Role of microglia in CNS inflammation

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.

Ketamine's mechanism of action with an emphasis on neuroimmune regulation: can the complement system complement ketamine's antidepressant effects?

Over 300 million people worldwide suffer from major depressive disorder (MDD). Unfortunately, only 30-40% of patients with MDD achieve complete remission after conventional monoamine antidepressant therapy. In recent years, ketamine has revolutionized the treatment of MDD, with its rapid antidepressant effects manifesting within a few hours as opposed to weeks with conventional antidepressants. Many research endeavors have sought to identify ketamine's mechanism of action in mood disorders; while many studies have focused on ketamine's role in glutamatergic modulation, several studies have implicated its role in regulating neuroinflammation. The complement system is an important component of the innate immune response vital for synaptic plasticity. The complement system has been implicated in the pathophysiology of depression, and studies have shown increases in complement component 3 (C3) expression in the prefrontal cortex of suicidal individuals with depression. Given the role of the complement system in depression, ketamine and the complement system's abilities to modulate glutamatergic transmission, and our current understanding of ketamine's anti-inflammatory properties, there is reason to suspect a common link between the complement system and ketamine's mechanism of action. This review will summarize ketamine's anti- inflammatory roles in the periphery and central nervous system, with an emphasis on complement system regulation.

Vagus nerve stimulation (VNS) preventing postoperative cognitive dysfunction (POCD): two potential mechanisms in cognitive function

Postoperative cognitive dysfunction (POCD) impacts a significant number of patients annually, frequently impairing their cognitive abilities and resulting in unfavorable clinical outcomes. Aimed at addressing cognitive impairment, vagus nerve stimulation (VNS) is a therapeutic approach, which was used in many mental disordered diseases, through the modulation of vagus nerve activity. In POCD model, the enhancement of cognition function provided by VNS was shown, demonstrating VNS effect on cognition in POCD. In the present study, we primarily concentrates on elucidating the role of the VNS improving the cognitive function in POCD, via two potential mechanisms: the inflammatory microenvironment and epigenetics. This study provided a theoretical support for the feasibility that VNS can be a potential method to enhance cognition function in POCD.

Platycodon grandiflorum exhibits anti-neuroinflammatory potential against beta-amyloid-induced toxicity in microglia cells

Background/objectives

Platycodon grandiflorum (PG) is used in traditional oriental medicine to treat several ailments.

Methods

The study investigated the anti-inflammatory and neuroprotective effects of PGW (P. grandiflorum) extract in Aβ25-35-induced inflammation in BV2 microglia cells.

Result

PGW demonstrated significant inhibition of nitric oxide (NO) production, with reductions of 30.4, 36.7, and 61.2% at concentrations of 50, 100, and 200 μg/mL, respectively. Moreover, PGW effectively suppressed the production of pro-inflammatory cytokines IL-1β and IL-6 and exhibited significant inhibitory activity against TNF-α at 200 μg/mL. Furthermore, PGW treatment mitigated apoptosis in Aβ-induced BV2 cells by modulating the mitochondrial apoptosis pathway, regulating Bcl-2 family protein synthesis, and inhibiting caspase activation. Mechanistically, PGW attenuated the activation of the MAPK (JNK, ERK, p38) pathway induced by Aβ, showing a concentration-dependent decrease in phosphorylation levels of these proteins. Additionally, PGW inhibited the NF-κB pathway activation by reducing the phosphorylation levels of p65 and IκBα in a concentration-dependent manner.

Conclusion

PGW demonstrated anti-inflammatory and neuroprotective effects in Aβ-induced neuronal cells, suggesting its potential as a therapeutic agent for neuroinflammatory associated with neurodegenerative diseases.

Targeted Repair of Spinal Cord Injury Based on miRNA-124-3p-Loaded Mesoporous Silica Camouflaged by Stem Cell Membrane Modified with Rabies Virus Glycoprotein

Spinal cord injury (SCI) has no effective treatment modalities. It faces a significant global therapeutical challenge, given its features of poor axon regeneration, progressive local inflammation, and inefficient systemic drug delivery due to the blood-spinal cord barrier (BSCB). To address these challenges, a new nano complex that achieves targeted drug delivery to the damaged spinal cord is proposed, which contains a mesoporous silica nanoparticle core loaded with microRNA and a cloaking layer of human umbilical cord mesenchymal stem cell membrane modified with rabies virus glycoprotein (RVG). The nano complex more readily crosses the damaged BSCB with its exosome-resembling properties, including appropriate size and a low-immunogenic cell membrane disguise and accumulates in the injury center because of RVG, where it releases abundant microRNAs to elicit axon sprouting and rehabilitate the inflammatory microenvironment. Culturing with nano complexes promotes axonal growth in neurons and M2 polarization in microglia. Furthermore, it showed that SCI mice treated with this nano complex by tail vein injection display significant improvement in axon regrowth, microenvironment regulation, and functional restoration. The efficacy and biocompatibility of the targeted delivery of microRNA by nano complexes demonstrate their immense potential as a noninvasive treatment for SCI.

Exploring the Role of Guanylate-Binding Protein-2 in Activated Microglia-Mediated Neuroinflammation and Neuronal Damage

Neuron damage by microglia, which act as macrophage cells in the brain, can result in various brain diseases. However, the function of pro-inflammatory or anti-inflammatory microglia in the neurons remains controversial. Guanylate-binding protein-2 (GBP2) is expressed and activated in the microglia in the early phase of the inflammatory response and plays an important role in controlling immune responses. In this study, we evaluated whether GBP2 initially reduces the immune response induced by microglia, and whether microglia induce pro-inflammatory functions in neurons via GBP2 expression. In lipopolysaccharide (LPS)-stimulated microglia, we assessed the expression of GBP2 and how it affects neurons via activated microglia. The biological functions of microglia due to the downregulation of the GBP2 gene were examined using short hairpin RNA (shRNA)-RNA-GBP2. Downregulated GBP2 affected the function of mitochondria in the microglia and showed reduced neuronal damage when compared to the control group in the co-culture system. Furthermore, this protein was observed to be highly expressed in the brains of dementia mice. Our results are the first to report that the downregulation of GBP2 in activated microglia has an anti-inflammatory function. This study suggests that the GBP2 gene can be used as a therapeutic target biomarker for inflammation-related neurodegenerative diseases.

Evaluation of microglia activation related markers following a clinical course of TBS: A non-human primate study

While the applicability and popularity of theta burst stimulation (TBS) paradigms remain, current knowledge of their neurobiological effects is still limited, especially with respect to their impact on glial cells and neuroinflammatory processes. We used a multimodal imaging approach to assess the effects of a clinical course of TBS on markers for microglia activation and tissue injury as an indirect assessment of neuroinflammatory processes. Healthy non-human primates received continuous TBS (cTBS), intermittent TBS (iTBS), or sham stimulation over the motor cortex at 90% of resting motor threshold. Stimulation was delivered to the awake subjects 5 times a week for 3-4 weeks. Translocator protein (TSPO) expression was evaluated using Positron Emission Tomography and [11C]PBR28, and myo-inositol (mI) and N-acetyl-aspartate (NAA) concentrations were assessed with Magnetic Resonance Spectroscopy. Animals were then euthanized, and immunofluorescence staining was performed using antibodies against TSPO. Paired t-tests showed no significant changes in [11C]PBR28 measurements after stimulation. Similarly, no significant changes in mI and NAA concentrations were found. Post-mortem TSPO evaluation showed comparable mean immunofluorescence intensity after active TBS and sham delivery. The current study suggests that in healthy brains a clinical course of TBS, as evaluated with in-vivo imaging techniques (PET and MRS), did not measurably modulate the expression of glia related markers and metabolite associated with neural viability.

