Characterization of the role of Rho activating signalling complexes in G protein-coupled receptor induced cardiac fibrosis

Dans certaines conditions pathologiques, telles que l'hypertension artérielle ou l'infarctus du myocarde, le coeur répond à une augmentation de la post-charge par des processus de remodelage aboutissant à une hypertrophie du ventricule gauche. L'hypertrophie cardiaque est caractérisée par une croissance hypertrophique des cardiomyocytes, ainsi que par une différenciation des fibroblastes en un phenotype présentant une capacité accrue de synthèse protéiques, nommés myofibroblastes. Ceci résulte en une accumulation excessive des constituants de la matrice extracellulaire, ou autrement dit fibrose. En raison de son effet délétère sur la contractilité du coeur, menant sur le long terme à une insuffisance cardiaque, de nombreux efforts ont été déployés, afin de définir les mécanismes moléculaires impliqués dans la réponse profibrotique. A ce jour, de nombreuses études indiquent que la petite GTPase RhoA pourrait être un médiateur important de la réponse profibrotique du myocarde. Cependant, les facteurs d'échanges impliqués dans la transduction de signaux profibrotiques, via la régulation de son activité au niveau des fibroblastes cardiaques, n'ont pas encore été identifiés. De précédentes études menées dans le laboratoire, ont identifiées une nouvelle protein d'ancrage de la PKA, exprimée majoritairement dans le coeur, nommée AKAP-Lbc. Il a été montré que cette protéine, en plus de sa fonction de protein d'ancrage, possédait une activité de facteur d'échange de nucléotide guanine (GEF) pour la petite GTPase RhoA. Au niveau des cardiomyocytes, il a été montré que l'AKAP-Lbc participe à une voie de signalisation pro-hypertrophique, incluant la sous-unité alpha de la protéine G hétérotrimerique G12 et RhoA. Chose intéressante, des observations antérieures à cette étude, indiquent que dans le coeur, l'AKAP-Lbc est également exprimée dans les fibroblastes. Cependant aucunes études n'a encore reporté de fonction pour ce facteur d'échange dans les fibroblastes cardiaques. Dans ce travail, les résultats obtenus indiquent que dans les fibroblastes cardiaques, I'activation de RhoA par l'AKAP-Lbc est impliquée dans la transmission de signaux profibrotiques, en aval des récépteurs à l'angiotensine II. En particulier, nous avons observé que la suppression de l'expression de l'AKAP-Lbc dans les fibroblastes ventriculaires de rat adultes, réduisait fortement Γ activation de Rho induite par l'angiotensine II, la déposition de collagène, la capacité migratoire des fibroblastes ainsi que leur différenciation en myofibroblastes. A notre connaissance, l'AKAP-Lbc est le premier RhoGEF identifié comme médiateur de la réponse profibrotique dans les fibroblastes cardiaques. - In pathological conditions such as chronic hypertension or myocardial infarction, the myocardium is subjected to various biomechanical and biochemical stresses, and undergoes an adverse ventricular remodelling process associated with cardiomyocytes hypertrophy and excess deposition of extracellular matrix proteins resulting in fibrosis. During the fibrotic response, cardiac fibroblasts differentiate into a more mobile and contractile phenotype termed myofibroblasts. These cells, possess a greater synthetic ability to produce ECM proteins and have been implicated in diseases with increased ECM deposition including cardiac fibrosis. Because fibrosis impairs myocardial contractility and is associated with the progression to heart failure, a major cause of lethality worldwide, many efforts have been made to define the molecular players involved in this process. During these last years, increasing evidence suggests a role for the small GTPase RhoA in mediating the fibrotic response in CFbs. However the identity of the exchange factors that modulate its activity and transduce fibrotic signals in CFbs is still unknown. Earlier work in our laboratory identified a novel PKA anchoring protein expressed in the heart termed AKAP-Lbc that has been shown to function as anchoring protein as well as a guanine nucleotide exchange factor (GEF) for the small GTPase RhoA. In response to several hypertrophic stimuli we have shown that RhoGEF activity of AKAP-Lbc mediated by Gan promotes the activation of a signaling pathway including RhoA, leading to cardiomyocytes hypertrophy. Within the heart, previous observations made in the laboratory indicated that AKAP-Lbc was also expressed in fibroblasts. However its role in cardiac fibroblasts remained to be determined. In the present study, we show that AKAP-Lbc is critical for activating RhoA and transducing profibrotic signals downstream of angiotensin II receptors in cardiac fibroblasts. In particular, our results indicate that suppression of AKAP-Lbc expression by infecting adult rat ventricular fibroblasts with lentiviruses encoding AKAP-Lbc specific short hairpin RNAs strongly reduces angiotensin II-induced RhoA activation, collagen deposition as well as cell migration and differentiation. These findings identify AKAP-Lbc as the first Rho-guanine nucleotide exchange factor involved in a profibrotic signalling pathway at the level of cardiac fibroblasts.

