Are vesicular neurotransmitter transporters potential treatment targets for temporal lobe epilepsy?

A new method for isolation and purification of fusion-competent inhibitory synaptic vesicles

Synaptic vesicles specific to inhibitory GABA-releasing neurons are critical for regulating neuronal excitability. To study the specific molecular composition, architecture, and function of inhibitory synaptic vesicles, we have developed a new method to isolate and purify GABA synaptic vesicles from mouse brains. GABA synaptic vesicles were immunoisolated from mouse brain tissue using an engineered fragment antigen-binding region (Fab) against the vesicular GABA transporter (vGAT) and purified. Western blot analysis confirmed that the GABA synaptic vesicles were specifically enriched for vGAT and largely depleted of contaminants from other synaptic vesicle types, such as vesicular glutamate transporter (vGLUT1), and other cellular organelles. This degree of purity was achieved despite the relatively low abundance of vGAT vesicles compared to the total synaptic vesicle pool in mammalian brains. Cryo-electron microscopy images of these isolated GABA synaptic vesicles revealed intact morphology with circular shape and protruding proteinaceous densities. The GABA synaptic vesicles are functional, as assessed by a hybrid (ex vivo/in vitro) vesicle fusion assay, and they undergo synchronized fusion with synthetic plasma membrane mimic vesicles in response to Ca2+-triggering, but, as a negative control, not to Mg2+-triggering. Our immunoisolation method could also be applied to other types of vesicles.

Preferential pruning of inhibitory synapses by microglia contributes to alteration of the balance between excitatory and inhibitory synapses in the hippocampus in temporal lobe epilepsy

BACKGROUND

A consensus has formed that neural circuits in the brain underlie the pathogenesis of temporal lobe epilepsy (TLE). In particular, the synaptic excitation/inhibition balance (E/I balance) has been implicated in shifting towards elevated excitation during the development of TLE.

METHODS

Sprague Dawley (SD) rats were intraperitoneally subjected to kainic acid (KA) to generate a model of TLE. Next, electroencephalography (EEG) recording was applied to verify the stability and detectability of spontaneous recurrent seizures (SRS) in rats. Moreover, hippocampal slices from rats and patients with mesial temporal lobe epilepsy (mTLE) were assessed using immunofluorescence to determine the alterations of excitatory and inhibitory synapses and microglial phagocytosis.

RESULTS

We found that KA induced stable SRSs 14 days after status epilepticus (SE) onset. Furthermore, we discovered a continuous increase in excitatory synapses during epileptogenesis, where the total area of vesicular glutamate transporter 1 (vGluT1) rose considerably in the stratum radiatum (SR) of cornu ammonis 1 (CA1), the stratum lucidum (SL) of CA3, and the polymorphic layer (PML) of the dentate gyrus (DG). In contrast, inhibitory synapses decreased significantly, with the total area of glutamate decarboxylase 65 (GAD65) in the SL and PML diminishing enormously. Moreover, microglia conducted active synaptic phagocytosis after the formation of SRSs, especially in the SL and PML. Finally, microglia preferentially pruned inhibitory synapses during recurrent seizures in both rat and human hippocampal slices, which contributed to the synaptic alteration in hippocampal subregions.

CONCLUSIONS

Our findings elaborately characterize the alteration of neural circuits and demonstrate the selectivity of synaptic phagocytosis mediated by microglia in TLE, which could strengthen the comprehension of the pathogenesis of TLE and inspire potential therapeutic targets for epilepsy treatment.

Designing the 5HT2BR structure and its modulation as a therapeutic target for repurposing approach in drug-resistant epilepsy

The study intends to repurpose FDA drugs and investigate the mechanism of (5HT_2BR) activation by comprehending inter-residue interactions. The 5HT_2BR is a novel thread, and its role in reducing seizures in Dravet syndrome is emerging. The crystal structure (5HT_2BR) is a chimera with mutations; hence 3D-structure is modeled (4IB4: 5HT_2BR_M). The structure is cross-validated to simulate the human receptor using enrichment analysis (ROC: 0.79) and SAVESv6.0. Virtual screening of 2456 approved drugs yielded the best hits that are subjected to MM/GBSA and molecular dynamic (MD) simulations. The 2 top drugs Cabergoline (-53.44 kcal/mol) and Methylergonovine (-40.42 kcal/mol), display strong binding affinity, and ADMET/SAR analysis also suggests their non-mutagenic or non-carcinogenic nature. Methylergonovine has a weaker binding affinity and lower potency than standards [Ergotamine (agonist) and Methysergide (antagonist)] due to its higher K_i (1.32 M) and K_d (6.44 ×10^-8 M) values. Compared to standards, Cabergoline has moderate binding affinity and potency [K_i = 0.85 M and K_d = 5.53 × 10-8 M]. The top 2 drugs primarily interact with conserved residues (ASP135, LEU209, GLY221, ALA225, and THR140) as in agonists, unlike the antagonist. The top 2 drugs, upon binding to the 5HT_2BR_M, modify the helices VI, V, and III and shift the RMSD 2.48 Å and 3.07 Å. LEU209 forms a latch with residues 207-214 (forms a lid) in the 5HT_2BR_M receptor, which enhances agonist binding and prevents drug escape. Methylergonovine and Cabergoline interact more stongly with ALA225 than the antagonist. The post-MD analysis of Cabergoline suggests a better MM/GBSA value (-89.21 kcal/mol) than Methylergonovine (-63.54 kcal/mol). In this study, Cabergoline and Methylergonovine's agonistic mechanism and solid binding properties suggest their strong role in regulating the 5HT_2BR and might target drug-resistant epilepsy.

