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.

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.

Abstract 162: Influence of Age and Ischemia on Cardiac Subsarcolemmal and Interfibrillar Mitochondria in a Novel Model of Estrogen Deficiency

Altered mitochondrial respiration (MR) and calcium retention capacity (CRC) are proposed cardiac cell death mechanisms exacerbated by aging in males. The present study aimed, for the first time, to determine changes in mitochondrial subpopulation function with age and ischemia/reperfusion (I/R) injury in the female heart. A novel model to recapitulate human menopause/age interactions was used in F344 female rats ovariectomized (OVX) at 15mo and studied at 24mo (MO OVX; n=15), vs adult (6mo; n=18). MR and CRC were assessed in isolated subsarcolemmal (SSM) and interfibrillar (IFM) mitochondria following in vivo coronary artery ligation (CAL; 31 min I and 10 min R) or sham. State 3 MR energized by either complex I (CI) or complex II (CII) substrates was selectively reduced by age in SSM (p<.02), and by I/R in IFM (p<.05). The I/R-dependent decrease in CRC was 64% (18 vs 29.5) greater in MO OVX vs. adult IFM, suggesting earlier mitochondrial permeability transition pore (MPTP) opening. At CI, but not CII, cyclosporine A (CsA) enhanced CRC 20% (103 vs 86) more in SSM and 75% (98 vs 56) more in IFM from adult compared to MO OVX, suggesting reduced protective efficacy with age and MPTP involvement. Additionally, mitochondrial cyclophilin D increases with age, while cytoplasmic RIP1 is increased with age and I/R further implicating the MPTP mechanism and link with programmed necrosis in the aged female heart. In contrast to males, our data suggest a sex-specific phenotype whereby reductions in both SSM and IFM dynamics may play an additive role in the enhanced susceptibility to I/R injury and myocardial infarction in the aged female heart, which remains the leading cause of death in older women.

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.

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.

Divergent effects of aging and sex on vasoconstriction to endothelin in coronary arterioles

OBJECTIVE

The risk for cardiovascular disease increases with advancing age; however, the chronological development of heart disease differs in males and females. The purpose of this study was to determine whether age-induced alterations in responses of coronary arterioles to the endogenous vasoconstrictor, endothelin, are sex-specific.

METHODS

Coronary arterioles were isolated from young and old male and female rats to assess vasoconstrictor responses to endothelin (ET), and ETa and ETb receptor inhibitors were used to assess receptor-specific signaling.

RESULTS

In intact arterioles from males, ET-induced vasoconstriction was reduced with age, whereas age increased vasoconstrictor responses to ET in intact arterioles from female rats. In intact arterioles from both sexes, blockade of either ETa or ETb eliminated age-related differences in responses to ET; however, denudation of arterioles from both sexes revealed age-related differences in ETa-mediated vasoconstriction. In arterioles from male rats, ETa receptor protein decreased, whereas ETb receptor protein increased with age. In coronary arterioles from females, neither ETa nor ETb receptor protein changed with age, suggesting age-related changes in ET signaling occur downstream of ET receptors.

CONCLUSIONS

Thus, aging-induced alterations in responsiveness of the coronary resistance vasculature to endothelin are sex-specific, possibly contributing to sexual dimorphism in the risk of cardiovascular disease with advancing age.

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.

Aging accentuates alcohol-induced decrease in protein synthesis in gastrocnemius

The present study sought to determine whether the protein catabolic response in skeletal muscle produced by chronic alcohol feeding was exaggerated in aged rats. Adult (3 mo) and aged (18 mo) female F344 rats were fed a nutritionally complete liquid diet containing alcohol (36% of total calories) or an isocaloric isonitrogenous control diet for 20 wk. Muscle (gastrocnemius) protein synthesis, as well as mTOR and proteasome activity did not differ between control-fed adult and aged rats, despite the increased TNF-α and IL-6 mRNA and decreased IGF-I mRNA in muscle of aged rats. Compared with alcohol-fed adult rats, aged rats demonstrated an exaggerated alcohol-induced reduction in lean body mass and protein synthesis (both sarcoplasmic and myofibrillar) in gastrocnemius. Alcohol-fed aged rats had enhanced dephosphorylation of 4E-BP1, as well as enhanced binding of raptor with both mTOR and Deptor, and a decreased binding of raptor with 4E-BP1. Alcohol feeding of both adult and aged rats reduced RagA binding to raptor. The LKB1-AMPK-REDD1 pathway was upregulated in gastrocnemius from alcohol-fed aged rats. These exaggerated alcohol-induced effects in aged rats were associated with a greater decrease in muscle but not circulating IGF-I, but no further increase in inflammatory mediators. In contrast, alcohol did not exaggerate the age-induced increase in atrogin-1 and MuRF1 mRNA or the increased proteasome activity. Our results demonstrate that, compared with adult rats, the gastrocnemius from aged rats is more sensitive to the catabolic effects of alcohol on protein synthesis, but not protein degradation, and this exaggerated response may be AMPK-dependent.

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.

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.

Comparison of the agar block and Lieber-DeCarli diets to study chronic alcohol consumption in an aging model of Fischer 344 female rats

INTRODUCTION

Post-menopausal women have a greater risk of developing alcoholic complications compared to age-matched men. Unfortunately, animal models of chronic ethanol consumption with estrogen deficiency are lacking. Here, we characterize the ability of the agar block and Lieber-DeCarli models of chronic ethanol consumption to produce elevated blood alcohol content (BAC) and liver pathology in the F344 postmenopausal animal model of aging.

METHODS

Adult (3 mo) and aged (18 mo) F344 ovary-intact or ovariectomized rats were administered ethanol for 14-20 weeks as follows: diet 1, standard chow access, 10% ethanol in drinking water, and 40% ethanol in agar blocks; diet 2, diet 1 plus low phytoestrogen chow (known to affect ethanol metabolism) for the final 4 weeks; diet 3, Lieber-DeCarli all liquid diet with 36% kcal ethanol. Control animals were matched isocalorically with dextrin.

RESULTS

For the agar block diet, average BAC was 13±4 mg/dL across groups. BAC was unaffected by reducing dietary phytoestrogen content (12±4 mg/dL), which is known to interfere with ethanol metabolism. Liver pathology was unaffected by the agar block diet. In contrast, the Lieber-DeCarli diet resulted in BAC of 45±5 mg/dL in conjunction with more severe hepatopathology.223

DISCUSSION

We conclude that the Lieber-DeCarli diet produces greater BAC and hepatopathology to study the effects of chronic ethanol administration in the F344 postmenopausal rodent model of aging when compared to an ethanol agar block diet.

