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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.


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Morphological glial cell responses are restricted to specific brain regions.(a) Severe astrogliosis is observed in the brain stem and thalamus of GSS/101LL but is not detected in NBH/101LL age-matched controls or in the cortex or cerebellum of GSS/101LL mice. (b) High magnification image demonstrating the change in astrocyte expression of GFAP in GSS/101LL mice compared to equivalent NBH/101LL brain regions. (c) A distinct change in cell morphology to that of a hypertrophied cell body and short thick processes could be observed in Iba1+ cells, indicative of activated microglia, in GSS/101LL brain stem and thalamus. No change in cell morphology was observed in either NBH/101LL age- and region-matched control samples or in GSS/101LL cortex and cerebellum samples. (d) High magnification image to highlight the shortening and thickening of microglial processes, a characteristic common to morphologically activated microglia. These findings are observed consistently across all animals tested; GSS/101LL (n = 9), NBH/101LL (n = 4). Scale bars = 100 μm.
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pbio.1002579.g003: Morphological glial cell responses are restricted to specific brain regions.(a) Severe astrogliosis is observed in the brain stem and thalamus of GSS/101LL but is not detected in NBH/101LL age-matched controls or in the cortex or cerebellum of GSS/101LL mice. (b) High magnification image demonstrating the change in astrocyte expression of GFAP in GSS/101LL mice compared to equivalent NBH/101LL brain regions. (c) A distinct change in cell morphology to that of a hypertrophied cell body and short thick processes could be observed in Iba1+ cells, indicative of activated microglia, in GSS/101LL brain stem and thalamus. No change in cell morphology was observed in either NBH/101LL age- and region-matched control samples or in GSS/101LL cortex and cerebellum samples. (d) High magnification image to highlight the shortening and thickening of microglial processes, a characteristic common to morphologically activated microglia. These findings are observed consistently across all animals tested; GSS/101LL (n = 9), NBH/101LL (n = 4). Scale bars = 100 μm.

Mentions: We performed an IHC analysis on the four regions from the prion-infected brains that were positive for prion seeds using the RT-QuIC (Fig 2; brain stem, thalamus, cortex, and cerebellum). Previous studies have demonstrated morphological changes associated with microglial activation and astrogliosis as valuable histological markers for early pathology, as both occur early in the course of disease before other early pathological changes as observed via histology, such as synaptic degeneration [23–27]. At clinical disease stage, we observe activated microglial and astrocyte glial cell responses. These are characterised by an up-regulation of glial-fibrillary acidic protein (GFAP), indicative of reactive astrocytes, or the hypertrophy of microglial cell bodies and thickening of microglial cell processes detected with Ionised calcium-binding adapter molecule 1 (Iba1) indicative of activated microglia. These glial cell responses were observed specifically restricted to brain stem and thalamus in GSS/101LL animals (Fig 3) but were not seen in cortex or cerebellum of GSS/101LL animals or in any NBH/101LL brain region (Fig 3).


Distribution of Misfolded Prion Protein Seeding Activity Alone Does Not Predict Regions of Neurodegeneration
Morphological glial cell responses are restricted to specific brain regions.(a) Severe astrogliosis is observed in the brain stem and thalamus of GSS/101LL but is not detected in NBH/101LL age-matched controls or in the cortex or cerebellum of GSS/101LL mice. (b) High magnification image demonstrating the change in astrocyte expression of GFAP in GSS/101LL mice compared to equivalent NBH/101LL brain regions. (c) A distinct change in cell morphology to that of a hypertrophied cell body and short thick processes could be observed in Iba1+ cells, indicative of activated microglia, in GSS/101LL brain stem and thalamus. No change in cell morphology was observed in either NBH/101LL age- and region-matched control samples or in GSS/101LL cortex and cerebellum samples. (d) High magnification image to highlight the shortening and thickening of microglial processes, a characteristic common to morphologically activated microglia. These findings are observed consistently across all animals tested; GSS/101LL (n = 9), NBH/101LL (n = 4). Scale bars = 100 μm.
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pbio.1002579.g003: Morphological glial cell responses are restricted to specific brain regions.(a) Severe astrogliosis is observed in the brain stem and thalamus of GSS/101LL but is not detected in NBH/101LL age-matched controls or in the cortex or cerebellum of GSS/101LL mice. (b) High magnification image demonstrating the change in astrocyte expression of GFAP in GSS/101LL mice compared to equivalent NBH/101LL brain regions. (c) A distinct change in cell morphology to that of a hypertrophied cell body and short thick processes could be observed in Iba1+ cells, indicative of activated microglia, in GSS/101LL brain stem and thalamus. No change in cell morphology was observed in either NBH/101LL age- and region-matched control samples or in GSS/101LL cortex and cerebellum samples. (d) High magnification image to highlight the shortening and thickening of microglial processes, a characteristic common to morphologically activated microglia. These findings are observed consistently across all animals tested; GSS/101LL (n = 9), NBH/101LL (n = 4). Scale bars = 100 μm.
Mentions: We performed an IHC analysis on the four regions from the prion-infected brains that were positive for prion seeds using the RT-QuIC (Fig 2; brain stem, thalamus, cortex, and cerebellum). Previous studies have demonstrated morphological changes associated with microglial activation and astrogliosis as valuable histological markers for early pathology, as both occur early in the course of disease before other early pathological changes as observed via histology, such as synaptic degeneration [23–27]. At clinical disease stage, we observe activated microglial and astrocyte glial cell responses. These are characterised by an up-regulation of glial-fibrillary acidic protein (GFAP), indicative of reactive astrocytes, or the hypertrophy of microglial cell bodies and thickening of microglial cell processes detected with Ionised calcium-binding adapter molecule 1 (Iba1) indicative of activated microglia. These glial cell responses were observed specifically restricted to brain stem and thalamus in GSS/101LL animals (Fig 3) but were not seen in cortex or cerebellum of GSS/101LL animals or in any NBH/101LL brain region (Fig 3).

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.


Related in: MedlinePlus