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INVITED REVIEW
HIGHLIGHTED TOPICS
Role of Exercise in Reducing the Risk of Diabetes and Obesity
Division of Geriatrics and Nutritional Sciences, Department of Internal Medicine, Washington University School of Medicine, St. Louis, Missouri
Submitted 1 February 2005 ; accepted in final form 1 March 2005
| ABSTRACT |
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-D-ribofuranoside to activate AMP-activated protein kinase. The postexercise increase in sensitivity of muscle glucose transport to activation is not specific for insulin but also involves an increased susceptibility to activation by a submaximal contraction/hypoxia stimulus. The increase in insulin sensitivity is mediated by translocation of more GLUT4 glucose transporters to the cell surface in response to a submaximal insulin stimulus. Although the postexercise increase in muscle insulin sensitivity has been characterized in considerable detail, the basic mechanisms underlying this phenomenon remain a mystery. AMP-activated protein kinase; GLUT4; hypoxia; muscle contractions
That exercise increases the sensitivity of the glucose transport process to insulin in skeletal muscle was first discovered by Richter et al. (45) in Neil Rudermans laboratory. At the time of this discovery, these investigators thought that the increase in muscle glucose uptake induced by exercise requires the presence of insulin. However, in an earlier study, it was found that muscle contractions increase glucose transport in the absence of insulin in frog sartorius muscle (26). This effect of contractions in frog muscle appeared to be mediated by a different mechanism than that caused by insulin.
At about the same time that Richter et al. (45) found that exercise increases insulin sensitivity, it was shown that a bout of swimming results in an increase in muscle glucose uptake in the absence of added insulin that can be measured in perfused rat muscles after cessation of exercise (31). This finding was confirmed by Rudermans group in a study in which they showed that enhanced glucose uptake after exercise occurs in two phases in perfused rat hindlimb muscles (14). The first phase is independent of added insulin, and, as this increase in glucose transport reverses, it is replaced by an increase in insulin sensitivity (14). Similar results were obtained in a later study in which rat epitrochlearis muscles were studied in vitro at various time points after exercise (55).
Subsequent studies have established that contractions stimulate glucose transport in the complete absence of insulin (38, 40, 56, 57), that the maximal effects of contractions and insulin are additive (6, 24, 38, 55, 69), and that contractions and insulin stimulate glucose transport by separate pathways (36, 37, 65). The initial steps in the pathways by which contractions stimulate glucose transport have been identified. One of these is the release of Ca2+ from the sarcoplasmic reticulum (SR) (66) resulting in activation of Ca2+/calmodulin-dependent protein kinase (CaMK) II, which is the isoform of CaMK found in skeletal muscle (64). This process can be studied using subcontraction concentrations of agents, such as caffeine, that release Ca2+ from the SR. Studies using this approach have shown that inhibition of Ca2+ release from the SR, or inhibition of CaMKII, prevents the increase in glucose transport induced by Ca2+ (63, 64). The other pathway involves the AMP-activated protein kinase (AMPK), which is activated by the decreases in ATP and creatine phosphate and increase in AMP induced by contractions. This phenomenon has been studied extensively using aminoimidazole-4-carboxamide-1-
-D-ribofuranoside (AICAR), which is converted to the AMP analog 5-aminoimidazole-4-carboxamide-1-
-D-ribofuraosyl 5'-monophosphate (22, 23, 49, 59, 60). Of these two pathways, the Ca2+-activated one appears to be the more important, because it functions in both fast-twitch and slow-twitch muscle, whereas the AMPK-mediated mechanism functions only in fast-twitch muscle (at least in the rat) (63). The steps downstream of CaMKII and AMPK remain to be elucidated.
| PERSISTENT EFFECT OF EXERCISE ON MUSCLE GLUCOSE TRANSPORT |
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50% of the increase in glucose uptake had worn off in rats fed a carbohydrate-free diet, whereas the increase in uptake had completely reversed in rats fed carbohydrate to raise muscle glycogen (68). Because there was no insulin in the perfusion medium, we erroneously attributed the persistent increase in glucose uptake 18 h after exercise to a slowing of reversal of the exercise-induced, insulin-independent increase in glucose uptake as a result of prevention of glycogen repletion. Subsequent studies on muscles incubated in vitro showed that the increase in muscle glucose transport induced by exercise reverses within 23 h even in the absence of glycogen repletion (19, 41, 67). Incubation of muscles with 33% rat serum or a very low concentration of insulin, 7.5 µU/ml, appeared to markedly slow reversal of the increase in glucose transport (67). However, what appeared to be a slowing of reversal actually turned out to be due to a large increase in insulin sensitivity (19). Thus the increase in glucose transport observed by Young et al. (68) 18 h after exercise in muscles perfused with insulin-free medium was likely due to the markedly enhanced action of endogenous insulin still bound to the muscle insulin receptors and to an increase in GLUT4 glucose transporters induced by the exercise (see below).
