Leukocyte infiltration, neuronal degeneration, and neurite outgrowth after ablation of scar-forming, reactive astrocytes in adult transgenic mice

Cell reprogramming therapy for Parkinson's disease

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

Resident immune responses to spinal cord injury: role of astrocytes and microglia

Spinal cord injury can be traumatic or non-traumatic in origin, with the latter rising in incidence and prevalence with the aging demographics of our society. Moreover, as the global population ages, individuals with co-existent degenerative spinal pathology comprise a growing number of traumatic spinal cord injury cases, especially involving the cervical spinal cord. This makes recovery and treatment approaches particularly challenging as age and comorbidities may limit regenerative capacity. For these reasons, it is critical to better understand the complex milieu of spinal cord injury lesion pathobiology and the ensuing inflammatory response. This review discusses microglia-specific purinergic and cytokine signaling pathways, as well as microglial modulation of synaptic stability and plasticity after injury. Further, we evaluate the role of astrocytes in neurotransmission and calcium signaling, as well as their border-forming response to neural lesions. Both the inflammatory and reparative roles of these cells have eluded our complete understanding and remain key therapeutic targets due to their extensive structural and functional roles in the nervous system. Recent advances have shed light on the roles of glia in neurotransmission and reparative injury responses that will change how interventions are directed. Understanding key processes and existing knowledge gaps will allow future research to effectively target these cells and harness their regenerative potential.

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

Central nervous system (CNS) lesions become surrounded by neuroprotective borders of newly proliferated reactive astrocytes; however, fundamental features of these cells are poorly understood. Here we show that following spinal cord injury or stroke, 90% and 10% of border-forming astrocytes derive, respectively, from proliferating local astrocytes and oligodendrocyte progenitor cells in adult mice of both sexes. Temporal transcriptome analysis, single-nucleus RNA sequencing and immunohistochemistry show that after focal CNS injury, local mature astrocytes dedifferentiate, proliferate and become transcriptionally reprogrammed to permanently altered new states, with persisting downregulation of molecules associated with astrocyte-neuron interactions and upregulation of molecules associated with wound healing, microbial defense and interactions with stromal and immune cells. These wound repair astrocytes share morphologic and transcriptional features with perimeningeal limitans astrocytes and are the predominant source of neuroprotective borders that re-establish CNS integrity around lesions by separating neural parenchyma from stromal and immune cells as occurs throughout the healthy CNS.

Mechanobiological Modulation of In Vitro Astrocyte Reactivity Using Variable Gel Stiffness

After traumatic brain injury, the brain extracellular matrix undergoes structural rearrangement due to changes in matrix composition, activation of proteases, and deposition of chondroitin sulfate proteoglycans by reactive astrocytes to produce the glial scar. These changes lead to a softening of the tissue, where the stiffness of the contusion "core" and peripheral "pericontusional" regions becomes softer than that of healthy tissue. Pioneering mechanotransduction studies have shown that soft substrates upregulate intermediate filament proteins in reactive astrocytes; however, many other aspects of astrocyte biology remain unclear. Here, we developed a platform for the culture of cortical astrocytes using polyacrylamide (PA) gels of varying stiffness (measured in Pascal; Pa) to mimic injury-related regions in order to investigate the effects of tissue stiffness on astrocyte reactivity and morphology. Our results show that substrate stiffness influences astrocyte phenotype; soft 300 Pa substrates led to increased GFAP immunoreactivity, proliferation, and complexity of processes. Intermediate 800 Pa substrates increased Aggrecan+, Brevican+, and Neurocan+ astrocytes. The stiffest 1 kPa substrates led to astrocytes with basal morphologies, similar to a physiological state. These results advance our understanding of astrocyte mechanotransduction processes and provide evidence of how substrates with engineered stiffness can mimic the injury microenvironment.

A comprehensive exploration of astrocytes in migraine: a bibliometric and visual analysis

BACKGROUND

Migraine, as a prevalent neurologic disorder, involves intricate and yet incompletely elucidated pathophysiological mechanisms. A plethora of research findings underscores the pivotal role played by astrocytes in the progression of migraines. In order to elucidate the current advances and directions in research pertaining to astrocytes in migraines, we conducted bibliometric analysis of relevant literature and visualized the results. Subsequently, we expound upon these findings to contribute to the evolving understanding of the role of astrocytes in migraine pathophysiology.

METHODS

On November 21, 2023, we conducted a search on Web of Science (WOS), restricting the document type to articles or reviews and language to English. Following a meticulous selection process involving three researchers, we identified the literature to be included in our analysis. Subsequently, we employed Microsoft Office Excel programs, R, VOSviewer, Scimago Graphica, and CiteSpace software to conduct visualization analysis of basic information and trends regarding journals, countries/regions, and influential authors, institutions, keywords, and papers.

RESULTS

As of November 21, 2023, relevant literature has been published in 71 journals across 27 countries/regions. This corpus comprises contributions from 576 authors affiliated with 220 institutions, encompassing 865 keywords and referencing 6065 scholarly articles. CEPHALALGIA stands out as the most influential journal in this field, while authors PIETROBON D and DALKARA T have significant impact. The United States is highly influential, with CNR and UNIV PADUA emerging as highly influential institutions. The predominant category is Neurosciences.

CONCLUSIONS

Future investigators may continue to focus on migraines with aura, familial hemiplegic migraine (FHM), and the crucial calcitonin gene-related peptide (CGRP) system. Employing advanced observational techniques, such as imaging, researchers should pay attention to cellular and tissue structures, such as microglia and the trigeminal ganglion, as well as mechanisms involving inflammation and central sensitization. Moreover, animal models are paramount in obtaining high-quality evidence.

Inhibition of Notch1 signal promotes brain recovery by modulating glial activity after stroke

BACKGROUND

Notch1 signaling inhibiton with N-[N-(3,5-difluorophenacetyl)-1-alanyl]-S-phenylglycine t-butylester] (DAPT) treatment could promote brain recovery and the intervention effect is different between striatum (STR) and cortex (CTX), which might be accounted for different changes of glial activities, but the in-depth mechanism is still unknown. The purpose of this study was to identify whether DAPT could modulate microglial subtype shifts and astroglial-endfeet aquaporin-4 (AQP4) mediated waste solute drainage.

METHODS

Sprague-Dawley rats (n=10) were subjected to 90min of middle cerebral artery occlusion (MCAO) and were treated with DAPT (n=5) or act as control with no treatment (n=5). Two groups of rats underwent MRI scans at 24h and 4 week, and sacrificed at 4 week after stroke for immunofluorescence (IF).

RESULTS

Compared with control rats, MRI data showed structural recovery in ipsilateral STR but not CTX. And IF showed decreased pro-inflammatory M1 microglia and increased anti-inflammatory M2 microglia in striatal lesion core and peri-lesions of STR, CTX. Meanwhile, IF showed decreased AQP4 polarity in ischemic brain tissue, however, AQP4 polarity in striatal peri-lesions of DAPT treated rats was higher than that in control rats but shows no difference in cortical peri-lesions between control and treated rats.

CONCLUSIONS

The present study indicated that DAPT could promote protective microglia subtype shift and striatal astrocyte mediated waste solute drainage, that the later might be the major contributor of waste solute metabolism and one of the accounts for discrepant recovery of STR and CTX.

Astrocytic Slc4a4 regulates blood-brain barrier integrity in healthy and stroke brains via a CCL2-CCR2 pathway and NO dysregulation

Astrocytes play vital roles in blood-brain barrier (BBB) maintenance, yet how they support BBB integrity under normal or pathological conditions remains poorly defined. Recent evidence suggests that ion homeostasis is a cellular mechanism important for BBB integrity. In the current study, we investigated the function of an astrocyte-specific pH regulator, Slc4a4, in BBB maintenance and repair. We show that astrocytic Slc4a4 is required for normal astrocyte morphological complexity and BBB function. Multi-omics analyses identified increased astrocytic secretion of CCL2 coupled with dysregulated arginine-NO metabolism after Slc4a4 deletion. Using a model of ischemic stroke, we found that loss of Slc4a4 exacerbates BBB disruption, which was rescued by pharmacological or genetic inhibition of the CCL2-CCR2 pathway in vivo. Together, our study identifies the astrocytic Slc4a4-CCL2 and endothelial CCR2 axis as a mechanism controlling BBB integrity and repair, while providing insights for a therapeutic approach against BBB-related CNS disorders.

