HDAC6 regulates microtubule stability and clustering of AChRs at neuromuscular junctions

Arf6 GTPase deficiency leads to porcine oocyte quality decline during aging

Arf6 is a member of ADP-ribosylation factor (Arf) family, which is widely implicated in the regulation of multiple physiological processes including endocytic recycling, cytoskeletal organization, and membrane trafficking during mitosis. In this study, we investigated the potential relationship between Arf6 and aging-related oocyte quality, and its roles on organelle rearrangement and cytoskeleton dynamics in porcine oocytes. Arf6 expressed in porcine oocytes throughout meiotic maturation, and it decreased in aged oocytes. Disruption of Arf6 led to the failure of cumulus expansion and polar body extrusion. Further analysis indicated that Arf6 modulated ac-tubulin for meiotic spindle organization and microtubule stability. Besides, Arf6 regulated cofilin phosphorylation and fascin for actin assembly, which further affected spindle migration, indicating the roles of Arf6 on cytoskeleton dynamics. Moreover, the lack of Arf6 activity caused the dysfunction of Golgi and ER for protein synthesis and signal transduction. Mitochondrial dysfunction was also observed in Arf6-deficient porcine oocytes, which was supported by the increased ROS level and abnormal membrane potential. In conclusion, our results reported that insufficient Arf6 was related to aging-induced oocyte quality decline through spindle organization, actin assembly, and organelle rearrangement in porcine oocytes.

Setdb1 protects genome integrity in murine muscle stem cells to allow for regenerative myogenesis and inflammation

The histone H3 lysine 9 methyltransferase SETDB1 controls transcriptional repression to direct stem cell fate. Here, we show that Setdb1 expression by adult muscle stem cells (MuSCs) is required for skeletal muscle regeneration. We find that SETDB1 represses the expression of endogenous retroviruses (ERVs) in MuSCs. ERV de-repression in Setdb1-null MuSCs prevents their amplification following exit from quiescence and promotes cell death. Multi-omics profiling shows that chromatin decompaction at ERV loci activates the DNA-sensing cGAS-STING pathway, entailing cytokine expression by Setdb1-null MuSCs. This is followed by aberrant infiltration of inflammatory cells, including pathological macrophages. The ensuing histiocytosis is accompanied by myofiber necrosis, which, in addition to progressive MuSCs depletion, completely abolishes tissue repair. In contrast, loss of Setdb1 in fibro-adipogenic progenitors (FAPs) does not impact immune cells. In conclusion, genome maintenance by SETDB1 in an adult somatic stem cell is necessary for both its regenerative potential and adequate reparative inflammation.

Oxyresveratrol-β-cyclodextrin mitigates streptozotocin-induced Alzheimer's model cognitive impairment, histone deacetylase activity in rats: in silico & in vivo studies

Alzheimer's disease (AD) is associated with cognitive deficits and epigenetic deacetylation that can be modulated by natural products. The role of natural oxyresveratrol-β-cyclodextrin (ORV) on cognition and histone deacetylase activity in AD is unclear. Herein, in-silico docking and molecular dynamics simulation analysis determined that oxyresveratrol potentially targets histone deacetylase-2 (HDAC2). We therefore evaluated the in vivo ameliorative effect of ORV against cognitive deficit, cerebral and hippocampal expression of HDAC in experimental AD rats. Intracerebroventricular injection of STZ (3 mg/kg) induced experimental AD and the rats were treated with low dose (200 mg/kg), high dose (400 mg/kg) of ORV and donepezil (10 mg/kg) for 21 days. The STZ-induced AD caused cognitive and behavioural deficits demonstrated by considerable increases in acetylcholinesterase activity and escape latency compared to sham control. The levels of malondialdehyde (MDA) and HDAC activity were significantly increased in AD disease group comparison to the sham. Interestingly, the ORV reversed the cognitive-behavioural deficit and prominently reduced the MDA and HDAC levels comparable to the effect of the standard drug, donepezil. The findings suggest anti-AD role of ORV via antioxidant effect and inhibition of HDAC in the hippocampal and frontal cortical area of rats for AD.

