Tumor necrosis factor receptor 1 signaling resistance in the female myocardium during ischemia

Tumor Necrosis Factor Family Members and Myocardial Ischemia-Reperfusion Injury: State of the Art and Therapeutic Implications

Ischemic heart disease is the principal cause of death worldwide and clinically manifests as myocardial infarction (MI), stable angina, and ischemic cardiomyopathy. Myocardial infarction is defined as an irreversible injury due to severe and prolonged myocardial ischemia inducing myocardial cell death. Revascularization is helpful in reducing loss of contractile myocardium and improving clinical outcome. Reperfusion rescues myocardium from cell death but also induces an additional injury called ischemia-reperfusion injury. Multiple mechanisms are involved in ischemia-reperfusion injury, such as oxidative stress, intracellular calcium overload, apoptosis, necroptosis, pyroptosis, and inflammation. Various members of the tumor necrosis factor family play a key role in myocardial ischemia-reperfusion injury. In this article, the role of TNFα, CD95L/CD95, TRAIL, and the RANK/RANKL/OPG axis in the regulation of myocardial tissue damage is reviewed together with their potential use as a therapeutic target.

Sex as Biological Variable in Cardiac Mitochondrial Bioenergetic Responses to Acute Stress

Cardiac dysfunction/damage following trauma, shock, sepsis, and ischemia impacts clinical outcomes. Acute inflammation and oxidative stress triggered by these injuries impair mitochondria, which are critical to maintaining cardiac function. Despite sex dimorphisms in consequences of these injuries, it is unclear whether mitochondrial bioenergetic responses to inflammation/oxidative stress are sex-dependent. We hypothesized that sex disparity in mitochondrial bioenergetics following TNFα or H2O2 exposure is responsible for reported sex differences in cardiac damage/dysfunction. Methods and Results: Cardiomyocytes isolated from age-matched adult male and female mice were subjected to 1 h TNFα or H2O2 challenge, followed by detection of mitochondrial respiration capacity using the Seahorse XF96 Cell Mito Stress Test. Mitochondrial membrane potential (ΔΨm) was analyzed using JC-1 in TNFα-challenged cardiomyocytes. We found that cardiomyocytes isolated from female mice displayed a better mitochondrial bioenergetic response to TNFα or H2O2 than those isolated from male mice did. TNFα decreased ΔΨm in cardiomyocytes isolated from males but not from females. 17β-estradiol (E2) treatment improved mitochondrial metabolic function in cardiomyocytes from male mice subjected to TNFα or H2O2 treatment. Conclusions: Cardiomyocyte mitochondria from female mice were more resistant to acute stress than those from males. The female sex hormone E2 treatment protected cardiac mitochondria against acute inflammatory and oxidative stress.

Sex-Related Effects on Cardiac Development and Disease

Cardiovascular diseases (CVD) are the leading cause of morbidity and mortality. Interestingly, male and female patients with CVD exhibit distinct epidemiological and pathophysiological characteristics, implying a potentially important role for primary and secondary sex determination factors in heart development, aging, disease and therapeutic responses. Here, we provide a concise review of the field and discuss current gaps in knowledge as a step towards elucidating the “sex determination–heart axis”. We specifically focus on cardiovascular manifestations of abnormal sex determination in humans, such as in Turner and Klinefelter syndromes, as well as on the differences in cardiac regenerative potential between species with plastic and non-plastic sexual phenotypes. Sex-biased cardiac repair mechanisms are also discussed with a focus on the role of the steroid hormone 17β-estradiol. Understanding the “sex determination–heart axis” may offer new therapeutic possibilities for enhanced cardiac regeneration and/or repair post-injury.

Pathological Responses of Cardiac Mitochondria to Burn Trauma

Despite advances in treatment and care, burn trauma remains the fourth most common type of traumatic injury. Burn-induced cardiac failure is a key factor for patient mortality, especially during the initial post-burn period (the first 24 to 48 h). Mitochondria, among the most important subcellular organelles in cardiomyocytes, are a central player in determining the severity of myocardial damage. Defects in mitochondrial function and structure are involved in pathogenesis of numerous myocardial injuries and cardiovascular diseases. In this article, we comprehensively review the current findings on cardiac mitochondrial pathological changes and summarize burn-impaired mitochondrial respiration capacity and energy supply, induced mitochondrial oxidative stress, and increased cell death. The molecular mechanisms underlying these alterations are discussed, along with the possible influence of other biological variables. We hope this review will provide useful information to explore potential therapeutic approaches that target mitochondria for cardiac protection following burn injury.

Mitochondrial connexin 43 in sex-dependent myocardial responses and estrogen-mediated cardiac protection following acute ischemia/reperfusion injury

Preserving mitochondrial activity is crucial in rescuing cardiac function following acute myocardial ischemia/reperfusion (I/R). The sex difference in myocardial functional recovery has been observed after I/R. Given the key role of mitochondrial connexin43 (Cx43) in cardiac protection initiated by ischemic preconditioning, we aimed to determine the implication of mitochondrial Cx43 in sex-related myocardial responses and to examine the effect of estrogen (17β-estradiol, E2) on Cx43, particularly mitochondrial Cx43-involved cardiac protection following I/R. Mouse primary cardiomyocytes and isolated mouse hearts (from males, females, ovariectomized females, and doxycycline-inducible Tnnt2-controlled Cx43 knockout without or with acute post-ischemic E2 treatment) were subjected to simulated I/R in culture or Langendorff I/R (25-min warm ischemia/40-min reperfusion), respectively. Mitochondrial membrane potential and mitochondrial superoxide production were measured in cardiomyocytes. Myocardial function and infarct size were determined. Cx43 and its isoform, Gja1-20k, were assessed in mitochondria. Immunoelectron microscopy and co-immunoprecipitation were also used to examine mitochondrial Cx43 and its interaction with estrogen receptor-α by E2 in mitochondria, respectively. There were sex disparities in stress-induced cardiomyocyte mitochondrial function. E2 partially restored mitochondrial activity in cardiomyocytes following acute injury. Post-ischemia infusion of E2 improved functional recovery and reduced infarct size with increased Cx43 content and phosphorylation in mitochondria. Ablation of cardiac Cx43 aggravated mitochondrial damage and abolished E2-mediated cardiac protection during I/R. Female mice were more resistant to myocardial I/R than age-matched males with greater protective role of mitochondrial Cx43 in female hearts. Post-ischemic E2 usage augmented mitochondrial Cx43 content and phosphorylation, increased mitochondrial Gja1-20k, and showed cardiac protection.

Melatonin and cardioprotection against ischaemia/reperfusion injury: What's new? A review

Melatonin is a pleiotropic hormone with several functions. It binds to specific receptors and to a number of cytosolic proteins, activating a vast array of signalling pathways. Its potential to protect the heart against ischaemia/reperfusion damage has attracted much attention, particularly in view of its possible clinical applications. This review will focus mainly on the possible signalling pathways involved in melatonin-induced cardioprotection. In particular, the role of the melatonin receptors and events downstream of receptor activation, for example, the reperfusion injury salvage kinase (RISK), survivor activating factor enhancement (SAFE) and Notch pathways, the sirtuins, nuclear factor E2-related factor 2 (Nrf2) and translocases in the outer membrane (TOM70) will be discussed. Particular attention is given to the role of the mitochondrion in melatonin-induced cardioprotection. In addition, a brief overview will be given regarding the status quo of the clinical application of melatonin in humans.

Postischemic application of estrogen ameliorates myocardial damage in an in vivo mouse model

BACKGROUND

Cardioprotection provided by estrogen has been recognized for many years. It is noteworthy that most of these studies employ a means of preinjury application in experimental research and the preventive usage in clinical studies. Compared to pretreatment, postischemic administration of estrogen will be more practical in treating myocardial ischemia. On the other hand, defect in circadian clock gene period2 (Per2) has been shown to aggravate ischemia-induced heart damage. Given that Per2 expression decreases as a consequence of menopause, in this study, we aim to determine (1) potential improvement of myocardial function by postischemic administration of 17β-estradiol (E2) using an in vivo mouse myocardial ischemia/reperfusion (I/R) model and (2) the role of E2 in regulating myocardial Per2 expression following I/R.

METHODS

Thirty-minute occlusion of left anterior descending artery followed by 24-h reperfusion was performed on adult C57BL ovariectomized female mice. Groups (n = 3-6/group) were as follows: (1) Sham, (2) I/R + vehicle, and (3) I/R + E2. Vehicle or 0.5 mg/kg of E2 was subcutaneously injected right after 30-min ischemia. Following 24-h reperfusion, myocardial function was determined. Heart tissue was collected for analysis of cleaved caspase-3 and Per2 expression by Western blotting, as well as proinflammatory cytokine production (IL-1β, IL-6, and TNF-α) by enzyme-linked immunosorbent assay.

