Lentiviral RNAi-induced downregulation of adenosine kinase in human mesenchymal stem cell grafts: a novel perspective for seizure control

Adenosine kinase gene modified mesenchymal stem cell transplantation retards seizure severity and associated cognitive impairment in a temporal lobe epilepsy rat model

PURPOSE

Temporal lobe epilepsy (TLE) has a high risk of developing drug resistant and cognitive comorbidities. Adenosine has potential anticonvulsant effects as an inhibitory neurotransmitter, but drugs targeting its receptors and metabolic enzyme has inevitable side effects. Therefore, we investigated adenosine augmentation therapy for seizure control and cognitive comorbidities in TLE animals.

METHODS

Using lentiviral vectors coexpressing miRNA inhibiting the expression of adenosine kinase (ADK), we produced ADK--rMSC (ADK knockdown rat mesenchymal stem cell). ADK--rMSC and LV-con-rMSC (rMSC transduced by randomized scrambled control sequence) were transplanted into the hippocampus of TLE rat respectively. ADK-+DPCPX group was transplanted with ADK--rMSC and intraperitoneally injected with DPCPX (adenosine A1 receptor antagonist). Seizure behavior, EEG, CA1 pyramidal neuron apoptosis, and behavior in Morris water maze and novel object recognition test were studied RESULTS: Adenosine concentration in the supernatants of 105 ADK--rMSCs was 13.8 ng/ml but not detectable in LV-con-rMSCs. ADK--rMSC (n = 11) transplantation decreased spontaneous recurrent seizure (SRS) duration compared to LV-con-rMSC (n = 11, P < 0.05). CA1 neuron apoptosis was decreased in ADK--rMSC (n = 3, P < 0.05). ADK--rMSC (n = 11) improved the Morris water maze performance of TLE rats compared to LV-con-rMSC (n = 11, escape latency, P < 0.01; entries in target quadrant, P < 0.05). The effect of ADK--rMSC on neuron apoptosis and spatial memory were counteracted by DPCPX. However, ADK--rMSC didn't improve the performance in novel object recognition test.

CONCLUSION

Adenosine augmentation-based ADK--rMSC transplantation is a promising therapeutic candidate for TLE and related cognitive comorbidities.

Vector-Mediated Delivery of Transgenes and RNA Interference-Based Gene Silencing Sequences to Astrocytes for Disease Management: Advances and Prospectives

Astrocytes are a type of important glial cell in the brain that serve crucial functions in regulating neuronal activity, facilitating communication between neurons, and keeping everything in balance. In this abstract, we explore current methods and future approaches for using vectors to precisely target astrocytes in the fight against various illnesses. In order to deliver therapeutic cargo selectively to astrocytes, researchers have made tremendous progress by using viral vectors such as adeno-associated viruses (AAVs) and lentiviruses. It has been established that engineered viral vectors are capable of either crossing the blood-brain barrier (BBB) or being delivered intranasally, which facilitates their entrance into the brain parenchyma. These vectors are able to contain transgenes that code for neuroprotective factors, synaptic modulators, or anti-inflammatory medicines, which pave the way for multiple approaches to disease intervention. Strategies based on RNA interference (RNAi) make vector-mediated astrocyte targeting much more likely to work. Small interfering RNAs (siRNAs) and short hairpin RNAs (shRNAs) are two types of RNA that can be made to silence disease-related genes in astrocytes. Vector-mediated delivery in conjunction with RNAi techniques provides a powerful toolkit for investigating the complex biological pathways that contribute to disease development. However, there are still a number of obstacles to overcome in order to perfect the specificity, safety, and duration of vector-mediated astrocyte targeting. In order to successfully translate research findings into clinical practise, it is essential to minimise off-target effects and the risk of immunogenicity. To demonstrate the therapeutic effectiveness of these strategies, rigorous preclinical investigation and validation are required.

Therapeutic Potential of Mesenchymal Stem Cells in the Treatment of Epilepsy and Their Interaction with Antiseizure Medications

Epilepsy is a life-threatening neurological disease that affects approximately 70 million people worldwide. Although the vast majority of patients may be successfully managed with currently used antiseizure medication (ASM), the search for alternative therapies is still necessary due to pharmacoresistance in about 30% of patients with epilepsy. Here, we review the effects of ASMs on stem cell treatment when they could be, as expected, co-administered. Indeed, it has been reported that ASMs produce significant effects on the differentiation and determination of stem cell fate. In addition, we discuss more recent findings on mesenchymal stem cells (MSCs) in pre-clinical and clinical investigations. In this regard, their ability to differentiate into various cell types, reach damaged tissues and produce and release biologically active molecules with immunomodulatory/anti-inflammatory and regenerative properties make them a high-potential therapeutic tool to address neuroinflammation in different neurological disorders, including epilepsy. Overall, the characteristics of MSCs to be genetically engineered, in order to replace dysfunctional elements with the aim of restoring normal tissue functioning, suggested that these cells could be good candidates for the treatment of epilepsy refractory to ASMs. Further research is required to understand the potential of stem cell treatment in epileptic patients and its interaction with ASMs.

Mesenchymal Stem Cell Therapy for Focal Epilepsy: A Systematic Review of Preclinical Models and Clinical Studies

Drug resistant epilepsy (DRE) is characterized by recurrent seizures despite appropriate treatment with antiseizure medication (ASM). Due to their regenerative and immunomodulatory potential, therapies with biologics such as mesenchymal stem cells (MSCs) offer a potential therapeutic benefit for structural causes of epilepsy, such as hippocampal sclerosis. In this manuscript, we report a systematic review of the literature evaluating the preclinical and clinical studies of MSCs for DRE. Medline, Ovid EMBASE, Scopus, and the Cochrane Databases were electronically searched from their dates of inception to November 2021 using the following keywords: (("mesenchymal") AND ("stem cell")) AND (("epilepsy") OR ("convulsion") OR ("seizures")). This review followed the PRISMA guidelines. The initial query identified 488 studies representing 323 unique manuscripts. After application of selection criteria, 15 studies were included in this systematic review; 11 were preclinical studies and 4 were clinical studies. All preclinical studies were performed in rodents and all clinical studies were phase 1 trials. Thus far, therapy with MSCs appears to be safe for use in humans, as no severe adverse events directly related to the therapy were reported. Furthermore, MSC therapy appears to provide a statistically significant clinical benefit by reducing the seizure burden of patients, reducing the electrophysiological biomarkers of epilepsy, and improving their comorbidities, such as depression and anxiety. Additionally, animal studies reveal that the therapy exerts its effect by reducing aberrant mossy fiber sprouting (reduce excitatory pathways) and increasing GABAergic interneurons (increase inhibitory pathways). Both preclinical and clinical studies have shown MSC therapy to be safe and preliminary effective, thus warranting further studies to investigate its therapeutic potential.