Involvement of protein L-isoaspartyl methyltransferase in the physiopathology of neurodegenerative diseases: Possible substrates associated with synaptic function

Synaptic dysfunction is a typical pathophysiologic change in neurodegenerative diseases (NDs) such as Alzheimer's disease (AD), Parkinson's disease (PD), Hintington's disease (HD) and amyotrophic lateral sclerosis (ALS), which involves protein post-translational modifications (PTMs) including L-isoaspartate (L-isoAsp) formed by isomerization of aspartate or deamidation of asparagine. The formation of L-isoAsp could be repaired by protein L-isoaspartyl methyltransferase (PIMT). Some synaptic proteins have been identified as PIMT potential substrates and play an essential role in ensuring synaptic function. In this review, we discuss the role of certain synaptic proteins as PIMT substrates in neurodegenerative disease, thus providing therapeutic synapse-centered targets for the treatment of NDs.

[Microtubular network and functionality of the striated skeletal muscle]

Striated skeletal muscles are made of post-mitotic and multinucleated cells: muscle fibers, in which nuclei are regularly spaced and positioned at their periphery. The specific positioning of nuclei, necessary for the proper functioning of the muscle, is mainly regulated by the microtubule network and partner proteins. Many muscular pathologies present alterations in both the organization of the microtubule network and nuclear positioning, as observed in Duchenne Muscular Dystrophy, centronuclear myopathies or various neuromuscular diseases. The importance of the microtubule interactome and its influence in the maintenance of skeletal muscle homeostasis is a key issue in understanding muscle diseases.

HIV Infection: Shaping the Complex, Dynamic, and Interconnected Network of the Cytoskeleton

HIV-1 has evolved a plethora of strategies to overcome the cytoskeletal barrier (i.e., actin and intermediate filaments (AFs and IFs) and microtubules (MTs)) to achieve the viral cycle. HIV-1 modifies cytoskeletal organization and dynamics by acting on associated adaptors and molecular motors to productively fuse, enter, and infect cells and then traffic to the cell surface, where virions assemble and are released to spread infection. The HIV-1 envelope (Env) initiates the cycle by binding to and signaling through its main cell surface receptors (CD4/CCR5/CXCR4) to shape the cytoskeleton for fusion pore formation, which permits viral core entry. Then, the HIV-1 capsid is transported to the nucleus associated with cytoskeleton tracks under the control of specific adaptors/molecular motors, as well as HIV-1 accessory proteins. Furthermore, HIV-1 drives the late stages of the viral cycle by regulating cytoskeleton dynamics to assure viral Pr55Gag expression and transport to the cell surface, where it assembles and buds to mature infectious virions. In this review, we therefore analyze how HIV-1 generates a cell-permissive state to infection by regulating the cytoskeleton and associated factors. Likewise, we discuss the relevance of this knowledge to understand HIV-1 infection and pathogenesis in patients and to develop therapeutic strategies to battle HIV-1.

TDP-43 Controls HIV-1 Viral Production and Virus Infectiveness

The transactive response DNA-binding protein (TARDBP/TDP-43) is known to stabilize the anti-HIV-1 factor, histone deacetylase 6 (HDAC6). TDP-43 has been reported to determine cell permissivity to HIV-1 fusion and infection acting on tubulin-deacetylase HDAC6. Here, we studied the functional involvement of TDP-43 in the late stages of the HIV-1 viral cycle. The overexpression of TDP-43, in virus-producing cells, stabilized HDAC6 (i.e., mRNA and protein) and triggered the autophagic clearance of HIV-1 Pr55^Gag and Vif proteins. These events inhibited viral particle production and impaired virion infectiveness, observing a reduction in the amount of Pr55^Gag and Vif proteins incorporated into virions. A nuclear localization signal (NLS)-TDP-43 mutant was not able to control HIV-1 viral production and infection. Likewise, specific TDP-43-knockdown reduced HDAC6 expression (i.e., mRNA and protein) and increased the expression level of HIV-1 Vif and Pr55^Gag proteins and α-tubulin acetylation. Thus, TDP-43 silencing favored virion production and enhanced virus infectious capacity, thereby increasing the amount of Vif and Pr55^Gag proteins incorporated into virions. Noteworthy, there was a direct relationship between the content of Vif and Pr55^Gag proteins in virions and their infection capacity. Therefore, for TDP-43, the TDP-43/HDAC6 axis could be considered a key factor to control HIV-1 viral production and virus infectiveness.

