (and other caveolar-residing proteins) at the luminal surface compared with no-flow controls. The density of morphologically identifiable caveolae was enhanced sixfold at the luminal cell surface of flow-conditioned cells. Laminar shear stress applied to static endothelial cultures (flow step of 5 dyn/cm2), enhanced the tyrosine phosphorylation of luminal surface proteins by 1.7-fold, including caveolin-1 by 1.3-fold, increased Ser1179 phosphorylation of endothelial nitric oxide synthase (eNOS) by 2.6-fold, and induced a 1.4-fold activation of mitogen-activated protein kinases (ERK1/2) over no-flow controls. The same shear step applied to endothelial cells preconditioned under 10 dyn/cm2 of laminar shear stress for 6 h and induced a sevenfold increase of total phosphotyrosine signal at the luminal endothelial cell surface enhanced caveolin-1 tyrosine phosphorylation 5.8-fold and eNOS phosphorylation by 3.3-fold over static control values. In addition, phosphorylated caveolin-1 and eNOS proteins were preferentially localized to caveolar microdomains. In contrast, ERK1/2 activation was not detected in conditioned cells after acute shear challenge. These data suggest that cultured endothelial cells respond to a sustained flow environment by directing caveolae to the cell surface where they serve to mediate, at least in part, mechanotransduction responses.     

Ivabradine Prevents Low Shear Stress Induced Endothelial Inflammation and Oxidative Stress via mTOR/eNOS Pathway

Ivabradine not only reduces heart rate but has other cardiac and vascular protective effects including anti-inflammation and anti-oxidation. Since endothelial nitric oxide synthase (eNOS) is a crucial enzyme in maintaining endothelial activity, we aimed to investigate the impact of ivabradine in low shear stress (LSS) induced inflammation and endothelial injury and the role of eNOS played in it. Endothelial cells (ECs) were subjected to LSS at 2dyne/cm², with 1 hour of ivabradine (0.04μM) or {"type":"entrez-nucleotide","attrs":{"text":"LY294002","term_id":"1257998346","term_text":"LY294002"}}LY294002 (10μM) pre-treatment. The mRNA expression of IL-6, VCAM-1 along with eNOS were measured by QPCR. Reactive oxygen species (ROS) was detected by dihydroethidium (DHE) and DCF, and protein phosphorylation was detected by western blot. It demonstrated that ivabradine decreased LSS induced inflammation and oxidative stress in endothelial cells. Western blot showed reduced rictor and Akt-Ser473 as well as increased eNOS-Thr495 phosphorylation. However, mTORC1 pathway was only increased when LSS applied within 30 minutes. These effects were reversed by ivabradine. It would appear that ivabradine diminish ROS generation by provoking mTORC2/Akt phosphorylation and repressing mTORC1 induced eNOS-Thr495 activation. These results together suggest that LSS induced endothelial inflammation and oxidative stress are suppressed by ivabradine via mTORC2/Akt activation and mTORC1/eNOS reduction.     

Induction of endothelial nitric-oxide synthase phosphorylation by the raloxifene analog LY117018 is differentially mediated by Akt and extracellular signal-regulated protein kinase in vascular endothelial cells

Raloxifene is a tissue-selective estrogen receptor modulator. The effect of estrogen on cardiovascular disease is mainly dependent on direct actions on the vascular wall involving activation of endothelial nitric oxide synthase (eNOS) via Akt and extracellular signal-regulated protein kinase (ERK) cascades. Although raloxifene is also known to activate eNOS in the vascular endothelium, the molecular mechanism responsible for this effect remains to be elucidated. In studies of both human umbilical vein endothelial cells and simian virus 40-transformed rat lung vascular endothelial cells (TRLECs), the raloxifene analog LY117018 caused acute phosphorylation of eNOS that was unaffected by actinomycin D and was blocked by the pure estrogen receptor antagonist ICI182,780. Activation of Akt by raloxifene reached a plateau at 15-30 min and declined thereafter, a similar time frame to that of Akt activation by 17beta-estradiol. On the other hand, both activation and phosphorylation of ERK by raloxifene showed a biphasic pattern (peaks at 5 min and 1 h), whereas ERK activation and phosphorylation by 17beta-estradiol reached a plateau at 5 min and declined thereafter. A MEK inhibitor, PD98059, had no effect on the raloxifene-induced Akt activity, suggesting an absence of cross-talk between the ERK and Akt cascades. Either exogenous expression of a dominant-negative Akt or pretreatment of TRLECs with PD98059 decreased the raloxifene-induced eNOS phosphorylation. Moreover, raloxifene stimulated the activation of Akt, ERK, and eNOS in Chinese hamster ovary cells expressing estrogen receptor alpha but not Chinese hamster ovary cells expressing estrogen receptor beta. Our findings suggest that raloxifene-induced eNOS phosphorylation is mediated by estrogen receptor alpha via a nongenomic mechanism and is differentially mediated by Akt- and ERK-dependent cascades.     

