Gender-related differences in proliferative response of cardiac fibroblasts to hypoxia: effects of estrogen

Cardiac Fibroblasts Mediate a Sexually Dimorphic Fibrotic Response to β-Adrenergic Stimulation

Background

Biological sex is an important modifier of cardiovascular disease and women generally have better outcomes compared with men. However, the contribution of cardiac fibroblasts (CFs) to this sexual dimorphism is relatively unexplored.

Methods and Results

Isoproterenol (ISO) was administered to rats as a model for chronic β‐adrenergic receptor (β‐AR)‐mediated cardiovascular disease. ISO‐treated males had higher mortality than females and also developed fibrosis whereas females did not. Gonadectomy did not abrogate this sex difference. To determine the cellular contribution to this phenotype, CFs were studied. CFs from both sexes had increased proliferation in vivo in response to ISO, but CFs from female hearts proliferated more than male cells. In addition, male CFs were significantly more activated to myofibroblasts by ISO. To investigate potential regulatory mechanisms for the sexually dimorphic fibrotic response, β‐AR mRNA and PKA (protein kinase A) activity were measured. In response to ISO treatment, male CFs increased expression of β1‐ and β2‐ARs, whereas expression of both receptors decreased in female CFs. Moreover, ISO‐treated male CFs had higher PKA activity relative to vehicle controls, whereas ISO did not activate PKA in female CFs.

Conclusions

Chronic in vivo β‐AR stimulation causes fibrosis in male but not female rat hearts. Male CFs are more activated than female CFs, consistent with elevated fibrosis in male rat hearts and may be caused by higher β‐AR expression and PKA activation in male CFs. Taken together, our data suggest that CFs play a substantial role in mediating sex differences observed after cardiac injury.

Sex related differences in the pathogenesis of organ fibrosis

The development of organ fibrosis has garnered rising attention as multiple diseases of increasing and/or high prevalence appear to progress to the chronic stage. Such is the case for heart, kidney, liver, and lung where diseases such as diabetes, idiopathic/autoimmune disorders, and nonalcoholic liver disease appear to notably drive the development of fibrosis. Noteworthy is that the severity of these pathologies is characteristically compounded by aging. For these reasons, research groups and drug companies have identified fibrosis as a therapeutic target for which currently, there are essentially no effective options. Although a limited body of published studies are available, most literature indicates that in multiple organs, premenopausal women are protected from developing severe forms of fibrosis suggesting an important role for sex hormones in mitigating this process. Investigators have implemented relevant animal models of organ disease linked to fibrosis supporting in general, these observations. In vitro studies and transgenic animals models have also been used in an attempt to understand the role that sex hormones and related receptors play in the development of fibrosis. However, in the setting of chronic disease in some organs such as the heart older (postmenopausal) women within a few years can quickly approach men in disease severity and develop significant degrees of fibrosis. This review summarizes the current body of relevant literature and highlights the imperative need for a major focus to be placed on understanding the manner in which sex and the presence or absence of related hormones modulates cell phenotypes so as to allow for fibrosis to develop.

Multi-Omics Integration Reveals Short and Long-Term Effects of Gestational Hypoxia on the Heart Development

Antenatal hypoxia caused epigenetic reprogramming of methylome and transcriptome in the developing heart and increased the risk of heart disease later in life. Herein, we investigated the impact of gestational hypoxia in proteome and metabolome in the hearts of fetus and adult offspring. Pregnant rats were treated with normoxia or hypoxia (10.5% O₂) from day 15 to 21 of gestation. Hearts were isolated from near-term fetuses and 5 month-old offspring, and proteomics and metabolomics profiling was determined. The data demonstrated that antenatal hypoxia altered proteomics and metabolomics profiling in the heart, impacting energy metabolism, lipid metabolism, oxidative stress, and inflammation-related pathways in a developmental and sex dependent manner. Of importance, integrating multi-omics data of transcriptomics, proteomics, and metabolomics profiling revealed reprogramming of the mitochondrion, especially in two clusters: (a) the cluster associated with "mitochondrial translation"/"aminoacyl t-RNA biosynthesis"/"one-carbon pool of folate"/"DNA methylation"; and (b) the cluster with "mitochondrion"/"TCA cycle and respiratory electron transfer"/"acyl-CoA dehydrogenase"/"oxidative phosphorylation"/"complex I"/"troponin myosin cardiac complex". Our study provides a powerful means of multi-omics data integration and reveals new insights into phenotypic reprogramming of the mitochondrion in the developing heart by fetal hypoxia, contributing to an increase in the heart vulnerability to disease later in life.

