Epidermal growth factor receptor transactivation by endogenous vasoactive peptides contributes to hyperproliferation of vascular smooth muscle cells of SHR

Effect of Dan-Lou tablets on coronary heart disease revealed by microarray analysis integrated with molecular mechanism studies

Dan-Lou tablets (DLT) effectively treat coronary heart disease (CHD). However, its pharmacological mechanism in CHD treatment requires further investigation. This study aimed to elucidate the underlying pharmacological mechanisms of DLT in the treatment of CHD through clinical trials, microarray research, bioinformatics analysis, and molecular mechanism research. In this study, DLT improved coagulation function, endothelial injury, and levels of lipids, metalloproteases, adhesion molecules, inflammatory mediators, and homocysteine. The results of molecular biology research demonstrated that DLT can increase the gene and protein expressions of meningioma expressed antigen 5 (MGEA5) and mouse doubleminute 2 (MDM2) and inhibited the gene and protein expressions of signal transcription and transcription activator 5 B (STAT5B), tropomyosin-1 (TPM1), and aromatic hydrocarbon receptor nuclear transpose (ARNT). The results indicate that DLT reduced the extent of vascular endothelial damage in CHD rats by reducing the expressions of STAT5B, TPM1, and MDM2; inhibiting the inflammatory reaction; and increasing the expressions of ARNT and MGEA5.

Role of Gi proteins in the regulation of blood pressure and vascular remodeling

Heterotrimeric guanine nucleotide regulatory proteins (G-proteins) through the activation of several signaling mechanisms including adenylyl cyclase/cAMP and phospholipase C (PLC)/phosphatidyl inositol (PI) turnover. regulate a variety of cellular functions, including vascular reactivity, proliferation and hypertrophy of VSMC. Activity of adenylyl cyclase is regulated by two G proteins, stimulatory (Gsα) and inhibitory (Giα). Gsα stimulates adenylyl cyclase activity and increases the levels of cAMP, whereas Giα inhibits the activity of adenylyl cyclase and results in the reduction of cAMP levels. Abnormalities in Giα protein expression and associated adenylyl cyclase\cAMP levels result in the impaired cellular functions and contribute to various pathological states including hypertension. The expression of Giα proteins is enhanced in various tissues including heart, kidney, aorta and vascular smooth muscle cells (VSMC) from genetic (spontaneously hypertensive rats (SHR)) and experimentally - induced hypertensive rats and contribute to the pathogenesis of hypertension. In addition, the enhanced expression of Giα proteins exhibited by VSMC from SHR is also implicated in the hyperproliferation and hypertrophy, the two key players contributing to vascular remodelling in hypertension. The enhanced levels of endogenous vasoactive peptides including angiotensin II (Ang II), endothelin-1 (ET-1) and growth factors contribute to the overexpression of Giα proteins in VSMC from SHR. In addition, enhanced oxidative stress, activation of c-Src, growth factor receptor transactivation and MAP kinase/PI3kinase signaling also contribute to the augmented expression of Giα proteins in VSMC from SHR. This review summarizes the role of Giα proteins, and the underlying molecular mechanisms implicated in the regulation of high blood pressure and vascular remodelling.

Downregulation of natriuretic peptide receptor-C in vascular smooth muscle cells from spontaneously hypertensive rats contributes to vascular remodeling

Hypertension is associated with vascular remodeling due to hyperproliferation and hypertrophy of vascular smooth muscle cells (VSMC). VSMC from several animal models of hypertensive rats including spontaneously hypertensive rats (SHR) exhibit hyperproliferation, hypertrophy and decreased expression of natriuretic peptide receptor-C (NPR-C). In addition, angiotensin II (Ang II) and growth factors that promotes vascular remodeling have also been shown to attenuate the expression of NPR-C in VSMC. The present study investigates the relationship between the decreased expression of NPR-C and vascular remodeling in SHR and the underlying molecular mechanisms. Aortic VSMC from SHR and their control Wistar Kyoto (WKY) rats were transfected with cDNA of NPR-C and used for the vascular remodeling studies. Transfection of VSMC with cDNA of NPR-C augmented the expression of NPR-C in both VSMC from SHR and WKY rats and resulted in the attenuation of hyperproliferation and hypertrophy of VSMC from SHR. The overexpression of NPR-C also resulted in the attenuation of increased expression of epidermal growth factor receptor (EGFR), platelet derived growth factor receptor (PDGFR), cell cycle proteins, cyclin D1, cyclin-dependent kinase 4 (Cdk4), phospho-retinoblastoma (pRb) and Giα-2 proteins, all these signaling molecules implicated in the hyperproliferation/hypertrophy of VSMC from SHR. In summary, these results indicate that augmenting the decreased expression of NPR-C in VSMC from SHR improves vascular remodeling by attenuating hyperproliferation and hypertrophy through decreasing the overexpression of several signaling molecules. It may be suggested that NPR-C plays a vasculoprotective role and that the downregulation of NPR-C contributes to the vascular remodeling in SHR.

Sirtuin1 contributes to the overexpression of Giα proteins and hyperproliferation of vascular smooth muscle cells from spontaneously hypertensive rats

BACKGROUND

We earlier demonstrated that vascular smooth muscle cells (VSMC) from spontaneously hypertensive rats (SHR) exhibit the overexpression of Giα proteins and hyperproliferation that is attributed to the enhanced levels of endogenous angiotensin II (Ang II). In addition, the implication of Sirtuin1 (Sirt1) a histone deacetylase class III family in Ang II-induced hypertension has also been shown. We recently demonstrated that Ang II increased the expression of Sirt1 in aortic VSMC that contributed to the overexpression of Giα proteins. However, whether Sirt1 is overexpressed in VSMC from SHR and is linked to the enhanced expression of Giα proteins and hyperproliferation remains unexplored.

METHOD AND RESULTS

In the present study, we show that Sirt1 is upregulated in VSMC from SHR and this upregulation was attenuated by AT1 receptor antagonist losartan. In addition, the inhibition or knockdown of Sirt1 by specific inhibitors EX 527 and NAM and/or siRNA attenuated the enhanced expression of Giα proteins, cell cycle proteins and hyperproliferation of VSMC from SHR. Furthermore, the enhanced levels of reactive oxygen species (ROS), hydrogen peroxide and NADPH oxidase subunits NOX2 and p47phox, increased phosphorylation of EGFR, ERK1/2 and AKT displayed by VSMC from SHR were also attenuated by knocking down of Sirt1 by siRNA.

CONCLUSION

In summary, our results demonstrate that Sirt1 is overexpressed in VSMC from SHR which through augmenting oxidative stress contributes to the enhanced expression of Giα proteins, cell cycle proteins and resultant hyperproliferation of VSMC.

Calcineurin (PPP3CB) regulates angiotensin II-dependent vascular remodelling by potentiating EGFR signalling in mice

AIM

This study investigates the role of calcineurin for angiotensin II (AngII)-induced vascular remodelling with the help of a mouse model lacking the catalytic beta subunit of calcineurin (PPP3CB KO).

METHODS

Wildtype (WT) and PPP3CB KO mice were treated for 4 weeks with AngII followed by assessment of blood pressure, histological evaluation of aortas and mRNA analysis of aortic genes PPP3CB-dependently regulated by AngII. Primary murine vascular smooth muscle cells (VSMCs) were used for qPCR, ELISA and Western Blot experiments as well as wound healing and cell proliferation assays.

RESULTS

Upon AngII treatment, PPP3CB KO mice showed less aortic media thickening, lumen dilation and systolic blood pressure compared to WT mice. Next-generation sequencing data of aortic tissue indicated an increase in extracellular matrix components (EMCs), cell migration and cell proliferation. A PPP3CB-dependent increase in EMC was confirmed by qPCR in aorta and VSMCs. PPP3CB-dependent stimulation of VSMC migration could be verified by wound healing assays but markers of enhanced cell proliferation were only detectable in aortic tissue of WT mice but not in isolated WT or KO VSMCs. We could demonstrate in VSMCs with pharmacological inhibitors that PPP3CB leads to enhanced heparin-binding EGF-like growth factor (HB-EGF) secretion, epidermal growth factor receptor (EGFR) activation and consecutive stimulation of transforming growth factor β(TGFβ) and connective tissue growth factor (CTGF) signalling that enhances collagen expression.

CONCLUSION

AngII-induced vascular remodelling involves PPP3CB, which leads to enhanced EMC production, VSMC migration and sustained increase in systolic blood pressure via HBEGF/EGFR-TGFβ-CTGF signalling.

Angiotensin II-Induced Vasoconstriction via Rho Kinase Activation in Pressure-Overloaded Rat Thoracic Aortas

Angiotensin II (Ang II) induces vasoconstriction through myosin light chain (MLC) kinase activation and MLC phosphatase inactivation via phosphorylation of myosin phosphatase targeting subunit 1 (MYPT1) by Rho kinase. However, the detailed mechanism underlying Rho kinase activation by Ang II is still unknown. We investigated the mechanism of Ang II-induced vasoconstriction mediated by Rho kinase in pressure-overloaded rat thoracic aortas. Pressure-overloaded rats were produced by coarctation of the suprarenal abdominal aorta in four-week-old male Wistar rats. The contractile response to Ang II was significantly enhanced in the pressure-overloaded rats. Ang II-induced vasoconstriction was attenuated by inhibitors of Rho kinase, extracellular signal-regulated kinase 1 and 2 (Erk1/2), and epidermal growth factor receptor (EGFR) in both the sham-operated and pressure-overloaded rats. The Ang II-induced vasoconstriction was attenuated by a Janus kinase 2 (JAK2) inhibitor in only the pressure-overloaded rats. The protein levels of MYPT1 and JAK2 increased only in the pressure-overloaded rat thoracic aortas. These results suggested that Ang II-induced contraction is mediated by Rho kinase activation via EGFR, Erk1/2, and JAK2 in pressure-overloaded rat thoracic aortas. Moreover, Ang II-induced contraction was enhanced in pressure-overloaded rats probably because the protein levels of MYPT1 and JAK2 increased in the thoracic aortas.

