[Show abstract][Hide abstract] ABSTRACT: Amyotrophic lateral sclerosis (ALS) is an adult-onset motor neuron disease characterized by degeneration of motor neuron and glial activation followed by the progressive muscle loss and paralysis. Numerous distinct therapeutic interventions have been examined but currently ALS does not have a cure or an efficacious treatment for the disorder. Glutamate-induced excitotoxicity, inflammation, mitochondrial dysfunction, oxidative stress, protein aggregation, transcription deregulation, and epigenetic modifications are associated with the pathogenesis of ALS and known to be therapeutic targets in ALS. In this review, we discuss translational pharmacological studies targeting epigenetic components to ameliorate ALS. Understanding of the epigenetic mechanisms will provide novel insights that will further identify potential biological markers and therapeutic approaches for treating ALS. A combination of treatments that modulate epigenetic components and multiple targets may prove to be the most effective therapy for ALS.
[Show abstract][Hide abstract] ABSTRACT: In Alzheimer's disease (AD), memory impairment is the most prominent feature that afflicts patients and their families. Although reactive astrocytes have been observed around amyloid plaques since the disease was first described, their role in memory impairment has been poorly understood. Here, we show that reactive astrocytes aberrantly and abundantly produce the inhibitory gliotransmitter GABA by monoamine oxidase-B (Maob) and abnormally release GABA through the bestrophin 1 channel. In the dentate gyrus of mouse models of AD, the released GABA reduces spike probability of granule cells by acting on presynaptic GABA receptors. Suppressing GABA production or release from reactive astrocytes fully restores the impaired spike probability, synaptic plasticity, and learning and memory in the mice. In the postmortem brain of individuals with AD, astrocytic GABA and MAOB are significantly upregulated. We propose that selective inhibition of astrocytic GABA synthesis or release may serve as an effective therapeutic strategy for treating memory impairment in AD.
[Show abstract][Hide abstract] ABSTRACT: Rubinstein-Taybi syndrome (RTS) is an incurable genetic disorder with combination of mental retardation and physical features including broad thumbs and toes, craniofacial abnormalities, and growth deficiency. While the autosomal dominant mode of transmission is limitedly known, the majority of cases are attributable to de novo mutations in RTS. The first identified gene associated with RTS is CREB-binding protein (CREBBP/CBP). Alterations of the epigenetic 'histone code' due to dysfunction of the CBP histone acetyltransferase activity deregulate gene transcriptions that are prominently linked to RTS pathogenesis. In this review, we discuss how CBP mutation contributes to modifications of histone and how histone deacetylase inhibitors are therapeutically applicable to epigenetic conditioning in RTS. Since most genetic mutations are irreversible and therapeutic approaches are limited, therapeutic targeting of reversible epigenetic components altered in RTS may be an ideal strategy. Expeditious further study on the role of the epigenetic mechanisms in RTS is encouraged to identify novel epigenetic markers and therapeutic targets to treat RTS.
Neuromolecular medicine 01/2014; · 5.00 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The remodeling of chromatin in the nucleolus is important for the control of ribosomal DNA (rDNA) transcription and ribosome biogenesis. Herein, we found that upstream binding factor (UBF) interacts with ESET, a histone H3K9 methyltransferase and is trimethylated at Lys (K) 232/254 by ESET. UBF trimethylation leads to nucleolar chromatin condensation and decreased rDNA transcriptional activity. UBF mutations at K232/254A and K232/254R restored rDNA transcriptional activity in response to ESET. Both ESET-ΔSET mutant and knockdown of ESET by short hairpin RNA reduced trimethylation of UBF and resulted in the restoration of rDNA transcription. Atomic force microscopy confirmed that UBF trimethylated by ESET modulates the plasticity of nucleolar chromatin. We further demonstrated that UBF trimethylation at K232/254 by ESET deregulates rDNA transcription in a cell model of Huntington's disease. Together, our findings show that a novel epigenetic modification of UBF is linked to impaired rDNA transcription and nucleolar chromatin remodeling, which may play key roles in the pathogenesis of neurodegeneration.
