A1 Astrocytes Research Articles

Kynurenic acid blunts A1 astrocyte activation against neurodegeneration in HIV-associated neurocognitive disorders

Despite extensive astrocyte activation in patients suffering from HIV-associated neurocognitive disorders (HAND), little is known about the contribution of astrocytes to HAND neuropathology. Here, we report that the robust activation of neurotoxic astrocytes (A1 astrocytes) in the CNS promotes neuron damage and cognitive deficits in HIV-1 gp120 transgenic mice. Notably, knockout of α7 nicotinic acetylcholine receptors (α7nAChR) blunted A1 astrocyte responses, ultimately facilitating neuronal and cognitive improvement in the gp120tg mice. Furthermore, we provide evidence that Kynurenic acid (KYNA), a tryptophan metabolite with α7nAChR inhibitory properties, attenuates gp120-induced A1 astrocyte formation through the blockade of α7nAChR/JAK2/STAT3 signaling activation. Meanwhile, compared with gp120tg mice, mice fed with tryptophan showed dramatic improvement in cognitive performance, which was related to the inhibition of A1 astrocyte responses. These initial and determinant findings mark a turning point in our understanding of the role of α7nAChR in gp120-mediated A1 astrocyte activation, opening up new opportunities to control neurotoxic astrocyte generation through KYNA and tryptophan administration.

C3aR in astrocytes mediates post-thoracotomy pain by inducing A1 astrocytes in male rats

BackgroundAstrocyte activation, which is polarized into classical neurotoxic A1, neuroprotective A2, A-pan, etc., is thought to be involved in the transition from acute to chronic post-thoracotomy pain. The C3aR receptor associated with astrocyte-neuron and -microglia interactions is necessary for A1 astrocytes polarization. This study aimed to determine whether C3aR in astrocytes mediates post-thoracotomy pain by inducing A1 expression in a rat thoracotomy pain model. MethodsA rat thoracotomy pain model was employed. The mechanical withdraw threshold was measured to evaluate pain behavior. Lipopolysaccharide (LPS) was injected intraperitoneally to induce A1. Intrathecal injection of AAV2/9-rC3ar1 shRNA-GFAP was used to knock down in vivo C3aR expression in astrocytes. The expression of associated phenotypic markers before and after intervention was assessed by RT-PCR, western blot, co-immunofluorescence, and single-cell RNA sequencing. ResultsC3aR downregulation was found to inhibit LPS-induced A1 astrocytes activation, decrease the expression of C3aR, C3, and GFAP, which were activated from acute to chronic pain, and alleviate the mechanical withdrawal threshold and chronic pain incidence. In addition, more A2 astrocytes were activated in the model group that did not develop chronic pain. C3aR downregulation increased the number of A2 astrocytes upon LPS exposure. Knockdown of C3aR also decreased the activation of M1 microglia induced by LPS or thoracotomy. ConclusionsOur study confirmed that C3aR-induced A1 polarization contributes to chronic post-thoracotomy pain. Inhibition of A1 activation via C3aR downregulation increases anti-inflammatory A2 and decreases pro-inflammatory M1 activation, which may also be involved in the mechanism of chronic post-thoracotomy pain.

LPS Triggers Acute Neuroinflammation and Parkinsonism Involving NLRP3 Inflammasome Pathway and Mitochondrial CI Dysfunction in the Rat

Whether neuroinflammation leads to dopaminergic nigrostriatal system neurodegeneration is controversial. We addressed this issue by inducing acute neuroinflammation in the substantia nigra (SN) with a single local administration (5 µg/2 µL saline solution) of lipopolysaccharide (LPS). Neuroinflammatory variables were assessed from 48 h to 30 days after the injury by immunostaining for activated microglia (Iba-1 +), neurotoxic A1 astrocytes (C3 + and GFAP +), and active caspase-1. We also evaluated NLRP3 activation and Il-1β levels by western blot and mitochondrial complex I (CI) activity. Fever and sickness behavior was assessed for 24 h, and motor behavior deficits were followed up until day 30. On this day, we evaluated the cellular senescence marker β-galactosidase (β-Gal) in the SN and tyrosine hydroxylase (TH) in the SN and striatum. After LPS injection, Iba-1 (+), C3 (+), and S100A10 (+) cells were maximally present at 48 h and reached basal levels on day 30. NLRP3 activation occurred at 24 h and was followed by a rise of active caspase-1 (+), Il-1β, and decreased mitochondrial CI activity until 48 h. A significant loss of nigral TH (+) cells and striatal terminals was associated with motor deficits on day 30. The remaining TH (+) cells were β-Gal (+), suggesting senescent dopaminergic neurons. All the histopathological changes also appeared on the contralateral side. Our results show that unilaterally LPS-induced neuroinflammation can cause bilateral neurodegeneration of the nigrostriatal dopaminergic system and are relevant for understanding Parkinson's disease (PD) neuropathology.

