Astrocytes and Microglia: In Sickness and in Health

Refining the interactions between microglia and astrocytes in Alzheimer's disease pathology

Microglia and astrocytes are central to the pathogenesis and progression of Alzheimer's Disease (AD), working both independently and collaboratively to regulate key pathological processes such as β-amyloid protein (Aβ) deposition, tau aggregation, neuroinflammation, and synapse loss. These glial cells interact through complex molecular pathways, including IL-3/IL-3Ra and C3/C3aR, which influence disease progression and cognitive decline. Emerging research suggests that modulating these pathways could offer therapeutic benefits. For instance, recombinant IL-3 administration in mice reduced Aβ plaques and improved cognitive functions, while C3aR inhibition alleviated Aβ and tau pathologies, restored synaptic function, and corrected immune dysregulation. However, the effects of these interactions are context-dependent. Acute C3/C3aR activation enhances microglial Aβ clearance, whereas chronic activation impairs it, highlighting the dual roles of glial signaling in AD. Furthermore, C3/C3aR signaling not only impacts Aβ clearance but also modulates tau pathology and synaptic integrity. Given AD's multifactorial nature, understanding the specific pathological environment is crucial when investigating glial cell contributions. The interplay between microglia and astrocytes can be both neuroprotective and neurotoxic, depending on the disease stage and brain region. This complexity underscores the need for targeted therapies that modulate glial cell activity in a context-specific manner. By elucidating the molecular mechanisms underlying microglia-astrocyte interactions, this research advances our understanding of AD and paves the way for novel therapeutic strategies aimed at mitigating neurodegeneration and cognitive decline in AD and related disorders.

Zeolite Imidazole Framework-8 Exacerbates Astrocyte Activation and Oxidative Stress in the Brain of Rats

Metal-organic frameworks (MOFs) have been gaining significant attention due to their potential application in medicine. Here, we investigated the effect of zeolite imidazole framework-8 (ZIF-8) on neuro-behavioral parameters, histopathology, inflammation, and oxidative stress levels of rats' brain samples. Forty-eight male Wistar rats were injected by four injections of saline or ZIF-8 at different doses of 5, 10, or 20 mg/kg via the caudal vein. Y-Maze, Morris-Water Maze (MWM), and three chamber tests were conducted to explore working memory, spatial learning and memory, and social interactions, respectively. Histological staining and immunohistochemistry were used to evaluate pathological changes and astrocyte activation levels. The inflammation levels were measured using quantitative real-time reverse-transcription polymerase chain reaction (qRT-PCR). The total antioxidant capacity (TAC) and oxidative stress production were assessed by biochemical assays. The results showed that ZIF-8 induces neuromotor impairment dose-dependently. Although histopathological studies indicated increased neuronal loss, inflammatory changes, and elevated active astrocytes in the hippocampus, the expression levels of IL-1β and TNF-α were not significantly increased in ZIF-8-treated rats. The TAC level significantly reduced and the malondialdehyde (MDA) level remarkably increased in the brain tissues. Our findings suggest that administration of ZIF-8 induce neuromotor impairment, probably through amplified inflammation and oxidative stress.

Long-term effects of PM2.5 constituents on childhood attention deficit hyperactivity disorder: evidence from a large population-based study in the Pearl River Delta Region, China

BACKGROUND

Evidence linking fine particulate matter (PM2.5) constituents to childhood attention deficit hyperactivity disorder (ADHD) was limited.

OBJECTIVES

To investigate the individual and joint effects of exposure to PM2.5 constituents on ADHD.

METHODS

We conducted a large population-based survey involving 110,818 school children aged 6-18 years across six cities in the Pearl River Delta region, China. The three-year average concentrations of PM2.5 constituents (black carbon (BC), organic matter (OM), sulfate, nitrate, and ammonium) were estimated using the ChinaHighAirPollutants dataset. Parents completed an ADHD checklist using the Diagnostic and Statistical Manual of Mental Disorders-IV criteria. The individual and joint associations between PM2.5 components and ADHD were estimated using generalized linear mixed models and the quantile g-computation regression model, respectively.

RESULTS

The exposure-response relationships between PM2.5 constituents and ADHD primarily exhibited a nonlinear pattern. Compared with the lowest tertile, the highest tertiles of PM2.5 and its components were linked to greater odds for ADHD (e.g., the adjusted odds ratio (OR) was 1.37 (95 % confidential interval (CI): 1.27, 1.47) for PM2.5, 1.51 (95 %CI: 1.40, 1.63) for OM, 1.29 (95 %CI: 1.20, 1.39) for BC, and 1.20 (95 %CI:1.08, 1.34) for sulfate). Similar positive associations were observed between BC and sulfate exposure and ADHD subtypes. Moreover, joint exposure to PM2.5 components was associated with ADHD (OR = 1.14, 95 % CI:1.10, 1.18), with OM and BC contributing more to the observed associations.

CONCLUSIONS

These findings highlight the varying contributions of PM2.5 constituents to ADHD and underscore the importance of reducing specific PM2.5 component emissions to mitigate the burden of PM2.5-associated neurodevelopmental diseases.

A neuroimmune circuit mediates cancer cachexia-associated apathy

Cachexia, a severe wasting syndrome associated with inflammatory conditions, often leads to multiorgan failure and death. Patients with cachexia experience extreme fatigue, apathy, and clinical depression, yet the biological mechanisms underlying these behavioral symptoms and their relationship to the disease remain unclear. In a mouse cancer model, cachexia specifically induced increased effort-sensitivity, apathy-like symptoms through a cytokine-sensing brainstem-to-basal ganglia circuit. This neural circuit detects elevated interleukin-6 (IL-6) at cachexia onset and translates inflammatory signals into decreased mesolimbic dopamine, thereby increasing effort sensitivity. We alleviated these apathy-like symptoms by targeting key circuit nodes: administering an anti-IL-6 antibody treatment, ablating cytokine sensing in the brainstem, and optogenetically or pharmacologically boosting mesolimbic dopamine. Our findings uncovered a central neural circuit that senses systemic inflammation and orchestrates behavioral changes, providing mechanistic insights into the connection between chronic inflammation and depressive symptoms.

Alzheimer's Disease-Derived Outer Membrane Vesicles Exacerbate Cognitive Dysfunction, Modulate the Gut Microbiome, and Increase Neuroinflammation and Amyloid-β Production

Although our understanding of the molecular biology of Alzheimer's disease (AD) continues to improve, the etiology of the disease, particularly the involvement of gut microbiota disturbances, remains a challenge. Outer membrane vesicles (OMVs) play a key role in central nervous system diseases, but the impact of OMVs on AD progression remains unclear. In this study, we hypothesized that AD-derived OMVs (OMVsAD) were a risk factor in AD pathology. To test our hypothesis, young APP/PS1 mice (AD mice) were given OMVsAD by gavage. Young AD mice were euthanized 120 days after gavage to assess the intestinal barrier, gut microbiota diversity, mediators of neuroinflammation, glial markers, amyloid burden, and short-chain fatty acid (SCFA) levels. Our results showed that OMVsAD accelerated cognitive dysfunction after 120 days of intragastric administration. Morris water maze experiment and new object recognition test showed that OMVsAD caused significantly poorer spatial ability learning and memory of the AD mice. We observed the OMVsAD-treated APP/PS1 mice display OMVs disrupting the intestinal barrier compared with controls of normal human-derived OMVs. Compared with the OMVsHC group, claudin-5 and ZO-1 related to the intestinal barrier were significantly downregulated in the OMVsAD group. The OMVsAD activate microglia in the cerebral cortex and hippocampus of AD mice, and the levels of IL-1β, IL-6, TNF-α, and NF-Κb were upregulated. We also found that OMVsAD increased Aβ production. 16S rRNA sequencing showed that OMVsAD negatively regulated the α- and β-diversity index of intestinal flora and reduced the levels of SCFA. OMVsAD may change the intestinal flora of young AD, damage the intestinal mucosa and blood-brain barrier, and accelerate AD neuropathological damage.

Curcumin Modulates PTPRZ1 Activity and RNA m6A Modifications in Neuroinflammation-Associated Microglial Response

Neuroinflammation is often characterized by an overactive microglial response. Curcumin, known for its anti-inflammatory and antioxidant properties, can mitigate microglial hyperactivity following epileptic seizures. The study delves into the molecular mechanisms underlying curcumin's modulation of RNA post-transcriptional N (6)-methyladenosine (m6A) modification. It is found that curcumin interacts with the Z1-type protein tyrosine phosphatase receptor (PTPRZ1), maintaining its enzymatic activity and thus regulating the phosphorylation of the m6A-reader YTH domain-containing family protein 2 (YTHDF2). This modulation affects the expression of critical genes, resulting in reduced inflammatory responses. These findings highlight the importance of post-transcriptional modifications of RNA in the neuroprotective and anti-inflammatory effects of curcumin, offering new insights for the treatment of related diseases.

