Small cytoplasmic domain peptides of natriuretic peptide receptor-C attenuate cell proliferation through Gialpha protein/MAP kinase/PI3-kinase/AKT pathways

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.

Molecular Mechanism of Naringenin Against High-Glucose-Induced Vascular Smooth Muscle Cells Proliferation and Migration Based on Network Pharmacology and Transcriptomic Analyses

Although the protective effects of naringenin (Nar) on vascular smooth muscle cells (VSMCs) have been confirmed, whether it has anti-proliferation and anti-migration effects in high-glucose-induced VSMCs has remained unclear. This study aimed to clarify the potential targets and molecular mechanism of Nar when used to treat high-glucose-induced vasculopathy based on transcriptomics, network pharmacology, molecular docking, and in vivo and in vitro assays. We found that Nar has visible anti-proliferation and anti-migration effects both in vitro (high-glucose-induced VSMC proliferation and migration model) and in vivo (type 1 diabetes mouse model). Based on the results of network pharmacology and molecular docking, vascular endothelial growth factor A (VEGFA), the proto-oncogene tyrosine-protein kinase Src (Src) and the kinase insert domain receptor (KDR) are the core targets of Nar when used to treat diabetic angiopathies, according to the degree value and the docking score of the three core genes. Interestingly, not only the Biological Process (BP), Molecular Function (MF), and KEGG enrichment results from network pharmacology analysis but also transcriptomics showed that phosphatidylinositol-3-kinase (PI3K)/protein kinase B (Akt) is the most likely downstream pathway involved in the protective effects of Nar on VSMCs. Notably, according to the differentially expressed genes (DEGs) in the transcriptomic analysis, we found that cAMP-responsive element binding protein 5 (CREB5) is a downstream protein of the PI3K/Akt pathway that participates in VSMCs proliferation and migration. Furthermore, the results of molecular experiments in vitro were consistent with the bioinformatic analysis. Nar significantly inhibited the protein expression of the core targets (VEGFA, Src and KDR) and downregulated the PI3K/Akt/CREB5 pathway. Our results indicated that Nar exerted anti-proliferation and anti-migration effects on high-glucose-induced VSMCs through decreasing expression of the target protein VEGFA, and then downregulating the PI3K/Akt/CREB5 pathway, suggesting its potential for treating diabetic angiopathies.

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.

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.

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.

The Role of Natriuretic Peptides in the Regulation of Cardiac Tolerance to Ischemia/Reperfusion and Postinfarction Heart Remodeling

In the past 10 years, mortality from acute myocardial infarction has not decreased despite the widespread introduction of percutaneous coronary intervention. The reason for this situation is the absence in clinical practice of drugs capable of preventing reperfusion injury of the heart with high efficiency. In this regard, noteworthy natriuretic peptides (NPs) which have the infarct-limiting effect, prevent reperfusion cardiac injury, prevent adverse post-infarction remodeling of the heart. Atrial natriuretic peptide does not have the infarct-reducing effect in rats with alloxan-induced diabetes mellitus. NPs have the anti-apoptotic and anti-inflammatory effects. There is indirect evidence that NPs inhibit pyroptosis and autophagy. Published data indicate that NPs inhibit reactive oxygen species production in cardiomyocytes, aorta, heart, kidney and the endothelial cells. NPs can suppress aldosterone, angiotensin II, endothelin-1 synthesize and secretion. NPs inhibit the effects aldosterone, angiotensin II on the post-receptor level through intracellular signaling events. NPs activate guanylyl cyclase, protein kinase G and protein kinase A, and reduce phosphodiesterase 3 activity. NO-synthase and soluble guanylyl cyclase are involved in the cardioprotective effect of NPs. The cardioprotective effect of natriuretic peptides is mediated via activation of kinases (AMPK, PKC, PI3 K, ERK1/2, p70s6 k, Akt) and inhibition of glycogen synthase kinase 3β. The cardioprotective effect of NPs is mediated via sarcolemmal K_ATP channel and mitochondrial K_ATP channel opening. The cardioprotective effect of brain natriuretic peptide is mediated via MPT pore closing. The anti-fibrotic effect of NPs may be mediated through inhibition TGF-β1 expression. Natriuretic peptides can inhibit NF-κB activity and activate GATA. Hemeoxygenase-1 and peroxisome proliferator-activated receptor γ may be involved in the infarct-reducing effect of NPs. NPs exhibit the infarct-limiting effect in patients with acute myocardial infarction. NPs prevent post-infarction remodeling of the heart. To finally resolve the question of the feasibility of using NPs in AMI, a multicenter, randomized, blind, placebo-controlled study is needed to assess the effect of NPs on the mortality of patients after AMI.

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.

Pulmonary Arterial Hypertension Due to NPR-C Mutation: A Novel Paradigm for Normal and Pathologic Remodeling?

Idiopathic Pulmonary Arterial Hypertension (IPAH) is a deadly and disabling disease characterized by severe vascular remodeling of small pulmonary vessels by fibroblasts, myofibroblasts and vascular smooth muscle cell proliferation. Recent studies suggest that the Natriuretic Peptide Clearance Receptor (NPR-C) signaling pathways may play a crucial role in the development of IPAH. Reduced expression or function of NPR-C signaling in pulmonary artery smooth muscle cells may contribute to the pulmonary vascular remodeling, which is characteristic of this disease. The likely mechanisms may involve an impaired interaction between NPR-C, specific growth factors and other signal transduction pathways including but not limited to Gqα/mitogen-activated protein kinase (MAPK)/PI3K and AKT signaling. The resulting failure of growth suppression in pulmonary artery smooth muscle cells provides critical clues to the cellular pathobiology of IPAH. The reciprocal regulation of NPR-C signaling in models of tissue remodeling may thus provide new insights to our understanding of IPAH.

