Astrocytes in human central nervous system diseases: a frontier for new therapies

Functional abnormalities of the glymphatic system in cognitive disorders

Various pathological mechanisms represent distinct therapeutic targets for cognitive disorders, but a balance between clearance and production is essential for maintaining the stability of the brain's internal environment. Thus, the glymphatic system may represent a common pathway by which to address cognitive disorders. Using the established model of the glymphatic system as our foundation, this review disentangles and analyzes the components of its clearance mechanism, including the initial inflow of cerebrospinal fluid, the mixing of cerebrospinal fluid with interstitial fluid, and the outflow of the mixed fluid and the clearance. Each section summarizes evidence from experimental animal models and human studies, highlighting the normal physiological properties of key structures alongside their pathological manifestations in cognitive disorders. The same pathologic manifestations of different cognitive disorders appearing in the glymphatic system and the same upstream influences are main points of interest of this review. We conclude this article by discussing new findings and outlining the limitations identified in current research progress.

Spatial transcriptomics combined with single-nucleus RNA sequencing reveals glial cell heterogeneity in the human spinal cord

JOURNAL/nrgr/04.03/01300535-202511000-00032/figure1/v/2024-12-20T164640Z/r/image-tiff Glial cells play crucial roles in regulating physiological and pathological functions, including sensation, the response to infection and acute injury, and chronic neurodegenerative disorders. Glial cells include astrocytes, microglia, and oligodendrocytes in the central nervous system, and satellite glial cells and Schwann cells in the peripheral nervous system. Despite the greater understanding of glial cell types and functional heterogeneity achieved through single-cell and single-nucleus RNA sequencing in animal models, few studies have investigated the transcriptomic profiles of glial cells in the human spinal cord. Here, we used high-throughput single-nucleus RNA sequencing and spatial transcriptomics to map the cellular and molecular heterogeneity of astrocytes, microglia, and oligodendrocytes in the human spinal cord. To explore the conservation and divergence across species, we compared these findings with those from mice. In the human spinal cord, astrocytes, microglia, and oligodendrocytes were each divided into six distinct transcriptomic subclusters. In the mouse spinal cord, astrocytes, microglia, and oligodendrocytes were divided into five, four, and five distinct transcriptomic subclusters, respectively. The comparative results revealed substantial heterogeneity in all glial cell types between humans and mice. Additionally, we detected sex differences in gene expression in human spinal cord glial cells. Specifically, in all astrocyte subtypes, the levels of NEAT1 and CHI3L1 were higher in males than in females, whereas the levels of CST3 were lower in males than in females. In all microglial subtypes, all differentially expressed genes were located on the sex chromosomes. In addition to sex-specific gene differences, the levels of MT-ND4 , MT2A , MT-ATP6 , MT-CO3 , MT-ND2 , MT-ND3 , and MT-CO2 in all spinal cord oligodendrocyte subtypes were higher in females than in males. Collectively, the present dataset extensively characterizes glial cell heterogeneity and offers a valuable resource for exploring the cellular basis of spinal cord-related illnesses, including chronic pain, amyotrophic lateral sclerosis, and multiple sclerosis.

Rutin Attenuates Distraction Spinal Cord Injury by Inhibiting Microglial Inflammation Through Downregulation of P38 MAPK/NF-κB/STAT3 Pathway

Distraction spinal cord injury (DSCI) is a severe complication following scoliosis correction surgery, for which there are currently no effective clinical treatments. This study aims to evaluate the inhibitory effects of rutin, a natural product, on inflammation in DSCI and to investigate the underlying mechanisms. In vitro, microglial cells were exposed directly to rutin to assess its ability to inhibit lipopolysaccharide (LPS)-induced inflammation. In rats with DSCI, the inhibitory effect of rutin on DSCI was evaluated using behavioral tests. mRNA sequencing was performed on spinal cord tissues to elucidate the mechanism of rutin's action. Rutin significantly suppressed the LPS-induced increase in inflammatory factors in microglial cells. In DSCI rats treated with rutin, scores in the Basso-Beattie-Bresnahan (BBB) were significantly improved. The mechanism of rutin's action was found to be related to its ability to reduce inflammatory infiltration in spinal cord tissue, protecting neurons from apoptosis and microstructural demyelination. Through assays of transcriptomic differentially expressed genes (DEGs), Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis, and RT-qPCR validation of the top DEGs, MAPK13 (also known as P38 MAPK) was finally identified as the key target gene in promoting DSCI development. Further molecular docking analysis indicated an interaction between rutin and P38 MAPK, supporting the rutin's action and the underlying mechanism in anti-inflammation. In conclusion, rutin effectively inhibited the development of DSCI in rats. The mechanism of rutin's action was associated with its activity in blocking the P38 MAPK/NF-κB/STAT3 pathway in the microglial cells of spinal cord. Rutin could be developed as a potential anti-DSCI drug for clinical applications.

Astrocyte morphological remodeling regulates consciousness state transitions induced by inhaled general anesthesia

General anesthetics (GAs) are conventionally thought to induce loss of consciousness (LOC) by acting on pre- and post-synaptic targets. However, the mechanism underlying the involvement of astrocytes in LOC remains unclear. Here we report that inhaled GAs cause reversible impairments in the fine processes of astrocytes within the somatosensory cortex, mediated by regulating the phosphorylation level of Ezrin, a protein critical for the fine morphology of astrocytes. Genetically deleting Ezrin or disrupting its phosphorylation was sufficient to decrease astrocyte-synapse interaction and enhance sensitivity to sevoflurane (Sevo) in vivo. Moreover, we show that disrupting astrocytic Ezrin phosphorylation boosted the inhibitory effect of Sevo on pyramidal neurons by enhancing tonic GABA and lowering excitability under anesthesia. Our work reveals previously unappreciated phosphorylation-dependent morphological dynamics, which enable astrocytes to regulate neuronal activity during the transition between two brain consciousness states.

Modification of Neural Circuit Functions by Microglial P2Y6 Receptors in Health and Neurodegeneration

Neural circuits consisting of neurons and glial cells help to establish all functions of the CNS. Microglia, the resident immunocytes of the CNS, are endowed with UDP-sensitive P2Y6 receptors (P2Y6Rs) which regulate phagocytosis/pruning of excessive synapses during individual development and refine synapses in an activity-dependent manner during adulthood. In addition, this type of receptor plays a decisive role in primary (Alzheimer's disease, Parkinson's disease, neuropathic pain) and secondary (epilepsy, ischemic-, mechanical-, or irradiation-induced) neurodegeneration. A whole range of microglial cytokines controlled by P2Y6Rs, such as the interleukins IL-1β, IL-6, IL-8, and tumor necrosis factor-α (TNF-α), leads to neuroinflammation, resulting in neurodegeneration. Hence, small molecular antagonists of P2Y6Rs and genetic knockdown of this receptor provide feasible ways to alleviate inflammation-induced neurological disorders but might also interfere with the regulation of the synaptic circuitry. The present review aims at investigating this dual role of P2Y6Rs in microglia, both in shaping neural circuits by targeted phagocytosis and promoting neurodegenerative illnesses by fostering neuroinflammation through multiple transduction mechanisms.

