Ischaemic stroke following tranexamic acid in young patients carrying heterozygosity of MTHFR C677T

The objective of this study is to report a new manifestation of acute stroke following antifibrinolytic agent administration in young women carrying heterozygosity for methylene-tetrahydrofolate reductase (MTHFR) C677T. The study included two young women who developed an acute ischaemic stroke following three days of tranexamic acid administration for bleeding gynaecological disorders. Case 1, a 44-year-old woman, presented left hemiplegia, mild dysarthria and anosognosia. Brain magnetic resonance imaging showed right ischaemic fronto-temporal lesion due to subocclusion of the right middle cerebral artery. Case 2, a 49-year-old woman, developed aphasia and right hemiplegia. Neuroimaging showed left capsular and periventricular infarcts due to near occlusion of the left internal carotid artery. Thrombophilia screening, coagulation parameters, homocysteine testing, 12-lead electrocardiography, and transthoracic and transoesophageal echocardiography were unremarkable. Genetic assay showed that both patients carried heterozygosity for MTHFR C677T, in which cytosine (C) is replaced by thymidine (T) at base position 677. To our knowledge, this is the first report describing the association between genetic factors and the onset of stroke following antifibrinolytic drugs intake. These data suggest a synergic effect of plasminogen activator inhibitor and heterozygosity for MTHFR C677T on the pathogenetic mechanisms leading to ischaemic stroke in young people.

Protein kinase Cθ is required for cardiomyocyte survival and cardiac remodeling

Protein kinase Cs (PKCs) constitute a family of serine/threonine kinases, which has distinguished and specific roles in regulating cardiac responses, including those associated with heart failure. We found that the PKCθ isoform is expressed at considerable levels in the cardiac muscle in mouse, and that it is rapidly activated after pressure overload. To investigate the role of PKCθ in cardiac remodeling, we used PKCθ^−/− mice. In vivo analyses of PKCθ^−/− hearts showed that the lack of PKCθ expression leads to left ventricular dilation and reduced function. Histological analyses showed a reduction in the number of cardiomyocytes, combined with hypertrophy of the remaining cardiomyocytes, cardiac fibrosis, myofibroblast hyper-proliferation and matrix deposition. We also observed p38 and JunK activation, known to promote cell death in response to stress, combined with upregulation of the fetal pattern of gene expression, considered to be a feature of the hemodynamically or metabolically stressed heart. In keeping with these observations, cultured PKCθ^−/− cardiomyocytes were less viable than wild-type cardiomyocytes, and, unlike wild-type cardiomyocytes, underwent programmed cell death upon stimulation with α1-adrenergic agonists and hypoxia. Taken together, these results show that PKCθ maintains the correct structure and function of the heart by preventing cardiomyocyte cell death in response to work demand and to neuro-hormonal signals, to which heart cells are continuously exposed.

Myocardial Pitx2 differentially regulates the left atrial identity and ventricular asymmetric remodeling programs

The Pitx2 gene regulates left-right (L/R) asymmetrical cardiac morphogenesis. Constitutive Pitx2 knock out (ko) mice die before birth and display, among other defects, right atrial isomerism, atrial and ventricular septal defects, and double outlet right ventricle. The myocardial role of the gene has not been dissected. In particular, how Pitx2 regulates the differential L/R cardiac identity program is not clear. Additionally, the relation between Pitx2 ko ventricular defects and the gene expression pattern is not understood. In this article we analyze Pitx2 myocardial function during mouse heart development. By in situ hybridization analysis we show that myocardial Pitx2 expression delineates the remodeling of the left atrioventricular canal, the inner curvature, the ventral part of the interventricular ring, and the ventral portion of the right and left ventricle. By genetic analysis using an allelic series of Pitx2 mutants, among which a myocardial specific ko (ko(myo)) we show it has a crucial role in this process. Pitx2 ko(myo) mutants survive to adulthood, when they present strong cardiac morphological and functional defects. Confocal analysis of embryonic Pitx2 ko(myo) hearts reveals delayed cardiomyocyte development in the ventricular but not in the atrial Pitx2 null areas. Conversely, selective left atrial BMP10 mRNA downregulation which normally occurs at fetal stages is not found in the Pitx2 ko(myo) mice. This is the first evidence for distinct Pitx2 action in mediating L/R atrial identity and asymmetrical ventricular remodeling.

