ENT1 inhibition attenuates epileptic seizure severity via regulation of glutamatergic neurotransmission

Transmembrane protein modulates seizure in epilepsy: evidence from temporal lobe epilepsy patients and mouse models

Transmembrane protein (TMEM230) is located in secretory/recycling vesicles, including synaptic vesicles in neurons. However, the functional relationship between TMEM230 and epilepsy is still a mystery. The aims of this study were to investigate the expression of TMEM230 in patients with temporal lobe epilepsy (TLE) and two different mice models of chronic epilepsy, and to determine the probable roles of TMEM230 in epilepsy. Our results showed that TMEM230 expression was increased in the temporal neocortex of epileptic patients and the hippocampus and cortex of epileptic mice compared with that in the control tissues. Moreover, TMEM230 was mainly expressed in the neurons in both humans and mice epileptic brain. TMEM230 co-localized with glutamate vesicular transporter 1 (VGLUT-1), but not with vesicular γ-aminobutyric acid (GABA) transporter (VGAT). Mechanistically, coimmunoprecipitation confirmed that TMEM230 interacted with VGLUT-1, but not with VGAT in the hippocampus of epileptic mice. Lentivirus mediated overexpression of TMEM230 increased mice susceptibility to epilepsy and behavioural phenotypes of epileptic seizures during the kainite (KA)-induced chronic phase of epileptic seizures and the pentylenetetrazole (PTZ) kindling process, whereas lentivirus-mediated TMEM230 downregulation had the opposite effect. These results shed light on the functions of TMEM230 in neurons, suggesting that TMEM230 may play a critical role in the regulation of epileptic activity via influencing excitatory neurotransmission.

Anticonvulsant effect of equilibrative nucleoside transporters 1 inhibitor in a mouse model of Dravet syndrome

There are limited therapeutic options for patients with Dravet syndrome (DS). The equilibrative nucleoside transporters 1 (ENT1) mediate both the influx and efflux of adenosine across the cell membrane exerted beneficial effects in the treatment of epilepsy. This study aimed to evaluate the anticonvulsant effect of the ENT1 inhibitor in an animal model of DS (Scn1aE1099X/+ mice). J7 (5 mg/kg) treatment was efficacious in elevating seizure threshold in Scn1aE1099X/+ mice after hyperthermia exposure. Moreover, the J7 treatment significantly reduced the frequency of spontaneous excitatory post-synaptic currents (sEPSCs, ~35% reduction) without affecting the amplitude in dentate gyrus (DG) granule cells. Pretreatment with the adenosine A1 receptor (A1R) antagonist, DPCPX, abolished the J7 effects on sEPSCs. These observations suggest that the J7 shows an anticonvulsant effect in hyperthermia-induced seizures in Scn1aE1099X/+ mice. This effect possibly acts on presynaptic A1R-mediated signaling modulation in granule cells.

PGC-1α Affects Epileptic Seizures by Regulating Mitochondrial Fusion in Epileptic Rats

BACKGROUND

Peroxisome proliferator-activated receptor γ coactivator-1α (PGC-1α), regulated by AMPK, is an important regulator of mitochondrial fusion. At present, whether the AMPK/PGC-1α signaling pathway regulates mitochondrial dynamics in epileptic rats is still unknown.

METHODS

Adult male Sprague-Dawley (SD) rats were randomly divided into fourgroups: the control group (0.9% saline, n = 5), the EP groups (lithium-pilocarpine was used to induce epilepsy, and tissues were harvested at 6 and 24 h, every time point, n = 5), the EP + Compound C group (the specific inhibitor of PGC-1α, 15 mg/kg in 2% DMSO, n = 5), and the EP + DMSO group (0.9% saline + 2% DMSO, n = 5). To investigate whether PGC-1α participates in seizures by regulating the expression of mitofusin1/2(MFN1/2)in rats.

RESULTS

In this study, the behavioral results indicate that the seizure susceptibility of the rats to epilepsy was increased when the expression of PGC-1α was inhibited. Subsequently, Western blot results suggested that the expression level of both MFN1 and MFN2 in the hippocampus was higher at 6 and 24 h after an epileptic seizure. Besides, the expression of PGC-1α and MFN2 was significantly decreased in the hippocampus when the epileptic rats were treated with Compound C. Furthermore, the immunofluorescence analysis of the localization of MFN1/2 and PGC-1α showed that MFN1/2 was mainly expressed in neurons but not astrocytes in the hippocampus and cerebral cortex of rats. Meanwhile, PGC-1α colocalized with the excitatory post-synaptic marker PSD95, suggesting that PGC-1α may regulate the seizure susceptibility of the rats by mediating excitatory post-synaptic signaling.

