Exercise training promotes cardioprotection through oxygen-sparing action in high fat-fed mice.

Although exercise training has been demonstrated to have beneficial cardiovascular effects in diabetes, the effect of exercise training on hearts from obese/diabetic models is unclear. In the present study, mice were fed a high-fat diet, which led to obesity, reduced aerobic capacity, development of mild diastolic dysfunction, and impaired glucose tolerance. Following 8 wk on high-fat diet, mice were assigned to 5 weekly high-intensity interval training (HIT) sessions (10 × 4 min at 85-90% of maximum oxygen uptake) or remained sedentary for the next 10 constitutive weeks. HIT increased maximum oxygen uptake by 13%, reduced body weight by 16%, and improved systemic glucose homeostasis. Exercise training was found to normalize diastolic function, attenuate diet-induced changes in myocardial substrate utilization, and dampen cardiac reactive oxygen species content and fibrosis. These changes were accompanied by normalization of obesity-related impairment of mechanical efficiency due to a decrease in work-independent myocardial oxygen consumption. Finally, we found HIT to reduce infarct size by 47% in ex vivo hearts subjected to ischemia-reperfusion. This study therefore demonstrated for the first time that exercise training mediates cardioprotection following ischemia in diet-induced obese mice and that this was associated with oxygen-sparing effects. These findings highlight the importance of optimal myocardial energetics during ischemic stress.

The cardiokine secreted Frizzled-related protein 3, a modulator of Wnt signalling, in clinical and experimental heart failure.

OBJECTIVES: Experimental studies have shown involvement of Wnt signalling in heart failure (HF). We hypothesized that secreted frizzled-related protein 3 (sFRP3), a modulator of Wnt signalling, is related to the progression of HF. DESIGN: Circulating sFRP3 was measured in 153 HF patients and compared with 25 healthy controls. The association of sFRP3 with mortality was evaluated in 1202 patients (GISSI-HF trial). sFRP3 mRNA expression was assessed in failing human and murine left ventricles (LV), and cellular localization was determined after fractioning of myocardial tissue. In vitro studies were carried out in cardiac fibroblasts subjected to cyclic mechanical stretch. RESULTS: (i) Heart failure patients had significantly raised serum sFRP3 levels compared with controls, (ii) during a median follow-up of 47 months, 315 patients died in the GISSI-HF substudy. In univariable Cox regression, tertiles of baseline sFRP3 concentration were significantly associated with all-cause and cardiovascular mortality. After adjustment for demographic and clinical variables, but not for CRP and NT-proBNP, the associations with mortality remained significant for the third tertile (all-cause, HR 1.45, P = 0.011; cardiovascular, HR 1.66, P = 0.003), (iii) sFRP3 mRNA expression was increased in failing human LV, with a decline following LV assist device therapy. LV from post-MI mice showed an increased sFRP3 mRNA level, particularly in cardiac fibroblasts, and (iv) mechanical stretch enhanced sFRP3 expression and release in myocardial fibroblasts. CONCLUSION: There is an association between increased sFRP3 expression and adverse outcome in HF, suggesting that the failing myocardium itself contributes to an increase in circulating sFRP3.

Activin A inhibits organization of sarcomeric proteins in cardiomyocytes induced by leukemia inhibitory factor.

Cytokine systems are activated in heart failure, and it is believed that interaction between such systems may be important during progression of this disorder. We have previously shown that failing hearts have increased levels of the interleukin-6 related cytokine leukemia inhibitory factor (LIF) and activin A, a member of the transforming growth factor-beta family. The aim of this study was to examine the effects of activin A on cardiomyocytes and a potential interaction with LIF-mediated changes in cell signaling and growth. Cardiomyocytes were isolated from 1- to 3-day-old Wistar rats, and the cells were treated with LIF, activin A or a combination thereof. Our main findings were: (i) activin A treatment reduced the LIF-mediated increase in cardiomyocyte length, perimeter and sarcomeric organization and was accompanied by a substantially decreased alpha-skeletal actin gene expression. (ii) The activin A-mediated phosphorylation of Smad2 was markedly enhanced by LIF. (iii) Activin A markedly induced SOCS3 gene expression, while LIF potently increased the expression of Smad7 mRNA, representing inhibitors of LIF and activin A signaling pathways, respectively. (iv) Inhibiting activation of the Smad2/3 pathway abolished the effects of activin A on LIF-induced changes in cell length, perimeter and sarcomeric organization. In conclusion, activin A markedly attenuates LIF-induced changes in cardiomyocytes, reflecting a potentially important role for both activin A and the Smad2/3 pathway in regulation of myocardial remodeling.

Regulation of neuronal type genes in congestive heart failure rats.