Nucleic Acids Research 11/2013; · 8.81 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: EWS (Ewing's Sarcoma) gene encodes an RNA/DNA-binding protein that is ubiquitously expressed and involved in various cellular processes. EWS deficiency leads to impaired development and early senescence through unknown mechanisms. We found that EWS regulates the expression of Drosha and microRNAs (miRNAs). EWS deficiency resulted in increased expression of Drosha, a well-known microprocessor, and increased levels of miR-29b and miR-18b. Importantly, miR-29b and miR-18b were directly involved in the post-transcriptional regulation of collagen IV alpha 1 (Col4a1) and connective tissue growth factor (CTGF) in EWS knock-out (KO) mouse embryonic fibroblast cells. The upregulation of Drosha, miR-29b and miR-18b and the sequential downregulation of Col4a1 and CTGF contributed to the deregulation of dermal development in EWS KO mice. Otherwise, knockdown of Drosha rescued miRNA-dependent downregulation of Col4a1 and CTGF proteins. Taken together, our data indicate that EWS is involved in post-transcriptional regulation of Col4a1 and CTGF via a Drosha-miRNA-dependent pathway. This finding suggests that EWS has a novel role in dermal morphogenesis through the modulation of miRNA biogenesis.Cell Death and Differentiation advance online publication, 1 November 2013; doi:10.1038/cdd.2013.144.
Cell death and differentiation 11/2013; · 8.24 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Huntington's disease (HD) is a fatal genetic disorder characterized by triad clinical symptoms of chorea, emotional distress, and cognitive decline. Genetic mutation in HD is identified by an expansion of CAG repeats coding for glutamine (Q) in exon 1 of the huntingtin (htt) gene. The exact mechanism on how mutant htt leads to the selective loss of medium spiny neurons (MSNs) in the striatum is still unknown. Recent studies suggest that nucleolar stress and dysfunction is linked to the pathogenesis of HD. Alterations of the nucleolar activity and integrity contributes to deregulation of ribosomal DNA (rDNA) transcription in HD pathogenesis. Furthermore, epigenetic modifications in the nucleolus are associated with neuronal damage in HD. In this review, we discuss about how post-translational modifications of upstream binding factor (UBF) are affected by histone acetyltransferase and histone methyltransferase and involved in the transcriptional regulation of rDNA in HD. The understanding of epigenetic modulation of UBF-dependent rDNA transcription in the nucleolus may lead to the identification of novel pathological markers and new therapeutic targets to treat HD. This article is part of a Special Issue entitled: Role of the Nucleolus in Human Disease.
Biochimica et Biophysica Acta 10/2013; · 4.66 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Huntington's disease (HD) is an incurable and fatal hereditary neurodegenerative disorder of mid-life onset characterized by chorea, emotional distress, and progressive cognitive decline. HD is caused by an expansion of CAG repeats coding for glutamine (Q) in exon 1 of the huntingtin gene. Recent studies suggest that epigenetic modifications may play a key role in HD pathogenesis. Alterations of the epigenetic "histone code" lead to chromatin remodeling and deregulation of neuronal gene transcription that are prominently linked to HD pathogenesis. Furthermore, specific noncoding RNAs and microRNAs are associated with neuronal damage in HD. In this review, we discuss how DNA methylation, post-translational modifications of histone, and noncoding RNA function are affected and involved in HD pathogenesis. In addition, we summarize the therapeutic effects of histone deacetylase inhibitors and DNA binding drugs on epigenetic modifications and neuropathological sequelae in HD. Our understanding of the role of these epigenetic mechanisms may lead to the identification of novel biological markers and new therapeutic targets to treat HD.
