Exosomes as agents of change in the cardiovascular system

Exosomes have an evolving role in paracrine and autocrine signaling, which is enhanced because these lipid vesicles are quite stable and can deliver miRNA, DNA, protein and other molecules to cells throughout the body. Most cell types release exosomes, and exosomes are found in all biological fluids, making them accessible biomarkers. Significantly, exosomes can carry a biologically potent cargo, which can alter the phenotype of recipient cells. In the cardiovascular system exosomes have been primarily studied for their role in mediating the beneficial effects of mesenchymal stem cells after myocardial injury. Exosomes released by cardiac cells in disease states, such as myocardial ischemia, can potentially have important pathophysiologic effects on other cardiac cells as well as on distant organs.

Mitochondrial Dynamics and Heart Failure

Mitochondrial dynamics, fission and fusion, were first identified in yeast with investigation in heart cells beginning only in the last 5 to 7 years. In the ensuing time, it has become evident that these processes are not only required for healthy mitochondria, but also, that derangement of these processes contributes to disease. The fission and fusion proteins have a number of functions beyond the mitochondrial dynamics. Many of these functions are related to their membrane activities, such as apoptosis. However, other functions involve other areas of the mitochondria, such as OPA1's role in maintaining cristae structure and preventing cytochrome c leak, and its essential (at least a 10 kDa fragment of OPA1) role in mtDNA replication. In heart disease, changes in expression of these important proteins can have detrimental effects on mitochondrial and cellular function.

TLR4 mutation and HSP60-induced cell death in adult mouse cardiac myocytes

Extracellular (ex) HSP60 is increasingly recognized as an agent of cell injury. Previously, we reported that low endotoxin exHSP60 causes cardiac myocyte apoptosis. Our findings supported a role for Toll-like receptor (TLR) 4 in HSP60 mediated apoptosis. To further investigate the involvement of TLR4 in cardiac injury, we studied adult cardiac myocytes from C3H/HeJ (HeJ) mice, which have a mutant, nonfunctional TLR4, and compared the results with parallel studies using wild-type (WT) mice. Nuclear factor κB (NFκB) activation is an early step downstream of TLR4. NFκB was activated 1 h after treatment with HSP60 in WT, but not HeJ mouse myocytes. ExHSP60 caused apoptosis in cardiac myocytes from WT mice, but not in myocytes from the HeJ mutants. To further elucidate the importance of exHSP60 in cardiac myocyte injury, both WT and HeJ mutant isolated mouse adult cardiac myocytes were exposed to hypoxia/reoxygenation. Anti-HSP60 antibody treatment reduced apoptosis in the WT group, but had no effect on the HeJ mutant myocytes. Unexpectedly, necrosis was also decreased in the HeJ mutants. Necrosis after hypoxia/reoxygenation in WT cardiac myocytes was mediated in part by TLR2 and TLR4 through rapid activation of PKCα, followed by increased expression of Nox2, and this was ameliorated by blocking antibodies to TLR2/4. These studies provide further evidence that TLR4 mediates exHSP60-associated apoptosis and that exHSP60 has an important role in cardiac myocyte injury, both apoptotic and necrotic.

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.

Cardiac myocyte exosomes: stability, HSP60, and proteomics

Exosomes, which are 50- to 100-nm-diameter lipid vesicles, have been implicated in intercellular communication, including transmitting malignancy, and as a way for viral particles to evade detection while spreading to new cells. Previously, we demonstrated that adult cardiac myocytes release heat shock protein (HSP)60 in exosomes. Extracellular HSP60, when not in exosomes, causes cardiac myocyte apoptosis via the activation of Toll-like receptor 4. Thus, release of HSP60 from exosomes would be damaging to the surrounding cardiac myocytes. We hypothesized that 1) pathological changes in the environment, such as fever, change in pH, or ethanol consumption, would increase exosome permeability; 2) different exosome inducers would result in different exosomal protein content; 3) ethanol at "physiological" concentrations would cause exosome release; and 4) ROS production is an underlying mechanism of increased exosome production. We found the following: first, exosomes retained their protein cargo under different physiological/pathological conditions, based on Western blot analyses. Second, mass spectrometry demonstrated that the protein content of cardiac exosomes differed significantly from other types of exosomes in the literature and contained cytosolic, sarcomeric, and mitochondrial proteins. Third, ethanol did not affect exosome stability but greatly increased the production of exosomes by cardiac myocytes. Fourth, ethanol- and hypoxia/reoxygenation-derived exosomes had different protein content. Finally, ROS inhibition reduced exosome production but did not completely inhibit it. In conclusion, exosomal protein content is influenced by the cell source and stimulus for exosome formation. ROS stimulate exosome production. The functions of exosomes remain to be fully elucidated.

Mitochondrial dynamics in heart failure

Mitochondria have been widely studied for their critical role in cellular metabolism, energy production, and cell death. New developments in research on mitochondria derived from studies in yeast have led to the discovery of entirely new mitochondrial processes that have implications for mitochondrial function in heart failure. Recent studies have identified that maintaining normal mitochondrial morphology and function depends on the dynamic balance of mitochondrial fusion and fission (division). Mitochondrial fusion and fission are constant ongoing processes, which are essential for the maintenance of normal mitochondrial function. Studies in heart failure have been limited but suggest a possible reduction in mitochondrial fusion. As mitochondrial fusion and fission have important links to apoptosis, a key mechanism of loss of cardiac myocytes in heart failure, there are many implications for both heart failure research and treatment.

Impact of aging vs. estrogen loss on cardiac gene expression: estrogen replacement and inflammation

Despite an abundance of evidence to the contrary from animal studies, large clinical trials on humans have shown that estrogen administered to postmenopausal women increases the risk of cardiovascular disease. However, timing may be everything, as estrogen is often administered immediately after ovariectomy (Ovx) in animal studies, while estrogen administration in human studies occurred many years postmenopause. This study investigates the discrepancy by administering 17β-estradiol (E2) in a slow-release capsule to Norway Brown rats both immediately following Ovx and 9 wk post-Ovx (Late), and studying differences in gene expression between these two groups compared with age-matched Ovx and sham-operated animals. Two different types of microarray were used to analyze the left ventricles from these groups: an Affymetrix array (n = 3/group) and an inflammatory cytokines and receptors PCR array (n = 4/group). Key genes were analyzed by Western blotting. Ovx without replacement led to an increase in caspase 3, caspase 9, calpain 2, matrix metalloproteinase (MMP)9, and TNF-α. Caspase 6, STAT3, and CD11b increased in the Late group, while tissue inhibitor of metalloproteinase 2, MMP14, and collagen I α1 were decreased. MADD and fibronectin were increased in both Ovx and Late. TNF-α and inducible nitric oxide synthase (iNOS) protein levels increased with Late replacement. Many of these changes were prevented by early E2 replacement. These findings suggest that increased expression of inflammatory genes, such as TNF-α and iNOS, may be involved in some of the deleterious effects of delayed E2 administration seen in human studies.