Angiotensin II-induced overexpression of sirtuin 1 contributes to enhanced expression of Giα proteins and hyperproliferation of vascular smooth muscle cells

Angiotensin II (ANG II) plays an important role in the regulation of various physiological functions including proliferation, hypertrophy of vascular smooth muscle cells (VSMCs) through the overexpression of Giα proteins. Sirtuin 1 (Sirt1), a class III histone deacetylase and epigenetic regulator is implicated in a wide range of cellular functions, including migration and growth of VSMCs and in ANG II-induced hypertension. The present study was undertaken to examine the role of Sirt1 in ANG II-induced overexpression of Giα proteins and hyperproliferation of aortic VSMCs. We show that ANG II treatment of VSMCs increased the expression of Sirt1, which was attenuated by AT₁ and AT₂ receptor antagonists, losartan, and PD123319, respectively. In addition, the knockdown of Sirt1 by siRNA attenuated ANG II-induced overexpression of Giα-2 and Giα-3 proteins, hyperproliferation of VSMCs and the overexpression of cell cycle proteins, cyclin D1, Cdk4, and phosphorylated retinoblastoma proteins. Furthermore, ANG II-induced increased levels of superoxide anion (O₂^-) and NADPH oxidase activity and increased phosphorylation of ERK1/2 and Akt that are implicated in enhanced expression of Giα proteins and hyperproliferation of VSMCs were also attenuated to control levels by silencing of Sirt1. In addition, depletion of Sirt1 by siRNA also attenuated ANG II-induced enhanced phosphorylation of platelet-derived growth factor receptor (PDGFR), epidermal growth factor receptor (EGFR), and insulin-like growth factor receptor (IGFR) in VSMCs. In summary, our results demonstrate that ANG II increased the expression of Sirt1, which through oxidative stress, growth factor receptor-mediated mitogen-activated protein (MAP) kinase/Akt signaling pathway enhances the expression of Giα proteins and cell cycle proteins and results in the hyperproliferation of VSMCs.NEW & NOTEWORTHY ANG II regulates various physiological functions including proliferation of VSMCs through the overexpression of Giα proteins. Sirt1, a class III histone deacetylase, is implicated in several cellular functions, including VSMC growth and ANG II-induced hypertension. We showed for the first time that ANG II increased the expression of Sirt1, which through oxidative stress, growth factor receptor-mediated MAP kinase/Akt signaling pathway enhances the levels of Giα and cell cycle proteins resulting in the hyperproliferation of VSMCs.

Mapping the transcriptomic changes of endothelial compartment in human hippocampus across aging and mild cognitive impairment

Compromise of the vascular system has important consequences on cognitive abilities and neurodegeneration. The identification of the main molecular signatures present in the blood vessels of human hippocampus could provide the basis to understand and tackle these pathologies. As direct vascular experimentation in hippocampus is problematic, we achieved this information by computationally disaggregating publicly available whole microarrays data of human hippocampal homogenates. Three conditions were analyzed: 'Young Adults', 'Aged', and 'aged with Mild Cognitive Impairment' (MCI). The genes identified were contrasted against two independent data-sets. Here we show that the endothelial cells from the Younger Group appeared in an 'activated stage'. In turn, in the Aged Group, the endothelial cells showed a significant loss of response to shear stress, changes in cell adhesion molecules, increased inflammation, brain-insulin resistance, lipidic alterations, and changes in the extracellular matrix. Some specific changes in the MCI group were also detected. Noticeably, in this study the features arisen from the Aged Group (high tortuosity, increased bifurcations, and smooth muscle proliferation), pose the need for further experimental verification to discern between the occurrence of arteriogenesis and/or vascular remodeling by capillary arterialization. This article has an associated First Person interview with the first author of the paper.

Role of the JAK2/STAT3 pathway in angiotensin II-induced enhanced expression of Giα proteins and hyperproliferation of aortic vascular smooth muscle cells

We earlier showed that angiotensin (Ang) II-induced overexpression of Giα proteins contributes to the hyperproliferation of vascular smooth muscle cells (VSMC). In addition, the implication of the JAK2/STAT3 pathway in Ang II-induced hyperproliferation of VSMC has also been reported. However, the role of the JAK2/STAT3 pathway in Ang II-induced overexpression of Giα proteins and hyperproliferation of VSMC remains unexplored. In the present study, we show that inhibition or knockdown of the JAK2/STAT3 pathway by a specific inhibitor "cucurbitacin I" (CuI) or siRNAs attenuated Ang II-induced overexpression of Giα proteins and hyperproliferation of VSMC. In addition, the enhanced expression of cell cycle proteins induced by Ang II was also attenuated by CuI. Furthermore, Ang II-induced enhanced production of the superoxide anion (O2 -), H2O2, and NADPH oxidase activity, as well as the enhanced expression of NADPH oxidase subunits implicated in enhanced expression of Giα proteins and hyperproliferation, were also attenuated by inhibition of the JAK2/STAT3 pathway. On the other hand, Ang II-induced inhibition and augmentation of the levels of nitric oxide and peroxynitrite, respectively, in VSMC were restored to control levels by CuI. In summary, our results demonstrate that Ang II through the JAK2/STAT3 pathway increases nitroxidative stress, which contributes to the overexpression of Giα proteins and cell cycle proteins and the hyperproliferation of VSMC.

Oxidative Stress: A Unifying Paradigm in Hypertension

The etiology of hypertension involves complex interactions among genetic, environmental, and pathophysiologic factors that influence many regulatory systems. Hypertension is characteristically associated with vascular dysfunction, cardiovascular remodelling, renal dysfunction, and stimulation of the sympathetic nervous system. Emerging evidence indicates that the immune system is also important and that activated immune cells migrate and accumulate in tissues promoting inflammation, fibrosis, and target-organ damage. Common to these processes is oxidative stress, defined as an imbalance between oxidants and antioxidants in favour of the oxidants that leads to a disruption of oxidation-reduction (redox) signalling and control and molecular damage. Physiologically, reactive oxygen species (ROS) act as signalling molecules and influence cell function through highly regulated redox-sensitive signal transduction. In hypertension, oxidative stress promotes posttranslational modification (oxidation and phosphorylation) of proteins and aberrant signalling with consequent cell and tissue damage. Many enzymatic systems generate ROS, but NADPH oxidases (Nox) are the major sources in cells of the heart, vessels, kidneys, and immune system. Expression and activity of Nox are increased in hypertension and are the major systems responsible for oxidative stress in cardiovascular disease. Here we provide a unifying concept where oxidative stress is a common mediator underlying pathophysiologic processes in hypertension. We focus on some novel concepts whereby ROS influence vascular function, aldosterone/mineralocorticoid actions, and immunoinflammation, all important processes contributing to the development of hypertension.

HUWE1 promotes EGFR ubiquitination and degradation to protect against renal tubulointerstitial fibrosis

Injury of renal tubular epithelial cells is a key feature of the pathogenicity associated with tubulointerstitial fibrosis and other kidney diseases. HUWE1, an E3 ubiquitin ligase, acts by participating in ubiquitination and degradation of its target proteins. However, the detailed mechanisms by which HUWE1 might regulate fibrosis in renal tubular epithelial cells have not been established. Here, the possible regulation of renal tubulointerstitial fibrosis by HUWE1 was investigated by examining the expression of HUWE1 and EGFR in unilateral ureteral obstruction (UUO) mice. Markedly consistent reciprocal changes in HUWE1 and EGFR expression were observed at the protein and mRNA levels in the kidney after UUO injury. Expression of HUWE1 inhibited TGF-β-induced injury to HK-2 cells, while HUWE1 overexpression decreased the expression of EGFR. Further analysis indicated that HUWE1 physically interacted with EGFR and promoted its ubiquitination and degradation. HUWE1 expression also showed clinical relevance in renal disease, as it notably decreased in multiple types of clinical nephropathy, while EGFR expression significantly increased when compared to the normal kidney. Therefore, this study demonstrated that HUWE1, which serves as an E3 ubiquitin ligase specific for EGFR, promotes EGFR ubiquitination and degradation, thereby regulating EGFR expression and providing protection against kidney injury.

Sodium nitroprusside attenuates hyperproliferation of vascular smooth muscle cells from spontaneously hypertensive rats through the inhibition of overexpression of AT1 receptor, cell cycle proteins, and c-Src/growth factor receptor signaling pathways

We recently showed that sodium nitroprusside (SNP), a NO donor, attenuated hypertension in spontaneously hypertensive rats (SHR). Since hypertension is associated with enhanced proliferation and hypertrophy of vascular smooth muscle cells (VSMC), the present study examines whether in vivo treatment of SHR with SNP could also inhibit the augmented proliferation of VSMC and explore the signaling mechanisms. Treatment of 8 week old SHR and Wistar Kyoto rats with SNP twice a week for 2 weeks inhibited the enhanced proliferation of VSMC from SHR, the enhanced expression of angiotensin II type 1 (AT1) receptor, and enhanced activation of c-Src and growth factor receptors and ERK1/2 signaling pathways. In addition, SNP also inhibited the overexpression of cell cycle proteins including cyclins D1, Cdk4, and phosphorylated pRB and restored the downregulated Cdk inhibitors p21Cip1 and p27Kip1 expression towards control levels. Furthermore, SNP-induced inhibition of enhanced levels of the AT1 receptor and enhanced proliferation was reversed by L-NAME, an inhibitor of nitric oxide synthase. These results suggest that the SNP-induced antiproliferative effect may be mediated through the inhibition of enhanced expression of the AT1 receptor, cell cycle proteins and activation of c-Src, growth factor receptors, and MAP kinase signaling.

