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The cellular response to stress involves the recruitment and coordination of molecular signaling pathways that prevent cell death. D-dopachrome tautomerase (DDT) is an enzyme that lacks physiologic substrates in mammalian cells, but shares partial sequence and structural homology with macrophage migration inhibitory factor (MIF). Here, we observed that DDT is highly expressed in murine cardiomyocytes and secreted by the heart after ischemic stress. Antibody-dependent neutralization of secreted DDT exacerbated both ischemia-induced cardiac contractile dysfunction and necrosis. We generated cardiomyocyte-specific DDT knockout mice (Myh6-Cre [Ddtf.sup.fl/fl]), which demonstrated normal baseline cardiac size and function, but had an impaired physiologic response to ischemia-reperfusion. Hearts from Myh6-Cre [Ddtf.sup.fl/fl] mice exhibited more necrosis and LV contractile dysfunction than control hearts after coronary artery ligation and reperfusion. Furthermore, treatment with DDT protected isolated hearts against injury and contractile dysfunction after ischemia-reperfusion. The protective effect of DDT required activation of the metabolic stress enzyme AMP-activated protein kinase (AMPK), which was mediated by a CD74/CaMKK2-dependent mechanism. Together, our data indicate that cardiomyocyte secretion of DDT has important autocrine/paracrine effects during ischemia-reperfusion that protect the heart against injury., Introduction Myocardial ischemia resulting from coronary arterial occlusion leads to myocardial necrosis, arrhythmias, contractile dysfunction, and heart failure. Cellular adaptation to ischemic stress requires the coordination of cellular metabolic pathways [...]

Myocardial hypertrophy is an adaptation to increased hemodynamic demands. An increase in heart tissue must be matched by a corresponding expansion of the coronary vasculature to maintain and adequate supply [...]

Macrophage migration inhibitory factor (MIF) is a proinflammatory cytokine that also modulates physiologic cell signaling pathways. MIF is expressed in cardiomyocytes and limits cardiac injury by enhancing AMPK activity during ischemia. Reperfusion injury is mediated in part by activation of the stress kinase JNK, but whether MIF modulates JNK in this setting is unknown. We examined the role of MIF in regulating JNK activation and cardiac injury during experimental ischemia/reperfusion in mouse hearts. Isolated perfused [Mif.sup.[-/-]] hearts had greater contractile dysfunction, necrosis, and JNK activation than WT hearts, with increased upstream MAPK kinase 4 phosphorylation, following ischemia/reperfusion. These effects were reversed if recombinant MIF was present during reperfusion, indicating that MIF deficiency during reperfusion exacerbated injury. Activated JNK acts in a proapoptotic manner by regulating BCL2-associated agonist of cell death (BAD) phosphorylation, and this effect was accentuated in [Mif.sup.[-/-]] hearts after ischemia/reperfusion. Similar detrimental effects of MIF deficiency were observed in vivo following coronary occlusion and reperfusion in [Mif.sup.[-/-]] mice. Importantly, excess JNK activation also was observed after hypoxia-reoxygenation in human fibroblasts homozygous for the MIF allele with the lowest level of promoter activity. These data indicate that endogenous MIF inhibits JNK pathway activation during reperfusion and protects the heart from injury. These findings have clinical implications for patients with the low-expression MIF allele., Introduction Macrophage migration inhibitory factor (MIF) is a proinflammatory cytokine that is released from immune cells (1) and is involved in inflammatory diseases, including rheumatoid arthritis (1), atherosclerosis (2), and [...]

A study was conducted to evaluate the benefits of coronary artery disease (CAD) screening in identifying those high-risk patients with type 2 diabetes and also whether it improved their outcomes. Results indicated that cardiac event rates were low in diabetic patients and also that CAD screening did not really impact the outcomes.

Understanding cellular response to environmental stress has broad implications for human disease. AMP-activated protein kinase (AMPK) orchestrates the regulation of energy-generating and-consuming pathways, and protects the heart against ischaemic injury [...]

