Mitochondrial energy metabolism in a model of undernutrition induced by dexamethasone

Reduced PGC-1β protein expression may underlie corticosterone inhibition of mitochondrial biogenesis and oxidative phosphorylation in chicken muscles

To uncover the molecular mechanism underlying glucocorticoid-induced loss of mitochondrial integrity in skeletal muscles, studies were performed to investigate whether the peroxisome proliferator-activated receptor γ coactivator 1 (PGC-1)-mediated pathway was involved in this process. In an in vivo trial, 3 groups of 30-d-old Arbor Acres male broilers were randomly subjected to one of the following treatments for 7 days: corticosterone (CORT, 30 mg/kg diet), control (blank), and pair-feeding (restricted to the same feed intake as for the CORT treatment), each with 6 replicates of 15 birds. Mitochondrial abundance, morphology, and function were determined in the pectoralis major and biceps femoris muscles. In an in vitro trial, a primary culture of embryonic chick myotubes was incubated with a serum-free medium for 24 h in the presence or absence of CORT (0, 200, and 1,000 nM). Results showed that CORT destroyed mitochondrial ultrastructure (p < 0.01), and decreased the enzymatic activity and protein expression of respiratory chain complexes (p < 0.05), leading to an inferior coupling efficiency (p < 0.05). As reflected by a decline in mitochondrial density (p < 0.01) and mitochondrial DNA copy number (p < 0.05), CORT reduced mitochondrial contents. Among all three PGC-1 family members, only PGC-1β was down-regulated by CORT at the protein level (p < 0.05). Some aspects of these responses were tissue-specific and seemed to result from the depressed feed intake. Overall, CORT may impair mitochondrial biogenesis and oxidative phosphorylation in a PGC-1β-dependent manner in chicken muscles.

Mitochondrial oxidative phosphorylation response overrides glucocorticoid-induced stress in a reptile

Stress hormones and their impacts on whole organism metabolic rates are usually considered as appropriate proxies for animal energy budget that is the foundation of numerous concepts and models aiming at predicting individual and population responses to environmental stress. However, the dynamics of energy re-allocation under stress make the link between metabolism and corticosterone complex and still unclear. Using ectopic application of corticosterone for 3, 11 and 21 days, we estimated a time effect of stress in a lizard (Zootoca vivipara). We then investigated whole organism metabolism, muscle cellular O₂ consumption and liver mitochondrial oxidative phosphorylation processes (O₂ consumption and ATP production) and ROS production. The data showed that while skeletal muscle is not impacted, stress regulates the liver mitochondrial functionality in a time-dependent manner with opposing pictures between the different time expositions to corticosterone. While 3 days exposition is characterized by lower ATP synthesis rate and high H₂O₂ release with no change in the rate of oxygen consumption, the 11 days exposition reduced all three fluxes of about 50%. Oxidative phosphorylation capacities in liver mitochondria of lizard treated with corticosterone for 21 days was similar to the hepatic mitochondrial capacities in lizards that received no corticosterone treatment but with 40% decrease in H₂O₂ production. This new mitochondrial functioning allows a better capacity to respond to the energetic demands imposed by the environment but do not influence whole organism metabolism. In conclusion, global mitochondrial functioning has to be considered to better understand the proximal causes of the energy budget under stressful periods.

The Effect of Long-Lasting Swimming on Rats Skeletal Muscles Energy Metabolism after Nine Days of Dexamethasone Treatment

This study investigates the effect of Dexamethasone (Dex) treatment on blood and skeletal muscle metabolites level and skeletal muscle activity of enzymes related to energy metabolism after long-duration swimming. To evaluate whether Dex treatment, swimming, and combining these factors act on analyzed data, rats were randomly divided into four groups: saline treatment non-exercise and exercise and Dex treatment non-exercised and exercised. Animals in both exercised groups underwent long-lasting swimming. The concentration of lipids metabolites, glucose, and lactate were measured in skeletal muscles and blood according to standard colorimetric and fluorimetric methods. Also, activities of enzymes related to aerobic and anaerobic metabolism were measured in skeletal muscles. The results indicated that Dex treatment induced body mass loss and increased lipid metabolites in the rats’ blood but did not alter these changes in skeletal muscles. Interestingly, prolonged swimming applied after 9 days of Dex treatment significantly intensified changes induced by Dex; however, there was no difference in skeletal muscle enzymatic activities. This study shows for the first time the cumulative effect of exercise and Dex on selected elements of lipid metabolism, which seems to be essential for the patient’s health due to the common use of glucocorticoids like Dex.

