Type-2 diabetes (T2DM), a disease that now of epidemic proportions across the world with enormous social and medical costs. Failure of (-cells to adequately sense glucose and release insulin is the critical event leading to diabetes. Mitochondrial metabolism of (-cells senses blood glucose levels and thus a seminal question to understanding glucose stimulated insulin secretion is how mitochondrial fuel metabolism is """"""""sensed."""""""" Thus the molecular mechanisms by which mitochondria """"""""sense"""""""" metabolic flux are essential to understand the pathophysiology of T2DM. From observations in a pediatric disorder of hyperinsulinemic hypoglycemia I hypothesized that mitochondrial GTP (mtGTP) produced by the TCA cycle enzyme Succinyl CoA Synthetase (SCS) was an essential molecular signal that coupled mitochondrial metabolism to insulin secretion. A key insight was that mtGTP, unlike ATP, is an intramitochondrial signal produced stoichiometrically by each turn of the TCA cycle. By virtue of its tight coupling rates of TCA cycle oxidation, mtGTP might serve as a molecular tachometer for the TCA cycle. By altering mtGTP synthesis rates via gene silencing, a direct relationship between mtGTP and insulin secretion was observed. Surprisingly, mtGTP dramatically altered the function of mitochondria from ATP-synthesis to organelles that harness the energy of metabolism to pump calcium in and out of the mitochondria. Furthermore, the mtGTP signal provoked insulin secretion via a non-canonical KATP-independent mechanism by was dependent upon cytosolic calcium increases. Because of its isolated location, mtGTP is likely to be a very early signal dependent upon other mediators to transmit its signal to the secretory vesicles in the cytosol. Here I propose to: 1) To assess the role of mtGTP in metabolism and insulin secretion by over-expression of SCS isoforms. 2) To assess mtGTP regulation of mitochondrial anaplerosis. 3) To assess how mtGTP converts mitochondria from ATP synthesis to transporting calcium and phosphate. The projects outlined in this proposal are designed to answer not only essential questions about diabetes, but also to ensure my development as a well rounded clinical investigator and support from this award will provide an intensive, supervised research experience that is necessary to be an independent researcher and competitive at the R01 level. As fuel sensing is the essential mechanism that leads to insulin secretion, this signal will have profound implications for understanding and treatment of T2DM.

National Institute of Health (NIH)
National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)
Clinical Investigator Award (CIA) (K08)
Project #
Application #
Study Section
Diabetes, Endocrinology and Metabolic Diseases B Subcommittee (DDK)
Program Officer
Hyde, James F
Project Start
Project End
Budget Start
Budget End
Support Year
Fiscal Year
Total Cost
Indirect Cost
Yale University
Internal Medicine/Medicine
Schools of Medicine
New Haven
United States
Zip Code
Alves, Tiago C; Pongratz, Rebecca L; Zhao, Xiaojian et al. (2015) Integrated, Step-Wise, Mass-Isotopomeric Flux Analysis of the TCA Cycle. Cell Metab 22:936-47
Stark, Romana; Guebre-Egziabher, Fitsum; Zhao, Xiaojian et al. (2014) A role for mitochondrial phosphoenolpyruvate carboxykinase (PEPCK-M) in the regulation of hepatic gluconeogenesis. J Biol Chem 289:7257-63
Kibbey, Richard G; Choi, Cheol Soo; Lee, Hui-Young et al. (2014) Mitochondrial GTP insensitivity contributes to hypoglycemia in hyperinsulinemia hyperammonemia by inhibiting glucagon release. Diabetes 63:4218-29
Stark, Romana; Kibbey, Richard G (2014) The mitochondrial isoform of phosphoenolpyruvate carboxykinase (PEPCK-M) and glucose homeostasis: has it been overlooked? Biochim Biophys Acta 1840:1313-30
Alves, Tiago C; Befroy, Douglas E; Kibbey, Richard G et al. (2011) Regulation of hepatic fat and glucose oxidation in rats with lipid-induced hepatic insulin resistance. Hepatology 53:1175-81
Jamison, Rachel A; Stark, Romana; Dong, Jianying et al. (2011) Hyperglucagonemia precedes a decline in insulin secretion and causes hyperglycemia in chronically glucose-infused rats. Am J Physiol Endocrinol Metab 301:E1174-83
Jurczak, Michael J; Lee, Hui-Young; Birkenfeld, Andreas L et al. (2011) SGLT2 deletion improves glucose homeostasis and preserves pancreatic beta-cell function. Diabetes 60:890-8
Stark, Romana; Pasquel, Francisco; Turcu, Adina et al. (2009) Phosphoenolpyruvate cycling via mitochondrial phosphoenolpyruvate carboxykinase links anaplerosis and mitochondrial GTP with insulin secretion. J Biol Chem 284:26578-90
Pongratz, Rebecca L; Kibbey, Richard G; Kirkpatrick, Clare L et al. (2009) Mitochondrial dysfunction contributes to impaired insulin secretion in INS-1 cells with dominant-negative mutations of HNF-1alpha and in HNF-1alpha-deficient islets. J Biol Chem 284:16808-21
Pongratz, Rebecca L; Kibbey, Richard G; Cline, Gary W (2009) Investigating the roles of mitochondrial and cytosolic malic enzyme in insulin secretion. Methods Enzymol 457:425-50