Class-IIa Histone Deacetylase Inhibition Promotes the Growth of Neural Processes and Protects Them Against Neurotoxic Insult

Design and radiosynthesis of class-IIa HDAC inhibitor with high molar activity via repositioning the 18F-radiolabel

The design and radiosynthesis of [18F]NT376, a high potency inhibitor of class-IIa histone deacetylases (HDAC) is reported. We utilized a three-step radiochemical approach that led to the radiosynthesis of [18F]NT376 in a good radiochemical yield, (17.0 ± 3%, decay corrected), high radiochemical purity (> 97%) and relatively high molar activity of 185.0 GBq/µmol (> 5.0 Ci/µmol). The repositioning of the 18F-radiolabel into a phenyl ring (18F-Fluoro-aryl) of the class-IIa HDAC inhibitor avoided the shortcomings of the direct radiolabeling of the 5-trifluoromethyl-1,2,4-oxadiazole moiety that was reported by us previously and was associated with low molar activity (0.74-1.51 GBq/µmol, 20-41 mCi/µmol). This radiochemical approach could find a wider application for radiolabeling similar molecules with good radiochemical yield and high molar activity.

Role of histone modifications in neurogenesis and neurodegenerative disease development

Progressive neuronal dysfunction and death are key features of neurodegenerative diseases; therefore, promoting neurogenesis in neurodegenerative diseases is crucial. With advancements in proteomics and high-throughput sequencing technology, it has been demonstrated that histone post-transcriptional modifications (PTMs) are often altered during neurogenesis when the brain is affected by disease or external stimuli and that the degree of histone modification is closely associated with the development of neurodegenerative diseases. This review aimed to show the regulatory role of histone modifications in neurogenesis and neurodegenerative diseases by discussing the changing patterns and functional significance of histone modifications, including histone methylation, acetylation, ubiquitination, phosphorylation, and lactylation. Finally, we explored the control of neurogenesis and the development of neurodegenerative diseases by artificially modulating histone modifications.

Unlocking the epigenetic symphony: histone acetylation's impact on neurobehavioral change in neurodegenerative disorders

Recent genomics and epigenetic advances have empowered the exploration of DNA/RNA methylation and histone modifications crucial for gene expression in response to stress, aging and disease. Interest in understanding neuronal plasticity's epigenetic mechanisms, influencing brain rewiring amid development, aging and neurodegenerative disorders, continues to grow. Histone acetylation dysregulation, a commonality in diverse brain disorders, has become a therapeutic focus. Histone acetyltransferases and histone deacetylases have emerged as promising targets for neurodegenerative disorder treatment. This review delves into histone acetylation regulation, potential therapies and future perspectives for disorders like Alzheimer's, Parkinson's and Huntington's. Exploring genetic-environmental interplay through models and studies reveals molecular changes, behavioral insights and early intervention possibilities targeting the epigenome in at-risk individuals.

Targeting epigenetic modifications in Parkinson's disease therapy

Parkinson's disease (PD) is a multifactorial disease due to a complex interplay between genetic and epigenetic factors. Recent efforts shed new light on the epigenetic mechanisms involved in regulating pathways related to the development of PD, including DNA methylation, posttranslational modifications of histones, and the presence of microRNA (miRNA or miR). Epigenetic regulators are potential therapeutic targets for neurodegenerative disorders. In the review, we aim to summarize mechanisms of epigenetic regulation in PD, and describe how the DNA methyltransferases, histone deacetylases, and histone acetyltransferases that mediate the key processes of PD are attractive therapeutic targets. We discuss the use of inhibitors and/or activators of these regulators in PD models or patients, and how these small molecule epigenetic modulators elicit neuroprotective effects. Further more, given the importance of miRNAs in PD, their contributions to the underlying mechanisms of PD will be discussed as well, together with miRNA-based therapies.

The Bidirectional Interplay of α-Synuclein with Lipids in the Central Nervous System and Its Implications for the Pathogenesis of Parkinson's Disease

The alteration and aggregation of alpha-synuclein (α-syn) play a crucial role in neurodegenerative diseases collectively termed as synucleinopathies, including Parkinson's disease (PD). The bidirectional interaction of α-syn with lipids and biomembranes impacts not only α-syn aggregation but also lipid homeostasis. Indeed, lipid composition and metabolism are severely perturbed in PD. One explanation for lipid-associated alterations may involve structural changes in α-syn, caused, for example, by missense mutations in the lipid-binding region of α-syn as well as post-translational modifications such as phosphorylation, acetylation, nitration, ubiquitination, truncation, glycosylation, and glycation. Notably, different strategies targeting the α-syn-lipid interaction have been identified and are able to reduce α-syn pathology. These approaches include the modulation of post-translational modifications aiming to reduce the aggregation of α-syn and modify its binding properties to lipid membranes. Furthermore, targeting enzymes involved in various steps of lipid metabolism and exploring the neuroprotective potential of lipids themselves have emerged as novel therapeutic approaches. Taken together, this review focuses on the bidirectional crosstalk of α-syn and lipids and how alterations of this interaction affect PD and thereby open a window for therapeutic interventions.

