Unraveling the enigma: housekeeping gene Ugt1a7c as a universal biomarker for microglia

Background

Microglia, brain resident macrophages, play multiple roles in maintaining homeostasis, including immunity, surveillance, and protecting the central nervous system through their distinct activation processes. Identifying all types of microglia-driven populations is crucial due to the presence of various phenotypes that differ based on developmental stages or activation states. During embryonic development, the E8.5 yolk sac contains erythromyeloid progenitors that go through different growth phases, eventually resulting in the formation of microglia. In addition, microglia are present in neurological diseases as a diverse population. So far, no individual biomarker for microglia has been discovered that can accurately identify and monitor their development and attributes.

Summary

Here, we highlight the newly defined biomarker of mouse microglia, UGT1A7C, which exhibits superior stability in expression during microglia development and activation compared to other known microglia biomarkers. The UGT1A7C sensing chemical probe labels all microglia in the 3xTG AD mouse model. The expression of Ugt1a7c is stable during development, with only a 4-fold variation, while other microglia biomarkers, such as Csf1r and Cx3cr1, exhibit at least a 10-fold difference. The UGT1A7C expression remains constant throughout its lifespan. In addition, the expression and activity of UGT1A7C are the same in response to different types of inflammatory activators' treatment in vitro.

Conclusion

We propose employing UGT1A7C as the representative biomarker for microglia, irrespective of their developmental state, age, or activation status. Using UGT1A7C can reduce the requirement for using multiple biomarkers, enhance the precision of microglia analysis, and even be utilized as a standard for gene/protein expression.

Treadmill exercise improves hippocampal neural plasticity and relieves cognitive deficits in a mouse model of epilepsy

Epilepsy frequently leads to cognitive dysfunction and approaches to treatment remain limited. Although regular exercise effectively improves learning and memory functions across multiple neurological diseases, its application in patients with epilepsy remains controversial. Here, we adopted a 14-day treadmill-exercise paradigm in a pilocarpine injection-induced mouse model of epilepsy. Cognitive assays confirmed the improvement of object and spatial memory after endurance training, and electrophysiological studies revealed the maintenance of hippocampal plasticity as a result of physical exercise. Investigations of the mechanisms underlying this effect revealed that exercise protected parvalbumin interneurons, probably via the suppression of neuroinflammation and improved integrity of blood-brain barrier. In summary, this work identified a previously unknown mechanism through which exercise improves cognitive rehabilitation in epilepsy.

Advantages of nanocarriers for basic research in the field of traumatic brain injury

A major challenge for the efficient treatment of traumatic brain injury is the need for therapeutic molecules to cross the blood-brain barrier to enter and accumulate in brain tissue. To overcome this problem, researchers have begun to focus on nanocarriers and other brain-targeting drug delivery systems. In this review, we summarize the epidemiology, basic pathophysiology, current clinical treatment, the establishment of models, and the evaluation indicators that are commonly used for traumatic brain injury. We also report the current status of traumatic brain injury when treated with nanocarriers such as liposomes and vesicles. Nanocarriers can overcome a variety of key biological barriers, improve drug bioavailability, increase intracellular penetration and retention time, achieve drug enrichment, control drug release, and achieve brain-targeting drug delivery. However, the application of nanocarriers remains in the basic research stage and has yet to be fully translated to the clinic.

Effectiveness of Combinational Treatments for Alzheimer's Disease with Human Neural Stem Cells and Microglial Cells Over-Expressing Functional Genes

Alzheimer's disease (AD) is one of the most common neurodegenerative diseases. In AD patients, amyloid-β (Aβ) peptide-mediated degeneration of the cholinergic system utilizing acetylcholine (ACh) for memory acquisition is observed. Since AD therapy using acetylcholinesterase (AChE) inhibitors are only palliative for memory deficits without reversing disease progress, there is a need for effective therapies, and cell-based therapeutic approaches should fulfil this requirement. We established F3.ChAT human neural stem cells (NSCs) encoding the choline acetyltransferase (ChAT) gene, an ACh-synthesizing enzyme, HMO6.NEP human microglial cells encoding the neprilysin (NEP) gene, an Aβ-degrading enzyme, and HMO6.SRA cells encoding the scavenger receptor A (SRA) gene, an Aβ-uptaking receptor. For the efficacy evaluation of the cells, first, we established an appropriate animal model based on Aβ accumulation and cognitive dysfunction. Among various AD models, intracerebroventricular (ICV) injection of ethylcholine mustard azirinium ion (AF64A) induced the most severe Aβ accumulation and memory dysfunction. Established NSCs and HMO6 cells were transplanted ICV to mice showing memory loss induced by AF64A challenge, and brain Aβ accumulation, ACh concentration and cognitive function were analyzed. All the transplanted F3.ChAT, HMO6.NEP and HMO6.SRA cells were found to survive up to 4 weeks in the mouse brain and expressed their functional genes. Combinational treatment with the NSCs (F3.ChAT) and microglial cells encoding each functional gene (HMO6.NEP or HMO6.SRA) synergistically restored the learning and memory function of AF64A-challenged mice by eliminating Aβ deposits and recovering ACh level. The cells also attenuated inflammatory astrocytic (glial fibrillary acidic protein) response by reducing Aβ accumulation. Taken together, it is expected that NSCs and microglial cells over-expressing ChAT, NEP or SRA genes could be strategies for replacement cell therapy of AD.