Chronic stress, energy transduction, and free-radical production in a reptile

Stress hormones, such as corticosterone, play a crucial role in orchestrating physiological reaction patterns shaping adapted responses to stressful environments. Concepts aiming at predicting individual and population responses to environmental stress typically consider that stress hormones and their effects on metabolic rate provide appropriate proxies for the energy budget. However, uncoupling between the biochemical processes of respiration, ATP production, and free-radical production in mitochondria may play a fundamental role in the stress response and associated life histories. In this study, we aim at dissecting sub-cellular mechanisms that link these three processes by investigating both whole-organism metabolism, liver mitochondrial oxidative phosphorylation processes (O₂ consumption and ATP production) and ROS emission in Zootoca vivipara individuals exposed 21 days to corticosterone relative to a placebo. Corticosterone enhancement had no effect on mitochondrial activity and efficiency. In parallel, the corticosterone treatment increased liver mass and mitochondrial protein content suggesting a higher liver ATP production. We also found a negative correlation between mitochondrial ROS emission and plasma corticosterone level. These results provide a proximal explanation for enhanced survival after chronic exposure to corticosterone in this species. Importantly, none of these modifications affected resting whole-body metabolic rate. Oxygen consumption, ATP, and ROS emission were thus independently affected in responses to corticosterone increase suggesting that concepts and models aiming at linking environmental stress and individual responses may misestimate energy allocation possibilities.

Functional proteomic analysis of corticosteroid pharmacodynamics in rat liver: Relationship to hepatic stress, signaling, energy regulation, and drug metabolism

Corticosteroids (CS) are anti-inflammatory agents that cause extensive pharmacogenomic and proteomic changes in multiple tissues. An understanding of the proteome-wide effects of CS in liver and its relationships to altered hepatic and systemic physiology remains incomplete. Here, we report the application of a functional pharmacoproteomic approach to gain integrated insight into the complex nature of CS responses in liver in vivo. An in-depth functional analysis was performed using rich pharmacodynamic (temporal-based) proteomic data measured over 66h in rat liver following a single dose of methylprednisolone (MPL). Data mining identified 451 differentially regulated proteins. These proteins were analyzed on the basis of temporal regulation, cellular localization, and literature-mined functional information. Of the 451 proteins, 378 were clustered into six functional groups based on major clinically-relevant effects of CS in liver. MPL-responsive proteins were highly localized in the mitochondria (20%) and cytosol (24%). Interestingly, several proteins were related to hepatic stress and signaling processes, which appear to be involved in secondary signaling cascades and in protecting the liver from CS-induced oxidative damage. Consistent with known adverse metabolic effects of CS, several rate-controlling enzymes involved in amino acid metabolism, gluconeogenesis, and fatty-acid metabolism were altered by MPL. In addition, proteins involved in the metabolism of endogenous compounds, xenobiotics, and therapeutic drugs including cytochrome P450 and Phase-II enzymes were differentially regulated. Proteins related to the inflammatory acute-phase response were up-regulated in response to MPL. Functionally-similar proteins showed large diversity in their temporal profiles, indicating complex mechanisms of regulation by CS.

SIGNIFICANCE

Clinical use of corticosteroid (CS) therapy is frequent and chronic. However, current knowledge on the proteome-level effects of CS in liver and other tissues is sparse. While transcriptomic regulation following methylprednisolone (MPL) dosing has been temporally examined in rat liver, proteomic assessments are needed to better characterize the tissue-specific functional aspects of MPL actions. This study describes a functional pharmacoproteomic analysis of dynamic changes in MPL-regulated proteins in liver and provides biological insight into how steroid-induced perturbations on a molecular level may relate to both adverse and therapeutic responses presented clinically.

Reproduction Does Not Adversely Affect Liver Mitochondrial Respiratory Function but Results in Lipid Peroxidation and Increased Antioxidants in House Mice

Reproduction is thought to come at a cost to longevity. Based on the assumption that increased energy expenditure during reproduction is associated with increased free-radical production by mitochondria, oxidative damage has been suggested to drive this trade-off. We examined the impact of reproduction on liver mitochondrial function by utilizing post-reproductive and non-reproductive house mice (Mus musculus) living under semi-natural conditions. The age-matched post-reproductive and non-reproductive groups were compared after the reproductive females returned to a non-reproductive state, so that both groups were in the same physiological state at the time the liver was collected. Despite increased oxidative damage (p = 0.05) and elevated CuZnSOD (p = 0.002) and catalase (p = 0.04) protein levels, reproduction had no negative impacts on the respiratory function of liver mitochondria. Specifically, in a post-reproductive, maintenance state the mitochondrial coupling (i.e., respiratory control ratio) of mouse livers show no negative impacts of reproduction. In fact, there was a trend (p = 0.059) to suggest increased maximal oxygen consumption by liver mitochondria during the ADP stimulated state (i.e., state 3) in post-reproduction. These findings suggest that oxidative damage may not impair mitochondrial respiratory function and question the role of mitochondria in the trade-off between reproduction and longevity. In addition, the findings highlight the importance of quantifying the respiratory function of mitochondria in addition to measuring oxidative damage.

