Heat shock transcription factor 1 protects cardiomyocytes from ischemia/reperfusion injury.

BACKGROUND: Because cardiomyocyte death causes heart failure, it is important to find the molecules that protect cardiomyocytes from death. The death trap is a useful method to identify cell-protective genes. METHODS AND RESULTS: In this study, we isolated the heat shock transcription factor 1 (HSF1) as a protective molecule by the death trap method. Cell death induced by hydrogen peroxide was prevented by overexpression of HSF1 in COS7 cells. Thermal preconditioning at 42 degrees C for 60 minutes activated HSF1, which played a critical role in survival of cardiomyocytes from oxidative stress. In the heart of transgenic mice overexpressing a constitutively active form of HSF1, ischemia followed by reperfusion-induced ST-segment elevation in ECG was recovered faster, infarct size was smaller, and cardiomyocyte death was less than wild-type mice. Protein kinase B/Akt was more strongly activated, whereas Jun N-terminal kinase and caspase 3 were less activated in transgenic hearts than wild-type ones. CONCLUSIONS: These results suggest that HSF1 protects cardiomyocytes from death at least in part through activation of Akt and inactivation of Jun N-terminal kinase and caspase 3.

Leukemia inhibitory factor enhances survival of cardiomyocytes and induces regeneration of myocardium after myocardial infarction.

BACKGROUND: Myocardial infarction (MI) is a leading cause of cardiac morbidity and mortality in many countries; however, the treatment of MI is still limited. METHODS AND RESULTS: We demonstrate a novel gene therapy for MI using leukemia inhibitory factor (LIF) cDNA. We injected LIF plasmid DNA into the thigh muscle of mice immediately after inducing MI. Intramuscular injection of LIF cDNA resulted in a marked increase in circulating LIF protein concentrations. Two weeks later, left ventricular remodeling, such as infarct extent and myocardial fibrosis, was markedly attenuated in the LIF cDNA-injected mice compared with vehicle-injected mice. More myocardium was preserved and cardiac function was better in the LIF-treated mice than in the vehicle-injected mice. Injection of LIF cDNA not only prevented the death of cardiomyocytes in the ischemic area but also induced neovascularization in the myocardium. Furthermore, LIF cDNA injection increased the number of cardiomyocytes in cell cycle and enhanced mobilization of bone marrow cells to the heart and their differentiation into cardiomyocytes. CONCLUSIONS: The intramuscular injection of LIF cDNA may induce regeneration of myocardium and provide a novel treatment for MI.

3-Hydroxy-3-methylglutaryl coenzyme A reductase inhibitors prevent the development of cardiac hypertrophy and heart failure in rats.

OBJECTIVES: The aim of the present study was to determine whether 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors (statins) have preventive effects on the development of cardiac hypertrophy and heart failure. BACKGROUND: Statins have been reported to have various pleiotropic effects, such as inhibition of inflammation and cell proliferation. METHODS: Dahl rats were divided into three groups: LS, the rats fed the low-salt diet (0.3% NaCl); HS, the rats fed the high-salt diet (8% NaCl) from the age of 6 weeks; and CERI, the rats fed the high-salt diet with cerivastatin 1 mg/kg/d by gavage from the age of 6 weeks. RESULTS: In HS rats, cardiac function was markedly impaired and all rats showed the signs of heart failure within 17 weeks of age. In CERI rats, cardiac function was better than that of HS and no rats were dead up to 17 weeks of age. The development of cardiac hypertrophy and fibrosis was attenuated, and the number of apoptotic cells and expression of proinflammatory cytokine interleukin (IL)-1beta gene were less as compared with HS rats. Pretreatment of cerivastatin suppressed the adriamycin-induced apoptosis of cultured cardiomyocytes of neonatal rats. CONCLUSIONS: These results suggest that statins have a protective effect on cardiac myocytes and may be useful to prevent the development of hypertensive heart failure.

Beating is necessary for transdifferentiation of skeletal muscle-derived cells into cardiomyocytes.

