Search PubMed⌕ Search

Biomedical subjects

W H Dillmann

Publications and source records attributed to W H Dillmann.

At least 37 records · Page 2Linked to original sources
PubMed1999

Heat shock proteins and protection against ischemic injury.

Heat shock proteins present a complex family of proteins exerting chaperone-like activities that are classified according to their molecular weight. We especially explored protective functions of inducible heat shock protein 70, the mitochondrial heat shock protein 60 and 10, and the small heat shock proteins HSP27 and alphaB-crystallin against ischemic, reoxygenation-mediated injury using transgenic animals and hearts under in vivo conditions and in isolated cardiac myocyte-derived cells using adenoviral vectors. We noted with great interest that differential protective effects are exerted by specific hsps. For example, alpha-B-crystallin and constitutive hsp70 markedly protect microtubular structure in cardiac myocytes from ischemia-induced injury. Inducible hsp70, hsp60 and hsp10 when coexpressed, and hsp27 and alphaB-crystallin have an overall protective effect against ischemic injury as determined by the release of enzymes like creatine kinase and LDH. We did not note inflammatory or immune responses elicited by the expression of hsps in transgenic animals and cardiac myocytes. The specific cell types in which hsps are expressed may contribute to the protective effect of hsps versus their inflammatory and immunogenic effects when expressed in other cell types.

Animals↗
PubMed1999

Altered cardiac phenotype in transgenic mice carrying the delta337 threonine thyroid hormone receptor beta mutant derived from the S family.

The heart has been recognized as a major target of thyroid hormone action. Our study investigates both the regulation of cardiac-specific genes and contractile behavior of the heart in the presence of a mutant thyroid hormone receptor beta1 (T3Rbeta1-delta337T) derived from the S kindred. The mutant receptor was originally identified in a patient with generalized resistance to thyroid hormone. Cardiac expression of the mutant receptor was achieved by a transgenic approach in mice. As the genes for myosin heavy chains (MHC alpha and MHC beta) and the cardiac sarcoplasmic reticulum Ca2+ adenosine triphosphatase (SERCA2) are known to be regulated by T3, their cardiac expression was analyzed. The messenger RNA levels for MHC alpha and SERCA2 were markedly down-regulated, MHC beta messenger RNA was up-regulated. Although T3 levels were normal in these animals, this pattern of cardiac gene expression mimics a hypothyroid phenotype. Cardiac muscle contraction was significantly prolonged in papillary muscles from transgenic mice. The electrocardiogram of transgenic mice showed a substantial prolongation of the QRS interval. Changes in cardiac gene expression, cardiac muscle contractility, and electrocardiogram are compatible with a hypothyroid cardiac phenotype despite normal T3 levels, indicating a dominant negative effect of the T3Rbeta mutant.

Animals↗
PubMed1999

Influence of phosphorylation and oligomerization on the protective role of the small heat shock protein 27 in rat adult cardiomyocytes.

Recent reports have demonstrated that the heat shock proteins (hsp) and in particular the hsp70 confer protection against cardiac ischemic damage. More recently, we have shown that increased expression of another heat shock protein, the hsp27, through an adenovirus vector system protects adult cardiomyocytes against ischemic injury. This small heat shock protein undergoes phosphorylation when the cell is under stress. This has led many to speculate that phosphorylation of hsp27 is required for the protective role this protein plays in the cell. In order to investigate this possibility, we have mutated the serines that are the sites of phosphorylation on the hsp27, to glycines or alanines. These nonphosphorylatable mutants of hsp27 were cloned into adenoviral vectors and used to infect adult rat cardiomyocytes to assess their ability in protecting against ischemic injury. In addition, we used a specific inhibitor of p38 MAP kinase that is a key member of the kinase pathway responsible for phosphorylating the hsp27. Our present results show that the nonphosphorylated hsp27 forms larger oligomeric complexes than the phosphorylated hsp27. Interestingly, phosphorylation of hsp27 seems not to play a role in its ability to protect adult rat cardiomyocytes against ischemic damage.