Targeted Microglial Attenuation through Dendrimer-Drug Conjugates Improves Glaucoma Neuroprotection.

Retinal microglial/macrophage activation and optic nerve (ON) microglial/macrophage activation are glaucoma biomarkers and potential therapeutic targets for this blinding disease. We report targeting of activated microglia by PAMAM dendrimers in a rat glaucoma model and neuroprotection by N-acetylcysteine-conjugated dendrimer (D-NAC) conjugates in a post-injury rescue experiment. Intravitreally delivered fluorescently labeled dendrimer (D-Cy5) conjugates targeted and were retained in Iba-1-positive cells (90% at 7 days and 55% after 28 days) in the retina following intraocular pressure (IOP) elevation, while systemically delivered D-Cy5 targeted ON cells. A single intravitreal D-NAC dose given 1 week after IOP elevation significantly reduced transcription of pro-inflammatory (IL-6, MCP-1, IL-1β) and A1 astrocyte (Serping1, Fkbp5, Amigo2) markers and increased survival of retinal ganglion cells (39 ± 12%) versus BSS- (20 ± 15%, p = 0.02) and free NAC-treated (26 ± 14%, p = 0.15) eyes. These results highlight the potential of dendrimer-targeted microglia and macrophages for early glaucoma detection and as a neuroprotective therapeutic target.

The critical role of KLF4 in regulating the activation of A1/A2 reactive astrocytes following ischemic stroke

BackgroundWe have previously demonstrated that the expression of kruppel-like transcription factor-4 (KLF-4) is upregulated in astrocytes following acute ischemic stroke (AIS) and found that KLF4 confers vascular protection against cerebral ischemic injury. However, the functional role of KLF4 in astrocyte after AIS is far from clear.MethodsThe intrinsic relationship between KLF4 and A1/A2 reactive astrocytes and the impact of astrocytic KLF4 on the activation of A1/A2 subtype astrocytes were evaluated in middle cerebral artery occlusion (MCAO) mice and oxygen–glucose deprivation and restoration (OGD/R) astrocytes.ResultsOur results demonstrated that astrocytic KLF4 expression and complement C3-positive A1 and S100 calcium binding protein A10 (S100A10)-positive A2 astrocytes were induced in the ischemic penumbra following focal cerebral ischemia, and the time course of upregulation of astrocytic KLF4 correlated closely with the activation of A2 astrocytes. The dual immunofluorescent studies displayed that in the ischemic hemisphere, where the high levels of KLF4 were expressed, there were relatively low levels of C3 expressed in the reactive astrocytes and vice versa, but KLF4 was always co-stained well with S100A10. Mechanistic analyses revealed that astrocytic KLF4 inhibited the activation of A1 astrocyte but promoted A2 astrocyte polarization after OGD/R by modulating expressions of nuclear factor-kB.ConclusionsAstrocyte-derived KLF4 has a critical role in regulating the activation of A1/A2 reactive astrocytes following AIS.