Emilin1 links TGF-beta maturation to blood pressure homeostasis

TGF-beta proteins are main regulators of blood vessel development and maintenance. Here, we report an unprecedented link between TGF-beta signaling and arterial hypertension based on the analysis of mice mutant for Emilin1, a cysteine-rich secreted glycoprotein expressed in the vascular tree. Emilin1 knockout animals display increased blood pressure, increased peripheral vascular resistance, and reduced vessel size. Mechanistically, we found that Emilin1 inhibits TGF-beta signaling by binding specifically to the proTGF-beta precursor and preventing its maturation by furin convertases in the extracellular space. In support of these findings, genetic inactivation of Emilin1 causes increased TGF-beta signaling in the vascular wall. Strikingly, high blood pressure observed in Emilin1 mutants is rescued to normal levels upon inactivation of a single TGF-beta1 allele. This study highlights the importance of modulation of TGF-beta availability in the pathogenesis of hypertension.

Integrin signalling: the tug-of-war in heart hypertrophy

The mechanical stress imposed by hemodynamic overload on heart walls is a primary event in triggering the cardiac hypertrophic response. Integrins, a class of membrane receptors, are major players in transmitting the mechanical force across the plasma membrane and sensing the mechanical load in cardiomyocytes. In fact, integrins, together with a number of associated cytoskeletal proteins, connect the sarcomeric contractile apparatus to the extracellular matrix across the plasma membrane and trigger intracellular signaling pathways activating the cardiomyocyte hypertrophy program. In this review, we will discuss the role of the muscle-specific integrin isoform beta1D and of associated proteins such as FAK, melusin, vinculin, zyxin, VASP, and migfilin that are the most upstream elements ("initiators") activated by mechanical strain. These molecules trigger a coordinated downstream signaling cascade involving proteins such as AKT, RAS, and MAPKs that execute the biochemical program leading to cardiomyocyte hypertrophy. Better understanding of the functional role of the initiator elements is of key importance to developing novel strategies to control cardiac hypertrophy and prevent heart failure.

Selective Rac-1 Inhibition Protects From Diabetes-Induced Vascular Injury

Diabetes mellitus is a main risk factor for vascular diseases. Vascular injury induced by diabetes mellitus is characterized by endothelial dysfunction attributable to an increased oxidative stress. So far, the molecular mechanisms involved in the vasculotoxic effects of diabetes are only partially known. We examined the effect of diabetes mellitus on oxidative stress and Rac-1 activation, a small G-protein involved in the activation of NADPH oxidase. Our results show that oxidative stress in vessels of different murine models of diabetes mellitus and in endothelial cells treated with high glucose is associated with an increased Rac-1/PAK binding and Rac-1 translocation from cytosol to plasma membrane, thus demonstrating an enhanced Rac-1 activity. More important, selective Rac-1 inhibition by an adenoviral vector carrying a dominant negative mutant of Rac-1 protected from oxidative stress and vascular dysfunction induced by diabetes mellitus. Our study demonstrates that Rac-1 plays a crucial role in diabetes-induced vascular injury, and it could be a target of novel therapeutic approaches to reduce vascular risk in diabetes mellitus.

Replacement of K-Ras with H-Ras supports normal embryonic development despite inducing cardiovascular pathology in adult mice

Ras proteins are highly related GTPases that have key roles in regulating growth, differentiation and tumorigenesis. Gene-targeting experiments have shown that, out of the three mammalian ras genes, only K-ras is essential for normal mouse embryogenesis, and that mice deprived of H-ras and/or N-ras show no major phenotype. We generated mice (HrasKI) in which the K-ras gene had been modified to encode H-Ras protein. HrasKI mice produce undetectable amounts of K-Ras but-in contrast to mice homozygous for a null K-ras allele-they are born at the expected mendelian frequency, indicating that H-Ras can be substituted for K-Ras in embryonic development. However, adult HrasKI mice show dilated cardiomyopathy associated with arterial hypertension. Our results show that K-Ras can be replaced by H-Ras in its essential function in embryogenesis, and indicate that K-Ras has a unique role in cardiovascular homeostasis.

Cardiac Overexpression of Melusin Protects From Dilated Cardiomyopathy Due to Long-Standing Pressure Overload

We have previously shown that genetic ablation of melusin, a muscle specific beta 1 integrin interacting protein, accelerates left ventricle (LV) dilation and heart failure in response to pressure overload. Here we show that melusin expression was increased during compensated cardiac hypertrophy in mice subjected to 1 week pressure overload, but returned to basal levels in LV that have undergone dilation after 12 weeks of pressure overload. To better understand the role of melusin in cardiac remodeling, we overexpressed melusin in heart of transgenic mice. Echocardiography analysis indicated that melusin over-expression induced a mild cardiac hypertrophy in basal conditions (30% increase in interventricular septum thickness) with no obvious structural and functional alterations. After prolonged pressure overload (12 weeks), melusin overexpressing hearts underwent further hypertrophy retaining concentric LV remodeling and full contractile function, whereas wild-type LV showed pronounced chamber dilation with an impaired contractility. Analysis of signaling pathways indicated that melusin overexpression induced increased basal phosphorylation of GSK3beta and ERK1/2. Moreover, AKT, GSK3beta and ERK1/2 were hyper-phosphorylated on pressure overload in melusin overexpressing compared with wild-type mice. In addition, after 12 weeks of pressure overload LV of melusin overexpressing mice showed a very low level of cardiomyocyte apoptosis and stromal tissue deposition, as well as increased capillary density compared with wild-type. These results demonstrate that melusin overexpression allows prolonged concentric compensatory hypertrophy and protects against the transition toward cardiac dilation and failure in response to long-standing pressure overload.