The role of peptidyl-prolyl isomerase Pin1 in neuronal signaling in epilepsy

Epilepsy is a common symptom of many neurological disorders and can lead to neuronal damage that plays a major role in seizure-related disability. The peptidyl-prolyl isomerase Pin1 has wide-ranging influences on the occurrence and development of neurological diseases. It has also been suggested that Pin1 acts on epileptic inhibition, and the molecular mechanism has recently been reported. In this review, we primarily focus on research concerning the mechanisms and functions of Pin1 in neurons. In addition, we highlight the significance and potential applications of Pin1 in neuronal diseases, especially epilepsy. We also discuss the molecular mechanisms by which Pin1 controls synapses, ion channels and neuronal signaling pathways to modulate epileptic susceptibility. Since neurotransmitters and some neuronal signaling pathways, such as Notch1 and PI3K/Akt, are vital to the nervous system, the role of Pin1 in epilepsy is discussed in the context of the CaMKII-AMPA receptor axis, PSD-95-NMDA receptor axis, NL2/gephyrin-GABA receptor signaling, and Notch1 and PI3K/Akt pathways. The effect of Pin1 on the progression of epilepsy in animal models is discussed as well. This information will lead to a better understanding of Pin1 signaling pathways in epilepsy and may facilitate development of new therapeutic strategies.

Neuroprotective Effect of Exogenous Galectin-1 in Status Epilepticus

Intrahippocampal pilocarpine microinjection (H-PILO) induces status epilepticus (SE) that can lead to spontaneous recurrent seizures (SRS) and neurodegeneration in rodents. Studies using animal models have indicated that lectins mediate a variety of biological activities with neuronal benefits, especially galectin-1 (GAL-1), which has been identified as an effective neuroprotective compound. GAL-1 is associated with the regulation of cell adhesion, proliferation, programmed cell death, and immune responses, as well as attenuating neuroinflammation. Here, we administrated GAL-1 to Wistar rats and evaluated the severity of the SE, neurodegenerative and inflammatory patterns in the hippocampal formation. Administration of GAL-1 caused a reduction in the number of class 2 and 4 seizures, indicating a decrease in seizure severity. Furthermore, we observed a reduction in inflammation and neurodegeneration 24 h and 15 days after SE. Overall, these results suggest that GAL-1 has a neuroprotective effect in the early stage of epileptogenesis and provides new insights into the roles of exogenous lectins in temporal lobe epilepsy (TLE).

Insight into carbon quantum dot-vesicles interactions: role of functional groups

Understanding carbon quantum dot–cell membrane interaction is essential for designing an effective nanoparticle-based drug delivery system. In this study, an attempt has been made to study the interaction involving phosphatidylcholine vesicles (PHOS VES, as model cell membrane) and four different carbon quantum dots bearing different functional groups (–COOH, –NH₂, –OH, and protein bovine serum albumin coated) using various tools such as PL behavior, surface charge on vesicles, QCM, ITC, TEM, LSV, and FTIR. From the above studies, it was observed that the –NH₂ terminating carbon dots were capable of binding strongly with the vesicles whereas other functional groups bearing carbon dots were not significantly interacting. This observation was also supported by direct visual evidence as shown by transmission electron microscopy, which shows that the polyethyleneimine carbon dot (PEICD) bearing –NH₂ functionality has greater affinity towards PHOS VES. The mechanistic insight presented in the paper indicates greater possibility of higher H-bonding, signifying better interaction between –NH₂ functionalized carbon dots and PHOS VES supported by FTIR, QCM, ITC and TEM. Moreover, the transport of neurotransmitters (which are generally amine compound) in neurons for cellular communication through synapse is only possible through vesicular platforms, showing that in our body, such interactions are already present. Such studies on the nano–bio interface will help biomedical researchers design efficient carbon-based nanomaterial as drug/gene delivery vehicles.

An interaction study at the nano–bio interface involving phosphatidylcholine vesicles (as a model cell membrane) and four different carbon dots bearing different functional groups (–COOH, –NH₂, –OH, and BSA-coated).

Nigrostriatal dopamine depletion promoted an increase in inhibitory markers (parvalbumin, GAD67, VGAT) and cold allodynia

Pain constitutes the major non-motor symptom in Parkinson's disease (PD). Its mechanism is still poorly understood although an increase in excitation or a decrease in inhibition have been reported in preclinical studies. The aim of this study was to investigate gamma aminobutyric acid (GABA) inhibition in the 6-hydroxydopamine (6-OHDA) PD rat model. Therefore, the expression of three inhibitory markers parvalbumin, glutamate decarboxylase 67 (GAD67) and vesicular GABA transporter (VGAT) was evaluated, besides cold allodynia, in bilateral 6-OHDA lesioned rat. There was a significant increase in the expression of the three markers labeling within the spinal dorsal horn (SDH) of 6-OHDA lesioned rats. In parallel, there was also an increase of the excitatory marker protein kinase C gamma (PKCγ) . PKCγ cells have a crucial role in pain chronicity and are regulated by GABAergic influences. Central dopamine depletion induced an increase in excitation as reveled by an increase in cFOS expression upon acetone stimulus and the presence of cold allodynia. In addition, dopamine depletion induced increased expression in inhibitory markers, which may reflect a disinhibition or a decreased inhibition in 6-OHDA lesioned rats.