The contribution of the meningeal immune interface to neuroinflammation in traumatic brain injury

Traumatic brain injury (TBI) is a major cause of disability and mortality worldwide, particularly among the elderly, yet our mechanistic understanding of what renders the post-traumatic brain vulnerable to poor outcomes, and susceptible to neurological disease, is incomplete. It is well established that dysregulated and sustained immune responses elicit negative consequences after TBI; however, our understanding of the neuroimmune interface that facilitates crosstalk between central and peripheral immune reservoirs is in its infancy. The meninges serve as the interface between the brain and the immune system, facilitating important bi-directional roles in both healthy and disease settings. It has been previously shown that disruption of this system exacerbates neuroinflammation in age-related neurodegenerative disorders such as Alzheimer's disease; however, we have an incomplete understanding of how the meningeal compartment influences immune responses after TBI. In this manuscript, we will offer a detailed overview of the holistic nature of neuroinflammatory responses in TBI, including hallmark features observed across clinical and animal models. We will highlight the structure and function of the meningeal lymphatic system, including its role in immuno-surveillance and immune responses within the meninges and the brain. We will provide a comprehensive update on our current knowledge of meningeal-derived responses across the spectrum of TBI, and identify new avenues for neuroimmune modulation within the neurotrauma field.

Hyperglycemia enhances brain susceptibility to lipopolysaccharide-induced neuroinflammation via astrocyte reprogramming

Hyperglycemia has been shown to modulate the immune response of peripheral immune cells and organs, but the impact of hyperglycemia on neuroinflammation within the brain remains elusive. In the present study, we provide evidences that streptozotocin (STZ)-induced hyperglycemic condition in mice drives a phenotypic switch of brain astrocytes to a proinflammatory state, and increases brain vulnerability to mild peripheral inflammation. In particular, we found that hyperglycemia led to a significant increase in the astrocyte proliferation as determined by flow cytometric and immunohistochemical analyses of mouse brain. The increased astrocyte proliferation by hyperglycemia was reduced by Glut1 inhibitor BAY-876. Transcriptomic analysis of isolated astrocytes from Aldh1l1CreERT2;tdTomato mice revealed that peripheral STZ injection induced astrocyte reprogramming into proliferative, and proinflammatory phenotype. Additionally, STZ-induced hyperglycemic condition significantly enhanced the infiltration of circulating myeloid cells into the brain and the disruption of blood-brain barrier in response to mild lipopolysaccharide (LPS) administration. Systemic hyperglycemia did not alter the intensity and sensitivity of peripheral inflammation in mice to LPS challenge, but increased the inflammatory potential of brain microglia. In line with findings from mouse experiments, a high-glucose environment intensified the LPS-triggered production of proinflammatory molecules in primary astrocyte cultures. Furthermore, hyperglycemic mice exhibited a significant impairment in cognitive function after mild LPS administration compared to normoglycemic mice as determined by novel object recognition and Y-maze tasks. Taken together, these results demonstrate that hyperglycemia directly induces astrocyte reprogramming towards a proliferative and proinflammatory phenotype, which potentiates mild LPS-triggered inflammation within brain parenchymal regions.

Mature astrocytes as source for astrocyte repopulation after deletion in the medial prefrontal cortex: Implications for depression

The adult brain retains a high repopulation capacity of astrocytes after deletion, and both mature astrocytes in the neocortex and neural stem cells in neurogenic regions possess the potential to generate astrocytes. However, the origin and the repopulation dynamics of the repopulating astrocytes after deletion remain largely unclear. The number of astrocytes is reduced in the medial prefrontal cortex (mPFC) of patients with depression, and selective elimination of mPFC astrocytes is sufficient to induce depression-like behaviors in rodents. However, whether astrocyte repopulation capacity is impaired in depression is unknown. In this study, we used different transgenic mouse lines to genetically label different cell types and demonstrated that in the mPFC of normal adult mice of both sexes, mature astrocytes were a major source of the repopulating astrocytes after acute deletion induced by an astrocyte-specific toxin, L-alpha-aminoadipic acid (L-AAA), and astrocyte regeneration was accomplished within two weeks accompanied by reversal of depression-like behaviors. Furthermore, re-ablation of mPFC astrocytes post repopulation led to reappearance of depression-like behaviors. In adult male mice subjected to 14-day chronic restraint stress, a well-validated mouse model of depression, the number of mPFC astrocytes was reduced; however, the ability of mPFC astrocytes to repopulate after L-AAA-induced deletion was largely unaltered. Our study highlights a potentially beneficial role for repopulating astrocytes in depression and provides novel therapeutic insights into enhancing local mature astrocyte generation in depression.

Astrocytes adopt a progenitor-like migratory strategy for regeneration in adult brain

Mature astrocytes become activated upon non-specific tissue damage and contribute to glial scar formation. Proliferation and migration of adult reactive astrocytes after injury is considered very limited. However, the regenerative behavior of individual astrocytes following selective astroglial loss, as seen in astrocytopathies, such as neuromyelitis optica spectrum disorder, remains unexplored. Here, we performed longitudinal in vivo imaging of cortical astrocytes after focal astrocyte ablation in mice. We discovered that perilesional astrocytes develop a remarkable plasticity for efficient lesion repopulation. A subset of mature astrocytes transforms into reactive progenitor-like (REPL) astrocytes that not only undergo multiple asymmetric divisions but also remain in a multinucleated interstage. This regenerative response facilitates efficient migration of newly formed daughter cell nuclei towards unoccupied astrocyte territories. Our findings define the cellular principles of astrocyte plasticity upon focal lesion, unravelling the REPL phenotype as a fundamental regenerative strategy of mature astrocytes to restore astrocytic networks in the adult mammalian brain. Promoting this regenerative phenotype bears therapeutic potential for neurological conditions involving glial dysfunction.

Vagus nerve stimulation enhances remyelination and decreases innate neuroinflammation in lysolecithin-induced demyelination

BACKGROUND

Current treatments for Multiple Sclerosis (MS) poorly address chronic innate neuroinflammation nor do they offer effective remyelination. The vagus nerve has a strong regulatory role in inflammation and Vagus Nerve Stimulation (VNS) has potential to affect both neuroinflammation and remyelination in MS.

OBJECTIVE

This study investigated the effects of VNS on demyelination and innate neuroinflammation in a validated MS rodent model.

METHODS

Lysolecithin (LPC) was injected in the corpus callosum (CC) of 46 Lewis rats, inducing a demyelinated lesion. 33/46 rats received continuously-cycled VNS (cVNS) or one-minute per day VNS (1minVNS) or sham VNS from 2 days before LPC-injection until perfusion at 3 days post-injection (dpi) (corresponding with a demyelinated lesion with peak inflammation). 13/46 rats received cVNS or sham from 2 days before LPC-injection until perfusion at 11 dpi (corresponding with a partial remyelinated lesion). Immunohistochemistry and proteomics analyses were performed to investigate the extend of demyelination and inflammation.

RESULTS

Immunohistochemistry showed that cVNS significantly reduced microglial and astrocytic activation in the lesion and lesion border, and significantly reduced the Olig2+ cell count at 3 dpi. Furthermore, cVNS significantly improved remyelination with 57.4 % versus sham at 11 dpi. Proteomic gene set enrichment analyses showed increased activation of (glutamatergic) synapse pathways in cVNS versus sham, most pronounced at 3 dpi.

CONCLUSION

cVNS improved remyelination of an LPC-induced lesion. Possible mechanisms might include modulation of microglia and astrocyte activity, increased (glutamatergic) synapses and enhanced oligodendrocyte clearance after initial injury.

Insertional effect following electrode implantation: an underreported but important phenomenon

Deep brain stimulation has revolutionized the treatment of movement disorders and is gaining momentum in the treatment of several other neuropsychiatric disorders. In almost all applications of this therapy, the insertion of electrodes into the target has been shown to induce some degree of clinical improvement prior to stimulation onset. Disregarding this phenomenon, commonly referred to as 'insertional effect', can lead to biased results in clinical trials, as patients receiving sham stimulation may still experience some degree of symptom amelioration. Similar to the clinical scenario, an improvement in behavioural performance following electrode implantation has also been reported in preclinical models. From a neurohistopathologic perspective, the insertion of electrodes into the brain causes an initial trauma and inflammatory response, the activation of astrocytes, a focal release of gliotransmitters, the hyperexcitability of neurons in the vicinity of the implants, as well as neuroplastic and circuitry changes at a distance from the target. Taken together, it would appear that electrode insertion is not an inert process, but rather triggers a cascade of biological processes, and, as such, should be considered alongside the active delivery of stimulation as an active part of the deep brain stimulation therapy.

