Social stress-enhanced severity of Citrobacter rodentium-induced colitis is CCL2-dependent and attenuated by probiotic Lactobacillus reuteri

Abstract

Psychological stressors are known to affect colonic diseases but the mechanisms by which this occurs, and whether probiotics can prevent stressor effects, are not understood. Because inflammatory monocytes that traffic into the colon can exacerbate colitis, we tested whether CCL2, a chemokine involved in monocyte recruitment, was necessary for stressor-induced exacerbation of infectious colitis. Mice were exposed to a social disruption stressor that entails repeated social defeat. During stressor exposure, mice were orally challenged with Citrobacter rodentium to induce a colonic inflammatory response. Exposure to the stressor during challenge resulted in significantly higher colonic pathogen levels, translocation to the spleen, increases in colonic macrophages, and increases in inflammatory cytokines and chemokines. The stressor-enhanced severity of C. rodentium-induced colitis was not evident in CCL2−/− mice, indicating the effects of the stressor are CCL2-dependent. Additionally, we tested whether probiotic intervention could attenuate stressor-enhanced infectious colitis by reducing monocyte/macrophage accumulation. Treating mice with probiotic Lactobacillus reuteri reduced CCL2 mRNA levels in the colon, and attenuated stressor-enhanced infectious colitis. These data demonstrate that probiotic L. reuteri can prevent the exacerbating effects of stressor exposure on pathogen-induced colitis, and suggest that one mechanism by which this occurs is through a down-regulation of the chemokine CCL2.

Stressor exposure has prolonged effects on colonic microbial community structure in Citrobacter rodentium-challenged mice

“…We have previously demonstrated that stressor-induced increases in C. rodentium levels are associated with increases in C. rodentium -induced colonic pathology, and that L. reuteri can attenuate the effects of the stressor on colonic pathology18. Thus, markers of colonic inflammation were assessed to verify that the L. reuteri attenuated the effects of the stressor in the current study.…”

“…Thus, markers of colonic inflammation were assessed to verify that the L. reuteri attenuated the effects of the stressor in the current study. We previously found that colon mass strongly correlates with colonic histopathology18. Thus, we assessed colon mass as a surrogate marker of colonic pathology.…”

“…Lactobacillus reuteri is an immunomodulatory probiotic that can ameliorate the severity of colonic infection17 and can down-regulate CCL2, TNF-α, and iNOS mRNA levels in SDR-exposed C. rodentium -infected mice, as well as abrogate the heightened colonic pathology in stressor-exposed mice18. Probiotic microbes like L. reuteri can act directly upon host immunity, such as by modulating phagocytosis and cytokine release by macrophages and monocytes or intestinal epithelial cells1318, but they can also affect overall microbiome diversity, which is associated with host health14192021. Thus, it is possible that L. reuteri prevents the exacerbating effects of stressor exposure on C. rodentium -induced intestinal inflammation by preventing stressor-induced dysbiosis.…”

The role of the commensal microbiota in adaptive and maladaptive stressor-induced immunomodulation

“…However, like studies in rats (Reber et al, 2006; Reber et al, 2008; Veenema et al, 2008), exposure to stress enhances the response to inflammatory challenge in the colon. For example, we have shown that exposing mice to either the prolonged restraint stressor or to the SDR stressor significantly increases the inflammatory response to the colonic pathogen Citrobacter rodentium (Mackos et al, 2013; Mackos et al, 2016). This excessive inflammatory response is associated with immunopathology in the colon, and is consistent with clinical studies indicating that the symptoms of colonic diseases, such as the inflammatory bowel diseases, tend to be more severe during stressful periods.…”

“…This led to a series of experiments in which mice were given probiotic lactobacilli to determine whether increasing Lactobacillus levels in the intestines would prevent the deleterious effects of the stressor on colonic inflammation. Administering probiotic Lactobacillus reuteri (ATCC23272) was shown to restore barrier function in outbred CD-1 mice exposed to the restraint stressor during C. rodentium challenge (Mackos et al, 2013), and prevented the exacerbating effects of the SDR stressor on colonic immunopathology in inbred C57BL/6 mice challenged with C. rodentium (Mackos et al, 2016). When considered together, these studies demonstrate that stressor exposure changes the composition of the microbiota and that microbes are involved with stressor-induced changes in mucosal and systemic immune responses.…”