ATP and adenosine-Two players in the control of seizures and epilepsy development

Despite continuous advances in understanding the underlying pathogenesis of hyperexcitable networks and lowered seizure thresholds, the treatment of epilepsy remains a clinical challenge. Over one third of patients remain resistant to current pharmacological interventions. Moreover, even when effective in suppressing seizures, current medications are merely symptomatic without significantly altering the course of the disease. Much effort is therefore invested in identifying new treatments with novel mechanisms of action, effective in drug-refractory epilepsy patients, and with the potential to modify disease progression. Compelling evidence has demonstrated that the purines, ATP and adenosine, are key mediators of the epileptogenic process. Extracellular ATP concentrations increase dramatically under pathological conditions, where it functions as a ligand at a host of purinergic receptors. ATP, however, also forms a substrate pool for the production of adenosine, via the action of an array of extracellular ATP degrading enzymes. ATP and adenosine have assumed largely opposite roles in coupling neuronal excitability to energy homeostasis in the brain. This review integrates and critically discusses novel findings regarding how ATP and adenosine control seizures and the development of epilepsy. This includes purine receptor P1 and P2-dependent mechanisms, release and reuptake mechanisms, extracellular and intracellular purine metabolism, and emerging receptor-independent effects of purines. Finally, possible purine-based therapeutic strategies for seizure suppression and disease modification are discussed.

An Analysis of Mechanisms for Cellular Uptake of miRNAs to Enhance Drug Delivery and Efficacy in Cancer Chemoresistance

Up until recently, it was believed that pharmaceutical drugs and their metabolites enter into the cell to gain access to their targets via simple diffusion across the hydrophobic lipid cellular membrane, at a rate which is based on their lipophilicity. An increasing amount of evidence indicates that the phospholipid bilayer-mediated drug diffusion is in fact negligible, and that drugs pass through cell membranes via proteinaceous membrane transporters or carriers which are normally used for the transportation of nutrients and intermediate metabolites. Drugs can be targeted to specific cells and tissues which express the relevant transporters, leading to the design of safe and efficacious treatments. Furthermore, transporter expression levels can be manipulated, systematically and in a high-throughput manner, allowing for considerable progress in determining which transporters are used by specific drugs. The ever-expanding field of miRNA therapeutics is not without its challenges, with the most notable one being the safe and effective delivery of the miRNA mimic/antagonist safely to the target cell cytoplasm for attaining the desired clinical outcome, particularly in miRNA-based cancer therapeutics, due to the poor efficiency of neo-vascular systems revolting around the tumour site, brought about by tumour-induced angiogenesis. This acquisition of resistance to several types of anticancer drugs can be as a result of an upregulation of efflux transporters expression, which eject drugs from cells, hence lowering drug efficacy, resulting in multidrug resistance. In this article, the latest available data on human microRNAs has been reviewed, together with the most recently described mechanisms for miRNA uptake in cells, for future therapeutic enhancements against cancer chemoresistance.

Role of Adenosine in Epilepsy and Seizures

Adenosine is an endogenous anticonvulsant and neuroprotectant of the brain. Seizure activity produces large quantities of adenosine, and it is this seizure-induced adenosine surge that normally stops a seizure. However, within the context of epilepsy, adenosine plays a wide spectrum of different roles. It not only controls seizures (ictogenesis), but also plays a major role in processes that turn a normal brain into an epileptic brain (epileptogenesis). It is involved in the control of abnormal synaptic plasticity and neurodegeneration and plays a major role in the expression of comorbid symptoms and complications of epilepsy, such as sudden unexpected death in epilepsy (SUDEP). Given the important role of adenosine in epilepsy, therapeutic strategies are in development with the goal to utilize adenosine augmentation not only for the suppression of seizures but also for disease modification and epilepsy prevention, as well as strategies to block adenosine A_2A receptor overfunction associated with neurodegeneration. This review provides a comprehensive overview of the role of adenosine in epilepsy.

Targeting Purinergic Signaling and Cell Therapy in Cardiovascular and Neurodegenerative Diseases

Extracellular purines exert several functions in physiological and pathophysiological mechanisms. ATP acts through P2 receptors as a neurotransmitter and neuromodulator and modulates heart contractility, while adenosine participates in neurotransmission, blood pressure, and many other mechanisms. Because of their capability to differentiate into mature cell types, they provide a unique therapeutic strategy for regenerating damaged tissue, such as in cardiovascular and neurodegenerative diseases. Purinergic signaling is pivotal for controlling stem cell differentiation and phenotype determination. Proliferation, differentiation, and apoptosis of stem cells of various origins are regulated by purinergic receptors. In this chapter, we selected neurodegenerative and cardiovascular diseases with clinical trials using cell therapy and purinergic receptor targeting. We discuss these approaches as therapeutic alternatives to neurodegenerative and cardiovascular diseases. For instance, promising results were demonstrated in the utilization of mesenchymal stem cells and bone marrow mononuclear cells in vascular regeneration. Regarding neurodegenerative diseases, in general, P2X7 and A_2A receptors mostly worsen the degenerative state. Stem cell-based therapy, mainly through mesenchymal and hematopoietic stem cells, showed promising results in improving symptoms caused by neurodegeneration. We propose that purinergic receptor activity regulation combined with stem cells could enhance proliferative and differentiation rates as well as cell engraftment.

Astrocyte adenosine deaminase loss increases motor neuron toxicity in amyotrophic lateral sclerosis

As clinical evidence supports a negative impact of dysfunctional energy metabolism on the disease progression in amyotrophic lateral sclerosis, it is vital to understand how the energy metabolic pathways are altered and whether they can be restored to slow disease progression. Possible approaches include increasing or rerouting catabolism of alternative fuel sources to supplement the glycolytic and mitochondrial pathways such as glycogen, ketone bodies and nucleosides. To analyse the basis of the catabolic defect in amyotrophic lateral sclerosis we used a novel phenotypic metabolic array. We profiled fibroblasts and induced neuronal progenitor-derived human induced astrocytes from C9orf72 amyotrophic lateral sclerosis patients compared to normal controls, measuring the rates of production of reduced nicotinamide adenine dinucleotides from 91 potential energy substrates. This approach shows for the first time that C9orf72 human induced astrocytes and fibroblasts have an adenosine to inosine deamination defect caused by reduction of adenosine deaminase, which is also observed in induced astrocytes from sporadic patients. Patient-derived induced astrocyte lines were more susceptible to adenosine-induced toxicity, which could be mimicked by inhibiting adenosine deaminase in control lines. Furthermore, adenosine deaminase inhibition in control induced astrocytes led to increased motor neuron toxicity in co-cultures, similar to the levels observed with patient derived induced astrocytes. Bypassing metabolically the adenosine deaminase defect by inosine supplementation was beneficial bioenergetically in vitro, increasing glycolytic energy output and leading to an increase in motor neuron survival in co-cultures with induced astrocytes. Inosine supplementation, in combination with modulation of the level of adenosine deaminase may represent a beneficial therapeutic approach to evaluate in patients with amyotrophic lateral sclerosis.

