Project description:Existing controversy regarding the importance of AMP-activated protein kinase (AMPK) in fatty acid (FA) oxidation in skeletal muscle with contraction/exercise may to some extent pertain to redundant AMPKα1 signaling. Using a mouse model lacking both AMPKα1 and -α2 in skeletal muscle specifically (mdKO) we hypothesized that FA utilization would be impaired in skeletal muscle. Calorimetric analysis showed a similar respiratory exchange ratio (RER) of AMPKα WT and mdKO mice when fed normal chow, a high fat diet or with prolonged fasting. Though, in vivo treadmill exercise at the same relative intensity induced a higher RER in mdKO mice compared to WT (WT=0.81; mdKO=0.87; p<0.01) indicating a decreased utilization of FA. Ex vivo incubation of soleus muscle revealed that basal and contraction-induced FA oxidation was impaired in mdKO mice, suggesting that the increased RER during in vivo running exercise originated from decreased skeletal muscle FA oxidation. A decreased muscle protein expression of CD36 and FABPpm (by 17-40%) together with abolishment of TBC1D1 Ser237 phosphorylation in mdKO mice, may result in lower FA transport capacity and FA transport protein translocation to sarcolemma, respectively. In summary this study shows that the catalytically active AMPKα subunits are required for normal stimulation of FA utilization during exercise and contractions.
Project description:Influx of Ca2+ across the inner mitochondrial membrane via the mitochondrial Ca2+ uniporter (MCU) enhances the activity of several electron transport chain dehydrogenases and the F1F0 ATP synthase. In this study, we investigated the role of MCUb, an MCU complex gene product that is a direct inhibitor of MCU mediated Ca2+ influx. We find MCUb expression to be induced by caloric restriction in heart, skeletal muscle, liver and kidney where it functions as a metabolic activator of mitochondrial fatty acid utilization. Mice selectively deficient for Mcub in skeletal muscle showed a metabolic signature of deficient fatty acid utilization in muscle, associated with progressive age-related obesity, glucose intolerance and metabolic syndrome. To define transcriptional changes underlying, and potentially contributing to this regulation of Ca2+-dependent mitochondrial fatty acid utilization, microarray analyses of tibialis anterior (TA) muscle from control and knockout mice was carried out. We used microarrays to elucidate effects of MCU and MCUb ablation on transcriptional profiles of TA muscle
Project description:Time-restricted feeding (TRF) has gained attention as a dietary regimen that promotes metabolic health. This study sought to determine if ketone flux in skeletal and cardiac muscles plays an essential role in conferring the health benefits of an intermittent TRF (iTRF) schedule. Notably, we found that the ketolytic enzyme, beta-hydroxybutyrate dehydrogenase 1 (BDH1), is uniquely enriched in isolated mitochondria derived from heart and red/oxidative skeletal muscles, which also have high capacity for fatty acid oxidation (FAO). Using mice with muscle/heart-specific BDH1 deficiency, we discover that this enzyme is required for optimal FAO efficiency and exercise tolerance during acute fasting. Additionally, iTRF leads to robust molecular remodeling of muscle tissues and BDH1 flux is indeed required for the full adaptive benefits of this regimen, including increased lean mass, mitochondrial hormesis, and metabolic rerouting of pyruvate. In sum, ketone utilization enhances mitochondrial bioenergetics and supports iTRF-induced remodeling of skeletal muscle and heart.
Project description:Exercise stimulates systemic and tissue-specific adaptations that protect against lifestyle related diseases including obesity and type 2 diabetes. Exercise places high mechanical and energetic demands on contracting skeletal muscle, which require finely-tuned protein post-translational modifications involving signal transduction (e.g. phosphorylation) to elicit appropriate short- and long-term adaptive responses. To uncover the breadth of protein phosphorylation events underlying the adaptive responses to endurance exercise and skeletal muscle contraction, we performed global, unbiased mass spectrometry-based phosphoproteomic analyses of skeletal muscle from two rodent models, in situ muscle contraction in rats and treadmill-based endurance exercise in mice.
Project description:To investigate microRNAs related to mitochondria biogenesis in skeletal muscle, microRNA expressions during skeletal muscle differentiation and exercise were analyzed in vivo and in vitro. Murine skeletal muscle cell (C2C12) were assigned to undifferentiated, differentiated, and passively stretched (exercise mimicked). C57BL/6S mice were assigned to resting, acute exercise (1day), and chronic exercise (7days). Low molecular weight RNA (< 200 nucleotides) was isolated from C2C12 cell or tibialis anterior muscle of mice and hybridized to Ncode microRNA microarrays. The experiment was performed using a loop design for the data analysis.