Cardiovascular influences of alpha1b-adrenergic receptor defect in mice.

BACKGROUND: The alpha1-adrenergic receptors (alpha1-ARs) play a key role in cardiovascular homeostasis. However, the functional role of alpha1-AR subtypes in vivo is still unclear. The aim of this study was to evaluate the cardiovascular influences of alpha1b-AR. METHODS AND RESULTS: In transgenic mice lacking alpha1-AR (KO) and their wild-type controls (WT), we evaluated blood pressure profile and cardiovascular remodeling induced by the chronic administration (18 days via osmotic pumps) of norepinephrine, angiotensin II, and subpressor doses of phenylephrine. Our results indicate that norepinephrine induced an increase in blood pressure levels only in WT mice. In contrast, the hypertensive state induced by angiotensin II was comparable between WT and KO mice. Phenylephrine did not modify blood pressure levels in either WT or KO mice. The cardiac hypertrophy and eutrophic vascular remodeling evoked by norepinephrine was observed only in WT mice, and this effect was independent of the hypertensive state because it was similar to that observed during subpressor phenylephrine infusion. Finally, the cardiac hypertrophy induced by thoracic aortic constriction was comparable between WT and KO mice. CONCLUSIONS: Our data demonstrate that the lack of alpha1b-AR protects from the chronic increase of arterial blood pressure induced by norepinephrine and concomitantly prevents cardiovascular remodeling evoked by adrenergic activation independently of blood pressure levels.

Pharmacodynamic and humoral effects of single intravenous doses of captopril in normal subjects.

The blood pressure, heart rate and humoral responses to single intravenous doses of the angiotensin converting enzyme inhibitor captopril were evaluated in 5 volunteers on a free salt intake. Each subject was given at one-week intervals a 1, 5 and 25 mg intravenous dose of captopril as well as the vehicle of captopril. The study was conducted in a single-blind fashion and the order of treatment phases was randomized. Captopril was found to inhibit the renin-angiotensin system in a dose-dependent fashion. A fall in circulating angiotensin II was observed with doses of 1 and 5 mg. Plasma angiotensin II was not detectable 15 min after the 25 mg dose. Acute inhibition of angiotensin converting enzyme with intravenous captopril had no effect on blood pressure and heart rate.

Effects of neuropeptide Y on the blood pressure response to various vasoconstrictor agents.