Animals↗
PubMed1998

Influences of increased expression of the Ca2+ ATPase of the sarcoplasmic reticulum by a transgenic approach on cardiac contractility.

Congestive heart failure is a significant clinical problem and leads to abnormalities in Ca2+ transients and to decreases in the level of the Ca2+ ATPase of the sarcoplasmic reticulum according to reports to some investigators. The Ca2+ ATPase of the sarcoplasmic reticulum (SERCA2) contributes in an important manner to diastolic Ca2+ lowering and relaxation of the heart. To determine the contractile alterations resulting from increased SERCA2 expression, we generated transgenic mice overexpressing a rat SERCA2 transgene. In these mice, SERCA2 mRNA was increased 2.6-fold, the relative synthesis rate of SERCA2 protein 1.8-fold, and SERCA2 protein levels 1.2-fold. Functional analysis of Ca2+ handling and contractile parameters in isolated cardiac myocytes indicated that the intracellular Ca2+ decline and myocyte relengthening were each accelerated by 22-23%. In addition, studies in isolated papillary muscles showed that the time to half-maximal post-rest potentiation was significantly shorter, hinting at an increased Ca2+ loading of the sarcoplasmic reticulum. Furthermore, in vivo cardiac functional studies demonstrated a significant accelerated contraction and relaxation in SERCA2 transgenic mice. We also cloned a SERCA2 transgene and mutants of the phospholamban gene into E1 deleted replication-deficient human adenovirus 5 viral vectors and infected cardiac myocytes. In the cardiac myocytes, endogenous SERCA2 levels were decreased by PMA treatment. Infection of such myocytes with a SERCA2 expressing adenovirus could reconstitute the Ca2+ transient, and augmented oxalate facilitated SERCA2 Ca2+ uptake. In addition, phospholamban mutants with changes of basic to acidic amino acids in the cytoplasmic domain increased SERCA2 activity by 30-35%. These findings, therefore, suggest that increased SERCA2 activity can be achieved by increasing SERCA2 levels or by expressing phospholamban mutants. Increased SERCA2 activity can lead to significant enhancements of Ca2+ transients and myocardial contractility.

Animals↗
PubMed1998

The Raf-MEK-ERK cascade represents a common pathway for alteration of intracellular calcium by Ras and protein kinase C in cardiac myocytes.

Ras and protein kinase C (PKC), which regulate the Raf-MEK-ERK cascade, may participate in the development of cardiac hypertrophy, a condition characterized by diminished and prolonged contractile calcium transients. To directly examine the influence of this pathway on intracellular calcium ([Ca2+]i), cardiac myocytes were cotransfected with effectors of this pathway and with green fluorescent protein, which allowed the living transfected myocytes to be identified and examined for [Ca2+]i via indo-1. Transfection with constitutively active Ras (Ha-RasV12) increased cell size, decreased expression of the myofibrils and the calcium-regulatory enzyme SERCA2, and reduced the magnitude and prolonged the decay phase of the contractile [Ca2+]i transients. Similar effects on [Ca2+]i were obtained with Ha-RasV12S35, a Ras mutant that selectively couples to Raf, and with constitutively active Raf. In contrast, Ha-RasV12C40, a Ras mutant that activates the phosphatidylinositol 3-kinase pathway, had a lesser effect. The PKC-activating phorbol ester, phorbol 12-myristate 13-acetate, also prolonged the contractile [Ca2+]i transients. Cotransfection with dnMEK inhibited the effects of Ha-RasV12, Raf, and phorbol 12-myristate 13-acetate on [Ca2+]i. The effects of Ha-RasV12 and Raf on [Ca2+]i were also counteracted by SERCA2 overexpression. Both Ras and PKC may thus regulate cardiac [Ca2+]i via the Raf-MEK-ERK cascade, and this pathway may represent a critical determinant of cardiac physiological function.

