Reduced influence of perceptual context in mild traumatic brain injury is not an illusion

Perceptual grouping is impaired following mild traumatic brain injury (mTBI). This may affect visual size perception, a process influenced by perceptual grouping abilities. We conducted two experiments to evaluate visual size perception in people with self-reported history of mTBI, using two different size-contrast illusions: the Ebbinghaus Illusion (Experiment 1) and the Müller-Lyer illusion (Experiment 2). In Experiment 1, individuals with mTBI and healthy controls were asked to compare the size of two target circles that were either the same size or different sizes. The target circles appeared by themselves (no-context condition), or were surrounded by smaller or larger circles (context condition). Similar levels of accuracy were evident between the groups in the no-context condition. However, size judgements by mTBI participants were more accurate in the context condition, suggesting that they processed the target circles separately from the surrounding circles. In Experiment 2, individuals with mTBI and healthy controls judged the length of parallel lines that appeared with arrowheads (context condition) or without arrowheads (no context condition). Consistent with Experiment 1, size judgements by mTBI participants were more accurate than size judgements by control participants in the context condition. These findings suggest that mTBI influences size perception by impairing perceptual grouping of visual stimuli in near proximity.

Modified conventional gait model vs. Six degrees of freedom model: A comparison of lower limb kinematics and associated error

BACKGROUND

The conventional gait model (CGM) is commonly utilised within clinical motion analysis but has a number of inherent limitations. To overcome some of these limitations modifications have been made to the CGM and six-degrees of freedom models (6DoF) have been developed.

RESEARCH QUESTION

How comparable are lower limb kinematics calculated using modified CGM and 6DoF models and what is the error associated with the output of each model during walking?

METHODS

Ten healthy males attended two gait analysis sessions, in which they walked at a self-selected pace, while a 10-camera motion capture system recorded lower limb kinematics. Hip, knee and ankle joint kinematics in all three anatomical planes were calculated using a modified CGM, with medial anatomical markers and a three-dimensional foot added, and 6DoF. Mean absolute differences were calculated on a point-by-point basis over the walking gait cycle and interpreted relative to a 5° threshold to explore the comparability of model outputs. The standard error of the measurement (SEM) was also calculated on a point-by-point basis over the walking gait cycle for each model.

RESULTS

Mean absolute differences above 5° were reported between the two model outputs in 58-86% of the walking gait cycle at the knee in the frontal plane, and over the entire walking gait cycle at the hip and knee in the transverse plane. SEM was typically larger for the modified CGM compared to the 6DoF, with the highest SEM values reported at the knee in the frontal plane, and the hip and the knee in the transverse plane.

SIGNIFICANCE

Caution should be taken when looking to compare findings between studies utilising modified CGM and 6DoF outside of the sagittal plane, especially at the hip and knee. The reduced SEM associated with the 6DoF suggests this modelling approach may be preferable.

Tetrahydroquinoline-Capped Histone Deacetylase 6 Inhibitor SW-101 Ameliorates Pathological Phenotypes in a Charcot-Marie-Tooth Type 2A Mouse Model

Histone deacetylase 6 (HDAC6) is a promising therapeutic target for the treatment of neurodegenerative disorders. SW-100 (1a), a phenylhydroxamate-based HDAC6 inhibitor (HDAC6i) bearing a tetrahydroquinoline (THQ) capping group, is a highly potent and selective HDAC6i that was shown to be effective in mouse models of Fragile X syndrome and Charcot-Marie-Tooth disease type 2A (CMT2A). In this study, we report the discovery of a new THQ-capped HDAC6i, termed SW-101 (1s), that possesses excellent HDAC6 potency and selectivity, together with markedly improved metabolic stability and druglike properties compared to SW-100 (1a). X-ray crystallography data reveal the molecular basis of HDAC6 inhibition by SW-101 (1s). Importantly, we demonstrate that SW-101 (1s) treatment elevates the impaired level of acetylated α-tubulin in the distal sciatic nerve, counteracts progressive motor dysfunction, and ameliorates neuropathic symptoms in a CMT2A mouse model bearing mutant MFN2. Taken together, these results bode well for the further development of SW-101 (1s) as a disease-modifying HDAC6i.

HDAC6 inhibition promotes α-tubulin acetylation and ameliorates CMT2A peripheral neuropathy in mice

Charcot-Marie-Tooth type 2A (CMT2A) peripheral neuropathy, the most common axonal form of CMT, is caused by dominantly inherited point mutations in the Mitofusin 2 (Mfn2) gene. It is characterized by progressive length-dependent degeneration of motor and sensory nerves with corresponding clinical features of motor and sensory impairment. There is no cure for CMT, and therapeutic approaches are limited to physical therapy, orthopedic devices, surgery, and analgesics. In this study we focus on histone deacetylase 6 (HDAC6) as a therapeutic target in a mouse model of mutant MFN2 (MFN2^R94Q)-induced CMT2A. We report that these mice display progressive motor and sensory dysfunction as well as a significant decrease in α-tubulin acetylation in distal segments of long peripheral nerves. Treatment with a new, highly selective HDAC6 inhibitor, SW-100, was able to restore α-tubulin acetylation and ameliorate motor and sensory dysfunction when given either prior to or after the onset of symptoms. To confirm HDAC6 is the target for ameliorating the CMT2A phenotype, we show that genetic deletion of Hdac6 in CMT2A mice prevents the development of motor and sensory dysfunction. Our findings suggest α-tubulin acetylation defects in distal parts of nerves as a pathogenic mechanism and HDAC6 as a therapeutic target for CMT2A.

