Local delivery of a PKCε-activating peptide limits ischemia reperfusion injury in the aged female rat heart

PKCε inhibition prevents ischemia‑induced dendritic spine impairment in cultured primary neurons

Brain ischemia is an independent risk factor for Alzheimer's disease (AD); however, the mechanisms underlining ischemic stroke and AD remain unclear. The present study aimed to investigate the function of the ε isoform of protein kinase C (PKCε) in brain ischemia-induced dendritic spine dysfunction to elucidate how brain ischemia causes AD. In the present study, primary hippocampus and cortical neurons were cultured while an oxygen-glucose deprivation (OGD) model was used to simulate brain ischemia. In the OGD cell model, in vitro kinase activity assay was performed to investigate whether the PKCε kinase activity changed after OGD treatment. Confocal microscopy was performed to investigate whether inhibiting PKCε kinase activity protects dendritic spine morphology and function. G-LISA was used to investigate whether small GTPases worked downstream of PKCε. The results showed that PKCε kinase activity was significantly increased following OGD treatment in primary neurons, leading to dendritic spine dysfunction. Pre-treatment with PKCε-inhibiting peptide, which blocks PKCε activity, significantly rescued dendritic spine function following OGD treatment. Furthermore, PKCε could activate Ras homolog gene family member A (RhoA) as a downstream molecule, which mediated OGD-induced dendritic spine morphology changes and caused dendritic spine dysfunction. In conclusion, the present study demonstrated that the PKCε/RhoA signalling pathway is a novel mechanism mediating brain ischemia-induced dendritic spine dysfunction. Developing therapeutic targets for this pathway may protect against and prevent brain ischemia-induced cognitive impairment and AD.

iTRAQ-based quantitative proteomic analysis of the improved effects of total flavones of Dracocephalum Moldavica L. in chronic mountain sickness

To use isobaric tags for relative and absolute quantification (iTRAQ) technology to study the pathogenesis of chronic mountain sickness (CMS), identify biomarkers for CMS, and investigate the effect of total flavones of Dracocephalum moldavica L. (TFDM) on a rat model of CMS. We simulated high altitude hypobaric hypoxia conditions and generated a rat model of CMS. Following the administration of TFDM, we measured the pulmonary artery pressure and serum levels of hemoglobin (Hb), the hematocrit (Hct), and observed the structure of the pulmonary artery in experimental rats. Furthermore, we applied iTRAQ-labeled quantitative proteomics technology to identify differentially expressed proteins (DEPs) in the serum, performed bioinformatics analysis, and verified the DEPs by immunohistochemistry. Analysis showed that the pulmonary artery pressure, serum levels of Hb, and the Hct, were significantly increased in a rat model of CMS (P < 0.05). Pathological analysis of lung tissue and pulmonary artery tissue showed that the alveolar compartment had obvious hyperplasia and the pulmonary artery degree of muscularization was enhanced. Both pulmonary artery pressure and tissue morphology were improved following the administration of TFDM. We identified 532 DEPs by quantitative proteomics; gene ontology (GO)and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis further revealed that metabolic pathways associated with coagulation and complement play crucial roles in the occurrence of CMS. Immunohistochemistry verified that several DEPs (α-1-acid glycoprotein, collagen, fibulin, haptoglobin, PLTP, and TAGLN2) are important biological markers for CMS. Our analyses demonstrated that TFDM can improve CMS and exert action by influencing the metabolic pathways associated with coagulation and complement. This process relieves pulmonary artery pressure and improves lung function. We also identified that α-1-acid glycoprotein, collagen, fibulin, haptoglobin, PLTP, and TAGLN2 may represent potential biomarkers for CMS.

Inhibition of programmed necrosis limits infarct size through altered mitochondrial and immune responses in the aged female rat heart

