Microglial autophagy-associated phagocytosis is essential for recovery from neuroinflammation

Diosgenin alleviates neuropathic pain based on the enhancement of autophagy and promotion of M2 polarization

Neuropathic pain has serious impacts on the quality of people's life. Diosgenin extracted from yams has shown significant potential in the treatment of nervous system diseases. To investigate the potential mechanism of diosgenin fighting against neuropathic pain, we established a chronic compression injury (CCI) model. The pain-related behaviors were determined by Von Frey, hot plate, and sciatic nerve index test. As a result, diosgenin significantly lowered the pain threshold, improved the sciatic nerve index, and decreased the damage of sciatic nerve structure in CCI model mice. It increased the protein levels of LC3-II and Beclin-1, the number of the lysosomes, decreased the protein level of P62 and the number of the autophagosomes, and therefore activated autophagy. Diosgenin also inhibited the proliferation of microglia cells and the translocation of NF-κB p65, while promoting promoted M2 polarization of microglia cells. Autophagy inhibitor like chloroquine inhibited the M2 polarization of microglia cells, and reversed the therapeutic effect of diosgenin. All in all, diosgenin alleviated neuropathic pain in CCI mice based on the enhancement of autophagy and the promotion of M2 polarization.

The regulation of microglia by aging and autophagy in multiple sclerosis

Multiple sclerosis (MS) is an inflammatory disease that is often characterized by the development of irreversible clinical disability. Age is a strong risk factor that is strongly associated with the clinical course and progression of MS. Several lines of evidence suggest that with aging, microglia have an aging-related gene expression signature and are close to disease-associated microglia (DAM), which exhibit decreased phagocytosis but increased production of inflammatory factors. The gene expression signatures of microglia in MS overlap with those in aging, inflammation and DAM. Moreover, the clearance of damaged myelin by microglia is impaired in the aged brain. Autophagy is a cellular process that decreases in activity with age. In this review, we provide an overview of the role of autophagy and aging in MS. We describe the impact of autophagy and aging on microglial activation in MS and the molecules involved in autophagy and aging, which are related to the phagocytosis and activation of microglia. We propose that a decrease in autophagy in microglia occurs with aging, leading to a decrease in phagocytosis. Decreases in phagocytosis and increases in the production of inflammatory factors by microglia contribute to chronic inflammation in the aged brain and disease progression in MS. Thus, the modulation of autophagy in microglia serves as a potential therapeutic target for MS.

Anti-IL-6R antibody treatment changes microglial phenotype in AQP4 peptide-immunized mice, leading to suppression of myelitis severity

Neuromyelitis optica spectrum disorder (NMOSD) is a rare autoimmune disease characterized by periods of remission and relapse; severe relapses often lead to permanent neurological disability. Satralizumab, an anti-interleukin-6 receptor (anti-IL-6R) antibody, has been proven in previous studies to reduce the frequency and severity of relapses in patients with NMOSD. There are several reports on the mechanisms through which anti-IL-6R antibodies are thought to suppress relapse. However, the mechanisms underlying how anti-IL-6R antibodies reduce the severity of myelitis have not been elucidated. We investigated the effect of an anti-IL-6R antibody (MR16-1) on the severity of myelitis in an AQP4 peptide-immunized mice model. This mouse model exhibits NMOSD-like pathological characteristics and the production of anti-AQP4 autoantibodies. Unlike the previously reported experimental protocol where antibody and peptide are administered simultaneously, we tested delayed administration of MR16-1 (9 days after peptide immunization). We found that delayed MR16-1 administration suppressed the clinical score of AQP4 peptide-immunized mice experiencing myelitis. Mice treated with MR16-1 showed a greater percentage of CD11c+ microglia in the spinal cord, along with upregulated expression of phagocytosis-related genes. Blockade of IL-6R by anti-IL-6R antibodies may suppress the severity of myelitis by increasing CD11c+ microglia and enhancing phagocytic function in AQP4 peptide-immunized mice.

The mechanism of disease progression by aging and age-related gut dysbiosis in multiple sclerosis

Multiple sclerosis (MS) is the most common demyelinating disease caused by a multifaceted interplay of genetic predispositions and environmental factors. Most patients initially experience the relapsing-remitting form of the disease (RRMS), which is characterized by episodes of neurological deficits followed by periods of symptom resolution. However, over time, many individuals with RRMS advance to a progressive form of the disease, known as secondary progressive MS (SPMS), marked by a gradual worsening of symptoms without periods of remission. The mechanisms underlying this transition remain largely unclear, and current disease-modifying therapies (DMTs) are partially effective in treating SPMS. Age is widely acknowledged as a risk factor for the transition from RRMS to SPMS. One factor associated with aging that may influence the progression of MS is gut dysbiosis. This review discusses how aging and age-related gut dysbiosis affect the progression of MS.

Unlocking the therapeutic promise of miRNAs in promoting amyloid-β clearance for Alzheimer's disease

Alzheimer's disease (AD) is a neurological disorder that affects cognition and behavior, accounting for 60-70 % of dementia cases. Its mechanisms involve amyloid aggregates, hyperphosphorylated tau tangles, and loss of neural connections. Current treatments have limited efficacy due to a lack of specific targets. Recently, microRNAs (miRNAs) have emerged as key modulators in AD, regulating gene expression through interactions with mRNA. Dysregulation of specific miRNAs contributes to disease progression by disrupting clearance pathways. Antisense oligonucleotide (ASO)-based therapies show promise for AD treatment, particularly when combined with miRNA mimics or antagonists, targeting complex regulatory networks. However, miRNAs can interact with each other, complicating cellular processes and potentially leading to side effects. Our review emphasizes the role of miRNAs in regulating amyloid-beta (Aβ) clearance and highlights their potential as therapeutic targets and early biomarkers for AD, underscoring the need for further research to enhance their efficacy and safety.

Loss of ATG7 in microglia impairs UPR, triggers ferroptosis, and weakens amyloid pathology control

Microglia impact brain development, homeostasis, and pathology. One important microglial function in Alzheimer's disease (AD) is to contain proteotoxic amyloid-β (Aβ) plaques. Recent studies reported the involvement of autophagy-related (ATG) proteins in this process. Here, we found that microglia-specific deletion of Atg7 in an AD mouse model impaired microglia coverage of Aβ plaques, increasing plaque diffusion and neurotoxicity. Single-cell RNA sequencing, biochemical, and immunofluorescence analyses revealed that Atg7 deficiency reduces unfolded protein response (UPR) while increasing oxidative stress. Cellular assays demonstrated that these changes lead to lipoperoxidation and ferroptosis of microglia. In aged mice without Aβ buildup, UPR reduction and increased oxidative damage induced by Atg7 deletion did not impact microglia numbers. We conclude that reduced UPR and increased oxidative stress in Atg7-deficient microglia lead to ferroptosis when exposed to proteotoxic stress from Aβ plaques. However, these microglia can still manage misfolded protein accumulation and oxidative stress as they age.

Anthraquinones and Aloe Vera Extracts as Potential Modulators of Inflammaging Mechanisms: A Translational Approach from Autoimmune to Onco-Hematological Diseases

Inflammaging is a chronic, low-grade inflammatory state that contributes to age-related diseases, including cardiovascular disorders, osteoporosis, neurodegeneration, and cancer. This process involves immunosenescence, oxidative stress, and immune aging, all of which contribute to the breakdown of immune tolerance and the onset of autoimmune disorders. Aloe vera (AV) has recently gained attention for its immunomodulatory, anti-inflammatory, and antioxidant properties. This review explores the effects of AV extracts and anthraquinones (e.g., aloe-emodin, emodin, aloin) on key inflammaging-driven mechanisms in autoimmunity. Our analysis highlights AV's ability to regulate hormone balance, autoantibody production, and cytokine/chemokine signaling (such as interleukin-1β, tumor necrosis factor-α, and interferon-γ). It modulates inflammatory pathways, including mitogen-activated protein kinases (MAPKs) and phosphatidylinositol 3-kinase/protein kinase B (PI3K/AKT), thereby inhibiting nuclear factor kappa-light-chain-enhancer of activated B-cell (NF-κB) activation. Additionally, AV enhances antioxidant defenses and restores immune balance by reducing Th1/Th17 subsets while promoting Th2-mediated regulation. Notably, AV also modulates inflammasome-mediated mechanisms and counteracts immunosenescence, which is driven by autophagy-related processes. These effects position AV as a potential integrative approach to mitigating inflammaging-driven autoimmunity. Furthermore, as inflammaging is increasingly recognized in onco-hematological diseases, AV-based strategies may offer novel therapeutic avenues. Future studies should focus on clinical validation, optimizing formulations, and expanding applications to broader age-related and immune-mediated disorders.

