New tools for studying microglia in the mouse and human CNS

Hippocampal microglial activation induces cognitive impairment and allodynia through neuronal plasticity changes in male mice with neuropathic pain

Clinical evidence indicates that cognitive impairment is a common comorbidity of chronic pain, including neuropathic pain, but the mechanism underlying this comorbidity remains unclear. Neuroinflammation plays a critical role in the development of both neuropathic pain and cognitive impairment. A previous study showed that minocycline, an inhibitor of microglia, ameliorated allodynia and cognitive impairment in partial sciatic nerve ligation (PSNL) mice. Therefore, the current study examined a potential role of brain microglia in allodynia and cognitive impairment in male mice with neuropathic pain due to PSNL. Immunohistochemistry of the microglial markers ionized calcium-binding adapter molecule 1 (Iba1), transmembrane protein 119 (TMEM119), and purinergic receptor P2Y12 (P2RY12) was performed to examine microglial status. Two weeks after PSNL, significant microglial activation was observed in the hippocampus and amygdala, but not in the perirhinal cortex. Inhibition of brain-region-specific microglia with a local microinjection of clodronate liposomes was examined to elucidate the involvement of these microglia in PSNL-induced allodynia and cognitive impairment. Local clodronate liposome microinjection to the hippocampus, but not the amygdala, ameliorated allodynia and cognitive impairment. Other changes in the hippocampus of PSNL mice, e.g., decreased hippocampal dendrite length and intersections number, were prevented by microinjection of clodronate liposomes. The current findings suggest hippocampal microglia are related to cognitive impairment and allodynia through neuronal plasticity changes observed in PSNL mice. Blocking hippocampal microglia-mediated neuroinflammation may be a novel approach for reducing comorbidities such as cognitive impairment associated with neuropathic pain.

Drivers and shapers of macrophages specification in the developing brain

The brain harbors two major macrophage populations: microglia reside within the brain parenchyma, while border-associated macrophages (BAMs) are situated at central nervous system (CNS) interfaces. BAMs can be further classified into distinct subsets based on their localization: perivascular macrophages surround blood vessels, meningeal macrophages reside in the leptomeninges, dura macrophages in the dura mater, and choroid plexus macrophages are confined to the choroid plexus. The environmental factors and molecular mechanisms driving the specification of these macrophage populations are still being elucidated. Deciphering the communication pathways between CNS macrophages and their tissue niches during development, homeostasis, and pathologic conditions offers significant potential for treating a wide range of brain disorders, from neurodevelopmental and neuroinflammatory diseases to neurovascular and neurodegenerative conditions. With this short review, we will address the current understanding and knowledge gaps in the field, as well as the future directions for the upcoming years.

Inhibiting 15-PGDH blocks blood-brain barrier deterioration and protects mice from Alzheimer's disease and traumatic brain injury

Alzheimer's disease (AD) and traumatic brain injury (TBI) are currently untreatable neurodegenerative disorders afflicting millions of people worldwide. These conditions are pathologically related, and TBI is one of the greatest risk factors for AD. Although blood-brain barrier (BBB) disruption drives progression of both AD and TBI, strategies to preserve BBB integrity have been hindered by lack of actionable targets. Here, we identify 15-hydroxyprostaglandin dehydrogenase (15-PGDH), an enzyme that catabolizes eicosanoids and other anti-inflammatory mediators, as a therapeutic candidate that protects the BBB. We demonstrate that 15-PGDH is enriched in BBB-associated myeloid cells and becomes markedly elevated in human and mouse models of AD and TBI, as well as aging, another major risk factor for AD. Pathological increase in 15-PGDH correlates with pronounced oxidative stress, neuroinflammation, and neurodegeneration, alongside profound BBB structural degeneration characterized by astrocytic endfeet swelling and functional impairment. Pharmacologic inhibition or genetic reduction of 15-PGDH in AD and TBI models strikingly mitigates oxidative damage, suppresses neuroinflammation, and restores BBB integrity. Most notably, inhibiting 15-PGDH not only halts neurodegeneration but also preserves cognitive function at levels indistinguishable from healthy controls. Remarkably, these neuroprotective effects in AD are achieved without affecting amyloid pathology, underscoring a noncanonical mechanism for treating AD. In a murine microglia cell line exposed to amyloid beta oligomer, major protection was demonstrated by multiple anti-inflammatory substrates that 15-PGDH degrades. Thus, our findings position 15-PGDH inhibition as a broad-spectrum strategy to protect the BBB and thereby preserve brain health and cognition in AD and TBI.

Loss of insulin signaling in microglia impairs cellular uptake of Aβ and neuroinflammatory response exacerbating AD-like neuropathology

Insulin receptors are present on cells throughout the body, including the brain. Dysregulation of insulin signaling in neurons and astrocytes has been implicated in altered mood, cognition, and the pathogenesis of Alzheimer's disease (AD). To define the role of insulin signaling in microglia, the primary phagocytes in the brain critical for maintenance and damage repair, we created mice with an inducible microglia-specific insulin receptor knockout (MG-IRKO). RiboTag profiling of microglial mRNAs revealed that loss of insulin signaling results in alterations of gene expression in pathways related to innate immunity and cellular metabolism. In vitro, loss of insulin signaling in microglia results in metabolic reprogramming with an increase in glycolysis and impaired uptake of Aβ. In vivo, MG-IRKO mice exhibit alterations in mood and social behavior, and when crossed with the 5xFAD mouse model of AD, the resultant mice exhibit increased levels of Aβ plaque and elevated neuroinflammation. Thus, insulin signaling in microglia plays a key role in microglial cellular metabolism and the ability of the cells to take up Aβ, such that reduced insulin signaling in microglia alters mood and social behavior and accelerates AD pathogenesis. Together, these data indicate key roles of insulin action in microglia and the potential of targeting insulin signaling in microglia in treatment of AD.

Chronic Stress Modulates Microglial Activation Dynamics, Shaping Priming Responses to Subsequent Stress

(1) Background: The high recurrence rate and individual differences in stress susceptibility contribute to the diverse symptoms of depression, making full recovery and relapse prevention challenging. Emerging evidence suggests that fluctuations in microglial activity are closely linked to depression progression under chronic stress exposure. Changes in the brain microenvironment can elicit microglial priming, enhancing their sensitivity to external stimuli. However, few studies have longitudinally examined how microglial characteristics evolve throughout depression progression. (2) Methods: In this study, we investigated microglial morphological changes and their responses to acute stress at different stages of depression using the chronic unpredictable mild stress (CUMS) paradigm in mice. (3) Results: Our findings reveal that in the dentate gyrus, microglial activation indices, including cell number and morphology, exhibit distinct dynamic patterns depending on CUMS exposure duration. Notably, after 2 and 4 weeks of CUMS exposure followed by acute stress re-exposure, microglia display opposing response patterns. In contrast, after 6 weeks of CUMS exposure, primed microglia exhibit dysfunction, failing to respond to acute stress. Notably, depressive behaviors are not prominent after 2 weeks of CUMS exposure but become more pronounced after 4 and 6 weeks of exposure. Additionally, regardless of CUMS duration, body weight demonstrates an intrinsic capacity to normalize after stress cessation. (4) Conclusions: These findings suggest that microglial priming responses are state-dependent, either enhancing or suppressing secondary stimulus responses, or exceeding physiological limits, thereby preventing further activation. This study provides novel insights into the role of microglial priming in stress vulnerability and its contribution to depression progression.

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.

Revisiting the Pathogenesis of X-Linked Adrenoleukodystrophy

BACKGROUND

X-ALD is a white matter (WM) disease caused by mutations in the ABCD1 gene encoding the transporter of very-long-chain fatty acids (VLCFAs) into peroxisomes. Strikingly, the same ABCD1 mutation causes either devastating brain inflammatory demyelination during childhood or, more often, progressive spinal cord axonopathy starting in middle-aged adults. The accumulation of undegraded VLCFA in glial cell membranes and myelin has long been thought to be the central mechanism of X-ALD.

