Functions of microglia in the central nervous system--beyond the immune response

Cannabidiol improves the cognitive function of SAMP8 AD model mice involving the microbiota-gut-brain axis

Cannabidiol (CBD), a natural component extracted from Cannabis sativa L. exerts neuroprotective, antioxidant, and anti-inflammatory effects in Alzheimer's disease (AD), a disease characterized by impaired cognition and accumulation of amyloid-B peptides (Aβ). Interactions between the gut and central nervous system (microbiota-gut-brain axis) play a critical role in the pathogenesis of neurodegenerative disorder AD. At present investigations into the mechanisms underlying the neuroprotective action of CBD in AD are not conclusive. The aim of this study was thus to examine the influence of CBD on cognition and involvement of the microbiota-gut-brain axis using a senescence-accelerated mouse prone 8 (SAMP8) model. Data demonstrated that administration of CBD to SAMP8 mice improved cognitive function as evidenced from the Morris water maze test and increased hippocampal activated microglia shift from M1 to M2. In addition, CBD elevated levels of Bacteriodetes associated with a fall in Firmicutes providing morphologically a protective intestinal barrier which subsequently reduced leakage of intestinal toxic metabolites. Further, CBD was found to reduce the levels of hippocampal and colon epithelial cells lipopolysaccharide (LPS), known to be increased in AD leading to impaired gastrointestinal motility, thereby promoting neuroinflammation and subsequent neuronal death. Our findings demonstrated that CBD may be considered a beneficial therapeutic drug to counteract AD-mediated cognitive impairment and restore gut microbial functions associated with the observed neuroprotective mechanisms.

A novel in vitro model for investigating oligodendroglial maturation and myelin deposition under demyelinating and remyelinating conditions: Impact of microglial depletion and repopulation

Experimental models of multiple sclerosis (MS) have significantly contributed to our understanding of pathophysiology and the development of therapeutic interventions. Various in vivo animal models have successfully replicated key features of MS and associated pathophysiological processes, shedding light on the sequence of events leading to disease initiation, progression, and resolution. Nevertheless, these models often entail substantial costs and prolonged treatment periods. In contrast, in vitro models offer distinct advantages, including cost-effectiveness and precise control over experimental conditions, thereby facilitating more reproducible results. We have developed a novel in vitro model tailored to the study of oligodendroglial maturation and myelin deposition under demyelinating and remyelinating conditions, which encompasses all the cell types present in the central nervous system (CNS). Of note, our model enables the evaluation of microglial cell commitment through a protocol involving their depletion and subsequent repopulation. Given that the development and survival of microglia are critically reliant on colony-stimulating factor-1 receptor (CSF-1R) signaling, we have employed CSF-1R inhibition to effectively deplete microglia. This versatile model holds promise for the assessment of potential therapies aimed at promoting oligodendroglial differentiation to safeguard and repair myelin, hence mitigate neurodegenerative processes.

Quantifying microglial morphology: an insight into function

Microglia are specialized immune cells unique to the central nervous system (CNS). Microglia have a highly plastic morphology that changes rapidly in response to injury or infection. Qualitative and quantitative measurements of ever-changing microglial morphology are considered a cornerstone of many microglia-centric research studies. The distinctive morphological variations seen in microglia are a useful marker of inflammation and severity of tissue damage. Although a wide array of damage-associated microglial morphologies has been documented, the exact functions of these distinct morphologies are not fully understood. In this review, we discuss how microglia morphology is not synonymous with microglia function, however, morphological outcomes can be used to make inferences about microglial function. For a comprehensive examination of the reactive status of a microglial cell, both histological and genetic approaches should be combined. However, the importance of quality immunohistochemistry-based analyses should not be overlooked as they can succinctly answer many research questions.

A review of concepts and methods for FTIR imaging of biomarker changes in the post-stroke brain

Stroke represents a core area of study in neurosciences and public health due to its global contribution toward mortality and disability. The intricate pathophysiology of stroke, including ischemic and hemorrhagic events, involves the interruption in oxygen and nutrient delivery to the brain. Disruption of these crucial processes in the central nervous system leads to metabolic dysregulation and cell death. Fourier transform infrared (FTIR) spectroscopy can simultaneously measure total protein and lipid content along with a number of key biomarkers within brain tissue that cannot be observed using conventional techniques. FTIR imaging provides the opportunity to visualize this information in tissue which has not been chemically treated prior to analysis, thus retaining the spatial distribution and in situ chemical information. Here we present a review of FTIR imaging methods for investigating the biomarker responses in the post-stroke brain.

Is the Central Nervous System Reservoir a Hurdle for an HIV Cure?

There is currently no cure for HIV infection although adherence to effective antiretroviral therapy (ART) suppresses replication of the virus in blood, increases CD4+ T-cell counts, reverses immunodeficiency, and increases life expectancy. Despite these substantial advances, ART is a lifelong treatment for people with HIV (PWH) and upon cessation or interruption, the virus quickly rebounds in plasma and anatomic sites, including the central nervous system (CNS), resulting in disease progression. With recent advances in quantifying viral burden, detection of genetically intact viral genomes, and isolation of replication-competent virus from brain tissues of PWH receiving ART, it has become apparent that the CNS viral reservoir (largely comprised of macrophage type cells) poses a substantial challenge for HIV cure strategies. Other obstacles impacting the curing of HIV include ageing populations, substance use, comorbidities, limited antiretroviral drug efficacy in CNS cells, and ART-associated neurotoxicity. Herein, we review recent findings, including studies of the proviral integration sites, reservoir decay rates, and new treatment/prevention strategies in the context of the CNS, together with highlighting the next steps for investigations of the CNS as a viral reservoir.

Microglia in pediatric brain tumors: The missing link to successful immunotherapy

Brain tumors are the leading cause of cancer-related mortality in children. Despite the development of immunotherapeutic strategies for adult brain tumors, progress in pediatric neuro-oncology has been hindered by the complex and poorly understood nature of the brain's immune system during early development, a phase that is critical for the onset of many pediatric brain tumors. A defining characteristic of these tumors is the abundance of microglia, the resident immune cells of the central nervous system. In this review, we explore the concept of microglial diversity across brain regions and throughout development and discuss how their maturation stage may contribute to tumor growth in children. We also summarize the current knowledge on the roles of microglia in common pediatric brain tumor entities and provide examples of myeloid-based immunotherapeutic strategies. Our review underscores the importance of microglial plasticity in pediatric brain tumors and its significance for developing effective immunotherapeutic strategies.

Proteomic discovery of prognostic protein biomarkers for persisting problems after mild traumatic brain injury

Some individuals with mild traumatic brain injury (mTBI), also known as concussion, have neuropsychiatric and physical problems that last longer than a few months. Symptoms following mTBI are not only impacted by the kind and severity of the injury but also by the post-injury experience and the individual's responses to it, making the persistence of mTBI particularly difficult to predict. We aimed to identify prognostic blood-based protein biomarkers predicting 6-month outcomes, in light of the clinical course after the injury, in a longitudinal mTBI cohort (N = 42). Among 420 target proteins quantified by multiple-reaction monitoring-mass spectrometry assays of blood samples, 31, 43, and 15 proteins were significantly associated with the poor recovery of neuropsychological symptoms at < 72 h, 1 week, and 1 month after the injury, respectively. Sequential associations among clinical assessments (depressive symptoms and cognitive function) affecting the 6-month outcomes were evaluated. Then, candidate biomarker proteins indirectly affecting the outcome via neuropsychological symptoms were identified. Using the identified proteins, prognostic models that can predict the 6-month outcome of mTBI were developed. These protein biomarkers established in the context of the clinical course of mTBI may have potential for clinical application.