Resveratrol prevents the development of high blood pressure in spontaneously hypertensive rats through the inhibition of enhanced expression of Giα proteins

Resveratrol (RV), a polyphenolic component of red wine, has been shown to attenuate high blood pressure (BP) in spontaneously hypertensive rats (SHRs). We previously found that the enhanced expression of Giα proteins plays a role in the pathogenesis of hypertension in SHRs. In the present study, we investigated whether this RV-induced decrease in BP in SHRs can be attributed to the ability of RV to inhibit the enhanced expression of Giα proteins and the upstream signaling molecules implicated in the overexpression of Giα proteins. Administration of RV (50 mg/kg per day) to prehypertensive 2-week-old SHRs for 6 weeks prevented the development of high BP and inhibited the enhanced expression of Giα proteins, the enhanced levels of superoxide anion (O2−) and NADPH oxidase activity, the enhanced activation (phosphorylation) of c-Src and growth factor receptors, as well as the enhanced levels of extracellular signal-regulated kinase 1/2 (ERK1/2) and protein kinase B (Akt) exhibited by vascular smooth muscle cells isolated from SHRs. In conclusion, these results indicate that RV attenuates the development of high BP in SHRs through the inhibition of enhanced levels of Giα proteins, oxidative stress, and the upstream signaling molecules that contribute to the overexpression of Giα proteins. These findings suggest that RV could potentially be used as a therapeutic agent in the treatment of cardiovascular complications including hypertension.

Inhibition of overexpression of Giα proteins and nitroxidative stress contribute to sodium nitroprusside-induced attenuation of high blood pressure in SHR

We earlier showed that vascular smooth muscle cells (VSMC) from spontaneously hypertensive rats (SHR) exhibit enhanced expression of Giα proteins which was attributed to the decreased levels of nitric oxide (NO), because elevation of the intracellular levels of NO by NO donors; sodium nitroprusside (SNP) and S-Nitroso-N-acetyl-DL-penicillamine (SNAP), attenuated the enhanced expression of Giα proteins. Since the enhanced expression of Giα proteins is implicated in the pathogenesis of hypertension, the present study was undertaken to investigate if treatment of SHR with SNP could also attenuate the development of high blood pressure (BP) and explore the underlying molecular mechanisms. Intraperitoneal injection of SNP at a concentration of 0.5 mg/kg body weight twice a week for 2 weeks into SHR attenuated the high blood pressure by about 80 mmHg without affecting the BP in WKY rats. SNP treatment also attenuated the enhanced levels of superoxide anion (O₂^- ), hydrogen peroxide (H₂ O₂ ), peroxynitrite (ONOO^- ), and NADPH oxidase activity in VSMC from SHR to control levels. In addition, the overexpression of different subunits of NADPH oxidase; Nox-1, Nox-2, Nox-4, P^22phox , and P^47phox , and Giα proteins in VSMC from SHR were also attenuated by SNP treatment. On the other hand, SNP treatment augmented the decreased levels of intracellular NO, eNOS, and cGMP in VSMC from SHR. These results suggest that SNP treatment attenuates the development of high BP in SHR through the elevation of intracellular levels of cGMP and inhibition of the enhanced levels of Giα proteins and nitroxidative stress.

Natriuretic peptide receptor-C-mediated attenuation of vascular smooth muscle cell hypertrophy involves Gqα/PLCβ1 proteins and ROS-associated signaling

Hypertension is associated with vascular remodeling due to hyperproliferation and hypertrophy of vascular smooth muscle cells (VSMC). Recently, we showed the implication of enhanced expression of Gqα and PLCβ1 proteins in hypertrophy of VSMCs from 16‐week‐old spontaneously hypertensive rats (SHR). The aim of this study was to investigate whether C‐ANP_4‐23, a natriuretic peptide receptor‐C (NPR‐C) ligand that was shown to inhibit vasoactive peptide‐induced enhanced protein synthesis in A10 VSMC could also attenuate hypertrophy of VSMC isolated from rat model of cardiac hypertrophy and to further explore the possible involvement of Gqα/PLCβ1 proteins and ROS‐mediated signaling in this effect. The protein synthesis and cell volume, markers of hypertrophy were significantly enhanced in VSMC from 16‐week‐old SHR compared with age‐matched WKY rats and C‐ANP_4‐23 treatment attenuated both to WKY levels. In addition, C‐ANP_4‐23 treatment also attenuated the enhanced expression of AT1 receptor, Gqα, PLCβ1, Nox4, and p47^phox proteins, the enhanced activation of EGFR, PDGFR, IGF‐1R, enhanced phosphorylation of ERK1/2/AKT and c‐Src in VSMC from SHR. Furthermore, the enhanced levels of superoxide anion and NADPH oxidase activity exhibited by VSMC from SHR were also attenuated to control levels by C‐ANP_4‐23 treatment. These results indicate that C‐ANP_4‐23 via the activation of NPR‐C attenuates VSMC hypertrophy through decreasing the overexpression of Gqα/PLCβ1 proteins, enhanced oxidative stress, increased activation of growth factor receptors, and enhanced phosphorylation of MAPK/AKT signaling pathways. Thus, it can be suggested that C‐ANP_4‐23 may be used as a therapeutic agent for the treatment of vascular complications associated with hypertension and atherosclerosis.

Contribution of oxidative stress and growth factor receptor transactivation in natriuretic peptide receptor C-mediated attenuation of hyperproliferation of vascular smooth muscle cells from SHR

Earlier studies have shown the implication of growth factor receptor activation in angiotensin II (Ang II)-induced hyperproliferation of aortic VSMC as well as in hyperproliferation of VSMC from spontaneously hypertensive rats (SHR). We previously showed that NPR-C specific agonist C-ANP_4-23 attenuates the hyperproliferation of VSMC from SHR through the inhibition of MAP kinase, Giα protein signaling and overexpression of cell cycle proteins. The aim of the present study was to investigate if C-ANP_4-23- mediated attenuation of hyperproliferation of VSMC from SHR also involves growth factor receptor activation and upstream signaling molecules. For this study, C-ANP _4–23 (10 nmole/kg body weight) was injected intraperitoneally into 2 week-old prehypertensive SHR and Wistar Kyoto (WKY) rats twice per week for 6 weeks. The blood pressure in SHR was significantly attenuated by C-ANP_4-23 treatment. In addition, C-ANP_4-23 treatment also attenuated the hyperproliferation of VSMC from SHR as well as the enhanced phosphorylation of EGF-R, PDGF-R, IGF-R and c-Src. Furthermore, the enhanced levels of superoxide anion, NADPH oxidase activity, and enhanced expression of Nox4,Nox1,Nox2 and P47^phox in SHR compared to WKY rats was also significantly attenuated by C-ANP_4-23 treatment. In addition, N-acetyl cysteine (NAC), a scavenger of O₂^-, inhibitors of growth factor receptors and of c-Src, all inhibited the overexpression of cell cycle proteins cyclin D1 and cdk4 in VSMC from SHR. These results suggest that in vivo treatment of SHR with C-ANP_4-23 inhibits the enhanced oxidative stress, c-Src and EGF-R, PDGF-R, IGF-R activation which through the inhibition of overexpression of cell cycle proteins result in the attenuation of hyperproliferation of VSMC.

Resveratrol prevents angiotensin II-induced hypertrophy of vascular smooth muscle cells through the transactivation of growth factor receptors

We previously showed that augmented levels of endogenous angiotensin II (AngII) contribute to vascular smooth muscle cell (VSMC) hypertrophy through the transactivation of growth factor receptors in spontaneously hypertensive rats. Resveratrol (RV), a polyphenolic component of red wine, has also been shown to attenuate AngII-evoked VSMC hypertrophy; however, the molecular mechanism mediating this response is obscure. The present study was therefore undertaken to examine whether RV could prevent AngII-induced VSMC hypertrophy through the transactivation of growth factor receptor and associated signaling pathways. AngII treatment of VSMC enhanced the protein synthesis that was attenuated towards control levels by RV pretreatment as well as by the inhibitors of NADPH oxidase, c-Src, and growth factor receptors. Furthermore, RV pretreatment also inhibited enhanced levels of superoxide anion, NADPH oxidase activity, increased expression of NADPH oxidase subunits, and phosphorylation of c-Src, EGF-R, PDGE-R, ERK1/2, and AKT1/2. In conclusion, these results indicate that RV attenuates AngII-induced VSMC hypertrophy through the inhibition of enhanced oxidative stress and activation of c-Src, growth factor receptors, and MAPK/AKT signaling. We suggest that RV could be used as a therapeutic agent in the treatment of vascular complications associated with hypertension and hypertrophy.

Nitric oxide attenuates overexpression of Giα proteins in vascular smooth muscle cells from SHR: Role of ROS and ROS-mediated signaling

Vascular smooth muscle cells (VSMC) from spontaneously hypertensive rats (SHR) exhibit decreased levels of nitric oxide (NO) that may be responsible for the overexpression of Giα proteins that has been shown as a contributing factor for the pathogenesis of hypertension in SHR. The present study was undertaken to investigate if increasing the intracellular levels of NO by NO donor S-Nitroso-N-acetyl-DL-penicillamine (SNAP) could attenuate the enhanced expression of Giα proteins in VSMC from SHR and explore the underlying mechanisms responsible for this response. The expression of Giα proteins and phosphorylation of ERK1/2, growth factor receptors and c-Src was determined by Western blotting using specific antibodies. Treatment of VSMC from SHR with SNAP for 24 hrs decreased the enhanced expression of Giα-2 and Giα-3 proteins and hyperproliferation that was not reversed by 1H (1, 2, 4) oxadiazole (4, 3-a) quinoxalin-1-one (ODQ), an inhibitor of soluble guanylyl cyclase, however, PD98059, a MEK inhibitor restored the SNAP-induced decreased expression of Giα proteins towards control levels. In addition, the increased production of superoxide anion, NAD(P)H oxidase activity, overexpression of AT1 receptor, Nox4, p22phox and p47phox proteins, enhanced levels of TBARS and protein carbonyl, increased phosphorylation of PDGF-R, EGF-R, c-Src and ERK1/2 in VSMC from SHR were all decreased to control levels by SNAP treatment. These results suggest that NO decreased the enhanced expression of Giα-2/3 proteins and hyperproliferation of VSMC from SHR by cGMP-independent mechanism and involves ROS and ROS-mediated transactivation of EGF-R/PDGF-R and MAP kinase signaling pathways.

