A novel HDAC6 inhibitor, CKD-504, is effective in treating preclinical models of huntington's disease

Histone Deacetylases in Metabolism: the Known and the Unexplored

Histone deacetylases (HDACs) are enzymes that catalyze the removal of acetyl groups from key lysine residues on histone and nonhistone proteins and thereby regulate gene transcription. They have been implicated in several biological processes in both healthy and pathological settings. This review discusses the role of HDACs in multiple metabolically active tissues and highlights their contribution to the pathogenesis of tissue-specific maladaptation and diseases. We also summarize the current knowledge gaps and potential ways to address them in future studies.

Histone H3 lysine 9 tri-methylation is associated with pterygium

BACKGROUND

Pterygium, abnormal growths of conjunctival tissue onto the cornea, are common ocular surface conditions with a high risk of recurrence after surgery and potential ophthalmic complications. The exact cause of pterygium remains unclear, and the triggers are still unknown. This study aims to investigate the relationship between pterygium and epigenetics to uncover the cause of pterygium and identify biomarkers for its diagnosis.

METHODS

We performed a ChIP-seq assay to compare genome-wide histone modification levels between normal conjunctiva and stage 3 pterygium samples.

RESULTS

In this study, we investigate the epigenetic profiles of patients with pterygium, focusing on histone H3 lysine 4 (H3K4) and lysine 9 (H3K9) trimethylation (me3). While H3K4me3 levels showed no significant genome-wide change, they were significantly altered in genes related to development and ocular diseases. Conversely, H3K9me3 levels were markedly elevated genome-wide, particularly at the promoters of 82 genes involved in developmental pathways. Furthermore, we identify six genes, ANK2, AOAH, CBLN2, CDH8, CNTNAP4, and DPP6, with decreased gene expression correlated with substantially increased H3K9me3, suggesting their potential as biomarkers for pterygium.

CONCLUSION

This study represents the first report linking histone modification to pterygium progression, providing valuable insights into therapeutic strategies and potential drug targets.

The Role of Brain-Derived Neurotrophic Factor as an Essential Mediator in Neuronal Functions and the Therapeutic Potential of Its Mimetics for Neuroprotection in Neurologic and Psychiatric Disorders

Among neurotrophins, including nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), neurotrophin-3 (NT-3), and neurotrophin-4 (NT-4/5), BDNF has been extensively studied for its physiological role in cell survival and synaptic regulation in the central nervous system's (CNS's) neurons. BDNF binds to TrkB (a tyrosine kinase) with high affinity, and the resulting downstream intracellular signaling cascades play crucial roles in determining cell fate, including neuronal differentiation and maturation of the CNS neurons. It has been well demonstrated that the downregulation/dysregulation of the BDNF/TrkB system is implicated in the pathogenesis of neurologic and psychiatric disorders, such as Alzheimer's disease (AD) and depression. Interestingly, the effects of BDNF mimetic compounds including flavonoids, small molecules which can activate TrkB-mediated signaling, have been extensively investigated as potential therapeutic strategies for brain diseases, given that p75NTR, a common neurotrophin receptor, also contributes to cell death under a variety of pathological conditions such as neurodegeneration. Since the downregulation of the BDNF/TrkB system is associated with the pathophysiology of neurodegenerative diseases and psychiatric disorders, understanding how alterations in the BDNF/TrkB system contribute to disease progression could provide valuable insight for the prevention of these brain diseases. The present review shows recent advances in the molecular mechanisms underlying the BDNF/TrkB system in neuronal survival and plasticity, providing critical insights into the potential therapeutic impact of BDNF mimetics in the pathophysiology of brain diseases.

Curcumin prevents neurodegeneration by blocking HDAC6-NLRP3 pathway-dependent neuroinflammation in Parkinson's disease

Curcumin is a hydrophobic polyphenolic compound with potent anti-inflammatory properties. However, whether it can achieve therapeutic effects by alleviating neuroinflammation in patients with Parkinson's disease (PD) and its potential mechanism are still unknown. This study explored the effects of curcumin on neuroinflammation in dopaminergic neurons and deciphered its direct target in the histone deacetylase 6 (HDAC6)-Nucleotide-binding domain, leucine-rich repeat, and pyrin domain-containing protein 3 (NLRP3) pathway, revealing the potential role of curcumin in the treatment of Parkinson's disease. Here, we show that curcumin alleviated the degeneration of neurons in a PD model by mitigating the activation of the NLRP3-mediated inflammatory response both in vivo and in vitro. Furthermore, we discovered that curcumin prevented neuroinflammation by blocking the HDAC6-NLRP3 pathway in a PD model. Moreover, overexpression of HDAC6 could eliminate the effect of curcumin on the neuroinflammatory response mediated by NLRP3. Curcumin and the HDAC6 inhibitor WT161 could alleviate neurodegeneration. In addition, activated HDAC6 directly deacetylated NLRP3 at lysine 84 to maintain its stability, which increased the inflammatory response and promoted neurodegeneration. These findings show that curcumin, a neuroinflammation inhibitor, blocks neurodegeneration via the HDAC6-NLRP3 pathway and represents a potentially practical pharmacological approach for treating neuroinflammation-driven neurodegenerative diseases. For the first time, HDAC6 was shown to directly regulate the acetylation of NLRP3.