RESULTS

I/R significantly impaired left ventricular function and increased myocardial levels of active caspase-3, IL-1β, and IL-6. Importantly, postischemic treatment of E2 markedly restored I/R-depressed myocardial function, reduced caspase-3 activation, and decreased proinflammatory cytokine production (IL-1β, IL-6, and TNF-α). Intriguingly, a trend of the decreased Per2 level was observed in ovariectomized female hearts subjected to I/R, whereas E2 treatment upregulated myocardial Per2 expression.

CONCLUSIONS

Our study represents the initial evidence that postischemic administration of E2 effectively preserves the myocardium against I/R injury and this protective effect of E2 may involve upregulation of Per2 in ischemic heart.

Effects of inhaled nitric oxide on outcome after prolonged cardiac arrest in mild therapeutic hypothermia treated rats

Guidelines endorse targeted temperature management to reduce neurological sequelae and mortality after cardiac arrest (CA). Additional therapeutic approaches are lacking. Inhaled nitric oxide (iNO) given post systemic ischemia/reperfusion injury improves outcomes. Attenuated inflammation by iNO might be crucial in brain protection. iNO augmented mild therapeutic hypothermia (MTH) may improve outcome after CA exceeding the effect of MTH alone. Following ten minutes of CA and three minutes of cardiopulmonary resuscitation, 20 male Sprague-Dawley rats were randomized to receive MTH at 33 °C for 6hrs or MTH + 20ppm iNO for 5hrs; one group served as normothermic control. During the experiment blood was taken for biochemical evaluation. A neurological deficit score was calculated daily for seven days post CA. On day seven, brains and hearts were harvested for histological evaluation. Treatment groups showed a significant decrease in lactate levels six hours post resuscitation in comparison to controls. TNF-α release was significantly lower in MTH + iNO treated animals only at four hours post ROSC. While only the combination of MTH and iNO improved neurological function in a statistically significant manner in comparison to controls on days 4–7 after CA, there was no significant difference between groups treated with MTH and MTH + iNO.

Sex Differences of Human Cardiac Progenitor Cells in the Biological Response to TNF-α Treatment

Adult cardiac progenitor cells (CPCs), isolated as cardiosphere-derived cells (CDCs), represent promising candidates for cardiac regenerative therapy. CDCs can be expanded in vitro manyfolds without losing their differentiation potential, reaching numbers that are appropriate for clinical applications. Since mechanisms of successful CDC survival and engraftment in the damaged myocardium are still critical and unresolved issues, we aimed at deciphering possible key factors capable of bolstering CDC function. In particular, the response and the phenotype of CDCs exposed to low concentrations of the multifunctional cytokine tumor necrosis factor α (TNF-α), known to be capable of activating cell survival pathways, have been investigated. Furthermore, differential biological responses of CDCs from male and female donors, in terms of cell cycle progression and cell spreading, have also been assessed. The results obtained indicate that (i) the intracellular signaling activated in our experimental conditions is most likely due to the prosurvival and proliferative signaling of TNF-α receptor 2 and that (ii) cells from female patients appear more responsive to TNF-α treatment in terms of cell cycle progression and migration ability. In conclusion, the present report highlights the hypothesis that TNF-stimulated CDCs isolated from females may represent a promising candidate for cardiac regenerative therapy applications.

Regulation of myocardial stromal cell-derived factor 1α/CXCL12 by tumor necrosis factor signaling

BACKGROUND

Global myocardial ischemia-reperfusion (I/R) occurs during cardiac operations. This I/R injury leads to increased production of tumor necrosis factor α (TNF) instantly and upregulated expression of stromal cell-derived factor 1 α (SDF-1). On the basis of the published data from our laboratory and other groups, locally produced TNF contributes to cardiac dysfunction mainly via binding to its receptor (tumor necrosis factor receptor 1 [TNFR1]), whereas ischemia-induced myocardial SDF-1 mediates cardioprotection. Although TNF has been shown to work as an upstream initiator for induction of other cytokines and chemokines, there is no information regarding the interaction among TNF, TNFRs, and myocardial SDF-1 expression. In this study, given that TNF downregulated SDF-1 in vascular endothelial cells, we therefore hypothesized that TNF would have a negative effect on myocardial SDF-1 production, which is attributable to TNFR-initiated actions.

METHODS

Using a Langendorff model, isolated male mouse hearts were infused with TNF for 45 min. Male adult mouse hearts from wild type, TNFR1 knockout (TNFR1KO), TNFR2KO, and TNFR1/2KO were subjected to global I/R. H9c2 cells with small interfering RNA transfection were used as an in vitro model. The levels of SDF-1 (protein and messenger RNA) were detected by enzyme-linked immunosorbent assay and quantitative reverse transcription-polymerase chain reaction . Protein kinases of IκB (nuclear factor of kappa light polypeptide gene enhancer in B-cells inhibitor α) and c-jun N-terminal kinase were also determined using Western blot assay.

RESULTS

TNF infusion downregulated myocardial SDF-1 production in a dose-dependent manner in the hearts. In addition, using TNF significantly decreased SDF-1 expression in cardiomyoblasts (H9c2 cells), which was associated with reduced IκB level. Knockdown of TNFR1 or TNFR2 by small interfering RNAs neutralized TNF-suppressed SDF-1 in H9c2 cells. Furthermore, deletion of TNFR1/2 or TNFR2 increased SDF-1 production in the hearts after I/R.

CONCLUSIONS

Our study represents the initial evidence showing that TNF plays an inhibitory role in modulating myocardial SDF-1 production and blockade of TNF signaling by ablation of TNFR1 and TNFR2 genes increased SDF-1 expression in the heart. These data expand on TNF signaling-initiated mechanisms in myocardium, which may lend a more complete understanding of SDF-1 and TNFR-derived actions in hopes of advancing ischemic heart injury treatments.

G Protein-Coupled Estrogen Receptor 1 Mediates Acute Estrogen-Induced Cardioprotection via MEK/ERK/GSK-3β Pathway after Ischemia/Reperfusion

Three types of estrogen receptors (ER) exist in the heart, Esr1, Esr2 and the G protein-coupled estrogen receptor 1, Gper1. However, their relative importance in mediating estrogen protective action is unknown. We found that, in the male mouse ventricle, Gper1 transcripts are three- and seventeen-fold more abundant than Esr1 and Esr2 mRNAs, respectively. Analysis of the three ER knockouts (Esr1^-/-, Esr2^-/- and Gper1^-/-) showed that only the Gper1^-/- hearts lost their ability to be protected by 40 nM estrogen as measured by heart function, infarct size and mitochondrial Ca²⁺ overload, an index of mitochondrial permeability transition pore (mPTP) activity. Analysis of Akt, ERK_1/2 and GSK-3β salvage kinases uncovered Akt and ERK_1/2 transient activation by estrogen whose phosphorylation increased during the first 5 min of non-ischemic perfusion. All these increase in phosphorylation effects were abrogated in Gper1^-/-. Inhibition of MEK_1/2/ERK_1/2 (1 μM U0126) and PI-3K/Akt (10 μM LY294002) signaling showed that the MEK_1/2/ERK_1/2 pathway via GSK-3β exclusively was responsible for cardioprotection as an addition of U0126 prevented estrogen-induced GSK-3β increased phosphorylation, resistance to mitochondrial Ca²⁺-overload, functional recovery and protection against infarction. Further, inhibiting PKC translocation (1 μM chelerythrin-chloride) abolished estrogen-induced cardioprotection. These data indicate that estrogen-Gper1 acute coupling plays a key role in cardioprotection against ischemia/reperfusion injury in male mouse via a cascade involving PKC translocation, ERK_1/2/GSK-3β phosphorylation leading to the inhibition of the mPTP opening.

Gender disparity in the role of TLR2 in post-ischemic myocardial inflammation and injury

It is unclear whether Toll-like receptor (TLR) 2 plays a role in post-ischemic myocardial inflammatory response and cardiac dysfunction in both males and females. Permanent ischemia was induced in male and female C57BL/6J (wild-type, WT) and TLR2 knockout (KO) mice. Infarct size and left ventricular (LV) function were analyzed at day 7. Myocardial levels of monocyte chemoattractant protein-1 (MCP-1) and intercellular adhesion molecule-1 (ICAM-1), as well as neutrophil infiltration, were assessed at day 3, and mononuclear cell accumulation was determined at day 7. Lower MCP-1 and ICAM-1 levels, and reduced leukocyte accumulation correlated with smaller infarct size and improved LV function in male TLR2 KO mice. Female WT mice exhibited attenuated myocardial inflammatory response and injury, and TLR2 KO in females did not provide a protective effect although myocardial TLR2 levels in female WT mice were unaltered, and their cardiac cells responded to bacterial TLR2 agonist properly. TLR2 KO in male mice reduced post-ischemic myocardial inflammatory response, resulting in smaller infarct sizes and improved cardiac function. However, TLR2 KO was not beneficial in female mice. The gender disparity in the role of TLR2 in post-ischemic myocardial inflammatory response and myocardial injury suggests that interception with TLR2 signaling may have therapeutic potentials only in males.

