Figure 1.

Key structural and functional components of adipose tissue and adipose tissue-secreted factors to key biological properties of skeletal muscle and mobility in aging. Adipose tissue arises from adipose-derived stem cells (ASCs). The ability of ASCs to self-renew is critical for maintenance of healthy adipocytes and adipose tissue. While some ASCs retain the capacity for ongoing regeneration, others change their self-renewal cycle to become mature adipocytes. Mature “healthy” adipocytes have several potential fates that may contribute to “adipose pathology:” cell death (in which cells usually develop necrosis and are engulfed by macrophage, forming crown-like structures), senescence (in which cells cease to divide and enter a quiescent, metabolically inactive state), inflammation (in which inflammatory cells infiltrate adipose tissues and produce inflammatory cytokines), metabolic inflexibility (in which typically hypertrophic cells develop reduced ability to adjust substrate utilization in response to physiological stimuli such as insulin and catecholamines). These adipose “fates,” in turn, influence secretion of bioactive factors that can ultimately mediate inter-organ pathology, including skeletal muscle pathology. SASP, secretory-associated senescent phenotype; FFAs, free fatty acids; M1, macrophage 1; M2, macrophage 2.