Fluid shear stress activates proline-rich tyrosine kinase via reactive oxygen species-dependent pathway

Inhibition of proline-rich tyrosine kinase 2 restores cardioprotection by remote ischaemic preconditioning in type 2 diabetes

BACKGROUND AND PURPOSE

Remote ischaemic preconditioning (rIPC) for cardioprotection is severely impaired in diabetes, and therapeutic options to restore it are lacking. The vascular endothelium plays a key role in rIPC. Given that the activity of endothelial nitric oxide synthase (eNOS) is inhibited by proline-rich tyrosine kinase 2 (Pyk2), we hypothesized that pharmacological Pyk2 inhibition could restore eNOS activity and thus restore remote cardioprotection in diabetes.

EXPERIMENTAL APPROACH

New Zealand obese (NZO) mice that demonstrated key features of diabetes were studied. The consequence of Pyk2 inhibition on endothelial function, rIPC and infarct size after myocardial infarction were evaluated. The impact of plasma from mice and humans with or without diabetes was assessed in isolated buffer perfused murine hearts and aortic rings.

KEY RESULTS

Plasma from nondiabetic mice and humans, both subjected to rIPC, caused remote tissue protection. Similar to diabetic humans, NZO mice demonstrated endothelial dysfunction. NZO mice had reduced circulating nitrite levels, elevated arterial blood pressure and a larger infarct size after ischaemia and reperfusion than BL6 mice. Pyk2 increased the phosphorylation of eNOS at its inhibitory site (Tyr656), limiting its activity in diabetes. The cardioprotective effects of rIPC were abolished in diabetic NZO mice. Pharmacological Pyk2 inhibition restored endothelial function and rescued cardioprotective effects of rIPC.

CONCLUSION AND IMPLICATIONS

Endothelial function and remote tissue protection are impaired in diabetes. Pyk2 is a novel target for treating endothelial dysfunction and restoring cardioprotection through rIPC in diabetes.

The hollow porous sphere cell carrier for the dynamic 3D cell culture

Large-scale mammalian cell culture is essential in stem cell-based therapy, the production of the vaccine, and the manufacturing of therapeutic protein drugs. Due to the adherent growth characteristic of most mammalian cell types, the combination of cell carrier and bioreactor is a common choice in large-scale mammalian cell culture. Cell carriers are usually developed by polymer crosslinking, lithography, and emulsion drops; however, all these methods are difficult to control the uniformed porous structure and porous interior design. Therefore, unable to optimize the dynamic culture condition for cell proliferation, matrix production, and cell differentiation. Here we use fused deposition modelling (FDM) 3D printing technology to fabricate hollow porous spheres (HPS), based on which a novel dynamic 3D culture system has been established. In the meantime, computational fluid dynamics (CFD) simulations were conducted to study liquid flow behaviour in HPS. A dynamic cell seeding was developed and refined using the 3D culture system, which increased 32% (roughly) seeding efficiency compared to the traditional static cell seeding method. The cell proliferation analysis demonstrated that HPSs could speed up cell growth in dynamic cell culture. The HPS with a honeycomb-like structure showed the highest inner pore velocity (CFD analysis) and achieved the fastest cell proliferation and the highest cell viability. Overall, our study, for the first time, developed a 3D printed HPS cell culture device with a uniformed porous structure, which can effectively facilitate cell adhesion and proliferation in the dynamic cultural environment, thereby could be considered an ideal carrier candidate for the manufacturing of cells and cell-based products. Furthermore, this study provides a novel 3D dynamic culture system that can be further applied in cell culture and research in the future.

LED Light-Induced ROS Differentially Regulates Focal Adhesion Kinase Activity in HaCaT Cell Viability

In this study, changes in cell signaling mechanisms in skin cells induced by various wavelengths and intensities of light-emitting diodes (LED) were investigated, focusing on the activity of focal adhesion kinase (FAK) in particular. We examined the effect of LED irradiation on cell survival, the generation of intracellular reactive oxygen species (ROS), and the activity of various cell-signaling proteins. Red LED light increased cell viability at all intensities, whereas strong green and blue LED light reduced cell viability, and this effect was reversed by NAC or DPI treatment. Red LED light caused an increase in ROS formation according to the increase in the intensity of the LED light, and green and blue LED lights led to sharp increases in ROS formation. In the initial reaction to LEDs, red LED light only increased the phosphorylation of FAK and extracellular-signal regulated protein kinase (ERK), whereas green and blue LED lights increased the phosphorylation of inhibitory-κB Kinase α (IKKα), c-jun N-terminal kinase (JNK), and p38. The phosphorylation of these intracellular proteins was reduced via FAK inhibitor, NAC, and DPI treatments. Even after 24 h of LED irradiation, the activity of FAK and ERK appeared in cells treated with red LED light but did not appear in cells treated with green and blue LED lights. Furthermore, the activity of caspase-3 was confirmed along with cell detachment. Therefore, our results suggest that red LED light induced mitogenic effects via low levels of ROS–FAK–ERK, while green and blue LED lights induced cytotoxic effects via cellular stress and apoptosis signaling resulting from high levels of ROS.

Zika virus NS1 affects the junctional integrity of human brain microvascular endothelial cells

Zika virus (ZIKV) infection leads to microcephaly in newborns. Flaviviruses are known to secrete NS1 protein extracellularly and its concentration in serum directly co-relate to disease severity. The presence of ZIKV-NS1 near the brain microvascular endothelial cells (BMVECs) affects blood-brain-barrier, which is composed of tight junctions (TJs) and adherens junctions (AJs). Viruses utilize different strategies to circumvent this barrier to enter in brain. The present study demonstrated the mechanism of junctional integrity disruption in BMVECs by ZIKV-NS1 protein exposure. The Transendothelial Electrical Resistance and sodium fluorescein migration assays revealed the endothelial barrier disruption in BMVECs exposed to ZIKV-NS1 at different time (12hr and 24hr) and doses (500 ng/mL, 1000 ng/mL and 1500 ng/mL). The exposure of ZIKV-NS1 on BMVECs led to the phosphorylation of AJs and suppression of TJs through secreted ZIKV-NS1 in a bystander fashion. The activation of NADPH dependent reactive oxygen species activity and redox sensitive tyrosine kinase further increased the phosphorylation of AJs. The reduced expression of the phosphatase led to the increased phosphorylation of the AJs. The treatment with Diphenyleneiodonium chloride rescued the phosphatase and TJs expression and suppressed the expression of kinase and AJs in BMVECs exposed to ZIKV-NS1.

Whole-Genome Uterine Artery Transcriptome Profiling and Alternative Splicing Analysis in Rat Pregnancy

During pregnancy, the uterine artery (UA) undergoes extensive remodeling to permit a 20–40 fold increase in blood flow with associated changes in the expression of a multitude of genes. This study used next-gen RNA sequencing technology to identify pathways and genes potentially involved in arterial adaptations in pregnant rat UA (gestation day 20) compared with non-pregnant rat UA (diestrus). A total of 2245 genes were differentially expressed, with 1257 up-regulated and 970 down-regulated in pregnant UA. Gene clustering analysis revealed a unique cluster of suppressed genes implicated in calcium signaling pathway and vascular smooth muscle contraction in pregnant UA. Transcription factor binding site motif scanning identified C2H2 ZF, AP-2 and CxxC as likely factors functional on the promoters of down-regulated genes involved in calcium signaling and vascular smooth muscle contraction. In addition, 1686 genes exhibited alternative splicing that were mainly implicated in microtubule organization and smooth muscle contraction. Cross-comparison analysis identified novel genes that were both differentially expressed and alternatively spliced; these were involved in leukocyte and B cell biology and lipid metabolism. In conclusion, this first comprehensive study provides a valuable resource for understanding the molecular mechanism underlying gestational uterine arterial adaptations during pregnancy.

A Quantitative Method to Measure Low Levels of ROS in Nonphagocytic Cells by Using a Chemiluminescent Imaging System

Chemiluminescence (CL) is one of the most useful methods for detecting reactive oxygen species (ROS). Although fluorescence dyes or genetically encoded biosensors have been developed, CL is still used due to its high sensitivity, ease of use, and low cost. While initially established and used to measure high levels of ROS in phagocytic cells, CL assays are not ideal for measuring low levels of ROS. Here, we developed a newly modified CL assay using a chemiluminescent imaging system for measuring low concentrations of ROS in nonphagocytic cells. We found that dissolving luminol in NaOH, rather than DMSO, increased the H2O2-induced CL signal and that the addition of 4-iodophenylboronic acid (4IPBA) further increased CL intensity. Our new system also increased the rate and intensity of the CL signal in phorbol 12-myristate 13-acetate- (PMA-) treated HT-29 colon cancer cells compared to those in luminol only. We were able to quantify ROS levels from both cells and media in parallel using an H2O2 standard. A significant benefit to our system is that we can easily measure stimulus-induced ROS formation in a real-time manner and also investigate intracellular signaling pathways from a single sample simultaneously. We found that PMA induced tyrosine phosphorylation of protein tyrosine kinases (PTKs), such as focal adhesion kinase (FAK), protein tyrosine kinase 2 (Pyk2), and Src, and increased actin stress fiber formation in a ROS-dependent manner. Interestingly, treatment with either N-acetyl-L-cysteine (NAC) or diphenyleneiodonium (DPI) reduced the PMA-stimulated phosphorylation of these PTKs, implicating a potential role in cellular ROS signaling. Thus, our newly optimized CL assay using 4IPBA and a chemiluminescent imaging method provides a simple, real-time, and low-cost method for the quantification of low levels of ROS.

