Adipocyte and adipogenesis.

Adipocytes are the main constituent of adipose tissue and are considered to be a corner stone in the homeostatic control of whole body metabolism. Their primary function is to control energy balance by storing triacylglycerol in periods of energy excess and mobilizing it during energy deprivation. Besides the classical function of storing fat, adipocytes secrete numerous lipid and protein factors. Collectively they are considered to constitute a major endocrine organ which has a profound impact on the metabolism of other tissues, the regulation of appetite, insulin sensitivity, immunological responses and vascular disease. Adipogenesis is the process during which fibroblast like preadipocytes developed into mature adipocytes. Adipogenesis is a well-orchestrated multistep process that requires the sequential activation of numerous transcription factors, including the CCAAT/enhancer-binding protein (C/EBP) gene family and peroxisome proliferator activated receptor-γ (PPAR-γ). In order to reach maturity, these cells must go through two vital steps: adipocyte determination and adipocyte differentiation. Although many of the molecular details of adipogenesis are still unknown, several factors involved in this processes have been identified. Some stimulators include peroxisome proliferator-activated receptor γ (PPAR γ), insulin-like growth factor I (IGF-l), macrophage colony stimulating factor, fatty acids, prostaglandins and glucocorticoids. Inhibitors include glycoproteins, transforming growth factor-β (TGF-β), inflammatory cytokines and growth hormone. Beside these factors, there are others for example age, gender and life style that may affect this process in one way or another. An increase in the number and size of adipocytes causes white adipose tissue (WAT) to expand and this can lead to obesity. Adipogenesis can lead to central obesity if it occurs in the abdominal fat depot and peripheral obesity if it occurs in subcutaneous tissue.