Deacetylation of Miro1 by HDAC6 blocks mitochondrial transport and mediates axon growth inhibition

Inhibition of histone deacetylase 6 (HDAC6) was shown to support axon growth on the nonpermissive substrates myelin-associated glycoprotein (MAG) and chondroitin sulfate proteoglycans (CSPGs). Though HDAC6 deacetylates α-tubulin, we find that another HDAC6 substrate contributes to this axon growth failure. HDAC6 is known to impact transport of mitochondria, and we show that mitochondria accumulate in distal axons after HDAC6 inhibition. Miro and Milton proteins link mitochondria to motor proteins for axon transport. Exposing neurons to MAG and CSPGs decreases acetylation of Miro1 on Lysine 105 (K105) and decreases axonal mitochondrial transport. HDAC6 inhibition increases acetylated Miro1 in axons, and acetyl-mimetic Miro1 K105Q prevents CSPG-dependent decreases in mitochondrial transport and axon growth. MAG- and CSPG-dependent deacetylation of Miro1 requires RhoA/ROCK activation and downstream intracellular Ca²⁺ increase, and Miro1 K105Q prevents the decrease in axonal mitochondria seen with activated RhoA and elevated Ca²⁺ These data point to HDAC6-dependent deacetylation of Miro1 as a mediator of axon growth inhibition through decreased mitochondrial transport.

Epigenetic changes following traumatic brain injury and their implications for outcome, recovery and therapy

Traumatic brain injury (TBI) contributes to nearly a third of all injury-related deaths in the United States. For survivors of TBI, depending on severity, patients can be left with devastating neurological disabilities that include impaired cognition or memory, movement, sensation, or emotional function. Despite the efforts to identify novel therapeutics, the only strategy to combat TBI is risk reduction (helmets, seatbelts, removal of fall hazards, etc.). Enormous heterogeneity exists within TBI, and it depends on the severity, the location, and whether the injury was focal or diffuse. Evidence from recent studies support the involvement of epigenetic mechanisms such as DNA methylation, chromatin post-translational modification, and miRNA regulation of gene expression in the post-injured brain. In this review, we discuss studies that have assessed epigenetic changes and mechanisms following TBI, how epigenetic changes might not only be limited to the nucleus but also impact the mitochondria, and the implications of these changes with regard to TBI recovery.

Thiol-Based Potent and Selective HDAC6 Inhibitors Promote Tubulin Acetylation and T-Regulatory Cell Suppressive Function

Several new mercaptoacetamides were synthesized and studied as HDAC6 inhibitors. One compound, 2b, bearing an aminoquinoline cap group, was found to show 1.3 nM potency at HDAC6, with >3000-fold selectivity over HDAC1. 2b also showed excellent efficacy at increasing tubulin acetylation in rat primary cortical cultures, inducing a 10-fold increase in acetylated tubulin at 1 μM. To assess possible therapeutic effects, compounds were assayed for their ability to increase T-regulatory (Treg) suppressive function. Some but not all of the compounds increased Treg function, and thereby decreased conventional T cell activation and proliferation in vitro.

A brief review of recent Charcot-Marie-Tooth research and priorities

This brief review of current research progress on Charcot-Marie-Tooth (CMT) disease is a summary of discussions initiated at the Hereditary Neuropathy Foundation (HNF) scientific advisory board meeting on November 7, 2014. It covers recent published and unpublished in vitro and in vivo research. We discuss recent promising preclinical work for CMT1A, the development of new biomarkers, the characterization of different animal models, and the analysis of the frequency of gene mutations in patients with CMT. We also describe how progress in related fields may benefit CMT therapeutic development, including the potential of gene therapy and stem cell research. We also discuss the potential to assess and improve the quality of life of CMT patients. This summary of CMT research identifies some of the gaps which may have an impact on upcoming clinical trials. We provide some priorities for CMT research and areas which HNF can support. The goal of this review is to inform the scientific community about ongoing research and to avoid unnecessary overlap, while also highlighting areas ripe for further investigation. The general collaborative approach we have taken may be useful for other rare neurological diseases.

Antihelminthic benzimidazoles are novel HIF activators that prevent oxidative neuronal death via binding to tubulin

AIMS

Pharmacological activation of the adaptive response to hypoxia is a therapeutic strategy of growing interest for neurological conditions, including stroke, Huntington's disease, and Parkinson's disease. We screened a drug library with known safety in humans using a hippocampal neuroblast line expressing a reporter of hypoxia-inducible factor (HIF)-dependent transcription.

RESULTS

Our screen identified more than 40 compounds with the ability to induce hypoxia response element-driven luciferase activity as well or better than deferoxamine, a canonical activator of hypoxic adaptation. Among the chemical entities identified, the antihelminthic benzimidazoles represented one pharmacophore that appeared multiple times in our screen. Secondary assays confirmed that antihelminthics stabilized the transcriptional activator HIF-1α and induced expression of a known HIF target gene, p21(cip1/waf1), in post-mitotic cortical neurons. The on-target effect of these agents in stimulating hypoxic signaling was binding to free tubulin. Moreover, antihelminthic benzimidazoles also abrogated oxidative stress-induced death in vitro, and this on-target effect also involves binding to free tubulin.

