Derivation and transcriptional reprogramming of border-forming wound repair astrocytes after spinal cord injury or stroke in mice

PD-L1/PD-1 checkpoint pathway regulates astrocyte morphogenesis and myelination during brain development

Programmed cell death protein 1 (PD-1) and its primary ligand PD-L1 are integral components of a significant immune checkpoint pathway, widely recognized for its central role in cancer immunotherapy. However, emerging evidence highlights their broader involvement in both the central and peripheral nervous systems. In this study, we demonstrate that PD-L1/PD-1 signaling in astrocytes during mouse brain development regulates astrocyte maturation and morphogenesis via the MEK/ERK pathway by targeting the downstream effector cysteine and glycine rich protein 1 (CSRP1). This enhanced astrocyte morphological complexity results in increased end-foot coverage of blood vessels. Additionally, aberrant secretion of CSRP1 by astrocytes interacts with oligodendrocyte precursor cells (OPCs) membrane proteins annexin A1 (ANXA1) and annexin A2 (ANXA2), leading to the exclusion of migrating OPCs from blood vessels. This disruption in OPC migration and differentiation results in abnormal myelination and is associated with cognitive deficits in the mice. Our results provide critical insights into the function of PD-L1/PD-1 signaling in astrocyte-OPC interactions and underscore its relevance to glial cell development and pathogenesis in neurodevelopmental disorders.

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.

Delayed atorvastatin delivery promotes recovery after experimental spinal cord injury

Spinal cord injury (SCI) significantly alters gene expression, potentially impeding functional recovery. This study investigated the effects of atorvastatin, a widely prescribed cholesterol-lowering drug, on gene expression and functional recovery in a chronic murine SCI model. Female C57BL/6J mice underwent moderate 0.25 ​mm lateral compression SCI and received daily atorvastatin (10 ​mg/kg) or vehicle-only injections from two weeks post-injury for four weeks. Sensorimotor functions were assessed using the Basso Mouse Scale (BMS), its subscore, and the inclined plane test. RNA sequencing of spinal cord tissues identified robust transcriptomic changes from SCI and a smaller subset from atorvastatin treatment. Atorvastatin enhanced sensorimotor recovery within two weeks of treatment initiation, with effects persisting to the experimental endpoint. Pathway analysis showed atorvastatin enriched neural regeneration processes including Fatty Acid Transport, Axon Guidance, and the Endocannabinoid Developing Neuron Pathway; improved mitochondrial function via increased TCA Cycle II and reduced Mitochondrial Dysfunction; and decreased Inhibition of Matrix Metalloproteases. Key gene drivers included Fabp7, Unc5c, Rest, and Klf4. Together, these results indicate atorvastatin's potential in chronic SCI recovery, especially where already indicated for cardiovascular protection.

Glial Cell Reprogramming in Ischemic Stroke: A Review of Recent Advancements and Translational Challenges

Ischemic stroke, the second leading cause of death worldwide and the leading cause of long-term disabilities, presents a significant global health challenge, particularly in aging populations where the risk and severity of cerebrovascular events are significantly increased. The aftermath of stroke involves neuronal loss in the infarct core and reactive astrocyte proliferation, disrupting the neurovascular unit, especially in aged brains. Restoring the balance between neurons and non-neuronal cells within the perilesional area is crucial for post-stroke recovery. The aged post-stroke brain mounts a fulminant proliferative astroglial response, leading to gliotic scarring that prevents neural regeneration. While countless therapeutic techniques have been attempted for decades with limited success, alternative strategies aim to transform inhibitory gliotic tissue into an environment conducive to neuronal regeneration and axonal growth through genetic conversion of astrocytes into neurons. This concept gained momentum following discoveries that in vivo direct lineage reprogramming in the adult mammalian brain is a feasible strategy for reprogramming non-neuronal cells into neurons, circumventing the need for cell transplantation. Recent advancements in glial cell reprogramming, including transcription factor-based methods with factors like NeuroD1, Ascl1, and Neurogenin2, as well as small molecule-induced reprogramming and chemical induction, show promise in converting glial cells into functional neurons. These approaches leverage the brain's intrinsic plasticity for neuronal replacement and circuit restoration. However, applying these genetic conversion therapies in the aged, post-stroke brain faces significant challenges, such as the hostile inflammatory environment and compromised regenerative capacity. There is a critical need for safe and efficient delivery methods, including viral and non-viral vectors, to ensure targeted and sustained expression of reprogramming factors. Moreover, addressing the translational gap between preclinical successes and clinical applications is essential, emphasizing the necessity for robust stroke models that replicate human pathophysiology. Ethical considerations and biosafety concerns are critically evaluated, particularly regarding the long-term effects and potential risks of genetic reprogramming. By integrating recent research findings, this comprehensive review provides an in-depth understanding of the current landscape and future prospects of genetic conversion therapy for ischemic stroke rehabilitation, highlighting the potential to enhance personalized stroke management and regenerative strategies through innovative approaches.

