Leptin

Leptin belongs to the long-chain helical cytokine family (Matarese G 2000). Leptin is expressed by adipose tissue, gastric epithelium and brain cells (Bado A et al. 1998). In the hypothalamus, leptin stimulates metabolic rate and has appetite inhibitory effects. Leptin has regulatory functions in angiogenesis, homeostasis, hematopoiesis, thermogenesis, and chondrogenesis. Leptin also influences neuroendocrine and immunological processes (Fantuzzi G et al. 2000). For example, leptin acts by acting as a proinflammatory cytokine in monocytes and lymphocytes, thereby promoting the production of Th1-type cytokines.

Furthermore, leptin influences reproductive processes. During pregnancy, the maternal leptin concentration increases and decreases again after birth. Leptin influences the course of pregnancy by regulating ovarian function and maturation and embryonic development (Cervero A et al. 2004). In addition, leptin promotes trophoblast proliferation, fetal growth, and lactation.In osteoblasts, monocytes, eosinophilic granulocytes, and other cells, leptin has anti-apoptotic effects (Conus S et al 2005).

Leptin is a ligand of the leptin receptor (ObR, LEPR). The leptin receptor belongs to the gp130 family of cytokine receptors (Tartaglia LA et al 1995). Through its cytosolic domain, the leptin receptor is associated with tyrosine kinases. It has no tyrosine kinase activity of its own. Alternative splicing gives rise to the 6 leptin receptor isoforms: ObRa, ObRb, ObRc, ObRd, ObRe and ObRf (Harvey J et al 2003).

Leptin itself is a target gene of the nuclear receptor PPARγ and thus also a target gene of RXRα, the heterodimeric partner of PPARγ. RXRα and PPARγ are also likely involved in the regulation of leptin in the placenta. RXR agonists are able to regulate leptin expression and thereby positively influence pregnancy outcome. Furthermore, leptin influences reproductive processes. During pregnancy the maternal leptin concentration increases and decreases after birth. Leptin influences the course of pregnancy by regulating the function and maturation of the ovaries and the development of the embryo (Cervero A et al. 2004).

In addition, leptin promotes trophoblast proliferation, fetal growth and lactation, and has anti-apoptotic effects in osteoblasts, monocytes, eosinophil granulocytes and other cells (Conus S et al. 2005).

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