Impact of dietary manipulation on cardiac hypertrophy

Left ventricular hypertrophy (LVH) is a significant risk factor for the development of heart failure (HF), the incidence of which is increased by obesity. Diets high in fat and sugar have been linked with the development of the metabolic syndrome and obesity, and may expose the heart to a unique environment via the differential actions of dietary macronutrients. The main objectives of this study were to determine the effect of differing dietary regimens upon (i) the progression of LVH and whole organism morphology (ii) function and metabolism in the hypertrophied heart, and (iii) cardiac ceramide content.Cardiac hypertrophy was surgically induced in male Sprague-Dawley rats via abdominal aortic constriction (AC). Animals were assigned to either a diet containing 5% sucrose/7% fat (standard diet, SD), 9 % sucrose/45 % fat (high-fat diet, HFD), or 14% sucrose/44% fat (western diet, WD) for 9 weeks. LVH was observed in all AC groups but was greatest in those fed a SD or WD. Both HFD and WD resulted in a significant increase in abdominal fat mass, which was positively associated with serum concentrations of leptin.In vitro cardiac function was unaltered by any dietary regimen alone, but was significantly enhanced in hypertrophied hearts from HFD and WD-fed animals, consistent with a compensated phase of hypertrophic remodelling. This was accompanied by a small reduction in palmitate oxidation and increased reliance upon lactate, an effect which was exacerbated in hearts from WD-fed animals. In WD-fed animals, there was a substantial increase in cardiac triglyceride (TG), which was not affected by AC. PPARα protein was reduced following AC in the hearts of animals fed a SD or WD, whereas the HFD prevented this decline. CD36 protein expression was not different between control and AC animals, but was highest in those fed a WD.In addition to elevated TG, WD hearts also exhibited a significant accumulation of long-chain ceramide species (C16-C24) compared with other dietary groups; consistent with metabolic remodelling. This effect was observed independent of AC. In order to simulate a model of HF, WD animals were treated with adriamycin (ADR), and cardiac ceramide content was further increased with the specific accumulation of C16 and C18 ceramide.These findings suggest that dietary macronutrient composition can have a profound effect upon the progression of LVH. Furthermore, the enhanced ceramide content in WD hearts indicates that the macronutrient composition of this dietary profile is most deleterious to the hypertrophied heart. Prolonged exposure of the hypertrophied heart to the WD may lead to increased apoptosis and accelerate the transition to HF

Impact of Diet Composition on Insulin Resistance

Insulin resistance is a key player in the pathology of cardiometabolic diseases - obesity, hypertension, dyslipidaemia, type 2 diabetes and NAFLD. These diseases are commonly associated with a peripheral insulin resistance, but an important role of insulin is played at brain circuitries that control food behaviour and autonomic activity. Brain insulin resistance is also associated with cognition impairment and Alzheimer Disease and other neurodegenerative diseases. Disruptions in diet composition, e.g. hypercaloric diets, and patterns, as well as nutritional status contribute to the genesis of insulin resistance. In contrast, hypocaloric diets, different feed regimens and some nutrients have beneficial impacts on insulin resistance and disease development. This special issue “Impact of diet composition on insulin resistance” is developed to compile studies that highlight the beneficial or deleterious impact of different nutritional plans on insulin sensitivity and metabolism and that unravel mechanistic links between diet composition and nutritional status and the development of insulin resistance, both periphery and centrally

The pathophysiological role of physical inactivity and fat-diet to development of metabolic syndrome in an animal model