METHODS

This review discusses studies in mouse and drosophila models that have modified our views of X-ALD pathogenesis.

RESULTS

In the Abcd1 knockout (KO) mouse that mimics the spinal cord disease, the late manifestations of axonopathy are rapidly reversed by ABCD1 gene transfer into spinal cord oligodendrocytes (OLs). In a peroxin-5 KO mouse model, the selective impairment of peroxisomal biogenesis in OLs achieves an almost perfect phenocopy of cerebral ALD. A drosophila knockout model revealed that VLCFA accumulation in glial myelinating cells causes the production of a toxic lipid able to poison axons and activate inflammatory cells. Other mouse models showed the critical role of OLs in providing energy substrates to axons. In addition, studies on microglial changing substates have improved our understanding of neuroinflammation.

CONCLUSIONS

Animal models supporting a primary role of OLs and axonal pathology and a secondary role of microglia allow us to revisit of X-ALD mechanisms. Beyond ABCD1 mutations, pathogenesis depends on unidentified contributors, such as genetic background, cell-specific epigenomics, potential environmental triggers, and stochasticity of crosstalk between multiple cell types among billions of glial cells and neurons.

Direct microglia replacement reveals pathologic and therapeutic contributions of brain macrophages to a monogenic neurological disease

Krabbe disease, also named globoid cell (GC) leukodystrophy (GLD) for its distinct lipid-laden macrophages, is a severe leukodystrophy caused by galactosylceramidase (GALC) mutations. Hematopoietic stem cell transplant (HSCT) ameliorates disease and is associated with central nervous system (CNS) engraftment of GALC+ donor macrophages. Yet, the role of macrophages in GLD pathophysiology and HSCT remains unclear. Using single-cell sequencing, we revealed early interferon response signatures that preceded progressively severe macrophage dyshomeostasis and identified a molecular signature of GCs, which we validated in human brain specimens. Genetic depletion and direct microglia replacement by CNS monocyte injection rapidly replaced >80% of endogenous microglia with healthy macrophages in the twitcher (GalcW355∗) mouse model of GLD. Perinatal microglia replacement completely normalized transcriptional signatures, rescued histopathology, and doubled average survival. Overall, we uncovered distinct forms of microglial dysfunction and evidence that direct, CNS-limited microglia replacement improves a monogenic neurodegenerative disease, identifying a promising therapeutic target.

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

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

Microglial TMEM119 binds to amyloid-β to promote its clearance in an Aβ-depositing mouse model of Alzheimer's disease

The progression of Alzheimer's disease (AD) involves temporal dynamics of microglial activation. Restoring or maintaining microglial homeostasis has emerged as a promising therapeutic strategy to combat AD. Transmembrane protein 119 (TMEM119) is a homeostatic marker of microglia but has not been fully studied under AD pathological conditions. Here, we observed that amyloid-beta (Aβ) induced a decrease in TMEM119 expression in microglia, and TMEM119 deficiency increased AD progression in the 5×FAD mouse model. TMEM119 bound to Aβ oligomers and recruited low-density lipoprotein receptor 1, which in turn degraded TMEM119 itself. Overexpression of TMEM119 in microglia enhanced their phagocytic activity and alleviated cognitive deficits in 5xFAD mice. Administration of the small molecules Kartogenin and SRI-011381, which we found enhanced TMEM119 expression, substantially promoted Aβ clearance and improved cognitive function in AD mice, even during the mid-stage of the disease. These findings identify TMEM119 as a promising therapeutic target for AD.

Beyond relapses: How BTK inhibitors are shaping the future of progressive MS treatment

Multiple sclerosis is a biologically and clinically heterogenous inflammatory demyelinating disease, driven by relapsing and progressive mechanisms, all individuals experiencing varying degrees of both. Existing highly effective therapies target peripheral inflammation and reduce relapse rates but have limited efficacy in progressive MS due to poor blood-brain barrier penetration and inability to address neurodegeneration. Bruton's tyrosine kinase (BTK) inhibitors represent an emerging therapeutic class offering a novel mechanism targeting BTK, which is expressed by both B cells and myeloid cells, including microglia within the CNS. Pre-clinical, Phase II, and Phase III clinical trials have demonstrated promising results in modulating progressive disease in both relapsing and non-relapsing MS patients. In contrast, the evidence regarding impact on relapse biology remains mixed and somewhat inconclusive. This review highlights gaps in current therapeutic strategies, examines the latest evidence for the efficacy and safety of BTK inhibitors in MS, and explores the future landscape of MS treatment.

PLA2G15 is a BMP hydrolase and its targeting ameliorates lysosomal disease

Lysosomes catabolize lipids and other biological molecules, maintaining cellular and organismal homeostasis. Bis(monoacylglycero)phosphate (BMP), a major lipid constituent of intralysosomal vesicles, stimulates lipid-degrading enzymes and is altered in various human conditions, including neurodegenerative diseases1,2. Although lysosomal BMP synthase was recently discovered3, the enzymes mediating BMP turnover remain elusive. Here we show that lysosomal phospholipase PLA2G15 is a physiological BMP hydrolase. We further demonstrate that the resistance of BMP to lysosomal hydrolysis arises from its unique sn2, sn2' esterification position and stereochemistry, as neither feature alone confers resistance. Purified PLA2G15 catabolizes most BMP species derived from cell and tissue lysosomes. Furthermore, PLA2G15 efficiently hydrolyses synthesized BMP stereoisomers with primary esters, challenging the long-held thought that BMP stereochemistry alone ensures resistance to acid phospholipases. Conversely, BMP with secondary esters and S,S stereoconfiguration is stable in vitro and requires acyl migration for hydrolysis in lysosomes. Consistent with our biochemical data, PLA2G15-deficient cells and tissues accumulate several BMP species, a phenotype reversible by supplementing wild-type PLA2G15 but not its inactive mutant. Targeting PLA2G15 reduces the cholesterol accumulation in fibroblasts of patients with Niemann-Pick disease type C1 and significantly ameliorates disease pathologies in Niemann-Pick disease type C1-deficient mice, leading to an extended lifespan. Our findings established the rules governing BMP stability in lysosomes and identified PLA2G15 as a lysosomal BMP hydrolase and a potential target for therapeutic intervention in neurodegenerative diseases.

Macrophage Lyn Kinase Is a Sex-Specific Regulator of Post-Subarachnoid Hemorrhage Neuroinflammation

BACKGROUND

Lyn kinase is a member of the Src family of tyrosine kinases, primarily known for its role in regulating immune cell signaling. It can phosphorylate and modulate the activity of various proteins involved in immune responses, including Toll-like receptor 4 (TLR4). TLR4-mediated inflammatory pathways have been extensively studied; however, the sex-specific interaction of TLR4 and Lyn in neuroinflammation after aneurysmal subarachnoid hemorrhage (SAH) has yet to be investigated. SAH occurs due to a ruptured aneurysm, and the consequences often lead to neuroinflammation and cognitive impairments. In our study, we investigated the sex-specific involvement of Lyn kinase in regulating TLR4 signaling to understand the TLR4-mediated inflammatory response after SAH.

METHODS

Cell-specific Lyn knockout mice of both sexes were used for this study. Wild-type and conditional knockout mouse brains were analyzed by multicolor flow cytometry, immunohistochemistry, and western blotting at postoperative day 7 following SAH surgery. An unbiased spatial transcriptomic analysis was performed with the frozen mouse brain tissues. A 3-dimensional brain stroke model and cerebrospinal fluid samples of patients with SAH were also used for this study.

