Adipose tissue development: The role of precursor cells and adipogenic factors

Summary Obesity is regarded as a heterogeneous syndrome, which may appear in different forms. Various causes have been found to contribute to its pathogenesis. During recent years investigations of adipose tissue cellularity and its dynamic changes have gained growing interest. An important progress was the discovery of adipose tissue precursor cells. These cells have not yet been precisely identified by morphological and biochemical methods in intact tissue. However, due to methodological developments such precursor cells can be cultured both as primary cultures and as established cell lines. These culture systems have proven to be valuable models for the study of the processes involved in the formation of new fat cells.Abbreviations cAMP Cyclic adenosine monophosphate - cDNA Complementary desoxyribonucleic acid - DHAP Dihydroxy-acetone phosphate - GPDH Glycero-3-phosphate dehydrogenase - IGF-I Insulin-like growth factor I - MIX 1-Methyl-3-isobutylxanthine - mRNA Messenger ribonucleic acid - TNF Tumor necrosis factorExperiments carried out in the authors' laboratories and published in this review were supported by the Deutsche Forschungsgemeinschaft, Sonderforschungsbereich 43Terms: A number of terms have been used to describe the process of adipocyte development. These are defined as follows [11]:Adipoblast: the pluripotent mesenchymal stem cell of the adipose tissue, which at present is still putative and has not been identified biochemically and morphologicallyPreadipocyte: the cell already committed or determined to become a fat cell with the ability to synthesize lipogenic enzymes and to store lipids; these cells may even contain small lipid droplets or become quickly filled with triglyceridesAdipocyte precursor cells: a precise distinction between adipoblast and preadipocyte is usually not possible and therefore this term is frequently used to describe both differentiation phases, particularly in primary cultureAdipocyte: a cell with a central large lipid vacuole, showing the characteristic signet-ring form, with high activities for enzymes of triglyceride synthesis and releaseDetermination or commitment: the irreversible recruitment of the pluripotent stem cell to a preadipocyte, which may be preceded by one or more cell divisionsAdipogenic conversion: the development of a preadipocyte to the morphological and biochemical appearance of an adipocyte by the expression of a genetic programAdipogenic (adipose) differentiation: the continuous gradual development of an adipoblast to a mature fat cell