Research at the University
2005 Diabetes Research Highlights
Adeli, Khosrow
Department of Laboratory Medicine & Pathobiology, & Department of Biochemistry, University of Toronto
Head, Clinical Biochemistry, Pediatric Laboratory Medicine, Hospital for Sick Children
Our research program is focused on molecular mechanisms underlying lipid and lipoprotein disorders in insulin resistant states, such as obesity and type 2 diabetes. The incidence of obesity in children and adolescents has been increasing at an alarming rate in recent years, mostly as a result of decreased physical activity and increased availability of high calorie foods. This in turn has contributed to higher incidence of insulin resistance and type 2 diabetes in this population which are frequently accompanied by hyperlipidemia and increased risk of cardiovascular disease later in life. A common finding in these conditions is hepatic overproduction of apolipoprotein B (apoB) and thus increased plasma levels of atherogenic lipoproteins. Our research program is aimed at elucidating the key genetic and environmental factors that link insulin resistance, lipoprotein abnormalities, and cardiovascular disease. We are thus investigating the mechanisms that underlie the development of metabolic dyslipidemia in insulin resistant states at the cellular and molecular levels. Diet-induced animal models of insulin resistance and obesity are deployed to investigate the link between the insulin signaling pathway and deregulation of hepatic and intestinal lipoprotein metabolism. These animal models are also applied to the investigation of the mechanisms of action of hypolipidemic and insulin sensitizing pharmaceutical drugs at the cellular and molecular level. Proteomic profiling of hepatic ER proteins in an animal model of insulin resistance and metabolic dyslipidemia. J. Biol Chem. 2005, 280(18):17626-33 and Fructose, insulin resistance, and metabolic dyslipidemia. Nutr. Metab (Lond). 2005 Feb 21;2(1):5, pages 1-14. [Epub] (Invited Review)
Belsham, Denise D.
Department of Physiology
Recently several researchers in the diabetes field have made the provocative proposal that diabetes is "a disease of the hypothalamus", a specific part of the brain controlling food intake. This statement may be over-reaching, but in the past few years it has been well-established that coordinated regulation of gene expression from the hypothalamus is critical to maintain energy balance. Specifically, it has been proposed that the central nervous system uses overlapping metabolic pathways to control food intake and glucose homeostasis. Recent studies suggest that in addition to regulating food intake, hypothalamic circuits also regulate insulin action, providing some insight into the potential link between type 2 diabetes mellitus and obesity; therefore research is essential to determine the contribution of the hypothalamus. Major efforts are currently underway in our laboratory to dissect the brain pathways involved, with the hope of discovering novel targets for the treatment of these complex disorders. We have generated 38 clonal hypothalamic cell lines with unique phenotypic profiles. Since they express many neuropeptides associated to the control of feeding behaviour, they can be used to study complex cell biology involved in the regulation of proteins linked to the control of feeding and energy homeostasis. The generation of the cell lines are considered by many to be significant progress as only a couple of other hypothalamic cell lines are currently available. The initial paper on the cell lines was published in Endocrinology (145: 393-400, 2004). We have also recently published a study on the regulation of neurotensin (NT) by leptin, insulin, and alpha-MSH (Anorexigenic hormones leptin, insulin, and alpha-melanocyte-stimulating hormone directly induce neurotensin (NT) gene expression in novel NT-expressing cell models. J. Neurosci., 25: 9497-9506, 2005). We have many ongoing studies to understand the control of hypothalamic neuropeptides by nutrients and hormones, such as leptin, insulin, glucose, and ghrelin.
Bendeck, Michelle
Department of Laboratory Medicine and Pathobiology
The focus of research in the Bendeck lab is on atherosclerosis. During the past year we have published a paper reporting the interaction of smooth muscle cells with type VIII collagen, a matrix protein upregulated after vascular injury, which enables cell migration by acting as a slippery substrate. These results elucidate the function of type VIII collagen in the vessel wall, and suggest that inhibition of type VIII collagen may be a good target to reduce vessel thickening in atherosclerosis. Migration and growth are attenuated in vascular smooth muscle cells with type VIII collagen-null alleles. Arterioscler Thromb Vasc Biol. 2006 Jan;26(1):56-61. Doxycycline is an antibiotic with MMP inhibitory activity, and it increases cell-cell and cell-matrix adhesion of smooth muscle cells. The net effect of doxycycline was to inhibit cell growth and migration, making it an attractive candidate for the treatment of atherosclerosis and restenotic vascular disease. (Franco et al. In press, American Journal of Pathology; 2006). In collaboration with Dr. Adria Giacca, we are studying the effect of high glucose and insulin on SMC growth and matrix remodeling in atherosclerosis. We published a paper showing that hyperinsulinemia has atheroprotective effects, inhibiting intimal thickening following balloon injury in the rat carotid artery. Anti-atherogenic effect of insulin in vivo. J Vasc Res. 2005 Nov-Dec;42(6):455-62.
Boyd, Shelley
Department of Ophthalmology & Vision Sciences
Our research focuses on the NeuroVascular aspects of visual loss in diabetes. From a clinical point of view, we challenge the dogma that diabetic retinopathy is a disease of the retinal vessels exclusively. Working in collaboration with the Hospital for Sick Children we are evaluating the changes in neuronal function, from retina to visual cortex, that precede detectable vascular change. In the laboratory, we are studying molecules such as VEGF and erythropoietin, both of which have angiogenic and neuroprotective functions. We are also interested in the mechanisms of neuronal cell death in diabetic retinopathy. Finally, our lab also is investigating the potential role of adult retinal stem cells in tissue repair and regeneration.
Brubaker, Patricia L.
Departments of Physiology and Medicine
Research in the Brubaker lab is focused on the intestinal glucagon-like peptides, GLP-1 and GLP-2, which are released into the circulation following nutrient ingestion. GLP-1 has recently been approved in the USA for the treatment of patients with type 2 diabetes, due to its ability to stimulate insulin secretion, enhance beta cell growth and reduce food intake. GLP-2 is also in clinical trials for the treatment of intestinal insufficiency and inflammation, due to its actions to increase the growth and function of the intestine. A recent study has demonstrated that the mechanism of action of GLP-1 to suppress food intake is mediated through the peripheral vagus nerve, in Peripheral exendin-4 and peptide YY(3-36) synergistically reduce food intake through different mechanisms in mice. Endocrinology. 2005 Sep;146(9):3748-56. The mechanism of action of GLP-1 to protect the pancreatic beta cell from damage has also been examined, in Glucagon-like peptide-1 protects beta cells from cytokine-induced apoptosis and necrosis: role of protein kinase B. Diabetologia. 2005 Jul;48(7):1339-49. Finally, the role of GLP-2 as a physiological regulator of intestinal growth following a prolonged fast was demonstrated, in Mucosal adaptation to enteral nutrients is dependent on the physiologic actions of glucagon-like peptide-2 in mice. Gastroenterology. 2005 May;128(5):1340-53.
