The Emerging Nature of Astrocyte Diversity

Astrocyte Loss Augments Body Weight Through Reduction in Adipose Sympathetic Outflows

Emerging evidence indicates that astrocytes modulate energy metabolism and homeostasis. However, one important but poorly understood element is the necessity of astrocytes in the control of body weight. Here, we apply viral vector-assisted brain-region selective loss of astrocytes to define physiological roles played by astrocytes in the arcuate nucleus of the hypothalamus (ARH) and to elucidate the involved mechanism. We find that astrocyte loss potently augments body weight in adult mice fed chow or high-fat diet. Mechanistically, we find that the loss of astrocytes reduces adipose tissue norepinephrine (NE) contents and chemogenetic stimulation of adipose tissue sympathetic inputs reverses the astrocyte loss-induced increase in body weight. Collectively, our findings in this study suggest a crucial physiological role of astrocytes in preventing diet-induced energy surfeit and obesity by modulating adipose tissue lipid metabolism through central sympathetic outflows to adipose tissues.

Activation of ATF6 Signaling Confers Long-Term Beneficial Effects in Young and Aged Mice After Permanent Stroke

Ischemic stroke disrupts protein homeostasis in brain cells, causes endoplasmic reticulum (ER) stress, and consequently activates the unfolded protein response (UPR). The primary function of UPR activation is to help cells restore ER function, thereby promoting cell survival. A major adaptive UPR branch is mediated by activating transcription factor 6 (ATF6). We previously provided experimental evidence that activation of ATF6 signaling in neurons improves short-term outcome after both transient and permanent stroke. However, the effect of ATF6 activation in astrocytes on stroke outcome remains undetermined, and critically, the long-term therapeutic potential of targeting this UPR branch in permanent stroke has not been evaluated. The current study aimed to address these two critical unknowns. First, using conditional knock-in mice in which functional short-form ATF6 (sATF6) is specifically expressed in astrocytes, we demonstrated that astrocytic ATF6 activation modestly improved outcome after permanent stroke. Then, our pharmacokinetic analysis indicated that compound AA147, an ATF6-specific activator, can cross the blood-brain barrier. Lastly, we found that post-stroke treatment with AA147 had no significant beneficial effect on short-term outcome, but improved long-term functional recovery in both young and aged mice after permanent stroke. Together with previous findings, our data support the notion that the ATF6 pathway is a promising target for stroke therapy.

The roles of immune factors in neurodevelopment

The development of the nervous system is a highly complex process orchestrated by a multitude of factors, including various immune elements. These immune components play a dual role, not only regulating the immune response but also actively influencing brain development under both physiological and pathological conditions. The brain's immune barrier includes microglia in the brain parenchyma, which act as resident macrophages, astrocytes that support neuronal function and contribute to the inflammatory response, as well as circulating immune cells that reside at the brain's borders, including the choroid plexus, meninges, and perivascular spaces. Cytokines-soluble signaling molecules released by immune cells-play a crucial role in mediating communication between immune cells and the developing nervous system. Cytokines regulate processes such as neurogenesis, synaptic pruning, and inflammation, helping to shape the neural environment. Dysregulation of these immune cells, astrocytes, or cytokine signaling can lead to alterations in neurodevelopment, potentially contributing to neurodevelopmental abnormalities. This article reviews the central role of microglia, astrocytes, cytokines, and other immune factors in neurodevelopment, and explores how neuroinflammation can lead to the onset of neurodevelopmental disorders, shedding new light on their pathogenesis.

Transcriptomic and morphologic vascular aberrations underlying FCDIIb etiology

Focal cortical dysplasia type II (FCDII) is a major cause of drug-resistant epilepsy, but genetic factors explain only some cases, suggesting other mechanisms. In this study, we conduct a molecular analysis of brain lesions and adjacent areas in FCDIIb patients. By analyzing over 217,506 single-nucleus transcriptional profiles from 15 individuals, we find significant changes in smooth muscle cells (SMCs) and astrocytes. We identify abnormal vascular malformations and a unique type of SMC that we call "Firework cells", which migrate from blood vessels into the brain parenchyma and associate with VIM+ cells. These abnormalities create localized ischemic-hypoxic (I/H) microenvironments, as confirmed by clinical data, further impairing astrocyte function, activating the HIF-1α/mTOR/S6 pathway, and causing neuronal loss. Using zebrafish models, we demonstrate that vascular abnormalities resulting in I/H environments promote seizures. Our results highlight vascular malformations as a factor in FCDIIb pathogenesis, suggesting potential therapeutic avenues.

Astrocyte-conditional knockout of MOB2 inhibits the phenotypic conversion of reactive astrocytes from A1 to A2 following spinal cord injury in mice

After spinal cord injury (SCI), reactive astrocytes in the injured area are triggered after spinal cord injury (SCI) and to polarize into A1 astrocytes with a proinflammatory phenotype or A2 astrocytes with an anti-inflammatory phenotype. Monopolar spindle binder 2 (MOB2) induces astrocyte stellation, maintains cell homeostasis, and promotes neurite outgrowth; however, its role in the phenotypic transformation of reactive astrocytes remains unclear. Here, we confirmed for the first time that MOB2 is associated with A1/A2 phenotypic switching in reactive astrocytes following SCI in mice. MOB2 modulated A1/A2 transformation in a primary astrocyte reactive cell model. Therefore, we constructed MOB2 conditional knockout mice (MOB2GFAP-CKO) and discovered that conditional knockout of MOB2 inhibited the conversion of reactive astrocytes from A1 to A2 and hindered spinal cord function recovery. Mechanistically, MOB2 increased the activation of PI3K-AKT signaling to promote A1/A2 transformation in vitro, whereas sc79 (an AKT activator) reversed the subtype transformation of reactive astrocytes and improved functional recovery in MOB2GFAP-CKO mice after SCI. Taken together, study provides the first insights into how MOB2 acts as a novel regulator to promote the conversion this of the reactive astrocyte phenotype from A1 to A2, showing great potential for the treatment of SCI.

The Astrocytic Zinc Transporter ZIP12 Is a Synaptic Protein That Contributes to Synaptic Zinc Levels in the Mouse Auditory Cortex

Synaptically released zinc is a neuronal signaling system that arises from the actions of the presynaptic vesicular zinc transporter protein zinc transporter 3 (ZnT3). Mechanisms that regulate the actions of zinc at synapses are of great importance for many aspects of synaptic signaling in the brain. Here, we identify the astrocytic zinc transporter protein ZIP12 as a candidate mechanism that contributes to zinc clearance at cortical synapses. We identify small-molecule compounds that antagonize the function of ZIP12 in heterologous expression systems, and we use one of these compounds, ZIP12 modulator 8, to increase the concentration of ZnT3-dependent zinc at synapses in the brain of male and female mice to inhibit the activity of neuronal AMPA and NMDA glutamate receptors. These results identify a cellular mechanism and provide a pharmacological toolbox to target the molecular machinery that supports the actions of synaptic zinc in the brain.

Defining the molecular identity and morphology of glia limitans superficialis astrocytes in vertebrates

Astrocytes are a highly abundant glial cell type and perform critical homeostatic functions in the central nervous system. Like neurons, astrocytes have many discrete heterogeneous subtypes. The subtype identity and functions are, at least in part, associated with their anatomical location and can be highly restricted to strategically important anatomical domains. Here, we report that astrocytes forming the glia limitans superficialis, the outermost border of the brain and spinal cord, are a highly specialized astrocyte subtype and can be identified by a single marker: myocilin (Myoc). We show that glia limitans superficialis astrocytes cover the entire brain and spinal cord surface, exhibit an atypical morphology, and are evolutionarily conserved from zebrafish, rodents, and non-human primates to humans. Identification of this highly specialized astrocyte subtype will advance our understanding of CNS homeostasis and potentially be targeted for therapeutic intervention to combat peripheral inflammatory effects on the CNS.

