Rho-kinase inhibition reduces neointima formation after vascular injury by enhancing Bax expression and apoptosis

Cylindrospermopsin impairs vascular smooth muscle cells by P53-mediated apoptosis due to ROS overproduction

Cylindrospermopsin (CYN) is a toxic secondary metabolite from cyanobacteria that can cause cardiovascular disease. However, the study of CYN-induced cardiovascular toxicity in vitro is very limited and the mechanism is remain to be clarified. Vascular smooth muscle cells (VMSCs) have an important function in maintaining the structural and functional integrity of the aortic wall, and are an important in vitro model for cardiovascular research. Thus, the effects of CYN exposure (2, 20, 200, and 2000 nM) on VMSCs were analyzed. In vitro study, results showed that CYN exposure decreased VMSCs viability, inhibited VMSCs migration, induced DNA damage, destroyed cytoskeleton, changed cell morphology, promoted VMSCs apoptosis, and increased intracellular reactive oxygen species (ROS) levels. In addition, CYN could induce the activities of SOD, CAT and GPX, and promote the expressions of SOD1, CAT, GPx1, p53 and Bax genes and inhibit the expression of Bcl-2 gene, leading to a higher ratio of Bax/Bcl-2. Taken together, CYN may induce ROS overproduction, leading to increased p53 expression and ultimately promoting VSMC apoptosis. Therefore, the present study demonstrates that CYN could impair VMSCs, leading to vascular developmental defects and angiocardiopathy.

Apoptosis in vascular pathology: present and future

Apoptosis is recognized as a programmed cell death controlled by genetic mechanisms and required for normal existence of an organism. Its main task is elimination of defective or mutant cells. The particles of dead cells are engulfed by macrophages with no development of inflammatory reaction. Apoptosis actively participates in embryogenesis, cellular homeostasis, elimination of tumor cells, and may be divided to three phases: signal, effector, and degradation. Its main components are cytoplasmic proteases caspases. Caspases exist in the cytoplasm in inactive condition in the form pf procaspases. Being activated, they break down to subunits. Proteins of Bcl-2 family are active participants of the mitochondrial pathway of apoptosis. They influence permeability of the outer membrane of mitochondria. Disorders in the mechanisms of apoptosis underlie many diseases including ischemic lesions, autoimmune disorders, malignant neoplasms. The ability to influence survival or death of cell is known to possess enormous therapeutic potential. At present, active research is under way to study signal pathways that control cell cycle and apoptosis. The article discusses the mechanisms participating in death of vascular endothelium and smooth muscle cells, potential role of apoptosis in atherosclerosis is also described.

Cylindrospermopsin induces abnormal vascular development through impairing cytoskeleton and promoting vascular endothelial cell apoptosis by the Rho/ROCK signaling pathway

Cylindrospermopsin (CYN) is a widely distributed cyanobacterial toxin in water bodies and is considered to pose growing threats to human and environmental health. Although its potential toxicity has been reported, its effects on the vascular system are poorly understood. In this study, we examined the toxic effects of CYN on vascular development and the possible mechanism of vascular toxicity induced by CYN using zebrafish embryos and human umbilical vein endothelial cells (HUVECs). CYN exposure induced abnormal vascular development and led to an increase in the growth of common cardinal vein (CCV), in which CCV remodeling was delayed as reflected by the larger CCV area and wider ventral diameter. CYN decreased HUVECs viability, inhibited HUVECs migration, promoted HUVECs apoptosis, destroyed cytoskeleton, and increased intracellular ROS levels. Additionally, CYN could promote the expression of Bax, Bcl-2, and MLC-1 and inhibit the expression of ITGB1, Rho, ROCK, and VIM-1. Taken together, CYN may induce cytoskeleton damage and promote vascular endothelial cell apoptosis by the Rho/ROCK signaling pathway, leading to abnormal vascular development. The current results provide potential insight into the mechanism of CYN toxicity in angiocardiopathy and are beneficial for understanding the environmental risks of CYN for aquatic organisms and human health.

