Emerging Roles for CSF-1 Receptor and its Ligands in the Nervous System

Spinal astrocyte-derived M-CSF mediates microglial reaction and drives visceral hypersensitivity following DSS-induced colitis

Visceral hypersensitivity is one of the most prevalent symptoms of inflammatory bowel disease (IBD), and it can be difficult to cure despite achieving endoscopic remission. Accumulating studies have described that macrophage colony-stimulating factor (M-CSF) modulates neuroinflammation in the central nervous system (CNS) and the development of chronic pain, while the underlying mechanism for whether and how M-CSF/CSF1R signaling pathway regulates visceral hypersensitivity following colitis remains unknown. In the present study, using the dextran sulfate sodium (DSS)-induced colitis model, we determined that microglial accumulation occurred in the spinal dorsal horn during remission phase. The reactive microglia released inflammatory factor, increased neuronal excitability in the dorsal horn, and produced chronic visceral pain behaviors in DSS-treated adult male mice. In addition, we also found significantly increased signaling mediated by astrocytic M-CSF and microglial CSF1R in dorsal horn in the mice with colitis. Exogenous M-CSF induced microglial activation, neuronal hyperactivity and behavioral hypersensitivity in the control group, inhibition of astrocyte/microglia by fluorocitrate/minocycline significantly suppressed microglial and neuronal activity, and relieved the visceral hypersensitivity in the model mice. Overall, our experimental study uncovers the critical involvement of spinal astrocyte-derived M-CSF and reactive microglia in the initiation and maintenance of visceral hypersensitivity following colitis, thereby identifying spinal M-CSF as a target for treating chronic visceral pain. This may provide more accurate theoretical guidance for clinical patients with IBD.

Microglial depletion prevents visual deficits and retinal ganglion cell loss induced by early life stress in adult animals

Early life stress (ELS), a prenatal/early postnatal period of severe trauma, social deprivation, or neglect, among other adversities, constitutes a risk factor for developing psychopathologies and different health complications in adulthood. Maternal separation with early weaning (MSEW) induces long-term consequences in mouse retinal function and structure. We analyzed microglia involvement in adult retina ELS-induced sequelae. C57Bl/6 J mice were separated from the dams at postnatal days (PND) 4-6, 7-9, 10-12, and 13-16, for 2 h, 3 h, 4 h, and 6 h, respectively, and were weaned at PND 17. Control pups were left undisturbed and weaned at PND 21. At PND 45, MSEW induced microgliosis and decreased retinal ganglion cell (RGC) function, followed by RGC loss at PND 60. Microglial phenotypic alterations correlated with a pro-inflammatory profile (i.e., increase in the nuclear levels of nuclear factor kappa B -subunit p65, and C3-, nitric oxide synthase-2, and interleukin-1β-immunoreactivity in Iba-1 ( +) cells). Depleting microglia between PND 35 and 60 did not affect the retina from naïve mice. However, in early stressed mice, it preserved RGC function and number, visually mediated behavior, and contrast sensitivity. Therefore, microglial reactivity could be one of the key factors linking progressive alterations provoked by ELS in adult mice retinal function and structure.

Cyclooxygenase-1 and cyclooxygenase-2 densities measured using positron emission tomography are not altered in the brains of individuals with stable multiple sclerosis

Multiple sclerosis (MS) is a chronic inflammatory disease affecting the central nervous system that involves immune-mediated demyelination and axonal degeneration. Clinical imaging techniques play a critical role in diagnosing and assessing the prognosis of MS. Magnetic resonance imaging has been most frequently used to visualize demyelination and detect acute and chronic active lesions, which are key indicators of clinical course of illness. Previous research has also highlighted the effectiveness of translocator protein 18-kDa (TSPO) positron emission tomography (PET) imaging for identifying chronic active lesions and progressive pathology. Building on this work, the present study used PET imaging to explore the role of cyclooxygenase-1 and -2 (COX-1 and COX-2)-key enzymes involved in neuroinflammation-in individuals with MS. Five participants with MS were recruited, and lesions were identified using 7 Tesla MRI. No significant differences in COX radioligand binding were observed in the co-registered PET images between lesioned areas and normal-appearing brain tissues, nor between individuals with MS and healthy volunteers. The negative findings underscore the complexity of MS pathology and raise several important considerations for planning future studies using COX PET for imaging in MS.

Microglial dynamics and emerging therapeutic strategies in CNS homeostasis and pathology

Microglia, the resident immune cells of the central nervous system (CNS), are highly dynamic and play critical roles in maintaining CNS homeostasis. Under normal conditions, microglia continuously monitor their environment, clear cellular debris, and regulate homeostasis. In response to disease or injury, however, they undergo rapid morphological and functional changes, often adopting an amoeboid shape that facilitates phagocytosis of abnormal cells, pathogens, and external antigens. Microglia also proliferate in areas of injury or pathology, contributing to immune responses and tissue remodeling. Recently, pharmacological approaches targeting microglial depletion and repopulation have gained attention as a means to reset or modulate microglial function. Techniques such as CSF1R inhibition enable transient depletion of microglia, followed by rapid repopulation, potentially restoring homeostatic functions and mitigating chronic inflammation. This review explores the current understanding of microglial dynamics and highlights emerging therapeutic applications of microglial depletion and repopulation within the CNS.

The Basis for Targeting the Tumor Macrophage Compartment in Glioblastoma Immunotherapy

Background: Glioblastoma (GBM) remains the most aggressive primary brain tumor with limited treatment options. The immunosuppressive tumor microenvironment (TME), largely shaped by tumor-associated macrophages (TAMs), represents a significant barrier to effective immunotherapy. Objective: This review aims to explore the role of TAMs within the TME, highlighting the phenotypic plasticity, interactions with tumor cells, and potential therapeutic targets to enhance anti-tumor immunity. Findings: TAMs constitute a substantial portion of the TME, displaying functional plasticity between immunosuppressive and pro-inflammatory phenotypes. Strategies targeting TAMs include depletion, reprogramming, and inhibition of pro-tumor signaling pathways. Preclinical studies show that modifying TAM behavior can shift the TME towards a pro-inflammatory state, enhancing antitumor immune responses. Clinical trials investigating inhibitors of TAM recruitment, polarization, and downstream signaling pathways reveal promising yet limited results, necessitating further research to optimize approaches. Conclusions: Therapeutic strategics targeting TAM plasticity through selective depletion, phenotypic reprogramming, or modulation of downstream immunosuppressive signals represent promising avenues to overcome GBM-associated immunosuppression. Early clinical trials underscore their safety and feasibility, yet achieving meaningful clinical efficacy requires deeper mechanistic understanding and combinatorial approaches integrating macrophage-direct therapies with existing immunotherapeutic modalities.

Neurons as Immunomodulators: From Rapid Neural Activity to Prolonged Regulation of Cytokines and Microglia

Regulation of the brain's neuroimmune system is central to development, normal function, and disease. Neuronal communication to microglia, the primary immune cells of the brain, is well known to involve purinergic signaling mediated via ATP secretion and the cytokine fractalkine. Recent evidence shows that neurons release multiple cytokines beyond fractalkine, yet these are less studied and poorly understood. In contrast to ATP, cytokines are a class of signaling molecule that are much larger, with longer signaling and farther diffusion. We posit that neuron-expressed cytokines are an essential mechanism of neuron-microglia communication that arises as part of both normal learning and memory and in response to tissue pathology. Thus, neurons are underappreciated immunomodulatory cells that express diverse immunomodulatory signals. While neuronally sourced cytokines have been understudied, new technical advances make this a timely topic. The goal of this review is to define what is known about the cytokines expressed from neurons, how they are regulated, and the effects of these cytokines on microglia. We delineate key knowledge gaps and needs for new tools to define and analyze neuronal roles in immunomodulation. Given that cytokines are central regulators of microglial function, a broad new body of work is required to illuminate functional links between these neuronally expressed cytokines and sustained and transient microglial function.