Endothelial nitric oxide synthase is dynamically expressed during bone marrow stem cell differentiation into endothelial cells

This study was designed to investigate the developmental expression of endothelial nitric oxide synthase (eNOS) during stem cell differentiation into endothelial cells and to examine the functional status of the newly differentiated endothelial cells. Mouse adult multipotent progenitor cells (MAPCs) were used as the source of stem cells and were induced to differentiate into endothelial cells with vascular endothelial growth factor (VEGF) in serum-free medium. Expression of eNOS in the cells during differentiation was evaluated with real-time PCR, nitric oxide synthase (NOS) activity, and Western blot analysis. It was found that eNOS, but no other NOS, was present in undifferentiated MAPCs. eNOS expression disappeared in the cells immediately after induction of differentiation. However, eNOS expression reoccurred at day 7 during differentiation. Increasing eNOS mRNA, protein content, and activity were observed in the cells at days 14 and 21 during differentiation. The differentiated endothelial cells formed dense capillary networks on growth factor-reduced Matrigel. VEGF-stimulated phosphorylation of extracellular signal-regulated kinase (ERK)-1 and ERK-2 occurred in these cells, which was inhibited by NOS inhibitor N(G)-nitro-L-arginine methyl ester. In conclusion, these data demonstrate that eNOS is present in MAPCs and is dynamically expressed during the differentiation of MAPCs into endothelial cells in vitro.     

Kruppel-like Factor 4 Is a Novel Mediator of Kallistatin in Inhibiting Endothelial Inflammation via Increased Endothelial Nitric-oxide Synthase Expression

Kallistatin is a plasma protein that exhibits pleiotropic effects in vasodilation, anti-angiogenesis, and anti-inflammation. To isolate a kallistatin-binding protein that mediates the vascular actions of kallistatin, we screened and identified a positive clone from a human heart cDNA expression library by using an alkaline phosphatase-kallistatin fusion protein binding assay. Sequence analysis revealed that kallistatin-binding protein is human Kruppel-like factor 4 (KLF4). KLF4 was localized on the plasma membrane of HEK-293 cells and endothelial cells overexpressing KLF4. KLF4 and kallistatin complex formation was identified in endothelial cells by immunoprecipitation followed by immunoblotting. We showed that kallistatin inhibits tumor necrosis factor-α-induced NF-κB activation, as well as vascular cell adhesion molecule-1 and monocyte chemoattractant protein-1 expression in endothelial cells, whereas knockdown of KLF4 by small interfering RNA oligonucleotide abolished the effect of kallistatin. Kallistatin increased endothelial nitric-oxide synthase (eNOS) expression and nitric oxide levels, and these effects were also blocked by KLF4 small interfering RNA oligonucleotide. Moreover, inhibition of eNOS by RNA interference or by NOS inhibitor abolished the blocking effect of kallistatin on vascular cell adhesion molecule-1 and monocyte chemoattractant protein-1 expression. In summary, we identified KLF4 as a kallistatin-binding protein, which has a novel role in mediating the anti-inflammatory actions of kallistatin via increasing eNOS expression in endothelial cells. This study provides a new target for modulating endothelial function in vascular disease.     

Signaling pathway of nitric oxide production induced by ginsenoside Rb1 in human aortic endothelial cells: a possible involvement of androgen receptor

Ginsenosides have been shown to stimulate nitric oxide (NO) production in aortic endothelial cells. However, the signaling pathways involved have not been well studied in human aortic endothelial cells. The present study was designed to examine whether purified ginsenoside Rb1, a major active component of ginseng could actually induce NO production and to clarify the signaling pathway in human aortic endothelial cells. NO production was rapidly increased by Rb1. The rapid increase in NO production was abrogated by treatment with nitric oxide synthetase inhibitor, L-NAME. Rb1 stimulated rapid phosphorylation of Akt (Ser473), ERK1/2 (Thr202/Thr204) and eNOS (Ser1177). Rapid phosphorylation of eNOS (Ser1177) was prevented by SH-5, an Akt inhibitor or wortmannin, PI3-kinase inhibitor and partially attenuated by PD98059, an upstream inhibitor for ERK1/2. Interestingly, NO production and eNOS phosphorylation at Ser1177 by Rb1 were abolished by androgen receptor antagonist, nilutamide. The results suggest that PI3kinase/Akt and MEK/ERK pathways and androgen receptor are involved in the regulation of acute eNOS activation by Rb1 in human aortic endothelial cells.     