Histone Deacetylases: Molecular Mechanisms and Therapeutic Implications for Muscular Dystrophies

Histone deacetylases (HDACs) are enzymes that regulate the deacetylation of numerous histone and non-histone proteins, thereby affecting a wide range of cellular processes. Deregulation of HDAC expression or activity is often associated with several pathologies, suggesting potential for targeting these enzymes for therapeutic purposes. For example, HDAC expression and activity are higher in dystrophic skeletal muscles. General pharmacological blockade of HDACs, by means of pan-HDAC inhibitors (HDACi), ameliorates both muscle histological abnormalities and function in preclinical studies. A phase II clinical trial of the pan-HDACi givinostat revealed partial histological improvement and functional recovery of Duchenne Muscular Dystrophy (DMD) muscles; results of an ongoing phase III clinical trial that is assessing the long-term safety and efficacy of givinostat in DMD patients are pending. Here we review the current knowledge about the HDAC functions in distinct cell types in skeletal muscle, identified by genetic and -omic approaches. We describe the signaling events that are affected by HDACs and contribute to muscular dystrophy pathogenesis by altering muscle regeneration and/or repair processes. Reviewing recent insights into HDAC cellular functions in dystrophic muscles provides new perspectives for the development of more effective therapeutic approaches based on drugs that target these critical enzymes.

The myonuclear domain in adult skeletal muscle fibres: past, present and future

Most cells in the body are mononuclear whereas skeletal muscle fibres are uniquely multinuclear. The nuclei of muscle fibres (myonuclei) are usually situated peripherally which complicates the equitable distribution of gene products. Myonuclear abundance can also change under conditions such as hypertrophy and atrophy. Specialised zones in muscle fibres have different functions and thus distinct synthetic demands from myonuclei. The complex structure and regulatory requirements of multinuclear muscle cells understandably led to the hypothesis that myonuclei govern defined 'domains' to maintain homeostasis and facilitate adaptation. The purpose of this review is to provide historical context for the myonuclear domain and evaluate its veracity with respect to mRNA and protein distribution resulting from myonuclear transcription. We synthesise insights from past and current in vitro and in vivo genetically modified models for studying the myonuclear domain under dynamic conditions. We also cover the most contemporary knowledge on mRNA and protein transport in muscle cells. Insights from emerging technologies such as single myonuclear RNA-sequencing further inform our discussion of the myonuclear domain. We broadly conclude: (1) the myonuclear domain can be flexible during muscle fibre growth and atrophy, (2) the mechanisms and role of myonuclear loss and motility deserve further consideration, (3) mRNA in muscle is actively transported via microtubules and locally restricted, but proteins may travel far from a myonucleus of origin and (4) myonuclear transcriptional specialisation extends beyond the classic neuromuscular and myotendinous populations. A deeper understanding of the myonuclear domain in muscle may promote effective therapies for ageing and disease.

The role of altered protein acetylation in neurodegenerative disease

Acetylation is a key post-translational modification (PTM) involved in the regulation of both histone and non-histone proteins. It controls cellular processes such as DNA transcription, RNA modifications, proteostasis, aging, autophagy, regulation of cytoskeletal structures, and metabolism. Acetylation is essential to maintain neuronal plasticity and therefore essential for memory and learning. Homeostasis of acetylation is maintained through the activities of histone acetyltransferases (HAT) and histone deacetylase (HDAC) enzymes, with alterations to these tightly regulated processes reported in several neurodegenerative diseases including Alzheimer's disease (AD), Parkinson's disease (PD), Huntington's disease (HD), and amyotrophic lateral sclerosis (ALS). Both hyperacetylation and hypoacetylation can impair neuronal physiological homeostasis and increase the accumulation of pathophysiological proteins such as tau, α-synuclein, and Huntingtin protein implicated in AD, PD, and HD, respectively. Additionally, dysregulation of acetylation is linked to impaired axonal transport, a key pathological mechanism in ALS. This review article will discuss the physiological roles of protein acetylation and examine the current literature that describes altered protein acetylation in neurodegenerative disorders.

