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Amira
Klip
Professor
Ph.D., Mexico City, 1976 |
Hospital
for Sick Children, McMaster Building, Room
5004B
416-813-6392
amira@sickkids.ca |
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Regulation of Glucose Transport
and Membrane Proteins in Muscle
Research Synopsis
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Glucose is the major energy substrate for most cells, and it is avidly stored as glycogen in the liver and muscle tissue, as well as processed into fat in adipose tissue. During a meal, insulin derived from the pancreas vigorously promotes glucose uptake into muscle and fat cells, and stops the liver from releasing glucose to the blood. The mechanism whereby insulin increases glucose uptake into muscle/fat has received much attention but remains incompletely understood. Insulin resistance, a key defect in type 2 diabetes, involves defective responses to insulin in muscle, adipose and hepatic tissues.
My laboratory has been studying the mechanism of glucose uptake into muscle cells through glucose transporters or GLUTs, using cell biology and biochemical approaches. Our work focuses on how a series of signal transduction pathways activated by insulin within muscle cells impinge on intracellularly stored GLUT4, to move to the cell surface to promote glucose uptake. We also study how these processes of signal transduction and vesicle traffic fail during conditions of insulin resistance, and we re-create in vitro cellular models of muscle-macrophage crosstalk that reveal a participation of inflammatory cues in the genesis of insulin resistance.
Specifically, our studies have revealed that insulin signals bifurcate at the level of the Insulin Receptor Substrates 1 and 2 (IRS1 and IRS2), and then again downstream of phosphatidylinositol 3-kinase (PI 3-kinase). Here two signalling arms emanate, one activating the kinase Akt/PKB and the other activating the small G protein Rac1. Akt phosphorylates and thereby inactivates the Rab-GAP AS160, resulting in activation (GTP loading) of Rab8A and Rab13, which regulate distinct steps in GLUT4 intracellular traffic. Downstream of Rac1 actin filaments are remodelled via a dynamic cycle of branching and severing, culminating in GLUT4 interacting with ACTN4. Both arms contribute to the final fusion of GLUT4 vesicles with the plasma membrane. Further, GLUTs arrive at the cell surface in a state of low activity, but are soon activated by a pathway that may involve the removal of Hexokinase II from the transporter complex. Regarding insulin resistance, we have found that treating muscle cells with saturated fatty acids makes them attract macrophages, which in turn, in the context of the saturated fatty acids, produce inflammatory cytokines that render muscle cells insulin resistant.
Future Research
* Identify how insulin activates Rac1 and what lies downstream of Rabs in the insulin signalling transduction pathway
* Discern the intracellular itinerary of GLUT4 returning from the membrane, through endocytosis and sorting
* Hone in on the crosstalk between muscle cells and macrophages
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Selected Publications
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JeBailey L, Wanono O, Niu W, Roessler J, Rudich A, Klip A. (2007) Ceramide- and Oxidant-Induced Insulin Resistance Involve Loss of Insulin-Dependent Rac-Activation and Actin Remodeling in Muscle Cells. Diabetes 56: 394-403.
Thong FSL, Bilan PJ, Klip A. (2007) The Rab GTPase-Activating Protein AS160 integrates Akt, Protein Kinase C, and AMP-Activated Protein Kinase signals regulating GLUT4 traffic. Diabetes 56: 414-23.
Antonescu CN, Díaz M, Femia G, Planas J, Klip A. (2008) Clathrin-Dependent and Independent Endocytosis of Glucose Transporter 4 (GLUT4) in Myoblasts: Regulation by Mitochondrial Uncoupling. Traffic 9: 1173-90.
Talior-Volodarsky I, Randhawa VK, Zaid H, Klip A. (2008) a - Actinin-4 Is selectively required for insulin-induced GLUT4 translocation. J. Biol. Chem. 283: 25115-23.
Randhawa VK, Ishikura S, Talior-Volodarksy I, Cheng AW, Patel N, Hartwig JH, Klip A. (2008) GLUT4 vesicle recruitment and fusion are differentially regulated by Rac, AS160, and Rab8A in muscle cells. J. Biol. Chem. 283: 27208-19.
Ishikura S, Klip A. (2008) Muscle cells engage Rab8A and myosin Vb in insulin-dependent GLUT4 translocation. Am. J. Physiol. Cell Physiol. 295: C1016-25.
Samokhvalov V, Bilan PJ, Schertzer JD, Antonescu CN, Klip A. (2009) Palmitate- and LPS-activated macro- phages evoke contrasting insulin responses in muscle cells. Am. J. Physiol. Endocrinol. Metab. 296: E37-46.
Zaid H, Talior-Volodarsky I, Antonescu C, Liu Z, Klip A. (2009) GAPDH binds GLUT4 reciprocally to hexokinase-II and regulates glucose transport activity. Biochem. J. 419: 475-84.
Schertzer JD, Antonescu CN, Bilan PJ, Jain S, Huang X, Liu Z, Bonen A, Klip A. (2009) A transgenic mouse model to study GLUT4 myc regulation in skeletal muscle. Endocrinol. 150: 1935-40.
Niu W, Bilan PJ, Ishikura S, Schertzer J, Contreras-Ferrat A, Fu Z, Liu J, Boguslavsky S , Foley K, Liu Z, Li J, Chu G,Panakkezhum T, Lopaschuk G, Lavandero S,Yao Z, Klip A. (2010) Contraction-related stimuli regulate GLUT4 traffic in C 2 C 12 -GLUT4 myc skeletal muscle cells. Am. J. Physiol. Endocrinol. Metab. 298: E1058-71.
Chiu TT, Patel N, Shaw AE, Bamburg JR, Klip A. (2010) Arp2/3- and cofilin-coordinated actin dynamics is required for insulin-mediated GLUT4 translocation to the surface of muscle cells. Mol. Biol. Cell 21: 3529-39.
Tamrakar AK, Schertzer JD, Chiu TT, Foley KP, Bilan PJ, Philpott DJ, Klip A. (2010) NOD2 Activation Induces Muscle Cell-Autonomous Innate Immune Responses and Insulin Resistance. Endocrinol. 151: 5624-37.
Sun Y, Bilan PJ, Liu Z, Klip A. (2010) Rab8A and Rab13 are activated by insulin and regulate GLUT4 translocation in muscle cells. Proc. Natl. Acad. Sci. USA . 107: 19909-14.
Niu W, Bilan PJ, Yu J, Gao J, Boguslavsky S, Schertzer JD, Chu G, Yao Z, Klip A. (2011) PKC e Regulates contraction-stimulated GLUT4 traffic in skeletal muscle cells. J. Cell. Physiol . 226: 173-80.
Schertzer JD, Tamrakar AK, Magalhães JG, Pereira S, Bilan PJ, Fullerton MD, Liu Z, Steinberg GR, Giacca A, Philpott DJ, Klip A. (2011) NOD1 Activators Link Innate Immunity to Insulin Resistance. Diabetes 60: 2206-15.
Yu J, Shi L, Wang H, Bilan PJ, Yao Z, Samaan MC, He Q, Klip A, Niu W. (2011) Conditioned medium from hypoxia-treated adipocytes renders muscle cells insulin resistant. Eur. J. Cell Biol. , Sep 29 Epub ahead of print.
Kewalramani G, Nielsen Fink L, Asadi F, Klip A. (2011) Palmitate-activated macrophages confer insulin resistance to muscle cells by a mechanism involving Protein Kinase C ? and e. PLoS One , Oct 6 accepted/in press.
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