Cell transplantation could be a potential therapy for heart damage. Skeletal myoblasts have been expected to be a good cell source for autologous transplantation; however, the safety and efficacy of their transplantation are still controversial. Recent studies have revealed that skeletal muscle possesses the stem cell population that is distinct from myoblasts. To elucidate whether skeletal muscle stem cells can transdifferentiate into cardiomyocytes, we cocultured skeletal muscle cells isolated from transgenic mice expressing green fluorescent protein with cardiomyocytes of neonatal rats. Skeletal muscle-derived cells expressed cardiac-specific proteins such as cardiac troponin T and atrial natriuretic peptide as well as cardiac-enriched transcription factors such as Nkx2E (formerly called Csx/Nkx2.5) and GATA4 by coculture with cardiomyocytes. Skeletal muscle-derived cells also expressed cadherin and connexin 43 at the junctions with neighboring cardiomyocytes. Cardiomyocyte-like action potentials were recorded from beating skeletal muscle-derived cells. Treatment of nifedipine or culture in Ca2+-free media suppressed contraction of cardiomyocytes and inhibited skeletal muscle cells to express cardiac-specific proteins. Cyclic stretch completely restored this inhibitory effect. These results suggest that some part of skeletal muscle cells can transdifferentiate into cardiomyocytes and that direct cell-to-cell contact and contraction of neighboring cardiomyocytes are important for the transdifferentiation.

Gene expression profile revealed different effects of angiotensin II receptor blockade and angiotensin-converting enzyme inhibitor on heart failure.

Although recent clinical studies have indicated that angiotensin II receptor blocker is as effective in treating heart failure as an angiotensin-converting enzyme inhibitor, it is unknown whether their effects are different. Dahl salt-sensitive rats were treated with an angiotensin-converting enzyme inhibitor benazepril, and an angiotensin II receptor blocker candesartan from 11 weeks old. We examined cardiac geometry and function by echocardiography, and histology and gene expression by high-density oligonucleotide arrays using Affymetrix U34 (Affymetrix, Santa Clara, CA, U.S.A.). Dahl salt-sensitive rats fed a high salt diet showed a marked increase in blood pressure and developed concentric hypertrophy at 11 weeks, followed by left ventricle dilation and congestive heart failure by 20 weeks after birth. Although both medications had only a mild antihypertensive effect, they strongly suppressed the development of cardiac hypertrophy, fibrosis and heart failure to the same extent. Gene expression pattern examined by Affymetrix GeneChip (Affymetrix) is quite different between the two drug groups, indicating that angiotensin II receptor blocker and angiotensin-converting enzyme inhibitor prevent heart failure by different mechanisms.

Inhibitory molecules in signal transduction pathways of cardiac hypertrophy.

Cardiac hypertrophy is induced by a variety of diseases, such as hypertension, valvular diseases, myocardial infarction, and endocrine disorders. Although cardiac hypertrophy may initially be a beneficial response that normalizes wall stress and maintains normal cardiac function, prolonged hypertrophy is a leading cause of heart failure and sudden death. A number of studies have elucidated molecules responsible for the development of cardiac hypertrophy, including the mitogen-activated protein (MAP) kinases pathway, Janus kinase (JAK)/signal transducer and activator of transcription (STAT) pathway, and calcium/calmodulin-dependent protein phosphatase calcineurin pathway. These molecules may be targets for therapies designed to prevent the progression of cardiac hypertrophy. Numerous studies have focused on characterization of the intracellular signal transduction molecules that promote cardiac hypertrophy in order to clarify the molecular mechanisms, but there have been only a few reports on the inhibitory regulators of hypertrophic response. Recently, several molecules have attracted much attention as endogenous inhibitory regulators of cardiac hypertrophy. Enhancement of these inhibitory regulators would also seem to be a potential approach for the pharmacological treatment of hypertrophy. In this review, we summarize the inhibitory molecules of cardiac hypertrophy.

Angiotensin II type 1a receptor mediates doxorubicin-induced cardiomyopathy.