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.

Puerarin inhibits vascular smooth muscle cells proliferation induced by fine particulate matter via suppressing of the p38 MAPK signaling pathway

Background

Fine particulate matter (PM2.5) is a major risk factor for the development and progression of atherosclerosis. Proliferation and infiltration of vascular smooth muscle cells (VSMCs) from the blood vessel media into the intima is a crucial step in the pathophysiology of atherosclerosis. Puerarin, a natural extract from Radix Puerariae, possesses significant anti-atherosclerosis properties. However, the underlying molecular mechanisms responsible for the effect of puerarin on the VSMCs proliferation induced by PM2.5 remain unclear. The present study was designed to examine the effect of puerarin on PM2.5-induced VSMCs proliferation, and to explore the p38 mitogen-activated protein kinase (p38 MAPK) signal mechanism involved.

Methods

VSMCs viability was measured by CCK-8 assay, VSMCs proliferation was assessed by BrdU immunofluorescence, the levels of superoxide dismutase (SOD) and malonaldehyde (MDA) were assayed by colorimetric assay kits, the levels of nitric oxide (NO) and endothelin-1 (ET-1) were determined by nitrate reductase method and radioimmunoassay, the levels of vascular cell adhesion molecule-1 (VCAM-1), interleukin-6 (IL-6) and tumor necrosis factor-alpha (TNF-α) were measured by ELISA. The protein expressions of phospho-p38 MAPK (p-p38 MAPK) and proliferating cell nuclear antigen (PCNA) in the VSMCs were subjected by Western blot.

Results

Compared to the PM2.5-treated cells, in addition to inhibiting the PM2.5-induced VSMCs proliferation, puerarin also down-regulated the protein expressions of p-p38 MAPK and PCNA, decreased the levels of ET-1, VCAM-1, IL-6, TNF-α and MDA, increased the levels of NO and SOD. Moreover, the anti-proliferative effects of puerarin were significantly enhanced by the co-incubation of puerarin with SB203580, a selective inhibitor of p38 MAPK, as compared to the puerarin-treated cells.

Conclusion

These results suggest that puerarin might suppress the PM2.5-induced VSMCs proliferation via the inhibition of the p38 MAPK signaling pathway.

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.

Receptor signaling and neutral endopeptidase are involved in the resistance of C-type natriuretic peptide to human mesangial proliferation and collagen-IV expression

C-type natriuretic peptide (CNP) is regarded as a local, paracrine hormone to regulate vascular tone and cell proliferation. Although several in vivo studies have documented that CNP exerts the inhibitory effects on mesangial cells (MCs) proliferation and collagen production, a limited number of studies exist about the resistance of CNP to MCs proliferation in vitro. Besides, whether its receptor signaling and neutral endopeptidase (NEP) are involved remains unclear. In the present study, human MCs were incubated in serum-containing medium in the absence or presence of CNP (0, 10 and 100 pM) for 24, 48 and 72 hours, respectively. CNP administration significantly suppresses MCs proliferation and collagen-IV (Col-IV) expression in a time-dependent and dose-dependent manner. As a down-stream signal molecule of CNP activation, the expressions of natriuretic peptide receptor (NPR)-B, cyclic guanosine monophosphate-dependent protein kinases II and NPR-C were obviously augmented, whereas NEP expression was significantly decreased after CNP treatment. In conclusion, receptor signaling and NEP are involved in the resistance of CNP to human mesangial proliferation and Col-IV expression.

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.

Mice, double deficient in lysosomal serine carboxypeptidases Scpep1 and Cathepsin A develop the hyperproliferative vesicular corneal dystrophy and hypertrophic skin thickenings

Vasoactive and mitogenic peptide, endothelin-1 (ET-1) plays an important role in physiology of the ocular tissues by regulating the growth of corneal epithelial cells and maintaining the hemodynamics of intraocular fluids. We have previously established that ET-1 can be degraded in vivo by two lysosomal/secreted serine carboxypeptidases, Cathepsin A (CathA) and Serine Carboxypeptidase 1 (Scpep1) and that gene-targeted CathA^S190A/Scpep1^-/- mice, deficient in CathA and Scpep1 have a prolonged half-life of circulating ET-1 associated with systemic hypertension. In the current work we report that starting from 6 months of age, ~43% of CathA^S190A/Scpep1^-/- mice developed corneal clouding that eventually caused vision impairment. Histological evaluation of these mice demonstrated a selective fibrotic thickening and vacuolization of the corneas, resembling human hyperproliferative vesicular corneal stromal dystrophy and coexisting with a peculiar thickening of the skin epidermis. Moreover, we found that cultured corneal epithelial cells, skin fibroblasts and vascular smooth muscle cells derived from CathA/Scpep1-deficient mice, demonstrated a significantly higher proliferative response to treatment with exogenous ET-1, as compared with cells from wild type mice. We also detected increased activation level of ERK1/2 and AKT kinases involved in cell proliferation in the ET-1-treated cultured cells from CathA/Scpep1 deficient mice. Together, results from our experimental model suggest that; in normal tissues the tandem of serine carboxypeptidases, Scpep1 and CathA likely constitutes an important part of the physiological mechanism responsible for the balanced elimination of heightened levels of ET-1 that otherwise would accumulate in tissues and consequently contribute to development of the hyper-proliferative corneal dystrophy and abnormal skin thickening.