Effects of trace element dysregulation on brain structure and function in spinocerebellar Ataxia type 3

Spinocerebellar ataxia type 3 (SCA3), a neurodegenerative disorder caused by excess CAG repeats in the ATXN3 gene, leads to progressive cerebellar ataxia and other symptoms. The results of previous studies suggest that trace element dysregulation contributes to neurodegenerative disorder onset. Here, we investigated the relationships of trace element dysregulation with CAG repeat length, clinical severity, and brain structural and functional connectivity in 45 patients with SCA3 and 44 healthy controls (HCs). Blood levels of lithium (Li), selenium (Se), and copper (Cu) were significantly lower in patients with SCA3 than in HCs; Li and Se levels were negatively correlated with CAG repeat length, especially in the manifest subgroup. Diffusion tensor imaging combined with resting-state functional magnetic resonance imaging revealed that Li levels were negatively correlated with fractional anisotropy in the white matter (WM) of bilateral frontal and parietal regions; tractography mapping showed disorder structural connectivity of Li-associated region nerve fiber pathways in patients with SCA3. Dynamic causal modeling analyses showed bidirectional causal connectivity from the inferior parietal lobule(IPL) to the cerebellum was significantly correlated with the blood level of Li in patients with SCA3. Time series correlation-based functional connectivity analysis revealed that the intrinsic connectivities of the bilateral dorsal premotor cortex(PMd) and IPL with local cerebellar regions were significantly weaker in patients with SCA3 than in HCs. Our results suggest that trace element dysregulation, especially Li deficiency, induces brain alterations and clinical manifestations in patients with SCA3; Li supplementation may be beneficial for WM or astrocytes in this patient population.

Development and in vitro evaluation of biomimetic injectable hydrogels from decellularized human nerves for central nervous system regeneration

Injuries to the central nervous system (CNS) often lead to persistent inflammation and limited regeneration. This study developed a clinically relevant injectable hydrogel derived from decellularized human peripheral nerves, with mechanical properties biomimicking native CNS tissue. Using a modified Hudson method, human sciatic nerves were decellularized, effectively removing immunogenic cellular debris while retaining the extracellular matrix. Two delipidation solvents, dichloromethane: ethanol (2:1 v/v) and n-hexane: isopropanol (3:1 v/v), were evaluated, with the former achieving optimal lipid removal and better digestion. The resulting solution was crosslinked with genipin, forming an injectable hydrogel (iHPN) that gelled within 12 min at 37 °C and exhibited mechanical stiffness of approximately 400 Pa. Human astrocytes, human microglial cell clone 3 (HMC3), and mouse RAW 264.7 macrophages were cultured individually within iHPN, with lipopolysaccharide (LPS) added to mimic CNS inflammation following injury. Compared to LPS-activated cells on tissue culture plates (TCP), astrocytes within iHPN maintained a quiescent state, as evidenced by reduced GFAP expression and IL-1β secretion. RAW 264.7 and HMC3 cells in iHPN displayed an anti-inflammatory phenotype, as shown by increased CD206 and decreased CD86/CD68 expression, along with higher IL-4 and lower TNF-α/IL-1β secretion. Human SH-SY5Y neuroblastoma cells exhibited higher viability and improved neuronal differentiation in iHPN compared to TCP. Human brain neurons had higher neuronal differentiation within iHPN compared to TCP or collagen hydrogels. Overall, iHPN is a novel injectable hydrogel that has potential for minimally invasive CNS applications, such as a carrier for cell or drug delivery and/or a biomaterial to support axonal growth.

The value of serum glial fibrillary acidic protein as a biomarker of astrogliosis in different neurological diseases

BACKGROUND

Glial Fibrillary Acidic Protein (GFAP) is a well-established biomarker of astrocytes and astrogliosis, a pathological response observed in various neurological diseases. This study aimed to evaluate the diagnostic performance of serum GFAP in Alzheimer's disease (AD), multiple sclerosis (MS), and transthyretin amyloidosis (ATTR) polyneuropathy.

METHODS

We performed a retrospective observational study, including 498 participants (337 healthy controls and 161 patients with AD, MS, or ATTR amyloidosis). Serum GFAP levels were measured using the Lumipulse G1200 platform, and statistical analyses were performed to compare levels across disease groups and assess their diagnostic accuracy.

RESULTS

GFAP levels were significantly elevated in all neurological disease groups compared to age-matched controls, with the highest levels found in AD (79.4 pg/mL vs. 39.5 pg/mL, p = 2.55 × 10-12). ROC curve analysis revealed that GFAP had strong diagnostic performance for AD (AUC = 0.86), moderate performance for ATTR amyloidosis (AUC = 0.67), and poor performance for MS (AUC = 0.61).

CONCLUSIONS

These findings suggest that GFAP is a promising biomarker for AD, reflecting astrocytic activation and neuroinflammatory processes. Its diagnostic utility in ATTR amyloidosis is moderate, while its role in MS remains limited.

ATP Alters the Oxylipin Profiles in Astrocytes: Modulation by High Glucose and Metformin

Background: Astrocytes play a key role in the inflammatory process accompanying various neurological diseases. Extracellular ATP accompanies inflammatory processes in the brain, but its effect on lipid mediators (oxylipins) in astrocytes remains elusive. Metformin is a hypoglycemic drug with an anti-inflammatory effect that has been actively investigated in the context of therapy for neuroinflammation, but its mechanisms of action are not fully elucidated. Therefore, we aimed to characterize the effects of ATP on inflammatory markers and oxylipin profiles; determine the dependence of these effects on the adaptation of astrocytes to high glucose levels; and evaluate the possibility of modulating ATP effects using metformin. Methods: We estimated the ATP-mediated response of primary rat astrocytes cultured at normal (NG, 5 mM) and high (HG, 22.5 mM) glucose concentrations for 48 h before stimulation. Cell responses were assessed by monitoring changes in the expression of inflammatory markers (TNFα, IL-6, IL-10, IL-1β, iNOS, and COX-2) and the synthesis of oxylipins (41 compounds), assayed with ultra-high-performance liquid chromatography and tandem mass spectrometry (UPLC-MS/MS). Intracellular pathways were assessed by analyzing the phosphorylation of p38; ERK MAPK; transcription factors STAT3 and NF-κB; and the enzymes mediating oxylipin synthesis, COX-1 and cPLA2. Results: The stimulation of cells with ATP does not affect the expression of pro-inflammatory markers, increases the activities of p38 and ERK MAPKs, and activates oxylipin synthesis, shifting the profiles toward an increase in anti-inflammatory compounds (PGD2, PGA2, 12-HHT, and 18-HEPE). The ATP effects are reduced in HG astrocytes. Metformin potentiated ATP-induced oxylipin synthesis (11-HETE, PGD2, 12-HHT, 15-HETE, 13-HDoHE, and 15-HETrE), which was predominantly evident in NG cells. Conclusions: Our data provide new evidence showing that ATP induces the release of anti-inflammatory oxylipins, and metformin enhances these effects. These results should be considered in the development of anti-inflammatory therapeutic approaches aimed at modulating astrocyte function in various pathologies.