Animals↗
PubMed1998

Protection against myocardial dysfunction after a brief ischemic period in transgenic mice expressing inducible heat shock protein 70.

Brief ischemic periods lead to myocardial dysfunction without myocardial infarction. It has been shown that expression of inducible HSP70 in hearts of transgenic mice leads to decreased infarct size, but it remains unclear if HSP70 can also protect against myocardial dysfunction after brief ischemia. To investigate this question, we developed a mouse model in which regional myocardial function can be measured before and after a temporary ischemic event in vivo. In addition, myocardial function was determined after brief episodes of global ischemia in an isolated Langendorff heart. HSP70-positive mice and transgene negative littermates underwent 8 min of regional myocardial ischemia created by occlusion of the left descending coronary artery, followed by 60 min of reperfusion. This procedure did not result in a myocardial infarction. Regional epicardial strain was used as a sensitive indicator for changes in myocardial function after cardiac ischemia. Maximum principal strain was significantly greater in HSP70-positive mice with 88+/-6% of preischemic values vs. 58+/-6% in transgene-negative mice (P < 0.05). Similarly, in isolated Langendorff perfused hearts of HSP70-positive and transgene-negative littermates exposed to 10 min of global ischemia and 90 min of reperfusion, HSP70 transgenic hearts showed a better-preserved ventricular peak systolic pressure. Thus, we conclude that expression of HSP70 protects against postischemic myocardial dysfunction as shown by better preserved myocardial function.

Animals↗
PubMed1998

Constitutive and inducible hsp70s are involved in oxidative resistance evoked by heat shock or ethanol.

Improved cardiac post-ischemic recovery after whole-body hyperthermia is correlated with an increased expression of the heat shock proteins (hsps). The inducible hsp70 (hsp70i) has a known cardioprotective effect against ischemia/reperfusion injury. Here, we studied whether other hsps are also involved in cardioprotection. Using rat heart-derived H9c2 myocytes, we observed that preheating at 43 degreesC for 20 min conferred resistance to hydrogen peroxide (H2O2). The resistance to mild H2O2 toxicity (3-5 micro mol/10(7) cells) appeared early and persisted, whereas the resistance to moderate H2O2 toxicity (6-9 micro mol/10(7) cells) was detectable only at 20-44 h post heat shock. No resistance was observed at higher doses of hydrogen peroxide (10-12 micro mol/10(7) cells), indicating that severe toxicity exceeds the capacity of the induced protective mechanism. Coincidentally, this thermal regimen elicited a rapid and prolonged increase in the cellular level of hsp70i, and a delayed and transient induction of the constitutive hsp70 (hsp70c). Nuclear translocations of hsp70i and hsp70c also occurred upon heat stimulation. A homogeneous distribution of the accumulated hsp70i and hsp70c throughout the nuclei and cytoplasm paralleled the development of heat-induced resistance to moderate H2O2 challenge. Application of another hsp inducer, ethyl alcohol, evoked a similar pattern of H2O2 resistance, and hsp induction and distribution. Our results suggest that induction and subcellular distribution of hsp70s contribute importantly to cellular antioxidant defenses, and that a co-operation between hsp70i and hsp70c may improve cardiac preservation during oxidative insult.

Animals↗
PubMed1998

Sarcoplasmic reticulum function in murine ventricular myocytes overexpressing SR CaATPase.

