? Hyperglycemia is one of the hallmarks of diabetes. Understanding the molecular mechanisms responsible for the elevated blood glucose is crucial for the prevention and cure of this rapidly rising disease. This investigator is currently using mouse genetic approaches to elucidate regulatory mechanisms controlling hepatic glucose homeostasis. Insulin receptor substrate (IRS) 1 and 2 mediate most of the insulin action in the liver. Mice that are deficient of both IRS1 and IRS2 in the hepatocytes (LDKO) develop severe diabetes with hyperglycemia and insulin resistance. Intriguingly, expression of well known gluconeogenic genes including phosphoenolpyruvate carboxykinase (Pepck) and glucose-6 phosphatase (G6Pase) is not altered in the LDKO liver. In contrast, expression of pyruvate dehydrogenase kinase 4 (PDK4) is dramatically increased in the liver of these mice. PDK4 is important because it regulates the critical substrate (pyruvate) supply for gluconeogenesis. Substrate availability is the most important driving force for gluconeogenesis. For the short-term goal in the mentored phase, this investigator will investigate whether suppression of hepatic PDK4 expression by adenovirus-mediated siRNA can attenuate the gluconeogenesis and improve hyperglycemia in diabetic animal models. Meanwhile, mechanisms responsible for the PDK4 induced hyperglycemia will also be investigated. For the long-term goal in the independent phase and beyond, how PDK4 is regulated by hormonal and nutritional signals will be mechanistically studied. Specifically, nutrients such as pyruvate, the primary substrate for gluconeogenesis, will be investigated for its potential role in the regulation of PDK4 gene. SIRT1, a candidate for metabolic sensor, will be explored for its function in the nutrient-regulated PDK4 expression. Furthermore, the mechanisms responsible for the PDK4 dysregulation in diabetes will be elucidated using animal models, particularly Foxo1 (A Forkhead transcription factor) mediated regulation. Understanding how PDK4 contributes to hepatic nutrient homeostasis can reveal novel target for the treatment of metabolic syndrome and type 2 diabetes. The overall goal of the proposed project will be accomplished in the following three specific aims: ? 1. Role of PDK4 in gluconeogenesis in the IRS1 and IRS2 dual liver-specific knockout mice. ? 2. Nutrient sensing in the regulation of PDK4 expression. ? 3. Role of Foxo1 in the regulation of PDK4 and hepatic glucose homeostasis. ? ?
| Xiong, Xiwen; Tao, Rongya; DePinho, Ronald A et al. (2013) Deletion of hepatic FoxO1/3/4 genes in mice significantly impacts on glucose metabolism through downregulation of gluconeogenesis and upregulation of glycolysis. PLoS One 8:e74340 |
| Tao, Rongya; Xiong, Xiwen; Harris, Robert A et al. (2013) Genetic inactivation of pyruvate dehydrogenase kinases improves hepatic insulin resistance induced diabetes. PLoS One 8:e71997 |
| Cheng, Zhiyong; Guo, Shaodong; Copps, Kyle et al. (2009) Foxo1 integrates insulin signaling with mitochondrial function in the liver. Nat Med 15:1307-11 |
| Guo, Shaodong; Copps, Kyle D; Dong, Xiaocheng et al. (2009) The Irs1 branch of the insulin signaling cascade plays a dominant role in hepatic nutrient homeostasis. Mol Cell Biol 29:5070-83 |
| Dong, Xiaocheng C; Copps, Kyle D; Guo, Shaodong et al. (2008) Inactivation of hepatic Foxo1 by insulin signaling is required for adaptive nutrient homeostasis and endocrine growth regulation. Cell Metab 8:65-76 |