Molecular signature of primate astrocytes reveals pathways and regulatory changes contributing to human brain evolution

Astrocytes contribute to the development and regulation of the higher-level functions of the brain, the critical targets of evolution. However, how astrocytes evolve in primates is unsettled. Here, we obtain human, chimpanzee, and macaque induced pluripotent stem-cell-derived astrocytes (iAstrocytes). Human iAstrocytes are bigger and more complex than the non-human primate iAstrocytes. We identify new loci contributing to the increased human astrocyte. We show that genes and pathways implicated in long-range intercellular signaling are activated in the human iAstrocytes and partake in controlling iAstrocyte complexity. Genes downregulated in human iAstrocytes frequently relate to neurological disorders and were decreased in adult brain samples. Through regulome analysis and machine learning, we uncover that functional activation of enhancers coincides with a previously unappreciated, pervasive gain of "stripe" transcription factor binding sites. Altogether, we reveal the transcriptomic signature of primate astrocyte evolution and a mechanism driving the acquisition of the regulatory potential of enhancers.

Molecular Motors in Blood-Brain Barrier Maintenance by Astrocytes

The blood-brain barrier (BBB) comprises distinct cell types, including endothelial cells, pericytes, and astrocytes, and is essential for central nervous system (CNS) homeostasis by selectively regulating molecular transport and maintaining integrity. In particular, astrocytes are essential for BBB function, as they maintain BBB integrity through their end-feet, which form a physical and biochemical interface that enhances endothelial cell function and barrier selectivity. Moreover, they secrete growth factors like vascular endothelial growth factor (VEGF) and transforming growth factor-beta (TGF-β), which regulate tight junction (TJ) proteins (e.g., claudins and occludins) crucial for limiting paracellular permeability. Molecular motors like kinesins, dynein, and myosins are essential for these astrocyte functions. By facilitating vesicular trafficking and protein transport, they are essential for various functions, including trafficking of junctional proteins to support BBB integrity, the proper mitochondria localization within astrocyte processes for efficient energy supply, the polarized distribution of aquaporin (AQP)-4 at astrocyte end-feet for regulating water homeostasis across the BBB, and the modulation of neuroinflammatory responses. Moreover, myosin motors modulate actomyosin dynamics to regulate astrocyte process outgrowth, adhesion, migration, and morphology, facilitating their functional roles. Thus, motor protein dysregulation in astrocytes can compromise BBB function and integrity, increasing the risk of neurodegeneration. This review explores the complex interplay between astrocytes and molecular motors in regulating BBB homeostasis, which represents an attractive but poorly explored area of research.

Integrated transcriptomic profiling reveals a STING-mediated Type II Interferon signature in SOD1-mutant amyotrophic lateral sclerosis models

Inflammation is a hallmark of amyotrophic lateral sclerosis (ALS), particularly in cases with SOD1 mutations. Using integrative transcriptomics, we analyzed gene expression changes in mouse models throughout progression, human induced-pluripotent stem cells (hiPSCs), and post-mortem spinal cord tissue from ALS patients. We identified a conserved upregulation of interferon (IFN) genes and IFN-stimulating genes (ISGs) in both mouse models and human ALS, with a predominance Type I IFNs (IFN-α/β) in mice and Type II IFNs (IFN-γ) in humans. In mouse models, we observed robust and sustained upregulation of Type I and II ISGs, including ATF3, beginning at disease onset stage and persisting throughout disease progression. Single-cell transcriptomics further pinpointed vascular endothelial cells as a major source of ISGs. Furthermore, we found that the STING-TBK1 axis is essential for the induction of Type II ISGs in ALS, as its deletion impaired their expression. Our study uncovers a conserved ISGs signature across ALS models and patients, highlighting the potential role of innate immune activation in ALS pathogenesis. These findings suggest that ISGs may serve as potential biomarkers and therapeutic targets for ALS.

Uncovering Astrocyte Morphological Dynamics Using Optical Diffraction Tomography and Shape-Based Trajectory Inference

Astrocytes, integral components of the central nervous system, are increasingly recognized for their multifaceted roles beyond support cells. Despite their acknowledged importance, understanding the intricacies of astrocyte morphological dynamics remains limited. Our study marks the first exploration of astrocytes using optical diffraction tomography (ODT), establishing a label-free, quantitative method to observe morphological changes in astrocytes over a 7-day in-vitro period. ODT offers quantitative insights into cell volume, dry mass, and area through label-free, real-time measurements-capabilities that are challenging to achieve with conventional imaging techniques. Through comprehensive analysis of 3D refractive index maps and shape characterization techniques, we capture the developmental trajectory and dynamic morphological transformations of astrocytes. Specifically, our observations reveal increased area and a transition to larger, flattened shapes, with alterations in cell volume and density, indicating shifts in cellular composition. By employing unsupervised clustering and pseudotime trajectory analysis, we introduce a novel morphological trajectory inference for neural cells, tracking the morphological evolution of astrocytes from elongated to evenly spread shapes. This analysis marks the first use of trajectory inference based solely on morphology for neural cell types, laying a foundation for future studies employing ODT to examine astrocyte dynamics and neural cell interactions across diverse substrates.

The Glutamate/GABA-Glutamine Cycle: Insights, Updates, and Advances

Synaptic homeostasis of the principal neurotransmitters glutamate and GABA is tightly regulated by an intricate metabolic coupling between neurons and astrocytes known as the glutamate/GABA-glutamine cycle. In this cycle, astrocytes take up glutamate and GABA from the synapse and convert these neurotransmitters into glutamine. Astrocytic glutamine is subsequently transferred to neurons, serving as the principal precursor for neuronal glutamate and GABA synthesis. The glutamate/GABA-glutamine cycle integrates multiple cellular processes, including neurotransmitter release, uptake, synthesis, and metabolism. All of these processes are deeply interdependent and closely coupled to cellular energy metabolism. Astrocytes display highly active mitochondrial oxidative metabolism and several unique metabolic features, including glycogen storage and pyruvate carboxylation, which are essential to sustain continuous glutamine release. However, new roles of oligodendrocytes and microglia in neurotransmitter recycling are emerging. Malfunction of the glutamate/GABA-glutamine cycle can lead to severe synaptic disruptions and may be implicated in several brain diseases. Here, I review central aspects and recent advances of the glutamate/GABA-glutamine cycle to highlight how the cycle is functionally connected to critical brain functions and metabolism. First, an overview of glutamate, GABA, and glutamine transport is provided in relation to neurotransmitter recycling. Then, central metabolic aspects of the glutamate/GABA-glutamine cycle are reviewed, with a special emphasis on the critical metabolic roles of glial cells. Finally, I discuss how aberrant neurotransmitter recycling is linked to neurodegeneration and disease, focusing on astrocyte metabolic dysfunction and brain lipid homeostasis as emerging pathological mechanisms. Instead of viewing the glutamate/GABA-glutamine cycle as individual biochemical processes, a more holistic and integrative approach is needed to advance our understanding of how neurotransmitter recycling modulates brain function in both health and disease.

