Regulation of the tyrosine hydroxylase gene promoter by histone deacetylase inhibitors

Transcription Factors Phox2a/2b Upregulate Expression of Noradrenergic and Dopaminergic Phenotypes in Aged Rat Brains

The present study investigated the effects of forced overexpression of Phox2a/2b, two transcription factors, in the locus coeruleus (LC) of aged rats on noradrenergic and dopaminergic phenotypes in brains. Results showed that a significant increase in Phox2a/2b mRNA levels in the LC region was paralleled by marked enhancement in expression of DBH and TH per se. Furthermore, similar increases in TH protein levels were observed in the substantial nigra and striatum, as well as in the hippocampus and frontal cortex. Overexpression of Phox2 genes also significantly increased BrdU-positive cells in the hippocampal dentate gyrus and NE levels in the striatum. Moreover, this manipulation significantly improved the cognition behavior. The in vitro experiments revealed that norepinephrine treatments may increase the transcription of TH gene through the epigenetic action on the TH promoter. The results indicate that Phox2 genes may play an important role in improving the function of the noradrenergic and dopaminergic neurons in aged animals, and regulation of Phox2 gene expression may have therapeutic utility in aging or disorders involving degeneration of noradrenergic neurons.

The influence of TSA and VPA on the in vitro differentiation of bone marrow mesenchymal stem cells into neuronal lineage cells: Gene expression studies

INTRODUCTION

Epigenetic mechanisms regulate the transcription of genes, which can affect the differentiation of MSCs. The aim of the current work is to determine how the histone deacetylase inhibitors TSA and VPA affect the expression of neuronal lineage genes in a culture of rat MSCs (rMSCs).

MATERIALS AND METHODS

We analyzed the expression of early neuron marker gene (Tubb3), mature neuron markers genes (Vacht, Th, Htr2a) and the oligodendrocyte progenitor marker gene (GalC). Moreover, changes in the gene expression after three different periods of exposure to TSA and VPA were investigated for the first time.

RESULTS

After six days of exposition to TSA and VPA, the expression of Tubb3 and GalC decreased, while the expression of Th increased. The highest increase of VAChT expression was observed after three days of TSA and VPA treatment. A decrease in Htr2a gene expression was observed after TSA treatment and an increase was observed after VPA treatment. We also observed that TSA and VPA inhibited cell proliferation and the formation of neurospheres in the rMSCs culture.

DISCUSSION

The central findings of our study are that TSA and VPA affect the expression of neuronal lineage genes in an rMSCs culture. After exposure to TSA or VPA, the expression of early neuronal gene decreases but equally the expression of mature neuron genes increases. After TSA and VPA treatment ER of the oligodendrocyte progenitor marker decreased. TSA and VPA inhibit cell proliferation and the formation of neurospheres in rMSCs culture.

Neuroprotection by Epigenetic Modulation in a Transgenic Model of Multiple System Atrophy

Similar to Parkinson disease, multiple system atrophy (MSA) presents neuropathologically with nigral neuronal loss; however, the hallmark intracellular α-synuclein (αSyn) accumulation in MSA affects typically oligodendrocytes to form glial cytoplasmic inclusions. The underlying pathogenic mechanisms remain unclear. As MSA is predominantly sporadic, epigenetic mechanisms may play a role. We tested the effects of the pan-histone deacetylase inhibitor (HDACi) sodium phenylbutyrate in aged mice overexpressing αSyn under the control of the proteolipid protein promoter (PLP-αSyn) designed to model MSA and characterized by αSyn accumulation in oligodendrocytes and nigral neurodegeneration. HDACi improved motor behavior and survival of nigral neurons in PLP-αSyn mice. Furthermore, HDACi reduced the density of oligodendroglial αSyn aggregates, which correlated with the survival of nigral neurons in PLP-αSyn mice. For the first time, we suggest a role of HDACi in the pathogenesis of MSA-like neurodegeneration and support the future development of selective HDACi for MSA therapy.