Histone Deacetylase 4 Inhibition Reduces Rotenone-Induced Alpha-Synuclein Accumulation via Autophagy in SH-SY5Y Cells

(1) Background: Parkinson's disease (PD) is the most common movement disorder. Imbalanced protein homeostasis and α-syn aggregation are involved in PD pathogenesis. Autophagy is related to the occurrence and development of PD and can be regulated by histone deacetylases (HDACs). Various inhibitors of HDACs exert neuroprotective effects within in vitro and in vivo models of PD. HDAC4, a class Ⅱ HDAC, colocalizes with α-synuclein and ubiquitin in Lewy bodies and also accumulates in the nuclei of dopaminergic neurons in PD models. (2) Methods: In the present study, the gene expression profile of HDACs from two previously reported datasets in the GEO database was analyzed, and the RNA levels of HDAC4 in brain tissues were compared between PD patients and healthy controls. In vitro, SH-SY5Y cells transfected with HDAC4 shRNA or pretreated with mc1568 were treated with 1 μM of rotenone for 24 h. Then, the levels of α-syn, LC3, and p62 were detected using Western blot analysis and immunofluorescent staining, and cell viabilities were detected using Cell Counting Kit-8 (CCK-8). (3) Results: HDAC4 was highly expressed in PD substantia nigra and locus coeruleus. Mc1568, an inhibitor of HDAC4, decreased α-synuclein levels in rotenone-treated SH-SY5Y cells in a concentration-dependent manner and activated autophagy, which was impaired by rotenone. The knockdown of HDAC4 reversed rotenone-induced α-syn accumulation in SH-SY5Y cells and protected the neurons by enhancing autophagy. (4) Conclusions: HDAC4 is a potential therapeutic target for PD. The inhibition of HDAC4 by mc1568 or a gene block can reduce α-syn levels by regulating the autophagy process in PD. Mc1568 is a promising therapeutic agent for PD and other disorders related to α-syn accumulation.

Histone Deacetylases as Epigenetic Targets for Treating Parkinson's Disease

Parkinson's disease (PD) is a chronic progressive neurodegenerative disease that is increasingly becoming a global threat to the health and life of the elderly worldwide. Although there are some drugs clinically available for treating PD, these treatments can only alleviate the symptoms of PD patients but cannot completely cure the disease. Therefore, exploring other potential mechanisms to develop more effective treatments that can modify the course of PD is still highly desirable. Over the last two decades, histone deacetylases, as an important group of epigenetic targets, have attracted much attention in drug discovery. This review focused on the current knowledge about histone deacetylases involved in PD pathophysiology and their inhibitors used in PD studies. Further perspectives related to small molecules that can inhibit or degrade histone deacetylases to treat PD were also discussed.

Peripheral administration of the Class-IIa HDAC inhibitor MC1568 partially protects against nigrostriatal neurodegeneration in the striatal 6-OHDA rat model of Parkinson's disease

Parkinson's disease (PD) is a neurodegenerative disorder characterised by nigrostriatal dopaminergic (DA) neurodegeneration. There is a critical need for neuroprotective therapies, particularly those that do not require direct intracranial administration. Small molecule inhibitors of histone deacetylases (HDIs) are neuroprotective in in vitro and in vivo models of PD, however it is unknown whether Class IIa-specific HDIs are neuroprotective when administered peripherally. Here we show that 6-hydroxydopamine (6-OHDA) treatment induces protein kinase C (PKC)-dependent nuclear accumulation of the Class IIa histone deacetylase (HDAC)5 in SH-SY5Y cells and cultured DA neurons in vitro. Treatment of these cultures with the Class IIa-specific HDI, MC1568, partially protected against 6-OHDA-induced cell death. In the intrastriatal 6-OHDA lesion in vivo rat model of PD, MC1568 treatment (0.5 mg/kg i.p.) for 7 days reduced forelimb akinesia and partially protected DA neurons in the substantia nigra and their striatal terminals from 6-OHDA-induced neurodegeneration. MC1568 treatment prevented 6-OHDA-induced increases in microglial activation in the striatum and substantia nigra. Furthermore, MC1568 treatment decreased 6-OHDA-induced increases in nuclear HDAC5 in nigral DA neurons. These data suggest that peripheral administration of Class IIa-specific HDIs may be a potential therapy for neuroprotective in PD.

Chromatin Alterations in Neurological Disorders and Strategies of (Epi)Genome Rescue

Neurological disorders (NDs) comprise a heterogeneous group of conditions that affect the function of the nervous system. Often incurable, NDs have profound and detrimental consequences on the affected individuals' lives. NDs have complex etiologies but commonly feature altered gene expression and dysfunctions of the essential chromatin-modifying factors. Hence, compounds that target DNA and histone modification pathways, the so-called epidrugs, constitute promising tools to treat NDs. Yet, targeting the entire epigenome might reveal insufficient to modify a chosen gene expression or even unnecessary and detrimental to the patients' health. New technologies hold a promise to expand the clinical toolkit in the fight against NDs. (Epi)genome engineering using designer nucleases, including CRISPR-Cas9 and TALENs, can potentially help restore the correct gene expression patterns by targeting a defined gene or pathway, both genetically and epigenetically, with minimal off-target activity. Here, we review the implication of epigenetic machinery in NDs. We outline syndromes caused by mutations in chromatin-modifying enzymes and discuss the functional consequences of mutations in regulatory DNA in NDs. We review the approaches that allow modifying the (epi)genome, including tools based on TALENs and CRISPR-Cas9 technologies, and we highlight how these new strategies could potentially change clinical practices in the treatment of NDs.

