Cholesterol regulates insulin-induced mTORC1 signaling

Area of Science:

• Cellular signaling and metabolism
• Molecular mechanisms of growth regulation

Background:

• Insulin-stimulated mechanistic target of rapamycin complex-1 (mTORC1) signaling is vital for mammalian cell growth.
• The precise regulatory factors governing insulin-induced mTORC1 activation remain incompletely understood.

Purpose of the Study:

• To elucidate the role of cholesterol in regulating insulin-stimulated mTORC1 signaling.
• To investigate how cholesterol influences mTORC1 localization and activation.
• To explore cholesterol's role in mTORC1 reactivation during starvation and its implications in Smith-Lemli-Opitz Syndrome (SLOS).

Main Methods:

• Depletion and repletion of cellular cholesterol.
• Analysis of mTORC1 recruitment to lysosomes and TSC complex dissociation.
• Investigation of cholesterol's interaction with autophagy for mTORC1 reactivation.
• Assessment of insulin-mTORC1 signaling in SLOS fibroblasts and HeLa-SLOS cells.

Main Results:

• Insulin-induced mTORC1 signaling is impaired in cholesterol-depleted cells and restored upon cholesterol repletion.
• Cholesterol facilitates mTORC1 recruitment to lysosomes, promoting complete activation without altering TSC complex dynamics.
• Cholesterol collaborates with autophagy to enable mTORC1 reactivation under starvation, rescuing insulin responsiveness.
• SLOS cells, deficient in cholesterol biosynthesis, exhibit defective insulin-mTORC1 signaling, which is rescued by cholesterol supplementation or activated Rag GTPase.

Conclusions:

• Cholesterol is a critical regulator of insulin-stimulated mTORC1 signaling, essential for cell growth.
• Cholesterol orchestrates the spatial and temporal control of mTORC1 activation through lysosomal recruitment.
• Defects in cholesterol biosynthesis lead to impaired mTORC1 signaling, highlighting cholesterol's importance in growth regulation and disease.