Early life stress drives sustained reductions in circulating butyrate and propionate short-chain fatty acids in pre-pubertal and adult mice.

Exposure to early life stress (ELS) is associated with a greater risk of developing cardiovascular disease (CVD) later in life. Using a mouse model of ELS, we have recently showed that 4-week-old pre-pubertal mice exposed to ELS have lower microbial diversity and reduced abundances of Lachnospiraceae and Ruminococcaceae taxa, which are important producers of short-chain fatty acids (SCFAs). An essential mechanism by which gut microbes influence host physiology is through the production of SCFAs that act as vasoactive mediators, histone deacetylase inhibitors, and immunomodulators. Therefore, we hypothesized that ELS-induced changes in the gut microbiota would result in reduced circulating SCFAs. To test this hypothesis, we subjected mice to maternal separation (MaSep) in which pups underwent daily separation for 4 h on postnatal days (PDs) 2-5 and 8 h on PDs 6-16 until weaning on PD17. Normally reared (NR) mice remained undisturbed with dams until weaning on PD21. All mice were maintained on standard chow (NIH-31) following weaning. Plasma was collected at PD28 (n=17 MaSep mice from 7 litters and 13 NR mice from 7 litters) and at PD84 (n=8 MaSep from 3 litters and 11 NR mice from 3 litters) for analysis of lactate and the SCFAs acetate, butyrate, isovalerate, propionate, and succinate by gas chromatography/mass spectrometry. Acetate, succinate, and lactate were not different between MaSep and NR mice at either timepoint. However, ELS exposure resulted in significantly reduced butyrate plasma concentrations at PD28 (14.38 ± 0.50 µM in MaSep mice compared to 18.58 ± 1.87 µM in NR mice; P = 0.02) and PD84 (11.94 ± 0.18 µM in MaSep mice compared to 15.03 ± 0.21 µM in NR mice; P < 0.001). ELS also reduced propionate plasma concentrations at PD28 (35.96 ± 1.47 µM in MaSep mice compared to 43.70 ± 1.44 µM in NR mice; P = 0.001) and PD84 (32.16 ± 0.92 µM in MaSep mice compared to 42.53 ± 1.05 µM in NR mice; P < 0.001). Isovalerate plasma concentration was greater in MaSep mice at PD84 (1.11 ± 0.13 µM) compared to NR mice (0.45 ± 0.11 µM; P = 0.002), while there was no difference in isovalerate between MaSep and NR mice at PD28. These data indicate that exposure to stress in early life can result in sustained reductions in butyrate (~22%) and propionate (~21%) concentrations in circulation. Recent advances have determined that butyrate and propionate are involved in blood pressure regulation and vascular physiology. Much less is known about the branched SCFA isovalerate. Future studies will determine if decreases in circulating butyrate and propionate, or increases in circulating isovalerate, play a role in ELS-induced increased risk of CVD.