RESULTS

Our overall animal and patient data from flow cytometry, immunohistochemistry, western blot, cognitive function tests, and spatial transcriptomic data revealed that Lyn kinase is a sex-specific regulator in inflammatory cytokine production, red blood cell phagocytosis, neuronal apoptosis, and cognitive function, as well as a negative regulator of TLR4 signaling pathways.

CONCLUSIONS

Our results highlight sex-specific modulation of Lyn kinase activity in TLR4 signaling after hemorrhagic stroke and indicate that successful treatment of neuroinflammation may require sex-specific treatments.

Exploring tumor-associated macrophages in glioblastoma: from diversity to therapy

Glioblastoma is the most aggressive and lethal cancer of the central nervous system, presenting substantial treatment challenges. The current standard treatment, which includes surgical resection followed by temozolomide and radiation, offers limited success. While immunotherapies, such as immune checkpoint inhibitors, have proven effective in other cancers, they have not demonstrated significant efficacy in GBM. Emerging research highlights the pivotal role of tumor-associated macrophages (TAMs) in supporting tumor growth, fostering treatment resistance, and shaping an immunosuppressive microenvironment. Preclinical studies show promising results for therapies targeting TAMs, suggesting potential in overcoming these barriers. TAMs consist of brain-resident microglia and bone marrow-derived macrophages, both exhibiting diverse phenotypes and functions within the tumor microenvironment. This review delves into the origin, heterogeneity, and functional roles of TAMs in GBM, underscoring their dual roles in tumor promotion and suppression. It also summarizes recent progress in TAM-targeted therapies, which may, in combination with other treatments like immunotherapy, pave the way for more effective and personalized strategies against this aggressive malignancy.

Neuronal CCL2 responds to hyperglycaemia and contributes to anxiety disorders in the context of diabetes

Anxiety disorders are frequently observed in patients with diabetes and can be associated with several diabetes-related factors. Here we determine that hyperglycaemia is a major cause for the development of anxiety disorders through a C-C motif chemokine ligand 2 (CCL2)-dependent mechanism. By adopting complementary strategies, we demonstrate that neuron-specific (not peripheral) CCL2 mediates anxiety-like behaviours in streptozotocin-induced diabetic mice. Mechanistically, high glucose levels induce Tonicity-responsive enhancer-binding protein (TonEBP)-dependent CCL2 expression in neurons, leading to microglial activation in a paracrine manner. Similar phenotypes are also observed in high-fat diet-induced diabetic mice, independent of insulin signalling. Furthermore, we reveal that neuronal CCL2 in the medial prefrontal cortex and ventral hippocampus synergistically induces anxiety-like behaviours, indicating brain region-specific effects on diabetic mice. Finally, we confirm that the neuronal TonEBP-CCL2 axis and inflammatory pathways are both upregulated in patients with diabetes. Conclusively, neuronal CCL2 is specifically increased by hyperglycaemia and contributes to anxiety disorders, providing additional insights into the link between diabetes and mental health disorders.

Attenuation of Blood-Brain Barrier Disruption in Traumatic Brain Injury via Inhibition of NKCC1 Cotransporter: Insights into the NF-κB/NLRP3 Signaling Pathway

Following traumatic brain injury (TBI), inhibition of the Na+-K+-Cl- cotransporter1 (NKCC1) has been observed to alleviate damage to the blood-brain barrier (BBB). However, the underlying mechanism for this effect remains unclear. This study aimed to investigate the mechanisms by which inhibiting the NKCC1 attenuates disruption of BBB integrity in TBI. The TBI model was induced in C57BL/6 mice through a controlled cortical impact device, and an in vitro BBB model was established using Transwell chambers. Western blot (WB) analysis was used to evaluate NOD-like receptor family pyrin domain containing 3 (NLRP3) inflammasome and nuclear factor-kappaB (NF-κB) pathway proteins. Flow cytometry and transendothelial electrical resistance (TEER) were employed to assess endothelial cell apoptosis levels and BBB integrity. ELISA was utilized to measure cytokines interleukin-1β (IL-1β) and matrix metalloproteinase-9 (MMP-9). Immunofluorescence techniques were used to evaluate protein levels and the nuclear translocation of the rela (p65) subunit. The Evans blue dye leakage assay and the brain wet-dry weight method were utilized to assess BBB integrity and brain swelling. Inhibition of NKCC1 reduced the level of NLRP3 inflammasome and the secretion of IL-1β and MMP-9 in microglia. Additionally, NKCC1 inhibition suppressed the activation of the NF-κB signaling pathway, which in turn decreased the level of NLRP3 inflammasome. The presence of NLRP3 inflammasome in BV2 cells led to compromised BBB integrity within an inflammatory milieu. Following TBI, an upregulation of NLRP3 inflammasome was observed in microglia, astrocytes, vascular endothelial cells, and neurons. Furthermore, inhibiting NKCC1 resulted in a decrease in the positive rate of NLRP3 inflammasome in microglia and the levels of inflammatory cytokines IL-1β and MMP-9 after TBI, which correlated with BBB damage and the development of cerebral edema. These findings demonstrate that the suppression of the NKCC1 cotransporter protein alleviates BBB disruption through the NF-κB/NLRP3 signaling pathway following TBI.

Brain region and sex differences in human microglia morphology and function

Microglia exhibit complex and dynamic morphology that is linked to function. Altered microglia function has been implicated in multiple diseases of the brain, including elevated phagocytosis of neuronal dendritic spines in schizophrenia. However, understanding the relationship between altered microglia and pathophysiology first requires a clearer picture of microglia morphology in the non-diseased brain, which has yet to be fully established. Here, we deploy immunostaining and confocal microscopy to sample over 1,300 microglia from two prefrontal cortex (PFC) subregions in postmortem human brain (3 males, 3 females). We use Neurolucida 360 to trace the 3-dimensional structure of these microglia and quantify interactions with dendritic spines. We find that PFC microglia in male subjects display overall more complex branching than in female subjects, and subgenual anterior cingulate cortex (sgACC) microglia are more complexly branched with more round somas than those in the dorsolateral PFC (DLPFC), irrespective of sex. Furthermore, a lower proportion of phagocytic burden in sgACC microglia involves engulfment of dendritic spines compared to DLPFC. Overall, our results paint a detailed and nuanced picture of microglia morphology and function in subjects unaffected by psychiatric or neurologic illness that can be used as a benchmark for future studies of the diseased brain.

Research on Peripheral Nerve Aging and Degeneration: Cellular Changes and Mechanism Exploration From the Perspective of Single-Cell Sequencing

As age increases, there are structural and functional alterations in the peripheral nervous system (PNS), significantly affecting movement, sensation and autonomic function. Understanding the characteristics and mechanisms of PNS aging is crucial for preventing and treating related diseases. This study employed single-cell sequencing technology to analyse the dorsal root ganglia (DRG) and sciatic nerve (SN) of aging rats, in comparison with adult rats. The research investigated the mechanisms underlying PNS aging and degeneration, revealing the transcriptional profiles of various cell types. Significant differences were observed in the proportion of Schwann cells between the DRG and SN of adult and aged rats. The Kyoto Encyclopedia of Genes and Genomes (KEGG), Gene Ontology (GO) and Gene Set Enrichment Analysis (GSEA) revealed that pathways related to neurodegeneration were upregulated in Schwann cells. Additionally, lipid metabolism pathways were upregulated in the SN of aged rats, suggesting that certain lipid signalling molecules may influence cell proliferation. Through further re-clustering of myelinating Schwann cells, six distinct subtypes were identified. The anti-aging protein protocadherin 9 (PCDH9) was preliminarily screened and found to be significantly downregulated with age. In vitro experiments confirmed that PCDH9 expression is associated with Schwann cell proliferation and differentiation. By using gene expression analysis and cell type across several age groups, this study offers important insights into the mechanisms of PNS aging and degeneration.