The microglial response to inhibition of Colony-stimulating-factor-1 receptor by PLX3397 differs by sex in adult mice

Microglia, the resident macrophages of the brain, are derived from the yolk sac and colonize the brain before the blood-brain barrier forms. Once established, they expand locally and require Colony-stimulating-factor-1 receptor (CSF1R) signaling for their development and maintenance. CSF1R inhibitors have been used extensively to deplete microglia in the healthy and diseased brain. In this study, we demonstrated sex-dependent differences in the microglial response to the CSF1R inhibitor PLX3397. Male mice exhibited greater microglial depletion compared to females. Transcriptomic and flow cytometry analysis revealed sex-specific differences in the remaining microglia population, with female microglia upregulating autophagy and proteostasis pathways while male microglia increased mitobiogenesis. Furthermore, manipulating key microglial receptors by using different transgenic mouse lines resulted in changes in depletion efficacies that were also sex dependent. These findings suggest sex-dependent microglial survival mechanisms, which might contribute to the well-documented sex differences in various neurological disorders.

Distinct UPR and Autophagic Functions Define Cell-Specific Responses to Proteotoxic Stress in Microglial and Neuronal Cell Lines

Autophagy is a catabolic process involved in different cellular functions. However, the molecular pathways governing its potential roles in different cell types remain poorly understood. We investigated the role of autophagy in the context of proteotoxic stress in two central nervous system cell types: the microglia-like cell line BV2 and the neuronal-like cell line N2a. Proteotoxic stress, induced by proteasome inhibition, produced early apoptosis in BV2 cells, due in part to a predominant activation of the PERK-CHOP pathway. In contrast, N2a cells showcased greater resistance and robust induction of the IRE1α-sXbp1 arm of the UPR. We also demonstrated that proteotoxic stress activated autophagy in both cell lines but with different kinetics and cellular functions. In N2a cells, autophagy restored cellular proteostasis, while in BV2 cells, it participated in regulating phagocytosis. Finally, proteotoxic stress predominantly activated the mTORC2-AKT-FOXO1-β-catenin pathway in BV2 cells, while N2a cells preferentially induced the PDK1-AKT-FOXO3 axis. Collectively, our findings suggest that proteotoxic stress triggers cell-specific responses in microglia and neurons, with different physiological outcomes.

New insight in treating autoimmune diseases by targeting autophagy

Autophagy is a highly conserved biological process in eukaryotes, which degrades cellular misfolded proteins, damaged organelles and invasive pathogens in the lysosome-dependent manner. Autoimmune diseases caused by genetic elements, environments and aberrant immune responses severely impact patients' living quality and even threaten life. Recently, numerous studies have reported autophagy can regulate immune responses, and play an important role in autoimmune diseases. In this review, we summarised the features of autophagy and autophagy-related genes, enumerated some autophagy-related genes involved in autoimmune diseases, and further overviewed how to treat autoimmune diseases through targeting autophagy. Finally, we outlooked the prospect of relieving and curing autoimmune diseases by targeting autophagy pathway.

A critical role for microglia in regulating metabolic homeostasis and neural repair after spinal cord injury

Traumatic spinal cord injury (SCI) often results in severe immune and metabolic disorders, aggravating neurological damage and inhibiting locomotor functional recovery. Microglia, as resident immune cells of the spinal cord, play crucial roles in maintaining neural homeostasis under physiological conditions. However, the precise role of microglia in regulating immune and metabolic functions in SCI is still unclear and is easily confused with that of macrophages. In this study, we pharmacologically depleted microglia to explore the role of microglia after SCI. We found that microglia are beneficial for the recovery of locomotor function. Depleting microglia disrupted glial scar formation, reducing neurogenesis and angiogenesis. Using liquid chromatography tandem mass spectrometry (LC‒MS/MS), we discovered that depleting microglia significantly inhibits lipid metabolism processes such as fatty acid degradation, unsaturated fatty acid biosynthesis, glycophospholipid metabolism, and sphingolipid metabolism, accompanied by the accumulation of multiple organic acids. Subsequent studies demonstrated that microglial depletion increased the inhibition of FASN after SCI. FASN inhibition exacerbated malonyl-CoA accumulation and significantly impeded the activity of mTORC1. Moreover, microglial depletion exacerbated the oxidative stress of neurons. In summary, our results indicate that microglia alleviate neural damage and metabolic disorders after SCI, which is beneficial for achieving optimal neuroprotection and neural repair.

Fueling neurodegeneration: metabolic insights into microglia functions

Microglia, the resident immune cells of the central nervous system, emerge in the brain during early embryonic development and persist throughout life. They play essential roles in brain homeostasis, and their dysfunction contributes to neuroinflammation and the progression of neurodegenerative diseases. Recent studies have uncovered an intricate relationship between microglia functions and metabolic processes, offering fresh perspectives on disease mechanisms and possible treatments. Despite these advancements, there are still significant gaps in our understanding of how metabolic dysregulation affects microglial phenotypes in these disorders. This review aims to address these gaps, laying the groundwork for future research on the topic. We specifically examine how metabolic shifts in microglia, such as the transition from oxidative phosphorylation and mitochondrial metabolism to heightened glycolysis during proinflammatory states, impact the disease progression in Alzheimer's disease, multiple sclerosis, Parkinson's disease, amyotrophic lateral sclerosis, and Huntington's disease. Additionally, we explore the role of iron, fatty and amino acid metabolism in microglial homeostasis and repair. Identifying both distinct and shared metabolic adaptations in microglia across neurodegenerative diseases could reveal common therapeutic targets and provide a deeper understanding of disease-specific mechanisms underlying multiple CNS disorders.

Myelin debris phagocytosis in demyelinating disease

Demyelinating diseases are often caused by a variety of triggers, including immune responses, viral infections, malnutrition, hypoxia, or genetic factors, all of which result in the loss of myelin in the nervous system. The accumulation of myelin debris at the lesion site leads to neuroinflammation and inhibits remyelination; therefore, it is crucial to promptly remove the myelin debris. Initially, Fc and complement receptors on cellular surfaces were the primary clearance receptors responsible for removing myelin debris. However, subsequent studies have unveiled the involvement of additional receptors, including Mac-2, TAM receptors, and the low-density lipoprotein receptor-related protein 1, in facilitating the removal process. In addition to microglia and macrophages, which serve as the primary effector cells in the disease phase, a variety of other cell types such as astrocytes, Schwann cells, and vascular endothelial cells have been demonstrated to engage in the phagocytosis of myelin debris. Furthermore, we have concluded that oligodendrocyte precursor cells, as myelination precursor cells, also exhibit this phagocytic capability. Moreover, our research group has innovatively identified the low-density lipoprotein receptor as a potential phagocytic receptor for myelin debris. In this article, we discuss the functional processes of various phagocytes in demyelinating diseases. We also highlight the alterations in signaling pathways triggered by phagocytosis, and provide a comprehensive overview of the various phagocytic receptors involved. Such insights are invaluable for pinpointing potential therapeutic strategies for the treatment of demyelinating diseases by targeting phagocytosis.

Senolytic treatment diminishes microglia and decreases severity of experimental autoimmune encephalomyelitis

BACKGROUND

The role of senescence in disease contexts is complex, however there is considerable evidence that depletion of senescent cells improves outcomes in a variety of contexts particularly related to aging, cognition, and neurodegeneration. Much research has shown previously that inflammation can promote cellular senescence. Microglia are a central nervous system innate immune cell that undergo senescence with aging and during neurodegeneration. The contribution of senescent microglia to multiple sclerosis, an inflammatory neurodegenerative disease, is not clear, but microglia are strongly implicated in chronic active lesion pathology, tissue injury, and disease progression. Drugs that could specifically eliminate dysregulated microglia in multiple sclerosis are therefore of great interest to the field.