Epigenetic regulation contributes to urocortin-enhanced midbrain dopaminergic neuron differentiation

The production of midbrain dopaminergic (mDA) neurons requires precise extrinsic inductive signals and intrinsic transcriptional cascade at a specific time point in development. Urocortin (UCN) is a peptide of the corticotropin-releasing hormone family that mediates various responses to stress. UCN was first cloned from adult rat midbrain. However, the contribution of UCN to the development of mDA neurons is poorly understood. Here, we show that UCN is endogenously expressed in the developing ventral midbrain (VM) and its receptors are exhibited in Nurr1(+) postmitotic mDA precursors and TH(+) neurons, suggesting possible roles in regulating their terminal differentiation. UCN treatment increased DA cell numbers in rat VM precursor cultures by promoting the conversion of Nurr1(+) precursors into DA neurons. Furthermore, neutralization of secreted UCN with anti-UCN antibody resulted in a reduction in the number of DA neurons. UCN induced an abundance of acetylated histone H3 and enhanced late DA regulator Nurr1, Foxa2, and Pitx3 expressions. Using pharmacological and RNA interference approaches, we further demonstrated that histone deacetylase (HDAC) inhibition and late transcriptional factors upregulation contribute to UCN-mediated DA neuron differentiation. Chromatin immunoprecipitation analyses revealed that UCN promoted histone acetylation of chromatin surrounding the TH promoter by directly inhibiting HDAC and releasing of methyl CpG binding protein 2-CoREST-HDAC1 repressor complex from the promoter, ultimately leading to an increase in Nurr1/coactivators-mediated transcription of TH gene. Moreover, UCN treatment in vivo also resulted in increased DA neuron differentiation. These findings suggest that UCN might contribute to regulate late mDA neuron differentiation during VM development.

Nurr1 represses tyrosine hydroxylase expression via SIRT1 in human neural stem cells

Nurr1 is an orphan nuclear receptor best known for its essential role in the development and maintenance of midbrain dopaminergic (DA) neurons. During DA neurogenesis, Nurr1 directly targets human tyrosine hydroxylase (hTH). Here we investigated this targeting to identify the molecular mechanisms by which Nurr1 regulates DA neurogenesis. We previously cloned the hTH promoter and found three consensus elements for Nurr1 binding: NBRE-A, -B, and -C. In the present study, gel retardation and luciferase assays using hTH constructs showed that Nurr1 preferentially bound to NBRE-A, through which it mediated transcriptional activity. Furthermore, Nurr1 displayed dual-function transcriptional activities depending on the cell type. In DA-like SH-SY5Y cells, Nurr1 dose-dependently stimulated hTH-3174 promoter activity by 7- to 11-fold. However, in the human neural stem cell (hNSC) line HB1.F3, Nurr1 strongly repressed transcription from the same promoter. This repression was relieved by mutation of only the NBRE-A element and by nicotinamide [an inhibitor of class III histone deacetylases (HDACs), such as SIRT1], but not by trichostatin A (an inhibitor of class I and II HDACs). SIRT1 was strongly expressed in the nucleus of HB1.F3 cells, while it was localized in the cytoplasm in SH-SY5Y cells. ChIP assays of HB1.F3 cells showed that Nurr1 overexpression significantly increased the SIRT1 occupancy of the NBRE-A hTH promoter region, while low SIRT1 levels were observed in control cells. In contrast, no significant SIRT1 recruitment was observed in SH-SY5Y cells. These results indicate that differential SIRT1 localization may be involved in hTH gene regulation. Overall, our findings suggest that Nurr1 exists in dual transcriptional complexes, including co-repressor complexes that can be remodeled to become co-activators and can fine-tune hTH gene transcription during human DA neurogenesis.

Epigenetic mechanisms in the development and maintenance of dopaminergic neurons

Mesodiencephalic dopaminergic (mdDA) neurons are located in the ventral mesodiencephalon and are involved in psychiatric disorders and severely affected in neurodegenerative diseases such as Parkinson's disease. mdDA neuronal development has received much attention in the last 15 years and many transcription factors involved in mdDA specification have been discovered. More recently however, the impact of epigenetic regulation has come into focus, and it's emerging that the processes of histone modification and DNA methylation form the basis of genetic switches that operate during mdDA development. Here, we review the epigenetic control of mdDA development, maturation and maintenance. As we highlight, epigenetic mechanisms play a pivotal role in all of these processes and the knowledge gathered from studying epigenetics in these contexts may aid our understanding of mdDA-related pathologies.

Sodium butyrate improves locomotor impairment and early mortality in a rotenone-induced Drosophila model of Parkinson's disease