LMK235, a small molecule inhibitor of HDAC4/5, protects dopaminergic neurons against neurotoxin- and α-synuclein-induced degeneration in cellular models of Parkinson's disease

Epigenetic modifications in neurodegenerative disease are under investigation for their roles in disease progression. Alterations in acetylation rates of certain Parkinson's disease (PD)-linked genes have been associated with the pathological progression of this disorder. In light of this, and given the lack of disease-modifying therapies for PD, HDAC inhibitors (HDIs) are under consideration as potential pharmacological agents. The neuroprotective effects of pan-HDACs and some class-specific inhibitors have been tested in in vivo and in vitro models of PD, with varying outcomes. Here we used gene co-expression analysis to identify HDACs that are associated with human dopaminergic (DA) neuron development. We identified HDAC3, HDAC5, HDAC6 and HDAC9 as being highly correlated with the DA markers, SLC6A3 and NR4A2. RT-qPCR revealed that mRNA expression of these HDACs exhibited similar temporal profiles during embryonic mouse midbrain DA (mDA) neuron development. We tested the neuroprotective potential of a number of class-specific small molecule HDIs on human SH-SY5Y cells, using neurite growth as a phenotypic readout of neurotrophic action. Neither the class I-specific HDIs, RGFP109 and RGFP966, nor the HDAC6 inhibitor ACY1215, had significant effects on neurite outgrowth. However, the class IIa HDI, LMK235 (a HDAC4/5 inhibitor), significantly increased histone acetylation and neurite outgrowth. We found that LMK235 increased BMP-Smad-dependent transcription in SH-SY5Y cells and that this was required for its neurite growth-promoting effects on SH-SY5Y cells and on DA neurons in primary cultures of embryonic day (E) 14 rat ventral mesencephalon (VM). These effects were also seen in SH-SY5Y cells transfected with HDAC5 siRNA. Furthermore, LMK235 treatment exerted neuroprotective effects against degeneration induced by the DA neurotoxin 1-methyl-4-phenylpyridinium (MPP⁺), in both SH-SY5Y cells and cultured DA neurons. Treatment with LMK235 was also neuroprotective against axonal degeneration induced by overexpression of wild-type (WT) or A53T mutant α-synuclein in both SH-SY5Y cells and primary cultures of DA neurons. In summary, these data show the neuroprotective potential of the class IIa HDI, LMK235, in cell models of relevance to PD.

Novel late-stage radiosynthesis of 5-[18F]-trifluoromethyl-1,2,4-oxadiazole (TFMO) containing molecules for PET imaging

Small molecules that contain the (TFMO) moiety were reported to specifically inhibit the class-IIa histone deacetylases (HDACs), an important target in cancer and the disorders of the central nervous system (CNS). However, radiolabeling methods to incorporate the [18F]fluoride into the TFMO moiety are lacking. Herein, we report a novel late-stage incorporation of [18F]fluoride into the TFMO moiety in a single radiochemical step. In this approach the bromodifluoromethyl-1,2,4-oxadiazole was converted into [18F]TFMO via no-carrier-added bromine-[18F]fluoride exchange in a single step, thus producing the PET tracers with acceptable radiochemical yield (3–5%), high radiochemical purity (> 98%) and moderate molar activity of 0.33–0.49 GBq/umol (8.9–13.4 mCi/umol). We validated the utility of the novel radiochemical design by the radiosynthesis of [18F]TMP195, which is a known TFMO containing potent inhibitor of class-IIa HDACs.

Acetylation of NDUFV1 induced by a newly synthesized HDAC6 inhibitor HGC rescues dopaminergic neuron loss in Parkinson models

It has been shown that histone deacetylase (HDAC) inhibitors hold considerable therapeutic potentials for treating neurodegeneration-related diseases including Parkinson disease (PD). Here, we synthesized an HDAC inhibitor named as HGC and examined its neuroprotective roles in PD models. Our results showed that HGC protects dopaminergic neurons from 1-methyl-4-phenylpyridinium (MPP⁺)-induced insults. Furthermore, in 1-methyl-4-phenyl-1, 2, 3, 6-tetrahydropyridine (MPTP)-induced PD model mice, HGC application rectifies behavioral defects, improves tyrosine hydroxylase-positive neurons in the midbrain, and maintains mitochondrial integrity and functions. Mechanistically, mass spectrometry data revealed that HGC stimulates acetylation modification at lysine 28 of NDUFV1. Inhibition of HDAC6 by HGC is responsible for this acetylation modification. Functional tests showed that, as well as HGC, NDUFV1 exhibits beneficial roles against MPP⁺ injuries. Moreover, knockdown of NDUFV1 abolishes the neuroprotective roles of HGC. Taken together, our data indicate that HGC has a great therapeutic potential for treating PD and NDUFV1 might be a target for developing drugs against PD.