Neuropeptide Y (NPY) is known to potentiate the pressor effect of norepinephrine. In the present work, we evaluated in unanesthetized normotensive rats the effect of NPY on blood pressure responsiveness not only to norepinephrine, but also to tyramine, a sympathomimetic agent acting indirectly to B-HT933, a selective alpha-2 adrenoceptor stimulant, to angiotensin II and vasopressin. Dose-response curves to the various pressor agents were established starting at the 45th min of an i.v. infusion with either NPY (0.025 and 0.1 microgram/min) or its vehicle. The two doses of NPY increased blood pressure by an average of approximately 6 mm Hg, which was not significantly different from the vehicle-induced blood pressure changes. NPY significantly enhanced the pressor effect of norepinephrine, tyramine and angiotensin II, but not that of B-HT933 and vasopressin. We also tested whether NPY inhibits the enzyme activity of Na, K-adenosine triphosphatase using a purified toad kidney preparation. Concentrations of NPY from 10(-14) M up to 10(-6) M had no effect on the enzyme activity. It appears therefore that the blood pressure potentiating effect of NPY is not restricted to alpha adrenoceptor stimulation with norepinephrine, but involves also the vasoconstrictor hormone angiotensin II. This NPY-induced potentiation does not seem to depend upon stimulation of alpha-2 adrenoceptors or inhibition of Na,K-adenosine triphosphatase.

Cellular localization, expression and regulation of neuropeptide Y in kidneys of hypertensive rats.

Neuropeptide Y (NPY) is a key modulator of the autonomic nervous system playing pivotal roles in cardiovascular and neuronal functions. In this study, we assessed the cellular localization and gene expression of NPY in rat kidneys. We also examined the relationship between NPY gene expression and renin in two rat models of hypertension (two-kidney, one-clip renal hypertension (2K1C), and deoxycorticosterone-salt-induced hypertension (DOCA-salt)) characterized by a similar blood pressure elevation. In situ hybridization and immunohistochemistry, using anti-NPY or anti-C-flanking peptide of NPY (CPON) antibodies, showed that NPY transcript and protein were colocalized in the tubules of rat kidneys. During experimental hypertension, NPY mRNA was decreased in both kidneys of the 2K1C animals, but not in the kidney of DOCA-salt rats. In 2K1C rats, renal NPY content was also decreased. The difference in NPY gene expression between 2K1C rats (a high renin model of hypertension) and DOCA-salt rats (a low renin model of hypertension) suggests that circulating angiotensin II plays a role in local renal NPY gene expression and that the elevated blood pressure per se is not the primary factor responsible for the control of NPY gene expression in the kidney.

Clinical pharmacology of atrial natriuretic (3-28) eicosahexapeptide.

The clinical pharmacology of a synthetic rat atrial natriuretic peptide (rANP) was evaluated in normal volunteers. During a dose-ranging study at 1-40 micrograms/min we observed a dose-dependent decrease in mean intra-arterial blood pressure, an acceleration of the heart rate and a transient increase in blood flow to the skin. During a 4-h constant-dose infusion at 0.5 and 5.0 micrograms/min, inulin clearance remained unchanged but there was a dose-related fall in paraaminohippurate (PAH) clearance and an increase in the filtration fraction. Urinary excretion of sodium, chloride and calcium increased in a dose-related fashion, but with the high dose the excretion curve had a bell-shape. No change in plasma renin activity, angiotensin II and aldosterone was observed during the rANP infusion despite the excretion of large amounts of sodium and a blood pressure reduction with the high dose. Indocyanine green clearance, a measure of hepatic blood flow, was significantly decreased by a 2-h rANP infusion at 1.0 microgram/min. In normal volunteers, therefore, rANP induced vasodilation and blood pressure reduction, a decrease in renal and hepatic blood flow and a natriuretic and transient diuretic effect without activation of the renin-angiotensin-aldosterone system.

Angiotensinergic and noradrenergic neurons in the rat and human heart.

