Genomic analysis of reactive astrogliosis. J Neurosci. 2012;32:6391-6410. [PMID: 22553043 DOI: 10.1523/jneurosci.6221-11.2012]

Vascular depression: A comprehensive exploration of the definition, mechanisms, and clinical challenges

Vascular depression (VaDep), which was proposed over two decades ago, is a distinct subtype of depression primarily observed in patients with stroke and cerebral small-vessel disease and is characterized by white matter hyperintensities; however, the lack of standardized diagnostic criteria and consensus limits its clinical application. This review explores the pathological conditions and vascular risk factors that may precipitate VaDep, particularly in relation to stroke and cerebral small-vessel disease. VaDep is distinguished by unique pathophysiological mechanisms and treatment responses. We categorize these mechanisms into three groups: 1) macroscopic mechanisms, including vascular aging, cerebral hypoperfusion, blood-brain barrier disruption, and neural circuit dysfunction; 2) microscopic mechanisms, involving the inflammatory response, hypothalamic-pituitary-adrenal axis dysregulation, impaired monoamine synthesis, and mitochondrial dysfunction; and 3) undetermined mechanisms, such as microbiota-gut-brain axis dysbiosis. These insights support VaDep as a distinct depression subtype, differentiating it from late-life depression and major depressive disorder. Treatment is challenging, as patients with VaDep often exhibit resistance to conventional antidepressants. Addressing vascular risk factors and protecting vascular integrity are essential for effective management. Future research should validate these mechanisms and develop novel diagnostic and therapeutic approaches to improve VaDep outcomes.

Response of astrocytes and their interaction with surrounding brain cells after acute ischemia-reperfusion analyzed by single-cell transcriptome sequencing

Astrocytes play a key role in the occurrence and development of ischemic stroke. However, reactive astrocytes have both detrimental and protective roles in ischemic stroke. Regrettably, the stimulation signals associated with the transformation of astrocytes into different subclusters lack systemic analysis, and the mechanism by which astrocytes produce multiple effects is not entirely clear. We investigated the heterogeneity of mouse astrocytes 12 h after cerebral ischemia-reperfusion via Single-cell RNA sequencing and verified gene expressions by reverse transcription-polymerase chain reaction. We acquired astrocyte subclusters' transcriptional characteristics involved in diversified functions. To explore what stimulus signals cause astrocyte heterogeneity, we present a blueprint for cellular communication between astrocyte subclusters and other surrounding brain cells 12 h after ischemia-reperfusion, and identified 9 genes which are potential and promising for being therapeutic targets and 6 genes were specific to astrocyte subcluster 2 that tend to resist ischemia-reperfusion injury. At 12 h after ischemia-reperfusion, each subcluster of astrocytes is characteristic in terms of function and communication with surrounding cells, which is based on the activation genes and transcription molecules that we have revealed with subcluster characteristics. Our results provide a basis for revealing the anti-injury response of astrocytes to cerebral ischemia-reperfusion, which involves coordination of different subclusters and the coordination of astrocytes with surrounding brain cells.

Contributions of Genetic Variation in Astrocytes to Cell and Molecular Mechanisms of Risk and Resilience to Late-Onset Alzheimer's Disease

Reactive astrocytes are associated with Alzheimer's disease (AD), and several AD genetic risk variants are associated with genes highly expressed in astrocytes. However, the contribution of genetic risk within astrocytes to cellular processes relevant to the pathogenesis of AD remains ill-defined. Here, we present a resource for studying AD genetic risk in astrocytes using a large collection of induced pluripotent stem cell (iPSC) lines from deeply phenotyped individuals with a range of neuropathological and cognitive outcomes. IPSC lines from 44 individuals were differentiated into astrocytes followed by unbiased molecular profiling using RNA sequencing and tandem mass tag-mass spectrometry. We demonstrate the utility of this resource in examining gene- and pathway-level associations with clinical and neuropathological traits, as well as in analyzing genetic risk and resilience factors through parallel analyses of iPSC-astrocytes and brain tissue from the same individuals. Our analyses reveal that genes and pathways altered in iPSC-derived astrocytes from individuals with AD are concordantly dysregulated in AD brain tissue. This includes increased levels of prefoldin proteins, extracellular matrix factors, COPI-mediated trafficking components and reduced levels of proteins involved in cellular respiration and fatty acid oxidation. Additionally, iPSC-derived astrocytes from individuals resilient to high AD neuropathology show elevated basal levels of interferon response proteins and increased secretion of interferon gamma. Correspondingly, higher polygenic risk scores for AD are associated with lower levels of interferon response proteins in astrocytes. This study establishes an experimental system that integrates genetic information with a matched iPSC lines and brain tissue data from a large cohort of individuals to identify genetic contributions to molecular pathways affecting AD risk and resilience.

Non-neuronal brain biology and its relevance to animal welfare

Non-neuronal cells constitute a significant portion of brain tissue and are seen as having key roles in brain homeostasis and responses to challenges. This review illustrates how non-neuronal biology can bring new perspectives to animal welfare through understanding mechanisms that determine welfare outcomes and highlighting interventions to improve welfare. Most obvious in this respect is the largely unrecognised relevance of neuroinflammation to animal welfare which is increasingly found to have roles in determining how animals respond to challenges. We start by introducing non-neuronal cells and review their involvement in affective states and cognition often seen as core psychological elements of animal welfare. We find that the evidence for a causal involvement of glia in cognition is currently more advanced than the corresponding evidence for affective states. We propose that translational research on affective disorders could usefully apply welfare science derived approaches for assessing affective states. Using evidence from translational research, we illustrate the involvement of non-neuronal cells and neuroinflammatory processes as mechanisms modulating resilience to welfare challenges including disease, pain, and social stress. We review research on impoverished environments and environmental enrichment which suggests that environmental conditions which improve animal welfare also improve resilience to challenges through balancing pro- and anti-inflammatory non-neuronal processes. We speculate that non-neuronal biology has relevance to animal welfare beyond neuro-inflammation including facilitating positive affective states. We acknowledge the relevance of neuronal biology to animal welfare whilst proposing that non-neuronal biology provides additional and relevant insights to improve animals' lives.

Astrocyte heterogeneity in ischemic stroke: Molecular mechanisms and therapeutic targets

Ischemic stroke is one of the major causes of death and disability in adults, bringing a significant economic burden to the society and families. Despite significant advancements in stroke treatment, focusing solely on neurons is insufficient for improving disease progression and prognosis. Astrocytes are the most ubiquitous cells in the brain, and they undergo morphological and functional changes after brain insults, which has been known as astrocyte reactivity. Transcriptomics have shown that reactive astrocytes (RA) are heterogeneous, and they can be roughly classified into neurotoxic and neuroprotective types, thereby affecting the development of central nervous system (CNS) diseases. However, the relationship between stroke and reactive astrocyte heterogeneity has not been fully elucidated, and regulating the heterogeneity of astrocytes to play a neuroprotective role may provide a new perspective for the treatment of stroke. Here we systematically review current advancements in astrocyte heterogeneity following ischemic stroke, elucidate the molecular mechanisms underlying their activation, and further summarize promising therapeutic agents and molecular targets capable of modulating astrocyte heterogeneity.

Inflammasome links traumatic brain injury, chronic traumatic encephalopathy, and Alzheimer's disease

Traumatic brain injury, chronic traumatic encephalopathy, and Alzheimer's disease are three distinct neurological disorders that share common pathophysiological mechanisms involving neuroinflammation. One sequela of neuroinflammation includes the pathologic hyperphosphorylation of tau protein, an endogenous microtubule-associated protein that protects the integrity of neuronal cytoskeletons. Tau hyperphosphorylation results in protein misfolding and subsequent accumulation of tau tangles forming neurotoxic aggregates. These misfolded proteins are characteristic of traumatic brain injury, chronic traumatic encephalopathy, and Alzheimer's disease and can lead to downstream neuroinflammatory processes, including assembly and activation of the inflammasome complex. Inflammasomes refer to a family of multimeric protein units that, upon activation, release a cascade of signaling molecules resulting in caspase-induced cell death and inflammation mediated by the release of interleukin-1β cytokine. One specific inflammasome, the NOD-like receptor protein 3, has been proposed to be a key regulator of tau phosphorylation where it has been shown that prolonged NOD-like receptor protein 3 activation acts as a causal factor in pathological tau accumulation and spreading. This review begins by describing the epidemiology and pathophysiology of traumatic brain injury, chronic traumatic encephalopathy, and Alzheimer's disease. Next, we highlight neuroinflammation as an overriding theme and discuss the role of the NOD-like receptor protein 3 inflammasome in the formation of tau deposits and how such tauopathic entities spread throughout the brain. We then propose a novel framework linking traumatic brain injury, chronic traumatic encephalopathy, and Alzheimer's disease as inflammasome-dependent pathologies that exist along a temporal continuum. Finally, we discuss potential therapeutic targets that may intercept this pathway and ultimately minimize long-term neurological decline.