•

HGC is a potent inhibitor for HDACs, especially HDAC1/6

•

HGC protects dopaminergic neurons and alleviates PD symptoms in PD models

•

HDAC6/NDUFV1 axis is responsible for transducing its anti-PD activities

•

HGC holds great therapeutic potentials for treating PD

HDAC4 and HDAC5 form a complex with DREAM that epigenetically down-regulates NCX3 gene and its pharmacological inhibition reduces neuronal stroke damage

The histone deacetylases (HDACs)-dependent mechanisms regulating gene transcription of the Na⁺/Ca⁺ exchanger isoform 3 (ncx3) after stroke are still unknown. Overexpression or knocking-down of HDAC4/HDAC5 down-regulates or increases, respectively, NCX3 mRNA and protein. Likewise, MC1568 (class IIa HDACs inhibitor), but not MS-275 (class I HDACs inhibitor) increased NCX3 promoter activity, gene and protein expression. Furthermore, HDAC4 and HDAC5 physically interacted with the transcription factor downstream regulatory element antagonist modulator (DREAM). As MC1568, DREAM knocking-down prevented HDAC4 and HDAC5 recruitment to the ncx3 promoter. Importantly, DREAM, HDAC4, and HDAC5 recruitment to the ncx3 gene was increased in the temporoparietal cortex of rats subjected to transient middle cerebral artery occlusion (tMCAO), with a consequent histone-deacetylation of ncx3 promoter. Conversely, the tMCAO-induced NCX3 reduction was prevented by intracerebroventricular injection of siDREAM, siHDAC4, and siHDAC5. Notably, MC1568 prevented oxygen glucose deprivation plus reoxygenation and tMCAO-induced neuronal damage, whereas its neuroprotective effect was abolished by ncx3 knockdown. Collectively, we found that: (1) DREAM/HDAC4/HDAC5 complex epigenetically down-regulates ncx3 gene transcription after stroke, and (2) pharmacological inhibition of class IIa HDACs reduces stroke-induced neurodetrimental effects.

JUP/plakoglobin is regulated by salt-inducible kinase 2, and is required for insulin-induced signalling and glucose uptake in adipocytes

BACKGROUND

Salt-inducible kinase 2 (SIK2) is abundant in adipocytes, but downregulated in adipose tissue from individuals with obesity and insulin resistance. Moreover, SIK isoforms are required for normal insulin signalling and glucose uptake in adipocytes, but the underlying molecular mechanisms are currently not known. The adherens junction protein JUP, also termed plakoglobin or γ-catenin, has recently been reported to promote insulin signalling in muscle cells.

OBJECTIVE

The objective of this study was to analyse if JUP is required for insulin signalling in adipocytes and the underlying molecular mechanisms of this regulation.

METHODS

Co-expression of SIK2 and JUP mRNA levels in adipose tissue from a human cohort was analysed. siRNA silencing and/or pharmacological inhibition of SIK2, JUP, class IIa HDACs and CRTC2 was employed in 3T3-L1- and primary rat adipocytes. JUP protein expression was analysed by western blot and mRNA levels by qPCR. Insulin signalling was evaluated by western blot as levels of phosphorylated PKB/Akt and AS160, and by monitoring the uptake of ³H-2-deoxyglucose.

RESULTS

mRNA expression of SIK2 correlated with that of JUP in human adipose tissue. SIK2 inhibition or silencing resulted in downregulation of JUP mRNA and protein expression in 3T3-L1- and in primary rat adipocytes. Moreover, JUP silencing reduced the expression of PKB and the downstream substrate AS160, and consequently attenuated activity in the insulin signalling pathway, including insulin-induced glucose uptake. The known SIK2 substrates CRTC2 and class IIa HDACs were found to play a role in the SIK-mediated regulation of JUP expression.

CONCLUSIONS

These findings identify JUP as a novel player in the regulation of insulin sensitivity in adipocytes, and suggest that changes in JUP expression could contribute to the effect of SIK2 on insulin signalling in these cells.

The class II histone deacetylases as therapeutic targets for Parkinson's disease

Parkinson’s disease (PD) is a progressive neurodegenerative disorder characterised by specific motor impairments. The neuropathological hallmarks of PD include progressive degeneration of midbrain dopaminergic neurons, and loss of their axonal projections to the striatum. Additionally, there is progressive accumulation and spread of intracellular aggregates of α-synuclein. Although dopamine-replacement pharmacotherapy can treat PD symptoms in the short-term, there is a critical need for the development of disease-modifying therapies based on an understanding of the underlying disease mechanisms. One such mechanism is histone acetylation, which is a common epigenetic modification that alters gene transcription. A number of studies have described alterations in histone acetylation in the brains of PD patients. Moreover, α-synuclein accumulation has been linked to alterations in histone acetylation and pharmacological strategies aimed at modulating histone acetylation are under investigation as novel approaches to disease modification in PD. Currently, such strategies are focused predominantly on pan-inhibition of histone deacetylase (HDAC) enzymes. Inhibition of specific individual HDAC enzymes is a more targeted strategy that may allow for future clinical translation. However, the most appropriate class of HDACs that should be targeted for neuroprotection in PD is still unclear. Recent work has shed new light on the role of class-II HDACs in dopaminergic degeneration. For this reason, here we describe the regulation of histone acetylation, outline the evidence for alterations in histone acetylation in the PD brain, and focus on the roles of class II HDACs and the potential of class-II HDAC inhibition as a therapeutic approach for neuroprotection in PD.