Associations of prenatal metal exposure with child neurodevelopment and mediation by perturbation of metabolic pathways

Prenatal exposure to metals has been associated with impaired neurodevelopment in children, but the detailed molecular mechanisms remain largely unknown. Based on the Wuhan Healthy Baby Cohort, China (N = 1088), eleven metals were measured in maternal urine during early pregnancy (13.1 ± 1.1 weeks) and metabolomics profiling was conducted in cord blood. Neurodevelopment was evaluated using the Bayley Scales of Infant Development in 2-year-old children to obtain the mental development index (MDI) and psychomotor development index (PDI). After false discovery rate correction, higher maternal urinary levels of manganese, nickel, aluminum, rubidium, gallium, and the summary score of metals were only significantly associated with lower MDI scores. The weighted quantile sum index of the metal mixture showed a significant inverse association with MDI and PDI scores, with aluminum contributing the most to the associations. Histidine, beta-alanine, purine, and pyrimidine metabolism significantly mediated the above associations, suggesting that disturbances in amino acids, neurotransmitter and neuroendocrine metabolism may be important mediators in contributing to impaired neurodevelopment of children.

Synthesis of Naringenin and Senecioic Acid Ester Derivatives and Biological Evaluation of the Astrocyte Antioxidant Mechanism and Reactivity After Inflammatory Stimulus

The imbalance between the overproduction of reactive species and antioxidant mechanisms can result in astrogliosis and oxidative stress associated with neurodegeneration. Based on the described antioxidant activity of naturally occurring flavonoids, this study evaluated the antioxidant mechanisms of the flavonoid naringenin and the senecioic acid ester derivatives in cortical astrocytes. Naringenin and (S)-naringenin were purified from Citrus paradisi, and from them 7,4-O-disenecioic ester naringenin, (S)-7,4-O-disenecioic ester naringenin, and 7-O-senecioic ester naringenin were synthesized and tested for antioxidant activity by the free-radical scavenging reaction with DPPH. The flavonoids' toxicity and glutathione (GS) depletion were determined in rat astrocyte cultures; the effects on the astrocytes' reactivity was determined by the expression of the glial fibrillary acidic protein (GFAP) and by measuring nitric oxide (NO) production in astrocytes treated with lipopolysaccharide (LPS, 1 µg/mL/24 h). The compounds (1-10 μM) presented antioxidant effects, and the (S)-7,4'-O-disenecioic ester naringenin was the most effective. The compounds (1-100 μM) were not toxic to the astrocytes, also promoting an antioxidant effect by increasing GSH. Moreover, naringenin, (S)-7,4'-O-disenecioic ester naringenin, and 7-O-senecioc ester naringenin mitigated the astrocyte reactivity induced by LPS, reducing GFAP expression and NO production. These findings indicate that naringenin and senecioic acid ester derivatives present a pharmacological potential as antioxidant and anti-inflammatory compounds for brain diseases via the modulation of astrocyte response.

Uncovering the Signatures of Cellular Senescence in the Human Dorsolateral Prefrontal Cortex

Identifying senescent cells poses challenges due to their rarity, heterogeneity, and lack of a definitive marker. We performed Visium spatial transcriptomics (ST) and single nucleus RNA sequencing (snRNA-seq) on non-pathological human tissue to build a transcriptomic atlas of aging and senescence in the dorsolateral prefrontal cortex (dlPFC). We identified markers characteristic of aging dlPFC cortical layers and cell types. We also observed an increase in astrocyte abundance and decrease in somatostatin expressing inhibitory neurons. Overall, the senescence profile in the dlPFC was highly heterogeneous and heavily influenced by cell type identity and cortical layer. Combined unbiased analysis of ST and snRNA-seq datasets revealed gene expression modules encoding for communities of microglia and endothelial cells in the white matter and regional astrocytes programs that were strongly enriched with age and for senescence-related genes. These findings will help facilitate future studies exploring the function of senescent cell subpopulations in the aging brain.

Unveiling the Mechanisms of Pain in Endometriosis: Comprehensive Analysis of Inflammatory Sensitization and Therapeutic Potential

Endometriosis is a complicated, estrogen-dependent gynecological condition with a high morbidity rate. Pain, as the most common clinical symptom of endometriosis, severely affects women's physical and mental health and exacerbates socioeconomic burden. However, the specific mechanisms behind the occurrence of endometriosis-related pain remain unclear. It is currently believed that the occurrence of endometriosis pain is related to various factors, such as immune abnormalities, endocrine disorders, the brain-gut axis, angiogenesis, and mechanical stimulation. These factors induce systemic chronic inflammation, which stimulates the nerves and subsequently alters neural plasticity, leading to nociceptive sensitization and thereby causing chronic pain. In this paper, we compile and review the articles published on the study of nociceptive sensitization and endometriosis pain mechanisms. Starting from the factors influencing the chronic pain associated with endometriosis, we explain the relationship between these factors and chronic inflammation and further elaborate on the potential mechanisms by which chronic inflammation induces nociceptive sensitization. We aim to reveal the possible mechanisms of endometriosis pain, as well as nociceptive sensitization, and offer potential new targets for the treatment of endometriosis pain.

Neurobiological perturbations in bipolar disorder compared to schizophrenia - evidence from cell cultures and brain organoids

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

Cell-cell communications in the brain of hepatic encephalopathy: The neurovascular unit

Many patients with liver diseases are exposed to the risk of hepatic encephalopathy (HE). The incidence of HE in liver patients is high, showing various symptoms ranging from mild symptoms to coma. Liver transplantation is one of the ways to overcome HE. However, not all patients can receive liver transplantation. Moreover, patients who have received liver transplantation have limitations in that they are vulnerable to hepatocellular carcinoma, allograft rejection, and infection. To find other therapeutic strategies, it is important to understand pathological factors and mechanisms that lead to HE after liver disease. Oxidative stress, inflammatory response, hyperammonaemia and metabolic disorders seen after liver diseases have been reported as risk factors of HE. These are known to affect the brain and cause HE. These peripheral pathological factors can impair the blood-brain barrier, cause it to collapse and damage the neurovascular unit component of multiple cells, including vascular endothelial cells, astrocytes, microglia, and neurons, leading to HE. Many previous studies on HE have suggested the impairment of neurovascular unit and cell-cell communication in the pathogenesis of HE. This review focuses on pathological factors that appear in HE, cell type-specific pathological mechanisms, miscommunication/incorrect relationships, and therapeutic candidates between brain cells in HE. This review suggests that regulating communications and interactions between cells may be important in overcoming HE.

