Browsing by Author "Lochner, Amanda"
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- ItemAMP kinase activation and glut4 translocation in isolated cardiomyocytes(Clinics Cardive Publishing, 2010-04) Webste, Ingrid; Friedrich, Sven O.; Lochner, Amanda; Huisamen, BarbaraActivation of AMP-activated protein kinase (AMPK) results in glucose transporter 4 (GLUT4) translocation from the cytosol to the cell membrane, and glucose uptake in the skeletal muscles. This increased activation of AMPK can be stimulated by a pharmacological agent, AICAR (5’-aminoimidazole-4-carboxamide ribonucleoside), which is converted intracellularly into ZMP (5’-aminoimidazole-4-carboxamideribonucleosidephosphate), an AMP analogue. We utilised AICAR and ZMP to study GLUT4 translocation and glucose uptake in isolated cardiomyocytes. Adult ventricular cardiomyocytes were treated with AICAR or ZMP, and glucose uptake was measured via [3H]-2-deoxyglucose accumulation. PKB/Akt, AMPK and acetyl-CoA-carboxylase phosphorylation and GLUT4 translocation were detected by Western blotting or flow cytometry. AICAR and ZMP promoted AMPK phosphorylation. Neither drug increased glucose uptake but on the contrary, inhibited basal glucose uptake, although GLUT4 translocation from the cytosol to the membrane occurred. Using flow cytometry to detect the exofacial loop of the GLUT4 protein, we showed ineffective insertion in the membrane under these conditions. Supplementing with nitric oxide improved insertion in the membrane but not glucose uptake. We concluded that activation of AMPK via AICAR or ZMP was not sufficient to induce GLUT4-mediated glucose uptake in isolated cardiomyocytes. Nitric oxide plays a role in proper insertion of the protein in the membrane but not in glucose uptake.
- ItemAMP kinase activation and glut4 translocation in isolated cardiomyocytes(http://www.cvja.co.za/index.php, 2010-03) Webster, Ingrid; Huisamen, Barbara; Lochner, Amanda; Friedrich, Sven O; Biomedical Sciences: Medical Physiology
- ItemAtaxia telangiectasia mutated protein kinase : a potential master puppeteer of oxidative stress-induced metabolic recycling(Hindawi, 2021) Blignaut, Marguerite; Harries, Sarah; Lochner, Amanda; Huisamen, BarbaraENGLISH ABSTRACT: Ataxia Telangiectasia Mutated protein kinase (ATM) has recently come to the fore as a regulatory protein fulfilling many roles in the fine balancing act of metabolic homeostasis. Best known for its role as a transducer of DNA damage repair, the activity of ATM in the cytosol is enjoying increasing attention, where it plays a central role in general cellular recycling (macroautophagy) as well as the targeted clearance (selective autophagy) of damaged mitochondria and peroxisomes in response to oxidative stress, independently of the DNA damage response. The importance of ATM activation by oxidative stress has also recently been highlighted in the clearance of protein aggregates, where the expression of a functional ATM construct that cannot be activated by oxidative stress resulted in widespread accumulation of protein aggregates. This review will discuss the role of ATM in general autophagy, mitophagy, and pexophagy as well as aggrephagy and crosstalk between oxidative stress as an activator of ATM and its potential role as a master regulator of these processes.
- ItemEditorial: Role of Mitochondrial Quality Control in Myocardial and Microvascular Physiology and Pathophysiology(Frontiers Media S.A, 2021-09) Lochner, Amanda; Wang, Hsueh-Hsiao; Reiter, Russel J.; Guo, Rui; Zhou, HaoMitochondrial quality control (MQC) involves a series of adaptive responses of mitochondrial morphological alterations and functional modifications, such as mitochondrial fusion, mitochondrial fission, mitophagy, mitochondrial biogenesis, mitochondrial bioenergetics, and mitochondria-mediated death pathways (Akbari et al., 2019; Del Campo, 2019; Shanmughapriya et al., 2020; Wang et al., 2020c). Mitochondrial damage or impaired MQC has been reported to play an important role in regulating the physiology and/or pathology of myocardium and vessels (Heusch, 2019; Hughes et al., 2020; Wang and Zhou, 2020; Wang et al., 2020b). The objective role of the Research Topic “Role of Mitochondrial Quality Control in Myocardial and Microvascular Physiology and Pathophysiology” (https://www.frontiersin.org/research-topics/13532/role-of-mitochondrial-quality-control-in-myocardial-and-microvascular-physiology-and-pathophysiology#research-topic-overview) was to gather original research articles and/or reviews to highlight the recent findings regarding the impact of MQC on various cardiovascular disorders. The article “Physical exercise: a novel tool to protect mitochondrial health” by Sorriento et al. reviews the effects of physical activity on cardiac mitochondrial function underlying the ability to modulate specific steps in mitochondrial quality control in both physiological and pathophysiological conditions. Topics were discussed ranged from the effects of exercise on mitochondrial phenotypes, biogenesis, turnover, morphology and respiration to cardiac pathophysiological conditions such as, aging, ischemia/reperfusion injury (I/R), diabetic cardiomyopathy, and anthracyclines dependent heart failure. From these studies, physical exercise emerges as a non-pharmacological tool (“mitochondrial medicine for muscle”) to improve cardiovascular fitness in healthy people as well as to attenuate mitochondrial dysfunction in patients with pathophysiological conditions, particularly cardiac I/R damage.
