Leptin is a hormone that is primarily made from adipose cells that assist in regulating energy balance by inhibiting hunger. Leptin is the opposite of ghrelin which is known as the hunger hormone. Both of these hormones act on receptors found in the arcuate nucleus of the hypothalamus to regulate appetite and also help to achieve energy homeostasis. Regulation of fat stores is the primary function of leptin, but it also plays a part in other physiological processes. These functions are evidenced by the synthesis at multiple sites other than the fat cells, but many of these have yet to be defined and require more research.
Several discoveries were found between 1950 and 1995 that lead to the identification of leptin. In 1949, a non-obese colon of mice being studied at the Jackson Laboratory produced a strain of obese offspring, suggesting that a mutation had occured in the hormones that regulated hunger and energy expenditure. In 1960, a second mutation was observed by Douglas Coleman, also at the Jackson Laboratory and was named diabetes (db) as both ob/bo and db/db were obese. In 1990, Rudolph Leibel and Jeffrey M. Freidman reported that they had mapped the db gene. In 1994, Freidman’s laboratory reported that they had identified the ob gene.
Location of Action
Leptin acts directly on leptin receptors in the cell membrane of various different cells in the human body. In particular, it acts on vertebrates in general. The leptin receptor is located in a variety of different cell types. It is a single-transmembrane-domain type I cytokine receptor. This is a special class of cytokine receptors. Furthermore, leptin interacts with other hormones and energy regulators to indirectly mediate the effects of glucagon, insulin, insulin-like growth factor, growth hormone, glucocorticoids, cytokines and metabolites.
Mode of Action
The central location of action of fat cell-specific leptin is the hypothalamus, which is a party of the brain. This is the part of which the central nervous system is located. Non-hypothalamic targets of leptin are often referred to as peripheral targets. There is a difference between central and peripheral leptin interactions under different physiological states and variations between different species.
The main function of leptin is to regulate the adipose tissue mass through central hypothalamus mediated effects on hunger, physical exercise, energy balance and food energy use. In the body, leptin’s secondary functions include the modulation of energy expenditure, modulation between fetal and maternal metabolism, and plays a permissive role in puberty, activator of beta islet cells, activator of immune cells and growth factor.
Human leptin is a 16-kDa protein of 167 amino acids. The Ob(Lep) gene (Obese, Leptin) is found on the chromosome 7 in humans.