M2 microglia and macrophages drive oligodendrocyte differentiation during CNS remyelination

Infiltration by monocytes of the central nervous system and its role in multiple sclerosis: reflections on therapeutic strategies

Mononuclear macrophage infiltration in the central nervous system is a prominent feature of neuroinflammation. Recent studies on the pathogenesis and progression of multiple sclerosis have highlighted the multiple roles of mononuclear macrophages in the neuroinflammatory process. Monocytes play a significant role in neuroinflammation, and managing neuroinflammation by manipulating peripheral monocytes stands out as an effective strategy for the treatment of multiple sclerosis, leading to improved patient outcomes. This review outlines the steps involved in the entry of myeloid monocytes into the central nervous system that are targets for effective intervention: the activation of bone marrow hematopoiesis, migration of monocytes in the blood, and penetration of the blood-brain barrier by monocytes. Finally, we summarize the different monocyte subpopulations and their effects on the central nervous system based on phenotypic differences. As activated microglia resemble monocyte-derived macrophages, it is important to accurately identify the role of monocyte-derived macrophages in disease. Depending on the roles played by monocyte-derived macrophages at different stages of the disease, several of these processes can be interrupted to limit neuroinflammation and improve patient prognosis. Here, we discuss possible strategies to target monocytes in neurological diseases, focusing on three key aspects of monocyte infiltration into the central nervous system, to provide new ideas for the treatment of neurodegenerative diseases.

Microglia: a promising therapeutic target in spinal cord injury

Microglia are present throughout the central nervous system and are vital in neural repair, nutrition, phagocytosis, immunological regulation, and maintaining neuronal function. In a healthy spinal cord, microglia are accountable for immune surveillance, however, when a spinal cord injury occurs, the microenvironment drastically changes, leading to glial scars and failed axonal regeneration. In this context, microglia vary their gene and protein expression during activation, and proliferation in reaction to the injury, influencing injury responses both favorably and unfavorably. A dynamic and multifaceted injury response is mediated by microglia, which interact directly with neurons, astrocytes, oligodendrocytes, and neural stem/progenitor cells. Despite a clear understanding of their essential nature and origin, the mechanisms of action and new functions of microglia in spinal cord injury require extensive research. This review summarizes current studies on microglial genesis, physiological function, and pathological state, highlights their crucial roles in spinal cord injury, and proposes microglia as a therapeutic target.

Lupenone improves motor dysfunction in spinal cord injury mice through inhibiting the inflammasome activation and pyroptosis in microglia via the nuclear factor kappa B pathway

JOURNAL/nrgr/04.03/01300535-202408000-00034/figure1/v/2023-12-16T180322Z/r/image-tiff Spinal cord injury-induced motor dysfunction is associated with neuroinflammation. Studies have shown that the triterpenoid lupenone, a natural product found in various plants, has a remarkable anti-inflammatory effect in the context of chronic inflammation. However, the effects of lupenone on acute inflammation induced by spinal cord injury remain unknown. In this study, we established an impact-induced mouse model of spinal cord injury, and then treated the injured mice with lupenone (8 mg/kg, twice a day) by intraperitoneal injection. We also treated BV2 cells with lipopolysaccharide and adenosine 5'-triphosphate to simulate the inflammatory response after spinal cord injury. Our results showed that lupenone reduced IκBα activation and p65 nuclear translocation, inhibited NLRP3 inflammasome function by modulating nuclear factor kappa B, and enhanced the conversion of proinflammatory M1 microglial cells into anti-inflammatory M2 microglial cells. Furthermore, lupenone decreased NLRP3 inflammasome activation, NLRP3-induced microglial cell polarization, and microglia pyroptosis by inhibiting the nuclear factor kappa B pathway. These findings suggest that lupenone protects against spinal cord injury by inhibiting inflammasomes.

Targeted DeSUMOylation as a therapeutic strategy for multiple sclerosis

SUMO (small ubiquitin like modifier) conjugated proteins have emerged as an important post translational modifier of cellular function. SUMOylation modulates several cellular processes involved in transcriptional regulation of genes, protein-protein interactions and DNA damage and repair. Since abnormalities in SUMOylation has been observed in neoplastic and neurodegenerative disorders, the SUMO pathway has become an attractive site for targeting of new therapies to regulate SUMOylation and reduce disease burden. Conjugation of SUMO to their respective substrates is orchestrated by an enzymatic cascade involving three main enzymes, E1, activation enzyme, E2, conjugating enzyme and E3, a protein ligase. Each of these enzymes are therefore potential "druggable" sites for future therapeutics. SUMOylation is a well-known mechanism by which the innate immune response is regulated in response to viral infections and in the adaptive immune response to tumor immunity. We have shown that small molecules which inhibit the SUMO activation pathway are also capable of inhibiting autoimmune response. TAK981 which forms adducts with SUMO and anacardic acid which inhibits the E1 enzyme of the SUMO pathway were effective in preventing the development of experimental allergic encephalitis (EAE), a mouse model of multiple sclerosis. Anacardic acid and TAK981 inhibited activation of TH17 cells and reduced clinical and pathological injury in IL-17 mediated myelin oligodendrocyte glycoprotein (MOG) induced EAE. Ginkgolic acid, another known inhibitor of SUMO pathway, was also shown to be effective in reducing the severity of inflammatory arthropathies which is also IL-17 mediated. In addition, the increase in the transcription of myelin genes with TAK981 and anacardic acid improved remyelination in experimental models of demyelination. In the present review paper, we examine the mechanism of action of inhibitors of the SUMO pathway on regulating the immune response and the possibility of the use of these agents as therapeutics for MS.

Electrical stimulation of the vagus nerve ameliorates inflammation and disease activity in a rat EAE model of multiple sclerosis

Multiple sclerosis (MS) is a demyelinating central nervous system (CNS) disorder that is associated with functional impairment and accruing disability. There are multiple U.S. Food and Drug Administration (FDA)-approved drugs that effectively dampen inflammation and slow disability progression. However, these agents do not work well for all patients and are associated with side effects that may limit their use. The vagus nerve (VN) provides a direct communication conduit between the CNS and the periphery, and modulation of the inflammatory reflex via electrical stimulation of the VN (VNS) shows efficacy in ameliorating pathology in several CNS and autoimmune disorders. We therefore investigated the impact of VNS in a rat experimental autoimmune encephalomyelitis (EAE) model of MS. In this study, VNS-mediated neuroimmune modulation is demonstrated to effectively decrease EAE disease severity and duration, infiltration of neutrophils and pathogenic lymphocytes, myelin damage, blood-brain barrier disruption, fibrinogen deposition, and proinflammatory microglial activation. VNS modulates expression of genes that are implicated in MS pathogenesis, as well as those encoding myelin proteins and transcription factors regulating new myelin synthesis. Together, these data indicate that neuroimmune modulation via VNS may be a promising approach to treat MS, that not only ameliorates symptoms but potentially also promotes myelin repair (remyelination).

Inosine pretreatment of pregnant rats ameliorates maternal inflammation-mediated hypomyelination in pups via microglia polarization switch

Periventricular leukomalacia (PVL) is a neurological condition observed in premature infants, characterized by hypomyelination and activation of microglia. Maternal inflammation-induced brain injury in offspring significantly contributes to the development of PVL. Currently, there are no clinical pharmaceutical interventions available for pregnant women to prevent maternal inflammation-mediated brain injury in their offspring. Inosine has been shown to modulate the immune response in diverse stressful circumstances, such as injury, ischemia, and inflammation. The aim of this investigation was to examine the potential prophylactic impact of inosine on offspring PVL induced by maternal inflammation. This was accomplished by administering a 1 mg/ml inosine solution (40 ml daily) to pregnant Sprague-Dawley (SD) rats for 16 consecutive days prior to their intraperitoneal injection of lipopolysaccharide (350 µg/kg, once a day, for two days). The results showed that maternal inosine pretreatment significantly reversed the reduction in MBP and CNPase (myelin-related markers), CC-1 and Olig2 (oligodendrocyte-related markers) in their PVL pups (P7), suggesting that inosine administration during pregnancy could improve hypomyelination and enhance the differentiation of oligodendrocyte precursor cells (OPCs) in their PVL pups. Furthermore, the protective mechanism of inosine against PVL is closely associated with the activation and polarization of microglia. This is evidenced by a notable reduction in the quantity of IBA 1-positive microglia, a decrease in the level of CD86 (a marker for M1 microglia), an increase in the level of Arg 1 (a marker for M2 microglia), as well as a decrease in the level of pro-inflammatory factors TNF-α, IL-1β, and IL-6, and an increase in the level of anti-inflammatory factors IL-4 and IL-10 in the brain of PVL pups following maternal inosine pretreatment. Taken together, inosine pretreatment of pregnant rats can improve hypomyelination in their PVL offspring by triggering the M1/M2 switch of microglia.