Activity of human-specific Interlaminar Astrocytes in a Chimeric Mouse Model of Fragile X Syndrome

Astrocytes, a type of glial cells, have multiple roles in regulating neuronal development and homeostasis. In addition to the typical mammalian astrocytes, in the primate cortex interlaminar astrocytes are located in the superficial layer and project long processes traversing multiple layers of the cerebral cortex. Previously, we described a human stem cell based chimeric mouse model where interlaminar astrocytes develop. Here, we utilized this model to study the calcium signaling properties of interlaminar astrocytes. To determine how interlaminar astrocytes could contribute to neurodevelopmental disorders, we generated a chimeric mouse model for Fragile X syndrome. We report that FXS interlaminar astrocytes exhibit hyperexcitable calcium signaling and cause an increase in dendritic spine dynamics.

Neurobiological Perturbations in Bipolar Disorder Compared With Schizophrenia: Evidence From Cell Cultures and Brain Organoids

Bipolar disorder (BD) and schizophrenia (SCZ) are uniquely human disorders with a complex pathophysiology that involves adverse neuropathological events in brain development. High disease polygenicity and limited access to live human brain tissue make these disorders exceedingly challenging to study mechanistically. Cellular cultures and brain organoids generated from human-derived pluripotent stem cells preserve the genetic background of the donor cells and recapitulate some of the defining characteristics of human brain architecture and early spatiotemporal development. These model systems have already proven successful in deciphering some of the neuropathological perturbations in BD and SCZ, and methodological advancements, such as the functional integration of 2 or more region-specific organoids and organoid transplantation in animals, promise to deliver increasingly refined insights. Here, we review a selection of recent discoveries achieved by stem cell-based models, with a particular focus on patterns of cellular and molecular convergence and divergence between BD and SCZ. First, we provide a brief overview of the evidence from glial and neuronal cell cultures and brain organoids, centering our discussion on several key functional domains, including neuroinflammation, neuronal excitability, and mitochondrial function. Then, we review recent findings demonstrating the power of integrating stem cell-based systems with gene editing technologies to elucidate the functional consequences of risk variants identified through genetic association studies. We end with a discussion of current challenges and some promising avenues for future research.

Mitochondria and astrocyte reactivity: Key mechanism behind neuronal injury

In this special issue to celebrate the 30th anniversary of the Uruguayan Society for Neuroscience (SNU), we find it pertinent to highlight that research on glial cells in Uruguay began almost alongside the history of SNU and contributed to the understanding of neuron-glia interactions within the international scientific community. Glial cells, particularly astrocytes, traditionally regarded as supportive components in the central nervous system (CNS), undergo notable morphological and functional alterations in response to neuronal damage, a phenomenon referred to as glial reactivity. Among the myriad functions of astrocytes, metabolic support holds significant relevance for neuronal function, given the high energy demand of the nervous system. Although astrocytes are typically considered to exhibit low mitochondrial respiratory chain activity, they possess a noteworthy mitochondrial network. Interestingly, both the morphology and activity of these organelles change following glial reactivity. Despite receiving less attention compared to studies on neuronal mitochondria, recent studies indicate that mitochondria play a crucial role in driving the transition of astrocytes from a quiescent to a reactive state in various neurological disorders. Notably, stimulating mitochondria in astrocytes has been shown to reduce damage associated with the neurodegenerative disease amyotrophic lateral sclerosis. Here, we focus on studies supporting the emerging paradigm that metabolic reprogramming occurs in astrocytes following damage, which is associated with their phenotypic shift to a new functional state that significantly influences the progression of pathology. Thus, exploring mitochondrial activity and metabolic reprogramming within glial cells may provide valuable insights for developing innovative therapeutic approaches to mitigate neuronal damage. In this review, we focus on studies supporting the emerging paradigm that metabolic reprogramming occurs in astrocytes following damage, which is associated with their phenotypic shift to a new functional state that significantly influences the progression of pathology. Thus, exploring mitochondrial activity and metabolic reprogramming within glial cells may provide valuable insights for developing innovative therapeutic approaches to mitigate neuronal damage.

Understanding the molecular diversity of synapses

Synapses are composed of thousands of proteins, providing the potential for extensive molecular diversity to shape synapse type-specific functional specializations. In this Review, we explore the landscape of synaptic diversity and describe the mechanisms that expand the molecular complexity of synapses, from the genotype to the regulation of gene expression to the production of specific proteoforms and the formation of localized protein complexes. We emphasize the importance of examining every molecular layer and adopting a systems perspective to understand how these interconnected mechanisms shape the diverse functional and structural properties of synapses. We explore current frameworks for classifying synapses and methodologies for investigating different synapse types at varying scales, from synapse-type-specific proteomics to advanced imaging techniques with single-synapse resolution. We highlight the potential of synapse-type-specific approaches for integrating molecular data with cellular functions, circuit organization and organismal phenotypes to enable a more holistic exploration of neuronal phenomena across different scales.

FAST: Fast, Free, Consistent, and Unsupervised Oligodendrocyte Segmentation and Tracking System

To develop reparative therapies for neurological disorders like multiple sclerosis (MS), we need to better understand the physiology of loss and replacement of oligodendrocytes, the cells that make myelin and are the target of damage in MS. In vivo two-photon fluorescence microscopy allows direct visualization of oligodendrocytes in the intact brain of transgenic mouse models, promising a deeper understanding of the longitudinal dynamics of replacing oligodendrocytes after damage. However, the task of tracking the fate of individual oligodendrocytes requires extensive effort for manual annotation and is especially challenging in three-dimensional images. While several models exist for annotating cells in two-dimensional images, few models exist to annotate cells in three-dimensional images and even fewer are designed for tracking cells in longitudinal imaging. Notably, existing options often come with a substantial financial investment, being predominantly commercial or confined to proprietary software. Furthermore, the complexity of processes and myelin formed by individual oligodendrocytes can result in the failure of algorithms that are specifically designed for tracking cell bodies alone. Here, we propose a fast, free, consistent, and unsupervised beta-mixture oligodendrocyte segmentation system (FAST) that is written in open-source software, and can segment and track oligodendrocytes in three-dimensional images over time with minimal human input. We showed that the FAST model can segment and track oligodendrocytes similarly to a blinded human observer. Although FAST was developed to apply to our studies on oligodendrocytes, we anticipate that it can be modified to study four-dimensional in vivo data of any brain cell with associated complex processes.

Ezrin-mediated astrocyte-synapse signaling regulates cognitive function via astrocyte morphological changes in fine processes in male mice

Astrocytes, which actively participate in cognitive processes, have a complex spongiform morphology, highlighted by extensive ramified fine processes that closely enwrap the pre- and post-synaptic compartments, forming tripartite synapses. However, the role of astrocyte morphology in cognitive processes remains incompletely understood and even controversial. The actin-binding protein Ezrin is highly expressed in astrocytes and is a key structural determinant of astrocyte morphology. Here, we found that Ezrin expression and astrocyte fine process volume in the hippocampus of male mice increased after learning but decreased after lipopolysaccharide injection and in a mouse model of postoperative cognitive dysfunction, both of which involved models with impaired cognitive function. Additionally, astrocytic Ezrin knock-out led to significantly decreased astrocytic fine process volumes, decreased astrocyte-neuron proximity, and induced anxiety-like behaviors and cognitive dysfunction. Astrocytic Ezrin deficiency in the hippocampus was achieved by using a microRNA silencing technique delivered by adeno-associated viruses. Down-regulation of Ezrin in hippocampal astrocytes led to disrupted astrocyte-synapse interactions and impaired synaptic functions, including synaptic transmission and synaptic plasticity, which could be rescued by exogenous administration of D-serine. Remarkably, decreased Ezrin expression and reduced astrocyte fine processes volumes were also observed in aged mice with decreased cognitive function. Moreover, overexpression of astrocytic Ezrin increased astrocyte fine process volumes and improved cognitive function in aged mice. Overall, our results indicate Ezrin-mediated astrocyte fine processes integrity shapes astrocyte-synapse signaling contributing to cognitive function.

