Novel signaling pathways contributing to vascular changes in hypertension

In hypertension, increased peripheral resistance maintains elevated levels of arterial blood pressure. The increase in peripheral resistance results, in part, from abnormal constrictor and dilator responses and vascular remodeling. In this review, we consider four cellular signaling pathways as possible explanations for these abnormal vascular responses: (1) augmented signaling via the epidermal growth factor receptor to cause remodeling of the cerebrovasculature; (2) reduced sphingolipid signaling leading to blunted vasodilation and increased smooth muscle proliferation; (3) increased signaling via Rho/Rho kinase leading to enhanced vasoconstriction, and (4) a relative state of microtubular depolymerization favoring vasoconstriction in hypertension. These novel cell signaling pathways provide new pharmacological targets to reduce total peripheral vascular resistance in hypertension.     

RHO SIGNALING in vascular diseases

Rho signaling pathways in vascular smooth muscle cells are highly activated in hypertension, a condition associated with a variety of vascular diseases, including restenosis injury and atherosclerosis. In this review we suggest that inflammatory cytokines and agonists of G protein-coupled receptors that activate Rho are effective triggers of vascular disease. Accordingly, Rho kinase inhibitors and statins may have therapeutic potential for preventing vascular disease characterized by Rho-mediated cell proliferation and gene expression.     

Animal models of pulmonary hypertension: Rho kinase inhibition

Pulmonary Hypertension is a terminology encompassing a range of etiologically different pulmonary vascular diseases. The most common is that termed pulmonary arterial hypertension or PAH; a rare but often fatal disease characterized by a mean pulmonary arterial pressure of >25?mmHg. PAH is associated with a complex etiology highlighted by core characteristics of increased pulmonary vascular resistance and elevation of mean pulmonary artery pressure. When sustained, pulmonary vascular remodeling occurs and eventually patients pass away due to right heart failure. Hypoxic pulmonary vasoconstriction is an early event occurring in pulmonary hypertension due to chronic exposure to hypoxia. While the underlying mechanisms of hypoxic pulmonary vasoconstriction may be controversial, a role for RhoA/Rho kinase mediated regulation of intracellular Ca(2+) has been recently identified. Further study suggests that RhoA may have an integral role in other pathophysiological processes such as cell proliferation and migration occurring in all forms of PH. Indeed Rho proteins are known to play essential roles in actin cytoskeleton organization in all eukaryotic cells and thus Rho and Rho-GTPases are implicated in fundamental cellular processes such as cellular proliferation, migration, adhesion, apoptosis and gene expression. This review focuses on providing an overview of the role of RhoA/Rho kinase in currently available animal models of pulmonary hypertension.     

Involvement of RhoA/Rho kinase signaling in pulmonary hypertension of the fawn-hooded rat.

The fawn-hooded rat (FHR) develops severe pulmonary hypertension (PH) when raised for the first 3-4 wk of life in the mild hypoxia of Denver's altitude (5,280 ft.). The PH is associated with sustained pulmonary vasoconstriction and pulmonary artery remodeling. Furthermore, lung alveolarization and vascularization are reduced in the Denver FHR. We have recently shown that RhoA/Rho kinase signaling is involved in both vasoconstriction and vascular remodeling in animal models of hypoxic PH. In this study, we investigated the role of RhoA/Rho kinase signaling in the PH of Denver FHR. In alpha-toxin permeabilized pulmonary arteries from Denver FHR, the contractile sensitivity to Ca2+ was increased compared with those from sea-level FHR. RhoA activity and Rho kinase I protein expression in pulmonary arteries of Denver FHR (10-wk-old) were higher than in those of sea-level FHR. Acute inhalation of the Rho kinase inhibitor fasudil selectively reduced the elevated pulmonary arterial pressure in Denver FHR in vivo. Chronic fasudil treatment (30 mg.kg-1.day-1, from birth to 10 wk old) markedly reduced the development of PH and improved lung alveolarization and vascularization in Denver FHR. These results suggest that Rho kinase-mediated sustained vasoconstriction, through increased Ca2+ sensitivity, plays an important role in the established PH and that RhoA/Rho kinase signaling contributes significantly to the development of PH and lung dysplasia in mild hypoxia-exposed FHR.     

