title: Leptin-dependent STAT3 phosphorylation in postnatal mouse hypothalamus.
abstract: Leptin, a hormone produced by adipose tissue, reduces food intake and boosts energy expenditure via activation of the JAK2-STAT3 signalling pathway in adult mammal hypothalamic neurons. It is found in blood early after birth, peaking around postnatal day (P) 10. The hypothalamus of neonatal mice administered intraperitoneal leptin (3 mg/kg of body weight) was investigated for phospho-STAT3-positive cells to gain insights into the timing of maturation of the leptin signal transduction system. Leptin responsiveness was first detected in arcuate nucleus, where it was faint at P1 and evident from P5. It was then identified in medial preoptic area, anterior hypothalamus, retrochiasmatic area, dorsomedial nucleus and premammillary nucleus from P7, and in ventromedial nucleus and lateral hypothalamus from P11. From P13 onwards, hypothalamic P-STAT3 staining was indistinguishable from that of adult mice. Significant hypothalamic STAT3 activation was also detected by Western blotting at P11 and P15. The level of activation seen in adults was comparable to that observed at P15 although, remarkably, leptin-induced feeding reduction is observed only after the fourth postnatal week. Neuronal and glial markers and double-labelling immunohistochemistry showed that leptin-stimulated hypothalamic cells that had already reached their final position in a given area or nucleus were neurons; however, leptin responsiveness preceded positivity for the neuronal markers, suggesting a not fully differentiated status. Interestingly, leptin also increased P-STAT3 and c-Fos immunoreactivity in a distinctive and transient (from P5 to P13) cell population found in the dorsal part of the third ventricle and in subependymal position. These cells did not express mature or immature neuronal or glial markers. Their ultrastructural appearance, though suggestive of differentiating cells, was not conclusive for a specific phenotype.
authors.affiliation: Institute of Normal Human Morphology, Marche Polytechnic University, Via Tronto 10/A, 60020 Ancona, Italy.
authors.forename: Andrea
authors.initials: A
authors.lastname: Frontini
authors.forename: Paola
authors.initials: P
authors.lastname: Bertolotti
authors.forename: Cristina
authors.initials: C
authors.lastname: Tonello
authors.forename: Alessandra
authors.initials: A
authors.lastname: Valerio
authors.forename: Enzo
authors.initials: E
authors.lastname: Nisoli
authors.forename: Saverio
authors.initials: S
authors.lastname: Cinti
authors.forename: Antonio
authors.initials: A
authors.lastname: Giordano
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D001069:Appetite Regulation / Q000502:physiology; D001111:Arcuate Nucleus of Hypothalamus / Q000254:growth & development / Q000378:metabolism*; D002454:Cell Differentiation / Q000502:physiology; D005260:Female; D018507:Gene Expression Regulation, Developmental / Q000502:physiology; D007031:Hypothalamus / Q000254:growth & development / Q000378:metabolism; D007150:Immunohistochemistry; D066298:In Vitro Techniques; D020738:Leptin / Q000378:metabolism*; D051379:Mice; D008810:Mice, Inbred C57BL; D008817:Mice, Mutant Strains; D008820:Mice, Obese; D009474:Neurons / Q000378:metabolism*; D050796:STAT3 Transcription Factor / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology*; D014018:Tissue Distribution
chemical_list: D020738:Leptin; D050796:STAT3 Transcription Factor; C494087:Stat3 protein, mouse