Mechanisms and Therapeutic Prospects of Microglia-Astrocyte Interactions in Neuropathic Pain Following Spinal Cord Injury

Neuropathic pain is a prevalent and debilitating condition experienced by the majority of individuals with spinal cord injury (SCI). The complex pathophysiology of neuropathic pain, involving continuous activation of microglia and astrocytes, reactive gliosis, and altered neuronal plasticity, poses significant challenges for effective treatment. This review focuses on the pivotal roles of microglia and astrocytes, the two major glial cell types in the central nervous system, in the development and maintenance of neuropathic pain after SCI. We highlight the extensive bidirectional interactions between these cells, mediated by the release of inflammatory mediators, neurotransmitters, and neurotrophic factors, which contribute to the amplification of pain signaling. Understanding the microglia-astrocyte crosstalk and its impact on neuronal function is crucial for developing novel therapeutic strategies targeting neuropathic pain. In addition, this review discusses the fundamental biology, post-injury pain roles, and therapeutic prospects of microglia and astrocytes in neuropathic pain after SCI and elucidates the specific signaling pathways involved. We also speculated that the extracellular matrix (ECM) can affect the glial cells as well. Furthermore, we also mentioned potential targeted therapies, challenges, and progress in clinical trials, as well as new biomarkers and therapeutic targets. Finally, other relevant cell interactions in neuropathic pain and the role of glial cells in other neuropathic pain conditions have been discussed. This review serves as a comprehensive resource for further investigations into the microglia-astrocyte interaction and the detailed mechanisms of neuropathic pain after SCI, with the aim of improving therapeutic efficacy.

IL-17 A Exacerbated Neuroinflammatory and Neurodegenerative Biomarkers in Intranasal Amyloid-Beta Model of Alzheimer's Disease

Proinflammatory cytokines, especially interleukin-17 A (IL-17 A) have been found to be significantly associated with AD patients. IL-17 A amplifies neuroinflammation during AD pathology. This study highlighted the ability of IL-17 A to exacerbate amyloid-beta-induced pathology in animals. The AD pathology was induced with repeated intranasal administration of Aβ along with recombinant mouse IL-17 A (rmIL-17) at 1, 2 and 4 µg/kg for seven alternate days. Although, the combination of rmIL-17 and Aβ did not have severe effects on memory of the animals, but it drastically increased the IL-17 A mediated signaling, level of proinflammatory cytokines, oxidative stress and reduced antioxidants in the hippocampus and cortex regions of the animal brains. Interestingly, combining rmIL-17 with Aβ also triggered the expression of AD structural markers like pTau, amyloid-beta and BACE1 in the brain regions. Furthermore, rmIL-17 with Aβ exposure stimulated astrocytes and microglia leading to activation of proinflammatory signaling in the brain of the animals. These results showed the propensity of IL-17 A to promote severity of AD pathology and suggest IL-17 A as potent therapeutic target to control AD progression.

Potential roles for microglia in drug addiction: Adolescent neurodevelopment and beyond

Adolescence is a sensitive period for development of addiction-relevant brain circuits, and it is also when people typically start experimenting with drugs. Unfortunately, such substance use may cause lasting impacts on the brain, and might increase vulnerability to later-life addictions. Microglia are the brain's immune cells, but their roles in shaping neural connectivity and synaptic plasticity, especially in developmental sensitive periods like adolescence, may also contribute to addiction-related phenomena. Here, we overview how drugs of abuse impact microglia, and propose that they may play poorly-understood, but important roles in addiction vulnerability and progression.

Reactive Astrocytes in Glioma: Emerging Opportunities and Challenges

Gliomas are the most prevalent malignant tumors in the adult central nervous system (CNS). Glioblastoma (GBM) accounts for approximately 60-70% of primary gliomas. It is a great challenge to human health because of its high degree of malignancy, rapid progression, short survival time, and susceptibility to recurrence. Owing to the specificity of the CNS, the glioma microenvironment often contains numerous glial cells. Astrocytes are most widely distributed in the human brain and form reactive astrocyte proliferation regions around glioma tissue. In addition, astrocytes are activated under pathological conditions and regulate tumor and microenvironmental cells through cell-to-cell contact or the secretion of active substances. Therefore, astrocytes have attracted attention as important components of the glioma microenvironment. Here, we focus on the mechanisms of reactive astrocyte activation under glioma conditions, their contribution to the mechanisms of glioma genesis and progression, and their potential value as targets for clinical intervention in gliomas.

Drug delivery strategy of hemostatic drugs for intracerebral hemorrhage

Intracerebral hemorrhage (ICH) is associated with high rates of mortality and disability, underscoring an urgent need for effective therapeutic interventions. The clinical prognosis of ICH remains limited, primarily due to the absence of targeted, precise therapeutic options. Advances in novel drug delivery platforms, including nanotechnology, gel-based systems, and exosome-mediated therapies, have shown potential in enhancing ICH management. This review delves into the pathophysiological mechanisms of ICH and provides a thorough analysis of existing treatment strategies, with an emphasis on innovative drug delivery approaches designed to address critical pathological pathways. We assess the benefits and limitations of these therapies, offering insights into future directions in ICH research and highlighting the transformative potential of next-generation drug delivery systems in improving patient outcomes.

Nanotechnology to Overcome Blood-Brain Barrier Permeability and Damage in Neurodegenerative Diseases

The blood-brain barrier (BBB) is a critical structure that maintains brain homeostasis by selectively regulating nutrient influx and waste efflux. Not surprisingly, it is often compromised in neurodegenerative diseases. In addition to its involvement in these pathologies, the BBB also represents a significant challenge for drug delivery into the central nervous system. Nanoparticles (NPs) have been widely explored as drug carriers capable of overcoming this barrier and effectively transporting therapies to the brain. However, their potential to directly address and ameliorate BBB dysfunction has received limited attention. In this review, we examine how NPs enhance drug delivery across the BBB to treat neurodegenerative diseases and explore emerging strategies to restore the integrity of this vital structure.

Exploring the microbiota-gut-brain axis: impact on brain structure and function

The microbiota-gut-brain axis (MGBA) plays a significant role in the maintenance of brain structure and function. The MGBA serves as a conduit between the CNS and the ENS, facilitating communication between the emotional and cognitive centers of the brain via diverse pathways. In the initial stages of this review, we will examine the way how MGBA affects neurogenesis, neuronal dendritic morphology, axonal myelination, microglia structure, brain blood barrier (BBB) structure and permeability, and synaptic structure. Furthermore, we will review the potential mechanistic pathways of neuroplasticity through MGBA influence. The short-chain fatty acids (SCFAs) play a pivotal role in the MGBA, where they can modify the BBB. We will therefore discuss how SCFAs can influence microglia, neuronal, and astrocyte function, as well as their role in brain disorders such as Alzheimer's disease (AD), and Parkinson's disease (PD). Subsequently, we will examine the technical strategies employed to study MGBA interactions, including using germ-free (GF) animals, probiotics, fecal microbiota transplantation (FMT), and antibiotics-induced dysbiosis. Finally, we will examine how particular bacterial strains can affect brain structure and function. By gaining a deeper understanding of the MGBA, it may be possible to facilitate research into microbial-based pharmacological interventions and therapeutic strategies for neurological diseases.

