[Show abstract][Hide abstract] ABSTRACT: DNA repair defends against naturally occurring or disease-associated DNA damage during the long lifespan of neurons and is implicated in polyglutamine disease pathology. In this study, we report that mutant huntingtin (Htt) expression in neurons causes double-strand breaks (DSBs) of genomic DNA, and Htt further promotes DSBs by impairing DNA repair. We identify Ku70, a component of the DNA damage repair complex, as a mediator of the DNA repair dysfunction in mutant Htt-expressing neurons. Mutant Htt interacts with Ku70, impairs DNA-dependent protein kinase function in nonhomologous end joining, and consequently increases DSB accumulation. Expression of exogenous Ku70 rescues abnormal behavior and pathological phenotypes in the R6/2 mouse model of Huntington's disease (HD). These results collectively suggest that Ku70 is a critical regulator of DNA damage in HD pathology.
The Journal of Cell Biology 05/2010; 189(3):425-43. DOI:10.1083/jcb.200905138 · 9.83 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: HMGB1 is an evolutionarily conserved non-histone chromatin-associated protein with key roles in maintenance of nuclear homeostasis; however, the function of HMGB1 in the brain remains largely unknown. Recently, we found that the reduction of nuclear HMGB1 protein level in the nucleus associates with DNA double-strand break (DDSB)-mediated neuronal damage in Huntington’s disease [M.L. Qi, K. Tagawa, Y. Enokido, N. Yoshimura, Y. Wada, K. Watase, S. Ishiura, I. Kanazawa, J. Botas, M. Saitoe, E.E. Wanker, H. Okazawa, Proteome analysis of soluble nuclear proteins reveals that HMGB1/2 suppress genotoxic stress in polyglutamine diseases, Nat. Cell Biol. 9 (2007) 402–414]. In this study, we analyze the region- and cell type-specific changes of HMGB1 and DDSB accumulation during the aging of mouse brain. HMGB1 is localized in the nuclei of neurons and astrocytes, and the protein level changes in various brain regions age-dependently. HMGB1 reduces in neurons, whereas it increases in astrocytes during aging. In contrast, DDSB remarkably accumulates in neurons, but it does not change significantly in astrocytes during aging. These results indicate that HMGB1 expression during aging is differentially regulated between neurons and astrocytes, and suggest that the reduction of nuclear HMGB1 might be causative for DDSB in neurons of the aged brain.
Biochemical and Biophysical Research Communications 11/2008; 376(1-376):128-133. DOI:10.1016/j.bbrc.2008.08.108 · 2.30 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Selective vulnerability of neurons is a critical feature of neurodegenerative diseases, but the underlying molecular mechanisms remain largely unknown. We here report that Omi/HtrA2, a mitochondrial protein regulating survival and apoptosis of cells, decreases selectively in striatal neurons that are most vulnerable to the Huntington's disease (HD) pathology. In microarray analysis, Omi/HtrA2 was decreased under the expression of mutant huntingtin (htt) in striatal neurons but not in cortical or cerebellar neurons. Mutant ataxin-1 (Atx-1) did not affect Omi/HtrA2 in any type of neuron. Western blot analysis of primary neurons expressing mutant htt also confirmed the selective reduction of the Omi/HtrA2 protein. Immunohistochemistry with a mutant htt-transgenic mouse line and human HD brains confirmed reduction of Omi/HtrA2 in striatal neurons. Overexpression of Omi/HtrA2 by adenovirus vector reverted mutant htt-induced cell death in primary neurons. These results collectively suggest that the homeostatic but not proapoptotic function of Omi/HtrA2 is linked to selective vulnerability of striatal neurons in HD pathology.