Carlen, Peter L.
Departments of Medicine (Neurology) and Physiology
One of the scourges of especially juvenile diabetes is hypoglycemic seizures. Prolonged seizures resulting from low blood sugar can lead to brain damage The Carlen lab has developed an in vitro model to study the pathophysiology of this condition. We use the isolated intact juvenile mouse hippocampus preparation to measure, using mainly electrophysiological techniques, seizure activity accompanying low glucose perfusion. The hippocampus is a brain area intimately involved with memory function and quite susceptible to seizure generation. To date we have discovered that hypoglycemia associated with seizures produces irreversible brain dysfunction. Preventing seizures pharmacologically is neuroprotective as measured by recovery of impaired brain electrical activity and by neuropathological examination. We have demonstrated that losing the glycogen reserves in the brain plays a key role in the generation of hypoglycemic seizures. We have shown that the cerebral cortex is less sensitive to the hypoglycemic insult than the hippocampus. We are now examining the cellular electrophysiological bases for the generation of hypoglycemic seizures in vitro, and studying the electrophysiological and neuropathological concomitants of hypoglycemic seizures in vivo in rats. This work is funded by the Juvenile Diabetes Research Foundation.
Daneman, Denis
Department of Pediatrics
Chief, Division of Endocrinology, The Hospital for Sick Children.
In the past year my research has continued in three areas in type 1 diabetes in children and teens: (i) the epidemiology of diabetic ketoacidosis (DKA) and its complications; (ii) psychosocial determinants of diabetes-related outcomes; and (iii) interventions to improve metabolic control in teens. The DKA research included a country-wide surveillance for cerebral edema to determine which therapeutic factors may predispose to this complication. We also found that many children presenting in DKA at disease onset are seen by physicians in the days preceding diagnosis, when the opportunity to prevent progression to DKA may be missed. Our collaborative research in eating disorders in teenage girls with type 1 diabetes continues into the natural history of this association, with its important short- and long-term consequences. Finally, our group has completed a second study using an adjunctive agent, the insulin sensitizer , Pioglitazone, to improve metabolic control in teens with poorly controlled diabetes. Unlike our previous studies with metformin this TZD was ineffective in lowering A1c levels. We are also involved in an intensive psychosocial intervention in teens with persistently high A1c levels. Population-based study of incidence and risk factors for cerebral edema in pediatric diabetic ketoacidosis. J Pediatr. 2005 May;146(5):688-92, and School attendance in children with Type 1 diabetes. Diabet Med. 2005 Apr;22(4):421-6.
Danska, Jayne
Departments of Immunology & Medical Biophysics
Our objective is identification of Type 1 diabetes (T1D) genes and to obtain a clear understanding of how they orchestrate autoimmune attack of -islet cells. Rodent models have helped advance understanding of the genetic susceptibility, pathology and testing therapies for T1D. Both the complex genetic and autoimmune basis of T1D is shared between humans and the non-obese diabetic (NOD) mouse strain. Many regions of mouse and human genomes have been implicated in T1D but few genes have been identified. Since T1D likely results from many genes working in complex pathways, the influence of single genes is hard to observe. We have studied early steps in autoimmune islet inflammation in the NOD and related mouse strains reasoning that these events might reveal the effects of one or only a few T1D genes. We have found that two chromosomal regions control T cell infiltration into the islets, and the progression from early to severe islet inflammation. We isolated these chromosomal intervals by breeding to generate novel mouse strains and refined their location using information from the mouse and human genome projects. Our goals are to identify the genes at these two mouse chromosomal regions, and to learn how and in what cell types they exert their effects. We use genomic, immunological and computational methods to refine the locations of, and examine the functions of genes controlling diabetes susceptibility. Sex-specific control of type 1 diabetes pathogenesis by the Idd4 locus in the NOD mouse. Journal of Immunology, 2005 Jun 1; 174 (11):7129-40.
Dosch, Hans-Michael
Department of Immunology
- Mouse studies: We have now worked for over 4 yr to identify links between the nervous system and autoimmunity, mainly, but not exclusively, Type 1 Diabetes. Last year we completed characterising an unexpected, critical role for TRPV1+ sensory nerves in islet inflammation & diabetes, with removal of these nerves, systemically or through nerve transsections, preventing islet attack in NOD mice. We cloned TRPV1NOD and identified it as hypofunctional mutant. Our observations describe a new regulatory circuit between b-cells and (insulin-receptor+) TRPV1+ nerves in the pancreas that sets levels of insulin resistance. The hypofunctional TRPV1NOD mediates elevated insulin resistance with hyperinsulinemia and, consequently, progressive b-cell stress. Removal of that circuit ablates that b-cell stress, a critical element of prediabetes progression. We analyzed B6 strain mice, which can develop an insulin resistance syndrome reminiscent of Type 2 diabetes. B6 mice carrying a TRPV1 null genotype were found to be protected from insulin resistance as predicted. Type 1 and Type 2 diabetes may share insulin resistance as mayor disease progression element. We completed the generation and characterization of 5 new transgenic NOD mouse lines generated to determine the role of peri-islet Schwann cells (pSC) in diabetes progression. These mice carry immunomodulatory molecules (B7-1, B7H-1, SOD, TK in Schwann cells or b-cells, several lines express transgenic MHC class I on these Schwann cells, in mice deficient for class I expression systemically. Collectively, the data generated determine that pSC are an integral part of prediabetes, with cognate interactions at the pSC surface mediated by CD8+ T effector cells. We are developing immunotherapy specifically targeting this element of prediabetes.
- Human studies: The past 4 years were exciting for our human studies, with respect to the global TRIGR diabetes prevention trial: recruitment of over 6000 HLA-selected newborns will be completed this year, the lab is involved in several trial aspects, in particular measurements of diabetes-relevant T cell autoreactivity for the entire North American trial branch. Canada leads the world in recruitment, Toronto is the world most successful recruitment center.
