Astrocytes induce hemeoxygenase-1 expression in microglia: a feasible mechanism for preventing excessive brain inflammation

Microglia in Ischemic Stroke: Pathogenesis Insights and Therapeutic Challenges

Ischemic stroke is the most common type of stroke, which is the main cause of death and disability on a global scale. As the primary immune cells in the brain that are crucial for preserving homeostasis of the central nervous system microenvironment, microglia have been found to exhibit dual or even multiple effects at different stages of ischemic stroke. The anti-inflammatory polarization of microglia and release of neurotrophic factors may provide benefits by promoting neurological recovery at the lesion in the early phase after ischemic stroke. However, the pro-inflammatory polarization of microglia and secretion of inflammatory factors in the later phase of injury may exacerbate the ischemic lesion, suggesting the therapeutic potential of modulating the balance of microglial polarization to predispose them to anti-inflammatory transformation in ischemic stroke. Microglia-mediated signaling crosstalk with other cells may also be key to improving functional outcomes following ischemic stroke. Thus, this review provides an overview of microglial functions and responses under physiological and ischemic stroke conditions, including microglial activation, polarization, and interactions with other cells. We focus on approaches that promote anti-inflammatory polarization of microglia, inhibit microglial activation, and enhance beneficial cell-to-cell interactions. These targets may hold promise for the creation of innovative therapeutic strategies.

Exploring the pathophysiological influence of heme oxygenase-1 on neuroinflammation and depression: A study of phytotherapeutic-based modulation

BACKGROUND

The heme oxygenase (HO) system plays a significant role in neuroprotection and reduction of neuroinflammation and neurodegeneration. The system, via isoforms HO-1 and HO-2, regulates cellular redox balance. HO-1, an antioxidant defense enzyme, is highlighted due to its association with depression, characterized by heightened neuroinflammation and impaired oxidative stress responses.

METHODOLOGY

We observed the pathophysiology of HO-1 and phytochemicals as its modulator. We explored Science Direct, Scopus, and PubMed for a comprehensive literature review. Bibliometric and temporal trend analysis were done using VOSviewer.

RESULTS

Several phytochemicals can potentially alleviate neuroinflammation and oxidative stress-induced depressive symptoms. These effects result from inhibiting the MAPK and NK-κB pathways - both implicated in the overproduction of pro-inflammatory factors - and from the upregulation of HO-1 expression mediated by Nrf2. Bibliometric and temporal trend analysis further validates these associations.

CONCLUSION

In summary, our findings suggest that antidepressant agents can mitigate neuroinflammation and depressive disorder pathogenesis via the upregulation of HO-1 expression. These agents suppress pro-inflammatory mediators and depressive-like symptoms, demonstrating that HO-1 plays a significant role in the neuroinflammatory process and the development of depression.

A One-Stone-Two-Birds Strategy of Targeting Microbubbles with "Dual" Anti-Inflammatory and Blood-Brain Barrier "Switch" Function for Ischemic Stroke Treatment

Inflammation is considered to be the main target of the development of new stroke therapies. There are three key issues in the treatment of stroke inflammation: the first one is how to overcome the blood-brain barrier (BBB) to achieve drug delivery, the second one is how to select drugs to treat stroke inflammation, and the third one is how to achieve targeted drug delivery. In this study, we constructed hydrocortisone-phosphatidylserine microbubbles and combined them with ultrasound (US)-targeted microbubble destruction technology to successfully open the BBB to achieve targeted drug delivery. Phosphatidylserine on the microbubbles was used for its "eat me" effect to increase the targeting of the microvesicles. In addition, we found that hydrocortisone can accelerate the closure of the BBB, achieving efficient drug delivery while reducing the entry of peripheral toxins into the brain. In the treatment of stroke inflammation, it was found that hydrocortisone itself has anti-inflammatory effects and can also change the polarization of microglia from the harmful pro-inflammatory M1 phenotype to the beneficial anti-inflammatory M2 phenotype, thus achieving dual anti-inflammatory effects and enhancing the anti-inflammatory effects in ischemic areas after stroke, well reducing the cerebellar infarction volume by inhibiting the inflammatory response after cerebral ischemia. A confocal microendoscope was used to directly observe the polarization of microglial cells in living animal models for dynamic microscopic visualization detection showing the advantage of being closer to clinical work. Taken together, this study constructed a multifunctional targeted US contrast agent with the function of "one-stone-two-birds", which can not only "on-off" the BBB but also have "two" anti-inflammatory functions, providing a new strategy of integrated anti-inflammatory targeted delivery and imaging monitoring for ischemic stroke treatment.

Astrocyte-Derived Exosomal miR-148a-3p Suppresses Neuroinflammation and Restores Neurological Function in Traumatic Brain Injury by Regulating the Microglial Phenotype

Interactions between astrocytes and microglia play an important role in the regeneration and repair of traumatic brain injury (TBI), and exosomes are involved in cell-cell interactions. A TBI model was constructed in rats. Brain extract (Ext) was isolated 1 d after TBI. Astrocyte-derived exosomes were obtained by coculturing Ext with primary astrocytes, and the morphology of exosomes was observed by electron microscopy. The isolated exosomes were cocultured with microglia to observe phenotypic changes in M1 and M2 markers. Aberrant RNA expression was detected in necrotic brain tissue and edematous brain tissue. The role of miR-148a-3p in regulating microglial phenotype was explored by knocking down or overexpressing miR-148a-3p. Finally, the effect of miR-148a-3p on TBI was studied in a rat TBI model. Astrocyte-derived exosomes stimulated by Ext promoted the transition of microglia from the M1 phenotype to the M2 phenotype. MiR-148a-3p was highly expressed in TBI. Transfecting miR-148a-3p promoted the transition of microglia from the M1 phenotype to the M2 phenotype and inhibited the lipopolysaccharide-induced inflammatory response in pre-microglia. In a rat TBI model, miR-148a-3p significantly improved the modified neurological severity score and attenuated brain injury, which promoted the transition of microglia from the M1 phenotype to the M2 phenotype. MiR-148a-3p alleviated TBI by inhibiting the nuclear factor κB pathway. Astrocyte-derived exosomal miR-148a-3p regulates the microglial phenotype, inhibits neuroinflammation, and restores neurological function in TBI. These results provide new potential targets for the treatment of TBI.

Glaucoma: from pathogenic mechanisms to retinal glial cell response to damage

Glaucoma is a neurodegenerative disease of the retina characterized by the irreversible loss of retinal ganglion cells (RGCs) leading to visual loss. Degeneration of RGCs and loss of their axons, as well as damage and remodeling of the lamina cribrosa are the main events in the pathogenesis of glaucoma. Different molecular pathways are involved in RGC death, which are triggered and exacerbated as a consequence of a number of risk factors such as elevated intraocular pressure (IOP), age, ocular biomechanics, or low ocular perfusion pressure. Increased IOP is one of the most important risk factors associated with this pathology and the only one for which treatment is currently available, nevertheless, on many cases the progression of the disease continues, despite IOP control. Thus, the IOP elevation is not the only trigger of glaucomatous damage, showing the evidence that other factors can induce RGCs death in this pathology, would be involved in the advance of glaucomatous neurodegeneration. The underlying mechanisms driving the neurodegenerative process in glaucoma include ischemia/hypoxia, mitochondrial dysfunction, oxidative stress and neuroinflammation. In glaucoma, like as other neurodegenerative disorders, the immune system is involved and immunoregulation is conducted mainly by glial cells, microglia, astrocytes, and Müller cells. The increase in IOP produces the activation of glial cells in the retinal tissue. Chronic activation of glial cells in glaucoma may provoke a proinflammatory state at the retinal level inducing blood retinal barrier disruption and RGCs death. The modulation of the immune response in glaucoma as well as the activation of glial cells constitute an interesting new approach in the treatment of glaucoma.

