Striatal astrocytes transdifferentiate into functional mature neurons following ischemic brain injury

DNA methylation controls stemness of astrocytes in health and ischaemia

Astrocytes are the most abundant cell type in the mammalian brain and provide structural and metabolic support to neurons, regulate synapses and become reactive after injury and disease. However, a small subset of astrocytes settles in specialized areas of the adult brain where these astrocytes instead actively generate differentiated neuronal and glial progeny and are therefore referred to as neural stem cells1-3. Common parenchymal astrocytes and quiescent neural stem cells share similar transcriptomes despite their very distinct functions4-6. Thus, how stem cell activity is molecularly encoded remains unknown. Here we examine the transcriptome, chromatin accessibility and methylome of neural stem cells and their progeny, and of astrocytes from the striatum and cortex in the healthy and ischaemic adult mouse brain. We identify distinct methylation profiles associated with either astrocyte or stem cell function. Stem cell function is mediated by methylation of astrocyte genes and demethylation of stem cell genes that are expressed later. Ischaemic injury to the brain induces gain of stemness in striatal astrocytes7. We show that this response involves reprogramming the astrocyte methylome to a stem cell methylome and is absent if the de novo methyltransferase DNMT3A is missing. Overall, we unveil DNA methylation as a promising target for regenerative medicine.

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.

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.

A promise for neuronal repair: reprogramming astrocytes into neurons in vivo

Massive loss of neurons following brain injury or disease is the primary cause of central nervous system dysfunction. Recently, much research has been conducted on how to compensate for neuronal loss in damaged parts of the nervous system and thus restore functional connectivity among neurons. Direct somatic cell differentiation into neurons using pro-neural transcription factors, small molecules, or microRNAs, individually or in association, is the most promising form of neural cell replacement therapy available. This method provides a potential remedy for cell loss in a variety of neurodegenerative illnesses, and the development of reprogramming technology has made this method feasible. This article provides a comprehensive review of reprogramming, including the selection and methods of reprogramming starting cell populations as well as the signaling methods involved in this process. Additionally, we thoroughly examine how reprogramming astrocytes into neurons can be applied to treat stroke and other neurodegenerative diseases. Finally, we discuss the challenges of neuronal reprogramming and offer insights about the field.

Astrocyte Regulation of Neuronal Function and Survival in Stroke Pathophysiology

The interactions between astrocytes and neurons in the context of stroke play crucial roles in the disease's progression and eventual outcomes. After a stroke, astrocytes undergo significant changes in their morphology, molecular profile, and function, together termed reactive astrogliosis. Many of these changes modulate how astrocytes relate to neurons, inducing mechanisms both beneficial and detrimental to stroke recovery. For example, excessive glutamate release and astrocytic malfunction contribute to excitotoxicity in stroke, eventually causing neuronal death. Astrocytes also provide essential metabolic support and neurotrophic signals to neurons after stroke, ensuring homeostatic stability and promoting neuronal survival. Furthermore, several astrocyte-secreted molecules regulate synaptic plasticity in response to stroke, allowing for the rewiring of neural circuits to compensate for damaged areas. In this chapter, we highlight the current understanding of the interactions between astrocytes and neurons in response to stroke, explaining the varied mechanisms contributing to injury progression and the potential implications for future therapeutic interventions.

Targeting Neurogenesis in Seeking Novel Treatments for Ischemic Stroke

The interruption of cerebral blood flow leads to ischemic cell death and results in ischemic stroke. Although ischemic stroke is one of the most important causes of long-term disability and mortality, limited treatments are available for functional recovery. Therefore, extensive research has been conducted to identify novel treatments. Neurogenesis is regarded as a fundamental mechanism of neural plasticity. Therefore, therapeutic strategies targeting neurogenesis are thought to be promising. Basic research has found that therapeutic intervention including cell therapy, rehabilitation, and pharmacotherapy increased neurogenesis and was accompanied by functional recovery after ischemic stroke. In this review, we consolidated the current knowledge of the relationship between neurogenesis and treatment for ischemic stroke. It revealed that many treatments for ischemic stroke, including clinical and preclinical ones, have enhanced brain repair and functional recovery post-stroke along with neurogenesis. However, the intricate mechanisms of neurogenesis and its impact on stroke recovery remain areas of extensive research, with numerous factors and pathways involved. Understanding neurogenesis will lead to more effective stroke treatments, benefiting not only stroke patients but also those with other neurological disorders. Further research is essential to bridge the gap between preclinical discoveries and clinical implementation.

Astrocytes in stroke-induced neurodegeneration: a timeline

Stroke is a condition characterized by sudden deprivation of blood flow to a brain region and defined by different post-injury phases, which involve various molecular and cellular cascades. At an early stage during the acute phase, fast initial cell death occurs, followed by inflammation and scarring. This is followed by a sub-acute or recovery phase when endogenous plasticity mechanisms may promote spontaneous recovery, depending on various factors that are yet to be completely understood. At later time points, stroke leads to greater neurodegeneration compared to healthy controls in both clinical and preclinical studies, this is evident during the chronic phase when recovery slows down and neurodegenerative signatures appear. Astrocytes have been studied in the context of ischemic stroke due to their role in glutamate re-uptake, as components of the neurovascular unit, as building blocks of the glial scar, and synaptic plasticity regulators. All these roles render astrocytes interesting, yet understudied players in the context of stroke-induced neurodegeneration. With this review, we provide a summary of previous research, highlight astrocytes as potential therapeutic targets, and formulate questions about the role of astrocytes in the mechanisms during the acute, sub-acute, and chronic post-stroke phases that may lead to neurorestoration or neurodegeneration.

Modulation of neurotrophic factors in the treatment of dementia, stroke and TBI: Effects of Cerebrolysin

Neurotrophic factors (NTFs) are involved in the pathophysiology of neurological disorders such as dementia, stroke and traumatic brain injury (TBI), and constitute molecular targets of high interest for the therapy of these pathologies. In this review we provide an overview of current knowledge of the definition, discovery and mode of action of five NTFs, nerve growth factor, insulin-like growth factor 1, brain derived NTF, vascular endothelial growth factor and tumor necrosis factor alpha; as well as on their contribution to brain pathology and potential therapeutic use in dementia, stroke and TBI. Within the concept of NTFs in the treatment of these pathologies, we also review the neuropeptide preparation Cerebrolysin, which has been shown to resemble the activities of NTFs and to modulate the expression level of endogenous NTFs. Cerebrolysin has demonstrated beneficial treatment capabilities in vitro and in clinical studies, which are discussed within the context of the biochemistry of NTFs. The review focuses on the interactions of different NTFs, rather than addressing a single NTF, by outlining their signaling network and by reviewing their effect on clinical outcome in prevalent brain pathologies. The effects of the interactions of these NTFs and Cerebrolysin on neuroplasticity, neurogenesis, angiogenesis and inflammation, and their relevance for the treatment of dementia, stroke and TBI are summarized.

Inhibition of Notch 1 signaling in the subacute stage after stroke promotes striatal astrocyte-derived neurogenesis

Inhibition of Notch1 signaling has been shown to promote astrocyte-derived neurogenesis after stroke. To investigate the regulatory role of Notch1 signaling in this process, in this study, we used a rat model of stroke based on middle cerebral artery occlusion and assessed the behavior of reactive astrocytes post-stroke. We used the γ-secretase inhibitor N-[N-(3,5-diuorophenacetyl)-1-alanyl]-S-phenylglycine t-butylester (DAPT) to block Notch1 signaling at 1, 4, and 7 days after injury. Our results showed that only administration of DAPT at 4 days after stroke promoted astrocyte-derived neurogenesis, as manifested by recovery of white matter fiber bundle integrity on magnetic resonance imaging, which is consistent with recovery of neurologic function. These findings suggest that inhibition of Notch1 signaling at the subacute stage post-stroke mediates neural repair by promoting astrocyte-derived neurogenesis.

