NFAT5-dependent expression of AQP4 in astrocytes

Amygdala-specific changes in Cacna1c, Nfat5, and Bdnf expression are associated with stress responsivity in mice: A possible mechanism for psychiatric disorders

The CACNA1C gene encodes the alpha-1c subunit of the Cav1.2 calcium channel, a regulator of neuronal calcium influx involved in neurotransmitter release and synaptic plasticity. Genetic data show a role for CACNA1C in depressive symptoms underlying different psychiatric diagnoses. However, the mechanisms involved still require further exploration. This study aimed to investigate sex and region-specific changes in the Cacna1c gene and behavioral outcomes in mice exposed to chronic stress. Moreover, we evaluated the Nuclear factor of activated T-cells 5 (Nfat5) and the Brain-derived neurotrophic factor (Bdnf) as potential upstream and downstream Cacna1c targets and their correlation in stressed mice and humans with depression. Male and female Swiss mice were exposed to chronic unpredictable stress (CUS) for 21 days. Animal-integrated emotionality was assessed using the sucrose splash test, the tail suspension, the open-field test, and the elevated-plus-maze. Gene expression analysis was performed in the amygdala, prefrontal cortex, and hippocampus. Human data for in silico analysis was obtained from the Gene Expression Omnibus. CUS-induced impairment in integrated emotional regulation was observed in males. Gene expression analysis showed decreased levels of Cacna1c and Nfat5 and increased levels of Bdnf transcripts in the amygdala of stressed male mice. In contrast, there were no major changes in behavioral responses or gene expression in female mice after stress. The expression of the three genes was significantly correlated in the amygdala of mice and humans. The strong and positive correlation between Canac1c and Nfat5 suggests a potential role for this transcription factor in Canac1c expression. These changes could impact amygdala reactivity and emotional responses, making them a potential target for psychiatric intervention.

Inhibition of NFAT5-Dependent Astrocyte Swelling Alleviates Neuropathic Pain

Astrocyte swelling is implicated in various neurological disorders. However, whether astrocyte swelling contributes to neuropathic pain remains elusive. This study elucidates the pivotal role of the nuclear factor of activated T-cells 5 (NFAT5) emerges as a master regulator of astrocyte swelling in the spinal dorsal horn (SDH) during neuropathic pain. Despite the ubiquitous expression of NFAT5 protein in SDH cell types, it selectively induces swelling specifically in astrocytes, not in microglia. Mechanistically, NFAT5 directly controls the expression of the water channel aquaporin-4 (AQP4), a key regulator exclusive to astrocytes. Additionally, aurora kinase B (AURKB) orchestrates NFAT5 phosphorylation, enhancing its protein stability and nuclear translocation, thereby regulating AQP4 expression. The findings establish NFAT5 as a crucial regulator for neuropathic pain through the modulation of astrocyte swelling. The AURKB-NFAT5-AQP4 pathway in astrocytes emerges as a potential therapeutic target to combat neuropathic pain.

The Glymphatic System May Play a Vital Role in the Pathogenesis of Hepatic Encephalopathy: A Narrative Review

Hepatic encephalopathy (HE) is a neurological complication of liver disease resulting in cognitive, psychiatric, and motor symptoms. Although hyperammonemia is a key factor in the pathogenesis of HE, several other factors have recently been discovered. Among these, the impairment of a highly organized perivascular network known as the glymphatic pathway seems to be involved in the progression of some neurological complications due to the accumulation of misfolded proteins and waste substances in the brain interstitial fluids (ISF). The glymphatic system plays an important role in the clearance of brain metabolic derivatives and prevents aggregation of neurotoxic agents in the brain ISF. Impairment of it will result in aggravated accumulation of neurotoxic agents in the brain ISF. This could also be the case in patients with liver failure complicated by HE. Indeed, accumulation of some metabolic by-products and agents such as ammonia, glutamine, glutamate, and aromatic amino acids has been reported in the human brain ISF using microdialysis technique is attributed to worsening of HE and correlates with brain edema. Furthermore, it has been reported that the glymphatic system is impaired in the olfactory bulb, prefrontal cortex, and hippocampus in an experimental model of HE. In this review, we discuss different factors that may affect the function of the glymphatic pathways and how these changes may be involved in HE.

LncRNA OIP5-AS1 Mitigates Bupivacaine-Induced Neurotoxicity in Dorsal Root Ganglion Neurons Through Regulating NFAT5 Expression via Sponging miR-34b

Bupivacaine (BUP), which is widely used in anesthesia, can cause neurotoxicity and neurological abnormalities. This work intended to study the function of long non-coding RNA (lncRNA) OIP5 antisense RNA 1 (OIP5-AS1) in BUP-triggered neurotoxicity. OIP5-AS1, microRNA (miR)-34b, and nuclear factor of activated T cells 5 (NFAT5) levels were examined via real-time quantitative PCR (RT-qPCR). Cell proliferation, caspase-3 activity, and apoptosis were assessed via 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide (MTT), caspase-3 activity, and terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assays. The regulatory relationships between miR-34b and OIP5-AS1 or NFAT5 were validated via RNA binding protein immunoprecipitation (RIP) and dual-luciferase reporter assays. Our data demonstrated that OIP5-AS1 and NFAT5 levels were downregulated and miR-34b was upregulated upon exposure to BUP. Functional assays implied that the OIP5-AS1 deficiency impeded cell proliferation and enhanced the apoptosis of DRG neurons, while OIP5-AS1 addition reversed these changes. Moreover, OIP5-AS1 could bind to miR-34b and OIP5-AS1 regulated BUP-induced neurotoxicity via miR-34b. Besides, miR-34b could directly interact with NFAT5. Augmentation of miR-34b impeded cell proliferation and expedited the apoptosis and caspase-3 activity, while NFAT5 addition neutralized these impacts. Finally, it was verified that OIP5-AS1 could upregulate NFAT5 through sponging miR-34b. In sum, our results disclosed that OIP5-AS1 ameliorated BUP-caused neurotoxicity via regulating the miR-34b/NFAT5 axis, suggesting that OIP5-AS1 might be a promising therapeutic target for the treatment of BUP-induced neurotoxicity.