Severe Acute Liver Dysfunction Induces Delayed Hepatocyte Swelling and Cytoplasmic Vacuolization, and Delayed Cortical Neuronal Cell Death

Liver dysfunction is the main cause of hepatic encephalopathy. However, histopathological changes in the brain associated with hepatic encephalopathy remain unclear. Therefore, we investigated pathological changes in the liver and brain using an acute hepatic encephalopathy mouse model. After administering ammonium acetate, a transient increase in the blood ammonia level was observed, which returned to normal levels after 24 h. Consciousness and motor levels also returned to normal. It was revealed that hepatocyte swelling, and cytoplasmic vacuolization progressed over time in the liver tissue. Blood biochemistry also suggested hepatocyte dysfunction. In the brain, histopathological changes, such as perivascular astrocyte swelling, were observed 3 h after ammonium acetate administration. Abnormalities in neuronal organelles, especially mitochondria and rough endoplasmic reticulum, were also observed. Additionally, neuronal cell death was observed 24 h post-ammonia treatment when blood ammonia levels had returned to normal. Activation of reactive microglia and increased expression of inducible nitric oxide synthase (iNOS) were also observed seven days after a transient increase in blood ammonia. These results suggest that delayed neuronal atrophy could be iNOS-mediated cell death due to activation of reactive microglia. The findings also suggest that severe acute hepatic encephalopathy causes continued delayed brain cytotoxicity even after consciousness recovery.

Turmeronols (A and B) from Curcuma longa have anti-inflammatory effects in lipopolysaccharide-stimulated BV-2 microglial cells by reducing NF-κB signaling

Turmeronols (A and B), bisabolane-type sesquiterpenoids found in turmeric, reduce inflammation outside the brain in animals; however, their effects on neuroinflammation, a common pathology of various neurodegenerative diseases, are not understood. Inflammatory mediators produced by microglial cells play a key role in neuroinflammation, so this study evaluated the anti-inflammatory effects of turmeronols in BV-2 microglial cells stimulated with lipopolysaccharide (LPS). Pretreatment with turmeronol A or B significantly inhibited LPS-induced nitric oxide (NO) production; mRNA expression of inducible NO synthase; production of interleukin (IL)-1β, IL-6, and tumor necrosis factor α and upregulation of their mRNA expression; phosphorylation of nuclear factor-κB (NF-κB) p65 proteins and inhibitor of NF-κB kinase (IKK); and nuclear translocation of NF-κB. These results suggest that these turmeronols may prevent the production of inflammatory mediators by inhibiting the IKK/NF-κB signaling pathway in activated microglial cells and can potentially treat neuroinflammation associated with microglial activation.

Different Contacted Cell Types Contribute to Acquiring Different Properties in Brain Microglial Cells upon Intercellular Interaction

Microglial cells (MGs), originally derived from progenitor cells in a yolk sac during early development, are glial cells located in a physiological and pathological brain. Since the brain contains various cell types, MGs could frequently interact with different cells, such as astrocytes (ACs), pericytes (PCs), and endothelial cells (ECs). However, how microglial traits are regulated via cell-cell interactions by ACs, PCs, or ECs and how they are different depending on the contacted cell types is unclear. This study aimed to clarify these questions by coculturing MGs with ACs, PCs, or ECs using mouse brain-derived cells, and microglial phenotypic changes were investigated under culture conditions that enabled direct cell-cell contact. Our results showed that ACs or PCs dose-dependently increased the number of MG, while ECs decreased it. Microarray and gene ontology analysis showed that cell fate-related genes (e.g., cell cycle, proliferation, growth, death, and apoptosis) of MGs were altered after a cell-cell contact with ACs, PCs, and ECs. Notably, microarray analysis showed that several genes, such as gap junction protein alpha 1 (Gja1), were prominently upregulated in MGs after coincubation with ACs, PCs, or ECs, regardless of cell types. Similarly, immunohistochemistry showed that an increased Gja1 expression was observed in MGs after coincubation with ACs, PCs, or ECs. Immunofluorescent and fluorescence-activated cell sorting analysis also showed that calcein-AM was transferred into MGs after coincubation with ACs, PCs, or ECs, confirming that intercellular interactions occurred between these cells. However, while Gja1 inhibition reduced the number of MGs after coincubation with ACs and PCs, this was increased after coincubation with ECs; this indicates that ACs and PCs positively regulate microglial numbers via Gja1, while ECs decrease it. Results show that ACs, PCs, or ECs exert both common and specific cell type-dependent effects on MGs through intercellular interactions. These findings also suggest that brain microglial phenotypes are different depending on their surrounding cell types, such as ACs, PCs, or ECs.

Testing a Polygenic Risk Score for Morphological Microglial Activation in Alzheimer's Disease and Aging

BACKGROUND

Neuroinflammation and the activation of microglial cells are among the earliest events in Alzheimer's disease (AD). However, direct observation of microglia in living people is not currently possible. Here, we indexed the heritable propensity for neuroinflammation with polygenic risk scores (PRS), using results from a recent genome-wide analysis of a validated post-mortem measure of morphological microglial activation.

OBJECTIVE

We sought to determine whether a PRS for microglial activation (PRSmic) could augment the predictive performance of existing AD PRSs for late-life cognitive impairment.

METHODS

First, PRSmic were calculated and optimized in a calibration cohort (Alzheimer's Disease Neuroimaging Initiative (ADNI), n = 450), with resampling. Second, predictive performance of optimal PRSmic was assessed in two independent, population-based cohorts (total n = 212,237). Finally, we explored associations of PRSmic with a comprehensive set of imaging and fluid AD biomarkers in ADNI.

RESULTS

Our PRSmic showed no significant improvement in predictive power for either AD diagnosis or cognitive performance in either external cohort. Some nominal associations were found in ADNI, but with inconsistent effect directions.