Serotonergic mediation of the brain-wide neurogenesis: Region-dependent and receptor-type specific roles on neurogenic cellular transformation

Brain serotonin (5-hydroxytryptamine, 5-HT) is a key molecule for the mediation of depression-related brain states, but the neural mechanisms underlying 5-HT mediation need further investigation. A possible mechanism of the therapeutic antidepressant effects is neurogenic cell production, as stimulated by 5-HT signaling. Neurogenesis, the proliferation of neural stem cells (NSCs), and cell differentiation and maturation occur across brain regions, particularly the hippocampal dentate gyrus and the subventricular zone, throughout one's lifespan. 5-HT plays a major role in the mediation of neurogenic processes, which in turn leads to the therapeutic effect on depression-related states. In this review article, we aim to identify how the neuronal 5-HT system mediates the process of neurogenesis, including cell proliferation, cell-type differentiation and maturation. First, we will provide an overview of the neurogenic cell transformation that occurs in brain regions containing or lacking NSCs. Second, we will review brain region-specific mechanisms of 5-HT-mediated neurogenesis by comparing regions localized to NSCs, i.e., the hippocampus and subventricular zone, with those not containing NSCs. Highlighting these 5-HT mechanisms that mediate neurogenic cell production processes in a brain-region-specific manner would provide unique insights into the role of 5-HT in neurogenesis and its associated effects on depression.

Formation of Three-Dimensional Spheres Enhances the Neurogenic Potential of Stem Cells from Apical Papilla

Cell-based neural regeneration is challenging due to the difficulty in obtaining sufficient neural stem cells with clinical applicability. Stem cells from apical papilla (SCAPs) originating from embryonic neural crests with high neurogenic potential could be a promising cell source for neural regeneration. This study aimed to investigate whether the formation of 3D spheres can promote SCAPs' neurogenic potential.

MATERIAL AND METHODS

Three-dimensional SCAP spheres were first generated in a 256-well agarose microtissue mold. The spheres and single cells were individually cultured on collagen I-coated μ-slides. Cell morphological changes, neural marker expression, and neurite outgrowth were evaluated by confocal microscope, ELISA, and RT-qPCR.

RESULTS

Pronounced morphological changes were noticed in a time-dependent manner. The migrating cells' morphology changed from fibroblast-like cells to neuron-like cells. Compared to the 2D culture, neurite length, number, and the expression of multiple progenitors, immature and mature neural markers were significantly higher in the 3D spheres. BDNF and NGF-β may play a significant role in the neural differentiation of SCAP spheres.

CONCLUSION

The formation of 3D spheres enhanced the neurogenic potential of SCAPs, suggesting the advantage of using the 3D spheres of SCAPs for treating neural diseases.

Astrocyte-Derived Neuronal Transdifferentiation as a Therapy for Ischemic Stroke: Advances and Challenges

After the onset of ischemic stroke, ischemia–hypoxic cascades cause irreversible neuronal death. Neurons are the fundamental structures of the central nervous system, and mature neurons do not renew or multiply after death. Functional and structural recovery from neurological deficits caused by ischemic attack is a huge task. Hence, there remains a need to replace the lost neurons relying on endogenous neurogenesis or exogenous stem cell-based neuronal differentiation. However, the stem cell source difficulty and the risk of immune rejection of the allogeneic stem cells might hinder the wide clinical application of the above therapy. With the advancement of transdifferentiation induction technology, it has been demonstrated that astrocytes can be converted to neurons through ectopic expression or the knockdown of specific components. The progress and problems of astrocyte transdifferentiation will be discussed in this article.

Astrocyte Reprogramming in Stroke: Opportunities and Challenges

Stroke is a major cause of morbidity and mortality worldwide. In the early stages of stroke, irreversible damage to neurons leads to high mortality and disability rates in patients. However, there are still no effective prevention and treatment measures for the resulting massive neuronal death in clinical practice. Astrocyte reprogramming has recently attracted much attention as an avenue for increasing neurons in mice after cerebral ischemia. However, the field of astrocyte reprogramming has recently been mired in controversy due to reports questioning whether newborn neurons are derived from astrocyte transformation. To better understand the process and controversies of astrocyte reprogramming, this review introduces the method of astrocyte reprogramming and its application in stroke. By targeting key transcription factors or microRNAs, astrocytes in the mouse brain could be reprogrammed into functional neurons. Additionally, we summarize some of the current controversies over the lack of cell lineage tracing and single-cell sequencing experiments to provide evidence of gene expression profile changes throughout the process of astrocyte reprogramming. Finally, we present recent advances in cell lineage tracing and single-cell sequencing, suggesting that it is possible to characterize the entire process of astrocyte reprogramming by combining these techniques.

Changes and roles of IL-17A, VEGF-A and TNF-α in patients with cerebral infarction during the acute phase and early stage of recovery

BACKGROUND AND PURPOSE

Interleukin 17A (IL-17A), vascular endothelial growth factor A (VEGF-A) and tumour necrosis factor alpha (TNF-α) are important cytokines detected mostly within two weeks after stroke in previous clinical studies. Longer clinical studies investigating these cytokines are lacking. We aimed to explore the roles of these cytokines in patients within 35 days after cerebral infarction.

METHODS

Thirty patients with cerebral infarction and 30 healthy individuals were enrolled. Venous blood was collected from each patient at specific times and from each healthy individual only once. Coma and neurological functional deficits of the patients were evaluated by the Glasgow Coma Scale (GCS) and the National Institutes of Health Stroke Scale (NIHSS), respectively. Three cytokines were measured. The correlations among the three cytokines and between each cytokine and the GCS/NIHSS scores were analysed.

RESULTS

IL-17A and TNF-α began to increase on day 1 after cerebral infarction, peaked on day 4, then decreased, and increased again on day 18. IL-17A returned to normal on day 35, but TNF-α remained higher than normal on day 35. VEGF-A began to increase on day 1, peaked on day 7, and returned to normal on day 35. From days 18 to 35, IL-17A was positively correlated with the GCS scores, and both IL-17A and VEGF-A were negatively correlated with the NIHSS scores.

CONCLUSION

After cerebral infarction, VEGF-A from the acute phase and IL-17A from the early stage of recovery may be important for nerve protection and repair; TNF-α plays a complex role within 35 days.

Does astrocyte gap junction protein expression level differ during development in the absence epileptic rats?

Intercellular communication via gap junctions (GJ) has a wide variety of complex and essential functions in the CNS. In the present developmental study, we aimed to quantify the number of astrocytic GJ protein connexin 30 (Cx30) of genetic absence epilepsy rats from Strasbourg (GAERS) at postnatal P10, P30, and P60 days in the epileptic focal areas involved in the cortico-thalamic circuit. We compared the results with Wistar rats using immunohistochemistry and Western Blotting. The number of Cx30 immunopositive astrocytes in per unit area were quantified for the somatosensory cortex (SSCx), ventrobasal (VB), and lateral geniculate (LGN) of the two strains and Cx30 Western Blot was applied to the tissue samples from the same regions. Both immunohistochemical and Western Blot results revealed the presence of Cx30 in all regions studied at P10 in both Wistar and GAERS animals. The SSCx, VB, and LGN of Wistar animals showed progressive increase in the number of Cx30 immunopositive labelled astrocytes from P10 to P30 and reached a peak at P30; then a significant decline was observed from P30 to P60 for the SSCx and VB. However, in GAERS Cx30 immunopositive labelled astrocytes showed a progressive increase from P10 to P60 for all brain regions studied. The immunohistochemical data highly corresponded with Western Blotting results. We conclude that the developmental disproportional expression of Cx30 in the epileptic focal areas in GAERS may be related to the onset of absence seizures or may be related to the neurogenesis of absence epilepsy. This article is protected by copyright. All rights reserved.