Mitochondria and heart failure: new insights into an energetic problem

Cardiac mitochondria are powerful organelles supplying energy to support the high adenosine triphosphate (ATP) consumption of the beating heart. The progression of HF (HF) is characterized by diminished energy metabolism, calcium mishandling, reactive oxygen species (ROS) generation and apoptotic cell death. Although the etiologies of HF are multifactoral, many of the changes of HF are associated with cardiac mitochondrial dysfunction either directly or indirectly. A number of studies have established the role of calcium mishandling and reduced ATP production in mitochondrial dysfunction in HF. More recent work has contributed to our understanding of the role of ROS and proapoptotic protein release by the mitochondria in HF. New interest has been generated in mitochondria by the relatively recent identification of the processes of fusion and fission, which are critical to the maintenance of healthy mitochondria. Fission and fusion also have significant roles in apoptosis. Other studies have shown that estrogen has important functions in the mitochondria, including regulation of mitochondrial gene expression. Aging alone contributes to the development of HF through multiple mechanisms. These new insights into HF have implications for our understanding of this important disease, and will be reviewed here.

Regulation of heat shock protein 60 and 72 expression in the failing heart

Heart failure, a progressive, fatal disease of the heart muscle, is a state of chronic inflammation and injury. Heat shock protein (HSP) 72, a ubiquitous protective protein that is well-established as cardioprotective, is not increased in heart failure. In contrast, HSP60 levels are doubled in the failing heart. We hypothesized that HSF-1 is not activated in heart failure and that the increased expression of HSP60 was driven by NFkappaB activation. To test this hypothesis, we measured levels of heat shock factor (HSF) -1 and -2, the transcription factors controlling HSP expression, which were increased in heart failure. There was no increased phosphorylation of serine 230 or serine 303/307 in HSF-1, which are thought to regulate its activity; EMSA showed no increase in HSF binding activity with heart failure. Nonetheless, mRNA was increased for HSP60, but not HSP72. In contrast to HSF, NFkappaB activity was increased in heart failure. HSP60, but not HSP72, contained NFkappaB binding elements. ChIP assay demonstrated increased binding of NFkappaB to both of the NFkappaB binding elements in the heart failure HSP60 gene. TNFalpha treatment was used to test the role of NFkappaB activation in HSP60 expression in a cardiac cell line. TNFalpha increased HSP60 expression, and this could be prevented by pretreatment with siRNA inhibiting p65 expression. In conclusion, HSP72 is not increased in heart failure because HSF activity is not changed; increased expression of HSP60 may be driven by NFkappaB activation.

Role of aging versus the loss of estrogens in the reduction in vascular function in female rats

Although aging is known to lead to increased vascular stiffness, the role of estrogens in the prevention of age-related changes in the vasculature remains to be elucidated. To address this, we measured vascular function in the thoracic aorta in adult and old ovariectomized (ovx) rats with and without immediate 17beta-estradiol (E2) replacement. In addition, aortic mRNA and protein were analyzed for proteins known to be involved in vasorelaxation. Aging in combination with the loss of estrogens led to decreased vasorelaxation in response to acetylcholine and sodium nitroprusside, indicating either smooth muscle dysfunction and/or increased fibrosis. Loss of estrogens led to increased vascular tension in response to phenylephrine, which could be partially restored by E2 replacement. Levels of endothelial nitric oxide synthase and inducible nitric oxide synthase did not differ among the groups, nor did total nitrite plus nitrate levels. Old ovx exhibited decreased expression of both the alpha and beta-subunits of soluble guanylyl cyclase (sGC) and had impaired nitric oxide signaling in the vascular smooth muscle. Immediate E2 replacement in the aged ovx prevented both the impairment in vasorelaxation, and the decreased sGC receptor expression and abnormal sGC signaling within the vascular smooth muscle.

HSP60 in heart failure: abnormal distribution and role in cardiac myocyte apoptosis

Heat shock protein (HSP) 60 is a mitochondrial and cytosolic protein. Previously, we reported that HSP60 doubled in end-stage heart failure, even though levels of the protective HSP72 were unchanged. Furthermore, we observed that acute injury in adult cardiac myocytes resulted in movement of HSP60 to the plasma membrane. We hypothesized that the inflammatory state of heart failure would cause translocation of HSP60 to the plasma membrane and that this would provide a pathway for cardiac injury. Two models were used to test this hypothesis: 1) a rat model of heart failure and 2) human explanted failing hearts. We found that HSP60 localized to the plasma membrane and was also found in the plasma early in heart failure. Plasma membrane HSP60 localized to lipid rafts and was detectable on the cell surface with the use of both flow cytometry and confocal microscopy. Localization of HSP60 to the cell surface correlated with increased apoptosis. In heart failure, HSP60 is in the plasma membrane fraction, on the cell surface, and in the plasma. Membrane HSP60 correlated with increased apoptosis. Release of HSP60 may activate the innate immune system, promoting a proinflammatory state, including an increase in TNF-alpha. Thus abnormal trafficking of HSP60 to the cell surface may be an early trigger for myocyte loss and the progression of heart failure.

HSP60 trafficking in adult cardiac myocytes: role of the exosomal pathway

The heat shock proteins (HSP) are a highly conserved family of proteins with critical functions in protein folding, protein trafficking, and cell signaling. These proteins also protect the cell against injury. HSP60 has been found in the extracellular space and has been identified in the plasma of some individuals. HSP60 is thought to be a "danger signal" to the immune system and is also highly immunogenic. Thus extracellular HSP60 is possibly toxic to the cell. The mechanism by which HSP60 is released into the extracellular space is unknown, as is whether it is released by cardiac myocytes. We investigated several different pathways controlling protein release including the classic, Golgi-mediated pathway. We found that HSP60 is released via exosomes, and that within the exosome, HSP60 is tightly attached to the exosome membrane.

Toll-like receptor 4, nitric oxide, and myocardial depression in endotoxemia

The molecular mechanisms that mediate gram-negative sepsis-associated myocardial dysfunction remain elusive. Myocardial expression of inflammatory mediators is Toll-like receptor 4 (TLR4) dependent. However, it remains to be elucidated whether TLR4, expressed on cardiac myocytes, mediates impairment of cardiac contractility after lipopolysaccharide (LPS) application. Cardiac myocyte contractility, measured as sarcomere shortening of isolated cardiac myocytes from C3H/HeJ (with nonfunctional TLR4) and C3H/HeN (control), were recorded at stimulation frequencies between 0.5 and 10 Hz and after incubation with 1 and 10 mug/mL LPS for up to 8 h. Control cells treated with LPS were investigated with and without a competitive LPS inhibitor (E5564) and a specific inducible nitric oxide synthase (iNOS) inhibitor S-methylisothiourea. In control mice, LPS reduced sarcomere shortening amplitude and prolonged duration of relaxation, whereas sarcomere shortening of C3H/HeJ cells was insensitive to LPS. NFkappaB and iNOS were upregulated after LPS application in control mice compared with C3H/HeJ. Inhibition of TLR4 by E5564 as well as inhibition of iNOS prevented the influence of LPS on contractile activity in control myocytes. LPS-dependent suppression of cardiac myocyte contractility was significantly blunted in C3H/HeJ mice. Competitive inhibition of functional TLR4 with E5564 protects cardiac myocyte contractility against LPS. These findings suggest that TLR4, expressed on cardiac myocytes, contributes to sepsis-induced myocardial dysfunction. E5564, currently under investigation in two clinical phase II trials, seems to be a new therapeutic option for the treatment of myocardial dysfunction in sepsis associated with endotoxemia.