Localization, proteomics, and metabolite profiling reveal a putative vesicular transporter for UDP-glucose

Vesicular neurotransmitter transporters (VNTs) mediate the selective uptake and enrichment of small-molecule neurotransmitters into synaptic vesicles (SVs) and are therefore a major determinant of the synaptic output of specific neurons. To identify novel VNTs expressed on SVs (thus identifying new neurotransmitters and/or neuromodulators), we conducted localization profiling of 361 solute carrier (SLC) transporters tagging with a fluorescent protein in neurons, which revealed 40 possible candidates through comparison with a known SV marker. We parallelly performed proteomics analysis of immunoisolated SVs and identified seven transporters in overlap. Ultrastructural analysis further supported that one of the transporters, SLC35D3, localized to SVs. Finally, by combining metabolite profiling with a radiolabeled substrate transport assay, we identified UDP-glucose as the principal substrate for SLC35D3. These results provide new insights into the functional role of SLC transporters in neurotransmission and improve our understanding of the molecular diversity of chemical transmitters.

The Pin1-CaMKII-AMPA Receptor Axis Regulates Epileptic Susceptibility

Pin1 is a unique isomerase that regulates protein conformation and function after phosphorylation. Pin1 aberration contributes to some neurological diseases, notably Alzheimer's disease, but its role in epilepsy is not fully understood. We found that Pin1-deficient mice had significantly increased seizure susceptibility in multiple chemical inducing models and developed age-dependent spontaneous epilepsy. Electrophysiologically, Pin1 ablation enhanced excitatory synaptic transmission to prefrontal cortex (PFC) pyramidal neurons without affecting their intrinsic excitability. Biochemically, Pin1 ablation upregulated AMPA receptors and GluA1 phosphorylation by acting on phosphorylated CaMKII. Clinically, Pin1 was decreased significantly, whereas phosphorylated CaMKII and GluA1 were increased in the neocortex of patients with epilepsy. Moreover, Pin1 expression restoration in the PFC of Pin1-deficient mice using viral gene transfer significantly reduced phosphorylated CaMKII and GluA1 and effectively suppressed their seizure susceptibility. Thus, Pin1-CaMKII-AMPA receptors are a novel axis controlling epileptic susceptibility, highlighting attractive new therapeutic strategies.

The Role of Phospholipase C in GABAergic Inhibition and Its Relevance to Epilepsy

Epilepsy is characterized by recurrent seizures due to abnormal hyperexcitation of neurons. Recent studies have suggested that the imbalance of excitation and inhibition (E/I) in the central nervous system is closely implicated in the etiology of epilepsy. In the brain, GABA is a major inhibitory neurotransmitter and plays a pivotal role in maintaining E/I balance. As such, altered GABAergic inhibition can lead to severe E/I imbalance, consequently resulting in excessive and hypersynchronous neuronal activity as in epilepsy. Phospholipase C (PLC) is a key enzyme in the intracellular signaling pathway and regulates various neuronal functions including neuronal development, synaptic transmission, and plasticity in the brain. Accumulating evidence suggests that neuronal PLC is critically involved in multiple aspects of GABAergic functions. Therefore, a better understanding of mechanisms by which neuronal PLC regulates GABAergic inhibition is necessary for revealing an unrecognized linkage between PLC and epilepsy and developing more effective treatments for epilepsy. Here we review the function of PLC in GABAergic inhibition in the brain and discuss a pathophysiological relationship between PLC and epilepsy.

Modulation of Glucose Availability and Effects of Hypo- and Hyperglycemia on Status Epilepticus: What We Do Not Know Yet?

Status epilepticus (SE) can lead to serious neuronal damage and act as an initial trigger for epileptogenic processes that may lead to temporal lobe epilepsy (TLE). Besides promoting neurodegeneration, neuroinflammation, and abnormal neurogenesis, SE can generate an extensive hypometabolism in several brain areas and, consequently, reduce intracellular energy supply, such as adenosine triphosphate (ATP) molecules. Although some antiepileptic drugs show efficiency to terminate or reduce epileptic seizures, approximately 30% of TLE patients are refractory to regular antiepileptic drugs (AEDs). Modulation of glucose availability may provide a novel and robust alternative for treating seizures and neuronal damage that occurs during epileptogenesis; however, more detailed information remains unknown, especially under hypo- and hyperglycemic conditions. Here, we review several pathways of glucose metabolism activated during and after SE, as well as the effects of hypo- and hyperglycemia in the generation of self-sustained limbic seizures. Furthermore, this study suggests the control of glucose availability as a potential therapeutic tool for SE.

LSP5-2157 a new inhibitor of vesicular glutamate transporters

Vesicular glutamate transporters (VGLUT1-3) mediate the uptake of glutamate into synaptic vesicles. VGLUTs are pivotal actors of excitatory transmission and of almost all brain functions. Their implication in various pathologies has been clearly documented. Despite their functional importance, the pharmacology of VGLUTs is limited to a few dyes such as Trypan Blue, Rose Bengal or Brilliant Yellow type. Here, we report the design and evaluation of new potent analogs based on Trypan Blue scaffold. Our best compound, named LSP5-2157, has an EC50 of 50 nM on glutamate vesicular uptake. Using a 3D homology model of VGLUT1 and docking experiments, we determined its putative binding subdomains within vesicular glutamate transporters and validated the structural requirement for VGLUT inhibition. To better estimate the specificity and potency of LSP5-2157, we also investigated its ability to block glutamatergic transmission in autaptic hippocampal cells. Neither glutamate receptors nor GABAergic transmission or transmission machinery were affected by LSP5-2157. Low doses of compound reversibly reduce glutamatergic neurotransmission in hippocampal autpases. LSP5-2157 had a low and depressing effect on synaptic efficacy in hippocampal slice. Furthermore, LSP5-2157 had no effect on NMDA-R- mediated fEPSP but reduce synaptic plasticity induced by 3 trains of 100 Hz. Finally, LSP5-2157 had the capacity to inhibit VGLUT3-dependent auditory synaptic transmission in the guinea pig cochlea. In this model, it abolished the compound action potential of auditory nerve at high concentration showing the limited permeation of LSP5-2157 in an in-vivo model. In summary, the new ligand LSP5-2157, has a high affinity and specificity for VGLUTs and shows some permeability in isolated neuron, tissue preparations or in vivo in the auditory system. These findings broaden the field of VGLUTs inhibitors and open the way to their use to assess glutamatergic functions in vitro and in vivo.