Exploring the multifaceted role of NRF2 in brain physiology and cancer: A comprehensive review

Chronic oxidative stress plays a critical role in the development of brain malignancies due to the high rate of brain oxygen utilization and concomitant production of reactive oxygen species. The nuclear factor-erythroid-2-related factor 2 (NRF2), a master regulator of antioxidant signaling, is a key factor in regulating brain physiology and the development of age-related neurodegenerative diseases. Also, NRF2 is known to exert a protective antioxidant effect against the onset of oxidative stress-induced diseases, including cancer, along with its pro-oncogenic activities through regulating various signaling pathways and downstream target genes. In glioblastoma (GB), grade 4 glioma, tumor resistance, and recurrence are caused by the glioblastoma stem cell population constituting a small bulk of the tumor core. The persistence and self-renewal capacity of these cell populations is enhanced by NRF2 expression in GB tissues. This review outlines NRF2's dual involvement in cancer and highlights its regulatory role in human brain physiology and diseases, in addition to the development of primary brain tumors and therapeutic potential, with a focus on GB.

Endogenous GDNF Is Unable to Halt Dopaminergic Injury Triggered by Microglial Activation

Overactivation of microglial cells seems to play a crucial role in the degeneration of dopaminergic neurons occurring in Parkinson's disease. We have previously demonstrated that glial cell line-derived neurotrophic factor (GDNF) present in astrocytes secretome modulates microglial responses induced by an inflammatory insult. Therefore, astrocyte-derived soluble factors may include relevant molecular players of therapeutic interest in the control of excessive neuroinflammatory responses. However, in vivo, the control of neuroinflammation is more complex as it depends on the interaction between different types of cells other than microglia and astrocytes. Whether neurons may interfere in the astrocyte-microglia crosstalk, affecting the control of microglial reactivity exerted by astrocytes, is unclear. Therefore, the present work aimed to disclose if the control of microglial responses mediated by astrocyte-derived factors, including GDNF, could be affected by the crosstalk with neurons, impacting GDNF's ability to protect dopaminergic neurons exposed to a pro-inflammatory environment. Also, we aimed to disclose if the protection of dopaminergic neurons by GDNF involves the modulation of microglial cells. Our results show that the neuroprotective effect of GDNF was mediated, at least in part, by a direct action on microglial cells through the GDNF family receptor α-1. However, this protective effect seems to be impaired by other mediators released in response to the neuron-astrocyte crosstalk since neuron-astrocyte secretome, in contrast to astrocytes secretome, was unable to protect dopaminergic neurons from the injury triggered by lipopolysaccharide-activated microglia. Supplementation with exogenous GDNF was needed to afford protection of dopaminergic neurons exposed to the inflammatory environment. In conclusion, our results revealed that dopaminergic protective effects promoted by GDNF involve the control of microglial reactivity. However, endogenous GDNF is insufficient to confer dopaminergic neuron protection against an inflammatory insult. This reinforces the importance of further developing new therapeutic strategies aiming at providing GDNF or enhancing its expression in the brain regions affected by Parkinson's disease.

Crosstalk of Highly Purified Microglia and Astrocytes in the Frame of Toll-like Receptor (TLR)2/1 Activation

The major immune cells of the central nervous systems (CNS) are microglia and astrocytes, subsets of the glial cell population. The crosstalk between glia via soluble signaling molecules plays an indispensable role for neuropathologies, brain development as well as homeostasis. However, the investigation of the microglia-astrocyte crosstalk has been hampered due to the lack of suitable glial isolation methods. In this study, we investigated for the first time the crosstalk between highly purified Toll-like receptor (TLR)2-knock out (TLR2-KO) and wild-type (WT) microglia and astrocytes. We examined the crosstalk of TLR2-KO microglia and astrocytes in the presence of WT supernatants of the respective other glial cell type. Interestingly, we observed a significant TNF release by TLR2-KO astrocytes, which were activated with Pam3CSK4-stimulated WT microglial supernatants, strongly indicating a crosstalk between microglia and astrocytes after TLR2/1 activation. Furthermore, transcriptome analysis using RNA-seq revealed a wide range of significant up- and down-regulated genes such as Cd300, Tnfrsf9 or Lcn2, which might be involved in the molecular conversation between microglia and astrocytes. Finally, co-culturing microglia and astrocytes confirmed the prior results by demonstrating a significant TNF release by WT microglia co-cultured with TLR2-KO astrocytes. Our findings suggest a molecular TLR2/1-dependent conversation between highly pure activated microglia and astrocytes via signaling molecules. Furthermore, we demonstrate the first crosstalk experiments using ∼100% pure microglia and astrocyte mono-/co-cultures derived from mice with different genotypes highlighting the urgent need of efficient glial isolation protocols, which particularly holds true for astrocytes.

Microglia and the Blood-Brain Barrier: An External Player in Acute and Chronic Neuroinflammatory Conditions

Microglia are the resident immune cells of the central nervous system that guarantee immune surveillance and exert also a modulating role on neuronal synaptic development and function. Upon injury, microglia get activated and modify their morphology acquiring an ameboid phenotype and pro- or anti-inflammatory features. The active role of microglia in blood-brain barrier (BBB) function and their interaction with different cellular components of the BBB-endothelial cells, astrocytes and pericytes-are described. Here, we report the specific crosstalk of microglia with all the BBB cell types focusing in particular on the involvement of microglia in the modulation of BBB function in neuroinflammatory conditions that occur in conjunction with an acute event, such as a stroke, or in a slow neurodegenerative disease, such as Alzheimer's disease. The potential of microglia to exert a dual role, either protective or detrimental, depending on disease stages and environmental conditioning factors is also discussed.

Network pharmacology to explore the mechanism of scutellarin in the treatment of brain ischaemia and experimental verification of JAK2/STAT3 signalling pathway

Scutellarin is used to treat brain ischaemia. However, its underlying mechanism of action remains unclear. This study aimed to elucidate the potential mechanism of action of scutellarin in brain ischaemia through network pharmacology and experimental verification. The JAK2/STAT3 signalling pathway was identified and experimentally verified. Expression of JAK2/STAT3 signalling related proteins in TNC-1 astrocytes with BV-2 microglia-conditioned medium (CM), CM + lipopolysaccharide (LPS) (CM + L), and CM pretreated with scutellarin + LPS (CM + SL) was analysed by Western Blot and immunofluorescence staining. Expression levels of JAK2, p-JAK2, STAT3, and p-STAT3 were evaluated in astrocytes pre-treated with AG490. Middle cerebral artery occlusion (MCAO) in rats was performed in different experimental groups to detect expression of the above biomarkers. Network pharmacology suggested that the JAK2/STAT3 signalling pathway is one of the mechanisms by which scutellarin mitigates cerebral ischaemic damage. In TNC-1 astrocytes, p-JAK2 and p-STAT3 expression were significantly up-regulated in the CM + L group. Scutellarin promoted the up-regulation of various markers and AG490 neutralised the effect of scutellarin. In vivo, up-regulation of p-JAK2 and p-STAT3 after ischaemia is known. These results are consistent with previous reports. Scutellarin further enhanced this upregulation at 1, 3, and 7 d after MCAO. Scutellarin exerts its therapeutic effects on cerebral ischaemia by activating the astrocyte JAK2/STAT3 signalling, which provides a firm experimental basis for its clinical application.

