Ting I. Lee

Tumor necrosis factor-α decreases sarcoplasmic reticulum Ca2+-ATPase expressions via the promoter methylation in cardiomyocytes

Objectives:Sarcoplasmic reticulum Ca2+-ATPases (SERCA2a) plays an essential role in the Ca2+ homeostasis and cardiac functions. Tumor necrosis factor-&agr; (TNF-&agr;) decreases the SERCA2a, which may underlie cardiac dysfunction during sepsis and heart failure. Because the promoter region of SERCA2a contains CpG islands, gene methylation should be critical in regulating SERCA2a. The present study was to evaluate whether TNF-&agr; can modulate SERCA2a via enhancing methylation and to investigate the underlying mechanisms. Design:Controlled laboratory experiment. Setting:University research laboratory. Subjects:HL-1 cardiomyocytes. Interventions:TNF-&agr; (1-50 ng/mL) was administered in HL-1 cardiomyocytes with and without co-administration of an NF-&kgr;B inhibitor (SN-50, 50 &mgr;g/mL), antioxidant agents (ascorbic acid, 100 &mgr;M, or coenzyme Q10, 10 &mgr;M), or methylation inhibitor (5-aza-2′-deoxycytidine, 0.1, 1 &mgr;M). Measurements and Main Results:TNF-&agr; (50 ng/mL) decreased the SERCA2a RNA and protein by quantitative polymerase chain reaction and immunoblot. Furthermore, TNF-&agr; (50 ng/mL) increased the methylation in the SERCA2a promoter region, which was not influenced by the co-administration of SN-50, ascorbic acid, or coenzyme Q10, but was attenuated by 5-aza-2′-deoxycytidine (0.1 &mgr;M). Additionally, TNF-&agr; (50 ng/mL) increased the expression of DNA methyltransferase 1. Conclusions:TNF-&agr; increased DNA methyltransferase levels, thus enhancing the methylation in the SERCA2a promoter region with a result of reducing SERCA2a. These findings suggest that inhibition of hypermethylation may be a novel treatment strategy for cardiac dysfunction.

Calcitriol modulates receptor for advanced glycation end products (RAGE) in diabetic hearts

BACKGROUND Receptor for advanced glycation end products (RAGE) signaling pathway plays a vital role in diabetic cardiovascular complications. Calcitriol has been shown to exert various beneficial cardiovascular effects. The purpose of this study is to determine whether calcitriol can modulate RAGE expression, and study the potential mechanisms in diabetic hearts. METHODS Streptozotocin (65 mg/kg, intraperitoneal injection once) induced diabetic rats were treated with or without subcutaneous injections of calcitriol at a dose of 150 ng/kg/day for 4 weeks. Western blot was used to evaluate protein expressions of myocardial RAGE, TNF-α, p65 subunit of NF-κB (p65), α subunit of inhibitor of κB (IκBα), subunits of NADPH oxidase (NOX4 and p22(phox)), angiotensin II type 1 receptor (AT1R), TGF-β1, TGF-β receptor I, total and phosphorylated SMAD2/3 and ERK, matrix metalloproteinases 2 (MMP2), tissue inhibitors of metalloproteinases 2 (TIMP2) and procollagen I. RESULTS As compared to control, diabetic rats had increased expressions of cardiac RAGE, TNF-α, p22(phox), AT1R, and TGF-β1, which were significantly attenuated in the diabetic rats treated with calcitriol. Calcitriol-treated diabetic hearts also had lesser expressions of p-SMAD2/3 and p-ERK signaling than those of diabetic hearts. Moreover, diabetic hearts had increased expressions of MMP2 and procollagen I and decreased TIMP2. However, calcitriol reverted the diabetic effects in procollagen I but not in MMP2 or TIMP2. CONCLUSIONS Calcitriol decreased diabetic effects on RAGE and fibrosis, which may be caused by its modulation on AT1R and the anti-inflammatory and antioxidative potentials. Therefore, calcitriol may attenuate diabetic cardiomyopathy.

Hydralazine-induced promoter demethylation enhances sarcoplasmic reticulum Ca2+ -ATPase and calcium homeostasis in cardiac myocytes.

