Elevated Expression of Acid-Sensing Ion Channel 3 Inhibits Epilepsy via Activation of Interneurons

Acidosis-related pain and its receptors as targets for chronic pain

Sensing acidosis is an important somatosensory function in responses to ischemia, inflammation, and metabolic alteration. Accumulating evidence has shown that acidosis is an effective factor for pain induction and that many intractable chronic pain diseases are associated with acidosis signaling. Various receptors have been known to detect extracellular acidosis and all express in the somatosensory neurons, such as acid sensing ion channels (ASIC), transient receptor potential (TRP) channels and proton-sensing G-protein coupled receptors. In addition to sense noxious acidic stimulation, these proton-sensing receptors also play a vital role in pain processing. For example, ASICs and TRPs are involved in not only nociceptive activation but also anti-nociceptive effects as well as some other non-nociceptive pathways. Herein, we review recent progress in probing the roles of proton-sensing receptors in preclinical pain research and their clinical relevance. We also propose a new concept of sngception to address the specific somatosensory function of acid sensation. This review aims to connect these acid-sensing receptors with basic pain research and clinical pain diseases, thus helping with better understanding the acid-related pain pathogenesis and their potential therapeutic roles via the mechanism of acid-mediated antinociception.

Insights into the Cellular Interactions and Molecular Mechanisms of Ketogenic Diet for Comprehensive Management of Epilepsy

A high-fat diet with appropriate protein and low carbohydrate content, widely known as the ketogenic diet (KD), is considered as an effective non-pharmacotherapeutic treatment option for certain types of epilepsies. Several preclinical and clinical studies have been carried out to elucidate its mechanism of antiepileptic action. Ketone bodies produced after KD's breakdown interact with cellular excito-inhibitory processes and inhibit abnormal neuronal firing. The generated ketone bodies decrease glutamate release by inhibiting the vesicular glutamate transporter 1 and alter the transmembrane potential by hyperpolarization. Apart from their effect on the well-known pathogenic mechanisms of epilepsy, some recent studies have shown the interaction of KD metabolites with novel neuronal targets, particularly adenosine receptors, adenosine triphosphate-sensitive potassium channel, mammalian target of rapamycin, histone deacetylase, hydroxycarboxylic acid receptors, and the NLR family pyrin domain containing 3 inflammasomes to suppress seizures. The role of KD in augmenting gut microbiota as a potential mechanism for epileptic seizure suppression has been established. Furthermore, some recent findings also support the beneficial effect of KD against epilepsy- associated comorbidities. Despite several advantages of the KD in epilepsy management, its use is also associated with a wide range of side effects. Hypoglycemia, excessive ketosis, acidosis, renal stones, cardiomyopathies, and other metabolic disturbances are the primary adverse effects observed with the use of KD. However, in some recent studies, modified KD has been tested with lesser side effects and better tolerability. The present review discusses the molecular mechanism of KD and its role in managing epilepsy and its associated comorbidities.

Mechanisms of Action of the Peptide Toxins Targeting Human and Rodent Acid-Sensing Ion Channels and Relevance to Their In Vivo Analgesic Effects

Acid-sensing ion channels (ASICs) are voltage-independent H⁺-gated cation channels largely expressed in the nervous system of rodents and humans. At least six isoforms (ASIC1a, 1b, 2a, 2b, 3 and 4) associate into homotrimers or heterotrimers to form functional channels with highly pH-dependent gating properties. This review provides an update on the pharmacological profiles of animal peptide toxins targeting ASICs, including PcTx1 from tarantula and related spider toxins, APETx2 and APETx-like peptides from sea anemone, and mambalgin from snake, as well as the dimeric protein snake toxin MitTx that have all been instrumental to understanding the structure and the pH-dependent gating of rodent and human cloned ASICs and to study the physiological and pathological roles of native ASICs in vitro and in vivo. ASICs are expressed all along the pain pathways and the pharmacological data clearly support a role for these channels in pain. ASIC-targeting peptide toxins interfere with ASIC gating by complex and pH-dependent mechanisms sometimes leading to opposite effects. However, these dual pH-dependent effects of ASIC-inhibiting toxins (PcTx1, mambalgin and APETx2) are fully compatible with, and even support, their analgesic effects in vivo, both in the central and the peripheral nervous system, as well as potential effects in humans.