To examine the effects of the overexpression of sarcoplasmic reticulum (SR) CaATPase on function of the SR and Ca2+ homeostasis, we measured [Ca2+]i transients (fluo-3), and L-type Ca2+ currents (ICa.L), Na/Ca exchanger currents (INa/Ca), and SR Ca2+ content with voltage clamp in ventricular myocytes isolated from wild type (WT) mice and transgenic (SRTG) mice. The amplitude of [Ca2+]i transients was insignificantly increased in SRTG myocytes, while the diastolic [Ca2+]i tended to be lower. The initial and terminal declines of [Ca2+]i transients were significantly accelerated in SRTG myocytes, implying a functional upregulation of the SR CaATPase. We examined the functional contribution of only the SR CaATPase to the initial and the terminal phase of the decline of [Ca2+]i, by abruptly inhibiting Na/Ca exchange with a rapid switcher device. The rate of [Ca2+] decline mediated by the SR CaATPase was increased by 40% in SRTG compared with WT myocytes. The function of the L-type Ca2+ channel was unchanged in SRTG myocytes, while INa/Ca density was slightly (10%) decreased. Measured SR Ca2+ content was significantly increased by 29% in SRTG myocytes. Thus, overexpression of SR CaATPase markedly accelerates the decline of [Ca2+]i transients, and induces in increase in SR Ca2+ content, with some downregulation of the Na/Ca exchanger.

Animals↗
PubMed1998

Sarcoplasmic reticulum Ca(2+)-ATPase overexpression by adenovirus mediated gene transfer and in transgenic mice.

The sarcoplasmic reticulum Ca(2+)-ATPase (SERCA2a) is a major determinant of cardiac relaxation. It has been demonstrated that the steady state levels of the mRNA coding for this pump are reduced in human heart failure due to dilated cardiomyopathy. Although results regarding the protein level are controversial, most functional studies indicate decreased SERCA2a activity in heart failure. The extent to which a potential decrease in the calcium sequestering function of this protein could contribute to the contractile dysfunction in heart failure, and whether a reconstitution of SERCA2a could alleviate heart failure, are yet unknown. To further investigate these questions two methodological approaches were chosen. Adenovirus mediated gene transfer provides an approach to study functional consequences of SERCA2a overexpression in cardiac myocytes in vitro [1], and a transgenic mouse model allows the effects of cardiac overexpression of SERCA2a to be examined in vivo [2].

Adenoviridae↗
PubMed1998

Thermodynamic limitation for Ca2+ handling contributes to decreased contractile reserve in rat hearts.

The free energy release from ATP hydrolysis (|DeltaG approximately p|) is decreased by inhibiting the creatine kinase (CK) reaction, which may limit the thermodynamic driving force for the sarcoplasmic reticulum (SR) Ca2+ pumps and thereby cause a decrease in contractile reserve. To determine whether a decrease in |DeltaG approximately p| results in decreased contractile reserve by impairing Ca2+ handling, we measured left ventricular pressure and cytosolic Ca2+concentration ([Ca2+]c; by indo 1 fluorescence) in isolated perfused rat hearts, with >95% inhibition of CK with 90 micromol iodoacetamide. Iodoacetamide did not directly alter SR Ca2+-ATPase activity, baseline left ventricular developed pressure, or baseline [Ca2+]c. When perfusate Ca2+ concentration was increased from 1.2 to 3.3 mM, LV developed pressure increased from 67 +/- 6 to 119 +/- 8 mmHg in control hearts (P < 0.05) but did not significantly increase in CK-inhibited hearts. Similarly, the amplitude of the [Ca2+]c transient increased from 548 +/- 54 to 852 +/- 140 nM in control hearts (P < 0.05) but did not significantly increase in CK-inhibited hearts. We conclude that decreased |DeltaG approximately p| limits intracellular Ca2+ handling and thereby limits contractile reserve.

Animals↗
PubMed1998

Specific heat shock proteins protect microtubules during simulated ischemia in cardiac myocytes.