Ultrasonically actuated neural probes for reduced trauma and inflammation in mouse brain

Electrical neural recordings measured using direct electrical interfaces with neural tissue suffer from a short lifespan because the signal strength decreases over time. The inflammatory response to the inserted microprobe can create insulating tissue over the electrical interfaces, reducing the recorded signal below noise levels. One of the factors contributing to this inflammatory response is the tissue damage caused during probe insertion. Here, we explore the use of ultrasonic actuation of the neural probe during insertion to minimize tissue damage in mice. Silicon neural microprobes were designed and fabricated with integrated electrical recording sites and piezoelectric transducers. The microprobes were actuated at ultrasonic frequencies using integrated piezoelectric transducers. The microprobes were inserted into mouse brains under a glass window over the brain surface to image the tissue surrounding the probe using two-photon microscopy. The mechanical force required to penetrate the tissue was reduced by a factor of 2-3 when the microprobe was driven at ultrasonic frequencies. Tissue histology at the probe insertion site showed a reduced area of damage and decreased microglia counts with increasing ultrasonic actuation of the probes. Two-photon imaging of the microprobe over weeks demonstrated stabilization of the inflammatory response. Recording of electrical signals from neurons over time suggests that microprobes inserted using ultrasound have a higher signal-to-noise ratio over an extended time period.

The different facets of heme-oxygenase 1 in innate and adaptive immunity

Heme oxygenase (HO) enzymes are responsible for the main oxidative step in heme degradation, generating equimolar amounts of free iron, biliverdin and carbon monoxide. HO-1 is induced as a crucial stress response protein, playing protective roles in physiologic and pathological conditions, due to its antioxidant, anti-apoptotic and anti-inflammatory effects. The mechanisms behind HO-1-mediated protection are being explored by different studies, affecting cell fate through multiple ways, such as reduction in intracellular levels of heme and ROS, transcriptional regulation, and through its byproducts generation. In this review we focus on the interplay between HO-1 and immune-related signaling pathways, which culminate in the activation of transcription factors important in immune responses and inflammation. We also discuss the dual interaction of HO-1 and inflammatory mediators that govern resolution and tissue damage. We highlight the dichotomy of HO-1 in innate and adaptive immune cells development and activation in different disease contexts. Finally, we address different known anti-inflammatory pharmaceuticals that are now being described to modulate HO-1, and the possible contribution of HO-1 in their anti-inflammatory effects.

Methylmalonic acid induces inflammatory response and redox homeostasis disruption in C6 astroglial cells: potential glioprotective roles of melatonin and resveratrol

Methylmalonic acidemia is a neurometabolic disorder biochemically characterized by the accumulation of methylmalonic acid (MMA) in different tissues, including the central nervous system (CNS). In this sense, it has been shown that high levels of this organic acid have a key role in the progressive neurological deterioration in patients. Astroglial cells actively participate in a wide range of CNS functions, such as antioxidant defenses and inflammatory response. Considering the role of these cells to maintain brain homeostasis, in the present study, we investigated the effects of MMA on glial parameters, focusing on redox homeostasis and inflammatory process, as well as putative mediators of these events in C6 astroglial cells. MMA decreased cell viability, glutathione levels, and antioxidant enzyme activities, increased inflammatory response, and changed the expression of nuclear factor erythroid 2-related factor 2 (Nrf2), nuclear factor kappa B (NFκB), peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α), inducible nitric oxide synthase (iNOS), cyclooxygenase 2 (COX-2), and adenosine receptors, suggesting that these transcriptional factors and proteins may underlie the glial responses induced by MMA. Moreover, we also demonstrated the protective roles of melatonin and resveratrol against MMA-induced inflammation and decrease in glutathione levels. In summary, our findings support the hypothesis that astroglial changes are associated with pathogenesis of methylmalonic acidemia. In addition, we showed that these cells might be potential targets for preventive/therapeutic strategies by using molecules, such as melatonin and resveratrol, which mediated glioprotection in this inborn error of metabolism.

GSK-3β-mediated regulation of Nrf2/HO-1 signaling as a new therapeutic approach in the treatment of movement disorders

Movement disorders are neurological conditions characterized by involuntary motor movements, such as dystonia, ataxia, chorea myoclonus, tremors, Huntington's disease (HD), and Parkinson's disease (PD). It is classified into two categories: hypokinetic and hyperkinetic movements. Globally, movement disorders are a major cause of death. The pathophysiological process is initiated by excessive ROS generation, mitochondrial dysfunction, neuroinflammation, and neurotransmitters imbalance that lead to motor dysfunction in PD and HD patients. Several endogenous targets including Nrf2 maintain oxidative balance in the body. Activation of Nrf2 signaling is regulated by the enzyme glycogen synthase kinase (GSK-3β). In the cytoplasm, inhibition of GSK-3β regulates cellular proliferation, homeostasis, and apoptotic process by stimulating the nuclear factor erythroid 2 (Nrf2) pathway which is involved in the elevation of the cellular antioxidant enzymes which controls the ROS generation. The activation of Nrf2 increases the expression of antioxidant response elements (ARE), such as (Hemeoxygenase-1) HO-1, which decreases excessive cellular stress, mitochondrial dysfunction, apoptosis, and neuronal degeneration, which is the major cause of motor dysfunction. The present review explores the GSK-3β-mediated neuroprotection in various movement disorders through the Nrf2/HO-1 antioxidant pathway. This review provides a link between GSK-3β and the Nrf2/HO-1 signaling pathway in the treatment of PD and HD. In addition to that it highlights various GSK-3β inhibitors and the Nrf2/HO-1 activators, which exert robust neuroprotection against motor disorders. Therefore, the present review will help in the discovery of new therapy for PD and HD patients.

Dimethyl itaconate reprograms neurotoxic to neuroprotective primary astrocytes through the regulation of NLRP3 inflammasome and NRF2/HO-1 pathways

The activation of neurotoxic reactive astrocytes contributes to the pathogenesis of many neurodegenerative diseases. Itaconate, a product of cellular metabolism, is released from activated macrophage/microglia and has been shown to regulate inflammatory responses in several mammalian cells. This study was designed to investigate the impact of cell-permeable dimethyl itaconate (DI) on reactive astrocyte-dependent neurotoxicity. Primary murine astrocyte cells were isolated and stimulated with lipopolysaccharide (LPS) to generate reactive astrocytes. Treating these activated cells with DI was able to diminish the neurotoxic phenotype of reactive astrocytes, as we found reduced LPS-induced Nod-like receptor protein 3 (NLRP3) inflammasome activation and interleukin-1β (IL-1β) secretion. DI reduced the level of inflammasome components, attenuated inflammasome assembly and subsequently reduced caspase-1 cleavage and IL-1β levels. Additionally, DI attenuated nuclear factor-kappa B (NF-κB) phosphorylation in LPS-activated astrocytes and also protected astrocytes from LPS-induced cytotoxicity, including a lowering of Bax and caspase3. DI-treated reactive astrocytes showed an elevated GSH/GSSG ratio and improved antioxidant defense factors including catalase and superoxide dismutase, while lipid peroxidation was reduced. We found that DI activated the nuclear factor 2 (NRF2) and heme oxygenase-1 (HO-1) pathway in astrocytes and thereby potentially control redox-regulation and the inflammatory state of astrocytes. Collectively, these results indicate the neuroprotective role of DI by reprogramming astrocytes from neurotoxic A1 to neuroprotective A2 states and thereby reveal a novel potential strategy for the treatment of neurodegenerative diseases.

