Awardees 2005

PI:Kendra K. Bence, Ph.D.
Abstract:Proper control of body mass, which is accomplished by balancing food intake and energy expenditure, is vital for survival. Until recently, however, little was known about the pathways that control body mass. It is now clear that many of these pathways involve tyrosyl phosphorylation. Protein-tyrosine phosphatase-1B (PTP1B) is an abundant non-receptor tyrosine phosphatase and is classically known as an insulin receptor phosphatase. PTP1B-/- mice are insulin hyper-sensitive, consistent with a role for PTP1B as a negative regulator of insulin signaling. An unexpected feature of PTP1B-/- mice, however, is that owing to increased energy expenditure, they display remarkably low adiposity and are resistant to high fat diet-induced obesity. We have previously shown that PTP1B-/- mice are hyper-sensitive to the adipocyte-secreted hormone leptin and hypothesized that PTP1B plays an important role in the hypothalamic response to insulin and leptin. These findings provided a potential mechanism for the body mass defect, but the critical site(s) of PTP1B action had remained a subject of controversy.

To definitively resolve this issue I generated mice containing an inducible (floxed) allele of PTP1B. In my initial studies, I have found the brain to be the primary site of PTP1B action to control body mass. I plan to utilize this genetic mouse model to create mice with neuron-specific deletions by crossing the inducible mice with various Cre recombinase-expressing strains. My research plan will focus initially on several important areas that are not well understood, and will utilize unique genetic models to definitively answer key questions in the field: (1) The contribution of PTP1B specifically in leptin receptor (LepR)-expressing neurons to the leanness and increased energy expenditure phenotypes of PTP1B-/- mice (2) How PTP1B deletion in hypothalamic POMC and NPY neurons affects the overall metabolic phenotype of these animals and the electrophysiological properties of these neurons, and (3) How CNS-specific deletion of PTP1B regulates leptin levels in mice.

 

PI: Jack Strominger, M.D.
Abstract:A random amino acid copolymer (Copolymer 1, Glatiramer acetate, Copaxone®) is in wide use for the treatment of multiple sclerosis in which it reduces the relapse frequency by about 30%. We developed modifications of Copolymer 1 that have improved efficacy in amelioration of experimental autoimmune encephpalomyelitis (EAE), the rodent model of MS. Most recently peptide 15mers of defined sequence that are just as effective as random amino acid copolymers have been obtained. The purpose of the present proposal is to develop random amino acid copolymers and/or peptide 15mers that ameliorate Type 1 Diabetes in the NOD mouse.


PI: Mariano Ubeda-Minarro, M.D., Ph.D.
Abstract:The purpose of this application is to address the current controversy surrounding the existence and functional significance of stem cells in the adult pancreas. The findings of these studies will be especially relevant for the understanding of the dynamics by which the insulin producing beta cells are generated. Terminally differentiated beta cells respond to variations in the extracellular concentration of glucose by secreting appropriate amounts of insulin that are required to maintain energy homeostasis at any given time. Since, an absolute or relative deficit of beta cell number is responsible for both type 1 and type 2 diabetes the development of strategies to generate new beta cells could have important therapeutical implications. A large number of studies performed in vitro or in animal models of pancreatic regeneration have suggested that new beta cells form from precursor cells through a process called neogenesis. However, other studies indicate that new beta cells originate through replication of preexisting beta cells and find no evidence for neogenesis. In order to resolve this controversy and in an attempt to identify markers and techniques that could be useful in the isolation of pancreatic precursor cells suitable for transplantation, we have established the following aims for this proposal. 1) To generate an animal model in which the hypothetical pancreatic stem cells can be labeled based on their expected slow cycling properties. We intend to use a method recently described by Dr. Elaine Fuchs (1), in which a double transgenic animal is generated expressing the vital marker H2B-GFP under the control of a tetracycline responsive promoter. Expression of the marker during the pulse phase of the experiment is mediated by the concomitant presence of the tTA (tetR) regulator fused to VP16 (tetR-VP16). Expression of the tetR-VP16 regulator will be restricted to the pancreas by using the Pdx1 promoter. Addition of doxycycline induces a complete block on the expression of the H2B-GFP marker, and allows a chase period in which the label dissipates through successive cell divisions. In these conditions only slow cycling cells are able to retain the label. 2.) Once, we achieve the first goal, we plan to determine the possible existence of a pancreatic stem cell niche by investigating the location of the label retaining cells within the pancreas and their contribution the pancreatic regeneration after surgical and chemical injury. We also plan to isolate the label retaining cells by fluorescent cell sorting and determine their gene expression profile as well as to evaluate their in vitro and in vivo proliferation capability and potentiality to differentiate into the different pancreatic lineages, especially beta cells.


 

 

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