ABSTRACT
Obesity is a growing health concern, mainly caused by poor dietary habits. Yet, accurately tracking the diet and food intake of individuals with obesity is challenging. Although 3D motion capture technology is becoming increasingly important in healthcare, its potential for detecting early signs of obesity has not been fully explored. In this research, we used a deep LSTM network trained with individual identity (identity-trained deep LSTM network) to analyze 3D time-series skeleton data from mouse models with diet-induced obesity. First, we analyzed the data from two different viewpoints: allocentric and egocentric. Second, we trained various deep recurrent networks (e.g., RNN, GRU, LSTM) to predict the identity. Lastly, we tested whether these models effectively encode obese-like motion representations by training a support vector classifier with the latent features from the last layer. Our experimental results indicate that the optimal performance is achieved when utilizing an identity-trained deep LSTM network in conjunction with an egocentric viewpoint. This approach suggests a new way to use deep learning to spot health risks in mouse models of obesity and should be useful for detecting early signs of obesity in humans.
ABSTRACT
The μ-opioid receptor (MOR) is a class of opioid receptors characterized by a high affinity for β-endorphin and morphine. MOR is a G proteincoupled receptor (GPCR) that plays a role in reward and analgesic effects. While expression of MOR has been well established in neurons and microglia, astrocytic MOR expression has been less clear. Recently, we have reported that MOR is expressed in hippocampal astrocytes, and its activation has a critical role in the establishment of conditioned place preference. Despite this critical role, the expression and function of astrocytic MOR from other brain regions are still unknown. Here, we report that MOR is significantly expressed in astrocytes and GABAergic neurons from various brain regions including the hippocampus, nucleus accumbens, periaqueductal gray, amygdala, and arcuate nucleus. Using the MORmCherry reporter mice and Imaris analysis, we demonstrate that astrocytic MOR expression exceeded 60% in all tested regions. Also, we observed similar MOR expression of GABAergic neurons as shown in the previous distribution studies and it is noteworthy that MOR expression is particularly in parvalbumin (PV)-positive neurons. Furthermore, consistent with the normal MOR function observed in the MOR-mCherry mouse, our study also demonstrates intact MOR functionality in astrocytes through iGluSnFr-mediated glutamate imaging. Finally, we show the sex-difference in the expression pattern of MOR in PV-positive neurons, but not in the GABAergic neurons and astrocytes. Taken together, our findings highlight a substantial astrocytic MOR presence across various brain regions.
ABSTRACT
Developing social strategies to share limited resources equally and maximize the long-term benefits of conflict resolution is critical for appropriate social interactions. During social interactions, social decision-making depends not only on the external environment, but also on internal factors, such as hunger, thirst, or fatigue. In particular, hunger, which is related to food as a physical need, plays a dominant role in social decision-making. However, the consequences of food deprivation on social decision-making are not well understood. We have previously shown that mice with rule-observance behavior are capable of resolving conflict during social decision-making by observing a well-established social strategy based on reward zone allocation. Here, we developed a rule-observance behavior paradigm wherein the hunger state is achieved by applying food restrictions on mice prior to social behavior experiments. We found that the hunger state in mice deteriorated the established social strategy by decreasing reaction time, implying an increase in impulsivity. In contrast, the hunger state did not affect reward zone allocation, indicating no effect on spatial memory. This decrease in reaction time led to a significant increase in the percentage of violations during rule observance and a significant decrease in the amount of reward (payoff equity). Our study proposes that the hunger state exerts a detrimental effect on appropriate social decisionmaking by decreasing reaction time, increasing violation, and decreasing payoff equity in rule-observance behavior.
