Chicken LEAP2 Level Substantially Changes with Feed Intake and May Be Regulated by CDX4 in Small Intestine

SIMPLE SUMMARY: Feed-intake optimization is important for the efficient growth of livestock and poultry, and the identification of factors regulating feed intake is crucial for efficient animal husbandry. Liver-expressed antimicrobial peptide 2 (LEAP2) has been reported as an endogenous antagonist of the growth hormone secretagogue receptor (GHSR) and plays an important role in feed intake and energy homeostasis in mammals. In chickens, LEAP2 function is thought to be mainly antimicrobial, and its role in appetite regulation remains unexplored. This study aimed to outline the expression profiles of genes related to the ghrelin system in 20 different tissues of broiler chicks in different energy states. The expression levels of LEAP2 in the liver and small intestine varied significantly with changes in diet, and CDX4 may be a potential regulator of LEAP2 expression in the small intestine. Overall, the results of this study highlight the importance of LEAP2 for avian feed intake. ABSTRACT: Ghrelin O-acyltransferase (GOAT), ghrelin, and GHSR have been reported to play important roles that influence feed intake in mammals. LEAP2, an endogenous antagonist of GHSR, plays an important role in the regulation of feed intake. However, chicken ghrelin has also been reported to have an inhibitory effect on feed intake. The role of the GOAT–Ghrelin–GHSR–LEAP2 axis in chicken-feed intake remains unclear. Therefore, it is necessary to systematically evaluate the changes in the tissue expression levels of these genes under different energy states. In this study, broiler chicks in different energy states were subjected to starvation and feeding, and relevant gene expression levels were measured using quantitative real-time PCR. Different energy states significantly modulated the expression levels of LEAP2 and GHSR but did not significantly affect the expression levels of GOAT and ghrelin. A high expression level of LEAP2 was detected in the liver and the whole small intestine. Compared to the fed group, the fasted chicks showed significantly reduced LEAP2 expression levels in the liver and the small intestine; 2 h after being refed, the LEAP2 expression of the fasted chicks returned to the level of the fed group. Transcription factor prediction and results of a dual luciferase assay indicated that the transcription factor CDX4 binds to the LEAP2 promoter region and positively regulates its expression. High expression levels of GHSR were detected in the hypothalamus and pituitary. Moreover, we detected GHSR highly expressed in the jejunum—this finding has not been previously reported. Thus, GHSR may regulate intestinal motility, and this aspect needs further investigation. In conclusion, this study revealed the function of chicken LEAP2 as a potential feed-intake regulator and identified the potential mechanism governing its intestine-specific expression. Our study lays the foundations for future studies on avian feed-intake regulation.