Age-Dependent Electrocorticogram Dynamics and Epileptogenic Responsiveness in Rats Subjected to Prenatal Hypoxia

Using electrocorticogram (ECoG) analysis, we compared age-related dynamics of general neuronal activity and convulsive epileptiform responsiveness induced by intracortical microinjections of 4-aminopyridine (4-AP) in control Wistar rats and those subjected to prenatal hypoxia (Hx; E14; 7% O2, 3 h). The studies were carried out in three age periods roughly corresponding to childhood (P20-27), adolescence (P30-45), and adulthood (P90-120). It was found that in the process of postnatal development of the control rats, the peak of the ECoG power spectrum density (PSD) of the theta rhythm during wakefulness shifted from the low to the higher frequency, while in the Hx rats this shift had the opposite direction. Moreover, the Hx rats had different frequency characteristics of the ECoG PSD and longer episodes of spike-and-wave discharges caused by 4-AP injections compared to the controls. The total ECoG PSD of slow-wave sleep (1-5 Hz) was also dramatically decreased in the process of development of the Hx rats. Such alterations in PSD could be explained by the changes in balance of the excitation and inhibition processes in the cortical networks. Analyzing protein levels of neurotransmitter transporters in the brain structures of the Hx rats, we found that the content of the glutamate transporter EAAT1 was higher in the parietal cortex in all age groups of Hx rats while in the hippocampus it decreased during postnatal development compared to controls. Furthermore, the content of the vesicular acetylcholine transporter in the parietal cortex, and of the inhibitory GABA transporter 1 in the hippocampus, was also affected by prenatal Hx. These data suggest that prenatal Hx results in a shift in the excitatory and inhibitory balance in the rat cortex towards excitation, making the rat's brain more vulnerable to the effects of proconvulsant drugs and predisposing animals to epileptogenesis during postnatal life.

The autism/neuroprotection-linked ADNP/NAP regulate the excitatory glutamatergic synapse

Activity-dependent neuroprotective protein (ADNP), essential for brain formation, was discovered as a leading de novo mutated gene causing the autism-like ADNP syndrome. This syndrome is phenotypically characterized by global developmental delays, intellectual disabilities, speech impediments, and motor dysfunctions. The Adnp haploinsufficient mouse mimics the human ADNP syndrome in terms of synapse density and gene expression patterns, as well as in developmental, motor, and cognitive abilities. Peripheral ADNP was also discovered as a biomarker for Alzheimer's disease and schizophrenia, with nasal administration of the ADNP snippet peptide NAP (enhancing endogenous ADNP activity) leading to partial cognitive and functional protection at the cellular, animal and clinical settings. Here, a novel formulation for effective delivery of NAP is provided with superior brain penetration capabilities. Also provided are methods for treating pertinent clinical implications such as autism, cognitive impairments, olfactory deficits, and muscle strength using the formulation in the Adnp haploinsufficient mouse. Results showed a dramatically specific increase in brain/body bioavailability with the new formulation, without breaching the blood brain barrier. Additional findings included improvements using daily intranasal treatments with NAP, at the behavioral and brain structural levels, diffusion tensor imaging (DTI), translatable to clinical practice. Significant effects on hippocampal and cerebral cortical expression of the presynaptic Slc17a7 gene encoding vesicular excitatory glutamate transporter 1 (VGLUT1) were observed at the RNA and immunohistochemical levels, explaining the DTI results. These findings tie for the first time a reduction in presynaptic glutamatergic synapses with the autism/Alzheimer's/schizophrenia-linked ADNP deficiency coupled with amelioration by NAP (CP201).

Effects of agomelatine on electrocorticogram activity on penicillin-induced seizure model of rats

Agomelatine is a new antidepressant drug acting as an antagonist of 5-hydroxytryptamine receptor 2C (5-HTR_2C) and agonist of melatonergic receptors 1 and 2 (MT₁ and MT₂). Because of this dual action, it is an atypical antidepressant. The aim of this study was to investigate chronic anticonvulsant effects of agomelatine on penicillin-induced epilepsy model. Adult male Sprague-Dawley rats divided into four groups and were administered with tap water (vehicle), and agomelatine doses of 10 mg/kg, 50 mg/kg and 100 mg/kg for 14 days via oral gavage. After the last doses were given, epileptic seizures were induced by intracortical penicillin (500 IU/2.5 μl) application in rats under urethane (1.25 g/kg intraperitoneal) anesthesia. Electrocorticogram (ECoG) recordings were obtained from the somatomotor cortex through 90 min, and spike frequencies and amplitudes were analyzed. The spike frequency analyses revealed that only 50 mg/kg agomelatine administration decreased the spike frequencies of hypersynchronous discharge of neurons caused by penicillin (p < 0.05). No significant differences in amplitudes between experimental groups were observed. In addition, mRNA expressions of vesicular glutamate transporter 1 (VGLUT1) and vesicular gamma-aminobutyric acid transporter (VGAT) in response to the agomelatine active dose, 50 mg/kg, showed no significant effect of agomelatine on the mRNA expression. Our results indicate that chronic treatment with agomelatine may have potential anticonvulsant effects. Agomelatine may be a promising drug for epilepsy patients having depression due to its antiepileptic and antidepressant effects.