GAL-201 as a Promising Amyloid-β-Targeting Small-Molecule Approach for Alzheimer's Disease Treatment: Consistent Effects on Synaptic Plasticity, Behavior and Neuroinflammation

Soluble oligomeric forms of Amyloid-β (Aβ) are considered the major toxic species leading to the neurodegeneration underlying Alzheimer's disease (AD). Therefore, drugs that prevent oligomer formation might be promising. The atypical dipeptide GAL-201 is orally bioavailable and interferes as a modulator of Aβ aggregation. It binds to aggregation-prone, misfolded Aβ monomers with high selectivity and affinity, thereby preventing the formation of toxic oligomers. Here, we demonstrate that the previously observed protective effect of GAL-201 on synaptic plasticity occurs irrespective of shortages and post-translational modifications (tested isoforms: Aβ1-42, Aβ(p3-42), Aβ1-40 and 3NTyr(10)-Aβ). Interestingly, the neuroprotective activity of a single dose of GAL-201 was still present after one week and correlated with a prevention of Aβ-induced spine loss. Furthermore, we could observe beneficial effects on spine morphology as well as the significantly reduced activation of proinflammatory microglia and astrocytes in the presence of an Aβ1-42-derived toxicity. In line with these in vitro data, GAL-201 additionally improved hippocampus-dependent spatial learning in the "tgArcSwe" AD mouse model after a single subcutaneous administration. By this means, we observed changes in the deposition pattern: through the clustering of misfolded monomers as off-pathway non-toxic Aβ agglomerates, toxic oligomers are removed. Our results are in line with previously collected preclinical data and warrant the initiation of Investigational New Drug (IND)-enabling studies for GAL-201. By demonstrating the highly efficient detoxification of β-sheet monomers, leading to the neutralization of Aβ oligomer toxicity, GAL-201 represents a promising drug candidate against Aβ-derived pathophysiology present in AD.

MSC transplantation ameliorates depression in lupus by suppressing Th1 cell-shaped synaptic stripping

Systemic lupus erythematosus (SLE), an autoimmune disease, can cause psychiatric disorders, particularly depression, via immune activation. Human umbilical cord mesenchymal stromal cell (hUCMSC) transplantation (MSCT) has been shown to ameliorate immune dysfunction in SLE by inducing immune tolerance. However, whether MSCT can relieve the depressive symptoms in SLE remains incompletely understood. Here, we demonstrate that MSCT relieved early-onset depression-like behavior in both genetically lupus-prone (MRL/lpr) and pristane-induced lupus mice by rescuing impaired hippocampal synaptic connectivity. Transplanted hUCMSCs targeted Th1 cell-derived IFN-γ to inhibit neuronal JAK/STAT1 signaling and downstream CCL8 expression, reducing phagocytic microglia apposition to alleviate synaptic engulfment and neurological dysfunction in young (8-week-old) lupus mice. Systemic delivery of exogenous IFN-γ blunted MSCT-mediated alleviation of synaptic loss and depressive behavior in lupus mice, suggesting that the IFN-γ/CCL8 axis may be an effective therapeutic target and that MSCT is a potential therapy for lupus-related depression. In summary, transplanted hUCMSCs can target systemic immunity to ameliorate psychiatric disorders by rescuing synaptic loss, highlighting the active role of neurons as intermediaries between systemic immunity and microglia in this process.

Inactivation of microglial LXRβ in early postnatal mice impairs microglia homeostasis and causes long-lasting cognitive dysfunction

Microglia, the largest population of brain immune cells, play an essential role in regulating neuroinflammation by removing foreign materials and debris and in cognition by pruning synapses. Since liver X receptor β (LXRβ) has been identified as a regulator of microglial homeostasis, this study examined whether its removal from microglia affects neuroinflammation and cognitive function. We used a cell-specific tamoxifen-inducible Cre-loxP-mediated recombination to remove LXRβ from microglia specifically. We now report that ablation of LXRβ in microglia in early postnatal life led to a reduction in microglial numbers, distinct morphological changes indicative of microglial activation, and enhanced synapse engulfment accompanied by cognitive deficits. Removal of LXRβ from microglia in adult mice caused no cognitive defects. RNAseq analysis of microglia revealed that loss of LXRβ led to reduced expression of SAll1, a master regulator of microglial homeostasis, while increasing expression of genes associated with microglial activation and CNS disease. This study demonstrates distinctly different functions of microglial LXRβ in developing and adult mice and points to long-term consequences of defective LXRβ signaling in microglia in early life.

Noradrenergic signaling controls Alzheimer's disease pathology via activation of microglial β2 adrenergic receptors

Norepinephrine (NE) is a potent anti-inflammatory agent in the brain. In Alzheimer's disease (AD), the loss of NE signaling heightens neuroinflammation and exacerbates amyloid pathology. NE inhibits surveillance activity of microglia, the brain's resident immune cells, via their β2 adrenergic receptors (β2ARs). Here, we investigate the role of microglial β2AR signaling in AD pathology in the 5xFAD mouse model of AD. We found that loss of cortical NE projections preceded the degeneration of NE-producing neurons and that microglia in 5xFAD mice, especially those microglia that were associated with plaques, significantly downregulated β2AR expression early in amyloid pathology. Importantly, dampening microglial β2AR signaling worsened plaque load and the associated neuritic damage, while stimulating microglial β2AR signaling attenuated amyloid pathology. Our results suggest that microglial β2AR could be explored as a potential therapeutic target to modify AD pathology.

Differential tissue and cellular distribution of chemokine C-C motif ligand 2 in grey/white matters of healthy and simian immunodeficiency virus infected monkey

Previous studies have shown that CCL2 concentration is higher in cerebrospinal fluid than in plasma of health and human immunodeficiency virus (HIV) infected individuals, suggesting an extra source of CCL2 in brain. Brain cellular CCL2 has been broadly studied in cultured cells and its in-vivo cellular distribution has been investigated in rodent experimental autoimmune encephalomyelitis model. However, its cellular distribution in grey and white matter (GM, WM) remains elusive. We explored this issue using healthy and simian immunodeficiency virus (SIV) infected monkeys and found: 1) Neurons were a major source of CCL2-like immunoreactivity (CCL2-ir) in normal GM, and corpus callosum (CC) ependyma showed high density of CCL2-ir. 2) Upon SIV infection, CCL2-ir was strikingly raised in GM neurons, and in CC ependyma. 3) Brain vascular-perivascular cells were a large source of CCL2-ir in normal GM and WM, which was relatively larger in CC WM than in GM. 4) Vascular-perivascular CCL2-ir proportional areas were significantly enhanced by SIV infection in both GM and CC WM. 5) Microglia seemed not to express CCL2 in healthy brain. Microglia-marker and CCL2-ir co-labeled cells were significantly increased by SIV infection. 6) A vast of macrophage-like cells were situated along infected CC ependyma, suggesting a large number of monocytes be crossing ependyma, which may be related to establishment of viral reservoir. In conclusion, our study provides valuable insights into the cellular sources and alterations of CCL2 in the monkey brain under normal and SIV-infected conditions, which may promote better understanding of CCL2 in related neurological processes.

TDP-43 Cryptic RNAs in Perry Syndrome: Differences across Brain Regions and TDP-43 Proteinopathies

BACKGROUND

Perry syndrome (PS) is a rare and fatal hereditary autosomal dominant neurodegenerative disorder caused by mutations in dynactin (DCTN1). PS brains accumulate inclusions positive for ubiquitin, transactive-response DNA-binding protein of 43 kDa (TDP-43), and to a lesser extent dynactin.

OBJECTIVES

Little is known regarding the contributions of TDP-43, an RNA binding protein that represses cryptic exon inclusion, in PS. Therefore, we sought to identify the degree of TDP-43 dysfunction in two regions of PS brains.

METHODS

We evaluated the levels of insoluble pTDP-43 and TDP-43-regulated cryptic RNAs and protein in the caudate nucleus and substantia nigra of 7 PS cases, 12 cases of frontotemporal lobar degeneration (FTLD) with TDP-43 pathology, and 11 cognitively healthy controls without TDP-43 pathology.

