Adipose tissue is a dynamic organ In the sense that its cells are gradually replaced, though at a slowpace. It is generally believed that it is replace in about 10 years. Positive calorie balance and consequent additional triglyceride deposition in adipose tissueis intially accommodated by adipocyte hypertrophy.
The further positive caloriebalace is associated with the process of adipogenesis. During the process ofadipogenesis mesenchymal stem cells are recruited and prolifeated. Subsequentlythey are committed to preadipocytes and further mature into a adipocyte. Thisadipose tissue development and expansion is highly regulated process and is controlledby the concerted actions of a number of factors that include a number of environmental, genetic, epigenetic, andpharmacological factors. This highly regulated and integrated homeostatic network primarily designedto maintain energy homeostasis. This process of adipogenesishas been extensivly studied in vitro cell lines as well as animal models.
Theseexperiment have identified a sequential cascade oftranscriptional events that control the process of adipogenesis. Fig. 1 shows the cmplexcities of thsis process. The most important among them are peroxisome proliferator-activated receptor? (PPAR?) and CCAAT/enhancer binding protein a (C/EBPa). Both of thesetranscription factors coordinate and control the expression ofadipogenic genes.
Additionally these master regulators also controls the factorthat binds to inducer of short transcripts (FBI) as well as extracellularregulators such as Dickkopf proteins (Dkks) and Insulin-like Growth FactorBinding Protein 2 (IGFBP2) (aP2, pyruvate carboxylate) 5-7. The expression of these genes characterize thephenotype of terminally differentiated adipocytes. Their expression can befurther regulated by additional transcription factors, such assterol-regulatory element binding protein 1c (SREBP1c). Wnt signaling pathway, has also recentlybeen implicated in lineage determination and maintenance of the preadipocytephenotype 8.
