Regulation of colonic epithelial cell homeostasis by mTORC1

Area of Science:

• Gastroenterology
• Molecular Biology
• Cell Biology

Background:

• Colonic epithelial cell (CEC) homeostasis relies on intricate cell signaling pathways.
• Mammalian target of rapamycin complex 1 (mTORC1) regulates critical cellular functions like proliferation and autophagy.
• The role of mTORC1 in colonic epithelial cell regulation is not fully elucidated.

Purpose of the Study:

• To investigate the role of tuberous sclerosis complex 2 (Tsc2) as a negative regulator of mTORC1 in colonic epithelial cells.
• To determine the impact of Tsc2 ablation on CEC proliferation, stem cell populations, and Wnt signaling.
• To assess the effect of Tsc2 deficiency on colonic organoid development and susceptibility to colitis.

Main Methods:

• Conditional knockout (CKO) mouse model with Tsc2 specifically ablated in intestinal epithelial cells.
• Analysis of mTORC1 activity, CEC proliferation markers, and Lgr5-positive stem cell populations.
• Assessment of Wnt target gene expression and phosphorylation of key signaling molecules (Akt, GSK3β).
• In vitro colonic organoid culture and in vivo dextran sulfate sodium (DSS)-induced colitis model.

Main Results:

• Tsc2 ablation in CECs led to increased mTORC1 activity and enhanced CEC proliferation.
• Reduced Lgr5-positive colonic stem cells and decreased Wnt target gene expression were observed.
• Key signaling pathways, including Akt and GSK3β phosphorylation, were altered.
• Tsc2 CKO mice exhibited enhanced colonic organoid formation and increased susceptibility to DSS-induced colitis.

Conclusions:

• mTORC1 activation, driven by Tsc2 loss, promotes CEC proliferation and Wnt target gene expression.
• This signaling pathway is crucial for colonic organogenesis and maintaining homeostasis.
• Dysregulation of mTORC1 signaling in CECs contributes to intestinal inflammation and disease susceptibility.