Metabolic regulation of ghrelin O-acyl transferase (GOAT) expression in the mouse hypothalamus, pituitary, and stomach.
Ghrelin acts as an endocrine link connecting physiological processes regulating food intake, body composition, growth, and energy balance. Ghrelin is the only peptide known to undergo octanoylation. The enzyme mediating this process, ghrelin O-acyltransferase (GOAT), is expressed in the gastrointestinal tract (GI; primary source of circulating ghrelin) as well as other tissues. The present study demonstrates that stomach GOAT mRNA levels correlate with circulating acylated-ghrelin levels in fasted and diet-induced obese mice. In addition, GOAT was found to be expressed in both the pituitary and hypothalamus (two target tissues of ghrelin's actions), and regulated in response to metabolic status. Using primary pituitary cell cultures as a model system to study the regulation of GOAT expression, we found that acylated-ghrelin, but not desacyl-ghrelin, increased GOAT expression. In addition, growth-hormone-releasing hormone (GHRH) and leptin increased, while somatostatin (SST) decreased GOAT expression. The physiologic relevance of these later results is supported by the observation that pituitary GOAT expression in mice lacking GHRH, SST and leptin showed opposite changes to those observed after in vitro treatment with the corresponding peptides. Therefore, it seems plausible that these hormones directly contribute to the regulation of pituitary GOAT. Interestingly, in all the models studied, pituitary GOAT expression paralleled changes in the expression of a dominant spliced-variant of ghrelin (In2-ghrelin) and therefore this transcript may be a primary substrate for pituitary GOAT. Collectively, these observations support the notion that the GI tract is not the only source of acylated-ghrelin, but in fact locally produced des-acylated-ghrelin could be converted to acylated-ghrelin within target tissues by locally active GOAT, to mediate its tissue-specific effects.
Gahete
Manuel D
MD
Department of Cell Biology, Physiology and Immunology, University of Cordoba, Instituto Maimónides de Investigación Biomédica de Córdoba (IMIBIC), and CIBER Fisiopatología de la Obesidad y Nutrición, 14004 Córdoba, Spain.
Córdoba-Chacón
Jose
J
Salvatori
Roberto
R
Castaño
Justo P
JP
Kineman
Rhonda D
RD
Luque
Raul M
RM
D000217:Acyltransferases / Q000235:genetics / Q000378:metabolism*; D000818:Animals; D002478:Cells, Cultured; D005215:Fasting; D018628:Gene Dosage; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects; D054439:Ghrelin / Q000494:pharmacology; D013007:Growth Hormone-Releasing Hormone / Q000494:pharmacology; D007031:Hypothalamus / Q000187:drug effects / Q000201:enzymology*; D007328:Insulin / Q000494:pharmacology; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology; D020738:Leptin / Q000494:pharmacology; D008565:Membrane Proteins; D051379:Mice; D009478:Neuropeptide Y / Q000494:pharmacology; D009765:Obesity / Q000201:enzymology; D010902:Pituitary Gland / Q000166:cytology / Q000187:drug effects / Q000201:enzymology*; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D013004:Somatostatin / Q000494:pharmacology; D013270:Stomach / Q000187:drug effects / Q000201:enzymology*
D054439:Ghrelin; D007328:Insulin; D020738:Leptin; D008565:Membrane Proteins; D009478:Neuropeptide Y; D012333:RNA, Messenger; C422650:ghrelin, des-n-octanoyl; D013004:Somatostatin; D007334:Insulin-Like Growth Factor I; D013007:Growth Hormone-Releasing Hormone; D000217:Acyltransferases; C526983:Mboat4 protein, mouse