The protective effects of heat shock proteins (HSPs) during myocardial ischemia are now well documented, but little is known about the mechanisms of protection and the specificity of different HSPs. Because cytoskeletal injury plays a crucial role in the pathogenesis of irreversible ischemic damage, we tested whether overexpression of specific HSPs protects the integrity of microtubules during simulated ischemia in rat neonatal cardiac myocytes. Overexpression of specific HSPs was achieved by adenovirus-mediated transgene expression. Damage was assessed by comparing control cells to cells that were subjected to a simulated ischemia protocol. Microtubular integrity was measured by indirect immunofluorescence, confocal microscopy, and image analysis. Within 14 h of simulated ischemia, microtubular integrity decreased significantly in uninfected myocytes (from 24.6 +/- 1.2 to 13.2 +/- 0.4) and in myocytes infected with a control virus that expressed no transgene (from 25.9 +/- 1.8 to 13.1 +/- 1.4). Microtubular integrity after ischemia was significantly better preserved in cells overexpressing constitutive Hsp70 (21.7 +/- 1.6) or alphaB-crystallin (18.0 +/- 2.7) but not in cells overexpressing inducible Hsp70 (11.5 +/- 0.8) or Hsp27 (14.0 +/- 2.2). We conclude that specific HSPs protect the microtubules during simulated cardiac ischemia.

Animals↗
PubMed1997

Small heat shock proteins and protection against ischemic injury in cardiac myocytes.

BACKGROUND: Overexpression of the inducible hsp70 protects against ischemic cardiac damage. However, it is unclear whether the small heat shock proteins hsp27 and alphaB-crystallin protect against ischemic injury. METHODS AND RESULTS: Our aim was to examine whether the overexpression of hsp27 and alphaB-crystallin in neonatal and adult rat cardiomyocytes would protect against ischemic injury. Recombinant adenovirus expressing hsp27 or alphaB-crystallin under the control of the cytomegalovirus promoter was used to infect cardiac myocytes at high efficiency as assessed by immunostaining. Overexpression was confirmed by Western blot analysis. Cardiomyocytes were subjected to simulated ischemic stress, and survival was estimated through assessment of lactate dehydrogenase and creatine phosphokinase release. The hsp27 overexpression decreased lactate dehydrogenase release by 45+/-7.5% in adult cardiomyocytes but had no effect in the neonatal cells. In contrast, alphaB-crystallin overexpression was associated with a decrease in cytosolic enzyme release in both adult (29+/-6.6%) and neonatal (32+/-5.4%) cardiomyocytes. Decreased endogenous hsp25 with an antisense adenovirus produced a 29+/-9.9% increase in damage with simulated ischemia. Overexpression of the inducible hsp70 in adult cardiomyocytes was associated with a 34+/-4.6% decrease in lactate dehydrogenase release and is in line with our previous results in neonatal cardiomyocytes. CONCLUSIONS: The increased expression of hsp27 and alphaB-crystallin through an adenovirus vector system protects against ischemic injury in adult cardiomyocytes. Likewise, the overexpression of alphaB-crystallin protects against ischemic damage in neonatal cardiomyocytes. Decreasing the high levels of endogenous hsp25 present in neonatal cardiomyocytes renders them more susceptible to damage caused by simulated ischemia.

Adenoviridae↗
PubMed1997

Adenovirus-mediated gene transfer reconstitutes depressed sarcoplasmic reticulum Ca2+-ATPase levels and shortens prolonged cardiac myocyte Ca2+ transients.

BACKGROUND: Decreased expression of the sarcoplasmic reticulum (SR) Ca2+-ATPase of the cardiac myocyte (SERCA2) and abnormal Ca2+ regulation have been independently linked to human heart failure. This study was designed to determine whether expression of a SERCA2 transgene could reconstitute depressed cardiac myocyte SERCA2 levels, augment SR Ca2+ uptake, and shorten prolonged excitation-contraction (EC)-associated Ca2+ transients in neonatal rat cardiac myocytes (NM). METHODS AND RESULTS: Cultured NM were treated with phorbol-12-myristate-13-acetate (PMA), a compound that decreases endogenous SERCA2 expression and results in prolongation of EC-associated Ca2+ transients. PMA-treated NM had a 75% reduction in SERCA2 mRNA and a 40% reduction in SERCA2 protein levels. SERCA2 adenovirus infection increased SERCA2 mRNA expression to 2.5 times control and reconstituted SERCA2 protein levels in PMA-treated cells. This reconstitution was associated with a 32.4% reduction in the time for decline of the Indo-1 Ca2+ transient to half-maximum levels (t(1/2) [Ca2+]i) (P<.05). A 34.5% augmentation of oxalate-facilitated SR Ca2+ uptake was also documented in SERCA2 adenovirus-infected cells (P<.05). CONCLUSIONS: Adenovirus-mediated expression of a SERCA2 transgene can reconstitute depressed endogenous SERCA2 levels, shorten prolonged Ca2+ transients, and augment SR Ca2+ uptake. It is conceivable that such an approach might be used in vivo to normalize altered Ca2+ regulation in human heart failure.