AAV8 vector induced gliosis following neuronal transgene expression

Introduction

Expression of light sensitive ion channels by selected neurons has been achieved by viral mediated transduction with gene constructs, but for this to have therapeutic uses, for instance in treating epilepsy, any adverse effects of viral infection on the cerebral cortex needs to be evaluated. Here, we assessed the impact of adeno-associated virus 8 (AAV8) carrying DNA code for a soma targeting light activated chloride channel/FusionRed (FR) construct under the CKIIa promoter.

Methods

Viral constructs were harvested from transfected HEK293 cells in vitro and purified. To test functionality of the opsin, cultured rodent neurons were transduced and the light response of transduced neurons was assayed using whole-cell patch-clamp recordings. In vivo expression was confirmed by immunofluorescence for FR. Unilateral intracranial injections of the viral construct were made into the mouse neocortex and non-invasive fluorescence imaging of FR expression made over 1-4 weeks post-injection using an IVIS Spectrum system. Sections were also prepared from injected mouse cortex for immunofluorescence staining of FR, alongside glial and neuronal marker proteins.

Results

In vitro, cortical neurons were successfully transduced, showing appropriate physiological responses to light stimulation. Following injections in vivo, transduction was progressively established around a focal injection site over a 4-week period with spread of transduction proportional to the concentration of virus introduced. Elevated GFAP immunoreactivity, a marker for reactive astrocytes, was detected near injection sites associated with, and proportional to, local FR expression. Similarly, we observed reactive microglia around FR expressing cells. However, we found that the numbers of NeuN+ neurons were conserved close to the injection site, indicating that there was little or no neuronal loss. In control mice, injected with saline only, astrocytosis and microgliosis was limited to the immediate vicinity of the injection site. Injections of opsin negative viral constructs resulted in comparable levels of astrocytic reaction as seen with opsin positive constructs.

Discussion

We conclude that introduction of an AAV8 vector transducing expression of a transgene under a neuron specific promotor evokes a mild inflammatory reaction in cortical tissue without causing extensive short-term neuronal loss. The expression of an opsin in addition to a fluorescent protein does not significantly increase neuroinflammation.

Glial cells react to closed head injury in a distinct and spatiotemporally orchestrated manner

Traumatic brain injury (TBI) is a leading cause of mortality and disability worldwide. Acute neuroinflammation is a prominent reaction after TBI and is mostly initiated by brain-resident glial cells such as microglia, NG2-glia and astrocytes. The magnitude of this reaction paves the way for long-lasting consequences such as chronic neurological pathologies, for which therapeutic options remain limited. The neuroinflammatory response to TBI is mostly studied with craniotomy-based animal models that are very robust but also rather artificial. Here, we aimed to analyze the reaction of glial cells in a highly translational but variable closed head injury (CHI) model and were able to correlate the severity of the trauma to the degree of glial response. Furthermore, we could show that the different glial cell types react in a temporally and spatially orchestrated manner in terms of morphological changes, proliferation, and cell numbers in the first 15 days after the lesion. Interestingly, NG2-glia, the only proliferating cells in the healthy brain parenchyma, divided at a rate that was correlated with the size of the injury. Our findings describe the previously uncharacterized posttraumatic response of the major brain glial cell types in CHI in order to gain a detailed understanding of the course of neuroinflammatory events; such knowledge may open novel avenues for future therapeutic approaches in TBI.

A Brain-Protective Sterol from Soft Coral Inhibits Lipopolysaccharide-Induced Matrix Metalloproteinase-9-Mediated Astrocytic Migration

Matrix metalloproteinases (MMPs), which are proteolytic enzymes, promote blood-brain barrier (BBB) disruption, leading to neuronal damage and neuroinflammation. Among them, MMP-9 upregulation serves as an inflammatory biomarker in the central nervous system (CNS). Currently, the development of marine organism-derived bioactive compounds or metabolites as anti-inflammatory drugs has received considerable attention. The 9,11-secosteroid, 3β,11-dihydroxy-9,11-secogorgost-5-en-9-one (4p3f), is a novel sterol compound extracted from the soft coral Sinularia leptoclado with potential anti-inflammatory activity. However, the effect of and potential for brain protection of 4p3f on brain astrocytes remain unclear. Herein, we used rat brain astrocytes (RBAs) to investigate the effects and signaling mechanisms of 4p3f on lipopolysaccharide (LPS)-induced MMP-9 expression via zymographic, quantitative reverse transcription-polymerase chain reaction (qRT-PCR), Western blot, immunofluorescence staining, promoter-reporter, and cell migration analyses. We first found that 4p3f blocked LPS-induced MMP-9 expression in RBAs. Next, we demonstrated that LPS induced MMP-9 expression via the activation of ERK1/2, p38 MAPK, and JNK1/2, which is linked to the STAT3-mediated NF-κB signaling pathway. Finally, 4p3f effectively inhibited LPS-induced upregulation of MMP-9-triggered RBA cell migration. These data suggest that a novel sterol from soft coral, 4p3f, may have anti-inflammatory and brain-protective effects by attenuating these signaling pathways of MMP-9-mediated events in brain astrocytes. Accordingly, the soft coral-derived sterol 4p3f may emerge as a potential candidate for drug development or as a natural compound with neuroprotective properties.

Exosome-mediated repair of spinal cord injury: a promising therapeutic strategy

Spinal cord injury (SCI) is a catastrophic injury to the central nervous system (CNS) that can lead to sensory and motor dysfunction, which seriously affects patients' quality of life and imposes a major economic burden on society. The pathological process of SCI is divided into primary and secondary injury, and secondary injury is a cascade of amplified responses triggered by the primary injury. Due to the complexity of the pathological mechanisms of SCI, there is no clear and effective treatment strategy in clinical practice. Exosomes, which are extracellular vesicles of endoplasmic origin with a diameter of 30-150 nm, play a critical role in intercellular communication and have become an ideal vehicle for drug delivery. A growing body of evidence suggests that exosomes have great potential for repairing SCI. In this review, we introduce exosome preparation, functions, and administration routes. In addition, we summarize the effect and mechanism by which various exosomes repair SCI and review the efficacy of exosomes in combination with other strategies to repair SCI. Finally, the challenges and prospects of the use of exosomes to repair SCI are described.

Injury-specific factors in the cerebrospinal fluid regulate astrocyte plasticity in the human brain

The glial environment influences neurological disease progression, yet much of our knowledge still relies on preclinical animal studies, especially regarding astrocyte heterogeneity. In murine models of traumatic brain injury, beneficial functions of proliferating reactive astrocytes on disease outcome have been unraveled, but little is known regarding if and when they are present in human brain pathology. Here we examined a broad spectrum of pathologies with and without intracerebral hemorrhage and found a striking correlation between lesions involving blood-brain barrier rupture and astrocyte proliferation that was further corroborated in an assay probing for neural stem cell potential. Most importantly, proteomic analysis unraveled a crucial signaling pathway regulating this astrocyte plasticity with GALECTIN3 as a novel marker for proliferating astrocytes and the GALECTIN3-binding protein LGALS3BP as a functional hub mediating astrocyte proliferation and neurosphere formation. Taken together, this work identifies a therapeutically relevant astrocyte response and their molecular regulators in different pathologies affecting the human cerebral cortex.

A systematic review and meta-analysis of chondroitinase ABC promotes functional recovery in rat models of spinal cord injury

BACKGROUND

To comprehensively assess the neurologic recovery potential of chondroitinase ABC (ChABC) in rats after spinal cord injury (SCI).

METHODS

The PubMed, Embase, ScienceDirect, Web of Science, and China National Knowledge Infrastructure databases were searched for animal experiments that evaluated the use of ChABC in the treatment of SCI up to November 2022. Studies reporting neurological function using the Basso, Beattie, and Bresnahan (BBB) scale, as well as assessments of cavity area, lesion area, and glial fibrillary acidic protein (GFAP) levels, were included in the analysis.

RESULTS

A total of 46 studies were ultimately selected for inclusion. The results of the study showed that rats with SCI that received ChABC therapy exhibited a significant improvement in locomotor function after 7 days compared with controls (32 studies, weighted mean difference (WMD) = 0.58, [0.33, 0.83], p < 0.00001). Furthermore, the benefits of ChABC therapy were maintained for up to 28 days according to BBB scale. The lesion area was reduced by ChABC (5 studies, WMD = -20.94, [-28.42, -13.46], p < 0.00001). Meanwhile, GFAP levels were reduced in the ChABC treatment group (8 studies, WMD = -29.15, [-41.57, -16.72], p < 0.00001). Cavity area is not statistically significant. The subgroup analysis recommended that a single injection of 10 μL (8 studies, WMD = 2.82, [1.99, 3.65], p < 0.00001) or 20 U/mL (4 studies, WMD = 2.21, [0.73, 3.70], p = 0.003) had a better effect on improving the function. The funnel plot of the BBB scale was found to be essentially symmetrical, indicating a low risk of publication bias.