- ItemHigh carbohydrate and high fat diets protect the heart against ischaemia/reperfusion injury(BioMed Central Ltd., 2014-07-18) Salie, Ruduwaan; Huisamen, Barbara; Lochner, AmandaBackground: Although obesity is still considered a risk factor in the development of cardiovascular disorders, recent studies suggested that it may also be associated with reduced morbidity and mortality, the so-called “obesity paradox”. Experimental data on the impact of diabetes, obesity and insulin resistance on myocardial ischaemia/reperfusion injury are controversial. Similar conflicting data have been reported regarding the effects of ischaemic preconditioning on ischaemia/reperfusion injury in hearts from such animals. The aim of the present study was to evaluate the susceptibility to myocardial ischaemia/reperfusion damage in two models of diet-induced obesity as well as the effect of ischaemic and pharmacological preconditioning on such hearts. Methods: Three groups of rats were fed with: (i) normal rat chow (controls) (ii) a sucrose-supplemented diet (DIO) (iii) a high fat diet (HFD). After 16 weeks, rats were sacrificed and isolated hearts perfused in the working mode and subjected to 35 min regional ischaemia/60 min reperfusion. Endpoints were infarct size and functional recovery. Infarct size was determined, using tetrazolium staining. Activation of PKB/Akt and ERKp44/p42 (RISK pathway) during early reperfusion was determined using Western blot. Statistical evaluation was done using ANOVA and the Bonferroni correction. Results: Infarct sizes of non-preconditioned hearts from the two obese groups were significantly smaller than those of the age-matched controls. Ischaemic as well as pharmacological (beta-adrenergic) preconditioning with a beta2-adrenergic receptor agonist, formoterol, caused a significant reduction in infarct size of the controls, but were without effect on infarct size of hearts from the obese groups. However, ischaemic as well as beta-preconditioning caused an improvement in functional performance during reperfusion in all three groups. A clear-cut correlation between the reduction in infarct size and activation of ERKp44/p42 and PKB/Akt was not observed: The reduction in infarct size observed in the non-preconditioned hearts from the obese groups was not associated with activation of the RISK pathway. However, beta-adrenergic preconditioning caused a significant activation of ERKp44/p42, but not PKB/Akt, in all three groups. Conclusions: Relatively long-term administration of the two obesity-inducing diets resulted in cardioprotection against ischaemia/reperfusion damage. Further protection by preconditioning was, however, without effect on infarct size, while an improvement in functional recovery was observed.
- ItemThe impact of sugar-sweetened beverage intake on rat cardiac function(Elsevier, 2019-03-12) Driescher, Natasha; Joseph, Danzil E.; Human, Veronique R.; Ojuka, Edward; Cour, Martin; Hadebe, Nkanyiso; Bester, Dirk; Marnewick, Jeanine L.; Lecour, Sandrine; Lochner, Amanda; Essop, M. FaadielAims: Although there is evidence linking sugar-sweetened beverage (SSB) intake with the development of cardio-metabolic diseases, the underlying mechanisms remain unclear. The current study therefore evaluated the effects of SSB consumption by establishing a unique in-house in vivo experimental model. Main methods: Male Wistar rats were divided into two groups: a) one consuming a popular local SSB (SSB- Jive), and b) a control group (Control-water) for a period of three and six months (n = 6 per group), respectively. Rats were gavaged on a daily basis with an experimental dosage amounting to half a glass per day (in human terms) (SSB vs. water). Cardiac function was assessed at baseline (echocardiography) and following ex vivo ischemia-reperfusion of the isolated perfused working rat heart. Oral glucose tolerance tests and mitochondrial respiratory analyses were also performed. In addition, the role of non-oxidative glucose pathways (NOGPs), i.e. the polyol pathway, hexosamine biosynthetic pathway (HBP) and PKC were assessed. Key findings: These data show that SSB intake: a) resulted in increased weight gain, but did not elicit major effects in terms of insulin resistance and cardiac function after three and six months, respectively; b) triggered myocardial NOGP activation after three months with a reversion after six months; and c) resulted in some impairment in mitochondrial respiratory capacity in response to fatty acid substrate supply after six months. Significance: SSB intake did not result in cardiac dysfunction or insulin resistance. However, early changes at the molecular level may increase risk in the longer term.