Application and advantages of zebrafish model in the study of neurovascular unit

The concept of "Neurovascular Unit" (NVU) was put forward, so that the research goal of Central Nervous System (CNS) diseases gradually transitioned from a single neuron to the structural and functional integrity of the NVU. Zebrafish has the advantages of high homology with human genes, strong reproductive capacity and visualization of neural circuits, so it has become an emerging model organism for NVU research and has been applied to a variety of CNS diseases. Based on CNKI (https://www.cnki.net/) and PubMed (https://pubmed.ncbi.nlm.nih.gov/about/) databases, the author of this article sorted out the relevant literature, analyzed the construction of a zebrafish model of various CNS diseases，and the use of diagrams showed the application of zebrafish in the NVU, revealed its relationship, which would provide new methods and references for the treatment and research of CNS diseases.

Kir4.1 is coexpressed with stemness markers in activated astrocytes in the injured brain and a Kir4.1 inhibitor BaCl2 negatively regulates neurosphere formation in culture

Astrocytes are activated in response to brain damage. Here, we found that expression of Kir4.1, a major potassium channel in astrocytes, is increased in activated astrocytes in the injured brain together with upregulation of the neural stem cell markers, Sox2 and Nestin. Expression of Kir4.1 was also increased together with that of Nestin and Sox2 in neurospheres formed from dissociated P7 mouse brains. Using the Kir4.1 blocker BaCl₂ to determine whether Kir4.1 is involved in acquisition of stemness, we found that inhibition of Kir4.1 activity caused a concentration-dependent increase in sphere size and Sox2 levels, but had little effect on Nestin levels. Moreover, induction of differentiation of cultured neural stem cells by withdrawing epidermal growth factor and fibroblast growth factor from the culture medium caused a sharp initial increase in Kir4.1 expression followed by a decrease, whereas Sox2 and Nestin levels continuously decreased. Inhibition of Kir4.1 had no effect on expression levels of Sox2 or Nestin, or the astrocyte and neuron markers glial fibrillary acidic protein and β-tubulin III, respectively. Taken together, these results indicate that Kir4.1 may control gain of stemness but not differentiation of stem cells.

The Influence of Striatal Astrocyte Dysfunction on Locomotor Activity in Dopamine-depleted Rats

Introduction

Astrocyte dysfunction is the common pathology failing astrocyte-neuron interaction in neurological diseases, including Parkinson's Disease (PD). The present study aimed to evaluate the impacts of astrocytic dysfunction caused by striatal injections of selective glial toxin L-Aminoadipic Acid (L-AA) on the rats' locomotor activity in normal conditions and under alpha-methyl-p-tyrosine depletion of catecholamines synthesis.

Methods

Thirty-three male Wistar rats were used in the experiments. Intrastriatal L-AA injections (100 μg) were performed into the right striatum. Alpha-methyl-p-tyrosine (a-MT, 100 mg/kg, inhibitor of tyrosine hydroxylase) was intraperitoneally injected for catecholamine depletion. The animals were divided into 5 groups, as follows: 1. L-AA treated (n=7), 2. L-AA+a-MT treated (n=5), 3. Sham-operated (n=7), 4. Sham+a-MT treated (n=5), 5. Intact control (n=9). For assessing motor function, open field and beam walking tests were used on the third day after the operation. Neuronal and astrocyte markers (glial fibrillary acidic protein, glutamine synthetase, tyrosine hydroxylase, & neuronal nuclear antigen) were examined in the striatum by immunohistochemistry.

Results

Administrating L-AA led to astrocytic degeneration in the striatum. No neuronal death and disruption of dopaminergic terminals were detected. L-AA and a-MT-treated animals' distance traveled was significantly (P=0.047) shorter than the Sham-operated group injected with a-MT. In the walking beam test, the number of unilateral paw slippings was significantly (P<0.01) higher in the L-AA-treated group than Sham-operated animals. Administrating a-MT alone and L-AA did not change rats' performance in walking beam tests.

Conclusion

Astrocyte ablation in dopamine depleted striatum resulted in reduced motor activity and asymmetrical gait disturbances. These findings demonstrated the role of astroglia in motor function regulation in the nigrostriatal system and suggest the possible association of glial dysfunction with motor dysfunction in PD.

Highlights

The local administration of gliotoxin L-aminoadipate in the striatum of rats causes astrocytic degeneration without affecting the neurons and nigrostriatal fibers.The failure of astrocyte-neuron coupling in the striatum leads to motor dysfunction such as gait disturbances and bradykinesia.The influence of astrocytic degeneration on behavior is preserved and enhanced in dopamine-depleted rats.

Plain Language Summary

Astrocytes are the nervous system's cells supporting the function of neurons. The failure of astrocyte-neuron interaction is observed in neurological diseases, including Parkinson's disease. We induced the aminoadipate-induced rat model of astrocytic dysfunction to evaluate the role of these cells in movement regulation. In our study, astrocytic dysfunction led to gait disturbances and impaired motor function. The results suggest a possible role of glial pathology in motor impairment in parkinsonism.

The Role of Stem Cells in the Therapy of Stroke

Background: Stroke is a major challenge in neurology due to its multifactorial genesis and irreversible consequences. Processes of endogenous post-stroke neurogenesis, although insufficient, may indicate possible direction of future therapy. Multiple research considers stem-cell-based approaches in order to maximize neuroregeneration and minimize post-stroke deficits.

Objective: Aim of this study is to review current literature considering post-stroke stem-cell-based therapy and possibilities of inducing neuroregeneration after brain vascular damage.

Methods: Papers included in this article were obtained from PubMed and MEDLINE databases. The following medical subject headings (MeSH) were used: “stem cell therapy”, “post-stroke neurogenesis”, “stem-cells stroke”, “stroke neurogenesis”, “stroke stem cells”, “stroke”, “cell therapy”, “neuroregeneration”, “neurogenesis”, “stem-cell human”, “cell therapy in human”. Ultimate inclusion was made after manual review of the obtained reference list.

Results: Attempts of stimulating neuroregeneration after stroke found in current literature include supporting endogenous neurogenesis, different routes of exogenous stem cells supplying and extracellular vesicles used as a method of particle transport.

Conclusion: Although further research in this field is required, post stroke brain recovery supported by exogenous stem cells seems to be promising future therapy revolutionizing modern neurology.