CONCLUSION

The AMPK/PGC-1α signaling pathway may play an important role in the lithium-pilocarpine-induced epileptic rat model by mediating the expression of fusion proteins.

Emerging roles of dysregulated adenosine homeostasis in brain disorders with a specific focus on neurodegenerative diseases

In modern societies, with an increase in the older population, age-related neurodegenerative diseases have progressively become greater socioeconomic burdens. To date, despite the tremendous effort devoted to understanding neurodegenerative diseases in recent decades, treatment to delay disease progression is largely ineffective and is in urgent demand. The development of new strategies targeting these pathological features is a timely topic. It is important to note that most degenerative diseases are associated with the accumulation of specific misfolded proteins, which is facilitated by several common features of neurodegenerative diseases (including poor energy homeostasis and mitochondrial dysfunction). Adenosine is a purine nucleoside and neuromodulator in the brain. It is also an essential component of energy production pathways, cellular metabolism, and gene regulation in brain cells. The levels of intracellular and extracellular adenosine are thus tightly controlled by a handful of proteins (including adenosine metabolic enzymes and transporters) to maintain proper adenosine homeostasis. Notably, disruption of adenosine homeostasis in the brain under various pathophysiological conditions has been documented. In the past two decades, adenosine receptors (particularly A₁ and A_2A adenosine receptors) have been actively investigated as important drug targets in major degenerative diseases. Unfortunately, except for an A_2A antagonist (istradefylline) administered as an adjuvant treatment with levodopa for Parkinson's disease, no effective drug based on adenosine receptors has been developed for neurodegenerative diseases. In this review, we summarize the emerging findings on proteins involved in the control of adenosine homeostasis in the brain and discuss the challenges and future prospects for the development of new therapeutic treatments for neurodegenerative diseases and their associated disorders based on the understanding of adenosine homeostasis.

Metabolic Aspects of Adenosine Functions in the Brain

Adenosine, acting both through G-protein coupled adenosine receptors and intracellularly, plays a complex role in multiple physiological and pathophysiological processes by modulating neuronal plasticity, astrocytic activity, learning and memory, motor function, feeding, control of sleep and aging. Adenosine is involved in stroke, epilepsy and neurodegenerative pathologies. Extracellular concentration of adenosine in the brain is tightly regulated. Adenosine may be generated intracellularly in the central nervous system from degradation of AMP or from the hydrolysis of S-adenosyl homocysteine, and then exit via bi-directional nucleoside transporters, or extracellularly by the metabolism of released nucleotides. Inactivation of extracellular adenosine occurs by transport into neurons or neighboring cells, followed by either phosphorylation to AMP by adenosine kinase or deamination to inosine by adenosine deaminase. Modulation of the nucleoside transporters or of the enzymatic activities involved in the metabolism of adenosine, by affecting the levels of this nucleoside and the activity of adenosine receptors, could have a role in the onset or the development of central nervous system disorders, and can also be target of drugs for their treatment. In this review, we focus on the contribution of 5'-nucleotidases, adenosine kinase, adenosine deaminase, AMP deaminase, AMP-activated protein kinase and nucleoside transporters in epilepsy, cognition, and neurodegenerative diseases with a particular attention on amyotrophic lateral sclerosis and Huntington's disease. We include several examples of the involvement of components of the adenosine metabolism in learning and of the possible use of modulators of enzymes involved in adenosine metabolism or nucleoside transporters in the amelioration of cognition deficits.

Purinergic signaling in nervous system health and disease: Focus on pannexin 1

Purinergic signaling encompasses the cycle of adenosine 5' triphosphate (ATP) release and its metabolism into nucleotide and nucleoside derivatives, the direct release of nucleosides, and subsequent receptor-triggered downstream intracellular pathways. Since the discovery of nerve terminal and glial ATP release into the neuropil, purinergic signaling has been implicated in the modulation of nervous system development, function, and disease. In this review, we detail our current understanding of the roles of the pannexin 1 (PANX1) ATP-release channel in neuronal development and plasticity, glial signaling, and neuron-glial-immune interactions. We additionally provide an overview of PANX1 structure, activation, and permeability to orientate readers and highlight recent research developments. We identify areas of convergence between PANX1 and purinergic receptor actions. Additional highlights include data on PANX1's participation in the pathophysiology of nervous system developmental, degenerative, and inflammatory disorders. Our aim in combining this knowledge is to facilitate the movement of our current understanding of PANX1 in the context of other nervous system purinergic signaling mechanisms one step closer to clinical translation.

