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Changes in Purkinje cell firing and gene expression precede behavioral pathology in a mouse model of SCA2.

Hansen ST, Meera P, Otis TS, Pulst SM - Hum. Mol. Genet. (2012)

Bottom Line: Although motor performance began to deteriorate at 8 weeks of age, reductions in PC number were not seen until after 12 weeks.Transcription changes in several PC-specific genes such as Calb1 and Pcp2 mirrored the time course of changes in PC physiology with calbindin-28 K changes showing the first small, but significant decreases at 4 weeks.These results emphasize that in this model of SCA2, physiological and behavioral phenotypes precede morphological changes by several weeks and provide a rationale for future studies examining the effects of restoration of firing frequency on motor function and prevention of future loss of PCs.

View Article: PubMed Central - PubMed

Affiliation: Department of Neurology, University of Utah, UT, USA.

ABSTRACT
Spinocerebellar ataxia type 2 (SCA2) is an autosomal dominantly inherited disorder, which is caused by a pathological expansion of a polyglutamine (polyQ) tract in the coding region of the ATXN2 gene. Like other ataxias, SCA2 most overtly affects Purkinje cells (PCs) in the cerebellum. Using a transgenic mouse model expressing a full-length ATXN2(Q127)-complementary DNA under control of the Pcp2 promoter (a PC-specific promoter), we examined the time course of behavioral, morphologic, biochemical and physiological changes with particular attention to PC firing in the cerebellar slice. Although motor performance began to deteriorate at 8 weeks of age, reductions in PC number were not seen until after 12 weeks. Decreases in the PC firing frequency first showed at 6 weeks and paralleled deterioration of motor performance with progression of disease. Transcription changes in several PC-specific genes such as Calb1 and Pcp2 mirrored the time course of changes in PC physiology with calbindin-28 K changes showing the first small, but significant decreases at 4 weeks. These results emphasize that in this model of SCA2, physiological and behavioral phenotypes precede morphological changes by several weeks and provide a rationale for future studies examining the effects of restoration of firing frequency on motor function and prevention of future loss of PCs.

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Changes in PC number and molecular layer thickness occur late in ATXN2Q127 mice. Representative confocal images stained for calbindin 28-k from the ‘fissura prima’ of the cerebellar vermis: WT animals (A–E) and ATXN2Q127 transgenic mice (F–J) at 4, 8, 12 and 24 weeks of age are shown. (K) Graphical representation of changes in the molecular layer thickness. (L) PC count of ATXN2Q127 (gray bars) and WT (white bars) animals across age. N = 2–3 animals for each category. Two-way ANOVA comparing the age × genotype; Bonferroni post-hoc tests. *P < 0.05; **P < 0.01; ***P < 0.001. Error bars represent ±SEM. Scale bar = 200 μm
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DDS427F2: Changes in PC number and molecular layer thickness occur late in ATXN2Q127 mice. Representative confocal images stained for calbindin 28-k from the ‘fissura prima’ of the cerebellar vermis: WT animals (A–E) and ATXN2Q127 transgenic mice (F–J) at 4, 8, 12 and 24 weeks of age are shown. (K) Graphical representation of changes in the molecular layer thickness. (L) PC count of ATXN2Q127 (gray bars) and WT (white bars) animals across age. N = 2–3 animals for each category. Two-way ANOVA comparing the age × genotype; Bonferroni post-hoc tests. *P < 0.05; **P < 0.01; ***P < 0.001. Error bars represent ±SEM. Scale bar = 200 μm

Mentions: Along with the overt motor phenotype, we observed anatomical abnormalities associated with expression of the transgene in mutant mice, although at latter ages. Figure 2A–J shows representative images of WT (top row) and ATXN2Q127 cerebellar sections (bottom row) across five different age points (columns). Two-way ANOVA detected a significant main effect of genotype (F = 47.21, 20). Bonferroni post-hoc tests determined that mutant animals at 12 (P < 0.05), 24 (P < 0.01) and 40 (P < 0.001) weeks of age exhibited a significant loss of molecular layer thickness (Fig. 2K). Overall cell loss in ATXN2Q127 animals exhibited a significant main effect of genotype (F = 7.161, 20). Bonferroni post-hoc tests indicated that only 40-week-old ATXN2Q127 differed from WT (Fig. 2L). Despite normal motor behavior at the age of 4 weeks, perinuclear ataxin-2 aggregates were already detectable at that time in some PCs with an antibody targeting an epitope shared by human and mouse ATXN2 (Fig. 3). The number of PCs showing inclusions and the size of inclusions increased with age, whereas diffuse cytoplasmic staining became nearly undetectable at advanced ages.Figure 2.