Regulation of aquaporin-4 expression in the central nervous system investigated using M23-AQP4 null mouse

In astrocytes, unknown mechanisms regulate the expression of M1 and M23 isoforms of water channel aquaporin-4 (M1-AQP4 and M23-AQP4). The ratio between these two isoforms controls the AQP4 assembly state in the plasma membrane known as orthogonal arrays of particles (OAPs). To give new insights into these mechanisms, here, we explore the regulation of AQP4 expression in the spinal cord of a CRISPR/Cas9 M23-null mouse model (M23-null). In the M23-null spinal cord OAP assembly, the perivascular localization of AQP4 and M1-AQP4 protein were drastically reduced. In heterozygous, M1-AQP4 was proportionally reduced with M23-AQP4, maintaining the isoform ratio unaffected. We hypothesize a role of the M23-AQP4 in the regulation of M1-AQP4 expression. M1-AQP4 transcription, splicing and M1-AQP4 protein degradation were found to be unaffected in M23-null spinal cord and in M23-null astrocyte primary culture. The translational control was investigated by mRNA-protein pull down and quantitative mass spectrometry, to isolate and quantify AQP4 mRNA binding proteins (AQP4-RBPs). Compared to WT, in M23-null spinal cord, the interaction between AQP4 mRNA and polypyrimidine tract binding protein 1, a positive regulator of AQP4 translation, was higher, while interaction with the RNA helicase DDX17 was lower. In astrocyte primary cultures, DDX17 knockdown upregulated AQP4 protein expression and increased cell swelling, leaving AQP4 mRNA levels unchanged. Here, we identify AQP4-RBPs and provide evidence that in mouse spinal cord M23-AQP4 deletion changes the interaction between AQP4 mRNA and some RBPs involved in AQP4 translation. We describe for the first time the RNA helicase DDX17 as a regulator of AQP4 expression in astrocytes.

Long Noncoding RNA X-Inactive-Specific Transcript Promotes the Secretion of Inflammatory Cytokines in LPS Stimulated Astrocyte Cell Via Sponging miR-29c-3p and Regulating Nuclear Factor of Activated T cell 5 Expression

BACKGROUND

Astrocyte activation promotes glutamate accumulation and secretion of inflammatory factors, mainly responsible for epilepsy. Long noncoding RNA (lncRNA) X-inactive-specific transcript (XIST) regulates inflammation; however, the biological role and regulatory mechanism of XIST during astrocyte activation remain unclear.

METHODS

In the present study, rat epilepsy model and lipopolysaccharide (LPS)-treated CTX-TNA2 were established. XIST and miR-29c-3p expression were evaluated using quantitative real-time polymerase chain reaction. Nuclear factor of activated T cells 5 (NFAT5) was measured using western blot analysis. Interleukin (IL)-1β, IL-6, tumor necrosis factor-α, and L-glutamate levels in the culture supernatants were assessed using enzyme-linked immunosorbent assay. The binding between XIST and miR-29c-3p and between miR-29c-3p and the 3'-UTR of NFAT5 was analyzed using dual-luciferase reporter, RNA-binding protein immunoprecipitation (RIP), and Biotin pull-down assay. The proliferation and apoptosis were evaluated using CCK8 and flow cytometry, respectively.

RESULTS

XIST expression and NFAT5 protein level was increased, whereas miR-29c-3p expression was decreased in the epilepsy rat model and LPS-treated CTX-TNA2 cells. Silenced XIST expression, miR-29c-3p overexpression, or silenced NFAT5 expression inhibited the secretion of IL-1β, IL-6, and TNF-α and promoted glutamate transport in LPS-treated CTX-TNA2 cells. miR-29c-3p was the potential miRNA sponged by XIST. NFAT5 acted as a direct binding target of miR-29c-3p. Silenced miR-29c-3p expression or NFAT5 overexpression reversed the effect of silenced XIST expression on LPS-treated CTX-TNA2.XIST and miR-29c-3p treatment does not affect NFAT5 mRNA expression, but affects NFAT5 protein level. Furthermore, underexpressed XIST or overexpressed miR-29c-3p in LPS-stimulated CTX-TNA2 can attenuate neuronal apoptosis induced by LPS-stimulated CTX-TNA2.

CONCLUSION

LncRNA XIST promotes the secretion of inflammatory cytokines in LPS- treated CTX-TNA2 via sponging miR-29c-3p and regulating NFAT5 expression.

Exosomes Derived from MicroRNA-146a-5p-Enriched Bone Marrow Mesenchymal Stem Cells Alleviate Intracerebral Hemorrhage by Inhibiting Neuronal Apoptosis and Microglial M1 Polarization

Introduction

Intracerebral hemorrhage (ICH) is a devastating type of stroke with high mortality, and the effective therapies for ICH remain to be explored. Exosomes (Exos) have been found to play important roles in cell communication by transferring molecules, including microRNAs (miRNAs/miRs). MiRNAs are critical regulators of genes involved in many various biological processes and have been demonstrated to aggravate or alleviate brain damages induced by ICH. The aim of the present study was to investigate the effect of Exos derived from miR-146a-5p-enriched bone marrow mesenchymal stem cells (BMSCs-miR-146a-5p-Exos) on experimental ICH.

Methods

ICH was induced in adult male Sprague-Dawley rats by an intrastriatal injection of collagenase type IV. At 24 h after surgery, Exos were administrated. For detecting apoptotic cells, TUNEL staining was performed using an in situ Cell Death Detection Kit. Fluoro-Jade B staining was performed to detect degenerating neurons. Immunofluorescence assay was performed to detect the expression of myeloperoxidase (MPO) and OX-42. The binding of miR-146a-5p and its target genes was confirmed by luciferase reporter assay.