Anti-inflammatory activities of novel heat shock protein 90 isoform selective inhibitors in BV-2 microglial cells

Heat shock protein 90 (Hsp90) is a family of chaperone proteins that consists of four isoforms: Hsp90α, Hsp90β, glucose-regulated protein 94 (Grp94), and tumor necrosis factor type 1 receptor-associated protein (TRAP1). They are involved in modulating the folding, maturation, and activation of their client proteins to regulate numerous intracellular signaling pathways. Previous studies demonstrated that pan-Hsp90 inhibitors reduce inflammatory signaling pathways resulting in a reduction of inflammation and pain but show toxicities in cancer-related clinical trials. Further, the role of Hsp90 isoforms in inflammation remains poorly understood. This study aimed to determine anti-inflammatory activities of Hsp90 isoforms selective inhibitors on the lipopolysaccharide (LPS)-induced inflammation in BV-2 cells, a murine microglial cell line. The production of inflammatory mediators such as nitric oxide (NO), interleukin 1 beta (IL-1β), and tumor necrosis factor-alpha (TNF-α) was measured. We also investigated the impact of Hsp90 isoform inhibitors on the activation of nuclear factor kappa B (NF-κB), nuclear factor erythroid 2-related factor 2 (Nrf2), and mitogen-activated protein kinases (MAPKs). We found that selective inhibitors of Hsp90β reduced the LPS-induced production of NO, IL-1β, and TNF-α via diminishing the activation of NF-κB and Extracellular signal-regulated kinases (ERK) MAPK. The Hsp90α, Grp94, TRAP1 inhibitors had limited effect on the production of inflammatory mediators. These findings suggest that Hsp90β is the key player in LPS-induced neuroinflammation. Thereby providing a more selective drug target for development of medications involved in pain management that can potentially contribute to the reduction of adverse side effects associated with Hsp90 pan inhibitors.

Macrophage activation contributes to diabetic retinopathy

Diabetic retinopathy (DR) is recognized as a neurovascular complication of diabetes, and emerging evidence underscores the pivotal role of inflammation in its pathophysiology. Macrophage activation is increasingly acknowledged as a key contributor to the onset and progression of DR. Different populations of macrophages originating from distinct sources contribute to DR-associated inflammation. Retinal macrophages can be broadly categorized into two main groups based on their origin: intrinsic macrophages situated within the retina and vitreoretinal interface and macrophages derived from infiltrating monocytes. The former comprises microglia (MG), perivascular macrophages, and macrophage-like hyalocytes. Retinal MG, as the principal population of tissue-resident population of mononuclear phagocytes, exhibits high heterogeneity and plasticity while serving as a crucial connector between retinal capillaries and synapses. This makes MG actively involved in the pathological processes across various stages of DR. Activated hyalocytes also contribute to the pathological progression of advanced DR. Additionally, recruited monocytes, displaying rapid turnover in circulation, augment the population of retinal macrophages during DR pathogenesis, exerting pathogenic or protective effect based on different subtypes. In this review, we examine novel perspectives on macrophage biology based on recent studies elucidating the diversity of macrophage identity and function, as well as the mechanisms influencing macrophage behavior. These insights may pave the way for innovative therapeutic strategies in the management of DR.

The case for neuregulin-1 as a clinical treatment for stroke

Ischemic stroke is the leading cause of serious long-term disability and the 5th leading cause of death in the United States. Revascularization of the occluded cerebral artery, either by thrombolysis or endovascular thrombectomy, is the only effective, clinically-approved stroke therapy. Several potentially neuroprotective agents, including glutamate antagonists, anti-inflammatory compounds and free radical scavenging agents were shown to be effective neuroprotectants in preclinical animal models of brain ischemia. However, these compounds did not demonstrate efficacy in clinical trials with human patients following stroke. Proposed reasons for the translational failure include an insufficient understanding on the cellular and molecular pathophysiology of ischemic stroke, lack of alignment between preclinical and clinical studies and inappropriate design of clinical trials based on the preclinical findings. Therefore, novel neuroprotective treatments must be developed based on a clearer understanding of the complex spatiotemporal mechanisms of ischemic stroke and with proper clinical trial design based on the preclinical findings from specific animal models of stroke. We and others have demonstrated the clinical potential for neuregulin-1 (NRG-1) in preclinical stroke studies. NRG-1 significantly reduced ischemia-induced neuronal death, neuroinflammation and oxidative stress in rodent stroke models with a therapeutic window of >13 h. Clinically, NRG-1 was shown to be safe in human patients and improved cardiac function in multisite phase II studies for heart failure. This review summarizes previous stroke clinical candidates and provides evidence that NRG-1 represents a novel, safe, neuroprotective strategy that has potential therapeutic value in treating individuals after acute ischemic stroke.

Microglia cells treated with synthetic vasoactive intestinal peptide or transduced with LentiVIP protect neuronal cells against degeneration

A common pathological hallmark of neurodegenerative disorders is neuronal cell death, accompanied by neuroinflammation and oxidative stress. The vasoactive intestinal peptide (VIP) is a pleiotropic peptide that combines neuroprotective and immunomodulatory actions. The gene therapy field shows long-term promise for treating a wide range of neurodegenerative diseases (ND). In this study, we aimed to investigate the in vitro efficacy of transduction of microglia using lentiviral gene therapy vectors encoding VIP (LentiVIP). Additionally, we tested the protective effects of the secretome derived from LentiVIP-infected "immortalized human" microglia HMC3 cells, and cells treated with Synthetic VIP (SynVIP), against toxin-induced neurodegeneration. First, LentiVIP, which stably expresses VIP, was generated and purified. VIP secretion in microglial conditioned media (MG CM) for LentiVIP-infected HMC3 microglia cells was confirmed. Microglia cells were activated with lipopolysaccharide, and groups were formed as follows: 1) Control, 2) SynVIP-treated, or 3) LentiVIP-transduced. These MG CM were applied on an in vitro neurodegenerative model formed by differentiated (d)-SH-SY5Y cells. Then, cell survival analysis and apoptotic nuclear staining, besides measurement of oxidative/inflammatory parameters in CM of cells were performed. Activated MG CM reduced survival rates of both control and toxin-applied (d)-SH-SY5Y cells, whereas LentiVIP-infected MG CM and SynVIP-treated ones exhibited better survival rates. These findings were supported by apoptotic nuclear evaluations of (d)-SH-SY5Y cells, alongside oxidative/inflammatory parameters in their CM. LentiVIP seems worthy of further studies for the treatment of ND because of the potential of gene therapy to treat diseases effectively with a single injection.

Sesquiterpenoids and hexanorcucurbitacin from Aquilaria malaccensis agarwood with anti-inflammatory effects by inhibiting the STAT1/AKT/MAPK/NLRP3 pathway

Seven unknown compounds 1-7, including four sesquiterpenoids, one azulene-type, one indene-type, and one rare hexanorcucurbitacin, together with eleven knowns ones (8-16), were isolated from the agarwood chips of Aquilaria malaccensis. The structures of the isolated compounds were elucidated by extensive spectroscopic methods such as mass spectrometry, UV, IR, NMR spectroscopy. The precise stereo-chemical configurations of new compounds were determined by calculated ECD spectra data, as well as a single-crystal X-ray diffraction analysis. The isolated compounds 1-7 were evaluated by estimating the levels of nitric oxide (NO), TNF-α, and the expression of enzyme iNOS, and COX-2. Among them, a rare hexanortriterpenoid (7) derived from a cucurbitane-type triterpenoid showed the significantly attenuated neuro-inflammatory effects via the STAT1/AKT/MAPK/NLRP3 signaling pathway on the mechanistic studies.

Serum concentrations of complement C3 and C4 in dogs with idiopathic epilepsy

BACKGROUND

High concentrations of complement factors are presented in serum of animal epilepsy models and human patients with epilepsy.

OBJECTIVES

To determine whether complement dysregulation occurs in dogs with idiopathic epilepsy (IE).

