The global epidemic of obesity is rapidly becoming a major public health problem in many parts of the world. Unhealthy diets and physical inactivity are two modifiable risk factors for prevention of obesity and its associated chronic diseases. Their influence on muscle energy metabolism and fat mass is not completely elucidated. A decreased capacity for fatty acid oxidation (FAO) may be a metabolic risk factor for weight gain and is found to be depressed in obese individuals; and exercise training may promote an increased capacity for FAO. In addition to the interest in whole-body FAO, the role of site specific lipid accumulation including visceral adipose tissue (VAT), intrahepatic lipids (IHL) and intramyocellular lipids (IMCL) has become a focus of interest because of their reported association with insulin resistance (IR), a key metabolic defect associated with obesity and type 2 diabetes mellitus (T2DM). However, ambiguity persists regarding the importance of IMCL as a metabolic substrate for energy production in obesity. A better understanding of the factors regulating FAO, body fat distribution and IMCL mobilisation is important for the development of interventions allowing effective treatment of conditions in which these are disturbed. The study of individuals with metabolic myopathies can give more information about the energy metabolism of muscle. McArdle disease (MD) affects glucose availability to muscle for energy production. Investigations into IMCL storage and mobilisation in MD have not been reported. The aims of this thesis are to investigate 1) the effects of weight-loss via dietary restriction plus modest but clinically-relevant exercise training on FAO, body fat distribution and mobilisation of IMCL during exercise in obese non-diabetic adults; 2) the effect of an exercise training intervention on IMCL storage and mobilisation in a subject with MD. All obese subjects underwent a 4 month lifestyle intervention with weekly meetings with a dietitian and an exercise physiologist. Of the 92 subjects, 73 completed the intervention. They showed significant decreases in body weight (8%), fat mass (14%) and total cholesterol (5%). The exercise prescription of 1500 kcal.week-1 resulted in variable compliance with the prescription (1224 ± 1085 kcal.week-1) measured by heart rate monitor. Those who did most exercise and also those who had less weekly variability in their exercise, had greater reductions in body weight and fat mass. The total activity energy expenditure measured by accelerometry did not change post-intervention but there was a reduction in low intensity activity and an increase in moderate and high intensity activity. A submaximal treadmill test and resting metabolic rate (RMR) using indirect calorimetry was measured before and after the intervention to investigate factors regulating FAO and energy expenditure. Subjects showed increases in FAO without change in energy expenditure for the same walking speed post intervention, but the volume of exercise completed during the intervention was not associated with these changes. To investigate body fat distribution in obesity, VAT, IHL and soleus muscle IMCL was measured in a sub-group of 18 males by magnetic resonance imaging (MRI) and spectroscopy (MRS) along with measurement of maximal aerobic capacity. Fitness increased significantly with significant decreases in VAT (29%) and IHL (54%), without significant change in IMCL. Subjects who had the greatest decrease in VAT were those who exercised for longer durations during the intervention. IHL was the only measure of excess lipid that correlated with IR. The measurement of IMCL before and after 1-hour of cycle ergometer exercise showed no significant mobilisation of IMCL either at baseline or after the lifestyle intervention. The intensity of the acute exercise was adjusted to correspond to each individual’s maximal fatty acid oxidation (MFAO) which increased by over 60% post intervention. In the subject with MD, an 8 week exercise training intervention without dietary intervention increased IMCL stores by 27%, but there was no marked change in IMCL with acute exercise at both time points. The findings of this thesis demonstrate that a clinically relevant and achievable lifestyle intervention incorporating weight loss through diet and objectively measured exercise can achieve improvements in blood lipid profile, body composition and FAO. The differential effects of the intervention on the various fat depots and their associations to metabolic markers suggest that individualised strategies may be required dependent upon body fat distribution. The non detection of mobilisation of IMCL by MRS suggests that these lipids may not be present as a substrate source in this population but rather an ectopic lipid depot related to increased energy consumption in diet. The relatively low capacity for FAO in both the obese and MD subjects may have affected the results. This thesis discusses implications for clinical practice, discusses novel findings related to the energy metabolism in obesity and MD and informs clinical and basic science about important future directions.

