SERCA2 mRNA Research Articles

Elevated Afterload, Neuroendocrine Stimulation, and Human Heart Failure Increase BNP Levels and Inhibit Preload-Dependent SERCA Upregulation

In heart failure, brain-type natriuretic peptide (BNP) is elevated and the sarcoplasmic reticulum Ca(2+)-ATPase (SERCA) downregulated. We previously showed that preload-induced SERCA-upregulation is suppressed by exogenous BNP. Here we tested the hypothesis that afterload and neurohumoral activation would counterregulate preload-dependent SERCA upregulation through BNP, which finally results in decreased SERCA levels. We studied the effects of 6 hours preload, afterload, and isoproterenol stimulation on BNP and SERCA mRNA expression in rabbit and human failing muscles strips. Preload resulted in a pronounced upregulation of SERCA by 149% (isotonic versus slack, P<0.01). This upregulation was largely suppressed in afterloaded muscles (isometric versus slack: +32%; P<0.05). Similarly, presence of isoproterenol prevented SERCA upregulation in isotonic muscles. Afterload and isoproterenol resulted in a pronounced increase in BNP expression compared with slack by 225% (P<0.05) and 198% (P<0.01), respectively. Isoproterenol also increased expression of phospholamban by 84% (P<0.01). SERCA upregulation in preloaded muscles is associated with frequency-dependent potentiation of contractile force, which is absent in afterloaded muscles. In failing human myocardium, BNP expression was upregulated compared with nonfailing (+631%; P<0.05). Neither unloading nor preload or afterload induced a change in SERCA or BNP expression after 6 hours. Afterload and neuroendocrine stimulation increase BNP expression thereby causing inhibition of preload-dependent SERCA upregulation. In failing human myocardium, high BNP expression may underlie the loss of preload-dependent upregulation of SERCA. BNP may thus contribute to adverse myocardial remodelling in heart failure.

Mitochondrial transcription factors, Tfam and Tfb2 m regulate the SERCA2 gene transcription. A coordinate regulatory mechanism of energy production and expenditure

Background: The heart consumes ATP, which is mainly produced in mitochondria. Mitochondrial enzymes are produced under the control of mitochondrial specific transcription factor, Tfam and its enhancer, Tfb2 m. SERCA2 plays a central role in cardiac function by using ATP. Therefore, we tested if Tfam and Tfb2 m activate SERCA2 gene transcription as well as mitochondrial gene in the normal and diseased heart. Results: Localization of Tfam/Tfb2 m in the nucleus was demonstrated by immunostaining. ChIP assay revealed Tfam and Tfb2 m bound to the −479 to −1nt region of the SERCA2 gene promoter. Fluorescence correlation spectroscopy further revealed Tfam and Tfb2 m bound to the −122 to −114nt and the −122 to −117nt region, respectively. Overexpression of Tfam and Tfb2 m increased the SERCA2 gene transcription by 96% and their ablation diminished the SERCA2 transcription by 65 %. In the rat myocardial infarction model, SERCA2 mRNA level was significantly correlated with Tfam(r = 0.52, p < 0.001) and Tfb2m(r = 0.72, p < 0.001) mRNA. In the neonatal rat cultured myocytes, mutation of either Tfam or Tfb2 m binding sites decreased basal SERCA2 luciferase activity. Norepinephrine, an inducer of heart failure, decreased SERCA2 luciferase activity and its effect was further enhanced when mutations were induced. Conclusion: Our study revealed a novel machanism of the coordinate regulation of the transcription of genes for ATP production and expenditure. This mechanism will become a therapeutic target for heart failure.

Effect of Chaiqinchengqi decoction on sarco/endoplasmic reticulum Ca2+-ATPase mRNA expression of pancreatic tissues in acute pancreatitis rats