European Journal of Neuroscience 08/2008; 28(1):30-40. DOI:10.1111/j.1460-9568.2008.06323.x · 3.18 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: CBS is a vitamin B6-dependent transsulfuration enzyme needed to synthesize cysteine from methionine, catalyzing the condensation of serine with homocysteine to form cystathionine. A deficiency of CBS causes homocystinuria (MIM 236200), one of the most prevalent inborn errors, characterized by mental retardation, seizures, psychiatric disturbances, skeletal abnormalities and vascular disorders. Patients with CBS deficiency exhibit a major biochemical abnormality, hyperhomocysteinemia (HHcy), a condition associated with highly elevated plasma homocysteine levels. HHcy is recognized as a risk factor for several neurological diseases, such as cognitive impairment, dementia and Alzheimer's disease. Although the link between CBS deficiency and homocystinuria was first described over 40 years ago and mental retardation was the first clinical feature of the disease to be classified, very little is known about the role of CBS in the CNS. Here we show the regional and cellular distribution of CBS in the adult and developing mouse brain. In the adult mouse brain, CBS was expressed ubiquitously, but most intensely in the cerebellar molecular layer and hippocampal dentate gyrus. Immunohistochemical analysis revealed that CBS is preferentially expressed in cerebellar Bergmann glia and in astrocytes throughout the brain. At early developmental stages, CBS was expressed in neuroepithelial cells in the ventricular zone, but its expression changed to radial glial cells and then to astrocytes during the late embryonic and neonatal periods. Moreover, CBS was significantly accumulated in reactive astrocytes in the hippocampus after kainic acid-induced seizures, and cerebellar morphological abnormalities were observed in CBS-deficient mice. These results support the role of CBS in the development and maintenance of the CNS, and suggest that radial glia/astrocyte dysfunction might be involved in the complex neuropathological features associated with abnormal homocysteine metabolism.
Brain and nerve = Shinkei kenkyū no shinpo 08/2007; 59(7):731-7.
[Show abstract][Hide abstract] ABSTRACT: Nuclear dysfunction is a key feature of the pathology of polyglutamine (polyQ) diseases. It has been suggested that mutant polyQ proteins impair functions of nuclear factors by interacting with them directly in the nucleus. However, a systematic analysis of quantitative changes in soluble nuclear proteins in neurons expressing mutant polyQ proteins has not been performed. Here, we perform a proteome analysis of soluble nuclear proteins prepared from neurons expressing huntingtin (Htt) or ataxin-1 (AT1) protein, and show that mutant AT1 and Htt similarly reduce the concentration of soluble high mobility group B1/2 (HMGB1/2) proteins. Immunoprecipitation and pulldown assays indicate that HMGBs interact with mutant AT1 and Htt. Immunohistochemistry showed that these proteins were reduced in the nuclear region outside of inclusion bodies in affected neurons. Compensatory expression of HMGBs ameliorated polyQ-induced pathology in primary neurons and in Drosophila polyQ models. Furthermore, HMGBs repressed genotoxic stress signals induced by mutant Htt or transcriptional repression. Thus, HMGBs may be critical regulators of polyQ disease pathology and could be targets for therapy development.
[Show abstract][Hide abstract] ABSTRACT: The reason why vulnerabilities to mutant polyglutamine (polyQ) proteins are different among neuronal subtypes is mostly unknown. In this study, we compared the gene expression profiles of three types of primary neurons expressing huntingtin (htt) or ataxin-1. We found that heat shock protein 70 (hsp70), a well known chaperone molecule protecting neurons in the polyQ pathology, was dramatically upregulated only by mutant htt and selectively in the granule cells of the cerebellum. Granule cells, which are insensitive to degeneration in the human Huntington's disease (HD) pathology, lost their resistance by suppressing hsp70 with siRNA, whereas cortical neurons, affected in human HD, gained resistance by overexpressing hsp70. This indicates that induction levels of hsp70 are a critical factor for determining vulnerabilities to mutant htt among neuronal subtypes. CAT (chloramphenicol acetyltransferase) assays showed that CBF (CCAAT box binding factor, CCAAT/enhancer binding protein zeta) activated, but p53 repressed transcription of the hsp70 gene in granule cells. Basal and mutant htt-induced expression levels of p53 were remarkably lower in granule cells than in cortical neurons, suggesting that different magnitudes of p53 are linked to distinct induction levels of hsp70. Surprisingly, however, heat shock factor 1 was not activated in granule cells by mutant htt. Collectively, different levels of hsp70 among neuronal subtypes might be involved in selective neuronal death in the HD pathology.
