Type-2 Astrocytes Research Articles

A stroke organoids-multiomics platform to study injury mechanism and drug response

Stroke is one of the top causes of death and disability worldwide, and its pathogenesis and mechanism have not been fully elucidated. Several agents have shown protective effects against stroke in animal models; however, few studies have shown obvious effects in clinical practice. This might be due to differences in brain structure and physiological function between humans and rodents. In this study, we established a hypoxic stroke model in human-induced pluripotent stem cell (hiPSC)-derived brain organoids to simulate the hypoxic stroke caused by ischemia. Then, by combining proteomics, single-cell transcriptome analysis, and histopathological analysis, a significant increase of three types of astrocytes was identified and they showed different responses to hypoxic environments; also the main type of astrocyte that cause brain tissue hyperplasia in ischemia brains was identified. In addition, the cortical excitatory neurons had signs of apoptosis and aging after hypoxia both in vivo and in vitro. Most importantly, we identified a possible role of a traditional Chinese medicine formula called DengZhanShengMai capsule in ischemic and hypoxic stroke treatment through regulation of lipid metabolism related biological functions. These results indicate that the combination of brain organoids and multiomics method is helpful for developing a new strategy to direct study stroke, and could provide a promising platform for drug screening of stroke in the future.

Morphological and physiological features of human cerebral cortical astrocytes in regenerative medicine: a narrative review

Astrocytes are essential for various functions in the brain, including regulating synaptic transmission, maintaining ion homeostasis, and supporting neuronal network activity. Despite over a century of recognition that human astrocytes differ morphologically from those of other mammals, detailed functional studies have been limited due to challenges in obtaining live human brain tissue. This narrative review revisits recent findings on the morphological and physiological properties of human astrocytes, particularly those focusing on cortical astrocytes. I summarize the main anatomical and functional features of the different types of human astrocytes and briefly compare human astrocytes with what is known about astrocytes in mice and/or primates. I greatly summarize the physiological properties of human astrocytes, with emphasis on their intrinsic properties, potassium ion uptake and syncytium connectivity, emphasizing recent advances that have enhanced our understanding of astrocytic functionality in the human brain and their possible role in regenerative medicine.

HPSC-Derived Astrocytes at the Forefront of Translational Applications in Neurological Disorders.

Astrocytes, the most abundant glial cell type in the brain, play crucial roles in maintaining homeostasis within the central nervous system (CNS). Impairment or abnormalities of typical astrocyte functions in the CNS serve as a causative or contributing factor in numerous neurodevelopmental, neurodegenerative, and neuropsychiatric disorders. Currently, disease-modeling and drug-screening approaches, primarily focused on human astrocytes, rely on human pluripotent stem cell (hPSC)-derived astrocytes. However, it is important to acknowledge that these hPSC-derived astrocytes exhibit notable differences across studies and when compared to their in vivo counterparts. These differences may potentially compromise translational outcomes if not carefully accounted for. This review aims to explore state-of-the-art in vitro models of human astrocyte development, focusing on the developmental processes, functional maturity, and technical aspects of various hPSC-derived astrocyte differentiation protocols. Additionally, it summarizes their successful application in modeling neurological disorders. The discussion extends to recent advancements in the large-scale production of human astrocytes and their application in developing high-throughput assays conducive to therapeutic drug discovery.

Intrinsic ecto-5'-Nucleotidase/A1R Coupling may Confer Neuroprotection to the Cerebellum in Experimental Autoimmune Encephalomyelitis.