Knockdown of Inhibitory Guanine Nucleotide Binding Protein Giα-2 by Antisense Oligodeoxynucleotides Attenuates the Development of Hypertension and Tachycardia in Spontaneously Hypertensive Rats

BACKGROUND

We previously showed that the levels of both Giα-2 and Giα-3 proteins were augmented in spontaneously hypertensive rats (SHRs) before the onset of hypertension. In addition, intraperitoneal injection of pertussis toxin, which inactivates both Giα proteins, prevented the development of hypertension in SHRs. The aim of the present study was to determine the specific contributions of Giα-2 and Giα-3 proteins to the development of hypertension.

METHODS AND RESULTS

Antisense oligodeoxynucleotide of Giα-2 and Giα-3 encapsulated in PEG/DOTAP/DOPE cationic liposomes were administrated intravenously into 3-week-old prehypertensive SHRs and Wistar Kyoto rats, whereas the control Wistar Kyoto rats and SHRs received PBS, empty liposomes, or sense. The knockdown of Giα-2 but not Giα-3 protein attenuated tachycardia and prevented the development of hypertension up to age 6 weeks; thereafter, blood pressure started increasing and reached the same level as that of untreated SHRs at 9 weeks. Furthermore, Giα-2 and Giα-3 antisense oligodeoxynucleotide treatments significantly decreased the enhanced levels of Giα-2 and Giα-3 proteins, respectively, and enhanced levels of superoxide anion and NADPH oxidase activity in heart, aorta, and kidney and hyperproliferation of vascular smooth muscle cells from SHRs aged 6 weeks. In addition, antisense oligodeoxynucleotide treatment with Giα-2 but not Giα-3 restored enhanced inhibition of adenylyl cyclase by oxotremorine to WKY levels.

CONCLUSIONS

These results suggested that the enhanced expression of Giα-2 but not Giα-3 protein plays an important role in the pathogenesis of hypertension and tachycardia in SHRs.

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.

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.

Natriuretic peptides in cardiometabolic regulation and disease

In the 30 years since the identification of the natriuretic peptides, their involvement in regulating fluid and blood pressure has become firmly established. Data indicating a role for these hormones in lifestyle-related metabolic and cardiovascular disorders have also accumulated over the past decade. Dysregulation of the natriuretic peptide system has been associated with obesity, glucose intolerance, type 2 diabetes mellitus, and essential hypertension. Moreover, the natriuretic peptides have been implicated in the protection against atherosclerosis, thrombosis, and myocardial ischaemia. All these conditions can coexist and potentially lead to heart failure, a syndrome associated with a functional natriuretic peptide deficiency despite high circulating concentrations of immunoreactive peptides. Therefore, dysregulation of the natriuretic peptide system, a 'natriuretic handicap', might be an important factor in the initiation and progression of metabolic dysfunction and its accompanying cardiovascular complications. This Review provides a summary of the natriuretic peptide system and its involvement in these cardiometabolic conditions. We propose that these peptides might have an integrating role in lifestyle-related metabolic and cardiovascular disorders.

A functional genetic variant (N521D) in natriuretic peptide receptor 3 is associated with diastolic dysfunction: the prevalence of asymptomatic ventricular dysfunction study

Objectives

To evaluate the impact of a functional genetic variant in the natriuretic peptide clearance receptor, NPR3, on circulating natriuretic peptides (NPs) and myocardial structure and function in the general community.

Background

NPR3 plays an important role in the clearance of NPs and through direct signaling mechanisms modulates smooth muscle cell function and cardiac fibroblast proliferation. A NPR3 nonsynonymous single nucleotide polymorphism (SNP) rs2270915, resulting in a N521D substitution in the intracellular catalytic domain that interacts with Gi could affect receptor function. Whether this SNP is associated with alterations in NPs levels and altered cardiac structure and function is unknown.

Methods

DNA samples of 1931 randomly selected residents of Olmsted County, Minnesota were genotyped. Plasma NT-proANP_1-98, ANP_1-28, proBNP_1-108, NT-proBNP_1-76, BNP_1-32 and BNP_3-32 levels were measured. All subjects underwent comprehensive echocardiography.

Results

Genotype frequencies for rs2270915 were as follows: (A/A 60%, A/G 36%, G/G 4%). All analyses performed were for homozygotes G/G versus wild type A/A plus the heterozygotes A/G. Diastolic dysfunction was significantly more common (p = 0.007) in the homozygotes G/G (43%) than the A/A+A/G (28%) group. Multivariate regression adjusted for age, sex, body mass index and hypertension demonstrated rs2270915 to be independently associated with diastolic dysfunction (odds ratio 1.94, p = 0.03). There was no significant difference in NPs levels between the 2 groups suggesting that the clearance function of the receptor was not affected.

Conclusions

A nonsynonymous NPR3 SNP is independently associated with diastolic dysfunction and this association does not appear to be related to alterations in circulating levels of natriuretic peptides.