The Journal of Neuroscience : The Official Journal of the Society for Neuroscience 02/2007; 27(4):868-80. DOI:10.1523/JNEUROSCI.4522-06.2007 · 6.34 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Hepatoma-derived growth factor (HDGF) is a nuclear protein homologous to the high-mobility group B1 family of proteins. It is known to be released from cells and to act as a trophic factor for dividing cells. In this study HDGF was increased in spinal motor neurons of a mouse model of motor neuron degeneration, polyglutamine-tract-binding protein-1 (PQBP-1) transgenic mice, before onset of degeneration. HDGF promoted neurite extension and survival of spinal motor neurons in primary culture. HDGF repressed cell death of motor neurons after facial nerve section in newborn rats in vivo. We also found a significant increase in p53 in spinal motor neurons of the transgenic mice. p53 bound to a sequence in the upstream of the HDGF gene in a gel mobility shift assay, and promoted gene expression through the cis-element in chloramphenicol acetyl transfer (CAT) assay. Finally, we found that HDGF was increased in CSF of PQBP-1 transgenic mice. Collectively, our results show that HDGF is a novel trophic factor for motor neurons and suggest that it might play a protective role against motor neuron degeneration in PQBP-1 transgenic mice.
Journal of Neurochemistry 11/2006; 99(1):70-83. DOI:10.1111/j.1471-4159.2006.04021.x · 4.28 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Transcriptional disturbance is implicated in the pathology of polyglutamine diseases, including Huntington's disease (HD). However, it is unknown whether transcriptional repression leads to neuronal death or what forms that death might take. We found transcriptional repression-induced atypical death (TRIAD) of neurons to be distinct from apoptosis, necrosis, or autophagy. The progression of TRIAD was extremely slow in comparison with other types of cell death. Gene expression profiling revealed the reduction of full-length yes-associated protein (YAP), a p73 cofactor to promote apoptosis, as specific to TRIAD. Furthermore, novel neuron-specific YAP isoforms (YAPDeltaCs) were sustained during TRIAD to suppress neuronal death in a dominant-negative fashion. YAPDeltaCs and activated p73 were colocalized in the striatal neurons of HD patients and mutant huntingtin (htt) transgenic mice. YAPDeltaCs also markedly attenuated Htt-induced neuronal death in primary neuron and Drosophila melanogaster models. Collectively, transcriptional repression induces a novel prototype of neuronal death associated with the changes of YAP isoforms and p73, which might be relevant to the HD pathology.
The Journal of Cell Biology 03/2006; 172(4):589-604. DOI:10.1083/jcb.200509132 · 9.83 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Down's syndrome (DS) or trisomy 21 is the most common genetic cause of mental retardation, and adults with DS develop Alzheimer type of disease (AD). Cystathionine beta-synthase (CBS) is encoded on chromosome 21 and deficiency in its activity causes homocystinuria, the most common inborn error of sulfur amino acid metabolism and characterized by mental retardation and vascular disease. Here, we show that the levels of CBS in DS brains are approximately three times greater than those in the normal individuals. CBS is localized to astrocytes and those surrounding senile plaques in the brains of DS patients with AD. The over-expression of CBS may cause the developmental abnormality in cognition in DS children and that may lead to AD in DS adults.
