Role of smooth muscle cGMP/cGKI signaling in murine vascular restenosis

Phosphodiesterase in heart and vessels: from physiology to diseases

Phosphodiesterases (PDEs) are a superfamily of enzymes that hydrolyze cyclic nucleotides, including cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP). Both cyclic nucleotides are critical secondary messengers in the neurohormonal regulation in the cardiovascular system. PDEs precisely control spatiotemporal subcellular distribution of cyclic nucleotides in a cell- and tissue-specific manner, playing critical roles in physiological responses to hormone stimulation in the heart and vessels. Dysregulation of PDEs has been linked to the development of several cardiovascular diseases, such as hypertension, aneurysm, atherosclerosis, arrhythmia, and heart failure. Targeting these enzymes has been proven effective in treating cardiovascular diseases and is an attractive and promising strategy for the development of new drugs. In this review, we discuss the current understanding of the complex regulation of PDE isoforms in cardiovascular function, highlighting the divergent and even opposing roles of PDE isoforms in different pathogenesis.

Cysteine-Rich LIM-Only Protein 4 (CRP4) Promotes Atherogenesis in the ApoE-/- Mouse Model

Vascular smooth muscle cells (VSMCs) can switch from their contractile state to a synthetic phenotype resulting in high migratory and proliferative capacity and driving atherosclerotic lesion formation. The cysteine-rich LIM-only protein 4 (CRP4) reportedly modulates VSM-like transcriptional signatures, which are perturbed in VSMCs undergoing phenotypic switching. Thus, we hypothesized that CRP4 contributes to adverse VSMC behaviours and thereby to atherogenesis in vivo. The atherogenic properties of CRP4 were investigated in plaque-prone apolipoprotein E (ApoE) and CRP4 double-knockout (dKO) as well as ApoE-deficient CRP4 wildtype mice. dKO mice exhibited lower plaque numbers and lesion areas as well as a reduced content of α-smooth muscle actin positive cells in the lesion area, while lesion-associated cell proliferation was elevated in vessels lacking CRP4. Reduced plaque volumes in dKO correlated with significantly less intra-plaque oxidized low-density lipoprotein (oxLDL), presumably due to upregulation of the antioxidant factor peroxiredoxin-4 (PRDX4). This study identifies CRP4 as a novel pro-atherogenic factor that facilitates plaque oxLDL deposition and identifies the invasion of atherosclerotic lesions by VSMCs as important determinants of plaque vulnerability. Thus, targeting of VSMC CRP4 should be considered in plaque-stabilizing pharmacological strategies.

Role of PDE10A in vascular smooth muscle cell hyperplasia and pathological vascular remodelling

AIMS

Intimal hyperplasia is a common feature of vascular remodelling disorders. Accumulation of synthetic smooth muscle cell (SMC)-like cells is the main underlying cause. Current therapeutic approaches including drug-eluting stents are not perfect due to the toxicity on endothelial cells and novel therapeutic strategies are needed. Our preliminary screening for dysregulated cyclic nucleotide phosphodiesterases (PDEs) in growing SMCs revealed the alteration of PDE10A expression. Herein, we investigated the function of PDE10A in SMC proliferation and intimal hyperplasia both in vitro and in vivo.

METHODS AND RESULTS

RT-qPCR, immunoblot, and in situ proximity ligation assay were performed to determine PDE10A expression in synthetic SMCs and injured vessels. We found that PDE10A mRNA and/or protein levels are up-regulated in cultured SMCs upon growth stimulation, as well as in intimal cells in injured mouse femoral arteries. To determine the cellular functions of PDE10A, we focused on its role in SMC proliferation. The anti-mitogenic effects of PDE10A on SMCs were evaluated via cell counting, BrdU incorporation, and flow cytometry. We found that PDE10A deficiency or inhibition arrested the SMC cell cycle at G1-phase with a reduction of cyclin D1. The anti-mitotic effect of PDE10A inhibition was dependent on cGMP-dependent protein kinase Iα (PKGIα), involving C-natriuretic peptide (CNP) and particulate guanylate cyclase natriuretic peptide receptor 2 (NPR2). In addition, the effects of genetic depletion and pharmacological inhibition of PDE10A on neointimal formation were examined in a mouse model of femoral artery wire injury. Both PDE10A knockout and inhibition decreased injury-induced intimal thickening in femoral arteries by at least 50%. Moreover, PDE10A inhibition decreased ex vivo remodelling of cultured human saphenous vein segments.

CONCLUSIONS

Our findings indicate that PDE10A contributes to SMC proliferation and intimal hyperplasia at least partially via antagonizing CNP/NPR2/cGMP/PKG1α signalling and suggest that PDE10A may be a novel drug target for treating vascular occlusive disease.

