Further study on the role of HSP70 on Ca2+ homeostasis in rat ventricular myocytes subjected to simulated ischemia

Heat shock proteins: Biological functions, pathological roles, and therapeutic opportunities

The heat shock proteins (HSPs) are ubiquitous and conserved protein families in both prokaryotic and eukaryotic organisms, and they maintain cellular proteostasis and protect cells from stresses. HSP protein families are classified based on their molecular weights, mainly including large HSPs, HSP90, HSP70, HSP60, HSP40, and small HSPs. They function as molecular chaperons in cells and work as an integrated network, participating in the folding of newly synthesized polypeptides, refolding metastable proteins, protein complex assembly, dissociating protein aggregate dissociation, and the degradation of misfolded proteins. In addition to their chaperone functions, they also play important roles in cell signaling transduction, cell cycle, and apoptosis regulation. Therefore, malfunction of HSPs is related with many diseases, including cancers, neurodegeneration, and other diseases. In this review, we describe the current understandings about the molecular mechanisms of the major HSP families including HSP90/HSP70/HSP60/HSP110 and small HSPs, how the HSPs keep the protein proteostasis and response to stresses, and we also discuss their roles in diseases and the recent exploration of HSP related therapy and diagnosis to modulate diseases. These research advances offer new prospects of HSPs as potential targets for therapeutic intervention.

Heat Shock Protein 70 Protects the Heart from Ischemia/Reperfusion Injury through Inhibition of p38 MAPK Signaling

Background

Heat shock protein 70 (Hsp70) has been shown to exert cardioprotection. Intracellular calcium ([Ca²⁺]_i) overload induced by p38 mitogen-activated protein kinase (p38 MAPK) activation contributes to cardiac ischemia/reperfusion (I/R) injury. However, whether Hsp70 interacts with p38 MAPK signaling is unclear. Therefore, this study investigated the regulation of p38 MAPK by Hsp70 in I/R-induced cardiac injury.

Methods

Neonatal rat cardiomyocytes were subjected to oxygen-glucose deprivation for 6 h followed by 2 h reoxygenation (OGD/R), and rats underwent left anterior artery ligation for 30 min followed by 30 min of reperfusion. The p38 MAPK inhibitor (SB203580), Hsp70 inhibitor (Quercetin), and Hsp70 short hairpin RNA (shRNA) were used prior to OGD/R or I/R. Cell viability, lactate dehydrogenase (LDH) release, serum cardiac troponin I (cTnI), [Ca²⁺]_i levels, cell apoptosis, myocardial infarct size, mRNA level of IL-1β and IL-6, and protein expression of Hsp70, phosphorylated p38 MAPK (p-p38 MAPK), sarcoplasmic/endoplasmic reticulum Ca²⁺-ATPase2 (SERCA2), phosphorylated signal transducer and activator of transcription3 (p-STAT3), and cleaved caspase3 were assessed.

Results

Pretreatment with a p38 MAPK inhibitor, SB203580, significantly attenuated OGD/R-induced cell injury or I/R-induced myocardial injury, as evidenced by improved cell viability and lower LDH release, resulted in lower serum cTnI and myocardial infarct size, alleviation of [Ca²⁺]_i overload and cell apoptosis, inhibition of IL-1β and IL-6, and modulation of protein expressions of p-p38 MAPK, SERCA2, p-STAT3, and cleaved-caspase3. Knockdown of Hsp70 by shRNA exacerbated OGD/R-induced cell injury, which was effectively abolished by SB203580. Moreover, inhibition of Hsp70 by quercetin enhanced I/R-induced myocardial injury, while SB203580 pretreatment reversed the harmful effects caused by quercetin.

Conclusions

Inhibition of Hsp70 aggravates [Ca²⁺]_i overload, inflammation, and apoptosis through regulating p38 MAPK signaling during cardiac I/R injury, which may help provide novel insight into cardioprotective strategies.

Stress Effects on Meat Quality: A Mechanistic Perspective

Stress inevitably occurs from the farm to abattoir in modern livestock husbandry. The effects of stress on the behavioral and physiological status and ultimate meat quality have been well documented. However, reports on the mechanism of stress effects on physiological and biochemical changes and their consequent effects on meat quality attributes have been somewhat disjointed and limited. Furthermore, the causes of variability in meat quality traits among different animal species, muscle fibers within an animal, and even positions within a piece of meat in response to stress are still not entirely clear. This review 1st summarizes the primary stress factors, including heat stress, preslaughter handling stress, oxidative stress, and other stress factors affecting animal welfare; carcass quality; and eating quality. This review further delineates potential stress-induced pathways or mediators, including AMP-activated protein kinase-mediated energy metabolism, crosstalk among calcium signaling pathways and reactive oxygen species, protein modification, apoptosis, calpain and cathepsin proteolytic systems, and heat shock proteins that exert effects that cause biochemical changes during the early postmortem period and affect the subsequent meat quality. To obtain meat of high quality, further studies are needed to unravel the intricate mechanisms involving the aforementioned signaling pathways or mediators and their crosstalk.

Polystyrene–divinylbenzene based nano-CaCO3composites for the efficient removal of human tumor necrosis factor-α

PS-DVB/nano-CaCO₃, a novel abundant mesoporous structured polymer nano-composite, exhibits significantly enhanced performances in the adsorption of TNF-α from plasma.

Potential hepatoprotective effects of fullerenol nanoparticles on alcohol-induced oxidative stress by ROS

The free radical scavenging ability of fullerenols is their most exploited property in biomedical studies.

Diagnosis and Therapy of Atrial Fibrillation: The Past, The Present and The Future

Atrial fibrillation (AF) is the most common age-related cardiac arrhythmia. It is a progressive disease, which makes treatment difficult. The progression of AF is caused by the accumulation of damage in cardiomyocytes which makes the atria more vulnerable for AF. Especially structural remodeling and electrical remodeling, together called electropathology are sustainable in the atria and impair functional recovery to sinus rhythm after cardioversion. The exact electropathological mechanisms underlying persistence of AF are at present unknown. High resolution wavemapping studies in patients with different types of AF showed that longitudinal dissociation in conduction and epicardial breakthrough were the key elements of the substrate of longstanding persistent AF. A double layer of electrically dissociated waves propagating transmurally can explain persistence of AF (Double Layer Hypothesis) but the molecular mechanism is unknown. Derailment of proteasis -defined as the homeostasis in protein synthesis, folding, assembly, trafficking, guided by chaperones, and clearance by protein degradation systems - may play an important role in remodeling of the cardiomyocyte. As current therapies are not effective in attenuating AF progression, step-by-step analysis of this process, in order to identify potential targets for drug therapy, is essential. In addition, novel mapping approaches enabling assessment of the degree of electropathology in the individual patient are mandatory to develop patient-tailored therapies. The aims of this review are to 1) summarize current knowledge of the electrical and molecular mechanisms underlying AF 2) discuss the shortcomings of present diagnostic instruments and therapeutic options and 3) to present potential novel diagnostic tools and therapeutic targets.

