The islet-specific glucose-6-phosphatase catalytic subunit-related protein (IGRP) is approximately 50% identical at the amino acid level to the glucose-6-phosphatase catalytic subunit and has recently been identified as a major autoantigen in the mouse Non-Obese Diabetic (NOD) model of type 1 diabetes.
In Aim 1 we propose cross- breeding NOD mice and IGRP knockout mice to determine whether the absence of the IGRP gene in the NOD background is sufficient to prevent the onset of type 1 diabetes. If diabetes is prevented, we will perform (i) a detailed analysis of immune system function in the NOD/LtJ IGRP-/- mice to evaluate whether IGRP reactive T-cells persist in these animals and the impact on the autoimmune response directed at other islet autoantigens (ii) gene rescue experiments to determine whether re-introduction of IGRP as a BAG or cDNA restores diabetes susceptibility; only the former will be spliced and preliminary data suggest that differential splicing of IGRP RNA in thymus and islets may explain how IGRP escapes central tolerance. Alternatively, if diabetes is not prevented, we will (iii) perform a detailed analysis of cellular and humoral autoreactivity targeted at IGRP and other islet autoantigens, especially insulin and (iv) generate combined NOD/LtJ IGRP-/- and insulin I -/- mice to determine whether the absence of IGRP expression combined with a reduction in insulin expression is now sufficient to prevent the development of diabetes. Preliminary data show that deletion of the IGRP gene in mice only results in mild hypoglycemia.
In Aim 2 we propose investigating the physiological basis for this observation. Since IGRP catalyzes glucose-6-phosphate hydrolysis and is expressed exclusively in pancreatic islet beta cells, we hypothesize that IGRP deletion alters the Km of glucose-stimulated insulin secretion. Therefore, oral glucose tolerance tests and hyperglycemic clamps will be used to compare insulin secretion in IGRP knockout mice and wild type littermates in vivo. In addition, insulin secretion from wild type and IGRP knockout mouse perfused pancreata will be compared in situ. Finally, insulin secretion from isolated wild type and IGRP knockout mouse islets will be compared in vitro. Relevance: A protein called IGRP has been implicated in the development of type 1 diabetes. This project will assess whether the absence of IGRP in mice is sufficient to preven the onset of diabetes. ? ? ?
|Pound, Lynley D; Sarkar, Suparna A; Cauchi, Stéphane et al. (2011) Characterization of the human SLC30A8 promoter and intronic enhancer. J Mol Endocrinol 47:251-9|
|Oeser, James K; Parekh, Vrajesh V; Wang, Yingda et al. (2011) Deletion of the G6pc2 gene encoding the islet-specific glucose-6-phosphatase catalytic subunit-related protein does not affect the progression or incidence of type 1 diabetes in NOD/ShiLtJ mice. Diabetes 60:2922-7|
|Pound, Lynley D; Hang, Yan; Sarkar, Suparna A et al. (2011) The pancreatic islet ?-cell-enriched transcription factor Pdx-1 regulates Slc30a8 gene transcription through an intronic enhancer. Biochem J 433:95-105|
|Hutton, John C; O'Brien, Richard M (2009) Glucose-6-phosphatase catalytic subunit gene family. J Biol Chem 284:29241-5|
|Pound, Lynley D; Sarkar, Suparna A; Benninger, Richard K P et al. (2009) Deletion of the mouse Slc30a8 gene encoding zinc transporter-8 results in impaired insulin secretion. Biochem J 421:371-6|
|Wang, Y; Martin, C C; Oeser, J K et al. (2007) Deletion of the gene encoding the islet-specific glucose-6-phosphatase catalytic subunit-related protein autoantigen results in a mild metabolic phenotype. Diabetologia 50:774-8|