Involvement of androgen receptor in nitric oxide production induced by icariin in human umbilical vein endothelial cells

Icariin, a flavonoid isolated from Epimedii herba, stimulated phosphorylation of endothelial nitric oxide synthase (eNOS) at Ser1177, Akt (Ser473) and ERK1/2 (Thr202/Tyr204). The icariin-induced eNOS phosphorylation was abolished by an androgen receptor (AR) antagonist, nilutamide in human umbilical vein endothelial cells (HUVECs). Furthermore, it was also reduced in the cells transfected with small interfering RNA in which the expression of AR was broken down. The icariin-induced eNOS phosphorylation was inhibited by wortmannin, a phosphatidylinositol 3-kinase (PI3K) inhibitor and partially attenuated by PD98059, an upstream inhibitor for ERK1/2. These data suggest that icariin stimulates release of NO by AR-dependent activation of eNOS in HUVECs. PI3K/Akt and MAPK-ERK kinase (MEK)/ERK1/2 pathways were involved in the phosphorylation of eNOS by icariin.     

l-Theanine promotes nitric oxide production in endothelial cells through eNOS phosphorylation

Consumption of tea (Camellia sinensis) improves vascular function and is linked to lowering the risk of cardiovascular disease. Endothelial nitric oxide is the key regulator of vascular functions in endothelium. In this study, we establish that l-theanine, a non-protein amino-acid found in tea, promotes nitric oxide (NO) production in endothelial cells. l-theanine potentiated NO production in endothelial cells was evaluated using Griess reaction, NO sensitive electrode and a NO specific fluorescent probe (4-amino-5-methylamino-2',7'-difluororescein diacetate). l-Theanine induced NO production was partially attenuated in presence of l-NAME or l-NIO and completely abolished using eNOS siRNA. eNOS activation was Ca^2 + and Akt independent, as assessed by fluo-4AM and immunoblotting experiments, respectively and was associated with phosphorylation of eNOS Ser 1177. eNOS phosphorylation was inhibited in the presence of ERK1/2 inhibitor, PD-98059 and partially inhibited by PI3K inhibitor, LY-294002 and Wortmanin suggesting PI3K-ERK1/2 dependent pathway. Increased NO production was associated with vasodilation in ex ovo (chorioallantoic membrane) model. These results demonstrated that l-theanine administration in vitro activated ERK/eNOS resulting in enhanced NO production and thereby vasodilation in the artery. The results of our experiments are suggestive of l-theanine mediated vascular health benefits of tea.     

Flow-dependent regulation of endothelial nitric oxide synthase: role of protein kinases

Vascular endothelial cells are directly and continuously exposed to fluid shear stress generated by blood flow. Shear stress regulates endothelial structure and function by controlling expression of mechanosensitive genes and production of vasoactive factors such as nitric oxide (NO). Though it is well known that shear stress stimulates NO production from endothelial nitric oxide synthase (eNOS), the underlying molecular mechanisms remain unclear and controversial. Shear-induced production of NO involves Ca²⁺/calmodulin-independent mechanisms, including phosphorylation of eNOS at several sites and its interaction with other proteins, including caveolin and heat shock protein-90. There have been conflicting results as to which protein kinases—protein kinase A, protein kinase B (Akt), other Ser/Thr protein kinases, or tyrosine kinases—are responsible for shear-dependent eNOS regulation. The functional significance of each phosphorylation site is still unclear. We have attempted to summarize the current status of understanding in shear-dependent eNOS regulation. shear stress; nitric oxide; endothelial cells; protein kinases     

Endothelial argininosuccinate synthetase 1 regulates nitric oxide production and monocyte adhesion under static and laminar shear stress conditions

