Vanesa Muncan

Wound healing is critical to homeostasis in particular in tissues exposed to environmental insults such as the skin and the intestine. At the intersection of these tissues a particular form of wounding occurs in the form of perianal fistula, i.e. abnormal tracts connecting the intestine with the skin. Importantly, a natural disparity is found in healing efficiency in perianal fistula depending on the underlying medical condition, which is currently not well understood. Using this disparity, we modelled appropriate and defective wound healing by comparing Crohn’s disease related fistula (poor healing) and non-IBD/idiopathic fistula (well healing). We show that during wound healing, cytokines TNFα and IL6 in conjunction with TGF-β induce differentiation of columnar intestinal mucosa into squamous epithelium with high expression of keratins 5 and 13 and WFDC2 . Specifically in poorly healing wounds, cytokines including IL17, IL22 and IFNγ induced expression of S100A8/9 in this intestinal derived tissue. Surprisingly, S100A8/9 was not released but rather functioned as a transcriptional (co)regulator, affecting downstream inflammatory mediators such as C3 and CXCL17. These data identify separate immune pathways contributing to healing in general and deficient healing, allowing for more targeted intervention approaches.

Background: Nutritional intake in preterm infants is associated with short- and long-term outcomes. The favorable outcomes of preterm infants who predominantly receive their mother’s own milk (MOM) are thought to be mediated partly through beneficial effects on the gut microbiome. When MOM is not available, donor human milk (DHM) is recommended as the best alternative. However, DHM is less effective in preventing adverse outcomes, which may be explained by compositional differences between MOM and DHM, resulting in different microbiome development. This systematic review focuses on the effects of predominant DHM vs. MOM feeding on the gut microbiota composition in preterm infants. Methods: A comprehensive search was conducted across MEDLINE, Embase, and Cochrane databases. Eight out of the 717 publications identified were included. Data on gut microbiota composition, alpha diversity, and taxonomic differences between DHM- and MOM-fed preterm infants were extracted and analyzed. Results: The microbiome composition was distinct between the two feeding groups. Alpha diversity measures were lower in DHM-fed infants, particularly when preterm formula (PF) was also provided. DHM-fed infants showed higher abundances of Staphylococcaceae and Clostridiaceae , and lower abundances of Bacteroidetes and Bifidobacterium . Conclusion: The observed gut microbiome differences in DHM-fed preterm infants have previously been linked to adverse health outcomes. This underlines the importance of increasing the awareness of MOM intake in preterm infants. Further studies should explore the mechanisms through which human milk affects health outcomes.

The association between prolonged antibiotic (AB) use in neonates and increased incidence of later life diseases is not yet fully understood. AB treatment in early life alters intestinal epithelial cell composition, functioning, and maturation, which could be the basis for later life health effects. Here, we investigated whether AB-induced changes in the neonatal gut persisted up to adulthood and whether early life AB had additional long-term consequences for gut functioning. Mice received AB orally from postnatal day 10 to 20. Intestinal morphology, permeability, and gene and protein expression at 8 weeks were analyzed. Our data showed that the majority of the early life AB-induced gut effects did not persist into adulthood, yet early life AB did impact later life gut functioning. Specifically, the proximal small intestine (SI) of adult mice treated with AB in early life was characterized by hyperproliferative crypts, increased number of Paneth cells, and alterations in enteroendocrine cell-specific gene expression profiles. The distal SI of adult mice displayed a reduced expression of antibacterial defense markers. Together, our results suggest that early life AB leads to structural and physiological changes in the adult gut, which may contribute to disease development when homeostatic conditions are under challenge.