Experimental autoimmune encephalomyelitis (EAE) is widely used animal model of multiple sclerosis (MS). The disease is characterized by demyelination and neurodegeneration triggered by infiltrated autoimmune cells and their interaction with astrocytes and microglia. While neuroinflammation is most common in the spinal cord and brainstem, it is less prevalent in the cerebellum, where it predisposes to rapid disease progression. Because the induction and progression of EAE are tightly regulated by adenosinergic signaling, in the present study we compared the adenosine-producing and -degrading enzymes, ecto-5'-nucleotidase (eN/CD73) and adenosine deaminase (ADA), as well as the expression levels of adenosine receptors A1R and A2AR subtypes in nearby areas around the fourth cerebral ventricle-the pontine tegmentum, the choroid plexus (CP), and the cerebellum. Significant differences in histopathological findings were observed between pontine tegmentum and cerebellum on the same horizontal section level. Reactive astrogliosis and massive infiltration of CD4 + cells and macrophages in CP and pontine tegmentum resulted in local demyelination. In cerebellum, there was no evidence of infiltrates, microgliosis and neuroinflammation at the same sectional level. In addition, Bergman glia showed no signs of reactive gliosis. As for adenosinergic signaling, significant upregulation of eN/CD73 was observed in all areas studied, but in association with different adenosine receptor subtypes. In CP and pons, overexpression of eN/CD73 was coupled with induction of A2AR, whereas in cerebellum, a modest increase in eN/CD73 in resident Bergman glia was accompanied by a strong induction of A1R in the same type of astrocytes. Thus, the presence of specialized astroglia and intrinsic differences in adenosinergic signaling may play a critical role in the differential regional susceptibility to EAE inflammation.

KYNA Ameliorates Glutamate Toxicity of HAND by Enhancing Glutamate Uptake in A2 Astrocytes.

Reactive astrocytes are key players in HIV-associated neurocognitive disorders (HAND), and different types of reactive astrocytes play opposing roles in the neuropathologic progression of HAND. A recent study by our group found that gp120 mediates A1 astrocytes (neurotoxicity), which secrete proinflammatory factors and promote HAND disease progression. Here, by comparing the expression of A2 astrocyte (neuroprotective) markers in the brains of gp120 tgm mice and gp120+/α7nAChR-/- mice, we found that inhibition of alpha 7 nicotinic acetylcholine receptor (α7nAChR) promotes A2 astrocyte generation. Notably, kynurenine acid (KYNA) is an antagonist of α7nAChR, and is able to promote the formation of A2 astrocytes, the secretion of neurotrophic factors, and the enhancement of glutamate uptake through blocking the activation of α7nAChR/NF-κB signaling. In addition, learning, memory and mood disorders were significantly improved in gp120 tgm mice by intraperitoneal injection of kynurenine (KYN) and probenecid (PROB). Meanwhile, the number of A2 astrocytes in the mouse brain was significantly increased and glutamate toxicity was reduced. Taken together, KYNA was able to promote A2 astrocyte production and neurotrophic factor secretion, reduce glutamate toxicity, and ameliorate gp120-induced neuropathological deficits. These findings contribute to our understanding of the role that reactive astrocytes play in the development of HAND pathology and provide new evidence for the treatment of HAND via the tryptophan pathway.

Morphological and electrophysiological characterization of a novel displaced astrocyte in the mouse retina.

Astrocytes throughout the central nervous system are heterogeneous in both structure and function. This diversity leads to tissue-specific specialization where morphology is adapted to the surrounding neuronal circuitry, as seen in Bergman glia of the cerebellum and Müller glia of the retina. Because morphology can be a differentiating factor for cellular classification, we recently developed a mouse where glial-fibrillary acidic protein (GFAP)-expressing cells stochastically label for full membranous morphology. Here we utilize this tool to investigate whether morphological and electrophysiological features separate types of mouse retinal astrocytes. In this work, we report on a novel glial population found in the inner plexiform layer and ganglion cell layer which expresses the canonical astrocyte markers GFAP, S100β, connexin-43, Sox2 and Sox9. Apart from their retinal layer localization, these cells are unique in their radial distribution. They are notably absent from the mid-retina but are heavily concentrated near the optic nerve head, and to a lesser degree the peripheral retina. Additionally, their morphology is distinct from both nerve fiber layer astrocytes and Müller glia, appearing more similar to amacrine cells. Despite this structural similarity, these cells lack protein expression of common neuronal markers. Additionally, they do not exhibit action potentials, but rather resemble astrocytes and Müller glia in their small amplitude, graded depolarization to both light onset and offset. Their structure, protein expression, physiology, and intercellular connections suggest that these cells are astrocytic, displaced from their counterparts in the nerve fiber layer. As such, we refer to these cells as displaced retinal astrocytes.

