Primary Culture and Differentiation of Human Adipocyte Precursor Cells

Adipose or fat tissue is of mesenchymal origin and is comprised of adipocytes, adipose precursor cells, blood cells, endothelial cells, fibroblasts, and monocytes/macrophages. The adipocytes represent roughly two-thirds of the total cell number and, owing to their enormous cell size, make up more than 90% of the tissue volume. Adipocytes are major participants in the energy homeostasis of the human body by storing excess energy in the form of triglycerides and by releasing fatty acids to meet the energy needs of other organs depending on substrate balance and hormonal regulation (1 ,2 ). In addition, adipocytes exert multiple auto-, para-, and endocrine functions; they secrete numerous signaling factors that are involved in the regulation of energy homeostasis and a variety of neuroendocrine, metabolic, and immune functions (3 -5 ). The cytokines leptin, tumor necrosis factor-α (TNF-α), interleukin 6 (IL-6), as well as angiotensinogen and plasminogen activator inhibitor-1 (PAI-1) are some of the products secreted by adipocytes (3 -5 ). When the balance between energy intake and expenditure is such that the intake exceeds the need of the body, adipose tissue expands and the individual becomes obese. During adipose tissue enlargement, most of the adipocyte factors are increasingly produced and it has been suggested that some of them might be involved in the pathogenesis of the complications associated with obesity, such as insulin resistance (TNF-α), hypertension (angiotensinogen), enhanced thrombogenesis (PAI-1), and premature atherosclerosis (IL-6) (3 ).