INNOVATION AND CONCLUSIONS

These studies demonstrate that tubulin-binding drugs can activate a component of the hypoxic adaptive response, specifically the stabilization of HIF-1α and its downstream targets. Tubulin-binding drugs, including antihelminthic benzimidazoles, also abrogate oxidative neuronal death in primary neurons. Given their safety in humans and known ability to penetrate into the central nervous system, antihelminthic benzimidazoles may be considered viable candidates for treating diseases associated with oxidative neuronal death, including stroke.

Sirtuin deacetylases as therapeutic targets in the nervous system

Sirtuins are a conserved family of deacetylases whose activities are dependent on nicotinamide adenine dinucleotide (NAD+). Sirtuins act in different cellular compartments, such as the nucleus where they deacetylate histones and transcriptional factors, in the cytoplasm where they modulate cytoskeletal and signaling molecules, and in the mitochondria where they engage components of the metabolic machinery. Collectively, they tune metabolic processes to energy availability, and modulate stress responses, protein aggregation, inflammatory processes, and genome stability. As such, they have garnered much interest and have been widely studied in aging and age-related neurodegeneration. In this chapter, we review the identification of sirtuins and their biological targets. We focus on their biological mechanisms of action and how they might be regulated, including via NAD metabolism, transcriptional and posttranscriptional control, and as targets of pharmacological agents. Lastly, we highlight the numerous studies suggesting that sirtuins are efficacious therapeutic targets in neurodegenerative disease and injury.

Chromatin modifications associated with DNA double-strand breaks repair as potential targets for neurological diseases

The integrity of the genome is continuously challenged by both endogenous and exogenous DNA damaging agents. Neurons, due to their post-mitotic state, high metabolism, and longevity are particularly prone to the accumulation of DNA lesions. Indeed, DNA damage has been suggested as a major contributor to both age-associated neurodegenerative diseases and acute neurological injury. The DNA damage response is a key factor in maintaining genome integrity. It relies on highly dynamic posttranslational modifications of the chromatin and DNA repair proteins to allow signaling, access, and repair of the lesion. Drugs that modulate the activity of the enzymes responsible for these modifications have emerged as attractive therapeutic compounds to treat neurodegeneration. In this review, we discuss the role of DNA double-strand breaks and abnormal chromatin modification patterns in a range of neurodegenerative conditions, and the chromatin modifiers that might ameliorate them. Finally, we suggest that understanding the epigenetic modifications specific to neuronal DNA repair is crucial for the development of efficient neurotherapeutic strategies.

A screen for inducers of p21(waf1/cip1) identifies HIF prolyl hydroxylase inhibitors as neuroprotective agents with antitumor properties

Preventing neuronal death is a priority for treating neurological diseases. However, therapies that inhibit pathological neuron loss could promote tumorigenesis by preventing the physiological death of cancerous cells. To avert this, we targeted the transcriptional upregulation of p21(waf1/cip1) (p21), an endogenous tumor suppressor with neuroprotective and pro-regenerative activity. We identified potential p21 indcuers by screening a FDA-approved drug and natural product small molecule library against hippocampal HT22 cells stably expressing a luciferase reporter driven by the proximal 60bp of the p21 promoter, and tested them for neuroprotection from glutathione depletion mediated oxidative stress, and cytotoxicity to cancer cell lines (DLD-1, Neuro-2A, SH-SY5Y, NGP, CHLA15, CHP212, and SK-N-SH) in vitro. Of the p21 inducers identified, only ciclopirox, a hypoxia-inducible factor prolyl-4-hydroxylase (HIF-PHD) inhibitor, simultaneously protected neurons from glutathione depletion and decreased cancer cell proliferation at concentrations that were not basally toxic to neurons. We found that other structurally distinct HIF-PHD inhibitors (desferrioxamine, 3,4-dihydroxybenzoate, and dimethyloxalyl glycine) also protected neurons at concentrations that killed cancer cells. HIF-PHD inhibitors stabilize HIF transcription factors, mediating genetic adaptation to hypoxia. While augmenting HIF stability is believed to promote tumorigenesis, we found that chronic HIF-PHD inhibition killed cancer cells, suggesting a protumorigenic role for these enzymes. Moreover, our findings suggest that PHD inhibitors can be used to treat neurological disease without significant concern for cell-autonomous tumor promotion.

Rational design and simple chemistry yield a superior, neuroprotective HDAC6 inhibitor, tubastatin A

Structure-based drug design combined with homology modeling techniques were used to develop potent inhibitors of HDAC6 that display superior selectivity for the HDAC6 isozyme compared to other inhibitors. These inhibitors can be assembled in a few synthetic steps, and thus are readily scaled up for in vivo studies. An optimized compound from this series, designated Tubastatin A, was tested in primary cortical neuron cultures in which it was found to induce elevated levels of acetylated alpha-tubulin, but not histone, consistent with its HDAC6 selectivity. Tubastatin A also conferred dose-dependent protection in primary cortical neuron cultures against glutathione depletion-induced oxidative stress. Importantly, when given alone at all concentrations tested, this hydroxamate-containing HDAC6-selective compound displayed no neuronal toxicity, thus, forecasting the potential application of this agent and its analogues to neurodegenerative conditions.