Deficiency in Heat Shock Factor 1 (HSF-1) Expression Exacerbates Sepsis-induced Inflammation and Cardiac Dysfunction

In the present study, we investigated whether absence of heat shock factor 1 (HSF-1) and inability to increase myocardial expression of heat shock proteins alter septic responses of inflammatory cytokines and myocardial contractility. HSF-1 knockout (hsf ^-/-) mice and wild type litter mates underwent a sterile (lipopolysaccharide; LPS) or infectious (Streptococcus pneumoniae or Klebsiella pneumoniae) septic challenge. Production of cytokines, TNF, IL-1β, IL-6 and IL-10, in the blood and from cardiomyocytes was exaggerated in the hsf ^-/- mice compared to responses measured in wild type mice given an identical septic challenge. This enhanced compartmentalized myocardial inflammation was associated with significantly decreased cardiac contraction and diminished relaxation in the hsf ^-/- mice. However, lacking HSF-1 expression did not affect intracellular calcium and sodium responses in cardiomyocytes isolated from septic challenged mice, suggesting that ion loading was not a major or sustaining cause of the greater myocardial contractile defects in hsf ^-/- mice. In conclusion, our data indicated that HSF-1 and downstream heat shock proteins are essential components to support cardiac function in sepsis. Further studies are warranted to further define the precise mechanisms of HSF-1 mediated cardiac protection.

Mutation in integrin-linked kinase (ILK(R211A)) and heat-shock protein 70 comprise a broadly cardioprotective complex

Rationale

Integrin-linked kinase (ILK) has been proposed as a novel molecular target that has translational potential in diverse cardiac diseases, since its upregulation promotes a broadly cardioprotective phenotype. However, ILK has been implicated as both a cardioprotective and oncogenic target, which imposes therapeutic constraints that are generally relevant to the translational potential of many kinases.

Objective

To study the cardioprotective properties of the activation-resistant, non-oncogenic, mutation of ILK (ILK^R211A) against experimental MI invivo and Doxorubicin induced apoptosis invitro and it’s relationships to stress induced heat shock proteins.

Methods/Results

The transgenic mouse heart over-expressing a point mutation in the ILK pleckstrin homology (PH) domain (Tg^R211A) exhibits a highly cardioprotective phenotype based on LAD-ligation-induced MI reduction invivo, and on protection against doxorubicin (DOX)-induced cardiomyocyte apoptosis when overexpressed in human induced pluripotent stem cell (iPS)-derived cardiomyocytes invitro. Intriguingly, the degree of cardioprotection seen with the ILK^R211A mutation exceeded that with the ILK^S343D mutation. Microarray and immunoprecipitation analyses revealed upregulation of expression levels and specific binding of ILK^WT, ILK^S343D and ILK^R211A to both constitutively active heat-shock protein 70 (Hsc70) and inducible Hsp70 in response to MI, and to acute ILK overexpression in iPSC-cardiomyocytes. ILK-mediated cardioprotection was shown to depend upon Hsp70 ATPase activity.

Conclusions

These findings indicate that wild type ILK and the non-oncogenic ILK^R211A mutation comprise a cardioprotective module with Hsp/c70. These results advance a novel target discovery theme in which kinase mutations can be safely engineered to enhance cardioprotective effects.

Parvalbumin is overexpressed in the late phase of pharmacological preconditioning in skeletal muscle

Pharmacological preconditioning (PPC) with mitochondrial ATP-sensitive K(+) channel openers such as diazoxide, provides protection against ischemia in cardiac muscle, skeletal muscle, and other tissues. Effects on Ca(2+) homeostasis during the late phase of PPC have been described in cardiomyocytes, but no information is available regarding intracellular Ca(2+) changes in skeletal muscle fibers during late PPC. Intracellular Ca(2+) signals were measured in single fibers of adult mouse skeletal muscle, with fluorescent probes, 48 h after the administration of diazoxide. Parvalbumin levels in the myofibers were quantitated by Western blot. Diazoxide induction of late PPC was confirmed by partial protection of muscles from peroxide-induced damage. Late PPC was associated with a significant decrease in the duration of Ca(2+) signals during single twitches and tetanus with no changes in peak values. This effect was prevented by the reactive oxygen species (ROS) scavenger tiron. Late PPC was accompanied by a 30% increase in parvalbumin levels, and this effect was also blocked by tiron. Our data show, for the first time, a role of parvalbumin in late PPC in skeletal muscle.

Heat shock protein inducer modifies arrhythmogenic substrate and inhibits atrial fibrillation in the failing heart

BACKGROUND

Geranylgeranylacetone (GGA) has been reported up-regulating heat shock protein (HSP) expression, and protecting against atrial remodeling. This study aimed to investigate the effects of GGA on atrial electrophysiology and inducibility of atrial fibrillation (AF) in heart failure (HF) model.

METHODS AND RESULTS

HF rabbits were created 4 weeks after coronary artery ligation. Monophasic action potential recordings and multielectrode array were used to record the electrophysiological characteristics of left atrium (LA) in normal, or HF rabbits with (HF-GGA) and without (HF-control) oral administration of GGA (200 mg/kg, 24 h before experiments). The mRNA and protein expressions of ionic channels were measured by Western blot and PCR. HF-GGA LA (n = 10), similar to normal LA (n = 10) had a shorter action potential duration (APD) and effective refractory period than HF-control LA (n = 10). HF-GGA LA had less triggered activity and APD alternans (20% vs. 100%, P = 0.001), lower maxima slope of restitution curve of APD (0.94 ± 0.04 vs.1.69 ± 0.04, P < 0.001), and less inducibility of AF (50% vs. 100%, P = 0.033) than HF-control LA. HF-GGA LA had a shorter activation time and higher conduction velocity than HF-control LA. HF-GGA LA had a higher mRNA expression of Cav1.2, Nav1.5, Kir2.1, Kv1.4, Kv7.1, Kv11.1, sarcoplasmic reticulum Ca(2+)-ATPase, and higher phosphorylation of phospholamban than HF-control LA.

CONCLUSIONS

GGA decreases triggered activity, dispersion of APD and inducibility of AF in failing heart through induction of HSP, and modulation of ionic channels and calcium homeostasis.

A model of poorly controlled type 1 Diabetes Mellitus and its treatment with aerobic exercise training

BACKGROUND

Modern exogenous insulin therapy can improve the quality of life of Type 1 Diabetic Mellitus (T1DM) patients, although maintenance of normal glycaemic levels is often a challenge given the variety of factors that alter it. A number of studies have examined the effect of exercise in T1DM; however, the majority of experimental studies have utilized diabetic rodents with severe hyperglycaemia. Given that T1DM patients are likely to refrain from hyperglycaemia, studies examining the effects of regular exercise in which blood glucose is poorly controlled would better represent the T1DM population.

METHODS

The current study examined the ability of a ten-week aerobic exercise training program to modify markers of cardiovascular function and bone health in STZ-induced diabetic rodents maintained in the 9-15 mM glycaemic range through insulin therapy.

RESULTS

Moderate hyperglycaemia, when prolonged, leads to significant changes in cardiac structure, bone health, and glucose handling capacity. Ten weeks of exercise was able to alleviate many of these deleterious events as no significant cardiovascular functional alterations were evident except a reduction in resting heart rate and an increase in stroke volume index. Further, despite changes in cardiac dimensions, exercise was able to elevate cardiac output index and increase the E/A ratio of exercising diabetic animals which would be indicative of improvements of cardiac function.