- ItemIschaemic postconditioning : from bench to bedside …(Clinics Cardiv Publishing, 2008-12) Van Vuuren, Derick; Lochner, AmandaThe increase in the incidence of ischaemic heart disease and acute myocardial infarction (AMI) in both high- and lowincome countries necessitates the development of myocardial salvaging/protection interventions, to be applied alongside standard reperfusion therapies. Although the phenomenon of ischaemic preconditioning (IPC) is associated with the desired protective capacity, the necessity of its application before sustained ischaemia limits its clinical potential. The recently described phenomenon of postconditioning (postC), or short cycles of reperfusion/ischaemia applied at the onset of reperfusion, falls within the clinically relevant time period of reperfusion, but can it elicit reliable and potent cardioprotection? The answer to this problem is intimately related to the question whether postC can be translated from a laboratory technique to a clinical therapy. In this brief overview of postconditioning, the experimental set-ups and postC algorithms utilised, and their associated outcomes in all animal models studied (dog, rabbit, mouse, rat and pig) are discussed. The therapeutic potential of postC is also addressed by discussing reported preliminary studies on the efficacy and feasibility of postC (both ischaemic and pharmacological) in humans.
- ItemSanguinarine Non- Versus Re-Circulation During Isolated Heart Perfusion - A Jekyll and Hyde Effect?(Springer, 2014) Webster, Ingrid; Smith, Angelique; Huisamen, Barbara; Lochner, Amanda; Biomedical Sciences: Medical Physiology
- ItemSignalling pathways activated by glucagon-like peptide-1 (7-36) amide in the rat heart and their role in protection against ischaemia(Clinics Cardiv Publishing, 2008-04) Huisamen, Barbara; Genade, Sonia; Lochner, AmandaGlucagon-like peptide-1 is an incretin hormone proposed to have insulinomimetic effects on peripheral insulin-sensitive tissue. We examined these effects on the heart by using isolated, perfused rat hearts and adult ventricular myocytes. During normoxic perfusion, no effects of escalating concentrations of GLP-1 on either heart rate or left ventricular developed pressure were found. With functional performance as readout, we found that GLP-1 directly protected the heart against damage incurred by global low-flow ischaemia. This protection was sensitive to the presence of iodo-acetate, implicating activation of glycolysis, and was abolished by wortmannin, indicative of PI-3-kinase as mediator of protection. I n addition, GLP-1 had an infarct-sparing effect when supported by the presence of the dipeptidyl peptidase-IV inhibitor valine pyrrolidide. GLP-1 could not directly activate protein kinase B (also called Akt) or the extracellular regulated kinases Erk1/2 in hearts or cardiocytes under normoxic conditions, but phosphorylation of the AMP-activated kinase (AMPK) on Thr172 was enhanced. I n addition, the glycolytic enzyme phosphofructokinase- 2 was activated dose dependently. During reperfusion after ischaemia, modulation of the phosphorylation of PKB/Akt as well as AMPK was evident. GLP-1 therefore directly protected the heart against low-flow ischaemia by enhancing glycolysis, probably via activation of AMP kinase and by modulating the profile of activation of the survival kinase PKB/Akt.
- ItemTreatment with a fixed dose combination antiretroviral therapy drug containing tenofovir, emtricitabine and efavirenz is associated with cardioprotection in high calorie diet-induced obese rats(Public Library of Science, 2018-12-05) Everson, Frans; Genis, Amanda; Ogundipe, Temitope; De Boever, Patrick; Goswami, Nandu; Lochner, Amanda; Blackhurst, Dee; Strijdom, HansHIV-infection, certain antiretroviral drug classes, especially protease inhibitors (PI), and obesity are associated with increased ischaemic heart disease (IHD) risk. However, the effect of PI-free fixed dose combination (FDC) antiretroviral therapy (ART) on hearts exposed to ischaemia-reperfusion injury (I/R) is unknown, particularly in obesity. This is becoming relevant as World Health Organisation guidelines recommend a FDC ART containing (non-) nucleoside reverse transcriptase inhibitors (tenofovir (TDF), emtricitabine (FTC) and efavirenz (EFV)) as first-line HIV treatment. Additionally, obesity rates are rising in HIV-infected populations, not only in ART-experienced individuals, but also at the time of ART initiation, which may further increase the risk of IHD. Therefore, we investigated the effects of PI-free FDC ART in myocardial I/R-exposed hearts from obese rats. Obesity was induced in male wistar rats via a 16-week high calorie diet. At week 10, treatment with a FDC ART drug containing TDF/FTC/EFV was initiated. Biometric and metabolic parameters, as well as myocardial functional recovery and infract size (IS), and myocardial signalling proteins following I/R were assessed after 16 weeks. Obese rats presented with increased body and intraperitoneal fat mass, elevated triglyceride and TBARS levels, whilst the hearts responded to I/R with impaired functional performance and increased IS. The FDC ART treatment did not alter biometric and metabolic parameters in obese rats. In a novel finding, ART protected obese hearts against I/R as shown by improved functional performance and smaller IS vs. untreated obese hearts. Cardioprotection was underscored by increased myocardial phosphorylated endothelial nitric oxide synthase (eNOS) and reduced AMP-kinase levels. In conclusion, these results demonstrate for the first time, that 6-weeks treatment of obese rats with a FDC ART drug specifically containing TDF/FTC/EFV conferred cardioprotection against I/R. The FDC ART-induced cardioprotection was seemingly unrelated to metabolic changes, but rather due to direct cardiac mechanisms including the up-regulation of myocardial eNOS.