Adipose tissue (AT) expands through hypertrophy and hyperplasia. Hyperplasic AT expansion requires an adequate number of adipose progenitor cells. This study investigates the influence of depot origin on the susceptibility of adipose progenitors to cell death, and measures the effect of macrophage-secreted factors on adipose progenitor survival. Using serum deprivation alone or in the presence of TNFα, omental (OM) versus subcutaneous (SC) adipose progenitors, obtained from human AT, displayed a 3- and 1.7-fold-increase in apoptosis, respectively, as assessed by Hoechst staining, (p<0.05). Similar results were observed with cell enumeration. The ratio of OM/SC cell death from serum deprivation positively correlated with body mass index (BMI). The depot-specific difference in cell death was lost when TNFα and cycloheximide (CHX) were used. Monocyte-derived macrophages (MD-macrophages), isolated from human blood, did not have an effect on apoptosis. Depot-related differences in adipose progenitor apoptosis may influence AT remodeling and alter metabolic functionality in obesity.

White adipose tissue (WAT) is a metabolic organ with flexibility to retract and expand based on energy storage and utilization needs, processes that are driven via the coordination of different cells within adipose tissue. WAT is comprised of mature adipocytes (MA) and cells of the stromal vascular cell fraction (SVF), which include adipose progenitor cells (APCs), adipose endothelial cells (AEC) and infiltrating immune cells. APCs have the ability to proliferate and undergo adipogenesis to form MA, the main constituents ofWAT being predominantly composed of white, triglyceride-storing adipocytes with unilocular lipid droplets. While adiposity and adipose tissue health are controlled by diet and aging, the endogenous circadian (24-h) biological clock of the body is highly active in adipose tissue, from adipocyte progenitor cells to mature adipocytes, and may play a unique role in adipose tissue health and function. To some extent, 24-h rhythms in adipose tissue rely on rhythmic energy intake, but individual circadian clock proteins are also thought to be important for healthy fat. Here we discuss how and why the clock might be so important in this metabolic depot, and how temporal and qualitative aspects of energy intake play important roles in maintaining healthy fat throughout aging.