Early Life Stress in Mice Alters Microbial Composition
Authors: Kemp Keri M. , McPherson Kasi C. , Maynard Craig L. , Pollock Jennifer S. 
Published: April 2020

Early‐life stress (ELS) increases the risk of developing cardiovascular disease (CVD) and other chronic inflammatory diseases including inflammatory bowel disease (IBD). Early‐life perturbations in the gut microbiota that enhance a pro‐inflammatory state or reduce microbial metabolites that are important for regulating metabolic homeostasis may predispose children to developing IBD or CVD later in life. Previous investigations of ELS and the gut microbiota have not focused on early stages of gut microbial colonization and community development. We used a mouse model of ELS, maternal separation with early weaning (MSEW), and hypothesized that MSEW would lead to changes in the gut microbiota indicative of a pro‐inflammatory community composition. MSEW mice were subjected to maternal separation for 4 h per day on postnatal days (PDs) 2–5, and 8 h per day on PDs 6–16, and were subsequently weaned at PD 17. Normally reared (NR) mice remained undisturbed with dams until weaning on PD 21. All mice were maintained on standard chow (NIH‐31; NSN 8710‐01‐005‐8438) following weaning. We examined colonic microbiota composition in the MSEW and NR groups via Illumina sequencing of the 16s rRNA gene at PD 10 (n = 9 NR; 14 MSEW) during the separation protocol, and PD 28 (n = 13 NR; 12 MSEW) subsequent to weaning. Fecal microbiota of dams (n = 6) were also sequenced to evaluate potential maternal contribution of microbiota to their pups. Cardiac norepinephrine (NE) levels confirmed a stress phenotype; male MSEW mice had significantly greater NE at PD 28 (P = 0.01, 3.54 ± 0.38 NE/protein (ng/mg), n = 5) compared to NR male mice (2.06 ± 0.38 NE/protein (ng/mg), n = 4). Differences in microbial composition and diversity were not evident between MSEW and NR mice at PD 10 but were significant at PD 28. There were no changes in the microbial composition of dams when they were assigned to MSEW or NR (P = 0.55), providing evidence that microbiota differences detected at PD 28 were not inherited from their mothers. The microbiota of MSEW mice at PD 28 displayed reduced phylogenetic diversity (P = 0.03), a reflection of microbial functional trait diversity. Linear discriminant analysis (LDA) effect size (LEfSe) was used to identify microbial taxa with differential abundances between MSEW and NR mice at PD 28. MSEW mice were enriched in the bacterial families Lactobacillaceae (P = 0.011) and Peptostreptococcaceae (P = 0.017). Microbial communities of NR mice were enriched in the short‐chain fatty acid (SCFA) fermenting families Ruminococcaceae (P = 0.011) and Bacteroidaceae (P = 0.004). Microbial‐produced SCFAs promote colonic homeostasis as well as regulate metabolic health and CVD risk. Further studies are on‐going to determine SCFAs in MSEW and NR mice. In summary, MSEW mice had lower relative abundances of SCFA fermenting taxa and were enriched in taxa, Peptostreptococcacea and Lactobacillaceae, that promote inflammation and degradation of the colonic mucus barrier in mice.Support or Funding InformationFunding SourcesThis work was supported by National Institute of Health Institutional Research and Academic Career Development Award (to KMK), T32 DK007545 and PhRMA Translational Medicine and Therapeutics Postdoctoral Fellowship (to KCM), and a Research Initiatives Award from the Crohn’s and Colitis Foundation (to CLM and JSP).