An Astroglial Basis of Major Depressive Disorder: Molecular, Cellular, and Circuit Features

Major depressive disorder is a common psychiatric disorder and a leading cause of disability worldwide. Astrocytes play a role in the maintenance of the function of the central nervous system, both physiologically and pathologically. Accumulated evidence indicates that the astrocyte is an important contributor to the pathophysiology of major depressive disorder including blood-brain barrier integrity, gap junctions, gliotransmission, glutamate homeostasis, and energy metabolism. Here, we comprehensively summarize an astroglial basis for major depressive disorder based on molecular, cellular, and circuit properties, suggesting that astrocytes appear to be highly sensitive to stress and are likely to be uniquely positioned to integrate peripheral and central stress responses.

Sex-specific astrocyte regulation of spinal motor circuits by Nkx6.1

Astrocytes exhibit diverse cellular and molecular properties across the central nervous system (CNS). Recent studies identified region-specific transcription factors (TF) that oversee these diverse properties; how sex differences intersect with region-specific transcriptional programs to regulate astrocyte function is unknown. Here, we show that the TF Nkx6.1 is specifically expressed in ventral astrocytes of the spinal cord and that its deletion results in sex-specific effects on astrocyte morphology. Astrocytes from males exhibit enhanced morphological complexity, accompanied by increased motor function and cholinergic synapses. In contrast, female astrocytes exhibit reduced complexity and no changes in motor function. Mechanistically, we found that Nkx6.1 exhibits sex-specific DNA-binding properties and epigenomic remodeling, identifying Semaphorin 4A (Sema4A) and Gabbr1 as targets regulating astrocyte morphology and cholinergic synapse formation. Collectively, our studies identify astrocytic Nkx6.1 as a key regulator of astrocyte properties in the spinal cord while adding sexual dimorphism as a layer of transcriptional regulation to astrocyte function and circuit activity.

The Role of Glial Cells in the Pathophysiology of Epilepsy

Epilepsy is a chronic neurological disorder marked by recurrent seizures, significantly impacting individuals worldwide. Current treatments are often ineffective for a third of patients and can cause severe side effects, necessitating new therapeutic approaches. Glial cells, particularly astrocytes, microglia, and oligodendrocytes, are emerging as crucial targets in epilepsy management. Astrocytes regulate neuronal homeostasis, excitability, and synaptic plasticity, playing key roles in maintaining the blood-brain barrier (BBB) and mediating neuroinflammatory responses. Dysregulated astrocyte functions, such as reactive astrogliosis, can lead to abnormal neuronal activity and seizure generation. They release gliotransmitters, cytokines, and chemokines that may exacerbate or mitigate seizures. Microglia, the innate immune cells of the CNS, contribute to neuroinflammation, glutamate excitotoxicity, and the balance between excitatory and inhibitory neurotransmission, underscoring their dual role in seizure promotion and protection. Meanwhile, oligodendrocytes, primarily involved in myelination, also modulate axonal excitability and contribute to the neuron-glia network underlying seizure pathogenesis. Understanding the dynamic interactions of glial cells with neurons provides promising avenues for novel epilepsy therapies. Targeting these cells may lead to improved seizure control and better clinical outcomes, offering hope for patients with refractory epilepsy.

Astrocytes phenomics as new druggable targets in healthy aging and Alzheimer's disease progression

For over a century after their discovery astrocytes were regarded merely as cells located among other brain cells to hold and give support to neurons. Astrocytes activation, "astrocytosis" or A1 functional state, was considered a detrimental mechanism against neuronal survival. Recently, the scientific view on astrocytes has changed. Accumulating evidence indicate that astrocytes are not homogeneous, but rather encompass heterogeneous subpopulations of cells that differ from each other in terms of transcriptomics, molecular signature, function and response in physiological and pathological conditions. In this review, we report and discuss the recent literature on the phenomic differences of astrocytes in health and their modifications in disease conditions, focusing mainly on the hippocampus, a region involved in learning and memory encoding, in the age-related memory impairments, and in Alzheimer's disease (AD) dementia. The morphological and functional heterogeneity of astrocytes in different brain regions may be related to their different housekeeping functions. Astrocytes that express diverse transcriptomics and phenomics are present in strictly correlated brain regions and they are likely responsible for interactions essential for the formation of the specialized neural circuits that drive complex behaviors. In the contiguous and interconnected hippocampal areas CA1 and CA3, astrocytes show different, finely regulated, and region-specific heterogeneity. Heterogeneous astrocytes have specific activities in the healthy brain, and respond differently to physiological or pathological stimuli, such as inflammaging present in normal brain aging or beta-amyloid-dependent neuroinflammation typical of AD. To become reactive, astrocytes undergo transcriptional, functional, and morphological changes that transform them into cells with different properties and functions. Alterations of astrocytes affect the neurovascular unit, the blood-brain barrier and reverberate to other brain cell populations, favoring or dysregulating their activities. It will be of great interest to understand whether the differential phenomics of astrocytes in health and disease can explain the diverse vulnerability of the hippocampal areas to aging or to different damaging insults, in order to find new astrocyte-targeted therapies that might prevent or treat neurodegenerative disorders.

Orchestrating the neuroglial compartment: Ontogeny and developmental interaction of astrocytes, oligodendrocytes, and microglia

Neuroglial cells serve as the master regulators of the central nervous system, making it imperative for glial development to be tightly regulated both spatially and temporally to ensure optimal brain function. In this chapter, we will discuss the origin and development of the three major glia cells such as astrocytes, oligodendrocytes, and microglia in the central nervous system. While much of our understanding of neuroglia development stems from studies using animal models, we will also explore recent insights into human glial development and potential differences from rodent models. Finally, the extensive crosstalk between glia cells will be highlighted, discussing how interactions among astrocyte, oligodendrocyte, and microglial influence their respective developmental pathways.

Astrocytic G Protein-Coupled Receptors in Drug Addiction

Understanding the cellular mechanisms of drug addiction remains a key task in current brain research. While neuron-based mechanisms have been extensively explored over the past three decades, recent evidence indicates a critical involvement of astrocytes, the main type of non-neuronal cells in the brain. In response to extracellular stimuli, astrocytes modulate the activity of neurons, synaptic transmission, and neural network properties, collectively influencing brain function. G protein-coupled receptors (GPCRs) expressed on astrocyte surfaces respond to neuron- and environment-derived ligands by activating or inhibiting astrocytic signaling, which in turn regulates adjacent neurons and their circuitry. In this review, we focus on the dopamine D1 receptors (D1R) and metabotropic glutamate receptor 5 (mGLUR5 or GRM5)-two GPCRs that have been critically implicated in the acquisition and maintenance of addiction-related behaviors. Positioned as an introductory-level review, this article briefly discusses astrocyte biology, outlines earlier discoveries about the role of astrocytes in substance-use disorders (SUDs), and provides detailed discussion about astrocytic D1Rs and mGLUR5s in regulating synapse and network functions in the nucleus accumbens (NAc)-a brain region that mediates addiction-related emotional and motivational responses. This review serves as a stepping stone for readers of Engineering to explore links between astrocytic GPCRs and drug addiction and other psychiatric disorders.

Deciphering the spectrum of astrocyte diversity: Insights into molecular, morphological, and functional dimensions in health and neurodegenerative diseases

Astrocytes are the most abundant and morphologically complex glial cells that play active roles in the central nervous system (CNS). Recent research has identified shared and region-specific astrocytic genes and functions, elucidated the cellular origins of their regional diversity, and uncovered the molecular networks for astrocyte morphology, which are essential for their functional complexity. Reactive astrocytes exhibit a wide range of functional diversity in a context-specific manner in CNS disorders. This review discusses recent advances in understanding the molecular and morphological diversity of astrocytes in healthy individuals and those with neurodegenerative diseases, such as Alzheimer's disease, Huntington's disease, and amyotrophic lateral sclerosis.