Microglial phagocytosis of single dying oligodendrocytes is mediated by CX3CR1 but not MERTK

Oligodendrocyte death is common in aging and neurodegenerative disease. In these conditions, dying oligodendrocytes must be efficiently removed to allow remyelination and to prevent a feedforward degenerative cascade. Removal of this cellular debris is thought to primarily be carried out by resident microglia. To investigate the cellular dynamics underlying how microglia do this, we use a single-cell cortical demyelination model combined with longitudinal intravital imaging of dual-labeled transgenic mice. Following phagocytosis, single microglia clear the targeted oligodendrocyte and its myelin sheaths in one day via a precise, rapid, and stereotyped sequence. Deletion of the fractalkine receptor, CX3CR1, delays the microglial phagocytosis of the cell soma but has no effect on clearance of myelin sheaths. Unexpectedly, deletion of the phosphatidylserine receptor, MERTK, has no effect on oligodendrocyte or myelin sheath clearance. Thus, separate molecular signals are used to detect, engage, and clear distinct sub-compartments of dying oligodendrocytes to maintain tissue homeostasis.

The combined administration of LNC-encapsulated retinoic acid and calcitriol stimulates oligodendrocyte progenitor cell differentiation in vitro and in vivo after intranasal administration

Intranasal administration is an efficient strategy for bypassing the BBB, favoring drug accumulation in the brain, and improving its efficiency. Lipid nanocapsules (LNC) are suitable nanocarriers for the delivery of lipophilic drugs via this route and can be used to encapsulate lipophilic molecules such as retinoic acid (RA) and calcitriol (Cal). As the hallmarks of multiple sclerosis (MS) are neuroinflammation and oligodendrocyte loss, our hypothesis was that by combining two molecules known for their pro-differentiating properties, encapsulated in LNC, and delivered by intranasal administration, we would stimulate oligodendrocyte progenitor cells (OPC) differentiation into oligodendrocytes and provide a new pro-remyelinating therapy. LNC loaded with RA (LNC-RA) and Cal (LNC-Cal) were stable for at least 8 weeks. The combination of RA and Cal was more efficient than the molecules alone, encapsulated or not, on OPC differentiation in vitro and decreased microglia cell activation in a dose-dependent manner. After the combined intranasal administration of LNC-RA and LNC-Cal in a mouse cuprizone model of demyelination, increased MBP staining was observed in the corpus callosum. In conclusion, intranasal delivery of lipophilic drugs encapsulated in LNC is a promising strategy for myelinating therapies.

MiR-223 enhances lipophagy by suppressing CTSB in microglia following lysolecithin-induced demyelination in mice

BACKGROUND

Lipid droplet (LD)-laden microglia is a key pathological hallmark of multiple sclerosis. The recent discovery of this novel microglial subtype, lipid-droplet-accumulating microglia (LDAM), is notable for increased inflammatory factor secretion and diminished phagocytic capability. Lipophagy, the autophagy-mediated selective degradation of LDs, plays a critical role in this context. This study investigated the involvement of microRNAs (miRNAs) in lipophagy during demyelinating diseases, assessed their capacity to modulate LDAM subtypes, and elucidated the potential underlying mechanisms involved.

METHODS

C57BL/6 mice were used for in vivo experiments. Two weeks post demyelination induction at cervical level 4 (C4), histological assessments and confocal imaging were performed to examine LD accumulation in microglia within the lesion site. Autophagic changes were observed using transmission electron microscopy. miRNA and mRNA multi-omics analyses identified differentially expressed miRNAs and mRNAs under demyelinating conditions and the related autophagy target genes. The role of miR-223 in lipophagy under these conditions was specifically explored. In vitro studies, including miR-223 upregulation in BV2 cells via lentiviral infection, validated the bioinformatics findings. Immunofluorescence staining was used to measure LD accumulation, autophagy levels, target gene expression, and inflammatory mediator levels to elucidate the mechanisms of action of miR-223 in LDAM.

RESULTS

Oil Red O staining and confocal imaging revealed substantial LD accumulation in the demyelinated spinal cord. Transmission electron microscopy revealed increased numbers of autophagic vacuoles at the injury site. Multi-omics analysis revealed miR-223 as a crucial regulatory gene in lipophagy during demyelination. It was identified that cathepsin B (CTSB) targets miR-223 in autophagy to integrate miRNA, mRNA, and autophagy gene databases. In vitro, miR-223 upregulation suppressed CTSB expression in BV2 cells, augmented autophagy, alleviated LD accumulation, and decreased the expression of the inflammatory mediator IL-1β.

CONCLUSION

These findings indicate that miR-223 plays a pivotal role in lipophagy under demyelinating conditions. By inhibiting CTSB, miR-223 promotes selective LD degradation, thereby reducing the lipid burden and inflammatory phenotype in LDAM. This study broadens the understanding of the molecular mechanisms of lipophagy and proposes lipophagy induction as a potential therapeutic approach to mitigate inflammatory responses in demyelinating diseases.

Transcriptome analysis identifies an ASD-Like phenotype in oligodendrocytes and microglia from C58/J amygdala that is dependent on sex and sociability

BACKGROUND

Autism Spectrum Disorder (ASD) is a group of neurodevelopmental disorders with higher incidence in males and is characterized by atypical verbal/nonverbal communication, restricted interests that can be accompanied by repetitive behavior, and disturbances in social behavior. This study investigated brain mechanisms that contribute to sociability deficits and sex differences in an ASD animal model.

METHODS

Sociability was measured in C58/J and C57BL/6J mice using the 3-chamber social choice test. Bulk RNA-Seq and snRNA-Seq identified transcriptional changes in C58/J and C57BL/6J amygdala within which DMRseq was used to measure differentially methylated regions in amygdala.

RESULTS

C58/J mice displayed divergent social strata in the 3-chamber test. Transcriptional and pathway signatures revealed immune-related biological processes differ between C58/J and C57BL/6J amygdala. Hypermethylated and hypomethylated genes were identified in C58/J versus C57BL/6J amygdala. snRNA-Seq data in C58/J amygdala identified differential transcriptional signatures within oligodendrocytes and microglia characterized by increased ASD risk gene expression and predicted impaired myelination that was dependent on sex and sociability. RNA velocity, gene regulatory network, and cell communication analysis showed diminished oligodendrocyte/microglia differentiation. Findings were verified using Bulk RNA-Seq and demonstrated oxytocin's beneficial effects on myelin gene expression.

LIMITATIONS

Our findings are significant. However, limitations can be noted. The cellular mechanisms linking reduced oligodendrocyte differentiation and reduced myelination to an ASD phenotype in C58/J mice need further investigation. Additional snRNA-Seq and spatial studies would determine if effects in oligodendrocytes/microglia are unique to amygdala or if this occurs in other brain regions. Oxytocin's effects need further examination to understand its' potential as an ASD therapeutic.

CONCLUSIONS

Our work demonstrates the C58/J mouse model's utility in evaluating the influence of sex and sociability on the transcriptome in concomitant brain regions involved in ASD. Our single-nucleus transcriptome analysis elucidates potential pathological roles of oligodendrocytes and microglia in ASD. This investigation provides details regarding regulatory features disrupted in these cell types, including transcriptional gene dysregulation, aberrant cell differentiation, altered gene regulatory networks, and changes to key pathways that promote microglia/oligodendrocyte differentiation. Our studies provide insight into interactions between genetic risk and epigenetic processes associated with divergent affiliative behavior and lack of positive sociability.

Cystatin F attenuates neuroinflammation and demyelination following murine coronavirus infection of the central nervous system

BACKGROUND

Cystatin F is a secreted lysosomal cysteine protease inhibitor that has been implicated in affecting the severity of demyelination and enhancing remyelination in pre-clinical models of immune-mediated demyelination. How cystatin F impacts neurologic disease severity following viral infection of the central nervous system (CNS) has not been well characterized and was the focus of this study. We used cystatin F null-mutant mice (Cst7-/-) with a well-established model of murine coronavirus-induced neurologic disease to evaluate the contributions of cystatin F in host defense, demyelination and remyelination.

METHODS

Wildtype controls and Cst7-/- mice were intracranially (i.c.) infected with a sublethal dose of the neurotropic JHM strain of mouse hepatitis virus (JHMV), with disease progression and survival monitored daily. Viral plaque assays and qPCR were used to assess viral levels in CNS. Immune cell infiltration into the CNS and immune cell activation were determined by flow cytometry and 10X genomics chromium 3' single cell RNA sequencing (scRNA-seq). Spinal cord demyelination was determined by luxol fast blue (LFB) and Hematoxylin/Eosin (H&E) staining and axonal damage assessed by immunohistochemical staining for SMI-32. Remyelination was evaluated by electron microscopy (EM) and calculation of g-ratios.

RESULTS

JHMV-infected Cst7-/- mice were able to control viral replication within the CNS, indicating that cystatin F is not essential for an effective Th1 anti-viral immune response. Infiltration of T cells into the spinal cords of JHMV-infected Cst7-/- mice was increased compared to infected controls, and this correlated with increased axonal damage and demyelination associated with impaired remyelination. Single-cell RNA-seq of CD45 + cells enriched from spinal cords of infected Cst7-/- and control mice revealed enhanced expression of transcripts encoding T cell chemoattractants, Cxcl9 and Cxcl10, combined with elevated expression of interferon-g (Ifng) and perforin (Prf1) transcripts in CD8 + T cells from Cst7-/- mice compared to controls.