Drucker, Daniel J.
Department of Medicine, Division of Endocrinology & Metabolism
The Drucker lab is carrying out studies focused on understanding the factors regulating proglucagon gene expression in the gut and pancreas , as well as the actions of the glucagon-like peptides, GLP-1, and GLP-2, on their target tissues. GLP-1 is a promising gut-derived peptide that is being evaluated as a new treatment for subjects with diabetes. The first GLP-1R agonist, exendin-4, has been approved for the treatment of type 2 diabetes, and the laboratory is studying mechanisms of GLP-1 action in different target tissues beta-Cell Pdx1 expression is essential for the glucoregulatory, proliferative, and cytoprotective actions of glucagon-like peptide-1. Diabetes. 2005 Feb;54(2):482-91. We are also interested in developing new more potent and longer-acting GLP-1R agonists. An alternative strategy for potentiating incretin action follows from the known importance of the enzyme, dipeptidyl peptidase-4, in the control of incretin degradation. Our lab has pursued studies of DPP-4 inhibitor action through characterization of these agents in mice with genetic mutations in incretin receptors. The lab is also interested in the mechanism of action of GLP-2, a 33 amino acid peptide co-secreted together with GLP-1 from gut endocrine cells. GLP-2 is in late stage clinical trials for the treatment of intestinal disorders, and our studies are focused on understanding the molecular mechanisms mediating GLP-2 action The glucagon-like peptide-2 receptor C terminus modulates beta-arrestin-2 association but is dispensable for ligand-induced desensitization, endocytosis, and G-protein-dependent effector activation. J Biol Chem. 2005 Jun 10;280(23):22124-34 and The HeLa cell glucagon-like peptide-2 receptor is coupled to regulation of apoptosis and ERK1/2 activation through divergent signaling pathways.Mol Endocrinol. 2005 Feb;19(2):459-73.
Elsholtz, Harry
Department of Laboratory Medicine & Pathobiology
Our lab studies the molecular biology of pituitary hormones. Prolactin and growth hormone regulate key reproductive events and somatic growth, respectively, and affect the development of specific tissues including the pancreatic islets. Prolactin receptor deficient mice, for example, exhibit reduced islet beta cell mass, decreased insulin gene expression, and an impaired insulin response to glucose. We have investigated prolactin gene regulation, notably how transcription of the gene is controlled: (1) Our studies have identified pathways that mediate transcriptional repression of prolactin, showing that dopamine can cause transrepression by a novel G-protein specific, MAP kinase dependent pathway. We are using molecular strategies to target and identify critical components in this regulatory mechanism, including kinases downstream of MAP kinases, ERK 1/2 (2) We are investigating the chromatin-dependent changes that mediate endocrine regulation of prolactin gene transcription. We use chromatin immunoprecipitation techniques to identify early and late epigenetic changes in the prolactin promoter region in response to dopamine, glucocorticoids, and selective inhibitors of MAP kinase signaling. Specifically we are addressing the role of (a) transcription factors that bind directly to prolactin promoter DNA, (b) coregulatory activators and repressors, and (c) covalent modifications of histones. Epigenetic mechanisms in the dopamine D2 receptor-dependent inhibition of the prolactin gene. Mol Endocrinol. 19:1904-17, 2005.
Fantus, I. George
Departments of Medicine and Physiology
The Fantus lab is involved in two major areas of diabetes-related research. The first is focused on insulin resistance, its mechanisms and associations, and the second, on glucose toxicity and the pathogenesis of the chronic microvascular complications of diabetes.
In a previous study we demonstrated that insulin resistance induced by hyperglycemia both in vitro (Lu B et al J. Biol. Chem. 276: 35589-35598, 2001) and in vivo (Haber A et al Am. J. Physiol. Endocrinol. Metab 4: E744-753, 2003) was associated with oxidative stress, i.e. the formation of ROS (reactive oxygen species) greater than the ability of the tissues to remove them. In the latter study, our ability to prevent the insulin resistance in rodents induced by high glucose and insulin with either of two antioxidants, N-acetylcysteine (NAC) or taurine, strongly implicated ROS as a key pathophysiologic component in this model. Other investigators had implicated inflammatory cytokines as inducers of insulin resistance. In collaboration with Dr. Philipp Scherer (Albert Einstein College of Medicine, NY), we showed that NAC could prevent the increased gene expression of PAI-1 (plasminogen activator inhibitor-1), an inflammatory marker, in adipose tissue supporting the role of ROS in insulin resistance and potentially, its associated manifestations (The hyperglycemia-induced inflammatory response in adipocytes: the role of reactive oxygen species. J Biol Chem. 2005 Feb 11;280(6):4617-26).
We have also begun to explore the relationship between insulin resistance and cancer, specifically breast cancer. In collaboration with Dr. Pam Goodwin (Mount Sinai Hospital, University of Toronto), we showed that elevated levels of basal insulin, a marker of insulin resistance, was associated with increased risk of breast cancer in pre-menopausal women. (DelGiudice ME et al Insulin and related factors in premenopausal breast cancer risk. Breast Cancer Research and Treatment 47: 111-120, 1998). Leptin is known to be elevated in obesity- associated insulin resistance and it was suggested to perhaps contribute to either development or progression of breast cancer. Although Goodwin found that elevated levels of insulin also conferred an increased risk of recurrence and death in women with diagnosed breast cancer, this was not true for leptin (Is leptin a mediator of adverse prognostic effects of obesity in breast cancer? J Clin Oncol. 2005 Sep 1;23(25):6037-42). For clinical information on insulin resistance and oral hypoglycemic agents in type 2 diabetes mellitus see Oral antihyperglycemic therapy for type 2 diabetes mellitus. CMAJ. 2005 Jan 18;172(2):213-26.
