Microglia sense astrocyte dysfunction and prevent disease progression in an Alexander disease model

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.

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.

Single-Cell Cortical Transcriptomics Reveals Common and Distinct Changes in Cell-Cell Communication in Alzheimer's and Parkinson's Disease

Alzheimer's disease (AD) and Parkinson's disease (PD) cause significant neuronal loss and severely impair daily living. Despite different clinical manifestations, these disorders share common pathological molecular hallmarks, including mitochondrial dysfunction and synaptic degeneration. A detailed comparison of molecular changes at single-cell resolution in the cortex, as one of the main brain regions affected in both disorders, may reveal common susceptibility factors and disease mechanisms. We performed single-cell transcriptomic analyses of post-mortem cortical tissue from AD and PD subjects and controls to identify common and distinct disease-associated changes in individual genes, cellular pathways, molecular networks, and cell-cell communication events, and to investigate common mechanisms. The results revealed significant disease-specific, shared, and opposing gene expression changes, including cell type-specific signatures for both diseases. Hypoxia signaling and lipid metabolism emerged as significantly modulated cellular processes in both AD and PD, with contrasting expression alterations between the two diseases. Furthermore, both pathway and cell-cell communication analyses highlighted shared significant alterations involving the JAK-STAT signaling pathway, which has been implicated in the inflammatory response in several neurodegenerative disorders. Overall, the analyses revealed common and distinct alterations in gene signatures, pathway activities, and gene regulatory subnetworks in AD and PD. The results provide insights into coordinated changes in pathway activity and cell-cell communication that may guide future diagnostics and therapeutics.

Neuroglia in leukodystrophies

Leukodystrophies are a heterogeneous group of rare genetic neurologic disorders characterized by white matter degeneration resulting from mutations affecting glial cells. This review focuses on the primary subtypes-astroglial, oligodendroglial, and microglial leukodystrophies-offering a detailed description of their neuropathologic features and clinical manifestations. It delves into key aspects of the pathogenesis, emphasizing the distinct cellular mechanisms that drive white matter damage. Advances in disease modeling, including the development of animal models with pathologic gene expressions and patient-derived iPS-cell models, have significantly enhanced our understanding of these rare disorders. Insights into the roles of different glial cell types highlight the complexity of leukodystrophies and provide a foundation for the development of targeted therapeutic strategies.

Establishment and Use of Primary Cultured Astrocytes from Alexander Disease Model Mice

Alexander disease (AxD) is an intractable neurodegenerative disease caused by mutations in glial fibrillary acidic protein (GFAP), which is predominantly expressed in astrocytes. Thus, AxD is a primary astrocyte disease. However, it remains unclear how GFAP mutations affect astrocytes and cause AxD pathology. Three features are characteristic of AxD astrocytes in vivo: (1) Rosenthal fibers (RFs), the hallmark of AxD; (2) aberrant Ca2+ signals (AxCa); and (3) upregulation of disease-associated genes (AxGen). We established a primary culture system for astrocytes from an AxD transgenic mouse model, and used it to analyze the above features of AxD pathogenesis in astrocytes in vitro. We observed the formation of RFs in AxD primary cultures. The abundance of RFs was greater in AxD-transgene-homozygous compared with -hemizygous astrocytes, indicating a gene dosage effect, and this abundance increased with time in culture, indicating a developmental process effect. However, cultured AxD astrocytes did not exhibit changes in either AxCa or AxGen. We therefore conclude that RFs in astrocytes form via a cell-autonomous mechanism, whereas AxCa and AxGen are likely to occur via a non-cell-autonomous mechanism through interactions with other cells, such as neurons, microglia, and vascular cells. Although primary cultured AxD astrocytes are suitable for elucidating the mechanisms of RFs formation and for intervention studies, it should be noted that they cannot reflect the pathophysiology of non-cell-autonomous events in astrocytes.

The hemostatic system in chronic brain diseases: A new challenging frontier?

Neurological diseases (ND), including neurodegenerative diseases (NDD) and psychiatric disorders (PD), present a significant public health challenge, ranking third in Europe for disability and premature death, following cardiovascular diseases and cancers. In 2017, approximately 540 million cases of ND were reported among Europe's 925 million people, with strokes, dementia, and headaches being most prevalent. Nowadays, more and more evidence highlight the hemostasis critical role in cerebral homeostasis and vascular events. Indeed, hemostasis, thrombosis, and brain abnormalities contributing to ND form a complex and poorly understood equilibrium. Alterations in vascular biology, particularly involving the blood-brain barrier, are implicated in ND, especially dementia, and PD. While the roles of key coagulation players such as thrombin and fibrinogen are established, the roles of other hemostasis components are less clear. Moreover, the involvement of these elements in psychiatric disease pathogenesis is virtually unstudied, except in specific pathological models such as antiphospholipid syndrome. Advanced imaging techniques, primarily functional magnetic resonance imaging and its derivatives like diffusion tensor imaging, have been developed to study brain areas affected by ND and to improve our understanding of the pathophysiology of these diseases. This literature review aims to clarify the current understanding of the connections between hemostasis, thrombosis, and neurological diseases, as well as explore potential future diagnostic and therapeutic strategies.