Gene expression profiles and signaling mechanisms in α2B-adrenoceptor-evoked proliferation of vascular smooth muscle cells

BACKGROUND

α2-adrenoceptors are important regulators of vascular tone and blood pressure. Regulation of cell proliferation is a less well investigated consequence of α2-adrenoceptor activation. We have previously shown that α2B-adrenoceptor activation stimulates proliferation of vascular smooth muscle cells (VSMCs). This may be important for blood vessel development and plasticity and for the pathology and therapeutics of cardiovascular disorders. The underlying cellular mechanisms have remained mostly unknown. This study explored pathways of regulation of gene expression and intracellular signaling related to α2B-adrenoceptor-evoked VSMC proliferation.

RESULTS

The cellular mechanisms and signaling pathways of α2B-adrenoceptor-evoked proliferation of VSMCs are complex and include redundancy. Functional enrichment analysis and pathway analysis identified differentially expressed genes associated with α2B-adrenoceptor-regulated VSMC proliferation. They included the upregulated genes Egr1, F3, Ptgs2 and Serpine1 and the downregulated genes Cx3cl1, Cav1, Rhoa, Nppb and Prrx1. The most highly upregulated gene, Lypd8, represents a novel finding in the VSMC context. Inhibitor library screening and kinase activity profiling were applied to identify kinases in the involved signaling pathways. Putative upstream kinases identified by two different screens included PKC, Raf-1, Src, the MAP kinases p38 and JNK and the receptor tyrosine kinases EGFR and HGF/HGFR. As a novel finding, the Src family kinase Lyn was also identified as a putative upstream kinase.

CONCLUSIONS

α2B-adrenoceptors may mediate their pro-proliferative effects in VSMCs by promoting the activity of bFGF and PDGF and the growth factor receptors EGFR, HGFR and VEGFR-1/2. The Src family kinase Lyn was also identified as a putative upstream kinase. Lyn is known to be expressed in VSMCs and has been identified as an important regulator of GPCR trafficking and GPCR effects on cell proliferation. Identified Ser/Thr kinases included several PKC isoforms and the β-adrenoceptor kinases 1 and 2. Cross-talk between the signaling mechanisms involved in α2B-adrenoceptor-evoked VSMC proliferation thus appears to involve PKC activation, subsequent changes in gene expression, transactivation of EGFR, and modulation of kinase activities and growth factor-mediated signaling. While many of the identified individual signals were relatively small in terms of effect size, many of them were validated by combining pathway analysis and our integrated screening approach.

Endothelin B Receptors on Primary Chicken Müller Cells and the Human MIO-M1 Müller Cell Line Activate ERK Signaling via Transactivation of Epidermal Growth Factor Receptors

Injury to the eye or retina triggers Müller cells, the major glia cell of the retina, to dedifferentiate and proliferate. In some species they attain retinal progenitor properties and have the capacity to generate new neurons. The epidermal growth factor receptor (EGFR) system and extracellular signal-regulated kinase (ERK) signaling are key regulators of these processes in Müller cells. The extracellular signals that modulate and control these processes are not fully understood. In this work we studied whether endothelin receptor signaling can activate EGFR and ERK signaling in Müller cells. Endothelin expression is robustly upregulated at retinal injury and endothelin receptors have been shown to transactivate EGFRs in other cell types. We analyzed the endothelin signaling system in chicken retina and cultured primary chicken Müller cells as well as the human Müller cell line MIO-M1. The Müller cells were stimulated with receptor agonists and treated with specific blockers to key enzymes in the signaling pathway or with siRNAs. We focused on endothelin receptor mediated transactivation of EGFRs by using western blot analysis, quantitative reverse transcriptase PCR and immunocytochemistry. The results showed that chicken Müller cells and the human Müller cell line MIO-M1 express endothelin receptor B. Stimulation by the endothelin receptor B agonist IRL1620 triggered phosphorylation of ERK1/2 and autophosphorylation of (Y1173) EGFR. The effects could be blocked by Src-kinase inhibitors (PP1, PP2), EGFR-inhibitor (AG1478), EGFR-siRNA and by inhibitors to extracellular matrix metalloproteinases (GM6001), consistent with a Src-kinase mediated endothelin receptor response that engage ligand-dependent and ligand-independent EGFR activation. Our data suggest a mechanism for how injury-induced endothelins, produced in the retina, may modulate the Müller cell responses by Src-mediated transactivation of EGFRs. The data give support to a view in which endothelins among several other functions, serve as an injury-signal that regulate the gliotic response of Müller cells.

Smooth muscle contraction and growth of stromal cells in the human prostate are both inhibited by the Src family kinase inhibitors, AZM475271 and PP2

BACKGROUND AND PURPOSE

In benign prostatic hyperplasia, increased prostate smooth muscle tone and prostate volume may contribute alone or together to urethral obstruction and voiding symptoms. Consequently, it is assumed there is a connection between smooth muscle tone and growth in the prostate, but any molecular basis for this is poorly understood. Here, we examined effects of Src family kinase (SFK) inhibitors on prostate contraction and growth of stromal cells.

EXPERIMENTAL APPROACH

SFK inhibitors, AZM475271 and PP2, were applied to human prostate tissues to assess effects on smooth muscle contraction, and to cultured stromal (WPMY-1) and c-Src-deficient cells to examine effects on proliferation, actin organization and viability.

KEY RESULTS

SFKs were detected by real time PCR, western blot and immunofluorescence in human prostate tissues, some being located to smooth muscle cells. AZM475271 (10 μM) and PP2 (10 μM) inhibited SFK in prostate tissues and WPMY-1 cells. Both inhibitors reduced α₁ -adrenoceptor-mediated and neurogenic contraction of prostate strips. This may result from cytoskeletal deorganization, which was observed in response to AZM475271 and PP2 in WPMY-1 cells by staining of actin filaments with phalloidin. This was paralleled by reduced proliferation of wildtype but not of c-Src-deficient cells; cytotoxicity was mainly observed at higher concentrations (>50 μM).

CONCLUSIONS AND IMPLICATIONS

In human prostate, smooth muscle tone and growth are both controlled by an SFK-dependent process, which may explain their common role in bladder outlet obstruction. Targeting prostate smooth muscle tone and prostate growth simultaneously by a single compound may, in principal, be possible.

Influence of Endothelin 1 Receptor Blockers and a Nitric Oxide Synthase Inhibitor on Reactive Oxygen Species Formation in Rat Lungs

This study was designated to estimate protective role of ETA and ETB receptor antagonist against endothelin 1 (ET-1)-induced oxidative stress in lungs and determine whether these effects are mediated by nitric oxide (NO) synthase. Experiments were performed on Wistar rats divided into the following groups: I – saline (0.9 % NaCl); II – ET-1 (3 μg/kg b.w.), III – BQ123 (1 mg/kg b.w.) + ET-1 (3 μg/kg b.w.), IV – BQ788 (3 mg/kg b.w.) + ET-1 (3 μg/kg b.w.), V – N-nitro-L-arginine methyl ester (L-NAME) (5 mg/kg b.w.) + ET-1 (3 μg/kg b.w.). ETA and ETB receptor antagonists or L-NAME were administered 30 min before ET-1 injection. The levels of the following substances were measured in the lungs homogenates: thiobarbituric acid reactive substances (TBARS), hydrogen peroxide (H2O2), reduced glutathione (GSH) and tumor necrosis factor-alpha (TNF-α). The results showed that ET-1 significantly increased TBARS, H2O2 (respectively: p<0.001, p<0.02) and TNF-α levels (p<0.02) and decreased the GSH level (p<0.01) vs. control group. On the other hand, prior administration of ETA receptor blocker (BQ123) significantly attenuated TBARS (p<0.01), H2O2 (p<0.02), TNF-α (p<0.02) and increased GSH (p<0.02) levels vs. ET-1. However, prior administration of ETB receptor blocker BQ788 did not cause significant changes in the: TBARS, H2O2 and TNF-α (p>0.05) levels, but significantly increased the GSH level and GSH/GSSG ratio (p<0.05). Administration of L-NAME significantly attenuated TBARS (p<0.001), H2O2 (p<0.05), TNF-α (p<0.01) and increased GSH (p<0.05) levels vs. ET-1. In conclusion, we demonstrated that ET-1 induced oxidative stress in the lungs is mediated by ETA receptors. ETA receptor blockage inhibited generation of free radicals and TNF-α and ameliorated antioxidant properties. Moreover, generation of reactive oxygen species is mediated by NOS in the lungs.