Parkinson's disease (PD) is a neurodegenerative disorder primarily affecting the dopaminergic neurons in the nigrastriatal pathway resulting in debilitating motor impairment in both familial and sporadic cases. Histone deacetylase (HDAC) inhibitors have been recently implicated as a therapeutic candidate because of their ability to correct the disrupted HDAC activity in PD and other neurodegenerative diseases. Sodium butyrate (SB), an HDAC inhibitor, reduces degeneration of dopaminergic neurons in a mutant alpha-synuclein Drosophila transgenic model of familial PD. Chronic exposure to the pesticide rotenone also causes selective degeneration of dopaminergic neurons and causes locomotor impairment and early mortality in a Drosophila model of chemically induced PD. This study investigated the effects of sodium butyrate on locomotor impairment and early mortality in a rotenone-induced PD model. We show that treatment with 10mM SB-supplemented food rescued the rotenone-induced locomotor impairment and early mortality in flies. Additionally, flies with the genetic knockdown of HDAC activity through Sin3A loss-of-function mutation (Sin3A(lof)) were resistant to rotenone-induced locomotor impairment and early mortality. Furthermore, SB-supplemented Sin3A(lof) flies had a modest additive effect for improving locomotor impairment. We also show SB-mediated improvement of rotenone-induced locomotor impairment was associated with elevated dopamine levels in the brain. However, the possibility of SB-mediated protective role through mechanisms independent from dopamine system is also discussed. These findings demonstrate that HDAC inhibitors like SB can ameliorate locomotor impairment in a rotenone-induced PD model.

Epigenetic, transcriptional and posttranscriptional regulation of the tyrosine hydroxylase gene

The activity of tyrosine hydroxylase (TH, EC 1.14.16.2) gene and protein determines the catecholamine level, which, in turn, is crucial for the organism homeostasis. The TH gene expression is regulated by near all possible regulatory mechanisms on epigenetic, transcriptional and posttranscriptional levels. Ongoing molecular characteristic of the TH gene reveals some of the cis and trans elements necessary for its proper expression but most of them especially these responsible for tissue specific expression remain still obscure. This review will focus on some aspects of TH regulation including spatial chromatin organization of the TH locus and TH gene, regulatory elements mediating basal, induced and cell-specific activity, transcriptional elongation, alternative TH RNA processing, and the regulation of TH RNA stability in the cell.

Multiple coregulatory control of tyrosine hydroxylase gene transcription

Despite ubiquitous expression and a high level of metastasis-associated protein 1 (MTA1) coregulator, the physiological role of the MTA1 coactivator remains unknown. We found that MTA1 is a bona fide coactivator and stimulator of tyrosine hydroxylase (TH) transcription in neuronal cells and that MTA1-null mice had lower TH expression in the striatum and substantial nigra. MTA1 physically achieves these functions by interacting directly with DJ1 (Parkinson disease 7) and in turn recruits the DJ1/MTA1/RNA polymerase II complex to the bicoid binding element (BBE) in the TH promoter. Furthermore, we found that the MTA1/DJ1 complex is required for optimum stimulation of the TH expression by paired like homeodomain transcription factor (Pitx3) homeodomain transcription factor and that the MTA1/DJ1 complex is recruited to the TH gene chromatin via the direct interaction of MTA1 with Pitx3. These findings reveal a role for MTA1 as an upstream coactivator of TH and advance the notion of polygenic regulation of a disease-causing gene by coordinated interactions of three regulatory proteins.

A novel function of microRNA let-7d in regulation of galectin-3 expression in attention deficit hyperactivity disorder rat brain

In this study we investigated the locomotor activity and non-selective attention in spontaneously hypertensive rats (SHR) with control Wistar-Kyoto (WKY) rats, which were employed as an attention deficit hyperactivity disorder (ADHD) model. In open-field test and làt maze, SHR rats were found to be much more spontaneously active than WKY rats. As compared with WKY rats, a lower level of galectin-3 was observed in SHR brain prefrontal cortex (PFC), which was the major affected brain area of ADHD. Through miRNA microarray screening, rno-let-7d was noted to be solely upregulated in SHR PFC. Interestingly, rno-let-7d had a binding site at galectin-3 mRNA and was shown to regulate galectin-3 3' untranslated region (UTR) directly. Mutation of galectin-3 3'UTR by one nucleotide of the seed sequence prevented rno-let-7d regulation of the 3' UTR completely. Although rno-let-7d did not directly regulate tyrosine hydroxylase (TH) 3'UTR, the level of galectin-3 was important for cAMP response element binding protein, the major transcript factor for TH gene. Either overexpression or downexpression of galectin-3 could result in modulation of TH expression in both PC12H and PC12L cells. In conclusion, our data suggested a novel function of rno-let-7d in regulation of galectin-3 and in ADHD development. Rno-let-7d, which is increased in the PFC of SHR brain, negatively regulated galectin-3, which is coupled with TH expression regulation.