Adenoviridae↗
PubMed1997

Overexpression of the rat sarcoplasmic reticulum Ca2+ ATPase gene in the heart of transgenic mice accelerates calcium transients and cardiac relaxation.

The Ca2+ ATPase of the sarcoplasmic reticulum (SERCA2) plays a dominant role in lowering cytoplasmic calcium levels during cardiac relaxation and reduction of its activity has been linked to delayed diastolic relaxation in hypothyroid and failing hearts. To determine the contractile alterations resulting from increased SERCA2 expression, we generated transgenic mice overexpressing a rat SERCA2 transgene. Characterization of a heterozygous transgenic mouse line (CJ5) showed that the amount of SERCA2 mRNA and protein increased 2. 6-fold and 1.2-fold, respectively, relative to control mice. Determination of the relative synthesis rate of SERCA2 protein showed an 82% increase. The mRNA levels of some of the other genes involved in calcium handling, such as the ryanodine receptor and calsequestrin, remained unchanged, but the mRNA levels of phospholamban and Na+/Ca2+ exchanger increased 1.4-fold and 1.8-fold, respectively. The increase in phospholamban or Na+/Ca2+ exchanger mRNAs did not, however, result in changes in protein levels. Functional analysis of calcium handling and contractile parameters in isolated cardiac myocytes indicated that the intracellular calcium decline (t1/2) and myocyte relengthening (t1/2) were accelerated by 23 and 22%, respectively. In addition, the rate of myocyte shortening was also significantly faster. In isolated papillary muscle from SERCA2 transgenic mice, the time to half maximum postrest potentiation was significantly shorter than in negative littermates. Furthermore, cardiac function measured in vivo, demonstrated significantly accelerated contraction and relaxation in SERCA2 transgenic mice that were further augmented in both groups with isoproterenol administration. Similar results were obtained for the contractile performance of myocytes isolated from a separate line (CJ2) of homozygous SERCA2 transgenic mice. Our findings suggest, for the first time, that increased SERCA2 expression is feasible in vivo and results in enhanced calcium transients, myocardial contractility, and relaxation that may have further therapeutic implications.

Animals↗
PubMed1997

Induction of heat shock proteins by tyrosine kinase inhibitors in rat cardiomyocytes and myogenic cells confers protection against simulated ischemia.

Previous studies have shown that in rodent myogenic cells and in the hearts of transgenic mice in which heat shock protein expression is increased there is a marked tolerance to ischemic/reperfusion injury. Furthermore, a recent study has shown that the benzoquinoid ansamycin antibiotic and tyrosine kinase inhibitor, herbimycin A, is capable of inducing the expression of heat shock proteins in fibroblasts. Our intention, in the present study, was to investigate if exposure of rat cardiomyocytes and the myogenic cell line H9c2 to herbimycin A would induce these proteins and, thus, confer protection against ischemic stress. For this purpose, we exposed both rat neonatal cardiomyocytes and H9c2 cells to herbimycin A and another related benzoquinoid ansamycin antibiotic, geldanamycin. We found that cells exposed to these compounds overexpressed heat shock proteins and are also rendered more tolerant to simulated ischemia as measured by the release of cytoplasmic enzymes. In addition, we found that the mechanism of induction of heat shock proteins by these compounds is similar, if not identical, to that of a heat shock (42 degrees C, 60 min). These results suggest that these benzoquinoid ansamycin antibiotics, or closely related analogues, may offer a pharmacological means of increasing the level of heat shock proteins in cardiac tissue and thus protect the heart against ischemic/reperfusion injury.