The cGMP system: components and function

The cyclic guanosine monophosphate (cGMP) signaling system is one of the most prominent regulators of a variety of physiological and pathophysiological processes in many mammalian and non-mammalian tissues. Targeting this pathway by increasing cGMP levels has been a very successful approach in pharmacology as shown for nitrates, phosphodiesterase (PDE) inhibitors and stimulators of nitric oxide-guanylyl cyclase (NO-GC) and particulate GC (pGC). This is an introductory review to the cGMP signaling system intended to introduce those readers to this system, who do not work in this area. This article does not intend an in-depth review of this system. Signal transduction by cGMP is controlled by the generating enzymes GCs, the degrading enzymes PDEs and the cGMP-regulated enzymes cyclic nucleotide-gated ion channels, cGMP-dependent protein kinases and cGMP-regulated PDEs. Part A gives a very concise introduction to the components. Part B gives a very concise introduction to the functions modulated by cGMP. The article cites many recent reviews for those who want a deeper insight.

Novel Approaches to Fine-Tune Therapeutic Targeting of Platelets in Atherosclerosis: A Critical Appraisal

The pathogenesis of atherosclerotic vascular disease is driven by a multitude of risk factors intertwining metabolic and inflammatory pathways. Increasing knowledge about platelet biology sheds light on how platelets take part in these processes from early to later stages of plaque development. Recent insights from experimental studies and mouse models substantiate platelets as initiators and amplifiers in atherogenic leukocyte recruitment. These studies are complemented by results from genetics studies shedding light on novel molecular mechanisms which provide an interesting prospect as novel targets. For instance, experimental studies provide further details how platelet-decorated von Willebrand factor tethered to activated endothelial cells plays a role in atherogenic monocyte recruitment. Novel aspects of platelets as atherogenic inductors of neutrophil extracellular traps and particularities in signaling pathways such as cyclic guanosine monophosphate and the inhibitory adaptor molecule SHB23/LNK associating platelets with atherogenesis are shared. In summary, it was our intention to balance insights from recent experimental data that support a plausible role for platelets in atherogenesis against a paucity of clinical evidence needed to validate this concept in humans.

cGMP Signaling and Vascular Smooth Muscle Cell Plasticity

Cyclic GMP regulates multiple cell types and functions of the cardiovascular system. This review summarizes the effects of cGMP on the growth and survival of vascular smooth muscle cells (VSMCs), which display remarkable phenotypic plasticity during the development of vascular diseases, such as atherosclerosis. Recent studies have shown that VSMCs contribute to the development of atherosclerotic plaques by clonal expansion and transdifferentiation to macrophage-like cells. VSMCs express a variety of cGMP generators and effectors, including NO-sensitive guanylyl cyclase (NO-GC) and cGMP-dependent protein kinase type I (cGKI), respectively. According to the traditional view, cGMP inhibits VSMC proliferation, but this concept has been challenged by recent findings supporting a stimulatory effect of the NO-cGMP-cGKI axis on VSMC growth. Here, we summarize the relevant studies with a focus on VSMC growth regulation by the NO-cGMP-cGKI pathway in cultured VSMCs and mouse models of atherosclerosis, restenosis, and angiogenesis. We discuss potential reasons for inconsistent results, such as the use of genetic versus pharmacological approaches and primary versus subcultured cells. We also explore how modern methods for cGMP imaging and cell tracking could help to improve our understanding of cGMP’s role in vascular plasticity. We present a revised model proposing that cGMP promotes phenotypic switching of contractile VSMCs to VSMC-derived plaque cells in atherosclerotic lesions. Regulation of vascular remodeling by cGMP is not only an interesting new therapeutic strategy, but could also result in side effects of clinically used cGMP-elevating drugs.

Amplified pathogenic actions of angiotensin II in cysteine-rich LIM-only protein 4-negative mouse hearts

LIM domain proteins have been identified as essential modulators of cardiac biology and pathology; however, it is unclear which role the cysteine-rich LIM-only protein (CRP)4 plays in these processes. In studying CRP4 mutant mice, we found that their hearts developed normally, but lack of CRP4 exaggerated multiple parameters of the cardiac stress response to the neurohormone angiotensin II (Ang II). Aiming to dissect the molecular details, we found a link between CRP4 and the cardioprotective cGMP pathway, as well as a multiprotein complex comprising well-known hypertrophy-associated factors. Significant enrichment of the cysteine-rich intestinal protein (CRIP)1 in murine hearts lacking CRP4, as well as severe cardiac defects and premature death of CRIP1 and CRP4 morphant zebrafish embryos, further support the notion that depleting CRP4 is incompatible with a proper cardiac development and function. Together, amplified Ang II signaling identified CRP4 as a novel antiremodeling factor regulated, at least to some extent, by cardiac cGMP.-Straubinger, J., Boldt, K., Kuret, A., Deng, L., Krattenmacher, D., Bork, N., Desch, M., Feil, R., Feil, S., Nemer, M., Ueffing, M., Ruth, P., Just, S., Lukowski, R. Amplified pathogenic actions of angiotensin II in cysteine-rich LIM-only protein 4 negative mouse hearts.