RESULTS

Insoluble pTDP-43 protein levels were detected in PS brains to a similar extent in the caudate nucleus and substantia nigra but lower than those in FTLD brains. The caudate nucleus of PS showed accumulation of eight TDP-43-regulated cryptic RNAs (ACTL6B, CAMK2B, STMN2, UNC13A, KCNQ2, ATG4B, GPSM2, and HDGFL2) and cryptic protein (HDGFL2) characteristic of FTLD. Conversely, only one cryptic target, UNC13A, reached significance in the substantia nigra despite similar pTDP-43 levels.

CONCLUSION

We detected TDP-43 cryptic RNAs and protein in PS caudate nucleus. Given the importance of cryptic exon biology in the development of biomarkers, and the identification of novel targets for therapeutic intervention, it is imperative we understand the consequences of TDP-43 dysfunction across different brain regions and determine the targets that are specific and common to TDP-43 proteinopathies. © 2025 The Author(s). Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Novel application of cycloastragenol target microglia for the treatment of Alzheimer's disease: Evidence from single-cell analysis, network pharmacology and experimental assessment

BACKGROUND

Cycloastragenol (CAG), a compound extracted from Astragalus, is known for its telomerase activation and anti-inflammatory, antioxidant properties. However, its potential pharmacological effects on Alzheimer's disease (AD) remain unclear.

PURPOSE

This study aimed to explore potential targets and molecular mechanisms for the role of CAG in alzheimer's disease (AD) treatment.

METHODS

CAG was administered to 5 × FAD mice. The senescent cell count was verified by senescence-associated β-galactosidase (SA-β-gal) staining. The impact of CAG on microglial phagocytosis was assessed by in vitro and in vivo assays. The potential targets of CAG were identified by network pharmacology and single-nucleus RNA sequencing (snRNA-seq). The underlying mechanism was validated by molecular docking, surface plasmon resonance (SPR) and western blotting.

RESULTS

CAG effectively ameliorated cognitive impairments and microglial senescence in 5 × FAD mice. In vivo and in vitro experiments revealed that CAG modulated microglial phagocytic activity and reduced hippocampal Aβ deposition The analysis of single-nucleus RNA sequencing data of AD patients reported 13 microglial targets for AD intervention. Phosphodiesterase 4B (PDE4B) was identified as the target through which CAG regulated microglial activity by utilizing network pharmacology, molecular docking and SPR. Western blotting revealed that the PDE4B/CREB/BDNF pathway may mediate the regulatory effect of CAG.

CONCLUSION

CAG can enhance microglial phagocytosis and alleviate memory dysfunction and amyloid plaque pathology. Our findings suggest that CAG may regulate microglial function through its interaction with PDE4B, providing a novel therapeutic strategy for AD.

Microglia-derived sEV: Friend or foe in the pathogenesis of cognitive impairment

As immune cells, microglia serve a dual role in cognition. Microglia-derived sEV actively contribute to the development of cognitive impairment by selectively targeting specific cells through various substances such as proteins, RNA, DNA, lipids, and metabolic waste. In recent years, there has been an increasing focus on understanding the pathogenesis and therapeutic potential of sEV. This comprehensive review summarizes the detrimental effects of M1 microglial sEV on pathogenic protein transport, neuroinflammation, disruption of the blood-brain barrier (BBB), neuronal death and synaptic dysfunction in relation to cognitive damage. Additionally, it highlights the beneficial effects of M2 microglia on alleviating cognitive impairment based on evidence from cellular experiments and animal studies. Furthermore, since microglial-secreted sEV can be found in cerebrospinal fluid or cross the BBB into plasma circulation, they play a crucial role in diagnosing cognitive impairment. However, using sEV as biomarkers is still at an experimental stage and requires further clinical validation. Future research should aim to explore the mechanisms underlying microglial involvement in various nervous system disorders to identify novel targets for clinical interventions.

Itaconate restrains acute proinflammatory activation of microglia after traumatic brain injury in mice

Traumatic brain injury (TBI) rapidly triggers proinflammatory activation of microglia, contributing to secondary brain damage post-TBI. Although the governing role of energy metabolism in shaping the inflammatory phenotype and function of immune cells has been increasingly recognized, the specific alterations in microglial bioenergetics post-TBI remain poorly understood. Itaconate, a metabolite produced by the enzyme aconitate decarboxylase 1 [IRG1; encoded by immune responsive gene 1 (Irg1)], is a pivotal metabolic regulator in immune cells, particularly in macrophages. Because microglia are macrophages of the brain parenchyma, the IRG1/itaconate pathway likely modulates microglial inflammatory responses. In this study, we explored the role of the IRG1/itaconate pathway in regulating microglial bioenergetics and inflammatory activation post-TBI using a mouse controlled cortical impact (CCI) model. We isolated microglia before and 4 and 12 hours after TBI and observed a swift but transient increase in glycolysis coupled with a prolonged disruption of mitochondrial metabolism after injury. Despite an up-regulation of Irg1 expression, itaconate in microglia declined after TBI. Microglia-specific Irg1 gene knockout (Irg1-Mi-KO) exacerbated metabolic changes, intensified proinflammatory activation and neurodegeneration, and worsened certain long-term neurological deficits. Supplementation with 4-octyl itaconate (OI) reinstated the use and oxidative metabolism of glucose, glutamine, and fatty acid, thereby enhancing microglial bioenergetics post-TBI. OI supplementation also attenuated proinflammatory activation and neurodegeneration and improved long-term neurological outcomes. These results suggest that therapeutically targeting the itaconate pathway could improve microglial energy metabolism and neurological outcomes after TBI.

Microglial reprogramming enhances antitumor immunity and immunotherapy response in melanoma brain metastases

Melanoma is one of the tumor types with the highest risk of brain metastasis. However, the biology of melanoma brain metastasis and the role of the brain immune microenvironment in treatment responses are not yet fully understood. Using preclinical models and single-cell transcriptomics, we have identified a mechanism that enhances antitumor immunity in melanoma brain metastasis. We show that activation of the Rela/Nuclear Factor κB (NF-κB) pathway in microglia promotes melanoma brain metastasis. Targeting this pathway elicits microglia reprogramming toward a proinflammatory phenotype, which enhances antitumor immunity and reduces brain metastatic burden. Furthermore, we found that proinflammatory microglial markers in melanoma brain metastasis are associated with improved responses to immune checkpoint inhibitors in patients and targeting Rela/NF-κB pathway in mice improves responses to these therapies in the brain, suggesting a strategy to enhance antitumor immunity and responses to immune checkpoint inhibitors in patients with melanoma brain metastasis.

FKBP51 inhibition ameliorates neurodegeneration and motor dysfunction in the neuromelanin-SNCA mouse model of Parkinson's disease

Parkinson's disease (PD) is characterized by the loss of neuromelanin (NM)-containing dopaminergic (DA) neurons in the substantia nigra (SN) pars compacta (SNpc) and the buildup of α-synuclein (α-syn) inclusions, called Lewy bodies. To investigate the roles of NM and α-syn in DA neuron degeneration, we modeled PD by inducing NM accumulation in a humanized α-syn mouse model (Snca-; PAC-Tg(SNCAWT)) via the expression of human tyrosinase in the SN. We found that this mouse strain develops naturally progressive motor dysfunction and dopaminergic neuronal loss in the SN with aging. Upon tyrosinase injection, NM-containing neurons developed p62 and ubiquitin inclusions. Furthermore, the upregulation of genes associated with microglial activation in the midbrain indicated a role of pro-inflammatory factors in neurodegeneration. Midbrain RNA sequencing confirmed the microglial response and identified Fkbp5 as one of the more dysregulated genes. Next, we showed that FKBP51(51 kDa) was significantly upregulated with aging and in PD human brains. Pharmacological treatment with SAFit2, a potent FKBP51 inhibitor, led to a reduction in ubiquitin-positive inclusions, prevention of neurodegeneration in the SNpc, and improved motor function in NM-SNCAWT mice. These results highlight the critical role of FKBP51 in PD and propose SAFit2 as a promising therapeutic candidate for reducing neurodegeneration in PD.