Neurodegeneration in Multiple Sclerosis: The Role of Nrf2-Dependent Pathways

Multiple sclerosis (MS) encompasses a chronic, irreversible, and predominantly immune-mediated disease of the central nervous system that leads to axonal degeneration, neuronal death, and several neurological symptoms. Although various immune therapies have reduced relapse rates and the severity of symptoms in relapsing-remitting MS, there is still no cure for this devastating disease. In this brief review, we discuss the role of mitochondria dysfunction in the progression of MS, focused on the possible role of Nrf2 signaling in orchestrating the impairment of critical cellular and molecular aspects such as reactive oxygen species (ROS) management, under neuroinflammation and neurodegeneration in MS. In this scenario, we propose a new potential downstream signaling of Nrf2 pathway, namely the opening of hemichannels and pannexons. These large-pore channels are known to modulate glial/neuronal function and ROS production as they are permeable to extracellular Ca²⁺ and release potentially harmful transmitters to the synaptic cleft. In this way, the Nrf2 dysfunction impairs not only the bioenergetics and metabolic properties of glial cells but also the proper antioxidant defense and energy supply that they provide to neurons.

Microglia: The Hub of Intercellular Communication in Ischemic Stroke

Communication between microglia and other cells has recently been at the forefront of research in central nervous system (CNS) disease. In this review, we provide an overview of the neuroinflammation mediated by microglia, highlight recent studies of crosstalk between microglia and CNS resident and infiltrating cells in the context of ischemic stroke (IS), and discuss how these interactions affect the course of IS. The in-depth exploration of microglia-intercellular communication will be beneficial for therapeutic tools development and clinical translation for stroke control.

Crosstalk Between the Oxidative Stress and Glia Cells After Stroke: From Mechanism to Therapies

Stroke is the second leading cause of global death and is characterized by high rates of mortality and disability. Oxidative stress is accompanied by other pathological processes that together lead to secondary brain damage in stroke. As the major component of the brain, glial cells play an important role in normal brain development and pathological injury processes. Multiple connections exist in the pathophysiological changes of reactive oxygen species (ROS) metabolism and glia cell activation. Astrocytes and microglia are rapidly activated after stroke, generating large amounts of ROS via mitochondrial and NADPH oxidase pathways, causing oxidative damage to the glial cells themselves and neurons. Meanwhile, ROS cause alterations in glial cell morphology and function, and mediate their role in pathological processes, such as neuroinflammation, excitotoxicity, and blood-brain barrier damage. In contrast, glial cells protect the Central Nervous System (CNS) from oxidative damage by synthesizing antioxidants and regulating the Nuclear factor E2-related factor 2 (Nrf2) pathway, among others. Although numerous previous studies have focused on the immune function of glial cells, little attention has been paid to the role of glial cells in oxidative stress. In this paper, we discuss the adverse consequences of ROS production and oxidative-antioxidant imbalance after stroke. In addition, we further describe the biological role of glial cells in oxidative stress after stroke, and we describe potential therapeutic tools based on glia cells.

Agmatine Mitigates Inflammation-Related Oxidative Stress in BV-2 Cells by Inducing a Pre-Adaptive Response

Neuroinflammation and microglial activation, common components of most neurodegenerative diseases, can be imitated in vitro by challenging microglia cells with Lps. We here aimed to evaluate the effects of agmatine pretreatment on Lps-induced oxidative stress in a mouse microglial BV-2 cell line. Our findings show that agmatine suppresses nitrosative and oxidative burst in Lps-stimulated microglia by reducing iNOS and XO activity and decreasing O₂^- levels, arresting lipid peroxidation, increasing total glutathione content, and preserving GR and CAT activity. In accordance with these results, agmatine suppresses inflammatory NF-kB, and stimulates antioxidant Nrf2 pathway, resulting in decreased TNF, IL-1 beta, and IL-6 release, and reduced iNOS and COX-2 levels. Together with increased ARG1, CD206 and HO-1 levels, our results imply that, in inflammatory conditions, agmatine pushes microglia towards an anti-inflammatory phenotype. Interestingly, we also discovered that agmatine alone increases lipid peroxidation end product levels, induces Nrf2 activation, increases total glutathione content, and GPx activity. Thus, we hypothesize that some of the effects of agmatine, observed in activated microglia, may be mediated by induced oxidative stress and adaptive response, prior to Lps stimulation.

Integrated Metabolomics and Lipidomics Reveal High Accumulation of Glycerophospholipids in Human Astrocytes under the Lipotoxic Effect of Palmitic Acid and Tibolone Protection

Lipotoxicity is a metabolic condition resulting from the accumulation of free fatty acids in non-adipose tissues which involves a series of pathological responses triggered after chronic exposure to high levels of fatty acids, severely detrimental to cellular homeostasis and viability. In brain, lipotoxicity affects both neurons and other cell types, notably astrocytes, leading to neurodegenerative processes, such as Alzheimer (AD) and Parkinson diseases (PD). In this study, we performed for the first time, a whole lipidomic characterization of Normal Human Astrocytes cultures exposed to toxic concentrations of palmitic acid and the protective compound tibolone, to establish and identify the set of potential metabolites that are modulated under these experimental treatments. The study covered 3843 features involved in the exo- and endo-metabolome extracts obtained from astrocytes with the mentioned treatments. Through multivariate statistical analysis such as PCA (principal component analysis), partial least squares (PLS-DA), clustering analysis, and machine learning enrichment analysis, it was possible to determine the specific metabolites that were affected by palmitic acid insult, such as phosphoethanolamines, phosphoserines phosphocholines and glycerophosphocholines, with their respective metabolic pathways impact. Moreover, our results suggest the importance of tibolone in the generation of neuroprotective metabolites by astrocytes and may be relevant to the development of neurodegenerative processes.

Antimony-induced astrocyte activation via mitogen-activated protein kinase activation-dependent CREB phosphorylation

Recent studies suggest that the chemical element antimony (Sb) is neurotoxic; however, the molecular mechanisms behind Sb-related neuronal damage are currently unknown. In this study, we found that Sb exposure promoted astrocyte proliferation and increased the expression of inducible nitric oxide synthase (iNOS) and glial fibrillary acidic protein (GFAP), two key protein markers of reactive astrogliosis, at both the gene and protein level, suggesting that Sb induced astrocyte activation. Moreover, the p38 mitogen-activated protein kinase (p38 MAPK) and extracellular signal-related kinase (ERK) pathways were activated following Sb exposure. Inhibition of p38 MAPK reduced Sb-induced iNOS and GFAP upregulation, while inhibiting ERK reduced GFAP expression only, in Sb-exposed C6 cells. Sb treatment also induced the phosphorylation of cyclic adenosine monophosphate (cAMP) response element-binding protein (CREB), and the inhibition of CREB caused a reduction in Sb-induced GFAP and iNOS expression. Furthermore, inhibiting both p38 MAPK and ERK effectively alleviated CREB phosphorylation in Sb-exposed C6 cells. Taken together, our results suggest that p38 MAPK and ERK activation mediate Sb-induced astrocyte activation through CREB phosphorylation. These results help to clarify the molecular mechanisms underlying Sb-associated neurotoxicity.

Contribution of the Nrf2 Pathway on Oxidative Damage and Mitochondrial Failure in Parkinson and Alzheimer's Disease

The increase in human life expectancy has become a challenge to reduce the deleterious consequences of aging. Nowadays, an increasing number of the population suffer from age-associated neurodegenerative diseases including Parkinson's disease (PD) and Alzheimer's disease (AD). These disorders present different signs of neurodegeneration such as mitochondrial dysfunction, inflammation, and oxidative stress. Accumulative evidence suggests that the transcriptional factor nuclear factor (erythroid-derived 2)-like 2 (Nrf2) plays a vital defensive role orchestrating the antioxidant response in the brain. Nrf2 activation promotes the expression of several antioxidant enzymes that exert cytoprotective effects against oxidative damage and mitochondrial impairment. In this context, several studies have proposed a role of Nrf2 in the pathogenesis of PD and AD. Thus, we consider it important to summarize the ongoing literature related to the effects of the Nrf2 pathway in the context of these diseases. Therefore, in this review, we discuss the mechanisms involved in Nrf2 activity and its connection with mitochondria, energy supply, and antioxidant response in the brain. Furthermore, we will lead our discussion to identify the participation of the Nrf2 pathway in mitochondrial impairment and neurodegeneration present in PD and AD. Finally, we will discuss the therapeutic effects that the Nrf2 pathway activation could have on the cognitive impairment, neurodegeneration, and mitochondrial failure present in PD and AD.