Mechanisms of primordial follicle activation and new pregnancy opportunity for premature ovarian failure patients

Primordial follicles are the starting point of follicular development and the basic functional unit of female reproduction. Primordial follicles are formed around birth, and most of the primordial follicles then enter a dormant state. Since primordial follicles are limited in number and can't be renewed, dormant primordial follicles cannot be reversed once they enter the growing state. Thus, the orderly occurrence of primordial follicles selective activation directly affects the rate of follicle consumption and thus determines the length of female reproductive lifespan. Studies have found that appropriately inhibiting the activation rate of primordial follicles can effectively slow down the rate of follicle consumption, maintain fertility and delay ovarian aging. Based on the known mechanisms of primordial follicle activation, primordial follicle in vitro activation (IVA) technique has been clinically developed. IVA can help patients with premature ovarian failure, middle-aged infertile women, or infertile women due to gynecological surgery treatment to solve infertility problems. The study of the mechanism of selective activation of primordial follicles can contribute to the development of more efficient and safe IVA techniques. In this paper, recent mechanisms of primordial follicle activation and its clinical application are reviewed.

Ste20-like kinase activity promotes meiotic resumption and spindle microtubule stability in mouse oocytes

Ste20-like kinase (SLK) is involved in cell proliferation and migration in somatic cells. This study aims to explore SLK expression and function in mouse oocyte meiosis. Western blot, immunofluorescence, Co-immunoprecipitation, drug treatment, cRNA construct and in vitro transcription, microinjection of morpholino oilgo (MO) and cRNA were performed in oocytes. High and stable protein expression of SLK was detected in mouse oocyte meiosis, with dynamic distribution in the nucleus, chromosomes and spindle apparatus. SLK phosphorylation emerges around meiotic resumption and reaches a peak during metaphase I (MI) and metaphase II. SLK knockdown with MO or expression of kinase-dead SLK K63R dramatically delays meiotic resumption due to sequentially suppressed phosphorylation of Polo-like kinase 1 (Plk1) and cell division cycle 25C (CDC25C) and dephosphorylation of cyclin-dependent kinase 1 (CDK1). SLK depletion promotes ubiquitination-mediated degradation of paxillin, an antagonist to α-tubulin deacetylation, and thus destroys spindle assembly and chromosome alignment; these phenotypes can be substantially rescued by exogenous expression of SLK kinase active fragment. Additionally, exogenous SLK effectively promotes meiotic progression and spindle assembly in aging oocytes with reduced SLK. Collectively, this study reveals SLK is required for meiotic resumption and spindle assembly in mouse oocyte meiosis.

[HDAC6, a very specific deacetylase with a potential therapeutic role]

The cytoplasmic histone deacetylase 6 (HDAC6) is defined today as a new key player in the treatment of many diseases. Overexpression of HDAC6 was observed in a variety of diseases. Over the past ten years, plenty of new selective inhibitors of HDAC6 activity have been synthesized and characterized. Many studies have shown the high efficiency and beneficial effects of HDAC6 inhibitors in many diseases such as cancers, neurodegenerative, inflammatory, or neuromuscular diseases. The mechanisms of HDAC6 action that explain the benefit of its inhibition in various pathologies are still unknown. We have recently shown that HDAC6, via the regulation of the microtubule network, plays a role at the level of neuromuscular junctions by controlling acetylcholine receptor delivery.

Pharmacological inhibition of HDAC6 improves muscle phenotypes in dystrophin-deficient mice by downregulating TGF-β via Smad3 acetylation

The absence of dystrophin in Duchenne muscular dystrophy disrupts the dystrophin-associated glycoprotein complex resulting in skeletal muscle fiber fragility and atrophy, associated with fibrosis as well as microtubule and neuromuscular junction disorganization. The specific, non-conventional cytoplasmic histone deacetylase 6 (HDAC6) was recently shown to regulate acetylcholine receptor distribution and muscle atrophy. Here, we report that administration of the HDAC6 selective inhibitor tubastatin A to the Duchenne muscular dystrophy, mdx mouse model increases muscle strength, improves microtubule, neuromuscular junction, and dystrophin-associated glycoprotein complex organization, and reduces muscle atrophy and fibrosis. Interestingly, we found that the beneficial effects of HDAC6 inhibition involve the downregulation of transforming growth factor beta signaling. By increasing Smad3 acetylation in the cytoplasm, HDAC6 inhibition reduces Smad2/3 phosphorylation, nuclear translocation, and transcriptional activity. These findings provide in vivo evidence that Smad3 is a new target of HDAC6 and implicate HDAC6 as a potential therapeutic target in Duchenne muscular dystrophy.