Although the physiological and pharmacological evidences suggest a role for angiotensin II (Ang II) with the mammalian heart, the source and precise location of Ang II are unknown. To visualize and quantitate Ang II in atria, ventricular walls and interventricular septum of the rat and human heart and to explore the feasibility of local Ang II production and function, we investigated by different methods the expression of proteins involved in the generation and function of Ang II. We found mRNA of angiotensinogen (Ang-N), of angiotensin converting enzyme, of the angiotensin type receptors AT(1A) and AT(2) (AT(1B) not detected) as well as of cathepsin D in any part of the hearts. No renin mRNA was traceable. Ang-N mRNA was visualized by in situ hybridization in atrial ganglial neurons. Ang II and dopamine-β-hydroxylase (DβH) were either colocalized inside the same neuronal cell or the neurons were specialized for Ang II or DβH. Within these neurons, the vesicular acetylcholine transporter (VAChT) was neither colocalized with Ang II nor DβH, but VAChT-staining was found with synapses en passant encircle these neuronal cells. The fibers containing Ang II exhibited with blood vessels and with cardiomyocytes supposedly angiotensinergic synapses en passant. In rat heart, right atrial median Ang II concentration appeared higher than septal and ventricular Ang II. The distinct colocalization of neuronal Ang II with DβH in the heart may indicate that Ang II participates together with norepinephrine in the regulation of cardiac functions: Produced as a cardiac neurotransmitter Ang II may have inotropic, chronotropic or dromotropic effects in atria and ventricles and contributes to blood pressure regulation.

Nerve growth factor (NGF) stimulation of cholinergic telencephalic neurons in aggregating cell cultures.

The addition of nerve growth factor (2.5S NGF) to serum-free aggregating cell cultures of fetal rat telencephalon greatly stimulated the developmental increase in choline acetyltransferase activity. Two other neuronal enzymes, acetylcholinesterase and glutamic acid decarboxylase, showed only slightly increased activities after NGF treatment whereas the total protein content of the cultures and the activity of 2',3'- cyclic nucleotide phosphodiesterase remained unchanged. The stimulation of choline acetyltransferase was dependent on the NGF media concentrations, showing a 50% maximum effect (120% increase) at approximately 3 ng/ml (10-10 M 2.5S NGF). NGF treatments during different culture periods showed that the cholinergic neurons remained responsive for at least 19 days. The continued treatment was the most effective; however, an initial treatment for only 5 days still caused a significant stimulation of choline acetyltransferase on day 19. The observed stimulation appeared to be specific to NGF. Univalent antibody fragments (Fab) against 2.5S NGF completely abolished the NGF-dependent increase in choline acetyltransferase activity, whereas Fab fragments of control IgG were ineffective. Furthermore, angiotensin II, added in high amounts to the cultures, showed no stimulatory effect. The present results suggest that certain populations of rat brain neurons are responsive to nerve growth factor.

Increased Expression of Renal Cyclooxygenase-2 and Neuronal Nitric Oxide Synthase in Hypertensive Cx40-Deficient Mice.

Cx40-deficient mice (Cx40-/-) are hypertensive due to increased renin secretion. We evaluated the renal expression of neuronal nitric oxide synthase (nNOS) and cyclooxygenases COX-1 and COX-2, three macula densa enzymes. The levels of nNOS were increased in kidneys of Cx40-/- mice, as well as in those of wild-type (WT) mice subjected to the two-kidney one-clip model of hypertension. In contrast, the levels of COX-2 expression were only increased in the hypoperfused kidney of Cx40-/- mice. Treatment with indomethacin lowered blood pressure and renin mRNA in Cx40-/- mice without affecting renin levels, indicating that changes in COX-2 do not cause the altered secretion of renin. Suppression of NOS activity by N(G)-nitro-L-arginine methyl ester (L-NAME) decreased renin levels in Cx40-/- animals, indicating that NO regulates renin expression in the absence of Cx40. Treatment with candesartan normalized blood pressure in Cx40-/- mice, and decreased the levels of both COX-2 and nNOS. After a treatment combining candesartan and L-NAME, the blood pressure of Cx40-/- mice was higher than that of WT mice, showing that NO may counterbalance the vasoconstrictor effects of angiotensin II in Cx40-/- mice. These data document that renal COX-2 and nNOS are differentially regulated due to the elevation of renin-dependent blood pressure in mice lacking Cx40.