Effects of exercise and metformin on the prevention of glucose intolerance: a comparative study

We aimed to evaluate the effects of aerobic exercise training (4 days) and metformin exposure on acute glucose intolerance after dexamethasone treatment in rats. Forty-two adult male Wistar rats (8 weeks old) were divided randomly into four groups: sedentary control (SCT), sedentary dexamethasone-treated (SDX), training dexamethasone-treated (DPE), and dexamethasone and metformin treated group (DMT). Glucose tolerance tests and in situ liver perfusion were undertaken on fasting rats to obtain glucose profiles. The DPE group displayed a significant decrease in glucose values compared with the SDX group. Average glucose levels in the DPE group did not differ from those of the DMT group, so we suggest that exercise training corrects dexamethasone-induced glucose intolerance and improves glucose profiles in a similar manner to that observed with metformin. These data suggest that exercise may prevent the development of glucose intolerance induced by dexamethasone in rats to a similar magnitude to that observed after metformin treatment.

High mitochondrial respiration and glycolytic capacity represent a metabolic phenotype of human tolerogenic dendritic cells

Human dendritic cells (DCs) regulate the balance between immunity and tolerance through selective activation by environmental and pathogen-derived triggers. To characterize the rapid changes that occur during this process, we analyzed the underlying metabolic activity across a spectrum of functional DC activation states, from immunogenic to tolerogenic. We found that in contrast to the pronounced proinflammatory program of mature DCs, tolerogenic DCs displayed a markedly augmented catabolic pathway, related to oxidative phosphorylation, fatty acid metabolism, and glycolysis. Functionally, tolerogenic DCs demonstrated the highest mitochondrial oxidative activity, production of reactive oxygen species, superoxide, and increased spare respiratory capacity. Furthermore, assembled, electron transport chain complexes were significantly more abundant in tolerogenic DCs. At the level of glycolysis, tolerogenic and mature DCs showed similar glycolytic rates, but glycolytic capacity and reserve were more pronounced in tolerogenic DCs. The enhanced glycolytic reserve and respiratory capacity observed in these DCs were reflected in a higher metabolic plasticity to maintain intracellular ATP content. Interestingly, tolerogenic and mature DCs manifested substantially different expression of proteins involved in the fatty acid oxidation (FAO) pathway, and FAO activity was significantly higher in tolerogenic DCs. Inhibition of FAO prevented the function of tolerogenic DCs and partially restored T cell stimulatory capacity, demonstrating their dependence on this pathway. Overall, tolerogenic DCs show metabolic signatures of increased oxidative phosphorylation programing, a shift in redox state, and high plasticity for metabolic adaptation. These observations point to a mechanism for rapid genome-wide reprograming by modulation of underlying cellular metabolism during DC differentiation.

Amelioration of an undesired action of deguelin

The pharmaceutical world has greatly benefited from the well-characterized structure-function relationships of toxins with endogenous biomolecules, such as ion-channels, receptors, and signaling molecules. Thus, therapeutics derived from toxins have been aggressively pursued. However, the multifunctional role of various toxins may lead to undesirable off-target effects, hindering their use as therapeutic agents. In this paper, we suggest that previously unsuccessful toxins (due to off-target effects) may be revisited with mixtures by utilizing the pharmacodynamic response to the potential primary therapeutic as a starting point for finding new targets to ameliorate the unintended responses. In this proof of principle study, the pharmacodynamic response of HepG2 cells to a potential primary therapeutic (deguelin, a plant-derived chemopreventive agent) was monitored, and a possible secondary target (p38MAPK) was identified. As a single agent, deguelin decreased cellular viability at higher doses (>10 μM), but inhibited oxygen consumption over a wide dosing range (1.0-100 μM). Our results demonstrate that inhibition of oxygen consumption is related to an increase in p38MAPK phosphorylation, and may only be an undesired side effect of deguelin (i.e., one that does not contribute to the decrease in HepG2 viability). We further show that deguelin's negative effect on oxygen consumption can be diminished while maintaining efficacy when used as a therapeutic mixture with the judiciously selected secondary inhibitor (SB202190, p38MAPK inhibitor). These preliminary findings suggest that an endogenous response-directed mixtures approach, which uses a pharmacodynamic response to a primary therapeutic to determine a secondary target, allows previously unsuccessful toxins to be revisited as therapeutic mixtures.

A cell-autonomous role for the glucocorticoid receptor in skeletal muscle atrophy induced by systemic glucocorticoid exposure