Astrocytic proteostasis in the tale of aging and neurodegeneration

Homeostasis of proteins (proteostasis), which governs protein processing, folding, quality control, and degradation, is a fundamental cellular process that plays a pivotal role in various neurodegenerative diseases and in the natural aging process of the mammalian brain. While the role of neuronal proteostasis in neuronal physiology is well characterized, the contribution of proteostasis of glial cells, particularly of astrocytes, has received fairly less attention in this context. Here, we summarize recent data highlighting proteostasis dysfunction in astrocytes and its putative implication to neurodegenerative diseases and aging. We discuss how distinct proteostasis nodes and pathways in astrocytes may specifically contribute to brain function and different age-associated pathologies. Finally, we argue that the understanding of astrocytic proteostasis role in neuronal physiology and functional decay may arise as a potential new avenue of intervention in neurodegenerative diseases and grant relevant data in the biology of aging.

A Wonderful Journey: The Diverse Roles of Adenosine Deaminase Action on RNA 1 (ADAR1) in Central Nervous System Diseases

BACKGROUND

Adenosine deaminase action on RNA 1 (ADAR1) can convert the adenosine in double-stranded RNA (dsRNA) molecules into inosine in a process known as A-to-I RNA editing. ADAR1 regulates gene expression output by interacting with RNA and other proteins; plays important roles in development, including growth; and is linked to innate immunity, tumors, and central nervous system (CNS) diseases.

RESULTS

In recent years, the role of ADAR1 in tumors has been widely discussed, but its role in CNS diseases has not been reviewed. It is worth noting that recent studies have shown ADAR1 has great potential in the treatment of neurodegenerative diseases, but the mechanisms are still unclear. Therefore, it is necessary to elaborate on the role of ADAR1 in CNS diseases.

CONCLUSIONS

Here, we focus on the effects and mechanisms of ADAR1 on CNS diseases such as Aicardi-AicardiGoutières syndrome, Alzheimer's disease, Parkinson's disease, glioblastoma, epilepsy, amyotrophic lateral sclerosis, and autism. We also evaluate the impact of ADAR1-based treatment strategies on these diseases, with a particular focus on the development and treatment strategies of new technologies such as microRNAs, nanotechnology, gene editing, and stem cell therapy. We hope to provide new directions and insights for the future development of ADAR1 gene editing technology in brain science and the treatment of CNS diseases.

An Astrocyte Transplantation Method to Investigate Astrocyte Development and Diversity in the Central Nervous System (CNS)

Astrocytes have rich structural, molecular, and physiological properties and show remarkable diversity in form and function that supports circuit-specific physiology within the central nervous system (CNS). However, the developmental mechanisms and cellular interactions that help to locally and globally diversify astrocytes with the CNS remain to be better understood. Understanding these processes will help to understand how astrocytes establish specialized microenvironments in the healthy brain and how they may differentially respond to CNS injury and disease. Here, we describe a cell transplantation method that enables the study of cell-autonomous and non-cell-autonomous determinants of astrocyte diversification by tracking the developmental trajectory of astrocytes transferred to the same or different regions of the mouse brain. With this method, it is possible to evaluate how astrocytes mature in "familiar" or "foreign" environmental contexts, for example, by transplanting cortical astrocytes into the cortex (a familiar context) or cerebellum (a foreign context). Also, with this method, the effect of developmental state on the ability of transplanted astrocytes to integrate into the brain environment can be studied, for example, by transplanting embryonically or postnatally derived cortical astrocytes into the cerebellum and monitoring their maturation within the recipient brain. We find that this transplantation method provides a flexible and robust approach to investigate how intrinsic cell properties and extrinsic cues from the extracellular environment shape astrocyte diversity.

Single-nucleus RNA sequencing of human periventricular white matter in vascular dementia

Vascular dementia (VaD) refers to a variety of dementias driven by cerebrovascular disease and is the second leading cause of dementia globally. VaD may be caused by ischemic strokes, intracerebral hemorrhage, and/or cerebral small vessel disease, commonly identified as white matter hyperintensities on MRI. The mechanisms underlying these white matter lesions in the periventricular brain are poorly understood. In this study we perform an extensive transcriptomic analysis on human postmortem periventricular white matter lesions in patients with VaD with the goal of identifying molecular pathways in the disease. We find increased cellular stress responses in astrocytes, oligodendrocytes, and oligodendrocyte precursor cells as well as transcriptional and translational repression in microglia in our dataset. We show that several genes identified by GWAS as being associated with white matter disease are differentially expressed in cells in VaD. Finally, we compare our dataset to an independent snRNAseq dataset of PVWM in VaD and a scRNAseq dataset on human iPSC-derived microglia exposed to oxygen glucose deprivation (OGD). We identify the increase of the heat shock protein response as a conserved feature of VaD across celltypes and show that this increase is not linked to OGD exposure. Overall, our study is the first to show that increased heat shock protein responses are a common feature of lesioned PVWM in VaD and may represent a potential therapeutic target.

Physiological and Pathological Role of mTOR Signaling in Astrocytes

The mammalian target of rapamycin (mTOR) signaling pathway is one of the key regulators of cellular energy metabolism. It senses diverse alterations in the extracellular environment such as availability of nutrients and growth factors, and mediates the corresponding intracellular response. In the brain, astrocytes crucially contribute to energy and neurotransmitter metabolism, and numerous other functions. However, the relevance of physiological, astrocytic mTOR signaling in maintaining brain homeostasis and function is not well understood. Pathophysiological mTOR signaling is involved in manifold diseases in the central nervous system and most of the knowledge about astrocytic mTOR signaling has been derived from observations on these disorders. Dysregulation of the mTOR signaling pathway impairs important functions of astrocytes including neurotransmitter uptake and -signaling as well as energy metabolism. Some of these alterations could trigger neuropathological conditions such as epilepsy. This review focuses on how mTOR signaling regulates properties of astrocytes, and how these signaling events might contribute to the physiological function of the brain.

The role of astrocytes response triggered by hyperglycaemia during spinal cord injury

OBJECTIVE

This manuscript aimed to provide a comprehensive overview of the physiological, molecular, and cellular mechanisms triggered by reactive astrocytes (RA) in the context of spinal cord injury (SCI), with a particular focus on cases involving hyperglycaemia.

METHODS

The compilation of articles related to astrocyte responses in neuropathological conditions, with a specific emphasis on those related to SCI and hyperglycaemia, was conducted by searching through databases including Science Direct, Web of Science, and PubMed.

RESULTS AND CONCLUSIONS

This article explores the dual role of astrocytes in both neurophysiological and neurodegenerative conditions within the central nervous system (CNS). In the aftermath of SCI and hyperglycaemia, astrocytes undergo a transformation into RA, adopting a distinct phenotype. While there are currently no approved therapies for SCI, various therapeutic strategies have been proposed to alleviate the detrimental effects of RAs following SCI and hyperglycemia. These strategies show promising potential in the treatment of SCI and its likely comorbidities.

Immune checkpoint inhibitors as first-line treatment for brain metastases in stage IV NSCLC patients without driver mutations

Immune checkpoint inhibitors (ICI) therapy with or without chemotherapy has been established as the first-line treatment for patients with non-oncogene addicted advanced Non-Small Cell Lung Cancer (NSCLC). Yet some clinical settings, such as the treatment sequence in patients with brain metastases, have barely been evidenced. Although ICIs cannot directly cross the blood-brain barrier (BBB), evidence suggests that BBB damage could allow ICIs into the central nervous system, or that they can have an indirect effect on the tumor immune microenvironment (TIME) and cause an anti-tumor response. Pivotal phase III trials have included a highly selected population but offer few data on these patients. Here we first review how ICIs can indirectly shape the brain metastases microenvironment through different mechanisms, and some possible causes of ICIs resistance. We also analyze the evidence reported in pivotal phase III trials and phase II trials focused on NSCLC brain metastases for first-line treatment, and the evidence for upfront or delayed local brain therapy. Finally, we discuss the best evidence-based approach to treat NSCLC patients with brain metastases and propose future research.

