Objective: To validate the human mesenchymal stem cells (hMSCs) as a new in vitro model for the study of human adipogenesis, to develop the optimal protocol for the differentiation of hMSCs into adipocytes, and to describe effect of mitogen‐activated protein kinase on hMSC differentiation into adipocytes.

Research Methods and Procedures: hMSCs, obtained commercially, were differentiated by exposure to insulin, dexamethasone, indomethacin, and 3‐isobutyl‐1‐methylxanthine three times for 3 days each. Various differentiation conditions were examined to optimize differentiation as measured by Oil Red O staining. The gene expression during adipogenic conversion was assessed by reverse‐transcription polymerase chain reaction, real‐time reverse‐transcription polymerase chain reaction, and Western blotting.

Results: hMSCs differentiated into adipocytes to a different extent depending on the experimental conditions. We have found that differentiation medium based on medium 199 and containing 170 nM insulin, 0.5 mM 3‐isobutyl‐1‐methylxanthine, 0.2 mM indomethacin, 1 μM dexamethasone, and 5% fetal bovine serum was optimal. However, the replacement of fetal bovine serum with rabbit serum (15%) led to further enhancement of differentiation. Inhibition of mitogen‐activated protein kinase activation also facilitated adipogenic conversion of hMSCs. The pattern of genes expressed during hMSC differentiation into adipocytes (adipsin, peroxisome proliferator‐activated receptor‐γ, CCAAT/enhancer‐binding protein‐β, GLUT4, and leptin) was similar to that observed in other in vitro adipocyte models.

Discussion: hMSCs are renewable sources of noncommitted precursors that are able to differentiate into mature adipocytes under the proper hormonal and pharmacological stimuli. Thus, hMSCs represent a new model for the study of human adipogenesis.