Embryonic exposure to acetamiprid insecticide induces CD68-positive microglia and Purkinje cell arrangement abnormalities in the cerebellum of neonatal rats

Concerns have been raised regarding acetamiprid (ACE), a neonicotinoid insecticide, due to its potential neurodevelopmental toxicity. ACE, which is structurally similar to nicotine, acts as an agonist of nicotinic acetylcholine receptors (nAChRs) and resists degradation by acetylcholinesterase. Furthermore, ACE has been reported to disrupt neuronal transmission and induce developmental neurotoxicity and ataxia in animal models. However, the prenatal ACE exposure and its pathological changes, including impacts on motor control, remains unclear. In this study, we investigated the effects of ACE exposure, focusing on the development of cerebellar neurons and glia, which are linked to motor impairment. ACE at doses of 20, 40-, and 60 mg/kg body weight was administered to Pregnant Wistar rats via feed on gestational day (G) 15. The developing cerebellum of the pups was examined on postnatal days (P) 7, 14, and 18, corresponding to the critical periods of cerebellar maturation in rodents. Our data revealed that ACE exposure at 40 and 60 mg/kg induced abnormal neuronal alignment on P14, and neuronal cell loss on P18. Additionally, ACE altered microglial behavior, with an increase in the number of CD68-positive microglia, suggesting that the exposure results in an increase in phagocytic microglia in response to neuronal abnormalities, ultimately leading to neuronal cell loss. Pups exposed to 60 mg/kg ACE exhibited hindlimb clasping during the hindlimb suspension test, indicating motor impairment. These findings suggest that ACE exposure causes neuronal cell loss of developing Purkinje cells and promotes a phase shift to the activate mode of microglia. This study further highlights the crucial role of neuron-glia interactions in ACE-induced motor impairment, thus contributing to our understanding of the potential risks associated with prenatal ACE exposure.

Glia-glia crosstalk via semaphorins: Emerging implications in neurodegeneration

The central nervous system (CNS) is wired by a complex network of integrated glial and neuronal signals, which is critical for its development and homeostasis. In this context, glia-glia communication is a complex and dynamic process that is essential for ensuring optimal CNS function. Semaphorins, which include secreted and transmembrane molecules, and their receptors, mainly found in the plexin and neuropilin families, are expressed in a wide range of cell types, including glia. In the CNS, semaphorin signalling is involved in a spectrum of processes, including neurogenesis, neuronal migration and wiring, and glial cell recruitment. Recently, semaphorins and plexins have attracted intense research aimed at elucidating their roles in instructing glial cell behavior during development or in response to inflammatory stimuli. In this review, we provide an overview of the multifaceted role of semaphorins in glia-glia communication, highlighting recent discoveries about semaphoring-dependent regulation of glia functions in healthy conditions. We also discuss the mechanisms of gliaglia crosstalk mediated by semaphorins under pathological conditions, and how these interactions may provide potential avenues for therapeutic intervention in neuroinflammation-mediated neurodegeneration.

Role of Glial Cells and Receptors in Schizophrenia Pathogenesis

The specific pathogeneses of schizophrenia (SCZ) remain an enigma despite extensive research that has implicated both genetic and environmental factors. Recent revelations that dysregulated immune system caused by glial cell overactivation result in neuroinflammation, a key player in neurodegenerative as well as neuropsychiatric disorders including SCZ are providing novel clues on potential therapeutic interventions. Here, we review the roles of glial cells (Dr. Arne Schousboe's passion) and two of their most implicated receptors, toll-like receptors (TLRs), and nicotinic cholinergic receptors, in SCZ pathology with suggestions as potential targets in this devastating neuropsychiatric condition.

Akkermansia muciniphila and its metabolite propionic acid maintains neuronal mitochondrial division and autophagy homeostasis during Alzheimer's disease pathologic process via GPR41 and GPR43

BACKGROUND

Alzheimer's disease (AD) is a prevalent neurodegenerative disease (ND). In recent years, multiple clinical and animal studies have shown that mitochondrial dysfunction may be involved in the pathogenesis of AD. In addition, short-chain fatty acids (SCFA) produced by intestinal microbiota metabolism have been considered to be important factors affecting central nervous system (CNS) homeostasis. Among the main mediators of host-microbe interactions, volatile fatty acids play a crucial role. Nevertheless, the influence and pathways of microorganisms and their metabolites on Alzheimer's disease (AD) remain uncertain.

RESULTS

In this study, we present distinctions in blood and fecal SCFA levels and microbiota composition between healthy individuals and those diagnosed with AD. We found that AD patients showed a decrease in the abundance of Akkermansia muciniphila and a decrease in propionic acid both in fecal and in blood. In order to further reveal the effects and the mechanisms of propionic acid on AD prevention, we systematically explored the effects of propionic acid administration on AD model mice and cultured hippocampal neuronal cells. Results showed that oral propionate supplementation ameliorated cognitive impairment in AD mice. Propionate downregulated mitochondrial fission protein (DRP1) via G-protein coupled receptor 41 (GPR41) and enhanced PINK1/PARKIN-mediated mitophagy via G-protein coupled receptor 43 (GPR43) in AD pathophysiology which contribute to maintaining mitochondrial homeostasis both in vivo and in vitro. Administered A. muciniphila to AD mice before disease onset showed improved cognition, mitochondrial division and mitophagy in AD mice.

CONCLUSIONS

Taken together, our results demonstrate that A. muciniphila and its metabolite propionate protect against AD-like pathological events in AD mouse models by targeting mitochondrial homeostasis, making them promising therapeutic candidates for the prevention and treatment of AD. Video Abstract.

From Physiology to Pathology of Astrocytes: Highlighting Their Potential as Therapeutic Targets for CNS Injury

In the mammalian central nervous system (CNS), astrocytes are the ubiquitous glial cells that have complex morphological and molecular characteristics. These fascinating cells play essential neurosupportive and homeostatic roles in the healthy CNS and undergo morphological, molecular, and functional changes to adopt so-called 'reactive' states in response to CNS injury or disease. In recent years, interest in astrocyte research has increased dramatically and some new biological features and roles of astrocytes in physiological and pathological conditions have been discovered thanks to technological advances. Here, we will review and discuss the well-established and emerging astroglial biology and functions, with emphasis on their potential as therapeutic targets for CNS injury, including traumatic and ischemic injury. This review article will highlight the importance of astrocytes in the neuropathological process and repair of CNS injury.

C3/C3aR Bridges Spinal Astrocyte-Microglia Crosstalk and Accelerates Neuroinflammation in Morphine-Tolerant Rats

AIMS

Communication within glial cells acts as a pivotal intermediary factor in modulating neuroimmune pathology. Meanwhile, an increasing awareness has emerged regarding the detrimental role of glial cells and neuroinflammation in morphine tolerance (MT). This study investigated the influence of crosstalk between astrocyte and microglia on the evolution of morphine tolerance.

METHODS

Sprague-Dawley rats were intrathecally treated with morphine twice daily for 9 days to establish morphine-tolerant rat model. Tail-flick latency test was performed to identify the analgesic effect of morphine. The role of microglia, astrocyte and C3-C3aR axis in morphine tolerance were elucidated by real-time quantitative polymerase chain reaction, Western blot, and immunofluorescence.

RESULTS

Chronic morphine treatment notably promoted the activation of microglia, upregulated the production of proinflammatory mediators (interleukin-1 alpha (IL-1α), tumor necrosis factor alpha (TNFα), and complement component 1q (C1q)). Simultaneously, it programed astrocytes to a pro-inflammatory phenotype (A1), which mainly expresses complement 3 (C3) and serping1. PLX3397 (a colony-stimulating factor 1 receptor (CSF1R) inhibitor), Compstain (a C3 inhibitor) and SB290157(a C3aR antagonist) could reverse the above pathological process and alleviate morphine tolerance to different extents.

CONCLUSION

Our findings identify C3-C3aR axis as an amplifier of microglia-astrocyte crosstalk, neuroinflammation and a node for therapeutic intervention in morphine tolerance.

Efficient derivation of functional astrocytes from human induced pluripotent stem cells (hiPSCs)

Astrocytes are specialized glial cell types of the central nervous system (CNS) with remarkably high abundance, morphological and functional diversity. Astrocytes maintain neural metabolic support, synapse regulation, blood-brain barrier integrity and immunological homeostasis through intricate interactions with other cells, including neurons, microglia, pericytes and lymphocytes. Due to their extensive intercellular crosstalks, astrocytes are also implicated in the pathogenesis of CNS disorders, such as ALS (amyotrophic lateral sclerosis), Parkinson's disease and Alzheimer's disease. Despite the critical importance of astrocytes in neurodegeneration and neuroinflammation are recognized, the lack of suitable in vitro systems limits their availability for modeling human brain pathologies. Here, we report the time-efficient, reproducible generation of astrocytes from human induced pluripotent stem cells (hiPSCs). Our hiPSC-derived astrocytes expressed characteristic astrocyte markers, such as GFAP, S100b, ALDH1L1 and AQP4. Furthermore, hiPSC-derived astrocytes displayed spontaneous calcium transients and responded to inflammatory stimuli by the secretion of type A1 and type A2 astrocyte-related cytokines.

