Induction of HSP70 in cultured rat neonatal cardiomyocytes by hypoxia and metabolic stress

BACKGROUND

A cultured neonatal rat cardiomyocyte model is used to investigate the expression of the inducible heat shock protein 70 (HSP70i) during hypoxia/reoxygenation and metabolic stress.

METHODS AND RESULTS

The major HSP70i is increased in its expression at the mRNA and protein level in myocytes exposed to hypoxia/reoxygenation and metabolic stress by the addition of 2-deoxyglucose and sodium cyanide, which are inhibitors known to block ATP production. Surprisingly, the appearance of HSP70 mRNA precedes the intracellular ATP depletion caused by hypoxia, which is contrary to what we observe when the cardiomyocytes are subjected to metabolic stress.

CONCLUSIONS

It has been postulated recently that the decrease in intracellular ATP content in cells under stress may be the trigger that leads to the induction of HSP70i by reducing the pool of free HSP70, thus activating the stress response. Our results indicate that although this may be the case during metabolic stress, another route of activation must be used during the early stages of hypoxia in cardiomyocytes. The induction of HSP70i also appears to precede the onset of cellular damage as measured by the release of cytoplasmic enzymes and preincorporated arachidonic acid. This indicates that cardiomyocytes are able to respond to hypoxia/reoxygenation and metabolic stress with increased HSP70i production and points to a potential protective role of heat shock proteins during ischemia/reperfusion injury.

Surgical management of the thyroid nodule: patient selection based on the results of fine-needle aspiration cytology

To determine whether the routine use of fine-needle aspiration (FNA) cytology reduces the rate of unnecessary surgery, the surgical pathology of 54 thyroidectomy patients who had preoperative FNA was compared to the results obtained with 24 thyroidectomy patients who did not have preoperative FNA. Twenty-nine (85.3%) of the 34 patients who had a positive FNA were confirmed by histology to have a thyroid neoplasm; in 24 patients, the neoplasm was malignant. Two of the 17 patients who had a negative FNA but underwent thyroidectomy based on other factors were found to have thyroid cancer. Only 8 (33.3%) of the 24 surgical specimens of patients who did not have an FNA were found to be malignant. FNA had a sensitivity of 93.5% and a specificity of 75.0%. The results indicate that the routine use of FNA for patients with thyroid nodules reduces the incidence of unnecessary surgery. Furthermore, FNA alone is sufficient to identify most patients at risk and is, therefore, cost-effective. However, the presence of other findings suspicious of malignancy should preclude clinical decision making based on FNA alone.

Thyroid hormone response of slow and fast sarcoplasmic reticulum Ca2+ ATPase mRNA in striated muscle

The thyroid status markedly influences the contractile function of muscle, and changes in the activity of the Ca2+ ATPase of the sarcoplasmic reticulum (SR) contribute to these alterations. Two separate genes encode the major isoforms of SR Ca2+ ATPase. In fast skeletal muscle, sarcoplasmic endoplasmic reticulum Ca2+ ATPase type 1 (SERCa1) presents the major isoform, whereas in slow skeletal muscle SERCa type 2 (SERCa2) predominates. Cardiac muscle contains only SERCa2. To examine the mechanisms responsible for changes in contractile function, we quantitated SERCa1 and SERCa2 mRNA levels in fast extensor digitorum longus muscle (EDL), slow soleus muscle, and cardiac muscle in rats of different thyroid status. Hypothyroidism led in soleus to a marked decrease in SERCa1 mRNA and SERCa2 mRNA levels, in cardiac muscle SERCa2 mRNA decreased markedly, as previously shown by us, and in EDL SERCa1 mRNA decreased. These findings are compatible with a hypothyroidism induced decrease in SR Ca2+ ATPase activity and a delay in muscle relaxation. In contrast, SERCa2 mRNA of EDL, representing only a small percent of total SERCa mRNA in this muscle, increased to 175% of control values. Muscle specific and SERCa gene specific changes also occur after acute triiodothyronine (T3) administration to hypothyroid rats. T3 does not induce a significant change in SERCa1 or SERCa2 mRNA levels in soleus, but in the heart SERCa2 mRNA increases about 3-fold. In EDL, T3 increases SERCa1 mRNA from a hypothyroid level of 59 +/- 6% to 138 +/- 4% of control values but SERCa2 mRNA is decreased to 75 +/- 5% of control levels.(ABSTRACT TRUNCATED AT 250 WORDS)

Selective reduction of creatine kinase subunit mRNAs in striated muscle of diabetic rats

Creatine kinase (CK) is important for energy transfer and is composed of mitochondrial (mitCK), muscle (MCK), and brain (BCK) subunits, each being the product of separate nuclear genes. The concentrations of MCK and BCK mRNAs have been shown to decrease in streptozotocin-hypoinsulinemic rat hearts, and in this report, we examined in detail the diabetic effect on CK gene expression in cardiac muscle and in two types of skeletal muscle. The level of sarcomeric mitCK mRNA was not altered in the diabetic myocardium, but was reduced by 86 and 67% in diabetic slow-twitch soleus muscle and fast-twitch extensor digitorum longus (EDL) muscle, respectively. MCK mRNA was also lowered in diabetic soleus muscle by 56%, while it remained at control levels in diabetic EDL. In both skeletal muscles, at either state, BCK mRNA was not detectable. There was a 33% decrease in total CK activity in diabetic cardiac and soleus muscle, but not in EDL. Diabetes thus exerts a widespread, muscle type-dependent adverse effect on CK expression that we found to be insulin therapy revertible. This study adds to our understanding of defective energy transduction in diabetic muscle.

Cardiac hypertrophy-induced changes in mRNA levels for TGF-beta 1, fibronectin, and collagen

Cardiac hypertrophy induced by pressure overload is accompanied by increases in the deposition of extracellular matrix (ECM) proteins. We wanted to determine in this study whether changes in mRNA coding for transforming growth factor (TGF)-beta 1, TGF-beta 3, and the ECM proteins, fibronectin and collagen, occur during the early phases of cardiac hypertrophy. Steady-state mRNA levels were determined in sham-operated and thoracic-banded hypertrophied rat myocardium from 6 h to 30 days after surgery. TGF-beta 1 mRNA increased significantly (1.7-fold vs. control) 12 h after aortic banding, decreasing to control levels by 14 days. No significant changes were observed for TGF-beta 3 message. Fibronectin mRNA levels increased twofold at day 1 and peaked to approximately threefold at day 3. Type I and III collagen mRNA expression was similar to control levels at day 1 but increased significantly 3 days after banding. Cardiac hypertrophy also resulted in an induction of mRNA for an embryonic isoform of fibronectin (EIIIA+) that is generated through alternative splicing of the gene. These findings indicate that, with myocardial hypertrophy, mRNAs for fibronectin are increased as early as 1 day after banding, which may allow for an initial increase in the production of fibronectin followed by the deposition of collagen. These increased mRNA levels for the ECM proteins are preceded by marked increases in TGF-beta 1 mRNAs.