Abstract 342: Increased Mitochondrial Permeability Transition Pore Opening Dominates Ischemia-Reperfusion Injury in the Aged Female Rat Heart

Background: Cardiovascular disease remains the leading cause of death in older post-menopausal women. Ischemia/Reperfusion (I/R) injury triggers mitochondrial calcium (Ca 2+ ) overload inducing mitochondrial permeability transition pore (MPTP) opening, mitochondrial dysfunction, and cell death potentially by necrosis, apoptosis, and/or autophagy.

Purpose: We sought to determine if age-associated estrogen deficiency increases mitochondrial Ca 2+ sensitivity, providing a possible mechanism for increased vulnerability to I/R injury in older women.

Methods: Mitochondrial respiration (MR) was assessed in isolated mitochondria from ventricles of adult (6 mo; n=15) and aged (24 mo; n=18) ovary-intact or ovariectomized (OVX) female F344 rats. MR at complexes I and II was compared in the absence (State 2) and presence (State 3) of ADP to calculate respiratory control index (RCI; state3/state 2). Reduced RCI following Ca 2+ addition was used to assess Ca 2+ sensitivity, while mitochondrial Ca 2+ retention capacity was measured to quantify MPTP opening (CRC; n=4-5/group) prior to and following coronary artery ligation (55 min I and 6 hr R). Apoptosis was examined using DNA laddering and terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL). Markers of autophagy were evaluated by western blotting and mitochondrial morphology through electron microscopy (EM).

Results: Significant age-dependent decreases in RCI for complex I (12%) and complex II (8%) were observed in the absence of Ca 2+ , and correlated with increased necrosis in aged hearts revealed by triphenyltetrazolium chloride (TTC) staining (p < 0.05). Ca 2+ exposure decreased MR (18-30%; p < 0.05) in Complex I of aged and OVX mitochondria vs adults. Furthermore, CRC worsened with age requiring less Ca 2+ to open the MPTP. Reduced DNA laddering and TUNEL staining combined with increased beclin-1 and cathepsinD expression in aged vs. adult further support a dominant role for necrosis over apoptosis underlying cell death in aged females (n=4-5/group). EM revealed morphological alterations with age and OVX.

Conclusion: Decreased MR and increased MPTP opening with aging are likely causal in necrotic cell death mechanisms associated with I/R injury observed in post-menopausal women.

Age-dependent reductions in mitochondrial respiration are exacerbated by calcium in the female rat heart

BACKGROUND

Cardiovascular disease mortality increases rapidly after menopause by poorly defined mechanisms.

OBJECTIVE

Because mitochondrial function and Ca(2+) sensitivity are important regulators of cell death after myocardial ischemia, we sought to determine whether aging and/or estrogen deficiency (ovariectomy) increased mitochondrial Ca(2+) sensitivity.

METHODS

Mitochondrial respiration was measured in ventricular mitochondria isolated from adult (6 months; n = 26) and aged (24 months; n = 25), intact or ovariectomized female rats using the substrates α-ketoglutarate/malate (complex I); succinate/rotenone (complex II); ascorbate/N,N,N',N'-tetramethyl-p-phenylenediamine/antimycin (complex IV). State 2 and 3 respiration was initiated by sequential addition of mitochondria and adenosine diphosphate. Ca(2+) sensitivity was assessed by Ca(2+)-induced swelling of de-energized mitochondria and reduction in state 3 respiration. Propylpyrazole triol (PPT) was administered intraperitoneally 45 minutes before euthanasia to assess mitochondrial protective effects through estrogen receptor (ER) α activation.

RESULTS

Aging decreased the respiratory control index (RCI; state 3/state 2) for complexes I and II by 12% and 8%, respectively, independent of ovary status (P < 0.05). Of interest, Ca(2+) induced a greater decrease (18%-30%; P < 0.05) in complex I state 3 respiration in aged and ovariectomized animals, and mitochondrial swelling occurred twice as quickly in aged (vs adult) female rats (P < 0.05). Pretreatment with PPT increased RCI by 8% and 7% at complexes I and II, respectively (P < 0.05) but surprisingly increased Ca(2+) sensitivity.

CONCLUSIONS

Age-dependent decreases in RCI and sensitization to Ca(2+) may explain in part the age-associated reductions in female ischemic tolerance; however, protection afforded by ER agonism involves more complex mechanisms.

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

Reduced efficacy of cardioprotective interventions in the aged female heart, including estrogen replacement, highlights the need for alternative therapeutics to reduce myocardial ischemia-reperfusion (I/R) injury in postmenopausal women. Here, we sought to determine the efficacy of protein kinase-Cε (PKCε)-mediated cardioprotection in the aged, estradiol-deficient rat heart. Infarct size and functional recovery were assessed in Langendorff-perfused hearts from adult (5 mo) or aged (23 mo) female Fisher 344 ovary-intact or ovariectomized (OVX) rats administered a PKCε-activator, receptor for activated C kinase (ψεRACK) prior to 47-min ischemia and 60-min reperfusion. Proteomic analysis was conducted on left ventricular mitochondrial fractions treated with ψεRACK prior to I/R, utilizing isobaric tags for relative and absolute quantitation (iTRAQ) 8plex labeling and tandem mass spectrometry. Real-time PCR was utilized to assess connexin 43 (Cx43) and RACK2 mRNA post-I/R. Greater infarct size in aged OVX (78%) vs. adult (37%) was reduced by ψεRACK (35%, P < 0.0001) and associated with greater mitochondrial PKCε localization (P < 0.0003). Proteomic analysis revealed three novel mitochondrial targets of PKCε-mediated cardioprotection with aging (P < 0.05): the antioxidant enzymes glutathione peroxidase (GPX) and MnSOD2, and heat shock protein 10. Finally, decreased levels of Cx43 and RACK2 mRNA seen with age were partially abrogated by administration of ψεRACK (P < 0.05). The mechanisms described here may represent important therapeutic candidates for the treatment of acute myocardial infarction in postmenopausal women and age-associated estradiol deficiency.

Increased estrogen receptor β in adipose tissue is associated with increased intracellular and reduced circulating adiponectin protein levels in aged female rats

BACKGROUND

Obesity and associated metabolic and cardiovascular disease risk are correlated with reduced circulating adiponectin (APN) levels. Metabolic and cardiovascular disease risk is also increased after menopause and may be linked to disturbances in estrogen receptor (ER) signaling in adipose.