Unraveling the Role of the Blood-Brain Barrier in the Pathophysiology of Depression: Recent Advances and Future Perspectives

Depression is a highly prevalent psychological disorder characterized by persistent dysphoria, psychomotor retardation, insomnia, anhedonia, suicidal ideation, and a remarkable decrease in overall well-being. Despite the prevalence of accessible antidepressant therapies, many individuals do not achieve substantial improvement. Understanding the multifactorial pathophysiology and the heterogeneous nature of the disorder could lead the way toward better outcomes. Recent findings have elucidated the substantial impact of compromised blood-brain barrier (BBB) integrity on the manifestation of depression. BBB functions as an indispensable defense mechanism, tightly overseeing the transport of molecules from the periphery to preserve the integrity of the brain parenchyma. The dysfunction of the BBB has been implicated in a multitude of neurological disorders, and its disruption and consequent brain alterations could potentially serve as important factors in the pathogenesis and progression of depression. In this review, we extensively examine the pathophysiological relevance of the BBB and delve into the specific modifications of its components that underlie the complexities of depression. A particular focus has been placed on examining the effects of peripheral inflammation on the BBB in depression and elucidating the intricate interactions between the gut, BBB, and brain. Furthermore, this review encompasses significant updates on the assessment of BBB integrity and permeability, providing a comprehensive overview of the topic. Finally, we outline the therapeutic relevance and strategies based on BBB in depression, including COVID-19-associated BBB disruption and neuropsychiatric implications. Understanding the comprehensive pathogenic cascade of depression is crucial for shaping the trajectory of future research endeavors.

The Neuroimmune System and the Cerebellum

The recognition that there is an innate immune system of the brain, referred to as the neuroimmune system, that preforms many functions comparable to that of the peripheral immune system is a relatively new concept and much is yet to be learned. The main cellular components of the neuroimmune system are the glial cells of the brain, primarily microglia and astrocytes. These cell types preform many functions through secretion of signaling factors initially known as immune factors but referred to as neuroimmune factors when produced by cells of the brain. The immune functions of glial cells play critical roles in the healthy brain to maintain homeostasis that is essential for normal brain function, to establish cytoarchitecture of the brain during development, and, in pathological conditions, to minimize the detrimental effects of disease and injury and promote repair of brain structure and function. However, dysregulation of this system can occur resulting in actions that exacerbate or perpetuate the detrimental effects of disease or injury. The neuroimmune system extends throughout all brain regions, but attention to the cerebellar system has lagged that of other brain regions and information is limited on this topic. This article is meant to provide a brief introduction to the cellular and molecular components of the brain immune system, its functions, and what is known about its role in the cerebellum. The majority of this information comes from studies of animal models and pathological conditions, where upregulation of the system facilitates investigation of its actions.

The role of astrocytes response triggered by hyperglycaemia during spinal cord injury

OBJECTIVE

This manuscript aimed to provide a comprehensive overview of the physiological, molecular, and cellular mechanisms triggered by reactive astrocytes (RA) in the context of spinal cord injury (SCI), with a particular focus on cases involving hyperglycaemia.

METHODS

The compilation of articles related to astrocyte responses in neuropathological conditions, with a specific emphasis on those related to SCI and hyperglycaemia, was conducted by searching through databases including Science Direct, Web of Science, and PubMed.

RESULTS AND CONCLUSIONS

This article explores the dual role of astrocytes in both neurophysiological and neurodegenerative conditions within the central nervous system (CNS). In the aftermath of SCI and hyperglycaemia, astrocytes undergo a transformation into RA, adopting a distinct phenotype. While there are currently no approved therapies for SCI, various therapeutic strategies have been proposed to alleviate the detrimental effects of RAs following SCI and hyperglycemia. These strategies show promising potential in the treatment of SCI and its likely comorbidities.

M1 Microglia-Derived Exosomes Promote A1 Astrocyte Activation and Aggravate Ischemic Injury via circSTRN3/miR-331-5p/MAVS/NF-κB Pathway

Background

After ischemic stroke (IS), microglia and astrocytes undergo polarization, transforming into a pro-inflammatory phenotype (M1 or A1). According to previous studies, exosomes might play an important role in the interplay between M1 microglia and A1 astrocytes after IS.

Methods

We used the microglial oxygen-glucose deprivation/reperfusion (OGD/R) model and ultracentrifugation to extract M1 microglial exosomes (M1-exos). Subsequently, we identified circSTRN3 enriched in exosomes through RNA sequencing and detected the role of circSTRN3 in astrocyte activation based on bioinformatics analysis, immunofluorescence, Western blotting, and polymerase chain reaction analysis. We validated these findings in the middle cerebral artery occlusion/reperfusion (MCAO/R) model of adult male C57BL/6J mice. Finally, we confirmed the correlation among circSTRN3, miR-331-5p, and stroke severity score in exosomes isolated from peripheral blood of IS patients.

Results

Our findings revealed that M1-exos promoted A1 astrocyte activation. CircSTRN3 was abundant in M1-exos, which could sponge miR-331-5p to affect mitochondrial antiviral signaling protein (MAVS), activate NF-κB pathway, and participate in A1 astrocyte activation. In addition, overexpressed circSTRN3 augmented the infarct size and neurological dysfunction in MCAO/R models, while miR-331-5p mimics reversed the effect. Furthermore, circSTRN3 in IS patients was positively correlated with stroke severity score (R 2 = 0.83, P < 0.001), while miR-331-5p demonstrated a negative correlation with the same score (R 2 = 0.81, P < 0.001).

Conclusion

Taken together, our research indicated that circSTRN3 from M1-exos could promote A1 astrocyte activation and exacerbate ischemic brain injury via miR331-5p/MAVS/NF-κB axis.

New insights on targeting extracellular vesicle release by GW4869 to modulate lipopolysaccharide-induced neuroinflammation in mice model

Aim: This study aims to elucidate the regulatory role of extracellular vesicle (EV) release in glial cell activation, microglia-astrocyte interactions and neurological outcomes.Materials & methods: We employed a pharmacological intervention using GW4869 to modulate EV release, investigating its impact on primary cultures of microglia and astrocytes, microglia-astrocyte interactions, neuroinflammation and behavioral changes in lipopolysaccharide (LPS)-induced cell and animal models.Results: We isolated the EVs from glial cells and confirmed their positivity for CD9, CD63 and CD81. Our findings demonstrate that GW4869 significantly reduced EV protein concentrations secreted by glial cells within 6-12 h. Utilizing ELISA, immunostaining and western blot analyses, we observed that treatment with GW4869 attenuated glial cell activation and inflammatory responses both in vitro and in vivo. Transwell assays indicated that controlled EV release from activated microglia and astrocytes mitigated neurotoxic reactivity in normal astrocytes and microglia, respectively. Furthermore, GW4869 administration in LPS-injected mice resulted in notable improvements in spatial memory, anxiety-like behaviors and exploratory activity compared with vehicles.Conclusion: Our study suggests that modulating glia-derived EV dynamics effectively reduce neuroinflammation and enhance behavioral outcomes in mice. These findings underscore the potential of targeting EV release as a novel therapeutic approach for neurological disorders.

Hypoxic postconditioning modulates neuroprotective glial reactivity in a 3D cortical ischemic-hypoxic injury model

Stroke remains one of the major health challenges due to its high rates of mortality and long-term disability, necessitating the development of effective therapeutic treatment. This study aims to explore the neuroprotective effects of hypoxic postconditioning (HPC) using a cell-based 3D cortical ischemic-hypoxic injury model. Our model employs murine cells to investigate HPC-induced modulation of glial cell reactivity and intercommunication post-oxygen-glucose deprivation-reoxygenation (OGD-R) injury. We found that a single HPC session (1HPC) provided the most significant neuroprotection post-OGD-R compared to multiple intermittent hypoxic treatments, evidenced by improved spheroidal structure, enhanced cell survival and reduced apoptosis, optimal modulation of neuronal phenotypes, dampened ischemic responses, and augmented neurite outgrowth of spheroids. Furthermore, 1HPC suppressed both pro-inflammatory A1 and anti-inflammatory A2 astrocyte phenotypes despite the induction of astrocyte activation while reducing microglial activation with inhibited M1 and M2 reactive states. This was accompanied by a decrease in gene expression of the pro-inflammatory cytokines essential to microglia-astrocyte signaling, collectively suggesting a shift of glial cells away from their traditional reactive states for neuroprotection. This study highlights the potential of 1HPC as a novel therapeutic intervention for ischemic injury via the modulation of neuroprotective glial reactivity. Moreover, the 3D cortical ischemic-hypoxic injury model employed here holds enormous potential serving as a disease model to further elucidate the underlying mechanism of HPC, which can also extend to the applications in brain regeneration, drug development, and the modeling of neural diseases.