A review of the literature on cardiac electrical activity between fibroblasts and myocytes

Myocardial injuries often lead to fibrotic deposition. This review presents evidence supporting the concept that fibroblasts in the heart electrically couple to myocytes.

Activation of GPR30 inhibits cardiac fibroblast proliferation

The incidence of left ventricular diastolic dysfunction significantly increases in postmenopausal women suggesting the association between estrogen loss and diastolic dysfunction. The in vivo activation of G protein-coupled estrogen receptor (GPR30) attenuates the adverse effects of estrogen loss on cardiac fibrosis and diastolic dysfunction in mRen2.Lewis rats. This study was designed to address the effects of GPR30 on cardiac fibroblast proliferation in rats. The expression of GPR30 in cardiac fibroblasts isolated from adult Sprague-Dawley rats was confirmed by RT-PCR, Western blot analysis, and immunofluorescence staining. Results from BrdU incorporation assays, cell counting, carboxyfluorescein diacetate succinimidyl ester labeling in conjunction with flow cytometry, and Ki-67 staining showed that treatment with G1, a specific agonist of GPR30, inhibited cardiac fibroblast proliferation in a dose-dependent manner, which was associated with decreases in CDK1 and cyclin B1 protein expressions. In the GPR30-KO cells, BrdU incorporation, and CDK1 and cyclin B1 expressions significantly increased when compared to GPR30-intact cells. G1 had no effect on BrdU incorporation, CDK1 and cyclin B1 mRNA levels in GPR30-KO cells. In vivo studies showed increases in CDK1 and cyclin B1 mRNA levels, Ki-67-positive cells, and the immunohistochemistry staining of vimentin, a fibroblast marker, in the left ventricles from ovariectomized mRen2.Lewis rats versus hearts from ovary-intact littermates; 2 weeks of G1 treatment attenuated these adverse effects of estrogen loss. This study demonstrates that GPR30 is expressed in rat cardiac fibroblasts, and activation of GPR30 limits proliferation of these cells likely via suppression of the cell cycle proteins, cyclin B1, and CDK1.

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.

Fibroblasts in post-infarction inflammation and cardiac repair

Fibroblasts are the predominant cell type in the cardiac interstitium. As the main matrix-producing cells in the adult mammalian heart, fibroblasts maintain the integrity of the extracellular matrix network, thus preserving geometry and function. Following myocardial infarction fibroblasts undergo dynamic phenotypic alterations and direct the reparative response. Due to their strategic location, cardiac fibroblasts serve as sentinel cells that sense injury and activate the inflammasome secreting cytokines and chemokines. During the proliferative phase of healing, infarct fibroblasts undergo myofibroblast transdifferentiation forming stress fibers and expressing contractile proteins (such as α-smooth muscle actin). Mechanical stress, transforming growth factor (TGF)-β/Smad3 signaling and alterations in the composition of the extracellular matrix induce acquisition of the myofibroblast phenotype. In the highly cellular and growth factor-rich environment of the infarct, activated myofibroblasts produce matrix proteins, proteases and their inhibitors regulating matrix metabolism. As the infarct matures, "stress-shielding" of myofibroblasts by the cross-linked matrix and growth factor withdrawal may induce quiescence and ultimately cause apoptotic death. Because of their critical role in post-infarction cardiac remodeling, fibroblasts are promising therapeutic targets following myocardial infarction. However, the complexity of fibroblast functions and the pathophysiologic heterogeneity of post-infarction remodeling in the clinical context discourage oversimplified approaches in clinical translation. This article is part of a Special Issue entitled: Cardiomyocyte Biology: Cardiac Pathways of Differentiation, Metabolism and Contraction.

