The increased angiotensin II (type 1) receptor density in myocardium of type 2 diabetic patients is prevented by blockade of the renin-angiotensin system

Identification of membrane palmitoylated protein 1 (MPP1) as a heart-failure-promoting protein triggered by cardiovascular risk factors and aging

Membrane-Associated Guanylate Kinase (MAGUK) proteins are scaffold proteins with well-established functions in the neuronal system. A role of MAGUK protein up-regulation in the pathogenesis of heart failure is not established. This study identified the up-regulation of the MAGUK family protein MPP1 (Membrane Palmitoylated Protein 1), in cardiac transcriptome data of three different heart failure models. MPP1 was up-regulated in failing hearts of B6 mice with long-term chronic pressure overload, in failing hearts of aged Apoe-/- mice with long-term atherosclerosis, and in failing hearts of RKIP-transgenic mice with cardiotoxic lipid overload. MPP1-transgenic mice revealed that moderately (2-fold) increased cardiac MPP1 levels caused symptoms of heart failure with a significantly reduced left ventricular ejection fraction of 39.0 ± 6.9 % in Tg-MPP1 mice compared to 55.2 ± 3.7 % of non-transgenic B6 controls. Echocardiographic and histological analyses detected cardiac enlargement and cardiac dilation in Tg-MPP1 mice. The angiotensin II AT1 receptor (AGTR1) and MPP1 were co-localized on sarcolemmal membranes in vivo, and Tg-MPP1 mice had increased levels of cardiac AGTR1, which has an established heart failure-promoting function. The increased AGTR1 protein could be directly triggered by elevated MPP1 because MPP1 also increased the AGTR1 protein in non-cardiomyocyte HEK cells, which was detected by fluorescence measurement of AGTR1eYFP. MPP1 was not only up-regulated by major cardiovascular risk factors but also by old age, which is a major contributor to heart failure. Thus, the aging-induced MPP1 exerts a previously unrecognized role in heart failure pathogenesis by upregulation of the angiotensin II AT1 receptor (AGTR1) protein.

Role of Ang1-7 in renal haemodynamics and excretion in streptozotocin diabetic rats

The contribution of angiotensin (1-7) (Ang1-7) to control of extrarenal and renal function may be modified in diabetes. We investigated the effects of Ang1-7 supplementation on blood pressure, renal circulation and intrarenal reactivity (IVR) to vasoactive agents in normoglycaemic (NG) and streptozotocin diabetic rats (DM). In Sprague Dawley DM and NG rats, 3 weeks after streptozotocin (60 mg/kg i.p.) or solvent injection, Ang1-7 was administered (400 ng/min) over the next 2 weeks using subcutaneously implanted osmotic minipumps. For a period of 5 weeks, blood pressure (BP), 24 h water intake and diuresis were determined weekly. In anaesthetised rats, BP, renal total and cortical (CBF), outer (OMBF) and inner medullary (IMBF) perfusion and urine excretion were determined. To check IVR, a short-time infusion of acetylcholine or norepinephrine was randomly given to the renal artery. Unexpectedly, BP did not differ between NG and DM, and this was not modified by Ang-1-7 supplementation. Baseline IMBF was higher in NG vs. DM, and Ang1-7 treatment did not change it in NG but decreased it in DM. In the latter, Ang1-7 increased cortical IVR to vasoconstrictor and vasodilator stimuli. IMBF decrease after high acetylcholine dose seen in untreated NG was reverted to an increase in Ang1-7 treated rats. Irrespective of the glycaemia level, Ang1-7 did not modify BP. However, it impaired medullary circulation in DM, whereas in NG it rendered the medullary vasculature more sensitive to vasodilators. Possibly, the medullary hypoperfusion in DM was mediated by Ang1-7 activation of angiotensin AT-1 receptors which are upregulated by hyperglycaemia.

