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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.


Detection of misfolded PrP using IHC at different time-points in different brain regions.(a) At 150 dpi, small quantities of fine-punctate misfolded PrP deposits can be detected in the midbrain. This positive staining could be observed in five of twelve GSS/101LL mice tested, but no staining was observed in any NBH/101LL animal in any brain region (n = 12). At 220 dpi, fine-punctate misfolded PrP deposits were detectable in both the midbrain and brain stem, which was observed in four of six GSS/101LL mice tested, but no staining was observed in any NBH/101LL animal in any brain region (n = 6). At clinical onset of disease (291.1 ± 5.3 dpi), misfolded PrP staining could be observed in midbrain, brain stem, and the thalamus but not in cortex or cerebellum in GSS/101LL mice. This staining pattern was observed in all mice tested at this stage (n = 9), whereas no staining was observed in any NBH/101LL animal in any brain region tested (n = 4). Scale bars: midbrain = 100 μm, brain stem, thalamus, cortex, and cerebellum = 200 μm. (b) Quantification of PrP+ staining intensity. The levels of PrP+ staining are originally high in the midbrain, but at later time-points in other brain regions, such as brain stem and thalamus, the levels of PrP+ staining increase to comparable levels to that of the midbrain. In cortex and cerebellum, no change in PrP+ staining was observed. Quantitation was performed using colour deconvolution plug-in to Image-J software.
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pbio.1002579.g001: Detection of misfolded PrP using IHC at different time-points in different brain regions.(a) At 150 dpi, small quantities of fine-punctate misfolded PrP deposits can be detected in the midbrain. This positive staining could be observed in five of twelve GSS/101LL mice tested, but no staining was observed in any NBH/101LL animal in any brain region (n = 12). At 220 dpi, fine-punctate misfolded PrP deposits were detectable in both the midbrain and brain stem, which was observed in four of six GSS/101LL mice tested, but no staining was observed in any NBH/101LL animal in any brain region (n = 6). At clinical onset of disease (291.1 ± 5.3 dpi), misfolded PrP staining could be observed in midbrain, brain stem, and the thalamus but not in cortex or cerebellum in GSS/101LL mice. This staining pattern was observed in all mice tested at this stage (n = 9), whereas no staining was observed in any NBH/101LL animal in any brain region tested (n = 4). Scale bars: midbrain = 100 μm, brain stem, thalamus, cortex, and cerebellum = 200 μm. (b) Quantification of PrP+ staining intensity. The levels of PrP+ staining are originally high in the midbrain, but at later time-points in other brain regions, such as brain stem and thalamus, the levels of PrP+ staining increase to comparable levels to that of the midbrain. In cortex and cerebellum, no change in PrP+ staining was observed. Quantitation was performed using colour deconvolution plug-in to Image-J software.

Mentions: Granular deposits of misfolded PrP were detected in the midbrain at 150 dpi by IHC (Fig 1). Specifically, the staining observed is associated with the interpeduncular nuclei and substantia nigra, pars compacta (SNc). No staining could be observed in any other brain region (Fig 1); therefore, the initial IHC-detectable misfolded PrP targets specific midbrain nuclei. At 200 dpi, IHC-detectable misfolded PrP remained restricted only to midbrain nuclei. At later time-points (>220 dpi), additional IHC-detectable PrP could also be detected in brain stem regions such as the medial and dorsal raphe nuclei in GSS/101LL animals. No IHC-detectable PrP was observed in any other brain region at this time-point. At clinical onset of disease, IHC detection of misfolded PrP could be observed restricted to specific neuronal populations in three major brain regions: the midbrain, brain stem, and thalamus (Fig 1). No IHC-detectable misfolded PrP was observed in other brain regions.


Distribution of Misfolded Prion Protein Seeding Activity Alone Does Not Predict Regions of Neurodegeneration
Detection of misfolded PrP using IHC at different time-points in different brain regions.(a) At 150 dpi, small quantities of fine-punctate misfolded PrP deposits can be detected in the midbrain. This positive staining could be observed in five of twelve GSS/101LL mice tested, but no staining was observed in any NBH/101LL animal in any brain region (n = 12). At 220 dpi, fine-punctate misfolded PrP deposits were detectable in both the midbrain and brain stem, which was observed in four of six GSS/101LL mice tested, but no staining was observed in any NBH/101LL animal in any brain region (n = 6). At clinical onset of disease (291.1 ± 5.3 dpi), misfolded PrP staining could be observed in midbrain, brain stem, and the thalamus but not in cortex or cerebellum in GSS/101LL mice. This staining pattern was observed in all mice tested at this stage (n = 9), whereas no staining was observed in any NBH/101LL animal in any brain region tested (n = 4). Scale bars: midbrain = 100 μm, brain stem, thalamus, cortex, and cerebellum = 200 μm. (b) Quantification of PrP+ staining intensity. The levels of PrP+ staining are originally high in the midbrain, but at later time-points in other brain regions, such as brain stem and thalamus, the levels of PrP+ staining increase to comparable levels to that of the midbrain. In cortex and cerebellum, no change in PrP+ staining was observed. Quantitation was performed using colour deconvolution plug-in to Image-J software.
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pbio.1002579.g001: Detection of misfolded PrP using IHC at different time-points in different brain regions.(a) At 150 dpi, small quantities of fine-punctate misfolded PrP deposits can be detected in the midbrain. This positive staining could be observed in five of twelve GSS/101LL mice tested, but no staining was observed in any NBH/101LL animal in any brain region (n = 12). At 220 dpi, fine-punctate misfolded PrP deposits were detectable in both the midbrain and brain stem, which was observed in four of six GSS/101LL mice tested, but no staining was observed in any NBH/101LL animal in any brain region (n = 6). At clinical onset of disease (291.1 ± 5.3 dpi), misfolded PrP staining could be observed in midbrain, brain stem, and the thalamus but not in cortex or cerebellum in GSS/101LL mice. This staining pattern was observed in all mice tested at this stage (n = 9), whereas no staining was observed in any NBH/101LL animal in any brain region tested (n = 4). Scale bars: midbrain = 100 μm, brain stem, thalamus, cortex, and cerebellum = 200 μm. (b) Quantification of PrP+ staining intensity. The levels of PrP+ staining are originally high in the midbrain, but at later time-points in other brain regions, such as brain stem and thalamus, the levels of PrP+ staining increase to comparable levels to that of the midbrain. In cortex and cerebellum, no change in PrP+ staining was observed. Quantitation was performed using colour deconvolution plug-in to Image-J software.
Mentions: Granular deposits of misfolded PrP were detected in the midbrain at 150 dpi by IHC (Fig 1). Specifically, the staining observed is associated with the interpeduncular nuclei and substantia nigra, pars compacta (SNc). No staining could be observed in any other brain region (Fig 1); therefore, the initial IHC-detectable misfolded PrP targets specific midbrain nuclei. At 200 dpi, IHC-detectable misfolded PrP remained restricted only to midbrain nuclei. At later time-points (>220 dpi), additional IHC-detectable PrP could also be detected in brain stem regions such as the medial and dorsal raphe nuclei in GSS/101LL animals. No IHC-detectable PrP was observed in any other brain region at this time-point. At clinical onset of disease, IHC detection of misfolded PrP could be observed restricted to specific neuronal populations in three major brain regions: the midbrain, brain stem, and thalamus (Fig 1). No IHC-detectable misfolded PrP was observed in other brain regions.

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.