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Human Molecular Genetics, 2004, Vol. 13, No. 11 1183-1192
DOI: 10.1093/hmg/ddh131
Human Molecular Genetics, Vol. 13, No. 11 © Oxford University Press 2004; all rights reserved

Sodium butyrate ameliorates phenotypic expression in a transgenic mouse model of spinal and bulbar muscular atrophy

Makoto Minamiyama, Masahisa Katsuno, Hiroaki Adachi, Masahiro Waza, Chen Sang, Yasushi Kobayashi, Fumiaki Tanaka, Manabu Doyu, Akira Inukai and Gen Sobue*

Department of Neurology, Nagoya University Graduate School of Medicine, Nagoya 466-8550, Japan

Received February 23, 2004; Revised March 24, 2004; Accepted April 5, 2004


   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 RESULTS
 DISCUSSION
 MATERIALS AND METHODS
 REFERENCES
 
Spinal and bulbar muscular atrophy (SBMA) is an inherited motor neuron disease caused by the expansion of a polyglutamine (polyQ) tract within the androgen receptor. Unifying mechanisms have been implicated in the pathogenesis of polyQ-dependent neurodegenerative diseases including SBMA, Huntington disease and spinocerebellar ataxias. It has been suggested that mutant protein containing polyQ inhibits histone acetyltransferase activity, resulting in transcriptional dysfunction and subsequent neuronal dysfunction. Histone deacetylase (HDAC) inhibitors alleviate neurological phenotypes in fly and mouse models of polyQ disease, although the therapeutic effect is limited by the toxicity of these compounds. We studied the therapeutic effects of sodium butyrate (SB), an HDAC inhibitor, in a transgenic mouse model of SBMA. Oral administration of SB ameliorated neurological phenotypes as well as increased acetylation of nuclear histone in neural tissues. These therapeutic effects, however, were seen only within a narrow range of SB dosage. Our results indicate that SB is a possible therapeutic agent for SBMA and other polyQ diseases, although an appropriate dose should be determined for clinical application.


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
RESULTS
 DISCUSSION
 MATERIALS AND METHODS
 REFERENCES
 
Polyglutamine (polyQ) diseases are inherited neurodegenerative disorders caused by the expansion of a trinucleotide CAG repeat in the causative genes (1,2). To date, nine polyQ diseases have been identified (3). Spinal and bulbar muscular atrophy (SBMA) is a polyQ disease affecting males, and is characterized by proximal muscle atrophy, weakness, contraction fasciculations and bulbar involvement (4–6). The number of CAG repeats in the first exon of androgen receptor (AR) gene is polymorphic with a range of 11–35 in normal population; the repeat expands to 40–62 CAGs in SBMA patients (7,8) with minimal somatic mosaicism (9). There is an inverse correlation between the CAG repeat size in AR and the age at onset, or the disease severity (10–12) as observed in other polyQ diseases (1). The major pathological finding of SBMA is motor neuron loss in the spinal cord and brainstem accompanied by a subclinical loss of sensory neurons in the dorsal root ganglia (5). Nuclear inclusions (NIs) containing mutant AR have been observed in the residual motor neurons and non-neuronal cells (13,14). The presence of NIs, which is a clue to the pathogenesis, is also striking in other polyQ diseases (15). These observations pointed to the cell nucleus as a crucial site of polyQ toxicity in the majority of polyQ diseases, although the exact role of NIs in the pathogenesis is yet to be elucidated (16). Our previous studies with a transgenic (Tg) mouse model of SBMA clearly demonstrated that reduction in the amount of nuclear-accumulated mutant AR results in marked improvement of SBMA phenotypes (17–19).