Stearoyl-CoA Desaturase (SCD) Induces Cardiac Dysfunction with Cardiac Lipid Overload and Angiotensin II AT1 Receptor Protein Up-Regulation

Heart failure is a major cause of death worldwide with insufficient treatment options. In the search for pathomechanisms, we found up-regulation of an enzyme, stearoyl-CoA desaturase 1 (Scd1), in different experimental models of heart failure induced by advanced atherosclerosis, chronic pressure overload, and/or volume overload. Because the pathophysiological role of Scd1/SCD in heart failure is not clear, we investigated the impact of cardiac SCD upregulation through the generation of C57BL/6-Tg(MHCSCD)Sjaa mice with myocardium-specific expression of SCD. Echocardiographic examination showed that 4.9-fold-increased SCD levels triggered cardiac hypertrophy and symptoms of heart failure at an age of eight months. Tg-SCD mice had a significantly reduced left ventricular cardiac ejection fraction of 25.7 ± 2.9% compared to 54.3 ± 4.5% of non-transgenic B6 control mice. Whole-genome gene expression profiling identified up-regulated heart-failure-related genes such as resistin, adiponectin, and fatty acid synthase, and type 1 and 3 collagens. Tg-SCD mice were characterized by cardiac lipid accumulation with 1.6- and 1.7-fold-increased cardiac contents of saturated lipids, palmitate, and stearate, respectively. In contrast, unsaturated lipids were not changed. Together with saturated lipids, apoptosis-enhancing p53 protein contents were elevated. Imaging by autoradiography revealed that the heart-failure-promoting and membrane-spanning angiotensin II AT1 receptor protein of Tg-SCD hearts was significantly up-regulated. In transfected HEK cells, the expression of SCD increased the number of cell-surface angiotensin II AT1 receptor binding sites. In addition, increased AT1 receptor protein levels were detected by fluorescence spectroscopy of fluorescent protein-labeled AT1 receptor-Cerulean. Taken together, we found that SCD promotes cardiac dysfunction with overload of cardiotoxic saturated lipids and up-regulation of the heart-failure-promoting AT1 receptor protein.

Diabetic cardiomyopathy: pathophysiology and clinical features

Since diabetic cardiomyopathy was first reported four decades ago, substantial information on its pathogenesis and clinical features has accumulated. In the heart, diabetes enhances fatty acid metabolism, suppresses glucose oxidation, and modifies intracellular signaling, leading to impairments in multiple steps of excitation–contraction coupling, inefficient energy production, and increased susceptibility to ischemia/reperfusion injury. Loss of normal microvessels and remodeling of the extracellular matrix are also involved in contractile dysfunction of diabetic hearts. Use of sensitive echocardiographic techniques (tissue Doppler imaging and strain rate imaging) and magnetic resonance spectroscopy enables detection of diabetic cardiomyopathy at an early stage, and a combination of the modalities allows differentiation of this type of cardiomyopathy from other organic heart diseases. Circumstantial evidence to date indicates that diabetic cardiomyopathy is a common but frequently unrecognized pathological process in asymptomatic diabetic patients. However, a strategy for prevention or treatment of diabetic cardiomyopathy to improve its prognosis has not yet been established. Here, we review both basic and clinical studies on diabetic cardiomyopathy and summarize problems remaining to be solved for improving management of this type of cardiomyopathy.

Late-life enalapril administration induces nitric oxide-dependent and independent metabolic adaptations in the rat skeletal muscle

Recently, we showed that administration of the angiotensin-converting enzyme inhibitor enalapril to aged rats attenuated muscle strength decline and mitigated apoptosis in the gastrocnemius muscle. The aim of the present study was to investigate possible mechanisms underlying the muscle-protective effects of enalapril. We also sought to discern the effects of enalapril mediated by nitric oxide (NO) from those independent of this signaling molecule. Eighty-seven male Fischer 344 × Brown Norway rats were randomly assigned to receive enalapril (n = 23), the NO synthase (NOS) inhibitor N(G)-nitro-L-arginine methyl ester (L-NAME; n = 22), enalapril + L-NAME (n = 19), or placebo (n = 23) from 24 to 27 months of age. Experiments were performed on the tibialis anterior muscle. Total NOS activity and the expression of neuronal, endothelial, and inducible NOS isoforms (nNOS, eNOS, and iNOS) were determined to investigate the effects of enalapril on NO signaling. Transcript levels of tumor necrosis factor-alpha (TNF-α) and peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α) were assessed to explore actions of enalapril on inflammation and mitochondrial biogenesis, respectively. Protein expression of energy-sensing and insulin signaling mediators, including protein kinase B (Akt-1), phosphorylated Akt-1 (pAkt-1), mammalian target of rapamycin (mTOR), AMP-activated protein kinase subunit alpha (AMPKα), phosphorylated AMPKα (pAMPKα), and the glucose transporter GLUT-4, was also determined. Finally, the generation of hydrogen peroxide (H2O2) was quantified in subsarcolemmal (SSM) and intermyofibrillar (IFM) mitochondria. Enalapril increased total NOS activity, which was prevented by L-NAME co-administration. eNOS protein content was enhanced by enalapril, but not by enalapril + L-NAME. Gene expression of iNOS was down-regulated by enalapril either alone or in combination with L-NAME. In contrast, protein levels of nNOS were unaltered by treatments. The mRNA abundance of TNF-α was reduced by enalapril relative to placebo, with no differences among any other group. PCG-1α gene expression was unaffected by enalapril and lowered by enalapril + L-NAME. No differences in protein expression of Akt-1, pAkt-1, AMPKα, pAMPKα, or GLUT-4 were detected among groups. However, mTOR protein levels were increased by enalapril compared with placebo. Finally, all treatment groups displayed reduced SSM, but not IFM H2O2 production relative to placebo. Our data indicate that enalapril induces a number of metabolic adaptations in aged skeletal muscle. These effects result from the concerted modulation of NO and angiotensin II signaling, rather than from a dichotomous action of enalapril on the two pathways. Muscle protection by enalapril administered late in life appears to be primarily mediated by mitigation of oxidative stress and pro-inflammatory signaling.

