Transcriptional modulation of monoaminergic neurotransmission genes by the histone deacetylase inhibitor trichostatin A in neuroblastoma cells

Fusobacterium nucleatum determines the expression of amphetamine-induced behavioral responses through an epigenetic phenomenon

Amphetamines (AMPHs) are psychostimulants commonly used for the treatment of neuropsychiatric disorders. They are also misused (AMPH use disorder; AUD), with devastating outcomes. Recent studies have implicated dysbiosis in the pathogenesis of AUD. However, the mechanistic roles of microbes in AUD are unknown. Fusobacterium nucleatum (Fn) is a bacterium that increases in abundance in both rats and humans upon AMPH exposure. Fn releases short-chain fatty acids (SCFAs), bacterial byproducts thought to play a fundamental role in the gut-brain axis as well as the pathogenesis of AUD. We demonstrate that in gnotobiotic Drosophila melanogaster, colonization with Fn or dietary supplementation of the SCFA butyrate, a potent inhibitor of histone deacetylases (HDACs), enhances the psychomotor and rewarding properties of AMPH as well as its ability to promote male sexual motivation. Furthermore, solely HDAC1 RNAi targeted inhibition recapitulates these enhancements, pointing to a specific process underlying this Fn phenomenon. Of note is that the expression of these AMPH behaviors is determined by the increase in extracellular dopamine (DA) levels that result from AMPH-induced reversal of DA transporter (DAT) function, termed non-vesicular DA release (NVDR). The magnitude of AMPH-induced NVDR is dictated, at least in part, by DAT expression levels. Consistent with our behavioral data, we show that Fn, butyrate, and HDAC1 inhibition enhance NVDR by elevating DAT expression. Thus, the participation of Fn in AUD stems from its ability to release butyrate and inhibit HDAC1. These data offer a microbial target and probiotic interventions for AUD treatment.

Aromatic Amino Acid Hydroxylases as Off-Targets of Histone Deacetylase Inhibitors

The aromatic amino acid hydroxylases (AAAHs) phenylalanine hydroxylase, tyrosine hydroxylase, and tryptophan hydroxylases 1 and 2 are structurally related enzymes that contain an active site iron atom and depend on tetrahydrobiopterin (BH4) as cosubstrate. Due to their important roles in synthesis of serotonin, dopamine, noradrenaline, and adrenaline and their involvement in cardiovascular, neurological, and endocrine disorders, AAAHs have been targeted by substrate analogs, iron chelators, and allosteric ligands. Phenylalanine hydroxylase is also off-target of the histone deacetylase (HDAC) inhibitor panobinostat. To systematically explore the binding of HDAC inhibitors to AAAHs, we screened a library of 307 HDAC inhibitors and structural analogs against tryptophan hydroxylase 1 using a fluorescence-based thermal stability assay, followed by activity assays. Selected hits were enzymatically tested against all four purified human AAAHs. Cellular thermal shift assay was performed for phenylalanine hydroxylase. We show that panobinostat and structurally related compounds such as TB57, which similarly to panobinostat also contains a cinnamoyl hydroxamate, bind to human AAAHs and inhibit these enzymes with high selectivity within the class (panobinostat inhibition (IC50): phenylalanine hydroxylase (18 nM) > tyrosine hydroxylase (450 nM) > tryptophan hydroxylase 1 (1960 nM). This study shows that panobinostat and related hydroxamic acid type HDAC inhibitors inhibit all AAAHs at therapeutically relevant concentrations. Our results warrant further investigations of the off-target relevance of HDAC inhibitors intended for clinical use and provide directions for new dual HDAC/AAAH and selective AAAH inhibitors. These findings may also provide a new mechanistic link between regulation of histone modification, AAAH function, and monoaminergic neurotransmission.

