Programmed cell death and expression of the protooncogene bcl-2 in myocytes during postnatal maturation of the heart

Sensitivity and activation of endoplasmic reticulum stress response and apoptosis in the perinatal sheep heart

Although the unfolded protein response (UPR) contributes to survival by removing misfolded proteins, endoplasmic reticulum (ER) stress also activates proapoptotic pathways. Changed sensitivity to normal developmental stimuli may underlie observed cardiomyocyte apoptosis in the healthy perinatal heart. We determined in vitro sensitivity to thapsigargin in sheep cardiomyocytes from four perinatal ages. In utero cardiac activation of ER stress and apoptotic pathways was determined at these same ages. Thapsigargin-induced phosphorylation of eukaryotic initiation factor 2 (EIF2A) was decreased by 72% between 135 and 143 dGA (P = 0.0096) and remained low at 1 dPN (P = 0.0080). Conversely, thapsigargin-induced caspase cleavage was highest around the time of birth: cleaved caspase 3 was highest at 1 dPN (3.8-fold vs. 135 dGA, P = 0.0380; 7.8-fold vs. 5 dPN, P = 0.0118), cleaved caspase 7 and cleaved caspase 12 both increased between 135 and 143 dGA (25-fold and 6.9-fold respectively, both P < 0.0001) and remained elevated at 1 dPN. Induced apoptosis, measured by TdT-mediated dUTP nick-end labeling (TUNEL) assay, was highest around the time of birth (P < 0.0001). There were changes in myocardial ER stress pathway components in utero. Glucose (78 kDa)-regulated protein (GRP78) protein levels were high in the fetus and declined after birth (P < 0.0001). EIF2A phosphorylation was profoundly depressed at 1 dPN (vs. 143 dGA, P = 0.0113). In conclusion, there is dynamic regulation of ER proteostasis, ER stress, and apoptosis cascade in the perinatal heart. Apoptotic signaling is more readily activated in fetal cardiomyocytes near birth, leading to widespread caspase cleavage in the newborn heart. These pathways are important for the regulation of normal maturation in the healthy perinatal heart.NEW & NOTEWORTHY Cardiomyocyte apoptosis occurs even in the healthy, normally developing perinatal myocardium. As cardiomyocyte number is a critical contributor to heart health, the sensitivity of cardiomyocytes to endoplasmic reticulum stress leading to apoptosis is an important consideration. This study suggests that the heart has less robust protective mechanisms in response to endoplasmic reticulum stress immediately before and after birth, and that more cardiomyocyte death can be induced by stress in this period.

Developmental Aspects of Cardiac Adaptation to Increased Workload

The heart is capable of extensive adaptive growth in response to the demands of the body. When the heart is confronted with an increased workload over a prolonged period, it tends to cope with the situation by increasing its muscle mass. The adaptive growth response of the cardiac muscle changes significantly during phylogenetic and ontogenetic development. Cold-blooded animals maintain the ability for cardiomyocyte proliferation even in adults. On the other hand, the extent of proliferation during ontogenetic development in warm-blooded species shows significant temporal limitations: whereas fetal and neonatal cardiac myocytes express proliferative potential (hyperplasia), after birth proliferation declines and the heart grows almost exclusively by hypertrophy. It is, therefore, understandable that the regulation of the cardiac growth response to the increased workload also differs significantly during development. The pressure overload (aortic constriction) induced in animals before the switch from hyperplastic to hypertrophic growth leads to a specific type of left ventricular hypertrophy which, in contrast with the same stimulus applied in adulthood, is characterized by hyperplasia of cardiomyocytes, capillary angiogenesis and biogenesis of collagenous structures, proportional to the growth of myocytes. These studies suggest that timing may be of crucial importance in neonatal cardiac interventions in humans: early definitive repairs of selected congenital heart disease may be more beneficial for the long-term results of surgical treatment.

Myocardial Injury, Troponin Release and Cardiomyocyte Death in Brief Ischemia, Failure and Ventricular Remodeling

Troponin released from irreversibly injured myocytes is the gold standard biomarker for the rapid identification of an acute coronary syndrome. In acute myocardial infarction, necrotic cell death is characterized by sarcolemmal disruption in response to a critical level of energy depletion after more than 15-minutes of ischemia. While troponin I and T are highly specific for cardiomyocyte death, high-sensitivity assays have demonstrated that measurable circulating levels of troponin are present in the majority of normal subjects. In addition, transient as well as chronic elevations have been demonstrated in many disease states not clearly associated with myocardial ischemia. The latter observations have given rise to the clinical concept of myocardial injury. This review will summarize evidence supporting the notion that circulating troponin levels parallel the extent of myocyte apoptosis in normal ventricular remodeling and in pathophysiological conditions not associated with infarction or necrosis. It will review the evidence that myocyte apoptosis can be accelerated by both diastolic strain from elevated ventricular preload as well as systolic strain from dyskinesis after brief episodes of ischemia too short to cause a critical level of myocyte energy depletion. We then show how chronic, low rates of myocyte apoptosis from endogenous myocyte turnover, repetitive ischemia or repetitive elevations in LV diastolic pressure can lead to significant myocyte loss in the absence of neurohormonal stimulation. Finally, we posit that the differential response to strain-induced injury in heart failure may determine whether progressive myocyte loss and HFrEF or interstitial fibrosis and HFpEF become the heart failure phenotype.

Transport viable heart tissue at physiological temperature yielded higher human cardiomyocytes compared to the conventional temperature

This study investigated the optimum transport condition for heart tissue to recover single-cell cardiomyocytes for future in-vitro or in-vivo studies. The heart tissues were obtained from removing excessive myocardium discharged during the repair surgery of an excessive right atrial hypertrophy due to a congenital disease. The transportation temperature studied was the most used temperature (4 °C) or the conventional condition, compared to a physiological temperature(37 °C). The heart tissues were transported from the operating theatre to the lab maintained less than 30 min consistently. Single-cell isolation was enzymatically and mechanically performed using collagenase-V (160 U/mg) and proteinase-XXIV (7-14 U/mg) following the previously described protocol. The impact of temperature differences was observed by the density of cells harvested per mg tissue, cell viability, and the senescence signals, identified by the p21, p53 and caspase-9 mRNA expressions. Results the heart tissue transported at 37 °C yielded significantly higher viable cell density (p < 0.01) yielded viable cells significantly higher density (p < 0.01) than the 4 °C; 2,335 ± 849 cells per mg tissue, and 732 ± 425 cells per mg tissue, respectively. The percentage of viable cells in both groups showed no difference. Although the 37 °C group expressed the apoptosis genes such as p21, p53 and caspase9 by 2.5-, 5.41-, 5-fold respectively (p > 0.05). Nonetheless, the Nk×2.5 and MHC genes were expressed 1,7- and 3.56-fold higher than the 4 °C. and the c-Kit+ expression was 17.56-fold, however, statistically insignificant. Conclusion When needed for single-cell isolation, a heart tissue transported at 37 °C yielded higher cell density per mg tissue compared to at 4 °C, while other indicators of gene expressions for apoptosis, cardiac structural proteins, cardiac progenitor cells showed no difference. Further investigations of the isolated cells at different temperature conditions towards their proliferation and differentiation capacities in a 3-D scaffold would be essential.

Synergistic effects of Ficus Carica extract and extra virgin olive oil against oxidative injury, cytokine liberation, and inflammation mediated by 5-Fluorouracil in cardiac and renal tissues of male albino rats

5-Fluorouracil (5-FU), a chemotherapeutic drug, has adverse effects on heart and kidney functions. Ficus Carica (fig) and extra virgin olive oil (EVOO) are natural sources which have antioxidant effects. This study investigated the synergistic effects of fig extract and EVOO against cardiac and renal damage induced by 5-FU. Forty rats were equally divided into five groups and treated with physiological saline (control), five intravenous injections of 5-FU (40 mg/kg b.w) (5-FU), fig (1 g/kg b.w/day, orally) with 5-FU (Fig/5-FU), EVOO (7 g/kg b.w/day, orally) with 5-FU (EVOO/5-FU), combined treatment of fig and EVOO with five 5-FU injections (Fig/EVOO/5-FU). After 30 days, blood and tissue samples (Heart and kidney) were collected to be used in the examinations. 5-FU significantly increased serum creatine kinase activity, renal biomarkers, cholesterol, triglycerides, C-reactive protein, tumor necrosis factor-α, and interleukin-1β as well as cardiac and renal lipid peroxides (malondialdehyde). Meanwhile, serum levels of immunoglobulins, interleukins (IL-10, IL-12), and antioxidants of heart and kidney tissues were significantly decreased in 5-FU group. It also downregulated cardiac and renal Bcl2, and upregulated cardiac troponin and renin gene expressions. As well, histological alterations clarified that 5-FU induced cardiac cell damage, distorted renal corpuscles and tubules, inflammatory cell infiltrations, and severe congestion and hemorrhage in the blood vessels. The treatment with fig and olive oil, especially the combined treatment, modulated the toxic effect of 5-FU on the heart and kidney. Our results revealed that fig extract and EVOO have a powerful antioxidant and many protective effects against cardiac and renal toxicity induced by 5-FU, especially when using fig and EVOO together as a combined treatment.