ABSTRACT
Monoamine oxidase B (MAOB) is a key enzyme for GABA production in astrocytes in several brain regions. To date, the role of astrocytic MAOB has been studied in MAOB null knockout (KO) mice, although MAOB is expressed throughout the body. Therefore, there has been a need for genetically engineered mice in which only astrocytic MAOB is targeted. Here, we generated an astrocyte-specific MAOB conditional KO (cKO) mouse line and characterized it in the cerebellar and striatal regions of the brain. Using the CRISPR-Cas9 gene-editing technique, we generated Maob floxed mice (B6-Maob em1Cjl /Ibs) which have floxed exons 2 and 3 of Maob with two loxP sites. By crossing these mice with hGFAP-CreER T2 , we obtained Maob floxed::hGFAP-CreER T2 mice which have a property of tamoxifen-inducible ablation of Maob under the human GFAP (hGFAP) promoter. When we treated Maob floxed::hGFAP-CreER T2 mice with tamoxifen for 5 consecutive days, MAOB and GABA immunoreactivity were significantly reduced in striatal astrocytes as well as in Bergmann glia and lamellar astrocytes in the cerebellum, compared to sunflower oil-injected control mice. Moreover, astrocyte-specific MAOB cKO led to a 74.6% reduction in tonic GABA currents from granule cells and a 76.8% reduction from medium spiny neurons. Our results validate that astrocytic MAOB is a critical enzyme for the synthesis of GABA in astrocytes. We propose that this new mouse line could be widely used in studies of various brain diseases to elucidate the pathological role of astrocytic MAOB in the future.
ABSTRACT
The principal inhibitory transmitter, γ-aminobutyric acid (GABA), is critical for maintaining hypothalamic homeostasis and released from neurons phasically, as well as from astrocytes tonically. Although astrocytes in the arcuate nucleus (ARC) of the hypothalamus are shown to transform into reactive astrocytes, the tonic inhibition by astrocytic GABA has not been adequately investigated in diet-induced obesity (DIO). Here, we investigated the expression of monoamine oxidase- B (MAOB), a GABA-synthesizing enzyme, in reactive astrocytes in obese mice. We observed that a chronic high-fat diet (HFD) significantly increased astrocytic MAOB and cellular GABA content, along with enhanced hypertrophy of astrocytes in the ARC. Unexpectedly, we found that the level of tonic GABA was unaltered in chronic HFD mice using whole-cell patch-clamp recordings in the ARC. Furthermore, the GABA-induced current was increased with elevated GABA A receptor α5 (GABRA5) expression. Surprisingly, we found that a nonselective GABA transporter (GAT) inhibitor, nipecotic acid (NPA)-induced current was significantly increased in chronic HFD mice. We observed that GAT1 inhibitor, NO711-induced current was significantly increased, whereas GAT3 inhibitor, SNAP5114-induced current was not altered. The unexpected unaltered tonic inhibition was due to an increase of GABA clearance in the ARC by neuronal GAT1 rather than astrocytic GAT3. These results imply that increased astrocytic GABA synthesis and neuronal GABA A receptor were compensated by GABA clearance, resulting in unaltered tonic GABA inhibition in the ARC of the hypothalamus in obese mice. Taken together, GABA-related molecular pathways in the ARC dynamically regulate the tonic inhibition to maintain hypothalamic homeostasis against the HFD challenge.
ABSTRACT
Central neurocytoma (CN) has been known as a benign neuronal tumor. In rare cases, CN undergoes malignant transformation to glioblastomas (GBM). Here we examined its cellular origin by characterizing differentiation potential and gene expression of CN-spheroids. First, we demonstrate that both CN tissue and cultured primary cells recapitulate the hierarchal cellular composition of subventricular zone (SVZ), which is comprised of neural stem cells (NSCs), transit amplifying progenitors (TAPs), and neuroblasts. We then derived spheroids from CN which displayed EGFR+/ MASH+ TAP and BLBP+ radial glial cell (RGC) characteristic, and mitotic neurogenesis and gliogenesis by single spheroids were observed with cycling multipotential cells. CN-spheroids expressed increased levels of pluripotency and tumor stem cell genes such as KLF4 and TPD5L1, when compared to their differentiated cells and human NSCs. Importantly, Gene Set Enrichment Analysis showed that gene sets of GBM-Spheroids, EGFR Signaling, and Packaging of Telomere Ends are enriched in CN-spheroids in comparison with their differentiated cells. We speculate that CN tumor stem cells have TAP and RGC characteristics, and upregulation of EGFR signaling as well as downregulation of eph-ephrin signaling have critical roles in tumorigenesis of CN. And their ephemeral nature of TAPs destined to neuroblasts, might reflect benign nature of CN.