Astrocytes of the hippocampus and responses to periprandial neuroendocrine hormones

Astrocytes have risen as stars in the field of energy homeostasis and neurocognitive function, acting as a bridge of communication between the periphery and the brain, providing metabolic support, signaling via gliotransmitters, and altering synaptic communication. Dietary factors and energy state have a profound influence on hippocampal function, and the hippocampus is critical for appropriate behavioral responses associated with feeding and internal hunger cues (being in the fasted or full state), but how the hippocampus senses periprandial status and is impacted by diet is largely unknown. Periprandial hormones act within the hippocampus to modulate processes involved in hippocampal-dependent learning and memory function and astrocytes likely play an important role in modulating this signaling. In addition to periprandial hormones, astrocytes are positioned to respond to changes in circulating nutrients like glucose. Here, we review literature investigating how astrocytes mediate changes in hippocampal function, highlighting astrocyte location, morphology, and function in the context of integrating glucose metabolism, neuroendocrine hormone action, and/or cognitive function in the hippocampus. Specifically, we discuss research findings on the effects of insulin, ghrelin, leptin, and GLP-1 on glucose homeostasis, neural activity, astrocyte function, and behavior in the hippocampus. Because obesogenic diets impact neuroendocrine hormones, astrocytes, and cognitive function, we also discuss the effects of diet and diet-induced obesity on these parameters.

Spatiotemporal transcriptomic maps of mouse intracerebral hemorrhage at single-cell resolution

Intracerebral hemorrhage (ICH) is a prevalent disease with high mortality. Despite advances in clinical care, the prognosis of ICH remains poor due to an incomplete understanding of the complex pathological processes. To address this challenge, we generated single-cell-resolution spatiotemporal transcriptomic maps of the mouse brain following ICH. This dataset is the most extensive resource available, providing detailed information about the temporal expression of genes along with a high-resolution cellular profile and preserved cellular organization. We identified 100 distinct cell subclasses, 17 of which were found to play significant roles in the pathophysiology of ICH. We also report similarities and differences between two experimental ICH models and human postmortem ICH brain tissue. This study advances the understanding of the local and global responses of brain cells to ICH. It provides a valuable resource that can facilitate future research and aid the development of novel therapies for this devastating condition.

GADD45G operates as a pathological sensor orchestrating reactive gliosis and neurodegeneration

Reactive gliosis is a hallmark of neuropathology and offers a potential target for addressing numerous neurological diseases. Here, we show that growth arrest and DNA damage inducible gamma (GADD45G), a stress sensor in astrocytes, is a nodal orchestrator of reactive gliosis and neurodegeneration. GADD45G expression in astrocytes is sufficient to incite astrogliosis, microgliosis, synapse loss, compromised animal behavior, and the aggravation of Alzheimer's disease (AD). Conversely, silencing GADD45G specifically in astrocytes preserves synapses and rescues the histological and behavioral phenotypes of AD. Mechanistically, GADD45G controls the mitogen-activated protein kinase kinase kinase 4 (MAP3K4) and neuroimmune signaling pathways, including nuclear factor κB (NF-κB) and interferon regulatory factor 3 (IRF3), leading to profound molecular changes and the secretion of various factors that regulate both cell-autonomous and cell-nonautonomous reactive gliosis and glia-neuron interactions. These results uncover GADD45G signaling as a promising therapeutic target for AD and potentially for numerous other neurological disorders.

Incorporation of graphene oxide into collagenous biomaterials attenuates scar-forming phenotype transition of reactive astrocytes in vitro

The integrin-mediated interaction between collagen type I and reactive astrocytes was recently shown to induce a detrimental, scar-forming phenotype transformation following spinal cord injury (SCI), which severely limits the therapeutic potential of commonly used collagen-based biomaterials. Graphene oxide (GO) is a promising candidate to disrupt the collagen-integrin interaction, since it is capable of altering the surface topography of biomaterials applied as SCI treatment. Moreover, free GO contributes towards potassium and glutamate transport, which is often implicated following SCI. However, it remains unclear whether both the integrin-mediated binding and astrocytic transport of potassium and glutamate are affected by GO, when inserted into collagenous biomaterials. Therefore, in the current study GO was incorporated into collagen-based hydrogels in an attempt to prevent the scar-forming phenotype transition and promote the expression of astrocytic potassium channels and glutamate transporters. Primary astrocytes were cultured either on top of or embedded within GO-enriched collagen type I or adipose tissue-derived extracellular matrix (ECM) gels. The impact of GO incorporation on integrin β1-mediated binding, astrocyte phenotype and potassium and glutamate transport was assessed by gene expression analysis and immunofluorescence studies. Upon GO incorporation into ECM gels, expression of integrin β1 and N-cadherin was significantly decreased. Moreover, GO decreased proteoglycan-associated gene expression by four-fold. Finally, GO incorporation led to a decrease in expression of both potassium channels and glutamate transporters. In conclusion, the incorporation of GO into collagen-based materials attenuated the transition of reactive astrocytes into a scar-forming phenotype.

Neuroimmune regulation of the prefrontal cortex tetrapartite synapse

The prefrontal cortex (PFC) is an essential driver of cognitive, affective, and motivational behavior. There is clear evidence that the neuroimmune system directly influences PFC synapses, in addition to its role as the first line of defense against toxins and pathogens. In this review, we first describe the core structures that form the tetrapartite PFC synapse, focusing on the signaling microdomain created by astrocytic cradling of the synapse as well as the emerging role of the extracellular matrix in synaptic organization and plasticity. Neuroimmune signals (e.g. pro-inflammatory interleukin 1β) can impact the function of each core structure within the tetrapartite synapse, as well as promote intra-synaptic crosstalk, and we will provide an overview of recent advances in this field. Finally, evidence from post mortem human brain tissue and preclinical studies indicate that inflammation may be a key contributor to PFC dysfunction. Therefore, we conclude with a mechanistic discussion of neuroimmune-mediated maladaptive plasticity in neuropsychiatric disorders, with a focus on alcohol use disorder (AUD). Growing recognition of the neuroimmune system's role as a critical regulator of the PFC tetrapartite synapse provides strong support for targeting the neuroimmune system to develop new pharmacotherapeutics.

A single-cell transcriptomic atlas of all cell types in the brain of 5xFAD Alzheimer mice in response to dietary inulin supplementation

BACKGROUND

Alzheimer's disease (AD) is a progressive neurodegenerative disease that is a major threat to the aging population. Due to lack of effective therapy, preventive treatments are important strategies to limit AD onset and progression, of which dietary regimes have been implicated as a key factor. Diet with high fiber content is known to have beneficial effects on cognitive decline in AD. However, a global survey on microbiome and brain cell dynamics in response to high fiber intake at single-cell resolution in AD mouse models is still missing.

RESULTS

Here, we show that dietary inulin supplementation synergized with AD progression to specifically increase the abundance of Akkermansia muciniphila in gut microbiome of 5 × Familial AD (FAD) mice. By performing single-nucleus RNA sequencing on different regions of the whole brain with three independent biological replicates, we reveal region-specific changes in the proportion of neuron, astrocyte, and granule cell subpopulations upon inulin supplementation in 5xFAD mice. In addition, we find that astrocytes have more pronounced region-specific diversity than microglia. Intriguingly, such dietary change reduces amyloid-β plaque burden and alleviates microgliosis in the forebrain region, without affecting the spatial learning and memory.

CONCLUSIONS

These results provide a comprehensive overview on the transcriptomic changes in individual cells of the entire mouse brain in response to high fiber intake and a resourceful foundation for future mechanistic studies on the influence of diet and gut microbiome on the brain during neurodegeneration.

Knowing the enemy: strategic targeting of complement to treat Alzheimer disease

The complement system protects against infection, positively responds to tissue damage, clears cell debris, directs and modulates the adaptive immune system, and functions in neuronal development, normal synapse elimination and intracellular metabolism. However, complement also has a role in aberrant synaptic pruning and neuroinflammation - processes that lead to a feedforward loop of inflammation, injury and neuronal death that can contribute to neurodegenerative and neurological disorders, including Alzheimer disease. This Review provides justification, largely from preclinical mouse models but also from correlates with human tissue and biomarkers, for targeting specific complement components for therapeutic intervention in Alzheimer disease. We discuss promising strategies to slow the progression of cognitive loss with minimal undesired effects. The diverse interactions and functions of complement system components can influence biological processes in the healthy and diseased brain; here, these functions are described as a prerequisite to selecting appropriate, safe and effective therapeutic targets for translation to the clinic.

Transcription Factor-Based Gene Therapy Enables Functional Repair of Rat Following Chronic Ischemic Stroke

OBJECTIVE

In vivo transcription factor (TF) -mediated gene therapy through astrocyte-to-neuron (AtN) conversion has shown therapeutic effects on rodent and non-human primate cortical ischemic injury in the subacute phase. However, in the clinic, subcortical regions including striatum as well as white matter are vulnerable regions of stroke, with millions of patients beyond subacute phase. In this study, we investigate whether TF-mediated AtN conversion therapy can be extended to treat chronic-phase ischemic stroke involving subcortical regions (e.g., striatum) and white matter, beyond cortical injuries.

