Minocycline selectively inhibits M1 polarization of microglia

Differential response of injured and healthy retinas to syngeneic and allogeneic transplantation of a clonal cell line of immortalized olfactory ensheathing glia: a double-edged sword

JOURNAL/nrgr/04.03/01300535-202508000-00029/figure1/v/2024-09-30T120553Z/r/image-tiff Olfactory ensheathing glia promote axonal regeneration in the mammalian central nervous system, including retinal ganglion cell axonal growth through the injured optic nerve. Still, it is unknown whether olfactory ensheathing glia also have neuroprotective properties. Olfactory ensheathing glia express brain-derived neurotrophic factor, one of the best neuroprotectants for axotomized retinal ganglion cells. Therefore, we aimed to investigate the neuroprotective capacity of olfactory ensheating glia after optic nerve crush. Olfactory ensheathing glia cells from an established rat immortalized clonal cell line, TEG3, were intravitreally injected in intact and axotomized retinas in syngeneic and allogeneic mode with or without microglial inhibition or immunosuppressive treatments. Anatomical and gene expression analyses were performed. Olfactory bulb-derived primary olfactory ensheathing glia and TEG3 express major histocompatibility complex class II molecules. Allogeneically and syngenically transplanted TEG3 cells survived in the vitreous for up to 21 days, forming an epimembrane. In axotomized retinas, only the allogeneic TEG3 transplant rescued retinal ganglion cells at 7 days but not at 21 days. In these retinas, microglial anatomical activation was higher than after optic nerve crush alone. In intact retinas, both transplants activated microglial cells and caused retinal ganglion cell death at 21 days, a loss that was higher after allotransplantation, triggered by pyroptosis and partially rescued by microglial inhibition or immunosuppression. However, neuroprotection of axotomized retinal ganglion cells did not improve with these treatments. The different neuroprotective properties, different toxic effects, and different responses to microglial inhibitory treatments of olfactory ensheathing glia in the retina depending on the type of transplant highlight the importance of thorough preclinical studies to explore these variables.

Short-term PS-NP exposure in early adulthood induces neuronal damage in middle-aged mice via microglia-mediated neuroinflammation

Nanoplastics (NPs) are ubiquitous environmental pollutants that have garnered considerable attention for their potential adverse health effects. In this study, male C57BL/6 J mice were orally treated with a mixture of 50-nm and 200-nm polystyrene (PS)-NPs for one week followed by measurements of their neurobehavioral performance and neuronal damage 10 months later. Notably, PS-NPs were detected in the brains of the mice by transmission electron microscopy (TEM) and a nanoscale hyperspectral microscope imaging system 10 months after the PS-NP exposure. The mice exposed to short-term PS-NPs exhibited cognitive dysfunction and anxiety-like symptoms, neuronal damage and synapse loss, and an increase in the number of M1-polarized microglia and A1-reactive astrocytes. Interestingly, the inhibition of microglial activation by minocycline significantly mitigated the PS-NP-induced synapse loss and neuron damage. In vitro studies showed that PS-NPs could be readily internalized by three types of neurovascular unit (NVU) cells, including microglia, astrocytes, and brain microvascular endothelial cells, via multiple pathways. RNA-seq analysis confirmed that microglia-mediated neuronal injury was associated with disturbances in synapse and cell death signaling pathways. Collectively, these findings suggest that short-term PS-NP exposure-induced neuroinflammation in early adulthood may not be resolved naturally but may deteriorate under the interaction of microglia and astrocytes, leading to synapse loss, neuron degeneration, and cognitive dysfunction in middle age. The results of the present study provide important insights into the potential neurological impacts of NPs and suggest that targeting microglia to suppress inflammation might be a potential intervention strategy for neurodegeneration induced by NPs.

Myelination Trajectory and Microglial Dynamics Following Repeated Sevoflurane Exposure in Developing Brain

The myelination is a critical process during brain development. This study aimed to explore the impact of volatile anesthetic sevoflurane on developing myelination and the role of microglial activation in this process. Neonatal C57BL/6J mice were exposed to sevoflurane at their postnatal 6-8 days. Neurobehavioral tests were used to assess fine motor and cognitive functions. Myelination of hippocampus (HC) and corpus callosum (CC), as well as microglial activation, were determined by western blotting and immunostaining. Lipid droplets were assessed by Oil-Red-O and Bodipy staining. Further, primary microglia were co-cultured with oligodendrocyte precursor cell (OPC) to determine the role of microglia in the proliferation and differentiation of OPC. And microglial inhibitor minocycline and CSF1R inhibitor PLX5622 were administered to assess the effects of microglial activation on developing myelination. The results showed that repeated sevoflurane exposure impaired both fine motor and cognitive functions and induced abnormal expressions of myelin-related proteins myelin basic protein (MBP) and platelet-derived growth factor α receptor (PDGFR-α). And accumulations of lipid droplets were found in the microglia of HC and CC after sevoflurane exposure. Further, the spatiotemporal response to repeated sevoflurane exposure in glial cells exhibited an aberrant myelination process and microglial polarization. The conditioned medium from sevoflurane-treated microglia inhibited the OPC proliferation and differentiation, while minocycline or PLX5622 alleviated sevoflurane-induced neuroinflammation and hypomyelination. Therefore, repeated sevoflurane exposure negatively affected OPC differentiation and myelination trajectory through hyperactivating microglia in developing brain, leading to motor and cognitive impairments, while microglial inhibition/depletion could protect against sevoflurane-induced damage on developing myelination.

Microglial repopulation reverses radiation-induced cognitive dysfunction by restoring medial prefrontal cortex activity and modulating leukotriene-C4 synthesis

Cranial radiotherapy and environmental radiation exposure are associated with increased risk of cognitive dysfunction, including memory deficits and mood disorders, yet the underlying mechanisms remain poorly understood. In this study, we demonstrate that cranial irradiation induces hypoactivity in the medial prefrontal cortex (mPFC) of mice, leading to anxiety-like behaviors and memory impairments, which can be prevented by optogenetic activation of mPFC excitatory neurons. Radiaiton exposure also causes a significant reduction in microglial density within the mPFC, accompanied by morphological and transcriptional alterations in the remaining microglia. Notably, microglial repopulation, achieved through CSF1R antagonist-mediated depletion prior to irradiation and subsequent repopulation, restores mPFC neuronal acitivity and reverses cognitive and behavioral deficits. Integrated bulk RNA sequencing and microglial proteomic analysis of the mPFC reveal that microglial repopulation specifically modulates the leukotriene-C4 biosynthesis pathway, without significant changes in canonical pro-inflammatory cytokines or chemokines. Importantly, pharmacological inhibition of leukotriene-C4 synthase ameliorates radiation-induced anxiety and memory impairments. These findings identify leukotriene-C4 signaling as a critical mechanism underlying radiation-induced cognitive dysfunction and suggest that microglial repopulation and targted inhibition of leukotriene-C4 represent potential therapeutic strategies for mitigating radiation-associated cognitive disorders.

Hypercholesterolemia, oxidative stress, and low-grade inflammation: a potentially dangerous scenario to blood-brain barrier

For more than a century, hypercholesterolemia has been linked to atherosclerotic cardiovascular disease. Notably, this metabolic condition has also been pointed out as a risk factor for neurodegenerative diseases, such as Alzheimer's disease (AD). Oxidative stress seems to be the connective factor between hypercholesterolemia and cardio and neurological disorders. By disturbing redox homeostasis, hypercholesterolemia impairs nitric oxide (NO) availability, an essential vasoprotective element, and jeopardizes endothelial function and selective permeability. The central nervous system (CNS) is partially protected from peripheral insults due to an arrangement between endothelial cells, astrocytes, microglia, and pericytes that form the blood-brain barrier (BBB). The endothelial dysfunction related to hypercholesterolemia increases the risk of developing cardiovascular diseases and also initiates BBB breakdown, which is a cause of brain damage characterized by neuroinflammation, oxidative stress, mitochondrial dysfunction, and, ultimately, neuronal and synaptic impairment. In this regard, we reviewed the mechanisms by which hypercholesterolemia-induced oxidative stress affects peripheral vessels, BBB, and leads to memory deficits. Finally, we suggest oxidative stress as the missing link between hypercholesterolemia and dementia.

Microglial IKKβ Alters Central and Peripheral Immune Activity at Distinct Time Points After Spinal Cord Injury

After high-level spinal cord injury (SCI), persistently reactive microglia drive widespread plasticity throughout the neuraxis. Plasticity in the thoracolumbar cord, a region corresponding to the spinal sympathetic reflex (SSR) circuit, contributes to the development of sympathetic dysfunction and associated immune disorders. The transcription factor NF-κB is activated after SCI, promoting a pro-inflammatory loop by driving the expression of inflammatory mediators which further activate NF-κB signaling. We hypothesize that microglial NF-κB signaling via IKKβ modulates microglial activity, impacting central and peripheral immune activity related to the SSR circuit post-SCI. We assessed the effect of deleting canonical IKKβ in CNS-resident microglia, its impact on microglial activation, polarization, central transcriptional activity, and peripheral immune activity at 1- and 4-week post-SCI (wpi). Transcriptomic analyses reveal microglial IKKβ influences immune-related pathways in the thoracolumbar cord at 1 wpi. We show that inhibition of microglial NF-κB signaling via deletion of the activator IKKβ mitigates injury-induced increases in "proinflammatory" M1 microglia in the thoracolumbar cord at 4 wpi and increases the quantity of splenocytes at 1 wpi. This study advances our understanding of how microglial IKKβ signaling shapes the neuroimmune response and a peripheral immune organ after SCI.