Adverse effects of fetal exposure of electronic-cigarettes and high-fat diet on male neonatal hearts

Epidemiological studies have shown an increased risk of cardiovascular diseases in children born to mothers who smoked during pregnancy. The cardiovascular risk in the offspring associated with in utero nicotine exposure is further exaggerated by maternal obesity. The consumption of electronic cigarettes (e-cigarettes) is alarmingly increasing among adolescents and young adults without the knowledge of their harmful health effects. There has also been a substantial increase in e-cigarette use by women of reproductive age. This study investigates the detrimental effects of gestational exposure of e-cigarette and a high-fat diet (HFD) on neonatal hearts. Time-mated pregnant mice were fed a HFD and exposed to saline or e-cigarette aerosol with 2.4% nicotine from embryonic day 4 (E4) to E20. We demonstrated that in utero exposure of e-cigarettes and HFD from E4 to E20 triggers cardiomyocyte (CM) apoptosis in the offspring at postnatal day1 (PND1), PND3, and PND14. Induction of CM apoptosis following gestational exposure of e-cigarettes and HFD was associated with inactivation of AMP-activated protein kinase (AMPK), increased cardiac oxidative stress coupled with perturbation of cardiac BAX/ BCL-2 ratio and activation of caspase 3 at PND 14. Electron microscopy further revealed that left ventricles of pups at PND14 after e-cigarette exposure exhibited apoptotic nuclei, convoluted nuclear membranes, myofibrillar derangement, and enlarged mitochondria occasionally showing signs of crystolysis, indicative of cardiomyopathy and cardiac dysfunction. Our results show profound adverse effects of prenatal exposure of e-cigarette plus HFD in neonatal hearts that may lead to long-term adverse cardiac consequences in the adult.

TBX3 deficiency accelerates apoptosis in cardiomyoblasts through regulation of P21 expression

Congenital heart disease (CHD) is the most common birth defect in newborns. There is increasing evidence that apoptosis and remodeling of the cardiomyoblasts are the major pathology of CHD. Previous research found that T-box transcription factor 3 (TBX3) was compulsory for the regulation of proliferation, cell cycle arrest and apoptosis in various cells. Hence, TBX3 might be involved in the treatment of CHD. The primary aim of this study was to study the effects of TBX3 on apoptosis in aged cardiomyoblasts and investigate the latent mechanism. In the present study, we found TBX3 knockdown induced proliferation inhibition, cell cycle arrest and apoptosis accompanied by mitochondrial dysfunction in cardiomyoblasts at passage 10 to 15. Apoptosis-inducing effects of TBX3 silence could be neutralized by silencing P21 using specific siRNA. In addition, the mRNA and protein expression levels of TBX3 in the heart tissues of sporadic type CHD donors were obviously down-regulated. In conclusion, we demonstrated that TBX3 deficiency accelerated apoptosis via directly regulating P21 expression in senescent cardiomyoblasts.

Right Ventricular Involution: Big Changes in Small Hearts

BACKGROUND

Before birth, the fetal right ventricle (RV) is the pump for the systemic circulation and is about as thick as the left ventricle (LV). After birth, the RV becomes the pump for the lower pressure pulmonary circulation, and the RV chamber elongates without change in its wall thickness. We hypothesize that the fetal RV may be a model of compensated RV hypertrophy, and understanding this process may aid in discovering therapeutic strategies for RV failure.

METHODS

We performed a literature review and identified pertinent articles from 1980 to present.

RESULTS

The following topics were identified to be most pertinent in right ventricular involution: morphologic and histologic changes of the RV, cellular proliferation and terminal differentiation, the effect of stress on RV development, excitation contraction coupling and inotropic response change over time, and the amount of apoptosis through RV development.

CONCLUSIONS

The RV changes on multiple levels after its transition from systemic to pulmonary circulation. Although published literature has variable results due partly from differences between animal models, the literature shows a clear need for more research in the field.

Serum apoptotic marker M30 is positively correlated with early diastolic dysfunction in adolescent obesity

Purpose

Obesity in adolescence has been shown to be related to cardiac geometric and functional changes. Cardiac dysfunction in adults with obesity could be attributed to chronic low-grade inflammation, apoptosis of cardiomyocyte, and glucose metabolic disorder. The aforementioned association in adolescents with obesity have never been well studied. Our aim was to determine the types of cardiac dysfunction in adolescents with obesity and survey the association between cardiac dysfunction and chronic low-grade inflammation, apoptosis, and glucose dysregulation in adolescents with obesity.

Methods

Adolescents aged between 10 and 20 years were enrolled in this study. Body mass index, waist-to-hip ratio, blood pressure, glucose metabolism, and high-sensitivity C-reactive protein (hs-CRP), interleukin-6 (IL-6), tumor necrosis factor-a (TNF-α), and apoptosis marker M30 levels were measured. Echocardiographic indices were also measured. The association between serum biomarkers and echocardiographic function parameters was analyzed.

Results

Diastolic dysfunction was the major finding in the cardiac functional assessment. The main changes in glucose metabolism were elevated C-peptide level and insulin resistance. Hs-CRP, IL-6, and M30 levels also increased with adolescent obesity. M30 was the major biomarker that was highly correlated to diastolic dysfunction indices in adolescents with obesity.

Conclusions

Diastolic dysfunction was the main change in adolescent obesity. Insulin resistance, apoptotic marker M30, hs-CRP, and IL-6 were all elevated in adolescents with obesity. Only M30 was related to indices of left ventricular diastolic dysfunction among adolescents with obesity, rather than inflammation or insulin resistance.

Differential Response to Injury in Fetal and Adolescent Sheep Hearts in the Immediate Post-myocardial Infarction Period

Aim: Characterizing the response to myocardial infarction (MI) in the regenerative sheep fetus heart compared to the post-natal non-regenerative adolescent heart may reveal key morphological and molecular differences that equate to the response to MI in humans. We hypothesized that the immediate response to injury in (a) infarct compared with sham, and (b) infarct, border, and remote tissue, in the fetal sheep heart would be fundamentally different to the adolescent, allowing for repair after damage.

Methods: We used a sheep model of MI induced by ligating the left anterior descending coronary artery. Surgery was performed on fetuses (105 days) and adolescent sheep (6 months). Sheep were randomly separated into MI (n = 5) or Sham (n = 5) surgery groups at both ages. We used magnetic resonance imaging (MRI), histological/immunohistochemical staining, and qRT-PCR to assess the morphological and molecular differences between the different age groups in response to infarction.

Results: Magnetic resonance imaging showed no difference in fetuses for key functional parameters; however there was a significant decrease in left ventricular ejection fraction and cardiac output in the adolescent sheep heart at 3 days post-infarction. There was no significant difference in functional parameters between MRI sessions at Day 0 and Day 3 after surgery. Expression of genes involved in glucose transport and fatty acid metabolism, inflammatory cytokines as well as growth factors and cell cycle regulators remained largely unchanged in the infarcted compared to sham ventricular tissue in the fetus, but were significantly dysregulated in the adolescent sheep. Different cardiac tissue region-specific gene expression profiles were observed between the fetal and adolescent sheep.

Conclusion: Fetuses demonstrated a resistance to cardiac damage not observed in the adolescent animals. The manipulation of specific gene expression profiles to a fetal-like state may provide a therapeutic strategy to treat patients following an infarction.