Ferritin H induction by histone deacetylase inhibitors

Because both iron deficiency and iron excess are deleterious to normal cell function, the intracellular level of iron must be tightly controlled. Ferritin, an iron binding protein, regulates iron balance by storing iron in a bioavailable but nontoxic form. Ferritin protein comprises two subunits: ferritin H, which contains ferroxidase activity, and ferritin L. Here we demonstrate that ferritin H mRNA and protein are induced by histone deacetylase inhibitors (HDAC inhibitors), a promising class of anti-cancer drugs, in cultured human cancer cells. Deletion analysis and EMSA assays reveal that the induction of ferritin H occurs at a transcriptional level via Sp1 and NF-Y binding sites near the transcriptional start site of the human ferritin H promoter. Classically, HDAC inhibitors modulate gene expression by increasing histone acetylation. However, ChIP assays demonstrate that HDAC inhibitors induce ferritin H transcription by increasing NF-Y binding to the ferritin H promoter without changes in histone acetylation. These results identify ferritin H as a new target of HDAC inhibitors, and recruitment of NF-Y as a novel mechanism of action of HDAC inhibitors.

Histone deacetylase inhibitors de-repress tyrosine hydroxylase expression in the olfactory bulb and rostral migratory stream

Most olfactory bulb (OB) interneurons are derived from neural stem cells in the subventricular zone (SVZ) and migrate to the OB via the rostral migratory stream (RMS). Mature dopaminergic interneurons in the OB glomerular layer are readily identified by their synaptic activity-dependent expression of tyrosine hydroxylase (TH). Paradoxically, TH is not expressed in neural progenitors migrating in the RMS, even though ambient GABA and glutamate depolarize these progenitors. In forebrain slice cultures prepared from transgenic mice containing a GFP reporter gene under the control of the Th 9kb upstream regulatory region, treatment with histone deacetylase (HDAC) inhibitors (either sodium butyrate, Trichostatin A or Scriptaid) induced Th-GFP expression specifically in the RMS independently of depolarizing conditions in the culture media. Th-GFP expression in the glomerular layer was also increased in slices treated with Trichostatin A, but this increased expression was dependent on depolarizing concentrations of KCl in the culture media. Th-GFP expression was also induced in the RMS in vivo by intra-peritoneal injections with either sodium butyrate or valproic acid. Quantitative RT-PCR analysis of neurosphere cultures confirmed that HDAC inhibitors de-repressed Th expression in SVZ-derived neural progenitors. Together, these findings suggest that HDAC function is critical for regulating Th expression levels in both neural progenitors and mature OB dopaminergic neurons. However, the differential responses to the combinatorial exposure of HDAC inhibitors and depolarizing culture conditions indicate that Th expression in mature OB neurons and neural progenitors in the RMS are regulated by distinct HDAC-mediated mechanisms.

Human embryonic stem cells which express hrGFP in the undifferentiated state and during dopaminergic differentiation

PURPOSE

Human embryonic stem cells (hESCs) which express a reporter gene consistently during all phases of differentiation would be valuable for basic research on cell transplantation. In this study, we describe karyotypically-abnormal variant hESCs, BGO1V2-EFG, which express hrGFP driven by the EF1 promoter.

METHODS

BGO1V2-EFG cells were analyzed by using immunocytochemistry, single cell-based confocal image, and in vitro differentiation, including dopaminergic differentiation.

RESULTS

Undifferentiated BGO1V2-EFG cells expressed pluripotent ESC markers and retained the ability to differentiate into cell types of all three germ layers. BGO1V2-EFG cells maintained stable and robust hrGFP expression in vitro in the undifferentiated state and during differentiation. The EF1 promoter retained activity during dopaminergic differentiation, as 76% of tyrosine hydroxlase (TH)-positive cells co-expressed hrGFP by confocal analysis. Treated with sodium butyrate (0.02 mM to 2.0 mM), an inhibitor of histone deacetylase (HDAC), during differentiation did not affect hrGFP expression, although TH expression was reduced by higher concentrations of sodium butyrate.

CONCLUSION

BGO1V2-EFG cells maintain stable and robust hrGFP expression in the undifferentiated state and during neural differentiation. Especially, the EF1 promoter was effective in driving hrGFP expression during dopaminergic differentiation. BGO1V2-EFG cells may be useful for transplantation studies in Parkinson disease animal models.

SIRT1 regulates tyrosine hydroxylase expression and differentiation of neuroblastoma cells via FOXO3a

To examine the function of SIRT1 in neuronal differentiation, we employed all-trans retinoic acid (ATRA)-induced differentiation of neuroblastoma cells. Nicotinamide inhibited neurite outgrowth and tyrosine hydroxylase (TH) expression. Inhibition of PARP or histone deacetylase did not inhibit TH expression, showing the effect to be SIRT1 specific. Expression of FOXO3a and its target proteins were increased during the differentiation and reduced by nicotinamide. FOXO3a deacetylation was increased by ATRA and blocked by nicotinamide. SIRT1 and FOXO3a siRNA inhibited ATRA-induced up-regulation of TH and differentiation. Taken together, these results indicate that SIRT1 is involved in ATRA-induced differentiation of neuroblastoma cells via FOXO3a.