ANIMALS

The study included 49 dogs with IE subgrouped into treatment (n = 19), and nontreatment (n = 30), and 29 healthy dogs.

METHODS

In this case-control study, the serum concentrations of the third (C3) and fourth (C4) components of the complement system were measured using a canine-specific ELISA kit.

RESULTS

Serum C3 and C4 concentrations were significantly higher in dogs with IE (C3, median; 4.901 [IQR; 3.915-6.673] mg/mL, P < .001; C4, 0.327 [0.134-0.557] mg/mL, P = .03) than in healthy control dogs (C3, 3.550 [3.075-4.191] mg/mL; C4, 0.267 [0.131-0.427] mg/mL). No significant differences were observed in serum C3 and C4 concentrations between dogs in the treatment (C3, median; 4.894 [IQR; 4.192-5.715] mg/mL; C4, 0.427 [0.143-0.586] mg/mL) and nontreatment groups (C3, 5.051 [3.702-7.132] mg/mL; C4, 0.258 [0.130-0.489] mg/mL). Dogs with a seizure frequency >3 times/month had significantly higher serum C3 (6.461 [4.695-8.735] mg/mL; P < .01) and C4 (0.451 [0.163-0.675] mg/mL; P = .01) concentrations than those with a seizure frequency ≤3 times/month (C3, 3.859 [3.464-5.142] mg/mL; C4, 0.161 [0.100-0.325] mg/mL).

CONCLUSIONS AND CLINICAL IMPORTANCE

Dysregulation of classical complement pathway was identified in IE dogs. Serum C3 and C4 concentrations could be diagnostic biomarkers for IE in dogs with higher seizure frequency.

Oxidative stress and inflammation cause auditory system damage via glial cell activation and dysregulated expression of gap junction proteins in an experimental model of styrene-induced oto/neurotoxicity

BACKGROUND

Redox imbalance and inflammation have been proposed as the principal mechanisms of damage in the auditory system, resulting in functional alterations and hearing loss. Microglia and astrocytes play a crucial role in mediating oxidative/inflammatory injury in the central nervous system; however, the role of glial cells in the auditory damage is still elusive.

OBJECTIVES

Here we investigated glial-mediated responses to toxic injury in peripheral and central structures of the auditory pathway, i.e., the cochlea and the auditory cortex (ACx), in rats exposed to styrene, a volatile compound with well-known oto/neurotoxic properties.

METHODS

Male adult Wistar rats were treated with styrene (400 mg/kg daily for 3 weeks, 5/days a week). Electrophysiological, morphological, immunofluorescence and molecular analyses were performed in both the cochlea and the ACx to evaluate the mechanisms underlying styrene-induced oto/neurotoxicity in the auditory system.

RESULTS

We showed that the oto/neurotoxic insult induced by styrene increases oxidative stress in both cochlea and ACx. This was associated with macrophages and glial cell activation, increased expression of inflammatory markers (i.e., pro-inflammatory cytokines and chemokine receptors) and alterations in connexin (Cxs) and pannexin (Panx) expression, likely responsible for dysregulation of the microglia/astrocyte network. Specifically, we found downregulation of Cx26 and Cx30 in the cochlea, and high level of Cx43 and Panx1 in the ACx.

CONCLUSIONS

Collectively, our results provide novel evidence on the role of immune and glial cell activation in the oxidative/inflammatory damage induced by styrene in the auditory system at both peripheral and central levels, also involving alterations of gap junction networks. Our data suggest that targeting glial cells and connexin/pannexin expression might be useful to attenuate oxidative/inflammatory damage in the auditory system.

History of Microglia

The term 'microglia' was first introduced into the scientific literature a century ago. The various eras of microglial research have been defined not only by the number of reports subsequently generated but, more critically, also by the concepts that have shaped our present-day views and understanding of microglia. Key methods, technologies, and models, as well as seminal discoveries made possible through their deployment have enabled breakthroughs, and now pave the way for lines of investigation that could not have been anticipated even a decade ago. Advances in our understanding of the microglial origin, forms, and functions have relied fundamentally on parallel developments in immunology. As the 'neuro-immune' cells of the brain, microglia are now under the spotlight in various disciplines. This chapter surveys the gradual processes and precipitous events that helped form ideas concerning the developmental origin of microglia and their roles in health and disease. It first covers the dawning phase during which the early pioneers of microglial research discovered cellular entities and already assigned functions to them. Following a recess period, the 1960s brought about a renaissance of active interest, with the development of tools and models-and fundamental notions on microglial contributions to central nervous system (CNS) pathologies. These seminal efforts laid the foundation for the awakening of a sweeping research era beginning in the 1980s and spurred on by a blast of immunological discoveries. Finally, this chapter stresses the advancements in molecular, genetic, and imaging approaches to the study of microglia with the turn of the millennium, enabling insights into virtually all facets of microglial physiology. Moving forward, it is clear that the future holds substantial promise for further discoveries. The next epoch in the history of microglial research has just begun.

C/EBPβ: The structure, regulation, and its roles in inflammation-related diseases

Inflammation, a mechanism of the human body, has been implicated in many diseases. Inflammatory responses include the release of inflammatory mediators by activating various signaling pathways. CCAAT/enhancer binding protein β (C/EBPβ), a transcription factor in the C/EBP family, contains the leucine zipper (bZIP) domain. The expression of C/EBPβ is mediated at the transcriptional and post-translational levels, such as phosphorylation, acetylation, methylation, and SUMOylation. C/EBPβ has been involved in inflammatory responses by mediating several signaling pathways, such as MAPK/NF-κB and IL-6/JAK/STAT3 pathways. C/EBPβ plays an important role in the pathological development of inflammation-related diseases, such as osteoarthritis, pneumonia, hepatitis, inflammatory bowel diseases, and rheumatoid arthritis. Here, we comprehensively discuss the structure and biological effects of C/EBPβ and its role in inflammatory diseases.

Advances in immune checkpoint-based immunotherapies for multiple sclerosis: rationale and practice

Beyond the encouraging results and broad clinical applicability of immune checkpoint (ICP) inhibitors in cancer therapy, ICP-based immunotherapies in the context of autoimmune disease, particularly multiple sclerosis (MS), have garnered considerable attention and hold great potential for developing effective therapeutic strategies. Given the well-established immunoregulatory role of ICPs in maintaining a balance between stimulatory and inhibitory signaling pathways to promote immune tolerance to self-antigens, a dysregulated expression pattern of ICPs has been observed in a significant proportion of patients with MS and its animal model called experimental autoimmune encephalomyelitis (EAE), which is associated with autoreactivity towards myelin and neurodegeneration. Consequently, there is a rationale for developing immunotherapeutic strategies to induce inhibitory ICPs while suppressing stimulatory ICPs, including engineering immune cells to overexpress ligands for inhibitory ICP receptors, such as program death-1 (PD-1), or designing fusion proteins, namely abatacept, to bind and inhibit the co-stimulatory pathways involved in overactivated T-cell mediated autoimmunity, and other strategies that will be discussed in-depth in the current review. Video Abstract.

K252a Prevents Microglial Activation Induced by Anoxic Stimulation of Carotid Bodies in Rats

Inducing carotid body anoxia through the administration of cyanide can result in oxygen deprivation. The lack of oxygen activates cellular responses in specific regions of the central nervous system, including the Nucleus Tractus Solitarius, hypothalamus, hippocampus, and amygdala, which are regulated by afferent pathways from chemosensitive receptors. These receptors are modulated by the brain-derived neurotrophic factor receptor TrkB. Oxygen deprivation can cause neuroinflammation in the brain regions that are activated by the afferent pathways from the chemosensitive carotid body. To investigate how microglia, a type of immune cell in the brain, respond to an anoxic environment resulting from the administration of NaCN, we studied the effects of blocking the TrkB receptor on this cell-type response. Male Wistar rats were anesthetized, and a dose of NaCN was injected into their carotid sinus to induce anoxia. Prior to the anoxic stimulus, the rats were given an intracerebroventricular (icv) infusion of either K252a, a TrkB receptor inhibitor, BDNF, or an artificial cerebrospinal fluid (aCSF). After the anoxic stimulus, the rats were perfused with paraformaldehyde, and their brains were processed for microglia immunohistochemistry. The results indicated that the anoxic stimulation caused an increase in the number of reactive microglial cells in the hypothalamic arcuate, basolateral amygdala, and dentate gyrus of the hippocampus. However, the infusion of the K252a TrkB receptor inhibitor prevented microglial activation in these regions.