Equilibrative Nucleoside Transporters-1 Inhibitors Act as Anti-epileptic Agents by Inhibiting Glutamatergic Transmission

Background and Purpose: Adenosine dysregulation is associated with the occurrence of the epilepsy and equilibrative nucleoside transporters-1 (ENT-1) functions as an important regulator of extracellular adenosine in the brain. This study was aimed to prove the anti-epileptic effect of BBB permeable ENT-1 inhibitors, JMF1907 and J4, on animal models of various epilepsy, and the mechanisms that are involved. Experimental Approach: Maximal electroshock seizure (MES), pentylenetetrazol (PTZ)-induced seizure and kindling models were used as mouse models of generalized tonic-clonic epilepsy, generalized myoclonic epilepsy, and partial epilepsy, respectively. The epilepsy frequency, duration, and Racine score were evaluated. Whole-cell recordings were made from the hippocampal dentate granule cells by using a patch-clamp technique in the brain slice of the mice. Key Results: In MES, JMF1907 at a dose of 5 mg kg^-1 was efficacious in decreasing hindlimb extension, while J4 did not decrease hindlimb extension until a higher dose (10 mg kg^-1). Both JMF1907 and J4 were more potent in lengthening onset latency than ethosuximide (ETH) in PTZ-induced myoclonic epilepsy model, whereas ETH had better effects on the Racine score. In kindling model, JMF1907 and J4 at a dose of 1 mg kg^-1 had effects on seizure frequency and duration, and the effects of JMF1907 were comparable with those of carbamazepine. Both JMF1907 and J4 can reduce the glutamatergic spontaneous excitatory post-synaptic currents (sEPSCs) frequency. The maximal inhibition was about 50% for JMF1907 at a concentration of 1 μg L^-1, whereas J4 only inhibited 40% of sEPSCs frequency at a dose of 10 μg L^-1. Conclusion and Implications: ENT-1 inhibitors, JMF1907 and J4, showed anti-epileptic effects in different epilepsy models and the effects involved pre-synaptic neuronal modulation.

Inhibition of p38 MAPK regulates epileptic severity by decreasing expression levels of A1R and ENT1

Epilepsy is a chronic nervous system disease. Excessive increase of the excitatory neurotransmitter glutamate in the body results in an imbalance of neurotransmitters and excessive excitation of neurons, leading to epileptic seizures. Long‑term recurrent seizures lead to behavior and cognitive changes, and even increase the risk of death by 2‑ to 3‑fold relative to the general population. Adenosine A1 receptor (A1R), a member of the adenosine system, has notable anticonvulsant effects, and adenosine levels are controlled by the type 1 equilibrative nucleoside transporter (ENT1); in addition the p38 MAPK signaling pathway is involved in the regulation of ENT1, although the effect of its inhibitors on the expression levels of A1R and ENT1 is unclear. Therefore, in the present study, SB203580 was used to inhibit the p38 MAPK signaling pathway in rats, and the expression levels of A1R and ENT1 in the brain tissue of rats with acute LiCl‑pilocarpine‑induced status epilepticus was detected. SB203580 decreased pathological damage of hippocampal neurons, prolonged seizure latency, reduced the frequency of seizures, and decreased levels of A1R and ENT1 protein in rats.

Dynamic-related protein 1 inhibitor eases epileptic seizures and can regulate equilibrative nucleoside transporter 1 expression

Background

Dynamic-related protein 1 (Drp1) is a key protein involved in the regulation of mitochondrial fission, and it could affect the dynamic balance of mitochondria and appears to be protective against neuronal injury in epileptic seizures. Equilibrative nucleoside transporter 1 (ENT1) is expressed and functional in the mitochondrial membrane that equilibrates adenosine concentration across membranes. Whether Drp1 participates in the pathogenesis of epileptic seizures via regulating function of ENT1 remains unclear.

Methods

In the present study, we used pilocarpine to induce status epilepticus (SE) in rats, and we used mitochondrial division inhibitor 1 (Mdivi-1), a selective inhibitor to Drp1, to suppress mitochondrial fission in pilocarpine-induced SE model. Mdivi-1administered by intraperitoneal injection before SE induction, and the latency to firstepileptic seizure and the number of epileptic seizures was thereafter observed. The distribution of Drp1 was detected by immunofluorescence, and the expression patterns of Drp1 and ENT1 were detected by Western blot. Furthermore, the mitochondrial ultrastructure of neurons in the hippocampal CA1 region was observed by transmission electron microscopy.