The role of adenosine in epilepsy

Adenosine is a well-characterized endogenous anticonvulsant and seizure terminator of the brain. Through a combination of adenosine receptor-dependent and -independent mechanisms, adenosine affects seizure generation (ictogenesis), as well as the development of epilepsy and its progression (epileptogenesis). Maladaptive changes in adenosine metabolism, in particular increased expression of the astroglial enzyme adenosine kinase (ADK), play a major role in epileptogenesis. Increased expression of ADK has dual roles in both reducing the inhibitory tone of adenosine in the brain, which consequently reduces the threshold for seizure generation, and also driving an increased flux of methyl-groups through the transmethylation pathway, thereby increasing global DNA methylation. Through these mechanisms, adenosine is uniquely positioned to link metabolism with epigenetic outcome. Therapeutic adenosine augmentation therefore not only holds promise for the suppression of seizures in epilepsy, but moreover the prevention of epilepsy and its progression overall. This review will focus on adenosine-related mechanisms implicated in ictogenesis and epileptogenesis and will discuss therapeutic opportunities and challenges.

Research progress on adenosine in central nervous system diseases

As an endogenous neuroprotectant agent, adenosine is extensively distributed and is particularly abundant in the central nervous system (CNS). Under physiological conditions, the concentration of adenosine is low intra- and extracellularly, but increases significantly in response to stress. The majority of adenosine functions are receptor-mediated, and primarily include the A1, A2A, A2B, and A3 receptors (A1R, A2AR, A2BR, and A3R). Adenosine is currently widely used in the treatment of diseases of the CNS and the cardiovascular systems, and the mechanisms are related to the disease types, disease locations, and the adenosine receptors distribution in the CNS. For example, the main infarction sites of cerebral ischemia are cortex and striatum, which have high levels of A1 and A2A receptors. Cerebral ischemia is manifested with A1R decrease and A2AR increase, as well as reduction in the A1R-mediated inhibitory processes and enhancement of the A2AR-mediated excitatory process. Adenosine receptor dysfunction is also involved in the pathology of Alzheimer's disease (AD), depression, and epilepsy. Thus, the adenosine receptor balance theory is important for brain disease treatment. The concentration of adenosine can be increased by endogenous or exogenous pathways due to its short half-life and high inactivation properties. Therefore, we will discuss the function of adenosine and its receptors, adenosine formation, and metabolism, and its role for the treatment of CNS diseases (such as cerebral ischemia, AD, depression, Parkinson's disease, epilepsy, and sleep disorders). This article will provide a scientific basis for the development of novel adenosine derivatives through adenosine structure modification, which will lead to experimental applications.

Genome Editing in Neuroepithelial Stem Cells to Generate Human Neurons with High Adenosine-Releasing Capacity

As a powerful regulator of cellular homeostasis and metabolism, adenosine is involved in diverse neurological processes including pain, cognition, and memory. Altered adenosine homeostasis has also been associated with several diseases such as depression, schizophrenia, or epilepsy. Based on its protective properties, adenosine has been considered as a potential therapeutic agent for various brain disorders. Since systemic application of adenosine is hampered by serious side effects such as vasodilatation and cardiac suppression, recent studies aim at improving local delivery by depots, pumps, or cell-based applications. Here, we report on the characterization of adenosine-releasing human embryonic stem cell-derived neuroepithelial stem cells (long-term self-renewing neuroepithelial stem [lt-NES] cells) generated by zinc finger nuclease (ZFN)-mediated knockout of the adenosine kinase (ADK) gene. ADK-deficient lt-NES cells and their differentiated neuronal and astroglial progeny exhibit substantially elevated release of adenosine compared to control cells. Importantly, extensive adenosine release could be triggered by excitation of differentiated neuronal cultures, suggesting a potential activity-dependent regulation of adenosine supply. Thus, ZFN-modified neural stem cells might serve as a useful vehicle for the activity-dependent local therapeutic delivery of adenosine into the central nervous system. Stem Cells Translational Medicine 2018;7:477-486.

Stable Knockdown of Adenosine Kinase by Lentiviral Anti-ADK miR-shRNAs in Wharton's Jelly Stem Cells

Objective

In this study, we describe an efficient approach for stable knockdown of adenosine kinase (ADK) using lentiviral system, in an astrocytoma cell line and in human Wharton’s jelly mesenchymal stem cells (hWJMSCs). These sources of stem cells besides having multilineage differentiation potential and immunomodulatory activities, are easily available in unlimited numbers, do not raise ethical concerns and are attractive for gene manipulation and cell-based gene therapy.

Materials and Methods

In this experimental study, we targeted adenosine kinase mRNA at 3' and performed coding sequences using eight miR-based expressing cassettes of anti-ADK short hairpin RNA (shRNAs). First, these cassettes with scrambled control sequences were cloned into expressing lentiviral pGIPZ vector. Quantitative real time-polymerase chain reaction (qRT-PCR) was used to screen multi-cassettes anti-ADK miR-shRNAs in stably transduced U-251 MG cell line and measuring ADK gene expression at mRNA level. Extracted WJMSCs were characterized using flow cytometry for expressing mesenchymal specific marker (CD44+) and lack of expression of hematopoietic lineage marker (CD45-). Then, the lentiviral vector that expressed the most efficient anti-ADK miR-shRNA, was employed to stably transduce WJMSCs.

Results

Transfection of anti-ADK miR-shRNAs in HEK293T cells using CaPO₄ method showed high efficiency. We successfully transduced U-251 cell line by recombinant lentiviruses and screened eight cassettes of anti-ADK miR- shRNAs in stably transduced U-251 MG cell line by qRT-PCR. RNAi-mediated down-regulation of ADK by lentiviral system indicated up to 95% down-regulation of ADK. Following lentiviral transduction of WJMSCs with anti-ADK miR- shRNA expression cassette, we also implicated, down-regulation of ADK up to 95% by qRT-PCR and confirmed it by western blot analysis at the protein level.

Conclusion

Our findings indicate efficient usage of shRNA cassette for ADK knockdown. Engineered WJMSCs with genome editing methods like CRISPR/cas9 or more safe viral systems such as adeno-associated vectors (AAV) might be an attractive source in cell-based gene therapy and may have therapeutic potential for epilepsy.

Engineering Human Mesenchymal Stem Cells to Release Adenosine Using miRNA Technology

Adenosine is an important modulator of metabolic activity with powerful tissue and cell protective functions. Adenosine kinase (ADK), the major adenosine-regulating enzyme, is critical to adapt its intra- and extracellular levels in response to environmental changes. Lentiviral RNAi-mediated downregulation of ADK in human mesenchymal stem cells (hMSCs) has therefore been considered an effective tool for engineering therapeutically effective adenosine-releasing cell grafts that could constitute patient-identical autologous implants for clinical application. We constructed lentiviral vectors that co-express miRNA directed against ADK and an emerald green fluorescent protein (EmGFP) reporter gene. Following lentiviral transduction of hMSCs, we demonstrated up to 80% downregulation of ADK and 98% transduction efficiency. Transduced hMSCs continued to express EmGFP after four to six consecutive passages, and EmGFP-positive hMSC grafts survived in the hippocampal fissure of mouse brains and provided efficient adenosine-dependent neuroprotection in a mouse model of seizure-induced cell loss.