RESULTS

A single-cell analysis of brain tissue from mice subjected to experimental autoimmune encephalomyelitis (EAE), a mouse model of CNS inflammation that models aspects of multiple sclerosis (MS), identified microglia with a strong transcriptional signature of senescence including the presence of BCL2-family gene transcripts. Microglia expressing Bcl2l1 had higher expression of pro-inflammatory and senescence associated genes than their Bcl2l1 negative counterparts in EAE, suggesting they may exacerbate inflammation. Notably, in human single-nucleus sequencing from MS, BCL2L1 positive microglia were enriched in lesions with active inflammatory pathology, and likewise demonstrated increased expression of immune genes suggesting they may be proinflammatory and contribute to disease processes in chronic active lesions. Employing a small molecule BCL2-family inhibitor, Navitoclax (ABT-263), significantly reduced the presence of microglia and macrophages in the EAE spinal cord, suggesting that these cells can be targeted by senolytic treatment. ABT-263 treatment had a profound effect on EAE mice: decreasing motor symptom severity, improving visual acuity, promoting neuronal survival, and decreasing white matter inflammation.

CONCLUSION

These results support the hypothesis that microglia and macrophages exhibit transcriptional features of cellular senescence in EAE and MS, and that microglia expressing Bcl2l1 demonstrate a proinflammatory signature that may exacerbate inflammation resulting in negative outcomes in neuroinflammatory disease. Depleting microglia and macrophages using a senolytic results in robust improvement in EAE disease severity, including across measures of neurodegeneration, inflammation, and demyelination, and may therefore represent a novel strategy to address disease progression in multiple sclerosis.

Distinct olfactory mucosal macrophage populations mediate neuronal maintenance and pathogen defense

The olfactory mucosa is important for both the sense of smell and as a mucosal immune barrier to the upper airway and brain. However, little is known about how the immune system mediates the conflicting goals of neuronal maintenance and inflammation in this tissue. A number of immune cell populations reside within the olfactory mucosa and yet we have little understanding of how these resident olfactory immune cells functionally interact with the chemosensory environment. Identifying these interactions will allow therapeutic manipulations that treat disorders such as post-viral olfactory dysfunction. Macrophages are the most prevalent immune cell type in the uninflamed olfactory mucosa and here, we identify two distinct tissue macrophage populations in murine olfactory mucosa. P2ry12hi macrophages are transcriptionally specialized for neuron interactions, closely associated with olfactory neuron cell bodies, long-term tissue residents, and functionally specialized to phagocytose cells and debris, including olfactory neurons. Conversely, MHC Class IIhi macrophages are transcriptionally dedicated to cytokine production and antigen presentation, localized primarily within the olfactory lamina propria, more rapidly replaced by blood monocytes, and rapidly produce chemokines in response to viral infection. We further show that these macrophage signatures are present in human olfactory biopsies, and P2ry12-like olfactory macrophages are reduced in patients with long-term smell loss following COVID-19. Together, these data show that two olfactory macrophage populations regulate neurons and initiate the immune response, contributing to our understanding of both olfactory immunity and tissue-resident macrophage biology.

Rapid phagosome isolation enables unbiased multiomic analysis of human microglial phagosomes

Microglia are the resident macrophages of the central nervous system (CNS). Their phagocytic activity is central during brain development and homeostasis-and in a plethora of brain pathologies. However, little is known about the composition, dynamics, and function of human microglial phagosomes under homeostatic and pathological conditions. Here, we developed a method for rapid isolation of pure and intact phagosomes from human pluripotent stem cell-derived microglia under various in vitro conditions, and from human brain biopsies, for unbiased multiomic analysis. Phagosome profiling revealed that microglial phagosomes were equipped to sense minute changes in their environment and were highly dynamic. We detected proteins involved in synapse homeostasis, or implicated in brain pathologies, and identified the phagosome as the site where quinolinic acid was stored and metabolized for de novo nicotinamide adenine dinucleotide (NAD+) generation in the cytoplasm. Our findings highlight the central role of phagosomes in microglial functioning in the healthy and diseased brain.

Autophagy in Multiple Sclerosis: Phagocytosis and Autophagy of Oligodendrocyte Precursor Cells

Multiple sclerosis (MS) is a leading cause of chronic neurological dysfunction in young to middle-aged adults, affecting approximately 2.5 million people worldwide. It is characterized by inflammation, multifocal demyelination, axonal loss, and white and gray matter gliosis. Autophagy is a highly conserved protein degradation pathway. Polymorphisms in autophagy-related genes have been implicated in a variety of autoimmune diseases, including systemic lupus erythematosus, rheumatoid arthritis, psoriasis and MS. However, the significance of autophagy in MS remains to be elucidated. This paper aims to explore the potential role of autophagy-related genes in MS diseases by using bioinformatics combined with machine learning methods. Finally, we obtained 9 autophagy genes with the highest correlation with MS, and further changes in these autophagy genes were verified in the experimental autoimmune encephalomyelitis (EAE) model and oligodendrocyte precursor cells (OPCs) engulfed myelin debris (MD). Combined with bioinformatic analysis and experimental data, Becn1 showed obvious expression abnormalities suggesting that this gene has vital functions in autophagy and MD engulfed by OPCs. This work will be of great significance for the further exploration of autophagy-related genes in demyelinating diseases.

Identification of Autophagy-Related Biomarkers and Diagnostic Model in Alzheimer's Disease

Alzheimer's disease (AD) is the most prevalent neurodegenerative disease. Its accurate pathogenic mechanisms are incompletely clarified, and effective therapeutic treatments are still inadequate. Autophagy is closely associated with AD and plays multiple roles in eliminating harmful aggregated proteins and maintaining cell homeostasis. This study identified 1191 differentially expressed genes (DEGs) based on the GSE5281 dataset from the GEO database, intersected them with 325 autophagy-related genes from GeneCards, and screened 26 differentially expressed autophagy-related genes (DEAGs). Subsequently, GO and KEGG enrichment analysis was performed and indicated that these DEAGs were primarily involved in autophagy-lysosomal biological process. Further, eight hub genes were determined by PPI construction, and experimental validation was performed by qRT-PCR on a SH-SY5Y cell model. Finally, three hub genes (TFEB, TOMM20, GABARAPL1) were confirmed to have potential application for biomarkers. A multigenic prediction model with good predictability (AUC = 0.871) was constructed in GSE5281 and validated in the GSE132903 dataset. Hub gene-targeted miRNAs closely associated with AD were also retrieved through the miRDB and HDMM database, predicting potential therapeutic agents for AD. This study provides new insights into autophagy-related genes in brain tissues of AD patients and offers more candidate biomarkers for AD mechanistic research as well as clinical diagnosis.

Extracellular vesicles promote autophagy in human microglia through lipid raft-dependent mechanisms

Autophagy dysfunction has been closely related with pathogenesis of many neurodegenerative diseases and therefore represents a potential therapeutic target. Extracellular vesicles (EVs) may act as potent anti-inflammatory agents and also modulators of autophagy in target cells. However, the molecular mechanisms by which EVs modulate autophagy flux in human microglia remain largely unexplored. In the present study, we investigated the effects of EVs derived from human oral mucosa stem cells on the autophagy in human microglia. We demonstrate that EVs promoted autophagy and autophagic flux in human microglia and that this process was dependent on the integrity of lipid rafts. Lipopolysaccharide (LPS) also activated autophagy, but combined treatment with EVs and LPS suppressed autophagy response, indicating interference between these signaling pathways. Blockage of Toll-like receptor 4 (TLR4) with anti-TLR4 antibody suppressed EV-induced autophagy. Furthermore, inhibition of the EV-associated heat shock protein (HSP70) chaperone which is one of the endogenous ligands of the TLR4 also suppressed EV-induced lipid raft formation and autophagy. Pre-treatment of microglia with a selective inhibitor of αvβ3/αvβ5 integrins cilengitide inhibited EV-induced autophagy. Finally, blockage of purinergic P2X4 receptor (P2X4R) with selective inhibitor 5-BDBD also suppressed EV-induced autophagy. In conclusion, we demonstrate that EVs activate autophagy in human microglia through interaction with HSP70/TLR4, αVβ3/αVβ5, and P2X4R signaling pathways and that these effects depend on the integrity of lipid rafts. Our findings could be used to develop new therapeutic strategies targeting disease-associated microglia.