Disease-Associated Neurotoxic Astrocyte Markers in Alzheimer Disease Based on Integrative Single-Nucleus RNA Sequencing

Alzheimer disease (AD) is an irreversible neurodegenerative disease, and astrocytes play a key role in its onset and progression. The aim of this study is to analyze the characteristics of neurotoxic astrocytes and identify novel molecular targets for slowing down the progression of AD. Single-nucleus RNA sequencing (snRNA-seq) data were analyzed from various AD cohorts comprising about 210,654 cells from 53 brain tissue. By integrating snRNA-seq data with bulk RNA-seq data, crucial astrocyte types and genes associated with the prognosis of patients with AD were identified. The expression of neurotoxic astrocyte markers was validated using 5 × FAD and wild-type (WT) mouse models, combined with experiments such as western blot, quantitative real-time PCR (qRT-PCR), and immunofluorescence. A group of neurotoxic astrocytes closely related to AD pathology was identified, which were involved in inflammatory responses and pathways related to neuron survival. Combining snRNA and bulk tissue data, ZEP36L, AEBP1, WWTR1, PHYHD1, DST and RASL12 were identified as toxic astrocyte markers closely related to disease severity, significantly elevated in brain tissues of 5 × FAD mice and primary astrocytes treated with Aβ. Among them, WWTR1 was significantly increased in astrocytes of 5 × FAD mice, driving astrocyte inflammatory responses, and has been identified as an important marker of neurotoxic astrocytes. snRNA-seq analysis reveals the biological functions of neurotoxic astrocytes. Six genes related to AD pathology were identified and validated, among which WWTR1 may be a novel marker of neurotoxic astrocytes.

The Diverse Roles of Reactive Astrocytes in the Pathogenesis of Amyotrophic Lateral Sclerosis.

Astrocytes displaying reactive phenotypes are characterized by their ability to remodel morphologically, molecularly, and functionally in response to pathological stimuli. This process results in the loss of their typical astrocyte functions and the acquisition of neurotoxic or neuroprotective roles. A growing body of research indicates that these reactive astrocytes play a pivotal role in the pathogenesis of amyotrophic lateral sclerosis (ALS), involving calcium homeostasis imbalance, mitochondrial dysfunction, abnormal lipid and lactate metabolism, glutamate excitotoxicity, etc. This review summarizes the characteristics of reactive astrocytes, their role in the pathogenesis of ALS, and recent advancements in astrocyte-targeting strategies.

The identification of a Distinct Astrocyte Subtype that Diminishes in Alzheimer's Disease.

Alzheimer's disease (AD) is characterized by the presence of two hallmark pathologies: the accumulation of Amyloid beta (Aβ) and tau proteins in the brain. There is a growing body of evidence suggesting that astrocytes, a type of glial cell in the brain, play crucial roles in clearing Aβ and binding to tau proteins. However, due to the heterogeneity of astrocytes, the specific roles of different astrocyte subpopulations in response to Aβ and tau remain unclear. To enhance the understanding of astrocyte subpopulations in AD, we investigated astrocyte lineage cells based on single-nuclei transcriptomic data obtained from both human and mouse samples. We characterized the diversity of astrocytes and identified global and subpopulation-specific transcriptomic changes between control and AD samples. Our findings revealed the existence of a specific astrocyte subpopulation marked by low levels of GFAP and the presence of AQP4 and CD63 expression, which showed functional enrichment in Aβ clearance and tau protein binding, and diminished in AD. We verified this type of astrocytes in mouse models and in AD patient brain samples. Furthermore, our research also unveiled significant alterations of the ligand-receptor interactions between astrocytes and other cell types. These changes underscore the complex interplay between astrocytes and neighboring cells in the context of AD. Overall, our work gives insights into astrocyte heterogeneity in the context of AD and reveals a distinct astrocyte subpopulation that holds potential for therapeutic interventions in AD. Targeting specific astrocyte subpopulations may offer new avenues for the development of novel treatments for AD.