Acute Neurobehavioral and Glial Responses to Explosion Gas Inhalation in Rats

Military personnel, firefighters, and fire survivors exhibit a higher prevalence of mental health conditions such as depression and post-traumatic stress disorder (PTSD) compared to the general population. While numerous studies have examined the neurological impacts of physical trauma and psychological stress, research on acute neurobehavioral effects of gas inhalation from explosions or fires is limited. This study investigates the early-stage neurobehavioral and neuronal consequences of acute explosion gas inhalation in Sprague-Dawley rats. Rats were exposed to simulated explosive gas and subsequently assessed using behavioral tests and neurobiological analyses. The high-dose exposure group demonstrated significant depression-like behaviors, including reduced mobility and exploration. However, neuronal damage was not evident in histological analyses. Immunofluorescence revealed increased density of radial glia and oligodendrocytes in specific brain regions, suggesting hypoxia and axon damage induced by gas inhalation as a potential mechanism for the observed neurobehavioral changes. These findings underscore the acute impact of explosion gas inhalation on mental health, highlighting the habenula and dentate gyrus of hippocampus as the possible target regions. The findings are expected to support early diagnosis and treatment strategies for brain injuries caused by explosion gas, offering insights into early intervention for depression and PTSD in affected populations.

Neuroinflammation in Post COVID-19 Sequelae: Neuroinvasion and Neuroimmune Crosstalk

The emergence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in December 2019 triggered a swift global spread, leading to a devastating pandemic. Alarmingly, approximately one in four individuals diagnosed with coronavirus disease 2019 (COVID-19) experience varying degrees of cognitive impairment, raising concerns about a potential increase in neurological sequelae cases. Neuroinflammation seems to be the key pathophysiological hallmark linking mild respiratory COVID-19 to cognitive impairment, fatigue, and neurological sequelae in COVID-19 patients, highlighting the interaction between the nervous and immune systems following SARS-CoV-2 infection. Several hypotheses have been proposed to explain how the virus disrupts physiological pathways to trigger inflammation within the CNS, potentially leading to neuronal damage. These include neuroinvasion, systemic inflammation, disruption of the lung and gut-brain axes, and reactivation of latent viruses. This review explores the potential origins of neuroinflammation and the underlying neuroimmune cross-talk, highlighting important unanswered questions in the field. Addressing these fundamental issues could enhance our understanding of the virus's impact on the CNS and inform strategies to mitigate its detrimental effects.

Multi-Protective Effects of Petunidin-3-O-(trans-p-coumaroylrutinoside)-5-O-glucoside on D-Gal-Induced Aging Mice

Petunidin-3-O-(trans-p-coumaroylrutinoside)-5-O-glucoside (PtCG), the primary anthocyanin ingredient in Lycium ruthenicum Murr., possesses a range of biological activities, including antioxidative properties and melanin inhibition. This study aimed to investigate the protective effect of PtCG on D-galactose (D-gal)-induced aging in female mice and elucidate the underlying molecular pathways. Behavioral experiments, including the MWW and Y-maze tests, revealed that PtCG significantly ameliorated cognitive decline and enhanced learning and memory abilities in aging mice. Regarding biochemical indicators, PtCG considerably improved superoxide dismutase (SOD) and glutathione (GSH) activity while reducing malondialdehyde (MDA) and acetylcholinesterase (AChE) levels in the hippocampus and serum. Furthermore, PtCG ingestion alleviated liver injury by decreasing alanine transaminase (ALT), aspartate transaminase (AST), and alkaline phosphatase (AKP) levels, and attenuated renal damage by reducing blood urea nitrogen (BUN) and uric acid (UA) levels. Transmission electron microscopy (TEM) results demonstrated that PtCG restored the function and quantity of synapses in the hippocampus. Hematoxylin and eosin (H&E), Masson's trichrome, and Nissl staining revealed that PtCG significantly improved the relevant pathological characteristics of liver and hippocampal tissues in aging mice. The molecular mechanism investigation showed that PtCG downregulated the protein expression of microglial marker ionized calcium-binding adapter molecule 1 (Iba1), astrocytic marker glial fibrillary acidic protein (GFAP), β-secretase 1 (BACE-1), and amyloid-beta1-42 (Aβ1-42) in the hippocampus of aging mice. The protein expression of inflammatory pathway components, including nuclear factor-kappa B (NF-κB), cyclooxygenase-2 (COX2), inducible nitric oxide synthase (iNOS), and interleukin-1 beta (IL-1β), was also suppressed. These findings suggest that PtCG may possess anti-aging properties, with its mechanism of action potentially linked to the attenuation of neuroinflammation, oxidative stress, and liver and kidney damage. PtCG may have future applications as a functional food for the treatment of aging-related disorders.

Sex-dependent astrocyte reactivity: Unveiling chronic stress-induced morphological changes across multiple brain regions

Chronic stress is a major precursor to various neuropsychiatric disorders and is linked with increased inflammation in the brain. However, the bidirectional association between inflammation and chronic stress has yet to be fully understood. Astrocytes are one of the key inflammatory regulators in the brain, and the morphological change in reactive astrocytes serves as an important indicator of inflammation. In this study, we evaluated the sex-specific astrocyte response to chronic stress or systemic inflammation in key brain regions associated with mood disorders. We conducted the unpredictable chronic mild stress (UCMS) paradigm to model chronic stress, or lipopolysaccharide (LPS) injection to model systemic inflammation. To evaluate stress-induced morphological changes in astrocyte complexity, we measured GFAP fluorescent intensity for astrocyte expression, branch bifurcation by quantifying branch points and terminal points, branch arborization by conducting Sholl analysis, and calculated the ramification index. Our analysis indicated that chronic stress-induced morphological changes in astrocytes in all brain regions investigated. The effects of chronic stress were region and sex specific. Notably, females had greater stress or inflammation-induced astrocyte activation in the hypothalamus (HYPO), CA1, CA3, and amygdala (AMY) than males. These findings indicate that chronic stress induces astrocyte activation that may drive sex and region-specific effects in females, potentially contributing to sex-dependent mechanisms of disease.

Astrocytes and microglia in the coordination of CNS development and homeostasis

Glia have emerged as important architects of central nervous system (CNS) development and maintenance. While traditionally glial contributions to CNS development and maintenance have been studied independently, there is growing evidence that either suggests or documents that glia may act in coordinated manners to effect developmental patterning and homeostatic functions in the CNS. In this review, we focus on astrocytes, the most abundant glia in the CNS, and microglia, the earliest glia to colonize the CNS highlighting research that documents either suggestive or established coordinated actions by these glial cells in various CNS processes including cell and/or debris clearance, neuronal survival and morphogenesis, synaptic maturation, and circuit function, angio-/vasculogenesis, myelination, and neurotransmission. Some molecular mechanisms underlying these processes that have been identified are also described. Throughout, we categorize the available evidence as either suggestive or established interactions between microglia and astrocytes in the regulation of the respective process and raise possible avenues for further research. We conclude indicating that a better understanding of coordinated astrocyte-microglial interactions in the developing and mature brain holds promise for developing effective therapies for brain pathologies where these processes are perturbed.

Nimodipine attenuates neuroinflammation and delayed apoptotic neuronal death induced by trimethyltin in the dentate gyrus of mice

L-type voltage-gated calcium channels (L-VGCCs) are thought to be involved in epileptogenesis and acute excitotoxicity. However, little is known about the role of L-VGCCs in neuroinflammation or delayed neuronal death following excitotoxic insult. We examined the effects of repeated treatment with the L-VGCC blocker nimodipine on neuroinflammatory changes and delayed neuronal apoptosis in the dentate gyrus following trimethyltin (TMT)-induced convulsions. Male C57BL/6 N mice were administered TMT (2.6 mg/kg, i.p.), and the expression of the Cav1.2 and Cav1.3 subunits of L-VGCC were evaluated. The expression of both subunits was significantly decreased; however, the astroglial expression of Cav1.3 L-VGCC was significantly induced at 6 and 10 days after TMT treatment. Furthermore, astroglial Cav1.3 L-VGCCs colocalized with both the pro-inflammatory phenotype marker C3 and the anti-inflammatory phenotype marker S100A10 of astrocytes. Nimodipine (5 mg/kg, i.p. × 5 at 12-h intervals) did not significantly affect TMT-induced astroglial activation. However, nimodipine significantly attenuated the pro-inflammatory phenotype changes, while enhancing the anti-inflammatory phenotype changes in astrocytes after TMT treatment. Consistently, nimodipine reduced the levels of pro-inflammatory astrocytes-to-microglia mediators, while increasing the levels of anti-inflammatory astrocytes-to-microglia mediators. These effects were accompanied by an increase in the phosphorylation of extracellular signal-regulated kinase (ERK), supporting our previous finding that p-ERK is a signaling factor that regulates astroglial phenotype changes. In addition, nimodipine significantly attenuated TMT-induced microglial activation and delayed apoptosis of dentate granule neurons. Our results suggest that L-VGCC blockade attenuates neuroinflammation and delayed neurotoxicity following TMT-induced convulsions through the regulation of astroglial phenotypic changes by promoting ERK signaling.