Transplantation of A2 type astrocytes promotes neural repair and remyelination after spinal cord injury

BackgroundLimited progress in terms of an effective treatment for spinal cord injury (SCI) emphasizes the urgent need for novel therapies. As a vital central nervous system component, the resident astrocytes play crucial roles in regulating recovery after SCI. In this study, recovery after SCI was compared following the transplantation of either A1 or A2 astrocytes. A1 astrocytes are harmful as they upregulate the neurotoxic classical complement cascade genes. Conversely, A2 astrocytes are characterized as neuroprotective as they upregulate the production of many neurotrophic factors.MethodsWe used different supernatant obtained from microglia stimulated with lipopolysaccharide or interleukin-4 to generate A1 and A2 astrocytes. We detected the influence of astrocytes on neurons by co-culturing A1 and A2 astrocytes with neurons. We transplanted astrocytes into the lesion site of the spinal cord and assessed lesion progression, neural restoration, glia formation and locomotor recovery.ResultsAstrocytes were polarized into A1 and A2 phenotypes following culture in the supernatant obtained from microglia stimulated with lipopolysaccharide or interleukin-4, respectively. Furthermore, co-culturing A2 astrocytes with neurons significantly suppressed glutamate-induced neuronal apoptosis and promoted the degree of neuron arborization. Transplantation of these A2 astrocytes into the lesion site of the spinal cord of mice significantly improved motor function recovery, preserved spared supraspinal pathways, decreased glia scar deposition, and increased neurofilament formation at the site of injury compared to the transplantation of A1 astrocytes. Additionally, enhanced A2 astrocytes with potentially beneficial A2-like genes were also detected in the A2 group. Moreover, luxol fast blue staining and electron microscopy indicated increased preservation of myelin with organized structure after transplantation of A2 astrocytes than of A1 astrocytes.ConclusionsA2 astrocyte transplantation could be a promising potential therapy for SCI.Graphical -k_-1M1wXF49hQ9JfigvAZVideo abstract

Roles of prokineticin 2 in electroconvulsive shock-induced memory impairment via regulation of phenotype polarization in astrocytes

Electroconvulsive shock (ECT) is the most effective treatment for depression but can impair learning and memory. ECT is increasingly being shown to activate astrocytes and induce neuroinflammation, resulting in cognitive decline. Activated astrocytes can differentiate into two subtypes, A1-type astrocytes and A2-type astrocytes. Regarding cognitive function, neurotoxic A1 astrocytes and neuroprotective A2 astrocytes may exhibit opposite effects. Specifically, prokineticin 2 (PK2) functions as an essential mediator of inflammation and induces a selective A2-protective phenotype in astrocytes. This study aimed to clarify how PK2 promotes improved learning memory following electroconvulsive shock (ECS). As part of the study, rats were modeled using chronic unpredictable mild stress. Behavioral experiments were conducted to assess their cognitive abilities and depression-like behaviors. Western blot was used to determine the expression of PK2. Immunohistochemical and electron microscopy analyses of the hippocampal CA1 region were conducted to study the activation of astrocyte subtypes and synaptic ultrastructure, respectively. In this study, rats' spatial learning and memory impairment began to improve as activated A1-subtype astrocytes gradually decreased, and PK2 and A2 phenotype activation peaked on the third day after ECS. PKRA7 (PK2 antagonist) inhibits A2-type astrocyte activation partially and suppresses spatial learning and memory improvement. Collectively, our findings support that PK2 may induce a selective modulation of astrocytic polarization to a protective phenotype to promote learning and memory improvement after ECS

Daphnetin Improves Neuropathic Pain by Inhibiting the Expression of Chemokines and Inflammatory Factors in the Spinal Cord and Interfering with Glial Cell Polarization.

Neuropathic pain (NP) is a common pain disease that seriously affects the quality of life and physical and mental health of patients. Daphnetin is extracted from the Daphne giraldii Nitsche and has the structure of 7,8-dihydroxy coumarin. As a natural product, daphnetin displays a wide range of pharmacological activities, such as analgesia and anti-inflammatory activities, but whether it is able to improve NP through anti-inflammatory effects is unknown. Therefore, this paper intends to investigate the mechanism of daphnetin in improving NP rats affected by the intrathecal injection of tumor necrosis factor-α (TNF-α) from the perspective of anti-inflammation. Our results showed that daphnetin significantly improved hyperalgesia in NP rats. Daphnetin inhibited the activation and polarization of glial cells and neurons in the spinal cord of NP rats and reduced the expression of mRNA and protein of inflammatory factors and chemokine pairs in the spinal cord. Daphnetin inhibited the polarization of human microglia cell 3 (HMC3) cells and human glioma cells (U251) cells toward M1 microglia and A1 astrocytes, respectively, and induced the conversion of M1 microglia and A1 astrocytes to M2 microglia and A2 astrocytes, respectively. In conclusion, daphnetin ameliorates NP by inhibiting the expression of inflammatory factors and chemokines and the polarization of glial cells in the spinal cord of NP rats. This study provides a theoretical basis for the treatment of NP with daphnetin to expand the clinical application of daphnetin.

