56 Early Weaning Stress Relocates Epithelial Enteroendocrine Cells and Alters Intestinal Nutrient Sensing and Transport Functions in Pigs
Authors: Yu Liang-en , Mann Peter , Schlitzkus Lydia , Chakradhar Jiniya , Li Yihang 
Published: October 2023

Abstract
Intestinal nutrient sensing and enteroendocrine functions are critical in controlling feed intake and nutrient transport, yet have been overlooked in agricultural animals. Enteroendocrine cells (EECs) residing on intestinal epithelium monitor luminal chemical environment and orchestrate body neuronal and hormonal responses. After nutrient stimulation, the EECs release hormones, such as glucagon-like peptide 2 (GLP2), which dynamically regulates intestinal nutrient transport and epithelial barrier homeostasis. In pigs, early weaning stress has negatively impacted intestinal development and functions. The objective of the present study is to evaluate effects of early weaning on intestinal nutrient sensing functions, EEC-derived GLP2 production, and epithelial nutrient transport in pigs. Commercial pig littermates (females, n = 9) were split-weaned at the age of d15 (early weaning, EW) and d 26 (late weaning, LW). Piglets were all raised under the same conditions and euthanized at 35 days of age. Intestinal tissues were collected and preserved for later immunohistochemistry staining and gene expression analyses. Immediately post euthanasia, the mucosal layers from jejunum and ileum were mounted on the Ussing chambers to investigate physiological functions. Nutrients transport activities were measured by short circuit current changes (ΔIsc) in response to luminal nutrients (glucose, alanine, lysine, and di-peptide) applications. Nutrient sensing function was measured by GLP2 release rate following glucose stimulation in Ussing chambers. Serum and intestinal tissue concentrations of GLP2 were also measured by ELISA. Data were analyzed by the student’s t-test. Our results showed altered electrogenic nutrients and ion transport activities between EW and LW pigs. The ileal basal Isc was significantly less in EW pigs, indicating a reduction in ions transport. The EW pigs significantly downregulated electrogenic lysine transport, while upregulated active transport of dipeptide. The EECs number in ileum was reduced in EW pigs, indicated by less ChgA (EEC cell marker) mRNA and significantly less ChgA positive-stained cells. In addition, EW pigs exhibited a pattern of EECs relocation, in which the ChgA-positive cells enriched towards the lower half of villi. Nutrient sensing activities of the EECs were suppressed in both jejunum and ileum in EW pigs, indicated by a significant reduction in the glucose-stimulated GLP2 release on Ussing chambers. Moreover, in contrast with the significantly greater GLP2 concentration in ileum, the serum GLP2 concentration was significantly less in the EW pigs, which reflected a decreased GLP2 release rate. In summary, our results suggested that early weaning stress altered EECs number and locations on epithelium, reduced EECs nutrient sensing activities and endogenous GLP2 release, and changed nutrient transport activities. Understanding the mechanism by which early weaning stress regulates intestinal nutrient sensing and transport functions will lead to novel feeding strategies that improve intestinal health and animal production.