Tyrosine phosphorylation of eNOS regulates myocardial survival after an ischaemic insult: role of PYK2

Aims

Endothelial nitric oxide (NO) synthase (eNOS) is known to play a cardioprotective protective. However, the molecular mechanisms regulating eNOS activity during ischaemia/reperfusion (I/R) injury are incompletely understood. eNOS is a substrate for several kinases that positively or negatively affect its enzymatic activity. Herein, we sought to correlate eNOS phosphorylation status with cardiomyocyte survival and we investigated the contribution of the proline-rich tyrosine kinase 2 (PYK2)/eNOS axis to the regulation of myocardial infarct size in vivo.

Methods and results

Exposure of H9c2 cardiomyocytes to H2O2 lead to PYK2 phosphorylation on its activator site (Y402) and eNOS phosphorylation on the inhibitor site Y656 and the activator site S1176. Both H2O2-induced eNOS phosphorylation events were abolished by PYK2 pharmacological inhibition or gene knockdown. Activity assays demonstrated that phosphorylation of the tyrosine inhibitory site exerts a dominant effect over S1176. In cardiomyocytes subjected to oxidative stress or oxygen-glucose deprivation, inhibition of PYK2 limited cell injury; this effect was prevented by inhibition of NO production. In vivo, ischaemia-reperfusion induced an early activation of PYK2, leading to eNOS phosphorylation on Y656, which, in turn, reduced NO output, as judged by the low tissue levels of its downstream effector cGMP. Moreover, pharmacological blockade of PYK2 alleviated eNOS inhibition and prevented cardiac damage following I/R injury in wild-type, but not in eNOS KO mice.

Conclusion

The current studies demonstrate that PYK2 is a pivotal regulator of eNOS function in myocardial infarction and identify PYK2 as a novel therapeutic target for cardioprotection.

Hydrogen Sulfide Preserves Endothelial Nitric Oxide Synthase Function by Inhibiting Proline-Rich Kinase 2: Implications for Cardiomyocyte Survival and Cardioprotection

Hydrogen sulfide (H₂S) exhibits beneficial effects in the cardiovascular system, many of which depend on nitric oxide (NO). Proline-rich tyrosine kinase 2 (PYK2), a redox-sensitive tyrosine kinase, directly phosphorylates and inhibits endothelial NO synthase (eNOS). We investigated the ability of H₂S to relieve PYK2-mediated eNOS inhibition and evaluated the importance of the H₂S/PYK2/eNOS axis on cardiomyocyte injury in vitro and in vivo. Exposure of H9c2 cardiomyocytes to H₂O₂ or pharmacologic inhibition of H₂S production increased PYK2 (Y402) and eNOS (Y656) phosphorylation. These effects were blocked by treatment with Na₂S or by overexpression of cystathionine γ-lyase (CSE). In addition, PYK2 overexpression reduced eNOS activity in a H₂S-reversible manner. The viability of cardiomyocytes exposed to Η₂Ο₂ was reduced and declined further after the inhibition of H₂S production. PYK2 downregulation, l-cysteine supplementation, or CSE overexpression alleviated the effects of H₂O₂ on H9c2 cardiomyocyte survival. Moreover, H₂S promoted PYK2 sulfhydration and inhibited its activity. In vivo, H₂S administration reduced reactive oxygen species levels, as well as PYK2 (Y402) and eNOS (Y656) phosphorylation. Pharmacologic blockade of PYK2 or inhibition of PYK2 activation by Na₂S reduced myocardial infarct size in mice. Coadministration of a PYK2 inhibitor and Na₂S did not result in additive effects on infarct size. We conclude that H₂S relieves the inhibitory effect of PYK2 on eNOS, allowing the latter to produce greater amounts of NO, thereby affording cardioprotection. Our results unravel the existence of a novel H₂S-NO interaction and identify PYK2 as a crucial target for the protective effects of H₂S under conditions of oxidative stress.

Modulation of Local and Systemic Heterocellular Communication by Mechanical Forces: A Role of Endothelial Nitric Oxide Synthase

In this review, we discuss the role of nitric oxide (NO) as a key physiological mechanotransducer modulating both local and systemic heterocellular communication and contributing to the integrated (patho)physiology of the cardiovascular system. A deeper understanding of mechanotransduction-mediated local and systemic nodes controlling heterocellular communication between the endothelium, blood cells, and other cell types (e.g., cardiomyocytes) may suggest novel therapeutic strategies for endothelial dysfunction and cardiovascular disease. Recent Advances: Mechanical forces acting on mechanoreceptors on endothelial cells activate the endothelial NO synthase (eNOS) to produce NO. NO participates in (i) abluminal heterocellular communication, inducing vasorelaxation, and thereby regulating vascular tone and blood pressure; (ii) luminal heterocellular communication, inhibiting platelet aggregation, and controlling hemostasis; and (iii) systemic heterocellular communication, contributing to adaptive physiological processes in response to exercise and remote ischemic preconditioning. Interestingly, shear-induced eNOS-dependent activation of vascular heterocellular communication constitutes the molecular basis of all methods applied in the clinical routine for evaluation of endothelial function. Critical Issues and Future Directions: The integrated physiology of heterocellular communication is still not fully understood. Dedicated experimental models are needed to analyze messengers and mechanisms underpinning heterocellular communication in response to physical forces in the cardiovascular system (and elsewhere). Antioxid. Redox Signal. 26, 917-935.

A cell-based sensor of fluid shear stress for microfluidics

Microsystems designed for cell-based studies or applications inherently require fluid handling. Flows within such systems inevitably generate fluid shear stress (FSS) that may adversely affect cell health. Simple assays of cell viability, morphology or growth are typically reported to indicate any gross disturbances to cell physiology. However, no straightforward metric exists to specifically evaluate physiological implications of FSS within microfluidic devices, or among competing microfluidic technologies. This paper presents the first genetically encoded cell sensors that fluoresce in a quantitative fashion upon FSS pathway activation. We picked a widely used cell line (NIH3T3s) and created a transcriptional cell-sensor where fluorescence turns on when transcription of a relevant FSS-induced protein is initiated. Specifically, we chose Early Growth Factor-1 (a mechanosensitive protein) upregulation as the node for FSS detection. We verified our sensor pathway specificity and functionality by noting induced fluorescence in response to chemical induction of the FSS pathway, seen both through microscopy and flow cytometry. Importantly, we found our cell sensors to be inducible by a range of FSS intensities and durations, with a limit of detection of 2 dynes cm(-2) when applied for 30 minutes. Additionally, our cell-sensors proved their versatility by showing induction sensitivity when made to flow through an inertial microfluidic device environment with typical flow conditions. We anticipate these cell sensors to have wide application in the microsystems community, allowing the device designer to engineer systems with acceptable FSS, and enabling the end-user to evaluate the impact of FSS upon their assay of interest.

Post-ovulatory aging of oocytes disrupts kinase signaling pathways and lysosome biogenesis

Post-ovulatory aging of oocytes results in the progressive loss of fertilization and developmental competence. This degradation of oocyte quality has been the object of numerous investigations, primarily focused on individual signaling pathways which provide limited insight into the status of global signaling events. The purpose of the present investigation was to comprehensively assess broad patterns of signaling pathway activity during in vitro aging as an initial step in defining control points that can be targeted to prevent the reduction in oocyte quality during prolonged culture. An antibody microarray-based phospho-proteome analysis performed on oocytes before and after eight hours of culture revealed significant changes in the abundance or activation state of 43 proteins that function in a wide variety of protein kinase-mediated signaling pathways. Several of the most significantly affected kinases were studied by Western blot and confocal immunofluorescence to corroborate the array results. Prolonged culture resulted in global changes in the abundance and activity of protein kinases that regulate the response to calcium, stress, and cell-cycle control. Examination of intracellular structures revealed a previously unrecognized increase in the abundance of large autophogagic lysosomes, which correlates with changes in protein kinase pathways. These results provide insight into the stresses experienced by oocytes during culture and the diversity of responses that results from them. The observed increase in autophagy-related activity, together with the disruptions in calcium signaling, cell-cycle, and stress-response pathways, have the potential to negatively impact oocyte quality by interfering with the normal sequence of biochemical changes that constitute egg activation following fertilization.