Impact of O -GlcNAcylation elevation on mitophagy and glia in the dentate gyrus

O -GlcNAcylation is a dynamic and reversible protein post-translational modification of serine or threonine residues which modulates the activity of transcriptional and signaling pathways and controls cellular responses to metabolic and inflammatory stressors. We and others have shown that O -GlcNAcylation has the potential to regulate autophagy and mitophagy to play a critical role in mitochondrial quality control, but this has not been assessed in vivo in the brain. This is important since mitochondrial dysfunction contributes to the development of neurodegenerative disease. We used mito-QC reporter mice to assess mitophagy in diverse cells in the dentate gyrus in response to pharmacological inhibition of OGA with thiamet G which leads to elevation of protein O -GlcNAcylation. We demonstrate that mitophagy occurs predominantly in the GFAP positive astrocytes and is significantly decreased in response to elevated O -GlcNAcylation. Furthermore, with increased O -GlcNAcylation, the levels of astrocyte makers GFAP and S100B, and microglial cell marker IBA1 were decreased in the dentate gyrus, while the levels of microglial cell marker TMEM119 were increased, indicating significant changes in glia homeostasis. These results provide strong evidence of the regulation of mitophagy and glia signatures by the O -GlcNAc pathway.

Intercellular Adhesion Molecule 1 (ICAM-1): An Inflammatory Regulator with Potential Implications in Ferroptosis and Parkinson's Disease

Intercellular adhesion molecule 1 (ICAM-1/CD54), a transmembrane glycoprotein, has been considered as one of the most important adhesion molecules during leukocyte recruitment. It is encoded by the ICAM1 gene and plays a central role in inflammation. Its crucial role in many inflammatory diseases such as ulcerative colitis and rheumatoid arthritis are well established. Given that neuroinflammation, underscored by microglial activation, is a key element in neurodegenerative diseases such as Parkinson's disease (PD), we investigated whether ICAM-1 has a role in this progressive neurological condition and, if so, to elucidate the underpinning mechanisms. Specifically, we were interested in the potential interaction between ICAM-1, glial cells, and ferroptosis, an iron-dependent form of cell death that has recently been implicated in PD. We conclude that there exist direct and indirect (via glial cells and T cells) influences of ICAM-1 on ferroptosis and that further elucidation of these interactions can suggest novel intervention for this devastating disease.

Protective effects of docosahexaenoic acid supplementation on cognitive dysfunction and hippocampal synaptic plasticity impairment induced by early postnatal PM2.5 exposure in young rats

PM2.5 exposure is a challenging environmental issue that is closely related to cognitive development impairment; however, currently, relevant means for prevention and treatment remain lacking. Herein, we determined the preventive effect of docosahexaenoic acid (DHA) supplementation on the neurodevelopmental toxicity induced by PM2.5 exposure. Neonatal rats were divided randomly into three groups: control, PM2.5, and DHA + PM2.5 groups. DHA could ameliorate PM2.5-induced learning and memory dysfunction, as well as reverse the impairment of hippocampal synaptic plasticity, evidenced by enhanced long-term potentiation, recovered synaptic ultrastructure, and increased expression of synaptic proteins. Moreover, DHA increased CREB phosphorylation and BDNF levels and attenuated neuroinflammation and oxidative stress, reflected by lower levels of IBA-1, IL-1β, and IL-6 and increased levels of SOD1 and Nrf2. In summary, our findings demonstrated that supplementation of DHA effectively mitigated the cognitive dysfunction and synaptic plasticity impairment induced by early postnatal exposure to PM2.5. These beneficial effects may be attributed to the upregulation of the CREB/BDNF signaling pathway, as well as the reduction of neuroinflammation and oxidative stress.

Autism-associated CHD8 controls reactive gliosis and neuroinflammation via remodeling chromatin in astrocytes

Reactive changes of glial cells during neuroinflammation impact brain disorders and disease progression. Elucidating the mechanisms that control reactive gliosis may help us to understand brain pathophysiology and improve outcomes. Here, we report that adult ablation of autism spectrum disorder (ASD)-associated CHD8 in astrocytes attenuates reactive gliosis via remodeling chromatin accessibility, changing gene expression. Conditional Chd8 deletion in astrocytes, but not microglia, suppresses reactive gliosis by impeding astrocyte proliferation and morphological elaboration. Astrocyte Chd8 ablation alleviates lipopolysaccharide-induced neuroinflammation and septic-associated hypothermia in mice. Astrocytic CHD8 plays an important role in neuroinflammation by altering the chromatin landscape, regulating metabolic and lipid-associated pathways, and astrocyte-microglia crosstalk. Moreover, we show that reactive gliosis can be directly mitigated in vivo using an adeno-associated virus (AAV)-mediated Chd8 gene editing strategy. These findings uncover a role of ASD-associated CHD8 in the adult brain, which may warrant future exploration of targeting chromatin remodelers in reactive gliosis and neuroinflammation in injury and neurological diseases.

Suppression of inner blood-retinal barrier breakdown and pathogenic Müller glia activation in ischemia retinopathy by myeloid cell depletion

Ischemic retinopathies including diabetic retinopathy are major causes of vision loss. Inner blood-retinal barrier (BRB) breakdown with retinal vascular hyperpermeability results in macular edema. Although dysfunction of the neurovascular unit including neurons, glia, and vascular cells is now understood to underlie this process, there is a need for fuller elucidation of the underlying events in BRB dysfunction in ischemic disease, including a systematic analysis of myeloid cells and exploration of cellular cross-talk. We used an approach for microglia depletion with the CSF-1R inhibitor PLX5622 (PLX) in the retinal ischemia-reperfusion (IR) model. Under non-IR conditions, PLX treatment successfully depleted microglia in the retina. PLX suppressed the microglial activation response following IR as well as infiltration of monocyte-derived macrophages. This occurred in association with reduction of retinal expression of chemokines including CCL2 and the inflammatory adhesion molecule ICAM-1. In addition, there was a marked suppression of retinal neuroinflammation with reduction in expression of IL-1b, IL-6, Ptgs2, TNF-a, and Angpt2, a protein that regulates BRB permeability. PLX treatment significantly suppressed inner BRB breakdown following IR, without an appreciable effect on neuronal dysfunction. A translatomic analysis of Müller glial-specific gene expression in vivo using the Ribotag approach demonstrated a strong suppression of Müller cell expression of multiple pro-inflammatory genes following PLX treatment. Co-culture studies of Müller cells and microglia demonstrated that activated microglia directly upregulates Müller cell-expression of these inflammatory genes, indicating Müller cells as a downstream effector of myeloid cells in retinal IR. Co-culture studies of these two cell types with endothelial cells demonstrated the ability of both activated microglia and Müller cells to compromise EC barrier function. Interestingly, quiescent Müller cells enhanced EC barrier function in this co-culture system. Together this demonstrates a pivotal role for myeloid cells in inner BRB breakdown in the setting of ischemia-associated disease and indicates that myeloid cells play a major role in iBRB dysregulation, through direct and indirect effects, while Müller glia participate in amplifying the neuroinflammatory effect of myeloid cells.