OBJECTIVE

We hypothesized that age-associated estrogen (E(2))-deficiency alters the ERα/β ratio in adipose tissue and increases risk for metabolic disease via APN-ac activated mechanisms.

METHODS

Visceral adipose was isolated from adult (6 months) and aged (24 months) female Fisher 344 rats (n = 5-6/group) with ovaries intact or removed by surgical ovariectomy (OVX) and subjected to western blotting.

RESULTS

Notably, weight was greatest in aged OVX rats (P < 0.01) and associated with a 2-fold increase in ERβ protein versus adult intact rats (P < 0.001). ER levels were increased in aged OVX versus adult OVX rats. Intra-adipocyte APN was also increased in aged OVX rats versus all groups (P < 0.01), whereas circulating APN levels decreased in aged OVX versus adult OVX rats (P < 0.05). Endoplasmic reticulum protein of 44 kDa (Erp44) levels remained the same (P = 0.09). Adiponectin receptor-1 (AdipoR1) and peroxisome proliferator-activated receptor-α (PPAR-α) were also unchanged. AdipoR2, PPAR-γ, and phosphorylated adenosine monophosphate-dependant kinase (pAMPK) to total AMPK ratio all decreased with age (P < 0.05).

CONCLUSIONS

Collectively, these data suggested that age-associated increases in ERβ paired with decreased PPAR-γ levels might predispose E(2)-deficient postmenopausal women for increased adiposity and associated metabolic and cardiovascular disease risk. Reduced circulating APN and AdipoR2 levels might contribute to age and E(2)-deficiency linked disease progression.

Estrogen receptor beta does not influence ischemic tolerance in the aged female rat heart

INTRODUCTION

Ischemic heart disease remains the leading cause of morbidity and mortality in aged women, with a 2- to 3-fold increase in incidence following menopause. Clinical trials have failed to demonstrate cardioprotective benefit from chronic estrogen (E(2)) replacement therapy, yet protective effects of E(2) have been demonstrated in adult animal models and are mediated by the estrogen receptor (ER) subtypes ERα and ERβ.

AIMS

The aim of this study was to determine the effects of acute ERβ activation on ischemia/reperfusion (I/R) injury in adult, aged, and aged E(2)-deficient female rats.

METHODS

Hearts were isolated from adult (6 months; n = 9), aged (24 months; n = 13), and aged ovariectomized (OVX; n = 14) female Fischer 344 rats and subjected to 47 min of global I and 60 min of R. Rats were acutely treated with the ERβ-agonist diarylpropionitrile (DPN; 5 μg/kg) or vehicle 45 min prior to I/R; ERβ mRNA and protein levels were also assessed.

RESULTS

Acute treatment with DPN had no effect on functional recovery following I/R injury in adult, aged, or aged OVX female rats. Additionally, we were unable to detect ERβ mRNA or protein in the adult or aged female rat myocardium.

CONCLUSIONS

Here, for the first time, our data suggest that acute ERβ activation does not impact ischemic tolerance in the adult or aged female Fischer 344 rat myocardium and this likely due to a lack of detectable ERβ.

From syncitium to regulated pump: a cardiac muscle cellular update

The primary purpose of this article is to present a basic overview of some key teaching concepts that should be considered for inclusion in an six- to eight-lecture introductory block on the regulation of cardiac performance for graduate students. Within the context of cardiac excitation-contraction coupling, this review incorporates information on Ca(2+) microdomains and local control theory, with particular emphasis on the role of Ca(2+) sparks as a key regulatory component of ventricular myocyte contraction dynamics. Recent information pertaining to local Ca(2+) cycling in sinoatrial nodal cells (SANCs) as a mechanism underlying cardiac automaticity is also presented as part of the recently described coupled-clock pacemaker system. The details of this regulation are emerging; however, the notion that the sequestration and release of Ca(2+) from internal stores in SANCs (similar to that observed in ventricular myocytes) regulates the rhythmic excitation of the heart (i.e., membrane ion channels) is an important advancement in this area. The regulatory role of cardiac adrenergic receptors on cardiac rate and function is also included, and fundamental concepts related to intracellular signaling are discussed. An important point of emphasis is that whole organ cardiac dynamics can be traced back to cellular events regulating intracellular Ca(2+) homeostasis and, as such, provides an important conceptual framework from which students can begin to think about whole organ physiology in health and disease. Greater synchrony of Ca(2+)-regulatory mechanisms between ventricular and pacemaker cells should enhance student comprehension of complex regulatory phenomenon in cardiac muscle.

Rapid estrogen receptor-alpha activation improves ischemic tolerance in aged female rats through a novel protein kinase C epsilon-dependent mechanism

The effects of estrogen deficiency on the loss of cardioprotection with advancing age are complex and poorly understood. A major focus of the current study was to uncover a cardioprotective role for rapid, nongenomic estrogen receptor (ER) signaling in the aged female myocardium. We hypothesized that selective ERalpha activation in aged females would reduce infarct size in part, through reversal of age-associated reductions in mitochondrial protein kinase Cepsilon (PKCepsilon). Hearts isolated from adult (6 month old) and aged (23-24 months old) female F344 rats with ovaries removed (n = 20 per group) were subjected to ischemia/reperfusion (47 min global ischemia). Rats were injected sc with the ERalpha agonist propylpyrazole triol (PPT) or vehicle 45 min before heart isolation (5 microg/kg). Infarct size was greatest in aged vs. adult ovariectomized rats, significantly reduced by PPT, and the protection reversed by prior administration of the ER inhibitor ICI 182,780 (3 mg/kg). Increased ERalpha particulate targeting occurred after PPT in conjunction with reversal of age-related reductions in nuclear PKCepsilon, mitochondrial PKCepsilon and pAkt (P < 0.05). PPT also increased mRNA levels for the PKCepsilon anchoring protein, receptor for activated C kinase2 (RACK2; P < 0.05). Our data suggest, for the first time, that selective ERalpha activation reduces ischemic injury in the aged, estrogen-deficient heart through a mechanism involving nongenomic redistribution of ERalpha and PKCepsilon activation. A novel feed-forward transcriptional mechanism to potentially enhance PKCepsilon-RACK2 interactions was also observed. Collectively, our findings may provide key insight into developing targeted therapeutic interventions in postmenopausal women to reduce ischemia/reperfusion injury, including selective ERalpha mimetics.