METHODS

Rat middle cerebral artery occlusion (MCAO)-like models were established to induce broad ischemic injuries including cortical and striatal regions. Then multiple rounds of TF-mediated gene therapy treatments through adeno-associated virus (AAV) system to cover the large-scaled infarct areas were conducted in the chronic phase of the stroke models. Magnetic resonance imaging (MRI), [18F] FDG-PET/CT, behavioral tests, immunohistochemistry and bulk-RNA seq were applied to evaluate the AtN conversion, tissue repair and functional recovery.

RESULTS

Our results revealed that administrated in the chronic phase of ischemic stroke, TF-mediated gene therapy can efficiently regenerate new neurons in both cortical and striatal regions, and promote tissue repair in both grey and white matter. Compared with single round of AAV administration, multiple rounds of treatment regenerated more neurons and led to a significant functional recovery.

CONCLUSIONS

Our study demonstrates that TF-mediated gene therapy has a broad therapeutic time window and can be applied multiple rounds to treat severe ischemic stroke, making it an attractive therapeutic intervention in the chronic phase after stroke, when current approaches are largely ineffective.

Prostaglandin synthesis mediates the suppression of arcuate Kiss1 neuron activation and pulsatile luteinizing hormone secretion during immune/inflammatory stress in female mice

Stress induces a series of compensatory mechanisms with the objective of restoration or adaptation of physiological function. A common casualty of the response to stress is impaired reproduction via the inhibition of pulsatile luteinizing hormone (LH) secretion; however, how stressors convey LH inhibition remains unclear and may be dependent on stress type. Immune/inflammatory stress, modeled with peripheral lipopolysaccharide (LPS) exposure, induces a systemic inflammatory response which may contrast with the neural mechanisms employed by psychosocial stressors. We examined the suppressive effect of LPS versus psychosocial stress, modeled with restraint, on pulsatile LH secretion and investigated the neural mechanisms underlying LPS-induced LH suppression in ovariectomized (OVX) female mice. We observed that both LPS and restraint significantly suppressed mean LH concentrations; however, the dynamics of pulse suppression displayed stress-type dependency. LPS induced a reduction in both LH pulse frequency and amplitude, whereas restraint suppressed LH pulse frequency without compromising pulse amplitude. Next, we investigated the mediatory role of immune/inflammatory signaling for LPS to impair LH secretion and upstream arcuate Kiss1 cell function. Peripheral administration of flurbiprofen, a prostaglandin synthesis inhibitor, blocked the suppressive effect of LPS on LH pulse frequency and amplitude. Interestingly, flurbiprofen only partially prevented the suppressive effect of LPS on arcuate Kiss1 cell activity, as measured by c-Fos expression. These data demonstrate that immune/inflammatory stress inhibits the activity of the LH pulse generator, in part, via a prostaglandin-dependent pathway and supports the role of differential neural mechanisms mediating LH pulse suppression during stress.

Peripheral Inflammation and Insulin Resistance: Their Impact on Blood-Brain Barrier Integrity and Glia Activation in Alzheimer's Disease

Alzheimer's disease (AD) is a progressive neurodegenerative disorder characterized by cognitive decline, memory impairment, and synaptic dysfunction. The accumulation of amyloid beta (Aβ) plaques and hyperphosphorylated tau protein leads to neuronal dysfunction, neuroinflammation, and glial cell activation. Emerging evidence suggests that peripheral insulin resistance and chronic inflammation, often associated with type 2 diabetes (T2D) and obesity, promote increased proinflammatory cytokines, oxidative stress, and immune cell infiltration. These conditions further damage the blood-brain barrier (BBB) integrity and promote neurotoxicity and chronic glial cell activation. This induces neuroinflammation and impaired neuronal insulin signaling, reducing glucose metabolism and exacerbating Aβ accumulation and tau hyperphosphorylation. Indeed, epidemiological studies have linked T2D and obesity with an increased risk of developing AD, reinforcing the connection between metabolic disorders and neurodegeneration. This review explores the relationships between peripheral insulin resistance, inflammation, and BBB dysfunction, highlighting their role in glial activation and the exacerbation of AD pathology.

Biomarkers in Aneurysmatic and Spontaneous Subarachnoid Haemorrhage: A Clinical Prospective Multicentre Biomarker Panel Study of S100B, Claudin-5, Interleukin-10, TREM-1, TREM-2 and Neurofilament Light Chain As Well As Immunoglobulin G and M

Following aneurysmatic subarachnoid haemorrhage (SAH), complex pathophysiological processes take place which result in ischaemia, dysfunction of the blood-brain barrier and the clinical development of vasospasms and delayed cerebral ischaemia (DCI). The aim of this study was to present a biomarker panel that can be used for temporal assignment in the pathophysiological process after haemorrhage, a prediction of vasospasm, DCI or outcome. In a prospective multicentre approach, complex laboratory chemistry tests were used to determine the value of the biomarkers S100B, Claudin-5, Interleukin (IL) -10, Triggering receptor expresses on myeloid cells (TREM)-1 and TREM-2, and neurofilament light chain (NfL) as well as IgG and IgM in plasma and Cerebro-spinal-fluid (CSF) in SAH patients. The predictive power of mentioned biomarkers with regard to the occurrence of vasospasms, DCI and the outcome (Glasgow Outcome Scale) were defined by using sophisticated statistical methods with the level of significance at p ≤ 0.05. Mean age of the 12 patients included was 56 (SD:14) years with 67% female patients and that of the 11 control subjects was 74 (SD:3) years with 55% female subjects. S100B showed higher concentrations compared to the control patients on the first four days (p ≤ 0.0141). For IL-10, the CSF concentrations showed a continuous increase: day 2 (p = 0.0074), day 4 (p = 0.0012), and day 5 (p < 0.0001). Regarding the TREM1 and TREM2 balance, CSF concentrations of TREM1 increased until day eight (p ≤ 0.0055). TREM-2 plasma concentrations decreased below the levels of control patients and appeared unchanged for the further course. The greatest difference in the CSF concentration of NfL between the patients and the control group was seen on day 8 (p = 0.0104). The differentiation between patients with and without DCI showed different concentration curves of the TREM1 CSF-plasma index with increasing concentrations for patients with DCI. The TREM 2 CSF-plasma index showed higher concentrations for patients with DCI. Patients without DCI showed a decreasing concentration of the NfL CSF-plasma index compared to an increase when vasospasm was detected. NfL, TREM-1 and TREM-2 have the potential to be relevant biomarkers for SAH in the intermediate and delayed injury phase.

Adhesion-Related Pathways and Functional Polarization of Astrocytes in Traumatic Brain Injury: Insights from Single-cell RNA Sequencing

Traumatic brain injury (TBI) induces profound functional heterogeneity in astrocytes, yet the regulatory mechanisms underlying this diversity remain poorly understood. In this study, we analyzed single-cell RNA sequencing data from the cortex and hippocampus of TBI mouse models to characterize astrocyte subtypes and their functional dynamics. We identified two major reactive subtypes: A1 astrocytes, enriched in inflammatory response, synaptic regulation, and neurodegenerative disease-related pathways; and A2 astrocytes, enriched in lipid metabolism, extracellular matrix (ECM) remodeling, and phagosome formation pathways. These functional differences were consistently observed across datasets with varying injury severities. Notably, adhesion-related pathways-including gap junctions, adherens junctions, and calcium-dependent adhesion-showed significant subtype-specific expression patterns and temporal shifts. Pseudotime trajectory analysis further suggested a potential transition between A1 and A2 states, accompanied by dynamic regulation of adhesion-related genes. Our findings highlight the complex and context-dependent roles of astrocytes in TBI and propose cell adhesion as a key modulator of astrocyte functional polarization.

The Role of Astrocytes in the Molecular Pathophysiology of Schizophrenia: Between Neurodevelopment and Neurodegeneration

Schizophrenia is a chronic and severe psychiatric disorder affecting approximately 1% of the global population, characterized by disrupted synaptic plasticity and brain connectivity. While substantial evidence supports its classification as a neurodevelopmental disorder, non-canonical neurodegenerative features have also been reported, with increasing attention given to astrocytic dysfunction. Overall, in this study, we explore the role of astrocytes as a structural and functional link between neurodevelopment and neurodegeneration in schizophrenia. Specifically, we examine how astrocytes contribute to forming an aberrant substrate during early neurodevelopment, potentially predisposing individuals to later neurodegeneration. Astrocytes regulate neurotransmitter homeostasis and synaptic plasticity, influencing early vulnerability and disease progression through their involvement in Ca2⁺ signaling and dopamine-glutamate interaction-key pathways implicated in schizophrenia pathophysiology. Astrocytes differentiate via nuclear factor I-A, Sox9, and Notch pathways, occurring within a neuronal environment that may already be compromised in the early stages due to the genetic factors associated with the 'two-hits' model of schizophrenia. As a result, astrocytes may contribute to the development of an altered neural matrix, disrupting neuronal signaling, exacerbating the dopamine-glutamate imbalance, and causing excessive synaptic pruning and demyelination. These processes may underlie both the core symptoms of schizophrenia and the increased susceptibility to cognitive decline-clinically resembling neurodegeneration but driven by a distinct, poorly understood molecular substrate. Finally, astrocytes are emerging as potential pharmacological targets for antipsychotics such as clozapine, which may modulate their function by regulating glutamate clearance, redox balance, and synaptic remodeling.

