Paul F. Pilch, Ph.D.

Insulin action in fat and muscle

The modern Western diet coupled with a sedentary lifestyle has led to an epidemic of obesity, a consequence of which is a dramatic rise in the incidence of type II diabetes, a malfunction in insulin-regulated metabolism. At the cellular level, type II diabetes is characterized by failure of insulin to act in liver, muscle and fat, and we study aspects of insulin signaling and action in the latter two tissues. Insulin resistance in muscle (and fat) derives from the failure of insulin to activate the tissue-specific glucose transporter GLUT4. The activation mechanism for this process involves vesicle trafficking and protein targeting with regard to GLUT4 and the insulin receptor. We are characterizing the formation and protein content of GLUT4-containing vesicles; we are trying to identify the organelles through which they pass on their way to and from the cell surface and we are determining the communication mechanism(s) from the insulin receptor to the GLUT4-containing vesicles (refs. 1, 3, 5 & 8). These studies involve both fat (refs. 1, 3, 8) and muscle cells (refs. 4, 5, 8), and we are also studying the physiological role of cell surface (plasma membrane) microdomains called caveolae that are particularly abundant in fat and muscle (ref. 7). We are testing the hypothesis that caveolae (for little caves that are small invaginations of the plasma membrane into the cytosol) are involved in lipid trafficking (ref. 6). A consequence of high circulating levels of lipid (fatty acids) is rapid induction of the muscle specific mitochondrial uncoupling protein (UCP-3 ) (ref. 2). We continue to study the regulation of this protein and other aspects of muscle cell biology to understand the interplay between glucose and fat metabolism as well as the interplay between adipocytes and muscle required for overall metabolic homeostasis. Indeed, we wish to uncover the mechanism(s) by exercise also regulates some of these same parameters independent of insulin. Understanding these pathways will help us to figure out how they are compromised in pathophysiological states such as diabetes.

References:

1. El-Jack, A.K., Kandror, K. V, and Pilch, P.F. (1999) The formation of an insulin-responsive vesicular cargo compartment is an early event in 3T3-L1 adipocyte differentiation. Mol. Biol. Cell, 10, 1581-1594.

2. Zhou, M., Lin, B.-Z., Coughlin, S., Vallega, G. and Pilch, P.F. (2000) UCP-3 expression in skeletal muscle: effects of exercise, hypoxia, and AMP-activated protein kinase. Am. J. Physiol., 279, E622-E629

3. Martinez, C., Vallega, G., and Pilch P.F.(2000) Insulin-Dependent Phosphorylation of a 70-kDa Protein in Light Microsomes from Rat Adipocytes. Biochem. Biophys. Res. Commun.276, 1302-1305.

4. Tortorella, L.L., Milasincic, D. J. and Pilch, P.F. (2001) Critical Proliferation-independent Window for Basic Fibroblast Growth Factor Repression of Myogenesis via the p42/p44 MAPK Signaling Pathway. J Biol Chem. 276,13709-13717.

5. Tortorella, L.L. and Pilch, P.F. (2002) C2C12 myocytes lack an insulin responsive vesicular compartment despite dexamethasone-induced Glut4 expression. Am. J. Physiol., Endocrinol Metab. 283: E514-524.

6. Kamp ,F., Guo, W., Souto, R., Pilch, P.F., Corkey, B.E., and Hamilton, J.A. (2003) Rapid flip-flop of oleic acid across the plasma membrane of adipocytes. J Biol Chem. 278, 7988-7995.

7. Souto RP, Vallega G, Wharton J, Vinten J, Tranum-Jensen J, Pilch PF. (2003) Immunopurification and characterization of rat adipocyte caveolae suggest their dissociation from insulin signaling. J Biol Chem. 278, 18321-18329.

8. Tojo. H., Kaieda , I., Hattori, H., Katayama, N., Yoshimura, K., Kakimoto, S., Fujisawa, Y., Presman, E., Brooks, C.C., and Pilch, P.F. (2003) The Formin family protein, formin homolog overexpressed in spleen, interacts with the insulin-responsive aminopeptidase and profilin IIa. Mol Endocrinol. 17, 1216-1229.

9. Tojo H, Kaieda I, Hattori H, Katayama N, Yoshimura K, Kakimoto S, Fujisawa Y, Presman E, Brooks CC, Pilch PF. The Formin family protein, formin homolog overexpressed in spleen, interacts with the insulin-responsive aminopeptidase and profilin IIa. Mol Endocrinol. 2003;17:1216-29.


