Brief report: the differential roles of mTORC1 and mTORC2 in mesenchymal stem cell differentiation

Area of Science:

• Cell Biology
• Stem Cell Biology
• Molecular Biology

Background:

• Mesenchymal stem cells (MSCs) differentiate into adipocytes (AdCs) and osteoblasts (OBs) through a transcriptionally controlled, mutually exclusive process.
• The mammalian target of rapamycin (mTOR) pathway is implicated in determining MSC fate, with mTOR inhibition favoring OB differentiation.
• mTOR functions in two complexes, mTORC1 and mTORC2, but their distinct roles in MSC lineage commitment are unclear due to inhibitor study limitations.

Purpose of the Study:

• To elucidate the specific roles of mTORC1 and mTORC2 in regulating mesenchymal stem cell (MSC) differentiation into adipocytes and osteoblasts.
• To overcome the confounding effects of broad mTOR inhibitors on MSC fate determination.

Main Methods:

• Generated primary mouse MSCs with genetic deficiencies in Rptor (RapKO) or Rictor (RicKO) using the Cre/loxP system.
• Assessed MSC differentiation capacity towards adipogenic and osteogenic lineages under inductive culture conditions.
• Confirmed impaired mTORC1 signaling in RapKO MSCs and impaired mTORC2 signaling in RicKO MSCs.

Main Results:

• RapKO MSCs showed reduced adipogenesis and enhanced osteogenesis.
• RicKO MSCs exhibited reduced osteogenesis and enhanced adipogenesis.
• These findings demonstrate distinct and opposing roles for mTORC1 and mTORC2 in MSC lineage commitment.

Conclusions:

• mTORC1 signaling, mediated by raptor, promotes adipocyte differentiation and suppresses osteoblast differentiation.
• mTORC2 signaling, mediated by rictor, promotes osteoblast differentiation and suppresses adipocyte differentiation.
• Distinct roles of mTORC1 and mTORC2 are critical for regulating MSC lineage commitment, offering potential therapeutic targets.