DNA topoisomerase I inhibitors ameliorate seizure-like behaviors and paralysis in a Drosophila model of epilepsy

Recent developments of topoisomerase inhibitors: Clinical trials, emerging indications, novel molecules and global sales

The nucleic acid topoisomerases (TOP) are an evolutionary conserved mechanism to solve topological problems within DNA and RNA that have been historically well-established as a chemotherapeutic target. During investigation of trends within clinical trials, we have identified a very high number of clinical trials involving TOP inhibitors, prompting us to further evaluate the current status of this class of therapeutic agents. In total, we have identified 233 unique molecules with TOP-inhibiting activity. In this review, we provide an overview of the clinical drug development highlighting advances in current clinical uses and discussing novel drugs and indications under development. A wide range of bacterial infections, along with solid and hematologic neoplasms, represent the bulk of clinically approved indications. Negative ADR profile and drug resistance among the antibacterial TOP inhibitors and anthracycline-mediated cardiotoxicity in the antineoplastic TOP inhibitors are major points of concern, subject to continuous research efforts. Ongoing development continues to focus on bacterial infections and cancer; however, there is a degree of diversification in terms of novel drug classes and previously uncovered indications, such as glioblastoma multiforme or Clostridium difficile infections. Preclinical studies show potential in viral, protozoal, parasitic and fungal infections as well and suggest the emergence of a novel target, TOP IIIβ. We predict further growth and diversification of the field thanks to the large number of experimental TOP inhibitors emerging.

Effects of valproate on seizure-like activity in Drosophila melanogaster with a knockdown of Ube3a in different neuronal populations as a model of Angelman Syndrome

Angelman Syndrome is a rare, genetically induced neurodevelopmental disorder. This disorder stems from a mutation or deletion of the maternal UBE3A gene. Characteristics of this disease include developmental delay, recurring seizures, and severe intellectual disabilities. We studied seizure activity in male Drosophila melanogaster with a knockdown of Ube3a in different neuronal populations (GABAergic, glutamatergic, mushroom body, and all neurons) and investigated the effects of the antiseizure medication (ASM) on seizure-like activity. Epileptiform activity was monitored in individual fruit flies using imaging chambers and mechanically induced seizures using a vortex assay. A positive control was also used: eas (easily shocked seizure phenotype). Seizure activity was analyzed for sums of seizure durations, number of seizures, and total time to return to normal activity. Ube3a knockdowns in GABAergic neurons elicited more seizure-like episodes than knockdowns in glutamatergic neurons and were on par with the positive control group and those with knockdowns in the mushroom bodies. We have established a method whereby valproate could be administered through food rather than through injections to effectively treat epileptiform activity. We demonstrated that if Ube3a is not knocked down pan-neuronally, Angelman Syndrome seizure-like activity can be studied using Drosophila melanogaster and therefore allows for high-throughput drug discovery.

Seizure-suppressor genes: can they help spearhead the discovery of novel therapeutic targets for epilepsy?

INTRODUCTION

Epilepsies are disorders of neuronal excitability characterized by spontaneously recurrent focal and generalized seizures, some of which result from genetic mutations. Despite the availability of antiseizure medications, pharmaco-resistant epilepsy is seen in about 23% of epileptic patients worldwide. Therefore, there is an urgent need to develop novel therapeutic strategies for epilepsies. Several epilepsy-associated genes have been found in humans. Seizure susceptibility can also be induced in Drosophila mutants, some showing features resembling human epilepsies. Interestingly, several second-site mutation gene products have been found to suppress seizure susceptibility in the seizure genetic model Drosophila. Thus, these so-called 'seizure-suppressor' gene variants may lead to developing a novel class of antiseizure medications.

AREA COVERED

This review evaluates the potential therapeutic of seizure-suppressor gene variants.

EXPERT OPINION

Studies on epilepsy-associated genes have allowed analyses of mutations linked to human epilepsy by reproducing these mutations in Drosophila using reverse genetics to generate potential antiseizure therapeutics. As a result, about fifteen seizure-suppressor gene mutants have been identified. Furthermore, some of these epilepsy gene mutations affect ligand-and voltage-gated ion channels. Therefore, a better understanding of the antiseizure activity of seizure-suppressor genes is essential in advancing gene therapy and precision medicine for epilepsy.