Ending Restenosis: Inhibition of Vascular Smooth Muscle Cell Proliferation by cAMP

Increased vascular smooth muscle cell (VSMC) proliferation contributes towards restenosis after angioplasty, vein graft intimal thickening and atherogenesis. The second messenger 3′ 5′ cyclic adenosine monophosphate (cAMP) plays an important role in maintaining VSMC quiescence in healthy vessels and repressing VSMC proliferation during resolution of vascular injury. Although the anti-mitogenic properties of cAMP in VSMC have been recognised for many years, it is only recently that we gained a detailed understanding of the underlying signalling mechanisms. Stimuli that elevate cAMP in VSMC inhibit G₁-S phase cell cycle progression by inhibiting expression of cyclins and preventing S-Phase Kinase Associated Protein-2 (Skp2-mediated degradation of cyclin-dependent kinase inhibitors. Early studies implicated inhibition of MAPK signalling, although this does not fully explain the anti-mitogenic effects of cAMP. The cAMP effectors, Protein Kinase A (PKA) and Exchange Protein Activated by cAMP (EPAC) act together to inhibit VSMC proliferation by inducing Cyclic-AMP Response Element Binding protein (CREB) activity and inhibiting members of the RhoGTPases, which results in remodelling of the actin cytoskeleton. Cyclic-AMP induced actin remodelling controls proliferation by modulating the activity of Serum Response Factor (SRF) and TEA Domain Transcription Factors (TEAD), which regulate expression of genes required for proliferation. Here we review recent research characterising these mechanisms, highlighting novel drug targets that may allow the anti-mitogenic properties of cAMP to be harnessed therapeutically to limit restenosis.

Rho-associated coiled-coil kinase 1 activation mediates amyloid precursor protein site-specific Ser655 phosphorylation and triggers amyloid pathology

Rho‐associated coiled‐coil kinase 1 (ROCK1) is proposed to be implicated in Aβ suppression; however, the role for ROCK1 in amyloidogenic metabolism of amyloid precursor protein (APP) to produce Aβ was unknown. In the present study, we showed that ROCK1 kinase activity and its APP binding were enhanced in AD brain, resulting in increased β‐secretase cleavage of APP. Furthermore, we firstly confirmed that APP served as a substrate for ROCK1 and its major phosphorylation site was located at Ser655. The increased level of APP Ser655 phosphorylation was observed in the brain of APP/PS1 mice and AD patients compared to controls. Moreover, blockade of APP Ser655 phosphorylation, or inhibition of ROCK1 activity with either shRNA knockdown or Y‐27632, ameliorated amyloid pathology and improved learning and memory in APP/PS1 mice. These findings suggest that activated ROCK1 targets APP Ser655 phosphorylation, which promotes amyloid processing and pathology. Inhibition of ROCK1 could be a potential therapeutic approach for AD.

ROCK Inhibition Drives Resolution of Acute Inflammation by Enhancing Neutrophil Apoptosis

Uncontrolled inflammation leads to tissue damage and it is central for the development of chronic inflammatory diseases and autoimmunity. An acute inflammatory response is finely regulated by the action of anti-inflammatory and pro-resolutive mediators, culminating in the resolution of inflammation and restoration of homeostasis. There are few studies investigating intracellular signaling pathways associated with the resolution of inflammation. Here, we investigate the role of Rho-associated kinase (ROCK), a serine/threonine kinase, in a model of self-resolving neutrophilic inflammatory. We show that ROCK activity, evaluated by P-MYPT-1 kinetics, was higher during the peak of lipopolysaccharide-induced neutrophil influx in the pleural cavity of mice. ROCK inhibition by treatment with Y-27632 decreased the accumulation of neutrophils in the pleural cavity and was associated with an increase in apoptotic events and efferocytosis, as evaluated by an in vivo assay. In a model of gout, treatment with Y-27632 reduced neutrophil accumulation, IL-1β levels and hypernociception in the joint. These were associated with reduced MYPT and IκBα phosphorylation levels and increased apoptosis. Finally, inhibition of ROCK activity also induced apoptosis in human neutrophils and destabilized cytoskeleton, extending the observed effects to human cells. Taken together, these data show that inhibition of the ROCK pathway might represent a potential therapeutic target for neutrophilic inflammatory diseases.

The Function of Rho-Associated Kinases ROCK1 and ROCK2 in the Pathogenesis of Cardiovascular Disease