Reactive oxygen species in inflammation and tissue injury

Abstract Reactive oxygen species (ROS) are key signaling molecules that play an important role in the progression of inflammatory disorders. An enhanced ROS generation by polymorphonuclear neutrophils (PMNs) at the site of inflammation causes endothelial dysfunction and tissue injury. The vascular endothelium plays an important role in passage of macromolecules and inflammatory cells from the blood to tissue. Under the inflammatory conditions, oxidative stress produced by PMNs leads to the opening of inter-endothelial junctions and promotes the migration of inflammatory cells across the endothelial barrier. The migrated inflammatory cells not only help in the clearance of pathogens and foreign particles but also lead to tissue injury. The current review compiles the past and current research in the area of inflammation with particular emphasis on oxidative stress-mediated signaling mechanisms that are involved in inflammation and tissue injury.

Shear stress-induced redistribution of vascular endothelial-protein-tyrosine phosphatase (VE-PTP) in endothelial cells and its role in cell elongation

Vascular endothelial cells (ECs) are continuously exposed to shear stress (SS) generated by blood flow. Such stress plays a key role in regulation of various aspects of EC function including cell proliferation and motility as well as changes in cell morphology. Vascular endothelial-protein-tyrosine phosphatase (VE-PTP) is an R3-subtype PTP that possesses multiple fibronectin type III-like domains in its extracellular region and is expressed specifically in ECs. The role of VE-PTP in EC responses to SS has remained unknown, however. Here we show that VE-PTP is diffusely localized in ECs maintained under static culture conditions, whereas it undergoes rapid accumulation at the downstream edge of the cells relative to the direction of flow in response to SS. This redistribution of VE-PTP triggered by SS was found to require its extracellular and transmembrane regions and was promoted by integrin engagement of extracellular matrix ligands. Inhibition of actin polymerization or of Cdc42, Rab5, or Arf6 activities attenuated the SS-induced redistribution of VE-PTP. VE-PTP also underwent endocytosis in the static and SS conditions. SS induced the polarized distribution of internalized VE-PTP. Such an effect was promoted by integrin engagement of fibronectin but prevented by inhibition of Cdc42 activity or of actin polymerization. In addition, depletion of VE-PTP by RNA interference in human umbilical vein ECs blocked cell elongation in the direction of flow induced by SS. Our results suggest that the polarized redistribution of VE-PTP in response to SS plays an important role in the regulation of EC function by blood flow.

Molecular biology of atherosclerosis

At least 468 individual genes have been manipulated by molecular methods to study their effects on the initiation, promotion, and progression of atherosclerosis. Most clinicians and many investigators, even in related disciplines, find many of these genes and the related pathways entirely foreign. Medical schools generally do not attempt to incorporate the relevant molecular biology into their curriculum. A number of key signaling pathways are highly relevant to atherogenesis and are presented to provide a context for the gene manipulations summarized herein. The pathways include the following: the insulin receptor (and other receptor tyrosine kinases); Ras and MAPK activation; TNF-α and related family members leading to activation of NF-κB; effects of reactive oxygen species (ROS) on signaling; endothelial adaptations to flow including G protein-coupled receptor (GPCR) and integrin-related signaling; activation of endothelial and other cells by modified lipoproteins; purinergic signaling; control of leukocyte adhesion to endothelium, migration, and further activation; foam cell formation; and macrophage and vascular smooth muscle cell signaling related to proliferation, efferocytosis, and apoptosis. This review is intended primarily as an introduction to these key signaling pathways. They have become the focus of modern atherosclerosis research and will undoubtedly provide a rich resource for future innovation toward intervention and prevention of the number one cause of death in the modern world.

Monoamine Oxidases Are Mediators of Endothelial Dysfunction in the Mouse Aorta

Monoamine oxidases (MAOs) generate H 2 O 2 as a by-product of their catalytic cycle. Whether MAOs are mediators of endothelial dysfunction is unknown and was determined here in the angiotensin II and lipopolysaccharide-models of vascular dysfunction in mice. Quantitative real-time polymerase chain reaction revealed that mouse aortas contain enzymes involved in catecholamine generation and MAO-A and MAO-B mRNA. MAO-A and -B proteins could be detected by Western blot not only in mouse aortas but also in human umbilical vein endothelial cells. Ex vivo incubation of mouse aorta with recombinant MAO-A increased H 2 O 2 formation and induced endothelial dysfunction that was attenuated by polyethylene glycol-catalase and MAO inhibitors. In vivo lipopolysaccharide (8 mg/kg IP overnight) or angiotensin II (1 mg/kg per day, 2 weeks, minipump) treatment induced vascular MAO-A and -B expressions and resulted in attenuated endothelium-dependent relaxation of the aorta in response to acetylcholine. MAO inhibitors reduced the lipopolysaccharide- and angiotensin II–induced aortic reactive oxygen species formation by 50% (ferrous oxidation xylenol orange assay) and partially normalized endothelium-dependent relaxation. MAO-A and MAO-B inhibitors had an additive effect; combined application completely restored endothelium-dependent relaxation. To determine how MAO-dependent H 2 O 2 formation induces endothelial dysfunction, cyclic GMP was measured. Histamine stimulation of human umbilical vein endothelial cells to activate endothelial NO synthase resulted in an increase in cyclic GMP, which was almost abrogated by MAO-A exposure. MAO inhibition prevented this effect, suggesting that MAO-induced H 2 O 2 formation is sufficient to attenuate endothelial NO release. Thus, MAO-A and MAO-B are both expressed in the mouse aorta, induced by in vivo lipopolysaccharide and angiotensin II treatment and contribute via the generation of H 2 O 2 to endothelial dysfunction in vascular disease models.

The atherosusceptible endothelium: endothelial phenotypes in complex haemodynamic shear stress regions in vivo

Atherosclerosis initiates at predictable focal sites and develops to a spatially regional disease with limited distribution. There is compelling evidence that links haemodynamics to the localized origin of atherosclerotic lesions. Arterial flow in vivo is unsteady, dynamically complex, and regionally variable. Sites susceptible to atherosclerosis near arterial branches and curves are associated with regions of disturbed blood flow that contain repetitive phases of flow reversal resulting in steep multidirectional temporal and spatial gradients of wall shear stresses. Endothelium in atherosusceptible regions relative to protected sites shows activation of endoplasmic reticulum (ER) stress and the unfolded protein response (UPR), the altered expression of pro-inflammatory Nuclear Factor kappa B (NFκB) and oxidant/antioxidant pathways, and low expression of major protective factors, notably endothelial nitric oxide synthase and Kruppel-like Factors KLF2 and KLF4. At some atherosusceptible locations, reactive oxygen species levels are significantly elevated. Here we describe flow-related phenotypes identified in steady-state in vivo and outline some of the molecular mechanisms that may contribute to pre-lesional atherosusceptibility as deduced from complementary cell experiments in vitro. We conclude that disturbed flow is a significant local risk factor for atherosclerosis that induces a chronic low-level inflammatory state, an adaptive response to ensure continued function at the expense of increased susceptibility to atherogenesis. Surprisingly, when challenged by short-term hypercholesterolaemia in vivo, atherosusceptible endothelial phenotype was resistant to greater pro-inflammatory expression, suggesting that sustained hyperlipidaemia is required to overcome these protective characteristics.

Cyclic strain delays the expression of tissue factor induced by thrombin in human umbilical vein endothelial cells

Most studies of tissue factor (TF) expression in endothelial cells (EC) are performed under stationary culture conditions. The purpose of this study was to determine the influence of mechanical stimuli such as cyclic strain (CS) on the expression of TF in EC exposed to thrombin (Thr). Human umbilical vein endothelial cells (HUVEC) were exposed to 4 U·mL(-1) Thr in the presence or absence of 10% average CS at 60 cycles·min(-1) and then TF expression was measured. TF messenger RNA (mRNA) expression peaked at 2 hours in HUVEC exposed to Thr, but at 4 hours in HUVEC exposed to both Thr + CS. TF expression was inhibited by p38 and extracellular signal-regulated protein kinase (ERK) inhibitors. For both Thr or Thr + CS stimuli, p38 and ERK activity peaked at 5 minutes (p < 0.05). Nuclear factor-kappa B levels remained high in the Thr group but not in the Thr + CS group, while Egr-1 levels were elevated in the Thr + CS group. We demonstrated CS-delayed, Thr-induced TF mRNA expression in HUVEC, which may be modulated by p38 and ERK inhibitors.

