The peptide hormone ghrelin is the only known protein modified with an O-linked octanoyl side group, which occurs on its third serine residue. This modification is crucial for ghrelin's physiological effects including regulation of feeding, adiposity, and insulin secretion. Despite the crucial role for octanoylation in the physiology of ghrelin, the lipid transferase that mediates this novel modification has remained unknown. Here we report the identification and characterization of human GOAT, the ghrelin O-acyl transferase. GOAT is a conserved orphan membrane-bound O-acyl transferase (MBOAT) that specifically octanoylates serine-3 of the ghrelin peptide. Transcripts for both GOAT and ghrelin occur predominantly in stomach and pancreas. GOAT is conserved across vertebrates, and genetic disruption of the GOAT gene in mice leads to complete absence of acylated ghrelin in circulation. The occurrence of ghrelin and GOAT in stomach and pancreas tissues demonstrates the relevance of GOAT in the acylation of ghrelin and further implicates acylated ghrelin in pancreatic function.G hrelin is a 28-aa peptide hormone produced principally by stomach tissue with an unusual acyl modification on its critical serine-3 residue. Ghrelin is the endogenous ligand for the growth hormone secretagogue receptor 1a (GHSR1a), and its acyl modification is critical for the activation of the GHSR1a (1). In addition to stimulating growth hormone release from pituitary, ghrelin also promotes food intake, carbohydrate utilization, and adiposity (2-5). Accordingly, ghrelin levels are modulated by changes in nutritional status such as feeding and fasting or exposure to high-fat diets (5, 6). Importantly, ghrelin is the only peptide hormone of peripheral tissue origin that increases food intake (2).More recent studies have identified roles for acylated ghrelin in regulating insulin secretion and blood glucose. Acylated ghrelin occurs in pancreas tissues, and GHSR1a receptor blockade with specific antagonists or treatments with antiserum against acylated ghrelin enhance glucose-induced increases in insulin release whereas acylated ghrelin decreases insulin release (5, 7-10). These observations have further implicated acylated ghrelin in the regulation of metabolism.In stomach tissue and in circulation, acylated forms of ghrelin are modified via an ester linkage with n-octanoic acid and to a lesser extent with decanoyl and decenoyl fatty acids (1, 3). Importantly, the acyl modification in ghrelin is essential for function, with octanoyl and decanoyl fatty acids being optimal (11). Ghrelin is highly conserved in vertebrates, and the third serine residue, which is uniquely modified by the ester-linked acyl group, occurs in all mammal, avian, and fish species (3).The enzyme(s) responsible for acylation of ghrelin has remained unknown. Work by Takada et al. (12) described that porcupine, an enzyme with structural similarities to membrane-bound O-acyl transferases (MBOAT), is required for serine-209 acylation with palmitoleic acid and for transport of...

CNS nutrient sensing and afferent endocrine signalling are established as parallel systems communicating metabolic status and energy availability in vertebrates. The only afferent endocrine signal known to require modification with a fatty acid side chain is the orexigenic hormone ghrelin. We find that the ghrelin O-acyl transferase (GOAT) which is essential for ghrelin acylation, is regulated by nutrient availability, depends on specific dietary lipids as acylation substrates and modulates body fat mass in mice.Two discoveries have softened the traditional differentiation between the classic model of nutrient sensing 1 and the concept of endocrine signals controlling energy status 2 and drawn attention to the regulation of energy homeostasis by circulating long chain fatty acids (LCFAs). Hotamisligil and colleagues recently reported that one specific adipocyte derived long chain fatty acid (C16:1n7), the lipokine palmitoleate, functions as a hormone regulating systemic insulin sensitivity 3. A recent study followed with the discovery that a gastrointestinal lipid metabolite, N-acylphosphatidylethanolamine (NAPE), can function as an endocrine signal which targets hypothalamic energy balance centers to control food intake, particularly when the acyl NAPE species is C16:0 4. Ten years after the discovery of the only orexigenic gut hormone ghrelin 5,6, this unique medium-chain fatty acid (MCFA)-peptide chimera is now revealing itself as yet another nutrient-hormone hybrid with the specific role of linking macronutrient composition with CNS energy balance regulation. It is further intriguing that the only peptide hormone known to require a fatty acid modification 5 is also the only known afferent endocrine factor which depends on intra-neuronal fatty acid metabolism 7. Unique characteristics of the predominantly stomach derived ghrelin include Users may view, print, copy, and download text and data-mine the content in such documents, for the purposes of academic research, subject always to the full Conditions of use