Gene Co-expression Analysis Identifies Histone Deacetylase 5 and 9 Expression in Midbrain Dopamine Neurons and as Regulators of Neurite Growth via Bone Morphogenetic Protein Signaling

Parkinson's disease is characterized by the intracellular accumulation of α-synuclein which has been linked to early dopaminergic axonal degeneration. Identifying druggable targets that can promote axonal growth in cells overexpressing α-synuclein is important in order to develop strategies for early intervention. Class-IIa histone deacetylases (HDACs) have previously emerged as druggable targets, however, it is not known which specific class-IIa HDACs should be targeted to promote neurite growth in dopaminergic neurons. To provide insight into this, we used gene co-expression analysis to identify which, if any, of the class-IIa HDACs had a positive correlation with markers of dopaminergic neurons in the human substantia nigra. This revealed that two histone deacetylases, HDAC5 and HDAC9, are co-expressed with TH, GIRK2 and ALDH1A1 in the human SN. We further found that HDAC5 and HDAC9 are expressed in dopaminergic neurons in the adult mouse substantia nigra. We show that siRNAs targeting HDAC5 or HDAC9 can promote neurite growth in SH-SY5Y cells, and that their pharmacological inhibition, using the drug MC1568, promoted neurite growth in cultured rat dopaminergic neurons. Moreover, MC1568 treatment upregulated the expression of the neurotrophic factor, BMP2, and its downstream transcription factor, SMAD1. In addition, MC1568 or siRNAs targeting HDAC5 or HDAC9 led to an increase in Smad-dependent GFP expression in a reporter assay. Furthermore, MC1568 treatment of cultured rat dopaminergic neurons increased cellular levels of phosphorylated Smad1, which was prevented by the BMP receptor inhibitor, dorsomorphin. Dorsomorphin treatment prevented the neurite growth-promoting effects of siRNAs targeting HDAC5, as did overexpression of dominant-negative Smad4 or of the inhibitory Smad7, demonstrating a functional link to BMP signaling. Supplementation with BMP2 prevented the neurite growth-inhibitory effects of nuclear-restricted HDAC5. Finally, we report that siRNAs targeting HDAC5 or HDAC9 promoted neurite growth in cells overexpressing wild-type or A53T-α-synuclein and that MC1568 protected cultured rat dopaminergic neurons against the neurotoxin, MPP+. These findings establish HDAC5 and HDAC9 as novel regulators of BMP-Smad signaling, that additionally may be therapeutic targets worthy of further exploration in iPSC-derived human DA neurons and in vivo models of Parkinson's disease.

Histone deacetylase inhibitors: Isoform selectivity improves survival in a hemorrhagic shock model

BACKGROUND

Hemorrhage is a leading preventable cause of death. Nonselective histone deacetylase inhibitors (HDACIs), such as valproic acid (VPA), have been shown to improve outcomes in hemorrhagic shock (HS). The HDACs can be divided into four functional classes (I, IIa/IIb, III, and IV). Classes I, IIa/IIb, and III have previously been implicated in the pathophysiology of HS. This study aimed to determine which HDAC class, or classes, are responsible for the survival benefit observed with nonselective HDACIs.

METHODS

Survival study: Sprague-Dawley rats were subjected to lethal HS (50% hemorrhage) and randomized to the following groups (n = 8): (1) no treatment, (2) normal saline vehicle, (3) cyclodextrin vehicle, (4) MS275 (class I HDACI), (5) VPA (class I/IIa HDACI), (6) MC1568 (class IIa HDACI), (7) ACY1083 (class IIb HDACI), and (8) EX527 (class III HDACI). Survival was monitored for 24 hours. Mechanistic study: Sprague-Dawley rats were subjected to sublethal HS (40% hemorrhage) and randomized to the same groups (n = 3), excluding EX527, based on results of the survival study. Tissues were harvested at 3 hours posttreatment, and expression of phosphorylated-AKT, β-catenin, acetylated histones H3 and H4, and acetylated α-tubulin were analyzed in myocardial tissue.

RESULTS

Survival rate was 12.5% in the untreated group, and did not improve with vehicle or MS275 treatment. EX527 improved survival to 50%, although this did not achieve statistical significance (p = 0.082). However, treatment with VPA, MC1568, and ACY1083 improved survival rates to 87.5%, 75%, and 75%, respectively (p < 0.05). The VPA-induced acetylation of both histones H3 and H4, while MC1568 and ACY1083 increased acetylation of histone H4. ACY1083 also induced acetylation of α-tubulin. All treatment groups, except MS275, increased phosphorylated-AKT, and β-catenin.

CONCLUSION

Inhibition of HDAC classes IIa or IIb, but not class I, activates prosurvival pathways, which may be responsible for the improved outcomes in rodent models of HS.