First-in-Class Dual Mechanism Ferroptosis-HDAC Inhibitor Hybrids

HDAC inhibitors are an attractive class of cytotoxic agents for the design of hybrid molecules. Several HDAC hybrids have emerged over the years, but none combines HDAC inhibition with ferroptosis, a combination which is being extensively studied because it leads to enhanced cytotoxicity and attenuated neuronal toxicity. We combined the pharmacophores of SAHA and CETZOLE molecules to design the first-in-class dual mechanism hybrid molecules, which induce ferroptosis and inhibit HDAC proteins. The involvement of both mechanisms in cytotoxicity was confirmed by a series of biological assays. The cytotoxic effects were evaluated in a series of cancer and neuronal cell lines. Analogue HY-1 demonstrated the best cytotoxic profile with GI50 values as low as 20 nM. Although the increase in activity of the hybrids over the combinations is modest in cellular systems, they have the potential advantage of homogeneous spatiotemporal distribution in in vivo systems.

Stepwise progression of β-selection during T cell development involves histone deacetylation

During T cell development, the first step in creating a unique T cell receptor (TCR) is genetic recombination of the TCRβ chain. The quality of the new TCRβ is assessed at the β-selection checkpoint. Most cells fail this checkpoint and die, but the coordination of fate at the β-selection checkpoint is not yet understood. We shed new light on fate determination during β-selection using a selective inhibitor of histone deacetylase 6, ACY1215. ACY1215 disrupted the β-selection checkpoint. Characterising the basis for this disruption revealed a new, pivotal stage in β-selection, bookended by up-regulation of TCR co-receptors, CD28 and CD2, respectively. Within this "DN3b^Pre" stage, CD5 and Lef1 are up-regulated to reflect pre-TCR signalling, and their expression correlates with proliferation. These findings suggest a refined model of β-selection in which a coordinated increase in expression of pre-TCR, CD28, CD5 and Lef1 allows for modulating TCR signalling strength and culminates in the expression of CD2 to enable exit from the β-selection checkpoint.

Simple Methods for Permanent or Transient Denervation in Mouse Sciatic Nerve Injury Models

Our ability to move and breathe requires an efficient communication between nerve and muscle that mainly takes place at the neuromuscular junctions (NMJs), a highly specialized synapse that links the axon of a motor neuron to a muscle fiber. When NMJs or axons are disrupted, the control of muscle fiber contraction is lost and muscle are paralyzed. Understanding the adaptation of the neuromuscular system to permanent or transient denervation is a challenge to understand the pathophysiology of many neuromuscular diseases. There is still a lack of in vitro models that fully recapitulate the in vivo situation, and in vivo denervation, carried out by transiently or permanently severing the nerve afferent to a muscle, remains a method of choice to evaluate reinnervation and/or the consequences of the loss of innervation. We describe here a simple surgical intervention performed at the hip zone to expose the sciatic nerve in order to obtain either permanent denervation (nerve-cut) or transient and reversible denervation (nerve-crush). These two methods provide a convenient in vivo model to study adaptation to denervation. Graphical abstract.

Therapeutic Potential of CKD-504, a Novel Selective Histone Deacetylase 6 Inhibitor, in a Zebrafish Model of Neuromuscular Junction Disorders

The neuromuscular junction (NMJ), which is a synapse for signal transmission from motor neurons to muscle cells, has emerged as an important region because of its association with several peripheral neuropathies. In particular, mutations in GARS that affect the formation of NMJ result in Charcot-Marie-Tooth disease and distal hereditary motor neuropathy. These disorders are mainly considered to be caused by neuronal axon abnormalities; however, no treatment is currently available. Therefore, in order to determine whether the NMJ could be targeted to treat neurodegenerative disorders, we investigated the NMJ recovery effect of HDAC6 inhibitors, which have been used in the treatment of several peripheral neuropathies. In the present study, we demonstrated that HDAC6 inhibition was sufficient to enhance movement by restoring NMJ impairments observed in a zebrafish disease model. We found that CKD-504, a novel HDAC6 inhibitor, was effective in repairing NMJ defects, suggesting that treatment of neurodegenerative diseases via NMJ targeting is possible.