CONCLUSIONS

This systematic review and meta-analysis has indicated that ChABC could improve functional recovery in rats after SCI.

The function of astrocytes and their role in neurological diseases

Astrocytes have countless links with neurons. Previously, astrocytes were only considered a scaffold of neurons; in fact, astrocytes perform a variety of functions, including providing support for neuronal structures and energy metabolism, offering isolation and protection and influencing the formation, function and elimination of synapses. Because of these functions, astrocytes play an critical role in central nervous system (CNS) diseases. The regulation of the secretiory factors, receptors, channels and pathways of astrocytes can effectively inhibit the occurrence and development of CNS diseases, such as neuromyelitis optica (NMO), multiple sclerosis, Alzheimer's disease (AD), Parkinson's disease (PD) and Huntington's disease. The expression of aquaporin 4 in AS is directly related to NMO and indirectly involved in the clearance of Aβ and tau proteins in AD. Connexin 43 has a bidirectional effect on glutamate diffusion at different stages of stroke. Interestingly, astrocytes reduce the occurrence of PD through multiple effects such as secretion of related factors, mitochondrial autophagy and aquaporin 4. Therefore, this review is focused on the structure and function of astrocytes and the correlation between astrocytes and CNS diseases and drug treatment to explore the new functions of astrocytes with the astrocytes as the target. This, in turn, would provide a reference for the development of new drugs to protect neurons and promote the recovery of nerve function.

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

Astroglia are a broad class of neural parenchymal cells primarily dedicated to homoeostasis and defence of the central nervous system (CNS). Astroglia contribute to the pathophysiology of all neurological and neuropsychiatric disorders in ways that can be either beneficial or detrimental to disorder outcome. Pathophysiological changes in astroglia can be primary or secondary and can result in gain or loss of functions. Astroglia respond to external, non-cell autonomous signals associated with any form of CNS pathology by undergoing complex and variable changes in their structure, molecular expression, and function. In addition, internally driven, cell autonomous changes of astroglial innate properties can lead to CNS pathologies. Astroglial pathophysiology is complex, with different pathophysiological cell states and cell phenotypes that are context-specific and vary with disorder, disorder-stage, comorbidities, age, and sex. Here, we classify astroglial pathophysiology into (i) reactive astrogliosis, (ii) astroglial atrophy with loss of function, (iii) astroglial degeneration and death, and (iv) astrocytopathies characterised by aberrant forms that drive disease. We review astroglial pathophysiology across the spectrum of human CNS diseases and disorders, including neurotrauma, stroke, neuroinfection, autoimmune attack and epilepsy, as well as neurodevelopmental, neurodegenerative, metabolic and neuropsychiatric disorders. Characterising cellular and molecular mechanisms of astroglial pathophysiology represents a new frontier to identify novel therapeutic strategies.

Reinventing the Penumbra - the Emerging Clockwork of a Multi-modal Mechanistic Paradigm

The concept of the ischemic penumbra was originally defined as the area around a necrotic stroke core and seen as the tissue at imminent risk of further damage. Today, the penumbra is generally considered as time-sensitive hypoperfused brain tissue with decreased oxygen and glucose availability, salvageable tissue as treated by intervention, and the potential target for neuroprotection in focal stroke. The original concept entailed electrical failure and potassium release but one short of neuronal cell death and was based on experimental stroke models, later confirmed in clinical imaging studies. However, even though the basic mechanisms have translated well, conferring brain protection, and improving neurological outcome after stroke based on the pathophysiological mechanisms in the penumbra has yet to be achieved. Recent findings shape the modern understanding of the penumbra revealing a plethora of molecular and cellular pathophysiological mechanisms. We now propose a new model of the penumbra, one which we hope will lay the foundation for future translational success. We focus on the availability of glucose, the brain's central source of energy, and bioenergetic failure as core pathophysiological concepts. We discuss the relation of mitochondrial function in different cell types to bioenergetics and apoptotic cell death mechanisms, autophagy, and neuroinflammation, to glucose metabolism in what is a dynamic ischemic penumbra.

Lipocalin-2: a therapeutic target to overcome neurodegenerative diseases by regulating reactive astrogliosis

Glial cell activation precedes neuronal cell death during brain aging and the progression of neurodegenerative diseases. Under neuroinflammatory stress conditions, lipocalin-2 (LCN2), also known as neutrophil gelatinase-associated lipocalin or 24p3, is produced and secreted by activated microglia and reactive astrocytes. Lcn2 expression levels are known to be increased in various cells, including reactive astrocytes, through the activation of the NF-κB signaling pathway. In the central nervous system, as LCN2 exerts neurotoxicity when secreted from reactive astrocytes, many researchers have attempted to identify various strategies to inhibit LCN2 production, secretion, and function to minimize neuroinflammation and neuronal cell death. These strategies include regulation at the transcriptional, posttranscriptional, and posttranslational levels, as well as blocking its functions using neutralizing antibodies or antagonists of its receptor. The suppression of NF-κB signaling is a strategy to inhibit LCN2 production, but it may also affect other cellular activities, raising questions about its effectiveness and feasibility. Recently, LCN2 was found to be a target of the autophagy‒lysosome pathway. Therefore, autophagy activation may be a promising therapeutic strategy to reduce the levels of secreted LCN2 and overcome neurodegenerative diseases. In this review, we focused on research progress on astrocyte-derived LCN2 in the central nervous system.

Fate Specification of GFAP-Negative Primitive Neural Stem Cells and Their Progeny at Clonal Resolution

The mature brain contains an incredible number and diversity of cells that are produced and maintained by heterogeneous pools of neural stem cells (NSCs). Two distinct types of NSCs exist in the developing and adult mouse brain: Glial Fibrillary Acidic Protein (GFAP)-negative primitive (p)NSCs and downstream GFAP-positive definitive (d)NSCs. To better understand the embryonic functions of NSCs, we performed clonal lineage tracing within neurospheres grown from either pNSCs or dNSCs to enrich for their most immediate downstream neural progenitor cells (NPCs). These clonal progenitor lineage tracing data allowed us to construct a hierarchy of progenitor subtypes downstream of pNSCs and dNSCs that were then validated using single-cell transcriptomics. Further, we identify Nexn as required for neuronal specification from neuron/astrocyte progenitor cells downstream of rare pNSCs. Combined, these data provide single-cell resolution of NPC lineages downstream of rare pNSCs that likely would be missed from population-level analyses in vivo.

Astrocyte-specific Ca2+ activity: Mechanisms of action, experimental tools, and roles in ethanol-induced dysfunction

Astrocytes are a subtype of non-neuronal glial cells that reside in the central nervous system. Astrocytes have extensive peripheral astrocytic processes that ensheathe synapses to form the tripartite synapse. Through a multitude of pathways, astrocytes can influence synaptic development and structural maturation, respond to neuronal signals, and modulate synaptic transmission. Over the last decade, strong evidence has emerged demonstrating that astrocytes can influence behavioral outcomes in various animal models of cognition. However, the full extent of how astrocytes influence brain function is still being revealed. Astrocyte calcium (Ca2+) signaling has emerged as an important driver of astrocyte-neuronal communication allowing intricate crosstalk through mechanisms that are still not fully understood. Here, we will review the field's current understanding of astrocyte Ca2+ signaling and discuss the sophisticated state-of-the-art tools and approaches used to continue unraveling astrocytes' interesting role in brain function. Using the field of pre-clinical ethanol (EtOH) studies in the context of alcohol use disorder, we focus on how these novel approaches have helped to reveal an important role for astrocyte Ca2+ function in regulating EtOH consumption and how astrocyte Ca2+ dysfunction contributes to the cognitive deficits that emerge after EtOH exposure in a rodent model.

Astrocyte-Neuronal Communication and Its Role in Stroke

Astrocytes are the most abundant glial cells in the central nervous system. These cells are an important hub for intercellular communication. They participate in various pathophysiological processes, including synaptogenesis, metabolic transformation, scar production, and blood-brain barrier repair. The mechanisms and functional consequences of astrocyte-neuron signaling are more complex than previously thought. Stroke is a disease associated with neurons in which astrocytes also play an important role. Astrocytes respond to the alterations in the brain microenvironment after stroke, providing required substances to neurons. However, they can also have harmful effects. In this review, we have summarized the function of astrocytes, their association with neurons, and two paradigms of the inflammatory response, which suggest that targeting astrocytes may be an effective strategy for treating stroke.