Sildenafil Does Not Prevent Heart Hypertrophy and Fibrosis Induced by Cardiomyocyte Angiotensin II Type 1 Receptor Signaling

Analyses of several mouse models imply that the phosphodiesterase 5 (PDE5) inhibitor sildenafil (SIL), via increasing cGMP, affords protection against angiotensin II (Ang II)-stimulated cardiac remodeling. However, it is unclear which cell types are involved in these beneficial effects, because Ang II may exert its adverse effects by modulating multiple renovascular and cardiac functions via Ang II type 1 receptors (AT1Rs). To test the hypothesis that SIL/cGMP inhibit cardiac stress provoked by amplified Ang II/AT1R directly in cardiomyocytes (CMs), we studied transgenic mice with CM-specific overexpression of the AT1R under the control of the α-myosin heavy chain promoter (αMHC-AT1R(tg/+)). The extent of cardiac growth was assessed in the absence or presence of SIL and defined by referring changes in heart weight to body weight or tibia length. Hypertrophic marker genes, extracellular matrix-regulating factors, and expression patterns of fibrosis markers were examined in αMHC-AT1R(tg/+) ventricles (with or without SIL) and corroborated by investigating different components of the natriuretic peptide/PDE5/cGMP pathway as well as cardiac functions. cGMP levels in heart lysates and intact CMs were measured by competitive immunoassays and Förster resonance energy transfer. We found higher cardiac and CM cGMP levels and upregulation of the cGMP-dependent protein kinase type I with AT1R overexpression. However, even a prolonged SIL treatment regimen did not limit the progressive CM growth, fibrosis, or decline in cardiac functions in the αMHC-AT1R(tg/+) model, suggesting that SIL does not interfere with the pathogenic actions of amplified AT1R signaling in CMs. Hence, the cardiac/noncardiac cells involved in the cross-talk between SIL-sensitive PDE activity and Ang II/AT1R still need to be identified.

Role of sGC-dependent NO signalling and myocardial infarction risk

The NO/cGMP pathway plays an important role in many physiological functions and pathophysiological conditions. In the last few years, several genetic and functional studies pointed to an underestimated role of this pathway in the development of atherosclerosis. Indeed, several genetic variants of key enzymes modulating the generation of NO and cGMP have been strongly associated with coronary artery disease and myocardial infarction risk. In this review, we aim to place the genomic findings on components of the NO/cGMP pathway, namely endothelial nitric oxide synthase, soluble guanylyl cyclase and phosphodiesterase 5A, in context of preventive and therapeutic strategies for treating atherosclerosis and its sequelae.

Targeted ablation of the Pde6h gene in mice reveals cross-species differences in cone and rod phototransduction protein isoform inventory

Phosphodiesterase-6 (PDE6) is a multisubunit enzyme that plays a key role in the visual transduction cascade in rod and cone photoreceptors. Each type of photoreceptor utilizes discrete catalytic and inhibitory PDE6 subunits to fulfill its physiological tasks, i.e. the degradation of cyclic guanosine-3',5'-monophosphate at specifically tuned rates and kinetics. Recently, the human PDE6H gene was identified as a novel locus for autosomal recessive (incomplete) color blindness. However, the three different classes of cones were not affected to the same extent. Short wave cone function was more preserved than middle and long wave cone function indicating that some basic regulation of the PDE6 multisubunit enzyme was maintained albeit by a unknown mechanism. To study normal and disease-related functions of cone Pde6h in vivo, we generated Pde6h knock-out (Pde6h(-/-)) mice. Expression of PDE6H in murine eyes was restricted to both outer segments and synaptic terminals of short and long/middle cone photoreceptors, whereas Pde6h(-/-) retinae remained PDE6H-negative. Combined in vivo assessment of retinal morphology with histomorphological analyses revealed a normal overall integrity of the retinal organization and an unaltered distribution of the different cone photoreceptor subtypes upon Pde6h ablation. In contrast to human patients, our electroretinographic examinations of Pde6h(-/-) mice suggest no defects in cone/rod-driven retinal signaling and therefore preserved visual functions. To this end, we were able to demonstrate the presence of rod PDE6G in cones indicating functional substitution of PDE6. The disparities between human and murine phenotypes caused by mutant Pde6h/PDE6H suggest species-to-species differences in the vulnerability of biochemical and neurosensory pathways of the visual signal transduction system.