Journal of the American Society for Experimental NeuroTherapeutics 09/2013; · 5.38 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Amyotrophic lateral sclerosis (ALS) is an adult-onset neurodegenerative disorder characterized by loss of motor neurons. Dominant mutations in the gene for superoxide dismutase 1 (SOD1) give rise to familial ALS by an unknown mechanism. Here we show that genetic deficiency of mammalian sterile 20-like kinase 1 (MST1) delays disease onset and extends survival in mice expressing the ALS-associated G93A mutant of human SOD1. SOD1(G93A) induces dissociation of MST1 from a redox protein thioredoxin-1 and promotes MST1 activation in spinal cord neurons in a reactive oxygen species-dependent manner. Moreover, MST1 was found to mediate SOD1(G93A)-induced activation of p38 mitogen-activated protein kinase and caspases as well as impairment of autophagy in spinal cord motoneurons of SOD1(G93A) mice. Our findings implicate MST1 as a key determinant of neurodegeneration in ALS.
Proceedings of the National Academy of Sciences 07/2013; · 9.74 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Huntington's disease (HD) is an autosomal dominant neurodegenerative disease caused by an expanded trinucleotide CAG repeat in the gene coding for huntingtin. Deregulation of chromatin remodeling is linked to the pathogenesis of HD but the mechanism remains elusive. To identify what genes are deregulated by trimethylated histone H3K9 (H3K9me3)-dependent heterochromatin, we performed H3K9me3-ChIP genome-wide sequencing combined with RNA sequencing followed by platform integration analysis in stable striatal HD cell lines (STHdhQ7/7 and STHdhQ111/111) cells. We found that genes involving neuronal synaptic transmission including cholinergic receptor M1 (CHRM1), cell motility, and neuronal differentiation pathways are downregulated while their promoter regions are highly occupied with H3K9me3 in HD. Moreover, we found that repression of CHRM1 gene expression by H3K9me3 impairs Ca2+-dependent neuronal signal transduction in stable cell lines expressing mutant HD protein. Thus, our data indicate that the epigenetic modifications, such as aberrant H3K9me3-dependent heterochromatin plasticity, directly contribute to the pathogenesis of HD.
[Show abstract][Hide abstract] ABSTRACT: Mitochondrial dysfunction and synaptic damage are critical early features of Alzheimer’s disease (AD) associated with amyloid β (Aβ) and τ. We previously reported that the scaffolding protein RanBP9, which is overall increased in AD, simultaneously promotes Aβ generation and focal adhesion disruption by accelerating the endocytosis of APP and β1-integrin, respectively. Moreover, RanBP9 induces neurodegeneration in vitro and in vivo and mediates Aβ-induced neurotoxicity. However, little is known regarding the mechanisms underlying such neurotoxic processes. Here, we show that RanBP9 induces the loss of mitochondrial membrane potential and increase in mitochondrial superoxides associated with decrease in Bcl-2, increase in Bax protein and oligomerization, fragmentation of mitochondria, and cytochrome c release. RanBP9-induced neurotoxic changes are significantly prevented by the mitochondrial fission inhibitor Mdivi-1 and by classical inhibitors of the mitochondrial apoptosis, XIAP, Bcl-2, and Bcl-xl. RanBP9 physically interacts with the tumor suppressor p73 and increases endogenous p73α levels at both transcriptional and post-translational levels;moreover, the knockdown of endogenous p73 by siRNA effectively blocks RanBP9 and Aβ1-42-induced mitochondria-mediated cell death. Conversely, siRNA knockdown of endogenous RanBP9 also suppresses p73-induced apoptosis, suggesting that RanBP9 and p73 have cooperative roles in inducing cell death. Taken together, these finding implicate the RanBP9/p73 complex in mitochondria-mediated apoptosis in addition to its role in enhancing Aβ generation.