Angiotensin II type 1 and type 2 receptor expression in circulating monocytes of diabetic and hypercholesterolemic patients over 3-month rosuvastatin treatment

Background

In diabetes, a variety of pro-inflammatory cellular changes has been found in various cell types, including monocytes which are known to be involved in all the phases of atherogenesis. Angiotensin II (Ang II) type 1 receptor (AT₁R) mediates the pro-atherogenic effects of Ang II whereas the type 2 receptor (AT₂R) seems associated with atheroprotection. We sought to investigate the potential changes of AT₁R-AT₂R expression in human monocytes of type 2 diabetic- hypercholesterolemic patients and in hypercholesterolemic subjects, upon clinical treatment with rosuvastatin.

Methods

The AT₁R membrane protein and mRNA AT₁R and AT₂R expression in monocytes were investigated in 10 type 2 diabetic-hypercholesterolemic patients and in 10 hypercholesterolemic subjects, before and after 3-month rosuvastatin treatment. Moreover, the serum cytokine levels of interferon-γ (IFN-γ) and interleukin-4 (IL-4) were detected.

Results

As expected, rosuvastatin was associated with a change in the lipid profile in the two groups. Both the membrane protein (P = 0.008) and the AT₁R mRNA expression (P = 0.038) were significantly reduced during treatment in the absence of AT₂R expression change in diabetic-hypercholesterolemic patients whereas no significant difference was observed in hypercholesterolemic subjects. The serum IL-4 levels were increased during treatment whereas no change was observed in IFN-γ in diabetic-hypercholesterolemic patients. No cytokine change was observed in hypercholesterolemic subjects.

Conclusions

Our study on monocytes of diabetic-hypercholesterolemic patients, showing a reduced AT₁R but not AT₂R expression during rosuvastatin treatment, suggests that statin therapy may modulate favorably the AT₁-AT₂ receptor balance in subjects with coexistent type 2 diabetes.

Ryanodine receptor: a new therapeutic target to control diabetic cardiomyopathy

Diabetes mellitus is a major risk factor for cardiovascular complications. Intracellular Ca(2+) release plays an important role in the regulation of muscle contraction. Sarcoplasmic reticulum Ca(2+) release is controlled by dedicated molecular machinery, composed of a complex of cardiac ryanodine receptors (RyR2s). Acquired and genetic defects in this complex result in a spectrum of abnormal Ca(2+) release phenotypes in heart. Cardiovascular dysfunction is a leading cause for mortality of diabetic individuals due, in part, to a specific cardiomyopathy, and to altered vascular reactivity. Cardiovascular complications result from multiple parameters, including glucotoxicity, lipotoxicity, fibrosis, and mitochondrial uncoupling. In diabetic subjects, oxidative stress arises from an imbalance between production of reactive oxygen and nitrogen species and capability of the system to readily detoxify reactive intermediates. To date, the etiology underlying diabetes-induced reductions in myocyte and cardiac contractility remains incompletely understood. However, numerous studies, including work from our laboratory, suggest that these defects stem in part from perturbation in intracellular Ca(2+) cycling. Since the RyR2s are one of the well-characterized redox-sensitive ion channels in heart, this article summarizes recent findings on redox regulation of cardiac Ca(2+) transport systems and discusses contributions of redox regulation to pathological cardiac function in diabetes.