Neuroglial Advances: New Roles for Established Players

Neuroglial cells perform numerous physiological functions and contribute to the pathogenesis of all diseases of the nervous system. Neuroglial neuroprotection defines the resilience of the nervous tissue to exo- and endogenous pathological challenges, while neuroglial defence determines the progression and outcome of neurological disorders. IN this paper, we overview previously unknown but recently discovered roles of various types of neuroglial cells in diverse physiological and pathological processes. First, we describe the role of ependymal glia in the regulation of cerebrospinal fluid flow from the spinal cord to peripheral tissues through the spinal nerves. This newly discovered pathway provides a highway for the CNS-body volume transmission. Next, we present the mechanism by which astrocytes control migration and differentiation of oligodendrocyte precursor cells (OPCs). In pre- and early postnatal CNS, OPCs migrate using vasculature (which is yet free from glia limitans perivascularis) as a pathfinder. Newly forming astrocytic perivascular endfeet signal (through semaphorin-plexin cascade) to OPCs that detach from the vessels and start to differentiate into myelinating oligodendrocytes. We continue the astrocyte theme by demonstrating the neuroprotective role of APOE-laden astrocytic extracellular vesicles in neuromyelitis optica. Next, we explore the link between astrocytic morphology and stress-induced depression. We discuss the critical role of astrocytic ezrin, the cytosolic linker defining terminal astrocyte arborisation and resilience to stress: overexpression of ezrin in prefrontal cortical astrocytes makes mice resistant to stress, whereas ezrin knockdown increases animals vulnerability to stress. Subsequently, we highlight the pathophysiological role of oligodendroglial lineage in schizophrenia by describing novel hypertrophied OPCs in the post-mortem patient's tissue and in a mouse model with OPCs overexpressing alternative splice variant DISC1-Δ3. These DISC1-Δ3-OPCs demonstrated overactivated Wnt/β-catenin signalling pathway and were sufficient to trigger pathological behaviours. Finally, we deliberate on the pathological role of astrocytic and microglial connexin 43 hemichannels in Alzheimer's disease and present a new formula of Cx43 hemichannel inhibitor with increased blood-brain barrier penetration and brain retention.

miR-484 in Hippocampal Astrocytes of Aged and Young Rats Targets CSF-1 to Regulate Neural Progenitor/Stem Cell Proliferation and Differentiation Into Neurons

AIM

Aging-related cognitive decline is closely linked to the reduced function of neural progenitor/stem cells (NPSCs), which can be influenced by the neural microenvironment, particularly astrocytes. The aim of this study was to explore how astrocytes affect NPSCs and cognitive function during aging.

METHODS

H2O2-treated astrocytes were used to mimic the aging phenotype of astrocytes. Proteomic analysis identified altered protein expression, revealing high levels of colony-stimulating factor-1 (CSF-1) in the supernatant of H2O2-treated astrocytes. Primary NPSCs were isolated and cultured in vitro, then stimulated with varying concentrations of recombinant CSF-1 protein to assess its effects on NPSC proliferation, differentiation, and apoptosis. Transcriptome sequencing identified miR-484 related to CSF-1 in H2O2-treated astrocytes, and a dual-luciferase assay verified the interaction between miR-484 and CSF-1. The impact of miR-484 overexpression on NPSC function and cognitive restoration was evaluated both in vitro and in vivo (in 20-month-old rats).

RESULTS

High concentration of CSF-1 inhibited the NPSC proliferation and differentiation into neurons while inducing apoptosis. Overexpression of miR-484 downregulated CSF-1 expression by binding to its 3' untranslated region, thereby promoting the NPSC proliferation and differentiation into neurons. In 20-month-old rats, miR-484 overexpression improved spatial learning and memory in the Morris water maze, increased NPSC proliferation, and reduced apoptosis.

CONCLUSION

Our findings reveal that miR-484 regulates CSF-1 to influence NPSC proliferation, differentiation into neurons, and apoptosis, consequently improving cognitive function in 20-month-old rats. This study provides a foundation for developing therapeutic strategies targeting age-related hippocampal cognitive impairments.

Evaluation of [18F]JNJ-CSF1R-1 as a Positron Emission Tomography Ligand Targeting Colony-Stimulating Factor 1 Receptor

PURPOSE

Colony-stimulating factor 1 receptor (CSF1R) signaling plays a pivotal role in neuroinflammation, driving microglia proliferation and activation. CSF1R is considered a hallmark of inflammation in many neurodegenerative diseases, such as Alzheimer's disease (AD) and Parkinson's disease (PD). Our study aims to evaluate the potential value of 5-cyano-N-(4-(4-(2-([18F]fluoro)ethyl)piperazin-1-yl)-2-(piperidin-1-yl)phenyl)furan-2-carboxamide ([18F]JNJ-CSF1R-1) as a positron emission tomography (PET) ligand targeting CSF1R in preclinical models of neuroinflammation.

PROCEDURES

A cell-based MSD assay was used to measure the IC50 of 5-cyano-N-(4-(4-(2-(fluoro)ethyl)piperazin-1-yl)-2-(piperidin-1-yl)phenyl)furan-2-carboxamide (JNJ-CSF1R-1). JNJ-CSF1R-1 was radiolabeled with fluorine-18. PET imaging was used to evaluate brain uptake, and target engagement of [18F]JNJ-CSF1R-1 in two neuroinflammation mouse models, including systemic lipopolysaccharide (LPS) and AppSAA knock in (KI). CSF1R protein levels in brain tissue were determined by western blot and ELISA assays. [18F]JNJ-CSF1R-1 brain uptake was also measured in a non-human primate (NHP) PET study.

RESULTS

JNJ-CSF1R-1 is a 12 nM (IC50) inhibitor of CSF1R. ​[18F]JNJ-CSF1R-1 demonstrated significantly higher brain uptake in both LPS and AD mouse models as measured by the area under the time activity curves (AUC) compared to control animals. In the AppSAA KI model, CSF1R levels increased near amyloid plaques as detected by IHC. ​[18F]JNJ-CSF1R-1 PET imaging signal showed a good correlation with CSF1R expression levels measured by western blot and ELISA. In an NHP study, ​[18F]JNJ-CSF1R-1 readily entered the brain and demonstrated reversible kinetics.

CONCLUSION

​[18F]JNJ-CSF1R-1 is a potent and promising CSF1R PET tracer with translational potential for measuring microglia-based neuroinflammatory processes and for tracking the impact of anti-inflammatory therapies.

Microglia contribute to nociception via CSF-1R signaling pathway in rat orofacial carcinoma

OBJECTIVE

Cancer-induced pain is the most common complication of the head and neck cancer. The microglia colony-stimulating factor receptor 1 (CSF1R) plays a crucial role in the inflammation and neuropathic pain. However, the effect of CSF1R on orofacial cancer-induced pain is unclear. Here, we aimed to determine the role of CSF1R in orofacial pain caused by cancer.

METHODS

We established an animal model of cancer-induced orofacial pain with Walker 256B cells. Von Frey filament test and laser-intensity pain tester were used to evaluate tumor-induced mechanical and thermal hypersensitivity. Minocycline and PLX3397 were used to alter tumor-induced mechanical and thermal hyperalgesia. Additionally, we evaluated the effect of PLX3397 on immunoinflammatory mediators and neuronal activation within the trigeminal spinal subnucleus caudalis (Vc).

RESULTS

Walker 256B cell-induced tumor growth resulted in mechanical and thermal hyperalgesia, accompanying by microglia activation and CSF1R upregulation. Treatment with minocycline or PLX3397 reversed the associated nocifensive behaviors and microglia activation triggered by tumor. As a result of PLX3397 treatment, tumor-induced increases in pro-inflammatory cytokine expression and neuronal activation of the Vc were significantly inhibited.

CONCLUSIONS

The results of our study showed that blocking microglial activation via CSF1R may help prevent cancer-induced orofacial pain.

Interleukin-34 orchestrates bone formation through its binding to bone morphogenic proteins

Rationale: During development, the contribution of IL34, a ligand of macrophage colony stimulating factor receptor (MCSFR), has not been fully defined. Together with its twin cytokine MCSF, they display an essential role in macrophage differentiation and activation, including tissue specialized macrophages. The mechanism of action of each molecule involves the phosphorylation of MCSFR in varying intensity and kinetics. Furthermore, IL34 can interact with other receptors and cofactors, opening a wide range of modulations during development. The aim of this work was to investigate these effects through the suppression of IL34 in different animal models and study molecular interactions, with a particular focus on osteoclast / osteoblast regulation. Methods: Two different and unique models of IL34-/- were generated in zebrafish and mouse. The skeleton of both species was analyzed and compared by histological and morphometric (Micro-CT) approaches. The role of IL34 and new partners in osteoclast and osteoblast differentiation was analyzed by multiple techniques including mineralization assays, tartrate resistant acid phosphatase (TRAP) staining, receptor phosphorylation and activation assays, and gene expression (real-time quantitative PCR) studies. Furthermore, protein interactions were studied by surface plasmon resonance approach and protein-protein docking ClusPro analysis. Results: Significant growth delay and hypo-mineralization of skeletal elements were observed in both IL34-/- models, as well as craniofacial dysmorphoses in mice. With regard to bone cells, an unexpected increase in the number of osteoclasts and an accumulation of pre-osteoblasts were observed in mice lacking IL34. For the first time, in vitro analyses complemented by protein binding and molecular docking studies established that IL34 interacts directly with certain Bone Morphogenetic Proteins (BMPs), modulating their various activities such as the stimulation of osteoblast differentiation. Conclusions: A new mechanism of action for IL34 through BMPs has been characterized. IL34 interactions with MCSFR and BMPs appear crucial for both osteoclastogenesis and osteoblastogenesis, impacting bone tissue homeostasis and development. The potential interaction of IL34 with different members of the BMP family and their functional impact, including pathological situations such as cancer, should be further explored, opening new therapeutic perspectives.

