BADERC- Laurie J. Goodyear

Laurie J. Goodyear, Ph.D.

Exercise Regulation of Glucose Transport in Skeletal Muscle

The 1996 report of the US Surgeon General states that the performance of regular physical exercise results in numerous health benefits including a reduced risk of developing type 2 diabetes. Physical exercise is also widely accepted as a clinically important modality to decrease blood glucose concentrations in patients with diabetes, due largely to an increase in the rate of glucose transport into the contracting skeletal muscles and an increase in insulin sensitivity in the period following exercise. Despite the profound clinical importance of the metabolic effects of exercise, until recently, there was little focus on understanding the underlying molecular mechanisms that mediate these responses. A major goal of the work in the Goodyear laboratory is to elucidate the mechanisms through which physical exercise increases glucose transport and insulin sensitivity in skeletal muscle. Studies in our laboratory and by other groups have shown that both exercise and insulin increase glucose transport through the translocation of the GLUT4 glucose transporter. Furthermore, we and others have suggested that the intracellular signal transduction mechanisms that lead to the stimulation of GLUT4 translocation by exercise and insulin are distinct. The mechanism responsible for this “insulin-independent” activation of glucose transport has long been elusive. However, our recent work, along with studies from other groups, have provided strong evidence that the AMP-activated protein kinase (AMPK) is part of the signaling mechanism by which exercise increases glucose transport in skeletal muscle. One of our current goals is to understand the mechanism by which AMPK regulates glucose transport in muscle, including studies to identify AMPK substrates. In addition to AMPK, it is now clear that there must be other molecules involved in the regulation of exercise-stimulated glucose transport. Thus, another major focus of our work is to identify novel signaling mechanisms for the regulation of insulin-independent glucose transport. To determine the molecular basis for post-exercise increases in insulin action, our work is focussed on elucidating novel proteins and to investigate the roles of Akt and GSK-3 signaling in this phenomenon, protein kinases that we have recently discovered are regulated in contracting skeletal muscle.

In addition to the acute effects of a single bout of exercise on muscle glucose metabolism, exercise training can lead to numerous chronic adaptations to skeletal muscle. These adaptations are fundamental for the salutary effects of increased physical activity on several human diseases including diabetes and congestive heart failure. The stimulus for these changes is thought to be initiated by each individual bout of exercise, as a single exercise session can significantly alter rates of gene transcription and protein synthesis. In working to understand how the contraction stimulus signals the transcriptional and protein synthetic processes, we have discovered that exercise robustly increases MAP kinase signaling cascades, including ERK, c-jun kinase, and p38 kinase. Since these molecules have been implicated in the regulation of multiple transcriptional processes, studies are underway to determine if the effects of chronic exercise to cause skeletal muscle remodeling involves the activation of these intracellular signal transduction cascades.

To address all of these questions we use a combination of molecular and physiological approaches including contraction of rodent skeletal muscles in vitro and in situ, knockout and transgenic mice, as well as our recent development of a technique to overexpress foreign proteins into adult rodent skeletal muscle using electroporation. Our discoveries using animal experimentation have provided the basis for our multiple studies investigating glucose transport regulation in the skeletal muscle of people with diabetes. All of this work should help define the molecular basis for the important adaptations that occur in skeletal muscle in response to exercise, and will have important ramifications for patients with diabetes.

References:

1. Hayashi T, Hirshman MF, Kurth EJ, Winder WW, Goodyear LJ. Evidence for 5’AMP-activated protein kinase mediation of the effect of muscle contraction on glucose transport. Diabetes 1998;47(8);1369-1373.

2. Higaki Y, Wojtaszewski JFP, Hirshman MF, Withers DJ, Towery H, White MF, Goodyear LJ. Insulin receptor substrate-2 is not necessary for insulin- and exercise-stimulated glucose transport in skeletal muscle. J. Biol. Chem. 1999;274:20791-20795.

3. Markuns, JF, Wojtaszewski JFP, Goodyear LJ. Insulin and exercise decrease glycogen synthase kinase-3 activity by different mechanisms in rat skeletal muscle. J. Biol. Chem. 1999;274:24896-24900.

4. Wojtaszewski JFP, Higaki Y, Hirshman MF, Michael MD, Dufresne SD, Kahn CR, Goodyear LJ. Exercise modulates postreceptor insulin signaling and glucose transport in muscle-specific insulin receptor knockout mice. J. Clin. Invest. 1999;104:1257-1264.

