Inhibition of Rho-kinase attenuates hypoxia-induced angiogenesis in the pulmonary circulation

Effect of all-trans-retinoic acid on the development of chronic hypoxia-induced pulmonary hypertension

BACKGROUND

An earlier study showed that all-trans-retinoic acid (ATRA) prevents the development of monocrotalin-induced pulmonary hypertension (PH). The purpose of the present study was to determine the effect of ATRA on another model of chronic hypoxia-induced PH.

METHODS AND RESULTS

Male Sprague-Dawley rats were given 30 mg/kg ATRA or vehicle only by gavage once daily for 14 days during hypobaric hypoxic exposure. Chronic hypoxic exposure induced PH, right ventricular hypertrophy (RVH), and hypertensive pulmonary vascular changes. Quantitative morphometry of the pulmonary arteries showed that ATRA treatment significantly reduced the percentage of muscularized arteries in peripheral pulmonary arteries only with an external diameter between 15 and 50 microm. ATRA treatment also significantly reduced the medial wall thickness in small muscular arteries only with an external diameter between 50 and 100 microm. Unfortunately, these reductions did not accompany the lowering of pulmonary artery pressure nor decrease in RVH. Chronic hypoxia-induced PH rats with ATRA had a loss in body weight. Chronic hypoxia increased the expression of endothelial nitric oxide synthase in the lung on western blotting and immunohistochemistry, in which ATRA treatment had no effect.

CONCLUSIONS

The administration of ATRA might not have a therapeutic role in preventing the development of chronic hypoxia-induced PH, because of body weight loss and the subtle preventable effects of vascular changes.

ROCK as a Therapeutic Target of Diabetic Retinopathy

The increasing global prevalence of diabetes is a critical problem for public health. In particular, diabetic retinopathy, a prevalent ocular complication of diabetes mellitus, causes severe vision loss in working population. A better understanding of the pathogenesis and the development of new pharmacologic treatments are needed. This paper describes the relevance between Rho/ROCK pathway and the pathogenesis of diabetic retinopathy from its early to late stages. Moreover, the therapeutic potential of ROCK inhibitor in the total management of diabetic retinopathy is discussed.

Heparin inhibits pulmonary artery smooth muscle cell proliferation through guanine nucleotide exchange factor-H1/RhoA/Rho kinase/p27

Ras homolog gene family member A (RhoA) through Rho kinase kinase (ROCK), one of its downstream effectors, regulates a wide range of cell physiological functions, including vascular smooth muscle cell (SMC) proliferation, by degrading cyclin-dependent kinase inhibitor, p27. Our previous studies found that heparin inhibition of pulmonary artery SMC (PASMC) proliferation and pulmonary hypertension was dependent on p27 up-regulation. To investigate whether ROCK, a regulator of p27, is involved in regulation of heparin inhibition of PASMC proliferation, we analyzed ROCK expression in the lungs from mice and from human PASMCs exposed to hypoxia, and investigated the effect of ROCK expression in vitro by RhoA cDNA transfection. We also investigated the effect of guanine nucleotide exchange factor (GEF)-H1, an upstream regulator of RhoA, on heparin inhibition of PASMC proliferation by GEF-H1 cDNA transfection. We found that: (1) hypoxia increased ROCK expression in mice and PASMCs; (2) overexpression of RhoA diminished the inhibitory effect of heparin on PASMC proliferation and down-regulated p27 expression; and (3) overexpression of GEF-H1 negated heparin inhibition of PASMC proliferation, which was accompanied by increased GTP-RhoA and decreased p27. This study demonstrates that the RhoA/ROCK pathway plays an important role in heparin inhibition on PASMC proliferation, and reveals that heparin inhibits PASMC proliferation through GEF-H1/RhoA/ROCK/p27 signaling pathway, by down-regulating GEF-H1, RhoA, and ROCK, and then up-regulating p27.

The role of hypoxia in bone marrow-derived mesenchymal stem cells: considerations for regenerative medicine approaches

Bone marrow-derived mesenchymal stem cells (MSCs) have demonstrated potential for regenerative medicine strategies. Knowledge of the way these cells respond to their environment in in vitro culture and after implantation in vivo is crucial for successful therapy. Oxygen tension plays a pivotal role in both situations. In vivo, a hypoxic environment can lead to apoptosis, but hypoxic preconditioning of MSCs and overexpression of prosurvival genes like Akt can reduce hypoxia-induced cell death. In cell culture, hypoxia can increase proliferation rates and enhance differentiation along the different mesenchymal lineages. Hypoxia also modulates the paracrine activity of MSCs, causing upregulation of various secretable factors, among which are important angiogenic factors such as vascular endothelial growth factor and interleukin-6 (IL6). Finally, hypoxia plays an important role in mobilization and homing of MSCs, primarily by its ability to induce stromal cell-derived factor-1 expression along with its receptor CXCR4. This article reviews the current literature on the effects of hypoxia on MSCs and aims to elucidate its potential role in regenerative medicine strategies.

Sonic hedgehog induces angiogenesis via Rho kinase-dependent signaling in endothelial cells

The morphogen Sonic hedgehog (Shh) promotes neovascularization in adults by inducing pro-angiogenic cytokine expression in fibroblasts; however, the direct effects of Shh on endothelial cell (EC) function during angiogenesis are unknown. Our findings indicate that Shh promotes capillary morphogenesis (tube length on Matrigel increased to 271+/-50% of the length in untreated cells, p=0.00003), induces EC migration (modified Boyden chamber assay, 191+/-35% of migration in untreated cells, p=0.00009), and increases EC expression of matrix metalloproteinase 9 (MMP-9) and osteopontin (OPN) mRNA (real-time RT-PCR), which are essential for Shh-induced angiogenesis both in vitro and in vivo. Shh activity in ECs is mediated by Rho, rather than through the "classic" Shh signaling pathway, which involves the Gli transcription factors. The Rho dependence of Shh-induced EC angiogenic activity was documented both in vitro, with dominant-negative RhoA and Rho kinase (ROCK) constructs, and in vivo, with the ROCK inhibitor Y27632 in the mouse corneal angiogenesis model. Finally, experiments performed in MMP-9- and OPN-knockout mice confirmed the roles of the ROCK downstream targets MMP-9 and OPN in Shh-induced angiogenesis. Collectively, our results identify a "nonclassical" pathway by which Shh directly modulates EC phenotype and angiogenic activity.

Effects of rho-kinase inhibition on pulmonary hypertension, lung growth, and structure in neonatal rats chronically exposed to hypoxia

Rho-kinase (ROCK) inhibitors prevent pulmonary hypertension (PHT) in adult rodents, but little is known about their effects on the neonatal lung. Our objective was to examine the effects of ROCK inhibition on chronic hypoxia (CH)-induced PHT and abnormal lung structure in the neonatal rat. Pups were exposed to air or CH from postnatal d 1-14 while receiving Y-27632 (5 or 10 mg x kg(-1) x d(-1)), fasudil (20 mg x kg(-1) x d(-1)), or saline intraperitoneally. Relative to air, CH-exposed pups had increased pulmonary vascular resistance, right ventricular hypertrophy, arterial medial wall thickening, and abnormal distal airway morphology characterized by septal thinning and decreased secondary septation. Treatment with 10 mg/kg Y-27632 or fasudil attenuated the structural and hemodynamic changes of PHT while having no effect on septal thinning or inhibited secondary septation. In addition, Y-27632 (10 mg/kg) and fasudil augmented CH-induced somatic growth restriction. Pulmonary arteries of CH-exposed pups had increased ROCK activity, up-regulated expression of PDGF-BB and increased smooth muscle DNA synthesis, all of which were attenuated by treatment with 10 mg/kg Y-27632. Systemically administered ROCK inhibitors prevented PHT in the CH-exposed neonatal rat but at the cost of inhibited somatic growth. Limiting effects on vascular remodeling likely resulted, in major part, from attenuated vascular PDGF-BB/beta-receptor signaling.