Results

At 24 h after surgery, BMSCs-miR-146a-5p-Exos administration significantly improved neurological function, reduced apoptotic and degenerative neurons, and inhibited inflammatory response. Furthermore, miR-146a-5p-enriched Exos obviously inhibited the M1 polarization of microglia after ICH in rats, accompanied by the reduced expression of pro-inflammatory mediators releasing by M1 microglia including inducible nitric oxide synthase (iNOS), cyclooxygenase-2 (COX-2) and monocyte chemoattractant protein-1 (MCP-1). Finally, we observed that miR-146a-5p directly targeted interleukin-1 receptor-associated kinase1 (IRAK1) and nuclear factor of activated T cells 5 (NFAT5), which contributed to the inflammation response and the polarization of M1 microglia/macrophages.

Conclusion

We demonstrated that miR-146a-5p-riched BMSCs-Exos could offer neuroprotection and functional improvements after ICH through reducing neuronal apoptosis, and inflammation associated with the inhibition of microglial M1 polarization by downregulating the expression of IRAK1 and NFAT5.

DDC expression is not regulated by NFAT5 (TonEBP) in dopaminergic neural cell lines

The nuclear factor of activated T-cells 5 (NFAT5), also known as tonicity-responsive enhancer-binding protein (TonEBP), is a transcription factor that regulates osmoadaptive response in multiple tissues and is highly expressed in the developing central nervous system. A former study reported that NFAT5 activation through hypertonic stress increases the expression of the dopa decarboxylase enzyme (DDC), also known as aromatic-l-amino-acid decarboxylase (AADC), in human renal proximal tubule cells, leading to an increase of dopamine synthesis. In a previous study, we identified NFAT5 as a candidate gene for cocaine dependence, a complex psychiatric disorder in which dopaminergic neurotransmission plays an important role. Therefore, to test the hypothesis that NFAT5 may also affect dopamine levels in the nervous system through the regulation of DDC expression, we examined this regulation using two neural dopaminergic cell lines, SH-SY5Y and PC12. The effect of NFAT5 on the expression of the neuronal isoform of DDC was evaluated by qRT-PCR. Upon hypertonic stress, NFAT5 was activated and accumulated into the nuclei and, subsequently, the expression of NFAT5 and its known targets sodium/myo-inositol cotransporter 1 (SMIT) and sodium chloride/taurine cotransporter (TAUT) increased, as expected. However, the expression of DDC decreased. When silencing the expression of NFAT5 with a specific shRNA we observed that the downregulation of DDC is independent from NFAT5 in both cell lines and is due to hypertonic stress. In conclusion, NFAT5 does not regulate the expression of the neuronal isoform of DDC in neural dopaminergic cell lines and, consequently, it does not modulate dopamine synthesis through DDC.

Gliomas display distinct sex-based differential methylation patterns based on molecular subtype

Background

Gliomas are the most common type of primary brain tumor and one of many cancers where males are diagnosed with greater frequency than females. However, little is known about the sex-based molecular differences in glioblastomas (GBMs) or lower grade glioma (non-GBM) subtypes. DNA methylation is an epigenetic mechanism involved in regulating gene transcription. In glioma and other cancers, hypermethylation of specific gene promoters downregulates transcription and may have a profound effect on patient outcome. The purpose of this study was to determine if sex-based methylation differences exist in different glioma subtypes.

Methods

Molecular and clinical data from glioma patients were obtained from The Cancer Genome Atlas and grouped according to tumor grade and molecular subtype (IDH1/2 mutation and 1p/19q chromosomal deletion). Sex-specific differentially methylated probes (DMPs) were identified in each subtype and further analyzed to determine if they were part of differentially methylated regions (DMRs) or associated with differentially methylated DNA transcription regulatory binding motifs.

Results

Analysis of methylation data in 4 glioma subtypes revealed unique sets of both sex-specific DMPs and DMRs in each subtype. Motif analysis based on DMP position also identified distinct sex-based sets of DNA-binding motifs that varied according to glioma subtype. Downstream targets of 2 of the GBM-specific transcription binding sites, NFAT5 and KLF6, showed differential gene expression consistent with increased methylation mediating downregulation.

Conclusion

DNA methylation differences between males and females in 4 glioma molecular subtypes suggest an important, sex-specific role for DNA methylation in epigenetic regulation of gliomagenesis.

Hypertonic Stress Causes Cytoplasmic Translocation of Neuronal, but Not Astrocytic, FUS due to Impaired Transportin Function

The primarily nuclear RNA-binding protein FUS (fused in sarcoma) forms pathological cytoplasmic inclusions in a subset of early-onset amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD) patients. In response to cellular stress, FUS is recruited to cytoplasmic stress granules, which are hypothesized to act as precursors of pathological inclusions. We monitored the stress-induced nucleocytoplasmic shuttling of endogenous FUS in an ex vivo mouse CNS model and human neural networks. We found that hyperosmolar, but not oxidative, stress induced robust cytoplasmic translocation of neuronal FUS, with transient nuclear clearance and loss of function. Surprisingly, this reaction is independent of stress granule formation and the molecular pathways activated by hyperosmolarity. Instead, it represents a mechanism mediated by cytoplasmic redistribution of Transportin 1/2 and is potentiated by transcriptional inhibition. Importantly, astrocytes, which remain unaffected in ALS/FTD-FUS, are spared from this stress reaction that may signify the initial event in the development of FUS pathology.