CONCLUSION

While genetic scores capable of indexing risk for neuroinflammatory processes in aging are highly desirable, more well-powered genome-wide studies of microglial activation are required. Further, biobank-scale studies would benefit from phenotyping of proximal neuroinflammatory processes to improve the PRS development phase.

Gastrodin From Gastrodia elata Enhances Cognitive Function and Neuroprotection of AD Mice via the Regulation of Gut Microbiota Composition and Inhibition of Neuron Inflammation

Gastrodin (Gas) is known to exhibit neuroprotective effects in Alzheimer’s disease (AD). However, the detailed mechanism of action is still unclear. In the present study, we focused on the microbiome–gut–brain axis to investigate the mechanism of action of Gas using a D-galactose (Dgal)–induced AD model. Gas reversed the memory dysfunction of Dgal-administered mice. Neurons in the cerebral cortex and hippocampus were reduced in the Dgal-administered group, and the decrease of neurons was suppressed in 90 and 210 mg/kg Gas treatment groups. 16S rRNA sequence analysis was carried out to explore the composition of gut microbiota in fecal samples of mice. Gas treatment had a positive correlation with Firmicutes and had a negative correlation with Cyanobacteria, Proteobacteria, and Deferribaceters. Importantly, the LPS and proinflammatory cytokines in the brain increased in Dgal-administered mice, but these parameters recovered to normal levels after oral administration of Gas. To determine whether the microbiota–gut–brain axis is involved in the neuroprotective effect of Gas, the mice were given antibiotic cocktail before and during the trial period to decrease the gut microbiota of mice. The antibiotic cocktail partially eliminated the neuroprotective effect of Gas by changing the gut microbiome composition. These results indicated that Gas improves the memory of the AD mouse model via partly targeting the microbiota–gut–brain axis and mitigating neuron inflammation.

Inhibition of vascular endothelial growth factor alleviates neovascular retinopathy with regulated neurotrophic/proinflammatory cytokines through the modulation of DBI-TSPO signaling

Diazepam binding inhibitor (DBI)-translocator protein (18kDa) (TSPO) signaling in the retina was reported to possess coordinated macroglia-microglia interactions. We investigated DBI-TSPO signaling and its correlation with vascular endothelial growth factor (VEGF), neurotrophic or inflammatory cytokines in neovascular retinopathy, and under hypoxic conditions. The vitreous expression of DBI, VEGF, nerve growth factor (NGF), and interleukin-1beta (IL-1β) were examined in proliferative diabetic retinopathy (PDR) patients with or without anti-VEGF therapy and nondiabetic controls. Retinal DBI-TSPO signaling and the effect of the anti-VEGF agent were evaluated in a mouse model of oxygen-induced retinopathy (OIR). Interactions between Müller cell-derived VEGF and DBI, as well as cocultured microglial cells under hypoxic conditions, were studied, using Western blot, real-time RT-PCR, enzyme-linked immunosorbent assay (ELISA), flow cytometry, and immunofluorescent labeling. Results showed that vitreous levels of DBI, VEGF, NGF, and IL-1β were significantly higher in PDR patients compared with controls, which further changed after anti-VEGF therapy. A statistical association was found between vitreous DBI and VEGF, NGF, IL-1β, and age. The application of the anti-VEGF agent in the OIR model induced retinal expression of DBI and NGF, and attenuated inflammation and microglial cell activation. Inhibition of Müller cell-derived VEGF could increase its DBI expression under hypoxic conditions, while the DBI-TSPO signaling pathway is essential for anti-VEGF agents exerting anti-inflammatory and neuroprotective effects, as well as limiting inflammatory magnitude, promoting its neurotrophin production and anti-inflammatory (M2) polarization in microglial cells. These findings suggest the beneficial effect of anti-VEGF therapy on inflammation and neurotrophy of retinal glial cells through modulation of the DBI-TSPO signaling pathway.

Anti-oxidant Effect of High Dilutions of Arnica montana, Arsenicum Album, and Lachesis Mutus in Microglial Cells in Vitro

Microglial cells play important roles in inflammatory responses. The level of oxidative stress is a well-known marker of inflammation. Homeopathic medicines are often used clinically to alleviate inflammation. We evaluated the anti-oxidative effect of high dilutions of Arnica montana (Arnica m.), Arsenicum album (Arsenicum a.), and Lachesis mutus (Lachesis m.) on production of reactive oxygen species (ROS) in inflamed microglial cells in vitro. Microglial cells, on exposure to lipopolysaccharide (LPS), have induced production of ROS compared with resting cells. The dilutions significantly reduced the oxidative stress by decreasing the level of ROS produced. Arnica m. 1C, 3C, 5C, 7C, 9C, and 30C dilutions had a range of ROS reduction between 15 and 42.1%; Arsenicum a. 3C, 5C, 7C, 15C, and 30C dilutions had a range of ROS reduction between 17.6 and 35.3%; and Lachesis m. 3C, 5C, 7C, 9C, 15C, and 30C dilutions had a range of ROS reduction between 25 and 41.7%. To summarize, the dilutions with the greatest effect were Arnica m. 1C (42.1%), Arsenicum a. 30C (35.3%), and Lachesis m. 7C (41.7%). Arnica m., Arsenicum a., and Lachesis m. did not have the same effect on ROS production and were not dose-dependent.