Senescent Microglia: The Key to the Ageing Brain?

Ageing represents the single biggest risk factor for development of neurodegenerative disease. Despite being such long-lived cells, microglia have been relatively understudied for their role in the ageing process. Reliably identifying aged microglia has proven challenging, not least due to the diversity of cell populations, and the limitations of available models, further complicated by differences between human and rodent cells. Consequently, the literature contains multiple descriptions and categorisations of microglia with neurotoxic phenotypes, including senescence, without any unifying markers. The role of microglia in brain homeostasis, particularly iron storage and metabolism, may provide a key to reliable identification.

Astrocyte phenotypes: Emphasis on potential markers in neuroinflammation

Astrocytes, the most abundant glial cells in the central nervous system (CNS), have numerous integral roles in all CNS functions. They are essential for synaptic transmission and support neurons by providing metabolic substrates, secreting growth factors and regulating extracellular concentrations of ions and neurotransmitters. Astrocytes respond to CNS insults through reactive astrogliosis, in which they go through many functional and molecular changes. In neuroinflammatory conditions reactive astrocytes exert both beneficial and detrimental functions, depending on the context and heterogeneity of astrocytic populations. In this review we profile astrocytic diversity in the context of neuroinflammation; with a specific focus on multiple sclerosis (MS) and its best-described animal model experimental autoimmune encephalomyelitis (EAE). We characterize two main subtypes, protoplasmic and fibrous astrocytes and describe the role of intermediate filaments in the physiology and pathology of these cells. Additionally, we outline a variety of markers that are emerging as important in investigating astrocytic biology in both physiological conditions and neuroinflammation.

Cellular infiltration in traumatic brain injury

Traumatic brain injury leads to cellular damage which in turn results in the rapid release of damage-associated molecular patterns (DAMPs) that prompt resident cells to release cytokines and chemokines. These in turn rapidly recruit neutrophils, which assist in limiting the spread of injury and removing cellular debris. Microglia continuously survey the CNS (central nervous system) compartment and identify structural abnormalities in neurons contributing to the response. After some days, when neutrophil numbers start to decline, activated microglia and astrocytes assemble at the injury site—segregating injured tissue from healthy tissue and facilitating restorative processes. Monocytes infiltrate the injury site to produce chemokines that recruit astrocytes which successively extend their processes towards monocytes during the recovery phase. In this fashion, monocytes infiltration serves to help repair the injured brain. Neurons and astrocytes also moderate brain inflammation via downregulation of cytotoxic inflammation. Depending on the severity of the brain injury, T and B cells can also be recruited to the brain pathology sites at later time points.

Astrocyte-derived VEGF increases cerebral microvascular permeability under high salt conditions

Excess salt (NaCl) intake is closely related to a variety of central nervous system (CNS) diseases characterized by increased cerebral microvascular permeability. However, the link between a high salt diet (HSD) and the breakdown of tight junctions (TJs) remains unclear. In the present study, we found that high salt does not directly influence the barrier between endothelial cells, but it suppresses expression of TJ proteins when endothelial cells are co-cultured with astrocytes. This effect is independent of blood pressure, but depends on the astrocyte activation via the NFκB/MMP-9 signaling pathway, resulting in a marked increase in VEGF expression. VEGF, in turn, induces disruption of TJs by inducing phosphorylation and activation of ERK and eNOS. Correspondingly, the HSD-induced disruption of TJ proteins is attenuated by blocking VEGF using the specific monoclonal antibody Bevacizumab. These results reveal a new axis linking a HSD to increased cerebral microvascular permeability through a VEGF-initiated inflammatory response, which may be a potential target for preventing the deleterious effects of HSD on the CNS.

Extracellular Vesicles miRNA Cargo for Microglia Polarization in Traumatic Brain Injury

Traumatic brain injury (TBI) is one of the major causes of death and disability worldwide, and despite its high dissemination, effective pharmacotherapies are lacking. TBI can be divided into two phases: the instantaneous primary mechanical injury, which occurs at the moment of insult, and the delayed secondary injury, which involves a cascade of biological processes that lead to neuroinflammation. Neuroinflammation is a hallmark of both acute and chronic TBI, and it is considered to be one of the major determinants of the outcome and progression of disease. In TBI one of the emerging mechanisms for cell–cell communication involved in the immune response regulation is represented by Extracellular Vesicles (EVs). These latter are produced by all cell types and are considered a fingerprint of their generating cells. Exosomes are the most studied nanosized vesicles and can carry a variety of molecular constituents of their cell of origin, including microRNAs (miRNAs). Several miRNAs have been shown to target key neuropathophysiological pathways involved in TBI. The focus of this review is to analyze exosomes and their miRNA cargo to modulate TBI neuroinflammation providing new strategies for prevent long-term progression of disease.

Hippo/YAP Pathway Plays a Critical Role in Effect of GDNF Against Aβ-Induced Inflammation in Microglial Cells

Neuroinflammation is a critical mechanism responsible for the progression of Alzheimer's disease (AD). Recent studies reveal that Hippo/Yes-associated protein (YAP) signaling pathway is highly associated with a series of inflammation-related disorders. Glial cell line-derived neurotrophic factor (GDNF), with its neurotrophic and anti-apoptotic functions for nervous system, has been demonstrated to decrease the expression of proinflammatory mediators. Here we investigated whether Hippo/YAP signaling may affect amyloid-β (Aβ)-induced proinflammatory cytokine production in microglial cells and explored its relationship with the anti-inflammation function of GDNF. The results showed that Aβ induced a decrease in the expression of YAP in microglia cells. YAP agonist XMU-MP-1 or its overexpression in microglial cells caused decreased expression of proinflammatory cytokines, whereas YAP antagonist Verteporfin or knockdown of YAP had the opposite effect. Treatment with GDNF resulted in upregulation of YAP expression and reduced the production of proinflammatory cytokines. Meanwhile YAP knockdown weakened the function of GDNF in microglial cells. In conclusion, Hippo/YAP pathway plays a critical role in effect of GDNF against Aβ-induced inflammatory response in microglia. Targeting GDNF or Hippo/YAP signaling may be promising therapeutic approach for the treatment of AD.

Resilience to Injury: A New Approach to Neuroprotection?

Despite thousands of neuroprotectants demonstrating promise in preclinical trials, a neuroprotective therapeutic has yet to be approved for the treatment of acute brain injuries such as stroke or traumatic brain injury. Developing a more detailed understanding of models and populations demonstrating "neurological resilience" in spite of brain injury can give us important insights into new translational therapies. Resilience is the process of active adaptation to a stressor. In the context of neuroprotection, models of preconditioning and unique animal models of extreme physiology (such as hibernating species) reliably demonstrate resilience in the laboratory setting. In the clinical setting, resilience is observed in young patients and can be found in those with specific genetic polymorphisms. These important examples of resilience can help transform and extend the current neuroprotective framework from simply countering the injurious cascade into one that anticipates, monitors, and optimizes patients' physiological responses from the time of injury throughout the process of recovery. This review summarizes the underpinnings of key adaptations common to models of resilience and how this understanding can be applied to new neuroprotective approaches.