Both advancing age and estrogen loss exacerbate acute myocardial infarction in the female heart. However, the mechanistic underpinnings of age-related differences in cell death after ischemia-reperfusion (I/R) injury in female subjects and reductions in cardioprotective reserve capacity remain largely unexplored. The aim of the present study was to determine the efficacy of programmed necrosis inhibition on infarct size reduction and preservation of left ventricular (LV) function after I/R injury with female aging. Fischer 344 rats were ovariectomized (OVX) at 15 mo and studied at 24 mo (MO OVX) versus adult rats with intact ovaries (6 mo). After in vivo coronary artery ligation (55-min ischemia and 2- or 6-h reperfusion), necrostatin-1 (Nec-1; 3.5 or 5.7 mg/kg) delivered upon reperfusion significantly reduced infarct size by 37% and improved LV function in the MO OVX group ( P < 0.01). Although age-associated elevations in cyclophilin D and mitochondrial acetylation ( P < 0.001) were unaffected by Nec-1, profound reductions in IL-1, IL-6, and TNF-α ( P < 0.05) as well as cardiac immune cell infiltration were observed in MO OVX but not adult rats. We conclude that chronic inflammation and postmenopausal estrogen deficiency conspire to exacerbate acute infarction through a mechanism involving exaggerated mitochondria-mediated programmed necrosis through receptor-interacting protein 1 signaling. Modulatory effects of programmed necrosis inhibition on proinflammatory cytokine production after I/R reveal a potentially important mechanistic target to restore and preserve cardiac function in the OVX aged female heart. NEW & NOTEWORTHY Myocardial infarct size reduction by inhibition of programmed necrosis in aged female subjects suggests a dominant cell death pathway. Alterations in mitochondrial protein levels and acetylation underscore a mitochondria-dependent mechanism, whereas the profound cytokine reduction in aged subjects alone points to a divergent role for immune modulation of programmed necrosis and viable therapeutic target.

Connexins in Cardiovascular and Neurovascular Health and Disease: Pharmacological Implications

Connexins are ubiquitous channel forming proteins that assemble as plasma membrane hemichannels and as intercellular gap junction channels that directly connect cells. In the heart, gap junction channels electrically connect myocytes and specialized conductive tissues to coordinate the atrial and ventricular contraction/relaxation cycles and pump function. In blood vessels, these channels facilitate long-distance endothelial cell communication, synchronize smooth muscle cell contraction, and support endothelial-smooth muscle cell communication. In the central nervous system they form cellular syncytia and coordinate neural function. Gap junction channels are normally open and hemichannels are normally closed, but pathologic conditions may restrict gap junction communication and promote hemichannel opening, thereby disturbing a delicate cellular communication balance. Until recently, most connexin-targeting agents exhibited little specificity and several off-target effects. Recent work with peptide-based approaches has demonstrated improved specificity and opened avenues for a more rational approach toward independently modulating the function of gap junctions and hemichannels. We here review the role of connexins and their channels in cardiovascular and neurovascular health and disease, focusing on crucial regulatory aspects and identification of potential targets to modify their function. We conclude that peptide-based investigations have raised several new opportunities for interfering with connexins and their channels that may soon allow preservation of gap junction communication, inhibition of hemichannel opening, and mitigation of inflammatory signaling.

Age and ischemia differentially impact mitochondrial ultrastructure and function in a novel model of age-associated estrogen deficiency in the female rat heart

Altered mitochondrial respiration, morphology, and quality control collectively contribute to mitochondrial dysfunction in the aged heart. Because myocardial infarction remains the leading cause of death in aged women, the present study utilized a novel rodent model to recapitulate human menopause to interrogate the combination of age and estrogen deficiency on mitochondrial ultrastructure and function with cardiac ischemia/reperfusion (I/R) injury. Female F344 rats were ovariectomized (OVX) at 15 months and studied at 24 months (MO OVX; n = 40) vs adult ovary intact (6 months; n = 41). Temporal declines in estrogen concomitant with increased visceral adipose tissue were observed in MO OVX vs adult. Following in vivo coronary artery ligation or sham surgery, state 3 mitochondrial respiration was selectively reduced by age in subsarcolemmal mitochondria (SSM) and by I/R in interfibrillar mitochondria (IFM); left ventricular maximum dP/dt was reduced in MO OVX (p < 0.05). Elevated cyclophilin D and exacerbated I/R-induced mitochondrial acetylation in MO OVX suggest permeability transition pore involvement and reduced protection vs adult (p < 0.05). Mitochondrial morphology by TEM revealed an altered time course of autophagy coordinate with attenuated Drp1 and LC3BII protein levels with age-associated estrogen loss (p < 0.05). Here, reductions in both SSM and IFM function may play an additive role in enhanced susceptibility to regional I/R injury in aged estrogen-deficient female hearts. Moreover, novel insight into altered cardiac mitochondrial quality control garnered here begins to unravel the potentially important regulatory role of mitochondrial dynamics on sustaining respiratory function in the aged female heart.