Histone deacetylase 5 represses the transcription of cyclin D3

Histone deacetylases (HDACs) modulate the transcription of a subset of genes by various means. HDAC5 is a class II HDAC whose subcellular location is signal-dependent. At present, its known gene targets are few in number. Here we identify a new HDAC5 target: the gene encoding the cell cycle-regulatory protein cyclin D3. When overexpressed in Balb/c-3T3 cells or mouse embryo fibroblasts, HDAC5 substantially reduced the activity of the cyclin D3 promoter and the abundance of endogenous cyclin D3 protein. Conversely, conditions that blocked HDAC5 function increased cyclin D3 expression: treatment of cells with the class I/II HDAC inhibitor trichostatin A (TSA), depletion of HDAC5 from cells by RNA interference, and cytoplasmic sequestration of HDAC5 by co-expression of catalytically active calcium/calmodulin-dependent protein kinase. HDAC5 interacted with the cyclin D3 promoter in vivo, and the HDAC5-responsive element was within 118 base pairs upstream of the transcription start site. Mutation of the Sp1 site and the cyclic AMP response element within this region did not affect the responsiveness of the cyclin D3 promoter to HDAC5 or TSA.

Semi-quantitative analysis of alpha-synuclein in subcellular pools of rat brain neurons: an immunogold electron microscopic study using a C-terminal specific monoclonal antibody

Alpha-synuclein (alpha-Syn) is a brain-enriched protein of 140 amino acids. Despite of strong evidence showing the implication of the protein in the pathogenesis of several neurodegenerative diseases, its physiological function remains poorly understood. To study the physiological function of alpha-Syn, a depiction of its precise subcellular localization is necessary. Although alpha-Syn expression in the brain has been extensively investigated using several different antibodies, its precise subcellular localization in neurons remains elusive. In this study, immunogold electron microscopy with a newly produced 3D5 monoclonal antibody recognizing the C-terminal 115-121 amino acids of alpha-Syn was used to examine its subcellular localization in rat brain neurons. In addition, the relative amount of the protein in different subcellular pools of the neurons in several brain regions was evaluated and compared. The results showed that alpha-Syn-positive gold particles were unevenly distributed in axons, presynaptic terminals, cytoplasm and nucleus in the neuron, with the density of gold particles being greater in presynaptic terminals and nucleus than in other subcellular pools. In the cytoplasmic region, relatively dense gold particles were seen in some mitochondria. In the same subcellular pools, the density of gold particles was varied among the neurons from different brain regions. Although the cortical neurons showed much higher density of gold particles in the presynaptic terminals and nuclei than in striatal, hippocampal and substantia nigral neurons, the density of gold particles in their mitochondria was much lower compared with the mitochondria of striatal, hippocampal and substantia nigral neurons. The relative high level of mitochondrial alpha-Syn in hippocampus, striatum and substantia nigral neurons may have special pathophysiological significance, which deserves further investigation.

Dibutyryl cyclic AMP induces differentiation of human neuroblastoma SH-SY5Y cells into a noradrenergic phenotype

Dibutyryl cyclic AMP (dbcAMP) and retinoic acid (RA) have been demonstrated to be the inducers of morphological differentiation in SH-SY5Y cells, a human catecholaminergic neuroblastoma cell line. However, it remains unclear whether morphologically differentiated SH-SY5Y cells by these compounds acquire catecholaminergic properties. We focused on the alteration of tyrosine hydroxylase (TH) expression and intracellular content of noradrenaline (NA) as the indicators of functional differentiation. Three days treatment with dbcAMP (1mM) and RA (10microM) induced morphological changes and an increase of TH-positive cells using immunocytochemical analysis in SH-SY5Y cells. The percentage of TH-expressing cells in dbcAMP (1mM) treatment was larger than that in RA (10microM) treatment. In addition, dbcAMP increased intracellular NA content, whereas RA did not. The dbcAMP-induced increase in TH-expressing cells is partially inhibited by KT5720, a protein kinase A (PKA) inhibitor. We also investigated the effect of butyrate on SH-SY5Y cells, because dbcAMP is enzymatically degraded by intracellular esterase, thereby resulting in the formation of butyrate. Butyrate induced the increase of NA content at lower concentrations than dbcAMP, although the increase in TH-expressing cells by butyrate was smaller than that by dbcAMP. The dbcAMP (1mM)- and butyrate (0.3mM)-induced increase in NA content was completely suppressed by alpha-methyl-p-tyrosine (1mM), an inhibitor of TH. These results suggest that dbcAMP induces differentiation into the noradrenergic phenotype through both PKA activation and butyrate.