ABSTRACT
The cause of Parkinson’s disease has been traditionally believed to be the dopaminergic neuronal death in the substantia nigra pars compacta (SNpc).This traditional view has been recently challenged by the proposal that reactive astrocytes serve as key players in the pathology of Parkinson’s disease through excessive GABA release. This aberrant astrocytic GABA is synthesized by the enzymatic action of monoamine oxidase B (MAOB), whose pharmacological inhibition and gene-silencing are reported to significantly alleviate parkinsonian motor symptoms in animal models of Parkinson’s disease. However, whether genetic ablation and over-expression of MAOB can bidirectionally regulate parkinsonian motor symptoms has not been tested. Here we demonstrate that genetic ablation of MAOB blocks the MPTP-induced augmentation of astrocytic GABA-mediated tonic inhibition of neighboring dopaminergic neurons as well as parkinsonian motor symptoms, indicating the necessity of MAOB for parkinsonian motor symptoms. Furthermore, we demonstrate that GFAP-MAOB transgenic mice, in which MAOB is over-expressed under the GFAP promoter for astrocyte-specific over-expression, display exacerbated MPTP-induced tonic inhibition and parkinsonian motor symptoms compared to wild-type mice, indicating the importance of astrocytic MAOB for parkinsonian motor symptoms. Our study provides genetic pieces of evidence for the causal link between the pathological role of astrocytic MAOB-dependent tonic GABA synthesis and parkinsonian motor symptoms.
ABSTRACT
Parkinson’s disease (PD) is the most prevalent neurodegenerative motor disorder. While PD has been attributed to dopaminergic neuronal death in substantia nigra pars compacta (SNpc), accumulating lines of evidence have suggested that reactive astrogliosis is critically involved in PD pathology. These pathological changes are associated with α-synuclein aggregation, which is more prone to be induced by an A53T mutation. Therefore, the overexpression of A53T-mutated α-synuclein (A53T-α-syn) has been utilized as a popular animal model of PD. However, this animal model only shows marginal-to-moderate extents of reactive astrogliosis and astrocytic α-synuclein accumulation, while these phenomena are prominent in human PD brains. Here we show that Adeno-GFAP-GFP virus injection into SNpc causes severe reactive astrogliosis and exacerbates the A53Tα-syn-mediated PD pathology. In particular, we demonstrate that AAV-CMV-A53T-α-syn injection, when combined with Adeno-GFAP-GFP, causes more significant loss of dopaminergic neuronal tyrosine hydroxylase level and gain of astrocytic GFAP and GABA levels. Moreover, the combination of AAV-CMV-A53T-α-syn and Adeno-GFAP-GFP causes an extensive astrocytic α-syn expression, just as in human PD brains. These results are in marked contrast to previous reports that AAV-CMV-A53T-α-syn alone causes α-syn expression mostly in neurons but rarely in astrocytes. Furthermore, the combination causes a severe PD-like motor dysfunction as assessed by rotarod and cylinder tests within three weeks from the virus injection, whereas Adeno-GFAP-GFP alone or AAV-CMV-A53T-α-syn alone does not. Our findings implicate that inducing reactive astrogliosis exacerbates PD-like pathologies and propose the virus combination as an advanced strategy for developing a new animal model of PD.