The effects of self-assembling peptide on glial cell activation

Glial cells play a critical role in the healthy and diseased phases of the central nervous system (CNS). CNS diseases involve a wide range of pathological conditions characterized by poor recovery of neuronal function. Glial cell-related target therapies are progressively gaining interest in inhibiting secondary injury-related death. Modulation of the extracellular matrix by artificial scaffolds plays a critical role in the behavior of glial cells after injury. Among numerous types of scaffolds, self-assembling peptides (SAPs) notably give attention to the design of a proper biophysical and biomechanical microenvironment for cellular homeostasis and tissue regeneration. Implementing SAPs in an injured brain can induce neural differentiation in transplanted stem cells, reducing inflammation and inhibiting glial scar formation. In this review, we investigate the recent findings to elucidate the pivotal role of SAPs in orchestrating the most pivotal secondary response following CNS injury. Notably, we explore their impact on the activation of glial cells and their modulatory effects on microglial and astrocytic polarization.

An Expanded Narrative Review of Neurotransmitters on Alzheimer's Disease: The Role of Therapeutic Interventions on Neurotransmission

Alzheimer's disease (AD) is a progressive neurodegenerative disease. The accumulation of amyloid-β (Aβ) plaques and tau neurofibrillary tangles are the key players responsible for the pathogenesis of the disease. The accumulation of Aβ plaques and tau affect the balance in chemical neurotransmitters in the brain. Thus, the current review examined the role of neurotransmitters in the pathogenesis of Alzheimer's disease and discusses the alterations in the neurochemical activity and cross talk with their receptors and transporters. In the presence of Aβ plaques and neurofibrillary tangles, changes may occur in the expression of neuronal receptors which in turn triggers excessive release of glutamate into the synaptic cleft contributing to cell death and neuronal damage. The GABAergic system may also be affected by AD pathology in a similar way. In addition, decreased receptors in the cholinergic system and dysfunction in the dopamine neurotransmission of AD pathology may also contribute to the damage to cognitive function. Moreover, the presence of deficiencies in noradrenergic neurons within the locus coeruleus in AD suggests that noradrenergic stimulation could be useful in addressing its pathophysiology. The regulation of melatonin, known for its effectiveness in enhancing cognitive function and preventing Aβ accumulation, along with the involvement of the serotonergic system and histaminergic system in cognition and memory, becomes remarkable for promoting neurotransmission in AD. Additionally, nitric oxide and adenosine-based therapeutic approaches play a protective role in AD by preventing neuroinflammation. Overall, neurotransmitter-based therapeutic strategies emerge as pivotal for addressing neurotransmitter homeostasis and neurotransmission in the context of AD. This review discussed the potential for neurotransmitter-based drugs to be effective in slowing and correcting the neurodegenerative processes in AD by targeting the neurochemical imbalance in the brain. Therefore, neurotransmitter-based drugs could serve as a future therapeutic strategy to tackle AD.

Excitatory amino acids as therapeutic agents: Reversing neurodegenerative trajectory by tackling excitotoxicity

Neurodegenerative diseases pose significant challenges to healthcare systems globally due to their complex etiology and relentless progression, often rendering conventional treatments ineffective. Recent advances have spotlighted excitatory amino acids, particularly D-amino acids, once considered as products of metabolism of the microbiota or deriving from food intake. This review explores the role of D-amino acids in mitigating excitotoxicity-a process characterized by excessive calcium influx through aberrant N-methyl-D-aspartate receptor (NMDAR) activation, which is implicated in the pathogenesis of diseases like Alzheimer's disease. By providing alternative pathways for neuronal signaling and protecting against excitotoxic damage, D-amino acids offer a novel approach to reversing neurodegenerative trajectories. Future research should focus on elucidating the detailed mechanisms of action of these compounds, evaluating their therapeutic potential through rigorous preclinical and clinical trials, and developing effective delivery systems to optimize their neuroprotective effects. This emerging field holds promise for developing innovative treatment strategies that could significantly improve outcomes for patients with neurodegenerative disorders.

Neuron-Astrocyte Interactions in Aging and Alzheimer's Disease: Dysregulation of Amyloid Precursor Protein

Amyloid precursor protein (APP) is central to Alzheimer's disease (AD) by its role in Aβ build-up and in neuronal and astrocytic malfunction. The major risk factor for late-onset AD is aging, which increases APP processing in both neurons and astrocytes, and consequently increases Aβ production. This focused review covers the subjects of how aging and AD affect APP dynamics within the both cell types and how astrocytes dysfunction can enhance neuroinflammation and neuronal dysfunction and injury. We discuss the interplay between neurons and astrocytes in aging and AD brains, where bi-directional cellular interactions accelerate neurodegeneration.

Astrocytes in Primary Familial Brain Calcification (PFBC): Emphasis on the Importance of Induced Pluripotent Stem Cell-Derived Human Astrocyte Models

Primary familial brain calcification (PFBC) is a rare, progressive central nervous system (CNS) disorder without a cure, and the current treatment methodologies primarily aim to relieve neurological and psychiatric symptoms of the patients. The disease is characterized by abnormal bilateral calcifications in the brain, however, our mechanistic understanding of the biology of the disease is still limited. Determining the roles of the specific cell types and molecular mechanisms involved in the pathophysiological processes of the disease is of great importance for the development of novel and effective treatment methodologies. There is a growing interest in the involvement of astrocytes in PFBC, as recent studies have suggested that astrocytes play a central role in the disease and that functional defects in these cells are critical for the development and progression of the disease. This review aims to discuss recent findings on the roles of astrocytes in PFBC pathophysiology, with a focus on known expression and roles of PFBC genes in astrocytes. Additionally, we discuss the importance of human astrocytes for PFBC disease modeling, and astrocytes as a potential therapeutic target in PFBC. Utilization of species-specific and physiologically relevant PFBC model systems can open new avenues for basic research, drug development, and regenerative medicine.

P2Y1R-IGFBP2 signaling: new contributor to astrocyte-neuron communication

In a recent article published in Nature Communications (Shigetomi et al Nat Commun 15(1):6525, 2024), Shigetomi et al. identified that upregulated astrocytic purinergic P2Y1 receptors (P2Y1R), acting via the downstream molecule, insulin-like growth factor binding protein 2 (IGFBP2), play a crucial role in neuronal hyperexcitability. In epilepsy and stroke models, P2Y1R-IGFBP2 signaling was found to mediate astrocyte-driven neuronal hyperexcitability and so is a new contributor to astrocyte-neuron communication. Thus, IGFBP2 could be an alternative target for treating the effects of upregulated P2Y1R activity in reactive astrocytes in neurological diseases.