Tetra-acetylajugasterone a new constituent of Vitex cienkowskii with vasorelaxant activity

Tetra-acetylajugasterone C (TAAC) was found to be one of the naturally occurring compounds of the Cameroonian medicinal plant Vitex cienkowskii which is responsible for a vasorelaxant activity of an extract of this plant. The evaluation of the underlying mechanisms for the relaxing effect of TAAC was determined using aortic rings of rats and mice. TAAC produced a concentration-dependent relaxation in rat artery rings pre-contracted with 1μM noradrenaline (IC50: 8.40μM) or 60mM KCl (IC50: 36.30μM). The nitric oxide synthase inhibitor l-NAME (100μM) and the soluble guanylate cyclase inhibitor ODQ (10μM) significantly attenuated the vasodilatory effect of TAAC. TAAC also exerted a relaxing effect in aorta of wild-type mice (cGKI(+/+); IC50=13.04μM) but a weaker effect in aorta of mice lacking cGMP-dependent protein kinase I (cGKI(-/-); IC50=36.12μM). The involvement of calcium channels was studied in rings pre-incubated in calcium-free buffer and primed with 1μM noradrenaline prior to addition of calcium to elicit contraction. TAAC (100μM) completely inhibited the resulting calcium-induced vasoconstriction. The same concentration of TAAC showed a stronger effect on the tonic than on the phasic component of noradrenaline-induced contraction. This study shows that TAAC, a newly detected constituent of Vitex cienkowskii contributes to the relaxing effect of an extract of the plant. The effect is partially mediated by the involvement of the NO/cGMP pathway of the smooth muscle but additionally inhibition of calcium influx into the cell may play a role.

Sildenafil citrate increases fetal weight in a mouse model of fetal growth restriction with a normal vascular phenotype

Fetal growth restriction (FGR) is defined as the inability of a fetus to achieve its genetic growth potential and is associated with a significantly increased risk of morbidity and mortality. Clinically, FGR is diagnosed as a fetus falling below the 5(th) centile of customised growth charts. Sildenafil citrate (SC, Viagra™), a potent and selective phosphodiesterase-5 inhibitor, corrects ex vivo placental vascular dysfunction in FGR, demonstrating potential as a therapy for this condition. However, many FGR cases present without an abnormal vascular phenotype, as assessed by Doppler measures of uterine/umbilical artery blood flow velocity. Thus, we hypothesized that SC would not increase fetal growth in a mouse model of FGR, the placental-specific Igf2 knockout mouse, which has altered placental exchange capacity but normal placental blood flow. Fetal weights were increased (by 8%) in P0 mice following maternal SC treatment (0.4 mg/ml) via drinking water. There was also a trend towards increased placental weight in treated P0 mice (P = 0.056). Additionally, 75% of the P0 fetal weights were below the 5(th) centile, the criterion used to define human FGR, of the non-treated WT fetal weights; this was reduced to 51% when dams were treated with SC. Umbilical artery and vein blood flow velocity measures confirmed the lack of an abnormal vascular phenotype in the P0 mouse; and were unaffected by SC treatment. (14)C-methylaminoisobutyric acid transfer (measured to assess effects on placental nutrient transporter activity) per g placenta was unaffected by SC, versus untreated, though total transfer was increased, commensurate with the trend towards larger placentas in this group. These data suggest that SC may improve fetal growth even in the absence of an abnormal placental blood flow, potentially affording use in multiple sub-populations of individuals presenting with FGR.

The role of cGMP/cGKI signalling and Trpc channels in regulation of vascular tone

AIMS

Signalling via cGMP-dependent protein kinase I (cGKI) is the major pathway in vascular smooth muscle (SM), by which endothelial NO regulates vascular tone. Recent evidence suggests that canonical transient receptor potential (Trpc) channels are targets of cGKI in SM and mediate the relaxant effects of cGMP signalling. We tested this concept by investigating the role of cGMP/cGKI signalling on vascular tone and peripheral resistance using Trpc6(-/-), Trpc3(-/-), Trpc3(-/-)/6(-/-), Trpc1(-/-)/3(-/-)/6(-/-), and SM-specific cGKI(-/-) (sm-cGKI(-/-)) mice.

METHODS AND RESULTS

α-Adrenergic stimulation induced similar contractions in L-NG-nitroarginine methyl ester (l-NAME)-treated aorta and comparably increased peripheral pressure in hind limbs from all mouse lines investigated. After α-adrenergic stimulation, 8-Br-cGMP diminished similarly aortic tone and peripheral pressure in control, Trpc6(-/-), Trpc3(-/-), Trpc3(-/-)/6(-/-), and Trpc1(-/-)/3(-/-)/6(-/-) mice but not in sm-cGKI(-/-) mice. In untreated aorta, α-adrenergic stimulation induced similar contractions in the aorta from control and Trpc3(-/-) mice but larger contractions in sm-cGKI(-/-), Trpc6(-/-), Trpc3(-/-)/6(-/-), and Trpc1(-/-)/3(-/-)/6(-/-) mice, indicating a functional link between cGKI and Trpc6 channels. Trpc3 channels were detected by immunocytochemistry in both isolated aortic smooth muscle cells (SMCs) and aortic endothelial cells (ECs), whereas Trpc6 channels were detected only in ECs. Phenylephrine-stimulated Ca(2+) levels were similar in SMCs from control (Ctr) and Trpc6(-/-) mice. Carbachol-stimulated Ca(2+) levels were reduced in ECs from Trpc6(-/-) mice. Stimulated Ca(2+) levels were lowered by 8-Br-cGMP in Ctr but not in Trpc6(-/-) ECs.