Numerous studies have indicated that transcriptional dysregulation is the pivotal mechanism of neuronal dysfunction in polyQ disease. Transcriptional co-activators such as cAMP-response element binding protein-binding protein (CBP) are sequestrated into the NIs through protein–protein interaction in mouse models and patients with polyQ diseases (20,21). Alternatively, the interaction between transcriptional co-activators and soluble mutant protein has also been demonstrated in fly and mouse models as well as in post-mortem tissues of Huntington disease (HD) patients (22,23). The histone acetyltransferase (HAT) activity of CBP is inhibited in a fly model of HD and restored by histone deacetylase (HDAC) inhibitors, resulting in less neurodegeneration (24,25). Oral administration of suberoylanilide hydroxamic acid (SAHA), an HDAC inhibitor, ameliorates motor impairment in a mouse model of HD (26), but its beneficial effect is restricted by lethal toxicity. In the present study, we report that oral administration of sodium butyrate (SB) ameliorates symptomatic and histopathological phenotypes of a mouse model of SBMA through upregulation of histone acetylation in nervous tissues. Although SB is less toxic than SAHA, this compound yielded beneficial effects within a narrow therapeutic window of dosage. Our results indicate the importance of dose determination in the clinical application of HDAC inhibitors, which are a promising new therapy for polyQ disease.


   RESULTS
TOP
 ABSTRACT
 INTRODUCTION
 RESULTS
DISCUSSION
 MATERIALS AND METHODS
 REFERENCES
 
SB improves motor impairment in SBMA mouse model within a narrow optimal dose
SB did not alter the neuromuscular phenotypes in wild-type (Wt) mice at any of the doses we tested (data not shown). Oral administration of SB markedly ameliorated muscle atrophy, body posture and footprint pattern on walking in male Tg mice at a dose of 4 g/l (Fig. 1A and B). We quantitatively assessed motor impairment by rotarod analysis and cage activity measurement, and found remarkable amelioration of motor impairment with oral SB administration in a narrow SB dose range (Figs 2 and 3A–C). SB significantly delayed the onset (at 4 and 8 g/l) and the progression (at 4 g/l) of motor deficit detected by rotarod performance (Figs 2 and 3C). SB also elongated the period during which each motor activity declines to 50% of its maximal value (Fig. 3B). SB did not produce a substantial improvement in such motor performance at 2 g/l (Figs 2 and 3A–C). It should be noted that 16 g/l of SB accelerated the onset by ~2 weeks (Figs 2 and 3C). The number of days for 50% impairment of rotarod and cage activity were not changed with 2 and 8 g/l, but even worsened with 16 g/l (Fig. 3B). Tg mice treated with 16 g/l of SB showed swelling of the kidneys (data not shown), which was also obvious in Wt mice treated with a higher dose, 40 g/l, of SB.



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  		Figure 1. SB ameliorates neuromuscular phenotypes of SBMA Tg mouse. (A) The male Tg mouse treated with 4 g/l of SB does not show the muscular atrophy seen in the non-treated male mouse (12 weeks old). (B) Footprints of the SB-treated and non-treated male Tg mice. Front paws are in red, and hind paws in blue. SB markedly ameliorated gait disturbance.

 


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  		Figure 2. SB ameliorates motor abilities of SBMA Tg mice. Rotarod activity, cage activity, body weight and survival rate (Kaplan–Meier) of Tg mice treated with or without SB (n=6 in SB 2 and 16 g/l, n=12 in SB 4 and 8 g/l, n=15 in water).

 


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  		Figure 3. SB exerts therapeutic effects within a narrow dose range. (A) Rotarod performance of Tg mice at 8, 12, 16 and 20 weeks of age. The dose effect was bell-shaped at each examined week of age. (B) At the dose of 4 g/l, SB prolonged the period during which motor function, assessed by rotarod task and cage activity, declines to 50% of its maximal value, as well as 50% survival. These effects are also observed at 8 g/l, although to a lesser extent than at 4 g/l. (C) The onset of rotarod task decline and the period from the onset to death in each treatment group. The symptomatic onset is retarded by SB at 4 or 8 g/l, whereas the progression is slowed only at the dose of 4 g/l. (A, B and C: n=6 in SB 2 and 16 g/l, n=12 in SB 4 and 8 g/l, n=15 in water).

 
Assessment of survival rate also demonstrated a similar pattern of dose-dependent response to that of motor performance. SB significantly improved the survival rate (4 g/l, P<0.0001; 8 g/l, P=0.004) and time to 50% survival at the dose of 4 and 8 g/l (Figs 2 and 3B), whereas 2 g/l doses of SB did not alter the survival rate (Figs 2 and 3B). On the other hand, the lifespan of Tg mice was shortened at the dose of 16 g/l (Fig. 2, P=0.0009). SB treatment at 4 g/l resulted in body weight gain, whereas Tg mice given other doses of SB showed earlier declines in weight, as did those not treated with SB (Fig. 2).