CONCLUSIONS

Together, this study demonstrates that despite moderate hyperglycaemia, the combined role of a ten-week exercise training program coupled with insulin therapy is able to alleviate many of the well-known complications associated with diabetes progression.

Role of physical activity in tumor patients and possible underlying mechanisms

A growing knowledge regarding the influence of exercise on adverse physiologic outcomes associated with cancer and its treatment exists. Aside from its effects on psychological behavior, quality of life, and cancer-related fatigue, physical exercise can target physical and cardio-respiratory fitness, insulin regulation and metabolic syndrome, body weight and composition, and immune function in tumor patients. The increasing number of study results for different cancer types, which prove the positive influences of physical activity in cancer patients, changed the contradictory opinions which existed until the end of the last century. Although an increasing number of studies showing the positive effects of physical activity and more specifically of endurance and resistance training in cancer patients have been published, the underlying mechanisms are mostly unknown. Thus, we summarized the current knowledge of the effects of physical activity and specific training in different tumor entities with specific respect to the possible underlying mechanisms. Especially, the association between physical activity and (1) the improvement of fatigue and the role of free radicals in this process, (2) the counterbalance of tumor-induced cachexia, (3) the improvement of the immune system for supportive tumor treatment, and (4) the possible role of epigenetic modulation against tumor and tumor treatment-dependent adverse physiologic outcomes is focused.

Loss of proteostatic control as a substrate for atrial fibrillation: a novel target for upstream therapy by heat shock proteins

Atrial fibrillation (AF) is the most common, sustained clinical tachyarrhythmia associated with significant morbidity and mortality. AF is a persistent condition with progressive structural remodeling of the atrial cardiomyocytes due to the AF itself, resulting in cellular changes commonly observed in aging and in other heart diseases. While rhythm control by electrocardioversion or drug treatment is the treatment of choice in symptomatic AF patients, its efficacy is still limited. Current research is directed at preventing first-onset AF by limiting the development of substrates underlying AF progression and resembles mechanism-based therapy. Upstream therapy refers to the use of non-ion channel anti-arrhythmic drugs that modify the atrial substrate- or target-specific mechanisms of AF, with the ultimate aim to prevent the occurrence (primary prevention) or recurrence of the arrhythmia following (spontaneous) conversion (secondary prevention). Heat shock proteins (HSPs) are molecular chaperones and comprise a large family of proteins involved in the protection against various forms of cellular stress. Their classical function is the conservation of proteostasis via prevention of toxic protein aggregation by binding to (partially) unfolded proteins. Our recent data reveal that HSPs prevent electrical, contractile, and structural remodeling of cardiomyocytes, thus attenuating the AF substrate in cellular, Drosophila melanogaster, and animal experimental models. Furthermore, studies in humans suggest a protective role for HSPs against the progression from paroxysmal AF to persistent AF and in recurrence of AF. In this review, we discuss upregulation of the heat shock response system as a novel target for upstream therapy to prevent derailment of proteostasis and consequently progression and recurrence of AF.

Embryonic lethality in mice lacking the nuclear factor of activated T cells 5 protein due to impaired cardiac development and function

Nuclear factor of activated T cells 5 protein (NFAT5) is thought to be important for cellular adaptation to osmotic stress by regulating the transcription of genes responsible for the synthesis or transport of organic osmolytes. It is also thought to play a role in immune function, myogenesis and cancer invasion. To better understand the function of NFAT5, we developed NFAT5 gene knockout mice. Homozygous NFAT5 null (NFAT5^−/−) mouse embryos failed to develop normally and died after 14.5 days of embryonic development (E14.5). The embryos showed peripheral edema, and abnormal heart development as indicated by thinner ventricular wall and reduced cell density at the compact and trabecular areas of myocardium. This is associated with reduced level of proliferating cell nuclear antigen and increased caspase-3 in these tissues. Cardiomyocytes from E14.5 NFAT5^−/− embryos showed a significant reduction of beating rate and abnormal Ca²⁺ signaling profile as a consequence of reduced sarco(endo)plasmic reticulum Ca²⁺-ATPase (SERCA) and ryanodine receptor (RyR) expressions. Expression of NFAT5 target genes, such as HSP 70 and SMIT were reduced in NFAT5^−/− cardiomyocytes. Our findings demonstrated an essential role of NFAT5 in cardiac development and Ca²⁺ signaling. Cardiac failure is most likely responsible for the peripheral edema and death of NFAT5^−/− embryos at E14.5 days.

The second window of preconditioning (SWOP) where are we now?

A standard ischemic preconditioning (IPC) stimulus of one or more brief episodes of non-lethal myocardial ischemia and reperfusion elicits a bi-phasic pattern of cardioprotection. The first phase manifests almost immediately following the IPC stimulus and lasts for 1-2 h, after which its effect disappears (termed classical or early IPC). The second phase of cardioprotection appears 12-24 h later and lasts for 48-72 h (termed the Second Window of Protection [SWOP] or delayed or late IPC). The cardioprotection conferred by delayed IPC is robust and ubiquitous but is not as powerful as early IPC. Although there are some similarities in the mechanisms underlying early and delayed IPC, one of the major distinctions between the two is the latter's requirement for de novo protein synthesis of distal mediators such as iNOS and COX-2 which mediate the cardioprotection 24 h after the IPC stimulus. The phenomenon of delayed IPC has been demonstrated in man using a variety of experimental models. However, its clinical application has been limited by the same factors which affect early IPC- i.e. the need to intervene before the onset of myocardial ischemia, thereby restricting its potential clinical utility to planned settings of acute myocardial ischemia-reperfusion injury such as coronary artery bypass graft surgery, cardiac transplantation and percutaneous coronary intervention. In this article, the focus will be on the origins of delayed IPC, the mechanisms underlying its delayed cardioprotective effect, and the potential areas for its clinical application.

Cytokine-associated drug toxicity in human hepatocytes is associated with signaling network dysregulation

Idiosyncratic drug hepatotoxicity is a major problem in pharmaceutical development due to poor prediction capability of standard preclinical toxicity assessments and limited knowledge of its underlying mechanisms. Findings in animal models have shown that adverse effects of numerous drugs with idiosyncratic hepatotoxicity in humans can be reproduced in the presence of coincident inflammatory cytokine signaling. Following these observations, we have recently developed an in vitro drug/inflammatory cytokine co-treatment approach that can reproduce clinical drug hepatotoxicity signatures-particularly for idiosyncratic drugs-in cultured primary human hepatocytes. These observations have suggested that drug-induced stresses may interact with cytokine signaling to induce hepatic cytotoxicity, but the hepatocyte signaling mechanisms governing these interactions are poorly understood. Here, we collect high-throughput phosphoprotein signaling and cytotoxicity measurements in cultured hepatocytes, from multiple human donors, treated with combinations of hepatotoxic drugs (e.g. trovafloxacin, clarithromycin) and cytokines (tumor necrosis factor-alpha, interferon-gamma, interleukin-1 alpha, and interleukin-6). We demonstrate, through orthogonal partial least-squares regression (OPLSR) modeling of these signal-response data, that drug/cytokine hepatic cytotoxicity is integratively controlled by four key signaling pathways: Akt, p70 S6 kinase, MEK-ERK, and p38-HSP27. This modeling predicted, and experimental studies confirmed, that the MEK-ERK and p38-HSP27 pathways contribute pro-death signaling influences in drug/cytokine hepatic cytotoxicity synergy. Further, our four-pathway OPLSR model produced successful prediction of drug/cytokine hepatic cytotoxicities across different human donors, even though signaling and cytotoxicity responses were both highly donor-specific. Our findings highlight the critical role of kinase signaling in drug/cytokine hepatic cytotoxicity synergies and reveal that hepatic cytotoxicity responses are governed by multi-pathway signaling network balance.