Contribution of histone acetylation to the serotonin-mediated long-term synaptic plasticity in terrestrial snails

Serotonin plays a decisive role in long-term synaptic plasticity and long-term memory in mollusks. Previously, we demonstrated that histone acetylation is a regulatory mechanism of long-term memory in terrestrial snail. At the behavioral level, many studies were done in Helix to elucidate the role of histone acetylation and serotonin. However, the impact of histone acetylation on long-term potentiation of synaptic efficiency in electrophysiological studies in Helix has been studied only in one paper. Here we investigated effects of serotonin, histone deacetylases inhibitors sodium butyrate and trichostatin A, and a serotonergic receptor inhibitor methiothepin on long-term potentiation of synaptic responses in vitro. We demonstrated that methiothepin drastically declined the EPSPs amplitudes when long-term potentiation was induced, while co-application either of histone deacetylase inhibitors sodium butyrate or trichostatin A with methiothepin prevented the weakening of potentiation. We showed that single serotonin application in combination with histone deacetylase blockade could mimic the effect of repeated serotonin applications and be enough for sustained long-lasting synaptic changes. The data obtained demonstrated that histone deacetylases blockade ameliorated deficits in synaptic plasticity induced by different paradigms (methiothepin treatment, the weak training protocol with single application of serotonin), suggesting that histone acetylation contributes to the serotonin-mediated synaptic plasticity.

The regulatory role of AP-2β in monoaminergic neurotransmitter systems: insights on its signalling pathway, linked disorders and theragnostic potential

Monoaminergic neurotransmitter systems play a central role in neuronal function and behaviour. Dysregulation of these systems gives rise to neuropsychiatric and neurodegenerative disorders with high prevalence and societal burden, collectively termed monoamine neurotransmitter disorders (MNDs). Despite extensive research, the transcriptional regulation of monoaminergic neurotransmitter systems is not fully explored. Interestingly, certain drugs that act on these systems have been shown to modulate central levels of the transcription factor AP-2 beta (AP-2β, gene: TFAP2Β). AP-2β regulates multiple key genes within these systems and thereby its levels correlate with monoamine neurotransmitters measures; yet, its signalling pathways are not well understood. Moreover, although dysregulation of TFAP2Β has been associated with MNDs, the underlying mechanisms for these associations remain elusive. In this context, this review addresses AP-2β, considering its basic structural aspects, regulation and signalling pathways in the controlling of monoaminergic neurotransmitter systems, and possible mechanisms underpinning associated MNDS. It also underscores the significance of AP-2β as a potential diagnostic biomarker and its potential and limitations as a therapeutic target for specific MNDs as well as possible pharmaceutical interventions for targeting it. In essence, this review emphasizes the role of AP-2β as a key regulator of the monoaminergic neurotransmitter systems and its importance for understanding the pathogenesis and improving the management of MNDs.

Histone deacetylase inhibitor, panobinostat, exerts anti-proliferative effect with partial normalization from aberrant epigenetic states on granulosa cell tumor cell lines

The prognosis of the patients with inoperable or advanced granulosa cell tumors (GCTs) is still poor, and therefore it is important to establish a novel treatment strategy. Here we investigated the in vitro effects of a histone deacetylase inhibitor, panobinostat (PS) on two GCT cell lines (KGN and COV434). GCT cell lines were found to be susceptible to PS treatment and it inhibited cell growth mainly by apoptosis. In cell cycle analysis, PS reduced only the ratio of S phase in GCT cell lines. Combined treatment of PS with a deubiquitinase inhibitor, VLX1570 enhanced the expression of p21, cleaved PARP, cleaved caspase-9, heme oxygenase-1, and the acetylation of histone H4 and α-tubulin, leading to an additive anti-proliferative effect on KGN and COV434. The gene set enrichment analysis revealed that PS treatment suppressed DNA replication- or cell cycle-related gene expression which led to chemotherapeutic cell death and in addition, this treatment induced activation of the gene set of adherens junction towards a normalized direction as well as activation of neuron-related gene sets that might imply unexpected differentiation potential due to epigenetic modification by a HDAC inhibitor in KGN cells. Exposure of KGN and COV434 cells to PS increased the expression of E-cadherin, one of the principal regulators associated with adherens junction in quantitative RT-PCR and immunoblotting analysis. In the present study, we indicate a basis of a novel therapeutic availability of a HDAC inhibitor for the treatment of GCTs and further investigations will be warranted.