Diagnostic reactive astrogliosis biomarkers in Alzheimer´s disease continuum

AbstractBackgroundThe Alzheimer’s disease (AD) biomarker field is moving rapidly. Creating a platform where multi‐PET tracer approaches and various fluid biomarkers with discriminative power in the early pathological stages could provide deeper insight into the role of reactive astrogliosis in the AD continuum. Accumulating data indicates that reactive astrogliosis may play a critical role in the early stages and, perhaps, precedes other pathological hallmarks of AD. Different PET tracers for imaging reactive astrogliosis are now available along with plasma GFAP showing a direct correlation with increased brain amyloid‐PET. We also propose that alpha‐7‐nicotinic acetylcholine receptors (α7nAChRs) might be early modulators of reactive astrogliosis and Aβ‐pathology in AD. New α7nAChRs‐PET‐tracers might be promising future new biomarkers of reactive astrogliosis with potential early diagnostic properties.MethodTranslational molecular imaging studies including in vivo multimodal PET investigations ([11C]‐deprenyl, [11C]‐PIB, [18F]‐Flutemematol, [18F]‐FDG, [18F]‐RO‐948), MRI, plasma GFAP analyses in control, presymptomatic ADAD, MCI to AD dementia and in vitro PET tracer binding studies (deprenyl, SMBT‐1, and BU99008) in postmortem brains using small/large section‐autoradiography and tissue‐homogenates.ResultWe hypothesize from our in vivo PET/in vitro brain imaging translational/clinical studies a ‘first and second wave of reactive astrogliosis’ with distinct close‐loop relationships with other pathological biomarkers across AD continuum. Validation of newly developed PET‐tracers BU99008 and SMBT‐1 for mapping and visualizing reactive astrogliosis in the brain demonstrated multiple binding properties in AD brain and highlighted the crucial need of multi‐PET tracer approach for understanding the complexity of reactive astrogliosis in AD. We have observed a significant positive correlation between plasma GFAP levels and [18F]‐flutemetamol binding in patients undergoing memory assessment. In presymtomatic ADAD patients, high [11C] deprenyl binding is observed earlier in the disease evolution than increase in plasma GFAP levels following a divergent direction. This clearly suggests plasma GFAP as a later biomarker than [11C]‐deprenyl in AD trajectory, possibly reflecting different types of reactive astrocytes at different stages of AD.ConclusionIt’s an exciting time for the AD field with several new biomarkers/PET‐tracers for reactive astrogliosis, which will improve our understanding of underlying astrocytic complexity and add power to the existing diagnostic criteria in AD.

Deficits in mitochondrial function and glucose metabolism seen in sporadic and familial Alzheimer’s disease derived Astrocytes are ameliorated by increasing hexokinase 1

AbstractBackgroundAstrocytes have multiple roles including providing neurons with metabolic substrates and maintaining neurotransmitters at neuronal synapses. Astrocyte glucose metabolism plays a key role in learning and memory with astrocytic glycogen a key substrate supporting memory encoding. The homeostatic role the astrocyte provides for neurons leads to metabolic demands, meaning that abnormalities in the function of astrocyte mitochondria and glycolysis could affect this relationship. Changes to cellular metabolism are seen early in Alzheimer’s disease (AD). Understanding cellular metabolism changes in AD astrocytes could be exploited as a new biomarker or synergistic therapeutic agent when combined with anti‐amyloid treatments in AD.MethodsIn this project, we characterised mitochondrial and glycolytic dysfunction in astrocytes derived from patients with sporadic (n = 6) and familial (PSEN1, n = 3) AD, and associated controls (n = 9). Astrocytes were derived using direct reprogramming technology. Astrocyte metabolic outputs; ATP, and extracellular lactate levels were measured using luminescent and fluorescent protocols. Mitochondrial respiration and glycolytic function were measured using a Seahorse XF Analyzer. Hexokinase deficits identified where corrected by transfecting astrocytes with an adenovirus viral vector containing the hexokinase 1 gene.ResultsIn sAD astrocytes a 20% reduction (p = 0.05) and in fAD a 48% (p<0.01) reduction in total cellular ATP was seen. A 44% reduction (p<0.05), and 80% reduction in Mitochondrial spare capacity was seen in sAD and fAD respectively. Reactive oxygen species (ROS) where increased in both AD astrocyte types (p = 0.05). Mitochondrial complex I and II was significantly increased in sAD (p<0.05) but not in fAD. Astrocyte glycolytic reserve and extracellular lactate was significantly reduced when compared to controls in both sAD and fAD (p<0.05). We identified that astrocytes had a deficit in the glycolytic pathway enzyme hexokinase, and that correcting this deficit restored total cellular ATP levels, extracellular lactate and reduced ROS in sAD but not fAD astrocytes.ConclusionAD astrocytes have abnormalities in functional capacity of mitochondria and the process of glycolysis. These deficits are likely to impede metabolic support for neurons. These functional deficits can be improved by correcting hexokinase deficits. This suggests that hexokinase 1 deficiency could potentially be exploited as a new therapeutic target for AD.