Although the serious cardiotoxicity of doxorubicin (DOX), a useful chemotherapeutic agent, limits the use of this agent, the mechanism of DOX-induced cardiomyopathy remains unclear. Since accumulating evidence suggests that activation of the renin-angiotensin system is involved in the development of various types of cardiovascular remodeling, we examined the role of angiotensin II (Ang II) in DOX-induced cardiotoxicity using Ang II type 1a receptor (AT1) knockout (KO) mice. To examine the role of AT1 in the acute effects of DOX, we injected a single 20 mg/kg dose of DOX into AT1KO mice, wild type (WT) mice and WT mice treated with an AT1 antagonist, RNH-6270; to examine the role of AT1 in the chronic effects of DOX, we injected mice of the same groups with 1 mg/kg DOX once a week for 12 weeks. Echocardiography revealed that cardiac function was significantly impaired in WT mice, but not in AT1KO mice or WT mice administered RNH-6270, by both acute and chronic DOX treatment. Histological analysis showed that DOX induced myofibrillar loss and increased the number of apoptotic cells in WT mice, but not in AT1KO mice or WT mice administered RNH-6270. Expression of the ANP gene was downregulated by DOX treatment in WT mice, and this alteration was attenuated in AT1KO mice and in RNH-6270-treated mice. We conclude that the AT1-mediated Ang II signaling pathway plays an important role in DOX-induced cardiac impairment, suggesting that an AT1 antagonist can be used to prevent DOX-induced cardiomyopathy.

Molecular and cellular mechanisms of mechanical stress-induced cardiac hypertrophy.

Congestive heart failure is one of the major issues for cardiologists. Since cardiac hypertrophy deteriorates into heart failure, it is important to elucidate the mechanisms of cardiac hypertrophy. Hemodynamic overload, namely mechanical stress, is a major cause for cardiac hypertrophy. Mechanical stress induces various hypertrophic responses such as activation of phosphorylation cascades of many protein kinases, expression of specific genes and an increase in protein synthesis. During this process, secretion and production of vasoactive peptides such as angiotensin II and endothelin-1, are increased and play critical roles in the induction of these hypertrophic responses. Recently, a Ca2+ dependent protein kinase, CaMK, and a Ca2+ dependent protein phosphatase, calcineurin, have attracted great attention as critical molecules that induce cardiac hypertrophy. In this review, we described the mechanisms by which mechanical stress induces cardiac hypertrophy, especially focusing on the role of calcineurin in the development of cardiac hypertrophy.

Csx/Nkx2-5 is required for homeostasis and survival of cardiac myocytes in the adult heart.

Csx/Nkx2-5, which is essential for cardiac development of the embryo, is abundantly expressed in the adult heart. We here examined the role of Csx/Nkx2-5 in the adult heart using two kinds of transgenic mice. Transgenic mice that overexpress a dominant negative mutant of Csx/Nkx2-5 (DN-TG mice) showed degeneration of cardiac myocytes and impairment of cardiac function. Doxorubicin induced more marked cardiac dysfunction in DN-TG mice and less in transgenic mice that overexpress wild type Csx/Nkx2-5 (WT-TG mice) compared with non-transgenic mice. Doxorubicin induced cardiomyocyte apoptosis, and the number of apoptotic cardiomyocytes was high in the order of DN-TG mice, non-transgenic mice, and WT-TG mice. Overexpression of the dominant negative mutant of Csx/Nkx2-5 induced apoptosis in cultured cardiomyocytes, while expression of wild type Csx/Nkx2-5 protected cardiomyocytes from doxorubicin-induced apoptotic death. These results suggest that Csx/Nkx2-5 plays a critical role in maintaining highly differentiated cardiac phenotype and in protecting the heart from stresses including doxorubicin.

Sodium calcium exchanger plays a key role in alteration of cardiac function in response to pressure overload.

The Na+-Ca2+ exchanger (NCX) on the plasma membrane is thought to be the main calcium extrusion system from the cytosol to the extracellular space in many mammalian excitable cells, including cardiac myocytes. However, the pathophysiological role of NCX in the heart is still unclear because of the lack of known specific inhibitors of NCX. To determine the role of NCX in cardiac contraction and the development of cardiac hypertrophy, we imposed pressure overload on the heart of heterozygous NCX knockout (KO) mice by constricting transverse aorta, and examined cardiac function and morphology 3 wk after operation. Although there was no difference in cardiac function between sham-operated KO mice and sham-operated wild-type (WT) mice, KO mice showed higher left ventricular pressure and better systolic function than WT mice in response to pressure overload. Northern blot analysis revealed that mRNA levels of sarcoplasmic reticulum Ca2+-ATPase were reduced by pressure overload in left ventricles of WT but not of KO mice. However, hypertrophic changes with interstitial fibrosis were more prominent in KO mice than WT mice. These results suggest that reduction of NCX results in supernormalized cardiac function and causes marked cardiac hypertrophy in response to pressure overload.