Rho kinase-mediated vasoconstriction in pulmonary hypertension

Rho kinase-mediated vasoconstriction rather than fixed arterial wall thickening is responsible for increased pulmonary vascular resistance and pulmonary hypertension in chronically hypoxic and monocrotaline-injected rats. In the absence of vascular tone, the medial and adventitial thickening in these models has only minimal impact on the cross-sectional area of the pulmonary arterial bed. In contrast, increased pulmonary vascular resistance in left-pneumonectomized plus monocrotaline-injected rats and VEGF receptor blocker-injected plus chronic hypoxia rats is attributable to both Rho kinase-mediated vasoconstriction and formation of lumen obliterating lesions in small pulmonary arteries. The upstream signals responsible for activation of RhoA/Rho kinase signaling in hypertensive pulmonary arteries and whether or not they differ in different forms of pulmonary hypertension are unclear. The RhoA/Rho kinase pathway is a convergence point of several different vasoconstrictor signals, including those mediated by G protein-coupled receptors, receptor tyrosine kinases, and integrin clustering. Both isoforms of Rho kinase can also be constitutively activated by cleavage, and cleaved Rho kinase 1 has been detected in the hypertensive lungs of left-pneumonectomized plus monocrotaline-injected rats. That such diverse stimuli can lead to activation of Rho kinase, which may cause hypercontraction of smooth muscle by promoting both actomyosin interaction and remodeling of the cytoskeleton, may explain why in various rat models of pulmonary hypertension Rho kinase inhibitors are more effective pulmonary vasodilators than conventional agents such as nitric oxide, prostacyclin, and nifedipine. We suspect the same will be true in at least some forms of human pulmonary arterial hypertension.

ROCK pathway participates in the processes that 15-hydroxyeicosatetraenoic acid (15-HETE) mediated the pulmonary vascular remodeling induced by hypoxia in rat

15-Hydroxyeicosatetraenoic acid (15-HETE), a product of arachidonic acid (AA) catalyzed by 15-lipoxygenase (15-LO), plays an essential role in hypoxic pulmonary arterial hypertension. We have previously shown that 15-HETE inhibits apoptosis in pulmonary artery smooth muscle cells (PASMCs). To test the hypothesis that such an effect is attributable to the hypoxia-induced pulmonary vascular remodeling (PVR), we performed these studies. We found subtle thickening of proximal media/adventitia of the pulmonary arteries (PA) in rats that had been exposed to hypoxia. This was associated with an up-regulation of the anti-apoptotic Bcl-2 expression and down-regulation of pro-apoptotic caspase-3 and Bax expression in PA homogenates. Nordihydroguaiaretic acid (NDGA), which inhibits the generation of endogenous 15-HETE, reversed all the alterations following hypoxia. In situ hybridization histochemistry and immunocytochemistry showed that the 15-LO-1 mRNA and protein were localized in pulmonary artery endothelial cells (PAECs), while the 15-LO-2 mRNA and protein were localized in both PAECs and PASMCs. Furthermore, the Rho-kinase (ROCK) pathway was activated by both endogenous and exogenous 15-HETE, alleviating the serum deprivation (SD)-induced PASMC apoptosis. Thus, these findings indicate that 15-HETE protects PASMC from apoptosis, contributing to pulmonary vascular medial thickening, and the effect is, at least in part, mediated via the ROCK pathway.

Reactive oxygen species and RhoA signaling in vascular smooth muscle: role in chronic hypoxia-induced pulmonary hypertension

Increases in myofilament Ca2+ sensitivity resulting from stimulation of RhoA and Rho kinase represent a primary mechanism of vasoconstriction and associated pulmonary hypertension resulting from chronic hypoxia (CH). This chapter summarizes recent advances in the understanding of RhoA/Rho kinase signaling mechanisms in pulmonary vascular smooth muscle (VSM) that increase the sensitivity of the contractile apparatus to Ca2+ and contribute to vasoconstriction in this setting. Such advances include the discovery of myogenic tone in small pulmonary arteries from CH rats that contributes to vasoconstriction through a mechanism inherent to the VSM, dependent on Rho kinase-induced Ca2+ sensitization but independent of L-type voltage-gated Ca2+ channels. Additional studies have revealed an important contribution of superoxide anion (O2-)-induced RhoA activation to both receptor-mediated and membrane depolarization-induced myofilament Ca2+ sensitization in hypertensive pulmonary arteries. Xanthine oxidase and NADPH oxidase isoforms are potential sources of O2- that mediate RhoA-dependent vasoconstriction and associated pulmonary hypertension.

Chronic hypoxia augments depolarization-induced Ca2+ sensitization in pulmonary vascular smooth muscle through superoxide-dependent stimulation of RhoA

Rho kinase (ROCK)-dependent vasoconstriction has been implicated as a major factor in chronic hypoxia (CH)-induced pulmonary hypertension. This component of pulmonary hypertension is associated with arterial myogenicity and increased vasoreactivity to receptor-mediated agonists and depolarizing stimuli resulting from ROCK-dependent myofilament Ca(2+) sensitization. On the basis of separate lines of evidence that CH increases pulmonary arterial superoxide (O(2)(-)) generation and that O(2)(-) stimulates RhoA/ROCK signaling in vascular smooth muscle (VSM), we hypothesized that depolarization-induced O(2)(-) generation mediates enhanced RhoA-dependent Ca(2+) sensitization in pulmonary VSM following CH. To test this hypothesis, we determined effects of the ROCK inhibitor HA-1077 and the O(2)(-)-specific spin trap tiron on vasoconstrictor reactivity to depolarizing concentrations of KCl in isolated lungs and Ca(2+)-permeabilized, pressurized small pulmonary arteries from control and CH (4 wk at 0.5 atm) rats. Using the same vessel preparation, we examined effects of CH on KCl-dependent VSM membrane depolarization and O(2)(-) generation using sharp electrodes and the fluorescent indicator dihydroethidium, respectively. Finally, using a RhoA-GTP pull-down assay, we investigated the contribution of O(2)(-) to depolarization-induced RhoA activation. We found that CH augmented KCl-dependent vasoconstriction through a Ca(2+) sensitization mechanism that was inhibited by HA-1077 and tiron. Furthermore, CH caused VSM membrane depolarization that persisted with increasing concentrations of KCl, enhanced KCl-induced O(2)(-) generation, and augmented depolarization-dependent RhoA activation in a O(2)(-)-dependent manner. These findings reveal a novel mechanistic link between VSM membrane depolarization, O(2)(-) generation, and RhoA activation that mediates enhanced myofilament Ca(2+) sensitization and pulmonary vasoconstriction following CH.

Angioplasticity in asthma

Plasticity of the lung vasculature is intrinsically more complex than other organs due to the presence of two blood supply systems under different arterial pressures, the pulmonary and bronchial arterial systems. The bronchial and pulmonary circulations may both contribute to vascular remodelling in lungs after injury or inflammation. Vascular remodelling in the airway is a long recognized component in asthma. Growing numbers of reports suggest that a pro-angiogenic milieu is not a consequence of, but rather dictates the chronic inflammation of asthma. The fairly recent discovery of EPCs (endothelial progenitor cells) has enabled us to study the bone-marrow-derived cells that regulate lung vascular plasticity in asthma. This mini review provides a concise synopsis of our present knowledge about vascular plasticity in adult lungs, summarizes our current view of angioplasticity in asthma and highlights yet unresolved areas of potential interest.

RhoA/Rho-kinase signaling: a therapeutic target in pulmonary hypertension

Pulmonary arterial hypertension (PAH) is a devastating disease characterized by progressive elevation of pulmonary arterial pressure and vascular resistance due to pulmonary vasoconstriction and vessel remodeling as well as inflammation. Rho-kinases (ROCKs) are one of the best-described effectors of the small G-protein RhoA, and ROCKs are involved in a variety of cellular functions including muscle cell contraction, proliferation and vascular inflammation through inhibition of myosin light chain phosphatase and activation of downstream mediators. A plethora of evidence in animal models suggests that heightened RhoA/ROCK signaling is important in the pathogenesis of pulmonary hypertension by causing enhanced constriction and remodeling of the pulmonary vasculature. Both animal and clinical studies suggest that ROCK inhibitors are effective for treatment of severe PAH with minimal risk, which supports the premise that ROCKs are important therapeutic targets in pulmonary hypertension and that ROCK inhibitors are a promising new class of drugs for this devastating disease.