Natriuretic peptide receptor-C agonist attenuates the expression of cell cycle proteins and proliferation of vascular smooth muscle cells from spontaneously hypertensive rats: role of Gi proteins and MAPkinase/PI3kinase signaling

Vascular smooth muscle cells (VSMC) from spontaneously hypertensive rats (SHR) exhibit hyperproliferation and overexpression of cell cycle proteins. We earlier showed that small peptide fragments of cytoplasmic domain of natriuretic receptor-C (NPR-C) attenuate vasoactive peptide-induced hyperproliferation of VSMC. The present study investigated if C-ANP_4–23, a specific agonist of NPR-C, could attanuate the hyperproliferation of VSMC from SHR by inhibiting the overexpression of cell cycle proteins and examine the underlying signaling pathways contributing to this inhibition. The proliferation of VSMC was determined by [³H] thymidine incorporation and the expression of proteins was determined by Western blotting. The hyperproliferation of VSMC from SHR and overexpression of cyclin D1,cyclin A, cyclin E, cyclin-dependent kinase 2 (cdk2), phosphorylated retinoblastoma protein (pRb), Giα proteins and enhanced phosphorylation of ERK1/2 and AKT exhibited by VSMC from SHR were attenuated by C-ANP_4–23 to control levels. In addition, in vivo treatment of SHR with C-ANP_4–23 also attenuated the enhanced proliferation of VSMC. Furthemore, PD98059, wortmannin and pertussis toxin, the inhibitors of MAP kinase, PI3kinase and Giα proteins respectively, also attenuated the hyperproliferation of VSMC from SHR and overexpression of cell cycle proteins to control levels. These results indicate that NPR-C activation by C-ANP_4–23 attenuates the enhanced levels of cell cycle proteins through the inhibition of enhanced expression of Giα proteins and enhanced activation of MAPkinase/PI3kinase and results in the attenuation of hyperproliferation of VSMC from SHR. It may be suggested that C-ANP_4–23 could be used as a therapeutic agent in the treatment of vascular complications associated with hypertension, atherosclerosis and restenosis.

Natriuretic peptide receptors regulate cytoprotective effects in a human ex vivo 3D/bioreactor model

INTRODUCTION

The present study examined the effect of C-type natriuretic peptide (CNP) and biomechanical signals on anabolic and catabolic activities in chondrocyte/agarose constructs.

METHODS

Natriuretic peptide (Npr) 2 and 3 expression were compared in non-diseased (grade 0/1) and diseased (grade IV) human cartilage by immunofluoresence microscopy and western blotting. In separate experiments, constructs were cultured under free-swelling conditions or subjected to dynamic compression with CNP, interleukin-1β (IL-1β), the Npr2 antagonist P19 or the Npr3 agonist cANF⁴⁻²³. Nitric oxide (NO) production, prostaglandin E₂ (PGE₂) release, glycosaminoglycan (GAG) synthesis and CNP concentration were quantified using biochemical assays. Gene expression of Npr2, Npr3, CNP, aggrecan and collagen type II were assessed by real-time qPCR. Two-way ANOVA and a post hoc Bonferroni-corrected t-test were used to analyse the data.

RESULTS

The present study demonstrates increased expression of natriuretic peptide receptors in diseased or older cartilage (age 70) when compared to non-diseased tissue (age 60) which showed minimal expression. There was strong parallelism in the actions of CNP on cGMP induction resulting in enhanced GAG synthesis and reduction of NO and PGE₂ release induced by IL-1β. Inhibition of Npr2 with P19 maintained catabolic activities whilst specific agonism of Npr3 with cANF⁴⁻²³ had the opposite effect and reduced NO and PGE₂ release. Co-stimulation with CNP and dynamic compression enhanced anabolic activities and inhibited catabolic effects induced by IL-1β. The presence of CNP and the Npr2 antagonist abolished the anabolic response to mechanical loading and prevented loading-induced inhibition of NO and PGE₂ release. In contrast, the presence of the Npr3 agonist had the opposite effect and increased GAG synthesis and cGMP levels in response to mechanical loading and reduced NO and PGE₂ release comparable to control samples. In addition, CNP concentration and natriuretic peptide receptor expression were increased with dynamic compression.

CONCLUSIONS

Mechanical loading mediates endogenous CNP release leading to increased natriuretic peptide signalling. The loading-induced CNP/Npr2/cGMP signalling route mediates anabolic events and prevents catabolic activities induced by IL-1β. The CNP pathway therefore represents a potentially chondroprotective intervention for patients with OA, particularly when combined with physiotherapeutic approaches to stimulate biomechanical signals.

C2238 atrial natriuretic peptide molecular variant is associated with endothelial damage and dysfunction through natriuretic peptide receptor C signaling

RATIONALE

C2238 atrial natriuretic peptide (ANP) minor allele (substitution of thymidine with cytosine in position 2238) associates with increased risk of cardiovascular events.

OBJECTIVE

We investigated the mechanisms underlying the vascular effects of C2238-αANP.

METHODS AND RESULTS

In vitro, human umbilical vein endothelial cell were exposed to either wild-type (T2238)- or mutant (C2238)-αANP. Cell survival and apoptosis were tested by Trypan blue, annexin V, and cleaved caspase-3 assays. C2238-αANP significantly reduced human umbilical vein endothelial cell survival and increased apoptosis. In addition, C2238-αANP reduced endothelial tube formation, as assessed by matrigel. C2238-αANP did not differentially modulate natriuretic peptide receptor (NPR)-A/B activity with respect to T2238-αANP, as evaluated by intracellular cGMP levels. In contrast, C2238-αANP, but not T2238-αANP, markedly reduced intracellular cAMP levels in an NPR-C-dependent manner. Accordingly, C2238-αANP showed higher affinity binding to NPR-C, than T2238-αANP. Either NPR-C inhibition by antisense oligonucleotide or NPR-C gene silencing by small interfering RNA rescued survival and tube formation of human umbilical vein endothelial cell exposed to C2238-αANP. Similar data were obtained in human aortic endothelial cell with NPR-C knockdown. NPR-C activation by C2238-αANP inhibited the protein kinase A/Akt1 pathway and increased reactive oxygen species. Adenovirus-mediated Akt1 reactivation rescued the detrimental effects of C2238-αANP. Overall, these data indicate that C2238-αANP affects endothelial cell integrity through NPR-C-dependent inhibition of the cAMP/protein kinase A/Akt1 pathway and increased reactive oxygen species production. Accordingly, C2238-αANP caused impairment of acetylcholine-dependent vasorelaxation ex vivo, which was rescued by NPR-C pharmacological inhibition. Finally, subjects carrying C2238 minor allele showed early endothelial dysfunction, which highlights the clinical relevance of our results.