These observations indicate that oral administration of SB improves motor impairment, survival rate and failure of weight gain in the male Tg mice within a narrow dose range. Nevertheless, a higher dose of SB has deleterious effects on the neurological phenotypes of Tg mice.

SB ameliorates histopathological impairments of motor neurons and muscles
Oral administration of SB at the dose of 4 g/l significantly improved histopathological impairments in the muscles, spinal motor neurons and their axons in the male Tg mice (Fig. 4). The SBMA Tg mice show atrophy of spinal motor neurons and their axons in the ventral nerve root accompanied by neurogenic amyotrophy (17). SB administration significantly increased the diameter of muscles, spinal roots and motor neurons as compared with non-treated mice. Although small angulated fibers and grouped atrophy were observed in the muscles of the non-treated group, SB markedly ameliorated these histopathological appearances of denervation pattern (Fig. 4A–C). SB also improved axonal atrophy in the L5 ventral nerve root (Fig. 4D–F). There was a significant difference in the size of large motor neurons in the lumbar anterior horn between SB-treated and non-treated male Tg mice (Fig. 4G–I). Quantitative assessment showed a significant improvement in the mean diameter of muscles (45.7±5.7 µm in the SB-treated Tg mice versus 27.2±12 µm in the non-treated Tg mice, P=0.005), the diameter of large axons in the ventral root (>6 µm) (11.2±0.7 µm in the SB Tg mice versus 9.5±0.4 µm in non-treated Tg mice, P=0.02) and the size of large (>300 µm2) motor neurons in the lumbar anterior horn (453.0±32.4 µm2 in the SB-treated Tg mice versus 372.0±38.1 µm2 in non-treated Tg mice, P=0.04) with oral SB administration at 4 g/l (Fig. 4C, F and I).



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  		Figure 4. Amelioration of neuropathological findings by SB treatment. (A–C). Muscle H&E staining (A and B) of the SB-treated and non-treated male Tg mice (12 weeks old), and the histogram of muscle fiber diameter (C, n=3 in each group). (D–F) Toluidine blue staining of the L5 ventral root of male Tg mice treated with or without SB (D and E), and the histogram of myelinated fiber diameter (F, n=3). (G–I) Nissl staining of the lumbar anterior horn of Tg mice of each treatment group (G and H), and the histogram of motor neuron size (I, n=3).

 
SB does not inhibit nuclear localization and aggregation of mutant androgen receptor protein
As we reported earlier (17), nuclear localization and aggregate formation of the mutant AR protein are the major pathways of neuronal dysfunction and phenotypic expression in SBMA. Thus, we examined whether SB administration alters the amount of nuclear-localized mutant AR and the large complex form of mutant AR protein in male Tg mice, using immunohistochemistry with an anti-polyQ antibody, 1C2 and western blotting analysis. As predicted, SB did not decrease the number of neurons and glial cells harboring diffuse nuclear stain with 1C2 and nuclear inclusions in the spinal cord and other central nervous tissues (Fig. 5A). Similarly, SB did not change the 1C2 nuclear staining in visceral organs such as muscle (Fig. 5A). The amount of slowly migrating large complex mass and aggregates of the mutant AR in the spinal cords and muscles (Fig. 5B) as well as in their nuclear fractions (Fig. 5C) was assessed by western blotting with an anti-AR antibody, N-20. SB did not alter the amount of smearing mutant AR protein in the stacking gel. Although CBP was sequestered into the nuclear inclusion in Tg mice, oral SB had no influence on CBP distribution (Fig. 5D).