RESUMO Esta tese é suportada por uma revisão narrativa da literatura, perspetivando fornecer uma visão geral dos principais aspetos etiológicos, fisiopatológicos e clínicos da síndrome metabólica, assim como por três artigos originais, utilizando um modelo animal, que objetivaram identificar a contribuição isolada e conjugada da inatividade física e de uma dieta hiperlipídica no desenvolvimento da síndrome metabólica. Para tal, ratos Wistar machos foram alimentados com dieta hiperlipídica e/ou tiveram a atividade física restrita ao espaço da gaiola por 21 semanas. Os resultados revelaram que a dieta hiperlipídica e a inatividade física induziram um característico fenótipo adulto, com ratos maiores e mais leves, possuindo órgãos mais leves e uma expressiva deposição de gordura retroperitoneal sem, contudo, ganho de peso. Os trabalhos empíricos também revelaram a predominância da dieta gorda sobre a inatividade física na indução de desarranjos metabólicos, uma vez que apenas os animais alimentados com dieta gorda desenvolveram síndrome metabólica, independentemente dos níveis de atividade física, com maladaptações hepáticas e do pâncreas endócrino evidenciando uma intensa resposta inflamatória, aumento do conteúdo local de colágeno e da apoptose celular em ambos os órgãos. Estes resultados permitem concluir que a dieta rica em gordura é um fator patogénico predominante na indução da síndrome metabólica e das maladaptações hepáticas e pancreáticas em um modelo animal, comparativamente à inatividade física. Ainda assim, comparativamente à dieta gorda, mais determinante na indução da intolerância à glicose, a inatividade física parece ser mais decisiva no comprometimento da sensibilidade à insulina. Níveis mais elevados de atividade física não parecem prevenir o desenvolvimento da síndrome metabólica e das alterações orgânicas associadas após 21 semanas de protocolo experimental, mas atenuam os transtornos metabólicos e estruturais induzidos pela dieta gorda. Palavras Chave: Physical inactivity, fat diet, metabolic syndrome, liver disorder, and endocrine pancreas disarrangement.This thesis is supported by a literature narrative review aiming to provide an overview of the metabolic syndrome main etiological, pathophysiological and clinical aspects, as well as three original articles using an animal model that aimed to identify the physical inactivity and the hyperlipidic diet isolated and conjugated contribution in the metabolic syndrome development. For this, male Wistar rats were fed with a high-fat diet and/or had the physical activity restricted to the cage space for 21 weeks. The results revealed that the high-fat diet and physical inactivity induced a singular adult phenotype, with larger and lighter rats, having lighter organs and an expressive retroperitoneal fat deposition without, however, gaining weight. The empirical studies also revealed the high-fat diet predominance over physical inactivity in inducing metabolic disorders, since only high-fat diet fed-animals developed metabolic syndrome, regardless of physical activity levels, with the hepatic and endocrine pancreas maladaptations evidencing an intense inflammatory response, increased local collagen content and cellular apoptosis in both organs. These results allow us to conclude that the high-fat diet is a predominant pathogenic factor in inducing the metabolic syndrome and the hepatic and pancreatic maladaptations in an animal model, compared to physical inactivity. Nevertheless, in comparison to the high-fat diet, which is more important in the glucose intolerance induction, physical inactivity seems to be more decisive in the impairment of insulin sensitivity. Higher levels of physical activity do not seem to prevent the metabolic syndrome development and related organic changes after 21 weeks of experimental protocol but attenuate the metabolic and structural disorders induced by the high-fat diet