Glial polarization in neurological diseases: Molecular mechanisms and therapeutic opportunities

Glial cell polarization plays a pivotal role in various neurological disorders. In response to distinct stimuli, glial cells undergo polarization to either mitigate neurotoxicity or facilitate neural repair following injury, underscoring the importance of glial phenotypic polarization in modulating central nervous system function. This review presents an overview of glial cell polarization, focusing on astrocytes and microglia. It explores the involvement of glial polarization in neurological diseases such as Alzheimer's disease, Parkinson's disease, stroke, epilepsy, traumatic brain injury, amyotrophic lateral sclerosis, multiple sclerosis and meningoencephalitis. Specifically, it emphasizes the role of glial cell polarization in disease pathogenesis through mechanisms including neuroinflammation, neurodegeneration, calcium signaling dysregulation, synaptic dysfunction and immune response. Additionally, it summarizes various therapeutic strategies including pharmacological treatments, dietary supplements and cell-based therapies, aimed at modulating glial cell polarization to ameliorate brain dysfunction. Future research focused on the spatio-temporal manipulation of glial polarization holds promise for advancing precision diagnosis and treatment of neurological diseases.

Characterizing progenitor cells in developing and injured spinal cord: Insights from single-nucleus transcriptomics and lineage tracing

Various mature tissue-resident cells exhibit progenitor characteristics following injury. However, the existence of endogenous stem cells with multiple lineage potentials in the adult spinal cord remains a compelling area of research. In this study, we present a cross-species investigation that extends from development to injury. We used single-nucleus transcriptomic sequencing and genetic lineage tracing to characterize neural cells in the spinal cord. Our findings show that ciliated ependymal cells lose neural progenitor gene signatures and proliferation ability following the differentiation of NPCs within the ventricular zone. By combining single-nucleus transcriptome datasets from the rhesus macaque spinal cord injury (SCI) model with developmental human spinal cord datasets, we revealed that ciliated ependymal cells respond minimally to injury and cannot revert to a developmental progenitor state. Intriguingly, we observed astrocytes transdifferentiating into mature oligodendrocytes postinjury through lineage tracing experiments. Further analysis identifies an intermediate-state glial cell population expressing both astrocyte and oligodendrocyte feature genes in adult spinal cords. The transition ratio from astrocytes into oligodendrocytes increased after remodeling injury microenvironment by functional scaffolds. Overall, our results highlight the remarkable multilineage potential of astrocytes in the adult spinal cord.

The immunology of stroke and dementia

Ischemic stroke and vascular cognitive impairment, caused by a sudden arterial occlusion or more subtle but protracted vascular insufficiency, respectively, are leading causes of morbidity and mortality worldwide with limited therapeutic options. Innate and adaptive immunity have long been implicated in neurovascular injury, but recent advances in methodology and new experimental approaches have shed new light on their contributions. A previously unappreciated dynamic interplay of brain-resident, meningeal, and systemic immune cells with the ischemic brain and its vasculature has emerged, and new insights into the frequent overlap between vascular and Alzheimer pathology have been provided. Here, we critically review these recent findings, place them in the context of current concepts on neurovascular pathologies and Alzheimer's disease, and highlight their impact on recent stroke and Alzheimer therapies.

