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Mutant huntingtin fragment selectively suppresses Brn-2 POU domain transcription factor to mediate hypothalamic cell dysfunction.

Yamanaka T, Tosaki A, Miyazaki H, Kurosawa M, Furukawa Y, Yamada M, Nukina N - Hum. Mol. Genet. (2010)

Bottom Line: We found a reduction of DNA binding of Brn-2, a POU domain transcription factor involved in differentiation and function of hypothalamic neurosecretory neurons.We provide evidence supporting that Brn-2 loses its function through two pathways, its sequestration by mutant Nhtt and its reduced transcription, leading to reduced expression of hypothalamic neuropeptides.Our data indicate that functional suppression of Brn-2 together with a region-specific lack of compensation by Brn-1 mediates hypothalamic cell dysfunction by mutant Nhtt.

View Article: PubMed Central - PubMed

Affiliation: Laboratory for Structural Neuropathology, RIKEN Brain Science Institute, Saitama 351-0198, Japan.

ABSTRACT
In polyglutamine diseases including Huntington's disease (HD), mutant proteins containing expanded polyglutamine stretches form nuclear aggregates in neurons. Although analysis of their disease models suggested a significance of transcriptional dysregulation in these diseases, how it mediates the specific neuronal cell dysfunction remains obscure. Here we performed a comprehensive analysis of altered DNA binding of multiple transcription factors using R6/2 HD model mice brains that express an N-terminal fragment of mutant huntingtin (mutant Nhtt). We found a reduction of DNA binding of Brn-2, a POU domain transcription factor involved in differentiation and function of hypothalamic neurosecretory neurons. We provide evidence supporting that Brn-2 loses its function through two pathways, its sequestration by mutant Nhtt and its reduced transcription, leading to reduced expression of hypothalamic neuropeptides. In contrast to Brn-2, its functionally related protein, Brn-1, was not sequestered by mutant Nhtt but was upregulated in R6/2 brain, except in hypothalamus. Our data indicate that functional suppression of Brn-2 together with a region-specific lack of compensation by Brn-1 mediates hypothalamic cell dysfunction by mutant Nhtt.

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Reduction of Brn-2 and Arnt2 proteins in R6/2 hypothalamus. (A) Coronal sections prepared from paraffin-embedded brain of 12-week-old R6/2 (TG) or control (WT) mice were stained with antibody against Brn-2 (C-2AP), Brn-1/2 (sc), Brn-1 (C-2AP) or Arnt2. (B) Magnified images of the PVN stained with antibody against Brn-2 (C-2AP), Brn-1/2 (sc) or Arnt2. Scale bars = 400 µm (A) and 100 µm (B).
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DDQ087F5: Reduction of Brn-2 and Arnt2 proteins in R6/2 hypothalamus. (A) Coronal sections prepared from paraffin-embedded brain of 12-week-old R6/2 (TG) or control (WT) mice were stained with antibody against Brn-2 (C-2AP), Brn-1/2 (sc), Brn-1 (C-2AP) or Arnt2. (B) Magnified images of the PVN stained with antibody against Brn-2 (C-2AP), Brn-1/2 (sc) or Arnt2. Scale bars = 400 µm (A) and 100 µm (B).

Mentions: We next examined whether Brn-2 protein was also reduced in R6/2 hypothalamus. In control mice, anti-Brn-2 signals were predominantly observed in PVN and SON neurons in its hypothalamus (Fig. 5A), consistently with previous observations (19,25). Importantly, these signals were clearly reduced in 12-week-old R6/2 hypothalamus (Fig. 5A). Similar results were also observed by staining with another antibody, anti-Brn-1/2 (Fig. 5A), which recognizes both Brn-2 and Brn-1 (Supplementary Material, Fig. S2A and B). In contrast, specific staining was not observed by anti-Brn-1 in PVN and SON in wild-type mice as previously reported (Fig. 5A) (25), suggesting that anti-Brn-1/2 stained only Brn-2 in these regions. Magnified images showed that although the level of Brn-2 was severely reduced, the number of Brn-2-positive cells seemed to stay consistent (Fig. 5B), suggesting that the reduction of Brn-2 is not caused by a loss of Brn-2-positive cells. Accumulations of Nhtt and ubiquitin, as well as formations of inclusions positive for them were confirmed in PVN cells of R6/2 mouse (Supplementary Material, Fig. S11). Thus, Brn-2 protein was reduced in association with accumulation of mutant Nhtt inclusions in 12-week-old R6/2 hypothalamus.