Ischemia-Triggered Glutamate Excitotoxicity From the Perspective of Glial Cells

A plethora of neurological disorders shares a final common deadly pathway known as excitotoxicity. Among these disorders, ischemic injury is a prominent cause of death and disability worldwide. Brain ischemia stems from cardiac arrest or stroke, both responsible for insufficient blood supply to the brain parenchyma. Glucose and oxygen deficiency disrupts oxidative phosphorylation, which results in energy depletion and ionic imbalance, followed by cell membrane depolarization, calcium (Ca²⁺) overload, and extracellular accumulation of excitatory amino acid glutamate. If tight physiological regulation fails to clear the surplus of this neurotransmitter, subsequent prolonged activation of glutamate receptors forms a vicious circle between elevated concentrations of intracellular Ca²⁺ ions and aberrant glutamate release, aggravating the effect of this ischemic pathway. The activation of downstream Ca²⁺-dependent enzymes has a catastrophic impact on nervous tissue leading to cell death, accompanied by the formation of free radicals, edema, and inflammation. After decades of “neuron-centric” approaches, recent research has also finally shed some light on the role of glial cells in neurological diseases. It is becoming more and more evident that neurons and glia depend on each other. Neuronal cells, astrocytes, microglia, NG2 glia, and oligodendrocytes all have their roles in what is known as glutamate excitotoxicity. However, who is the main contributor to the ischemic pathway, and who is the unsuspecting victim? In this review article, we summarize the so-far-revealed roles of cells in the central nervous system, with particular attention to glial cells in ischemia-induced glutamate excitotoxicity, its origins, and consequences.

Astrocyte-derived exosomes enriched with miR-873a-5p inhibit neuroinflammation via microglia phenotype modulation after traumatic brain injury

BACKGROUND

The interaction between astrocytes and microglia plays a vital role in the damage and repair of brain lesions due to traumatic brain injury (TBI). Recent studies have shown that exosomes act as potent mediators involved in intercellular communication.

METHODS

In the current study, the expression of inflammatory factors and miR-873a-5p in the lesion area and oedema area was evaluated in 15 patients with traumatic brain injury. Exosomes secreted by astrocytes were detected by immunofluorescence, Western blot and electron microscopy. A mouse model of TBI and an in vitro model of LPS-induced primary microglia were established to study the protective mechanism of exosomes from miR-873a-5p overexpressing in TBI-induced nerve injury.

RESULTS

We discovered that exosomes derived from activated astrocytes promote microglial M2 phenotype transformation following TBI. More than 100 miRNAs were detected in these astrocyte-derived exosomes. miR-873a-5p is a major component that was highly expressed in human traumatic brain tissue. Moreover, miR-873a-5p significantly inhibited LPS-induced microglial M1 phenotype transformation and the subsequent inflammation through decreased phosphorylation of ERK and NF-κB p65. This effect also greatly improved the modified neurological severity score (mNSS) and attenuated brain injury in a strictly controlled cortical impact mouse model.

CONCLUSIONS

Taken together, our research indicates that miRNAs in the exosomes derived from activated astrocytes play a key role in the astrocyte-microglia interaction. miR-873a-5p, as one of the main components of these astrocyte-derived exosomes, attenuated microglia-mediated neuroinflammation and improved neurological deficits following TBI by inhibiting the NF-κB signalling pathway. These findings suggest a potential role for miR-873a-5p in treating traumatic brain injury.

Potential microglia-based interventions for stroke

A large number of families worldwide suffer from the physical and mental burden posed by stroke. An increasing number of studies aimed at the prevention and treatment of stroke have been conducted. Specifically, manipulating the immune response to stroke is under intense investigation. Microglia are the principal immune cells in the brain and are the first line of defense against the pathophysiology induced by stroke. Increasing evidence has suggested that microglia play diverse roles that depend on dynamic interactions with neurons, astrocytes, and other neighboring cells both in the normal brain and under pathological conditions, including stroke. Moreover, there are dynamic alterations in microglial functions with respect to aging and sex differences in the human brain, which offer a deep understanding of the conditions of stroke patients of different ages and sex. Hence, we review the dynamic microglial reactions caused by aging, sex, and crosstalk with neighboring cells both in normal conditions and after stroke and relevant potential interventions.

The role of astrocytes in oxidative stress of central nervous system: A mixed blessing

Central nervous system (CNS) maintains a high level of metabolism, which leads to the generation of large amounts of free radicals, and it is also one of the most vulnerable organs to oxidative stress. Emerging evidences have shown that, as the key homeostatic cells in CNS, astrocytes are deeply involved in multiple aspects of CNS function including oxidative stress regulation. Besides, the redox level in CNS can in turn affect astrocytes in morphology and function. The complex and multiple roles of astrocytes indicate that their correct performance is crucial for the normal functioning of the CNS, and its dysfunction may result in the occurrence and progression of various neurological disorders. To date, the influence of astrocytes in CNS oxidative stress is rarely reviewed. Therefore, in this review we sum up the roles of astrocytes in redox regulation and the corresponding mechanisms under both normal and different pathological conditions.

Cellular Model of Endotoxin Tolerance in Astrocytes: Role of Interleukin 10 and Oxylipins

A phenomenon of endotoxin tolerance where prior exposure of cells to minute amounts of lipopolysaccharide (LPS) causes them to become refractory to a subsequent high-amount endotoxin challenge is well described for innate immune cells such as monocytes/macrophages, but it is still obscure for brain cells. We exposed primary rat cortical astrocytes to a long-term low-grade concentration of LPS, followed by stimulation with a middle-grade concentration of LPS. Inflammatory markers, i.e., pro-inflammatory cytokine TNFα, inducible enzymes COX-2 and iNOS, anti-inflammatory cytokine interleukin 10 (IL-10) detected at the mRNA and protein levels reveal similarities between astrocytes and macrophages in the model, i.e., tolerance in pro-inflammatory markers and priming in IL-10. Long-term or short-term treatment with IL-10 does not change cell sensitivity for LPS, which makes doubtful its involvement in the mechanisms of cell tolerance development. Significant changes occur in the oxylipin profiles measured by UPLC-MS/MS analysis. The priming occurs in the following compounds: 11-HETE, PGD₂, PGE₂, cyclopentenone prostaglandins, and TXB₂. Tolerance is observed for 12-HHT, PGF_2α, and 6-keto-PGF_1α. As far as we know, this is the first report on changes in oxylipin profiles in the endotoxin tolerance model. The data can greatly improve the understanding of oxylipins’ role in inflammatory and resolution processes in the brain and mechanisms of astrocyte involvement in neuroinflammation.

Blood-Related Toxicity after Traumatic Brain Injury: Potential Targets for Neuroprotection

Emergency visits, hospitalizations, and deaths due to traumatic brain injury (TBI) have increased significantly over the past few decades. While the primary early brain trauma is highly deleterious to the brain, the secondary injury post-TBI is postulated to significantly impact mortality. The presence of blood, particularly hemoglobin, and its breakdown products and key binding proteins and receptors modulating their clearance may contribute significantly to toxicity. Heme, hemin, and iron, for example, cause membrane lipid peroxidation, generate reactive oxygen species, and sensitize cells to noxious stimuli resulting in edema, cell death, and increased morbidity and mortality. A wide range of other mechanisms such as the immune system play pivotal roles in mediating secondary injury. Effective scavenging of all of these pro-oxidant and pro-inflammatory metabolites as well as controlling maladaptive immune responses is essential for limiting toxicity and secondary injury. Hemoglobin metabolism is mediated by key molecules such as haptoglobin, heme oxygenase, hemopexin, and ferritin. Genetic variability and dysfunction affecting these pathways (e.g., haptoglobin and heme oxygenase expression) have been implicated in the difference in susceptibility of individual patients to toxicity and may be target pathways for potential therapeutic interventions in TBI. Ongoing collaborative efforts are required to decipher the complexities of blood-related toxicity in TBI with an overarching goal of providing effective treatment options to all patients with TBI.