Rho-associated kinases ROCK1 and ROCK2 are serine/threonine kinases that are downstream targets of the small GTPases RhoA, RhoB, and RhoC. ROCKs are involved in diverse cellular activities including actin cytoskeleton organization, cell adhesion and motility, proliferation and apoptosis, remodeling of the extracellular matrix and smooth muscle cell contraction. The role of ROCK1 and ROCK2 has long been considered to be similar; however, it is now clear that they do not always have the same functions. Moreover, depending on their subcellular localization, activation, and other environmental factors, ROCK signaling can have different effects on cellular function. With respect to the heart, findings in isoform-specific knockout mice argue for a role of ROCK1 and ROCK2 in the pathogenesis of cardiac fibrosis and cardiac hypertrophy, respectively. Increased ROCK activity could play a pivotal role in processes leading to cardiovascular diseases such as hypertension, pulmonary hypertension, angina pectoris, vasospastic angina, heart failure, and stroke, and thus ROCK activity is a potential new biomarker for heart disease. Pharmacological ROCK inhibition reduces the enhanced ROCK activity in patients, accompanied with a measurable improvement in medical condition. In this review, we focus on recent findings regarding ROCK signaling in the pathogenesis of cardiovascular disease, with a special focus on differences between ROCK1 and ROCK2 function.

Mixed-lineage kinase 3 deficiency promotes neointima formation through increased activation of the RhoA pathway in vascular smooth muscle cells

OBJECTIVE

Mitogen-activated protein kinase pathways play an important role in neointima formation secondary to vascular injury, in part by promoting proliferation of vascular smooth muscle cells (VSMC). Mixed-lineage kinase 3 (MLK3) is a mitogen-activated protein kinase kinase kinase that activates multiple mitogen-activated protein kinase pathways and has been implicated in regulating proliferation in several cell types. However, the role of MLK3 in VSMC proliferation and neointima formation is unknown. The aim of this study was to determine the function of MLK3 in the development of neointimal hyperplasia and to elucidate the underlying mechanisms.

APPROACH AND RESULTS

Neointima formation was analyzed after endothelial denudation of carotid arteries from wild-type and MLK3-deficient mice. MLK3 deficiency promoted injury-induced neointima formation and increased proliferation of primary VSMC derived from aortas isolated from MLK3-deficient mice compared with wild-type mice. Furthermore, MLK3 deficiency increased the activation of p63Rho guanine nucleotide exchange factor, RhoA, and Rho kinase in VSMC, a pathway known to promote neointimal hyperplasia, and reconstitution of MLK3 expression attenuated Rho kinase activation. Furthermore, cJun NH2-terminal kinase activation was decreased in MLK3-deficient VSMC, and proliferation of wild-type but not MLK3 knockout cells treated with a cJun NH2-terminal kinase inhibitor was attenuated.

CONCLUSIONS

We demonstrate that MLK3 limits RhoA activation and injury-induced neointima formation by binding to and inhibiting the activation of p63Rho guanine nucleotide exchange factor, a RhoA activator. In MLK3-deficient cells, activation of p63Rho guanine nucleotide exchange factor proceeds in an unchecked manner, leading to a net increase in RhoA pathway activation. Reconstitution of MLK3 expression restores MLK3/p63Rho guanine nucleotide exchange factor interaction, which is attenuated by feedback from activated cJun NH2-terminal kinase.

The protective effect of Bcl-xl overexpression against oxidative stress-induced vascular endothelial cell injury and the role of the Akt/eNOS pathway

Restenosis after intraluminal or open vascular reconstruction remains an important clinical problem. Vascular endothelial cell (EC) injury induced by oxidative stress plays an important role in the development of intimal hyperplasia. In this study, we sought to evaluate the protective effects of Bcl-xl overexpression in vitro on oxidative stress-induced EC injury and the role of the Akt/endothelial nitric oxide synthase (eNOS) pathway. Human umbilical vein endothelial cells (HUVECs) exposed to hydrogen peroxide (H₂O₂, 0.5 mM) were used as the experimental oxidative stress model. The Bcl-xl gene was transferred into HUVECs through recombinant adenovirus vector pAdxsi-GFP-Bcl-xl before oxidative treatment. Cell apoptosis was evaluated by Annexin V/propidium iodide and Hoechst staining, caspase-7 and PARP cleavage. Cell viability was assessed using the cell counting kit-8 assay, proliferating cell nuclear antigen (PCNA) immunocytochemical detection and the scratching assay. Expressions of Akt, phospho-Akt and eNOS were detected by Western blotting. Our results showed that H₂O₂ induced apoptosis and decreased the cell viability of HUVECs. Bcl-xl overexpression significantly protected cells from H₂O₂-induced cell damage and apoptosis and maintained the cell function. Furthermore, the level of phospho-Akt and eNOS protein expression was significantly elevated when pretreated with Bcl-xl gene transferring. These findings suggest that Bcl-xl overexpression exerts an anti-apoptotic and protective effect on EC function. The Akt/eNOS signaling pathway is probably involved in these processes.