Fluid shear stress induces differentiation of circulating phenotype endothelial progenitor cells

Endothelial progenitor cells (EPCs) are mobilized from bone marrow to peripheral blood, and contribute to angiogenesis in tissue. In the process, EPCs are exposed to shear stress generated by blood flow and tissue fluid flow. Our previous study showed that shear stress induces differentiation of mature EPCs in adhesive phenotype into mature endothelial cells and, moreover, arterial endothelial cells. In this study we investigated whether immature EPCs in a circulating phenotype differentiate into mature EPCs in response to shear stress. When floating-circulating phenotype EPCs derived from ex vivo expanded human cord blood were exposed to controlled levels of shear stress in a flow-loading device, the bioactivities of adhesion, migration, proliferation, antiapoptosis, tube formation, and differentiated type of EPC colony formation increased. The surface protein expression rate of the endothelial markers VEGF receptor 1 (VEGF-R1) and -2 (VEGF-R2), VE-cadherin, Tie2, VCAM1, integrin α(v)/β(3), and E-selectin increased in shear-stressed EPCs. The VEGF-R1, VEGF-R2, VE-cadherin, and Tie2 protein increases were dependent on the magnitude of shear stress. The mRNA levels of VEGF-R1, VEGF-R2, VE-cadherin, Tie2, endothelial nitric oxide synthase, matrix metalloproteinase 9, and VEGF increased in shear-stressed EPCs. Inhibitor analysis showed that the phosphoinositide 3-kinase (PI3K)/Akt/mammalian target of rapamycin (mTOR) signal transduction pathway is a potent activator of adhesion, proliferation, tube formation, and differentiation in response to shear stress. Western blot analysis revealed that shear stress activated the VEGF-R2 phosphorylation in a ligand-independent manner. These results indicate that shear stress increases differentiation, adhesion, migration, proliferation, antiapoptosis, and vasculogenesis of circulating phenotype EPCs by activation of VEGF-R2 and the PI3K/Akt/mTOR signal transduction pathway.

Statins reverse renal inflammation and endothelial dysfunction induced by chronic high salt intake

High salt intake (HS) is a risk factor for cardiovascular and kidney disease. Indeed, HS may promote blood-pressure-independent tissue injury via inflammatory factors. The lipid-lowering 3-hydroxy 3-methylglutaryl-coenzyme A (HMG-CoA) reductase inhibitors exert beneficial lipid-independent effects, reducing the expression and synthesis of inflammatory factors. We hypothesized that HS impairs kidney structure and function in the absence of hypertension, and these changes are reversed by atorvastatin. Four groups of rats were treated for 6 wk in metabolic cages with their diets: normal salt (NS); HS, NS plus atorvastatin and HS plus atorvastatin. We measured basal and final body weight, urinary sodium and protein excretion (UProtV), and systolic blood pressure (SBP). At the end of the experimental period, cholesterolemia, creatinine clearance, renal vascular reactivity, glomerular volume, cortical and glomerular endothelial nitric oxide synthase (eNOS), and transforming growth factor (TGF)-β1 expression were measured. We found no differences in SBP, body weight, and cholesterolemia. HS rats had increased creatinine clearence, UProtV, and glomerular volume at the end of the study. Acetylcholine-induced vasodilatation decreased by 40.4% in HS rats ( P < 0.05). HS decreased cortical and glomerular eNOS and caused mild glomerular sclerosis, interstitial mononuclear cell infiltration, and increased cortical expression of TGF-β1. All of these salt-induced changes were reversed by atorvastatin. We conclude that long-term HS induces inflammatory and hemodynamic changes in the kidney that are independent of SBP. Atorvastatin corrected all, suggesting that the nitric oxide-oxidative stress balance plays a significant role in the earlier stages of salt induced kidney damage.

Role of increased guanosine triphosphate cyclohydrolase-1 expression and tetrahydrobiopterin levels upon T cell activation

Tetrahydrobiopterin (BH(4)) is an essential co-factor for the nitric-oxide (NO) synthases, and in its absence these enzymes produce superoxide (O(2)(·-)) rather than NO. The rate-limiting enzyme for BH(4) production is guanosine triphosphate cyclohydrolase-1 (GTPCH-1). Because endogenously produced NO affects T cell function, we sought to determine whether antigen stimulation affected T cell GTPCH-1 expression and ultimately BH(4) levels. Resting T cells had minimal expression of inducible NOS (NOS2), endothelial NOS (NOS3), and GTPCH-1 protein and nearly undetectable levels of BH(4). Anti-CD3 stimulation of T cells robustly stimulated the coordinated expression of NOS2, NOS3, and GTPCH-1 and markedly increased both GTPCH-1 activity and T cell BH(4) levels. The newly expressed GTPCH-1 was phosphorylated on serine 72 and pharmacological inhibition of casein kinase II reduced GTPCH-1 phosphorylation and blunted the increase in T cell BH(4). Inhibition of GTPCH-1 with diaminohydroxypyrimidine (1 mmol/liter) prevented T cell BH(4) accumulation, reduced NO production, and increased T cell O(2)(·-) production, due to both NOS2 and NOS3 uncoupling. GTPCH-1 inhibition also promoted TH(2) polarization in memory CD4 cells. Ovalbumin immunization of mice transgenic for an ovalbumin receptor (OT-II mice) confirmed a marked increase in T cell BH(4) in vivo. These studies identify a previously unidentified consequence of T cell activation, promoting BH(4) levels, NO production, and modulating T cell cytokine production.

Early inflammatory reactions in atherosclerosis are induced by proline-rich tyrosine kinase/reactive oxygen species-mediated release of tumor necrosis factor-alpha and subsequent activation of the p21Cip1/Ets-1/p300 system

OBJECTIVE

Reactive oxygen species (ROS) are involved in the initial process of atherosclerosis, whereas it remains to be determined how atherogenic stimulus causes ROS-mediated proinflammatory reactions. Here, we focused on proline-rich tyrosine kinase (PYK2)-mediated ROS generation and examined how atherogenic stimulus causes early proinflammatory reactions.

METHODS AND RESULTS

PYK2-deficient (knockout [KO]) (PYK2-KO) mice were crossbred with apolipoprotein E (ApoE)-deficient (PYK2-KO/ApoE-KO) mice. PYK2-KO/ApoE-KO mice and endothelial cells (EC) were used for the study. Aortic atherogenic lesions in PYK2-KO/ApoE-KO mice were markedly decreased (55% versus ApoE-KO) after 8 weeks of a Western diet. Aortic PYK2 was activated as early as 7 days after the Western diet, when inflammatory cells were not yet activated. Addition of the proatherogenic oxidized phospholipid lysophosphatidylcholine caused activation of endothelial PYK2. Lysophosphatidylcholine-activated PYK2 induced NADPH oxidase-mediated ROS generation and ROS-mediated synthesis of tumor necrosis factor-α (TNFα), vascular cell adhesion molecule-1 (VCAM-1), monocyte chemotactic protein-1 (MCP-1), and p21Cip1/Ets-1. Neutralizing anti-TNFα antibody or knockdown of p21Cip1/Ets-1 system blocked the induction of VCAM-1 and MCP-1. PYK2 deficiency abolished these ROS-mediated proinflammatory reactions. Further analysis revealed that PYK2/ROS-mediated p21Cip1/Ets-1 activation upregulated the transcription of the MCP-1 gene in collaboration with p300 transcription coactivator.

CONCLUSIONS

PYK2 is a key tyrosine kinase activated by high cholesterol exposure, which causes ROS-mediated TNFα release and induces TNFα-dependent expression of proinflammatory molecules via the p21Cip1/Ets-1/p300 transcription system.

Ageing and neurodegenerative diseases

Ageing, which all creatures must encounter, is a challenge to every living organism. In the human body, it is estimated that cell division and metabolism occurs exuberantly until about 25 years of age. Beyond this age, subsidiary products of metabolism and cell damage accumulate, and the phenotypes of ageing appear, causing disease formation. Among these age-related diseases, neurodegenerative diseases have drawn a lot of attention due to their irreversibility, lack of effective treatment, and accompanied social and economical burdens. In seeking to ameliorate ageing and age-related diseases, the search for anti-ageing drugs has been of much interest. Numerous studies have shown that the plant polyphenol, resveratrol (3,5,4'-trihydroxystilbene), extends the lifespan of several species, prevents age-related diseases, and possesses anti-inflammatory, and anti-cancer properties. The beneficial effects of resveratrol are believed to be associated with the activation of a longevity gene, SirT1. In this review, we discuss the pathogenesis of age-related neurodegenerative diseases including Alzheimer's disease, Parkinson's disease and cerebrovascular disease. The therapeutic potential of resveratrol, diet and the roles of stem cell therapy are discussed to provide a better understanding of the ageing mystery.

Resveratrol protects human endothelium from H(2)O(2)-induced oxidative stress and senescence via SirT1 activation

AIM

Silencing information regulator (SirT1), a NAD-dependent histone deacetylase, is an essential mediator of longevity in normal cells by calorie restriction. SirT1 has many biological functions, including transcription regulation, cell differentiation inhibition, cell cycle regulation, and anti-apoptosis. Resveratrol (RV)-induced SirT1 activation also improves endothelial dysfunction and suppresses vascular inflammation. In this study, we investigated the roles of RV-induced SirT1 activation in endothelial cells under oxidative stress.

METHODS

SirT1 mRNA expression levels were examined in the endothelium layer (endothelial cells) of cardiac coronary vessels from patients receiving coronary artery bypass graft surgery (CABG) surgery and aged rats using reverse transcriptase polymerase chain reaction (RT-PCR). To further explore the effect of SirT1 activation on oxidative stress-induced aging, senescence-associated β-galactosidase (SA-β-gal) expression in RV-treated human umbilical vein endothelial cells (HUVECs) with or without H(2)O(2) treatment was evaluated.