Molecular imaging of multiple sclerosis: from the clinical demand to novel radiotracers

Background

Brain PET imaging with different tracers is mainly clinically used in the field of neurodegenerative diseases and brain tumors. In recent years, the potential usefulness of PET has also gained attention in the field of MS. In fact, MS is a complex disease and several processes can be selected as a target for PET imaging. The use of PET with several different tracers has been mainly evaluated in the research setting to investigate disease pathophysiology (i.e. phenotypes, monitoring of progression) or to explore its use a surrogate end-point in clinical trials.

Results

We have reviewed PET imaging studies in MS in humans and animal models. Tracers have been grouped according to their pathophysiological targets (ie. tracers for myelin kinetic, neuroinflammation, and neurodegeneration). The emerging clinical indication for brain PET imaging in the differential diagnosis of suspected tumefactive demyelinated plaques as well as the clinical potential provided by PET images in view of the recent introduction of PET/MR technology are also addressed.

Conclusion

While several preclinical and fewer clinical studies have shown results, full-scale clinical development programs are needed to translate molecular imaging technologies into a clinical reality that could ideally fit into current precision medicine perspectives.

The detrimental effects of lipopolysaccharide-induced neuroinflammation on adult hippocampal neurogenesis depend on the duration of the pro-inflammatory response

Adult hippocampal neurogenesis is a finely tuned process regulated by extrinsic factors. Neuroinflammation is a hallmark of several pathological conditions underlying dysregulation of neurogenesis. In animal models, lipopolysaccharide (LPS)-induced neuroinflammation leads to a neurogenic decrease mainly associated to the early inflammatory response. However, it is not well understood how the neuroinflammatory response progresses over time and if neurogenesis continues to be diminished during the late neuroinflammatory response. Moreover, it is unknown if repeated intermittent administration of LPS along time induces a greater reduction in neurogenesis. We administered one single intraperitoneal injection of LPS or saline or four repeated injections (one per week) of LPS or saline to young-adult mice. A cohort of new cells was labeled with three 5-bromo-2-deoxyuridine injections (one per day) 4 days after the last LPS injection. We evaluated systemic and neuroinflammation-associated parameters and compared the effects of the late neuroinflammatory response on neurogenesis induced by each protocol. Our results show that 1) a single LPS injection leads to a late pro-inflammatory response characterized by microglial activation, moderate astrocytic reaction and increased interleukin-6 levels. This response correlates in time with decreased neurogenesis and 2) a repeated intermittent injection of LPS does not elicit a late pro-inflammatory response although activated microglia persists. The latter profile is not accompanied by a continued long-term hippocampal neurogenic decrease. Hereby, we provide evidence that the neuroinflammatory response is a dynamic process that progresses in a milieu-dependent manner and does not necessarily lead to a neurogenic decrease, highlighting the complex interaction between the immune system and neurogenesis.

Effect of the Lipid Peroxidation Product 4-Hydroxynonenal on Neuroinflammation in Microglial Cells: Protective Role of Quercetin and Monochloropivaloylquercetin

Objectives

The lipid peroxidation-derived aldehyde 4-hydroxynonenal (HNE) has been implicated in a number of oxidative stress-induced inflammatory pathologies such as neurodegenerative diseases and aging. In this regard, we investigated the effects of HNE on neuroinflammatory responses by measuring cyclooxygenase-2 (COX-2) and inducible nitric oxide synthase (iNOS) induction with cytokine production. In addition, we measured nuclear factor erythroid 2-related factor 2 (Nrf-2)/Kelch-like ECH-associated protein 1 (Keap1) signaling proteins, and antioxidant enzymes heme oxygenase-1 (HO-1) and nicotinamide adenine dinucleotide phosphate dehydrogenase, quinone 1 (NQO1), and compared the results with quercetin and monochloropivaloylquercetin (MPQ) pretreated microglial cells.

Materials and Methods

Cytotoxicity was determined by MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay and production of cytokines was determined by cytokine array. Furthermore, intracellular Nfr2/Keap1 signaling proteins, HO-1, NQO1, and COX-2 expression were analyzed by western blot in 2.5 μM HNE treated BV-2 cells.

Results

Inducible nitric oxide synthase (iNOS) and COX-2 mRNA levels were measured with reverse transcription-quantitative polymerase chain reaction. HNE induced both COX-2 mRNA and protein levels, iNOS mRNA expression, and cytokine production. In addition, HNE markedly increased Keap1 levels and decreased cytoplasmic Nrf-2 expression with antioxidant enzyme HO-1 levels. Quercetin and monochloropivaloylquercetin treatment alleviated neuroinflammatory responses in microglial cells, by decreasing COX-2 mRNA expression. Monochloropivaloylquercetin decreased cytoplasmic Keap1 levels and increased nuclear translocation of Nrf-2 resulted in induction of HO-1 and NQO1 expression.

Conclusion

These results suggest that HNE could be a link between oxidative stress and inflammation in BV-2 microglia cells. In particular, monochloropivaloylquercetin alleviated inflammation, probably by decreasing the expression of proinflammatory genes and strengthening the antioxidant defense system.

Stress and aging act through common mechanisms to elicit neuroinflammatory priming

Over the course of an animal's lifespan, there is a protracted breakdown in basic homeostatic functions. Stressors (both psychological and physiological) can accelerate this process and compromise multiple homeostatic mechanisms. For example, both stress and aging can modulate neuroinflammatory function and cause a primed phenotype resulting in a heightened neuroinflammatory profile upon immune activation. Microglia, the brain's resident myeloid cell, produce "silent" immune machinery in response to stress and aging that does not cause immediate immune activation; rather, these changes prime the cell for a subsequent immune insult. Primed microglia exhibit a hyperinflammatory response upon immune activation that can exacerbate pathology. In this review, we will explore parallels between stress- and aging-induced neuroinflammatory priming. First, we will provide a background on the basic principles of neuroimmunology. Next, we will discuss evidence that neuroinflammatory responses become primed in the context of both stress and aging. We will also describe cell-specific contributions to neuroinflammatory priming with a focus on microglia. Finally, common mechanisms underlying priming in the context of stress and aging will be discussed: these mechanisms include glucocorticoid signaling; accumulation of danger signals; dis-inhibition of microglia; and breakdown of circadian rhythms. Overall, there are multifarious parallels between stress- and aging-elicited neuroinflammatory priming, suggesting that stress may promote a form of premature aging. Further unravelling mechanisms underlying priming could lead to improved treatments for buffering against stress- and aging-elicited behavioral pathologies.

Microglia-Astrocyte Crosstalk: An Intimate Molecular Conversation

Microglia-astrocyte crosstalk has recently been at the forefront of glial research. Emerging evidence illustrates that microglia- and astrocyte-derived signals are the functional determinants for the fates of astrocytes and microglia, respectively. By releasing diverse signaling molecules, both microglia and astrocytes establish autocrine feedback and their bidirectional conversation for a tight reciprocal modulation during central nervous system (CNS) insult or injury. Microglia, the constant sensors of changes in the CNS microenvironment and restorers of tissue homeostasis, not only serve as the primary immune cells of the CNS but also regulate the innate immune functions of astrocytes. Similarly, microglia determine the functions of reactive astrocytes, ranging from neuroprotective to neurotoxic. Conversely, astrocytes through their secreted molecules regulate microglial phenotypes and functions ranging from motility to phagocytosis. Altogether, the microglia-astrocyte crosstalk is fundamental to neuronal functions and dysfunctions. This review discusses the current understanding of the intimate molecular conversation between microglia and astrocytes and outlines its potential implications in CNS health and disease.

