Activation of group 2 metabotropic glutamate receptors reduces behavioral and electrographic correlates of pilocarpine induced status epilepticus

Downregulatory effect of miR-342-3p on epileptogenesis in the PTZ-kindling model

BACKGROUND

Epileptogenesis is a process that results in neurons firing abnormally, causing seizures. Increasing evidence has shown that miRNAs expressed in the epileptic hippocampus are involved in epileptogenesis. We demonstrated the expression changes of miRNAs that may be effective in epileptogenesis in silico analysis in the kindling model created with Pentylenetetrazole (PTZ). Thus, we aimed to identify the target genes responsible for epileptogenesis.

METHODS AND RESULTS

Fifteen male Wistar-albino rats (200-230 g) were randomly divided into two groups control (n = 6) and PTZ (n = 9). The control group received 0.5 ml saline, and the PTZ group (35 mg/kg i.p.) intraperitoneally (i.p.) (11 times, every other day) to induce tonic-clonic seizures. Seizures were observed and scored 30 min after PTZ injection. After the last dose of PTZ (75 mg/kg) administration, the hippocampus tissues of the rats were removed by anesthesia. Analysis of miRNAs was performed with the Affymetrix gene chip miRNA sequence (728 miRNA) and confirmed by the Real-Time Polymerase Chain Reaction (Real-Time PCR) method (29 miRNAs). We evaluated the expression change of the target gene of miRNA, whose expression change was detected using in silico analysis, by q-RT PCR. Eight miRNAs with changes in expression were detected. Of these miRNAs, miR-342-p was downregulated in the PTZ group and was statistically significant (p < 0.005). Ultimately, we determined that the target gene of miR-342-p is a metabotropic glutamate receptor 2 (GRM2) and that GRM2 expression is upregulated.

CONCLUSIONS

Downregulation of miR-342-3p in the PTZ kindling model may result in the upregulation of GRM2.

N-Acetyl-Aspartyl-Glutamate in Brain Health and Disease

N-acetyl-aspartyl-glutamate (NAAG) is the most abundant dipeptide in the brain, where it acts as a neuromodulator of glutamatergic synapses by activating presynaptic metabotropic glutamate receptor 3 (mGluR3). Recent data suggest that NAAG is selectively localized to postsynaptic dendrites in glutamatergic synapses and that it works as a retrograde neurotransmitter. NAAG is released in response to glutamate and provides the postsynaptic neuron with a feedback mechanisms to inhibit excessive glutamate signaling. A key regulator of synaptically available NAAG is rapid degradation by the extracellular enzyme glutamate carboxypeptidase II (GCPII). Increasing endogenous NAAG—for instance by inhibiting GCPII—is a promising treatment option for many brain disorders where glutamatergic excitotoxicity plays a role. The main effect of NAAG occurs through increased mGluR3 activation and thereby reduced glutamate release. In the present review, we summarize the transmitter role of NAAG and discuss the involvement of NAAG in normal brain physiology. We further present the suggested roles of NAAG in various neurological and psychiatric diseases and discuss the therapeutic potential of strategies aiming to enhance NAAG levels.

Identification and Development of a New Positron Emission Tomography Ligand 4-(2-Fluoro-4-[11C]methoxyphenyl)-5-((1-methyl-1H-pyrazol-3-yl)methoxy)picolinamide for Imaging Metabotropic Glutamate Receptor Subtype 2 (mGlu2)

Metabotropic glutamate receptor 2 (mGlu₂) is a known target for treating several central nervous system (CNS) disorders. To develop a viable positron emission tomography (PET) ligand for mGlu₂, we identified new candidates 5a-i that are potent negative allosteric modulators (NAMs) of mGlu₂. Among these candidates, 4-(2-fluoro-4-methoxyphenyl)-5-((1-methyl-1H-pyrazol-3-yl)methoxy)picolinamide (5i, also named as [¹¹C]MG2-1812) exhibited high potency, high subtype selectivity, and favorable lipophilicity. Compound 5i was labeled with positron-emitting carbon-11 (¹¹C) to obtain [¹¹C]5i in high radiochemical yield and high molar activity by O-[¹¹C]methylation of the phenol precursor 12 with [¹¹C]CH₃I. In vitro autoradiography with [¹¹C]5i showed heterogeneous radioactive accumulation in the brain tissue sections, ranked in the order: cortex > striatum > hippocampus > cerebellum ≫ thalamus > pons. PET study of [¹¹C]5i indicated in vivo specific binding of mGlu₂ in the rat brain. Based on the [¹¹C]5i scaffold, further optimization for new candidates is underway to identify a more suitable ligand for imaging mGlu₂.

