Leptin regulates prothyrotropin-releasing hormone biosynthesis. Evidence for direct and indirect pathways

• Published in: The Journal of biological chemistry Vol. 275; no. 46; pp. 36124 - 36133
• Main Authors: Nillni, E A, Vaslet, C, Harris, M, Hollenberg, A, Bjørbak, C, Flier, J S
• Format: Journal Article
• Language: English
• Published: United States 17.11.2000
• Subjects: alpha-MSH - pharmacology; Animals; Antibody Specificity; Carrier Proteins - genetics; Carrier Proteins - metabolism; Cells, Cultured; Fluorescent Antibody Technique; Hypothalamus - cytology; Hypothalamus - embryology; Leptin - metabolism; Models, Biological; Neurons - drug effects; Neurons - metabolism; Neuropeptide Y - pharmacology; Promoter Regions, Genetic; Protein Precursors - biosynthesis; Protein Precursors - genetics; Pyrrolidonecarboxylic Acid - analogs & derivatives; Radioimmunoassay; Rats; Rats, Sprague-Dawley; Receptors, Cell Surface; Receptors, Leptin; RNA, Messenger - genetics; RNA, Messenger - metabolism; Signal Transduction - drug effects; Thyrotropin-Releasing Hormone - biosynthesis; Thyrotropin-Releasing Hormone - genetics; Thyrotropin-Releasing Hormone - metabolism
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M003549200

The hypothalamic-pituitary-thyroid axis is down-regulated during starvation, and falling levels of leptin are a critical signal for this adaptation, acting to suppress preprothyrotropin-releasing hormone (prepro-TRH) mRNA expression in the paraventricular nucleus of the hypothalamus. This study addresses the mechanism for this regulation, using primary cultures of fetal rat hypothalamic neurons as a model system. Leptin dose-dependently stimulated a 10-fold increase in pro-TRH biosynthesis, with a maximum response at 10 nm. TRH release was quantified using immunoprecipitation, followed by isoelectric focusing gel electrophoresis and specific TRH radioimmunoassay. Leptin stimulated TRH release by 7-fold. Immunocytochemistry revealed that a substantial population of cells expressed TRH or leptin receptors and that 8-13% of those expressing leptin receptors coexpressed TRH. Leptin produced a 5-fold induction of luciferase activity in CV-1 cells transfected with a TRH promoter and the long form of the leptin receptor cDNA. Although the above data are consistent with a direct ability of leptin to promote TRH biosynthesis through actions on TRH neurons, addition of alpha-melanocyte-stimulating hormone produced a 3.5-fold increase in TRH biosynthesis and release, whereas neuropeptide Y treatment suppressed pro-TRH biosynthesis approximately 3-fold. Furthermore, the melanocortin-4 receptor antagonist SHU9119 partially inhibited leptin-stimulated TRH release from the neuronal culture. Consequently, our data suggest that leptin regulates the TRH neurons through both direct and indirect pathways.