Potential Role of Gene Regulator NFAT5 in the Pathogenesis of Diabetes Mellitus

Nuclear factor of activated T cells 5 (NFAT5), a Rel/nuclear factor- (NF-) κB family member, is the only known gene regulator of the mammalian adaptive response to osmotic stress. Exposure to elevated glucose increases the expression and nuclear translocation of NFAT5, as well as NFAT5-driven transcriptional activity in vivo and in vitro. Increased expression of NFAT5 is closely correlated with the progression of diabetes in patients. The distinct structure of NFAT5 governs its physiological and pathogenic roles, indicating its opposing functions. The ability of NFAT5 to maintain cell homeostasis and proliferation is impaired in patients with diabetes. NFAT5 promotes the formation of aldose reductase, pathogenesis of diabetic vascular complications, and insulin resistance. Additionally, NFAT5 activates inflammation at a very early stage of diabetes and induces persistent inflammation. Recent studies revealed that NFAT5 is an effective therapeutic target for diabetes. Here, we describe the current knowledge about NFAT5 and its relationship with diabetes, focusing on its diverse regulatory functions, and highlight the importance of this protein as a potential therapeutic target in patients with diabetes.

Uncoupled Endothelial Nitric Oxide Synthase Enhances p-Tau in Chronic Traumatic Encephalopathy Mouse Model

AIMS

Chronic traumatic encephalopathy (CTE) is a progressive neurodegenerative disease thought to be caused by repetitive traumatic brain injury (TBI) and subconcussive injuries. While hyperphosphorylation of tau (p-Tau), which is attributed to astrocytic tangles (ATs) and neurofibrillary tangles, is known to be involved in CTE, there are limited neuropathological or molecular data. By utilizing repetitive mild TBI (rmTBI) mouse models, our aim was to examine the pathological changes of CTE-associated structures, specifically the ATs.

RESULTS

Our rmTBI mouse models showed symptoms of depressive behavior and memory deficit, alongside an increased p-Tau expression in their neurons and astrocytes in both the hippocampus and cortex. rmTBI induced oxidative stress in endothelial cells and nitric oxide (NO) generation in astrocytes, which were mediated by hypoxia and increased hypoxia-inducible factor 1-α (HIF1α). There was also correlated decreased regional cerebral tissue perfusion units, mild activation of astrocytes and NFκB phosphorylation, increased expression of inducible nitric oxide synthase (iNOS), increased endothelial nitric oxide synthase (eNOS) uncoupling with decreased tetrahydrobiopterin, and increased expression of nitrotyrosine, NADPH oxidase 2 (Nox2)/nuclear factor (erythroid-derived 2) factor 2 (Nrf2) signaling proteins. Combined, these effects induced peroxynitrite formation and hyperphosphorylation of tau in the hippocampus and cortex toward the formation of ATs.

INNOVATION

Our model features molecular pathogenesis events of CTE with clinically relevant latency periods. In particular, this is the first demonstration of an increased astrocytic iNOS expression in an in vivo model.

CONCLUSION

We propose a novel mechanism of uncoupled eNOS and NO contribution to Tau phosphorylation and AT formation in rmTBI brain, toward an increased molecular understanding of the pathophysiology of human CTE.

Sevoflurane enhanced the clearance of Aβ1-40 in hippocampus under surgery via up-regulating AQP-4 expression in astrocyte

The neurotoxicity of anesthetics on developing brain has been a focused issue for years. However, controversy exists between human and animal studies and surgery may be a potential reason for this. The discovery of glymphatic system, a pathway eliminating soluble substance from central nervous system (CNS), together with recent evidence that surgery-induced Aβ increase contributes to cognition dysfunction made us rethink about the influence of anesthetics on cognitive function. The function of glymphatic system was proved to be enhanced by sleep and sedation, so we assumed that under clinical situation Aβ1-40 whose accumulation played important role in cognitive dysfunction was increased by surgery and eliminated from CNS by glymphatic system. The function of glymphatic system is facilitated by aquaporin-4 (AQP-4), a water channel expressed in highly polarized manor in astrocytic endfeet, whose transcription is regulated by nuclear factor of activated T cells 5 (NFAT5). Our results suggest that under brief operation and sevoflurane exposure, surgery may be the main cause of Aβ increase and sevoflurane increase the elimination of Aβ by up-regulating AQP-4 which is the key component in glymphatic system.

NFAT5 Has a Job in the Brain

Nuclear factor of activated T cells 5 (NFAT5) has recently been classified as a new member of the Rel family. In addition, there are 5 more well-defined members (NF-κB and NFAT1-4) in the Rel family, which participate in regulating the expression of immune and inflammatory response-related genes. NFAT5 was initially identified in renal medullary cells where it regulated the expression of osmoprotective-related genes during the osmotic response. Many studies have demonstrated that NFAT5 is highly expressed in the nuclei of neurons in fetal and adult brains. Additionally, its expression is approximately 10-fold higher in fetal brains. With the development of detection technologies (laser scanning confocal microscopy, transgene technology, etc.), recent studies suggest that NFAT5 is also expressed in glial cells and plays a more diverse functional role. This article aims to summarize the current knowledge regarding the expression of NFAT5, its regulation of activation, and varied biological functions in the brain.

GRHL2 Is Required for Collecting Duct Epithelial Barrier Function and Renal Osmoregulation

Collecting ducts make up the distal-most tubular segments of the kidney, extending from the cortex, where they connect to the nephron proper, into the medulla, where they release urine into the renal pelvis. During water deprivation, body water preservation is ensured by the selective transepithelial reabsorption of water into the hypertonic medullary interstitium mediated by collecting ducts. The collecting duct epithelium forms tight junctions composed of barrier-enforcing claudins and exhibits a higher transepithelial resistance than other segments of the renal tubule exhibit. However, the functional relevance of this strong collecting duct epithelial barrier is unresolved. Here, we report that collecting duct-specific deletion of an epithelial transcription factor, grainyhead-like 2 (GRHL2), in mice led to reduced expression of tight junction-associated barrier components, reduced collecting duct transepithelial resistance, and defective renal medullary accumulation of sodium and other osmolytes. In vitro, Grhl2-deficient collecting duct cells displayed increased paracellular flux of sodium, chloride, and urea. Consistent with these effects, Grhl2-deficient mice had diabetes insipidus, produced dilute urine, and failed to adequately concentrate their urine after water restriction, resulting in susceptibility to prerenal azotemia. These data indicate a direct functional link between collecting duct epithelial barrier characteristics, which appear to prevent leakage of interstitial osmolytes into urine, and body water homeostasis.