Cell Death & Disease 01/2013; · 6.04 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Promyelocytic leukemia (PML) is a major component of macromolecular multiprotein complexes called PML nuclear-bodies (PML-NBs). These PML-NBs recruit numerous proteins including CBP, p53 and HIPK2 in response to DNA damage, senescence and apoptosis. In this study, we investigated the effect of presenilin (PS), the main component of the γ-secretase complex, in PML/p53 expression and downstream consequences during DNA damage-induced cell death using camptothecin (CPT). We found that the loss of PS in PS knockout (KO) MEFs (mouse embryonic fibroblasts) results in severely blunted PML expression and attenuated cell death upon CPT exposure, a phenotype that is fully reversed by re-expression of PS1 in PS KO cells and recapitulated by γ-secretase inhibitors in hPS1 MEFs. Interestingly, the γ-secretase cleavage product, APP intracellular domain (AICD), together with Fe65-induced PML expression at the protein and transcriptional levels in PS KO cells. PML and p53 reciprocally positively regulated each other during CPT-induced DNA damage, both of which were dependent on PS. Finally, elevated levels of PML-NB, PML protein and PML mRNA were detected in the brain tissues from Alzheimer's disease (AD) patients, where γ-secretase activity is essential for pathogenesis. Our data provide for the first time, a critical role of the PS/AICD-PML/p53 pathway in DNA damage-induced apoptosis, and implicate this pathway in AD pathogenesis.Cell Death and Differentiation advance online publication, 11 January 2013; doi:10.1038/cdd.2012.162.
Cell death and differentiation 01/2013; · 8.24 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Amyotrophic lateral sclerosis (ALS) is a fatal neurological disorder characterized by progressive paralysis caused by the degeneration of motor neurons throughout the central nervous system. Mutations of the free radical scavenging enzyme Cu/Zn superoxide dismutase 1 (SOD1) are a cause of familial ALS. In the present study, we demonstrated an age-dependent increase in taurine transporter (TauT) immunoreactivity in spinal cord motor neurons of ALS transgenic mice (mutant SOD1 (G93A)) and a similar increase in TauT in spinal motor neurons of patients with ALS. Chromatin immunoprecipitation analysis verified that heat shock factor 1 (HSF1) preferentially occupies the HSF1 binding element in the promoter of TauT under oxidative stress conditions. Knockdown of HSF1 by small interfering RNA reduced the transcriptional activity of TauT. Using [(3)H] taurine, we confirmed that an elevated expression of TauT directly contributes to increased taurine uptake in ALS motor neurons. In addition, we showed that taurine plays an antioxidant role and may prevent motor neuron loss due to oxidative stress in ALS. Our findings suggest that HSF1-induced TauT expression partially protects motor neurons by compensating for constitutive oxidative stress, which is thought to be a key mechanism contributing to the pathogenesis of ALS. Taken together, our results suggest that TauT is a novel pathological marker for stressed motor neurons in ALS and that modulation of TauT and taurine may slow neuronal degeneration in ALS.
[Show abstract][Hide abstract] ABSTRACT: Alzheimer disease (AD) brains are deficient in brain-derived neurotrophic factor (BDNF), which regulates synaptic plasticity and memory. MicroRNAs (miRNAs) are ∼22-nucleotide small noncoding RNAs that control a variety of physiological and disease processes. Here, we show that miR-206 regulates BDNF and memory function in AD mice.
Expression of miRNAs was analyzed in Tg2576 AD transgenic mice and human AD brain samples. Regulation of BDNF by a selected miRNA was validated by in silico prediction, target gene luciferase assay, and dendritic spine responses in neurons. AM206, a neutralizing inhibitor of miR-206 (antagomir), was injected into the third ventricle of Tg2576 mice, after which memory function, synaptogenesis, neurogenesis, and target gene expression were assessed. For noninvasive delivery, antagomirs were administered intranasally.
The brains of Tg2576 mice and the temporal cortex of human AD brains had increased levels of miR-206. This miRNA targeted BDNF transcripts, and AM206 prevented the detrimental effects of amyloid-β42 on BDNF and dendritic spine degeneration in Tg2576 neurons. Injection of AM206 into the cerebral ventricles of AD mice increased the brain levels of BDNF and improved their memory function. In parallel, AM206 enhanced the hippocampal synaptic density and neurogenesis. Furthermore, intranasally administered AM206 also reached the brain and increased BDNF levels and memory function in AD mice.
Our findings demonstrate a novel miRNA-dependent regulation of BDNF in AD and suggest possible therapeutic approaches, such as noninvasive intranasal delivery of AM206.