Brain Repair by Cell Replacement via In Situ Neuronal Reprogramming

Neurodegenerative diseases, characterized by progressive neural loss, have been some of the most challenging medical problems in aging societies. Treatment strategies such as symptom management have little impact on dis-ease progression, while intervention with specific disease mechanisms may only slow down disease progression. One therapeutic strategy that has the potential to reverse the disease phenotype is to replenish neurons and re-build the pathway lost to degeneration. Although it is generally believed that the central nervous system has lost the capability to regenerate, increasing evidence indicates that the brain is more plastic than previously thought, containing perhaps the biggest repertoire of cells with latent neurogenic programs in the body. This review focuses on key advances in generating new neurons through in situ neuronal reprogramming, which is tied to fun-damental questions regarding adult neurogenesis, cell source, and mecha-nisms for neuronal reprogramming, as well as the ability of new neurons to integrate into the existing circuitry. Expected final online publication date for the Annual Review of Genetics, Volume 55 is November 2021. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Recent insights on astrocyte mechanisms in CNS homeostasis, pathology, and repair

Astrocytes play essential roles in development, homeostasis, injury, and repair of the central nervous system (CNS). Their development is tightly regulated by distinct spatial and temporal cues during embryogenesis and into adulthood throughout the CNS. Astrocytes have several important responsibilities such as regulating blood flow and permeability of the blood-CNS barrier, glucose metabolism and storage, synapse formation and function, and axon myelination. In CNS pathologies, astrocytes also play critical parts in both injury and repair mechanisms. Upon injury, they undergo a robust phenotypic shift known as "reactive astrogliosis," which results in both constructive and deleterious outcomes. Astrocyte activation and migration at the site of injury provides an early defense mechanism to minimize the extent of injury by enveloping the lesion area. However, astrogliosis also contributes to the inhibitory microenvironment of CNS injury and potentiate secondary injury mechanisms, such as inflammation, oxidative stress, and glutamate excitotoxicity, which facilitate neurodegeneration in CNS pathologies. Intriguingly, reactive astrocytes are increasingly a focus in current therapeutic strategies as their activation can be modulated toward a neuroprotective and reparative phenotype. This review will discuss recent advancements in knowledge regarding the development and role of astrocytes in the healthy and pathological CNS. We will also review how astrocytes have been genetically modified to optimize their reparative potential after injury, and how they may be transdifferentiated into neurons and oligodendrocytes to promote repair after CNS injury and neurodegeneration.

Aging-Related Tau Astrogliopathy in Aging and Neurodegeneration

Astrocytes are of vital importance to neuronal function and the health of the central nervous system (CNS), and astrocytic dysfunction as a primary or secondary event may predispose to neurodegeneration. Until recently, the main astrocytic tauopathies were the frontotemporal lobar degeneration with tau (FTLD-tau) group of disorders; however, aging-related tau astrogliopathy (ARTAG) has now been defined. This condition is a self-describing neuropathology mainly found in individuals over 60 years of age. Astrocytic tau accumulates with a thorny or granular/fuzzy morphology and is commonly found in normal aging as well as coexisting with diverse neurodegenerative disorders. However, there are still many unknown factors associated with ARTAG, including the cause/s, the progression, and the nature of any clinical associations. In addition to FTLD-tau, ARTAG has recently been associated with chronic traumatic encephalopathy (CTE), where it has been proposed as a potential precursor to these conditions, with the different ARTAG morphological subtypes perhaps having separate etiologies. This is an emerging area of exciting research that encompasses complex neurobiological and clinicopathological investigation.

The metabesity factor HMG20A potentiates astrocyte survival and reactive astrogliosis preserving neuronal integrity

Rationale: We recently demonstrated that the 'Metabesity' factor HMG20A regulates islet beta-cell functional maturity and adaptation to physiological stress such as pregnancy and pre-diabetes. HMG20A also dictates central nervous system (CNS) development via inhibition of the LSD1-CoREST complex but its expression pattern and function in adult brain remains unknown. Herein we sought to determine whether HMG20A is expressed in the adult CNS, specifically in hypothalamic astrocytes that are key in glucose homeostasis and whether similar to islets, HMG20A potentiates astrocyte function in response to environmental cues. Methods: HMG20A expression profile was assessed by quantitative PCR (QT-PCR), Western blotting and/or immunofluorescence in: 1) the hypothalamus of mice exposed or not to either a high-fat diet or a high-fat high-sucrose regimen, 2) human blood leukocytes and adipose tissue obtained from healthy or diabetic individuals and 3) primary mouse hypothalamic astrocytes exposed to either high glucose or palmitate. RNA-seq and cell metabolic parameters were performed on astrocytes treated or not with a siHMG20A. Astrocyte-mediated neuronal survival was evaluated using conditioned media from siHMG20A-treated astrocytes. The impact of ORY1001, an inhibitor of the LSD1-CoREST complex, on HMG20A expression, reactive astrogliosis and glucose metabolism was evaluated in vitro and in vivo in high-fat high-sucrose fed mice. Results: We show that Hmg20a is predominantly expressed in hypothalamic astrocytes, the main nutrient-sensing cell type of the brain. HMG20A expression was upregulated in diet-induced obesity and glucose intolerant mice, correlating with increased transcript levels of Gfap and Il1b indicative of inflammation and reactive astrogliosis. Hmg20a transcript levels were also increased in adipose tissue of obese non-diabetic individuals as compared to obese diabetic patients. HMG20A silencing in astrocytes resulted in repression of inflammatory, cholesterol biogenesis and epithelial-to-mesenchymal transition pathways which are hallmarks of reactive astrogliosis. Accordingly, HMG20A depleted astrocytes exhibited reduced mitochondrial bioenergetics and increased susceptibility to apoptosis. Neuron viability was also hindered in HMG20A-depleted astrocyte-derived conditioned media. ORY1001 treatment rescued expression of reactive astrogliosis-linked genes in HMG20A ablated astrocytes while enhancing cell surface area, GFAP intensity and STAT3 expression in healthy astrocytes, mimicking the effect of HMG20A. Furthermore, ORY1001 treatment protected against obesity-associated glucose intolerance in mice correlating with a regression of hypothalamic HMG20A expression, indicative of reactive astrogliosis attenuation with improved health status. Conclusion: HMG20A coordinates the astrocyte polarization state. Under physiological pressure such as obesity and insulin resistance that induces low grade inflammation, HMG20A expression is increased to induce reactive astrogliosis in an attempt to preserve the neuronal network and re-establish glucose homeostasis. Nonetheless, a chronic metabesity state or functional mutations will result in lower levels of HMG20A, failure to promote reactive astrogliosis and increase susceptibility of neurons to stress-induced apoptosis. Such effects could be reversed by ORY1001 treatment both in vitro and in vivo, paving the way for a new therapeutic approach for Type 2 Diabetes Mellitus.

Icarisid II promotes proliferation and neuronal differentiation of neural stem cells via activating Wnt/β-catenin signaling pathway

Adult neurogenesis plays a vital role in maintaining cognitive functions in mammals and human beings. Mobilization of hippocampal neurogenesis has been regarded as a promising therapeutic approach to restore injured neurons in neurodegenerative diseases including Alzheimer's disease (AD). Icarisid II (ICS II), an active ingredient derived from Epimedii Folium, has been reported to exhibit multiple neuroprotective effects. In the present study, we investigated the effects of ICS II on the proliferation and differentiation of neural stem cells (NSCs) and amyloid precusor protein (APP)-overexpressing NSCs (APP-NSCs) in vitro. Our results demonstrated that ICS II dose-dependently suppressed apoptosis and elevated viability of APP-NSCs. ICS II (1 μM) potently promoted proliferation and neuronal differentiation of NSCs and APP-NSCs. ICS II (1 μM) significantly upregulated Wnt-3a expression, increased the phosphorylation of glycogen synthase kinase-3β and enhanced the nuclear transfer of β-catenin. Moreover, ICS II also promoted astrocytes to secrete Wnt-3a, which positively modulates Wnt/β-catenin signaling pathway. These findings demonstrate that ICS II promotes NSCs proliferation and neuronal differentiation partly by activating the Wnt/β-catenin signaling pathway.

Therapeutic application of exosomes in ischaemic stroke

Ischaemic stroke is a leading cause of long-term disability in the world, with limited effective treatments. Increasing evidence demonstrates that exosomes are involved in ischaemic pathology and exhibit restorative therapeutic effects by mediating cell–cell communication. The potential of exosome therapy for ischaemic stroke has been actively investigated in the past decade. In this review, we mainly discuss the current knowledge of therapeutic applications of exosomes from different cell types, different exosomal administration routes, and current advances of exosome tracking and targeting in ischaemic stroke. We also briefly summarised the pathology of ischaemic stroke, exosome biogenesis, exosome profile changes after stroke as well as registered clinical trials of exosome-based therapy.