Cardiac contractile dysfunction during acute hyperglycemia due to impairment of SERCA by polyol pathway-mediated oxidative stress

Hyperglycemia is an indication of poor outcome for heart attack patients, even for nondiabetic patients with stress-induced hyperglycemia. Previous studies showed that inhibition of aldose reductase, the first and rate-limiting enzyme of the polyol pathway, attenuated contractile dysfunction in diabetic animals, but the mechanism is unclear. We therefore wanted to find out whether the polyol pathway also contributes to acute hyperglycemia-induced cardiac contractile dysfunction, and determine the mechanism involved. Rat hearts were isolated and retrogradely perfused with Krebs buffer containing either normal or high concentrations of glucose for 2 h. Short exposure to high-glucose medium led to contractile dysfunction as indicated by decreased -dP/dt(max), as well as elevation in left ventricular end-diastolic pressure. Cardiomyocytes incubated in high-glucose medium showed abnormal Ca2+ signaling, most likely because of decreased activity of sarco(endo)plasmic reticulum Ca2+-ATPase (SERCA) inactivated by oxidative stress. Inhibition of aldose reductase or sorbitol dehydrogenase, the second enzyme in the polyol pathway, ameliorated contractile dysfunction, attenuated oxidative stress, and normalized Ca2+ signaling and SERCA activity caused by high glucose, indicating that the polyol pathway is the major contributor to acute hyperglycemia-induced oxidative stress leading to the inactivation of SERCA and contractile dysfunction.

Polyol pathway impairs the function of SERCA and RyR in ischemic-reperfused rat hearts by increasing oxidative modifications of these proteins

A number of studies have shown that the polyol pathway, consisting of aldose reductase (AR) and sorbitol dehydrogenase (SDH), contributes to ischemia-reperfusion (I/R)-induced myocardial infarction due to depletion of ATP. In this report we show that the polyol pathway in I/R heart also contributes to the impairment of sacro/endoplasmic reticulum Ca(2+)-ATPase (SERCA) and ryanodine receptor (RyR), two key players in Ca(2+) signaling that regulate cardiac contraction. Rat hearts were isolated and retrogradely perfused with either Krebs' buffer containing 1 microM AR inhibitor, zopolrestat, or 200 nM SDH inhibitor, CP-170,711, and challenged by 30 min of regional ischemia and 45 min of reperfusion. We found that post-ischemic contractile function of the isolated perfused hearts was improved by pharmacological inhibition of the polyol pathway. I/R-induced contractile dysfunction is most likely due to impairment in Ca(2+) signaling and the activities of SERCA and RyR. All these abnormalities were significantly ameliorated by treatment with ARI or SDI. We showed that the polyol pathway activities increase the level of peroxynitrite, which enhances the tyrosine nitration of SERCA and irreversibly modifies it to form SERCAC674-SO(3)H. This leads to reduced level of S-glutathiolated SERCA, contributing to its inactivation. The polyol pathway activities also deplete the level of GSH, leading to decreased active RyR, the S-glutathiolated RyR. Thus, in I/R heart, inhibition of polyol pathway improved the function of SERCA and RyR by protecting them from irreversible oxidation.

Protective effects of Hsp70 on the structure and function of SERCA2a expressed in HEK-293 cells during heat stress

Heat shock protein 70 (Hsp70) can physically interact with and prevent thermal inactivation of sarco(endo)plasmic reticulum Ca(2+)-ATPase (SERCA) 1a, the SERCA isoform expressed in adult fast-twitch skeletal muscle. This study examined whether Hsp70 could physically interact with and prevent thermal inactivation of SERCA2a, the SERCA isoform expressed in heart. HEK-293 cells were cotransfected with cDNAs encoding human Hsp70 and rabbit SERCA2a (S2a/Hsp70). Cells cotransfected with SERCA2a cDNA and pMT2 (S2a/pMT2) were used as control. One-half of the cells was heat shocked at 40 degrees C for 1 h (HS), and one-half was maintained at 37 degrees C before harvesting the cells and isolating microsomes. Western blot analysis showed that Hsp70 and SERCA2a were colocalized in the microsomal fraction. The levels of Hsp70 were approximately fivefold higher (P < 0.05) in S2a/Hsp70 compared with S2a/pMT2 and approximately twofold higher (P < 0.05) following HS in all cells. Coimmunoprecipitation demonstrated that Hsp70 directly binds to SERCA2a. Following HS, maximal SERCA2a activity was reduced ( approximately 52%, P < 0.05) in S2a/pMT2 but was increased ( approximately 33%, P < 0.05) in S2a/Hsp70. Thermal inactivation of SERCA2a in S2a/pMT2 was associated with decreased ( approximately 49%, P < 0.05) binding capacity for fluorescein isothiocyanate (FITC) and increased carbonyl ( approximately 42%, P < 0.05) and nitrotyrosine ( approximately 40%, P < 0.05) levels in SERCA2a. By contrast, the HS-induced increase in maximal SERCA2a activity observed in S2a/Hsp70 corresponded with no change (P > 0.05) in FITC-binding capacity and reductions in carbonyl ( approximately 40%, P < 0.05) and nitrotyrosine ( approximately 23%, P < 0.05) levels in SERCA2a compared with S2a/pMT2. These results show that Hsp70 forms a protective interaction with SERCA2a during HS actually reducing oxidation and nitrosylation of SERCA2a thus increasing its maximal activity.

Alpha2-AMPK activity is not essential for an increase in fatty acid oxidation during low-intensity exercise

A single bout of exercise increases glucose uptake and fatty acid oxidation in skeletal muscle, with a corresponding activation of AMP-activated protein kinase (AMPK). While the exercise-induced increase in glucose uptake is partly due to activation of AMPK, it is unclear whether the increase of fatty acid oxidation is dependent on activation of AMPK. To examine this, transgenic mice were produced expressing a dominant-negative (DN) mutant of alpha(1)-AMPK (alpha(1)-AMPK-DN) in skeletal muscle and subjected to treadmill running. alpha(1)-AMPK-DN mice exhibited a 50% reduction in alpha(1)-AMPK activity and almost complete loss of alpha(2)-AMPK activity in skeletal muscle compared with wild-type littermates (WT). The fasting-induced decrease in respiratory quotient (RQ) ratio and reduced body weight were similar in both groups. In contrast with WT mice, alpha(1)-AMPK-DN mice could not perform high-intensity (30 m/min) treadmill exercise, although their response to low-intensity (10 m/min) treadmill exercise was not compromised. Changes in oxygen consumption and the RQ ratio during sedentary and low-intensity exercise were not different between alpha(1)-AMPK-DN and WT. Importantly, at low-intensity exercise, increased fatty acid oxidation in response to exercise in soleus (type I, slow twitch muscle) or extensor digitorum longus muscle (type II, fast twitch muscle) was not impaired in alpha(1)-AMPK-DN mice, indicating that alpha(1)-AMPK-DN mice utilize fatty acid in the same manner as WT mice during low-intensity exercise. These findings suggest that an increased alpha(2)-AMPK activity is not essential for increased skeletal muscle fatty acid oxidation during endurance exercise.