Drosophila melanogaster as a versatile model organism to study genetic epilepsies: An overview

Epilepsy is one of the most prevalent neurological disorders, affecting more than 45 million people worldwide. Recent advances in genetic techniques, such as next-generation sequencing, have driven genetic discovery and increased our understanding of the molecular and cellular mechanisms behind many epilepsy syndromes. These insights prompt the development of personalized therapies tailored to the genetic characteristics of an individual patient. However, the surging number of novel genetic variants renders the interpretation of pathogenetic consequences and of potential therapeutic implications ever more challenging. Model organisms can help explore these aspects in vivo. In the last decades, rodent models have significantly contributed to our understanding of genetic epilepsies but their establishment is laborious, expensive, and time-consuming. Additional model organisms to investigate disease variants on a large scale would be desirable. The fruit fly Drosophila melanogaster has been used as a model organism in epilepsy research since the discovery of "bang-sensitive" mutants more than half a century ago. These flies respond to mechanical stimulation, such as a brief vortex, with stereotypic seizures and paralysis. Furthermore, the identification of seizure-suppressor mutations allows to pinpoint novel therapeutic targets. Gene editing techniques, such as CRISPR/Cas9, are a convenient way to generate flies carrying disease-associated variants. These flies can be screened for phenotypic and behavioral abnormalities, shifting of seizure thresholds, and response to anti-seizure medications and other substances. Moreover, modification of neuronal activity and seizure induction can be achieved using optogenetic tools. In combination with calcium and fluorescent imaging, functional alterations caused by mutations in epilepsy genes can be traced. Here, we review Drosophila as a versatile model organism to study genetic epilepsies, especially as 81% of human epilepsy genes have an orthologous gene in Drosophila. Furthermore, we discuss newly established analysis techniques that might be used to further unravel the pathophysiological aspects of genetic epilepsies.

Vps54 Regulates Lifespan and Locomotor Behavior in Adult Drosophila melanogaster

Vps54 is an integral subunit of the Golgi-associated retrograde protein (GARP) complex, which is involved in tethering endosome-derived vesicles to the trans-Golgi network (TGN). A destabilizing missense mutation in Vps54 causes the age-progressive motor neuron (MN) degeneration, muscle weakness, and muscle atrophy observed in the wobbler mouse, an established animal model for human MN disease. It is currently unclear how the disruption of Vps54, and thereby the GARP complex, leads to MN and muscle phenotypes. To develop a new tool to address this question, we have created an analogous model in Drosophila by generating novel loss-of-function alleles of the fly Vps54 ortholog (scattered/scat). We find that null scat mutant adults are viable but have a significantly shortened lifespan. Like phenotypes observed in the wobbler mouse, we show that scat mutant adults are male sterile and have significantly reduced body size and muscle area. Moreover, we demonstrate that scat mutant adults have significant age-progressive defects in locomotor function. Interestingly, we see sexually dimorphic effects, with scat mutant adult females exhibiting significantly stronger phenotypes. Finally, we show that scat interacts genetically with rab11 in MNs to control age-progressive muscle atrophy in adults. Together, these data suggest that scat mutant flies share mutant phenotypes with the wobbler mouse and may serve as a new genetic model system to study the cellular and molecular mechanisms underlying MN disease.

Critical roles of Rad54 in tolerance to apigenin-induced Top1-mediated DNA damage

Apigenin (APG), a flavone sub-class of flavonoids, possesses a diverse range of biological activities, including anti-cancer and anti-inflammatory effects. Previous studies identified the genotoxicity of APG in certain cancer cells, which may be associated with its anticancer effect. However, the DNA damage repair mechanism induced by APG has remained elusive. In order to clarify the molecular mechanisms, the present study determined the toxicity of APG to the wild-type (WT) DT40 chicken B-lymphocyte cell line, as well as to DT40 cells with deletions in various DNA repair genes, and their sensitivities were compared. It was demonstrated that cells deficient of Rad54, a critical homologous recombination gene, were particularly sensitive to APG. Cell-cycle analysis demonstrated that APG caused an increase in the G₂/M-phase population of Rad54^{- / -} cells that was greater than that in WT cells. Furthermore, it was demonstrated by immunofluorescence assay that Rad54^{- / -} cells exhibited significantly increased numbers of γ-phosphorylated H2AX variant histone foci and chromosomal aberrations compared to the WT cells in response to APG. Of note, the in vitro complex of enzyme assay indicated that APG induced increased topoisomerase I (Top1) covalent protein DNA complex in Rad54^{- / -} cells compared to WT cells. Finally, these results were verified using the TK6 human lymphoblastoid cell line and it was demonstrated that, as for DT40 cells, Rad54 deficiency sensitized TK6 cells to APG. The present study demonstrated that Rad54 was involved in the repair of APG-induced DNA damage, which was associated with Top1 inhibition.