To investigate the effect of Chaiqinchengqi decoction (CQCQD) on sarco/endoplasmic reticulum Ca2+-ATPase (SERCA) mRNA expression of pancreatic tissues in acute pancreatitis (AP) rats. Thirty Sprague-Dawley (SD) rats were randomized into control group, AP group and CQCQD group (n = 3 x 10). The rats in the CQCQD group were intragastrically administered with CQCQD (10 mL/kg every 2 h) after induction of AP by intraperitoneal injection of caerulein (50 microg/kg.h x 5) within 4 h. At 6 h after the induction of AP model, pancreatic tissues were collected for the pathological observation, mRNA extraction for determination of SERCA1 and SERCA2 mRNA expression or pancreatic acinar cell isolation for measurement of fluorescence intensity (FI) of intracellular calcium ion concentration [Ca2+]i. There was no expression of pancreatic SERCA1 mRNA in the control group and the AP group. The expression of pancreatic SERCA2 mRNA in the AP group was down-regulated (expression ratio = 0.536; P = 0.001) compared with the control group, while that in the CQCQD group was up-regulated (expression ratio = 2.00; P = 0.012) compared with AP group. The FI of intracellular [Ca2+] of pancreatic acinar cells in the AP group (138.2 +/- 23.1) was higher than the C group (111.0 +/- 18.4) and the CQCQD group (118.7 +/- 15.2 ) (P < 0.05) and the pancreatic pathological score in the CQCQD group was lower than that in the AP group (5.7 +/- 1.9 vs 9.2 +/- 2.7, P < 0.05). CQCQD can up-regulate the expression of SERCA2 mRNA of pancreatic tissues, reduce intracellular calcium overload and relieve pancreatic tissue lesions.

Prostaglandin F2.ALPHA. Inhibits SERCA2 Gene Transcription Through an Induction of Egr-1 in Cultured Neonatal Rat Cardiac Myocytes

Prostaglandin F(2alpha) (PGF(2alpha)) stimulates hypertrophic growth of neonatal rat cardiac myocytes, a feature of which includes downregulation of the Ca(2+)-ATPase (SERCA2), a major Ca(2+) transport protein in SR. The molecular mechanisms by which PGF(2alpha) inhibits SERCA2 gene expression remain unknown. We determined the cis-regulatory elements responsible for the regulation of the SERCA2 gene expression in cultured neonatal rat cardiac myocytes exposed to PGF(2alpha). The role of Egr-1 was evaluated by transient transfection of its expression vector and antisense oligonucleotide. Signaling pathways were determined by using the pharmacological inhibitors or cDNA expression plasmids coding for dominant negative forms of Ras and Rac. PGF(2alpha) reduced the SERCA2 mRNA levels in a time- and dose-dependent manner in cultured rat cardiac myocytes. Transient transfection analyses showed that PGF(2alpha) -responsive elements are located between -284 and -72 of the SERCA2 promoter, which contains G+C-rich sequences homologous to Sp1, Egr-1 and AP2-binding sites. PGF(2alpha) significantly increased Egr-1 expression, and overexpression of Egr-1 largely reduced the transcription of the SERCA2 gene. Egr-1 antisense oligonucleotides blocked the PGF(2alpha) -mediated decrease in SERCA2 mRNA expression. Furthermore, inhibitors for either genistein-sensitive tyrosine kinase or p38 MAPK, and dominant negative forms of either Ras or Rac, prevented PGF(2alpha) -induced repression of SERCA2 mRNA levels. These results suggest that Egr-1, as well as Ras, Rac, and p38 MAPK, plays a crucial role in the repression of SERCA2 gene expression during PGF(2alpha) -induced cardiac hypertrophy.

Effects of sex hormones on genioglossal muscle contractility and SR Ca 2+-ATPase activity in aged rat

This investigation was designed to examine whether short-term administration of sex hormones could produce changes in contractile properties and the sarcoplasmic reticulum Ca 2+-ATPase (SERCA) function in genioglossal muscle (GG) of aged male rats. Twenty-four aged male rats were randomly divided into three groups to receive an intramuscular injection of either 0.1 mg/kg oestrogen (group A), 2.5 mg/kg testosterone (group B), or 0.2 ml sterile peanut oil (group C, control), twice a week, during 4 weeks. After hormone treatment, in vivo isometric contractile properties were determined using surgically prepared GG muscles with platinum electrodes for stimulation of the medial branch of the hypoglossus nerve. Sarcoplasmic reticulum Ca 2+-ATPase activity was measured in muscle homogenates by detecting the amount of inorganic phosphorus ion released in a standard coupled enzyme assay. SERCA1 mRNA level was observed using a real-time quantitative reverse transcription-polymerase chain reaction (Q-RT-PCR). It was found that, compared with group C, testosterone treatment decreased the fatigue resistance in GG muscles ( p < .05), whereas no change was observed in the isometric twitch ( P t) and tetanic tension ( P 0) ( p > .05). By contrast, in oestrogen treated GG muscles, no significant modification was found either in the contractile or in endurance properties ( p > .05). The change in GG fatigue resistance of group B was associated with a marked decrease in SR Ca 2+-ATPase activity when compared with that of the control group ( p < .01). Furthermore, SERCA1 mRNA level was also down regulated in group B ( p < .05). No prominent differences in SR Ca 2+-ATPase activity and SERCA1 mRNA expression existed between group A and group C ( p > .05). The present results show that exogenous testosterone produces more pronounced changes in GG muscle fatigue resistance than oestrogen does by acting at SR Ca 2+-ATPase activity and SERCA gene expression.