Local delivery of PKCepsilon-activating peptide mimics ischemic preconditioning in aged hearts through GSK-3beta but not F1-ATPase inactivation

In adult heart, selective PKCepsilon activation limits ischemia (I)-reperfusion (R) damage and mimics the protection associated with ischemic preconditioning. We sought to determine whether local delivery of PKCepsilon activator peptide psiepsilon-receptor for activated C-kinase (psiepsilon-RACK) is sufficient to produce a similarly protected phenotype in aged hearts. Langendorff-perfused hearts isolated from adult (5 mo; n = 9) and aged (24 mo; n = 9) male Fisher 344 rats were perfused with psiepsilon-RACK conjugated to Tat (500 nM) or Tat only (500 nM) for 10 min before global 31-min ischemia. Western blotting was used to measure mitochondrial targeting of PKCepsilon, PKCdelta, phospho (p)-GSK-3beta (Ser(9)) and GSK-3beta in hearts snap-frozen during I. Recovery of left ventricular developed pressure was significantly improved by psiepsilon-RACK (P < 0.01) and infarct size reduced in 24-mo rats vs. age-matched controls (60% vs. 34%; P < 0.01). Mitochondrial PKCepsilon levels were 30% greater during I with psiepsilon-RACK in aged vs. control rats (P < 0.01). Interestingly, mitochondrial GSK-3beta levels were threefold greater in aged vs. adult rats during I, and psiepsilon-RACK prevented this increase (P < 0.01). Mitochondrial p-GSK-3beta levels were also greater in aged rats after psiepsilon-RACK (P < 0.01), and subsequent inhibition of GSK-3beta with SB-216763 (3 muM) before I/R elicited protection similar to that of psiepsilon-RACK (n = 3/group). Mitochondrial proteomic analysis further identified group differences in the F(1)-ATPase beta-subunit, and coimmunoprecipitation studies revealed a novel interaction with PKCepsilon. F(1)-ATPase-PKCepsilon association was affected by psiepsilon-RACK in adult but not aged rats. Our results provide evidence, for the first time, for PKCepsilon-mediated protection in aged rat heart after I/R and suggest a central role for mitochondrial GSK-3beta but not F(1)-ATPase as a potential target of PKCepsilon to limit I/R damage with aging.

PKCδ mediates anti-proliferative, pro-apoptic effects of testosterone on coronary smooth muscle

Sex hormone status has emerged as an important modulator of coronary physiology and cardiovascular disease risk in both males and females. Our previous studies have demonstrated that testosterone increases protein kinase C (PKC) δ expression and activity in coronary smooth muscle (CSMC). Because PKCδ has been implicated in regulation of proliferation and apoptosis in other cell types, we sought to determine if testosterone modulates CSMC proliferation and/or apoptosis through PKCδ. Porcine CSMC cultures (passages 2–6) from castrated males were treated with testosterone for 24 h. Testosterone (20 and 100 nM) decreased [3H]thymidine incorporation in proliferating CSMC to 59 ± 5.3 and 33.1 ± 4.5% of control. Flow cytometric analysis demonstrated that testosterone induced G1arrest in CSMC with a concomitant reduction in the S phase cells. Testosterone reduced protein levels of cyclins D1and E and phosphorylation of retinoblastoma protein while elevating levels of p21cip1and p27kip1. There were no significant differences in the levels of cyclins D3, CDK2, CDK4, or CDK6. Testosterone significantly reduced kinase activity of CDK2 and -6, but not CDK4, -7, or -1. PKCδ small interfering RNA (siRNA) prevented testosterone-mediated G1arrest, p21cip1upregulation, and cyclin D1and E downregulation. Furthermore, testosterone increased CSMC apoptosis in a dose-dependent manner, which was blocked by either PKCδ siRNA or caspase 3 inhibition. These findings demonstrate that the anti-proliferative, pro-apoptotic effects of testosterone on CSMCs are substantially mediated by PKCδ.

Estrogen deficiency decreases ischemic tolerance in the aged rat heart: roles of PKCδ, PKCε, Akt, and GSK3β

The mechanisms underlying the age-dependent reversal of female cardioprotection are poorly understood and complicated by findings that estrogen replacement is ineffective at reducing cardiovascular mortality in postmenopausal women. Although several protective signals have been identified in young animals, including PKC and Akt, how these signals are affected by age, estrogen deficiency, and ischemia-reperfusion (I/R) remains unknown. To determine the independent and combined effects of age and estrogen deficiency on I/R injury and downstream PKC-Akt signaling, adult and aged female F344 rats ( n = 12/age) with ovaries intact or ovariectomy (Ovx) were subjected to I/R using Langendorff perfusion (31-min global-ischemia). Changes in cytosolic (s), nuclear (n), mitochondrial (m) PKC (δ, ε) levels, and changes in total Akt and mGSK-3β phosphorylation after I/R were assessed by Western blot analysis. Senescence increased infarct size 50% in ovary-intact females ( P < 0.05), whereas no differences in LV functional recovery or estradiol levels were observed. Ovx reduced functional recovery to a greater extent in aged compared with adult rats ( P < 0.05). In aged (vs. adult), levels of m- and nPKC(-δ, -ε) were markedly decreased, whereas mGSK3β levels were increased ( P < 0.05). Ovx led to greater levels of sPKC(-δ, -ε) independent of age ( P < 0.05). I/R reduced p-Akt(Ser473) levels by 57% and increased mGSK-3β accumulation 1.77-fold ( P < 0.05) in aged, ovary-intact females. These data suggest, for the first time, that estrogen alone cannot protect the aged female myocardium from I/R damage and that age- and estrogen-dependent alterations in PKC, Akt, and GSK-3β signaling may contribute to loss of ischemic tolerance.

Effects of gradual coronary artery occlusion and exercise training on gene expression in swine heart

Gradual occlusion (O) of the swine left circumflex coronary artery (LCX) with an ameroid occluder results in complete O within 3 weeks, collateral vessel development, and compensatory hypertrophy. The purpose of this investigation was to determine the independent and combined effects of O and exercise training (E) on gene expression in the swine heart. Adult Yucatan miniature swine were assigned to one of the following groups (n=6-9/group): sedentary control (S), exercise-trained (E), sedentary swine subjected to LCX occlusion (SO), and exercise-trained swine with LCX occlusion (EO). Exercise consisted of progressive treadmill running conducted 5 d/wk for 16 weeks. Gene expression was studied in myocardium isolated from the collateral-dependent left ventricle free wall (LV) and the collateral-independent septum (SEP) by RNA blotting. E and O each stimulated cardiac hypertrophy independently (p<0.001) with no interaction. O but not E increased atrial natriuretic factor expression in the LV, but not in the SEP. E decreased the expression of beta-myosin heavy chain in the LV, but not in the SEP. E retarded the expression of collagen III mRNA in SEP; but not in the LV. Exercise training and coronary artery occlusion each stimulate cardiac hypertrophy independently and induce different patterns of gene expression.

