SnapShot: Adipocyte Life Cycle

Adipose stem cells, which reside in a vascular niche, are essential to the development and maintenance of adipose tissue. Data from humans and rodents show that maintenance of adult adipose tissue is a dynamic process. Adipocyte turnover in young adult mice is estimated to be greater than 10% per month. The adipose stem cell niche is just as active, generating new adipocytes and replenishing the niche. This cycle occurs throughout life and responds to myriad environmental stimuli, including diet, pharmacological agents, and tissue injury. Adipose tissue deficiency (lipodystrophy) or excess (obesity) cause disease and serious secondary conditions, including diabetes, hypertension, hyper-lipidemia, and even cancer. It is therefore critical to understand the life cycle of adipose tissue and how it is regulated. In this SnapShot, we integrate a variety of studies—cell culture, animal model, human retrospective, and clinical trials—to summarize what is currently known about the molecular basis of adipose tissue formation, its stem cell niche, and the pathogenesis of obesity. Adipocyte Formation and Expansion: Key Events and Molecules Adipose depot and adipocyte formation are multistep processes, involving stem cell commitment, quiescence, and proliferation, as well as early (recruitment) and late (lipid filling) differentiation. These highly orchestrated processes involve many cell types in adipose tissue, including mature adipocytes and stromal-vascular cells (SVCs). The SVCs include fibroblasts, smooth muscle cells, pericytes, endothelial cells, and adipogenic stem/progenitor cells. The perivascular location of the stem cells places them in an appropriate position to help coordinate these interactions as well as respond to blood-borne signals, such as nutrients and drugs. Adipose Stem Cell Proliferation Stem cells are poised in a delicate balance between quiescence and division. Cell division may create additional stem cells or cells that are destined to differentiate. To maintain the appropriate balance of stem cells and various progeny, decisions are tightly regulated by an assortment of inhibitory and stimulatory factors, which can be subdivided into at least three groups (1): cell-cycle regulators (e. Significant progress has been made toward identifying the origin, location, and niche of adipose stem cells, as well as their molecular signature. The expression of PPARγ marks the adipose stem compartment. Lineage-tracing studies based on the expression of PPARγ indicate a perivascular location of adipose stem cells and highlight the vasculature as a critical stem cell niche (Tang et al., 2008). Stem cells reside in this niche as mural cells (those which physically surround the endothelial cells to provide …