Two-photon live imaging of direct glia-to-neuron conversion in the mouse cortex.

JOURNAL/nrgr/04.03/01300535-202408000-00032/figure1/v/2023-12-16T180322Z/r/image-tiff Over the past decade, a growing number of studies have reported transcription factor-based in situ reprogramming that can directly convert endogenous glial cells into functional neurons as an alternative approach for neuroregeneration in the adult mammalian central nervous system. However, many questions remain regarding how a terminally differentiated glial cell can transform into a delicate neuron that forms part of the intricate brain circuitry. In addition, concerns have recently been raised around the absence of astrocyte-to-neuron conversion in astrocytic lineage-tracing mice. In this study, we employed repetitive two-photon imaging to continuously capture the in situ astrocyte-to-neuron conversion process following ectopic expression of the neural transcription factor NeuroD1 in both proliferating reactive astrocytes and lineage-traced astrocytes in the mouse cortex. Time-lapse imaging over several weeks revealed the step-by-step transition from a typical astrocyte with numerous short, tapered branches to a typical neuron with a few long neurites and dynamic growth cones that actively explored the local environment. In addition, these lineage-converting cells were able to migrate radially or tangentially to relocate to suitable positions. Furthermore, two-photon Ca2+ imaging and patch-clamp recordings confirmed that the newly generated neurons exhibited synchronous calcium signals, repetitive action potentials, and spontaneous synaptic responses, suggesting that they had made functional synaptic connections within local neural circuits. In conclusion, we directly visualized the step-by-step lineage conversion process from astrocytes to functional neurons in vivo and unambiguously demonstrated that adult mammalian brains are highly plastic with respect to their potential for neuroregeneration and neural circuit reconstruction.

Transcriptomic analysis of the ocular posterior segment completes a cell atlas of the human eye

Although the visual system extends through the brain, most vision loss originates from defects in the eye. Its central element is the neural retina, which senses light, processes visual signals, and transmits them to the rest of the brain through the optic nerve (ON). Surrounding the retina are numerous other structures, conventionally divided into anterior and posterior segments. Here, we used high-throughput single-nucleus RNA sequencing (snRNA-seq) to classify and characterize cells in six extraretinal components of the posterior segment: ON, optic nerve head (ONH), peripheral sclera, peripapillary sclera (PPS), choroid, and retinal pigment epithelium (RPE). Defects in each of these tissues are associated with blinding diseases-for example, glaucoma (ONH and PPS), optic neuritis (ON), retinitis pigmentosa (RPE), and age-related macular degeneration (RPE and choroid). From ~151,000 single nuclei, we identified 37 transcriptomically distinct cell types, including multiple types of astrocytes, oligodendrocytes, fibroblasts, and vascular endothelial cells. Our analyses revealed a differential distribution of many cell types among distinct structures. Together with our previous analyses of the anterior segment and retina, the data presented here complete a "Version 1" cell atlas of the human eye. We used this atlas to map the expression of >180 genes associated with the risk of developing glaucoma, which is known to involve ocular tissues in both anterior and posterior segments as well as the neural retina. Similar methods can be used to investigate numerous additional ocular diseases, many of which are currently untreatable.

Characterization of tumor-associated reactive astrocytes in gliomas by single-cell and bulk tumor sequencing.