Western diet and its effect on motivation, learning and memory

In Western society, the prevalence of a hyper-caloric diet consisting of a high consumption of fat and simple sugars has coincided with an exponential rise in diabetes as well as cardiovascular diseases and several types of cancer. While some of these medical comorbidities are themselves associated with adverse cognitive effects, recent studies have also linked the western diet to an increased incidence of Alzheimer’s disease and mild cognitive impairment. Moreover, these disorders are considered to be major risk factors for dementia indicating that these metabolic effects have both peripheral and central effects. Rats that have been a fed high fat diet (HFD) have shown indications to be cognitively impaired compared to those fed a normal chow diet. Research suggests that HFD consumption has a deleterious effect on spatial learning and memory, and this effect consequently may be mediated by damage to the hippocampus. To date however, there is conflicting results regarding the motivational and other types of learning implications after HFD consumption. The primary animal model of obesity used in this thesis is the western diet (WD) model of obesity in rats. This model mimics the ‘western’ diet typically consumed in developed ‘western’ countries by feeding rats a WD chow (containing 22% w/w fat) or a control chow diet (containing 6% w/w fat). Using this model, we explored the ability of 8 weeks of WD consumption to influence changes to Pavlovian & instrumental conditioning as well as motivation. This study used well characterised tests to assess whether learnt feeding behaviour can be affected by WD consumption. The ability for WD consumption to alter motivational drive in varying states of food deprivation was also investigated. Results from this study found that rats fed a WD for 8 weeks did not affect Pavlovian conditioning or motivational state. The effect of WD consumption on instrumental conditioning is still indeterminate with conflicting results. There was no change in instrumental conditioning in rats fed a WD. However, WD fed rats were impaired in progressive ratio instrumental conditioning acquisition. Additionally, WD exposed rats were no different to changes in states of food deprivation compared to control diet counterparts. A further study investigated whether a period of 12 weeks WD consumption can affect spatial working and reference memory. No changes in spatial working or reference memory were observed in WD rats. Due to the assumed role of c-Fos, an immediate-early gene and corresponding protein, in learning and use as a surrogate marker of neuronal activation, neuronal activation in selected brain regions was evaluated. We demonstrated that WD consumption increased neuronal activation after environmental novelty in the striatum. Other brain regions involved in memory and learning were also investigated with no differences in neuronal activation before and after environmental novelty between control and WD animals. In a series of experiments, we explored the ability of WD consumption to influence change in neurotransmitters involved in memory and learning. The expression of serotonin (5-HT) receptors 5-HT2A, 5-HT2C and the 5-HT transporter within the striatum was also investigated, as previous studies have shown that serotonin is implicated in feeding behaviour following WD consumption. Both 5-HT2C receptor and 5-HT transporter expression were found to be increased in WD rats. In contrast, 5-HT2A receptor expression was unchanged in the striatum. This suggests that WD consumption has a selective capacity to alter the serotoninergic system. Furthermore due to the well-recognised role of dopamine in cognition, including motivation, reward, punishment and working memory, the modification of dopamine metabolism was evaluated. High performance liquid chromatography analysis found reduced levels of striatal dopamine, with alterations in dopamine metabolism and turnover also evident in the hippocampus after WD consumption. These neurotransmitter changes were also observed to be independent of any change in cognitive ability. This suggests that WD consumption may instigate dopaminergic and serotoninergic adaptations before cognitive impairment transpire. The early life nutritional environment was also investigated to ascertain if early life obesity may contribute to cognitive impairment using a neonatal overfeeding rat model of obesity. As early life is a critical window of vulnerability to long-term programming of health, cognitive assessment was performed by utilizing spatial memory function in the Y-maze test and also spatial reference and working memory using the delayed win-shift task (DWSh) in the radial arm maze. Neonatally overfed rats took longer to learn the DWSh task indicating a poorer memory acquisition compared to control. No change of spatial memory in the less cognitively demanding Y-maze test was observed in neonatally overfed rats. The potential of a synergistic effect of WD consumption in the APPswe/PS1dE9 double transgenic Alzheimer’s mice model (APDE9) animal model memory and anxiety-like behaviour was assessed. Metabolically, this study identified that APDE9 mice fed a WD showed impaired glucose tolerance but not in wild-type WD mice or ADPE9 mice fed the control diet indicating impaired insulin receptor signalling. Both APDE9 mice fed control or WD showed a spatial memory deficit in the Y-maze when compared to their wild-type counterparts. There was no observed synergistic effect of WD consumption and APDE9 phenotype in the Y-maze. Additionally no change in anxiety-like behaviour was discerned using the open field test and the light/dark preference test. Findings from this thesis indicate that WD consumption alone does not affect cognition using a variety of behavioural tasks. Whilst central changes in the dopaminergic and serotoninergic system ensue following WD consumption however, whether these changes occur before cognitive impairment is still unclear. The time period in which the obese phenotype transpires appears to play a factor in cognitive impairment as shown by the results in the neonatal overfeeding study. Additionally we demonstrated that WD consumption does not affect spatial memory but a possible synergistic interplay between the APDE9 mice phenotype and WD consumption may have a deleterious effect of spatial memory. Further work is necessary to elucidate the factors that contribute to the onset of cognitive impairment observed in rat models of obesity

Cellular & Molecular Mechanisms That Contribute to the Early Development of Skeletal Muscle & Systemic Insulin Resistance

