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. 2015 Jul 29;35(30):10821-30.
doi: 10.1523/JNEUROSCI.0575-15.2015.

Probiotics Improve Inflammation-Associated Sickness Behavior by Altering Communication between the Peripheral Immune System and the Brain

Affiliations

Probiotics Improve Inflammation-Associated Sickness Behavior by Altering Communication between the Peripheral Immune System and the Brain

Charlotte D'Mello et al. J Neurosci. .

Abstract

Patients with systemic inflammatory diseases (e.g., rheumatoid arthritis, inflammatory bowel disease, chronic liver disease) commonly develop debilitating symptoms (i.e., sickness behaviors) that arise from changes in brain function. The microbiota-gut-brain axis alters brain function and probiotic ingestion can influence behavior. However, how probiotics do this remains unclear. We have previously described a novel periphery-to-brain communication pathway in the setting of peripheral organ inflammation whereby monocytes are recruited to the brain in response to systemic TNF-α signaling, leading to microglial activation and subsequently driving sickness behavior development. Therefore, we investigated whether probiotic ingestion (i.e., probiotic mixture VSL#3) alters this periphery-to-brain communication pathway, thereby reducing subsequent sickness behavior development. Using a well characterized mouse model of liver inflammation, we now show that probiotic (VSL#3) treatment attenuates sickness behavior development in mice with liver inflammation without affecting disease severity, gut microbiota composition, or gut permeability. Attenuation of sickness behavior development was associated with reductions in microglial activation and cerebral monocyte infiltration. These events were paralleled by changes in markers of systemic immune activation, including decreased circulating TNF-α levels. Our observations highlight a novel pathway through which probiotics mediate cerebral changes and alter behavior. These findings allow for the potential development of novel therapeutic interventions targeted at the gut microbiome to treat inflammation-associated sickness behaviors in patients with systemic inflammatory diseases.

Significance statement: This research shows that probiotics, when eaten, can improve the abnormal behaviors (including social withdrawal and immobility) that are commonly associated with inflammation. Probiotics are able to cause this effect within the body by changing how the immune system signals the brain to alter brain function. These findings broaden our understanding of how probiotics may beneficially affect brain function in the context of inflammation occurring within the body and may open potential new therapeutic alternatives for the treatment of these alterations in behavior that can greatly affect patient quality of life.

Keywords: TNF-alpha; cerebral intravital microscopy; microglia; monocytes.

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Figures

Figure 1.
Figure 1.
VSL#3 treatment does not alter markers of liver injury or gut permeability. A, B, Change in body weight (A) and ALT and bilirubin values (B) for placebo- and VSL#3-treated sham and BDL mice. All data represented as mean ± SEM, n = 5–10/group, *p < 0.05 vs sham mice. Representative images of liver sections depicting histology (H&E; C) and Sirius red-fast green staining (for collagen; D) in placebo- and VSL#3-treated sham and BDL mice. E, No change in colonic or small intestinal barrier function in BDL- or VSL#3-treated BDL mice. FITC–dextran flux (arbitrary fluorescence units) was assessed in colonic (A, n = 6–10) and small intestinal (B, n = 4–7) tissue mounted in Ussing chambers from sham and BDL mice. No significant differences in macromolecular flux were observed.
Figure 2.
Figure 2.
VSL#3 treatment improves sickness behavior in BDL mice. Total time in seconds an adult test mouse spent in social exploration (A) or remaining immobile (B) during a 10 min observation period; n = 5–14/group, *p < 0.05, **p < 0.01, ***p < 0.0001. All data are represented as mean ± SEM.
Figure 3.
Figure 3.
VSL#3 treatment does not affect the composition of gut microbiota in BDL mice. A, Average α-diversity measures for each group using Chao1 and Shannon diversity indices. The values were calculated using QIIME with 10 rarefactions to a depth of 10,000 sequences. B, Principal coordinate analysis based on Bray–Curtis distance shows distinct clustering of samples based on whether the mice had undergone BDL, but no distinct separation was observed based on VSL#3 administration. The axis labels represent the first two principal coordinate axis and the numbers in brackets the percentage variation explained. This separation of groups is supported by the Unweighted Pair Group Method with Arithmetic Mean (UPGMA) tree of weighted UniFrac distance with jackknife support (data not shown). C, Taxonomic summary at the phyla level for each of the four treatment groups. D, Taxonomic profiles of fecal pellets for each mice. The data are presented at the phyla level (i) and highest resolved taxonomic level for the 25 most abundant groups (ii) for each of the four treatment groups. Taxa summaries are indicated as being resolved to the class (c) order (o), family (f), or genus (g) level where indicated. Groups in C and D are as follows: A, sham placebo; B, sham VSL#3; C, BDL placebo; D, BDL VSL#3.
Figure 4.
Figure 4.
VSL#3 treatment reduces circulating TNF-α levels in BDL mice. Plasma TNF-α and G-CSF levels as determined using Luminex technology for placebo- or VSL#3-treated sham and BDL mice. All data are represented as mean ± SEM, n = 6–8/group, *p < 0.05, **p < 0.01, ***p < 0.001.
Figure 5.
Figure 5.
VSL#3 treatment attenuates microglial activation in BDL mice. A, Representative images from brain sections depicting Iba-1+ microglia in cortical region of placebo- and VSL#3-treated sham and BDL mice. Arrows indicate activated microglia; arrowheads indicate resting microglia; Scale bar, 50 μm. B, Representative histogram depicting number of CD11b+ CD45low, CD11b+ CD45intermediate, and CD11b+ CD45high cells in sham-, BDL placebo-, and BDL VSL#3-treated mice. Bar graph indicates number of activated microglia (CD11b+ CD45intermediate cells) as isolated from cerebral cortices of placebo- and VSL#3-treated sham and BDL mice and characterized using flow cytometry. C, Number of activated microglia (CD11b+ CD45intermediate cells) isolated from cerebral cortices of placebo- and VSL#3-treated sham and BDL mice that expressed TNF-α. All data represented as mean ± SEM, n = 5–8/group, *p < 0.05, **p < 0.01, ***p < 0.001. int, Intermediate.
Figure 6.
Figure 6.
VSL#3 treatment reduces monocyte:CEC adhesive interactions and monocyte infiltration into brain in BDL. A, Representative images of cerebral vasculature in sham-, placebo-, and VSL#3-treated BDL mice. Circulating leukocytes were labeled with rhodamine (red); CECs were labeled with FITC anti-CD31 (green). Bar graph indicates number of rolling leukocytes (cells/min/100 μm; B) and adherent leukocytes (cells/100 μm; C) along CECs in placebo- and VSL#3-treated sham and BDL mice. D, Representative flow cytometry profiles from sham placebo, BDL placebo, and BDL VSL#3 mice. E, Total number of CD11b+ CD45high cells as isolated from cerebral cortices of placebo- and VSL#3-treated sham and BDL mice and characterized using flow cytometry. F, Total number of CD11b+ CD45high cells isolated from cerebral cortices of placebo- and VSL#3-treated sham and BDL mice that expressed TNF-α. All data represented as mean ± SEM, n = 5–8/group, *p < 0.05, **p < 0.01, ***p < 0.001.

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