Modulation of anxiety-like behavior in galactooligosaccharide-fed mice: A potential role for bacterial tryptophan metabolites and reduced microglial reactivity.

Prebiotic galactooligosaccharides (GOS) reduce anxiety-like behaviors in mice and humans. However, the biological pathways behind these behavioral changes are not well understood. To begin to study these pathways, we utilized C57BL/6 mice that were fed a standard diet with or without GOS supplementation for 3 weeks prior to testing on the open field. After behavioral testing, colonic contents and serum were collected for bacteriome (16S rRNA gene sequencing, colonic contents only) and metabolome (UPLC-MS, colonic contents and serum data) analyses. As expected, GOS significantly reduced anxiety-like behavior (i.e., increased time in the center) and decreased cytokine gene expression (Tnfa and Ccl2) in the prefrontal cortex. Notably, time in the center of the open field was significantly correlated with serum methyl-indole-3-acetic acid (methyl-IAA). This metabolite is a methylated form of indole-3-acetic acid (IAA) that is derived from bacterial metabolism of tryptophan. Sequencing analyses showed that GOS significantly increased Lachnospiraceae UCG006 and Akkermansia; these taxa are known to metabolize both GOS and tryptophan. To determine the extent to which methyl-IAA can affect anxiety-like behavior, mice were intraperitoneally injected with methyl-IAA. Mice given methyl-IAA had a reduction in anxiety-like behavior in the open field, along with lower Tnfa in the prefrontal cortex. Methyl-IAA was also found to reduce TNF-α (as well as CCL2) production by LPS-stimulated BV2 microglia. Together, these data support a novel pathway through which GOS reduces anxiety-like behaviors in mice and suggests that the bacterial metabolite methyl-IAA reduces microglial cytokine and chemokine production, which in turn reduces anxiety-like behavior.

T Cell-Induced Colitis Is Exacerbated by Prolonged Stress: A Comparison in Male and Female Mice.

Psychological stress exposure is well recognized to exacerbate inflammatory bowel disease (IBD) but the mechanisms involved remain poorly understood. In this study, chronic T cell-mediated colitis was induced by adoptively transferring CD4+CD45RBhigh splenic T cells from C57BL/6 WT donor mice into Rag1tm1Mom mice. Two weeks after T cell transfer, mice were exposed to a prolonged restraint stressor (RST) for 8 h per day for 6 consecutive days. The colitis phenotype was assessed via histopathology and semi-quantitative rt-PCR at humane endpoints or 10 weeks post-T-cell transfer. Mice that received the T cell transplant developed chronic colitis marked by increases in colonic histopathology and inflammatory cytokines. Colonic histopathology was greater in males than females regardless of RST exposure but RST exposure increased histopathology scores in females such that they reached scores observed in the males. This pattern was consistent with cytokine gene expression and protein levels in the colon (especially for IFN-γ, IL-17A, and TNF-α). Serum cytokine levels were not strongly affected by exposure to the stressor. Using a murine model of chronic T cell-mediated colitis, this study demonstrates that biological sex strongly influences colonic inflammation and exposure to chronic stress has a more pronounced effect in females than in males.

Human Complement C4B Allotypes and Deficiencies in Selected Cases With Autoimmune Diseases.

Human complement C4 is one of the most diverse but heritable effectors for humoral immunity. To help understand the roles of C4 in the defense and pathogenesis of autoimmune and inflammatory diseases, we determined the bases of polymorphisms including the frequent genetic deficiency of C4A and/or C4B isotypes. We demonstrated the diversities of C4A and C4B proteins and their gene copy number variations (CNVs) in healthy subjects and patients with autoimmune disease, such as type 1 diabetes, systemic lupus erythematosus (SLE) and encephalitis. We identified subjects with (a) the fastest migrating C4B allotype, B7, or (b) a deficiency of C4B protein caused by genetic mutation in addition to gene copy-number variation. Those variants and mutants were characterized, sequenced and specific techniques for detection developed. Novel findings were made in four case series. First, the amino acid sequence determinant for C4B7 was likely the R729Q variation at the anaphylatoxin-like region. Second, in healthy White subject MS630, a C-nucleotide deletion at codon-755 led to frameshift mutations in his single C4B gene, which was a private mutation. Third, in European family E94 with multiplex lupus-related mortality and low serum C4 levels, the culprit was a recurrent haplotype with HLA-A30, B18 and DR7 that segregated with two defective C4B genes and identical mutations at the donor splice site of intron-28. Fourth, in East-Asian subject E133P with anti-NMDA receptor encephalitis, the C4B gene had a mutation that changed tryptophan-660 to a stop-codon (W660x), which was present in a haplotype with HLA-DRB1*04:06 and B*15:27. The W660x mutation is recurrent among East-Asians with a frequency of 1.5% but not detectable among patients with SLE. A meticulous annotation of C4 sequences revealed clusters of variations proximal to sites for protein processing, activation and inactivation, and binding of interacting molecules.