CONCLUSIONS

Cystatin F is not required for immune-mediated control of JHMV replication within the CNS. However, JHMV-infected Cst7-/- mice exhibited more severe clinical disease associated with increased demyelination and impaired remyelination. The increase in disease severity was associated with elevated expression of T cell chemoattractant chemokines, concurrent with increased neuroinflammation. These findings support the idea that cystatin F influences expression of proinflammatory gene expression impacting neuroinflammation, T cell activation and/or glia cell responses ultimately impacting neuroinflammation and neurologic disease.

Trametinib, an anti-tumor drug, promotes oligodendrocytes generation and myelin formation

Oligodendrocytes (OLs) are differentiated from oligodendrocyte precursor cells (OPCs) in the central nervous system (CNS). Demyelination is a common feature of many neurological diseases such as multiple sclerosis (MS) and leukodystrophies. Although spontaneous remyelination can happen after myelin injury, nevertheless, it is often insufficient and may lead to aggravated neurodegeneration and neurological disabilities. Our previous study has discovered that MEK/ERK pathway negatively regulates OPC-to-OL differentiation and remyelination in mouse models. To facilitate possible clinical evaluation, here we investigate several MEK inhibitors which have been approved by FDA for cancer therapies in both mouse and human OPC-to-OL differentiation systems. Trametinib, the first FDA approved MEK inhibitor, displays the best effect in stimulating OL generation in vitro among the four MEK inhibitors examined. Trametinib also significantly enhances remyelination in both MOG-induced EAE model and LPC-induced focal demyelination model. More exciting, trametinib facilitates the generation of MBP+ OLs from human embryonic stem cells (ESCs)-derived OPCs. Mechanism study indicates that trametinib promotes OL generation by reducing E2F1 nuclear translocation and subsequent transcriptional activity. In summary, our studies indicate a similar inhibitory role of MEK/ERK in human and mouse OL generation. Targeting the MEK/ERK pathway might help to develop new therapies or repurpose existing drugs for demyelinating diseases.

[Oxytocin as a neuroprotective strategy in neonates: concept and preclinical evidence]

OBJECTIVE

Prematurity and intra-uterine growth retardation are responsible for brain damage associated with various neurocognitive and behavioral disorders in more than 9 million children each year. Most pharmacological strategies aimed at preventing perinatal brain injury have not demonstrated substantial clinical benefits so far. In contrast, enrichment of the newborn's environment appears to have positive effects on brain structure and function, influences newborn hormonal responses, and has lasting neurobehavioral consequences during infancy and adulthood. Oxytocin (OT), a neuropeptide released by the hypothalamus, may represent the hormonal basis for these long-term effects.

METHOD

This review of the literature summarizes the knowledge concerning the effect of OT in the newborn and the preclinical data supporting its neuroprotective effect.

RESULTS

OT plays a role during the perinatal period, in parent-child attachment and in social behavior. Furthermore, preclinical studies strongly suggest that endogenous and synthetic OT is capable of regulating the inflammatory response of the central nervous system in response to situations of prematurity or more generally insults to the developing brain. The long-term effect of synthetic OT administration during labor is also discussed.

CONCLUSION

All the conceptual and experimental data converge to indicate that OT would be a promising candidate for neonatal neuroprotection, in particular through the regulation of neuroinflammation.

Immunomodulatory effects of Kaempferol on microglial and Macrophage cells during the progression of diabetic retinopathy

BACKGROUND

Diabetic retinopathy (DR) stands as a prevalent secondary complication of diabetes, notably Type 1 Diabetes Mellitus (T1D), characterized by immune system involvement potentially impacting the retinal immune response mediated by microglia. Early stages of DR witness blood-retinal barrier permeabilization, facilitating peripheral immune cell interaction with the retinal immune system. Kaempferol (Kae), known for its potent anti-inflammatory activity, presents a promising avenue in DR treatment by targeting the immune mechanisms underlying its onset and progression. Our investigation delves into the molecular intricacies of innate immune cell interaction during DR progression and the attenuation of inflammatory processes pivotal to its pathology.

METHODS

Employing in vitro studies, we exposed HAPI microglial and J774.A1 macrophage cells to pro-inflammatory stimuli in the presence or absence of Kae. Ex vivo and in vivo experiments utilized BB rats, a T1D animal model. Retinal explants from BB rats were cultured with Kae, while intraperitoneal Kae injections were administered to BB rats for 15 days. Quantitative PCR, Western blotting, immunofluorescence, and Spectral Domain - Optical Coherence Tomography (SD-OCT) facilitated survival assessment, cellular signaling analysis, and inflammatory marker determination.

RESULTS

Results demonstrate Kae significantly mitigates inflammatory processes across in vitro, ex vivo, and in vivo DR models, primarily targeting immune cell responses. Kae administration notably inhibits proinflammatory responses during DR progression while promoting an anti-inflammatory milieu, chiefly through microglia-mediated synthesis of Arginase-1 and Hemeoxygenase-1(HO-1). In vivo, Kae administration effectively preserves retinal integrity amid DR progression.

CONCLUSIONS

Our findings elucidate the interplay between retinal and systemic immune cells in DR progression, underscoring a differential treatment response predominantly orchestrated by microglia's anti-inflammatory action. Kae treatment induces a phenotypic and functional shift in immune cells, delaying DR progression, thereby spotlighting microglial cells as a promising therapeutic target in DR management.

Microglia in Ischemic Stroke: Pathogenesis Insights and Therapeutic Challenges

Ischemic stroke is the most common type of stroke, which is the main cause of death and disability on a global scale. As the primary immune cells in the brain that are crucial for preserving homeostasis of the central nervous system microenvironment, microglia have been found to exhibit dual or even multiple effects at different stages of ischemic stroke. The anti-inflammatory polarization of microglia and release of neurotrophic factors may provide benefits by promoting neurological recovery at the lesion in the early phase after ischemic stroke. However, the pro-inflammatory polarization of microglia and secretion of inflammatory factors in the later phase of injury may exacerbate the ischemic lesion, suggesting the therapeutic potential of modulating the balance of microglial polarization to predispose them to anti-inflammatory transformation in ischemic stroke. Microglia-mediated signaling crosstalk with other cells may also be key to improving functional outcomes following ischemic stroke. Thus, this review provides an overview of microglial functions and responses under physiological and ischemic stroke conditions, including microglial activation, polarization, and interactions with other cells. We focus on approaches that promote anti-inflammatory polarization of microglia, inhibit microglial activation, and enhance beneficial cell-to-cell interactions. These targets may hold promise for the creation of innovative therapeutic strategies.

The role of glial cells in amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) has traditionally been considered a neuron-centric disease. This view is now outdated, with increasing recognition of cell autonomous and non-cell autonomous contributions of central and peripheral nervous system glia to ALS pathomechanisms. With glial research rapidly accelerating, we comprehensively interrogate the roles of astrocytes, microglia, oligodendrocytes, ependymal cells, Schwann cells and satellite glia in nervous system physiology and ALS-associated pathology. Moreover, we highlight the inter-glial, glial-neuronal and inter-system polylogue which constitutes the healthy nervous system and destabilises in disease. We also propose classification based on function for complex glial reactive phenotypes and discuss the pre-requisite for integrative modelling to advance translation. Given the paucity of life-enhancing therapies currently available for ALS patients, we discuss the promising potential of harnessing glia in driving ALS therapeutic discovery.

Mechanistic advances of hyperoxia-induced immature brain injury

The impact of hyperoxia-induced brain injury in preterm infants is being increasingly investigated. However, the parameters and protocols used to study this condition in animal models lack consistency. Research is further hampered by the fact that hyperoxia exerts both direct and indirect effects on oligodendrocytes and neurons, with the precise underlying mechanisms remaining unclear. In this article, we aim to provide a comprehensive overview of the conditions used to induce hyperoxia in animal models of immature brain injury. We discuss what is known regarding the mechanisms underlying hyperoxia-induced immature brain injury, focusing on the effects on oligodendrocytes and neurons, and briefly describe therapies that may counteract the effects of hyperoxia. We also identify further studies required to fully elucidate the effects of hyperoxia on the immature brain as well as discuss the leading therapeutic options.

Diagnostic efficacy of long non-coding RNAs in multiple sclerosis: a systematic review and meta-analysis

Background

Currently, an increasing body of research suggests that blood-based long non-coding RNAs (lncRNAs) could serve as biomarkers for diagnosing multiple sclerosis (MS). This meta-analysis evaluates the diagnostic capabilities of selected lncRNAs in distinguishing individuals with MS from healthy controls and in differentiating between the relapsing and remitting phases of the disease.