Effect of mutation of amino acids 246-251 (KRKHKK) in HSP72 on protein synthesis and recovery from hypoxic injury

Heat shock protein (HSP)72, the inducible form of HSP70, protects cells against a variety of injuries, but underlying mechanisms are poorly defined. To investigate the protective effects of HSP72, multiple clones expressing wild-type (WT) HSP72 and two mutants with defective nucleolar and nuclear localization (M45 and 985A, respectively) were made with the tet-off system in C2C12 cells. Four different parameters of cell function/injury were examined after simulated ischemia: protein synthesis, polysome formation, DNA synthesis, and lactate dehydrogenase (LDH release). Overexpression of WT HSP72 was also compared to nontransfected C2C12 cells. As expected, overexpression of HSP72 protected against simulated ischemia and reoxygenation for all parameters. In contrast, both M45 and 985A showed abnormal protein synthesis and polysome formation, both after simulated ischemia and under control conditions. Total RNA was slightly reduced in M45 and 985A at baseline, but 1 h after hypoxia, RNA levels were protected in all clones but significantly decreased in nontransfected C2C12 cells. Clones expressing 985A had nuclear retention of mRNA, suggesting that HSP72 is needed for nuclear export of RNA. All clones, both WT and mutant, had protection of DNA synthesis compared to C2C12 cells, but 985A had greater release of LDH after injury than any other group. These results support a multifactoral protective effect of HSP72, some aspects dependent on nuclear localization with stress and some not. The protection of protein synthesis and polysome formation, and abnormalities in these with the mutants, support a role for HSP72 in these processes both in the normal cell and in injury.

HSP60, Bax, apoptosis and the heart

HSP60 has primarily been known as a mitochondrial protein that is important for folding key proteins after import into the mitochondria. It is now clear that a significant amount of HSP60 is also present in the extra-mitochondrial cytosol of many cells. In the heart, this cytosolic HSP60 complexes with Bax, Bak and Bcl-XL, but not with Bcl-2. Reduction in HSP60 expression precipitates apoptosis, but does not alter mitochondrial function. During hypoxia, HSP60 cellular distribution changes, with HSP60 leaving the cytosol, and translocating to the plasma membrane. Total cellular HSP60 does not change until 10 h of reoxygenation; however, release of cytochrome c from the mitochondria occurs prior to reoxygenation, coinciding with the redistribution of HSP60. The changes in HSP60, Bax and cytochrome c during hypoxia can be replicated by ATP depletion. HSP60 has also been shown to accelerate the cleavage of pro-caspase3. Thus, HSP60 has a complex role in apoptosis in the cell. Its binding to Bax under normal conditions suggests a key regulatory role in apoptosis.

Estrogen, heat shock proteins, and NFkappaB in human vascular endothelium

BACKGROUND

We hypothesized that estrogen would increase HSP72 in human coronary artery endothelial cells (HCAEC), and that these would be more sensitive to estrogen than our previous observations in myocytes.

METHODS AND RESULTS

HCAEC were treated with 17beta-estradiol or tamoxifen, ranging from physiological to pharmacological(1 nM to 10 micromol/L) for either 24 hours (early) or 7 days (chronic). HSP expression was assessed by Western blots. Both early and chronic 17beta-estradiol and tamoxifen increased HSP72. Electromobility shift assays (EMSA) showed activation of HSF-1 with early, but not chronic, 17beta-estradiol. 17beta-Estradiol activated NFkappaB within 10 minutes, and the ER-alpha selective inhibitor, ICI 182 780, abolished this effect. Transcription factor decoys containing the heat shock element blocked HSP72 induction. Estrogen pretreatment decreased lactate dehydrogenase release with hypoxia. This protective effect persisted despite blockade of HSF-1 by decoys. However, an NF-kappaB decoy prevented the increase in HSP72 and abolished the estrogen-associated protection during hypoxia.

CONCLUSIONS

17beta-Estradiol upregulates HSP72 early and chronically via different mechanisms in HCAEC, and provides cytoprotection during hypoxia, independent of HSP72 induction. NF-kappaB mediates the early increase in HSP72, suggesting that estrogen activates NF-kappaB via a nongenomic, receptor-dependent mechanism, and this leads to activation of HSF-1. Activation of NF-kappaB was critical for estrogen-associated protection. Further studies are needed to elucidate the involved signaling pathways. We hypothesized that estrogen would increase HSP72 in human coronary artery endothelial cells (HCAEC). Both early and chronic treatment increased HSP72. EMSA showed activation of HSF-1 with early, but not chronic, 17beta-estradiol. Transcription factor decoys blocked estrogen-related HSP72 induction. Estrogen decreased LDH release with hypoxia. An NF-kappaB decoy blocked the HSP72 increase and estrogen-associated protection.

Estrogen and regulation of heat shock protein expression in female cardiomyocytes: cross-talk with NFкB signaling

Estrogen is associated with increased heat shock protein (HSP)72 and protection during hypoxia-reoxygenation in cardiomyocytes from adult male rats, as previously reported. We have also reported that female rats have more cardiac HSP72 than males. We hypothesized that, despite higher endogenous estrogen levels and higher baseline HSP72, 17 beta-estradiol treatment would still result in increased HSP72 and protection during hypoxia-reoxygenation in cardiomyocytes from females.

METHODS/RESULTS

Cardiac cells isolated from adult female rats were treated for 12 hr with 17 beta-estradiol (0.1, 10, or 50 microM), tamoxifen, (10 or 25 microM; estrogen receptor agonist/antagonist), geldanamycin (2, 5, or 10 microg/ml; inactivates HSP90, preventing interaction with HSF1), or vehicle. Western blot analyses revealed that treatment with 17 beta-estradiol (10 or 50 microM), tamoxifen (25 microM), and geldanamycin (all doses) resulted in significant increases in HSP72. Electromobility shift assays revealed activation of HSF1 by 2 to 3 hr, and NF kappa B activation by 15 min. HSP72 induction via HSF1 activation was confirmed using transcription factor decoys containing the heat shock element, which prevented the estrogen-related HSP72 induction. Estrogen pretreatment resulted in decreased LDH release during 24 hr hypoxia. This protective effect persisted despite decoy-mediated blockade of nuclear HSF1 binding. However, transfection with an NF?B decoy not only prevented an estrogen-associated increase in HSP72, but also abolished the estrogen-related protection during hypoxia.

CONCLUSIONS

Despite higher endogenous estrogen, 17 beta-estradiol and the selective estrogen receptor modulator, tamoxifen, upregulate HSP72 in cardiomyocytes from adult females, and provide cytoprotection during hypoxia, independent of HSP induction. NF kappa B activation is necessary for the increase in HSP72, suggesting that estrogen treatment activates NF kappa B, with subsequent HSF1 activation. NF kappa B activation is critical for estrogen-associated HSP induction, and protection during hypoxia in female cardiocytes. Treatment with 17 beta-estradiol and tamoxifen may provide a novel means of protecting both male and female cardiac myocytes against hypoxia-induced damage. Further studies are needed to define the cross-talk between HSF1 and NF kappa B signaling pathways.

