Feeding resveratrol to rodents has no effect on mitochondrial biogenesis, and deacetylation of PGC-1α results in a decrease, not an increase, in its coactivator activity.

It has been reported that supplementation with the antioxidant vitamins C and E prevents the adaptive increases in mitochondrial biogenesis and GLUT4 expression induced by endurance exercise. We reevaluated the effects of these antioxidants on the adaptive responses of rat skeletal muscle to swimming in a short-term study consisting of 9 days of vitamins C and E with exercise during the last 3 days and a longer-term study consisting of 8 wk of antioxidant vitamins with exercise during the last 3 wk. The rats in the antioxidant groups were given 750 mg·kg body wt Ϫ1 ·day Ϫ1 vitamin C and 150 mg·kg body wt Ϫ1 ·day Ϫ1 vitamin E. In rats euthanized immediately after exercise, plasma TBARs were elevated in the control rats but not in the antioxidant-supplemented rats, providing evidence for an antioxidant effect. In rats euthanized 18 h after exercise there were large increases in insulin responsiveness of glucose transport in epitrochlearis muscles mediated by an approximately twofold increase in GLUT4 expression in both the short-and long-term treatment groups. The protein levels of a number of mitochondrial marker enzymes were also increased about twofold. Superoxide dismutases (SOD) 1 and 2 were increased about twofold in triceps muscle after 3 days of exercise, but only SOD2 was increased after 3 wk of exercise. There were no differences in the magnitudes of any of these adaptive responses between the control and antioxidant groups. These results show that very large doses of antioxidant vitamins do not prevent the exercise-induced adaptive responses of muscle mitochondria, GLUT4, and insulin action to exercise and have no effect on the level of these proteins in sedentary rats. ascorbic acid; ␣-tocopherol; peroxisome proliferator-activated receptor-␥ coactivator-1␣; mitochondria; superoxide dismutase TWO ARTICLES HAVE BEEN PUBLISHED RECENTLY reporting that taking the vitamin ascorbic acid (vitamin C) or the combination of ascorbic acid and ␣-tocopherol (vitamin E) prevents the adaptive responses of skeletal muscle to endurance exercise. In the first study, Gomez-Cabrera et al. (6) reported that men taking 1.0 g/day ascorbic acid (vitamin C) had a markedly reduced increase in maximal oxygen uptake (V O 2 max ) in response to 8 wk of endurance training. They also reported that giving rats ascorbic acid prevented adaptive increases in enzyme levels in skeletal muscle and severely reduced the increase in endurance induced by a treadmill-running program. In the other study, Ristow et al. (23) evaluated the effects of taking ascorbic acid and ␣-tocopheral on adaptive responses to a 4-wk-long exercise program, the major component of which was circuit training. The study involved two groups of men, one trained and the other untrained, at the start of the study.Ristow et al. (23) interpreted their findings as evidence that antioxidant vitamins prevent exercise training-induced increases in insulin sensitivity and in skeletal muscle peroxisome proliferator-activated receptor-␥ (PPAR␥) coactivator-1␣ PGC-1␣, PPAR␥, and s...

It has been reported that 30% calorie restriction (CR) for 3 mo results in large increases in mitochondrial biogenesis in heart, brain, liver, and adipose tissue, with concomitant increases in respiration and ATP synthesis. We found these results surprising, and performed this study to determine whether 30% CR does induce an increase in mitochondria in heart, brain, liver, adipose tissue, and/or skeletal muscle. To this end, we measured the levels of a range of mitochondrial proteins, and mRNAs. With the exception of long-chain acyl-CoA dehydrogenase protein level, which was increased ∼60% in adipose tissue, none of the mitochondrial proteins or mRNAs that we measured were increased in rats subjected to 30% CR for 14 wk. There was also no increase in citrate synthase activity. Because it is not possible to have an increase in mitochondria without any increase in key mitochondrial proteins, we conclude that 30% CR does not induce an increase in mitochondria in heart, brain, liver, adipose tissue, or skeletal muscle in laboratory rodents.

SUMMARY The objective of this study was to evaluate the specific mechanism(s) by which PPARβ regulates mitochondrial content in skeletal muscle. We discovered that PPARβ increases PGC-1α by protecting it from degradation by binding to PGC-1α and limiting ubiquitination. PPARβ also induces an increase in nuclear respiratory factor 1 (NRF-1) expression, resulting in increases in mitochondrial respiratory chain proteins and MEF2A, for which NRF-1 is a transcription factor. There was also an increase in AMP kinase phosphorylation mediated by an NRF-1-induced increase in CAM kinase kinase-β (CaMKKβ). Knockdown of PPARβ resulted in large decreases in the levels of PGC-1α and mitochondrial proteins and a marked attenuation of the exercise-induced increase in mitochondrial biogenesis. In conclusion, PPARβ induces an increase in PGC-1α protein, and PPARβ is a transcription factor for NRF-1. Thus, PPARβ plays essential roles in the maintenance and adaptive increase in mitochondrial enzymes in skeletal muscle by exercise.

