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Distribution of Misfolded Prion Protein Seeding Activity Alone Does Not Predict Regions of Neurodegeneration

View Article: PubMed Central - PubMed

ABSTRACT

Protein misfolding is common across many neurodegenerative diseases, with misfolded proteins acting as seeds for "prion-like" conversion of normally folded protein to abnormal conformations. A central hypothesis is that misfolded protein accumulation, spread, and distribution are restricted to specific neuronal populations of the central nervous system and thus predict regions of neurodegeneration. We examined this hypothesis using a highly sensitive assay system for detection of misfolded protein seeds in a murine model of prion disease. Misfolded prion protein (PrP) seeds were observed widespread throughout the brain, accumulating in all brain regions examined irrespective of neurodegeneration. Importantly, neither time of exposure nor amount of misfolded protein seeds present determined regions of neurodegeneration. We further demonstrate two distinct microglia responses in prion-infected brains: a novel homeostatic response in all regions and an innate immune response restricted to sites of neurodegeneration. Therefore, accumulation of misfolded prion protein alone does not define targeting of neurodegeneration, which instead results only when misfolded prion protein accompanies a specific innate immune response.

No MeSH data available.


Disease-associated gene expression changes can be predominantly attributed to microglia in all GSS/101LL brain regions tested.(a) Spider graph representation of component B genes after filtering. Up-regulation of genes in all GSS/101LL brain regions, but particularly increased in GSS/101LL brain stem and thalamus compared to GSS/101LL cerebellum and cortex. N = number of genes present after data are filtered that constitute the average intensity value. The number of genes represented is highest in GSS/101LL brain stem but lowest in GSS/101LL cortex. (b) Gene expression can be attributed to specific cell types when overlaid onto previous microarray datasets. These data show a simplified version to demonstrate how different genes that are known to have selective expression in specific cell types in vivo can be attributed to their expected cell type. For example, Cd11b is a gene generally regarded as a pan-macrophage marker, and hence we show the increased expression of this gene in macrophage/microglial cell populations compared to other cell types. Colony-stimulating factor 1 (Csf1) is a gene that is up-regulated during immune cell activation, shown here by its increased expression in lipopolysaccharide-activated macrophages. Gfap is a gene expressed highly in astrocytes, and, indeed, we show the high and specific expression of Gfap in astrocytes in this dataset. Finally, synapsin I is a synaptic-specific protein and therefore will most commonly be expressed in neurons, as is shown here. (c) Attribution of genes that are identified in component b to their respective cell type shows that a majority of genes that are identified in component b can be attributed to macrophage/microglia. (d) Representation of the macrophage/microglia gene list overlap of different brain regions tested.
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pbio.1002579.g007: Disease-associated gene expression changes can be predominantly attributed to microglia in all GSS/101LL brain regions tested.(a) Spider graph representation of component B genes after filtering. Up-regulation of genes in all GSS/101LL brain regions, but particularly increased in GSS/101LL brain stem and thalamus compared to GSS/101LL cerebellum and cortex. N = number of genes present after data are filtered that constitute the average intensity value. The number of genes represented is highest in GSS/101LL brain stem but lowest in GSS/101LL cortex. (b) Gene expression can be attributed to specific cell types when overlaid onto previous microarray datasets. These data show a simplified version to demonstrate how different genes that are known to have selective expression in specific cell types in vivo can be attributed to their expected cell type. For example, Cd11b is a gene generally regarded as a pan-macrophage marker, and hence we show the increased expression of this gene in macrophage/microglial cell populations compared to other cell types. Colony-stimulating factor 1 (Csf1) is a gene that is up-regulated during immune cell activation, shown here by its increased expression in lipopolysaccharide-activated macrophages. Gfap is a gene expressed highly in astrocytes, and, indeed, we show the high and specific expression of Gfap in astrocytes in this dataset. Finally, synapsin I is a synaptic-specific protein and therefore will most commonly be expressed in neurons, as is shown here. (c) Attribution of genes that are identified in component b to their respective cell type shows that a majority of genes that are identified in component b can be attributed to macrophage/microglia. (d) Representation of the macrophage/microglia gene list overlap of different brain regions tested.

Mentions: Data from component B were filtered stringently by first removing transcripts not annotated to known or predicted protein coding regions of the genome. Annotated genes were then filtered by Mann–Whitney U test (p ≤ 0.05) to define significantly altered genes by comparison of GSS/101LL brain regions to their respective NBH/101LL-matched control brain regions. Furthermore, of those statistically significant genes, only those that exhibited a >1.5-fold change between control and disease were analysed further. This group of genes exhibited an increase in gene expression across all brain regions, with the greatest increases observed in regions of neurodegeneration (brain stem and thalamus) and lower but significant increases in gene expression in brain regions that do not show neurodegeneration (cerebellum and cortex) (Fig 7A). Within component B, only a few significant gene expression changes were noted in the cortex (11 genes) compared with a much larger number in the other regions, and therefore the cortex was not included in further analyses in the current study.