Glucocorticoids (GCs) are important regulators of skeletal muscle mass, and prolonged exposure will induce significant muscle atrophy. To better understand the mechanism of skeletal muscle atrophy induced by elevated GC levels, we examined three different models: exogenous synthetic GC treatment [dexamethasone (DEX)], nutritional deprivation, and denervation. Specifically, we tested the direct contribution of the glucocorticoid receptor (GR) in skeletal muscle atrophy by creating a muscle-specific GR-knockout mouse line (MGR(e3)KO) using Cre-lox technology. In MGR(e3)KO mice, we found that the GR is essential for muscle atrophy in response to high-dose DEX treatment. In addition, DEX regulation of multiple genes, including two important atrophy markers, MuRF1 and MAFbx, is eliminated completely in the MGR(e3)KO mice. In a condition where endogenous GCs are elevated, such as nutritional deprivation, induction of MuRF1 and MAFbx was inhibited, but not completely blocked, in MGR(e3)KO mice. In response to sciatic nerve lesion and hindlimb muscle denervation, muscle atrophy and upregulation of MuRF1 and MAFbx occurred to the same extent in both wild-type and MGR(e3)KO mice, indicating that a functional GR is not required to induce atrophy under these conditions. Therefore, we demonstrate conclusively that the GR is an important mediator of skeletal muscle atrophy and associated gene expression in response to exogenous synthetic GCs in vivo and that the MGR(e3)KO mouse is a useful model for studying the role of the GR and its target genes in multiple skeletal muscle atrophy models.

Neonatal corticosterone programs for thrifty phenotype adult diabetic manifestations and oxidative stress: countering effect of melatonin as a deprogrammer

OBJECTIVE

The present study assesses the thrifty phenotype response of neonatal corticosterone programming to a diabetogenic challenge in adult rats and the role of melatonin as a deprogrammer.

METHODS

Neonates of both sexes, born of healthy male and female rats maintained under standard conditions of temperature and light, were separated and, equal number of pups was assigned to lactating mothers. Pups treated with either saline or corticosterone or, a combination of corticosterone and melatonin from postnatal day (PND) 2 to PND 14 and, at 120 days of age, six animals from each treatment group were rendered diabetic by alloxanization. Various serum and tissue parameters pertaining to glycaemic regulation, dyslipidemia, hepatic and renal distress and oxidative stress were analysed in adult rats of all groups.

RESULTS

The results indicate compromised feed efficiency, hyperglycaemia, hypoinsulinemia, decreased glycogen content, elevated serum and tissue lipids and serum markers of hepatic and renal stress, together with increased lipid peroxidation, and decreased levels of non-enzymatic and enzymatic antioxidants in corticosterone programmed diabetic animals than in the non-programmed diabetic rats. However, treatment with melatonin simultaneously prevented to a significant extent the alterations in carbohydrate and lipid metabolism and oxidative stress.

CONCLUSIONS

Melatonin is a potent deprogrammer of neonatal corticosterone programming effects and the adult thrifty phenotype alteration to a diabetogenic challenge.

Plasticity changes in adult metabolic homeostasis and tissue oxidative stress: neonatal programming by corticosterone and melatonin as deprogrammer

OBJECTIVE

To evaluate the long-term plasticity changes induced by neonatal corticosterone programming on adult metabolic status and the deprogramming effect of melatonin.

METHODS

Male and female Wistar rats were maintained under standard conditions and when mated females delivered pups, neonates of both sexes were separated and equal number of pups was assigned to lactating mothers. Pups treated with saline, corticosterone or a combination of corticosterone and melatonin from PND 2 to PND 14, were maintained until 120 days of age. Various serum and tissue parameters pertaining to glycaemic regulation, dyslipidemia, hepatic and renal distress and oxidative stress were analyzed in adult rats.

RESULTS

Neonatal corticosterone exposure induced dyslipidemia, increased fed and fasting glucose levels, insulin resistance, lipid peroxidation, serum levels of insulin, corticosterone and hepatic and renal dysfunction markers and decreased the levels of enzymatic and non-enzymatic antioxidants, relatively more in males. Melatonin proved as an effective deprogrammer of corticosterone induced plasticity changes.

CONCLUSIONS

Neonatal corticosterone exposure induces long lasting effects on adult physiology and metabolism. Concurrent treatment with melatonin effectively deprograms the changes.

High levels of whole-body energy expenditure are associated with a lower coupling of skeletal muscle mitochondria in C57Bl/6 mice

Considerable variation in energy expenditure is observed in C57Bl/6 mice on a high-fat diet. Because muscle tissue is a major determinant of whole-body energy expenditure, we set out to determine the variation in energy expenditure and its possible association with skeletal muscle mitochondrial function upon high-fat diet intervention. Metabolic cages using indirect calorimetry were used to assess whole-body energy metabolism in C57Bl/6 male mice during the first 3 days of high-fat diet intervention. Mice were grouped in a negative or positive residual nocturnal energy expenditure group after correction of total nocturnal energy expenditure for body mass by residual analysis. The positive residual energy expenditure group was characterized by higher uncorrected total nocturnal energy expenditure and food intake. On day 7, mitochondria were isolated from the skeletal muscle of the hind limb. Mitochondrial density was determined by mitochondrial protein content and did not differ between the positive and negative residual energy expenditure groups. Using high-resolution respirometry, mitochondrial oxidative function was assessed using various substrates. Mitochondria from the positive residual energy expenditure group were characterized by a lower adenosine diphosphate-stimulated respiration and lower respiratory control rates using palmitoyl-coenzyme A as substrate. These results indicate that reduced mitochondrial coupling is associated with positive residual energy expenditure and high rates of total energy expenditure in vivo.