Methods

We conducted comprehensive searches across seven databases in both Chinese and English to identify relevant studies, applying stringent inclusion and exclusion criteria. The quality of the selected references was rigorously assessed using the QUADAS-2 tool. The analysis involved calculating summarized sensitivity (SSEN), specificity (SSPE), positive likelihood ratio (SPLR), negative likelihood ratio (SNLR), and diagnostic odds ratio (DOR) with 95% confidence intervals (CIs). Accuracy was assessed using summary receiver operating characteristic (SROC) curves.

Results

Thirteen high-quality studies were selected for inclusion in the meta-analysis. Our meta-analysis assessed the combined diagnostic performance of lncRNAs in distinguishing MS patients from healthy controls. We found a SSEN of 0.81 (95% CI: 0.74-0.87), SSPE of 0.84 (95% CI: 0.78-0.89), SPLR of 5.14 (95% CI: 3.63-7.28), SNLR of 0.22 (95% CI: 0.16-0.31), and DOR of 23.17 (95% CI: 14.07-38.17), with an AUC of 0.90 (95% CI: 0.87-0.92). For differentiating between relapsing and remitting MS, the results showed a SSEN of 0.79 (95% CI: 0.71-0.85), SSPE of 0.76 (95% CI: 0.64-0.85), SPLR of 3.34 (95% CI: 2.09-5.33), SNLR of 0.28 (95% CI: 0.19-0.40), and DOR of 12.09 (95% CI: 5.70-25.68), with an AUC of 0.84 (95% CI: 0.81-0.87).

Conclusion

This analysis underscores the significant role of lncRNAs as biomarkers in MS diagnosis and differentiation between its relapsing and remitting forms.

Tryptophan Metabolism in Alzheimer's Disease with the Involvement of Microglia and Astrocyte Crosstalk and Gut-Brain Axis

Alzheimer's disease (AD) is an age-dependent neurodegenerative disease characterized by extracellular Amyloid Aβ peptide (Aβ) deposition and intracellular Tau protein aggregation. Glia, especially microglia and astrocytes are core participants during the progression of AD and these cells are the mediators of Aβ clearance and degradation. The microbiota-gut-brain axis (MGBA) is a complex interactive network between the gut and brain involved in neurodegeneration. MGBA affects the function of glia in the central nervous system (CNS), and microbial metabolites regulate the communication between astrocytes and microglia; however, whether such communication is part of AD pathophysiology remains unknown. One of the potential links in bilateral gut-brain communication is tryptophan (Trp) metabolism. The microbiota-originated Trp and its metabolites enter the CNS to control microglial activation, and the activated microglia subsequently affect astrocyte functions. The present review highlights the role of MGBA in AD pathology, especially the roles of Trp per se and its metabolism as a part of the gut microbiota and brain communications. We (i) discuss the roles of Trp derivatives in microglia-astrocyte crosstalk from a bioinformatics perspective, (ii) describe the role of glia polarization in the microglia-astrocyte crosstalk and AD pathology, and (iii) summarize the potential of Trp metabolism as a therapeutic target. Finally, we review the role of Trp in AD from the perspective of the gut-brain axis and microglia, as well as astrocyte crosstalk, to inspire the discovery of novel AD therapeutics.

Neural regeneration in the human central nervous system-from understanding the underlying mechanisms to developing treatments. Where do we stand today?

Mature neurons in the human central nervous system (CNS) fail to regenerate after injuries. This is a common denominator across different aetiologies, including multiple sclerosis, spinal cord injury and ischemic stroke. The lack of regeneration leads to permanent functional deficits with a substantial impact on patient quality of life, representing a significant socioeconomic burden worldwide. Great efforts have been made to decipher the responsible mechanisms and we now know that potent intra- and extracellular barriers prevent axonal repair. This knowledge has resulted in numerous clinical trials, aiming to promote neuroregeneration through different approaches. Here, we summarize the current understanding of the causes to the poor regeneration within the human CNS. We also review the results of the treatment attempts that have been translated into clinical trials so far.

The Emerging Role of Microglial Hv1 as a Target for Immunomodulation in Myelin Repair

In the central nervous system (CNS), the myelin sheath ensures efficient interconnection between neurons and contributes to the regulation of the proper function of neuronal networks. The maintenance of myelin and the well-organized subtle process of myelin plasticity requires cooperation among myelin-forming cells, glial cells, and neural networks. The process of cooperation is fragile, and the balance is highly susceptible to disruption by microenvironment influences. Reactive microglia play a critical and complicated role in the demyelination and remyelination process. Recent studies have shown that the voltage-gated proton channel Hv1 is selectively expressed in microglia in CNS, which regulates intracellular pH and is involved in the production of reactive oxygen species, underlying multifaceted roles in maintaining microglia function. This paper begins by examining the molecular mechanisms of demyelination and emphasizes the crucial role of the microenvironment in demyelination. It focuses specifically on the role of Hv1 in myelin repair and its therapeutic potential in CNS demyelinating diseases.

OV Modulators of the Paediatric Brain TIME: Current Status, Combination Strategies, Limitations and Future Directions

Oncolytic viruses (OVs) are characterised by their preference for infecting and replicating in tumour cells either naturally or after genetic modification, resulting in oncolysis. Furthermore, OVs can elicit both local and systemic anticancer immune responses while specifically infecting and lysing tumour cells. These characteristics render them a promising therapeutic approach for paediatric brain tumours (PBTs). PBTs are frequently marked by a cold tumour immune microenvironment (TIME), which suppresses immunotherapies. Recent preclinical and clinical studies have demonstrated the capability of OVs to induce a proinflammatory immune response, thereby modifying the TIME. In-depth insights into the effect of OVs on different cell types in the TIME may therefore provide a compelling basis for using OVs in combination with other immunotherapy modalities. However, certain limitations persist in our understanding of oncolytic viruses' ability to regulate the TIME to enhance anti-tumour activity. These limitations primarily stem from the translational limitations of model systems, the difficulties associated with tracking reliable markers of efficacy throughout the course of treatment and the role of pre-existing viral immunity. In this review, we describe the different alterations observed in the TIME in PBTs due to OV treatment, combination therapies of OVs with different immunotherapies and the hurdles limiting the development of effective OV therapies while suggesting future directions based on existing evidence.

H3K27M mutant glioma: Disease definition and biological underpinnings

High-grade glioma (HGG) is the most common cause of cancer death in children and the most common primary central nervous system tumor in adults. While pediatric HGG was once thought to be biologically similar to the adult form of disease, research has shown these malignancies to be significantly molecularly distinct, necessitating distinct approaches to their clinical management. However, emerging data have shown shared molecular events in pediatric and adult HGG including the histone H3K27M mutation. This somatic missense mutation occurs in genes encoding one of two isoforms of the Histone H3 protein, H3F3A (H3.3), or HIST1H3B (H3.1), and is detected in up to 80% of pediatric diffuse midline gliomas and in up to 60% of adult diffuse gliomas. Importantly, the H3K27M mutation is associated with poorer overall survival and response to therapy compared to patients with H3 wild-type tumors. Here, we review the clinical features and biological underpinnings of pediatric and adult H3K27M mutant glioma, offering a groundwork for understanding current research and clinical approaches for the care of patients suffering with this challenging disease.

Pelizaeus-Merzbacher disease: on the cusp of myelin medicine

Pelizaeus-Merzbacher disease (PMD) is caused by mutations in the proteolipid protein 1 (PLP1) gene encoding proteolipid protein (PLP). As a major component of myelin, mutated PLP causes progressive neurodegeneration and eventually death due to severe white matter deficits. Medical care has long been limited to symptomatic treatments, but first-in-class PMD therapies with novel mechanisms now stand poised to enter clinical trials. Here, we review PMD disease mechanisms and outline rationale for therapeutic interventions, including PLP1 suppression, cell transplantation, iron chelation, and intracellular stress modulation. We discuss available preclinical data and their implications on clinical development. With several novel treatments on the horizon, PMD is on the precipice of a new era in the diagnosis and treatment of patients suffering from this debilitating disease.

Myeloid cell replacement is neuroprotective in chronic experimental autoimmune encephalomyelitis

Multiple sclerosis (MS) is an autoimmune disease characterized by demyelination of the central nervous system (CNS). Autologous hematopoietic cell transplantation (HCT) shows promising benefits for relapsing-remitting MS in open-label clinical studies, but the cellular mechanisms underlying its therapeutic effects remain unclear. Using single-nucleus RNA sequencing, we identify a reactive myeloid cell state in chronic experimental autoimmune encephalitis (EAE) associated with neuroprotection and immune suppression. HCT in EAE mice results in an increase of the neuroprotective myeloid state, improvement of neurological deficits, reduced number of demyelinated lesions, decreased number of effector T cells and amelioration of reactive astrogliosis. Enhancing myeloid cell incorporation after a modified HCT further improved these neuroprotective effects. These data suggest that myeloid cell manipulation or replacement may be an effective therapeutic strategy for chronic inflammatory conditions of the CNS.