Features that distinguish age-related macular degeneration from aging

Age-related macular degeneration (AMD) is a complex, multifactorial retinal degenerative disease that is influenced by both genetic and environmental factors. However, the strongest risk factor for AMD is advanced age. Several physiological processes are observed in aging tissues including a low level of chronic inflammation (inflammaging), changed lipid and energy metabolism, and senescence. Nevertheless, whereas everyone ages, only a subset of the population develops AMD. The purpose of this review is to delineate the differences on a cellular and molecular level between natural aging changes and those observed in AMD. We provide a unique perspective on how genetic and environmental components modulate aging in the eye, as well as the specific role of the aging RPE and retina in the pathogenesis of AMD. Topics discussed include the mechanism of aging and its relation to the mechanism of AMD, current animal models that can be used to recapitulate some aspects of the pathology, and potential interventions that shift the balance towards healthy aging and therefore attenuate, prevent or delay the initiation of the disease.

The (neuro)inflammatory system in anxiety disorders and PTSD: Potential treatment targets

Targeting the immune system has recently garnered attention in the treatment of stress- associated psychiatric disorders resistant to existing pharmacotherapeutics. While such approaches have been studied in considerable detail in depression, the role of (neuro)inflammation in anxiety-related disorders, or in anxiety as an important transdiagnostic symptom, is much less clear. In this review we first critically review clinical and in part preclinical evidence of central and peripheral immune dysregulation in anxiety disorders and post-traumatic stress disorder (PTSD) and briefly discuss proposed mechanisms of how inflammation can affect anxiety-related symptoms. We then give an overview of existing and potential future targets in inflammation-associated signal transduction pathways and discuss effects of different immune-modulatory drugs in anxiety-related disorders. Finally, we discuss key gaps in current clinical trials such as the lack of prospective studies involving anxiety patient stratification strategies based on inflammatory biomarkers. Overall, although evidence is rather limited so far, there is data to indicate that increased (neuro)inflammation is present in subgroups of anxiety disorder patients. Although exact identification of such immune subtypes of anxiety disorders and PTSD is still challenging, these patients will likely particularly benefit from therapeutic targeting of aspects of the inflammatory system. Different anti-inflammatory treatment approaches (microglia-directed treatments, pro-inflammatory cytokine inhibitors, COX-inhibitors, phytochemicals and a number of novel anti-inflammatory agents) have indeed shown some efficacy even in non-stratified anxiety patient groups and appear promising as novel alternative or complimentary therapeutic options in specific ("inflammatory") subtypes of anxiety disorder and PTSD patients.

Effect of microglial Pd1 on glial scar formation after spinal cord injury in mice

The cross talk between microglia and astrocytes following spinal cord injury (SCI) greatly decides the prognosis. However, a comprehensive understanding of the molecular mechanisms by which microglia regulate astrocytic activity post-SCI is lacking. Programmed cell death protein 1 (Pdcd1, Pd1) plays a crucial role in modulating immune responses by exerting suppressive effects on microglia and peripheral immune cells within the central nervous system. Previous studies have shown the involvement of Pd1 in the pathogenesis of SCI; however, the role of microglial Pd1 in astrocytic activation and the following glial scar formation remains elusive. Here, we demonstrated that the pharmacological depletion of microglia using minocycline decreased the expression of tumor necrosis factor-alpha and interleukin-6 while concurrently increasing the expression of interleukin-10 following SCI, thereby facilitating motor function recovery in mice. We observed an increase in Pd1 expression in the injured spinal cord after SCI, with precise localization of Pd1 within microglia. Based on Pd1 knockout (KO) mice, we further revealed that Pd1 deficiency disrupted glial scar formation, leading to increased inflammation, impeded nerve regeneration, enlarged tissue damage, and compromised functional recovery following SCI. In vitro study showed that siRNA-mediated inhibition of Pd1 in microglia followed by lipopolysaccharide treatment significantly inhibited astrocyte migration and upregulated the secretion of tumor necrosis factor-alpha and CXCL9 from microglia, indicating that microglial Pd1 regulates glial scar formation through modulating the inflammatory microenvironment. Our study gains a new mechanistic insight into how microglial Pd1 decides the fate of SCI and promotes microglial Pd1 as a promising therapeutic target for SCI.

Olfactory bulb microglia activation mediates neuronal pyroptosis in ozone-exposed mice with olfactory and cognitive dysfunction

In recent years, there has been a notable increase in the concentration of air pollutants in the troposphere, especially ozone. However, limited research has gone beyond examining histopathological alterations in the olfactory bulb (OB) to explore the effects of ozone exposure on olfactory and cognitive functions. In our study, we exposed nine-month-old C57BL/6 mice to ozone at a concentration of 1.0 ppm for 13 weeks to examine the effects of ozone on the OB. The results indicated that ozone exposure induces olfactory and cognitive impairments in the mice. Subsequently, microglia in the OB are activated, leading to neuroinflammation. Ozone-induced downregulation of PSD95 and Synaptophysin, which was accompanied by a decrease in dendritic length and spine density. Simultaneously, increasing in the co-labeling of C1q, Iba1, and PSD95 after ozone exposure indicated that C1q-mediated synaptic phagocytosis by microglia might play a role in synaptic damage. Furthermore, the co-labeling of GSDMD-N and NEUN results suggests that ozone exposure triggers pyroptosis in neurons. Additionally, minocycline administration can alleviate ozone-induced olfactory and cognitive impairments by suppressing microglial activation. This study illustrates that prolonged ozone exposure leads to microglial activation in the OB, causing synaptic damage, neuronal pyroptosis, and subsequent deficits in olfactory and cognitive functions.

Microglia-Mediated Synaptic Dysfunction Contributes to Chemotherapy-Related Cognitive Impairment

Chemotherapy-related cognitive impairment (CRCI) significantly impacts cancer survivors. Due to unclear mechanisms, effective treatments for cognitive deficits are lacking. Here, we examined if microglia-mediated deficits in synaptic plasticity drive CRCI. Adult male mice were treated with the chemotherapeutic drugs 5-fluorouracil and leucovorin (5-Fu/LV, intraperitoneal injection, I.P.) on Days 1, 8, and 15 at a dosage of 50 mg/kg for 5-Fu and 90 mg/kg for LV for 3 weeks. Cognitive function was assessed using a novel object recognition (NOR) test 4 weeks after completion of 5-Fu/LV treatment. Compared with vehicle treatment, 5-Fu/LV treatment reduced the preference for exploring novel objects in the NOR test. Treatment with 5-Fu/LV increased the numbers of Iba1-positive microglial and CD68-positive/Iba1-positive microglia with shortened process lengths and diminished endpoints but decreased the number of phagocytotic (≤ 1 FITC-labeled beads) Iba1-positive microglia. Furthermore, 5-Fu/LV treatment reduced the long-term potentiation (LTP) recorded in the hippocampal CA1 region in response to a theta burst stimulation of the CA3-CA1 pathway and decreased the evoked N-methyl-D-aspartic acid receptor (NMDAR)-excitatory postsynaptic currents (NMDAR-EPSCs) in CA1 neurons. Cotreatment with the microglial inhibitor minocycline (33 mg/kg, daily for 3 weeks) restored cognitive deficits and microglial ramification, decreased the number of CD68-positive microglia, and reversed the reductions in LTP and the amplitude of NMDAR-EPSCs in 5-Fu/LV-treated mice. Our data suggest that microglial dysfunction and related synaptic dysfunction contribute to 5-Fu/LV-induced cognitive impairment.

Central amygdala neuroimmune signaling in alcohol use disorder

Alcohol Use Disorder (AUD) is a prevalent and debilitating condition characterized by an inability to control alcohol consumption despite adverse consequences. Current treatments for AUD, including FDA-approved medications such as naltrexone and acamprosate, have limited efficacy and compliance, underscoring the need for novel therapeutic approaches. The central amygdala (CeA) plays a crucial role in the development and maintenance of AUD, particularly aspects associated with stress and binge behaviors. Recent research indicates neuroimmune signaling in the CeA is emerging as a key factor in this process. Chronic alcohol consumption disrupts neuroimmune signaling, leading to altered cytokine expression and activation of glial cells, including astrocytes and microglia. These changes contribute to the dysregulation of neural circuits involved in reward and stress, perpetuating alcohol-seeking behavior and relapse. This review delves into how chronic alcohol exposure affects neuroimmune signaling in the CeA, contributing to the pathophysiology of AUD. By focusing on the impact of cytokine expression and glial cell activation, this review aims to elucidate the mechanisms by which neuroinflammation in the CeA influences alcohol-related behaviors. By providing a comprehensive overview of the current state of research, this review identifies potential therapeutic targets for AUD. Understanding the complex interplay between neuroimmune signaling and alcohol-related behaviors may pave the way for more effective treatments and improved outcomes for individuals struggling with AUD.