Annals of Neurology 08/2012; 72(2):269-77. · 11.19 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Huntington's disease (HD) is an autosomal dominant neurodegenerative disorder of mid-life onset characterized by involuntary movements and progressive cognitive decline caused by a CAG repeat expansion in exon 1 of the Huntingtin (Htt) gene. Neuronal DNA damage is one of the major features of neurodegeneration in HD, but it is not known how it arises or relates to the triplet repeat expansion mutation in the Htt gene. Herein, we found that imbalanced levels of non-phosphorylated and phosphorylated BRCA1 contribute to the DNA damage response in HD. Notably, nuclear foci of γ-H2AX, the molecular component that recruits various DNA damage repair factors to damage sites including BRCA1, were deregulated when DNA was damaged in HD cell lines. BRCA1 specifically interacted with γ-H2AX via the BRCT domain, and this association was reduced in HD. BRCA1 overexpression restored γ-H2AX level in the nucleus of HD cells, while BRCA1 knockdown reduced the spatiotemporal propagation of γ-H2AX foci to the nucleoplasm. The deregulation of BRCA1 correlated with an abnormal nuclear distribution of γ-H2AX in striatal neurons of HD transgenic (R6/2) mice and BRCA1(+/-) mice. Our data indicate that BRCA1 is required for the efficient focal recruitment of γ-H2AX to the sites of neuronal DNA damage. Taken together, our results show that BRCA1 directly modulates the spatiotemporal dynamics of γ-H2AX upon genotoxic stress and serves as a molecular maker for neuronal DNA damage response in HD.
[Show abstract][Hide abstract] ABSTRACT: Aberrant chromatin remodeling is involved in the pathogenesis of Huntington's disease (HD) but the mechanism is not known. Herein, we report that mutant huntingtin (mtHtt) induces the transcription of alpha thalassemia/mental retardation X linked (ATRX), an ATPase/helicase and SWI/SNF-like chromatin remodeling protein via Cdx-2 activation. ATRX expression was elevated in both a cell line model and transgenic model of HD, and Cdx-2 occupancy of the ATRX promoter was increased in HD. Induction of ATRX expanded the size of promyelocytic leukemia nuclear body (PML-NB) and increased trimethylation of H3K9 (H3K9me3) and condensation of pericentromeric heterochromatin, while knockdown of ATRX decreased PML-NB and H3K9me3 levels. Knockdown of ATRX/dXNP improved the hatch rate of fly embryos expressing mtHtt (Q127). ATRX/dXNP overexpression exacerbated eye degeneration of eye-specific mtHtt (Q127) expressing flies. Our findings suggest that transcriptional alteration of ATRX by mtHtt is involved in pericentromeric heterochromatin condensation and contributes to the pathogenesis of HD.
Cell death and differentiation 01/2012; 19(7):1109-16. · 8.24 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Huntington's disease (HD), an inherited neurodegenerative disorder, is caused by an expansion of cytosine-adenine-guanine repeats in the huntingtin gene. The aggregation of mutant huntingtin (mtHTT) and striatal cell loss are representative features to cause uncontrolled movement and cognitive defect in HD. However, underlying mechanism of mtHTT aggregation and cell toxicity remains still elusive. Here, to find new genes modulating mtHTT aggregation, we performed cell-based functional screening using the cDNA expression library and isolated IRE1 gene, one of endoplasmic reticulum (ER) stress sensors. Ectopic expression of IRE1 led to its self-activation and accumulated detergent-resistant mtHTT aggregates. Treatment of neuronal cells with ER stress insults, tunicamycin and thapsigargin, increased mtHTT aggregation via IRE1 activation. The kinase activity of IRE1, but not the endoribonuclease activity, was necessary to stimulate mtHTT aggregation and increased death of neuronal cells, including SH-SY5Y and STHdhQ111/111 huntingtin knock-in striatal cells. Interestingly, ER stress impaired autophagy flux via IRE1-TRAF2 pathway, thus enhancing cellular accumulation of mtHTT. Atg5 deficiency in M5-7 cells increased mtHTT aggregation but blocked ER stress-induced mtHTT aggregation. Further, ER stress markers including p-IRE1 and autophagy markers such as p62 were up-regulated exclusively in the striatal tissues of HD mouse models and in HD patients. Moreover, down-regulation of IRE1 expression rescues the rough-eye phenotype by mtHTT in a HD fly model. These results suggest that IRE1 plays an essential role in ER stress-mediated aggregation of mtHTT via the inhibition of autophagy flux and thus neuronal toxicity of mtHTT aggregates in HD.
