Autophagic degradation of mitochondria in white adipose tissue differentiation.

Recent work has revealed that autophagy plays a significant role in the process of white adipocyte differentiation. In both in vitro and in vivo model systems, autophagy inactivation by targeted deletion of essential autophagy genes results in alterations in white adipocyte structure. In both models, postdifferentiation cells exhibit atypical morphology, with many small lipid droplets and large numbers of mitochondria, rather than the single large lipid droplet and relatively few mitochondria observed in normal white adipocytes. The role of autophagy as the primary means of the degradation of mitochondria has long been studied, and it is likely that a deficiency in the degradation of mitochondria contributes to the unusual phenotypes observed in mice with autophagy-deficient adipose tissue, including reduced adiposity, resistance to diet-induced obesity, and increased insulin sensitivity. What is not yet known is whether the process of mitochondria-specific autophagy, often referred to as "mitophagy," is specifically induced during adipogenesis or if a general increase in the nonspecific autophagic degradation of mitochondria plays a role in normal adipose differentiation. Despite remaining questions, these findings not only establish the critical role of autophagy in white adipose tissue development, but also suggest that the manipulation of autophagy in adipose tissue may provide novel therapeutic opportunities for metabolic diseases.