Sex-related differences in gene expression by porcine aortic valvular interstitial cells

While many large-scale risk factors for calcific aortic valve disease (CAVD) have been identified, the molecular etiology and subsequent pathogenesis of CAVD have yet to be fully understood. Specifically, it is unclear what biological phenomena underlie the significantly higher occurrence of CAVD in the male population. We hypothesized the existence of intrinsic, cellular-scale differences between male and female valvular interstitial cells (VICs) that contribute to male sex being a risk factor for CAVD. Differences in gene expression profiles between healthy male and female porcine VICs were investigated via microarray analysis. Mean expression values of each probe set in the male samples were compared to the female samples, and biological processes were analyzed for overrepresentation using Gene Ontology term enrichment analysis. There were 183 genes identified as significantly (fold change>2; P<0.05) different in male versus female aortic valve leaflets. Within this significant gene list there were 298 overrepresented biological processes, several of which are relevant to pathways identified in CAVD pathogenesis. In particular, pathway analysis indicated that cellular proliferation, apoptosis, migration, ossification, angiogenesis, inflammation, and extracellular matrix reorganization were all significantly represented in the data set. These gene expression findings also translated into functional differences in VIC behavior in the in vitro environment, as sex-related differences in proliferation and apoptosis were confirmed in VIC populations cultured in vitro. These data suggest that a sex-related propensity for CAVD exists on the cellular level in healthy subjects, a phenomenon that could have significant clinical implications. These findings also strongly support discontinuing the use of mixed-sex VIC cultures, thereby changing the current standard in the field.

Female sex and estrogen receptor-beta attenuate cardiac remodeling and apoptosis in pressure overload

We investigated sex differences and the role of estrogen receptor-beta (ERbeta) on myocardial hypertrophy in a mouse model of pressure overload. We performed transverse aortic constriction (TAC) or sham surgery in male and female wild-type (WT) and ERbeta knockout (ERbeta(-/-)) mice. All mice were characterized by echocardiography and hemodynamic measurements and were killed 9 wk after surgery. Left ventricular (LV) samples were analyzed by microarray profiling, real-time RT-PCR, and histology. After 9 wk, WT males showed more hypertrophy and heart failure signs than WT females. Notably, WT females developed a concentric form of hypertrophy, while males developed eccentric hypertrophy. ERbeta deletion augmented the TAC-induced increase in cardiomyocyte diameter in both sexes. Gene expression profiling revealed that WT male hearts had a stronger induction of matrix-related genes and a stronger repression of mitochondrial genes than WT female hearts. ERbeta(-/-) mice exhibited a different transcriptional response. ERbeta(-/-)/TAC mice of both sexes exhibited induction of proapoptotic genes with a stronger expression in ERbeta(-/-) males. Cardiac fibrosis was more pronounced in male WT/TAC than in female mice. This difference was abolished in ERbeta(-/-) mice. The number of apoptotic nuclei was increased in both sexes of ERbeta(-/-)/TAC mice, most prominent in males. Female sex offers protection against ventricular chamber dilation in the TAC model. Both female sex and ERbeta attenuate the development of fibrosis and apoptosis, thus slowing the progression to heart failure.

17beta-Estradiol inhibits matrix metalloproteinase-2 transcription via MAP kinase in fibroblasts

AIMS

Female sex and sex hormones contribute to cardiac remodelling. 17beta-estradiol (E2) is involved in the modulation of extracellular matrix composition and function. Here, we analysed the effect of E2 on matrix metalloproteinase (MMP)-2 gene expression and studied the underlying molecular mechanisms in rat cardiac fibroblasts and in a human fibroblast cell line.

METHODS AND RESULTS

In adult rat cardiac fibroblasts, E2 significantly decreased MMP-2 gene expression in an estrogen receptor (ER)-dependent manner. Transient transfection experiments of human MMP-2 (hMMP-2) promoter deletion constructs in a human fibroblast cell line revealed a regulatory region between -324 and -260 bp that is involved in E2/ERalpha-mediated repression of hMMP-2 gene transcription. Electrophoretic mobility shift assays (EMSA) and supershift analysis demonstrated the binding of transcription factor Elk-1 within this promoter region. Elk-1 was phosphorylated by E2 via the mitogen-activated protein kinase (MAPK) signalling pathway as shown by western blotting. Treatment of cells with the MAPK inhibitor PD98059 blocked the E2-dependent repression of hMMP-2 promoter activity as well as the endogenous MMP-2 mRNA levels in both human fibroblast cells and rat cardiac fibroblasts.