Evidence of Altered Mitochondrial Protein Expression After Chronic Ethanol Consumption in the Aged Estrogen-Deficient Female Rat Heart

BACKGROUND

Estrogen loss has been implicated to increase the risk of alcoholic cardiomyopathy in postmenopausal women. The purpose of this study was to identify novel mitochondrial protein targets for the treatment of alcoholic cardiomyopathy in aged women using a state-of-the-art proteomic approach. We hypothesized that chronic ethanol (EtOH) ingestion exacerbates maladaptive mitochondrial protein expression in the aged female heart.

METHODS

Adult (3 months) and aged (18 months) F344 ovary-intact or ovariectomized (OVX) rats were randomly assigned an EtOH or control Lieber-DeCarli "all-liquid" diet for 20 weeks. Proteomic analyses were conducted in mitochondria isolated from left ventricles using isobaric tags for relative and absolute quantification (iTRAQ) 8plex labeling and mass spectrometry (n = 3 to 5/group).

RESULTS

After EtOH, significant differences (false discovery rate <5%) were observed in electron transport chain components (NADH dehydrogenase [ubiquinone] flavoprotein 2) as well as proteins involved in lipid metabolism (2,4 dienoyl-CoA reductase) and cellular defense (catalase), suggesting a possible link to congestive heart failure. Directional changes in protein levels were confirmed by Western blotting. Additionally, EtOH significantly reduced state 3 mitochondrial respiration in all groups, yet only reduced respiratory control index in the aged OVX rat heart (p < 0.05).

CONCLUSIONS

Collectively, the data reveal that EtOH-induced changes in the mitochondrial proteome exacerbate cardiac dysfunction in aged and estrogen-deficient hearts, but not in adult. In conclusion, iTRAQ is a powerful tool for investigating new mitochondrial targets of alcoholic cardiomyopathy.

A new flavonoid glycoside (APG) isolated from Clematis tangutica attenuates myocardial ischemia/reperfusion injury via activating PKCε signaling

Clematis tangutica has been shown to be beneficial for the heart; however, the mechanism of this effectremains unknown. Apigenin-7-O-β-D-(-6″-p-coumaroyl)-glucopyranoside (APG) is a new flavonoid glycoside isolated from Clematis tangutica. This study investigates the effects of APG on myocardial ischemia/reperfusion (IR) injury (IRI). An IRI model of primary myocardial cells and mice was used in this study. Compared with the IR group, APG preconditioning is protective against IRI in primary myocardial cells and in mice hearts in a dose-dependent manner. The cardioprotective mechanisms of APG may involve a significant PKCε translocation into the mitochondria and an activation of the Nrf2/HO-1 pathway, which respectively suppressesmitochondrial oxidative stress and inhibits apoptosis. In addition, PKCε-targeted siRNA and a PKCε specialized inhibitor (ε-V1-2) were used to inhibit PKCε expression and activity. The inhibition of PKCε reversed the cardioprotective effect of APG, with an inhibition of Nrf2/HO-1 activation and increased mitochondrial oxidative stress and cardiomyocyte apoptosis. In conclusion, PKCε activation plays an important role in the cardioprotective effects of APG. PKCε activation induced by APG preconditioning reduces mitochondrial oxidative stress and promotes Nrf2/HO-1-mediated anti-apoptosis signaling.

Interaction of risk factors, comorbidities, and comedications with ischemia/reperfusion injury and cardioprotection by preconditioning, postconditioning, and remote conditioning

Pre-, post-, and remote conditioning of the myocardium are well described adaptive responses that markedly enhance the ability of the heart to withstand a prolonged ischemia/reperfusion insult and provide therapeutic paradigms for cardioprotection. Nevertheless, more than 25 years after the discovery of ischemic preconditioning, we still do not have established cardioprotective drugs on the market. Most experimental studies on cardioprotection are still undertaken in animal models, in which ischemia/reperfusion is imposed in the absence of cardiovascular risk factors. However, ischemic heart disease in humans is a complex disorder caused by, or associated with, cardiovascular risk factors and comorbidities, including hypertension, hyperlipidemia, diabetes, insulin resistance, heart failure, altered coronary circulation, and aging. These risk factors induce fundamental alterations in cellular signaling cascades that affect the development of ischemia/reperfusion injury per se and responses to cardioprotective interventions. Moreover, some of the medications used to treat these risk factors, including statins, nitrates, and antidiabetic drugs, may impact cardioprotection by modifying cellular signaling. The aim of this article is to review the recent evidence that cardiovascular risk factors and their medication may modify the response to cardioprotective interventions. We emphasize the critical need to take into account the presence of cardiovascular risk factors and concomitant medications when designing preclinical studies for the identification and validation of cardioprotective drug targets and clinical studies. This will hopefully maximize the success rate of developing rational approaches to effective cardioprotective therapies for the majority of patients with multiple risk factors.

