Author: Gianpiero Pescarmona Date: 2010-02-09
Leptin (Greek leptos meaning thin) is a 16 kDa protein hormone that plays a key role in regulating energy intake and energy expenditure, including appetite and metabolism. It is one of the most important adipose derived hormones. The Ob(Lep) gene (Ob for obese, Lep for leptin) is located on chromosome 7 in humans.
Vagal stimulation rapidly increases leptin secretion in human stomach. 2002
Leptin plays a critical role in regulating muscle protein metabolism by binding with leptin receptors in a 1:1 stoichiometry. However, the role for leucine in the regulation of leptin receptor expression in muscle has not been investigated. The present study was conducted to test the hypothesis that leucine regulates leptin receptor levels in C2C12 myotubes. Cells were cultured in the presence of DMEM/F12 medium containing supplemental 0 or 5 mM L: -leucine. Leptin receptor expression by C2C12 myotubes peaked at 2 h post-supplementation. Additionally, leucine stimulated leptin receptor expression at both mRNA and protein levels in a dose-dependent manner. Furthermore, leucine enhanced the phosphorylation of mammalian target of rapamycin (mTOR). Addition of rapamycin (an inhibitor of mTOR) to culture medium completely suppressed leucine-induced activation of mTOR and inhibited leucine-stimulated leptin receptor production. These results indicate that leucine affects leptin receptor expression in muscle cells via the mTOR signaling pathway. (Mol Biol Rep. 2010 Feb 12)
Leptin is a 16 kDa protein hormone that plays a key role in regulating energy intake and energy expenditure, including appetite and metabolism. It is one of the most important adipose derived hormones.
Contents in aminoacids, % of total:
Leptin functions directly in the regulation of food energy intake and expenditure. At the level of the central nervous system, leptin exerts an anorexigenic effect by signalling satiety and decreasing the sensation of hunger .
The control of energy homeostasis, food intake and body composition by leptin begins in early life, when the hormone also controls foetal growth and development. Growth during foetal life is linked with specific changes in leptin levels: small-for-gestational age (SGA) neonates have lower leptin levels at birth than appropriate-for-gestational age ones, and large-for-gestational age (LGA) neonates have higher leptin levels than the other infants. The observation of a surge in leptin soon after birth in mice suggests that leptin is essential for the development of the hypothalamic pathways involved in the regulation of energy balance and appetite, and that this activity could be restricted to a critical neonatal window. Interestingly, there is evidence that serum leptin concentration reflects body fat mass in adults, in children, during foetal life and also in infants.
The leptin gene is expressed in the mammary gland of lactating women and that leptin is produced by mammary epithelial cells; leptin can be secreted into milk by the mammary gland and it can be transferred from the blood. Leptin receptors have been identified in gastric epithelial cells and in the absorptive cells of small intestine, which suggests that leptin could pass from milk to infant blood.
The mean target of Leptin are arcuate nucleus cells that express Ob-Rb receptors. Leptin inhibits NPY/AGRP neurons and enhances POMC/CART (pro-opiomelanocortin) neurons. When leptin binds its receptor, activates the JAK-STAT pathways inducing SOCS-3 (suppressors of cytokine signaling). Leptin receptor were found also in cortex and thalamus, and in peripherical organs: adipocytes, lung, liver, skeletal muscle, lymphonode, kidney, spleen, adrenals and testis.