Indiana University-Purdue University Indianapolis (IUPUI)Insulin resistance starts years before type 2 diabetes (T2D) diagnosis, even before recognition of prediabetes. Mice on a high fat diet have a similar early onset of insulin resistance, yet the mechanism remains unknown. Several studies have demonstrated that skeletal muscle insulin resistance resulting from obesity or high fat feeding does not stem from defects in proximal insulin signaling. Our lab discovered that excess plasma membrane cholesterol impairs insulin action. Excess cholesterol in the plasma membrane causes a loss of cortical actin filaments that are essential for glucose transporter GLUT4 regulation by insulin. Our cell studies further revealed that increased hexosamine biosynthesis pathway (HBP) activity increases O-linked N-acetylglucosamine modification of the transcription factor Sp1, leading to transcription of HMG-CoA reductase (HMGR), the rate-limiting enzyme in cholesterol biosynthesis. Our central hypothesis is that cholesterol accumulation mediated by HBP activity is an early reversible mechanism of high-fat diet-induced insulin resistance. We performed a series of studies and found that early high-fat feeding-induced insulin resistance is associated with a buildup of cholesterol in skeletal muscle membranes (SMM). Akin to the antidiabetic effect of caloric restriction, we found that high-fat diet removal fully mitigated SMM cholesterol accumulation and insulin resistance. Furthermore, using the cholesterol-binding agent methyl-β-cyclodextrin (MβCD), studies established causality between excess SMM cholesterol and insulin resistance. To begin to assess the role of the HBP/Sp1 in contributing to de novo cholesterol biosynthesis, SMM accumulation, and insulin resistance we treated high-fat fed mice with an Sp1 inhibitor, mithramycin. We found that mithramycin prevented SMM cholesterol accumulation and insulin resistance. This series of studies provide evidence that HBP/Sp1-mediated cholesterol accumulation in SMM is a causal, early and reversible mechanism of whole body insulin resistance

The effects of polyphenol-rich extracts on obesity-linked metabolic diseases

Tableau d'honneur de la FÉSPL'obésité et son large spectre de maladies associées ont atteint des proportions pandémiques inquiétantes, soulignant la nécessité d’identifier des stratégies alternatives afin de lutter contre ce problème. À ce titre, les régimes riches en fruits et légumes représentent des déterminants bien établis d'une incidence plus faible de ces désordres métabolique. Grandement soutenus par des évidences épidémiologiques reliant les régimes riches en polyphénols et un meilleur état de santé, des efforts considérables ont été déployés afin d’étudier les bienfaits de ces métabolites secondaires des plantes. Malgré tout, les mécanismes par lesquels ces phytoéléments améliorent la santé métabolique demeurent encore mal compris, ce qui en justifie une étude plus approfondie. D’autre part, de plus en plus d’évidences indiquent que les bactéries intestinales exercent un important contrôle sur des aspects clés du métabolisme, et on comprend aujourd’hui que plusieurs phytoéléments de baies ont une biodisponibilité limitée, atteignant ainsi le colon qui abrite la plus vaste part du microbiote intestinal. Le travail présenté dans cette thèse vise donc à étudier l’impact de phytoéléments de baies sur le syndrome métabolique de souris soumises à une diète obèsogène et d’en comprendre le rôle du microbiote intestinal dans ces effets. En traitant quotidiennement ces animaux avec des extraits riches en polyphénols d'une gamme de baies aux compositions polyphénoliques variées, nous avons montré que les extraits les plus bioactifs (c.- à-d., canneberge, cloudberry, alpine bearberry, lingonberry et camu camu) partagent la capacité de diminuer l'inflammation intestinale, l’entotoxémie métabolique, la stéatose hépatique et la résistance à l'insuline. L'analyse des populations microbiennes fécales par séquençage du gène 16S ARNr a révélé que l'état métabolique amélioré lié à l'administration de ces extraits était associé à un remodelage draconien du microbiote intestinal, marqué par une expansion d'Akkermansia muciniphila. Cette bactérie intestinale est fortement associée à un faible niveau d’adiposité chez l’humain et son administration à des souris obèses a été montrée suffisante pour renverser le syndrome métabolique. Par ailleurs, les résultats présentés dans cette thèse suggèrent que les polymères de polyphénols, à savoir les proanthocyanidines et les ellagitannins, pourraient bien être des iv molécules clés dans les effets bénéfiques observés, ouvrant la voie à plus de recherche en ce sens. L’ingestion régulière de ces polyphénols par la consommation de canneberges, de cloudberry, d'alpine bearberry, de lingonberry et de camu camu représentent donc une stratégie efficace pour la prévention de désordres métaboliques associés à l’obésité. Cet ouvrage ouvre ainsi à de nouveaux concepts mécanistiques, ciblant l’axe intestin-foie et le microbiote intestinal pour expliquer les effets bénéfiques des polyphénols sur la santé métabolique.Obesity and its wide spectrum of associated diseases have reached worrisome pandemic proportions, underscoring the need for alternative strategies to fight this problem. Plant-rich diets are well-established determinants of a lower incidence of obesity-related diseases, and fruits are important components of these diets. Supported by strong epidemiological evidence linking polyphenol-rich diets and better health status, research has been focused on the potential health effects of these plant secondary metabolites, albeit the mechanisms by which these poorly bioavailable phytonutrients improve metabolic health remains are not yet fully understood. Since there is compelling evidence for a relationship between host metabolic control and the gut microbiota, the work presented in this thesis aimed to investigate the impact of polyphenol-rich berry extracts on features of the metabolic syndrome in diet-induced obese mice. The work presented in this thesis also focuses on the relationship between putative gut microbial alterations driven by dietary polyphenols and its relevance to host metabolism. By daily treating dietinduced obese mice with polyphenol-rich extracts of a wide range of berries (with varied polyphenolic concentration and composition) we demonstrated that the most bioactive extracts (i.e., cranberry, cloudberry, alpine bearberry, lingonberry and camu camu) shared in common the ability to dampen intestinal inflammation and bacterial lipopolysaccharide leakage to systemic circulation, findings associated with reduced hepatic steatosis and improved insulin resistance. 16S rRNA genebased analysis of fecal DNA revealed that the improved metabolic status linked to the administration of these polyphenolic extracts was associated with a drastic gut microbial remodeling, marked by a consistent bloom of Akkermansia muciniphila. This gut bacterium is strongly associated with leanness in humans and its administration to obese mice reversed features of the metabolic syndrome. The findings presented in this thesis suggest that polymers of polyphenols, namely proanthocyanidins and ellagitannins, may have a superior impact on the gut-liver homeostasis, supporting further research on these particular classes of phenolic phytonutrients. While bringing evidence that substantiate the regular consumption of sources of proanthocyanidins and ellagitannins as a strategy to prevent prevalent chronic diseases associated with obesity, this work provides novel mechanistic insights pointing to the gut-liver axis and the gut microbiota as primary targets of dietary polyphenols in order to improve metabolic health