Application of an exercise intervention on the evolution of diastolic dysfunction in patients with diabetes mellitus: efficacy and effectiveness

BACKGROUND

Diastolic dysfunction (DD) is associated with adverse cardiovascular outcomes. We studied the impact of an exercise-based lifestyle intervention on the evolution of DD in patients with type 2 diabetes mellitus (T2DM) and prospectively investigated the clinical correlates of DD progression.

METHODS AND RESULTS

A total of 223 outpatients with T2DM were randomized to supervised exercise-based lifestyle intervention (initial gym-based program and lifestyle and diet advice followed by telephone-guided supervision) or usual care. Patients underwent echocardiographic assessment of diastolic function and metabolic and clinical evaluation at baseline and 3 years. Changes in prevalence and evolution of DD were assessed and correlations sought with clinical and metabolic variables. DD was present in 50% of patients at baseline and 54% at 3 years, with no difference between the usual care and intervention groups (60% versus 48%, P=0.10). Abnormal DD at the final visit was independently associated with older age and a decrease in peak oxygen consumption over time (P<0.05). There was no impact on glycemic control or exercise capacity. In a subanalysis restricted to patients who finished the full 3-year follow-up, control subjects were independently associated with DD at 3 years (β=0.90; odds ratio, 2.46; P=0.034), with the only other independent correlate being older age (β=0.05; odds ratio, 1.06; P=0.019).

CONCLUSIONS

Despite being efficacious in the subgroup who completed 3 years of exercise-based lifestyle intervention, randomization to this program was not effective in reducing progression of subclinical DD in patients with T2DM, which may reflect the recognized difficulty of adherence to prolonged exercise intervention.

CLINICAL TRIAL REGISTRATION

URL: http://www.anzctr.org.au. Unique identifier: ACTRN12607000060448.

Application of angiotensin II to healthy rat sciatic nerve can produce neuropathy without associated vasculopathy

Elevated angiotensin II (AII) levels have been associated with hypertension, diabetes, and polyneuropathy. It is unknown whether AII applied to healthy nerve can be used to model a confined neuronal injury by producing localized vasculopathy and associated neuropathy. In this study, angiotensin II (2.2 μg/ml) or saline was infused constantly via osmotic pump onto the sciatic nerve of 20 rats for 12 weeks. Nerve conduction studies were repeated every 4 weeks, and sciatic nerve was collected for pathological analysis at 12 weeks. Animals infused with AII showed a significant decrease in nerve fiber diameter (P < 0.001), axon diameter (P < 0.001), and myelin thickness (P < 0.001), despite the absence of electrophysiological changes. Surprisingly, there was no significant difference in vessel diameter or wall thickness. AII can cause structural alterations in healthy nerve without associated changes in vasculature, implying the existence of additional previously unrecognized mechanisms of AII-induced neuronal injury.

Diabetes-related defects in sarcoplasmic Ca2+ release are prevented by inactivation of G(alpha)11 and G(alpha)q in murine cardiomyocytes

Neurohumoral stimulation of Gq-coupled receptors has been proposed as a central mechanism in the pathogenesis of diabetic heart disease. The resulting contractile dysfunction is closely related to abnormal intracellular Ca(2+) handling with functional defects of the sarcoplasmic reticulum (SR). The present study was therefore designed to determine the role of G(q)-protein signaling via G(alpha)(11) and G(alpha)(q) in diabetes for the induction of functional and structural changes in the Ca(2+) release complex of the SR. An experimental type 1-diabetes was induced in wild type, G(alpha)(11) knockout, and G(alpha)(11/q)-knockout mice by injection of streptozotocin. Cardiac morphology and function was assessed in vivo by echocardiography. SR Ca(2+) leak was tested in vitro based on a (45)Ca(2+) assay and protein densities as well as gene expression of ryanodine receptor (RyR2), FKBP12.6, sorcin, and annexin A7 were analyzed by immunoblot and RT-PCR. In wild type animals 8 weeks of diabetes resulted in cardiac hypertrophy and SR Ca(2+) leak was increased. In addition, diabetic wild type animals showed reduced protein levels of FKBP12.6 and annexin A7. In G(alpha)(11)- and G(alpha)(11/q)-knockout animals, however, SR Ca(2+) release and cardiac phenotype remained unchanged upon induction of diabetes. Densities of the proteins that we presently analyzed were also unaltered in G(alpha)(11)-knockout mice. G(alpha)(11/q)-knockout animals even showed increased expression of sorcin and annexin A7. Thus, based on the present study we suggest a signaling pathway via the G(q)-proteins, G(alpha)(11) and G(alpha)(q), that could link increased neurohumoral stimulation in diabetes with defective RyR2 channel function by regulating protein expression of FKBP12.6, annexin A7, and sorcin.