Review on pharmacological effects of gastrodin

Gastrodia elata Blume is a well-known traditional Chinese medicine that is mainly used to treat diseases related to the nervous system, such as stroke, epilepsy, and headache. Gastrodin is the main bioactive component of Gastrodia elata Blume, and studies have shown that it has extensive pharmacological activity. This narrative review aims to systematically review relevant studies on the pharmacological effects of gastrodin to provide researchers with the latest and most useful information. Studies have shown that gastrodin has prominent neuroprotective effects and can treat or improve epilepsy, Tourette syndrome, Alzheimer's disease, Parkinson's disease, emotional disorders, cerebral ischemia-reperfusion injury, cognitive impairment, and neuropathic pain. Gastrodin can also improve myocardial hypertrophy, hypertension, and myocardial ischemia-reperfusion injury. In addition, gastrodin can mitigate liver, kidney, and bone tissue damage caused by oxidative stress and inflammation. In short, gastrodin is expected to treat many diseases, and it is worth investing more effort in research on this compound.

Adult IDH Wild-Type Glioblastoma Ultrastructural Investigation Suggests a Possible Correlation between Morphological Biomarkers and Ki-67 Index

Glioblastoma is an aggressive brain tumor with an average life expectancy between 14 and 16 months after diagnosis. The Ki-67 labeling index (LI), a measure of cellular proliferation, is emerging as a prognostic marker in GBM. In this study, we investigated the ultrastructure of glioblastoma tissue from 9 patients with the same molecular profile (adult IDH wild-type glioblastoma, wild-type ATRX, and positive for TP53 expression, GFAP expression, and EGFR overexpression) to find possible ultrastructural features to be used as biomarkers and correlated with the only parameter that differs among our samples, the Ki-67 LI. Our main results were the visualization of the anatomical basis of astrocyte-endothelial cells crosstalk; the ultrastructural in situ imaging of clusters of hyperactivated microglia cells (MsEVs); the ultrastructural in situ imaging of microglia cells storing lipid vesicles (MsLVs); the ultrastructural in situ imaging of neoplastic cells mitophagy (NCsM). The statistical analysis of our data indicated that MsEVs and MsLVs correlate with the Ki-67 LI value. We can thus assume they are good candidates to be considered morphological biomarkers correlating to Ki-67 LI. The role of NCsM instead must be further evaluated. Our study findings demonstrate that by combining ultrastructural characteristics with molecular information, we can discover biomarkers that have the potential to enhance diagnostic precision, aid in treatment decision-making, identify targets for therapy, and enable personalized treatment plans tailored to each patient. However, further research with larger sample sizes is needed to validate these findings and fully utilize the potential of ultrastructural analysis in managing glioblastoma.

Pivotal role of the protein corona in the cell uptake of fluorinated nanoparticles with increased sensitivity for 19F-MR imaging

In vivo cell tracking by non-invasive imaging technologies is needed to accelerate the clinical translation of innovative cell-based therapies. In this regard, ¹⁹F-MRI has recently gained increased attention for unbiased localization of labeled cells over time. To push forward the use of ¹⁹F-MRI for cell tracking, the development of highly performant ¹⁹F-probes is required. PLGA-based NPs containing PERFECTA, a multibranched superfluorinated molecule with an optimal MRI profile thanks to its 36 magnetically equivalent fluorine atoms, are promising ¹⁹F-MRI probes. In this work we demonstrate the importance of the surface functionalization of these NPs in relation to their interaction with the biological environment, stressing the pivotal role of the formation of the protein corona (PC) in their cellular labelling efficacy. In particular, our studies showed that the formation of PC NPs strongly promotes the cellular internalization of these NPs in microglia cells. We advocate that the formation of PC NPs in the culture medium can be a key element to be used for the optimization of cell labelling with a considerable increase of the detection sensitivity by ¹⁹F-MRI.

Neurodegeneration and inflammation crosstalk: Therapeutic targets and perspectives

Glia, which was formerly considered to exist just to connect neurons, now plays a key function in a wide range of physiological events, including formation of memory, learning, neuroplasticity, synaptic plasticity, energy consumption, and homeostasis of ions. Glial cells regulate the brain's immune responses and confers nutritional and structural aid to neurons, making them an important player in a broad range of neurological disorders. Alzheimer's, ALS, Parkinson's, frontotemporal dementia (FTD), and epilepsy are a few of the neurodegenerative diseases that have been linked to microglia and astroglia cells, in particular. Synapse growth is aided by glial cell activity, and this activity has an effect on neuronal signalling. Each glial malfunction in diverse neurodegenerative diseases is distinct, and we will discuss its significance in the progression of the illness, as well as its potential for future treatment.

Aurantiamide suppresses the activation of NLRP3 inflammasome to improve the cognitive function and central inflammation in mice with Alzheimer's disease

AIM

This study was aimed at exploring the mechanism by which aurantiamide (Aur) targeted NLRP3 to suppress microglial cell polarization.

METHODS

The 7-month-old APP/PS1 mice and C57BL/6 mice were applied to be the study objects, and Aur was administered intragastrically to APP/PS1 mice at 10 mg/kg and 20 mg/kg. The changes in the neurocognitive function of mice were measured by Morris Water Maze (MWM) test. In the in vitro experiments, the mouse BV2 cells were employed as the study objects, which were subject to treatment with 10 μM and 20 μM Aur and induced with LPS and IFN-γ in order to activate BV2 cells and induce their M1 polarization.

RESULTS

Aur was found to suppress the M1 polarization of mouse microglia, reduce central neuroinflammation, and improve the cognitive function in mice. Meanwhile, Aur suppressed the activation and the expression of NLRP3 inflammasome. The results of experiments in vitro demonstrated that Aur inhibited the activation and M1 polarization of BV2 cells.

CONCLUSION

Aur targets NLRP3 and suppresses the activation of NLRP3 inflammasome.

GDNF-Loaded Polydopamine Nanoparticles-Based Anisotropic Scaffolds Promote Spinal Cord Repair by Modulating Inhibitory Microenvironment

Spinal cord injury (SCI) is a devastating injury that causes permanent loss of sensation and motor function. SCI repair is a significant challenge due to the limited regenerating ability of adult neurons and the complex inflammatory microenvironment. After SCI, the oxidative stress induced by excessive reactive oxygen species (ROS) often leads to prolonged neuroinflammation that results in sustained damage to the spinal cord tissue. Polydopamine (PDA) shows remarkable capability in scavenging ROS to treat numerous inflammatory diseases. In this study, glial cell-derived neurotrophic factor (GDNF)-loaded PDA nanoparticle-based anisotropic scaffolds for spinal cord repair are developed. It is found that mesoporous PDA nanoparticles (mPDA NPs) in the scaffolds efficiently scavenge ROS and promote microglia M2 polarization, thereby inhibiting inflammatory response at the injury site and providing a favorable microenvironment for nerve cell survival. Furthermore, the GDNF encapsulated in mPDA NPs promotes corticospinal tract motor axon regeneration and its locomotor functional recovery. Together, findings from this study reveal that the GDNF-loaded PDA/Gelatin scaffolds hold potential as an effective artificial transplantation material for SCI treatment.