Prior alcohol use enhances vulnerability to compulsive cocaine self-administration by promoting degradation of HDAC4 and HDAC5

Addiction to cocaine is commonly preceded by experiences with legal or decriminalized drugs, such as alcohol, nicotine, and marijuana. The biological mechanisms by which these gateway drugs contribute to cocaine addiction are only beginning to be understood. We report that in the rat, prior alcohol consumption results in enhanced addiction-like behavior to cocaine, including continued cocaine use despite aversive consequences. Conversely, prior cocaine use has no effect on alcohol preference. Long-term, but not short-term, alcohol consumption promotes proteasome-mediated degradation of the nuclear histone deacetylases HDAC4 and HDAC5 in the nucleus accumbens, a brain region critical for reward-based memory. Decreased nuclear HDAC activity results in global H3 acetylation, creating a permissive environment for cocaine-induced gene expression. We also find that selective degradation of HDAC4 and HDAC5, facilitated by the class II-specific HDAC inhibitor MC1568, enhances compulsive cocaine self-administration. These results parallel our previously reported findings that the gateway drug nicotine enhances the behavioral effects of cocaine via HDAC inhibition. Together, our findings suggest a shared mechanism of action for the gateway drugs alcohol and nicotine, and reveal a novel mechanism by which environmental factors may alter the epigenetic landscape of the reward system to increase vulnerability to cocaine addiction.

Targeting bone morphogenetic protein signalling in midbrain dopaminergic neurons as a therapeutic approach in Parkinson's disease

Parkinson's disease (PD) is the second most common neurodegenerative disease, characterized by the degeneration of midbrain dopaminergic (mDA) neurons and their axons, and aggregation of α-synuclein, which leads to motor and late-stage cognitive impairments. As the motor symptoms of PD are caused by the degeneration of a specific population of mDA neurons, PD lends itself to neurotrophic factor therapy. The goal of this therapy is to apply a neurotrophic factor that can slow down, halt or even reverse the progressive degeneration of mDA neurons. While the best known neurotrophic factors are members of the glial cell line-derived neurotrophic factor (GDNF) family, their lack of clinical efficacy to date means that it is important to continue to study other neurotrophic factors. Bone morphogenetic proteins (BMPs) are naturally secreted proteins that play critical roles during nervous system development and in the adult brain. In this review, we provide an overview of the BMP ligands, BMP receptors (BMPRs) and their intracellular signalling effectors, the Smad proteins. We review the available evidence that BMP-Smad signalling pathways play an endogenous role in mDA neuronal survival in vivo, before outlining how exogenous application of BMPs exerts potent effects on mDA neuron survival and axon growth in vitro and in vivo. We discuss the molecular mechanisms that mediate these effects, before highlighting the potential of targeting the downstream effectors of BMP-Smad signalling as a novel neuroprotective approach to slow or stop the degeneration of mDA neurons in PD.

Class-Specific Histone Deacetylase Inhibitors Promote 11-Beta Hydroxysteroid Dehydrogenase Type 2 Expression in JEG-3 Cells

Exposure to maternal cortisol plays a crucial role in fetal organogenesis. However, fetal overexposure to cortisol has been linked to a range of short- and long-term adverse outcomes. Normally, this is prevented by the expression of an enzyme in the placenta called 11-beta hydroxysteroid dehydrogenase type 2 (11β-HSD2) which converts active cortisol to its inactive metabolite cortisone. Placental 11β-HSD2 is known to be reduced in a number of adverse pregnancy complications, possibly through an epigenetic mechanism. As a result, a number of pan-HDAC inhibitors have been examined for their ability to promote 11β-HSD2 expression. However, it is not known if the effects of pan-HDAC inhibition are a general phenomenon or if the effects are dependent upon a specific class of HDACs. Here, we examined the ability of pan- and class-specific HDAC inhibitors to regulate 11β-HSD2 expression in JEG3 cells. We find that pan-, class I, or class IIa HDAC inhibition promoted 11β-HSD2 expression and prevented cortisol or interleukin-1β-induced decrease in its expression. These results demonstrate that targeting a specific class of HDACs can promote 11β-HSD2 expression in JEG3 cells. This adds to the growing body of evidence suggesting that HDACs may be crucial in maintaining normal fetal development.

Endocytosis contributes to BMP2-induced Smad signalling and neuronal growth

Bone morphogenetic protein 2 (BMP2) is a neurotrophic factor which induces the growth of midbrain dopaminergic (DA) neurons in vitro and in vivo, and its neurotrophic effects have been shown to be dependent on activation of BMP receptors (BMPRs) and Smad 1/5/8 signalling. However, the precise intracellular cascades that regulate BMP2-BMPR-Smad-signalling-induced neurite growth remain unknown. Endocytosis has been shown to regulate Smad 1/5/8 signalling and differentiation induced by BMPs. However, these studies were carried out in non-neural cells. Indeed, there are scant reports regarding the role of endocytosis in BMP-Smad signalling in neurons. To address this, and to further characterise the mechanisms regulating the neurotrophic effects of BMP2, the present study examined the role of dynamin-dependent endocytosis in BMP2-induced Smad signalling and neurite growth in the SH-SY5Y neuronal cell line. The activation, temporal kinetics and magnitude of Smad 1/5/8 signalling induced by BMP2 were significantly attenuated by dynasore-mediated inhibition of endocytosis in SH-SY5Y cells. Furthermore, BMP2-induced increases in neurite length and neurite branching in SH-SY5Y cells were significantly reduced following inhibition of dynamin-dependent endocytosis using dynasore. This study demonstrates that BMP2-induced Smad signalling and neurite growth is regulated by dynamin-dependent endocytosis in a model of human midbrain dopaminergic neurons.