Immune mechanisms and shared immune targets in neurodegenerative diseases

The immune system plays a major part in neurodegenerative diseases. In some, such as multiple sclerosis, it is the primary driver of the disease. In others, such as Alzheimer disease, amyotrophic lateral sclerosis and Parkinson disease, it has an amplifying role. Immunotherapeutic approaches that target the adaptive and innate immune systems are being explored for the treatment of almost all neurological diseases, and the targets and approaches are often common across diseases. Microglia are the primary immune cells in the brain that contribute to disease pathogenesis, and are consequently a common immune target for therapy. Other therapeutic approaches target components of the peripheral immune system, such as regulatory T cells and monocytes, which in turn act within the CNS. This Review considers in detail how microglia, monocytes and T cells contribute to the pathogenesis of multiple sclerosis, Alzheimer disease, amyotrophic lateral sclerosis and Parkinson disease, and their potential as shared therapeutic targets across these diseases. The microbiome is also highlighted as an emerging therapeutic target that indirectly modulates the immune system. Therapeutic approaches being developed to target immune function in neurodegenerative diseases are discussed, highlighting how immune-based approaches developed to treat one disease could be applicable to multiple other neurological diseases.

New targets in spontaneous intracerebral hemorrhage

PURPOSE OF REVIEW

Intracerebral hemorrhage (ICH) is a devastating stroke with limited medical treatments; thus, timely exploration of emerging therapeutic targets is essential. This review focuses on the latest strategies to mitigate secondary brain injury post-ICH other than targeting surgery or hemostasis, addressing a significant gap in clinical practice and highlighting potential improvements in patient outcomes.

RECENT FINDINGS

Promising therapeutic targets to reduce secondary brain injury following ICH have recently been identified, including attenuation of iron toxicity and inhibition of ferroptosis, enhancement of endogenous resorption of hematoma, and modulation of perihematomal inflammatory responses and edema. Additionally, novel insights suggest the lymphatic system of the brain may potentially play a role in hematoma clearance and edema management. Various experimental and early-phase clinical trials have demonstrated these approaches may potentially offer clinical benefits, though most research remains in the preliminary stages.

SUMMARY

Continued research is essential to identify multifaceted treatment strategies for ICH. Clinical translation of these emerging targets could significantly enhance the efficacy of therapeutic interventions and potentially reduce secondary brain damage and improve neurological recovery. Future efforts should focus on large-scale clinical trials to validate these approaches, to pave the way for more effective treatment protocols for spontaneous ICH.

The Role of Microglia in Perioperative Pain and Pain Treatment: Recent Advances in Research

Microglia play a crucial role in monitoring the microenvironment of the central nervous system. Over the past decade, the role of microglia in the field of pain has gradually been unraveled. Microglia activation not only releases proinflammatory factors that enhance nociceptive signaling, but also participates in the resolving of pain. Opioids induce microglia activation, which enhances phagocytic activity and release of neurotoxic substances. Conversely, microglia activation reduces opioid efficacy and results in opioid tolerance. The application of microglia research to clinical pain management and drug development is a promising but challenging area. Microglia-targeted therapies may provide new avenues for pain management.

Minocycline ameliorates cognitive impairment in rats with trigeminal neuralgia by regulating microglial polarization

Trigeminal neuralgia (TN)-related cognitive impairment is a common cause of decreased quality of life in patients and is closely associated with neuroinflammation. Although minocycline has demonstrated anti-inflammatory, analgesic, and neuroprotective functions, its role in treating TN-related cognitive impairment remains unreported. In this study, we used an in vivo TN model and an in vitro model of primary microglial neuroinflammation to investigate the potential effects of minocycline on cognitive function and microglial polarization in TN rats. Our results suggested that minocycline treatment attenuated cognitive deficits by alleviating hippocampal neuronal damage and enhancing synaptic plasticity in TN rats. Furthermore, both in vitro and in vivo assays demonstrated that minocycline polarized activated microglia to the M2 phenotype, leading to the reduction of pro-inflammatory factors, including tumor necrosis factor-α and interleukin-1, and an increase in the anti-inflammatory factors, such as interleukin-4 and interleukin-10, thereby attenuating neuroinflammation. Moreover, it was found that the TLR4/MyD88/NF-κB pathway was involved in the shift of microglia from a pro-inflammatory (M1) to an anti-inflammatory (M2). In summary, minocycline likely mediated the process of microglia polarization partly via the TLR4/MyD88/NF-κB pathway, promoting neuronal survival and restoring synaptic plasticity, thereby improving TN-related cognitive impairment.

Impact of Neuroimmune System Activation by Adolescent Binge Alcohol Exposure on Adult Neurobiology

Adolescence is a conserved neurodevelopmental period encompassing maturation of glia and the innate immune system that parallels refinement of brain structures, neurotransmitter systems, and neurocircuitry. Given the vast neurodevelopmental processes occurring during adolescence, spanning brain structural and neurocircuitry refinement to maturation of neurotransmitter systems, glia, and the innate immune system, insults incurred during this critical period of neurodevelopment, could have profound effects on brain function and behavior that persist into adulthood. Adolescent binge drinking is common and associated with many adverse outcomes that may underlie the lifelong increased risk of alcohol-related problems and development of an alcohol use disorder (AUD). In this chapter, we examined the impact of adolescent binge drinking models using the adolescent intermittent ethanol (AIE) model on adult neurobiology. These studies implicate proinflammatory neuroimmune signaling across glia and neurons in persistent AIE-induced neuropathology. Some of these changes are reversible, providing unique opportunities for the development of treatments to prevent many of the long-term consequences of adolescent alcohol misuse.

Unraveling the complexity of microglial responses in traumatic brain and spinal cord injury

Microglia, the resident innate immune cells of the central nervous system (CNS), play an important role in neuroimmune signaling, neuroprotection, and neuroinflammation. In the healthy CNS, microglia adopt a surveillant and antiinflammatory phenotype characterized by a ramified scanning morphology that maintains CNS homeostasis. In response to acquired insults, such as traumatic brain injury (TBI) or spinal cord injury (SCI), microglia undergo a dramatic morphologic and functional switch to that of a reactive state. This microglial switch is initially protective and supports the return of the injured tissue to a physiologic homeostatic state. However, there is now a significant body of evidence that both TBI and SCI can result in a chronic state of microglial activation, which contributes to neurodegeneration and impairments in long-term neurologic outcomes in humans and animal models. In this review, we discuss the complex role of microglia in the pathophysiology of TBI and SCI, and recent advancements in knowledge of microglial phenotypic states in the injured CNS. Furthermore, we highlight novel therapeutic strategies targeting chronic microglial responses in experimental models and discuss how they may ultimately be translated to the clinic for human brain and SCI.

Dopamine D3 receptor mediates natural and methamphetamine rewards via regulating the expression of miR-29c in the nucleus accumbens of mice

The dopamine D3 receptor (D3R), principally confined to the nucleus accumbens (NAc), is involved in regulating natural and drug rewards; however, the molecular mechanisms underlying the associated process remain unclear. Earlier research has reported the concurrent influence of D3R and miR-29c expressed in the NAc on methamphetamine (METH)-induced reward behaviors and microglial activation, hinting at regulatory roles in reward processing. Herein, we performed viral manipulation-mediating D3R/miR-29c overexpression and inhibition in the whole NAc in male D3R knockout and wild-type mice to investigate this potential relationship. Behavioral responses to the rewarding stimuli were assessed using sucrose preference score, METH-induced locomotor sensitization, and METH-induced conditioned place preference tests. Overall, we observed a notable decrease in the behavioral response to sucrose and METH in D3R-deficient mice, accompanied by the downregulation of miR-29c expression in the NAc. Diminished responses to those rewarding stimuli in D3R-deficient mice primarily stemmed from the reduction of GSK3β activity and subsequent down-regulation of miR-29c in the NAc. Microglial activation in the NAc mediates the effect of D3R-miR-29c deficiency on the reward effects of sucrose and METH. Pharmacological suppression of microglial activity rescued the reduced response in mice lacking D3R-miR-29c in the NAc. Overall, this study revealed the mechanism by which D3R regulates both natural and drug rewards via miR-29c in the murine NAc, highlighting the role of the NAc D3R-miR-29c pathway as a critical regulator of rewards, and providing new insights into the role of NAc D3R-miR-29c in encoding rewarding experiences.

Effective Nose-to-Brain Delivery of Blood-Brain Barrier Impermeant Anti-IL-1β Antibody via the Minimally Invasive Nasal Depot (MIND) Technique

Treatment of neuroinflammation and neurodegenerative diseases using biologic therapies is limited due to the blood-brain barrier (BBB). This study explores a clinically validated approach to bypass the BBB for the purposes of direct central nervous system (CNS) delivery of antibodies using the Minimally Invasive Nasal Depot (MIND) technique. Using a lipopolysaccharide (LPS)-induced mouse model of neuroinflammation, we evaluated the efficacy of MIND in delivering a BBB impermeant full-length anti-IL-1β antibody. The results demonstrated that MIND delivery resulted in a significant reduction in IL-1β levels and microglial activation in relevant brain regions, notably outperforming conventional intravenous (IV) administration. These results underscore the ability of the MIND approach to transform the treatment landscape for a range of neurodegenerative diseases by enabling the targeted delivery of otherwise BBB impermeant therapeutics.