Anti-Neuroinflammatory Potential of a Nectandra angustifolia (Laurel Amarillo) Ethanolic Extract

Microglia, the resident macrophage-like population in the CNS, plays an important role in the pathogenesis of many neurodegenerative disorders. Nectandra genus is known to produce different metabolites with anti-inflammatory, anti-oxidant and analgesic properties. Although the species Nectandra angustifolia is popularly used for the treatment of different types of inflammatory processes, its biological effects on neuroinflammation have not yet been addressed. In this study, we have investigated the role of a Nectandra angustifolia ethanolic extract (NaE) in lipopolysaccharide (LPS)-induced neuroinflammation in vitro and in vivo. In LPS-activated BV2 microglial cells, NaE significantly reduced the induced proinflammatory mediators TNF-α, IL-1β, IL-6, COX-2 and iNOS, as well as NO accumulation, while it promoted IL-10 secretion and YM-1 expression. Likewise, reduced CD14 expression levels were detected in microglial cells in the NaE+LPS group. NaE also attenuated LPS-induced ROS and lipid peroxidation build-up in BV2 cells. Mechanistically, NaE prevented NF-κB and MAPKs phosphorylation, as well as NLRP3 upregulation when added before LPS stimulation, although it did not affect the level of some proteins related to antioxidant defense such as Keap-1 and HO-1. Additionally, we observed that NaE modulated some activated microglia functions, decreasing cell migration, without affecting their phagocytic capabilities. In LPS-injected mice, NaE pre-treatment markedly suppressed the up-regulated TNF-α, IL-6 and IL-1β mRNA expression induced by LPS in brain. Our findings indicate that NaE is beneficial in preventing the neuroinflammatory response both in vivo and in vitro. NaE may regulate microglia homeostasis, not only restraining activation of LPS towards the M1 phenotype but promoting an M2 phenotype.

Mitochondrial quality control in the brain: The physiological and pathological roles

The human brain has high energetic expenses and consumes over 20% of total oxygen metabolism. Abnormal brain energy homeostasis leads to various brain diseases. Among multiple factors that contribute to these diseases, mitochondrial dysfunction is one of the most common causes. Maintenance of mitochondrial integrity and functionality is of pivotal importance to brain energy generation. Mitochondrial quality control (MQC), employing the coordination of multiple mechanisms, is evolved to overcome many mitochondrial defects. Thus, not surprisingly, aberrant mitochondrial quality control results in a wide range of brain disorders. Targeting MQC to preserve and restore mitochondrial function has emerged as a promising therapeutic strategy for the prevention and treatment of brain diseases. Here, we set out to summarize the current understanding of mitochondrial quality control in brain homeostasis. We also evaluate potential pharmaceutically and clinically relevant targets in MQC-associated brain disorders.

Opposing effects of apoE2 and apoE4 on microglial activation and lipid metabolism in response to demyelination

BACKGROUND

Abnormal lipid accumulation has been recognized as a key element of immune dysregulation in microglia whose dysfunction contributes to neurodegenerative diseases. Microglia play essential roles in the clearance of lipid-rich cellular debris upon myelin damage or demyelination, a common pathogenic event in neuronal disorders. Apolipoprotein E (apoE) plays a pivotal role in brain lipid homeostasis; however, the apoE isoform-dependent mechanisms regulating microglial response upon demyelination remain unclear.

METHODS

To determine how apoE isoforms impact microglial response to myelin damage, 2-month-old apoE2-, apoE3-, and apoE4-targeted replacement (TR) mice were fed with normal diet (CTL) or 0.2% cuprizone (CPZ) diet for four weeks to induce demyelination in the brain. To examine the effects on subsequent remyelination, the cuprizone diet was switched back to regular chow for an additional two weeks. After treatment, brains were collected and subjected to immunohistochemical and biochemical analyses to assess the myelination status, microglial responses, and their capacity for myelin debris clearance. Bulk RNA sequencing was performed on the corpus callosum (CC) to address the molecular mechanisms underpinning apoE-mediated microglial activation upon demyelination.

RESULTS

We demonstrate dramatic isoform-dependent differences in the activation and function of microglia upon cuprizone-induced demyelination. ApoE2 microglia were hyperactive and more efficient in clearing lipid-rich myelin debris, whereas apoE4 microglia displayed a less activated phenotype with reduced clearance efficiency, compared with apoE3 microglia. Transcriptomic profiling revealed that key molecules known to modulate microglial functions had differential expression patterns in an apoE isoform-dependent manner. Importantly, apoE4 microglia had excessive buildup of lipid droplets, consistent with an impairment in lipid metabolism, whereas apoE2 microglia displayed a superior ability to metabolize myelin enriched lipids. Further, apoE2-TR mice had a greater extent of remyelination; whereas remyelination was compromised in apoE4-TR mice.

CONCLUSIONS

Our findings provide critical mechanistic insights into how apoE isoforms differentially regulate microglial function and the maintenance of myelin dynamics, which may inform novel therapeutic avenues for targeting microglial dysfunctions in neurodegenerative diseases.

Diabetic Macular Edema: Current Understanding, Molecular Mechanisms and Therapeutic Implications

Diabetic retinopathy (DR), with increasing incidence, is the major cause of vision loss and blindness worldwide in working-age adults. Diabetic macular edema (DME) remains the main cause of vision impairment in diabetic patients, with its pathogenesis still not completely elucidated. Vascular endothelial growth factor (VEGF) plays a pivotal role in the pathogenesis of DR and DME. Currently, intravitreal injection of anti-VEGF agents remains as the first-line therapy in DME treatment due to the superior anatomic and functional outcomes. However, some patients do not respond satisfactorily to anti-VEGF injections. More than 30% patients still exist with persistent DME even after regular intravitreal injection for at least 4 injections within 24 weeks, suggesting other pathogenic factors, beyond VEGF, might contribute to the pathogenesis of DME. Recent advances showed nearly all the retinal cells are involved in DR and DME, including breakdown of blood-retinal barrier (BRB), drainage dysfunction of Müller glia and retinal pigment epithelium (RPE), involvement of inflammation, oxidative stress, and neurodegeneration, all complicating the pathogenesis of DME. The profound understanding of the changes in proteomics and metabolomics helps improve the elucidation of the pathogenesis of DR and DME and leads to the identification of novel targets, biomarkers and potential therapeutic strategies for DME treatment. The present review aimed to summarize the current understanding of DME, the involved molecular mechanisms, and the changes in proteomics and metabolomics, thus to propose the potential therapeutic recommendations for personalized treatment of DME.

Selective GSK3β Inhibition Mediates an Nrf2-Independent Anti-inflammatory Microglial Response

Glycogen synthase kinase 3 (GSK3) is associated with the proinflammatory phenotype of microglia and has been shown to act in concert with nuclear factor kappa B (NF-κB). GSK3 is also a suppressor of nuclear factor erythroid 2-related factor 2 (Nrf2), the principal regulator of redox homeostasis. Agreeing with the oxidative paradigm of aging, Nrf2 is often deregulated in parainflammatory and neurodegenerative diseases. In this study, we aimed to explore a multimodal disease-modifying utility of GSK3 inhibition, beyond neuronal proteopathologies. Furthermore, we aimed to underscore the difference in therapeutic value between the two GSK3 paralogs by isoform-selective chemical inhibition. The anti-inflammatory effects of paralog-selective GSK3 inhibitors were evaluated as a function of the reductive capacity of each to mitigate LPS-induced activation of SIM-A9 microglia. The Griess method was employed to detect the nitrate-lowering capacity of selective GSK3 inhibition. Real-time PCR was used to assess post-treatment expression levels of pro-inflammatory markers and antioxidant genes; pro-inflammatory cytokines were assayed by ELISA. Nuclear lysates of treated cells were examined for Nrf2 and NF-κB accumulation by immunoblotting. Finally, to infer whether the counter-inflammatory activity of GSK3 inhibition was Nrf2-dependent, DsiRNA-mediated knockdown of Nrf2 was attempted. Results from our experiments reveal a superior anti-inflammatory and anti-oxidative efficacy for GSK3β-selective inhibition, compared to GSK3α-selective and non-selective pan-inhibition; hence, use of selective GSK3β inhibitors is likely to be more propitious than non-selective dual inhibitors administered at comparable doses. Moreover, our results suggest that the anti-inflammatory effects of GSK3 inhibition are not Nrf2 dependent.

