Biogen
Multiple Sclerosis Research Unit

Author Of 2 Presentations

Pathogenesis – Role of Glia Poster Presentation

P0941 - Anti-myelin oligodendrocyte glycoprotein autoantibodies trigger an Fc-Receptor and BTK-dependent proliferative response in microglia (ID 1382)

Speakers
Presentation Number
P0941
Presentation Topic
Pathogenesis – Role of Glia

Abstract

Background

Autoantibodies are a hallmark feature of numerous neurologic disorders, including multiple sclerosis (MS) and Neuromyelitis optica (NMO) even though the exact pathogenic role(s) and mechanism(s) associated with these autoantibodies are not fully understood. Within the CNS, antibodies can bind to both activating and inhibitory Fc-Receptors (FcRs) that are expressed on barrier-associated macrophages, microglia and other trafficking immune subsets. While well understood in peripheral myeloid cells, the pathophysiological significance of autoantibody-induced FcR signaling in microglia remains unknown, in part due to the lack of a robust in vivo model.

Objectives

Develop an in vivo model to assess Fc Receptor (FcR) and Bruton's tyrosine kinase (BTK) dependent antibody-induced microglia activation.

Methods

Anti-Myelin oligodendrocyte glycoprotein (MOG) monoclonal antibodies (mAbs) were generated and injected peripherally. Anti-MOG CNS target engagement and microglia activation were measured by immunohistochemistry and flow cytometry. Microglia transcriptomics were assessed by RNAseq.

Results

Here, we report that peripheral injection of anti-Myelin oligodendrocyte glycoprotein (MOG) monoclonal antibodies (mAbs) triggers a rapid and tightly regulated microglia Ki-67+ proliferative burst in both brain and spinal cord. This microglia activation was FcR-dependent as only Fc effector-competent but not Fc effectorless aglycosylated antibodies triggered the proliferative response. Accordingly, anti-MOG induced microglia proliferation was fully abrogated in FcR knockout mice. The anti-MOG driven microglia proliferative response was associated with a transient and tightly-regulated gene expression signature of largely proliferation-associated genes. Moreover, we determined that anti-MOG-induced microglia activation in vivo was dependent on BTK, a signaling node downstream of FcRs. Specifically, we found that anti-MOG microglia response was amplified in BTKe41K knock-in mice that express a constitutively active form of BTK and was blunted in mice treated with ibrutinib, a CNS penetrant small molecule BTK inhibitor.

Conclusions

Together, these results demonstrate the first report of an in vivo physiological function for FcR and BTK signaling in microglia and we propose that this model provides a novel tool to further dissect the roles of microglia-specific FcR and BTK driven responses to antibodies in CNS homeostasis and disease.

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Pathogenesis – Role of Glia Poster Presentation

P0943 - Autofluorescence identifies two subsets of microglia in healthy brain and defines their differential modulation by aging.  (ID 128)

Speakers
Presentation Number
P0943
Presentation Topic
Pathogenesis – Role of Glia

Abstract

Background

Microglia are a unique type of brain-resident immune cell that secretes essential neurotrophic factors, promotes myelinogenesis, provides immune defense, clears debris and phagocytoses apoptotic cells. While this wide array of functional properties is suggestive of microglia heterogeneity, few microglia subsets have been described in the healthy brain thus far.

Objectives

To identify novel microglia subsets present in the steady-state brain and to characterize their unique functional roles.

Methods

Microglia isolated from mice and non-human primates were characterized by flow cytometry, electron microscopy and proteomics.

Results

In microglia isolated from mice and non-human primates and then analyzed by flow cytometry, we serendipitously observed that cellular autofluorescence (AF) presented as a bimodally-distributed signal which identified two subsets of microglia: AF-positive (AF+) and AF-negative (AF). While these subsets were present across the brain and maintained at a roughly 2:1 ratio (AF+:AF) throughout most of adulthood, microglia AF increased linearly and exclusively within the AF+ subset, while the AF subset continued to remain free of AF. Electron microscopy of FACS-isolated AF+ microglia revealed large and frequent lysosomal storage bodies, which contained lipids and electron dense material that increased in size and complexity withaging. Proteomic analysis of AF subsets revealed an overrepresentation of endolysosomal, autophagic, catabolic, and mTOR-related proteins in AF+ microglia, pointing to a unique dependence of the AF+ subset on lysosomal function. Accordingly, genetic disruption of lysosomal or autophagic pathways increased and decreased, respectively, the accumulation of AF in the AF+ subset while the AF subset remained unaffected. Lastly, both aging and lysosomal disruption differentially impacted AF subsets, as demonstrated by the increased cellular ROS content and apoptotic rates in AF+ microglia, which also correlated with diminished cell numbers of AF+ microglia at advanced ages.

Conclusions

AF+ and AF subsets represent discrete populations of microglia, present in healthy brain and marked by distinct subcellular content likely reflective of unique functional roles, and in particular distinct CNS clearance functions in steady-state and aging. The increased accumulation of AF material, restricted to AF+ microglia, uniquely impacts their physiology as indicated by elevated cellular ROS and their decreased survival in aging, factors possibly contributing to age-related cognitive decline.

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Presenter Of 1 Presentation

Pathogenesis – Role of Glia Poster Presentation

P0943 - Autofluorescence identifies two subsets of microglia in healthy brain and defines their differential modulation by aging.  (ID 128)

Speakers
Presentation Number
P0943
Presentation Topic
Pathogenesis – Role of Glia

Abstract

Background

Microglia are a unique type of brain-resident immune cell that secretes essential neurotrophic factors, promotes myelinogenesis, provides immune defense, clears debris and phagocytoses apoptotic cells. While this wide array of functional properties is suggestive of microglia heterogeneity, few microglia subsets have been described in the healthy brain thus far.

Objectives

To identify novel microglia subsets present in the steady-state brain and to characterize their unique functional roles.

Methods

Microglia isolated from mice and non-human primates were characterized by flow cytometry, electron microscopy and proteomics.

Results

In microglia isolated from mice and non-human primates and then analyzed by flow cytometry, we serendipitously observed that cellular autofluorescence (AF) presented as a bimodally-distributed signal which identified two subsets of microglia: AF-positive (AF+) and AF-negative (AF). While these subsets were present across the brain and maintained at a roughly 2:1 ratio (AF+:AF) throughout most of adulthood, microglia AF increased linearly and exclusively within the AF+ subset, while the AF subset continued to remain free of AF. Electron microscopy of FACS-isolated AF+ microglia revealed large and frequent lysosomal storage bodies, which contained lipids and electron dense material that increased in size and complexity withaging. Proteomic analysis of AF subsets revealed an overrepresentation of endolysosomal, autophagic, catabolic, and mTOR-related proteins in AF+ microglia, pointing to a unique dependence of the AF+ subset on lysosomal function. Accordingly, genetic disruption of lysosomal or autophagic pathways increased and decreased, respectively, the accumulation of AF in the AF+ subset while the AF subset remained unaffected. Lastly, both aging and lysosomal disruption differentially impacted AF subsets, as demonstrated by the increased cellular ROS content and apoptotic rates in AF+ microglia, which also correlated with diminished cell numbers of AF+ microglia at advanced ages.

Conclusions

AF+ and AF subsets represent discrete populations of microglia, present in healthy brain and marked by distinct subcellular content likely reflective of unique functional roles, and in particular distinct CNS clearance functions in steady-state and aging. The increased accumulation of AF material, restricted to AF+ microglia, uniquely impacts their physiology as indicated by elevated cellular ROS and their decreased survival in aging, factors possibly contributing to age-related cognitive decline.

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