Effective Perturbations on the Amplitude and Hysteresis of Erg-Mediated Potassium Current Caused by 1-Octylnonyl 8-[(2-hydroxyethyl)[6-oxo-6(undecyloxy)hexyl]amino]-octanoate (SM-102), a Cationic Lipid

SM-102 (1-octylnonyl 8-[(2-hydroxyethyl)[6-oxo-6-(undecyloxy)hexyl]amino]-octanoate) is an amino cationic lipid that has been tailored for the formation of lipid nanoparticles and it is one of the essential ingredients present in the Moderna^TM COVID-19 vaccine. However, to what extent it may modify varying types of plasmalemmal ionic currents remains largely uncertain. In this study, we investigate the effects of SM-102 on ionic currents either in two types of endocrine cells (e.g., rat pituitary tumor (GH₃) cells and mouse Leydig tumor (MA-10) cells) or in microglial (BV2) cells. Hyperpolarization-activated K⁺ currents in these cells bathed in high-K⁺, Ca²⁺-free extracellular solution were examined to assess the effects of SM-102 on the amplitude and hysteresis of the erg-mediated K⁺ current (I_K(erg)). The SM-102 addition was effective at blocking I_K(erg) in a concentration-dependent fashion with a half-maximal concentration (IC₅₀) of 108 μM, a value which is similar to the K_D value (i.e., 134 μM) required for its accentuation of deactivation time constant of the current. The hysteretic strength of I_K(erg) in response to the long-lasting isosceles-triangular ramp pulse was effectively decreased in the presence of SM-102. Cell exposure to TurboFectin^TM 8.0 (0.1%, v/v), a transfection reagent, was able to inhibit hyperpolarization-activated I_K(erg) effectively with an increase in the deactivation time course of the current. Additionally, in GH₃ cells dialyzed with spermine (30 μM), the I_K(erg) amplitude progressively decreased; moreover, a further bath application of SM-102 (100 μM) or TurboFectin (0.1%) diminished the current magnitude further. In MA-10 Leydig cells, the I_K(erg) was also blocked by the presence of SM-102 or TurboFectin. The IC₅₀ value for SM-102-induced inhibition of I_K(erg) in MA-10 cells was 98 μM. In BV2 microglial cells, the amplitude of the inwardly rectifying K⁺ current was inhibited by SM-102. Taken together, the presence of SM-102 concentration-dependently inhibited I_K(erg) in endocrine cells (e.g., GH₃ or MA-10 cells), and such action may contribute to their functional activities, assuming that similar in vivo findings exist.

Positive Allosteric Modulation of CB1 and CB2 Cannabinoid Receptors Enhances the Neuroprotective Activity of a Dual CB1R/CB2R Orthosteric Agonist

Preclinical studies highlighted that compounds targeting cannabinoid receptors could be useful for developing novel therapies against neurodegenerative disorders. However, the chronic use of orthosteric agonists alone has several disadvantages, limiting their usefulness as clinically relevant drugs. Positive allosteric modulators might represent a promising approach to achieve the potential therapeutic benefits of orthosteric agonists of cannabinoid receptors through increasing their activity and limiting their adverse effects. The aim of the present study was to show the effects of positive allosteric ligands of cannabinoid receptors on the activity of a potent dual orthosteric agonist for neuroinflammation and excitotoxic damage by excessive glutamate release. The results indicate that the combination of an orthosteric agonist with positive allosteric modulators could represent a promising therapeutic approach to the treatment of neurodegenerative disorders.

[Role of pyroptosis in bilirubin-induced microglial injury]

OBJECTIVE

To study whether pyroptosis is involved in the bilirubin-induced injury of primary cultured rat cortical microglial cells.

METHODS

Primary cultured rat cortical microglial cells were randomly administered with 30 μmol/L bilirubin (bilirubin group), 30 μmol/L bilirubin following 30 μmol/L VX-765 pretreatment (VX-765+bilirubin group), or an equal volume of dimethyl sulfoxide (control group). Modified MTT assay was used to measure the viability of microglial cells. Western blot was used to measure the expression of the pyroptosis-related proteins Caspase-1 and gasdermin D (GSDMD). Lactate dehydrogenase (LDH)-release assay was used to evaluate the cytotoxicity of microglial cells. EtBr/EthD2 with different molecular weights (394 Da/1 293 Da) was used to measure the size of plasma membrane pores. ELISA was used to measure the level of the inflammatory factor interleukin-1β (IL-1β) in culture supernatant.

RESULTS

After bilirubin stimulation, the viability of microglial cells decreased and LDH release increased, both in a time-dependent manner. Compared with the control group, the bilirubin group had a significantly higher positive rate of small-molecule EtBr passing through the cell membrane (P<0.001), while there was no significant difference in the pass rate of large-molecule EthD2 between groups (P>0.05). The expression of activated Caspase-1 significantly increased at 0.5 hour after bilirubin stimulation (P<0.05), and that of activated GSDMD significantly increased at 6 hours after bilirubin stimulation (P<0.05). The release of IL-1β significantly increased at 6 hours after bilirubin stimulation and reached the peak at 24 hours (P<0.001). Compared with the bilirubin group, the VX-765+bilirubin group had a significant increase in cell viability (P<0.05) and significant reductions in the expression of activated GSDMD, the pass rate of EtBr, and the release of LDH and IL-1β (P<0.05).

CONCLUSIONS

Pyroptosis is involved in bilirubin-induced injury of primary cultured microglial cells.