An Insight into Molecular Mechanisms and Novel Therapeutic Approaches in Epileptogenesis

Epilepsy is the second most common neurological disease with abnormal neural activity involving the activation of various intracellular signalling transduction mechanisms. The molecular and system biology mechanisms responsible for epileptogenesis are not well defined or understood. Neuroinflammation, neurodegeneration and Epigenetic modification elicit epileptogenesis. The excessive neuronal activities in the brain are associated with neurochemical changes underlying the deleterious consequences of excitotoxicity. The prolonged repetitive excessive neuronal activities extended to brain tissue injury by the activation of microglia regulating abnormal neuroglia remodelling and monocyte infiltration in response to brain lesions inducing axonal sprouting contributing to neurodegeneration. The alteration of various downstream transduction pathways resulted in intracellular stress responses associating endoplasmic reticulum, mitochondrial and lysosomal dysfunction, activation of nucleases, proteases mediated neuronal death. The recently novel pharmacological agents modulate various receptors like mTOR, COX-2, TRK, JAK-STAT, epigenetic modulators and neurosteroids are used for attenuation of epileptogenesis. Whereas the various molecular changes like the mutation of the cell surface, nuclear receptor and ion channels focusing on repetitive episodic seizures have been explored by preclinical and clinical studies. Despite effective pharmacotherapy for epilepsy, the inadequate understanding of precise mechanisms, drug resistance and therapeutic failure are the current fundamental problems in epilepsy. Therefore, the novel pharmacological approaches evaluated for efficacy on experimental models of epilepsy need to be identified and validated. In addition, we need to understand the downstream signalling pathways of new targets for the treatment of epilepsy. This review emphasizes on the current state of novel molecular targets as therapeutic approaches and future directions for the management of epileptogenesis. Novel pharmacological approaches and clinical exploration are essential to make new frontiers in curing epilepsy.

Investigating Developmental and Epileptic Encephalopathy Using Drosophila melanogaster

Developmental and epileptic encephalopathies (DEEs) are the spectrum of severe epilepsies characterized by early-onset, refractory seizures occurring in the context of developmental regression or plateauing. Early infantile epileptic encephalopathy (EIEE) is one of the earliest forms of DEE, manifesting as frequent epileptic spasms and characteristic electroencephalogram findings in early infancy. In recent years, next-generation sequencing approaches have identified a number of monogenic determinants underlying DEE. In the case of EIEE, 85 genes have been registered in Online Mendelian Inheritance in Man as causative genes. Model organisms are indispensable tools for understanding the in vivo roles of the newly identified causative genes. In this review, we first present an overview of epilepsy and its genetic etiology, especially focusing on EIEE and then briefly summarize epilepsy research using animal and patient-derived induced pluripotent stem cell (iPSC) models. The Drosophila model, which is characterized by easy gene manipulation, a short generation time, low cost and fewer ethical restrictions when designing experiments, is optimal for understanding the genetics of DEE. We therefore highlight studies with Drosophila models for EIEE and discuss the future development of their practical use.

A Systematic Review on Non-mammalian Models in Epilepsy Research

Epilepsy is a common neurological disorder characterized by seizures which result in distinctive neurobiological and behavioral impairments. Not much is known about the causes of epilepsy, making it difficult to devise an effective cure for epilepsy. Moreover, clinical studies involving epileptogenesis and ictogenesis cannot be conducted in humans due to ethical reasons. As a result, animal models play a crucial role in the replication of epileptic seizures. In recent years, non-mammalian models have been given a primary focus in epilepsy research due to their advantages. This systematic review aims to summarize the importance of non-mammalian models in epilepsy research, such as in the screening of anti-convulsive compounds. The reason for this review is to integrate currently available information on the use and importance of non-mammalian models in epilepsy testing to aid in the planning of future studies as well as to provide an overview of the current state of this field. A PRISMA model was utilized and PubMed, Springer, ScienceDirect and SCOPUS were searched for articles published between January 2007 and November 2017. Fifty-one articles were finalized based on the inclusion/exclusion criteria and were discussed in this review. The results of this review demonstrated the current use of non-mammalian models in epilepsy research and reaffirmed their potential to supplement the typical rodent models of epilepsy in future research into both epileptogenesis and the treatment of epilepsy. This review also revealed a preference for zebrafish and fruit flies in lieu of other non-mammalian models, which is a shortcoming that should be corrected in future studies due to the great potential of these underutilized animal models.

