Cardioprotective effects of severe calorie restriction from birth in adult ovariectomized rats

AIMS

Menopause is a female condition induced by a reduction of ovarian hormone and is related to an increase in cardiovascular diseases in women. We have shown that severe calorie restriction (SCR) from birth reduces the cardiometabolic risk in adult male Wistar rats. In this study, we investigated the effects of SCR from birth to adulthood on cardiovascular function of ovariectomized rats.

MAIN METHODS

From birth to adulthood, rats were daily fed ad libitum (control group - C) or with 50% of the amount consumed by the control group (calorie-restricted group - R). At 90 days, half of the rats in each group underwent bilateral ovariectomy (OVX), totaling 4 groups: C-Sham, C-OVX, R-Sham, R-OVX. Systolic blood pressure (SBP), heart rate (HR) and, double product (DP) index were recorded by tail-cuff plethysmography. Cardiac function was analyzed by the Langendorff technique and cardiomyocyte diameter was accessed by histologic analysis. Additionally, cardiac SERCA2 content and redox status were evaluated.

KEY FINDINGS

C-OVX rats exhibited reduced cardiac function and cardiac non-enzymatic total antioxidant capacity (TAC). R-Sham animals showed reduced SBP, DP, HR, improved cardiac function, reduced cardiac protein carbonyl derivatives and increased TAC, catalase, and superoxide dismutase activities. R-OVX rats maintained reduced SBP, DP, HR, and increased contractility and relaxation indexes. R-Sham and R-OVX rats exhibited preserved heart mass and reduced cardiomyocyte diameter. Cardiac SERCA2 content did not differ between the groups.

SIGNIFICANCE

Taken together, our findings show cardioprotective effects of SCR from birth in adult ovariectomized rats.

The Link Between Sex Hormones and Susceptibility to Cardiac Arrhythmias: From Molecular Basis to Clinical Implications

It is well-known that gender is an independent risk factor for some types of cardiac arrhythmias. For example, males have a greater prevalence of atrial fibrillation and the Brugada Syndrome. In contrast, females are at increased risk for the Long QT Syndrome. However, the underlying mechanisms of these gender differences have not been fully identified. Recently, there has been accumulating evidence indicating that sex hormones may have a significant impact on the cardiac rhythm. In this review, we describe in-depth the molecular interactions between sex hormones and the cardiac ion channels, as well as the clinical implications of these interactions on the cardiac conduction system, in order to understand the link between these hormones and the susceptibility to arrhythmias.

Decreasing myocardial estrogen receptors and antioxidant activity may be responsible for increasing ischemia- and reperfusion-induced ventricular arrhythmia in older female rats

AIMS

This study aimed to investigate the relationship between ischemia- and reperfusion-induced arrhythmia and blood serum estrogen levels, myocardial estrogen receptor levels, antioxidant enzyme activities, and the effects of the estrogen receptor blocker, fulvestrant (ICI 182 780).

MAIN METHODS

A total of 102 female Sprague-Dawley rats of different ages (2-3, 6-7, 14-15, and 20-21 months) were used in this study. Myocardial ischemia was produced by ligation of the descending branch of the left anterior descending coronary artery, and reperfusion was produced by releasing this artery. An electrocardiogram (ECG) and blood pressure were recorded for 6 min of ischemia and 6 min of reperfusion. The levels of superoxide dismutase (SOD), malondialdehyde (MDA), catalase (CAT), estrogen receptor α (ERα), and estrogen receptor β (ERβ) in myocardial tissue and 17 beta-estradiol (E2) in blood serum were measured via enzyme-linked immunosorbent assay (ELISA). The results were compared using a Mann-Whitney U test, one-way analysis of variance (ANOVA), and a student's t-test.

KEY FINDINGS

It is not the changes in serum estrogen levels but the decreasing myocardial estrogen receptors and antioxidant activities that could be responsible for the occurrence of more severe arrhythmia in response to reperfusion in older female rats.

SIGNIFICANCE

The death rate due to a heart attack in younger men is higher than in women. However, it equalizes after the menopausal stage in women. In this study, the reason for the increasing sudden post-menopausal death rate in women was investigated experimentally.