Effects of a novel selective androgen receptor modulator on dexamethasone-induced and hypogonadism-induced muscle atrophy

Glucocorticoids are the most widely used antiinflammatory drugs in the world. However, prolonged use of glucocorticoids results in undesirable side effects such as muscle wasting, osteoporosis, and diabetes. Skeletal muscle wasting, which currently has no approved therapy, is a debilitating condition resulting from either reduced muscle protein synthesis or increased degradation. The imbalance in protein synthesis could occur from increased expression and function of muscle-specific ubiquitin ligases, muscle atrophy F-box (MAFbx)/atrogin-1 and muscle ring finger 1 (MuRF1), or decreased function of the IGF-I and phosphatidylinositol-3 kinase/Akt kinase pathways. We examined the effects of a nonsteroidal tissue selective androgen receptor modulator (SARM) and testosterone on glucocorticoid-induced muscle atrophy and castration-induced muscle atrophy. The SARM and testosterone propionate blocked the dexamethasone-induced dephosphorylation of Akt and other proteins involved in protein synthesis, including Forkhead box O (FoxO). Dexamethasone caused a significant up-regulation in the expression of ubiquitin ligases, but testosterone propionate and SARM administration blocked this effect by phosphorylating FoxO. Castration induced rapid myopathy of the levator ani muscle, accompanied by up-regulation of MAFbx and MuRF1 and down-regulation of IGF-I, all of which was attenuated by a SARM. The results suggest that levator ani atrophy caused by hypogonadism may be the result of loss of IGF-I stimulation, whereas that caused by glucocorticoid treatment relies almost solely on up-regulation of MAFbx and MuRF1. Our studies provide the first evidence that glucocorticoid- and hypogonadism-induced muscle atrophy are mediated by distinct but overlapping mechanisms and that SARMs may provide a more effective and selective pharmacological approach to prevent glucocorticoid-induced muscle loss than steroidal androgen therapy.

Abundance of some skeletal muscle mitochondrial proteins is associated with increased blood serum insulin in bovine fetuses

The aim of this study was to investigate the evolution of the abundance of cytochrome oxidase c subunit IV (NCOIV) and beta subunit of ATP synthase (β-ATP) during the last third of gestation in bovine skeletal muscles. Semitendinosus, longissimus thoracis and rectus abdominis muscles were chosen for the immunoblotting of the respective protein levels. Muscle and blood samples from bovine fetuses of randomly selected breeds were collected at 180, 210, and 260 days post-conception (dpc). The muscle tissue expressions of NCOIV, β-ATP were compared to blood glucose and insulin. At 260 dpc, protein levels of NCOIV raised in skeletal muscles. Additionally, β-ATP in semitendinosus and longissimus thoracis were elevated and paralleled by higher concentrations of blood serum insulin. It corroborates our previous observations indicating that accelerated metabolic differentiation of bovine skeletal muscles is associated with elevated blood insulin and occurs during the last trimester of gestation. Our observations point to the connection between insulin-sensitivity and the molecular mechanisms of mitochondrial contribution to ontogenesis of skeletal muscles.

Time course expression of Foxo transcription factors in skeletal muscle following corticosteroid administration

Increased expression of forkhead box O (Foxo) transcription factors were reported in cultured myotubes and mouse limb muscle with corticosteroid (CS) treatment. We previously reported that administration of CS to rats resulted in muscle fiber atrophy only by day 7. The aim of this study, therefore, was to evaluate the time-course changes in the expression of Foxo transcription factors and muscle-specific ubiquitin E3 ligases in rat limb muscle following CS administration. Triamcinolone (TRI; 1 mg x kg(-1) x day(-1) im) was administered for 1, 3, or 7 days. Control (CTL) rats were given saline. Muscle mRNA was analyzed by real-time RT-PCR. Compared with CTL, body weights of TRI-treated animals decreased by 3, 12, and 21% at days 1, 3, and 7, respectively. Muscle IGF-1 mRNA levels decreased by 33, 65, and 58% at days 1, 3, and 7 in TRI-treated rats compared with CTL. Levels of phosphorylated Akt were 28, 50, and 36% lower in TRI animals at these time points. Foxo1 mRNA increased progressively by 1.2-, 1.4-, and 2.5-fold at days 1, 3, and 7 in TRI animals. Similar changes were noted in the expression of Foxo3a mRNA (1.3-, 1.4-, and 2.6-fold increments). By contrast, Foxo4 mRNA was not significantly changed in TRI animals. With TRI, muscle atrophy F box/Atrogin-1 increased by 1.8-, 4.1-, and 7.5-fold at days 1, 3, and 7 compared with CTL rats. By contrast, muscle RING finger 1 increased only from day 7 (2.7-fold). Gradual reduction in IGF-I expression with TRI over the time series paralleled that of Akt. These findings are consistent with a progressive stimulus to muscle protein degradation and the need to process/remove disassembled muscle proteins via the ubiquitin-proteasome system. Elucidating the dynamic catabolic responses to CS challenge is important in understanding the mechanisms underlying muscle atrophy and therapeutic measures to offset this.