RESULTS

SirT1 expression was decreased in aged and atherosclerotic vessels in vivo, and significantly reduced in endothelial cells purified from vessel tissues. Furthermore, SirT1 levels were dose-dependently increased in RV-treated HUVECs. The SA-β gal assay showed that RV inhibited the senescent phenotype of H(2)O(2)-treated HUVECs. Reactive oxygen species (ROS) production and the percentage of cells positive for SA-β gal were significantly increased in siRNA-SirT1 (knockdown of SirT1 expression)-treated HUVEC cells. Importantly, the treatment effect of RV was significantly abolished in the oxidative effects of H(2)O(2)-treated HUVECs by siRNA-SirT1.

CONCLUSION

Our data suggested that SirT1 could be a crucial factor involved in the endothelial cells of atherosclerotic CAGB patients and aging rats. RV is a potential candidate for preventing oxidative stress-induced aging in endothelial cells. RV may also prevent ROS-induced damage via increased endothelial SirT1 expression.

Molecular mechanisms underlying the activation of eNOS

Endothelial cells situated at the interface between blood and the vessel wall play a crucial role in controlling vascular tone and homeostasis, particularly in determining the expression of pro- and anti-atherosclerotic genes. Many of these effects are mediated by changes in the generation and release of the vasodilator nitric oxide (NO) in response to hemodynamic stimuli exerted on the luminal surface of endothelial cells by the streaming blood (shear stress) and the cyclic strain of the vascular wall. The endothelial NO synthase (eNOS) is activated in response to fluid shear stress and numerous agonists via cellular events such as; increased intracellular Ca(2+), interaction with substrate and co-factors, as well as adaptor and regulatory proteins, protein phosphorylation, and through shuttling between distinct sub-cellular domains. Dysregulation of these processes leads to attenuated eNOS activity and reduced NO output which is a characteristic feature of numerous patho-physiological disorders such as diabetes and atherosclerosis. This review summarizes some of the recent findings relating to the molecular events regulating eNOS activity.

Angiotensin II impairs endothelial function via tyrosine phosphorylation of the endothelial nitric oxide synthase

Proline-rich tyrosine kinase 2 (PYK2) can be activated by angiotensin II (Ang II) and reactive oxygen species. We report that in endothelial cells, Ang II enhances the tyrosine phosphorylation of endothelial NO synthase (eNOS) in an AT₁-, H₂O₂-, and PYK2-dependent manner. Low concentrations (1–100 µmol/liter) of H₂O₂ stimulated the phosphorylation of eNOS Tyr657 without affecting that of Ser1177, and attenuated basal and agonist-induced NO production. In isolated mouse aortae, 30 µmol/liter H₂O₂ induced phosphorylation of eNOS on Tyr657 and impaired acetylcholine-induced relaxation. Endothelial overexpression of a dominant-negative PYK2 mutant protected against H₂O₂-induced endothelial dysfunction. Correspondingly, carotid arteries from eNOS^−/− mice overexpressing the nonphosphorylatable eNOS Y657F mutant were also protected against H₂O₂. In vivo, 3 wk of treatment with Ang II considerably increased levels of Tyr657-phosphorylated eNOS in the aortae of wild-type but not Nox2^y/− mice, and this was again associated with a clear impairment in endothelium-dependent vasodilatation in the wild-type but not in the Nox2^y/− mice. Collectively, endothelial PYK2 activation by Ang II and H₂O₂ causes the phosphorylation of eNOS on Tyr657, attenuating NO production and endothelium-dependent vasodilatation. This mechanism may contribute to the endothelial dysfunction observed in cardiovascular diseases associated with increased activity of the renin–angiotensin system and elevated redox stress.

Reactive Oxygen Species–Mediated Signal Transduction in the Endothelium

The endothelium is an important component of vascular homeostasis that is a target for injury in the setting of vascular disease. One means of promoting a maladaptive endothelial cell phenotype such as that seen in atherosclerosis is excess oxidative stress. Although this term once was almost exclusively used to describe low-density lipoprotein (LDL) and lipid oxidation in the vasculature, we now understand that the intracellular oxidant milieu is an important modulator of vascular cell function. Indeed, considerable data indicate that reactive oxygen species (ROS) are an important means of cellular signaling, although the precise mechanisms whereby ROS accomplish this are still under investigation. In this review, the data linking ROS to kinase activation and cell signaling in the endothelium is discussed, with a particular emphasis on the roles of protein thiol modification.

Hemodynamic forces, vascular oxidative stress, and regulation of BMP-2/4 expression

Changes in the hemodynamic environment (e.g., hypertension, disturbed-flow conditions) are known to promote atherogenesis by inducing proinflammatory phenotypic alterations in endothelial and smooth muscle cells; however, the mechanisms underlying mechanosensitive induction of inflammatory gene expression are not completely understood. Bone morphogenetic protein-2 and -4 (BMP-2/4) are TGF-beta superfamily cytokines that are expressed by both endothelial and smooth muscle cells and regulate a number of cellular processes involved in atherogenesis, including vascular calcification and endothelial activation. This review considers how hemodynamic forces regulate BMP-2/4 expression and explores the role of mechanosensitive generation of reactive oxygen species by NAD(P)H oxidases in the control of BMP signaling.

eNOS activation by physical forces: from short-term regulation of contraction to chronic remodeling of cardiovascular tissues

Nitric oxide production in response to flow-dependent shear forces applied on the surface of endothelial cells is a fundamental mechanism of regulation of vascular tone, peripheral resistance, and tissue perfusion. This implicates the concerted action of multiple upstream "mechanosensing" molecules reversibly assembled in signalosomes recruiting endothelial nitric oxide synthase (eNOS) in specific subcellular locales, e.g., plasmalemmal caveolae. Subsequent short- and long-term increases in activity and expression of eNOS translate this mechanical stimulus into enhanced NO production and bioactivity through a complex transcriptional and posttranslational regulation of the enzyme, including by shear-stress responsive transcription factors, oxidant stress-dependent regulation of transcript stability, eNOS regulatory phosphorylations, and protein-protein interactions. Notably, eNOS expressed in cardiac myocytes is amenable to a similar regulation in response to stretching of cardiac muscle cells and in part mediates the length-dependent increase in cardiac contraction force. In addition to short-term regulation of contractile tone, eNOS mediates key aspects of cardiac and vascular remodeling, e.g., by orchestrating the mobilization, recruitment, migration, and differentiation of cardiac and vascular progenitor cells, in part by regulating the stabilization and transcriptional activity of hypoxia inducible factor in normoxia and hypoxia. The continuum of the influence of eNOS in cardiovascular biology explains its growing implication in mechanosensitive aspects of integrated physiology, such as the control of blood pressure variability or the modulation of cardiac remodeling in situations of hemodynamic overload.

NADPH oxidase-dependent signaling in endothelial cells: role in physiology and pathophysiology

Reactive oxygen species (ROS) including superoxide (O(2)(.-)) and hydrogen peroxide (H(2)O(2)) are produced endogenously in response to cytokines, growth factors; G-protein coupled receptors, and shear stress in endothelial cells (ECs). ROS function as signaling molecules to mediate various biological responses such as gene expression, cell proliferation, migration, angiogenesis, apoptosis, and senescence in ECs. Signal transduction activated by ROS, "oxidant signaling," has received intense investigation. Excess amount of ROS contribute to various pathophysiologies, including endothelial dysfunction, atherosclerosis, hypertension, diabetes, and acute respiratory distress syndrome (ARDS). The major source of ROS in EC is a NADPH oxidase. The prototype phagaocytic NADPH oxidase is composed of membrane-bound gp91phox and p22hox, as well as cytosolic subunits such as p47(phox), p67(phox) and small GTPase Rac. In ECs, in addition to all the components of phagocytic NADPH oxidases, homologues of gp91(phox) (Nox2) including Nox1, Nox4, and Nox5 are expressed. The aim of this review is to provide an overview of the emerging area of ROS derived from NADPH oxidase and oxidant signaling in ECs linked to physiological and pathophysiological functions. Understanding these mechanisms may provide insight into the NADPH oxidase and oxidant signaling components as potential therapeutic targets.

Vascular consequences of dietary salt intake

Animal and human studies support an untoward effect of excess dietary NaCl (salt) intake on cardiovascular and renal function and life span. Recent work has promoted the concept that the endothelium, in particular, reacts to changes in dietary salt intake through a complex series of events that are independent of blood pressure and the renin-angiotensin-aldosterone axis. The cellular signaling events culminate in the intravascular production of transforming growth factor-beta (TGF-beta) and nitric oxide in response to increased salt intake. Plasticity of the endothelium is integral in the vascular remodeling consequences associated with excess salt intake, because nitric oxide serves as a negative regulator of TGF-beta production. Impairment of nitric oxide production, such as occurs with endothelial dysfunction in a variety of disease states, results in unopposed excess vascular TGF-beta production, which promotes reduced vascular compliance and augmented peripheral arterial constriction and hypertension. Persistent alterations in vascular function promote the increase in cardiovascular events and reductions in renal function that reduce life span during increased salt intake.