Acute PKCdelta inhibition limits ischaemia-reperfusion injury in the aged rat heart: role of GSK-3beta

OBJECTIVE

Age is a leading risk factor for the development of ischaemic heart disease and failure. However, the efficacy of cardioprotective strategies designed to rescue the aged myocardium remains controversial. We have previously demonstrated increased levels of basal cardiac protein kinase Cdelta (PKCdelta) with ageing, a well-known mediator of apoptotic cell death following ischaemia and reperfusion (I/R) in adult hearts. Our objective was to determine the contribution of PKCdelta signaling mechanisms to reperfusion injury in the aged heart using local delivery of a novel PKCdelta inhibitory peptide (KID1-1).

METHODS

Contractile responses were assessed in hearts isolated from adult (4 months, n=38) and aged (24 months, n=45) male Fisher 344 rats treated with either KID1-1 (500 nM) or Tat vehicle peptide (500 nM) upon reperfusion for 10 min following 31-min global ischaemia.

RESULTS

Recovery of left ventricular (LV) developed pressure was significantly improved by KID1-1 and associated with smaller infarct size in 24 months vs. age-matched controls (p<0.005). We also observed significant reductions in DNA laddering and cytochrome c and caspase 3 levels in aged hearts treated with KID1-1. Interestingly, KID1-1 attenuated mitochondrial and nuclear PKCdelta levels during reperfusion in aged vs. age-matched controls (p<0.01). Further, increases in mitochondrial phosphorylated glycogen synthase kinase-3beta (pGSK-3beta) levels were hastened in aged and adult hearts following KID1-1 (p<0.05), increasing the pGSK-3beta/GSK-3beta ratio.

CONCLUSIONS

These results provide novel evidence for cardioprotection through acute PKCdelta inhibition in aged rat heart following I/R. Our results also suggest, for the first time, a key role for mitochondrial GSK-3beta as a cellular basis for the protection associated with PKCdelta inhibition with ageing.

PKCδ Mediates Testosterone-induced Increases in Coronary Smooth Muscle Cav1.2

Sex hormones have emerged as important modulators of cardiovascular physiology and pathophysiology. Our previous studies demonstrated that testosterone increases expression and activity of L-type, voltage-gated calcium channels (Cav1.2) in coronary arteries of males. The purpose of the present study was to determine whether testosterone (T) alters coronary protein kinase C delta (PKCdelta) expression and whether PKCdelta plays a role in coronary Cav1.2 expression. For in vitro studies, porcine right coronary arteries (RCA) and post-confluent (passages 3-6) 5-day, serum-restricted coronary smooth muscle cell cultures (CSMC) were incubated in the presence and absence of T or dihydrotestosterone (10 and 100 nm) for 18 h at 37 degrees C in a humidified chamber. For sex and endogenous testosterone-dependent effects, RCA were obtained from intact males, castrated males, castrated males with T replacement, and intact females. In vitro T and dihydrotestosterone caused an approximately 2-3-fold increase in PKCdelta protein levels, approximately 1.5-2-fold increase in PKCdelta kinase activity, and localization of PKCdelta toward the plasma membrane and nuclear envelope. PKCdelta protein levels were higher in coronary arteries of intact males compared with intact females. Elimination of endogenous testosterone by castration reduced RCA PKCdelta protein levels, an effect partially (approximately 45%) reversed by exogenous T (castrated males with T replacement). In CSMC, PKC inhibition with either the general PKC inhibitor, cheylerythrine, or the putative PKCdelta inhibitor, rottlerin, completely inhibited the T-mediated increase in coronary Cav1.2 protein levels. Conversely, Go6976, a conventional PKC isoform inhibitor, failed to inhibit T-induced increases in coronary Cav1.2 protein levels. PKCdelta short interference RNA completely blocked T-induced increases in Cav1.2 protein levels in CSMC. These results demonstrate for the first time that 1) endogenous T is a primary modulator of coronary PKCdelta protein and activity in males and 2) T increases Cav1.2 protein expression in a PKCdelta-dependent manner.

Exercise and hypercholesterolemia produce disparate shifts in coronary PKC expression

INTRODUCTION

Sedentary lifestyle and high-fat, high-cholesterol diets are each associated with elevated risk for coronary heart disease (CHD); however, the mechanisms by which they increase risk are unclear. Specific PKC isoforms have been implicated in the development of CHD, regulation of coronary vasoreactivity, as well as exercise-induced cardioprotection. Thus, diet and physical inactivity may increase CHD risk by altering coronary protein kinase C (PKC) isoform profiles.

PURPOSE

To determine whether coronary PKC isoform profiles are altered in a model of early CHD and whether exercise can prevent these changes.

METHODS

Male and female Yucatan miniature swine were either fed a normal (NF) or high-fat (HF) diet (8 vs 46% kilocalories from fat) and remained sedentary (Sed) or were treadmill-trained (Ex) at 75% of; VO2max (6 mph, 60 min) for 16 wk. Groups were as follows: NFSed (N=8/N=7), NFEx (N=8/N=7), HFSed (N=8/N=7), and HFEx (N=8/N=7). Western blotting was performed on right coronary conduit artery (CCA) segments (>1 mm I.D.) to measure total protein levels of PKC-alpha, -betaI, -betaII, -delta, -epsilon, and -zeta.

RESULTS

HF diet increased total cholesterol by more than sixfold with no increase in triglycerides. Hypercholesterolemia increased PKC-betaII and -epsilon protein levels in CCA of both male and female pig; Ex had no effect on this response. Ex-induced increases in PKC-betaI, PKC-delta, and PKC-zeta were observed in HF male pigs. Female pigs had higher baseline amounts of PKC-alpha (25%), PKC-betaI (33%), PKC-betaII (39%), and PKC-epsilon (29%), whereas male pigs had higher amounts of PKC-delta (308%). Further analyses revealed a direct relationship between androgens and PKC-delta levels.

CONCLUSION

Hypercholesterolemia and exercise exert disparate effects on coronary PKC expression. Observed sex differences in PKC protein profiles may also contribute to altered cardiovascular risk patterns in males versus females.