Increased seizure sensitivity in pregnant mice with genetic knockdown of acid sensing ion channel 2a is associated with impaired hippocampal inflammatory response

Acid sensing ion channels (ASICs) are mechano- and chemo-receptor channels that are activated by drops in extracellular pH as occurs after neurotransmission. In our previous study, we demonstrated that mice subjected to reduced utero-placental perfusion pressure during pregnancy, to mimic the pregnancy complication of preeclampsia, have reduced hippocampal expression of ASIC2a protein. We also showed that pregnant mice with heterozygous expression of ASIC2a (+/-) had increased sensitivity and severity to pentylenetetrazol-induced seizures; however, the mechanisms by which this occurs remain unclear. The purpose of this study was to investigate key molecular targets involving neurotransmission and inflammation that are differentially changed following seizure exposure in pregnant ASIC2a +/- mice. On gestational day 18.5, ASIC2a wild-type (+/+, n = 7) and +/- (n = 14) mice were injected with 40 mg/kg pentylenetetrazol and monitored for 30 min. Western blot and ELISA analysis revealed no difference in hippocampal synaptosome glutamate-related proteins but an increase in GABA concentration in pregnant +/- mice. Using ELISA and multiplex assays, we found a significant decrease in serum TNFα, and a decreased concentration of pro-inflammatory cytokines and chemokines in hippocampal cytosolic fraction. Significant reductions in IL-1β, IL-3, IL-12 (p70), eotaxin, interferon gamma, and macrophage inflammatory protein (MIP-1β), in the hippocampal cytosolic fractions of +/- mice were observed compared to +/+ mice. Additionally, there was no difference in hippocampal microglia density or activation in pregnant ASIC2a+/+ vs. +/- mice. These results support the hypothesis that pregnant mice with reduced ASIC2a may not be able to mount an inflammatory response following acute seizure exposure.

Acetazolamide: Old drug, new evidence?

Acetazolamide is an old drug used as an antiepileptic agent, amongst other indications. The drug is seldom used, primarily due to perceived poor efficacy and adverse events. Acetazolamide acts as a noncompetitive inhibitor of carbonic anhydrase, of which there are several subtypes in humans. Acetazolamide causes an acidification of the intracellular and extracellular environments activating acid‐sensing ion channels, and these may account for the anti‐seizure effects of acetazolamide. Other potential mechanisms are modulation of neuroinflammation and attenuation of high‐frequency oscillations. The overall effect increases the seizure threshold in critical structures such as the hippocampus. The evidence for its clinical efficacy was from 12 observational studies of 941 patients. The 50% responder rate was 49%, 20% of patients were rendered seizure‐free, and 30% were noted to have had at least one adverse event. We conclude that the evidence from several observational studies may overestimate efficacy because they lack a comparator; hence, this drug would need further randomized placebo‐controlled trials to assess effectiveness and harm.

Acid-sensing ion channel 3: An analgesic target

Acid-sensing ion channel 3 (ASIC3) belongs to the epithelial sodium channel/degenerin (ENaC/DEG) superfamily. There are 7 different ASIC subunits encoded by 5 different genes. Most ASIC subunits form trimeric ion channels that upon activation by extracellular protons mediate a transient inward current inducing cellular excitability. ASIC subunits exhibit differential tissue expression and biophysical properties, and the ability of subunits to form homo- and heteromeric trimers further increases the complexity of currents measured and their pharmacological properties. ASIC3 is of particular interest, not only because it exhibits high expression in sensory neurones, but also because upon activation it does not fully inactivate: a transient current is followed by a sustained current that persists during a period of extracellular acidity, i.e. ASIC3 can encode prolonged acidosis as a nociceptive signal. Furthermore, certain mediators sensitize ASIC3 enabling smaller proton concentrations to activate it and other mediators can directly activate the channel at neutral pH. Moreover, there is a plethora of evidence using transgenic mouse models and pharmacology, which supports ASIC3 as being a potential target for development of analgesics. This review will focus on current understanding of ASIC3 function to provide an overview of how ASIC3 contributes to physiology and pathophysiology, examining the mechanisms by which it can be modulated, and highlighting gaps in current understanding and future research directions.