Molecular mechanism of HDAC6-mediated pyroptosis in neurological function recovery after cardiopulmonary resuscitation in rats

Brain injury after cardiac arrest (CA) and cardiopulmonary resuscitation (CPR) is the leading cause of neurological dysfunction and death. This study aimed to explore the mechanism of histone deacetylase 6 (HDAC6) in neurofunctional recovery following CA/CPR in rats. A rat model was established by CA/CPR treatment. Adenovirus-packaged sh-HDAC6 was injected into the tail vein. To evaluate the neurofunction of rats, survival time, neurofunctional scores, serum NSE/S100B, and brain water content were measured and Morris water maze test was performed. HDAC6, microRNA (miR)-138-5p, Nod-like receptor protein 3 (NLRP3), and pyroptotic factor levels were determined by real-time quantitative polymerase chain reaction or Western blot assay. HDAC6 and H3K9ac enrichment on miR-138-5p promoter were examined by chromatin immunoprecipitation. miR-138-5p-NLRP3 binding was analyzed by dual-luciferase reporter assay. NLRP3 inflammasome was activated with nigericin sodium salt. After CPR treatment, HDAC6 was highly expressed, while miR-138-5p was downregulated. HDAC6 downregulation improved neurofunction and reduced pyroptosis. HDAC6 enrichment on the miR-138-5p promoter deacetylated H3K9ac, inhibiting miR-138-5p, and promoting NLRP3-mediated pyroptosis. Downregulating miR-138-5p partially reversed the protective effect of HDAC6 inhibition after CPR. In Conclusion, HDAC6 enrichment on miR-138-5p promoter deacetylated H3K9ac, inhibiting miR-138-5p expression and promoting NLRP3-mediated pyroptosis, worsening neurological dysfunction in rats after CPR.

The role of neuron-like cell lines and primary neuron cell models in unraveling the complexity of neurodegenerative diseases: a comprehensive review

Neurodegenerative diseases (NDs) are characterized by the progressive loss of neurons. As to developing effective therapeutic interventions, it is crucial to understand the underlying mechanisms of NDs. Cellular models have become invaluable tools for studying the complex pathogenesis of NDs, offering insights into disease mechanisms, determining potential therapeutic targets, and aiding in drug discovery. This review provides a comprehensive overview of various cellular models used in ND research, focusing on Alzheimer's disease, Parkinson's disease, Huntington's disease, and amyotrophic lateral sclerosis. Cell lines, such as SH-SY5Y and PC12 cells, have emerged as valuable tools due to their ease of use, reproducibility, and scalability. Additionally, co-culture models, involving the growth of distinct cell types like neurons and astrocytes together, are highlighted for simulating brain interactions and microenvironment. While cell lines cannot fully replicate the complexity of the human brain, they provide a scalable method for examining important aspects of neurodegenerative diseases. Advancements in cell line technologies, including the incorporation of patient-specific genetic variants and improved co-culture models, hold promise for enhancing our understanding and expediting the development of effective treatments. Integrating multiple cellular models and advanced technologies offers the potential for significant progress in unraveling the intricacies of these debilitating diseases and improving patient outcomes.

Therapeutic indications for HDAC6 inhibitors in the peripheral and central nervous disorders

INTRODUCTION

Inhibition of the enzymatic function of HDAC6 is currently being explored in clinical trials ranging from peripheral neuropathies to cancers. Advances in selective HDAC6 inhibitor discovery allowed studying highly efficacious brain penetrant and peripheral restrictive compounds for treating PNS and CNS indications.