Estradiol treatment promotes cardiac stem cell (CSC)-derived growth factors, thus improving CSC-mediated cardioprotection after acute ischemia/reperfusion

INTRODUCTION

Studies from our group and others have indicated that paracrine function is one of major mechanisms underlying stem cell-mediated cardioprotection. To improve therapeutic efficacy of cardiac stem cells (CSCs), modification of CSCs to enhance their paracrine actions is of great interest. We have shown previously that stem cells from female sex produced greater levels of protective growth factors compared with male stem cells. In addition, 17β-estradiol (E2)-treated mesenchymal stem cells provided better protection in the ischemia/reperfusion (I/R)-injured myocardium compared with untreated cells. In this study, therefore, we hypothesized that (1) treatment with E2 would improve CSC-mediated acute protection of cardiac function after global I/R; and (2) this greater protection in E2-treated CSCs would be attributable to the beneficial effect of E2 on paracrine actions of CSCs.

METHOD

CSCs were harvested from C57BL mouse hearts. Myocardial I/R was performed in isolated mouse hearts via a Langendorff model. A total of 0.1 × 10(6)/mL of untreated CSCs or E2-treated CSCs was infused into mouse hearts before ischemia or during the initiation of reperfusion. Heart tissue was used for analysis of activation of caspase-3 and STAT3. Secretion of vascular endothelial growth factor and stromal cell-derived factor 1α by CSCs and E2-treated CSCs was determined. In addition, the conditioned medium from the cultivation of CSCs and E2-modified CSCs was used to treat cardiomyocytes during hypoxia.

RESULTS

E2-treated CSCs produced greater levels of vascular endothelial growth factor and stromal cell-derived factor 1α compared with untreated CSCs. Preischemic infusion of CSCs and E2-treated CSCs improved myocardial function, increased activation of myocardial STAT3 (a prosurvival signaling), and reduced active caspase-3 after acute I/R compared with the vehicle group. The greater protection was observed in E2-treated CSC group than in CSC group. Additionally, infusion of E2-treated CSCs, but not untreated CSCs, during the initiation of reperfusion protected cardiac function after I/R, further indicating the beneficial effect of E2 on CSC protective function.

CONCLUSION

Treatment with E2 enhanced CSC-derived protective factor production and improved CSC-mediated protection of cardiac function and myocyte survival after acute I/R, suggesting that in vitro modification of CSCs may improve their therapeutic outcome.

Sex difference in urocortin production is contributory to the gender disparity in a rat model of vasculitis induced by sodium laurate

Cardiovascular diseases, the most common leading death diseases, occur more in men than women of the same ages. Increasing evidence shows that urocortin (Ucn1), an autocrine or paracrine pro-inflammatory factor, can be regulated by sex hormones. The purpose of the study is to investigate the role of Ucn1 in gender disparity in a sodium laurate-induced vasculitis model. Rats exhibited visible signs of vasculitis on the 14th day after sodium laurate injection. Inflammatory states of the rat femoral artery were observed by histological examination. Significant gender disparity, with the symptoms much grosser in males than females, was seen. In males, the serum levels of Ucn1, prostaglandin estradiol, and soluble intercellular adhesion molecule-1 and the expressions of Ucn1, cyclooxygenase-2, and intercellular adhesion molecule-1 in femoral artery were higher than those in females. Orchidectomy significantly ameliorated the symptoms of vasculitis accompanied with a decrease in the plasma Ucn1 level. However, estradiol supplement after orchidectomy failed to improve the inflammatory states further. In females, ovariectomy and/or dihydrotestosterone supplement significantly increased Ucn1 level and exacerbated symptoms of vasculitis. Furthermore, ip administration of rabbit antiserum to Ucn1 almost abolished the gender differences in vasculitis. These results demonstrated that vasculitis of this model is androgen-responsive and hormonal manipulation by surgical orchidectomy could substantially attenuate the symptoms of vasculitis. Moreover, Ucn1 is a contributory factor to the gender disparity in vasculitis and dihydrotestosterone-promoted Ucn1 secretion exacerbated the development of vasculitis.

The selective 5-LOX inhibitor 11-keto-β-boswellic acid protects against myocardial ischemia reperfusion injury in rats: involvement of redox and inflammatory cascades

Myocardial ischemia induces 5-lipoxygenase (LOX) translocation and leukotriene production in the heart. Leukotrienes increase inflammatory responses aggravating, thereby, ischemia-reperfusion (I/R) injury. This study aimed to investigate whether the selective 5-LOX inhibitor 11-keto-β-boswellic acid (11-keto BA), in three different dose levels, exert a protective effect on myocardial I/R injury in an in vivo rat heart model. Sixty male Wister rats were used in this study and divided into five equal groups (n=12): GP1, sham-operated receiving normal saline; Gp 2, rats were subjected to 45 min left anterior descending coronary artery ligation followed by 4 h reperfusion to serve as I/R group. Gps 3-5 received 11-keto BA in doses 250, 500, 1,000 mg/kg, respectively, via an oral gavage for 7 days then were exposed to I/R. I/R injury induced a significant elevation in myeloperoxidase activity and gene expression of intracellular adhesion molecules, cyclooxygenase-2, 5-lipooxygenasae, nuclear factor kappa-beta, tumor necrosis factor alpha, nuclear factor (erythroid-derived 2)-like 2, and hemeoxygenease-1 consequently with reduction in glutathione peroxidase in heart tissues. Furthermore, immunohistochemical examination of the heart tissues showed positive immuostaining for both 3-nitrotyrosine and caspase-3 with DNA-ladder formation in all diseased rats. 11-keto BA in three dose levels exerted dose dependent cardioprotective effect manifested by dose-dependent reduction in serum lactate dehydrogenase and infract size through mechanisms related to enhancement of antioxidant capacity and prevention of inflammatory cascades.

Valsartan attenuates oxidative stress and NF-κB activation and reduces myocardial apoptosis after ischemia and reperfusion

Myocardial apoptosis is primarily triggered during reperfusion. Various mechanisms are involved, including oxidative stress which activates the translocation of nuclear factor-kappa B (NF-κB) and stimulates the release of tumor necrosis factor-alpha (TNF-α). However, the relative contribution of the renin angiotensin system (RAS) to the development of myocardial apoptosis during reperfusion remains unknown. In the present study, we examined whether inhibition of RAS with Valsartan, an Angiotensin II 1 receptor (AT1) antagonist, could reduce apoptosis during reperfusion. We constructed a rat model of myocardial ischemia reperfusion injury. Rats were pretreated with Valsartan for 2 weeks, and then subjected to 30 min ischemia and 4h reperfusion. Apoptosis was detected by terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL). Levels of malondialdehyde (MDA), superoxide dismutase (SOD), TNF-α, and caspase-3 were detected by ELISA. NF-κB, Nicotinamide Adenine Dinucleotide Phosphate (NADPH) oxidase expression was assessed by Western blot analysis. Valsartan inhibited apoptosis (TUNEL staining) in ischemic myocardium (P<0.05), consistent with reduced caspase-3 activity. Valsartan also inhibited of NF-κB translocation to nucleus (P<0.05), and decreased plasma TNF-α levels (P<0.05). Valsartan pretreatment suppressed MDA content and preserved SOD activity, consistent with reduced NADPH oxidase expression (P<0.01). These data provided substantial evidence that RAS was involved in NF-κB activation, mediated by AT1 dependent oxidative stress; thus, RAS might ultimately promote myocardial apoptosis during reperfusion pathogenesis.

Sca-1+ cardiac stem cells mediate acute cardioprotection via paracrine factor SDF-1 following myocardial ischemia/reperfusion

Background

Cardiac stem cells (CSCs) promote myocardial recovery following ischemia through their regenerative properties. However, little is known regarding the implication of paracrine action by CSCs in the setting of myocardial ischemia/reperfusion (I/R) injury although it is well documented that non-cardiac stem cells mediate cardioprotection via the production of paracrine protective factors. Here, we studied whether CSCs could initiate acute protection following global myocardial I/R via paracrine effect and what component from CSCs is critical to this protection.