Hyperhomocysteinemia-induced VCID results in visual deficits, reduced neuroinflammation and vascular alterations in the retina

Over recent years, the retina has been increasingly investigated as a potential biomarker for dementia. A number of studies have looked at the effect of Alzheimer's disease (AD) pathology on the retina and the associations of AD with visual deficits. However, while OCT-A has been explored as a biomarker of cerebral small vessel disease (cSVD), studies identifying the specific retinal changes and mechanisms associated with cSVD are lacking. Using our model of hyperhomocysteinemia-induced cSVD, we aimed to identify the effects of cSVD on visual sensitivity and cognition, retinal glial and vascular cells, and neuroinflammatory and cardiovascular gene expression changes. We placed C57Bl6/SJL mice on a HHcy-inducing diet, a model that has been well characterized to have vascular pathologies in the brain similar to pathologic cSVD. After 14 weeks on diet, mice underwent the Visual-Stimuli 4-arm Maze to identify visual deficits. Whole mount retinas were stained for vessels, microglia and astrocytes to identify glial and vascular changes. Finally, neuroinflammatory and cardiovascular gene expression was measured using NanoString's nCounter system. Ultimately, HHcy led to visual changes that specifically affected the reaction to blue and white light, slightly decreased vascular volume and significantly decreased interaction of microglia with the vasculature, as well as downregulation of inflammatory and vascular genes. These changes provide novel insights and reproduce some prior observations. These studies highlight retinal changes in association with cSVD and serve as a precaution when interpreting vision-dependent cognitive testing of cSVD models.

Neurological impact of HIV/AIDS and substance use alters brain function and structure

Human immunodeficiency virus (HIV) infection is the cause of acquired immunodeficiency syndrome (AIDS). Combination antiretroviral therapy (cART) has successfully controlled AIDS, but HIV-associated neurocognitive disorders (HANDs) remain prevalent among people with HIV. HIV infection is often associated with substance use, which promotes HIV transmission and viral replication and exacerbates HANDs even in the era of cART. Thus, the comorbid effects of substance use exacerbate the neuropathogenesis of HANDs. Unraveling the mechanism(s) of this comorbid exacerbation at the molecular, cell-type, and brain region levels may provide a better understanding of HAND persistence. This review aims to highlight the comorbid effects of HIV and substance use in specific brain regions and cell types involved in the persistence of HANDs. This review includes an overview of post-translational modifications, alterations in microglia-specific biomarkers, and possible mechanistic pathways that may link epigenomic modifications to functional protein alterations in microglia. The impairment of the microglial proteins that are involved in neural circuit function appears to contribute to the breakdown of cellular communication and neurodegeneration in HANDs. The epigenetic modification of N-terminal acetylation is currently understudied, which is discussed in brief to demonstrate the important role of this epigenetic modification in infected microglia within specific brain regions. The discussion also explores whether combined antiretroviral therapy is effective in preventing HIV infection or substance-use-mediated post-translational modifications and protein alterations in the persistence of neuropathogenesis in HANDs.

Animal-based approaches to understanding neuroglia physiology in vitro and in vivo

This chapter describes the pivotal role of animal models for unraveling the physiology of neuroglial cells in the central nervous system (CNS). The two rodent species Mus musculus (mice) and Rattus norvegicus (rats) have been indispensable in scientific research due to their remarkable resemblance to humans anatomically, physiologically, and genetically. Their ease of maintenance, short gestation times, and rapid development make them ideal candidates for studying the physiology of astrocytes, oligodendrocyte-lineage cells, and microglia. Moreover, their genetic similarity to humans facilitates the investigation of molecular mechanisms governing neural physiology. Mice are largely the predominant model of neuroglial research, owing to advanced genetic manipulation techniques, whereas rats remain invaluable for applications requiring larger CNS structures for surgical manipulations. Next to rodents, other animal models, namely, Danio rerio (zebrafish) and Drosophila melanogaster (fruit fly), will be discussed to emphasize their critical role in advancing our understanding of glial physiology. Each animal model provides distinct advantages and disadvantages. By combining the strengths of each of them, researchers can gain comprehensive insights into glial function across species, ultimately promoting the understanding of glial physiology in the human CNS and driving the development of novel therapeutic interventions for CNS disorders.

Long-term reprogramming of primed microglia after moderate inhibition of CSF1R signaling

In acute neuroinflammation, microglia activate transiently, and return to a resting state later on. However, they may retain immune memory of such event, namely priming. Primed microglia are more sensitive to new stimuli and develop exacerbated responses, representing a risk factor for neurological disorders with an inflammatory component. Strategies to control the hyperactivation of microglia are, hence, of great interest. The receptor for colony stimulating factor 1 (CSF1R), expressed in myeloid cells, is essential for microglia viability, so its blockade with specific inhibitors (e.g. PLX5622) results in significant depletion of microglial population. Interestingly, upon inhibitor withdrawal, new naïve microglia repopulate the brain. Depletion-repopulation has been proposed as a strategy to reprogram microglia. However, substantial elimination of microglia is inadvisable in human therapy. To overcome such drawback, we aimed to reprogram long-term primed microglia by CSF1R partial inhibition. Microglial priming was induced in mice by acute neuroinflammation, provoked by intracerebroventricular injection of neuraminidase. After 3-weeks recovery, low-dose PLX5622 treatment was administrated for 12 days, followed by a withdrawal period of 7 weeks. Twelve hours before euthanasia, mice received a peripheral lipopolysaccharide (LPS) immune challenge, and the subsequent microglial inflammatory response was evaluated. PLX5622 provoked a 40%-50% decrease in microglial population, but basal levels were restored 7 weeks later. In the brain regions studied, hippocampus and hypothalamus, LPS induced enhanced microgliosis and inflammatory activation in neuraminidase-injected mice, while PLX5622 treatment prevented these changes. Our results suggest that PLX5622 used at low doses reverts microglial priming and, remarkably, prevents broad microglial depletion.

Microglial CD2AP deficiency exerts protection in an Alzheimer's disease model of amyloidosis

BACKGROUND

The CD2-associated protein (CD2AP) was initially identified in peripheral immune cells and regulates cytoskeleton and protein trafficking. Single nucleotide polymorphisms (SNPs) in the CD2AP gene have been associated with Alzheimer's disease (AD). However, the functional role of CD2AP, especially its role in microglia during AD onset, remains elusive.

METHODS

CD2AP protein levels in cultured primary cells and in 5xFAD mice was studied. Microglial CD2AP-deficient mice were crossed with 5xFAD mice and the offspring were subjected to neuropathological assessment, behavioral tests, electrophysiology, RNA-seq, Golgi staining, and biochemistry analysis. Primary microglia were also isolated for assessing their uptake and morphology changes.

RESULTS

We find that CD2AP is abundantly expressed in microglia and its levels are elevated in the brain of AD patients and the 5xFAD model mice at pathological stages. We demonstrate that CD2AP haploinsufficiency in microglia significantly attenuates cognitive and synaptic deficits, weakens the response of microglia to Aβ and the formation of disease-associated microglia (DAM), and alleviates synapse loss in 5xFAD mice. We show that CD2AP-deficient microglia exhibit compromised uptake ability. In addition, we find that CD2AP expression is positively correlated with the expression of the complement C1q that is important for synapse phagocytosis and the formation of DAM in response to Aβ deposition. Moreover, we reveal that CD2AP interacts with colony stimulating factor 1 receptor (CSF1R) and regulates CSF1R cell surface levels, which may further affect C1q expression.