Intranasal Delivery of miR-155-5p Antagomir Alleviates Acute Seizures Likely by Inhibiting Hippocampal Inflammation

INTRODUCTION

To confront the resistance to existing antiepileptic drugs, studies have gradually begun to investigate alternative pathologies distinct from the traditional treatments that overwhelmingly target ion channels. Microglia activation is the first inflammatory response in the brain, in which miR-155-5p plays a key proinflammatory role and thus represents a promising target for inflammatory modulation in epilepsy pathologies.

METHODS

In this study, a pentetrazol-induced acute seizure model was established, and the seizure degree was evaluated within 60 min after pentetrazol administration. Animals were then sacrificed for hippocampal tissue collection for biological experiments.

RESULTS

Intranasal delivery of miR-155-5p antagomir (30 min before pentetrazol administration) increased the percentage of animals with no induced seizures by 20%, extended the latency to generalized convulsions, and decreased seizure severity. In addition, miR-155-5p antagomir treatment alleviated hippocampal damage and decreased the expression of typical inflammatory modulators (TNF-α, IL-1β and IL-6). Further research revealed that intranasal delivery of miR-155-5p antagomir significantly decreased the relative level of miR-155-5p and increased the expression of its targets LXRα and SOCS1 in IBA1-labeled microglial cells in the hippocampus.

CONCLUSION

These findings demonstrate that intranasal delivery of miR-155-5p antagomir alleviated acute seizures, likely by blocking hippocampal inflammation. However, other potential mechanisms of the effects of miR-155-5p antagomir and its long-term safety for epilepsy treatment remain to be investigated.

Kainic acid-induced status epilepticus decreases mGlu5 receptor and phase-specifically downregulates Homer1b/c expression

Globally, over 50 million people are affected by epilepsy, which is characterized by the occurrence of spontaneous recurrent seizures. Almost one-third of the patients show resistance to current anti-epileptic drugs, making the exploration of new molecular targets necessary. An interesting target may be Homer1, due to its diverse roles in epileptogenesis and synaptic plasticity. Indeed, Homer1 regulates group I metabotropic glutamate (mGlu) receptors (i.e. mGlu₁ and mGlu₅) scaffolding and signaling in neurons. In the present work, using the systemic kainic acid (KA)-induced status epilepticus (SE) model in adult rats, we investigated the mRNA and protein expression patterns of the mGlu₅ receptor, Homer1a and Homer1b/c at 10, 80 and 120 days post-SE (i.e. T10, T80 and T120). Epileptogenesis was validated by electrophysiological recordings of seizures via electroencephalography (EEG) monitoring and through upregulation of glial fibrillary acidic protein. At the protein level, the mGlu₅ receptor was downregulated in the late latent phase (T10) and the early- and late exponential growth phase (T80 and T120, respectively), which was best observed in the hippocampal CA1 region. At mRNA level, significant downregulation of the mGlu₅ receptor was only detected in the late exponential growth phase. Homer1a expression did not change at any investigated time point. Interestingly, Homer1b/c was only downregulated in the late latent phase, a period where spontaneous seizures are extremely rare. Thus, this phase-specific downregulation may be indicative of an endogenous neuroprotective mechanism. In conclusion, these results suggest that Homer1b/c may be an interesting molecular target to prevent epileptogenesis and/or control seizures.