CONCLUSIONS

The results suggest that cGKI and Trpc1,3,6 channels are not functionally coupled in vascular SM. Deletion of Trpc6 channels impaired endothelial cGKI signalling and vasodilator tone in the aorta.

cGMP-Dependent Protein Kinase Inhibitors in Health and Disease

cGMP-dependent protein kinases (PKG) exhibit diverse physiological functions in the mammalian system e.g., in vascular and gastrointestinal smooth muscles, in platelets, in kidney, in bone growth, nociception and in the central nervous system. Furthermore, PKG were found in insects and in the malaria parasite Plasmodium falciparum. Two different genes of PKG exist: a) the PKG-I gene that is expressed as cytosolic PKG-Iα or PKG-Iβ isoform, and b) the PKG-II gene, which expresses the membrane associated PKG-II protein. The enzyme kinetics, the localization and the substrates of these PKG enzymes differ utilizing different physiological functions. Various inhibitors of PKG were developed directed against diverse functional regions of the kinase. These inhibitors of PKG have been used to analyse the specific functions of these enzymes. The review article will summarize these different inhibitors regarding their specificity and their present applications in vitro and in vivo. Furthermore, it will be discussed that the distinct inhibition of the PKG enzymes could be used as a valuable pharmacological target e.g., in the treatment of cardiovascular diseases, diarrhea, cancer or malaria.

cGMP-dependent protein kinases (cGK)

cGMP-dependent protein kinases (cGK) are serine/threonine kinases that are widely distributed in eukaryotes. Two genes-prkg1 and prkg2-code for cGKs, namely, cGKI and cGKII. In mammals, two isozymes, cGKIα and cGKIβ, are generated from the prkg1 gene. The cGKI isozymes are prominent in all types of smooth muscle, platelets, and specific neuronal areas such as cerebellar Purkinje cells, hippocampal neurons, and the lateral amygdala. The cGKII prevails in the secretory epithelium of the small intestine, the juxtaglomerular cells, the adrenal cortex, the chondrocytes, and in the nucleus suprachiasmaticus. Both cGKs are major downstream effectors of many, but not all, signalling events of the NO/cGMP and the ANP/cGMP pathways. cGKI relaxes smooth muscle tone and prevents platelet aggregation, whereas cGKII inhibits renin secretion, chloride/water secretion in the small intestine, the resetting of the clock during early night, and endochondral bone growth. This chapter focuses on the involvement of cGKs in cardiovascular and non-cardiovascular processes including cell growth and metabolism.

Nitric oxide reduces NADPH oxidase 5 (Nox5) activity by reversible S-nitrosylation

The NADPH oxidases (Noxs) are a family of transmembrane oxidoreductases that produce superoxide and other reactive oxygen species (ROS). Nox5 was the last of the conventional Nox isoforms to be identified and is a calcium-dependent enzyme that does not depend on accessory subunits for activation. Recently, Nox5 was shown to be expressed in human blood vessels and therefore the goal of this study was to determine whether nitric oxide (NO) can modulate Nox5 activity. Endogenously produced NO potently inhibited basal and stimulated Nox5 activity and this inhibition was reversible with chronic, but not acute, exposure to L-NAME. Nox5 activity was reduced by NO donors, iNOS, and eNOS and in endothelial cells and LPS-stimulated smooth muscle cells in a manner dependent on NO concentration. ROS production was diminished by NO in an isolated enzyme activity assay replete with surplus calcium and NADPH. There was no evidence for NO-dependent changes in tyrosine nitration, glutathiolation, or phosphorylation of Nox5. In contrast, there was evidence for the increased nitrosylation of Nox5 as determined by the biotin-switch assay and mass spectrometry. Four S-nitrosylation sites were identified and of these, mutation of C694 dramatically lowered Nox5 activity, NO sensitivity, and biotin labeling. Furthermore, coexpression of the denitrosylation enzymes thioredoxin 1 and GSNO reductase prevented NO-dependent inhibition of Nox5. The potency of NO against other Nox enzymes was in the order Nox1 ≥ Nox3 > Nox5 > Nox2, whereas Nox4 was refractory. Collectively, these results suggest that endogenously produced NO can directly S-nitrosylate and inhibit the activity of Nox5.