The role of myelin in neurodegeneration: implications for drug targets and neuroprotection strategies

Myelination of axons in the central nervous system offers numerous advantages, including decreased energy expenditure for signal transmission and enhanced signal speed. The myelin sheaths surrounding an axon consist of a multi-layered membrane that is formed by oligodendrocytes, while specific glycoproteins and lipids play various roles in this formation process. As beneficial as myelin can be, its dysregulation and degeneration can prove detrimental. Inflammation, oxidative stress, and changes in cellular metabolism and the extracellular matrix can lead to demyelination of these axons. These factors are hallmark characteristics of certain demyelinating diseases including multiple sclerosis. The effects of demyelination are also implicated in primary degeneration in diseases such as glaucoma and Alzheimer's disease, as well as in processes of secondary degeneration. This reveals a relationship between myelin and secondary processes of neurodegeneration, including resultant degeneration following traumatic injury and transsynaptic degeneration. The role of myelin in primary and secondary degeneration is also of interest in the exploration of strategies and targets for remyelination, including the use of anti-inflammatory molecules or nanoparticles to deliver drugs. Although the use of these methods in animal models of diseases have shown to be effective in promoting remyelination, very few clinical trials in patients have met primary end points. This may be due to shortcomings or considerations that are not met while designing a clinical trial that targets remyelination. Potential solutions include diversifying disease targets and requiring concomitant interventions to promote rehabilitation.

Gut Microbiota Shape Oligodendrocyte Response after Traumatic Brain Injury

White matter injury (WMI) is thought to be a major contributor to long-term cognitive dysfunctions after traumatic brain injury (TBI). This damage occurs partly due to apoptotic death of oligodendrocyte lineage cells (OLCs) after the injury, triggered directly by the trauma or in response to degenerating axons. Recent research suggests that the gut microbiota modulates the inflammatory response through the modulation of peripheral immune cell infiltration after TBI. Additionally, T-cells directly impact OLCs differentiation and proliferation. Therefore, we hypothesized that the gut microbiota plays a critical role in regulating the OLC response to WMI influencing T-cells differentiation and activation. Gut microbial depletion early after TBI chronically reduced re-myelination, acutely decreased OLCs proliferation, and was associated with increased myelin debris accumulation. Surprisingly, the absence of T-cells in gut microbiota depleted mice restored OLC proliferation and remyelination after TBI. OLCs co-cultured with T-cells derived from gut microbiota depleted mice resulted in impaired proliferation and increased expression of MHC-II compared with T cells from control-injured mice. Furthermore, MHC-II expression in OLCs appears to be linked to impaired proliferation under gut microbiota depletion and TBI conditions. Collectively our data indicates that depletion of the gut microbiota after TBI impaired remyelination, reduced OLCs proliferation with concomitantly increased OLC MHCII expression and required the presence of T cells. This data suggests that T cells are an important mechanistic link by which the gut microbiota modulate the oligodendrocyte response and white matter recovery after TBI.

LXR agonism for CNS diseases: promises and challenges

The unfavorable prognosis of many neurological conditions could be attributed to limited tissue regeneration in central nervous system (CNS) and overwhelming inflammation, while liver X receptor (LXR) may regulate both processes due to its pivotal role in cholesterol metabolism and inflammatory response, and thus receives increasing attentions from neuroscientists and clinicians. Here, we summarize the signal transduction of LXR pathway, discuss the therapeutic potentials of LXR agonists based on preclinical data using different disease models, and analyze the dilemma and possible resolutions for clinical translation to encourage further investigations of LXR related therapies in CNS disorders.

Effects of sleep fragmentation on white matter pathology in a rat model of cerebral small vessel disease

STUDY OBJECTIVES

Mounting evidence indicated the correlation between sleep and cerebral small vessel disease (CSVD). However, little is known about the exact causality between poor sleep and white matter injury, a typical signature of CSVD, as well as the underlying mechanisms.

METHODS

Spontaneously hypertensive rats (SHR) and control Wistar Kyoto rats were subjected to sleep fragmentation (SF) for 16 weeks. The effects of chronic sleep disruption on the deep white matter and cognitive performance were observed.

RESULTS

SHR were validated as a rat model for CSVD. Fragmented sleep induced strain-dependent white matter abnormalities, characterized by reduced myelin integrity, impaired oligodendrocytes precursor cells (OPC) maturation and pro-inflammatory microglial polarization. Partially reversible phenotypes of OPC and microglia were observed in parallel following sleep recovery.

CONCLUSIONS

Long-term SF-induced pathological effects on the deep white matter in a rat model of CSVD. The pro-inflammatory microglial activation and the block of OPC maturation may be involved in the mechanisms linking sleep to white matter injury.

Hexahydrocurcumin attenuated demyelination and improved cognitive impairment in chronic cerebral hypoperfusion rats

Age-related white matter lesions (WML) frequently present vascular problems by decreasing cerebral blood supply, resulting in the condition known as chronic cerebral hypoperfusion (CCH). This study aimed to investigate the effect of hexahydrocurcumin (HHC) on the processes of demyelination and remyelination induced by the model of the Bilateral Common Carotid Artery Occlusion (BCCAO) for 29 days to mimic the CCH condition. The pathological appearance of myelin integrity was significantly altered by CCH, as evidenced by Transmission Electron Microscopy (TEM) and Luxol Fast Blue (LFB) staining. In addition, CCH activated A1-astrocytes and reactive-microglia by increasing the expression of Glial fibrillary acidic protein (GFAP), complement 3 (C3d) and pro-inflammatory cytokines. However, S100a10 expression, a marker of neuroprotective astrocytes, was suppressed, as were regenerative factors including (IGF-1) and Transglutaminase 2 (TGM2). Therefore, the maturation step was obstructed as shown by decreases in the levels of myelin basic protein (MBP) and the proteins related with lipid synthesis. Cognitive function was therefore impaired in the CCH model, as evidenced by the Morris water maze test. By contrast, HHC treatment significantly improved myelin integrity, and inhibited A1-astrocytes and reactive-microglial activity. Consequently, pro-inflammatory cytokines and A1-astrocytes were attenuated, and regenerative factors increased assisting myelin maturation and hence improving cognitive performance. In conclusion, HHC improves cognitive function and also the integrity of white matter in CCH rats by reducing demyelination, and pro-inflammatory cytokine production and promoting the process of remyelination.

5Z-7-Oxozaenol attenuates cuprizone-induced demyelination in mice through microglia polarization regulation

INTRODUCTION

Demyelination is a key factor in axonal degeneration and neural loss, leading to disability in multiple sclerosis (MS) patients. Transforming growth factor beta activated kinase 1 (TAK1) is a critical molecule involved in immune and inflammatory signaling pathways. Knockout of microglia TAK1 can inhibit autoimmune inflammation of the brain and spinal cord and improve the outcome of MS. However, it is unclear whether inhibiting TAK1 can alleviate demyelination.

METHODS

Eight-week-old male c57bl/6j mice were randomly divided into five groups: (a) the control group, (b) the group treated with cuprizone (CPZ) only, (c) the group treated with 5Z-7-Oxozaenol (OZ) only, and (d) the group treated with both cuprizone and 15 μg/30 μg OZ. Demyelination in the mice of this study was induced by administration of CPZ (ig) at a daily dose of 400 mg/kg for consecutive 5 weeks. OZ was intraperitoneally administered at mentioned doses twice a week, starting from week 3 after beginning cuprizone treatment. Histology, rotarod test, grasping test, pole test, Western blot, RT-PCR, and ELISA were used to evaluate corpus callosum demyelination, behavioral impairment, oligodendrocyte differentiation, TAK1 signaling pathway expression, microglia, and related cytokines.

RESULTS

Our results demonstrated that OZ protected against myelin loss and behavior impairment caused by CPZ. Additionally, OZ rescued the loss of oligodendrocytes in CPZ-induced mice. OZ inhibited the activation of JNK, p65, and p38 pathways, transformed M1 polarized microglia into M2 phenotype, and increased brain-derived neurotrophic factor (BDNF) expression to attenuate demyelination in CPZ-treated mice. Furthermore, OZ reduced the expression of proinflammatory cytokines and increases anti-inflammatory cytokines in CPZ-treated mice.

CONCLUSION

These findings suggest that inhibiting TAK1 may be an effective approach for treating demyelinating diseases.

Dynamics of myelin deficits in the 5xFAD mouse model for Alzheimer's disease and the protective role of BDNF

Recent findings highlight myelin breakdown as a decisive early event in Alzheimer's Disease (AD) acting as aggravating factor of its progression. However, it is still unclear whether myelin loss is attributed to increased oligodendrocyte vulnerability, reduced repairing capacity or toxic stimuli. In the present study, we sought to clarify the starting point of myelin disruption accompanied with Oligodendrocyte Progenitor Cell (OPC) elimination in the brain of the 5xFAD mouse model of AD at 6 months of age in Dentate Gyrus of the hippocampus in relation to neurotrophin system. Prominent inflammation presence was detected since the age of 6 months playing a key role in myelin disturbance and AD progression. Expression analysis of neurotrophin receptors in OPCs was performed to identify new targets that could increase myelination in health and disease. OPCs in both control and 5xFAD mice express TrkB, TrkC and p75 receptors but not TrkA. Brain-derived neurotrophic factor (BDNF) that binds to TrkB receptor is well-known about its pro-myelination effect, promoting oligodendrocytes proliferation and differentiation, so we focused our investigation on its effects in OPCs under neurodegenerative conditions. Our in vitro results showed that BDNF rescues OPCs from death and promotes their proliferation and differentiation in presence of the toxic Amyloid-β 1-42. Collectively, our results indicate that BDNF possess an additional neuroprotective role through its actions on oligodendrocytic component and its use could be proposed as a drug-based myelin-enhancing strategy, complementary to amyloid and tau centered therapies in AD.

