Impacts of PI3K/protein kinase B pathway activation in reactive astrocytes: from detrimental effects to protective functions

Astrocytes are the most abundant type of glial cell in the central nervous system.Upon injury and inflammation,astrocytes become reactive and undergo morphological and functional changes.Depending on their phenotypic classification as A1 or A2,reactive astrocytes contribute to both neurotoxic and neuroprotective responses,respectively.However,this binary classification does not fully capture the diversity of astrocyte responses observed across different diseases and injuries.Transcriptomic analysis has revealed that reactive astrocytes have a complex landscape of gene expression profiles,which emphasizes the heterogeneous nature of their reactivity.Astrocytes actively participate in regulating central nervous system inflammation by interacting with microglia and other cell types,releasing cytokines,and influencing the immune response.The phosphoinositide 3-kinase(PI3K)/protein kinase B(AKT)signaling pathway is a central player in astrocyte reactivity and impacts various aspects of astrocyte behavior,as evidenced by in silico,in vitro,and in vivo results.In astrocytes,inflammatory cues trigger a cascade of molecular events,where nuclear factor-κB serves as a central mediator of the pro-inflammatory responses.Here,we review the heterogeneity of reactive astrocytes and the molecular mechanisms underlying their activation.We highlight the involvement of various signaling pathways that regulate astrocyte reactivity,including the PI3K/AKT/mammalian target of rapamycin(mTOR),αvβ3 integrin/PI3K/AKT/connexin 43,and Notch/PI3K/AKT pathways.While targeting the inactivation of the PI3K/AKT cellular signaling pathway to control reactive astrocytes and prevent central nervous system damage,evidence suggests that activating this pathway could also yield beneficial outcomes.This dual function of the PI3K/AKT pathway underscores its complexity in astrocyte reactivity and brain function modulation.The review emphasizes the importance of employing astrocyte-exclusive models to understand their functions accurately and these models are essential for clarifying astrocyte behavior.The findings should then be validated using in vivo models to ensure real-life relevance.The review also highlights the significance of PI3K/AKT pathway modulation in preventing central nervous system damage,although further studies are required to fully comprehend its role due to varying factors such as different cell types,astrocyte responses to inflammation,and disease contexts.Specific strategies are clearly necessary to address these variables effectively.

Maraviroc promotes recovery from traumatic brain injury in mice by suppression of neuroinflammation and activation of neurotoxic reactive astrocytes

Neuroinflammation and the NACHT,LRR,and PYD domains-containing protein 3 inflammasome play crucial roles in secondary tissue damage following an initial insult in patients with traumatic brain injury(TBI).Maraviroc,a C-C chemokine receptor type 5 antagonist,has been viewed as a new therapeutic strategy for many neuroinflammatory diseases.We studied the effect of maraviroc on TBI-induced neuroinflammation.A moderate-TBI mouse model was subjected to a controlled cortical impact device.Maraviroc or vehicle was injected intraperitoneally 1 hour after TBI and then once per day for 3 consecutive days.Western blot,immunohistochemistry,and TUNEL(terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling)analyses were performed to evaluate the molecular mechanisms of maraviroc at 3 days post-TBI.Our results suggest that maraviroc administration reduced NACHT,LRR,and PYD domains-containing protein 3 inflammasome activation,modulated microglial polarization from M1 to M2,decreased neutrophil and macrophage infiltration,and inhibited the release of inflammatory factors after TBI.Moreover,maraviroc treatment decreased the activation of neurotoxic reactive astrocytes,which,in turn,exacerbated neuronal cell death.Additionally,we confirmed the neuroprotective effect of maraviroc using the modified neurological severity score,rotarod test,Morris water maze test,and lesion volume measurements.In summary,our findings indicate that maraviroc might be a desirable pharmacotherapeutic strategy for TBI,and C-C chemokine receptor type 5 might be a promising pharmacotherapeutic target to improve recovery after TBI.

Dynamic reactive astrocytes after focal ischemia

Astrocytes are specialized and most numerous glial cell type in the central nervous system and play important roles in physiology. Astrocytes are also critically involved in many neural disorders including focal ischemic stroke, a leading cause of brain injury and human death. One of the prominent pathological features of focal ischemic stroke is reactive astrogliosis and glial scar formation associated with morphological changes and proliferation. This review paper discusses the recent advances in spatial and temporal dynamics of morphology and proliferation of reactive astrocytes after ischemic stroke based on results from experimental animal studies. As reactive astrocytes exhibit stem cell-like properties, knowledge of dynamics of reactive astrocytes and glial scar formation will provide important insiehts for astrocvte-based cell therapy in stroke.