Apoptosis and epicardial contributions act as complementary factors in remodeling of the atrioventricular canal myocardium and atrioventricular conduction patterns in the embryonic chick heart

BACKGROUND

During heart development, it has been hypothesized that apoptosis of atrioventricular canal myocardium and replacement by fibrous tissue derived from the epicardium are imperative to develop a mature atrioventricular conduction. To test this, apoptosis was blocked using an established caspase inhibitor and epicardial growth was delayed using the experimental epicardial inhibition model, both in chick embryonic hearts.

RESULTS

Chicken embryonic hearts were either treated with the peptide caspase inhibitor zVAD-fmk by intrapericardial injection in ovo (ED4) or underwent epicardial inhibition (ED2.5). Spontaneously beating embryonic hearts isolated (ED7-ED8) were then stained with voltage-sensitive dye Di-4-ANEPPS and imaged at 0.5-1 kHz. Apoptotic cells were quantified (ED5-ED7) by whole-mount LysoTracker Red and anti-active caspase 3 staining. zVAD-treated hearts showed a significantly increased proportion of immature (base to apex) activation patterns at ED8, including ventricular activation originating from the right atrioventricular junction, a pattern never observed in control hearts. zVAD-treated hearts showed decreased numbers of apoptotic cells in the atrioventricular canal myocardium at ED7. Hearts with delayed epicardial outgrowth showed also increased immature activation patterns at ED7.5 and ED8.5. However, the ventricular activation always originated from the left atrioventricular junction. Histological examination showed no changes in apoptosis rates, but a diminished presence of atrioventricular sulcus tissue compared with controls.

CONCLUSIONS

Apoptosis in the atrioventricular canal myocardium and controlled replacement of this myocardium by epicardially derived HCN4-/Trop1- sulcus tissue are essential determinants of mature ventricular activation pattern. Disruption can lead to persistence of accessory atrioventricular connections, forming a morphological substrate for ventricular pre-excitation. Developmental Dynamics 247:1033-1042, 2018. © 2018 Wiley Periodicals, Inc.

Cardiac injury biomarkers in paediatric age: Are we there yet?

The aim of this article is to evaluate the clinical utility of cardiac injury biomarkers in paediatric age. In December 2015, a literature search was performed (PubMed access to MEDLINE citations; http://www.ncbi.nlm.nih.gov/PubMed/ ). The search strategy included the following medical subject headings and text terms for the key words: "cardiac injury biomarkers", "creatine kinase-MB", "myoglobin", "troponin", "children", "neonate/s", "newborn/s", "infant/s" and echocardiography. In the paediatric population, troponins show a good correlation with the extent of myocardial damage following cardiac surgery and cardiotoxic medication and can be used as predictors of subsequent cardiac recovery and mortality. Elevation of cardiac injury biomarkers may also have diagnostic value in cases when cardiac contusion or pericarditis is suspected. Cardiac injury biomarkers are very sensitive markers for the detection of myocardial injury and have been studied in healthy newborns, after tocolysis, intrauterine growth restriction, respiratory distress and asphyxia. The proportion of newborns with elevated troponin was higher than that in ill infants, children, and adolescents and in healthy adults, suggesting that myocardial injury, although clinically occult, is common in this young age group. Results suggest that significant elevation of cord troponin is an excellent early predictor of severity of hypoxic-ischaemic encephalopathy and mortality in term infants. Cardiac biomarkers may also benefit centres without on-site echocardiography with evidence showing good correlation with echo-derived markers of myocardial function. Further studies are needed to better clarify the role of cardiac biomarkers in paediatric age and their correlation with echocardiographic parameters.

MiR-31a-5p protects myocardial cells against apoptosis by targeting Tp53

The pathogenesis and progression of heart failure (HF) involves multiple mechanisms, including the increased activity of the renin-angiotensin-aldosterone system, apoptosis and differential expression of microRNAs (miRNAs/miRs). Our previous study revealed an increase in miR‑31a‑5p levels in the failing hearts of a rat HF model. In the present study, whether and how miR‑31a‑5p mediates angiotensin II (AngII)‑induced apoptosis in the cardiac H9C2 cell line, was investigated using molecular biological approaches, including reverse transcription followed by quantitative polymerase chain reaction, western blotting, RNA arrays, and mutagenesis. It was demonstrated that AngII stimulation increased apoptosis and decreased miR‑31a‑5p expression, which coincided with increased tumor protein p53 (Tp53) levels. Overexpression of miR‑31a‑5p significantly suppressed the AngII‑induced apoptotic rate and caspase‑3 activity, while suppression of miR‑31a‑5p did the opposite. A total of 16 proapoptotic genes that were downregulated and 4 antiapoptotic genes that were upregulated in the miR‑31a‑5p‑overexpressed cells were identified. It was also revealed that Tp53 mRNA contained the seed sequence in its 3'‑untranslated region for miR‑31a‑5p binding. The luciferase reporter analysis showed that miR‑31a‑5p repressed the luciferase activity of the wild‑type seed sequence, but not the mutated seed sequence fused to a reporter construct. Thus, it was demonstrated that miR‑31a‑5p mediated AngII‑triggered apoptosis in myocardial cells at least partially through targeting Tp53. These findings advance the understanding of the functional interaction between miRNAs and Tp53 in the setting of cardiac diseases. Further work is required to explore whether miR‑31a‑5p can serve as a therapeutic target for HF treatment in vivo.

Nicotine plus a high-fat diet triggers cardiomyocyte apoptosis

Cigarette smoking is an important risk factor for diabetes, cardiovascular disease and non-alcoholic fatty liver disease. The health risk associated with smoking can be aggravated by obesity. Smoking might also trigger cardiomyocyte (CM) apoptosis. Given that CM apoptosis has been implicated as a potential mechanism in the development of cardiomyopathy and heart failure, we characterize the key signaling pathways in nicotine plus high-fat diet (HFD)-induced CM apoptosis. Adult C57BL6 male mice were fed a normal diet (ND) or HFD and received twice-daily intraperitoneal (IP) injections of nicotine (0.75 mg/kg body weight [BW]) or saline for 16 weeks. An additional group of nicotine-treated mice on HFD received twice-daily IP injections of mecamylamine (1 mg/kg BW), a non-selective nicotinic acetylcholine receptor antagonist, for 16 weeks. Nicotine when combined with HFD led to a massive increase in CM apoptosis that was fully prevented by mecamylamine treatment. Induction of CM apoptosis was associated with increased oxidative stress and activation of caspase-2-mediated intrinsic pathway signaling coupled with inactivation of AMP-activated protein kinase (AMPK). Furthermore, nicotine treatment significantly (P < 0.05) attenuated the HFD-induced decrease in fibroblast growth factor 21 (FGF21) and silent information regulator 1 (SIRT1). We conclude that nicotine, when combined with HFD, triggers CM apoptosis through the generation of oxidative stress and inactivation of AMPK together with the activation of caspase-2-mediated intrinsic apoptotic signaling independently of FGF21 and SIRT1.

Endocrine and other physiologic modulators of perinatal cardiomyocyte endowment

Immature contractile cardiomyocytes proliferate to rapidly increase cell number, establishing cardiomyocyte endowment in the perinatal period. Developmental changes in cellular maturation, size and attrition further contribute to cardiac anatomy. These physiological processes occur concomitant with a changing hormonal environment as the fetus prepares itself for the transition to extrauterine life. There are complex interactions between endocrine, hemodynamic and nutritional regulators of cardiac development. Birth has been long assumed to be the trigger for major differences between the fetal and postnatal cardiomyocyte growth patterns, but investigations in normally growing sheep and rodents suggest this may not be entirely true; in sheep, these differences are initiated before birth, while in rodents they occur after birth. The aim of this review is to draw together our understanding of the temporal regulation of these signals and cardiomyocyte responses relative to birth. Further, we consider how these dynamics are altered in stressed and suboptimal intrauterine environments.

Uhl's anomaly detected in-utero

Uhl's anomaly is rarely diagnosed antenatally. It is a condition characterised by partial or complete absence of the right ventricular myocardium and the heart conducting system. We present a case of Uhl's anomaly diagnosed during fetal life on prenatal ultrasound, with eight years postnatal follow‐up.

