Affective Immunology: The Crosstalk Between Microglia and Astrocytes Plays Key Role?

Astrocyte-Microglia Crosstalk: A Novel Target for the Treatment of Migraine

Migraine is a pervasive neurologic disease closely related to neurogenic inflammation. The astrocytes and microglia in the central nervous system are vital in inducing neurogenic inflammation in migraine. Recently, it has been found that there may be a crosstalk phenomenon between microglia and astrocytes, which plays a crucial part in the pathology and treatment of Alzheimer's disease and other central nervous system diseases closely related to inflammation, thus becoming a novel hotspot in neuroimmune research. However, the role of the crosstalk between microglia and astrocytes in the pathogenesis and treatment of migraine is yet to be discussed. Based on the preliminary literature reports, we have reviewed relevant evidence of the crosstalk between microglia and astrocytes in the pathogenesis of migraine and summarized the crosstalk pathways, thereby hoping to provide novel ideas for future research and treatment.

The microbiome-gut-brain axis in epilepsy: pharmacotherapeutic target from bench evidence for potential bedside applications

The gut-brain axis augments the bidirectional communication between the gut and brain and modulates gut homeostasis and the central nervous system through the hypothalamic-pituitary-adrenal axis, enteroendocrine system, neuroendocrine system, inflammatory and immune pathways. Preclinical and clinical reports showed that gut dysbiosis might play a major regulatory role in neurological diseases such as epilepsy, Parkinson's, multiple sclerosis, and Alzheimer's disease. Epilepsy is a chronic neurological disease that causes recurrent and unprovoked seizures, and numerous risk factors are implicated in developing epilepsy. Advanced consideration of the gut-microbiota-brain axis can reduce ambiguity about epilepsy pathology, antiepileptic drugs, and effective therapeutic targets. Gut microbiota sequencing analysis reported that the level of Proteobacteria, Verrucomicrobia, Fusobacteria, and Firmicutes was increased and the level of Actinobacteria and Bacteroidetes was decreased in epilepsy patients. Clinical and preclinical studies also indicated that probiotics, ketogenic diet, faecal microbiota transplantation, and antibiotics can improve gut dysbiosis and alleviate seizure by enhancing the abundance of healthy biota. This study aims to give an overview of the connection between gut microbiota, and epilepsy, how gut microbiome changes may cause epilepsy, and whether gut microbiome restoration could be used as a treatment for epilepsy.

Neuroprotective astroglial response to neural damage and its relevance to affective disorders

Astrocytes not only support neuronal function with essential roles in synaptic neurotransmission, action potential propagation, metabolic support, or neuroplastic and developmental adaptations. They also respond to damage or dysfunction in surrounding neurons and oligodendrocytes by releasing neurotrophic factors and other molecules that increase the survival of the supported cells or contribute to mechanisms of structural and molecular restoration. The neuroprotective responsiveness of astrocytes is based on their ability to sense signals of degeneration, metabolic jeopardy and structural damage, and on their aptitude to locally deliver specific molecules to remedy threats to the molecular and structural features of their cellular partners. To the extent that neuronal and other glial cell disturbances are known to occur in affective disorders, astrocyte responsiveness to those disturbances may help to better understand the roles astrocytes play in affective disorders. The astrocytic sensing apparatus supporting those responses involves receptors for neurotransmitters, purines, cell adhesion molecules and growth factors. Astrocytes also share with the immune system the capacity of responding to cytokines released upon neuronal damage. In addition, in responses to specific signals astrocytes release unique factors such as clusterin or humanin that have been shown to exert potent neuroprotective effects. Astrocytes integrate the signals above to further deliver structural lipids, removing toxic metabolites, stabilizing the osmotic environment, normalizing neurotransmitters, providing anti-oxidant protection, facilitating synaptogenesis and acting as barriers to contain varied deleterious signals, some of which have been described in brain regions relevant to affective disorders and related animal models. Since various of the injurious signals that activate astrocytes have been implicated in different aspects of the etiopathology of affective disorders, particularly in relation to the diagnosis of depression, potentiating the corresponding astrocyte neuroprotective responses may provide additional opportunities to improve or complement available pharmacological and behavioral therapies for affective disorders.