Regulation of signaling pathways downstream of IGF-I/insulin by androgen in skeletal muscle of glucocorticoid-treated rats

BACKGROUND

The mechanisms by which androgens ameliorate glucocorticoid-induced muscle wasting are still under investigation. In the present study, we tested the hypothesis that androgen's effects in reversing muscle wasting are related to activating the signaling pathways downstream of insulin-like growth factor-1 (IGF-I)/insulin.

METHODS

Forty female Sprague-Dawley rats were randomly divided into four groups: control group, dexamethasone (DEX) group, testosterone (TES) group, and TES + DEX group. Each group was injected with saline or DEX (0.1 mg/100 g/d) for 10 days and sesame oil or TES (0.5 mg/100 g/d) for 13 days. Several downstream targets of IGF-I/insulin in skeletal muscle including protein kinase B (Akt), p70 ribosomal protein S6 kinase (p70S6K), and glycogen synthase kinase-3beta (GSK-3beta) that are associated with protein synthesis were examined. Two proteolysis-related ubiquitin E3-ligases, muscle atrophy F-box, and muscle RING finger-1 that are also regulated by IGF-I/insulin were also assessed.

RESULTS

TES attenuated gastrocnemius muscle atrophy induced by DEX. TES prevented the DEX-induced decrease of IGF-I expression in gastrocnemius muscle, but not in serum. TES ameliorated DEX-induced dephosphorylation of Akt and p70S6K and promoted the phosphorylation of GSK-3beta in gastrocnemius muscle. The total amount of Akt, p70S6K, or GSK-3beta proteins was not changed among these groups. TES did not show any effects on the DEX-induced upregulation of muscle atrophy F-box, and muscle RING finger-1 mRNA in gastrocnemius muscle.

CONCLUSION

This findings suggest that the effects of TES in reversing DEX-induced muscle atrophy are related to signaling pathways downstream of IGF-I/insulin that are associated with protein synthesis.

Adenine nucleotide translocator promotes oxidative phosphorylation and mild uncoupling in mitochondria after dexamethasone treatment

The composition of the mitochondrial inner membrane and uncoupling protein [such as adenine nucleotide translocator (ANT)] contents are the main factors involved in the energy-wasting proton leak. This leak is increased by glucocorticoid treatment under nonphosphorylating conditions. The aim of this study was to investigate mechanisms involved in glucocorticoid-induced proton leak and to evaluate the consequences in more physiological conditions (between states 4 and 3). Isolated liver mitochondria, obtained from dexamethasone-treated rats (1.5 mg.kg(-1).day(-1)), were studied by polarography, Western blotting, and high-performance thin-layer chromatography. We confirmed that dexamethasone treatment in rats induces a proton leak in state 4 that is associated with an increased ANT content, although without any change in membrane surface or lipid composition. Between states 4 and 3, dexamethasone stimulates ATP synthesis by increasing both the mitochondrial ANT and F1-F0 ATP synthase content. In conclusion, dexamethasone increases mitochondrial capacity to generate ATP by modifying ANT and ATP synthase. The side effect is an increased leak in nonphosphorylating conditions.

The metabolic changes caused by dexamethasone in the adjuvant-induced arthritic rat

The action of orally administered dexamethasone (0.2 mg kg(-1) day(-1)) on metabolic parameters of adjuvant-induced arthritic rats was investigated. The body weight gain and the progression of the disease were also monitored. Dexamethasone was very effective in suppressing the Freund's adjuvant-induced paw edema and the appearance of secondary lesions. In contrast, the body weight loss of dexamethasone-treated arthritic rats was more accentuated than that of untreated arthritic or normal rats treated with dexamethasone, indicating additive harmful effects. The perfused livers from dexamethasone-treated arthritic rats presented high content of glycogen in both fed and fasted conditions, as indicated by the higher rates of glucose release in the absence of exogenous substrate. The metabolization of exogenous L: -alanine was increased in livers from dexamethasone-treated arthritic rats in comparison with untreated arthritic rats, but there was a diversion of carbon flux from glucose to L: -lactate and pyruvate. Plasmatic levels of insulin and glucose were significantly higher in arthritic rats following dexamethasone administration. Most of these changes were also found in livers from normal rats treated with dexamethasone. The observed changes in L: -alanine metabolism and glycogen synthesis indicate that insulin was the dominant hormone in the regulation of the liver glucose metabolism even in the fasting condition. The prevalence of the metabolic effects of dexamethasone over those ones induced by the arthritis disease suggests that dexamethasone administration was able to suppress the mechanisms implicated in the development of the arthritis-induced hepatic metabolic changes. It seems thus plausible to assume that those factors responsible for the inflammatory responses in the paws and for the secondary lesions may be also implicated in the liver metabolic changes, but not in the body weight loss of arthritic rats.