CONCLUSIONS

C2238-αANP reduces endothelial cell survival and impairs endothelial function through NPR-C signaling. NPR-C targeting represents a potential strategy to reduce cardiovascular risk in C2238 minor-allele carriers.

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.

Atrial natriuretic peptide attenuates agonist-induced pulmonary edema in mice with targeted disruption of the gene for natriuretic peptide receptor-A

Atrial natriuretic peptide (ANP) inhibits agonist-induced pulmonary edema formation, but the signaling pathway responsible is not well defined. To investigate the role of the particulate guanylate cyclase-linked receptor, natriuretic peptide receptor-A (NPR-A), we measured acute lung injury responses in intact mice and pulmonary microvascular endothelial cells (PMVEC) with normal and disrupted expression of NPR-A. NPR-A wild-type (NPR-A+/+), heterozygous (NPR-A+/-), and knockout (NPR-A-/-) mice were anesthetized and treated with thrombin receptor agonist peptide (TRAP) or lipopolysaccharide (LPS). Lung injury was assessed by lung wet-to-dry (W/D) weight and by protein and cell concentration of bronchoalveolar lavage (BAL) fluid. No difference in pulmonary edema formation was seen between NPR-A genotypes under baseline conditions. TRAP and LPS increased lung W/D weight and BAL fluid cell counts more in NPR-A-/- mice than in NPR-A+/- or NPR-A+/+ mice, but no genotype-related differences were seen in TRAP-induced increases in bloodless lung W/D weight or LPS-induced increases in BAL protein concentration. Pretreatment with ANP infusion completely blocked TRAP-induced increases in lung W/D weight and blunted LPS-induced increases in BAL cell counts and protein concentration in both NPR-A-/- and NPR-A+/+ mice. Thrombin decreased transmembrane electrical resistance in monolayers of PMVECs in vitro, and this effect was attenuated by ANP in PMVECs isolated from both genotypes. Administration of the NPR-C-specific ligand, cANF, also blocked TRAP-induced increases in lung W/D weight and LPS-induced increases in BAL cell count and protein concentration in NPR-A+/+ and NPR-A-/- mice. We conclude that ANP is capable of attenuating agonist-induced lung edema in the absence of NPR-A. The protective effect of ANP on agonist-induced lung injury and pulmonary barrier function may be mediated by NPR-C.

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.

Signal protein-derived peptides as functional probes and regulators of intracellular signaling

The functionally important regions of signal proteins participating in their specific interaction and responsible for transduction of hormonal signal into cell are rather short in length, having, as a rule, 8 to 20 amino acid residues. Synthetic peptides corresponding to these regions are able to mimic the activated form of full-size signal protein and to trigger signaling cascades in the absence of hormonal stimulus. They modulate protein-protein interaction and influence the activity of signal proteins followed by changes in their regulatory and catalytic sites. The present review is devoted to the achievements and perspectives of the study of signal protein-derived peptides and to their application as selective and effective regulators of hormonal signaling systems in vitro and in vivo. Attention is focused on the structure, biological activity, and molecular mechanisms of action of peptides, derivatives of the receptors, G protein α subunits, and the enzymes generating second messengers.

Kinin B1 receptor upregulation by angiotensin II and endothelin-1 in rat vascular smooth muscle cells: receptors and mechanisms

Oxidative stress upregulates the kinin B1 receptor (B1R) in diabetes and hypertension. Since angiotensin II (ANG II) and endothelin-1 (ET-1) are increased in these disorders, this study aims at determining the role of these two prooxidative peptides in B1R expression in rat vascular smooth muscle cells (VSMC). In the A10 cell line and aortic VSMC, ANG II enhanced B1R protein expression in a concentration- and time-dependent manner (maximal at 1 μM and 6 h). In A10 cells, ANG II (1 μM) also increased B1R mRNA expression at 3 h and the activation of induced B1R with the agonist [Sar-d-Phe8]-des-Arg9-BK (10 nM, 5 min) significantly enhanced mitogen -activated protein kinase (MAPK1/2) phosphorylation. The enhancing effect of ANG II on B1R protein expression in A10 cells was normalized by the AT1 (losartan) but not by the AT2 (PD123319) receptor antagonist. Furthermore, it was inhibited by inhibitors of phosphatidylinositol 3-kinase (wortmannin) and NF-κB (MG132) but not of MAPK (PD098059). Whereas the ETB receptor antagonist (BQ788) had no effect, the ETA receptor antagonist (BQ123) blocked the effect of ANG II at 6–8 h but not at an early time point. BQ123 and BQ788 also blocked the increasing effect of ET-1 on B1R protein expression. Antioxidants ( N-acetyl-l-cysteine and diphenyleneiodonium) abolished ANG II- and ET-1-increased B1R protein expression. In conclusion, B1R induction is linked to oxidative stress and activation of phosphatidylinositol 3-kinase and NF-κB. The newly synthesized B1R is functional and can activate MAPK signaling in VSMC. The effect of ANG II is mediated by the AT1 receptor and the subsequent activation of ETA through ET-1 release.