Blocking Two-Pore Domain Potassium Channel TREK-1 Inhibits the Activation of A1-Like Reactive Astrocyte Through the NF-κB Signaling Pathway in a Rat Model of Major Depressive Disorder

Major depressive disorder (MDD) refers to a widespread psychiatric disorder. Astrocytes play a pivotal role in regulating inflammation which is a well-acknowledged key component in depression pathogenesis. However, the effects of the neuroinflammation-inducing A1-like astrocytes on MDD are still unknown. TWIK-related K+ channel 1 (TREK-1) has been demonstrated to regulate the action of antidepressants. Nevertheless, its mechanisms and effects on A1-like astrocyte stimulation in MDD are not clear. Therefore, we conducted in vivo and in vitro experiments using TREK-1 specific inhibitor spadin. In vivo, rats were subjected to a 6-week chronic unpredictable mild stress (CUMS) followed by spadin treatment. Behavioral tests were employed to surveil depressive-like behaviors. Hippocampal proteomic analysis was carried out with the purpose of identifying differentially expressed proteins after CUMS and spadin treatments. In vitro, astrocyte-conditioned medium and spadin were used to treat rat astrocyte cell line. The activated microglia, inflammatory factors, A1 astrocyte markers, and activated nuclear factor kappa B (NF-κB) pathway were later analyzed using immunofluorescence, western blot, and RT-qPCR. Our findings indicated that blockage of TREK-1 reduced CUMS-induced depressive-like behavior in rats, inhibited the microglial stimulation, reduced inflammatory factor levels, and suppressed the activation of A1-like reactive astrocytes in the hippocampus. We also verified that the suppression of A1-like astrocytes by spadin necessitated the NF-κB pathway. According to the findings, blocking TREK-1 inhibited the activation of A1-like reactive astrocytes via the NF-κB signaling pathway in MDD. Our study preliminarily identifies a novel antidepressant mechanism of TREK-1 action and provides a therapeutic path for MDD.

Total flavones of Rhododendron induce the transformation of A1/A2 astrocytes via promoting the release of CBS-produced H2S

BackgroundWe previously found that total flavones of Rhododendron (TFR) protected against the cerebral ischemia/reperfusion (I/R) injury. But the detailed mechanism is not clear. Recent research revealed that reactive astrocytes were divided into A1 and A2 phenotypes for their morphological and functional remodeling and neurotoxic- vs-neuroprotective effect on the injury of the central nervous system (CNS). PurposeThe present study was undertaken to explore the role and mechanism of TFR on the phenotypic change of astrocytes following cerebral I/R in vivo and oxygen glucose deprivation/re-oxygenation (OGD/R) in vitro. Study design and methodsWe tested the expression of astrocytes marker glial fibrillary acidic protein (GFAP), A1 astrocytes marker C3 protein and A2 astrocytes marker S100a10, as well as the BrdU/GFAP-positive cells, GFAP/S100a10-positive cells and GFAP/C3-positive cells in mice hippocampal tissues to evaluate the phenotypic change of astrocytes. Besides, we assessed the change of astrocyte phenotypes following OGD/R in vitro. ResultsWe found that mice cerebral I/R promoted the astrocytes proliferation of both A1 and A2 phenotypes in hippocampal tissues. While treatment with TFR could promote the proliferation of A2 astrocytes but inhibit the A1 astrocytes proliferation in mice hippocampal tissues, suggesting that TFR could accelerate the astrocytes transformation into A2 subtype following cerebral I/R. Whereas, in OGD/R model of astrocytes, we found that TFR inhibited the proliferation of both A1 and A2 astrocytes. Besides, we found that TFR could up-regulate the release of cystathionine β-synthase (CBS)-produced hydrogen sulfide (H2S) and inhibit RhoA/Rho kinase pathway, and revealed that the inhibitory effect of TFR on astrocytes proliferation could be blocked by aminooxyacetic acid (AOAA), an CBS inhibitor. Furthermore, TFR could ameliorate the mice cerebral I/R injury and the OGD/R-induced astrocytic damage. ConclusionThese findings suggested that TFR could affect the transformation of astrocytes subtypes following cerebral I/R, which may be related to up-regulation of CBS-produced H2S and subsequent inhibition of RhoA/ROCK pathway.