Glial reactivity is linked to synaptic dysfunction across the aging and Alzheimer's disease spectrum

Previous studies have shown that glial and neuronal changes may trigger synaptic dysfunction in Alzheimer's disease(AD). However, the link between glial and neuronal markers and synaptic abnormalities in the living brain is poorly understood. Here, we investigated the association between biomarkers of astrocyte and microglial reactivity and synaptic dysfunction in 478 individuals across the aging and AD spectrum from two cohorts with available CSF measures of amyloid-β(Aβ), phosphorylated tau(pTau181), astrocyte reactivity(GFAP), microglial activation(sTREM2), and synaptic biomarkers(GAP43 and neurogranin). Elevated CSF GFAP levels were linked to presynaptic and postsynaptic dysfunction, regardless of cognitive status or Aβ presence. CSF sTREM2 levels were associated with presynaptic biomarkers in cognitively unimpaired and impaired Aβ + individuals and postsynaptic biomarkers in cognitively impaired Aβ + individuals. Notably, CSF pTau181 levels mediated all associations between GFAP or sTREM2 levels and synaptic dysfunction biomarkers. These results suggest that neuronal-related synaptic biomarkers could be used in clinical trials targeting glial reactivity in AD.

Neurodegenerative disorders: Mechanisms of degeneration and therapeutic approaches with their clinical relevance

Neurodegenerative disorders (NDs) are expected to pose a significant challenge for both medicine and public health in the upcoming years due to global demographic changes. NDs are mainly represented by degeneration/loss of neurons, which is primarily accountable for severe mental illness. This neuronal degeneration leads to many neuropsychiatric problems and permanent disability in an individual. Moreover, the tight junction of the brain, blood-brain barrier (BBB)has a protective feature, functioning as a biological barrier that can prevent medicines, toxins, and foreign substances from entering the brain. However, delivering any medicinal agent to the brain in NDs (i.e., Multiple sclerosis, Alzheimer's, Parkinson's, etc.) is enormously challenging. There are many approved therapies to address NDs, but most of them only help treat the associated manifestations. The available therapies have failed to control the progression of NDs due to certain factors, i.e., BBB and drug-associated undesirable effects. NDs have extremely complex pathology, with many pathogenic mechanisms involved in the initiation and progression; thereby, a limited survival rate has been observed in ND patients. Hence, understanding the exact mechanism behind NDs is crucial to developing alternative approaches for improving ND patients' survival rates. Thus, the present review sheds light on different cellular mechanisms involved in NDs and novel therapeutic approaches with their clinical relevance, which will assist researchers in developing alternate strategies to address the limitations of conventional ND therapies. The current work offers the scope into the near future to improve the therapeutic approach of NDs.

Beyond PDE4 inhibition: A comprehensive review on downstream cAMP signaling in the central nervous system

Cyclic adenosine monophosphate (cAMP) is a key second messenger that regulates signal transduction pathways pivotal for numerous biological functions. Intracellular cAMP levels are spatiotemporally regulated by their hydrolyzing enzymes called phosphodiesterases (PDEs). It has been shown that increased cAMP levels in the central nervous system (CNS) promote neuroplasticity, neurotransmission, neuronal survival, and myelination while suppressing neuroinflammation. Thus, elevating cAMP levels through PDE inhibition provides a therapeutic approach for multiple CNS disorders, including multiple sclerosis, stroke, spinal cord injury, amyotrophic lateral sclerosis, traumatic brain injury, and Alzheimer's disease. In particular, inhibition of the cAMP-specific PDE4 subfamily is widely studied because of its high expression in the CNS. So far, the clinical translation of full PDE4 inhibitors has been hampered because of dose-limiting side effects. Hence, focusing on signaling cascades downstream activated upon PDE4 inhibition presents a promising strategy, offering novel and pharmacologically safe targets for treating CNS disorders. Yet, the underlying downstream signaling pathways activated upon PDE(4) inhibition remain partially elusive. This review provides a comprehensive overview of the existing knowledge regarding downstream mediators of cAMP signaling induced by PDE4 inhibition or cAMP stimulators. Furthermore, we highlight existing gaps and future perspectives that may incentivize additional downstream research concerning PDE(4) inhibition, thereby providing novel therapeutic approaches for CNS disorders.

Rapamycin Alleviates Neuronal Injury and Modulates Microglial Activation After Cerebral Ischemia

Neurons and microglia are sensitive to cerebral microcirculation and their responses play a crucial part in the pathological processes, while they are also the main target cells of many drugs used to treat brain diseases. Rapamycin exhibits beneficial effects in many diseases; however, whether it can affect neuronal injury or alter the microglial activation after global cerebral ischemia remains unclear. In this study, we performed global cerebral ischemia combined with rapamycin treatment in CX3CR1GFP/+ mice and explored the effects of rapamycin on neuronal deficit and microglial activation. Our results showed that rapamycin reduced neuronal loss, neurodegeneration, and ultrastructural damage after ischemia by histological staining and transmission electron microscopy (TEM). Interestingly, rapamycin suppressed de-ramification and proliferation of microglia and reduced the density of microglia. Immunofluorescence staining indicated that rapamycin skewed microglial polarization toward an anti-inflammatory state. Furthermore, rapamycin as well suppressed the activation of astrocytes. Meanwhile, quantitative real-time polymerase chain reaction (qRT-PCR) analyses revealed a significant reduction of pro-inflammatory factors as well as an elevation of anti-inflammatory factors upon rapamycin treatment. As a result of these effects, behavioral tests showed that rapamycin significantly alleviated the brain injury after stroke. Together, our study suggested that rapamycin attenuated neuronal injury, altered microglial activation state, and provided a more beneficial immune microenvironment for the brain, which could be used as a promising therapeutic approach to treat ischemic cerebrovascular diseases.

Glial scarring around intra-cortical MEA implants with flexible and free microwires inserted using biodegradable PLGA needles

Introduction: Many invasive and noninvasive neurotechnologies are being developed to help treat neurological pathologies and disorders. Making a brain implant safe, stable, and efficient in the long run is one of the requirements to conform with neuroethics and overcome limitations for numerous promising neural treatments. A main limitation is low biocompatibility, characterized by the damage implants create in brain tissue and their low adhesion to it. This damage is partly linked to friction over time due to the mechanical mismatch between the soft brain tissue and the more rigid wires. Methods: Here, we performed a short biocompatibility assessment of bio-inspired intra-cortical implants named "Neurosnooper" made of a microelectrode array consisting of a thin, flexible polymer-metal-polymer stack with microwires that mimic axons. Implants were assembled into poly-lactic-glycolic acid (PLGA) biodegradable needles for their intra-cortical implantation. Results and Discussion: The study of glial scars around implants, at 7 days and 2 months post-implantation, revealed a good adhesion between the brain tissue and implant wires and a low glial scar thickness. The lowest corresponds to electrode wires with a section size of 8 μm × 10 μm, compared to implants with the 8 μm × 50 μm electrode wire section size, and a straight shape appears to be better than a zigzag. Therefore, in addition to flexibility, size and shape parameters are important when designing electrode wires for the next generation of clinical intra-cortical implants.

Heavy Metal Interactions with Neuroglia and Gut Microbiota: Implications for Huntington's Disease

Huntington's disease (HD) is a rare but progressive and devastating neurodegenerative disease characterized by involuntary movements, cognitive decline, executive dysfunction, and neuropsychiatric conditions such as anxiety and depression. It follows an autosomal dominant inheritance pattern. Thus, a child who has a parent with the mutated huntingtin (mHTT) gene has a 50% chance of developing the disease. Since the HTT protein is involved in many critical cellular processes, including neurogenesis, brain development, energy metabolism, transcriptional regulation, synaptic activity, vesicle trafficking, cell signaling, and autophagy, its aberrant aggregates lead to the disruption of numerous cellular pathways and neurodegeneration. Essential heavy metals are vital at low concentrations; however, at higher concentrations, they can exacerbate HD by disrupting glial-neuronal communication and/or causing dysbiosis (disturbance in the gut microbiota, GM), both of which can lead to neuroinflammation and further neurodegeneration. Here, we discuss in detail the interactions of iron, manganese, and copper with glial-neuron communication and GM and indicate how this knowledge may pave the way for the development of a new generation of disease-modifying therapies in HD.

Primary mitochondrial diseases: The intertwined pathophysiology of bioenergetic dysregulation, oxidative stress and neuroinflammation

OBJECTIVES AND SCOPE

Primary mitochondrial diseases (PMDs) are rare genetic disorders resulting from mutations in genes crucial for effective oxidative phosphorylation (OXPHOS) that can affect mitochondrial function. In this review, we examine the bioenergetic alterations and oxidative stress observed in cellular models of primary mitochondrial diseases (PMDs), shedding light on the intricate complexity between mitochondrial dysfunction and cellular pathology. We explore the diverse cellular models utilized to study PMDs, including patient-derived fibroblasts, induced pluripotent stem cells (iPSCs) and cybrids. Moreover, we also emphasize the connection between oxidative stress and neuroinflammation.