Maternal uterine vascular remodeling during pregnancy

Sufficient uteroplacental blood flow is essential for normal pregnancy outcome and is accomplished by the coordinated growth and remodeling of the entire uterine circulation, as well as the creation of a new fetal vascular organ: the placenta. The process of remodeling involves a number of cellular processes, including hyperplasia and hypertrophy, rearrangement of existing elements, and changes in extracellular matrix. In this review, we provide information on uterine blood flow increases during pregnancy, the influence of placentation type on the distribution of uterine vascular resistance, consideration of the patterns, nature, and extent of maternal uterine vascular remodeling during pregnancy, and what is known about the underlying cellular mechanisms.

Dietary salt activates an endothelial proline-rich tyrosine kinase 2/c-Src/phosphatidylinositol 3-kinase complex to promote endothelial nitric oxide synthase phosphorylation

Although many laboratories have shown that dietary NaCl (salt) intake increases NO production in rodents and humans, the mechanism has not been uncovered. In the present study, pharmacological and dominant-negative strategies were used to show that feeding a formulated diet containing increased amounts of salt to young male Sprague-Dawley rats induced the formation of an endothelial cell-signaling complex that contained proline-rich tyrosine kinase 2, c-Src (also known as pp60(c-src)), and phosphatidylinositol 3-kinase. In the setting of a high-salt diet, proline-rich tyrosine kinase 2 served as the scaffold for c-Src-mediated phosphatidylinositol 3-kinase activation. Phosphatidylinositol 3-kinase was the upstream activator of protein kinase B (Akt), which was responsible for phosphorylation of the rat endothelial isoform of NO synthase at S1176 and thereby promoted the increase in NO production. The combined findings illustrated the crucial role for a proline-rich tyrosine kinase 2-signaling complex in the endothelial response to salt intake.

Cell cycle regulation by oncogenic tyrosine kinases in myeloid neoplasias: from molecular redox mechanisms to health implications

Neoplastic expansion of myeloid cells is associated with specific genetic changes that lead to chronic activation of signaling pathways, as well as altered metabolism. It has become increasingly evident that transformation relies on the interdependency of both events. Among the various genetic changes, the oncogenic BCR-ABL tyrosine kinase in patients with Philadelphia chromosome positive chronic myeloid leukemia (CML) has been a focus of extensive research. Transformation by this oncogene is associated with elevated levels of intracellular reactive oxygen species (ROS). ROS have been implicated in processes that promote viability, cell growth, and regulation of other biological functions such as migration of cells or gene expression. Currently, the BCR-ABL inhibitor imatinib mesylate (Gleevec) is being used as a first-line therapy for the treatment of CML. However, BCR-ABL transformation is associated with genomic instability, and disease progression or resistance to imatinib can occur. Imatinib resistance is not known to cause or significantly alter signaling requirements in transformed cells. Elevated ROS are crucial for transformation, making them an ideal additional target for therapeutic intervention. The underlying mechanisms leading to elevated oxidative stress are reviewed, and signaling mechanisms that may serve as novel targeted approaches to overcome ROS-dependent cell growth are discussed.

Role of the cytoskeleton in flow (shear stress)-induced dilation and remodeling in resistance arteries

Cytoskeletal proteins determine cell shape and integrity and membrane-bound structures connected to extracellular components allow tissue integrity. These structural elements have an active role in the interaction of blood vessels with their environment. Shear stress due to blood flow is the most important force stimulating the endothelium. The role of cytoskeletal proteins in endothelial responses to flow has been studied in resistance arteries using pharmacological tools and transgenic models. Shear stress activates extracellular "flow sensing" elements associated with a thick glycocalyx communicating the signal to membrane-bound complexes (integrins and/or dystrophin-dystroglycans) and to eNOS through a pathway involving the intermediate filament vimentin, the microtubule network and actin. When blood flow increases chronically the endothelium triggers diameter enlargement and medial hypertrophy. This is facilitated by the genetic absence of the intermediate filaments, vimentin and desmin suggesting that these elements oppose the process.

KLF2 Primes the Antioxidant Transcription Factor Nrf2 for Activation in Endothelial Cells

Objective— Atheroprotective blood flow induces expression of anti-inflammatory Krüppel-like factor 2 (KLF2) and activates antioxidant transcription factor nuclear factor erythroid 2-related factor 2 (Nrf2) in vascular endothelium. Previously, we obtained KLF2-induced gene expression profiles in ECs, containing several Nrf2 target genes. Our aim was to investigate the role of KLF2 in shear stress–mediated activation of Nrf2 in human umbilical vein endothelial cells (HUVECs).

Methods and Results— Expression of Nrf2 and its targets NAD(P)H dehydrogenase quinone 1 (NQO1) and heme oxygenase (HO-1) was elevated by shear and KLF2. KLF2 knockdown showed that shear-induced expression of NQO1 but not Nrf2 was dependent on KLF2. KLF2 overexpression in absence of flow resulted in more efficient activation of Nrf2 by tert-butyl hydroquinone (tBHQ) through enhanced nuclear localization, and promoted expression of a large panel of Nrf2-dependent genes resulting in superior protection against oxidative stress. Comparison of shear-, KLF2-, and Nrf2-induced transcriptomes showed that the majority of shear-modulated gene sets is influenced by KLF2 or Nrf2.

Conclusions— We report that KLF2 substantially enhances antioxidant activity of Nrf2 by increasing its nuclear localization and activation. The synergistic activity of these two transcription factors forms a major contribution to the shear stress–elicited transcriptome in endothelial cells.

Mechanism of dietary salt-mediated increase in intravascular production of TGF-beta1

Clinical and preclinical studies have demonstrated an important effect of arterial pathobiology on the progressive loss of renal function that occurs in chronic kidney disease. Chronic kidney disease, in turn, promotes alterations in vascular function. A modulating role for dietary salt has been suggested, with the amount of salt intake regulating endothelial cell production of transforming growth factor-beta1 (TGF-beta1), a fibrogenic growth factor that promotes arteriosclerosis and glomerulosclerosis. The purpose of the present studies was to determine how the interaction between dietary salt intake and vasculature promoted the production of TGF-beta1 in rats. Two different vascular tissues, aortic rings and glomeruli, were chosen for study. Dietary salt induced, in a dose-dependent fashion, activation of proline-rich tyrosine kinase-2 (Pyk2) and further identified c-Src as an important binding partner of Pyk2 in these tissues. Use of pharmacological inhibitors and dominant negative strategies confirmed that dietary salt induced complex formation of Pyk2 and c-Src with downstream activation of p38 and p42/44 mitogen-activated protein kinases and generation of TGF-beta1. The experiments defined the molecular signaling events that promoted the production of TGF-beta1, a key growth factor involved in the vascular response to increased salt intake.

Inhibition of endothelial nitric oxide synthase activity by proline-rich tyrosine kinase 2 in response to fluid shear stress and insulin

In native and primary cultures of endothelial cells, fluid shear stress elicits the tyrosine phosphorylation of the endothelial NO synthase (eNOS), however, the consequences of this modification on enzyme activity are unclear. We found that fluid shear stress induces the association of eNOS with the proline-rich tyrosine kinase 2 (PYK2) in endothelial cells and that the eNOS immunoprecipitated from eNOS- and PYK2-overexpressing HEK293 cells was tyrosine-phosphorylated on Tyr657. In mouse carotid arteries, the overexpression of wild-type PYK2, but not a dominant-negative PYK2, decreased eNOS activity (approximately 50%), whereas in murine lung endothelial cells, the downregulation of PYK2 (small interfering RNA) increased ionomycin-induced NO production. Mutation of Tyr657 to the phosphomimetic residues aspartate (D) or glutamate (E) abolished enzyme activity, whereas a nonphosphorylatable mutant (phenylalanine [F]) showed activity comparable to the wild-type enzyme. Moreover, normal flow-induced vasodilatation was apparent in carotid arteries from eNOS(-/-) mice overexpressing either the wild-type eNOS or the Y657F mutant, whereas no flow-induced vasodilatation was apparent in arteries expressing the Y657E eNOS mutant. Insulin also activated PYK2 and stimulated eNOS in endothelial cells expressing the Y657F mutant but not wild-type eNOS. These data indicate that PYK2 mediates the tyrosine phosphorylation of eNOS on Tyr657 in response to fluid shear stress and insulin stimulation and that this modification attenuates the activity of the enzyme. The PYK2-dependent inhibition of NO production may serve to keep eNOS activity low and limit the detrimental consequences of maintained high NO output, ie, the generation of peroxynitrite.

