Mechanisms involved in the development of the small intestine mucosal layer in postnatal piglets

Multi-Omics Uncover Neonatal Cecal Cell Development Potentials

Although, the cecum plays vital roles in absorption of water, electrolytes, and other small molecules, and harbors trillions of commensal bacteria to shape large intestine immune functions, it is unknown the cecum development potentials at single cell level during the very crucial neonatal developmental period. Using singe cell RNA-seq and proteomics, we have characterized six major types of cecal cells: undifferentiated cells; immune cells (Ims); cecumocytes (CCs); goblet, Paneth like cells (PLCs), and enteroendocrine cells (EECs) with specific markers. CCs mature with a gradual decrease in proportion of cells; however, Ims develop with a continuing increase in proportion of cells. Meanwhile, goblet and EEC cells reduced in proportion of cells from do to d14 or d21; PLCs increased in proportion of cells from d0 to d7 then decreased at d14 and d21. The cells exhibit specific development and maturation trends controlled by transcriptional factors, ligand-receptor pairs, and other factors. As piglets grow, cecal content and mucosal microbial diversity increases dramatically with population of beneficial microbiota, such as lactobacillus. Moreover, cecal mucosal-associated and cecal content microbiota are positively correlated and both show significant correlation with different types of cecal cells and plasma metabolites. This is the first presentation of neonatal cecal cell development and maturation naturally at single cell level with transcript, protein, microbiota and metabolism perspectives. Furthermore, this study provides an important tool for the determination of novel interventions in cecal drug delivery and metabolism studies.

Developmental Profiling of Dietary Carbohydrate Digestion in Piglets

Carbohydrates are the main source of energy in the diet, accounting for the largest proportion in the diets of humans and monogastric animals. Although recent progress has been made in the study of intestinal carbohydrate digestion in piglets, there is a lack of comprehensive study on the dynamic changes in intestinal carbohydrate digestion with age in the early growth stage of piglets. To fill in this gap of knowledge, we collected samples of the small intestine, pancreatic tissues, and colonic digesta from 42 piglets during newborn [day (d) 0], lactation (d 7, 14), weaning (d 21), and nursery (d 28, 35, and 42) stages. Intestinal and pancreatic tissues and colonic digesta were collected at necropsy and analyzed for morphology, digestive enzyme activities, short-chain fatty acids (SCFA), and microbial abundance. Villus height reached a maximum at 1 week (d 7) in the duodenum and jejunum (P <0.01), and a higher ratio of villus height to crypt depth and lactase activity were observed on d 0 and 7 (P < 0.001) compared to other ages. However, the sucrase and maltase activities were increased with piglets' age. Similar activities of sucrase and maltase were found in the small intestine. In addition, amylase, lipase, and protease activities were assayed in the pancreas. The activity of amylase increased with age, while lipase and protease decreased gradually from birth to weaning (d 21, 28) and then increased after weaning (d 35, 42). Compared with d 0, d 42 increased the abundance of Firmicutes and Bacteroidetes with a higher concentration of total SCFA (P < 0.001) and decreased the abundance of Proteobacteria, but weaning (d 21, 28) increased the abundance of Proteobacteria in the colon. These results indicate that with the increase in piglet age, the carbohydrate digestive function gradually increased, but weaning hindered the development of intestinal function. These results provide us with new insights into the healthy development of piglets' intestines, which may help us to better regulate the physiological health of piglets in the future.

Changes in progenitors and differentiated epithelial cells of neonatal piglets

This study aimed to assess the changes of small intestinal morphology, progenitors, differentiated epithelial cells, and potential mechanisms in neonatal piglets. Hematoxylin and eosin staining of samples from 36 piglets suggested that dramatic changes were observed in the jejunum crypts depth and crypt fission index of neonatal piglets (P < 0.001). The number of intestinal stem cells (ISC) tended to increase (P < 0.10), and a decreased number of enteroendocrine cells appeared in the jejunal crypt on d 7 (P < 0.05). Furthermore, the mRNA expression of jejunal chromogranin A (ChgA) was down-regulated in d 7 piglets (P < 0.05). There was an up-regulation of the adult ISC marker gene of SPARC related modular calcium binding 2 (Smoc2), and Wnt/β-catenin target genes on d 7 (P < 0.05). These results were further verified in vitro enteroid culture experiments. A mass of hollow spheroids was cultured from the fetal intestine of 0-d-old piglets (P < 0.001), whereas substantial organoids with budding and branching structures were cultured from the intestine of 7-d-old piglets (P < 0.001). The difference was reflected by the organoid budding efficiency, crypt domains per organoid, and the surface area of the organoid. Furthermore, spheroids on d 0 had more Ki67-positive cells and enteroendocrine cells (P < 0.05) and showed a decreasing trend in the ISC and goblet cells (P < 0.10). Moreover, the mRNA expression of spheroids differed markedly from that of organoids, with low expression of intestinal differentiation gene (Lysozyme; P < 0.05), epithelial-specific markers (Villin, E-cadherin; P < 0.05), and adult ISC markers (leucine-rich repeat-containing G protein-coupled receptor 5 [Lgr5], Smoc2; P < 0.001), and up-regulation of fetal marker (connexin 43 [Cnx43]; P < 0.05). The mRNA expression of relevant genes was up-regulated, and involved in Wnt/β-catenin, epidermal growth factor (EGF), Notch, and bone morphogenetic protein (BMP) signaling on d 7 organoids (P < 0.05). Spheroids displayed low differentiated phenotype and high proliferation, while organoids exhibited strong differentiation potential. These results indicated that the conversion from the fetal progenitors (spheroids) to adult ISC (normal organoids) might largely be responsible for the fast development of intestinal epithelial cells in neonatal piglets.