Small G Proteins in the Cardiovascular System: Physiological and Pathological Aspects

Small G proteins exist in eukaryotes from yeast to human and constitute the Ras superfamily comprising more than 100 members. This superfamily is structurally classified into five families: the Ras, Rho, Rab, Arf, and Ran families that control a wide variety of cell and biological functions through highly coordinated regulation processes. Increasing evidence has accumulated to identify small G proteins and their regulators as key players of the cardiovascular physiology that control a large panel of cardiac (heart rhythm, contraction, hypertrophy) and vascular functions (angiogenesis, vascular permeability, vasoconstriction). Indeed, basal Ras protein activity is required for homeostatic functions in physiological conditions, but sustained overactivation of Ras proteins or spatiotemporal dysregulation of Ras signaling pathways has pathological consequences in the cardiovascular system. The primary object of this review is to provide a comprehensive overview of the current progress in our understanding of the role of small G proteins and their regulators in cardiovascular physiology and pathologies.

Inhibition of the Rho/ROCK pathway enhances the efficacy of cisplatin through the blockage of hypoxia-inducible factor-1α in human ovarian cancer cells

Rho, a Ras-related small GTPase, and Rho-associated coiled coil-containing protein kinase (Rho kinase, ROCK1 and ROCK2) are key regulators of focal adhesion, actomyosin contraction, and thus cell motility. Rho/ROCK kinases also play roles in proliferation, differentiation, apoptosis and oncogenic transformation. In the present study, we have shown that Rho/ROCK pathway inhibition by fasudil, an orally administered inhibitor of Rho kinases, enhanced cisplatin-induced growth inhibition and apoptosis in human ovarian cancer cell lines. Fasudil inhibited hypoxia inducible factor (HIF)-1α protein expression. Knockdown of RhoA, ROCK1 or ROCK2 also attenuated the expression of HIF-1α. Furthermore, knockdown of HIF-1α using small interfering RNA enhanced cisplatin-induced growth inhibition and apoptosis as did inhibition of the Rho/ROCK pathway by fasudil, the Rho/ROCK inhibitor Y27632, or by Rho/ROCK knockdown. Therefore, the Rho/ROCK pathway may modulate HIF-1α signal transduction and blockade of Rho/ROCK enhances the efficacy of cisplatin by inhibiting HIF-1α in ovarian cancer cells. Our findings suggested that the Rho/ROCK pathway may be a new target for molecular targeting therapies against ovarian cancer.

Effects of exercise training and RhoA/ROCK inhibition on plaque in ApoE-/- mice

BACKGROUND

The molecular mechanisms of exercise-induced cardioprotection are poorly understood. We recently reported that exercise training down-regulated gene expression of the Ras homolog gene family member A (RhoA). RhoA and its first effectors, the Rho-kinases (ROCK), have already been implicated in the pathogenesis of cardiovascular disease. The aim of this study was to compare the effects of a RhoA/ROCK inhibitor (fasudil) and exercise in the Apolipoprotein E knockout (ApoE(-/-)) mouse model of atherosclerosis.

METHODS

Four groups of 14 week old ApoE(-/-) mice were randomised as follows (n=12/group): i) sedentary controls (Cont); ii) fasudil (Fas) treatment (100mg/kg bodyweight/day) for 8 weeks; iii) exercise intervention (Ex:free access to running wheel for 8 weeks) and iv) exercise intervention and fasudil treatment (ExFas) for 8 weeks.

RESULTS

Phosphorylation of myosin light chain was significantly reduced in the brachiocephalic artery of all treatment groups compared with sedentary controls, implying an inhibitory effect of exercise and fasudil on the RhoA/ROCK pathway. Furthermore, atherosclerotic lesions were significantly smaller in all treatment and intervention groups compared with the control group (Fas: 34.7%, Ex: 48.3%, ExFas: 40.9% less than Control). The intima:media ratio was reduced by both exercise intervention and fasudil treatment alone or in combination (Fas: 23.6%, Ex: 35.5%, ExFas: 43.9% less than Control). Exercise alone and fasudil treatment alone also showed similar effects on plaque composition, increasing both smooth muscle cell and macrophage density.

CONCLUSION

These results suggest that the protective effects of exercise on atherogenesis are similar to the inhibitory effects on the RhoA/ROCK signalling pathway.