CONCLUSIONS

Our results demonstrate that CD2AP regulates microgliosis and identify a protective function of microglial CD2AP deficiency against Aβ deposition, suggesting the importance of detailed investigation of AD-associated genes in different brain cells for thoroughly understanding their exact contribution to AD.

Vaccines for immunological defense against traumatic brain injury

Traumatic brain injury (TBI) and subsequent neurodegeneration is partially driven by chronic inflammation both locally and systemically. Yet, current clinical intervention strategies do not mitigate inflammation sequalae necessitating the development of innovative approaches to reduce inflammation and minimize deleterious effects of TBI. Herein, a subcutaneous formulation based on polymer of alpha-ketoglutarate (paKG) delivering glycolytic inhibitor PFK15 (PFKFB3 inhibitor, a rate limiting step in glycolysis), alpha-ketoglutarate (to fuel Krebs cycle) and peptide antigen from myelin proteolipid protein (PLP139-151) was utilized as the prophylactic immunosuppressive formulation in a mouse model of TBI. In vitro, the paKG(PFK15+PLP) vaccine formulation stimulated proliferation of immunosuppressive regulatory T cells and induced generation of T helper-2 cells. When given subcutaneously in the periphery to two weeks prior to mice sustaining a TBI, the active vaccine formulation increased frequency of immunosuppressive macrophages and dendritic cells in the periphery and the brain at day 7 post- TBI and by 28 days post-TBI enhanced PLP-specific immunosuppressive cells infiltrated the brain. While immunohistology measurements of neuroinflammation were not altered 28 days post-TBI, the vaccine formulation improved motor function and enhanced autophagy mediated genes in a spatial manner in the brain. Overall, these data suggest that the TBI vaccine formulation successfully induced an anti-inflammatory profile and decreased TBI-associated inflammation.

Teaser

In this study, a vaccine formulation was generated to develop central nervous specific immunosuppressive responses for TBI.

Mouse and human macrophages and their roles in cardiovascular health and disease

The past 15 years have witnessed a leap in understanding the life cycle, gene expression profiles, origins and functions of mouse macrophages in many tissues, including macrophages of the artery wall and heart that have critical roles in cardiovascular health. Here, we review the phenotypical and functional diversity of macrophage populations in multiple organs and discuss the roles that proliferation, survival, and recruitment and replenishment from monocytes have in maintaining macrophages in homeostasis and inflammatory states such as atherosclerosis and myocardial infarction. We also introduce emerging data that better characterize the life cycle and phenotypic profiles of human macrophages. We discuss the similarities and differences between murine and human macrophages, raising the possibility that tissue-resident macrophages in humans may rely more on bone marrow-derived monocytes than in mouse.

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.

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

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

Discerning potent CSF-1r inhibitors for targeting and therapy of neuroinflammation using computational approaches

Microglia, the primary cellular mediator of neuroinflammation, plays a pivotal role in numerous neurological disorders. Precise and non-invasive quantification of microglia is of paramount importance. Despite various investigations into cell-specific biomarkers for assessing neuroinflammation, many suffer from poor cellular specificity and low signal-to-noise ratios. Colony-stimulating factor-1 receptor (CSF-1R), also known as FMS kinase, has emerged as a promising neuroinflammation biomarker with significant relevance to inflammatory diseases. Additionally, CSF-1R inhibitors (CSF-1Ri) have shown therapeutic potential in central nervous system (CNS) pathological conditions by depleting microglia. Therefore, the development of more specific CSF-1R inhibitors for targeting and treating various CNS insults and neurological disorders is imperative. This study focuses on the search for novel CSF-1R inhibitors. Based on the literature on CSF-1R inhibitors, we proposed and investigated ten ligands as novel CSF-1R inhibitors. Among these, the top three ligands, selected based on their maximum binding scores in docking calculations, are subjected to 100 nanoseconds of molecular dynamics (MD) simulation, alongside three reference ligands. All protein-ligand complexes remain stable throughout the dynamics and exhibit minimal fluctuations during the analysis. The results obtained through this study may prove significant for the future design of CSF-1R inhibitors with potential applications in the field of biomedicine.

Unveiling the impact of TREM-2+ Macrophages in metabolic disorders

The Triggering Receptor Expressed on Myeloid cells 2 (TREM-2) has been widely known by its anti-inflammatory activity. It can be activated in response to microbes and tissue damage, leading to phagocytosis, autophagy, cell polarization and migration, counter inflammation, and tissue repair. So far, the receptor has been largely explored in neurodegenerative disorders, however, a growing number of studies have been investigating its contribution in different pathological conditions, including metabolic diseases, in which (resident) macrophages play a crucial role. In this regard, TREM-2 + macrophages have been implicated in the onset and development of obesity, atherosclerosis, and fibrotic liver disease. These macrophages can be detected in the brain, white adipose tissue, liver, and vascular endothelium. In this review we discuss how different murine models have been demonstrating the ability of such cells to contribute to tissue and body homeostasis by phagocytosing cellular debris and lipid structures, besides contributing to lipid homeostasis in metabolic diseases. Therefore, understanding the role of TREM-2 in metabolic disorders is crucial to expand our current knowledge concerning their immunopathology as well as to foster the development of more targeted therapies to treat such conditions.

The evolving pathophysiology of TBI and the advantages of temporally-guided combination therapies

Several clinical and experimental studies have demonstrated that traumatic brain injury (TBI) activates cascades of biochemical, molecular, structural, and pathological changes in the brain. These changes combine to contribute to the various outcomes observed after TBI. Given the breadth and complexity of changes, combination treatments may be an effective approach for targeting multiple detrimental pathways to yield meaningful improvements. In order to identify targets for therapy development, the temporally evolving pathophysiology of TBI needs to be elucidated in detail at both the cellular and molecular levels, as it has been shown that the mechanisms contributing to cognitive dysfunction change over time. Thus, a combination of individual mechanism-based therapies is likely to be effective when maintained based on the time courses of the cellular and molecular changes being targeted. In this review, we will discuss the temporal changes of some of the key clinical pathologies of human TBI, the underlying cellular and molecular mechanisms, and the results from preclinical and clinical studies aimed at mitigating their consequences. As most of the pathological events that occur after TBI are likely to have subsided in the chronic stage of the disease, combination treatments aimed at attenuating chronic conditions such as cognitive dysfunction may not require the initiation of individual treatments at a specific time. We propose that a combination of acute, subacute, and chronic interventions may be necessary to maximally improve health-related quality of life (HRQoL) for persons who have sustained a TBI.

Contemporaneous Inflammatory, Angiogenic, Fibrogenic, and Angiostatic Cytokine Profiles of the Time-to-Tumor Development by Cancer Cells to Orchestrate Tumor Neovascularization, Progression, and Metastasis

Cytokines can promote various cancer processes, such as angiogenesis, epithelial to mesenchymal transition (EMT), invasion, and tumor progression, and maintain cancer stem-cell-like (CSCs) cells. The mechanism(s) that continuously promote(s) tumors to progress in the TME still need(s) to be investigated. The data in the present study analyzed the inflammatory, angiogenic, fibrogenic, and angiostatic cytokine profiles in the host serum during tumor development in a mouse model of human pancreatic cancer. Pancreatic MiaPaCa-2-eGFP cancer cells were subcutaneously implanted in RAG2xCγ double mutant mice. Blood samples were collected before cancer cell implantation and every week until the end point of the study. The extracted serum from the blood of each mouse at different time points during tumor development was analyzed using a Bio-Plex microarray analysis and a Bio-Plex 200 system for proinflammatory (IL-1β, IL-10, IFN-γ, and TNF-α) and angiogenic and fibrogenic (IL-15, IL-18, basic FGF, LIF, M-CSF, MIG, MIP-2, PDGF-BB, and VEGF) cytokines. Here, we find that during cancer cell colonization for tumor development, host angiogenic, fibrogenic, and proinflammatory cytokine profiling in the tumor-bearing mice has been shown to significantly reduce host angiostatic and proinflammatory cytokines that restrain tumor development and increase those for tumor growth. The proinflammatory cytokines IL-15, IL-18, and IL-1β profiles reveal a significant host serum increase after day 35 when the tumor began to progress in growth. In contrast, the angiostatic cytokine profiles of TNFα, MIG, M-CSF, IL-10, and IFNγ in the host serum revealed a dramatic and significant decrease after day 5 post-implantation of cancer cells. OP treatment of tumor-bearing mice on day 35 maintained high levels of angiostatic and fibrogenic cytokines. The data suggest an entirely new regulation by cancer cells for tumor development. The findings identify for the first time how pancreatic cancer cells use host cytokine profiling to orchestrate the initiation of tumor development.