Constituents of Gastrodia elata and Their Neuroprotective Effects in HT22 Hippocampal Neuronal, R28 Retinal Cells, and BV2 Microglial Cells

Gastrodia elata is widely used in traditional medicine and contains various types of metabolites with pharmacological activity. In the course of searching for neuroprotective molecules associated with the potential of G. elata in the treatment of neurodegenerative disorders, two new phenolic compounds (1 and 2) and a new tripeptide (3), together with 16 known compounds (4–19), were isolated from the rhizomes of G. elata. The structures of the compounds were determined by the interpretation of spectroscopic data, including nuclear magnetic resonance and mass spectrometry data. All obtained compounds were assessed for their ability to protect neuronal cells against neurotoxicity and neuroinflammation. Of these, 4 and 5 were found to possess moderate activities in HT22 hippocampal neuronal cells, whereas 2, 6, and 7 showed weak activities in R28 retinal cells. Additionally, compound 9 showed moderate inhibitory activity on lipopolysaccharide-induced nitric oxide production in BV2 microglial cells.

Bone marrow stromal cells-derived exosomes target DAB2IP to induce microglial cell autophagy, a new strategy for neural stem cell transplantation in brain injury

Bone marrow stromal cells (MSCs) are a useful source of stem cells for the treatment of various brain injury diseases due to their abundant supply and fewer ethical problems compared with transplant treatment. However, the clinical application of MSCs is limited due to allograft rejection and immunosuppression in the process of MSCs transplantation. According to previous studies, microglial cell autophagy occurs following co-culture with MSCs. In the present study, exosomes were obtained from MSCs and subsequently characterized using transmission electron microscopy, atomic force microscopy and dynamic light scattering particle size analysis. The type of microRNAs (miRs) found in the exosomes was then analyzed via gene chip. The results demonstrated that microglial cell autophagy could be induced by exosomes. This mechanism was therefore investigated further via reverse transcription-quantitative PCR, western blotting and luciferase assays. These results demonstrated that exosomes from MSCs could induce microglial cell autophagy through the miR-32-mediated regulation of disabled homolog 2-interacting protein, thus providing a theoretical basis for the clinical application of miRs in MSCs.

[Regulatory mechanism of MS275 on the p38 MAPK signaling pathway in rats with convulsion in the developmental stage]

OBJECTIVE

To study the regulatory mechanism of MS275, a histone deacetylase inhibitor, on the p38 MAPK signaling pathway in rats with convulsion in the developmental stage.

METHODS

Thirty-two male rats were randomly divided into four groups: control, pentylenetetrazol (PTZ), PTZ+3 mg/kg MS275, and PTZ+6 mg/kg MS275 (n=8 each). A rat model of convulsion in the developmental stage was prepared by an intraperitoneal injection of PTZ. The rats in the control group were given an injection of normal saline alone. MS275 was given by an intraperitoneal injection at 2 hours before PTZ injection. At 24 hours after successful modeling, 6 rats were taken from each group. Western blot and qRT-PCR were used to measure the protein and mRNA expression of p38, MK2, cAMP response element-binding protein (CREB), and interleukin-6 (IL-6) in the hippocampus. Hematoxylin-eosin (HE) staining was used to observe brain pathological changes. Western blot was used to measure the expression of CD11b as a marker for the activation of microglial cells.

RESULTS

Compared with the control group, the PTZ group had significant increases in the mRNA and protein expression of p38, MK2, CREB, and IL-6 (P<0.05). MS275 significantly inhibited the mRNA and protein expression of the above markers in the rats with convulsion in the developmental stage (P<0.05), and 6 mg/kg MS275 had a significantly better inhibitory effect on the mRNA and protein expression of IL-6 and CREB than 3 mg/kg MS275 (P<0.05). HE staining showed that the PTZ group had marked neuron apoptosis, cellular edema, and inflammatory cell infiltration, while MS275 intervention alleviated neuron apoptosis and cellular edema and reduced inflammatory cell infiltration in the rats with convulsion. The PTZ group had a significant increase in the activation of microglial cells, while MS275 significantly inhibited the activation of microglial cells in the rats with convulsion (P<0.05); 6 mg/kg MS275 had a significantly better inhibitory effect than 3 mg/kg MS275 (P<0.05).

CONCLUSIONS

In rats with convulsion in the developmental stage, the histone deacetylase inhibitor MS275 can inhibit the p38 MAPK signaling pathway, the apoptosis of hippocampal neurons, and the activation of microglial cells and thus reduce inflammatory response and convulsion-induced brain injury in a dose-dependent manner.

[Regulatory mechanism of MS275 on the p38 MAPK signaling pathway in rats with convulsion in the developmental stage]

OBJECTIVE

To study the regulatory mechanism of MS275, a histone deacetylase inhibitor, on the p38 MAPK signaling pathway in rats with convulsion in the developmental stage.

METHODS

Thirty-two male rats were randomly divided into four groups: control, pentylenetetrazol (PTZ), PTZ+3 mg/kg MS275, and PTZ+6 mg/kg MS275 (n=8 each). A rat model of convulsion in the developmental stage was prepared by an intraperitoneal injection of PTZ. The rats in the control group were given an injection of normal saline alone. MS275 was given by an intraperitoneal injection at 2 hours before PTZ injection. At 24 hours after successful modeling, 6 rats were taken from each group. Western blot and qRT-PCR were used to measure the protein and mRNA expression of p38, MK2, cAMP response element-binding protein (CREB), and interleukin-6 (IL-6) in the hippocampus. Hematoxylin-eosin (HE) staining was used to observe brain pathological changes. Western blot was used to measure the expression of CD11b as a marker for the activation of microglial cells.