Assessment of Ventricular Repolarization in Sickle Cell Anemia Patients: The Role of QTc Interval, Tp-e Interval and Tp-e/QTc Ratio and Its Gender Implication

Background

Many specific and non-specific electrocardiographic abnormalities including ventricular arrhythmias have been reported in subjects with sickle cell anemia (SCA). In SCA patients, cardiac electrical abnormalities may be the leading cause of increased risk of arrhythmias. The corrected QT (QTc) interval, peak to the end of the T wave (Tp-e) interval and associated Tp-e/QTc ratio are promising measures of altered ventricular repolarization and increased arrhythmogenesis risk.

Aim

This study assessed ventricular repolarization abnormalities in subjects with SCA using the QTc interval, Tp-e interval and Tp-e/QTc ratio, and also evaluated the gender differences in these parameters, as well as their determinants.

Methods

Sixty subjects with SCA and 60 healthy control subjects, matched for age and gender, were studied. All participants underwent physical examination, hematological and biochemical evaluation, and 12-lead electrocardiography (ECG) recording. QT and Tp-e intervals were measured from the ECG, and the QTc interval was calculated using Bazett’s formula. Tp-e/QT and Tp-e/QTc ratios were also derived.

Results

QT and QTc intervals were prolonged in subjects with SCA. Tp-e interval, Tp-e/QT ratio and Tp-e/QTc ratio were prolonged in male SCA subjects, with a paradoxical shortening in female SCA subjects. Plasminogen activator inhibitor-1 (PAI-1) was an independent determinant of QTc, while body mass index (BMI) was an independent determinant of both Tp-e interval and Tp-e/QTc ratio.

Conclusion

Our results suggest an elevated risk for ventricular arrhythmogenesis in male SCA subjects. Furthermore, increased BMI and PAI-1 level are possible markers of ventricular repolarization abnormalities in SCA subjects.

Short term methylphenidate treatment does not increase myocardial injury in the ischemic rat heart

Methylphenidate is commonly used for the treatment of attention deficit hyperactivity disorder. The cardiovascular safety of methylphenidate has been a subject of debate with some studies indicating that methylphenidate increases the likelihood of experiencing a myocardial infarction. However, it is unknown whether methylphenidate worsens the extent of injury during an ischemic insult. The purpose of this study was to determine whether short term exposure to methylphenidate increases the extent of myocardial injury during an ischemic insult. Male and female rats received methylphenidate (5 mg/kg/day) or saline for 10 days by oral gavage. Hearts were subjected to 20 min of ischemia and 2 h of reperfusion on a Langendorff isolated heart apparatus on day 11. Cardiac contractile function was monitored via an intraventricular balloon and myocardial injury was assessed by triphenyltetrazolium chloride staining. Methylphenidate significantly increased locomotor activity in male and female rats, confirming absorption of this psychostimulant into the central nervous system. Male hearts had significantly larger infarcts than female hearts, but methylphenidate had no impact on infarct size or postischemic recovery of contractile function in hearts of either sex. These data indicate that methylphenidate does not increase the extent of injury induced by an ischemic insult.

The Effect of Estrogen on Intracellular Ca2+ and Na+ Regulation in Heart Failure

•

During the progression toward heart failure, indicators of in vivo whole-heart function suggest greater impairment in the absence of estrogen.

•

At the single cardiac myocyte level, the absence of estrogen results in further reduction of Ca²⁺ transient amplitudes, further slowing of transient decay kinetics, less SR Ca²⁺ content, and a further increase in Ca²⁺ spark frequencies and spark-mediated SR leak compared with animals with normal estrus cycles.

•

Cardiac myocyte Na⁺ regulation is also more disrupted in the absence of estrogen.

Contradictory findings of estrogen supplementation in cardiac disease highlight the need to investigate the involvement of estrogen in the progression of heart failure in an animal model that lacks traditional comorbidities. Heart failure was induced by aortic constriction (AC) in female guinea pigs. Selected AC animals were ovariectomized (ACOV), and a group of these received 17β-estradiol supplementation (ACOV+E). One hundred-fifty days post-AC surgery, left-ventricular myocytes were isolated, and their electrophysiology and Ca²⁺ and Na⁺ regulation were examined. Long-term absence of ovarian hormones exacerbates the decline in cardiac function during the progression to heart failure. Estrogen supplementation reverses these aggravating effects.