Modulatory Role of Nitric Oxide/cGMP System in Endothelin-1-Induced Signaling Responses in Vascular Smooth Muscle Cells

Nitric oxide (NO) is an important vasoprotective molecule that serves not only as a vasodilator but also exerts antihypertrophic and antiproliferative effects in vascular smooth muscle cells (VSMC). The precise mechanism by which the antihypertrophic and antiproliferative responses of NO are mediated remains obscure. However, recent studies have suggested that one of the mechanisms by which this may be achieved includes the attenuation of signal transduction pathways responsible for inducing the hypertrophic and proliferative program in VSMC. Endothelin-1 is a powerful vasoconstrictor peptide with mitogenic and growth stimulatory properties and exerts its effects by activating multiple signaling pathways which include ERK 1/2, PKB and Rho-ROCK. Both cGMP-dependent and independent events have been reported to mediate the effect of NO on these pathways leading to its vasoprotective response. This review briefly summarizes some key studies on the modulatory effect of NO on these signaling pathways and discusses the possible role of cGMP system in this process.

Animal, in vitro, and ex vivo models of flow-dependent atherosclerosis: role of oxidative stress

Atherosclerosis is an inflammatory disease preferentially occurring in curved or branched arterial regions, whereas straight parts of the arteries are protected, suggesting a close relationship between flow and atherosclerosis. However, evidence directly linking disturbed flow to atherogenesis is just emerging, thanks to the recent development of suitable animal models. In this article, we review the status of various animal, in vitro, and ex vivo models that have been used to study flow-dependent vascular biology and atherosclerosis. For animal models, naturally flow-disturbed regions such as branched or curved arterial regions as well as surgically created models, including arterio-venous fistulas, vascular grafts, perivascular cuffs, and complete, incomplete, or partial ligation of arteries, are used. Although in vivo models provide the environment needed to mimic the complex pathophysiological processes, in vitro models provide simple conditions that allow the study of isolated factors. Typical in vitro models use cultured endothelial cells exposed to various flow conditions, using devices such as cone-and-plate and parallel-plate chambers. Ex vivo models using isolated vessels have been used to bridge the gap between complex in vivo models and simple in vitro systems. Here, we review these flow models in the context of the role of oxidative stress in flow-dependent inflammation, a critical proatherogenic step, and atherosclerosis.

PKGIα inhibits the proliferation of cerebral arterial smooth muscle cell induced by oxyhemoglobin after subarachnoid hemorrhage

The purpose of the present study was to observe the proliferation of cerebral arterial smooth muscle cell (CASMC) induced by oxyhemoglobin (Oxyhb) and interfered by Adenovirus-mediate-PKGI (Ad-PKGI), and to investigate the potential regulative role of the PKGI gene in the molecule mechanism of cerebral vasospasm (CVS) after Subarachnoid hemorrhage (SAH). Tissue-sticking method was used for primary cultured rat CASMCs. Semi-quantitative reverse transcription and polymerase chain reaction (RT-PCR) and western blot were used to examine the PKGI mRNA and protein expressions after CASMC were transfected by Ad-PKG. The proliferation of CASMCs was determined by MTT assay and 3H-TdR incorporation. Ad-PKGI could be transfected into CASMCS and highly express. Oxyhemoglobin could stimulate the proliferation of CASMC; the value of 3H-TdR incorporation and the absorbance value of MTT increased and could block up after CASMC was transfected by Ad-PKG. The results suggested that the PKG signaling pathway might play an important role in CVS after SAH, and the PKG gene might be a target point of gene therapy.

cGMP-dependent protein kinases and cGMP phosphodiesterases in nitric oxide and cGMP action

To date, studies suggest that biological signaling by nitric oxide (NO) is primarily mediated by cGMP, which is synthesized by NO-activated guanylyl cyclases and broken down by cyclic nucleotide phosphodiesterases (PDEs). Effects of cGMP occur through three main groups of cellular targets: cGMP-dependent protein kinases (PKGs), cGMP-gated cation channels, and PDEs. cGMP binding activates PKG, which phosphorylates serines and threonines on many cellular proteins, frequently resulting in changes in activity or function, subcellular localization, or regulatory features. The proteins that are so modified by PKG commonly regulate calcium homeostasis, calcium sensitivity of cellular proteins, platelet activation and adhesion, smooth muscle contraction, cardiac function, gene expression, feedback of the NO-signaling pathway, and other processes. Current therapies that have successfully targeted the NO-signaling pathway include nitrovasodilators (nitroglycerin), PDE5 inhibitors [sildenafil (Viagra and Revatio), vardenafil (Levitra), and tadalafil (Cialis and Adcirca)] for treatment of a number of vascular diseases including angina pectoris, erectile dysfunction, and pulmonary hypertension; the PDE3 inhibitors [cilostazol (Pletal) and milrinone (Primacor)] are used for treatment of intermittent claudication and acute heart failure, respectively. Potential for use of these medications in the treatment of other maladies continues to emerge.