Physiology of Astroglia

Astrocytes are neural cells of ectodermal, neuroepithelial origin that provide for homeostasis and defense of the central nervous system (CNS). Astrocytes are highly heterogeneous in morphological appearance; they express a multitude of receptors, channels, and membrane transporters. This complement underlies their remarkable adaptive plasticity that defines the functional maintenance of the CNS in development and aging. Astrocytes are tightly integrated into neural networks and act within the context of neural tissue; astrocytes control homeostasis of the CNS at all levels of organization from molecular to the whole organ.

Physiology of Astroglia

Astrocytes are neural cells of ectodermal, neuroepithelial origin that provide for homeostasis and defense of the central nervous system (CNS). Astrocytes are highly heterogeneous in morphological appearance; they express a multitude of receptors, channels, and membrane transporters. This complement underlies their remarkable adaptive plasticity that defines the functional maintenance of the CNS in development and aging. Astrocytes are tightly integrated into neural networks and act within the context of neural tissue; astrocytes control homeostasis of the CNS at all levels of organization from molecular to the whole organ.

Altered MT1 and MT2 melatonin receptors expression in the hippocampus of pilocarpine-induced epileptic rats

Clinical and experimental findings show that melatonin may be used as an adjuvant to the treatment of epilepsy-related complications by alleviates sleep disturbances, circadian alterations and attenuates seizures alone or in combination with AEDs. In addition, it has been observed that there is a circadian component on seizures, which cause changes in circadian system and in melatonin production. Nevertheless, the dynamic changes of the melatoninergic system, especially with regard to its membrane receptors (MT₁ and MT₂) in the natural course of TLE remain largely unknown. The aim of this study was to evaluate the 24-hour profile of MT₁ and MT₂ mRNA and protein expression in the hippocampus of rats submitted to the pilocarpine-induced epilepsy model analyzing the influence of the circadian rhythm in the expression pattern during the acute, silent, and chronic phases. Melatonin receptor MT₁ and MT₂ mRNA expression levels were increased in the hippocampus of rats few hours after SE, with MT₁ returning to normal levels and MT₂ reducing during the silent phase. During the chronic phase, mRNA expression levels of both receptors return to levels close to control, however, presenting a different daily profile, showing that there is a circadian change during the chronic phase. Also, during the acute and silent phase it was possible to verify MT₁ label only in CA2 hippocampal region with an increased expression only in the dark period of the acute phase. The MT₂ receptor was present in all hippocampal regions, however, it was reduced in the acute phase and it was found in astrocytes. In chronic animals, there is a reduction in the presence of both receptors especially in regions where there is a typical damage derived from epilepsy. Therefore, we conclude that SE induced by pilocarpine is able to change melatonin receptor MT₁ and MT₂ protein and mRNA expression levels in the hippocampus of rats few hours after SE as well as in silent and chronic phases.

Down-regulation of Pin1 in Temporal Lobe Epilepsy Patients and Mouse Model

Peptidyl-prolyl cis-trans isomerase NIMA-interacting 1 (Pin1) is a unique PPIase belonging to the parvulin family, and it isomerizes peptide bond between phospho-(Ser/Thr) and Pro. Pin1 has been linked to the pathogenesis of various human diseases; however, its exact biological functions remain unclear. The aim of the present study is to explore the expression pattern of Pin1 in patients with refractory epilepsy and in a chronic pilocarpine-induced epileptic mouse model. Using Western blot, immunofluorescence and immunoprecipitation analysis, we found that Pin1 protein was mainly distributed in neurons, demonstrated by colocalization with the dendritic marker, MAP2. However, the expression of Pin1 decreased remarkably in epileptic patients and experimental mice. Furthermore, the reciprocal coimmunoprecipitation analysis showed that Pin1 interacted with NR2A and NR2B-containing NMDA receptors not AMPA receptors in epileptic mouse models. Our results are the first to indicate that the expression of Pin1 in epileptic brain tissue could play important roles in epilepsy.

Neurochemical Markers in the Mammalian Brain: Structure, Roles in Synaptic Communication, and Pharmacological Relevance

BACKGROUND

Knowledge of molecular marker (typically protein or mRNA) expression in neural systems can provide insight to the chemical blueprint of signal processing and transmission, assist in tracking developmental or pathological progressions, and yield key information regarding potential medicinal targets. These markers are particularly relevant in the mammalian brain in the light of its unsurpassed cellular diversity. Accordingly, molecular expression profiling is rapidly becoming a major approach to classify neuron types. Despite a profusion of research, however, the biological functions of molecular markers commonly used to distinguish neuron types remain incompletely understood. Furthermore, most molecular markers of mammalian neuron types are also present in other organs, therefore complicating considerations of their potential pharmacological interactions.

OBJECTIVE

Here, we survey 15 prominent neurochemical markers from five categories, namely membrane transporters, calcium-binding proteins, neuropeptides, receptors, and extracellular matrix proteins, explaining their relation and relevance to synaptic communication.

METHOD

For each marker, we summarize fundamental structural features, cellular functionality, distributions within and outside the brain, as well as known drug effectors and mechanisms of action.

CONCLUSION

This essential primer thus links together the cellular complexity of the brain, the chemical properties of key molecular players in neurotransmission, and possible biomedical opportunities.