Src tyrosine kinase mediates endothelin-1-induced early growth response protein-1 expression via MAP kinase-dependent pathways in vascular smooth muscle cells

We have previously demonstrated that the non-receptor protein tyrosine kinase (NR-PTK) c-Src is an upstream regulator of endothelin-1 (ET-1) and angiotensin II-induced activation of protein kinase B (PKB) signaling in vascular smooth muscle cells (VSMCs). We have also demonstrated that ET-1 potently induces the expression of the early growth response protein-1 (Egr-1), a zinc finger transcription factor that is overexpressed in models of vascular diseases, such as atherosclerosis. However, the involvement of c-Src in ET-1‑induced Egr-1 expression has not yet been investigated and its role in mitogen-activated protein kinase (MAPK) signaling remains controversial. Therefore, the aim of the present study was to examine the role of c-Src in the ET-1-induced phosphorylation of extracellular signal-regulated kinase (ERK)1/2, c-Jun N-terminal kinase (JNK) and p38 MAPK, 3 key members of the MAPK family and in the regulation of Egr-1 expression in rat aortic A10 VSMCs. ET-1 rapidly induced the phosphorylation of MAPKs, as well as the expression of Egr-1; however, treatment of the VSMCs with PP2, a specific pharmacological inhibitor of c-Src, dose-dependently reduced the phosphorylation of the 3 MAPKs and the expression of Egr-1 induced by ET-1. Furthermore, in mouse embryonic fibroblasts (MEFs) deficient in c-Src (SYF), the ET-1-induced Egr-1 expression and MAPK phosphorylation were significantly suppressed, as compared to MEFs expressing normal Src levels. These results suggest that c-Src plays a critical role in mediating ET-1-induced MAPK phosphorylation and Egr-1 expression in VSMCs.

Role of PKCδ in Enhanced Expression of Gqα/PLCβ1 Proteins and VSMC Hypertrophy in Spontaneously Hypertensive Rats

Gqα signaling has been implicated in cardiac hypertrophy. In addition, angiotensin II (Ang II) was also shown to induce its hypertrophic effect through Gqα and PKCδ activation. We recently showed the role of enhanced expression of Gqα/PLCβ1 proteins in vascular smooth muscle cell (VSMC) hypertrophy, however, the role of PKCδ in VSMC hypertrophy in animal model is still lacking. The present study was therefore undertaken to examine the role of PKCδ and the associated signaling mechanisms in VSMC hypertrophy using 16-week-old spontaneously hypertensive rats (SHR). VSMC from 16-week-old SHR exhibited enhanced phosphorylation of PKCδ-Tyr311 and increased protein synthesis, marker of hypertrophy, as compared to WKY rats which was attenuated by rottlerin, an inhibitor of PKCδ. In addition, knocking down of PKCδ by PKCδ-siRNA also attenuated enhanced protein synthesis in VSMC from SHR. Furthermore, rottlerin attenuated the increased production of superoxide anion, NAD(P)H oxidase activity, increased expression of Gqα, phospholipase C (PLC)β1, insulin like growth factor-1 receptor (IGF-1R) and epidermal growth factor receptor (EGFR) proteins in VSMC from SHR. In addition, the enhanced phosphorylation of c-Src, PKCδ-Tyr311, IGF-1R, EGFR and ERK1/2 exhibited by VSMC from SHR was also attenuated by rottlerin. These results suggest that VSMC from SHR exhibit enhanced activity of PKCδ and that PKCδ is the upstream molecule of reactive oxygen species (ROS) and contributes to the enhanced expression of Gqα and PLCβ1 proteins and resultant VSMC hypertrophy involving c-Src, growth factor receptor transactivation and MAP kinase signaling.

Expression and Function of the Epidermal Growth Factor Receptor in Physiology and Disease

The epidermal growth factor receptor (EGFR) is the prototypical member of a family of membrane-associated intrinsic tyrosine kinase receptors, the ErbB family. EGFR is activated by multiple ligands, including EGF, transforming growth factor (TGF)-α, HB-EGF, betacellulin, amphiregulin, epiregulin, and epigen. EGFR is expressed in multiple organs and plays important roles in proliferation, survival, and differentiation in both development and normal physiology, as well as in pathophysiological conditions. In addition, EGFR transactivation underlies some important biologic consequences in response to many G protein-coupled receptor (GPCR) agonists. Aberrant EGFR activation is a significant factor in development and progression of multiple cancers, which has led to development of mechanism-based therapies with specific receptor antibodies and tyrosine kinase inhibitors. This review highlights the current knowledge about mechanisms and roles of EGFR in physiology and disease.

Endothelin-1: Biosynthesis, Signaling and Vasoreactivity

Endothelin-1 (ET-1) is an extremely potent vasoconstrictor peptide originally isolated from endothelial cells. Its synthesis, mainly regulated at the gene transcription level, involves processing of a precursor by a furin-type proprotein convertase to an inactive intermediate, big ET-1. The latter peptide can then be cleaved directly by an endothelin-converting enzyme (ECE) into ET-1 or reach the active metabolite through a two-step process involving chymase hydrolyzing big ET-1 to ET-1 (1-31), itself needing conversion to ET-1 by neprilysin (NEP) to exert physiological activity. ET-1 signals through two G protein-coupled receptors, endothelin receptor A (ETA) and endothelin receptor B (ETB). Both receptors induce an increase in intracellular Ca(2+), mainly from the extracellular space through voltage-independent mechanisms, the receptor-operated channels and store-operated channels. ET-1 also induces signaling through epidermal growth factor receptor transactivation, oxidative stress induction, rho-kinase, and the activation (ETA) or inhibition (ETB) of the adenylate cyclase/cyclic adenosine monophosphate pathway. Arterial vasoconstriction is mediated mainly by the ETA receptor. ET-1, via endothelium-located ETB, relaxes arteries or constricts vessels following activation of the same receptor type on the smooth muscle, where it can interact with ETA. In addition, ETB-dependent vasoconstriction seems more prominent in the venous vasculature. A better understanding of how ET-1 is synthesized and how ETA and ETB receptors interact could help design better pharmacological agents in the treatment of cardiovascular diseases where targeting the ET-1 system is indicated.

Substance-specific importance of EGFR for vascular smooth muscle cells motility in primary culture

Besides their importance for the vascular tone, vascular smooth muscle cells (VSMC) also contribute to pathophysiological vessel alterations. Various G-protein coupled receptor ligands involved in vascular dysfunction and remodeling can transactivate the epidermal growth factor receptor (EGFR) of VSMC, yet the importance of EGFR transactivation for the VSMC phenotype is incompletely understood. The aims of this study were (i) to characterize further the importance of the VSMC-EGFR for proliferation, migration and marker gene expression for inflammation, fibrosis and reactive oxygen species (ROS) homeostasis and (ii) to test the hypothesis that vasoactive substances (endothelin-1, phenylephrine, thrombin, vasopressin and ATP) rely differentially on the EGFR with respect to the abovementioned phenotypic alterations. In primary, aortic VSMC from mice without conditional deletion of the EGFR, proliferation, migration, marker gene expression (inflammation, fibrosis and ROS homeostasis) and cell signaling (ERK 1/2, intracellular calcium) were analyzed. VSMC-EGFR loss reduced collective cell migration and single cell migration probability, while no difference between the genotypes in single cell velocity, chemotaxis or marker gene expression could be observed under control conditions. EGF promoted proliferation, collective cell migration, chemokinesis and chemotaxis and leads to a proinflammatory gene expression profile in wildtype but not in knockout VSMC. Comparing the impact of five vasoactive substances (all reported to transactivate EGFR and all leading to an EGFR dependent increase in ERK1/2 phosphorylation), we demonstrate that the importance of EGFR for their action is substance-dependent and most apparent for crowd migration but plays a minor role for gene expression regulation.

c-Src, ERK1/2 and Rho kinase mediate hydrogen peroxide-induced vascular contraction in hypertension: role of TXA2, NAD(P)H oxidase and mitochondria

AIM

: The aim of this study was to analyse the signalling pathways involved in H2O2 vascular responses in hypertension.

METHODS

Vascular function, thromboxane A2 (TXA2) production, oxidative stress and protein expression were determined in mesenteric resistance arteries (MRAs) from hypertensive (spontaneously hypertensive rats, SHR) and normotensive Wistar Kyoto (WKY) rats.

RESULTS

H2O2 and the TP agonist U46619 induced greater contractile responses in MRA from SHR than WKY. Moreover, H2O2 increased TXA2 production more in SHR than in WKY. The c-Src inhibitor PP1 reduced H2O2 and U46619-induced contraction and TXA2 release in both strains. The ERK1/2 inhibitor PD98059 reduced H2O2 but not U46619-induced contraction only in SHR arteries. The Rho kinase inhibitor Y26372 reduced H2O2 and U46619-induced contractions only in SHR arteries. Basal c-Src, ERK1/2 and Rho kinase expression were greater in MRA from SHR than WKY. In SHR, the combination of PD98059 with the TP antagonist SQ29548 but not with Y27632 inhibited the H2O2 contraction more than each inhibitor alone. H2O2 and U46619 increased NAD(P)H oxidase activity and O2 production and decreased mitochondrial membrane potential in vessels from SHR. The effects induced by H2O2 were abolished by inhibitors of TXA2 synthase, ERK1/2 and c-Src. The mitochondrial antioxidant mitoTEMPO reduced H2O2-induced contraction and NAD(P)H oxidase activation.

CONCLUSION

In arteries from WKY, c-Src mediates H2O2 contractile responses by modulating TXA2 release and TXA2 effect. In SHR, H2O2 induces c-Src dependent TXA2 release that provokes vascular contractile responses through Rho kinase, c-Src and O2 from NAD(P)H Oxidase and mitochondria. Moreover, ERK1/2 activation contributes to H2O2 contraction in SHR through effects on mitochondria/NAD(P)H Oxidase.