Microglia and Astrocytes in Alzheimer's Disease: Significance and Summary of Recent Advances

Alzheimer's disease, one of the most common forms of dementia, is characterized by a slow progression of cognitive impairment and neuronal loss. Currently, approved treatments for AD are hindered by various side effects and limited efficacy. Despite considerable research, practical treatments for AD have not been developed. Increasing evidence shows that glial cells, especially microglia and astrocytes, are essential in the initiation and progression of AD. During AD progression, activated resident microglia increases the ability of resting astrocytes to transform into reactive astrocytes, promoting neurodegeneration. Extensive clinical and molecular studies show the involvement of microglia and astrocyte-mediated neuroinflammation in AD pathology, indicating that microglia and astrocytes may be potential therapeutic targets for AD. This review will summarize the significant and recent advances of microglia and astrocytes in the pathogenesis of AD in three parts. First, we will review the typical pathological changes of AD and discuss microglia and astrocytes in terms of function and phenotypic changes. Second, we will describe microglia and astrocytes' physiological and pathological role in AD. These roles include the inflammatory response, "eat me" and "don't eat me" signals, Aβ seeding, propagation, clearance, synapse loss, synaptic pruning, remyelination, and demyelination. Last, we will review the pharmacological and non-pharmacological therapies targeting microglia and astrocytes in AD. We conclude that microglia and astrocytes are essential in the initiation and development of AD. Therefore, understanding the new role of microglia and astrocytes in AD progression is critical for future AD studies and clinical trials. Moreover, pharmacological, and non-pharmacological therapies targeting microglia and astrocytes, with specific studies investigating microglia and astrocyte-mediated neuronal damage and repair, may be a promising research direction for future studies regarding AD treatment and prevention.

Cognitive Functions, Neurotransmitter Alterations, and Hippocampal Microstructural Changes in Mice Caused by Feeding on Western Diet

Metabolic Dysfunction Associated Steatotic Liver Disease (MASLD) is the most common chronic liver disease in Western countries. It is becoming increasingly evident that peripheral organ-centered inflammatory diseases, including liver diseases, are linked with brain dysfunctions. Therefore, this study aims to unravel the effect of MASLD on brain histology, cognitive functions, and neurotransmitters. For this purpose, mice fed for 48 weeks on standard (SD) or Western diet (WD) were evaluated by behavioral tests, followed by sacrifice and analysis of the liver-brain axis including histopathology, immunohistochemistry, and biochemical analyses. Histological analysis of the liver showed features of Metabolic Dysfunction-Associated Steatohepatitis (MASH) in the WD-fed mice including lipid droplet accumulation, inflammation, and fibrosis. This was accompanied by an elevation of transaminase and alkaline phosphatase activities, increase in inflammatory cytokine and bile acid concentrations, as well as altered amino acid concentrations in the blood. Interestingly, compromised blood capillary morphology coupled with astrogliosis and microgliosis were observed in brain hippocampus of the WD mice, indicating neuroinflammation or a disrupted neurovascular unit. Moreover, attention was impaired in WD-fed mice along with the observations of impaired motor activity and balance, enhanced anxiety, and stereotyped head-twitch response (HTR) behaviors. Analysis of neurotransmitters and modulators including dopamine, serotonin, GABA, glutamate, and acetylcholine showed region-specific dysregulation in the brain of the WD-fed mice. In conclusion, the induction of MASH in mice is accompanied by the alteration of cellular morphology and neurotransmitter expression in the brain, associated with compromised cognitive functions.

Serum Levels of S100B Protein and Myelin Basic Protein as a Potential Biomarkers of Recurrent Depressive Disorders

Nowadays, nervous tissue damage proteins in serum are considered promising drug targets and biomarkers of Mood Disorders. In a cross-sectional naturalistic study, the S100B, MBP and GFAP levels in the blood serum were compared between two diagnostic groups (patients with Depressive Episode (DE, n = 28) and patients with Recurrent Depressive Disorder (RDD, n = 21)), and healthy controls (n = 25). The diagnostic value of serum markers was assessed by ROC analysis. In the DE group, we did not find changed levels of S100B, MBP and GFAP compared with controls. In the RDD group, we found decreased S100B level (p = 0.011) and increased MBP level (p = 0.015) in comparison to those in healthy controls. Provided ROC analysis indicates that MBP contributes to the development of a DE (AUC = 0.676; 95%Cl 0.525-0.826; p = 0.028), and S100B and MBP have a significant effect on the development of RDD (AUC = 0.732; 95%Cl 0.560-0.903; p = 0.013 and AUC = 0.712; 95%Cl 0.557-0.867; p = 0.015, correspondingly). The study of serum markers of nervous tissue damage in patients with a current DE indicates signs of disintegration of structural and functional relationships, dysfunction of gliotransmission, and impaired secretion of neurospecific proteins. Modified functions of astrocytes and oligodendrocytes are implicated in the pathophysiology of RDD.