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

We showed previously that vascular smooth muscle cells (VMSC) from spontaneously hypertensive rats (SHR) exhibit increased proliferation. The present study was undertaken to examine whether the enhanced levels of endogenous angiotensin (ANG) II and endothelin (ET)-1 contribute to the enhanced proliferation of VSMC from SHR and to further investigate the underlying mechanisms responsible for this response. The enhanced proliferation of VSMC from SHR compared with Wistar-Kyoto (WKY) rats was attenuated by losartan, BQ-123, BQ-788, and AG-1478, inhibitors of AT(1), ET(A), ET(B) and epidermal growth factor (EGF-R) receptors, respectively. In addition, BQ-123 and BQ-788 also attenuated the enhanced production of superoxide anion (O(2)(-)) and NADPH oxidase activity. Furthermore, diphenyleneiodonium (DPI, inhibitor of NADPH oxidase), N-acetyl-L-cysteine (NAC, O(2)(-) scavenger), and PP2 (inhibitor of c-Src) also inhibited the augmented proliferation of VSMC from SHR to WKY levels. In addition, the enhanced phosphorylation of EGF-R in VSMC from SHR compared with WKY was also attenuated by inhibitors of AT(1), ET(A), ET(B), and EGF-R but not by inhibitors of platelet-derived growth factor receptor or insulin-like growth factor receptor. Furthermore, the enhanced phosphorylation of ERK1/2 in VSMC from SHR was also attenuated by AT(1), ET(A), ET(B), c-Src, and EGF-R inhibitors. The phosphorylation of c-Src was significantly augmented in VSMC from SHR compared with VSMC from WKY and was attenuated by DPI and NAC. These data suggest that endogenous vasoactive peptides, through increased oxidative stress and resultant activation of c-Src, transactivate EGF-R, which through mitogen-activated protein (MAP) kinase signaling may contribute to the hyperproliferation of VSMC from SHR.

Atrial natriuretic peptide inhibits angiotensin II-stimulated proliferation in fetal cardiomyocytes

The role of atrial natriuretic peptide (ANP) in regulating fetal cardiac growth is poorly understood. Angiotensin II (Ang II) stimulates proliferation in fetal sheep cardiomyocytes when growth is dependent on the activity of the mitogen-activated protein kinase (MAPK) and phosphoinositol-3-kinase (PI3K) pathways. We hypothesized that ANP would suppress near-term fetal cardiomyocyte proliferation in vitro and inhibit both the MAPK and PI3K pathways. Forty-eight hour 5-bromodeoxyuridine (BrdU) uptake (used as an index of proliferation) was measured in cardiomyocytes isolated from fetal sheep (135 day gestational age) in response to 100 nm Ang II with or without ANP (0.003-100 nm) or 1 microm 8-bromo-cGMP. The effects of these compounds on the MAPK and PI3K pathways were assessed by measuring extracellular signal-regulated kinase (ERK) and AKT phosphorylation following 10 min of treatment with Ang II, ANP or 8-bromo-cGMP. In right ventricular myocytes (RV), the lowest dose of ANP (0.003 nm) inhibited Ang II-stimulated BrdU uptake by 68%. Similarly, 8-bromo-cGMP suppressed Ang II-stimulated proliferation by 62%. The same effects were observed in left ventricular (LV) cardiomyocytes but the RV was more sensitive to the inhibitory effects of ANP than the LV (P < 0.0001). Intracellular cGMP was increased by 4-fold in the presence of 100 nm ANP. Ang II-stimulated ERK and Akt phosphorylation was inhibited by 100 nm ANP. The activity of ANP may in part be cGMP dependent, as 8-bromo-cGMP had similar effects on the cardiomyocytes.

Involvement of insulin-like growth factor 1 receptor transactivation in endothelin-1-induced signaling in vascular smooth muscle cells

Endothelin-1 (ET-1) is a potent vasoactive peptide that exerts hypertrophic, migratory, and mitogenic effects in vascular smooth muscle cells. ET-1-induced activation of several signaling events has been shown to mediate the cellular effects of ET-1. In the past several years, transactivation of growth factor receptor has gained much recognition in transducing the signaling responses of ET-1. Among various growth factor receptors studied, the involvement of epidermal growth factor receptor transactivation in triggering ET-1-induced responses has been studied in some detail. However, recent studies have implicated insulin-like growth factor 1 receptor transactivation in this process. There are also some suggestions for a role of the Src family of nonreceptor protein tyrosine kinases, such as c-Src, in transducing the signaling responses of vasoactive peptides. In this review, we will examine the contribution of both insulin-like growth factor 1 receptor and c-Src in mediating ET-1-induced signaling responses in vascular smooth muscle cells.