ABSTRACT
Bestrophin-1 (Best1) is a GABA- and glutamate-permeable, Ca 2+ -activated Cl - channel, which is mainly expressed in astrocytes and localized at the microdomain or perisynaptic junction of the tripartite synapse. Distribution of Best1 is dramatically changed in pathological conditions such as Alzheimer’s disease. However, it is still unknown whether Best1 is located at the glutamatergic or GABAergic tripartite synapses. Here, we utilized the Lattice structured illumination microscopy (Lattice SIM) to visualize Best1 expression at the perisynaptic junctions of the tripartite synapses in CA1 of mouse hippocampus. We performed co-labeling with antibodies against 1) Best1 and vesicular glutamate transporter-2 (vGLUT2) or 2) Best1 and vesicular GABA transporter (vGAT) to measure the proximity of Best1-containing perisynapse to glutamatergic or GABAergic presynapse, respectively. In addition, we examined two transgenic mouse lines of 1) APP/PS1 mouse showing high astrocytic MAOB activity and cytosolic GABA and 2) MAOB-KO mouse showing low astrocytic GABA. Lattice SIM images were further processed by Imaris, which allowed 3Drendering and spot identification. We found that astrocytic Best1 was distributed closer to the glutamatergic synapses than GABAergic synapses in the wild-type mice. In APP/PS1 mice, Best1 distribution was significantly changed by moving away from the glutamatergic synapses while moving closer to the GABAergic synapses. On the contrary, in MAOB-KO mice, the Best1 distribution was dramatically changed by moving closer to the glutamatergic synapses and moving far away from the GABAergic synapses. Our findings propose that the proximity of Best1-containing perisynapses to presynapses dynamically changes according to the level of astrocytic cytosolic GABA.
ABSTRACT
In the era of COVID-19 outbreak, various efforts are undertaken to develop a quick, easy, inexpensive, and accurate way for diagnosis. Although many commercial diagnostic kits are available, detailed scientific evaluation is lacking, making the public vulnerable to fear of false-positive results.Moreover, current tissue sampling method from respiratory tract requires personal contact of medical staff with a potential asymptomatic SARSCOV-2 carrier and calls for safe and less invasive sampling method. Here, we have developed a convenient detection protocol for SARS-COV-2 based on a non-invasive saliva self-sampling method by extending our previous studies on development of a laboratory-safe and low-cost detection protocol based on qRT-PCR. We tested and compared various self-sampling methods of self-pharyngeal swab and self-saliva sampling from non-carrier volunteers. We found that the self-saliva sampling procedure gave expected negative results from all of the non-carrier volunteers within 2 hours, indicating cost-effectiveness, speed and reliability of the saliva-based method. For an automated assessment of the sampling quality and degree of positivity for COVID-19, we developed scalable formulae based on a logistic classification model using both cycle threshold and melting temperature from the qRT-PCR results. Our newly developed protocol will allow easy sampling and spatial-separation between patient and experimenter for guaranteed safety. Furthermore, our newly established risk assessment formula can be applied to a large-scale diagnosis in health institutions and agencies around the world.
ABSTRACT
Central neurocytoma (CN) has been known as a benign neuronal tumor. In rare cases, CN undergoes malignant transformation to glioblastomas (GBM). Here we examined its cellular origin by characterizing differentiation potential and gene expression of CN-spheroids. First, we demonstrate that both CN tissue and cultured primary cells recapitulate the hierarchal cellular composition of subventricular zone (SVZ), which is comprised of neural stem cells (NSCs), transit amplifying progenitors (TAPs), and neuroblasts. We then derived spheroids from CN which displayed EGFR+/ MASH+ TAP and BLBP+ radial glial cell (RGC) characteristic, and mitotic neurogenesis and gliogenesis by single spheroids were observed with cycling multipotential cells. CN-spheroids expressed increased levels of pluripotency and tumor stem cell genes such as KLF4 and TPD5L1, when compared to their differentiated cells and human NSCs. Importantly, Gene Set Enrichment Analysis showed that gene sets of GBM-Spheroids, EGFR Signaling, and Packaging of Telomere Ends are enriched in CN-spheroids in comparison with their differentiated cells. We speculate that CN tumor stem cells have TAP and RGC characteristics, and upregulation of EGFR signaling as well as downregulation of eph-ephrin signaling have critical roles in tumorigenesis of CN. And their ephemeral nature of TAPs destined to neuroblasts, might reflect benign nature of CN.