Methodology/Principal Findings

A murine model of global myocardial I/R was utilized to investigate paracrine effect of Sca-1+ CSCs on cardiac function. Intracoronary delivery of CSCs or CSC conditioned medium (CSC CM) prior to ischemia significantly improved myocardial function following I/R. siRNA targeting of VEGF in CSCs did not affect CSC-preserved myocardial function in response to I/R injury. However, differentiation of CSCs to cardiomyocytes (DCSCs) abolished this protection. Through direct comparison of the protein expression profiles of CSCs and DCSCs, SDF-1 was identified as one of the dominant paracrine factors secreted by CSCs. Blockade of the SDF-1 receptor by AMD3100 or downregulated SDF-1 expression in CSCs by specific SDF-1 siRNA dramatically impaired CSC-induced improvement in cardiac function and increased myocardial damage following I/R. Of note, CSC treatment increased myocardial STAT3 activation after I/R, whereas downregulation of SDF-1 action by blockade of the SDF-1 receptor or SDF-1 siRNA transfection abolished CSC-induced STAT3 activation. In addition, inhibition of STAT3 activation attenuated CSC-mediated cardioprotection following I/R. Finally, post-ischemic infusion of CSC CM was shown to significantly protect I/R-caused myocardial dysfunction.

Conclusions/Significance

This study suggests that CSCs acutely improve post-ischemic myocardial function through paracrine factor SDF-1 and up-regulated myocardial STAT3 activation.

SDF-1/CXCR4 mediates acute protection of cardiac function through myocardial STAT3 signaling following global ischemia/reperfusion injury

Stromal cell-derived factor-1α (SDF-1) has been reported to mediate cardioprotection through the mobilization of stem cells into injured tissue and an increase in local angiogenesis after myocardial infarction. However, little is known regarding whether SDF-1 induces acute protection following global myocardial ischemia/reperfusion (I/R) injury and if so, by what molecular mechanism. SDF-1 binding to its cognate receptor CXCR4 has been shown to activate STAT3 in a variety of cells. STAT3 is a cardioprotective factor and may mediate SDF-1/CXCR4-induced acute protection. We hypothesized that SDF-1 would improve myocardial function through CXCR4-increased STAT3 activation following acute I/R. Isolated mouse hearts were subjected to 25-min global ischemia/40-min reperfusion and divided into groups of 1) vehicle; 2) SDF-1; 3) AMD3100, a CXCR4 inhibitor; 4) SDF-1 + AMD3100; 5) Stattic, a STAT3 inhibitor; 6) SDF-1 + Stattic; 7) cardiomyocyte-restricted ablation of STAT3 (STAT3KO); 8) STAT3KO + SDF-1; 9) Ly294002, an inhibitor of the Akt pathway; and 10) SDF-1 + Ly294002. Reagents were infused into hearts within 5 min before ischemia. SDF-1 administration significantly improved postischemic myocardial functional recovery in a dose-dependent manner. Additionally, pretreatment with SDF-1 reduced cardiac apoptotic signaling and increased myocardial STAT3 activation following acute I/R. Inhibition of the SDF-1 receptor CXCR4 neutralized these protective effects by SDF-1 in hearts subjected to I/R. Notably, inhibition of the STAT3 pathway or use of STAT3KO hearts abolished SDF-1-induced acute protection following myocardial I/R. Our results represent the first evidence that the SDF-1/CXCR4 axis upregualtes myocardial STAT3 activation and, thereby, mediates acute cardioprotection in response to global I/R.

Myocarditis in CD8-depleted SIV-infected rhesus macaques after short-term dual therapy with nucleoside and nucleotide reverse transcriptase inhibitors

BACKGROUND

Although highly active antiretroviral therapy (HAART) has dramatically reduced the morbidity and mortality associated with HIV infection, a number of antiretroviral toxicities have been described, including myocardial toxicity resulting from the use of nucleotide and nucleoside reverse transcriptase inhibitors (NRTIs). Current treatment guidelines recommend the use of HAART regimens containing two NRTIs for initial therapy of HIV-1 positive individuals; however, potential cardiotoxicity resulting from treatment with multiple NRTIs has not been addressed.

METHODOLOGY/PRINCIPAL FINDINGS

We examined myocardial tissue from twelve CD8 lymphocyte-depleted adult rhesus macaques, including eight animals infected with simian immunodeficiency virus, four of which received combined antiretroviral therapy (CART) consisting of two NRTIs [(9-R-2-Phosphonomethoxypropyl Adenine) (PMPA) and (+/-)-beta-2',3'-dideoxy-5-fluoro-3'-thiacytidine (RCV)] for 28 days. Multifocal infiltrates of mononuclear inflammatory cells were present in the myocardium of all macaques that received CART, but not untreated SIV-positive animals or SIV-negative controls. Macrophages were the predominant inflammatory cells within lesions, as shown by immunoreactivity for the macrophage markers Iba1 and CD68. Heart specimens from monkeys that received CART had significantly lower virus burdens than untreated animals (p<0.05), but significantly greater quantities of TNF-α mRNA than either SIV-positive untreated animals or uninfected controls (p<0.05). Interferon-γ (IFN-γ), IL-1β and CXCL11 mRNA were upregulated in heart tissue from SIV-positive monkeys, independent of antiretroviral treatment, but CXCL9 mRNA was only upregulated in heart tissue from macaques that received CART.

CONCLUSIONS/SIGNIFICANCE

These results suggest that short-term treatment with multiple NRTIs may be associated with myocarditis, and demonstrate that the CD8-depleted SIV-positive rhesus monkey is a useful model for studying the cardiotoxic effects of combined antiretroviral therapy in the setting of immunodeficiency virus infection.

Gender dimorphisms in progenitor and stem cell function in cardiovascular disease

Differences in cardiovascular disease outcomes between men and women have long been recognized and attributed, in part, to gender and sex steroids. Gender dimorphisms also exist with respect to the roles of progenitor and stem cells in post-ischemic myocardial and endothelial repair and regeneration. Understanding how these cells are influenced by donor gender and the recipient hormonal milieu may enable researchers to further account for the gender-related disparities in clinical outcomes as well as utilize the beneficial effects of these hormones to optimize transplanted cell function and survival. This review discusses (1) the cardiovascular effects of sex steroids (specifically estradiol and testosterone); (2) the therapeutic potentials of endothelial progenitor cells, mesenchymal stem cells, and embryonic stem cells; and (3) the direct effect of sex steroids on these cell types.

TNF receptor 2, not TNF receptor 1, enhances mesenchymal stem cell-mediated cardiac protection following acute ischemia

Mesenchymal stem cells (MSCs) may improve myocardial function after I/R injury via paracrine effects, including the release of growth factors. Genetic modification of MSCs is an appealing method to enhance MSC paracrine action. Ablation of TNF receptor 1 (TNFR1), but not TNFR2, increases MSC growth factor production. In this study, therefore, we hypothesized that 1) preischemic infusion of MSCs derived from TNFR1 knockout (TNFR1KO) mice will further improve myocardial functional recovery and that 2) TNFR2KO and TNFR1/2KO will abolish MSC-mediated protection in the heart after I/R injury. Mesenchymal stem cells were harvested from adult C57BL/6J (wild-type 1 [WT1]), B6129SF2 (WT2), TNFR1KO, TNFR2KO, and TNFR1/2KO mice. Mesenchymal stem cells were cultured and adopted for experiments after passage 3. Isolated hearts from adult male Sprague-Dawley rats were subjected to 25 min of ischemia and 40 min of reperfusion (Langendorff model), during which time myocardial function was continuously monitored. Before ischemia, 1 mL of vehicle or 1 x 10(6) MSCs/mL from WT1, WT2, TNFR1KO, TNFR2KO, or TNFR1/2KO was infused into the hearts (n = 4-6 per group). Treatment of C57BL/6J mice with MSC before ischemia significantly increased cardiac function. TNFR1 knockout MSCs demonstrated greater cardioprotection when compared with WT MSCs after I/R, as exhibited by improved left ventricular developed pressure and +/-dp/dt. However, infusion of MSCs from TNFR2KO and TNFR1/2KO mice either offered no benefit or decreased MSC-mediated cardiac functional recovery in response to I/R when compared with WT MSCs. TNFR1 signaling may damage MSC paracrine effects and decrease MSC-mediated cardioprotection, whereas TNFR2 likely mediates beneficial effects in MSCs.