Role of growth factor receptor transactivation in high glucose-induced increased levels of Gq/11alpha and signaling in vascular smooth muscle cells

We have recently shown that high glucose increased the expression of Gq/11alpha, PLCbeta and mediated signaling in A10 vascular smooth muscle cells (VSMC). Since high glucose has been shown to increase growth factor receptor activation, we investigated the role of epidermal growth factor receptor (EGF-R) and platelet-derived growth factor receptor (PDGF-R) transactivation in high glucose-induced enhanced expression of Gq/11alpha and PLCbeta. Pre-treatment of A10 VSMC with high glucose (26 mM) for 3 days, increased the levels of Gqalpha, G11alpha, PLCbeta-1 and PLCbeta-2 proteins which were restored to control levels by AG1478, an inhibitor of EGF-R, AG1295, an inhibitor of PDGF-R and PP2, an inhibitor of c-Src but not by PP3. In addition, endothelin-1 (ET-1)-stimulated production of IP(3) that was enhanced by high glucose was also restored towards control levels by AG1478, AG1295 and PP2. High glucose also increased the phosphorylation of EGF-R and PDGF-R which was abolished by AG1478, AG1295 and PP2. Furthermore, high glucose-induced enhanced levels of Gqalpha, G11alpha and PLCbeta were also attenuated by PD98059, an inhibitor of mitogen-activated protein kinase (MAPK) and wortmannin, an inhibitor of phosphatidylinositol 3-kinase (PI3-K). In addition, AG1478 and AG1295, also attenuated high glucose-induced enhanced phosphorylation of ERK1/2 and AKT. Furthermore, high glucose augmented the phosphorylation of c-Src which was attenuated by antioxidant, DPI. These results suggest that oxidative stress through the activation of c-Src and resultant transactivation of growth factor receptor contributes to the high glucose-induced enhanced expression of Gq/11alpha/PLC and -mediated cell signaling through MAPK/PI3K pathway.

Contribution of epidermal growth factor receptor transactivation in angiotensin II-induced enhanced expression of Gi protein and proliferation in A10 vascular smooth muscle cellsThis article is one of a selection of papers published in a special issue on Advances in Cardiovascular Research

We have recently shown that vasoactive peptides such as angiotensin II (Ang II) and endothelin-1 (ET-1) increased the expression of Gi proteins and proliferation of A10 vascular smooth muscle cells (VSMC) through MAP kinase / PI3 kinase pathways. The present study was undertaken to examine the implication of growth factor receptor activation in Ang II-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 and the phosphorylation of ERK1/2 and epidermal growth factor receptor (EGFR) was determined by Western blotting. Treatment of A10 VSMC with Ang II enhanced the expression of Gi proteins, which was attenuated by Ang II AT1 receptor antagonist but not by AT2 receptor antagonist. The inhibitor of EGFR also attenuated the enhanced expression of Gi proteins induced by Ang II to control levels. In addition, Ang II enhanced the phosphorylation of EGFR in A10 VSMC, and this was restored to control levels by the EGFR inhibitor and antioxidants. Furthermore, Ang II also augmented the proliferation and ERK1/2 phosphorylation of A10 VSMC, which were restored to control levels by the EGFR inhibitor. These data suggest that the Ang II-induced increase in oxidative stress transactivates EGFR, which through MAP kinase signaling may contribute to the enhanced expression of Gi proteins and thereby to the increased proliferation of A10 VSMC.

Role of insulin-like growth factor 1 receptor and c-Src in endothelin-1- and angiotensin II-induced PKB phosphorylation, and hypertrophic and proliferative responses in vascular smooth muscle cellsThis article is one of a selection of papers published in a special issue on Advances in Cardiovascular Research

Endothelin-1 (ET-1) and angiotensin II (Ang II) are vasoactive peptides believed to contribute to the pathogenesis of vascular abnormalities such as hypertension, atherosclerosis, hypertrophy, and restenosis. The concept of transactivation of growth factor receptors, such as epidermal growth factor receptor (EGFR), in triggering vasoactive peptide-induced signaling events has gained much recognition during the past several years. We have demonstrated that insulin-like growth factor type 1 receptor (IGF-1R) plays a role in transducing the effect of H2O2, leading to protein kinase B (PKB) phosphorylation. Since vasoactive peptides elicit their responses through generation of reactive oxygen species, including H2O2, we investigated whether IGF-1R transactivation plays a similar role in ET-1- and Ang II-induced PKB phosphorylation and hypertrophic responses in vascular smooth muscle cells (VSMC). AG1024, a specific inhibitor of IGF-1R protein tyrosine kinase (PTK), attenuated both ET-1- and Ang II-induced PKB phosphorylation in a dose-dependent manner. ET-1 and Ang II treatment also induced the phosphorylation of tyrosine residues in the autophosphorylation sites of IGF-1R, which were blocked by AG1024. In addition, both ET-1 and Ang II evoked tyrosine phosphorylation of c-Src, a nonreceptor PTK, whereas pharmacological inhibition of c-Src PTK activity by PP2, a specific inhibitor of Src-family tyrosine kinase, significantly reduced PKB phosphorylation as well as tyrosine phosphorylation of IGF-1R induced by the 2 vasoactive peptides. Furthermore, protein and DNA synthesis enhanced by ET-1 and Ang II were attenuated by AG1024 and PP2. In conclusion, these data suggest that IGF-1R PTK and c-Src PTK play a critical role in mediating PKB phosphorylation as well as hypertrophic and proliferative responses induced by ET-1 and Ang II in A10 VSMC.

Biology of the natriuretic peptides

The biology of the natriuretic peptide (NP) system is complex, yet highly phylogenetically preserved. It regulates salt and water handling, promotes vasodilatation, and exerts favorable effects on the heart in the context of processes such as heart failure. Prior assumptions about the production of B-type NP (BNP) and its amino-terminal precursor fragment (NT-proBNP) have recently been refuted. It is now recognized that rather than a 1:1 secretion of these 2 NPs, a mixture of cleaved and uncleaved NPs is released by the cardiomyocyte. It is also recognized that BNP is rapidly modified into a mixture of various fragments. Commercial assays for the detection of BNP and NT-proBNP measure a mixture of cleaved and uncleaved NPs as well as varying amounts of degraded BNP. BNP and NT-proBNP are cleared differentially: BNP is actively removed from the bloodstream and also has passive clearance mechanisms, including renal clearance; NT-proBNP is cleared more passively by organs with high rates of blood flow, including the kidney.