PI3K, Rho, and ROCK play a key role in hypoxia-induced ATP release and ATP-stimulated angiogenic responses in pulmonary artery vasa vasorum endothelial cells

We recently reported that vasa vasorum expansion occurs in the pulmonary artery (PA) adventitia of chronically hypoxic animals and that extracellular ATP is a pro-angiogenic factor for isolated vasa vasorum endothelial cells (VVEC). However, the sources of extracellular ATP in the PA vascular wall, as well as the molecular mechanisms underlying its release, remain elusive. Studies were undertaken to explore whether VVEC release ATP in response to hypoxia and to determine signaling pathways involved in this process. We found that hypoxia (1-3% O2) resulted in time- and O2-dependent ATP release from VVEC. Preincubation with the inhibitors of vesicular transport (monensin, brefeldin A, and N-ethylmaleimide) significantly decreased ATP accumulation in the VVEC conditioned media, suggesting that hypoxia-induced ATP release occurs through vesicular exocytosis. Additionally, both hypoxia and exogenously added ATP resulted in the activation of PI3K and accumulation of GTP-bound RhoA in a time-dependent manner. Pharmacological inhibition of PI3K and ROCK or knockout of RhoA by small interfering RNA significantly abolished hypoxia-induced ATP release from VVEC. Moreover, RhoA and ROCK play a critical role in ATP-induced increases in VVEC DNA synthesis, migration, and tube formation, indicating a functional contribution of PI3K, Rho, and ROCK to both the autocrine mechanism of ATP release and ATP-mediated angiogenic activation of VVEC. Taken together, our findings provide novel evidence for the signaling mechanisms that link hypoxia-induced increases in extracellular ATP and vasa vasorum expansion.

L-Arginine promotes angiogenesis in the chronically hypoxic lung: a novel mechanism ameliorating pulmonary hypertension

Chronic alveolar hypoxia, whether due to residence at high altitude or lung disease, leads to a sustained increase in pulmonary vascular resistance and pulmonary hypertension (PH). Strategies that augment endogenous nitric oxide production or activity, including l-arginine supplementation, attenuate the development of PH. This action has been attributed to inhibition of vessel wall remodeling, thus preventing structural narrowing of the vascular lumen. However, more recent evidence suggests that structural changes are not responsible for the elevated vascular resistance observed in chronic hypoxic PH, calling into question the previous explanation for the action of l-arginine. We examined the effect of dietary l-arginine supplementation on pulmonary vasoconstriction, structurally determined maximum vascular lumen diameter, and vessel length in rats during 2 wk of exposure to hypoxia. l-Arginine attenuated the development of hypoxic PH by preventing increased arteriolar resistance. It did not alter mean maximal vascular lumen diameter, nor did it augment nitric oxide-mediated vasodilatation, in chronically hypoxic lungs. However, the total length of vessels within the gas exchange region of the hypoxic lungs was significantly increased after l-arginine supplementation. These findings suggest that dietary l-arginine ameliorated hypoxic PH, but not by an effect on the structurally determined lumen diameter of pulmonary blood vessels. l-Arginine enhanced angiogenesis in the hypoxic pulmonary circulation, which may attenuate hypoxic PH by producing new parallel vascular pathways through the lung.

Targeting cerebrovascular Rho-kinase in stroke

BACKGROUND

Rho and Rho-associated kinase (ROCK) play pivotal roles in pathogenesis of vascular diseases including stroke. ROCK is expressed in all cell types relevant to stroke, and regulates a range of physiological processes.

OBJECTIVE

To provide an overview of ROCK as an experimental therapeutic target in cerebral ischemia, and the translational opportunities and obstacles in the prophylaxis and treatment of stroke.

METHODS

Relevant literature was reviewed.

RESULTS

ROCK activity is upregulated in chronic vascular risk factors such as diabetes, hyperlipidemia and hypertension, and more acutely by cerebral ischemia. ROCK activation is predicted to increase the risk of cerebral ischemia, and worsen the ischemic tissue outcome and functional recovery. Evidence suggests that ROCK inhibition is protective in models of cerebral ischemia. The benefit is mediated through multiple mechanisms.

CONCLUSION

ROCK is a promising therapeutic target in all stages of stroke.

Dexfenfluramine discontinuous treatment does not worsen hypoxia-induced pulmonary vascular remodeling but activates RhoA/ROCK pathway: consequences on pulmonary hypertension

The anorectic drug, dexfenfluramine has been associated with an increase in the relative risk of developing pulmonary hypertension. 5-hydroxytryptamine (5-HT) is a mitogen for smooth muscle cell, an effect that relies on 5-HT transporter expression and which has been proposed to explain pulmonary side effect of dexfenfluramine, and more particularly its effect on vascular remodeling. However recent data supported a major role of pulmonary artery vasoconstriction through the RhoA/Rho-kinase pathway. We questioned whether or not anorectic treatment aggravates pulmonary hypertension through vascular remodeling and if RhoA/Rho-kinase (ROCK) was potentially involved. In rats exposed to hypoxia, concomitant dexfenfluramine treatment (5 mg/kg/day, i.v.) for 4 weeks had no effect on pulmonary hypertension development. When exposure to 2 weeks of chronic hypoxia followed discontinuation of dexfenfluramine treatment (dexfenfluramine-hypoxic rats), echocardiographic parameters of pulmonary artery flow and right ventricle were further altered (P<0.05) as well as right ventricle systolic pressure was further increased (P<0.001) when compared to hypoxic rats treated with vehicle (hypoxic rats). However, the total number of muscularized distal pulmonary arteries artery was similar in dexfenfluramine-hypoxic vs. hypoxic rats (P>0.05). Western blot, RT-PCR and immunofluorescence analysis revealed a greater expression of 5-HT transporter and ROCK, as well as a greater activation of RhoA in dexfenfluramine-hypoxic rats compared to hypoxic rats. These data show that increased 5-HT transporter expression that follows dexfenfluramine discontinuation is not associated to a greater vascular remodeling despite worsening the development of pulmonary hypertension. Furthermore dexfenfluramine discontinuation promotes a greater RhoA/ROCK pathway activation. This pathway, involved in many cardiovascular diseases, might explain the cardiac and pulmonary toxicity of serotoninergic agonists.

Preservation of cGMP-induced relaxation of pulmonary veins of fetal lambs exposed to chronic high altitude hypoxia: role of PKG and Rho kinase

The roles of Rho kinase (ROCK) and cGMP-dependent protein kinase (PKG) in cGMP-mediated relaxation of fetal pulmonary veins exposed to chronic hypoxia (CH) were investigated. Fourth generation pulmonary veins were dissected from near-term fetuses ( approximately 140 days of gestation) delivered from ewes exposed to chronic high altitude hypoxia for approximately 110 days (CH) and from control ewes. After constriction with endothelin-1, 8-bromoguanosine 3',5'-cyclic monophosphate (8-Br-cGMP) caused a similar relaxation of both control and CH vessels. Rp-8-Br-PET-cGMPS (a PKG inhibitor) inhibited whereas Y-27632 (a ROCK inhibitor) augmented relaxation of control veins to 8-Br-cGMP. These effects were significantly diminished in CH veins. PKG protein expression and activity were greater whereas ROCK protein expression and activity were less in CH vessels compared with controls. Phosphorylation of threonine 696 (ROCK substrate) and serine 695 (PKG substrate) of the regulatory myosin phosphatase targeting subunit MYPT1 of myosin light chain (MLC) phosphatase was stimulated to a lesser extent in CH than in control veins by endothelin-1 (ROCK stimulant) and 8-Br-cGMP (PKG stimulant), respectively. The phosphorylation and dephosphorylation of MLC caused by endothelin-1 and 8-Br-cGMP, respectively, were less in CH veins than in controls. These results suggest that CH in utero upregulates PKG activity but attenuates PKG action in fetal pulmonary veins. These effects are offset by the diminished ROCK action on MYPT1 and MLC and thus lead to an unaltered response to cGMP.