We examined whether a mixed lactate and caffeine compound (LC) could effectively elicit proliferation and differentiation of satellite cells or activate anabolic signals in skeletal muscles. We cultured C2C12 cells with either lactate or LC for 6 h. We found that lactate significantly increased myogenin and follistatin protein levels and phosphorylation of P70S6K while decreasing the levels of myostatin relative to the control. LC significantly increased protein levels of Pax7, MyoD, and Ki67 in addition to myogenin, relative to control. LC also significantly increased follistatin expression relative to control and stimulated phosphorylation of mTOR and P70S6K. In an in vivo study, male F344/DuCrlCrlj rats were assigned to control (Sed, n = 10), exercise (Ex, n = 12), and LC supplementation (LCEx, n = 13) groups. LC was orally administered daily. The LCEx and Ex groups were exercised on a treadmill, running for 30 min at low intensity every other day for 4 wk. The LCEx group experienced a significant increase in the mass of the gastrocnemius (GA) and tibialis anterior (TA) relative to both the Sed and Ex groups. Furthermore, the LCEx group showed a significant increase in the total DNA content of TA compared with the Sed group. The LCEx group experienced a significant increase in myogenin and follistatin expression of GA relative to the Ex group. These results suggest that administration of LC can effectively increase muscle mass concomitant with elevated numbers of myonuclei, even with low-intensity exercise training, via activated satellite cells and anabolic signals.

Ogasawara R, Sato K, Higashida K, Nakazato K, Fujita S. Ursolic acid stimulates mTORC1 signaling after resistance exercise in rat skeletal muscle.

AMP activated protein kinase (AMPK) plays a key role in the regulatory network responsible for maintaining systemic energy homeostasis during exercise or nutrient deprivation. To understand the function of the regulatory ␤2 subunit of AMPK in systemic energy metabolism, we characterized ␤2 subunit-deficient mice. Using these mutant mice, we demonstrated that the ␤2 subunit plays an important role in regulating glucose, glycogen, and lipid metabolism during metabolic stress. The ␤2 mutant animals failed to maintain euglycemia and muscle ATP levels during fasting. In addition, ␤2-deficient animals showed classic symptoms of metabolic syndrome, including hyperglycemia, glucose intolerance, and insulin resistance when maintained on a high-fat diet (HFD), and were unable to maintain muscle ATP levels during exercise. Cell surface-associated glucose transporter levels were reduced in skeletal muscle from ␤2 mutant animals on an HFD. In addition, they displayed poor exercise performance and impaired muscle glycogen metabolism. These mutant mice had decreased activation of AMPK and deficits in PGC1␣-mediated transcription in skeletal muscle. Our results highlight specific roles of AMPK complexes containing the ␤2 subunit and suggest the potential utility of AMPK isoform-specific pharmacological modulators for treatment of metabolic, cardiac, and neurological disorders. AMP activated protein kinase (AMPK) plays a crucial role in maintaining systemic energy homeostasis through its coordinated actions on the central nervous system and peripheral tissues (54). Loss of AMPK function causes metabolic abnormalities in mice and defects in development and growth, cell polarity, and structure in plants, Drosophila, and rodents (1, 10, 33). Moreover, AMPK is necessary for caloric restriction-mediated longevity in Caenorhabditis elegans (19). AMPK is an intracellular energy sensor. When intracellular levels of ATP decrease, a corresponding increase in AMP leads to activation of AMPK, a step that is vital for restoring intracellular energy balance via AMPK-dependent inhibition of energy-consuming biosynthetic processes and concomitant activation of pathways that increase ATP production.AMPK is a multisubstrate, heterotrimeric serine/threonine kinase consisting of one ␣, one ␤, and one ␥ subunit. The mammalian genome encodes two ␣, two ␤, and three ␥ subunits. The N terminus of the ␣ subunit contains the catalytic domain as well as a phosphorylation site for upstream kinases that regulate its activity (9). The ␥ subunits are nucleotide binding regulatory subunits that bind AMP. The conserved C terminus of the ␤ subunit interacts with both the ␣ and ␥ subunits and plays an obligatory role in AMPK complex formation (10, 46). In addition, ␤ subunits contain a conserved carbohydrate-binding domain that allows AMPK to function as a glycogen sensor (37,42).While AMPK is present in all tissues, the individual AMPK subunits display considerable variation in tissue-specific expression, subunit association, and subcellular localization. Earlie...

BackgroundIt has been proposed that muscle insulin resistance in type 2 diabetes is due to a selective decrease in the components of the mitochondrial electron transport chain and results from accumulation of toxic products of incomplete fat oxidation. The purpose of the present study was to test this hypothesis.Methodology/Principal FindingsRats were made severely iron deficient, by means of an iron-deficient diet. Iron deficiency results in decreases of the iron containing mitochondrial respiratory chain proteins without affecting the enzymes of the fatty acid oxidation pathway. Insulin resistance was induced by feeding iron-deficient and control rats a high fat diet. Skeletal muscle insulin resistance was evaluated by measuring glucose transport activity in soleus muscle strips. Mitochondrial proteins were measured by Western blot. Iron deficiency resulted in a decrease in expression of iron containing proteins of the mitochondrial respiratory chain in muscle. Citrate synthase, a non-iron containing citrate cycle enzyme, and long chain acyl-CoA dehydrogenase (LCAD), used as a marker for the fatty acid oxidation pathway, were unaffected by the iron deficiency. Oleate oxidation by muscle homogenates was increased by high fat feeding and decreased by iron deficiency despite high fat feeding. The high fat diet caused severe insulin resistance of muscle glucose transport. Iron deficiency completely protected against the high fat diet-induced muscle insulin resistance.Conclusions/SignificanceThe results of the study argue against the hypothesis that a deficiency of the electron transport chain (ETC), and imbalance between the ETC and β-oxidation pathways, causes muscle insulin resistance.