Natriuretic peptides in vascular physiology and pathology

Four major natriuretic peptides have been isolated: atrial natriuretic peptide (ANP), brain natriuretic peptide (BNP), C-type natriuretic peptide (CNP), and Dendroaspis-type natriuretic peptide (DNP). Natriuretic peptides play an important role in the regulation of cardiovascular homeostasis maintaining blood pressure and extracellular fluid volume. The classical endocrine effects of natriuretic peptides to modulate fluid and electrolyte balance and vascular smooth muscle tone are complemented by autocrine and paracrine actions that include regulation of coronary blood flow and, therefore, myocardial perfusion; modulation of proliferative responses during myocardial and vascular remodeling; and cytoprotective anti-ischemic effects. The actions of natriuretic peptides are mediated by the specific binding of these peptides to three cell surface receptors: type A natriuretic peptide receptor (NPR-A), type B natriuretic peptide receptor (NPR-B), and type C natriuretic peptide receptor (NPR-C). NPR-A and NPR-B are guanylyl cyclase receptors that increase intracellular cGMP concentration and activate cGMP-dependent protein kinases. NPR-C has been presented as a clearance receptor and its activation also results in inhibition of adenylyl cyclase activity. The wide range of effects of natriuretic peptides might be the base for the development of new therapeutic strategies of great benefit in patients with cardiovascular problems including coronary artery disease or heart failure. This review summarizes current literature concerning natriuretic peptides, their receptors and their effects on fluid/electrolyte balance, and vascular and cardiac physiology and pathology, including primary hypertension and myocardial infarction. In addition, we will attempt to provide an update on important issues regarding natriuretic peptides in congestive heart failure.

Peroxynitrite inhibits the expression of G(i)alpha protein and adenylyl cyclase signaling in vascular smooth muscle cells

We previously showed that S-nitroso-N-acetylpenicillamine, a nitric oxide donor, decreased the levels and functions of G(i)alpha proteins by formation of peroxynitrite (ONOO(-)) in vascular smooth muscle cells (VSMC). The present studies were undertaken to investigate whether ONOO(-) can modulate the expression of G(i)alpha protein and associated adenylyl cyclase signaling in VSMC. Treatment of A-10 and aortic VSMC with ONOO(-) for 24 h decreased the expression of G(i)alpha-2 and G(i)alpha-3, but not G(s)alpha, protein in a concentration-dependent manner; expression was restored toward control levels by (111)Mn-tetralis(benzoic acid porphyrin) and uric acid, but not by 1H[1,2,4]oxadiazole[4,3-a]quinoxaline-1-one (ODQ) and KT-5823. cGMP levels were increased by approximately 50% and 150% by 0.1 and 0.5 mM ONOO(-), respectively, and attenuated toward control levels by ODQ. In addition, 0.5 mM ONOO(-) attenuated the inhibition of adenylyl cyclase by ANG II and C-type atrial natriuretic peptide (C-ANP(4-23)), as well as the inhibition of forskolin-stimulated adenylyl cyclase activity by GTPgammaS, whereas, the G(s)-mediated stimulations were augmented. In addition, 0.5 mM ONOO(-) decreased phosphorylation of ERK1/2 and p38 MAP kinase and enhanced JNK phosphorylation but did not affect AKT1/3 phosphorylation. These results suggest that ONOO(-) decreased the expression of G(i) proteins and associated functions in VSMC through a cGMP-independent mechanism and may involve the MAP kinase signaling pathway.

Natriuretic peptide C receptor signalling in the heart and vasculature

Natriuretic peptides (NPs), including atrial, brain and C-type natriuretic peptides (ANP, BNP and CNP), bind two classes of cell surface receptors: the guanylyl cyclase-linked A and B receptors (NPR-A and NPR-B) and the C receptor (NPR-C). The biological effects of NPs have been mainly attributed to changes in intracellular cGMP following their binding to NPR-A and NPR-B. NPR-C does not include a guanylyl cyclase domain. It has been denoted as a clearance receptor and is thought to bind and internalize NPs for ultimate degradation. However, a substantial body of biochemical work has demonstrated the ability of NPR-C to couple to inhibitory G proteins (Gi) and cause inhibition of adenylyl cyclase and activation of phospholipase-C. Recently, novel physiological effects of NPs, mediated specifically by NPR-C, have been discovered in the heart and vasculature. We have described the ability of CNP, acting via NPR-C, to selectively inhibit L-type calcium currents in atrial and ventricular myocytes, as well as in pacemaker cells (sinoatrial node myocytes). In contrast, our studies of the electrophysiological effects of CNP on cardiac fibroblasts demonstrated an NPR-C-Gi-phospholipase-C-dependent activation of a non-selective cation current mediated by transient receptor potential (TRP) channels. It is also known that CNP and BNP have important anti-proliferative effects in cardiac fibroblasts that appear to involve NPR-C. In the mammalian resistance vessels, including mesenteric and coronary arteries, CNP has been found to function as an NPR-C-dependent endothelium-derived hyperpolarizing factor that regulates local blood flow and systemic blood pressure by hyperpolarizing smooth muscle cells. In this review we highlight the role of NPR-C in mediating these NP effects in myocytes and fibroblasts from the heart as well as in vascular smooth muscle cells.