Interactive role of tyrosine kinase,protein kinase C,and Rho/Rho kinase systems in the mechanotransduction of vascular smooth muscles

Blood vessels are always subjected to hemodynamic stresses including blood pressure and blood flow. The cerebral artery is particularly sensitive to hemodynamic stresses such as pressure and stretch, and shows contractions that are myogenic in nature; i.e., the mechanical response is generated by the vascular smooth muscle itself. The artery constricts in response to an increase in intraluminal pressure, and dilates in response to a decrease in the intraluminal pressure. We provide herein some insights into the mechanotransduction of vascular tissue; i.e., we discuss how the tissue is receptive to mechanical force and how the latter induces the specific signals leading to myogenic contraction in terms of mechanosensor action and subsequent intracellular signaling. The interactive role of tyrosine kinase, protein kinase C, and Rho/Rho-kinase systems in the mechanotransduction process is discussed, which systems also seem to play an important role in the development of experimental cerebral vasospasm. The study of the mechanotransduction in vascular tissue may aid in clarifying the mechanisms underlying vasospastic episodes and pathologic remodeling in cardiovascular diseases, and may potentially have therapeutic consequences.     

The Lbc Rho Guanine Nucleotide Exchange Factor/α-Catulin Axis Functions in Serotonin-induced Vascular Smooth Muscle Cell Mitogenesis and RhoA/ROCK Activation

Serotonin (5-hydroxytryptamine, 5-HT) is mitogenic for several cell types including pulmonary arterial smooth muscle cells (PASMC), and is associated with the abnormal vascular smooth muscle remodeling that occurs in pulmonary arterial hypertension. RhoA/Rho kinase (ROCK) function is required for 5-HT-induced PASMC mitogenesis, and 5-HT activates RhoA; however, the signaling steps are poorly defined. Rho guanine nucleotide exchange factors (Rho GEFs) transduce extracellular signals to Rho, and we found that 5-HT treatment of PASMC led to increased membrane-associated Lbc Rho GEF, suggesting modulation by 5-HT. Lbc knockdown by siRNA attenuated 5-HT-induced thymidine uptake in PASMC, indicating a role in PASMC mitogenesis. 5-HT triggered Rho-dependent serum response factor-mediated reporter activation in PASMC, and this was reduced by Lbc depletion. Lbc knockdown reduced 5-HT-induced RhoA/ROCK activation, but not p42/44 ERK MAP kinase activation, suggesting that Lbc is an intermediary between 5-HT and RhoA/ROCK, but not ERK. 5-HT stimulation of PASMC led to increased association between Lbc, RhoA, and the α-catulin scaffold. Furthermore, α-catulin knockdown attenuated 5-HT-induced PASMC thymidine uptake. 5-HT-induced PASMC mitogenesis was reduced by dominant-negative G_q protein, suggesting cooperation with Lbc/α-catulin. These results for the first time define a Rho GEF involved in vascular smooth muscle cell growth and serotonin signaling, and suggest that Lbc Rho GEF family members play distinct roles. Thus, the Lbc/α-catulin axis participates in 5-HT-induced PASMC mitogenesis and RhoA/ROCK signaling, and may be an interventional target in diseases involving vascular smooth muscle remodeling.     

G12-G13-LARG-mediated signaling in vascular smooth muscle is required for salt-induced hypertension

The tone of vascular smooth muscle cells is a primary determinant of the total peripheral vascular resistance and hence the arterial blood pressure. Most forms of hypertension ultimately result from an increased vascular tone that leads to an elevated total peripheral resistance. Regulation of vascular resistance under normotensive and hypertensive conditions involves multiple mediators, many of which act through G protein-coupled receptors on vascular smooth muscle cells. Receptors that mediate vasoconstriction couple with the G-proteins G(q)-G11 and G12-G13 to stimulate phosphorylation of myosin light chain (MLC) via the Ca2+/MLC kinase- and Rho/Rho kinase-mediated signaling pathways, respectively. Using genetically altered mouse models that allow for the acute abrogation of both signaling pathways by inducible Cre/loxP-mediated mutagenesis in smooth muscle cells, we show that G(q)-G11-mediated signaling in smooth muscle cells is required for maintenance of basal blood pressure and for the development of salt-induced hypertension. In contrast, lack of G12-G13, as well as of their major effector, the leukemia-associated Rho guanine nucleotide exchange factor (LARG), did not alter normal blood pressure regulation but did block the development of salt-induced hypertension. This identifies the G12-G13-LARG-mediated signaling pathway as a new target for antihypertensive therapies that would be expected to leave normal blood pressure regulation unaffected.     