Genetic delineation of the pathways mediated by bid and JNK in tumor necrosis factor-alpha-induced liver injury in adult and embryonic mice

Tumor necrosis factor-alpha (TNFalpha)-induced hepatocyte death and liver injury can be mediated by multiple mechanisms, which could be evaluated by different animal models. Previous studies have defined the importance of Bid in mitochondrial apoptosis activation in adult mice treated with lipopolysaccharides in the presence of galactosamine (GalN), which suppresses NF-kappaB activation, but not in embryonic mice in which NF-kappaB activation is suppressed by genetic deletion of p65RelA. JNK has also been found important in TNFalpha-induced mitochondria activation and liver injury in the lipopolysaccharide/GalN and concanavalin A (ConA)/GalN models, but not in a ConA-only model in which NF-kappaB activation was not suppressed. To determine the mechanistic relationship of pathways mediated by Bid and JNK, we investigated these two molecules in TNFalpha injury models that had not been previously examined. Most importantly, we created and studied mice deficient in both Bid and JNK. We found that, like JNK, Bid was also required for TNFalpha-induced injury induced by concanavalin A/GalN but not by ConA alone. Furthermore, our results indicate that these two molecules function in a largely overlapped manner, with Bid being downstream of JNK in the adult livers. However, JNK, but not Bid, was able to contribute to the TNFalpha-induced liver apoptosis in RelA-deficient embryos. The Bid-independent role of JNK was also observed in the adult mice, mainly in the promotion of the lethal progression of the TNFalpha injury. This work defined both linear and parallel relationships of Bid and JNK in TNFalpha-induced hepatocyte apoptosis and liver injury.

The alpha-subunit of AMPK is essential for submaximal contraction-mediated glucose transport in skeletal muscle in vitro

AMP-activated protein kinase (AMPK) is a key signaling protein in the regulation of skeletal muscle glucose uptake, but its role in mediating contraction-induced glucose transport is still debated. The effect of contraction on glucose transport is impaired in EDL muscle of transgenic mice expressing a kinase-dead, dominant negative form of the AMPKalpha(2) subunit (KD-AMPKalpha(2) mice). However, maximal force production is reduced in this muscle, raising the possibility that the defect in glucose transport was due to a secondary decrease in force production and not impaired AMPKalpha(2) activity. Generation of force-frequency curves revealed that muscle force production is matched between wild-type (WT) and KD-AMPKalpha(2) mice at frequencies < or =50 Hz. Moreover, AMPK activation is already maximal at 50 Hz in muscles of WT mice. When EDL muscles from WT mice were stimulated at a frequency of 50 Hz for 2 min (200-ms train, 1/s, 30 volts), contraction caused an approximately 3.5-fold activation of AMPKalpha(2) activity and an approximately 2-fold stimulation of glucose uptake. Conversely, whereas force production was similar in EDL of KD-AMPKalpha(2) animals, no effect of contraction was observed on AMPKalpha(2) activity, and glucose uptake stimulation was reduced by 50% (P < 0.01) As expected, 5-aminoimidazole-4-carboxamide-1-beta-d-ribofuranosyl 5'-monophosphate (AICAR) caused a 2.3-fold stimulation of AMPKalpha(2) activity and a 1.7-fold increase in glucose uptake in EDL from WT mice, whereas no effect was detected in muscle from KD-AMPKalpha(2) mice. These data demonstrate that AMPK activation is essential for both AICAR and submaximal contraction-induced glucose transport in skeletal muscle but that AMPK-independent mechanisms are also involved.

The effect of cardiac ischemic preconditioning on rat left ventricular gene expression profile

Ischemic preconditioning (IPC) is a phenomenon where heart is rendered more resistant to subsequent ischemia-reperfusion (I-R)-induced injury by one or more brief episodes of I-R. The mechanisms responsible for cardio-protective effects of IPC are not well characterized. The objective of the study was to characterize gene expression profiles in the left ventricle of male Wistar rat hearts exposed to I-R or IPC followed by I-R. Group 1 included hearts that were only perfused for 30 min. Group 2 included hearts that underwent 30 min perfusion followed by 40 min I and 30 min R. Group 3 comprised 30 min perfused hearts that were subjected to IPC (5 min I + 10 min R + 5 min I + 10 min R) followed by I-R. Total RNAs were isolated from left ventricular tissues. Codelink gene expression system (GE Healthcare) was used for cRNA target preparation, hybridization of microarrays (Rat UniSet 10 K CodeLink bioarrays, GE Healthcare) and detection. Microarrays were scanned with Affymetrix 428 Array scanner. Data analyses were carried out with GeneSifter microarray data analysis software. We determined a total of 140 transcripts (> or =2-fold change) whose expressions were changed (44 up-regulated and 96 down-regulated) accompanying to I-R injury compared to perfused only hearts. Twenty-three transcripts including Ryr3, Crk, Dio1, Npy1r, Ptpra, Cyp51 that were down-regulated by I-R injury, were up-regulated by cardiac IPC. IPC down-regulated the expression of several transcripts including Atf3 (activating transcription factor 3), carboxypeptidase A1 (Cpa1), Slc38a4, Blk which were up-regulated by I-R. In conclusion, evaluation of global gene expression profiling via microarray-based technologies provides a molecular portrait of cardiac IPC of the left ventricular tissue of rat heart.

Interaction between Hsp70 and the SR Ca2+pump: a potential mechanism for cytoprotection in heart and skeletal muscle

The overexpression of heat shock protein 70 (Hsp70) provides cytoprotection to cells, making them resistant to otherwise lethal levels of stress. In this review, the role Hsp70 plays in protecting both cardiac and skeletal muscle against the pathophysiological effects of oxidative stress are examined, with a focus on the molecular basis for the cytoprotective effects of Hsp70. The ability of Hsp70 to maintain cell survival undoubtedly involves the regulation of multiple steps within apoptotic pathways, but could also involve the regulation of key upstream mediators of apoptosis (i.e., oxidative stress, Ca2+overload). Hsp70 can stabilize the structure and function of both the skeletal muscle and cardiac Ca2+pump under heat stress conditions. Given that Ca2+overload has long been implicated in cell death, Hsp70 might protect muscle cells by maintaining cellular Ca2+homeostasis, thereby preventing the initiation of apoptosis. The functional interaction between Hsp70 and Ca2+pumps might also promote improvements in muscle contractility after exposure to oxidative stress.