Microbiota-gut-brain axis and ketogenic diet: how close are we to tackling epilepsy?

The microbiota-gut-brain axis refers to the intricate bidirectional communication between commensal microorganisms residing in the digestive tract and the central nervous system, along neuroendocrine, metabolic, immune, and inflammatory pathways. This axis has been suggested to play a role in several neurological disorders, such as Parkinson's disease, Alzheimer's disease, multiple sclerosis, and epilepsy, paving the way for microbiome-based intervention strategies for the mitigation and treatment of symptoms. Epilepsy is a multifaceted neurological condition affecting more than 50 million individuals worldwide, 30% of whom do not respond to conventional pharmacological therapies. Among the first-hand microbiota modulation strategies, nutritional interventions represent an easily applicable option in both clinical and home settings. In this narrative review, we summarize the mechanisms underlying the microbiota-gut-brain axis involvement in epilepsy, discuss the impact of antiepileptic drugs on the gut microbiome, and then the impact of a particular dietary pattern, the ketogenic diet, on the microbiota-gut-brain axis in epileptic patients. The investigation of the microbiota response to non-pharmacological therapies is an ever-expanding field with the potential to allow the design of increasingly accessible and successful intervention strategies.

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.

Astrocytes as a target for therapeutic strategies in epilepsy: current insights

Astrocytes are specialized non-neuronal glial cells of the central nervous system, contributing to neuronal excitability and synaptic transmission (gliotransmission). Astrocytes play a key roles in epileptogenesis and seizure generation. Epilepsy, as a chronic disorder characterized by neuronal hyperexcitation and hypersynchronization, is accompanied by substantial disturbances of glial cells and impairment of astrocytic functions and neuronal signaling. Anti-seizure drugs that provide symptomatic control of seizures primarily target neural activity. In epileptic patients with inadequate control of seizures with available anti-seizure drugs, novel therapeutic candidates are needed. These candidates should treat epilepsy with anti-epileptogenic and disease-modifying effects. Evidence from human and animal studies shows that astrocytes have value for developing new anti-seizure and anti-epileptogenic drugs. In this review, we present the key functions of astrocytes contributing to neuronal hyperexcitability and synaptic activity following an etiology-based approach. We analyze the role of astrocytes in both development (epileptogenesis) and generation of seizures (ictogenesis). Several promising new strategies that attempted to modify astroglial functions for treating epilepsy are being developed: (1) selective targeting of glia-related molecular mechanisms of glutamate transport; (2) modulation of tonic GABA release from astrocytes; (3) gliotransmission; (4) targeting the astrocytic Kir4.1-BDNF system; (5) astrocytic Na+/K+/ATPase activity; (6) targeting DNA hypo- or hypermethylation of candidate genes in astrocytes; (7) targeting astrocytic gap junction regulators; (8) targeting astrocytic adenosine kinase (the major adenosine-metabolizing enzyme); and (9) targeting microglia-astrocyte communication and inflammatory pathways. Novel disease-modifying therapeutic strategies have now been developed, such as astroglia-targeted gene therapy with a broad spectrum of genetic constructs to target astroglial cells.

Microbiota-gut-brain axis mechanisms in the complex network of bipolar disorders: potential clinical implications and translational opportunities

Bipolar disorders (BD) represent a severe leading disabling mental condition worldwide characterized by episodic and often progressive mood fluctuations with manic and depressive stages. The biological mechanisms underlying the pathophysiology of BD remain incompletely understood, but it seems that there is a complex picture of genetic and environmental factors implicated. Nowadays, gut microbiota is in the spotlight of new research related to this kind of psychiatric disorder, as it can be consistently related to several pathophysiological events observed in BD. In the context of the so-called microbiota-gut-brain (MGB) axis, it is shown to have a strong influence on host neuromodulation and endocrine functions (i.e., controlling the synthesis of neurotransmitters like serotonin or mediating the activation of the hypothalamic-pituitary-adrenal axis), as well as in modulation of host immune responses, critically regulating intestinal, systemic and brain inflammation (neuroinflammation). The present review aims to elucidate pathophysiological mechanisms derived from the MGB axis disruption and possible therapeutic approaches mainly focusing on gut microbiota in the complex network of BD. Understanding the mechanisms of gut microbiota and its bidirectional communication with the immune and other systems can shed light on the discovery of new therapies for improving the clinical management of these patients. Besides, the effect of psychiatric drugs on gut microbiota currently used in BD patients, together with new therapeutical approaches targeting this ecosystem (dietary patterns, probiotics, prebiotics, and other novelties) will also be contemplated.