Maresin-like 1 Ameliorates Neuropathology of Alzheimer's Disease in Brains of a Transgenic Mouse Model

(1) Background: Impeded resolution of inflammation contributes substantially to the pathogenesis of Alzheimer's disease (AD); consequently, resolving inflammation is pivotal to the amelioration of AD pathology. This can potentially be achieved by the treatment with specialized pro-resolving lipid mediators (SPMs), which should resolve neuroinflammation in brains. (2) Methods: Here, we report the histological effects of long-term treatment with an SPM, maresin-like 1 (MarL1), on AD pathogenesis in a transgenic 5xFAD mouse model. (3) Results: MarL1 treatment reduced Aβ overload, curbed the loss of neurons in brains especially cholinergic neurons associated with cleaved-caspase-3-associated apoptotic degeneration, reduced microgliosis and the pro-inflammatory M1 polarization of microglia, curbed the AD-associated decline in anti-inflammatory Iba1+Arg-1+-M2 microglia, inhibited phenotypic switching to pro-inflammatory N1 neutrophils, promoted the blood-brain barrier-associated tight-junction protein claudin-5 and decreased neutrophil leakage in 5xFAD brains, and induced the switch of neutrophils toward the inflammation-resolving N2 phenotype. (4) Conclusions: Long-term administration of MarL1 mitigates AD-related neuropathogenesis in brains by curbing neuroinflammation and neurodegeneration, based on the histological results. These findings provide preclinical leads and mechanistic insights for the development of MarL1 into an effective modality to ameliorate AD pathogenesis.

Estrogen receptor α regulates the IKKs/NF-kB activity involved in the development of mechanical allodynia induced by REM sleep deprivation in rats

Several signaling pathways that converge in NF-kB activation have been linked to developing and maintaining different types of pathological pain. In addition, some mechanisms implied in the establishment of chronic pain have been demonstrated to have a sex-dependent correlation. This study aimed to determine if the IKKs/NF-kB signaling pathway is involved in establishing REM sleep deprivation (REMSD) induced mechanical allodynia in rats and its possible regulation depending on estradiol and estrogen receptors. Intrathecal administration of BMS-345541 or minocycline, two drugs that reduce the IKKs/NF-kB activity, avoided the development of mechanical allodynia in female but not in male rats subjected to 48 h of REMSD. Ovariectomy in female rats abolished the effect of BMS-345541 and minocycline. Meanwhile, the 17-β-estradiol restitution restored it. Intrathecal administration of MPP, a selective ERα antagonist, but not PHTPP, a selective ERβ antagonist, avoided the effect of BMS-345541 in female rats without hormonal manipulation. In addition, the transient run-down of ERα in female rats abolished the effect of BMS-345541. All data suggest an important role of ERα as a regulator of the IKKs/NF-kB activity. REMSD increased the ERα protein expression in the dorsal root ganglia and the dorsal spinal cord in females but not in male rats. Interestingly, ERα activation or ERα overexpression allowed the effect of BMS-345541 in male rats. Data suggest an important regulatory role of ERα in the IKKs/NF-kB activity on establishing mechanical allodynia induced by REMSD in female rats.

Minocycline reduces neurobehavioral deficits evoked by chronic unpredictable stress in adult zebrafish

Chronic stress-related brain disorders are widespread and debilitating, and often cause lasting neurobehavioral deficits. Minocycline, a common antibiotic and an established inhibitor of microglia, emerges as potential treatment of these disorders. The zebrafish (Danio rerio) is an important emerging model organism in translational neuroscience and stress research. Here, we evaluated the potential of minocycline to correct microglia-mediated behavioral, genomic and neuroimmune responses induced by chronic unpredictable stress (CUS) in adult zebrafish. We demonstrated that CUS evoked overt behavioral deficits in the novel tank, light-dark box and shoaling tests, paralleled by elevated stress hormones (CRH, ACTH and cortisol), and upregulated brain expression of the 'neurotoxic M1' microglia-specific biomarker gene (MHC-2) and pro-inflammatory cytokine genes (IL-1β, IL-6 and IFN-γ). CUS also elevated peripheral (whole-body) pro-inflammatory (IL-1β, IFN-γ) and lowered anti-inflammatory cytokines (IL-4 and IL-10), as well as reduced whole-brain serotonin, dopamine and norepinephrine levels, and increased brain dopamine and serotonin turnover. In contrast, minocycline attenuated most of these effects, also reducing CUS-elevated peripheral levels of IL-6 and IFN-γ. Collectively, this implicates microglia in zebrafish responses to chronic stress, and suggests glial pathways as potential evolutionarily conserved drug targets for treating stress-evoked neuropathogenesis. Our findings also support the growing translational value of zebrafish models for understanding complex molecular mechanisms of brain pathogenesis and its therapy.

Minocycline inhibits microglial activation in the CA1 hippocampal region and prevents long-term cognitive sequel after experimental cerebral malaria

Cerebral malaria is the worst complication of malaria infection, has a high mortality rate, and may cause different neurodysfunctions, including cognitive decline. Neuroinflammation is an important cause of cognitive damage in neurodegenerative diseases, and microglial cells can be activated in a disease-associated profile leading to tissue damage and neuronal death. Here, we demonstrated that treatment with minocycline reduced blood-brain barrier breakdown and modulated ICAM1 mRNA expression; reduced proinflammatory cytokines, such as TNF-α, IL-1β, IFN-γ, and IL-6; and prevented long-term cognitive decline in contextual and aversive memory tasks. Taken together, our data suggest that microglial cells are activated during experimental cerebral malaria, leading to neuroinflammatory events that end up in cognitive damage. In addition, pharmacological modulation of microglial activation, by drugs such as minocycline may be an important therapeutic strategy in the prevention of long-term memory impairment.

Microglial polarization pathways and therapeutic drugs targeting activated microglia in traumatic brain injury

Traumatic brain injury can be categorized into primary and secondary injuries. Secondary injuries are the main cause of disability following traumatic brain injury, which involves a complex multicellular cascade. Microglia play an important role in secondary injury and can be activated in response to traumatic brain injury. In this article, we review the origin and classification of microglia as well as the dynamic changes of microglia in traumatic brain injury. We also clarify the microglial polarization pathways and the therapeutic drugs targeting activated microglia. We found that regulating the signaling pathways involved in pro-inflammatory and anti-inflammatory microglia, such as the Toll-like receptor 4 / nuclear factor-kappa B, mitogen-activated protein kinase, Janus kinase/signal transducer and activator of transcription, phosphoinositide 3-kinase/protein kinase B, Notch, and high mobility group box 1 pathways, can alleviate the inflammatory response triggered by microglia in traumatic brain injury, thereby exerting neuroprotective effects. We also reviewed the strategies developed on the basis of these pathways, such as drug and cell replacement therapies. Drugs that modulate inflammatory factors, such as rosuvastatin, have been shown to promote the polarization of anti-inflammatory microglia and reduce the inflammatory response caused by traumatic brain injury. Mesenchymal stem cells possess anti-inflammatory properties, and clinical studies have confirmed their significant efficacy and safety in patients with traumatic brain injury. Additionally, advancements in mesenchymal stem cell-delivery methods-such as combinations of novel biomaterials, genetic engineering, and mesenchymal stem cell exosome therapy-have greatly enhanced the efficiency and therapeutic effects of mesenchymal stem cells in animal models. However, numerous challenges in the application of drug and mesenchymal stem cell treatment strategies remain to be addressed. In the future, new technologies, such as single-cell RNA sequencing and transcriptome analysis, can facilitate further experimental studies. Moreover, research involving non-human primates can help translate these treatment strategies to clinical practice.

Maternal exposure to 4-tert-octylphenol causes alterations in the morphology and function of microglia in the offspring mouse brain

4-tert-Octylphenol (OP), an endocrine disrupting chemical is widely used in the production of industrial products. Prenatal exposure to endocrine-disrupting chemicals negatively affects the brain. However, the influence of OP exposure during neurodevelopment in adult offspring remains unclear. Thus, in the present study, we investigated the effects of maternal OP exposure on brain development in adult offspring by analyzing primary glial cell cultures and mice. Our findings revealed that OP exposure led to a specific increase in the mRNA expression of the ionized calcium-binding adapter molecule 1 (Iba-1) and the proportion of amoeboid microglia in the primary glial cell culture and adult offspring mice. Exposure to OP increased the transcriptional activation of Iba-1 and estrogen response element, which were counteracted by estrogen receptor antagonists ICI 182,780. Moreover, OP exposure increased the nuclear localization of the estrogen receptor. Remarkably, OP exposure decreased the mRNA expression levels of proinflammatory cytokines and genes associated with immune response in the brains of the offspring. OP exposure upregulated actin filament-related genes and altered cytoskeletal gene expression, as demonstrated by microarray analysis. The morphological changes in microglia did not result in an inflammatory response following lipopolysaccharide treatment. Taken together, the effects of OP exposure during neurodevelopment persist into adulthood, resulting in microglial dysfunction mediated by estrogen receptor signaling pathways in the brains of adult offspring mice.