Theoretical design for covering Engeletin with functionalized nanostructure-lipid carriers as neuroprotective agents against Huntington's disease via the nasal-brain route

Objective: To propose a theoretical formulation of engeletin-nanostructured lipid nanocarriers for improved delivery and increased bioavailability in treating Huntington's disease (HD). Methods: We conducted a literature review of the pathophysiology of HD and the limitations of currently available medications. We also reviewed the potential therapeutic benefits of engeletin, a flavanol glycoside, in treating HD through the Keap1/nrf2 pathway. We then proposed a theoretical formulation of engeletin-nanostructured lipid nanocarriers for improved delivery across the blood-brain barrier (BBB) and increased bioavailability. Results: HD is an autosomal dominant neurological illness caused by a repetition of the cytosine-adenine-guanine trinucleotide, producing a mutant protein called Huntingtin, which degenerates the brain's motor and cognitive functions. Excitotoxicity, mitochondrial dysfunction, oxidative stress, elevated concentration of ROS and RNS, neuroinflammation, and protein aggregation significantly impact HD development. Current therapeutic medications can postpone HD symptoms but have long-term adverse effects when used regularly. Herbal medications such as engeletin have drawn attention due to their minimal side effects. Engeletin has been shown to reduce mitochondrial dysfunction and suppress inflammation through the Keap1/NRF2 pathway. However, its limited solubility and permeability hinder it from reaching the target site. A theoretical formulation of engeletin-nanostructured lipid nanocarriers may allow for free transit over the BBB due to offering a similar composition to the natural lipids present in the body a lipid solubility and increase bioavailability, potentially leading to a cure or prevention of HD. Conclusion: The theoretical formulation of engeletin-nanostructured lipid nanocarriers has the potential to improve delivery and increase the bioavailability of engeletin in the treatment of HD, which may lead to a cure or prevention of this fatal illness.

Microglial tissue surveillance: The never-resting gardener in the developing and adult CNS

Immunosurveillance by microglia is a dynamic process in the central nervous system (CNS) with versatile functions to maintain tissue homeostasis and provide immune defense. A tightly controlled microglia network throughout the CNS parenchyma facilitates efficient immunosurveillance, where each cell guards a certain tissue territory. Each cell is constantly surveilling its environment and the surrounding cells, screening for pathogens but also removing cell debris and metabolites, grooming neighboring cells and facilitating cellular crosstalk. In the absence of inflammation, this "tissue surveillance" by microglia presents an essential process for CNS homeostasis and development. In this review, we provide a summary on different tissue surveillance functions mediated by microglia, the underlying molecular machineries, and how defects, such as genetic mutations, can alter these surveillance mechanisms and cause disease onset.

Inhibition of Galectins and the P2X7 Purinergic Receptor as a Therapeutic Approach in the Neurovascular Inflammation of Diabetic Retinopathy

Diabetic retinopathy (DR) is the most frequent microvascular retinal complication of diabetic patients, contributing to loss of vision. Recently, retinal neuroinflammation and neurodegeneration have emerged as key players in DR progression, and therefore, this review examines the neuroinflammatory molecular basis of DR. We focus on four important aspects of retinal neuroinflammation: (i) the exacerbation of endoplasmic reticulum (ER) stress; (ii) the activation of the NLRP3 inflammasome; (iii) the role of galectins; and (iv) the activation of purinergic 2X7 receptor (P2X7R). Moreover, this review proposes the selective inhibition of galectins and the P2X7R as a potential pharmacological approach to prevent the progression of DR.

Xeno-Free Biomimetic ECM Model for Investigation of Matrix Composition and Stiffness on Astrocyte Cell Response

Astrocytes, highly specialized glial cells, play a critical role in neuronal function. Variations in brain extracellular matrix (ECM) during development and disease can significantly alter astrocyte cell function. Age-related changes in ECM properties have been linked to neurodegenerative diseases such as Alzheimer's disease. The goal of this study was to develop hydrogel-based biomimetic ECM models with varying stiffness and evaluate the effects of ECM composition and stiffness on astrocyte cell response. Xeno-free ECM models were synthesized by combining varying ratios of human collagen and thiolated hyaluronic acid (HA) crosslinked with polyethylene glycol diacrylate. Results showed that modulating ECM composition yielded hydrogels with varying stiffnesses that match the stiffness of the native brain ECM. Collagen-rich hydrogels swell more and exhibit greater stability. Higher metabolic activity and greater cell spreading was observed in hydrogels with lower HA. Soft hydrogels trigger astrocyte activation indicated by greater cell spreading, high GFAP expression and low ALDH1L1 expression. This work presents a baseline ECM model to investigate the synergistic effects of ECM composition and stiffness on astrocytes, which could be further developed to identify key ECM biomarkers and formulate new therapies to alleviate the impact of ECM changes on the onset and progression of neurodegenerative diseases.

The Central Nervous System Source Modulates Microglia Function and Morphology In Vitro

The regional heterogeneity of microglia was first described a century ago by Pio del Rio Hortega. Currently, new information on microglia heterogeneity throughout central nervous system (CNS) regions is being revealed by high-throughput techniques. It remains unclear whether these spatial specificities translate into different microglial behaviors in vitro. We cultured microglia isolated from the cortex and spinal cord and analyzed the effect of the CNS spatial source on behavior in vitro by applying the same experimental protocol and culture conditions. We analyzed the microglial cell numbers, function, and morphology and found a distinctive in vitro phenotype. We found that microglia were present in higher numbers in the spinal-cord-derived glial cultures, presenting different expressions of inflammatory genes and a lower phagocytosis rate under basal conditions or after activation with LPS and IFN-γ. Morphologically, the cortical microglial cells were more complex and presented longer ramifications, which were also observed in vivo in CX3CR1^+/GFP transgenic reporter mice. Collectively, our data demonstrated that microglial behavior in vitro is defined according to specific spatial characteristics acquired by the tissue. Thus, our study highlights the importance of microglia as a source of CNS for in vitro studies.

CK2 inhibitor DMAT ameliorates spinal cord injury by increasing autophagy and inducing anti-inflammatory microglial polarization

Spinal cord injury (SCI) is a destructive and disabling nerve injury from which complete recovery has not yet been achieved due to complex pathology. Casein kinase II (CK2) is a pleiotropic serine/threonine protein kinase that plays an essential role in the nervous system. This study aimed to investigate the role of CK2 in SCI to understand the pathogenesis of SCI and explore new therapeutic methods. The SCI rat model of C5 unilateral clamp was established by modified clamp method in male adult SD rats. Then, CK2 inhibitor DMAT was used to treat SCI rats, and the behaviour, pathological changes in the spinal cord and microglial polarization were analysed. Additionally, the effects of DMAT on the polarization and autophagy of microglial BV-2 cells were investigated in vitro, and the effects of BV-2 polarization on spinal cord neuronal cells were analysed by Transwell coculture. Results showed that DMAT significantly increased the BBB score, improved histopathological injury, decreased the expression of inflammatory cytokines, and promoted M2 polarization of microglia in SCI rats. In vitro experiments further confirmed that DMAT could promote the polarization of BV-2 to the M2 type, promote autophagy, and reverse the LPS-induced decline in cell viability and increase in apoptosis of neuronal cells. The use of 3-MA confirmed that autophagy plays an important role in DMAT promoting M2 polarization of BV-2 to improve neuronal cell viability. In conclusion, CK2 inhibitor DMAT improved SCI by inducing anti-inflammatory polarization of microglia through autophagy and is a potential therapeutic target for SCI.

Neuro-Nutraceutical Polyphenols: How Far Are We?

The brain, composed of billions of neurons, is a complex network of interacting dynamical systems controlling all body functions. Neurons are the building blocks of the nervous system and their impairment of their functions could result in neurodegenerative disorders. Accumulating evidence shows an increase of brain-affecting disorders, still today characterized by poor therapeutic options. There is a strong urgency to find new alternative strategies to prevent progressive neuronal loss. Polyphenols, a wide family of plant compounds with an equally wide range of biological activities, are suitable candidates to counteract chronic degenerative disease in the central nervous system. Herein, we will review their role in human healthcare and highlight their: antioxidant activities in reactive oxygen species-producing neurodegenerative pathologies; putative role as anti-acetylcholinesterase inhibitors; and protective activity in Alzheimer’s disease by preventing Aβ aggregation and tau hyperphosphorylation. Moreover, the pathology of these multifactorial diseases is also characterized by metal dyshomeostasis, specifically copper (Cu), zinc (Zn), and iron (Fe), most important for cellular function. In this scenario, polyphenols’ action as natural chelators is also discussed. Furthermore, the critical importance of the role exerted by polyphenols on microbiota is assumed, since there is a growing body of evidence for the role of the intestinal microbiota in the gut–brain axis, giving new opportunities to study molecular mechanisms and to find novel strategies in neurological diseases.