5. Dufresne SD, Bjorbaek C, El-Hashimi K, Zhao Y, Aschenbach WG, Moller DE, Goodyear LJ. Altered extracellular signal-regulated kinase signaling and glycogen metabolism in skeletal muscle from p90 ribosomal S6 kinase 2 knockout mice. Mol. Cell Biol. 2001; 21:81-87.

6. Tian R, Musi N, D’Agostino J, Hirshman MF, Goodyear LJ. Increased adenosine momophosphated-activated protein kinase activity in rat hearts with pressure overload hypertrophy. Circulation 2001; 104(14):1664-1669.

7. Sakamoto K, Hirshman MF, Aschenbach WG, Goodyear LJ. Contraction regulation of Akt in rat skeletal muscle. J. Biol. Chem. 2002; 277:11910-11917.

8. Musi N, Hirshman MF, Nygren J, Svanfeldt M, Bavenholm P, Rooyackers O, Zhou G, Williamson J, Ljunqvist O, Efendic S, Moller DE, Thorell A, Goodyear LJ. Metformin increases AMP-activated protein kinase activity in skeletal muscle of subjects with type 2 diabetes. Diabetes 2002; 51:2074-2081.

9. Sakamoto K, Aschenbach WG, Hirshman MF, Goodyear LJ. Akt signaling in skeletal muscle: regulation by exercise and passive stretch. Am J Physiol Endocrinol Metab. 2003;285:E1081-8.

10. Ho RC, Alcazar O, Fujii N, Hirshman MF, Goodyear LJ. p38gamma MAPK regulation of glucose transporter expression and glucose uptake in L6 myotubes and mouse skeletal muscle. Am J Physiol Regul Integr Comp Physiol. 2004;286:R342-9.

11. Yu H, Fujii N, Hirshman MF, Pomerleau JM, Goodyear LJ. Cloning and characterization of mouse 5'-AMP-activated protein kinase gamma3 subunit. Am J Physiol Cell Physiol. 2004;286:C283-92.

12. Fujii N, Boppart MD, Dufresne SD, Crowley PF, Jozsi AC, Sakamoto K, Yu H, Aschenbach WG, Kim S, Miyazaki H, Rui L, White MF, Hirshman MF, Goodyear LJ. Overexpression or ablation of JNK in skeletal muscle has no effect on glycogen synthase activity.Am J Physiol Cell Physiol. 2004;287:C200-8.