HSP60, Bax, and cardiac apoptosis

HSP60 has long been known as an important chaperonin and as having key folding functions within the mitochondria. However, it has now become evident that significant amounts of HSP60 are found in extra-mitochondrial locations. This extra-mitochondrial HSP60 in the heart has key anti-apoptotic functions. Extra-mitochondrial HSP60 complexes with both bax and bak, but not with bcl-2. Reduction in HSP60 is sufficient to precipitate apoptosis. In the setting of hypoxia and reoxygenation HSP60 decreases with reoxygenation, but the apoptotic cascade has already been triggered by end-hypoxia. Redistribution of cytosolic HSP60 to the plasma membrane during hypoxia appears to contribute to the initiation of the apoptotic cascade with hypoxia and reoxygenation.

Gender differences in the expression of heat shock proteins: the effect of estrogen

The heat shock proteins (HSPs) are an important family of endogenous, protective proteins that are found in all tissues. In the heart, HSP72, the inducible form of HSP70, has been the most intensely studied. It is well established that HSP72 is induced with ischemia and is cardioprotective. Overexpression of other HSPs also is protective against cardiac injury. Recently, we observed that 17beta-estradiol increases levels of HSPs in male rat cardiac myocytes. We hypothesized that there were gender differences in HSP72 expression in the heart secondary to estrogen. To test this hypothesis, we examined cardiac levels of HSP72 by ELISA in male and female Sprague-Dawley rats. In addition, three other HSPs were assessed by Western blot (HSP27, HSP60, and HSP90). To determine whether estrogen status affected HSP72 expression in other muscles or tissues, two other muscle tissues, slow twitch muscle (soleus muscle) and fast twitch muscle (gastrocnemius muscle), were studied as well as two other organs, the kidney and liver. Because HSP72 is cardioprotective, and females are known to have less cardiovascular disease premenopause, the effects of ovariectomy were examined. We report that female Sprague-Dawley rat hearts have twice as much HSP72 as male hearts. Ovariectomy reduced the level of HSP72 in female hearts, and this could be prevented by estrogen replacement therapy. These data show that the expression of cardiac HSP72 is greater in female rats than in male rats, due to upregulation by estrogen.

Complications of inappropriate use of spironolactone in heart failure: when an old medicine spirals out of new guidelines

OBJECTIVES

This study was designed to investigate the appropriateness and complications of the use of spironolactone for heart failure (HF) in clinical practice.

BACKGROUND

Spironolactone was reported by one prospective randomized trial to decrease morbidity and mortality in patients with New York Heart Association (NYHA) class III and IV HF. With this report (Randomized Spironolactone Evaluation Study [RALES] trial), we noted a marked increase in widespread use of spironolactone in patients with HF. Long-term outcome data with respect to safety and utilization of this medication in HF are not available.

METHODS

To investigate the use of spironolactone for HF in a clinical setting, we analyzed the application of the RALES trial protocol to the care of 104 patients, whom we identified as being started on spironolactone for HF after prerelease of the RALES trial.

RESULTS

We found broader use, less intensive follow-up, and increased complications with spironolactone treatment compared with the RALES trial. Cardiologists provided more appropriate care than did primary care providers.

CONCLUSIONS

These data suggest that spironolactone is being used widely in HF without consideration of the NYHA class and ejection fraction, and without optimization of background treatment with angiotensin-converting enzyme inhibitors and beta-blockers. Clinical follow-up does not adhere to the RALES trial guidelines, resulting in higher complications. We conclude that long-term studies with further safety and efficacy data are needed.

Cytosolic heat shock protein 60, hypoxia, and apoptosis

BACKGROUND

Heat shock protein (HSP)60 is an abundant protein found primarily in the mitochondria, though 15% to 20% is found in the cytosol. Previously we observed that HSP60 complexes with bax in the cytosol. Reduction in HSP60 precipitates translocation of bax to the mitochondria and apoptosis. We hypothesized that HSP60 would decrease with hypoxia/reoxygenation and that this would precipitate bax translocation to the mitochondria and release of cytochrome c.

METHODS AND RESULTS

Adult rat cardiac myocytes were studied at end-hypoxia and at 10 and 24 hours of reoxygenation. HSP60 levels were unchanged at end-hypoxia and decreased 33% and 40% at 10 and 24 hours of reoxygenation, whereas HSP72 increased 80% and 110%. Bax and bcl-2 decreased during reoxygenation. However, cytochrome c release occurred at end-hypoxia, before reoxygenation. Cell fractionation was done to analyze this further. In normal myocytes, bax and HSP60 were present in the cytosol, and bax coimmunoprecipitated with cytosolic HSP60. At end-hypoxia, mitochondrial HSP60 was unchanged, but cytosolic HSP60 had disappeared and was now in the plasma membrane fraction. Concurrently, bax was no longer in the cytosol but now in the mitochondria. Thus, although total HSP60 remained the same, it no longer complexed with bax, and bax was free to translocate to the mitochondria and precipitate apoptosis. Reduction in ATP had a similar effect.

CONCLUSIONS

These studies show that hypoxia results in disassociation of the HSP60-bax complex with translocation of cytosolic HSP60 to the plasma membrane and bax to the mitochondria. This is sufficient to trigger apoptosis.

Cytosolic heat shock protein 60, apoptosis, and myocardial injury

BACKGROUND

Heat shock proteins (HSPs) are well known for their ability to "protect" the structure and function of native macromolecules, particularly as they traffic across membranes. Considering the role of key mitochondrial proteins in apoptosis and the known antiapoptotic effects of HSP27 and HSP72, we postulated that HSP60, primarily a mitochondrial protein, also exerts an antiapoptotic effect. Methods and Results- To test this hypothesis, we used an antisense phosphorothioate oligonucleotide to effect a 50% reduction in the levels of HSP60 in cardiac myocytes, a cell type that has abundant mitochondria. The induced decrease in HSP60 precipitated apoptosis, as manifested by the release of cytochrome c, activation of caspase 3, and induction of DNA fragmentation. Antisense treatment was associated with an increase in bax and a decrease in bcl-2 secondary to increased synthesis of bax and degradation of bcl-2. A control oligonucleotide had no effect on these measurements. We further demonstrated that cytosolic HSP60 forms a macromolecular complex with bax and bak in vitro suggesting that complex formation with HSP60 may block the ability of bax and bak to effect apoptosis in vivo. Lastly, we show that as cytosolic (nonmitochondrial) HSP60 decreases, a small unbound fraction of bax appears and that the amount of bax associated with the mitochondria and cell membranes increases.

CONCLUSIONS

These results support a key antiapoptotic role for cytosolic HSP60. To our knowledge, this is the first report suggesting that interactions of HSP60 with bax and/or bak regulate apoptosis.