Estrogen Contributions to Microvascular Dysfunction Evolving to Heart Failure With Preserved Ejection Fraction

Heart failure with preserved ejection fraction (HFpEF) is a syndrome involving microvascular dysfunction. No treatment is available yet and as the HFpEF patient group is expanding due to the aging population, more knowledge on dysfunction of the cardiac microvasculature is required. Endothelial dysfunction, impaired angiogenesis, (perivascular) fibrosis and the pruning of capillaries (rarefaction) may all contribute to microvascular dysfunction in the heart and other organs, e.g., the kidneys. The HFpEF patient group consists mainly of post-menopausal women and female sex itself is a risk factor for this syndrome. This may point toward a role of estrogen depletion after menopause in the development of HFpEF. Estrogens favor the ratio of vasodilating over vasoconstricting factors, which results in an overall lower blood pressure in women than in men. Furthermore, estrogens improve angiogenic capacity and attenuate (perivascular) fibrosis formation. Therefore, we hypothesize that the drop of estrogen levels after menopause contributes to myocardial microvascular dysfunction and renders post-menopausal women more vulnerable for heart diseases that involve the microvasculature. This review provides a detailed summary of molecular targets of estrogen, which might guide future research and treatment options.

Estrogen and DPP-4 inhibitor share similar efficacy in reducing brain pathology caused by cardiac ischemia-reperfusion injury in both lean and obese estrogen-deprived rats

OBJECTIVE

Cardiac ischemia-reperfusion injury (I/R) caused an oxidative burst, increased beta-amyloid production, and decreased dendritic spine density in the brain. However, the effect of cardiac I/R in the brain of estrogen-deprived rats who were or were not obese have not been investigated. Moreover, the benefits of estrogen or dipeptidyl peptidase-4 (DDP-4) inhibitor therapies in those conditions have never been determined. We hypothesized that cardiac I/R aggravates brain pathology in estrogen-deprived obese rats, to a greater extent when compared with estrogen-deprived lean rats, and treatment with either estrogen or a DPP-4 inhibitor attenuates those adverse effects.

METHODS

In protocol 1, rats were divided into sham operation (n = 12) or ovariectomy (n = 24). Sham-operated rats were fed with normal diet (ND) and ovariectomized rats were fed with either ND or high-fat diet (HF) for 12 weeks. Then, rats were subdivided to sham operation or cardiac I/R injury. In protocol 2, ovariectomized rats were given either ND (n = 18) or HF (n = 18). At week 13, ovariectomized rats were subdivided to receive vehicle, estradiol, or DPP-4 inhibitor for 4 weeks. Then, all rats were subjected to cardiac I/R.

RESULTS

Cardiac I/R injury aggravated brain oxidative stress, beta-amyloid production, and decreased dendritic spine density in either sham-operated or ovariectomized ND-fed rats, but not in ovariectomized HF-fed rats. Either estrogen or DPP-4 inhibitor therapies reduced those conditions in all rats with cardiac I/R.

CONCLUSIONS

Cardiac I/R aggravates brain toxicity in estrogen-deprived lean rats, but not in the estrogen-deprived obese rats. Estrogen and DPP-4 inhibitor treatments attenuate those effects in all groups.

MiR-770-5p inhibits cisplatin chemoresistance in human ovarian cancer by targeting ERCC2

In this study, we examined the role of the miRNA miR-770-5p in cisplatin chemotherapy resistance in ovarian cancer (OVC) patients. miR-770-5p expression was reduced in platinum-resistant patients. Using a 6.128-fold in expression as the cutoff value, miR-770-5p expression served as a prognostic biomarker and predicted the response to cisplatin treatment and survival among OVC patients. Overexpression of miR-770-5p in vitro reduced survival in chemoresistant cell lines after cisplatin treatment. ERCC2, a target gene of miR-770-5p that participates in the NER system, was negatively regulated by miR-770-5p. siRNA-mediated silencing of ERCC2 reversed the inhibition of apoptosis resulting from miR-770-5p downreglation in A2780S cells. A comet assay confirmed that this restoration of cisplatin chemosensitivity was due to the inhibition of DNA repair. These findings suggest that endogenous miR-770-5p may function as an anti-oncogene and promote chemosensitivity in OVC, at least in part by downregulating ERCC2. miR-770-5p may therefore be a useful biomarker for predicting chemosensitivity to cisplatin in OVC patients and improve the selection of effective, more personalized, treatment strategies.