TNFα protects cardiac mitochondria independently of its cell surface receptors

Our novel proposal is that TNFα exerts a direct effect on mitochondrial respiratory function in the heart, independently of its cell surface receptors. TNFα-induced cardioprotection is known to involve reactive oxygen species (ROS) and sphingolipids. We therefore further propose that this direct mitochondrial effect is mediated via ROS and sphingolipids. The protective concentration of TNFα (0.5 ng/ml) was added to isolated heart mitochondria from black 6 × 129 mice (WT) and double TNF receptor knockout mice (TNFR1&2(-/-)). Respiratory parameters and inner mitochondrial membrane potential were analyzed in the presence/absence of two antioxidants, N-acetyl-L: -cysteine or N-tert-butyl-α-(2-sulfophenyl)nitrone or two antagonists of the sphingolipid pathway, N-oleoylethanolamine (NOE) or imipramine. In WT, TNFα reduced State 3 respiration from 279.3 ± 3 to 119.3 ± 2 (nmol O₂/mg protein/min), increased proton leak from 15.7 ± 0.6% (control) to 36.6 ± 4.4%, and decreased membrane potential by 20.5 ± 3.1% compared to control groups. In TNFR1&2(-/-) mice, TNFα reduced State 3 respiration from 205.2 ± 4 to 75.7 ± 1 (p < 0.05 vs. respective control). In WT mice, both antioxidants added with TNFα restored State 3 respiration to 269.2 ± 2 and 257.6 ± 2, respectively. Imipramine and NOE also restored State 3 respiration to 248.4 ± 2 and 249.0 ± 2, respectively (p < 0.01 vs. TNFα alone). Similarly, both antioxidant and inhibitors of the sphingolipid pathway restored the proton leak to pre-TNF values. TNFα-treated mitochondria or isolated cardiac muscle fibers showed an increase in respiration after anoxia-reoxygenation, but this effect was lost in the presence of an antioxidant or NOE. Similar data were obtained in TNFR1&2(-/-) mice. TNFα exerts a protective effect on respiratory function in isolated mitochondria subjected to an anoxia-reoxygenation insult. This effect appears to be independent of its cell surface receptors, but is likely to be mediated by ROS and sphingolipids.

MEK, p38, and PI-3K mediate cross talk between EGFR and TNFR in enhancing hepatocyte growth factor production from human mesenchymal stem cells

Human bone marrow mesenchymal stem cells (MSCs) are a potent source of growth factors, which are partly responsible for their beneficial paracrine effects. We reported previously that transforming growth factor-alpha (TGF-alpha), a putative mediator of wound healing and the injury response, increases the release of vascular endothelial growth factor (VEGF), augments tumor necrosis factor-alpha (TNF-alpha)-stimulated VEGF production, and activates mitogen-activated protein kinases and phosphatidylinositol 3-kinase (PI-3K) pathway in human MSCs. The experiments described in this report indicate that TGF-alpha increases MSC-derived hepatocyte growth factor (HGF) production. TGF-alpha-stimulated HGF production was abolished by inhibition of MEK, p38, PI-3K, or by small interfering RNA (siRNA) targeting TNF receptor 2 (TNFR2), but was not attenuated by siRNA targeting TNF receptor 1 (TNFR1). Ablation of TNFR1 significantly increased basal and stimulated HGF. A potent synergy between TGF-alpha and TNF-alpha was noted in MSC HGF production. This synergistic effect was abolished by MEK, P38, PI-3K inhibition, or by ablation of both TNF receptors using siRNA. We conclude that 1) novel cross talk occurs between tumor necrosis factor receptor and TGF-alpha/epidermal growth factor receptor in stimulating MSC HGF production; 2) this cross talk is mediated, at least partially, via activation of MEK, p38, and PI-3K; 3) TGF-alpha stimulates MSCs to produce HGF by MEK, p38, PI-3K, and TNFR2-dependent mechanisms; and 4) TNFR1 acts to decrease basal TGF-alpha and TNF-alpha-stimulated HGF.

Both endogenous and exogenous testosterone decrease myocardial STAT3 activation and SOCS3 expression after acute ischemia and reperfusion

BACKGROUND

Signal transducer and activator of transduction 3 (STAT3) pathway has been shown to be cardioprotective. We observed decreased STAT3/suppressor of cytokine signaling 3 (SOCS3) in male hearts, which was associated with worse postischemic myocardial function compared with females. However, it is unclear whether this downregulation of myocardial STAT3/SOCS3 is due to testosterone in males. We hypothesized that after ischemia/reperfusion (I/R), (1) endogenous testosterone decreases myocardial STAT3 and SOCS3 in males, and (2) administration of exogenous testosterone reduces myocardial STAT3/SOCS3 in female and castrated male hearts.

METHODS

To study this, hearts from I/R injury (Langendorff) were homogenized and assessed for phosphorylated-STAT3 (p-STAT3), total-STAT3 (T-STAT3), SOCS3, and GAPDH by Western blot. We grouped age-matched adult males, females, castrated males, males with androgen receptor blocker-flutamide implantation, females, and castrated males with chronic (3-week) 5alpha-dihydrotestosterone (DHT) release pellet implantation or acute (5-minute) testosterone infusion (ATI) before ischemia (n = 5-9 per group).

RESULTS

Castration or flutamide treatment significantly increased SOCS3 expression in male hearts after I/R. However, only castration increased myocardial STAT3 activation. Notably, DHT replacement or ATI decreased markedly myocardial STAT3/SOCS3 in castrated males and females subjected to I/R.

CONCLUSION

These results suggest that endogenous and exogenous testosterone decrease myocardial STAT3 activation and SOCS3 expression after I/R. This represents the initial demonstration of testosterone-downregulated STAT3/SOCS3 signaling in myocardium.

Deficiency in TLR4 signal transduction ameliorates cardiac injury and cardiomyocyte contractile dysfunction during ischemia

Toll-like receptor 4 (TLR4), a proximal signalling receptor in innate immune responses to lipopolysaccharide of gram-negative pathogens, is expressed in the heart. Accumulating evidence have consolidated the notion that TLR4 plays an essential role in the pathogenesis of cardiac dysfunction. However, the molecular mechanisms of TLR4 responsible for ischemia-induced cardiac dysfunction remain unclear. To address the signalling mechanisms of TLR4-deficiency cardioprotection against ischemic injury, in vivo regional ischemia was induced by occlusion of the left anterior descending coronary artery in wild-type (WT) C3H/HeN and TLR4-mutated C3H/HeJ mice. The results demonstrated that blunted ischemic activation of p38 mitogen-activated protein kinase and JNK signalling occurred in C3H/HeJ hearts versus C3H/HeN hearts, while ERK and AMP-activated protein kinase (AMPK) signalling pathways were augmented during ischemia in C3H/HeJ hearts versus C3H/HeN hearts. Intriguingly, ischemia-stimulated endoplasmic reticulum stress was higher in C3H/HeN hearts than that in C3H/HeJ as demonstrated by up-regulation of Grp78/BiP, Gadd153/CHOP and IRE-1α. Myocardial infarct, caspase-3 activity and terminal deoxynucleotidyl transferase dUTP nick end labelling (TUNEL) staining demonstrated that C3H/HeN hearts suffered more damage than those of C3H/HeJ hearts during ischemia. Moreover, isolated cardiomyocytes from C3H/HeJ hearts showed resistance to hypoxia-induced contractile dysfunction compared to those from C3H/HeN hearts, which are associated with greater hypoxic activation of AMPK and ERK signalling, better intracellular Ca²⁺ handling in C3H/HeJ versus C3H/HeN cardiomyocytes. These findings suggest that the cardioprotective effects against ischemic injury of hearts with deficiency in TLR4 signalling may be mediated through modulating AMPK and ERK signalling pathway during ischemia.

Estrogen receptor beta mediates increased activation of PI3K/Akt signaling and improved myocardial function in female hearts following acute ischemia

Females have a lower incidence of heart failure and improved survival after myocardial ischemia-reperfusion (I/R) compared with males. Although estrogen-suppressed cardiomyocyte apoptosis may be mediated through the phosphatidylinositol 3-kinase (PI3K)/protein kinase B (Akt) pathway, it is unclear whether this action is mediated via estrogen receptor beta (ERbeta). Therefore, we hypothesized that ERbeta mediates estrogen-induced cardioprotection through PI3K/Akt and antiapoptotic signaling in females but not in males. Isolated male and female hearts from ERbeta knockout (ERbetaKO) and wild-type (WT) mice (n = 5 mice/group) were subjected to 20-min ischemia followed by 60-min reperfusion (Langendorff). Ablation of ERbeta significantly decreased postischemic recovery of left ventricular developed pressure in female, but not male, hearts. Reduced activation of PI3K and Akt was noted in female ERbetaKO hearts, which was associated with increased expression of caspase-3 and -8, as well as decreased Bcl-2 levels compared with WT. However, myocardial STAT3, SOCS3 (suppressor of cytokine signaling 3), VEGF, and TNF receptors 1 and 2 levels did not change in ERbetaKO of either sex following I/R. Furthermore, deficiency of ERbeta increased myocardial JNK activation in females but increased ERK1/2 activity in males during acute I/R. We conclude that ERbeta mediates myocardial protection via upregulation of PI3K/Akt activation, decreased caspase-3 and -8, and increased Bcl-2 in female hearts following I/R. These findings provide evidence of ERbeta-mediated PI3K/Akt and antiapoptotic signaling in the myocardium and may lend insight into the mechanistic pathways behind the observed variation in clinical outcomes between males and females after myocardial infarction.