Reactive astrocytes promote axonal remodeling and neurological recovery after stroke

Stroke is a leading cause of death and disability in adults worldwide. For decades, the primary approach and goal of therapy for stroke has focused on neuroprotection, namely treating the injured tissue, with interventions designed to reduce the volume of cerebral infarction. Enormous effort in the laboratory has been devoted to the development of neuroprotective agents in an attempt to salvage ischemic neurons in the brain from irreversible injury; however, all these efforts have failed to demonstrate efficacy in clinical trials of stroke. In order to treat stroke, we have to re-con- ceptualize and redefine our therapeutic targets. Acute neu- roprotective treatments for stroke fight a temporal battle of salvaging cerebral tissue before the onset of death, as well as a physiological impediment of delivery of therapy to tissue which has inadequate blood flow.

Emerging roles of astrocytes in blood-brain barrier disruption upon amyloid-beta insults in Alzheimer's disease

Blood-brain barrier disruption occurs in the early stages of Alzheimer’s disease.Recent studies indicate a link between blood-brain barrier dysfunction and cognitive decline and might accelerate Alzheimer’s disease progression.Astrocytes are the most abundant glial cells in the central nervous system with important roles in the structural and functional maintenance of the blood-brain barrier.For example,astrocytic cove rage around endothelial cells with perivascular endfeet and secretion of homeostatic soluble factors are two major underlying mechanisms of astrocytic physiological functions.Astrocyte activation is often observed in Alzheimer’s disease patients,with astrocytes expressing a high level of glial fibrillary acid protein detected around amyloid-beta plaque with the elevated phagocytic ability for amyloid-beta.Structural alte rations in Alzheimer’s disease astrocytes including swollen endfeet,somata shrinkage and possess loss contribute to disruption in vascular integrity at capillary and arte rioles levels.In addition,Alzheimer’s disease astrocytes are skewed into proinflammatory and oxidative profiles with increased secretions of vasoactive mediators inducing endothelial junction disruption and immune cell infiltration.In this review,we summarize the findings of existing literature on the relevance of astrocyte alte ration in response to amyloid pathology in the context of blood-brain barrier dysfunction.First,we briefly describe the physiological roles of astrocytes in blood-brain barrier maintenance.Then,we review the clinical evidence of astrocyte pathology in Alzheimer’s disease patients and the preclinical evidence in animal and cellular models.We further discuss the structural changes of blood-brain barrier that correlates with Alzheimer’s disease astrocyte.Finally,we evaluate the roles of soluble factors secreted by Alzheimer’s disease astrocytes,providing potential molecular mechanisms underlying blood-brain barrier modulation.We conclude with a perspective on investigating the therapeutic potential of targeting astrocytes for blood-brain barrier protection in Alzheimer’s disease.

Proliferation and differentiation of reactive nestin^+/GFAP^+ cells in an adult rat model of compression-induced spinal cord injury

BACKGROUND： Studies have demonstrated that astrocytes may possess similar properties to neural stem cells/neural precursor cells and have the potential to differentiate into neurons. OBJECTIVE： To observe neuroepithelial stem cell protein （nestin） and glial fibrillary acidic protein （GFAP） expression following spinal cord injury, and to explore whether nestin＋/GFAP＋ cells, which are detected at peak levels in gray and white matter around the ependymal region of the central canal in injured spinal cord, possess similar properties of neural stem cells. DESIGN, TIME AND SETTING： A randomized, controlled experiment. The study was performed at the Key Laboratory of Environment and Genes Related to Diseases （Xi＇an Jiaotong University）, Ministry of Education between January 2004 and December 2006. MATERIALS： Rabbit anti-rat nestin, β-tubulinⅢ, mouse anti-rat GFAP, galactocerebroside （GaLC） antibodies were utilized, as well as flow cytometry. METHODS： A total of 60 male, Sprague Dawley rats, aged 8 weeks, were randomly assigned to control （n = 12） and model （n = 48） groups. The spinal cord injury model was established in the model group by aneurysm clip compression, while the control animals were not treated. The gray and white matter around the ependymal region of the central canal exhibited peak expression of nestin＋/GFAP＋ cells. These cells were harvested and prepared into single cell suspension, followed by primary and passage cultures. The cells were incubated with serum-containing neural stem cell complete medium. MAINOUTCOME MEASURES： Nestin and GFAP expression in injured spinal cord was determined using immunohistochemistry and double-labeled immunofluorescence at 1, 3, 5, 7, 14, 28, and 56 days post-injury. In addition, cell proliferation and differentiation were detected using immunofluorescence cytochemistry and flow cytometry. RESULTS： Compared with the control group, the model group exhibited significantly increased nestin and GFAP expression （P 〈 0.05）, which reached peak levels between 3 and 7 days. The majority of cells in the ependymal region around the central canal were nestin＋/GFAP- cells, while the gray and white matter around the ependymal region were full of nestin＋/GFAP＋ cells, with an astrocytic-like appearance. A large number of nestin＋/GFAP＋cells were observed in the model group cell culture, and the cells formed clonal spheres and displayed strong nestin-positive immunofluorescence staining. Following induced differentiation, a large number of GaLC-nestin, β-tubulin Ⅲ-nestin, and GFAP-nestin positive cells were observed. However, no obvious changes were seen in the control group. Cells in S stage, as well as the percentage of proliferating cells, in the model group were significantly greater than in the control group （P 〈 0.01）, CONCLUSION： Spinal cord injury in the adult rat induced high expression of nestin＋/GFAP＋ in the gray and white matter around the ependymal region of the central canal. These nestin＋/GFAP＋ cells displayed the potential to self-renew and differentiate into various cells. The cells could be neural stem cells of the central nervous system.