The Role of PGK1 in Promoting Ischemia/Reperfusion Injury-Induced Microglial M1 Polarization and Inflammation by Regulating Glycolysis

Stroke is a leading cause of death, with a continuously increasing incidence. As a metabolic process that catabolizes glucose pyruvate and provides adenosine triphosphate (ATP), glycolysis plays a crucial role in different diseases. Phosphoglycerate kinase 1 (PGK1) facilitates energy production with biosynthesis in many diseases, including stroke. However, the exact role of PGK1/glycolysis in stroke remains to be elucidated. A rat model of middle cerebral artery occlusion (MCAO) was used to mimic ischemia/reperfusion injuries. Oxygen glucose deprivation/re-oxygenation (OGD/R) was used to induce injury to highly aggressively proliferating immortalized (HAPI) rat microglial cells. The extracellular acidification rate (ECAR) was determined using an XFe24 Extracellular Flux Analyzer. ATP, lactate dehydrogenase, tumor necrosis factor-alpha, and interleukin-6 levels were measured using commercial kits. Chromatin immunoprecipitation assay was performed to examine the interaction between H3K27ac or p300 and the PGK1 promoter region. PGK1 was either knocked down or overexpressed by lentivirus. Thus, to examine its role in stroke, real-time polymerase chain reaction and immunoblotting were used to measure gene expression. The expression of PGK1 was increased and associated with M1 polarization and glycolysis in MCAO rat models. OGD/R promoted M1 polarization and HAPI microglial cell inflammation by regulating glycolysis. Silencing PGK1 reduced OGD/R-increased M1 polarization, inflammation, and glycolysis. Conversely, the overexpression of PGK1 promoted HAPI microglial cell inflammation by regulating glycolysis. The mechanism showed that histone acetyltransferase p300 promoted PGK1 expression through H3K27 acetylation. Finally, data indicated that silencing PGK1 inhibited microglia M1 polarization, inflammation, and glycolysis in MCAO rat models. PGK1 could promote ischemia/reperfusion injury-induced microglial M1 polarization and inflammation by regulating glycolysis, which might provide a novel direction in developing new therapeutic medications for preventing or treating stroke.

Image processing and supervised machine learning for retinal microglia characterization in senescence

The process of senescence impairs the function of cells and can ultimately be a key factor in the development of disease. With an aging population, senescence-related diseases are increasing in prevalence. Therefore, understanding the mechanisms of cellular senescence within the central nervous system (CNS), including the retina, may yield new therapeutic pathways to slow or even prevent the development of neuro- and retinal degenerative diseases. One method of probing the changing functions of senescent retinal cells is to observe retinal microglial cells. Their morphological structure may change in response to their surrounding cellular environment. In this chapter, we show how microglial cells in the retina, which are implicated in aging and diseases of the CNS, can be identified, quantified, and classified into five distinct morphotypes using image processing and supervised machine learning algorithms. The process involves dissecting, staining, and mounting mouse retinas, before image capture via fluorescence microscopy. The resulting images can then be classified by morphotype using a support vector machine (SVM) we have recently described showing high accuracy. This SVM model uses shape metrics found to correspond with qualitative descriptions of the shape of each morphotype taken from existing literature. We encourage more objective and widespread use of methods of quantification such as this. We believe automatic delineation of the population of microglial cells in the retina, could potentially lead to their use as retinal imaging biomarkers for disease prediction in the future.

Current Understanding on the Role of Lipids in Macrophages and Associated Diseases

Lipid metabolism is the major intracellular mechanism driving a variety of cellular functions such as energy storage, hormone regulation and cell division. Lipids, being a primary component of the cell membrane, play a pivotal role in the survival of macrophages. Lipids are crucial for a variety of macrophage functions including phagocytosis, energy balance and ageing. However, functions of lipids in macrophages vary based on the site the macrophages are residing at. Lipid-loaded macrophages have recently been emerging as a hallmark for several diseases. This review discusses the significance of lipids in adipose tissue macrophages, tumor-associated macrophages, microglia and peritoneal macrophages. Accumulation of macrophages with impaired lipid metabolism is often characteristically observed in several metabolic disorders. Stress signals differentially regulate lipid metabolism. While conditions such as hypoxia result in accumulation of lipids in macrophages, stress signals such as nutrient deprivation initiate lipolysis and clearance of lipids. Understanding the biology of lipid accumulation in macrophages requires the development of potentially active modulators of lipid metabolism.

Role of microglia in blood pressure and respiratory responses to acute hypoxic exposure in rats

Microglia modulate cardiorespiratory activities during chronic hypoxia. It has not been clarified whether microglia are involved in the cardiorespiratory responses to acute hypoxia. Here we investigated this issue by comparing cardiorespiratory responses to two levels of acute hypoxia (13% O₂ for 4 min and 7% O₂ for 5 min) in conscious unrestrained rats before and after systemic injection of minocycline (MINO), an inhibitor of microglia activation. MINO increased blood pressure but not lung ventilation in the control normoxic condition. Acute hypoxia stimulated cardiorespiratory responses in MINO-untreated rats. MINO failed to significantly affect the magnitude of hypoxia-induced blood pressure elevation. In contrast, MINO tended to suppress the ventilatory responses to hypoxia. We conclude that microglia differentially affect cardiorespiratory regulation depending on the level of blood oxygenation. Microglia suppressively contribute to blood pressure regulation in normoxia but help maintain ventilatory augmentation in hypoxia, which underscores the dichotomy of central regulatory pathways for both systems.

Reactive morphology of dividing microglia following kainic acid administration

The microglial response to a pathological microenvironment is hallmarked by a change in cellular morphology. Following a pathological stimulus, microglia become reactive and simultaneously divide to create daughter cells. Although a wide array of microglial morphologies has been observed, the exact functions of these distinct morphologies are unknown, as are the morphology and reactivity status of dividing microglia. In this study, we used kainic acid to trigger microglial activation and cell division. Following a cortical kainic acid injection, microglial morphology and proliferation were examined at 3 days post-injection using immunohistochemistry for ionized calcium binding adapter molecule 1 (Iba1) to stain for microglia, and KI67 as a marker of cell division. Individual microglial cells were isolated from photomicrographs and skeletal and fractal analyses were used to examine cell size and spatial complexity. We examined the morphology of microglia in both wildtype and microglia-specific tumor necrosis factor (TNF)-α knockout mice. Data were analyzed using generalized linear mixed models or a two-way ANOVA. We found that dividing microglia had a more reactive morphology (larger cell body area, longer cell perimeter, and less ramification) compared to microglia that were not dividing, regardless of microglial release of TNF-α. However, we also observed dividing microglia with a complex, more ramified morphology. Changes in microglial morphology and division were greatest near the kainic acid injection site. This study uses robust and quantitative techniques to better understand microglial cell division, morphology, and population dynamics, which are essential for the development of novel therapeutics that target microglia.

Brain Bioenergetics in Chronic Hypertension: Risk Factor for Acute Ischemic Stroke

Chronic hypertension is one of the key modifiable risk factors for acute ischemic stroke, also contributing to determine greater neurological deficits and worse functional outcome when an acute cerebrovascular event would occur. A tight relationship exists between cerebrovascular autoregulation, neuronal activity and brain bioenergetics. In chronic hypertension, progressive adaptations of these processes occur as an attempt to cope with the demanding necessity of brain functions, creating a new steady-state homeostatic condition. However, these adaptive modifications are insufficient to grant an adequate response to possible pathological perturbations of the established fragile hemodynamic and metabolic homeostasis. In this narrative review, we will discuss the main mechanisms by which alterations in brain bioenergetics and mitochondrial function in chronic hypertension could lead to increased risk of acute ischemic stroke, stressing the interconnections between hemodynamic factors (i.e. cerebral autoregulation and neurovascular coupling) and metabolic processes. Both experimental and clinical pieces of evidence will be discussed. Moreover, the potential role of mitochondrial dysfunction in determining, or at least sustaining, the pathogenesis and progression of chronic neurogenic hypertension will be considered. In the perspective of novel therapeutic strategies aiming at improving brain bioenergetics, we propose some determinant factors to consider in future studies focused on the cause-effect relationships between chronic hypertension and brain bioenergetic abnormalities (and vice versa), so to help translational research in this so-far unfilled gap.