Sex- and OGG1-dependent reversal of in utero ethanol-initiated changes in postnatal behaviour by neonatal treatment with the histone deacetylase inhibitor trichostatin A (TSA) in oxoguanine glycosylase 1 (Ogg1) knockout mice

Oxoguanine glycosylase 1 (OGG1) is both a DNA repair enzyme and an epigenetic modifier. We assessed behavioural abnormalities in OGG1-deficient progeny exposed once in utero to a low dose of ethanol (EtOH) and treated postnatally with a global histone deacetylase inhibitor, trichostatin A (TSA). The goal of this study was to determine if neurodevelopmental disorders initiated in the fetal brain by in utero exposure to EtOH could be mitigated by postnatal treatment with TSA. EtOH and TSA alone improved preference for novel location (short-term, 90 min) and novel object (long-term, 24 h) sex- and OGG1-dependently. Combined EtOH/TSA treatment reversed these effects in the short-term novel location test sex- and OGG1-dependently. In females but not males, the incidence of high shredders of nesting material was not altered by either TSA or EtOH alone, but was reduced by combined EtOH/TSA treatment in +/+ progeny. Similar but non-significant effects were observed in Ogg1 -/- females. Accelerated rotarod performance was enhanced by both EtOH and TSA alone in only male Ogg1 +/+ but not -/- progeny, and was not altered by combined EtOH/TSA exposure. The OGG1-dependent effects of EtOH and TSA particularly on novel location and the incidence of high shredders, and the reversal of EtOH effects on these parameters by combined EtOH/TSA treatment, suggests both xenobiotics may alter behaviour via a mechanism involving OGG1 acting as an epigenetic modifier, in addition to repairing DNA damage. These preliminary results suggest that the postnatal use of more selective epigenetic modifying agents may constitute a novel strategy for mitigating some components of ROS-initiated neurodevelopmental disorders.

The correlation between DNA methylation and transcriptional expression of human dopamine transporter in cell lines

This study aims to investigate the relationship between DNA methylation and expression of human dopamine transporter (hDAT). We examined methylation status of hDAT in cells with various hDAT expression levels, including two dopaminergic neural cell lines (SK-N-AS and SH-SY-5Y) and one non-dopaminergic cell line (HEK293) by bisulfite sequencing PCR(BSP). The effects of DNA methyltransferase inhibitor 5-aza-dC or/and histone deacetylase inhibitor (HDACi, sodium butyrate, NaB) on the DNA methylation status and mRNA expression levels of hDAT were examined. The results revealed marked hypomethylation of the two promoter regions (-1214 to -856bp and -48 to 439bp, the first base of exon 1 was taken as +1 bp)of hDAT in SK-N-AS (4.7%±2.0^mC and 3.5%±1.0^mC, respectively) compared with SH-SY-5Y (88.0%±4.4%^mC and 81.1%±8.8%^mC) and HEK293 (90.7%±2.4^mC and 84.4%±8.6% ^mC) cell lines, indicating a cell-specific methylation regulation of hDAT. 5-aza-dC and NaB decreased hypermethylation,while increase hDAT expression in SH-SY-5Y cells and recovered hDAT mRNA expression in HEK293 cells. DNA methylation enabled the cell-specific differential expression of the hDAT gene. hDAT silencing was reversed by the introduction of DNA hypomethylation via 5-aza-dC or/and NaB.

Valproate increases dopamine transporter expression through histone acetylation and enhanced promoter binding of Nurr1

The dopamine transporter (DAT) is the key regulator of dopaminergic transmission and is a target of several xenobiotics, including pesticides and pharmacological agents. Previously, we identified a prominent role for histone deacetylases in the regulation of DAT expression. Here, we utilized a rat dopaminergic cell line (N27) to probe the responsiveness of DAT mRNA expression to inhibitors of histone acetylation. Inhibition of histone deacetylases (HDACs) by valproate, butyrate and Trichostatin A led to a 3-10-fold increase in DAT mRNA expression, a 50% increase in protein levels, which were accompanied by increased H3 acetylation levels. To confirm the mechanism of valproate-mediated increase in DAT mRNA, chromatin immunoprecipitation (ChIP) assays were used and demonstrated a significant increase in enrichment of acetylation of histone 3 on lysines 9 and 14 (H3K9/K14ac) in the DAT promoter. Expression of Nurr1 and Pitx3, key regulators of DAT expression, were increased following valproate treatment and Nurr1 binding was enriched in the DAT promoter. Together, these results indicate that histone acetylation and subsequent enhancement of transcription factor binding are plausible mechanisms for DAT regulation by valproate and, perhaps, by other xenobiotics.