Astrocytes constitute approximately 30% of cells in gliomas and play important roles in synapse construction and survival. Recently, JAK/STAT pathway activation associated with a new type of astrocyte was reported. However, the implications of these tumor-associated reactive astrocytes (TARAs) in glioma are not known. We comprehensively assessed TARAs in gliomas, both in single cells and at the bulk tumor level, by analyzing five independent datasets. First, we analyzed two single-cell RNA sequencing datasets of 35,563 cells from 23 patients to estimate the infiltration level of TARAs in gliomas. Second, we collected clinical information and genomic and transcriptomic data of 1,379 diffuse astrocytoma and glioblastoma samples from the Chinese Glioma Genome Atlas (CGGA) and The Cancer Genome Atlas datasets to evaluate the genomic, transcriptomic and clinical characteristics of TARA infiltration. Third, we downloaded expression profiles of recurrent glioblastoma samples from patients receiving PD-1 inhibitors to analyze the predictive value of TARAs for immune checkpoint inhibition. Single-cell RNA sequencing data showed TARAs were abundant in the glioma micro-environment (15.7% in the CGGA dataset and 9.1% in the Gene Expression Omnibus GSE141383 dataset, respectively). Bulk tumor sequencing data showed that the extent of TARA infiltration was highly associated with major clinical and molecular features of astrocytic gliomas. Patients with more TARA infiltration were more likely to have MUC16, FLG, and PICK3A mutations, chromosome 9p21.3, 10q23.3, and 13q14.2 deletions and 7p11.2 amplification. Gene Ontology analysis revealed that the high level of astrocyte infiltration was characterized by immune and oncogenic pathways, such as the inflammatory response, positive regulation of the JAK-STAT cascade, positive regulation of NIK/NF-kappa B signaling and the tumor necrosis factor biosynthetic process. Patients with greater TARA infiltration showed inferior prognosis. Meanwhile, the extent of reactive astrocyte infiltration exhibited a predictive value for recurrent glioblastoma patients undergoing anti-PD-1 immune therapy. TARA infiltration might promote glioma tumor progression and can be used as a diagnostic, predictive and prognostic marker in gliomas. Prevention of TARA infiltration might be a new therapeutic strategy for glioma.

Tracking reactive astrocytes in autosomal dominant Alzheimer disease with plasma GFAP and multi‐modal PET imaging

AbstractBackgroundWe have proposed astrogliosis as a “first wave” of response to AD pathology with diverging longitudinal changes of reactive astrocytes and amyloid‐β positron emission tomography (PET) retention in pre‐symptomatic autosomal dominant AD (ADAD). It has been suggested that plasma glial fibrillary acidic protein (GFAP) could be a marker of neuroinflammation in AD brain, although this hypothesis remains unproven. We therefore compared plasma GFAP levels with 11C‐deprenyl (DED) with a multi‐modal PET design in ADAD mutation carriers (MC) and non‐carriers (NC).MethodTwenty‐three individuals from families with known ADAD mutations were included (MC = 9; NC = 14). All individuals underwent PET imaging with 11C‐DED, 11C‐PIB and 18F‐FDG, for assessing monoamine oxidase B as a marker of reactive astrocytes, amyloid‐beta deposition, and glucose metabolism, respectively. Plasma sampling was performed after a median of 3 (interquartile range 1.5‐5.5) months. GFAP levels were measured using single molecule array technology. Eleven individuals had follow‐up imaging investigations and plasma sampling after a median of 2.7 (interquartile range 2.5‐2.9) years.ResultPlasma GFAP levels and 11C‐PIB binding increased significantly from pre‐symptomatic to symptomatic stage while 11C‐DED binding and 18F‐FDG uptake significantly decreased towards estimated onset of clinical symptoms in MC. Cross‐sectionally, plasma GFAP showed negative correlations with [18F]FDG uptake in widespread cortical areas, in contrast to no correlations with 11C‐DED or 11C‐PIB binding. 11C‐DED binding showed a positive correlation with 18F‐FDG uptake. Across the follow‐up interval, plasma GFAP levels showed a four‐fold greater intraindividual variation relative to 11C‐DED binding variation (longitudinal Δ variance = 1.67 vs 0.39 z‐scores, respectively). When averaging plasma GFAP values and tracer binding across consecutive time points for the same individual, strong negative correlations were found between plasma GFAP and 11C‐DED binding and 18F‐FDG uptake, but no significant correlation was found between plasma GFAP levels and 11C‐PIB binding in MC.ConclusionDivergent plasma GFAP levels and PET 11C‐DED brain binding in pre‐symptomatic ADAD carriers may reflect different but associated underlying processes, including different types of reactive astrocytes. However, the levels of plasma GFAP show large intraindividual variation over time and the assessment of reactive astrocytes based solely on cross‐sectional plasma GFAP levels poses great challenges and warrants further investigations.

