Emilie Chanseaume

Mitochondrial dysfunction results from oxidative stress in the skeletal muscle of diet-induced insulin-resistant mice

Mitochondrial dysfunction in skeletal muscle has been implicated in the development of type 2 diabetes. However, whether these changes are a cause or a consequence of insulin resistance is not clear. We investigated the structure and function of muscle mitochondria during the development of insulin resistance and progression to diabetes in mice fed a high-fat, high-sucrose diet. Although 1 month of high-fat, high-sucrose diet feeding was sufficient to induce glucose intolerance, mice showed no evidence of mitochondrial dysfunction at this stage. However, an extended diet intervention induced a diabetic state in which we observed altered mitochondrial biogenesis, structure, and function in muscle tissue. We assessed the role of oxidative stress in the development of these mitochondrial abnormalities and found that diet-induced diabetic mice had an increase in ROS production in skeletal muscle. In addition, ROS production was associated with mitochondrial alterations in the muscle of hyperglycemic streptozotocin-treated mice, and normalization of glycemia or antioxidant treatment decreased muscle ROS production and restored mitochondrial integrity. Glucose- or lipid-induced ROS production resulted in mitochondrial alterations in muscle cells in vitro, and these effects were blocked by antioxidant treatment. These data suggest that mitochondrial alterations do not precede the onset of insulin resistance and result from increased ROS production in muscle in diet-induced diabetic mice.

Subcutaneous Adipose Tissue Remodeling during the Initial Phase of Weight Gain Induced by Overfeeding in Humans

CONTEXT Deciphering the early processes occurring in adipose tissue during weight gain is a major issue for understanding the development of fat mass and obesity. Experimental overfeeding in humans is a unique situation to tackle these events. OBJECTIVE Our aim was to identify the pathways involved in sc adipose tissue remodeling during the initial phase of weight gain. RESEARCH DESIGN AND METHODS Forty-four healthy men were involved in an overfeeding protocol with a lipid-enriched diet (+760 kcal/d) for 2 months. Subcutaneous abdominal adipose tissue biopsies were taken for histology, transcriptomics, and Western blotting in the basal state, after 14 d, and at the end of the protocol. RESULTS Overfeeding significantly increased body weight (+2.5 kg) and fat mass. Reorganization of gene expression patterns occurred in adipose tissue with an up-regulation of numerous genes involved in lipid metabolism and storage, followed by clusters of genes related to angiogenesis and extracellular matrix remodeling. Histological examination showed increased microvascular density and connective tissue deposition after 56 d of overfeeding, with no changes in the number of macrophages or inflammatory cells. Inhibition of the canonical Wnt/β-catenin signaling pathway and induction of the renin-angiotensin system might be implicated in the remodeling of sc adipose tissue. CONCLUSIONS We characterize the coordinated and time-dependent processes that occur in human adipose tissue during the early phase of weight gain in healthy subjects and identify pathways representing potential targets in pathologies of adipose development, including obesity.

Visceral Fat Accumulation During Lipid Overfeeding Is Related to Subcutaneous Adipose Tissue Characteristics in Healthy Men

CONTEXT The hypothesis of a limited expansion of sc adipose tissue during weight gain provides an attractive explanation for the reorientation of excess lipids toward ectopic sites, contributing to visceral adipose depots and metabolic syndrome. OBJECTIVE Our objective was to define whether the characteristics of sc adipose tissue influence the partition of lipids toward abdominal fat depots during weight gain in healthy men. RESEARCH DESIGN AND METHODS Forty-one healthy nonobese volunteers performed a 56-day overfeeding protocol (+760 kcal/d). Insulin sensitivity was estimated by euglycemic hyperinsulinemic clamp. Changes in abdominal visceral and sc adipose tissue depots were measured by magnetic resonance imaging. The fate of ingested lipids before and after overfeeding was investigated using a [d31]palmitate test meal, and gene expression was measured by real-time PCR in sc fat biopsies. RESULTS Overfeeding led to a 2.5-kg body weight increase with large interindividual variations in abdominal sc and visceral adipose tissues. There was no relationship between the relative expansions of these 2 depots, but the increase in visceral depot was positively associated with the magnitude of the postprandial exogenous fatty acid release in the circulation during the test meal. The regulation of lipid storage-related genes (DGAT2, SREBP1c, and CIDEA) was defective in the sc fat of the subjects exhibiting the largest accumulation in visceral depot. CONCLUSIONS Characteristics of sc adipose tissue appear therefore to contribute to the development of visceral fat depot, supporting the adipose tissue expandability theory and extending it to early stages of weight gain in nonobese subjects.

