Leptin Regulation of Agrp and Npy mRNA in the Rat Hypothalamus

Agouti‐related protein (AGRP) is synthesized in the same neurones in the arcuate nucleus as neuropeptide Y (NPY), another potent orexigenic peptide. AGRP antagonizes the action of α‐melanocyte stimulating hormone, a derivative of pro‐opiomelanocortin (POMC) at the hypothalamic MC4 receptor to increase food intake. Although leptin has been shown to regulate Agrp/Npy and Pomc‐expressing neurones, there are differences with respect to Agrp regulation in leptin receptor‐deficient mice and rats. Unlike the obese leptin receptor‐deficient db/db mouse, which exhibits upregulation of Agrp mRNA expression in the medial basal hypothalamus (MBH) compared to lean controls, the obese leptin receptor‐deficient (faf; Koletsky) rat does not exhibit upregulation of Agrp expression. To determine whether this represents a general difference between leptin receptor‐deficient mice and rats, neuropeptide gene expression was analysed in the MBH of lean and obese rats segregating for a different leptin receptor mutation, Leprfa (Zucker). Fasting in lean rats (+/fa) for 72 h significantly increased Agrp and Npy mRNA expression, and decreased Pomc mRNA expression as detected by a sensitive solution hybridization/S1 nuclease protection assay. Npy mRNA levels were significantly increased in fed obese fa/fa compared to lean rats, and further increased in the obese animals after fasting. In contrast, Agrp mRNA levels did not differ between fed lean and fed obese rats, and fasting did not significantly change Agrp levels in obese rats. To determine whether the change in Agrp expression that occurs with food deprivation in lean rats could be prevented by leptin replacement, Sprague‐Dawley rats were fasted and infused via subcutaneous osmotic micropumps for 48 h with either saline or recombinant mouse leptin. Fasting significantly increased Agrp and Npy, and decreased Pomc mRNA levels. Leptin infusion almost completely reversed these changes such that there was no significant difference between the levels in the fasted rats and those that were fed ad libitum. Thus, in fasted lean rats, Agrp and Npy are upregulated in parallel when leptin levels fall and are downregulated by leptin infusion. By contrast, the absence of a functional leptin receptor results in the upregulation of Npy but not Agrp mRNA.

[1]  Roy J Martin,et al.  Evidence for a Central Mechanism of Obesity in the Zucker Rat: Role of Neuropeptide Y and Leptin 1 , 1997, Proceedings of the Society for Experimental Biology and Medicine. Society for Experimental Biology and Medicine.

[2]  R. Leibel,et al.  Effects of changes in body weight on carbohydrate metabolism, catecholamine excretion, and thyroid function. , 2000, The American journal of clinical nutrition.

[3]  S. Chua,et al.  Food deprivation and hypothalamic neuropeptide gene expression: effects of strain background and the diabetes mutation. , 1991, Brain research. Molecular brain research.

[4]  L. Aronne,et al.  Synergy of sibutramine and low-dose leptin in treatment of diet-induced obesity in rats. , 2001, Metabolism: clinical and experimental.

[5]  J. Flier,et al.  Distinct Physiologic and Neuronal Responses to Decreased Leptin and Mild Hyperleptinemia , 1999 .

[6]  C. Priest,et al.  Hypothalamic pro-opiomelanocortin mRNA is reduced by fasting and [corrected] in ob/ob and db/db mice, but is stimulated by leptin. , 1998, Diabetes.

[7]  R. Adan,et al.  AgRP(83-132) acts as an inverse agonist on the human-melanocortin-4 receptor. , 2001, Molecular endocrinology.

[8]  G. Barsh,et al.  Antagonism of central melanocortin receptors in vitro and in vivo by agouti-related protein. , 1997, Science.

[9]  R. Steiner,et al.  Regulation of hypothalamic proopiomelanocortin mRNA by leptin in ob/ob mice. , 1997, Endocrinology.

[10]  C. Mantzoros,et al.  Role of leptin in the neuroendocrine response to fasting , 1996, Nature.

[11]  S. Woods,et al.  Central insulin administration reduces neuropeptide Y mRNA expression in the arcuate nucleus of food-deprived lean (Fa/Fa) but not obese (fa/fa) Zucker rats. , 1991, Endocrinology.

[12]  M. Phillips,et al.  Leptin receptor missense mutation in the fatty Zucker rat , 1996, Nature Genetics.

[13]  R. G. Allen,et al.  Corticotropin-releasing factor differentially regulates anterior and intermediate pituitary lobe proopiomelanocortin gene transcription, nuclear precursor RNA and mature mRNA in vivo. , 1990, Neuroendocrinology.

[14]  C. Priest,et al.  Hypothalamic Pro-Opiomelanocortin mRNA Is Reduced By Fasting in ob/ob and db/db Mice, but Is Stimulated by Leptin , 1998, Diabetes.