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.

Triggering receptor expressed on myeloid cells 2 (TREM2) regulates phagocytosis in glioblastoma

BACKGROUND

Glioblastomas (GBMs) are central nervous system tumors that resist standard-of-care interventions and even immune checkpoint blockade. Myeloid cells in the tumor microenvironment can contribute to GBM progression; therefore, emerging immunotherapeutic approaches include reprogramming these cells to achieve desirable antitumor activity. Triggering receptor expressed on myeloid cells 2 (TREM2) is a myeloid signaling regulator that has been implicated in a variety of cancers and neurological diseases with contrasting functions, but its role in GBM immunopathology and progression is still under investigation.

METHODS

Our reverse translational investigations leveraged single-cell RNA sequencing and cytometry of human gliomas to characterize TREM2 expression across myeloid subpopulations. Using 2 distinct murine glioma models, we examined the role of Trem2 on tumor progression and immune modulation of myeloid cells. Furthermore, we designed a method of tracking phagocytosis of glioma cells in vivo and employed in vitro assays to mechanistically understand the influence of TREM2 signaling on tumor uptake.

RESULTS

We discovered that TREM2 expression does not correlate with immunosuppressive pathways, but rather showed strong a positive association with the canonical phagocytosis markers lysozyme (LYZ) and macrophage scavenger receptor (CD163) in gliomas. While Trem2 deficiency was found to be dispensable for gliomagenesis, Trem2+ myeloid cells display enhanced tumor uptake compared to Trem2- cells. Mechanistically, we demonstrate that TREM2 mediates phagocytosis via Syk signaling.

CONCLUSIONS

These results indicate that TREM2 is not associated with immunosuppression in gliomas. Instead, TREM2 is an important regulator of phagocytosis that may be exploited as a potential therapeutic strategy for brain tumors.

Autophagy in neural stem cells and glia for brain health and diseases

Autophagy is a multifaceted cellular process that not only maintains the homeostatic and adaptive responses of the brain but is also dynamically involved in the regulation of neural cell generation, maturation, and survival. Autophagy facilities the utilization of energy and the microenvironment for developing neural stem cells. Autophagy arbitrates structural and functional remodeling during the cell differentiation process. Autophagy also plays an indispensable role in the maintenance of stemness and homeostasis in neural stem cells during essential brain physiology and also in the instigation and progression of diseases. Only recently, studies have begun to shed light on autophagy regulation in glia (microglia, astrocyte, and oligodendrocyte) in the brain. Glial cells have attained relatively less consideration despite their unquestioned influence on various aspects of neural development, synaptic function, brain metabolism, cellular debris clearing, and restoration of damaged or injured tissues. Thus, this review composes pertinent information regarding the involvement of autophagy in neural stem cells and glial regulation and the role of this connexion in normal brain functions, neurodevelopmental disorders, and neurodegenerative diseases. This review will provide insight into establishing a concrete strategic approach for investigating pathological mechanisms and developing therapies for brain diseases.

ATG5 (autophagy related 5) in microglia controls hippocampal neurogenesis in Alzheimer disease

Macroautophagy/autophagy is the intracellular degradation process of cytoplasmic content and damaged organelles. Autophagy is strongly associated with the progression of Alzheimer disease (AD). Microglia are brain-resident macrophages, and recent studies indicate that autophagy in microglia protects neurons from neurodegeneration. Postnatal neurogenesis, the generation of new neurons from adult neural stem cells (NSCs), is impaired in AD patients as well as in AD animal models. However, the extent to which microglial autophagy influences adult NSCs and neurogenesis in AD animal models has not been studied. Here, we showed that conditional knock out (cKO) of Atg5 (autophagy related 5) in microglia inhibited postnatal neurogenesis in the dentate gyrus (DG) of the hippocampus, but not in the subventricular zone (SVZ) of a 5×FAD mouse model. Interestingly, the protection of neurogenesis by Atg5 in microglia was only observed in female AD mice. To confirm the roles of autophagy in microglia for postnatal hippocampal neurogenesis, we generated additional cKO mice to delete autophagy essential genes Rb1cc1 or Atg14 in microglia. However, these rb1cc1 cKO and atg14 cKO mice did not exhibit neurogenesis defects in the context of a female AD mouse model. Last, we used the CSF1R antagonist to deplete ATG5-deficient microglia and this intervention restored neurogenesis in the hippocampus of 5×FAD mice. These results indicate that microglial ATG5 is essential to maintain postnatal hippocampal neurogenesis in a mouse model of AD. Our findings further support the notion that ATG5 in microglia supports NSC health and may prevent neurodegeneration.Abbreviations: 5×FAD: familial Alzheimer disease; Aβ: β-amyloid; AD: Alzheimer disease; AIF1: allograft inflammatory factor 1; ATG: autophagy related; BrdU: 5-bromo-2'-deoxyuridine; CA: Cornu Ammonis; cKO: conditional knock out; CSF1R: colony stimulating factor 1 receptor; Ctrl: control; DCX: doublecortin; DG: dentate gyrus; GFAP: glial fibrillary acidic protein; GZ: granular zone; H&E: hematoxylin and eosin; IF: immunofluorescence; LD: lipid droplet; LDAM: lipid droplets accumulated microglia; LPS: lipopolysaccharides; MAP1LC3B/LC3: microtubule-associated protein 1 light chain 3 beta; NSCs: neural stem cells; RB1CC1: RB1-inducible coiled-coil 1; SOX2: SRY (sex determining region Y)-box 2; SGZ: subgranular zone; SVZ: subventricular zone; WT: wild type.

Targeting autophagy to counteract neuroinflammation: A novel antidepressant strategy

Depression is a common disease that affects physical and mental health and imposes a considerable burden on afflicted individuals and their families worldwide. Depression is associated with a high rate of disability and suicide. It causes a severe decline in productivity and quality of life. Unfortunately, the pathophysiological mechanisms underlying depression have not been fully elucidated, and the risk of its treatment is still presented. Studies have shown that the expression of autophagic markers in the brain and peripheral inflammatory mediators are dysregulated in depression. Autophagy-related genes regulate the level of autophagy and change the inflammatory response in depression. Depression is related to several aspects of immunity. The regulation of the immune system and inflammation by autophagy may lead to the development or deterioration of mental disorders. This review highlights the role of autophagy and neuroinflammation in the pathophysiology of depression, sumaries the autophagy-targeting small moleculars, and discusses a novel therapeutic strategy based on anti-inflammatory mechanisms that target autophagy to treat the disease.

The Multiple Roles of Autophagy in Neural Function and Diseases

Autophagy involves the sequestration and delivery of cytoplasmic materials to lysosomes, where proteins, lipids, and organelles are degraded and recycled. According to the way the cytoplasmic components are engulfed, autophagy can be divided into macroautophagy, microautophagy, and chaperone-mediated autophagy. Recently, many studies have found that autophagy plays an important role in neurological diseases, including Alzheimer's disease, Parkinson's disease, Huntington's disease, neuronal excitotoxicity, and cerebral ischemia. Autophagy maintains cell homeostasis in the nervous system via degradation of misfolded proteins, elimination of damaged organelles, and regulation of apoptosis and inflammation. AMPK-mTOR, Beclin 1, TP53, endoplasmic reticulum stress, and other signal pathways are involved in the regulation of autophagy and can be used as potential therapeutic targets for neurological diseases. Here, we discuss the role, functions, and signal pathways of autophagy in neurological diseases, which will shed light on the pathogenic mechanisms of neurological diseases and suggest novel targets for therapies.