Contraction-stimulated glucose transport in rat skeletal muscle is sustained despite reversal of increased PAS-phosphorylation of AS160 and TBC1D1

Akt substrate of 160 kDa (AS160), the most distal insulin signaling protein known to be important for insulin-stimulated glucose transport, becomes phosphorylated with skeletal muscle contraction. Akt, AMP-activated protein kinase (AMPK), and Ca(2+)/calmodulin-dependent kinase II (CaMKII) have been implicated in regulating AS160 and/or glucose transport. Our primary aim was to assess time courses for contraction's effects on glucose transport and phosphorylation of Akt, AMPK, CaMKII, and AS160. Isolated rat epitrochlearis muscles were studied without or with contraction (5, 10, 20, 40, 60 min). Phospho-Akt substrate (PAS) antibody was used to measure AS160 PAS phosphorylation by quantifying the approximately 160-kDa band on PAS immunoblots (PAS-160); a separate band at 150 kDa (PAS-150) that responded similarly to contraction was also identified. Using specific antibodies for AS160 or TBC1D1 on immunoblots, the molecular mass of PAS-160 was found to correspond with that of AS160 and not TBC1D1, whereas PAS-150 corresponded with TBC1D1 and not AS160. Furthermore, supernatant of sample immunodepleted with anti-AS160 had greatly reduced PAS-160, whereas supernatant of sample immunodepleted with anti-TBC1D1 had greatly reduced PAS-150, providing further evidence that PAS-160 and PAS-150 correspond with PAS-AS160 and PAS-TBC1D1, respectively. Contraction induced transient increases in PAS-160, PAS-150, phospho-glycogen synthase kinase 3 (an Akt substrate) and phospho-CaMKII; glucose transport and phospho-AMPK increases were maintained for 60 min of contraction. These data suggest the following: 1) PAS-160 (AS160) and PAS-150 (TBC1D1) respond to contraction transiently, despite sustained stimulation; 2) continual AMPK activation was insufficient for sustained increase in PAS-160 or PAS-150; and 3) sustained elevation of PAS-160 or PAS-150 was unnecessary to maintain contraction-stimulated glucose transport for up to 60 min.

Kinase-specific responsiveness to incremental contractile activity in skeletal muscle with low and high mitochondrial content

Muscle contractions activate protein kinases, leading to signal transduction. We hypothesized that kinase activation would be influenced by mitochondrial content, as well as by contractile activity-induced increases in muscle O(2) consumption (Vo(2)). Kinase phosphorylation in high-oxidative red and low-oxidative white tibialis anterior (TA) muscle (RTA and WTA, respectively) with 2.5-fold differences in mitochondrial content were compared. Stimulation of the TA muscle elicited large increases in Vo(2) (3- to 6-fold and 4- to 60-fold above resting levels in WTA and RTA, respectively). At rest, AMP-activated protein kinase (AMPK), p38, p42, and p44 activation were nearly twofold greater in WTA than in RTA, suggesting an inverse relationship between mitochondrial content and kinase activation in resting muscle. During contractions, similar degrees of phosphorylation in RTA and WTA were evident as a function of Vo(2) for p38 and p42. During increases in Vo(2) up to sixfold above rest, greater responses were observed in RTA than in WTA for AMPK and p44, whereas Akt activation was greater in WTA. In RTA, elevations in Vo(2) elicited increases in AMPK and p44 activation, whereas Akt, p38, and p42 were less sensitive to increments in Vo(2). Reactive oxygen species (ROS) production was greater in mitochondria from white muscle, but when it was calculated in the context of the whole muscle, ROS production was twofold greater in red than in white myofibers. Thus mitochondrial content influences ROS production and is inversely related to kinase activation in resting muscle. During contractions, kinases are differentially sensitive to contraction-induced increments in Vo(2), suggesting that muscle mitochondrial content is important, but it is not the sole determinant of kinase activation during exercise of different intensities.

Role of JNK translocation to mitochondria leading to inhibition of mitochondria bioenergetics in acetaminophen-induced liver injury

Previously, we demonstrated JNK plays a central role in acetaminophen (APAP)-induced liver injury (Gunawan, B. K., Liu, Z. X., Han, D., Hanawa, N., Gaarde, W. A., and Kaplowitz, N. (2006) Gastroenterology 131, 165-178). In this study, we examine the mechanism involved in activating JNK and explore the downstream targets of JNK important in promoting APAP-induced liver injury in vivo. JNK inhibitor (SP600125) was observed to significantly protect against APAP-induced liver injury. Increased mitochondria-derived reactive oxygen species were implicated in APAP-induced JNK activation based on the following: 1) mitochondrial GSH depletion (maximal at 2 h) caused increased H2O2 release from mitochondria, which preceded JNK activation (maximal at 4 h); 2) treatment of isolated hepatocytes with H2O2 or inhibitors (e.g. antimycin) that cause increased H2O2 release from mitochondria-activated JNK. An important downstream target of JNK following activation was mitochondria based on the following: 1) JNK translocated to mitochondria following activation; 2) JNK inhibitor treatment partially protected against a decline in mitochondria respiration caused by APAP treatment; and 3) addition of purified active JNK to mitochondria isolated from mice treated with APAP plus JNK inhibitor (mitochondria with severe GSH depletion, covalent binding) directly inhibited respiration. Cyclosporin A blocked the inhibitory effect of JNK on mitochondria respiration, suggesting JNK was directly inducing mitochondrial permeability transition in isolated mitochondria from mice treated with APAP plus JNK inhibitor. Addition of JNK to mitochondria isolated from control mice did not affect respiration. Our results suggests that APAP-induced liver injury involves JNK activation, due to increased reactive oxygen species generated by GSH-depleted mitochondria, and translocation of activated JNK to mitochondria where JNK induces mitochondrial permeability transition and inhibits mitochondria bioenergetics.

Skeletal muscle protein anabolic response to resistance exercise and essential amino acids is delayed with aging

Skeletal muscle loss during aging leads to an increased risk of falls, fractures, and eventually loss of independence. Resistance exercise is a useful intervention to prevent sarcopenia; however, the muscle protein synthesis (MPS) response to resistance exercise is less in elderly compared with young subjects. On the other hand, essential amino acids (EAA) increase MPS equally in both young and old subjects when sufficient EAA is ingested. We hypothesized that EAA ingestion following a bout of resistance exercise would stimulate anabolic signaling and MPS similarly between young and old men. Each subject ingested 20 g of EAA 1 h following leg resistance exercise. Muscle biopsies were obtained before and 1, 3, and 6 h after exercise to measure the rate of MPS and signaling pathways that regulate translation initiation. MPS increased early in young (1-3 h postexercise) and later in old (3-6 h postexercise). At 1 h postexercise, ERK1/2 MNK1 phosphorylation increased and eIF2alpha phosphorylation decreased only in the young. mTOR signaling (mTOR, S6K1, 4E-BP1, eEF2) was similar between groups at all time points, but MNK1 phosphorylation was lower at 3 h and AMP-activated protein kinase-alpha (AMPKalpha) phosphorylation was higher in old 1-3 h postexercise. We conclude that the acute MPS response after resistance exercise and EAA ingestion is similar between young and old men; however, the response is delayed with aging. Unresponsive ERK1/2 signaling and AMPK activation in old muscle may be playing a role in the delayed activation of MPS. Notwithstanding, the combination of resistance exercise and EAA ingestion should be a useful strategy to combat sarcopenia.