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

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

Putting the 'HAT' back on survival signalling: the promises and challenges of HDAC inhibition in the treatment of neurological conditions

Decreased histone acetyltransferase activity and transcriptional dysfunction have been implicated in almost all neurodegenerative conditions. Increasing net histone acetyltransferase activity through inhibition of the histone deacetylases (HDACs) has been shown to be an effective strategy to delay or halt progression of neurological disease in cellular and rodent models. These findings have provided firm rationale for Phase I and Phase II clinical trials of HDAC inhibitors in Huntington's disease, spinal muscular atrophy, and Freidreich's ataxia. In this review, we discuss the current findings and promise of HDAC inhibition as a strategy for treating neurological disorders. Despite the fact that HDAC inhibitors are in an advanced stage of development, we suggest other approaches to modulating HDAC function that may be less toxic and more efficacious than the canonical agents developed so far.

Searching for disease modifiers-PKC activation and HDAC inhibition - a dual drug approach to Alzheimer's disease that decreases Abeta production while blocking oxidative stress

A series of benzolactam compounds were synthesized, some of which caused a concentration-dependent increase in sAPPalpha and decrease in Abeta production in the concentration range of 0.1-10 microM. Moreover, some compounds showed neuroprotective effects in the 10-20 microM range in the HCA cortical neuron model of oxidative stress and no toxicity in measurements of neuron viability by MTT assay, even at the highest concentrations tested (20 microM). Alzheimer's disease (AD) is a well-studied neurodegenerative process characterized by the presence of amyloid plaques and neurofibrillary tangles. In this study, a series of protein kinase C (PKC) activators were investigated, some of which also exhibit histone deacetylase (HDAC) inhibitory activity, under the hypothesis that such compounds might provide a new path forward in the discovery of drugs for the treatment of AD. The PKC-activating properties of these drugs were expected to enhance the alpha-secretase pathway in the processing of amyloid precursor protein (APP), while their HDAC inhibition was anticipated to confer neuroprotective activity. We found that benzolactams 9 and 11-14 caused a concentration-dependent increase in sAPPalpha and decrease in beta-amyloid (Abeta) production in the concentration range of 0.1-10 microM, consistent with a shift of APP metabolism toward the alpha-secretase-processing pathway. Moreover, compounds 9-14 showed neuroprotective effects in the 10-20 microM range in the homocysteate (HCA) cortical neuron model of oxidative stress. In parallel, we found that the most neuroprotective compounds caused increased levels of histone acetylation (H4), thus indicating their likely ability to inhibit HDAC activity. As the majority of the compounds studied also show nanomolar binding affinities for PKC, we conclude that it is possible to design, de novo, agents that combine both PKC-activating properties along with HDAC inhibitory properties. Such agents would be capable of modulating amyloid processing while showing neuroprotection. These findings may offer a new approach to therapies that exhibit disease-modifying effects, as opposed to symptomatic relief, in the treatment of AD.

Targeting histone deacetylases as a multifaceted approach to treat the diverse outcomes of stroke

Achieving therapeutic efficacy in ischemic stroke represents one of the biggest challenges in translational neurobiology. Despite extensive efforts, tissue plasminogen activator remains the only available intervention for enhancing functional recovery in humans once a stroke has occurred. To expand the repertoire of therapeutic options in stroke, one must consider and target its diverse pathophysiologies that trigger cell loss in a manner that also permits and enhances neuronal plasticity and repair. Several converging lines of inquiry suggest that histone deacetylase (HDAC) inhibition could be a strategy to achieve these goals. Here, we review evidence that targeting HDACs with low-molecular-weight inhibitors significantly decreases neuronal injury and improves functional outcome in multiple preclinical models of focal ischemia. These salutary effects emanate, in part, from modifications of chromatin and nonchromatin proteins that enhance adaptive gene expression or adaptive protein function. Together, the findings suggest that HDAC inhibition is a strategy capable of targeting diverse pathophysiologies of stroke with a wide therapeutic window.

Small molecule activation of adaptive gene expression: tilorone or its analogs are novel potent activators of hypoxia inducible factor-1 that provide prophylaxis against stroke and spinal cord injury

A major challenge for neurological therapeutics is the development of small molecule drugs that can activate a panoply of downstream pathways without toxicity. Over the past decade our group has shown that a family of enzymes that regulate posttranscriptional and transcriptional adaptive responses to hypoxia are viable targets for neuronal protection and repair. The family is a group of iron, oxygen, and 2-oxoglutarate-dependent dioxygenases, known as the HIF prolyl 4-hydroxylases (HIF PHDs). We have previously shown that pluripotent protection offered by iron chelators is mediated, in part, via the ability of these agents to inhibit the HIF PHDs. Our group and others have implicated the transcriptional activator HIF-1 in some of the salutary effects of iron chelation-induced PHD inhibition. While some iron chelators are currently employed in humans for conditions such as hemochromatosis, the diverse utilization of iron in physiological processes in the brain makes the development of HIF activators that do not bind iron a high priority. Here we report the development of a high throughput screen to develop novel HIF activators and/or PHD inhibitors for therapeutic use in the central nervous system (CNS). We show that tilorone, a low-molecular weight, antiviral, immunomodulatory agent is the most effective activator of the HIF pathway in a neuronal line. We also show that tilorone enhances HIF protein levels and increases the expression of downstream target genes independent of iron chelation and HIF PHD inhibition in vitro. We further demonstrate that tilorone can activate an HIF-regulated reporter gene in the CNS. These studies confirm that tilorone can penetrate the blood-brain barrier to activate HIF in the CNS. As expected from these findings, we show that tilorone provides effective prophylaxis against permanent ischemic stroke and traumatic spinal cord injury in male rodents. Altogether these findings identify tilorone as a novel and potent modulator of HIF-mediated gene expression in neurons with neuroprotective properties.