NR4A1 Knockdown Suppresses Seizure Activity by Regulating Surface Expression of NR2B

Nuclear receptor subfamily 4 group A member 1 (NR4A1), a downstream target of CREB that is a key regulator of epileptogenesis, has been implicated in a variety of biological processes and was previously identified as a seizure-associated molecule. However, the relationship between NR4A1 and epileptogenesis remains unclear. Here, we showed that NR4A1 protein was predominantly expressed in neurons and up-regulated in patients with epilepsy as well as pilocarpine-induced mouse epileptic models. NR4A1 knockdown by lentivirus transfection (lenti-shNR4A1) alleviated seizure severity and prolonged onset latency in mouse models. Moreover, reciprocal coimmunoprecipitation of NR4A1 and NR2B demonstrated their interaction. Furthermore, the expression of p-NR2B (Tyr1472) in epileptic mice and the expression of NR2B in the postsynaptic density (PSD) were significantly reduced in the lenti-shNR4A1 group, indicating that NR4A1 knockdown partly decreased surface NR2B by promoting NR2B internalization. These results are the first to indicate that the expression of NR4A1 in epileptic brain tissues may provide new insights into the molecular mechanisms underlying epilepsy.

Monoaminergic Mechanisms in Epilepsy May Offer Innovative Therapeutic Opportunity for Monoaminergic Multi-Target Drugs

A large body of experimental and clinical evidence has strongly suggested that monoamines play an important role in regulating epileptogenesis, seizure susceptibility, convulsions, and comorbid psychiatric disorders commonly seen in people with epilepsy (PWE). However, neither the relative significance of individual monoamines nor their interaction has yet been fully clarified due to the complexity of these neurotransmitter systems. In addition, epilepsy is diverse, with many different seizure types and epilepsy syndromes, and the role played by monoamines may vary from one condition to another. In this review, we will focus on the role of serotonin, dopamine, noradrenaline, histamine, and melatonin in epilepsy. Recent experimental, clinical, and genetic evidence will be reviewed in consideration of the mutual relationship of monoamines with the other putative neurotransmitters. The complexity of epileptic pathogenesis may explain why the currently available drugs, developed according to the classic drug discovery paradigm of "one-molecule-one-target," have turned out to be effective only in a percentage of PWE. Although, no antiepileptic drugs currently target specifically monoaminergic systems, multi-target directed ligands acting on different monoaminergic proteins, present on both neurons and glia cells, may represent a new approach in the management of seizures, and their generation as well as comorbid neuropsychiatric disorders.

Sleep-Dependent Structural Synaptic Plasticity of Inhibitory Synapses in the Dendrites of Hypocretin/Orexin Neurons

Sleep is tightly regulated by the circadian clock and homeostatic mechanisms. Although the sleep/wake cycle is known to be associated with structural and physiological synaptic changes that benefit the brain, the function of sleep is still debated. The hypothalamic hypocretin/orexin (Hcrt) neurons regulate various functions including feeding, reward, sleep, and wake. Continuous imaging of single neuronal circuits in live animals is vital to understanding the role of sleep in regulating synaptic dynamics, and the transparency of the zebrafish model enables time-lapse imaging of single synapses during both day and night. Here, we use the gephyrin (Gphnb) protein, a central inhibitory synapse organizer, as a fluorescent post-synaptic marker of inhibitory synapses. Double labeling showed that Gphnb-tagRFP and collybistin-EGFP clusters co-localized in dendritic inhibitory synapses. Using a transgenic hcrt:Gphnb-EGFP zebrafish, we showed that the number of inhibitory synapses in the dendrites of Hcrt neurons was increased during development. To determine the effect of sleep on the inhibitory synapses, we performed two-photon live imaging of Gphnb-EGFP in Hcrt neurons during day and night, under light/dark and constant light and dark conditions, and following sleep deprivation (SD). We found that synapse number increased during the night under light/dark conditions but that these changes were eliminated under constant light or dark conditions. SD reduced synapse number during the night, and the number increased during post-deprivation daytime sleep rebound. These results suggest that rhythmic structural plasticity of inhibitory synapses in Hcrt dendrites is independent of the circadian clock and is modulated by consolidated wake and sleep.

Dorsal horn neurons release extracellular ATP in a VNUT-dependent manner that underlies neuropathic pain

Activation of purinergic receptors in the spinal cord by extracellular ATP is essential for neuropathic hypersensitivity after peripheral nerve injury (PNI). However, the cell type responsible for releasing ATP within the spinal cord after PNI is unknown. Here we show that PNI increases expression of vesicular nucleotide transporter (VNUT) in the spinal cord. Extracellular ATP content ([ATP]_e) within the spinal cord was increased after PNI, and this increase was suppressed by exocytotic inhibitors. Mice lacking VNUT did not show PNI-induced increase in [ATP]_e and had attenuated hypersensitivity. These phenotypes were recapitulated in mice with specific deletion of VNUT in spinal dorsal horn (SDH) neurons, but not in mice lacking VNUT in primary sensory neurons, microglia or astrocytes. Conversely, ectopic VNUT expression in SDH neurons of VNUT-deficient mice restored PNI-induced increase in [ATP]_e and pain. Thus, VNUT is necessary for exocytotic ATP release from SDH neurons which contributes to neuropathic pain.

Purinergic receptor activation by extracellular ATP in the dorsal horn contributes to neuropathic pain, but which cell types release ATP in this context is not known. The authors show in a mouse model of neuropathic pain that ATP is released by dorsal horn neurons, a process requiring the vesicular nucleotide transporter, VNUT.