Tumor necrosis factor-related apoptosis-inducing ligand activates a lysosomal pathway of apoptosis that is regulated by Bcl-2 proteins

The present studies were performed to determine whether lysosomal permeabilization contributes to tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) cytotoxicity and to reconcile a role for lysosomes with prior observations that Bcl-2 family members regulate TRAIL-induced apoptosis. In KMCH cholangiocarcinoma cells stably expressing Mcl-1 small interference RNA (siRNA), treatment with TRAIL induced a redistribution of the cathepsin B from lysosomes to the cytosol. Pharmacological and small hairpin RNA-targeted inhibition of cathepsin B attenuated TRAIL-mediated apoptosis as assessed by morphological, biochemical, and clonogenic assays. Neither Bid siRNA nor Bak siRNA prevented cathepsin B release. In contrast, treatment of the cells with Bim siRNA or the JNK inhibitor SP600125 attenuated lysosomal permeabilization and cell death. Moreover, Bim and active Bax co-localized to lysosomes in TRAIL-treated cells in a JNK-dependent manner, and Bax siRNA reduced TRAIL-induced lysosomal permeabilization and cell death. Finally, BH3 domain peptides permeabilized isolated lysosomes in the presence of Bax. Collectively, these data suggest that TRAIL can trigger an apoptotic pathway that involves JNK-dependent activation of Bim, which in turn induces Bax-mediated permeabilization of lysosomes.

Caffeine-induced Ca(2+) release increases AMPK-dependent glucose uptake in rodent soleus muscle

Previous studies have proposed that caffeine-induced activation of glucose transport in skeletal muscle is independent of AMP-activated protein kinase (AMPK) because alpha-AMPK Thr172 phosphorylation was not increased by caffeine. However, our previous studies, as well as the present, show that AMPK phosphorylation measured in whole muscle lysate is not a good indicator of AMPK activation in rodent skeletal muscle. In lysates from incubated rat soleus muscle, a predominant model in previous caffeine-studies, both acetyl-CoA carboxylase-beta (ACCbeta) Ser221 and immunoprecipitated alpha(1)-AMPK activity increased with caffeine incubation, without changes in AMPK phosphorylation or immunoprecipitated alpha(2)-AMPK activity. This pattern was also observed in mouse soleus muscle, where only ACCbeta and alpha(1)-AMPK phosphorylation were increased following caffeine treatment. Preincubation with the selective CaMKK inhibitor STO-609 (5 microM), the CaM-competitive inhibitor KN-93 (10 microM), or the SR Ca(2+) release blocking agent dantrolene (10 microM) all inhibited ACCbeta phosphorylation and alpha(1)-AMPK phosphorylation, suggesting that SR Ca(2+) release may work through a CaMKK-AMPK pathway. Caffeine-stimulated 2-deoxyglucose (2DG) uptake reflected the AMPK activation pattern, being increased with caffeine and inhibited by STO-609, KN-93, or dantrolene. The inhibition of 2DG uptake is likely causally linked to AMPK activation, since muscle-specific expression of a kinase-dead AMPK construct greatly reduced caffeine-stimulated 2DG uptake in mouse soleus. We conclude that a SR Ca(2+)-activated CaMKK may control alpha(1)-AMPK activation and be necessary for caffeine-stimulated glucose uptake in mouse soleus muscle.

Catalase takes part in rat liver mitochondria oxidative stress defense

Highly purified rat liver mitochondria (RLM) when exposed to tert-butylhydroperoxide undergo matrix swelling, membrane potential collapse, and oxidation of glutathione and pyridine nucleotides, all events attributable to the induction of mitochondrial permeability transition. Instead, RLM, if treated with the same or higher amounts of H2O2 or tyramine, are insensitive or only partially sensitive, respectively, to mitochondrial permeability transition. In addition, the block of respiration by antimycin A added to RLM respiring in state 4 conditions, or the addition of H2O2, results in O2 generation, which is blocked by the catalase inhibitors aminotriazole or KCN. In this regard, H2O2 decomposition yields molecular oxygen in a 2:1 stoichiometry, consistent with a catalytic mechanism with a rate constant of 0.0346 s(-1). The rate of H2O2 consumption is not influenced by respiratory substrates, succinate or glutamate-malate, nor by N-ethylmaleimide, suggesting that cytochrome c oxidase and the glutathione-glutathione peroxidase system are not significantly involved in this process. Instead, H2O2 consumption is considerably inhibited by KCN or aminotriazole, indicating activity by a hemoprotein. All these observations are compatible with the presence of endogenous heme-containing catalase with an activity of 825 +/- 15 units, which contributes to mitochondrial protection against endogenous or exogenous H2O2. Mitochondrial catalase in liver most probably represents regulatory control of bioenergetic metabolism, but it may also be proposed for new therapeutic strategies against liver diseases. The constitutive presence of catalase inside mitochondria is demonstrated by several methodological approaches as follows: biochemical fractionating, proteinase K sensitivity, and immunogold electron microscopy on isolated RLM and whole rat liver tissue.

Targeting HSP70 to motoneurons protects locomotor activity from hyperthermia in Drosophila

Heat shock preconditioning can enhance locomotor and synaptic performance during subsequent hyperthermia. The molecular basis underlying this neural phenotypic modification is largely unknown. Here we report that directing the expression of the 70 kDa heat shock protein (HSP70) to motoneurons protected larval locomotor activity of Drosophila. Tissue-specific expression showed that motoneurons were critical for developing HSP70-mediated thermoprotection of locomotor activity, whereas peripheral sensory neurons, dopaminergic neurons, serotonergic neurons, and muscle cells alone were insufficient. Targeting HSP70 to motoneurons caused structural plasticity of axonal terminals associated with increased transmitter release at neuromuscular junctions at high temperature. The thermoprotection induced by motoneuronal expression of HSP70 mimicked the protective effect of a prior heat shock (36 degrees C, 1 h; 25 degrees C, 1 h) but the effects of heat shock and motoneuronal expression of HSP70 were not additive. In the absence of heat shock pretreatment, ubiquitously expressed transgenic HSP70 activated the transcription of endogenous hsp70 genes. These results demonstrate that motoneurons were critical for HSP70-mediated thermoprotection, and that transgenic HSP70 activated the transcription of endogenous hsp70 in motoneurons with the result that a mix of transgenic and endogenous HSP70 conferred thermoprotection in Drosophila larva.

Possible CaMKK-dependent regulation of AMPK phosphorylation and glucose uptake at the onset of mild tetanic skeletal muscle contraction

The Ca(2+)/calmodulin (CaM) competitive inhibitor KN-93 has previously been used to evaluate 5'-AMP-activated protein kinase (AMPK)-independent Ca(2+)-signaling to contraction-stimulated glucose uptake in muscle during intense electrical stimulation ex vivo. With the use of low-intensity tetanic contraction of mouse soleus and extensor digitorum longus (EDL) muscles ex vivo, this study demonstrates that KN-93 can potently inhibit AMPK phosphorylation and activity after 2 min but not 10 min of contraction while strongly inhibiting contraction-stimulated 2-deoxyglucose uptake at both the 2- and 10-min time points. These data suggest inhibition of Ca(2+)/CaM-dependent signaling events upstream of AMPK, the most likely candidate being the novel AMPK kinase CaM-dependent protein kinase kinase (CaMKK). CaMKK protein expression was detected in mouse skeletal muscle. Similar to KN-93, the CaMKK inhibitor STO-609 strongly reduced AMPK phosphorylation and activity at 2 min and less potently at 10 min. Pretreatment with STO-609 inhibited contraction-stimulated glucose uptake at 2 min in soleus, but not EDL, and in both muscles after 10 min. Neither KN-93 nor STO-609 inhibited 5-aminoimidazole-4-carboxamide-1-beta-4-ribofuranoside-stimulated glucose uptake, AMPK phosphorylation, or recombinant LKB1 activity, suggestive of an LKB1-independent effect. Finally, neither KN-93 nor STO-609 had effects on the reductions in glucose uptake seen in mice overexpressing a kinase-dead AMPK construct, indicating that the effects of KN-93 and STO-609 on glucose uptake require inhibition of AMPK activity. We propose that CaMKKs act in mouse skeletal muscle regulating AMPK phosphorylation and glucose uptake at the onset of mild tetanic contraction and that an intensity- and/or time-dependent switch occurs in the relative importance of AMPKKs during contraction.