ICAM-1-Mediated, Src- and Pyk2-Dependent Vascular Endothelial Cadherin Tyrosine Phosphorylation Is Required for Leukocyte Transendothelial Migration

Leukocyte transendothelial migration (TEM) has been modeled as a multistep process beginning with rolling adhesion, followed by firm adhesion, and ending with either transcellular or paracellular passage of the leukocyte across the endothelial monolayer. In the case of paracellular TEM, endothelial cell (EC) junctions are transiently disassembled to allow passage of leukocytes. Numerous lines of evidence demonstrate that tyrosine phosphorylation of adherens junction proteins, such as vascular endothelial cadherin (VE-cadherin) and beta-catenin, correlates with the disassembly of junctions. However, the role of tyrosine phosphorylation in the regulation of junctions during leukocyte TEM is not completely understood. Using human leukocytes and EC, we show that ICAM-1 engagement leads to activation of two tyrosine kinases, Src and Pyk2. Using phospho-specific Abs, we show that engagement of ICAM-1 induces phosphorylation of VE-cadherin on tyrosines 658 and 731, which correspond to the p120-catenin and beta-catenin binding sites, respectively. These phosphorylation events require the activity of both Src and Pyk2. We find that inhibition of endothelial Src with PP2 or SU6656 blocks neutrophil transmigration (71.1 +/- 3.8% and 48.6 +/- 3.8% reduction, respectively), whereas inhibition of endothelial Pyk2 also results in decreased neutrophil transmigration (25.5 +/- 6.0% reduction). Moreover, overexpression of the nonphosphorylatable Y658F or Y731F mutants of VE-cadherin impairs transmigration of neutrophils compared with overexpression of wild-type VE-cadherin (32.7 +/- 7.1% and 38.8 +/- 6.5% reduction, respectively). Our results demonstrate that engagement of ICAM-1 by leukocytes results in tyrosine phosphorylation of VE-cadherin, which is required for efficient neutrophil TEM.

Glucocorticoids induce osteocyte apoptosis by blocking focal adhesion kinase-mediated survival. Evidence for inside-out signaling leading to anoikis

Bone fragility induced by chronic glucocorticoid excess is due, at least in part, to induction of osteocyte apoptosis through direct actions on these cells. However, the molecular mechanism by which glucocorticoids shorten osteocyte life span has remained heretofore unknown. We report that apoptosis of osteocytic MLO-Y4 cells induced by the synthetic glucocorticoid dexamethasone is abolished by the glucocorticoid receptor antagonist RU486, but not by inhibition of protein or RNA synthesis. Dexamethasone-induced apoptosis is preceded by a decrease in the number of cytoplasmic processes, an indicator of cell detachment. In addition, the focal adhesion kinase FAK prevents dexamethasone-induced apoptosis, whereas the FAK-related kinase Pyk2 increases the basal levels of apoptosis. Dexamethasone-induced apoptosis is also prevented in cells expressing kinase-deficient or phosphorylation-defective (Y402F) dominant negative mutants of Pyk2. Consistent with the requirement of tyrosine 402, dexamethasone induces rapid Pyk2 phosphorylation in this residue. Moreover, knocking down Pyk2 expression abolishes apoptosis and cell detachment induced by dexamethasone, and transfection with human Pyk2 rescues both responses. Furthermore, induction of apoptosis as well as cell detachment by dexamethasone is abolished by inhibiting the activity of JNK, a recognized downstream target of Pyk2 activation. These results demonstrate that glucocorticoids promote osteocyte apoptosis via a receptor-mediated mechanism that does not require gene transcription and that is mediated by rapid activation of Pyk2 and JNK, followed by inside-out signaling that leads to cell detachment-induced apoptosis or anoikis.

Hydrogen peroxide-induced Ca2+ responses in CNS pericytes

OBJECTIVE

The aims of the present study were to elucidate the interaction of reactive oxygen species (ROS) and Ca(2+) response in central nervous system (CNS) pericytes.

METHODS

The intracellular Ca(2+) concentration was measured using fluorescent Ca(2+) indicator, fura-2, in cultured CNS pericytes.

RESULTS

Hydrogen peroxide evoked a dose-dependent increase in cytosolic Ca(2+), which was completely inhibited by catalase. Removal of external Ca(2+) or addition of nicardipine (1 microM) during application of hydrogen peroxide did not affect Ca(2+) response. Incubation of the cells in Ca(2+) free solution did not abolish but slightly reduced Ca(2+) response by hydrogen peroxide. Ca(2+) response to hydrogen peroxide was not altered by the depletion of intracellular Ca(2+) by thapsigargin (1 microM). Pretreatment of the cells with tyrosine kinase inhibitor genistein (100 microM) or tyrphostin A47 (30 microM) significantly reduced Ca(2+) increase by hydrogen peroxide.

CONCLUSIONS

These results indicate that hydrogen peroxide evokes Ca(2+) increase predominantly by release from intracellular Ca(2+) store, which may be regulated by tyrosine kinases.

Alpha1-adrenergic receptors activate AKT via a Pyk2/PDK-1 pathway that is tonically inhibited by novel protein kinase C isoforms in cardiomyocytes

AKT is a potent antiapoptotic kinase, but its role in the cardioprotective actions of alpha(1)-adrenergic receptors (ARs) remains uncertain, because alpha(1)-ARs typically induce little-to-no AKT activation in most cardiomyocyte models. This study identifies a prominent alpha(1)-AR-dependent AKT activation pathway that is under tonic inhibitory control by novel protein kinase Cs (nPKCs) in neonatal rat cardiomyocyte cultures. We also implicate Pyk2, Pyk2 complex formation with PDK-1 and paxillin, and increased PDK-1-Y373/376 phosphorylation as the mechanism that links alpha(1)-AR activation to increased AKT phosphorylation. nPKCs (which are prominent alpha(1)-AR effectors) interfere with this alpha(1)-AR-dependent AKT activation by blocking Pyk2/PDK-1/paxillin complex formation and PDK-1-Y373/376 phosphorylation. Additional studies used an adenoviral-mediated overexpression strategy to show that Pyk2 exerts dual controls on antiapoptotic PDK-1/AKT and proapoptotic c-Jun N-terminal kinase (JNK) pathways. Although the high nPKC activity of most cardiomyocyte models favors Pyk2 signaling to JNK (and cardiac apoptosis), the cardioprotective actions of Pyk2 through the PDK-1/AKT pathway are exposed when PKC or JNK activation is prevented. Collectively, these studies identify JNK and AKT as functionally distinct downstream components of the alpha(1)-AR/Pyk2 signaling pathway. We also implicate nPKCs as molecular switches that control the balance of signaling via proapoptotic JNK and antiapoptotic PDK-1/AKT pathways, exposing a novel mechanism for nPKC-dependent regulation of cardiac hypertrophy and failure.

Mechanosensitive production of reactive oxygen species in endothelial and smooth muscle cells: role in microvascular remodeling?

Changes in the hemodynamic environment (e.g., hypertension, increased blood flow/shear stress) are known to lead to vascular remodeling; however, the underlying mechanisms by which hemodynamic forces control gene expression in vascular cells are not yet completely understood. This review considers how mechanosensitive generation of reactive oxygen species (ROS) by NAD(P)H oxidases and other sources interacts with downstream signaling systems [including activation of nuclear factor kappa B (NF-kappaB) and AP-1] that modulate the phenotype of endothelial and smooth muscle cells, leading to vascular remodeling. We propose a model for an interaction between direct mechanosensitive ROS signaling and pathways activated by pressure-induced upregulation of prooxidant paracrine signaling mechanisms [local renin-angiotensin system, TNF-alpha- converting enzyme (TACE)/tumor necrosis factor alpha (TNF-alpha) system, and endothelin signaling].

Subcellular targeting of oxidants during endothelial cell migration

Endogenous oxidants participate in endothelial cell migration, suggesting that the enzymatic source of oxidants, like other proteins controlling cell migration, requires precise subcellular localization for spatial confinement of signaling effects. We found that the nicotinamide adenine dinucleotide phosphate reduced (NADPH) oxidase adaptor p47^phox and its binding partner TRAF4 were sequestered within nascent, focal complexlike structures in the lamellae of motile endothelial cells. TRAF4 directly associated with the focal contact scaffold Hic-5, and the knockdown of either protein, disruption of the complex, or oxidant scavenging blocked cell migration. An active mutant of TRAF4 activated the NADPH oxidase downstream of the Rho GTPases and p21-activated kinase 1 (PAK1) and oxidatively modified the focal contact phosphatase PTP-PEST. The oxidase also functioned upstream of Rac1 activation, suggesting its participation in a positive feedback loop. Active TRAF4 initiated robust membrane ruffling through Rac1, PAK1, and the oxidase, whereas the knockdown of PTP-PEST increased ruffling independent of oxidase activation. Our data suggest that TRAF4 specifies a molecular address within focal complexes that is targeted for oxidative modification during cell migration.

Signaling Mechanisms Regulating Endothelial Permeability

The microvascular endothelial cell monolayer localized at the critical interface between the blood and vessel wall has the vital functions of regulating tissue fluid balance and supplying the essential nutrients needed for the survival of the organism. The endothelial cell is an exquisite “sensor” that responds to diverse signals generated in the blood, subendothelium, and interacting cells. The endothelial cell is able to dynamically regulate its paracellular and transcellular pathways for transport of plasma proteins, solutes, and liquid. The semipermeable characteristic of the endothelium (which distinguishes it from the epithelium) is crucial for establishing the transendothelial protein gradient (the colloid osmotic gradient) required for tissue fluid homeostasis. Interendothelial junctions comprise a complex array of proteins in series with the extracellular matrix constituents and serve to limit the transport of albumin and other plasma proteins by the paracellular pathway. This pathway is highly regulated by the activation of specific extrinsic and intrinsic signaling pathways. Recent evidence has also highlighted the importance of the heretofore enigmatic transcellular pathway in mediating albumin transport via transcytosis. Caveolae, the vesicular carriers filled with receptor-bound and unbound free solutes, have been shown to shuttle between the vascular and extravascular spaces depositing their contents outside the cell. This review summarizes and analyzes the recent data from genetic, physiological, cellular, and morphological studies that have addressed the signaling mechanisms involved in the regulation of both the paracellular and transcellular transport pathways.

