Longevity, lipotoxicity and leptin: the adipocyte defense against feasting and famine

In this review, we propose that actions of the lipid-lowering, apoptosis-inhibiting effects of certain "longevity genes" oppose the life-shortening consequences of lipotoxicity and lipoapoptosis. We note that lipotoxicity occurs whenever leptin action is deficient, or whenever satiety is overridden, as in forced or voluntary overfeeding ("supersizing"). The role of hyperleptinemia, we suggest, is to extend survival during famine by permitting the storage of surplus calories in adipocytes without concomitant injury to nonadipose tissues from ectopic lipid deposits. It achieves this lipid partitioning by (1) restraining the level of overnutrition so as not to exceed the available adipocyte storage space and (2) enhancing oxidation of any ectopic lipid overflow: The mechanisms of lipoapoptosis are discussed, and the possibility that metabolic syndrome is the human equivalent of rodent lipotoxicity is suggested.