Glucose uptake in the heart is mediated by specific glucose transporters (GLUTs) present on cardiomyocyte cell surface membranes. Metabolic stress and insulin both increase glucose transport by stimulating the translocation of glucose transporters from intracellular storage vesicles to the cell surface. Isolated perfused transgenic mouse hearts are commonly used to investigate the molecular regulation of heart metabolism; however, current methods to quantify cell surface glucose transporter content in intact mouse hearts are limited. Therefore, we developed a novel technique to directly assess the cell surface content of the cardiomyocyte glucose transporter GLUT4 in perfused mouse hearts, using a cell surface impermeant biotinylated his-glucose photolabeling reagent (bio-LC-ATB-BGPA). Bio-LC-ATB-BGPA was infused through the aorta and cross-linked to cell surface GLUTs. Bio-LCATB-BGPA-labeled GLUT4 was recovered from cardiac membranes by streptavidin isolation and quantified by immunoblotting. Bio-LCATB-BGPA-labeling of GLUT4 was saturable and competitively inhibited by D-glucose. Stimulation of glucose uptake by insulin in the perfused heart was associated with parallel increases in bio-LC-ATB-BGPA-labeling of cell surface GLUT4. Bio-LC-ATB-BGPA also labeled cell surface GLUT1 in the perfused heart. Thus, photolabeling provides a novel approach to assess cell surface glucose transporter content in the isolated perfused mouse heart and may prove useful to investigate the mechanisms through which insulin, ischemia, and other stimuli regulate glucose metabolism in the heart and other perfused organs. glucose transport; perfused mouse heart; photolabeling; glucose transporter 4 doi:10.1152/ajpendo.00170.2006

AMP-activated protein kinase (AMPK) plays a key role in modulating cellular metabolic processes. AMPK, a serine-threonine kinase, is a heterotrimeric complex of catalytic [alpha]-subunits and regulatory [beta]- and [gamma]-subunits with multiple isoforms. Mutations in the cardiac [[gamma].sub.2]-isoform have been associated with hypertrophic cardiomyopathy and pre-excitation syndromes. However, physiological regulation of AMPK complexes containing different subunit isoforms is not well defined and is important for an understanding of the function of this signaling pathway in the intact heart. We evaluated the kinase activity associated with heart AMPK complexes containing specific or- and y-subunit isoforms of AMPK in an in vivo rat model of regional ischemia. Left coronary artery occlusion activated the immunoprecipitated [[alpha].sub.1]-isoform (6-fold, P < 0.01) and [[alpha].sub.2]-isoform (9-fold, P < 0.01) in the ischemic left ventricle compared with sham controls. The degree of a-subunit activation depended on the extent of ischemia and paralleled echocardiographic contractile dysfunction. The regulatory [[gamma].sub.1]- and [[gamma].sub.2]-isoforms were expressed in the heart. The [[gamma].sub.1]- and [[gamma].sub.2]-isoforms coimmunoprecipitated with [[alpha].sub.1]- and [[alpha].sub.2]-isoforms in proportion to [alpha]-subunit content, [[gamma].sub.1]-Isoform immunocomplexes accounted for 70% of AMPK activity and AMPK phosphorylation ([Thr.sup.172]) in hearts. Ischemia similarly increased AMPK activity associated with the [[gamma].sub.1]- and [[gamma].sub.2]-isoform complexes threefold (P < 0.01 for each). Thus AMPK catalytic [[alpha].sub.1]-and [[alpha].sub.2]-isoforms are activated by regional ischemia in vivo in the heart, irrespective of the regulatory [[gamma].sub.1]- or [[gamma].sub.2]-isoforms to which they are complexed. Despite the pathophysiological importance of [[gamma].sub.2]-isoform mutations, [[gamma].sub.1]-isoform complexes account for most of the AMPK activity in the ischemic heart. adenosine monophosphate-activated protein kinase; ischemia; subunits; isoforms