Propranolol causes a paradoxical enhancement of cardiomyocyte foetal gene response to hypertrophic stimuli

Pathological cardiac hypertrophy is associated with the expression of a gene profile reminiscent of foetal development. The non selective beta-adrenoceptor antagonist propranolol is able to blunt cardiomyocyte hypertrophic response in pressure-overloaded hearts. It remains to be determined whether propranolol also attenuates the expression of hypertrophy-associated foetal genes. To address this question, the foetal gene programme, of which atrial natriuretic peptide (ANP), the beta-isoform of myosin heavy chain (beta-MHC), and the alpha-skeletal muscle isoform of actin (skACT) are classical members, was induced by thoracic aortic coarctation (TAC) in C57BL/6 mice, or by phenylephrine, a selective alpha(1)-adrenoceptor agonist, in cultured rat neonatal cardiomyocytes. In TAC mice, the left ventricular weight-to-body weight (LVW/BW) ratio increased by 35% after 2 weeks. Levels of ANP, beta-MHC and skACT mRNA in the left ventricles increased 2.2-fold, 2.0-fold and 12.1-fold, respectively, whereas alpha-MHC and SERCA mRNA levels decreased by approximately 50%. Although propranolol blunted cardiomyocyte growth, with approximately an 11% increase in the LVW/BW ratio, it enhanced the expression of ANP, beta-MHC and skACT genes (10.5-fold, 27.7-fold and 22.7-fold, respectively). Propranolol also enhanced phenylephrine-stimulated ANP and beta-MHC gene expression in cultured cardiomyocytes. Similar results were obtained with metoprolol, a selective beta(1)-adrenoceptor antagonist, but not with ICI 118551, a beta(2)-adrenoceptor antagonist. Propranolol enhances expression of the hypertrophy-associated foetal genes mainly via the beta(1)-adrenoceptor blockade. Our results also suggest that, in pressure-overloaded hearts, cardiomyocyte growth and foetal gene expression occur as independent processes.

Activation of the androgen receptor alters the intracellular calcium response to glutamate in primary hippocampal neurons and modulates sarco/endoplasmic reticulum calcium ATPase 2 transcription

Androgens have been shown to have a number of effects on hippocampal function. Although androgen receptors (AR) are found at high levels in hippocampal neurons, the intracellular mechanisms responsible for androgen’s actions are unknown. If androgens were capable of altering internal calcium concentration ([Ca 2+] i), they could influence a variety of intracellular signaling pathways, maintain neuronal homeostasis and Ca 2+ induced excitotoxicity. In the present study, calcium imaging was used to measure the [Ca 2+] i in rat primary hippocampal neurons treated with either the AR agonist dihydrotestosterone (DHT), DHT+flutamide (AR antagonist), flutamide alone, or vehicle for 24 h and subsequently presented with an excitatory glutamate stimulus. In the absence of glutamate stimulation, DHT treatment caused a significant upward shift in baseline [Ca 2+] i when compared with neurons from all other groups. Glutamate had a greater effect on [Ca 2+] i in DHT-treated neurons and DHT-treated neurons returned to baseline levels significantly faster than all other groups. Cyclopiazonic acid, an inhibitor of sarco/endoplasmic reticulum calcium ATPase (SERCA) had a larger response in DHT-treated neurons compared with controls, suggesting increased Ca 2+ stores in DHT-treated neurons. In all cases the effects of DHT were blocked by treatment with flutamide indicating an AR-mediated mechanism. To determine a possible mechanism by which AR activation could be influencing [Ca 2+] i, SERCA2 mRNA levels were measured in primary hippocampal neurons. SERCA2 is inserted into the endoplasmic reticulum (ER) membrane and functions to rapidly pump [Ca 2+] i into the ER. Following treatment of primary hippocampal neurons with DHT, SERCA2 mRNA was increased, an effect that was blocked in the presence of flutamide. Taken together these results indicate that DHT, working through AR, causes an up-regulation of SERCA2, which increases the sequestering of [Ca 2+] i in the endoplasmic reticulum of hippocampal neurons. Such changes may allow the neurons to respond more robustly to a stimulus and recover more quickly following a highly stimulatory challenge.

