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Expression of mutant huntingtin in glial cells contributes to neuronal excitotoxicity.

Shin JY, Fang ZH, Yu ZX, Wang CE, Li SH, Li XJ - J. Cell Biol. (2005)

Bottom Line: Here, we report that mutant huntingtin accumulates in glial nuclei in HD brains and decreases the expression of glutamate transporters.Mutant htt in cultured astrocytes decreased their protection of neurons against glutamate excitotoxicity.These findings suggest that decreased glutamate uptake caused by glial mutant htt may critically contribute to neuronal excitotoxicity in HD.

View Article: PubMed Central - PubMed

Affiliation: Department of Human Genetics, Emory University School of Medicine, Atlanta, GA 30322, USA.

ABSTRACT
Huntington disease (HD) is characterized by the preferential loss of striatal medium-sized spiny neurons (MSNs) in the brain. Because MSNs receive abundant glutamatergic input, their vulnerability to excitotoxicity may be largely influenced by the capacity of glial cells to remove extracellular glutamate. However, little is known about the role of glia in HD neuropathology. Here, we report that mutant huntingtin accumulates in glial nuclei in HD brains and decreases the expression of glutamate transporters. As a result, mutant huntingtin (htt) reduces glutamate uptake in cultured astrocytes and HD mouse brains. In a neuron-glia coculture system, wild-type glial cells protected neurons against mutant htt-mediated neurotoxicity, whereas glial cells expressing mutant htt increased neuronal vulnerability. Mutant htt in cultured astrocytes decreased their protection of neurons against glutamate excitotoxicity. These findings suggest that decreased glutamate uptake caused by glial mutant htt may critically contribute to neuronal excitotoxicity in HD.

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Age-dependent nuclear accumulation of mutant htt in cultured glial cells. (A) Immunofluorescence double labeling showing that GFAP (green) positive astrocytes display htt aggregates (red) in the nuclei of R6/2 glial cells. (B) Some intranuclear htt aggregates are also labeled by antibody to ubiquitin. (C) Immunofluorescent images of cultured glial cells that were cultured for 2 and 12 wk showing the increase of glial htt aggregates with time. (D) Western blotting of cultured astrocytes that were isolated from the cortex of postnatal Hdh CAG(150) knock-in (KI) and littermate control (WT) mice and had been cultured for 4 wk. The blot was probed with antitubulin (bottom) and 1C2 (top), an antibody that is specific to expanded polyQ tracts and reacts with NH2-terminal htt fragments containing 150Q. Arrow indicates full-length mutant htt. (E) Immunofluorescent images of glial culture from Hdh CAG KI. GFAP (green) positive astrocytes (arrows) contain intranuclear htt (red) aggregates. Some GFAP-negative cells (arrowhead) also show intranuclear htt, suggesting that they might be immature astrocytes or other types of cells. Bars, 5 μm.
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fig4: Age-dependent nuclear accumulation of mutant htt in cultured glial cells. (A) Immunofluorescence double labeling showing that GFAP (green) positive astrocytes display htt aggregates (red) in the nuclei of R6/2 glial cells. (B) Some intranuclear htt aggregates are also labeled by antibody to ubiquitin. (C) Immunofluorescent images of cultured glial cells that were cultured for 2 and 12 wk showing the increase of glial htt aggregates with time. (D) Western blotting of cultured astrocytes that were isolated from the cortex of postnatal Hdh CAG(150) knock-in (KI) and littermate control (WT) mice and had been cultured for 4 wk. The blot was probed with antitubulin (bottom) and 1C2 (top), an antibody that is specific to expanded polyQ tracts and reacts with NH2-terminal htt fragments containing 150Q. Arrow indicates full-length mutant htt. (E) Immunofluorescent images of glial culture from Hdh CAG KI. GFAP (green) positive astrocytes (arrows) contain intranuclear htt (red) aggregates. Some GFAP-negative cells (arrowhead) also show intranuclear htt, suggesting that they might be immature astrocytes or other types of cells. Bars, 5 μm.

Mentions: Cell culture provides a good system to validate the specific effect of mutant htt on glia. As expected, cultured GFAP-positive astrocytes from R6/2 mice showed intranuclear htt aggregates (Fig. 4 A). Only a fraction of these nuclear aggregates were ubiquitinated (Fig. 4 B), and the formation of these nuclear htt aggregates increased with culturing time (Fig. 4 C). The cells containing htt aggregates were not labeled by antibodies to markers of microglia and oligodendrocytes (not depicted), suggesting that NH2-terminal mutant htt forms aggregates more readily in astrocytic nuclei.


Expression of mutant huntingtin in glial cells contributes to neuronal excitotoxicity.