Sodium butyrate modifies the stabilizing complexes of tyrosine hydroxylase mRNA

Multiple mechanisms regulate the expression of the tyrosine hydroxylase (Th) gene, which encodes the rate-limiting enzyme in the biosynthesis of catecholamines. Sodium butyrate (SOB), a physiological histone deacetylase (HDAC) inhibitor, was reported to stimulate the Th gene promoter activity in reporter gene assays. However, the expression of the endogenous Th gene in PC12 cells was reported to be either stimulated or inhibited by SOB. Here, we report that SOB and other HDAC inhibitors drastically (up to 90%) and reversibly decrease the level of TH mRNA in PC12 cells. We also show that SOB does not influence the transcription initiation rate of the Th gene but perturbs the formation of protein-RNA complexes at the 3'UTR of the gene. Our results suggest that SOB inhibits the expression of the Th gene by destabilizing TH mRNAs.

Transcription and epigenetic profile of the promoter, first exon and first intron of the human tyrosine hydroxylase gene

The transcriptional and chromatin profile of the promoter, first exon and first intron of the human TH gene were analyzed in human neuroblastoma BE(2)-C-16 and human renal carcinoma 293FT cell lines. The latter is a cell culture system that is not permissive for TH gene expression, whereas the former has a 50% cell fraction that tests positive for TH. The engineering of a 6.3 kb recombinant human TH promoter revealed the presence of repressors of transcription between positions (-6,244/-194). The addition of a 1.2 kb fragment of the first intron of the human TH gene (+730/+1,653) enhanced transcriptional activity of the recombinant promoter. However, both constructs were not specific for TH-positive BE(2)-C-16 cells. Chromatin immunoprecipitation (Chip) analysis was carried out on BE(2)-C-16 and 293FT cells to probe sequences of promoter, first exon and first intron of the human TH gene from position (-448/+1,204). The presence of nucleosomes was observed approximately from position (-20/+473) in both cell lines. Chip analysis was then conducted to determine the acetylation of various lysine residues of H3 and H4 in both cell lines. All analyzed lysine residues of H3 and H4 were acetylated in BE(2)-C-16 cells, whereas 293FT cells tested positive for acetylation only in the external lysine residues of the histone tail. Our data are compatible with an active TH gene expression in a 50% cell fraction of BE(2)-C-16 cells. Further analysis of epigenetic programming might lead to the identification of the factors that determine TH gene expression specifically in dopaminergic neurons.

Differential regulation of the tyrosine hydroxylase and enkephalin neuropeptide transmitter genes in rat PC12 cells by short chain fatty acids: Concentration-dependent effects on transcription and RNA stability

At physiologic concentrations, butyrate regulates the expression of individual genes involving at least three mechanisms: (i) through induction of cis- and trans-acting butyrate-dependent transcription factors for selected genes, (ii) by inhibition of histone deacetylation and attendant chromatin remodeling and (iii) by affecting turnover of mRNAs. Our previous work illustrated gradual accumulation of mRNA for tyrosine hydroxylase (TH), the rate-limiting enzyme in catecholamine biosynthesis and the neuropeptide transmitter proenkephalin (ppEnk) in butyrate-differentiated PC12 cells (Nankova, B.B., Chua, J., Mishra, R., Kobasiuk, C.D., La Gamma, E.F. 2003. Nicotinic induction of preproenkephalin and tyrosine hydroxylase gene expression in butyrate-differentiated rat PC12 cells: a model for adaptation to gut-derived environmental signals. Pediatr. Res. 53, 113-118.). However, at higher physiological concentrations (6 mM), TH mRNA levels are significantly reduced while ppEnk mRNA transcripts remained elevated. These differential effects suggest suppression of endogenous TH gene transcription, targeted degradation of TH mRNA or both. By using nuclear run-on assays, we found that transcription increased for both endogenous TH and ppEnk genes, even at time points and concentrations when reduced steady-state levels of TH mRNA were observed. The reduction in TH mRNA was blocked by cycloheximide consistent with a protein-dependent mechanism. We also observed a dose-dependent accumulation of luciferase reporter molecules driven by TH promoter in transient transfection experiments, data that provide additional support for separate regulatory pathways. Significantly, butyrate-dependent decreases in TH mRNA were also reflected in a reduction in TH protein. Our results suggest a novel mode of regulation for TH by butyrate operating via both transcriptional and post-transcriptional mechanisms. We speculate that, depending on plasma concentrations of butyrate, this naturally occurring signaling molecule can function as an in vivo molecular switch to alter levels of TH mRNA, its protein and thus the biosynthesis of endogenous catecholamines.