Neurotoxic A1 astrocytes promote neuronal ferroptosis via CXCL10/CXCR3 axis in epilepsy

Epilepsy is a common neurological disorder with a complex etiology. Ferroptosis, a new form of programmed cell death, is characterized by the accumulation of lipid peroxides and associated with seizures. However, the underlying mechanism of ferroptosis in epilepsy remains elusive. Here, we found that GPX4-GSH-dependent neuronal ferroptosis was detected in epileptic mice, which was attenuated with ferroptosis inhibitors. Moreover, activated neurotoxic A1 astrocytes facilitated seizure-related neuronal ferroptosis in epileptic brains. Inhibition of ferroptosis blocked A1 astrocyte-induced neurotoxicity. A1 astrocyte-secreted CXCL10 enhanced STAT3 phosphorylation but suppressed SLC7A11 in neurons via CXCR3, leading to ferroptosis-associated lipid peroxidation in a GPX4-dependent manner. This was in line with clinical findings, showing a significant correlation between neuronal ferroptosis and A1 astrocytes in epileptic patients. In summary, the present data show that A1 astrocyte-induced neuronal ferroptosis contributes to the pathogenesis of epilepsy, which offers a novel therapeutic target for precision medicine.

Arterial Baroreflex Dysfunction Promotes Neuroinflammation by Activating the Platelet CD40L/Nuclear Factor Kappa B Signaling Pathway in Microglia and Astrocytes

Arterial baroreflex (ABR) dysfunction has previously been associated with neuroinflammation, the most common pathological feature of neurological disorders. However, the mechanisms mediating ABR dysfunction-induced neuroinflammation are not fully understood. In the present study, we investigated the role of platelet CD40 ligand (CD40L) in neuroinflammation in an in vivo model of ABR dysfunction, and microglia and astrocyte activation in vitro. ABR dysfunction was induced in Sprague‒Dawley rats by sinoaortic denervation (SAD). We used ELSA and immunofluorescence to assess the effect of platelet CD40L on glial cell polarization and the secretion of inflammatory factors. By flow cytometry, we found that rats subjected to SAD showed a high level of platelet microaggregation and upregulation of CD40L on the platelet surface. The promotion of platelet invasion and accumulation was also observed in the brain tissues of rats subjected to SAD. In the animal model and cultured N9 microglia/C6 astrocytoma cells, platelet CD40L overexpression promoted neuroinflammation and activated M1 microglia, A1 astrocytes, and the nuclear factor kappa B (NFκB) signaling pathway. These effects were partially blocked by inhibiting platelet activity with clopidogrel or inhibiting CD40L-mediated signaling. Our results suggest that during ABR dysfunction, CD40L signaling in platelets converts microglia to the M1 phenotype and astrocytes to the A1 phenotype, activating NFκB and resulting in neuroinflammation. Thus, our study provides a novel understanding of the pathogenesis of ABR dysfunction-induced neuroinflammation and indicates that targeting platelet CD40L is beneficial for treating central nervous system (CNS) disorders associated with ABR dysfunction.

Astrocyte-derived exosome-transported GJA1-20k attenuates traumatic brain injury in rats.

Astrocyte-derived exosome-transported GJA1-20k attenuates traumatic brain injury in rats.