The gut-immune-brain axis in neurodevelopment and neurological disorders

The gut-brain axis is gaining momentum as an interdisciplinary field addressing how intestinal microbes influence the central nervous system (CNS). Studies using powerful tools, including germ-free, antibiotic-fed, and fecal microbiota transplanted mice, demonstrate how gut microbiota perturbations alter the fate of neurodevelopment. Probiotics are also becoming more recognized as potentially effective therapeutic agents in alleviating symptoms of neurological disorders. While gut microbes may directly communicate with the CNS through their effector molecules, including metabolites, their influence on neuroimmune populations, including newly discovered brain-resident T cells, underscore the host immunity as a potent mediator of the gut-brain axis. In this review, we examine the unique immune populations within the brain, the effects of the gut microbiota on the CNS, and the efficacy of specific probiotic strains to propose the novel concept of the gut-immune-brain axis.

T-2 Toxin Induces Apoptotic Cell Death and Protective Autophagy in Mouse Microglia BV2 Cells

T-2 toxin exposure could cause neurotoxicity; however, the precise molecular mechanisms remain unclear. In the present study, we investigated T-2 toxin-induced cytotoxicity and underlying molecular mechanisms using a mouse microglia BV2 cell line. The results show that T-2 toxin treatment-induced cytotoxicity of BV2 cells was dose- and time-dependent. Compared to the control, T-2 toxin treatment at 1.25–5 ng/mL significantly increased reactive oxygen species (ROS) production and triggered oxidative stress. T-2 toxin treatment also caused mitochondrial dysfunction in BV2 cells, which was evidenced by decreased mitochondrial transmembrane potential, upregulated expression of Bax protein, and decreased expression of Bcl-2 protein. Meanwhile, T-2 toxin treatment upregulated the expression of cleaved-caspase-3, cleaved-PARP-1 proteins, and downregulated the expression of HO-1 and nuclear Nrf2 proteins, finally inducing cell apoptosis in BV2 cells. N-acetylcysteine (NAC) supplementation significantly attenuated T-2 toxin-induced cytotoxicity. Moreover, T-2 toxin treatment activated autophagy and upregulated autophagy flux, and the inhibition of autophagy significantly promoted T-2 toxin-induced cell apoptosis. Taken together, our results reveal that T-2 toxin-induced cytotoxicity in BV2 cells involves the production of ROS, the activation of the mitochondrial apoptotic pathway, and the inhibition of the Nrf2/HO-1 pathway. Our study offers new insight into the underlying molecular mechanisms in T-2 toxin-mediated neurotoxicity.

Immunomodulatory effects of microbiota-derived metabolites at the crossroad of neurodegenerative diseases and viral infection: network-based bioinformatics insights

Bidirectional cross-talk between commensal microbiota and the immune system is essential for the regulation of immune responses and the formation of immunological memory. Perturbations of microbiome-immune system interactions can lead to dysregulated immune responses against invading pathogens and/or to the loss of self-tolerance, leading to systemic inflammation and genesis of several immune-mediated pathologies, including neurodegeneration. In this paper, we first investigated the contribution of the immunomodulatory effects of microbiota (bacteria and fungi) in shaping immune responses and influencing the formation of immunological memory cells using a network-based bioinformatics approach. In addition, we investigated the possible role of microbiota-host-immune system interactions and of microbiota-virus interactions in a group of neurodegenerative diseases (NDs): Amyotrophic Lateral Sclerosis (ALS), Multiple Sclerosis (MS), Parkinson’s disease (PD) and Alzheimer’s disease (AD). Our analysis highlighted various aspects of the innate and adaptive immune response systems that can be modulated by microbiota, including the activation and maturation of microglia which are implicated in the development of NDs. It also led to the identification of specific microbiota components which might be able to influence immune system processes (ISPs) involved in the pathogenesis of NDs. In addition, it indicated that the impact of microbiota-derived metabolites in influencing disease-associated ISPs, is higher in MS disease, than in AD, PD and ALS suggesting a more important role of microbiota mediated-immune effects in MS.

Peridontitis as a Risk Factor for Attention Deficit Hyperactivity Disorder: Possible Neuro-inflammatory Mechanisms

Periodontitis is a condition caused mostly by the creation of a biofilm by the bacterium P. gingivalis, which releases toxins and damages the tooth structure. Recent research studies have reported association between dental health and neuropsychiatric illnesses. Neuroinflammation triggered by the first systemic inflammation caused by the bacterium present in the oral cavities is a plausible explanation for such a relationship. Substantial amount of evidence supports the role of neuroinflammation and dysfunction of the dopaminergic system in the pathology of ADHD (Attention deficit hyperactivity disorders). Recent epidemiological, microbiological and inflammatory findings strengthen that, periodontal bacteria, which cause systemic inflammation can contribute to neuroinflammation and finally ADHD. Although both diseases are characterized by inflammation, the specific pathways and crosslink's between periodontitis and ADHD remain unknown. Here, the authors describe the inflammatory elements of periodontitis, how this dental illness causes systemic inflammation, and how this systemic inflammation contributes to deteriorating neuroinflammation in the evolution of ADHD. Therefore, the aim of this review is to present possible links and mechanisms that could confirm the evidence of this association.

The Influence of Adverse Childhood Experiences in Pain Management: Mechanisms, Processes, and Trauma-Informed Care

Adverse childhood experiences (ACEs) increase the likelihood of reduced physical and psychological health in adulthood. Though understanding and psychological management of traumatic experiences is growing, the empirical exploration of ACEs and physical clinical outcomes remains under-represented and under-explored. This topical review aimed to highlight the role of ACEs in the experience of chronic pain, pain management services and clinical decision making by: (1) providing an overview of the relationship between ACEs and chronic pain; (2) identifying biopsychosocial mechanisms through which ACEs may increase risk of persistent pain; (3) highlighting the impact of ACEs on patient adherence and completion of pain management treatment; and (4) providing practical clinical implications for pain management. Review findings demonstrated that in chronic pain, ACEs are associated with increased pain complications, pain catastrophizing and depression and the combination of these factors further heightens the risk of early treatment attrition. The pervasive detrimental impacts of the COVID-19 pandemic on ACEs and their cyclical effects on pain are discussed in the context of psychological decline during long treatment waitlists. The review highlights how people with pain can be further supported in pain services by maintaining trauma-informed practices and acknowledging the impact of ACEs on chronic pain and detrimental health outcomes. Clinicians who are ACE-informed have the potential to minimize the negative influence of ACEs on treatment outcomes, ultimately optimizing the impact of pain management services.

Ski regulates the inflammatory response of reactive astrocytes induced by oxygen glucose deprivation/reoxygenation (OGD/R) through the NF-κB pathway

Spinal cord injury (SCI) is a common disease of the nervous system, including primary and secondary injuries.Neuronal inflammation after SCI is the most important pathological process of SCI and a chemical barrier to nerve function recovery after injury.Ski, an evolutionarily conserved functional transcriptional regulator protein, is upregulated in reactive astrocytes after SCI and regulates the biological characteristics of astrocytes. However, its role in the glial inflammatory response triggered by reactive astrocytes after spinal cord ischemia and its exact mechanism remains unclear. This study investigated the role and mechanism of Ski in the inflammatory response triggered by reactive astrocytes induced by oxygen and sugar deprivation/reoxygenation (OGD/R) model in vitro. In the ODG/R model, Ski expression was upregulated.In contrast, Ski upregulation was accompanied by increased levels of iNOS, IL-1β, IL-6, TNF-α, and other inflammation-related factors.These results indicated that the inflammatory response triggered by astrocytes was significantly enhanced in OGD/R-stimulated astrocytes. Astrocytes were transfected with Ski specific siRNA to knock out Ski and subsequently attenuate OGD-induced astrocyte-triggered inflammation.Our results also suggest that Ski downregulation downregulates the expression of iNOS, IL-1β, IL-6, and TNF-α in OGD/R-induced reactive astrocytes by inhibiting the activity of the NF-κB signaling pathway. In conclusion, downregulation of Ski can effectively inhibit glial inflammation in SCI by inhibiting the activity of the NF-κB pathway.These findings suggest that Ski is a promising therapeutic target for inflammatory responses after SCI.In conclusion, Ski downregulation can effectively inhibit glial inflammation in SCI by inhibiting the activity of the NF-κB pathway. These findings suggest that Ski might serve as a promising target for the treatment of inflammatory responses after SCI.