GPR37L1 identifies spinal cord astrocytes and protects neuropathic pain after nerve injury

Astrocytes in the spinal cord dorsal horn (SDH) play a pivotal role in synaptic transmission and neuropathic pain. However, the precise classification of SDH astrocytes in health and disease remains elusive. Here, we reveal Gpr37l1 as a marker and functional regulator of spinal astrocytes. Through single-nucleus RNA sequencing, we identified Gpr37l1 as a selective G-protein-coupled receptor (GPCR) marker for spinal cord astrocytes. Notably, SDH displayed reactive astrocyte phenotypes and exacerbated neuropathic pain following nerve injury combined with Gpr37l1 deficiency. In naive animals, Gpr37l1 knockdown in SDH astrocytes induces astrogliosis and pain hypersensitivity, while Gpr37l1-/- mice fail to recover from neuropathic pain. GPR37L1 activation by maresin 1 increased astrocyte glutamate transporter 1 (GLT-1) activity and reduced spinal EPSCs and neuropathic pain. Selective overexpression of Gpr37l1 in SDH astrocytes reversed neuropathic pain and astrogliosis after nerve injury. Our findings illuminate astrocyte GPR37l1 as an essential negative regulator of pain, which protects against neuropathic pain through astrocyte signaling in SDH.

Exosome-shuttled miR-5121 from A2 astrocytes promotes BSCB repair after traumatic SCI by activating autophagy in vascular endothelial cells

Spinal cord injury (SCI) is a severe neurological disorder that significantly impacts patients' quality of life. Following SCI, the blood-spinal cord barrier (BSCB) is destroyed, leading to ischemia and hypoxia, which further exacerbates the imbalance in the spinal cord microenvironment. A2-type astrocytes, which arise under ischemic and hypoxic conditions, have been reported to promote SCI repair. However, the roles of exosomes derived from A2 astrocytes (A2-Exos) in SCI have not been explored. This study aims to investigate the role of A2-Exos in SCI repair, particularly in BSCB restoration, and to elucidate its potential mechanisms. GEO database analysis, western blotting, and immunofluorescence were used to detect A2 astrocyte polarization after SCI in mice. In vitro, A2 astrocytes were obtained through hypoxia induction, and A2-Exos were extracted via ultracentrifugation. An in vivo SCI model and a series of in vitro experiments demonstrated the reparative effects of A2-Exos on BSCB following SCI. Furthermore, miRNA sequencing analysis and rescue experiments confirmed the role of miRNAs in A2-Exos-mediated BSCB repair. Finally, luciferase assays and western blotting were performed to investigate the underlying mechanisms. The results showed that A2-Exos promote motor function recovery and BSCB repair in mice following SCI. In vitro, A2-Exos facilitated BSCB reconstruction and endothelial cell autophagy. miRNA sequencing identified miR-5121 as the most significantly enriched miRNA in A2-Exos, suggesting its involvement in BSCB repair and autophagy regulation. AKT2 was identified as a potential downstream target of miR-5121. Functional gain- and loss-of-function experiments further validated the miR-5121/AKT2 axis. Finally, we demonstrated that the AKT2/mTOR/p70S6K pathway may mediate the effects of miR-5121 in A2-Exos on BSCB repair.

Astrocytic RNA editing regulates the host immune response to alpha-synuclein

RNA editing is a posttranscriptional mechanism that targets changes in RNA transcripts to modulate innate immune responses. We report the role of astrocyte-specific, ADAR1-mediated RNA editing in neuroinflammation in Parkinson's disease (PD). We generated human induced pluripotent stem cell-derived astrocytes, neurons and cocultures and exposed them to small soluble alpha-synuclein aggregates. Oligomeric alpha-synuclein triggered an inflammatory glial state associated with Toll-like receptor activation, viral responses, and cytokine secretion. This reactive state resulted in loss of neurosupportive functions and the induction of neuronal toxicity. Notably, interferon response pathways were activated leading to up-regulation and isoform switching of the RNA deaminase enzyme, ADAR1. ADAR1 mediates A-to-I RNA editing, and increases in RNA editing were observed in inflammatory pathways in cells, as well as in postmortem human PD brain. Aberrant, or dysregulated, ADAR1 responses and RNA editing may lead to sustained inflammatory reactive states in astrocytes triggered by alpha-synuclein aggregation, and this may drive the neuroinflammatory cascade in Parkinson's.

Cannabidiol-Rich Cannabis sativa L. Extract Alleviates LPS-Induced Neuroinflammation Behavioral Alterations, and Astrocytic Bioenergetic Impairment in Male Mice

Neuroinflammation is a hallmark of various neurodegenerative disorders, yet effective treatments remain limited. This study investigates the neuroprotective potential of a cannabidiol (CBD)-Rich Cannabis sativa L. (CS) extract in a lipopolysaccharide (LPS)-induced neuroinflammation mouse model. The effects on anxiety-like behavior, cognitive function, and locomotor activity were assessed using behavioral tests (open field, elevated plus maze, novel object recognition, and Morris water maze). Antioxidant activity was measured by assaying glutathione (GSH) levels and lipid peroxidation by-products (TBARs). Anti-inflammatory properties were evaluated using quantitative reverse transcription polymerase chain reaction (QRt-PCR) for proinflammatory cytokines (IL-6 and TNF-α), glial fibrillary acidic protein (GFAP), and cannabinoid receptor 1 (CB1) mRNAs in the prefrontal cortex (PFC). Astrocytic bioenergetics were analyzed using extracellular flux assays. Additionally, computational inference with a deep learning approach was conducted to evaluate the synergistic interactions among CS phytocompounds on the CB1 receptors. Compared with synthetic CBD, the CS extract (20.0 mg/kg) demonstrated superior efficacy in mitigating LPS-induced anxiety-like behavior, cognitive deficits, and locomotor impairments. It also significantly mitigated oxidative stress (increased GSH, reduced TBARs) and suppressed proinflammatory cytokines and GFAP mRNAs, indicating potent anti-inflammatory properties. The extract modulated CB1 receptor expression and preserved metabolic homeostasis in cortical astrocytes, preventing their shift from glycolysis to oxidative phosphorylation under neuroinflammatory conditions. Computational modeling highlighted conformational changes in CB1 receptor residues induced by Delta-9-THC that enhanced CBD binding. These findings underscore the potential of CS extract as a therapeutic candidate for managing neuroinflammation and its associated neurodegenerative consequences, warranting further clinical exploration.

Astrocytes, reactive astrogliosis, and glial scar formation in traumatic brain injury

Traumatic brain injury is a global health crisis, causing significant death and disability worldwide. Neuroinflammation that follows traumatic brain injury has serious consequences for neuronal survival and cognitive impairments, with astrocytes involved in this response. Following traumatic brain injury, astrocytes rapidly become reactive, and astrogliosis propagates from the injury core to distant brain regions. Homeostatic astroglial proteins are downregulated near the traumatic brain injury core, while pro-inflammatory astroglial genes are overexpressed. This altered gene expression is considered a pathological remodeling of astrocytes that produces serious consequences for neuronal survival and cognitive recovery. In addition, glial scar formed by reactive astrocytes is initially necessary to limit immune cell infiltration, but in the long term impedes axonal reconnection and functional recovery. Current therapeutic strategies for traumatic brain injury are focused on preventing acute complications. Statins, cannabinoids, progesterone, beta-blockers, and cerebrolysin demonstrate neuroprotective benefits but most of them have not been studied in the context of astrocytes. In this review, we discuss the cell signaling pathways activated in reactive astrocytes following traumatic brain injury and we discuss some of the potential new strategies aimed to modulate astroglial responses in traumatic brain injury, especially using cell-targeted strategies with miRNAs or lncRNA, viral vectors, and repurposed drugs.