Timing of cardiomyocyte growth, maturation, and attrition in perinatal sheep

Studies in altricial rodents attribute dramatic changes in perinatal cardiomyocyte growth, maturation, and attrition to stimuli associated with birth. Our purpose was to determine whether birth is a critical trigger controlling perinatal cardiomyocyte growth, maturation and attrition in a precocial large mammal, sheep (Ovis aries). Hearts from 0-61 d postnatal lambs were dissected or enzymatically dissociated. Cardiomyocytes were measured by micromorphometry, cell cycle activity assessed by immunohistochemistry, and nuclear number counted after DNA staining. Integration of this new data with published fetal data from our laboratory demonstrate that a newly appreciated >30% decrease in myocyte number occurred in the last 10 d of gestation (P < 0.0005) concomitant with an increase in cleaved poly (ADP-ribose) polymerase 1 (P < 0.05), indicative of apoptosis. Bisegmental linear regressions show that most changes in myocyte growth kinetics occur before birth (median = 15.2 d; P < 0.05). Right ventricular but not left ventricular cell number increases in the neonate, by 68% between birth and 60 d postnatal (P = 0.028). We conclude that in sheep few developmental changes in cardiomyocytes result from birth, excepting the different postnatal degrees of free wall hypertrophy between the ventricles. Furthermore, myocyte number is reduced in both ventricles immediately before term, but proliferation increases myocyte number in the neonatal right ventricle.

Sexual dimorphism in the expression of mitochondria-related genes in rat heart at different ages

Cardiovascular disease (CVD) is the leading cause of mortality worldwide. Moreover, sex and age are considered major risk factors in the development of CVDs. Mitochondria are vital for normal cardiac function, and regulation of mitochondrial structure and function may impact susceptibility to CVD. To identify potential role of mitochondria in sex-related differences in susceptibility to CVD, we analyzed the basal expression levels of mitochondria-related genes in the hearts of male and female rats. Whole genome expression profiling was performed in the hearts of young (8-week), adult (21-week), and old (78-week) male and female Fischer 344 rats and the expression of 670 unique genes related to various mitochondrial functions was analyzed. A significant (p<0.05) sexual dimorphism in expression levels of 46, 114, and 41 genes was observed in young, adult and old rats, respectively. Gene Ontology analysis revealed the influence of sex on various biological pathways related to cardiac energy metabolism at different ages. The expression of genes involved in fatty acid metabolism was significantly different between the sexes in young and adult rat hearts. Adult male rats also showed higher expression of genes associated with the pyruvate dehydrogenase complex compared to females. In young and adult hearts, sexual dimorphism was not noted in genes encoding oxidative phosphorylation. In old rats, however, a majority of genes involved in oxidative phosphorylation had higher expression in females compared to males. Such basal differences between the sexes in cardiac expression of genes associated with energy metabolism may indicate a likely involvement of mitochondria in susceptibility to CVDs. In addition, female rats showed lower expression levels of apoptotic genes in hearts compared to males at all ages, which may have implications for better preservation of cardiac mass in females than in males.

The influence of age on serum concentrations of cardiac troponin I: results in rats, monkeys, and commercial sera

Cardiac troponins serve as serum biomarkers of myocardial injury. The current study examined the influence of age on serum concentrations of cardiac troponin I (cTnI). An ultrasensitive immunoassay was used to monitor cTnI concentrations in Sprague-Dawley (SD) rats and Erythrocebus patas monkeys of different ages. The mean cTnI concentrations were highest in 10-day-old rats compared to 25-, 40-, and 80-day-old SD rats. Cardiomyocyte remodeling was apparent in hearts from 10-day-old SD rats as evident by hypercellularity, irregularly shaped nuclei, and moderate numbers of myocytes undergoing mitosis and apoptosis. The mean concentration of cTnI in 5 newborn monkeys was considerably higher than that of three 1-year-old monkeys. Evidence of cardiomyocyte remodeling was also observed in these newborn hearts (loss of myofibrils and cytoplasmic vacuolation). Commercial animal serum samples were also analyzed. The concentrations of cTnI detected in fetal equine and porcine serum were considerably higher than that found in adult equine and porcine serum samples Likewise, fetal bovine serum had higher cTnI concentrations (>2,400 pg/ml) than did adult caprine and laprine samples (2.5-2.7 pg/ml). The present study found age-related differences in cTnI concentrations, with higher levels occurring at younger ages. This effect was consistent across several animal species.

Early origins of heart disease: low birth weight and determinants of cardiomyocyte endowment

1. World-wide epidemiological and experimental animal studies demonstrate that adversity in fetal life, resulting in intrauterine growth restriction, programmes the offspring for a greater susceptibility to ischaemic heart disease and heart failure in adult life. 2. After cardiogenesis, cardiomyocyte endowment is determined by a range of hormones and signalling pathways that regulate cardiomyocyte proliferation, apoptosis and the timing of multinucleation/terminal differentiation. 3. The small fetus may have reduced cardiomyocyte endowment owing to the impact of a suboptimal intrauterine environment on the signalling pathways that regulate cardiomyocyte proliferation, apoptosis and the timing of terminal differentiation.

Early maternal separation has mild effects on cardiac autonomic balance and heart structure in adult male rats

Early life adverse experiences have long-term physiologic and behavioral effects and enhance stress sensitivity. This study examined the effects of maternal separation (MS) on cardiac stress responsivity and structure in adulthood. Male Wistar rats were separated from the dams for 3 h per day from postnatal days 2 through 15. When exposed to 5-day intermittent restraint stress (IRS) as adults, MS, and control rats showed similar acute modifications of cardiac sympathovagal balance, quantified via heart rate variability analysis. In addition, MS had no effect on cardiac pacemaker intrinsic activity (as revealed by autonomic blockade with scopolamine and atenolol) and did not affect the circadian rhythmicity of heart rate, neither before nor after IRS. However, MS differed from control rats in cardiac parasympathetic drive following IRS, which was heightened in the latter but remained unchanged in the former, both during the light and dark phases of the daily rhythm. The evaluation of adult cardiac structure indicated that stress experienced during a crucial developmental period induced only modest changes, involving cardiomyocyte hypertrophy, increased density of vascular structures, and myocardial fibrosis. The mildness of these functional-structural effects questions the validity of MS as a model for early stress-induced cardiac disease in humans.

Β-adrenergic receptor stimulation induces endoplasmic reticulum stress in adult cardiac myocytes: role in apoptosis

Accumulation of misfolded proteins and alterations in calcium homeostasis induces endoplasmic reticulum (ER) stress, leading to apoptosis. In this study, we tested the hypothesis that β-AR stimulation induces ER stress, and induction of ER stress plays a pro-apoptotic role in cardiac myocytes. Using thapsigargin and brefeldin A, we demonstrate that ER stress induces apoptosis in adult rat ventricular myocytes (ARVMs). β-AR-stimulation (isoproterenol; 3h) significantly increased expression of ER stress proteins, such as GRP-78, Gadd-153, and Gadd-34, while activating caspase-12 in ARVMs. In most parts, these effects were mimicked by thapsigargin. β-AR stimulation for 15 min increased PERK and eIF-2α phosphorylation. PERK phosphorylation remained higher, while eIF-2α phosphorylation declined thereafter, reaching to ~50% below basal levels at 3 h after β-AR stimulation. This decline in eIF-2α phosphorylation was prevented by β1-AR, not by β2-AR antagonist. Forskolin, adenylyl cyclase activator, simulated the effects of ISO on eIF-2α phosphorylation. Salubrinal (SAL), an ER stress inhibitor, maintained eIF-2α phosphorylation and inhibited β-AR-stimulated apoptosis. Furthermore, inhibition of caspase-12 using z-ATAD inhibited β-AR-stimulated and thapsigargin-induced apoptosis. In vivo, β-AR stimulation induced ER stress in the mouse heart as evidenced by increased expression of GRP-78 and Gadd-153, activation of caspase-12, and dephosphorylation of eIF-2α. SAL maintained phosphorylation of eIF-2α, inhibited activation of caspase-12, and decreased β-AR-stimulated apoptosis in the heart. Thus, β-AR stimulation induces ER stress in cardiac myocytes and in the heart, and induction of ER stress plays a pro-apoptotic role.