Alpha-1 antichymotrypsin is involved in astrocyte injury in concert with arginine-vasopressin during the development of acute hepatic encephalopathy

Background and aims

We developed a bio-artificial liver (BAL) using a radial-flow bioreactor and rescued mini-pig models with lethal acute liver failure (ALF). The point of the rescue is the recovery from hepatic encephalopathy (HE). HE on ALF has sometimes resulted in brain death following brain edema with astrocyte swelling. Several factors, including ammonia and glutamine, have been reported to induce astrocyte swelling and injury. However, many clinicians believe that there are any other factors involved in the development of HE. Therefore, the aim of this study was to identify novel HE-inducible factors, particularly those inducing astrocyte dysfunction.

Methods

Mini-pig plasma samples were collected at three time points: before the administration of toxins (α-amanitin and LPS), when HE occurred after the administration of toxins, and after treatment with extracorporeal circulation (EC) by the BAL. To identify the causative factors of HE, each plasma sample was subjected to a comparative proteome analysis with two-dimensional gel electrophoresis and mass spectrometry. To assess the direct effects of candidate factors on the astrocyte function and injury, in vitro experiments with human astrocytes were performed.

Results

Using a proteome analysis, we identified alpha-1 antichymotrypsin (ACT), which was increased in plasma samples from mini-pigs with HE and decreased in those after treatment with EC by BAL. In in vitro experiments with human astrocytes, ACT showed growth-inhibitory and cytotoxic effects on astrocytes. In addition, the expression of water channel protein aquaporin-4, which is induced in injured astrocytes, was increased following ACT treatment. Interestingly, these effects of ACT were additively enhanced by adding arginine-vasopressin (AVP) and were canceled by adding an AVP receptor antagonist.

Conclusions

These results suggest that ACT is involved in astrocyte injury and dysfunction in concert with AVP during the development of acute HE.

The anti-inflammatory role of extranuclear apurinic/apyrimidinic endonuclease 1/redox effector factor-1 in reactive astrocytes

Apurinic/apyrimidinic endonuclease 1 (APE1), a ubiquitous multipurpose protein, is also known as redox effector factor-1 (Ref-1). It is involved in DNA repair and redox signaling and, in turn, oxidative stress-induced neurodegeneration. Although previous studies have demonstrated that APE1/Ref-1 functions as a negative regulator of inflammatory response via several mechanisms in neuronal cells, little is known about the roles of APE1/Ref-1 in glial cells. In this study, we found that cytoplasmic APE1/Ref-1 expression was upregulated in reactive astrocytes of the kainic acid- or lipopolysaccharide (LPS)-injected hippocampus. Analysis of the inflammatory response induced by extranuclear APE1/Ref-1 (ΔNLS-Ref-1) in cultured primary astrocytes revealed that it markedly suppressed inducible nitric oxide synthase (iNOS) expression and tumor necrosis factor-α (TNF-α) secretion induced by LPS to a similar extent as did wild type APE1/Ref-1 (WT-Ref-1), supporting the concept an anti-inflammatory role of extranuclear APE1/Ref-1 in astrocytes. Additionally, overexpression of WT- and ΔNLS-Ref-1 suppressed the transcriptional activity of nuclear factor-κB (NF-κB), although it effectively enhanced activator protein 1 (AP-1) activity. The blunting effect of APE1/Ref-1 on LPS-induced NF-κB activation was not mediated by IκB kinase (IKK) activity. Instead, APE1/Ref-1 inhibited p300-mediated acetylation of p65 by suppressing intracellular reactive oxygen species (ROS) levels following LPS treatment. Taken together, our results showed that altered expression and/or subcellular distribution of APE1/Ref-1 in activated astrocytes regulated the neuroinflammatory response to excitotoxin and endotoxin insults used in model of neurodegenerative brain diseases.

Astrocytic Expression of CTMP Following an Excitotoxic Lesion in the Mouse Hippocampus

Akt (also known as protein kinase B, PKB) has been seen to play a role in astrocyte activation of neuroprotection; however, the underlying mechanism on deregulation of Akt signaling in brain injuries is not fully understood. We investigated the role of carboxy-terminal modulator protein (CTMP), an endogenous Akt inhibitor, in brain injury following kainic acid (KA)-induced neurodegeneration of mouse hippocampus. In control mice, there was a weak signal for CTMP in the hippocampus, but CTMP was markedly increased in the astrocytes 3 days after KA treatment. To further investigate the effectiveness of Akt signaling, the phosphorylation of CTMP was examined. KA treatment induced an increased p-CTMP expression in the astrocytes of hippocampus at 1 day. LPS/IFN-γ-treatment on primary astrocytes promoted the p-CTMP was followed by phosphorylation of Akt and finally upregulation of CTMP and p-CREB. Time-dependent expression of p-CTMP, p-Akt, p-CREB, and CTMP indicate that LPS/IFN-γ-induced phosphorylation of CTMP can activate Akt/CREB signaling, whereas lately emerging enhancement of CTMP can inhibit it. These results suggest that elevation of CTMP in the astrocytes may suppress Akt activity and ultimately negatively affect the outcome of astrocyte activation (astroglisiois). Early time point enhancers of phosphorylation of CTMP and/or late time inhibitors specifically targeting CTMP may be beneficial in astrocyte activation for neuroprotection within treatment in neuroinflammatory conditions.