Whole-body heat shock protects the ischemic rat heart by stimulating mitochondria respiration

Whole-body heat shock (HS) leads to an enhancement of postischemic mechanical function and an improvement in glucose use by the rat heart. Here, we examine the effect of HS on isolated mitochondrial metabolism during reperfusion in the working rat heart. Rats were anesthetized, and their body temperature was raised to 41-42 degrees C for 15 min. Control rats were treated the same way but were not exposed to hyperthermia. Twenty-four hours after HS or sham treatment, rats were reanesthetized and the hearts were removed for perfusion with Krebs-Henseleit buffer, containing 11 mmol glucose/L and 1.2 mmol palmitate/L prebound to 3% albumin. Hearts were subjected to 25 min of global ischemia followed by 30 min of reperfusion. At the end of reperfusion, heart mitochondria were isolated using differential centrifugation and respiration measured in the presence of pyruvate, glutamate, or palmitoylcarnitine. Hearts subjected to HS showed an enhanced recovery of function, expressed as aortic flow, during the reperfusion period, compared with sham hearts. This improved functional status was associated with a significant increase in state 3 respiration in the presence of pyruvate, glutamate, or palmitoylcarnitine. These results show that HS offers protection against ischemic damage, and that a possible mechanism might be the enhanced myocardial metabolism of fuels.

Alpha-lipoic acid protects against hepatic ischemia-reperfusion injury in rats

BACKGROUND AND AIM

To evaluate the protective effect of alpha-lipoic acid in reducing oxidative damage after severe hepatic ischemia/reperfusion (IR) injury.

METHODS

Wistar albino rats were subjected to 45 min of hepatic ischemia, followed by 60 min reperfusion period. Lipoic acid (100 mg/kg i.p.) was administered 15 min prior to ischemia and immediately before reperfusion period. At the end of the reperfusion period aspartate aminotransferase (AST), alanine aminotransferase (ALT), lactate dehydrogenase (LDH) activity, and cytokine, TNF-alpha and IL-1beta levels were determined in serum samples. Malondialdehyde (MDA), and glutathione (GSH) levels and myeloperoxidase (MPO) activity were determined in the liver tissue samples while formation of reactive oxygen species was monitored by using chemiluminescence (CL) technique with luminol and lucigenin probes. Tissues were also analyzed histologically.

RESULTS

Serum ALT, AST, and LDH activities and TNF-alpha and IL-1beta levels were elevated in the I/R group, while this increase was significantly lower in the group of animals treated concomitantly with lipoic acid. Hepatic GSH levels, significantly depressed by I/R, were elevated back to control levels in lipoic acid-treated I/R group. Furthermore, increases in tissue luminol and lucigenin CL, MDA levels and MPO activity due to I/R injury were reduced back to control levels with lipoic acid treatment.

CONCLUSION

Since lipoic acid administration alleviated the I/R-induced liver injury and improved the hepatic structure and function, it seems likely that lipoic acid with its antioxidant and oxidant-scavenging properties may be of potential therapeutic value in protecting the liver against oxidative injury due to ischemia-reperfusion.

Mild exercise training, cardioprotection and stress genes profile

To improve current knowledge of the molecular mechanisms underlying exercise-induced cardioprotection in a rat model of mild exercise training, Sprague-Dawley rats were trained to run on a treadmill up to 55% of their maximal oxygen uptake for 1 h/day, 3 days/week, 14 weeks, with age-matched sedentary controls (n = 20/group). Rats were sacrificed 48 h after the last training session. Despite lack of cardiac hypertrophy, training decreased blood hemoglobin (7.94 +/- 0.21 mM vs. 8.78 +/- 0.23 mM, mean +/- SE, P = 0.01) and increased both plasma malondialdehyde (0.139 +/- 0.005 mM vs. 0.085 +/- 0.009 mM, P = 0.05) and the activity of Mn-superoxide dismutase (11.6 +/- 0.6 vs. 16.5 +/- 1.6 mU/microg, P = 0.01), whereas total superoxide dismutase activity was unaffected. When subjected to 30-min ischemia followed by 90-min reperfusion, hearts from trained rats (n = 5) displayed reduced infarct size as compared to controls (37.26 +/- 0.92% vs. 49.09 +/- 2.11% of risk area, P = 0.04). The biochemical analyses in the myocardium, which included gene expression profiles, real-time PCR, Western blot and determination of enzymatic activity, showed training-induced upregulation of the following mRNAs and/or proteins: growth-arrest and DNA-damage induced 153 (GADD153/CHOP), heme-oxygenase-1 (HO-1), cyclooxygenase-2 (Cox-2), heat-shock protein 70/72 (HSP70/72), whereas heat-shock protein 60 (HSP60) and glucose-regulated protein 75 (GRP75) were decreased. As a whole, these data indicate that mild exercise training activates a second window of myocardial protection against ischemia/reperfusion by upregulating a number of protective genes, thereby warranting further investigation in man.

Testosterone is required for delayed cardioprotection and enhanced heat shock protein 70 expression induced by preconditioning

Ischemic preconditioning fails to confer immediate cardioprotection in the absence of testosterone, indicating that the hormone is required for the process. Here we set out to determine whether testosterone is also necessary for delayed cardioprotection and, if so, how it acts. Male Sprague Dawley rats (7-8 wk) underwent sham operation or gonadectomy without (G) or with testosterone replacement (GT) for 8 wk. Isolated ventricular myocytes were preconditioned either by metabolic inhibition or with U50,488H, a kappa-opioid receptor agonist. In intact rats, U50,488H was administered systemically and 24 h later the hearts were removed. Ventricular myocytes were then subjected to metabolic inhibition and anoxia and isolated hearts to regional ischemia, followed by reperfusion to induce injury. Both types of preconditioning significantly increased the viability and decreased the lactate dehydrogenase release in ventricular myocytes from sham rats. They also activated heat shock transcription factor-1 and increased heat shock protein 70 expression. In contrast, all these effects were absent in myocytes from G rats and were restored by testosterone replacement. Parallel results were found in isolated hearts. In addition, preconditioning improved contractile functions impaired by ischemic insults in sham and rats gonadectomized with testosterone replacement but not G rats. The effects of testosterone replacement in ventricular myocytes were abolished by androgen receptor blockade. In conclusion, preconditioning requires testosterone to increase heat shock protein 70 synthesis, which mediates delayed cardioprotection in the male. These effects of testosterone are mediated by the androgen receptor.