Overexpression of phospholipase D enhances Bcl-2 expression by activating STAT3 through independent activation of ERK and p38MAPK in HeLa cells

The purpose of this study was to identify the role of phospholipase D (PLD) isozymes in Bcl-2 expression. Overexpression of PLD1 or PLD2 increased Bcl-2 expression and phosphatidic acid (PA), the product of PLDs, also upregulated Bcl-2 expression. Treatment with PA activated the phospholipase A(2) (PLA(2))/G(i)/ERK1/2, RhoA/Rho-associated kinase (ROCK)/p38 MAPK, and Rac1/p38 MAPK pathways. PA-induced phosphorylation of ERK1/2 was attenuated by a PLA(2) inhibitor (mepacrine) and, a G(i) protein inhibitor (pertussis toxin, PTX). On the other hand, p38 MAPK phosphorylation was attenuated by a dominant negative Rac1 and a specific Rho-kinase inhibitor (Y-27632). These results suggest that PLA(2)/G(i) acts at the upstream of ERK1/2, while Rac1 and RhoA/ROCK act upstream of p38 MAPK. We next, tried to determine which transcription factor is involved in PLD-related Bcl-2 expression. When signal transducer and activator of transcription 3 (STAT3) activity was blocked by a STAT3 specific siRNA, PA-induced Bcl-2 expression was remarkably decreased, suggesting that STAT3 is an essential transcription factor linking PLD to Bcl-2 upregulation. Taken together, these findings indicate that PLD acts as an important regulator in Bcl-2 expression by activating STAT3 involving the phosphorylation of Ser727 through the PLA(2)/G(i)/ERK1/2, RhoA/ROCK/p38 MAPK, and Rac1/p38 MAPK pathways.

Rho-associated coiled-coil-forming kinases (ROCKs): potential targets for the treatment of atherosclerosis and vascular disease

ROCKs are important regulators of the actin cytoskeleton. Because changes in the actin cytoskeleton underlie vascular contractility and remodeling, inflammatory cell recruitment, and cell proliferation, it is likely that the Rho/ROCK pathway will play a central role in mediating vascular function. Indeed, increased ROCK activity is observed in cerebral and coronary vasospasm, hypertension, vascular inflammation, arteriosclerosis, and atherosclerosis. Recent experimental and clinical studies suggest that inhibition of ROCK could be a promising target for the treatment of cardiovascular disease. For example, inhibition of ROCK might be the underlying mechanism by which statins or HMG-CoA reductase inhibitors exert their therapeutic benefits beyond cholesterol reduction. In this review we summarize current understanding of the crucial role of RhoA/ROCK pathway in the regulation of vascular function and discuss its therapeutic potential in the treatment of atherosclerosis and vascular disease.

Rho-kinase/ROCK: A key regulator of the cytoskeleton and cell polarity

Rho-associated kinase (Rho-kinase/ROCK/ROK) is an effector of the small GTPase Rho and belongs to the AGC family of kinases. Rho-kinase has pleiotropic functions including the regulation of cellular contraction, motility, morphology, polarity, cell division, and gene expression. Pharmacological analyses have revealed that Rho-kinase is involved in a wide range of diseases such as vasospasm, pulmonary hypertension, nerve injury, and glaucoma, and is therefore considered to be a potential therapeutic target. This review focuses on the structure, function, and modes of activation and action of Rho-kinase.

Key role of the RhoA/Rho kinase system in pulmonary hypertension

Pulmonary hypertension (PH) is a general term comprising a spectrum of pulmonary hypertensive disorders which have in common an elevation of mean pulmonary arterial pressure (mPAP). The prototypical form of the disease, termed pulmonary arterial hypertension (PAH), is a rare but lethal syndrome with a complex aetiology characterised by increased pulmonary vascular resistance (PVR) and progressive elevation of mPAP; patients generally die from heart failure. Current therapies are inadequate and median survival is less than three years. PH due to chronic hypoxia (CH) is a condition separate from PAH and is strongly associated with chronic obstructive pulmonary disease (COPD). An early event in the pathogenesis of this form of PH is hypoxic pulmonary vasoconstriction (HPV), an acute homeostatic process that maintains the ventilation-perfusion ratio during alveolar hypoxia. The mechanisms underlying HPV remain controversial, but RhoA/Rho kinase (ROK)-mediated Ca²+-sensitisation is considered important. Increasing evidence also implicates RhoA/ROK in PASMC proliferation, inflammatory cell recruitment and the regulation of cell motility, all of which are involved in the pulmonary vascular remodelling occurring in all forms of PH. ROK is therefore a potential therapeutic target in treating PH of various aetiologies. Here, we examine current concepts regarding the aetiology of PAH and also PH due to CH, focusing on the contribution that RhoA/ROK-mediated processes may make to their development and on ROK inhibitors as potential therapies.