Single-Cell Transcriptome Sequencing and Proteomics Reveal Neonatal Ileum Dynamic Developmental Potentials

The neonatal period is a crucial time during development of the mammalian small intestine. Moreover, neonatal development and maturation of the small intestine are exceptionally important for early growth, successful weaning, and postweaning growth and development, in order to achieve species-specific milestones. Although several publications recently characterized intestinal epithelial cell diversity at the single-cell level, it remains unclear how differentiation and molecular interactions take place between types and subtypes of epithelial cells during the neonatal period. A single-cell RNA sequencing (scRNA-seq) survey of 40,186 ileal epithelial cells and proteomics analysis of ileal samples at 6 time points in the swine neonatal period were performed. The results revealed previously unknown developmental changes: specific increases in undifferentiated cells, unique enterocyte differentiation, and time-dependent reduction in secretory cells. Moreover, we observed specific transcriptional factors, ligand-receptor pairs, G protein-coupled receptors, transforming growth factor β, bone morphogenetic protein signaling pathways, and gut mucosal microbiota playing vital roles in ileal development during the neonatal window. This work offers new comprehensive information regarding ileal development throughout the neonatal period. Reference to this data set may assist in the creation of novel interventions for inflammation-, metabolism-, and proliferation-related gut pathologies. IMPORTANCE We found previously unknown neonatal ileum developmental potentials: specific increases in undifferentiated cells, unique enterocyte differentiation, and time dependent reduction in secretory cells. Specific transcriptional factors (TFs), ligand-receptor pairs, G protein-coupled receptors, transforming growth factor β, bone morphogenetic protein signaling pathways, and the gut mucosal microbiota are involved in this process. Our results may assist in the creation of novel interventions for inflammation-, metabolism-, and proliferation-related gut pathologies.

Differences in Intestinal Barrier Development between Intrauterine Growth Restricted and Normal Birth Weight Piglets

Simple Summary

Animals with intrauterine growth restriction (IUGR) are defined as neonates born at term but with low birth weight and a characteristic shape of the head. A number of structural and functional modifications in the IUGR intestine affecting its digestive and absorptive function and impairing intestinal barrier function have been reported in the past. Far less is known about the immune system in the gut of IUGR pigs. Therefore, the aim of the present study was to evaluate the structures of the immune system of the gut mucosa in IUGR neonates. We found that the immune deficiency in the gut mucosa that results from restricted intrauterine development occurs at postnatal day (PD) 7, but it disappears thereafter within a week. However, all examined IUGR piglets had an increased number of intraepithelial leukocytes in the gut mucosa on PD 14. We have shown that the immune system of the gut of IUGR piglets is able to quickly compensate for the immunological deficiency postnatally and hardly shows any morphological disabilities in later life.

Abstract

Intrauterine growth restricted (IUGR) piglets are born at term but have low birth mass and a characteristic shape of the head. Impaired general condition, especially in intestinal function, leads to an increase in the occurrence of diarrhoea and high mortality in the first days of life. So far, the mechanical and immunological gut barrier functions in IUGR are poorly understood. The aim of this study was to microscopically evaluate the early postnatal changes in the gut mucosa occurring in IUGR piglets. Whole-tissue small intestine samples were collected from littermate pairs (IUGR and normal) on postnatal day (PD) 7, 14 and 180 and analysed by light microscopy. We found that in the IUGR piglets, the percentage of intraepithelial leukocytes was reduced in the duodenum on PD 7, but it increased in the proximal and middle jejunum both on PD 7 and PD 14, which suggested the development of an inflammatory process. The number of goblet cells was also reduced on PD 14. The average size of the Peyer’s patches in the distal jejunum and ileum showed significant reduction on PD 7 as compared to normal pigs; however, on PD 14, it returned to normal. On PD 180, we did not find any differences in the measured parameters between the IUGR and the normal pigs. In conclusion, we found that in one-week-old IUGR pig neonates, the gut barrier and the immune system structures display signs of retarded development but recover within the second postnatal week of life.