Persistence of post-stress blood pressure elevation requires activation of astrocytes

The reflexive excitation of the sympathetic nervous system in response to psychological stress leads to elevated blood pressure, a condition that persists even after the stress has been alleviated. This sustained increase in blood pressure, which may contribute to the pathophysiology of hypertension, could be linked to neural plasticity in sympathetic nervous activity. Given the critical role of astrocytes in various forms of neural plasticity, we investigated their involvement in maintaining elevated blood pressure during the post-stress phase. Specifically, we examined the effects of arundic acid, an astrocytic inhibitor, on blood pressure and heart rate responses to air-jet stress. First, we confirmed that the inhibitory effect of arundic acid is specific to astrocytes. Using c-Fos immunohistology, we then observed that psychological stress activates neurons in cardiovascular brain regions, and that this stress-induced neuronal activation was suppressed by arundic acid pre-treatment in rats. By evaluating astrocytic process thickness, we also confirmed that astrocytes in the cardiovascular brain regions were activated by stress, and this activation was blocked by arundic acid pre-treatment. Next, we conducted blood pressure measurements on unanesthetized, unrestrained rats. Air-jet stress elevated blood pressure, which remained high for a significant period during the post-stress phase. However, pre-treatment with arundic acid, which inhibited astrocytic activation, suppressed stress-induced blood pressure elevation both during and after stress. In contrast, arundic acid had no significant impact on heart rate. These findings suggest that both neurons and astrocytes play integral roles in stress-induced blood pressure elevation and its persistence after stress, offering new insights into the pathophysiological mechanisms underlying hypertension.

Extracellular ATP/adenosine dynamics in the brain and its role in health and disease

Extracellular ATP and adenosine are neuromodulators that regulate numerous neuronal functions in the brain. Neuronal activity and brain insults such as ischemic and traumatic injury upregulate these neuromodulators, which exert their effects by activating purinergic receptors. In addition, extracellular ATP/adenosine signaling plays a pivotal role in the pathogenesis of neurological diseases. Virtually every cell type in the brain contributes to the elevation of ATP/adenosine, and various mechanisms underlying this increase have been proposed. Extracellular adenosine is thought to be mainly produced via the degradation of extracellular ATP. However, adenosine is also released from neurons and glia in the brain. Therefore, the regulation of extracellular ATP/adenosine in physiological and pathophysiological conditions is likely far more complex than previously thought. To elucidate the complex mechanisms that regulate extracellular ATP/adenosine levels, accurate methods of assessing their spatiotemporal dynamics are needed. Several novel techniques for acquiring spatiotemporal information on extracellular ATP/adenosine, including fluorescent sensors, have been developed and have started to reveal the mechanisms underlying the release, uptake and degradation of ATP/adenosine. Here, we review methods for analyzing extracellular ATP/adenosine dynamics as well as the current state of knowledge on the spatiotemporal dynamics of ATP/adenosine in the brain. We focus on the mechanisms used by neurons and glia to cooperatively produce the activity-dependent increase in ATP/adenosine and its physiological and pathophysiological significance in the brain.

Severity of Peripheral Infection Differentially Affects Brain Functions in Mice via Microglia-Dependent and -Independent Mechanisms

Peripheral infection induces inflammation in peripheral tissues and the brain, impacting brain function. Glial cells are key players in this process. However, the effects of peripheral infection on glial activation and brain function remain unknown. Here, we showed that varying degrees of peripheral infection had different effects on the regulation of brain functions by microglia-dependent and -independent mechanisms. Acute mild infection (one-day LPS challenge: 1LPS) exacerbated middle cerebral artery occlusion (MCAO) injury, and severe infection (four-day LPS challenge: 4LPS) for one week suppressed it. MCAO injury was assessed by triphenyltetrazolium chloride staining. We observed early activation of microglia in the 1LPS and 4LPS groups. Depleting microglia with a colony-stimulating factor-1 receptor (CSF1R) antagonist had no effect on 1LPS-induced brain injury exacerbation but abolished 4LPS-induced protection, indicating microglial independence and dependence, respectively. Microglia-independent exacerbation caused by 1LPS involved peripheral immune cells including macrophages. RNA sequencing analysis of 4LPS-treated microglia revealed increased factors related to anti-inflammatory and neuronal tissue repair, suggesting their association with the protective effect. In conclusion, varying degrees of peripheral inflammation had contradictory effects (exacerbation vs. protection) on MCAO, which may be attributed to microglial dependence. Our findings highlight the significant impact of peripheral infection on brain function, particularly in relation to glial cells.