Pathobiology of pulmonary hypertension

A variety of conditions can lead to the development of pulmonary arterial hypertension (PAH). Current treatments can improve symptoms and reduce the severity of the hemodynamic abnormality, but most patients remain quite limited, and deterioration in their condition necessitates a lung transplant. This review discusses current experimental and clinical studies that investigate the pathobiology of PAH. An emerging theme is the consideration of ways in which one might reverse the advanced occlusive structural changes in the pulmonary circulation causing PAH. The current debate concerning the role of regeneration through stem cells is presented. This review also highlights investigations in a number of laboratories relating the pathobiology of PAH to mutations causing loss of function of bone morphogenetic protein receptor II in patients with familial PAH, as well as sporadic cases.

Novel interactions between the 5-HT transporter, 5-HT1B receptors and Rho kinase in vivo and in pulmonary fibroblasts

BACKGROUND AND PURPOSE

While the 5-HT and Rho-kinase (ROCK) pathways have been implicated in the development of pulmonary arterial hypertension (PAH), the nature of any interactions between them remain unclear. This study investigated a role for ROCK in 5-HT-regulated proliferative responses in lung fibroblasts in vivo and in vitro.

EXPERIMENTAL APPROACH

PAH was examined in mice over-expressing human 5-HT transporters (SERT+), from which pulmonary artery fibroblasts (PFs) were isolated to assess ROCK expression. In vitro analysis of 5-HT signalling employed CCL39 hamster lung fibroblasts.

KEY RESULTS

ROCK inhibition ablated increased pulmonary remodelling and hypertension observed in SERT+ mice, and ROCK1/2 protein levels were elevated in SERT+ PFs. ROCK inhibition also reduced 5-HT-stimulated proliferation by suppressing MEK-stimulated ERK phosphorylation. While optimal 5-HT-stimulated proliferation required 5-HT(1B) and 5-HT(2A) receptors and SERT, receptor sensitivity to Y27632 was restricted to the 5-HT(1B) receptor. Also, while hypoxia-induced pulmonary vascular remodelling and hypertension were sensitive to Y27632 in WT and SERT+ animals, the proportions sensitive to ROCK inhibition were increased by SERT over-expression.

CONCLUSIONS AND IMPLICATIONS

SERT over-expression increased ROCK-dependent pulmonary remodelling in normoxia and hypoxia and SERT over-expression was associated with elevated ROCK1/2 levels. ROCK also potentiated 5-HT(1B) receptor-stimulated ERK activation and proliferation in vitro by facilitating MEK-ERK interaction.

Hypoxia selectively activates the CREB family of transcription factors in the in vivo lung

RATIONALE

Pulmonary hypertension is a common complication of chronic hypoxic lung diseases and is associated with increased morbidity and reduced survival. The pulmonary vascular changes in response to hypoxia, both structural and functional, are unique to this circulation.

OBJECTIVES

To identify transcription factor pathways uniquely activated in the lung in response to hypoxia.

METHODS

After exposure to environmental hypoxia (10% O(2)) for varying periods (3 h to 2 wk), lungs and systemic organs were isolated from groups of adult male mice. Bioinformatic examination of genes the expression of which changed in the hypoxic lung (assessed using microarray analysis) identified potential lung-selective transcription factors controlling these changes in gene expression. In separate further experiments, lung-selective activation of these candidate transcription factors was tested in hypoxic mice and by comparing hypoxic responses of primary human pulmonary and cardiac microvascular endothelial cells in vitro.

MEASUREMENTS AND MAIN RESULTS

Bioinformatic analysis identified cAMP response element binding (CREB) family members as candidate lung-selective hypoxia-responsive transcription factors. Further in vivo experiments demonstrated activation of CREB and activating transcription factor (ATF)1 and up-regulation of CREB family-responsive genes in the hypoxic lung, but not in other organs. Hypoxia-dependent CREB activation and CREB-responsive gene expression was observed in human primary lung, but not cardiac microvascular endothelial cells.

CONCLUSIONS

These findings suggest that activation of CREB and AFT1 plays a key role in the lung-specific responses to hypoxia, and that lung microvascular endothelial cells are important, proximal effector cells in the specific responses of the pulmonary circulation to hypoxia.

Changes in the structure-function relationship of elastin and its impact on the proximal pulmonary arterial mechanics of hypertensive calves

Extracellular matrix remodeling has been proposed as one mechanism by which proximal pulmonary arteries stiffen during pulmonary arterial hypertension (PAH). Although some attention has been paid to the role of collagen and metallomatrix proteins in affecting vascular stiffness, much less work has been performed on changes in elastin structure-function relationships in PAH. Such work is warranted, given the importance of elastin as the structural protein primarily responsible for the passive elastic behavior of these conduit arteries. Here, we study structure-function relationships of fresh arterial tissue and purified arterial elastin from the main, left, and right pulmonary artery branches of normotensive and hypoxia-induced pulmonary hypertensive neonatal calves. PAH resulted in an average 81 and 72% increase in stiffness of fresh and digested tissue, respectively. Increase in stiffness appears most attributable to elevated elastic modulus, which increased 46 and 65%, respectively, for fresh and digested tissue. Comparison between fresh and digested tissues shows that, at 35% strain, a minimum of 48% of the arterial load is carried by elastin, and a minimum of 43% of the change in stiffness of arterial tissue is due to the change in elastin stiffness. Analysis of the stress-strain behavior revealed that PAH causes an increase in the strains associated with the physiological pressure range but had no effect on the strain of transition from elastin-dominant to collagen-dominant behavior. These results indicate that mechanobiological adaptations of the continuum and geometric properties of elastin, in response to PAH, significantly elevate the circumferential stiffness of proximal pulmonary arterial tissue.

Adaptative modifications of right coronary myocytes voltage-gated K+ currents in rat with hypoxic pulmonary hypertension

Chronic hypoxia (CH)-induced pulmonary hypertension (PHT) is well known to alter K+ channels in pulmonary myocytes. PHT induces right ventricle hypertrophy that increases oxygen demand; however, coronary blood flow and K+ channel adaptations of coronary myocytes during PHT remain unknown. We determined whether CH and PHT altered K+ currents and coronary reactivity and what impact they might have on right myocardial perfusion. Right ventricle perfusion, as attested by microspheres, was redistributed toward hypertrophied right ventricle [RV/LV (%)=0.59+/-0.07% in CH rats vs. 0.29+/-0.03 in control rats, P<0.05]. Whole-cell patch clamping showed a reduction of global outward current in hypoxic right coronary artery myocytes (H-RCA), whereas hypoxic left coronary artery myocytes exhibited an increase. K+ channel blockers revealed that a 4-aminopyridine (4AP)-sensitive current (Kv current) was decreased in H-RCA (14.3+/-1.1 vs. 23.4+/-2.5 pA/pF at 60 mV in control RCA, P<0.05) and increased in hypoxic left coronary artery myocytes (H-LCA; 26.4+/-3.8 vs. 11.8+/-1.6 pA/pF at 60 mV in control LCA, P<0.05). Constriction to 4AP was decreased in H-RCA when compared to normoxic control and increased in H-LCA when compared to LCA. Finally, we observed that the expression of Kv1.2 and Kv1.5 were lower in H-RCA than that in H-LCA. This study reveals that CH differentially regulates Kv channels in coronary myocytes. Hypoxia decreases Kv currents and therefore reduces vasoreactivity that contributes to an adaptative response leading to right hypertrophied ventricle perfusion enhancement at rest.