Laminar shear stress (LSS) is known to increase endothelial nitric oxide (NO) production, which is essential for vascular health, through expression and activation of nitric oxide synthase 3 (NOS3). Recent studies demonstrated that LSS also increases the expression of argininosuccinate synthetase 1 (ASS1) that regulates the provision of L-arginine, the substrate of NOS3. It was thus hypothesized that ASS1 might contribute to vascular health by enhancing NO production in response to LSS. This hypothesis was pursued in the present study by modulating NOS3 and ASS1 levels in cultured endothelial cells. Exogenous expression of either NOS3 or ASS1 in human umbilical vein endothelial cells increased NO production and decreased monocyte adhesion stimulated by tumor necrosis factor-α (TNF-α). The latter effect of overexpressed ASS1 was reduced when human umbilical vein endothelial cells were co-treated with small interfering RNAs (siRNAs) for ASS1 or NOS3. SiRNAs of NOS3 and ASS1 attenuated the increase of NO production in human aortic endothelial cells stimulated by LSS (12 dynes·cm(-2)) for 24 h. LSS inhibited monocyte adhesion to human aortic endothelial cells stimulated by TNF-α, but this effect of LSS was abrogated by siRNAs of NOS3 and ASS1 that recovered the expression of vascular cell adhesion molecule-1. The current study suggests that the expression of ASS1 harmonized with that of NOS3 may be important for the optimized endothelial NO production and the prevention of the inflammatory monocyte adhesion to endothelial cells.     

Rho GTPase/Rho kinase negatively regulates endothelial nitric oxide synthase phosphorylation through the inhibition of protein kinase B/Akt in human endothelial cells

Endothelial nitric oxide synthase (eNOS) is an important regulator of cardiovascular homeostasis by production of nitric oxide (NO) from vascular endothelial cells. It can be activated by protein kinase B (PKB)/Akt via phosphorylation at Ser-1177. We are interested in the role of Rho GTPase/Rho kinase (ROCK) pathway in regulation of eNOS expression and activation. Using adenovirus-mediated gene transfer in human umbilical vein endothelial cells (HUVECs), we show here that both active RhoA and ROCK not only downregulate eNOS gene expression as reported previously but also inhibit eNOS phosphorylation at Ser-1177 and cellular NO production with concomitant suppression of PKB activation. Moreover, coexpression of a constitutive active form of PKB restores the phosphorylation but not gene expression of eNOS in the presence of active RhoA. Furthermore, we show that thrombin inhibits eNOS phosphorylation, as well as expression via Rho/ROCK pathway. Expression of the active PKB reverses eNOS phosphorylation but has no effect on downregulation of eNOS expression induced by thrombin. Taken together, these data demonstrate that Rho/ROCK pathway negatively regulates eNOS phosphorylation through inhibition of PKB, whereas it downregulates eNOS expression independent of PKB.     

The isoflavone Equol mediates rapid vascular relaxation: Ca2+-independent activation of endothelial nitric-oxide synthase/Hsp90 involving ERK1/2 and Akt phosphorylation in human endothelial cells

We recently reported that soy isoflavones increase gene expression of endothelial nitric-oxide synthase (eNOS) and antioxidant defense enzymes, resulting in improved endothelial function and lower blood pressure in vivo. In this study, we establish that equol (1-100 nM) causes acute endothelium- and nitric oxide (NO)-dependent relaxation of aortic rings and rapidly (2 min) activates eNOS in human aortic and umbilical vein endothelial cells. Intracellular Ca2+ and cyclic AMP levels were unaffected by treatment (100 nM, 2 min) with equol, daidzein, or genistein. Rapid phosphorylation of ERK1/2, protein kinase B/Akt, and eNOS serine 1177 by equol was paralleled by association of eNOS with heat shock protein 90 (Hsp90) and NO synthesis in human umbilical vein endothelial cells, expressing estrogen receptors (ER)alpha and ERbeta. Inhibition of phosphatidylinositol 3-kinase and ERK1/2 inhibited eNOS activity, whereas pertussis toxin and the ER antagonists ICI 182,750 and tamoxifen had negligible effects. Our findings provide the first evidence that nutritionally relevant plasma concentrations of equol (and other soy protein isoflavones) rapidly stimulate phosphorylation of ERK1/2 and phosphatidylinositol 3-kinase/Akt, leading to the activation of NOS and increased NO production at resting cytosolic Ca2+ levels. Identification of the nongenomic mechanisms by which equol mediates vascular relaxation provides a basis for evaluating potential benefits of equol in the treatment of postmenopausal women and patients at risk of cardiovascular disease.     