RESULTS

Compared with the control group, the PTZ group had significant increases in the mRNA and protein expression of p38, MK2, CREB, and IL-6 (P<0.05). MS275 significantly inhibited the mRNA and protein expression of the above markers in the rats with convulsion in the developmental stage (P<0.05), and 6 mg/kg MS275 had a significantly better inhibitory effect on the mRNA and protein expression of IL-6 and CREB than 3 mg/kg MS275 (P<0.05). HE staining showed that the PTZ group had marked neuron apoptosis, cellular edema, and inflammatory cell infiltration, while MS275 intervention alleviated neuron apoptosis and cellular edema and reduced inflammatory cell infiltration in the rats with convulsion. The PTZ group had a significant increase in the activation of microglial cells, while MS275 significantly inhibited the activation of microglial cells in the rats with convulsion (P<0.05); 6 mg/kg MS275 had a significantly better inhibitory effect than 3 mg/kg MS275 (P<0.05).

CONCLUSIONS

In rats with convulsion in the developmental stage, the histone deacetylase inhibitor MS275 can inhibit the p38 MAPK signaling pathway, the apoptosis of hippocampal neurons, and the activation of microglial cells and thus reduce inflammatory response and convulsion-induced brain injury in a dose-dependent manner.

Effects of FGF2/FGFR1 Pathway on Expression of A1 Astrocytes After Infrasound Exposure

Two types of reactive astrocytes, A1 and A2 astrocytes, are induced following neuroinflammation and ischemia. In this study, we evaluated the effects of the fibroblast growth factor (FGF)2/FGF receptor (FGFR)1 pathway on A1 and A2 astrocytes in the rat hippocampus using double-labeling immunofluorescence following infrasound exposure. A1 astrocytes were induced in the CA1 region of the hippocampus after exposure to infrasound for 3 days. The number of microglial cells was also increased, and we investigated if these might be responsible for the reactivity of A1 astrocytes. Accordingly, expression levels of C3 and Iba-1, as markers of A1 astrocytes and microglial cells, respectively, were both up-regulated in rat hippocampus following infrasound exposure, as demonstrated by western blot. We also explored the effect of the FGF2/FGFR1 pathway on A1 astrocyte reactivity by pretreating rats with FGF2 or the specific FGFR1 antagonist, PD173074. A1 astrocytes were gradually down-regulated by activation of the FGF2/FGFR1 pathway and were up-regulated by inhibition of the FGF2/FGFR1 pathway after infrasound damage. These results further our understanding of the role of reactive astrocytes in infrasound-induced central nervous system injury and will thus facilitate the development of new treatments for these injuries.

Neuron-glia interaction is a key mechanism underlying persistent orofacial pain

Excitability of neurons in the trigeminal ganglion (TG), trigeminal spinal subnucleus caudalis (Vc), and upper cervical spinal cord (C1-C2) is greatly enhanced after orofacial inflammation and trigeminal nerve injury, and TG, Vc, and C1-C2 neurons remain sensitized long after such episodes. Sensitized neurons generate various molecules, which are released from nociceptive neurons in these areas and are involved in modulating the excitability of TG, Vc, and C1-C2 nociceptive neurons. Hyperexcitable nociceptive neurons also activate satellite glial cells in the TG and microglial cells and astrocytes in the Vc and C1-C2. Glial cell activation spreads throughout the TG, Vc, and C1-C2 and triggers the release of various molecules involved in modulating nociceptive neurons in TG, Vc, and C1-C2 neurons. These findings suggest that functional interaction between neurons and glial cells is critical in persistent orofacial pain associated with orofacial inflammation and trigeminal nerve injury.

Effects of apelin on retinal microglial cells in a rat model of oxygen-induced retinopathy of prematurity

This study explores the effects of apelin on retinal microglial cells in rat models of oxygen-induced retinopathy of prematurity (ROP). Totally, 274 rats were selected for establishing oxygen-induced retinopathy (OIR) models, and 92 healthy rats for control group. OIR rats were assigned into OIR, 10^-5  g/L apelin, 10^-4  g/L apelin, and 10^-3  g/L apelin groups. Immunohistochemistry was employed to determine morphology of microglial cells and cell number. CDllb, ionized calcium-binding adapter molecule 1 (IBA-1), TNF-α, and iNOS mRNA and protein expressions were identified using RT-qPCR and Western blotting, respectively. ELISA was employed to determine the levels of VEGF and glial fibrillary acidic protein (GFAP). The amoeboid microglial cells were found in the OIR and 10^-3  g/L apelin groups, while bipolar microglial cells were found in the normal control, 10^-5  g/L apelin and 10^-4  g/L apelin groups. In the 1, 2, 3, and 4th week after apelin treatment, there were significantly decreased bipolar microglial cells, lower mRNA and protein expressions of CDllb, IBA-1, TNF-α and iNOS, and the levels of VEGF and GFAP in the 10^-4  g/L apelin group than in the OIR, 10^-3  g/L apelin and 10^-5  g/L apelin groups. The differences between the normal control and 10^-4  g/L apelin groups are not significant. Compared with the OIR group, the 10^-5  g/L apelin and 10^-3  g/L apelin groups presented decreased microglial cells and mRNA and protein expressions of CDllb, IBA-1, TNF-α, and iNOS. Appropriate concentration of apelin may reduce retinal microglial cells in a rat model of oxygen-induced ROP.

Establishment of mouse neuron and microglial cell co-cultured models and its action mechanism

OBJECTIVE

The objective of this study is to establish a co-culture model of mouse neurons and microglial cells, and to analyze the mechanism of action of oxygen glucose deprivation (OGD) and transient oxygen glucose deprivation (tOGD) preconditioning cell models.