Astrocytes in functional recovery following central nervous system injuries

Astrocytes are increasingly recognised as partaking in complex homeostatic mechanisms critical for regulating neuronal plasticity following central nervous system (CNS) insults. Ischaemic stroke and traumatic brain injury are associated with high rates of disability and mortality. Depending on the context and type of injury, reactive astrocytes respond with diverse morphological, proliferative and functional changes collectively known as astrogliosis, which results in both pathogenic and protective effects. There is a large body of research on the negative consequences of astrogliosis following brain injuries. There is also growing interest in how astrogliosis might in some contexts be protective and help to limit the spread of the injury. However, little is known about how astrocytes contribute to the chronic functional recovery phase following traumatic and ischaemic brain insults. In this review, we explore the protective functions of astrocytes in various aspects of secondary brain injury such as oedema, inflammation and blood-brain barrier dysfunction. We also discuss the current knowledge on astrocyte contribution to tissue regeneration, including angiogenesis, neurogenesis, synaptogenesis, dendrogenesis and axogenesis. Finally, we discuss diverse astrocyte-related factors that, if selectively targeted, could form the basis of astrocyte-targeted therapeutic strategies to better address currently untreatable CNS disorders.

Morphofunctional Investigation in a Transgenic Mouse Model of Alzheimer's Disease: Non-Reactive Astrocytes Are Involved in Aβ Load and Reactive Astrocytes in Plaque Build-Up

The term neuroinflammation defines the reactions of astrocytes and microglia to alterations in homeostasis in the diseased central nervous system (CNS), the exacerbation of which contributes to the neurodegenerative effects of Alzheimer's disease (AD). Local environmental conditions, such as the presence of proinflammatory molecules, mechanical properties of the extracellular matrix (ECM), and local cell-cell interactions, are determinants of glial cell phenotypes. In AD, the load of the cytotoxic/proinflammatory amyloid β (Aβ) peptide is a microenvironmental component increasingly growing in the CNS, imposing time-evolving challenges on resident cells. This study aimed to investigate the temporal and spatial variations of the effects produced by this process on astrocytes and microglia, either directly or by interfering in their interactions. Ex vivo confocal analyses of hippocampal sections from the mouse model TgCRND8 at different ages have shown that overproduction of Aβ peptide induced early and time-persistent disassembly of functional astroglial syncytium and promoted a senile phenotype of reactive microglia, hindering Aβ clearance. In the late stages of the disease, these patterns were altered in the presence of Aβ-plaques, surrounded by typically reactive astrocytes and microglia. Morphofunctional characterization of peri-plaque gliosis revealed a direct contribution of astrocytes in plaque buildup that might result in shielding Aβ-peptide cytotoxicity and, as a side effect, in exacerbating neuroinflammation.

Cellular and molecular mechanisms in vascular repair after traumatic brain injury: a narrative review

Traumatic brain injury (TBI) disrupts normal brain function and is associated with high morbidity and fatality rates. TBI is characterized as mild, moderate or severe depending on its severity. The damage may be transient and limited to the dura matter, with only subtle changes in cerebral parenchyma, or life-threatening with obvious focal contusions, hematomas and edema. Blood vessels are often injured in TBI. Even in mild TBI, dysfunctional cerebral vascular repair may result in prolonged symptoms and poor outcomes. Various distinct types of cells participate in vascular repair after TBI. A better understanding of the cellular response and function in vascular repair can facilitate the development of new therapeutic strategies. In this review, we analyzed the mechanism of cerebrovascular impairment and the repercussions following various forms of TBI. We then discussed the role of distinct cell types in the repair of meningeal and parenchyma vasculature following TBI, including endothelial cells, endothelial progenitor cells, pericytes, glial cells (astrocytes and microglia), neurons, myeloid cells (macrophages and monocytes) and meningeal lymphatic endothelial cells. Finally, possible treatment techniques targeting these unique cell types for vascular repair after TBI are discussed.

The kinase inhibitory region of SOCS3 attenuates reactive astrogliosis and astroglial scar in mice after traumatic brain injury

Traumatic brain injury (TBI) leads to reactive astrogliosis that impedes neural repair/regeneration. It has been proven that SOCS3 attenuates astrocyte activation by inhibiting the JAK2-STAT3 pathway. However, whether the kinase inhibitory region (KIR) of SOCS3 can be directly applied to mediate astrocyte activation after TBI is not clear. The present study aimed at investigating the inhibitory effect of KIR on reactive astrogliosis and its potential neuroprotection after TBI insult. For this purpose, A TBI model was developed by the free impact of heavy objects in adult mice. KIR was linked to the TAT peptide (TAT-KIR) to facilitate cell membrane penetration and intracranially injected into the cerebral cortex adjacent to the TBI lesion. Then reactive astrogliosis, activity of JAK2-STAT3 pathway, neuron loss, and function deficit were observed. Our results showed a decrease in neuron loss and an improvement in neural function. Meanwhile, Intracranial injection of TAT-KIR in TBI mice demonstrated a reduction of GFAP-positive astrocytes as well as C3/GFAP double-labeled A1 reactive astrocytes. Western blot analysis illustrated that the activity of the JAK2-STAT3 pathway was significantly inhibited by TAT-KIR. We conclude that exogenous treatment TAT-KIR, through suppression of JAK2-STAT3 activity, inhibits TBI -induced reactive astrogliosis induced, thereby alleviating the loss of neurons and relieving the neural function deficit. This investigation suggests that TAT-KIR could be a potential therapeutic strategy for enhancing neural regeneration following.

Astrocyte-mediated mechanisms contribute to traumatic brain injury pathology

Astrocytes respond to traumatic brain injury (TBI) with changes to their molecular make-up and cell biology, which results in changes in astrocyte function. These changes can be adaptive, initiating repair processes in the brain, or detrimental, causing secondary damage including neuronal death or abnormal neuronal activity. The response of astrocytes to TBI is often-but not always-accompanied by the upregulation of intermediate filaments, including glial fibrillary acidic protein (GFAP) and vimentin. Because GFAP is often upregulated in the context of nervous system disturbance, reactive astrogliosis is sometimes treated as an "all-or-none" process. However, the extent of astrocytes' cellular, molecular, and physiological adjustments is not equal for each TBI type or even for each astrocyte within the same injured brain. Additionally, new research highlights that different neurological injuries and diseases result in entirely distinctive and sometimes divergent astrocyte changes. Thus, extrapolating findings on astrocyte biology from one pathological context to another is problematic. We summarize the current knowledge about astrocyte responses specific to TBI and point out open questions that the field should tackle to better understand how astrocytes shape TBI outcomes. We address the astrocyte response to focal versus diffuse TBI and heterogeneity of reactive astrocytes within the same brain, the role of intermediate filament upregulation, functional changes to astrocyte function including potassium and glutamate homeostasis, blood-brain barrier maintenance and repair, metabolism, and reactive oxygen species detoxification, sex differences, and factors influencing astrocyte proliferation after TBI. This article is categorized under: Neurological Diseases > Molecular and Cellular Physiology.

Astrocytes in the Optic Nerve Are Heterogeneous in Their Reactivity to Glaucomatous Injury

The optic nerve head is thought to be the site of initial injury to retinal ganglion cell injury in glaucoma. In the initial segment of the optic nerve directly behind the globe, the ganglion cell axons are unmyelinated and come into direct contact to astrocytes, suggesting that astrocytes may play a role in the pathology of glaucoma. As in other parts of the CNS, optic nerve head astrocytes respond to injury by characteristic changes in cell morphology and gene expression profile. Using RNA-sequencing of glaucomatous optic nerve heads, single-cell PCR, and an in-vivo assay, we demonstrate that an up-regulation of astrocytic phagocytosis is an early event after the onset of increased intraocular pressure. We also show that astrocytes in the glial lamina of the optic nerve are apparently functionally heterogeneous. At any time, even in naïve nerves, some of the cells show signs of reactivity-process hypertrophy, high phagocytic activity, and expression of genetic markers of reactivity whereas neighboring cells apparently are inactive. A period of increased intraocular pressure moves more astrocytes towards the reactive phenotype; however, some cells remain unreactive even in glaucomatous nerves.