Fixed-dose combinations as initial therapy for hypertension : a review of approved agents and a guide to patient selection.

Recent guidelines recommend initiation of antihypertensive therapy with fixed-dose combinations in high-risk patients because such patients usually need two or more blood pressure (BP)-lowering agents in order to normalize their BP. Agents that block the renin-angiotensin system (ACE inhibitors or angiotensin II receptor antagonists [angiotensin receptor blockers; ARBs]) are preferred for the management of hypertension in most patients exhibiting subclinical target organ damage, or established cardiovascular or renal diseases. Unless contraindicated they should be one of the components of fixed-dose combinations, whereas the other component may be either a calcium channel antagonist or a thiazide diuretic. Fixed-dose combinations containing an ACE inhibitor or ARB plus a calcium channel antagonist appear particularly effective in preventing complications of coronary heart disease.

Pharmacokinetic evaluation of losartan.

Introduction: Blockade of the renin-angiotensin system is one of the major therapeutic strategies in the management of patients with essential hypertension, congestive heart failure and diabetic as well as non-diabetic renal diseases. As the first angiotensin II receptor blocker (ARB) on the market, losartan belongs to the most frequently prescribed ARB. Area covered : The present review examines the pharmacokinetics of losartan with a special discussion on the dose of losartan that should be used in clinical practice to obtain the maximal benefits of the drug. Readers are provided with arguments suggesting that the dose of 50 mg losartan is probably too low and that losartan should preferably be prescribed at the dose of 100 mg/day or higher. Expert opinion : Losartan is an effective antagonist of angiotensin II AT(1) receptors which has been shown to provide important clinical benefits in patients with hypertension, congestive heart failure and renal diseases. Losartan should be prescribed at the dose of 100 mg/day and the use of higher doses should be reconsidered in future studies to improve its clinical efficacy.

Rôle de la bradykinine dans l'hypotension induite par le fragment actif dérivé du facteur XII [Role of bradykinin in hypotension induced by the active factor derived from factor XII]

The active fragment derived from factor XII (factor XIIf) was purified from human plasma and administered intravenously to normotensive conscious rats. Factor XIIf-mediated hypotension was dose-dependent and augmented by pretreatment with captopril, an inhibitor of the angiotensin I- and bradykinin-processing enzyme. In contrast, factor XIIf-induced hypotension was not enhanced by blockade of the renin-angiotensin system by saralasin, a competitive antagonist of angiotensin II at the vascular receptor level. These results suggest that factor XIIf-mediated hypotension is due to the formation of bradykinin.

Blood pressure, cardiac, and renal responses to salt and deoxycorticosterone acetate in mice: role of Renin genes.

Several studies have demonstrated that mice are polymorphic for the number of renin genes, with some inbred strains harboring one gene (Ren-1(c)) and other strains containing two genes (Ren-1(d) and Ren-2). In this study, the effects of 1% salt and deoxycorticosterone acetate (DOCA)/salt were investigated in one- and two-renin gene mice, for elucidation of the role of renin in the modulation of BP, cardiac, and renal responses to salt and DOCA. The results demonstrated that, under baseline conditions, mice with two renin genes exhibited 10-fold higher plasma renin activity, 100-fold higher plasma renin concentrations, elevated BP (which was angiotensin II-dependent), and an increased cardiac weight index, compared with one-renin gene mice (all P < 0.01). The presence of two renin genes markedly increased the BP, cardiac, and renal responses to salt. The number of renin genes also modulated the responses to DOCA/salt. In one-renin gene mice, DOCA/salt induced significant renal and cardiac hypertrophy (P < 0.01) even in the absence of any increase in BP. Treatment with losartan, an angiotensin II AT(1) receptor antagonist, decreased BP in two-renin gene mice but not in one-renin gene mice. However, losartan prevented the development of cardiac hypertrophy in both groups of mice. In conclusion, these data demonstrate that renin genes are important determinants of BP and of the responses to salt and DOCA in mice. The results confirm that the Ren-2 gene, which controls renin production mainly in the submaxillary gland, is physiologically active in mice and is not subject to the usual negative feedback control. Finally, these data provide further evidence that mineralocorticoids promote cardiac hypertrophy even in the absence of BP changes. This hypertrophic process is mediated in part by the activation of angiotensin II AT(1) receptors.