Mutant huntingtin fragment selectively suppresses Brn-2 POU domain transcription factor to mediate hypothalamic cell dysfunction.

Yamanaka T, Tosaki A, Miyazaki H, Kurosawa M, Furukawa Y, Yamada M, Nukina N - Hum. Mol. Genet. (2010)

Reduction of Brn-2 and Arnt2 proteins in R6/2 hypothalamus. (A) Coronal sections prepared from paraffin-embedded brain of 12-week-old R6/2 (TG) or control (WT) mice were stained with antibody against Brn-2 (C-2AP), Brn-1/2 (sc), Brn-1 (C-2AP) or Arnt2. (B) Magnified images of the PVN stained with antibody against Brn-2 (C-2AP), Brn-1/2 (sc) or Arnt2. Scale bars = 400 µm (A) and 100 µm (B).
© Copyright Policy - creative-commons
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC2865370&req=5

DDQ087F5: Reduction of Brn-2 and Arnt2 proteins in R6/2 hypothalamus. (A) Coronal sections prepared from paraffin-embedded brain of 12-week-old R6/2 (TG) or control (WT) mice were stained with antibody against Brn-2 (C-2AP), Brn-1/2 (sc), Brn-1 (C-2AP) or Arnt2. (B) Magnified images of the PVN stained with antibody against Brn-2 (C-2AP), Brn-1/2 (sc) or Arnt2. Scale bars = 400 µm (A) and 100 µm (B).
Mentions: We next examined whether Brn-2 protein was also reduced in R6/2 hypothalamus. In control mice, anti-Brn-2 signals were predominantly observed in PVN and SON neurons in its hypothalamus (Fig. 5A), consistently with previous observations (19,25). Importantly, these signals were clearly reduced in 12-week-old R6/2 hypothalamus (Fig. 5A). Similar results were also observed by staining with another antibody, anti-Brn-1/2 (Fig. 5A), which recognizes both Brn-2 and Brn-1 (Supplementary Material, Fig. S2A and B). In contrast, specific staining was not observed by anti-Brn-1 in PVN and SON in wild-type mice as previously reported (Fig. 5A) (25), suggesting that anti-Brn-1/2 stained only Brn-2 in these regions. Magnified images showed that although the level of Brn-2 was severely reduced, the number of Brn-2-positive cells seemed to stay consistent (Fig. 5B), suggesting that the reduction of Brn-2 is not caused by a loss of Brn-2-positive cells. Accumulations of Nhtt and ubiquitin, as well as formations of inclusions positive for them were confirmed in PVN cells of R6/2 mouse (Supplementary Material, Fig. S11). Thus, Brn-2 protein was reduced in association with accumulation of mutant Nhtt inclusions in 12-week-old R6/2 hypothalamus.

Bottom Line: We found a reduction of DNA binding of Brn-2, a POU domain transcription factor involved in differentiation and function of hypothalamic neurosecretory neurons.We provide evidence supporting that Brn-2 loses its function through two pathways, its sequestration by mutant Nhtt and its reduced transcription, leading to reduced expression of hypothalamic neuropeptides.Our data indicate that functional suppression of Brn-2 together with a region-specific lack of compensation by Brn-1 mediates hypothalamic cell dysfunction by mutant Nhtt.

View Article: PubMed Central - PubMed

Affiliation: Laboratory for Structural Neuropathology, RIKEN Brain Science Institute, Saitama 351-0198, Japan.

ABSTRACT
In polyglutamine diseases including Huntington's disease (HD), mutant proteins containing expanded polyglutamine stretches form nuclear aggregates in neurons. Although analysis of their disease models suggested a significance of transcriptional dysregulation in these diseases, how it mediates the specific neuronal cell dysfunction remains obscure. Here we performed a comprehensive analysis of altered DNA binding of multiple transcription factors using R6/2 HD model mice brains that express an N-terminal fragment of mutant huntingtin (mutant Nhtt). We found a reduction of DNA binding of Brn-2, a POU domain transcription factor involved in differentiation and function of hypothalamic neurosecretory neurons. We provide evidence supporting that Brn-2 loses its function through two pathways, its sequestration by mutant Nhtt and its reduced transcription, leading to reduced expression of hypothalamic neuropeptides. In contrast to Brn-2, its functionally related protein, Brn-1, was not sequestered by mutant Nhtt but was upregulated in R6/2 brain, except in hypothalamus. Our data indicate that functional suppression of Brn-2 together with a region-specific lack of compensation by Brn-1 mediates hypothalamic cell dysfunction by mutant Nhtt.

Show MeSH
Related in: MedlinePlus