Acid-sensing ion channels as potential therapeutic targets

Tissue acidification is associated with a variety of disease states, and acid-sensing ion channels (ASICs) that can sense changes in pH have gained traction as possible pharmaceutical targets. An array of modulators, ranging from small molecules to large biopharmaceuticals, are known to inhibit ASICs. Here, we summarize recent insights from animal studies to assess the therapeutic potential of ASICs in disorders such as ischemic stroke, various pain-related processes, anxiety, and cardiac pathologies. We also review the factors that present a challenge in the pharmacological targeting of ASICs, and which need to be taken into careful consideration when developing potent and selective modulators in the future.

Acid-Sensing Ion Channels: Expression and Function in Resident and Infiltrating Immune Cells in the Central Nervous System

Peripheral and central immune cells are critical for fighting disease, but they can also play a pivotal role in the onset and/or progression of a variety of neurological conditions that affect the central nervous system (CNS). Tissue acidosis is often present in CNS pathologies such as multiple sclerosis, epileptic seizures, and depression, and local pH is also reduced during periods of ischemia following stroke, traumatic brain injury, and spinal cord injury. These pathological increases in extracellular acidity can activate a class of proton-gated channels known as acid-sensing ion channels (ASICs). ASICs have been primarily studied due to their ubiquitous expression throughout the nervous system, but it is less well recognized that they are also found in various types of immune cells. In this review, we explore what is currently known about the expression of ASICs in both peripheral and CNS-resident immune cells, and how channel activation during pathological tissue acidosis may lead to altered immune cell function that in turn modulates inflammatory pathology in the CNS. We identify gaps in the literature where ASICs and immune cell function has not been characterized, such as neurotrauma. Knowledge of the contribution of ASICs to immune cell function in neuropathology will be critical for determining whether the therapeutic benefits of ASIC inhibition might be due in part to an effect on immune cells.

Acid Sensing Ion Channel 2a Is Reduced in the Reduced Uterine Perfusion Pressure Mouse Model and Increases Seizure Susceptibility in Pregnant Mice

Eclampsia is diagnosed in pregnant women who develop novel seizures. Our laboratory showed that the reduced uterine perfusion pressure (RUPP) rat model of preeclampsia displays reduced latency to drug-induced seizures. While acid sensing ion channels (ASIC1a and 3) are important for reducing seizure longevity and severity, the role of ASIC2a in mediating seizure sensitivity in pregnancy has not been investigated. We hypothesized that 1) RUPP reduces hippocampal ASIC2a, and 2) pregnant mice with reduced ASIC2a (ASIC2a+/-) have increased seizure sensitivity. On gestational day 18.5, hippocampi from sham and RUPP C57BL/6 mice were harvested, and ASIC2a was assessed using Western blot. Pregnant wild-type and ASIC2a+/- mice received 40 mg/kg of pentylenetetrazol (i.p.) and were video recorded for 30 min. Behaviors were scored using a modified Racine scale (0-7: 0 = no seizure; 7 = respiratory arrest/death). Seizure severity was classified as mild (score = 1-3) or severe (score = 4-7). RUPP mice had reduced hippocampal and placental ASIC2a protein. ASIC2a+/- mice had reduced latency to seizures, increased seizure duration, increased severe seizure duration, and higher maximum seizure scores. Reduced hippocampal ASIC2a in RUPP mice and increased seizure activity in pregnant ASIC2a+/- mice support the hypothesis that reduced ASIC2a increases seizure sensitivity associated with the RUPP.

Ketone Bodies Inhibit the Opening of Acid-Sensing Ion Channels (ASICs) in Rat Hippocampal Excitatory Neurons in vitro

Objectives: Despite the long-term efficacy of antiepileptic drug treatments, frequent attacks of drug-resistant epilepsy necessitate the development of new antiepileptic drug therapy targets. The ketogenic diet is a high-fat, low-carbohydrate diet that has been shown to be effective in treating drug-resistant epilepsy, although the mechanism is yet unclear. In the ketogenic diet, excess fat is metabolized into ketone bodies (including acetoacetic acid, β-hydroxybutyric acid, and acetone). The present study explored the effect of ketone bodies on acid-sensing ion channels and provided a theoretical basis for the study of new targets of antiepileptic drugs based on “ketone body-acid sensing ion channels.”