Nociceptin/Orphanin FQ Inhibits the Survival and Axon Growth of Midbrain Dopaminergic Neurons Through a p38-MAPK Dependent Mechanism

Nociceptin/orphanin FQ (N/OFQ) is an opioid-like neuropeptide that binds and signals through a G-protein-coupled receptor called the N/OFQ peptide (NOP) receptor. N/OFQ and the NOP receptor are expressed in the midbrain and have been implicated in the pathogenesis of Parkinson's disease (PD). Genetic removal of the N/OFQ precursor partially protects midbrain dopaminergic neurons from 1-methyl-4-phenylpyridine-induced toxicity, suggesting that endogenous N/OFQ may be detrimental to dopaminergic neurons. However, whether N/OFQ directly affects the survival and growth of dopaminergic neurons is unknown. Here, we show that N/OFQ has a detrimental effect on the survival of dopaminergic neurons and the growth of their axons in primary cultures of the E14 rat ventral mesencephalon. N/OFQ potentiates the effects of the neurotoxins 6-hydroxydopamine and 1-methyl-4-phenylpyridinium through p38-MAPK signalling. We also show that like α-synuclein, there is a significant reduction in N/OFQ messenger RNA (mRNA) expression in the midbrain of patients with Parkinson's disease. These results demonstrate for the first time that N/OFQ is detrimental to the survival and growth of dopaminergic neurons and that its expression is altered in the midbrain of patients with Parkinson's disease.

MC1568 Inhibits Thimerosal-Induced Apoptotic Cell Death by Preventing HDAC4 Up-Regulation in Neuronal Cells and in Rat Prefrontal Cortex

Ethylmercury thiosalicylate (thimerosal) is an organic mercury-based compound commonly used as an antimicrobial preservative that has been found to be neurotoxic. In contrast, histone deacetylases (HDACs) inhibition has been found to be neuroprotective against several environmental contaminants, such as polychlorinated biphenyls, di-2-ethylhexyl phthalate, and methylmercury. The aim of this study was to investigate the effect of HDAC inhibition on thimerosal-induced neurotoxicity in neuroblastoma cells and cortical neurons. Interestingly, we found that thimerosal, at 0.5 μM in SH-SY5Y cells and at 1 μM in neurons, caused cell death by activation of apoptosis, which was prevented by the HDAC class IIA inhibitor MC1568 but not the class I inhibitor MS275. Furthermore, thimerosal specifically increased HDAC4 protein expression but not that of HDACs 5, 6, 7, and 9. Western blot analysis revealed that MC1568 prevented thimerosal-induced HDAC4 increase. In addition, both HDAC4 knocking-down and MC1568 inhibited thimerosal-induced cell death in SH-SY5Y cells and cortical neurons. Importantly, intramuscular injection of 12 μg/kg thimerosal on postnatal days 7, 9, 11, and 15 increased HDAC4 levels in the prefrontal cortex (PFC), which decreased histone H4 acetylation in infant male rats, in parallel increased motor activity changes. In addition, coadministration of 40 mg/kg MC1568 (intraperitoneal injection) moderated the HDAC4 increase which reduced histone H4 deacetylation and caspase-3 cleavage in the PFC. Finally, open-field testing showed that thimerosal-induced motor activity changes are reduced by MC1568. These findings indicate that HDAC4 regulates thimerosal-induced cell death in neurons and that treatment with MC1568 prevents thimerosal-induced activation of caspase-3 in the rat PFC.

Protocol for evaluation of neurotrophic strategies in Parkinson's disease-related dopaminergic and sympathetic neurons in vitro

Parkinson’s disease (PD) is a neurodegenerative disease that is characterized by motor and non-motor symptoms which result from the progressive degeneration of nigrostriatal ventral midbrain (VM) dopaminergic (DA) neurons, as well as peripheral sympathetic neurons. PD is incurable, with current therapeutic strategies providing symptomatic relief. Neurotrophic factor (NTF) therapy has the potential to protect degenerating neurons in PD. However, there has been limited success in PD clinical trials due to neurotrophic strategies that are invasive, inefficient in delivering sustained neurotrophic support, do not protect all degenerating neurons and may have a compromised mechanism of action in the PD brain. Therefore, while neurotrophic therapy remains a promising disease-modifying approach for PD, it is important to identify novel neurotrophic strategies that can protect all neurons affected by PD. To address this need, we report an integrated approach for pre-clinical evaluation of potential neurotrophic strategies, e.g., pharmacological agents (e.g., drugs/small molecules), signaling proteins (e.g., morphogens) and/or genetic (gene/mRNA) modifications, in cellular models of the neuronal populations that are affected by PD. Herein, we describe, in detail, an in vitro protocol that allows a step-wise evaluation of the efficacy, and mechanism(s) of action, of novel neurotrophic strategies in VM DA neurons and sympathetic neurons, following an initial evaluation in a human cell line model of these cells, SH-SY5Y cells. The protocol uses the induction of neurite growth as the primary measure of neurotrophic action. Indeed, the neuro-protection/-restoration of PD-affected axons is widely thought to be an appropriate target for effective therapeutic intervention in PD.