Biochemical and Biophysical Research Communications 01/2006; 338(3):1547-50. DOI:10.1016/j.bbrc.2005.10.118 · 2.30 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Cystathionine beta-synthase (CBS; EC 22.214.171.124) is a key enzyme in the generation of cysteine from methionine. A deficiency of CBS leads to homocystinuria, an inherited human disease characterized by mental retardation, seizures, psychiatric disturbances, skeletal abnormalities, and vascular disorders; however, the underlying mechanisms remain largely unknown. Here, we show the regional and cellular distribution of CBS in the adult and developing mouse brain. In the adult mouse brain, CBS was expressed ubiquitously, but it is expressed most intensely in the cerebellar molecular layer and hippocampal dentate gyrus. Immunohistochemical analysis revealed that CBS is preferentially expressed in cerebellar Bergmann glia and in astrocytes throughout the brain. At early developmental stages, CBS was expressed in neuroepithelial cells in the ventricular zone, but its expression changed to radial glial cells and then to astrocytes during the late embryonic and neonatal periods. CBS was most highly expressed in juvenile brain, and a striking induction was observed in cultured astrocytes in response to EGF, TGF-alpha, cAMP, and dexamethasone. Moreover, CBS was significantly accumulated in reactive astrocytes in the hippocampus after kainic acid-induced seizures, and cerebellar morphological abnormalities were observed in CBS-deficient mice. Taken together, these results suggest that CBS plays a crucial role in the development and maintenance of the CNS and that radial glia/astrocyte dysfunction might be involved in the complex neuropathological features associated with abnormal homocysteine metabolism.
The FASEB Journal 12/2005; 19(13):1854-6. DOI:10.1096/fj.05-3724fje · 5.04 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Hyperhomocysteinemia (HHCY) is a consequence of impaired methionine/cysteine metabolism and is caused by deficiency of vitamins and/or enzymes such as cystathionine beta-synthase (CBS). Although HHCY is an important and independent risk factor for cardiovascular diseases that are commonly associated with hepatic steatosis, the mechanism by which homocysteine promotes the development of fatty liver is poorly understood. CBS-deficient (CBS(-/-)) mice were previously generated by targeted deletion of the Cbs gene and exhibit pathological features similar to HHCY patients, including endothelial dysfunction and hepatic steatosis. Here we show abnormal lipid metabolism in CBS(-/-) mice. Triglyceride and nonesterified fatty acid levels were markedly elevated in CBS(-/-) mouse liver and serum. The activity of thiolase, a key enzyme in beta-oxidation of fatty acids, was significantly impaired in CBS(-/-) mouse liver. Hepatic apolipoprotein B100 levels were decreased, whereas serum apolipoprotein B100 and very low density lipoprotein levels were elevated in CBS(-/-) mice. Serum levels of cholesterol/phospholipid in high density lipoprotein fractions but not of total cholesterol/phospholipid were decreased, and the activity of lecithin-cholesterol acyltransferase was severely impaired in CBS(-/-) mice. Abnormal high density lipoprotein particles with higher mobility in polyacrylamide gel electrophoresis were observed in serum obtained from CBS(-/-) mice. Moreover, serum cholesterol/triglyceride distribution in lipoprotein fractions was altered in CBS(-/-) mice. These results suggest that hepatic steatosis in CBS(-/-) mice is caused by or associated with abnormal lipid metabolism.
[Show abstract][Hide abstract] ABSTRACT: The modifier of cell adhesion protein (MOCA), or Dock3, initially identified as presenilin-binding protein (PBP), belongs to the Dock180 family of proteins and is localized specifically in neurons. Here we demonstrate that MOCA binds to Rac1 and enhances its activity, which leads to the activation of c-Jun NH(2)-terminal kinase (JNK) and causes changes in cell morphology. Farnesylated MOCA, which is localized in the plasma membrane, enhances the activation of Rac1 and JNK more markedly than wild-type MOCA, and cells expressing farnesylated MOCA show flattened morphology similar to those expressing a constitutive active mutant of Rac1, Rac1Q61L. On poly-d-lysine-coated dishes, endogenous MOCA is concentrated on the leading edge of broad membrane protrusions (lamellipodia) where actin filaments are co-localized. MOCA is also concentrated with actin on the growth cone in primary cultures of cortical neurons. These observations suggest that MOCA may induce cytoskeletal reorganization and changes in cell adhesion by regulating the activity of Rac1.