Proteolytic processing of myostatin is auto-regulated during myogenesis

Myostatin, a potent negative regulator of myogenesis, is proteolytically processed by furin proteases into active mature myostatin before secretion from myoblasts. Here, we show that mature myostatin auto-regulates its processing during myogenesis. In a cell culture model of myogenesis, Northern blot analysis revealed no appreciable change in myostatin mRNA levels between proliferating myoblasts and differentiated myotubes. However, Western blot analysis confirmed a relative reduction in myostatin processing and secretion by differentiated myotubes as compared to proliferating myoblasts. Furthermore, in vivo results demonstrate a lower level of myostatin processing during fetal muscle development when compared to postnatal adult muscle. Consequently, high levels of circulatory mature myostatin were detected in postnatal serum, while fetal circulatory myostatin levels were undetectable. Since Furin proteases are important for proteolytically processing members of the TGF-beta superfamily, we therefore investigated the ability of myostatin to control the transcription of furin and auto-regulate the extent of its processing. Transfection experiments indicate that mature myostatin indeed regulates furin protease promoter activity. Based on these results, we propose a mechanism whereby myostatin negatively regulates its proteolytic processing during fetal development, ultimately facilitating the differentiation of myoblasts by controlling both furin protease gene expression and subsequent active concentrations of mature myostatin peptide.

Transcriptional therapy with the histone deacetylase inhibitor trichostatin A ameliorates experimental autoimmune encephalomyelitis

We demonstrate that the histone deacetylase (HDAC) inhibitor drug trichostatin A (TSA) reduces spinal cord inflammation, demyelination, neuronal and axonal loss and ameliorates disability in the relapsing phase of experimental autoimmune encephalomyelitis (EAE), a model of multiple sclerosis (MS). TSA up-regulates antioxidant, anti-excitotoxicity and pro-neuronal growth and differentiation mRNAs. TSA also inhibits caspase activation and down-regulates gene targets of the pro-apoptotic E2F transcription factor pathway. In splenocytes, TSA reduces chemotactic, pro-Th1 and pro-proliferative mRNAs. A transcriptional imbalance in MS may contribute to immune dysregulation and neurodegeneration, and we identify HDAC inhibition as a transcriptional intervention to ameliorate this imbalance.

Remodeling chromatin and stress resistance in the central nervous system: histone deacetylase inhibitors as novel and broadly effective neuroprotective agents

Acetylation and deacetylation of histone protein plays a critical role in regulating gene expression in a host of biological processes including cellular proliferation, development, and differentiation. Accordingly, aberrant acetylation and deacetylation resulting from the misregulation of histone acetyltransferases (HATs) and/or histone deacetylases (HDACs) has been linked to clinical disorders such as Rubinstein-Taybi syndrome, fragile X syndrome, leukemia, and various cancers. Of significant import has been the development of small molecule HDAC inhibitors that permit pharmacological manipulation of histone acetylation levels and treatment of some of these diseases including cancer. In this Review we discuss evidence that aberrant HAT and HDAC activity may also be a common underlying mechanism contributing to neurodegeneration during acute and chronic neurological diseases, including stroke, Huntington's disease Amyotrophic Lateral Sclerosis and Alzheimer's disease. With this in mind, a number of studies examining the use of HDAC inhibitors as therapy for restoring histone acetylation and transcriptional activation in in vitro and in vivo neurodegenerative models are discussed. These studies demonstrate that pharmacological HDAC inhibition is a promising therapeutic approach for the treatment of a range of central nervous system disorders.

Chemotherapy for the brain: the antitumor antibiotic mithramycin prolongs survival in a mouse model of Huntington's disease

Huntington's disease (HD) is a fully penetrant autosomal-dominant inherited neurological disorder caused by expanded CAG repeats in the Huntingtin gene. Transcriptional dysfunction, excitotoxicity, and oxidative stress have all been proposed to play important roles in the pathogenesis of HD. This study was designed to explore the therapeutic potential of mithramycin, a clinically approved guanosine-cytosine-rich DNA binding antitumor antibiotic. Pharmacological treatment of a transgenic mouse model of HD (R6/2) with mithramycin extended survival by 29.1%, greater than any single agent reported to date. Increased survival was accompanied by improved motor performance and markedly delayed neuropathological sequelae. To identify the functional mechanism for the salubrious effects of mithramycin, we examined transcriptional dysfunction in R6/2 mice. Consistent with transcriptional repression playing a role in the pathogenesis of HD, we found increased methylation of lysine 9 in histone H3, a well established mechanism of gene silencing. Mithramycin treatment prevented the increase in H3 methylation observed in R6/2 mice, suggesting that the enhanced survival and neuroprotection might be attributable to the alleviation of repressed gene expression vital to neuronal function and survival. Because it is Food and Drug Administration-approved, mithramycin is a promising drug for the treatment of HD.

Oxidative stress-induced death in the nervous system: cell cycle dependent or independent?