INSIGHTS

The central nervous system (CNS) is particularly vulnerable to mitochondrial dysfunction due to its dependence on aerobic metabolism and the correct functioning of OXPHOS. Similar to other neurodegenerative diseases affecting the CNS, individuals with PMDs exhibit several neuroinflammatory hallmarks alongside neurodegeneration, a pattern also extensively observed in mouse models of mitochondrial diseases. Based on histopathological analysis of postmortem human brain tissue and findings in mouse models of PMDs, we posit that neuroinflammation is not merely a consequence of neurodegeneration but a potential pathogenic mechanism for disease progression that deserves further investigation. This recognition may pave the way for novel therapeutic strategies for this group of devastating diseases that currently lack effective treatments.

SUMMARY

In summary, this review provides a comprehensive overview of bioenergetic alterations and redox imbalance in cellular models of PMDs while underscoring the significance of neuroinflammation as a potential driver in disease progression.

P7C3 suppresses astrocytic senescence to protect dopaminergic neurons: Implication in the mouse model of Parkinson's disease

AIMS

Astrocytic senescence is inextricably linked to aging and neurodegenerative disorders, including Parkinson's disease (PD). P7C3 is a small, neuroprotective aminopropyl carbazole compound that exhibits anti-inflammatory properties. However, the effects of P7C3 on astrocytic senescence in PD remain to be elucidated.

METHODS

An in vitro, long culture-induced, replicative senescence cell model and a 1-methyl-4-phenylpyridinium (MPP+)/rotenone-induced premature senescence cell model were used to investigate the effects of P7C3 on astrocytic senescence. An in vivo, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced mouse PD model was used to study the role of P7C3 in astrocytic senescence. Immunoblotting, real-time quantitative RT-PCR (qPCR), immunofluorescence, subcellular fractionation assays, and immunohistochemistry were utilized to confirm the effects of P7C3 on astrocytic senescence and elucidate its underlying mechanisms.

RESULTS

This study determined that P7C3 suppressed the senescence-associated secretory phenotype (SASP) in both cell models, as demonstrated by the reduction in the critical senescence marker p16 and proinflammatory factors (IL-6, IL-1β, CXCL10, and MMP9) and increased laminB1 levels, implying that P7C3 inhibited replicative astrocytic senescence and MPP+/rotenone-induced premature astrocytic senescence, Most importantly, we demonstrated that P7C3 prevented the death of dopamine (DA) neurons and reduced the behavioral deficits in the MPTP-induced mouse model of PD, which is accompanied by a decrease in senescent astrocytes in the substantia nigra compacta (SNc). Mechanistically, P7C3 promoted Nrf2/Sirt3-mediated mitophagy and reduced mitochondrial reactive oxygen species (mitoROS) generation, which contributed to the suppression of astrocytic senescence. Furthermore, Sirt3 deficiency obviously abolished the inhibitory effects of P7C3 on astrocytic senescence.

CONCLUSION

This study revealed that P7C3 inhibited astrocytic senescence via increased Nrf2/Sirt3-mediated mitophagy and suppression of mitoROS, which further protected against DA neuronal loss. These observations provide a prospective theoretical basis for P7C3 in the treatment of age-associated neurodegenerative diseases, such as PD.

Evolution of glial cells: a non-bilaterian perspective

Nervous systems of bilaterian animals generally consist of two cell types: neurons and glial cells. Despite accumulating data about the many important functions glial cells serve in bilaterian nervous systems, the evolutionary origin of this abundant cell type remains unclear. Current hypotheses regarding glial evolution are mostly based on data from model bilaterians. Non-bilaterian animals have been largely overlooked in glial studies and have been subjected only to morphological analysis. Here, we provide a comprehensive overview of conservation of the bilateral gliogenic genetic repertoire of non-bilaterian phyla (Cnidaria, Placozoa, Ctenophora, and Porifera). We overview molecular and functional features of bilaterian glial cell types and discuss their possible evolutionary history. We then examine which glial features are present in non-bilaterians. Of these, cnidarians show the highest degree of gliogenic program conservation and may therefore be crucial to answer questions about glial evolution.

Animal models to study cognitive impairment of chronic kidney disease

Mild cognitive impairment (MCI) is common in people with chronic kidney disease (CKD), and its prevalence increases with progressive loss of kidney function. MCI is characterized by a decline in cognitive performance greater than expected for an individual age and education level but with minimal impairment of instrumental activities of daily living. Deterioration can affect one or several cognitive domains (attention, memory, executive functions, language, and perceptual motor or social cognition). Given the increasing prevalence of kidney disease, more and more people with CKD will also develop MCI causing an enormous disease burden for these individuals, their relatives, and society. However, the underlying pathomechanisms are poorly understood, and current therapies mostly aim at supporting patients in their daily lives. This illustrates the urgent need to elucidate the pathogenesis and potential therapeutic targets and test novel therapies in appropriate preclinical models. Here, we will outline the necessary criteria for experimental modeling of cognitive disorders in CKD. We discuss the use of mice, rats, and zebrafish as model systems and present valuable techniques through which kidney function and cognitive impairment can be assessed in this setting. Our objective is to enable researchers to overcome hurdles and accelerate preclinical research aimed at improving the therapy of people with CKD and MCI.

Origin, identity, and function of terminal Schwann cells

The highly specialized nonmyelinating glial cells present at somatic peripheral nerve endings, known collectively as terminal Schwann cells (TSCs), play critical roles in the development, function and repair of their motor and sensory axon terminals and innervating tissue. Over the past decades, research efforts across various vertebrate species have revealed that while TSCs are a diverse group of cells, they share a number of features among them. In this review, we summarize the state-of-knowledge about each TSC type and explore the opportunities that TSCs provide to treat conditions that afflict peripheral axon terminals.

Psilocybin for dementia prevention? The potential role of psilocybin to alter mechanisms associated with major depression and neurodegenerative diseases

Major depression is an established risk factor for subsequent dementia, and depression in late life may also represent a prodromal state of dementia. Considering current challenges in the clinical development of disease modifying therapies for dementia, the focus of research is shifting towards prevention and modification of risk factors to alter the neurodegenerative disease trajectory. Understanding mechanistic commonalities underlying affective symptoms and cognitive decline may reveal biomarkers to aid early identification of those at risk of progressing to dementia during the preclinical phase of disease, thus allowing for timely intervention. Adult hippocampal neurogenesis (AHN) is a phenomenon that describes the birth of new neurons in the dentate gyrus throughout life and it is associated with spatial learning, memory and mood regulation. Microglia are innate immune system macrophages in the central nervous system that carefully regulate AHN via multiple mechanisms. Disruption in AHN is associated with both dementia and major depression and microgliosis is a hallmark of several neurodegenerative diseases. Emerging evidence suggests that psychedelics promote neuroplasticity, including neurogenesis, and may also be immunomodulatory. In this context, psilocybin, a serotonergic agonist with rapid-acting antidepressant properties has the potential to ameliorate intersecting pathophysiological processes relevant for both major depression and neurodegenerative diseases. In this narrative review, we focus on the evidence base for the effects of psilocybin on adult hippocampal neurogenesis and microglial form and function; which may suggest that psilocybin has the potential to modulate multiple mechanisms of action, and may have implications in altering the progression from major depression to dementia in those at risk.

Allopregnanolone and its antagonist modulate neuroinflammation and neurological impairment

Neuroinflammation accompanies several brain disorders, either as a secondary consequence or as a primary cause and may contribute importantly to disease pathogenesis. Neurosteroids which act as Positive Steroid Allosteric GABA-A receptor Modulators (Steroid-PAM) appear to modulate neuroinflammation and their levels in the brain may vary because of increased or decreased local production or import from the systemic circulation. The increased synthesis of steroid-PAMs is possibly due to increased expression of the mitochondrial cholesterol transporting protein (TSPO) in neuroinflammatory tissue, and reduced production may be due to changes in the enzymatic activity. Microglia and astrocytes play an important role in neuroinflammation, and their production of inflammatory mediators can be both activated and inhibited by steroid-PAMs and GABA. What is surprising is the finding that both allopregnanolone, a steroid-PAM, and golexanolone, a novel GABA-A receptor modulating steroid antagonist (GAMSA), can inhibit microglia and astrocyte activation and normalize their function. This review focuses on the role of steroid-PAMs in neuroinflammation and their importance in new therapeutic approaches to CNS and liver disease.