Prevention of myocardial fibrosis by N-acetyl-seryl-aspartyl-lysyl-proline in diabetic rats

Ac-SDKP (N-acetyl-seryl-aspartyl-lysyl-proline) is a physiological tetrapeptide hydrolysed by ACE (angiotensin-converting enzyme). In experimental models of hypertension, Ac-SDKP has antifibrotic effects in the heart; however, the role of Ac-SDKP in diabetic cardiomyopathy is currently unknown. The aim of the present study was to evaluate the effect of Ac-SDKP on cardiac systolic and diastolic function, and interstitial and perivascular fibrosis in the heart of diabetic rats.Diabetes was induced in 55 Sprague-Dawley rats by streptozotocin injection. Control rats (n=18)underwent only buffer injection.Out of the 55 diabetic rats, 19 were chronically treated with insulin and 13 with the ACEI (ACE inhibitor) ramipril (3 mg x kg(-1 )of body weight x day(-1)). At 2 months after the onset of diabetes, Ac-SDKP (1 mg x kg(-1) of body weight x day(-1)) was administered by osmotic minipumps for 8 weeks to eight control rats, 13 diabetic rats, seven diabetic rats treated with ramipril and nine insulin-treated diabetic rats. Diabetic rats had a significant increase in blood glucose levels. Left ventricular interstitial and perivascular fibrosis, and TGF-beta1 (transforming growth factor-beta1) protein levels were increased in diabetic rats, but not in insulin-treated diabetic rats and ramipril-treated diabetic rats, compared with control rats. Ac-SDKP administration significantly reduced left ventricular interstitial and perivascular fibrosis in diabetic rats and in diabetic rats treated with ramipril. This was accompanied by a significant reduction in active TGF-beta1 and phospho-Smad2/3 protein levels in myocardial tissue of diabetic rats. Echocardiography showed that diabetes was associated with increased end-systolic diameters, and depressed global systolic function and diastolic dysfunction, as assessed by transmitral Doppler velocity profile. These changes were completely reversed by insulin or ramipril treatment. Ac-SDKP treatment partially restored diastolic function in diabetic rats. In conclusion, Ac-SDKP administration in diabetic rats reduces left ventricular interstitial and perivascular fibrosis, active TGF-beta1 and phospho-Smad2/3levels, and improves diastolic function. Taken together, these findings suggest that, by inhibiting theTGF-beta/Smad pathway, Ac-SDKP protects against the development of diabetic cardiomyopathy

Effects of angiotensin-converting enzyme inhibitor versus valsartan on cellular signaling events in heart transplant

BACKGROUND

Angiotensin-converting enzyme (ACE) inhibitors and angiotensin receptor blockers (ARBs) provide similar biologic effects in model systems and similar clinical impacts in humans. The changes in the cardiac angiotensin system signaling pathways in the human heart in response to ACE inhibitors versus ARBs have been incompletely studied.

OBJECTIVE

To investigate the effects of ACE inhibitors versus valsartan on the angiotensin II signal transduction pathways in the transplanted human heart.

METHODS

Twenty-seven stable cardiac transplant recipients were randomized to remain on ACE inhibitor therapy (n = 8) or to receive valsartan (n = 19). Two additional endomyocardial biopsy samples were obtained at baseline and after 9 months of therapy. The expression of cardiac angiotensin type I and II receptors and atrial natriuretic factor (ANF) was measured by quantitative polymerase chain reaction. The expression and phosphorylation levels of selected signal transduction pathways were analyzed by immunoblotting.

RESULTS

The mean dose of valsartan was 114 +/- 41 mg/day. The use of valsartan resulted in a similar impact on blood pressure and biochemistry profile. There were no significant changes in the expression of angiotensin type I and II receptors and ANF with valsartan. Similarly, no significant changes in the expression and phosphorylation of Jun N-terminal kinase, extracellular signal-regulated kinase 1 and 2, and p38 mitogen-activated protein kinases or AKT, and mammalian target of rapamycin was observed in the valsartan-treated group.

CONCLUSIONS

Valsartan use is associated with similar clinical and molecular cardiac effects as ACE inhibitor therapy in stable long-term cardiac transplant recipients.