PI3Kgamma modulates the cardiac response to chronic pressure overload by distinct kinase-dependent and -independent effects

The G protein-coupled, receptor-activated phosphoinositide 3-kinase gamma (PI3Kgamma) mediates inflammatory responses and negatively controls cardiac contractility by reducing cAMP concentration. Here, we report that mice carrying a targeted mutation in the PI3Kgamma gene causing loss of kinase activity (PI3KgammaKD/KD) display reduced inflammatory reactions but no alterations in cardiac contractility. We show that, in PI3KgammaKD/KD hearts, cAMP levels are normal and that PI3Kgamma-deficient mice but not PI3KgammaKD/KD mice develop dramatic myocardial damage after chronic pressure overload induced by transverse aortic constriction (TAC). Finally, our data indicate that PI3Kgamma is an essential component of a complex controlling PDE3B phosphodiesterase-mediated cAMP destruction. Thus, cardiac PI3Kgamma participates in two distinct signaling pathways: a kinase-dependent activity that controls PKB/Akt as well as MAPK phosphorylation and contributes to TAC-induced cardiac remodeling, and a kinase-independent activity that relies on protein interactions to regulate PDE3B activity and negatively modulates cardiac contractility.

Adaptive and maladaptive hypertrophic pathways: points of convergence and divergence

Myocardial hypertrophy is a response of cardiac muscle to altered conditions of haemodynamic overload caused by a large number of physiological and pathological conditions. Traditionally, it has been considered a beneficial mechanism. However, sustained hypertrophy has been associated with a significant increase in the risk of cardiovascular disease and mortality. Actually, many researchers are trying to understand whether left ventricular hypertrophy is a 'good' mechanism to stimulate or a 'bad' process to prevent. In this review we investigate the most common biochemical signaling pathways involved in the hypertrophic response to identify the precise role, either 'adaptive' or 'maladaptive', of each molecular pathway. Delinealing intracellular signaling pathways involved in the different aspects of cardiac hypertrophy will permit future improvements in the signaling that controls beneficial growth.

Left ventricular hypertrophy is associated with asymptomatic cerebral damage in hypertensive patients

BACKGROUND AND PURPOSE

It has been demonstrated that left ventricular hypertrophy (LVH) confers an increased risk for major cerebrovascular events. However, it is still uncertain whether there is an association between LVH and asymptomatic cerebrovascular damage in hypertensive patients. In this study, we investigated the relation between LVH, evaluated by both echocardiography (Echo-LVH) and electrocardiography (ECG-LVH), and preclinical cerebral damage, as identified by magnetic resonance imaging.

METHODS

One hundred ninety-five consecutive patients were enrolled in the study. We evaluated other risk factors such as age, sex, presence of diabetes, cholesterol levels, smoking status, heart rate, and systolic and diastolic blood pressure. Asymptomatic cerebrovascular damage was considered silent cerebral lesions: punctate lesions, lacunes, and territorial lesions. Patients were divided into 2 groups according to the presence of asymptomatic brain lesions.

RESULTS

The 2 groups of patients differed only in terms of age and systolic pressure. More importantly, the prevalence of Echo-LVH (83% versus 47.7%, P<0.001) and ECG-LVH (56% versus 22%, P<0.001) was significantly higher in patients with asymptomatic brain lesions. A multivariate analysis allowed us to recognize LVH as the only independent predictor for the presence of ischemic lacunes (P<0.001). Moreover, we evaluated the impact of left ventricular geometry on asymptomatic cerebrovascular damage, and we found that hypertensives with concentric hypertrophy displayed more pronounced asymptomatic cerebrovascular damage compared with patients with eccentric hypertrophy.

CONCLUSIONS

Our study demonstrates that LVH is associated with cerebral damage even in the absence of clinical symptoms. Thus, the presence of cardiac damage provides important prognostic clues about the presence of asymptomatic cerebral damage.

