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Regulation of ghrelin signaling by a leptin-induced gene, negative regulatory element-binding protein, in the hypothalamic neurons.

ABSTRACT: Leptin, the product of the ob gene, plays important roles in the regulation of food intake and body weight through its receptor in the hypothalamus. To identify novel transcripts induced by leptin, we performed cDNA subtraction based on selective suppression of the polymerase chain reaction by using mRNA prepared from the forebrain of leptin-injected ob/ob mice. One of the genes isolated was a mouse homolog of human negative regulatory element-binding protein (NREBP). Its expression was markedly increased by leptin in the growth hormone secretagogue-receptor (GHS-R)-positive neurons of the arcuate nucleus and ventromedial hypothalamic nucleus. The promoter region of GHS-R contains one NREBP binding sequence, suggesting that NREBP regulates GHS-R transcription. Luciferase reporter assays showed that NREBP repressed GHS-R promoter activity in a hypothalamic neuronal cell line, GT1-7, and its repressive activity was abolished by the replacement of negative regulatory element in GHS-R promoter. Overexpression of NREBP reduced the protein expression of endogenous GHS-R without affecting the expression of ob-Rb in GT1-7 cells. To determine the functional importance of NREBP in the hypothalamus, we assessed the effects of NREBP on ghrelin action. Although phosphorylation of AMP-activated protein kinase ? (AMPK?) was induced by ghrelin in GT1-7 cells, NREBP repressed ghrelin-induced AMPK? phosphorylation. These results suggest that leptin-induced NREBP is an important regulator of GHS-R expression in the hypothalamus and provides a novel molecular link between leptin and ghrelin signaling.

SUBMITTER: Komori T

PROVIDER: S-EPMC2988391 | biostudies-literature | 2010 Nov

REPOSITORIES: biostudies-literature

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Regulation of ghrelin signaling by a leptin-induced gene, negative regulatory element-binding protein, in the hypothalamic neurons.

Komori Tadasuke T Doi Asako A Furuta Hiroto H Wakao Hiroshi H Nakao Naoyuki N Nakazato Masamitsu M Nanjo Kishio K Senba Emiko E Morikawa Yoshihiro Y

The Journal of biological chemistry 20100928 48

Leptin, the product of the ob gene, plays important roles in the regulation of food intake and body weight through its receptor in the hypothalamus. To identify novel transcripts induced by leptin, we performed cDNA subtraction based on selective suppression of the polymerase chain reaction by using mRNA prepared from the forebrain of leptin-injected ob/ob mice. One of the genes isolated was a mouse homolog of human negative regulatory element-binding protein (NREBP). Its expression was markedly ...[more]

PMID: 20876580

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Project description:ObjectivesAssess direct versus indirect action(s) of ghrelin on hypothalamic NPY neurons.Materials and methodsElectrophysiology was used to measure ion channel activity in NPY-GFP neurons in slice preparations. Ca2+ imaging was used to monitor ghrelin activation of isolated NPY GFP-labeled neurons. Immunohistochemistry was used to localize Trpm4, SUR1 and Kir6.2 in the hypothalamus.ResultsAcylated ghrelin depolarized the membrane potential (MP) of NPY-GFP neurons in brain slices. Depolarization resulted from a decreased input resistance (IR) in ~70% of neurons (15/22) or an increased IR in the remainder (7/22), consistent with the opening or closing of ion channels, respectively. Although tetrodotoxin (TTX) blockade of presynaptic action potentials reduced ghrelin-induced changes in MP and IR, ghrelin still significantly depolarized the MP and decreased IR in TTX-treated neurons, suggesting that ghrelin directly opens cation channel(s) in NPY neurons. In isolated NPY-GFP neurons, ghrelin produced a sustained rise of [Ca2+]c, with an EC50 ~110 pM. Pharmacologic studies confirmed that the direct action of ghrelin was through occupation of the growth hormone secretagogue receptor, GHS-R, and demonstrated the importance of the adenylate cyclase/cAMP/protein kinase A (PKA) and phospholipase C/inositol triphosphate (PLC/IP3) pathways as activators of 5' AMP-activated protein kinase (AMPK). Activation of isolated neurons was not affected by CNQX or TTX, but reducing [Na+]o suppressed activation, suggesting a role for Na+-permeable cation channels. SUR1 and two channel partners, Kir6.2 and Trpm4, were identified immunologically in NPY-GFP neurons in situ. The actions of SUR1 and Trpm4 modulators were informative: like ghrelin, diazoxide, a SUR1 agonist, elevated [Ca2+]c and glibenclamide, a SUR1 antagonist, partially suppressed ghrelin action, while 9-phenanthrol and flufenamic acid, selective Trpm4 antagonists, blocked ghrelin actions on isolated neurons. Ghrelin activation was unaffected by nifedipine and ω-conotoxin, inhibitors of L- and N-type Ca2+ channels, respectively, while Ni2+, mibefradil, and TTA-P2 completely or partially inhibited ghrelin action, implicating T-type Ca2+ channels. Activation was also sensitive to a spider toxin, SNX-482, at concentrations selective for R-type Ca2+ channels. Nanomolar concentrations of GABA markedly inhibited ghrelin-activation of isolated NPY-GFP neurons, consistent with chronic suppression of ghrelin action in vivo.ConclusionsNPY neurons express all the molecular machinery needed to respond directly to ghrelin. Consistent with recent studies, ghrelin stimulates presynaptic inputs that activate NPY-GFP neurons in situ. Ghrelin can also directly activate a depolarizing conductance. Results with isolated NPY-GFP neurons suggest the ghrelin-activated, depolarizing current is a Na+ conductance with the pharmacologic properties of SUR1/Trpm4 non-selective cation channels. In the isolated neuron model, the opening of SUR1/Trpm4 channels activates T- and SNX482-sensitive R-type voltage dependent Ca2+ channels, which could contribute to NPY neuronal activity in situ.

Dataset Information

Regulation of ghrelin signaling by a leptin-induced gene, negative regulatory element-binding protein, in the hypothalamic neurons.

Publications

Regulation of ghrelin signaling by a leptin-induced gene, negative regulatory element-binding protein, in the hypothalamic neurons.

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