Down-regulation of the cardiac sarcoplasmic reticulum ryanodine channel in severely food-restricted rats

We have shown that myocardial dysfunction induced by food restriction is related to calcium handling. Although cardiac function is depressed in food-restricted animals, there is limited information about the molecular mechanisms that lead to this abnormality. The present study evaluated the effects of food restriction on calcium cycling, focusing on sarcoplasmic Ca2+-ATPase (SERCA2), phospholamban (PLB), and ryanodine channel (RYR2) mRNA expressions in rat myocardium. Male Wistar-Kyoto rats, 60 days old, were submitted to ad libitum feeding (control rats) or 50% diet restriction for 90 days. The levels of left ventricle SERCA2, PLB, and RYR2 were measured using semi-quantitative RT-PCR. Body and ventricular weights were reduced in 50% food-restricted animals. RYR2 mRNA was significantly decreased in the left ventricle of the food-restricted group (control = 5.92 +/- 0.48 vs food-restricted group = 4.84 +/- 0.33, P < 0.01). The levels of SERCA2 and PLB mRNA were similar between groups (control = 8.38 +/- 0.44 vs food-restricted group = 7.96 +/- 0.45, and control = 1.52 +/- 0.06 vs food-restricted group = 1.53 +/- 0.10, respectively). Down-regulation of RYR2 mRNA expressions suggests that chronic food restriction promotes abnormalities in sarcoplasmic reticulum Ca2+ release.

Mechanism of reduced colonic contractility in experimental colitis: role of sarcoplasmic reticulum pump isoform-2

Inflammatory bowel diseases (IBD) such as Crohn's disease and ulcerative colitis are inflammatory disorders associated with decreased colonic contractility. Here we show that, in experimental colitis in rat induced by trinitrobenzenesulfonic acid, there is a decrease in contraction in response to carbamoylcholine and the sarco/endoplasmic reticulum Ca(+2) (SERCA) pump inhibitor thapsigargin. However, the decrease in contractility may occur due to decrease in the SERCA pump levels or their inactivation. Therefore, we examined the protein and mRNA levels for SERCA2 isoform, which is predominant isoform in colonic smooth muscle. There was a decrease in the levels of SERCA2 protein and mRNA levels in inflamed colonic muscle. These findings suggest that decreased SERCA pump levels is responsible for a decrease in the Ca(+2) stores in the sarco/endoplasmic reticulum that causes a decrease in the contractility in colonic smooth muscle leading to poor bowel movements.

Chronic allopurinol administration ameliorates maladaptive alterations in Ca2+ cycling proteins and β-adrenergic hyporesponsiveness in heart failure

Xanthine oxidase (XO) activity contributes to both abnormal excitation-contraction (EC) coupling and cardiac remodeling in heart failure (HF). beta-Adrenergic hyporesponsiveness and abnormalities in Ca(2+) cycling proteins are mechanistically linked features of the HF phenotype. Accordingly, we hypothesized that XO influences beta-adrenergic responsiveness and expression of genes whose products participate in deranged EC coupling. We measured inotropic (dP/dt(max)), lusitropic (tau), and vascular (elastance; E(a)) responses to beta-adrenergic (beta-AR) stimulation with dobutamine in conscious dogs administered allopurinol (100 mg po daily) or placebo during a 4-wk induction of pacing HF. With HF induction, the decreases in both baseline and dobutamine-stimulated inotropic responses were offset by allopurinol. Additionally, allopurinol converted a vasoconstrictor effect to dobutamine to a vasodilator response and enhanced both lusitropic and preload reducing effects. To assess molecular correlates for this phenotype, we measured myocardial sarcoplasmic reticulum Ca(2+)-ATPase 2a (SERCA), phospholamban (PLB), phosphorylated PLB (P-PLB), and Na(+)/Ca(2+) transporter (NCX) gene expression and protein. Although SERCA mRNA and protein concentrations did not change with HF, both PLB and NCX were upregulated (P < 0.05). Additionally, P-PLB and protein kinase A activity were greatly reduced. Allopurinol ameliorated all of these molecular alterations and preserved the PLB-to-SERCA ratio. Preventing maladaptive alterations of Ca(2+) cycling proteins represents a novel mechanism for XO inhibition-mediated preservation of cardiac function in HF, raising the possibility that anti-oxidant therapies for HF may ameliorate transcriptional changes associated with adverse cardiac remodeling and beta-adrenergic hyporesponsiveness.