Distribution of Misfolded Prion Protein Seeding Activity Alone Does Not Predict Regions of Neurodegeneration
Disease-associated gene expression changes can be predominantly attributed to microglia in all GSS/101LL brain regions tested.(a) Spider graph representation of component B genes after filtering. Up-regulation of genes in all GSS/101LL brain regions, but particularly increased in GSS/101LL brain stem and thalamus compared to GSS/101LL cerebellum and cortex. N = number of genes present after data are filtered that constitute the average intensity value. The number of genes represented is highest in GSS/101LL brain stem but lowest in GSS/101LL cortex. (b) Gene expression can be attributed to specific cell types when overlaid onto previous microarray datasets. These data show a simplified version to demonstrate how different genes that are known to have selective expression in specific cell types in vivo can be attributed to their expected cell type. For example, Cd11b is a gene generally regarded as a pan-macrophage marker, and hence we show the increased expression of this gene in macrophage/microglial cell populations compared to other cell types. Colony-stimulating factor 1 (Csf1) is a gene that is up-regulated during immune cell activation, shown here by its increased expression in lipopolysaccharide-activated macrophages. Gfap is a gene expressed highly in astrocytes, and, indeed, we show the high and specific expression of Gfap in astrocytes in this dataset. Finally, synapsin I is a synaptic-specific protein and therefore will most commonly be expressed in neurons, as is shown here. (c) Attribution of genes that are identified in component b to their respective cell type shows that a majority of genes that are identified in component b can be attributed to macrophage/microglia. (d) Representation of the macrophage/microglia gene list overlap of different brain regions tested.
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pbio.1002579.g007: Disease-associated gene expression changes can be predominantly attributed to microglia in all GSS/101LL brain regions tested.(a) Spider graph representation of component B genes after filtering. Up-regulation of genes in all GSS/101LL brain regions, but particularly increased in GSS/101LL brain stem and thalamus compared to GSS/101LL cerebellum and cortex. N = number of genes present after data are filtered that constitute the average intensity value. The number of genes represented is highest in GSS/101LL brain stem but lowest in GSS/101LL cortex. (b) Gene expression can be attributed to specific cell types when overlaid onto previous microarray datasets. These data show a simplified version to demonstrate how different genes that are known to have selective expression in specific cell types in vivo can be attributed to their expected cell type. For example, Cd11b is a gene generally regarded as a pan-macrophage marker, and hence we show the increased expression of this gene in macrophage/microglial cell populations compared to other cell types. Colony-stimulating factor 1 (Csf1) is a gene that is up-regulated during immune cell activation, shown here by its increased expression in lipopolysaccharide-activated macrophages. Gfap is a gene expressed highly in astrocytes, and, indeed, we show the high and specific expression of Gfap in astrocytes in this dataset. Finally, synapsin I is a synaptic-specific protein and therefore will most commonly be expressed in neurons, as is shown here. (c) Attribution of genes that are identified in component b to their respective cell type shows that a majority of genes that are identified in component b can be attributed to macrophage/microglia. (d) Representation of the macrophage/microglia gene list overlap of different brain regions tested.
Mentions: Data from component B were filtered stringently by first removing transcripts not annotated to known or predicted protein coding regions of the genome. Annotated genes were then filtered by Mann–Whitney U test (p ≤ 0.05) to define significantly altered genes by comparison of GSS/101LL brain regions to their respective NBH/101LL-matched control brain regions. Furthermore, of those statistically significant genes, only those that exhibited a >1.5-fold change between control and disease were analysed further. This group of genes exhibited an increase in gene expression across all brain regions, with the greatest increases observed in regions of neurodegeneration (brain stem and thalamus) and lower but significant increases in gene expression in brain regions that do not show neurodegeneration (cerebellum and cortex) (Fig 7A). Within component B, only a few significant gene expression changes were noted in the cortex (11 genes) compared with a much larger number in the other regions, and therefore the cortex was not included in further analyses in the current study.

View Article: PubMed Central - PubMed

ABSTRACT

Protein misfolding is common across many neurodegenerative diseases, with misfolded proteins acting as seeds for "prion-like" conversion of normally folded protein to abnormal conformations. A central hypothesis is that misfolded protein accumulation, spread, and distribution are restricted to specific neuronal populations of the central nervous system and thus predict regions of neurodegeneration. We examined this hypothesis using a highly sensitive assay system for detection of misfolded protein seeds in a murine model of prion disease. Misfolded prion protein (PrP) seeds were observed widespread throughout the brain, accumulating in all brain regions examined irrespective of neurodegeneration. Importantly, neither time of exposure nor amount of misfolded protein seeds present determined regions of neurodegeneration. We further demonstrate two distinct microglia responses in prion-infected brains: a novel homeostatic response in all regions and an innate immune response restricted to sites of neurodegeneration. Therefore, accumulation of misfolded prion protein alone does not define targeting of neurodegeneration, which instead results only when misfolded prion protein accompanies a specific innate immune response.

No MeSH data available.