Exaggerated coronary vasoreactivity to endothelin-1 in aged rats: Role of protein kinase C

OBJECTIVE

The interaction between advanced age and increased susceptibility to ischemic insult is well documented. Age-related increases in coronary vascular resistance, in part due to impaired dilator responses, have been reported. Our aim was to determine the role of endothelin-1 (ET-1) on enhanced constrictor responses in aged coronary arteries (CAs) and whether protein kinase C (PKC) signaling mechanisms impact ET-1 responses.

METHODS

Vasoreactivity was assessed in CAs isolated from aged (24 months; n=16) and adult (4 months; n=21) male F344 rats following ET-1 (10(-10)-10(-8)) with and without specific ETA/ETB receptor antagonists (BQ-123, 1 microM; BQ-788, 30 nM) or the PKC inhibitor bisindolylmaleimide (Bis; 10(-6) M). Constrictor responses to KCl (80 mM) were also measured and voltage-gated Ca2+ channel (VGCC) determined in isolated coronary smooth muscle cells. Dilator responses to acetylcholine (ACH) and sodium nitroprusside (SNP) were assessed.

RESULTS

Passive diameter was greater (357+/-19 vs. 309+/-9; p<0.02) while spontaneous tone was similar in 24 months vs. 4 months. ET-1 resulted in greater constriction in 24 months vs. 4 months (79% vs. 67%; p<0.01). Group differences persisted following selective ETB inhibition with BQ-788 (p<0.02), while BQ-123 abolished contractile responses to ET-1. Importantly, inhibition of ET-1 constriction by Bis occurred in 24 months but not 4 months (p<0.01). Constrictor responses to KCl and peak VGCC current density were similar in 24 months vs. 4 months (48% vs. 50%). No age-related differences were observed in ACH- or SNP-mediated dilation. Western blotting revealed increases in Ca2+-sensitive PKCalpha, -betaI, and -betaII levels with age, while eNOS and ETA receptor protein levels were unchanged.

CONCLUSION

Aberrant ETA constrictor responses and directional changes in PKC are likely to contribute to coronary vascular pathology with advanced age.

Isoform-specific modulation of coronary artery PKC by glucocorticoids

Glucocorticoids (GC) exert diverse cellular effects in response to both acute and chronic stress, the functional consequences of which have been implicated in the development of cardiovascular pathology such as hypertension and atherosclerosis. However, the mechanisms by which GCs activate divergent signaling pathways are poorly understood. The present study examined the direct effects of natural (cortisol) and synthetic (dexamethasone) GCs on protein kinase C (PKC) isoform expression in coronary arteries. Porcine right coronary arteries were treated in vitro for 18 h in the presence and absence of either dexamethasone (10, 100, or 500 nM) or cortisol (50, 125, 250, or 500 nM). PKC isoform levels and subcellular distribution were determined by immmunoblotting of whole cell homogenates and immunocytofluorescence using PKC-alpha, -betaII, -epsilon, -delta, and -zeta specific antibodies. Dexamethasone caused a approximately 4-fold increase in PKC-alpha, a approximately 2.5-fold increase in PKC-betaII, and a 2-fold increase in PKC-epsilon (p<0.05). In contrast, dexamethasone had no effect on PKC-delta or PKC- zeta levels. Dexamethasone also caused an increase in the activity of PKC-alpha (285%), -betaII (170%), and -epsilon (210%). Cortisol produced similar effects on PKC isoform expression. Confocal microscopy revealed that while dexamethasone altered localization patterns for PKC-alpha, -betaII and -epsilon, no such effect was observed for PKC-delta or PKC-zeta. The stimulatory effects of dexamethasone and cortisol on coronary PKC levels and translocation were prevented by the GC receptor (GR) blocker, RU486. These results demonstrate, for the first time, that GCs modulate coronary PKC expression and subcellular distribution in an isoform-specific manner through a GR-dependent mechanism.

Age- and sex-dependent alterations in protein kinase C (PKC) and extracellular regulated kinase 1/2 (ERK1/2) in rat myocardium

Cardiovascular morbidity and mortality increase significantly with advancing age, with proportionally higher rates occurring in aged women when compared to aged men. The signaling alterations responsible for age-related reductions in ischemic stress reserves, particularly in aged women, are poorly understood. Accordingly, we sought to determine whether alterations in the cellular location and formation of specific protein kinase C (PKC)-extracellular regulated 1/2 (ERK1/2) signaling modules (SMS) might provide insight into known age- and sex-related differences in cardiovascular disease outcomes. Cytosolic (Cyto), mitochondrial (Mito) and nuclear (Nuc) fractions were isolated from left ventricles of male (M) and female (F) adult (6 mo), castrated or aged (23 mo) F344 rats by centrifugation. Western blotting was used to assess PKC (alpha, delta, epsilon), p-ERK1/2 and p-Bad(Ser112) levels, and immunoprecipitation to assess PKC-ERK1/2 SMS. Cyto-PKCalpha levels increased with age (p<0.0001), whereas increases in cyto-PKCalpha-ERK1/2 SMS were only observed in aged F (60%; p<0.01). Mito-PKCdelta and Mito-PKCdelta-ERK1/2 SMS increased in M and F with age (p<0.0001); however increases in Cyto-PKCdelta were only observed in aged M (80% p<0.0001). It is important to note that Nuc- and Mito-PKCdelta-ERK1/2 SMS were 3.5- and 4.8-fold greater in males versus females, respectively (p<0001). Increases in Mito-PKCepsilon-ERK1/2 SMS (216%) were also specific to aged M (p<0.0001), however, Mito-p-Bad(Ser112) levels were decreased with age in both M and F. Differences in sex hormone status could not fully account for observed age-related differences in PKC. Collectively, our results provide novel evidence for age and sex-related differences in the magnitude and distribution of cardiac PKC-ERK1/2 SMS consistent with previously described pathological and protective phenotypes, respectively.

Protein kinase C distribution and translocation in rat myocardium: Methodological considerations

INTRODUCTION

Protein kinase C (PKC) is an important modifier of several cardiovascular phenomena, including cardioprotection, apoptosis, and hypertrophy. Although pharmacological activation of PKC is often assessed by translocation, the effects of isolation procedures on left ventricular (LV) PKC distribution have not been systematically examined. Accordingly, we sought to determine whether homogenization methods (Polytron, glass-glass tissue grinder), detergent selection and concentration, or centrifugation protocols affect PKC (alpha, epsilon) distribution or phorbol-12-myristate-13-acetate (PMA)-induced translocation.