Minocycline suppresses oxidative stress and attenuates fetal cardiac myocyte apoptosis triggered by in utero cocaine exposure

This study investigates the molecular mechanisms by which minocycline, a second generation tetracycline, prevents cardiac myocyte death induced by in utero cocaine exposure. Timed mated pregnant Sprague-Dawley (SD) rats received one of the following treatments twice daily from embryonic (E) day 15-21 (E15-E21): (i) intraperitoneal (IP) injections of saline (control); (ii) IP injections of cocaine (15 mg/kg BW); and (iii) IP injections of cocaine + oral administration of 25 mg/kg BW of minocycline. Pups were killed on postnatal day 15 (P15). Additional pregnant dams received twice daily IP injections of cocaine (from E15-E21) + oral administration of a relatively higher (37.5 mg/kg BW) dose of minocycline. Minocycline treatment continued from E15 until the pups were sacrificed on P15. In utero cocaine exposure resulted in an increase in oxidative stress and fetal cardiac myocyte apoptosis through activation of c-Jun-NH(2)-terminal kinase (JNK) and p38 mitogen-activated protein kinase (MAPK)-mediated mitochondria-dependent apoptotic pathway. Continued minocycline treatment from E15 through P15 significantly prevented oxidative stress, kinase activation, perturbation of BAX/BCL-2 ratio, cytochrome c release, caspase activation, and attenuated fetal cardiac myocyte apoptosis after prenatal cocaine exposure. These results demonstrate in vivo cardioprotective effects of minocycline in preventing fetal cardiac myocyte death after prenatal cocaine exposure. Given its proven clinical safety and ability to cross the placental barrier and enter into the fetal circulation, minocycline may be an effective therapy for preventing cardiac consequences of in utero cocaine exposure.

Myocyte proliferation in the developing heart

Regulation of organ growth is critical during embryogenesis. At the cellular level, mechanisms controlling the size of individual embryonic organs include cell proliferation, differentiation, migration, and attrition through cell death. All these mechanisms play a role in cardiac morphogenesis, but experimental studies have shown that the major determinant of cardiac size during prenatal development is myocyte proliferation. As this proliferative capacity becomes severely restricted after birth, the number of cell divisions that occur during embryogenesis limits the growth potential of the postnatal heart. We summarize here current knowledge concerning regional control of myocyte proliferation as related to cardiac morphogenesis and dysmorphogenesis. There are significant spatial and temporal differences in rates of cell division, peaking during the preseptation period and then gradually decreasing toward birth. Analysis of regional rates of proliferation helps to explain the mechanics of ventricular septation, chamber morphogenesis, and the development of the cardiac conduction system. Proliferation rates are influenced by hemodynamic loading, and transduced by autocrine and paracrine signaling by means of growth factors. Understanding the biological response of the developing heart to such factors and physical forces will further our progress in engineering artificial myocardial tissues for heart repair and designing optimal treatment strategies for congenital heart disease.

The defects in development and apoptosis of cardiomyocytes in mice lacking the transcriptional factor Pax-8

BACKGROUND

Cardiac-specific deletion of ALK3 is lethal in mid-gestation with ventricular septum malformations (VSM). This study was designed to define the Pax-8's role in heart development and cardiomyocyte apoptosis.

METHODS

Pathologic changes in the hearts of Pax-8 or ALK3 knockout and wild type control mice were determined by light and electron microscopy. Analysis of cardiomyocyte apoptosis was performed by TUNEL. The effect of Pax-8 gene deficiency on caspase-3 activity was examined after transfecting Pax-8 siRNA into cultured myoblast cell line.

RESULTS

Mice with ALK3 or Pax-8 gene knockout but not wild type control animals showed the development of VSM. Increased cardiomyocyte apoptosis was found in homozygotes. Echocardiography showed that Pax-8 homozygote mice developed malfunction of the heart. Furthermore, the caspase-3 activity was significantly higher in the cells treated with Pax-8 siRNA as compared to those treated with negative control siRNA in H9C2 (2-1) cell line.

CONCLUSIONS

The Pax-8 gene may play a crucial role in heart development and regulating cardiocyte apoptosis. Knockout of Pax-8 may exert a similar effect on myocardial morphology and apoptosis as those seen in ALK3 knockouts. Furthermore, the ventricular septum malformations could be partially attributed to accelerated cardiomyocyte apoptosis.

Obesogenic high fat western diet induces oxidative stress and apoptosis in rat heart

Feeding Wistar rats a high calorie "Western" diet (45% fat) for up to 48 weeks induces obesity and cardiac dysfunction, while a high fat diet (60% fat) induces obesity only. Here we investigated the molecular "footprints" of the two forms of diet-induced obesity in the heart. In rats fed Western diet for a long term, cardiac mRNA transcript levels of malic enzyme were decreased (-72%, P < 0.05), suggesting impaired anaplerotic flux of the Krebs cycle (KC) and mitochondrial dysfunction. In addition, there was a marked decrease in the expression of the transcription factor MEF2C (myocyte enhancer factor 2C) and its target gene SERCA2a (sarco-endo-plasmic reticulum Ca(2+)-ATPase). Oxidative stress was reflected in reduced transcript levels of manganese superoxide dismutase, glutathione peroxidase 1, and increased protein levels of mitochondrial transcription factor A, suggesting compensatory mitochondrial biogenesis in the face of increased mitochondrial damage. Oxidant injury was accompanied by increased protein glycosylation, increased transcript levels of glutamine fructose 6-phosphate amidotransferase 2, and decreased protein levels of acetyl Co-A carboxylase. Lastly, apoptosis was evident by TUNEL positivity and elevated mRNA transcript levels and activity of caspase 3. Consistent with these results, protein levels of Bcl2 were markedly reduced. We conclude that inadequate supplementation of KC intermediates due to reduced levels of malic enzyme, downregulation of MEF2C and its target gene SERCA2a, oxidative stress, and programmed cell death are all potential contributors to contractile dysfunction of the heart.

Nitric oxide and oxygen radicals induced apoptosis via bcl-2 and p53 pathway in hypoxia-reoxygenated cardiomyocytes

Neonatal rat cardiomyocytes were subjected to 24 h of hypoxia 95%N2/5%CO2 and 24 h of hypoxia plus 4 h of reoxygenation 95%O2/5%CO2. 24 h of hypoxia increased the levels of NO, NO2-/NO3-, TBARS and LDH. 24 h of hypoxia plus 4 h of reoxygenation decreased the levels of NO, NO2-/NO3-, but further increased TBARS and LDH. The hypoxia up-regulated the expression of bcl-2, p53 and p21/waf1/cip1 but the reoxygenation down-regulated the expression of bcl-2, and further up-regulated p53 and p21/waf1/cip1. The hypoxia increased cell apoptosis and reoxygenation further increased both apoptotic and necrotic cell death. NO, NO2-/NO3- TBARS, DNA fragmentation and cell apoptosis were enhanced by SNP and inhibited by L-NAME respectively. In addition, SOD/catalase down-regulated the expression of p53, p21/wafl/cipl and TBARS but up-regulated bcl-2 and increased indirectly the level of NO, NO2-/NO3-, and inhibited DNA fragmentation. The results suggest that hypoxia-induced cell death is associated with the activation of NO, bcl-2 and p53 pathway, while hypoxia-reoxygenation induced cell death via the generation of reactive oxygen species and activation of p53 pathway. The present study clarified that NO may be an initiative signal to apoptotic cell death and the activation of bcl-2, p53 and p21/waf1/cip1 pathway in hypoxic and hypoxia-reoxygenated cardiomyocytes.

Apoptosis is not involved in the mechanism of myocardial dysfunction after resuscitation in a rat model of cardiac arrest and cardiopulmonary resuscitation

OBJECTIVE

To investigate the presence of apoptosis after the global myocardial ischemia of cardiopulmonary resuscitation and the regional myocardial ischemia after left anterior descending coronary artery occlusion and relate it to the severity of postresuscitation myocardial dysfunction.

DESIGN

Prospective animal study.

SETTING

University-affiliated animal research laboratory.

SUBJECTS

Male Sprague-Dawley rats.

INTERVENTIONS

Fifteen male Sprague-Dawley rats weighing 450-550 g were randomized to: (1) 8 mins of untreated cardiac arrest followed by 6 mins of cardiopulmonary resuscitation; (2)left anterior descending coronary artery occlusion for 45 mins followed by 4 hrs of reperfusion; and (3) left anterior descending coronary artery sham group. Cardiac functions, including ejection fraction, analog differentiation of left ventricular pressure at 40 mm Hg, and rate of maximal left ventricular pressure decline were continuously measured for 4 hrs. The hearts were then harvested for the terminal transferase-mediated 2'-deoxyuridine, 5'-triphosphate nick end-labeling assay analysis.