Single cell molecular alterations reveal target cells and pathways of conditioned fear memory.

Recent evidence indicates that hippocampus is important for conditioned fear memory (CFM). Though few studies consider the roles of various cell types' contribution to such a process, as well as the accompanying transcriptome changes during this process. The purpose of this study was to explore the transcriptional regulatory genes and the targeted cells that are altered by CFM reconsolidation. A fear conditioning experiment was established on adult male C57 mice, after day 3 tone-cued CFM reconsolidation test, hippocampus cells were dissociated. Using single cell RNA sequencing (scRNA-seq) technique, alterations of transcriptional genes expression were detected and cell cluster analysis were performed and compared with those in sham group. Seven non-neuronal and eight neuronal cell clusters (including four known neurons and four newly identified neuronal subtypes) has been explored. Among them, CA subtype 1 has characteristic gene markers of Ttr and Ptgds, which is speculated to be the outcome of acute stress and promotes the production of CFM. The results of KEGG pathway enrichment indicate the differences in the expression of certain molecular protein functional subunits in long-term potentiation (LTP) pathway between two types of neurons (DG and CA1) and astrocytes, thus providing a new transcriptional perspective for the role of hippocampus in the CFM reconsolidation. More importantly, the correlation between the reconsolidation of CFM and neurodegenerative diseases-linked genes is substantiated by the results from cell-cell interactions and KEGG pathway enrichment. Further analysis shows that the reconsolidation of CFM inhibits the risk-factor genes App and ApoE in Alzheimer's Disease (AD) and activates the protective gene Lrp1. This study reports the transcriptional genes expression changes of hippocampal cells driven by CFM, which confirm the involvement of LTP pathway and suggest the possibility of CFM-like behavior in preventing AD. However, the current research is limited to normal C57 mice, and further studies on AD model mice are needed to prove this preliminary conclusion.

Striatal spatial heterogeneity, clustering, and white matter association of GFAP+ astrocytes in a mouse model of Huntington's disease.

Huntington's disease (HD) is a neurodegenerative disease that primarily affects the striatum, a brain region that controls movement and some forms of cognition. Neuronal dysfunction and loss in HD is accompanied by increased astrocyte density and astrocyte pathology. Astrocytes are a heterogeneous population classified into multiple subtypes depending on the expression of different gene markers. Studying whether mutant Huntingtin (HTT) alters specific subtypes of astrocytes is necessary to understand their relative contribution to HD. Here, we studied whether astrocytes expressing two different markers; glial fibrillary acidic protein (GFAP), associated with astrocyte activation, and S100 calcium-binding protein B (S100B), a marker of matured astrocytes and inflammation, were differentially altered in HD. First, we found three distinct populations in the striatum of WT and symptomatic zQ175 mice: GFAP+, S100B+, and dual GFAP+S100B+. The number of GFAP+ and S100B+ astrocytes throughout the striatum was increased in HD mice compared to WT, coinciding with an increase in HTT aggregation. Overlap between GFAP and S100B staining was expected, but dual GFAP+S100B+ astrocytes only accounted for less than 10% of all tested astrocytes and the number of GFAP+S100B+ astrocytes did not differ between WT and HD, suggesting that GFAP+ astrocytes and S100B+ astrocytes are distinct types of astrocytes. Interestingly, a spatial characterization of these astrocyte subtypes in HD mice showed that while S100B+ were homogeneously distributed throughout the striatum, GFAP+ preferentially accumulated in "patches" in the dorsomedial (dm) striatum, a region associated with goal-directed behaviors. In addition, GFAP+ astrocytes in the dm striatum of zQ175 mice showed increased clustering and association with white matter fascicles and were preferentially located in areas with low HTT aggregate load. In summary, we showed that GFAP+ and S100B+ astrocyte subtypes are distinctly affected in HD and exist in distinct spatial arrangements that may offer new insights to the function of these specific astrocytes subtypes and their potential implications in HD pathology.