			Laurie J. Goodyear, Ph.D. Exercise Regulation of Glucose Transport in Skeletal Muscle The 1996 report of the US Surgeon General states that the performance of regular physical exercise results in numerous health benefits including a reduced risk of developing type 2 diabetes. Physical exercise is also widely accepted as a clinically important modality to decrease blood glucose concentrations in patients with diabetes, due largely to an increase in the rate of glucose transport into the contracting skeletal muscles and an increase in insulin sensitivity in the period following exercise. Despite the profound clinical importance of the metabolic effects of exercise, until recently, there was little focus on understanding the underlying molecular mechanisms that mediate these responses. A major goal of the work in the Goodyear laboratory is to elucidate the mechanisms through which physical exercise increases glucose transport and insulin sensitivity in skeletal muscle. Studies in our laboratory and by other groups have shown that both exercise and insulin increase glucose transport through the translocation of the GLUT4 glucose transporter. Furthermore, we and others have suggested that the intracellular signal transduction mechanisms that lead to the stimulation of GLUT4 translocation by exercise and insulin are distinct. The mechanism responsible for this “insulin-independent” activation of glucose transport has long been elusive. However, our recent work, along with studies from other groups, have provided strong evidence that the AMP-activated protein kinase (AMPK) is part of the signaling mechanism by which exercise increases glucose transport in skeletal muscle. One of our current goals is to understand the mechanism by which AMPK regulates glucose transport in muscle, including studies to identify AMPK substrates. In addition to AMPK, it is now clear that there must be other molecules involved in the regulation of exercise-stimulated glucose transport. Thus, another major focus of our work is to identify novel signaling mechanisms for the regulation of insulin-independent glucose transport. To determine the molecular basis for post-exercise increases in insulin action, our work is focussed on elucidating novel proteins and to investigate the roles of Akt and GSK-3 signaling in this phenomenon, protein kinases that we have recently discovered are regulated in contracting skeletal muscle. In addition to the acute effects of a single bout of exercise on muscle glucose metabolism, exercise training can lead to numerous chronic adaptations to skeletal muscle. These adaptations are fundamental for the salutary effects of increased physical activity on several human diseases including diabetes and congestive heart failure. The stimulus for these changes is thought to be initiated by each individual bout of exercise, as a single exercise session can significantly alter rates of gene transcription and protein synthesis. In working to understand how the contraction stimulus signals the transcriptional and protein synthetic processes, we have discovered that exercise robustly increases MAP kinase signaling cascades, including ERK, c-jun kinase, and p38 kinase. Since these molecules have been implicated in the regulation of multiple transcriptional processes, studies are underway to determine if the effects of chronic exercise to cause skeletal muscle remodeling involves the activation of these intracellular signal transduction cascades. To address all of these questions we use a combination of molecular and physiological approaches including contraction of rodent skeletal muscles in vitro and in situ, knockout and transgenic mice, as well as our recent development of a technique to overexpress foreign proteins into adult rodent skeletal muscle using electroporation. Our discoveries using animal experimentation have provided the basis for our multiple studies investigating glucose transport regulation in the skeletal muscle of people with diabetes. All of this work should help define the molecular basis for the important adaptations that occur in skeletal muscle in response to exercise, and will have important ramifications for patients with diabetes. References: 1. Hayashi T, Hirshman MF, Kurth EJ, Winder WW, Goodyear LJ. Evidence for 5’AMP-activated protein kinase mediation of the effect of muscle contraction on glucose transport. Diabetes 1998;47(8);1369-1373. 2. Higaki Y, Wojtaszewski JFP, Hirshman MF, Withers DJ, Towery H, White MF, Goodyear LJ. Insulin receptor substrate-2 is not necessary for insulin- and exercise-stimulated glucose transport in skeletal muscle. J. Biol. Chem. 1999;274:20791-20795. 3. Markuns, JF, Wojtaszewski JFP, Goodyear LJ. Insulin and exercise decrease glycogen synthase kinase-3 activity by different mechanisms in rat skeletal muscle. J. Biol. Chem. 1999;274:24896-24900. 4. Wojtaszewski JFP, Higaki Y, Hirshman MF, Michael MD, Dufresne SD, Kahn CR, Goodyear LJ. Exercise modulates postreceptor insulin signaling and glucose transport in muscle-specific insulin receptor knockout mice. J. Clin. Invest. 1999;104:1257-1264. 5. Dufresne SD, Bjorbaek C, El-Hashimi K, Zhao Y, Aschenbach WG, Moller DE, Goodyear LJ. Altered extracellular signal-regulated kinase signaling and glycogen metabolism in skeletal muscle from p90 ribosomal S6 kinase 2 knockout mice. Mol. Cell Biol. 2001; 21:81-87. 6. Tian R, Musi N, D’Agostino J, Hirshman MF, Goodyear LJ. Increased adenosine momophosphated-activated protein kinase activity in rat hearts with pressure overload hypertrophy. Circulation 2001; 104(14):1664-1669. 7. Sakamoto K, Hirshman MF, Aschenbach WG, Goodyear LJ. Contraction regulation of Akt in rat skeletal muscle. J. Biol. Chem. 2002; 277:11910-11917. 8. Musi N, Hirshman MF, Nygren J, Svanfeldt M, Bavenholm P, Rooyackers O, Zhou G, Williamson J, Ljunqvist O, Efendic S, Moller DE, Thorell A, Goodyear LJ. Metformin increases AMP-activated protein kinase activity in skeletal muscle of subjects with type 2 diabetes. Diabetes 2002; 51:2074-2081. 9. Sakamoto K, Aschenbach WG, Hirshman MF, Goodyear LJ. Akt signaling in skeletal muscle: regulation by exercise and passive stretch. Am J Physiol Endocrinol Metab. 2003;285:E1081-8. 10. Ho RC, Alcazar O, Fujii N, Hirshman MF, Goodyear LJ. p38gamma MAPK regulation of glucose transporter expression and glucose uptake in L6 myotubes and mouse skeletal muscle. Am J Physiol Regul Integr Comp Physiol. 2004;286:R342-9. 11. Yu H, Fujii N, Hirshman MF, Pomerleau JM, Goodyear LJ. Cloning and characterization of mouse 5'-AMP-activated protein kinase gamma3 subunit. Am J Physiol Cell Physiol. 2004;286:C283-92. 12. Fujii N, Boppart MD, Dufresne SD, Crowley PF, Jozsi AC, Sakamoto K, Yu H, Aschenbach WG, Kim S, Miyazaki H, Rui L, White MF, Hirshman MF, Goodyear LJ. Overexpression or ablation of JNK in skeletal muscle has no effect on glycogen synthase activity.Am J Physiol Cell Physiol. 2004;287:C200-8.