MEASUREMENTS AND MAIN RESULTS

Myocardial function was significantly impaired after resuscitation from cardiac arrest and reperfusion from left anterior descending coronary artery occlusion(p < .01). There was no difference in the percentage of apoptotic cells between the cardiopulmonary resuscitation animals and sham-operated animals. Fewer apoptotic cells were observed in cardiac arrest/cardiopulmonary resuscitation animals in comparison to left anterior descending coronary artery occlusion animals (p < .05), even though myocardial function was more severely impaired after resuscitation (p < .01).

CONCLUSIONS

Myocardial function was significantly impaired after cardiac arrest/cardiopulmonary resuscitation and ischemia/reperfusion. However, apoptosis was not involved in the mechanism of postresuscitation myocardial dysfunction in this setting.

Early origins of cardiac hypertrophy: does cardiomyocyte attrition programme for pathological 'catch-up' growth of the heart?

1. Epidemiological and experimental evidence suggests that adult development of cardiovascular disease is influenced by events of prenatal and early postnatal life. Cardiac hypertrophy is recognized as an important predictor of cardiovascular morbidity and mortality, but the developmental origins of this condition are not well understood. 2. In the heart, a switch from hyperplastic to hypertrophic cellular growth occurs during late prenatal or early postnatal life. Postnatal growth of the heart is almost entirely reliant on hypertrophy of individual cardiomyocytes, and damage to heart muscle in adulthood is typically not reparable by cell replacement. Therefore, a reduced number of cardiomyocytes may render the heart more vulnerable in situations where an increased workload is required. 3. A number of different animal models have been used to study fetal programming of adult diseases, including nutritional, hypoxic, maternal/neonatal endocrine stress and genetic models. Although studies investigating the cellular basis of myocardial disease in growth-restricted models are limited, a reduction in cardiomyocyte number through either reduced cellular proliferation or increased apoptosis appears to be a central feature. 4. The mechanisms responsible for the programming of adult cardiovascular disease are poorly understood. We hypothesize that cardiac hypertrophy can have a developmental origin in excess cardiomyocyte attrition during a critical perinatal growth window. Findings that have directly assessed the impact of fetal growth restriction on the myocardium are considered and cellular and molecular mechanisms involved in the potential pathological 'catch-up' growth of the heart during later maturation are identified.

Briana D, Baka S, Vraila VM, Kontara L, Hassiakos D, Malamitsi-Puchner A. Perinatal changes of cardiac troponin-I in normal and intrauterine growth-restricted pregnancies

Intrauterine growth restriction (IUGR) implies fetal hypoxia, resulting in blood flow redistribution and sparing of vital organs (brain, heart). Serum cardiac Troponin-I (cTnI), a well-established marker of myocardial ischaemia, was measured in 40 mothers prior to delivery, the doubly clamped umbilical cords (representing fetal state), and their 20 IUGR and 20 appropriate-forgestational-age (AGA) neonates on day 1 and 4 postpartum. At all time points, no differences in cTnI levels were observed between the AGA and IUGR groups. Strong positive correlations were documented between maternal and fetal/neonatal values (r ≥ .498, P ≤ .025 in all cases in the AGA and r ≥ .615, P ≤ .009 in all cases in the IUGR group). These results may indicate (a) normal heart function, due to heart sparing, in the IUGR group (b) potential crossing of the placental barrier by cTnI in both groups.

Chronic right ventricular pressure overload results in a hyperplastic rather than a hypertrophic myocardial response

Myocardial hyperplasia is generally considered to occur only during fetal development. However, recent evidence suggests that this type of response may also be triggered by cardiac overload after birth. In congenital heart disease, loading conditions are frequently abnormal, thereby affecting ventricular function. We hypothesized that chronic right ventricular pressure overload imposed on neonatal hearts initiates a hyperplastic response in the right ventricular myocardium. To test this, young lambs (aged 2-3 weeks) underwent adjustable pulmonary artery banding to obtain peak right ventricular pressures equal to left ventricular pressures for 8 weeks. Transmural cardiac tissue samples from the right and left ventricles of five banded and five age-matched control animals were studied. We found that chronic right ventricular pressure overload resulted in a twofold increase in right-to-left ventricle wall thickness ratio. Morphometric right ventricular myocardial tissue analysis revealed no changes in tissue composition between the two groups; nor were right ventricular myocyte dimensions, relative number of binucleated myocytes, or myocardial DNA concentration significantly different from control values. In chronic pressure overloaded right ventricular myocardium, significantly (P < 0.01) more myocyte nuclei were positive for the proliferation marker proliferating cellular nuclear antigen than in control right ventricular myocardium. Chronic right ventricular pressure overload applied in neonatal sheep hearts results in a significant increase in right ventricular free wall thickness which is primarily the result of a hyperplastic myocardial response.

Detection of TUNEL-positive cardiomyocytes and C-kit-positive progenitor cells in children with congenital heart disease

The loss of cardiomyocytes by apoptosis and the subsequent replacement by fibrous connective tissues are important features of cardiac remodeling in adult heart disease. In children with CHD, however, the cellular and molecular mechanisms of heart failure have not yet been fully understood because of the anatomical and hemodynamic complexities. To investigate the apoptotic death of cardiomyocytes and mobilization of cardiac progenitor cells in children with congenital heart disease (CHD), terminal deoxynucleotidyl-transferase-mediated dUTP nick end-labeling (TUNEL) assay and immunohistochemistry with antibody against c-kit were performed. The incidence of TUNEL-positive cardiomyocytes in children with CHD (n=17) was higher (0.39+/-0.21%) than that in the child controls (0.072+/-0.037%, p<0.001, n=6), however, the incidence was lower than that in adults with heart disease (1.35+/-0.54%, p<0.005, n=7). Significant cardiomyocyte hypertrophy or fibrosis was not observed in children with CHD. The CHD patients hemodynamically demonstrating a volume overload showed more TUNEL-positive cardiomyocytes (0.58+/-0.17%, n=4) than those with severe cyanosis (0.20+/-0.12%, p<0.05, n=4). C-kit-positive cells were more abundantly detected in CHD in comparison to the child control (p<0.01) and the adults with heart disease (p<0.005). The incidence of c-kit-positive cells correlated with that of TUNEL-positive cardiomyocytes (r=0.513). In contrast to adult patients with heart disease where cardiomyocyte apoptosis and the subsequent replacement by fibrous connective tissue are characteristic features of remodeling process, stress in children with CHD was found to induce less cardiomyocyte apoptosis and fibrosis. This study also provides a possible relationship between cardiomyocyte apoptosis and mobilization of c-kit-positive cells in children with CHD.

Dose and time-dependent apoptotic effects by angiotensin II infusion on left ventricular cardiomyocytes

OBJECTIVE

To gain insight into the regulation of cardiac apoptosis we studied the dose-response and time-course effects of angiotensin II (Ang II) infusion on ventricular cardiomyocyte apoptosis and on the expression of Bax and Bcl-2 genes and proteins.

STUDY DESIGN AND METHODS

In the dose-response study, Ang II was infused subcutaneously at doses of 100, 200, 400, 800 and 1200 ng/kg per min for 14 days. In the time-course study, rats infused with Ang II at doses of 200 and 400 ng/kg per min were followed for 7 and 14 days. The cardiomyocyte apoptotic density was assessed by DNA end labelling (terminal deoxynucleotide nick-end labelling; TUNEL). Gene and protein expression of Bcl-2 and Bax were evaluated by reverse transcriptase-polymerase chain reaction and by Western blots.

RESULTS

Systolic blood pressure and left ventricular mass were increased in a dose-dependent manner in Ang II-infused rats. A statistically significant increase in the rate of cardiac apoptosis and pro-apoptotic changes of Bcl-2 and Bax gene and protein expression was observed when high doses of Ang II (800-1200 ng/kg per min) were infused. A positive correlation of apoptotic density with Bax and a negative correlation with Bcl-2 and Bcl-2/Bax ratio were found. Cardiac apoptosis was greatly influenced by the timing of Ang II infusion. Losartan-treated Ang II-infused rats exhibited normalized systolic blood pressure, left ventricular weight, apoptosis, and Bax and Bcl-2 levels.