The global epidemic of obesity is rapidly becoming a major public health problem in many parts of the world. Unhealthy diets and physical inactivity are two modifiable risk factors for prevention of obesity and its associated chronic diseases. Their influence on muscle energy metabolism and fat mass is not completely elucidated. A decreased capacity for fatty acid oxidation (FAO) may be a metabolic risk factor for weight gain and is found to be depressed in obese individuals; and exercise training may promote an increased capacity for FAO. In addition to the interest in whole-body FAO, the role of site specific lipid accumulation including visceral adipose tissue (VAT), intrahepatic lipids (IHL) and intramyocellular lipids (IMCL) has become a focus of interest because of their reported association with insulin resistance (IR), a key metabolic defect associated with obesity and type 2 diabetes mellitus (T2DM). However, ambiguity persists regarding the importance of IMCL as a metabolic substrate for energy production in obesity. A better understanding of the factors regulating FAO, body fat distribution and IMCL mobilisation is important for the development of interventions allowing effective treatment of conditions in which these are disturbed. The study of individuals with metabolic myopathies can give more information about the energy metabolism of muscle. McArdle disease (MD) affects glucose availability to muscle for energy production. Investigations into IMCL storage and mobilisation in MD have not been reported. The aims of this thesis are to investigate 1) the effects of weight-loss via dietary restriction plus modest but clinically-relevant exercise training on FAO, body fat distribution and mobilisation of IMCL during exercise in obese non-diabetic adults; 2) the effect of an exercise training intervention on IMCL storage and mobilisation in a subject with MD. All obese subjects underwent a 4 month lifestyle intervention with weekly meetings with a dietitian and an exercise physiologist. Of the 92 subjects, 73 completed the intervention. They showed significant decreases in body weight (8%), fat mass (14%) and total cholesterol (5%). The exercise prescription of 1500 kcal.week-1 resulted in variable compliance with the prescription (1224 ± 1085 kcal.week-1) measured by heart rate monitor. Those who did most exercise and also those who had less weekly variability in their exercise, had greater reductions in body weight and fat mass. The total activity energy expenditure measured by accelerometry did not change post-intervention but there was a reduction in low intensity activity and an increase in moderate and high intensity activity. A submaximal treadmill test and resting metabolic rate (RMR) using indirect calorimetry was measured before and after the intervention to investigate factors regulating FAO and energy expenditure. Subjects showed increases in FAO without change in energy expenditure for the same walking speed post intervention, but the volume of exercise completed during the intervention was not associated with these changes. To investigate body fat distribution in obesity, VAT, IHL and soleus muscle IMCL was measured in a sub-group of 18 males by magnetic resonance imaging (MRI) and spectroscopy (MRS) along with measurement of maximal aerobic capacity. Fitness increased significantly with significant decreases in VAT (29%) and IHL (54%), without significant change in IMCL. Subjects who had the greatest decrease in VAT were those who exercised for longer durations during the intervention. IHL was the only measure of excess lipid that correlated with IR. The measurement of IMCL before and after 1-hour of cycle ergometer exercise showed no significant mobilisation of IMCL either at baseline or after the lifestyle intervention. The intensity of the acute exercise was adjusted to correspond to each individual’s maximal fatty acid oxidation (MFAO) which increased by over 60% post intervention. In the subject with MD, an 8 week exercise training intervention without dietary intervention increased IMCL stores by 27%, but there was no marked change in IMCL with acute exercise at both time points. The findings of this thesis demonstrate that a clinically relevant and achievable lifestyle intervention incorporating weight loss through diet and objectively measured exercise can achieve improvements in blood lipid profile, body composition and FAO. The differential effects of the intervention on the various fat depots and their associations to metabolic markers suggest that individualised strategies may be required dependent upon body fat distribution. The non detection of mobilisation of IMCL by MRS suggests that these lipids may not be present as a substrate source in this population but rather an ectopic lipid depot related to increased energy consumption in diet. The relatively low capacity for FAO in both the obese and MD subjects may have affected the results. This thesis discusses implications for clinical practice, discusses novel findings related to the energy metabolism in obesity and MD and informs clinical and basic science about important future directions.