Iodide induces transforming growth factor beta 1 (TGF-beta 1) mRNA in sheep thyroid cells

We examined TGF-beta mRNA levels in primary sheep thyroid cell cultures to determine whether the inhibitory effects of iodide on thyroid cells could be explained by an induction of TGF-beta mRNA and if this induction was mediated by iodine organification. Thyroid cells were incubated with TSH and five additives (insulin, somatostatin, growth hormone, transferrin, and glycyl-L-histidyl-L-lysin) for 2-3 weeks and then were exposed to sodium iodide (NaI) or 1-methylimidazole-2-thiol (methimazole, MMI), or both for 72 h. Iodide at 10(-6) M and 10(-4) M significantly increased the amount of TGF-beta mRNA as determined by Northern blot analysis with a rat TGF-beta 1 cDNA probe. This increase in TGF-beta 1 mRNA was abolished by the addition of methimazole, an inhibitor of organification. These data indicate that the effects of iodide on thyroid growth and function may be mediated by a process that involves organification of iodide and increases in TGF-beta 1 mRNA levels.

Insulin responsiveness of CK-M and CK-B mRNA in the diabetic rat heart

Decreased cardiac performance is a known complication of diabetes mellitus, but the detailed molecular mechanisms that are responsible for this contractile abnormality are only incompletely explored, and cardiac gene products of known function, which are markedly and actively insulin responsive, have not been described. Recently, we found that creatine kinase (CK) enzyme activity and CK-M subunit mRNA levels are decreased in the heart of rats with experimental diabetes mellitus. These abnormalities could be restored to normal with chronic insulin administration. The CK-M and CK-B genes are expressed in the heart, and we wanted to determine whether diabetes also induces a change in CK-B mRNA levels. Quantitation of CK-M and CK-B mRNA levels on Northern blots with specific cDNA probes showed that, in diabetic hearts, CK-B mRNA levels represent only 19.8% of control levels and are more markedly depressed than CK-M mRNA levels, which are 46.5% of control values. Acute injection of insulin led to a significant 1.6-fold increase in CK-M mRNA and a 2.2-fold increase of CK-B mRNA 5 h after insulin injection. CK-M mRNA levels were restored to normal within 12 h, but 48 h were required to restore CK-B mRNA levels to normal values. After 1 mo of insulin therapy, CK-B mRNA levels had risen 9.7-fold, exceeding normal values by 90%, whereas CK-M mRNA levels were at the normal level as previously shown. CK enzyme activity showed only a small response to insulin administration 48 h postinjection. Diabetes leads therefore to a marked lowering of CK-M and CK-B mRNA levels in the rat heart.(ABSTRACT TRUNCATED AT 250 WORDS)

Influence of thyroid hormone and retinoic acid on slow sarcoplasmic reticulum Ca2+ ATPase and myosin heavy chain alpha gene expression in cardiac myocytes. Delineation of cis-active DNA elements that confer responsiveness to thyroid hormone but not to retinoic acid

The mRNA encoding the sarcoplasmic reticulum (SR) Ca2+ ATPase is highly influenced by thyroid hormone (T3) in the hearts of intact animals. We show here that this effect of T3 can be mimicked in primary neonatal rat cardiocytes, both in serum-containing and in serum-free media; the expression of SR Ca2+ ATPase mRNA is myocyte-specific and is also modulated by retinoic acid (RA). RA also induces myosin heavy chain (MHC) alpha-mRNA in this system. The induction of Ca2+ ATPase mRNA is sensitive to T3 (EC50 approximately 30 pM) and less sensitive to RA (EC50 approximately 2 nM). Transient transfection experiments utilizing various segments of the Ca2+ATPase promoter fused to the reporter gene chloramphenicol acetyltransferase (CAT) indicate a minimal thyroid hormone response element (TRE) between nucleotides -262 and -322, while sequences between -322 and -559 are required for maximal trans-activation. RA is not able to regulate these constructs. Likewise, a clear effect of T3 but no effect of RA was observed when the CAT gene was driven by a TRE derived from the rat alpha-MHC gene. In contrast, CAT expression was induced by either hormone when placed under the control of a synthetic palindromic TRE. Taken together, these results indicate that T3 and RA induce gene expression in primary cardiac myocytes, but through distinct response elements and/or mechanisms.

Age-induced decreases in the messenger RNA coding for the sarcoplasmic reticulum Ca2(+)-ATPase of the rat heart

Age-associated slowing of cardiac relaxation related to the decline in the Ca2+ pump function of cardiac sarcoplasmic reticulum (SR) has been previously described. It is unclear if the decreased Ca2+ pump function results from a lower amount of Ca2(+)-ATPase protein or a decreased pumping activity of the enzyme. To determine if these alterations could be mediated by changes in the amount of the protein itself, the level of the messenger RNA (mRNA) coding for the Ca2(+)-ATPase of the SR of Fischer rat hearts (4- and 30-month-old rats) were quantitated with a Northern blotting technique. We observed that the levels of SR Ca2(+)-ATPase mRNA were 60% lower in old rats as compared with young rats, suggesting that a quantitative reduction in the levels of the corresponding protein could occur during aging to explain the delayed diastolic relaxation documented in old animals as opposed to a change in the specific activity of this enzyme. The thyroid hormone responsiveness of SR Ca2(+)-ATPase mRNA has been previously established. We have found in this study that the thyroxine levels were consistently lower in old rats; however, this difference was relatively small (4.3 +/- 0.7 and 3.1 +/- 0.8 micrograms/dl [mean +/- SD), respectively, in young and old rats). In addition, no age-induced decrease in 3,5,3'-triiodothyronine levels was observed, suggesting that the aging process itself may be responsible for the changes in SR Ca2(+)-ATPase mRNA levels.