Impacts of PI3K/protein kinase B pathway activation in reactive astrocytes: from detrimental effects to protective functions

Astrocytes are the most abundant type of glial cell in the central nervous system. Upon injury and inflammation, astrocytes become reactive and undergo morphological and functional changes. Depending on their phenotypic classification as A1 or A2, reactive astrocytes contribute to both neurotoxic and neuroprotective responses, respectively. However, this binary classification does not fully capture the diversity of astrocyte responses observed across different diseases and injuries. Transcriptomic analysis has revealed that reactive astrocytes have a complex landscape of gene expression profiles, which emphasizes the heterogeneous nature of their reactivity. Astrocytes actively participate in regulating central nervous system inflammation by interacting with microglia and other cell types, releasing cytokines, and influencing the immune response. The phosphoinositide 3-kinase (PI3K)/protein kinase B (AKT) signaling pathway is a central player in astrocyte reactivity and impacts various aspects of astrocyte behavior, as evidenced by in silico , in vitro , and in vivo results. In astrocytes, inflammatory cues trigger a cascade of molecular events, where nuclear factor-κB serves as a central mediator of the pro-inflammatory responses. Here, we review the heterogeneity of reactive astrocytes and the molecular mechanisms underlying their activation. We highlight the involvement of various signaling pathways that regulate astrocyte reactivity, including the PI3K/AKT/mammalian target of rapamycin (mTOR), α v β 3 integrin/PI3K/AKT/connexin 43, and Notch/PI3K/AKT pathways. While targeting the inactivation of the PI3K/AKT cellular signaling pathway to control reactive astrocytes and prevent central nervous system damage, evidence suggests that activating this pathway could also yield beneficial outcomes. This dual function of the PI3K/AKT pathway underscores its complexity in astrocyte reactivity and brain function modulation. The review emphasizes the importance of employing astrocyte-exclusive models to understand their functions accurately and these models are essential for clarifying astrocyte behavior. The findings should then be validated using in vivo models to ensure real-life relevance. The review also highlights the significance of PI3K/AKT pathway modulation in preventing central nervous system damage, although further studies are required to fully comprehend its role due to varying factors such as different cell types, astrocyte responses to inflammation, and disease contexts. Specific strategies are clearly necessary to address these variables effectively.

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.

SERPINA3 predicts long-term neurological outcomes and mortality in patients with intracerebral hemorrhage

Intracerebral hemorrhage (ICH) is a severe stroke subtype with high mortality and disability rates, and long-term outcomes among survivors remain unpredictable due to the lack of reliable biomarkers. In this study, spatial transcriptomics was used to analyze molecular profiles in autopsy brain tissues from chronic ICH patients, revealing distinct transcriptomic features in the thalamus and cortex, with common inflammatory characteristics such as gliosis, apoptosis, and immune activation. Serine proteinase inhibitor NA3 (SERPINA3) was significantly upregulated in both regions and co-expressed with astrocytes in the thalamus. Pathological studies in postmortem human tissues and mouse models confirmed elevated SERPINA3 expression, with murine Serpina3n showing a similar pattern in mice. Plasma analysis of 250 ICH patients and 250 healthy controls revealed significantly higher SERPINA3 levels in ICH patients, correlating with hemorrhage severity, National Institutes of Health Stroke Scale (NIHSS), and Glasgow Coma Scale (GCS) scores, and long-term functional outcomes. Higher SERPINA3 levels within 72 hours of hemorrhage onset were independently associated with worse functional recovery (mRS ≥ 3) and increased all-cause mortality at 6 and 12 months. Additionally, SERPINA3 levels at 7 days post-ictus correlated with white matter hyperintensities and poor cognitive performance at 6 months. These findings highlight SERPINA3 as a potential prognostic biomarker for ICH, warranting further investigation into its role in long-term neurological dysfunction and validation in larger prospective cohorts.

ALS molecular subtypes are a combination of cellular and pathological features learned by deep multiomics classifiers

Amyotrophic lateral sclerosis (ALS) is a complex syndrome with multiple genetic causes and wide variation in disease presentation. Despite this heterogeneity, large-scale genomics studies revealed that ALS postmortem samples can be grouped into a small number of subtypes, defined by transcriptomic signatures of mitochondrial dysfunction and oxidative stress (ALS-Ox), microglial activation and neuroinflammation (ALS-Glia), or TDP-43 pathology and associated transposable elements (ALS-TE). In this study, we present a deep ALS neural net classifier (DANCer) for ALS molecular subtypes. Applying DANCer to an expanded cohort from the NYGC ALS Consortium highlights two subtypes that strongly correlate with disease duration: ALS-TE in cortex and ALS-Glia in spinal cord. Finally, single-nucleus transcriptomes demonstrate that ALS subtypes are recapitulated in neurons and glia, with both ALS-wide and subtype-specific alterations in all cell types. In summary, ALS molecular subtypes represent a combination of cellular and pathological features that correlate with clinical features of ALS.

Activation of Nuclear Factor-kappa B in the nucleus accumbens core is necessary for chronic stress-induced glutamate and neuro-immune alterations that facilitate cocaine self-administration

Stressful events are associated with impaired glutamate signaling and neuroimmune adaptations that may increase the vulnerability of individuals to cocaine addiction. We previously demonstrated that chronic stress induced reactive microglia and increased TNF-α expression in the nucleus accumbens core (NAcore), both alterations strongly linked with impaired glutamate homeostasis and the facilitation of cocaine self-administration. The nuclear factor kappa-B (NF-κB) is a critical regulator of many immune- and addiction-related genes, such as the gene coding for glutamate transporter (GLT-1), and it is considered a master regulator of inflammation, reported to be a key driver of microglia activation in psychiatric diseases. However, no studies have examined the role of NF-κB signaling within the NAcore in the neuroimmune and glutamate mechanism, underpinning stress-induced vulnerability to cocaine self-administration. Here we investigate whether viral dominant negative inhibition of I kappa B kinase (IKKdn), a signaling molecule responsible for NF-κB activation, would prevent stress-induced facilitation to cocaine self-administration and associated changes in accumbal GLT-1 and TNF-α expression. We also explore N-myc proto-oncogene protein (N-myc) levels as a link between NF-κB and stress-induced GLT-1 downregulation. For seven days (days 1-7), adult male rats were restrained for 2 h/day. Animals were administered an intra-NAcore with IKKdn or empty lentiviruses on day 14 after the first restraint stress session. Marked activation of NF-κB was detected in the NAcore of stressed subjects, along with increased NF-κB expression in astrocytes. Consistently, viral NF-κB inhibition prevented stress-induced facilitation of cocaine self-administration. Moreover, NF-κB blockade results in the restoration of stress-induced reduction in GLT-1 levels and was effective in suppressing stress-induced TNF-α within the NAcore. These findings suggest that accumbal NF-κB signaling exerts a central control over stress-altered downstream neuroimmune and glutamate function underlying vulnerability to cocaine use disorders.

Coordinated regulation of cortical astrocyte maturation by OLIG1 and OLIG2 through BMP7 signaling modulation

Astrocyte maturation is crucial for brain function, yet the mechanisms regulating this process remain poorly understood. In this study, we identify the bHLH transcription factors Olig1 and Olig2 as essential coordinators of cortical astrocyte maturation. We demonstrate that Olig1 and Olig2 work synergistically to regulate cortical astrocyte maturation by modulating Bmp7 expression. Genetic ablation of both Olig1 and Olig2 results in defective astrocyte morphology, including reduced process complexity and an immature gene expression profile. Single-cell RNA sequencing reveals a shift towards a less mature astrocyte state, marked by elevated levels of HOPX and GFAP, resembling human astrocytes. Mechanistically, Olig1 and Olig2 bind directly to the Bmp7 enhancer, repressing its expression to promote astrocyte maturation. Overexpression of Bmp7 in vivo replicates the astrocyte defects seen in Olig1/2 double mutants, confirming the critical role of BMP7 signaling in this process. These findings provide insights into the transcriptional and signaling pathways regulating astrocyte development and highlight Olig1 and Olig2 as key regulators of cortical astrocyte maturation, with potential implications for understanding glial dysfunction in neurological diseases.

Reactive Astrocytes in Glioma: Emerging Opportunities and Challenges

Gliomas are the most prevalent malignant tumors in the adult central nervous system (CNS). Glioblastoma (GBM) accounts for approximately 60-70% of primary gliomas. It is a great challenge to human health because of its high degree of malignancy, rapid progression, short survival time, and susceptibility to recurrence. Owing to the specificity of the CNS, the glioma microenvironment often contains numerous glial cells. Astrocytes are most widely distributed in the human brain and form reactive astrocyte proliferation regions around glioma tissue. In addition, astrocytes are activated under pathological conditions and regulate tumor and microenvironmental cells through cell-to-cell contact or the secretion of active substances. Therefore, astrocytes have attracted attention as important components of the glioma microenvironment. Here, we focus on the mechanisms of reactive astrocyte activation under glioma conditions, their contribution to the mechanisms of glioma genesis and progression, and their potential value as targets for clinical intervention in gliomas.

Astroglia's role in synchronized spontaneous neuronal activity: from physiology to pathology

The nervous system relies on a balance of excitatory and inhibitory signals. Aberrant neuronal hyperactivity is a pathological phenotype associated with several neurological disorders, with its most severe effects observed in epilepsy patients. This review explores the literature on spontaneous synchronized neuronal activity, its physiological role, and its aberrant forms in disease. Emphasizing the importance of targeting underlying disease mechanisms beyond traditional neuron-focused therapies, the review delves into the role of astroglia in epilepsy progression. We detail how astroglia transitions from a normal to a pathological state, leading to epileptogenic seizures and cognitive decline. Astroglia activity is correlated with epileptiform activity in both animal models and human tissue, indicating their potential role in seizure induction and modulation. Understanding astroglia's dual beneficial and detrimental roles could lead to novel treatments for epilepsy and other neurological disorders with aberrant neuronal activity as the underlying disease substrate.