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  		Figure 5. SB does not prevent nuclear accumulation of mutant AR. (A) Immunohistochemistry with anti-polyQ antibody of the spinal cord and muscle of Tg mice treated with or without SB (12 weeks old). (B) Western blot analysis with an anti-AR antibody, N-20, of total homogenates from the spinal cord and muscle of the SB-treated and non-treated male Tg mice (12 weeks old). Densitometric analysis demonstrated no difference in the amount of smearing mutant AR protein between SB-treated and non-treated Tg mice (n=3, P=0.79 for spinal cord and P=0.93 for muscle). (C) Western blot analysis of nuclear fraction from the muscle of male mice with N-20 (12 weeks old). In the densitometric analysis, SB did not reduce the amount of smearing mutant AR in the nuclear fraction (n=3, P=0.89). (D) Immunohistochemistry of the muscle demonstrates that CBP is sequestrated into the nuclear inclusion in Tg mice (12 weeks old) regardless of SB treatment.

 
Oral SB increases histone acetylation level in the central nervous system
It is important to assess the augmentation of histone acetylation in the central nervous system tissue by the oral administration of SB. To determine whether SB increases the acetylation level of histone, we analyzed western blotting of spinal cord homogenate with antibodies against histones H2A, H2B, H3 and H4, and those for acetylated isoforms (Fig. 6A). Without SB treatment, histone acetylation levels are significantly reduced in Tg compared with Wt. Oral SB resulted in a significant increase in the H3 histone acetylation level in male Tg mice at 4 g/l or higher doses, although this effect was not observed at the dose of 2 g/l. The acetylation of histone H3 was also significantly enhanced in Wt mice treated with oral SB (Fig. 6A and B). In contrast to H3, acetylation of histones H2A, H2B and H4 was not significantly augmented by oral SB administration at any dose (Fig. 6A). Similar effects were observed in the brain and muscle (data not shown).



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  		Figure 6. SB induces acetylation of nuclear histone in mice. (A) Western blot analysis of the spinal cord of Wt and Tg mice with the antibodies against histones: H3, H4, H2A and H2B. Each blot was reprobed with the antibodies against the acetylated isoform of the histones. (B) The acetylation level of histone H3 was quantitated using densitometry (n=6 for each group). (C) Immunohistochemistry of the spinal cord of the SB-treated and non-treated Tg mice with antibodies against acetylated H3. (D) Densitometric analysis of immunohistochemistry shows that the acetylation level of both neurons and glial cells are upregulated at 4 g/l of SB.

 
Immunohistochemistry with the antibody specific to acetylated H3 demonstrated that the nuclei of the spinal cord motor neurons and glial cells were more densely stained in mice given oral SB than in non-treated mice. The staining intensity was proportional to the oral SB doses (Fig. 6C). The numbers of anti-acetylated histone H3 positive neurons and glia cells were significantly greater in SB-treated Tg mice than in non-treated mice (Fig. 6D).

These observations indicate that SB is capable of crossing the blood–brain barrier and increasing the level of H3 acetylation in the spinal cord and brain, providing the theoretical basis for this SBMA treatment.


   DISCUSSION
TOP
 ABSTRACT
 INTRODUCTION
 RESULTS
 DISCUSSION
MATERIALS AND METHODS
 REFERENCES
 
A growing number of polyQ diseases share salient clinical features including anticipation and selective distribution of pathology, and their symptoms are influenced by the number of CAG repeats in the causative gene (1,2). Although the gene products are unrelated except for the presence of polyQ tract, some nervous tissues, including the spinal anterior horn, brainstem and cerebellum, are preferentially affected in polyQ diseases. NIs detected in these lesions are the pathological hallmark of the disorders. The observations of common phenotypes led to the hypothesis that unifying mechanisms underlie the pathogenesis of polyQ diseases. Transcriptional dysregulation (16,27,28), aggregate formation (29,30), proteolysis of causative protein (31), transglutaminase activation (32) and mitochondrial deficits (33) have been implicated in the pathogenesis, and have been expected to be targets of medical intervention. Among these hypotheses, altered transcription appears to be convincing, supported by the fact that most polyQ proteins have been implicated in transcriptional regulation (34).