Oxidative stress contributes to the enhanced expression of Gqα/PLCβ1 proteins and hypertrophy of VSMC from SHR: role of growth factor receptor transactivation

We showed previously that vascular smooth muscle cells (VSMCs) from spontaneously hypertensive rats (SHRs) exhibit overexpression of Gqα/PLCβ1 proteins, which contribute to increased protein synthesis through the activation of MAP kinase signaling. Because oxidative stress has been shown to be increased in hypertension, the present study was undertaken to examine the role of oxidative stress and underlying mechanisms in enhanced expression of Gqα/PLCβ1 proteins and VSMC hypertrophy. Protein expression was determined by Western blotting, whereas protein synthesis and cell volume, markers for VSMC hypertrophy, were determined by [3H]-leucine incorporation and three-dimensional confocal imaging, respectively. The increased expression of Gqα/PLCβ1 proteins, increased protein synthesis, and augmented cell volume exhibited by VSMCs from SHRs were significantly attenuated by antioxidants N-acetyl-cysteine (NAC), a scavenger of superoxide anion, DPI, an inhibitor of NAD(P)H oxidase. In addition, PP2, AG1024, AG1478, and AG1295, inhibitors of c-Src, insulin-like growth factor receptor (IGFR), epidermal growth factor receptor (EGFR), and platelet-derived growth factor receptor (PDGFR), respectively, also attenuated the enhanced expression of Gqα/PLCβ1 proteins and enhanced protein synthesis in VSMCs from SHRs toward control levels. Furthermore, the levels of IGF-1R and EGFR proteins and not of PDGFR were also enhanced in VSMCs from SHRs, which were attenuated significantly by NAC, DPI, and PP2. In addition, NAC, DPI, and PP2 also attenuated the enhanced phosphorylation of IGF-1R, PDGFR, EGFR, c-Src, and EKR1/2 in VSMCs from SHRs. These data suggest that enhanced oxidative stress in VSMCs from SHRs activates c-Src, which through the transactivation of growth factor receptors and MAPK signaling contributes to enhanced expression of Gqα/PLCβ1 proteins and resultant VSMC hypertrophy.

NOX signaling in molecular cardiovascular mechanisms involved in the blood pressure homeostasis

Blood pressure homeostasis is maintained by several mechanisms regulating cardiac output, vascular resistances, and blood volume. At cellular levels, reactive oxygen species (ROS) signaling is involved in multiple molecular mechanisms controlling blood pressure. Among ROS producing systems, NADPH oxidases (NOXs), expressed in different cells of the cardiovascular system, are the most important enzymes clearly linked to the development of hypertension. NOXs exert a central role in cardiac mechanosensing, endothelium-dependent relaxation, and Angiotensin-II (Ang-II) redox signaling regulating vascular tone. The central role of NOXs in redox-dependent cardiovascular cell functions renders these enzymes a promising pharmacological target for the treatment of cardiovascular diseases, including hypertension. The aim of the present review is to focus on the physiological role of the cardiovascular NOX-generating ROS in the molecular and cellular mechanisms affecting blood pressure.

Enhanced expression of Giα proteins contributes to the hyperproliferation of vascular smooth muscle cells from spontaneously hypertensive rats via MAP kinase- and PI3 kinase-independent pathways

Vascular smooth muscle cells (VSMC) from spontaneously hypertensive rats (SHR) exhibit hyperproliferation, enhanced MAP kinase (MAPK) activity, and overexpression of Giα proteins. This study was undertaken to examine whether the overexpression of Giα proteins contributes to the hyperproliferation of VSMC of SHR through MAPK signaling. The hyperproliferation of VSMC from SHR in the absence and presence of angiotensin II was restored towards those in Wistar-Kyoto (WKY) rats levels by pertussis toxin (PT) treatment. In addition, siRNA knockdown of Giα proteins also resulted in the attenuation of hyperproliferation towards control levels. The overexpression of Giα proteins was also inhibited by MAPK and PI3 kinase (PI3K) inhibitors. In addition, the hyperproliferation and enhanced phosphorylation of ERK1/2 and Akt in VSMC from SHR were attenuated towards WKY levels by the inhibitors of MAPK, PI3K, c-Src, and antioxidants, whereas PT was unable to attenuate the enhanced phosphorylation of ERK1/2 and Akt. Furthermore, 8Br-cAMP and forskolin also attenuated the hyperproliferation of VSMC from SHR. These results suggest that the hyperproliferation of VSMC from SHR may be attributed to the enhanced expression of Giα proteins and increased activation of MAPK and PI3 kinase. However, Giα-mediated hyperproliferation may not be mediated through MAPK- and PI3 kinase-dependent pathways and may involve decreased levels of intracellular cAMP.

Hypertension risk in Dutch women with symptomatic uterine fibroids

BACKGROUND

Female-specific risk factors for cardiovascular disease are understudied. We assessed whether women with uterine fibroids have a greater hypertension risk, independent of the shared risk factors for both conditions.

METHODS

Blood pressure was measured in women scheduled for fibroid surgery compared to women scheduled for nonfibroid gynecological surgery and women randomly sampled from the general population. We used multivariable binary logistic regression to assess whether hypertension was more common with surgically treated fibroids, independent of age, body mass index, and African ancestry.

RESULTS

We included 1,342 women (542 of African ancestry), of which 272 scheduled for fibroid surgery, 385 controls scheduled for nonfibroid gynecological surgery, and 685 random population controls, with a mean age (SD) of, respectively, 43.4 (6.6), 41.3 (10.2), and 45.1 (6.6) years; and a mean body mass index (SD) of, respectively, 27.4 (5.3), 25.7 (5.7), and 28.2 (5.6) kg/m(2). Hypertension was found more frequently with surgically treated fibroids, with an occurrence of 41.9% in women with fibroids vs. 27.5% in surgical controls, and 28.3% in population controls (P < 0.001 for fibroids vs. controls). The association with hypertension was independent of age, body mass index, and African ancestry (odds ratio, 2.4; 95% confidence interval, 1.7-3.4).

CONCLUSIONS

Hypertension risk is higher in Dutch women with surgically treated fibroids than in surgery or population controls, independent of age, body mass index, and African ancestry. Our data add to the body of evidence indicating that women with uterine fibroids are eligible for hypertension screening.

Protein disulfide isomerase expression increases in resistance arteries during hypertension development. Effects on Nox1 NADPH oxidase signaling

NADPH oxidases derived reactive oxygen species (ROS) play an important role in vascular function and remodeling in hypertension through redox signaling processes. Previous studies demonstrated that protein disulfide isomerase (PDI) regulates Nox1 expression and ROS generation in cultured vascular smooth muscle cells. However, the role of PDI in conductance and resistance arteries during hypertension development remains unknown. The aim of the present study was to investigate PDI expression and NADPH oxidase dependent ROS generation during hypertension development. Mesenteric resistance arteries (MRA) and thoracic aorta were isolated from 6, 8, and 12 week-old spontaneously hypertensive (SHR) and Wistar rats. ROS production (dihydroethidium fluorescence), PDI (WB, imunofluorescence), Nox1 and NOX4 (RT-PCR) expression were evaluated. Results show a progressive increase in ROS generation in MRA and aorta from 8 to 12 week-old SHR. This effect was associated with a concomitant increase in PDI and Nox1 expression only in MRA. Therefore, suggesting a positive correlation between PDI and Nox1 expression during the development of hypertension in MRA. In order to investigate if this effect was due to an increase in arterial blood pressure, pre hypertensive SHR were treated with losartan (20 mg/kg/day for 30 days), an AT1 receptor antagonist. Losartan decreased blood pressure and ROS generation in both vascular beds. However, only in SHR MRA losartan treatment lowered PDI and Nox1 expression to control levels. In MRA PDI inhibition (bacitracin, 0.5 mM) decreased Ang II redox signaling (p-ERK 1/2). Altogether, our results suggest that PDI plays a role in triggering oxidative stress and vascular dysfunction in resistance but not in conductance arteries, increasing Nox1 expression and activity. Therefore, PDI could be a new player in oxidative stress and functional alterations in resistance arteries during the establishment of hypertension.

The Affymetrix DMET Plus platform reveals unique distribution of ADME-related variants in ethnic Arabs

Background. The Affymetrix Drug Metabolizing Enzymes and Transporters (DMET) Plus Premier Pack has been designed to genotype 1936 gene variants thought to be essential for screening patients in personalized drug therapy. These variants include the cytochrome P450s (CYP450s), the key metabolizing enzymes, many other enzymes involved in phase I and phase II pharmacokinetic reactions, and signaling mediators associated with variability in clinical response to numerous drugs not only among individuals, but also between ethnic populations. Materials and Methods. We genotyped 600 Saudi individuals for 1936 variants on the DMET platform to evaluate their clinical potential in personalized medicine in ethnic Arabs. Results. Approximately 49% each of the 437 CYP450 variants, 56% of the 581 transporters, 56% of 419 transferases, 48% of the 104 dehydrogenases, and 58% of the remaining 390 variants were detected. Several variants, such as rs3740071, rs6193, rs258751, rs6199, rs11568421, and rs8187797, exhibited significantly either higher or lower minor allele frequencies (MAFs) than those in other ethnic groups. Discussion. The present study revealed some unique distribution trends for several variants in Arabs, which displayed partly inverse allelic prevalence compared to other ethnic populations. The results point therefore to the need to verify and ascertain the prevalence of a variant as a prerequisite for engaging it in clinical routine screening in personalized medicine in any given population.

Role of epidermal growth factor receptor in vascular structure and function

PURPOSE OF THE REVIEW

The epidermal growth factor receptor (EGFR) is a receptor tyrosine kinase with a wide implication in tumor biology, wound healing and development. Besides acting as a growth factor receptor activated by ligands such as EGF, the EGFR can also be transactivated and thereby mediate cross-talk with different signaling pathways. The aim of this review is to illustrate the Janus-faced function of the EGFR in the vasculature with its relevance for vascular biology and disease.