Our work on the complications of diabetes is focused on diabetic nephropathy, a major cause of morbidity and mortality. We have shown that in high glucose, increased flux through the HBP (hexosamine biosynthetic pathway) leads to activation of gene transcription. In our model of cultured glomerular mesangial cells, the stimulation of PAI-1 gene expression was dependent on the transcription factor Sp1 and the activation of PKC (protein kinase C) (Goldberg H et al J. Biol. Chem. 277:33833-33841, 2002). The increased flux via the HBP, one of several glucose metabolic pathways activated by hyperglycemia and believed to contribute to diabetic nephropathy, can lead to increased oxidative stress as well as to intracellular protein O-glycosylation, the addition of a single N-acetylglucosamine (GlcNAc) to Ser and/or Thr residues. Using genetic and pharmacological approaches, e.g. expression of dominant negative O-GlcNAc transferase (OGT), overexpression of O-GlcNAcase, we recently demonstrated that O-glycosylation is the critical mediator of high glucose induced PAI-1 gene expression (Posttranslational, reversible O-glycosylation is stimulated by high glucose and mediates plasminogen activator inhibitor-1 gene expression and Sp1 transcriptional activity in glomerular mesangial cells. Endocrinology. 2006 Jan;147(1):222-31). In collaboration with Dr. C. Whiteside (Department of Medicine, University of Toronto), we continued the studies of signaling in mesangial cells by high glucose and showed that PKC activation leads to NADPH oxidase upregulation, a potential source of toxic ROS in addition to mitochondria (Mesangial cell NADPH oxidase upregulation in high glucose is protein kinase C dependent and required for collagen IV expression. Am J Physiol Renal Physiol. 2006 Feb;290(2):F345-56. [Epub ahead of print], 2005).
For more general information on glucose toxicity see Fantus IG. Glucose Toxicity in ENDOTEXT, De Groot, L. (ed), MDTEXT.com http://www.endotext.org/diabetes/diabetes12new/diabetesframe12.htm.
Gaisano, Herbert
Departments of Medicine and Physiology
The Gaisano laboratory has been investigating the mechanisms by which SNARE proteins, originally described to mediate exocytosis in neurons, regulate insulin secretion. The central working hypothesis is that SNARE proteins act to link together the distal components of insulin secretion, including not only exocytosis of the insulin granule, but also K+ and Ca2+ channels, priming and mobilization of insulin granule pools, into the fine sequence of events leading to secretion. We reported that levels of SNARE proteins are severely reduced in human type 2 diabetes islets (Diabetes, in press), which is therefore a major contributing factor to dysregulated insulin secretion. The current areas we are focused on are:
- Having demonstrated that SNARE proteins bind both membrane depolarizing KATP and membrane-depolarizing Kv2.1 channels in islet b-cells, our lab has began to elucidate the putative functional binding domains between the SNARE and these channels. Open form of syntaxin-1A is a more potent inhibitor than wild-type syntaxin-1A of Kv2.1 channels. Biochem J. 2005 Apr 1;387(Pt 1):195-202 and Transgenic mouse overexpressing syntaxin-1A as a diabetes model. Diabetes. 2005 Sep;54(9):2744-54.
- Our lab showed that the key receptor activated by diacylglycerol to prime insulin secretion is not PKC as broadly believed, but rather a novel protein called Munc13-1, which we now definitely demonstrated using a Munc13-1 deleted mouse. (Diabetes in press.) We are now examining how this pathway converges with the cAMP coupled priming proteins.
- Much is known about granule-plasma membrane exocytosis. We now demonstrate that insulin granule-granule fusion also occurs that can carry more insulin cargo for export (by compound exocytosis), and which is acted upon by GLP-1. Transgenic mouse overexpressing syntaxin-1A as a diabetes model. Diabetes. 2005 Sep;54(9):2744-54. We will now identify the specific molecules mediating compound exocytosis.
- Abnormal glycemic control in diabetes is contributed not only by abnormal beta cell insulin secretion but also abnormal alpha cell glucagon secretion. We are now exploring this new area, including new aspects of alpha cell biology and beta cell-alpha cell crosstalk. Electrophysiological characterization of pancreatic islet cells in the mouse insulin promoter-green fluorescent protein mouse. Endocrinology. 2005 Nov;146(11):4766-75. (Endo in press.)
Our lab has in place state-of-the-art single cell patch clamp and exocytic imaging assays (epifluorescence, evanescent and confocal microscopy), pancreatic islet perifusion, complementary biochemical and molecular biology tools, and genetically-modified mouse models to unequivocally dissect these complicated secretory pathways.
Hamilton, Jill
Department of Pediatrics
My research focus has continued in the area of insulin resistance disorders in childhood. Over the past year we have: (i) completed a treatment trial examining whether the oral medication, pioglitazone, used commonly to treat type 2 diabetes, combined with insulin may be helpful to improve diabetes control in type 1 diabetes; (ii) evaluated quality of life issues and diabetes knowledge in youth with type 2 diabetes; (iii) evaluated risk for diabetes and the metabolic syndrome in children with a tumor located in the brain centre regulating body weight and appetite; (iv) initiated a study to look at risk factors related to future development of obesity and diabetes in babies born to women who had diabetes during pregnancy.
Hanley, Anthony
Department of Nutritional Sciences
- Obesity has many health consequences, including diabetes, hypertension, and heart disease. Recently, a novel liver complication of obesity, called non-alcoholic fatty liver disease (NAFLD) has been described. NAFLD is related to insulin resistance and blood markers of NAFLD, including the liver enzymes ALT and AST, are known to predict the development of diabetes. Whether NAFLD also predicts the development of diabetes precursors, such as the Metabolic Syndrome, has not been studied extensively. We assessed the relationship of blood markers of NAFLD with risk of developing Metabolic Syndrome in a large multi-ethnic cohort. We found that subjects in the upper quartiles of ALT had a 2-fold increased risk of developing Metabolic Syndrome after 5 years, even after taking into account other diabetes risk factors including central adiposity and insulin resistance. The results were essentially identical when we excluded former and heavy drinkers from the analysis. Liver markers and development of the metabolic syndrome: the insulin resistance atherosclerosis study. Diabetes 2005;54:3140-7.
- Both diabetes and heart disease are characterized and predicted by a cluster of cardiovascular risk factors, commonly referred to as the Metabolic Syndrome. Several sets of standard criteria have been proposed to define the syndrome, including those from the World Health Organization and the National Cholesterol Education Program. Recently it has been suggested that new components be added to the definitions or existing components be modified. Whether different Metabolic Syndrome definitions (with or without suggested modifications) differ in their prediction of type 2 diabetes has not been extensively evaluated. We addressed this issue using data from a large multi-ethnic cohort and found Metabolic Syndrome definitions that used simple variables that are readily available in clinical settings (including lipids, glucose, blood pressure and waist circumference) predicted diabetes just as well as definitions that used more complex, less readily available measures (such as insulin resistance, CRP and microalbuminuria). Prediction of type 2 diabetes mellitus with alternative definitions of the metabolic syndrome: the Insulin Resistance Atherosclerosis Study. Circulation 2005;112:3713-21.