Neuronal death, attributable to perturbed redox homeostasis, is the underlying factor in many acute and chronic neurological disorders. The mechanisms employed by oxidatively stressed neurons to commit to cell death pathways are beginning to be characterized, but this is hampered by a lack of good models that extrapolate readily to redox-dependent neuronal death paradigms. In this Mini-Review, we discuss mechanisms by which oxidative stress can result in neurodegeneration. We examine evidence on which terminally differentiated neurons might commit to death under conditions of oxidative stress. In some cases, death may be linked to an aberrant and uncoordinated reentry into the cell cycle and mitotic catastrophe. Other evidence suggests that cell cycle reentry is not mandatory for death execution. Rather, the reexpression of cell cycle proteins may induce apoptotic pathways in a cell cycle-independent manner. In contrast to these models, there is also evidence that oxidative neuronal death is independent of cell cycle proteins. We conclude that oxidative stress-induced neuronal death may be promoted via several pathways, which may be cycle protein dependent or independent. The determining factor for which or how many pathways are induced appears to be context dependent and determined by the level and duration of oxidative stress.

Neuroprotective effects of phenylbutyrate in the N171-82Q transgenic mouse model of Huntington's disease

Huntington's disease (HD) is caused by an expansion of exonic CAG triplet repeats in the gene encoding the huntingtin protein (Htt), however, the means by which neurodegeneration occurs remains obscure. There is evidence that mutant Htt interacts with transcription factors leading to reduced histone acetylation. We report that administration of the histone deacetylase inhibitor phenylbutyrate after onset of symptoms in a transgenic mouse model of HD significantly extends survival and attenuates both gross brain and neuronal atrophy. Administration of phenylbutyrate increased brain histone acetylation and decreased histone methylation levels as assessed by both immunocytochemistry and Western blots. Phenylbutyrate increased mRNA for components of the ubiquitin-proteosomal pathway and down-regulated caspases implicated in apoptotic cell death, and active caspase 3 immunoreactivity in the striatum. These results show that administration of phenylbutyrate, at doses that are well tolerated in man, exerts significant neuroprotective effects in a transgenic mouse model of HD, and therefore represents a very promising therapeutic approach for HD.

Translation of ischemic preconditioning to the patient: prolyl hydroxylase inhibition and hypoxia inducible factor-1 as novel targets for stroke therapy

Effective therapies for stroke must interdict multiple parallel and sequential pathophysiological events. A paradigm which offers insight into multivalent but thoughtfully coordinated protective programs is ischemic preconditioning. A central hypothesis of our group and others is that pharmacological agents that activate programs of gene expression normally induced by ischemic preconditioning will be effective agents for the prevention and treatment of stroke. Inhibitors of a class of enzymes, the hypoxia inducible factor-1 (HIF-1) prolyl hydroxylases stabilize the transcriptional activator HIF-1 and activate target genes involved in compensation for ischemia, including erythropoeitin (Epo) and vascular endothelial growth factor (VEGF). Here, we review evidence suggesting that the HIF-1 prolyl hyroxylases are inhibited during ischemic preconditioning and that pharmacological inhibitors of these enzymes are viable targets for stroke therapy.

Novel roles for arginase in cell survival, regeneration, and translation in the central nervous system

In this review the current knowledge about the arginine-degrading enzyme arginase and its unexpected roles in survival and regeneration in the central nervous system will be discussed. Recent data suggest the neuroprotective effects of extracellularly applied arginase can be attributed to an activation of the endoplasmic reticulum stress response with a consequent change of the pro-survival gene expression profile. However, the activation of neural regeneration pathways caused by an upregulation of endogenous arginase I is mediated by polyamines, a group of arginase downstream products with widespread biological effects. In light of these new discoveries, there is heightened interest in the regulation of arginase I gene expression within the central nervous system. A number of transcription factors such as Sp1, C/EBP (CCATT/enhancer-binding protein), and CREB seem to be involved in the transcriptional control of arginase I and may contribute to the complex expression pattern of arginase I in distinct brain regions and during development. Beyond molecular mechanisms, this review will also include relevant clinical findings in patients with neurodegenerative diseases.

Myostatin inhibits rhabdomyosarcoma cell proliferation through an Rb-independent pathway

Rhabdomyosarcoma (RMS) tumors are the most common soft-tissue sarcomas in childhood. In this investigation, we show that myostatin, a skeletal muscle-specific inhibitor of growth and differentiation is expressed and translated in the cultured RMS cell line, RD. The addition of exogenous recombinant myostatin inhibits the proliferation of RD cells cultured in growth media, consistent with the role of myostatin in normal myoblast proliferation inhibition. However, unlike normal myoblasts, upregulation of p21 was not observed. Rather, myostatin signalling resulted in the specific downregulation of both Cdk2 and its cognate partner, cyclin-E. The analysis of Rb reveals that there was no change in its phosphorylation status with myostatin treatment, consistent with D-type-cyclin-Cdk4/6 complexes being active in the absence of p21. Moreover, the activity of Rb appeared to be unchanged between treated and nontreated RD cells, as determined by the ability of Rb to bind E2F1. The examination of NPAT, a substrate of cyclin-E-Cdk2 involved in the transcriptional activation of replication-dependent histone gene expression, revealed that it undergoes a loss of phosphorylation with myostatin treatment. Supporting this, a downregulation in H4-histone gene expression was observed. These results suggest that myostatin could potentially be used as an inhibitor of RMS proliferation and define a previously uncharacterized, Rb-independent mechanism for the inhibition of muscle precursor cell proliferation by myostatin.