M2 microglial small extracellular vesicles reduce glial scar formation via the miR-124/STAT3 pathway after ischemic stroke in mice

Rationale: Glial scars present a major obstacle for neuronal regeneration after stroke. Thus, approaches to promote their degradation and inhibit their formation are beneficial for stroke recovery. The interaction of microglia and astrocytes is known to be involved in glial scar formation after stroke; however, how microglia affect glial scar formation remains unclear. Methods: Mice were treated daily with M2 microglial small extracellular vesicles through tail intravenous injections from day 1 to day 7 after middle cerebral artery occlusion. Glial scar, infarct volume, neurological score were detected after ischemia. microRNA and related protein were examined in peri-infarct areas of the brain following ischemia. Results: M2 microglial small extracellular vesicles reduced glial scar formation and promoted recovery after stroke and were enriched in miR-124. Furthermore, M2 microglial small extracellular vesicle treatment decreased the expression of the astrocyte proliferation gene signal transducer and activator of transcription 3, one of the targets of miR-124, and glial fibrillary acidic protein and inhibited astrocyte proliferation both in vitro and in vivo. It also decreased Notch 1 expression and increased Sox2 expression in astrocytes, which suggested that astrocytes had transformed into neuronal progenitor cells. Finally, miR-124 knockdown in M2 microglial small extracellular vesicles blocked their effects on glial scars and stroke recovery. Conclusions: Our results showed, for the first time, that microglia regulate glial scar formation via small extracellular vesicles, indicating that M2 microglial small extracellular vesicles could represent a new therapeutic approach for stroke.

Evidence for Decreased Density of Calretinin-Immunopositive Neurons in the Caudate Nucleus in Patients With Schizophrenia

Schizophrenia (SCH) and autism spectrum disorder (ASD) share several common aetiological and symptomatic features suggesting they may be included in a common spectrum. For example, recent results suggest that excitatory/inhibitory imbalance is relevant in the etiology of SCH and ASD. Numerous studies have investigated this imbalance in regions like the ventromedial and dorsolateral prefrontal cortex (DLPFC). However, relatively little is known about neuroanatomical changes that could reduce inhibition in subcortical structures, such as the caudate nucleus (CN), in neuropsychiatric disorders. We recently showed a significant decrease in calretinin-immunopositive (CR-ip) interneuronal density in the CN of patients with ASD without significant change in the density of neuropeptide Y-immunopositive (NPY-ip) neurons. These subtypes together constitute more than 50% of caudate interneurons and are likely necessary for maintaining excitatory/inhibitory balance. Consequently, and since SCH and ASD share characteristic features, here we tested the hypothesis, that the density of CR-ip neurons in the CN is decreased in patients with SCH. We used immunohistochemistry and qPCR for CR and NPY in six patients with schizophrenia and six control subjects. As expected, small, medium and large CR-ip interneurons were detected in the CN. We found a 38% decrease in the density of all CR-ip interneurons (P < 0.01) that was driven by the loss of the small CR-ip interneurons (P < 0.01) in patients with SCH. The densities of the large CR-ip and of the NPY-ip interneurons were not significantly altered. The lower density detected could have been due to inflammation-induced degeneration. However, the state of microglial activation assessed by quantification of ionized calcium-binding adapter molecule 1 (Iba1)- and transmembrane protein 119 (TMEM119)-immunopositive cells showed no significant difference between patients with SCH and controls. Our results warrant further studies focussing on the role of CR-ip neurons and on the striatum being a possible hub for information selection and regulation of associative cortical fields whose function have been altered in SCH.

Astrocytes: News about Brain Health and Diseases

Astrocytes, the most numerous glial cells in the brains of humans and other mammalian animals, have been studied since their discovery over 100 years ago. For many decades, however, astrocytes were believed to operate as a glue, providing only mechanical and metabolic support to adjacent neurons. Starting from a "revolution" initiated about 25 years ago, numerous astrocyte functions have been reconsidered, some previously unknown, others attributed to neurons or other cell types. The knowledge of astrocytes has been continuously growing during the last few years. Based on these considerations, in the present review, different from single or general overviews, focused on six astrocyte functions, chosen due in their relevance in both brain physiology and pathology. Astrocytes, previously believed to be homogeneous, are now recognized to be heterogeneous, composed by types distinct in structure, distribution, and function; their cooperation with microglia is known to govern local neuroinflammation and brain restoration upon traumatic injuries; and astrocyte senescence is relevant for the development of both health and diseases. Knowledge regarding the role of astrocytes in tauopathies and Alzheimer's disease has grow considerably. The multiple properties emphasized here, relevant for the present state of astrocytes, will be further developed by ongoing and future studies.

Expression of Nestin and Glial Fibrillary Acidic Protein in the Marginal Ischemic Zone of the Brain in SHR Rats

We studied spatial organization and structural characteristics of striatal glial cells in spontaneously hypertensive rats (SHR) in 48 h after 30-min focal ischemia. Immunocytochemical analysis of nestin and glial fibrillar acidic protein (GFAP) revealed 3 types of activated astrocytes: expressing only nestin, only GFAP, or both markers. There were no nestin-immunopositive astrocytes in the striatum of sham-operated rats. In cells expressing nestin and GFAP, localization of these markers did not completely coincide, which can be explained by different functions of these proteins or formation of heterodimers of nestin with other intermediate filament proteins.

Troxerutin flavonoid has neuroprotective properties and increases neurite outgrowth and migration of neural stem cells from the subventricular zone

Troxerutin (TRX) is a water-soluble flavonoid which occurs commonly in the edible plants. Recent studies state that TRX improves the functionality of the nervous system and neutralizes Amyloid-ß induced neuronal toxicity. In this study, an in vitro assay based upon Neural stem cell (NSCs) isolated from the subventricular zone of the postnatal balb/c mice was established to explore the impact of TRX on individual neurogenesis processes in general and neuroprotective effect against ß-amyloid 1-42 (Aß42) induced inhibition in differentiation in particular. NSCs were identified exploiting immunostaining of the NSCs markers. Neurosphere clonogenic assay and BrdU/Ki67 immunostaining were employed to unravel the impact of TRX on proliferation. Differentiation experiments were carried out for a time span lasting from 48 h to 7 days utilizing ß-tubulin III and GFAP as neuronal and astrocyte marker respectively. Protective effects of TRX on Aß42 induced depression of NSCs differentiation were determined after 48 h of application. A neurosphere migration assay was carried out for 24 h in the presence and absence of TRX. Interestingly, TRX enhanced neuronal differentiation of NSCs in a dose-dependent manner after 48 h and 7 days of incubation and significantly enhanced neurite growth. A higher concentration of TRX also neutralized the inhibitory effects of Aß42 on neurite outgrowth and length after 48 h of incubation. TRX significantly stimulated cell migration. Overall, TRX not only promoted NSCs differentiation and migration but also neutralized the inhibitory effects of Aß42 on NSCs. TRX, therefore, offers an interesting lead structure from the perspective of drug design especially to promote neurogenesis in neurological disorders i.e. Alzheimer's disease.