ABSTRACT
The cause of Parkinson’s disease has been traditionally believed to be the dopaminergic neuronal death in the substantia nigra pars compacta (SNpc).This traditional view has been recently challenged by the proposal that reactive astrocytes serve as key players in the pathology of Parkinson’s disease through excessive GABA release. This aberrant astrocytic GABA is synthesized by the enzymatic action of monoamine oxidase B (MAOB), whose pharmacological inhibition and gene-silencing are reported to significantly alleviate parkinsonian motor symptoms in animal models of Parkinson’s disease. However, whether genetic ablation and over-expression of MAOB can bidirectionally regulate parkinsonian motor symptoms has not been tested. Here we demonstrate that genetic ablation of MAOB blocks the MPTP-induced augmentation of astrocytic GABA-mediated tonic inhibition of neighboring dopaminergic neurons as well as parkinsonian motor symptoms, indicating the necessity of MAOB for parkinsonian motor symptoms. Furthermore, we demonstrate that GFAP-MAOB transgenic mice, in which MAOB is over-expressed under the GFAP promoter for astrocyte-specific over-expression, display exacerbated MPTP-induced tonic inhibition and parkinsonian motor symptoms compared to wild-type mice, indicating the importance of astrocytic MAOB for parkinsonian motor symptoms. Our study provides genetic pieces of evidence for the causal link between the pathological role of astrocytic MAOB-dependent tonic GABA synthesis and parkinsonian motor symptoms.
ABSTRACT
Parkinson’s disease (PD) is the most prevalent neurodegenerative motor disorder. While PD has been attributed to dopaminergic neuronal death in substantia nigra pars compacta (SNpc), accumulating lines of evidence have suggested that reactive astrogliosis is critically involved in PD pathology. These pathological changes are associated with α-synuclein aggregation, which is more prone to be induced by an A53T mutation. Therefore, the overexpression of A53T-mutated α-synuclein (A53T-α-syn) has been utilized as a popular animal model of PD. However, this animal model only shows marginal-to-moderate extents of reactive astrogliosis and astrocytic α-synuclein accumulation, while these phenomena are prominent in human PD brains. Here we show that Adeno-GFAP-GFP virus injection into SNpc causes severe reactive astrogliosis and exacerbates the A53Tα-syn-mediated PD pathology. In particular, we demonstrate that AAV-CMV-A53T-α-syn injection, when combined with Adeno-GFAP-GFP, causes more significant loss of dopaminergic neuronal tyrosine hydroxylase level and gain of astrocytic GFAP and GABA levels. Moreover, the combination of AAV-CMV-A53T-α-syn and Adeno-GFAP-GFP causes an extensive astrocytic α-syn expression, just as in human PD brains. These results are in marked contrast to previous reports that AAV-CMV-A53T-α-syn alone causes α-syn expression mostly in neurons but rarely in astrocytes. Furthermore, the combination causes a severe PD-like motor dysfunction as assessed by rotarod and cylinder tests within three weeks from the virus injection, whereas Adeno-GFAP-GFP alone or AAV-CMV-A53T-α-syn alone does not. Our findings implicate that inducing reactive astrogliosis exacerbates PD-like pathologies and propose the virus combination as an advanced strategy for developing a new animal model of PD.