Microglia in retinal diseases: From pathogenesis towards therapeutic strategies

Microglia, a widely dispersed cohort of immune cells in the retina, are intricately involved in a diverse range of pivotal biological processes, including inflammation, vascular development, complement activation, antigen presentation, and phagocytosis. Within the retinal milieu, microglia are crucial for the clearance of dead cells and cellular debris, release of anti-inflammatory agents, and orchestration of vascular network remodeling to maintain homeostasis. In addition, microglia are key mediators of neuroinflammation. Triggered by oxidative stress, elevated intraocular pressure, genetic anomalies, and immune dysregulation, microglia release numerous inflammatory cytokines, contributing to the pathogenesis of various retinal disorders. Recent studies on the ontogeny and broad functions of microglia in the retina have elucidated their characteristics during retinal development, homeostasis, and disease. Furthermore, therapeutic strategies that target microglia and their effector cytokines have been developed and shown positive results for some retinal diseases. Therefore, we systematically review the microglial ontogeny in the retina, elucidate their dual roles in retinal homeostasis and disease pathogenesis, and demonstrate microglia-based targeted therapeutic strategies for retinal diseases.

Astragalus polysaccharide treatment relieves cerebral ischemia‒reperfusion injury by promoting M2 polarization of microglia by enhancing O-GlcNAcylation

Cerebral ischemia‒reperfusion (I/R) injury seriously threatens the lives of patients. Astragalus polysaccharide (APS) is the main active ingredient of Astragalus membranaceus and has a wide range of pharmacological activities. Here, we aimed to explore the impacts of APS on cerebral I/R injury and its specific mechanisms. We established a cerebral I/R injury model using middle cerebral artery occlusion (MCAO)-treated rats and oxygen glucose deprivation/reoxygenation (OGD/R)-treated BV2 cells. The interleukin 1β (IL-1β), interleukin 6 (IL-6) and interleukin (IL-10) levels were determined using corresponding ELISA kits and RT‒qPCR. The levels of M1 microglial markers (INOS and CD16) and M2 microglial markers (Arg-1 and CD206) were measured by RT‒qPCR. The O-linked N-acetylglucosamine modification (O-GlcNAcylation), O-GlcNAc transfer (OGT) and O-GlcNAc glycosidase (OGA) protein levels were measured by Western blot. Our results showed that APS treatment decreased IL-1β (179.72 ± 9.08 vs. 81.33 ± 6.30) and IL-6 (445.56 ± 33.09 vs. 234.75 ± 27.62) levels and increased IL-10 (41.95 ± 4.18 vs. 86.40 ± 7.16) levels in OGD/R-treated BV2 cells (p < 0.001). In addition, APS promoted the M2 polarization of OGD/R-treated BV2 cells, manifested by an increase in Arg-1 (0.43 ± 0.04 vs. 0.76 ± 0.03) and CD206 (0.36 ± 0.03 vs. 0.65 ± 0.06) and a decrease in INOS (2.84 ± 0.39 vs. 1.56 ± 0.19) and CD16 (4.04 ± 0.36 vs. 1.88 ± 0.09) in OGD/R-treated BV2 cells (p < 0.001). Additionally, APS treatment increased the O-GlcNAcylation and OGT levels in OGD/R-treated BV2 cells, while OGT knockdown reversed the effect of APS in OGD/R-treated BV2 cells and MCAO-treated rats (p < 0.05). Our study demonstrated that APS alleviated cerebral I/R injury by promoting the M2 polarization of microglia by enhancing OGT-mediated O-GlcNAcylation.

Microglial depletion rescues spatial memory impairment caused by LPS administration in adult mice

Recent studies have highlighted the importance of microglia, the resident macrophages in the brain, in regulating cognitive functions such as learning and memory in both healthy and diseased states. However, there are conflicting results and the underlying mechanisms are not fully understood. In this study, we examined the effect of depleting adult microglia on spatial learning and memory under both physiological conditions and lipopolysaccharide (LPS)-induced neuroinflammation. Our results revealed that microglial depletion by PLX5622 caused mild spatial memory impairment in mice under physiological conditions; however, it prevented memory deficits induced by systemic LPS insult. Inactivating microglia through minocycline administration replicated the protective effect of microglial depletion on LPS-induced memory impairment. Furthermore, our study showed that PLX5622 treatment suppressed LPS-induced neuroinflammation, microglial activation, and synaptic dysfunction. These results strengthen the evidence for the involvement of microglial immunoactivation in LPS-induced synaptic and cognitive malfunctions. They also suggest that targeting microglia may be a potential approach to treating neuroinflammation-associated cognitive dysfunction seen in neurodegenerative diseases.

Cobalt Toxicity Induces Retinopathy and Optic Neuropathy in Mice

Purpose

To explore the effect of cobalt toxicity on vision.

Methods

A total of 103 wild-type (WT) mice were injected with cobalt chloride by two routes in different concentrations: single intravenous (IV) high or low doses (total, n = 43); or daily repeated intraperitoneal (IP) high (three days) or low (28 days, 56 days) dose, and low-dose cobalt with added minocycline (56 days) (total, n = 60); 10 WT mice served as a control group. An additional group of 17 immunodeficient NOD scid gamma (NSG) mice were injected IV or IP with cobalt, and 10 NSG mice served as control. Cobalt levels were measured in blood, urine, and tears by particle-induced X-ray emission (PIXE). Macroscopic, immunohistochemical, electroretinography (ERG), and molecular studies were done.

Results

PIXE revealed cobalt elimination from the blood by two hours, with increased levels in urine but under the detection limit in tears. In the retina, ERG recordings showed decreased b-wave amplitude. Apoptosis mainly involved the inner retina, with inner retinal inflammatory reaction in both WT and less in the NSG mice. In the optic nerves, an increased microglial and astrocytic activation was noted.

Conclusions

This study demonstrated functional visual impairment with extensive inflammatory reaction secondary to cobalt toxicity in mice.

Polymer nanotherapeutics: A promising approach toward microglial inhibition in neurodegenerative diseases

Nanoparticles (NPs) that target multiple transport mechanisms facilitate targeted delivery of active therapeutic agents to the central nervous system (CNS) and improve therapeutic transport and efficacy across the blood-brain barrier (BBB). CNS nanotherapeutics mostly target neurons and endothelial cells, however, microglial immune cells are the first line of defense against neuronal damage and brain infections. Through triggering release of inflammatory cytokines, chemokines and proteases, microglia can however precipitate neurological damage-a significant factor in neurodegenerative diseases. Thus, microglial inhibitory agents are attracting much attention among those researching and developing novel treatments for neurodegenerative disorders. The most established inhibitors of microglia investigated to date are resveratrol, curcumin, quercetin, and minocycline. Thus, there is great interest in developing novel agents that can bypass or easily cross the BBB. One such approach is the use of modified-nanocarriers as, or for, delivery of, therapeutic agents to the brain and wider CNS. For microglial inhibition, polymeric NPs are the preferred vehicles for choice. Here, we summarize the immunologic and neuroinflammatory role of microglia, established microglia inhibitor agents, challenges of CNS drug delivery, and the nanotherapeutics explored for microglia inhibition to date. We also discuss applications of the currently considered "most useful" polymeric NPs for microglial-inhibitor drug delivery in CNS-related diseases.

NF-κB in Alzheimer's Disease: Friend or Foe? Opposite Functions in Neurons and Glial Cells

Alzheimer's disease (AD) is a devasting neurodegenerative disease afflicting mainly glutamatergic neurons together with a massive neuroinflammation mediated by the transcription factor NF-κB. A 65%-plus increase in Alzheimer's patients by 2050 might be a major threat to society. Hallmarks of AD are neurofibrillary tangles (NFTs) composed of hyperphosphorylated tau and amyloid beta (Aβ) plaques. Here, we review the potential involvement of transcription factor NF-κB by hereditary mutations of the tumor necrosis factor pathway in AD patients. One of the greatest genetic risk factors is APOE4. Recently, it was shown that the APOE4 allele functions as a null allele in human astrocytes not repressing NF-κB anymore. Moreover, NF-κB seems to be involved in the repair of DNA double-strand breaks during healthy learning and memory, a function blunted in AD. NF-κB could be a friend to healthy neurons by repressing apoptosis and necroptosis. But a loss of neuronal NF-κB and activation of glial NF-κB in AD makes it a foe of neuronal survival. Hopeful therapies include TNFR2 receptor bodies relieving the activation of glial NF-κB by TNFα.

TLR2/NF-κB signaling in macrophage/microglia mediated COVID-pain induced by SARS-CoV-2 envelope protein

Pain has become a major symptom of long COVID-19 without effective therapy. Apart from viral infection pathological process, SARS-CoV-2 membranal proteins (envelope [S2E], spike [S2S] and membrane [S2M]) also present pro-inflammatory feature independently. Here, we aim to uncover the neuroinflammatory mechanism of COVID-pain induced by SARS-CoV-2 membranal proteins. We detected the three proteins in both peripheral sensory ganglions and spinal dorsal horn of COVID-19 donors. After intradermal and intrathecal injection, only S2E triggered pain behaviors, accompanied with upregulated-phosphorylation nuclear factor kappa B (NF-κB), which was significantly attenuated by minocycline in mice. We further identified Toll-like receptor 2 (TLR2) among TLRs as the target of S2E to evoke inflammatory responses leading to COVID-pain. This study identified the nociceptive effect of S2E through directly interacting with macrophage/microglia TLR2 and inducing the following NF-κB inflammatory storm. Clearing away S2E and inhibiting macrophage/microglia TLR2 served as perspective therapeutic strategies for COVID-19 pain.