Synthetic bioreducible lipid-based nanoparticles for miRNA delivery to mesenchymal stem cells to induce neuronal differentiation

MicroRNA (miRNA) functions in tissue regeneration and determines the fate of stem cells. Nanoparticle‐based miRNA delivery systems for therapeutic applications have been studied in clinical settings. However, gene delivery to stem cells is still a challenging issue. Lipid‐like nanoparticles produced using combinatorial approaches have recently been used for delivery of a variety of biologics. In this study, we investigated the ability of these lipids to deliver miRNA to human mesenchymal stem cells (hMSCs). First, small library screening of bioreducible lipids was performed using fluorophore‐conjugated miRNA to determine the optimal chemical structure for miRNA delivery to hMSCs. Next, miRNA‐9 (miR‐9), which promotes neuronal differentiation of stem cells, was delivered to hMSCs using the lipids identified from the library screening. Morphological changes of the cells and upregulation of neuronal marker genes were observed after the delivery of miR‐9. The synthetic bioreducible lipids are effective in facilitating miRNA delivery to hMSCs and promoting the neuronal differentiation.

Comorbidities in Neurology: Is adenosine the common link?

Comorbidities in Neurology represent a major conceptual and therapeutic challenge. For example, temporal lobe epilepsy (TLE) is a syndrome comprised of epileptic seizures and comorbid symptoms including memory and psychiatric impairment, depression, and sleep dysfunction. Similarly, Alzheimer's disease (AD), Parkinson's disease (PD), and Amyotrophic Lateral Sclerosis (ALS) are accompanied by various degrees of memory dysfunction. Patients with AD have an increased likelihood for seizures, whereas all four conditions share certain aspects of psychosis, depression, and sleep dysfunction. This remarkable overlap suggests common pathophysiological mechanisms, which include synaptic dysfunction and synaptotoxicity, as well as glial activation and astrogliosis. Astrogliosis is linked to synapse function via the tripartite synapse, but astrocytes also control the availability of gliotransmitters and adenosine. Here we will specifically focus on the 'adenosine hypothesis of comorbidities' implying that astrocyte activation, via overexpression of adenosine kinase (ADK), induces a deficiency in the homeostatic tone of adenosine. We present evidence from patient-derived samples showing astrogliosis and overexpression of ADK as common pathological hallmark of epilepsy, AD, PD, and ALS. We discuss a transgenic 'comorbidity model', in which brain-wide overexpression of ADK and resulting adenosine deficiency produces a comorbid spectrum of seizures, altered dopaminergic function, attentional impairment, and deficits in cognitive domains and sleep regulation. We conclude that dysfunction of adenosine signaling is common in neurological conditions, that adenosine dysfunction can explain co-morbid phenotypes, and that therapeutic adenosine augmentation might be effective for the treatment of comorbid symptoms in multiple neurological conditions.

Adenosinergic signaling in epilepsy

Despite the introduction of at least 20 new antiepileptic drugs (AEDs) into clinical practice over the past decades, about one third of all epilepsies remain refractory to conventional forms of treatment. In addition, currently used AEDs have been developed to suppress neuronal hyperexcitability, but not necessarily to address pathogenic mechanisms involved in epilepsy development or progression (epileptogenesis). For those reasons endogenous seizure control mechanisms of the brain may provide alternative therapeutic opportunities. Adenosine is a well characterized endogenous anticonvulsant and seizure terminator of the brain. Several lines of evidence suggest that endogenous adenosine-mediated seizure control mechanisms fail in chronic epilepsy, whereas therapeutic adenosine augmentation effectively prevents epileptic seizures, even those that are refractory to conventional AEDs. New findings demonstrate that dysregulation of adenosinergic mechanisms are intricately involved in the development of epilepsy and its comorbidities, whereas adenosine-associated epigenetic mechanisms may play a role in epileptogenesis. The first goal of this review is to discuss how maladaptive changes of adenosinergic mechanisms contribute to the expression of seizures (ictogenesis) and the development of epilepsy (epileptogenesis) by focusing on pharmacological (adenosine receptor dependent) and biochemical (adenosine receptor independent) mechanisms as well as on enzymatic and transport based mechanisms that control the availability (homeostasis) of adenosine. The second goal of this review is to highlight innovative adenosine-based opportunities for therapeutic intervention aimed at reconstructing normal adenosine function and signaling for improved seizure control in chronic epilepsy. New findings suggest that transient adenosine augmentation can have lasting epigenetic effects with disease modifying and antiepileptogenic outcome. This article is part of the Special Issue entitled 'Purines in Neurodegeneration and Neuroregeneration'.

Defective Self-Renewal and Differentiation of GBA-Deficient Neural Stem Cells Can Be Restored By Macrophage Colony-Stimulating Factor

Gaucher disease (GD) is an autosomal recessive lysosomal storage disorder caused by mutations in the glucocerebrosidase gene (GBA), which encodes the lysosomal enzyme glucosylceramidase (GCase). Deficiency in GCase leads to characteristic visceral pathology and lethal neurological manifestations in some patients. Investigations into neurogenesis have suggested that neurodegenerative disorders, such as GD, could be overcome or at least ameliorated by the generation of new neurons. Bone marrow-derived mesenchymal stem cells (BM-MSCs) are potential candidates for use in the treatment of neurodegenerative disorders because of their ability to promote neurogenesis. Our objective was to examine the mechanism of neurogenesis by BM-MSCs in GD. We found that neural stem cells (NSCs) derived from a neuronopathic GD model exhibited decreased ability for self-renewal and neuronal differentiation. Co-culture of GBA-deficient NSCs with BM-MSCs resulted in an enhanced capacity for self-renewal, and an increased ability for differentiation into neurons or oligodendrocytes. Enhanced proliferation and neuronal differentiation of GBA-deficient NSCs was associated with elevated release of macrophage colony-stimulating factor (M-CSF) from BM-MSCs. Our findings suggest that soluble M-CSF derived from BM-MSCs can modulate GBA-deficient NSCs, resulting in their improved proliferation and neuronal differentiation.

Mesenchymal stem/stromal cells as a delivery platform in cell and gene therapies

Regenerative medicine relying on cell and gene therapies is one of the most promising approaches to repair tissues. Multipotent mesenchymal stem/stromal cells (MSC), a population of progenitors committing into mesoderm lineages, are progressively demonstrating therapeutic capabilities far beyond their differentiation capacities. The mechanisms by which MSC exert these actions include the release of biomolecules with anti-inflammatory, immunomodulating, anti-fibrogenic, and trophic functions. While we expect the spectra of these molecules with a therapeutic profile to progressively expand, several human pathological conditions have begun to benefit from these biomolecule-delivering properties. In addition, MSC have also been proposed to vehicle genes capable of further empowering these functions. This review deals with the therapeutic properties of MSC, focusing on their ability to secrete naturally produced or gene-induced factors that can be used in the treatment of kidney, lung, heart, liver, pancreas, nervous system, and skeletal diseases. We specifically focus on the different modalities by which MSC can exert these functions. We aim to provide an updated understanding of these paracrine mechanisms as a prerequisite to broadening the therapeutic potential and clinical impact of MSC.