Synergistic effects of caloric restriction with maintained protein intake on skeletal muscle performance in 21-month-old rats: a mitochondria-mediated pathway

Caloric restriction (CR) delays the onset of age‐related mitochondrial abnormalities but does not prevent the decline in ATP production needed to sustain muscle protein fractional synthesis rate (FSR) and contractile activity. We hypothesized that improving mitochondrial activity and FSR using a CR diet with maintained protein intakes could enhance myofibrillar protein FSR and consequently improve muscle strength in aging rats. Wistar rats (21 months old) were fed either an ad libitum (AL), 40% protein‐energy restricted (PER) or 40% AL‐isonitrogenous energy restricted (ER) diet for 5 months. ATP production, electron transport chain activity, reactive oxygen species (ROS) generation, protein carbonyl content and FSR were determined in both tibialis anterior (TA) and soleus muscle mitochondria. Myosin and actin FSR and grip force were also investigated. The ER diet led to improved mitochondrial activity and ATP production in the TA and soleus muscles in comparison with PER. Furthermore, mitochondrial FSR in the TA was enhanced under the ER diet but diminished under the PER. Mitochondrial protein carbonyl content was decreased by both the ER and PER diets. The ER diet was able to improve myosin and actin FSR and grip force. Therefore, the synergistic effects of CR with maintained protein intake may help to limit the progression of sarcopenia by optimizing the turnover rates and functions of major proteins in skeletal muscle.—Zangarelli, A., Chanseaume, E., Morio, B., Brugère, C., Mosoni, L., Rousset, P., Giraudet, C., Patrac, V., Gachon, P., Boirie, Y., Walrand, S. Synergistic effects of caloric restriction with maintained protein intake on skeletal muscle performance in 21‐month‐old rats: a mitochondria‐mediated pathway. FASEB J. 20, 2439–2450 (2006)

Overfeeding increases postprandial endotoxemia in men: Inflammatory outcome may depend on LPS transporters LBP and sCD14

SCOPE Low-grade inflammation is a recognized hallmark of obesity. Endotoxins absorbed after high-fat meals have recently been implicated. Plasma lipopolysaccharides binding protein (LBP) and soluble cluster of differentiation 14 (sCD14) have also been suggested as clinical markers of endotoxemia. In mice, the ratio LBP/sCD14 has been associated with high fat diet induced inflammation. We tested the hypothesis that healthy subjects develop inflammation differently during weight gain according to changes of LBP/sCD14 ratio. METHODS AND RESULTS Eighteen healthy men were overfed during 8 wk (+760 kcal/day). Endotoxemia, sCD14, LBP, and IL-6 were measured before and after overfeeding (OF) at fasting (n = 18) and postprandially (subcohort, n = 8). OF did not modify fasting IL-6 but increased the LBP/sCD14 ratio (P = 0.017). Subjects were categorized into tertiles for LBP/sCD14 ratio variation. Subjects in the highest tertile (+90% LBP/sCD14) increased plasma IL-6 (+26%) versus the lowest tertile due to a decrease of sCD14 associated with high LBP. The postprandial accumulation of endotoxins increased after OF (+160%). However, only four responding subjects presented increased postprandial IL-6 accumulation. CONCLUSION OF increases postprandial endotoxemia but the inflammatory outcome may be modulated by endotoxin handling in plasma. This study supports a new concept whereby inflammation setup during the initial phase of weight gain is linked to the relative variations of LBP and sCD14.

Chronological Approach of Diet-induced Alterations in Muscle Mitochondrial Functions in Rats

Objective: Mitochondrial dysfunction might predispose individuals to develop insulin resistance. Our objective was to determine whether mitochondrial dysfunction or insulin resistance was the primary event during high‐fat (HF) diet.

Enhanced Muscle Mixed and Mitochondrial Protein Synthesis Rates after a High-fat or High-sucrose Diet

Objective: Obesity and insulin resistance are associated with muscle mitochondrial dysfunction, which might be related to impairment of mitochondrial protein synthesis. This study aimed at investigating mixed and mitochondrial protein synthesis in skeletal muscle in response to dietary manipulations.