Ischemia-induced endogenous Nrf2/HO-1 axis activation modulates microglial polarization and restrains ischemic brain injury

Cerebral ischemic stroke accounts for more than 80% of all stroke cases. During cerebral ischemia, reactive oxygen species produced in the ischemic brain induce oxidative stress and inflammatory responses. Nrf2 is a transcription factor responsible for regulating cellular redox balance through the induction of protective antioxidant and phase II detoxification responses. Although the induction of endogenous Nrf2/HO-1 axis activation has been observed in the ischemic brain, whether ischemia-induced endogenous Nrf2/HO-1 axis activation plays a role in modulating microglia (MG) phenotypes and restraining ischemic brain injury is not characterized and requires further exploration. To investigate that, we generated mice with Nrf2 knockdown specifically in MG to rigorously assess the role of endogenous Nrf2 activation in ischemic brain injury after stroke. Our results showed that MG-specific Nrf2 knockdown exacerbated ischemic brain injury after stroke. We found that Nrf2 knockdown altered MG phenotypes after stroke, in which increased frequency of inflammatory MG and decreased frequency of anti-inflammatory MG were detected in the ischemic brain. Moreover, we identified attenuated Nrf2/HO-1 axis activation led to increased CD68/IL-1β and suppressed CD206 expression in MG, resulting in aggravated inflammatory MG in MG-specific Nrf2 knockdown mice after stroke. Intriguingly, using type II diabetic preclinical models, we revealed that diabetic mice exhibited attenuated Nrf2/HO-1 axis activation in MG and exacerbated ischemic brain injury after stroke that phenocopy mice with MG-specific Nrf2 knockdown. Finally, the induction of exogenous Nrf2/HO-1 axis activation in MG through pharmacological approaches ameliorated ischemic brain injury in diabetic mice. In conclusion, our findings provide cellular and molecular insights demonstrating ischemia-induced endogenous Nrf2/HO-1 axis activation modulates MG phenotypes and restrains ischemic brain injury. These results further strengthen the therapeutic potential of targeting Nrf2/HO-1 axis in MG for the treatment of ischemic stroke and diabetic stroke.

Minocycline prevents early age-related cognitive decline in a mouse model of intellectual disability caused by ZBTB18/RP58 haploinsufficiency

Haploinsufficiency of the transcriptional repressor ZBTB18/RP58 is associated with intellectual disability. However, the mechanisms causing this disability are unknown, and preventative measures and treatments are not available. Here, we assessed multiple behaviors in Zbtb18/Rp58 heterozygous-knockout mice, and examined local field potentials, DNA fragmentation, mitochondrial morphology, and performed histochemical and transcriptome analyses in the hippocampus to evaluate chronic inflammation. In wild-type mice, object location memory was present at a similar level at 2 and 4-5 months of age, and became impaired at 12-18 months. In contrast, Zbtb18/Rp58 heterozygous-knockout mice displayed early onset impairments in object location memory by 4-5 months of age. These mice also exhibited earlier accumulation of DNA and mitochondrial damage, and activated microglia in the dentate gyrus, which are associated with defective DNA repair. Notably, chronic minocycline therapy, which has neuroprotective and anti-inflammatory effects, attenuated age-related phenotypes, including accumulation of DNA damage, increased microglial activation, and impairment of object location memory. Our results suggest that Zbtb18/Rp58 activity is required for DNA repair and its reduction results in DNA and mitochondrial damage, increased activation of microglia, and inflammation, leading to accelerated declines in cognitive functions. Minocycline has potential as a therapeutic agent for the treatment of ZBTB18/RP58 haploinsufficiency-associated cognitive dysfunction.

Microglia Signatures: A Cause or Consequence of Microglia-Related Brain Disorders?

Microglia signatures refer to distinct gene expression profiles or patterns of gene activity that are characteristic of microglia. Advances in gene expression profiling techniques, such as single-cell RNA sequencing, have allowed us to study microglia at a more detailed level and identify unique gene expression patterns that are associated, but not always, with different functional states of these cells. Microglial signatures depend on the developmental stage, brain region, and specific pathological conditions. By studying these signatures, it has been possible to gain insights into the underlying mechanisms of microglial activation and begin to develop targeted therapies to modulate microglia-mediated immune responses in the CNS. Historically, the first two signatures coincide with M1 pro-inflammatory and M2 anti-inflammatory phenotypes. The first one includes upregulation of genes such as CD86, TNF-α, IL-1β, and iNOS, while the second one may involve genes like CD206, Arg1, Chil3, and TGF-β. However, it has long been known that many and more specific phenotypes exist between M1 and M2, likely with corresponding signatures. Here, we discuss specific microglial signatures and their association, if any, with neurodegenerative pathologies and other brain disorders.

Discovery of novel protective agents for infection-related delirium through bispectral electroencephalography

Delirium is a multifactorial medical condition of waxing and waning impairment across various domains of mental functioning over time. Importantly, delirium is also one of the greatest risk factors for prolonged hospitalization, morbidity, and mortality. Studying this important condition is challenging due to the difficulty in both objective diagnosis in patients and validation of laboratory models. As a result, there is a lack of protective treatments for delirium. Our recent studies report the efficacy of bispectral electroencephalography (BSEEG) in diagnosing delirium in patients and predicting patient outcomes, advancing the concept that this simple measure could represent an additional vital sign for patients. Here, we applied BSEEG to characterize and validate a novel lipopolysaccharide (LPS) mouse model of infection-related delirium. We then applied this model to evaluate the protective efficacy of three putative therapeutic agents: the conventional antipsychotic medication haloperidol, the neuroprotective compound P7C3-A20, and the antibiotic minocycline. Aged mice were more susceptible than young mice to LPS-induced aberration in BSEEG, reminiscent of the greater vulnerability of older adults to delirium. In both young and old mice, P7C3-A20 and minocycline administration prevented LPS-induced BSEEG abnormality. By contrast, haloperidol did not. P7C3-A20 and minocycline have been shown to limit different aspects of LPS toxicity, and our data offers proof of principle that these agents might help protect patients from developing infection-related delirium. Thus, utilization of BSEEG in a mouse model for infection-related delirium can identify putative therapeutic agents for applications in patient clinical trials.

Astragaloside IV ameliorated neuroinflammation and improved neurological functions in mice exposed to traumatic brain injury by modulating the PERK-eIF2α-ATF4 signaling pathway

Increasing evidence suggests that endoplasmic reticulum stress (ER stress) and neuroinflammation are involved in the complex pathological process of traumatic brain injury (TBI). However, the pathological mechanisms of their interactions in TBI remain incompletely elucidated. Therefore, investigating and ameliorating neuroinflammation and ER stress post-TBI may represent effective strategies for treating secondary brain injury. Astragaloside IV (AS-IV) has been reported as a potential neuroprotective and anti-inflammatory agent in neurological diseases. This study utilized a mouse TBI model to investigate the pathological mechanisms and crosstalk of ER stress, neuroinflammation, and microglial cell morphology in TBI, as well as the mechanisms and potential of AS-IV in improving TBI. The research revealed that post-TBI, inflammatory factors IL-6, IL-1β, and TNF-α increased, microglial cells were activated, and the specific inhibitor of PERK phosphorylation, GSK2656157, intervened to alleviate neuroinflammation and inhibit microglial cell activation. Post-TBI, levels of ER stress-related proteins (p-PERK, p-eIF2a, ATF4, ATF6, and p-IRE1a) increased. Following AS-IV treatment, neurological dysfunction in TBI mice improved. Levels of p-PERK, p-eIF2a, and ATF4 decreased, along with reductions in inflammatory factors IL-6, IL-1β, and TNF-α. Changes in microglial/macrophage M1/M2 polarization were observed. Additionally, the PERK activator CCT020312 intervention eliminated the impact of AS-IV on post-TBI inflammation and ER stress-related proteins p-PERK, p-eIF2a, and ATF4. These results indicate that AS-IV alleviates neuroinflammation and brain damage post-TBI through the PERK pathway, offering new directions and theoretical insights for TBI treatment.

Sovateltide (ILR-1620) Improves Motor Function and Reduces Hyperalgesia in a Rat Model of Spinal Cord Injury

BACKGROUND

Spinal cord injury (SCI) presents a major global health challenge, with rising incidence rates and substantial disability. Although progress has been made in understanding SCI's pathophysiology and early management, there is still a lack of effective treatments to mitigate long-term consequences. This study investigates the potential of sovateltide, a selective endothelin B receptor agonist, in improving clinical outcomes in an acute SCI rat model.

METHODS

Thirty male Sprague-Dawley rats underwent sham surgery (group A) or SCI and treated with vehicle (group B) or sovateltide (group C). Clinical tests, including Basso, Beattie, and Bresnahan scoring, inclined plane, and allodynia testing with von Frey hair, were performed at various time points. Statistical analyses assessed treatment effects.