Inhibition of P2X4 and P2X7 receptors improves histological and behavioral outcomes after experimental traumatic brain injury in rats

Release of large amounts of adenosine triphosphate (ATP), a gliotransmitter, into the extracellular space by traumatic brain injury (TBI) is considered to activate the microglia followed by release of inflammatory cytokines resulting in excessive inflammatory response that induces secondary brain injury. The present study investigated whether antagonists of ATP receptors (P2X4 and/or P2X7) on microglia are beneficial for reducing the post-injury inflammatory response that leads to secondary injury, a prognostic aggravation factor of TBI. Adult male Sprague-Dawley rats were subjected to cortical contusion injury (CCI) and randomly assigned to injury and drug treatment conditions, as follows: i) No surgical intervention (naïve group); ii) dimethyl sulfoxide treatment after CCI (CCI-control group); iii) 5-BDBD (antagonist of P2X4 receptor) treatment after CCI (CCI-5-BDBD group); iv) CCI-AZ11645373 (antagonist of P2X7 receptor) treatment after CCI (CCI-AZ11645373 group); v) or 5-BDBD and AZ11645373 treatment after CCI (CCI-5-BDBD + AZ11645373 group). In the CCI-5-BDBD, CCI-AZ11645373, and CCI-5-BDBD + AZ11645373 groups, expression of activated microglia was suppressed in the ipsilateral cortex and hippocampus 3 days after the CCI. Western blotting with ionized calcium-binding adaptor molecule 1 antibody revealed that administration of CCI-5-BDBD and/or CCI-AZ11645373 suppressed expression of microglia and reduced expression of inflammatory cytokine mRNA 3 days after the CCI. Furthermore, the plus maze test, which reflects the spatial memory function and involves the hippocampal function, showed improvement 28 days after secondary injury to the hippocampus. These findings confirmed that blocking the P2X4 and P2X7 receptors, which are ATP receptors central in gliotransmission, suppresses microglial activation and subsequent cytokine expression after brain injury, and demonstrates the potential as an effective treatment for reducing secondary brain injury.

Pilot Study of Cytoprotective Mechanisms of Selenium Nanorods (SeNrs) under Ischemia-like Conditions on Cortical Astrocytes

The cytoprotective properties of the trace element selenium, its nanoparticles, and selenium nanocomplexes with active compounds are shown using a number of models. To date, some molecular mechanisms of the protective effect of spherical selenium nanoparticles under the action of ischemia/reoxygenation on brain cells have been studied. Among other things, the dependence of the effectiveness of the neuroprotective properties of nanoselenium on its diameter, pathways, and efficiency of penetration into astrocytes was established. In general, most research in the field of nanomedicine is focused on the preparation and study of spherical nanoparticles of various origins due to the ease of their preparation; in addition, spherical nanoparticles have a large specific surface area. However, obtaining and studying the mechanisms of action of nanoparticles of a new form are of great interest since nanorods, having all the positive properties of spherical nanoparticles, will also have a number of advantages. Using the laser ablation method, we managed to obtain and characterize selenium nanorods (SeNrs) with a length of 1 μm and a diameter of 100 nm. Using fluorescence microscopy and inhibitory analysis, we were able to show that selenium nanorods cause the generation of Ca2+ signals in cortical astrocytes in an acute experiment through the mobilization of Ca2+ ions from the thapsigargin-sensitive pool of the endoplasmic reticulum. Chronic use of SeNrs leads to a change in the expression pattern of genes encoding proteins that regulate cell fate and protect astrocytes from ischemia-like conditions and reoxygenation through the inhibition of a global increase in the concentration of cytosolic calcium ([Ca2+]i). An important component of the cytoprotective effect of SeNrs during ischemia/reoxygenation is the induction of reactive A2-type astrogliosis in astrocytes, leading to an increase in both baseline and ischemia/reoxygenation-induced phosphoinositide 3-kinase (PI3K) activity and suppression of necrosis and apoptosis. The key components of this cytoprotective action of SeNrs are the actin-dependent process of endocytosis of nanoparticles into cells and activation of the Ca2+ signaling system of astrocytes.

Astrocytic scar restricting glioblastoma via glutamate-MAO-B activity in glioblastoma-microglia assembloid

BACKGROUND

Glial scar formation is a reactive glial response confining injured regions in a central nervous system. However, it remains challenging to identify key factors formulating glial scar in response to glioblastoma (GBM) due to complex glia-GBM crosstalk.

METHODS

Here, we constructed an astrocytic scar enclosing GBM in a human assembloid and a mouse xenograft model. GBM spheroids were preformed and then co-cultured with microglia and astrocytes in 3D Matrigel. For the xenograft model, U87-MG cells were subcutaneously injected to the Balb/C nude female mice.

RESULTS

Additional glutamate was released from GBM-microglia assembloid by 3.2-folds compared to GBM alone. The glutamate upregulated astrocytic monoamine oxidase-B (MAO-B) activity and chondroitin sulfate proteoglycans (CSPGs) deposition, forming the astrocytic scar and restricting GBM growth. Attenuating scar formation by the glutamate-MAO-B inhibition increased drug penetration into GBM assembloid, while reducing GBM confinement.

CONCLUSIONS

Taken together, our study suggests that astrocytic scar could be a critical modulator in GBM therapeutics.

Understanding the Role of the Glial Scar through the Depletion of Glial Cells after Spinal Cord Injury

Spinal cord injury (SCI) is a condition that affects between 8.8 and 246 people in a million and, unlike many other neurological disorders, it affects mostly young people, causing deficits in sensory, motor, and autonomic functions. Promoting the regrowth of axons is one of the most important goals for the neurological recovery of patients after SCI, but it is also one of the most challenging goals. A key event after SCI is the formation of a glial scar around the lesion core, mainly comprised of astrocytes, NG2⁺-glia, and microglia. Traditionally, the glial scar has been regarded as detrimental to recovery because it may act as a physical barrier to axon regrowth and release various inhibitory factors. However, more and more evidence now suggests that the glial scar is beneficial for the surrounding spared tissue after SCI. Here, we review experimental studies that used genetic and pharmacological approaches to ablate specific populations of glial cells in rodent models of SCI in order to understand their functional role. The studies showed that ablation of either astrocytes, NG2⁺-glia, or microglia might result in disorganization of the glial scar, increased inflammation, extended tissue degeneration, and impaired recovery after SCI. Hence, glial cells and glial scars appear as important beneficial players after SCI.

Astrocyte Endfeet in Brain Function and Pathology: Open Questions

Astrocyte endfeet enwrap the entire vascular tree within the central nervous system, where they perform important functions in regulating the blood-brain barrier (BBB), cerebral blood flow, nutrient uptake, and waste clearance. Accordingly, astrocyte endfeet contain specialized organelles and proteins, including local protein translation machinery and highly organized scaffold proteins, which anchor channels, transporters, receptors, and enzymes critical for astrocyte-vascular interactions. Many neurological diseases are characterized by the loss of polarization of specific endfoot proteins, vascular dysregulation, BBB disruption, altered waste clearance, or, in extreme cases, loss of endfoot coverage. A role for astrocyte endfeet has been demonstrated or postulated in many of these conditions. This review provides an overview of the development, composition, function, and pathological changes of astrocyte endfeet and highlights the gaps in our knowledge that future research should address.

Stem cell-derived brainstem mouse astrocytes obtain a neurotoxic phenotype in vitro upon neuroinflammation

BACKGROUND

Astrocytes respond to injury and disease through a process known as reactive astrogliosis, of which inflammatory signaling is one subset. This inflammatory response is heterogeneous with respect to the inductive stimuli and the afflicted central nervous system region. This is of plausible importance in e.g. traumatic axonal injury (TAI), where lesions in the brainstem carries a particularly poor prognosis. In fact, astrogliotic forebrain astrocytes were recently suggested to cause neuronal death following axotomy. We therefore sought to assess if ventral brainstem- or rostroventral spinal astrocytes exert similar effects on motor neurons in vitro.

METHODS

We derived brainstem/rostroventral spinal astrocyte-like cells (ES-astrocytes) and motor neurons using directed differentiation of mouse embryonic stem cells (ES). We activated the ES-astrocytes using the neurotoxicity-eliciting cytokines interleukin- (IL-) 1α and tumor necrosis factor-(TNF-)α and clinically relevant inflammatory mediators. In co-cultures with reactive ES-astrocytes and motor neurons, we assessed neurotoxic ES-astrocyte activity, similarly to what has previously been shown for other central nervous system (CNS) regions.