Hux, Janet E.
Department of Medicine and Department of Health Policy, Management and Evaluation
Dr. Hux and her team are carrying out a broad range of health services research in the area of diabetes. Linked healthcare administrative data are being used to define the burden of diabetes and temporal and geographic trends in this emerging chronic disease epidemic. Current projects are aimed at improving the sensitivity and specificity of administrative data algorithms for detecting diabetes in special populations - pregnant women, children and persons receiving care in non-fee for service settings. Within the defined population of persons with diagnosed diabetes, we continue to examine processes of care delivery, for instance, utilization of HbA1c testing and delivery of non-diabetes related services (Utilization and outcomes of HbA1c testing: a population-based study. CMAJ, 2006;174(3):327-9; and Reduced screening mammography among women with diabetes. Arch Intern Med 2005;165(18):2090-5.) We also continue to examine treatment of diabetes and in particular differences in the care delivered under differing service models (Clinical inertia in response to inadequate glycemic control: do specialists differ from primary care physicians? Diabetes Care 2005;28(3):600-6). Health services research has inherent ties to health policy and our group has provided important leadership to the Ontario Task Force on the Prevention of Diabetes Complications.
Irwin, David M.
Department of Laboratory Medicine and Pathobiology
The Irwin lab is investigating the expression and evolution of the proglucagon gene. The proglucagon gene encodes several hormones that are important in regulating metabolism, including glucagon, glucagon-like peptide 1 (GLP-1), and glucagon-like peptide 2 (GLP-2). While the regulation of expression of the rat proglucagon gene has been extensively studied, we have found that comparable regulatory gene sequences previously identified for the rat proglucagon gene do not appear to be important in regulating the human proglucagon gene. Our recent shows that sequences within intron 1 of the human proglucagon gene are essential for expression in islet cells. We also investigate the evolution of receptors for proglucagon derived peptides. GLP-1 is an incretin hormone in mammals but acts like glucagon in fish. Our work has led to new model to explain contrasting factions of GLP-1 in fish and mammals. Intron 1 Sequences are Required for Pancreatic Expression of the Human Proglucagon Gene. Am J Physiol Regul Integr Comp Physiol. 2006 in press, and Evolution of new hormone function: loss and gain of a receptor. J Hered. 2005 May-Jun;96(3):205-11.
Jin, Tianru
Departments of Medicine; Laboratory Medicine and Pathobiology; and Physiology
Div. of Cell and Molecular Biology, Toronto General Research Institute, University Health Network
The second messenger cAMP plays important roles in regulating hormone production and secretion. We found that in glucagon and GLP-1 producing cells, cAMP stimulates caudal homeobox gene Cdx-2 expression through a newly discovered pathway, the Epac pathway. This discovery opened new research directions to study: 1) role of Epac in glucagon/GLP-1 producing cells, and 2) how signaling molecules and transcription factors work together in regulating hormone production. PKA independent and cell type specific activation of the expression of caudal homeobox gene Cdx-2 by cyclic AMP. FEBS J. 2005 Jun;272(11):2746-59. Although Cdx2 expression in insulin producing cells has been previously detected, whether it stimulates endogenous insulin production has not been studied. Using an inducible gene expression system, we demonstrated that Cdx-2 up-regulates endogenous insulin mRNA expression and insulin synthesis. Our observations also suggested that Cdx-2 serve as a mediator for cAMP in insulin-producing cells. Role of Cdx-2 in insulin and proglucagon gene expression: a study using the RIN-1056A cell line with an inducible gene expression system. J Endocrinol. 2005 Jul;186(1):179-92. We have shown previous that proglucagon expression/GLP-1 synthesis in gut, but not in pancreas, could be activated by the Wnt signaling pathway. We show here that the activated is mediated by a cis-element in proglucagon promoter, and cell-type specific activation is attributed to cell specific expression of a Wnt mediator, TCF-4. TCF-4 Mediates Cell Type-specific Regulation of Proglucagon Gene Expression by ß-Catenin and Glycogen Synthase Kinase-3 ß. J Biol Chem. 2005 Jan 14;280(2):1457-64. More recently, it is suggested that TCF-4 could be a diabetes gene, based on a genetic linkage analysis by deCODE company.
Klip, Amira
The Hospital for Sick Children
Departments of Biochemistry, Physiology and Peadiatrics of the University of Toronto
Our work focuses on the mechanisms whereby insulin causes a gain in glucose carrier molecules at the surface of muscle cells. This is a fundamental process that allows the dietary sugar glucose to be stored. Interestingly, exercise also increases these carrier molecules, independently of insulin and without engaging the signals that insulin releases inside the cell. We established a model system of muscle cells to study how exercise increases glucose carriers at the surface, by subjecting cells to the first trigger of muscle contraction, namely a change in the electrical gradient across the cell membrane. Upon such 'depolarization' we observed a gain in surface glucose carriers, and that this process requires the ion calcium and possibly protein kinase C. Since these muscle cells culture do not contract (unlike exercising muscle) we concluded that the signal to increase glucose carriers is independent of the work developed during contraction. Even more strikingly, the gain in surface glucose carriers resulted from a slow-down in the return of the carriers from the membrane to the cell interior, rather than to an acceleration of their movement to the membrane -the step stimulated by insulin. This work, carried out by doctoral student Nadeeja Wijeseekara, along with Amanda Tung and Farah Thung, is in press in the Amer J Physiol: Endocrinol/Metab.
A second achievement of 2005 was the discovery that insulin regulates the fusion of glucose carrier vesicles with the plasma membrane, and that this occurs through participation of a specific signalling lipid molecule, PI3,4,5P3. Using electron microscopy, we visualized the vesicles below the membrane, but precluded from fusing upon inhibition of the enzyme that produces PI3,4,5P3. This work, pioneered by postdoctoral fellow Manabu Ishiki and involving Varinder Randhawa, Vincent Poon and Lellean JeBailey: Insulin regulates the membrane arrival, fusion, and C-terminal unmasking of glucose transporter-4 via distinct phosphoinositides. J Biol Chem. 2005 Aug 5;280(31):28792-802. PMID: 15955810.