Reactive oxygen species mediate RhoA/Rho kinase-induced Ca2+ sensitization in pulmonary vascular smooth muscle following chronic hypoxia

Recent evidence supports a prominent role for Rho kinase (ROK)-mediated pulmonary vasoconstriction in the development and maintenance of chronic hypoxia (CH)-induced pulmonary hypertension. Endothelin (ET)-1 contributes to the pulmonary hypertensive response to CH, and recent studies by our laboratory and others indicate that pulmonary vascular reactivity following CH is largely independent of changes in vascular smooth muscle (VSM) intracellular free calcium concentration ([Ca(2+)](i)). In addition, CH increases generation of reactive oxygen species (ROS) in pulmonary arteries, which may underlie the shift toward ROK-dependent Ca(2+) sensitization. Therefore, we hypothesized that ROS-dependent RhoA/ROK signaling mediates ET-1-induced Ca(2+) sensitization in pulmonary VSM following CH. To test this hypothesis, we determined the effect of pharmacological inhibitors of ROK, myosin light chain kinase (MLCK), tyrosine kinase (TK), and PKC on ET-1-induced vasoconstriction in endothelium-denuded, Ca(2+)-permeabilized small pulmonary arteries from control and CH (4 wk at 0.5 atm) rats. Further experiments examined ET-1-mediated, ROK-dependent phosphorylation of the regulatory subunit of myosin light chain phosphatase (MLCP), MYPT1. Finally, we measured ET-1-induced ROS generation in dihydroethidium-loaded small pulmonary arteries and investigated the role of ROS in mediating ET-1-induced, RhoA/ROK-dependent Ca(2+) sensitization using the superoxide anion scavenger, tiron. We found that CH increases ET-1-induced Ca(2+) sensitization that is sensitive to inhibition of ROK and MLCK, but not PKC or TK, and correlates with ROK-dependent MYPT1(Thr696) phosphorylation. Furthermore, tiron inhibited basal and ET-1-stimulated ROS generation, RhoA activation, and VSM Ca(2+) sensitization following CH. We conclude that CH augments ET-1-induced Ca(2+) sensitization through ROS-dependent activation of RhoA/ROK signaling in pulmonary VSM.

Chronic intrauterine pulmonary hypertension increases endothelial cell Rho kinase activity and impairs angiogenesis in vitro

Persistent pulmonary hypertension of the newborn (PPHN) is characterized by endothelial dysfunction and decreased vascular growth. The role of Rho kinase activity in modulating endothelial function and regulating angiogenesis during normal lung development and in PPHN is unknown. We hypothesized that PPHN increases Rho kinase activity in fetal pulmonary artery endothelial cells (PAECs) and impairs angiogenesis in vitro. Proximal PAECs were harvested from fetal sheep with partial ligation of the ductus arteriosus in utero (PPHN) and age-matched controls. Rho kinase activity was measured by RhoA, Rho GTP, and phosphorylated MYPT-1 protein content. The effects of Rho kinase activity on angiogenesis, endothelial nitric oxide (NO) synthase (eNOS) protein expression, and NO production were determined in normal and PPHN PAECs. Angiogenesis was assessed by tube formation in vitro with/without Y-27632 (a Rho kinase inhibitor) and calpeptin (a Rho kinase activator) in the presence/absence of N-nitro-l-arginine (l-NA, an NOS inhibitor). RhoA, Rho GTP, and phosphorylated MYPT-1 protein were increased in PPHN PAECs. Tube formation was reduced 29% in PPHN PAECs (P < 0.001) and increased with Y-27632 treatment in normal and PPHN PAECs, with PPHN PAECs achieving levels similar to those of normal PAECs. l-NA inhibited the Y-27632-induced increase in tube formation in normal, but not PPHN, PAECs. Calpeptin reduced tube formation in normal and PPHN PAECs. eNOS expression was reduced 42% in PPHN PAECs (P < 0.01). Y-27632 increased eNOS protein and NO production in normal and PPHN PAECs. Calpeptin decreased eNOS protein only in normal PAECs but reduced NO production in normal and PPHN PAECs. We conclude that Rho kinase activity is increased in PPHN PAECs and impairs angiogenesis and downregulates eNOS protein and NO production in vitro.

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.

Pulmonary hypertension: therapeutic targets within the serotonin system

Pulmonary arterial hypertension (PAH) is characterized by a sustained and progressive elevation in pulmonary arterial pressure and pulmonary vascular remodelling leading to right heart failure and death. Prognosis is poor and novel therapeutic approaches are needed. The serotonin hypothesis of PAH originated in the 1960s after an outbreak of the disease was reported among patients taking the anorexigenic drugs aminorex and fenfluramine. These are indirect serotonergic agonists and serotonin transporter substrates. Since then many advances have been made in our understanding of the role of serotonin in the pathobiology of PAH. The rate-limiting enzyme in the synthesis of serotonin is tryptophan hydroxylase (Tph). Serotonin is synthesized, through Tph1, in the endothelial cells of the pulmonary artery and can then act on underlying pulmonary arterial smooth muscle cells and pulmonary arterial fibroblasts in a paracrine fashion causing constriction and remodelling. These effects of serotonin can be mediated through both the serotonin transporter and serotonin receptors. This review will discuss our current understanding of 'the serotonin hypothesis' of PAH and highlight possible therapeutic targets within the serotonin system.

Lung-selective gene responses to alveolar hypoxia: potential role for the bone morphogenetic antagonist gremlin in pulmonary hypertension

Pulmonary hypoxia is a common complication of chronic lung diseases leading to the development of pulmonary hypertension. The underlying sustained increase in vascular resistance in hypoxia is a response unique to the lung. Thus we hypothesized that there are genes for which expression is altered selectively in the lung in response to alveolar hypoxia. Using a novel subtractive array strategy, we compared gene responses to hypoxia in primary human pulmonary microvascular endothelial cells (HMVEC-L) with those in cardiac microvascular endothelium and identified 90 genes (forming 9 clusters) differentially regulated in the lung endothelium. From one cluster, we confirmed that the bone morphogenetic protein (BMP) antagonist, gremlin 1, was upregulated in the hypoxic murine lung in vivo but was unchanged in five systemic organs. We also demonstrated that gremlin protein was significantly increased by hypoxia in vivo and inhibited HMVEC-L responses to BMP stimulation in vitro. Furthermore, significant upregulation of gremlin was measured in lungs of patients with pulmonary hypertensive disease. From a second cluster, we showed that CXC receptor 7, a receptor for the proangiogenic chemokine CXCL12, was selectively upregulated in the hypoxic lung in vivo, confirming that our subtractive strategy had successfully identified a second lung-selective hypoxia-responsive gene. We conclude that hypoxia, typical of that encountered in pulmonary disease, causes lung-specific alterations in gene expression. This gives new insights into the mechanisms of pulmonary hypertension and vascular loss in chronic lung disease and identifies gremlin 1 as a potentially important mediator of vascular changes in hypoxic pulmonary hypertension.

Involvement of RhoA/Rho kinase signaling in protection against monocrotaline-induced pulmonary hypertension in pneumonectomized rats by dehydroepiandrosterone

RhoA/Rho kinase (ROCK) signaling plays a key role in the pathogenesis of experimental pulmonary hypertension (PH). Dehydroepiandrosterone (DHEA), a naturally occurring steroid hormone, effectively inhibits chronic hypoxic PH, but the responsible mechanisms are unclear. This study tested whether DHEA was also effective in treating monocrotaline (MCT)-induced PH in left pneumonectomized rats and whether inhibition of RhoA/ROCK signaling was involved in the protective effect of DHEA. Three weeks after MCT injection, pneumonectomized rats developed PH with severe vascular remodeling, including occlusive neointimal lesions in pulmonary arterioles. In lungs from these animals, we detected cleaved (constitutively active) ROCK I as well as increases in activities of RhoA and ROCK and increases in ROCK II protein expression. Chronic DHEA treatment (1%, by food for 3 wk) markedly inhibited the MCT-induced PH (mean pulmonary artery pressures after treatment with 0% and 1% DHEA were 33+/-5 and 16+/-1 mmHg, respectively) and severe pulmonary vascular remodeling in pneumonectomized rats. The MCT-induced changes in RhoA/ROCK-related protein expression were nearly normalized by DHEA. A 3-wk DHEA treatment (1%) started 3 wk after MCT injection completely inhibited the progression of PH (mean pulmonary artery pressures after treatment with 0% and 1% DHEA were 47+/-3 and 30+/-3 mmHg, respectively), and this treatment also resulted in 100% survival in contrast to 30% in DHEA-untreated rats. These results suggest that inhibition of RhoA/ROCK signaling, including the cleavage and constitutive activation of ROCK I, is an important component of the impressive protection of DHEA against MCT-induced PH in pneumonectomized rats.

