PhD, Center for Research and Advanced Studies, Mexico City, 1976
|Address||The Hospital for Sick Children
686 Bay Street Room 19.9-709
Toronto, ON M5G 0A4
|Lab||Amira Klip Lab|
Following her PhD in Biochemistry (on the use of photolabels to study protein structure/function) Dr. Klip did 2 years of postdoctoral studies at The University of Toronto with Dr. D. MacLennan followed by 1 year at the ETH in Zurich with Dr. G. Semenza. This turned her interest to membrane transport proteins, SERCA and SGLT. In 1980 Dr. Klip was appointed as Scientist at SickKids and began her independent career on the regulation of glucose transport by the other family of mammalian transporters, GLUTs. This led her to investigating insulin signal transduction and set her lab on a path to unravel the signals from the insulin receptor to the responding glucose transporters. In parallel, she characterized biochemically the muscle glucose transporter (GLUT4) and discovered its regulation by insulin and exercise through distinct recruitment mechanisms. Her lab’s signal transduction studies revealed the unexpected involvement of the small molecular G proteins Rac1, Rab 8 and Rab13 as molecular switches linking to mechanical effectors mobilizing GLUT4-containing vesicles.
In addition to normal insulin action the Klip lab also investigated insulin resistance, its molecular origins and complex causes in the body resulting from lipid overload and obesity. They currently study how immune cells become inflamed in obesity and how they impact on muscle cells. They recently discovered that saturated lipids turn macrophages inflammatory and products thereof in turn activate signals within muscle cells that interfere with insulin signalling. Conversely, saturated fatty acids make muscle cells express pannexins that release nucleotides which chemoattract monocytes. This cellular crosstalk may underpin their observed infiltration of muscle by immune cells during obesity and its contribution to insulin resistance. This work was performed by over 70 graduate students and fellows, that she mentors with passion.
Dr. Klip was an Associate Chief of Research at SickKids for over 15 years, where she created and directed for 14 years the Research Training Centre as a hub of information and opportunities for students and fellows of all disciplines. She has organized international meetings, is a past Editor-in-Chief of the American Journal of Physiology-Endocrinology & Metabolism, and continues to serve on a number of editorial boards, as well as on national and international grant panels. Her work is supported by CIHR, the Canadian Diabetes Association and the Banting and Best Diabetes Centre. Klip holds a Tier I Canada Research Chair on the Cell Biology of Insulin Action.
Cellular and biochemical basis of insulin action and insulin resistance: focus on glucose transport
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. The liver provides the rest of the body with glucose between meals, especially the brain. However, 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 is not completely understood. Insulin resistance, a key defect in type 2 diabetes, involves defective responses to insulin in muscle, adipose and hepatic tissues.
Klip’s laboratory has been studying the regulation of glucose uptake by insulin and muscle contraction, using an array of rat and mouse stable muscle cell lines that they have generated. The focus is the intracellular traffic of vesicles containing glucose transporters, primarily GLUT4. Current work focuses on how a series of signal transduction pathways activated by insulin within muscle cells impinge on intracellular stores of GLUT4, how the vesicles move to the cell surface, and how they are further turned-on into faster carriers. This recruitment of transporters and their subsequent activation requires participation of the actin cytoskeleton for faithful congregation of the pertinent signals and gathering of GLUT4 below the plasma membrane.
Her lab’s studies have revealed two important bifurcations in insulin action, one defined by different outcomes of the insulin receptor substrate 1 (IRS-1) protein and insulin receptor substrate 2 (IRS-2) protein, the other defined by two signalling arms downstream of phosphatidylinositol 3-kinase (PI 3-kinase). The Akt/PKB arm, a serine/threonine protein kinase that plays a key role in multiple cellular processes such as glucose metabolism, cell proliferation, apoptosis, transcription and cell migration, leads to the inactivation of the RAb-GAP AS160 (Akt substrate of 160 kDa), which acts through distinct Rab molecules to mobilize and position GLUT4 vesicles. In muscle cells, their work identifies Rab8A, Rab13 and Rab14 as important mediators of these steps. On the other hand, the Rac activation arm functions to rapidly remodel actin filaments into a cortical mesh below the cell surface, as shown through a dynamic cycle of actin branching mediated by Arp2/3 and severing mediated by actin-binding proteins know as cofilin. Vesicles mobilized to the cell cortex interact with the actin mesh through actinin-4, possibly in preparation for optimal docking and fusion with the membrane. Klip’s team has also identified the SNARE molecules VAMP2, syntaxin4 and SNAP23 as mediators of this docking/fusion step. GLUT4 arrives at the cell surface in a state of low activity but are soon activated by a pathway that may involve the removal of ancillary inhibitors or the binding of activators of GLUT4. In particular, GAPDH binds to GLUT4 as Hexokinase II is displaced, possibly accounting for the activation of the transporter.
In a new series of studies, the Klip lab has also established cellular models to study insulin resistance:
- Exposure of muscle cell cultures to high glucose and high insulin, emulating the environment in type 2 diabetes;
- Exposure to high saturated fats or their derivative ceramides and reactive oxygen species, emulating the lipotoxic component of the metabolic syndrome; and
- Exposure to conditioned media from palmitate-treated macrophages, emulating the inflammation component of insulin resistance.
In each case, GLUT4 translocation in response to insulin was dampened, but interestingly through distinct signalling defects, respectively: reduction in IRS-1 phosphorylation, in Rac activation and in Akt and AS160 phosphorylation. These findings suggest that insulin resistance in vivo must be analyzed at each signalling level and may require distinct and specific interventional therapies.
View all publications on PubMed
Calcium signaling in insulin action on striated muscle.
Contreras-Ferrat A, Lavandero S, Jaimovich E, Klip A.
Cell Calcium. 2014 Sep 6. pii: S0143-4160(14)00135-3. Read
Nucleotides released from palmitate-challenged muscle cells through pannexin-3 attract monocytes.
Pillon NJ, Li YE, Fink LN, Brozinick JT, Nikolayev A, Kuo MS, Bilan PJ, Klip A.
Diabetes. 2014 Nov;63(11):3815-26. Read
Mice lacking NOX2 are hyperphagic and store fat preferentially in the liver.
Costford SR, Castro-Alves J, Chan KL, Bailey LJ, Woo M, Belsham DD, Brumell JH, Klip A.
Am J Physiol Endocrinol Metab. 2014 Jun 15;306(12):E1341-53. Read
Dynamic GLUT4 sorting through a syntaxin-6 compartment in muscle cells is derailed by insulin resistance-causing ceramide.
Foley KP, Klip A.
Biol Open. 2014 Apr 4;3(5):314-25. Read