Parthenolide regulates microglial and astrocyte function in primary cultures from ALS mice and has neuroprotective effects on primary motor neurons

Over the last twenty years, the role of microgliosis and astrocytosis in the pathophysiology of neurodegenerative diseases has increasingly been recognized. Dysregulation of microglial and astrocyte properties and function has been described also in the fatal degenerative motor neuron disease amyotrophic lateral sclerosis (ALS). Microglia cells, the immune cells of the nervous system, can either have an immunonegative neurotoxic or immunopositive neuroprotective phenotype. The feverfew plant (Tanacetum parthenium) derived compound parthenolide has been found to be capable of interfering with microglial phenotype and properties. Positive treatment effects were shown in animal models of neurodegenerative diseases like Alzheimer's disease and Parkinson's disease. Now we were able to show that PTL has a modulating effect on primary mouse microglia cells, both wild type and SOD1, causing them to adopt a more neuroprotective potential. Furthermore, we were able to show that PTL, through its positive effect on microglia, also has an indirect positive impact on motor neurons, although PTL itself has no direct effect on these primary motor neurons. The results of our study give reason to consider PTL as a drug candidate for ALS.

Astrocytes in the mouse brain respond bilaterally to unilateral retinal neurodegeneration

Glaucomatous optic neuropathy, or glaucoma, is the world's primary cause of irreversible blindness. Glaucoma is comorbid with other neurodegenerative diseases, but how it might impact the environment of the full central nervous system to increase neurodegenerative vulnerability is unknown. Two neurodegenerative events occur early in the optic nerve, the structural link between the retina and brain: loss of anterograde transport in retinal ganglion cell (RGC) axons and early alterations in astrocyte structure and function. Here, we used whole-mount tissue clearing of full mouse brains to image RGC anterograde transport function and astrocyte responses across retinorecipient regions early in a unilateral microbead occlusion model of glaucoma. Using light sheet imaging, we found that RGC projections terminating specifically in the accessory optic tract are the first to lose transport function. Although degeneration was induced in one retina, astrocytes in both brain hemispheres responded to transport loss in a retinotopic pattern that mirrored the degenerating RGCs. A subpopulation of these astrocytes in contact with large descending blood vessels were immunopositive for LCN2, a marker associated with astrocyte reactivity. Together, these data suggest that even early stages of unilateral glaucoma have broad impacts on the health of astrocytes across both hemispheres of the brain, implying a glial mechanism behind neurodegenerative comorbidity in glaucoma.

Calycosin regulates astrocyte reactivity and astrogliosis after spinal cord injury by targeting STAT3 phosphorylation

BACKGROUND

Astrocytes are the most populous glial cells in the central nervous system (CNS), which can exert detrimental effects through a process of reactive astrogliosis. Our previous study has indicated the potential effect of Calycosin in preventing spinal cord injury (SCI). This study aims to investigate the mechanism by which calycosin regulates the polarization of A1 astrocytes, a neurotoxic subtype of reactive astrocytes, in SCI models.

MATERIALS AND METHODS

The SCI model was induced by applying mechanical compression to the spinal cord using vascular clamps. A1 astrocyte differentiation was induced by treating astrocytes with microglia supernatant obtained after Lipopolysaccharide (LPS) stimulation. Key protein expression levels were analyzed by Western blotting, and astrocyte markers such as CS56, GFAP, C3, S100A10 were assessed through immunofluorescence staining.

RESULTS

Calycosin treatment significantly reduced glial scar formation and C3 expression in SCI rats. However, S100A10 expression remained unchanged. Further analysis showed that Calycosin inhibited A1 astrocyte activation, migration, and invasion, which was associated with STAT3 phosphorylation. Calycosin downregulated p-STAT3 levels in both A1 astrocytes and SCI rats. These effects were reversed by Colivelin (a STAT3 activator) in A1 astrocytes.

CONCLUSION

Calycosin treatment can modulate p-STAT3 expression, thereby altering the functionality of astrocytes during the recovery phase and positively impacting the treatment and rehabilitation of SCI.

Interrogating mediators of single-cell transcriptional changes in the acute damaged cerebral cortex: Insights into endothelial-astrocyte interactions

Traumatic brain injury (TBI) induces complex cellular and molecular changes, challenging recovery and therapeutic development. Although molecular pathways have been implicated in TBI pathology, the cellular specificity of these mechanisms remains underexplored. Here, we investigate the role of endothelial cell (EC) EphA4, a receptor tyrosine kinase receptor involved in axonal guidance, in modulating cell-specific transcriptomic changes within the damaged cerebral cortex. Utilizing single-cell RNA sequencing (scRNA-seq) in an experimental TBI model, we mapped transcriptional changes across various cell types, with a focus on astrocytes and ECs. Our analysis reveals that EC-specific knockout (KO) of EphA4 triggers significant alterations in astrocyte gene expression and shifts predominate subclusters. We identified six distinct astrocyte clusters (C0-C5) in the damaged cortex including as C0-Mobp/Plp1+; C1-Slc1a3/Clu+; C2-Hbb-bs/Hba-a1/Ndrg2+; C3-GFAP/Lcn2+; C4-Gli3/Mertk+, and C5-Cox8a+. We validate a new Sox9+ cluster expressing Mertk and Gas, which mediates efferocytosis to facilitate apoptotic cell clearance and anti-inflammatory responses. Transcriptomic and CellChat analyses of EC-KO cells highlights upregulation of neuroprotective pathways, including increased amyloid precursor protein (APP) and Gas6. Key pathways predicted to be modulated in astrocytes from EC-KO mice include oxidative phosphorylation and FOXO signaling, mitochondrial dysfunction and ephrin B signaling. Concurrently, metabolic and signaling pathways in endothelial cells-such as ceramide and sphingosine phosphate metabolism and NGF-stimulated transcription-indicate an adaptive response to a metabolically demanding post-injury hypoxic environment. These findings elucidate potential interplay between astrocytic and endothelial responses as well as transcriptional networks underlying cortical tissue damage.

Glial Cells in Spinal Muscular Atrophy: Speculations on Non-Cell-Autonomous Mechanisms and Therapeutic Implications

Spinal muscular atrophy (SMA) is a neuromuscular disorder caused by homozygous deletions or mutations in the SMN1 gene, leading to progressive motor neuron degeneration. While SMA has been classically viewed as a motor neuron-autonomous disease, increasing evidence indicates a significant role of glial cells-astrocytes, microglia, oligodendrocytes, and Schwann cells-in the disease pathophysiology. Astrocytic dysfunction contributes to motor neuron vulnerability through impaired calcium homeostasis, disrupted synaptic integrity, and neurotrophic factor deficits. Microglia, through reactive gliosis and complement-mediated synaptic stripping, exacerbate neurodegeneration and neuroinflammation. Oligodendrocytes exhibit impaired differentiation and metabolic support, while Schwann cells display abnormalities in myelination, extracellular matrix composition, and neuromuscular junction maintenance, further compromising motor function. Dysregulation of pathways such as NF-κB, Notch, and JAK/STAT, alongside the upregulation of complement proteins and microRNAs, reinforces the non-cell-autonomous nature of SMA. Despite the advances in SMN-restorative therapies, they do not fully mitigate glial dysfunction. Targeting glial pathology, including modulation of reactive astrogliosis, microglial polarization, and myelination deficits, represents a critical avenue for therapeutic intervention. This review comprehensively examines the multifaceted roles of glial cells in SMA and highlights emerging glia-targeted strategies to enhance treatment efficacy and improve patient outcomes.

TSG-6 Protects Against Cerebral Ischemia-Reperfusion Injury via Upregulating Hsp70-1B in Astrocytes

AIMS

This study aimed to investigate the relationship between tumor necrosis factor alpha-induced protein (TNFAIP6/TSG-6) and astrocytes in cerebral ischemia/reperfusion (I/R) injury.

METHODS

Utilizing in vivo and in vitro cerebral I/R models, cerebral infarct volumes, neurobehavioral outcomes, blood-brain barrier (BBB) permeability, as well as indicators of astrocyte apoptosis, reactivity, and A1 phenotype were assessed to evaluate the effects of recombinant rattus TSG-6 (rrTSG-6) on astrocytes in acute cerebral I/R injury. Following mRNA sequencing of all astrocyte groups, astrocyte apoptosis and reactivity were analyzed through a combined intervention of rrTSG-6 and Apoptozole, a heat shock protein 70-1B (Hsp70-1B) inhibitor, in vitro.