Late chronic local inflammation, synaptic alterations, vascular remodeling and arteriovenous malformations in the brains of male rats exposed to repetitive low-level blast overpressures

In the course of military operations in modern war theaters, blast exposures are associated with the development of a variety of mental health disorders associated with a post-traumatic stress disorder-related features, including anxiety, impulsivity, insomnia, suicidality, depression, and cognitive decline. Several lines of evidence indicate that acute and chronic cerebral vascular alterations are involved in the development of these blast-induced neuropsychiatric changes. In the present study, we investigated late occurring neuropathological events associated with cerebrovascular alterations in a rat model of repetitive low-level blast-exposures (3 × 74.5 kPa). The observed events included hippocampal hypoperfusion associated with late-onset inflammation, vascular extracellular matrix degeneration, synaptic structural changes and neuronal loss. We also demonstrate that arteriovenous malformations in exposed animals are a direct consequence of blast-induced tissue tears. Overall, our results further identify the cerebral vasculature as a main target for blast-induced damage and support the urgent need to develop early therapeutic approaches for the prevention of blast-induced late-onset neurovascular degenerative processes.

Astrocyte-derived exosomal lncRNA 4933431K23Rik modulates microglial phenotype and improves post-traumatic recovery via SMAD7 regulation

Astrocyte-microglial interaction plays a crucial role in brain injury-associated neuroinflammation. Our previous data illustrated that astrocytes secrete microRNA, leading to anti-inflammatory effects on microglia. Long non-coding RNAs participate in neuroinflammation regulation after traumatic brain injury. However, the effect of astrocytes on microglial phenotype via long non-coding RNAs and the underlying molecular mechanisms remain elusive. We used long non-coding RNA sequencing on murine astrocytes and found that exosomal long non-coding RNA 4933431K23Rik attenuated traumatic brain injury-induced microglial activation in vitro and in vivo and ameliorated cognitive function deficiency. Furthermore, microRNA and messenger RNA sequencing together with binding prediction illustrated that exosomal long non-coding RNA 4933431K23Rik up-regulates E2F7 and TFAP2C expression by sponging miR-10a-5p. Additionally, E2F7 and TFAP2C, as transcription factors, regulated microglial Smad7 expression. Using Cx3cr1-Smad7 overexpression of adeno-associated virus, microglia specifically overexpressed Smad7 in the attenuation of neuroinflammation, resulting in less cognitive deficiency after traumatic brain injury. Mechanically, overexpressed Smad7 physically binds to IκBα and inhibits its ubiquitination, preventing NF-κB signaling activation. The Smad7 activator asiaticoside alleviates neuroinflammation and protects neuronal function in traumatic brain injury mice. This study revealed that an exosomal long non-coding RNA from astrocytes attenuates microglial activation after traumatic brain injury by up-regulating Smad7, providing a potential therapeutic target.

Glioma-associated microglia/macrophages (GAMs) in glioblastoma: Immune function in the tumor microenvironment and implications for immunotherapy

Glioma is a mixed solid tumor composed of neoplastic and non-neoplastic components. Glioma-associated macrophages and microglia (GAMs) are crucial elements of the glioma tumor microenvironment (TME), regulating tumor growth, invasion, and recurrence. GAMs are also profoundly influenced by glioma cells. Recent studies have revealed the intricate relationship between TME and GAMs. In this updated review, we provide an overview of the interaction between glioma TME and GAMs based on previous studies. We also summarize a series of immunotherapies targeting GAMs, including clinical trials and preclinical studies. Specifically, we discuss the origin of microglia in the central nervous system and the recruitment of GAMs in the glioma background. We also cover the mechanisms through which GAMs regulate various processes associated with glioma development, such as invasiveness, angiogenesis, immunosuppression, recurrence, etc. Overall, GAMs play a significant role in the tumor biology of glioma, and a better understanding of the interaction between GAMs and glioma could catalyze the development of new and effective immunotherapies for this deadly malignancy.