Epigenetic regulation of autophagy in neuroinflammation and synaptic plasticity

Autophagy is a conserved cellular mechanism that enables the degradation and recycling of cellular organelles and proteins via the lysosomal pathway. In neurodevelopment and maintenance of neuronal homeostasis, autophagy is required to regulate presynaptic functions, synapse remodeling, and synaptic plasticity. Deficiency of autophagy has been shown to underlie the synaptic and behavioral deficits of many neurological diseases such as autism, psychiatric diseases, and neurodegenerative disorders. Recent evidence reveals that dysregulated autophagy plays an important role in the initiation and progression of neuroinflammation, a common pathological feature in many neurological disorders leading to defective synaptic morphology and plasticity. In this review, we will discuss the regulation of autophagy and its effects on synapses and neuroinflammation, with emphasis on how autophagy is regulated by epigenetic mechanisms under healthy and diseased conditions.

The beneficial role of autophagy in multiple sclerosis: Yes or No?

Multiple sclerosis (MS) is a chronic progressive demyelinating disease of the central nervous system (CNS) due to an increase of abnormal peripherally auto-reactive T lymphocytes which elicit autoimmunity. The main pathophysiology of MS is myelin sheath damage by immune cells and a defect in the generation of myelin by oligodendrocytes. Macroautophagy/autophagy is a critical degradation process that eliminates dysfunctional or superfluous cellular components. Autophagy has the property of a double-edged sword in MS in that it may have both beneficial and detrimental effects on MS neuropathology. Therefore, this review illustrates the protective and harmful effects of autophagy with regard to this disease. Autophagy prevents the progression of MS by reducing oxidative stress and inflammatory disorders. In contrast, over-activated autophagy is associated with the progression of MS neuropathology and in this case the use of autophagy inhibitors may alleviate the pathogenesis of MS. Furthermore, autophagy provokes the activation of different immune and supporting cells that play an intricate role in the pathogenesis of MS. Autophagy functions in the modulation of MS neuropathology by regulating cell proliferation related to demyelination and remyelination. Autophagy enhances remyelination by increasing the activity of oligodendrocytes, and astrocytes. However, autophagy induces demyelination by activating microglia and T cells. In conclusion, specific autophagic activators of oligodendrocytes, and astrocytes, and specific autophagic inhibitors of dendritic cells (DCs), microglia and T cells induce protective effects against the pathogenesis of MS.Abbreviations: ALS: amyotrophic lateral sclerosis; APCs: antigen-presenting cells; BBB: blood-brain barrier; CSF: cerebrospinal fluid; CNS: central nervous system; DCs: dendritic cells; EAE: experimental autoimmune encephalomyelitis; ER: endoplasmic reticulum; LAP: LC3-associated phagocytosis; MS: multiple sclerosis; NCA: non-canonical autophagy; OCBs: oligoclonal bands; PBMCs: peripheral blood mononuclear cells; PD: Parkinson disease; ROS: reactive oxygen species; UPR: unfolded protein response.

The aging mouse CNS is protected by an autophagy-dependent microglia population promoted by IL-34

Microglia harness an unutilized health-promoting potential in age-related neurodegenerative and neuroinflammatory diseases, conditions like progressive multiple sclerosis (MS). Our research unveils an microglia population emerging in the cortical brain regions of aging mice, marked by ERK1/2, Akt, and AMPK phosphorylation patterns and a transcriptome indicative of activated autophagy - a process critical for cellular adaptability. By deleting the core autophagy gene Ulk1 in microglia, we reduce this population in the central nervous system of aged mice. Notably, this population is found dependent on IL-34, rather than CSF1, although both are ligands for CSF1R. When aging mice are exposed to autoimmune neuroinflammation, the loss of autophagy-dependent microglia leads to neural and glial cell death and increased mortality. Conversely, microglial expansion mediated by IL-34 exhibits a protective effect. These findings shed light on an autophagy-dependent neuroprotective microglia population as a potential target for treating age-related neuroinflammatory conditions, including progressive MS.

Microglia regulation of central nervous system myelin health and regeneration

Microglia are resident macrophages of the central nervous system that have key functions in its development, homeostasis and response to damage and infection. Although microglia have been increasingly implicated in contributing to the pathology that underpins neurological dysfunction and disease, they also have crucial roles in neurological homeostasis and regeneration. This includes regulation of the maintenance and regeneration of myelin, the membrane that surrounds neuronal axons, which is required for axonal health and function. Myelin is damaged with normal ageing and in several neurodegenerative diseases, such as multiple sclerosis and Alzheimer disease. Given the lack of approved therapies targeting myelin maintenance or regeneration, it is imperative to understand the mechanisms by which microglia support and restore myelin health to identify potential therapeutic approaches. However, the mechanisms by which microglia regulate myelin loss or integrity are still being uncovered. In this Review, we discuss recent work that reveals the changes in white matter with ageing and neurodegenerative disease, how this relates to microglia dynamics during myelin damage and regeneration, and factors that influence the regenerative functions of microglia.

Melatonin prevents EAAC1 deletion-induced retinal ganglion cell degeneration by inhibiting apoptosis and senescence

Normal tension glaucoma (NTG) is referred to as a progressive degenerative disorder of the retinal ganglion cells (RGCs), resulting in nonreversible visual defects, despite intraocular pressure levels within the statistically normal range. Current therapeutic strategies for NTG yield limited benefits. Excitatory amino acid carrier 1 (EAAC1) knockout (EAAC1-/- ) in mice has been shown to induce RGC degeneration without elevating intraocular pressure, mimicking pathological characteristics of NTG. In this study, we explored whether daily oral administration of melatonin could block RGCs loss and prevent retinal morphology and function defects associated with EAAC1 deletion. We also explored the molecular mechanisms underlying EAAC1 deletion-induced RGC degeneration and the neuroprotective effects of melatonin. Our RNA sequencing and in vivo data indicated EAAC1 deletion caused elevated oxidative stress, activation of apoptosis and cellular senescence pathways, and neuroinflammation in RGCs. However, melatonin administration efficiently prevented these detrimental effects. Furthermore, we investigated the potential role of apoptosis- and senescence-related redox-sensitive factors in EAAC1 deletion-induced RGCs degeneration and the neuroprotective effects of melatonin administration. We observed remarkable upregulation of p53, whereas NRF2 and Sirt1 expression were significantly decreased in EAAC1-/- mice, which were prevented by melatonin treatment, suggesting that melatonin exerted its neuroprotective effects possibly through modulating NRF2/p53/Sirt1 redox-sensitive signaling pathways. Overall, our study provided a solid foundation for the application of melatonin in the management of NTG.

Studying Autophagy in Microglia: Overcoming the Obstacles

In this chapter, we provide an overview of the main techniques and experimental approaches that can be used to analyze autophagy flux in microglia, the brain-resident macrophages. For this purpose, we first briefly introduce the main peculiarities of microglial biology, describe the basic mechanisms and functions of autophagy, and summarize the evidence accumulated so far on the role of autophagy in the regulation of microglial survival and functions, mainly phagocytosis and inflammation. Then, we highlight conceptual and technical aspects of autophagic recycling and microglial physiology that need to be taken into account for the accurate evaluation of autophagy flux in microglia. Finally, we describe the main assays that can be used to analyze the complete sequence of autophagosome formation and degradation or autophagy flux, mainly in cultured microglia and in vivo. The main approaches include indirect tracking of autophagosomes by autophagic enzymes such as LC3 by western blot and fluorescence-based confocal microscopy, as well as direct analysis of autophagic vesicles by electron microscopy. We also discuss the advantages and disadvantages of using these methods in specific experimental contexts and highlight the need to complement LC3 and/or electron microscopy data with analysis of other autophagic effectors and lysosomal proteins that participate in the initiation and completion of autophagy flux, respectively. In summary, we provide an experimental guide for the analysis of autophagosome turnover in microglia, emphasizing the need to combine as many markers and complementary approaches as possible to fully characterize the status of autophagy flux in microglia.