Renin Angiotensin system as a regulator of cell volume. Implications to myocardial ischemia

It is known that long lasting changes in cell volume are incompatible with cellular functions. In the present review, I discussed the role of cell volume on gene expression and protein synthesis as well as the importance of the renin angiotensin system on the regulation of cell volume in the failing heart. Moreover, the relationship between mechanical stretch, cell volume and the renin angiotensin system as well some translational studies are also described and their relevance to the prevention or reduction of cardiac damage during myocardial ischemia is emphasized.

Proestrus female rats are more resistant to right ventricular pressure overload

Multiple studies of left ventricular dysfunction suggest that females may be more resistant to ischemia or endotoxemia. However, sex differences in right ventricular (RV) responses to pressure overload and/or endotoxemia have not been elucidated. We hypothesized that females would maintain better RV function during acute pressure overload (APO), endotoxemia, or a simultaneous insult from both processes. Age-matched male and proestrus female Sprague-Dawley rats were given an intraperitoneal injection of either phosphate buffered saline or LPS. Six hours after injection, hearts were removed by median sternotomy and isolated via Langendorff. End-diastolic pressures were sequentially elevated past physiologic levels by increasing the volume of a latex balloon that was inserted into the RV. Male RV function was depressed to a greater degree after APO injury compared with that in females (developed pressure: male, 44.97 mmHg vs. female, 58.23 mmHg). Interestingly though, at a physiologic end-diastolic pressure of 5 mmHg, endotoxic males and females maintained equivalent RV function. However, with concurrent endotoxic insult and APO, RV function was better maintained in males as compared with that in females (developed pressure: male, 59% of control versus female, 41% of control). Furthermore, tissue levels of IL-1 and IL-6, but not IL-10, were increased after endotoxin exposure but did not differ based on sex. Through this study, we have shown that sex differences exist in RV dysfunction, and that different cardiac insults diversely affect myocardial function. Understanding these differences may allow for the implementation of novel therapeutic treatment options that are designed to attenuate RV cardiovascular collapse.

Mechanisms of sex differences in TNFR2-mediated cardioprotection

BACKGROUND

TNFR1/TNFR2 signaling may mediate different cellular and molecular responses (injury versus protection) and the balance may be affected by sex hormones. Previous studies have shown that females have improved myocardial functional recovery, TNFR1 signaling resistance, and increased SOCS3 expression after acute ischemia/reperfusion when compared with males. However, it is unknown whether the TNFR2 pathway protects the myocardium from ischemia/reperfusion injury, and if so, whether sex differences exist in TNFR2-mediated cardioprotection. Therefore, we hypothesized that (1) TNFR2 mediates myocardial protection from ischemia/reperfusion through STAT3, SOCS3, and vascular endothelial growth factor in both sexes; and (2) TNFR2 elicits greater protective signaling in females compared with males.

METHODS AND RESULTS

Isolated male and female mouse hearts from TNFR2 knockout, TNFR1/2 knockout, and wild-type (C57BL/6J or B6129SF2/J; n=5 to 6/group) were subjected to 20 minutes ischemia followed by 60 minutes reperfusion. TNFR2 deficiency decreased postischemic myocardial recovery in both sexes but had a greater effect on females. The deleterious effects of TNFR2 ablation were associated with a decrease in mRNA and protein levels of SOCS3, STAT3, and vascular endothelial growth factor as well as an increase in myocardial interleukin-1-beta production in female hearts. However, a significant increase in JNK activation and interleukin-1-beta protein levels was noted in male TNFR2KO hearts after ischemia/reperfusion. Additionally, TNFR1/2 knockout decreased myocardial function in female hearts but not males. This observation was associated with a decrease in mRNA levels of SOCS3, STAT3, and vascular endothelial growth factor and an increase in myocardial p38 mitogen-activated protein kinase activation in females.

CONCLUSIONS

Sex differences in the mechanisms of TNFR2-mediated cardioprotection occur by increasing STAT3, SOCS3, and vascular endothelial growth factor in females and by decreasing JNK in males.

Aprotinin exacerbates left ventricular dysfunction after ischemia/reperfusion in mice lacking tumor necrosis factor receptor I

Aprotinin is a serine protease inhibitor with diverse biological effects; until recently, it was utilized in the context of ischemia/reperfusion (I/R). It has been hypothesized that a signaling pathway modulated by aprotinin in the context of I/R is the tumor necrosis factor-alpha receptor (TNFR) pathway. An intact mouse model of I/R (30 min ischemia and 60 min reperfusion) was used and left ventricular (LV) peak + maximal rate of left ventricular (LV) peak pressure (dP/dt) was measured in wild-type mice (WT, C57BL/6; n = 10), WT mice with aprotinin (4 mL/kg; n = 10), transgenic mice devoid of the TNFRI (TNFRI-null; n = 10), and TNFRI-null with aprotinin (n=10). Following I/R, LV peak + dP/dt decreased in both WT groups, but remained similar to baseline values in the TNFRI-null group. In contrast, aprotinin caused a marked reduction in LV peak + dP/dt in the TNFRI-null group following I/R. Soluble plasma TNF levels increased in the WT and TNFRI-null mice with I/R and was reduced with aprotinin. Soluble TNFRI and TNFRII levels, indicative of TNF activation, increased in the WT mice following I/R and remained elevated with aprotinin. Soluble TNFRII levels were increased in the TNFRI-null mice following I/R and remained elevated with aprotinin. The new and unique findings of this study were twofold. First, aprotinin failed to improve LV function after I/R despite a reduction in circulating TNF levels. Second, genetic ablation of TNFRI uncovered a negative inotropic effect of aprotinin. These findings demonstrate that complex biological pathways and interactions are affected with broad spectrum serine protease inhibition, which are relevant to myocardial function in the context of I/R.

TNFR1 signaling resistance associated with female stem cell cytokine production is independent of TNFR2-mediated pathways

End-organ ischemia is a common source of patient morbidity and mortality. Stem cell therapy represents a novel treatment modality for ischemic diseases and may aid injured tissues through the release of beneficial paracrine mediators. Female bone marrow mesenchymal stem cells (MSCs) have demonstrated a relative resistance to detrimental TNF receptor 1 (TNFR1) signaling and are thought to be superior to male stem cells in limiting inflammation. However, it is not known whether sex differences exist in TNF receptor 2 (TNFR2)-ablated MSCs. Therefore, we hypothesized that 1) sex differences would be observed in wild-type (WT) and TNFR2-ablated MSC cytokine signaling, and 2) the production of IL-6, VEGF, and IGF-1 in males, but not females, would be mediated through TNFR2. MSCs were harvested from male and female WT and TNFR2 knockout (TNFR2KO) mice and were subsequently exposed to TNF (50 ng/ml) or LPS (100 ng/ml). After 24 h, supernatants were collected and measured for cytokines. TNF and LPS stimulated WT stem cells to produce cytokines, but sex differences were only seen in IL-6 and IGF-1 after TNF stimulation. Ablation of TNFR2 increased VEGF and IGF-1 production in males compared with wild-type, but no difference was observed in females. Female MSCs from TNFR2KOs produced significantly lower levels of VEGF and IGF-1 compared with male TNFR2KOs. The absence of TNFR2 signaling appears to play a greater role in male MSC cytokine production. As a result, male, but not female stem cell cytokine production may be mediated through TNFR2 signaling cascades.

The effects of endogenous sex hormones and acute hypoxia on vasoconstriction in isolated rat pulmonary artery rings

BACKGROUND

Studies have noted gender differences in various models but have not investigated whether hormone depletion will abolish these differences. Therefore, we measured isometric force displacement in normal males, castrated males, normal females, and ovarectomized females.

MATERIALS AND METHODS

Adult male, adult female, castrated male, and ovarectomized female (250-350 g) Sprague Dawley rat pulmonary arteries (n = 7-8/group) were isolated and suspended in physiological organ baths. Force displacement was continuously recorded for 60 min of hypoxia. Data (mean +/- SEM) was analyzed with two-way analysis of variance with post-hoc Bonferroni test or Student's t-test.