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.

Serum starvation induces cytosolic DNA trafficking via exosome and autophagy-lysosome pathway in microglia

The imbalance of microglial homeostasis is highly associated with age-related neurological diseases, where cytosolic endogenous DNA is also likely to be found. As the main medium for storing biological information, endogenous DNA could be localized to cellular compartments normally free of DNA when cells are stimulated. However, the intracellular trafficking of endogenous DNA remains unidentified. In this study, we demonstrated that nuclear DNA (nDNA) and mitochondrial DNA (mtDNA), as the components of endogenous DNA, undergo different intracellular trafficking under conditions of microglial homeostasis imbalance induced by serum starvation. Upon detecting various components of endogenous DNA in the cytoplasmic and extracellular microglia, we found that cytosolic nDNA primarily exists in a free form and undergoes degradation through the autophagy-lysosome pathway. In contrast, cytosolic mtDNA predominantly exists in a membrane-wrapped form and is trafficked through both exosome and autophagy-lysosome pathways, with the exosome pathway serving as the primary one. When the autophagy-lysosome pathway was inhibited, there was an increase in exosomes. More importantly, the inhibition of the autophagy-lysosome pathway resulted in enhanced trafficking of mtDNA through the exosome pathway. These findings unveiled the crosstalk between these two pathways in the trafficking of microglial cytosolic DNA and thus provide new insights into intervening in age-related neurological diseases.

Microglia-like cells from patient monocytes demonstrate increased phagocytic activity in probable Alzheimer's disease

Alzheimer's disease (AD) is a neurodegenerative disorder that is characterized by the accumulation of amyloid plaques, phosphorylated tau tangles and microglia toxicity, resulting in neuronal death and cognitive decline. Since microglia are recognized as one of the key players in the disease, it is crucial to understand how microglia operate in disease conditions and incorporate them into models. The studies on human microglia functions are thought to reflect the post-symptomatic stage of the disease. Recently developed methods involve induced microglia-like cells (iMGs) generated from patients' blood monocytes or induced pluripotent stem cells (iPSCs) as an alternative to studying the microglia cells in vitro. In this research, we aimed to investigate the phenotype and inflammatory responses of iMGs from AD patients. Monocytes derived from blood using density gradient centrifugation were differentiated into iMGs using a cytokine cocktail, including granulocyte-macrophage colony-stimulating factor (GM-CSF) and interleukin-34 (IL-34). After differentiation, cells were assessed by morphological analysis and a microglia surface marker, TMEM119. We used stimulants, lipopolysaccharide (LPS) and beta-amyloid, to examine iMGs' functions. Results showed that iMGs derived from AD patients exhibited increased secretion of pro-inflammatory cytokines upon LPS stimulation. Furthermore, their phagocytic ability was also heightened in stimulated and unstimulated conditions, with cells derived from patients showing increased phagocytic activity compared to healthy controls. Overall, these findings suggest that iMGs derived from patients using the direct conversion method possess characteristics of human microglia, making them an easy and promising model for studying microglia function in AD.

Sex and Region-Specific Differences in Microglial Morphology and Function Across Development

Microglia are exceptionally dynamic resident innate immune cells within the central nervous system, existing on a continuum of morphologies and functions throughout their lifespan. They play vital roles in response to injuries and infections, clearing cellular debris, and maintaining neural homeostasis throughout development. Emerging research suggests that microglia are strongly influenced by biological factors, including sex, developmental stage, and their local environment. This review synthesizes findings on sex differences in microglial morphology and function in key brain regions, including the frontal cortex, hippocampus, amygdala, hypothalamus, basal ganglia, and cerebellum, across the lifespan. Where available, we examine how gonadal hormones influence these microglial characteristics. Additionally, we highlight the limitations of relying solely on morphology to infer function and underscore the need for comprehensive, multimodal approaches to guide future research. Ultimately, this review aims to advance the dialogue on these spatiotemporally heterogeneous cells and their implications for sex differences in brain function and vulnerability to neurological and psychiatric disorders.

The roles of glioma-associated macrophages/microglia and potential targets for anti-glioma therapy

Glioblastoma (GBM) is the central nervous system tumor with the most aggressive behavior, and no definitive therapy has yet been found. The tumor microenvironment of GBM is immunosuppressive and is considered a 'cold tumor' with low lymphocytic infiltration, but is characterized by a high proportion of glioma-associated macrophages/microglia (GAMs). GAMs promote tumor growth and also affect treatment resistance in GBM. In this review, we describe the origin and classification of GAMs in humans and describe the mechanisms of their activation and the cell-cell interactions between tumor cells and GAMs. We also describe the history of GAM detection methods, especially immunohistochemistry, and discusses the merits and limitations of these techniques. In addition, we summarized chemotactic factors for GAMs and the therapies targeting these factors. Recent single-cell RNA analysis and spatial analysis add new insights to our previous knowledge of GAMs. Based on these studies, GBM therapies targeting GAMs are expected to be further developed.

WebSEQ: A New Tool for Democratizing Omics Data Sharing

The relative ease of generation and proliferation of omics datasets has moved considerably faster than the effective dissemination of these data to the scientific community. Despite advancements in making raw data publicly available, many researchers struggle with data analysis and integration. We propose sharing analyzed data through user-friendly platforms to enhance accessibility. Here, we present a free, online tool, for sharing basic omics data in a searchable and user-friendly format. Importantly, it requires no coding or prior computational knowledge to build-only a data spreadsheet. Overall, this tool facilitates the exploration of transcriptomic, proteomic, and metabolomics data, which is crucial for understanding glial diversity and function. This initiative underscores the importance of accessible molecular data in advancing neuroscience research.

Exogenous L-fucose attenuates depression induced by chronic unpredictable stress: Implicating core fucosylation has an antidepressant potential

Core fucosylation is one of the most essential modifications of the N-glycans, catalyzed by α1,6-fucosyltransferase (Fut8), which transfers fucose from guanosine 5'-diphosphate (GDP)-fucose to the innermost N-acetylglucosamine residue of N-glycans in an α1-6 linkage. Our previous studies demonstrated that lipopolysaccharide (LPS) can induce a more robust neuroinflammatory response in Fut8 homozygous knockout (KO) (Fut8-/-) and heterozygous KO (Fut8+/-) mice contrasted to the wild-type (Fut8+/+) mice. Exogenous administration of L-fucose suppressed LPS-induced neuroinflammation. Numerous studies indicate that neuroinflammation plays a vital role in the development of depression. Here, we investigated whether core fucosylation regulates depression induced by chronic unpredictable stress (CUS), a well-established model for depression. Our results showed that Fut8+/- mice exhibited depressive-like behaviors and increased neuroinflammation earlier than Fut8+/+ mice. Administration of L-fucose significantly reduced CUS-induced depressive-like behaviors and pro-inflammatory cytokine levels in Fut8+/- mice. The L-fucose treatment produced antidepressant effects by attenuating the complex formation between gp130 and the interleukin-6 (IL-6) receptor and the JAK2/STAT3 signaling pathway. Notably, L-fucose treatment increased dendritic spine density and postsynaptic density protein 95 (PSD-95) expression, which were suppressed in CUS-induced depression. Furthermore, the effects of L-fucose on the CUS-induced depression were also observed in Fut8+/+ mice. Our results clearly demonstrate that L-fucose ameliorates neuroinflammation and synaptic defects in CUS-induced depression, implicating that core fucosylation has significant anti-neuroinflammatory activity and an antidepressant potential.