No abstract

The purpose of this study was to determine if the accumulation of the 72-kDa heat shock protein (HSP70) is elevated in response to a prolonged bout of submaximal exercise in which colonic temperature (Tco) remained at control levels. Sprague-Dawley rats were randomly assigned to one of four testing groups [n = 8 per group; ambient temperatures (Ta) for each condition are included]: 1) control (cool/rest; Ta = 24 degrees C); 2) cool and exercise (cool/exercise; Ta = 14 degrees C); 3) nonexertional heating (heat/rest; Ta = 42 degrees C); 4) heat and exercise (heat/exercise; Ta = 32 degrees C). All interventions were approximately 60 min in duration. An exercise bout consisted of treadmill running at 17 m/min and 0% grade, while the heat/rest and heat/exercise experiments consisted of heat exposure that was terminated when Tco reached 41 degrees C. Baseline Tco was similar for all four groups. In the cool/rest and cool/exercise groups, final Tco was not different from the baseline values, nor was it different between these two groups. In the heat/rest and heat/exercise groups, heating rates were similar. Tissue samples were obtained from the gastrocnemius, soleus, and extensor digitorum longus (EDL) muscles of the left hindlimb and the left ventricle 30 min after a trial was completed. An enzyme-linked immunosorbent assay specific for HSP70 was used to directly quantitate absolute levels of HSP70 in tissues. There were significant main effects of both heating and exercise for HSP70 levels in the gastrocnemius, soleus, and left ventricle (P < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

A stimulator of Fe transport (SFT) was identified by functional expression cloning in Xenopus oocytes. SFT-mediated transport has properties defined for transferrin-independent Fe uptake, but its cytolocalization in recycling endosomes and the observed stimulation of transferrin-bound Fe assimilation indicate a key role in intracellular Fe membrane transport as well. SFT has six predicted transmembranous domains and a functionally important RExxE motif that resembles domains involved in yeast Fe transport and Fe-binding by ferritin L-chains. The observation that SFT oligomerizes, along with other structural and mechanistic features, suggests it may be a member of either the ATP-binding cassette or cation diffusion facilitator families. The 3′ untranslated region of SFT contains a translation inhibitory element and inhibition of SFT expression in Xenopus oocytes was found to be relieved by coinjection of transcripts from other defined cDNAs that are also described in this report. SFT is the first component of the mammalian Fe membrane transport machinery to be identified.

Reductions in levels of the hunger-stimulating hormone ghrelin have been proposed to mediate part of the effects of vertical sleeve gastrectomy (VSG) and Roux-en-Y gastric bypass surgeries for obesity. We studied circulating levels of acyl and desacyl ghrelin in rats after these surgeries. We found that blood levels of ghrelin were reduced after VSG, but not after Roux-en-Y gastric bypass, based on enzyme-linked immunosorbent assay and mass-spectrometry analyses. We compared the effects of VSG in ghrelin-deficient mice and wild-type mice on food intake, body weight, dietary fat preference, and glucose tolerance. We found that VSG produced comparable outcomes in each strain. Reduced ghrelin signaling therefore does not appear to be required for these effects of VSG.

Iterated games are well-known in the game theory literature. We study iterated Boolean games. These are games in which players repeatedly choose truth values for Boolean variables they have control over. Our model of iterated Boolean games assumes that players have goals given by formulae of Linear Temporal Logic (LTL), a formalism for expressing properties of state sequences. In order to represent the strategies of players in such games, we use a finite state machine model. After introducing and formally defining iterated Boolean games, we investigate the computational complexity of their associated game-theoretic decision problems, as well as semantic conditions characterising classes of LTL properties that are preserved by equilibrium points (pure-strategy Nash equilibria) whenever they exist.

Proteolytic cleavage of FGF21, evaluated in human plasma, confirmed three known proline hydrolysis sites. Although DPP-IV participates in consecutive cleavages from the N-terminus, fibroblast activation protein was implicated as the enzyme responsible for the C-terminal cleavage that inactivates FGF21.