In light of evidence that glycogen depletion enhances, and glycogen supercompensation reduces insulin action (9, 30, 70), Cartee et al. (4) compared the effects of a high-carbohydrate diet and a carbohydrate-free diet on persistence of the increase in muscle insulin sensitivity after exercise. Three hours after exercise, insulin sensitivity of glucose transport was increased in epitrochlearis muscles in both carbohydrate fed and fasted rats. However, 18 h after exercise, the increase in insulin action had completely reversed, whereas it persisted for at least 48 h in rats fed a carbohydrate-free diet. We interpreted these findings to indicate that carbohydrate restriction results in a marked prolongation of the increase in insulin sensitivity. In retrospect, I think this interpretation was incorrect. The following year it was discovered that endurance exercise induces an adaptive increase in the GLUT4 isoform of the glucose transporter in skeletal muscle (11, 42, 48).
In these and a number of subsequent studies of this phenomenon, prolonged training programs were used, because it was thought that the adaptation of muscle to exercise is a slow process. However, it turned out that the GLUT4 protein has a very short half-life and that the increase in GLUT4 protein occurs very rapidly in response to a single bout of exercise (18, 44). In a study by Ren et al. (44), it was found that GLUT4 protein expression was increased by
50% in epitrochlearis muscles 16 h after a bout of swimming. This study and others showed that maximal insulin- or contraction-stimulated glucose transport is increased in proportion to the increase in GLUT4 protein (28, 29, 34, 35, 44). This increase in glucose transport is mediated by translocation of more GLUT4 to the cell surface (34, 35, 44). Feeding a high-carbohydrate diet, with development of glycogen supercompensation, prevents the increase in insulin responsiveness (28, 34, 35). On the other hand, the increase in GLUT4 and insulin responsiveness persists for days if glycogen supercompensation is prevented by feeding a carbohydrate-free diet (13). In light of this information, I now think that the increase in insulin action that we observed 18 and 48 h after exercise was due to an increase in GLUT4 rather than a persistent increase in insulin sensitivity.
This raises the question: Why did we not detect an increase in insulin responsiveness? We calculated insulin responsiveness as the increase in glucose transport above basal in response to a maximal insulin stimulus. However, "basal" transport was significantly increased 18 h after exercise in the muscles from rats not fed carbohydrate. The absolute rate of glucose transport, which reflects the total number of GLUT4 molecules at the cell surface, was actually significantly higher in the glycogen-depleted muscles exposed to a maximal insulin stimulus 18 h after exercise. However, maximally insulin-stimulated glucose transport was only
22% higher in the glycogen-depleted muscles 18 h after exercise than in the muscles from nonexercised controls. This effect is much smaller than the 60% increase in insulin responsiveness that we have subsequently observed 16 h after one exercise bout (44).
It is not possible at this point to explain this discrepancy; however, a difference in study design that could have influenced the results is the duration of the swimming, 2 h in the study by Cartee et al. (4) and 6 h in the study of GLUT4 biogenesis by Ren et al. (44). Although the exercise-induced increase in GLUT4 is responsible for the increase in insulin- and contraction-stimulated glucose transport 16 h or longer after exercise, an increase in GLUT4 is clearly not involved in the increase in muscle insulin sensitivity seen 24 h after exercise. Evidence for this conclusion includes the finding that inhibition of protein synthesis does not prevent the increase in insulin sensitivity (10).
| EXERCISE INCREASES THE SUSCEPTIBILITY OF MUSCLE GLUCOSE TRANSPORT TO VARIOUS STIMULI |
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| REQUIREMENT FOR A SERUM FACTOR |
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| EXERCISE MIMETICS |
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| STUDIES OF THE MECHANISMS BY WHICH THE INCREASE IN MUSCLE INSULIN SENSITIVITY IS MEDIATED |
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It has been argued that this conclusion is incorrect and that the increase in GLUT4 photolabeling may be explained by an increase in GLUT4 intrinsic activity that results in both an increase in glucose transport and an increase in binding of the photolabel to GLUT4. Direct testing of this alternative hypothesis will require development of new technology. However, available evidence argues against it. It has been shown, using the same protocol, that unlike the increase in insulin sensitivity, the response of glucose transport to a maximal insulin stimulus is not augmented 3 h after exercise (19). If GLUT4 intrinsic activity were increased 3 h after exercise, the effect of a maximal insulin stimulus on glucose transport, i.e., responsiveness, would also be increased.