The Glial Scar: To Penetrate or Not for Motor Pathway Restoration?

Although notable progress has been made, restoring motor function from the brain to the muscles continues to be a substantial clinical challenge in motor neuron diseases/disorders such as spinal cord injury (SCI). While cell transplantation has been widely explored as a potential therapeutic method for reconstructing functional motor pathways, there remains considerable opportunity for enhancing its therapeutic effectiveness. We reviewed studies on motor pathway regeneration to identify molecular and ultrastructural cues that could enhance the efficacy of cell transplantation. While the glial scar is often cited as an intractable barrier to axon regeneration, this mainly applies to axons trying to penetrate its "core" to reach the opposite side. However, the glial scar exhibits a "duality," with an anti-regenerative core and a pro-regenerative "surface." This surface permissiveness is attributed to pro-regenerative molecules, such as laminin in the basement membrane (BM). Transplanting donor cells onto the BM, which forms plastically after injury, may significantly enhance the efficacy of cell transplantation. Specifically, forming detour pathways between transplanted cells and endogenous propriospinal neurons on the pro-regenerative BM may efficiently bypass the intractable scar core and promote motor pathway regeneration. We believe harnessing the tissue's innate repair capacity is crucial, and targeting post-injury plasticity in astrocytes and Schwann cells, especially those associated with the BM that has predominantly been overlooked in the field of SCI research, can advance motor system restoration to a new stage. A shift in cell delivery routes-from the traditional intra-parenchymal (InP) route to the transplantation of donor cells onto the pro-regenerative BM via the extra-parenchymal (ExP) route-may signify a transformative step forward in neuro-regeneration research. Practically, however, the complementary use of both InP and ExP methods may offer the most substantial benefit for restoring motor pathways. We aim for this review to deepen the understanding of cell transplantation and provide a framework for evaluating the efficacy of this therapeutic modality in comparison to others.

Single-cell RNA sequencing in stroke and traumatic brain injury: Current achievements, challenges, and future perspectives on transcriptomic profiling

Single-cell RNA sequencing (scRNA-seq) is a high-throughput transcriptomic approach with the power to identify rare cells, discover new cellular subclusters, and describe novel genes. scRNA-seq can simultaneously reveal dynamic shifts in cellular phenotypes and heterogeneities in cellular subtypes. Since the publication of the first protocol on scRNA-seq in 2009, this evolving technology has continued to improve, through the use of cell-specific barcodes, adoption of droplet-based systems, and development of advanced computational methods. Despite induction of the cellular stress response during the tissue dissociation process, scRNA-seq remains a popular technology, and commercially available scRNA-seq methods have been applied to the brain. Recent advances in spatial transcriptomics now allow the researcher to capture the positional context of transcriptional activity, strengthening our knowledge of cellular organization and cell-cell interactions in spatially intact tissues. A combination of spatial transcriptomic data with proteomic, metabolomic, or chromatin accessibility data is a promising direction for future research. Herein, we provide an overview of the workflow, data analyses methods, and pros and cons of scRNA-seq technology. We also summarize the latest achievements of scRNA-seq in stroke and acute traumatic brain injury, and describe future applications of scRNA-seq and spatial transcriptomics.

Cell type mapping reveals tissue niches and interactions in subcortical multiple sclerosis lesions

Multiple sclerosis (MS) is a chronic inflammatory disease of the central nervous system. Inflammation is gradually compartmentalized and restricted to specific tissue niches such as the lesion rim. However, the precise cell type composition of such niches, their interactions and changes between chronic active and inactive stages are incompletely understood. We used single-nucleus and spatial transcriptomics from subcortical MS and corresponding control tissues to map cell types and associated pathways to lesion and nonlesion areas. We identified niches such as perivascular spaces, the inflamed lesion rim or the lesion core that are associated with the glial scar and a cilia-forming astrocyte subtype. Focusing on the inflamed rim of chronic active lesions, we uncovered cell-cell communication events between myeloid, endothelial and glial cell types. Our results provide insight into the cellular composition, multicellular programs and intercellular communication in tissue niches along the conversion from a homeostatic to a dysfunctional state underlying lesion progression in MS.