Role of Exercise on Neuropathic Pain in Preclinical Models: Perspectives for Neuroglia

The benefits of exercise on neuropathic pain (NP) have been demonstrated in numerous studies. In recent studies, inflammation, neurotrophins, neurotransmitters, and endogenous opioids are considered as the main mechanisms. However, the role of exercise in alleviating NP remains unclear. Neuroglia, widely distributed in both the central and peripheral nervous systems, perform functions such as support, repair, immune response, and maintenance of normal neuronal activity. A large number of studies have shown that neuroglia play an important role in the occurrence and development of NP, and exercise can alleviate NP by regulating neuroglia. This article reviewed the involvement of neuroglia in the development of NP and their role in the exercise treatment of NP, intending to provide a theoretical basis for the exercise treatment strategy of NP.

Propagation of neuronal micronuclei regulates microglial characteristics

Microglia-resident immune cells in the central nervous system-undergo morphological and functional changes in response to signals from the local environment and mature into various homeostatic states. However, niche signals underlying microglial differentiation and maturation remain unknown. Here, we show that neuronal micronuclei (MN) transfer to microglia, which is followed by changing microglial characteristics during the postnatal period. Neurons passing through a dense region of the developing neocortex give rise to MN and release them into the extracellular space, before being incorporated into microglia and inducing morphological changes. Two-photon imaging analyses have revealed that microglia incorporating MN tend to slowly retract their processes. Loss of the cGAS gene alleviates effects on micronucleus-dependent morphological changes. Neuronal MN-harboring microglia also exhibit unique transcriptome signatures. These results demonstrate that neuronal MN serve as niche signals that transform microglia, and provide a potential mechanism for regulation of microglial characteristics in the early postnatal neocortex.

Integration and functionality of human iPSC-derived microglia in a chimeric mouse retinal model

INTRODUCTION

Microglia, the resident immune cells of the central nervous system, play a pivotal role in maintaining homeostasis, responding to injury, and modulating neuroinflammation. However, the limitations of rodent models in accurately representing human microglia have posed significant challenges in the study of retinal diseases.

METHODS

PLX5622 was used to eliminate endogenous microglia in mice through oral and intraperitoneal administration, followed by transplantation of human induced pluripotent stem cell-derived microglia (hiPSC-microglia, iMG) into retinal explants to create a novel ex vivo chimeric model containing xenotransplanted microglia (xMG). The number and proportion of xMG in the retina were quantified using retinal flat-mounting and immunostaining. To evaluate the proliferative capacity and synaptic pruning ability of xMG, the expression of Ki-67 and the phagocytosis of synaptic proteins SV2 and PSD95 was assessed. The chimeric model was stimulated with LPS, and single-cell RNA sequencing (scRNA-seq) was used to analyze transcriptomic changes in iMG and xMG. Mouse IL-34 antibody neutralization experiments were performed, and the behavior of xMG in retinal degenerative Pde6b-/- mice was examined.

RESULTS

We demonstrated that xenotransplanted microglia (xMG) successfully migrated to and localized within the mouse retina, adopting homeostatic morphologies. Our approach achieved over 86% integration of human microglia, which maintained key functions including proliferation, immune responsiveness, and synaptic pruning over a 14-day culture period. scRNA-seq of xMG revealed a shift in microglial signatures compared to monoculture iMG, indicating a transition to a more in vivo-like phenotype. In retinal degenerative Pde6b-/- mice, xMG exhibited activation and migrated toward degenerated photoreceptors.

CONCLUSION

This model provides a powerful platform for studying human microglia in the retinal context, offering significant insights for advancing research into retinal degenerative diseases and developing potential therapeutic strategies. Future applications of this model include using patient-derived iPSCs to investigate disease-specific microglial behaviors, thereby enhancing our understanding of microglia-related pathogenesis.

Activity-dependent regulation of microglia numbers by pyramidal cells during development shape cortical functions

Beyond their role as immune sentinels, microglia are actively involved in establishing and maintaining cortical circuits. Alteration in microglial numbers has been associated with abnormal behaviors akin to those observed in neurodevelopmental disorders. Consequently, establishing the appropriate microglial numbers during development is crucial for ensuring normal cortical function. Here, we uncovered a dynamic relationship between pyramidal cells and microglia that tunes microglial numbers and development through distinct phases of mouse postnatal development. Changes in pyramidal cell activity during development induce differential release of activity-dependent proteins such as Activin A, which, in turn, adjusts microglial numbers accordingly. Decoupling of this relationship not only changes microglial numbers but has a long-term consequence on their role as synaptic organizers, which ultimately affects cortical function. Our findings reveal that microglia adapt their numbers to changes in pyramidal cell activity during a critical time window in development, consequently adjusting their numbers and function to the demands of the developing local circuits.

Unraveling microglial spatial organization in the developing human brain with DeepCellMap, a deep learning approach coupled with spatial statistics

Mapping cellular organization in the developing brain presents significant challenges due to the multidimensional nature of the data, characterized by complex spatial patterns that are difficult to interpret without high-throughput tools. Here, we present DeepCellMap, a deep-learning-assisted tool that integrates multi-scale image processing with advanced spatial and clustering statistics. This pipeline is designed to map microglial organization during normal and pathological brain development and has the potential to be adapted to any cell type. Using DeepCellMap, we capture the morphological diversity of microglia, identify strong coupling between proliferative and phagocytic phenotypes, and show that distinct spatial clusters rarely overlap as human brain development progresses. Additionally, we uncover an association between microglia and blood vessels in fetal brains exposed to maternal SARS-CoV-2. These findings offer insights into whether various microglial phenotypes form networks in the developing brain to occupy space, and in conditions involving haemorrhages, whether microglia respond to, or influence changes in blood vessel integrity. DeepCellMap is available as an open-source software and is a powerful tool for extracting spatial statistics and analyzing cellular organization in large tissue sections, accommodating various imaging modalities. This platform opens new avenues for studying brain development and related pathologies.

Kinetic changes in microglia-related retinal transcripts in experimental autoimmune uveoretinitis (EAU) of B10.RIII mice

In this study the retinal transcriptome was investigated during the development of experimental autoimmune uveoretinitis (EAU) in mice. EAU was induced by immunizing B10.RIII mice with human interphotoreceptor retinoid binding protein (hIRBP) 161-180 peptide. Genome-wide transcriptional profiles of EAU (day 7, 14 or 21 after immunization) and of control retinas were generated using DNA-microarrays and bioinformatic data mining. Microglia-associated transcripts were identified. Quantitative real-time polymerase chain reaction was performed to validate the expression of differentially expressed genes. Retinal transcript validation revealed that complement and interferon-related pathways, as well as gene clusters specific for antigen-processing and -presentation, and immunosuppression are involved during the course of the disease. Immunofluorescence analysis confirm that upregulated transcripts in EAU are also expressed by retinal microglia. Furthermore, the heterogenous expression patterns observed in retinal microglia, suggests the presence of different subpopulations of retinal microglia in EAU. This study expands our knowledge of the local immune processes involved in EAU pathology.

Spatial proteomic differences in chronic traumatic encephalopathy, Alzheimer's disease, and primary age-related tauopathy hippocampi

INTRODUCTION

Alzheimer's disease (AD), primary age-related tauopathy (PART), and chronic traumatic encephalopathy (CTE) all feature hyperphosphorylated tau (p-tau)-immunoreactive neurofibrillary degeneration, but differ in neuroanatomical distribution and progression of neurofibrillary degeneration and amyloid beta (Aβ) deposition.

METHODS

We used Nanostring GeoMx Digital Spatial Profiling to compare the expression of 70 proteins in neurofibrillary tangle (NFT)-bearing and non-NFT-bearing neurons in hippocampal CA1, CA2, and CA4 subregions and entorhinal cortex of cases with autopsy-confirmed AD (n = 8), PART (n = 7), and CTE (n = 5).