Inhibition of sodium glucose cotransporters following status epilepticus induced by intrahippocampal pilocarpine affects neurodegeneration process in hippocampus

Temporal lobe epilepsy (TLE) is characterized by spontaneous recurrent seizures, starting from secondary functional disorders due to several insults, including self-sustaining continuous seizures identified as status epilepticus (SE). Although hypoglycemia has been associated with SE, the effect of inhibition of the Na(+)/glucose cotransporters (SGLTs) on hippocampus during SE is still unknown. Here we evaluated the functional role of SGLT in the pattern of limbic seizures and neurodegeneration process after pilocarpine (PILO)-induced SE. Vehicle (VEH, 1μL) or phlorizin, a specific SGLT inhibitor (PZN, 1μL, 50μg/μL), was administered in the hippocampus of rats 30min before PILO (VEH+PILO or PZN+PILO, respectively). The limbic seizures were classified using the Racine's scale, and the amount of wet dog shakes (WDS) was quantified before and during SE. Neurodegeneration process was evaluated by Fluoro-Jade C (FJ-C), and FJ-C-positive neurons (FJ-C+) were counted 24h and 15days after SE. The PZN-treated rats showed higher (p<0.05) number of WDS when compared with VEH+PILO. There was no difference in seizure severity between PZN+PILO and VEH+PILO groups. However, the pattern of limbic seizures significantly changed in PZN+PILO. Indeed, the class 5 seizures repeated themselves more times (p<0.05) than the other classes in the PZN group at 50min after SE induction. The PZN+PILO animals had a higher (p<0.05) number of FJ-C+ cells in the dentate gyrus (DG), hilus, and CA3 and CA1 of hippocampus, when compared with VEH+PILO. The PZN+PILO animals had a decreased number (p<0.05) of FJ-C+ cells in CA1 compared with VEH+PILO 15days after SE induction. Taken together, our data suggest that SGLT inhibition with PZN increased the severity of limbic seizures during SE and increased neurodegeneration in hippocampus 24h after SE, suggesting that SGLT1 and SGLT2 could participate in the modulation of earlier stages of epileptogenic processes.

Activation of lysosomal P2X4 by ATP transported into lysosomes via VNUT/SLC17A9 using V-ATPase generated voltage gradient as the driving force

KEY POINTS

SLC17A9 proteins function as a lysosomal ATP transporter responsible for lysosomal ATP accumulation. P2X4 receptors act as lysosomal ion channels activated by luminal ATP. SLC17A9-mediated ATP transport across the lysosomal membrane is suppressed by Bafilomycin A1, the V-ATPase inhibitor. SLC17A9 mainly uses voltage gradient but not pH gradient generated by the V-ATPase as the driving force to transport ATP into the lysosome to activate P2X4.

ABSTRACT

The lysosome contains abundant ATP which plays important roles in lysosome functions and in cell signalling. Recently, solute carrier family 17 member 9 (SLC17A9, also known as VNUT for vesicular nucleotide transporter) proteins were suggested to function as a lysosomal ATP transporter responsible for lysosomal ATP accumulation, and P2X4 receptors were suggested to be lysosomal ion channels that are activated by luminal ATP. However, the molecular mechanism of SLC17A9 transporting ATP and the regulatory mechanism of lysosomal P2X4 are largely unknown. In this study, we report that SLC17A9-mediated ATP transport across lysosomal membranes is suppressed by Bafilomycin A1, the V-ATPase inhibitor. By measuring P2X4 activity, which is indicative of ATP transport across lysosomal membranes, we further demonstrated that SLC17A9 mainly uses voltage gradient but not pH gradient as the driving force to transport ATP into lysosomes. This study provides a molecular mechanism for lysosomal ATP transport mediated by SLC17A9. It also suggests a regulatory mechanism of lysosomal P2X4 by SLC17A9.

The intravesicular cocktail and its role in the regulation of exocytosis

The accumulation of neurotransmitters within secretory vesicles (SVs) far exceeds the theoretical tonic concentrations in the cytosol, a phenomenon that has captivated the attention of scientists for decades. For instance, chromaffin granules can accumulate close to molar concentrations of catecholamines, along with many other products like ATP, calcium, peptides, chromogranins, ascorbate, and other nucleotides. In this short review, we will summarize the interactions that are currently believed to occur between the elements that make up the vesicular cocktail in the acidic environment of SVs, and how they permit the accumulation of such high concentrations of certain components. In addition, we will examine how the vesicular cocktail regulates the exocytosis of neurotransmitters. In this review, we have highlighted the mechanisms that permit the storage of neurotransmitters and hormones inside secretory vesicles. We also have proposed a novel model based in the intravesicular interactions of the main components of this inner cocktail - catecholamines, ATP, and chromogranins - to allow the accumulation of near molar concentrations of transmitters in secretory vesicles. This article is part of a mini review series on Chromaffin cells (ISCCB Meeting, 2015).

Increased expression of copine VI in patients with refractory epilepsy and a rat model

Copine VI (CPNE6) is a member of copines family, a calcium-dependent phospholipids-binding protein group found in many diverse eukaryotic organisms. Although earlier studies have shown that CPNE6 is almost exclusively expressed in brain, the exact biological functions remain unclear. The purpose of this study is to explore the relationship between epilepsy and CPNE6 expression. In present study, we investigated the expression pattern and distribution of CPNE6 in patients with refractory epilepsy and in a chronic pilocarpine-induced epileptic rat model by quantitative real-time PCR, Western blot and immunofluorescence. The results showed that the expression of CPNE6 increased remarkably in epileptic patients and in experimental epileptic rats. Double immunofluorescence labeling studies have revealed that CPNE6 protein is mainly expressed in neurons, demonstrated by co-localization with the dendritic marker, MAP2. Our results are the first to indicate that the abnormal expression of the CPNE6 in epileptic brain tissue may play an important role in epilepsy, especially refractory epilepsy.

The vacuolar-type H⁺-ATPase at a glance - more than a proton pump

The vacuolar H(+)-ATPase (V-ATPase) has long been appreciated to function as an electrogenic H(+) pump. By altering the pH of intracellular compartments, the V-ATPase dictates enzyme activity, governs the dissociation of ligands from receptors and promotes the coupled transport of substrates across membranes, a role often aided by the generation of a transmembrane electrical potential. In tissues where the V-ATPase is expressed at the plasma membrane, it can serve to acidify the extracellular microenvironment. More recently, however, the V-ATPase has been implicated in a bewildering variety of additional roles that seem independent of its ability to translocate H(+). These non-canonical functions, which include fusogenicity, cytoskeletal tethering and metabolic sensing, are described in this Cell Science at a Glance article and accompanying poster, together with a brief overview of the conventional functions of the V-ATPase.