Project description:Acute aerobic exercise has been shown to improve skeletal muscle mitochondrial function and completeness of fatty acid β-oxidation which contribute to improved insulin sensitivity. The effectiveness of acute exercise on improving mitochondrial adaptations, leading to improved insulin sensitivity, in overweight/obese (Ov/Ob) individuals is controversial. This study aimed to determine the effects of acute exercise on epigenetic regulation of genes involved in skeletal muscle mitochondrial adaptations in lean vs Ov/Ob men.
Project description:We performed the circadian transcriptome analysis using the skeletal muscle from sedentary and exercised mice either in the early rest phase (ZT3) or in the early active phase (ZT15). By the combination with circadian transcriptomic and metabolomic analysis, we revealed time-of-day-dependent remodeling of circadian muscular metabolic pathways involved in glucose and glycerol metabolism after exercise. We found that only exercise in the early active phase elevates the levels of genes encoding glycolytic enzymes followed by the activation of fatty acid oxidation, branched-chain amino acid catabolism and ketogenesis/ketosis. This study demonstrates that time-of-day is a critical factor to modulate the impact of exercise on metabolic pathways within skeletal muscle.
Project description:We address whether the functions of HDAC3 in skeletal muscle require its enzyme activity. By mutating the NCoR/SMRT corepressors in a knock-in mouse model named NS-DADm, we ablated the enzymatic activity of HDAC3 without affecting its protein levels. Compared to the control mice, skeletal muscles from NS-DADm mice showed lower force generation, enhanced fatigue resistance, enhanced fatty acid oxidation, reduced glucose uptake during exercise, upregulated expression of metabolic genes involved in branched-chain amino acids (BCAAs) catabolism, and aging-associated reduction in muscle mass, without changes in the muscle fiber type composition or mitochondrial protein content. These findings demonstrate that the metabolic function of HDAC3 in skeletal muscles requires its enzymatic activity.
Project description:Acute aerobic exercise has been shown to improve skeletal muscle mitochondrial function and completeness of fatty acid β-oxidation which contribute to improved insulin sensitivity. The effectiveness of acute exercise on improving mitochondrial adaptations, leading to improved insulin sensitivity, in overweight/obese (Ov/Ob) individuals is controversial. This study aimed to determine the effects of acute exercise on epigenetic regulation, specifically nucleosome positioning, of genes involved in skeletal muscle mitochondrial adaptations in lean vs Ov/Ob men.
Project description:This experiment was conducted to identify target genes of the peroxisome proliferator-activated receptor beta (PPARb) in skeletal muscle of transgenic mice that overexpressed PPARb. The following abstract from the submitted manuscript describes the major findings of this work. The Nuclear Receptor Transcription Factor PPARbeta/delta Programs Muscle Glucose Metabolism. Zhenji Gan, Eileen Burkart-Hartman, Dong-Ho Han, Brian Finck, Teresa C. Leone, John Holloszy, and Daniel P. Kelly. To identify new gene regulatory pathways controlling skeletal muscle energy metabolism, comparative studies were conducted on muscle-specific transgenic mouse lines expressing the nuclear receptors, PPARalpha (MCK-PPARalpha) or PPARbeta/delta (MCK-PPARbeta/delta). MCK-PPARbeta/delta mice are known to have enhanced exercise performance whereas MCK-PPARalpha mice perform at low levels. Transcriptional profiling revealed that the lactate dehydrogenase (Ldh)b/Ldha gene expression ratio is increased in MCK-PPARbeta/delta muscle, an isoenzyme shift that diverts pyruvate into the mitochondrion for the final steps of glucose oxidation. PPARbeta/delta gain- and loss-of-function studies in skeletal myotubes demonstrated that PPARbeta/delta, but not PPARalpha, interacts with the exercise inducible kinase, AMP-activated protein kinase (AMPK), to synergistically activate Ldhb gene transcription by cooperating with myocyte enhancer factor 2A (MEF2A), in a PPARbeta/delta ligand-independent manner. MCK-PPARbeta/delta muscle was shown to have high glycogen stores, increased levels of GLUT4, and augmented capacity for mitochondrial pyruvate oxidation suggesting a broad reprogramming of glucose utilization pathways. Lastly, exercise studies demonstrated that MCK-PPARbeta/delta mice had lower circulating levels of lactate compared to non-transgenic controls, while exhibiting supranormal performance on a high intensity exercise regimen. These results identify a transcriptional regulatory mechanism that increases capacity for muscle glucose utilization in a pattern that resembles the effects of exercise training. Keywords: muscle, exercise, nuclear receptors, glucose metabolism, gene regulation RNA from two wild-type (non-transgenic (NTG)) and two PPARbeta overexpressing (MCK-PPARb) mice was analyzed. Two replicates of each are provided.