Treatment with oestrogen-receptor agonists or oxytocin in conjunction with exercise protects against myocardial infarction in ovariectomized rats

NEW FINDINGS

What is the central question of this study? Could the activation of oxytocin or oestrogen receptors be protective against myocardial injury after ovariectomy? If so, would exercising have an additional ameliorating effect? What is the main finding and its importance? The results revealed that when accompanied by exercise, both oestrogen receptor agonists and oxytocin improved cardiac dysfunction, inhibited the generation of pro-inflammatory cytokines and reduced myocardial injury in ovariectomized female rats, suggesting a new approach for protecting postmenopausal women against ischaemia-induced myocardial injury. To investigate the putative protective effects of oxytocin or oestrogen receptor agonists against myocardial injury of ovariectomized sedentary or exercised rats, female Sprague-Dawley rats assigned to sham-operated control and ovariectomized (OVX) groups were kept sedentary or undertook swimming exercise for 4 weeks and were treated with saline, an oestrogen receptor (ER) β (DPN) or ERα agonist (PPT) or oxytocin. Ovariectomy increased weight gain and anxiety in sedentary rats, whereas exercise prevented weight gain. When accompanied by exercise, both ER agonists and oxytocin inhibited weight gain and anxiety; oxytocin, in the absence or presence of exercise, increased the left ventricular diastolic dimensions and ejection fraction, whereas ER agonists also increased left ventricular diameter when given to exercised rats. Upon the induction of myocardial ischaemia-reperfusion in the OVX rats, plasma creatine kinase-(muscle-brain) was depressed by PPT and oxytocin, whereas DPN, PPT and OT reduced plasminogen activator inhibitor-1 concentrations. The increased tumour necrosis factor-α concentration in OVX rats was also suppressed by exercise or DPN, PPT or oxytocin treatments, whereas the interleukin-6 concentration was diminished by all the treatments when given in conjunction with exercise. Disorganization of cardiac muscle fibres was reduced in all exercised rats. Oestrogen receptor agonists, as well as oxytocin, in conjunction with exercise may be effective new therapeutics to protect against myocardial ischaemia in postmenopausal women.

Effect of ovariectomy on intracellular Ca2+ regulation in guinea pig cardiomyocytes

This study addressed the hypothesis that long-term deficiency of ovarian hormones after ovariectomy (OVx) alters cellular Ca²⁺-handling mechanisms in the heart, resulting in the formation of a proarrhythmic substrate. It also tested whether estrogen supplementation to OVx animals reverses any alterations to cardiac Ca²⁺ handling and rescues proarrhythmic behavior. OVx or sham operations were performed on female guinea pigs using appropriate anesthetic and analgesic regimes. Pellets containing 17β-estradiol (1 mg, 60-day release) were placed subcutaneously in selected OVx animals (OVx + E). Cardiac myocytes were enzymatically isolated, and electrophysiological measurements were conducted with a switch-clamp system. In fluo-4-loaded cells, Ca²⁺ transients were 20% larger, and fractional sarcoplasmic reticulum (SR) Ca²⁺ release was 7% greater in the OVx group compared with the sham group. Peak L-type Ca²⁺ current was 16% larger in OVx myocytes with channel inactivation shifting to more positive membrane potentials, creating a larger "window" current. SR Ca²⁺ stores were 22% greater in the OVx group, and these cells showed a higher frequency of Ca²⁺ sparks and waves and shorter wave-free intervals. OVx myocytes showed higher frequencies of early afterdepolarizations, and a greater percentage of these cells showed delayed afterdepolarizations after exposure to isoprenaline compared with sham myocytes. The altered Ca²⁺ regulation occurring in the OVx group was not observed in the OVx + E group. These findings suggest that long-term deprivation of ovarian hormones in guinea pigs lead to changes in myocyte Ca²⁺-handling mechanisms that are considered proarrhythmogenic. 17β-Estradiol replacement prevented these adverse effects.NEW & NOTEWORTHY Ovariectomized guinea pig cardiomyocytes have higher frequencies of Ca²⁺ waves, and isoprenaline-challenged cells display more early afterdepolarizations, delayed afterdepolarizations, and extra beats compared with sham myocytes. These alterations to Ca²⁺ regulation were not observed in myocytes from ovariectomized guinea pigs supplemented with 17β-estradiol, suggesting that ovarian hormone deficiency modifies cardiac Ca²⁺ regulation, potentially creating proarrhythmic substrates.