Insulin Resistance

This book has been made possible by the contributions of leading scientists and clinicians from upcoming and interdisciplinary fields of research concerning the molecular and clinical features of insulin resistance. Multiple metabolic disturbances associated with Insulin Resistance include inflammatory cytokines, adipokines, endothelial dysfunction, tissue-specific defects in insulin action and signaling, oxidative stress, ectopic lipid deposition, and disordered neuroregulation. This book aims to encourage scientists and physicians - working separately on various aspects of Insulin resistance and metabolic syndrome for early detection of the first signs indicating the onset of a metabolic misbalance in order to prevent the consecutive cascades which lead to metabolic syndrome, resulting in the so-called diseases of modern civilization - cancer, diabetes and hypertension

Mitochondrial function in metabolic health

Inactivity-related diseases (such as obesity and insulin resistance) are a burden on Western society, with low cardiorespiratory fitness (maximal aerobic capacity, VO2max) a strong independent predictor of metabolic disease and all-cause mortality. The etiological basis of these disorders is polygenic and highly dependent on the environment (i.e., existing genes interact with environmental factors to result in phenotypic expression of these diseases). The work undertaken for this thesis comprised a series of independent but related studies aimed at enhancing our understanding of the relationship between genetic factors and environmental stimuli in determining the capacity for aerobic energy production in skeletal muscle and white adipose tissue (WAT). Rodent models of divergent intrinsic running capacity (and, by association, metabolic health profile) and environmental interventions (i.e., diet and exercise) were employed in order to explore some of the mechanisms that determine the capacity for mitochondrial energy production in these two insulin-responsive tissues. In the first investigation (Chapter 2), Long-Evans rats were given ad libitum access to either a Western Diet (WD; 40% energy (E) from fat, 17 % protein, and 43% carbohydrate (30% sucrose); n=12) or a control diet (CON; 16% E from fat, 21% protein, and 63% carbohydrate (10% sucrose); n=12) for 12 wk. Rats fed the WD consumed 23% more E than CON (P=0.0001), which was associated with greater increases in body mass (23%; P=0.0002) and adiposity (17%; P=0.03). There were no differences in fasting blood glucose concentration of glucose tolerance between diets, although fasting insulin was increased by 30% (P=0.007). Fasting serum triglycerides were also elevated in WD (86%; P=0.001). The maximal respiratory capacity of m. soleus (soleus) was greater following the WD (37%; P=0.02), as were the maximal activities of several mitochondrial enzymes (citrate synthase, CS; β-hydroxyacyl-CoA dehydrogenase, β-HAD; carnitine palmitoyltransferase). Protein expression of CS, uncoupling protein (UCP)-3, and individual respiratory complexes was greater after WD (all P<0.05) despite no differences in the expression of peroxisome proliferator activated receptor-γ coactivator-1α (PGC-1α) mRNA or protein. The finding that the mitochondrial machinery was increased in skeletal muscle in response to the WD led to the conclusion that mitochondrial energy production pathways were up-regulated in order to cope with the sudden increased flux of energy substrates to metabolically active tissues. It was suggested that elevated skeletal muscle respiratory capacity would be, at least in the short term, protective against lipid-induced impairments in glycemic control. Given that VO2max also has a genetic underpinning, the second investigation (Chapter 3) sought to identify whether intrinsic running capacity (and, by association, metabolic health) was associated with skeletal muscle mitochondrial