Melusin, a muscle-specific integrin beta1-interacting protein, is required to prevent cardiac failure in response to chronic pressure overload

Cardiac hypertrophy is an adaptive response to a variety of mechanical and hormonal stimuli, and represents an early event in the clinical course leading to heart failure. By gene inactivation, we demonstrate here a crucial role of melusin, a muscle-specific protein that interacts with the integrin beta1 cytoplasmic domain, in the hypertrophic response to mechanical overload. Melusin-null mice showed normal cardiac structure and function in physiological conditions, but when subjected to pressure overload--a condition that induces a hypertrophic response in wild-type controls--they developed an abnormal cardiac remodeling that evolved into dilated cardiomyopathy and contractile dysfunction. In contrast, the hypertrophic response was identical in wild-type and melusin-null mice after chronic administration of angiotensin II or phenylephrine at doses that do not increase blood pressure--that is, in the absence of cardiac biomechanical stress. Analysis of intracellular signaling events induced by pressure overload indicated that phosphorylation of glycogen synthase kinase-3beta (GSK-3beta) was specifically blunted in melusin-null hearts. Thus, melusin prevents cardiac dilation during chronic pressure overload by specifically sensing mechanical stress.

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.

The Role of Egr-1 in the Cardiac Remodeling During Chronic Pressure Overload

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Early growth response-1 (Egr-1) is a transcription factor which is activated in the left ventricle during the onset of myocardial hypertrophy in response to pressure overload, but its role in cardiac remodeling is still unclear. The recent generation by homologous recombination of mice which have ablated Egr-1 allows to explore this issue. In particular, we exposed Egr-1 null mice (-/-, n=18) and their wild-type littermates (+/+, n=20) to chronic pressure overload induced by transverse aortic constriction (TAC) between left carotid artery and truncus anonimus. In sham operated mice (+/+ n=6; -/- n=7) basal fractional shortening, as an index of left ventricular function evaluated by transthoracic echocardiography, (47.4±.6 vs 48.4±.7 %, n.s.) and left ventricular weight/body weight ratio (LVW/BW, mg/g), an index of left ventricular mass, (3.2±.1 vs 3.1±.1 mg/g, n.s.) were comparable in +/+ and -/- mice. After 7 days of chronic pressure overload, despite systolic pressure gradient across the stenosis was comparable between the two mice strains (62±5 vs 67±6 mmHg, n.s.), -/- mice showed a lower LVW/BW as compared to +/+ mice (4.4±.2 vs 5.7±.3 mg/g, p<0.01). Moreover, the histological analysis disclosed a markedly reduced left ventricle perivascular and interstitial fibrosis in -/- TAC mice as compared to that observed in +/+ TAC mice. Interestingly, left ventricular gene expression of fibronectin and collagen I and III was significantly reduced in -/- TAC mice when compared with +/+ TAC mice. These data demonstrate that Egr-1 activation affects the stromal reaction involved in the cardiac remodeling due to pressure overload, suggesting that Egr-1 may be a molecular target of novel therapeutic strategies focused to modulate specific features of the cardiac hypertrophic remodeling.

Increased cardiomyocyte apoptosis and changes in proapoptotic and antiapoptotic genes bax and bcl-2 during left ventricular adaptations to chronic pressure overload in the rat

BACKGROUND

Left ventricular hypertrophy (LVH) represents both an adaptive response to increased cardiac work load and a precursor state of heart failure. Recent evidence linked cardiac myocyte death by apoptosis with LVH and heart failure. It remained unclear, however, whether apoptosis participated in the transition from LVH to left ventricular dysfunction (LVD).

METHODS AND RESULTS

Cardiac myocyte apoptotic events and changes in apoptosis-specific genes were studied in a rat model of chronic pressure overload induced by transverse aortic constriction. The changes in left ventricular geometry and function were assessed by echocardiography. Transverse aortic constriction rats progressively developed "concentric" LVH and subsequently, LVD. A similar distribution of LVH and LVD was found 18 weeks after surgery. At this time point, we determined the occurrence of myocyte apoptosis by DNA laddering, in situ DNA TUNEL labeling, and light and electron microscopy. The monitoring of proapoptotic and antiapoptotic genes was determined by Western blot and immunohistochemistry. Our data demonstrated that cardiomyocyte apoptotic events increased from virtually undetectable (in sham-operated controls, SH) to 0.8/10(3) and 1.5/10(3) positive nuclei in LVH and LVD, respectively. Fibrosis also increased in the subendocardial and midwall regions of LVH and LVD rats compared with SH. Expression of the proapoptotic gene bax increased, whereas that of antiapoptotic gene bcl-2 decreased in LVH and LVD compared with SH.

CONCLUSIONS

These data suggest that in response to chronic pressure overload, cardiomyocyte-specific apoptosis contributed to the transition from LVH to LVD. LVH and LVD were accompanied by a dramatic cardiomyocyte upregulation of the proapoptotic gene bax and reduced bcl-2/bax ratio, predisposing cardiomyocytes to apoptosis.