Figure 2. Origin of different types of adipocytes.

Even though all types of adipocytes differentiate form mesenchymal/mesodermal stem cells,⁹⁸ brown, white and beige adipocytes arise from different progenitors. Interscapular brown adipocytes differentiate from Myf5⁺ precursors common to skeletal muscle cells.^{15, 27} Subcutaneous and visceral white and beige adipocytes derive from Pdgfr-α⁺ progenitors.²⁷ Aortic and mesenteric PVAT adipocytes are derived from SM22α-positive cells,²⁵ although it is unclear whether pre-adipocytes of PVAT share common precursors with VSMCs and whether VSMCs can trans-differentiate into PVAT adipocytes. Additionally, with ectopic expression of PRDM16, skeletal myocytes trans-differentiate into brown adipocytes,⁹⁹ and VSMCs into beige adipocytes.²⁸ White adipocytes can be “browned” by stimulation with cold temperature or certain factors such as irisin.^{9, 11} (Solid arrows indicate direct differentiation, and dashed arrows indicate trans-differentiation.)