The goal of this project is to decipher molecular signaling mechanisms for control of insulin biosynthesis and secretion, and the immediate focus is on dissecting the function of Shp2 tyrosine phosphatase in orchestrating signaling cascades in ? cells. Although pancreatic ? cell failure is a critical component in all forms of diabetes, the molecular basis underlying ? cell dysfunction is poorly understood. This is mainly because that little is known for the cytoplasmic components mediating glucose and insulin signals in ?-cells. Shp2 is a cytoplasmic tyrosine phosphatase with two SH2 domains that is implicated in regulation and coordination of signaling pathways. In particular, Shp2 has been shown to promote insulin-stimulated Erk activation in vitro, although the physiological significance of Shp2 function in insulin signaling is unclear. In recent studies, we have successfully created a conditional Shp2 knockout allele, Shp2flox, in mice, which allows us to investigate specific Shp2 functions in a specific cell type or tissue in vivo. We have generated mutant mice with Shp2 deleted in mature ?-cells or in Pdx1+ pancreatic precursor cells, and will characterize these novel mouse models to test the working hypothesis that Shp2 acts to coordinate and control the strength of several signaling pathways in orchestrating insulin biosynthesis and secretion in ?-cells. In complement with the gene targeting approach in vivo, we will also use siRNA- mediated gene knockdown technique to decipher the molecular signaling mechanisms in ? cells.
Our specific aims are: 1) to determine the physiological role of Shp2 in ?-cell function and glucose homeostasis;2) to dissect the molecular mechanism for Shp2 action in ?-cells;and 3) to investigate the Shp2 function in pancreatic development and ?-cell regeneration. Successful completion of the proposed experiments will fill in a gap in our knowledge for coordinated regulation of cytoplasmic signaling events in ?-cells, and may even lead to a new paradigm on regulation of ?-cell functions in glucose homeostasis and also in pathogenesis of type 2 diabetes.
The goal of this project is to understand the intracellular signaling mechanisms for control of insulin biosynthesis in ? cells and also the molecular basis for ? cell failure in Type 2 diabetes, the most common metabolic disease in the world. Type 2 diabetes is characterized by defective pancreatic ? cell insulin release in response to glucose and impaired insulin action on its target tissues. ?-cell failure is likely caused by inadequate expansion of the ?-cell mass and/or failure of the ?-cells to respond to glucose. Now, a crucial issue is to understand the molecular signaling scheme for ?-cell sensing of glucose and secretion of insulin. We originally cloned murine Shp2 (Syp) as a protein tyrosine phosphatase that contains two Src homology 2 (SH2) domains (Feng et al., Science 1993). Shp2 is a cytoplasmic enzyme and has been implicated in regulation of signaling events triggered by growth factors, cytokines and hormones. In particular, Shp2 binds the insulin receptor substrate (IRS) and Grb2-associated binder (GAB) proteins. Several groups have demonstrated a positive effect of Shp2 in mediating insulin-stimulated Erk activation in vitro. While these studies suggest a putative role of Shp2 in insulin action, the physiological evidence in vivo is yet to be obtained. To determine Shp2 function in ?-cells, we have generated mutant mouse lines with Shp2 selectively deleted in the pancreas or ?-cells. These mutant mice displayed impaired glucose tolerance and defective insulin secretion and production. Our central working hypothesis is that Shp2 acts as a coordinator to fine-tune and integrate multiple signals for insulin biosynthesis and secretion in ?-cells. Our preliminary experimental data suggest that Shp2 indeed has a critical role in promoting insulin biosynthesis and secretion in ?-cells for control of glucose homeostasis. Successful completion of the proposed experiments in these three Aims will not only fill in a gap in our knowledge in molecular signaling events in ?- cells, but may even refresh our current view on ?-cell functions in glucose-stimulated insulin secretion and also on the etiology of type 2 diabetes.
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