RECENT FINDINGS

Over recent years, the number of identified signaling partners of the EGFR has steadily increased, as have the biological processes in which the EGFR is thought to be involved. Recently, new models have allowed investigation of EGFR effects in vivo, shedding some light on the overall function of the EGFR in the vasculature. At the same time, EGFR inhibitors and antibodies have become increasingly established in cancer therapy, providing potential therapeutic tools for decreasing EGFR signaling.

SUMMARY

The EGFR is a versatile signaling pathway integrator associated with vascular homeostasis and disease. In addition to modulating basal vascular tone and tissue homeostasis, the EGFR also seems to be involved in proinflammatory, proliferative, migratory and remodeling processes, with enhanced deposition of extracellular matrix components, thereby promoting vascular diseases such as hypertension or atherosclerosis.

MiR-7-5p is frequently downregulated in glioblastoma microvasculature and inhibits vascular endothelial cell proliferation by targeting RAF1

The aberrant expression of microRNAs (miRNAs) is always associated with tumor development and progression. Microvascular proliferation is one of the unique pathologic features of glioblastoma (GBM) . In this study, the microvasculature from GBM or normal brain tissue derived from neurosurgeries was purified and total RNA was isolated from purified microvasculature. The difference of miRNA expression profiles between glioblastoma microvasculature and normal brain capillaries was investigated. It was found that miR-7-5p in GBM microvessels was significantly reduced compared with that in normal brain capillaries. In the in vitro experiments, overexpression of miR-7-5p significantly inhibited human umbilical vein endothelial cell proliferation. Forced expression of miR-7-5p in human umbilical vein endothelial cells in vitro significantly reduced the protein level of RAF1 and repressed the activity of the luciferase, a reporter vector carrying the 3'-untranslated region of RAF1. These findings indicate that RAF1 is one of the miR-7-5p target genes. Furthermore, a significant inverse correlation between miR-7-5p expression and RAF1 protein level in GBM microvasculature was found. These data suggest that miR-7-5p functions as a tumor suppressor gene to regulate GBM microvascular endothelial cell proliferation potentially by targeting the RAF1 oncogene, implicating an important role for miR-7-5p in the pathogenesis of GBM. It may serve as a guide for the antitumor angiogenesis drug development.

Role of endothelin in uteroplacental circulation and fetal vascular function

Endothelins are 21-amino acid peptides involved in vascular homeostasis. Three types of peptide have been identified, with endothelin-1 (ET-1) being the most potent vasoconstrictor currently known. Two endothelin receptor subtypes are found in various tissues, including the brain, heart, blood vessel, lung, and placenta. The ETA-receptor is associated with vasoconstriction in vascular smooth muscle. Conversely, the ETB-receptor can elicit a vasoconstrictor effect in vascular smooth muscle and a vasodilator effect via its action in endothelial cells. Both receptors play a key role in maintaining circulatory homeostasis and vascular function. Changes in ET-1 expression are found in various disease states, and overexpression of ET-1 is observed in hypertension and preeclampsia in pregnancy. Placental localization of ET-1 implies a key role in regulating the uteroplacental circulation. Additionally, ET-1 is important in the fetal circulation and is involved in the pulmonary circulation and closure of the ductus arteriosus after birth, as well as fetal growth constriction in utero. ET receptor antagonists and nitric oxide donors may provide therapeutic potential in treating conditions associated with overexpression of ET and hypertension.

Orthovanadate-induced vasocontraction is mediated by the activation of Rho-kinase through Src-dependent transactivation of epidermal growth factor receptor

Orthovanadate (OVA), a protein tyrosine phosphatase (PTPase) inhibitor, exerts contractile effects on smooth muscle in a Rho-kinase-dependent manner, but the precise mechanisms are not elucidated. The aim of this study was to determine the potential roles of Src and epidermal growth factor receptor (EGFR) in the OVA-induced contraction of rat aortas and the phosphorylation of myosin phosphatase target subunit 1 (MYPT1; an index of Rho-kinase activity) in vascular smooth muscle cells (VSMCs). Aortic contraction by OVA was significantly blocked not only by Rho kinase inhibitors Y-27632 [R-[+]-trans-N-[4-pyridyl]-4-[1-aminoethyl]-cyclohexanecarboxamide] and hydroxyfasudil [1-(1-hydroxy-5-isoquinolinesulfonyl)homopiperazine] but also by Src inhibitors PP2 [4-amino-3-(4-chlorophenyl)-1-(t-butyl)-1H-pyrazolo[3,4-d]pyrimidine] and Src inhibitor No. 5 [4-(3′-methoxy-6′-chloro-anilino)-6-methoxy-7(morpholino-3-propoxy)-quinazoline], and the EGFR inhibitors AG1478 [4-(3-chloroanilino)-6,7-dimethoxyquinazoline] and EGFR inhibitor 1 [cyclopropanecarboxylic acid-(3-(6-(3-trifluoromethyl-phenylamino)-pyrimidin-4-ylamino)-phenyl)-amide]. OVA induced rapid increases in the phosphorylation of MYPT1 (Thr-853), Src (Tyr-416), and EGFR (Tyr-1173) in VSMCs, and Src inhibitors abolished these effects. OVA-induced Src phosphorylation was abrogated by Src inhibitors, but not affected by inhibitors of EGFR and Rho-kinase. Inhibitors of Src and EGFR, but not Rho-kinase, also blocked OVA-induced EGFR phosphorylation. Furthermore, a metalloproteinase inhibitor TAPI-0 [N-(R)-[2-(hydroxyaminocarbonyl) methyl]-4-methylpentanoyl-l-naphthylalanyl-l-alanine amide] and an inhibitor of heparin-binding EGF (CRM 197) not only abrogated the OVA-induced aortic contraction, but also OVA-induced EGFR and MYPT1 phosphorylation, suggesting the involvement of EGFR transactivation. OVA also induced EGFR phosphorylation at Tyr-845, one of residues phosphorylated by Src. These results suggest that OVA-induced vasocontraction is mediated by the Rho-kinase-dependent inactivation of myosin light-chain phosphatase via signaling downstream of Src-induced transactivation of EGFR.

Endogenous endothelin 1 mediates angiotensin II-induced hypertrophy in electrically paced cardiac myocytes through EGFR transactivation, reactive oxygen species and NHE-1

Emerging evidence supports a key role for endothelin-1 (ET-1) and the transactivation of the epidermal growth factor receptor (EGFR) in angiotensin II (Ang II) action. We aim to determine the potential role played by endogenous ET-1, EGFR transactivation and redox-dependent sodium hydrogen exchanger-1 (NHE-1) activation in the hypertrophic response to Ang II of cardiac myocytes. Electrically paced adult cat cardiomyocytes were placed in culture and stimulated with 1 nmol l(-1) Ang II or 5 nmol l(-1) ET-1. Ang II increased ~45 % cell surface area (CSA) and ~37 % [(3)H]-phenylalanine incorporation, effects that were blocked not only by losartan (Los) but also by BQ123 (AT1 and ETA receptor antagonists, respectively). Moreover, Ang II significantly increased ET-1 messenger RNA (mRNA) expression. ET-1 similarly increased myocyte CSA and protein synthesis, actions prevented by the reactive oxygen species scavenger MPG or the NHE-1 inhibitor cariporide (carip). ET-1 increased the phosphorylation of the redox-sensitive ERK1/2-p90(RSK) kinases, main activators of the NHE-1. This effect was prevented by MPG and the antagonist of EGFR, AG1478. Ang II, ET-1 and EGF increased myocardial superoxide production (187 ± 9 %, 149 ± 8 % and 163.7 ± 6 % of control, respectively) and AG1478 inhibited these effects. Interestingly, Los inhibited only Ang II whilst BQ123 cancelled both Ang II and ET-1 actions, supporting the sequential and unidirectional activation of AT1, ETA and EGFR. Based on the present evidence, we propose that endogenous ET-1 mediates the hypertrophic response to Ang II by a mechanism that involves EGFR transactivation and redox-dependent activation of the ERK1/2-p90(RSK) and NHE-1 in adult cardiomyocytes.

Angiotensin II, NADPH oxidase, and redox signaling in the vasculature

SIGNIFICANCE

Angiotensin II (Ang II) influences the function of many cell types and regulates many organ systems, in large part through redox-sensitive processes. In the vascular system, Ang II is a potent vasoconstrictor and also promotes inflammation, hypertrophy, and fibrosis, which are important in vascular damage and remodeling in cardiovascular diseases. The diverse actions of Ang II are mediated via Ang II type 1 and Ang II type 2 receptors, which couple to various signaling molecules, including NADPH oxidase (Nox), which generates reactive oxygen species (ROS). ROS are now recognized as signaling molecules, critically placed in pathways activated by Ang II. Mechanisms linking Nox and Ang II are complex and not fully understood.

RECENT ADVANCES

Ang II regulates vascular cell production of ROS through various recently characterized Noxs, including Nox1, Nox2, Nox4, and Nox5. Activation of these Noxs leads to ROS generation, which in turn influences many downstream signaling targets of Ang II, including MAP kinases, RhoA/Rho kinase, transcription factors, protein tyrosine phosphatases, and tyrosine kinases. Activation of these redox-sensitive pathways regulates vascular cell growth, inflammation, contraction, and senescence.

CRITICAL ISSUES

Although there is much evidence indicating a role for Nox/ROS in Ang II function, there is still a paucity of information on how Ang II exerts cell-specific effects through ROS and how Nox isoforms are differentially regulated by Ang II. Moreover, exact mechanisms whereby ROS induce oxidative modifications of signaling molecules mediating Ang II actions remain elusive.