Identifying new antiepileptic drugs through genomics-based drug repurposing

Currently available antiepileptic drugs (AEDs) fail to control seizures in 30% of patients. Genomics-based drug repurposing (GBR) offers the potential of savings in the time and cost of developing new AEDs. In the current study, we used published data and software to identify the transcriptomic signature of chornic temporal lobe epilepsy and the drugs that reverse it. After filtering out compounds based on exclusion criteria, such as toxicity, 36 drugs were retained. 11 of the 36 drugs identified (>30%) have published evidence of the antiepileptic efficacy (for example, curcumin) or antiepileptogenic affect (for example, atorvastatin) in recognised rodent models or patients. By objectively annotating all ∼20,000 compounds in the LINCS database as either having published evidence of antiepileptic efficacy or lacking such evidence, we demonstrated that our set of repurposable drugs is ∼6-fold more enriched with drugs having published evidence of antiepileptic efficacy in animal models than expected by chance (P-value <0.006). Further, we showed that another of our GBR-identified drugs, the commonly-used well-tolerated antihyperglycemic sitagliptin, produces a dose-dependent reduction in seizures in a mouse model of pharmacoresistant epilepsy. In conclusion, GBR successfully identifies compounds with antiepileptic efficacy in animal models and, hence, it is an appealing methodology for the discovery of potential AEDs.

Bio-effectiveness of the main flavonoids of Achillea millefolium in the pathophysiology of neurodegenerative disorders- a review

The Achillea millefolium L. (Yarrow) is a common herb which is widely being used, worldwide. Achillea is being used for treatment of many disorders since centuries. It is considered safe for supplemental use and flavonoids such as kaempferol, luteolin and apigenin are of main constituents present in Achillea. Most of both antioxidant and anti-inflammatory properties of this herb have been attributed to its flavonoid content. Oxidative and inflammatory processes play important roles in pathogenesis of neurodegenerative diseases. Present review was aimed to review the latest literature evidences regarding application of Achillea and/or its three main flavonoid constituents on epilepsy, Alzheimer's disease, multiple sclerosis, Parkinson's disease and stroke.

Seizure control through genetic and pharmacological manipulation of Pumilio in Drosophila: a key component of neuronal homeostasis

Epilepsy is a significant disorder for which approximately one-third of patients do not respond to drug treatments. Next-generation drugs, which interact with novel targets, are required to provide a better clinical outcome for these individuals. To identify potential novel targets for antiepileptic drug (AED) design, we used RNA sequencing to identify changes in gene transcription in two seizure models of the fruit fly Drosophila melanogaster The first model compared gene transcription between wild type (WT) and bangsenseless¹ (para^bss), a gain-of-function mutant in the sole fly voltage-gated sodium channel (paralytic). The second model compared WT with WT fed the proconvulsant picrotoxin (PTX). We identified 743 genes (FDR≤1%) with significant altered expression levels that are common to both seizure models. Of these, 339 are consistently upregulated and 397 downregulated. We identify pumilio (pum) to be downregulated in both seizure models. Pum is a known homeostatic regulator of action potential firing in both flies and mammals, achieving control of neuronal firing through binding to, and regulating translation of, the mRNA transcripts of voltage-gated sodium channels (Na_v). We show that maintaining expression of pum in the CNS of para^bss flies is potently anticonvulsive, whereas its reduction through RNAi-mediated knockdown is proconvulsive. Using a cell-based luciferase reporter screen, we screened a repurposed chemical library and identified 12 compounds sufficient to increase activity of pum Of these compounds, we focus on avobenzone, which significantly rescues seizure behaviour in para^bss flies. The mode of action of avobenzone includes potentiation of pum expression and mirrors the ability of this homeostatic regulator to reduce the persistent voltage-gated Na⁺ current (I_NaP) in an identified neuron. This study reports a novel approach to suppress seizure and highlights the mechanisms of neuronal homeostasis as potential targets for next-generation AEDs.