ABSTRACT
Bestrophin-1 (Best1) is a GABA- and glutamate-permeable, Ca 2+ -activated Cl - channel, which is mainly expressed in astrocytes and localized at the microdomain or perisynaptic junction of the tripartite synapse. Distribution of Best1 is dramatically changed in pathological conditions such as Alzheimer’s disease. However, it is still unknown whether Best1 is located at the glutamatergic or GABAergic tripartite synapses. Here, we utilized the Lattice structured illumination microscopy (Lattice SIM) to visualize Best1 expression at the perisynaptic junctions of the tripartite synapses in CA1 of mouse hippocampus. We performed co-labeling with antibodies against 1) Best1 and vesicular glutamate transporter-2 (vGLUT2) or 2) Best1 and vesicular GABA transporter (vGAT) to measure the proximity of Best1-containing perisynapse to glutamatergic or GABAergic presynapse, respectively. In addition, we examined two transgenic mouse lines of 1) APP/PS1 mouse showing high astrocytic MAOB activity and cytosolic GABA and 2) MAOB-KO mouse showing low astrocytic GABA. Lattice SIM images were further processed by Imaris, which allowed 3Drendering and spot identification. We found that astrocytic Best1 was distributed closer to the glutamatergic synapses than GABAergic synapses in the wild-type mice. In APP/PS1 mice, Best1 distribution was significantly changed by moving away from the glutamatergic synapses while moving closer to the GABAergic synapses. On the contrary, in MAOB-KO mice, the Best1 distribution was dramatically changed by moving closer to the glutamatergic synapses and moving far away from the GABAergic synapses. Our findings propose that the proximity of Best1-containing perisynapses to presynapses dynamically changes according to the level of astrocytic cytosolic GABA.
ABSTRACT
The TMEM43 has been studied in human diseases such as arrhythmogenic right ventricular cardiomyopathy type 5 (ARVC5) and auditory neuropathy spectrum disorder (ANSD). In the heart, the p.(Ser358Leu) mutation has been shown to alter intercalated disc protein function and disturb beating rhythms. In the cochlea, the p.(Arg372Ter) mutation has been shown to disrupt connexin-linked function in glia-like supporting cells (GLSs), which maintain inner ear homeostasis for hearing. The TMEM43-p.(Arg372Ter) mutant knock-in mice displayed a significantly reduced passive conductance current in the cochlear GLSs, raising a possibility that TMEM43 is essential for mediating the passive conductance current in GLSs. In the brain, the two-pore-domain potassium (K2P) channels are generally known as the “leak channels” to mediate background conductance current, raising another possibility that K2P channels might contribute to the passive conductance current in GLSs. However, the possible association between TMEM43 and K2P channels has not been investigated yet. In this study, we examined whether TMEM43 physically interacts with one of the K2P channels in the cochlea, KCNK3 (TASK-1). Utilizing co-immunoprecipitation (IP) assay and Duolink proximity ligation assay (PLA), we revealed that TMEM43 and TASK-1 proteins could directly interact. Genetic modifications further delineated that the intracellular loop domain of TMEM43 is responsible for TASK-1 binding. In the end, gene-silencing of Task-1 resulted in significantly reduced passive conductance current in GLSs. Together, our findings demonstrate that TMEM43 and TASK-1 form a protein-protein interaction in the cochlea and provide the possibility that TASK-1 is a potential contributor to the passive conductance current in GLSs.
ABSTRACT
Sleep is indispensable for living animals to live and maintain a normal life. Due to the growing number of people suffering from sleep disorders such as insomnia, there have been increasing interests in environmentally friendly therapeutic approaches for sleep disorders to avoid any side effects of pharmacological treatment using synthetic hypnotics. It has been widely accepted that the various beneficial effects of forest, such as relieving stress and anxiety and enhancing immune system function, are caused by plant-derived products, also known as phytoncide. Recently, it has been reported that the sleep-enhancing effects of phytoncide are derived from pine trees such as (-)-α-pinene and 3-carene. These are the major constituents of pine tree that potentiate the inhibitory synaptic responses by acting as a positive modulator for GABAA-BZD receptor. In this review, we discuss the effects of phytoncide on sleep and review the latest approaches of sleep-related behavioral assay, electrophysiological recording, and molecular modeling technique.