Reduction in the Migration Activity of Microglia Treated with Silica-Coated Magnetic Nanoparticles and their Recovery Using Citrate

Nanoparticles have garnered significant interest in neurological research in recent years owing to their efficient penetration of the blood-brain barrier (BBB). However, significant concerns are associated with their harmful effects, including those related to the immune response mediated by microglia, the resident immune cells in the brain, which are exposed to nanoparticles. We analysed the cytotoxic effects of silica-coated magnetic nanoparticles containing rhodamine B isothiocyanate dye [MNPs@SiO2(RITC)] in a BV2 microglial cell line using systems toxicological analysis. We performed the invasion assay and the exocytosis assay and transcriptomics, proteomics, metabolomics, and integrated triple-omics analysis, generating a single network using a machine learning algorithm. The results highlight alteration in the mechanisms of the nanotoxic effects of nanoparticles using integrated omics analysis.

Resveratrol Glycosides Impede Microglial Apoptosis and Oxidative Stress in Rats for Spinal Cord Injury

Spinal cord injury (SCI) usually occurs after severe trauma, which can lead to detrimental and unpredictable secondary diseases, including dyskinesia, paraplegia and even quadriplegia, resulting in seriously reduced quality of life among these patients. Oxidative damage is one of the major pathogenic factors of SCI. Resveratrol biologically exerts a significant antioxidant activity by increasing the levels of antioxidants and sequentially scavenging free radicals, so as to protect multiple organs from damage. This study investigates whether resveratrol can function as a protective mediator in SCI and the underlying mechanisms, aiming to provide a theoretical hint for the treatment of SCI. After establishment of SCI model in rats, serial doses of resveratrol were administrated. Afterwards, the therapeutic effects of resveratrol glycosides were evaluated by analyzing the motor function, spinal cord edema, cellular apoptosis and oxidative reaction in rats. Eventually, the potential mechanisms of resveratrol glycosides were studied via Western blotting. Our results showed that the pro-apoptosis proteins were highly expressed in the spinal cord tissue of rats after SCI. In comparison with healthy rats, those with SCI exhibited significant widespread dead neurons, glial cell apoptosis, oxidative stress and more serious functional defects. Nevertheless, resveratrol glycosides can ameliorate oxidative stress, inhibit the apoptosis of glial cells and neuronal death after SCI. Importantly, it can induce the activation of the Nrf2/HO-1 signal transduction pathway that mediated the alleviation of SCI in rats. Resveratrol can improve motor dysfunction after SCI, which may be a result of its anti-oxidation and anti-apoptotic effects via modulating the Nrf2 signal transduction pathway of microglia, which provides a new idea for the treatment of SCI.

Human Microglia Extracellular Vesicles Derived from Different Microglia Cell Lines: Similarities and Differences

Microglial cells are a component of the innate immune system in the brain that support cell-to-cell communication via secreted molecules and extracellular vesicles (EVs). EVs can be divided into two major populations: large (LEVs) and small (SEVs) EVs, carrying different mediators, such as proteins, lipids, and miRNAs. The microglia EVs cargo crucially reflects the status of parental cells and can lead to both beneficial and detrimental effects in many physiopathological states. Herein, a workflow for the extraction and characterization of SEVs and LEVs from human C20 and HMC3 microglia cell lines derived, respectively, from adult and embryonic microglia is reported. EVs were gathered from the culture media of the two cell lines by sequential ultracentrifugation steps and their biochemical and biophysical properties were analyzed by Western blot, transmission electron microscopy, and dynamic light scattering. Although the C20- and HMC3-derived EVs shared several common features, C20-derived EVs were slightly lower in number and more polydispersed. Interestingly, C20- but not HMC3-SEVs were able to interfere with the proliferation of U87 glioblastoma cells. This correlated with the different relative levels of eight miRNAs involved in neuroinflammation and tumor progression in the C20- and HMC3-derived EVs, which in turn reflected a different basal activation state of the two cell types. Our data fill a gap in the community of microglia EVs, in which the preparations from human cells have been poorly characterized so far. Furthermore, these results shed light on both the differences and similarities of EVs extracted from different human microglia cell models, underlining the need to better characterize the features and biological effects of EVs for therein useful and correct application.

Astrocyte Activation, but not Microglia, Is Associated with the Experimental Mouse Model of Schizophrenia Induced by Chronic Ketamine

Ketamine is a noncompetitive antagonist of N-methyl-D-aspartate (NMDA) receptors. Many experimental studies have shown that ketamine can induce cognitive impairments and schizophrenia-like symptoms. While much data have demonstrated that glial cells are associated with the pathophysiology of psychiatric disorders, including schizophrenia, the response of glial cells to ketamine and its significance to schizophrenia are not clear. The present study was intended to explore whether chronic ketamine treatment would induce behavioral and glial changes in mice. First, ketamine was used to stimulate behavioral abnormalities similar to schizophrenia evaluated by the open field test, elevated plus-maze test, Y maze test, novel object recognition test, and tail suspension test. Secondly, histopathology and Nissl staining were performed. Meanwhile, immunofluorescence was used to evaluate the expression levels of IBA-1 (a microglial marker) and GFAP (an astrocyte marker) in the mouse hippocampus for any change. Then, ELISA was used to analyze proinflammatory cytokine levels for any change. Our results showed that ketamine (25 mg/kg, i.p., qid, 12 days) induced anxiety, recognition deficits, and neuronal injury in the hippocampus. Moreover, chronic ketamine treatment enhanced GFAP expression in CA1 and DG regions of the hippocampus but did not influence the expression of IBA-1. Ketamine also increased the levels of IL-1β, IL-6, and TNF-α in the mouse hippocampus. Our study created a new procedure for ketamine administration, which successfully induce negative symptoms and cognitive-behavioral defects in schizophrenia by chronic ketamine. This study further revealed that an increase in astrocytosis, but not microglia, is associated with the mouse model of schizophrenia caused by ketamine. In summary, hippocampal astrocytes may be involved in the pathophysiology of ketamine-induced schizophrenia-like phenotypes through reactive transformation and regulation of neuroinflammation.

Anxiety-like behavior and microglial activation in the amygdala after acute neuroinflammation induced by microbial neuraminidase

Short-term behavioral alterations are associated with infection and aid the recovery from sickness. However, concerns have raised that sustained behavioral disturbances after acute neuroinflammation could relate to neurological diseases in the long run. We aimed to explore medium- and long-term behavioral disturbances after acute neuroinflammation in rats, using a model based on the intracerebroventricular administration of the enzyme neuraminidase (NA), which is part of some pathogenic bacteria and viruses. Neurological and behavioral assessments were performed 2 and 10 weeks after the injection of NA, and neuroinflammation was evaluated by gene expression and histology. No alterations were observed regarding basic neurological functions or locomotor capacity in NA-injected rats. However, they showed a reduction in unsupported rearing, and increased grooming and freezing behaviors, which indicate anxiety-like behavior. A principal component analysis including a larger set of parameters further supported such anxiety-like behavior. The anxiety profile was observed 2 weeks after NA-injection, but not after 10 weeks. Concomitantly, the amygdala presented increased number of microglial cells showing a morphologic bias towards an activated state. A similar but subtler tendency was observed in hypothalamic microglia located in the paraventricular nucleus. Also, in the hypothalamus the pattern recognition receptor toll-like receptor 4 (TLR4) was slightly overexpressed 2 weeks after NA injection. These results demonstrate that NA-induced neuroinflammation provokes anxiety-like behavior in the medium term, which disappears with time. Concurrent microgliosis in the amygdala could explain such behavior. Further experiments should aim to explore subtle but long-lasting alterations observed 10 weeks after NA injection, both in amygdala and hypothalamus, as well as mild behavioral changes.