Le déficit héréditaire en Carnitine Palmitoyl Transférase 2 (CPT2), l’un des déficits de l’oxydation mitochondriale des acides gras (OAG) les plus fréquents, est caractérisé dans sa forme adulte par une myopathie métabolique avec des épisodes récurrents de douleurs musculaires, de myoglobinurie et de rhabdomyolyse, habituellement déclenchés par un exercice prolongé ou un jeûne. A l’heure actuelle, il n’y a pas de traitement pharmacologique efficace pour la correction de ce déficit à l’exception de prise en charge nutritionnelle. Mon travail de thèse a porté sur l’étude du potentiel thérapeutique du composé GSK773 un activateur direct de l’AMP-activated Protein Kinase (AMPK), un senseur énergétique de la cellule, dans des myotubes de quatre patients déficitaires en CPT2. En effet, l'AMPK est considérée comme une cible thérapeutique potentielle dans de nombreux troubles métaboliques ou neurodégénératifs courants associés aux dysfonctionnements mitochondriaux. Nous montrons que le composé GSK773 est capable de stimuler les capacités résiduelles de l’OAG et de corriger le flux d’OAG dans des myotubes déficitaires en CPT2 (n=4) après un traitement par 30µM pendant 48h. L’étude par western-blot et par immunofluorescence montre que le GSK773 augmente la quantité de protéine mutante CPT2. L'analyse des intermédiaires C16-acylcarnitines montre que les myotubes déficients en CPT2 présentent, comme prévu, une accumulation de C16-acylcarnitines significativement diminuée après le traitement par le GSK773. De manière intéressante, l'IF et l’xCELLigence, une nouvelle technique basée sur la mesure de l’impédance électrique en temps réel, montrent un processus de différenciation altéré dans les myotubes de patients déficitaires en CPT2 par rapport aux cellules témoins, qui est corrigé par le GSK773. Nous avons également montré que le GSK773 induit une conversion des fibres musculaires vers les fibres de type I lentes/oxydatives, mais aussi une amélioration générale de la qualité du réseau mitochondrial accompagnée d’une biogenèse mitochondriale et une augmentation du niveau de ROS suggérant que le GSK773 agirait sur la plasticité musculaire. D’un point de vue mécanistique, nous avons montré que les effets du GSK773 passent par l’AMPK, PGC-1α, p38 MAPK et les ROS. Ainsi, ces résultats suggèrent que le GSK773 améliore les paramètres métaboliques et structuraux dans les myotubes déficients en CPT2 et que l'AMPK pourrait représenter une cible thérapeutique hautement pertinente pour la correction pharmacologique du déficit en CPT2. / Carnitine Palmitoyl Transferase 2 (CPT2) deficiency is among the most common inherited defects of mitochondrial fatty acid oxidation (FAO). A frequent phenotype is an early adult-onset myopathy characterized by recurrent episodes of muscle pain, myoglobinuria and rhabdomyolysis usually triggered by prolonged exercise or fasting. To date, there is no treatment of this disorder other than dietary management. AMPK is considered as a potential therapeutic target in many common metabolic or neurodegenerative disorders associated to mitochondrial dysfunctions. Thus, we tested the therapeutic potential of the direct AMPK activator GSK773 in myotubes from four CPT2-deficient patients. We show that GSK773 is able to stimulate residual FAO capacities in a dose- and time-dependent manner. Correction of CPT2 defect is achieved after treatment with GSK773 at 30µM for 48h. Western-blots analysis and Immunostaining shows that GSK773 increases the amount of CPT2 mutant protein. Analysis of acylcarnitine intermediates in the culture media shows that CPT2-deficient myotubes exhibit, as expected, an accumulation of C16-acylcarnitines that is significantly decreased after GSK773 treatment. Surprisingly, immunofluorescence and xCELLigence (a real-time monitoring of cell culture technic) show an impaired differentiation process in CPT2-deficient myotubes that is corrected by GSK773. We also show that GSK773 induces a shift in myosin-heavy-chain isoforms toward slow oxidative fiber types, improves the quality of mitochondrial network with an induction of mitochondrial biogenesis and increases ROS levels, suggesting that GSK773 might induce muscle plasticity. Finally, from a mechanistic point of view, siRNAs experiments showed that the effects triggered by GSK773 implicate AMPK, PGC-1α, ROS and p38 MAPK. Altogether these results suggest that GSK773 improves metabolic and structural parameters in CPT2-deficient myotubes and that AMPK might represent a highly relevant therapeutic target for pharmacological correction of inborn CPT2 deficiency.

Es stellt sich die Frage, wie diese Zellen im entzündeten Gewebe überleben können und wie sie ihren Stoffwechsel an die dortigen Bedingungen anpassen. Diese Arbeit beschreibt am Beispiel der Juvenilen Idiopathischen Arthritis (JIA) die Analyse des Stoffwechsels von CD4+ T Lymphozyten, die chronische Entzündungen antreiben undim entzündeten Gewebe lange Zeit persistieren. Pathogene CD4+ CD45RO+ PD1+ CXCR5-T Zellen wurden hierfür aus Synovialflüssigkeit von Patienten mit JIA isoliert und gezeigt, dass auch bei diesen Zellen der Stoffwechsel auf Fettsäureoxidation beruht. Wurde die Fettsäureoxidation durch Etomoxir blockiert, starben die Zellen. Die Störung des Stoffwechsels dieser Zellen könnte somit eine Option für einen neuen Therapieansatzdarstellen. Zusätzlich war die Expression des Transkriptionsfaktors Twist 1 in diesen CD4+CD45RO+ PD1+ CXCR5- T Zellen hochreguliert. Twist 1 ist ein Marker für T Lymphozyten, die in entzündetem Gewebe von Patienten mit chronisch-entzündlichen Erkrankungen der Gelenke oder des Darmes persistieren. Untersuchung