Animals↗
PubMed1997

Transcription of the rat sarcoplasmic reticulum Ca2+ adenosine triphosphatase gene is increased by 3,5,3'-triiodothyronine receptor isoform-specific interactions with the myocyte-specific enhancer factor-2a.

Thyroid hormone (T3) increases the transcription of the sarcoplasmic reticulum Ca2+ adenosine triphosphatase (ATPase) gene (SERCA 2) through three thyroid hormone response elements. The existence of repetitive cis elements with different configurations is likely to serve specific functions such as interactions with nuclear transcription factors. In addition, the presence of different T3 receptor isoforms (T3Rs) may contribute to another level of complexity in providing specificity for T3 action. In this study, we investigated T3R alpha 1-vs. T3R beta 1-specific interactions with the myocyte enhancer-specific factor-2 (MEF-2) on the expression of the SERCA 2 gene in transient transfection assays in embryonal heart-derived H9c2 cells. MEF-2a in combination with either T3R alpha 1 or T3R beta 1 isoforms resulted in a 2.5-fold increase in SERCA 2 transgene expression in the absence of T3. Addition of T3 did not induce any further increase in SERCA 2 expression when T3R alpha 1 and MEF-2a expression vectors were cotransfected. In contrast, in the presence of T3R beta 1 and MEF-2, the addition of T3 increased chlorampenicol acetyltransferase activity by an additional 2.2-fold to a total 5.5-fold increase. The interaction between MEF-2a and T3R is transcription factor specific because another factor that binds to MEF-2 consensus sites (heart factor 1b) was not able to interact with T3R. In addition, MEF-2a failed to interact with other nuclear factors (cAMP response element-binding protein and Egr-1) that stimulate SERCA 2 gene transcription. In addition, we found that a single homologous thyroid hormone response element is not able to mediate the interactions between MEF-2a and T3Rs to increase SERCA 2 gene transcription. Our findings point to T3R isoform-specific interactions with a cell type-specific transcription factor (MEF-2) in the regulation of SERCA 2 gene expression.

Animals↗
PubMed1997

Alpha 1-adrenergic stimulation inhibits 3,5,3'-triiodothyronine-induced expression of the rat heart sarcoplasmic reticulum Ca2+ adenosine triphosphatase gene.

The interactions between the beta-adrenergic system and thyroid hormone (T3) on cardiac function have been investigated in detail. In addition to beta-adrenoceptors, alpha 1-adrenergic receptors are present in the mammalian heart. The interactions between T3 and the alpha 1-adrenergic system remain, however, poorly understood. T3 stimulates the expression and transcription of the sarcoplasmic reticulum Ca2+ adenosine triphosphatase (SERCA2) gene, a protein vital in the control of cardiac calcium transients and contractility. We show that in rat cardiac myocytes, the stimulatory effect of T3 on SERCA2 messenger RNA expression and gene transcription is inhibited by an alpha 1-adrenergic agonist. We demonstrate that direct activation of the alpha 1-adrenergic signaling pathway, using a mutant constitutively active G protein (Gq) similarly down-regulated the T3 effect on SERCA2 transcription. The combined effect of thyroid hormone receptor and retinoid X receptors on T3-stimulated SERCA2 gene transcription was also markedly attenuated by alpha 1-adrenergic stimulation. These results suggested that activation of the alpha 1-adrenergic signaling pathway has an inhibitor effect on T3-dependent SERCA2 gene transcription. As this inhibitory effect of alpha 1-adrenergic stimulation occurs when only one thyroid hormone response element (TRE) drives reporter expression, it is most likely mediated by an alteration of the nuclear factors binding to the TRE or by influencing the interaction of the TRE complex with the basal transcriptional machinery.

Animals↗