Shin JY, Fang ZH, Yu ZX, Wang CE, Li SH, Li XJ - J. Cell Biol. (2005)

Age-dependent nuclear accumulation of mutant htt in cultured glial cells. (A) Immunofluorescence double labeling showing that GFAP (green) positive astrocytes display htt aggregates (red) in the nuclei of R6/2 glial cells. (B) Some intranuclear htt aggregates are also labeled by antibody to ubiquitin. (C) Immunofluorescent images of cultured glial cells that were cultured for 2 and 12 wk showing the increase of glial htt aggregates with time. (D) Western blotting of cultured astrocytes that were isolated from the cortex of postnatal Hdh CAG(150) knock-in (KI) and littermate control (WT) mice and had been cultured for 4 wk. The blot was probed with antitubulin (bottom) and 1C2 (top), an antibody that is specific to expanded polyQ tracts and reacts with NH2-terminal htt fragments containing 150Q. Arrow indicates full-length mutant htt. (E) Immunofluorescent images of glial culture from Hdh CAG KI. GFAP (green) positive astrocytes (arrows) contain intranuclear htt (red) aggregates. Some GFAP-negative cells (arrowhead) also show intranuclear htt, suggesting that they might be immature astrocytes or other types of cells. Bars, 5 μm.
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Related In: Results  -  Collection

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getmorefigures.php?uid=PMC2171327&req=5

fig4: Age-dependent nuclear accumulation of mutant htt in cultured glial cells. (A) Immunofluorescence double labeling showing that GFAP (green) positive astrocytes display htt aggregates (red) in the nuclei of R6/2 glial cells. (B) Some intranuclear htt aggregates are also labeled by antibody to ubiquitin. (C) Immunofluorescent images of cultured glial cells that were cultured for 2 and 12 wk showing the increase of glial htt aggregates with time. (D) Western blotting of cultured astrocytes that were isolated from the cortex of postnatal Hdh CAG(150) knock-in (KI) and littermate control (WT) mice and had been cultured for 4 wk. The blot was probed with antitubulin (bottom) and 1C2 (top), an antibody that is specific to expanded polyQ tracts and reacts with NH2-terminal htt fragments containing 150Q. Arrow indicates full-length mutant htt. (E) Immunofluorescent images of glial culture from Hdh CAG KI. GFAP (green) positive astrocytes (arrows) contain intranuclear htt (red) aggregates. Some GFAP-negative cells (arrowhead) also show intranuclear htt, suggesting that they might be immature astrocytes or other types of cells. Bars, 5 μm.
Mentions: Cell culture provides a good system to validate the specific effect of mutant htt on glia. As expected, cultured GFAP-positive astrocytes from R6/2 mice showed intranuclear htt aggregates (Fig. 4 A). Only a fraction of these nuclear aggregates were ubiquitinated (Fig. 4 B), and the formation of these nuclear htt aggregates increased with culturing time (Fig. 4 C). The cells containing htt aggregates were not labeled by antibodies to markers of microglia and oligodendrocytes (not depicted), suggesting that NH2-terminal mutant htt forms aggregates more readily in astrocytic nuclei.

Bottom Line: Here, we report that mutant huntingtin accumulates in glial nuclei in HD brains and decreases the expression of glutamate transporters.Mutant htt in cultured astrocytes decreased their protection of neurons against glutamate excitotoxicity.These findings suggest that decreased glutamate uptake caused by glial mutant htt may critically contribute to neuronal excitotoxicity in HD.

View Article: PubMed Central - PubMed

Affiliation: Department of Human Genetics, Emory University School of Medicine, Atlanta, GA 30322, USA.

ABSTRACT
Huntington disease (HD) is characterized by the preferential loss of striatal medium-sized spiny neurons (MSNs) in the brain. Because MSNs receive abundant glutamatergic input, their vulnerability to excitotoxicity may be largely influenced by the capacity of glial cells to remove extracellular glutamate. However, little is known about the role of glia in HD neuropathology. Here, we report that mutant huntingtin accumulates in glial nuclei in HD brains and decreases the expression of glutamate transporters. As a result, mutant huntingtin (htt) reduces glutamate uptake in cultured astrocytes and HD mouse brains. In a neuron-glia coculture system, wild-type glial cells protected neurons against mutant htt-mediated neurotoxicity, whereas glial cells expressing mutant htt increased neuronal vulnerability. Mutant htt in cultured astrocytes decreased their protection of neurons against glutamate excitotoxicity. These findings suggest that decreased glutamate uptake caused by glial mutant htt may critically contribute to neuronal excitotoxicity in HD.

Show MeSH
Related in: MedlinePlus