Multiples étiologies de l'angioedème [The multiple etiologies of angioedema]

L'angioedème est une affection fréquente, dont les étiologies sont multiples. Les angioedèmes habituellement associés à une urticaire sont en général dus à une libération d'histamine et répondent en principe aux antihistaminiques et à l'adrénaline. Il s'agit des angioedèmes d'origine allergique, des réactions anaphylactoïdes, souvent d'origine médicamenteuse (AINS), des angioedèmes physiques et de l'angioedème récurrent idiopathique. La bradykinine joue certainement un rôle dans la genèse des angioedèmes associés aux inhibiteurs de l'enzyme de conversion de l'angiotensine et rarement aux antagonistes du récepteur de l'angiotensine II, ainsi que dans celle des rares angioedèmes héréditaires ou liés à un déficit acquis en Ci-inhibiteur. L'urticaire est alors absente et les antihistaminiques ainsi que l'adrénaline sont inefficaces. Angioedema is a frequent disorder with multiple aetiologies. Angioedemas associated with urticaria are usually caused by histamine release and respond to anti-histamines and adrenalin. They include allergic angioedemas, anaphylactoid reactions (mostly drug-induced, e.g. NSAID), physical angioedemas and recurrent idiopathic angioedema. Bradykinin probably plays a causative role in the pathogenesis of ACE-inhibitor or angiotensin II receptor blocker related angioedemas, as well as in the pathogenesis of the rare hereditary or acquired C1-inhibitor deficiency angioedemas. Urticaria is then typically absent and anti-histamines, as well as adrenalin, are ineffective

Extracellular superoxide dismutase is a major determinant of nitric oxide bioavailability: in vivo and ex vivo evidence from ecSOD-deficient mice.

The bioavailability of nitric oxide (NO) within the vascular wall is limited by superoxide anions (O2.-). The relevance of extracellular superoxide dismutase (ecSOD) for the detoxification of vascular O2.- is unknown. We determined the involvement of ecSOD in the control of blood pressure and endothelium-dependent responses in angiotensin II-induced hypertension and renovascular hypertension induced by the two-kidney, one-clip model in wild-type mice and mice lacking the ecSOD gene. Blood pressure was identical in sham-operated ecSOD+/+ and ecSOD-/- mice. After 6 days of angiotensin II-treatment and 2 and 4 weeks after renal artery clipping, blood pressure was significantly higher in ecSOD-/- than ecSOD+/+ mice. Recombinant ecSOD selectively decreased blood pressure in hypertensive ecSOD-/- mice, whereas ecSOD had no effect in normotensive and hypertensive ecSOD+/+ mice. Compared with sham-operated ecSOD+/+ mice, sham-operated ecSOD-/- mice exhibited attenuated acetylcholine-induced relaxations. These responses were further depressed in vessels from clipped animals. Vascular O2.-, as measured by lucigenin chemiluminescence, was higher in ecSOD-/- compared with ecSOD+/+ mice and was increased by clipping. The antioxidant tiron normalized relaxations in vessels from sham-operated and clipped ecSOD-/-, as well as from clipped ecSOD+/+ mice. In contrast, in vivo application of ecSOD selectively enhanced endothelium-dependent relaxation in vessels from ecSOD-/- mice. These data reveal that endogenous ecSOD is a major antagonistic principle to vascular O2.-, controlling blood pressure and vascular function in angiotensin II-dependent models of hypertension. ecSOD is expressed in such an abundance that even in situations of high oxidative stress no relative lack of enzyme activity occurs.