Human Molecular Genetics 09/2011; 21(1):101-14. · 7.69 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Huntington's disease (HD) is an autosomal-dominant neurological disorder caused by expanded CAG repeats in the Huntingtin (Htt) gene, but it is not known how this mutation causes neurodegeneration. Herein, we found that dysfunction of upstream binding factor-1 (UBF-1) is linked to reduced ribosomal DNA (rDNA) transcription in HD. We identified that UBF1 acetylation at Lys (K) 352 by CREB binding protein (CBP) is crucial for the transcriptional activity of rDNA. UBF1 mutation (K352A, K352Q, and K352R) decreased rDNA transcriptional activity. Moreover, both CBP-dHAT mutant and knockdown of CBP by siRNA reduced acetylation of UBF1 and resulted in the decreased transcription of rDNA into rRNA. ChIP analysis showed a significant reduction of UBF1 occupancy in the promoter of rDNA in STHdh(Q111) cell line model of HD. These results demonstrate that abnormal activity of UBF1 and its acetylation by CBP are linked to impaired rDNA transcription in HD. This novel mechanism suggests that modulation of UBF-mediated rDNA synthesis by CBP may be a therapeutic target for improving neuronal rDNA transcription in HD.
Cell death and differentiation 05/2011; 18(11):1726-35. · 8.24 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Human norepinephrine (NE) deficiency (or dopamine β-hydroxylase (DBH) deficiency) is a rare congenital disorder of primary
autonomic failure, in which neurotransmitters NE and epinephrine are undetectable. Although potential pathogenic mutations,
such as a common splice donor site mutation (IVS1+2T→C) and various missense mutations, in NE deficiency patients were identified,
molecular mechanisms underlying this disease remain unknown. Here, we show that the IVS1+2T→C mutation results in a non-detectable
level of DBH protein production and that all three missense mutations tested lead to the DBH protein being trapped in the
endoplasmic reticulum (ER). Supporting the view that mutant DBH induces an ER stress response, exogenous expression of mutant
DBH dramatically induced expression of BiP, a master ER chaperone. Furthermore, we found that a pharmacological chaperone,
glycerol, significantly rescued defective trafficking of mutant DBH proteins. Taken together, we propose that NE deficiency
is caused by the combined abnormal processing of DBH mRNA and defective protein trafficking and that this disease could be
treated by a pharmacological chaperone(s).
Journal of Biological Chemistry 03/2011; 286(11):9196-9204. · 4.65 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Human norepinephrine (NE) deficiency (or dopamine β-hydroxylase (DBH) deficiency) is a rare congenital disorder of primary autonomic failure, in which neurotransmitters NE and epinephrine are undetectable. Although potential pathogenic mutations, such as a common splice donor site mutation (IVS1+2T→C) and various missense mutations, in NE deficiency patients were identified, molecular mechanisms underlying this disease remain unknown. Here, we show that the IVS1+2T→C mutation results in a non-detectable level of DBH protein production and that all three missense mutations tested lead to the DBH protein being trapped in the endoplasmic reticulum (ER). Supporting the view that mutant DBH induces an ER stress response, exogenous expression of mutant DBH dramatically induced expression of BiP, a master ER chaperone. Furthermore, we found that a pharmacological chaperone, glycerol, significantly rescued defective trafficking of mutant DBH proteins. Taken together, we propose that NE deficiency is caused by the combined abnormal processing of DBH mRNA and defective protein trafficking and that this disease could be treated by a pharmacological chaperone(s).
Journal of Biological Chemistry 01/2011; 286(11):9196-204. · 4.65 Impact Factor