Peroxiredoxin 6 Regulates Glia Toxicity in Tau Mediated Neurodegeneration

AbstractBackgroundIn Alzheimer’s disease (AD) neurons, which accumulate hyperphosphorylated tau (p‐tau) are associated with neurodegenerative phenotype microglia (MGnD) and A1 neurotoxic astrocytes. MGnD display reduced ability to phagocytose p‐tau aggregates and neuronal remnants, while their pro‐inflammatory character furthers p‐tau accumulation and neuronal demise. Likewise, A1 astrocytes lose their neuron‐supporting function and promote neurodegeneration. Importantly, MGnD and A1 astrocytes reciprocally stimulate their pathological phenotypes. Factors protecting astrocytes form A1 phenotype transformation are unknown. In this work we explored the role of peroxiredoxin (PRDX) 6 in tau mediated neurodegeneration. PRDX6 is an enzymatic protein which in the CNS is unique to astrocytes. It possesses independent glutathione peroxidase and phospholipase 2 enzymatic activities, which confer ability to repair oxidatively damaged cell membranes and cell‐to‐cell signaling.Method MAPT P301S mutant mice (PS19/Prdx6 +/+) were once crossed to Prdx6 ‐/‐ mice and mice homozygous for the knock‐in of the Prdx6 129X1/SvJ allele overexpressing wild‐type PRDX6 to generate novel PS19/Prdx6 +/‐ and PS19/Prdx6 Tg lines, respectively. Eight weeks old PS19/Prdx6 +/‐, PS19/Prdx6 +/+, and PS19/Prdx6 Tg animals show 0.4:1:2 ratio of Prdx6 brain mRNA level, while levels of hTau and Gfap mRNA remain unchanged. Male mice were neuropathologically characterized at the age of 9.5 months.Result PS19/Prdx6 +/‐ mice feature increased hippocampal atrophy and ventricular enlargement and greater p‐tau accumulation compared to PS19/Prdx6 +/+ mice. Contrariwise, PS19/Prdx6 Tg animals show attenuated brain atrophy and p‐tau accumulation. The GFAP+ load used as a marker of global astrocytic activation and the C3+/GFAP+ ratio, used as a surrogate A1 phenotype marker, vary inversely with the Prdx6 gene dose. Likewise, the load of IBA1+ microglia vary inversely with the Prdx6 gene dose, while the CD68+/IBA1+ index, which determines relative microglia phagocytic activity, directly correlates with the Prdx6 expression.ConclusionExacerbation of the pathological phenotype in PS19/Prdx6 +/‐ mice reveals a neuroprotective effect of PRDX6 in tau mediated neurodegeneration, while attenuation of pathology in PS19/Prdx6 Tg mice suggests a merit of therapeutic PRDX6 upregulation. PRDX6 endows astrocytes with resistance to A1 phenotype transition. Astrocytic PRDX6 also reprograms microglia by downregulating their global activation level and selectively promoting phagocytic properties. Comparative analysis of astrocytic and microglia transcriptomic markers across PS19/Prdx6 +/‐, PS19/Prdx6 +/+, and PS19/Prdx6 Tg genotypes is underway.

Knockout of transient receptor potential ankyrin 1 (TRPA1) modulates the glial phenotype and alleviates perihematomal neuroinflammation after intracerebral hemorrhage in mice via MAPK/NF-κB signaling.

The objective is to explore the role of astrocytic transient receptor potential ankyrin 1 (TRPA1) in glial phenotype transformation in neuroinflammation after intracerebral hemorrhage (ICH). Wild-type astrocytes and TRPA1-/- astrocytes were subjected to 6-h hemin treatment, and the calcium ions and transcriptome sequencing were assessed. A mouse autologous blood injection ICH model was established to evaluate the proliferation and phenotypes of astrocytes and microglia around the hematoma. The neuroinflammation and behavioral performance of wild-type ICH mice and TRPA1-/- ICH mice were assessed. Knockout of astrocytic TRPA1 decreased calcium ions of astrocytes after hemin treatment in-vitro, and microglial and astrocytes around the hematoma proliferated after the ICH model. Furthermore, RNA-sequencing (RNA-seq), immunofluorescence, and Western blotting results showed that the activated astrocytes transformed into the A2 phenotype in TRPA1-/- ICH mice. The 'ameboid' microglia were observed around the hematoma in TRPA1-/- ICH mice. The proliferation of A2 astrocytes and 'ameboid' microglia ameliorated the neuroinflammation after ICH. The inflammatory response was reduced by inhibiting the mitogen-activated protein kinase/nuclear factor kappa-B signaling pathway, and neurologic deficits were improved in TRPA1-/- ICH mice compared with wild-type ICH mice. This research suggests that astrocytic TRPA1 is a new therapeutic target to rescue neuroinflammation by modulating the glial phenotype after ICH.

Inhibition of A1 Astrocytes and Activation of A2 Astrocytes for the Treatment of Spinal Cord Injury.