Mutations of the Calcium Channel Gene cacophony Suppress Seizures in Drosophila

Bang sensitive (BS) Drosophila mutants display characteristic seizure-like phenotypes resembling, in some aspects, those of human seizure disorders such as epilepsy. The BS mutant para^bss1, caused by a gain-of-function mutation of the voltage-gated Na⁺ channel gene, is extremely seizure-sensitive with phenotypes that have proven difficult to ameliorate by anti-epileptic drug feeding or by seizure-suppressor mutation. It has been presented as a model for intractable human epilepsy. Here we show that cacophony (cac^TS2), a mutation of the Drosophila presynaptic Ca⁺⁺ channel α₁ subunit gene, is a particularly potent seizure-suppressor mutation, reverting seizure-like phenotypes for para^bss1 and other BS mutants. Seizure-like phenotypes for para^bss1 may be suppressed by as much as 90% in double mutant combinations with cac^TS2. Unexpectedly, we find that para^bss1 also reciprocally suppresses cac^TS2 seizure-like phenotypes. The cac^TS2 mutant displays these seizure-like behaviors and spontaneous high-frequency action potential firing transiently after exposure to high temperature. We find that this seizure-like behavior in cac^TS2 is ameliorated by 85% in double mutant combinations with para^bss1.

Seizure disorders, such as epilepsy, are a serious health concern because of the large number of patients affected and a limited availability of treatment options. About 10% of the population will have at least one seizure during their lifetime, and 1% will experience persistent, recurrent epileptic seizures. Moreover, for about one-third of patients, epilepsy is intractable with seizures that are not controlled with any available drugs. Genetic seizure suppressors are modifier mutations that are capable of reverting seizure susceptibility to wild type levels when combined with seizure-prone mutants in double mutant individuals. Suppressors are valuable in providing an experimental approach that can provide insight into mechanisms underlying seizure susceptibility. Also, they identify novel gene products that may be targets for therapeutic drug development. In the present study we show that a severe seizure phenotype of the Drosophila paralytic^bss1(para^bss1) mutant is 90% suppressed by the N-type calcium channel mutation cacophony^TS2(cac^TS2). The effect of suppression is not restricted to para^bss1, but cac^TS2 can also revert seizure-like phenotypes of other Drosophila mutants like easily-shocked (eas) and slamdance (sda). Thus, cac^TS2 acts as a highly potent, general seizure suppressor mutation. A surprising finding in this study is co-suppression: para^bss1 also suppresses a seizure phenotype in cac^TS2 mutants induced by elevated temperature. A current view of complex diseases such as epilepsy, is that multiple genes and environmental factors can each contribute small, additive effects that can summate to produce a disease state when some threshold value is exceeded. Our findings indicate that different pathogenic ion channel mutations can sometimes form therapeutic combinations with effects that mask one another.

Seizure suppression through manipulating splicing of a voltage-gated sodium channel

Voltage-gated persistent sodium current (INaP) is a tractable target for antiepileptic drugs. Using a strategy focused on INaP reduction, Lin et al. identify 95 regulators of voltage-gated sodium channel splicing for which RNAi knockdown reduces seizure duration in Drosophila. Manipulation of splicing regulators could improve control of epilepsy.

Seizure can result from increased voltage-gated persistent sodium current expression. Although many clinically-approved antiepileptic drugs target voltage-gated persistent sodium current, none exclusively repress this current without also adversely affecting the transient voltage-gated sodium current. Achieving a more selective block has significant potential for the treatment of epilepsy. Recent studies show that voltage-gated persistent sodium current amplitude is regulated by alternative splicing offering the possibility of a novel route for seizure control. In this study we identify 291 splicing regulators that, on knockdown, alter splicing of the Drosophila voltage-gated sodium channel to favour inclusion of exon K, rather than the mutually exclusive exon L. This change is associated with both a significant reduction in voltage-gated persistent sodium current, without change to transient voltage-gated sodium current, and to rescue of seizure in this model insect. RNA interference mediated knock-down, in two different seizure mutants, shows that 95 of these regulators are sufficient to significantly reduce seizure duration. Moreover, most suppress seizure activity in both mutants, indicative that they are part of well conserved pathways and likely, therefore, to be optimal candidates to take forward to mammalian studies. We provide proof-of-principle for such studies by showing that inhibition of a selection of regulators, using small molecule inhibitors, is similarly effective to reduce seizure. Splicing of the Drosophila sodium channel shows many similarities to its mammalian counterparts, including altering the amplitude of voltage-gated persistent sodium current. Our study provides the impetus to investigate whether manipulation of splicing of mammalian voltage-gated sodium channels may be exploitable to provide effective seizure control.

