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.

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.

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.

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.

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.

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].

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.

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.

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.

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.

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.

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.

Adenovirus-mediated gene transfer of a heat shock protein 70 (hsp 70i) protects against simulated ischemia

We have recently shown that the overexpression of a heat shock protein 70 (hsp 70) in a rat myogenic cell line confers protection against simulated ischemia. We also developed and demonstrated that overexpression of this protein, in the hearts of transgenic mice, protects against ischemia/reperfusion injury. We have now inserted the hsp70 gene in an adenoviral vector and show that we are able to transfer and achieve overexpression of this protein in neonatal cardiomyocytes and in the rat myogenic cell line H9c2. We find that cells infected with the adenoviral-hsp70i construct are rendered tolerant to simulated ischemia as compared to cells infected with a control recombinant adenoviral construct. In conclusion, our results demonstrate the feasibility of using adenoviral vectors to overexpress the hsp70 in myogenic cells, specially in cardiomyocytes, and the efficiency of this approach for providing protection against myocardial ischemia.

Phorbol myristate acetate-induced hypertrophy of neonatal rat cardiac myocytes is associated with decreased sarcoplasmic reticulum Ca2+ ATPase (SERCA2) gene expression and calcium reuptake

The decreased expression of the sarcoplasmic reticulum Ca(2+)-ATPase associated with cardiac hypertrophy was investigated in cultured neonatal rat cardiac myocytes. Northern blot analysis indicated a significant 55-60% decrease in Ca(2+)-ATPase mRNA levels and after 12 and 24 h of treatment with the phorbol ester phorbol myristate acetate (PMA). Myocytes treated with the phorbol ester for 80 h showed a significant 34% decrease (relative to vehicle-treated control cells) in the levels of Ca(2+)-ATPase protein, and a significant 38% increase in the levels of alpha-sarcomeric actin, as assessed by Western blot analysis using specific antibodies. Immunocytochemistry of myocytes treated for 72 h with the phorbol ester revealed a hypertrophied cell morphology, and showed a marked decrease in Ca(2+)-ATPase staining intensity. Contractile calcium transients were evaluated through the use of indo-1. It was found that the t1/2 for the decline of calcium transient was significantly prolonged by PMA treatment (0.51 +/- 0.15) when compared to controls (0.38 +/- 0.17, P < 0.001). Treatment of myocytes with endothelin-1 also led to a 35% decrease in sarcoplasmic reticulum Ca(2+)-ATPase mRNA levels. It is concluded that phorbol ester treatment of neonatal rat cardiac myocytes induces similar changes in Ca(2+)-ATPase mRNA levels. It is concluded that phorbol ester treatment of neonatal rat cardiac myocytes induces similar changes in Ca(2+)-ATPase gene expression as observed in vivo in the hypertrophied and failing heart. The observed prolongation in t1/2 for [Ca2+]i decline might be due to the observed depressed levels for sarcoplasmic reticulum Ca(2+)-ATPase in PMA treated cells.

Overexpression of heat shock protein 72 in transgenic mice decreases infarct size in vivo

BACKGROUND

Previous studies have demonstrated that induction of heat shock protein (HSP) 72 by whole-body hyperthermia reduces infarct size in an in vivo model of ischemia and reperfusion. Furthermore, hearts obtained from transgenic mice that overexpress HSP72 demonstrate improved functional recovery and decreased infarct size in vitro after global ischemia and reperfusion.

METHODS AND RESULTS

To test the hypothesis that overexpression of HSP72 in transgenic mice reduces infarct size in vivo, transgenic mice that were heterozygous for a rat HSP70i gene ([+]HSP72) and transgene-negative littermate controls ([-]HSP72) were subjected to 30 minutes of left coronary artery occlusion followed by 120 minutes of reperfusion. Core body temperature was monitored with a rectal thermometer and maintained between 36.5 degrees C and 37.0 degrees C with a heating pad. Infarct size, determined by dual staining with triphenyltetrazolium chloride and phthalocyanine blue dye, was smaller in [+]HSP72 mice compared with [-]HSP72 mice (12.7 +/- 2.8% [n = 7] versus 33.4 +/- 4.5% [n = 6], infarct size/risk area, respectively; P < .05; mean +/- SEM).

CONCLUSIONS

Overexpression of HSP72 reduces infarct size in this in vivo transgenic mouse model of myocardial ischemia and reperfusion.