RESULTS

Mouse primary neurons and BV2 microglial cells were successfully cultured, and the OGD and tOGD models were also established. In the co-culture of mouse primary neurons and microglial cells, the cell number of tOGD mouse neurons and microglial cells was larger than the OGD cell number, observed by a microscope. CCK-8 assay result showed that at 1h after treatment, the OD value in the control group is lower compared to all the other three groups (P < 0.05). The treatment group exhibited the highest OD value among the four groups. The results observed at 5h were consistent with the results at 1 h. Flow cytometry results showed that at 1h after treatment the apoptosis percentages is higher in the control group compared to other three groups (P < 0.05).

MATERIALS AND METHODS

Mouse brain tissues were collected and primary neurons cells were cultured. In the meantime mouse BV2 microglia cells were cultured. Two types of cells were co-cultured, and OGD and tOGD cell models were established. There were four groups in the experiment: control group (OGD), treatment group (tOGD+OGD), placebo group (tOGD+OGD+saline) and minocycline intervention group (tOGD+OGD+minocycline). CCK-8 kit was used to detect cell viability and flow cytometry was used to detect apoptosis.

CONCLUSIONS

In this study, mouse primary neurons and microglial cells were co-cultured. The OGD and tOGD models were established successfully. tOGD was able to effectively protect neurons and microglial cells from damage, and inhibit the apoptosis caused by oxygen glucose deprivation.

Pleiotropic function of TRPV4 ion channels in the central nervous system

NEW FINDINGS

What is the topic of this review? In this concise review, we highlight insights into the role of transient receptor potential, vanilloid type 4 (TRPV4) ion channels in the CNS, results that have been contributed over the last 16 years since the initial discovery of the channel. What advances does it highlight? TRPV4 has been found to function in neurons, astroglia and microglia, both in physiological (e.g. astrocytic neurovascular coupling, neuronal membrane potential at physiological temperature) and in pathological conditions (e.g. mechanical trauma), so far recorded as exciting findings in need of more in-depth mechanistic clarification. Transient receptor potential, vanilloid type 4 (TRPV4) ion channels are osmo-mechano-TRP channels, with pleiotropic function and expression in many different types of tissues and cells. They have also been found to be involved in pain and inflammation. Studies have focused on the role of TRPV4 in peripheral sensory neurons, but its expression and function in central nervous glial cells and neurons has also been documented. In this overview, based on the senior author's (WL) lecture at the recent recent joint meeting of APS/The Physiological Society in Dublin, we concisely review evidence of TRPV4 expression and function in the CNS and how TRPV4 function can be modulated for therapeutic benefit of neuropsychiatric disorders. Novel TRPV4-inhibitory compounds developed recently in the authors' laboratory are also discussed.

Molecular determinants of Hv1 proton channel inhibition by guanidine derivatives

The voltage-gated proton channel Hv1 plays important roles in proton extrusion, pH homeostasis, and production of reactive oxygen species in a variety of cell types. Excessive Hv1 activity increases proliferation and invasiveness in cancer cells and worsens brain damage in ischemic stroke. The channel is composed of two subunits, each containing a proton-permeable voltage-sensing domain (VSD) and lacking the pore domain typical of other voltage-gated ion channels. We have previously shown that the compound 2-guanidinobenzimidazole (2GBI) inhibits Hv1 proton conduction by binding to the VSD from its intracellular side. Here, we examine the binding affinities of a series of 2GBI derivatives on human Hv1 channels mutated at positions located in the core of the VSD and apply mutant cycle analysis to determine how the inhibitor interacts with the channel. We identify four Hv1 residues involved in the binding: aspartate 112, phenylalanine 150, serine 181, and arginine 211. 2GBI appears to be oriented in the binding site with its benzo ring pointing to F150, its imidazole ring inserted between residue D112 and residues S181 and R211, and the guanidine group positioned in the proximity of R211. We also identify a modified version of 2GBI that is able to reach the binding site on Hv1 from the extracellular side of the membrane. Understanding how compounds like 2GBI interact with the Hv1 channel is an important step to the development of pharmacological treatments for diseases caused by Hv1 hyperactivity.

Cellular magnetic resonance with iron oxide nanoparticles: long-term persistence of SPIO signal in the CNS after transplanted cell death

AIM

To study the specificity of cellular MRI based on superparamagnetic iron oxide particles (SPIOs), especially within the CNS.

MATERIALS & METHODS

A microglial cell line was engineered for the expression of a suicide gene, the receptor of diphtheria toxin (DT), and two reporter genes, green fluorescent protein and luciferase, in order to induce, in a controlled manner, cell death and test it through bioluminescence. SPIO-labeled DT-sensitive and control DT-insensitive cells were transplanted into the brains of mice, which underwent serial MRI and bioluminescence studies before and up to 90 days after DT-induced cell death.

RESULTS

No variations in SPIO signal voids were detected along longitudinal monitoring in brain hemispheres transplanted with DT-sensitive cells. Ex vivo analyses showed persistence of iron nanoparticle deposits at transplantation sites.

CONCLUSION

Due to the long-term persistence of signal after transplanted cell death, caution is advised when SPIOs are employed for cell tracking.