METHODS

Hearts of male F344 or Wistar rats were Langendorff perfused with either 100 nM PMA or vehicle, and LV cytosolic and particulate PKC (alpha, epsilon) distributions were assessed by differential centrifugation and Western blotting.

RESULTS

Following 100000 xg centrifugation of the homogenate, resuspension of the pellet (P(1)) in 0.1% sodium dodecyl sulfate (SDS) increased electrophoretic mobility of PKC (alpha, epsilon) such that PKCepsilon comigrated with a nonspecific band. Resuspension of P(1) in Triton X-100 (TX) did not affect mobility but decreased P(1) PKC (alpha, epsilon) levels in a TX-concentration-dependent manner; however, this decrease was found to be due to differential protein solubilization. Decreased levels of PKC (alpha, epsilon) were also noted in soluble and P(2) (supernatant of 100000 xg centrifugation of P(1)) fractions due to increased Polytron burst and total homogenization times. Interestingly, the P(2) fraction also revealed Polytron-dependent decreases (47% vs. glass-glass tissue grinder; p<0.05) in PKCepsilon following an initial 1000 xg centrifugation and an increased PMA-dependent translocation of PKC (alpha, epsilon; 2.4-fold and 1.6-fold, respectively, vs. P(1); p<0.05).

DISCUSSION

Taken together, these results suggest that PKC isolation procedures should be carefully considered when designing or comparing LV PKC studies due to the potential effects isolation may have on PKC distribution and translocation.

Chronic Exercise Improves Myocardial Inotropic Reserve Capacity Through α1-Adrenergic and Protein Kinase C-Dependent Effects in Senescent Rats

We have previously demonstrated that α1-adrenergic (AR)-mediated contraction is diminished in the senescent rat heart, in part due to alterations in protein kinase C (PKC) signaling. Since chronic exercise training (EX) can exert independent effects on increasing α1-AR contraction in the adult rat heart, we sought to determine whether age-related defects in α1-AR contraction could be reversed by chronic EX. We further hypothesized that improved α1-AR contraction by EX may be PKC dependent. Adult (4 months; Y) and aged (24 months; O) male F344 rats were treadmill-trained (n = 12–13/group; TR) at ∼70% of VO2max for 12 weeks or remained sedentary (YSED, YTR, OSED, OTR). Training status was verified by plantaris citrate synthase activity and left ventricular (LV) contractile responses (dP/dt) to α1-AR stimulation were assessed in Langendorff-perfused hearts using the α1-AR agonist phenylephrine (PE; 10−5 M) with and without the PKC inhibitor chelerythrine (CE; 10−6 M). α1-AR stimulation elicited greater increases in LV dP/dt in hearts isolated from OTR (4525.4 ± 224.1 mmHg/s) versus OSED (3658.9 ± 291.0 mmHg/s), while CE abolished PE-induced effects (OTR, 4069.2 ± 341.2) versus (OSED, 3608.9 ± 321.2) (p &lt;.01). Upon western blotting, phosphospecific antibodies directed at PKCε (pSer729) revealed greater levels in LV isolated from YTR versus YSED, and EX ameliorated aged-related reductions in OSED (p &lt;.001). Basal PKCε mRNA levels were also greater in YTR and OTR versus YSED (p &lt;.01). PE-induced increases in phosphor-PKCδ (pThr507) levels observed in OSED were attenuated in OTR (p &lt;.03). Chronic EX was also associated with significant reductions in PKCα (pSer657) levels following PE in OTR (p &lt;.002). The results indicate that age-related reductions in α1-AR contraction can be partially reversed by EX in the rat heart. These results further suggest that alterations in PKC levels underlie, at least in part, EX-induced improvements in α1-AR contraction.

Control of the arteriolar myogenic response by transvascular fluid filtration

Mechanisms of the myogenic response have not been completely established. We hypothesized that transvascular fluid filtration from plasma across smooth muscle cells (SMC) and into the surrounding interstitium helps regulate arteriolar myogenic tone. Arteriolar diameters in the rat mesentery were monitored before and following vascular occlusion with a glass micropipette. Arteriolar occlusion not only gave an increase in hydrostatic pressure that initiated myogenic constriction upstream of the pipette, but also allowed measurement of fluid filtration rate by monitoring the movement of vascular red blood cells. A statistically significant correlation (P < 0.001) existed between basal myogenic tone and fluid filtration. Additionally, the myogenic response was attenuated by 47% +/- 7% (N = 10) when an osmotic solution of albumin or albumin plus Ficoll was infused into the bloodstream to decrease fluid filtration by 53% +/- 3%. Moreover, the same inhibition of myogenic tone was found in isolated, cannulated rat soleus muscle arterioles when filtration was osmotically attenuated by intravascular dextran. Taken together, these results are consistent with the hypothesis that shear stress on arteriolar smooth muscle, induced by transvascular fluid filtration, is a contributing factor that helps control myogenic tone.

Alterations in PKC signaling underlie enhanced myogenic tone in exercise-trained porcine coronary resistance arteries

The intracellular mechanisms underlying enhanced myogenic contraction (MC) in coronary resistance arteries (CRAs) from exercise-trained (EX) pigs have not been established. The purpose of this study was to test the hypothesis that exercise-induced alterations in protein kinase C (PKC) signaling underlie enhanced MC. Furthermore, we sought to determine whether modulation of intracellular Ca2+signaling by PKC underlies enhanced MC in EX animals. Male Yucatan miniature swine were treadmill trained ( n = 7) at ∼75% of maximal O2uptake for 16 wk (6 miles/h, 60 min) or remained sedentary (SED, n = 6). Diameter measurements in response to intraluminal pressure (60, 75, and 90 cmH2O) or 60 mM KCl were determined in single, cannulated CRAs (∼100 μm ID) with and without the PKC inhibitor chelerythrine (CE, 1 μM). Confocal imaging of Ca2+signaling [myogenic Ca2+(Cam)] was also performed in CRAs of similar internal diameter after abluminal loading of the Ca2+indicator dye fluo 4 (1 μM, 37°C, 30 min). We observed significantly greater MC in CRAs isolated from EX than from SED animals at 90 cmH2O, as well as greater reductions in MC after CE at all pressures studied. At intraluminal pressures of 75 and 90 cmH2O, CE produced greater decreases in Camin CRAs from EX than from SED animals (64% vs. 25%, P < 0.05). Inhibition of KCl constriction and Camby CE was also greater in EX animals ( P < 0.05). Western blotting revealed significant increases in Ca2+-dependent PKC-α (∼50%) but not Ca2+-independent PKC-ϵ levels in CRAs isolated from EX animals ( P < 0.05). We also observed significant group differences in phosphorylated PKC-α levels. Finally, voltage-gated Ca2+current (VGCC) was effectively blocked by CE, bisindolylmaleimide, and staurosporine in isolated smooth muscle cells from CRAs, providing evidence for a mechanistic link between VGCCs and PKC in our experimental paradigm. These results suggest that enhanced MC in CRAs from EX animals involves PKC-dependent modulation of intracellular Ca2+, including regulation of VGCCs.