in vitro ergaben außerdem, dass Twist 1 spezifisch von Th1 Lymphozyten exprimiert wird, die mehrfach restimuliert wurden. Dieser Transkriptionsfaktor wirkt einerseits der Gewebszerstörung, die von T Zellen verursacht wird, entgegen, und unterstützt anderseits die Persistenz der Zellen im Gewebe durch die Induktion der microRNA148a, die die Expression des pro-apoptotischen Proteins Bim reguliert. In dieser Arbeit zeigen wir dessen Einfluss auf die Regulation des Metabolismus von CD4+ T Lymphozyten bei chronischen Entzündungen. Dabei wird die Glycolyse verringert und vermehrt Fettsäuren synthetisiert, um die Zellen vor reaktiven oxidierenden Spezies (ROS) zu schützen. Zusätzlich konnten wir nachweisen, dass mehrfach re-stimulierte, Twist-defizienteTh1 Zellen unfähig sind, durch Fettsäureoxydation zu überleben, sondern den Stoffwechsel auf Lipid- Peroxidierung umstellen / How do CD4+ T cells adapt their metabolism for survival in the inflamed tissue? This thesis describes analysis of the metabolism of CD4 T lymphocytes driving chronic inflammation and persisting at the site of inflammation, exemplified by cells that reside in the inflamed tissue of patients with the rheumatic disease juvenile idiopathic arthritis. To specifically take aim at the CD4+ T lymphocytes persisting at the site of inflammation, it is important to determine how these cells adapt their metabolism. We show that pathogenic CD4+ CD45RO+ PD1+ CXCR5- T cells that were isolated from the synovial fluid of patients with juvenile idiopathic arthritis are dependent on a fatty acid oxidation for survival ex vivo. Their survival can be blocked by blocking FAO with Etomoxir, pointing to the option of targeting such cells by metabolic interference. Furthermore, CD4+ CD45RO+ PD1+ CXCR5- T cells had upregulated expression of Twist1, a hallmark transcription factor of T lymphocytes persisting in the inflamed tissues of patients with chronic-inflammatory diseases of joints or the gut. Expression of Twist1 is specific for Th1 lymphocytes which have repeatedly been re-stimulated in vitro, or isolated from inflamed. This transcription factor dampens immunopathology caused by the T cells and supports their persistence, by inducing microRNA148a, which regulates expression of the proapoptotic protein Bim. This thesis shows, through conditional genetic inactivation of Twist1 in CD4+ T lymphocytes, that Twist1 regulates the metabolism ofCD4 T lymphocytes of chronic inflammation, by downregulating glycolysis, promoting fatty acid synthesis and protecting the cells from ROS. Additionally, we show that Twist1 deficient repeatedly reactivated murine Th1 cells are unable to survive on fatty acid oxidation and have increased levels of lipid peroxidation.

Beta adrenergic antagonists and antianginal drugs are used with the aim to ultimately decrease mortality and enable patients to lead an improved quality of life by avoidance of anginal episodes. Each class of medications used for this purpose has a variety of actual or potential side effects associated with their use. Side effects and drug interactions involving these medications are discussed in the following chapter. Evidence presented should be used in the context of the patient populations described and may aid clinical decision making through avoidance or identification of actual or potential side effects. This review includes literature published from January 2019 to January 2020 written in English.

A variety of atherosclerosis and cardiovascular disease (ASCVD) phenotypes are tightly linked to changes in the cardiac energy metabolism that can lead to a loss of metabolic flexibility and to unfavorable clinical outcomes. We conducted an association analysis of 31 ASCVD phenotypes and 97 whole blood amino acids, acylcarnitines and derived ratios in the LIFE-Adult (n = 9646) and LIFE-Heart (n = 5860) studies, respectively. In addition to hundreds of significant associations, a total of 62 associations of six phenotypes were found in both studies. Positive associations of various amino acids and a range of acylcarnitines with decreasing cardiovascular health indicate disruptions in mitochondrial, as well as peroxisomal fatty acid oxidation. We complemented our metabolite association analyses with whole blood and peripheral blood mononuclear cell (PBMC) gene-expression analyses of fatty acid oxidation and ketone-body metabolism related genes. This revealed several differential expressions for the heart failure biomarker N-terminal prohormone of brain natriuretic peptide (NT-proBNP) in peripheral blood mononuclear cell (PBMC) gene expression. Finally, we constructed and compared three prediction models of significant stenosis in the LIFE-Heart study using (1) traditional risk factors only, (2) the metabolite panel only and (3) a combined model. Area under the receiver operating characteristic curve (AUC) comparison of these three models shows an improved prediction accuracy for the combined metabolite and classical risk factor model (AUC = 0.78, 95%-CI: 0.76–0.80). In conclusion, we improved our understanding of metabolic implications of ASCVD phenotypes by observing associations with metabolite concentrations and gene expression of the mitochondrial and peroxisomal fatty acid oxidation. Additionally, we demonstrated the predictive potential of the metabolite profile to improve classification of patients with significant stenosis.