Upregulation of Nox4 by TGF{beta}1 oxidizes SERCA and inhibits NO in arterial smooth muscle of the prediabetic Zucker rat

RATIONALE

Vascular smooth muscle cell (SMC) migration is an important pathological process in several vascular occlusive diseases, including atherosclerosis and restenosis, both of which are accelerated by diabetes mellitus.

OBJECTIVE

To determine the mechanisms of abnormal vascular SMC migration in type 2 diabetes, the obese Zucker rat (ZO), a model of obesity and insulin resistance, was studied.

METHODS AND RESULTS

In culture, ZO aortic SMCs showed a significant increase in Nox4 mRNA and protein levels compared with the control lean Zucker rat (ZL). The sarco-/endoplasmic reticulum Ca(2+) ATPase (SERCA) nitrotyrosine-294,295 and cysteine-674 (C674)-SO(3)H were increased in ZO SMCs, indicating oxidant stress. Unlike ZL SMC, nitric oxide (NO) failed to inhibit serum-induced SMC migration in ZO. Transfection of Nox4 small interference RNA or overexpression of SERCA2b wild type, but not C674S mutant SERCA, restored the response to NO. Knockdown of Nox4 also decreased SERCA oxidation in ZO SMCs. In addition, transforming growth factor-β1 via Smad2 was necessary and sufficient to upregulate Nox4, oxidize SERCA, and block the antimigratory action of NO in ZO SMCs. Corresponding to the results in cultured SMCs, immunohistochemistry confirmed that Nox4 and SERCA C674-SO(3)H were significantly increased in ZO aorta. After common carotid artery injury, knockdown of Nox4 by adenoviral Nox4 short hairpin RNA decreased Nox4 and SERCA C674-SO(3)H staining and significantly decreased injury-induced neointima.

CONCLUSION

These studies indicate that the upregulation of Nox4 by transforming growth factor-β1 in ZO SMCs is responsible for the impaired response to NO by a mechanism involving the oxidation of SERCA C674. Knockdown of Nox4 inhibits oxidation of SERCA, as well as neointima formation, after ZO common carotid artery injury.

Cardiac hypertrophy is not amplified by deletion of cGMP-dependent protein kinase I in cardiomyocytes

It has been suggested that cGMP kinase I (cGKI) dampens cardiac hypertrophy. We have compared the effect of isoproterenol (ISO) and transverse aortic constriction (TAC) on hypertrophy in WT [control (CTR)] mice, total cGKI-KO mice, and cGKIbeta rescue mice (betaRM) lacking cGKI specifically in cardiomyocytes (CMs). Infusion of ISO did not change the expression of cGKI in the hearts of CTR mice or betaRM but raised the heart weight by approximately 20% in both. An identical hypertrophic growth response was measured in CMs from CTR mice and betaRM and in isolated adult CMs cultured with or without 1 muM ISO. In both genotypes, ISO infusion induced similar changes in the expression of hypertrophy-associated cardiac genes and significant elevation of serum atrial natriuretic peptide and total cardiac cGMP. No differences in cardiac hypertrophy were obtained by 7-day ISO infusion in 4- to 6-week-old conventional cGKI-KO and CTR mice. Furthermore, TAC-induced hypertrophy of CTR mice and betaRM was not different and did not result in changes of the cGMP-hydrolyzing phosphodiesterase activities in hypertropic hearts or CMs. These results strongly suggest that cardiac myocyte cGKI does not affect the development of heart hypertrophy induced by pressure overload or chronic ISO infusion.

Cyclic GMP kinase and RhoA Ser188 phosphorylation integrate pro- and antifibrotic signals in blood vessels

Vascular fibrosis is a major complication of hypertension and atherosclerosis, yet it is largely untreatable. Natriuretic peptides (NPs) repress fibrogenic activation of vascular smooth muscle cells (VSMCs), but the intracellular mechanism mediating this effect remains undetermined. Here we show that inhibition of RhoA through phosphorylation at Ser188, the site targeted by the NP effector cyclic GMP (cGMP)-dependent protein kinase I (cGK I), is critical to fully exert antifibrotic potential. cGK I(+/-) mouse blood vessels exhibited an attenuated P-RhoA level and concurrently increased RhoA/ROCK signaling. Importantly, cGK I insufficiency caused dynamic recruitment of ROCK into the fibrogenic programs, thereby eliciting exaggerated vascular hypertrophy and fibrosis. Transgenic expression of cGK I-unphosphorylatable RhoA(A188) in VSMCs augmented ROCK activity, vascular hypertrophy, and fibrosis more prominently than did that of wild-type RhoA, consistent with the notion that RhoA(A188) escapes the intrinsic inhibition by cGK I. Additionally, VSMCs expressing RhoA(A188) became refractory to the antifibrotic effects of NPs. Our results identify cGK I-mediated Ser188 phosphorylation of RhoA as a converging node for pro- and antifibrotic signals and may explain how diminished cGMP signaling, commonly associated with vascular malfunction, predisposes individuals to vascular fibrosis.