Mitochondrial function, energy expenditure, aging and insulin resistance

Mitochondria are the cells' powerhouse that produce the ubiquitous energy currency (ATP) by consuming oxygen, producing water and building up the proton motive force. Oxygen consumption is a classical means of assessing energy expenditure, one component of energy balance. When energy balance is positive, weight increases. This is observed during the dynamic phase of obesity, and during body composition changes associated with aging. Whether intrinsic defaults in mitochondria occur is the matter of this review. Indeed, the ratio of ATP over oxygen consumed, which is not fixed, is one way of regulating heat release and ATP flux, but can also be the consequence of environmental conditions of mitochondrial work. For example, various hormones (T3, glucocorticoids), changes in lipid membrane composition, changes in food intake and exercise, and various drugs, can modify the ratio of ATP over oxygen consumed. Aging and insulin resistance are other regulators of this ratio. Finally there is a rising body of evidence linking diabetes to mitochondrial functions.

Hormonal regulation of mitochondrial energy production

PURPOSE OF REVIEW

It had been thought for a long time that thyroid hormones were the only ones to regulate energy production within mitochondria. Recent findings show that other hormones (steroids, leptin, insulin) regulate the efficiency of mitochondrial adenosine triphosphate production. Furthermore, a mismatch between oxygen consumption and energy intake may not be sufficient to understand body weight regulation. It appears that the efficiency of adenosine triphosphate production may play a role.

RECENT FINDINGS

Over the past 2 years a series of results argued that glucocorticoids influence energy balance, the efficiency of adenosine triphosphate production, and are thermogenic. The sites for this effect are discussed, probably both the liver and muscle. Evidence of the genes involved in this regulation is substantial for muscle but remains to be studied in the liver. On the other hand, leptin could be a thermogenic hormone, especially in situations of calorie restriction. Finally, recent data and opinions suggest that mitochondria and adenosine triphosphate production could be central in the pathogenesis of both insulin resistance and beta cell deficiency.

SUMMARY

The adaptation of mitochondrial adenosine triphosphate production appears to play a role in both diabetes and weight loss (voluntary and involuntary). Hormonal and nutritional manipulation could be a therapeutic possibility for weight management.

Kinetics and control of oxidative phosphorylation in rat liver mitochondria after dexamethasone treatment

The present investigation was undertaken in order to evaluate the contributions of ATP synthesis and proton leak reactions to the rate of active respiration of liver mitochondria, which is altered following dexamethasone treatment (1.5 mg/kg per day for 5 days). We applied top-down metabolic control analysis and its extension, elasticity analysis, to gain insight into the mechanisms of glucocorticoid regulation of mitochondrial bioenergetics. Liver mitochondria were isolated from dexamethasone-treated, pair-fed and control rats when in a fed or overnight fasted state. Injection of dexamethasone for 5 days resulted in an increase in the fraction of the proton cycle of phosphorylating liver mitochondria, which was associated with a decrease in the efficiency of the mitochondrial oxidative phosphorylation process in liver. This increase in proton leak activity occurred with little change in the mitochondrial membrane potential, despite a significant decrease in the rate of oxidative phosphorylation. Regulation analysis indicates that mitochondrial membrane potential homoeostasis is achieved by equal inhibition of the mitochondrial substrate oxidation and phosphorylation reactions in rats given dexamethasone. Our results also suggest that active liver mitochondria from dexamethasone-treated rats are capable of maintaining phosphorylation flux for cellular purposes, despite an increase in the energetic cost of mitochondrial ATP production due to increased basal proton permeability of the inner membrane. They also provide a complete description of the effects of dexamethasone treatment on liver mitochondrial bioenergetics.

Dexamethasone impairs muscle energetics, studied by (31)P NMR, in rats

AIMS/HYPOTHESIS

Glucocorticoid treatments are associated with increased whole-body oxygen consumption. We hypothesised that an impairment of muscle energy metabolism can participate in this increased energy expenditure.

METHODS

To investigate this possibility, we have studied muscle energetics of dexamethasone-treated rats (1.5 mg kg(-1) day(-1) for 6 days), in vivo by (31)P NMR spectroscopy. Results were compared with control and pair-fed (PF) rats before and after overnight fasting.

RESULTS

Dexamethasone treatment resulted in decreased phosphocreatine (PCr) concentration and PCr:ATP ratio, increased ADP concentration and higher PCr to gamma-ATP flux but no change in beta-ATP to beta-ADP flux in gastrocnemius muscle. Neither 4 days of food restriction (PF rats) nor 24 h fasting affected high-energy phosphate metabolism. In dexamethasone-treated rats, there was an increase in plasma insulin and non-esterified fatty acid concentration.

CONCLUSIONS/INTERPRETATION

We conclude that dexamethasone treatment altered resting in vivo skeletal muscle energy metabolism, by decreasing oxidative phosphorylation, producing ATP at the expense of PCr.