Reduced myocardial expression of calcium handling protein in patients with severe chronic mitral regurgitation☆☆☆

Left ventricle (LV) function was shown to be a principal determinant of morbidity and mortality in both uncorrected and surgically corrected mitral regurgitation (MR). However, the cellular mechanisms that develop in the LV remodeling secondary to volume overload in chronic severe MR is still not well defined. In single ventricular myocyte, a reduced contraction and slowed relaxation have been mainly attributed to defective intracellular Ca2+ currents. Between several Ca2+ handling proteins, sarcoplasmic reticulum Ca2+-ATPase 2 (SERCA2) expression and activity determines not only the extent and rate of relaxation, but also the rate and amplitude of contraction. The aim of the study was to determine whether modifications of SERCA2 gene expression occurs in LV wall remodeling process secondary to chronic severe MR. The LV samples were obtained from 12 patients presented LV wall remodeling (LV: diastolic/systolic diameter-70+/-7 mm vs 46+/-10 mm; diastolic/systolic volume-260+/-65 ml vs 102+/-68 ml) due to chronic, severe MR. Expressions of SERCA2 isoforms-SERCA2a and 2b mRNAs were estimated by semiquantitative RT-PCR and normalized to GAPDH. The protein levels of SERCA2 were determined by Western blot after normalization to actin. Results were compared with samples from non-failing human hearts (NFH). On SERCA2 mRNA levels, important reduction on both SERCA isoforms SERCA2a (-40%) and SERCA2b (-49%) compared to NFH, together with significant correlation between isoforms (r = 0.89; p = 0.01) were observed. SERCA2 protein levels were decreased (-38%) in MR compared to NFH. Also significant correlations between SERCA2a/2b and SERCA2 protein expression (r = 0.83, p = 0.017; r = 0.68, p = 0.05, respectively) were observed. Moreover, a negative correlation between protein levels of SERCA2 (r = -0.64, p = 0.053) and left ventricular diastolic diameter was observed. In chronic volume overload the down-regulation of SERCA2a and 2b at the mRNA and SERCA2 protein levels exist. Moreover, protein levels of SERCA2 tend to correlate to the grade of left ventricular diastolic dilatation and suggest an important role LV remodeling.

Sarco/Endoplasmic Reticulum Calcium-ATPase 2 Expression as a Tumor Marker in Colorectal Cancer

Maintaining a high calcium concentration in the endoplasmic reticulum through the action of sarco/endoplasmic reticulum calcium-ATPases (SERCAs) is crucial in many cell functions involved in intracellular signal transduction, control of proliferation, programmed cell death, or the synthesis of mature proteins. Recent studies have found that many SERCAs have altered expression patterns in various malignancies. The purpose of the current study was to quantify the expression of SERCA2 in colorectal cancer (CRC) tissues and the corresponding noncancerous tissues, and to statistically analyze whether the SERCA2 expression levels correlate with the clinico-pathologic features and prognosis of CRC patients. Paired colorectal tissue samples from cancerous and the corresponding noncancerous tissues were obtained from 50 patients who underwent surgical resection. Semiquantitative measurements of SERCA2 messenger RNA (mRNA) expression were done using the multiplex reverse transcriptase-polymerase chain reaction. CRC tissues were analyzed through immunohistochemistry for the SERCA2 protein. SERCA2 mRNA overexpression in cancerous tissues compared with normal counterparts was observed in 45 of 50 (90%) patients. The mean expression level of SERCA2 mRNA in cancerous tissues was significantly higher than that in noncancerous tissues (P = 0.01). Increased SERCA2 protein expression was significantly correlated with serosal invasion (P = 0.012), lymph node metastasis (P = 0.009), and advanced tumor stage (P = 0.004). Furthermore, patients with high SERCA2 expression had a significantly poorer overall survival rate than patients with low SERCA2 (P = 0.032). Multivariate analyses indicated that tumor stage (P = 0.015) and SERCA2 expression were independently correlated with overall survival (P = 0.018). The result of this study indicated that SERCA2 may be a molecular determinant in the development and progression of CRC. The molecular mechanisms underlying the SERCA-dependent calcium accumulation and CRC tumorigenesis are worthy of further investigations.

