Pioglitazone and dexamethasone induce adipogenesis in D1 bone marrow stromal cell line, but not through the peroxisome proliferator-activated receptor-gamma pathway

Osteoblasts and adipocytes share a common progenitor in bone marrow. Peroxisome proliferator-activated receptor-gamma (PPAR-gamma) plays a critical role in adipogenesis. Using a mouse pluripotent mesenchymal cell, D1, as a model, several reports have demonstrated that dexamethasone, a glucocorticoid, can induce adipogenesis. We first examined whether adipogenesis induction in D1 cells is initiated by activation of PPAR-gamma. The results revealed that pioglitazone induces adipogenesis in D1 cells in a dose-dependent manner and decreases alkaline phosphatase activity in D1 cells. Interestingly, this adipogenesis was not blocked by bisphenol A diglycidyl ether, a PPAR-gamma antagonist. A PPAR-gamma-mediated reporter gene assay showed no response to pioglitazone. We then asked whether dexamethasone-induced adipogenesis can be repressed by mifepristone (RU486), an antagonist of glucocorticoid receptor. The results disclosed that mifepristone cannot counteract dexamethasone-induced adipogenesis, and mifepristone itself induced adipogenesis in D1 cells. Moreover, glucocorticoid receptor-mediated reporter gene assay was not responsive to dexamethasone or mifepristone. We concluded that the adipogenesis induced by pioglitazone and dexamethasone in D1 cells may not occur via a PPAR-gamma and glucocorticoid receptor pathway. Finally, we analyzed the gene expression profile of D1 by cDNA microarray after treatment with dexamethasone. We found that the expression of several adipogenesis-related genes is highly provoked by this agent.