Biochemical basis of thyroid hormone action in the heart

Thyroid hormone-induced changes in cardiac function have been recognized for over 150 years; however, the biochemical basis of triiodothyronine (T3) action in the heart has been intensely investigated only during the last two decades. T3-induced changes in cardiac function can result from direct or indirect T3 effects. Direct T3 effects result from T3 action in the heart itself and are mediated by nuclear or extranuclear mechanisms. Extranuclear T3 effects, which occur independent of nuclear T3 receptor binding and increases in protein synthesis, influence primarily the transport of amino acids, sugars, and calcium across the cell membrane. Nuclear T3 effects are mediated by the binding of T3 to specific nuclear receptor proteins, which results in increased transcription of T3-responsive cardiac genes. The T3 receptor is a member of the ligand-activated transcription factor family and is encoded by cellular erythroblastosis A (c-erb A) genes. The c-erb A protein is the cellular homologue of the viral erythroblastosis A (v-erb A) protein, which causes red cell leukemia in chickens. Currently, three T3-binding isoforms of the c-erb protein and two non-T3-binding nuclear proteins that exert positive and negative effects on T3-responsive cardiac genes have been identified. T3 increases the heart transcription of the myosin heavy chain (MHC) alpha gene and decreases the transcription of the MHC beta gene, leading to an increase of myosin V1 and a decrease in myosin V3 isoenzymes. Myosin V1, which is composed of two MHC alpha, has a higher myosin ATPase activity than myosin V3, which contains two MHC beta. The globular head of myosin V1, with its higher ATPase activity, leads to a more rapid movement of the globular head of myosin along the thin filament, resulting in an increased velocity of contraction. T3 also leads to an increase in the speed of diastolic relaxation, which is caused by the more efficient pumping of the calcium ATPase of the sarcoplasmic reticulum (SR). This T3 effect results from T3-induced increases in the level of the mRNA coding for the SR calcium ATPase protein, leading to an increased number of calcium ATPase pump units in the SR. Overall, thyroid hormone leads to an increase in ATP consumption in the heart. In addition, less chemical energy of ATP is used for contractile purposes and more of it goes toward heat production, which causes a decreased efficiency of the contractile process in the hyperthyroid heart.

Diabetes decreases creatine kinase enzyme activity and mRNA level in the rat heart

Several of the adenosinetriphosphatase enzymes that are responsible for cardiac muscle contraction rely on high-energy phosphates supplied by the creatine kinase (CK) system. Experimental diabetes mellitus has been shown to cause a decrease in the maximal contractile performance of the heart. We postulated that the decrease in contractile performance may be explained in part by a decrease in CK enzyme activity. To evaluate this possibility, we determined the level of CK activity and isoenzyme distribution in ventricular homogenates from normal, diabetic, and insulin-treated diabetic rats. We found that total CK activity was decreased by 35% in diabetic hearts and that a 66% reduction in the cardiac-specific MB isoenzyme occurs. Using a cDNA probe for CK-muscle (M) RNA in Northern blot analysis, we determined that a 61.1% decrease in CK-M mRNA occurs in diabetes. Chronic insulin therapy for 1 mo restores CK-M mRNA levels and enzyme activity. In conclusion, diabetes-induced CK enzyme decreases are mediated in part by a lower level of CK-M mRNA that codes for the major CK-M subunit protein. Decreased performance of the CK system may contribute to diabetic cardiomyopathy.

Diabetes and thyroid-hormone-induced changes in cardiac function and their molecular basis

The heart is a major target organ for insulin and thyroid hormone action, and marked changes in cardiac function occur in patients with hyper- or hypothyroidism and diabetes mellitus. Cardiac contractility is increased in the hyperthyroid state and decreased in hypothyroidism, and changes in specific proteins mediating cardiac contraction accompany these alterations. Changes in thyroid status mediate their influence on cardiac function by a combination of direct thyroid hormone effects on the heart, alterations in the responsiveness of the cardiac sympathoadrenal system, and hemodynamic effects generated in the periphery. Cardiovascular complications of diabetes mellitus are a major contributor to mortality and morbidity in the diabetic population. In addition to cardiac small and large vessel disease, an autonomic neuropathy and a cardiomyopathy occur in diabetic patients. The cardiomyopathy results in congestive failure and is independent of large vessel disease. Studies in diabetic animal models point to a metabolic basis for the cardiomyopathy, which is accompanied by changes in specific contractile proteins.

Influence of thyroid hormone on myosin heavy chain mRNA and other messenger RNAs in the rat heart

The level of myosin heavy chain (MHC) alpha mRNA and of MHC-beta mRNA was quantitated in the rat heart using a specific cDNA probe. In hypothyroid and diabetic hearts MHC-beta mRNA predominates, whereas in normal hearts MHC-alpha mRNA represents 80% of all MHC mRNA. Administration of 0.2 mg T3/100 g body wt. to hypothyroid rats led to an increase in MHC-alpha mRNA beginning at 3 h after injection and continued to rise until at 24 h control level of MHC-alpha mRNA were reached. In contrast, after administration of 2 units regular insulin to diabetic rats, MHC-alpha mRNA levels showed a small but significant increase already 30 min after insulin administration reaching a peak at 3 h and returning to diabetic values 5 h after insulin. The T3 response of other cardiac mRNAs was quantitated using in vitro translation, separation of 35S methionine labeled translational products and their quantitation by digital matrix photometry. An mRNA (spot 72b) coding for a translational product with a Mr 81,000 and pI of 5.4 showed a 3-fold increase in its level 1 h after T3 administration. In view of the rapid response of spot 72b and the early response of MHC-alpha mRNA to insulin, it is currently unclear if the T3 response of MHC-alpha mRNA represents a primary effect of T3.

Ischemia induces changes in the level of mRNAs coding for stress protein 71 and creatine kinase M

Hyperthermia, hypoxia, and other conditions induce the appearance of heat shock or stress proteins in cells. We have previously shown that in the ischemic dog myocardium the level of a messenger RNA (mRNA) coding for a protein with migration characteristics similar to heat shock/stress protein 71 increases. Using a human heat-shock protein (hHSP) 70 genomic clone and anti-HSP70 antibodies as probes, we demonstrate in this report that heart stress protein (SP) 71 mRNA and its translational products (71 kDa polypeptides) are members of the stress protein family. In rabbit hearts, the ischemia-induced mRNAs translate into three isoforms with different isoelectric points (6.0, 6.1, and 6.15), in contrast to dog heart mRNA that translates into a protein with a pI of 5.8. The levels of SP71 mRNA in the dog and rabbit ischemic myocardium increased by sixfold and 18-fold, respectively. In the same samples, the levels of creatine kinase M mRNA decreased by about 40%, whereas those of myosin heavy chain mRNA remain unaltered. Our comparative analysis of three different mRNAs indicates that ischemia manifests its effects by differentially changing the levels of specific mRNAs coding for proteins with separate and distinct roles in the cell.