Results

We found that Drp1 was expressed mainly in neurons and Drp1 expression was significantly upregulated in the hippocampal and temporal neocortex tissues at 6 h and 24 h after induction of SE. Mitochondrial fission inhibitor 1 attenuated epileptic seizures after induction of SE, reduced mitochondrial damage and ENT1 expression.

Conclusions

These data indicate that Drp1 is upregulated in hippocampus and temporal neocortex after pilocarpine-induced SE and the inhibition of Drp1 may lead to potential therapeutic target for SE by regulating ENT1 after pilocarpine-induced SE.

ENT1 inhibition attenuates apoptosis by activation of cAMP/pCREB/Bcl2 pathway after MCAO in rats

BACKGROUND AND PURPOSE

The present study was designed to investigate the potential role and the mechanism of equilibrative nucleoside transporter 1 (ENT1) on neuronal apoptosis and neurological deficits after middle cerebral artery occlusion (MCAO) in rats.

METHODS

One hundred and thirty-four male Sprague-Dawley rats were subjected to two hours of MCAO followed by reperfusion. The time course of the expression level of ENT1 and phosphorylation of CREB were detected by western blot and immunofluorescence staining. Another set of animals were administrated with NBTI, the ENT1 inhibitor, by daily intraperitoneal injection starting at 0.5 h post-MCAO, infarction volume and neurological deficits were measured both at 24 h and 72 h post MCAO. We further explored the neuroprotection machenism by using H89, cAMP dependent protein kinase inhibitor, the expression of Bcl-2, Bax, phosphorylated CREB and Cleaved caspase-3 were quantified by Western blot, neuronal apoptosis were analyed by TUNEL staining.

RESULTS

The endogenous expression of ENT1 were significantly increased and peaked at 12 h after MCAO. High-dose of NBTI (15 mg/kg) reduced brain infarction volume and improved neurologic deficits both at 24 h and 72 h post MCAO. Moreover, NBTI significantly increased the level of CREB phosphorylation and extracellular adenosine concentration, and decreased the neuronal apoptosis 24 h after MCAO. NBTI treatment reduced the expression of Bax and cleaved caspase-3, while up-regulated Bcl-2 compared with vehicle group. These effects were abolished by H89 pretreatment.

CONCLUSIONS

ENT1 inhibition prevented neuronal apoptosis and improves neurological deficits through cAMP/PKA/CREB/Bcl-2 signaling pathway after MCAO in rats. ENT1 might be an effective target in the treatment strategy for ischemic stroke.

The Concept of an Epilepsy Brain Bank

Epilepsy comprises more than 40 clinical syndromes affecting millions of patients and families worldwide. To decode the molecular and pathological framework of epilepsy researchers, need reliable human epilepsy and control brain samples. Brain bank organizations collecting and supplying well-documented clinically and pathophysiologically tissue specimens are important for high-quality neurophysiology and neuropharmacology studies for epilepsy and other neurological diseases. New development in molecular mechanism and new treatment methods for neurological disorders have evoked increased demands for human brain tissue. An epilepsy brain bank is a storage source for both the frozen samples as well as the formaldehyde fixed paraffin embedded (FFPE) tissue from epilepsy surgery resections. In 2014, the University of Saskatchewan have started collecting human epilepsy brain tissues for the first time in Canada. This review highlights the necessity and importance of Epilepsy Brain bank that provides unique access for research to valuable source of brain tissue and blood samples from epilepsy patients.

Nitrobenzylthioinosine mimics adenosine to attenuate the epileptiform discharge of hippocampal neurons from epileptic rats

