Wolfgang H. Dillmann

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.

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 (FCF–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.

Myofibroblasts revert to an inactive phenotype during regression of liver fibrosis

Myofibroblasts produce the fibrous scar in hepatic fibrosis. In the carbon tetrachloride (CCl4) model of liver fibrosis, quiescent hepatic stellate cells (HSC) are activated to become myofibroblasts. When the underlying etiological agent is removed, clinical and experimental fibrosis undergoes a remarkable regression with complete disappearance of these myofibroblasts. Although some myofibroblasts apoptose, it is unknown whether other myofibroblasts may revert to an inactive phenotype during regression of fibrosis. We elucidated the fate of HSCs/myofibroblasts during recovery from CCl4- and alcohol-induced liver fibrosis using Cre-LoxP–based genetic labeling of myofibroblasts. Here we demonstrate that half of the myofibroblasts escape apoptosis during regression of liver fibrosis, down-regulate fibrogenic genes, and acquire a phenotype similar to, but distinct from, quiescent HSCs in their ability to more rapidly reactivate into myofibroblasts in response to fibrogenic stimuli and strongly contribute to liver fibrosis. Inactivation of HSCs was associated with up-regulation of the anti-apoptotic genes Hspa1a/b, which participate in the survival of HSCs in culture and in vivo.

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.

Expression of inducible stress protein 70 in rat heart myogenic cells confers protection against simulated ischemia-induced injury.

Myocardial ischemia markedly increases the expression of several members of the stress/heat shock protein (HSP) family, especially the inducible HSP70 isoforms. Increased expression of HSP70 has been shown to exert a protective effect against a lethal heat shock. We have examined the possibility of using this resistance to a lethal heat shock as a protective effect against an ischemic-like stress in vitro using a rat embryonic heart-derived cell line H9c2 (2-1). Myogenic cells in which the heat shock proteins have been induced by a previous heat shock are found to become resistant to a subsequent simulated ischemic stress. In addition, to address the question of how much does the presence of the HSP70 contribute to this protective effect, we have generated stably transfected cell lines overexpressing the human-inducible HSP70. Embryonal rat heart-derived H9c2(2-1) cells were used for this purpose. This stably transfected cell line was found to be significantly more resistant to an ischemic-like stress than control myogenic cells only expressing the selectable marker (neomycin) or the parental cell line H9c2(2-1). This finding implicates the inducible HSP70 protein as playing a major role in protecting cardiac cells against ischemic injury.

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.

Mice overexpressing rat heat shock protein 70 are protected against cerebral infarction

Increased expression of heat shock protein 70 (HSP70) in the brain has been extensively documented in association with a variety of insults, including ischemia, and is suggested to play a role in cell survival and recovery after ischemic injury. To more directly assess the protective role of HSP70 during ischemic brain damage, we used transgenic mice overexpressing the rat HSP70 (HSP70tg mice). In contrast to wild‐type (wt) littermates, high levels of HSP70 messenger RNA and protein were detected in brains of HSP70tg mice under normal conditions, and immunohistochemical analysis revealed primarily neuronal expression of HSP70. Heterozygous HSP70tg mice and their wt littermates were subjected to permanent focal cerebral ischemia by intraluminal blockade of the middle cerebral artery. Cerebral infarction after 6 hours of ischemia, as evaluated by Nissl staining, was significantly less in HSP70tg mice compared with wt mice. This reduction in infarction volume in HSP70tg mice was not attributable to an altered cardiovascular anatomy or to initial differences in body temperature or hemodynamic parameters. The HSP70tg mice were still protected against cerebral infarction 24 hours after permanent focal ischemia. The data suggest that HSP70 can markedly protect the brain against ischemic damage and that approaches aimed at inducing HSP70 may lead to new therapeutic interventions in cerebrovascular injuries. Ann Neurol 2000;47:782–791

Diabetes and the accompanying hyperglycemia impairs cardiomyocyte calcium cycling through increased nuclear O-GlcNAcylation.

Diabetic cardiomyopathy is characterized by impaired cardiac contractility leading to poor myocardial performance. We investigated the role that the hexosamine pathway, and especially altered nuclear O-Glc-NAcylation, plays in the development of diabetic cardiomyopathy. Incubating neonatal rat cardiomyocytes in high glucose (25 mm) resulted in prolonged calcium transients when compared with myocytes incubated in normal glucose (5.5 mm), which is consistent with delayed myocardial relaxation. High glucose-treated myocytes also exhibited reduced sarcoendoplasmic reticulum Ca2+-ATPase 2a (SERCA2a) mRNA and protein expression, decreased SERCA2a promoter activity, and increased O-GlcNAcylation of nuclear proteins compared with myocytes treated with normal glucose. Exposure of myocytes to 8 mm glucosamine or an adenovirus expressing O-GlcNAc-transferase (OGT) resulted in prolonged calcium transient decays and significantly reduced SERCA2a protein levels, whereas treatment with an adenovirus encoding O-GlcNAcase (GCA) resulted in improved calcium transients and SERCA2a protein levels in myocytes exposed to high glucose. Effects of elevated glucose or altered O-GlcNAcylation were also observed on essential transcription factors involved in cardiomyocyte function. High glucose-treated myocytes (with or without OGT adenovirus) exhibited increased levels of O-GlcNAcylated specificity protein 1 compared with control myocytes, whereas infecting high glucose-treated myocytes with GCA adenovirus reduced the degree of specificity protein 1 Glc-NAcylation. Treatment of myocytes with 25 mm glucose, 8 mm glucosamine, or OGT adenovirus also significantly reduced levels of myocytes enhancer factor-2A protein compared with control myocytes, whereas infection with GCA adenovirus resulted in improved myocytes enhancer factor-2 expression. Our results suggest that the hexosamine pathway, and O-GlcNAcylation in particular, is important in impaired cardiac myocyte function and the development of diabetic cardiomyopathy.

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.