Molecular differences caused by differentiation of 3T3-L1 preadipocytes in the presence of either dehydroepiandrosterone (DHEA) or 7-oxo-DHEA.

The effects of dehydroepiandrosterone (DHEA) and 7-oxo-DHEA on the cell size, adiposity, and fatty acid composition of differentiating 3T3-L1 preadipocyte cells are correlated with stearoyl-CoA desaturase (SCD) expression (mRNA and protein levels) and enzyme activity. Fluorescence-activated cell sorting shows that preadipocyte cells treated with methylisobutylxanthine, dexamethasone, and insulin (MDI) plus DHEA comprise a population distribution of predominantly large cells with reduced adiposity. In contrast, cells treated with MDI plus 7-oxo-DHEA comprise a population distribution of almost equal proportions of small and large cells that have an adiposity equivalent to cells differentiated with MDI alone. The cells treated with MDI plus DHEA have significantly reduced levels of total fatty acid, mainly due to a dramatic reduction in the level of palmitoleic (Delta(9)-16:1) acid. The cells treated with MDI plus 7-oxo-DHEA have a significantly increased level of total fat, primarily due to increased levels of Delta(9)-16:1 and palmitic (16:0) acids. At the molecular level, the DHEA-treated cells contain lowered amounts of SCD1 mRNA and antibody-detectable desaturase protein, while 7-oxo-DHEA-treated cells contained elevated levels of SCD1 mRNA and protein. Inhibition of differentiation in DHEA-treated cells was also suggested by a reduction in the mRNA level of the adipogenic gene aP2. At the level of microsomal enzymatic activity, SCD activity was decreased in DHEA-treated cells while the SCD activity was increased in 7-oxo-DHEA-treated cells. The changes in mRNA levels and enzyme activity were concentration-dependent and appeared as early as day 3 of the differentiation protocol. The results show that DHEA and 7-oxo-DHEA have distinct modes of action with respect to the complex transcriptional cascade required for differentiation. Furthermore, differences in the insulin-stimulated uptake of 2-deoxyglucose and in the activity of carnitine palmitoyl transferase observed from either DHEA- or 7-oxo-DHEA-treated cells support the ability of DHEA to produce a thermogenic effect in differentiating preadipocytes, while 7-oxo-DHEA promotes differentiation without other changes typical of thermogenesis.