Hsp72 expression enhances survival in adenosine triphosphate-depleted renal epithelial cells

Although prior heat stress (HS) inhibits apoptosis in adenosine phosphate (ATP)-depleted renal epithelial cells (REC), the specific stress protein(s) responsible for cytoprotection have not been identified. The present study evaluated the hypothesis that Hsp72, the major inducible member of the Hsp70 family, protects REC against ATP depletion injury. In the presence of isopropyl-beta-D-thiogalactoside (IPTG), a stable line of transfected opossum kidney cells was induced to overexpress human Hsp72 tagged with the flag epitope. Transfected cells from 2 clones that expressed Hsp72 at a level comparable with wild-type cells were subjected to transient heat stress (43 degrees C for 1 hour). To assess the cytoprotective effect of Hsp72, transfected cells were subjected to transient ATP depletion followed by recovery in the presence vs the absence of IPTG. ATP depletion resulted in nuclear chromatin condensation without cell membrane injury (ie, minimal leak of lactate dehydrogenase) and activation of caspase-3, confirming that apoptosis is the major cause of cell death. In both clones cell survival 1-3 days after ATP depletion was significantly improved in the presence of IPTG. Selective overexpression of Hsp72 reproduced nearly 60% of the protective effect on the survival afforded by prior heat stress. In transfected cells subjected to ATP depletion, Hsp72 overexpression significantly inhibited caspase activation. In native renal cells brief ATP depletion markedly induced the expression of native Hsp72, a finding identical to that observed after renal ischemia in vivo. These studies are the first to directly show that Hsp72 per se mediates acquired resistance to ischemic injury in REC.

Congestive heart failure and outpatient risk of venous thromboembolism: a retrospective, case-control study

Although CHF has been considered a risk factor for venous thromboembolism, this has not been directly studied. We hypothesized that congestive heart failure would increase the risk of venous thromboembolism in an outpatient population, and that this risk would increase as patients' ventricular function worsened. We conducted a case-control study to examine whether CHF due to left ventricular dysfunction was an independent risk factor for acute venous thromboembolism in outpatients, once established risk factors such as recent surgery and prior venous thromboembolism are taken into account. We reviewed 106 cases of DVT and 603 controls, admitted for diabetes mellitus or infection, matched for month of admission at a VA hospital. Assignment of a diagnosis of venous thromboembolism required a definitive test, as did classification as CHF. In a logistic regression model CHF was an independent predictor of venous thromboembolism. A second logistic regression model showed that the risk of venous thromboembolism increased as the ejection fraction (EF) decreased, with an EF < 20 associated with a venous thromboembolism OR of 38.3 (95% CI 9.6, 152.5). CHF is an independent risk factor for venous thromboembolism, and the risk increases markedly as the EF decreases. These results support the use of anticoagulation in selected patients with CHF.

Regulation of prostaglandin A1-induced heat shock protein expression in isolated cardiomyocytes

Prostaglandins of the A-type (PGAs) induce heat shock protein (HSP) synthesis in a wide variety of mammalian cells resulting in protection against cellular stresses. The effect of PGAs on HSP-induction in cardiac myocytes is unknown. Therefore, we investigated the effect of PGA1 on HSP synthesis in adult rat cardiac myocytes. After 24 h of treatment, HSP72 was significantly increased 2.9-, 5.6- and 5.0-fold by PGA1 used at concentrations of 10, 20 or 40 microg/ml, respectively (P<0.05). However, the PGA1-concentration of 40 microg/ml, was found to be cytotoxic as evidenced by the release of LDH. In addition to HSP72, HSP32 was significantly increased by PGA1. The HSP32 induction was more vigorous with a marked increase with only 4 microg/ml of PGA1. No differences in the levels of HSP27, HSP60 or HSP90 were detected. When isolated cardiac myocytes were treated with PGA1, clear activation of heat shock factor (HSF) 1, one of the transcription factors for HSPs, was observed. In addition, another stress-induced transcription factor NFkappaB was also activated by PGA exposure. Despite the significant upregulation of both HSP72 and HSP32 cytoprotective properties against hypoxia and reoxygenation were absent. In conclusion, these experiments show for the first time that PGA1 induces differential expression of heat shock proteins in cardiac myocytes probably mediated through the activation of both HSF1 and NFkappaB.

Activation of heat-shock factor by stretch-activated channels in rat hearts

BACKGROUND

Previously, we have observed that the isolated, erythrocyte-perfused rabbit heart has increased levels of heat-shock protein (HSP) 72 after a mild mechanical stress. We hypothesized that stretch-activated ion channels (SACs) mediated this increase. Methods and Results-- To test this hypothesis, we subjected isolated, perfused rat hearts to mechanical stretch. Gel mobility shift assay showed that heat-shock factor (HSF) was activated in hearts with mechanical stretch, but not in controls. Supershift experiments demonstrated that HSF1 was the transcription factor. Northern blots revealed the concomitant increase in HSP72 mRNA in stretched rat hearts. In a separate set of experiments, gadolinium, an inhibitor of SACs, was added to the perfusate. Gadolinium inhibited the activation of HSF and decreased HSP72 mRNA level. Because gadolinium can inhibit both SACs and L-type calcium channels, we perfused a group of hearts with diltiazem, a specific L-type calcium channel blocker, to eliminate the involvement of L-type calcium channels. Diltiazem failed to inhibit the activation of HSF.

CONCLUSIONS

Stretch in the rat heart results in activation of HSF1 and an increase in HSP72 mRNA through SACs. This represents a novel mechanism of HSF activation and may be an important cardiac signaling pathway for hemodynamic stress.

Activation of the heat shock response: relationship to energy metabolites. A (31)P NMR study in rat hearts

Heat shock factor (HSF), the transcription factor for the heat shock proteins, is activated by cardiac ischemia, but the mechanism of activation is unknown. Ischemia is accompanied by changes in the energy state and acid-base conditions. We hypothesized that decreased ATP and/or intracellular pH (pH(i)) might activate HSF. To test this hypothesis, we perfused rat hearts within an NMR spectrometer. NMR data showed that after 6.5, 13, and 20 min of ischemia, ATP dropped to 62.7, 23.1, and 6.9% of the control level, and pH(i) was 6.16, 5.94, and 5.79, respectively. Reperfusion after ischemia partially restored ATP levels, and this was associated with greater activation of HSF1. HSF1 was also activated after 6.5 min of ischemia. Activation of HSF1 was less after 13 min of ischemia and barely detectable after 20 min of ischemia. In conclusion, 1) a moderate decrease in intracellular ATP correlates with activation of HSF1 in the heart; and 2) a severe depletion in ATP correlates with an attenuation in HSF1 activation, and the restoration of ATP leads to greater activation of HSF1, suggesting that a critical ATP level is required for activation of HSF1.