Titin-cap associates with, and regulates secretion of, Myostatin

Myostatin, a secreted growth factor, is a key negative regulator of skeletal muscle growth. To identify modifiers of Myostatin function, we screened for Myostatin interacting proteins. Using a yeast two-hybrid screen, we identified Titin-cap (T-cap) protein as interacting with Myostatin. T-cap is a sarcomeric protein that binds to the N-terminal domain of Titin and is a substrate of the titin kinase. Mammalian two-hybrid studies, in vitro binding assays and protein truncations in the yeast two-hybrid system verified the specific interaction between processed mature Myostatin and full-length T-cap. Analysis of protein-protein interaction using surface plasmon resonance (Biacore, Uppsala, Sweden) kinetics revealed a high affinity between Myostatin and T-cap with a KD of 40 nM. When T-cap was stably overexpressed in C(2)C(12) myoblasts, the rate of cell proliferation was significantly increased. Western analyses showed that production and processing of Myostatin were not altered in cells overexpressing T-cap, but an increase in the retention of mature Myostatin indicated that T-cap may block Myostatin secretion. Bioassay for Myostatin confirmed that conditioned media from myoblasts overexpressing T-cap contained lower levels of Myostatin. Given that Myostatin negatively regulates myoblast proliferation, the increase in proliferation observed in myoblasts overexpressing T-cap could thus be due to reduced Myostatin secretion. These results suggest that T-cap, by interacting with Myostatin, controls Myostatin secretion in myogenic precursor cells without affecting the processing step of precursor Myostatin.

Myostatin inhibits myoblast differentiation by down-regulating MyoD expression

Myostatin, a negative regulator of myogenesis, is shown to function by controlling the proliferation of myoblasts. In this study we show that myostatin is an inhibitor of myoblast differentiation and that this inhibition is mediated through Smad 3. In vitro, increasing concentrations of recombinant mature myostatin reversibly blocked the myogenic differentiation of myoblasts, cultured in low serum media. Western and Northern blot analysis indicated that addition of myostatin to the low serum culture media repressed the levels of MyoD, Myf5, myogenin, and p21 leading to the inhibition of myogenic differentiation. The transient transfection of C(2)C(12) myoblasts with MyoD expressing constructs did not rescue myostatin-inhibited myogenic differentiation. Myostatin signaling specifically induced Smad 3 phosphorylation and increased Smad 3.MyoD association, suggesting that Smad 3 may mediate the myostatin signal by interfering with MyoD activity and expression. Consistent with this, the expression of dominant-negative Smad3 rescued the activity of a MyoD promoter-reporter in C(2)C(12) myoblasts treated with myostatin. Taken together, these results suggest that myostatin inhibits MyoD activity and expression via Smad 3 resulting in the failure of the myoblasts to differentiate into myotubes. Thus we propose that myostatin plays a critical role in myogenic differentiation and that the muscular hyperplasia and hypertrophy seen in animals that lack functional myostatin is because of deregulated proliferation and differentiation of myoblasts.

Single cysteine to tyrosine transition inactivates the growth inhibitory function of Piedmontese myostatin

Myostatin, a member of the transforming growth factor-beta superfamily, is a secreted growth factor that is proteolytically processed to give COOH-terminal mature myostatin and NH2-terminal latency-associated peptide in myoblasts. Piedmontese cattle are a heavy-muscled breed that express a mutated form of myostatin in which cysteine (313) is substituted with tyrosine. Here we have characterized the biology of this mutated Piedmontese myostatin. Northern and Western analyses indicate that there is increased expression of myostatin mRNA and precursor myostatin protein in the skeletal muscle of Piedmontese cattle. In contrast, a decrease in mature myostatin was observed in Piedmontese skeletal muscle. However, there is no detectable change in the circulatory levels of mature myostatin in Piedmontese cattle. Myoblast proliferation assay performed with normal and Piedmontese myostatin indicated that mature wild-type myostatin protein inhibited the proliferation of C2C12 myoblasts. Piedmontese myostatin, by contrast, failed to inhibit myoblast proliferation. In addition, when added in molar excess, Piedmontese myostatin acted as a potent "competitive inhibitor" molecule. These results indicate that, in Piedmontese myostatin, substitution of cysteine with tyrosine results in the distortion of the "cystine knot" structure and a loss of biological activity of the myostatin. This mutation also appears to affect either processing or stability of mature myostatin without altering the secretion of myostatin.

Myostatin in muscle growth and repair

Myostatin, a member of the TGF beta superfamily, regulates skeletal muscle size by controlling embryonic myoblast proliferation. Recent results show that myostatin may also have a role in muscle regeneration and muscle wasting of adult animals. This review summarizes the recent developments in the regulation of myostatin gene expression and mechanism of its function.

Myostatin, a negative regulator of muscle growth, functions by inhibiting myoblast proliferation

Myostatin, a member of the transforming growth factor-beta (TGF-beta) superfamily, has been shown to be a negative regulator of myogenesis. Here we show that myostatin functions by controlling the proliferation of muscle precursor cells. When C(2)C(12) myoblasts were incubated with myostatin, proliferation of myoblasts decreased with increasing levels of myostatin. Fluorescence-activated cell sorting analysis revealed that myostatin prevented the progression of myoblasts from the G(1)- to S-phase of the cell cycle. Western analysis indicated that myostatin specifically up-regulated p21(Waf1, Cip1), a cyclin-dependent kinase inhibitor, and decreased the levels and activity of Cdk2 protein in myoblasts. Furthermore, we also observed that in myoblasts treated with myostatin protein, Rb was predominately present in the hypophosphorylated form. These results suggests that, in response to myostatin signaling, there is an increase in p21 expression and a decrease in Cdk2 protein and activity thus resulting in an accumulation of hypophosphorylated Rb protein. This, in turn, leads to the arrest of myoblasts in G(1)-phase of cell cycle. Thus, we propose that the generalized muscular hyperplasia phenotype observed in animals that lack functional myostatin could be as a result of deregulated myoblast proliferation.