Thesis (MScMedSc (Dept. of Biomedical Sciences. Medical Physiology))University of Stellenbosch, 2010. / ENGLISH ABSTRACT: Background: Obesity is associated with dyslipidemia, insulin resistance and glucose intolerance and together these components characterise the metabolic syndrome (Dandona et al. 2005). In the state of obesity, there are high levels of circulating free fatty acids and increased rates of fatty oxidation which inhibit glucose oxidation. This: (i) reduce the heart‘s contractile ability, (ii) exacerbates ischemic/reperfusion injury and (iii) decreases cardiac mechanical function during reperfusion (Kantor et al. 2000; Liu et al. 2002; Taegtmeyer, 2000). Aim: The aim of our study was to investigate the effect of inhibiting fatty acid oxidation, with oxfenicine (4-Hydroxy-L-phenylglycine), on (i) cardiac mechanical function, (ii) mitochondrial respiration, (iii) myocardial tolerance to ischemia/reperfusion injury, (iv) CPT-I expression, MCAD expression, IRS-1 activation, total GLUT- 4 expression and (v) the RISK pathway (ERK42/44 and PKB/Akt). Methods: Male Wistar rats were fed a control rat chow diet or a high calorie diet (HCD) for 16 weeks. The HCD caused diet induced obesity (DIO). The animals were randomly divided into 4 groups [Control, DIO, Control + oxfen and DIO + oxfen]. The drug was administered for the last 8 weeks of feeding (200mg/kg/day). Animals were sacrificed and the hearts were perfused on the Langendorff perfusion system. After being subjected to regional ischemia and two hours of reperfusion, infarct size was determined. A separate series of animals were fed and/or treated and hearts were collected after 25 minutes global ischemia followed by 30 min reperfusion for determination of GLUT- 4, CPT-1, IRS -1, MCAD, ERK (42/44) and PKB/Akt expression/phosphorylation using Western blot analysis. A third series of hearts were excised and used for the isolation of mitochondria. Results: In the DIO rats, chronic oxfenicine treatment improved cardiac mechanical function by improving mitochondrial respiration. Oxfenicine inhibited CPT-1 expression but had no effect on MCAD or GLUT- 4 expression. Oxfenicine decreased IRS-1 iv expression, but not IRS-1 activation. Oxfenicine also improved myocardial tolerance to ischemia/reperfusion without activation of the RISK pathway (ERK & PKB). In the control rats, chronic oxfenicine treatment worsened cardiac mechanical function by adversely affecting mitochondrial respiration. Oxfenicine also worsened myocardial tolerance to ischemia/reperfusion in the control rats without changes in the RISK pathway (ERK & PKB). Oxfenicine had no effect on CPT-1, MCAD or GLUT- 4 expression. Oxfenicine increased IRS-1 expression, but not IRS-1 activity. Conclusion: Chronic oxfenicine treatment improved cardiac mechanical function and myocardial resistance to ischemia/reperfusion injury in obese animals, but worsened it in control animals. The improved cardiac mechanical function and tolerance to ischemia/reperfusion injury may be due to improvement in mitochondrial respiration. / AFRIKAANSE OPSOMMING: Agtergrond: Vetsug word geassosieer met dislipidemie, insulien weerstandigheid en glukose intoleransie, wat saam die metaboliese sindroom karakteriseer (Dandona et al. 2005). Met vetsug is daar ‗n hoë sirkulasie van vetsure, sowel as verhoogde vertsuur oksidasie wat gevolglik glukose oksidasie onderdruk. Dit: (i) verlaag die hart se vermoë om saam te trek, (ii) vererger isgemiese/herperfusie skade en (iv) verlaag kardiale effektiwiteit gedurende herperfusie (Kantor et al. 2000; Liu et al. 2002; Taegtmeyer, 2000). Doel: Die doel van die studie was om die effekte van vetsuur onderdrukking m.b.v. oksfenisien (4-Hidroksie-L-fenielglisien) op (i) meganiese hart funksie, (ii) mitokondriale respirasie, (iii) miokardiale toleransie teen isgemiese/herperfusie skade, (iv) CPT-I uitdrukking, MCAD uitdrukking, IRS-1 aktiwiteit, totale GLUT-4 uitdrukking en (v) die RISK pad (ERK42/44 en PKB/Akt) te ondersoek. Metodes: Manlike Wistar rotte was gevoer met ‗n kontrole rot dieet of ‗n hoë kalorie dieet (HKD) vir 16 weke. Die HKD lei tot dieet-geïnduseerde vetsug (DGV). Die diere was lukraak verdeel in 4 groepe [kontrole, DGV, kontrole + oksfen en DGV + oksfen]. Die behandeling met die middel was toegedien vir die laaste 8 weke van die voeding protokol (200mg/kg/dag). Die diere was geslag en die harte was geperfuseer op die Langendorff