Role of Focal Adhesion Kinase in Flow-Induced Dilation of Coronary Arterioles

Backgound— Flow-induced regulation of endothelial NO synthase (eNOS) depends on integrin signaling and tyrosine kinase activation. Integrins cluster in focal adhesion complexes, where the extracellular matrix is connected to the cytoskeleton and where focal adhesion kinase (FAK) is located. FAK plays a central role in integrin signaling and Src activation. Accordingly, we hypothesized that FAK plays an important role in flow-induced dilation (FID).

Methods and Results— To inactivate FAK-dependent signaling, anti-FAK, phosphospecific (Tyr 397 ) antibody (FAKab), which binds against the FAK autophosphorylation site, was incorporated into endothelium of rat coronary arterioles using liposomal transfection. The responses to flow, acetylcholine (Ach), or the NO donor MAHAMANONOate (NOC-9) were observed before and after FAKab. In control and vehicles (denatured antibody or transfecting reagent alone), flow produced progressive dilation to a maximal value of 35% increase in diameter, which was inhibited by N ω -nitro- l -arginine methyl ester ( l -NAME). However, FAKab prevented FID ( P <0.01 versus control). Combined treatment with FAKab and l -NAME did not produce inhibition greater than FAKab alone. FAKab did not blunt Ach- or NOC-9–induced dilation. Western analysis demonstrated that FAKab prevented flow-induced phosphorylation of FAK (pY397-FAK), Akt (pS473-Akt), and eNOS (pS1179-eNOS).

Conclusion— Our study demonstrates the pivotal role of FAK in NO-mediated FID. Inhibition of FAK signaling with FAKab impaired FID and phosphorylation of Akt and eNOS. Our data suggest that the activation of FAK is central to the mechanotransduction of FID via regulation of activation of Akt and eNOS.

Endothelial protein kinase C isoform identity and differential activity of PKCzeta in an athero-susceptible region of porcine aorta

Endothelial protein kinase C (PKC) signaling was investigated in different regions of normal porcine aorta. The locations map to differential atherosclerotic susceptibility and correlate with sites of disturbed (DF) or undisturbed (UF) local flow profiles. Endothelial lysates were isolated from the inner curvature of the aortic arch (DF; athero-susceptible) and a nearby UF region of the descending thoracic aorta (UF; athero-protected), and in some experiments a distant athero-protected UF site, the common carotid artery. Total endothelial PKC activity in the DF regions was 145% to 240% of that in both UF locations (P<0.05), whereas the UF regions were not significantly different from each other. PKC protein isoforms alpha, beta, epsilon, iota, lambda, and zeta were expressed in similar proportions in both aortic regions, suggesting that differences of kinase activity were not directly attributable to expression levels. Inhibition of members of the "conventional" and "novel" PKC families had no differential effect on regional kinase activity. However, inhibition of PKCzeta, a member of the "atypical" PKC family, reduced the DF lysate kinase activity to that of UF levels (NS P=0.35). Differential phosphorylation of PKCzeta Thr410 and Thr560, along with increased levels of PKCzeta degradation products in UF endothelial lysates, suggested posttranslational modification of PKCzeta as the basis for site-specific differences in vivo. Steady-state regional heterogeneity of an important family of regulatory proteins in intact arterial endothelium in vivo may link localized athero-susceptibility and the associated hemodynamic environment.

Flow activates ERK1/2 and endothelial nitric oxide synthase via a pathway involving PECAM1, SHP2, and Tie2

Blood flow modulates endothelial cell (EC) functions through specific signaling events. Previous data show that flow stimulates SHP2 translocation to cell membranes and binding to phosphotyrosine proteins. Flow-induced ERK1/2 phosphorylation depends on SHP2 phosphatase activity and SHP2 binding to phospho-PECAM1 (platelet endothelial adhesion molecule 1), suggesting that SHP2 forms a signaling module with PECAM1. We hypothesized that flow induces assembly of the multi-protein complexes with SHP2 that are required for downstream signaling. ECs were exposed to flow for 10 min, and endogenous SHP2 was immunoprecipitated. SHP2-associated proteins were analyzed by SDS-PAGE and identified by mass spectrometry. Tie2 and several known SHP2-binding proteins were identified in flow-induced SHP2 complexes. Flow significantly increased tyrosine phosphorylation of both Tie2 and PECAM1 and their association with SHP2. To evaluate their functional roles, ECs were treated with Tie2 or PECAM1 small interfering RNA (siRNA). Tie2 and PECAM1 expression decreased >80% after siRNA treatment, and flow-stimulated phosphorylation of ERK1/2, Akt, and endothelial nitric oxide synthase was significantly inhibited by Tie2 and PECAM1 siRNA. Tie2 phosphorylation by flow was significantly inhibited by PECAM1 siRNA treatment. These results establish Tie2 transactivation via PECAM1 as an early event in flow-mediated mechanotransduction and suggest an important role for a PECAM1-SHP2-Tie2 pathway in flow-mediated signal transduction.

Proline-rich Tyrosine Kinase 2 (Pyk2) Mediates Vascular Endothelial-Cadherin-based Cell-Cell Adhesion by Regulating β-Catenin Tyrosine Phosphorylation

Vascular endothelial-cadherin (VE-cadherin) controls endothelial cell-cell adhesion and preserves endothelial integrity. In order to maintain endothelial barrier function, VE-cadherin function is tightly regulated through mechanisms that involve protein phosphorylation and cytoskeletal dynamics. Here, we show that loss of VE-cadherin function results in intercellular gap formation and a drop in electrical resistance of monolayers of primary human endothelial cells. Detailed analysis revealed that loss of endothelial cell-cell adhesion, induced by VE-cadherin-blocking antibodies, is preceded by and dependent on a rapid activation of Rac1 and increased production of reactive oxygen species. Moreover, VE-cadherin-associated beta-catenin is tyrosine-phosphorylated upon loss of cell-cell contact. Finally, the redox-sensitive proline-rich tyrosine kinase 2 (Pyk2) is activated and recruited to cell-cell junctions following the loss of VE-cadherin homotypic adhesion. Conversely, the inhibition of Pyk2 activity in endothelial cells by the expression of CRNK (CADTK/CAKbeta-related non-kinase), an N-terminal deletion mutant that acts in a dominant negative fashion, not only abolishes the increase in beta-catenin tyrosine phosphorylation but also prevents the loss of endothelial cell-cell contact. These results implicate Pyk2 in the reduced cell-cell adhesion induced by the Rac-mediated production of ROS through the tyrosine phosphorylation of beta-catenin. This signaling is initiated upon loss of VE-cadherin function and is important for our insight in the modulation of endothelial integrity.

Flow shear stress stimulates Gab1 tyrosine phosphorylation to mediate protein kinase B and endothelial nitric-oxide synthase activation in endothelial cells

Fluid shear stress generated by blood flow modulates endothelial cell function via specific intracellular signaling events. We showed previously that flow activated the phosphatidylinositol 3-kinase (PI3K), Akt, and endothelial nitric-oxide synthase (eNOS) via Src kinase-dependent transactivation of vascular endothelial growth factor receptor 2 (VEGFR2). The scaffold protein Gab1 plays an important role in receptor tyrosine kinase-mediated signal transduction. We found here that laminar flow (shear stress = 12 dynes/cm2) rapidly stimulated Gab1 tyrosine phosphorylation in both bovine aortic endothelial cells and human umbilical vein endothelial cells, which correlated with activation of Akt and eNOS. Gab1 phosphorylation as well as activation of Akt and eNOS by flow was inhibited by the Src kinase inhibitor PP2 (4-amino-5-(4-chlorophenyl)-7-(t-butyl)pyrazolo[3,4-d]pyrimidine) and VEGFR2 kinase inhibitors SU1498 and VTI, suggesting that flow-mediated Gab1 phosphorylation is Src kinase-dependent and VEGFR2-dependent. Tyrosine phosphorylation of Gab1 by flow was functionally important, because flow stimulated the association of Gab1 with the PI3K subunit p85 in a time-dependent manner. Furthermore, transfection of a Gab1 mutant lacking p85 binding sites inhibited flow-induced activation of Akt and eNOS. Finally, knockdown of endogenous Gab1 by small interference RNA abrogated flow activation of Akt and eNOS. These data demonstrate a critical role of Gab1 in flow-stimulated PI3K/Akt/eNOS signal pathway in endothelial cells.