XB-ART-56679NPJ Regen Med January 1, 2020; 5 2.
Infections have numerous effects on the brain. However, possible roles of the brain in protecting against infection, and the developmental origin and role of brain signaling in immune response, are largely unknown. We exploited a unique Xenopus embryonic model to reveal control of innate immune response to pathogenic E. coli by the developing brain. Using survival assays, morphological analysis of innate immune cells and apoptosis, and RNA-seq, we analyzed combinations of infection, brain removal, and tail-regenerative response. Without a brain, survival of embryos injected with bacteria decreased significantly. The protective effect of the developing brain was mediated by decrease of the infection-induced damage and of apoptosis, and increase of macrophage migration, as well as suppression of the transcriptional consequences of the infection, all of which decrease susceptibility to pathogen. Functional and pharmacological assays implicated dopamine signaling in the bacteria-brain-immune crosstalk. Our data establish a model that reveals the very early brain to be a central player in innate immunity, identify the developmental origins of brain-immune interactions, and suggest several targets for immune therapies.
PubMed ID: 32047653
PMC ID: PMC7000827
Article link: NPJ Regen Med
Genes referenced: ctrl itih3 mmp7 nr2e1 slurp1l tub
GO keywords: immune response
Article Images: [+] show captions
|Fig. 1: The presence of a brain protects against systemic infection in Xenopus embryos. a) One day after fertilization (early- to mid-gastrula or stage 12), Xenopus embryos were microinjected with the pathogenic bacteria E. coli UTI89. The next day, surgeries were performed for removal of the brain (brainless or BR– embryos), a piece of cervical spinal cord (SC– embryos) or the tail bud (Tail– embryos). Embryos were collected for morphological and molecular analysis during the next three days post-surgery. The bacterial load is represented in red. b–e) Dorsal (left column) and lateral (right column) views of st. 48 embryos belonging Control or Intact (Ctrl; b, c) vs. Brainless (BR−; d, e) experimental groups. Green and red arrows point, respectively, the control or correct vs. aberrant morphologies after surgery removal. Eyes, gut and branchial arches (ba) are indicated for reference. Left: rostral is up. Right: rostral is left, dorsal is up. Rostral is left and dorsal is up. Scale bar = 500 μm. f, g) Survival rates (plotted as percentage, %) of each experimental group per each infection condition: without E. coli infection or not-infected animals (NI; f, one-way ANOVA P > 0.05) vs. E. coli UTI89 infected animals (UTI, evaluated four days after infection; g, one-way ANOVA P < 0.01). Data represent the mean and S.D. of, at least, five independent replicates. Each replicate is shown by one dot. h) Bacteria load measured and plotted as colony forming units per milliliter (cfu/ml) in independent embryos (dots) belonging each experimental group or surgery condition. Alive embryos were harvested for analysis 48 h after infection. Initial bacteria load or number of bacteria injected (average of three independent replicates) at t = 0 is plotted as a blue-dashed line. One-way ANOVA P > 0.05. i) Host-Pathogen Response Index (HPRI) = % survival/(1 + log10(CFU + 1)), for each experimental group, as a metric of tolerance. Data represent the mean and S.D. of five independent embryos. One-way ANOVA P < 0.01. g, i) P values after post hoc Bonferroni comparisons are indicated as **P < 0.01, *P < 0.05, ns P > 0.05. See also Supplementary Fig. S1.|
|Fig. 5: Transcriptional analysis of Control (Ctrl) and Brainless (BR–) datasets show quantitatively and qualitatively differences for regulated transcripts and cell processes after infection (UTI) or/and not-infection (NI) conditions. a, b) Venn diagram comparing genes (a) and sub-networks (b) differentially regulated for each experimental group-condition. c) Neural-related pathways unique to infection with a brain. d) Neural-related pathways unique to infection without a brain. e) Innate immunity response for brainless animals with infection. This network was significantly upregulated by 11%. f) Complement activation sub-network (classical pathway) exclusively present in infected embryos with absence of brain. Green = down gene, Red = up gene. Complete data are presented in Supplementary Data 1. All measured genes found in a pathway are located in Supplementary Data 2. See also Supplementary Figs S4 and S5.|
|Supplementary Figure S4. Gene networks and cell processes unique to infection in presence or absence of a brain during development. a–d) Pie chart of the functional classification of the pathways exclusively regulated after infection in Control animals (a), after infection in BR– animals (b), after brain removal without infection (c), and between infected Ctrl and infected BR– embryos (d). e) Upregulation of bacteria-related genes induced by infection in brainless animals. These networks were up-regulated by 20%. f) Innate immune response after infection in intact (or developed with a brain) animals. This pathway responds 11% less in presence of a brain than it does in absence of a brain (see Fig. 6c). Green = down gene, Red = up gene. Complete data are presented in Supplementary Data 1. All measured genes found in a pathway are located in Supplementary Data 2.|
|Supplementary Figure S5. Gene networks and cell processes unique to infection in presence of brain. a) Considering the role of the brain on macrophages, which in turn are required for regeneration1, we analyzed transcriptional sub-networks related to regeneration. Gene networks related to tissue regeneration/remodeling were exclusively regulated in intact animals (developing with brain) with presence of bacteria, suggesting a relationship between brain, bacteria, and regeneration. b) Membrane-Potential related genes. Likewise, genes related to membrane potential are exclusively up regulated by 12%, in the presence of brain, confirming our previous results on connection between electrical signaling from the brain and slow electrical flows in the long-distance somatic tissue2,3. c) Melanocyte-migration related genes are suppressed (12%) by infection in presence of a brain. Conversely, in absence of brain, this pathway is not affected. Green = down gene, Red = up gene. Complete data are presented in Supplementary Data 1. All measured genes found in a pathway are located in Supplementary Data 2.|
|Supplementary Figure S6. Quantitative LC/MS/MS Analysis of Dopamine (DA) in Control (Ctrl) and Brainless (BR–) Xenopus embryos. a) Chromatogram of DA, its metabolite DA-d4 and labelled versions from wholemount embryos homogenate. b) Standard curve used for DA quantification, r2=0.99897605. X-axis is concentration (μM) and Y-axis if for relative response of DA corrected by its internal standard (DA-d4).|
References [+] :
Agricola, Identification of genes expressed in the migrating primitive myeloid lineage of Xenopus laevis. 2016, Pubmed, Xenbase