Edaravone protects against oxygen-glucose-serum deprivation/restoration-induced apoptosis in spinal cord astrocytes by inhibiting integrated stress response

We previously found that oxygen-glucose-serum deprivation/restoration（OGSD/R） induces apoptosis of spinal cord astrocytes, possibly via caspase-12 and the integrated stress response, which involves protein kinase R-like endoplasmic reticulum kinase（PERK）, eukaryotic initiation factor 2-alpha（eIF2α） and activating transcription factor 4（ATF4）. We hypothesized that edaravone, a low molecular weight, lipophilic free radical scavenger, would reduce OGSD/R-induced apoptosis of spinal cord astrocytes. To test this, we established primary cultures of rat astrocytes, and exposed them to 8 hours/6 hours of OGSD/R with or without edaravone（0.1, 1, 10, 100 μM） treatment. We found that 100 μM of edaravone significantly suppressed astrocyte apoptosis and inhibited the release of reactive oxygen species. It also inhibited the activation of caspase-12 and caspase-3, and reduced the expression of homologous CCAAT/enhancer binding protein, phosphorylated（p）-PERK, p-eIF2α, and ATF4. These results point to a new use of an established drug in the prevention of OGSD/R-mediated spinal cord astrocyte apoptosis via the integrated stress response.

Unexpected BrdU inhibition on astrocyte-to-neuron conversion

5-Bromo-2′-deoxyuridine(BrdU)is a halogenated pyrimidine that can be incorporated into newly synthesized DNA during the S phase of the cell cycle.BrdU is widely used in fate-mapping studies of embryonic and adult neurogenesis to identify newborn neurons,however side effects on neural stem cells and their progeny have been reported.In vivo astrocyte-to-neuron(AtN)conversion is a new approach for generating newborn neurons by directly converting endogenous astrocytes into neurons.The BrdU-labeling strategy has been used to trace astrocyte-converted neurons,but whether BrdU has any effect on the AtN conversion is unknown.Here,while conducting a NeuroD1-mediated AtN conversion study using BrdU to label dividing reactive astrocytes following ischemic injury,we accidentally discovered that BrdU inhibited AtN conversion.We initially found a gradual reduction in BrdU-labeled astrocytes during NeuroD1-mediated AtN conversion in the mouse cortex.Although most NeuroD1-infected astrocytes were converted into neurons,the number of BrdU-labeled neurons was surprisingly low.To exclude the possibility that this BrdU inhibition was caused by the ischemic injury,we conducted an in vitro AtN conversion study by overexpressing NeuroD1 in cultured cortical astrocytes in the presence or absence of BrdU.Surprisingly,we also found a significantly lower conversion rate and a smaller number of converted neurons in the BrdU-treated group compared with the untreated group.These results revealed an unexpected inhibitory effect of BrdU on AtN conversion,suggesting more caution is needed when using BrdU in AtN conversion studies and in data interpretation.