NFAT5 protects astrocytes against oxygen-glucose-serum deprivation/restoration damage via the SIRT1/Nrf2 pathway

Nuclear factor of activated T cells (NFAT) is a multifunctional cytokine family. NFAT5 was recently reported to be involved in many neuronal functions, but its specific function remains unclear. In this study, our aim is to investigate whether NFAT5 overexpression can protect astrocytes against oxygen-glucose-serum deprivation/restoration (OGSD/R) damage. In vivo, rats were subjected to ischemia-reperfusion injury, resulting in increased water content, infarct volume, and expression of NFAT5 protein in rat spinal cord. After primary culture for spinal cord astrocytes, the in vitro OGSD/R model was established. The results of the CCK8 assay and flow cytometry showed that, in the OGSD/R group, astrocyte cell viability was downregulated, but astrocyte apoptosis increased. Caspase 3 activity increased as well. Levels of NFAT5, as detected by real-time quantitative PCR and western blot, decreased under OGSD/R, as did SIRT1. Commercial kits for activity assays were used to show that OGSD/R inhibited SIRT1 activation but accelerated SOD activation after OGSD/R. Next, pcDNA-NFAT5 or NFAT5 siRNA was transfected into astrocytes. Overexpression of NFAT5 not only promoted the survival of the astrocytes and SIRT1 activation under OGSD/R but also inhibited cell apoptosis and SOD activation. Moreover, overexpression of NFAT5 apparently diminished histone acetylation and promoted the nuclear transport of Nrf2. Our results show that NFAT5 protects spinal astrocytes in a manner that depends on activation of the SIRT1/Nrf2 pathway. These findings present a novel potential molecular mechanism for NFAT5 therapy in the context of spinal cord injury.

NFAT5 promotes proliferation and migration of lung adenocarcinoma cells in part through regulating AQP5 expression

The osmoregulated transcription factor nuclear factor of activated T-cells 5(NFAT5), has been found to play important roles in the development of many kinds of human cancers, including breast cancer, colon carcinoma, renal cell carcinoma and melanoma. The aim of the present study was to determine whether NFAT5 is involved in the proliferation and migration of lung adenocarcinoma cells. We found that NFAT5 was upregulated in lung adenocarcinoma cells and knockdown of NFAT5 decreased proliferation and migration of the cells, accompanied by a significant reduction in the expression of AQP5. AQP5 was upregulated in lung adenocarcinoma cells and knockdown of AQP5 also inhibited proliferation and migration of the cells as knockdown of NFAT5 did. Moreover, overexpression of NFAT5 promoted proliferation and migration of lung adenocarcinoma cells, accompanied by a significant increase in the expression of AQP5. These results indicate that NFAT5 plays important roles in proliferation and migration of human lung adenocarcinoma cells through regulating AQP5 expression, providing a new therapeutic option for lung adenocarcinoma therapy.

Growth Differentiation Factor 15 Expression in Astrocytes After Excitotoxic Lesion in the Mouse Hippocampus

Growth differentiation factor 15 (GDF15) is, a member of the transforming growth factor β (TGF-β) superfamily of proteins. Although GDF15 is well established as a potent neurotrophic factor for neurons, little is known about its role in glial cells under neuropathological conditions. We monitored GDF15 expression in astrocyte activation after a kainic acid (KA)-induced neurodegeneration in the ICR mice hippocampus. In control, GDF15 immunoreactivity (IR) was evident in the neuronal layer of the hippocampus; however, GDF15 expression had increased in activated astrocytes throughout the hippocampal region at day 3 after the treatment with KA. LPS treatment in astrocytes dramatically increased GDF15 expression in primary astrocytes. In addition, LPS treatment resulted in the decrease of the IκB-α degradation and increase of the phosphorylation level of RelA/p65. These results indicate that GDF15 has a potential link to NF-κB activation, making GDF15 a valuable target for modulating inflammatory conditions.

PKC-α contributes to high NaCl-induced activation of NFAT5 (TonEBP/OREBP) through MAPK ERK1/2

High NaCl in the renal medullary interstitial fluid powers the concentration of urine but can damage cells. The transcription factor nuclear factor of activated T cells 5 (NFAT5) activates the expression of osmoprotective genes. We studied whether PKC-α contributes to the activation of NFAT5. PKC-α protein abundance was greater in the renal medulla than in the cortex. Knockout of PKC-α reduced NFAT5 protein abundance and expression of its target genes in the inner medulla. In human embryonic kidney (HEK)-293 cells, high NaCl increased PKC-α activity, and small interfering RNA-mediated knockdown of PKC-α attenuated high NaCl-induced NFAT5 transcriptional activity. Expression of ERK1/2 protein and phosphorylation of ERK1/2 were higher in the renal inner medulla than in the cortex. Knockout of PKC-α decreased ERK1/2 phosphorylation in the inner medulla, as did knockdown of PKC-α in HEK-293 cells. Also, knockdown of ERK2 reduced high NaCl-dependent NFAT5 transcriptional activity in HEK-293 cells. Combined knockdown of PKC-α and ERK2 had no greater effect than knockdown of either alone. Knockdown of either PKC-α or ERK2 reduced the high NaCl-induced increase of NFAT5 transactivating activity. We have previously found that the high NaCl-induced increase of phosphorylation of Ser(591) on Src homology 2 domain-containing phosphatase 1 (SHP-1-S591-P) contributes to the activation of NFAT5 in cell culture, and here we found high levels of SHP-1-S591-P in the inner medulla. PKC-α has been previously shown to increase SHP-1-S591-P, which raised the possibility that PKC-α might be acting through SHP-1. However, we did not find that knockout of PKC-α in the renal medulla or knockdown in HEK-293 cells affected SHP-1-S591-P. We conclude that PKC-α contributes to high NaCl-dependent activation of NFAT5 through ERK1/2 but not through SHP-1-S591.