Shear stress stimulates phosphorylation of eNOS at Ser(635) by a protein kinase A-dependent mechanism

Shear stress stimulates nitric oxide (NO) production by phosphorylating endothelial NO synthase (eNOS) at Ser(1179) in a phosphoinositide-3-kinase (PI3K)- and protein kinase A (PKA)-dependent manner. The eNOS has additional potential phosphorylation sites, including Ser(116), Thr(497), and Ser(635). Here, we studied these potential phosphorylation sites in response to shear, vascular endothelial growth factor (VEGF), and 8-bromocAMP (8-BRcAMP) in bovine aortic endothelial cells (BAEC). All three stimuli induced phosphorylation of eNOS at Ser(635), which was consistently slower than that at Ser(1179). Thr(497) was rapidly dephosphorylated by 8-BRcAMP but not by shear and VEGF. None of the stimuli phosphorylated Ser(116). Whereas shear-stimulated Ser(635) phosphorylation was not affected by phosphoinositide-3-kinase inhibitors wortmannin and LY-294002, it was blocked by either treating the cells with a PKA inhibitor H89 or infecting them with a recombinant adenovirus-expressing PKA inhibitor. These results suggest that shear stress stimulates eNOS by two different mechanisms: 1) PKA- and PI3K-dependent and 2) PKA-dependent but PI3K-independent pathways. Phosphorylation of Ser(635) may play an important role in chronic regulation of eNOS in response to mechanical and humoral stimuli.     

Glomerular Endothelial Cell Injury and Damage Precedes That of Podocytes in Adriamycin-Induced Nephropathy

The role of podocytes in the development and progression of glomerular disease has been extensively investigated in the past decade. However, the importance of glomerular endothelial cells in the pathogenesis of proteinuria and glomerulosclerosis has been largely ignored. Recent studies have demonstrated that endothelial nitric oxide synthatase (eNOS) deficiency exacerbates renal injury in anti-GBM and remnant kidney models and accelerates diabetic kidney damage. Increasing evidence also demonstrates the importance of the glomerular endothelium in preventing proteinuria. We hypothesize that endothelial dysfunction can initiate and promote the development and progression of glomerulopathy. Administration of adriamycin (ADR) to C57BL/6 mice, normally an ADR resistant strain, with an eNOS deficiency induced overt proteinuria, severe glomerulosclerosis, interstitial fibrosis and inflammation. We also examined glomerular endothelial cell and podocyte injury in ADR-induced nephropathy in Balb/c mice, an ADR susceptible strain, by immunostaining, TUNEL and Western blotting. Interestingly, down-regulation of eNOS and the appearance of apoptotic glomerular endothelial cells occurred as early as 24 hours after ADR injection, whilst synaptopodin, a functional podocyte marker, was reduced 7 days after ADR injection and coincided with a significant increase in the number of apoptotic podocytes. Furthermore, conditioned media from mouse microvascular endothelial cells over-expressing GFP-eNOS protected podocytes from TNF-α-induced loss of synaptopodin. In conclusion, our study demonstrated that endothelial dysfunction and damage precedes podocyte injury in ADR-induced nephropathy. Glomerular endothelial cells may protect podocytes from inflammatory insult. Understanding the role of glomerular endothelial dysfunction in the development of kidney disease will facilitate in the design of novel strategies to treat kidney disease.     

3-Morpholinosyndnonimine inhibits 5-hydroxytryptamine-induced phosphorylation of nitric oxide synthase in endothelial cells.

5-Hydroxytryptamine (5-HT) is a vasoactive substance that is taken up by endothelial cells to activate endothelial nitrite oxide synthase (eNOS). The activation of eNOS results in the production of nitric oxide (NO), which is responsible for vasodilation of blood vessels. NO also interacts with superoxide anion (O2*-) to form peroxynitrite (ONOO-), a potent oxidant that has been shown to induce vascular endothelial dysfunction. We examined the ability of 3-morpholinosyndnonimine (SIN-1), an ONOO- generator, to inhibit 5-HT-induced phosphorylation of eNOS in cultured bovine aortic endothelial cells (BAECs). We observed that 5-HT phosphorylates Ser1179 eNOS in a time- and concentration-dependent manner. Maximum phosphorylation occurred at 30 sec using a concentration of 1.0 microM 5-HT. BAECs treated with SIN-1 (1-1000 microM) for 30 min showed no significant increase in eNOS phosphorylation. However, 5-HT-induced eNOS phosphorylation was inhibited in cells treated with various concentrations of SIN-1 for 30 min and stimulated with 5-HT. These data suggest that an increase in ONOO- as a result of an increase in the production of O2*-, may feedback to inhibit 5-HT-induced eNOS phosphorylation at Ser1179 and therefore, contribute to endothelial dysfunction associated with cardiovascular diseases.