Background: Prebiotic galacto-oligosaccharides (GOS) have an extensively demonstrated beneficial impact on intestinal health. In this study, we determined the mechanistic impact of GOS diets on hallmarks of gut aging: microbiome dysbiosis, inflammation, and intestinal barrier defects (“leaky gut”). We also evaluated if short-term GOS feeding influenced how the aging gut responded to antibiotic challenges, since these interventions are common and relevant in older adults. Finally, we assessed the ability of colonic organoids to reproduce in vivo responses to GOS.
Results: Old animals had a distinct microbiome characterized by lower diversity, increased ratios of non-saccharolytic versus saccharolytic bacteria and lower abundance of O-Glycosyl hydrolases . GOS treatment increased abundance of non-saccharolytic ( Akkermansia muciniphila ) and saccharolytic bacteria (species of Bacteroides and Lactobacillus ), and increased the abundance of β-galactosidases and β-glucosidases in young and old animals . Clyndamicin treatment reduced the abundance of beneficial bacteria including Bifidobacterium and Lactobacillus , while increasing Akkermansia, Clostridium, Coprococcus, Enterococcus, Bacillus, Bacteroides, and Paenibacillus . Prebiotics impacted the effects of the antibiotics decreasing the abundance of Akkermansia in the GOS-antibiotic groups compared to the control-antibiotics groups. GOS reduced the age-associated increased intestinal permeability via increased MUC2 expression and mucus biosynthesis. T ranscriptomics analysis of colon from old animals fed GOS diets showed increased expression of genes involved in small molecule metabolic processes and specifically the respirasome, which could indicate an increased oxidative metabolism and energetic efficiency. In young mice, GOS induced expression of binding-related genes and the galectin gene Lgals1 , a β-galactosyl-binding lectin that bridges molecules by their sugar moieties, forming a signaling and adhesion network. Further analysis showed higher expression levels of genes in focal adhesion, PI3K-Akt and ECM-receptor interaction pathways. GOS reduced the expression of TNF in old animals, and altered serum levels of inflammatory biomarkers IL-6, IL-17, IP-10 and Eotaxin. Stools from young mice exhibiting variable bifidogenic response to GOS, injected into colon organoids in the presence of prebiotics, reproduced the response and non-response phenotypes.
Conclusions: GOS modulation of intestinal homeostasis likely occurs through direct GOS-host interactions via modulation of host gene expression and mucus production, as well as through interactions mediated by the gut microbiota that result in increased or restored saccharolytic potential.