Spinal cord injury (SCI) is a serious injury to the central nervous system that causes significant physical and psychological trauma to the patient. SCI includes primary spinal cord injuries and secondary spinal cord injuries. The secondary injury refers to the pathological process or reaction after the primary injury. Although SCI has always been thought to be an incurable injury, the human nerve has the ability to repair itself after an injury. However, the reparability is limited because glial scar formation impedes functional recovery. There is a type of astrocyte that can differentiate into two forms of reactive astrocytes known as 'A1' and 'A2' astrocytes. A1 astrocytes release cytotoxic chemicals that cause neurons and oligodendrocytes to die and perform a harmful role. A2 astrocytes can produce neurotrophic factors and act as neuroprotectors. This article discusses ways to block A1 astrocytes while stimulating A2 astrocytes to formulate a new treatment for spinal cord injury.

The role and mechanism of NLRP3 inflammasome-mediated astrocyte activation in dehydrocorydaline against CUMS-induced depression.

Background: Depression is a common and potentially life-threatening mental illness, and currently, there is a lack of effective treatment. It has been reported that dehydrocorydaline (DHC) can inhibit monoamine transporter uptake in depressed CUMS mice, but more possible mechanisms of action remain to be further studied. Methods: C57BL/6 mice were exposed to chronic unpredictable mild stress (CUMS) for five consecutive weeks. The mice were administrated with dehydrocorydaline or fluoxetine (FLU) for four consecutive weeks. Behavioral tests including sucrose preference test (SPT), tail suspension test (TST), and forced swimming test (FST) were applied. In parallel, hematoxylin and eosin (H&E) staining and Nissl staining were used to explore the effect of DHC on pathological changes in the hippocampus. The concentrations of depression-related factors (5-HT and DA) and inflammatory factors (TNF-α, IL-6, and IL-1β) in the hippocampus and serum were assessed by ELISA assay. NLRP3 inflammasome pathway-related proteins (NLRP3, IL-18, IL-1 IL-1α, and caspase-1) were detected by western blot. The activation of microglia and astrocytes was subjected to immunofluorescent staining. Additionally, microglia were treated with DHC (100mg/L) for 24h following incubation with 100ng/ml LPS for 12h. ov-NC or ov-NLRP3 plasmid was transfected into microglia 6h before LPS induction for exploring the effect of NLRP3 overexpression on DHC-inhibited microglia activation. Then, conditioned media of microglia were collected from each group, followed by intervention of astrocytes for 24h to explore the effect of NLRP3 overexpression of microglia on astrocyte activation. Results: In vivo administration of DHC was found to ameliorate depressive-like behaviors and attenuate neuron damage of CUMS mice. DHC increased neurotransmitter concentration, reduced the proinflammatory factor levels, attenuated NLRP3 inflammasome activation, and decreased A1 astrocyte and microglia activation in the hippocampus of CUMS mice. Furthermore, in vivo results showed that activated microglia induced activation of A1 astrocytes but not A2 astrocytes. Conclusion: Taken together, we provided evidence that DHC exhibited antidepressive effects on CUMS mice possibly via NLRP3 inflammasome-mediated astrocyte activation.

Mitochondrial glutamine transporter SLC1A5_var, a potential target to suppress astrocyte reactivity in Parkinson’s Disease

SLC1A5 variant (SLC1A5_var) is identified as a mitochondrial glutamine transporter in cancer cells recently. However, the role of SLC1A5_var in Parkinson’s disease (PD) is completely unknown. Here, we found the significant downregulation of SLC1A5_var in astrocytes and midbrain of mice treated with MPTP/MPP+ and LPS. Importantly, overexpression of SLC1A5_var ameliorated but knockdown of SLC1A5_var exacerbated MPTP/MPP+- and LPS-induced mitochondrial dysfunction. Consequently, SLC1A5_var provided beneficial effects on PD pathology including improvement of PD-like motor symptoms and rescue of dopaminergic (DA) neuron degeneration through maintaining mitochondrial energy metabolism. Moreover, SLC1A5_var reduced astrocyte reactivity via inhibition of A1 astrocyte conversion. Further investigation demonstrated that SLC1A5_var restrained the secretion of astrocytic pro-inflammatory cytokines by blunting TLR4-mediated downstream pathways. This is the first study to prove that astrocytic SLC1A5_var inhibits neuroinflammation, and rescues the loss of DA neurons and motor symptoms involved in PD progression, which provides a novel target for PD treatment.