Regulation of cardiac excitation-contraction coupling: a cellular update

The primary purpose of this paper is to present a basic overview of some "relatively" new ideas related to the regulation of cardiac performance and underlying excitation-contraction (EC) coupling that have yet to be incorporated to textbooks currently used for introductory graduate-level physiology courses. Within the context of cardiac EC coupling, this review incorporates information on microdomains and local control theory, with particular emphasis on the role of Ca(2+) sparks as a key regulatory component of ventricular myocyte contraction dynamics. Recent information pertaining to Ca(2+) release mechanisms specific to the sarcoplasmic reticulum is also presented, as well as the idea of the ryanodine receptor as a macromolecular signaling complex. Because of the potential relationship to maladaptive functional responses under conditions of cardiovascular pathology, the regulatory role of cardiac adrenergic and additional G protein-coupled receptors known to regulate cardiac function is included, and fundamental concepts related to intracellular signaling are discussed. Finally, information on the roles of vascular and cardiac nitric oxide as an important regulator of cardiac performance is included to allow students to begin to think about the ubiquitous role of nitric oxide in the regulation of the cardiovascular system. An important point of emphasis is that whole organ cardiac dynamics can be traced back to the cellular events regulating intracellular Ca(2+) homeostasis and as such provides an important conceptual framework from which the students can begin to think about whole organ physiology in health and disease.

Alterations in rat coronary vasoreactivity and vascular protein kinase C isoforms in Type 1 diabetes

Vascular complications associated with diabetes mellitus (DM) have been linked to activation of PKC-dependent signaling pathways in both human and animal models of DM. To determine whether aberrant PKC signaling mechanisms specifically impact the coronary circulation, we assessed isolated coronary artery (CA) responses after the induction of Type 1 DM. Male Sprague-Dawley rats were subjected to partial pancreatectomy (DM; n = 23) and compared with age-matched controls (CTL; n = 19). Vasoreactivity was assessed in single CAs ( approximately 250 microm internal diameter) after abluminal administration of the Gq-dependent vasoconstrictors endothelin (ET)-1 (10(-10)-10(-9) M) and U-44619 (10(-9)-10(-5) M) or the voltage-gated Ca2+ channel agonist BAY K 8644 (10(-9)-10(-5) M) with and without the PKC inhibitor bisindolylmaleimide (Bis; 10(-6) M). Dilator responses to ACh (10(-9)-10(-5) M) were also assessed. ET-1 resulted in significantly greater constriction in the DM versus CTL group (50 +/- 4% vs. 33 +/- 5%, P < 0.0001), whereas responses to U-44619 and BAY K 8644 were similar between groups. Importantly, inhibition of ET-1 and U-44619 constriction by Bis occurred in the DM but not CTL group (P < 0.05). Western blotting on isolated CAs revealed greater levels of PKC-alpha, PKC-beta I, and PKC-beta II by 22%, 15.3%, and 17.6%, respectively, in the DM versus CTL group (P < 0.05), whereas PKC-delta and PKC-epsilon protein levels were unchanged. DM was also associated with attenuated CA dilation after ACh treatment (P < 0.0566) and reductions in endothelial nitric oxide synthase protein levels versus CTL (P < 0.03). These data suggest that Ca2+-dependent PKC signaling pathways, particularly for ET-1, play a greater role in modulating CA vasoconstrictor responses in DM versus CTL. These data further suggest that aberrant CA constrictor and dilator responses are likely to contribute to the coronary vascular pathology associated with DM.

Dose-dependent effects of acute exercise on PKC levels in rat heart: is PKC the heart's prophylactic?

Epidemiological studies have demonstrated that chronic exercise is cardioprotective, and recent evidence from our laboratory suggests a key role for protein kinase C (PKC)-dependent pathways, at least in part, as a cellular basis for this response. However, the dose-response relationship linking exercise volume and the time course of isoform-specific PKC activation are poorly understood.

AIM

The purpose of this investigation was to determine the effects of acute exercise of varying durations on PKC subcellular distribution and phosphorylation in the rat left ventricle.

METHODS

Adult (5 months) male Fischer-344 more rats were subjected to a single bout (OB) or 7 days (SB) of treadmill running (n = 6/group; 23 m min-1, 20 min), and compared with sedentary controls (SED; n = 8). Hearts were isolated immediately after [early window (EW); n = 3/group] or 24 h after the last exercise bout [late window (LW); n = 3/group] in OB and SD, respectively. Total PKC and subcellular distribution for the alpha, delta, epsilon, betaI, and betaII isoforms, as well as phosphorylated (phospho-) PKC epsilon (pSer729), PKC alpha (pSer657) and PKCdelta (pThr507) levels were assessed by western blotting. Protein kinase C epsilon and PKC alpha mRNA levels were assessed by real time polymerase chain reaction.

RESULTS

Following OB, PKCbetaI protein levels were reduced, while total phospho-PKC epsilon (pSer729), PKC alpha (pSer657) and PKC delta (pThr507) levels were increased during EW (P < 0.05). Interestingly, total PKC delta (31%) and membrane-associated PKC alpha (24%) levels decreased from EW to LW (P < 0.05). In contrast, SB yielded chronic increases in total PKC epsilon (80.5%) levels and PKC delta (20.0%) levels (P < 0.03), with reversal of effects on phospho-PKC epsilon (Ser729), phospho-PKC alpha (Ser657) and phospho-PKC delta (Thr507) levels observed with OB. Reductions in total phospho-PKC alpha (Ser657) persisted at SB (26.1%; P < 0.02). Interestingly, mRNA levels for PKC epsilon were significantly increased following SB while PKC alpha mRNA levels were reduced, respectively.

CONCLUSION

These data suggest that divergent patterns of PKC activation occur following OB and SB at both the transcriptional and translational levels. That similar patterns of PKC translocation are observed in experimental models of ischaemic preconditioning and genetic PKC manipulation provide evidence for a dose-dependent cardioprotective phenotype induced by physical activity.