Antagonistic effects of IL-17 and Astragaloside IV on cortical neurogenesis and cognitive behavior after stroke in adult mice through Akt/GSK-3β pathway

We aimed to investigate the exact effect of IL-17 on regulating neural stem cells (NSCs) stemness and adult neurogenesis in ischemic cortex after stroke, how Astragaloside IV(As-IV) regulated IL-17 expression and the underlying mechanism. Photochemical brain ischemia model was established and IL-17 protein expression was observed at different time after stroke in WT mice. At 3 days after stroke, when IL-17 expression peaked, IL-17 knock out (KO) mice were used to observe cell proliferation and neurogenesis in ischemic cortex. Then, As-IV was administered intravenously to assess cell apoptosis, proliferation, neurogenesis, and cognitive deficits by immunochemistry staining, western blots, and animal behavior tests in WT mice. Furthermore, IL-17 KO mice and As-IV were used simultaneously to evaluate the mechanism of cell apoptosis and proliferation after stroke in vivo. Besides, in vitro, As-IV and recombinant mouse IL-17A was administered, respectively, into NSCs culture, and then their diameters, viable cell proliferation and pathway relevant protein was assessed. The results showed knocking out IL-17 contributed to regulating PI3K/Akt pathway, promoting NSCs proliferation, and neurogenesis after ischemic stroke. Moreover, As-IV treatment helped inhibit neural apoptosis, promote the neurogenesis and eventually relieve mice anxiety after stroke. Unsurprisingly, IL-17 protein expression could be downregulated by As-IV in vivo and in vitro and they exerted antagonistic effect on neurogenesis by regulating Akt/GSK-3β pathway, with significant regulation for apoptosis. In conclusion, IL-17 exerts negative effect on promoting NSCs proliferation, neurogenesis and cognitive deficits after ischemic stroke, which could be reversed by As-IV.

Expression and Significance of MicroRNA155 in Serum of Patients with Cerebral Small Vessel Disease

Objective

This study aimed to investigate the changes and significance of microRNA155 levels in serum of patients with cerebral small vessel disease (CSVD).

Methods

Thirty patients with CSVD who met the inclusion criteria were selected and divided into eight patients with lacunar infarction (LI) group and 22 patients with multiple lacunar infarction (MLI) combined with white matter lesions (WML) group according to the results of head magnetic resonance imaging (MRI). Thirty samples from healthy volunteers without abnormalities after head MRI examination were selected as the control group. The levels of serum microRNA155 in each group were determined by real-time polymerase chain reaction, and the correlation between microRNA155 in the serum of patients with CSVD and the increase of imaging lesions was analyzed by Spearman correlation analysis.

Results

Compared with the control group, the serum microRNA155 level in the LI group, MLI combined with WML group increased, the difference was statistically significant (p<0.05); serum microRNA155 level was positively correlated with the increase of imaging lesions (p<0.05).

Conclusion

The change of serum microRNA155 level in patients with CSVD may be one of its self-protection mechanisms, and the intensity of this self-protection mechanism is positively correlated with the number of CSVD lesions.

Multiple lineages enable robust development of the neuropil-glia architecture in adult Drosophila

Neural remodeling is essential for the development of a functional nervous system and has been extensively studied in the metamorphosis of Drosophila Despite the crucial roles of glial cells in brain functions, including learning and behavior, little is known of how adult glial cells develop in the context of neural remodeling. Here, we show that the architecture of neuropil-glia in the adult Drosophila brain, which is composed of astrocyte-like glia (ALG) and ensheathing glia (EG), robustly develops from two different populations in the larva: the larval EG and glial cell missing-positive (gcm+ ) cells. Whereas gcm+ cells proliferate and generate adult ALG and EG, larval EG dedifferentiate, proliferate and redifferentiate into the same glial subtypes. Each glial lineage occupies a certain brain area complementary to the other, and together they form the adult neuropil-glia architecture. Both lineages require the FGF receptor Heartless to proliferate, and the homeoprotein Prospero to differentiate into ALG. Lineage-specific inhibition of gliogenesis revealed that each lineage compensates for deficiency in the proliferation of the other. Together, the lineages ensure the robust development of adult neuropil-glia, thereby ensuring a functional brain.

Balanced single-vector co-delivery of VEGF/PDGF-BB improves functional collateralization in chronic cerebral ischemia

The myoblast-mediated delivery of angiogenic genes represents a cell-based approach for targeted induction of therapeutic collateralization. Here, we tested the superiority of myoblast-mediated co-delivery of vascular endothelial growth factor-A (VEGF) together with platelet-derived growth factor-BB (PDGF-BB) on transpial collateralization of an indirect encephalomyosynangiosis (EMS) in a model of chronic cerebral ischemia. Mouse myoblasts expressing a reporter gene alone (empty vector), VEGF, PDGF-BB or VEGF and PDGF-BB through a single bi-cistronic vector (VIP) were implanted into the temporalis muscle of an EMS following permanent ipsilateral internal carotid artery occlusion in adult, male C57BL/6N mice. Over 84 days, myoblast engraftment and gene product expression, hemodynamic impairment, transpial collateralization, angiogenesis, pericyte recruitment and post-ischemic neuroprotection were assessed. By day 42, animals that received PDGF-BB in combination with VEGF (VIP) showed superior hemodynamic recovery, EMS collateralization and ischemic protection with improved pericyte recruitment around the parenchymal vessels and EMS collaterals. Also, supplementation of PDGF-BB resulted in a striking astrocytic activation with intrinsic VEGF mobilization in the cortex below the EMS. Our findings suggest that EMS surgery together with myoblast-mediated co-delivery of VEGF/PDGF-BB may have the potential to serve as a novel treatment strategy for augmentation of collateral flow in the chronically hypoperfused brain.

Post-stroke remodeling processes in animal models and humans

After cerebral ischemia, events like neural plasticity and tissue reorganization intervene in lesioned and non-lesioned areas of the brain. These processes are tightly related to functional improvement and successful rehabilitation in patients. Plastic remodeling in the brain is associated with limited spontaneous functional recovery in patients. Improvement depends on the initial deficit, size, nature and localization of the infarction, together with the sex and age of the patient, all of them affecting the favorable outcome of reorganization and repair of damaged areas. A better understanding of cerebral plasticity is pivotal to design effective therapeutic strategies. Experimental models and clinical studies have fueled the current understanding of the cellular and molecular processes responsible for plastic remodeling. In this review, we describe the known mechanisms, in patients and animal models, underlying cerebral reorganization and contributing to functional recovery after ischemic stroke. We also discuss the manipulations and therapies that can stimulate neural plasticity. We finally explore a new topic in the field of ischemic stroke pathophysiology, namely the brain-gut axis.

Developmental exposure to diacetoxyscirpenol reversibly disrupts hippocampal neurogenesis by inducing oxidative cellular injury and suppressed differentiation of granule cell lineages in mice

To investigate the developmental exposure effect of diacetoxyscirpenol (DAS) on postnatal hippocampal neurogenesis, pregnant ICR mice were provided a diet containing DAS at 0, 0.6, 2.0, or 6.0 ppm from gestational day 6 to day 21 on weaning after delivery. Offspring were maintained through postnatal day (PND) 77 without DAS exposure. On PND 21, neural stem cells (NSCs) and all subpopulations of proliferating progenitor cells were suggested to decrease in number in the subgranular zone (SGZ) at ≥ 2.0 ppm. At 6.0 ppm, increases of SGZ cells showing TUNEL⁺, metallothionein-I/II⁺, γ-H2AX⁺ or malondialdehyde⁺, and transcript downregulation of Ogg1, Parp1 and Kit without changing the level of double-stranded DNA break-related genes were observed in the dentate gyrus. This suggested induction of oxidative DNA damage of NSCs and early-stage progenitor cells, which led to their apoptosis. Cdkn2a, Rb1 and Trp53 downregulated transcripts, which suggested an increased vulnerability to DNA damage. Hilar PVALB⁺ GABAergic interneurons decreased and Grin2a and Chrna7 were downregulated, which suggested suppression of type-2-progenitor cell differentiation. On PND 77, hilar RELN⁺ interneurons increased at ≥ 2.0 ppm; at 6.0 ppm, RELN-related Itsn1 transcripts were upregulated and ARC⁺ granule cells decreased. Increased RELN signals may ameliorate the response to the decreases of NSCs and ARC-mediated synaptic plasticity. These results suggest that DAS reversibly disrupts hippocampal neurogenesis by inducing oxidative cellular injury and suppressed differentiation of granule cell lineages. The no-observed-adverse-effect level of DAS for offspring neurogenesis was determined to be 0.6 ppm (0.09-0.29 mg/kg body weight/day).

