BACKGROUND:Mechanical stress increases myocardial myostatin expression. However, the expression of myostatin in chronic heart failure resulting from volume-overload and after treatment with beta-blockers is little known. The authors hypothesize that myostatin plays a role in the failing myocardium because of volume-overload.MATERIALS AND METHODS:Aorto-caval shunt was created over a 4-week period in adult Sprague-Dawley rats to induce volume-overload heart failure.RESULTS:Heart weight and body weight ratio significantly increased after shunting. The left ventricular end-diastolic dimension also significantly increased. Treatment with carvedilol in the shunt group reversed the increase in heart weight and ventricular dimension to the baseline values. Myocardial and skeletal myostatin proteins were up-regulated in the shunt group. The mRNA of myocardial myostatin also increased in the shunt group. Treatment with carvedilol reversed both protein and mRNA of myocardial myostatin to the baseline values. Treatment with N-acetylcysteine and doxazosin partially decreased myostatin mRNA and protein expression as compared with the shunt group. Carvedilol normalized the increased immunohistochemical labelling of myocardial myostatin in the shunt group.CONCLUSION:Myocardial myostatin mRNA and protein expression were up-regulated in the rat model of volume-overload heart failure. Treatment with carvedilol is associated with a limitation of increased myostatin expression in the failing ventricular myocardium.

Type-I plasminogen activator inhibitor (PAI-1) is the primary inhibitor of both tissue- and urokinase-type plasminogen activators (t-PA, u-PA) and is thus a primary regulator of plasminogen activation and possibly of extracellular proteolysis. In anchorage-dependent cells, the PAI-1 gene was regulated by cell adhesion. PAI-1 gene expression was induced more evidently in cells adhered to the culture plate than in nonadherent cells. In this study, we investigated the signal pathway of the PAI-1 gene expression regulated by cell adhesion. We found the induction of both PAI-1 mRNA and protein, when cells adhered to culture dish, was inhibited by the PI-3 kinase specific inhibitors (Ly294002 and wortmannin). The cells seeded on collagen-1 coated plate with low serum further demonstrated that the PAI-1 gene expression was prolonged by the cell adhesion. The above-mentioned PI-3 kinase specific inhibitors also blocked the PAI-1 maintenance when cell adhered to collagen-1 coated plate. In addition, we found that both PI-3 kinase and its downstream molecule, Akt, were activated more evidently in adherent cells than in nonadherent cells. Furthermore, we transfected antisense oligodeoxynucleotides of Akt (AS-ODN-Akt) into cells to block the expression of Akt and found that the induction of PAI-1 mRNA was also inhibited. Hence, we conclude that the induction of PAI-1 gene expression is cell adhesion dependent and is through PI-3 kinase and Akt activation.

Objectives: The therapeutic utility of hypoxia-inducible factor-1 (HIF-1) transcriptional regulatory system for ischemic hindlimb has been demonstrated. It is not yet known whether this transcriptional regulatory system can be used as a therapeutic strategy to enhance collateral vessel formation in myocardial tissues, where acute hypoxia occurs due to inadequate perfusion. We aimed to test the hypothesis that exogenous administration of HIF-1alpha/VP16 could enhance collateral vessel formation in a rat acute myocardial infarction model. Methods: Sprague-Dawley rats received ligation of the proximal left interior descending, coronary artery to induce acute myocardial infarction. Immediately after the ligation, 50 mug total plasmid DNA (control, plasmid encoding, human vascular endothelial growth factor (pVEGF(165)). or pHIF-1alpha/VP16) was injected into the infarct area at three locations. Results: Reverse transcription polymerase chain reaction (RT-PCR) showed the presence of HIF-1alpha and VEGF mRNA in the myocardium, but not in other organs at days 3 and 7. The infarct size significantly decreased from 37 +/- 4% (control) to 24 +/- 2% in the VEGF-treated group and 23 +/- 2% in the HIF-1alpha/VP16 treated group (P<0.05). Capillary density also significantly increased from 550 +/- 75/mm(2)(control) to 850 +/- 75/mm(2) in the VEGF group and 850 +/- 50/mm(2) in the HIF-1alpha/VP16-treated group (P<0.01). Combined therapy with HIF-1alphaVP16 and VEGF resulted in higher capillary density (1230 +/- 50/mm(2)) than treatment with either therapy alone. Regional myocardial blood flow was also higher in the treated groups than in the control. Plasma levels of VEGF were also significantly higher in the HIf-1alpha/VP16 and VEGF-treated group than in the control group. Conclusions: The HIF-1alpha/VP16 hybrid transcription factor is able to reduce infarct size and enhance neovascularization in an acute ischemic myocardium. The potency of VEGF and hybrid as therapeutic angiogenic factors in acute hypoxic myocardium is similiar. (C) 2002 Elsevier Science B.V. All rights reserved.