perfusie sisteem. Na blootstelling aan streeks- of globale isgemie en 2 ure herperfusie was infark groottes bepaal. ‗n Aparte reeks diere was gevoer en/of behandel en die harte was versamel na 25 minute globale isgemie gevolg deur 30 minute herperfusie vir die bepaling van GLUT-4, CPT 1, IRS -1, MCAD, ERK (42/44) en PKB/Akt uitdrukking/aktivering d.m.v. Western blot analise. ‗n Derde reeks diere was gebruik vir die isolasie van mitokondria. Resultate: In die DGV diere, het kroniese oksfenisien behandeling meganiese hart funksie verbeter d.m.v. die verbetering van mitokondriale respirasie. Oksfenisien het CPT-1 uitdrukking verlaag terwyl GLUT- 4 en MCAD uitdrukking nie geaffekteer was vi nie. Oksfenisien het IRS-1 uitdrukking verlaag, maar nie IRS-1 aktiwiteit nie. Oksfenisien het ook miokardiale weerstand teen isgemiese/herperfusie verbeter met sonder aktivering van die RISK pad (ERK & PKB). In die kontrole diere, het kroniese oksfenisien behandeling die meganiese hart funksie versleg d.m.v. negatiewe effekte op mitokondriale respirasie. Oksfenisien het die miokardiale weerstand teen isgemiese/herperfusie van die kontrole rotte versleg sonder veranderinge in die RISK pad (ERK & PKB). Oksfenisien het geen effek gehad op CPT-1, MCAD en GLUT-4 uitdrukking nie. Oksfenisien het IRS-1 uitdrukking verhoog, maar nie IRS-1 aktiwiteit nie. Samevatting: Kroniese oksfenisien behandeling het die meganiese hart funksie en miokardiale weerstand teen isgemiese/herperfusie skade in die vet diere verbeter, maar versleg in die kontrole diere. Hierdie verbetering van meganiese hart funksie en weerstand teen isgemiese/herperfusie skade kon dalk wees a.g.v. ‗n verbetering in mitokondriale respirasie.

Les sécrétines de l’hormone de croissance (GHRPs) sont de petits peptides synthétiques capables de stimuler la sécrétion de l’hormone de croissance à partir de l’hypophyse via leur liaison au récepteur de la ghréline GHS-R1a. Le GHRP hexaréline a été utilisé afin d’étudier la distribution tissulaire de GHS-R1a et son effet GH-indépendant. Ainsi, par cette approche, il a été déterminé que l’hexaréline était capable de se lier à un deuxième récepteur identifié comme étant le récepteur scavenger CD36. Ce récepteur possède une multitude de ligands dont les particules oxLDL et les acides gras à longue chaîne. CD36 est généralement reconnu pour son rôle dans l’athérogénèse et sa contribution à la formation de cellules spumeuses suite à l’internalisation des oxLDL dans les macrophages/monocytes. Auparavant, nous avions démontré que le traitement des macrophages avec l’hexaréline menait à l’activation de PPARƔ via sa liaison à GHS-R1a, mais aussi à CD36. De plus, une cascade d’activation impliquant LXRα et les transporteurs ABC provoquait également une augmentation de l’efflux du cholestérol. Une stimulation de la voie du transport inverse du cholestérol vers les particules HDL entraînait donc une diminution de l’engorgement des macrophages de lipides et la formation de cellules spumeuses. Puisque CD36 est exprimé dans de multiples tissus et qu’il est également responsable du captage des acides gras à longue chaîne, nous avons voulu étudier l’impact de l’hexaréline uniquement à travers sa liaison à CD36. Dans le but d’approfondir nos connaissances sur la régulation du métabolisme des lipides par CD36, nous avons choisi des types cellulaires jouant un rôle important dans l’homéostasie lipidique n’exprimant pas GHS-R1a, soient les adipocytes et les hépatocytes. L’ensemble de mes travaux démontre qu’en réponse à son interaction avec l’hexaréline, CD36 a le potentiel de réduire le contenu lipidique des adipocytes et des hépatocytes. Dans les cellules adipeuses, l'hexaréline augmente l’expression de plusieurs gènes impliqués dans la mobilisation et l’oxydation des acides gras, et induit également l’expression des marqueurs thermogéniques PGC-1α et UCP-1. De même, hexaréline augmente l’expression des gènes impliqués dans la biogenèse mitochondriale, un effet accompagné de changements morphologiques des mitochondries; des caractéristiques observées dans les types cellulaires ayant une grande capacité oxydative. Ces résultats démontrent que les adipocytes blancs traités avec hexaréline ont la capacité de se transformer en un phénotype similaire aux adipocytes bruns ayant l’habileté de brûler les acides gras plutôt que de les emmagasiner. Cet effet est également observé dans les tissus adipeux de souris et est