Astrocytic endothelin-1 overexpression promotes neural progenitor cells proliferation and differentiation into astrocytes via the Jak2/Stat3 pathway after stroke

Background

Endothelin-1 (ET-1) is synthesized and upregulated in astrocytes under stroke. We previously demonstrated that transgenic mice over-expressing astrocytic ET-1 (GET-1) displayed more severe neurological deficits characterized by a larger infarct after transient middle cerebral artery occlusion (tMCAO). ET-1 is a known vasoconstrictor, mitogenic, and a survival factor. However, it is unclear whether the observed severe brain damage in GET-1 mice post stroke is due to ET-1 dysregulation of neurogenesis by altering the stem cell niche.

Methods

Non-transgenic (Ntg) and GET-1 mice were subjected to tMCAO with 1 h occlusion followed by long-term reperfusion (from day 1 to day 28). Neurological function was assessed using a four-point scale method. Infarct area and volume were determined by 2,3,5-triphenyltetra-zolium chloride staining. Neural stem cell (NSC) proliferation and migration in subventricular zone (SVZ) were evaluated by immunofluorescence double labeling of bromodeoxyuridine (BrdU), Ki67 and Sox2, Nestin, and Doublecortin (DCX). NSC differentiation in SVZ was evaluated using the following immunofluorescence double immunostaining: BrdU and neuron-specific nuclear protein (NeuN), BrdU and glial fibrillary acidic protein (GFAP). Phospho-Stat3 (p-Stat3) expression detected by Western-blot and immunofluorescence staining.

Results

GET-1 mice displayed a more severe neurological deficit and larger infarct area after tMCAO injury. There was a significant increase of BrdU-labeled progenitor cell proliferation, which co-expressed with GFAP, at SVZ in the ipsilateral side of the GET-1 brain at 28 days after tMCAO. p-Stat3 expression was increased in both Ntg and GET-1 mice in the ischemia brain at 7 days after tMCAO. p-Stat3 expression was significantly upregulated in the ipsilateral side in the GET-1 brain than that in the Ntg brain at 7 days after tMCAO. Furthermore, GET-1 mice treated with AG490 (a JAK2/Stat3 inhibitor) sh owed a significant reduction in neurological deficit along with reduced infarct area and dwarfed astrocytic differentiation in the ipsilateral brain after tMCAO.

Conclusions

The data indicate that astrocytic endothelin-1 overexpression promotes progenitor stem cell proliferation and astr ocytic differentiation via the Jak2/Stat3 pathway.

Chromosome Instability and Mosaic Aneuploidy in Neurodegenerative and Neurodevelopmental Disorders

Evidence from multiple laboratories has accumulated to show that mosaic neuronal aneuploidy and consequent apoptosis characterizes and may underlie neuronal loss in many neurodegenerative diseases, particularly Alzheimer’s disease and frontotemporal dementia. Furthermore, several neurodevelopmental disorders, including Seckel syndrome, ataxia telangiectasia, Nijmegen breakage syndrome, Niemann–Pick type C, and Down syndrome, have been shown to also exhibit mosaic aneuploidy in neurons in the brain and in other cells throughout the body. Together, these results indicate that both neurodegenerative and neurodevelopmental disorders with apparently different pathogenic causes share a cell cycle defect that leads to mosaic aneuploidy in many cell types. When such mosaic aneuploidy arises in neurons in the brain, it promotes apoptosis and may at least partly underlie the cognitive deficits that characterize the neurological symptoms of these disorders. These findings have implications for both diagnosis and treatment/prevention.

Genetic conversion of proliferative astroglia into neurons after cerebral ischemia: a new therapeutic tool for the aged brain?

Ischemic stroke represents the 2nd leading cause of death worldwide and the leading cause for long-term disabilities, for which no cure exists. After stroke, neurons are frequently lost in the infarct core. On the other hand, other cells such as astrocytes become reactive and proliferative, disrupting the neurovascular unit in the lesioned area, especially in the aged brain. Therefore, restoring the balance between neurons and nonneuronal cells within the perilesional area is crucial for post stroke recovery. In addition, the aged post stroke brain mounts a fulminant proliferative astroglial response leading to the buildup of gliotic scars that prevent neural regeneration. Therefore, "melting" glial scars has been attempted for decades, albeit with little success. Alternative strategies include transforming inhibitory gliotic tissue into an environment conducive to neuronal regeneration and axonal growth by genetic conversion of astrocytes into neurons. The latter idea has gained momentum following the discovery that in vivo direct lineage reprogramming in the adult mammalian brain is a feasible strategy for reprogramming nonneuronal cells into neurons. This exciting new technology emerged as a new approach to circumvent cell transplantation for stroke therapy. However, the potential of this new methodology has not been yet tested to improve restoration of structure and function in the hostile environment caused by the fulminant inflammatory reaction in the brains of aged animals.

New Neurons in the Post-ischemic and Injured Brain: Migrating or Resident?

The endogenous potential of adult neurogenesis is of particular interest for the development of new strategies for recovery after stroke and traumatic brain injury. These pathological conditions affect endogenous neurogenesis in two aspects. On the one hand, injury usually initiates the migration of neuronal precursors (NPCs) to the lesion area from the already existing, in physiological conditions, neurogenic niche - the ventricular-subventricular zone (V-SVZ) near the lateral ventricles. On the other hand, recent studies have convincingly demonstrated the local generation of new neurons near lesion areas in different brain locations. The striatum, cortex, and hippocampal CA1 region are considered to be locations of such new neurogenic zones in the damaged brain. This review focuses on the relative contribution of two types of NPCs of different origin, resident population in new neurogenic zones and cells migrating from the lateral ventricles, to post-stroke or post-traumatic enhancement of neurogenesis. The migratory pathways of NPCs have also been considered. In addition, the review highlights the advantages and limitations of different methodological approaches to the definition of NPC location and tracking of new neurons. In general, we suggest that despite the considerable number of studies, we still lack a comprehensive understanding of neurogenesis in the damaged brain. We believe that the advancement of methods for in vivo visualization and longitudinal observation of neurogenesis in the brain could fundamentally change the current situation in this field.

MicroRNA-365 Knockdown Prevents Ischemic Neuronal Injury by Activating Oxidation Resistance 1-Mediated Antioxidant Signals

MicroRNA-365 (miR-365) is upregulated in the ischemic brain and is involved in oxidative damage in the diabetic rat. However, it is unclear whether miR-365 regulates oxidative stress (OS)-mediated neuronal damage after ischemia. Here, we used a transient middle cerebral artery occlusion model in rats and the hydrogen peroxide-induced OS model in primary cultured neurons to assess the roles of miR-365 in neuronal damage. We found that miR-365 exacerbated ischemic brain injury and OS-induced neuronal damage and was associated with a reduced expression of OXR1 (Oxidation Resistance 1). In contrast, miR-365 antagomir alleviated both the brain injury and OXR1 reduction. Luciferase assays indicated that miR-365 inhibited OXR1 expression by directly targeting the 3'-untranslated region of Oxr1. Furthermore, knockdown of OXR1 abolished the neuroprotective and antioxidant effects of the miR-365 antagomir. Our results suggest that miR-365 upregulation increases oxidative injury by inhibiting OXR1 expression, while its downregulation protects neurons from oxidative death by enhancing OXR1-mediated antioxidant signals.