Silencing of microRNA-146a alleviates the neural damage in temporal lobe epilepsy by down-regulating Notch-1

This study aimed to evaluate the specific regulatory roles of microRNA-146a (miRNA-146a) in temporal lobe epilepsy (TLE) and explore the related regulatory mechanisms. A rat model of TLE was established by intraperitoneal injection of lithium chloride-pilocarpine. These model rats were injected intracerebroventricularly with an miRNA-146a inhibitor and Notch-1 siRNA. Then, neuronal damage and cell apoptosis in the cornu ammonis (CA) 1 and 3 regions of the hippocampus were assessed. SOD and MDA levels in the hippocampus were detected by chromatometry, and IL-1β, IL-6, and IL-18 levels were detected by ELISA. Then, we evaluated the expression levels of caspase-9, GFAP, Notch-1, and Hes-1 in the hippocampus. The interaction between Notch-1 and miRNA-146a was assessed by a dual luciferase reporter gene assay. A rat model of TLE was successfully established, which exhibited significantly increased miRNA-146a expression in the hippocampus. Silencing of miRNA-146a significantly alleviated the neuronal damage and cell apoptosis in the CA1 and CA3 regions of the hippocampus in TLE rats and decreased MDA, IL-1β, IL-6, and IL-18 levels and increased SOD levels in the hippocampus of TLE rats. In addition, silencing of miRNA-146a significantly decreased the expression levels of caspase-9, GFAP, Notch-1, and Hes-1 in the hippocampus of TLE rats. Notch-1 was identified as a target of miRNA-146a and silencing of Notch-1 aggravated the neuronal damage in the CA1 and CA3 regions. Silencing of miRNA-146a alleviated the neuronal damage in the hippocampus of TLE rats by down-regulating Notch-1.

Targeting metabotropic glutamate receptors in the treatment of epilepsy: rationale and current status

INTRODUCTION

Several drugs targeting the GABAergic system are used in the treatment of epilepsy, but only one drug targeting glutamate receptors is on the market. This is surprising because an imbalance between excitatory and inhibitory neurotransmission lies at the core of the pathophysiology of epilepsy. One possible explanation is that drug development has been directed towards the synthesis of molecules that inhibit the activity of ionotropic glutamate receptors. These receptors mediate fast excitatory synaptic transmission in the central nervous system (CNS) and their blockade may cause severe adverse effects such as sedation, cognitive impairment, and psychotomimetic effects. Metabotropic glutamate (mGlu) receptors are more promising drug targets because these receptors modulate synaptic transmission rather than mediate it. Areas covered: We review the current evidence that links mGlu receptor subtypes to the pathophysiology and experimental treatment of convulsive and absence seizures. Expert opinion: While mGlu₅ receptor negative allosteric modulators have the potential to be protective against convulsive seizures and hyperactivity-induced neurodegeneration, drugs that enhance mGlu₅ and mGlu₇ receptor function may have beneficial effects in the treatment of absence epilepsy. Evidence related to the other mGlu receptor subtypes is more fragmentary; further investigations are required for an improved understanding of their role in the generation and propagation of seizures.

Group II Metabotropic Glutamate Receptors: Role in Pain Mechanisms and Pain Modulation

Glutamate is the main excitatory neurotransmitter in the nervous system and plays a critical role in nociceptive processing and pain modulation. G-protein coupled metabotropic glutamate receptors (mGluRs) are widely expressed in the central and peripheral nervous system, and they mediate neuronal excitability and synaptic transmission. Eight different mGluR subtypes have been identified so far, and are classified into Groups I-III. Group II mGluR2 and mGluR3 couple negatively to adenylyl cyclase through Gi/Go proteins, are mainly expressed presynaptically, and typically inhibit the release of neurotransmitters, including glutamate and GABA. Group II mGluRs have consistently been linked to pain modulation; they are expressed in peripheral, spinal and supraspinal elements of pain-related neural processing. Pharmacological studies have shown anti-nociceptive/analgesic effects of group II mGluR agonists in preclinical models of acute and chronic pain, although much less is known about mechanisms and sites of action for mGluR2 and mGluR3 compared to other mGluRs. The availability of orthosteric and new selective allosteric modulators acting on mGluR2 and mGluR3 has provided valuable tools for elucidating (subtype) specific contributions of these receptors to the pathophysiological mechanisms of pain and other disorders and their potential as therapeutic targets. This review focuses on the important role of group II mGluRs in the neurobiology of pain mechanisms and behavioral modulation, and discusses evidence for their therapeutic potential in pain.