The Epigenome as a therapeutic target for Parkinson's disease

Parkinson's disease (PD) is a common, progressive neurodegenerative disease characterised by degeneration of nigrostriatal dopaminergic neurons, aggregation of α-synuclein and motor symptoms. Current dopamine-replacement strategies provide symptomatic relief, however their effectiveness wear off over time and their prolonged use leads to disabling side-effects in PD patients. There is therefore a critical need to develop new drugs and drug targets to protect dopaminergic neurons and their axons from degeneration in PD. Over recent years, there has been robust evidence generated showing that epigenetic dysregulation occurs in PD patients, and that epigenetic modulation is a promising therapeutic approach for PD. This article first discusses the present evidence implicating global, and dopaminergic neuron-specific, alterations in the methylome in PD, and the therapeutic potential of pharmacologically targeting the methylome. It then focuses on another mechanism of epigenetic regulation, histone acetylation, and describes how the histone acetyltransferase (HAT) and histone deacetylase (HDAC) enzymes that mediate this process are attractive therapeutic targets for PD. It discusses the use of activators and/or inhibitors of HDACs and HATs in models of PD, and how these approaches for the selective modulation of histone acetylation elicit neuroprotective effects. Finally, it outlines the potential of employing small molecule epigenetic modulators as neuroprotective therapies for PD, and the future research that will be required to determine and realise this therapeutic potential.

A novel histone deacetylase 1 and 2 isoform-specific inhibitor alleviates experimental Parkinson's disease

With increased histone deacetylase (HDAC) activity and histone hypoacetylation being implicated in neurodegeneration, HDAC inhibitors have been reported to have considerable therapeutic potential. Yet, existing inhibitors lack specificity and may show substantial adverse effect. In this study, we identified a novel HDAC1/2 isoform-specific inhibitor, K560, with protective effects against 1-methyl-4-phenylpyridinium (MPP(+))- and/or 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced neuronal death in both in vitro and in vivo Parkinson's disease model. K560 attenuated cell death induced by MPP(+) in differentiated SH-SY5Y cells through the sustained expression of an antiapoptotic protein, X-linked inhibitor of apoptosis (XIAP). Inhibition of XIAP expression by locked nucleic acid antisense oligonucleotides abolished the protective effect of K560. Inactivation of mitogen-activated protein kinase cascades, reduced p53 phosphorylation, and down-regulation of p53-upregulated modulator of apoptosis on K560 treatment were also observed. Furthermore, pre- and post-oral administration of K560 to mice prevented MPTP-induced loss of dopaminergic neurons in substantia nigra, suggesting that selective inhibition of HDAC1 and HDAC2 by K560 may pave the way to new strategies for Parkinson's disease treatment.

MS-275 inhibits aroclor 1254-induced SH-SY5Y neuronal cell toxicity by preventing the formation of the HDAC3/REST complex on the synapsin-1 promoter

Polychlorinated biphenyl (PCB) exposure has been associated with neurodegenerative diseases, such as Parkinson's disease, amyotrophic lateral sclerosis, and dementia. Neuronal death elicited by the PCB mixture Aroclor 1254 (A1254) has been attributed to an increase in RE-1-silencing transcription factor (REST), which, in turn, correlates with a decrease in the synapsin-1 promoter gene. Although histone deacetylase (HDAC) inhibitors are known to be neuroprotective in several neurologic disorders, the core mechanisms governing this effect are not yet understood. Here, to examine how HDAC class I [N-(2-aminophenyl)-4-[N-(pyridin-3-yl-methoxycarbonyl)aminomethyl]-benzamide (MS-275)] and HDAC class II [3-[5-(3-(3-fluorophenyl)-3-oxopropen-1-yl)-1-methyl-1H-pyrrol-2-yl]-N-hydroxy-2-propenamide (MC-1568)] inhibitors prevent A1254-induced neuronal cell death, we exposed SH-SY5Y neuroblastoma cells to A1254. Exposure to A1254 (30.6 μM) for 24 and 48 hours resulted in a time-dependent cell death. Indeed, after 48 hours, MS-275, but not MC-1568, reverted A1254-induced cell death in a dose-dependent manner. Furthermore, A1254 significantly increased HDAC3, but not HDAC1 or HDAC2. Interestingly, REST physically interacted with HDAC3 after A1254 exposure. Chromatin immunoprecipitation assays revealed that MS-275 reverted the increased levels of HDAC3 binding and decreased acetylation of histone H3 within the synapsin-1 promoter region, thus reverting synapsin-1 mRNA reduction. Moreover, REST knockdown by small interfering RNA (siRNA) prevented HDAC3 from binding to the synapsin-1 promoter. Likewise, HDAC3 siRNA significantly reduced A1254-induced cell toxicity in SH-SY5Y cells and cortical neurons. Hence, this study demonstrates that inhibition of HDAC class I attenuates A1254-induced neuronal cell death by preventing HDAC3 binding and histone deacetylation within the synapsin-1 promoter region.