Neuroinflammation in Tinnitus

Purpose of Review

The current review aims to explore recent studies that have illustrated a link between neuroinflammation and tinnitus and the consequential effect on neuronal functioning. We explore parallels amongst pain and tinnitus pathologies and a novel treatment option.

Recent Findings

Genetic and pharmacological blockage of pro-inflammatory cytokines mitigates the physiological and behavioral tinnitus phenotype in acute rodent models. In addition, recent pain studies target a signaling pathway to prevent the transition from acute to chronic neuropathic pain, which could translate to tinnitus.

Summary

Neuroinflammation likely mediates hyperexcitability of the auditory pathway, driving the development of acute tinnitus. In chronic tinnitus, we believe translational regulation plays a role in maintaining persistent tinnitus signaling. We therefore propose this pathway as a potential therapeutic strategy.

Schizophrenia and Inflammation Research: A Bibliometric Analysis

Background

Schizophrenia (SCZ) is a severe psychiatric disorder that involves inflammatory processes. The aim of this study was to explore the field of inflammation-related research in SCZ from a bibliometric perspective.

Methods

Regular and review articles on SCZ- and inflammation-related research were obtained from the Web of Science Core Collection (WOSCC) database from its inception to February 19, 2022. R package "bibliometrix" was used to summarize the main findings, count the occurrences of the top keywords, visualize the collaboration network between countries, and generate a three-field plot. VOSviewer software was applied to conduct both co-authorship and co-occurrence analyses. CiteSpace was used to identify the top references and keywords with the strongest citation burst.

Results

A total of 3,596 publications on SCZ and inflammation were included. Publications were mainly from the USA, China, and Germany. The highest number of publications was found in a list of relevant journals. Apart from "schizophrenia" and "inflammatory", the terms "bipolar disorder," "brain," and "meta-analysis" were also the most frequently used keywords.

Conclusions

This bibliometric study mapped out a fundamental knowledge structure consisting of countries, institutions, authors, journals, and articles in the research field of SCZ and inflammation over the past 30 years. The results provide a comprehensive perspective about the wider landscape of this research area.

Targeting Microglia in Alzheimer’s Disease: From Molecular Mechanisms to Potential Therapeutic Targets for Small Molecules

Alzheimer’s disease (AD) is a common, progressive, and devastating neurodegenerative disorder that mainly affects the elderly. Microglial dysregulation, amyloid-beta (Aβ) plaques, and intracellular neurofibrillary tangles play crucial roles in the pathogenesis of AD. In the brain, microglia play roles as immune cells to provide protection against virus injuries and diseases. They have significant contributions in the development of the brain, cognition, homeostasis of the brain, and plasticity. Multiple studies have confirmed that uncontrolled microglial function can result in impaired microglial mitophagy, induced Aβ accumulation and tau pathology, and a chronic neuroinflammatory environment. In the brain, most of the genes that are associated with AD risk are highly expressed by microglia. Although it was initially regarded that microglia reaction is incidental and induced by dystrophic neurites and Aβ plaques. Nonetheless, it has been reported by genome-wide association studies that most of the risk loci for AD are located in genes that are occasionally uniquely and highly expressed in microglia. This finding further suggests that microglia play significant roles in early AD stages and they be targeted for the development of novel therapeutics. In this review, we have summarized the molecular pathogenesis of AD, microglial activities in the adult brain, the role of microglia in the aging brain, and the role of microglia in AD. We have also particularly focused on the significance of targeting microglia for the treatment of AD.

Age-Associated Glia Remodeling and Mitochondrial Dysfunction in Neurodegeneration: Antioxidant Supplementation as a Possible Intervention

Aging induces substantial remodeling of glia, including density, morphology, cytokine expression, and phagocytic capacity. Alterations of glial cells, such as hypertrophy of lysosomes, endosomes and peroxisomes, and the progressive accumulation of lipofuscin, lipid droplets, and other debris have also been reported. These abnormalities have been associated with significant declines of microglial processes and reduced ability to survey the surrounding tissue, maintain synapses, and recover from injury. Similarly, aged astrocytes show reduced capacity to support metabolite transportation to neurons. In the setting of reduced glial activity, stressors and/or injury signals can trigger a coordinated action of microglia and astrocytes that may amplify neuroinflammation and contribute to the release of neurotoxic factors. Oxidative stress and proteotoxic aggregates may burst astrocyte-mediated secretion of pro-inflammatory cytokines, thus activating microglia, favoring microgliosis, and ultimately making the brain more susceptible to injury and/or neurodegeneration. Here, we discuss the contribution of microglia and astrocyte oxidative stress to neuroinflammation and neurodegeneration, highlight the pathways that may help gain insights into their molecular mechanisms, and describe the benefits of antioxidant supplementation-based strategies.

CD36-Binding Amphiphilic Nanoparticles for Attenuation of Alpha Synuclein-Induced Microglial Activation

Neuroinflammation is one of the hallmarks contributing to Parkinson's Disease (PD) pathology, where microglial activation occurs as one of the earliest events, triggered by extracellular alpha synuclein (aSYN) binding to the CD36 receptor. Here, CD36-binding nanoparticles (NPs) containing synthetic tartaric acid-based amphiphilic polymers (AMs) were rationally designed to inhibit this aSYN-CD36 binding. In silico docking revealed that four AMs with varying alkyl side chain lengths presented differential levels of CD36 binding affinity and that an optimal alkyl chain length would promote the strongest inhibitory activity towards aSYN-CD36 interactions. In vitro competitive binding assays indicated that the inhibitory activity of AM-based NPs plateaued at intermediate side chain lengths of 12- and 18-carbons, supporting the in silico docking predictions. These 12- and 18-carbon length AM NPs also had significantly stronger effects on reducing aSYN internalization and inhibiting the production of the proinflammatory molecules TNF-α and nitric oxide from aSYN-challenged microglia. All four NPs modulated the gene expression of aSYN-challenged microglia, downregulating the expression of the proinflammatory genes TNF, IL-6, and IL-1β, and upregulating the expression of the anti-inflammatory genes TGF-β and Arg1. Overall, this work represents a novel polymeric nanotechnology platform that can be used to modulate aSYN-induced microglial activation in PD.

Vagus Nerve Stimulation Reduces Neuroinflammation Through Microglia Polarization Regulation to Improve Functional Recovery After Spinal Cord Injury

Background

Spinal cord injury (SCI) is a devastating disease that lacks effective treatment. Interestingly, recent studies indicated that vagus nerve stimulation (VNS), neuromodulation that is widely used in a variety of central nervous system (CNS) diseases, improved motor function recovery after SCI. But the exact underlying mechanism of how VNS ameliorates SCI is unclear. This study aimed to confirm the efficacy and further explore the potential therapeutic mechanism of VNS in SCI.

Method

A T10 spinal cord compression model was established in adult female Sprague-Dawley rats. Then the stimulation electrode was placed in the left cervical vagus nerve (forming Sham-VNS, VNS, and VNS-MLA groups). Basso-Beattie-Bresnahan (BBB) behavioral scores and Motor evoked potentials (MEPs) analysis were used to detect motor function. A combination of histological and molecular methods was used to clarify the relevant mechanism.