ERM蛋白在微血管内皮细胞通透性调控中的研究进展

埃兹蛋白(Ezrin)/根蛋白(Radixin)/膜突蛋白(Moesin)(ERM)是细胞膜与胞内骨架的连接蛋白,具有高度同源性。细胞外刺激因子可通过多种信号通路磷酸化ERM蛋白,使细胞骨架重构,从而调控微血管内皮细胞通透性,在感染、炎症、代谢异常等病理过程中发挥作用。ERM功能调节的一个重要环节就是其羧基末端苏氨酸残基磷酸化后引起ERM构象的改变,暴露的羧基末端尾部的肌动蛋白(actin)-细胞骨架结合位点;故通过ERM的桥接作用,可将肌动蛋白微丝与细胞膜相连,使血管内皮细胞屏障功能发生变化。目前已知能使ERM磷酸化的激酶有蛋白激酶C(PKC)、促分裂原活化蛋白激酶(MAPK)、Rho相关激酶(ROCK),分别通过p38-MAPK、Rho/ROCK、PKC信号通路参与微血管内皮屏障功能的调控。本文旨在阐述ERM及其相关信号通路在微血管内皮细胞通透性调控中发挥的作用。     

Inhibition of serotonin-induced mitogenesis, migration, and ERK MAPK nuclear translocation in vascular smooth muscle cells by atorvastatin

The HMG-CoA reductase inhibitors, statins, have pleiotropic effects which may include interference with the isoprenylation of Ras and Rho small GTPases. Statins have beneficial effects in animal models of pulmonary hypertension, although their mechanisms of action remain to be determined. Serotonin [5-hydroxytryptamine (5-HT)] is implicated in the process of pulmonary artery smooth muscle (PASM) remodeling as part of the pathophysiology of pulmonary hypertension. We examined the effect of atorvastatin on 5-HT-induced PASM cell responses. Atorvastatin dose dependently inhibits 5-HT-induced mitogenesis and migration of cultured bovine PASM cells. Inhibition by atorvastatin was reversed by mevalonate and geranylgeranylpyrophosphate (GGPP) supplement, suggesting that the statin targets a geranylgeranylated protein such as Rho. Concordantly, atorvastatin inhibits 5-HT-induced cellular RhoA activation, membrane localization, and Rho kinase-mediated phosphorylation of myosin phosphatase-1 subunit. Atorvastatin reduced activated RhoA-induced serum response factor-mediated reporter activity in HEK293 cells, indicating that atorvastatin inhibits Rho signaling, and this was reversed by GGPP. While 5-HT-induced ERK MAP and Akt kinase activation were unaffected by atorvastatin, 5-HT-induced ERK nuclear translocation was attenuated in a GGPP-dependent fashion. These studies suggest that atorvastatin inhibits 5-HT-induced PASM cell mitogenesis and migration through targeting isoprenylation which may, in part, attenuate the Rho pathway, a mechanism that may apply to statin effects on in vivo models of pulmonary hypertension.     

Cellular signaling in Abdominal Aortic Aneurysm

Abdominal aortic aneurysms (AAAs) are highly lethal cardiovascular diseases without effective medications. However, the molecular and signaling mechanisms remain unclear. A series of pathological cellular processes have been shown to contribute to AAA formation, including vascular extracellular matrix remodeling, inflammatory and immune responses, oxidative stress, and dysfunction of vascular smooth muscle cells. Each cellular process involves complex cellular signaling, such as NF-κB, MAPK, TGFβ, Notch and inflammasome signaling. In this review, we discuss how cellular signaling networks function in various cellular processes during the pathogenesis and progression of AAA. Understanding the interaction of cellular signaling networks with AAA pathogenesis as well as the crosstalk of different signaling pathways is essential for the development of novel therapeutic approaches to and personalized treatments of AAA diseases.     

Cdc42 and RhoA are differentially regulated during arachidonate-mediated HeLa cell adhesion