Gene expression analysis indicates that transcriptional disruption is an early change in the pathogenesis of mouse models of polyQ diseases (35,36). The expression of genes regulated through cAMP-response element-mediated transcription is decreased in HD mouse models (37,38). The transcription co-activators are sequestrated into aggregation, and their function is inhibited by soluble polyQ-containing protein (2). As the HAT activity of CBP is suppressed in cellular models, a decrease in histone acetylation is likely to underlie the neurodegeneration in polyQ diseases. Although this hypothesis has been confirmed in vitro, it remains unclear whether the histone acetylation level is decreased in animal models (26,39). The present study demonstrates that the acetylation of nuclear histone is diminished in SBMA Tg mice, suggesting that the HAT activity of CBP is suppressed in vivo. The restoration of histone acetylation by HDAC inhibitors has been considered to be of therapeutic benefit in polyQ diseases (40). Although HDAC inhibitors mitigate polyQ-induced neurodegeneration in cell and fly models of polyQ diseases (24,25), SAHA is of limited therapeutic benefit in a mouse model of HD owing to its toxicity (26). Based on their ability to regulate transcriptional activity, HDAC inhibitors have also been employed in experimental therapies for malignancies and endocrinological disorders (41). In experimental cancer therapy, as observed in polyQ models, higher doses of HDAC inhibitor are required in animal models than in vitro, presumably because of the fast elimination and low bioavailability of these compounds in vivo. The cytotoxicity of HDAC inhibitor is considerable, especially in dividing cells, and this needs to be overcome for clinical use. SAHA demonstrated remarkable side effects, including leukopenia, thrombocytopenia, hypotension, acute respiratory distress, renal insufficiency, tumor-related pain and fatigue, in a phase I clinical trial for malignancies (42). Dose-limiting toxicities were neuro-cortical events such as somnolence and confusion in another phase I clinical trial with phenylbutyrate (43).

SB is less potent than SAHA, but has the advantage of less serious toxicity. Our present study demonstrates that oral SB exerts therapeutic effects with subtle side effects when it is used at an appropriate dose. Our results revealed that the most beneficial effects were achieved at the oral SB dose of 4 g/l, whereas the compound was partially effective at the dose of 8 g/l. The acetylation level of histone is increased at these doses, implying that improvement of transcription contributes to the amelioration of symptomatic and histopathological phenotypes. SB caused no amelioration of the pathogenesis at 2 g/l, presumably because it failed to augment histone acetylation.

It is intriguing that Tg mice had lower tolerance to the toxicity of SB than did Wt. The dose of 16 g/l, which did not harm Wt mice, aggravated motor dysfunction in the Tg mice. This appears to result from the adverse effect of SB, as the histone acetylation level was successfully increased in the central nervous system at this dose. SB induces metabolic acidosis and even death at high doses in mice (44). Immobility, dehydration and exhaustion may lower the threshold for adverse effects of SB in Tg mice. This observation should also be kept in mind during clinical trials.

Intraperitoneal delivery of SB has also been reported to ameliorate neurodegeneration in an HD mouse model (39). This study supports our findings that SB improves the pathogenesis of polyQ diseases at an appropriate dose. Although intraperitoneal administration of SB upregulates acetylation of both histones H3 and H4, the present study demonstrated H3 selectivity of the effect of oral SB treatment. As SB is rapidly eliminated in vivo (44), the route of SB administration may influence its effect on histone acetylation as well as its side effects. Alternatively, a higher dose of SB might be required for H4 acetylation; indeed, the most effective dose of SB in HD mouse study, 1200 mg/kg/day, was higher than that in our analysis, 800–900 mg/kg/day.

We have previously described therapeutic approaches for SBMA using our Tg mouse model (45). Reduction in the testosterone level by castration or leuprorelin administration diminished nuclear-localized mutant AR and markedly prevented phenotypic expression in the male Tg mice (17,18). Overexpression of heat shock protein 70, which is a molecular chaperone refolding mutant protein (46), resulted in acceleration of mutant AR degradation and phenotypic amelioration (19). Although these strategies show therapeutic promise, single therapeutic agents possess limited potential because of their side effects. As suggested for other neurodegenerative diseases (47), combinations of drugs appear to be useful in the attempts of obtaining maximal therapeutic effects and reducing harmful events. Although the exact mechanism remains to be clarified, SB also ameliorates neuromuscular phenotypes of spinal muscular atrophy, which is another lower motor neuron disease arising from a different gene mutation (48). This result might indicate the relatively potent effects of SB on affected lower motor neurons. SB is a promising candidate for combination therapy for SBMA, although its dose should be very carefully determined for clinical use.


