PI: Kazuhiro Eto, MD, PhD.
Title: Regulation of pancreatic beta-cells by Eg
Abstract: Maintenance of pancreatic beta-cell mass and production of insulin from beta-cells are crucially relevant to a therapy of diabetes. We hypothesize that a zinc finger transcription factor early growth response-1 (Egr-1) regulates both glucose-dependent insulin production and pancreatic beta-cell mass. Thus, we have newly observed that Egr-1 plays a pivotal role in the activation of the insulin promoter and in the regulation of the promoter activity of the Pdx-1 gene, the product of which is a key transcription factor for beta-cell development, differentiation and proliferation. We propose the following specific aims: 1) To identify mechanisms by which Egr-1 regulates insulin gene transcription. We will determine the cis-acting regulatory elements and trans-acting factors of the insulin promoter that respond to Egr-1, 2) To identify mechanisms by which Egr-1 modulates the transcriptional activity of the Pdx-1 promoter. We will determine the cis-acting regulatory elements and trans-acting factors of the Pdx-1 promoter that respond to Egr-1, and 3) To determine whether Egr-1 regulates beta-cell mass. We will determine a role of Egr-1 in the regulation of beta-cell proliferation and apoptosis. Through these studies, we envisage that new key factors and pathways that regulate insulin production, beta-cell gene expression and beta-cell mass may be identified to directly contribute to new therapies for diabetes.
PI: Jose Florez, M.D., Ph.D.
Title: The role of common variation in genes encoding hypoglycemic drug targets in the development of type 2 diabetes and response to preventative interventions
Abstract: The Principal Investigator in this proposal is an M.D./Ph.D. post-doctoral fellow currently training in Dr. David Altshuler's human genetics laboratory at the Massachusetts General Hospital (MGH), which has intellectual and technological ties to the Broad Institute. He will become an Instructor at the Harvard Medical School on July 1, 2004. He plans to extend the findings of diabetes genetics research into the clinical arena, and thus contribute to understand the heterogeneity of type 2 diabetes (T2D), the impact of common genetic variation on the development of diabetes and the role of an individual's genetic profile in therapeutic response.
In order to do so, during his post-doctoral fellowship he has been studying the role of common variation in genes encoding drug targets for T2D. Type 2 diabetes is a polygenic disease, and work in our and other laboratories has recently implicated single nucleotide polymorphisms in the peroxisome proliferator-activated receptor-gamma (PPARG, a target for thiazolidinediones) and the sulfonylurea receptor complex in the pathogenesis of the disease. A T2D association of common variants in AMP kinase (a presumed drug target for metformin) has not been reported.
As a way to determine whether common genetic variation in genes encoding drug targets predicts the development of T2D and/or response to preventive interventions, we have been granted access to the DNA samples collected during the Diabetes Prevention Program (DPP). During the initial phase of the project, common variants in the genes encoding the sulfonylurea receptor and the seven known subunits of AMP kinase will be tested for association with T2D in several family-based and case-control panels totalling 3400 subjects. All associated variants will be examined for an effect on the various preventive strategies proven to be successful in the DPP. Whether common genetic variation in the AMP kinase and PPARG genes affects the pharmacological response to metformin and/or troglitazone will be assessed. This proposal should serve as the foundation for a large pharmacogenomics trial designed to evaluate the feasibility of genetically-tailored therapy in T2D.
PI: Herbert Lin, M.D., Ph.D
Role of Novel BMP Receptors in Diabetic Nephropathy
Diabetic Nephropathy (DN) is an important cause of morbidity and mortality in diabetic patients, with up to 40% of type I diabetics and 15% of type II diabetics eventually developing end-stage renal disease requiring dialysis. In the United States, up to one-third of all ESRD patients have DN, and the proportion continues to rise. Thus, DN has rapidly approached epidemic numbers. Any new insight into the pathophysiology of DN that could lead to novel diagnostic and therapeutic options that do not exist today could be of immense significance.
Bone Morphogenetic Proteins (BMPs) are members of the transforming growth factor beta (TGF-beta) superfamily of growth factors that regulate many physiologic and pathophysiologic processes in the kidney including nephrogenesis, response to injury, and repair. Although their precise role in the adult kidney is not fully understood, BMPs appear to be protective against renal injury to a variety of insults including DN. We present Preliminary Studies that Dragon, a novel GPI-anchored protein which we have recently discovered, is highly expressed in the kidney in renal tubular epithelial cells and that its expression is dynamically altered during diabetic nephropathy. Importantly, we demonstrate that 1) Dragon can augment signaling via the BMP pathway, 2) Dragon can bind to specific BMPs, 3) Dragon signals via the BMP type IB receptor, ALK6, and 4) Dragon signals via the R-Smad, Smad1. We propose to investigate further the molecular and cellular mechanisms of Dragon-mediated signaling via the BMP pathway in kidney cells and to study in detail Dragon expression and its consequences in the kidney as it develops diabetic nephropathy.
PI: Janice Zabolotny, Ph.D
Title: Regulation of Protein Tyrosine Phosphatase 1B in Obesity
Abstract: Obesity, an insulin-resistant state, is a major risk factor for type 2 diabetes. Increased expression and activity of protein tyrosine phosphatase 1B (PTP1B) are observed in muscle and adipose tissue of obese, insulin-resistant animals and humans, and have been causally related to insulin resistance. PTP1B-deficient mice have increased insulin sensitivity in muscle and liver. PTP1B also regulates leptin action; PTP1B-deficient mice have reduced adiposity due to increased leptin sensitivity in hypothalamus. Conversely, preliminary data show that transgenic PTP1B overexpression in skeletal muscle of mice is sufficient to impair muscle insulin action and cause whole body insulin resistance. Although preliminary data show that PTP1B expression is not always increased in insulin- and leptin- target tissues of genetically obese animals, expression of PTP1B is increased in multiple insulin- and leptin target tissues of diet-induced obese mice. Preliminary data show that the proinflammatory cytokine tumor necrosis factor alpha (TNF-alpha), which is increased in diet-induced obesity and implicated in causing insulin resistance, induces PTP1B expression in 3T3-L1 adipocytes in vitro. Because transgenic overexpression of PTP1B can cause insulin-resistance, at least in muscle, it is important to understand how endogenous PTP1B overexpression is mediated in vivo. The overall goal of this project is to identify factors and mechanisms that mediate PTP1B overexpression in diet-induced obesity. The proposed studies will determine (1) whether PTP1B overexpression precedes insulin- and leptin-resistance in diet-induced obese mice, (2) whether macrophage recruitment to adipose tissue is necessary for PTP1B overexpression in diet-induced obesity, and (3) whether the TNF-alpha is necessary for PTP1B overexpression in diet-induced obesity. These experiments will aid understanding of when and how PTP1B overexpression negatively regulates insulin and leptin action in vivo, contributing to the development of insulin resistance, obesity, and diabetes.