Changes in Purkinje cell firing and gene expression precede behavioral pathology in a mouse model of SCA2.

Hansen ST, Meera P, Otis TS, Pulst SM - Hum. Mol. Genet. (2012)

Changes in PC number and molecular layer thickness occur late in ATXN2Q127 mice. Representative confocal images stained for calbindin 28-k from the ‘fissura prima’ of the cerebellar vermis: WT animals (A–E) and ATXN2Q127 transgenic mice (F–J) at 4, 8, 12 and 24 weeks of age are shown. (K) Graphical representation of changes in the molecular layer thickness. (L) PC count of ATXN2Q127 (gray bars) and WT (white bars) animals across age. N = 2–3 animals for each category. Two-way ANOVA comparing the age × genotype; Bonferroni post-hoc tests. *P < 0.05; **P < 0.01; ***P < 0.001. Error bars represent ±SEM. Scale bar = 200 μm
© Copyright Policy - creative-commons
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3526159&req=5

DDS427F2: Changes in PC number and molecular layer thickness occur late in ATXN2Q127 mice. Representative confocal images stained for calbindin 28-k from the ‘fissura prima’ of the cerebellar vermis: WT animals (A–E) and ATXN2Q127 transgenic mice (F–J) at 4, 8, 12 and 24 weeks of age are shown. (K) Graphical representation of changes in the molecular layer thickness. (L) PC count of ATXN2Q127 (gray bars) and WT (white bars) animals across age. N = 2–3 animals for each category. Two-way ANOVA comparing the age × genotype; Bonferroni post-hoc tests. *P < 0.05; **P < 0.01; ***P < 0.001. Error bars represent ±SEM. Scale bar = 200 μm
Mentions: Along with the overt motor phenotype, we observed anatomical abnormalities associated with expression of the transgene in mutant mice, although at latter ages. Figure 2A–J shows representative images of WT (top row) and ATXN2Q127 cerebellar sections (bottom row) across five different age points (columns). Two-way ANOVA detected a significant main effect of genotype (F = 47.21, 20). Bonferroni post-hoc tests determined that mutant animals at 12 (P < 0.05), 24 (P < 0.01) and 40 (P < 0.001) weeks of age exhibited a significant loss of molecular layer thickness (Fig. 2K). Overall cell loss in ATXN2Q127 animals exhibited a significant main effect of genotype (F = 7.161, 20). Bonferroni post-hoc tests indicated that only 40-week-old ATXN2Q127 differed from WT (Fig. 2L). Despite normal motor behavior at the age of 4 weeks, perinuclear ataxin-2 aggregates were already detectable at that time in some PCs with an antibody targeting an epitope shared by human and mouse ATXN2 (Fig. 3). The number of PCs showing inclusions and the size of inclusions increased with age, whereas diffuse cytoplasmic staining became nearly undetectable at advanced ages.Figure 2.

Bottom Line: Although motor performance began to deteriorate at 8 weeks of age, reductions in PC number were not seen until after 12 weeks.Transcription changes in several PC-specific genes such as Calb1 and Pcp2 mirrored the time course of changes in PC physiology with calbindin-28 K changes showing the first small, but significant decreases at 4 weeks.These results emphasize that in this model of SCA2, physiological and behavioral phenotypes precede morphological changes by several weeks and provide a rationale for future studies examining the effects of restoration of firing frequency on motor function and prevention of future loss of PCs.

View Article: PubMed Central - PubMed

Affiliation: Department of Neurology, University of Utah, UT, USA.

ABSTRACT
Spinocerebellar ataxia type 2 (SCA2) is an autosomal dominantly inherited disorder, which is caused by a pathological expansion of a polyglutamine (polyQ) tract in the coding region of the ATXN2 gene. Like other ataxias, SCA2 most overtly affects Purkinje cells (PCs) in the cerebellum. Using a transgenic mouse model expressing a full-length ATXN2(Q127)-complementary DNA under control of the Pcp2 promoter (a PC-specific promoter), we examined the time course of behavioral, morphologic, biochemical and physiological changes with particular attention to PC firing in the cerebellar slice. Although motor performance began to deteriorate at 8 weeks of age, reductions in PC number were not seen until after 12 weeks. Decreases in the PC firing frequency first showed at 6 weeks and paralleled deterioration of motor performance with progression of disease. Transcription changes in several PC-specific genes such as Calb1 and Pcp2 mirrored the time course of changes in PC physiology with calbindin-28 K changes showing the first small, but significant decreases at 4 weeks. These results emphasize that in this model of SCA2, physiological and behavioral phenotypes precede morphological changes by several weeks and provide a rationale for future studies examining the effects of restoration of firing frequency on motor function and prevention of future loss of PCs.

Show MeSH
Related in: MedlinePlus