Methods: In this study, rat primary cultured hippocampal neurons were used. The effects of acetoacetic acid, β-hydroxybutyric acid, and acetone on the open state of acid-sensing ion channels of hippocampal neurons were investigated by the patch-clamp technique.

Results: At pH 6.0, the addition of acetoacetic acid, β-hydroxybutyric acid, and acetone in the extracellular solution markedly weakened the currents of acid-sensing ion channels. The three ketone bodies significantly inhibited the opening of the acid-sensing ion channels on the surface of the hippocampal neurons, and 92, 47, and 77%, respectively.

Conclusions: Ketone bodies significantly inhibit the opening of acid-sensing ion channels. However, a new target for antiepileptic drugs on acid-sensing ion channels is yet to be investigated.

Protons as Messengers of Intercellular Communication in the Nervous System

In this review, evidence demonstrating that protons (H⁺) constitute a complex, regulated intercellular signaling mechanisms are presented. Given that pH is a strictly regulated variable in multicellular organisms, localized extracellular pH changes may constitute significant signals of cellular processes that occur in a cell or a group of cells. Several studies have demonstrated that the low pH of synaptic vesicles implies that neurotransmitter release is always accompanied by the co-release of H⁺ into the synaptic cleft, leading to transient extracellular pH shifts. Also, evidence has accumulated indicating that extracellular H⁺ concentration regulation is complex and implies a source of protons in a network of transporters, ion exchangers, and buffer capacity of the media that may finally establish the extracellular proton concentration. The activation of membrane transporters, increased production of CO₂ and of metabolites, such as lactate, produce significant extracellular pH shifts in nano- and micro-domains in the central nervous system (CNS), constituting a reliable signal for intercellular communication. The acid sensing ion channels (ASIC) function as specific signal sensors of proton signaling mechanism, detecting subtle variations of extracellular H⁺ in a range varying from pH 5 to 8. The main question in relation to this signaling system is whether it is only synaptically restricted, or a volume modulator of neuron excitability. This signaling system may have evolved from a metabolic activity detection mechanism to a highly localized extracellular proton dependent communication mechanism. In this study, evidence showing the mechanisms of regulation of extracellular pH shifts and of the ASICs and its function in modulating the excitability in various systems is reviewed, including data and its role in synaptic neurotransmission, volume transmission and even segregated neurotransmission, leading to a reliable extracellular signaling mechanism.

Expression of ASIC3 in the Trigeminal Nucleus Caudalis Plays a Role in a Rat Model of Recurrent Migraine

Acid-sensing ion channel 3 (ASIC3) is abundant in the trigeminal nervous system and is most sensitive to a slight pH decrease. Recent studies have indicated that ASIC3 in the peripheral trigeminal ganglia is likely involved in the pathogenesis of migraine pain. However, it is unclear whether this receptor plays a role in recurrent migraine, namely, migraine chronicity. Here, we aimed to investigate the role of ASIC3 in an animal model of recurrent migraine (RM). In this study, we established a rat model of RM through repeated administration of inflammatory soup (IS) onto the dura. Then, we tested the mechanical pain thresholds of the face and hindpaws by von Frey filaments. qRT-PCR, Western blot and immunofluorescence labelling were used to detect the expression and localization of ASIC3 in the trigeminal nucleus caudalis (TNC). The protein levels of calcitonin gene-related peptide (CGRP), its receptor component receptor activity modifying protein 1 (RAMP1) and c-Fos were analysed following treatment with the ASIC3 inhibitor APETx2 and activator 2-guanidine-4-methylquinazoline (GMQ). We found decreased pain thresholds after repeated dural inflammatory stimulation, which suggested the establishment of an RM model. Based on this model, we observed elevated expression of ASIC3 in the TNC group compared to that in the Sham group. ASIC3 was primarily expressed in neurons but not in astrocytes of the TNC. Moreover, APETx2 attenuated tactile allodynia and significantly decreased the expression of c-Fos, CGRP and RAMP1, while GMQ aggravated these effects compared to those observed in the IS + vehicle group. These findings indicate a critical role of ASIC3 channels in the pathophysiology of RM, and ASIC3 might represent a potential therapeutic target to prevent the progression of migraine.

