Brief Report: The Differential Roles of mTORC1 and mTORC2 in Mesenchymal Stem Cell Differentiation

• Published in: Stem cells (Dayton, Ohio) Vol. 33; no. 4; pp. 1359 - 1365
• Main Authors: Martin, Sally K., Fitter, Stephen, Dutta, Ankit K., Matthews, Mary P., Walkley, Carl R., Hall, Michael N., Ruegg, Markus A., Gronthos, Stan, Zannettino, Andrew C. W.
• Format: Journal Article
• Language: English
• Published: United States Oxford University Press 01.04.2015
• Subjects: Animals; Bone marrow; Cell Differentiation - physiology; Cell Proliferation - physiology; Mechanistic Target of Rapamycin Complex 1; Mechanistic Target of Rapamycin Complex 2; Mesenchymal stem cell; Mesenchymal Stromal Cells - physiology; Mice; Mice, Knockout; mTOR; Multiprotein Complexes - physiology; Raptor; Rictor; Stem cells; TOR Serine-Threonine Kinases - physiology; Mesenchymal stem cell; Rictor; mTOR; Raptor
• ISSN: 1066-5099; 1549-4918
• DOI: 10.1002/stem.1931

Adipocytes (AdCs) and osteoblasts (OBs) are derived from mesenchymal stem cells (MSCs) and differentiation toward either lineage is both mutually exclusive and transcriptionally controlled. Recent studies implicate the mammalian target of rapamycin (mTOR) pathway as important in determining MSC fate, with inhibition of mTOR promoting OB differentiation and suppressing AdC differentiation. mTOR functions within two distinct multiprotein complexes, mTORC1 and mTORC2, each of which contains the unique adaptor protein, raptor or rictor, respectively. While compounds used to study mTOR signaling, such as rapamycin and related analogs, primarily inhibit mTORC1, prolonged exposure can also disrupt mTORC2 function, confounding interpretation of inhibitor studies. As a result, the relative contribution of mTORC1 and mTORC2 to MSC fate determination remains unclear. In this study, we generated primary mouse MSCs deficient in either Rptor (RapKO) or Rictor (RicKO) using the Cre/loxP system. Cre‐mediated deletion of Rptor or Rictor resulted in impaired mTORC1 and mTORC2 signaling, respectively. Under lineage‐inductive culture conditions, RapKO MSCs displayed a reduced capacity to form lipid‐laden AdCs and an increased capacity to form a mineralized matrix. In contrast, RicKO MSCs displayed reduced osteogenic differentiation capacity and enhanced adipogenic differentiation potential. Taken together, our findings reveal distinct roles for mTORC1 and mTORC2 in MSC lineage commitment. Stem Cells 2015;33:1359–1365