Jiří Pácha

Recently, the bidirectional connection between the gastrointestinal microbiota and the brain has gained interest in many research studies. Findings have highlighted the potential role of stress and sex hormones in modulating the gut microbiome. To our knowledge, no study has investigated the effect of sex hormone perturbations on the gut microbiota in response to stress. To understand how stress may alter the gut microbiota differently depending on sex, gonadectomized and sham-operated male and female mice were subjected to 2 h of daily restraint stress for seven consecutive days. Body weight and plasma level of corticosterone were evaluated. Bacterial diversity and composition of colon and cecum were analyzed by sequencing of 16S rRNA gene. The bacterial communities were strongly altered by stress in the colon than in the cecum. A profound dysregulation of several metabolic and functional pathways was observed in sham mice. Alterations in the gut microbiome diversity and its functional pathways due to stress were more pronounced in males than in females. The present results provide potential sex-specific biomarkers and novel metabolic signatures in the gut microbiota related to stress disorders which may be used as potential targets in diagnostic and therapeutic approaches in neurogastroenterological diseases. Graphical Abstract

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.

Introduction: Solute Carrier (SLC) and ATP-binding cassette (ABC) transporters expressed in the intestine, liver, and kidney determine the absorption, distribution, and excretion of drugs. In addition, most molecular and cellular processes show circadian rhythmicity controlled by circadian clocks that leads to diurnal variations in the pharmacokinetics and pharmacodynamics of many drugs and affects their therapeutic efficacy and toxicity. Area covered: This review provides an overview of the current knowledge on the circadian rhythmicity of drug transporters and the molecular mechanisms of their circadian control. Evidence for coupling drug transporters to circadian oscillators and the plausible candidates conveying circadian clock signals to target drug transporters, particularly transcription factors operating as the output of clock genes, is discussed. Expert opinion: The circadian machinery has been demonstrated to interact with the uptake and efflux of various drug transporters. The evidence supports the concept that diurnal changes that affect drug transporters may influence the pharmacokinetics of the drugs. However, more systematic studies are required to better define the timing of pharmacologically important drug transporter regulation and determine tissue- and sex-dependent differences. Finally, the transfer of knowledge based on the results and conclusions obtained primarily from animal models will require careful validation before it is applied to humans.

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.

Stress is an important risk factors for human diseases. It activates the hypothalamic-pituitary-adrenal (HPA) axis and increases plasma glucocorticoids, which are powerful regulators of immune system. The response of the target cells to glucocorticoids depends not only on the plasma concentrations of cortisol and corticosterone but also on their local metabolism. This metabolism is catalysed by 11beta-hydroxysteroid dehydrogenases type 1 and 2, which interconvert glucocorticoid hormones cortisol and corticosterone and their 11-oxo metabolites cortisone and 11-dehydrocorticosterone. The goal of this study was to determine whether stress modulates glucocorticoid metabolism within lymphoid organs - the structures where immune cells undergo development and activation. Using the resident-intruder paradigm, we studied the effect of social stress on glucocorticoid metabolism in primary and secondary lymphoid organs of Fisher 344 (F344) and Lewis (LEW) rats, which exhibit marked differences in their HPA axis response to social stressors and inflammation. We show that repeated social defeat increased the regeneration of corticosterone from 11-dehydrocorticosterone in the thymus, spleen and mesenteric lymphatic nodes (MLN). Compared with the F344 strain, LEW rats showed higher corticosterone regeneration in splenocytes of unstressed rats and in thymic and MLN mobile cells after stress but corticosterone regeneration in the stroma of all lymphoid organs was similar in both strains. Inactivation of corticosterone to 11-dehydrocorticosterone was found only in the stroma of lymphoid organs but not in mobile lymphoid cells and was not upregulated by stress. Together, our findings demonstrate the tissue- and strain-dependent regeneration of glucocorticoids following social stress.

The presence of the enzymes of local metabolism of glucocorticoids in lymphoid organs and many other tissues suggests that the local glucocorticoid signal is not determined only by plasma level of glucocorticoids but also by the local activity of these enzymes. Using resident-intruder test the present study determined if chronic social stress modulates local metabolism of corticosterone and 11-dehydrocorticosterone in rats of Fisher 344 (F344) and Lewis (LEW) strains, which differ in their response to social stressors and inflammation. We demonstrated that social defeat significantly increased regeneration of corticosterone from 11-dehydrocorticosterone in thymus, spleen and mesenteric lymphatic nodes (MLN) but not pituitary of both strains. When compared with F344 strain, LEW rats showed lower corticosterone regeneration in pituitary of unstressed and stressed animals and higher corticosterone regeneration in thymic and MLN mobile cells after chronic stress. In contrast, stress-induced increase of corticosterone regeneration in stroma tissues of all lymphoid organs was similar in both strains. Social defeat was also associated with changes in expression of enzymes participating in local metabolism of glucocorticoids: 11β-hydroxysteroid dehydrogenase type 1 (11HSD1), 11β-hydroxysteroid dehydrogenase type 2 (11HSD2) and hexose-6-phosphate dehydrogenase (H6PDH). Whereas F344 rats exhibited significant upregulation of 11HSD1 mRNA, 11HSD2 mRNA and H6PDH mRNA expression in thymus and 11HSD1 mRNA in spleen, LEW rats showed an apparent insensitivity to stress in all lymphoid organs and neither of the transcripts was upregulated by stress. Our results indicate that social stress amplifies glucocorticoid regeneration in the lymphoid organs including the expression of genes involved in local metabolism of glucocorticoids and that this process is partly determined by the genetic background. The study was supported by Czech Science Foundation.