Effect of estrogen on calcium-handling proteins, β-adrenergic receptors, and function in rat heart

Regulation of cellular Ca 2+ cycling is central to myocardial contractile function. Loss of Ca 2+ regulation is associated with cardiac dysfunction and pathology. Estrogen has been shown to modify contractile function and to confer cardioprotection. Therefore, we investigated the effect of estrogen on expression of rat heart myocardial Ca 2+-handling proteins and beta-adrenergic receptor (β 1-AR) and examined functional correlates. Female rats were sham-operated (SHAM) or ovariectomized. Two weeks after ovariectomy rats were injected (i.p.) daily with estradiol benozoate (OVX + EB) or sesame oil (OVX) for 2 weeks. Protein abundance was measured by immunoblotting and mRNA was quantified by real-time RT-PCR. OVX significantly decreased estrogen and progesterone levels and EB replacement returned both estrogen and progesterone to physiological levels. OVX induced a 75% reduction of uterine weight and a gain in body weight. Replacement restored weights to SHAM level. OVX increased and estrogen-replacement normalized abundance of β 1-AR and L-type Ca 2+ channel (Cav1.2) protein. OVX decreased sodium–Ca 2+ exchange protein (NCX) and estrogen restored protein abundance to SHAM levels. Sarcoplasmic reticular ATPase (SERCA), phospholamban (PLB), and ryanodine receptor (RyR) abundance was not altered by hormone status. Levels of mRNA encoding for β 1-AR, Cav1.2, and NCX were not influenced by OVX or estrogen replacement. OVX had no effect on SERCA and PLB mRNA level but estrogen replacement elicited a significant increase compared to OVX and SHAM. Estrogen-dependent changes in Ca 2+-handling proteins and β 1-AR are theoretically consistent reduced myocellular Ca 2+ load. However, hormone-dependent alterations in protein were not associated with changes in contractile function.

Regulatory role of ovarian sex hormones in calcium uptake activity of cardiac sarcoplasmic reticulum

Alterations in the intracellular Ca2+ handling in cardiomyocytes may underlie the cardiac dysfunction observed in the ovarian sex hormone-deprived condition. To test the hypothesis that ovarian sex hormones had a significant role in the cardiac intracellular Ca2+ mobilization, the sarcoplasmic reticulum (SR) Ca2+ uptake and SR Ca2+-ATPase (SERCA) activity were determined in 10-wk ovariectomized rat hearts. With the use of left ventricular homogenate preparations, a significant suppression of maximum SR Ca2+ uptake activity, but with an increase in SR Ca2+ responsiveness, was demonstrated in ovariectomized hearts. In parallel measurements of SERCA activity in SR-enriched membrane preparations from ovariectomized hearts, a suppressed maximum SERCA activity with a leftward shift in the relationship between pCa (-log molar free Ca2+ concentration) and SERCA activity was also detected. A significant downregulation of SERCA proteins and reduction in the SERCA mRNA level were observed in association with suppressed maximum SERCA activity. While there were no changes in total phospholamban and phosphorylated Ser16 phospholamban levels, a decrease in phosphorylated Thr17 phospholamban as well as an increase in the suprainhibitory, monomeric form of phospholamban stoichiometry was found. Estrogen and progesterone supplementations were equally effective in preventing changes in ovariectomized hearts. Our data showed for the first time that female sex hormones played an important role in the regulation of the cardiac SR Ca2+ uptake. Under hormone-deficient conditions, there was an adaptive response of SERCA that escaped the regulatory effect of phospholamban.

CRNK Overexpression Alters Hypertrophic Gene Expression In Cultured Neonatal Rat Ventricular Myocytes