Pivotal Role of Cranial Irradiation-Induced Peripheral, Intrinsic, and Brain-Engrafting Macrophages in Malignant Glioma

Malignant (high-grade) gliomas are aggressive intrinsic brain tumors that diffusely infiltrate the brain parenchyma. They comprise of World Health Organization (WHO) grade III and IV gliomas. Ionizing radiation or irradiation (IR) is frequently utilized in the treatment of both primary as well as metastatic brain tumors. On the contrary, macrophages (MΦ) are the most copious infiltrating immune cells of all the different cell types colonizing glioma. MΦ at tumor milieu are referred to as tumor-associated macrophages (TAMΦ). In malignant gliomas milieu, TAMΦ are also polarized into two distinct phenotypes such as M1 TAMΦ or M2 TAMΦ, which are capable of inhibiting or promoting tumor growth, respectively. Cranial-IR such as x- and γ-IR are sufficient to induce the migration of peripherally derived MΦ into the brain parenchyma. The IR facilitate a more immunosuppressive milieu via the stimulation of efferocytosis in TAMΦ, and an upsurge of tumor cell engulfment by TAMΦ exhibited detrimental effect of the anti-tumoral immune response in glioma. The MΦ inside the tumor mass are associated with multiple phenomena that include IR resistance and enrichment of the M2 MΦ after IR is able to facilitate glioblastoma multiforme (GBM) recurrence. Reviews on the role of cranial IR-induced peripheral and brain-engrafting macrophages (BeMΦ) in glioma are lacking. Specifically, most studies on peripheral, intrinsic as well as beMΦ on IR focus on WHO grade III and IV. Thus, this review precisely focuses primary on WHO grade III as well as IV gliomas.

Tapeworm infection affects sleep-like behavior in three-spined sticklebacks

Sleep is a complex and conserved biological process that affects several body functions and behaviors. Evidence suggests that there is a reciprocal interaction between sleep and immunity. For instance, fragmented sleep can increase the probability of parasitic infections and reduce the ability to fight infections. Moreover, viral and bacterial infections alter the sleep patterns of infected individuals. However, the effects of macro-parasitic infections on sleep remain largely unknown, and measuring sleep in non-model organisms remains challenging. In this study, we investigated whether macro-parasite infections could alter sleep-like behavior of their hosts. We experimentally infected three-spined sticklebacks (Gasterosteus aculeatus), a freshwater fish, with the tapeworm Schistocephalus solidus and used a hidden Markov model to characterize sleep-like behavior in sticklebacks. One to four days after parasite exposure, infected fish showed no difference in sleep-like behavior compared with non-exposed fish, and fish that were exposed-but-not-infected only showed a slight reduction in sleep-like behavior during daytime. Twenty-nine to 32 days after exposure, infected fish showed more sleep-like behavior than control fish, while exposed-but-not-infected fish showed overall less sleep-like behavior. Using brain transcriptomics, we identified immune- and sleep-associated genes that potentially underlie the observed behavioral changes. These results provide insights into the complex association between macro-parasite infection, immunity, and sleep in fish and may thus contribute to a better understanding of reciprocal interactions between sleep and immunity.

Relative contributions of osteal macrophages and osteoclasts to postnatal bone development in CSF1R-deficient rats and phenotype rescue following wild-type bone marrow cell transfer

Macrophage and osteoclast proliferation, differentiation and survival are regulated by colony-stimulating factor 1 receptor (CSF1R) signaling. Osteopetrosis associated with Csf1 and Csf1r mutations has been attributed to the loss of osteoclasts and deficiency in bone resorption. Here, we demonstrate that homozygous Csf1r mutation in rat leads to delayed postnatal skeletal ossification associated with substantial loss of osteal macrophages in addition to osteoclasts. Osteosclerosis and site-specific skeletal abnormalities were reversed by intraperitoneal transfer of wild-type bone marrow cells (bone marrow cell transfer, BMT) at weaning. Following BMT, IBA1+ macrophages were detected before TRAP+ osteoclasts at sites of ossification restoration. These observations extend evidence that osteal macrophages independently contribute to bone anabolism and are required for normal postnatal bone growth and morphogenesis.

Multiple sclerosis: a narrative overview of current pharmacotherapies and emerging treatment prospects

Multiple sclerosis (MS) is a chronic autoimmune disease characterized by pathological processes of demyelination, subsequent axonal loss, and neurodegeneration within the central nervous system. Despite the availability of numerous disease-modifying therapies that effectively manage this condition, there is an emerging need to identify novel therapeutic targets, particularly for progressive forms of MS. Based on contemporary insights into disease pathophysiology, ongoing efforts are directed toward developing innovative treatment modalities. Primarily, monoclonal antibodies have been extensively investigated for their efficacy in influencing specific pathological pathways not yet targeted. Emerging approaches emphasizing cellular mechanisms, such as chimeric antigen receptor T cell therapy targeting immunological cells, are attracting increasing interest. The evolving understanding of microglia and the involvement of ferroptotic mechanisms in MS pathogenesis presents further avenues for targeted therapies. Moreover, innovative treatment strategies extend beyond conventional approaches to encompass interventions that target alterations in microbiota composition and dietary modifications. These adjunctive therapies hold promise as complementary methods for the holistic management of MS. This narrative review aims to summarize current therapies and outline potential treatment methods for individuals with MS.

Axatilimab in Recurrent or Refractory Chronic Graft-versus-Host Disease

BACKGROUND

Colony-stimulating factor 1 receptor (CSF1R)-dependent monocytes and macrophages are key mediators of chronic graft-versus-host disease (GVHD), a major long-term complication of allogeneic hematopoietic stem-cell transplantation. The CSF1R-blocking antibody axatilimab has shown promising clinical activity in chronic GVHD.

METHODS

In this phase 2, multinational, pivotal, randomized study, we evaluated axatilimab at three different doses in patients with recurrent or refractory chronic GVHD. Patients were randomly assigned to receive axatilimab, administered intravenously, at a dose of 0.3 mg per kilogram of body weight every 2 weeks (0.3-mg dose group), at a dose of 1 mg per kilogram every 2 weeks (1-mg dose group), or at a dose of 3 mg per kilogram every 4 weeks (3-mg dose group). The primary end point was overall response (complete or partial response) in the first six cycles; the key secondary end point was a patient-reported decrease in chronic GVHD symptom burden, as assessed by a reduction of more than 5 points on the modified Lee Symptom Scale (range, 0 to 100, with higher scores indicating worse symptoms). The primary end point would be met if the lower bound of the 95% confidence interval exceeded 30%.

RESULTS

A total of 241 patients were enrolled (80 patients in the 0.3-mg dose group, 81 in the 1-mg dose group, and 80 in the 3-mg dose group). The primary end point was met in all the groups; an overall response was observed in 74% (95% confidence interval [CI], 63 to 83) of the patients in the 0.3-mg dose group, 67% (95% CI, 55 to 77) of the patients in the 1-mg dose group, and 50% (95% CI, 39 to 61) of the patients in the 3-mg dose group. A reduction of more than 5 points on the modified Lee Symptom Scale was reported in 60%, 69%, and 41% of the patients in the three dose groups, respectively. The most common adverse events were dose-dependent transient laboratory abnormalities related to CSF1R blockade. Adverse events leading to discontinuation of axatilimab occurred in 6% of the patients in the 0.3-mg dose group, 22% in the 1-mg dose group, and 18% in the 3-mg dose group.

CONCLUSIONS

Targeting CSF1R-dependent monocytes and macrophages with axatilimab resulted in a high incidence of response among patients with recurrent or refractory chronic GVHD. (Funded by Syndax Pharmaceuticals and Incyte; AGAVE-201 ClinicalTrials.gov number, NCT04710576.).