Immunohistological Study of Monkey Foveal Retina

The fovea centralis, an anatomically concave pit located at the center of the macula, is avascular, hypoxic, and characteristic of stem-cell niches of other tissues. We hypothesized that in the fovea, undifferentiated retinal-stem-cell-like cells may exist, and that neurogenesis may occur. Hence, we performed an immunohistological study using cynomolgus monkey retinas. After preparing frozen tissue sections of the retina including the foveal pit, immunostaining was performed for glial fibrillary acidic protein (GFAP), nestin, vimentin, neuron-specific class III β-tubulin (Tuj-1), arrestin 4, neurofilament, CD117, CD44, Ki67, and cellular retinaldehyde-binding protein (CRALBP), followed by fluorescence and/or confocal microscopy examinations. Immunostaining of the tissue sections enabled clear observation of strongly GFAP-positive cells that corresponded to the inner-half layer of the foveolar Müller cell cone. The surface layer of the foveal slope was partially costained with GFAP and vimentin. Tuj-1-positive cells were observed in the innermost layer of the foveolar retina, which spanned to the surrounding ganglion cell layer. Moreover, colocalization of Tuj-1 and GFAP was observed at the foveal pit. The coexpression of CD117 and CD44 was found in the interphotoreceptor matrix of the fovea. The foveolar cone stained positive for both nestin and arrestin 4, however, the photoreceptor layer outside of the foveola displayed weak staining for nestin. Colocalization of nestin and vimentin was observed in the inner half of the Henle layer, while colocalization of nestin and neurofilament was observed in the outer half, predominantly. Scattered Ki67-positive cells were observed in the cellular processes of the outer plexiform layer and the ganglion cell layer around the foveola. Immunostaining for CRALBP was negative in most parts of the GFAP-positive area. The Müller cell cone was divided into GFAP-strongly positive cells, presumably astrocytes, in the inner layer and nestin-positive/GFAP-weakly positive radial glia-like cells in the outer layer. These findings indicated that groups of such undifferentiated cells in the foveola might be involved in maintaining morphology and regeneration.

Vascular endothelial growth factor increases the function of calcium-impermeable AMPA receptor GluA2 subunit in astrocytes via activation of protein kinase C signaling pathway

Astrocytic calcium signaling plays pivotal roles in the maintenance of neural functions and neurovascular coupling in the brain. Vascular endothelial growth factor (VEGF), an original biological substance of vessels, regulates the movement of calcium and potassium ions across neuronal membrane. In this study, we investigated whether and how VEGF regulates glutamate-induced calcium influx in astrocytes. We used cultured astrocytes combined with living cell imaging to detect the calcium influx induced by glutamate. We found that VEGF quickly inhibited the glutamate/hypoxia-induced calcium influx, which was blocked by an AMPA receptor antagonist CNQX, but not D-AP5 or UBP310, NMDA and kainate receptor antagonist, respectively. VEGF increased phosphorylation of PKCα and AMPA receptor subunit GluA2 in astrocytes, and these effects were diminished by SU1498 or calphostin C, a PKC inhibitor. With the pHluorin assay, we observed that VEGF significantly increased membrane insertion and expression of GluA2, but not GluA1, in astrocytes. Moreover, siRNA-produced knockdown of GluA2 expression in astrocytes reversed the inhibitory effect of VEGF on glutamate-induced calcium influx. Together, our results suggest that VEGF reduces glutamate-induced calcium influx in astrocytes via enhancing PKCα-mediated GluA2 phosphorylation, which in turn promotes the membrane insertion and expression of GluA2 and causes AMPA receptors to switch from calcium-permeable to calcium-impermeable receptors, thereby inhibiting astrocytic calcium influx. The present study reveals that excitatory neurotransmitter glutamate-mediated astrocytic calcium influx can be regulated by vascular biological factor via activation of AMPA receptor GluA2 subunit and uncovers a novel coupling mechanism between astrocytes and endothelial cells within the neurovascular unit.

Portrait of glial scar in neurological diseases

Fibrosis is formed after injury in most of the organs as a common and complex response that profoundly affects regeneration of damaged tissue. In central nervous system (CNS), glial scar grows as a major physical and chemical barrier against regeneration of neurons as it forms dense isolation and creates an inhibitory environment, resulting in limitation of optimal neural function and permanent deficits of human body. In neurological damages, glial scar is mainly attributed to the activation of resident astrocytes which surrounds the lesion core and walls off intact neurons. Glial cells induce the infiltration of immune cells, resulting in transient increase in extracellular matrix deposition and inflammatory factors which inhibit axonal regeneration, impede functional recovery, and may contribute to the occurrence of neurological complications. However, recent studies have underscored the importance of glial scar in neural protection and functional improvement depending on the specific insults which involves various pivotal molecules and signaling. Thus, to uncover the veil of scar formation in CNS may provide rewarding therapeutic targets to CNS diseases such as chronic neuroinflammation, brain stroke, spinal cord injury (SCI), traumatic brain injury (TBI), brain tumor, and epileptogenesis. In this article, we try to describe the new portrait of glial scar and trending of research in neurological diseases to readers.

Self-injurious behaviours in rhesus macaques: Potential glial mechanisms

BACKGROUND

Self-injurious behaviour (SIB) can be classified as intentional, direct injuring of body tissue usually without suicidal intent. In its non-suicidal form it is commonly seen as a clinical sign of borderline personality disorder, autism, PTSD, depression, and anxiety affecting a wide range of ages and conditions. In rhesus macaques SIB is most commonly manifested through hair plucking, self-biting, self-hitting, and head banging. SIB in the form of self-biting is observed in approximately 5-15% of individually housed monkeys. Recently, glial cells are becoming recognised as key players in regulating behaviours.

METHOD

The goal of this study was to determine the role of glial activation, including astrocytes, in macaques that had displayed SIB. To this end, we performed immunohistochemistry and next generation sequence of brain tissues from rhesus macaques with SIB.

RESULTS

Our studies showed increased vimentin, but not nestin, expression on astrocytes of macaques displaying SIB. Initial RNA Seq analyses indicate activation of pathways involved in tissue remodelling, neuroinflammation and cAMP signalling.

CONCLUSIONS

Glia are most probably activated in primates with self-injury, and are therefore potential novel targets for therapeutics.

The evolving role of neuro-immune interaction in brain repair after cerebral ischemic stroke

Stroke is the world's leading cause of disability with limited brain repair treatments which effectively improve long-term neurological deficits. The neuroinflammatory responses persist into the late repair phase of stroke and participate in all brain repair elements, including neurogenesis, angiogenesis, synaptogenesis, remyelination and axonal sprouting, shedding new light on post-stroke brain recovery. Resident brain glial cells, such as astrocytes not only contribute to neuroinflammation after stroke, but also secrete a wide range of trophic factors that can promote post-stroke brain repair. Alternatively, activated microglia, monocytes, and neutrophils in the innate immune system, traditionally considered as major damaging factors after stroke, have been suggested to be extensively involved in brain repair after stroke. The adaptive immune system may also have its bright side during the late regenerative phase, affecting the immune suppressive regulatory T cells and B cells. This review summarizes the recent findings in the evolving role of neuroinflammation in multiple post-stroke brain repair mechanisms and poses unanswered questions that may generate new directions for future research and give rise to novel therapeutic targets to improve stroke recovery.