Rictor/mTORC2 is essential for maintaining a balance between beta-cell proliferation and cell size

Area of Science:

• Endocrinology
• Cell Biology
• Metabolic Signaling

Background:

• The phosphotidylinositol-3-kinase (PI3K)/mammalian target of rapamycin complex 2 (mTORC2)/AKT signaling pathway regulates critical cellular processes.
• mTORC2, a key component of this pathway, is implicated in cell growth and survival, but its specific role in pancreatic beta-cell mass and function requires elucidation.

Purpose of the Study:

• To investigate the role of Rictor, an essential component of mTORC2, in regulating pancreatic beta-cell mass and function.
• To determine the impact of deleting Rictor and/or Pten on beta-cell proliferation, mass, and glucose homeostasis.

Main Methods:

• Generation of mice with beta-cell-specific deletions of Rictor or Pten.
• Analysis of beta-cell mass, proliferation, insulin content, and glucose-stimulated insulin secretion.
• Assessment of AKT phosphorylation (S473 and T308) and key protein expression (FoxO1, p27).

Main Results:

• Rictor deletion in beta-cells reduced beta-cell mass, proliferation, and insulin secretion, leading to hyperglycemia and glucose intolerance.
• Pten deletion increased beta-cell mass through enhanced proliferation and cell size.
• Mice lacking both Rictor and Pten had normal beta-cell mass but larger cells, with increased AKT-T308 phosphorylation despite reduced proliferation.

Conclusions:

• PI3K/AKT signaling via mTORC2 (specifically pAKT-S473) is vital for maintaining normal beta-cell mass.
• Phosphorylation of AKT-S473 negatively regulates AKT-T308 phosphorylation, balancing beta-cell proliferation and cell size in response to stimuli.