Cardiac response to pressure overload in the rat: the selective alteration of in vitro directed RNA translation products

As cardiac hypertrophy develops, total cardiac RNA and protein synthesis increase significantly. We have identified specific messenger RNAs that change in predominance with the induction of pressure-overload-stimulated cardiac hypertrophy. Total cardiac RNA was isolated from rats either undergoing cardiac hypertrophy secondary to subdiaphragmatic aortic constriction or subjected to sham surgery. The products translated in vitro were separated by two-dimensional gel electrophoresis and quantitated. The translation of four proteins decreased while the translation of four others increased in preparations from hypertrophied hearts compared with those from sham-treated rats. Two isoforms of creatine kinase M were translated in vitro. Only one of these isoforms decreased with cardiac hypertrophy, suggesting that the transcriptional or translational control for creatine kinase is much more complex than previously believed. Finally, since only eight of over 700 different translation products changed in relative predominance with cardiac hypertrophy, we conclude that the accumulation of existing RNA and protein products is the primary adaptive process responsible for cardiac hypertrophy.

Thyroid hormone markedly increases the mRNA coding for sarcoplasmic reticulum Ca2+-ATPase in the rat heart

Previous findings have shown that thyroid hormone markedly increases the speed of diastolic relaxation in the heart. This thyroid hormone-dependent change is also accompanied by an increased Ca2+ pumping ability in the sarcoplasmic reticulum. In an effort to determine the underlying cause of improved Ca2+ transport, mRNA levels of the slow Ca2+-ATPase of the sarcoplasmic reticulum were quantified on Northern blots. In hypothyroid rat hearts, the steady state level of Ca2+-ATPase mRNA was only 36% of control levels, whereas hyperthyroid rat heart mRNA levels were 136% of control. Ca2+-ATPase mRNA responded rapidly to T3, as the mRNA level was significantly increased by 2 h and normalized by 5 h after T3 injection into hypothyroid rats. The well established effect of thyroid hormone on improved myocardial contractility and increased speed of diastolic relaxation may in part relate to specific alterations in the level of the mRNA coding for Ca2+-ATPase, resulting in increased pump units.

Diabetes-induced changes of proteins synthesized by adult cardiac myocytes are partially reversed by insulin

In the rat heart diabetes mellitus leads to a change in myosin heavy chain (MHC) mRNAs and corresponding alterations in myosin isoenzymes as well as a decrease in total cardiac protein synthesis. However, it is still unknown whether cardiac proteins other than MHC are altered by diabetes and if so whether these abnormalities are mediated by insulin deficiency. To answer these questions we analyzed proteins synthesized by isolated cardiac myocytes in the presence or absence of insulin. Enzymatically dispersed adult cardiac myocytes from control and streptozotocin-induced diabetic rats were incubated in medium containing [35S]-methionine for 4 h; diabetic cells were incubated with or without the addition of 5 x 10(-7)M insulin. The labelled peptides were then separated by two-dimensional polyacrylamide gel electrophoresis and analyzed by fluorometry. The abundance of six individual polypeptides was consistently affected by diabetes: one protein was significantly decreased while four others were increased in diabetic myocytes. The remaining protein showed a shift in isoelectric point without a change in molecular weight possibly representing isoforms of a single polypeptide. The addition of insulin reverted the predominance of three proteins back to normal while it did not affect the other three at all. In conclusion diabetes induces changes in the abundance of a few proteins synthesized in vitro by cardiac myocytes and only half of them show an acute response to insulin.

Time course of response of individual messenger RNAs in the rat heart to T3

The time course of response of specific mRNAs following administration of triiodothyronine (T3) to hypothyroid rats was examined. We were particularly interested in identifying mRNAs showing a rapid response. Hypothyroid rats were injected with 0.2 mg of T3/100 g body wt and total cardiac RNA was prepared 0.5, 1, 2, 3, 5, 12 and 24 h later. RNA was translated in vitro in the presence of [35S]-methionine, the labeled peptides separated by two-dimensional electrophoresis and quantitated by digital matrix photometry. Of a total of 427 translational products 13 were identified to be selectively responsive to thyroid hormone. A specific mRNA coding for a protein designated as spot 72b (Mr 81,600, pI 5.34) was observed to show the most rapid response to T3. Administration of T3 to the hypothyroid animal resulted in an increase in the level of spot 72b by 2.6-fold within 1 h. The lag time between injection of T3 and response of other specific mRNA species varied between 5 to 24 h. These results demonstrate the diversity of response of individual cardiac mRNAs. The specific T3 responsive mRNA species described in the heart have not been demonstrated in other tissues indicating that induction of distinctive mRNA species is highly tissue specific. Relatively late responses may represent indirect effects of T3 mediated by interaction with other hormonal or metabolic signals. The rapid induction of spot 72b suggests it may result from the interaction of T3 with the nuclear receptor leading to a direct effect on the expression of this gene in the heart.(ABSTRACT TRUNCATED AT 250 WORDS)

Ischemia of the dog heart induces the appearance of a cardiac mRNA coding for a protein with migration characteristics similar to heat-shock/stress protein 71

Recent evidence indicates that different forms of stress, including hypoxia, can induce specific proteins called heat-shock or stress proteins in various types of mammalian cells. These studies examined whether myocardial ischemia can result in increased levels of proteins with molecular weight and isoelectric point characteristics similar to those described for heat-shock or stress proteins. The left anterior descending coronary artery of the dog heart was completely occluded; normal and ischemic myocardial samples were obtained 6 hours after occlusion; and total cardiac proteins and RNA were prepared. Ribonucleic acid was translated in vitro in a modified rabbit reticulocyte lysate system, and [35S]-methionine-labelled translational products as well as unlabelled cardiac proteins were separated by two-dimensional gel electrophoresis. Total proteins were visualized by silver staining and in vitro translation products quantified by fluorometry. A translatable mRNA coding for a 71,000 dalton peptide with an isoelectric point of 5.8 was markedly increased in the ischemic myocardium after 6 hours of ischemia. A protein with similar migration characteristics was detected in ischemic myocardium but not in normal myocardium. These results indicate that an mRNA coding for a translational product with similar migration characteristics of heat-shock protein 71 is induced by ischemia in the dog heart.