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

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

Sterol dysregulation in Smith-Lemli-Opitz syndrome causes astrocyte immune reactivity through microglia crosstalk

Owing to the need for de novo cholesterol synthesis and cholesterol-enriched structures within the nervous system, cholesterol homeostasis is critical to neurodevelopment. Diseases caused by genetic disruption of cholesterol biosynthesis, such as Smith-Lemli-Opitz syndrome, which is caused by mutations in 7-dehydrocholesterol reductase (DHCR7), frequently result in broad neurological deficits. Although astrocytes regulate multiple neural processes ranging from cell migration to network-level communication, immunological activation of astrocytes is a hallmark pathology in many diseases. However, the impact of DHCR7 on astrocyte function and immune activation remains unknown. We demonstrate that astrocytes from Dhcr7 mutant mice display hallmark signs of reactivity, including increased expression of glial fibrillary acidic protein (GFAP) and cellular hypertrophy. Transcript analyses demonstrate extensive Dhcr7 astrocyte immune activation, hyper-responsiveness to glutamate stimulation and altered calcium flux. We further determine that the impacts of Dhcr7 are not astrocyte intrinsic but result from non-cell-autonomous effects of microglia. Our data suggest that astrocyte-microglia crosstalk likely contributes to the neurological phenotypes observed in disorders of cholesterol biosynthesis. Additionally, these data further elucidate a role for cholesterol metabolism within the astrocyte-microglia immune axis, with possible implications in other neurological diseases.

The implication of a diversity of non-neuronal cells in disorders affecting brain networks

In the central nervous system (CNS) neurons are classically considered the functional unit of the brain. Analysis of the physical connections and co-activation of neurons, referred to as structural and functional connectivity, respectively, is a metric used to understand their interplay at a higher level. A myriad of glial cell types throughout the brain composed of microglia, astrocytes and oligodendrocytes are key players in the maintenance and regulation of neuronal network dynamics. Microglia are the central immune cells of the CNS, able to affect neuronal populations in number and connectivity, allowing for maturation and plasticity of the CNS. Microglia and astrocytes are part of the neurovascular unit, and together they are essential to protect and supply nutrients to the CNS. Oligodendrocytes are known for their canonical role in axonal myelination, but also contribute, with microglia and astrocytes, to CNS energy metabolism. Glial cells can achieve this variety of roles because of their heterogeneous populations comprised of different states. The neuroglial relationship can be compromised in various manners in case of pathologies affecting development and plasticity of the CNS, but also consciousness and mood. This review covers structural and functional connectivity alterations in schizophrenia, major depressive disorder, and disorder of consciousness, as well as their correlation with vascular connectivity. These networks are further explored at the cellular scale by integrating the role of glial cell diversity across the CNS to explain how these networks are affected in pathology.

Neurobiological mechanisms of mood disorders: Stress vulnerability and resilience

Stress is an important factor in the development of several human pathologies. The response of rodents and humans to stress depends on many factors; some people and rodents develop stress-related mood disorders, such as depression and anxiety in humans, depression-like and anxiety-like behavior in mice and rats, while others report no new psychological symptoms in response to chronic or acute stress, and are considered susceptible and resilient to stress, respectively. Resilience is defined as the ability to thrive in the face of adversity and is a learned process that can help protect against occupational stressors and mental illnesses. There is growing interest in the underlying mechanisms involved in resilience and vulnerability to depression caused by stress, and some studies have demonstrated that individual variability in the way animals and humans respond to stress depends on several mechanisms, such as oxidative stress, neuronal plasticity, immunology and genetic factors, among others not discussed in this review, this review provides a general overview about this mechanism.

Astrocyte reactivation in medial prefrontal cortex contributes to obesity-promoted depressive-like behaviors

BACKGROUND

Little is known about how the obesogenic environment influences emotional states associated with glial responses and neuronal function. Here, we investigated glial reactivation and neuronal electrophysiological properties in emotion-related brain regions of high-fat diet (HFD) and ob/ob mice under chronic stress.

METHODS

The glial reactivation and neuronal activities in emotion-related brain regions were analyzed among normal diet mice (ND), HFD mice, wild-type mice, and ob/ob mice. To further activate or inhibit astrocytes in medial prefrontal cortex (mPFC), we injected astrocytes specific Gq-AAV or Gi-AAV into mPFC and ongoing treated mice with CNO.