Intracoronary gene transfer of fibroblast growth factor-5 increases blood flow and contractile function in an ischemic region of the heart

Increased coronary blood vessel development could potentially benefit patients with ischemic heart disease. In a model of stress-induced myocardial ischemia, intracoronary injection of a recombinant adenovirus expressing human fibroblast growth factor-5 (FGF-5) resulted in messenger RNA and protein expression of the transferred gene. Two weeks after gene transfer, regional abnormalities in stress-induced function and blood flow were improved, effects that persisted for 12 weeks. Improved blood flow and function were associated with evidence of angiogenesis. This report documents, for the first time, successful amelioration of abnormalities in myocardial blood flow and function following in vivo gene transfer.

Regulation of expression of cardiac sarcoplasmic reticulum proteins under pathophysiological conditions

Congestive heart failure presents a significant medical problem and accumulating evidence indicates that slow relaxation during diastole maybe at least in part be medlated by decreased expression of the gene coding for the Ca2+ ATPase of the sarcoplasmic reticulum (SR). In order to determine if increased expression of the SR Ca2+ ATPase gene leads to alterations in calcium transients and in contractile behavior we constructed transgenic mice overexpressing the SERCA2 gene. Measuring dP/dt(max) and dpPdt(min) with a 2 French Milar catheter we found a significant Increase in systolic contraction and diastolic relaxation in transgene positive versus transgene negative mice. In addition we constructed adenoviruses overexpressing the gene coding for the Ca2+ ATPase of the sarcoplasmic reticulum. Infacting cardiac myocytes with the adenovirus expressing this transgene led to an accelerated calcium transient. Determining cell shortening and relengthening with a edge detection method indicated that increased expression of the SERCA2 transgene mediated by adenovirus Infection accelerated contractile parameters. In summary increased expression of the SERCA2 transgene leads to an enhancement of cardiac contrectile parameters under in vivo conditions in transgenic mice and in myocytes in cell culture using an adenovirus based approach to increase expression of the SERCAX gene.

Adenovirus-mediated overexpression of human transforming growth factor-beta 1 in rat cardiac fibroblasts, myocytes and smooth muscle cells

Transforming growth factor-beta 1 (TGF-beta 1) is known to regulate cardiac cell function and its overexpression in the heart is thought to contribute to the development of cardiac hypertrophy and fibrosis. We wished to develop a high efficiency gene transfer method that could be used both in vitro and in vivo and result in the overexpression of TGF-beta 1. For this purpose, we constructed a replication-deficient human adenovirus 5 vector encoding for human TGF-beta 1 and used for control purposes an adenovirus lacZ vector. The adenovirus 5 construct was capable of infecting neonatal rat cardiac myocytes, fibroblasts and VSMCs. Of the three cell types, cardiac myocytes appear more susceptible to infection by the adenovirus 5 construct as assessed through beta-galactosidase staining. Infection of cardiac fibroblasts, myocytes and VSMCs with the hTGF-beta 1 adenovirus leads to the expression of hTGF-beta 1 mRNA and enhanced levels of bioactive and total TGF-beta 1 protein. Infection with hTGF-beta 1 adenovirus also results in enhanced levels of collagen type III gene expression in VSMCs and fibroblasts whereas in cardiac myocytes it leads to increased levels for sarcomeric and beta-actin. Thus, this adenoviral vector might be used for the exploration of in vivo effects of altered levels of cardiac TGF-beta 1.

Angiotensin II stimulates the autocrine production of transforming growth factor-beta 1 in adult rat cardiac fibroblasts

Angiotensin II (Ang II) has been implicated in the development of cardiac hypertrophy and myocardial fibrosis. While recent in vivo and in vitro studies performed in cultured cardiac myocytes and fibroblasts support this role for Ang II, the mechanisms of Ang II action at the cellular level remain unclear. In the present study, we postulated that Ang II action in adult cardiac fibroblasts may stimulate the autocrine production and release of transforming growth factor-beta 1 (TGF-beta 1), a known regulator of cardiac fibroblast and myocyte function. We examined the ability of Ang II to regulate the gene expression, biological activity, and protein production of TGF-beta 1 in cultured adult rat cardiac fibroblasts. Treatment of fibroblast cultures with Ang II (10(-9) M) induced a two-fold increase in TGF-beta 1 mRNA levels within 4 h that was sustained through 24 h (P < 0.01). TGF-beta 1-like activity in Ang II-treated cultures was significantly increased compared with control as measured by bioassay (P < 0.001). Specificity for TGF-beta 1-like activity was confirmed through its neutralization with a TGF-beta 1 specific antibody (100 micrograms/ml). Total concentration of TGF-beta 1 (latent plus active forms) in conditioned media from Ang II-treated cardiac fibroblasts was also found to be greater than control (P < 0.01). These findings suggest that the effects of Ang II in the adult myocardium may be mediated in part by autocrine/paracrine mechanisms, including the production and release of TGF-beta 1 by cardiac fibroblasts.

