The tissue. However, recent studies showed that leptin is

The gene LEP (on 7alpha31.3) encodes for Leptin, a
vital homeostatic hormone that is secreted into the blood stream by the white adipose
tissue and it operates by stimulating energy expenditure and inhibiting food
intake in the hypothalamus (Anke
Hinney, Vogel, & Hebebrand, 2010). After the secretion of leptin into the
bloodstream where it attaches to proteins and get transported to the brain,
which stimulate or inhibit the release of various neurotransmitters. MNAJA1 Some orexigenic neuropeptide such as neuropeptide Y, melanin-concentrating
hormones gets down-regulated by leptin, while other orexigenic neuropeptide
gets up-regulated such as corticotrpin-releasing hormone and alpha melanocyte
stimulating hormones which acts on the melanocortin 4 receptor (Houseknecht
et al., 1996; Mullis, 2017)

Leptin expression is influenced by the status of energy
stores in fats. Previews studies indicated that leptin expression was only
synthesized in adipose tissue. However, recent studies showed that leptin is
also synthesized in extra adipose tissues including the skeletal muscles,
mammary epithelium, gastric fundic mucosa and the placenta but the amount of
body fat is the main determinant of the circulating level of leptin. Adipocyte
size plays an important role in determining leptin synthesis, the larger the
adipocyte size the more leptin it contains. The level of leptin in the blood
correlates with total body fat stores. It is not fully understood whether
factors such as increases in triglyceride level or lipid metabolism that are
associated with increase in adipocyte sizes affect leptin expression (Ahima
& Flier, 2000).

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Defect in leptin production can cause extreme obesity.

Regulation of leptin expression is mediated by insulin, the expression of
leptin increases by the increase of insulin during feeding cycle. Thus, leptin
level increases rapidly after several days of overeating and decreases within
hours of fasting 19. In addition, Leptin expression in the placenta is
stimulated by glucocorticoids, hypoxia and insulin. Leptin synthesis is
stimulated by many factors such as; infection, endotoxin and cytokines like,
tumor necrosis factors (TNF), interleukin 1 (IL-1), and leukemia inhibitory
factors (LIF). The increase in leptin level as the result of the rise in
cytokine levels may contribute to anorexia and weight loss (Ahima
& Flier, 2000).