Amygdala and anterior cingulate transcriptomes from individuals with bipolar disorder reveal downregulated neuroimmune and synaptic pathways

Recent genetic studies have identified variants associated with bipolar disorder (BD), but it remains unclear how brain gene expression is altered in BD and how genetic risk for BD may contribute to these alterations. Here, we obtained transcriptomes from subgenual anterior cingulate cortex and amygdala samples from post-mortem brains of individuals with BD and neurotypical controls, including 511 total samples from 295 unique donors. We examined differential gene expression between cases and controls and the transcriptional effects of BD-associated genetic variants. We found two coexpressed modules that were associated with transcriptional changes in BD: one enriched for immune and inflammatory genes and the other with genes related to the postsynaptic membrane. Over 50% of BD genome-wide significant loci contained significant expression quantitative trait loci (QTL) (eQTL), and these data converged on several individual genes, including SCN2A and GRIN2A. Thus, these data implicate specific genes and pathways that may contribute to the pathology of BP.

Tauopathies: the role of tau in cellular crosstalk and synaptic dysfunctions

Tauopathies are a group of neurodegenerative diseases among which are many of the most prevalent and with higher incidence worldwide, such as Alzheimer's disease (AD). According to the World Health Organization, this set of diseases will continue to increase their incidence, affecting millions of people by 2050. All of them are characterized by aberrant aggregation of tau protein in neurons and glia that are distributed in different brain regions according to their susceptibility. Numerous studies reveal that synaptic regulation not only has a neuronal component, but glia plays a fundamental role in it beyond its neuroinflammatory role. Despite this, it has not been emphasized how the glial inclusions of tau in this cell type directly affect this and many other essential functions, whose alterations have been related to the development of tauopathies. In this way, this review shows how tau inclusions in glia influence the synaptic dysfunctions that result in the cognitive symptoms characteristic of tauopathies. Thus, the mechanisms affected by inclusions in neurons, astrocytes, and oligodendrocytes are unraveled.

Reduced microglia activity in patients with long-term immunosuppressive therapy after liver transplantation

PURPOSE

Calcineurin inhibitors (CNI) can cause long-term impairment of brain function. Possible pathomechanisms include alterations of the cerebral immune system. This study used positron emission tomography (PET) imaging with the translocator protein (TSPO) ligand 18F-GE-180 to evaluate microglial activation in liver-transplanted patients under different regimens of immunosuppression.

METHODS

PET was performed in 22 liver-transplanted patients (3 CNI free, 9 with low-dose CNI, 10 with standard-dose CNI immunosuppression) and 9 healthy controls. The total distribution volume (VT) estimated in 12 volumes-of-interest was analyzed regarding TSPO genotype, CNI therapy, and cognitive performance.

RESULTS

In controls, VT was about 80% higher in high affinity binders (n = 5) compared to mixed affinity binders (n = 3). Mean VT corrected for TSPO genotype was significantly lower in patients compared to controls, especially in patients in whom CNI dose had been reduced because of nephrotoxic side effect.

CONCLUSION

Our results provide evidence of chronic suppression of microglial activity in liver-transplanted patients under CNI therapy especially in patients with high sensitivity to CNI toxicity.

Polarization of Type 1 Macrophages Is Associated with the Severity of Viral Encephalitis Caused by Japanese Encephalitis Virus and Dengue Virus

Infection with flaviviruses causes mild to severe diseases, including viral hemorrhagic fever, vascular shock syndrome, and viral encephalitis. Several animal models explore the pathogenesis of viral encephalitis, as shown by neuron destruction due to neurotoxicity after viral infection. While neuronal cells are injuries caused by inflammatory cytokine production following microglial/macrophage activation, the blockade of inflammatory cytokines can reduce neurotoxicity to improve the survival rate. This study investigated the involvement of macrophage phenotypes in facilitating CNS inflammation and neurotoxicity during flavivirus infection, including the Japanese encephalitis virus, dengue virus (DENV), and Zika virus. Mice infected with different flaviviruses presented encephalitis-like symptoms, including limbic seizure and paralysis. Histology indicated that brain lesions were identified in the hippocampus and surrounded by mononuclear cells. In those regions, both the infiltrated macrophages and resident microglia were significantly increased. RNA-seq analysis showed the gene profile shifting toward type 1 macrophage (M1) polarization, while M1 markers validated this phenomenon. Pharmacologically blocking C-C chemokine receptor 2 and tumor necrosis factor-α partly retarded DENV-induced M1 polarization. In summary, flavivirus infection, such as JEV and DENV, promoted type 1 macrophage polarization in the brain associated with encephalitic severity.

Ultrastructural analysis of the morphological phenotypes of microglia associated with neuroinflammatory cues

Microglia are the primary resident immune cells of the central nervous system that are responsible for the maintenance of brain homeostasis. There is a plethora of evidence to suggest that microglia display distinct phenotypes that are associated with the alteration of cell morphology under varying environmental cues. However, it has not been fully explored how the varying states of microglial activation are linked to the alteration of microglia morphology, especially in the microdomain. The objective of this study was to quantitatively characterize the ultrastructural morphology of human microglia under neuroinflammatory cues. To address this, a human cell line of microglia was stimulated by antiinflammatory (IL-4), proinflammatory (TNF-α), and Alzheimer's disease (AD)-associated cues (Aβ, Aβ + TNF-α). The resulting effects on microglia morphology associated with changes in microdomain were analyzed using a high-resolution scanning electron microscopy. Our findings demonstrated that microglial activation under proinflammatory and AD-cues were closely linked to changes not only in cell shape but also in cell surface topography and higher-order branching of processes. Furthermore, our results revealed that microglia under proinflammatory cues exhibited unique morphological features involving cell-to-cell contact and the formation of vesicle-like structures. Our study provides insight into the fine details of microglia morphology associated with varying status of microglial activation.

Food-Origin Mycotoxin-Induced Neurotoxicity: Intend to Break the Rules of Neuroglia Cells

Mycotoxins are key risk factors in human food and animal feed. Most of food-origin mycotoxins could easily enter the organism and evoke systemic toxic effects, such as aflatoxin B1 (AFB1), ochratoxin A (OTA), T-2 toxin, deoxynivalenol (DON), zearalenone (ZEN), fumonisin B1 (FB1), and 3-nitropropionic acid (3-NPA). For the last decade, the researches have provided much evidences in vivo and in vitro that the brain is an important target organ on mycotoxin-mediated neurotoxic phenomenon and neurodegenerative diseases. As is known to all, glial cells are the best regulator and defender of neurons, and a few evaluations about the effects of mycotoxins on glial cells such as astrocytes or microglia have been conducted. The fact that mycotoxin contamination may be a key factor in neurotoxicity and glial dysfunction is exactly the reason why we reviewed the activation, oxidative stress, and mitochondrial function changes of glial cells under mycotoxin infection and summarized the mycotoxin-mediated glial cell proliferation disorders, death pathways, and inflammatory responses. The purpose of this paper is to analyze various pathways in which common food-derived mycotoxins can induce glial toxicity and provide a novel perspective for future research on the neurodegenerative diseases.

Qki is an essential regulator of microglial phagocytosis in demyelination

The mechanism underpinning the regulation of microglial phagocytosis in demyelinating diseases is unclear. Here, we showed that the Quaking protein (Qki) in microglia was greatly induced by demyelination in the brains of both mice and humans. Deletion of the Quaking gene (Qk) in microglia severely impaired the clearance of myelin debris. Transcriptomic profiling indicated that depletion of Qki impaired total RNA levels and splicing of the genes involved in phagosome formation and maturation. RNA immunoprecipitation (RIP) confirmed the physical interactions between the Qki protein and the mRNAs of Qki targets that are involved in phagocytosis, indicating that Qki regulates their RNA stability. Both Qki depletion and inhibition of Qki target Cd36 greatly reduced the phagocytic activity of microglia and macrophages. The defective uptake and degradation of myelin debris caused by Qki depletion in microglia resulted in unresolved myelin debris that impaired axon integrity, oligodendrocyte maturation, and subsequent remyelination. Thus, our results demonstrate that Qki is an essential regulator of microglia’s phagocytic activity under demyelinating conditions.