PKC-α contributes to high NaCl-induced activation of NFAT5 (TonEBP/OREBP) through MAPK ERK1/2

High NaCl in the renal medullary interstitial fluid powers the concentration of urine but can damage cells. The transcription factor nuclear factor of activated T cells 5 (NFAT5) activates the expression of osmoprotective genes. We studied whether PKC-α contributes to the activation of NFAT5. PKC-α protein abundance was greater in the renal medulla than in the cortex. Knockout of PKC-α reduced NFAT5 protein abundance and expression of its target genes in the inner medulla. In human embryonic kidney (HEK)-293 cells, high NaCl increased PKC-α activity, and small interfering RNA-mediated knockdown of PKC-α attenuated high NaCl-induced NFAT5 transcriptional activity. Expression of ERK1/2 protein and phosphorylation of ERK1/2 were higher in the renal inner medulla than in the cortex. Knockout of PKC-α decreased ERK1/2 phosphorylation in the inner medulla, as did knockdown of PKC-α in HEK-293 cells. Also, knockdown of ERK2 reduced high NaCl-dependent NFAT5 transcriptional activity in HEK-293 cells. Combined knockdown of PKC-α and ERK2 had no greater effect than knockdown of either alone. Knockdown of either PKC-α or ERK2 reduced the high NaCl-induced increase of NFAT5 transactivating activity. We have previously found that the high NaCl-induced increase of phosphorylation of Ser(591) on Src homology 2 domain-containing phosphatase 1 (SHP-1-S591-P) contributes to the activation of NFAT5 in cell culture, and here we found high levels of SHP-1-S591-P in the inner medulla. PKC-α has been previously shown to increase SHP-1-S591-P, which raised the possibility that PKC-α might be acting through SHP-1. However, we did not find that knockout of PKC-α in the renal medulla or knockdown in HEK-293 cells affected SHP-1-S591-P. We conclude that PKC-α contributes to high NaCl-dependent activation of NFAT5 through ERK1/2 but not through SHP-1-S591.

RhoGDI2 expression in astrocytes after an excitotoxic lesion in the mouse hippocampus

The Rho GDP-dissociation inhibitor (RhoGDI) originally downregulates Rho family GTPases by preventing nucleotide exchange and membrane association. Although RhoGDI2 functions as a metastasis regulator, little is known in glial cells under neuropathological conditions. We monitored RhoGDI2 expression in the mouse brain after administering a kainic acid(KA)-induced excitotoxic lesion. In control, RhoGDI2 immunoreactivity (IR) was evident in the neuronal layer of the hippocampus. However, RhoGDI2 IR was increased in astrocytes markedly throughout the hippocampus at day 3 post-treatment with KA. To further investigate the molecular mechanism of RhoGDI2-induced cellular migration, primary astrocytes were transfected with the flag-tagged RhoGDI2 cDNA. Cell migration assay revealed that RhoGDI2 cDNA transfection inhibits astrocyte migration. Overexpression of RhoGDI2 leads to inhibit protein kinase B (PKB) activation and cdc42 and cAMP-responsive element-binding protein (CREB) phosphorylation. In conclusion, our results suggested for the first time that RhoGDI2 is required for PKB and CREB activation and cdc42 expression in astrocyte migration after KA-mediated excitotoxic lesion in mouse brain.

Tonicity-responsive enhancer binding protein haplodeficiency attenuates seizure severity and NF-κB-mediated neuroinflammation in kainic acid-induced seizures

Kainic acid (KA)-induced seizures followed by neuronal death are associated with neuroinflammation and blood-brain barrier (BBB) leakage. Tonicity-responsive enhancer binding protein (TonEBP) is known as a transcriptional factor activating osmoprotective genes, and in brain, it is expressed in neuronal nuclei. Thus dysregulation of TonEBP may be involved in the pathology of KA-induced seizures. Here we used TonEBP heterozygote (+/-) mice to study the roles of TonEBP. Electroencephalographic study showed that TonEBP (+/-) mice reduced seizure frequency and severity compared with wild type during KA-induced status epilepticus. Immunohistochemistry and western blotting analysis showed that KA-induced neuroinflammation and BBB leakage were dramatically reduced in TonEBP (+/-) mice. Similarly, TonEBP-specific siRNA reduced glutamate-induced death in HT22 hippocampal neuronal cells. TonEBP haplodeficiency prevented KA-induced nuclear translocation of NF-κB p65 and attenuated inflammation. Our findings identify TonEBP as a critical regulator of neuroinflammation and BBB leakage in KA-induced seizures, which suggests TonEBP as a good therapeutic target.

Morphological changes of cortical pyramidal neurons in hepatic encephalopathy

Background

Hepatic encephalopathy (HE) is a reversible neuropsychiatric syndrome associated with acute and chronic liver diseases. It includes a number of neuropsychiatric disturbances including impaired motor activity and coordination, intellectual and cognitive function.

Results

In the present study, we used a chronic rat HE model by ligation of the bile duct (BDL) for 4 weeks. These rats showed increased plasma ammonia level, bile duct hyperplasia and impaired spatial learning memory and motor coordination when tested with Rota-rod and Morris water maze tests, respectively. By immunohistochemistry, the cerebral cortex showed swelling of astrocytes and microglia activation. To gain a better understanding of the effect of HE on the brain, the dendritic arbors of layer V cortical pyramidal neurons and hippocampal CA1 pyramidal neurons were revealed by an intracellular dye injection combined with a 3-dimensional reconstruction. Although the dendritic arbors remained unaltered, the dendritic spine density on these neurons was significantly reduced. It was suggested that the reduction of dendritic spines may be the underlying cause for increased motor evoked potential threshold and prolonged central motor conduction time in clinical finding in cirrhosis.