RESULTS

The results showed that obesogenic factors per se had no significant effect on neuronal activities in emotion-related brain regions, or on behavioral performance. However, exposure to a chronic stressor profoundly reduced the frequency of spontaneous inhibitory postsynaptic currents (sIPSCs) and spontaneous excitatory postsynaptic currents (sEPSCs) in the mPFC; depressive-like behaviors were seen, accompanied by significant upregulation of astrocyte reactivation. We identified resilient and susceptible mice among chronic social defeat stress-exposed HFD mice. As expected, astrocyte reactivity was upregulated, while neuronal activity was depressed, in the mPFC of susceptible compared to resilient mice. Furthermore, activating astrocytes resulted in similar levels of neuronal activity and depressive-like behaviors between resilient and susceptible mice. Additionally, inhibiting astrocyte reactivation in the mPFC of HFD mice upregulated neuronal activities and inhibited depressive-like behaviors.

CONCLUSIONS

These observations indicate that obesogenic factors increase the risk of depression, and improve our understanding of the pathological relationship between obesity and depression.

Neonatal Rat Glia Cultured in Physiological Normoxia for Modeling Neuropathological Conditions In Vitro

Cell culture conditions were proven to highly affect crucial biological processes like proliferation, differentiation, intercellular crosstalk, and senescence. Oxygen tension is one of the major factors influencing cell metabolism and thus, modulating cellular response to pathophysiological conditions. In this context, the presented study aimed at the development of a protocol for efficient culture of rat neonatal glial cells (microglia, astrocytes, and oligodendrocytes) in oxygen concentrations relevant to the nervous tissue. The protocol allows for obtaining three major cell populations, which play crucial roles in sustaining tissue homeostasis and are known to be activated in response to a wide spectrum of external stimuli. The cells are cultured in media without supplement addition to avoid potential modulation of cell processes. The application of active biomolecules for coating culturing surfaces might be useful for mirroring physiological cell interactions with extracellular matrix components. The cell fractions can be assembled as cocultures to further evaluate investigated mechanisms, intercellular crosstalk, or cell response to tested pharmacological compounds. Applying additional procedures, like transient oxygen and glucose deprivation, allows to mimic in vitro the selected pathophysiological conditions. The presented culture system for neonatal rat glial cells is a highly useful tool for in vitro modeling selected neuropathological conditions.

Mechanistic Studies of Gypenosides in Microglial State Transition and its Implications in Depression-Like Behaviors: Role of TLR4/MyD88/NF-κB Signaling

Depression is a prevalent psychiatric disorder. Microglial state transition has been found in many neurological disorders including depression. Gypenosides (Gypenosides I-LXXVIII, Gps) are saponin extracts isolated from the traditional Chinese herb Gynostemma pentaphyllum (Thunb.) Makino that exert anti-inflammatory and neuroprotective activities and regulate depression-like behaviors. However, its effect on microglial state transition in depression remains unknown. We aimed to evaluate the potential relationship between Gps and TLR4/MyD88/NF-κB signaling in microglial state transition in vitro and in vivo. First, BV-2 cells (microglial cell line) were exposed to lipopolysaccharides (LPS) and treated with 10 or 5 μg/ml Gps. Second, the chronic unpredictable mild stress (CUMS)-induced depression mouse model was used to investigate the antidepressant-like behaviors effects of Gps (100 or 50 mg/kg). We determined depression-like behaviors using the open-field test (OFT), forced swim test (FST), and sucrose preference test (SPT). Proteins and inflammatory factors in the TLR4/MyD88/NF-κB signaling pathway and the different microglial reaction states markers were subsequently conducted using enzyme-linked immunosorbent assay, immunocytochemistry, immunofluorescence, qPCR, or Western blotting analyses to evaluate the anti-inflammatory and antidepressant properties of Gps and the underlying molecular mechanisms. We found that Gps regulated the microglial cell line state transition in LPS-exposed BV-2 cells, as evidenced by the significantly decreased expression of inflammatory parameters iNOS, IL-1β, IL-6, and TNF-α and significantly promoted anti-inflammatory microglial phenotypes markers CD206 (Mrc1) and IL-10. More importantly, Gps protected against the loss of monoamine neurotransmitters and depression-like behavior in a mouse model of depression, which was accompanied by a regulation of the microglial state transition. Mechanistically, Gps inhibited TLR4/MyD88/NF-κB signaling, which reduced the release of downstream inflammatory cytokines (IL-1β, IL-6, and TNF-α) and promoted microglial phenotype transition, which all together contributed to the antidepressant effect. Our results suggest that Gps prevents depression-like behaviors by regulating the microglial state transition and inhibiting the TLR4/MyD88/NF-κB signaling pathway. Thus, Gps could be a promising therapeutic strategy to prevent and treat depression-like behaviors and other psychiatric disorders.