Neurotrophic Effects of Foeniculum vulgare Ethanol Extracts on Hippocampal Neurons: Role of Anethole in Neurite Outgrowth and Synaptic Development

Foeniculum vulgare Mill, commonly known as fennel, is an aromatic herb traditionally used for culinary and medicinal purposes, with potential therapeutic effects on neurological disorders. However, limited research has focused on its neurotrophic impact, particularly on neuronal maturation and synaptic development. This study investigates the neurotrophic effects of F. vulgare ethanol extracts (FVSE) on the maturation of rat primary hippocampal neurons. Results show that FVSE and its prominent component, anethole, significantly promote neurite outgrowth in a dose-dependent manner. Optimal axonal and dendritic growth occurred at concentrations of 40 µg/mL FVSE and 20 µM anethole, respectively, without causing cytotoxicity, underscoring the safety of FVSE for neuronal health. Additionally, FVSE enhances the formation of synapses, essential for neuronal communication. Network pharmacology analysis revealed that FVSE components influence critical neurotrophic pathways, including PI3K-AKT and Alzheimer's disease pathways. Specifically, FVSE modulates key proteins, including tropomyosin receptor kinase (Trk), glycogen synthase kinase 3 (GSK3βser9), phosphatidylinositol 3-kinase (PI3K), and extracellular signal-regulated protein kinase (Erk1/2). Anethole was found to play a key role in regulating these pathways, which was confirmed by immunocytochemistry experiments demonstrating its effect on promoting neuronal growth and synaptic development. In conclusion, this study highlights the neurotrophic properties of FVSE, with anethole emerging as a critical bioactive compound. These findings provide valuable insights into the therapeutic potential of fennel in treating neurological disorders, offering a basis for future research into interventions promoting neuronal growth and survival.

Astrocytes release ATP/ADP and glutamate in flashes via vesicular exocytosis

Astrocytes regulate brain functions through gliotransmitters like ATP/ADP and glutamate, but their release patterns and mechanisms remain controversial. Here, we visualized ATP/ADP and glutamate response following astrocyte activation and investigated their mechanisms in vivo. Employing cOpn5-mediated optogenetic stimulation, genetically encoded fluorescent sensors, and two-photon imaging, we observed ATP/ADP released as temporally prolonged and spatially extended flashes that later converted to adenosine. This release occurs via Ca2+ and VNUT-dependent vesicular exocytosis. Additionally, astrocytes also release glutamate in flashes through TeNT-sensitive exocytosis, independent of ATP/ADP release. ATP/ADP released by astrocytes triggers further ATP/ADP release from microglia through P2Y12- and VNUT-dependent mechanisms. VNUT in astrocytes and microglia also contributes to ATP/ADP release under LPS-induced brain inflammation. These findings establish Ca2+-dependent vesicular exocytosis as a key mode of action, reveal intricate astrocyte-microglia interactions, and suggest a role for gliotransmission in brain inflammation. Furthermore, the methodologies may provide valuable tools for deciphering glial physiology and pathophysiology.

Understanding perspectives and research trends in Down syndrome neuropathogenesis: A bibliometric analysis

Down syndrome (DS), characterised by compromised brain development and intellectual challenges, often manifests Alzheimer's disease (AD) -like symptoms. Utilising the Web of Science Core Collection (WOSCC) database from January 1, 2000, to July 31, 2023, we conducted a comprehensive bibliometric analysis using VOSviewer, CiteSpace, and the R package "bibliometrix." Analyses included co-authorship, co-citation, co-occurrence, cooperative network, reference, and keyword burst citation. Analysing 5,082 papers, the U.S. demonstrated prominence with the highest number of research organisations and citations. Keyword analysis revealed promising research areas, including "Alzheimer's disease," "development," "inflammation," and "neurogenesis". This 22-year survey of the brain with trisomy 21 research unveils key trends, contributors, and focal areas in DS neuropathogenesis. Notably, Alzheimer 's-related genes and proteins play a pervasive role in DS neuropathological processes across patients' lifespans. The study contributes foundational knowledge for advancing research and care in the DS neuropathogenesis domain.

Role of Peripheral and Central Insulin Resistance in Neuropsychiatric Disorders

Insulin acts on different organs, including the brain, which helps it regulate energy metabolism. Insulin signaling plays an important role in the function of different cell types. In this review, we have summarized the key roles of insulin and insulin receptors in healthy brains and in different brain disorders. Insulin signaling, as well as insulin resistance (IR), is a major contributor in the regulation of mood, behavior, and cognition. Recent evidence showed that both peripheral and central insulin resistance play a role in the pathophysiology, clinical presentation, and management of neuropsychiatric disorders like Cognitive Impairment/Dementia, Depression, and Schizophrenia. Many human studies point out Insulin Resistance/Metabolic Syndrome can increase the risk of dementia especially Alzheimer's dementia (AD). IR has been shown to play a role in AD development but also in its progression. This review article discusses the pathophysiological pathways and mechanisms of insulin resistance in major neuropsychiatric disorders. The extent of insulin resistance can be quantified using IR biomarkers like insulin levels, HOMA-IR index, and Triglyceride glucose-body mass index (TyG-BMI) levels. IR has been shown to precede neurodegeneration. Human trials showed current treatment with certain antidiabetic drugs, as well as life style management, like weight loss and exercise for IR, have shown promise in the management of cognitive/neuropsychiatric disorders. This may pave the pathway to the development of new therapeutic approaches to these challenging disorders of dementia and psychiatric diseases. Recent clinical trials are showing some encouraging evidence for these pharmacological and nonpharmacological approaches for IR in psychiatric and cognitive disorders, even though more research is needed to apply this evidence into clinical practice. Early identification and management of IR may help as a strategy to potentially alter neuropsychiatric disorders onset as well as its progression.

Revisiting astrocytic calcium signaling in the brain

Astrocytes, characterized by complex spongiform morphology, participate in various physiological processes, and abnormal changes in their calcium (Ca2+) signaling are implicated in central nervous system disorders. However, medications targeting the control of Ca2+ have fallen short of the anticipated therapeutic outcomes in clinical applications. This underscores the fact that our comprehension of this intricate regulation of calcium ions remains considerably incomplete. In recent years, with the advancement of Ca2+ labeling, imaging, and analysis techniques, Ca2+ signals have been found to exhibit high specificity at different spatial locations within the intricate structure of astrocytes. This has ushered the study of Ca2+ signaling in astrocytes into a new phase, leading to several groundbreaking research achievements. Despite this, the comprehensive understanding of astrocytic Ca2+ signaling and their implications remains challenging area for future research.