Immune response of BV-2 microglial cells is impacted by peroxisomal beta-oxidation

Microglia are crucial for brain homeostasis, and dysfunction of these cells is a key driver in most neurodegenerative diseases, including peroxisomal leukodystrophies. In X-linked adrenoleukodystrophy (X-ALD), a neuroinflammatory disorder, very long-chain fatty acid (VLCFA) accumulation due to impaired degradation within peroxisomes results in microglial defects, but the underlying mechanisms remain unclear. Using CRISPR/Cas9 gene editing of key genes in peroxisomal VLCFA breakdown (Abcd1, Abcd2, and Acox1), we recently established easily accessible microglial BV-2 cell models to study the impact of dysfunctional peroxisomal β-oxidation and revealed a disease-associated microglial-like signature in these cell lines. Transcriptomic analysis suggested consequences on the immune response. To clarify how impaired lipid degradation impacts the immune function of microglia, we here used RNA-sequencing and functional assays related to the immune response to compare wild-type and mutant BV-2 cell lines under basal conditions and upon pro-inflammatory lipopolysaccharide (LPS) activation. A majority of genes encoding proinflammatory cytokines, as well as genes involved in phagocytosis, antigen presentation, and co-stimulation of T lymphocytes, were found differentially overexpressed. The transcriptomic alterations were reflected by altered phagocytic capacity, inflammasome activation, increased release of inflammatory cytokines, including TNF, and upregulated response of T lymphocytes primed by mutant BV-2 cells presenting peptides. Together, the present study shows that peroxisomal β-oxidation defects resulting in lipid alterations, including VLCFA accumulation, directly reprogram the main cellular functions of microglia. The elucidation of this link between lipid metabolism and the immune response of microglia will help to better understand the pathogenesis of peroxisomal leukodystrophies.

Neuroinflammation-Modulating Agent SB1617 Enhances LC3-Associated Phagocytosis to Mitigate Tau Pathology

Tau protein aggregation and propagation in neurons and surrounding microglia are well-known risk factors for neurodegenerative diseases. Therefore, emerging therapeutic strategies that target neuroinflammatory activity in microglia have the potential to prevent tauopathy. Here, we explored the microglia-mediated neuroprotective function of SB1617 against tau aggregation. Our study revealed that SB1617-inactivated pathogenic M1-like microglia, reduced the secretion of pro-inflammatory cytokines via translational regulation, and induced microglial polarization toward the M2 phenotype and phagocytic function. Furthermore, we observed that extracellular pathogenic tau aggregates were eliminated via LC3-associated phagocytosis. The in vivo efficacy of SB1617 was confirmed in mice with traumatic brain injury in which SB1617 exerted neuroprotective effects by reducing pathogenic tau levels through microglia-mediated anti-inflammatory activity. Our results indicated that SB1617-mediated microglial surveillance with LC3-associated phagocytosis is a critical molecular mechanism in the regulation of tau proteostasis. This study provides new insights into tauopathies and directions for developing novel therapies for neurodegenerative diseases.

Bilirubin impacts microglial autophagy via the Akt-mTOR signaling pathway

Bilirubin encephalopathy is a severe complication of neonatal hyperbilirubinemia. With elevation of serum unconjugated bilirubin (UCB) levels, UCB crosses the blood-brain barrier and possibly leads to neurological dysfunction. Neuroinflammation is recognized as a prominent pathological feature in bilirubin encephalopathy. Recent studies have suggested that autophagy plays a crucial role in the inflammatory response. However, the potential effect of microglial autophagy in the pathogenesis of bilirubin encephalopathy remains uncertain. The in vitro findings verified that in primary cultured microglia, UCB significantly reduced the ratio of LC3B-II to LC3B-I and downregulated the expression of ATG5, Beclin-1, and ATG7, while increasing the expression of p62/SQSTM1. The results showed that UCB could decrease the number of mCherry-EGFP-LC3 positive puncta, even when chloroquine (CQ) was applied to block the microglial autophagy flux. Mechanistically, UCB was found to upregulate the expression of TLR4 and increase the phosphorylation levels of Akt and mammalian target of rapamycin (mTOR). Promoting microglial autophagy by treatment with Rapamycin (RAPA), an mTOR inhibitor, decreased the levels of NOD-like receptor protein 3 (NLRP3) inflammasome components and IL-1β, rescued microglial overactivation, and improved neurological functions. These data indicated that UCB could impact microglial autophagy via the Akt-mTOR signaling pathway and synergistically promote neuroinflammatory responses. Enhancing autophagy might disrupt the assembly of NLRP3 inflammasome, attenuate UCB-induced neuroinflammation, and improve the prognosis of model rats with bilirubin encephalopathy. In conclusion, this study implies that regulating microglial autophagy might be a promising therapeutic strategy for bilirubin encephalopathy.

The role of glial autophagy in Alzheimer's disease

Although Alzheimer's disease is the most pervasive neurodegenerative disorder, the mechanism underlying its development is still not precisely understood. Available data indicate that pathophysiology of this disease may involve impaired autophagy in glial cells. The dysfunction is manifested as reduced ability of astrocytes and microglia to clear abnormal protein aggregates. Consequently, excessive accumulation of amyloid beta plaques and neurofibrillary tangles activates microglia and astrocytes leading to decreased number of mature myelinated oligodendrocytes and death of neurons. These pathologic effects of autophagy dysfunction can be rescued by pharmacological activation of autophagy. Therefore, a deeper understanding of the molecular mechanisms involved in autophagy dysfunction in glial cells in Alzheimer's disease may lead to the development of new therapeutic strategies. However, such strategies need to take into consideration differences in regulation of autophagy in different types of neuroglia.

Reactive nitrogen species as therapeutic targets for autophagy/mitophagy modulation to relieve neurodegeneration in multiple sclerosis: Potential application for drug discovery

Multiple sclerosis (MS) is a neuroinflammatory disease with limited therapeutic effects, eventually developing into handicap. Seeking novel therapeutic strategies for MS is timely important. Active autophagy/mitophagy could mediate neurodegeneration, while its roles in MS remain controversial. To elucidate the exact roles of autophagy/mitophagy and reveal its in-depth regulatory mechanisms, we conduct a systematic literature study and analyze the factors that might be responsible for divergent results obtained. The dynamic change levels of autophagy/mitophagy appear to be a determining factor for final neuron fate during MS pathology. Excessive neuronal autophagy/mitophagy contributes to neurodegeneration after disease onset at the active MS phase. Reactive nitrogen species (RNS) serve as key regulators for redox-related modifications and participate in autophagy/mitophagy modulation in MS. Nitric oxide (•NO) and peroxynitrite (ONOO-), two representative RNS, could nitrate or nitrosate Drp1/parkin/PINK1 pathway, activating excessive mitophagy and aggravating neuronal injury. Targeting RNS-mediated excessive autophagy/mitophagy could be a promising strategy for developing novel anti-MS drugs. In this review, we highlight the important roles of RNS-mediated autophagy/mitophagy in neuronal injury and review the potential therapeutic compounds with the bioactivities of inhibiting RNS-mediated autophagy/mitophagy activation and attenuating MS progression. Overall, we conclude that reactive nitrogen species could be promising therapeutic targets to regulate autophagy/mitophagy for multiple sclerosis treatment.

Prophylactic effect of chronic immunosuppression in a mouse model of CSF-1 receptor-related leukoencephalopathy

Mutations leading to colony-stimulating factor-1 receptor (CSF-1R) loss-of-function or haploinsufficiency cause CSF1R-related leukoencephalopathy (CRL), an adult-onset disease characterized by loss of myelin and neurodegeneration, for which there is no effective therapy. Symptom onset usually occurs in the fourth decade of life and the penetrance of disease in carriers is high. However, familial studies have identified a few carriers of pathogenic CSF1R mutations that remain asymptomatic even in their seventh decade of life, raising the possibility that the development and severity of disease might be influenced by environmental factors. Here we report new cases in which long-term glucocorticoid treatment is associated with asymptomatic status in elder carriers of pathogenic CSF-1R mutations. The main objective of the present study was to investigate the link between chronic immunosuppression initiated pre-symptomatically and resistance to the development of symptomatic CRL, in the Csf1r+/- mouse model. We show that chronic prednisone administration prevents the development of memory, motor coordination and social interaction deficits, as well as the demyelination, neurodegeneration and microgliosis associated with these deficits. These findings are in agreement with the preliminary clinical observations and support the concept that pre-symptomatic immunosuppression is protective in patients carrying pathogenic CSF1R variants associated with CRL. Proteomic analysis of microglia and oligodendrocytes indicates that prednisone suppresses processes involved in microglial activation and alleviates senescence and improves fitness of oligodendrocytes. This analysis also identifies new potential targets for therapeutic intervention.