AIM: After myocardial infarction (MI), complex changes in the heart occur during progression into congestive heart failure (CHF). This study sought to identify regulated genes that could have a functional role in some of the changes seen in CHF. METHODS: Myocardial infarction was induced by ligation of the left anterior descending coronary artery (LAD) in Wistar rats. Gene expression changes in 1- and 7-day MI left ventricular myocardium was analysed using complementary DNA (cDNA) filter arrays. Regulated genes were identified by repeated measurements and a ranked ratio analysis method. RESULTS: A total of 135 genes were identified as differentially expressed. A few genes were robustly regulated at 1-day MI. In 7-day CHF hearts, changes in the expression of neuronal type genes was prominent (32%, n = 28). Eleven of these genes with no described association with CHF were selected for validation. One gene failed the validation. In CHF hearts, the expression of the muscarinic m4 (Chrm4) and nicotinic alpha4 (Chrna4) acetylcholin receptors, the ATP receptor P2rx4, nerve growth factor receptor (Ngfr), discoidin domain receptor 1 (Ddr1), neuronal pentraxin receptor (Nptxr), peripheral myelin protein Pmp-22, leukocyte type 12-lipoxygenase (Alox15), cytochrome P450 4F5 (Cyp4F5) and cardiac Kcne1 were all increased (range 1.6-6.0-fold, P < 0.01 for all genes). The lack of significant regulation of these genes at 1-day post-MI, suggests that the induction of these genes at 7-day post-MI is not a short-term response induced by the infarct itself. CONCLUSION: These neuronal type genes may participate in underlying processes that affect contractility, intracardiac nerve function and development of arrhythmias in CHF hearts.

Leukaemia inhibitory factor stimulates glucose transport in isolated cardiomyocytes and induces insulin resistance after chronic exposure.

AIMS/HYPOTHESIS: Hypertrophic and failing hearts have increased utilisation of glucose, but also develop insulin resistance and reduced ability to produce ATP. Increased levels of the IL-6-related cytokine leukaemia inhibitory factor (LIF) are found in failing hearts, and we have recently shown that LIF reduces ATP production in isolated cardiomyocytes. In the present study we investigated effects of LIF on glucose metabolism, and how LIF-treated cells respond to insulin stimulation. METHODS: Cardiomyocytes were isolated from adult Wistar rats by collagen digestion, maintained in culture for 48 h, and then treated with 1 nmol/l LIF. RESULTS: Acute LIF treatment increased deoxyglucose uptake compared with controls, but no additive effect was observed in cardiomyocytes treated with LIF and insulin. The phosphatidylinositol 3-kinase inhibitor wortmannin did not affect LIF-induced glucose uptake. LIF had no effect on AMP-activated protein kinase phosphorylation. Cardiomyocytes treated with LIF for 48 h did not respond to insulin by increasing deoxyglucose uptake and showed a reduced insulin-mediated uptake of oleic acid and formation of complex lipids compared with control cells. Chronic LIF treatment increased gene expression of the suppressor of cytokine signalling (Socs) 3 and reduced expression of solute carrier family 2, member 4 (Slc2a4, previously known as glucose transporter 4 [Glut4]). In line with these observations, chronic LIF treatment reduced insulin-mediated phosphorylation of both Akt/protein kinase B (PKB) and glycogen synthase kinase (GSK)-3. CONCLUSIONS/INTERPRETATION: Acute LIF treatment increased glucose uptake in isolated cardiomyocytes by a pathway different from that of insulin. Chronic LIF treatment induced insulin resistance, possibly mediated by altered expression of Socs3 and Slc2a4, and impaired insulin-mediated phosphorylation of GSK-3 and Akt/PKB.

Leukaemia inhibitory factor alters expression of genes involved in rat cardiomyocyte energy metabolism.

AIM: Cardiac remodelling is associated with changes in contractile proteins and their performance, alterations in energy production and intracellular calcium homeostasis, as well as changes in extracellular matrix proteins. Some of these processes may be mediated through the gp130 receptor complex. Patients with heart failure have increased cardiac gene expression of leukaemia inhibitory factor (LIF), a cytokine that signals through the gp130 receptor. The aim of this study was to identify alterations in gene expression in LIF-stimulated neonatal cardiomyocytes. METHODS: Cardiomyocytes were isolated from 1- to 3-day-old Wistar rats and stimulated for 48 h with LIF. Gene expression was examined by repeated cDNA filter array analysis (n = 5) and key results verified by complementary methods. RESULTS: In LIF-stimulated cultures we observed increased cell area and changes in gene expression. The intracellular signal regulators signal transducer and activator of transcription 3, calcium/calmodulin-dependent protein kinase IV, protein kinase Cdelta and the transcription factor ID1 were upregulated. Adenylyl cyclase V was downregulated. LIF also induced altered expression of tissue inhibitor of metalloproteinase-1. Receptor genes for tumour necrosis factor, interleukin-4, neurotensin and somatostatin were upregulated. Finally, LIF reduced the expression of components in the adenosine triphosphate synthase complex, epidermal fatty acid-binding protein and insulin-like growth factor-binding proteins 1 and 6. CONCLUSIONS: Array analysis revealed changes in mRNA levels of several genes not previously associated with activation of the gp130/LIF receptor complex. Our findings indicate a role for LIF in regulation of cardiomyocyte energy metabolism.