Astrocyte transcriptomic analysis identifies glypican 5 downregulation as a contributor to synaptic dysfunction in Alzheimer's disease models

Synaptic dysfunction is an early feature in Alzheimer's disease (AD) and correlates with cognitive decline. Astrocytes are essential regulators of synapses, impacting synapse formation, maturation, elimination and function. To understand if synapse-supportive functions of astrocytes are altered in AD, we used astrocyte BacTRAP mice to generate a comprehensive dataset of hippocampal astrocyte transcriptional alterations in two mouse models of Alzheimer's pathology (APPswe/PS1dE9 and Tau P301S), characterizing sex and age-dependent changes. We found that astrocytes from both models downregulate genes important for synapse regulation and function such as the synapse-maturation factor Glypican 5. This transcriptional signature is shared with human post-mortem AD patients. Manipulating a key component of this signature by in vivo overexpression of Glypican 5 in astrocytes is sufficient to prevent early synaptic dysfunction and improve spatial learning in APPswe/PS1dE9 mice. These findings open new avenues to target astrocytic factors to mitigate AD synaptic dysfunction.

Dynamic spatiotemporal activation of a pervasive neurogenic competence in striatal astrocytes supports continuous neurogenesis following injury

Adult neural stem cells (NSCs) are conventionally regarded as rare cells restricted to two niches: the subventricular zone (SVZ) and the subgranular zone. Parenchymal astrocytes (ASs) can also contribute to neurogenesis after injury; however, the prevalence, distribution, and behavior of these latent NSCs remained elusive. To tackle these issues, we reconstructed the spatiotemporal pattern of striatal (STR) AS neurogenic activation after excitotoxic lesion in mice. Our results indicate that neurogenic potential is widespread among STR ASs but is focally activated at the lesion border, where it associates with different reactive AS subtypes. In this region, similarly to canonical niches, steady-state neurogenesis is ensured by the continuous stochastic activation of local ASs. Activated ASs quickly return to quiescence, while their progeny transiently expand following a stochastic behavior that features an acceleration in differentiation propensity. Notably, STR AS activation rate matches that of SVZ ASs indicating a comparable prevalence of NSC potential.

Emerging roles of astrocytes as immune effectors in the central nervous system

The astrocyte, a major glial cell type in the central nervous system (CNS), is widely regarded as a functionally diverse mediator of homeostasis. During development and throughout adulthood, astrocytes have essential roles, such as providing neuron metabolic support, modulating synaptic function, and maintaining the blood-brain barrier (BBB). Recent evidence continues to underscore their functional heterogeneity and importance for CNS maintenance, as well as how these cells ensure optimal CNS and immune responses to disease, acute trauma, and infection. Advances in our understanding of neuroimmune interactions complement our knowledge of astrocyte functional heterogeneity, where astrocytes are now regarded as key effectors and propagators of immune signaling. This shift in perspective highlights the role of astrocytes not merely as support cells, but as active participants in CNS immune responses.

Metabolic Reprogramming of Astrocytes in Pathological Conditions: Implications for Neurodegenerative Diseases

Astrocytes play a pivotal role in maintaining brain energy homeostasis, supporting neuronal function through glycolysis and lipid metabolism. This review explores the metabolic intricacies of astrocytes in both physiological and pathological conditions, highlighting their adaptive plasticity and diverse functions. Under normal conditions, astrocytes modulate synaptic activity, recycle neurotransmitters, and maintain the blood-brain barrier, ensuring a balanced energy supply and protection against oxidative stress. However, in response to central nervous system pathologies such as neurotrauma, stroke, infections, and neurodegenerative diseases like Alzheimer's and Huntington's disease, astrocytes undergo significant morphological, molecular, and metabolic changes. Reactive astrocytes upregulate glycolysis and fatty acid oxidation to meet increased energy demands, which can be protective in acute settings but may exacerbate chronic inflammation and disease progression. This review emphasizes the need for advanced molecular, genetic, and physiological tools to further understand astrocyte heterogeneity and their metabolic reprogramming in disease states.