RESULTS

We confirmed the brainstem/rostroventral ES-astrocyte identity using RNA-sequencing, immunocytochemistry, and by comparison with primary subventricular zone-astrocytes. Following cytokine stimulation, the c-Jun N-terminal kinase pathway down-stream product phosphorylated c-Jun was increased, thus demonstrating ES-astrocyte reactivity. These reactive ES-astrocytes conferred a contact-dependent neurotoxic effect upon co-culture with motor neurons. When exposed to IL-1β and IL-6, two neuroinflammatory cytokines found in the cerebrospinal fluid and serum proteome following human severe traumatic brain injury (TBI), ES-astrocytes exerted similar effects on motor neurons. Activation of ES-astrocytes by these cytokines was associated with pathways relating to endoplasmic reticulum stress and altered regulation of MYC.

CONCLUSIONS

Ventral brainstem and rostroventral spinal cord astrocytes differentiated from mouse ES can exert neurotoxic effects in vitro. This highlights how neuroinflammation following CNS lesions can exert region- and cell-specific effects. Our in vitro model system, which uniquely portrays astrocytes and neurons from one niche, allows for a detailed and translationally relevant model system for future studies on how to improve neuronal survival in particularly vulnerable CNS regions following e.g. TAI.

Spinal cord injury: molecular mechanisms and therapeutic interventions

Spinal cord injury (SCI) remains a severe condition with an extremely high disability rate. The challenges of SCI repair include its complex pathological mechanisms and the difficulties of neural regeneration in the central nervous system. In the past few decades, researchers have attempted to completely elucidate the pathological mechanism of SCI and identify effective strategies to promote axon regeneration and neural circuit remodeling, but the results have not been ideal. Recently, new pathological mechanisms of SCI, especially the interactions between immune and neural cell responses, have been revealed by single-cell sequencing and spatial transcriptome analysis. With the development of bioactive materials and stem cells, more attention has been focused on forming intermediate neural networks to promote neural regeneration and neural circuit reconstruction than on promoting axonal regeneration in the corticospinal tract. Furthermore, technologies to control physical parameters such as electricity, magnetism and ultrasound have been constantly innovated and applied in neural cell fate regulation. Among these advanced novel strategies and technologies, stem cell therapy, biomaterial transplantation, and electromagnetic stimulation have entered into the stage of clinical trials, and some of them have already been applied in clinical treatment. In this review, we outline the overall epidemiology and pathophysiology of SCI, expound on the latest research progress related to neural regeneration and circuit reconstruction in detail, and propose future directions for SCI repair and clinical applications.

Tackling the glial scar in spinal cord regeneration: new discoveries and future directions

Axonal regeneration and functional recovery are poor after spinal cord injury (SCI), typified by the formation of an injury scar. While this scar was traditionally believed to be primarily responsible for axonal regeneration failure, current knowledge takes a more holistic approach that considers the intrinsic growth capacity of axons. Targeting the SCI scar has also not reproducibly yielded nearly the same efficacy in animal models compared to these neuron-directed approaches. These results suggest that the major reason behind central nervous system (CNS) regeneration failure is not the injury scar but a failure to stimulate axon growth adequately. These findings raise questions about whether targeting neuroinflammation and glial scarring still constitute viable translational avenues. We provide a comprehensive review of the dual role of neuroinflammation and scarring after SCI and how future research can produce therapeutic strategies targeting the hurdles to axonal regeneration posed by these processes without compromising neuroprotection.

PirB negatively regulates the inflammatory activation of astrocytes in a mouse model of sleep deprivation

Reactive astrocytes play a potential regulatory role in sleep deprivation (SD). Paired immunoglobulin-like receptor B (PirB) is expressed in reactive astrocytes, suggesting that PirB may participate in regulating the inflammatory response of astrocytes. We used lentiviral and adeno-associated viral approaches to interfere with the expression of PirB in vivo and in vitro. C57BL/6 mice were sleep deprived for 7 days and neurological function was measured via behavioral tests. We found that overexpressed PirB in SD mice could decrease the number of neurotoxic reactive astrocytes, alleviate cognitive deficits, and promote reactive astrocytes tended to be neuroprotective state. IL-1α, TNFα, and C1q were used to induce neurotoxic reactive astrocytes in vitro. Overexpression of PirB relieved the toxicity of neurotoxic astrocytes. Silencing PirB expression had the opposite effect and exacerbated the transition of reactive astrocytes to a neurotoxic state in vitro. Moreover, PirB-impaired astrocytes demonstrated STAT3 hyperphosphorylation which could be reversed by stattic (p-STAT3 inhibitor). Furthermore, Golgi-Cox staining confirmed that dendrite morphology defects and synapse-related protein were significantly increased in PirB-overexpressed SD mice. Our data demonstrated that SD induced neurotoxic reactive astrocytes and contributed to neuroinflammation and cognitive deficits. PirB performs a negative regulatory role in neurotoxic reactive astrocytes via the STAT3 signaling pathway in SD.

Celsr2-mediated morphological polarization and functional phenotype of reactive astrocytes in neural repair

Neural repair is highly influenced by reactive astrocytes. Atypical cadherin Celsr2 regulates neuron development and axon regeneration, while its role in glial cells remains unexplored. In this study, we show that Celsr2 is highly expressed in spinal astrocytes of adult mice, and knockout of Celsr2 results in reactive astrocytes with longer protrusions preferentially orientated towards lesion borders in culture scratch assay and injured spinal cord, and elevation of total and active Cdc42 and Rac1 protein in western blots. Inactivation of Celsr2 enhances calcium influx in reactive astrocytes in time-lapse imaging. Morphological phenotypes of cultured Celsr2^-/- astrocytes are rescued by Cdc42 or Rac1 inhibitors. Following spinal cord injury (SCI), Celsr2^-/- mice exhibit smaller lesion cavity and glial scar, enhanced fiber regeneration, weaker microglial response, and improved functional recovery than control animals. Similar phenotypes are found in mice with conditional knockout of Celsr2 in astrocytes. In Celsr2^-/- mice, astrocyte phenotype is changed and neuroinflammation is alleviated after injury. Inhibiting Cdc42/Rac1 activities compromises astrocyte polarization and the improvement of neural repair and functional recovery in Celsr2^-/- mice with SCI. In conclusion, Celsr2 regulates morphological polarization and functional phenotype of reactive astrocytes and inactivating Celsr2 is a potential therapeutic strategy for neural repair.

Effects of 660-nm LED photobiomodulation on drebrin expression pattern and astrocyte migration

Photobiomodulation (PBM) is a therapeutic tool that uses red or near-infrared light in medical applications. It's applications in both central (CNS) and peripheral nervous system (PNS) are widely studied. Among glial cells, astrocytes are known to be activated in injured or damaged brains. Astrocytic cell migration is crucial for maintaining homeostasis in the brain. Our previous study showed that PBM led to astrocyte proliferation and differentiation, but the effects on migration has not been investigated. The aim of this study was to evaluate the effect of PBM on astrocyte migration, drebrin (DBN) expression and cytoplasmic morphology using primary cultured rat astrocyte. We applied a 660-nm light-emitting diode (LED) with fluence of 6, 12 and 18 J/cm². PBM effects on astrocyte migration were analyzed by two different migration assays (scratch assay and transwell assay). We used immunofluorescence microscopy for visualizing DBN and glial-fibrillary acidic protein (GFAP) and analysis of DBN expression and astrocyte cytoplasmic morphology. Both scratch assay and transwell assay showed significant difference in astrocyte migration following PBM irradiation. With these specific fluence conditions, differences in DBN expression and cell morphology were revealed. PBM could increase the astrocyte migration by altering the cell morphology and DBN expression pattern.

Acoustic Stress Induces Opposite Proliferative/Transformative Effects in Hippocampal Glia

The hippocampus is a brain region crucially involved in regulating stress responses and highly sensitive to environmental changes, with elevated proliferative and adaptive activity of neurons and glial cells. Despite the prevalence of environmental noise as a stressor, its effects on hippocampal cytoarchitecture remain largely unknown. In this study, we aimed to investigate the impact of acoustic stress on hippocampal proliferation and glial cytoarchitecture in adult male rats, using environmental noise as a stress model. After 21 days of noise exposure, our results showed abnormal cellular proliferation in the hippocampus, with an inverse effect on the proliferation ratios of astrocytes and microglia. Both cell lineages also displayed atrophic morphologies with fewer processes and lower densities in the noise-stressed animals. Our findings suggest that, stress not only affects neurogenesis and neuronal death in the hippocampus, but also the proliferation ratio, cell density, and morphology of glial cells, potentially triggering an inflammatory-like response that compromises their homeostatic and repair functions.