SIRT2 and ALDH1A1 as critical enzymes for astrocytic GABA production in Alzheimer's disease

BACKGROUND

Alzheimer's Disease (AD) is a neurodegenerative disease with drastically altered astrocytic metabolism. Astrocytic GABA and H2O2 are associated with memory impairment in AD and synthesized through the Monoamine Oxidase B (MAOB)-mediated multi-step degradation of putrescine. However, the enzymes downstream to MAOB in this pathway remain unidentified.

METHODS

Using transcriptomics analysis, we identified two candidate enzymes, Aldehyde Dehydrogenase 1 family member A1 (ALDH1A1) and Sirtuin 2 (SIRT2) for the steps following MAOB in the astrocytic GABA production pathway. We used immunostaining, metabolite analysis and electrophysiology, both in vitro and in vivo, to confirm the participation of these enzymes in astrocytic GABA production. We checked for the presence of SIRT2 in human AD patients as well as the mouse model APP/PS1 and finally, we selectively ablated SIRT2 in the astrocytes of APP/PS1 mice to observe its effects on pathology.

RESULTS

Immunostaining, metabolite analysis, and electrophysiology recapitulated the participation of ALDH1A1 and SIRT2 in GABA production. Inhibition of SIRT2 reduced the production of astrocytic GABA but not H2O2, a key molecule in neurodegeneration. Elevated expression of these enzymes was found in hippocampal astrocytes of AD patients and APP/PS1 mice. Astrocyte-specific gene-silencing of SIRT2 in APP/PS1 mice restored GABA production and partially improved memory function.

CONCLUSIONS

Our study is the first to identify the specific role of SIRT2 in reactive astrogliosis and determine the specific pathway and metabolic step catalyzed by the enzyme. We determine the partial, yet significant role of ALDH1A1 in this process, thereby highlighting 2 new players the astrocytic GABA production pathway. Our findings therefore, offer SIRT2 as a new tool to segregate GABA from H2O2 production, aiding future research in neurodegenerative diseases.

Astrocytes in aging

The mammalian nervous system is impacted by aging. Aging alters brain architecture, is associated with molecular damage, and can manifest with cognitive and motor deficits that diminish the quality of life. Astrocytes are glial cells of the CNS that regulate the development, function, and repair of neural circuits during development and adulthood; however, their functions in aging are less understood. Astrocytes change their transcriptome during aging, with astrocytes in areas such as the cerebellum, the hypothalamus, and white matter-rich regions being the most affected. While numerous studies describe astrocyte transcriptional changes in aging, many questions still remain. For example, how is astrocyte function altered by transcriptional changes that occur during aging? What are the mechanisms promoting astrocyte aged states? How do aged astrocytes impact brain function? This review discusses features of aged astrocytes and their potential triggers and proposes ways in which they may impact brain function and health span.

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

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

Investigating the Pathology-Related Astroglial Plasticity in the Human Cerebral Cortex

Evaluation of astrocyte proliferation in human brain pathology plays a key role in the diagnostic and prognostic assessment of diseases, especially in cases of benign or malignant brain neoplasms. However, the proliferative potential of nonneoplastic astrocytes within the affected human brain parenchyma has not been well defined. Given the beneficial functions of proliferating reactive astrocytes for brain repair in experimental models of stroke and trauma, investigating the context-specific potential of human astrocytes to proliferate will be a major step forward in exploiting their roles in the genesis, progression, and outcome of neurological diseases in patients. Here, we describe a step-by-step protocol for immunofluorescent staining and neurosphere-forming assay tailored to uncover the astrocyte proliferation and neural stem cell properties in samples of human brain tissue obtained during neurosurgical resections or in a small brain biopsy. This protocol allows for reliable assessment and evaluation of adoptive astrocyte plasticity in the context with various neuropathological conditions in the human brain.

Multifarious astrocyte-neuron dialog in shaping neural circuit architecture

Astrocytes are multifaceted glial cell types that perform structural, functional, metabolic, and homeostatic roles in the brain. Recent studies have revealed mechanisms underlying the diversity of bidirectional communication modes between astrocytes and neurons - the fundamental organizing principle shaping synaptic properties at tripartite synapses. These astrocyte-neuron interactions are critical for the proper functioning of synapses and neural circuits. This review focuses on molecular mechanisms that direct these interactions, highlighting the versatile roles of multiple adhesion-based paths that likely modulate them, often in a context-dependent manner. It also describes how astrocyte-mediated processes go awry in certain brain disorders and provides a timely insight on the pivotal roles of astrocyte-neuron interactions in synaptic integrity and their relevance to understanding and treating neurological disorders.

Postmortem evaluation of the striatum in an NTCELL trial participant five years after transplantation

In 2017 a novel growth factor administration therapy (termed NTCELL®) was trialled for safety and efficacy for Parkinson's disease treatment. NTCELL® administration is the transplantation of encapsulated porcine choroid plexus cells into the putamen. A clinical study demonstrated safety but failed to meet its primary clinical end-point. Here we describe the clinical and neuropathological characteristics of a case who died five years after receiving NTCELL® treatment. Using histochemical and immunohistochemical labelling, we demonstrate that the NTCELL® capsules remain in the striatum but are mainly devoid of cellular contents. A similar pattern of astrogliosis and microgliosis surrounds the capsule placement area to those surrounding the needle track for implanting the capsules. This study is important as it is the first exploration of the long-term clinical and anatomical outcomes of the NTCELL® clinical trial. The results of this study will help inform future studies aimed at regenerating neurons through the implantation of capsules.

Physiology and pathophysiology of the retinal neuroglia

Neuroglia of the retina are represented by Müller glia, parenchymal astrocytes, microglia and oligodendrocytes mainly associated with the optic nerve. Müller glia are the most numerous glia, endowed with multiple homeostatic functions and indispensable for the retinal morphofunctional organization. Müller cells integrate retinal neurons into individual functional units (known as retinal columns) and act as a living light guide, transmitting photons to photoreceptors. In pathology, retinal neuroglia undergo complex changes, which include upregulation of neuroprotection, reactive gliosis, and functional asthenia. The balance between all these changes defines the progression and outcome of retinal disorders.

Astrocytes and microglia in multiple sclerosis and neuromyelitis optica

Multiple sclerosis and neuromyelitis optica are autoimmune neurodegenerative diseases primarily targeting myelin sheath and neuroglia. In multiple sclerosis, autoantibodies destroy oligodendrocytes and myelin, which underlies primary neurologic symptoms. Focal damage to myelin triggers reactive astrogliosis and microgliosis, which contribute to and to a large extent define the disease progression. In neuromyelitis optica, autoantibodies against water channel aquaporin 4 (AQP4), which are localized at astrocytic endfeet mediate damage of the glia limitans thus facilitating infiltration of blood-borne molecules and cells that propagate the damage to nerves and neurons. This primary astrocytopathy recruits microglia, which contribute to the neuroinflammatory response. Neuroglial cells therefore are potential targets for cell-specific therapies.