Nitrobenzylthioinosine (NBTI), a specific inhibitor of type 1 equilibrative nucleoside transporter, could regulate the extracellular adenosine concentration and have protective roles in seizures. However, the protection mechanism of NBTI in seizures remains poorly understood. Here, the expression pattern and subcellular distribution of adenosine A1 receptor were detected by Western blot analysis and double-labeling immunofluorescence staining in Lithium Chloride-Pilocarpine induced epileptic rat model. At 24 h after pilocarpine induced rat seizures, hippocampal slices were prepared and the evoked excitatory postsynaptic currents (eEPSCs) amplitude of pyramidal neurons in hippocampus CA1 region was recorded using whole-cell patch clamp. In vivo, compared to control group, Western blotting analysis showed that the expression of adenosine A1 receptor protein was increased at 24 h and 72 h after seizure, didn't change at 0 min and 1 w, and decreased at 2 w. Double-label immunofluorescence revealed that adenosine A1 receptor was mainly expressed in the membrane and cytoplasm of neurons. In Vitro, adenosine decreased the eEPSCs amplitude of pyramidal neurons in hippocampus CA1 region, NBTI also had the same effect. Meantime, NBTI could further inhibit eEPSCs amplitude on the basis of lower concentration adenosine (50μM), and adenosine A1 receptor inhibitor DPCPX partially reversed this effect. Taken together, we confirmed that the expression of adenosine A1 receptor protein was increased in the early seizures and decreased in the late seizures. At the same time, NBTI mimics adenosine to attenuate the epileptiform discharge through adenosine A1 receptor, which might provide a novel therapeutic approach toward the control of epilepsy.

Functional Characterization of the Saccharomyces cerevisiae Equilibrative Nucleoside Transporter 1 (ScENT1)

Equilibrative nucleoside transporters (ENTs) are polytopic membrane transporters responsible for the translocation of nucleosides, nucleobases—to a lesser extent—and nucleoside analog therapeutics across cellular membranes. ENTs function in a diffusion controlled bidirectional manner and are thought to utilize an alternating access transport mechanism. However, a detailed understanding of ENT function at the molecular level has remained elusive. ScENT1 (formerly known as Function Unknown Now 26 or FUN26) is the only known ENT ortholog endogenously expressed in S. cerevisiae, and a proteoliposome assay system was used to study homogenously overexpressed and purified ScENT1 (wildtype relative to L390A and F249I mutants). L390 and F249 are highly conserved residues and were found to alter transporter function. L390A produced a reduction of mean transport activity while F249I increased mean substrate translocation relative to wildtype protein. However, both mutations resulted in transport of UTP—a novel gain of function for any ENT. These residues were then mapped onto an ab initio model of FUN26 which suggests they function in substrate translocation (L390) or cytoplasmic gating (F249). Furthermore, wildtype, L390A, and F249I were found to be sensitive to the presence of alcohols. Ethanol attenuated ScENT1-mediated transport of uridine by ~50%. These findings further demonstrate functional similarities between ScENT1 and human ENT isoforms and support identification of FUN26 as ScENT1, the first ENT isoform in S. cerevisiae.

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.

Expression and purification of human and Saccharomyces cerevisiae equilibrative nucleoside transporters

Nucleosides play an essential role in the physiology of eukaryotes by acting as metabolic precursors in de novo nucleic acid synthesis and energy metabolism. Nucleosides also act as ligands for purinergic receptors. Equilibrative nucleoside transporters (ENTs) are polytopic integral membrane proteins that aid in regulating plasmalemmal flux of purine and pyrimidine nucleosides and nucleobases. ENTs exhibit broad substrate selectivity across different isoforms and utilize diverse mechanisms to drive substrate flux across membranes. However, the molecular mechanisms and chemical determinants of ENT-mediated substrate recognition, binding, inhibition, and transport are poorly understood. To determine how ENT-mediated transport occurs at the molecular level, greater chemical insight and assays employing purified protein are essential. This article focuses on the expression and purification of human ENT1, human ENT2, and Saccharomyces cerevisiae ScENT1 using novel expression and purification strategies to isolate recombinant ENTs. ScENT1, hENT1, and hENT2 were expressed in W303 Saccharomyces cerevisiae cells and detergent solubilized from the membrane. After detergent extraction, these ENTs were further purified using immobilized metal affinity chromatography and size exclusion chromatography. This effort resulted in obtaining quantities of purified protein sufficient for future biophysical analysis.

Equilibrative nucleoside transporters-A review

Equilibrative nucleoside transporters (ENTs) are polytopic integral membrane proteins that mediate the transport of nucleosides, nucleobases, and therapeutic analogs. The best-characterized ENTs are the human transporters hENT1 and hENT2. However, non-mammalian eukaryotic ENTs have also been studied (e.g., yeast, parasitic protozoa). ENTs are major pharmaceutical targets responsible for modulating the efficacy of more than 30 approved drugs. However, the molecular mechanisms and chemical determinants of ENT-mediated substrate recognition, binding, inhibition, and transport are poorly understood. This review highlights findings on the characterization of ENTs by surveying studies on genetics, permeant and inhibitor interactions, mutagenesis, and structural models of ENT function.