Figure 3.

mTORC1 signalling has been implicated in promoting the three main steps of adipogenesis. Adipogenesis consists of the differentiation of a mesenchymal stem cell to a mature adipocyte, which makes up a significant part of adipose tissue in which energy is stored as lipids. The commitment of the mesenchymal stem cells to the adipocyte lineage is the first step of adipogenesis and is facilitated by S6K1 activity. C/EBP-β and -δ are the primary drivers of clonal expansion, which is crucial for preadipocyte maturation, and the former has been suggested to be activated by mTORC1 signalling. The terminal differentiation of preadipocytes to mature adipocytes is mediated by PPARγ and C/EBP-α. mTORC1 promotes this final step through both its inhibition of 4E-BP and its activation of PPARγ through a poorly understood mechanism. Although the precise molecular mechanisms have yet to be defined, rapamycin blocks adipogenesis. 4E-BP, eIF4E-binding protein; C/EBP-α/β/δ, CCAAT/enhancer-binding protein-α/β/δ; mTORC1, mechanistic target of rapamycin complex 1; PPARγ, peroxisome proliferator-activated receptor γ; S6K1, ribosomal S6 kinase 1.