Role of the nitric oxide pathway in AMPK-mediated glucose uptake and GLUT4 translocation in heart muscle. Am J Physiol Endocrinol Metab 287: E834-E841, 2004. First published July 20, 2004; doi:10.1152/ajpendo.00234.2004.--AMP-activated protein kinase (AMPK) is a serine-threonine kinase that regulates cellular metabolism and has an essential role in activating glucose transport during hypoxia and ischemia. The mechanisms responsible for AMPK stimulation of glucose transport are uncertain, but may involve interaction with other signaling pathways or direct effects on GLUT vesicular trafficking. One potential downstream mediator of AMPK signaling is the nitric oxide pathway. The aim of this study was to examine the extent to which AMPK mediates glucose transport through activation of the nitric oxide (NO)-signaling pathway in isolated heart muscles. Incubation with 1 mM 5-amino-4-imidazole-1-[beta]-carboxamide ribofuranoside (AICAR) activated AMPK (P < 0.01) and stimulated glucose uptake (P < 0.05) and translocation of the cardiomyocyte glucose transporter GLUT4 to the cell surface (P < 0.05). AICAR treatment increased phosphorylation of endothelial NO synthase (eNOS) ~1.8-fold (P < 0.05). eNOS, but not neuronal NOS, coimmunoprecipitated with both the [[alpha].sub.2] and [[alpha].sub.1] AMPK catalytic subunits in heart muscle. NO donors also increased glucose uptake and GLUT4 translocation (P < 0.05). Inhibition of NOS with [N.sup.[omega]]-nitro-L-arginine and [N.sup.[omega]]-methyl-L-arginine reduced AICAR-stimulated glucose uptake by 21 [+ or -] 3% (P < 0.05) and 25 [+ or -] 4% (P < 0.05), respectively. Inhibition of guanylate cyclase with ODQ and LY-83583 reduced AICAR-stimulated glucose uptake by 31 [+ or -] 4% (P < 0.05) and 22 [+ or -] 3% (P < 0.05), respectively, as well as GLUT4 translocation to the cell surface (P < 0.05). Taken together, these results indicate that activation of the NO-guanylate cyclase pathway contributes to, but is not the sole mediator of, AMPK stimulation of glucose uptake and GLUT4 translocation in heart muscle. nitric oxide synthase; AMP-activated protein kinase; glucose transporter

AMP-activated protein kinase (AMPK) is emerging as a key signaling pathway that modulates cellular metabolic processes. In skeletal muscle, AMPK is activated during exercise. Increased myocardial substrate metabolism during exercise could be explained by AMPK activation. Although AMPK is known to be activated during myocardial ischemia, it remains uncertain whether AMPK is activated in response to the physiological increases in cardiac work associated with exercise. Therefore, we evaluated cardiac AMPK activity in rats at rest and after 10 min of treadmill running at moderate (15% grade, 16 m/min) or high (15% grade, 32 m/min) intensity. Total AMPK activity in the heart increased in proportion to exercise intensity (P < 0.05). AMPK activity associated with the [[alpha].sub.2]-catalytic subunit increased 2.8 [+ or -] 0.4-fold (P < 0.02 vs. rest) and 4.5 [+ or -] 0.6-fold (P < 0.001 vs. rest) with moderate- and high-intensity exercise, respectively. AMPK activity associated with the [[alpha].sub.1]-subunit increased to a lesser extent. Phosphorylation of the [Thr.sup.172]-regulatory site on AMPK [alpha]-catalytic subunits increased during exercise (P < 0.001). There was no increase in Akt phosphorylation during exercise. The changes in AMPK activity during exercise were associated with physiological AMPK effects (GLUT4 translocation to the sarcolemma and ACC phosphorylation). Thus cardiac AMPK activity increases progressively with exercise intensity, supporting the hypothesis that AMPK has a physiological role in the heart. energy metabolism; signal transduction; glucose

Aims: Pioglitazone is a potent insulin‐sensitizing drug with anti‐atherosclerotic properties, but adverse effects have limited its use. We assessed the benefits and risks of lower versus higher doses of pioglitazone taken by participants in the Insulin Resistance Intervention in Stroke Trial. Materials and Methods: Efficacy [myocardial infarction (MI) or recurrent stroke] new‐onset diabetes) and adverse outcomes (oedema, weight gain, heart failure and bone fracture) were examined for subjects assigned to pioglitazone or placebo within strata defined by mode dose of study drug taken (i.e. the dose taken on most days in the study). Results: Among the 1938 patients randomized to pioglitazone, the mode dose was <15 mg/day in 546 participants, 15 mg/day in 128, 30 mg/day in 89, and 45 mg/day in 1175. There was no significant effect on stroke/MI or new‐onset diabetes with <15 mg/day. For 15 mg/30 mg/day pooled, the adjusted hazard ratios (95% CI) for stroke/MI were 0.48 (0.30, 0.76; p =.002) and 0.74 (0.69, 0.94) for 45 mg/day. For new‐onset diabetes, the adjusted hazard ratios were 0.34 (0.15, 0.81; p =.001) and 0.31 (0.59, 0.94; p =.001) respectively. For oedema, weight gain and heart failure, the risk estimates for pioglitazone were lower for subjects taking <45 mg daily. For fractures, the increased risk with pioglitazone was similar across all dose strata. Conclusions: Lower doses of pioglitazone appear to confer much of the benefit with less adverse effects than the full dose. Further study is needed to confirm these findings so that clinicians may optimize dosing of this secondary prevention strategy in patients with stroke. [ABSTRACT FROM AUTHOR]

* OBJECTIVES To examine the association between (1) comorbid conditions related to diabetes mellitus, clinical findings on arrival at the hospital and characteristics of the myocardial infarction and (2) risk [...]