Up-regulation of Dyrk1b promote astrocyte activation following lipopolysaccharide-induced neuroinflammation

Astrocytes become activated in response to different stimulation. Dyrk1b is an arginine-directed serine/threonineprotein kinase that is expressed at elevated levels in many cancers but remains unknown in the pathologies of neuroinflammation. In this study, in vivo, we demonstrated that Dyrk1b expression was significantly increased and reached a peak at 12 h after LPS injection via Western blot. Double immunofluorescence staining showed that Dyrk1b co-located with GFAP and Ki67. In vitro, the expression of Dyrk1b, Ki67 and cyclinD1 was gradually increased and reached a peak at 12 h in a time-dependent manner after 1 μg/mL LPS stimulation. Knockdown of Dyrk1b significantly reduced the expression of Ki67 and cyclinD1. In addition, the data exhibited that silenced Dyrk1b decreased the expression of p-STAT3 in primary astrocyte cells, and Dyrk1b interacted with STAT3 in LPS-induced neuroinflammation. In conclusion, these results suggested that Dyrk1b is increased and may play a crucial role in regulating astrocyte cell activation via interact with STAT3 in LPS-induced neuroinflammation.

Astrocytes, Microglia, and Parkinson's Disease

Astrocytes and microglia support well-being and well-function of the brain through diverse functions in both intact and injured brain. For example, astrocytes maintain homeostasis of microenvironment of the brain through up-taking ions and neurotransmitters, and provide growth factors and metabolites for neurons, etc. Microglia keep surveying surroundings, and remove abnormal synapses or respond to injury by isolating injury sites and expressing inflammatory cytokines. Therefore, their loss and/or functional alteration may be directly linked to brain diseases. Since Parkinson's disease (PD)-related genes are expressed in astrocytes and microglia, mutations of these genes may alter the functions of these cells, thereby contributing to disease onset and progression. Here, we review the roles of astrocytes and microglia in intact and injured brain, and discuss how PD genes regulate their functions.

Neuroprotective effect of polysaccharide separated from Perilla frutescens Britton var. acuta Kudo against H2O2-induced oxidative stress in HT22 hippocampus cells

This study was carried out to evaluate the neuroprotective activity of polysaccharide extracts isolated from Perilla frutescens (PEPF) in H₂O₂-treated HT22 hippocampus cells. The PEPF treatment was found to increase the anti-oxidant activities of HT22 hippocampus cells. PEPF treatment resulted in a significant protection of HT22 hippocampus cells against H₂O₂-induced neurotoxicity, this protection ultimately occurred through an inhibition of ROS-mediated intracellular Ca²⁺ levels leading to MAPKs and NF-κB, as well as the accumulation of PI3K/AKT and Nrf2-mediated HO-1/NQO1 pathways. Furthermore, PEPF not only decreased the expression of Bax, cytochrome c, and cleaved caspases-3, -8, and -9, but also increased the expression of PARP and Bcl-2 in the H₂O₂-treated HT22 hippocampus cells, which overall contributed to the neuroprotective action. PEPF retains its mitochondrial membrane potential and reduces the elevated levels of sub-G1 phase and apoptotic morphological features induced by H₂O₂. It also reduces the malondialdehyde levels and enhances the intracellular SOD activity.

Diversity of astroglial responses across human neurodegenerative disorders and brain aging

Astrogliopathy refers to alterations of astrocytes occurring in diseases of the nervous system, and it implies the involvement of astrocytes as key elements in the pathogenesis and pathology of diseases and injuries of the central nervous system. Reactive astrocytosis refers to the response of astrocytes to different insults to the nervous system, whereas astrocytopathy indicates hypertrophy, atrophy/degeneration and loss of function and pathological remodeling occurring as a primary cause of a disease or as a factor contributing to the development and progression of a particular disease. Reactive astrocytosis secondary to neuron loss and astrocytopathy due to intrinsic alterations of astrocytes occur in neurodegenerative diseases, overlap each other, and, together with astrocyte senescence, contribute to disease-specific astrogliopathy in aging and neurodegenerative diseases with abnormal protein aggregates in old age. In addition to the well-known increase in glial fibrillary acidic protein and other proteins in reactive astrocytes, astrocytopathy is evidenced by deposition of abnormal proteins such as β-amyloid, hyper-phosphorylated tau, abnormal α-synuclein, mutated huntingtin, phosphorylated TDP-43 and mutated SOD1, and PrPres , in Alzheimer's disease, tauopathies, Lewy body diseases, Huntington's disease, amyotrophic lateral sclerosis and Creutzfeldt-Jakob disease, respectively. Astrocytopathy in these diseases can also be manifested by impaired glutamate transport; abnormal metabolism and release of neurotransmitters; altered potassium, calcium and water channels resulting in abnormal ion and water homeostasis; abnormal glucose metabolism; abnormal lipid and, particularly, cholesterol metabolism; increased oxidative damage and altered oxidative stress responses; increased production of cytokines and mediators of the inflammatory response; altered expression of connexins with deterioration of cell-to-cell networks and transfer of gliotransmitters; and worsening function of the blood brain barrier, among others. Increased knowledge of these aspects will permit a better understanding of brain aging and neurodegenerative diseases in old age as complex disorders in which neurons are not the only players.

Pathogenic mechanisms following ischemic stroke

Stroke is the second most common cause of death and the leading cause of disability worldwide. Brain injury following stroke results from a complex series of pathophysiological events including excitotoxicity, oxidative and nitrative stress, inflammation, and apoptosis. Moreover, there is a mechanistic link between brain ischemia, innate and adaptive immune cells, intracranial atherosclerosis, and also the gut microbiota in modifying the cerebral responses to ischemic insult. There are very few treatments for stroke injuries, partly owing to an incomplete understanding of the diverse cellular and molecular changes that occur following ischemic stroke and that are responsible for neuronal death. Experimental discoveries have begun to define the cellular and molecular mechanisms involved in stroke injury, leading to the development of numerous agents that target various injury pathways. In the present article, we review the underlying pathophysiology of ischemic stroke and reveal the intertwined pathways that are promising therapeutic targets.

High salt-induced activation and expression of inflammatory cytokines in cultured astrocytes

Salt (sodium chloride, NaCl) accumulation in the brain is associated with various diseases of central nervous system (CNS). Activation of astrocytes is an important manifestation of pathophysiological processes in the CNS. However, the direct impact of high salt (HS) environment on astrocytes is unclear. In the current study, we found that high salt treatment can induce activation of astrocytes both in vivo and in vitro, manifested as morphological alteration coupled with increased expression of glial fibrillary acidic protein (GFAP). Additionally, HS upregulated the expression of tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6), interleukin-1β (IL-1β) and vascular endothelial growth factor (VEGF); however, its effects on transforming growth factor-β (TGF-β) expression were not evident. Furthermore, HS treatment induced increased phosphorylation of signal transducer and activator transcription 3 (STAT 3). Inhibition of Janus kinase 2 (JAK 2) by specific pharmacological antagonists, AG490, attenuated the activation of JAK2/STAT3 pathway and induction of GFAP and other pro-inflammatory factors, respectively. The results suggest that the aforementioned multiple inflammatory cytokines and mediators that may be linked to the HS induced pathogenesis of CNS via the JAK2/STAT3 signaling pathways.