SUMMARY Resveratrol, a polyphenol in red wine, has been reported as a calorie restriction mimetic with potential antiaging and antidiabetogenic properties. It is widely consumed as a nutritional supplement, but its mechanism of action remains a mystery. Here, we report that the metabolic effects of resveratrol result from competitive inhibition of cAMP-degrading phosphodiesterases, leading to elevated cAMP levels. The resulting activation of Epac1, a cAMP effector protein, increases intracellular Ca2+ levels and activates the CamKKβ-AMPK pathway via phospholipase C and the ryanodine receptor Ca2+-release channel. As a consequence, resveratrol increases NAD+ and the activity of Sirt1. Inhibiting PDE4 with rolipram reproduces all of the metabolic benefits of resveratrol, including prevention of diet-induced obesity and an increase in mitochondrial function, physical stamina, and glucose tolerance in mice. Therefore, administration of PDE4 inhibitors may also protect against and ameliorate the symptoms of metabolic diseases associated with aging.

Endurance exercise induces increases in mitochondria and the GLUT4 isoform of the glucose transporter in muscle. Although little is known about the mechanisms underlying these adaptations, new information has accumulated regarding how mitochondrial biogenesis and GLUT4 expression are regulated. This includes the findings that the transcriptional coactivator PGC-1 promotes mitochondrial biogenesis and that NRF-1 and NRF-2 act as transcriptional activators of genes encoding mitochondrial enzymes. We tested the hypothesis that increases in PGC-1, NRF-1, and NRF-2 are involved in the initial adaptive response of muscle to exercise. Five daily bouts of swimming induced increases in mitochondrial enzymes and GLUT4 in skeletal muscle in rats. One exercise bout resulted in approximately twofold increases in full-length muscle PGC-1 mRNA and PGC-1 protein, which were evident 18 h after exercise. A smaller form of PGC-1 increased after exercise. The exercise induced increases in muscle NRF-1 and NRF-2 that were evident 12 to 18 h after one exercise bout. These findings suggest that increases in PGC-1, NRF-1, and NRF-2 represent key regulatory components of the stimulation of mitochondrial biogenesis by exercise and that PGC-1 mediates the coordinated increases in GLUT4 and mitochondria.

Summary Calorie restriction, without malnutrition, has been shown to increase lifespan and is associated with a shift away from glycolysis toward beta-oxidation. The objective of this study was to mimic this metabolic shift using low-carbohydrate diets and to determine the influence of these diets on longevity and healthspan in mice. C57BL/6 mice were assigned to a ketogenic, low-carbohydrate, or control diet at 12 months of age and were either allowed to live their natural lifespan or tested for physiological function after 1 or 14 months of dietary intervention. The ketogenic diet (KD) significantly increased median lifespan and survival compared to controls. In aged mice, only those consuming a KD displayed preservation of physiological function. The KD increased protein acetylation levels and regulated mTORC1 signaling in a tissue-dependent manner. This study demonstrates that a KD extends longevity and healthspan in mice.

No abstract

The transition of a muscle cell from a differentiated myotube into an adult myofiber is largely unstudied. This is primarily due to the difficulty of isolating specific developmental stimuli in vivo and the inability to maintain viable myotubes in culture for sufficient lengths of time. To address these limitations, a novel method for rapidly generating three-dimensional engineered muscles using fibrin gel casting has been developed. Myoblasts were seeded and differentiated on top of a fibrin gel. Cell-mediated contraction of the gel around artificial anchors placed 12 mm apart culminates 10 days after plating in a tubular structure of small myotubes (10-microm diameter) surrounded by a fibrin gel matrix. These tissues can be connected to a force transducer and electrically stimulated between parallel platinum electrodes to monitor physiological function. Three weeks after plating, the three-dimensional engineered muscle generated a maximum twitch force of 329 +/- 26.3 microN and a maximal tetanic force of 805.8 +/- 55 microN. The engineered muscles demonstrated normal physiological function including length-tension and force-frequency relationships. Treatment with IGF-I resulted in a 50% increase in force production, demonstrating that these muscles responded to hormonal interventions. Although the force production was maximal at 3 wk, constructs can be maintained in culture for up to 6 wk with no intervention. We conclude that fibrin-based gels provide a novel method to engineer three-dimensional functional muscle tissue and that these tissues may be used to model the development of skeletal muscle in vitro.