Epigenetic Regulation of Dopamine Transporter mRNA Expression in Human Neuroblastoma Cells

The dopamine transporter (DAT) is a key regulator of dopaminergic neurotransmission. As such, proper regulation of DAT expression is important to maintain homeostasis, and disruption of DAT expression can lead to neurobehavioral dysfunction. Based on genomic features within the promoter of the DAT gene, there is potential for DAT expression to be regulated through epigenetic mechanisms, including DNA methylation and histone acetylation. However, the relative contribution of these mechanisms to DAT expression has not been empirically determined. Using pharmacologic and genetic approaches, we demonstrate that inhibition of DNA methyltransferase (DNMT) activity increased DAT mRNA approximately 1.5-2 fold. This effect was confirmed by siRNA knockdown of DNMT1. Likewise, the histone deacetylase (HDAC) inhibitors valproate and butyrate also increased DAT mRNA expression, but the response was much more robust with expression increasing over tenfold. Genetic knockdown of HDAC1 by siRNA also increased DAT expression, but not to the extent seen with pharmacological inhibition, suggesting additional isoforms of HDAC or other targets may contribute to the observed effect. Together, these data identify the relative contribution of DNMTs and HDACs in regulating expression. These finding may aid in understanding the mechanistic basis for changes in DAT expression in normal and pathophysiological states.

Alcohol-induced serotonergic modulation: the role of histone deacetylases

Previous studies have demonstrated that alcohol use disorders (AUDs) are regulated by multiple mechanisms such as neurotransmitters and enzymes. The neurotransmitter, serotonin (5-hydroxytryptamine, 5-HT) may contribute to alcohol effects and serotonin receptors, including 5-HT3, play an important role in AUDs. Recent studies have also implicated histone deacetylases (HDACs) and acetyltransferases (HATS) in regulation of drug addiction, and HDAC inhibitors (HDACi) have been reported as transcriptional modulators of monoaminergic neurotransmission. Therefore, we hypothesize that HDACs may play a role in ethanol-induced serotonergic modulation. The effects of ethanol on serotonin and 5-HT3, and the role HDACs, HDAC activity and the HDACi, trichostatin A (TSA), play in alcohol-induced serotonergic effects were studied. Human SK-N-MC and neurons, were treated with ethanol (0.05, 0.1 and 0.2%), and/or TSA (50 nM), and 5-HT3 levels were assessed at 24-72 h. Gene expression was evaluated by qRT-PCR and protein by western blot and flow cytometry. Serotonin release was assessed by ELISA and HDAC activity by fluorometric assay. Our results show an increase in 5-HT3 gene after ethanol treatment. Further, ethanol significantly increased HDACs 1 and 3 genes accompanied by an increased in HDAC activity while TSA significantly inhibited HDACs. Studies with TSA show a significant upregulation of ethanol effects on 5-HT3, while surprisingly TSA inhibited ethanol-induced serotonin production. These results suggest that ethanol affects 5-HT3 and serotonin through mechanisms involving HDACs and HATs. In summary, our studies demonstrate some of the novel properties of HDAC inhibitors and contribute to the understanding of the mechanisms involve in alcohol-serotonergic modulation in the CNS.

Different effects of histone deacetylase inhibitors nicotinamide and trichostatin A (TSA) in C17.2 neural stem cells

Histone deacetylase inhibitors are involved in proliferation, apoptosis, cell cycle, mRNA transcription, and protein expression in various cells. However, the molecular mechanism underlying such functions is still not fully clear. In this study, we used C17.2 neural stem cell (NSC) line as a model to evaluate the effects of nicotinamide and trichostatin A (TSA) on cell characteristics. Results show that nicotinamide and TSA greatly inhibit cell growth, lead to cell morphology changes, and effectively induce cell apoptosis in a dose-dependent manner. Western blot analyses confirmed that nicotinamide significantly decreases the expression of bcl-2 and p38. Further insight into the molecular mechanisms shows the suppression of phosphorylation in eukaryotic initiation factor 4E-binding protein 1 (4EBP1) by nicotinamide, whereas, an increased expression of bcl-2 and p38 and phosphorylation of 4EBP1 by TSA. However, both nicotinamide and TSA significantly increase the expression of cytochrome c (cyt c). These results strongly suggest that bcl-2, p38, cyt c, and p-4EBP1 could suppress proliferation and induce apoptosis of C17.2 NSCs mediated by histone deacetylase inhibitors, nicotinamide and TSA, involving different molecular mechanisms.