Inhibition of apoptotic signaling and neointimal hyperplasia by tempol and nitric oxide synthase following vascular injury

OBJECTIVES

We hypothesized that redox-mediated apoptosis of medial smooth muscle cells (SMC) during the acute phase of vascular injury contributes to the pathophysiology of vascular disease.

METHODS

Apoptosis of medial SMC (1-14 days following balloon injury) was identified in rat carotid arteries by in situ DNA labeling. NADPH-derived superoxide and expression of Bcl-xL, Bax, caspase-3 and caspase-9 were assessed. The antioxidant tempol was administered in drinking water throughout the experimental period, and local adenoviral-mediated gene transfer of eNOS was performed prior to vascular injury.

RESULTS

Balloon injury increased NADPH-dependent superoxide production, medial SMC apoptosis, Bax-positive medial SMC index, Bax/Bcl-xL ratio, and caspase-3 and caspase-9 expression in the injured arteries. Treatment with tempol or eNOS gene transfer decreased superoxide levels and medial SMC apoptosis, with a concomitant increase in medial SMC density. Inhibition of superoxide was associated with a decreased Bax/Bcl-xL ratio, and caspase-3 and -9 expression. Tempol treatment and eNOS gene therapy significantly reduced neointima formation.

CONCLUSION

Vascular generation of reactive oxygen species participates in Bax activation and medial SMC apoptosis. These effects likely contribute to the shedding of cell-cell adhesion molecules and promote medial SMC migration and proliferation responsible for neointimal hyperplasia.

Therapeutic potential of RhoA/Rho kinase inhibitors in pulmonary hypertension

A burgeoning body of evidence suggests that RhoA/Rho kinase (ROCK) signalling plays an important role in the pathogenesis of various experimental models of pulmonary hypertension (PH), including chronic hypoxia-, monocrotaline-, bleomycin-, shunt- and vascular endothelial growth factor receptor inhibition plus chronic hypoxia-induced PH. ROCK has been incriminated in pathophysiologic events ranging from mediation of sustained abnormal vasoconstriction to promotion of vascular inflammation and remodelling. In addition, the 3-hydroxy-3-methylglutaryl CoA reductase inhibitors, statins, which inhibit activation of RhoA by preventing post-translational isoprenylation of the protein and its translocation to the plasma membrane ameliorate PH in several different rat models, and may also be effective in PH patients. Also, phosphorylation of RhoA and prevention of its translocation to the plasma membrane are involved in the protective effect of the type 5-PDE inhibitor, sildenafil, against hypoxia- and bleomycin-induced PH. Collectively, these and other observations indicate that independent of the cause of PH, activation of the RhoA/ROCK pathway serves as a point of convergence of various signalling cascades in the pathogenesis of the disease. We propose that ROCK inhibitors and other drugs that inhibit this pathway might be useful in the treatment of various forms of PH.

Does it matter whether or not a lipid-lowering agent inhibits Rho kinase?

Lipid-lowering agents, such as 3-hydroxy-3-methylglutaryl coenzyme A (HMG CoA) reductase inhibitors, also known as statins, have been shown to reduce cardiovascular events. However, evidence from recent clinical trials suggests that some of the beneficial effects of statins may be unrelated to changes in low-density lipoprotein cholesterol. In animal studies, many of the cholesterol-independent or "pleiotropic" effects of statins are mediated by inhibition of Rho kinase (ROCK). Indeed, ROCK has been implicated in the regulation of vascular tone, proliferation, inflammation, and oxidative stress. To what extent ROCK activity is inhibited in patients on lipid-lowering therapy, and in particular on statins, is not known, but it may have important clinical and therapeutic implications. This review attempts to make the case that, in addition to lipid lowering, inhibition of ROCK contributes to some of the benefits of statin therapy in patients with cardiovascular disease.

Applications for ROCK kinase inhibition

ROCK kinases, which play central roles in the organization of the actin cytoskeleton, are tantalizing targets for the treatment of human diseases. Deletion of ROCK I in mice revealed a role in the pathophysiological responses to high blood pressure, and validated ROCK inhibition for the treatment of specific types of cardiovascular disease. To date, the only ROCK inhibitor employed clinically in humans is fasudil, which has been used safely in Japan since 1995 for the treatment of cerebral vasospasm. Clinical trials, mostly focusing on the cardiovascular system, have uncovered beneficial effects of fasudil for additional indications. Intriguing recent findings also suggest significant potential for ROCK inhibitors in the production and implantation of stem cells for disease therapies.