Langille, Lowell
Department of Laboratory Medicine and Pathobiology
Director, Cell Biology of Atherosclerosis Program (HSFO)
Vascular disorders underlie the most severe complications of diabetes including atherosclerosis, microangiopathy and diabetic retinopathy. Our laboratory examines how the functions of vascular cells, endothelium and vascular smooth muscle, contribute to these disorders. In 2005, we demonstrated a key role for a cell-cell adhesion molecule (N-cadherin) in controlling how smooth muscle cells migrate to the inner surface of arteries to narrow these vessels during atherosclerosis and during restenosis, the primary complication of treatments of the disease. Accordingly, when angioplasty and stents are used to open atherosclerotic arteries, endothelium is lost and underlying smooth muscle cells receive biased N-cadherin signaling from deeper smooth muscle cells. This polarized signaling provides a stimulus which induces inward migration and proliferation of these cells, which ultimately narrows the artery and compromises blood flow. Our current research examines the intracellular mechanism by which this signaling works in order to design interventions that can limit these processes and alleviate the consequences of restenosis. Additional work in the laboratory examines how physical forces influence remodeling of arterial tissues in ways that influence vascular pathologies. Recently we demonstrated that tensile forces that are transmitted to arteries from surrounding tissues profoundly influence their capacity to remodel and thereby influences adaptive responses to the altered hemodynamics that are associated with arterial occlusive diseases like atherosclerosis. Partial off-loading of longitudinal tension induces arterial tortuosity. Arterioscler Thromb Vasc Biol. 2005 May;25(5):957-62.
Lewis, Gary
Departments of Medicine and Physiology
Head, Division of Endocrinology and Metabolism, University Health Network and Mount Sinai Hospital
Dr. Lewis has published a number of studies over the past few years examining the mechanism of HDL (the 'good cholesterol') lowering in people with prediabetes or Type 2 diabetes. His work was recently summarized in a comprehensive paper that highlights three insights derived from recent research:
- The liver is responsible for approximately 80% of plasma HDL concentrations, challenging the concept that cholesterol transport in the body is entirely centripetal from extrahepatic tissues to the liver,
- Clearance and not production of HDL particles is the major determinant of plasma HDL-c concentration and intravascular modification of HDL particles by lipid exchange, lipolytic modification and receptor interaction all influence particle composition and hence subsequent clearance rates,
- The dominant cause of low plasma HDL-c in humans is the insulin resistant syndrome, with enhanced HDL clearance in this condition being due predominantly to hepatic lipase modification of triglyceride-enriched HDL particles.
Ng, Dominic
Department of Medicine and Institute of Medical Science
My lab focused on two main areas of research:
- Ongoing research studying novel linkage between lipoprotein metabolism and glucose homeostasis in a monogenic low HDL syndrome using the murine model of LCAT deficiency. Our initial work suggest that LCAT, a major modulator of HDL cholesterol levels, may play an important role in linking the phenotypes of dyslipidemia and abnormal glucose homeostasis in the metabolic syndrome, familial combined hyperlipidemia and diabetic dyslipidemia, all sharing the increased propensity for accelerated atherosclerosis. More recently, we reported a profound alteration in fatty acid metabolism in LCAT deficient mice and this novel observation may partially explain the glucose-lipid links. Several phenotypes seen in the animal models are apparently paradoxical and may provide a window of opportunity for discovery of novel metabolic regulatory pathways. Ongoing studies include examining the interaction between these genetic-based phenotypes and various diets in the development of atherosclerosis and diabetes.
- A new area of research exploring the role of lipoproteins, especially HDL, in diabetes. We are investigating the interaction of HDL in the modulation of the insulitis process. We will focus on the effect of HDL on the various effector arms of the immune-mediated inflammatory process in murine models of diabetes.
Book Chapter: D. Ng. "Insulin resistance, diabetes and its complications" Encyclopaedia of Molecular Cell Biology and Molecular Medicine. Ed. R.A.Myers, Wiley-VCH Publications, GmbH:Weiheim, Germany (2005) 7:23-72
Norwich, Kenneth H.
Professor, Department of Physiology
My primary research involves the construction of a mathematical model governing the regulation of glucose levels in health and disease. The result is a computer program that differs from its predecessors in its inclusion of the effects of the incretins, which are hormones secreted in response to an oral glucose load. Incretins increase the rate of insulin secretion by the beta cells, and hence, accelerate the reduction in plasma glucose. The model required formulation of a hepatic balance function, which modulates the input and output of the liver under varying glucose and insulin environments. The model was designed primarily to simulate changes in glucose, insulin and incretins during the oral glucose tolerance test. It also functions well simulating the intravenous glucose tolerance test. It correctly predicts changes accompanying hyper- and hypoglycemia, obesity, exercise, as well as in type 1 diabetes mellitus. With adjustment of parameters, it also simulates the effects of type 2 diabetes mellitus. The utility of the model lies in its ability to relate clinically observed changes to alterations in biochemical function, and its ability to simulate metabolic tracer studies without actually using tracers. The program is also used to allow students to simulate investigational studies on patients.
Ohashi, Pamela S.
Ontario Cancer Institute, Division of Signaling Biology
University of Toronto, Departments of Medical Biophysics and Immunology
A population of white blood cells called T lymphocytes (cells), are important in attacking and eliminating germs that cause disease. Unfortunately, T cells are also the culprits that can mistakenly attack our own tissues and cause autoimmune diseases such as diabetes. Because it is dangerous to keep cells that can attack our own bodies, mechanisms have evolved to eliminate or turn off these dangerous T cells. Therefore from the perspective of the T cell, it must be turned off in some cases when it is dangerous to the body, and in some cases it must be turned on to fight against germs. Currently we are trying to build a molecular map of the molecules that regulate T cell function. By understanding the signals that regulate the T cells, we may find new targets that can be used to design new drugs to turn off T cells involved in autoimmune disease. NF-kappaB couples protein kinase B/Akt signaling to distinct survival pathways and the regulation of lymphocyte homeostasis in vivo. J Immunol. 2005 Sep 15;175(6):3790-9.
Prud'homme, Gerald J.