Bilirubin Induces A1-Like Reactivity of Astrocyte.

Astrocytes play an important role in the pathogenesis of bilirubin neurotoxicity, and activated astrocytes might be potential mediators of neuroinflammation processes contributing to neuronal cell death and tissue injury. Recent studies have reported that activated microglia induce two types of reactive astrocytes. A1 astrocytes could cause neuronal death and synaptic damage, as well as impaired phagocytosis. Therefore, the purpose of this study was to investigate whether unconjugated bilirubin (UCB)-induced A1-like astrocytes take on a neuroinflammation type and the underlying regulatory mechanisms. In this study, primary cortical astrocytes were treated with UCB in vitro. We detected the expression of complement component 3 (C3), S100 calcium binding protein A10 (S100A10), nuclear factor kappa B (NF-κB), NLR family pyrin domain containing 3 (NLRP3), activated caspase-1, gasdermin D N-terminal (GSDMD-N), PSD95, synaptophysin (SYP), the transcription levels of interleukin (IL)-1β and IL-18, and the survival rate of astrocytes after UCB treatment. The results showed that an increase in C3 was accompanied by a decrease in S100A10, and that A1-like astrocytes were functionally expressed after UCB stimulation. Meanwhile, the NF-κB and caspase-1 pathways were activated after UCB stimulation. After adding the NF-κB-specific inhibitor trans-activator of transcriptional-NEMO-binding domain (TAT-NBD) and caspase-1 specific inhibitor VX-765, the survival rate of astrocytes and neurons increased, whereas the protein expression of C3, NF-κB, NLRP3, activated caspase-1, and GSDMD-N decreased, and the mRNA levels of IL-1β and IL-18 reduced. Thus, we concluded that UCB stimulates the activation of A1-like astrocytes. Inhibition of NF-κB and caspase-1 alleviated A1-like astrocytes and exerted anti-inflammatory protective effects.

TPM1 mediates inflammation downstream of TREM2 via the PKA/CREB signaling pathway

BackgroundMicroglia, the innate immune cells in the central nervous system, play an essential role in brain homeostasis, neuroinflammation and brain infections. Dysregulated microglia, on the other hand, are associated with neurodegenerative diseases, yet the mechanisms underlying pro-inflammatory gene expression in microglia are incompletely understood.MethodsWe investigated the role of the actin-associated protein tropomyosin 1 (TPM1) in regulating pro-inflammatory phenotype of microglia in the retina by using a combination of cell culture, immunocytochemistry, Western blot, qPCR, TUNEL, RNA sequencing and electroretinogram analysis. TREM2−/− mice were used to investigate whether TPM1 regulated pro-inflammatory responses downstream of TREM2. To conditionally deplete microglia, we backcrossed CX3CR1CreER mice with Rosa26iDTR mice to generate CX3CR1CreER:Rosa26iDTR mice.ResultsWe revealed a vital role for TPM1 in regulating pro-inflammatory phenotype of microglia. We found that TPM1 drove LPS-induced inflammation and neuronal death in the retina via the PKA/CREB pathway. TPM1 knockdown ameliorated LPS-induced inflammation in WT retinas yet exaggerated the inflammation in TREM2−/− retinas. RNA sequencing revealed that genes associated with M1 microglia and A1 astrocytes were significantly downregulated in LPS-treated WT retinas but upregulated in LPS-treated TREM2−/− retinas after TPM1 knockdown. Mechanistically, we demonstrated that CREB activated by TPM1 knockdown mediated anti-inflammatory genes in LPS-treated WT retinas but pro-inflammatory genes in LPS-treated TREM2−/− retinas, suggesting a novel role for TREM2 as a brake on TPM1-mediated inflammation. Furthermore, we identified that TPM1 regulated inflammation downstream of TREM2 and in a microglia-dependent manner.ConclusionsWe demonstrate that TPM1 mediates inflammation downstream of TREM2 via the PKA/CREB signaling pathway. Our findings suggest that TPM1 could be a potential target for therapeutic intervention in brain diseases.