Topoisomerase 1 inhibition reversibly impairs synaptic function

Topotecan is a topoisomerase 1 (TOP1) inhibitor that is used to treat various forms of cancer. We recently found that topotecan reduces the expression of multiple long genes, including many neuronal genes linked to synapses and autism. However, whether topotecan alters synaptic protein levels and synapse function is currently unknown. Here we report that in primary cortical neurons, topotecan depleted synaptic proteins that are encoded by extremely long genes, including Neurexin-1, Neuroligin-1, Cntnap2, and GABA(A)β3. Topotecan also suppressed spontaneous network activity without affecting resting membrane potential, action potential threshold, or neuron health. Topotecan strongly suppressed inhibitory neurotransmission via pre- and postsynaptic mechanisms and reduced excitatory neurotransmission. The effects on synaptic protein levels and inhibitory neurotransmission were fully reversible upon drug washout. Collectively, our findings suggest that TOP1 controls the levels of multiple synaptic proteins and is required for normal excitatory and inhibitory synaptic transmission.

Epilepsy research methods update: Understanding the causes of epileptic seizures and identifying new treatments using non-mammalian model organisms

This narrative review is intended to introduce clinicians treating epilepsy and researchers familiar with mammalian models of epilepsy to experimentally tractable, non-mammalian research models used in epilepsy research, ranging from unicellular eukaryotes to more complex multicellular organisms. The review focuses on four model organisms: the social amoeba Dictyostelium discoideum, the roundworm Caenorhabditis elegans, the fruit fly Drosophila melanogaster and the zebrafish Danio rerio. We consider recent discoveries made with each model organism and discuss the importance of these advances for the understanding and treatment of epilepsy in humans. The relative ease with which mutations in genes of interest can be produced and studied quickly and cheaply in these organisms, together with their anatomical and physiological simplicity in comparison to mammalian species, are major advantages when researchers are trying to unravel complex disease mechanisms. The short generation times of most of these model organisms also mean that they lend themselves particularly conveniently to the investigation of drug effects or epileptogenic processes across the lifecourse.

Rescue of easily shocked mutant seizure sensitivity in Drosophila adults

Genetic factors that influence seizure susceptibility can act transiently during the development of neural circuits or might be necessary for the proper functioning of existing circuits. We provide evidence that the Drosophila seizure-sensitive mutant easily shocked (eas) represents a neurological disorder in which abnormal functioning of existing neural circuits leads to seizure sensitivity. The eas(+) gene encodes for the protein Ethanolamine Kinase, involved in phospholipid biosynthesis. We show that induction of eas(+) in adult mutant flies rescues them from seizure sensitivity despite previously known developmental defects in brain morphology. Additionally, through cell-type-specific rescue, our results suggest a specific role for eas(+) in excitatory rather than inhibitory neural transmission. Overall, our findings emphasize an important role for proper phospholipid metabolism in normal brain function and suggest that certain classes of epilepsy syndromes could have the potential to be treated with gene therapy techniques.

Seizure-sensitivity in Drosophila is ameliorated by dorsal vessel injection of the antiepileptic drug valproate

Drosophila is a powerful model organism that can be used for the development of new drugs directed against human disease. A limitation is the ability to deliver drugs for testing. We report on a novel delivery system for treating Drosophila neurological mutants, direct injection into the circulatory system. Using this method, we show that injection of the antiepileptic drug valproate can ameliorate seizure-sensitive phenotypes in several mutant genotypes in the bang-sensitive (BS) paralytic mutant class, sda, eas, and para(bss1). This drug-injection method is superior to drug-feeding methods that we have employed previously, presumably because it bypasses potent detoxification systems present in the fly. In addition, we find that utilizing blood-brain barrier mutations in the background may further improve the injection results under certain circumstances. We propose that this method of drug delivery is especially effective when using Drosophila to model human pathologies, especially neurological syndromes.