Distinct non-inflammatory signature of microglia in post-mortem brain tissue of patients with major depressive disorder

Findings from epidemiological studies, biomarker measurements and animal experiments suggest a role for aberrant immune processes in the pathogenesis of major depressive disorder (MDD). Microglia, the resident immune cells of the brain, are likely to play a key role in these processes. Previous post-mortem studies reported conflicting findings regarding microglial activation and an in-depth profiling of those cells in MDD is lacking. The aim of this study was therefore to characterize the phenotype and function of microglia in MDD. We isolated microglia from post-mortem brain tissue of patients with MDD (n = 13-19) and control donors (n = 12-25). Using flow cytometry and quantitative Polymerase Chain Reaction (qPCR), we measured protein and mRNA levels of a panel of microglial markers across four different brain regions (medial frontal gyrus, superior temporal gyrus, thalamus, and subventricular zone). In MDD cases, we found a significant upregulation of CX3CR1 and TMEM119 mRNA expression and a downregulation of CD163 mRNA expression and CD14 protein expression across the four brain regions. Expression levels of microglial activation markers, such as HLA-DRA, IL6, and IL1β, as well as the inflammatory responses to lipopolysaccharide and dexamethasone were unchanged. Our findings suggest that microglia enhance homeostatic functions in MDD but are not immune activated.

Loss of vagal integrity disrupts immune components of the microbiota-gut-brain axis and inhibits the effect of Lactobacillus rhamnosus on behavior and the corticosterone stress response

The vagus nerve is one of the major signalling components between the gut microbiota and brain. However, the exact relationship between gut-brain signaling along the vagus and the effects of gut microbes on brain function and behaviour is unclear. In particular, the relationship between the vagus nerve and immune signaling, that also appears to play a critical role in microbiota-gut-brain communication, has not been delineated. The aim of the present study was to determine the effect of subdiaphragmatic vagotomy on peripheral and central immune changes associated with the anxiolytic actions of L.rhamnosus. Male mice underwent vagotomy or sham surgery, followed by administration of L.rhamnosus for 14 days. L.rhamnosus administration following sham surgery resulted in reduced anxiety-like behaviour, and an attenuation of the hypothalamic-pituitary-adrenal axis (HPA axis), as indicated by reduced plasma corticosterone after acute restraint stress. These effects were associated with an increase in splenic T regulatory cells and a decrease in activated microglia in the hippocampus. The anxiolytic effects, HPA modulation and increase in T regulatory cells were prevented by vagotomy, whereas vagotomy alone led to a significant increase in activated microglia in the hippocampus that was not altered with L.rhamnosus treatment. Thus, both microbe induced and constitutive vagal signaling influences critical immune components of the microbiota-gut-brain axis. These findings suggest that, rather than acting as a direct neural link to the central nervous system, the role of the vagus nerve in gut-microbe to brain signalling is as an integral component of a bi-directional neuroimmunoendocrine pathway.

Phosphoinositides: Roles in the Development of Microglial-Mediated Neuroinflammation and Neurodegeneration

Microglia are increasingly recognized as vital players in the pathology of a variety of neurodegenerative conditions including Alzheimer’s (AD) and Parkinson’s (PD) disease. While microglia have a protective role in the brain, their dysfunction can lead to neuroinflammation and contributes to disease progression. Also, a growing body of literature highlights the seven phosphoinositides, or PIPs, as key players in the regulation of microglial-mediated neuroinflammation. These small signaling lipids are phosphorylated derivates of phosphatidylinositol, are enriched in the brain, and have well-established roles in both homeostasis and disease.Disrupted PIP levels and signaling has been detected in a variety of dementias. Moreover, many known AD disease modifiers identified via genetic studies are expressed in microglia and are involved in phospholipid metabolism. One of these, the enzyme PLCγ2 that hydrolyzes the PIP species PI(4,5)P₂, displays altered expression in AD and PD and is currently being investigated as a potential therapeutic target.Perhaps unsurprisingly, neurodegenerative conditions exhibiting PIP dyshomeostasis also tend to show alterations in aspects of microglial function regulated by these lipids. In particular, phosphoinositides regulate the activities of proteins and enzymes required for endocytosis, toll-like receptor signaling, purinergic signaling, chemotaxis, and migration, all of which are affected in a variety of neurodegenerative conditions. These functions are crucial to allow microglia to adequately survey the brain and respond appropriately to invading pathogens and other abnormalities, including misfolded proteins. AD and PD therapies are being developed to target many of the above pathways, and although not yet investigated, simultaneous PIP manipulation might enhance the beneficial effects observed. Currently, only limited therapeutics are available for dementia, and although these show some benefits for symptom severity and progression, they are far from curative. Given the importance of microglia and PIPs in dementia development, this review summarizes current research and asks whether we can exploit this information to design more targeted, or perhaps combined, dementia therapeutics. More work is needed to fully characterize the pathways discussed in this review, but given the strength of the current literature, insights in this area could be invaluable for the future of neurodegenerative disease research.

Beneficial Impacts of Alpha-Eleostearic Acid from Wild Bitter Melon and Curcumin on Promotion of CDGSH Iron-Sulfur Domain 2: Therapeutic Roles in CNS Injuries and Diseases

Neuroinflammation and abnormal mitochondrial function are related to the cause of aging, neurodegeneration, and neurotrauma. The activation of nuclear factor κB (NF-κB), exaggerating these two pathologies, underlies the pathogenesis for the aforementioned injuries and diseases in the central nervous system (CNS). CDGSH iron-sulfur domain 2 (CISD2) belongs to the human NEET protein family with the [2Fe-2S] cluster. CISD2 has been verified as an NFκB antagonist through the association with peroxisome proliferator-activated receptor-β (PPAR-β). This protective protein can be attenuated under circumstances of CNS injuries and diseases, thereby causing NFκB activation and exaggerating NFκB-provoked neuroinflammation and abnormal mitochondrial function. Consequently, CISD2-elevating plans of action provide pathways in the management of various disease categories. Various bioactive molecules derived from plants exert protective anti-oxidative and anti-inflammatory effects and serve as natural antioxidants, such as conjugated fatty acids and phenolic compounds. Herein, we have summarized pharmacological characters of the two phytochemicals, namely, alpha-eleostearic acid (α-ESA), an isomer of conjugated linolenic acids derived from wild bitter melon (Momordica charantia L. var. abbreviata Ser.), and curcumin, a polyphenol derived from rhizomes of Curcuma longa L. In this review, the unique function of the CISD2-elevating effect of α-ESA and curcumin are particularly emphasized, and these natural compounds are expected to serve as a potential therapeutic target for CNS injuries and diseases.

Epigenetics and Communication Mechanisms in Microglia Activation with a View on Technological Approaches

Microglial cells, the immune cells of the central nervous system (CNS), play a crucial role for the proper brain development and function and in CNS homeostasis. While in physiological conditions, microglia continuously check the state of brain parenchyma, in pathological conditions, microglia can show different activated phenotypes: In the early phases, microglia acquire the M2 phenotype, increasing phagocytosis and releasing neurotrophic and neuroprotective factors. In advanced phases, they acquire the M1 phenotype, becoming neurotoxic and contributing to neurodegeneration. Underlying this phenotypic change, there is a switch in the expression of specific microglial genes, in turn modulated by epigenetic changes, such as DNA methylation, histones post-translational modifications and activity of miRNAs. New roles are attributed to microglial cells, including specific communication with neurons, both through direct cell–cell contact and by release of many different molecules, either directly or indirectly, through extracellular vesicles. In this review, recent findings on the bidirectional interaction between neurons and microglia, in both physiological and pathological conditions, are highlighted, with a focus on the complex field of microglia immunomodulation through epigenetic mechanisms and/or released factors. In addition, advanced technologies used to study these mechanisms, such as microfluidic, 3D culture and in vivo imaging, are presented.