CONCLUSION

E2 inhibits MMP-2 expression via the ER and the MAPK pathway in rat cardiac fibroblasts and in a human fibroblast cell line. These mechanisms may contribute to sex-specific differences in fibrotic processes that are observed in human heart and other diseases.

Cardiac fibroblasts: at the heart of myocardial remodeling

Cardiac fibroblasts are the most prevalent cell type in the heart and play a key role in regulating normal myocardial function and in the adverse myocardial remodeling that occurs with hypertension, myocardial infarction and heart failure. Many of the functional effects of cardiac fibroblasts are mediated through differentiation to a myofibroblast phenotype that expresses contractile proteins and exhibits increased migratory, proliferative and secretory properties. Cardiac myofibroblasts respond to proinflammatory cytokines (e.g. TNFalpha, IL-1, IL-6, TGF-beta), vasoactive peptides (e.g. angiotensin II, endothelin-1, natriuretic peptides) and hormones (e.g. noradrenaline), the levels of which are increased in the remodeling heart. Their function is also modulated by mechanical stretch and changes in oxygen availability (e.g. ischaemia-reperfusion). Myofibroblast responses to such stimuli include changes in cell proliferation, cell migration, extracellular matrix metabolism and secretion of various bioactive molecules including cytokines, vasoactive peptides and growth factors. Several classes of commonly prescribed therapeutic agents for cardiovascular disease also exert pleiotropic effects on cardiac fibroblasts that may explain some of their beneficial outcomes on the remodeling heart. These include drugs for reducing hypertension (ACE inhibitors, angiotensin receptor blockers, beta-blockers), cholesterol levels (statins, fibrates) and insulin resistance (thiazolidinediones). In this review, we provide insight into the properties of cardiac fibroblasts that underscores their importance in the remodeling heart, including their origin, electrophysiological properties, role in matrix metabolism, functional responses to environmental stimuli and ability to secrete bioactive molecules. We also review the evidence suggesting that certain cardiovascular drugs can reduce myocardial remodeling specifically via modulatory effects on cardiac fibroblasts.

Sex steroids and stem cell function

Gender dimorphisms exist in the pathogenesis of a variety of cardiovascular, cardiopulmonary, neurodegenerative, and endocrine disorders. Estrogens exert immense influence on myocardial remodeling following ischemic insult, partially through paracrine growth hormone production by bone marrow mesenchymal stem cells (MSCs) and endothelial progenitor cells. Estrogens also facilitate the mobilization of endothelial progenitor cells to the ischemic myocardium and enhance neovascularization at the ischemic border zone. Moreover, estrogens limit pathological myocardial remodeling through the inhibitory effects on the proliferation of the cardiac fibroblasts. Androgens also may stimulate endothelial progenitor cell migration from the bone marrow, yet the larger role of androgens in disease pathogenesis is not well characterized. The beneficial effects of sex steroids include alteration of lipid metabolism in preadipocytes, modulation of bone metabolism and skeletal maturation, and prevention of osteoporosis through their effects on osteogenic precursors. In an example of sex steroid-specific effects, neural stem cells exhibit enhanced proliferation in response to estrogens, whereas androgens mediate inhibitory effects on their proliferation. Although stem cells can offer significant therapeutic benefits in various cardiovascular, neurodegenerative, endocrine disorders, and disorders of bone metabolism, a greater understanding of sex hormones on diverse stem cell populations is required to improve their ultimate clinical efficacy. In this review, we focus on the effects of estrogen and testosterone on various stem and progenitor cell types, and their relevant intracellular mechanisms.

Cardiac fibroblasts: friend or foe?

Cardiac function is determined by the dynamic interaction of various cell types and the extracellular matrix that composes the heart. This interaction varies with the stage of development and the degree and duration of mechanical, chemical, and electrical signals between the various cell types and the ECM. Understanding how these complex signals interact at the molecular, cellular, and organ levels is critical to understanding the function of the heart under a variety of physiological and pathophysiological conditions. Quantitative approaches, both in vivo and in vitro, are essential to understand the dynamic interaction of mechanical, chemical, and electrical stimuli that govern cardiac function. The fibroblast can thus be a friend in normal function or a foe in pathophysiological conditions.

