Role of activation of microglia in neurodegenerative prion disease
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Vincenti2015.docx (69.65Mb)
Date
04/07/2015Author
Vincenti, James Edward
Metadata
Abstract
Prion diseases are a group of fatal neurodegenerative protein-misfolding diseases.
Microglia, the resident myeloid cells found within the brain, have been shown to
demonstrate a reactive morphology during the disease process with conflicting
evidence for both a neurotoxic and neuroprotective role. The studies presented here
aimed to investigate the role of microglia activation using transcriptomic and
morphological analysis of prion disease in mice.
Initially, the host immune response to prion disease was explored using a publically
available mouse prion disease dataset. Re-analysis of this dataset was performed
using BioLayout Express3D; a novel software tool that supports the visualisation and
clustering of correlation networks. Disease-associated genes up-regulated during the
later stages of infection were present in two main clusters. The cellular origin of these
genes was explored by examining their expression in a dataset comprised of pure
populations of cells. This demonstrated that the primary cluster of up-regulated
transcripts encompassed genes expressed mainly by microglia and to a lesser extent
astrocytes and neurons. The secondary cluster comprised almost exclusively of
interferon response genes. The conclusions of these analyses were different from
those of the original study that suggested disease-associated genes were primarily
neuronal in origin.
Mouse models of prion disease were established by infecting a novel line of BALB/cJ
inbred mice, expressing EGFP under control of a myeloid specific Csf1r promoter, with
the 79A prion strain. Quantification of the morphological changes of EGFP expressing
microglia suggested the cells accumulated in the medulla at sites of early misfolded
protein deposition with minimal change in their overall appearance. An activated
microglia morphology was not observed until protein deposition was extensive.
Isolation of EGFP expressing microglia was performed for transcriptome analysis. The
vast majority of disease associated genes demonstrated increased expression at the
onset of clinical symptoms. The gene list was found to be highly enriched for genes
associated with an innate immune response regulated by the NFκB signalling cascade.
Also highly enriched were processes associated with protein translation, energy
production and stress response. These data suggest a high metabolic load is
burdened by proliferating microglia; and as part of a response which is strikingly more
pro-inflammatory in nature than has previously been attributed to the microglia
phenotype within prion disease.
As an active contributor to normal homeostasis, microglia are more than just innate
immune surveillance and are now considered an integral component in both the
healthy and diseased brain. The ramifications of activation toward the microglia
phenotype shown here will have direct and potentially cytotoxic influence on
neighbouring microglia and other brain cell types implying microglia as major
contributors to the neurotoxic environment found within the CNS during prion
disease. Furthermore the identification of genes associated with metabolism offer
many intriguing possibilities for manipulating the activity of microglia in pre-clinical
therapeutic intervention.