Mutation of amino acids 566-572 (KKKVLDK) inhibits nuclear accumulation of heat shock protein 72 after heat shock

Heat shock protein (HSP) 72 translocates from the cytoplasm to the nucleus in response to a wide variety of stresses, including heat shock and tissue ischemia. It is thought that this concentration of HSP72 in the nucleus with stress is part of the protein's protective response. Therefore, further understanding of the regulation of this response would be of interest. The signals regulating HSP72's nuclear localization have not been completely defined. Previously, we observed that mutation of amino acids 246-251 (KRKHKK) reduced nuclear accumulation of HSP72 and that a KRKHKK-EGFP (enhanced green fluorescent protein) fusion protein concentrated in the nucleoli. In examining HSP72 for other potential nuclear localization signals, we identified an additional sequence, KKKVLDK, amino acids 566-572, that might effect nuclear accumulation. We now report that mutation of KKKVLDK inhibited nuclear concentration of HSP72 following heat shock, and the fusion protein KKKVLDK-EGFP concentrated in the nucleus. Cells overexpressing the KKKVLDK mutant showed reduced resistance to heat shock. Mutation of KKKVLDK and KRKHKK abolished nuclear accumulation of HSP72 and reduced cell viability following heat shock to a greater extent than mutation of either site alone. These findings suggest that these two sequences, KRKHKK and KKKVLDK, have complementary function(s) in cellular protection after heat shock.

Heat-shock factor-1, steroid hormones, and regulation of heat-shock protein expression in the heart

Heat-shock proteins (HSPs) are an important family of endogenous, protective proteins. Overexpression of HSPs is protective against cardiac injury. Previously, we observed that dexamethasone activated heat-shock factor-1 (HSF-1) and induced a 60% increase in HSP72 in adult cardiac myocytes. The mechanism responsible for this effect of dexamethasone is unknown. Because HSP90 is known to bind the intracellular hormone receptors, we postulated that the interaction between HSP90, the receptors, and HSF was an important element in activation of HSF-1 by hormones. We hypothesized that there is an equilibrium between HSP90 and the various receptors/enzymes that it binds and that alteration in levels of certain hormones will alter the intracellular distribution of HSP90 and activate HSF-1. We report that, in adult cardiac myocytes, HSF-1 coimmunoprecipitates with HSP90. HSP90 redistributes in cardiac myocytes after treatment with 17beta-estradiol or progesterone. Estrogen and progesterone activate HSF-1 in adult male isolated cardiac myocytes, and this is followed by an increase in HSP72 protein. Testosterone had no effect on HSP levels; however, no androgen receptor was found in cardiac myocytes; therefore, testosterone would not be expected to effect binding of HSP90 to HSF. Geldanamycin, which inactivates HSP90 and prevents it from binding to receptors, activates HSF-1 and stimulates HSP72 synthesis. Activation of HSF-1 by steroid hormones, resulting from a change in the interaction of HSP90 and HSF-1, represents a novel pathway for regulating expression of HSPs. These findings may explain some of the gender differences in cardiovascular disease.

Phosphorylation at tyrosine-524 influences nuclear accumulation of HSP72 with heat stress

Nuclear accumulation of heat shock protein (HSP) 72 occurs after cardiac ischemia. This nuclear accumulation of HSP72 with stress occurs in other tissues and species. We postulated that nuclear accumulation of HSP72 was important for the protective effect of HSP72 and that phosphorylation of a single tyrosine (Y(524)) regulated nuclear accumulation of HSP72. Western blots of immunoprecipitated HSP72 from Cos-1 cells demonstrated that tyrosine becomes phosphorylated after heat shock. Treatment with the tyrosine kinase inhibitor geldanamycin blocked nuclear accumulation of HSP72 with heat shock. Two epitope-tagged constructs were made: M17 converting Y(524) to aspartic acid (pseudophosphorylation) and M18 converting Y(524) to phenylalanine. When transfected into Cos-1 cells, M17 accumulates more rapidly and M18 less rapidly than wild-type (WT) HSP72 in the nucleus following heat shock. Cells expressing M18 had less viability after heat shock at 43.5 degrees C than other constructs. After heat shock at 45 degrees C, cells expressing M17 had superior survival compared with WT and M18. These data suggest that phosphorylation at Y(524) facilitates nuclear accumulation of HSP72 following heat stress, and substitution of aspartic acid at Y(524) enhances resistance to heat-shock injury.

Activation of HSF and selective increase in heat-shock proteins by acute dexamethasone treatment

Heat-shock proteins (HSPs) are an important family of endogenous protective proteins, which increase in response to myocardial ischemia and other stresses. Overexpression of HSP72 is cardioprotective. We were interested in the regulation of heat-shock factor (HSF), the transcription factor for HSP genes. Previously we have observed that the inflammatory cytokine tumor necrosis factor-alpha increases HSP72 levels and postulated that dexamethasone might effect the heat shock response. In the adult rat cardiac myocyte we found that treatment with either low (10 microM)- or high (100 microM)-dose dexamethasone activated HSF by 2-6 h as determined by gel shift assay without evidence of cytotoxicity. Although HSF activation is a key step in expression of HSP72, this may not result in an increase in HSP72. We found that 10 microM dexamethasone increased HSP72 38%, and 100 microM dexamethasone increased HSP72 62% (P < 0.05). HSP27 and HSP60 were unchanged. The selective increase in HSP72 was associated with protection of the cardiac myocytes from hypoxia and reoxygenation. We conclude that dexamethasone is a novel inducer of the heat shock response.

Expression of heat shock proteins in turtle and mammal hearts: relationship to anoxia tolerance

Heat shock proteins (HSPs) may play a cardioprotective role during hypoxia or ischemia. We hypothesized that cardiac tissue from hypoxia-tolerant animals might have high levels of specific HSPs. We measured myocardial HSP60 and HSP72/73 in painted and softshell turtles during normoxia and anoxia (12 h) and after recovery (12 or 24 h). We also measured myocardial HSPs in normoxic rats and rabbits. During normoxia, hearts from the most highly anoxia-tolerant species, the painted turtle, expressed the highest levels of HSP60 (22.6+/-2.0 mg/g total protein) followed by softshells (11.5+/-0.8 mg/g), rabbits (6.8+/-0.9 mg/g), and rats (4.5+/-0.5 mg/g). HSP72/73 levels, however, were not significantly different. HSP60 levels in hearts from both painted and softshell turtles did not deviate significantly from control values after either 12 h of anoxia or 12 or 24 h of recovery. The pattern of changes observed in HSP72/73 was quite different in the two turtle species. In painted turtles anoxia induced a significant increase in myocardial HSP72/73 (from 2.8+/-0.1 mg/g normoxic to 3.9+/-0.2 mg/g anoxic, P<0.05). By 12 h of recovery, HSP72/73 had returned to control levels (2.7+/-0.1 mg/g) and remained there through 24 h (2.6+/-0.2 mg/g). In softshell turtles, HSP72/73 decreased significantly after 12 h of anoxia (from 2.4+/-0.4 mg/g normoxic to 1.3+/-0.2 mg/g anoxic, P<0.05). HSP72/73 levels were still slightly below control after 12 h of recovery (2.1+/-0.1 mg/g) and then rose to significantly above control after 24 h of recovery (4.1+/-0.7 mg/g, P<0.05). We also conclude that anoxia-tolerant and anoxia-sensitive turtles exhibit different patterns of myocardial HSP changes during anoxia and recovery. Whether these changes correlate with their relative degrees of anoxia tolerance remains to be determined.

Prior heat stress inhibits apoptosis in adenosine triphosphate-depleted renal tubular cells

BACKGROUND

This study tested the following hypotheses: (a) renal tubular epithelial cells subjected to transient adenosine triphosphate (ATP) depletion undergo apoptosis, and (b) induction of heat stress proteins (HSPs) inhibits cell death following ATP depletion, possibly by interacting with anti-apoptotic signal proteins.