Effects of histone deacetylation inhibition on neuronal differentiation of embryonic mouse neural stem cells

Neural stem cells (NSCs) are multipotent cells that have the capacity for self-renewal and for differentiation into the major cell types of the nervous system, i.e. neurons, astrocytes and oligodendrocytes. The molecular mechanisms regulating gene transcription resulting in NSC differentiation and cell lineage specification are slowly being unraveled. An important mechanism in transcriptional regulation is modulation of chromatin by histone acetylation and deacetylation, allowing or blocking the access of transcriptional factors to DNA sequences. The precise involvement of histone acetyltransferases and histone deacetylases (HDACs) in the differentiation of NSCs into mature functional neurons is still to be revealed. In this in vitro study we have investigated the effects of the HDAC inhibitor trichostatin A (TSA) on the differentiation pattern of embryonic mouse NSCs during culture in a minimal, serum-free medium, lacking any induction or growth factor. We demonstrated that under these basic conditions TSA treatment increased neuronal differentiation of the NSCs and decreased astrocyte differentiation. Most strikingly, electrophysiological recordings revealed that in our minimal culture system only TSA-treated NSC-derived neurons developed normal electrophysiological membrane properties characteristic for functional, i.e. excitable and firing, neurons. Furthermore, TSA-treated NSC-derived neurons were characterized by an increased elongation and arborization of the dendrites. Our study shows that chromatin structure modulation by HDACs plays an important role in the transcriptional regulation of the neuronal differentiation of embryonic NSCs particularly as far as the development of functional properties are concerned. Manipulation of HDAC activity may be an important tool to generate specific neuronal populations from NSCs for transplantation purposes.

Histone deacetylase inhibitors and transforming growth factor-beta induce 15-hydroxyprostaglandin dehydrogenase expression in human lung adenocarcinoma cells

Histone deacetylase (HDAC) inhibitors have been actively exploited as potential anticancer agents. To identify gene targets of HDAC inhibitors, we found that HDAC inhibitors such as sodium butyrate, scriptaid, apicidin and oxamflatin induced the expression of 15-hydroxyprostaglandin dehydrogenase (15-PGDH), a potential cyclooxygenase-2 (COX-2) antagonist and tumor suppressor, in a time and concentration dependent manner in A549 and H1435 lung adenocarcinoma cells. Detailed analyses indicated that HDAC inhibitors activated the 15-PGDH promoter-luciferase reporter construct in transfected A549 cells. A representative HDAC inhibitor, scriptaid, and its negative structural analog control, nullscript, were further evaluated at the chromatin level. Scriptaid but not nullscript induced a significant accumulation of acetylated histones H3 and H4 which were associated with the 15-PGDH promoter as determined by chromatin immunoprecipitation assay. Transforming growth factor-beta1 (TGF-beta1) also induced the expression of 15-PGDH in a time and concentration dependent manner in A549 and H1435 cells. Induction of 15-PGDH expression by TGF-beta1 was synergistically stimulated by the addition of Wnt3A which was inactive by itself. However, combination of TGF-beta and an HDAC inhibitor, scriptaid, only resulted in an additive effect. Together, our results indicate that 15-PGDH is one of the target genes that HDAC inhibitors and TGF-beta may induce to exhibit tumor suppressive effects.

Short chain fatty acids regulate tyrosine hydroxylase gene expression through a cAMP-dependent signaling pathway