Compensatory Mechanisms Modulate the Neuronal Excitability in a Kainic Acid-Induced Epilepsy Mouse Model

Epilepsy is one of the most common neurological disorders affecting millions of people. Due to the complicated and unclear mechanisms of epilepsy, still a significant proportion of epilepsy patients remain poorly controlled. Epilepsy is characterized by convulsive seizures that are caused by increased excitability. In this study, by using kainic acid (KA)-induced epilepsy mice, we investigated the neuronal activities and revealed the neuronal compensatory mechanisms after KA-induced toxic hyperexcitability. The results indicate that both phasic inhibition induced by enhanced inhibitory synaptic activity and tonic inhibition mediated by activated astrocytes participate in the compensatory mechanisms. Compensatory mechanisms were already found in various neuronal disorders and were considered important in protecting nervous system from toxic hyperexcitability. This study hopefully will provide valuable clues in understanding the complex neuronal mechanisms of epilepsy, and exploring potential clinical treatment of the disease.

Soluble Ectodomain of Neuroligin 1 Decreases Synaptic Activity by Activating Metabotropic Glutamate Receptor 2

Synaptic cell adhesion molecules represent important targets for neuronal activity-dependent proteolysis. Postsynaptic neuroligins (NLs) form trans-synaptic complexes with presynaptic neurexins (NXs). Both NXs and NLs are cleaved from the cell surface by metalloproteases in an activity-dependent manner, releasing a soluble extracellular fragment and membrane-tethered C-terminal fragment. The cleavage of NL1 depresses synaptic transmission, but the mechanism by which this occurs is unknown. Metabotropic glutamate receptor 2 (mGluR2) are located primarily at the periphery of presynaptic terminals, where they inhibit the formation of cyclic adenosine monophosphate (cAMP) and consequently suppress the release of glutamate and decrease synaptic transmission. In the present study, we found that the soluble ectodomain of NL1 binds to and activates mGluR2 in both neurons and heterologous cells, resulting in a decrease in cAMP formation. In a slice preparation from the hippocampus of mice, NL1 inhibited the release of glutamate from mossy fibers that project to CA3 pyramidal neurons. The presynaptic effect of NL1 was abolished in the presence of a selective antagonist for mGluR2. Thus, our data suggest that the soluble extracellular domain of NL1 functionally interacts with mGluR2 and thereby decreases synaptic strength.

Efficacy of mGlu2 -positive allosteric modulators alone and in combination with levetiracetam in the mouse 6 Hz model of psychomotor seizures

OBJECTIVE

The metabotropic glutamate receptor subtype 2 (mGlu₂ ) possesses both orthosteric and allosteric modulatory sites, are expressed in the frontal cortex and limbic structures, and can affect excitatory synaptic transmission. Therefore, mGlu₂ is a potential therapeutic target in the treatment of epilepsy. The present study seeks to evaluate the anticonvulsant potential of mGlu₂ -acting compounds.

METHODS

The anticonvulsant efficacy of two selective mGlu₂ -positive allosteric modulators (PAMs) (JNJ-42153605 and JNJ-40411813/ADX71149) and one mGlu_2/3 receptor agonist (LY404039) were evaluated alone and in combination with the antiseizure drug levetiracetam (LEV) in the mouse 6 Hz model.

RESULTS

In the 6 Hz (32 mA stimulus intensity) model, median effective dose (ED₅₀ ) values were determined for JNJ-42153605 (3.8 mg/kg), JNJ-40411813 (12.2 mg/kg), and LY404039 (10.9 mg/kg). At the 44 mA stimulus intensity, ED₅₀ values were determined for JNJ-42153605 (5.9 mg/kg), JNJ-40411813 (21.0 mg/kg), LY404039 (14.1 mg/kg), and LEV (345 mg/kg). In addition, subprotective doses of each mGlu₂ -acting compound, administered in combination with various doses of LEV, were able to shift the 6 Hz 44 mA ED₅₀ for LEV by >25-fold. When JNJ-42153605 was administered at varying doses in combination with a single dose of LEV (10 mg/kg), the potency of JNJ-42153605 was increased 3.7-fold. Similarly, when a moderately effective dose of LEV (350 mg/kg) was administered in combination with varying doses of JNJ-40411813, the potency of JNJ-40411813 was increased approximately 14-fold. Plasma levels of JNJ-40411813 and LEV were not different when administered alone or in combination, suggesting that increases in potency are not due to pharmacokinetic effects.

