THIAZOLIDINEDIONES INHIBIT ALKALINE-PHOSPHATASE ACTIVITY WHILE INCREASING EXPRESSION OF UNCOUPLING PROTEIN, DEIODINASE, AND INCREASING MITOCHONDRIAL MASS IN C3H10T1 2 CELLS/

Although there are a number of cell lines committed to differentiate i nto brown adipocytes, the stem-cell origin of brown fat remains unclea r. To address this problem, we explored the effects of various pharmac ological agents on differentiation of C3H10T1/2 cells, a pluripotent s tem-cell line of mesodermal origin. Histochemical and biochemical anal ysis revealed that, when these cells were treated with retinoic acid, they expressed the osteoblastic marker alkaline phosphatase. Upon addi tion of thiazolidinediones and insulin, these cells accumulated lipid and expressed the adipocyte marker aP2, indicating differentiation int o adipocytes. Treatment during the growth phase with thiazolidinedione s resulted in maximal lipogenesis indicating a need for clonal expansi on for efficient adipogenic differentiation. Further analysis revealed that addition of thiazolidinediones to the cells increased (1) the li polytic response of the cells to beta(3)-agonists, (2) the expression of uncoupling protein (UCP), (3) the expression of mRNA for type II io dothyronine 5'-deiodinase (5'D-II): and (4) mitochondrial staining. Th ese results suggest the anti-diabetic effects of thiazolidinediones ma y, in part, involve increased brown adipocyte differentiation. Moreove r, this is the first direct evidence indicating that brown adipocytes and osteoblasts may arise from the same stem cell.