Glucocorticoids (GCs) are hormones that are released in response to stressors and exhibit many activities, including immunomodulatory and anti-inflammatory activities. They are primarily synthesized in the adrenal gland but are also produced in peripheral tissues via regeneration of adrenal 11-oxo metabolites or by de novo synthesis from cholesterol. The present study investigated the influence of the microbiota on de novo steroidogenesis and regeneration of corticosterone in the intestine of germ-free (GF) and specific pathogen-free mice challenged with a physical stressor (anti-CD3 antibody i.p. injection). In the small intestine, acute immune stress resulted in increased mRNA levels of the proinflammatory cytokines IL1β, IL6 and Tnfα and genes involved in de novo steroidogenesis (Stard3 and Cyp11a1), as well as in regeneration of active GCs from their 11-oxo metabolites (Hsd11b1). GF mice showed a generally reduced transcriptional response to immune stress, which was accompanied by decreased intestinal corticosterone production and reduced expression of the GC-sensitive marker Fkbp5. In contrast, the interaction between stress and the microbiota was not detected at the level of plasma corticosterone or the transcriptional response of adrenal steroidogenic enzymes. The results indicate a differential immune stress-induced intestinal response to proinflammatory stimuli and local corticosterone production driven by the gut microbiota.

• Keywords
• 11β-hydroxysteroid dehydrogenase, anti-CD3 antibody, extra-adrenal steroidogenesis, glucocorticoids, intestine, microbiome,
• MeSH
• 11-beta-Hydroxysteroid Dehydrogenases genetics   metabolism   MeSH
• Corticosterone metabolism   MeSH
• Real-Time Polymerase Chain Reaction MeSH
• Mice MeSH
• Steroids metabolism   MeSH
• Gastrointestinal Microbiome physiology   MeSH
• Tandem Mass Spectrometry MeSH
• Intestine, Small metabolism   MeSH
• Animals MeSH
• Check Tag
• Male MeSH
• Mice MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• 11-beta-Hydroxysteroid Dehydrogenases MeSH
• Corticosterone MeSH
• Steroids MeSH

The gut microbiota play an important role in shaping brain functions and behavior, including the activity of the hypothalamus-pituitary-adrenocortical (HPA) axis. However, little is known about the effect of the microbiota on the distinct structures (hypothalamus, pituitary, and adrenals) of the HPA axis. In the present study, we analyzed the influence of the microbiota on acute restraint stress (ARS) response in the pituitary, adrenal gland, and intestine, an organ of extra-adrenal glucocorticoid synthesis. Using specific pathogen-free (SPF) and germ-free (GF) male BALB/c mice, we showed that the plasma corticosterone response to ARS was higher in GF than in SPF mice. In the pituitary, stress downregulated the expression of the gene encoding CRH receptor type 1 (Crhr1), upregulated the expression of the Fkbp5 gene regulating glucocorticoid receptor sensitivity and did not affect the expression of the proopiomelanocortin (Pomc) and glucocorticoid receptor (Gr) genes. In contrast, the microbiota downregulated the expression of pituitary Pomc and Crhr1 but had no effect on Fkbp5 and Gr. In the adrenals, the steroidogenic pathway was strongly stimulated by ARS at the level of the steroidogenic transcriptional regulator Sf-1, cholesterol transporter Star and Cyp11a1, the first enzyme of steroidogenic pathway. In contrast, the effect of the microbiota was significantly detected at the level of genes encoding steroidogenic enzymes but not at the level of Sf-1 and Star. Unlike adrenal Sf-1, the expression of the gene Lrh-1, which encodes the crucial transcriptional regulator of intestinal steroidogenesis, was modulated by the microbiota and ARS and this effect differed between the ileum and colon. The findings demonstrate that gut microbiota have an impact on the response of the pituitary, adrenals and intestine to ARS and that the interaction between stress and the microbiota during activation of glucocorticoid steroidogenesis differs between organs. The results suggest that downregulated expression of pituitary Pomc and Crhr1 in SPF animals might be an important factor in the exaggerated HPA response of GF mice to stress.

• Keywords
• HPA axis, acute restraint stress, extra-adrenal glucocorticoid synthesis, germ-free, gut microbiota, intestine, mice,
• MeSH
• Cholesterol Side-Chain Cleavage Enzyme genetics   MeSH
• Phosphoproteins genetics   MeSH
• Restraint, Physical * MeSH
• Pituitary Gland metabolism   MeSH
• Ileum metabolism   microbiology   MeSH
• Colon metabolism   microbiology   MeSH
• Corticosterone blood   MeSH
• Mice, Inbred BALB C MeSH
• Adrenal Glands metabolism   MeSH
• Pro-Opiomelanocortin genetics   MeSH
• Stress, Psychological blood   microbiology   MeSH
• CRF Receptor, Type 1 MeSH
• Receptors, Corticotropin-Releasing Hormone genetics   MeSH
• Gene Expression Regulation MeSH
• Steroidogenic Acute Regulatory Protein MeSH
• Steroidogenic Factor 1 genetics   MeSH
• Gastrointestinal Microbiome * MeSH
• Pituitary-Adrenal System * MeSH
• Hypothalamo-Hypophyseal System * MeSH
• Animals MeSH
• Check Tag
• Male MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Cholesterol Side-Chain Cleavage Enzyme MeSH
• Phosphoproteins MeSH
• Corticosterone MeSH
• Pro-Opiomelanocortin MeSH
• CRF Receptor, Type 1 MeSH
• Receptors, Corticotropin-Releasing Hormone MeSH
• Steroidogenic Acute Regulatory Protein MeSH
• Steroidogenic Factor 1 MeSH