Rapid effects of insulin on in vitro translational activity of specific mRNA in diabetic rat heart

We studied the time course of response of specific cardiac mRNA after administration of insulin to diabetic rats. The primary aim was to identify specific cardiac mRNA, which show a rapid response to insulin administration. Diabetic rats were injected with 2 U of regular insulin intravenously, and total cardiac RNA was prepared 0.5, 1.5, 3, 5, 12, and 24 h later. RNA was translated in vitro in the presence of [35S]methionine and the translational products separated by two-dimensional electrophoresis and quantitated by digital matrix photometry. A rapid change in the translational activity of five specific mRNA species was observed within 0.5 h after administration of insulin to the diabetic animal. One translational product exhibits a more delayed response at 1.5 h. The predominance of three of these products was increased, while that of three was decreased. Two specific mRNA coding for translation products designated as spots 97 and 106 show the most significant change, with a dramatic decrease of 15-fold and 6.5-fold, respectively, within 0.5 h after insulin administration. The change in levels of these specific mRNA species could result from effects of insulin at various sites of mRNA synthesis or degradation. However, the rapidity of the response is compatible with a direct effect of insulin on gene expression. The very quick response of these specific mRNA species to insulin could thus serve as a useful model system to examine the molecular mechanisms of insulin action in the heart.

Mechanism of action of thyroid hormones

Thyroid hormones have ubiquitous effects and influence the function of most organs. The influences that thyroid hormones have on these diverse functions are primarily mediated through binding of T3 and T4 to specific nuclear receptor sites. The nuclear action of T3 results in organ-specific increases and decreases of specific mRNAs, leading to alteration in the level of the corresponding proteins. In addition to the well established nuclear action of T3, effects of thyroid hormone on other sites including cell membranes and mitochondria have been documented.

Diabetes-induced alterations in the translational activity of specific messenger ribonucleic acids isolated from rat hearts

During diabetes mellitus, total proteins and ribonucleic acids are significantly decreased in the rat heart, and these parameters can be increased by insulin administration. To determine whether all ribonucleic acids are equally sensitive to insulin, we examined the influence of this hormone on individual translatable ribonucleic acids. Cardiac ribonucleic acid prepared from control, untreated, and insulin-treated diabetic animals was translated in vitro in the presence of [35S]methionine. The radiolabeled peptides were separated by two-dimensional gel electrophoresis and were analyzed by fluorometry. We found that diabetes induces both qualitative and quantitative changes in the predominance of a few specific translatable messenger ribonucleic acid species. The translation of 11 messenger ribonucleic acid species was significantly decreased and that of eight messenger ribonucleic acid species was significantly increased in diabetic preparation. Twelve of the 19 translation products were quantified by digital matrix photometry: three labeled peptides were observed only when cardiac ribonucleic acid from diabetic animals was added to the cell-free translation system, four new peptides appeared when cardiac ribonucleic acid from control animals was added, and although the remaining five peptides were translated in vitro after either control or diabetic ribonucleic acid was added, their relative predominance was altered 2- to 200-fold. When translation products coded for by messenger ribonucleic acids prepared from either diabetic or hypothyroid hearts were compared, we found that most of the alterations induced by diabetes were also induced by hypothyroidism.(ABSTRACT TRUNCATED AT 250 WORDS)

Myosin isoenzyme distribution and Ca+2-activated myosin ATPase activity in the rat heart is influenced by fructose feeding and triiodothyronine

Studies were conducted to determine if the level of cardiac Ca+2-activated myosin ATPase activity and ventricular myosin isoenzyme distribution are influenced by both T3 administration and fructose feeding. Previous studies have shown that in the cardiac ventricle of hypothyroid rats, only myosin V3 is present, and the Ca+2-activated myosin ATPase activity is markedly decreased. Hypothyroid [thyroidectomized (Tx)] rats were fed a diet containing 60% fructose or a regular diet (47% complex carbohydrates) for 4 weeks. Fructose feeding of hypothyroid rats led to a significant increase in Ca+2-activated myosin ATPase activity (Tx regular diet, 0.33 +/- 0.02 mumol Pi/mg protein X min; Tx fructose diet, 0.54 +/- 0.04 mumol Pi/mg protein X min). In addition, myosin V1 was detectable in the heart of fructose-fed Tx rats, but was absent in Tx rats on the regular diet. To determine if fructose had an effect of similar magnitude in animals of different thyroid states, Tx rats were injected with 0.075, 0.150, 0.225, and 0.300 micrograms T3/100 g BW daily and placed on fructose or regular diets. The fructose-induced increase in Ca+2-myosin ATPase activity was between 24-27% in Tx rats receiving 0-0.15 micrograms T3/100 g BW daily. In animals receiving 0.225 and 0.300 micrograms T3/100 g BW daily, fructose feeding did not induce a significant increase in myosin ATPase activity. This is due to the fact that the Ca+2-activated myosin ATPase activities of euthyroid and hyperthyroid animals are not significantly different from each other. In hypothyroid rats receiving a 60% glucose diet, Ca+2-myosin ATPase activity showed a significant 20% increase above the value in regular diet-fed Tx rats. Fructose- and glucose-induced changes in Ca+2-myosin ATPase activity occurred in the absence of changes in thyroid hormone or insulin levels. Our findings may indicate that cardiac carbohydrate consumption influences the predominance of ventricular myosin isoenzymes in the rat heart.