The role of dopamine in NLRP3 inflammasome inhibition: Implications for neurodegenerative diseases

In the Central Nervous System (CNS), neuroinflammation orchestrated by microglia and astrocytes is an innate immune response to counteract stressful and dangerous insults. One of the most important and best characterized players in the neuroinflammatory response is the NLRP3 inflammasome, a multiproteic complex composed by NOD-like receptor family Pyrin domain containing 3 (NLRP3), apoptosis-associated speck-like protein (ASC) and pro-caspase-1. Different stimuli mediate NLRP3 activation, resulting in the NLRP3 inflammasome assembly and the pro-inflammatory cytokine (IL-1β and IL-18) maturation and secretion. The persistent and uncontrolled NLRP3 inflammasome activation has a leading role during the pathophysiology of neuroinflammation in age-related neurodegenerative diseases such as Parkinson's (PD) and Alzheimer's (AD). The neurotransmitter dopamine (DA) is one of the players that negatively modulate NLRP3 inflammasome activation through DA receptors expressed in both microglia and astrocytes. This review summarizes recent findings linking the role of DA in the modulation of NLRP3-mediated neuroinflammation in PD and AD, where early deficits of the dopaminergic system are well characterized. Highlighting the relationship between DA, its glial receptors and the NLRP3-mediated neuroinflammation can provide insights to novel diagnostic strategies in early disease phases and new pharmacological tools to delay the progression of these diseases.

Partial Ablation of Astrocytes Exacerbates Cerebral Infiltration of Monocytes and Neuronal Loss After Brain Stab Injury in Mice

In traumatic brain injury (TBI), mechanical injury results in instantaneous tissue damages accompanied by subsequent pro-inflammatory cascades composed of microgliosis and astrogliosis. However, the interactive roles between microglia and astrocytes during the pathogenesis of TBI remain unclear and sometimes debatable. In this study, we used a forebrain stab injury mouse model to investigate the pathological role of reactive astrocytes in cellular and molecular changes of inflammatory response following TBI. In the ipsilateral hemisphere of stab-injured brain, monocyte infiltration and neuronal loss, as well as increased elevated astrogliosis, microglia activation and inflammatory cytokines were observed. To verify the role of reactive astrocytes in TBI, local and partial ablation of astrocytes was achieved by stereotactic injection of diphtheria toxin in the forebrain of Aldh1l1-CreER^T2::Ai9::iDTR transgenic mice which expressed diphtheria toxin receptor (DTR) in astrocytes after tamoxifen induction. This strategy achieved about 20% of astrocytes reduction at the stab site as validated by immunofluorescence co-staining of GFAP with tdTomato-positive astrocytes. Interestingly, reduction of astrocytes showed increased microglia activation and monocyte infiltration, accompanied with increased severity in stab injury-induced neuronal loss when compared with DTR^-/- mice, together with elevation of inflammatory chemokines such as CCL2, CCL5 and CXCL10 in astrogliosis-reduced mice. Collectively, our data verified the interactive role of astrocytes as an immune modulator in suppressing inflammatory responses in the injured brain. Schematic diagram shows monocyte infiltration and neuronal loss, as well as increased elevated astrogliosis, microglia activation and chemokines were observed in the injured site after stab injury. Local and partial ablation of astrocytes led to increased microglia activation and monocyte infiltration, accompanied with increased severity in neuronal loss together with elevation of inflammatory chemokines as compared with control mice subjected stab injury.

The Role and Mechanism of Transglutaminase 2 in Regulating Hippocampal Neurogenesis after Traumatic Brain Injury

Traumatic brain injury usually results in neuronal loss and cognitive deficits. Promoting endogenous neurogenesis has been considered as a viable treatment option to improve functional recovery after TBI. However, neural stem/progenitor cells (NSPCs) in neurogenic regions are often unable to migrate and differentiate into mature neurons at the injury site. Transglutaminase 2 (TGM2) has been identified as a crucial component of neurogenic niche, and significantly dysregulated after TBI. Therefore, we speculate that TGM2 may play an important role in neurogenesis after TBI, and strategies targeting TGM2 to promote endogenous neural regeneration may be applied in TBI therapy. Using a tamoxifen-induced Tgm2 conditional knockout mouse line and a mouse model of stab wound injury, we investigated the role and mechanism of TGM2 in regulating hippocampal neurogenesis after TBI. We found that Tgm2 was highly expressed in adult NSPCs and up-regulated after TBI. Conditional deletion of Tgm2 resulted in the impaired proliferation and differentiation of NSPCs, while Tgm2 overexpression enhanced the abilities of self-renewal, proliferation, differentiation, and migration of NSPCs after TBI. Importantly, injection of lentivirus overexpressing TGM2 significantly promoted hippocampal neurogenesis after TBI. Therefore, TGM2 is a key regulator of hippocampal neurogenesis and a pivotal therapeutic target for intervention following TBI.

Development of opioid-induced hyperalgesia depends on reactive astrocytes controlled by Wnt5a signaling

Opioids are the frontline analgesics for managing various types of pain. Paradoxically, repeated use of opioid analgesics may cause an exacerbated pain state known as opioid-induced hyperalgesia (OIH), which significantly contributes to dose escalation and consequently opioid overdose. Neuronal malplasticity in pain circuits has been the predominant proposed mechanism of OIH expression. Although glial cells are known to become reactive in OIH animal models, their biological contribution to OIH remains to be defined and their activation mechanism remains to be elucidated. Here, we show that reactive astrocytes (a.k.a. astrogliosis) are critical for OIH development in both male and female mice. Genetic reduction of astrogliosis inhibited the expression of OIH and morphine-induced neural circuit polarization (NCP) in the spinal dorsal horn (SDH). We found that Wnt5a is a neuron-to-astrocyte signal that is required for morphine-induced astrogliosis. Conditional knock-out of Wnt5a in neurons or its co-receptor ROR2 in astrocytes blocked not only morphine-induced astrogliosis but also OIH and NCP. Furthermore, we showed that the Wnt5a-ROR2 signaling-dependent astrogliosis contributes to OIH via inflammasome-regulated IL-1β. Our results reveal an important role of morphine-induced astrogliosis in OIH pathogenesis and elucidate a neuron-to-astrocyte intercellular Wnt signaling pathway that controls the astrogliosis.

The role of immune cells and associated immunological factors in the immune response to spinal cord injury

Spinal cord injury (SCI) is a devastating neurological condition prevalent worldwide. Where the pathological mechanisms underlying SCI are concerned, we can distinguish between primary injury caused by initial mechanical damage and secondary injury characterized by a series of biological responses, such as vascular dysfunction, oxidative stress, neurotransmitter toxicity, lipid peroxidation, and immune-inflammatory response. Secondary injury causes further tissue loss and dysfunction, and the immune response appears to be the key molecular mechanism affecting injured tissue regeneration and functional recovery from SCI. Immune response after SCI involves the activation of different immune cells and the production of immunity-associated chemicals. With the development of new biological technologies, such as transcriptomics, the heterogeneity of immune cells and chemicals can be classified with greater precision. In this review, we focus on the current understanding of the heterogeneity of these immune components and the roles they play in SCI, including reactive astrogliosis and glial scar formation, neutrophil migration, macrophage transformation, resident microglia activation and proliferation, and the humoral immunity mediated by T and B cells. We also summarize findings from clinical trials of immunomodulatory therapies for SCI and briefly review promising therapeutic drugs currently being researched.

Regulation of axonal regeneration after mammalian spinal cord injury

One hundred years ago, Ramón y Cajal, considered by many as the founder of modern neuroscience, stated that neurons of the adult central nervous system (CNS) are incapable of regenerating. Yet, recent years have seen a tremendous expansion of knowledge in the molecular control of axon regeneration after CNS injury. We now understand that regeneration in the adult CNS is limited by (1) a failure to form cellular or molecular substrates for axon attachment and elongation through the lesion site; (2) environmental factors, including inhibitors of axon growth associated with myelin and the extracellular matrix; (3) astrocyte responses, which can both limit and support axon growth; and (4) intraneuronal mechanisms controlling the establishment of an active cellular growth programme. We discuss these topics together with newly emerging hypotheses, including the surprising finding from transcriptomic analyses of the corticospinal system in mice that neurons revert to an embryonic state after spinal cord injury, which can be sustained to promote regeneration with neural stem cell transplantation. These gains in knowledge are steadily advancing efforts to develop effective treatment strategies for spinal cord injury in humans.