Calcium ion influx in microglial cells: physiological and therapeutic significance

Microglial cells, the immunocompetent cells of the central nervous system (CNS), exhibit a resting phenotype under healthy conditions. In response to injury, however, they transform into an activated state, which is a hallmark feature of many CNS diseases. Factors or agents released from the neurons, blood vessels, and/or astrocytes could activate these cells, leading to their functional and structural modifications. Microglial cells are well equipped to sense environmental changes within the brain under both physiological and pathological conditions. Entry of calcium ions (Ca(2+)) plays a critical role in the process of microglial transformation; several channels and receptors have been identified on the surface of microglial cells. These include store-operated channel, Orai1, and its sensor protein, stromal interaction molecule 1 (STIM1), in microglial cells, and their functions are modulated under pathological stimulations. Transient receptor potential (TRP) channels and voltage- and ligand-gated channels (ionotropic and metabotropic receptors) are also responsible for Ca(2+) influx into the microglial cells. An elevation of intracellular Ca(2+) concentration subsequently regulates microglial cell functions by activating a diverse array of Ca(2+)-sensitive signaling cascades. Perturbed Ca(2+) homeostasis contributes to the progression of a number of CNS disorders. Thus, regulation of Ca(2+) entry into microglial cells could be a pharmacological target for several CNS-related pathological conditions. This Review addresses the recent insights into microglial cell Ca(2+) influx mechanisms, their roles in the regulation of functions, and alterations of Ca(2+) entry in specific CNS disorders.

Matrix metalloproteinase dependent cleavage of cell adhesion molecules in the pathogenesis of CNS dysfunction with HIV and methamphetamine

Physiologically appropriate levels of matrix metalloproteinases (MMPs) are likely important to varied aspects of CNS function. In particular, these enzymes may contribute to neuronal activity dependent synaptic plasticity and to cell mobility in processes including stem cell migration and immune surveillance. Levels of MMPs may, however, be substantially increased in the setting of HIV infection with methamphetamine abuse. Elevated MMP levels might in turn influence integrity of the blood brain barrier, as has been demonstrated in published work. Herein we suggest that elevated levels of MMPs can also contribute to microglial activation as well as neuronal and synaptic injury through a mechanism that involves cleavage of specific cell and synaptic adhesion molecules.

Naegleria fowleri lysate induces strong cytopathic effects and pro-inflammatory cytokine release in rat microglial cells

Naegleria fowleri, a ubiquitous free-living ameba, causes fatal primary amebic meningoencephalitis in humans. N. fowleri trophozoites are known to induce cytopathic changes upon contact with microglial cells, including necrotic and apoptotic cell death and pro-inflammatory cytokine release. In this study, we treated rat microglial cells with amebic lysate to probe contact-independent mechanisms for cytotoxicity, determining through a combination of light microscopy and scanning and transmission electron microscopy whether N. fowleri lysate could effect on both necrosis and apoptosis on microglia in a time- as well as dose-dependent fashion. A ⁵¹Cr release assay demonstrated pronounced lysate induction of cytotoxicity (71.5%) toward microglial cells by 24 hr after its addition to cultures. In an assay of pro-inflammatory cytokine release, microglial cells treated with N. fowleri lysate produced TNF-α, IL-6, and IL-1β, though generation of the former 2 cytokines was reduced with time, and that of the last increased throughout the experimental period. In summary, N. fowleri lysate exerted strong cytopathic effects on microglial cells, and elicited pro-inflammatory cytokine release as a primary immune response.

Increase in hemokinin-1 mRNA in the spinal cord during the early phase of a neuropathic pain state

BACKGROUND AND PURPOSE

Substance P (SP), a representative member of the tachykinin family, is involved in nociception under physiological and pathological conditions. Recently, hemokinin-1 (HK-1) was identified as a new member of this family. Although HK-1 acts on NK(1) tachykinin receptors that are thought to be innate for SP, the roles of HK-1 in neuropathic pain are still unknown.

EXPERIMENTAL APPROACH

Using rats that had been subjected to chronic constrictive injury (CCI) of the sciatic nerve as a neuropathic pain model, we examined the changes in expression of SP- and HK-1-encoding genes (TAC1 and TAC4, respectively) in the L4/L5 spinal cord and L4/L5 dorsal root ganglia (DRGs) in association with changes in pain-related behaviours in this neuropathic pain state.

KEY RESULTS

The TAC4 mRNA level was increased on the ipsilateral side of the dorsal spinal cord, but not in DRGs, at day 3 after CCI. In contrast, the TAC1 mRNA level was significantly increased in the DRGs at day 3 after CCI without any changes in the dorsal spinal cord. Analysis of a cultured microglial cell line revealed the presence of TAC4 mRNA in microglial cells. Minocycline, an inhibitor of microglial activation, blocked the increased expression of TAC4 mRNA after CCI and inhibited the associated pain-related behaviours and microglial activation in the spinal cord.

CONCLUSIONS AND IMPLICATIONS

The present results suggest that HK-1 expression is increased at least partly in activated microglial cells after nerve injury and is clearly involved in the early phase of neuropathic pain.

Rabies viruses infect primary cultures of murine, feline, and human microglia and astrocytes

Recent studies have reported the detection of rabies viral antigens and virions in astrocytes and microglia of rabies-infected animals. As a first step toward understanding whether these glial cells may be involved in rabies virus replication, persistence, and/or pathogenesis, we explored their potential to be infected in vitro. Primary cultures of murine, feline, and human microglia and astrocytes were infected with several different rabies viruses: two unpassaged street virus isolates, a cell culture-adapted strain, and a mouse brain-passaged strain. Infection, as determined by immunofluorescence, was detected in 15 of the 16 (94%) virus-glial cell combinations. Replication of infectious virus, determined by infectivity assay, was detected in 7 of the 8 (88%) virus-cell combinations. These results show that astrocytes and microglia can be infected by rabies viruses, suggesting that they may have a potential role in disease, perhaps contributing to viral spread, persistence and/or neuronal dysfunction.