Repeated exposure to methamphetamine induces sex-dependent hypersensitivity to ischemic injury in the adult rat heart

Background

We previously reported that adult female, but not male rats that were prenatally exposed to methamphetamine exhibit myocardial hypersensitivity to ischemic injury. However, it is unknown whether hypersensitivity to ischemic injury develops when rats are exposed to methamphetamine during adulthood. The goal of this study was to determine whether methamphetamine exposure during adulthood sensitizes the heart to ischemic injury.

Methods

Adult male and female rats received daily injections of methamphetamine (5 mg/kg) or saline for 10 days. Their hearts were isolated on day 11 and subjected to a 20 min ischemic insult on a Langendorff isolated heart apparatus. Cardiac contractile function was measured by an intraventricular balloon, and infarct size was measured by triphenyltetrazolium chloride staining.

Results

Hearts from methamphetamine-treated females exhibited significantly larger infarcts and suppressed postischemic recovery of contractile function compared to hearts from saline-treated females. In contrast, methamphetamine had no effect on infarct size or contractile recovery in male hearts. Subsequent experiments demonstrated that hypersensitivity to ischemic injury persisted in female hearts following a 1 month period of abstinence from methamphetamine. Myocardial protein kinase C-ε expression, Akt phosphorylation, and ERK phosphorylation were unaffected by adult exposure to methamphetamine.

Conclusions

Exposure of adult rats to methamphetamine sex-dependently increases the extent of myocardial injury following an ischemic insult. These data suggest that women who have a heart attack might be at risk of more extensive myocardial injury if they have a recent history of methamphetamine abuse.

Mechanistic Pathways of Sex Differences in Cardiovascular Disease

Major differences between men and women exist in epidemiology, manifestation, pathophysiology, treatment, and outcome of cardiovascular diseases (CVD), such as coronary artery disease, pressure overload, hypertension, cardiomyopathy, and heart failure. Corresponding sex differences have been studied in a number of animal models, and mechanistic investigations have been undertaken to analyze the observed sex differences. We summarize the biological mechanisms of sex differences in CVD focusing on three main areas, i.e., genetic mechanisms, epigenetic mechanisms, as well as sex hormones and their receptors. We discuss relevant subtypes of sex hormone receptors, as well as genomic and nongenomic, activational and organizational effects of sex hormones. We describe the interaction of sex hormones with intracellular signaling relevant for cardiovascular cells and the cardiovascular system. Sex, sex hormones, and their receptors may affect a number of cellular processes by their synergistic action on multiple targets. We discuss in detail sex differences in organelle function and in biological processes. We conclude that there is a need for a more detailed understanding of sex differences and their underlying mechanisms, which holds the potential to design new drugs that target sex-specific cardiovascular mechanisms and affect phenotypes. The comparison of both sexes may lead to the identification of protective or maladaptive mechanisms in one sex that could serve as a novel therapeutic target in one sex or in both.

DPP-4 Inhibitor and Estrogen Share Similar Efficacy Against Cardiac Ischemic-Reperfusion Injury in Obese-Insulin Resistant and Estrogen-Deprived Female Rats

Estrogen deprivation aggravates cardiac injury after myocardial ischemia and reperfusion (I/R) injury. Although either estrogen or the dipeptidyl peptidase-4 (DPP-4) inhibitor, vildagliptin, reduces myocardial damage following cardiac I/R, their effects on the heart in obese-insulin resistant and estrogen deprived conditions remain unknown. Ovariectomized (O) rats (n = 36) were divided to receive either normal diet (NDO) or high-fat diet (HFO) for 12 weeks, followed by treatment with a vehicle, estrogen or vildagliptin for 4 weeks. The setting of in vivo cardiac I/R injury, 30-min ischemia and 120-min reperfusion, was performed. At 12 weeks after ovariectomy, both NDO and HFO rats exhibited an obese-insulin resistant condition. Both NDO and HFO rats treated with estrogen and vildagliptin showed reduced fasting plasma glucose, insulin and HOMA index. Both treatments improved cardiac function indicated by restoration of heart rate variability and increased %left ventricular ejection fraction (%LVEF). The treatments similarly protected cardiac mitochondrial function against I/R injury, leading to a reduction in the infarct size, oxidative stress and apoptosis in the ischemic myocardium. These findings demonstrate that vildagliptin effectively improves metabolic status, and shares similar efficacy to estrogen in reducing myocardial infarction and protecting cardiac mitochondrial function against I/R injury in estrogen-deprived obese-insulin resistant rats.