Rho kinase (ROCK) inhibitors

The Rho kinase (ROCK) isoforms, ROCK1 and ROCK2, were initially discovered as downstream targets of the small GTP-binding protein Rho. Because ROCKs mediate various important cellular functions such as cell shape, motility, secretion, proliferation, and gene expression, it is likely that this pathway will intersect with other signaling pathways known to contribute to cardiovascular disease. Indeed, ROCKs have already been implicated in the regulation of vascular tone, proliferation, inflammation, and oxidative stress. However, it is not entirely clear how ROCKs are regulated, what some of their downstream targets are, and whether ROCK1 and ROCK2 mediate different cellular functions. Clinically, inhibition of ROCK pathway is believed to contribute to some of the cardiovascular benefits of statin therapy that are independent of lipid lowering (ie, pleiotropic effects). To what extent ROCK activity is inhibited in patients on statin therapy is not known, but it may have important clinical implications. Indeed, several pharmaceutical companies are already actively engaged in the development of ROCK inhibitors as the next generation of therapeutic agents for cardiovascular disease because evidence from animal studies suggests the potential involvement of ROCK in hypertension and atherosclerosis.

Rho kinases in cardiovascular physiology and pathophysiology

Rho kinases (ROCKs) are the first and the best-characterized effectors of the small G-protein RhoA. In addition to their effect on actin organization, or through this effect, ROCKs have been found to regulate a wide range of fundamental cell functions such as contraction, motility, proliferation, and apoptosis. Abnormal activation of the RhoA/ROCK pathway has been observed in major cardiovascular disorders such as atherosclerosis, restenosis, hypertension, pulmonary hypertension, and cardiac hypertrophy. This review, based on recent molecular, cellular, and animal studies, focuses on the current understanding of ROCK signaling and its roles in cardiovascular physiology and pathophysiology.

Involvement of G proteins of the Rho family in the regulation of Bcl-2-like protein expression and caspase 3 activation by Gastrins

Gastrins, including amidated gastrin (Gamide) and glycine-extended gastrin (Ggly), are known to accelerate the growth of gastric and colorectal cancer cells by stimulation of proliferation and inhibition of apoptosis. Gamide controls apoptosis by regulation of proteins of the Bcl-2 family and by regulation of the activation of caspases. However the interactions between Ggly and proteins of the Bcl-2 family and caspases are not known. Since in other systems G proteins of the Rho family inhibit apoptosis via interaction with proteins of the Bcl-2 family, leading to changes in caspase activities, we have compared the role of Rho family G proteins in regulation of Bcl-2-like (Bad/Bax/Bcl-xl) protein expression and caspase 3 activation by Ggly and Gamide. The effects of the specific inhibitors C3 (for Rho) and Y-27632 (for ROCK), and of dominant negative mutants of Rac, Cdc42 and PAK, were investigated in the gastric epithelial cell line IMGE-5. Apoptosis was induced by serum starvation and confirmed by annexin V staining and caspase 3 activation. Ggly inhibits caspase 3 activation via a Bcl-2-like protein-mediated pathway which requires activation of both Rho/ROCK and Rac/Cdc42/PAK. Gamide inhibits caspase 3 activation via redundant Bcl-2-like protein-mediated pathways which involve alternative activation of Rac/Cdc42/PAK and Rho/ROCK. Gamide and Ggly differentially activate members of Rho family G proteins which in turn regulate different proteins of the Bcl-2 family leading to changes in caspase 3 activity. The findings offer potential targets for blocking the growth-stimulating effects of these gastrins.

Rho kinase in the regulation of cell death and survival

Rho kinase (ROCK) belongs to a family of serine/threonine kinases that are activated via interaction with Rho GTPases. ROCK is involved in a wide range of fundamental cellular functions, such as contraction, adhesion, migration, and proliferation. Recent studies have shown that ROCK plays an important role in the regulation of apoptosis in various cell types and animal disease models. Two ROCK isoforms, ROCK1 and ROCK2, are assumed to be function redundant, this based largely on kinase construct overexpression and chemical inhibitors (Y27632 and fasudil) which inhibit both ROCK1 and ROCK2. Gene targeting and RNA interference approaches allow further dissection of distinct cellular, physiological, and patho-physiological functions of the two ROCK isoforms. This review, based on recent molecular, cellular, and animal studies, focuses on the current understanding of ROCK signaling in the regulation of apoptosis and highlights new findings from recently generated ROCK-deficient mice.