Neuronal and glial region dependent changes in female mice from a model of premature aging

Adult Premature Aging Mice (PAM) show premature immunosenescence, oxidative and inflammatory stress and consequently a shorter lifespan than Exceptional Non-Prematurely Aging Mice (E-NPAM) at the same age. Indeed, adult female PAM exhibit behavioral age-related declines and abnormalities in its brain neurochemistry. Nevertheless, it is not clear whether these impairments might be accompanied by previous changes related to the neuroinflammation process in their central nervous system (CNS). Therefore, the aim of the present work was to determine if adult female PAM may show brain neuroinflammation processes comparable to those observed in chronologically old female mice. Accordingly, ICR-CD1 female mice were classified in PAM, Regular Non-Prematurely Aging Mice (R-NPAM) and E-NPAM and compared to a group of chronologically old female mice (OLD) (24±1 months). Through the application of immunohistochemical techniques we evaluated changes in the expression of NeuN (a neuronal marker), Iba-1 (a microglia marker) and GFAP (an astrocyte marker) in brain areas related to the behavioral alterations previously detected in both PAM and chronologically old mice. In general, PAM showed a lower NeuN expression and a higher GFAP and Iba1 expression mainly in the Anterior Frontal Cortex and in the Medial Hippocampal Formation, when compared to E-NPAM; similar changes were observed in OLD. Other brain areas, such as the Hypothalamic Nuclei and Motor Cortex were less affected. In conclusion, adult PAM and OLD female mice share some region-dependent neuronal and glial changes that may underlie, at least in part, some of the behavioral abnormalities previously reported in these animals.

Microbiota, Immune System and Autism Spectrum Disorders: An Integrative Model towards Novel Treatment Options

BACKGROUND

Autism Spectrum Disorder (ASD) is a condition strongly associated with genetic predisposition and familial aggregation. Among ASD patients, different levels of symptoms severity are detectable, while the presence of intermediate autism phenotypes in close relatives of ASD probands is also known in literature. Recently, increasing attention has been paid to environmental factors that might play a role in modulating the relationship between genomic risk and development and severity of ASD. Within this framework, an increasing body of evidence has stressed a possible role of both gut microbiota and inflammation in the pathophysiology of neurodevelopment. The aim of this paper is to review findings about the link between microbiota dysbiosis, inflammation and ASD.

METHODS

Articles ranging from 1990 to 2018 were identified on PUBMED and Google Scholar databases, with keyword combinations as: microbiota, immune system, inflammation, ASD, autism, broad autism phenotype, adult.

RESULTS

Recent evidence suggests that microbiota alterations, immune system and neurodevelopment may be deeply intertwined, shaping each other during early life. However, results from both animal models and human samples are still heterogeneous, while few studies focused on adult patients and ASD intermediate phenotypes.

CONCLUSION

A better understanding of these pathways, within an integrative framework between central and peripheral systems, might not only shed more light on neural basis of ASD symptoms, clarifying brain pathophysiology, but it may also allow to develop new therapeutic strategies for these disorders, still poorly responsive to available treatments.

CISD2 Attenuates Inflammation and Regulates Microglia Polarization in EOC Microglial Cells-As a Potential Therapeutic Target for Neurodegenerative Dementia

Background: Accumulating evidence has demonstrated a significant association between microglia-driven inflammation in the brain and neurodegenerative dementia. We previously showed a significant decline in CISD2 expression in mice models with advanced age. Moreover, we observed that the knockdown of CISD2 led to remarkable inflammation and mitochondrial dysfunction in neural cells. In the present study, we investigated whether CISD2 attenuation influences anti-inflammatory effects and M1-M2 polarization in microglia.

Materials and Methods: The knockdown of CISD2 expression by siRNA (siCISD2) in EOC microglial cells was performed to mimic the age-driven decline of CISD2 expression. The extent of the inflammatory reaction, polarization in the M1/M2 spectrum, and NFκB activation were verified in EOC microglial cells exhibiting CISD2 deficiency.

Results: In the cellular model of microglia, loss of CISD2 function mediated by siCISD2 exhibited a significant augmentation of proinflammatory signaling, as well as reduced expression levels of Arg-1, Ym1, IL-10, and BCL2. Attenuation of CISD2 expression led to a decrease in the proportion of the M2 phenotype of microglia (compared to M1). Enhanced DNA-binding activity of the NFκB p65 subunit was confirmed in cells transfected with siCISD2, as demonstrated by enzyme-linked immunosorbent assay (ELISA).

Conclusions: To the best of our knowledge, this is the first report examining the following phenomena: (1) anti-inflammatory effects of CISD2 in microglia via NFκB regulation; and (2) microglial CISD2 assistance in the restoration of M2 microglia phenotype. The anti-inflammatory effects of CISD2 in microglia eventually augment anti-apoptotic effects, which provides a rationale for the development of potential therapeutic target for neurodegenerative diseases and neurodegenerative dementia.

Long-term environmental enrichment reduces microglia morphological diversity of the molecular layer of dentate gyrus

We investigated long-term environmental influences on morphology of microglia from the outer and middle thirds of molecular layer of the dentate gyrus (MolDG), and on microglia from dorsal and ventral dentate gyrus molecular layer. We also estimated the total number of MolDG microglia using stereology. For this purpose, microglia of the molecular layer of the dentate gyrus of 20-month-old female Swiss albino mice, housed from 21st postnatal day onwards, in the impoverished environment of the standard laboratory cages (SEA), or in a cage with an enriched environment (EEA), were reconstructed microscopically in three dimensions and compared with each other and with microglia of 6-month-old female Swiss albino mice, also housed from weaning onwards in an enriched cage (EEY). All mice had their brains sectioned and processed for immunolabeling for IBA-1, a selective microglia marker. Random and systematic microglia samples were reconstructed in three dimensions and classified morphologically using hierarchical cluster analysis, followed by discriminant function analysis. SEA and EEY showed two morphological phenotypes of microglia in both the outer and middle thirds of MolDG. EEA mice showed such a reduction in the morphological diversity of microglia that essentially a single morphotype was found. EEA mouse microglia showed an intermediate morphological complexity between types I and II SE microglia. We suggest that type I and type II microglia in SE mice may have different physiological roles and that long-term EE may be associated with adaptive responses of microglial phenotypes to somatomotor and cognitive stimuli.

Chronic hM3Dq signaling in microglia ameliorates neuroinflammation in male mice

Microglia express muscarinic G protein-coupled receptors (GPCRs) that sense cholinergic activity and are activated by acetylcholine to potentially regulate microglial functions. Knowledge about how distinct types of muscarinic GPCR signaling regulate microglia function in vivo is still poor, partly due to the fact that some of these receptors are also present in astrocytes and neurons. We generated mice expressing the hM3Dq Designer Receptor Exclusively Activated by Designer Drugs (DREADD) selectively in microglia to investigate the role of muscarinic M3Gq-linked signaling. We show that activation of hM3Dq using clozapine N-oxide (CNO) elevated intracellular calcium levels and increased phagocytosis of FluoSpheres by microglia in vitro. Interestingly, whereas acute treatment with CNO increased synthesis of cytokine mRNA, chronic treatment attenuated LPS-induced cytokine mRNA changes in the brain. No effect of CNO on cytokine expression was observed in DREADD-negative mice. Interestingly, CNO activation of M3Dq in microglia was able to attenuate LPS-mediated decrease in social interactions. These results suggest that chronic activation of M3 muscarinic receptors (the hM3Dq progenitor) in microglia, and potentially other Gq-coupled GPCRs, can trigger an inflammatory-like response that preconditions microglia to decrease their response to further immunological challenges. Our results indicate that hM3Dq can be a useful tool to modulate neuroinflammation and study microglial immunological memory in vivo, which may be applicable for manipulations of neuroinflammation in neurodegenerative and psychiatric diseases.