Antiangiogenic properties of fasudil, a potent Rho-Kinase inhibitor

PURPOSE

Vascular endothelial growth factor (VEGF) plays a pivotal role in pathological angiogenesis. In this study, we addressed the therapeutic potential of fasudil, a potent Rho-kinase inhibitor, for VEGF-elicited angiogenesis and also for the intracellular signalings induced by VEGF.

METHODS

In vitro, the inhibitory effects of fasudil on the VEGF-dependent VEGF receptor 2 (VEFGR2 or KDR), extracellular signal-related kinase (ERK) 1/2, Akt and myosin light chain (MLC) phosphorylation, as well as on the migration and proliferation of bovine retinal microvascular endothelial cells (BRECs) were analyzed with Western blotting, [3H]-thymidine uptake, and modified Boyden chamber assay. VEGF-elicited in vivo angiogenesis was analyzed with a mouse corneal micropocket assay coembedded with or without fasudil.

RESULTS

VEGF caused enhanced MLC phosphorylation of BRECs, which was almost completely attenuated by 10microM fasudil. VEGF-dependent phosphorylation of ERK1/2 and Akt were also partially but significantly attenuated by treatment with fasudil without affecting VEGFR2 (KDR) phosphorylation. Moreover, both VEGF-induced [3H]-thymidine uptake and the migration of BRECs were significantly inhibited in the presence of fasudil. Finally, VEGF-elicited angiogenesis in the corneal micropocket assay was potently attenuated by coembedding with fasudil (P < 0.01).

CONCLUSIONS

These findings indicate that fasudil might have a therapeutic potential for ocular angiogenic diseases. The antiangiogenic effect of fasudil appears to be mediated through the blockade not only of Rho-kinase signaling but also of ERK and Akt signaling.

Endothelin-1 and serotonin are involved in activation of RhoA/Rho kinase signaling in the chronically hypoxic hypertensive rat pulmonary circulation

We have previously reported that vasoconstrictor sensitivity to KCl (a receptor-independent and voltage-gated Ca influx-mediated vasoconstrictor) is augmented in the chronically hypoxic hypertensive rat pulmonary circulation probably through increased Rho kinase-mediated Ca sensitization. However, the upstream mechanism by which the RhoA/Rho kinase signaling pathway is activated is unknown. This study examined if endogenous endothelin-1 (ET-1) and serotonin (5-HT) play roles in the Rho kinase-mediated augmented vasoconstrictor response to KCl and the activation of RhoA in chronically hypoxic hypertensive rat pulmonary arteries. The augmented KCl vasoconstriction in hypertensive lungs was reduced by the ETA receptor antagonist BQ123, while a dual ETA/B antagonist had no further effects. A combination of BQ123 and a 5-HT1B/1D receptor antagonist, GR127935, was more effective than either agent alone. The combined antagonists also reduced augmented contractile sensitivity to KCl in hypertensive intrapulmonary arteries. Membrane-to-cytosol ratio of RhoA expression in hypertensive arteries was greater than that in normotensive arteries and was reduced by BQ123 and GR127935. These results suggest that stimulation of ETA and 5-HT1B/1D receptors by endogenous ET-1 and 5-HT, respectively, is involved in RhoA/Rho kinase-mediated increased Ca sensitization in the chronically hypoxic hypertensive rat pulmonary circulation.

A method for measuring Rho kinase activity in tissues and cells

The Rho-associated kinases (ROCKs) can regulate cell shape and function by modulating the actin cytoskeleton. ROCKs are serine-threonine protein kinases that can phosphorylate adducin, ezrin-radixin-moesin proteins, LIM kinase, and myosin light chain phosphatase. In the cardiovascular system, the RhoA/ROCK pathway has been implicated in angiogenesis, atherosclerosis, cerebral and coronary vasospasm, cerebral ischemia, hypertension, myocardial hypertrophy, and neointima formation after vascular injury. ROCKs consist of two isoforms: ROCK1 and ROCK2. They share overall 65% homology in their amino acid sequence and 92% homology in their amino kinase domains. However, these two isoforms have different subcellular localizations and exert biologically different functions. In particular, ROCK1 appears to be more important for immunological functions, whereas ROCK2 is more important for endothelial and vascular smooth muscle function. Thus, the ability to measure ROCK activity in tissues and cells would be important for understanding mechanisms underlying cardiovascular disease. This chapter describes a method for measuring ROCK activity in peripheral blood, tissues, and cells.

Rho kinase-mediated vasoconstriction in rat models of pulmonary hypertension

There is current controversy regarding whether vasoconstriction plays a significant role in the elevated pressure of severe, advanced stages of pulmonary hypertension. Results of acute vasodilator testing using conventional vasodilators in such patients suggest there is only a minor contribution of vasoconstriction. However, there is a possibility that these results may underestimate the contribution of vasoconstriction because the most effective vasodilators have not yet been tested. This issue has not been addressed even experimentally, due mainly to a lack of appropriate animal models. A few animal models that mimic the pathology of human severe pulmonary hypertension more closely (i.e., development of occlusive neointimal lesions in small pulmonary arteries/arterioles) have been introduced, including rat models of left lung pneumonectomy plus monocrotaline injection and vascular endothelial growth factor inhibition plus exposure to chronic hypoxia. We have observed that Rho kinase inhibitors, a novel class of potent vasodilators, reduce the high pulmonary artery pressure of these models acutely and markedly, suggesting that vasoconstriction can significantly be involved in pulmonary hypertension with severely remodeled (occluded) pulmonary vessels. This chapter describes methods used for evaluation of the involvement of Rho kinase-mediated vasoconstriction in rat models of pulmonary hypertension.

Pleiotropic effects of statin therapy: molecular mechanisms and clinical results

Statins inhibit the enzyme 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase, which is required for cholesterol biosynthesis, and are beneficial in the primary and secondary prevention of cardiovascular disease. Most of the benefits of statin therapy are owing to the lowering of serum cholesterol levels. However, by inhibiting HMG-CoA reductase, statins can also inhibit the synthesis of isoprenoids, which are important lipid attachments for intracellular signaling molecules, such as Rho, Rac and Cdc42. Therefore, it is possible that statins might exert cholesterol-independent or 'pleiotropic' effects through direct inhibition of these small GTP-binding proteins. Recent studies have shown that statins might have important roles in diseases that are not mediated by cholesterol. Here, we review data from recent clinical trials that support the concept of statin pleiotropy and provide a rationale for their clinical importance.