Department of Laboratory Medicine and Pathobiology
Defective regulation of the immune system is a key feature of autoimmune (juvenile-onset) diabetes, and vaccines can be designed to protect against this form of autoimmunity. The objective of our work is to block autoimmune responses by gene therapy and DNA vaccination (vaccination with genes rather than proteins) approaches. Genes coding for islet cell target molecules were co-delivered into mice with genes that block or alter the autoimmune response of diabetic NOD mice. This prevented diabetes when applied early in life, and reversed diabetes in mice that had recently developed diabetes. The prevention of autoimmunity by these methods is relevant to three important areas: 1) It could be used to prevent diabetes in subjects at high risk. 2) It would protect against the rejection of transplanted islets. 3) It would reduce immune attack against new islet cells produced from stem cells or by gene therapy.
Rozakis Adcock, Maria
Department of Laboratory Medicine and Pathobiology
The Rozakis lab is interested in understanding the mechanisms of Type II Diabetes. Type 2 diabetes is a progressive disease characterized by two major defects: insulin resistance and beta-cell dysfunction. The insulin signalling pathway is fundamental for regulation of growth and cell division. Upon insulin stimulation, the insulin receptor's intrinsic tyrosine kinase activity is activated to phosphorylate two major substrates, IRS1 and IRS2. Genetically modified mice lacking IRS2 exhibit marked alterations in insulin secretion and develop diabetes. We have identified a novel downstream component of the IRS2 pathway, PHIP (IRS pleckstrin homology domain interacting protein), which is expressed in pancreatic islets. We have generated transgenic mice which express PHIP under the control of the mouse insulin promoter, and are conducting studies to understand the role of PHIP in beta-cell growth and survival, insulin secretion, glucose tolerance and Type II diabetes.
Stewart, Donna
Department of Psychiatry
Dr Stewart is carrying out research focused on understanding psychosocial, behavioural, and clinical differences that exist between men and women as they related to diabetes management and health outcomes. Our research program is also interested in how self-management education services are being used and delivered in Canada. Specifically, who uses these services, predictors of program attrition and retention, and the impact on varying use of education services on health outcomes using both quantitative and qualitative methods. These research projects are still in progress.
Volchuk, Allen
Scientist, Cell & Molecular Biology, Toronto General Research Institute
Assistant Professor, Department of Biochemistry, University of Toronto
In the past year my laboratory has been exploring the mechanism of how elevated levels of free fatty acids cause pancreatic beta-cell death. Pancreatic beta-cell death is believed to contribute to the development of Type 2 diabetes. It has been established that chronic exposure to free fatty acids induces beta-cell apoptosis (programmed cell death). The mechanism by which this occurs is not completely understood. During the past year we have tested whether chronic free-fatty acids induce endoplasmic reticulum stress, which can induce apoptotic pathways. We have identified that high levels of palmitate induces beta-cell ER stress and markers of ER stress-associated pro-apoptotic factors. These findings suggest that free fatty acids may cause beta-cell death in part by creating a state of chronic stress in the ER. The exact mechanism by which palmitate induces ER stress is currently under investigation.
van der Kooy, Derek
Department of Medical Genetics and Microbiology
We have provided the first clonal identification of a putative mammalian pancreatic stem cell (Seaberg et al, Nat Biotechnol. 2004 Sep;22(9):1115-24). In the last year, our data have suggested that an insulin producing cell in vivo is the cell that in culture will form pancreatic multipotential colonies in our culture dishes, that activating the Wnt signaling pathway may allow the longer term self-renewal of this stem/progenitor cell in our culture dishes, and that a similar cell may exist in the adult human pancreas.
Vranic, Mladen* and Matthews, Steve* **
*Departments of Physiology and Medicine
**Department of Obstetrics and Gynaecology
In collaboration with Steve Matthews, we are addressing 2 questions:
- the physiological and molecular basis for dysfunction of the Hypothalamic-Pituitary-Adrenal (HPA) and sympathoadrenal axes in diabetes in rats. In the four papers published this year, we demonstrated that activity of the sympathoadrenal axis is elevated in diabetes with respect to the expression of stress hormones and their receptors. This can be normalized in part by insulin treatment and normalization of plasma glucose. During hypoglycemia there is a deficient response of this axis and this is mainly due to the lack of suppression of mineralocorticoid receptors in the hippocampus. This abnormality is normalized by normalizing glucose despite very low insulin levels in diabetic rats. In analyzing this defect it is important to differentiate between the effect of insulin injection and the effect of hypoglycemia. This is because insulin by itself can increase activity of some components of the HPA axis. Hyperglycemia does not increase basal hypothalamo-pituitary-adrenal activity in diabetes but it does impair the HPA response to insulin-induced hypoglycemia. Am J Physiol Regul Integr Comp Physiol. 2005 Jul;289(1):R235-46. The defective response of epinephrine to hypoglycemia is associated with decreased expression of adrenal medullary enzymes controlling epinephrine synthesis.
- Work in progress demonstrates that exercise can prevent the onset of diabetes in a rat model of type 2 diabetes by increasing proliferation of beta-cells and thus preserving beta-cell mass. Surprisingly, repetitive stress by itself can also delay onset of diabetes.
Wang, Qinghua
Departments of Physiology and Medicine
Hyperglycemia is a hallmark of diabetes mellitus and is mostly a result of insufficient insulin secretion and/or excessive secretion of glucagon. Excessive secretion of glucagon is a major contributor to the diabetic hyperglycemia. We are studying pancreatic islet function under physiological and diabetic conditions. In particular, we are investigating the molecular mechanism(s) of intra-pancreatic hormonal regulation, i.e., the mechanism(s) by which insulin suppresses glucagon secretion from the glucagon-secreting the alpha cells. Our recent study suggests that the "insulin resistance" occurs in the alpha cells may contribute to hyperglycemia in type 2 diabetes. On the other hand, the failure of glucagon counterregulation during hypoglycemia is a major factor limiting the intensive insulin treatment needed for normalization of glucose homeostasis in type 1 diabetes. We are investigating the biochemical nature of the impairment of counterregulation and hypoglycemia in type 1 diabetes subjects (with M. Vranic). Our aim is to identify the molecular defects that cause diabetes and to develop novel therapies for prevention and treatment of diabetic hyperglycemia (with G. Prud'homme).
