Effects of Early Life Stress on the Gut Microbiota of Mice

Abstract

Exposure to early life stress (ELS) is associated with a greater risk of chronic disease development including depression, cardiovascular disease (CVD), and inflammatory bowel disease (IBD). Changes in the gut microbiota have been linked to IBD and CVD. Rodent models of early life neglect are used to characterize the mechanistic links between ELS exposure and the risk of disease later in life. However, little is understood about ELS exposure and the gut microbiota. We used a mouse model of ELS, maternal separation with early weaning (MSEW) and normally-reared (NR) mice to determine whether the neonate microbiota is altered, and if so, whether the MSEW protocol induces changes in the dam microbiota that are then transmitted to their offspring. MSEW mice (n = 12) 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 PD17. NR mice (n = 13) remained undisturbed with dams until weaning on PD21. All mice were maintained on standard chow (NIH-31; NSN 8710-01-005-8438) following weaning. Paired-end Illumina sequencing was conducted on colonic content from PD28 mice and DADA2 was utilized to infer and assign taxonomy to individual amplicon sequence variants (ASVs). The fecal microbiota of dams (n= 5) was also sequenced. Analysis of composition of microbiomes (ANCOM) detected 32 ASVs that had statistically different abundance in MSEW compared to NR mice at PD28. Five of the nine ASVs that increased in MSEW mice were classified as Clostridium senso stricto 1 or Lachnoclostridium, while none the of the 23 ASVs enriched in NR animals belonged to these taxa. Fifty-seven percent (13 of 23) of the ASVs that had greater abundance in NR animals were classified as Lachnospiracea (other than Lachnoclostrium) or Ruminococcaceae. Compared to NR animals, MSEW PD28 mice had reduced phylogenetic diversity (18.7 ± 0.3 compared to 20.3 ± 0.3 in NR; P = 0.003) and Chao1ASV richness (175 ± 8 compared to 198 ± 8 in NR; P = 0.04). Microbial community composition was also altered at PD28 based permutational analysis of variance of Aitchison distance (F(1,24) = 2.29, P = 0.002). The composition, levels of diversity, and abundance of individual ASVs in the microbiota of dams were no different between MSEW and NR cohorts. Thus, the observed microbiota shifts in the young pups are likely driven by endogenous effects of MSEW in the offspring and independent of maternal inheritance. MSEW mice had lower microbial diversity and a reduction in Lachnospiraceae and Ruminococcaceae, which are important fermenters of short-chain fatty acids (SCFAs). Nine different SCFAs were measured in plasma of PD28 mice and MSEW animals had reduced butyrate (P = 0.02) compared to NR controls. Butyrate promote colonic homeostasis as well as regulates metabolic health and CVD risk. Studies are on-going to determine the impact of altered SCFA levels with ELS exposure. This study suggests a direct effect of ELS-exposure on the gut microbiota, which may impact the risk of chronic disease development.