Sex dimorphism in cardiac pathophysiology: experimental findings, hormonal mechanisms, and molecular mechanisms

The higher cardiovascular risk in men and post-menopausal women implies a protective action of estrogen. A large number of experimental studies have provided strong support to this concept. However, the recent clinical trials with negative outcomes regarding hormone replacement therapy call for "post hoc" reassessment of existing information, models, and research strategies as well as a summary of recent findings. Sex steroid hormones, in particular estrogen, regulate numerous processes that are related to the development and progression of cardiovascular disease through a variety of signaling pathways. Use of genetically modified models has resulted in interesting information on diverse actions mediated by steroid receptors. By focusing on experimental findings, we have reviewed hormonal, cellular, and signaling mechanisms responsible for sex dimorphism and actions of hormone replacement therapy and addressed current limitations and future directions of experimental research.

Sex-related bedside clinical variables associated with survival of older inpatients with heart failure

BACKGROUND

Little is known about sex-related differences in factors affecting prognosis of heart failure (HF). We prospectively investigated the relationship between bedside clinical variables and survival of older females vs. males with HF.

METHODS

Included were consecutive unselected inpatients, age >/=60 years, admitted for various acute conditions. HF was chronic and of diverse etiologies. Follow-up extended up to 5 years. All-cause mortality was registered and statistically analyzed for association with in-hospital clinical variables.

RESULTS

Included were 162 females and 200 males. Survival rates were 52.4% and 59%, respectively, (P=0.1). Advanced age and renal dysfunction (RD) were associated with low survival in both sexes (P<0.03 and 0.02, P<0.001 and 0.01, respectively). An association with low survival was found with respect to; admission for pulmonary edema (P<0.02), using furosemide >/=80 mg/day (P<0.005) and severe HF [NYHA class III-IV (P<0.01)] in females, as well as for hypokalemia (P<0.03) and hypocalcemia (P<0.03) in males. On multivariate analysis RD (P<0.001), increasing age (P=0.008) and furosemide dosage >/=80 mg (P=0.02) were most significantly associated with low survival in females, while RD only was significantly associated with low survival in males (P=0.03).

CONCLUSIONS

Several clinical variables, which affect prognosis in older HF patients are sex-related and probably carry practical significance.

Sex-differences in prevalence of electrocardiographic left ventricular hypertrophy in Type 2 diabetes: the Casale Monferrato Study

AIMS Although left ventricular hypertrophy (LVH) defined by either standard 12-lead ECG or echocardiography strongly predicts cardiovascular mortality, its prevalence in Type 2 diabetes is largely unknown. We have assessed prevalence of ECG-LVH and its relationship with clinical and metabolic variables in an Italian population-based cohort of subjects with Type 2 diabetes. METHODS The study-base was 965 (61.3%) subjects with Type 2 diabetes of the population-based cohort living in Casale Monferrato (Italy). LVH was defined by ECG Cornell voltage-duration product. All measurements were centralized. RESULTS ECG-LVH was diagnosed in 165/965 subjects, giving a prevalence of 17.1% (95% CI 14.7-19.5). Large sex differences were found, with higher prevalence in women (23.5%, 19.9-27.0) than in men (8.4%, 5.6-11.0), even after adjustment for age, BMI and hypertension (OR 3.83, 95% CI 2.5-5.9). At the examination, subjects with ECG-LVH were older than those without it. Similar age- and sex-adjusted values of HbA(1c), plasma lipids, fibrinogen, uric acid and creatinine were found in the two subgroups. No differences in prevalence of hypertension, CHD, increased QT duration or dispersion, micro- and macro-albuminuria were found between subjects with ECG-LVH and those without it. In logistic regression analysis, variables independently associated with ECG-LVH, after age-adjustment, were sex and diastolic blood pressure.

CONCLUSIONS

This population-based study shows: (i) a high prevalence of ECG-LVH in Type 2 diabetic subjects; (ii) 3-fold higher risk in women than in men, independently of age, BMI, and blood pressure; (iii) an independent association between ECG-LVH and diastolic blood-pressure. Screening for ECG-LVH in diabetic subjects is therefore recommended, particularly in diabetic women.