METHODS

To simulate ischemia in vivo, cells derived from opossum kidney proximal tubule (OK) were subjected to ATP depletion (5 mM cyanide, 5 mM 2-deoxy-D-glucose, and 0 mM glucose) for 1 to 1. 5 hours, followed by recovery (10 mM glucose without cyanide). The presence of apoptosis was assessed by morphological and biochemical criteria. The effect of prior heat stress or caspase inhibition on apoptosis and cell survival were assessed.

RESULTS

In the ATP-depleted cell, both Hoechst dye and electron microscopy revealed morphological features that are typical of apoptosis. On an agarose gel, a "ladder pattern" typical of endonucleosomal DNA degradation was observed. Prior heat stress reduced the number of apoptotic-appearing cells, significantly decreased DNA fragmentation, and improved cell survival compared with controls (73.0 +/- 1% vs. 53.0 +/- 1.5%; P < 0.05). Two different caspase inhibitors also improved survival, suggesting that apoptosis is a cause of cell death in this model. Compared with ATP-depleted controls, prior heat stress inhibited the pro-apoptotic changes in the ratio of Bcl2 to BAX, proteins known to regulate the apoptotic set point in renal cells. HSP 72, a known cytoprotectant, co-immunoprecipitated with Bcl2, an anti-apoptotic protein. Prior heat stress markedly increased the interaction between HSP 72 and Bcl2.

CONCLUSIONS

Transient ATP depletion causes apoptosis in tubular epithelial cells. Prior HS inhibits apoptosis and improves survival in these cells. Novel interactions between HSP 72 and Bcl2 may be responsible, at least in part, for the protection afforded by prior heat stress against ATP depletion injury.

Mutation of amino acids 246-251 alters nuclear accumulation of human heat shock protein (HSP) 72 with stress, but does not reduce viability

The stress response includes up-regulation of heat shock protein (HSP) 72 expression and accumulation of the protein in the nucleus. This nuclear accumulation of HSP72 is seen in many different settings, including the ischemic heart. The identity of the signal(s) regulating nuclear concentration of HSP72 are unknown. We theorized that nuclear accumulation of HSP72 with stress contributes to its protective properties in the ischemic heart and other tissues. Before we can test this hypothesis we need to alter accumulation of HSP72. Using site-directed mutagenesis we investigated the importance of amino acids 246-262 (KRKHKKDISQNKRAVRR), the presumed nuclear localization sequence (NLS), in nuclear accumulation in response to stress. Three mutant constructs of this sequence, 985A(AAAHAADISQNKRAVRR), 97M (KRKHKKDISQNAAAVAR), and B1 (AAAHAADISQNAAAVAR), were transfected into Cos cells. Analysis by exhaustive photon reassignment, which allowed examination of the nucleus in sections, showed that both 985A and B1 had decreased nuclear concentration with stress. A fusion protein with KRKHKK and EGFP localized to the nucleus in the absence of stress, with prominent accumulation in the nucleoli. Only B1, which also altered ATP binding, affected viability after heat shock. We conclude that amino acids 246-251 influence nucleolar accumulation of HSP72, but that this is not essential for early survival after injury.

Tumor necrosis factor-alpha confers resistance to hypoxic injury in the adult mammalian cardiac myocyte

BACKGROUND

Previous studies in isolated cardiac myocytes have shown that tumor necrosis factor (TNF)-alpha provokes increased expression of 27- and 70-kD stress proteins as well as manganese superoxide dismutase, suggesting that TNF-alpha might play a role in mediating stress responses in the heart.

METHODS AND RESULTS

To determine whether TNF-alpha stimulation would protect isolated cardiac myocytes against environmental stress, myocyte cultures were pretreated with TNF-alpha for 12 hours and then subjected to continuous hypoxic injury (O2 content, 3 to 5 ppm) for 12 hours, followed by reoxygenation. Cell injury was assessed in terms of lactic dehydrogenase (LDH) release, 45Ca2+ uptake, and MTT metabolism. Pretreatment with TNF-alpha concentrations > or = 50 U/mL significantly attenuated LDH release by hypoxic cells compared with diluent-treated hypoxic cells. Similar findings were observed with respect to 45Ca2+ uptake and MTT metabolism in TNF-alpha-pretreated cells that were subjected to prolonged hypoxia. To determine the mechanism for the TNF-alpha-induced protective effect, the cells were pretreated with heat shock protein (HSP) 72 antisense oligonucleotides. These studies showed that the protective effect of TNF-alpha was not inhibited by antisense oligonucleotides, despite use of a concentration of antisense that was sufficient to attenuate the TNF-alpha-induced increase in HSP 72 expression. Subsequent studies using mutated TNF ligands showed that activation of both types 1 and 2 TNF receptors was sufficient to confer a protective response in isolated cardiac myocytes through an as yet unknown pathway(s).

CONCLUSIONS

Taken together, the above observations demonstrate that TNF-alpha pretreatment confers resistance to hypoxic stress in the adult cardiac myocyte through a novel mechanism that appears to be different from but not necessarily exclusive of the protective response conferred by HSP 72 expression.

Differential expression of heat shock proteins in normal and failing human hearts

BACKGROUND

Heat shock proteins (hsp) constitute an endogenous stress response that protects cells from injury. Most work on these important proteins has focused on the immediate response to acute stress in cell culture systems and mammalian models of heart disease. Little is known about the expression of the hsps in human hearts. We were interested in whether there was increased expression of the hsps in heart failure, a setting of chronic, sustained stress. Five different hsps were examined: hsp27, hsp60, hsp72, hsc70 and hsp90.

METHODS AND RESULTS

Three groups of explanted hearts were studied: dilated cardiomyopathy (DCM), ischemic cardiomyopathy (IHD), and normal controls. Western-blotting with a standard curve of purified protein on each blot was used to quantify the expression of the hsps. Hsp27 was increased almost two-fold in DCM compared to normal hearts, and was significantly greater than in IHD hearts. Levels of hsp60 were doubled in both DCM and IHD hearts (P < 0.05). Hsp72, hsc70 and hsp90 were not significantly changed.

CONCLUSIONS

This study shows for the first time that differential changes in hsp levels occur in end-stage heart failure. Since hsps can render cells resistant to apoptosis, and are associated with the mitochondria and the cytoskeleton, which are known to be abnormal in heart failure, these studies may lead to new insights into the pathogenesis of cardiac decompensation.

Blocking the endogenous increase in HSP 72 increases susceptibility to hypoxia and reoxygenation in isolated adult feline cardiocytes

BACKGROUND

Heat shock protein (HSP) 72 is a ubiquitous protein that is rapidly induced in response to stress and is thought to constitute an endogenous protective response. Previously, work has focused on the effect of overexpression of HSP 72 in various cell types. We were interested in testing the hypothesis that blocking the increase in HSP 72 that occurs in response to hypoxia or ischemia would be deleterious, thus showing that the endogenous response in cells, particularly cardiac cells, is an important line of defense against cell injury.