Milk whey protein concentration and mRNA associated with beta-lactoglobulin phenotype

Two common genetic variants of β-lactoglobulin (β-lg), A and B, exist as co- dominant alleles in dairy cattle (Aschaffenburg, 1968). Numerous studies have shown that cows homozygous for β-lg A have more β-lg and less α-lactalbumin (α-la) and casein in their milk than cows expressing only the B variant of β-lg (Ng-Kwai-Hang et al. 1987; Graml et al. 1989; Hill, 1993; Hill et al. 1995, 1997). These differences have a significant impact on the processing characteristics of the milk. For instance, the moisture-adjusted yield of Cheddar cheese is up to 10% higher using milk from cows of the β-lg BB phenotype compared with milk from cows expressing only the A variant (Hill et al. 1997). All these studies, however, describe compositional differences associated with β-lg phenotype in established lactation only. No information is available on the first few weeks of lactation, when there are marked changes in the concentrations of β-lg and α-la (Pérez et al. 1990).

Introduction of a proximal Stat5 site in the murine alpha-lactalbumin promoter induces prolactin dependency in vitro and improves expression frequency in vivo

In order to establish a possible correlation between in vitro prolactin induction and the transcriptional activity of mammary gene promoters in transgenic mice, a functional Stat5-binding site was created by means of site-directed mutagenesis at position -70 on a 560 bp murine alpha-lactalbumin promotor linked to a CAT reporter gene. Surprisingly, the wild-type promoter was constitutively active in vitro and could not be induced by prolactin. Introducing the proximal Stat5 site abolished this constitutive activity and resulted in prolactin dependence in both CHO-K1- and HC11-transfected cells. In transgenic mice, both the frequency of lines expressing the transgene and the prevalence of mid to late pregnancy expression were increased.

Rescue of an MMTV transgene by co-integration reveals novel locus control properties of the ovine beta-lactoglobulin gene that confer locus commitment to heterogeneous tissues

In an attempt to enhance the frequency and level of expression of a poor-performing MMTV-driven transgene, we co-integrated this construct with the ovine beta-lactoglobulin (BLG) gene in transgenic mice. Seven lines of transgenic mice possessing co-integrated BLG and MMTV-RZ5 transgenes were compared with 12 lines of mice that possessed only the MMTV-RZ5 construct. Co-integration enhanced the frequency of expression in the mammary gland from two out of 12 lines for the MMTV-RZ5 transgene alone, to five out of seven when co-integrated with BLG. Surprisingly, co-integration also resulted in co-expression of the two transgenes in the salivary gland, lung and spleen in addition to the mammary gland. Furthermore, both transgenes were expressed in virgin animals, and throughout pregnancy and lactation, suggesting that the developmental regulation of the locus follows that of the MMTV-promoter. These findings represent a novel locus control property of the ovine BLG gene that confers commitment of the locus to the mammary gland, but also to a range of heterogeneous tissues possibly defined by the second promoter at the locus.

Perceptions, safety behaviors, and learning needs of parents of children brought to an emergency department

INTRODUCTION

This study was conducted at a level II Pediatric Trauma Center to assess the perceptions, safety behaviors, and learning needs of parents who brought their children to the emergency department.

METHODS

Surveys were distributed in the emergency department, and 412 parents/caretakers responded. A descriptive design provided the framework for data analysis.

RESULTS

A profile of caretakers of children in three age groups (1 to 4, 5 to 12, and 13 to 15 years) emerged. Whereas most parents and older children knew how to call 911, only half of the parents knew child CPR. Parents tended to underestimate their children's risks for motor vehicle-related and immersion injuries and were more concerned about kidnapping and assault. Less than half of the parents believed that most injuries can be prevented. Learning needs were indicated by 34% of parents, and CPR was mentioned most frequently. Parents' desires for learning tended to focus on care after injuries happened.

DISCUSSION

Health professionals need to spend more time teaching parents about the link between child development and risks for injury, to emphasize prevention. Interventions based on study results include the hospital Safety Helmet Discharge Plan.

Patterns of injury in pediatric patients in one Florida community and implications for prevention programs

OBJECTIVES

To meet community needs, injury prevention programs for children should be based on an understanding of the patterns of different mechanisms of injury. This study was conducted by the staff of a level II pediatric trauma center to describe the patterns of injury in pediatric patients with traumatic injuries.

METHODS

We conducted a retrospective review of medical records of all 184 pediatric "trauma alert" patients seen during a 1-year period. The trauma alert status is assigned to children with serious injuries or when the mechanism of injury is severe. Data analysis used descriptive statistics.

RESULTS

Pedestrian-versus-automobile injuries were the most common and most severe injuries, followed in frequency by falls, motor vehicle occupant, and bicycle-versus-automobile injuries. Younger children tended to have injuries as a result of falls; school-age children were involved more often in pedestrian and bicycle injuries, and adolescents had more motor vehicle occupant injuries. Failure to use safety devices, such as helmets and seat belts, was a common finding.

DISCUSSION

Patterns of injury were similar to those described in national studies. An extensive helmet campaign directed at child bicyclists was developed as a result of the priorities generated from the study. Other community programs included bicycle rodeos and a mix-off of nonalcoholic beverages.