RESULTS

There were numerous subregion-specific differences related to Aβ processing, autophagy/proteostasis, inflammation, gliosis, oxidative stress, neuronal/synaptic integrity, and p-tau epitopes among these different disorders.

DISCUSSION

These results suggest that there are subregion-specific proteomic differences among the neurons of these disorders, which appear to be influenced to a large degree by the presence of hippocampal Aβ. These proteomic differences may play a role in the differing hippocampal p-tau distribution and pathogenesis of these disorders.

HIGHLIGHTS

Alzheimer's disease neuropathologic change (ADNC), possible primary age-related tauopathy (PART), definite PART, and chronic traumatic encephalopathy (CTE) can be differentiated based on the proteomic composition of their neurofibrillary tangle (NFT)- and non-NFT-bearing neurons. The proteome of these NFT- and non-NFT-bearing neurons is largely correlated with the presence or absence of amyloid beta (Aβ). Neurons in CTE and definite PART (Aβ-independent pathologies) share numerous proteomic similarities that distinguish them from ADNC and possible PART (Aβ-positive pathologies).

Screening and Identification of Brain Pericyte-Selective Markers

BACKGROUND

Pericytes, a type of mural cells, exert important functions in the CNS. One major challenge in pericyte research is the lack of pericyte-specific and subpopulation-specific markers.

METHODS

To address this knowledge gap, we first generated a novel transgenic mouse line in which vascular smooth muscle cells (vSMCs) are permanently labeled with tdTomato. Next, we isolated PDGFRβ+tdTomato- pericytes and PDGFRβ+tdTomato+ vSMCs from the brains of these mice and subsequently performed RNAseq analysis to identify pericyte-enriched genes.

RESULTS

Using this approach, we successfully identified 40 pericyte-enriched genes and 158 vSMC-enriched genes, which are involved in different biological processes and molecular functions. Using ISH/IHC analysis, we found that Pla1a and Cox4i2 were predominantly enriched in subpopulations of brain pericytes, although they also marked some non-vascular parenchymal cells.

CONCLUSIONS

These findings suggest that Pla1a and Cox4i2 preferably label subpopulations of pericytes in the brain compared to vSMCs, and thus, they may be useful in distinguishing these populations.

The WAVE complex in developmental and adulthood brain disorders

Actin polymerization and depolymerization are fundamental cellular processes required not only for the embryonic and postnatal development of the brain but also for the maintenance of neuronal plasticity and survival in the adult and aging brain. The orchestrated organization of actin filaments is controlled by various actin regulatory proteins. Wiskott‒Aldrich syndrome protein-family verprolin-homologous protein (WAVE) members are key activators of ARP2/3 complex-mediated actin polymerization. WAVE proteins exist as heteropentameric complexes together with regulatory proteins, including CYFIP, NCKAP, ABI and BRK1. The activity of the WAVE complex is tightly regulated by extracellular cues and intracellular signaling to execute its roles in specific intracellular events in brain cells. Notably, dysregulation of the WAVE complex and WAVE complex-mediated cellular processes confers vulnerability to a variety of brain disorders. De novo mutations in WAVE genes and other components of the WAVE complex have been identified in patients with developmental disorders such as intellectual disability, epileptic seizures, schizophrenia, and/or autism spectrum disorder. In addition, alterations in the WAVE complex are implicated in the pathophysiology of Alzheimer's disease and Parkinson's disease, as well as in behavioral adaptations to psychostimulants or maladaptive feeding.

Microglial plasticity governed by state-specific enhancer landscapes

Single-cell transcriptomic studies have identified distinct microglial subpopulations with shared and divergent gene signatures across development, aging and disease. Whether these microglial subsets represent ontogenically separate lineages of cells, or they are manifestations of plastic changes of microglial states downstream of some converging signals is unknown. Furthermore, despite the well-established role of enhancer landscapes underlying the identity of microglia, to what extent histone modifications and DNA methylation regulate microglial state switches at enhancers have not been defined. Here, using genetic fate mapping, we demonstrate the common embryonic origin of proliferative-region-associated microglia (PAM) enriched in developing white matter, and track their dynamic transitions into disease-associated microglia (DAM) and white matter-associated microglia (WAM) states in disease and aging contexts, respectively. This study links spatiotemporally discrete microglial states through their transcriptomic and epigenomic plasticity, while revealing state-specific histone modification profiles that govern state switches in health and disease.

Assessing in-vitro models for microglial development and fetal programming: a critical review

This review evaluates in-vitro models for studying how maternal influences during pregnancy impact the development of offspring microglia, the immune cells of the central nervous system. The models examined include primary microglia cultures, microglia cell lines, iPSC-derived microglia, PBMC-induced microglia-like cells, 3D brain organoids derived from iPSCs, and Hofbauer cells. Each model is assessed for its ability to replicate the in-vivo environment of the developing brain, with a focus on their strengths, limitations, and practical challenges. Key factors such as scalability, genetic and epigenetic fidelity, and physiological relevance are highlighted. Microglia cell lines are highly scalable but lack genetic and epigenetic fidelity. iPSC-derived microglia provide moderate physiological relevance and patient-specific genetic insights but face operational and epigenetic challenges inherent to reprogramming. 3D brain organoids, derived from iPSCs, offer an advanced platform for studying complex neurodevelopmental processes but require extensive resources and technical expertise. Hofbauer cells, which are fetal macrophages located in the placenta and share a common developmental origin with microglia, are uniquely exposed to prenatal maternal factors and, depending on fetal barrier maturation, exhibit variable epigenetic fidelity. This makes them particularly useful for exploring the impact of maternal influences on fetal programming of microglial development. The review concludes that no single model comprehensively captures all aspects of maternal influences on microglial development, but it offers guidance on selecting the most appropriate model based on specific research objectives and experimental constraints.

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.

Characteristics of TSPO expression in marmoset EAE

Multiple sclerosis (MS) is an inflammatory demyelinating disease of the central nervous system (CNS) and is a leading non-traumatic cause of disability in young adults. The 18 kDa Translocator Protein (TSPO) is a mitochondrial protein and positron emission tomography (PET)-imaging target that is highly expressed in MS brain lesions. It is used as an inflammatory biomarker and has been proposed as a therapeutic target. However, its specific pathological significance in humans is not well understood. Experimental autoimmune encephalomyelitis (EAE) in the common marmoset is a well-established primate model of MS. Studying TSPO expression in this model will enhance our understanding of its expression in MS. This study therefore characterizes patterns of TSPO expression in fixed CNS tissues from one non-EAE control marmoset and 8 EAE marmosets using multiplex immunofluorescence. In control CNS tissue, we find that TSPO is expressed in the leptomeninges, ependyma, and over two-thirds of Iba1 + microglia, but not astrocytes or neurons. In Iba1 + cells in both control and acute EAE tissue, we find that TSPO is co-expressed with markers of antigen presentation (CD74), early activation (MRP14), phagocytosis (CD163) and anti-inflammatory phenotype (Arg1); a high level of TSPO expression is not restricted to a particular microglial phenotype. While TSPO is expressed in over 88% of activated Iba1 + cells in acute lesions in marmoset EAE, it also is sometimes observed in subsets of astrocytes and neurons. Additionally, we find the percentage of Iba1 + cells expressing TSPO declines significantly in lesions > 5 months old and may be as low as 13% in chronic lesions. However, we also find increased astrocytic TSPO expression in chronic-appearing lesions with astrogliosis. Finally, we find expression of TSPO in a subset of neurons, most frequently GLS2 + glutamatergic neurons. The shift in TSPO expression from Iba + microglia/macrophages to astrocytes over time is similar to patterns suggested by earlier neuropathology studies in MS. Thus, marmoset EAE appears to be a clinically relevant model for the study of TSPO in immune dysregulation in human disease.