dépendant de la présence de CD36. Dans les hépatocytes, nous avons démontré le potentiel de CD36 à moduler le métabolisme du cholestérol. En réponse au traitement des cellules avec hexaréline, une phosphorylation rapide de LKB1 et de l’AMPK est suivie d’une phosphorylation inhibitrice de l’HMG-CoA réductase (HMGR), l’enzyme clé dans la synthèse du cholestérol. De plus, la liaison d'hexaréline à CD36 provoque le recrutement d’insig-2 à HMGR, l’étape d’engagement dans sa dégradation. La dégradation de HMGR par hexaréline semble être dépendante de l’activité de PPARƔ et de l’AMPK. Dans le but d’élucider le mécanisme d’activation par hexaréline, nous avons démontré d’une part que sa liaison à CD36 provoque une déphosphorylation de Erk soulevant ainsi l’inhibition que celui-ci exerce sur PPARƔ et d’autre part, un recrutement de l’AMPK à PGC-1α expliquant ainsi une partie du mécanisme d’activation de PPARƔ par hexaréline. Les résultats générés dans cette thèse ont permis d’élucider de nouveaux mécanismes d’action de CD36 et d'approfondir nos connaissances de son influence dans la régulation du métabolisme des lipides. / Growth hormone releasing peptides (GHRPs) are small synthetic peptides aimed at stimulating GH release from the pituitary through their binding to ghrelin receptor known as growth hormone secretagogue receptor 1a (GHS-R1a). Using the GHRP, hexarelin to study tissue distribution of GHS-R1a and its GH-independent effect, it was observed that hexarelin was capable of binding to a second receptor identified as scavenger receptor CD36. While having multiple ligands, CD36 is mainly known for binding and internalizing oxLDL and long chain fatty acids. CD36 is thought to play a detrimental role in macrophage derived foam cell formation and development of atherosclerosis. Previously, we have shown that in macrophages, expressing both GHS-R1a and CD36, hexarelin promoted an activation of PPARƔ via GHS-R1a but also through its binding to CD36. This activation led to the induction of the LXRα-ABC transporters pathway and an increase in cholesterol efflux, reducing lipid-laden macrophage content. This positive effect on macrophages was reproduced in apolipoprotein E-null mice on a high fat diet treated with hexarelin. A significant reduction in the size of atherosclerotic lesions was observed while similar increases in the expression of PPARƔ, LXRα and ABC transporters occurred in isolated peritoneal macrophages. CD36 also plays a role in fatty acid uptake, and to further investigate the impact of the interaction of hexarelin with CD36, we aimed at evaluating the role of CD36 in regulating lipid metabolism in cells devoid of GHS-R1a such as adipocytes and hepatocytes. In the present thesis, we demonstrated through its interaction with hexarelin, the ability of CD36 to decrease intracellular lipid content in both adipocytes and hepatocytes. In adipocytes, hexarelin was able to increase the expression of several genes involved in fatty acid mobilization, fatty acid oxidation but also to induce the expression of the thermogenic markers, PGC-1α and UCP-1. In addition, hexarelin increased the expression of genes involved in mitochondrial biogenesis which was accompanied by mitochondrial morphological changes in agreement with what is usually seen in highly oxidative cells. In support of these findings, we also observed an increase in the activity of cytochrome c oxidase (a component of the respiratory chain) which could reflect an increase in oxidative phosphorylation. The results generated with cultured white adipocytes suggest the ability of hexarelin to promote changes toward a brown fat-like phenotype which also occurred in vivo and was dependent on the presence of CD36. In hepatocytes, CD36 was capable of regulating cholesterol metabolism by rapidly phosphorylating LKB1 and AMPK which subsequently resulted in the inactivating phosphorylation of HMG-CoA reductase, the rate-limiting enzyme in cholesterol synthesis. Hexarelin via CD36 also induced the recruitment of insig-2 to HMGR, the committed step in HMGR degradation while lifting the exerted inhibitory effect of Erk on nuclear receptor PPARƔ activity, and promoting the recruitment of AMPK to PPARƔ coactivator PGC-1α, suggesting an enhanced transcriptional potential of PPARƔ. The results generated during my graduate studies represent unique and novel mechanisms by which CD36 is capable of regulating lipid metabolism.