Exercise enhances insulin and leptin signaling in the cerebral cortex and hypothalamus during dexamethasone-induced stress in diabetic rats

Exercise and dexamethasone (DEX) are known to have opposite effects on peripheral insulin resistance. However, their effects and mechanism on brain glucose metabolism have been poorly defined. We investigated the modulation of the hypothalamo-pituitary-adrenal (HPA) axis and insulin/leptin signaling associated with glucose utilization in the brains of 90% pancreatectomized diabetic rats, which had been administered two dosages of DEX and exercised for 8 weeks. The data revealed that the administration of a high dose (0.1 mg/kg body weight/day) of DEX (HDEX) attenuated insulin signaling in the cerebral cortex and hypothalamus, whereas exercise potentiated their insulin signaling along with induction of IRS2 expression. In parallel with the modulated signaling, glucose utilization, such as glycogen storage and glycogen synthase activity, was suppressed by DEX in the cortex and hypothalamus, while exercise offset the DEX effects. Despite a decrease in epididymal fat mass, HDEX increased serum leptin levels, possibly due to an activated HPA axis, while exercise suppressed the increment. However, DEX reduced leptin-induced STAT3 phosphorylation in the cortex and hypothalamus, and it increased AMP-activated protein kinase (AMPK) phosphorylation only in the hypothalamus. Exercise reversed the phosphorylation of STAT3 and AMPK which had been modulated by DEX. In conclusion, exercise improves insulin and leptin signaling in the cerebral cortex and hypothalamus of diabetic rats exacerbated with HDEX, contributing to the regulation of body weight and glucose homeostasis.

Ghrelin regulates mitochondrial-lipid metabolism gene expression and tissue fat distribution in liver and skeletal muscle

Ghrelin is a gastric hormone increased during caloric restriction and fat depletion. A role of ghrelin in the regulation of lipid and energy metabolism is suggested by fat gain independent of changes in food intake during exogenous ghrelin administration in rodents. We investigated the potential effects of peripheral ghrelin administration (two times daily 200-micrograms [DOSAGE ERROR CORRECTED] sc injection for 4 days) on triglyceride content and mitochondrial and lipid metabolism gene expression in rat liver and muscles. Compared with vehicle, ghrelin increased body weight but not food intake and circulating insulin. In liver, ghrelin induced a lipogenic and glucogenic pattern of gene expression and increased triglyceride content while reducing activated (phosphorylated) stimulator of fatty acid oxidation, AMP-activated protein kinase (AMPK, all P < 0.05), with unchanged mitochondrial oxidative enzyme activities. In contrast, triglyceride content was reduced (P < 0.05) after ghrelin administration in mixed (gastrocnemius) and unchanged in oxidative (soleus) muscle. In mixed muscle, ghrelin increased (P < 0.05) mitochondrial oxidative enzyme activities independent of changes in expression of fat metabolism genes and phosphorylated AMPK. Expression of peroxisome proliferator-activated receptor-gamma, the activation of which reduces muscle fat content, was selectively increased in mixed muscle where it paralleled changes in oxidative capacities (P < 0.05). Thus ghrelin induces tissue-specific changes in mitochondrial and lipid metabolism gene expression and favors triglyceride deposition in liver over skeletal muscle. These novel effects of ghrelin in the regulation of lean tissue fat distribution and metabolism could contribute to metabolic adaptation to caloric restriction and loss of body fat.

Postnatal glucocorticoid exposure alters the adult phenotype

We examined the effect of six doses of dexamethasone (Dex) administered daily (2–7 days of age) to postnatal rats on body weight gain, food and water intake, peripheral hormonal/metabolic milieu, and hypothalamic neuropeptides that regulate food intake. We observed a Dex-induced acute (3 days of age) suppression of endogenous corticosterone and an increase in circulating leptin concentrations that were associated with a decrease in body weight in males and females. Followup during the suckling, postsuckling, and adult stages (7–120 days of age) revealed hypoleptinemia in males and females, and hypoinsulinemia, a relative increase in the glucose-to-insulin ratio, and a larger increase in skeletal muscle glucose transporter (GLUT 4) concentrations predominantly in the males, reflective of a catabolic state associated with a persistent decrease in body weight gain. The increase in the glucose-to-insulin ratio and hyperglycemia was associated with an increase in water intake. In addition, the changes in the hormonal/metabolic milieu were associated with an increase in hypothalamic neuropeptide Y content in males and females during the suckling phase, which persisted only in the 120-day-old female with a transient postnatal decline in α-melanocyte-stimulating hormone and corticotropin-releasing factor. This increase in neuropeptide Y (NPY) during the suckling phase in males and females was associated with a subsequent increase in adult food intake that outweighed the demands of body weight gain. In contrast to the adult hypothalamic findings, cerebral ventricular dilatation was more prominent in adult males. We conclude that postnatal Dex treatment causes permanent sex-specific changes in the adult phenotype, setting the stage for future development of diabetes (increased glucose:insulin ratio), obesity (increased NPY and food intake), and neurological impairment (loss of cerebral volume).