Endoplasmic reticulum stress transducer old astrocyte specifically induced substance contributes to astrogliosis after spinal cord injury

Old astrocyte specifically induced substance （OASIS） is an endoplasmic reticulum （ER） stress transducer specifically expressed in astrocytes and osteoblasts. OASIS regulates the differentiation of neural precursor cells into astrocytes in the central nervous system. This study aimed to elucidate the involvement of ER stress responses stimulated via OASIS in astrogliosis following spinal cord injury. In a mouse model of spinal cord contusion injury, OASIS mRNA and protein expression were evaluated at days 7 and 14. A significant increase in OASIS mRNA on day 7 and an increase in protein on days 7 and 14 was observed in injured spinal cords. Immunostaining on day 7 revealed co-localization of OASIS and astrocytes in the periphery of the injury site. Furthermore, anti-OASIS small interfering RNA （siRNA） was injected at the injury sites on day 5 to elucidate the function of OASIS. Treatment with anti-OASIS siRNA caused a significant decrease in OASIS mRNA on day 7 and protein on days 7 and 14, and was associated with the inhibition of astrogliosis and hindlimb motor function recovery. Results of our study show that OASIS expression synchronizes with astrogliosis and is functionally associated with astrogliosis after spinal cord injury.

Hub Genes of Astrocyte Involved in Glaucoma with Ocular Hypertension by Integrated Bioinformatics Analysis

This study was conducted to elucidate the potential key candidate genes and pathways in role of astrocyte involved in glaucoma with ocular hypertension.Methods Expression profiles GSE2378 and GSE758 including 27 reactive optic nerve head astrocytes(ONHAs)by hypertensions and 26 normal controls,were integrated and deeply analyzed.Differentially expressed genes(DEGs)were sorted and candidate genes and pathways enrichment were analyzed.DEGs-associated protein-protein interaction network(PPI)was performed.Results A total of 119 consistently expressed genes were identified from 281 commonly changed DEGs,including 68 up-regulated genes and 51 down-regulated genes.PPI network complex filtered 75 DEGs(43 up-regulated and 32 down-regulated genes)of the 119 consistently altered DEGs and developed 117 edges,and 10 hub genes were identified.The most significant 3 modules were filtered from PPI,pathway enrichment analysis showed that module 1 was associated with extracellular exosome.Module 2 was mainly associated with antibody-dependent cellular cytotoxicity(ADCC)and module 3 was mainly associated with Hippo signaling pathway.Conclusion Taken above,using integrated bioinformatical analysis,we have identified DEGs candidate genes and pathways in role of astrocyte involved in glaucoma with ocular hypertension,which could improve our understanding of the cause and underlying molecular events,and these candidate genes and pathways could be therapeutic targets for glaucoma.

Treadmill Exercise Reshapes Cortical Astrocytic and Neuronal Activity to Improve Motor Learning Deficits Under Chronic Alcohol Exposure

Alcohol abuse induces various neurological disorders including motor learning deficits,possibly by affecting neuronal and astrocytic activity.Physical exercise is one effective approach to remediate synaptic loss and motor deficits as shown by our previous works.In this study,we unrevealed the role of exercise training in the recovery of cortical neuronal and astrocytic functions.Using a chronic alcohol injection mouse model,we found the hyperreactivity of astrocytes along with dendritic spine loss plus lower neuronal activity in the primary motor cortex.Persistent treadmill exercise training,on the other hand,improved neural spine formation and inhibited reactive astrocytes,alleviating motor learning deficits induced by alcohol exposure.These data collectively support the potency of endurance exercise in the rehabilitation of motor functions under alcohol abuse.

Protection of Salidroside on Primary Astrocytes from Cell Death by Attenuating Oxidative Stress

Objective To investigate whether salidroside（SAL） has protective and anti-oxidative effects on astrocytes. Methods Firstly, SAL was extracted from the roots of Rhodiola rosea with 70% ethanol and butanol to obtain crude phenylethyl alcohol glycosides which have been known as bioactive part of R. rosea; Secondly, WST-1 assay was carried out to assess the cell viability of astrocytes and cortical neurons under the treatment of the purified（〉 95%） SAL. Moreover, WST-1 assay was also used to evaluate the cytoprotective effects of SAL preventing astrocytes from staurosporine-induced cell death; Thirdly, we examined the spontaneous reactive oxygen species（ROS） and staurosporine-induced ROS generation in astrocytes in the absence or presence of SAL.Results SAL was observed to improve the astrocytes viability but not cortical neurons. In addition, SAL was able to ameliorate staurosporine-induced cell death. Moreover, SAL was able to attenuate the spontaneous ROS and staurosporine-induced ROS generation. Conclusion We here confirm that the anti-oxidative effect of SAL on primary astrocytes might be an important mechanism accounting for the cytoprotective effects from SAL.