Estrogenic Impact on Cardiac Ischemic/Reperfusion Injury

The increase in cardiovascular disease and metabolic syndrome incidence following the onset of menopause has highlighted the role of estrogen as a cardiometabolic protective agent. Specifically regarding the heart, estrogen induced an improvement in cardiac function, preserved calcium homeostasis, and inhibited the mitochondrial apoptotic pathway. The beneficial effects of estrogen in relation to cardiac ischemia/reperfusion (I/R) injury, such as reduced infarction and ameliorated post-ischemic recovery, have also been shown. Nevertheless, controversial findings exist and estrogen therapy is reported to be related to a higher rate of thromboembolic events and atrial fibrillation in post-menopausal women. Therefore, greater clarification is needed to evaluate the exact potential of estrogen use in cases of cardiac I/R injury. This article reviews the effects of estrogen, in both acute and chronic treatment, and collates the studies with regard to their in vivo, in vitro, or clinical trial settings in cases of cardiac I/R injury and myocardial infarction.

The expression of miR-30a* and miR-30e* is associated with a dualistic model for grading ovarian papillary serious carcinoma

Histological grade has already been recognized as a very important prognostic factor for ovarian papillary serous carcinoma (OPSC). On the basis of pathogenetic mechanisms, recent findings suggest a dualistic model of OPSC consisting of types I (low-grade) and II (high-grade) cancers. High-grade OPSC is responsible for most ovarian cancer deaths. The goal of our investigation was to identify the differences in key miRNAs and possible regulators through miRNA microarray chip analysis, as well as functional target prediction and clinical outcome between the low and high-grade OPSC patients. The pathogenic basis in differentiation of ovarian cancer subtypes was studied to provide insight into diagnosis and therapy for high-grade cases. Through microarray analysis, we found that miR-30a* and miR-30e* were the top 2 significantly different miRNAs between type I and type II OPSC patients, and both were remarkably downregulated in the latter type. ATF3 and MYC were indicated as potential co-targets of miR-30a* and miR-30e*, and showed a significant upregulation in type II patients. As ATF3 and MYC are often associated with aggressive behavior and poor differentiation, especially in human cancers, these results are in good agreement with our findings and point toward a regulating differentiation function of the miR-30a* and miR-30e* genes. Further analysis using leave‑one-out cross predictions and Kaplan-Meier survival analysis strongly suggested that miR-30a* and miR-30e* can be used as biomarkers to tailor histological grade before starting the regimen, and they showed important roles in ovarian cancer differentiation resulting in poorer prognosis. In general, miR-30a* and miR-30e* coupled with expression data that reveal pathogenic regulation to predict histological differentiation, may operate to direct the formation of early detection and therapeutic approaches to individual OPSC patients, especially differentiation therapy to high-grade cases.

Sex and sex hormones in cardiac stress--mechanistic insights

Important sex differences in the onset and characteristics of cardiovascular disease are evident, yet the mechanistic details remain unresolved. Men are more susceptible to cardiovascular disease earlier in life, though younger women who have a cardiovascular event are more likely to experience adverse outcomes. Emerging evidence is prompting a re-examination of the conventional view that estrogen is protective and testosterone a liability. The heart expresses both androgen and estrogen receptors and is functionally responsive to circulating sex steroids. New evidence of cardiac aromatase expression indicates local estrogen production may also exert autocrine/paracrine actions in the heart. Cardiomyocyte contractility studies suggest testosterone and estrogen have contrasting inotropic actions, and modulate Ca(2+) handling and transient characteristics. Experimentally, sex differences are also evident in cardiac stress responses. Female hearts are generally less susceptible to acute ischemic damage and associated arrhythmias, and generally are more resistant to stress-induced hypertrophy and heart failure, attributed to the cardioprotective actions of estrogen. However, more recent data show that testosterone can also improve acute post-ischemic outcomes and facilitate myocardial function and survival in chronic post-infarction. The myocardial actions of sex steroids are complex and context dependent. A greater mechanistic understanding of the specific actions of systemic/local sex steroids in different cardiovascular disease states has potential to lead to the development of cardiac therapies targeted specifically for men and women.

Tbx20 functions as an important regulator of estrogen-mediated cardiomyocyte protection during oxidative stress

BACKGROUND

As a transcription factor mainly expressed in cardiovascular system, T-box 20 (Tbx20) plays an important role in embryonic cardiovascular system development and adult heart function. Here, we determined the mechanism by which Tbx20 regulates cardiomyocyte apoptosis and cardiomyopathies.