RESULTS

Maximum vasodilation of normal males was -79.47 +/- 3.34%, while normal adult females exhibited a maximum vasodilation of -88.70 +/- 6.21% (P = 0.8149). In addition, delayed, phase II vasoconstriction of male pulmonary arteries rings was 89.79 +/- 7.25%, while adult females demonstrated a maximum phase II vasoconstriction of 95.90 +/- 14.23% (P = 0.9342). Hormone depletion of males exhibited a maximum vasodilation of -70.45 +/- 5.08% for castrated males as compared to -79.47 +/- 3.34% for normal adult males (P = 0.3805). Castrated males exhibited a maximum phase II vasoconstriction of 86.20 +/- 15.76% compared to 89.79 +/- 7.25% exhibited by normal adult males (P = 0.9516).

CONCLUSIONS

Hormone depletion in males and females did not alter pulmonary vasoreactivity in acute hypoxia.

Prevention of atrial fibrillation following cardiac surgery: basis for a novel therapeutic strategy based on non-hypoxic myocardial preconditioning

Atrial fibrillation is the most common complication of cardiac surgical procedures performed with cardiopulmonary bypass. It contributes to increased hospital length of stay and treatment costs. At present, preventive strategies offer only suboptimal benefits, despite improvements in anesthesia, surgical technique, and medical therapy. The pathogenesis of postoperative atrial fibrillation is considered to be multifactorial. However oxidative stress is a major contributory factor representing the unavoidable consequences of ischemia/reperfusion cycle occurring in this setting. Considerable evidence suggests the involvement of reactive oxygen species (ROS) in the pathogenic mechanism of this arrhythmia. Interestingly, the deleterious consequences of high ROS exposure, such as inflammation, cell death (apoptosis/necrosis) or fibrosis, may be abrogated by a myocardial preconditioning process caused by previous exposure to moderate ROS concentration known to trigger survival response mechanisms. The latter condition may be created by n-3 PUFA supplementation that could give rise to an adaptive response characterized by increased expression of myocardial antioxidant enzymes and/or anti-apoptotic pathways. In addition, a further reinforcement of myocardial antioxidant defenses could be obtained through vitamins C and E supplementation, an intervention also known to diminish enzymatic ROS production. Based on this paradigm, this review presents clinical and experimental evidence supporting the pathophysiological and molecular basis for a novel therapeutic approach aimed to diminish the incidence of postoperative atrial fibrillation through a non-hypoxic preconditioning plus a reinforcement of the antioxidant defense system in the myocardial tissue.

Females exhibit relative resistance to depressive effects of tumor necrosis factor-alpha on the myocardium

BACKGROUND

Tumor necrosis factor-alpha (TNF-alpha) plays a critical role in myocardial dysfunction following acute injury. It is unknown, however, if a gender-specific response to TNF infusion exists in isolated rat hearts. Elucidating such mechanisms is important to understanding the myocardial gender differences during acute injury. We hypothesize that females will exhibit a relative resistance to TNF-induced myocardial dysfunction compared to males and that menstrual cycle would influence the degree of female myocardial resistance to TNF-induced myocardial functional depression.

MATERIALS AND METHODS

Adult male, proestrus female, and metestrus/diestrus female hearts were subjected to 60 min of TNF infusion at 10,000 pg/mL.min via Langendorff. Myocardial contractile function (left ventricular developed pressure, and the positive/negative first derivative of pressure) was continuously recorded.

RESULTS

10,000 pg/mL.min of TNF markedly depressed myocardial function in males compared with other doses of TNF. Myocardial function was significantly decreased in males compared to females following TNF infusion. Additionally, both the proestrus and the metestrus/diestrus females exhibited equal resistance to TNF-induced myocardial dysfunction.

CONCLUSION

Our study shows that females exhibit a significantly greater degree of resistance to TNF-induced myocardial depression. Moreover, data from this study suggest that fluctuations in estrogen during the reproductive cycle may have little to no influence on TNF-induced myocardial depression.

Sex differences in endothelial STAT3 mediate sex differences in myocardial inflammation

Recent studies have shown that females have improved myocardial functional recovery, TNF receptor 1 (TNFR1) signaling resistance, and increased STAT3 phosphorylation following acute ischemia/reperfusion (I/R) compared with males. We hypothesized that 1) STAT3 deficiency in endothelial cells (EC) impairs myocardial functional recovery in both sexes, 2) EC STAT3 deficiency equalizes sex differences in functional recovery, and 3) knockout of EC STAT3 decreases activation of myocardial STAT3 and increases p38 MAPK activation following acute I/R. Isolated male and female mouse hearts from WT and EC STAT3 knockout (STAT3KO) were subjected to 20-min ischemia/60-min reperfusion, and +/- dP/dt were continuously recorded. Heart tissue was analyzed for the active forms of STAT3 and p38 MAPK as well as expression of caspase-8 (Western blot) following I/R. EC STATKO had significantly decreased myocardial functional recovery in both sexes (%recovered +dP/dt: male 51.6 +/- 3.1 vs. 32.1 +/- 13.1%, female 79.1 +/- 3.6 vs. 43.6 +/- 9.1%; -dP/dt: male 52.2 +/- 3.3 vs. 28.9 +/- 12%, female 75.2 +/- 4.1 vs. 38.6 +/- 10%). In addition, EC STAT3KO neutralized sex differences in myocardial function, which existed in WT mice. Interestingly, EC STAT3 deficiency decreased myocardial STAT3 activation but increased myocardial p38 MAPK activation in both sexes; however, this was seen to a greater degree in females. We conclude that EC STAT3 deficiency resulted in decreased recovery of myocardial function in both sexes and neutralized sex differences in myocardial functional recovery following I/R. This observation was associated with decreased activation of myocardial STAT3 and increased activation of p38 MAPK in EC STAT3KO heart after I/R.

Endogenous estrogen attenuates pulmonary artery vasoreactivity and acute hypoxic pulmonary vasoconstriction: the effects of sex and menstrual cycle

Sex differences exist in a variety of cardiovascular disorders. Sex hormones have been shown to mediate pulmonary artery (PA) vasodilation. However, the effects of fluctuations in physiological sex hormone levels due to sex and menstrual cycle on PA vasoreactivity have not been clearly established yet. We hypothesized that sex and menstrual cycle affect PA vasoconstriction under both normoxic and hypoxic conditions. Isometric force displacement was measured in isolated PA rings from proestrus females (PF), estrus and diestrus females (E/DF), and male (M) Sprague-Dawley rats. The vasoconstrictor response under normoxic conditions (organ bath bubbled with 95% O(2)-5% CO(2)) was measured after stimulation with 80 mmol/l KCl and 1 mumol/l phenylephrine. Hypoxia was generated by changing the gas to 95% N(2)-5% CO(2). PA rings from PF demonstrated an attenuated vasoconstrictor response to KCl compared with rings from E/DF (75.58 +/- 3.2% vs. 92.43 +/- 4.24%, P < 0.01). Rings from M also exhibited attenuated KCl-induced vasoconstriction compared with E/DF (79.34 +/- 3.2% vs. 92.43 +/- 4.24%, P < 0.05). PA rings from PF exhibited an attenuated vasoconstrictor response to phenylephrine compared with E/DF (59.61 +/- 2.98% vs. 70.03 +/- 4.61%, P < 0.05). While the maximum PA vasodilation during hypoxia did not differ between PF, E/DF, and M, phase II of hypoxic pulmonary vasoconstriction was markedly diminished in the PA from PF (64.10 +/- 7.10% vs. 83.91 +/- 5.97% in M, P < 0.05). We conclude that sex and menstrual cycle affect PA vasoconstriction in isolated PA rings. Even physiological increases in circulating estrogen levels attenuate PA vasoconstriction under both normoxic and hypoxic conditions.

Endothelial STAT3 plays a critical role in generalized myocardial proinflammatory and proapoptotic signaling

Signal transducer and activator of transcription (STAT) 3 is involved in mediating a broad range of biological processes, including cell survival, proliferation, and immune response. Recent evidence has indicated that STAT3 in cardiomyocytes can be activated by ischemic-oxidative stress and exerts cardioprotection in the ischemic heart. There is no information, however, regarding the effect of endothelial cell-derived STAT3 on the myocardial response to ischemiareperfusion (I/R) injury. We hypothesized that the ablation of the STAT3 gene in endothelial cells would worsen postischemic myocardial function by affecting capillary network integrity, suppressing antiapoptotic signaling. Isolated hearts from wild-type and endothelial cell STAT3 knockout (STAT3KO) mice were subjected to 20 min of global ischemia followed by 60 min of reperfusion. Endothelial cell STAT3 deficiency decreased recovery of myocardial function in response to I/R, which was associated with higher levels of LDH release, decreased activation of myocardial STAT3, and elevated p38 MAPK activation in STAT3 endothelial knockout (KO) hearts. In addition, although no significant apoptosis was observed in wild-type and KO hearts, our results showed more expression of myocardial caspase-8 and more apoptosis in the myocardium around the capillary in STAT3KO mice subjected to I/R. Furthermore, endothelial cell STAT3 ablation resulted in increased myocardial expression of IL-6 and suppressor of cytokine signal 3. This study demonstrates that endothelial cell-derived STAT3 plays an important role in postischemic myocardial function.