Methyl palmoxirate increases Ca2+-myosin ATPase activity and changes myosin isoenzyme distribution in the diabetic rat heart

Previous studies have shown that in rats diabetes mellitus leads to a decrease in cardiac ventricle myosin V1 and an increase in myosin V3 levels. Insulin administration reverts myosin isoenzyme distribution to normal levels. It is currently unclear whether the effects of insulin on myosin isoenzyme distribution are a direct effect of the hormone or are mediated through insulin-induced alterations in cardiac metabolism. To gain further insight into this question diabetic rats received methyl palmoxirate, a potent inhibitor of long-chain fatty acid oxidation. Administration of 25 mg methyl palmoxirate X kg body wt-1 X day-1 to diabetic rats for 4 wk leads to a partial reversal of the effects of diabetes. Myosin V1 predominance is re-established and Ca2+-activated myosin ATPase activity increases by 60% (Ca2+-myosin ATPase normal rats 1.067 +/- 0.13 mumol Pi X mg protein-1 X min-1, diabetic rats 0.609 +/- 0.05 mumol Pi X mg protein-1 X min-1, diabetic + methyl palmoxirate rats 0.912 +/- 0.06 mumol Pi X mg protein-1 X min-1). The methyl palmoxirate-induced increase in myosin V1 levels and Ca2+-activated myosin ATPase activity occurred in the absence of changes in insulin and thyroid hormone levels. Methyl palmoxirate may have acted through its known inhibitory effect on cardiac beta-oxidation and/or the resultant stimulatory effect on glycolytic flux. Our findings may indicate that changes in cardiac substrate consumption can influence myosin isoenzyme predominance.

Fructose feeding increases Ca++-activated myosin ATPase activity and changes myosin isoenzyme distribution in the diabetic rat heart

Previous studies have shown that in rats, diabetes mellitus induces a 45% decrease in cardiac Ca++-activated myosin ATPase activity which is accompanied by a decrease in myosin isoenzyme V1 and an increase in myosin isoenzyme V3 levels. Insulin administration reverts Ca++-activated myosin ATPase activity and myosin isoenzyme distribution to normal levels. It is currently unclear whether the effects of insulin on Ca++-myosin ATPase activity and myosin isoenzyme distribution are direct effects of the hormone or are mediated through insulin-induced alterations in cardiac metabolism. To determine if insulin may exert part of its effects by the latter route, diabetic rats were fed a normal, glucose, or fructose diet. Unlike glucose, fructose can enter the initial steps of the glycolytic pathway in the absence of insulin. Placing diabetic rats on different forms of 60% fructose diets for 4 weeks led to a 20-35% increase in Ca++-activated myosin ATPase activity, which was highly significant (normal Ca++-activated myosin ATPase activity, 0.917 mumol Pi/mg protein X min; diabetic, 0.553 mumol Pi/mg protein X min; diabetic + fructose, 0.661 mumol Pi/mg protein X min). The increase in Ca++-activated myosin ATPase activity was accompanied by increased myosin isoenzyme V1 and decreased myosin isoenzyme V3 levels. Feeding animals a 60% glucose diet did not lead to changes in Ca++-activated myosin ATPase activity or myosin isoenzyme distribution. The fructose-induced increase in Ca++-activated myosin ATPase activity and alteration in myosin isoenzyme distribution occurred in the absence of changes in insulin and thyroid hormone levels or improvement in the general metabolic status of fructose-fed diabetic rats.

Hormonal influences on cardiac myosin ATPase activity and myosin isoenzyme distribution

It has been recognized for a long time that changes in hormone secretion can influence cardiac function; however, the biochemical basis for these changes has only recently been clarified. In this review the influences of hormonal status on the contractile protein myosin is discussed. Myosin has a rod-like portion and a globular head and consists of two myosin heavy chains (MHC) and four light chains (LC), two of which are identical. The globular head is the site of an ATP-splitting enzyme, the myosin ATPase, and increases in myosin ATPase activity are closely related to an increased velocity of contraction of the heart. Myosin ATPase activity shows marked response to alterations in thyroid hormone, insulin, glucocorticoid, testosterone and catecholamine levels, but marked animal species differences in this response occur. Thyroid hormone administration to normal rabbits, for example, increases myosin ATPase activity markedly, but the myosin ATPase activity of hyperthyroid rats remains unchanged. In contrast, in hypothyroid rats myosin ATPase activity is markedly decreased but the hypothyroid rabbit shows no such response. These species-related differences in the hormonal response of myosin ATPase activity result from the predominance pattern of specific myosin isoenzymes. In the normal rat heart three myosin isoenzymes, V1, V2 and V3, can be separated electrophoretically. Myosin V1 predominates (70% of total myosin), and has the highest myosin ATPase activity, whereas in rabbits myosin V3, which has a lower myosin ATPase activity, is the predominant isomyosin. Thyroid hormone administration to rabbits induces myosin V1 predominance and therefore increases myosin ATPase activity, whereas in hyperthyroid rats only a small further increase in V1 predominance can occur. The alterations in myosin isoenzyme predominance and myosin ATPase activity are closely correlated to changes in cardiac contractility. Hormone-induced alterations in myosin isoenzyme predominance are mediated through changes in the formation of two isoforms of myosin heavy chain. Changes in the expression of different myosin heavy chain genes are most likely responsible for the thyroid hormone and insulin-induced alterations in myosin isoenzyme predominance. Investigation of the control of myosin heavy chain formation can provide further insights into the hormonal control of a multigene family as well as broaden our understanding of the molecular events which result in altered cardiac contractility.(ABSTRACT TRUNCATED AT 400 WORDS)

Effect of diabetes and hypothyroidism on the predominance of cardiac myosin heavy chains synthesized in vivo or in a cell-free system

Rat cardiac ventricular myosins and RNA were prepared from normal, diabetic, insulin-treated diabetic, hypothyroid, and 3,3',5-triiodo-L-thyronine-treated hypothyroid rats. Myosin heavy chains isolated from purified myosin or synthesized in vitro from cardiac RNAs were subjected to partial protease digestion during sodium dodecyl sulfate-polyacrylamide gel electrophoresis. It was found that peptide maps obtained from cardiac myosin heavy chains of hypothyroid and diabetic rats were identical but differed from the maps of myosin heavy chain from control and hormone-treated animals. The same results were obtained, whether the heavy chains were isolated from purified myosin synthesized in the intact heart or from translation products coded for by cardiac RNAs added to the modified reticulocyte lysate. These results indicate that the myosin heavy chain RNA species present in the hypothyroid heart is also expressed during insulin deficiency but differs from the species expressed in normal animals. The expression of the two myosin heavy chain RNA species found in the rat cardiac ventricle appears to be independently regulated by these two hormones.