Targeted Acid-Sensing Ion Channel Therapies for Migraine

Acid-sensing ion channels (ASICs) are a family of ion channels, consisting of four members; ASIC1 to 4. These channels are sensitive to changes in pH and are expressed throughout the central and peripheral nervous systems-including brain, spinal cord, and sensory ganglia. They have been implicated in a number of neurological conditions such as stroke and cerebral ischemia, traumatic brain injury, and epilepsy, and more recently in migraine. Their expression within areas of interest in the brain in migraine, such as the hypothalamus and PAG, their demonstrated involvement in preclinical models of meningeal afferent signaling, and their role in cortical spreading depression (the electrophysiological correlate of migraine aura), has enhanced research interest into these channels as potential therapeutic targets in migraine. Migraine is a disorder with a paucity of both acute and preventive therapies available, in which at best 50% of patients respond to available medications, and these medications often have intolerable side effects. There is therefore a great need for therapeutic development for this disabling condition. This review will summarize the understanding of the structure and CNS expression of ASICs, the mechanisms for their potential role in nociception, recent work in migraine, and areas for future research and drug development.

Interactions between GHRH and GABAARs in the brains of patients with epilepsy and in animal models of epilepsy

Growth hormone releasing hormone (GHRH) has recently been shown to increase the level of γ-aminobutyric acid (GABA) and activate GABA receptors (GABARs) in the cerebral cortex. GABA is an inhibitory neurotransmitter that can inhibit seizures. Does GHRH enhance the inhibitory effect of GABA to prevent epilepsy by increasing the GABA level and activating GABARs? In this study, patients with epilepsy and C57/BL6 mice with epilepsy induced by kainic acid (KA) or pentylenetetrazol (PTZ) served as the research subjects. Western blots were used to observe the differences in GHRH expression between the normal group and the epilepsy group, immunofluorescence was performed to explore the localization of GHRH in the brain, and coimmunoprecipitation was used to observe the interaction between GHRH and GABARs. GHRH expression was significantly increased in both patients with temporal lobe epilepsy (TLE) and in two mouse models induced by KA or PTZ compared with that in the normal groups (P < 0.05 or P < 0.01). GHRH was expressed in neurons in both humans and mice. Additionally, GHRH co-localized with presynaptic and postsynaptic sites of inhibitory neurons. Coimmunoprecipitation confirmed that GHRH interacted with GABAAα1 and GABAAβ2 + 3. GHRH may play an important role in inhibiting seizures by activating GABAARs.

Acid-Sensing Ion Channels as Potential Therapeutic Targets in Neurodegeneration and Neuroinflammation

Acid-sensing ion channels (ASICs) are a family of proton-sensing channels that are voltage insensitive, cation selective (mostly permeable to Na⁺), and nonspecifically blocked by amiloride. Derived from 5 genes (ACCN1-5), 7 subunits have been identified, 1a, 1b, 2a, 2b, 3, 4, and 5, that are widely expressed in the peripheral and central nervous system as well as other tissues. Over the years, different studies have shown that activation of these channels is linked to various physiological and pathological processes, such as memory, learning, fear, anxiety, ischemia, and multiple sclerosis to name a few, so their potential as therapeutic targets is increasing. This review focuses on recent advances that have helped us to better understand the role played by ASICs in different pathologies related to neurodegenerative diseases, inflammatory processes, and pain.

An acidosis-sparing ketogenic (ASK) diet to improve efficacy and reduce adverse effects in the treatment of refractory epilepsy

Diets that increase production of ketone bodies to provide alternative fuel for the brain are evolving from the classic ketogenic diet for epilepsy devised nearly a century ago. The classic ketogenic diet and its more recent variants all appear to have similar efficacy with approximately 50% of users showing a greater than 50% seizure reduction. They all require significant medical and dietetic support, and there are tolerability issues. A review suggests that low-grade chronic metabolic acidosis associated with ketosis is likely to be an important contributor to the short term and long term adverse effects of ketogenic diets. Recent studies, particularly with the characterization of the acid sensing ion channels, suggest that chronic metabolic acidosis may increase the propensity for seizures. It is also known that low-grade chronic metabolic acidosis has a broad range of negative health effects and an increased risk of early mortality in the general population. The modified ketogenic dietary treatment we propose is formulated to limit acidosis by measures that include monitoring protein intake and maximizing consumption of alkaline mineral-rich, low carbohydrate green vegetables. We hypothesize that this acidosis-sparing ketogenic diet is expected to be associated with less adverse effects and improved efficacy. A case history of life-long intractable epilepsy shows this diet to be a successful long-term strategy but, clearly, clinical studies are needed.