There has been much interest in the possibility that the increase in insulin sensitivity after exercise is mediated by an amplification of the insulin signal. However, it seems well documented now that a submaximal insulin stimulus does not result in greater activation of any of the known steps of the insulin-signaling pathway in muscle after exercise (10, 16, 20, 54, 61, 62). This finding is in keeping with the evidence that the increase in sensitivity is not specific for insulin but that it also involves increased sensitivity to agents that activate glucose transport via the contraction/hypoxia-stimulated pathway (3, 10). Apparently, the increase in "insulin" sensitivity is mediated by a mechanism that lies downstream of the insulin-signaling and contraction/hypoxia-signaling pathways.
It has been suggested that the activation of p38 MAPK plays a role in mediating the increases in glucose transport induced by insulin and muscle contractions (50, 51). Thong et al. (53) found that the increase in p38 phosphorylation induced by exercise in skeletal muscle lasts for at least 3 h. This finding led Thong et al. to hypothesize that p38 activation may be involved in mediating the exercise-induced increase in muscle insulin sensitivity. To evaluate this possibility, Geiger et al. (15) tested the hypothesis that activation of p38 results in an increase in muscle insulin sensitivity. To activate p38, soleus and epitrochlearis muscles were exposed to anisomycin for 30 min. The treatment with anisomycin resulted in an increase in p38 phosphorylation and also stimulated glucose transport approximately threefold. Three hours later, when the acute effect of anisomycin on glucose transport had largely worn off, insulin sensitivity of muscle glucose transport was markedly increased. Pretreatment of muscles with the inhibitor of p38 SB-202190 completely prevented both the activation of p38 and the increase in insulin sensitivity. At this point of the study, it seemed likely that activation of p38 might be the mechanism by which exercise induces an increase in insulin sensitivity. So these findings generated considerable excitement until it was discovered that blocking activation of p38 with SB-202190 does not prevent the increase in muscle insulin sensitivity induced by contractions. Thus it appears that activation of p38 results in increased muscle insulin sensitivity, contractions activate p38, yet activation of p38 is not necessary for the contraction-induced increase in insulin sensitivity.
| A HYPOTHESIS REGARDING THE MECHANISM UNDERLYING INCREASED MUSCLE "INSULIN SENSITIVITY" |
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Our current working hypothesis is that the graded response is explained by generation of a weaker insulin, or contraction, signal in some regions of the muscle cell than in others. The GLUT4 that are translocated in response to a weak signal are in regions where the strongest signal is generated. Increasing the strength of the signal results in progressive recruitment of GLUT4 from regions in which the signal is more attenuated. In keeping with this hypothesis, the peroxovanadium compound bisperoxo(1,10-phenanthroline)oxovanadate anion, which generates a much more powerful insulin signal than does a maximally effective insulin concentration, results in increases in GLUT4 translocation and glucose transport that are twice as great as those induced by a maximal insulin stimulus (39).
In the context of this hypothesis, an increase in insulin sensitivity could be mediated by movement of a larger proportion of the GLUT4 that are available for translocation into regions in which the insulin signal is strongest. A finding that does not fit with this scenario is that sensitivity of glucose transport to activation by the exercise/hypoxia pathway is also increased after exercise. To accommodate this finding, it was necessary to modify and extend the hypothesis as follows: when the stimulus that caused GLUT4 translocation is removed, and its effect reverses, the GLUT4 leaves the cell surface and move into an intracellular compartment in which they are highly susceptible to recruitment by either a weak insulin signal or weak contraction/hypoxia signal. The increase in sensitivity of glucose transport to activation persists for as long as the GLUT4 remains in this "high-susceptibility compartment."
| CONCLUDING REMARKS |
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| GRANTS |
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| ACKNOWLEDGMENTS |
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| FOOTNOTES |
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The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
| REFERENCES |
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and
by insulin and contraction in rat skeletal muscle. Potential role in the stimulation of glucose transport. Diabetes 49: 17941800, 2000.
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