Biogen
Chemical Biology and Proteomics

Author 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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