Anti- and pro-inflammatory milieu differentially regulate differentiation and immune functions of oligodendrocyte progenitor cells

Oligodendrocyte progenitor cells (OPCs) were regarded for years solely for their regenerative role; however, their immune-modulatory roles have gained much attention recently, particularly in the context of multiple sclerosis (MS). Despite extensive studies on OPCs, there are limited data elucidating the interactions between their intrinsic regenerative and immune functions, as well as their relationship with the inflamed central nervous system (CNS) environment, a key factor in MS pathology. We examined the effects of pro-inflammatory cytokines, represented by interferon (IFN)-γ and tumour necrosis factor (TNF)-α, as well as anti-inflammatory cytokines, represented by interleukin (IL)-4 and IL-10, on OPC differentiation and immune characteristics. Using primary cultures, enzyme-linked immunosorbent assay and immunofluorescence stainings, we assessed differentiation capacity, phagocytic activity, major histocompatibility complex (MHC)-II expression, and cytokine secretion. We observed that the anti-inflammatory milieu (IL4 and IL10) reduced both OPC differentiation and immune functions. Conversely, exposure to TNF-α led to intact differentiation, increased phagocytic activity, high levels of MHC-II expression, and cytokines secretion. Those effects were attributed to signalling via TNF-receptor-2 and counteracted the detrimental effects of IFN-γ on OPC differentiation. Our findings suggest that a pro-regenerative, permissive inflammatory environment is needed for OPCs to execute both regenerative and immune-modulatory functions.

Macrophage senescence in health and diseases

Macrophage senescence, manifested by the special form of durable cell cycle arrest and chronic low-grade inflammation like senescence-associated secretory phenotype, has long been considered harmful. Persistent senescence of macrophages may lead to maladaptation, immune dysfunction, and finally the development of age-related diseases, infections, autoimmune diseases, and malignancies. However, it is a ubiquitous, multi-factorial, and dynamic complex phenomenon that also plays roles in remodeled processes, including wound repair and embryogenesis. In this review, we summarize some general molecular changes and several specific biomarkers during macrophage senescence, which may bring new sight to recognize senescent macrophages in different conditions. Also, we take an in-depth look at the functional changes in senescent macrophages, including metabolism, autophagy, polarization, phagocytosis, antigen presentation, and infiltration or recruitment. Furthermore, some degenerations and diseases associated with senescent macrophages as well as the mechanisms or relevant genetic regulations of senescent macrophages are integrated, not only emphasizing the possibility of regulating macrophage senescence to benefit age-associated diseases but also has an implication on the finding of potential targets or drugs clinically.

Enriched environment treatment promotes neural functional recovery together with microglia polarization and remyelination after cerebral ischemia in rats

BACKGROUND

Microglia activation and oligodendrocyte maturation are critical for remyelination after cerebral ischemia. Studies have shown that enriched environment (EE) can effectively alleviate stroke-induced neurological deficits. However, little is known about the mechanism associated with glial cells underlying the neuroprotection of EE. Therefore, this study focuses on investigating the effect of EE on activated microglia polarization as well as oligodendrogenesis in the progress of remyelination following cerebral ischemia.

METHODS

The ischemia/reperfusion (I/R) injury model was established by middle cerebral artery occlusion (MCAO) in rats. Animals executed 4 weeks of environmental intervention after performing MCAO or sham surgery and were divided into sham, MCAO, and MCAO+EE groups. Cognitive function, myelin damage, microglia activation and polarization, inflammation, oligodendrogenesis, remyelination, and protein expression of the PI3K/AKT/GSK3β signaling pathway were determined.

RESULTS

The staining of NeuN indicated that the infarct size of MCAO rats was decreased under EE. EE intervention improved animal performance in the Morris water maze test and novel object recognition test, promoting the recovery of cognitive function after I/R injury. EE treatment alleviated myelin damage in MCAO rats, as evidenced by the lower fluorescence intensity ratio of SMI-32/MBP in MCAO+EE group. EE increased the fluorescence intensity ratio of NG2+/Ki67+/Olig2+, MBP, and MOG, enhancing the proliferation and differentiation of OPCs and oligodendrogenesis after MCAO. In terms of remyelination, more myelinated axons and lower G/ratio were detected in MCAO+EE rats compared with MCAO group. Moreover, EE treatment decreased the number of Iba1+/CD86+ M1 microglia, increased the number of Iba1+/CD206+ M2 microglia, and suppressed the inflammation response after I/R injury, which could be attributed to the augmented expression of PI3K/AKT/GSK3β axis.

CONCLUSION

EE improved long‑term recovery of cognitive function after cerebral I/R injury, at least in part by promoting M2 microglia transformation through activation of the PI3K/AKT/GSK3β signaling pathway, inhibiting inflammation to provide a favorable microenvironment for oligodendrocyte maturation and remyelination. The effect of the EE on myelin and inflammation could account for the neuroprotection provided by EE.

The neurotropic schistosome vs experimental autoimmune encephalomyelitis: are there any winners?

The incidences of multiple sclerosis have risen worldwide, yet neither the trigger nor efficient treatment is known. Some research is dedicated to looking for treatment by parasites, mainly by helminths. However, little is known about the effect of helminths that infect the nervous system. Therefore, we chose the neurotropic avian schistosome Trichobilharzia regenti, which strongly promotes M2 polarization and tissue repair in the central nervous system, and we tested its effect on the course of experimental autoimmune encephalomyelitis (EAE) in mice. Surprisingly, the symptoms of EAE tended to worsen after the infection with T. regenti. The infection did not stimulate tissue repair, as indicated by the similar level of demyelination. Eosinophils heavily infiltrated the infected tissue, and the microglia number increased as well. Furthermore, splenocytes from T. regenti-infected EAE mice produced more interferon (IFN)-γ than splenocytes from EAE mice after stimulation with myelin oligodendrocyte glycoprotein. Our research indicates that the combination of increased eosinophil numbers and production of IFN-γ tends to worsen the EAE symptoms. Moreover, the data highlight the importance of considering the direct effect of the parasite on the tissue, as the migrating parasite may further tissue damage and make tissue repair even more difficult.

Biology of neurofibrosis with focus on multiple sclerosis

Tissue damage elicits a wound healing response of inflammation and remodeling aimed at restoring homeostasis. Dysregulation of wound healing leads to accumulation of effector cells and extracellular matrix (ECM) components, collectively termed fibrosis, which impairs organ functions. Fibrosis of the central nervous system, neurofibrosis, is a major contributor to the lack of neural regeneration and it involves fibroblasts, microglia/macrophages and astrocytes, and their deposited ECM. Neurofibrosis occurs commonly across neurological conditions. This review describes processes of wound healing and fibrosis in tissues in general, and in multiple sclerosis in particular, and considers approaches to ameliorate neurofibrosis to enhance neural recovery.

Deletion of Slc9a1 in Cx3cr1+ cells stimulated microglial subcluster CREB1 signaling and microglia-oligodendrocyte crosstalk

Microglial Na/H exchanger-1 (NHE1) protein, encoded by Slc9a1, plays a role in white matter demyelination of ischemic stroke brains. To explore underlying mechanisms, we conducted single cell RNA-seq transcriptome analysis in conditional Slc9a1 knockout (cKO) and wild-type (WT) mouse white matter tissues at 3 days post-stroke. Compared to WT, Nhe1 cKO brains expanded a microglial subgroup with elevated transcription of white matter myelination genes including Spp1, Lgals3, Gpnmb, and Fabp5. This subgroup also exhibited more acidic pHi and significantly upregulated CREB signaling detected by ingenuity pathway analysis and flow cytometry. Moreover, the Nhe1 cKO white matter tissues showed enrichment of a corresponding oligodendrocyte subgroup, with pro-phagocytosis and lactate shuffling gene expression, where activated CREB signaling is a likely upstream regulator. These findings demonstrate that attenuation of NHE1-mediated H+ extrusion acidifies microglia/macrophage and may underlie the stimulation of CREB1 signaling, giving rise to restorative microglia-oligodendrocyte interactions for remyelination.