Bergeron, Raynald, Jian Ming Ren, Kevin S. Cadman, Irene K. Moore, Pascale Perret, Marc Pypaert, Lawrence H. Young, Clay F. Semenkovich, and Gerald I. Shulman. Chronic activation of AMP kinase results in NRF-1 activation and mitochondrial biogenesis. Am J Physiol Endocrinol Metab 281: E1340-E1346, 2001.--The underlying mechanism by which skeletal muscle adapts to exercise training or chronic energy deprivation is largely unknown. To examine this question, rats were fed for 9 wk either with or without [beta]-guanadinopropionic acid ([beta]-GPA; 1% enriched diet), a creatine analog that is known to induce muscle adaptations similar to those induced by exercise training. Muscle phosphocreatine, ATP, and ATP/AMP ratios were all markedly decreased and led to the activation of AMP-activated protein kinase (AMPK) in the [beta]-GPA-fed rats compared with control rats. Under these conditions, nuclear respiratory factor-1 (NRF-1) binding activity, measured using a cDNA probe containing a sequence encoding for the promoter of [delta]-aminolevulinate (ALA) synthase, was increased by about eightfold in the muscle of [beta]-GPA-fed rats compared with the control group. Concomitantly, muscle ALA synthase mRNA and cytochrome c content were also increased. Mitochondrial density in both extensor digitorum longus and epitrochlearis from [beta]-GPA-fed rats was also increased by more than twofold compared with the control group. In conclusion, chronic phosphocreatine depletion during [beta]-GPA supplementation led to the activation of muscle AMPK that was associated with increased NRF-1 binding activity, increased cytochrome c content, and increased muscle mitochondrial density. Our data suggest that AMPK may play an important role in muscle adaptations to chronic energy stress and that it promotes mitochondrial biogenesis and expression of respiratory proteins through activation of NRF-1. nuclear respiratory factor-1; muscle adaptation; [delta]-aminolevulinate synthase; cytochrome c; [beta]-guanadinopropionic acid Received 9 July 2001; accepted in final form 21 August 2001

The activation of myocardial adenylic acid-activated protein kinase (AMPK) by 5-aminoimidazole-4-carboxyamide-1-beta-D-ribofuranoside (AICAR) was studied to determine whether it causes the translocation of heart GLUT-4 to the sarcolemma resulting in increased myocardial glucose uptake in vitro. The results showed that translocation of myocardial GLUT-4 through a pathway that includes AMPK is caused by metabolic stressors such as ischemia. This pathway is different from the insulin-stimulated pathway that needs the activation of P13K activation.

A study was conducted to analyze the effects of AMP-activated protein kinase activation on skeletal muscle glucose metabolism in rats. The animals were infused with 5-aminoimidazole-4-carboxamide 1-beta-D-ribofuranoside. An automated analyzer was utilized to determine plasma glucose and lactate concentrations. Results indicated that the cellular pathway may support a critical function in exercise-induced increase in glucose transport activity.

A study was conducted to analyze the influence of insulin-like growth factor I (IGF-I) on cardiac contractile protein synthesis in vivo in rats. The animals were anesthetized with intraperitoneal injections. Carotid arterial blood pressure and heart rate were then determined at 15-min intervals. Results indicated that low doses of IGF-I have a direct effect in vivo to acutely increase heart contractile protein synthesis.

Insulin-like growth factor I (IGF-I) induces protein synthesis in heart and skeletal muscles in normal awake rats. However, a decrease in insulin and amino acid levels that occurs due to IGF-I infusion restricts the promotion of protein synthesis by IGF-I. Infusion of IGF-I along with amino acids produces a significant increase in protein synthesis in gastrocnemius and soleus compared to the control group of rats infused with saline or to the levels produced by IGF-I alone. Decrease in plasma concentration and plasma insulin is reduced with the infusion of amino acids. Protein synthesis also increased with co-infusion of IGF-I and insulin.