Dysfunctional astrocyte glutamate uptake in the hypothalamic paraventricular nucleus contributes to visceral pain and anxiety-like behavior in mice with chronic pancreatitis

Abdominal visceral pain is a predominant symptom in patients with chronic pancreatitis (CP); however, the underlying mechanism of pain in CP remains elusive. We hypothesized that astrocytes in the hypothalamic paraventricular nucleus (PVH) contribute to CP pain pathogenesis. A mouse model of CP was established by repeated intraperitoneal administration of caerulein to induce abdominal visceral pain. Abdominal mechanical stimulation, open field and elevated plus maze tests were performed to assess visceral pain and anxiety-like behavior. Fiber photometry, brain slice Ca2+ imaging, electrophysiology, and immunohistochemistry were used to investigate the underlying mechanisms. Mice with CP displayed long-term abdominal mechanical allodynia and comorbid anxiety, which was accompanied by astrocyte glial fibrillary acidic protein reactivity, elevated Ca2+ signaling, and astroglial glutamate transporter-1 (GLT-1) deficits in the PVH. Specifically, reducing astrocyte Ca2+ signaling in the PVH via chemogenetics significantly rescued GLT-1 deficits and alleviated mechanical allodynia and anxiety in mice with CP. Furthermore, we found that GLT-1 deficits directly contributed to the hyperexcitability of VGLUT2PVH neurons in mice with CP, and that pharmacological activation of GLT-1 alleviated the hyperexcitability of VGLUT2PVH neurons, abdominal visceral pain, and anxiety in these mice. Taken together, our data suggest that dysfunctional astrocyte glutamate uptake in the PVH contributes to visceral pain and anxiety in mice with CP, highlighting GLT-1 as a potential therapeutic target for chronic pain in patients experiencing CP.

Astrocyte allocation during brain development is controlled by Tcf4-mediated fate restriction

Astrocytes in the brain exhibit regional heterogeneity contributing to regional circuits involved in higher-order brain functions, yet the mechanisms controlling their distribution remain unclear. Here, we show that the precise allocation of astrocytes to specific brain regions during development is achieved through transcription factor 4 (Tcf4)-mediated fate restriction based on their embryonic origin. Loss of Tcf4 in ventral telencephalic neural progenitor cells alters the fate of oligodendrocyte precursor cells to transient intermediate astrocyte precursor cells, resulting in mislocalized astrocytes in the dorsal neocortex. These ectopic astrocytes engage with neocortical neurons and acquire features reminiscent of dorsal neocortical astrocytes. Furthermore, Tcf4 functions as a suppressor of astrocyte fate during the differentiation of oligodendrocyte precursor cells derived from the ventral telencephalon, thereby restricting the fate to the oligodendrocyte lineage in the dorsal neocortex. Together, our findings highlight a previously unappreciated role for Tcf4 in regulating astrocyte allocation, offering additional insights into the mechanisms underlying neurodevelopmental disorders linked to Tcf4 mutations.

Bacterial lipopolysaccharide model of neuroinflammation-associated neurodegeneration in Wistar rats: A comparison between different durations of lipopolysaccharide induction

Background and Aim

Bacterial lipopolysaccharide (LPS)-induced neuroinflammation can be the most dependable animal model for studying neurodegeneration mechanisms driven by systemic inflammation-induced neuroinflammation. Hence, this study aimed to standardize the LPS model of neuroinflammation by comparing the effect of relatively low-dose LPS administered for different durations on the induction of neurodegeneration in Wistar rats.

Materials and Methods

Six groups of six adult Wistar rats per group were used in the study. Group 1 was the control group, and the other five were administered single weekly dose of LPS (170 μg/kg) for increasing durations, ranging from 4 weeks to 8 weeks. The study endpoints included behavioral parameters, neuronal assay results, and the expression of microglia and astrocytes in the frontal cortex, dentate gyrus, and hippocampus.

Results

We observed a significant reduction in the number of neurons and an increase in glial cells at 5 weeks of exposure, along with a decline in memory. Thereafter, these changes were gradual until 7 weeks of exposure. However, at 8 weeks of exposure, there was no further statistically significant worsening compared with the group exposed for 7 weeks.

Conclusion

To effectively induce neuroinflammation and cause neuronal damage, a minimum of five weekly LPS administrations at a dose of 170 μg/kg is required. Moreover, our results recommend a maximum of 7 weeks of LPS exposure to create a chronic inflammatory model of neuroinflammation.

Cell reprogramming therapy for Parkinson's disease

Parkinson's disease is typically characterized by the progressive loss of dopaminergic neurons in the substantia nigra pars compacta. Many studies have been performed based on the supplementation of lost dopaminergic neurons to treat Parkinson's disease. The initial strategy for cell replacement therapy used human fetal ventral midbrain and human embryonic stem cells to treat Parkinson's disease, which could substantially alleviate the symptoms of Parkinson's disease in clinical practice. However, ethical issues and tumor formation were limitations of its clinical application. Induced pluripotent stem cells can be acquired without sacrificing human embryos, which eliminates the huge ethical barriers of human stem cell therapy. Another widely considered neuronal regeneration strategy is to directly reprogram fibroblasts and astrocytes into neurons, without the need for intermediate proliferation states, thus avoiding issues of immune rejection and tumor formation. Both induced pluripotent stem cells and direct reprogramming of lineage cells have shown promising results in the treatment of Parkinson's disease. However, there are also ethical concerns and the risk of tumor formation that need to be addressed. This review highlights the current application status of cell reprogramming in the treatment of Parkinson's disease, focusing on the use of induced pluripotent stem cells in cell replacement therapy, including preclinical animal models and progress in clinical research. The review also discusses the advancements in direct reprogramming of lineage cells in the treatment of Parkinson's disease, as well as the controversy surrounding in vivo reprogramming. These findings suggest that cell reprogramming may hold great promise as a potential strategy for treating Parkinson's disease.

Astrocyte regional specialization is shaped by postnatal development

Astrocytes are an abundant class of glial cells with critical roles in neural circuit assembly and function. Though many studies have uncovered significant molecular distinctions between astrocytes from different brain regions, how this regionalization unfolds over development is not fully understood. We used single-nucleus RNA sequencing to characterize the molecular diversity of brain cells across six developmental stages and four brain regions in the mouse and marmoset brain. Our analysis of over 170,000 single astrocyte nuclei revealed striking regional heterogeneity among astrocytes, particularly between telencephalic and diencephalic regions, at all developmental time points surveyed in both species. At the stages sampled, most of the region patterning was private to astrocytes and not shared with neurons or other glial types. Though astrocytes were already regionally patterned in late embryonic stages, this region-specific astrocyte gene expression signature changed dramatically over postnatal development, and its composition suggests that regional astrocytes further specialize postnatally to support their local neuronal circuits. Comparing across species, we found divergence in the expression of astrocytic region- and age-differentially expressed genes and the timing of astrocyte maturation relative to birth between mouse and marmoset, as well as hundreds of species differentially expressed genes. Finally, we used expansion microscopy to show that astrocyte morphology is largely conserved across gray matter regions of prefrontal cortex, striatum, and thalamus in the mouse, despite substantial molecular divergence.

Astrocytic Ephrin-B1 Regulates Oligodendrocyte Development and Myelination

Astrocytes have been implicated in oligodendrocyte development and myelination, however, the mechanisms by which astrocytes regulate oligodendrocytes remain unclear. Our findings suggest a new mechanism that regulates astrocyte-mediated oligodendrocyte development through ephrin-B1 signaling in astrocytes. Using a mouse model, we examined the role of astrocytic ephrin-B1 signaling in oligodendrocyte development by deleting ephrin-B1 specifically in astrocytes during the postnatal days (P)14-P28 period and used mRNA analysis, immunohistochemistry, and mouse behaviors to study its effects on oligodendrocytes and myelination. We found that deletion of astrocytic ephrin-B1 downregulated many genes associated with oligodendrocyte development, myelination, and lipid metabolism in the hippocampus and the corpus callosum. Additionally, we observed a reduced number of oligodendrocytes and impaired myelination in the corpus callosum of astrocyte-specific ephrin-B1 KO mice. Finally, our data show reduced motor strength in these mice exhibiting clasping phenotype and impaired performance in the rotarod test most likely due to impaired myelination. Our studies provide new evidence that astrocytic ephrin-B1 positively regulates oligodendrocyte development and myelination, potentially through astrocyte-oligodendrocyte interactions.