Optineurin tunes outside-in signaling to regulate lysosome biogenesis and phagocytic clearance in the retina

Balancing the competing demands of phagolysosomal degradation and autophagy is a significant challenge for phagocytic tissues. Yet how this plasticity is accomplished in health and disease is poorly understood. In the retina, circadian phagocytosis and degradation of photoreceptor outer segments by the postmitotic retinal pigment epithelium (RPE) are essential for healthy vision. Disrupted autophagy due to mechanistic target of rapamycin (mTOR) overactivation in the RPE is associated with blinding macular degenerations; however, outer segment degradation is unaffected in these diseases, indicating that distinct mechanisms regulate these clearance mechanisms. Here, using advanced imaging and mouse models, we identify optineurin as a key regulator that tunes phagocytosis and lysosomal capacity to meet circadian demands and helps prioritize outer segment clearance by the RPE in macular degenerations. High-resolution live-cell imaging implicates optineurin in scissioning outer segment tips prior to engulfment, analogous to microglial trogocytosis of neuronal processes. Optineurin is essential for recruiting light chain 3 (LC3), which anchors outer segment phagosomes to microtubules and facilitates phagosome maturation and fusion with lysosomes. This dynamically activates transcription factor EB (TFEB) to induce lysosome biogenesis in an mTOR-independent, transient receptor potential-mucolipin 1 (TRPML1)-dependent manner. RNA-seq analyses show that expression of TFEB target genes temporally tracks with optineurin recruitment and that lysosomal and autophagy genes are controlled by distinct transcriptional programs in the RPE. The unconventional plasma membrane-to-nucleus signaling mediated by optineurin ensures outer segment degradation under conditions of impaired autophagy in macular degeneration models. Independent regulation of these critical clearance mechanisms would help safeguard the metabolic fitness of the RPE throughout the organismal lifespan.

Lysosomal acidification dysfunction in microglia: an emerging pathogenic mechanism of neuroinflammation and neurodegeneration

Microglia are the resident innate immune cells in the brain with a major role in orchestrating immune responses. They also provide a frontline of host defense in the central nervous system (CNS) through their active phagocytic capability. Being a professional phagocyte, microglia participate in phagocytic and autophagic clearance of cellular waste and debris as well as toxic protein aggregates, which relies on optimal lysosomal acidification and function. Defective microglial lysosomal acidification leads to impaired phagocytic and autophagic functions which result in the perpetuation of neuroinflammation and progression of neurodegeneration. Reacidification of impaired lysosomes in microglia has been shown to reverse neurodegenerative pathology in Alzheimer's disease. In this review, we summarize key factors and mechanisms contributing to lysosomal acidification impairment and the associated phagocytic and autophagic dysfunction in microglia, and how these defects contribute to neuroinflammation and neurodegeneration. We further discuss techniques to monitor lysosomal pH and therapeutic agents that can reacidify impaired lysosomes in microglia under disease conditions. Finally, we propose future directions to investigate the role of microglial lysosomal acidification in lysosome-mitochondria crosstalk and in neuron-glia interaction for more comprehensive understanding of its broader CNS physiological and pathological implications.

Modulation of the immunity and inflammation by autophagy

Autophagy, a highly conserved cellular self-degradation pathway, has emerged with novel roles in the realms of immunity and inflammation. Genome-wide association studies have unveiled a correlation between genetic variations in autophagy-related genes and heightened susceptibility to autoimmune and inflammatory diseases. Subsequently, substantial progress has been made in unraveling the intricate involvement of autophagy in immunity and inflammation through functional studies. The autophagy pathway plays a crucial role in both innate and adaptive immunity, encompassing various key functions such as pathogen clearance, antigen processing and presentation, cytokine production, and lymphocyte differentiation and survival. Recent research has identified novel approaches in which the autophagy pathway and its associated proteins modulate the immune response, including noncanonical autophagy. This review provides an overview of the latest advancements in understanding the regulation of immunity and inflammation through autophagy. It summarizes the genetic associations between variants in autophagy-related genes and a range of autoimmune and inflammatory diseases, while also examining studies utilizing transgenic animal models to uncover the in vivo functions of autophagy. Furthermore, the review delves into the mechanisms by which autophagy dysregulation contributes to the development of three common autoimmune and inflammatory diseases and highlights the potential for autophagy-targeted therapies.

Microglial expression of CD83 governs cellular activation and restrains neuroinflammation in experimental autoimmune encephalomyelitis

Microglial activation during neuroinflammation is crucial for coordinating the immune response against neuronal tissue, and the initial response of microglia determines the severity of neuro-inflammatory diseases. The CD83 molecule has been recently shown to modulate the activation status of dendritic cells and macrophages. Although the expression of CD83 is associated with early microglia activation in various disease settings, its functional relevance for microglial biology has been elusive. Here, we describe a thorough assessment of CD83 regulation in microglia and show that CD83 expression in murine microglia is not only associated with cellular activation but also with pro-resolving functions. Using single-cell RNA-sequencing, we reveal that conditional deletion of CD83 results in an over-activated state during neuroinflammation in the experimental autoimmune encephalomyelitis model. Subsequently, CD83-deficient microglia recruit more pathogenic immune cells to the central nervous system, deteriorating resolving mechanisms and exacerbating the disease. Thus, CD83 in murine microglia orchestrates cellular activation and, consequently, also the resolution of neuroinflammation.

Autophagy enables microglia to engage amyloid plaques and prevents microglial senescence

Dysfunctional autophagy has been implicated in the pathogenesis of Alzheimer's disease (AD). Previous evidence suggested disruptions of multiple stages of the autophagy-lysosomal pathway in affected neurons. However, whether and how deregulated autophagy in microglia, a cell type with an important link to AD, contributes to AD progression remains elusive. Here we report that autophagy is activated in microglia, particularly of disease-associated microglia surrounding amyloid plaques in AD mouse models. Inhibition of microglial autophagy causes disengagement of microglia from amyloid plaques, suppression of disease-associated microglia, and aggravation of neuropathology in AD mice. Mechanistically, autophagy deficiency promotes senescence-associated microglia as evidenced by reduced proliferation, increased Cdkn1a/p21Cip1, dystrophic morphologies and senescence-associated secretory phenotype. Pharmacological treatment removes autophagy-deficient senescent microglia and alleviates neuropathology in AD mice. Our study demonstrates the protective role of microglial autophagy in regulating the homeostasis of amyloid plaques and preventing senescence; removal of senescent microglia is a promising therapeutic strategy.

Emodin attenuates inflammation and demyelination in experimental autoimmune encephalomyelitis

Emodin, a substance extracted from herbs such as rhubarb, has a protective effect on the central nervous system. However, the potential therapeutic effect of emodin in the context of multiple sclerosis remains unknown. In this study, a rat model of experimental autoimmune encephalomyelitis was established by immune induction to simulate multiple sclerosis, and the rats were intraperitoneally injected with emodin (20 mg/kg/d) from the day of immune induction until they were sacrificed. In this model, the nucleotide-binding domain-like receptor family pyrin domain containing 3 (NLRP3) inflammasome and the microglia exacerbated neuroinflammation, playing an important role in the development of multiple sclerosis. In addition, silent information regulator of transcription 1 (SIRT1)/peroxisome proliferator-activated receptor-alpha coactivator (PGC-1α) was found to inhibit activation of the NLRP3 inflammasome, and SIRT1 activation reduced disease severity in experimental autoimmune encephalomyelitis. Furthermore, treatment with emodin decreased body weight loss and neurobehavioral deficits, alleviated inflammatory cell infiltration and demyelination, reduced the expression of inflammatory cytokines, inhibited microglial aggregation and activation, decreased the levels of NLRP3 signaling pathway molecules, and increased the expression of SIRT1 and PGC-1α. These findings suggest that emodin improves the symptoms of experimental autoimmune encephalomyelitis, possibly through regulating the SIRT1/PGC-1α/NLRP3 signaling pathway and inhibiting microglial inflammation. These findings provide experimental evidence for treatment of multiple sclerosis with emodin, enlarging the scope of clinical application for emodin.