Conclusions

We found that HE perturbs CNS functions by altering the dendritic morphology of cortical and hippocampal pyramidal neurons, which may be the underlying cause for the motor and intellectual impairments associated with HE patients.

Uwhangchungsimwon, a traditional herbal medicine, protects brain against oxidative injury via modulation of hypothalamus-pituitary-adrenal (HPA) response in a chronic restraint mice model

ETHNOPHARMACOLOGICAL RELEVANCE

Uwhangchungsimwon (UCW) is a representative traditional herbal medicine for central nervous system disorders in East Asia countries over thousand years. To evaluate the pharmacological effects of UCW against oxidative brain injury in a chronic restraint stress mice model.

METHODS AND MATERIALS

C57BL/6 male mice underwent daily oral administration of distilled water, UCW or ascorbic acid 1h before induction of restraint stress (5h of immobilization daily for 14 days). Nitric oxide (NO), total reactive oxygen species (ROS) levels, malondialdehyde, protein carbonyl contents, and activities of antioxidant enzymes, and concentrations of corticosterone, adrenaline, noradrenaline, and dopamine, were measured in brain tissues or sera.

RESULTS

Restraint stress notably increased NO and ROS levels, malondialdehyde and protein carbonyl contents in brain tissues, but decreased activities of catalase, glutathione reductase and glutathione peroxidase. These alterations were significantly ameliorated by UCW. UCW significantly attenuated the elevated serum concentrations of corticosterone, adrenaline and noradrenaline. UCW also significantly normalized the gene expressions in brain tissues altered by restraint stress; up-regulation of phenylethanolamine N-methyltransferase (PNMT) and N-methyl-d-aspartate type 1 receptor (NMDAR1), and down-regulation of gamma-Aminobutyric acid type A receptor (GABAAR), glutamate decarboxylase 1 (GAD 67), and glutamate decarboxylase 2 (GAD 65), respectively. Moreover, UCW considerably restored neurogenesis in the hippocampal regions which was disturbed by chronic restraint stress.

CONCLUSIONS

These results evidenced that UCW has pharmacological properties for brain protection and neurogenesis in status of stress-associated oxidative damage, and the underlying mechanisms involve the regulation of HPA axis in stress responses.

Astrocytic phosphorylation of PDK1 on Tyr9 following an excitotoxic lesion in the mouse hippocampus

3-phosphoinositide-dependent kinase-1 (PDK1) is suggested to play important roles in the regulation of synaptic plasticity and neuronal cell survival in the mature CNS. Although few studies have investigated the roles of PDK1, little is known about PDK1 changes in glial cells under neuropathological conditions. In current report, phosphorylation of PDK1 was monitored specially on tyrosine residues, following the induction of an excitotoxic lesion in rat brain by using kainic acid administration. In injured hippocampal CA3 region, Tyr9 phosphorylation of PDK1 was increased from 4h until 3 day post-injection. Double immunohistochemistry further evaluated that these phosphorylated forms of PDK1 were localized in astrocytes not other cells. Overexpression of unphosphorylatable mutant, PDK1-Y9F leads to inhibit Protein kinase B (PKB/Akt) activation and cAMP responsive element binding protein (CREB) phosphorylation. In conclusion, our results suggested for the first time that tyrosine phosphorylation of PDK1 is required for PKB and CREB activation in KA-mediated excitotoxic lesion in mouse brain.

IQGAP1 expression in spared CA1 neurons after an excitotoxic lesion in the mouse hippocampus

Repeated seizures induce permanent alterations in the hippocampal circuits in experimental models with intractable temporal lobe epilepsy. Sprouting and synaptic reorganization induced by seizures has been well-studied in the mossy fiber pathway. However, studies investigating sprouting and synaptic reorganization beyond the mossy fiber pathway are limited. The present study examined the biochemical changes of CA1 pyramidal neurons undergoing morphological changes after excitotoxicity-induced hippocampal CA3 neuronal death. IQ-domain GTPase-activating proteins (IQGAP1), is an effector of Rac1 and Cdc42 and an actin-binding protein, was upregulated in CA1 pyramidal neurons after kainic acid-induced hippocampal CA3 neuronal degeneration. IQGAP1 + cells were colocalized with Nestin, but not in astrocytes or mature neurons. Furthermore, IQGAP1 did not originate from newly divided local precursors or NG2 + cells. IQGAP1 and adenomatous polyposis coli localized in CA1 pyramidal neurons, and Cdc42 activation was followed by IQGAP1 recruitment. These findings suggest that IQGAP1 is upregulated in pre-existed sparing neurons of the CA1 layer undergoing morphological changes after excitoxicity-induced hippocampal CA3 neuronal death. It demonstrates the utility of IQGAP1 as a possible marker for spared pyramidal neurons, which may contribute to structural and functional alternations responsible for the development of epilepsy.

NFAT5 in cellular adaptation to hypertonic stress - regulations and functional significance

The Nuclear Factor of Activated T Cells-5 (NFAT5), also known as OREBP or TonEBP, is a member of the nuclear factors of the activated T cells family of transcription factors. It is also the only known tonicity-regulated transcription factor in mammals. NFAT5 was initially known for its role in the hypertonic kidney inner medulla for orchestrating a genetic program to restore the cellular homeostasis. Emerging evidence, however, suggests that NFAT5 might play a more diverse functional role, including a pivotal role in blood pressure regulation and the development of autoimmune diseases. Despite the growing significance of NFAT5 in physiology and diseases, our understanding of how its activity is regulated remains very limited. Furthermore, how changes in tonicities are converted into functional outputs via NFAT5 remains elusive. Therefore, this review aims to summarize our current knowledge on the functional roles of NFAT5 in osmotic stress adaptation and the signaling pathways that regulate its activity.