Glucose Deficiency Elevates Acid-Sensing Ion Channel 2a Expression and Increases Seizure Susceptibility in Temporal Lobe Epilepsy

Brain hypometabolism is a common epilepsy-related finding in both patients and animal models. Fluorodeoxyglucose positron emission tomography studies have shown that recurrent seizures lead to reduced glucose metabolism in certain brain regions, but no studies have definitively determined whether this induces epileptogenesis. There is evidence that acid-sensing ion channel 2a (ASIC2a) affects epilepsy susceptibility. Transcription factor CP2 (TFCP2) regulates ASIC2a expression. We report that suppressed TFCP2 expression and elevated ASIC2a expression were associated with glucose hypometabolism in the hippocampi of humans with epilepsy and of rat epilepsy model brains. In cultured PC12 cells, we determined that glucose deficiency led to TFCP2 downregulating ASIC2a. Moreover, electrophysiological recordings from cultured rat hippocampal slices showed that ASIC2a overexpression resulted in more action potentials in CA1 pyramidal neurons and increased seizure susceptibility. Our findings suggest that hippocampal glucose hypometabolism elevates ASIC2a expression by suppressing TFCP2 expression, which further enhances the intrinsic excitability of CA1 pyramidal neurons and increases seizure susceptibility in patients with temporal lobe epilepsy.

Tubulin β-III modulates seizure activity in epilepsy

Tubulin β-III (TUBB3) is the most dynamic β-tubulin isoform expressed in neurons, and is highly expressed in the central nervous system. However, the relationship between TUBB3 and epileptic seizures has not been thoroughly investigated. The aims of this study were to investigate the expression of TUBB3 in patients with temporal lobe epilepsy and two different rat models of chronic epilepsy, and to determine the specific roles of TUBB3 in epilepsy. TUBB3 expression was upregulated in human and rat epileptic tissue. Moreover, TUBB3 expression was associated with inhibitory GABAergic neurons and the inhibitory postsynaptic scaffold protein gephyrin. TUBB3 downregulation attenuated the behavioural phenotypes of epileptic seizures during the pilocarpine-induced chronic phase of epileptic seizures and the pentylenetetrazole kindling process, whereas TUBB3 overexpression had the opposite effect. Whole-cell clamp recordings and western blotting revealed that the amplitude of GABA-A receptor-mediated miniature inhibitory postsynaptic currents and the surface expression of the GABA-A receptor were increased in rats in which TUBB3 expression was downregulated. Importantly, TUBB3 interacted with GABA-A receptor-associated protein, which is known to be involved in GABA-A receptor trafficking. These results indicate that TUBB3 plays a critical role in the regulation of epileptic seizures via GABA-A receptor trafficking, suggesting a molecular mechanism for new therapeutic strategies. Copyright © 2017 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Astrocytic Acid-Sensing Ion Channel 1a Contributes to the Development of Chronic Epileptogenesis

Unraveling mechanisms underlying epileptogenesis after brain injury is an unmet medical challenge. Although histopathological studies have revealed that reactive astrogliosis and tissue acidosis are prominent features in epileptogenic foci, their roles in epileptogenesis remain unclear. Here, we explored whether astrocytic acid-sensing ion channel-1a (ASIC1a) contributes to the development of chronic epilepsy. High levels of ASIC1a were measured in reactive astrocytes in the hippocampi of patients with temporal lobe epilepsy (TLE) and epileptic mice. Extracellular acidosis caused a significant Ca²⁺ influx in cultured astrocytes, and this influx was sensitive to inhibition by the ASIC1a-specific blocker psalmotoxin 1 (PcTX1). In addition, recombinant adeno-associated virus (rAAV) vectors carrying a GFAP promoter in conjunction with ASIC1a shRNA or cDNA were generated to suppress or restore, respectively, ASIC1a expression in astrocytes. Injection of rAAV-ASIC1a-shRNA into the dentate gyrus of the wide type TLE mouse model resulted in the inhibition of astrocytic ASIC1a expression and a reduction in spontaneous seizures. By contrast, rAAV-ASIC1a-cDNA restored astrocytic ASIC1a expression in an ASIC1a knock-out TLE mouse model and increased the frequency of spontaneous seizures. Taken together, our results reveal that astrocytic ASIC1a may be an attractive new target for the treatment of epilepsy.