	Paul F. Pilch, Ph.D. Insulin action in fat and muscle The modern Western diet coupled with a sedentary lifestyle has led to an epidemic of obesity, a consequence of which is a dramatic rise in the incidence of type II diabetes, a malfunction in insulin-regulated metabolism. At the cellular level, type II diabetes is characterized by failure of insulin to act in liver, muscle and fat, and we study aspects of insulin signaling and action in the latter two tissues. Insulin resistance in muscle (and fat) derives from the failure of insulin to activate the tissue-specific glucose transporter GLUT4. The activation mechanism for this process involves vesicle trafficking and protein targeting with regard to GLUT4 and the insulin receptor. We are characterizing the formation and protein content of GLUT4-containing vesicles; we are trying to identify the organelles through which they pass on their way to and from the cell surface and we are determining the communication mechanism(s) from the insulin receptor to the GLUT4-containing vesicles (refs. 1, 3, 5 & 8). These studies involve both fat (refs. 1, 3, 8) and muscle cells (refs. 4, 5, 8), and we are also studying the physiological role of cell surface (plasma membrane) microdomains called caveolae that are particularly abundant in fat and muscle (ref. 7). We are testing the hypothesis that caveolae (for little caves that are small invaginations of the plasma membrane into the cytosol) are involved in lipid trafficking (ref. 6). A consequence of high circulating levels of lipid (fatty acids) is rapid induction of the muscle specific mitochondrial uncoupling protein (UCP-3 ) (ref. 2). We continue to study the regulation of this protein and other aspects of muscle cell biology to understand the interplay between glucose and fat metabolism as well as the interplay between adipocytes and muscle required for overall metabolic homeostasis. Indeed, we wish to uncover the mechanism(s) by exercise also regulates some of these same parameters independent of insulin. Understanding these pathways will help us to figure out how they are compromised in pathophysiological states such as diabetes. References: 1. El-Jack, A.K., Kandror, K. V, and Pilch, P.F. (1999) The formation of an insulin-responsive vesicular cargo compartment is an early event in 3T3-L1 adipocyte differentiation. Mol. Biol. Cell, 10, 1581-1594. 2. Zhou, M., Lin, B.-Z., Coughlin, S., Vallega, G. and Pilch, P.F. (2000) UCP-3 expression in skeletal muscle: effects of exercise, hypoxia, and AMP-activated protein kinase. Am. J. Physiol., 279, E622-E629 3. Martinez, C., Vallega, G., and Pilch P.F.(2000) Insulin-Dependent Phosphorylation of a 70-kDa Protein in Light Microsomes from Rat Adipocytes. Biochem. Biophys. Res. Commun.276, 1302-1305. 4. Tortorella, L.L., Milasincic, D. J. and Pilch, P.F. (2001) Critical Proliferation-independent Window for Basic Fibroblast Growth Factor Repression of Myogenesis via the p42/p44 MAPK Signaling Pathway. J Biol Chem. 276,13709-13717. 5. Tortorella, L.L. and Pilch, P.F. (2002) C2C12 myocytes lack an insulin responsive vesicular compartment despite dexamethasone-induced Glut4 expression. Am. J. Physiol., Endocrinol Metab. 283: E514-524. 6. Kamp ,F., Guo, W., Souto, R., Pilch, P.F., Corkey, B.E., and Hamilton, J.A. (2003) Rapid flip-flop of oleic acid across the plasma membrane of adipocytes. J Biol Chem. 278, 7988-7995. 7. Souto RP, Vallega G, Wharton J, Vinten J, Tranum-Jensen J, Pilch PF. (2003) Immunopurification and characterization of rat adipocyte caveolae suggest their dissociation from insulin signaling. J Biol Chem. 278, 18321-18329. 8. Tojo. H., Kaieda , I., Hattori, H., Katayama, N., Yoshimura, K., Kakimoto, S., Fujisawa, Y., Presman, E., Brooks, C.C., and Pilch, P.F. (2003) The Formin family protein, formin homolog overexpressed in spleen, interacts with the insulin-responsive aminopeptidase and profilin IIa. Mol Endocrinol. 17, 1216-1229. 9. Tojo H, Kaieda I, Hattori H, Katayama N, Yoshimura K, Kakimoto S, Fujisawa Y, Presman E, Brooks CC, Pilch PF. The Formin family protein, formin homolog overexpressed in spleen, interacts with the insulin-responsive aminopeptidase and profilin IIa. Mol Endocrinol. 2003;17:1216-29.