DESCRIPTION OF PROJECT RESEARCH AND DEVELOPMENT PROGRAM PRINCIPAL INVESTIGATOR(S) Lambrecht, Nils, M.D. TITLE OF PROGRAM PROJECT (Not to exceed 72 character spaces) The gastric X/A (ghrelin) cell: A peripheral regulator of food intake KEYWORDS (MeSH terms only; minimum three) ghrelin, nucleobindin2 (NUCB2), nesfatin-1, MBOAT4, ghrelin-O-acyl transferase (GOAT), food intake, peripheral regulation, gastric mucosal X/A cell, obesity, cachexia, LPS BRIEF STATEMENT OF RESEARCH OBJECTIVES (Do not use continuation sheets) Chronic changes in body weight result in significant health problems. Appetite control is vital in body weight regulation and is controlled centrally and peripherally. Chronically increased food intake contributes to morbid obesity, chronically decreased food intake contributes to cachectic wasting as severe complication in overwhelming infections and cancer. To target those conditions a deep understanding of food intake regulation is necessary. While many food intake inhibitory peptides are released in the gastrointestinal tract, only one peptide, ghrelin, elicits feed-forward characteristics. It is the only known peripheral orexigenic peptide hormone which rises in concentration in the circulation before the central phase of food intake. We have recently begun to sub-classify the endocrine cell population of the rat gastric oxyntic mucosa and found that in addition to ECL and D cells, most of the endocrine cells in the upper and mid portion of the glands contain ghrelin. These cells appear to represent the gastric endocrine X/A-like cells. Octanoylation of ghrelin by an octanoyl transferase (GOAT) seems to be essential for its orexigenic activity while non-octanoylated ghrelin appears to have an anorexigenic effect. The cellular site of GOAT expression in gastric oxyntic mucosa has not been shown. We have also shown, that the X/A-like cell also expresses the anorexigenic protein nesfatin-1/NUCB2. This enables the X/A-like cell to signal both hunger and satiety. The release of ghrelin and nesfatin-1/NUCB2 must be independently controlled. However, specific physiological or pathological conditions to regulate the differential release of ghrelin and nesfatin-1/NUCB2 in vivo have not been studied. We propose two model conditions to study changes in ghrelin and nesfatin- 1/NUCB2 cellular expression, peptide modification and release into the circulation: a) 24 h food deprivation compared to ad libitum feeding and b) acute inflammation compared to healthy rats (peritoneal injection of gram-negative bacteriallipopolysaccharides at non-toxic doses).
Specific Aims : 1) Characterization of rat gastric endocrine X/A-like cells: Coexpression of ghrelin, nesfatin-1/NUCB2 and GOAT. 2) Effect of fasting (24 hr food restriction) and re-feeding on (a) nesfatin-1/NUCB2 concentration and ghrelin/desacyl ghrelin (DAG) ratios in rat blood plasma and on (b) mRNA and protein expression of ghrelin, GOAT, and nesfatin-1/NUCB2 in enriched rat oxyntic mucosal endocrine cells. 3) Effect of LPS and interleukin-1ss in the presence and absence of indomethacin on (a) nesfatin- 1/NUCB2 concentration and ghrelin/DAG ratios in rat blood plasma and on (b) mRNA and protein expression of ghrelin, GOAT, and nesfatin-1/NUCB2 in enriched rat oxynticmucosal endocrine cells. VAAPRFO19R9M0(R) 10-1313-2 Page 2 of VA Form 10-1313 package
Project narrative: Dysregulation of body weight is associated with significant mortality in the United States and world wide. Obesity-attributable medical expenditures are estimated at $75 billion in 2003. Cachexia is a significant contributor to the overall increased morbidity and mortality in patients with overwhelming infections, and in patients with chronic inflammation and cancer, affecting up to 85% of patients with gastrointestinal malignancies. The mechanisms leading to the sensation of appetite and the release of gastrointestinal hormones in response to meal stimuli play an important role in the regulation of body weight homeostasis. A complete understanding of this mechanism will improve the quality of life in our veteran patients by preventing serious medical complications. It appears to us, that acute control of food intake and long-term maintenance of body weight are regulated by a concerted action of sensing peripheral nutrient status and energy metabolism to the brain which integrates the signals with central inputs of circadian rhythm and psychological stressors. One of the peripheral regulators of food intake appears to be the X/A- like cell of the gastric oxyntic glands. The proposed studies aim to show, that this cell appears to have mechanisms in place to acutely stimulate or inhibit food intake by opposing actions of released ghrelin or nesfatin- 1/NUCB2. The cell is also in a perfect anatomic location, to sense acutely, when nutrients become available. Postprandial nutrient exposure of the X/A-like cell may result in a rapid down-regulation of ghrelin release and in down regulation of expression or enzymatic activity of the acylating enzyme of ghrelin, GOAT. This may result in a further decrease of n-octanoyl- ghrelin with concurrent increase in des-acyl ghrelin concentration leading to the central sensation of satiety. Another fail-safe mechanism of this cell to confer satiety is the increased release of the anorexic peptide NUCB2/nesfatin-1, a mechanism in concert with other anorexic peptide hormones of the gut. Acute dysregulation of these physiological endocrine responses may cause declining food intake in states of inflammation in the body caused by infections or cancer; chronic dysregulation may represent one of the changes occurring in the pathophysiology of obesity. The present proposal will attempt to elucidate the exact cellular and molecular mechanisms related to this effect and may result in clinical targets to control body weight. Given that the VA Medical Care System is the largest of its type in the USA, and that the 158 medical facilities include over 5 million patients, strategies to reduce the incidence of obesity and cachexia related morbidity and mortality are likely to have a beneficial impact not only on patient care through prevention but result in significant savings in resources that could be better spent on other aspects of veteran healthcare. The proposed studies will address important pathophysiological questions regarding the mechanisms regulating appetite and satiety as well as provide potentially important clinical treatment strategies.