Computational modeling of the relationship between morphological heterogeneity and functional responses in mouse hippocampal astrocytes

Recent studies indicate that astrocytes show heterogeneity in morphology and physiological function. They integrate synaptic signals and release calcium in reaction to active neurons. These calcium signals are not yet fully understood as they are highly dependent on the cell's morphology, which can vary across and within brain regions. We found structural heterogeneity among mouse hippocampal CA1 astrocytes based on geometric features, clustering 741 cells into six classes. Of those, we selected 84 cells and reconstructed their morphology based on confocal microscope images and converted them into multi-compartment models with a high detailedness. We applied a computational biophysical model simulating the intracellular ion and IP3 signaling and diffusion in those 3D cell geometries. The cells were stimulated with three different glutamate stimuli. Calcium mainly oscillated in the stimulated and the neighboring compartment but not in the soma. Significant differences were found in the peak width, mean prominence, and mean peak amplitude of the calcium signal when comparing the signals in the stimulated and neighboring compartments. Overall, this study highlights the influence of the complex morphology of astrocytes on intracellular ionic signaling.

Neuron-Glial Interactions: Implications for Plasticity, Behavior, and Cognition

The traditional view of glial cells as mere supportive tissue has shifted, due to advances in technology and theoretical conceptualization, to include a diversity of other functions, such as regulation of complex behaviors. Astrocytes, the most abundant glial cells in the central nervous system (CNS), have been shown to modulate synaptic functions through gliotransmitter-mediated neurotransmitter reuptake, influencing neuronal signaling and behavioral functions. Contemporary studies further highlight astrocytes' involvement in complex cognitive functions. For instance, inhibiting astrocytes in the hippocampus can lead to memory deficits, suggesting their integral role in memory processes. Moreover, astrocytic calcium activity and astrocyte-neuron metabolic coupling have been linked to changes in synaptic strength and learning. Microglia, another type of glial cell, also extend beyond their supportive roles, contributing to learning and memory processes, with microglial reductions impacting these functions in a developmentally dependent manner. Oligodendrocytes, traditionally thought to have limited roles postdevelopment, are now recognized for their activity-dependent modulation of myelination and plasticity, thus influencing behavioral responses. Recent advancements in technology and computational modeling have expanded our understanding of glial functions, particularly how astrocytes influence neuronal circuits and behaviors. This review underscores the importance of glial cells in CNS functions and the need for further research to unravel the complexities of neuron-glia interactions, the impact of these interactions on brain functions, and potential implications for neurological diseases.

Mapping multi-regional functional connectivity of astrocyte-neuronal networks during behaviors

Significance

Diverse behaviors rely on coordinated activity and multi-regional functional connectivity within astrocyte-neuronal networks. However, current techniques for simultaneously measuring astrocytic and neuronal activities across multiple brain regions during behaviors remain limited.

Aim

We propose a multi-fiber solution that can simultaneously record activities of astrocyte-neuronal networks across multiple regions during behaviors.

Approach

We employed cell-specific dual-color genetically encoded calcium indicators (GECIs) and multi-fiber photometry to simultaneously measure astrocytic and neuronal Ca2+ transients across multiple brain regions in freely behaving animals.

Results

Our findings demonstrate that both movements and sensory stimuli induce synchronized and highly correlated Ca2+ transients in astrocytes and neurons of freely behaving mice. In addition, we recorded astrocytic and neuronal Ca2+ transients from multiple brain regions during mouse behaviors. Our observations reveal heightened synchronization of astrocytic and neuronal Ca2+ transients across different brain regions during movements or sensory stimuli, indicating enhanced functional connectivity within brain-wide astrocyte-neuronal networks.

Conclusions

Multi-fiber photometry, combined with cell-specific dual-color GECIs, represents a powerful approach for investigating astrocytic and neuronal activities across different brain regions during behaviors. This technique serves as a versatile tool for analyzing the multi-regional functional connectivity map of astrocyte-neuronal networks associated with specific behaviors.

Astrocytes modulate brain phosphate homeostasis via polarized distribution of phosphate uptake transporter PiT2 and exporter XPR1

Aberrant inorganic phosphate (Pi) homeostasis causes brain calcification and aggravates neurodegeneration, but the underlying mechanism remains unclear. Here, we found that primary familial brain calcification (PFBC)-associated Pi transporter genes Pit2 and Xpr1 were highly expressed in astrocytes, with importer PiT2 distributed over the entire astrocyte processes and exporter XPR1 localized to astrocyte end-feet on blood vessels. This polarized PiT2 and XPR1 distribution endowed astrocyte with Pi transport capacity competent for brain Pi homeostasis, which was disrupted in mice with astrocyte-specific knockout (KO) of either Pit2 or Xpr1. Moreover, we found that Pi uptake by PiT2, and its facilitation by PFBC-associated galactosidase MYORG, were required for the high Pi transport capacity of astrocytes. Finally, brain calcification was suppressed by astrocyte-specific PiT2 re-expression in Pit2-KO mice. Thus, astrocyte-mediated Pi transport is pivotal for brain Pi homeostasis, and elevating astrocytic Pi transporter function represents a potential therapeutic strategy for reducing brain calcification.

Astrocyte-Mediated Neuroinflammation in Neurological Conditions

Astrocytes are one of the key glial types of the central nervous system (CNS), accounting for over 20% of total glial cells in the brain. Extensive evidence has established their indispensable functions in the maintenance of CNS homeostasis, as well as their broad involvement in neurological conditions. In particular, astrocytes can participate in various neuroinflammatory processes, e.g., releasing a repertoire of cytokines and chemokines or specific neurotrophic factors, which result in both beneficial and detrimental effects. It has become increasingly clear that such astrocyte-mediated neuroinflammation, together with its complex crosstalk with other glial cells or immune cells, designates neuronal survival and the functional integrity of neurocircuits, thus critically contributing to disease onset and progression. In this review, we focus on the current knowledge of the neuroinflammatory responses of astrocytes, summarizing their common features in neurological conditions. Moreover, we highlight several vital questions for future research that promise novel insights into diagnostic or therapeutic strategies against those debilitating CNS diseases.

Metformin ameliorates neuroinflammatory environment for neurons and astrocytes during in vitro and in vivo stroke and tobacco smoke chemical exposure: Role of Nrf2 activation

Despite the protective nature of the blood-brain barrier (BBB) and brain-protecting tissues, some types of CNS injury or stress can cause cerebral cytokine production and profound alterations in brain function. Neuroinflammation, which can also be accompanied by increased cerebral cytokine production, has a remarkable impact on the pathogenesis of many neurological illnesses, including loss of BBB integrity and ischemic stroke, yet effective treatment choices for these diseases are currently lacking. Although little is known about the brain effects of Metformin (MF), a commonly prescribed first-line antidiabetic drug, prior research suggested that it may be useful in preventing BBB deterioration and the increased risk of stroke caused by tobacco smoking (TS). Therefore, reducing neuroinflammation by escalating anti-inflammatory cytokine production and declining pro-inflammatory cytokine production could prove an effective therapeutic strategy for ischemic stroke. Hence, the current investigation was planned to explore the potential role of MF against stroke and TS-induced neuroinflammation and reactive oxygen species (ROS) production. Our studies revealed that MF suppressed releasing pro-inflammatory mediators like tumor necrosis factor-α (TNF-α) and interleukin-1β (IL-1β) by aiming at the nuclear factor kappa B (NF-κB) signaling pathway in primary neurons and astrocytes. MF also upregulated anti-inflammatory mediators, like interleukin-10 (IL-10), and interleukin-4 (IL-4), by upregulating the Nrf2-ARE signaling pathway. Adolescent mice receiving MF along with TS exposure also showed a notable decrease in NF-κB expression compared to the mice not treated with MF and significantly decreased the level of TNF-α, IL-1β, MCP-1, and MIP-2 and increased the levels of IL-10 and IL-4 through the activation of Nrf2-ARE signaling pathway. These results suggest that MF has anti-neuroinflammatory effects via inhibiting NF-κB signaling by activating Nrf2-ARE. These studies support that MF could be a strong candidate drug for treating and or preventing TS-induced neuroinflammation and ischemic stroke.