Acetylated α-tubulin K394 regulates microtubule stability to shape the growth of axon terminals

Microtubules are essential to neuron shape and function. Acetylation of tubulin has the potential to directly tune the behavior and function of microtubules in cells. Although proteomic studies have identified several acetylation sites in α-tubulin, the effects of acetylation at these sites remains largely unknown. This includes the highly conserved residue lysine 394 (K394), which is located at the αβ-tubulin dimer interface. Using a fly model, we show that α-tubulin K394 is acetylated in the nervous system and is an essential residue. We found that an acetylation-blocking mutation in endogenous α-tubulin, K394R, perturbs the synaptic morphogenesis of motoneurons and reduces microtubule stability. Intriguingly, the K394R mutation has opposite effects on the growth of two functionally and morphologically distinct motoneurons, revealing neuron-type-specific responses when microtubule stability is altered. Eliminating the deacetylase HDAC6 increases K394 acetylation, and the over-expression of HDAC6 reduces microtubule stability similar to the K394R mutant. Thus, our findings implicate α-tubulin K394 and its acetylation in the regulation of microtubule stability and suggest that HDAC6 regulates K394 acetylation during synaptic morphogenesis.

Clinical-Like Cryotherapy in Acute Knee Arthritis Protects Neuromuscular Junctions of Quadriceps and Reduces Joint Inflammation in Mice

Rheumatoid arthritis is an autoimmune and inflammatory disease that affects synovial joint tissues and skeletal muscle. Clinical-like cryotherapy benefits signs of joint inflammation in knee osteoarthritis after 60 days of anterior cruciate ligament transection surgery. However, it is unknown whether it also benefits acute knee arthritis (e.g., reduces inflammatory process and protects neuromuscular junction [NMJ] and muscle fibers). We aimed to analyze the effects of clinical-like cryotherapy on NMJ and quadriceps muscle fibers in a model of acute knee arthritis. Twenty-four male C57BL/6 mice (20 to 25 g) were randomly allocated into three groups: control (mice with no intervention), antigen-induced arthritis (AIA; mice sensitized and immunized with intra-articular [i.a.] injection of methylated bovine serum albumin [mBSA]), and AIA+cryotherapy (mice sensitized, immunized with i.a. injection of mBSA, and submitted to a clinical-like cryotherapy protocol). Twenty-one days after sensitization, arthritis was induced in immunized mice via i.a. injection of mBSA (100 μg/joint). Two clinical-like cryotherapy sessions (crushed ice pack for 20 min) were applied two hours apart. The first session was applied immediately after i.a. injection of mBSA. The quadriceps was removed two hours after the second clinical-like cryotherapy session for morphological analysis of muscle fibers (cross-sectional area), frequency distribution of muscle fiber area (%), and NMJ (area, perimeter, and maximum diameter). Gene expressions of mRNA involved in NMJ signaling (γ-nAChR, α1-nAChR, ε-nAChR, Agrin-MusK-Rapsyn, α-dystrobrevin, and utrophin) and atrophy (muscle RING-finger protein-1 and Atrogin-1) pathways were analyzed. Inflammatory signs were assessed in knee joint (swelling, articular surface temperature, and neutrophil migration in synovial fluid). Regarding morphological analysis of muscle fibers, 180 to 270 and >270 μm2 classes were higher in the AIA+cryotherapy than the AIA group. Area, perimeter, and maximum diameter of NMJ also increased in the AIA+cryotherapy compared with the control group. Agrin mRNA expression increased in the AIA+cryotherapy compared with the control and AIA groups. In the atrophy pathway, Atrogin-1 increased compared with the control and AIA groups. The AIA+cryotherapy group reduced knee swelling and neutrophil migration compared with the AIA group. In conclusion, clinical-like cryotherapy increased Agrin expression, contributing to NMJ maintenance and increased Atrogin-1 expression, thus protecting NMJ and muscle fiber. Furthermore, clinical-like cryotherapy reduced inflammatory signs (swelling and neutrophil migration) of acute knee arthritis.