17 beta-estradiol inhibits cardiac fibroblast growth through both subtypes of estrogen receptor

The effect of 17 beta-estradiol (E2) on the proliferation of cardiac fibroblasts (CFs) remains controversial. This study investigated which subtype of estrogen receptor (ER), ER alpha or ER beta, mediated the effect of E2 on CF growth by the gain of function analysis using an adenovirus vector. One hundred nanomoles per liter of E2 attenuated DNA synthesis by up to 10%, and transactivated the estrogen-responsive element determined by luciferase assay in rat neonatal CFs. We constructed replication-deficient adenoviruses bearing the coding region of human ER alpha, ER beta, or the dominant-negative form of ER beta (designated AxCAER alpha, AxCAER beta, and AxCADNER beta, respectively). When CFs were infected with AxCAER alpha or AxCAER beta at multiplicity of infection of 20 or higher, DNA synthesis was decreased by 50% in response to E2 and the effect was abolished by co-infection with AxCADNER beta. Similarly, transcriptional activity of ER in CFs infected with AxCAER alpha or AxCAER beta was markedly enhanced and co-infection with AxCADNER beta abolished the effects. These results suggest that E2 inhibits CF growth and that both ER subtypes mediate the effect comparably and redundantly.

Morphological and functional changes in cardiac myocytes isolated from mice overexpressing TNF-alpha

Transgenic (TG) TNF1.6 mice, which cardiac specifically overexpress tumor necrosis factor-alpha (TNF-alpha), exhibit heart failure (HF) and increased mortality, which is markedly higher in young (<20 wk) males (TG-M) than females (TG-F). HF in this model may be partly caused by remodeling of the extracellular matrix and/or structure/function alterations at the single myocyte level. We studied left ventricular (LV) structure and function using echocardiography and LV myocyte morphometry, contractile function, and intracellular Ca(2+) (Ca(i)(2+)) handling using cell edge detection and fura 2 fluorescence, respectively, in 12-wk-old TG-M and TG-F mice and their wild-type (WT) littermates. TG-F mice showed LV hypertrophy without dilatation and only a small reduction of basal fractional shortening (FS) and response to isoproterenol (Iso). TG-M mice showed a large LV dilatation, higher mRNA levels of beta-myosin heavy chain and atrial natriuretic factor versus TG-F mice, reduced FS relative to both WT and TG-F mice, and minimal response to Iso. TG-F and TG-M myocytes were similarly elongated (by approximately 20%). The amplitude of Ca(i)(2+) transients and contractions and the response to Iso were comparable in WT and TG-F myocytes, whereas the time to 50% decline (TD(50%)) of the Ca(i)(2+) transient, an index of the rate of sarcoplasmic reticulum Ca(2+) uptake, was prolonged in TG-F myocytes. In TG-M myocytes, the amplitudes of Ca(i)(2+) transients and contractions were reduced, TD(50%) of the Ca(i)(2+) transient was prolonged, and the inotropic effect of Iso on Ca(i)(2+) transients was reduced approximately twofold versus WT myocytes. Protein expression of sarco(endo)plasmic reticulum Ca(2+)-ATPase 2 and phospholamban was unaltered in TG versus WT hearts, suggesting functional origins of impaired Ca(2+) handling in the former. These results indicate that cardiac-specific overexpression of TNF-alpha induces myocyte hypertrophy and gender-dependent alterations in Ca(i)(2+) handling and contractile function, which may at least partly account for changes in LV geometry and in vivo cardiac function in this model.