Changes in macrovessel pulmonary blood flow distribution following chronic hypoxia: assessed using synchrotron radiation microangiography

Structural and functional changes of the pulmonary circulation, particularly during the pathogenesis of pulmonary arterial hypertension (PAH), remain to be fully elucidated. In this study, we utilized monochromatic synchrotron radiation (SR) microangiography to assess changes in pulmonary arteriole blood flow in the intact-chest rat after 4 wk of chronic hypoxia. Sprague-Dawley rats were exposed to normoxia (N-rats) or chronic hypoxia (10% O2; CH-rats) for 28 days. Rats were anesthetized, and microangiography was performed on the left lung to assess 1) the branching distribution of pulmonary arteriole blood flow (internal diameter >80 μm) and 2) dynamic changes in vessel lumen diameter during acute hypoxic (8% O2 for 4 min) pulmonary vasoconstriction (HPV) before and after β-adrenoceptor blockade (2 mg/kg iv propranolol). Using SR angiography, we observed that the number of opaque third- and fourth-generation vessels (100–300 μm) for CH-rats was significantly fewer than the number for N-rats. The magnitude of HPV was not different between CH-rats and N-rats. β-Adrenoceptor blockade accentuated the HPV in 200- to 300-μm vessels for CH-rats, but even more so in N-rats. However, in CH-rats, β-adrenoceptor blockade also accentuated the HPV in 100- to 200-μm vessels. In summary, we utilized SR to assess gross blood flow changes and functional changes (i.e., HPV) of the pulmonary circulation in PAH. These results highlight the benefits of SR for assessing pulmonary circulatory pathology. Of particular importance, future use of SR will provide an effective method for assessing potential therapeutic treatments for PAH.

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 kinase and Ca2+ entry mediate increased pulmonary and systemic vascular resistance in l-NAME-treated rats

The small GTP-binding protein and its downstream effector Rho kinase play an important role in the regulation of vasoconstrictor tone. Rho kinase activation maintains increased pulmonary vascular tone and mediates the vasoconstrictor response to nitric oxide (NO) synthesis inhibition in chronically hypoxic rats and in the ovine fetal lung. However, the role of Rho kinase in mediating pulmonary vasoconstriction after NO synthesis inhibition has not been examined in the intact rat. To address this question, cardiovascular responses to the Rho kinase inhibitor fasudil were studied at baseline and after administration of an NO synthesis inhibitor. In the intact rat, intravenous injections of fasudil cause dose-dependent decreases in systemic arterial pressure, small decreases in pulmonary arterial pressure, and increases in cardiac output. l-NAME caused a significant increase in pulmonary and systemic arterial pressures and a decrease in cardiac output. The intravenous injections of fasudil after l-NAME caused dose-dependent decreases in pulmonary and systemic arterial pressure and increases in cardiac output, and the percent decreases in pulmonary arterial pressure in response to the lower doses of fasudil were greater than decreases in systemic arterial pressure. The Ca++ entry blocker isradipine also decreased pulmonary and systemic arterial pressure in l-NAME-treated rats. Infusion of sodium nitroprusside restored pulmonary arterial pressure to baseline values after administration of l-NAME. These data provide evidence in support of the hypothesis that increases in pulmonary and systemic vascular resistance following l-NAME treatment are mediated by Rho kinase and Ca++ entry through L-type channels, and that responses to l-NAME can be reversed by an NO donor.

Effect of hypoxia and Beraprost sodium on human pulmonary arterial smooth muscle cell proliferation: the role of p27kip1

BACKGROUND

Hypoxia induces the proliferation of pulmonary arterial smooth muscle cell (PASMC) in vivo and in vitro, and prostacyclin analogues are thought to inhibit the growth of PASMC. Previous studies suggest that p27kip1, a kind of cyclin-dependent kinase inhibitor, play an important role in the smooth muscle cell proliferation. However, the mechanism of hypoxia and the subcellular interactions between p27kip1 and prostacyclin analogues in human pulmonary arterial smooth muscle cell (HPASMC) are not fully understood.

METHODS

We investigated the role of p27kip1 in the ability of Beraprost sodium (BPS; a stable prostacyclin analogue) to inhibit the proliferation of HPASMC during hypoxia. To clarify the biological effects of hypoxic air exposure and BPS on HPASMC, the cells were cultured in a hypoxic chamber under various oxygen concentrations (0.1-21%). Thereafter, DNA synthesis was measured as bromodeoxyuridine (BrdU) incorporation, the cell cycle was analyzed by flow cytometry with propidium iodide staining. The p27kip1 mRNA and protein expression and it's stability was measured by real-time RT-PCR and Western blotting. Further, we assessed the role of p27kip1 in HPASMC proliferation using p27kip1 gene knockdown using small interfering RNA (siRNA) transfection.

RESULTS

Although severe hypoxia (0.1% oxygen) suppressed the proliferation of serum-stimulated HPASMC, moderate hypoxia (2% oxygen) enhanced proliferation in accordance with enhanced p27kip1 protein degradation, whereas BPS suppressed HPASMC proliferation under both hypoxic and normoxic conditions by suppressing p27kip1 degradation with intracellular cAMP-elevation. The 8-bromo-cyclic adenosine monophosphate (8-Br-cAMP), a cAMP analogue, had similar action as BPS in the regulation of p27kip1. Moderate hypoxia did not affect the stability of p27kip1 protein expression, but PDGF, known as major hypoxia-induced growth factors, significantly decreased p27kip1 protein stability. We also demonstrated that BPS and 8-Br-cAMP suppressed HPASMC proliferation under both hypoxic and normoxic conditions by blocking p27kip1 mRNA degradation. Furthermore, p27kip1 gene silencing partially attenuated the effects of BPS and partially restored hypoxia-induced proliferation.

CONCLUSION

Our study suggests that moderate hypoxia induces HPASMC proliferation, which is partially dependent of p27kip1 down-regulation probably via the induction of growth factors such as PDGF, and BPS inhibits both the cell proliferation and p27kip1 mRNA degradation through cAMP pathway.

Vascular adaptations to hypoxia: molecular and cellular mechanisms regulating vascular tone

Several molecular and cellular adaptive mechanisms to hypoxia exist within the vasculature. Many of these processes involve oxygen sensing which is transduced into mediators of vasoconstriction in the pulmonary circulation and vasodilation in the systemic circulation. A variety of oxygen-responsive pathways, such as HIF (hypoxia-inducible factor)-1 and HOs (haem oxygenases), contribute to the overall adaptive process during hypoxia and are currently an area of intense research. Generation of ROS (reactive oxygen species) may also differentially regulate vascular tone in these circulations. Potential candidates underlying the divergent responses between the systemic and pulmonary circulations may include Nox (NADPH oxidase)-derived ROS and mitochondrial-derived ROS. In addition to alterations in ROS production governing vascular tone in the hypoxic setting, other vascular adaptations are likely to be involved. HPV (hypoxic pulmonary vasoconstriction) and CH (chronic hypoxia)-induced alterations in cellular proliferation, ionic conductances and changes in the contractile apparatus sensitivity to calcium, all occur as adaptive processes within the vasculature.

Hypoxia-induced pulmonary hypertension: Different impact of iloprost, sildenafil, and nitric oxide

OBJECTIVES

Chronic alveolar hypoxia induces pulmonary hypertension, evident from elevated pulmonary artery pressure (PAP), pulmonary vascular resistance, right ventricular hypertrophy (RVH), and increased muscularization of the pulmonary vasculature. Additionally, the vasoconstrictor response to acute hypoxia (HPV) may be reduced in the remodeled vasculature. However, no direct comparison of different treatments on the various parameters characterizing pulmonary hypertension has been performed yet. Against this background, we compared the effects of inhaled NO, infused iloprost, a stable prostacyclin analogue, and oral sildenafil, a phosphodiesterase 5 inhibitor, on hypoxia-induced pulmonary hypertension.

METHODS

Exposure of rabbits to chronic hypoxia (FiO(2)=0.10) for 42 days. Treatment with infused iloprost, oral sildenafil, and inhaled nitric oxide.

RESULTS

We quantified PAP, pulmonary vascular resistance, RVH, vascular remodeling, vasoreactivity, and the strength of HPV. Chronic hypoxia resulted in an increase in (a) the right ventricle/(left ventricle+septum) ratio from 0.26+/-0.01 to 0.44+/-0.01, (b) PAP, and (c) the degree of muscularization from 14.0+/-4.0% to 43.5+/-5.3%. Treatment with iloprost and sildenafil, but not with NO, prevented the increase in muscularization. In contrast, RVH was strongly inhibited by sildenafil, whereas NO had some minor, and iloprost had no effect. Only iloprost reduced PAP compared to NO and sildenafil. The downregulation of HPV was abrogated only by NO.