   MATERIALS AND METHODS
TOP
 ABSTRACT
 INTRODUCTION
 RESULTS
 DISCUSSION
 MATERIALS AND METHODS
REFERENCES
 
Generation and maintenance of Tg mice and genotyping
Chicken ß-actin promoter-driven AR-24Q and AR-97Q constructs were prepared by digestion of pCAGGS vector as described earlier (17,49,50). Genotyping of mice was performed by PCR using mouse tail (17). Tg mice were maintained by crossing to F1 of C57BL/6J and BDF1. We analyzed a symptomatic line #4–6 of this mouse model throughout the present study.

Assessment of motor ability
All animal experiments were performed in accordance with the National Institute of Health Guide for the Care and Use of Laboratory Animals and were approved by the Nagoya University Animal Experiment Committee. Rotarod performance was assessed weekly using an Economex Rotarod (Colombus Instruments, Colombus, OH, USA) as described previously (51). Cage activity was measured weekly, with each mouse in a transparent acrylic cage within a soundproof box as described previously (17).

Administration of SB
Wt and SBMA Tg (AR-97Q #4–6) mice were orally supplied sterile water ad libitum. Three mice shared the same drinking water in each cage. SB was administered at a concentration of 2, 4, 8, 16 or 40 g/l in distilled water from 5 weeks of age until the end of analysis. Before the onset of motor symptoms, between the age of 6 and 8 weeks, the approximate daily amount of drinking water was similar for each treatment group of Tg mice; 4.0±0.26, 3.7±0.51, 4.5±0.19, 4.1±0.29 and 4.4±0.15 ml at the dose of 0, 2, 4, 8 and 16 g/l, respectively. There was no difference in the amount of water intake and body weight between Wt and Tg mice in that period.

Immunohistochemistry
An aliquot of 20 ml of 4% paraformaldehyde fixative in 0.1 M phosphate buffer (pH 7.4) was perfused through the left cardiac ventricle of mice (12 weeks old) deeply anesthetized with ketamine–xylazine, the tissues post-fixed in 10% phosphate-buffered formalin and then processed for paraffin embedding. Tissue sections (4 µm thick) were then deparaffinized, dehydrated with alcohol, and then treated for antigen retrieval (17). For the mutant AR immunohistochemical study, the paraffin sections were pretreated with formic acid for 5 min at room temperature. The tissue sections were blocked with normal horse serum (1 : 20) and incubated with mouse anti-expanded polyQ, 1C2 (1 : 10 000, Chemicon, Temecula, CA, USA). The sections were then incubated with biotinylated anti-mouse IgG (1 : 1000, Vector Laboratories, Burlingame, CA, USA). Immune complexes were visualized using streptavidin–horseradish peroxidase (Dako, Glostrup, Denmark) and 3,3'-diaminobenzidine (Dojindo, Kumamoto, Japan) substrate. Sections were counterstained with methyl green. For immunostaining of histone, sections were autoclaved at 121°C for 15 min, and incubated with anti-histone H3 (1 : 100, Upstate Biotechnology, Lake Placid, NY, USA) or anti-acetylated histone H3 (1 : 500, Upstate Biotechnology) antibodies.

The number of 1C2 or anti-acetylated H3-positive cells for one individual mouse was counted using a light microscope with a computer-assisted image analyzer (Luzex FS, Nikon, Tokyo, Japan). Fifty consecutive transverse sections of the thoracic spinal cord were prepared, and 1C2 or anti-acetylated H3-positive cells in the anterior horn on every fifth section were counted as described previously (51,52). For quantitative assessment, 1C2-positive cells in the muscle were calculated from counts of more than 500 fibers in randomly selected areas, and were expressed as the number per 100 muscle fibers.