RESULTS

The findings demonstrated that rrTSG-6 significantly reduced cerebral infarct volumes by nearly half, improved neurobehavioral outcomes, mitigated BBB damage, and suppressed the expressions of astrocyte apoptosis markers, reactivity indicators, and A1 phenotype markers. mRNA sequencing revealed that the Hsp70-1B protein level increased to approximately 1.6 times that of the rrTSG-6 non-intervention group. Furthermore, Apoptozole impeded the expressions of astrocyte apoptosis markers, reactivity indicators, and A1 phenotype markers.

CONCLUSION

TSG-6 inhibited nuclear factor kappa-B (NF-κB) phosphorylation by upregulating Hsp70-1B in oxygen-glucose deprivation/reoxygenation (OGD/R)-induced astrocytes, thereby exerting a protective effect through anti-apoptotic mechanisms and the suppression of astrocyte reactivity and A1 transformation following cerebral I/R injury.

The role of astrocyte metabolic reprogramming in ischemic stroke (Review)

Ischemic stroke, a leading cause of disability and mortality worldwide, is characterized by the sudden loss of blood flow in specific area of the brain. Intravenous thrombolysis with recombinant tissue plasminogen activator is the only approved pharmacological treatment for acute ischemic stroke; however, the aforementioned treatment has significant clinical limitations, thus there is an urgent need for the development of novel mechanisms and therapeutic strategies for ischemic stroke. Astrocytes, abundant and versatile cells in the central nervous system, offer crucial support to neurons nutritionally, structurally and physically. They also contribute to blood‑brain barrier formation and regulate neuronal extracellular ion concentrations. Accumulated evidence has revealed the involvement of astrocytes in the regulation of host neurotransmitter metabolism, immune response and tissue repair, and different metabolic characteristics of astrocytes can contribute to the process and development of ischemic stroke, suggesting that targeted regulation of astrocyte metabolic reprogramming may contribute to the treatment and prognosis of ischemic stroke. In the present review, the current understanding of the multifaceted mechanisms of astrocyte metabolic reprogramming in ischemic stroke, along with its regulatory factors and pathways, as well as the strategies to promote its polarization balance, which hold promise for astrocyte immunometabolism‑targeted therapies in the treatment of ischemic stroke, were summarized.

Modulating mTOR-dependent astrocyte substate transitions to alleviate neurodegeneration

Traditional approaches to studying astrocyte heterogeneity have mostly focused on analyzing static properties, failing to identify whether subtypes represent intermediate or final states of reactive astrocytes. Here we show that previously proposed neuroprotective and neurotoxic astrocytes are transitional states rather than distinct subtypes, as revealed through time-series multiomic sequencing. Neuroprotective astrocytes are an intermediate state of the transition from a nonreactive to a neurotoxic state in response to neuroinflammation, a process regulated by the mTOR signaling pathway. In Alzheimer's disease (AD) and aging, we observed an imbalance in neurotoxic and neuroprotective astrocytes in animal models and human patients. Moreover, targeting mTOR in astrocytes with rapamycin or shRNA mitigated astrocyte neurotoxic effects in neurodegenerative mouse models. Overall, our study uncovers a mechanism through which astrocytes exhibit neuroprotective functions before becoming neurotoxic under neuroinflammatory conditions and highlights mTOR modulation specifically in astrocytes as a potential therapeutic strategy for neurodegenerative diseases.

A2-Astrocyte Activation by Short-Term Hypoxia Rescues α-Synuclein Pre-Formed-Fibril-Induced Neuronal Cell Death

Background/Objectives: Parkinson's disease (PD) is a neuro-degenerative disease for which a radical cure is not available, only symptomatic control. Studies have shown that hypoxia may have disease-modifying effects on PD. Methods: Herein, we investigated whether short-term hypoxia activates astrocytes and whether it has a protective effect on pre-formed fibril (PFF)-treated primary cortical neurons. Results: Long-term hypoxia suppresses astrocyte activation and induces cell death, whereas short-term hypoxia activates astrocytes without affecting cellular apoptosis or viability. Short-term hypoxia restored the cellular apoptosis and viability of PFF-treated neurons and reduced toxic phospho-α-synuclein (p-α-syn) aggregation. Similarly, the short-term hypoxia-exposed astrocyte-conditioned medium rescued cellular apoptosis and the viability of PFF-treated neurons and p-α-syn expression. Quantitative polymerase chain reaction revealed that short-term hypoxia promotes protective A2 astrocytes and suppresses toxic A1 astrocytes. Conclusions: Our findings suggest that short-term hypoxia has a neuro-protective effect against PD by activating protective A2 astrocytes, which rescue PFF-induced neuronal cell death. This provides insights into the clinical implications of short-term hypoxia as a disease-modifying PD strategy.

Astrogliosis and glial scar in ischemic stroke - focused on mechanism and treatment

Ischemic stroke is a kind of neurological dysfunction caused by cerebral ischemia. Astrocytes, as the most abundant type of glial cells in the central nervous system, are activated into reactive astrocytes after cerebral ischemia, and this process involves the activation or change of a series of cell surface receptors, ion channels and ion transporters, GTPases, signaling pathways, and so on. The role of reactive astrocytes in the development of ischemic stroke is time-dependent. In the early stage of ischemia, reactive astrocytes proliferate moderately and surround the ischemic tissue to prevent the spread of the lesion. At the same time, reactive astrocytes release neuroprotective factors, ultimately relieving brain injury. In the late stage of ischemia, reactive astrocytes excessively proliferate and migrate to form dense glial scar tissue, which hinders the repair of damaged tissue. At the same time, reactive astrocytes in the glial scar release a large number of neurotoxic factors, ultimately aggravating ischemic stroke. In this paper, we focus on the molecular mechanism of astrogliosis and glial scar formation after cerebral ischemia, and explore the relevant studies using glial scar as a therapeutic target, providing a reference for the selection of therapeutic strategies for ischemic stroke and further research directions.

Forty-hertz sensory entrainment impedes kindling epileptogenesis and reduces amyloid pathology in an Alzheimer disease mouse model

OBJECTIVE

The 5xFAD mouse model of Alzheimer disease (AD) recapitulates amyloid-beta (Aβ) deposition and pronounced seizure susceptibility observed in patients with AD. Forty-hertz audiovisual stimulation is a noninvasive technique that entrains gamma neural oscillations and can reduce Aβ pathology and modulate glial expression in AD models. We hypothesized that 40-Hz sensory stimulation would improve seizure susceptibility in 5xFAD mice and this would be associated with reduction of plaques and modulation of glial phenotypes.

METHODS

5xFAD mice and wild-type (WT) littermates received 1 h/day 40-Hz audiovisual stimulation or sham (n = 7-11/group), beginning 2 weeks before and continuing throughout amygdala kindling epileptogenesis. Postmortem analyses included Aβ pathology and morphology of astrocytes and microglia.

RESULTS

5xFAD mice exhibited enhanced susceptibility to seizures compared to WT, evidenced by fewer stimulations to reach kindling endpoint (incidence rate ratio [IRR] = 1.46, p < .0001) and a trend to higher seizure severity (odds ratio [OR] = .34, p = .059). Forty-hertz stimulation reduced the behavioral severity of the first seizure (OR = 4.04, p = .02) and delayed epileptogenesis, increasing the number of stimulations required to reach kindling endpoint (IRR = .82, p = .01) compared to sham, regardless of genotype. 5xFAD mice receiving sensory stimulation exhibited ~50% reduction in amyloid pathology compared to sham. Furthermore, markers of astrocytes and microglia were upregulated in both genotypes receiving 40-Hz stimulation.

SIGNIFICANCE

Forty-hertz sensory entrainment slows epileptogenesis in the mouse amygdala kindling model. Although this intervention improves Aβ pathology in 5xFAD mice, the observed antiepileptogenic effect may also relate to effects on glia, because mice without Aβ plaques (i.e., WT) also experienced antiepileptogenic effects of the intervention.

New perspectives on heterogeneity in astrocyte reactivity in neuroinflammation

The inflammatory response is a fundamental aspect of all insults to the central nervous system (CNS), which includes acute trauma, infections, and chronic neurodegenerative conditions. As methods for investigating astrocytes have progressed, recent findings indicate that astrocytes can react to a diverse spectrum of insults affecting the central nervous system. Astrocytes respond to external and internal stimuli from the nervous system in a process called glial reactivity. Astrocyte reactivity, previously considered uniform and functionally inactive, is currently a very diverse event in different inflammatory processes. These differences can occur due to the nature, the intensity of the stimulus, the brain region involved and can range from subtle changes in astrocytic morphology to protein expression alteration, gene transcription profile shifts, and variations in the secretory pattern of molecules. The elucidation of the diverse roles of astrocytes in both normal and pathological conditions has led to increased interest in the notion that various astrocyte subtypes may exist, each contributing with distinct functions. Our study will prioritize the characterization of astrocytic response patterns in the context of the development and progression of neurodegenerative diseases, particularly Alzheimer's and Parkinson's. In addition, we will investigate the astrocyte's response during bacterial and viral infections, given the potential to enhance specific therapeutic interventions based on the reactivity profiles of astrocytes.