Passive immunization against phosphorylated tau improves features of Huntington's disease pathology

Huntington's disease is classically described as a neurodegenerative disorder of monogenic aetiology. The disease is characterized by an abnormal polyglutamine expansion in the huntingtin gene, which drives the toxicity of the mutated form of the protein. However, accumulation of the microtubule-associated protein tau, which is involved in a number of neurological disorders, has also been observed in patients with Huntington's disease. In order to unravel the contribution of tau hyperphosphorylation to hallmark features of Huntington's disease, we administered weekly intraperitoneal injections of the anti-tau pS202 CP13 monoclonal antibody to zQ175 mice and characterized the resulting behavioral and biochemical changes. After 12 weeks of treatment, motor impairments, cognitive performance and general health were improved in zQ175 mice along with a significant reduction in hippocampal pS202 tau levels. Despite the lack of effect of CP13 on neuronal markers associated with Huntington's disease pathology, tau-targeting enzymes and gliosis, CP13 was shown to directly impact mutant huntingtin aggregation such that brain levels of amyloid fibrils and huntingtin oligomers were decreased, while larger huntingtin protein aggregates were increased. Investigation of CP13 treatment of Huntington's disease patient-derived induced pluripotent stem cells (iPSCs) revealed a reduction in pS202 levels in differentiated cortical neurons and a rescue of neurite length. Collectively, these findings suggest that attenuating tau pathology could mitigate behavioral and molecular hallmarks associated with Huntington's disease.

The Crosstalk Between Neurons and Glia in Methamphetamine-Induced Neuroinflammation

Methamphetamine (METH), an illicit psycho-stimulant, is widely known as an addictive drug that may cause neurotoxic effects. Previous researches on METH abuse have mainly focused on neurotransmitters, such as dopamine and glutamate. However, there is growing evidence that neuroinflammation also plays an important role in the etiology and pathophysiology of brain dysfunction induced by METH abuse. This has cast a spotlight on the research of microglia and astrocyte, which are critical mediators of neuroimmune pathology in recent years. In the central nervous system (CNS) immunity, abnormalities of the microglia and astrocytes have been observed in METH abusers from both postmortem and preclinical studies. The bidirectional communication between neurons and glia is essential for the homeostasis and biological function of the CNS while activation of glia induces the release of cytokines and chemokines during pathological conditions, which will affect the neuron-glia interactions and lead to adverse behavioral consequences. However, the underlying mechanisms of interaction between neurons and glia in METH-induced neuroinflammation remain elusive. Notably, discovering and further understanding glial activity and functions, as well as the crosstalk between neurons and glia may help to explain the pathogenesis of METH abuse and behavioral changes in abusers. In this review, we will discuss the current understanding of the crosstalk between neurons and glia in METH-induced neuroinflammation. We also review the existing microglia-astrocyte interaction under METH exposure. We hope the present review will lead the way for more studies on the development of new therapeutic strategies for METH abuse in the near future.

Blood-Brain Barrier Dysfunction in the Pathogenesis of Major Depressive Disorder

Major depression represents a complex and prevalent psychological disease that is characterized by persistent depressed mood, impaired cognitive function and complicated pathophysiological and neuroendocrine alterations. Despite the multifactorial etiology of depression, one of the most recent factors to be identified as playing a critical role in the development of depression is blood-brain barrier (BBB) disruption. The occurrence of BBB integrity disruption contributes to the disturbance of brain homeostasis and leads to complications of neurological diseases, such as stroke, chronic neurodegenerative disorders, neuroinflammatory disorders. Recently, BBB associated tight junction disruption has been shown to implicate in the pathophysiology of depression and contribute to increased susceptibility to depression. However, the underlying mechanisms and importance of BBB damage in depression remains largely unknown. This review highlights how BBB disruption regulates the depression process and the possible molecular mechanisms involved in development of depression-induced BBB dysfunction. Moreover, insight on promising therapeutic targets for treatment of depression with associated BBB dysfunctions are also discussed.