Novel variants in CSF1R associated with adult-onset leukoencephalopathy with axonal spheroids and pigmented glia (ALSP)

The CSF1R gene, located on chromosome 5, encodes a 108 kDa protein and plays a critical role in regulating myeloid cell function. Mutations in CSF1R have been identified as a cause of a rare white matter disease called adult-onset leukoencephalopathy with axonal spheroids and pigmented glia (ALSP, also known as CSF1R-related leukoencephalopathy), characterized by progressive neurological dysfunction. This study aimed to broaden the genetic basis of ALSP by identifying novel CSF1R variants in patients with characteristic clinical and imaging features of ALSP. Genetic analysis was performed through whole-exome sequencing or panel analysis for leukodystrophy genes. Variant annotation and classification were conducted using computational tools, and the identified variants were categorized following the recommendations of the American College of Medical Genetics and Genomics (ACMG). To assess the evolutionary conservation of the novel variants within the CSF1R protein, amino acid sequences were compared across different species. The study identified six previously unreported CSF1R variants (c.2384G>T, c.2133_2919del, c.1837G>A, c.2304C>A, c.2517G>T, c.2642C>T) in seven patients with ALSP, contributing to the expanding knowledge of the genetic diversity underlying this rare disease. The analysis revealed considerable genetic and clinical heterogeneity among these patients. The findings emphasize the need for a comprehensive understanding of the genetic basis of rare diseases like ALSP and underscored the importance of genetic testing, even in cases with no family history of the disease. The study's contribution to the growing spectrum of ALSP genetics and phenotypes enhances our knowledge of this condition, which can be crucial for both diagnosis and potential future treatments.

Aged-Related Changes in Microglia and Neurodegenerative Diseases: Exploring the Connection

Microglial cells exhibit properties akin to macrophages, thereby enabling them to support and protect the central nervous system environment. Aging induces alterations in microglial polarization, resulting in a shift toward a neurotoxic phenotype characterized by increased expression of pro-inflammatory markers. Dysregulation of microglial cells' regulatory pathways and interactions with neurons contribute to chronic activation and neurodegeneration. A better understanding of the involvement of microglia in neurodegenerative diseases such as Alzheimer's and Parkinson's is a critical topic for studying the role of inflammatory responses in disease progression. Furthermore, the metabolic changes in aged microglia, including the downregulation of oxidative phosphorylation, are discussed in this review. Understanding these mechanisms is crucial for developing better preventive and therapeutic strategies.

Repopulated microglia after pharmacological depletion decrease dendritic spine density in adult mouse brain

Microglia are innate immune cells in the brain and show exceptional heterogeneity. They are key players in brain physiological development regulating synaptic plasticity and shaping neuronal networks. In pathological disease states, microglia-induced synaptic pruning mediates synaptic loss and targeting microglia was proposed as a promising therapeutic strategy. However, the effect of microglia depletion and subsequent repopulation on dendritic spine density and neuronal function in the adult brain is largely unknown. In this study, we investigated whether pharmacological microglia depletion affects dendritic spine density after long-term permanent microglia depletion and after short-term microglia depletion with subsequent repopulation. Long-term microglia depletion using colony-stimulating-factor-1 receptor (CSF1-R) inhibitor PLX5622 resulted in increased overall spine density, especially of mushroom spines, and increased excitatory postsynaptic current amplitudes. Short-term PLX5622 treatment with subsequent repopulation of microglia had an opposite effect resulting in activated microglia with increased synaptic phagocytosis and consequently decreased spine density and reduced excitatory neurotransmission, while Barnes maze and elevated plus maze testing was unaffected. Moreover, RNA sequencing data of isolated repopulated microglia showed an activated and proinflammatory phenotype. Long-term microglia depletion might be a promising therapeutic strategy in neurological diseases with pathological microglial activation, synaptic pruning, and synapse loss. However, repopulation after depletion induces activated microglia and results in a decrease of dendritic spines possibly limiting the therapeutic application of microglia depletion. Instead, persistent modulation of pathological microglia activity might be beneficial in controlling synaptic damage.

Inflammation is a critical factor for successful regeneration of the adult zebrafish retina in response to diffuse light lesion

Inflammation can lead to persistent and irreversible loss of retinal neurons and photoreceptors in mammalian vertebrates. In contrast, in the adult zebrafish brain, acute neural inflammation is both necessary and sufficient to stimulate regeneration of neurons. Here, we report on the critical, positive role of the immune system to support retina regeneration in adult zebrafish. After sterile ablation of photoreceptors by phototoxicity, we find rapid response of immune cells, especially monocytes/microglia and neutrophils, which returns to homeostatic levels within 14 days post lesion. Pharmacological or genetic impairment of the immune system results in a reduced Müller glia stem cell response, seen as decreased reactive proliferation, and a strikingly reduced number of regenerated cells from them, including photoreceptors. Conversely, injection of the immune stimulators flagellin, zymosan, or M-CSF into the vitreous of the eye, leads to a robust proliferation response and the upregulation of regeneration-associated marker genes in Müller glia. Our results suggest that neuroinflammation is a necessary and sufficient driver for retinal regeneration in the adult zebrafish retina.

GBM Immunotherapy: Macrophage Impacts

BACKGROUND

Glioblastoma (GBM) is an extremely aggressive form of brain tumor with low survival rates. Current treatments such as chemotherapy, radiation, and surgery are problematic due to tumor growth, invasion, and tumor microenvironment. GBM cells are resistant to these standard treatments, and the heterogeneity of the tumor makes it difficult to find a universal approach. Progression of GBM and acquisition of resistance to therapy are due to the complex interplay between tumor cells and the TME. A significant portion of the TME consists of an inflammatory infiltrate, with microglia and macrophages being the predominant cells.

METHODS

Analysis of the literature data over a course of 5 years suggest that the tumor-associated macrophages (TAMs) are capable of releasing cytokines and growth factors that promote tumor proliferation, survival, and metastasis while inhibiting immune cell function at the same time.

RESULTS

Thus, immunosuppressive state, provided with this intensively studied kind of TME cells, is supposed to promote GBM development through TAMs modulation of tumor treatment-resistance and aggressiveness. Therefore, TAMs are an attractive therapeutic target in the treatment of glioblastoma.

CONCLUSION

This review provides a comprehensive overview of the latest research on the nature of TAMs and the development of therapeutic strategies targeting TAMs, focusing on the variety of macrophage properties, being modulated, as well as molecular targets.

Single-nucleus analysis reveals microenvironment-specific neuron and glial cell enrichment in Alzheimer's disease

BACKGROUND

Alzheimer's disease (AD) is a complicated neurodegenerative disease. Neuron-glial cell interactions are an important but not fully understood process in the progression of AD. We used bioinformatic methods to analyze single-nucleus RNA sequencing (snRNA-seq) data to investigate the cellular and molecular biological processes of AD.

METHOD

snRNA-seq data were downloaded from Gene Expression Omnibus (GEO) datasets and reprocessed to identify 240,804 single nuclei from healthy controls and patients with AD. The cellular composition of AD was further explored using Uniform Manifold Approximation and Projection (UMAP). Enrichment analysis for the functions of the DEGs was conducted and cell development trajectory analyses were used to reveal underlying cell fate decisions. iTALK was performed to identify ligand-receptor pairs among various cell types in the pathological ecological microenvironment of AD.

RESULTS

Six cell types and multiple subclusters were identified based on the snRNA-seq data. A subcluster of neuron and glial cells co-expressing lncRNA-SNHG14, myocardin-related transcription factor A (MRTFA), and MRTFB was found to be more abundant in the AD group. This subcluster was enriched in mitogen-activated protein kinase (MAPK)-, immune-, and apoptosis-related pathways. Through molecular docking, we found that lncRNA-SNHG14 may bind MRTFA and MRTFB, resulting in an interaction between neurons and glial cells.

CONCLUSIONS

The findings of this study describe a regulatory relationship between lncRNA-SNHG14, MRTFA, and MRTFB in the six main cell types of AD. This relationship may contribute to microenvironment remodeling in AD and provide a theoretical basis for a more in-depth analysis of AD.

Microglia in Ischemic Stroke: Pathogenesis Insights and Therapeutic Challenges

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

Neuron Derived Cytokine Interleukin-34 Controls Developmental Microglia Function

Neuron-microglia interactions dictate the development of neuronal circuits in the brain. However, the factors that support and broadly regulate these processes across developmental stages are largely unknown. Here, we find that IL34, a neuron-derived cytokine, is upregulated in development and plays a critical role in supporting and maintaining neuroprotective, mature microglia in the anterior cingulate cortex (ACC) of mice. We show that IL34 mRNA and protein is upregulated in neurons in the second week of postnatal life and that this increase coincides with increases in microglia number and expression of mature, homeostatic markers, e.g., TMEM119. We also found that IL34 mRNA is higher in more active neurons, and higher in excitatory (compared to inhibitory) neurons. Genetic KO of IL34 prevents the functional maturation of microglia and results in an anxiolytic phenotype in these mice by adulthood. Acute, low dose blocking of IL34 at postnatal day (P)15 in mice decreased microglial TMEM119 expression and increased aberrant microglial phagocytosis of thalamocortical synapses within the ACC. In contrast, viral overexpression of IL34 early in life (P1-P8) caused early maturation of microglia and prevented microglial phagocytosis of thalamocortical synapses during the appropriate neurodevelopmental refinement window. Taken together, these findings establish IL34 as a key regulator of neuron-microglia crosstalk in postnatal brain development, controlling both microglial maturation and synapse engulfment.