Exploratory analysis of the proteomic profile in plasma in adults with Down syndrome in the context of Alzheimer's disease

INTRODUCTION

Adults with Down syndrome (DS) show increased risk for Alzheimer's disease (AD) due to the triplication of chromosome 21 encoding the amyloid precursor protein gene. Further, this triplication possibly contributes to dysregulation of the immune system, furthering AD pathophysiology.

METHODS

Using Olink Explore 3072, we measured ∼3000 proteins in plasma from 73 adults with DS and 15 euploid, healthy controls (HC). Analyses for differentially expressed proteins (DEP) were carried out, and pathway and protein network enrichment using Gene Ontology, Kyoto Encyclopedia of Genes and Genomes (KEGG), and STRING database was investigated. Within DS, the LASSO (least absolute shrinkage and selection operator) feature selection was applied.

RESULTS

We identified 253 DEP between DS and HC and 142 DEP between symptomatic and asymptomatic DS. Several pathways regarding inflammatory and neurodevelopmental processes were dysregulated in both analyses. LASSO feature selection within DS returned 15 proteins as potential blood markers.

DISCUSSION

This exploratory proteomic analysis found potential new blood biomarkers for diagnosing DS-AD in need of further investigation.

HIGHLIGHTS

Inflammatory pathways are dysregulated in symptomatic versus asymptomatic DS. NFL and GFAP are confirmed as powerful biomarkers in DS with clinical and/or cognitive decline. Further circulating proteins were identified as potential blood biomarkers for symptomatic DS.

3-HKA Promotes Vascular Remodeling After Stroke by Modulating the Activation of A1/A2 Reactive Astrocytes

Ischemic stroke is the most common cerebrovascular disease and the leading cause of permanent disability worldwide. Recent studies have shown that stroke development and prognosis are closely related to abnormal tryptophan metabolism. Here, significant downregulation of 3-hydroxy-kynurenamine (3-HKA) in stroke patients and animal models is identified. Supplementation with 3-HKA improved long-term neurological recovery, reduced infarct volume, and increased ipsilateral cerebral blood flow after distal middle cerebral artery occlusion (MCAO). 3-HKA promoted angiogenesis, functional blood vessel formation, and blood-brain barrier (BBB) repair. Moreover, 3-HKA inhibited A1-like (neurotoxic) astrocyte activation but promoted A2-like (neuroprotective) astrocyte polarization. Proteomic analysis revealed that 3-HKA inhibited AIM2 inflammasome activation after stroke, and co-labeling studies indicated that AIM2 expression typically increased in astrocytes at 7 and 14 days after stroke. Consistently, in co-cultures of primary mouse brain microvascular endothelial cells and astrocytes, 3-HKA promoted angiogenesis after oxygen-glucose deprivation (OGD). AIM2 overexpression in astrocytes abrogated 3-HKA-driven vascular remodeling in vitro and in vivo, suggesting that 3-HKA may regulate astrocyte-mediated vascular remodeling by impeding AIM2 inflammasome activation. In conclusion, 3-HKA may promote post-stroke vascular remodeling by regulating A1/A2 astrocyte activation, thereby improving long-term neurological recovery, suggesting that supplementation with 3-HKA may be an efficient therapy for stroke.

Cell polarization in ischemic stroke: molecular mechanisms and advances

Ischemic stroke is a cerebrovascular disease associated with high mortality and disability rates. Since the inflammation and immune response play a central role in driving ischemic damage, it becomes essential to modulate excessive inflammatory reactions to promote cell survival and facilitate tissue repair around the injury site. Various cell types are involved in the inflammatory response, including microglia, astrocytes, and neutrophils, each exhibiting distinct phenotypic profiles upon stimulation. They display either proinflammatory or anti-inflammatory states, a phenomenon known as 'cell polarization.' There are two cell polarization therapy strategies. The first involves inducing cells into a neuroprotective phenotype in vitro, then reintroducing them autologously. The second approach utilizes small molecular substances to directly affect cells in vivo. In this review, we elucidate the polarization dynamics of the three reactive cell populations (microglia, astrocytes, and neutrophils) in the context of ischemic stroke, and provide a comprehensive summary of the molecular mechanisms involved in their phenotypic switching. By unraveling the complexity of cell polarization, we hope to offer insights for future research on neuroinflammation and novel therapeutic strategies for ischemic stroke.

FGF21, a modulator of astrocyte reactivity, protects against ischemic brain injury through anti-inflammatory and neurotrophic pathways

Ischemic stroke is a frequent cause of mortality and disability, and astrocyte reactivity is closely associated with injury outcomes. Fibroblast growth factor 21 (FGF21), an endogenous regulator, has been shown to perform pleiotropic functions in central nervous system (CNS) disorders. However, studies on neurological diseases have paid little attention to the effects and detailed mechanisms of FGF21 in astrocytes. Here, we found elevated serum levels of FGF21 in stroke patients and transient middle cerebral artery occlusion (tMCAO) mice. In the peri-infarct cortex, microglia and astrocytes serve as sources of FGF21 in addition to neurons. MRI and neurobehavioral assessments of wild-type (WT) and FGF21-/- tMCAO model mice revealed a deteriorated consequence of the loss of FGF21, with exacerbated brain infarction and neurological deficits. Additionally, combined with the pharmacological treatment of WT mice with recombinant human FGF21 (rhFGF21) after tMCAO, FGF21 was identified to suppress astrocytic activation and astrocyte-mediated inflammatory responses after brain ischemia and participated in controlling the infiltration of peripheral inflammatory cells (including macrophages, neutrophils, monocytes, and T cells) by modulating chemokines expression (such as Ccl3, Cxcl1, and Cxcl2) in astrocytes. Furthermore, rhFGF21 was shown to boost the production of neurotrophic factors (BDNF and NGF) in astrocytes, and by which rescued neuronal survival and promoted synaptic protein expression (postsynaptic density protein-95 (PSD-95), synaptotagmin 1 (SYT1), and synaptophysin) in neurons after ischemic injury. Overall, our findings implicate that FGF21 acts as a suppressor of astrocyte activation, and exerts anti-inflammatory and neurotrophic effects after ischemic brain injury through its action on astrocytes, offering an alternative therapeutic target.

The meninges host a distinct compartment of regulatory T cells that preserves brain homeostasis

Our understanding of the meningeal immune system has recently burgeoned, particularly regarding how innate and adaptive effector cells are mobilized to meet brain challenges. However, information on how meningeal immunocytes guard brain homeostasis in healthy individuals remains limited. This study highlights the heterogeneous, polyfunctional regulatory T cell (Treg) compartment in the meninges. A Treg subtype specialized in controlling interferon-γ (IFN-γ) responses and another dedicated to regulating follicular B cell responses were substantial components of this compartment. Accordingly, punctual Treg ablation rapidly unleashed IFN-γ production by meningeal lymphocytes, unlocked access to the brain parenchyma, and altered meningeal B cell profiles. Distally, the hippocampus assumed a reactive state, with morphological and transcriptional changes in multiple glial cell types. Within the dentate gyrus, neural stem cells underwent more death and were blocked from further differentiation, which coincided with impairments in short-term spatial-reference memory. Thus, meningeal Tregs are a multifaceted safeguard of brain homeostasis at steady state.

The Biflavonoid Agathisflavone Regulates Microglial and Astrocytic Inflammatory Profiles via Glucocorticoid Receptor

Nuclear receptors such as glucocorticoid receptors (GRs) are transcription factors with prominent regulatory effects on neuroinflammation. Agathisflavone is a biflavonoid that demonstrates neurogenic, neuroprotective, anti-inflammatory, antioxidant, and pro-myelinogenic effects in vitro. This study investigated whether the control of glial reactivity by agathisflavone is mediated by GRs. Primary cultures of astrocytes and microglia were induced to neuroinflammation by lipopolysaccharides (LPSs) and exposed to agathisflavone or not in the presence or absence of mifepristone, a GR antagonist. The microglia morphology and reactivity were evaluated by immunofluorescence against calcium-binding ionized adapter (Iba-1) and CD68. The astrocyte morphology and reactivity were evaluated by immunofluorescence against glial fibrillary acidic protein (GFAP). The inflammatory profile was evaluated by RT-qPCR. Molecular docking was performed to characterize agathisflavone and GR interactions. Microglial branching was increased in response to agathisflavone, an effect that was inhibited by mifepristone. CD68 and GFAP expression was decreased by agathisflavone but not in the presence of mifepristone. Agathisflavone decreased the expression of the pro-inflammatory cytokine IL-1β and increased the expression of the regulatory cytokine IL-10. The increase in IL-10 mRNA was inhibited by the GR antagonist. The in silico analysis showed that agathisflavone binds to a pocket at the glucocorticoid receptor. These interactions were stronger than mifepristone, dexamethasone, and the agathisflavone monomer apigenin. These results indicate that the GR is involved in the regulatory effects of agathisflavone on microglia and astrocyte inflammation, contributing to the elucidation of the molecular mechanisms of agathisflavone's effects in the nervous system.