Cardiac norepinephrine release: modulation by ovariectomy and estrogen

Previously, we have demonstrated that in contrast to male rats, female rats do not show an age-related reduction of depolarization-elicited norepinephrine (NE) release from cardiac synaptosomes (resealed nerve terminals). These results suggest that sex hormones such as estrogen may modulate NE release from cardiac synaptosomes prepared from female rats. The present study was designed to test the hypotheses that long-term estrogen depletion, resulting from ovariectomy, and estrogen replacement alters depolarization-elicited NE release from cardiac synaptosomes. Female F344 rats were divided into two groups, one of which underwent bilateral ovariectomy, whereas the other underwent a sham operation. Three ovariectomized subgroups received daily injections of conjugated equine estrogens, delta8,9-dehydroestrone or 17 alpha-dihydroequilenin. Another ovariectomized control subgroup and the sham-operated animals received daily injections of vehicle. After 90 or 270 days of treatment, the animals were sacrificed. Cardiac synaptosomes were prepared from each heart, incubated with [(3)H]-NE, and used to evaluate NE release capacity by exposure to 50 mM K(+). The effectiveness of the ovariectomy and the estrogenic actions of the test compounds was confirmed by evaluating vaginal smears, determining uterine weights, and measuring serum luteinizing hormone (LH) concentrations. Ovariectomy (after both 90 and 270 days) significantly increased depolarization-induced NE release compared with sham-operated rats. Treatment with all three estrogenic preparations reduced NE release in ovariectomized rats to values similar to those observed in sham-operated animals. Interestingly, NE release rates from rats treated with conjugated estrogens for 270 but not 90 days were significantly below that observed in age-matched sham animals. These results demonstrate that estrogen modulates depolarization-elicited NE release from cardiac nerve terminals. Such modulation may represent a protective action by estrogen at the cardiac synapse.

Sex-based differences in the effect of digoxin for the treatment of heart failure

BACKGROUND

The Digitalis Investigation Group trial reported that treatment with digoxin did not decrease overall mortality among patients with heart failure and depressed left ventricular systolic function, although it did reduce hospitalizations slightly. Even though the epidemiologic features, causes, and prognosis of heart failure vary between men and women, sex-based differences in the effect of digoxin were not evaluated.

METHODS

We conducted a post hoc subgroup analysis to assess whether there were sex-based differences in the effect of digoxin therapy among the 6800 patients in the Digitalis Investigation Group study. The presence of an interaction between sex and digoxin therapy with respect to the primary end point of death from any cause was evaluated with the use of Mantel-Haenszel tests of heterogeneity and a multivariable Cox proportional-hazards model, adjusted for demographic and clinical variables.

RESULTS

There was an absolute difference of 5.8 percent (95 percent confidence interval, 0.5 to 11.1) between men and women in the effect of digoxin on the rate of death from any cause (P=0.034 for the interaction). Specifically, women who were randomly assigned to digoxin had a higher rate of death than women who were randomly assigned to placebo (33.1 percent vs. 28.9 percent; absolute difference, 4.2 percent, 95 percent confidence interval, -0.5 to 8.8). In contrast, the rate of death was similar among men randomly assigned to digoxin and men randomly assigned to placebo (35.2 percent vs. 36.9 percent; absolute difference, -1.6 percent; 95 percent confidence interval, -4.2 to 1.0). In the multivariable analysis, digoxin was associated with a significantly higher risk of death among women (adjusted hazard ratio for the comparison with placebo, 1.23; 95 percent confidence interval, 1.02 to 1.47), but it had no significant effect among men (adjusted hazard ratio, 0.93; 95 percent confidence interval, 0.85 to 1.02; P=0.014 for the interaction).

CONCLUSIONS

The effect of digoxin therapy differs between men and women. Digoxin therapy is associated with an increased risk of death from any cause among women, but not men, with heart failure and depressed left ventricular systolic function.

Estrogen pretreatment protects males against hypoxia-induced immune depression

Hypoxemia depresses cell-mediated immune functions in males, whereas proestrous females do not show such a depression. We hypothesized that elevated systemic estradiol levels in proestrous females prevent hypoxemia-induced immune depression. To study this hypothesis, male C3H/HeN mice were pretreated with 17 beta-estradiol (E(2), 40 microg/kg body wt sc) or vehicle for 3 days before induction of hypoxemia and again immediately before induction of hypoxia. The mice were subjected to hypoxemia (95% N(2)-5% O(2)) or sham hypoxemia (room air) for 60 min, and plasma and spleen cells were collected 2 h later. In vehicle-treated mice, splenocyte proliferation and interleukin-2 and interleukin-3 production were depressed after hypoxemia. E(2)-pretreated animals, however, displayed no such depression in splenic T cell parameters after hypoxemia. Splenic macrophage cytokine production was also depressed in vehicle-treated mice subjected to hypoxia, whereas it was normal in E(2)-pretreated mice. In summary, these findings indicate that administration of E(2) before hypoxemia prevented the depression of cell-mediated immune functions. Thus administration of 17 beta-estradiol in high-risk patients before major surgery might decrease hypoxemia-induced immune depression under those conditions.