CONCLUSIONS

Our results are consistent with the pathophysiological role of Ang II in induction of cardiac apoptosis, and explain the cardioprotective effect of Ang II receptor antagonists.

Adolescent feline heart contains a population of small, proliferative ventricular myocytes with immature physiological properties

Recent studies suggest that rather than being terminally differentiated, the adult heart is a self-renewing organ with the capacity to generate new myocytes from cardiac stem/progenitor cells (CS/PCs). This study examined the hypotheses that new myocytes are generated during adolescent growth, to increase myocyte number, and these newly formed myocytes are initially small, mononucleated, proliferation competent, and have immature properties. Ventricular myocytes (VMs) and cKit(+) (stem cell receptor) CS/PCs were isolated from 11- and 22-week feline hearts. Bromodeoxyuridine incorporation (in vivo) and p16(INK4a) immunostaining were measured to assess myocyte cell cycle activity and senescence, respectively. Telomerase activity, contractions, Ca(2+) transients, and electrophysiology were compared in small mononucleated (SMMs) and large binucleated (LBMs) myocytes. Heart mass increased by 101% during adolescent growth, but left ventricular myocyte volume only increased by 77%. Most VMs were binucleated (87% versus 12% mononucleated) and larger than mononucleated myocytes. A greater percentage of SMMs was bromodeoxyuridine positive (SMMs versus LBMs: 3.1% versus 0.8%; P<0.05), and p16(INK4a) negative and small myocytes had greater telomerase activity than large myocytes. Contractions and Ca(2+) transients were prolonged in SMMs versus LBMs and Ca(2+) release was disorganized in SMMs with reduced transient outward current and T-tubule density. The T-type Ca(2+) current, usually seen in fetal/neonatal VMs, was found exclusively in SMMs and in myocytes derived from CS/PC. Myocyte number increases during adolescent cardiac growth. These new myocytes are initially small and functionally immature, with patterns of ion channel expression normally found in the fetal/neonatal period.

Morphological aspects of apoptosis in heart diseases

It has been suggested that apoptosis may be responsible for a significant amount of cardiomyocyte death during acute myocardial infarction as well as for a progressive loss of surviving cells in failing hearts. Typical apoptosis can indeed be induced in cardiomyocytes at the experimental conditions. In actual heart diseases, in contrast, there is very little direct morphological evidence of apoptosis in cardiomyocytes occurring at any stage of myocardial infarction and heart failure, despite the availability of much indirect evidence that includes detection of DNA fragmentation and apoptosis-related factors. For that reason, the potential efficacy of therapeutic intervention to prevent apoptosis remains controversial. This review will survey available data from both animals and humans to critically assess the role of cardiomyocyte apoptosis during myocardial infarction and its relevance to myocardial remodeling and during progression to heart failure. Also considered will be nonmyocyte interstitial cells, which have received less attention than myocytes despite definitive evidence of their apoptosis in the infarcted heart and recent studies suggesting that blockade of apoptosis among these cells mitigates postinfarction cardiac remodeling and heart failure. We conclude from our survey that there are many hurdles to surmount before regulation of apoptosis can be clinically applied in the treatment of myocardial infarction and heart failure.

Physiopathology of the embryonic heart (with special emphasis on hypoxia and reoxygenation)

The adaptative response of the developing heart to adverse intrauterine environment such as reduced O2 delivery can result in alteration of gene expression with short- and long-term consequences including adult cardiovascular diseases. The tolerance of the developing heart of acute or chronic oxygen deprivation, its capacity to recover during reperfusion and the mechanisms involved in reoxygenation injury are still under debate. Indeed, the pattern of response of the immature myocardium to hypoxia-reoxygenation differs from that of the adult. This review deals with the structural and metabolic characteristics of the embryonic heart and the functional consequences of hypoxia and reoxygenation. The relative contribution of calcium and sodium overload, pH disturbances and oxidant stress to the hypoxia-induced cardiac dysfunction is examined, as well as various cellular signaling pathways (e.g. MAP kinases) involved in cell survival or death. In the context of the recent advances in developmental cardiology and fetal cardiac surgery, a better understanding of the physiopathology of the stressed developing heart is required.

Regulation of the sphingolipid signaling pathways in the growing and hypoxic rat heart

Sphingolipids (SLs) have a biomodulatory role in physiological as well as pathological cardiovascular conditions. This study aims to assess the variation of SL mediators and metabolizing enzymes in the growing and hypoxic rat heart. Sprague-Dawley rats were placed in a hypoxic environment at birth. Control animals remained in room air. In control animals, activities of acidic-sphingomyelinase (A-SMase), sphingomyelin synthase (SMS), glucosylceramide synthase (GCS), and ceramidase decreased with age in both ventricles whereas activity of neutral-sphingomyelinase (N-SMase) increased with age. Hypoxic RV mass was 171 and 229% that of controls, at 4 and 8 weeks, respectively. This was accompanied by an increase in RV myocardial ceramide synthesis, consumption and breakdown, with a net effect of suppression of ceramide accumulation and increase in diacylglycerol (DAG) concentration. In addition, significant increase in activities of: A-SMase by 26 and 29%, SMS by 108 and 40%, and ceramidase by 66 and 35%, in the hypoxic RV rats as compared to controls, was noted at 4 and 8 weeks of age, respectively. Sphingolipids and their regulating enzymes appear to play a role in adaptive responses to chronic hypoxia in the neonatal rat heart.

Genetic Deletion of the p66 Shc Adaptor Protein Protects From Angiotensin II–Induced Myocardial Damage

Angiotensin II (Ang II), acting through its G protein-coupled AT1 receptor (AT1), contributes to the precocious heart senescence typical of patients with hypertension, atherosclerosis, and diabetes. AT1 was suggested to transactivate an intracellular signaling controlled by growth factors and their tyrosin-kinase receptors. In cultured vascular smooth muscle cells, this downstream mechanism comprises the p66Shc adaptor protein, previously recognized to play a role in vascular cell senescence and death. The aim of the present study was 2-fold: (1) to characterize the cardiovascular phenotype of p66Shc knockout mice (p66Shc(-/-)), and (2) to test the novel hypothesis that disrupting the p66Shc might protect the heart from the damaging action of elevated Ang II levels. Compared with wild-type littermates (p66Shc(+/+)), p66Shc(-/-) showed similar blood pressure, heart rate, and left ventricular wall thickness. However, cardiomyocyte number was increased in mutant animals, indicating a condition of myocardial hyperplasia. In p66Shc(+/+), infusion of a sub-pressor dose of Ang II (300 nmol/kg body weight [BW] daily for 28 days) caused left ventricular hypertrophy and apoptotic death of cardiomyocytes and endothelial cells. In contrast, p66Shc(-/-) were resistant to the proapoptotic/hypertrophic action of Ang II. Consistently, in vitro experiments showed that Ang II causes apoptotic death of cardiomyocytes isolated from p66Shc(+/+) hearts to a greater extent as compared with p66Shc(-/-) cardiomyocytes. Our results indicate a fundamental role of p66Shc in Ang II-mediated myocardial remodeling. In perspective, p66Shc inhibition may be envisioned as a novel way to prevent the deleterious effects of Ang II on the heart.

Immediate and Long-Term Effects of Color Doppler Ultrasound on Myocardial Cell Apoptosis of Fetal Rats

The objective of this article is to evaluate the safety of diagnostic color Doppler ultrasound (CDUS) on embryos by observing its effects on myocardial cell apoptosis of fetal rats. Pregnant Sprague-Dawley rats were divided into fetal group and neonatal group according to the sample-drawing time averagely and randomly, and each group was subdivided into control group and insonification group. The control group was sham-insonificated, and the insonification group was insonificated by diagnostic ultrasound (3.0 MHz, Tis = 1.8, MI = 1.6) for 30 minutes. The fetal rats' hearts were removed 24 hours after insonification and the neonatal rats' hearts were removed 10 days after birth. Apoptosis cells were detected with TUNEL (in situ terminal deoxynucleotidyl transferase-mediated D-UTP nick end labeling), and ultrastructural changes were observed with transmission electron microscope. Myocardial cell apoptosis was significantly higher in the fetal insonification group than in the fetal control group (P < 0.05), and it was significantly higher in the fetal groups than in the neonatal groups (P < 0.05), but there was no significant difference in myocardial cell apoptosis between the neonatal groups (P < 0.05). Apoptotic changes of myocardial cells in the fetal insonification group were observed with transmission electron microscope, which showed margination, condensation of the nuclear chromatin, etc. It is concluded that apoptosis and ultrastructural changes could be induced if fetal rat's heart was irradiated continuously over 30 minutes by diagnostic CDUS, but this phenomenon would disappear after birth.