The cyclic GMP modulators YC-1 and zaprinast reduce vessel remodeling through antiproliferative and proapoptotic effects

Guanosine-specific cyclic nucleotide signaling is suggested to serve protective actions in the vasculature; however, the influence of selective pharmacologic modulation of cyclic guanosine monophosphate- synthesizing soluble guanylate cyclase or cyclic guanosine monophosphate-degrading phosphodiesterase on vessel remodeling has not been thoroughly examined. In this study, rat carotid artery balloon injury was performed and the growth-modulating effects of the soluble guanylate cyclase stimulator YC-1 or the cyclic guanosine monophosphate-dependent phosphodiesterase-V inhibitor zaprinast were examined. YC-1 or zaprinast elevated vessel cyclic guanosine monophosphate content, reduced medial wall and neointimal cell proliferation, stimulated medial and neointimal cellular apoptosis, and markedly attenuated neointimal remodeling in comparable fashion. Interestingly, soluble guanylate cyclase inhibition by 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one failed to noticeably alter neointimal growth, and concomitant zaprinast with YC-1 did not modify any parameter compared to individual treatments. These results provide novel in vivo evidence that YC-1 and zaprinast inhibit injury-induced vascular remodeling through antimitogenic and proapoptotic actions and may offer promising therapeutic approaches against vasoproliferative disorders.

cGMP in the vasculature

Cyclic guanosine 3', 5'-monophosphate (cGMP) plays an integral role in the control of vascular function. Generated from guanylate cyclases in response to the endogenous ligands, nitric oxide (NO) and natriuretic peptides (NPs), cGMP influences a number of vascular cell types and regulates vasomotor tone, endothelial permeability, cell growth and differentiation, as well as platelet and blood cell interactions. Reciprocal regulation of the NO-cGMP and NP-cGMP pathways is evident in the vasculature such that one cGMP generating system may compensate for the dysfunction of the other. Indeed, aberrant cGMP production and/or signalling accompanies many vascular disorders such as hypertension, atherosclerosis, coronary artery disease and diabetic complications. This chapter highlights the main vascular functions of cGMP, its role in disease and the resulting current and potential therapeutic applications. With respect to pulmonary hypertension, heart failure and erectile dysfunction, as well as cGMP signal transduction, the reader is specifically referred to other dedicated chapters.

cGMP regulated protein kinases (cGK)

cGMP-dependent protein kinases (cGK) are serine/threonine kinases that are widely distributed in eukaryotes. Two genes--prkg1 and prkg2--code for cGKs, namely cGKI and cGKII. In mammals, two isozymes, cGKIalpha and cGKIbeta, are generated from the prkg1 gene. The cGKI isozymes are prominent in all types of smooth muscle, platelets, and specific neuronal areas such as cerebellar Purkinje cells, hippocampal neurons, and the lateral amygdala. The cGKII prevails in the secretory epithelium of the small intestine, the juxta-glomerular cells, the adrenal cortex, the chondrocytes, and in the nucleus suprachiasmaticus. Both cGKs are major downstream effectors of many, but not all signalling events of the NO/cGMP and the ANP/cGMP pathways. cGKI relaxes smooth muscle tone and prevents platelet aggregation, whereas cGKII inhibits renin secretion, chloride/water secretion in the small intestine, the resetting of the clock during early night, and endochondreal bone growth. cGKs are also modulators of cell growth and many other functions.

Cyclic guanosine monophosphate-dependent protein kinase I promotes adhesion of primary vascular smooth muscle cells

The cyclic guanosine monophosphate (cGMP)/cGMP-dependent protein kinase type I (cGKI) pathway regulates many cellular functions. The current study shows that 8-Br-cGMP stimulates the number of attached primary but not that of subcultured murine vascular smooth muscle cells (VSMCs). These effects of 8-Br-cGMP require the presence of cGKI. In agreement with previous studies, cGKI inhibited the number of cells in repeatedly passaged murine VSMCs. Activation of the cGMP/cGKI pathway in freshly isolated primary VSMCs slightly decreased apoptosis and strongly increased cell adhesion. The stimulation of cell adhesion by cGKI involves an inhibition of the RhoA/Rho kinase pathway and increased exposure of beta(1) and beta(3) integrins on the cell surface. Together, these results identify a novel proadhesive function of cGMP/cGKI signaling in primary VSMCs and suggest that the opposing effects of this pathway on VSMC number depend on the phenotypic context of the cells.