The effects of amiodarone on serum thyroid hormones and hepatic thyroxine 5'-monodeiodination in rats

Amiodarone (2-n-butyl-3,4'-diethylaminoethoxy-3', 5'-diiodobenzoyl-benzofurane) is an antiarrhythmic drug which increases serum T4 and rT3 levels in patients and lowers serum T3 levels. To investigate its effects on T4 metabolism and its cardiac action, we fed amiodarone to male Fisher rats at doses of 5, 15, and 45 mg/kg BW X day; controls received potassium iodide for 4-7 weeks, and another group received sodium ipodate. At 4 weeks, amiodarone caused a dose-dependent increase in the serum T4 concentration and a slight reduction of serum TSH without a change in the serum T3 concentration. These changes were not present at 7 weeks. Sodium ipodate raised serum T4 concentrations at both times. Rats treated with T4 (150 micrograms/kg BW X day) to suppress thyroidal secretion of hormone and with amiodarone (15 mg/kg) had marked reduction of serum T3 concentrations compared with controls receiving T4 without amiodarone. Liver homogenates from rats treated with amiodarone showed marked reduction on T4 5'-monodeiodinase activity in a dose-related manner. Amiodarone added to liver homogenates in vitro at concentrations of 0.001-1 mM did not inhibit T3 production from T4, whereas ipodate added in vitro (0.01-1 mM) did inhibit T3 production. Rats treated with amiodarone showed a lowering of the resting heart rate and a reduction of the increment in heart rate after iv isoproterenol administration. The cardiac Ca++ myosin ATPase activity was reduced in rats receiving amiodarone (45 mg/kg) compared with that in controls. The data indicate that rats treated with amiodarone have reduced peripheral conversion of T4 to T3 owing to impaired hepatic T4 5'-monodeiodinase activity. In addition, these rats have slowing of heart rate and reduction of cardiac Ca++ myosin ATPase activity. These findings are consistent with the hypothesis that amiodarone blocks some effects of thyroid hormone on the heart, but additional studies are needed to test this hypothesis.

Influence of thyroid hormone on the in vitro translational activity of specific mRNAs in the rat heart

The influence of thyroid hormone on the translational activity of specific cardiac mRNA was determined by in vitro translation of RNA isolated from the heart of normal, hypothyroid, and 3,3',5-triiodo-L-thyronine-injected hypothyroid rats. Proteins synthesized in vitro in the presence of [35S]methionine were separated by two-dimensional gel electrophoresis and quantitated by a novel scanning procedure using digital matrix photometry. A total of 421 translational products were detected by fluorography and changes in the predominance of 12 of these were influenced by the thyroid state of the animals. The relative predominance of 8 species was increased in euthyroid animals, whereas 4 translational products were increased in hypothyroid animals. The majority of these thyroid hormone-related alterations occurred in spot pairs of similar molecular weights, but slightly different isoelectric points. In contrast, the relative predominance of mRNAs coding for the major contractile proteins, light chain 1, light chain 2, tropomyosin, actin, and myosin heavy chain was not altered by the thyroid status of the animals. The relative levels of these abundant mRNA species remained unaltered in spite of a thyroid hormone-related increase in total RNA levels. In vivo effects of thyroid hormone on cardiac RNA levels are complex. In addition to a general increase in total RNA and mRNA levels, increases or attenuations in the predominance of a small number of specific mRNA species are observed when euthyroid and hypothyroid animals are compared.

A physiological dose of triiodothyronine normalizes cardiac myosin adenosine triphosphatase activity and changes myosin isoenzyme distribution in semistarved rats

The possibility that the lowering of thyroid hormone levels which occurs in the nonthyroidal illness syndrome results in a hypothyroid state at the cardiac tissue level was examined in semistarved rats. Rats were fed 50% of their normal food intake in the form of a regular diet (R. diet) or low carbohydrate diet (L.C. diet) for 8 weeks. Animals semistarved for 8 weeks on the R. diet lost 42% of their body weight, while plasma T3 and T4 levels decreased by 45-50%. Semistarvation on the L.C. diet resulted in a 19% weight loss and a similar 46-49% decrease in plasma T3 and T4 levels. Ca++-activated myosin ATPase activity declined by 28% and 48% with the R. and L.C. diets, respectively [normal rats myosin ATPase, 1.30 +/- 0.18 mumol Pi/(mg protein . min) (mean +/- SD); semistarvation R diet, 0.93 +/- 0.15; semistarvation L.C. diet, 0.67 +/- 0.15]. The administration of physiological amounts of T3 (0.3 micrograms T3/100 g BW daily) restored the cardiac myosin ATPase activity in both groups. To confirm that the T3 effect was due to a normalization of the thyroid status at the tissue level, hypothyroid animals on a normal diet were injected with 0.3 micrograms T3 for 4 weeks, which resulted in normalization of myosin ATPase activity levels. Thyroidectomized rats receiving daily T3 injections, and when placed on a 50% reduction of food intake for 4 weeks still maintained normal myosin ATPase activity even though they lost 36% of their body weight. Distribution of cardiac myosin isoenzymes was determined by pyrophosphate polyacrylamide gel electrophoresis. In normal cardiac ventricles, myosin isoenzyme V1 predominates and represents 68 +/- 7% (+/- SD) of the total myosin. Semistarvation resulted in a redistribution of myosin isoenzymes so that V3 myosin was the predominant species (53 +/- 3% of the total myosin). The administration of 0.3 microgram T3/100 g BW daily for 4 weeks to semistarved rats reverted myosin isoenzyme distribution to V1 predominance (V1 myosin, 54 +/- 3% of the total myosin). These results indicate that the semistarvation-induced lowering plasma T3 and T4 levels is an important determinant of myosin ATPase activity and myosin isoenzyme distribution. Restoration of myosin ATPase activity to its normal level and return to myosin V1 predominance after T3 administration make it likely that these changes are related to the lowering of thyroid hormone levels.

