Commitment of Mouse Embryonic Stem Cells to the Adipocyte Lineage Requires Retinoic Acid Receptor β and Active GSK3

Key events leading to terminal differentiation of preadipocytes into adipocytes have been identified in recent years. However, signaling pathways involved in the decision of stem cells to follow the adipogenic lineage have not yet been characterized. We have previously shown that differentiating mouse embryonic stem (mES) cells give rise to functional adipocytes upon an early treatment with retinoic acid (RA). The goal of this work was to identify regulators of RA-induced commitment of mES cells to the adipocyte lineage. First, we investigated the role of RA receptor (RAR) isotypes in the induction of mES cell adipogenesis. Using synthetic retinoids selective of RAR isotypes, we show that RARβ activation is both sufficient and necessary to trigger commitment of mES cells to adipocytes. Then, we performed a small-scale drug screening to find signaling pathways involved in RARβ-induced mES cell adipogenesis. We show that pharmacological inhibitors of glycogen synthase kinase (GSK) 3, completely inhibit RARβ-induced adipogenesis in mES cells. This finding uncovers the requirement of active GSK3 in RARβ-induced commitment of mES cells toward the adipocyte lineage. Finally, we investigated the role of the Wnt pathway, in which GSK3 is a critical negative regulator, in adipocyte commitment by analyzing Wnt pathway activity in RA- and RARβ-induced mES cell adipogenesis. Our results suggest that although RARβ and active GSK3 are required for RA-induced adipogenesis, they might be acting through a Wnt pathway–independent mechanism.