A knock-in model of human epilepsy in Drosophila reveals a novel cellular mechanism associated with heat-induced seizure

Over 40 missense mutations in the human SCN1A sodium channel gene are linked to an epilepsy syndrome termed genetic epilepsy with febrile seizures plus (GEFS+). Inheritance of GEFS+ is dominant, but the underlying cellular mechanisms remain poorly understood. Here we report that knock-in of a GEFS+ SCN1A mutation (K1270T) into the Drosophila sodium channel gene, para, causes a semidominant temperature-induced seizure phenotype. Electrophysiological studies of GABAergic interneurons in the brains of adult GEFS+ flies reveal a novel cellular mechanism underlying heat-induced seizures: the deactivation threshold for persistent sodium currents reversibly shifts to a more negative voltage when the temperature is elevated. This leads to sustained depolarizations in GABAergic neurons and reduced inhibitory activity in the central nervous system. Furthermore, our data indicate a natural temperature-dependent shift in sodium current deactivation (exacerbated by mutation) may contribute to febrile seizures in GEFS+ and perhaps normal individuals.

Protein misfolding and oxidative stress promote glial-mediated neurodegeneration in an Alexander disease model

Although alterations in glial structure and function commonly accompany death of neurons in neurodegenerative diseases, the role glia play in modulating neuronal loss is poorly understood. We have created a model of Alexander disease in Drosophila by expressing disease-linked mutant versions of glial fibrillary acidic protein (GFAP) in fly glia. We find aggregation of mutant human GFAP into inclusions bearing the hallmarks of authentic Rosenthal fibers. We also observe significant toxicity of mutant human GFAP to glia, which is mediated by protein aggregation and oxidative stress. Both protein aggregation and oxidative stress contribute to activation of a robust autophagic response in glia. Toxicity of mutant GFAP to glial cells induces a non-cell-autonomous stress response and subsequent apoptosis in neurons, which is dependent on glial glutamate transport. Our findings thus establish a simple genetic model of Alexander disease and further identify cellular pathways critical for glial-induced neurodegeneration.

Neuroprotection by spice-derived nutraceuticals: you are what you eat!

Numerous lines of evidence indicate that chronic inflammation plays a major role in the development of various neurodegenerative diseases, including Alzheimer's disease, Parkinson's disease, multiple sclerosis, brain tumor, and meningitis. Why these diseases are more common among people from some countries than others is not fully understood, but lifestyle factors have been linked to the development of neurodegenerative diseases. For example, the incidence of certain neurodegenerative diseases among people living in the Asian subcontinent, where people regularly consume spices, is much lower than in countries of the western world. Extensive research over the last 10 years has indicated that nutraceuticals derived from such spices as turmeric, red pepper, black pepper, licorice, clove, ginger, garlic, coriander, and cinnamon target inflammatory pathways, thereby may prevent neurodegenerative diseases. How these nutraceuticals modulate various pathways and how they exert neuroprotection are the focus of this review.

Seizure and epilepsy: studies of seizure disorders in Drosophila

Despite the frequency of seizure disorders in the human population, the genetic and physiological basis for these defects has been difficult to resolve. Although many genetic contributions to seizure susceptibility have been identified, these involve disparate biological processes, many of which are not neural specific. The large number and heterogeneous nature of the genes involved makes it difficult to understand the complex factors underlying the etiology of seizure disorders. Examining the effect known genetic mutations have on seizure susceptibility is one approach that may prove fruitful. This approach may be helpful in both understanding how different physiological processes affect seizure susceptibility and identifying novel therapeutic treatments. We review here factors contributing to seizure susceptibility in Drosophila, a genetically tractable system that provides a model for human seizure disorders. Seizure-like neuronal activities and behaviors in the fruit fly are described, as well as a set of mutations that exhibit features resembling some human epilepsies and render the fly sensitive to seizures. Especially interesting are descriptions of a novel class of mutations that are second-site mutations that act as seizure suppressors. These mutations revert epilepsy phenotypes back to the wild-type range of seizure susceptibility. The genes responsible for seizure suppression are cloned with the goal of identifying targets for lead compounds that may be developed into new antiepileptic drugs.