The microRNA miR-124 suppresses seizure activity and regulates CREB1 activity

miR-124, a brain-specific microRNA, was originally considered as a key regulator in neuronal differentiation and the development of the nervous system. Here we showed that miR-124 expression was suppressed in patients with epilepsy and rats after drug induced-seizures. Intrahippocampal administration of a miR-124 duplex led to alleviated seizure severity and prolonged onset latency in two rat models (pentylenetetrazole- and pilocarpine-induced seizures), while miR-124 inhibitor led to shortened onset latency in pilocarpine-induced seizure rat models. Moreover, the result of local field potentials (LFPs) records further demonstrated miR-124 may have anti-epilepsy function. Inhibition of neuronal firing by miR-124 was associated with the suppression of mEPSC, AMPAR- and NMDAR-mediated currents, which were accompanied by decreased surface expression of NMDAR. In addition, miR-124 injection resulted in decreased activity and expression of cAMP-response element-binding protein1 (CREB1). a key regulator in epileptogenesis. A dual-luciferase reporter assay was used to confirm that miR-124 targeted directly the 3'UTR of CREB1 gene and repressed the CREB1 expression in HEK293T cells. Immunoprecipitation studies confirmed that the CREB1 antibody effectively precipitated CREB1 and NMDAR1 but not GLUR1 from rat brain hippocampus. These results revealed a previously unknown function of miR-124 in neuronal excitability and provided a new insight into molecular mechanisms underlying epilepsy.

Association of Microtubule Dynamics with Chronic Epilepsy

Approximately 30 % of epilepsy cases are refractory to current pharmacological treatments through unknown mechanisms. Much work has been done on the role of synaptic components in the pathogenesis of epilepsy, but relatively little attention has been given to the potential role of the microtubules. We investigated the level of microtubule dynamic in 30 human epileptic tissues and two different chronic epilepsy rat models. The administration of microtubule-modulating agent attenuated the progression of chronic epilepsy. By contrast, microtubule-depolymerizing agent aggravated the progression of chronic epilepsy. The electrophysiological index by whole-cell clamp was used to investigate the neuronal excitation and inhibitory synaptic transmission in brain slices after administration of microtubule-modulating agent and microtubule-depolymerizing agent. Interestingly, we found that microtubule-modulating agent significantly increased the frequency of action potential firing in interneurons, and significantly promoted the amplitudes and frequencies of miniature inhibitory postsynaptic currents. Microtubule-depolymerizing agent had an opposite effect. These findings suggest that modulating hyperdynamic microtubules may take an anti-epileptic effect via postsynaptic mechanisms in interneurons. It could represent a potential pharmacologic target in epilepsy treatment.

Increased expression of receptor for activated C kinase 1 in temporal lobe epilepsy

Mesial temporal lobe epilepsy (MTLE) is characterized by spontaneous recurrent complex partial seizures. Increased neurogenesis and neuronal plasticity have been reported in animal models of MTLE, but not in detail in human MTLE cases. Here, we showed that receptor for activated C kinase 1 (RACK1) was expressed in the hippocampus and temporal cortex of the MTLE human brain. Interestingly, most of the cells expressing RACK1 in the epileptic temporal cortices co-expressed both polysialylated neural cell adhesion molecules, the migrating neuroblast marker, and the beta-tubulin isotype III, an early neuronal marker, suggesting that these cells may be post-mitotic neurons in the early phase of neuronal development. A subpopulation of RACK1-positive cells also co-express neuronal nuclei, a mature neuronal marker, suggesting that epilepsy may promote the generation of new neurons. Moreover, in the epileptic temporal cortices, the co-expression of both axonal and dendritic markers in the majority of RACK1-positive cells hints at enhanced neuronal plasticity. The expression of b-tubulin II (TUBB2B) associated with neuronal migration and positioning, was decreased. This study is the first to successfully identify a single population of cells expressing RACK1 in the human temporal cortex and the brain of the animal model, which can be up-regulated in epilepsy. Therefore, it is possible that these cells are functionally relevant to the pathophysiology of epilepsy.