Cell adhesion to extracellular matrix requires stimulation of an eicosanoid signaling pathway through the metabolism of arachidonate by 5-lipoxygenase to leukotrienes and cyclooxygenase-1/2 to prostaglandins, as well as activation of the small GTPase signaling pathway involving Cdc42 and Rho. These signaling pathways direct remodeling of the actin cytoskeleton during the adhesion process, specifically the polymerization of actin during cell spreading and the bundling of actin filaments when cells migrate. However, few studies linking these signaling pathways have been described in the literature. We have previously shown that HeLa cell adhesion to collagen requires oxidation of arachidonic acid (AA) by lipoxygenase for actin polymerization and cell spreading, and cyclooxygenase for bundling actin filaments during cell migration. We demonstrate that small GTPase activity is required for HeLa cell spreading upon gelatin, and that Cdc42 is activated while Rho is downregulated during the spreading process. Using constitutively active and dominant negative expression studies, we show that Cdc42 is required for HeLa cell spreading and migration, while activated RhoA is antagonistic towards spreading. Constitutively active RhoA promotes cell migration and increases the degree of actin bundling in HeLa cells. Further, we demonstrate that activation of either the AA oxidation pathway or the small GTPase pathway cannot rescue inhibition of spreading when the alternate pathway is blocked. Our results suggest (1) both the eicosanoid signaling pathway and small GTPase activation are required during HeLa cell adhesion, and (2) these signaling pathways converge to properly direct remodeling of the actin cytoskeleton during HeLa cell spreading and migration upon collagen.     

Perspectives on endothelial-to-mesenchymal transition: potential contribution to vascular remodeling in chronic pulmonary hypertension

All forms of pulmonary hypertension are characterized by structural changes in pulmonary arteries. Increased numbers of cells expressing alpha-smooth muscle (alpha-SM) actin is a nearly universal finding in the remodeled artery. Traditionally, it was assumed that resident smooth muscle cells were the exclusive source of these newly appearing alpha-SM actin-expressing cells. However, rapidly emerging experimental evidence suggests other, alternative cellular sources of these cells. One possibility is that endothelial cells can transition into mesenchymal cells expressing alpha-SM actin and that this process contributes to the accumulation of SM-like cells in vascular pathologies. We review the evidence that endothelial-mesenchymal transition is an important contributor to cardiac and vascular development as well as to pathophysiological vascular remodeling. Recent work has provided evidence for the role of transforming growth factor-beta, Wnt, and Notch signaling in this process. The potential roles of matrix metalloproteinases and serine proteases are also discussed. Importantly, endothelial-mesenchymal transition may be reversible. Thus insights into the mechanisms controlling endothelial-mesenchymal transition are relevant to vascular remodeling and are important as we consider new therapies aimed at reversing pulmonary vascular remodeling.     

New mechanisms of pulmonary arterial hypertension: role of Ca²⁺ signaling

Pulmonary arterial hypertension (PAH) is a severe and progressive disease that usually culminates in right heart failure and death if left untreated. Although there have been substantial improvements in our understanding and significant advances in the management of this disease, there is a grim prognosis for patients in the advanced stages of PAH. A major cause of PAH is increased pulmonary vascular resistance, which results from sustained vasoconstriction, excessive pulmonary vascular remodeling, in situ thrombosis, and increased pulmonary vascular stiffness. In addition to other signal transduction pathways, Ca(2+) signaling in pulmonary artery smooth muscle cells (PASMCs) plays a central role in the development and progression of PAH because of its involvement in both vasoconstriction, through its pivotal effect of PASMC contraction, and vascular remodeling, through its stimulatory effect on PASMC proliferation. Altered expression, function, and regulation of ion channels and transporters in PASMCs contribute to an increased cytosolic Ca(2+) concentration and enhanced Ca(2+) signaling in patients with PAH. This review will focus on the potential pathogenic role of Ca(2+) mobilization, regulation, and signaling in the development and progression of PAH.     

Vascular smooth muscle cell proliferation as a therapeutic target. Part 1: molecular targets and pathways

Cardiovascular diseases are a major cause of human death worldwide. Excessive proliferation of vascular smooth muscle cells contributes to the etiology of such diseases, including atherosclerosis, restenosis, and pulmonary hypertension. The control of vascular cell proliferation is complex and encompasses interactions of many regulatory molecules and signaling pathways. Herein, we recapitulated the importance of signaling cascades relevant for the regulation of vascular cell proliferation. Detailed understanding of the mechanism underlying this process is essential for the identification of new lead compounds (e.g., natural products) for vascular therapies.     

平滑肌22α蛋白在血管稳态和血管重构中的作用

有关血管稳态和重构的分子机制一直是近年来的研究热点,也被视为治疗血管损伤性疾病的突破点.大量研究证实,血管损伤修复及病理性重构过程与血管平滑肌细胞(vascular smooth muscle cells,VSMCs)的表型转化、异常增殖与迁移、细胞衰老关系密切.平滑肌22α(smooth muscle 22α,SM2...     