ABSTRACT
The severe acute respiratory coronavirus 2 (SARS-CoV-2), which emerged in December 2019 in Wuhan, China, has spread rapidly to over a dozen countries. Especially, the spike of case numbers in South Korea sparks pandemic worries. This virus is reported to spread mainly through personto- person contact via respiratory droplets generated by coughing and sneezing, or possibly through surface contaminated by people coughing or sneezing on them. More critically, there have been reports about the possibility of this virus to transmit even before a virus-carrying person to show symptoms. Therefore, a low-cost, easy-access protocol for early detection of this virus is desperately needed. Here, we have established a real-time reverse-transcription PCR (rtPCR)-based assay protocol composed of easy specimen self-collection from a subject via pharyngeal swab, Trizolbased RNA purification, and SYBR Green-based rtPCR. This protocol shows an accuracy and sensitivity limit of 1-10 virus particles as we tested with a known lentivirus. The cost for each sample is estimated to be less than 15 US dollars. Overall time it takes for an entire protocol is estimated to be less than 4 hours. We propose a cost-effective, quick-and-easy method for early detection of SARS-CoV-2 at any conventional Biosafety Level II laboratories that are equipped with a rtPCR machine. Our newly developed protocol should be helpful for a first-hand screening of the asymptomatic virus-carriers for further prevention of transmission and early intervention and treatment for the rapidly propagating virus.
ABSTRACT
The neuronal activity-dependent change in the manner in which light is absorbed or scattered in brain tissue is called the intrinsic optical signal (IOS), and provides label-free, minimally invasive, and high spatial (~100 µm) resolution imaging for visualizing neuronal activity patterns. IOS imaging in isolated brain slices measured at an infrared wavelength (>700 nm) has recently been attributed to the changes in light scattering and transmittance due to aquaporin-4 (AQP4)-dependent astrocytic swelling. The complexity of functional interactions between neurons and astrocytes, however, has prevented the elucidation of the series of molecular mechanisms leading to the generation of IOS. Here, we pharmacologically dissected the IOS in the acutely prepared brain slices of the stratum radiatum of the hippocampus, induced by 1 s/20 Hz electrical stimulation of Schaffer-collateral pathway with simultaneous measurement of the activity of the neuronal population by field potential recordings. We found that 55% of IOSs peak upon stimulation and originate from postsynaptic AMPA and NMDA receptors. The remaining originated from presynaptic action potentials and vesicle fusion. Mechanistically, the elevated extracellular glutamate and K⁺ during synaptic transmission were taken up by astrocytes via a glutamate transporter and quinine-sensitive K2P channel, followed by an influx of water via AQP-4. We also found that the decay of IOS is mediated by the DCPIB- and NPPB-sensitive anion channels in astrocytes. Altogether, our results demonstrate that the functional coupling between synaptic activity and astrocytic transient volume change during excitatory synaptic transmission is the major source of IOS.
Subject(s)
Action Potentials , alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid , Amino Acid Transport System X-AG , Astrocytes , Brain , Electric Stimulation , Glutamic Acid , Hippocampus , Jupiter , Neurons , Receptors, N-Methyl-D-Aspartate , Synaptic Transmission , WaterABSTRACT
In the brain, a reduction in extracellular osmolality causes water-influx and swelling, which subsequently triggers Cl⁻- and osmolytes-efflux via volume-regulated anion channel (VRAC). Although LRRC8 family has been recently proposed as the pore-forming VRAC which is activated by low cytoplasmic ionic strength but not by swelling, the molecular identity of the pore-forming swelling-dependent VRAC (VRAC(swell)) remains unclear. Here we identify and characterize Tweety-homologs (TTYH1, TTYH2, TTYH3) as the major VRAC(swell) in astrocytes. Gene-silencing of all Ttyh1/2/3 eliminated hypo-osmotic-solution-induced Cl⁻ conductance (I(Cl,swell)) in cultured and hippocampal astrocytes. When heterologously expressed in HEK293T or CHO-K1 cells, each TTYH isoform showed a significant I(Cl,swell) with similar aquaporin-4 dependency, pharmacological properties and glutamate permeability as I(Cl,swell) observed in native astrocytes. Mutagenesis-based structure-activity analysis revealed that positively charged arginine residue at 165 in TTYH1 and 164 in TTYH2 is critical for the formation of the channel-pore. Our results demonstrate that TTYH family confers the bona fide VRAC(swell) in the brain.