Connexin 43 is an emerging therapeutic target in ischemia/reperfusion injury, cardioprotection and neuroprotection

Connexins are widely distributed proteins in the body that are crucially important for heart and brain functions. Six connexin subunits form a connexon or hemichannel in the plasma membrane. Interactions between two hemichannels in a head-to-head arrangement result in the formation of a gap junction channel. Gap junctions are necessary to coordinate cell function by passing electrical current flow between heart and nerve cells or by allowing exchange of chemical signals and energy substrates. Apart from its localization at the sarcolemma of cardiomyocytes and brain cells, connexins are also found in the mitochondria where they are involved in the regulation of mitochondrial matrix ion fluxes and respiration. Connexin expression is affected by age and gender as well as several pathophysiological alterations such as hypertension, hypertrophy, diabetes, hypercholesterolemia, ischemia, post-myocardial infarction remodeling or heart failure, and post-translationally connexins are modified by phosphorylation/de-phosphorylation and nitros(yl)ation which can modulate channel activity. Using knockout/knockin technology as well as pharmacological approaches, one of the connexins, namely connexin 43, has been identified to be important for cardiac and brain ischemia/reperfusion injuries as well as protection from it. Therefore, the current review will focus on the importance of connexin 43 for irreversible injury of heart and brain tissues following ischemia/reperfusion and will highlight the importance of connexin 43 as an emerging therapeutic target in cardio- and neuroprotection.

Angiotensin II and ischemic preconditioning synergize to improve mitochondrial function while showing additive effects on ventricular postischemic recovery

Recent studies indicate that the cardioprotective effects of ischemic preconditioning (IPC) against sustained ischemia/reperfusion can be replicated by angiotensin II (Ang II). However, it is not clear whether IPC and Ang II-induced preconditioning (APC) act through similar mechanisms or synergize to enhance cardioprotection. In this study, Langendorff-perfused rat hearts were subjected to IPC, APC, or their combination (IPC/APC) followed by ischemia/reperfusion. IPC, and less potently APC, significantly increased the percent recoveries of the left ventricular developed pressure, the first derivative of developed pressure, and the rate pressure product compared with control. Furthermore, the postischemic recovery of the heart was significantly higher for IPC/APC compared with IPC or APC. The improvements in cardiac function by IPC, APC, and IPC/APC were associated with similar reductions in lactate dehydrogenase release and infarct size. However, a significant improvement in mitochondrial respiration was observed with IPC/APC. The postischemic recovery observed with APC and IPC/APC was inhibited by treatment with losartan, an Ang II type-1 receptor blocker, during the preconditioning phase but not by chelerythrine, a pan-PKC inhibitor. Both drugs, however, abolished the enhanced mitochondrial respiration by IPC/APC. Altogether, these results indicate that APC and IPC interact through mechanisms that enhance cardioprotection by affecting cardiac function and mitochondrial respiration.

PKCε is a negative regulator of PVAT-derived vessel formation

RATIONALE

Vessel formation is a crucial event in tissue repair after injury. Thus, one assumption of innovative therapeutic approaches is the understanding of its molecular mechanisms. Notwithstanding our knowledge of the role of Protein Kinase C epsilon (PKCε) in cardio-protection and vascular restenosis, its role in vessel progenitor differentiation remains elusive.

OBJECTIVE

Given the availability of PKCε pharmacological modulators already tested in clinical trials, the specific aim of this study is to unravel the role of PKCε in vessel progenitor differentiation, with implications in vascular pathology and vasculogenesis.

METHODS AND RESULTS

Mouse Peri-Vascular Adipose Tissue (PVAT) was used as source of mesenchymal vessel progenitors. VEGF-induced differentiation of PVAT cells down-regulates both PKCε and p-PAK1 protein expression levels. PKCε overexpression and activation: i) reduced the expression levels of SMA and PECAM in endothelial differentiation of PVAT cells; ii) completely abrogated tubules formation in collagen gel assays; iii) increased the expression of p-PAK1.