Microglia pack a toolbox for life

After decades of being overlooked, a recent wave of studies have explored the roles of microglia in brain health and disease. Microglia perform important physiological functions to set up and maintain proper neural network functions, as well as orchestrate responses to toxic stimuli to limit harm. Many microglial transcriptional programs, extracellular sensing molecules, and functional outputs are seen throughout life. A stark example is the similarity of microglial responses to stressors during neurodevelopment and neurodegeneration. The same themes often match that of other tissue-resident macrophages, presenting an opportunity to apply known concepts as therapeutics develop. We argue that microglial signaling during development and neurologic disease overlap with one another and with other tissue-resident macrophage pathways, in part due to similar sensed stimuli and a conserved sensome of receptors and signaling molecules, akin to a toolkit.

CSF1R antagonism results in increased supraspinal infiltration in EAE

BACKGROUND

Colony stimulating factor 1 receptor (CSF1R) signaling is crucial for the maintenance and function of various myeloid subsets. CSF1R antagonism was previously shown to mitigate clinical severity in experimental autoimmune encephalomyelitis (EAE). The associated mechanisms are still not well delineated.

METHODS

To assess the effect of CSF1R signaling, we employed the CSF1R antagonist PLX5622 formulated in chow (PLX5622 diet, PD) and its control chow (control diet, CD). We examined the effect of PD in steady state and EAE by analyzing cells isolated from peripheral immune organs and from the CNS via flow cytometry. We determined CNS infiltration sites and assessed the extent of demyelination using immunohistochemistry of cerebella and spinal cords. Transcripts of genes associated with neuroinflammation were also analyzed in these tissues.

RESULTS

In addition to microglial depletion, PD treatment reduced dendritic cells and macrophages in peripheral immune organs, both during steady state and during EAE. Furthermore, CSF1R antagonism modulated numbers and relative frequencies of T effector cells both in the periphery and in the CNS during the early stages of the disease. Classical neurological symptoms were milder in PD compared to CD mice. Interestingly, a subset of PD mice developed atypical EAE symptoms. Unlike previous studies, we observed that the CNS of PD mice was infiltrated by increased numbers of peripheral immune cells compared to that of CD mice. Immunohistochemical analysis showed that CNS infiltrates in PD mice were mainly localized in the cerebellum while in CD mice infiltrates were primarily localized in the spinal cords during the onset of neurological deficits. Accordingly, during the same timepoint, cerebella of PD but not of CD mice had extensive demyelinating lesions, while spinal cords of CD but not of PD mice were heavily demyelinated.

CONCLUSIONS

Our findings suggest that CSF1R activity modulates the cellular composition of immune cells both in the periphery and within the CNS, and affects lesion localization during the early EAE stages.

Differentiated mesenchymal stem cells-derived exosomes immobilized in decellularized sciatic nerve hydrogels for peripheral nerve repair

Peripheral nerve injury (PNI) and the limitations of current treatments often result in incomplete sensory and motor function recovery, which significantly impact the patient's quality of life. While exosomes (Exo) derived from stem cells and Schwann cells have shown promise on promoting PNI repair following systemic administration or intraneural injection, achieving effective local and sustained Exo delivery holds promise to treat local PNI and remains challenging. In this study, we developed Exo-loaded decellularized porcine nerve hydrogels (DNH) for PNI repair. We successfully isolated Exo from differentiated human adipose-derived mesenchymal stem cells (hADMSC) with a Schwann cell-like phenotype (denoted as dExo). These dExo were further combined with polyethylenimine (PEI), and DNH to create polyplex hydrogels (dExo-loaded pDNH). At a PEI content of 0.1%, pDNH showed cytocompatibility for hADMSCs and supported neurite outgrowth of dorsal root ganglions. The sustained release of dExos from dExo-loaded pDNH persisted for at least 21 days both in vitro and in vivo. When applied around injured nerves in a mouse sciatic nerve crush injury model, the dExo-loaded pDNH group significantly improved sensory and motor function recovery and enhanced remyelination compared to dExo and pDNH only groups, highlighting the synergistic regenerative effects. Interestingly, we observed a negative correlation between the number of colony-stimulating factor-1 receptor (CSF-1R) positive cells and the extent of PNI regeneration at the 21-day post-surgery stage. Subsequent in vitro experiments demonstrated the potential involvement of the CSF-1/CSF-1R axis in Schwann cells and macrophage interaction, with dExo effectively downregulating CSF-1/CSF-1R signaling.

Emerging Molecular and Synaptic Targets for the Management of Chronic Pain Caused by Systemic Lupus Erythematosus

Patients with systemic lupus erythematosus (SLE) frequently experience chronic pain due to the limited effectiveness and safety profiles of current analgesics. Understanding the molecular and synaptic mechanisms underlying abnormal neuronal activation along the pain signaling pathway is essential for developing new analgesics to address SLE-induced chronic pain. Recent studies, including those conducted by our team and others using the SLE animal model (MRL/lpr lupus-prone mice), have unveiled heightened excitability in nociceptive primary sensory neurons within the dorsal root ganglia and increased glutamatergic synaptic activity in spinal dorsal horn neurons, contributing to the development of chronic pain in mice with SLE. Nociceptive primary sensory neurons in lupus animals exhibit elevated resting membrane potentials, and reduced thresholds and rheobases of action potentials. These changes coincide with the elevated production of TNFα and IL-1β, as well as increased ERK activity in the dorsal root ganglion, coupled with decreased AMPK activity in the same region. Dysregulated AMPK activity is linked to heightened excitability in nociceptive sensory neurons in lupus animals. Additionally, the increased glutamatergic synaptic activity in the spinal dorsal horn in lupus mice with chronic pain is characterized by enhanced presynaptic glutamate release and postsynaptic AMPA receptor activation, alongside the reduced activity of glial glutamate transporters. These alterations are caused by the elevated activities of IL-1β, IL-18, CSF-1, and thrombin, and reduced AMPK activities in the dorsal horn. Furthermore, the pharmacological activation of spinal GPR109A receptors in microglia in lupus mice suppresses chronic pain by inhibiting p38 MAPK activity and the production of both IL-1β and IL-18, as well as reducing glutamatergic synaptic activity in the spinal dorsal horn. These findings collectively unveil crucial signaling molecular and synaptic targets for modulating abnormal neuronal activation in both the periphery and spinal dorsal horn, offering insights into the development of analgesics for managing SLE-induced chronic pain.

Microglia-endothelial cross-talk regulates diabetes-induced retinal vascular dysfunction through remodeling inflammatory microenvironment

Inflammation-mediated crosstalk between neuroglial cells and endothelial cells (ECs) is a fundamental feature of many vascular diseases. Nevertheless, the landscape of inflammatory processes during diabetes-induced microvascular dysfunction remains elusive. Here, we applied single-cell RNA sequencing to elucidate the transcriptional landscape of diabetic retinopathy (DR). The transcriptome characteristics of microglia and ECs revealed two microglial subpopulations and three EC populations. Exploration of intercellular crosstalk between microglia and ECs showed that diabetes-induced interactions mainly participated in the inflammatory response and vessel development, with colony-stimulating factor 1 (CSF1) and CSF1 receptor (CSF1R) playing important roles in early cell differentiation. Clinically, we found that CSF1/CSF1R crosstalk dysregulation was associated with proliferative DR. Mechanistically, ECs secrete CSF1 and activate CSF1R endocytosis and the CSF1R phosphorylation-mediated MAPK signaling pathway, which elicits the differentiation of microglia and triggers the secretion of inflammatory factors, and subsequently foster angiogenesis by remodeling the inflammatory microenvironment through a positive feedback mechanism.