Live imaging of apoptotic cells in zebrafish

Many debilitating diseases, including neurodegenerative diseases, involve apoptosis. Several methods have been developed for visualizing apoptotic cells in vitro or in fixed tissues, but few tools are available for visualizing apoptotic cells in live animals. Here we describe a genetically encoded fluorescent reporter protein that labels apoptotic cells in live zebrafish embryos. During apoptosis, the phospholipid phosphatidylserine (PS) is exposed on the outer leaflet of the plasma membrane. The calcium-dependent protein Annexin V (A5) binds PS with high affinity, and biochemically purified, fluorescently labeled A5 probes have been widely used to detect apoptosis in vitro. Here we show that secreted A5 fused to yellow fluorescent protein specifically labels apoptotic cells in living zebrafish. We use this fluorescent probe to characterize patterns of apoptosis in living zebrafish larvae and to visualize neuronal cell death at single-cell resolution in vivo.

Immobilizing topoisomerase I on a surface plasmon resonance biosensor chip to screen for inhibitors

BACKGROUND

The topoisomerase I (TopI) reaction intermediate consists of an enzyme covalently linked to a nicked DNA molecule, known as a TopI-DNA complex, that can be trapped by inhibitors and results in failure of re-ligation. Attempts at new derivative designs for TopI inhibition are enthusiastically being pursued, and TopI inhibitors were developed for a variety of applications. Surface plasmon resonance (SPR) was recently used in TopI-inhibition studies. However, most such immobilized small molecules or short-sequence nucleotides are used as ligands onto sensor chips, and TopI was used as the analyte that flowed through the sensor chip.

METHODS

We established a sensor chip on which the TopI protein is immobilized to evaluate TopI inhibition by SPR. Camptothecin (CPT) targeting the DNA-TopI complex was used as a representative inhibitor to validate this label-free method.

RESULTS

Purified recombinant human TopI was covalently coupled to the sensor chip for the SPR assay. The binding of anti-human (h)TopI antibodies and plasmid pUC19, respectively, to the immobilized hTopI was observed with dose-dependent increases in resonance units (RU) suggesting that the immobilized hTopI retains its DNA-binding activity. Neither CPT nor evodiamine alone in the analyte flowing through the sensor chip showed a significant increase in RU. The combination of pUC19 and TopI inhibitors as the analyte flowing through the sensor chip caused increases in RU. This confirms its reliability for binding kinetic studies of DNA-TopI binders for interaction and for primary screening of TopI inhibitors.

CONCLUSIONS

TopI immobilized on the chip retained its bioactivities of DNA binding and catalysis of intermediates of the DNA-TopI complex. This provides DNA-TopI binders for interaction and primary screening with a label-free method. In addition, this biochip can also ensure the reliability of binding kinetic studies of TopI.

Evodiamine stabilizes topoisomerase I-DNA cleavable complex to inhibit topoisomerase I activity

Evodiamine (EVO), an alkaloidal compound isolated from Evodia rutaecarpa (Juss.), has been reported to affect many physiological functions. Topoisomerase inhibitors have been developed in a variety of clinical applications. In the present study, we report the topoisomerase I (TopI) inhibitory activity of EVO, which may have properties that lead to improved therapeutic benefits. EVO is able to inhibit supercoiled plasmid DNA relaxation catalyzed by TopI. Upon treatment 0-10 microM EVO TopI was depleted in MCF-7 breast cancer cells in a concentration-dependent and time-dependent manner in 0-120 min. A K-SDS precipitation assay was performed to measure the extent of Top I-trapped chromosomal DNA. The ability of EVO to cause the formation of a TopI-DNA complex increased in a concentration-dependent manner, in that the DNA trapped increased by 24.2% in cells treated with 30 microM. The results suggest that EVO inhibits TopI by stabilizing the enzyme and DNA covalent complex.

Drosophila melanogaster as a model organism of brain diseases

Drosophila melanogaster has been utilized to model human brain diseases. In most of these invertebrate transgenic models, some aspects of human disease are reproduced. Although investigation of rodent models has been of significant impact, invertebrate models offer a wide variety of experimental tools that can potentially address some of the outstanding questions underlying neurological disease. This review considers what has been gleaned from invertebrate models of neurodegenerative diseases, including Alzheimer’s disease, Parkinson’s disease, metabolic diseases such as Leigh disease, Niemann-Pick disease and ceroid lipofuscinoses, tumor syndromes such as neurofibromatosis and tuberous sclerosis, epilepsy as well as CNS injury. It is to be expected that genetic tools in Drosophila will reveal new pathways and interactions, which hopefully will result in molecular based therapy approaches.