Journal
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
Volume 105, Issue 27, Pages 9250-9255Publisher
NATL ACAD SCIENCES
DOI: 10.1073/pnas.0803047105
Keywords
mTOR; pancreas; islets
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Funding
- NIDDK NIH HHS [R01DK073716-01, R01 DK073716-02, R01 DK073716] Funding Source: Medline
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Regulation of pancreatic beta cell mass and function is a major determinant for the development of diabetes. Growth factors and nutrients are important regulators of beta cell mass and function. The signaling pathways by which these growth signals modulate these processes have not been completely elucidated. Tsc2 is an attractive candidate to modulate these processes, because it is a converging point for growth factor and nutrient signals. In these experiments, we generated mice with conditional deletion of Tsc2 in beta cells (beta Tsc2(-/-)). These mice exhibited decreased glucose levels and hyperinsulinemia in the fasting and fed state. Improved glucose tolerance in these mice was observed as early is 4 weeks of age and was still present in 52-week-old mice. Deletion of Tsc2 in beta cells induced expansion of beta cell mass by increased proliferation and cell size. Rapamycin treatment reversed the metabolic changes in beta Tsc2(-/-) mice by induction of insulin resistance and reduction of beta cell mass. The reduction of beta cell mass in beta Tsc2(-/-) mice by inhibition of the mTOR/Raptor (TORC1) complex with rapamycin treatment suggests that TORC1 mediates proliferative and growth signals induced by deletion of Tsc2 in beta cells. These studies uncover a critical role for the Tsc2/mTOR pathway in regulation of beta cell mass and carbohydrate metabolism in vivo.
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