[Show abstract][Hide abstract] ABSTRACT: The molecular mechanism of Bcl-2 phosphorylation and its relationship to Bax is largely unknown. Here we show that the phosphorylation of Bcl-2 is involved in the intracellular translocation of Bax from cytosol to mitochondria in NO-induced neuronal apoptosis. We examined how the phosphorylation of Bcl-2 is regulated during the apoptosis and found it to be mediated by the activation of p38 and ERK, members of the MAPK superfamily. Furthermore, we investigated whether Bcl-2 phosphorylation affected Bax translocation, using mutant Bcl-2 expression vectors. Cortical neuronal cells overexpressing the Bcl-2 mutant S70A (which cannot be phosphorylated) prevented the translocation of Bax. In contrast, transfection with Bcl-2 (S70D), a constitutively active Bcl-2 mutant, enhanced the translocation. Our results suggested that Bcl-2 phosphorylated at Ser-70 plays a critial role in the translocation of Bax from the cytosol to the mitochondria, and this may regulate NO-induced neuronal apoptosis.
[Show abstract][Hide abstract] ABSTRACT: The amyloid precursor protein (APP) is a transmembrane protein whose abnormal processing is associated with the pathogenesis of Alzheimer's disease. In this study, we examined the expression and role of cell-associated APP in primary dorsal root ganglion (DRG) neurons. When dissociated DRG cells prepared from mouse embryos were treated with nerve growth factor (NGF), neuronal APP levels were transiently elevated. DRG neurons treated with an antibody against cell surface APP failed to mature and underwent apoptosis. When NGF was withdrawn from the cultures after a 36-h NGF treatment, virtually all neurons underwent apoptosis by 48 h. During the course of apoptosis, some neurons with intact morphology contained increased levels of APP immunoreactivity, whereas the APP levels were greatly reduced in apoptotic neurons. Furthermore, affected neurons contained immunoreactivities for activated caspase-3, a caspase-cleaved APP fragment (APPDeltaC31), and Abeta. Downregulation of endogenous APP expression by treatment with an APP antisense oligodeoxynucleotide significantly increased the number of apoptotic neurons in NGF-deprived DRG cultures. Furthermore, overexpression of APP by adenovirus vector-mediated gene transfer reduced the number of apoptotic neurons deprived of NGF. These results suggest that endogenous APP is upregulated to exert an antiapoptotic effect on neurotrophin-deprived DRG neurons and subsequently undergoes caspase-dependent proteolysis.
Experimental Cell Research 07/2003; 286(2):241-51. DOI:10.1016/S0014-4827(03)00066-1 · 3.25 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: PQBP-1 is a polyglutamine tract binding protein implicated in transcription. We previously reported that PQBP-1 and mutant ataxin-1, product of the spinocerebellar atrophy type 1 (SCA1) causative gene, cooperatively induce cell death in culture cells. Simultaneously, we showed that mutant ataxin-1 promoted interaction between PQBP-1 and RNA polymerase II and enhanced repression of the basal transcription by PQBP-1. In this study, we have examined the effects of overexpression of PQBP-1 to the primary-cultured cerebellar neurons. Our results indicate that overexpression of PQBP-1 inhibits the basal transcription in cerebellar neurons and increases their vulnerability to low potassium conditions.