Attenuating Neuronal Autophagy Alleviates Inflammatory Injury in OGDDeprived Co-culture of HT22 with BV2

Neuronal CX3CL1 suppressed microglial inflammation by binding to its receptor CX3CR1 expressed on microglia. Neuronal autophagy was prominently activated by cerebral ischemia, whereas CX3CL1 expression in autophagic neurons was conversely down-regulated to exacerbate microglial inflammation. Accordingly, this study was meant to investigate whether ischemia-activated microglial inflammation could be repressed by promoting CX3CL1 expression via the attenuation of neuronal autophagy. Immunofluorescence showed that autophagy predominantly occurred in neurons but barely in microglia. Western blot and immunofluorescence demonstrated that attenuating HT22 autophagy significantly increased its CX3CL1 expression and subsequently mitigated the BV2-mediated inflammatory responses, as indicated by decreased inflammatory factors of NF-κB-p65, IL-6, IL-1β, TNF-α, and PGE2. Meanwhile, CCK-8, Nissl staining, and FJC staining showed that an OGD (Oxygen-glycogen deprivation)-created neuronal injury was greatly alleviated by CX3CL1-suppressed microglial inflammation. Contrarily, elevating HT22 autophagy markedly decreased its CX3CL1 expression, which consequently worsened microglial inflammation and the neuronal injury. Our data suggests that attenuating neuronal autophagy may be an effective method to alleviate a microglial inflammatory injury after an ischemic stroke.

Stem cell-derived brainstem mouse astrocytes obtain a neurotoxic phenotype in vitro upon neuroinflammation

BACKGROUND

Astrocytes respond to injury and disease through a process known as reactive astrogliosis, of which inflammatory signaling is one subset. This inflammatory response is heterogeneous with respect to the inductive stimuli and the afflicted central nervous system region. This is of plausible importance in e.g. traumatic axonal injury (TAI), where lesions in the brainstem carries a particularly poor prognosis. In fact, astrogliotic forebrain astrocytes were recently suggested to cause neuronal death following axotomy. We therefore sought to assess if ventral brainstem- or rostroventral spinal astrocytes exert similar effects on motor neurons in vitro.

METHODS

We derived brainstem/rostroventral spinal astrocyte-like cells (ES-astrocytes) and motor neurons using directed differentiation of mouse embryonic stem cells (ES). We activated the ES-astrocytes using the neurotoxicity-eliciting cytokines interleukin- (IL-) 1α and tumor necrosis factor-(TNF-)α and clinically relevant inflammatory mediators. In co-cultures with reactive ES-astrocytes and motor neurons, we assessed neurotoxic ES-astrocyte activity, similarly to what has previously been shown for other central nervous system (CNS) regions.

RESULTS

We confirmed the brainstem/rostroventral ES-astrocyte identity using RNA-sequencing, immunocytochemistry, and by comparison with primary subventricular zone-astrocytes. Following cytokine stimulation, the c-Jun N-terminal kinase pathway down-stream product phosphorylated c-Jun was increased, thus demonstrating ES-astrocyte reactivity. These reactive ES-astrocytes conferred a contact-dependent neurotoxic effect upon co-culture with motor neurons. When exposed to IL-1β and IL-6, two neuroinflammatory cytokines found in the cerebrospinal fluid and serum proteome following human severe traumatic brain injury (TBI), ES-astrocytes exerted similar effects on motor neurons. Activation of ES-astrocytes by these cytokines was associated with pathways relating to endoplasmic reticulum stress and altered regulation of MYC.

CONCLUSIONS

Ventral brainstem and rostroventral spinal cord astrocytes differentiated from mouse ES can exert neurotoxic effects in vitro. This highlights how neuroinflammation following CNS lesions can exert region- and cell-specific effects. Our in vitro model system, which uniquely portrays astrocytes and neurons from one niche, allows for a detailed and translationally relevant model system for future studies on how to improve neuronal survival in particularly vulnerable CNS regions following e.g. TAI.

SENP3-mediated deSUMOylation of c-Jun facilitates microglia-induced neuroinflammation after cerebral ischemia and reperfusion injury

Recent evidences have implicated that SENP3 is a deSUMOylase which possesses neuronal damage effects in cerebral ischemia. However, its role in microglia remains poorly understood. Here, we found that SENP3 was upregulated in the peri-infarct areas of mice following ischemic stroke. Furthermore, knockdown of SENP3 significantly inhibits the expression of proinflammatory cytokines and chemokines in microglial cells. Mechanistically, SENP3 can bind and then mediated the deSUMOylation of c-Jun, which activated its transcriptional activity, ultimately followed by the activation of MAPK/AP-1 signaling pathway. In addition, microglia-specific SENP3 knockdown alleviated ischemia-induced neuronal damage, and markedly diminished infract volume, ameliorated sensorimotor and cognitive function in animals subjected to ischemic stroke. These results indicated SENP3 functions as a novel regulator of microglia-induced neuroinflammation by activating the MAPK/AP-1 signaling pathway via mediating the deSUMOylation of c-Jun. Interventions of SENP3 expression or its interaction with c-Jun would be a new and promising therapeutic strategy for ischemic stroke.

Regulation of microglia polarization after cerebral ischemia

Stroke ranks second as a leading cause of death and permanent disability globally. Microglia, innate immune cells in the brain, respond rapidly to ischemic injury, triggering a robust and persistent neuroinflammatory reaction throughout the disease's progression. Neuroinflammation plays a critical role in the mechanism of secondary injury in ischemic stroke and is a significant controllable factor. Microglia activation takes on two general phenotypes: the pro-inflammatory M1 type and the anti-inflammatory M2 type, although the reality is more complex. The regulation of microglia phenotype is crucial to controlling the neuroinflammatory response. This review summarized the key molecules and mechanisms of microglia polarization, function, and phenotypic transformation following cerebral ischemia, with a focus on the influence of autophagy on microglia polarization. The goal is to provide a reference for the development of new targets for the treatment for ischemic stroke treatment based on the regulation of microglia polarization.

LC3-associated phagocytosis promotes glial degradation of axon debris after injury in Drosophila models

Glial engulfment of neuron-derived debris after trauma, during development, and in neurodegenerative diseases supports nervous system functions. However, mechanisms governing the efficiency of debris degradation in glia have remained largely unexplored. Here we show that LC3-associated phagocytosis (LAP), an engulfment pathway assisted by certain autophagy factors, promotes glial phagosome maturation in the Drosophila wing nerve. A LAP-specific subset of autophagy-related genes is required in glia for axon debris clearance, encoding members of the Atg8a (LC3) conjugation system and the Vps34 lipid kinase complex including UVRAG and Rubicon. Phagosomal Rubicon and Atg16 WD40 domain-dependent conjugation of Atg8a mediate proper breakdown of internalized axon fragments, and Rubicon overexpression in glia accelerates debris elimination. Finally, LAP promotes survival following traumatic brain injury. Our results reveal a role of glial LAP in the clearance of neuronal debris in vivo, with potential implications for the recovery of the injured nervous system.

Modulation of microglial metabolism facilitates regeneration in demyelination

Microglia exhibit diverse phenotypes in various central nervous system disorders and metabolic pathways exert crucial effects on microglial activation and effector functions. Here, we discovered two novel distinct microglial clusters, functionally associated with enhanced phagocytosis (PEMs) and myelination (MAMs) respectively, in human patients with multiple sclerosis by integrating public snRNA-seq data. Microglia adopt a PEMs phenotype during the early phase of demyelinated lesions, predominated in pro-inflammatory responses and aggravated glycolysis, while MAMs mainly emerged during the later phase, with regenerative signatures and enhanced oxidative phosphorylation. In addition, microglial triggering receptor expressed on myeloid cells 2 (Trem2) was greatly involved in the phenotype transition in demyelination, but not indispensable for microglia transition toward PEMs. Rosiglitazone could promote microglial phenotype conversion from PEMs to MAMs, thus favoring myelin repair. Taken together, these findings provide insights into therapeutic interventions targeting immunometabolism to switch microglial phenotypes and facilitate regenerative capacity in demyelination.