RESULTS

Sovateltide administration significantly improved motor function, reducing neurological deficits and enhancing locomotor recovery compared with vehicle-treated rats, starting from day 7 post injury. Additionally, the allodynic threshold improved, suggesting antinociceptive properties. Notably, the sovateltide group demonstrated sustained recovery, and even reached preinjury performance levels, whereas the vehicle group plateaued.

CONCLUSIONS

This study suggests that sovateltide may offer neuroprotective effects, enhancing neurogenesis and angiogenesis. Furthermore, it may possess anti-inflammatory and antinociceptive properties. Future clinical trials are needed to validate these findings, but sovateltide shows promise as a potential therapeutic strategy to improve functional outcomes in SCI. Sovateltide, an endothelin B receptor agonist, exhibits neuroprotective properties, enhancing motor recovery and ameliorating hyperalgesia in a rat SCI model. These findings could pave the way for innovative pharmacological interventions for SCI in clinical settings.

Microglial activation in the medial prefrontal cortex after remote fear recall participates in the regulation of auditory fear extinction

Excessive or inappropriate fear responses can lead to anxiety-related disorders, such as post-traumatic stress disorder (PTSD). Studies have shown that microglial activation occurs after fear conditioning and that microglial inhibition impacts fear memory. However, the role of microglia in fear memory recall remains unclear. In this study, we investigated the activated profiles of microglia after the recall of remote-cued fear memory and the role of activated microglia in the extinction of remote-cued fear in adult male C57BL/6 mice. The results revealed that the expression of the microglia marker Iba1 increased in the medial prefrontal cortex (mPFC) at 10 min and 1 h following remote-cued fear recall, which was accompanied by amoeboid morphology. Inhibiting microglial activation through PLX3397 treatment before remote fear recall did not affect recall, reconsolidation, or regular extinction but facilitated recall-extinction and mitigated spontaneous recovery. Moreover, our results demonstrated reduced co-expression of Iba1 and postsynaptic density protein 95 (PSD95) in the mPFC, along with decreases in the p-PI3K/PI3K ratio, p-Akt/Akt ratio, and KLF4 expression after PLX3397 treatment. Our results suggest that microglial activation after remote fear recall impedes fear extinction through the pruning of synapses in the mPFC, accompanied by alterations in the expression of the PI3K/AKT/KLF4 pathway. This finding can help elucidate the mechanism involved in remote fear extinction, contributing to the theoretical foundation for the intervention and treatment of PTSD.

miR-29a-5p rescues depressive-like behaviors in a CUMS-induced mouse model by facilitating microglia M2-polarization in the prefrontal cortex via TMEM33 suppression

BACKGROUND

Depression accounts for a high proportion of neuropsychiatric disorders and is associated with abnormal states of neurons in specific brain regions. Microglia play a pivotal role in the inflammatory state during depression development; however, the exact mechanism underlying chronic mood states remains unknown. Thus, the present study aimed to determine whether microRNAs (miRNAs) alleviate stress-induced depression-like behavior in mice by regulating the expression levels of their target genes, explore the role of neuroinflammation induced by microglial activation in the pathogenesis and progression of depression, and determine whether the role of the miR-29a-5p/transmembrane protein 33 (TMEM33) axis.

METHODS

In this study, chronic unpredictable mild stress (CUMS) mouse depression model, various behavioral tests, western blotting, dual-luciferase reporter assay, enzyme-linked immunosorbent assay, real-time quantitative reverse transcription PCR, immunofluorescence and lentivirus-mediated gene transfer were used.

RESULTS

After exposure to the CUMS paradigm, miR-29a-5p was significantly down-regulated. This downregulation subsequently promoted the polarization of microglia M1 by upregulating the expression of TMEM33, resulting in enhanced inflammatory chemokines affecting neurons. Conversely, the upregulation of miR-29a-5p within the prefrontal cortex (PFC) suppressed TMEM33 expression, facilitated microglia M2-polarization, and ameliorated depressive-like behavior.

LIMITATIONS

Only rodent models of depression were used, and human samples were not included.

CONCLUSIONS

The results of this study suggest that miR-29a-5p deficits within the PFC mediate microglial anomalies and contribute to depressive-like behaviors. miR-29a-5p and TMEM33 may, therefore, serve as potential therapeutic targets for the treatment of depression.

Genetic contribution to microglial activation in schizophrenia

Several lines of evidence indicate the involvement of neuroinflammatory processes in the pathophysiology of schizophrenia (SCZ). Microglia are brain resident immune cells responding toward invading pathogens and injury-related products, and additionally, have a critical role in improving neurogenesis and synaptic functions. Aberrant activation of microglia in SCZ is one of the leading hypotheses for disease pathogenesis, but due to the lack of proper human cell models, the role of microglia in SCZ is not well studied. We used monozygotic twins discordant for SCZ and healthy individuals to generate human induced pluripotent stem cell-derived microglia to assess the transcriptional and functional differences in microglia between healthy controls, affected twins and unaffected twins. The microglia from affected twins had increased expression of several common inflammation-related genes compared to healthy individuals. Microglia from affected twins had also reduced response to interleukin 1 beta (IL1β) treatment, but no significant differences in migration or phagocytotic activity. Ingenuity Pathway Analysis (IPA) showed abnormalities related to extracellular matrix signaling. RNA sequencing predicted downregulation of extracellular matrix structure constituent Gene Ontology (GO) terms and hepatic fibrosis pathway activation that were shared by microglia of both affected and unaffected twins, but the upregulation of major histocompatibility complex (MHC) class II receptors was observed only in affected twin microglia. Also, the microglia of affected twins had heterogeneous response to clozapine, minocycline, and sulforaphane treatments. Overall, despite the increased expression of inflammatory genes, we observed no clear functional signs of hyperactivation in microglia from patients with SCZ. We conclude that microglia of the patients with SCZ have gene expression aberrations related to inflammation response and extracellular matrix without contributing to increased microglial activation.

Fasudil attenuates syncytin-1-mediated activation of microglia and impairments of motor neurons and motor function in mice

Amyotrophic lateral sclerosis (ALS) is a devastating neurodegenerative disease. Syncytin-1 (Syn), an envelope glycoprotein encoded by the env gene of the human endogenous retrovirus-W family, has been resorted to be highly expressed in biopsies from the muscles from ALS patients; however, the specific regulatory role of Syn during ALS progression remains uncovered. In this study, C57BL/6 mice were injected with adeno-associated virus-overexpressing Syn, with or without Fasudil administration. The Syn expression was assessed by quantitative real-time polymerase chain reaction and immunohistochemistry analysis. The histological change of anterior tibial muscles was determined by hematoxylin-eosin staining. Qualitative ultrastructural analysis of electron micrographs obtained from lumbar spinal cords was carried out. Serum inflammatory cytokines were assessed by enzyme linked immunosorbent assay (ELISA) assay and motor function was recorded using Basso, Beattie, and Bresnahan (BBB) scoring, climbing test and treadmill running test. Immunofluorescence and western blot assays were conducted to examine microglial- and motor neurons-related proteins. Syn overexpression significantly caused systemic inflammatory response, muscle tissue lesions, and motor dysfunction in mice. Meanwhile, Syn overexpression promoted the impairment of motor neuron, evidenced by the damaged structure of the neurons and reduced expression of microtubule-associated protein 2, HB9, neuronal nuclei and neuron-specific enolase in Syn-induced mice. In addition, Syn overexpression greatly promoted the expression of CD16/CD32 and inducible nitric oxide synthase (M1 phenotype markers), and reduced the expression of CD206 and arginase 1 (M2 phenotype markers). Importantly, the above changes caused by Syn overexpression were partly abolished by Fasudil administration. This study provides evidence that Syn-activated microglia plays a pivotal role during the progression of ALS.

Post-weaning social isolation alters sociability in a sex-specific manner

Adolescence is a critical period for brain development in humans and stress exposure during this time can have lasting effects on behavior and brain development. Social isolation and loneliness are particularly salient stressors that lead to detrimental mental health outcomes particularly in females, although most of the preclinical work on social isolation has been done in male animals. Our lab has developed a model of post-weaning adolescent social isolation that leads to increased drug reward sensitivity and altered neuronal structure in limbic brain regions. The current study utilized this model to determine the impact of adolescent social isolation on a three-chamber social interaction task both during adolescence and adulthood. We found that while post-weaning isolation does not alter social interaction during adolescence (PND45), it has sex-specific effects on social interaction in young adulthood (PND60), potentiating social interaction in male mice and decreasing it in female mice. As early life stress can activate microglia leading to alterations in neuronal pruning, we next examined the impact of inhibiting microglial activation with daily minocycline administration during the first 3 weeks of social isolation on these changes in social interaction. During adolescence, minocycline dampened social interaction in male mice, while having no effect in females. In contrast, during young adulthood, minocycline did not alter the impact of adolescent social isolation in males, with socially isolated males exhibiting higher levels of social interaction compared to their group housed counterparts. In females, adolescent minocycline treatment reversed the effect of social isolation leading to increased social interaction in the social isolation group, mimicking what is seen in naïve males. Taken together, adolescent social isolation leads to sex-specific effects on social interaction in young adulthood and adolescent minocycline treatment alters the effects of social isolation in females, but not males.