Microbiota-Gut-Brain Axis and Epilepsy: A Review on Mechanisms and Potential Therapeutics

The gut-brain axis refers to the bidirectional communication between the gut and brain, and regulates intestinal homeostasis and the central nervous system via neural networks and neuroendocrine, immune, and inflammatory pathways. The development of sequencing technology has evidenced the key regulatory role of the gut microbiota in several neurological disorders, including Parkinson's disease, Alzheimer's disease, and multiple sclerosis. Epilepsy is a complex disease with multiple risk factors that affect more than 50 million people worldwide; nearly 30% of patients with epilepsy cannot be controlled with drugs. Interestingly, patients with inflammatory bowel disease are more susceptible to epilepsy, and a ketogenic diet is an effective treatment for patients with intractable epilepsy. Based on these clinical facts, the role of the microbiome and the gut-brain axis in epilepsy cannot be ignored. In this review, we discuss the relationship between the gut microbiota and epilepsy, summarize the possible pathogenic mechanisms of epilepsy from the perspective of the microbiota gut-brain axis, and discuss novel therapies targeting the gut microbiota. A better understanding of the role of the microbiota in the gut-brain axis, especially the intestinal one, would help investigate the mechanism, diagnosis, prognosis evaluation, and treatment of intractable epilepsy.

Plasma Levels of the Cytokines B Cell-Activating Factor (BAFF) and A Proliferation-Inducing Ligand (APRIL) in Schizophrenia, Bipolar, and Major Depressive Disorder: A Cross Sectional, Multisite Study

BACKGROUND

Immune dysfunction has been implicated in the pathogenesis of schizophrenia and other nonaffective psychosis (SCZ), bipolar spectrum disorder (BIP) and major depressive disorder (MDD). The cytokines B cell-activating factor (BAFF) and A proliferation-inducing ligand (APRIL) belong to the tumor necrosis factor (TNF) super family and are essential in orchestrating immune responses. Abnormal levels of BAFF and APRIL have been found in autoimmune diseases with CNS affection.

METHODS

We investigated if plasma levels of BAFF and APRIL differed between patients with SCZ, BIP, and MDD with psychotic symptoms (n = 2009) and healthy control subjects (HC, n = 1212), and tested for associations with psychotic symptom load, controlling for sociodemographic status, antipsychotic and other psychotropic medication, smoking, body-mass-index, and high sensitivity CRP.

RESULTS

Plasma APRIL level was significantly lower across all patient groups compared to HC (P < .001; Cohen's d = 0.33), and in SCZ compared to HC (P < .001; d = 0.28) and in BIP compared to HC (P < .001; d = 0.37). Lower plasma APRIL was associated with higher psychotic symptom load with nominal significance (P = .017), but not with any other clinical characteristics. Plasma BAFF was not significantly different across patient groups vs HC, but significantly higher in BIP compared to HC (P = .040; d = 0.12) and SCZ (P = .027; d = 0.10).

CONCLUSIONS

These results show aberrant levels of BAFF and APRIL and association with psychotic symptoms in patients with SCZ and BIP. This suggest that dysregulation of the TNF system, mediated by BAFF and APRIL, is involved in the pathophysiology of psychotic disorders.

What Guides Peripheral Immune Cells into the Central Nervous System?

Multiple sclerosis (MS), an immune-mediated demyelinating disease of the central nervous system (CNS), initially presents with a relapsing-remitting disease course. During this early stage of the disease, leukocytes cross the blood–brain barrier to drive the formation of focal demyelinating plaques. Disease-modifying agents that modulate or suppress the peripheral immune system provide a therapeutic benefit during relapsing-remitting MS (RRMS). The majority of individuals with RRMS ultimately enter a secondary progressive disease stage with a progressive accumulation of neurologic deficits. The cellular and molecular basis for this transition is unclear and the role of inflammation during the secondary progressive disease stage is a subject of intense and controversial debate. In this review article, we discuss the following main hypothesis: during both disease stages, peripheral immune cells are triggered by CNS-intrinsic stimuli to invade the brain parenchyma. Furthermore, we outline the different neuroanatomical routes by which peripheral immune cells might migrate from the periphery into the CNS.