AREAS COVERED

This review explores the multifactorial role of HDAC6 in cells, the common pathological hallmarks of PNS and CNS disorders, and how HDAC6 modulates these mechanisms. Pharmacological inhibition of HDAC6 and genetic knockout/knockdown studies as a therapeutic strategy in PNS and CNS indications were analyzed. Furthermore, we describe the recent developments in HDAC6 PET tracers and their utility in CNS indications. Finally, we explore the advancements and challenges with HDAC6 inhibitor compounds, such as hydroxamic acid, fluoromethyl oxadiazoles, HDAC6 degraders, and thiol-based inhibitors.

EXPERT OPINION

Based on extensive preclinical evidence, pharmacological inhibition of HDAC6 is a promising approach for treating both PNS and CNS disorders, given its involvement in neurodegeneration and aging-related cellular processes. Despite the progress in the development of selective HDAC6 inhibitors, safety concerns remain regarding their chronic administration in PNS and CNS indications, and the development of novel compound classes and modalities inhibiting HDAC6 function offer a way to mitigate some of these safety concerns.

Design, synthesis and neuroprotective biological evaluation of novel HDAC6 inhibitors incorporating benzothiadiazinyl systems as cap groups

Histone deacetylase 6 (HDAC6), as the key regulatory enzyme, plays an important role in the development of the nervous system. More and more studies indicate that HDAC6 has become a promising therapeutic target for CNS diseases. Herein we designed and synthesized a series of novel HDAC6 inhibitors with benzothiadiazinyl systems as cap groups and evaluated their activity in vitro and in vivo. Among them, compound 3 exhibited superior selective inhibitory activity against HDAC6 (IC50 = 5.1 nM, about 30-fold selectivity over HDAC1). The results of docking showed that compound 3 can interact well with the key amino acid residues of HDAC6. Compound 3 showed lower cytotoxicity (20 μM to SH-SY5Y cells, inhibition rate = 25.75%) and better neuroprotective activity against L-glutamate-induced SH-SY5Y cell injury model in vitro. Meanwhile, compound 3 exhibited weak cardiotoxicity (10 μM hERG inhibition rate = 17.35%) and possess good druggability properties. Especially, compound 3 could significantly reduce cerebral infarction from 49.87% to 32.18%, and similar with butylphthalide in MCAO model, indicating potential clinical application prospects for alleviating ischemic stroke-induced brain infarction.

Chemical Versatility in Catalysis and Inhibition of the Class IIb Histone Deacetylases

The zinc-dependent histone deacetylases (HDACs 1-11) belong to the arginase-deacetylase superfamily of proteins, members of which share a common α/β fold and catalytic metal binding site. While several HDACs play a role in epigenetic regulation by catalyzing acetyllysine hydrolysis in histone proteins, the biological activities of HDACs extend far beyond histones. HDACs also deacetylate nonhistone proteins in the nucleus as well as the cytosol to regulate myriad cellular processes. The substrate pool is even more diverse in that certain HDACs can hydrolyze other covalent modifications. For example, HDAC6 is also a lysine decrotonylase, and HDAC11 is a lysine-fatty acid deacylase. Surprisingly, HDAC10 is not a lysine deacetylase but instead is a polyamine deacetylase. Thus, the HDACs are biologically and chemically versatile catalysts as they regulate the function of diverse protein and nonprotein substrates throughout the cell.Owing to their critical regulatory functions, HDACs serve as prominent targets for drug design. At present, four HDAC inhibitors are FDA-approved for cancer chemotherapy. However, these inhibitors are active against multiple HDAC isozymes, and a lack of selectivity is thought to contribute to undesirable side effects. Current medicinal chemistry campaigns focus on the development of isozyme-selective inhibitors, and many such studies largely focus on HDAC6 and HDAC10. HDAC6 is a target for therapeutic intervention due to its cellular role as a tubulin deacetylase and tau deacetylase, and selective inhibitors are being studied in cancer chemotherapy and the treatment of peripheral neuropathy. Crystal structures of enzyme-inhibitor complexes reveal how various features of inhibitor design, such as zinc-coordinating groups, bifurcated capping groups, and aromatic fluorination patterns, contribute to affinity and isozyme selectivity. The polyamine deacetylase HDAC10 is also an emerging target for cancer chemotherapy. Crystal structures of intact substrates trapped in the HDAC10 active site reveal the molecular basis of strikingly narrow substrate specificity for N8-acetylspermidine hydrolysis. Active site features responsible for substrate specificity have been successfully exploited in the design of potent and selective inhibitors.In this Account, I review the structural chemistry and inhibition of HDACs, highlighting recent X-ray crystallographic and functional studies of HDAC6 and HDAC10 in my laboratory. These studies have yielded fascinating snapshots of catalysis as well as novel chemical transformations involving bound inhibitors. The zinc-bound water molecule in the HDAC active site is the catalytic nucleophile in the deacetylation reaction, but this activated water molecule can also react with inhibitor C═O or C═N groups to yield unanticipated reaction products that bind exceptionally tightly. Versatile active site chemistry unleashes the full inhibitory potential of such compounds, and X-ray crystallography allows us to view this chemistry in action.