CONCLUSION

PKCε negatively interferes with vessel progenitor differentiation via interaction with PAK-1.

Acute adiponectin delivery is cardioprotective in the aged female rat heart

AIM

The aged, post-menopausal female heart is characterized by reduced ischemic tolerance, and few therapies currently exist to limit ischemic damage. Adiponectin (APN), a cytokine produced in adipose tissue, limits infarct size and improves functional recovery after ischemia/reperfusion injury in adult hearts. The aim of the present study was to extend these previous studies and determine the cardioprotective efficacy of APN treatment in aged female rats.

METHODS

Hearts were isolated from adult (age 6-7 months; n = 10), aged (age 23 months; n = 14) and aged ovariectomized (n = 10) female rats, and subjected to ischemia/reperfusion injury. On ischemia, hearts were infused with 9 μg of APN or vehicle. Adiponectin receptor 1, adiponectin receptor 2 and adenosine monophosphate-dependent kinase (AMPK) were assessed by western blotting, tumor necrosis factor-α and nicotinamide adenine dinucleotide phosphate oxidase levels by real time polymerase chain reaction. Non-reducing western blotting for APN multimers in visceral adipose was also carried out.

RESULTS

APN infusion successfully improved post-ischemic left ventricular developed pressure (∼10-15%) and attenuated the rise in end diastolic pressure in all groups (P < 0.05). With ischemia/reperfusion injury, phospho-AMPK increased in all groups with additive effects of APN on increasing phospho-AMPK abundance in aged ovary-intact female rats only (P < 0.001). Age-associated increases in pre-ischemic tumor necrosis factor-α mRNA were unaffected by APN, whereas nicotinamide adenine dinucleotide phosphate oxidase 2 mRNA levels were attenuated by APN in adult and aged ovariectomized female rats. An age-associated decrease in cardiac adiponectin receptor 2 was observed in conjunction with elevated high molecular weight APN in adipose.

CONCLUSIONS

The present data suggest that APN might be a relevant therapy for protecting the aging female heart, albeit through divergent mechanisms that are likely influenced by age-associated estrogen availability.

Age-associated alterations of cardiac structure and function in the female F344xBN rat heart

The Fischer 344/NNiaHSD × Brown Norway/BiNia F1 (F344xBN) rat model exhibits an increased life span and fewer age-associated pathologies compared to commonly used Fischer 344 (F344). How aging may affect cardiac structure and function in these animals, has to our knowledge, not been investigated. Echocardiography was performed on female F344xBN rats at 6, 26, and 30 months of age using a Phillips 5500 Echocardiography system. Before sacrifice, electrocardiograms were measured in the female F344xBN in order to determine heart rhythm interval changes. Aging was associated with an increase in heart to body weight ratio, cardiomyocyte cross-sectional area, posterior wall thickening, and left ventricle chamber dilatation. Aging was associated with slight evidence of diastolic dysfunction. Alterations in heart rhythm intervals were associated with alterations in the spatial distribution of connexin 43. The incidence of arrhythmias was not different with age; however, valvular dysfunction was increased. These data suggest that aging in the female F344xBN rat heart is associated with changes in cardiac structure as well as function. Further investigation regarding other parameters of cardiac biochemistry and function is needed to better understand the normal compensated cardiovascular aging process in the female F344xBN.

Estrogen and the female heart

Estrogen has a plethora of effects in the cardiovascular system. Studies of estrogen and the heart span human clinical trials and basic cell and molecular investigations. Greater understanding of cell and molecular responses to estrogens can provide further insights into the findings of clinical studies. Differences in expression and cellular/intracellular distribution of the two main receptors, estrogen receptor (ER) α and β, are thought to account for the specificity and differences in responses to estrogen. Much remains to be learned in this area, but cellular distribution within the cardiovascular system is becoming clearer. Identification of GPER as a third ER has introduced further complexity to the system. 17β-estradiol (E2), the most potent human estrogen, clearly has protective properties activating a signaling cascade leading to cellular protection and also influencing expression of the protective heat shock proteins (HSP). E2 protects the heart from ischemic injury in basic studies, but the picture is more involved in the whole organism and clinical studies. Here the complexity of E2's widespread effects comes into play and makes interpretation of findings more challenging. Estrogen loss occurs primarily with aging, but few studies have used aged models despite clear evidence of differences between the response to estrogen deficiency in adult and aged animals. Thus more work is needed focusing on the effects of aging vs. estrogen loss on the cardiovascular system.