METHODS

We analyzed Tbx20 expression levels and apoptosis rates in normal and heart failure human autopsy heart samples. Female C57BL/6 mice were ovariectomized and treated with 17β-estradiol to determine Tbx20 expression levels. ROS production, TUNEL, DNA laddering, qRT-PCR, Western blot, immunohistochemistry and ChIP analyses were performed on male C57BL/6 transverse aortic constriction-induced heart failure samples and on neonatal rat ventricular myocytes that were treated with H2O2 to investigate the role of Tbx20 in estrogen-mediated heart protection.

RESULTS

Tbx20 expression was down regulated during heart failure, accompanied by elevated cardiomyocyte apoptotic levels in humans and mice. H2O2 led to a concurrent decrease in Tbx20 expression and increase in apoptosis in cultured neonatal rat cardiomyocytes. Tbx20 overexpression reduced H2O2-induced cardiomyocyte apoptosis and was associated with a profound inhibition of p38MAPK, Bax and caspase3 and the activation of Bcl-2. Estrogen was able to protect cardiomyocytes from H2O2-induced apoptosis by upregulating Tbx20 expression in a concentration-dependent manner. Tbx20 silencing increased oxidative stress-induced apoptosis in H9c2 cells. Moreover, Tbx20 directly regulated Esrra expression to enhance the heart-protective effect of estrogen.

CONCLUSIONS

These results indicate that Tbx20 functions as an important regulator of estrogen-mediated cardiomyocyte protection during oxidative stress, suggesting that estorgen-Tbx20-ERR-α may represent a crucial regulatory cascade and a potential therapeutic target for heart failure.

Effects of short-term administration of estradiol on reperfusion arrhythmias in rats of different ages

Little is known about age-related differences in short-term effects of estradiol on ischemia-reperfusion (I/R) insults. The present study was designed to evaluate the effects of short-term treatment with estradiol on reperfusion arrhythmias in isolated hearts of 6-7-week-old and 12-14-month-old female rats. Wistar rats were sham-operated, ovariectomized and treated with vehicle or ovariectomized and treated with 17β-estradiol (E₂; 5 µg·100 g⁻¹·day⁻¹) for 4 days. Hearts were perfused by the Langendorff technique. Reperfusion arrhythmias, i.e., ventricular tachycardia and/or ventricular fibrillation, were induced by 15 min of left coronary artery ligation and 30 min of reperfusion. The duration and incidence of I/R arrhythmias were significantly higher in young rats compared to middle-aged rats (arrhythmia severity index: 9.4 ± 1.0 vs 3.0 ± 0.3 arbitrary units, respectively, P < 0.05). In addition, middle-aged rats showed lower heart rate, systolic tension and coronary flow. Four-day E₂ treatment caused an increase in uterine weight. Although E₂ administration had no significant effect on the duration of I/R arrhythmias in middle-aged rats, it induced a marked reduction in the rhythm disturbances of young rats accompanied by a decrease in heart rate of isolated hearts. Also, this reduction was associated with an increase in QT interval. No significant changes were observed in the QT interval of middle-aged E₂-treated rats. These data demonstrate that short-term estradiol treatment protects against I/R arrhythmias in hearts of young female rats. The anti-arrhythmogenic effect of estradiol might be related to a lengthening of the QT interval.

Functional consequences of abnormal Cx43 expression in the heart

The major gap junction protein expressed in the heart, connexin43 (Cx43), is highly remodeled in the diseased heart. Usually, Cx43 is down-regulated and heterogeneously redistributed to the lateral sides of cardiomyocytes. Reverse remodeling of the impaired Cx43 expression could restore normal cardiac function and normalize electrical stability. In this review, the reduced and heterogeneous Cx43 expression in the heart will be addressed in hypertrophic, dilated and ischemic cardiomyopathy together with its functional consequences of conduction velocity slowing, dispersed impulse conduction, its interaction with fibrosis and propensity to generate arrhythmias. Finally, different therapies are discussed. Treatments aimed to improve the Cx43 expression levels show new potentially anti-arrhythmic therapies during heart failure, but those in the context of acute ischemia can be anti-arrhythmogenic at the cost of larger infarct sizes. This article is part of a Special Issue entitled: The Communicating junctions, composition, structure and characteristics.