The vesicular nucleotide transporter (VNUT) is involved in the extracellular ATP effect on neuronal differentiation

Before being released, nucleotides are stored in secretory vesicles through the vesicular nucleotide transporter (VNUT). Once released, extracellular ATP participates in neuronal differentiation processes. Thus, the expression of a functional VNUT could be an additional component of the purinergic system which regulates neuronal differentiation and axonal elongation. In vitro expression of VNUT decreases neuritogenesis in N2a cells differentiated by retinoic acid treatment, whereas silencing of VNUT expression increases the number and length of neurites in these cells. These results highlight the role of VNUT in the neuritogenic process because this transporter regulates the ATP content in neurosecretory vesicles.

Hsp60 response in experimental and human temporal lobe epilepsy

The mitochondrial chaperonin Hsp60 is a ubiquitous molecule with multiple roles, constitutively expressed and inducible by oxidative stress. In the brain, Hsp60 is widely distributed and has been implicated in neurological disorders, including epilepsy. A role for mitochondria and oxidative stress has been proposed in epileptogenesis of temporal lobe epilepsy (TLE). Here, we investigated the involvement of Hsp60 in TLE using animal and human samples. Hsp60 immunoreactivity in the hippocampus, measured by Western blotting and immunohistochemistry, was increased in a rat model of TLE. Hsp60 was also increased in the hippocampal dentate gyrus neurons somata and neuropil and hippocampus proper (CA3, CA1) of the epileptic rats. We also determined the circulating levels of Hsp60 in epileptic animals and TLE patients using ELISA. The epileptic rats showed circulating levels of Hsp60 higher than controls. Likewise, plasma post-seizure Hsp60 levels in patients were higher than before the seizure and those of controls. These results demonstrate that Hsp60 is increased in both animals and patients with TLE in affected tissues, and in plasma in response to epileptic seizures, and point to it as biomarker of hippocampal stress potentially useful for diagnosis and patient management.

Altered vesicular glutamate transporter expression in human temporal lobe epilepsy with hippocampal sclerosis

Vesicular glutamate transporters (VGLUTs) are responsible for loading glutamate into synaptic vesicles. Altered VGLUT protein expression has been suggested to affect quantal size and glutamate release under both physiological and pathological conditions. In this study, we investigated mRNA and protein expression levels of the three VGLUT subtypes in hippocampal tissue of patients suffering from temporal lobe epilepsy (TLE) with hippocampal sclerosis (HS), International League Against Epilepsy type 1 (ILAE type 1) compared to autopsy controls, using quantitative polymerase chain reaction and semi-quantitative western blotting. mRNA expression levels of the VGLUTs are unaffected in hippocampal epileptic tissue compared to autopsy controls. At the protein level, VGLUT1 expression remains unaltered, while VGLUT2 is significantly decreased and VGLUT3 protein is significantly increased in hippocampal biopsies from TLE patients compared to controls. Our findings at the protein level can be explained by previously described histopathological changes observed in HS. Although VGLUTs have been repeatedly investigated in distinct rodent epilepsy models, their expression levels were hitherto not fully unraveled in the most difficult-to-treat form of epilepsy: TLE with HS ILAE type 1. We here, demonstrate for the first time that VGLUT2 protein expression is significantly decreased and VGLUT3 protein is significantly increased in the hippocampus of patients suffering from TLE with HS ILAE type 1 compared to autopsy controls.

Reduction of phosphorylated synapsin I (ser-553) leads to spatial memory impairment by attenuating GABA release after microwave exposure in Wistar rats

Background

Abnormal release of neurotransmitters after microwave exposure can cause learning and memory deficits. This study investigated the mechanism of this effect by exploring the potential role of phosphorylated synapsin I (p-Syn I).

Methods

Wistar rats, rat hippocampal synaptosomes, and differentiated (neuronal) PC12 cells were exposed to microwave radiation for 5 min at a mean power density of 30 mW/cm². Sham group rats, synaptosomes, and cells were otherwise identically treated and acted as controls for all of the following post-exposure analyses. Spatial learning and memory in rats was assessed using the Morris Water Maze (MWM) navigation task. The protein expression and presynaptic distribution of p-Syn I and neurotransmitter transporters were examined via western blotting and immunoelectron microscopy, respectively. Levels amino acid neurotransmitter release from rat hippocampal synaptosomes and PC12 cells were measured using high performance liquid chromatograph (HPLC) at 6 hours after exposure, with or without synapsin I silencing via shRNA transfection.

Results

In the rat experiments, there was a decrease in spatial memory performance after microwave exposure. The expression of p-Syn I (ser-553) was decreased at 3 days post-exposure and elevated at later time points. Vesicular GABA transporter (VGAT) was significantly elevated after exposure. The GABA release from synaptosomes was attenuated and p-Syn I (ser-553) and VGAT were both enriched in small clear synaptic vesicles, which abnormally assembled in the presynaptic terminal after exposure. In the PC12 cell experiments, the expression of p-Syn I (ser-553) and GABA release were both attenuated at 6 hours after exposure. Both microwave exposure and p-Syn I silencing reduced GABA release and maximal reduction was found for the combination of the two, indicating a synergetic effect.

Conclusion

p-Syn I (ser-553) was found to play a key role in the impaired GABA release and cognitive dysfunction that was induced by microwave exposure.