Bradford, Barry

Tetlow, Laura

Mabbott, Neil

English

Aims: Neuropathological damage induced by prions within the CNS is a characteristic hallmark of prion diseases. Along with prion deposition and neuronal loss, striking changes in glial activation occur. Studying these changes within scrapie-infected mouse models reveals a tractable model to investigate the mechanisms of neurodegeneration. Recently there have been numerous reports that gut microbiota influence neurodegeneration via modulation of the CNS microglial population. Indeed studies in naive mice have suggested that lack of gut microbiota results in a reduction of microglial activation state and subsequent severity of CNS innate immune responses when subjected to stimulation by lipopolysaccharide (LPS). We therefore determined whether the host commensal microbiota may influence CNS prion disease pathogenesis and susceptibility.Methods: Germ-free mice were used to investigate the influence of the host microbiota on CNS prion disease pathogenesis and susceptibility. Germ-free mice and conventional mice (control) were injected with either the 22A and 22C mouse-passaged scrapie strains by the intracerebral or intraperitoneal routes. Following exposure, survival times were recorded and brains collected at the terminal stage of disease for histopathology. Brains from mice from each group were analysed by standard histopathological and immunohistochemistry, supplemented with image and morphometric analysis techniques.Results: Our data show that the host commensal microbiota did not influence prion disease duration or susceptibility, as survival times and disease incidences were identical in germ-free and conventional mice when infected by the same strain of agent via the same route. We observed previously characterised differences which occur in the severity and targeting of neuropathology within given brain regions based upon the strain of agent and route of infection. Germ-free mice have been shown to have altered microglial morphology in the naïve state when compared to those from conventional mice. However, our data show that at the terminal stage of prion disease, the neuropathological changes and microglial morphology were indistinguishable in brains from germ-free and conventional mice. Conclusions: Our data show that the presence or absence of the host commensal microbiota does not significantly influence the development of microglial activation or neuropathology within the CNS during prion disease. <br/

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     Edinburgh Research Explorer                                      Effect of the host gut microbiota on prion-inducedneurodegenerationCitation for published version:Bradford, B, Tetlow, L & Mabbott, N 2017, 'Effect of the host gut microbiota on prion-inducedneurodegeneration', Prion 2017, Edinburgh, United Kingdom, 23/05/17 - 26/05/17.Link:Link to publication record in Edinburgh Research ExplorerDocument Version:Publisher's PDF, also known as Version of recordGeneral rightsCopyright for the publications made accessible via the Edinburgh Research Explorer is retained by the author(s)and / or other copyright owners and it is a condition of accessing these publications that users recognise andabide by the legal requirements associated with these rights.Take down policyThe University of Edinburgh has made every reasonable effort to ensure that Edinburgh Research Explorercontent complies with UK legislation. If you believe that the public display of this file breaches copyright pleasecontact openaccess@ed.ac.uk providing details, and we will remove access to the work immediately andinvestigate your claim.Download date: 23. Jul. 2021IntroductionNeuropathological damage induced by prions within the CNS is a characteristic hallmark of prion diseases. Along with prion deposition and neuronalloss, striking changes in glial activation occur. Studying these changes within scrapie-infected mouse models reveals a tractable model toinvestigate the mechanisms of neurodegeneration. Recently there have been numerous reports that gut microbiota influence neurodegeneration viamodulation of the CNS microglial population. Indeed studies in naive mice have suggested that lack of gut microbiota results in a reduction ofmicroglial activation state and subsequent severity of CNS innate immune responses when subjected to stimulation by lipopolysaccharide (LPS). Wetherefore determined whether the host commensal microbiota may influence CNS prion disease pathogenesis and susceptibility.Effect of the host gut microbiota on prion-induced neurodegeneration MethodsGerm-free mice were used to investigate the influence of the hostmicrobiota on CNS prion disease pathogenesis and susceptibility.Germ-free mice and conventional mice (control) were injected with22C mouse-passaged scrapie strains by the intracerebral orintraperitoneal routes. Following exposure, survival times wererecorded and brains collected at the terminal stage of disease forhistopathology, image and morphometric analysis techniques.This project was supported by The Roslin Institute strategic programme grant funding (BB/J004332/1)ResultsOur data show that the host commensal microbiota did not influenceprion disease duration or susceptibility, as survival times, diseaseincidences and neuropathological changes were identical in germ-free and conventional mice when infected with the same strain ofprion disease agent via the same route.ConclusionsGerm-free mice have been shown to have alteredmicroglial morphology in the naïve state when compared tothose from conventional mice. However, our data show thatat the terminal stage of prion disease, the neuropathologicalchanges and microglial morphology were indistinguishablein brains from germ-free and conventional mice. Our datashow that the presence or absence of the host commensalmicrobiota does not significantly influence the developmentof disease-associated PrP deposition, prion-inducedvacuolation microglial activation and astrocyte activation,affecting neither targeting nor intensity of eachneuropathological hallmark within the CNS during priondisease.Barry M. Bradford, Laura Tetlow& Neil A. MabbottThe Roslin Institute and R(D)SVS the University of Edinburgh, EH25 9RG, United KingdomFigure 2. The commensal gutmicrobiota does not influence themagnitude or distribution of theprion-induced vacuolation within thebrain at the terminal stage of priondisease.A) H&E stained brain sections used forvacuolation scoring, each brain wasscored on a scale of 1–5 in nine greymatter areas: G1, dorsal medulla; G2,cerebellar cortex; G3, superiorcolliculus; G4, hypothalamus; G5,thalamus; G6, hippocampus; G7,septum; G8, retrosplenial and adjacentmotor cortex; G9, cingulate and adjacentmotor cortex from mice were infectedwith prions by the IC (B) or IP (C)routes.Figure 1. Absence of thecommensal gut microbiota ingermfree mice did not influencethe distribution of disease-specific PrP within the brain.Sections were immunostained todetect PrP (brown) andcounterstained with haematoxylin(blue), scale bar, 100 µmFigure 3. Absence of the commensal gut microbiota in germfreemice did not influence the distribution of microglia within thebrain.A) Sections were immunostained to detect Iba1+ cells (brown) andcounterstained with haematoxylin (blue) in the brains of clinically-affected conventionally-housed and germfree mice infected with prionsby the IC (B) or IP (C) routes. n = 6 mice/group, scale bar, 100 µm.Figure 4. No significant differences between groups were observed in thenumber of microglia within regions, or in the length of dendrites, number ofsegments, branching points or terminal points on individual microglia.A) Imaris-based reconstructions of Iba1+ microglia in the hippocampus region. B)Imaris-based quantitative cell morphometry of Iba1+ microglia in the dorsal medulla(left-hand panels) and hippocampus (right-hand panels) regions. From each group,six individual mice were sampled, and data were collected from at least 25 individualIba1+ microglia within each brain region. Solid bars, conventionally-housed mice;open bars, germfree mice.Figure 5. Absence of the commensal gut microbiota in germfreemice did not influence the distribution of microglia within thebrain.A) Sections were immunostained to detect astrocytes (GFAP+ cells,brown) and counterstained with haematoxylin (blue), scale bar, 100µm. Analysed as above (Figure 3).

Effect of the host gut microbiota on prion-induced neurodegeneration

https://www.research.ed.ac.uk/files/205022194/Prion_2017_245_Effect_of_the_host_gut_microbiota_on_prion_induced_neurodegeneration_.pdf

Effect of the host gut microbiota on prion-induced neurodegeneration

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