Distinct transcriptional profiles of adipogenesis in vivo and in vitro

Obesity, defined as an increase in adipose tissue mass, is the most prevale nt nutritional disorder in industrialized countries and is a growing proble m in developing countries. An increase in adipose tissue mass can be the re sult of the production of new fat cells through the process of adipogenesis and/or the deposition of increased amounts of cytoplasmic triglyceride per cell. Although much has been learned about the differentiation of adipocyt es in vitro, less is known about the molecular basis for the mechanisms reg ulating adipogenesis in vivo. Here oligonucleotide microarrays have been us ed to compare the patterns of gene expression in preadipocytes and adipocyt es in vitro and in vivo. These data indicate that the cellular programs ass ociated with adipocyte differentiation are considerably more complex than p reviously appreciated and that a greater number of heretofore uncharacteriz ed gene regulatory events are activated during this process in vitro. In ad dition, the gene expression changes associated with adipocyte development i n vivo and in vitro, while overlapping, are in some respects quite differen t. These data further suggest that one or more transcriptional programs are activated exclusively in vivo to generate the fall adipocyte phenotype. Th is gene expression survey now sets the stage for further studies to dissect the molecular differences between in vivo and in vitro adipocytes.