Transglutaminase-dependent RhoA activation and depletion by serotonin in vascular smooth muscle cells

The small G protein RhoA plays a major role in several vascular processes and cardiovascular disorders. Here we analyze the mechanisms of RhoA regulation by serotonin (5-HT) in arterial smooth muscle. 5-HT (0.1-10 microM) induced activation of RhoA followed by RhoA depletion at 24-72 h. Inhibition of 5-HT1 receptors reduced the early phase of RhoA activation but had no effect on 5-HT-induced delayed RhoA activation and depletion, which were suppressed by the 5-HT transporter inhibitor fluoxetine and the transglutaminase inhibitor monodansylcadaverin and in type 2 transglutaminase-deficient smooth muscle cells. Coimmunoprecipitations demonstrated that 5-HT associated with RhoA both in vitro and in vivo. This association was calcium-dependent and inhibited by fluoxetine and monodansylcadaverin. 5-HT promotes the association of RhoA with the E3 ubiquitin ligase Smurf1, and 5-HT-induced RhoA depletion was inhibited by the proteasome inhibitor MG132 and the RhoA inhibitor Tat-C3. Simvastatin, the Rho kinase inhibitor Y-27632, small interfering RNA-mediated RhoA gene silencing, and long-term 5-HT stimulation induced Akt activation. In contrast, inhibition of 5-HT-mediated RhoA degradation by MG132 prevented 5-HT-induced Akt activation. Long-term 5-HT stimulation also led to the inhibition of the RhoA/Rho kinase component of arterial contraction. Our data provide evidence that 5-HT, internalized through the 5-HT transporter, is transamidated to RhoA by transglutaminase. Transamidation of RhoA leads to RhoA activation and enhanced proteasomal degradation, which in turn is responsible for Akt activation and contraction inhibition. The observation of transamidation of 5-HT to RhoA in pulmonary artery of hypoxic rats suggests that this process could participate in pulmonary artery remodeling and hypertension.

CO as a cellular signaling molecule

Many biological functions of heme oxygenase (HO), such as cytoprotection against oxidative stress, vasodilation, neurotransmission in the central or peripheral nervous systems, and anti-inflammatory, anti-apoptotic, or anti-proliferative potential, have been attributed to its enzymatic byproduct carbon monoxide (CO), although roles for biliverdin/bilirubin and iron have also been proposed. In addition to these well-characterized effects, recent findings reveal that HO-derived CO may act as an oxygen sensor and circadian modulator of heme biosynthesis. In lymphocytes, CO may participate in regulatory T cell function. A number of the known signaling effects of CO depend on stimulation of soluble guanylate cyclase and/or activation of mitogen-activated protein kinases (MAPK). Furthermore, modulation of caveolin-1 status may serve as an essential component of certain aspects of CO action, such as growth control. In this review, we summarize recent findings of the beneficial or detrimental effects of endogenous CO with an emphasis on the signaling pathways and downstream targets that trigger the action of this gas.

Rho-kinase is an important therapeutic target in cardiovascular medicine

Rho-kinase has been identified as one of the effectors of the small GTP-binding protein Rho. Accumulating evidence has demonstrated that Rho/Rho-kinase pathway plays an important role in various cellular functions, not only in vascular smooth muscle cell (VSMC) contraction but also in actin cytoskeleton organization, cell adhesion and motility, cytokinesis, and gene expressions, all of which may be involved in the pathogenesis of cardiovascular disease. At molecular level, Rho-kinase upregulates various molecules that accelerate inflammation/oxidative stress, thrombus formation, and fibrosis, whereas it downregulates endothelial nitric oxide synthase. The expression of Rho-kinase itself is mediated by protein kinase C/NF-kappaB pathway with an inhibitory and stimulatory modulation by estrogen and nicotine, respectively. At cellular level, Rho-kinase mediates VSMC hypercontraction, stimulates VSMC proliferation and migration, and enhances inflammatory cell motility. In animal studies, Rho-kinase has been shown to be substantially involved in the pathogenesis of vasospasm, arteriosclerosis, ischemia/reperfusion injury, hypertension, pulmonary hypertension, stroke and heart failure, and to enhance central sympathetic nerve activity. Finally, in clinical studies, fasudil, a Rho-kinase inhibitor, is effective for the treatment of a wide range of cardiovascular disease, including cerebral and coronary vasospasm, angina, hypertension, pulmonary hypertension, and heart failure, with a reasonable safety. Thus, Rho-kinase is an important therapeutic target in cardiovascular medicine.