Sarcoplasmic reticulum (SR) Ca2+-ATPase (SERCA2a) plays an essential role in Ca2+ homeostasis and cardiac functions. The promoter region of SERCA2a has a high content of CpG islands; thus, epigenetic modification by inhibiting methylation can enhance SERCA2a expression in cardiomyocytes. Hydralazine, a drug frequently used in heart failure, is a potential DNA methylation inhibitor. We evaluated whether hydralazine can modulate Ca2+ handling through an increase in SERCA2a expression via regulating methylation. We used indo-1 fluorescence, real-time RT-PCR, immunoblotting, and methylation-specific PCR to investigate intracellular Ca2+, the expressions of RNA and protein, and methylation of SERCA2a in HL-1 cardiomyocytes with and without (control) the administration of hydralazine (1, 10, and 30 μM) for 72 h. Hydralazine (10 and 30 μM) increased the intracellular Ca2+ transients and SR Ca2+ contents. Hydralazine (10 and 30 μM) decreased methylation in the SERCA2a promoter region and increased the RNA and protein expressions of SERCA2a. Additionally, hydralazine (10 and 30 μM) decreased the expression of DNA methyltransferase 1. Moreover, treatment with hydralazine in isoproterenol-induced heart failure rats decreased the promoter methylation of SERCA2a and increased SERCA2a RNA expression. In conclusion, hydralazine-induced promoter demethylation may improve cardiac function through increasing SERCA2a and modulating calcium homeostasis in cardiomyocytes.

Rosiglitazone induces arrhythmogenesis in diabetic hypertensive rats with calcium handling alteration

BACKGROUND Diabetes and hypertension have significant effects on cardiac calcium (Ca(2+)) regulation, which plays an essential role in determining cardiac function. The effect of peroxisome proliferator-activated receptor (PPAR)-γ agonists on Ca(2+) regulation in the cardiomyocytes is unclear. OBJECTIVE The purpose of this study was to investigate the effects of hypertension, diabetes, and PPAR-γ agonist-rosiglitazone on the regulation of Ca(2+) and the electrophysiological characteristics of isolated ventricular myocytes. METHODS The indo-1 fluorometric ratio technique and whole-cell patch clamp were used to investigate intracellular Ca(2+) (Ca(2+)i), action potentials, and ionic currents in ventricular myocytes from rats of Wistar-Kyoto (WKY), diabetic WKY (induced by streptozotocin), diabetic WKY treated with rosiglitazone (5mg/kg), spontaneously hypertensive rats (SHR), diabetic SHR, and diabetic SHR treated with rosiglitazone. Western blot was used to evaluate protein expressions of sarcoplasmic reticulum ATPase (SERCA2a), Na(+)-Ca(2+) exchanger (NCX), and ryanodine receptor (RyR). RESULTS Diabetic WKY and diabetic SHR had smaller sarcoplasmic reticulum Ca(2+) contents, and Ca(2+)i transients with a prolonged decay portion, down-regulated SERCA2a, NCX, and RyR protein expressions and smaller L-type Ca(2+) currents than non-diabetic WKY and SHR, respectively. The Ca(2+) dysregulations in diabetes were attenuated in rats treated with rosiglitazone. Diabetes and hypertension both prolonged the action potential duration which were enhanced by the use of rosiglitazone, and induced the genesis of triggered activity. CONCLUSIONS Diabetes and hypertension modulate Ca(2+) handling. Rosiglitazone significantly changed the Ca(2+) regulation and electrophysiological characteristics, and may contain an arrhythmogenic potential in diabetes with hypertension.

Potential of vitamin D in treating diabetic cardiomyopathy

Cardiovascular disease is the leading cause of morbidity and mortality in patients with diabetes mellitus (DM), and patients with DM frequently develop diabetic cardiomyopathy. Currently, effective treatments for diabetic cardiomyopathy are limited. Vitamin D exerts pleiotropic effects on the cardiovascular system and is associated with DM. The purpose of this review was to evaluate published research on vitamin D in diabetic cardiomyopathy by searching PubMed databases. Herein, we reviewed vitamin D metabolism; evaluated the molecular, cellular, and neuroendocrine effects in native and bioactive vitamin D; and evaluated the role of vitamin D in treating cardiovascular disease and DM. Some evidence suggests that vitamin D may improve cardiovascular outcomes in diabetes through anti-inflammatory, antioxidative, antihypertrophic, antifibrotic, and antiatherosclerotic activities and by regulating advanced glycation end-product signaling, the renin-angiotensin system, and cardiac metabolism. This clinical and laboratory evidence suggests that vitamin D may be a potential agent in treating diabetic cardiomyopathy. However, using vitamin D entails possible adverse risks of hypercalcemia, hyperphosphatemia, and vascular calcifications. Therefore, future studies should be conducted that clarify the potential benefits of vitamin D through large-scale randomized clinical trials in well-defined groups of diabetic patients.

PPARs modulate cardiac metabolism and mitochondrial function in diabetes

Diabetic cardiomyopathy is a major complication of diabetes mellitus (DM). Currently, effective treatments for diabetic cardiomyopathy are limited. The pathophysiology of diabetic cardiomyopathy is complex, whereas mitochondrial dysfunction plays a vital role in the genesis of diabetic cardiomyopathy. Metabolic regulation targeting mitochondrial dysfunction is expected to be a reasonable strategy for treating diabetic cardiomyopathy. Peroxisome proliferator-activated receptors (PPARs) are master executors in regulating glucose and lipid homeostasis and also modulate mitochondrial function. However, synthetic PPAR agonists used for treating hyperlipidemia and DM have shown controversial effects on cardiovascular regulation. This article reviews our updated understanding of the beneficial and detrimental effects of PPARs on mitochondria in diabetic hearts.