Switch to phagocytic microglia by CSFR1 inhibition drives amyloid-beta clearance from glutamatergic terminals rescuing LTP in acute hippocampal slices

Microglia, traditionally regarded as innate immune cells in the brain, drive neuroinflammation and synaptic dysfunctions in the early phases of Alzheimer disease (AD), acting upstream to Aβ accumulation. Colony stimulating factor 1-receptor (CSF-1R) is predominantly expressed on microglia and its levels are significantly increased in neurodegenerative diseases, possibly contributing to the chronic inflammatory microglial response. On the other hand, CSF-1R inhibitors confer neuroprotection in preclinical models of neurodegenerative diseases. Here, we determined the effects of the CSF-1R inhibitor PLX3397 on the Aβ-mediated synaptic alterations in ex vivo hippocampal slices. Electrophysiological findings show that PLX3397 rescues LTP impairment and neurotransmission changes induced by Aβ. In addition, using confocal imaging experiments, we demonstrate that PLX3397 stimulates a microglial transition toward a phagocytic phenotype, which in turn promotes the clearance of Aβ from glutamatergic terminals. We believe that the selective pruning of Aβ-loaded synaptic terminals might contribute to the restoration of LTP and excitatory transmission alterations observed upon acute PLX3397 treatment. This result is in accordance with the mechanism proposed for CSF1R inhibitors, that is to eliminate responsive microglia and replace it with newly generated, homeostatic microglia, capable of promoting brain repair. Overall, our findings identify a connection between the rapid microglia adjustments and the early synaptic alterations observed in AD, possibly highlighting a novel disease-modifying target.

Interplay between microglia and environmental risk factors in Alzheimer's disease

Alzheimer's disease, among the most common neurodegenerative disorders, is characterized by progressive cognitive impairment. At present, the Alzheimer's disease main risk remains genetic risks, but major environmental factors are increasingly shown to impact Alzheimer's disease development and progression. Microglia, the most important brain immune cells, play a central role in Alzheimer's disease pathogenesis and are considered environmental and lifestyle "sensors." Factors like environmental pollution and modern lifestyles (e.g., chronic stress, poor dietary habits, sleep, and circadian rhythm disorders) can cause neuroinflammatory responses that lead to cognitive impairment via microglial functioning and phenotypic regulation. However, the specific mechanisms underlying interactions among these factors and microglia in Alzheimer's disease are unclear. Herein, we: discuss the biological effects of air pollution, chronic stress, gut microbiota, sleep patterns, physical exercise, cigarette smoking, and caffeine consumption on microglia; consider how unhealthy lifestyle factors influence individual susceptibility to Alzheimer's disease; and present the neuroprotective effects of a healthy lifestyle. Toward intervening and controlling these environmental risk factors at an early Alzheimer's disease stage, understanding the role of microglia in Alzheimer's disease development, and targeting strategies to target microglia, could be essential to future Alzheimer's disease treatments.

Microglia contribute to cognitive decline in hypercholesterolemic LDLr-/- mice

Familial hypercholesterolemia (FH) is caused by mutations in the gene that encodes the low-density lipoprotein (LDL) receptor, which leads to an excessive increase in plasma LDL cholesterol levels. Previous studies have shown that FH is associated with gliosis, blood-brain barrier dysfunction, and memory impairment, but the mechanisms associated with these events are still not fully understood. Therefore, we aimed to investigate the role of microgliosis in the neurochemical and behavioral changes associated with FH using LDL receptor knockout (LDLr-/-) mice. We noticed that microgliosis was more severe in the hippocampus of middle-aged LDLr-/- mice, which was accompanied by microglial morphological changes and alterations in the immunocontent of synaptic protein markers. At three months of age, the LDLr-/- mice already showed increased microgliosis and decreased immunocontent of claudin-5 in the prefrontal cortex (PFC). Subsequently, 6-month-old male C57BL/6 wild-type and LDLr-/- mice were treated once daily for 30 days with minocycline (a pharmacological inhibitor of microglial cell reactivity) or vehicle (saline). Adult LDLr-/- mice displayed significant hippocampal memory impairment, which was ameliorated by minocycline treatment. Non-treated LDLr-/- mice showed increased microglial density in all hippocampal regions analyzed, a process that was not altered by minocycline treatment. Region-specific microglial morphological analysis revealed different effects of genotype or minocycline treatment on microglial morphology, depending on the hippocampal subregion analyzed. Moreover, 6-month-old LDLr-/- mice exhibited a slight but not significant increase in IBA-1 immunoreactivity in the PFC, which was reduced by minocycline treatment without altering microglial morphology. Minocycline treatment also reduced the presence of microglia within the perivascular area in both the PFC and hippocampus of LDLr-/- mice. However, no significant effects of either genotype or minocycline treatment were observed regarding the phagocytic activity of microglia in the PFC and hippocampus. Our results demonstrate that hippocampal microgliosis, microglial morphological changes, and the presence of these glial cells in the perivascular area, but not increased microglial phagocytic activity, are associated with cognitive deficits in a mouse model of FH.

Exploring the Significance of Microglial Phenotypes and Morphological Diversity in Neuroinflammation and Neurodegenerative Diseases: From Mechanisms to Potential Therapeutic Targets

Studying various microglial phenotypes and their functions in neurodegenerative diseases is crucial due to the intricate nature of their phenomics and their vital immunological role. Microglia undergo substantial phenomic changes, encompassing morphological, transcriptional, and functional aspects, resulting in distinct cell types with diverse structures, functions, properties, and implications. The traditional classification of microglia as ramified, M1 (proinflammatory), or M2 (anti-inflammatory) phenotypes is overly simplistic, failing to capture the wide range of recently identified microglial phenotypes in various brain regions affected by neurodegenerative diseases. Altered and activated microglial phenotypes deviating from the typical ramified structure are significant features of many neurodegenerative conditions. Understanding the precise role of each microglial phenotype is intricate and sometimes contradictory. This review specifically focuses on elucidating recent modifications in microglial phenotypes within neurodegenerative diseases. Recognizing the heterogeneity of microglial phenotypes in diseased states can unveil novel therapeutic strategies for targeting microglia in neurodegenerative diseases. Moreover, the exploration of the use of healthy isolated microglia to mitigate disease progression has provided an innovative perspective. In conclusion, this review discusses the dynamic landscape of mysterious microglial phenotypes, emphasizing the need for a nuanced understanding to pave the way for innovative therapeutic strategies for neurodegenerative diseases.

Chronic rapid eye movement sleep deprivation aggravates the pathogenesis of Alzheimer's disease by decreasing brain O-GlcNAc cycling in mice

This study investigated the role of O-GlcNAc cycling in Alzheimer's disease-related changes in brain pathophysiology induced by chronic REM sleep deprivation (CSD) in mice. CSD increased amyloid beta (Aβ) and p-Tau accumulation and impaired learning and memory (L/M) function. CSD decreased dendritic length and spine density. CSD also increased the intensity of postsynaptic density protein-95 (PSD-95) staining. All of these Alzheimer's disease (AD) pathogenic changes were effectively reversed through glucosamine (GlcN) treatment by enhancing O-GlcNAcylation. Interestingly, the lelvel of O-GlcNAcylated-Tau (O-Tau) exhibited an opposite trend compared to p-Tau, as it was elevated by CSD and suppressed by GlcN treatment. CSD increased neuroinflammation, as indicated by elevated levels of glial fibrillary acidic protein and IBA-1-positive glial cells in the brain, which were suppressed by GlcN treatment. CSD promoted the phosphorylation of GSK3β and led to an upregulation in the expression of endoplasmic reticulum (ER) stress regulatory proteins and genes. These alterations were effectively suppressed by GlcN treatment. Minocycline not only suppressed neuroinflammation induced by CSD, but it also rescued the decrease in O-GlcNAc levels caused by CSD. Minocycline also reduced AD neuropathy without affecting CSD-induced ER stress. Notably, overexpressing O-GlcNAc transferase in the dentate gyrus region of the mouse brain rescued CSD-induced cognitive dysfunction, neuropathy, neuroinflammation, and ER stress responses. Collectively, our findings reveal that dysregulation of O-GlcNAc cycling underlies CSD-induced AD pathology and demonstrate that restoration of OGlcNAcylation protects against CSD-induced neurodegeneration.

Therapeutic potential of microglia-derived extracellular vesicles in ischemic stroke

Ischemic stroke (IS) is a debilitating neurological disorder with limited treatment options. Extracellular vesicles (EVs) have emerged as crucial lipid bilayer particles derived from various cell types that facilitate intercellular communication and enable the exchange of proteins, lipids, and genetic material. Microglia are resident brain cells that play a crucial role in brain development, maintenance of neuronal networks, and injury repair. They secrete numerous extracellular vesicles in different states. Recent evidence indicates that microglia-derived extracellular vesicles (M-EVs) actively participate in mediating various biological processes, such as neuroprotection and neurorepair, in stroke, making them an excellent therapeutic approach for treating this condition. This review comprehensively summarizes the latest research on M-EVs in stroke and explores their potential as novel therapeutic targets for this disorder. Additionally, it provides an overview of the effects and functions of M-EVs on stroke recovery to facilitate the development of clinically relevant therapies for IS.