Inhibition of Histone Deacetylase 6 (HDAC6) as a therapeutic strategy for Alzheimer's disease: A review (2010-2020)

Alzheimer's disease (AD) is one of the most common neurodegenerative disorders, which is characterized by the primary risk factor, age. Several attempts have been made to treat AD, while most of them end in failure. However, with the deepening study of pathogenesis of AD, the expression of HDAC6 in the hippocampus, which plays a major role of the memory formation, is becoming worth of notice. Neurofibrillary tangles (NFTs), a remarkable lesion in AD, has been characterized in association with the abnormal accumulation of hyperphosphorylated Tau, which is mainly caused by the high expression of HDAC6. On the other hand, the hypoacetylated tubulin induced by HDAC6 is also fatal for the neuronal transport, which is the key impact of the formation of axons and dendrites. Overall, the significantly increased expression of HDAC6 in brain regions is deleterious to neuron survival in AD patients. Based on the above research, the inhibition of HDAC6 seems to be a potential therapeutic method for the treatment of AD. Up to now, various types of HDAC6 inhibitors have been discovered. This review mainly analyzes the HDAC6 inhibitors reported amid 2010-2020 in terms of their structure, selectivity and pharmacological impact towards AD. And we aim at facilitating the design and development of better HDAC6 inhibitors in the future.

Drebrin Regulates Acetylcholine Receptor Clustering and Organization of Microtubules at the Postsynaptic Machinery

Proper muscle function depends on the neuromuscular junctions (NMJs), which mature postnatally to complex "pretzel-like" structures, allowing for effective synaptic transmission. Postsynaptic acetylcholine receptors (AChRs) at NMJs are anchored in the actin cytoskeleton and clustered by the scaffold protein rapsyn, recruiting various actin-organizing proteins. Mechanisms driving the maturation of the postsynaptic machinery and regulating rapsyn interactions with the cytoskeleton are still poorly understood. Drebrin is an actin and microtubule cross-linker essential for the functioning of the synapses in the brain, but its role at NMJs remains elusive. We used immunohistochemistry, RNA interference, drebrin inhibitor 3,5-bis-trifluoromethyl pyrazole (BTP2) and co-immunopreciptation to explore the role of this protein at the postsynaptic machinery. We identify drebrin as a postsynaptic protein colocalizing with the AChRs both in vitro and in vivo. We also show that drebrin is enriched at synaptic podosomes. Downregulation of drebrin or blocking its interaction with actin in cultured myotubes impairs the organization of AChR clusters and the cluster-associated microtubule network. Finally, we demonstrate that drebrin interacts with rapsyn and a drebrin interactor, plus-end-tracking protein EB3. Our results reveal an interplay between drebrin and cluster-stabilizing machinery involving rapsyn, actin cytoskeleton, and microtubules.

MACF1 controls skeletal muscle function through the microtubule-dependent localization of extra-synaptic myonuclei and mitochondria biogenesis

Skeletal muscles are composed of hundreds of multinucleated muscle fibers (myofibers) whose myonuclei are regularly positioned all along the myofiber's periphery except the few ones clustered underneath the neuromuscular junction (NMJ) at the synaptic zone. This precise myonuclei organization is altered in different types of muscle disease, including centronuclear myopathies (CNMs). However, the molecular machinery regulating myonuclei position and organization in mature myofibers remains largely unknown. Conversely, it is also unclear how peripheral myonuclei positioning is lost in the related muscle diseases. Here, we describe the microtubule-associated protein, MACF1, as an essential and evolutionary conserved regulator of myonuclei positioning and maintenance, in cultured mammalian myotubes, in Drosophila muscle, and in adult mammalian muscle using a conditional muscle-specific knockout mouse model. In vitro, we show that MACF1 controls microtubules dynamics and contributes to microtubule stabilization during myofiber's maturation. In addition, we demonstrate that MACF1 regulates the microtubules density specifically around myonuclei, and, as a consequence, governs myonuclei motion. Our in vivo studies show that MACF1 deficiency is associated with alteration of extra-synaptic myonuclei positioning and microtubules network organization, both preceding NMJ fragmentation. Accordingly, MACF1 deficiency results in reduced muscle excitability and disorganized triads, leaving voltage-activated sarcoplasmic reticulum Ca2+ release and maximal muscle force unchanged. Finally, adult MACF1-KO mice present an improved resistance to fatigue correlated with a strong increase in mitochondria biogenesis.