HDAC inhibition modulates cardiac PPARs and fatty acid metabolism in diabetic cardiomyopathy

Peroxisome proliferator-activated receptors (PPARs) regulate cardiac glucose and lipid homeostasis. Histone deacetylase (HDAC) inhibitor has anti-inflammatory effects which may play a key role in modulating PPARs and fatty acid metabolism. The aim of this study was to investigate whether HDAC inhibitor, MPT0E014, can modulate myocardial PPARs, inflammation, and fatty acid metabolism in diabetes mellitus (DM) cardiomyopathy. Electrocardiography, echocardiography, and western blotting were used to evaluate the electrophysiological activity, cardiac structure, fatty acid metabolism, inflammation, and PPAR isoform expressions in the control and streptozotocin-nicotinamide-induced DM rats with or without MPT0E014. Compared to control, DM and MPT0E014-treated DM rats had elevated blood glucose levels and lower body weights. However, MPT0E014-treated DM and control rats had smaller left ventricular end-diastolic diameter and shorter QT interval than DM rats. The control and MPT0E014-treated DM rats had greater cardiac PPAR-α and PPAR-δ protein expressions, but less cardiac PPAR-γ than DM rats. Moreover, control and MPT0E014-treated DM rats had lower concentrations of 5′ adenosine monophosphate-activated protein kinase 2α, PPAR-γ coactivator 1α, phosphorylated acetyl CoA carboxylase, cluster of differentiation 36, diacylglycerol acyltransferase 1 (DGAT1), DGAT2, tumor necrosis factor-α, and interleukin-6 protein than DM rats. HDAC inhibition significantly attenuated DM cardiomyopathy through modulation of cardiac PPARS, fatty acid metabolism, and proinflammatory cytokines.

Glucagon-like peptide-1 regulates calcium homeostasis and electrophysiological activities of HL-1 cardiomyocytes.

Glucagon like-peptide-1 (GLP-1) is an incretin hormone with antidiabetic effects through stimulating insulin secretion, β cell neogenesis, satiety sensation, and inhibiting glucagon secretion. Administration of GLP-1 provides cardioprotective effects through attenuating cardiac inflammation and insulin resistance. GLP-1 also modulates the heart rate and systolic pressure, which suggests that GLP-1 may have cardiac electrical effects. Therefore, the purposes of this study were to evaluate whether GLP-1 has direct cardiac effects and identify the underlying mechanisms. Patch clamp, confocal microscopy with Fluo-3 fluorescence, and Western blot analyses were used to evaluate the electrophysiological characteristics, calcium homeostasis, and calcium regulatory proteins in HL-1 atrial myocytes with and without GLP-1 (1 and 10nM) incubation for 24h. GLP-1 (1 and 10nM) and control cells had similar action potential durations. However, GLP-1 at 10nM significantly increased calcium transients and sarcoplasmic reticular Ca(2+) contents. Compared to the control, GLP-1 (10nM)-treated cells significantly decreased phosphorylation of the ryanodine receptor at S2814 and total phospholamban, but there were similar protein levels of sarcoplasmic reticular Ca(2+)-ATPase and the sodium-calcium exchanger. Moreover, exendin (9-39) amide (a GLP-1 receptor antagonist, 10nM) attenuated GLP-1-mediated effects on total SR content and phosphorylated ryanodine receptor S2814. This study demonstrates GLP-1 may regulate HL-1 cell arrhythmogenesis through modulating calcium handling proteins.

Aging Modulates the Substrate and Triggers Remodeling in Atrial Fibrillation

Aging plays a critical role in the genesis of atrial fibrillation (AF) and also increases the risks of cardiac dysfunction and stroke in AF patients. AF is caused by increased AF triggering from abnormalities of the thoracic vein and/or modulated substrate (atrial) with enhancement of AF maintenance. Clinical and laboratory evidence indicates that aging is significant in the creation of atrial electrical and structural remodeling that leads to increased susceptibility to AF occurrence. Aging is commonly associated with cardiovascular comorbidities, oxidative stress, calcium dysregulation, atrial myopathy with apoptosis, and fibrosis, which all contribute to the genesis of AF. This review updates the current understanding of the effects of aging on the pathophysiology of AF.

ADAM10 modulates calcitriol-regulated RAGE in cardiomyocytes

Receptor for advanced glycation end products (RAGE) signalling plays a critical role in the pathogenesis of cardiovascular disease. Calcitriol modulates cardiac RAGE expression. This study explored the mechanisms underlying the effect of calcitriol on RAGE and soluble RAGE (sRAGE) expression in cardiomyocytes.