Chronic alcohol consumption disrupts myocardial protein balance and function in aged, but not adult, female F344 rats

The purpose of this study was to assess whether the deleterious effect of chronic alcohol consumption differs in adult and aged female rats. To address this aim, adult (4 mo) and aged (18 mo) F344 rats were fed a nutritionally complete liquid diet containing alcohol (36% total calories) or an isocaloric isonitrogenous control diet for 20 wk. Cardiac structure and function, assessed by echocardiography, as well as myocardial protein synthesis and proteolysis did not differ in either alcohol- versus control-fed adult rats or in adult versus aged control-fed rats. In contrast, cardiac function was impaired in alcohol-fed aged rats compared with age-matched control rats. Additionally, alcohol feeding decreased cardiac protein synthesis that was associated with decreased phosphorylation of 4E-BP1 and S6K1. This reduction in mammalian target of rapamycin (mTOR) kinase activity was associated with reduced eIF3f and binding of both Raptor and eIF4G to eIF3. Proteasome activity was increased in alcohol-fed aged rats with a coordinate elevation in the E3 ligases atrogin-1 and muscle RING-finger protein-1 (MuRF1). These changes were associated with increased regulated in development and DNA damage response 1 (REDD1) and phosphorylation of AMP-activated protein kinase (AMPK) but no increase in AKT or forkhead transcription factor (FOXO)3 phosphorylation. Finally, markers of autophagy (e.g., LC3B, Atg7, Atg12) and TNF-α were increased to a greater extent in alcohol-fed aged rats. These data demonstrate that aged female rats exhibit an enhanced sensitivity to alcohol compared with adult animals. Our data are consistent with a model whereby alcohol increases proteolysis via FOXO-independent increase in atrogin-1, which degrades eIF3f and therefore impairs formation of a functional preinitiation complex and protein synthesis.

The impact of ovariectomy on calcium homeostasis and myofilament calcium sensitivity in the aging mouse heart

This study determined whether deficiency of ovarian estrogen starting very early in life promoted age-associated Ca(2+) dysregulation and contractile dysfunction in isolated ventricular myocytes. Myocytes were isolated from anesthetized C57BL/6 female mice. Animals received an ovariectomy or sham-operation at one month and were aged to ~24 months. Excitation-contraction coupling parameters were compared in fura-2 loaded myocytes (37°C). While Ca(2+) transients were larger and faster in field-stimulated myocytes from ovariectomized mice, ovariectomy had no effect on peak fractional shortening. Similarly, ovariectomy had no effect on fractional shortening measured in vivo by echocardiography (values were 60.5 ± 2.9 vs. 60.3 ± 2.5% in sham and ovariectomized, respectively; n=5 mice/group). Ovariectomy did decrease myofilament Ca(2+) sensitivity, as evidenced by a 26% increase in the Ca(2+) required to activate actomyosin MgATPase in ovariectomized hearts. Larger Ca(2+) transients were attributable to a 48% increase in peak Ca(2+) current, along with an increase in the amplitude, width and frequency of Ca(2+) sparks measured in fluo-4 loaded myocytes. These changes in Ca(2+) handling were not due to increased expression of Ca(2+) channels (Cav1.2), sarcoplasmic reticulum Ca(2+) ATPase (SERCA2) or Na(+)-Ca(2+) exchanger in ovariectomized hearts. However, ovariectomy increased sarcoplasmic reticulum Ca(2+) stores by ~90% and promoted spontaneous Ca(2+) release from the sarcoplasmic reticulum when compared to sham controls. These observations demonstrate that long-term ovariectomy promotes intracellular Ca(2+) dysregulation, reduces myofilament Ca(2+) sensitivity and increases spontaneous Ca(2+) release in the aging female heart.