Regenerative therapy for hippocampal degenerative diseases: lessons from preclinical studies

Increase in life expectancy has put neurodegenerative diseases on the rise. Amongst these, degenerative diseases involving hippocampus like Alzheimer's disease (AD) and temporal lobe epilepsy (TLE) are ranked higher as it is vulnerable to excitotoxicity induced neuronal dysfunction and death resulting in cognitive impairment. Modern medicines have not succeeded in halting the progression of these diseases rendering them incurable and often fatal. Under such scenario, regenerative studies employing stem cells or their by-products in animal models of AD and TLE have yielded encourageing results. This review focuses on the distinct cell types, such as hippocampal cell lines, neural precursor cells, embryonic stem cells derived neural precursor cells, induced pluripotent stem cells, induced neurons and mesenchymal stem cells, which can be employed to rescue hippocampal functions in neurodegenerative diseases like AD and TLE. Besides, the divergent mechanisms through which cell based therapy confer neuroprotection, current impediments and possible improvements in stem cell transplantation strategies are discussed. Authors are aware of the voluminous literature available on this issue and have made a sincere attempt to put forth the current status of research in the field of cell based therapy concurrently discussing the promise it holds for combating neurodegenerative diseases like AD and TLE in the near future. Copyright © 2015 John Wiley & Sons, Ltd.

Adenosine receptor neurobiology: overview

Adenosine is a naturally occurring nucleoside that is distributed ubiquitously throughout the body as a metabolic intermediary. In the brain, adenosine functions as an important upstream neuromodulator of a broad spectrum of neurotransmitters, receptors, and signaling pathways. By acting through four G-protein-coupled receptors, adenosine contributes critically to homeostasis and neuromodulatory control of a variety of normal and abnormal brain functions, ranging from synaptic plasticity, to cognition, to sleep, to motor activity to neuroinflammation, and cell death. This review begun with an overview of the gene and genome structure and the expression pattern of adenosine receptors (ARs). We feature several new developments over the past decade in our understanding of AR functions in the brain, with special focus on the identification and characterization of canonical and noncanonical signaling pathways of ARs. We provide an update on functional insights from complementary genetic-knockout and pharmacological studies on the AR control of various brain functions. We also highlight several novel and recent developments of AR neurobiology, including (i) recent breakthrough in high resolution of three-dimension structure of adenosine A2A receptors (A2ARs) in several functional status, (ii) receptor-receptor heterodimerization, (iii) AR function in glial cells, and (iv) the druggability of AR. We concluded the review with the contention that these new developments extend and strengthen the support for A1 and A2ARs in brain as therapeutic targets for neurologic and psychiatric diseases.

Adenosine-associated delivery systems

Adenosine is a naturally occurring purine nucleoside in every cell. Many critical treatments such as modulating irregular heartbeat (arrhythmias), regulation of central nervous system (CNS) activity and inhibiting seizural episodes can be carried out using adenosine. Despite the significant potential therapeutic impact of adenosine and its derivatives, the severe side effects caused by their systemic administration have significantly limited their clinical use. In addition, due to adenosine's extremely short half-life in human blood (<10 s), there is an unmet need for sustained delivery systems to enhance efficacy and reduce side effects. In this article, various adenosine delivery techniques, including encapsulation into biodegradable polymers, cell-based delivery, implantable biomaterials and mechanical-based delivery systems, are critically reviewed and the existing challenges are highlighted.

Adenosine kinase, glutamine synthetase and EAAT2 as gene therapy targets for temporal lobe epilepsy

Astrocytes are an attractive cell target for gene therapy, but the validation of new therapeutic candidates is needed. We determined whether adeno-associated viral (AAV) vector-mediated overexpression of glutamine synthetase (GS) or excitatory amino-acid transporter 2 (EAAT2), or expression of microRNA targeting adenosine kinase (miR-ADK) in hippocampal astrocytes in the rat brain could modulate susceptibility to kainate-induced seizures and neuronal cell loss. Transgene expression was found predominantly in astrocytes following direct injection of glial-targeting AAV9 vectors by 3 weeks postinjection. ADK expression in miR-ADK vector-injected rats was reduced by 94-96% and was associated with an ~50% reduction in the duration of kainate-induced seizures and greater protection of dentate hilar neurons but not CA3 neurons compared with miR-control vector-injected rats. In contrast, infusion of AAV-GS and EAAT2 vectors did not afford any protection against seizures or neuronal damage as the level of transcriptional activity of the glial fibrillary acidic promoter was too low to drive any significant increase in transgenic GS or EAAT2 relative to the high endogenous levels of these proteins. Our findings support ADK as a prime therapeutic target for gene therapy of temporal lobe epilepsy and suggest that alternative approaches including the use of stronger glial promoters are needed to increase transgenic GS and EAAT2 expression to levels that may be required to affect seizure induction and propagation.

A Molecular Approach to Epilepsy Management: from Current Therapeutic Methods to Preconditioning Efforts

Epilepsy is the most common and chronic neurological disorder characterized by recurrent unprovoked seizures. The key aim in treating patients with epilepsy is the suppression of seizures. An understanding of focal changes that are involved in epileptogenesis may therefore provide novel approaches for optimal treatment of the seizure. Although the actual pathogenesis of epilepsy is still uncertain, recently growing lines of evidence declare that microglia and astrocyte activation, oxidative stress and reactive oxygen species (ROS) production, mitochondria dysfunction, and damage of blood-brain barrier (BBB) are involved in its pathogenesis. Impaired GABAergic function in the brain is probably the most accepted hypothesis regarding the pathogenesis of epilepsy. Clinical neuroimaging of patients and experimental modeling have demonstrated that seizures may induce neuronal apoptosis. Apoptosis signaling pathways are involved in the pathogenesis of several types of epilepsy such as temporal lobe epilepsy (TLE). The quality of life of patients is seriously affected by treatment-related problems and also by unpredictability of epileptic seizures. Moreover, the available antiepileptic drugs (AED) are not significantly effective to prevent epileptogenesis. Thus, novel therapies that are proficient to control seizure in people who are suffering from epilepsy are needed. The preconditioning method promises to serve as an alternative therapeutic approach because this strategy has demonstrated the capability to curtail epileptogenesis. For this reason, understanding of molecular mechanisms underlying brain tolerance induced by preconditioning is crucial to delineate new neuroprotective ways against seizure damage and epileptogenesis. In this review, we summarize the work to date on the pathogenesis of epilepsy and discuss recent therapeutic strategies in the treatment of epilepsy. We will highlight that novel therapy targeting such as preconditioning process holds great promise. In addition, we will also highlight the role of gene reprogramming and mitochondrial biogenesis in the preconditioning-mediated neuroprotective events.

Glial adenosine kinase--a neuropathological marker of the epileptic brain

Experimental research over the past decade has supported the critical role of astrocytes activated by different types of injury and the pathophysiological processes that underlie the development of epilepsy. In both experimental and human epileptic tissues astrocytes undergo complex changes in their physiological properties, which can alter glio-neuronal communication, contributing to seizure precipitation and recurrence. In this context, understanding which of the molecular mechanisms are crucially involved in the regulation of glio-neuronal interactions under pathological conditions associated with seizure development is important to get more insight into the role of astrocytes in epilepsy. This article reviews current knowledge regarding the role of glial adenosine kinase as a neuropathological marker of the epileptic brain. Both experimental findings in clinically relevant models, as well as observations in drug-resistant human epilepsies will be discussed, highlighting the link between astrogliosis, dysfunction of adenosine homeostasis and seizure generation and therefore suggesting new strategies for targeting astrocyte-mediated epileptogenesis.