Results

Compared with the Sham-VNS group, the VNS group exhibited better functional recovery, reduced scar formation (both glial and fibrotic scars), tissue damage, and dark neurons, but these beneficial effects of VNS were diminished after alpha 7 nicotinic acetylcholine receptor (α7nAchR) blockade. Specifically, VNS inhibited the pro-inflammatory factors TNF-α, IL-1β, and IL-6 and increased the expression of the anti-inflammatory factors IL-10. Furthermore, we found that VNS promotes the shift of M1-polarized Iba-1+/CD86+ microglia to M2-polarized Iba-1+/CD206+ microglia via upregulating α7nAchR to alleviate neuroinflammation after SCI.

Conclusion

Our results demonstrated that VNS promotes microglial M2 polarization through upregulating α7nAChR to reduce neuroinflammation, thus improving motor function recovery after SCI. These findings indicate VNS might be a promising neuromodulation strategy for SCI.

Nitrogen-doped graphene quantum dots induce ferroptosis through disrupting calcium homeostasis in microglia

Background

Along with the wild applications of nitrogen-doped graphene quantum dots (N-GQDs) in the fields of biomedicine and neuroscience, their increasing exposure to the public and potential biosafety problem has gained more and more attention. Unfortunately, the understanding of adverse effects of N-GQDs in the central nervous system (CNS), considered as an important target of nanomaterials, is still limited.

Results

After we found that N-GQDs caused cell death, neuroinflammation and microglial activation in the hippocampus of mice through the ferroptosis pathway, microglia was used to assess the molecular mechanisms of N-GQDs inducing ferroptosis because it could be the primary target damaged by N-GQDs in the CNS. The microarray data suggested the participation of calcium signaling pathway in the ferroptosis induced by N-GQDs. In microglial BV2 cells, when the calcium content above the homeostatic level caused by N-GQDs was reversed, the number of cell death, ferroptosis alternations and excessive inflammatory cytokines release were all alleviated. Two calcium channels of L-type voltage-gated calcium channels (L-VGCCs) in plasma membrane and ryanodine receptor (RyR) in endoplasmic reticulum (ER) took part in N-GQDs inducing cytosolic calcium overload. L-VGCCs and RyR calcium channels were also involved in promoting the excess iron influx and triggering ER stress response, respectively, which both exert excessive ROS generation and result in the ferroptosis and inflammation in BV2 cells.

Conclusion

N-GQDs exposure caused ferroptosis and inflammatory responses in hippocampus of mice and cultured microglia through activating two calcium channels to disrupt intracellular calcium homeostasis. The findings not only posted an alert for biomedical applications of N-GQDs, but also highlighted an insight into mechanism researches of GQDs inducing multiple types of cell death in brain tumor therapy in the future.

Graphical abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s12989-022-00464-z.

MicroRNA let-7 and viral infections: focus on mechanisms of action

MicroRNAs (miRNAs) are fundamental post-transcriptional modulators of several critical cellular processes, a number of which are involved in host defense mechanisms. In particular, miRNA let-7 functions as an essential regulator of the function and differentiation of both innate and adaptive immune cells. Let-7 is involved in several human diseases, including cancer and viral infections. Several viral infections have found ways to dysregulate the expression of miRNAs. Extracellular vesicles (EV) are membrane-bound lipid structures released from many types of human cells that can transport proteins, lipids, mRNAs, and miRNAs, including let-7. After their release, EVs are taken up by the recipient cells and their contents released into the cytoplasm. Let-7-loaded EVs have been suggested to affect cellular pathways and biological targets in the recipient cells, and can modulate viral replication, the host antiviral response, and the action of cancer-related viruses. In the present review, we summarize the available knowledge concerning the expression of let-7 family members, functions, target genes, and mechanistic involvement in viral pathogenesis and host defense. This may provide insight into the development of new therapeutic strategies to manage viral infections.

Extracellular Vesicles of Mesenchymal Stromal Cells Can be Taken Up by Microglial Cells and Partially Prevent the Stimulation Induced by β-amyloid

Mesenchymal stromal/stem cells (MSCs) have great capacity for immune regulation. MSCs provide protective paracrine effects, which are partially exerted by extracellular vesicles (EVs). It has been reported that MSCs-derived EVs (MSC-EVs) contain soluble factors, such as cytokines, chemokines, growth factors and even microRNAs, which confer them similar anti-inflammatory and regenerative effects to MSCs. Moreover, MSCs modulate microglia activation through a dual mechanism of action that relies both on cell contact and secreted factors. Microglia cells are the central nervous system immune cells and the main mediators of the inflammation leading to neurodegenerative disorders. Here, we investigated whether MSC-EVs affect the activation of microglia cells by β-amyloid aggregates. We show that the presence of MSC-EVs can prevent the upregulation of pro-inflammatory mediators such as tumor necrosis factor (TNF)-α and nitric oxide (NO). Both are up-regulated in neurodegenerative diseases representing chronic inflammation, as in Alzheimer’s disease. We demonstrate that MSC-EVs are internalized by the microglia cells. Further, our study supports the use of MSC-EVs as a promising therapeutic tool to treat neuroinflammatory diseases.

Significance Statement

It has been reported that mesenchymal stromal/stem cells and MSC-derived small extracellular vesicles have therapeutic effects in the treatment of various degenerative and inflammatory diseases. Extracellular vesicles are loaded with proteins, lipids and RNA and act as intercellular communication mediators. Here we show that extracellular vesicles can be taken up by murine microglial cells. In addition, they partially reduce the activation of microglial cells against β-amyloid aggregates. This inhibition of microglia activation may present an effective strategy for the control/therapy of neurodegenerative diseases such as Alzheimer’s disease.

Modulation of Pacemaker Channel Function in a Model of Thalamocortical Hyperexcitability by Demyelination and Cytokines

A consensus is yet to be reached regarding the exact prevalence of epileptic seizures or epilepsy in multiple sclerosis (MS). In addition, the underlying pathophysiological basis of the reciprocal interaction among neuroinflammation, demyelination, and epilepsy remains unclear. Therefore, a better understanding of cellular and network mechanisms linking these pathologies is needed. Cuprizone-induced general demyelination in rodents is a valuable model for studying MS pathologies. Here, we studied the relationship among epileptic activity, loss of myelin, and pro-inflammatory cytokines by inducing acute, generalized demyelination in a genetic mouse model of human absence epilepsy, C3H/HeJ mice. Both cellular and network mechanisms were studied using in vivo and in vitro electrophysiological techniques. We found that acute, generalized demyelination in C3H/HeJ mice resulted in a lower number of spike–wave discharges, increased cortical theta oscillations, and reduction of slow rhythmic intrathalamic burst activity. In addition, generalized demyelination resulted in a significant reduction in the amplitude of the hyperpolarization-activated inward current (I_h) in thalamic relay cells, which was accompanied by lower surface expression of hyperpolarization-activated, cyclic nucleotide-gated channels, and the phosphorylated form of TRIP8b (pS237-TRIP8b). We suggest that demyelination-related changes in thalamic I_h may be one of the factors defining the prevalence of seizures in MS.

In Vitro Methodologies to Study the Role of Advanced Glycation End Products (AGEs) in Neurodegeneration

Advanced glycation end products (AGEs) can be present in food or be endogenously produced in biological systems. Their formation has been associated with chronic neurodegenerative diseases such as Alzheimer’s disease, Parkinson’s disease, multiple sclerosis, and amyotrophic lateral sclerosis. The implication of AGEs in neurodegeneration is related to their ability to bind to AGE-specific receptors and the ability of their precursors to induce the so-called “dicarbonyl stress”, resulting in cross-linking and protein damage. However, the mode of action underlying their role in neurodegeneration remains unclear. While some research has been carried out in observational clinical studies, further in vitro studies may help elucidate these underlying modes of action. This review presents and discusses in vitro methodologies used in research on the potential role of AGEs in neuroinflammation and neurodegeneration. The overview reveals the main concepts linking AGEs to neurodegeneration, the current findings, and the available and advisable in vitro models to study their role. Moreover, the major questions regarding the role of AGEs in neurodegenerative diseases and the challenges and discrepancies in the research field are discussed.