FUTURE DIRECTIONS

Future research should elucidate these issues to better understand the significance of Ang II and ROS in vascular (patho) biology.

cAMP attenuates the enhanced expression of Gi proteins and hyperproliferation of vascular smooth muscle cells from SHR: role of ROS and ROS-mediated signaling

We previously showed that angiotensin II (ANG II)-induced overexpression of inhibitory G proteins (Gi) was attenuated by dibutyryl-cAMP (db-cAMP) in A10 vascular smooth muscle cells (VSMC). Since enhanced levels of endogenous ANG II contributed to the overexpression of Gi protein and hyperproliferation of VSMC from spontaneously hypertensive rats (SHR), the present study was therefore undertaken to examine if cAMP could also attenuate the overexpression of Gi proteins and hyperproliferation of VSMC from SHR and to explore the underlying molecular mechanisms responsible for this response. The enhanced expression of Giα proteins in VSMC from SHR and Nω-nitro-L-arginine methyl ester hypertensive rats was decreased by db-cAMP. In addition, enhanced inhibition of adenylyl cyclase by inhibitory hormones and forskolin-stimulated adenylyl cyclase activity by low concentration of GTPγS in VSMC from SHR was also restored to Wistar-Kyoto (WKY) levels by db-cAMP. Furthermore, db-cAMP also attenuated the hyperproliferation and the increased production of superoxide anion, NAD(P)H oxidase activity, overexpression of Nox1/Nox2/Nox4 and p47phox proteins, increased phosphorylation of PDGF-receptor (R), EGF-R, c-Src, and ERK1/2 to control levels. In addition, the protein kinase A (PKA) inhibitor reversed the effects of db-cAMP on the expression of Nox4 and Giα proteins and hyperproliferation of VSMC from SHR to WKY levels, while stimulation of the exchange protein directly activated by cAMP did not have any effect on these parameters. These results suggest that cAMP via PKA pathway attenuates the overexpression of Gi proteins and hyperproliferation of VSMC from SHR through the inhibition of ROS and ROS-mediated transactivation of EGF-R/PDGF-R and MAPK signaling pathways.

Role of epidermal growth factor receptor transactivation in endothelin-1-induced enhanced expression of Gi protein and proliferation in A10 vascular smooth muscle cells

We have recently shown that vasoactive peptides such as angiotensin II (Ang II) and endothelin-1 (ET-1) increase the expression of Gi proteins and the proliferation of A10 vascular smooth muscle cells (VSMC) through mitogen-activated protein (MAP) kinase – phosphoinositide (PI) 3-kinase pathways. This study was intended to examine the implication of epidermal growth factor receptor (EGFR) activation in ET-1-induced enhanced expression of Gi proteins and proliferation of A10 VSMC, and to further investigate the underlying mechanisms responsible for these increases. Cell proliferation was determined by [3H]thymidine incorporation and the expression of Gi proteins; extracellular signal-regulated kinases 1 and 2 (ERK1/2) and EGFR phosphorylation was determined by Western blotting. Treatment of A10 VSMC with ET-1 enhanced the expression of Gi proteins, which was attenuated by BQ123 and BQ788, antagonists of ETA and ETB receptor respectively. In addition, ET-1 enhanced the phosphorylation of EGFR in A10 VSMC, which was restored to the control levels by EGFR inhibitor and ETA and ETB receptor antagonists. Furthermore, ET-1 also augmented the proliferation and ERK1/2 phosphorylation of A10 VSMC, which were restored to the control levels by inhibition of EGFR. These data suggest that ET-1 transactivates EGFR, which, through MAP kinase signaling, may contribute to the enhanced expression of Gi proteins and thus increased proliferation of A10 VSMC.

Gastrointestinal hormones stimulate growth of Foregut Neuroendocrine Tumors by transactivating the EGF receptor

Foregut neuroendocrine tumors [NETs] usually pursuit a benign course, but some show aggressive behavior. The treatment of patients with advanced NETs is marginally effective and new approaches are needed. In other tumors, transactivation of the EGF receptor (EGFR) by growth factors, gastrointestinal (GI) hormones and lipids can stimulate growth, which has led to new treatments. Recent studies show a direct correlation between NET malignancy and EGFR expression, EGFR inhibition decreases basal NET growth and an autocrine growth effect exerted by GI hormones, for some NETs. To determine if GI hormones can stimulate NET growth by inducing transactivation of EGFR, we examined the ability of EGF, TGFα and various GI hormones to stimulate growth of the human foregut carcinoid,BON, the somatostatinoma QGP-1 and the rat islet tumor,Rin-14B-cell lines. The EGFR tyrosine-kinase inhibitor, AG1478 strongly inhibited EGF and the GI hormones stimulated cell growth, both in BON and QGP-1 cells. In all the three neuroendocrine cell lines studied, we found EGF, TGFα and the other growth-stimulating GI hormones increased Tyr(1068) EGFR phosphorylation. In BON cells, both the GI hormones neurotensin and a bombesin analogue caused a time- and dose-dependent increase in EGFR phosphorylation, which was strongly inhibited by AG1478. Moreover, we found this stimulated phosphorylation was dependent on Src kinases, PKCs, matrix metalloproteinase activation and the generation of reactive oxygen species. These results raise the possibility that disruption of this signaling cascade by either EGFR inhibition alone or combined with receptor antagonists may be a novel therapeutic approach for treatment of foregut NETs/PETs.

Role of epidermal growth factor receptor in acute and chronic kidney injury

Epidermal growth factor receptor (EGFR) is a receptor tyrosine kinase. Its activation results in beneficial or detrimental consequences, depending on the particular setting. Earlier studies in the animal model of acute kidney injury showed that EGFR activation promotes renal tubular cell proliferation. Activation of EGFR by its exogenous ligands, like EGF, can enhance recovery of renal function and structure following acute kidney injury. However, recent studies indicated that EGFR activation also contributes to development and progression of renal diseases in animal models of obstructive nephropathy, diabetic nephropathy, hypertensive nephropathy, and glomerulonephritis through mechanisms involved in activation of renal interstitial fibroblasts, induction of tubular atrophy, overproduction of inflammatory factors, and/or promotion of glomerular and vascular injury. This review highlights the actions and mechanisms of EGFR in a variety of acute and chronic kidney injuries.

Attenuation of endothelin-1-induced PKB and ERK1/2 signaling, as well as Egr-1 expression, by curcumin in A-10 vascular smooth muscle cells

Endothelin-1 (ET-1) is implicated in the pathogenesis of vascular abnormalities through the hyperactivation of growth promoting pathways, including protein kinase B (PKB) and extracellular signal-regulated kinase 1/2 (ERK1/2) signaling. ET-1 has been shown to elicit its responses through the generation of reactive oxygen species (ROS). Curcumin, the main constituent of the spice turmeric, exhibits cardio-protective, anti-proliferative, and antioxidant properties; however, the precise molecular mechanism of its action is unclear. Therefore, in the present study, we investigated the effects of curcumin on ET-1-induced PKB and ERK1/2 signaling, as well as insulin-like growth factor type receptor (IGF-1R) phosphorylation. Curcumin dose-dependently inhibited ET-1-induced phosphorylation of PKB, ERK1/2, c-Raf, and insulin-like growth factor type 1 receptor (IGF-1R), in vascular smooth muscle cells (VSMC). Furthermore, curcumin also attenuated ET-1-induced expression of early growth response (Egr)-1, a transcription factor downstream of ERK1/2 that plays a regulatory role in several cardiovascular pathological processes. In conclusion, these data demonstrate that curcumin is a potent inhibitor of ET-1-induced mitogenic and proliferative signaling events in VSMC and suggest that the ability of curcumin to attenuate these events may contribute as a potential mechanism for its cardiovascular protective response.

c-Src-dependent EGF receptor transactivation contributes to ET-1-induced COX-2 expression in brain microvascular endothelial cells

Background

Endothelin-1 (ET-1) is elevated and participates in the regulation of several brain inflammatory disorders. The deleterious effects of ET-1 on endothelial cells may aggravate brain inflammation mediated through the upregulation of cyclooxygenase-2 (COX-2) gene expression. However, the signaling mechanisms underlying ET-1-induced COX-2 expression in brain microvascular endothelial cells remain unclear.

Objective

The goal of this study was to examine whether ET-1-induced COX-2 expression and prostaglandin E₂ (PGE₂) release were mediated through a c-Src-dependent transactivation of epidermal growth factor receptor (EGFR) pathway in brain microvascular endothelial cells (bEnd.3 cells).

Methods

The expression of COX-2 induced by ET-1 was evaluated by Western blotting and RT-PCR analysis. The COX-2 regulatory signaling pathways were investigated by pretreatment with pharmacological inhibitors, short hairpin RNA (shRNA) or small interfering RNA (siRNA) transfection, chromatin immunoprecipitation (ChIP), and promoter activity reporter assays. Finally, we determined the PGE₂ level as a marker of functional activity of COX-2 expression.

Results

First, the data showed that ET-1-induced COX-2 expression was mediated through a c-Src-dependent transactivation of EGFR/PI3K/Akt cascade. Next, we demonstrated that ET-1 stimulated activation (phosphorylation) of c-Src/EGFR/Akt/MAPKs (ERK1/2, p38 MAPK, and JNK1/2) and then activated the c-Jun/activator protein 1 (AP-1) via G_q/i protein-coupled ET_B receptors. The activated c-Jun/AP-1 bound to its corresponding binding sites within COX-2 promoter, thereby turning on COX-2 gene transcription. Ultimately, upregulation of COX-2 by ET-1 promoted PGE₂ biosynthesis and release in bEnd.3 cells.

Conclusions

These results demonstrate that in bEnd.3 cells, c-Src-dependent transactivation of EGFR/PI3K/Akt and MAPKs linking to c-Jun/AP-1 cascade is essential for ET-1-induced COX-2 upregulation. Understanding the mechanisms of COX-2 expression and PGE₂ release regulated by ET-1/ET_B system on brain microvascular endothelial cells may provide rational therapeutic interventions for brain injury and inflammatory diseases.