The emerging neuroimmune hypothesis of bipolar disorder: An updated overview of neuroimmune and microglial findings

Bipolar disorder (BD) is a severe and multifactorial disease, with onset usually in young adulthood, which follows a progressive course throughout life. Replicated epidemiological studies have suggested inflammatory mechanisms and neuroimmune risk factors as primary contributors to the onset and development of BD. While not all patients display overt markers of inflammation, significant evidence suggests that aberrant immune signaling contributes to all stages of the disease and seems to be mood phase dependent, likely explaining the heterogeneity of findings observed in this population. As the brain's immune cells, microglia orchestrate the brain's immune response and play a critical role in maintaining the brain's health across the lifespan. Microglia are also highly sensitive to environmental changes and respond to physiological and pathological events by adapting their functions, structure, and molecular expression. Recently, it has been highlighted that instead of a single population of cells, microglia comprise a heterogeneous community with specialized states adjusted according to the local molecular cues and intercellular interactions. Early evidence has highlighted the contribution of microglia to BD neuropathology, notably for severe outcomes, such as suicidality. However, the roles and diversity of microglial states in this disease are still largely undermined. This review brings an updated overview of current literature on the contribution of neuroimmune risk factors for the onset and progression of BD, the most prominent neuroimmune abnormalities (including biomarker, neuroimaging, ex vivo studies) and the most recent findings of microglial involvement in BD neuropathology. Combining these different shreds of evidence, we aim to propose a unifying hypothesis for BD pathophysiology centered on neuroimmune abnormalities and microglia. Also, we highlight the urgent need to apply novel multi-system biology approaches to characterize the diversity of microglial states and functions involved in this enigmatic disorder, which can open bright perspectives for novel biomarkers and therapeutic discoveries.

Lesion-remote astrocytes govern microglia-mediated white matter repair

Spared regions of the damaged central nervous system undergo dynamic remodeling and exhibit a remarkable potential for therapeutic exploitation. Here, lesion-remote astrocytes (LRAs), which interact with viable neurons, glia and neural circuitry, undergo reactive transformations whose molecular and functional properties are poorly understood. Using multiple transcriptional profiling methods, we interrogated LRAs from spared regions of mouse spinal cord following traumatic spinal cord injury (SCI). We show that LRAs acquire a spectrum of molecularly distinct, neuroanatomically restricted reactivity states that evolve after SCI. We identify transcriptionally unique reactive LRAs in degenerating white matter that direct the specification and function of local microglia that clear lipid-rich myelin debris to promote tissue repair. Fueling this LRA functional adaptation is Ccn1 , which encodes for a secreted matricellular protein. Loss of astrocyte CCN1 leads to excessive, aberrant activation of local microglia with (i) abnormal molecular specification, (ii) dysfunctional myelin debris processing, and (iii) impaired lipid metabolism, culminating in blunted debris clearance and attenuated neurological recovery from SCI. Ccn1 -expressing white matter astrocytes are specifically induced by local myelin damage and generated in diverse demyelinating disorders in mouse and human, pointing to their fundamental, evolutionarily conserved role in white matter repair. Our findings show that LRAs assume regionally divergent reactivity states with functional adaptations that are induced by local context-specific triggers and influence disorder outcome. Astrocytes tile the central nervous system (CNS) where they serve vital roles that uphold healthy nervous system function, including regulation of synapse development, buffering of neurotransmitters and ions, and provision of metabolic substrates 1 . In response to diverse CNS insults, astrocytes exhibit disorder-context specific transformations that are collectively referred to as reactivity 2-5 . The characteristics of regionally and molecularly distinct reactivity states are incompletely understood. The mechanisms through which distinct reactivity states arise, how they evolve or resolve over time, and their consequences for local cell function and CNS disorder progression remain enigmatic. Immediately adjacent to CNS lesions, border-forming astrocytes (BFAs) undergo transcriptional reprogramming and proliferation to form a neuroprotective barrier that restricts inflammation and supports axon regeneration 6-9 . Beyond the lesion, spared but dynamic regions of the injured CNS exhibit varying degrees of synaptic circuit remodeling and progressive cellular responses to secondary damage that have profound consequences for neural repair and recovery 10,11 . Throughout these cytoarchitecturally intact, but injury-reactive regions, lesion-remote astrocytes (LRAs) intermingle with neurons and glia, undergo little to no proliferation, and exhibit varying degrees of cellular hypertrophy 7,12,13 . The molecular and functional properties of LRAs remain grossly undefined. Therapeutically harnessing spared regions of the injured CNS will require a clearer understanding of the accompanying cellular and molecular landscape. Here, we leveraged integrative transcriptional profiling methodologies to identify multiple spatiotemporally resolved, molecularly distinct states of LRA reactivity within the injured spinal cord. Computational modeling of LRA-mediated heterotypic cell interactions, astrocyte-specific conditional gene deletion, and multiple mouse models of acute and chronic CNS white matter degeneration were used to interrogate a newly identified white matter degeneration-reactive astrocyte subtype. We define how this reactivity state is induced and its role in governing the molecular and functional specification of local microglia that clear myelin debris from the degenerating white matter to promote repair.

The proteomic landscape of microglia in health and disease

Microglia are the resident immune cells of the central nervous system (CNS) and as such play crucial roles in regulating brain homeostasis. Their presence in neurodegenerative diseases is known, with neurodegeneration-associated risk genes heavily expressed in microglia, highlighting their importance in contributing to disease pathogenesis. Transcriptomics studies have uncovered the heterogeneous landscape of microglia in health and disease, identifying important disease-associated signatures such as DAM, and insight into both the regional and temporal diversity of microglia phenotypes. Quantitative mass spectrometry methods are ever increasing in the field of neurodegeneration, utilised as ways to identify disease biomarkers and to gain deeper understanding of disease pathology. Proteins are the main mechanistic indicators of cellular function, yet discordance between transcript and proteomic findings has highlighted the need for in-depth proteomic phenotypic and functional analysis to fully understand disease kinetics at the cellular and molecular level. This review details the current progress of using proteomics to define microglia biology, the relationship between gene and protein expression in microglia, and the future of proteomics and emerging methods aiming to resolve heterogeneous cell landscapes.

Neuropeptide Calcitonin Gene-Related Peptide Promotes Immune Homeostasis of Bacterial Meningitis by Inducing Major Histocompatibility Complex Class II Ubiquitination

BACKGROUND

Calcitonin gene-related peptide (CGRP), an immunomodulatory neuropeptide, is important for regulating pain transmission, vasodilation, and the inflammatory response. However, the molecular mechanisms of the CGRP-mediated immune response remain unknown.

METHODS

The effects of CGRP on bacterial meningitis (BM) and its underlying mechanisms were investigated in BM mice in vivo and macrophages in vitro.

RESULTS

Peripheral injection of CGRP attenuated cytokine storms and protected mice from fatal pneumococcal meningitis, marked by increased bacterial clearance, improved neuroethology, and reduced mortality. When the underlying mechanisms were investigated, we found that CGRP induces proteasome-dependent degradation of major histocompatibility complex class II (MHC-II) in macrophages and then inhibits CD4+ T-cell activation. MARCH1 was identified as an E3 ligase that can be induced by CGRP engagement and promote K48-linked ubiquitination and degradation of MHC-II in macrophages. These results provide new insights into neuropeptide CGRP-mediated immune regulation mechanisms.

CONCLUSIONS

We conclude that targeting the nervous system and manipulating neuroimmune communication is a promising strategy for treating intracranial infections like BM.

Epilepsy and demyelination: Towards a bidirectional relationship

Demyelination stands out as a prominent feature in individuals with specific types of epilepsy. Concurrently, individuals with demyelinating diseases, such as multiple sclerosis (MS) are at a greater risk of developing epilepsy compared to non-MS individuals. These bidirectional connections raise the question of whether both pathological conditions share common pathogenic mechanisms. This review focuses on the reciprocal relationship between epilepsy and demyelination diseases. We commence with an overview of the neurological basis of epilepsy and demyelination diseases, followed by an exploration of how our comprehension of these two disorders has evolved in tandem. Additionally, we discuss the potential pathogenic mechanisms contributing to the interactive relationship between these two diseases. A more nuanced understanding of the interplay between epilepsy and demyelination diseases has the potential to unveiling the molecular intricacies of their pathological relationships, paving the way for innovative directions in future clinical management and treatment strategies for these diseases.

Automated analysis of gray matter damage in aged mice reveals impaired remyelination in the cuprizone model

Multiple sclerosis is a chronic autoimmune disease of the central nervous system characterized by myelin loss, axonal damage, and glial scar formation. Still, the underlying processes remain unclear, as numerous pathways and factors have been found to be involved in the development and progression of the disease. Therefore, it is of great importance to find suitable animal models as well as reliable methods for their precise and reproducible analysis. Here, we describe the impact of demyelination on clinically relevant gray matter regions of the hippocampus and cerebral cortex, using the previously established cuprizone model for aged mice. We could show that bioinformatic image analysis methods are not only suitable for quantification of cell populations, but also for the assessment of de- and remyelination processes, as numerous objective parameters can be considered for reproducible measurements. After cuprizone-induced demyelination, subsequent remyelination proceeded slowly and remained incomplete in all gray matter areas studied. There were regional differences in the number of mature oligodendrocytes during remyelination suggesting region-specific differences in the factors accounting for remyelination failure, as, even in the presence of oligodendrocytes, remyelination in the cortex was found to be impaired. Upon cuprizone administration, synaptic density and dendritic volume in the gray matter of aged mice decreased. The intensity of synaptophysin staining gradually restored during the subsequent remyelination phase, however the expression of MAP2 did not fully recover. Microgliosis persisted in the gray matter of aged animals throughout the remyelination period, whereas extensive astrogliosis was of short duration as compared to white matter structures. In conclusion, we demonstrate that the application of the cuprizone model in aged mice mimics the impaired regeneration ability seen in human pathogenesis more accurately than commonly used protocols with young mice and therefore provides an urgently needed animal model for the investigation of remyelination failure and remyelination-enhancing therapies.