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.

Histone deacetylase 6: at the interface of cancer and neurodegeneration

With the recognition in the early 1960s that histones can be post-translationally modified, the list of different post-translational modifications of histones and their biological consequences has continued to expand. In addition, the idea of the 'histone code' hypothesis, later introduced by David Allis and colleagues, further broaden the horizon of chromatin biology. Currently, there is a wealth of knowledge about the transition between the active and the repressive state of chromatin, and modifications of histones remains at the center of chromatin biology. Histone deacetylases (HDACs) in particular are of great importance for the therapeutic success of cancer treatment. Focusing primarily on HDAC6, herein we have briefly highlighted its unique involvement in cancer and also apparently in neurodegeneration.

Deciphering the Mysterious Relationship between the Cross-Pathogenetic Mechanisms of Neurodegenerative and Oncological Diseases

The relationship between oncological pathologies and neurodegenerative disorders is extremely complex and is a topic of concern among a growing number of researchers around the world. In recent years, convincing scientific evidence has accumulated that indicates the contribution of a number of etiological factors and pathophysiological processes to the pathogenesis of these two fundamentally different diseases, thus demonstrating an intriguing relationship between oncology and neurodegeneration. In this review, we establish the general links between three intersecting aspects of oncological pathologies and neurodegenerative disorders, i.e., oxidative stress, epigenetic dysregulation, and metabolic dysfunction, examining each process in detail to establish an unusual epidemiological relationship. We also focus on reviewing the current trends in the research and the clinical application of the most promising chemical structures and therapeutic platforms that have a modulating effect on the above processes. Thus, our comprehensive analysis of the set of molecular determinants that have obvious cross-functional pathways in the pathogenesis of oncological and neurodegenerative diseases can help in the creation of advanced diagnostic tools and in the development of innovative pharmacological strategies.

Brain-Derived Neurotrophic Factor Dysregulation as an Essential Pathological Feature in Huntington's Disease: Mechanisms and Potential Therapeutics

Brain-derived neurotrophic factor (BDNF) is a major neurotrophin whose loss or interruption is well established to have numerous intersections with the pathogenesis of progressive neurological disorders. There is perhaps no greater example of disease pathogenesis resulting from the dysregulation of BDNF signaling than Huntington's disease (HD)-an inherited neurodegenerative disorder characterized by motor, psychiatric, and cognitive impairments associated with basal ganglia dysfunction and the ultimate death of striatal projection neurons. Investigation of the collection of mechanisms leading to BDNF loss in HD highlights this neurotrophin's importance to neuronal viability and calls attention to opportunities for therapeutic interventions. Using electronic database searches of existing and forthcoming research, we constructed a literature review with the overarching goal of exploring the diverse set of molecular events that trigger BDNF dysregulation within HD. We highlighted research that investigated these major mechanisms in preclinical models of HD and connected these studies to those evaluating similar endpoints in human HD subjects. We also included a special focus on the growing body of literature detailing key transcriptomic and epigenetic alterations that affect BDNF abundance in HD. Finally, we offer critical evaluation of proposed neurotrophin-directed therapies and assessed clinical trials seeking to correct BDNF expression in HD individuals.

HDAC6 Deficiency Has Moderate Effects on Behaviors and Parkinson's Disease Pathology in Mice

Histone deacetylase 6 (HDAC6) is involved in the regulation of protein aggregation and neuroinflammation, but its role in Parkinson's disease (PD) remains controversial. In this study, Hdac6^-/- mice were generated by CRISPR-Cas9 technology for exploring the effect of HDAC6 on the pathological progression of PD. We found that male Hdac6^-/- mice exhibit hyperactivity and certain anxiety. In the acute 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced PD mice, though motor injury was slightly alleviated by HDAC6 deficiency, dopamine (DA) depletion in the striatum, the decrease in the number of DA neurons in the substantia nigra (SN) and the reduction in DA neuronal terminals were not affected. In addition, activation of glial cells and the expression of α-synuclein, as well as the levels of apoptosis-related proteins in the nigrostriatal pathway, were not changed in MPTP-injected wild-type and Hdac6^-/- mice. Therefore, HDAC6 deficiency leads to moderate alterations of behaviors and Parkinson's disease pathology in mice.