BACKGROUND AND PURPOSE Mechanical forces have profound effects on vascular smooth muscle cells (VSMCs). The mechanism by which mechanical stimuli regulate vascular endothelial growth factor (VEGF) expression and regulation has yet to be elucidated. We investigated the effect of cyclical mechanical stretching on regulation of the VEGF gene in VSMCs. MATERIALS AND METHODS Cultured rat VSMCs grown on a flexible membrane base were stretched by applying a vacuum at 60 cycles/minute. VEGF concentration in the cultured media was determined by enzyme-linked immunoassay. VEGF gene expression was determined by Western blot and Northern blot. The location of VEGF in the VSMC was studied immunohistochemically. Chimeric constructs of the VEGF promoter were deleted and the promoter activity was determined by luciferase activity. RESULTS VEGF concentration increased by 21 to 32% as early as 10 minutes after stretching and remained at this level for up to 12 hours. The concentration of VEGF reached a maximum of 2.8-fold over that in control cells by 2 hours after stretching and declined slightly thereafter. The amount of VEGF mRNA in stretched cells increased as early as 1 hour after stretching, reached a maximum of 3.2-fold over the amount in control cells by 2 hours, and remained at this level for up to 6 hours after stretching. Immunohistochemical study confirmed increased VEGF expression in VSMCs after stretching. Stretched cells transfected with a Sac-Nhe fragment showed only 46% of the luciferase activity of unstretched control cells. However, stretched cells transfected with chimeric plasmids containing a Spe-Nhe fragment showed 2.8-fold luciferase activity over that in control cells. CONCLUSIONS Cyclical mechanical stretching upregulates expression of the VEGF gene in VSMCs at the transcription level. The VEGF 5'-flanking region contains a negative stretch-response element located in the 0.4-kb Sac-Pst fragment and a positive stretch-response element located in the 0.6-kb Spe-Sac fragment.

BACKGROUND AND PURPOSE:Norepinephrine (NE) is elevated in heart failure and can induce apoptosis in adult cardiac myocytes. However, it is not known whether NE can induce apoptosis in neonatal cardiac myocytes. This study examined the ability of NE to stimulate apoptosis in rat neonatal cardiac myocytes in vitro.METHODS:Neonatal rat cardiac myocytes were exposed to NE alone, NE + propranolol, or NE + prazosin for 24 hours. Apoptosis was assayed by DNA laddering with agarose gel electrophoresis and immunofluorescent terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) staining. Reverse transcription polymerase chain reaction was used to evaluate the expression of Mcl-1. Creatine kinase activity in the cultured medium was used as a measure of the toxicity of NE on myocytes.RESULTS:NE increased DNA laddering on agarose gel electrophoresis and increased the number of apoptotic cells in a dose-dependent manner. No increase in apoptosis was found in response to NE doses between 1 and 50 mumol/L. NE at concentrations of 100 to 400 mumol/L increased apoptosis from 10% to 31% of cells. The ability of NE to stimulate apoptosis in rat neonatal cardiac myocytes was completely blocked by propranolol, but not prazosin. NE treatment at high concentrations sharply reduced the level of Mcl-1 mRNA, coincident with the increase in the number of apoptotic cells. Creatine kinase activity in the cultured medium was similar among the controls and NE-treated myocytes.CONCLUSIONS:Our results showed that NE at high concentrations stimulated apoptosis in rat neonatal cardiac myocytes in vitro. Apoptosis induced by NE was associated with down-regulation of Mcl-1. However, NE at the same concentration was not toxic to rat neonatal cardiac myocytes.