Prenatal hypoxia and cardiac programming

Epidemiologic studies have shown a clear association of adverse intrauterine environment and an increased risk of hypertension and coronary heart disease in the adult. Many studies have been focused on the effects of maternal undernutrition and fetal glucocorticoid exposure on fetal programming and later adult disease. Although it is relatively less clear, there is evidence that fetal exposure to hypoxia, alcohol, tobacco smoking, and cocaine may also cause in utero programming leading to an increased risk of adult disease. Chronic hypoxia during the course of pregnancy is thought to result in fetal intrauterine growth retardation. Among other effects, chronic hypoxia suppresses fetal cardiac function, alters cardiac gene expression, increases myocyte apoptosis, and results in a premature exit of the cell cycle of cardiomyocytes and myocyte hypertrophy. This review discusses recent evidence of an association of prenatal hypoxic exposure with an increased vulnerability of adult heart disease, and the possible mechanisms involved.

Prenatal cocaine exposure increases apoptosis of neonatal rat heart and heart susceptibility to ischemia-reperfusion injury in 1-month-old rat

Maternal cocaine administration during pregnancy increased apoptosis in near-term fetal rat heart. The present study tested the hypothesis that prenatal cocaine exposure increases the heart susceptibility to ischemia/reperfusion injury in the offspring. Pregnant Sprague-Dawley rats received cocaine (30 mg kg(-1) day(-1)) or saline from days 15 to 21 of gestational age. Maternal body weights were not significantly different at the end of cocaine treatment, but body weights of offspring were decreased slightly at ages of 1, 3, and 7 days. Although heart-to-body weight ratio was not affected at all ages examined, prenatal cocaine significantly increased left ventricular myocyte size at an age of 30 days. Additionally, prenatal cocaine increased DNA fragmentation measured in the hearts isolated from offspring of 1, 3, 7, and 21 days, but not of 30 days, with the peak at 3-day neonates. Antiapoptotic (Bcl-2 and Bcl-X(L)) and proapoptotic (Bax and Bad) proteins were expressed in neonatal rat hearts of both groups. Prenatal cocaine exposure decreased levels of Bcl-2 in 21-day and increased Bax in 21- and 30-day rat hearts. In addition, hearts of 30-day-old male progeny were studied using the Langendorff preparation, and were subjected to 25 min of ischemia and 60 min of reperfusion. Preischemic baseline values of left ventricular (LV) function were the same between the two groups. However, prenatal cocaine exposure significantly attenuated postischemic recovery of LV function, and significantly increased elevated LV end diastolic pressure during reperfusion. This was associated with a significant increase in ischemia/reperfusion-induced LV myocardial infarct size. The results suggest that prenatal cocaine exposure induces abnormal apoptosis and myocyte hypertrophy in postnatal heart, leading to an increased heart susceptibility to ischemic insults in postnatal life.

Role of apoptosis in remodeling after myocardial infarction

The magnitude of an acute myocardial infarction (MI; i.e., number of dead cardiomyocytes) is the most critical determinant of subsequent left ventricular remodeling and heart failure. Also affecting the post-infarction disease process, however, are events occurring during the subacute and chronic stages of the infarction, including late cardiomyocyte death, cardiomyocyte hypertrophy, fibrosis, and expression of various cytokines. Additionally, it has been suggested that apoptosis may be responsible for a significant amount of cardiomyocyte death during the acute ischemic stage, as well as for a progressive loss of surviving cells during the subacute and chronic stages. However, there is very little direct morphological evidence of apoptosis occurring at any stage of MI, despite the availability of much indirect evidence that includes detection of DNA fragmentation and apoptosis-related factors. For that reason, the potential efficacy of therapeutic intervention to prevent apoptosis remains controversial. This review will survey available data from both animals and humans to critically assess the role of cardiomyocyte apoptosis during MI and its relevance to myocardial remodeling and heart failure. Also considered will be nonmyocyte interstitial cells, which have received less attention than myocytes despite definitive evidence of their apoptosis in the infarcted heart and recent studies suggesting that blockade of apoptosis among these cells mitigates post-infarction cardiac remodeling and heart failure. We conclude from our survey that there are many hurdles to surmount before regulation of apoptosis can be clinically applied in the treatment of MI and other heart diseases.

Angiotensin II may mediate apoptosis via AT1-receptors in the rat cardiac conduction system

INTRODUCTION

Apoptosis and angiotensin II (Ang II) have been suggested as possible causes of arrhythmias. In addition, Ang II via Ang II type I (AT(1)-) receptors, has been demonstrated to induce cardiomyocyte apoptosis. The transgenic m(Ren-2)27 (TG) rat carries the additional Ren-2 gene, the expression of which results in an increase in cardiac Ang II, thus potentially affecting the cell growth/death equilibrium. In this study we have investigated the effect of Ang II, via AT(1)-receptors, on mediating apoptosis in a cardiac conduction system (SA node and AV nodes).

MATERIALS AND METHODS

Heart sections from male two-day, one-week and two-week TG and Sprague-Dawley (SD) rats were stained with Masson Trichrome to localise the SA and AV nodes. The sections containing SA or AV nodes were processed for quantitation of apoptotic nuclei and AT(1)-receptors.

RESULTS

The number of apoptotic nuclei/mm(2) in the SA and AV nodes were found to decrease from two days to two weeks in both the TG and the SD rats, and the number of apoptotic nuclei/mm(2) in the TG groups was significantly higher than that of the SD groups for all ages (p<0.05). The number of AT(1)-receptors/mm(2) in the SA node were found to decrease with increasing age, whereas the number of AT(1)-receptors/mm(2) in the AV node was increased in both TG and SD rats and the number of AT(1)-receptors/mm(2) in the three TG groups was significantly more than that of the three SD groups (p<0.05).

DISCUSSION AND CONCLUSION

As a consequence of the additional renin gene in the TG rats, which results in the alteration of the local renin-angiotensin system, the numbers of AT(1)-receptors/mm(2) and apoptotic nuclei/mm(2) are increased. The number of apoptotic nuclei/mm(2) and AT(1)-receptors/mm(2) in the SA node decrease with maturation, whereas, the number of AT(1)-receptors in the AV node increase. Thus, there may be a correlation between Ang II and apoptosis in the SA node, which does not appear to be present in the AV node.

Pretreatment with tyrosine kinase inhibitor attenuates the reduction of apoptosis 24 h after ischemic preconditioning

We investigated whether ischemic preconditioning (PC) attenuates ischemia/reperfusion-induced injury in part by decreasing apoptosis and whether tyrosine kinase (TK) can regulate the signaling pathway leading to apoptosis in delayed cardioprotection. Six groups of rabbits were studied in the early phase (EP) and in the delayed phase (DP): (1) sham-operated control animals were received vehicle only (Veh-sham); (2) rabbits that received I.V. genistein (a nonspecific TK inhibitor) 10 min before ischemia (Gen-sham); (3) rabbits that received I.V. daidzein (an inactive structural analog of genistein) 10 min before ischemia (Dzn-sham); (4) rabbits preconditioned with 4 cycles of 5-min occlusion of left anterior descending coronary artery (LAD) and 10-min reperfusion (PC); (5) rabbits that received I.V. genistein, 10 min before PC (Gen-PC); (6) rabbits that received I.V. daidzein 10 min before PC (Dzn-PC). All rabbits underwent 30-min ischemia followed by 180-min reperfusion. Infarct size in the PC, Gen-PC, and Dzn-PC groups in the EP was significantly (p < 0.0001) reduced relative to controls Gen and Dzn. Delayed cardioprotection was blocked significantly (p < 0.0001) by genistein. In the EP, apoptosis was significantly (p < 0.0001) decreased in PC, Gen-PC, and Dzn-PC groups relative to controls Gen and Dzn. In the DP, a reduction of apoptosis was not seen in the Gen-PC group. This study suggests that PC reduces ischemic injury in part by decreasing apoptosis after ischemia/reperfusion and also that TK phosphorylation is involved in the signal transduction cascade leading to the decline of apoptosis in the DP.