Revealing and Characterizing Astrocytic Atrophy in an Animal Model of Depression

Astrocyte atrophy is the main histopathological hallmark of major depressive disorder (MDD) in humans and in animal models of depression. In particular, depression and depressive-like behaviors are associated with a substantial decrease in size and complexity of astrocytes in the prefrontal cortex. This results in the reduced homeostatic support of synaptic transmission, which arguably translates into abnormal activity of neuronal networks and pathological changes in mood and behavior. Treatment of experimental animals with antidepressants as well as with acupuncture in the specific acupoints alleviates depressive-like behaviors and rescues astrocytic atrophy. Here, we describe the methodology for inducing and monitoring the depressive-like behaviors in mice using chronic unpredictable mild stress (CUMS), with subsequent in-depth analysis of astrocytic morphology using confocal microscopy in conjunction with astrocyte-specific labeling by virally transfected genetically encoded fluorescent probe mCherry and intracellular injection of Lucifer yellow. We also describe immunocytochemical visualization of astrocyte-specific cytoskeletal linker ezrin, which is involved in controlling perisynaptic astrocytic leaflets.

Neuroglia in hepatic encephalopathy

Neuroglia contribute to the pathophysiology of hepatic encephalopathy (HE) either beneficially or detrimentally. Pathogenesis of HE is linked to damage triggered by blood-derived toxins, with ammonia being the main causative factor. Neuroglial cells, especially astrocytes and microglia, respond to HE-associated systemic and central signals and undergo complex and variable changes in their metabolism, morphology, and function, which include ion and water dyshomeostasis in conjunction with neurotransmission imbalance and neuroinflammation. HE-induced alterations of astrocytes are defined as astrocytopathy, with aberrant astrocytes resulting in either gain or loss of functions. In the chronic HE, the presence of Alzheimer type II cells is a histologic hallmark, with asthenic astrocytes emerging as a newcomer. In acute HE, rapid swelling of astrocytes is a primary cause of cerebral edema and mortality. This chapter reviews the dominant role of astrocytes in the pathogenesis of HE resulting from acute and chronic liver failure, mainly in experimental models. The focus is on the loss of homeostatic function bearing upon the functioning of the glymphatic system, aberrant neurotransmission as a consequence of astrocyte-neuron miscommunication, and the concordant neuroinflammatory response of astrocytes and microglia. The chapter concludes with a delineation of concepts for future research.

Neuroglia in aging

Aging is associated with morphologic and functional decline of the brain active milieu and, in particular, of the neuroglia, which compromises homeostatic support and neuroprotection. Astrocytes in aging undergo complex and region specific changes, manifested by morphologic atrophy and widespread functional asthenia. Aging leads to mitochondrial malfunction and reduced protein/lipid ratio in human astrocytes. Oligodendrocyte lineage cells are the most affected cells by the aging process, which limits myelinating capacity, thus leading to a substantial reduction in the white matter and deficient brain connectome. Finally, microglia undergo a morphologic functional dystrophy in the aged human brain which curtails brain defenses and increases brain vulnerability to neuropathology and especially to age-dependent neurodegenerative disorders. Lifestyle modifications, such as enriched environment, physical exercise, and healthy dieting, boost neuroglial support, thus improving cognitive longevity.

Neuroglia in mood disorders

Multiple lines of evidence indicate that mood disorders, such as major depressive and bipolar disorder, are associated with abnormalities in neuroglial cells. This chapter discusses the existing literature investigating the potential role of astrocytes, oligodendrocytes, and microglia in mood pathology. We will describe evidence from in vivo imaging, postmortem, animal models based on (stress) paradigms that mimic depressive-like behavior, and biomarker studies in blood and cerebrospinal fluid in patients with mood disorders. The effect of medication used in the treatment of mood disorders, such as antidepressants and lithium, on glial function is discussed. Lastly, we highlight the most relevant findings about potential deficiencies in glia-glia crosstalk in mood disorders. Overall, decreased astrocyte and oligodendrocyte density and expression and microglial changes in homeostatic functions have frequently been put forward in MDD pathology. Studies of BD report similar findings to some extent; however, the evidence is less well established. Together, these findings are suggestive of reduced glial cell function leading to potential white matter abnormalities, glutamate dysregulation, disrupted neuronal functioning, and neurotransmission. However, more research is required to better understand the exact mechanisms underlying glial cell contributions to mood disorder development.

Role of astrocytes connexins - pannexins in acute brain injury

Acute brain injuries (ABIs) encompass a broad spectrum of primary injuries such as ischemia, hypoxia, trauma, and hemorrhage that converge into secondary injury where some mechanisms show common determinants. In this regard, astroglial connexin and pannexin channels have been shown to play an important role. These channels are transmembrane proteins sharing similar topology and form gateways between adjacent cells named gap junctions (GJs) and pores into unopposed membranes named hemichannels (HCs). In astrocytes, GJs and HCs enable intercellular communication and have active participation in normal brain physiological processes, such as calcium waves, synapsis modulation, regional blood flow regulation, and homeostatic control of the extracellular environment, among others. However, after acute brain injury, astrocytes can change their phenotype and modify the activity of both channels and hemichannels, which can result in the amplification of danger signals, increased mediators of inflammation, and neuronal death, contributing to the expansion of brain damage and neurological deterioration. This is known as secondary brain damage. In this review, we discussed the main biological mechanism of secondary brain damage with a particular focus on astroglial connexin and pannexin participation during acute brain injuries.

Neuroglia in neurodegeneration: Alzheimer, Parkinson, and Huntington disease

The conspicuous rise of chronic neurodegenerative diseases, including Alzheimer (AD), Parkinson (PD), and Huntington (HD) diseases, is currently without disease-modifying therapies and accompanied by an excessive rate of unsuccessful clinical trials. This reflects a profound lack of understanding of the pathogenesis of these diseases, indicating that the current paradigms guiding disease modeling and drug development are in need of reconsideration. The role of neuroglia, namely astrocytes, microglial cells, and oligodendrocytes, in the pathogenesis of neurodegenerative diseases emerged during the last decades. This chapter provides the state-of-the-art update on the changes of astrocytes, microglial cells, and oligodendrocytes in AD, PD, and HD. A growing body of evidence suggests that homeostatic and defensive functions of glial cells are compromised at different disease stages, leading to increased susceptibility of neurons to noxious stimuli, eventually resulting in their malfunction and degeneration. Investments are needed in the generation of novel preclinical models suitable for studying glial pathology, in "humanizing" research, and in-depth investigation of glial cell alterations to slow down and, possibly, halt and prevent the rise of neurodegenerative disease. Targeting glial cells opens new therapeutic avenues to treat AD, PD, and HD.