Attenuation of acute hypoxic pulmonary vasoconstriction and hypoxic pulmonary hypertension in mice by inhibition of Rho-kinase

RhoA GTPase mediates a variety of cellular responses, including activation of the contractile apparatus, growth, and gene expression. Acute hypoxia activates RhoA and, in turn, its downstream effector, Rho-kinase, and previous studies in rats have suggested a role for Rho/Rho-kinase signaling in both acute and chronically hypoxic pulmonary vasoconstriction. We therefore hypothesized that activation of Rho/Rho-kinase in the pulmonary circulation of mice contributes to acute hypoxic pulmonary vasoconstriction and chronic hypoxia-induced pulmonary hypertension and vascular remodeling. In isolated, salt solution-perfused mouse lungs, acute administration of the Rho-kinase inhibitor Y-27632 (1 x 10(-5) M) attenuated hypoxic vasoconstriction as well as that due to angiotensin II and KCl. Chronic treatment with Y-27632 (30 mg x kg(-1) x day(-1)) via subcutaneous osmotic pump decreased right ventricular systolic pressure, right ventricular hypertrophy, and neomuscularization of the distal pulmonary vasculature in mice exposed to hypobaric hypoxia for 14 days. Analysis of a small number of proximal pulmonary arteries suggested that Y-27632 treatment reduced the level of phospho-CPI-17, a Rho-kinase target, in hypoxic lungs. We also found that endothelial nitric oxide synthase protein in hypoxic lungs was augmented by Y-27632, suggesting that enhanced nitric oxide production might have played a role in the Y-27632-induced attenuation of chronically hypoxic pulmonary hypertension. In conclusion, Rho/Rho-kinase activation is important in the effects of both acute and chronic hypoxia on the pulmonary circulation of mice, possibly by contributing to both vasoconstriction and vascular remodeling.     

ACE2/Ang-(1–7) signaling and vascular remodeling

The renin-angiotensin system (RAS) regulates vascular tone and plays a critical role in vascular remodeling, which is the result of a complex interplay of alterations in vascular tone and structure. Inhibition of the RAS has led to important pharmacological tools to prevent and treat vascular diseases such as hypertension, diabetic vasculopathy and atherosclerosis. Angiotensin converting enzyme 2 (ACE2) was recently identified as a multifunctional monocarboxypeptidase responsible for the conversion of angiotensin (Ang) II to Ang-(1–7). The ACE2/Ang-(1–7) signaling has been shown to prevent cellular proliferation, pathological hypertrophy, oxidative stress and vascular fibrosis. Thus, the ACE2/Ang-(1–7) signaling is deemed to be beneficial to the cardiovascular system as a negative regulator of the RAS. The addition of the ACE2/Ang-(1–7) signaling to the complexities of the RAS may lead to the development of novel therapeutics for the treatment of hypertension and other vascular diseases. The present review considers recent findings regarding the ACE2/Ang-(1–7) signaling and focuses on its regulatory roles in processes related to proliferation, inflammation, vascular fibrosis and remodeling, providing proof of principle for the potential use of ACE2 as a novel therapy for vascular disorders related to vascular remodeling.     

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.     

Effect of antihypertensive treatment on small artery remodeling in hypertension

Blood vessels are remodeled in hypertension both structurally and functionally. The changes that occur in their structure, mechanical properties, and function contribute to blood pressure elevation and to complications of hypertension. We studied the remodeling of small arteries in experimental animals and humans. Smooth muscle cells of small arteries are restructured around a smaller lumen, with significant remodeling of the extracellular matrix and collagen and fibronectin deposition. Interestingly, there is no evidence of net growth of the vascular wall (which results in so-called eutrophic remodeling), particularly in the milder forms of human essential hypertension. Hypertrophic remodeling and increased small artery stiffness may be found in more severe forms of hypertension. Almost all hypertensive patients have vascular structural remodeling. However, only some exhibit endothelial dysfunction. This is particularly true in mild hypertension, in which endothelial dysfunction is less common. A 1-year treatment of hypertensive patients with angiotensin converting enzyme inhibitors, angiotensin AT1 receptor antagonists, and long acting calcium channel blockers corrected small artery structure and, to variable degrees depending on the agents used, impaired endothelial function. In contrast, beta blockers did not improve structure, function, or mechanics of vessels. When beta-blocker-treated patients were switched to an AT1 receptor antagonist, small artery structure and impaired endothelial function were corrected. The vascular protective action of some antihypertensive agents may contribute to improve outcome for hypertensive patients, although this is presently unproven.