Trophic effects of angiotensin II on neonatal rat cardiac myocytes are mediated by cardiac fibroblasts

Cultured neonatal rat cardiac fibroblasts (NF) and myocytes (NM) were used to examine the distribution of angiotensin II (ANG II) receptors and the potential role of NF in mediating the trophic response to ANG II in the heart. In NM preparations cultured for 2-5 days, specific binding to 125I-ANG II was < 10% of the specific binding in cultured NF. Binding assays, immunocytochemistry, and autoradiography in NM cultured for > 5 days identified two populations of cells, one with fibroblast-like morphology and high density of ANG II receptors and another with low binding, comparable to NM cultures at day 5 or earlier. Conditioned medium (CM) from untreated NF increased cell surface area and net [3H]leucine (Leu) incorporation 1.4-fold in NM. CM from ANG II-treated NF enhanced [3H]Leu incorporation 2.2-fold in NM. This potentiating effect of ANG II was inhibited by losartan and was absent when ANG II was added directly to NM. In addition, studies using antibodies and bioassay for transforming growth factor-beta 1 (TGF-beta 1) suggested that TGF-beta 1 does not mediate the trophic effects of ANG II on NM. We conclude that ANG II receptors are localized predominantly on NF and that ANG II can indirectly stimulate hypertrophy of NM by stimulating NF to produce a transferrable factor(s). These data suggest that cardiac fibroblasts may play a critical role in mediating the hypertrophic response to ANG II in the rat heart.

Overexpression of the rat inducible 70-kD heat stress protein in a transgenic mouse increases the resistance of the heart to ischemic injury

Myocardial protection and changes in gene expression follow whole body heat stress. Circumstantial evidence suggests that an inducible 70-kD heat shock protein (hsp70i), increased markedly by whole body heat stress, contributes to the protection. Transgenic mouse lines were constructed with a cytomegalovirus enhancer and beta-actin promoter driving rat hsp70i expression in heterozygote animals. Unstressed, transgene positive mice expressed higher levels of myocardial hsp70i than transgene negative mice after whole body heat stress. This high level of expression occurred without apparent detrimental effect. The hearts harvested from transgene positive mice and transgene negative littermates were Langendorff perfused and subjected to 20 min of warm (37 degrees C) zero-flow ischemia and up to 120 min of reflow while contractile recovery and creatine kinase efflux were measured. Myocardial infarction was demarcated by triphenyltetrazolium. In transgene positive compared with transgene negative hearts, the zone of infarction was reduced by 40%, contractile function at 30 min of reflow was doubled, and efflux of creatine kinase was reduced by approximately 50%. Our findings suggest for the first time that increased myocardial hsp70i expression results in protection of the heart against ischemic injury and that the antiischemic properties of hsp70i have possible therapeutic relevance.

Myocardial remodeling in hypertensive Ren-2 transgenic rats

Rats harboring the mouse Ren-2 transgene develop hypertension despite low levels of plasma renin. We determined the extent of left ventricular remodeling present in Ren-2 rats at 16 weeks of age by measuring blood pressure, ratio of heart weight to body weight, left ventricular wall thickness, passive (diastolic) left ventricular compliance, and left ventricular collagen content using hydroxyproline and collagen area fraction. Changes in perivascular fibronectin and collagen type I and III were examined with immunohistochemistry. Blood pressure values at time of death were 244 +/- 15 mm Hg for Ren-2 rats (mean +/- SD, n = 5). Ratios of heart weight to body weight (grams per kilogram) for Ren-2 animals were 4.1 +/- 0.2 versus 3.1 +/- 0.1 for controls (n = 6, P < .001). Wall thickness values for control animals were 2.6 +/- 0.1 versus 4.1 +/- 0.4 mm for Ren-2 animals (P < .001). Left ventricular Ren-2 hydroxyproline measurements were significantly decreased (3.4 +/- 0.2 versus 4.7 +/- 0.9 mg/g dry wt for controls). Significant decreases of approximately 30% were also observed in collagen area fraction in Ren-2 rats. Immunohistochemical and picrosirius red staining indicated increased amounts of perivascular fibrosis in all Ren-2 animals (when compared with controls) with enhanced levels of perivascular fibronectin and type I and type III collagen proteins. Left ventricular compliance measurements indicated a decrease in left ventricular volume for all left ventricular pressures (P = .07).(ABSTRACT TRUNCATED AT 250 WORDS)