Postischemic infusion of 17-beta-estradiol protects myocardial function and viability

BACKGROUND

Females demonstrate improved cardiac recovery after ischemia/reperfusion injury compared with males. Attenuation of myocardial dysfunction with preischemic estradiol suggests that estrogen may be an important mediator of this cardioprotection. However, it remains unclear whether post-injury estradiol may have clinical potential in the treatment of acute myocardial infarction. We hypothesize that postischemic administration of 17beta-estradiol will decrease myocardial ischemia/reperfusion injury and improve left ventricular cardiac function.

MATERIALS AND METHODS

Adult male Sprague Dawley rat hearts (n = 20) (Harlan, Indianapolis, IN) were isolated, perfused with Krebs-Henseleit solution via Langendorff model, and subjected to 15 min of equilibration, 25 min of warm ischemia, and 40 min reperfusion. Experimental hearts received postischemic 17beta-estradiol infusion, 1 nm (n = 4), 10 nm (n = 4), 25 nm (n = 4), or 50 nm (n = 4), throughout reperfusion. Control hearts (n = 4) were infused with perfusate vehicle.

RESULTS

Postischemic recovery of left ventricular developed pressure was significantly greater with 1 nm (51.6% +/- 7.4%) and 10 nm estradiol (47.7% +/- 8.6%) than with vehicle (37.8% +/- 9.7%) at end reperfusion. There was also greater recovery of the end diastolic pressure with 1 nm (47.8 +/- 4.0 mmHg) and 10 nm estradiol (54.0 +/- 4.0) compared with vehicle (75.3 +/- 7.5). Further, 1 nm and 10 nm estrogen preserved coronary flow after ischemia and decreased coronary effluent lactated dehydrogenase compared with controls. Estrogen at 25 nm and 50 nm did not provide additional benefit in terms of functional recovery. Estrogen at all concentrations increased extracellular signal-regulated protein kinase phosphorylation.

CONCLUSIONS

Postischemic infusion of 17beta-estradiol protects myocardial function and viability. The attractive potential for the clinical application of postischemic estrogen therapy warrants further study to elucidate the mechanistic pathways and differences between males and females.

Iron chelation acutely stimulates fetal human intestinal cell production of IL-6 and VEGF while decreasing HGF: the roles of p38, ERK, and JNK MAPK signaling

Bacteria have developed mechanisms to sequester host iron via chelators such as deferoxamine (DFO). Interestingly, DFO has been shown to stimulate acute intestinal epithelial cell inflammatory cytokine production in the absence of bacteria; however, this mechanism has not been elucidated. Intestinal epithelial cell production of IL-6 and TNF-alpha is elevated in various gastrointestinal pathologies, including acute intestinal ischemia. Similarly, VEGF and HGF are essential to intestinal epithelial cell integrity. Therapeutic strategies that decrease IL-6 and TNF-alpha while increasing VEGF and HGF therefore have theoretical appeal. We hypothesized that 1) fetal human intestinal epithelial cells acutely produce increased IL-6, TNF-alpha, VEGF, and HGF during iron chelation and 2) the MAPK pathway mediates these effects. Fetal human intestinal epithelial cells were stimulated by iron chelation (1 mM DFO) with and without p38 MAPK, ERK, or JNK inhibition. Supernatants were harvested after 24 h of incubation, and IL-6, TNF-alpha, VEGF, and HGF levels were quantified by ELISA. Activation of MAPK pathways was confirmed by Western blot analysis. DFO stimulation resulted in a significant increase in epithelial cell IL-6 and VEGF production while yielding a decrease in HGF production (P<0.05). Unexpectedly, TNF-alpha was not detectable. p38 MAPK, ERK, and JNK inhibition significantly decreased IL-6, VEGF, and HGF production (P<0.05). In conclusion, DFO acutely increases fetal human intestinal epithelial cell IL-6 and VEGF expression while causing an unexpected decrease in HGF expression and no detectable TNF-alpha production. Furthermore, chelator-induced intestinal epithelial cell cytokine expression depends on p38, ERK, and JNK MAPK pathways.

Deficiency of TNFR1 protects myocardium through SOCS3 and IL-6 but not p38 MAPK or IL-1beta

Tumor necrosis factor-alpha (TNF-alpha) plays an important role in the development of heart failure. There is a direct correlation between myocardial function and myocardial TNF levels in humans. TNF may induce local inflammation to exert tissue injury. On the other hand, suppressors of cytokine signaling (SOCS) proteins have been shown to inhibit proinflammatory signaling. However, it is unknown whether TNF mediates myocardial inflammation via STAT3/SOCS3 signaling in the heart and, if so, whether this effect is through the type 1 55-kDa TNF receptor (TNFR1). We hypothesized that TNFR1 deficiency protects myocardial function and decreases myocardial IL-6 production via the STAT3/SOCS3 pathway in response to TNF. Isolated male mouse hearts (n = 4/group) from wild-type (WT) and TNFR1 knockout (TNFR1KO) were subjected to direct TNF infusion (500 pg.ml(-1).min(-1) x 30 min) while left ventricular developed pressure and maximal positive and negative values of the first derivative of pressure were continuously recorded. Heart tissue was analyzed for active forms of STAT3, p38, SOCS3 and SOCS1 (Western blot analysis), as well as IL-1beta and IL-6 (ELISA). Coronary effluent was analyzed for lactate dehydrogenase (LDH) activity. As a result, TNFR1KO had significantly better myocardial function, less myocardial LDH release, and greater expression of SOCS3 (percentage of SOCS3/GAPDH: 45 +/- 4.5% vs. WT 22 +/- 6.5%) after TNF infusion. TNFR1 deficiency decreased STAT3 activation (percentage of phospho-STAT3/STAT3: 29 +/- 6.4% vs. WT 45 +/- 8.8%). IL-6 was decreased in TNFR1KO (150.2 +/- 3.65 pg/mg protein) versus WT (211.4 +/- 26.08) mice. TNFR1 deficiency did not change expression of p38 and IL-1beta following TNF infusion. These results suggest that deficiency of TNFR1 protects myocardium through SOCS3 and IL-6 but not p38 MAPK or IL-1beta.

Gender differences in injury induced mesenchymal stem cell apoptosis and VEGF, TNF, IL-6 expression: role of the 55 kDa TNF receptor (TNFR1)

Concomitant pro- and anti-inflammatory properties of bone marrow stem cells (BMSC) may be an important aspect of their ability to heal injured tissue. However, very few studies have examined whether gender differences exist in BMSC function. Indeed, it remains unknown whether gender differences exist in BMSC function and ability to resist apoptosis, and if so, whether TNF receptor 1 (TNFR1) plays a role in these differences. We hypothesized that TNFR1 ablation equalizes gender differences in bone marrow mesenchymal stem cell (MSC) apoptosis, as well as expression of vascular endothelial growth factor (VEGF), TNF and interleukin (IL)-6. Mouse MSCs from male wild type (WT), female WT, male TNFR1 knockouts (TNFR1KO) and female TNFR1KO were stressed by endotoxin 200 ng/ml or 1 h hypoxia. MSC activation was determined by measuring VEGF, TNF and IL-6 production (ELISA). Differences considered significant if p<0.05. LPS and hypoxia resulted in significant activation in all experimental groups compared to controls. Male WT demonstrated significantly greater TNF and IL-6 and significantly less VEGF release than female WT MSCs. However, release of TNF, IL-6 and VEGF in male TNFR1 knockouts differed from male WT, but was not different from female WT MSCs. Similarly apoptosis in hypoxic male TNFRIKO differed from male WT, but it was not different from apoptosis from WT female. Female WT did not differ in TNF, IL-6 and VEGF release compared to female TNFR1KO. Gender differences exist in injury induced BMSC VEGF, TNF and IL-6 expression. TNFR1 may autoregulate VEGF, TNF and IL-6 expression in males more than females. MSCs are novel therapeutic agents for organ protection, but further study of the disparate expression of VEGF, TNF and IL-6 in males and females as well as the role of TNFR1 in these gender differences is necessary to maximize this protection.