Leptin regulates prothyrotropin-releasing hormone biosynthesis. Evidence for direct and indirect pathways.
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.
Nillni
E A
EA
Division of Endocrinology, Brown University School of Medicine, Rhode Island Hospital, Providence, Rhode Island 02903, USA. Eduardo_Nillni@Brown.edu
Vaslet
C
C
Harris
M
M
Hollenberg
A
A
Bjørbak
C
C
Flier
J S
JS
D000818:Animals; D000918:Antibody Specificity; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism; D002478:Cells, Cultured; D005455:Fluorescent Antibody Technique; D007031:Hypothalamus / Q000166:cytology / Q000196:embryology; D020738:Leptin / Q000378:metabolism*; D008954:Models, Biological; D009474:Neurons / Q000187:drug effects / Q000378:metabolism; D009478:Neuropeptide Y / Q000494:pharmacology; D011401:Promoter Regions, Genetic; D011498:Protein Precursors / Q000096:biosynthesis* / Q000235:genetics; D011761:Pyrrolidonecarboxylic Acid / Q000031:analogs & derivatives; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D011863:Radioimmunoassay; D051381:Rats; D017207:Rats, Sprague-Dawley; D011956:Receptors, Cell Surface; D054411:Receptors, Leptin; D015398:Signal Transduction / Q000187:drug effects; D013973:Thyrotropin-Releasing Hormone / Q000096:biosynthesis* / Q000235:genetics / Q000378:metabolism; D000521:alpha-MSH / Q000494:pharmacology
D002352:Carrier Proteins; D020738:Leptin; D009478:Neuropeptide Y; D011498:Protein Precursors; D012333:RNA, Messenger; D011956:Receptors, Cell Surface; D054411:Receptors, Leptin; C063596:prepro-thyrotropin-releasing hormone; D000521:alpha-MSH; D013973:Thyrotropin-Releasing Hormone; C046418:pro-thyrotropin releasing hormone; D011761:Pyrrolidonecarboxylic Acid