Age-Related Alterations at Neuromuscular Junction: Role of Oxidative Stress and Epigenetic Modifications

With advancing aging, a decline in physical abilities occurs, leading to reduced mobility and loss of independence. Although many factors contribute to the physio-pathological effects of aging, an important event seems to be related to the compromised integrity of the neuromuscular system, which connects the brain and skeletal muscles via motoneurons and the neuromuscular junctions (NMJs). NMJs undergo severe functional, morphological, and molecular alterations during aging and ultimately degenerate. The effect of this decline is an inexorable decrease in skeletal muscle mass and strength, a condition generally known as sarcopenia. Moreover, several studies have highlighted how the age-related alteration of reactive oxygen species (ROS) homeostasis can contribute to changes in the neuromuscular junction morphology and stability, leading to the reduction in fiber number and innervation. Increasing evidence supports the involvement of epigenetic modifications in age-dependent alterations of the NMJ. In particular, DNA methylation, histone modifications, and miRNA-dependent gene expression represent the major epigenetic mechanisms that play a crucial role in NMJ remodeling. It is established that environmental and lifestyle factors, such as physical exercise and nutrition that are susceptible to change during aging, can modulate epigenetic phenomena and attenuate the age-related NMJs changes. This review aims to highlight the recent epigenetic findings related to the NMJ dysregulation during aging and the role of physical activity and nutrition as possible interventions to attenuate or delay the age-related decline in the neuromuscular system.

Human motor units in microfluidic devices are impaired by FUS mutations and improved by HDAC6 inhibition

Neuromuscular junctions (NMJs) ensure communication between motor neurons (MNs) and muscle; however, in MN disorders, such as amyotrophic lateral sclerosis (ALS), NMJs degenerate resulting in muscle atrophy. The aim of this study was to establish a versatile and reproducible in vitro model of a human motor unit to investigate the effects of ALS-causing mutations. Therefore, we generated a co-culture of human induced pluripotent stem cell (iPSC)-derived MNs and human primary mesoangioblast-derived myotubes in microfluidic devices. A chemotactic and volumetric gradient facilitated the growth of MN neurites through microgrooves resulting in the interaction with myotubes and the formation of NMJs. We observed that ALS-causing FUS mutations resulted in reduced neurite outgrowth as well as an impaired neurite regrowth upon axotomy. NMJ numbers were likewise reduced in the FUS-ALS model. Interestingly, the selective HDAC6 inhibitor, Tubastatin A, improved the neurite outgrowth, regrowth, and NMJ morphology, prompting HDAC6 inhibition as a potential therapeutic strategy for ALS.

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Human motor units with functional NMJs can be generated using microfluidic devices

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FUS-ALS motor units display impaired neurite regrowth, outgrowth and NMJ numbers

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HDAC6 inhibition alleviate FUS-ALS motor unit pathology in vitro

Tubulin polyglutamylation, a regulator of microtubule functions, can cause neurodegeneration

Neurodegenerative diseases lead to a progressive demise of neuronal functions that ultimately results in neuronal death. Besides a large variety of molecular pathways that have been linked to the degeneration of neurons, dysfunctions of the microtubule cytoskeleton are common features of many human neurodegenerative disorders. Yet, it is unclear whether microtubule dysfunctions are causative, or mere bystanders in the disease progression. A so-far little explored regulatory mechanism of the microtubule cytoskeleton, the posttranslational modifications of tubulin, emerge as candidate mechanisms involved in neuronal dysfunction, and thus, degeneration. Here we review the role of tubulin polyglutamylation, a prominent modification of neuronal microtubules. We discuss the current understanding of how polyglutamylation controls microtubule functions in healthy neurons, and how deregulation of this modification leads to neurodegeneration in mice and humans.