The epithelial signaling pathways involved in damage and regeneration, and neoplastic transformation are known to be similar. We noted upregulation of argininosuccinate synthetase (ASS1) in hyperproliferative intestinal epithelium. Since ASS1 leads to de novo synthesis of arginine, an important amino acid for the growth of intestinal epithelial cells, its upregulation can contribute to epithelial proliferation necessary to be sustained during oncogenic transformation and regeneration. Here we investigated the function of ASS1 in the gut epithelium during tissue regeneration and tumorigenesis, using intestinal epithelial conditionalAss1knockout mice and organoids, and tissue specimens from colorectal cancer patients. We demonstrate that ASS1 is strongly expressed in the regenerating andApc-mutated intestinal epithelium. Furthermore, we observe an arrest in amino acid flux of the urea cycle, which leads to an accumulation of intracellular arginine. However, loss of epithelialAss1does not lead to a reduction in proliferation or increase in apoptosis in vivo, also in mice fed an arginine-free diet. Epithelial loss ofAss1seems to be compensated by altered arginine metabolism in other cell types and the liver.

Human milk is the optimal diet for infant development, but infant milk formula (IMF) must be available as an alternative. To develop high-quality IMF, bovine milk processing is required to ensure microbial safety and to obtain a protein composition that mimics human milk. However, processing can impact the quality of milk proteins, which can influence gastro-intestinal (GI) tolerance by changing digestion, transit time and/or absorption. The aim of this study was to evaluate the impact of structural changes of proteins due to thermal processing on gastro-intestinal tolerance in the immature GI tract. Preterm and near-term piglets received enteral nutrition based on whey protein concentrate (WPC) either mildly pasteurized (MP-WPC) or extensively heated (EH-WPC). Clinical symptoms, transit time and gastric residuals were evaluated. In addition, protein coagulation and protein composition of coagulates formed during in vitro digestion were analyzed in more detail. Characterization of MP-WPC and EH-WPC revealed that mild pasteurization maintained protein nativity and reduced aggregation of β-lactoglobulin and α-lactalbumin, relative to EH-WPC. Mild pasteurization reduced the formation of coagulates during digestion, resulting in reduced gastric residual volume and increased intestinal tract content. In addition, preterm piglets receiving MP-WPC showed reduced mucosal bacterial adherence in the proximal small intestine. Finally, in vitro digestion studies revealed less protein coagulation and lower levels of β-lactoglobulin and α-lactalbumin in the coagulates of MP-WPC compared with EH-WPC. In conclusion, minimal heat treatment of WPC compared with extensive heating promoted GI tolerance in immature piglets, implying that minimal heated WPC could improve the GI tolerance of milk formulas in infants.

Background. The human digestive tract is structurally mature at birth, yet maturation of gut functions such as digestion and mucosal barrier continues for the next 1–2 years. Human milk and infant milk formulas (IMF) seem to impact maturation of these gut functions differently, which is at least partially related to high temperature processing of IMF causing loss of bioactive proteins and formation of advanced glycation end products (AGEs). Both loss of protein bioactivity and formation of AGEs depend on heating temperature and time. The aim of this study was to investigate the impact of mildly pasteurized whey protein concentrate (MP-WPC) compared to extensively heated WPC (EH-WPC) on gut maturation in a piglet model hypersensitive to enteral nutrition. Methods. WPC was obtained by cold filtration and mildly pasteurized (73 °C, 30 s) or extensively heat treated (73 °C, 30 s + 80 °C, 6 min). Preterm (~90% gestation) and near-term piglets (~96% gestation) received enteral nutrition based on MP-WPC or EH-WPC for five days. Macroscopic and histologic lesions in the gastro-intestinal tract were evaluated and intestinal responses were further assessed by RT-qPCR, immunohistochemistry and enzyme activity analysis. Results. A diet based on MP-WPC limited epithelial intestinal damage and improved colonic integrity compared to EH-WPC. MP-WPC dampened colonic IL1-β, IL-8 and TNF-α expression and lowered T-cell influx in both preterm and near-term piglets. Anti-microbial defense as measured by neutrophil influx in the colon was only observed in near-term piglets, correlated with histological damage and was reduced by MP-WPC. Moreover, MP-WPC stimulated iALP activity in the colonic epithelium and increased differentiation into enteroendocrine cells compared to EH-WPC. Conclusions. Compared to extensively heated WPC, a formula based on mildly pasteurized WPC limits gut inflammation and stimulates gut maturation in preterm and near-term piglets and might therefore also be beneficial for preterm and (near) term infants.