Age-related differences in cardiac ischemia-reperfusion injury: effects of estrogen deficiency

Despite conflicting evidence for the efficacy of hormone replacement therapy in cardioprotection of postmenopausal women, numerous studies have demonstrated reductions in ischemia/reperfusion (I/R) injury following chronic or acute exogenous estradiol (E2) administration in adult male and female, gonad-intact and gonadectomized animals. It has become clear that ovariectomized adult animals may not accurately represent the combined effects of age and E2 deficiency on reductions in ischemic tolerance seen in the postmenopausal female. E2 is known to regulate the transcription of several cardioprotective genes. Acute, non-genomic E2 signaling can also activate many of the same signaling pathways recruited in cardioprotection. Alterations in cardioprotective gene expression or cardioprotective signal transduction are therefore likely to result within the context of aging and E2 deficiency and may help explain the reduced ischemic tolerance and loss of cardioprotection in the senescent female heart. Quantification of the mitochondrial proteome as it adapts to advancing age and E2 deficiency may also represent a key experimental approach to uncover proteins associated with disruptions in cardiac signaling contributing to age-associated declines in ischemic tolerance. These alterations have important ramifications for understanding the increased morbidity and mortality due to ischemic cardiovascular disease seen in postmenopausal females. Functional perturbations that occur in mitochondrial respiration and Ca(2+) sensitivity with age-associated E2 deficiency may also allow for the identification of alternative therapeutic targets for reducing I/R injury and treatment of the leading cause of death in postmenopausal women.

Promoter methylation of Egr-1 site contributes to fetal hypoxia-mediated PKCε gene repression in the developing heart

Fetal hypoxia causes protein kinase Cε (PKCε) gene repression in the heart resulting in heightened ischemic injury in male offspring in a sex-dependent manner. The present study tested the hypothesis that heightened methylation of the early growth response factor-1 (Egr-1) binding site at PKCε gene promoter contributes to sex dimorphism of hypoxia-induced programming of PKCε gene repression in the developing heart. Pregnant rats were divided into normoxic and hypoxic (10.5% O2 from day 15 to 21 of gestation) groups. Hypoxia selectively decreased PKCε mRNA and protein abundance in the heart of male, but not female, near-term (21 days) fetuses. Methylation of the CpG site at the Egr-1 binding site of PKCε promoter was significantly increased in the male hearts by hypoxia, resulting in decreased Egr-1 binding affinity and reduced Egr-1 binding to the PKCε promoter. Nuclear Egr-1 levels were not affected by hypoxia. There was significantly higher abundance of estrogen receptor α (ERα) and β (ERβ) isoforms in female than in male fetal hearts, which were not significantly altered by hypoxia. Both ERα and ERβ bind to the Egr-1 binding site with significant greater levels in the female fetal hearts. The increased methylation with reduced Egr-1 binding and PKCε gene repression persisted in 3-mo-old adult male hearts in a sex-dependent manner. The results indicate a key role for heightened methylation of the Egr-1 binding site in hypoxia-mediated programming of PKCε gene repression in the developing heart and suggest a novel protective mechanism of ER by binding to the Egr-1 binding site in epigenetic regulation of PKCε gene expression patterns in the early developmental stage.

Quantitative proteomic analysis reveals novel mitochondrial targets of estrogen deficiency in the aged female rat heart

The incidence of myocardial infarction rises sharply at menopause, implicating a potential role for estrogen (E(2)) loss in age-related increases in ischemic injury. We aimed to identify quantitative changes to the cardiac mitochondrial proteome of aging females, based on the hypothesis that E(2) deficiency exacerbates age-dependent disruptions in mitochondrial proteins. Mitochondria isolated from left ventricles of adult (6 mo) and aged (24 mo) F344 ovary-intact or ovariectomized (OVX) rats were labeled with 8plex isobaric tags for relative and absolute quantification (iTRAQ; n = 5-6/group). Groups studied were adult, adult OVX, aged, and aged OVX. In vivo coronary artery ligation and in vitro mitochondrial respiration studies were also performed in a subset of rats. We identified 965 proteins across groups and significant directional changes in 67 proteins of aged and/or aged OVX; 32 proteins were unique to aged OVX. Notably, only six proteins were similarly altered in adult OVX (voltage-dependent ion channel 1, adenine nucleotide translocator 1, cytochrome c oxidase subunits VIIc and VIc, catalase, and myosin binding protein C). Proteins affected by aging were primarily related to cellular metabolism, oxidative stress, and cell death. The largest change occurred in monoamine oxidase-A (MAO-A), a source of oxidative stress. While acute MAO-A inhibition induced mild uncoupling in aged mitochondria, reductions in infarct size were not observed. Age-dependent alterations in mitochondrial signaling indicate a highly selective myocardial response to E(2) deficiency. The combined proteomic and functional approaches described here offer possibility of new protein targets for experimentation and therapeutic intervention in the aged female population.