Multiple intracellular and extracellular regulatory factors affect transcription of the tyrosine hydroxylase (TH) gene encoding the rate-limiting enzyme in the biosynthesis of the neurotransmitters dopamine, norepinephrine and epinephrine. Short chain fatty acids like butyrate are known to alter TH gene expression, but the mechanism of action is unknown. In this report, transient transfection assays identified the proximal TH promoter to contain sufficient genetic information to confer butyrate responsiveness to a reporter gene. Deletion studies and gel shift analyses revealed that the promoter region spanning the cAMP response element is an absolute requirement for transcriptional activation by butyrate. The branched short chain fatty acid valproate is used for seizure control in humans. Significantly, it has a similar aliphatic structure to butyrate, and it was found to have similar effects on TH in PC12 cells. Site-directed mutagenesis indicated that the effects of both fatty acids were mediated through the canonical CRE. Butyrate treatment also resulted in CREB phosphorylation without changing CREB protein levels. The increased phosphorylation of CREB correlated with accumulation of TH mRNA. The adenylate cyclase inhibitor dideoxyadenosine blocked both CREB phosphorylation and accumulation of TH mRNA. The data are consistent with the conclusion that butyrate induces post-translational modifications of pre-existing CREB molecules in a cAMP/PKA-dependent manner to alter TH transcription. These results support the role of butyrate as a novel exogenous regulatory factor in TH gene expression. Our data delineate a molecular mechanism through which diet-derived environmental signals (e.g. butyrate) can modulate catecholaminergic systems by affecting TH gene transcription.

Role of histone deacetylation in cell-specific expression of endothelial nitric-oxide synthase

Histone acetylation plays an important role in chromatin remodeling and gene expression. The molecular mechanisms involved in cell-specific expression of endothelial nitric-oxide synthase (eNOS) are not fully understood. In this study we investigated whether histone deacetylation was involved in repression of eNOS expression in non-endothelial cells. Induction of eNOS expression by histone deacetylase (HDAC) inhibitors trichostatin A (TSA) and sodium butyrate was observed in all four different types of non-endothelial cells examined. Chromatin immunoprecipitation assays showed that the induction of eNOS expression by TSA was accompanied by a remarkable increase of acetylation of histone H3 associated with the eNOS 5'-flanking region in the non-endothelial cells. Moreover, DNA methylation-mediated repression of eNOS promoter activity was partially reversed by TSA treatment, and combined treatment of TSA and 5-aza-2'-deoxycytidine (AzadC) synergistically induced eNOS expression in non-endothelial cells. The proximal Sp1 site is critical for basal activity of eNOS promoter. The induction of eNOS by inhibition of HDACs in non-endothelial cells, however, appeared not mediated by the changes in Sp1 DNA binding activity. We further showed that Sp1 bound to the endogenous eNOS promoter and associated with HDAC1 in non-endothelial HeLa cells. Combined TSA and AzadC treatment increased Sp1 binding to the endogenous eNOS promoter but decreased the association between HDAC1 and Sp1 in HeLa cells. Our data suggest that HDAC1 plays a critical role in eNOS repression, and the proximal Sp1 site may serve a key target for HDCA1-mediated eNOS repression in non-endothelial cells.

Role of Ca2+ in induction of neurotransmitter-related gene expression by butyrate

We examined the effect of butyrate on neurotransmitter-related gene expression and calcium homeostasis in PC12 cells. Pretreatment with Ca2+ chelators (EGTA or BAPTA-AM) attenuated the butyrate-triggered accumulation of TH and ppEnk mRNA indicating that Ca2+ plays a role in butyrate-induced regulation of neuronal genes. Butyrate alone did not alter intracellular Ca2+ levels as determined by Fura-PE3 fluorescence; however, pretreatment with butyrate (18-24 h) reduced the first Ca2+ peak and prevented the second sustained rise in [Ca2+]i as induced by nicotine or ryanodine. In contrast, butyrate had no effect on Ca2+ transients when added shortly before or during nicotine or ryanodine stimulation. These results suggest that chronic butyrate exposure can modulate cell responses by affecting intracellular Ca2+ signaling.

Activation of the growth-differentiation factor 11 gene by the histone deacetylase (HDAC) inhibitor trichostatin A and repression by HDAC3

Histone deacetylase (HDAC) inhibitors inhibit the proliferation of transformed cells in vitro, restrain tumor growth in animals, and are currently being actively exploited as potential anticancer agents. To identify gene targets of the HDAC inhibitor trichostatin A (TSA), we compared the gene expression profiles of BALB/c-3T3 cells treated with or without TSA. Our results show that TSA up-regulates the expression of the gene encoding growth-differentiation factor 11 (Gdf11), a transforming growth factor beta family member that inhibits cell proliferation. Detailed analyses indicated that TSA activates the gdf11 promoter through a conserved CCAAT box element. A comprehensive survey of human HDACs revealed that HDAC3 is necessary and sufficient for the repression of gdf11 promoter activity. Chromatin immunoprecipitation assays showed that treatment of cells with TSA or silencing of HDAC3 expression by small interfering RNA causes the hyperacetylation of Lys-9 in histone H3 on the gdf11 promoter. Together, our results provide a new model in which HDAC inhibitors reverse abnormal cell growth by inactivation of HDAC3, which in turn leads to the derepression of gdf11 expression.