An Update of Palmitoylethanolamide and Luteolin Effects in Preclinical and Clinical Studies of Neuroinflammatory Events

The inflammation process represents of a dynamic series of phenomena that manifest themselves with an intense vascular reaction. Neuroinflammation is a reply from the central nervous system (CNS) and the peripheral nervous system (PNS) to a changed homeostasis. There are two cell systems that mediate this process: the glia of the CNS and the lymphocites, monocytes, and macrophages of the hematopoietic system. In both the peripheral and central nervous systems, neuroinflammation plays an important role in the pathogenesis of neurodegenerative diseases, such as Parkinson’s and Alzheimer’s diseases, and in neuropsychiatric illnesses, such as depression and autism spectrum disorders. The resolution of neuroinflammation is a process that allows for inflamed tissues to return to homeostasis. In this process the important players are represented by lipid mediators. Among the naturally occurring lipid signaling molecules, a prominent role is played by the N-acylethanolamines, namely N-arachidonoylethanolamine and its congener N-palmitoylethanolamine, which is also named palmitoylethanolamide or PEA. PEA possesses a powerful neuroprotective and anti-inflammatory power but has no antioxidant effects per se. For this reason, its co-ultramicronization with the flavonoid luteolin is more efficacious than either molecule alone. Inhibiting or modulating the enzymatic breakdown of PEA represents a complementary therapeutic approach to treating neuroinflammation. The aim of this review is to discuss the role of ultramicronized PEA and co-ultramicronized PEA with luteolin in several neurological diseases using preclinical and clinical approaches.

Extracellular vesicles from mesenchymal stem cells reduce microglial-mediated neuroinflammation after cortical injury in aged Rhesus monkeys

Cortical injury, such as injuries after stroke or age-related ischemic events, triggers a cascade of degeneration accompanied by inflammatory responses that mediate neurological deficits. Therapeutics that modulate such neuroinflammatory responses in the aging brain have the potential to reduce neurological dysfunction and promote recovery. Extracellular vesicles (EVs) from mesenchymal stem cells (MSCs) are lipid-bound, nanoscale vesicles that can modulate inflammation and enhance recovery in rodent stroke models. We recently assessed the efficacy of intravenous infusions of MSC-EVs (24-h and 14-days post-injury) as a treatment in aged rhesus monkeys (Macaca mulatta) with cortical injury that induced impairment of fine motor function of the hand. Aged monkeys treated with EVs after injury recovered motor function more rapidly and more fully than aged monkeys given a vehicle control. Here, we describe EV-mediated inflammatory changes using histological assays to quantify differences in markers of neuroinflammation in brain tissue between EV and vehicle-treated aged monkeys. The activation status of microglia, the innate macrophages of the brain, is critical to cell fate after injury. Our findings demonstrate that EV treatment after injury is associated with greater densities of ramified, homeostatic microglia, along with reduced pro-inflammatory microglial markers. These findings are consistent with a phenotypic switch of inflammatory hypertrophic microglia towards anti-inflammatory, homeostatic functions, which was correlated with enhanced functional recovery. Overall, our data suggest that EVs reduce neuroinflammation and shift microglia towards restorative functions. These findings demonstrate the therapeutic potential of MSC-derived EVs for reducing neuroinflammation after cortical injury in the aged brain.

Pharmacological inhibition of CSF1R by GW2580 reduces microglial proliferation and is protective against neuroinflammation and dopaminergic neurodegeneration

Increased pro-inflammatory cytokine levels and proliferation of activated microglia have been found in Parkinson's disease (PD) patients and animal models of PD, suggesting that targeting of the microglial inflammatory response may result in neuroprotection in PD. Microglial proliferation is regulated by many factors, but colony stimulating factor-1 receptor (CSF1R) has emerged as a primary factor. Using data mining techniques on existing microarray data, we found that mRNA expression of the CSF1R ligand, CSF-1, is increased in the brain of PD patients compared to controls. In two different neurotoxic mouse models of PD, acute MPTP and sub-chronic LPS treatment, mRNA and protein levels of CSF1R and CSF-1 were significantly increased. Treatment with the CSF1R inhibitor GW2580 significantly attenuated MPTP-induced CSF1R activation and Iba1-positive cell proliferation, without a reduction of the basal Iba1-positive population in the substantia nigra. GW2580 treatment also significantly decreased mRNA levels of pro-inflammatory factors, without alteration of anti-inflammatory mediators, and significantly attenuated the MPTP-induced loss of dopamine neurons and motor behavioral deficits. Importantly, these effects were observed in the absence of overt microglial depletion, suggesting that targeting CSF1R signaling may be a viable neuroprotective strategy in PD that disrupts pro-inflammatory signaling, but maintains the beneficial effects of microglia.

Intranasal delivery of M2 macrophage-derived soluble products reduces neuropsychological deficit in patients with cerebrovascular disease: a pilot study

Objective:

We assessed the safety and clinical effectiveness of intranasal therapy with M2 macrophage-derived soluble products (M2-SPs) for treating patients with cerebrovascular disease (CVD).

Materials and methods:

The protocol of the study was registered at www.ClinicalTrails.gov (NCT02957123). The study group comprised 30 patients with chronic CVD. Neurological status was examined before therapy and at 1- and 6-month follow–up. Concentrations of 32 cytokines in the blood serum were evaluated before and 1 month after therapy onset. Neurological assessment was conducted with the following scales: Subjective Assessment of Clinical (neurological) Symptoms (SACS), Hospital Anxiety and Depression Scale (HADS), Functional Mobility Assessment in Eldery Patients (FMA), and Montreal Cognitive Assessment (MoCa).

Results:

M2-SPs treatment (once daily for 28~30 days) was found to be safe and well tolerated. Neuropsychological improvements showed the amelioration of neurological symptoms, reduction in anxiety and depression levels, improvement in balance and gait ability as well as cognitive functions. Clinical effects could be detected at the end of treatment course and was stable during 6-month follow-up. Blood serum cytokine evaluation demonstrated diminished baseline levels of many cytokines including those with neurotrophic activity (brain-derived neurotrophic factor, BDNF; hepatocyte growth factor, HGF; migration inhibitory factor, MIF). Upon treatment, most pronounced clinical responses were observed in patients with most severe cytokine deficiency and post-therapy normalization of MIF and HGF levels.

Conclusion:

Intranasal therapy with M2-SPs is safe and according to preliminary data reduces neuropsychological deficit in patients with chronic CVD. The positive effect of M2-SPs treatment seems to be HGF- and MIF-dependent.

Social stress during adolescence activates long-term microglia inflammation insult in reward processing nuclei

The experience of social stress during adolescence is associated with higher vulnerability to drug use. Increases in the acquisition of cocaine self-administration, in the escalation of cocaine-seeking behavior, and in the conditioned rewarding effects of cocaine have been observed in rodents exposed to repeated social defeat (RSD). In addition, prolonged or severe stress induces a proinflammatory state with microglial activation and increased cytokine production. The aim of the present work was to describe the long-term effects induced by RSD during adolescence on the neuroinflammatory response and synaptic structure by evaluating different glial and neuronal markers. In addition to an increase in the conditioned rewarding effects of cocaine, our results showed that RSD in adolescence produced inflammatory reactivity in microglia that is prolonged into adulthood, affecting astrocytes and neurons of two reward-processing areas of the brain (the prelimbic cortex, and the nucleus accumbens core). Considered as a whole these results suggest that social stress experience modulates vulnerability to suffer a loss of glia-supporting functions and neuronal functional synaptic density due to drug consumption in later life.

Positron emission tomography imaging in evaluation of MS pathology in vivo

Positron emission tomography (PET) gives an opportunity to quantitate the expression of specific molecular targets in vivo and longitudinally in brain and thus enhances our possibilities to understand and follow up multiple sclerosis (MS)-related pathology. For successful PET imaging, one needs a relevant target molecule within the brain, to which a blood–brain barrier–penetrating specific radioligand will bind. 18-kDa translocator protein (TSPO)-binding radioligands have been used to detect activated microglial cells at different stages of MS, and remyelination has been measured using amyloid PET. Several PET ligands for the detection of other inflammatory targets, besides TSPO, have been developed but not yet been used for imaging MS patients. Finally, synaptic density evaluation has been successfully tested in human subjects and gives opportunities for the evaluation of the development of cortical and deep gray matter pathology in MS. This review will discuss PET imaging modalities relevant for MS today.