Role of adenosine in status epilepticus: a potential new target?

The homeostatic bioenergetic network regulator adenosine is an endogenous anticonvulsant of the brain that plays critical roles in seizure termination and postictal refractoriness. Adenosine homeostasis in the adult brain is largely under the control of metabolic clearance through adenosine kinase (ADK), expressed predominantly in astrocytes. The role of adenosine in status epilepticus (SE) appears to be a double-edged sword. We demonstrated that the severity of an SE clearly depends on the expression levels of ADK. A genetic knockdown of ADK prevented SE in a mouse model, whereas transgenic overexpression of the enzyme aggravated the SE. Therefore, ADK inhibition or adenosine augmentation might be a therapeutic strategy to terminate or attenuate an SE. On the other hand, SE triggers a surge of endogenous adenosine, which may initiate secondary events leading to epileptogenesis. Two new findings point into this direction: (1) Elevated adenosine triggers changes in the epigenome; and (2) SE triggers transient changes in ADK expression, which have been linked to neurogenesis. Although the ADK/adenosine system is an attractive target for the attenuation of an SE, the same system may also trigger downstream events related to epileptogenesis.

Bone-marrow-derived mesenchymal stem cells promote proliferation and neuronal differentiation of Niemann-Pick type C mouse neural stem cells by upregulation and secretion of CCL2

Niemann-Pick type C (NP-C) disease is a neurodegenerative disorder characterized neuropathologically by ballooned neurons distended with lipid storage and widespread neuronal loss. Neural stem cells (NSC) derived from NP-C disease models have decreased ability for self-renewal and neuronal differentiation. Investigation of neurogenesis in the adult brain has suggested that NP-C disease can be overcome, or at least ameliorated, by the generation of new neurons. Bone-marrow-derived mesenchymal stem cells (BM-MSCs) are regarded as potential candidates for use in the treatment of neurodegenerative disorders because of their ability to promote neurogenesis. The underlying mechanisms of BM-MSC-induced promotion of neurogenesis, however, have not been resolved. The aim of the present study was to examine the mechanism of neurogenesis by BM-MSCs in NP-C disease. Coculture of embryonic NSCs from NP-C mice that exhibit impaired ability for self-renewal and decreased rates of neuronal differentiation with BM-MSCs resulted in an enhanced capacity for self-renewal and an increased ability for differentiation into neurons or oligodendrocytes. In addition, results of in vivo studies have demonstrated that transplantation of intracerebral BM-MSCs resulted in stimulated proliferation and neuronal differentiation of NSCs within the subventricular zone. Of particular interest, enhanced proliferation and neuronal differentiation of endogenous NP-C mouse NSCs showed an association with elevated release of the chemokine (C-C motif) ligand 2 (CCL2) from BM-MSCs. These effects suggest that soluble CCL2 derived from BM-MSCs can modulate endogenous NP-C NSCs, resulting in their improved proliferation and neuronal differentiation in mice.

The imbalanced expression of adenosine receptors in an epilepsy model corrected using targeted mesenchymal stem cell transplantation

Adenosine inhibits epileptic episodes by interacting with G-protein-coupled receptors. This study examined the mechanism by which the inhibitory effect of adenosine becomes impaired during epileptogenesis. Dynamic changes in adenosine A1 receptors (A1Rs) and A2a receptors (A2aRs) were investigated in a kindling model of epilepsy. RT-PCR, Western blotting, and immunofluorescence results indicated that expression of A1Rs was increased in the hippocampus 24 h after kindling, but progressively decreased 1 and 6 months after kindling. Opposite changes were seen in the expression of A2aRs. This bidirectional change resulted in an imbalance between A1Rs and A2aRs and dysregulation of the adenosine system. Autologous mesenchymal stem cell (MSC) transplantation was used to correct this disorder and avoid side effects of systematic adenosine therapy. Paramagnetic iron oxide particles were used to mark and track the MSCs in vivo using MRI. The results indicated that the transplanted cells migrated along the callosum and settled at the ependymal layer. The MSCs displayed a relatively long survival time, at least 3 months. The improved AR expression and EEG findings suggested that MSC transplantation was a potentially effective means of treating refractory epilepsy.

Adenosine kinase: exploitation for therapeutic gain

Adenosine kinase (ADK; EC 2.7.1.20) is an evolutionarily conserved phosphotransferase that converts the purine ribonucleoside adenosine into 5'-adenosine-monophosphate. This enzymatic reaction plays a fundamental role in determining the tone of adenosine, which fulfills essential functions as a homeostatic and metabolic regulator in all living systems. Adenosine not only activates specific signaling pathways by activation of four types of adenosine receptors but it is also a primordial metabolite and regulator of biochemical enzyme reactions that couple to bioenergetic and epigenetic functions. By regulating adenosine, ADK can thus be identified as an upstream regulator of complex homeostatic and metabolic networks. Not surprisingly, ADK dysfunction is involved in several pathologies, including diabetes, epilepsy, and cancer. Consequently, ADK emerges as a rational therapeutic target, and adenosine-regulating drugs have been tested extensively. In recent attempts to improve specificity of treatment, localized therapies have been developed to augment adenosine signaling at sites of injury or pathology; those approaches include transplantation of stem cells with deletions of ADK or the use of gene therapy vectors to downregulate ADK expression. More recently, the first human mutations in ADK have been described, and novel findings suggest an unexpected role of ADK in a wider range of pathologies. ADK-regulating strategies thus represent innovative therapeutic opportunities to reconstruct network homeostasis in a multitude of conditions. This review will provide a comprehensive overview of the genetics, biochemistry, and pharmacology of ADK and will then focus on pathologies and therapeutic interventions. Challenges to translate ADK-based therapies into clinical use will be discussed critically.

Cortical interneurons from human pluripotent stem cells: prospects for neurological and psychiatric disease

Cortical interneurons represent 20% of the cells in the cortex. These cells are local inhibitory neurons whose function is to modulate the firing activities of the excitatory projection neurons. Cortical interneuron dysfunction is believed to lead to runaway excitation underlying (or implicated in) seizure-based diseases, such as epilepsy, autism, and schizophrenia. The complex development of this cell type and the intricacies involved in defining the relative subtypes are being increasingly well defined. This has led to exciting experimental cell therapy in model organisms, whereby fetal-derived interneuron precursors can reverse seizure severity and reduce mortality in adult epileptic rodents. These proof-of-principle studies raise hope for potential interneuron-based transplantation therapies for treating epilepsy. On the other hand, cortical neurons generated from patient iPSCs serve as a valuable tool to explore genetic influences of interneuron development and function. This is a fundamental step in enhancing our understanding of the molecular basis of neuropsychiatric illnesses and the development of targeted treatments. Protocols are currently being developed for inducing cortical interneuron subtypes from mouse and human pluripotent stem cells. This review sets out to summarize the progress made in cortical interneuron development, fetal tissue transplantation and the recent advance in stem cell differentiation toward interneurons.