Biochemical and Biophysical Research Communications 07/2002; 294(2):268-71. DOI:10.1016/S0006-291X(02)00477-1 · 2.30 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: PQBP-1 was isolated on the basis of its interaction with polyglutamine tracts. In this study, using in vitro and in vivo assays, we show that the association between ataxin-1 and PQBP-1 is positively influenced by expanded polyglutamine sequences. In cell lines, interaction between the two molecules induces apoptotic cell death. As a possible mechanism underlying this phenomenon, we found that mutant ataxin-1 enhances binding of PQBP-1 to the C-terminal domain of RNA polymerase II large subunit (Pol II). This reduces the level of phosphorylated Pol II and transcription. Our results suggest the involvement of PQBP-1 in the pathology of spinocerebellar ataxia type 1 (SCA1) and support the idea that modified transcription underlies polyglutamine-mediated pathology.
[Show abstract][Hide abstract] ABSTRACT: Xeroderma pigmentosum (XP) and Cockayne syndrome (CS) are rare autosomal recessive disorders associated with a defect in the nucleotide excision repair (NER) pathway required for the removal of DNA damage induced by UV light and distorting chemical adducts. Although progressive neurological dysfunction is one of the hallmarks of CS and of some groups of XP patients, the causative mechanisms are largely unknown. Here we show that mice lacking both the XPA (XP-group A) and CSB (CS-group B) genes in contrast to the single mutants display severe growth retardation, ataxia, and motor dysfunction during early postnatal development. Their cerebella are hypoplastic and showed impaired foliation and stunted Purkinje cell dendrites. Reduced neurogenesis and increased apoptotic cell death occur in the cerebellar external granular layer. These findings suggest that XPA and CSB have additive roles in the mouse nervous system and support a crucial role for these genes in normal brain development.
Proceedings of the National Academy of Sciences 12/2001; 98(23):13379-84. DOI:10.1073/pnas.231329598 · 9.67 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: In the previous studies, we have demonstrated that the tumor suppressor gene p53 is required for DNA strand break-induced neuronal apoptosis in organotypic slice cultures of cerebellum as well as in dissociated cerebellar neuron cultures. In this study, we further investigated the role of p53 in neuronal apoptosis, by examining whether caspases and c-Jun N-terminal kinase (JNK) are involved in the DNA strand break-induced apoptosis. The protein level of phospho-JNK increased in p53 wild-type mouse cerebellar granule neurons after exposure to bleomycin. On the other hand, the response was not observed in cerebellar granule neurons of p53-deficient mice. Caspase-3-like protease was activated and poly(ADP-ribose) polymerase (PARP) was cleaved in the bleomycin-induced apoptosis. Caspase-3-like protease inhibitor decreased the number of TUNEL-positive but not p53- or c-Jun-positive neurons in bleomycin-induced death. These results suggest that JNK and caspase-3-like protease are involved in the signaling cascade of DNA strand break-induced, p53-dependent apoptosis.
Brain Research 07/2001; 904(2):270-8. DOI:10.1016/S0006-8993(01)02472-6 · 2.84 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Apoptosis occurs not only in mitotic cells but also in postmitotic neuronal cells. We previously suggested that the tumor suppressor gene p53 is required for DNA strand break-induced apoptosis in dissociated culture of cerebellar granule neurons. In this study, we examined the role of p53 in apoptosis using organotypic slice culture of cerebellum from p53 null and wild-type mice. Exposure to bleomycin significantly increased the numbers of TUNEL-, p53-, and c-Jun-positive neurons in the wild-type mouse cerebellar internal granular layer (IGL) and Purkinje cell layer (PL). However, in p53-deficient mice, these responses were not observed. These results are consistent with our previous observations in dissociated neuronal culture showing that the amount of c-Jun protein increases significantly after addition of bleomycin in p53 wild-type cerebellar granule cells. The results presented here also indicate that p53 is involved in DNA strand break-induced apoptosis of fully postmitotic central nervous system neurons and suggest that c-Jun expression occurs downstream of p53 expression.
Journal of Neuroscience Research 06/2000; 60(4):450-7. DOI:10.1002/(SICI)1097-4547(20000515)60:43.0.CO;2-P · 2.59 Impact Factor