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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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PolyQ-mediated intranuclear htt accumulation in glial cells. (A) Immunofluorescent images of adenovirus-infected astrocytes that express GFP-htt containing a 23- (23Q) or 130- (130Q) glutamine repeat. Immunostaining with EM48 confirms that htt-130Q is located in the nucleus and forms nuclear aggregates. Nuclei are stained with Hoechst. (B) Proteasomal inhibition by ALLN (10 μg/ml) for 5 d significantly increases the formation of nuclear aggregates of htt-130Q, but not htt-23Q, in infected glial cells. (C) MTT assay of cultured glial cells infected by adenoviral-GFP (+GFP), htt-23Q (+23Q), or htt-130Q (+130Q) for 9 d. (D) MTT assay of astrocytes from R6/2 mice (HD) or littermate controls (WT) cultured for 6 or 8 wk. The data are presented as mean ± SEM (n = 3–4) and p values for 6- and 8-wk group comparisons (WT vs. HD) are 0.23 and 0.014, respectively. Bars, 5 μm.
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fig6: PolyQ-mediated intranuclear htt accumulation in glial cells. (A) Immunofluorescent images of adenovirus-infected astrocytes that express GFP-htt containing a 23- (23Q) or 130- (130Q) glutamine repeat. Immunostaining with EM48 confirms that htt-130Q is located in the nucleus and forms nuclear aggregates. Nuclei are stained with Hoechst. (B) Proteasomal inhibition by ALLN (10 μg/ml) for 5 d significantly increases the formation of nuclear aggregates of htt-130Q, but not htt-23Q, in infected glial cells. (C) MTT assay of cultured glial cells infected by adenoviral-GFP (+GFP), htt-23Q (+23Q), or htt-130Q (+130Q) for 9 d. (D) MTT assay of astrocytes from R6/2 mice (HD) or littermate controls (WT) cultured for 6 or 8 wk. The data are presented as mean ± SEM (n = 3–4) and p values for 6- and 8-wk group comparisons (WT vs. HD) are 0.23 and 0.014, respectively. Bars, 5 μm.

Mentions: To identify the pathological changes that are specifically associated with an expanded repeat, we infected glial cells with adenoviral vectors expressing GFP fusion protein containing the first 208 amino acids of human htt with 23Q (htt-23Q) or 130Q (htt-130Q). Htt-23Q was predominantly diffuse in the cytoplasm, though its overexpression resulted in small puncta or aggregates in the cytoplasm but not in the nucleus. However, expanded polyQ caused htt-130Q to form significantly larger and more abundant inclusions in both the cytoplasm and nucleus (Fig. 6 A). Also, nuclear accumulation and aggregation of htt-130Q were elevated by treatment with the proteasome inhibitor N-acetyl-leucinal-leucinal-norleucinal (Fig. 6 B, ALLN). All of these results indicate a specific nuclear accumulation of htt mediated by a large polyQ tract.


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)

PolyQ-mediated intranuclear htt accumulation in glial cells. (A) Immunofluorescent images of adenovirus-infected astrocytes that express GFP-htt containing a 23- (23Q) or 130- (130Q) glutamine repeat. Immunostaining with EM48 confirms that htt-130Q is located in the nucleus and forms nuclear aggregates. Nuclei are stained with Hoechst. (B) Proteasomal inhibition by ALLN (10 μg/ml) for 5 d significantly increases the formation of nuclear aggregates of htt-130Q, but not htt-23Q, in infected glial cells. (C) MTT assay of cultured glial cells infected by adenoviral-GFP (+GFP), htt-23Q (+23Q), or htt-130Q (+130Q) for 9 d. (D) MTT assay of astrocytes from R6/2 mice (HD) or littermate controls (WT) cultured for 6 or 8 wk. The data are presented as mean ± SEM (n = 3–4) and p values for 6- and 8-wk group comparisons (WT vs. HD) are 0.23 and 0.014, respectively. Bars, 5 μm.
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Related In: Results  -  Collection

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getmorefigures.php?uid=PMC2171327&req=5

fig6: PolyQ-mediated intranuclear htt accumulation in glial cells. (A) Immunofluorescent images of adenovirus-infected astrocytes that express GFP-htt containing a 23- (23Q) or 130- (130Q) glutamine repeat. Immunostaining with EM48 confirms that htt-130Q is located in the nucleus and forms nuclear aggregates. Nuclei are stained with Hoechst. (B) Proteasomal inhibition by ALLN (10 μg/ml) for 5 d significantly increases the formation of nuclear aggregates of htt-130Q, but not htt-23Q, in infected glial cells. (C) MTT assay of cultured glial cells infected by adenoviral-GFP (+GFP), htt-23Q (+23Q), or htt-130Q (+130Q) for 9 d. (D) MTT assay of astrocytes from R6/2 mice (HD) or littermate controls (WT) cultured for 6 or 8 wk. The data are presented as mean ± SEM (n = 3–4) and p values for 6- and 8-wk group comparisons (WT vs. HD) are 0.23 and 0.014, respectively. Bars, 5 μm.
Mentions: To identify the pathological changes that are specifically associated with an expanded repeat, we infected glial cells with adenoviral vectors expressing GFP fusion protein containing the first 208 amino acids of human htt with 23Q (htt-23Q) or 130Q (htt-130Q). Htt-23Q was predominantly diffuse in the cytoplasm, though its overexpression resulted in small puncta or aggregates in the cytoplasm but not in the nucleus. However, expanded polyQ caused htt-130Q to form significantly larger and more abundant inclusions in both the cytoplasm and nucleus (Fig. 6 A). Also, nuclear accumulation and aggregation of htt-130Q were elevated by treatment with the proteasome inhibitor N-acetyl-leucinal-leucinal-norleucinal (Fig. 6 B, ALLN). All of these results indicate a specific nuclear accumulation of htt mediated by a large polyQ tract.

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