Bone marrow mesenchymal stem cells for post-myocardial infarction cardiac repair: microRNAs as novel regulators

Transplantation of bone marrow-derived mesenchymal stem cells (MSCs) is safe and may improve cardiac function and structural remodelling in patients following myocardial infarction (MI). Cardiovascular cell differentiation and paracrine effects to promote endogenous cardiac regeneration, neovascularization, anti-inflammation, anti-apoptosis, anti-remodelling and cardiac contractility, may contribute to MSC-based cardiac repair following MI. However, current evidence indicates that the efficacy of MSC transplantation was unsatisfactory, due to the poor viability and massive death of the engrafted MSCs in the infarcted myocardium. MicroRNAs are short endogenous, conserved, non-coding RNAs and important regulators involved in numerous facets of cardiac pathophysiologic processes. There is an obvious involvement of microRNAs in almost every facet of putative repair mechanisms of MSC-based therapy in MI, such as stem cell differentiation, neovascularization, apoptosis, cardiac remodelling, cardiac contractility and arrhythmias, and others. It is proposed that therapeutic modulation of individual cardiovascular microRNA of MSCs, either mimicking or antagonizing microRNA actions, will hopefully enhance MSC therapeutic efficacy. In addition, MSCs may be manipulated to enhance functional microRNA expression or to inhibit aberrant microRNA levels in a paracrine manner. We hypothesize that microRNAs may be used as novel regulators in MSC-based therapy in MI and MSC transplantation by microRNA regulation may represent promising therapeutic strategy for MI patients in the future.

Kainic Acid-induced neurotoxicity: targeting glial responses and glia-derived cytokines

Glutamate excitotoxicity contributes to a variety of disorders in the central nervous system, which is triggered primarily by excessive Ca²⁺ influx arising from overstimulation of glutamate receptors, followed by disintegration of the endoplasmic reticulum (ER) membrane and ER stress, the generation and detoxification of reactive oxygen species as well as mitochondrial dysfunction, leading to neuronal apoptosis and necrosis. Kainic acid (KA), a potent agonist to the α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)/kainate class of glutamate receptors, is 30-fold more potent in neuro-toxicity than glutamate. In rodents, KA injection resulted in recurrent seizures, behavioral changes and subsequent degeneration of selective populations of neurons in the brain, which has been widely used as a model to study the mechanisms of neurodegenerative pathways induced by excitatory neurotransmitter. Microglial activation and astrocytes proliferation are the other characteristics of KA-induced neurodegeneration. The cytokines and other inflammatory molecules secreted by activated glia cells can modify the outcome of disease progression. Thus, anti-oxidant and anti-inflammatory treatment could attenuate or prevent KA-induced neurodegeneration. In this review, we summarized updated experimental data with regard to the KA-induced neurotoxicity in the brain and emphasized glial responses and glia-oriented cytokines, tumor necrosis factor-α, interleukin (IL)-1, IL-12 and IL-18.

Reconstruction of the adenosine system by bone marrow-derived mesenchymal stem cell transplantation

In the present study, we transplanted bone marrow-derived mesenchymal stem cells into the CA3 area of the hippocampus of chronic epilepsy rats kindled by lithium chloride-pilocarpine. Immunofluorescence and western blotting revealed an increase in adenosine A1 receptor expression and a decrease in adenosine A2a receptor expression in the brain tissues of epileptic rats 3 months after transplantation. Moreover, the imbalance in the A1 adenosine receptor/A2a adenosine receptor ratio was improved. Electroencephalograms showed that frequency and amplitude of spikes in the hippocampus and frontal lobe were reduced. These results suggested that mesenchymal stem cell transplantation can reconstruct the normal function of the adenosine system in the brain and greatly improve epileptiform discharges.

Adenosine dysfunction in epilepsy

Extracellular levels of the brain's endogenous anticonvulsant and neuroprotectant adenosine largely depend on an astrocyte-based adenosine cycle, comprised of ATP release, rapid degradation of ATP into adenosine, and metabolic reuptake of adenosine through equilibrative nucleoside transporters and phosphorylation by adenosine kinase (ADK). Changes in ADK expression and activity therefore rapidly translate into changes of extracellular adenosine, which exerts its potent anticonvulsive and neuroprotective effects by activation of pre- and postsynaptic adenosine A(1) receptors. Increases in ADK increase neuronal excitability, whereas decreases in ADK render the brain resistant to seizures and injury. Importantly, ADK was found to be overexpressed and associated with astrogliosis and spontaneous seizures in rodent models of epilepsy, as well as in human specimen resected from patients with hippocampal sclerosis and temporal lobe epilepsy. Several lines of evidence indicate that overexpression of astroglial ADK and adenosine deficiency are pathological hallmarks of the epileptic brain. Consequently, adenosine augmentation therapies constitute a powerful approach for seizure prevention, which is effective in models of epilepsy that are resistant to conventional antiepileptic drugs. The adenosine kinase hypothesis of epileptogenesis suggests that adenosine dysfunction in epilepsy undergoes a biphasic response: an acute surge of adenosine that can be triggered by any type of injury might contribute to the development of astrogliosis via adenosine receptor-dependent and -independent mechanisms. Astrogliosis in turn is associated with overexpression of ADK, which was shown to be sufficient to trigger spontaneous recurrent electrographic seizures. Thus, ADK emerges as a promising target for the prediction and prevention of epilepsy.

Overexpression of ADK in human astrocytic tumors and peritumoral tissue is related to tumor-associated epilepsy

PURPOSE

Adenosine kinase (ADK), a largely astrocyte-based metabolic enzyme, regulates adenosine homeostasis in the brain. Overexpression of ADK decreases extracellular adenosine and consequently leads to seizures. We hypothesized that dysfunction in the metabolism of tumor astrocytes is related to changes in ADK expression and that those changes might be associated with the development of epilepsy in patients with tumors.

METHODS

We compared ADK expression and cellular distribution in surgically removed tumor tissue (n = 45) and peritumoral cortex (n = 20) of patients with glial and glioneuronal tumors to normal control tissue obtained at autopsy (n = 11). In addition, we compared ADK expression in tumor patients with and without epilepsy. To investigate ADK expression, we used immunohistochemistry and Western blot analysis. ADK activity measurement was performed in surgical specimens of astrocytomas World Health Organization (WHO) grade III (n = 3), peritumoral cortex (n = 3), and nonepileptic cortex (n = 3).

KEY FINDINGS

Immunohistochemistry predominantly showed cytoplasmic labeling in tumors and peritumoral tissue containing infiltrating tumor cells. ADK immunoreactivity was significantly stronger in tumor and peritumoral tissue compared to normal white matter and normal cortex, especially in astrocytoma WHO grade III, as confirmed by Western blot analysis and ADK activity measurements. Importantly, we found a significantly higher expression of ADK in the peritumoral infiltrated tissue of patients with epilepsy than in patients without epilepsy.

SIGNIFICANCE

These results suggest a dysregulation of ADK in astrocytic brain tumors. Moreover, the upregulation of ADK observed in peritumoral infiltrated tissue of glioma patients with epilepsy supports the role of this enzyme in tumor-associated epilepsy.