We previously showed that overexpression of PYK2, a Ca2+-dependent nonreceptor protein tyrosine kinase, activated the stress-activated protein kinases JNK1/2 and p38MAPK, and down-regulated SERCA2 gene transcription in neonatal rat ventricular myocytes (NRVM) (Heidkamp et al., AJP:Cell 289:C471-C482, 2005). In the present study, we examined the effects of adenovirally (Adv)-mediated overexpression of a C-terminal, dominant-negative inhibitor of PYK2, known as CRNK (Cell adhesion kinase-β Related NonKinase) on cellular growth and hypertrophic gene expression in similarly cultured NRVM. NRVM were maintained in serum-free culture medium (UI), or infected with either Adv-CRNK or control Adv expressing green fluorescent protein (Adv-GFP; 5 moi, 24–48h). Cell extracts were analyzed for JNK and p38MAPK phosphorylation by Western blotting, for total protein and DNA content by spectrophotometry and fluorometry, and for SERCA2 and ANF mRNA levels by real-time RT-PCR. CRNK overexpression had no effect on basal JNK or p38MAPK, but blocked the H2O2-induced increase in JNK1/2 (but not p38MAPK) phosphorylation. CRNK overexpression also did not affect basal total protein/DNA ratio, and did not prevent the increase in total protein/DNA ratio produced by treatment with phorbol myristate acetate (200nM, 24h). However, CRNK overexpression significantly (P<0.05) increased SERCA2 mRNA levels 2.1±0.5-fold as compared to UI or GFP-expressing NRVM. In contrast, ANF mRNA levels were significantly decreased to 36±14% of UI by CRNK overexpression. These data indicate that PYK2 is necessary to elicit specific aspects of the hypertrophic phenotype in cultured NRVM. Supported by NIH RO1 HL34328 and the Dr. Ralph and Marian Falk Medical Research Trust.

Regulation factors exploring for bone marrow mesenchymal stem cells transdifferentiate into cardiomyocytes

OBJECTIVE In order to understand the effects of cardiac microenvironment on the differentiation of Bone marrow mesenchymal stem cells (BMSCs) into cardiomyocyte-like cells (CLCs), the cardiac microenvironment was simulated in vitro by coculturing BMSCs with myocardial cells. METHODS BMSCs were isolated from human bone marrow and their phenotypes were identified with fluorescence-activated cell sorting (FACS). BMSCs were cocultured with neonatal rat ventricular myocytes by semipermeable membrane. This membrane allows the diffusion of secreted factors but prevents physical contact between the two cell populations. The transformation of BMSCs was confirmed by immunocytochemistry, RT-PCR and western blot analysis. The differential expression factors was analysed by gene chip. RESULTS After cocultured with myocytes, SERCA2, RyR2 and GATA-4 mRNA in BMSCs were increased significantly. Some BMSCs became sarcomeric alpha-actinin, desmin, cTnT, and cTnI positive cells, suggesting a developing cardiomyocyte phenotype. Gene chip showed that there were 532 genes upregulated and 325 genes down-regulated after coculturing. Many of these upregulated genes were transcription factor for promoting cardiomyogenesis and some genes encoded cardiac specific proteins. CONCLUSION These results showed that human BMSCs possesses the potential to differentiate into cardiomyocytes, and this process is independent of physical contact between BMSCs and myocytes. On-going investigations may lead to the discovery of mediators of BMSCs migration and differentiation that, in turn, will be more effective way to repair the injured heart. (This work was supported by grants from National Natural Science Foundation of China, No.30271287, 30571850)

Effects of angiotensin II receptor blocker (candesartan) in daunorubicin-induced cardiomyopathic rats

Background Daunorubicin is an anthracycline anti-tumor agent; anthracycline chemotherapy in cancer can cause severe cardiomyopathy leading to a frequently fatal congestive heart failure; the first-line treatment is diuretics and digoxin. Recently, angiotensin-converting enzyme inhibitors have been shown to be effective in the treatment of such toxicity. The purpose of this study was to investigate the effects of angiotensin II type-1 receptor antagonist (candesartan) in a rat model of daunorubicin-induced cardiomyopathy. Methods Rats were treated with a cumulative dose of 9 mg/kg body weight daunorubicin (i.v.). 28 days later, after the development of cardiomyopathy, animals were randomly assigned to candesartan-treated (5 mg/kg/day, p.o.) or vehicle-treated groups; age-matched normal rats were used as the control group. Candesartan treatment was continued for 28 days. Hemodynamic and echocardiographic parameters were measured, cardiac protein and mRNA were analyzed, and histopathological analyses of myocardial fibrosis, cell size and apoptosis were conducted. Results Following cardiomyopathy, left ventricular end diastolic pressure and left ventricular systolic dimension were significantly elevated; while % fractional shortening and Doppler E/ A ratio were significantly reduced. Cardiomyopathic hearts showed significant increases in % fibrosis, % apoptosis, and myocyte diameter/body weight ratio; candesartan treatment reversed these changes. Fas-L protein overexpression in myopathic hearts was significantly suppressed by treatment with candesartan. Moreover, SERCA2 mRNA and protein expression were both down-regulated in myopathic hearts and restored to normal by candesartan treatment, significantly. Conclusions Our findings suggest that candesartan treatment significantly improved the left ventricular function and reversed the myocardial pathological changes investigated in this model of daunorubicin-induced cardiomyopathy; suggesting its potentials in limiting daunorubicin cardiotoxicity.