Epigenetic Alterations of Brain Non-Neuronal Cells in Major Mental Diseases.

The tissue-specific expression and epigenetic dysregulation of many genes in cells derived from the postmortem brains of patients have been reported to provide a fundamental biological framework for major mental diseases such as autism, schizophrenia, bipolar disorder, and major depression. However, until recently, the impact of non-neuronal brain cells, which arises due to cell-type-specific alterations, has not been adequately scrutinized; this is because of the absence of techniques that directly evaluate their functionality. With the emergence of single-cell technologies, such as RNA sequencing (RNA-seq) and other novel techniques, various studies have now started to uncover the cell-type-specific expression and DNA methylation regulation of many genes (e.g., TREM2, MECP2, SLC1A2, TGFB2, NTRK2, S100B, KCNJ10, and HMGB1, and several complement genes such as C1q, C3, C3R, and C4) in the non-neuronal brain cells involved in the pathogenesis of mental diseases. Additionally, several lines of experimental evidence indicate that inflammation and inflammation-induced oxidative stress, as well as many insidious/latent infectious elements including the gut microbiome, alter the expression status and the epigenetic landscapes of brain non-neuronal cells. Here, we present supporting evidence highlighting the importance of the contribution of the brain's non-neuronal cells (in particular, microglia and different types of astrocytes) in the pathogenesis of mental diseases. Furthermore, we also address the potential impacts of the gut microbiome in the dysfunction of enteric and brain glia, as well as astrocytes, which, in turn, may affect neuronal functions in mental disorders. Finally, we present evidence that supports that microbiota transplantations from the affected individuals or mice provoke the corresponding disease-like behavior in the recipient mice, while specific bacterial species may have beneficial effects.

The Activity of Substance P (SP) on the Corneal Epithelium

In 1931, Von Euler and Gaddum isolated substance P (SP), an undecapeptide from the tachykinin family, from equine brain and intestine tissue extracts. Numerous types of cells, including neurons, astrocytes, microglia, epithelial, and endothelial cells, as well as immune cells including T-cells, dendritic cells, and eosinophils, are responsible for its production. The corneal epithelium, immune cells, keratocytes, and neurons all express the two isoforms of NK1R, which has the highest affinity for SP. The most recent research supports SP’s contribution to corneal healing by encouraging epithelial cell migration and proliferation. Additionally, when applied to the eyes, SP has proinflammatory effects that result in miosis, intraocular inflammation, and conjunctival hyperemia. In this review article, we examine the role of substance P within the eye. We focus on the role of SP with regards to maintenance and healing of the corneal epithelium.

Purkinje cell dopaminergic inputs to astrocytes regulate cerebellar-dependent behavior

Dopamine has a significant role in motor and cognitive function. The dopaminergic pathways originating from the midbrain have received the most attention; however, the relevance of the cerebellar dopaminergic system is largely undiscovered. Here, we show that the major cerebellar astrocyte type Bergmann glial cells express D1 receptors. Dopamine can be synthesized in Purkinje cells by cytochrome P450 and released in an activity-dependent fashion. We demonstrate that activation of D1 receptors induces membrane depolarization and Ca2+ release from the internal store. These astrocytic activities in turn modify Purkinje cell output by altering its excitatory and inhibitory synaptic input. Lastly, we show that conditional knockout of D1 receptors in Bergmann glial cells results in decreased locomotor activity and impaired social activity. These results contribute to the understanding of the molecular, cellular, and circuit mechanisms underlying dopamine function in the cerebellum, revealing a critical role for the cerebellar dopaminergic system in motor and social behavior.