Boosting Microglial Lipid Metabolism via TREM2 Signaling by Biomimetic Nanoparticles to Attenuate the Sevoflurane-Induced Developmental Neurotoxicity

Lipid metabolism has been considered as a potential therapeutic target in sevoflurane-induced neurotoxicity that can potentially affect the learning and memory function in the developmental brain. Recently, triggering receptor expressed on myeloid cells 2 (TREM2) is identified as a crucial step in regulating lipid metabolism and associated with the pathogenesis of neurodegenerative diseases. Herein, it is reported that quercetin modified Cu2- x Se (abbreviated as CSPQ) nanoparticles can ameliorate sevoflurane-induced neurotoxicity by tuning the microglial lipid metabolism and promoting microglial M2-like polarization via TREM2 signaling pathway, in which the apolipoprotein E (ApoE), and adenosine triphosphate-binding cassette transporters (ABCA1 and ABCG1) levels are upregulated. Furthermore, the protective effects of CSPQ nanoparticles against sevoflurane-induced neurotoxicity via TREM2 are further demonstrated by the small interfering RNA (siRNA)-TREM2 transfected BV2 cells, which are obviously not influenced by CSPQ nanoparticles. The cell membrane coated CSPQ (referred as CSPQ@CM) nanoparticles can significantly reduce sevoflurane-induced learning and memory deficits, improve lipid metabolism dysfunction, and promote the remyelination in the hippocampus of mice. The study shows great potential of targeting microglial lipid metabolism in promoting remyelination of neurons for treatment of neurotoxicity and neurodegenerative diseases.

Remyelination in the Central Nervous System

The inability of the mammalian central nervous system (CNS) to undergo spontaneous regeneration has long been regarded as a central tenet of neurobiology. However, while this is largely true of the neuronal elements of the adult mammalian CNS, save for discrete populations of granule neurons, the same is not true of its glial elements. In particular, the loss of oligodendrocytes, which results in demyelination, triggers a spontaneous and often highly efficient regenerative response, remyelination, in which new oligodendrocytes are generated and myelin sheaths are restored to denuded axons. Yet remyelination in humans is not without limitation, and a variety of demyelinating conditions are associated with sustained and disabling myelin loss. In this work, we will (1) review the biology of remyelination, including the cells and signals involved; (2) describe when remyelination occurs and when and why it fails, including the consequences of its failure; and (3) discuss approaches for therapeutically enhancing remyelination in demyelinating diseases of both children and adults, both by stimulating endogenous oligodendrocyte progenitor cells and by transplanting these cells into demyelinated brain.

Impact of calcitriol and PGD2-G-loaded lipid nanocapsules on oligodendrocyte progenitor cell differentiation and remyelination

Multiple sclerosis (MS) is a demyelinating and inflammatory disease of the central nervous system (CNS) in need of a curative treatment. MS research has recently focused on the development of pro-remyelinating treatments and neuroprotective therapies. Here, we aimed at favoring remyelination and reducing neuro-inflammation in a cuprizone mouse model of brain demyelination using nanomedicines. We have selected lipid nanocapsules (LNC) coated with the cell-penetrating peptide transactivator of translation (TAT), loaded with either a pro-remyelinating compound, calcitriol (Cal-LNC TAT), or an anti-inflammatory bioactive lipid, prostaglandin D2-glycerol ester (PGD2-G) (PGD2-G-LNC TAT). Following the characterization of these formulations, we showed that Cal-LNC TAT in combination with PGD2-G-LNC TAT increased the mRNA expression of oligodendrocyte differentiation markers both in the CG-4 cell line and in primary mixed glial cell (MGC) cultures. However, while the combination of Cal-LNC TAT and PGD2-G-LNC TAT showed promising results in vitro, no significant impact, in terms of remyelination, astrogliosis, and microgliosis, was observed in vivo in the corpus callosum of cuprizone-treated mice following intranasal administration. Thus, although calcitriol's beneficial effects have been abundantly described in the literature in the context of MS, here, we show that the different doses of calcitriol tested had a negative impact on the mice well-being and showed no beneficial effect in the cuprizone model in terms of remyelination and neuro-inflammation, alone and when combined with PGD2-G-LNC TAT.

Knockdown of IFIT3 ameliorates multiple sclerosis via selectively regulating M1 polarization of microglia in an experimental autoimmune encephalomyelitis model

The key to the treatment of multiple sclerosis (MS) is to promote the transition from inflammation-induced demyelination to remyelination. Polarization of microglia towards M1 or M2 phenotype is critical in this transition. Interferon induced protein with tetratricopeptide repeats 3 (IFIT3) is involved in inflammatory reaction and up-regulated in M1-polarized macrophages. However, its effect on microglia during MS has not been reported. In this paper, we demonstrated the important role of IFIT3 in selectively regulating microglia polarization. The expression of IFIT3 was increased when microglia were polarized towards M1, but did not change under M2 polarization. The knockdown of IFIT3 selectively inhibited M1 polarization, while M2 polarization was not affected by IFIT3 silencing. Furthermore, the activation of signal transducer and activator of transcription 1 (STAT1) and nuclear factor kappa-B (NF-ĸB) signaling in M1 polarized microglia was suppressed by downregulating IFIT3. In experimental autoimmune encephalitis (EAE) mice, an animal model of MS, IFIT3 expression was upregulated. The disease progression, inflammatory infiltration and demyelination in the EAE mice were alleviated by silencing IFIT3. The inhibitory effects of IFIT3 knockdown on M1 polarization and STAT1 and NF-ĸB pathways were also confirmed in the spinal cord of EAE mice. In summary, our findings suggest that IFIT3 selectively intensified microglia polarization towards the pro-inflammatory M1 phenotype, and may contribute to the progression of MS.

Multiple Sclerosis: Roles of miRNA, lcnRNA, and circRNA and Their Implications in Cellular Pathways

Multiple sclerosis (MS) is a degenerative condition characterized by axonal damage and demyelination induced by autoreactive immune cells that occur in the Central Nervous System (CNS). The interaction between epigenetic changes and genetic factors can be widely involved in the onset, development, and progression of the disease. Although numerous efforts were made to discover new therapies able to prevent and improve the course of MS, definitive curative treatments have not been found yet. However, in recent years, it has been reported that non-coding RNAs (ncRNAs), including microRNAs (miRNAs), long ncRNAs (lncRNAs), and circular RNAs (circRNAs), acting as gene expression regulators, could be used as potential therapeutic targets or biomarkers to diagnose and fight MS. In this review, we discussed the role of miRNAs, lncRNAs, and circRNAs, as well as their expression level changes and signaling pathways that are related to preclinical and human MS studies. Hence, the investigation of ncRNAs could be important to provide additional information regarding MS pathogenesis as well as promote the discovery of new therapeutic strategies or biomarkers.

Aerobic Glycolysis Induced by mTOR/HIF-1α Promotes Early Brain Injury After Subarachnoid Hemorrhage via Activating M1 Microglia

M1 microglial activation is crucial for the pathogenesis of early brain injury (EBI) following subarachnoid hemorrhage (SAH), and there is growing evidence that glucose metabolism is frequently involved in microglial activation. However, the molecular mechanism of glycolysis and its role in M1 microglial activation in the context of EBI are not yet fully understood. In this study, firstly, the relationship between aerobic glycolysis and M1 microglial activation as well as SAH-induced EBI was researched in vivo. Then, intervention on mammalian target of rapamycin (mTOR) was performed to investigate the effects on glycolysis-dependent M1 microglial activation and EBI and its relationship with hypoxia-inducible factor-1α (HIF-1α) in vivo. Next, Hif-1α was inhibited to analyze its role in aerobic glycolysis, M1 microglial activation, and EBI in vivo. Lastly, both in vivo and in vitro, mTOR inhibition and Hif-1α enhancement were administered simultaneously, and the combined effects were further confirmed again. The results showed that aerobic glycolysis and M1 microglial polarization were increased after SAH, and glycolytic inhibition could attenuate M1 microglial activation and EBI. Inhibition of mTOR reduced glycolysis-dependent M1 microglial polarization and EBI severity by down-regulating HIF-1α expression, while enhancement had the opposite effects. Blockading HIF-1α had the similar effects as suppressing mTOR, while HIF-1α agonist worked against mTOR antagonist when administered simultaneously. In conclusion, the present study showed new evidence that aerobic glycolysis induced by mTOR/HIF-1α might promote EBI after SAH by activating M1 microglia. This finding provided new insights for the treatment of EBI.