Transcriptional profiling of retinal astrocytes identifies a specific marker and points to functional specialization

Astrocyte heterogeneity is an increasingly prominent research topic, and studies in the brain have demonstrated substantial variation in astrocyte form and function, both between and within regions. In contrast, retinal astrocytes are not well understood and remain incompletely characterized. Along with optic nerve astrocytes, they are responsible for supporting retinal ganglion cell axons and an improved understanding of their role is required. We have used a combination of microdissection and Ribotag immunoprecipitation to isolate ribosome-associated mRNA from retinal astrocytes and investigate their transcriptome, which we also compared to astrocyte populations in the optic nerve. Astrocytes from these regions are transcriptionally distinct, and we identified retina-specific astrocyte genes and pathways. Moreover, although they share much of the "classical" gene expression patterns of astrocytes, we uncovered unexpected variation, including in genes related to core astrocyte functions. We additionally identified the transcription factor Pax8 as a highly specific marker of retinal astrocytes and demonstrated that these astrocytes populate not only the retinal surface, but also the prelaminar region at the optic nerve head. These findings are likely to contribute to a revised understanding of the role of astrocytes in the retina.

Retarded astrogliogenesis in response to hypoxia is facilitated by downregulation of CIRBP

The adverse impacts of chronic hypoxia on maternal and infant health at high altitudes warrant significant attention. However, effective protective measures against the resultant growth restrictions and neurodevelopmental disorders in infants and young children are still lacking. This study investigated the neurodevelopment of mice offspring under hypoxic conditions by exposing pregnant mice to a hypobaric oxygen chamber that simulated the hypobaric hypoxia at an altitude of 4000 m until 28 days after delivery. Our findings suggested that prolonged exposure to hypoxia might result in emotional abnormalities and social disorders in offspring. The significant reduction in astrogliogenesis was a characteristic feature associated with neurodevelopmental disorders induced by hypoxia. Further studies demonstrated that cold-induced RNA-binding protein (CIRBP) was a key transcriptional regulator in astrogliogenesis, which downregulated astrocytic differentiation under hypoxia through its crosstalk with the NFIA. Our study emphasized the crucial role of CIRBP in regulating astrogliogenesis and highlighted its potential as a promising target for therapeutic interventions in neurodevelopmental disorders associated with hypoxia.

Proteomic features of gray matter layers and superficial white matter of the rhesus monkey neocortex: comparison of prefrontal area 46 and occipital area 17

In this novel large-scale multiplexed immunofluorescence study we comprehensively characterized and compared layer-specific proteomic features within regions of interest of the widely divergent dorsolateral prefrontal cortex (A46) and primary visual cortex (A17) of adult rhesus monkeys. Twenty-eight markers were imaged in rounds of sequential staining, and their spatial distribution precisely quantified within gray matter layers and superficial white matter. Cells were classified as neurons, astrocytes, oligodendrocytes, microglia, or endothelial cells. The distribution of fibers and blood vessels were assessed by quantification of staining intensity across regions of interest. This method revealed multivariate similarities and differences between layers and areas. Protein expression in neurons was the strongest determinant of both laminar and regional differences, whereas protein expression in glia was more important for intra-areal laminar distinctions. Among specific results, we observed a lower glia-to-neuron ratio in A17 than in A46 and the pan-neuronal markers HuD and NeuN were differentially distributed in both brain areas with a lower intensity of NeuN in layers 4 and 5 of A17 compared to A46 and other A17 layers. Astrocytes and oligodendrocytes exhibited distinct marker-specific laminar distributions that differed between regions; notably, there was a high proportion of ALDH1L1-expressing astrocytes and of oligodendrocyte markers in layer 4 of A17. The many nuanced differences in protein expression between layers and regions observed here highlight the need for direct assessment of proteins, in addition to RNA expression, and set the stage for future protein-focused studies of these and other brain regions in normal and pathological conditions.

Primary cilia signaling in astrocytes mediates development and regional-specific functional specification

Astrocyte diversity is greatly influenced by local environmental modulation. Here we report that the majority of astrocytes across the mouse brain possess a singular primary cilium localized to the cell soma. Comparative single-cell transcriptomics reveals that primary cilia mediate canonical SHH signaling to modulate astrocyte subtype-specific core features in synaptic regulation, intracellular transport, energy and metabolism. Independent of canonical SHH signaling, primary cilia are important regulators of astrocyte morphology and intracellular signaling balance. Dendritic spine analysis and transcriptomics reveal that perturbation of astrocytic cilia leads to disruption of neuronal development and global intercellular connectomes in the brain. Mice with primary ciliary-deficient astrocytes show behavioral deficits in sensorimotor function, sociability, learning and memory. Our results uncover a critical role for primary cilia in transmitting local cues that drive the region-specific diversification of astrocytes within the developing brain.

Spatial-temporal representation of the astroglial markers in the developing human cortex

Specific spatiotemporal patterns of the normal glial differentiation during human brain development have not been thoroughly studied. Immunomorphological studies on postmortem material have remained a basic method for human neurodevelopmental studies so far. The main problem for the immunohistochemical research of astrogliogenesis is that now there are no universal astrocyte markers, that characterize the whole mature astrocyte population or precursors at each stage of development. To define the general course of astrogliogenesis in the developing human cortex, 25 fetal autopsy samples at the stages from eight postconceptional weeks to birth were collected for the immunomorphological analysis. Spatiotemporal immunoreactivity patterns with the panel of markers (ALDH1L1, GFAP, S100, SOX9, and Olig-2), related to glial differentiation were described and compared. The early S100 + cell population of ventral origin was described as well. This S100 + cell distribution deviated from the SOX9-immunoreactivity pattern and was similar to the Olig-2 one. In the given material the dorsal gliogenic wave was characterized by ALDH1L1-, GFAP-, and S100-immunoreactivity manifestation in the dorsal proliferative niche at the end of the early fetal period. The time point of dorsal astrogliogenesis was agreed upon not later than the 17 GW stage. ALDH1L1 + , GFAP + , S100 + , and SOX9 + cell expansion patterns from the ventricular and subventricular zones to the intermediate zone, subplate, and cortical plate were described at the end of early fetal, middle, and late fetal periods. The ALDH1L1-, GFAP-, and S100-immunoreactivity patterns were shown to be not completely identical.

Heterogeneous brain region-specific responses to astrocytic mitochondrial DNA damage in mice

Astrocytes display context-specific diversity in their functions and respond to noxious stimuli between brain regions. Astrocytic mitochondria have emerged as key players in governing astrocytic functional heterogeneity, given their ability to dynamically adapt their morphology to regional demands on ATP generation and Ca2+ buffering functions. Although there is reciprocal regulation between mitochondrial dynamics and mitochondrial Ca2+ signaling in astrocytes, the extent of this regulation in astrocytes from different brain regions remains unexplored. Brain-wide, experimentally induced mitochondrial DNA (mtDNA) loss in astrocytes showed that mtDNA integrity is critical for astrocyte function, however, possible diverse responses to this noxious stimulus between brain areas were not reported in these experiments. To selectively damage mtDNA in astrocytes in a brain-region-specific manner, we developed a novel adeno-associated virus (AAV)-based tool, Mito-PstI expressing the restriction enzyme PstI, specifically in astrocytic mitochondria. Here, we applied Mito-PstI to two brain regions, the dorsolateral striatum and dentate gyrus, and we show that Mito-PstI induces astrocytic mtDNA loss in vivo, but with remarkable brain-region-dependent differences on mitochondrial dynamics, Ca2+ fluxes, and astrocytic and microglial reactivity. Thus, AAV-Mito-PstI is a novel tool to explore the relationship between astrocytic mitochondrial network dynamics and astrocytic mitochondrial Ca2+ signaling in a brain-region-selective manner.