Transcriptional Control of the Mitochondrial Gene Determines the Cardiac Contractile: Possible Involvement of SERCA2 Gene Activation by Mitochondrial Transcription Factors

Background: Expression of mitochondrial (Mt) proteins is controlled by Mt-transcriptional machinery composed of Tfam, Tfb2m and Mt-RNA polymerase. Correlations among Mt-transcription factors, each Mt respiratory complex, SERCA2 mRNA level, and systolic and diastolic function were determined in rat failing heart. We next tested the hypothesis that Mt-transcription factors regulate the transcription of the SERCA2 gene as well as Mt-genes.

Cardiac Sympathetic Dysfunction Correlates With Abnormal Myocardial Contractile Reserve in Dilated Cardiomyopathy Patients

We investigated the relationship between iodine-123-metaiodobenzylguanidine (123I-MIBG) findings and myocardial contractile reserve in patients with mild to moderate dilated cardiomyopathy (DCM). Little is known regarding the relationship between cardiac sympathetic nervous function and myocardial contractile reserve in DCM. Twenty-four DCM patients who showed sinus rhythm underwent echocardiography, biventricular catheterization, and myocardial 123I-MIBG scintigraphy. Left ventricular (LV) pressures were measured using a micromanometer-tipped catheter. The myocardial contractile function (LV dP/dt(max)) was determined at rest and during atrial pacing. The messenger ribonucleic acid (mRNA) expressions of intracellular Ca2+-regulatory proteins were analyzed by real-time quantitative reverse transcription-polymerase chain reaction. Myocardial 123I-MIBG accumulation was quantified as a heart-mediastinum ratio (HMR). A significant correlation was observed between the delayed 123I-MIBG HMR and the percentage change in LV dP/dt(max) from the baseline to the peak or critical heart rate (r = 0.64; p < 0.001). The delayed 123I-MIBG HMR was significantly lower in patients showing a worsening change in LV dP/dt(max) than in those showing a favorable change (p < 0.005). The maximum LV dP/dt(max) during pacing and the sarcoplasmic reticulum Ca2+-ATPase (SERCA2) mRNA levels were significantly more reduced in patients with a delayed HMR < or =1.8 than in those with a delayed HMR >1.8 (p < 0.05, respectively). Abnormal myocardial 123I-MIBG accumulation is related to an impaired myocardial contractile reserve and down-regulation of SERCA2 mRNA in DCM. Myocardial 123I-MIBG scintigraphy can be useful in noninvasively evaluating myocardial contractile reserve in patients with mild to moderate DCM.

COMPARISON OF LOW and HIGH DOSES OF CARVEDILOL ON RESTORATION OF CARDIAC FUNCTION and CALCIUM‐HANDLING PROTEINS IN RAT FAILING HEART

1. The beta-adrenoceptor antagonist carvedilol reverses cardiac dysfunction in the failing heart. A recent study showed that beta-adrenoceptor antagonists indirectly normalize Ca(2+)-regulatory proteins. The relationship between these two phenomena and the suitable dosage of carvedilol remains unclear. 2. We investigated the change in left ventricular (LV) remodelling and function in a rat model of heart failure due to myocardial infarction (MI) with or without carvedilol (30 or 2 mg/kg per day) treatment for 6 weeks. The expression of mRNA and proteins of sarcoplasmic reticulum Ca(2+)-ATPase (SERCA) and phospholamban (PLB) in cardiomyocytes was also measured. 3. There was significant LV remodelling and cardiac contractile dysfunction in MI rats. The expression of SERCA mRNA and protein were downregulated (P < 0.01), but the expression of PLB mRNA and protein were upregulated (P < 0.01) in MI rats compared with sham-operated rats. After treatment with carvedilol, LV remodelling and cardiac contractile dysfunction were clearly improved. Low-dose carvedilol was better at improving some parameters of LV remodelling and function than the high dose. Carvedilol partially restored the low expression of SERCA (P < 0.05), but had no effect on PLB expression (P > 0.05). Moreover, low-dose carvedilol induced a more significant improvement in SERCA expression than did the high dose (P < 0.05). 4. The results of the present study suggest that carvedilol is effective in improving LV remodelling and cardiac contractile dysfunction after MI. This may be related to the normalization of SERCA expression.