METHODS AND RESULTS

Isolated adult feline cardiocytes were treated with a 14-mer phosphorothioate antisense (AS) to HSP 72 and then exposed to mild (8 hours) or severe (12 hours) hypoxia. With mild hypoxia, an increase in LDH release, a decrease in MTT uptake, and a decrease in live-to-dead ratios were seen in AS-treated cells compared with control cells and cells treated with the complementary sense sequence or with AS to major histocompatibility complex I. AS treatment converted mild hypoxic injury to a pattern of cell injury seen with severe injury. After severe hypoxia, all treatment groups showed an increase in LDH, a decrease in MTT uptake, and a decrease in live-to-dead ratios; AS-treated cells had the greatest increase in cell injury. AS treatment produced a 40% decrease in HSP 72 levels after hypoxia compared with control cells treated with hypoxia. A dose-response study showed inhibition of the increase in HSP 72 with as little as 5 micrograms (1.24 mumol/L) of AS.

CONCLUSIONS

(1) Blocking an increase in HSP 72 with AS increases the susceptibility of adult cardiac myocytes to hypoxic injury. (2) HSP 72 is an important part of the normal cell response to stress and is important in protecting cardiac myocytes from hypoxia and reoxygenation.

Tumor necrosis factor-alpha-induced expression of heat shock protein 72 in adult feline cardiac myocytes

Tumor necrosis factor-alpha (TNF-alpha) is a proinflammatory cytokine that is elaborated in a myriad of cardiac disease states. Although the biological role for TNF-alpha in the adult heart is not known, a recent study in fetal myocardial cells has shown that this cytokine increases the synthesis of low-molecular-weight stress proteins. These findings suggested the interesting possibility that TNF-alpha might play a functional role in the adult heart by increasing the expression of stress proteins in cardiac myocytes. Accordingly, the purpose of this study was to determine whether TNF-alpha would modulate the expression of heat shock protein 72 (HSP 72), a stress protein that is thought to exert protective effects in the adult heart. Stimulation of adult feline cardiac myocytes with a range of TNF-alpha concentrations (10-1,000 U/ml) for 12 h showed that concentrations of TNF-alpha < or = 10 U/ml had no effect on HSP 72 expression: increased HSP 72 expression was detected 3 h following cytokine stimulation, peaked by approximately 12 h, and then returned toward baseline by 48 h. Additional studies indicated that stimulation of the type 1 TNF receptor was responsible for the increase in HSP 72 expression. In summary, these studies constitute the initial demonstration that TNF-alpha exerts concentration- and time-dependent effects on the expression of HSP 72 in the adult mammalian cardiac myocytes, thus suggesting the interesting possibility that the elaboration of TNF-alpha may enable the heart to better withstand certain forms of stress.

Late preconditioning against myocardial stunning. An endogenous protective mechanism that confers resistance to postischemic dysfunction 24 h after brief ischemia in conscious pigs

Conscious pigs underwent a sequence of 10 2-min coronary occlusions, each separated by 2 min of reperfusion, for three consecutive days (days 1, 2, and 3 of stage I). The recovery of systolic wall thickening (WTh) after the 10th reperfusion was markedly improved on days 2 and 3 compared with day 1, indicating that the myocardium had become preconditioned against "stunning." 10 d after stage I, pigs underwent again a sequence of 10 2-min coronary occlusions for two consecutive days (days 1 and 2 of stage II). On day 1 of stage II, the recovery of WTh after the 10th reperfusion was similar to that noted on day 1 of stage I; on day 2 of stage II, however, the recovery of WTh was again markedly improved compared with day 1. Blockade of adenosine receptors with 8-p-sulfophenyl theophylline failed to prevent the development of preconditioning against stunning. Northern blot analysis demonstrated an increase in heat stress protein (HSP) 70 mRNA 2 h after the preconditioning ischemia; at this same time point, immunohistochemical analysis revealed a concentration of HSP70 in the nucleus and an overall increase in staining for HSP70. 24 h after the preconditioning ischemia, Western dot blot analysis demonstrated an increase in HSP70. This study indicates the existence of a new, previously unrecognized cardioprotective phenomenon. The results demonstrate that a brief ischemic stress induces a powerful, long-lasting (at least 48 h) adaptive response that renders the myocardium relatively resistant to stunning 24 h later (late preconditioning against stunning). This adaptive response disappears within 10 d after the last ischemic stress but can be reinduced by another ischemic stress. Unlike early and late preconditioning against infarction, late preconditioning against stunning is not blocked by adenosine receptor antagonists, and therefore appears to involve a mechanism different from that of other forms of preconditioning currently known. The increase in myocardial HSP70 is compatible with, but does not prove, a role of HSPs in the pathogenesis of this phenomenon.

Rapid expression of fibronectin in the rabbit heart after myocardial infarction with and without reperfusion

The expression of fibronectin in the repair process after myocardial infarction was studied using two protocols of coronary occlusion in the rabbit: a permanent occlusion or 3 h of occlusion followed by reperfusion (too late for salvage). We found a rapid and progressive increase in cardiac fibronectin expression in the infarcted region of the ventricle. Steady-state mRNA levels for fibronectin increased 13- and 16-fold, respectively, in the permanent and reperfused infarcts 1 d postinfarction. Immunological detection of the protein with a polyclonal antibody against plasma fibronectin showed significant increases of the protein fibronectin in the infarcted myocardium by day 3 in the reperfused group and by day 5 in the permanent coronary occlusion group. Ribonuclease protection assays established the induction of EIIIB containing fibronectin mRNA in both models by day 1 and use of a monoclonal antibody showed an increase in the EIIIA isoform 2 d postinfarction. Increases in steady-state mRNA levels for several collagen types were found in both groups, but these changes occurred after those noted for fibronectin. Thus fibronectin mRNA and protein expression increased rapidly postinfarction suggesting a functional role in the repair process.

A single myocardial stretch or decreased systolic fiber shortening stimulates the expression of heat shock protein 70 in the isolated, erythrocyte-perfused rabbit heart

The regulation of heat shock protein 70 (HSP 70) expression was examined in the isolated, red blood cell-perfused rabbit heart by Northern and Western blot analysis. In the isovolumic (balloon in left ventricle), isolated perfused heart, HSP 70 mRNA was increased threefold after 30 min and sevenfold at 2 and 4 h compared to normal, nonperfused hearts. To further elucidate the etiology of the increase in HSP 70 mRNA, the effects of decreased systolic shortening (isovolumic heart) and of a single ventricular stretch were examined. Perfusion without the application of a stretch or the presence of a balloon resulted in no increase in HSP 70 mRNA; while a single stretch resulted in a threefold increase in HSP 70 mRNA. These changes were accompanied by an increase in HSP 70 protein by Western blot analysis. To elucidate the signalling mechanism mediating the increase in HSP 70, hearts were perfused with H7, a protein kinase C inhibitor. H7 did not prevent the induction of HSP 70. These results indicate that initiation of expression of myocardial HSP 70 can be stimulated by a single myocardial stretch or by prevention of systolic shortening. These mechanisms may contribute to the rapid expression of HSP 70 after coronary occlusion when dyskinesis, reduced systolic shortening, and increased diastolic segment length all occur.