SIGNIFICANCE

These studies suggest a potential positive pharmacodynamic effect of mGlu₂ -acting compounds in combination with LEV. If this effect is translated in a clinical setting, it can support a rational polypharmacy concept in treatment of epilepsy patients.

Intranasal Delivery of miR-146a Mimics Delayed Seizure Onset in the Lithium-Pilocarpine Mouse Model

Unveiling the key mechanism of temporal lobe epilepsy (TLE) for the development of novel treatments is of increasing interest, and anti-inflammatory miR-146a is now considered a promising molecular target for TLE. In the current study, a C57BL/6 TLE mouse model was established using the lithium-pilocarpine protocol. The seizure degree was evaluated according to the Racine scale, and level 5 was considered the threshold for generalized convulsions. Animals were sacrificed to analyze the hippocampus at three time points (2 h and 4 and 8 weeks after pilocarpine administration to evaluate the acute, latent, and chronic phases, resp.). After intranasal delivery of miR-146a mimics (30 min before pilocarpine injection), the percent of animals with no induced seizures increased by 6.7%, the latency to generalized convulsions was extended, and seizure severity was reduced. Additionally, hippocampal damage was alleviated. While the relative miR-146a levels significantly increased, the expression of its target mRNAs (IRAK-1 and TRAF-6) and typical inflammatory modulators (NF-κB, TNF-α, IL-1β, and IL-6) decreased, supporting an anti-inflammatory role of miR-146a via the TLR pathway. This study is the first to demonstrate that intranasal delivery of miR-146a mimics can improve seizure onset and hippocampal damage in the acute phase of lithium-pilocarpine-induced seizures, which provides inflammation-based clues for the development of novel TLE treatments.

Metabotropic Glutamate Receptors and Interacting Proteins in Epileptogenesis

Neurotransmitter and receptor systems are involved in different neurological and neuropsychological disorders such as Parkinson's disease, depression, Alzheimer’s disease and epilepsy. Recent advances in studies of signal transduction pathways or interacting proteins of neurotransmitter receptor systems suggest that different receptor systems may share the common signal transduction pathways or interacting proteins which may be better therapeutic targets for development of drugs to effectively control brain diseases. In this paper, we reviewed metabotropic glutamate receptors (mGluRs) and their related signal transduction pathways or interacting proteins in status epilepticus and temporal lobe epilepsy, and proposed some novel therapeutical drug targets for controlling epilepsy and epileptogenesis.

Regulatory effect of miRNA 320a on expression of aquaporin 4 in brain tissue of epileptic rats

OBJECTIVE

To study the expression of miRNA 320a in the brain tissue of epileptic rats and analyze its effect on the expression of aquaporin 4 (AQP4).

METHODS

All rats were performed with the intraperitoneal injection of lithium chloride (3 mmol/kg) and then the intraperitoneal injection of pilocarpine (30 mg/kg) 24 h later (injected twice) to prepare the epileptic model of Wistar rats. Rats in the control group were injected with the equal volume of normal saline. According to the Racine scale, rats with over stage 3 of epilepsy were chosen and the brain tissue was separated quickly and then stored at -80 °C. The immunohistochemistry was used to detect the expression of aquaporin in the brain tissue of epileptic model and the Real-time PCR was employed to determine the difference in the expression of miRNA 320a and AQP4 in the brain tissue of rats between the epileptic model group and control group. Five 5-day neonatal Wistar rats were chosen to collect the cerebral cortex and their primary astrocytes were separated and cultured. They were transfected with miRNA mimic and imitated to the endogenous miRNA 320a to up-regulate the expression of miRNA 320a.

RESULTS

In the model group, the expression of AQP4 was significantly higher than the control group (P < 0.01). However, the expression of miRNA 320a in the model group was lower than control group (P < 0.05), which was negatively correlated to AQP4. In the primary astrocytes, the transfection of miRNA 320a mimic could significantly reduce the expression of AQP4, while its inhibitor could up-regulate the expression of AQP4, which indicated that miRNA 320a could reduce the expression of AQP4.

CONCLUSIONS

In the primary astrocytes of rats, the miRNA 320a could inhibit the expression of AQP4 and after adding the inhibitor of miRNA 320a, the expression of AQP4 was up-regulated.