Muscle Mitochondrial Oxidative Phosphorylation Activity, But Not Content, Is Altered with Abdominal Obesity in Sedentary Men: Synergism with Changes in Insulin Sensitivity

CONTEXT Abdominal obesity is a major risk factor for muscle insulin resistance. Mitochondria may play a key role in this etiology. OBJECTIVE Changes in muscle mitochondrial content and function were examined according to abdominal obesity and insulin sensitivity in men. STUDY DESIGN AND SETTING The descriptive MitHyCal study was conducted on the general population of Clermont-Ferrand, France. PARTICIPANTS Forty-two healthy sedentary men (41.7 +/- 4.3 yr) were divided into four groups according to waist circumference: 87 cm or less (group 1, n = 10); 88-93 cm (group 2, n = 12); 94-101 cm (group 3, n = 10); and 102 cm or greater (group 4, n = 10). INTERVENTION Plasma metabolic check-up was performed, and insulin sensitivity index was calculated from glucose and insulin responses to a 3-h oral glucose tolerance test. Muscle biopsies were obtained to assess mitochondrial content, oxidative phosphorylation activity, and superoxide anion (reactive oxygen species) production. MAIN OUTCOME MEASURES Assessment of muscle mitochondrial content and function was planned before data collection began. RESULTS Abdominal obesity was negatively correlated to insulin sensitivity index (r = -0.39; P < 0.01), and only group 4 was insulin-resistant (P < 0.05). There were no between-group differences in muscle mitochondrial content and maximal activity of key oxidative enzymes. In contrast, muscle mitochondrial ADP-stimulated respiration rate was 24% higher in groups 2 and 3 compared to groups 1 and 4 (P < 0.05). Mitochondrial ATP and reactive oxygen species production rates were 27 and 48% lower in group 4 than in group 1 (P < 0.05). CONCLUSION Abdominal obesity is associated with alterations in intrinsic muscle mitochondrial function but not content. These adaptations mainly result in reduced mitochondrial ATP production rate in response to insulin resistance.

Regulation of Energy Metabolism and Mitochondrial Function in Skeletal Muscle During Lipid Overfeeding in Healthy Men

CONTEXT/OBJECTIVE The aim of this study was to evaluate the regulation of the fuel partitioning and energy metabolism in skeletal muscle during lipid overfeeding in healthy men. Design/Participants/Intervention: Thirty-nine healthy volunteers were overfed for 56 days with a high-fat diet (3180 kJ/d). Energy metabolism (indirect calorimetry) was characterized in the fasting state and during a test meal before and at the end of the diet. Skeletal muscle biopsies were taken at day 0 and day 56. MAIN OUTCOME MEASURES Change in gene expression, mitochondrial respiration, nicotinamide adenine dinucleotide (NAD(+)) content, and acetylation of peroxisome proliferator-activated receptor-γ coactivator-1α (PGC-1α) in skeletal muscle was measured. RESULTS Overfeeding increased body weight (+2.6 kg) and fat mass concomitantly with a shift in the use of substrates as energy fuel toward preferential oxidation of carbohydrates instead of lipids. Changes in lipid metabolic gene expression supported this observation, with a reduction in pyruvate dehydrogenase kinase 4 expression that could be the consequences of decreased NAD(+) concentration and reduced deacetylase activity of the sirtuins, as supported by hyperacetylation of PGC-1α after overfeeding. Interestingly, this reduction of the sirtuin PGC-1α pathway was associated with increased mitochondrial gene expression and higher respiration rate under these conditions. CONCLUSION Adaptation to lipid overfeeding and regulation of fuel partitioning in human muscle appear to rely on a dissociation between the regulatory functions of the sirtuin-PGC-1α pathway on fatty acid oxidation and on mitochondrial regulation. This may facilitate lipid storage during a period of positive energy balance while maintaining mitochondrial functions and oxidative capacities.

Impaired Resting Muscle Energetics Studied by 31P-NMR in Diet-induced Obese Rats

Objective: Mitochondrial activity is altered in skeletal muscle of obese, insulin‐resistant or type 2 diabetic patients. We hypothesized that this situation was associated with profound adaptations in resting muscle energetics. For that purpose, we used in vivo 31P‐nuclear magnetic resonance (31P‐NMR) in male sedentary Wistar rats fed with obesogenic diets known to induce alterations in muscle mitochondrial activity.