Muscle histology and morphometric analysis of spinal motor neurons and ventral spinal roots
Cryostat sections of the gastrocnemius muscles (6 µm thick) were air-dried and stained with hematoxylin and eosin (H&E). The muscle fiber diameter was measured in randomly selected areas for three mice of each treatment group (12 weeks old) using a Luzex FS image analyzer (Nireco). To assess the neuronal populations and cross-sectional area of the anterior horn cells, 20 serial 5 µm thick sections from the fifth lumbar spinal cords of three mice of each group (12 weeks old) were prepared. Every other section was stained by the Nissl technique, and all neurons with an obvious nucleolus in the anterior horn were assessed using a Luzex FS image analyzer as described earlier (17). The diameter of myelinated fibers in the ventral spinal roots was measured on the transverse sections stained with toluidine blue, also as described earlier (17).

Western blots
Mice (12 weeks old) were exsanguinated under ketamine–xylazine anesthesia, and their tissues snap-frozen with powdered CO2 in acetone. Frozen tissue (0.1 g wet weight) was homogenized in 1000 µl of CelLytic-M mammalian cell lysis/extraction reagent (Sigma Chemical, St Louis, MO, USA) with 1 mM phenylmethylsulfonyl fluoride and aprotinin at 6 µg/ml. Homogenates were spun at 2500g for 15 min at 4°C. The protein concentration of the supernatant was determined using DC protein assay (Bio-Rad Laboratories, Hercules, CA, USA). Each lane on a 5–20% SDS–PAGE gel was loaded with 200 µg protein for the spinal cord and 80 µg for the muscle from the supernatant fraction, which was transferred to Hybond-P membranes (Amersham Pharmacia Biotech, Buckinghamshire, UK) using 25 mM Tris, 192 mM glycine and 10% methanol as transfer buffer. Kaleidoscope prestained standards were used as size markers (Bio-Rad Laboratories). Proteins were then transferred to Hybond-P membranes (Amersham Pharmacia Biotech), which were subsequently blocked in 5% milk in Tris-buffered saline containing 0.05% Tween-20, and incubated with appropriate primary antibodies using standard techniques. Primary antibodies were used at the following concentrations: anti-histone H3, 1 : 500 (Upstate Biotechnology); anti-acetylated histone H3, 1 : 250 (Upstate Biotechnology); anti-histone H4, 1 : 500 (Upstate Biotechnology); anti-acetylated histone H4, 1 : 200 (Upstate Biotechnology); anti-histone H2A, 1 : 500 (Upstate Biotechnology); anti-acetylated histone H2A, 1 : 200 (Upstate Biotechnology); anti-histone H2B, 1 : 500 (Upstate Biotechnology) and anti-acetylated histone H2B, 1 : 200 (Serotec, Kidlington, UK). Second antibody probing and detection were performed using the ECL+plus kit (Amersham Pharmacia Biotech) as described earlier (17). The signal intensity of the bands smearing from the top of the gel were quantified using the NIH Image program (NIH Image version 1.62). The quantitative data of three independent western blots were expressed as mean±SD.

Statistical analyses
Data were analyzed using Kaplan–Meier and log-rank test for survival rate in Figure 2, Dunnett test for multiple comparison in Figures 3A–C and 6B and unpaired t-test in Figures 4,5 and 6D from Statview software version 5 (HULINKS, Tokyo, Japan).


   ACKNOWLEDGEMENTS
 
We thank Dr Tamakoshi and Dr Yatsuya for their advice in the statistical analysis. This work was supported by a Center-of-Excellence (COE) grant from the Ministry of Education, Culture, Sports, Science and Technology, Japan, grants from the Ministry of Health, Labor and Welfare, Japan, a grant from the Naito Foundation and a grant from the Kanae Foundation.


   FOOTNOTES
 
* To whom correspondence should be addressed at: Department of Neurology, Nagoya University Graduate School of Medicine, 65 Tsurumai-cho, Showa-ku, Nagoya 466-8550, Japan. Tel: +81 527442385; Fax: +81 527442384; Email: sobueg{at}med.nagoya-u.ac.jp


   REFERENCES
TOP
 ABSTRACT
 INTRODUCTION
 RESULTS
 DISCUSSION
 MATERIALS AND METHODS
 REFERENCES
 

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