Unifying biology of neurodegeneration in lysosomal storage diseases

There are currently at least 70 characterised lysosomal storage diseases (LSD) resultant from inherited single-gene defects. Of these, at least 30 present with central nervous system (CNS) neurodegeneration and overlapping aetiology. Substrate accumulation and dysfunctional neuronal lysosomes are common denominator, but how variants in 30 different genes converge on this central cellular phenotype is unclear. Equally unresolved is how the accumulation of a diverse spectrum of substrates in the neuronal lysosomes results in remarkably similar neurodegenerative outcomes. Conversely, how is it that many other monogenic LSDs cause only visceral disease? Lysosomal substance accumulation in LSDs with CNS neurodegeneration (nLSD) includes lipofuscinoses, mucopolysaccharidoses, sphingolipidoses and glycoproteinoses. Here, we review the latest discoveries in the fundamental biology of four classes of nLSDs, comparing and contrasting new insights into disease mechanism with emerging evidence of unifying convergence.

Neuroglia in stroke

Stroke, ischemic or hemorrhagic, triggers a complex and coordinated glial response, which, to a large extent, defines the progression and outcome of this focal damage of the nervous tissue. Massive cell death in the infarction core results in a release of damage-associated molecular patterns, which, together with blood-borne factors entering the brain through either ruptured vessels or through compromised blood-brain barrier, trigger reactive gliosis. Microglia are the first to migrate toward the lesion, proliferate, and phagocytose cellular debris in and around the infarct core. Reactive astrogliosis occurs around the margins of the infarct core and is characterized by astrocytic proliferation, morphologic remodeling with loss of territorial domain segregation, and transcriptional reprogramming into wound repair astrocytes that form a periinfarct border that protects the healthy tissue and assists postlesional regeneration.

General pathophysiology of neuroglia

Neuroglia in the CNS, represented by astroglia, oligodendroglia, and microglia, are responsible for the homeostatic support and protection of the nervous tissue. Neuroglia are intimately involved in the pathogenesis of all neurologic diseases, and neuroglial changes to a large extent define the progression of these diseases and their neurologic outcome. In contrast to neurons, neuroglia are capable of mounting an evolutionary conserved response to pathology known as reactive gliosis. Reactive gliosis is initially protective and allostatic, and it is aimed at preserving the nervous tissue function and integrity. However, in many diseases, neuroglial cells undergo atrophy and functional asthenia, contributing to nervous tissue damage.

Neuroinflammation in Alzheimer disease

Increasing evidence points to a pivotal role of immune processes in the pathogenesis of Alzheimer disease, which is the most prevalent neurodegenerative and dementia-causing disease of our time. Multiple lines of information provided by experimental, epidemiological, neuropathological and genetic studies suggest a pathological role for innate and adaptive immune activation in this disease. Here, we review the cell types and pathological mechanisms involved in disease development as well as the influence of genetics and lifestyle factors. Given the decade-long preclinical stage of Alzheimer disease, these mechanisms and their interactions are driving forces behind the spread and progression of the disease. The identification of treatment opportunities will require a precise understanding of the cells and mechanisms involved as well as a clear definition of their temporal and topographical nature. We will also discuss new therapeutic strategies for targeting neuroinflammation, which are now entering the clinic and showing promise for patients.

X-ray fluorescence mapping of brain tissue reveals the profound extent of trace element dysregulation in stroke pathophysiology

The brain is a privileged organ with regard to its trace element composition and maintains a robust barrier system to sequester this specialized environment from the rest of the body and the vascular system. Stroke is caused by loss of adequate blood flow to a region of the brain. Without adequate blood flow ischaemic changes begin almost immediately, triggering an ischaemic cascade, characterized by ion dysregulation, loss of function, oxidative damage, cellular degradation, and breakdown of the barrier that helps maintain this environment. Ion dysregulation is a hallmark of stroke pathophysiology and we observe that most elements in the brain are dysregulated after stroke. X-ray fluorescence-based detection of physiological changes in the neurometallome after stroke reveals profound ion dysregulation within the lesion and surrounding tissue. Not only are most elements significantly dysregulated after stroke, but the level of dysregulation cannot be predicted from a cell-level description of dysregulation. X-ray fluorescence imaging reveals that the stroke lesion retains <25% of essential K+ after stroke, but this element is not concomitantly elevated elsewhere in the organ. Moreover, elements like Na+, Ca2+, and Cl- are vastly elevated above levels available in normal brain tissue (>400%, >200%, and >150%, respectively). We hypothesize that weakening of the blood-brain barrier after stroke allows elements to freely diffuse down their concentration gradient so that the stroke lesion is in equilibrium with blood (and the compartments containing brain interstitial fluid and cerebrospinal fluid). The change observed for the neurometallome likely has consequences for the potential to rescue infarcted tissue, but also presents specific targets for treatment.

Microglia contact cerebral vasculature through gaps between astrocyte endfeet

The close spatial relationship between microglia and cerebral blood vessels implicates microglia in vascular development, homeostasis and disease. In this study we used the publicly available Cortical MM^3 electron microscopy dataset to systematically investigate microglial interactions with the vasculature. Our analysis revealed that approximately 20% of microglia formed direct contacts with blood vessels through gaps between adjacent astrocyte endfeet. We termed these contact points "plugs". Plug-forming microglia exhibited closer proximity to blood vessels than non-plug forming microglia and formed multiple plugs, predominantly near the soma, ranging in surface area from ∼0.01 μm2 to ∼15 μm2. Plugs were enriched at the venule end of the vascular tree and displayed a preference for contacting endothelial cells over pericytes at a ratio of 3:1. In summary, we provide novel insights into the ultrastructural relationship between microglia and the vasculature, laying a foundation for understanding how these contacts contribute to the functional cross-talk between microglia and cells of the vasculature in health and disease.

Neuroglia in cognitive reserve

The concept of cognitive reserve was born to account for the disjunction between the objective extent of brain damage in pathology and its clinical and intellectual outcome. The cognitive reserve comprises structural (brain reserve) and functional (brain maintenance, resilience, compensation) aspects of the nervous tissue reflecting exposome-driven life-long plasticity, which defines the ability of the brain to withstand aging and pathology. The mechanistic background of this concept was primarily focused on adaptive changes in neurones and neuronal networks. We present arguments favoring the more inclusive view, positing that neuroglia are fundamental for defining the cognitive reserve through homeostatic, neuroprotective, and neurodegenerative mechanisms. Neuroglia are critical for the life-long shaping of synaptically connected neuronal circuits as well as the brain connectome thus defining cognitive reserve. Neuroglial homeostatic and protective physiological responses define brain maintenance and resilience, while neuroglia regenerative capabilities are critical for brain compensation in pathology. Targeting neuroglia may represent an untrodden path for prolonging cognitive longevity.