CONCLUSION

We demonstrated (a) that the parameters characterizing hypoxia-induced pulmonary hypertension are not functionally linked, (b) that the downregulation of HPV under chronic hypoxia can be prevented by inhaled NO but not by sildenafil and iloprost, and (c) that iloprost is particularly effective in preventing vascular remodeling and sildenafil in preventing RVH.

Regression of chronic hypoxic pulmonary hypertension by simvastatin

The 3-hydroxy-3-methylglutaryl CoA (HMG-CoA) reductase inhibitor, simvastatin, has been shown to attenuate chronic hypoxic pulmonary hypertension (CHPH). Here, we assess whether simvastatin is capable of inducing regression of established CHPH and explore potential mechanisms of statin effect. Rats ( n = 8 in each group) were exposed to chronic hypoxia (10% FiO2) for 2 or 4 wk. Simvastatin treatment (20 mg·kg−1·day−1) commenced after 2 wk of hypoxia, at which time CHPH was fully established, reduced mean pulmonary artery pressure (19 ± 0.5 vs. 27 ± 0.9 mmHg; P < 0.001), the ratio of right ventricular free wall to left ventricular plus septal weight (0.41 ± 0.03 vs. 0.54 ± 0.03; P < 0.001), and medial thickening of small pulmonary arteries (13 ± 0.4 vs. 16 ± 0.4%; P < 0.01) compared with 4-wk hypoxic controls. Supplementation with mevalonate (50 mg·kg−1·day−1) prevented the attenuation of CHPH induced by simvastatin during 2 wk of hypoxia. Because statins are known to inhibit Rho-kinase (ROCK), we determined expression of ROCK-1 and -2 in whole lung by Western blot and ROCK activity by phosphorylation of the myosin-binding subunit of myosin phosphatase. Expression of both ROCK-1 and -2 were markedly diminished in simvastatin-treated animals during normoxia and hypoxia (2- and 4-wk) exposure ( P < 0.01). ROCK activity was increased threefold under hypoxic conditions and normalized with simvastatin treatment ( P < 0.001). We conclude that simvastatin attenuates and induces regression of established CHPH through inhibition of HMG-CoA reductase. Inhibition of ROCK expression and activity may be an important mechanism of statin effect.

Rosiglitazone attenuates hypoxia-induced pulmonary arterial remodeling

Thiazolidinediones (TZDs) are insulin-sensitizing agents that also decrease systemic blood pressure, attenuate the formation of atherosclerotic lesions, and block remodeling of injured arterial walls. Recently, TZDs were shown to prevent pulmonary arterial (PA) remodeling in rats treated with monocrotaline. Presently we report studies testing the ability of the TZD rosiglitazone (ROSI) to attenuate pathological arterial remodeling in the lung and prevent the development of pulmonary hypertension (PH) in rats subjected to chronic hypoxia. PA remodeling was reduced in ROSI-treated animals exposed to hypoxia compared with animals exposed to hypoxia alone. ROSI treatment blocked muscularization of distal pulmonary arterioles and reversed remodeling and neomuscularization in lungs of animals previously exposed to chronic hypoxia. Decreased PA remodeling in ROSI-treated animals was associated with decreased smooth muscle cell proliferation, decreased collagen and elastin deposition, and increased matrix metalloproteinase-2 activity in the PA wall. Cells expressing the c-Kit cell surface marker were observed in the PA adventitia of untreated animals exposed to hypoxia but not in ROSI-treated hypoxic rats. Right ventricular hypertrophy and cardiomyocyte hypertrophy were also blunted in ROSI-treated hypoxic animals. Interestingly, mean PA pressures were elevated equally in the untreated and ROSI-treated groups, indicating that ROSI had no effect on the development of PH. However, mean PA pressure was normalized acutely in both groups of hypoxia-exposed animals by Fasudil, an agent that inhibits RhoA/Rho kinase-mediated vasoconstriction. We conclude that ROSI can attenuate and reverse PA remodeling and neomuscularization associated with hypoxic PH. However, this agent fails to block the development of PH, apparently because of its inability to repress sustained Rho kinase-mediated arterial vasoconstriction.

Rho kinase-mediated vasoconstriction is important in severe occlusive pulmonary arterial hypertension in rats

Vascular remodeling, rather than vasoconstriction, is believed to account for high vascular resistance in severe pulmonary arterial hypertension (PAH). We have found previously that acute Rho kinase inhibition nearly normalizes PAH in chronically hypoxic rats that have no occlusive neointimal lesions. Here we examined whether Rho kinase-mediated vasoconstriction was also important in a rat model of severe occlusive PAH. Adult rats were exposed to chronic hypoxia ( approximately 10% O(2)) after subcutaneous injection of the vascular endothelial growth factor receptor inhibitor SUGEN 5416. Hemodynamic measurements were made in anesthetized rats after 2 weeks of hypoxia (early group) and 3 weeks of hypoxia plus 2 weeks of normoxia (late group). Both groups developed PAH, with greater severity in the late group. In the early group, intravenous fasudil was more effective than intravenous bradykinin, inhaled NO, or intravenous iloprost in reducing right ventricular systolic pressure. Despite more occlusive vascular lesions, fasudil also markedly reduced right ventricular systolic pressure in late-stage rats. Blood-perfused lungs from late-stage rats showed spontaneous vasoconstriction, which was reversed partially by the endothelin A receptor blocker BQ123 and completely by fasudil or Y-27632. Phosphorylation of MYPT1, a downstream target of Rho kinase, was increased in lungs from both groups of rats, and fasudil (intravenous) reversed the increased phosphorylation in the late group. Thus, in addition to structural occlusion, Rho kinase-mediated vasoconstriction is an important component of severe PAH in SUGEN 5416/hypoxia-exposed rats, and PAH can be significantly reduced in the setting of a severely remodeled lung circulation if an unconventional vasodilator is used.

Dehydroepiandrosterone upregulates soluble guanylate cyclase and inhibits hypoxic pulmonary hypertension

OBJECTIVE

It has been reported that dehydroepiandrosterone is a pulmonary vasodilator and inhibits chronic hypoxia-induced pulmonary hypertension. Additionally, dehydroepiandrosterone has been shown to improve systemic vascular endothelial function. Thus, we hypothesized that chronic treatment with dehydroepiandrosterone would attenuate hypoxic pulmonary hypertension by enhancing pulmonary artery endothelial function.

METHODS AND RESULTS

Rats were randomly assigned to five groups. Three groups received food containing 0, 0.3, or 1% dehydroepiandrosterone during a 3-wk-exposure to simulated high altitude (HA). The other 2 groups were kept at Denver's low altitude (LA) and received food containing 0 or 1% dehydroepiandrosterone. Dehydroepiandrosterone dose-dependently inhibited hypoxic pulmonary hypertension (mean pulmonary artery pressures after treatment with 0, 0.3, and 1% dehydroepiandrosterone=45+/-5, 33+/-2*, and 25+/-1*# mmHg, respectively. *P<0.05 vs. 0% and # vs. 0.3%). Dehydroepiandrosterone (1%, 3 wks) treatment started after rats had been exposed to 3-wk hypoxia also effectively reversed established hypoxic pulmonary hypertension. Pulmonary artery rings isolated from both LA and HA rats treated with 1% dehydroepiandrosterone showed enhanced relaxations to acetylcholine and sodium nitroprusside, but not to 8-bromo-cGMP. In the pulmonary artery tissue from dehydroepiandrosterone-treated LA and HA rats, soluble guanylate cyclase, but not endothelial nitric oxide synthase, protein levels were increased.

CONCLUSION

These results indicate that the protective effect of dehydroepiandrosterone against hypoxic pulmonary hypertension may involve upregulation of pulmonary artery soluble guanylate cyclase protein expression and augmented pulmonary artery vasodilator responsiveness to nitric oxide.