Westall, Carol
Department of Ophthalmology and Vision Sciences, University of Toronto
and The Hospital for Sick Children
Our group has have shown recently that adolescent children with diabetes, with no retinopathy, have very specific changes in their visual response to coloured targets. We suggest that this shows evidence of damage to nerve cells in the brain and/or retina. This damage is occurs even before changes to the blood vessels are visible to the eye doctor. In collaboration with Dr Shelley Boyd (St Michael's Hospital) we secured funding from the Juvenile Diabetes Research Foundation to investigate non-invasive measures of Eye-Brain function in early diabetes. We will evaluate four nerve function tests together to see how well they detect diabetic damage, and also how well they can follow the worsening of diabetes over time. In addition, we will couple these nerve function tests with traditional tests of blood vessel disease in order to document their relationship. First we will ask if these two types of abnormality can be physically mapped onto each other, and secondly, we will ask if one change can predict the other over time.
We believe that this study can significantly change the way we think about, diagnose and treat the blinding complications of diabetes. If this is true, entirely new therapies aimed at detecting, slowing or repairing the damage to nerves might be possible. Color visual evoked potentials in children with type 1 diabetes: relationship to metabolic control. Invest Ophthalmol Vis Sci 2005; 46(11): 4107-13 and Detecting ocular-visual function changes in diabetes. Br J Ophthalmol 2005; 89(11): 1392-3.
Wheeler, Michael
Departments Physiology and Medicine
Head of the Endocrinology and Diabetes Research Group
Research in the Wheeler lab focuses on understanding pancreatic b-cell dysfunction in type 2 diabetes. A major controversy is the relationship between the two hallmarks of the disease, b-cell dysfunction and insulin resistance - specifically, whether one can cause the other. In the MKR mouse model of the disease, we have shown that insulin resistance of sufficient severity can indeed cause b-cell dysfunction (Insulin resistance causes increased beta-cell mass but defective glucose-stimulated insulin secretion in a murine model of type 2 diabetes. Diabetologia. 2006 Jan;49(1):90-99. Epub 2005 Dec 15). Furthermore, abnormally elevated lipids are a potential cause of b-cell dysfunction, and the laboratory has established that uncoupling protein-2, a protein crucial in regulating cellular energy levels, can mediate some of the detrimental effects of lipids on b-cell function (Free fatty acid-induced beta-cell defects are dependent on uncoupling protein 2 expression. J Biol Chem. 2004 Dec 3;279(49):51049-56. Epub 2004 Sep 23). However, understanding disease mechanisms requires knowledge of the basic biology of the pancreatic islet. Although the trace element, zinc, is crucial for insulin biosynthesis and exocytosis, little is known about its cellular regulation. Studies from the lab have revealed novel information about how and under what conditions zinc is transported into the b-cell (The Zn2+ transporting pathways in pancreatic beta-cells: A role for the L-type voltage-gated Ca2+ channel. J Biol Chem. 2005 Dec 30). In addition, little is known about the interaction between b-cells and a-cells. We have determined that the insulin receptor is required for glucose to regulate glucagon secretion (Glucose-regulated glucagon secretion requires insulin receptor expression in pancreatic alpha-cells. J Biol Chem. 2005 Sep 30;280(39):33487-96. Epub 2005 Jul 14). Moreover, with Dr. Qinghua Wang's laboratory, we have begun to elucidate how insulin signalling influences glucagon secretion (Intra-islet insulin suppresses glucagon release via GABA-GABAA receptor system. Cell Metab. 2006 Jan;3(1):47-58).
Wolever, Thomas
Department of Nutritional Sciences
Studies on the long-term effects of altering the source and amount of dietary carbohydrate or dietary fibre intakes in relation to the prevention and treatment of type 2 diabetes were on-going during 2005. In addition, studies examining the effect on blood glucose responses of adding fat and protein to carbohydrate, of enzymatically modifying carbohydrate and of different types of potatoes are ongoing or completed. Glycemic index of potatoes commonly consumed in North America. J Am Dietet Assoc 2005;105:557-562. In addition, we have looked at how freezing, a common method of storing foods, alters the structure of oat fibre incorporated into muffins and how this, in turn, affects the ability of the fibre to reduce blood glucose responses. We continue to be interested in how different methods affect the results of studies examining the glucose responses of foods and the glycaemic index. Evaluation of a glucose meter for determining the glycemic responses of foods. Clin Chim Acta 2005;356:191-98. In 2005 I finished writing a scientific book on the Glycaemic Index which was published in early 2006 by CABI Publishing, UK (www.cabi-publishing.org).
Woodgett, James
Department of Medical Biophysics
The Woodgett lab is primarily interested in the abrogation of signal transduction pathways in human disease, in particular the phosphatidylinositol 3' kinase pathway which is implicated in cancer and diabetes. We are studying several key regulatory enzymes in this pathway, such as Phosphoinositide-dependent Kinase-1 (PDK1), Protein Kinase B (PKB/Akt), Serum and Glucocorticoid-inducible Kinase 3 (SGK3) and Glycogen Synthase Kinase-3 (GSK-3). Insulin leads to inhibition of GSK-3 and several drugs are being tested as insulin sensitizers for type-2 diabetes. There are two mammalian genes for GSK-3, termed alpha and beta, and we have generated mouse strains in which each has been inactivated, either globally or in a tissue-specific manner. For example, we have engineered mice that specifically lack GSK-3beta in either skeletal muscle or liver and have characterized the insulin and glucose responses of these animals. We are also identifying novel targets for GSK-3 which will help us understand the molecular mechanisms by which GSK-3 influences blood glucose responses.
Recent relevant papers: Phosphoinositide-dependent phosphorylation of PDK1 regulates nuclear translocation. Mol Cell Biol. 2005 Mar;25(6):2347-63 and A dual-kinase mechanism for Wnt co-receptor phosphorylation and activation. Nature. 2005 Dec 8;438(7069):873-7.
Young, Kue
Department of Public Health Sciences
In 2005 I concluded the 5-year research project in Manitoba, studying the prevalence of diabetes complications among First Nations individuals with no diabetes, undiagnosed diabetes, and previously diagnosed diabetes. The project was undertaken in one reserve in the south and several reserves in the north of the province. There is one diabetes-related publication based on the MSc thesis of a student at U of T: Characteristics and prevalence of the metabolic syndrome among three ethnic groups in Canada. Int J Obes (Lond). 2005 Nov 22.