Upregulation of adenosine kinase in astrocytes in experimental and human temporal lobe epilepsy

PURPOSE

Adenosine kinase (ADK) represents the key metabolic enzyme for the regulation of extracellular adenosine levels in the brain. In adult brain, ADK is primarily present in astrocytes. Several lines of experimental evidence support a critical role of ADK in different types of brain injury associated with astrogliosis, which is also a prominent morphologic feature of temporal lobe epilepsy (TLE). We hypothesized that dysregulation of ADK is an ubiquitous pathologic hallmark of TLE.

METHODS

Using immunocytochemistry and Western blot analysis, we investigated ADK protein expression in a rat model of TLE during epileptogenesis and the chronic epileptic phase and compared those findings with tissue resected from TLE patients with mesial temporal sclerosis (MTS).

KEY FINDINGS

In rat control hippocampus and cortex, a low baseline expression of ADK was found with mainly nuclear localization. One week after the electrical induction of status epilepticus (SE), prominent up-regulation of ADK became evident in astrocytes with a characteristic cytoplasmic localization. This increase in ADK persisted at least for 3-4 months after SE in rats developing a progressive form of epilepsy. In line with the findings from the rat model, expression of astrocytic ADK was also found to be increased in the hippocampus and temporal cortex of patients with TLE. In addition, in vitro experiments in human astrocyte cultures showed that ADK expression was increased by several proinflammatory molecules (interleukin-1β and lipopolysaccharide).

SIGNIFICANCE

These results suggest that dysregulation of ADK in astrocytes is a common pathologic hallmark of TLE. Moreover, in vitro data suggest the existence of an additional layer of modulatory crosstalk between the astrocyte-based adenosine cycle and inflammation. Whether this interaction also can play a role in vivo needs to be further investigated.

Adenosine kinase as a target for therapeutic antisense strategies in epilepsy

PURPOSE

Given the high incidence of refractory epilepsy, novel therapeutic approaches and concepts are urgently needed. To date, viral-mediated delivery and endogenous expression of antisense sequences as a strategy to prevent seizures have received little attention in epilepsy therapy development efforts. Here we validate adenosine kinase (ADK), the astrocyte-based key negative regulator of the brain's endogenous anticonvulsant adenosine, as a potential therapeutic target for antisense-mediated seizure suppression.

METHODS

We developed adenoassociated virus 8 (AAV8)-based gene therapy vectors to selectively modulate ADK expression in astrocytes. Cell type selectivity was achieved by expressing an Adk-cDNA in sense or antisense orientation under the control of an astrocyte-specific gfaABC1D promoter. Viral vectors where injected into the CA3 of wild-type mice or spontaneously epileptic Adk-tg transgenic mice that overexpress ADK in brain. After virus injection, ADK expression was assessed histologically and biochemically. In addition, intracranial electroencephalography (EEG) recordings were obtained.

KEY FINDINGS

We demonstrate in wild-type mice that viral overexpression of ADK within astrocytes is sufficient to trigger spontaneous recurrent seizures in the absence of any other epileptogenic event, whereas ADK downregulation via AAV8-mediated RNA interference almost completely abolished spontaneous recurrent seizures in Adk-tg mice.

SIGNIFICANCE

Our data demonstrate that modulation of astrocytic ADK expression can trigger or prevent seizures, respectively. This is the first study to use an antisense approach to validate ADK as a rational therapeutic target for the treatment of epilepsy and suggests that gene therapies based on the knock down of ADK might be a feasible approach to control seizures in refractory epilepsy.

Methylxanthines, seizures, and excitotoxicity

Clinical evidence, in particular the wide use of theophylline as a bronchodilator, suggests that methylxanthines can cause seizures in patients without known underlying epilepsy. Theophylline is also known to be an added risk factor for seizure exacerbation in patients with epilepsy. The proconvulsant activity of methylxanthines can best be explained by their antagonizing the brain's own anticonvulsant adenosine. Recent evidence suggests that adenosine dysfunction is a pathological hallmark of epilepsy contributing to seizure generation and seizure spread. Conversely, adenosine augmentation therapies are effective in seizure suppression and prevention, whereas adenosine receptor antagonists such as methylxanthines generally exacerbate seizures. The impact of the methylxanthines caffeine and theophylline on seizures and excitotoxicity depends on timing, dose, and acute versus chronic use. New findings suggest a role of free radicals in theophylline-induced seizures, and adenosine-independent mechanisms for seizure generation have been proposed.

Inhibitory RNA in epilepsy: research tools and therapeutic perspectives

Since its discovery a decade ago, RNA interference (RNAi) has been developed not only into powerful experimental tools but also into promising novel therapeutics. In contrast to conventional antiepileptic drugs (AEDs) that target specific proteins such as ion channels or receptors, RNAi-based therapeutics exploit an endogenous regulatory mechanism of gene expression and thereby are poised to prevent or reverse pathogenetic mechanisms involved in seizure development. Therapeutic RNAi has been widely explored for dominant targets involved in neurodegenerative diseases; however, their use for epilepsy therapy has received less attention. This review discusses potential RNAi-based targets that are of interest for epilepsy therapy, including adenosine kinase (ADK), the key negative regulator of the brain's endogenous anticonvulsant adenosine. Overexpression of ADK, and the resulting adenosine deficiency, are pathologic hallmarks of the sclerotic epileptic brain, and have been implicated in seizure generation. Therefore, RNAi-strategies aimed at reducing ADK (and increasing adenosine) are based on a direct neurochemical rationale that has recently been explored experimentally using ex vivo and in vivo gene therapy approaches. Technical issues and challenges remain before those promising tools can be developed into future therapeutics for epilepsy.

Acadesine inhibits tissue factor induction and thrombus formation by activating the phosphoinositide 3-kinase/Akt signaling pathway

OBJECTIVE

Acadesine, an adenosine-regulating agent and activator of AMP-activated protein kinase, has been shown to possess antiinflammatory activity. This study investigated whether and how acadesine inhibits tissue factor (TF) expression and thrombus formation.

METHODS AND RESULTS

Human umbilical vein endothelial cells and human peripheral blood monocytes were stimulated with lipopolysaccharide to induce TF expression. Pretreatment with acadesine dramatically suppressed the clotting activity and expression of TF (protein and mRNA). These inhibitory effects of acadesine were unchanged for endothelial cells treated with ZM241385 (a specific adenosine A(2A) receptor antagonist) or AMP-activated protein kinase inhibitor compound C, and in macrophages lacking adenosine A(2A) receptor or alpha1-AMP-activated protein kinase. In endothelial cells and macrophages, acadesine activated the phosphoinositide 3-kinase/Akt signaling pathway, reduced the activity of mitogen-activated protein kinases, and consequently suppressed TF expression by inhibiting the activator protein-1 and NF-kappaB pathways. In mice, acadesine suppressed lipopolysaccharide-mediated increases in blood coagulation, decreased TF expression in atherosclerotic lesions, and reduced deep vein thrombus formation.

CONCLUSION

Acadesine inhibits TF expression and thrombus formation by activating the phosphoinositide 3-kinase/Akt pathway. This novel finding implicates acadesine as a potentially useful treatment for many disorders associated with thrombotic pathology, such as angina pain, deep vein thrombosis, and sepsis.