Influence of thyroid hormone administration on myosin ATPase activity and myosin isoenzyme distribution in the heart of diabetic rats

Previous studies have shown that diabetes mellitus leads in rats to a 45% decrease in cardiac Ca++ activated myosin ATPase, a change in myosin isoenzyme distribution and a lowering of plasma T4 and T3 levels. Hypothyroidism causes similar changes in myosin ATPase and myosin isoenzyme distribution. We determined if thyroid hormone administration in physiological replacement dose (0.3 microgram T3/100 g BW) or pharmacological doses (3 micrograms T3/100 g BW and 10 micrograms T4/100 g BW) can normalize myosin ATPase and isoenzyme distribution in diabetic rats. Control animals have a Ca++ myosin ATPase activity of 1.23 +/- 0.14 mumol Pi/mg protein/min and myosin V1 represented 70% and myosin V3 15% of total myosin. Four weeks after streptozotocin administration myosin ATPase was 0.61 +/- 0.14, and myosin V3 represented 67% of total myosin. Administration of 0.3 microgram T3/100 g BW/day for four weeks to diabetic animals resulted in no significant increase in myosin ATPase (0.69 +/- 0.07 mumol Pi/mg protein/min) or in myosin isoenzyme distribution. In contrast, administration of 3 micrograms T3/100 g BW/day or 10 micrograms T4/100 g BW/day for 4 wk led to a normalization of myosin ATPase activity (for T3 1.03 +/- 0.18, for T4 1.06 +/- 0.15). In addition the myosin isoenzyme distribution pattern normalized. These findings may point to a diminished thyroid hormone responsiveness in diabetic rats or could result from diabetes related disturbances of cellular metabolism, which are normalized by pharmacologic doses of thyroid hormone.

Diabetes mellitus induces changes in cardiac myosin of the rat

Decreased contractility has been reported in the diabetic heart. Because a close correlation exists between contractility and the activity of Ca2+ AT Pa se of purified actinomyosin and myosin, Ca2+ ATPase activity was determined in control and diabetic rats. In control rats, actinomyosin ATPase was 0.59 ± 0.05 μmol Pi/mg protein/min and had decreased by 35% to 0.38 ± 0.04 in diabetic rats (P < 0.025). Myosin ATPase activity was 1.25 ± 0.09 μmol Pi/mg protein/min in control rats and had decreased by 45% to 0.67 ± 0.05 in diabetic animals (P < 0.01). To investigate the decrease in myosin ATPase activity further, ventricular myosin was separated by pyrophosphate polyacrylamide electrophoresis into its three authentic components, V1, V2, and V3 myosin. V1 has the highest mobility and Ca2+ ATPase activity (1.27 ± 0.3 arbitrary units) and represents 72% of control myosin, whereas V3 has the lowest mobility and Ca2+ ATPase activity (0.16 ± 0.08 units) and constitutes 13% of myosin. A marked change in the predominance of V1 and V3 myosin components occurs in diabetic rats where V3 myosin predominates, representing 68% of total myosin with V1 myosin constituting only 15%. Ca2+ ATPase activities of V1, V2, and V3 myosin in control and diabetic hearts are similar; however, the predominance of V3 myosin in diabetic rats can account for the decreased Ca2+ ATPase activity of diabetic myosin. The diabetes-induced changes in myosin ATPase activity and myosin isoenzyme distribution can be reverted to control levels by insulin administration.

Glucagon administration decreases hepatic nuclear triiodothyronine binding capacity

The maximal binding capacity (MBC) of nuclear triiodothyronine (T3) receptor sites in rat liver decreases markedly after glucagon administration. Administration of serial doses of glucagon (2.5 microgram/100 g BW) resulted in a 33% decrease in MBC in 3.5 h and MBC was reduced by 45% in 6.25 h. The individual doses used were in the same order of magnitude as those used in the treatment of hypoglycemic human subjects (1.5 microgram/100 g BW). This report presents the first evidence that a peptide hormone can change the number of nuclear T3 receptor sites. The physiological significance of these findings remains to be clarified.

Alpha-amanitin administration results in a temporary inhibition of hepatic enzyme induction by triiodothyronine: further evidence favoring a long-lived mediator of thyroid hormone action

Alpha-amanitin was shown to inhibit triiodothyronine (T3)-induced increases in mitochondrial alpha-glycerophosphate dehydrogenase (alpha-GPD) and cytoplasmic malic enzyme activity in the livers of male Sprague-Dawley rats. A 3-fold increase in alpha-GPD observed 24 h after the iv injection of 3 microngT3/100 g BW was completely inhibited by administration of alpha-amanitin at 0 and 8 h. Similarly, alpha-amanitin blocked a two- to four-fold increase in malic enzyme 24 h following iv injection of 3 mg T3/100 g BW into euthyroid rats. After the initial inhibition of enzyme induction by alpha-amanitin was dissipated, however, a delayed but striking increase in enzyme activity occurred. In hypothyroid animals, alpha-GPD activity rose after the initial 24 h inhibition and reached levels at 72 h equal to those observed in hypothyroid rats treated with T3 only. In euthyroid animals treated with T3 and alpha-amanitin, a delayed increase in malic enzyme activity was observed at 72 h and attained values at 96 h similar to those in euthyroid animals injected with T3 only. The delayed rise in enzyme response is most easily explained by the formation of a long-lived intermediate during the exposure of the nuclear sites to T3.

Studies of a thyroid hormone and androgen dependent protein in rat liver cytosol

Sodium dodecyl sulphate (SDS) polyacrylamide gel electrophoresis of the liver cytosol of euthyroid male rats revealed a prominent band (molecular weight, 26 000 daltons), designated Protein II, which was virtually absent in the cytosol of hypothyroid animals. Injection of 500 mug triiodothyronine (T3) per 100 g body weight resulted in a maximal increase in the level of Protein II, reaching 90% of the euthyroidal level 3 days after hormone administration. Concomitant studies with the liver mitochondrial enzyme alpha-glycerophosphate dehydrogenase (alpha-GPD) indicated that this T3 dose also resulted in a maximal enzyme response in this time period. Since we have estimated that 500 mug of T3 will saturate nearly all nuclear T3 binding sites, these results support the concept that the synthesis of both proteins is limited by nuclear binding. Protein II was absent in the liver cytosol of female rats but could be induced in ovariectomized female rats by androgens. Treatment of male rats with oestradiol resulted in disappearance of Protein II. Since administration of testosterone to hypothyroid male rats caused only a minimal increase in the amount of Protein II, the absence of the protein in hypothyroid animals was not due to androgen deficiency. Similarities in the molecular weight and the response to hormonal manipulation of Protein II and of the urinary alpha2uglobulin, previously reported by Roy (1973) raise the possibility that these proteins are the same. The high concentration of Protein II in male rat cytosol and the relative ease in its identification by SDS polyacrylamide gel electrophoresis make it a potentially useful model protein for the study of thyroid hormone action at the cellular level.