content and/or oxidative capacity. Eleven-wk old genetically heterogeneous rats with inborn high- (HCR) and low- (LCR) running capacity were studied in the absence of exercise training. LCR rats (n=12) were 28% heavier (P=0.0001), and fasting serum insulin concentrations were 62% greater than in HCR rats (n=12; P=0.02). In contrast, HCR rats had better glucose tolerance (P=0.01) and reduced adiposity (P=0.02). In soleus, maximal respiratory capacity was 21% greater in HCR rats (P=0.001), for which the relative contribution of fat oxidation was 20% higher than LCR rats (P=0.02). This was associated with increased CS (33%; P=0.009) and β-HAD activities (33%; P=0.0003). In m. extensor digitorum longus (EDL), CS activity was 29% greater (P=0.01) and β-HAD activity was 41% greater (P=0.0004) in HCR compared to LCR rats. Mitochondrial DNA was also elevated in the EDL of HCR rats (35%; P=0.049) and soleus (44%; P=0.16). Additionally, HCR rats had increased protein abundance of individual mitochondrial respiratory complexes, CS, and UCP-3 in both muscle types (all P<0.05). The finding that both mitochondrial machinery and capacity were elevated in HCR compared to LCR rats is consistent with the observation that endurance trained individuals have a greater reliance on lipid-based fuels as an energy source, and explains, in part, how intrinsically determined skeletal muscle metabolism contributes to the phenotype of running capacity and its correlated traits. WAT plays a central role in regulating whole-body lipid metabolism, with the metabolic activity of WAT being a crucial factor for substrate metabolism in other peripheral tissues. Thus, the primary aim of the third investigation (Chapter 4) was to characterize the expression and activity of mitochondrial proteins important to energy production pathways in WAT from the LCR and HCR rat phenotypes. Additionally, since exercise training has recently been shown to alter important aspects of WAT energy metabolism (such as improved insulin action and elevated expression of PGC- 1α and UCP-1), the effect of a short-term treadmill running protocol (same cumulative distance (~10 km) over 6 wk) on WAT from LCR and HCR rats was also investigated. LCR and HCR rats (n=10 per group, 22 wk old) were studied with or without exercise training. In untrained rats, the abundance of individual mitochondrial respiratory complexes, CS, and PGC-1α was similar for both phenotypes, although, CS activity showed a tendency to be greater in HCR (50%; P=0.09). Exercise training increased CS activity in both phenotypes but did not alter mitochondrial protein content. Training increased the expression and phosphorylation of proteins with roles in β-adrenergic signaling, including the β3-adrenergic receptor (increased 16% in LCR; P<0.05), neuron-derived orphan receptor-1 (decreased 24% in LCR and 21% in HCR; both P<0.05), phosphor-adipose triglyceride lipase (increased 25% in HCR; P<0.05), perilipin (increased 25% in HCR; P<0.05), comparative gene identification-58 (increased 15% in LCR; P<0.05), and the glucose transport protein GLUT4 (increased 16% in HCR; P<0.0001). A training effect was also observed for the phosphorylation status of the stress kinases p38 mitogen-activated protein kinase (decreased 12% in LCR and 20% in HCR; both P<0.05) and c-JuN terminal kinase 1/2 (increased 29% in LCR and 20% in HCR; both P<0.05). It was concluded that in the LCR-HCR rat model system, mitochondrial protein expression in WAT is not affected by intrinsic running capacity or short-term exercise training. However, training does induce alterations in the activity and expression of several proteins that are essential to the intracellular regulation of WAT metabolism. In summary, this thesis has identified several novel mechanisms by which mitochondrial function/adaptations can influence the capacity for energy substrate metabolism in skeletal muscle and WAT