Bien que le changement dans le choix des substrats énergétiques des acides gras (AGs) vers les glucides soit considéré comme bénéfique pour le cœur insuffisant, il n’est pas clair à savoir pourquoi les patients atteints de désordres de la β-oxydation (β-OX) des AGs à chaîne longue (AGCLs) développent des troubles du rythme et des cardiomyopathies. De plus, le traitement actuel ne permet pas de prévenir l’apparition du phénotype clinique chez tous les patients, spécifiquement en condition de jeûne ou de stress. Ainsi, plusieurs modèles de souris déficientes pour des enzymes impliquées dans l’oxydation des acides gras ont été développés de manière à améliorer les connaissances de la maladie ainsi que les traitements offerts aux patients. À cet égard, cette étude vise à évaluer le phénotype métabolique et fonctionnel des cœurs de souris déficientes pour le récepteur activé de la prolifération des peroxysomes-α (PPARα), un facteur de transcription des gènes impliqués notamment dans la β-OX des AGs, et pour la déshydrogénase des acyl-CoA à très longue chaîne (very-long chain acyl-CoA dehydrogenase, VLCAD), le déficit de l’oxydation des AGCLs le plus commun chez l’humain. L’approche expérimentale utilisée comprend plusieurs techniques dont (i) la perfusion ex vivo de cœur de souris au travail combinée à l’utilisation de substrats marqués au carbone 13 (13C) et à l’analyse par chromatographie gazeuse-spectrométrie de masse (GCMS), (ii) l’analyse de l’expression génique par qPCR et (iii) l’analyse de l’activité électrique du cœur in vivo par télémétrie. De manière inattendue, les résultats de cette étude menée chez la souris ont permis de mettre en évidence que des déficits pour des protéines impliquées dans l’oxydation des AGCLs sont associés à des altérations du métabolisme (i) des glucides, (ii) des AGs polyinsaturés (AGPIs), et (iii) mitochondrial, incluant l’anaplérose, en plus d’être liés à des désordres de la fonction électrique du cœur, à savoir une prolongation du segment QTc. Pris dans leur ensemble, les résultats de cette thèse pourraient servir à l’élaboration de nouvelles interventions métaboliques destinées à améliorer les traitements possibles et donc, la qualité de vie des patients atteints de désordres héréditaires de la β-OX des AGCLs. / While a shift from fatty acids to carbohydrate is considered beneficial for the failing heart, it is unclear why patients with fatty acid oxidation disorders present clinical manifestations such as cardiomyopathy, arrhythmia and conduction defects. Unfortunately, the current nutritional treatment for these patients is limited in its ability to prevent these symptoms, especially under fasting and stress conditions. Many mouse models of fatty acid oxidation deficiency have been developed to improve the knowledge of the disease and the treatment of these patients. In this regard, this study aims to characterize the metabolic and functional phenotype of hearts from mice that are deficient for the peroxisome proliferator-activated receptor α, a transcription factor for gene involved in fatty acid oxidation, and very long chain acyl-CoA dehydrogenase, the most common inherited long chain fatty acid oxidation disorder in human, under various conditions. In this study, numerous approaches have been used, which includes validated experimental paradigms, namely, (i) ex vivo heart perfusion in the working mode with concomitant evaluation of myocardial contractility and metabolic fluxes, employing 13C-labeled substrates combined with mass isotopomer analysis by gas chromatography coupled to mass spectrometry, (ii) gene expression analysis by qPCR and (iii) electrocardiogram monitoring in vivo by telemetry. Unexpectedly, results from the present thesis demonstrate that fatty acid oxidation disorders cause alterations in metabolism of (i) carbohydrates (ii) polyunsaturated fatty acids of the omega-3 type, specifically docosahaexanoic acid, and (iii) mitochondria including anaplerosis, in addition to lead to functional abnormalities, namely a prolongation of the QT interval. Altogether, results from this thesis could contribute to new metabolic therapy development to improve the quality of life of the patients with inherited long chain fatty acid oxidation disorder.

O consumo de ácidos graxos n-3 tem sido associado à proteção contra a obesidade, inflamação e resistência à insulina. Os n-3 são ligantes fracos dos receptores nucleares PPARγ, e pela ativação deste podem exercer suas ações metabólicas e anti-inflamatórias. No presente trabalho, foi investigado se o aumento da disponibilidade dos n-3 geneticamente ou por dieta, via ativação de PPARγ, protege camundongos do desenvolvimento da obesidade, intolerância a glicose e inflamação do tecido adiposo. Foi visto em um modelo com camundongos fat-1 (elevados níveis endógenos de n-3) que dentre as ações dos ácidos graxos n-3, a proteção contra o aumento de peso/adiposidade associada à obesidade, bem como a melhora da intolerância à glicose são dependentes de PPARγ. Além disso, por meio da utilização de camundongos com deleção de PPARγ em hepatócitos os dados desse trabalho mostram que os PPARγ são, ao menos em parte, essenciais ao aumento da oxidação de ácidos graxos induzida pelos n-3 devido à modulação da expressão gênica e protéica de enzimas mitocondriais e peroxissomais. / The intake of n-3 fatty acids have been associated to the protection against obesity, inflammation and insulin resistance. The n-3 fatty acids are ligands of the nuclear receptor PPARγ, and by the activation of this receptor can promote their metabolic and anti-inflammatory effects. Herein, we investigated whether increasing body n-3 fatty acids levels either genetically or by a n-3 enriched diet protects mice from diet-induced obesity, glucose intolerance and adipose tissue inflammation through PPARγ activation. Fat-1 mice were protected from diet-induced obesity, glucose intolerance and adipose tissue inflammation. To better investigate PPARγ involvement in n-3 beneficial actions, mice with genetic deletion of PPARγ specifically in hepatocytes. In spite of the absence of changes in body weight and glucose homeostasis PPARγ deletion in hepatocytes completely abolished the increase in liver fatty acid oxidation and hepatic gene expression of genes associated to mitochondrial and peroxisomal activity.