[15]  S. Sabol,et al.  Rat neuropeptide Y precursor gene expression. mRNA structure, tissue distribution, and regulation by glucocorticoids, cyclic AMP, and phorbol ester. , 1988, The Journal of biological chemistry.

[16]  S. Wardlaw,et al.  Glucocorticoid Regulation of Hypothalamic Proopiomelanocortin , 1998, Neuroendocrinology.

[17]  L. Tartaglia,et al.  Constitutive and impaired signaling of leptin receptors containing the Gln --> Pro extracellular domain fatty mutation. , 1997, Proceedings of the National Academy of Sciences of the United States of America.

[18]  L. Tartaglia,et al.  Phenotype of fatty Due to Gln269Pro Mutation in the Leptin Receptor (Lepr) , 1996, Diabetes.

[19]  Michael W. Schwartz,et al.  Coexpression of Agrp and NPY in fasting-activated hypothalamic neurons , 1998, Nature Neuroscience.

[20]  G. Sanacora,et al.  Increased hypothalamic content of preproneuropeptide Y messenger ribonucleic acid in genetically obese Zucker rats and its regulation by food deprivation. , 1990, Endocrinology.

[21]  R J Tempelman,et al.  Codominant effects of the fatty (fa) gene during early development of obesity. , 1995, The American journal of physiology.

[22]  Y. Yoshimasa,et al.  Involvement of agouti-related protein, an endogenous antagonist of hypothalamic melanocortin receptor, in leptin action. , 1999, Diabetes.

[23]  S. Chua,et al.  Effects of Leptin Receptor Mutation on Agrp Gene Expression in Fed and Fasted Lean and Obese ( LA / Nfa f ) Rats * , 2000 .

[24]  A. Levine,et al.  ARC POMC mRNA and PVN α-MSH are lower in obese relative to lean Zucker rats , 2000, Brain Research.

[25]  R. Leibel,et al.  Changes in energy expenditure resulting from altered body weight. , 1995, The New England journal of medicine.

[26]  S. Chua,et al.  Critical effects of aging and nutritional state on hypothalamic neuropeptide Y and galanin gene expression in lean and genetically obese Zucker rats. , 1993, Brain research. Molecular brain research.

[27]  J. Roberts,et al.  Fasting regulates hypothalamic neuropeptide Y, agouti-related peptide, and proopiomelanocortin in diabetic mice independent of changes in leptin or insulin. , 1999, Endocrinology.

[28]  R. Steiner,et al.  Testosterone regulation of proopiomelanocortin messenger ribonucleic acid in the arcuate nucleus of the male rat. , 1989, Endocrinology.

[29]  C. Mobbs,et al.  Hypothalamic agouti-related protein messenger ribonucleic acid is inhibited by leptin and stimulated by fasting. , 1999, Endocrinology.

[30]  J. Shutter,et al.  Hypothalamic expression of ART, a novel gene related to agouti, is up-regulated in obese and diabetic mutant mice. , 1997, Genes & development.

[31]  T. Kowalski,et al.  The leptin receptor mediates apparent autocrine regulation of leptin gene expression. , 1997, Biochemical and biophysical research communications.

[32]  S. Woods,et al.  Leptin Increases Hypothalamic Pro-opiomelanocortin mRNA Expression in the Rostral Arcuate Nucleus , 1997, Diabetes.

[33]  R. Leibel,et al.  Regulation of Hypothalamic Proopiomelanocortin by Leptin in Lean and Obese Rats , 1999, Neuroendocrinology.

[34]  T. Wadden,et al.  Treatment of Obesity by Moderate and Severe Caloric Restriction: Results of Clinical Research Trials , 1993, Annals of Internal Medicine.

[35]  R. Huupponen,et al.  Hypothalamic neuropeptide expression after food restriction in Zucker rats: evidence of persistent neuropeptide Y gene activation. , 1992, Brain research. Molecular brain research.

[36]  M. Ghatei,et al.  Increased neuropeptide-Y messenger ribonucleic acid (mRNA) and decreased neurotensin mRNA in the hypothalamus of the obese (ob/ob) mouse. , 1993, Endocrinology.

[37]  T. Kowalski,et al.  Neuropeptide Y Overexpression in the Preweanling Zucker (fa/fa) Rat , 1999, Physiology & Behavior.

[38]  J. Flier,et al.  Clinical review 94: What's in a name? In search of leptin's physiologic role. , 1998, The Journal of clinical endocrinology and metabolism.

[39]  J. Roberts,et al.  Androgen regulation of proopiomelanocortin gene expression and peptide content in the basal hypothalamus. , 1989, Endocrinology.

[40]  J. Roberts,et al.  The effect of time of day on levels of hypothalamic proopiomelanocortin primary transcript, processing intermediate and messenger ribonucleic acid in proestrous and estrous rats. , 1994, Endocrinology.