title: Leptin inhibits hypothalamic Npy and Agrp gene expression via a mechanism that requires phosphatidylinositol 3-OH-kinase signaling.
abstract: Phosphatidylinositol 3-OH-kinase (PI3K) and STAT3 are signal transduction molecules activated by leptin in brain areas controlling food intake. To investigate their role in leptin-mediated inhibition of hypothalamic neuropeptide Y (Npy) and agouti-related peptide (Agrp) gene expression, male Sprague-Dawley rats (n = 5/group) were either fed ad libitum or subjected to a 52-h fast. At 12-h intervals, the PI3K inhibitor LY-294002 (LY, 1 nmol) or vehicle was injected intracerebroventricularly (ICV) as a pretreatment, followed 1 h later by leptin (3 microg icv) or vehicle. Fasting increased hypothalamic Npy and Agrp mRNA levels (P < 0.05), and ICV leptin administration prevented this increase. As predicted, LY pretreatment blocked this inhibitory effect of leptin, such that Npy and Agrp levels in LY-leptin-treated animals were similar to fasted controls. By comparison, leptin-mediated activation of hypothalamic STAT3 signaling, as measured by induction of both phospho-STAT3 immunohistochemistry and suppressor of cytokine signaling-3 (Socs3) mRNA, was not significantly attenuated by ICV LY pretreatment. Because NPY/AgRP neurons project to the hypothalamic paraventricular nucleus (PVN), we next investigated whether leptin activation of PVN neurons is similarly PI3K dependent. Compared with vehicle, leptin increased the number of c-Fos positive cells within the parvocellular PVN (P = 0.001), and LY pretreatment attenuated this effect by 35% (P = 0.043). We conclude that leptin requires intact PI3K signaling both to inhibit hypothalamic Npy and Agrp gene expression and activate neurons within the PVN. In addition, these data suggest that leptin activation of STAT3 is insufficient to inhibit expression of Npy or Agrp in the absence of PI3K signaling.
authors.affiliation: University of Washington, Harborview Medical Center, Box 359757, 325 Ninth Ave., Seattle, WA 98108, USA.
authors.forename: Christopher D
authors.initials: CD
authors.lastname: Morrison
authors.forename: Gregory J
authors.initials: GJ
authors.lastname: Morton
authors.forename: Kevin D
authors.initials: KD
authors.lastname: Niswender
authors.forename: Richard W
authors.initials: RW
authors.lastname: Gelling
authors.forename: Michael W
authors.initials: MW
authors.lastname: Schwartz
mesh_terms: D054369:Agouti-Related Protein; D000818:Animals; D001111:Arcuate Nucleus of Hypothalamus / Q000166:cytology / Q000378:metabolism; D002867:Chromones / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005215:Fasting; D005786:Gene Expression Regulation / Q000187:drug effects*; D007031:Hypothalamus / Q000737:chemistry / Q000378:metabolism; D007276:Injections, Intraventricular; D036341:Intercellular Signaling Peptides and Proteins; D020738:Leptin / Q000494:pharmacology*; D008297:Male; D009025:Morpholines / Q000494:pharmacology; D009474:Neurons / Q000737:chemistry / Q000187:drug effects / Q000502:physiology; D009478:Neuropeptide Y / Q000235:genetics*; D010286:Paraventricular Hypothalamic Nucleus / Q000166:cytology; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D000081082:Phosphoinositide-3 Kinase Inhibitors; D011506:Proteins / Q000235:genetics*; D016760:Proto-Oncogene Proteins c-fos / Q000032:analysis; D012333:RNA, Messenger / Q000032:analysis; D051381:Rats; D017207:Rats, Sprague-Dawley; D050796:STAT3 Transcription Factor / Q000187:drug effects / Q000502:physiology; D015398:Signal Transduction; D000071223:Suppressor of Cytokine Signaling 3 Protein; D050826:Suppressor of Cytokine Signaling Proteins / Q000235:genetics
chemical_list: D054369:Agouti-Related Protein; D002867:Chromones; D004791:Enzyme Inhibitors; D036341:Intercellular Signaling Peptides and Proteins; D020738:Leptin; D009025:Morpholines; D009478:Neuropeptide Y; D019869:Phosphatidylinositol 3-Kinases; D000081082:Phosphoinositide-3 Kinase Inhibitors; D011506:Proteins; D016760:Proto-Oncogene Proteins c-fos; D012333:RNA, Messenger; D050796:STAT3 Transcription Factor; D000071223:Suppressor of Cytokine Signaling 3 Protein; D050826:Suppressor of Cytokine Signaling Proteins; C491410:Socs3 protein, rat; C085911:2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one