Genetic Contributions to Recovery following Brain Trauma: A Narrative Review

Traumatic brain injury (TBI) is a frequently encountered form of injury that can have lifelong implications. Despite advances in prevention, diagnosis, monitoring, and treatment, the degree of recovery can vary widely between patients. Much of this is explained by differences in severity of impact and patient-specific comorbidities; however, even among nearly identical patients, stark disparities can arise. Researchers have looked to genetics in recent years as a means of explaining this phenomenon. It has been hypothesized that individual genetic factors can influence initial inflammatory responses, recovery mechanisms, and overall prognoses. In this review, we focus on cytokine polymorphisms, mitochondrial DNA (mtDNA) haplotypes, immune cells, and gene therapy given their associated influx of novel research and magnitude of potential. This discussion is prefaced by a thorough background on TBI pathophysiology to better understand where each mechanism fits within the disease process. Cytokine polymorphisms causing unfavorable regulation of genes encoding IL-1β, IL-RA, and TNF-α have been linked to poor TBI outcomes like disability and death. mtDNA haplotype H has been correlated with deleterious effects on TBI recovery time, whereas haplotypes K, T, and J have been depicted as protective with faster recovery times. Immune cell genetics such as microglial differentially expressed genes (DEGs), monocyte receptor genes, and regulatory factors can be both detrimental and beneficial to TBI recovery. Gene therapy in the form of gene modification, inactivation, and editing show promise in improving post-TBI memory, cognition, and neuromotor function. Limitations of this study include a large proportion of cited literature being focused on pre-clinical murine models. Nevertheless, favorable evidence on the role of genetics in TBI recovery continues to grow. We aim for this work to inform interested parties on the current landscape of research, highlight promising targets for gene therapy, and galvanize translation of findings into clinical trials.

Allogenic microglia replacement: A novel therapeutic strategy for neurological disorders

Microglia are resident immune cells in the central nervous system (CNS) that play vital roles in CNS development, homeostasis and disease pathogenesis. Genetic defects in microglia lead to microglial dysfunction, which in turn leads to neurological disorders. The correction of the specific genetic defects in microglia in these disorders can lead to therapeutic effects. Traditional genetic defect correction approaches are dependent on viral vector-based genetic defect corrections. However, the viruses used in these approaches, including adeno-associated viruses, lentiviruses and retroviruses, do not primarily target microglia; therefore, viral vector-based genetic defect corrections are ineffective in microglia. Microglia replacement is a novel approach to correct microglial genetic defects via replacing microglia of genetic defects with allogenic healthy microglia. In this paper, we systematically review the history, rationale and therapeutic perspectives of microglia replacement, which would be a novel strategy for treating CNS disorders.

The NF1+/- Immune Microenvironment: Dueling Roles in Neurofibroma Development and Malignant Transformation

Neurofibromatosis type 1 (NF1) is a common genetic disorder resulting in the development of both benign and malignant tumors of the peripheral nervous system. NF1 is caused by germline pathogenic variants or deletions of the NF1 tumor suppressor gene, which encodes the protein neurofibromin that functions as negative regulator of p21 RAS. Loss of NF1 heterozygosity in Schwann cells (SCs), the cells of origin for these nerve sheath-derived tumors, leads to the formation of plexiform neurofibromas (PNF)-benign yet complex neoplasms involving multiple nerve fascicles and comprised of a myriad of infiltrating stromal and immune cells. PNF development and progression are shaped by dynamic interactions between SCs and immune cells, including mast cells, macrophages, and T cells. In this review, we explore the current state of the field and critical knowledge gaps regarding the role of NF1(Nf1) haploinsufficiency on immune cell function, as well as the putative impact of Schwann cell lineage states on immune cell recruitment and function within the tumor field. Furthermore, we review emerging evidence suggesting a dueling role of Nf1+/- immune cells along the neurofibroma to MPNST continuum, on one hand propitiating PNF initiation, while on the other, potentially impeding the malignant transformation of plexiform and atypical neurofibroma precursor lesions. Finally, we underscore the potential implications of these discoveries and advocate for further research directed at illuminating the contributions of various immune cells subsets in discrete stages of tumor initiation, progression, and malignant transformation to facilitate the discovery and translation of innovative diagnostic and therapeutic approaches to transform risk-adapted care.

APOE from patient-derived astrocytic extracellular vesicles alleviates neuromyelitis optica spectrum disorder in a mouse model

Neuromyelitis optica spectrum disorder (NMOSD) is an autoimmune astrocytopathy of the central nervous system, mediated by antibodies against aquaporin-4 water channel protein (AQP4-Abs), resulting in damage of astrocytes with subsequent demyelination and axonal damage. Extracellular communication through astrocyte-derived extracellular vesicles (ADEVs) has received growing interest in association with astrocytopathies. However, to what extent ADEVs contribute to NMOSD pathogenesis remains unclear. Here, through proteomic screening of patient-derived ADEVs, we observed an increase in apolipoprotein E (APOE)-rich ADEVs in patients with AQP4-Abs-positive NMOSD. Intracerebral injection of the APOE-mimetic peptide APOE130-149 attenuated microglial reactivity, neuroinflammation, and brain lesions in a mouse model of NMOSD. The protective effect of APOE in NMOSD pathogenesis was further established by the exacerbated lesion volume in APOE-deficient mice, which could be rescued by exogenous APOE administration. Genetic knockdown of the APOE receptor lipoprotein receptor-related protein 1 (LRP1) could block the restorative effects of APOE130-149 administration. The transfusion ADEVs derived from patients with NMOSD and healthy controls also alleviated astrocyte loss, reactive microgliosis, and demyelination in NMOSD mice. The slightly larger beneficial effect of patient-derived ADEVs as compared to ADEVs from healthy controls was further augmented in APOE-/- mice. These results indicate that APOE from astrocyte-derived extracellular vesicles could mediate disease-modifying astrocyte-microglia cross-talk in NMOSD.

Deplete and repeat: microglial CSF1R inhibition and traumatic brain injury

Traumatic brain injury (TBI) is a public health burden affecting millions of people. Sustained neuroinflammation after TBI is often associated with poor outcome. As a result, increased attention has been placed on the role of immune cells in post-injury recovery. Microglia are highly dynamic after TBI and play a key role in the post-injury neuroinflammatory response. Therefore, microglia represent a malleable post-injury target that could substantially influence long-term outcome after TBI. This review highlights the cell specific role of microglia in TBI pathophysiology. Microglia have been manipulated via genetic deletion, drug inhibition, and pharmacological depletion in various pre-clinical TBI models. Notably, colony stimulating factor 1 (CSF1) and its receptor (CSF1R) have gained much traction in recent years as a pharmacological target on microglia. CSF1R is a transmembrane tyrosine kinase receptor that is essential for microglia proliferation, differentiation, and survival. Small molecule inhibitors targeting CSF1R result in a swift and effective depletion of microglia in rodents. Moreover, discontinuation of the inhibitors is sufficient for microglia repopulation. Attention is placed on summarizing studies that incorporate CSF1R inhibition of microglia. Indeed, microglia depletion affects multiple aspects of TBI pathophysiology, including neuroinflammation, oxidative stress, and functional recovery with measurable influence on astrocytes, peripheral immune cells, and neurons. Taken together, the data highlight an important role for microglia in sustaining neuroinflammation and increasing risk of oxidative stress, which lends to neuronal damage and behavioral deficits chronically after TBI. Ultimately, the insights gained from CSF1R depletion of microglia are critical for understanding the temporospatial role that microglia develop in mediating TBI pathophysiology and recovery.

Colony Stimulating Factor-1 Receptor: An emerging target for neuroinflammation PET imaging and AD therapy

Although neuroinflammation is a significant pathogenic feature of many neurologic disorders, its precise function in-vivo is still not completely known. PET imaging enables the longitudinal examination, quantification, and tracking of different neuroinflammation biomarkers in living subjects. Particularly, PET imaging of Microglia, specialised dynamic immune cells crucial for maintaining brain homeostasis in central nervous system (CNS), is crucial for staging the neuroinflammation. Colony Stimulating Factor- 1 Receptor (CSF-1R) PET imaging is a novel method for the quantification of neuroinflammation. CSF-1R is mainly expressed on microglia, and neurodegenerative disorders greatly up-regulate its expression. The present review primarily focuses on the development, pros and cons of all the CSF-1R PET tracers reported for neuroinflammation imaging. Apart from neuroinflammation imaging, CSF-1R inhibitors are also reported for the therapy of neurodegenerative diseases such as Alzheimer's disease (AD). AD is a prevalent, advancing, and fatal neurodegenerative condition that have the characteristic feature of persistent neuroinflammation and primarily affects the elderly. The aetiology of AD is profoundly influenced by amyloid-beta (Aβ) plaques, intracellular neurofibrillary tangles, and microglial dysfunction. Increasing evidence suggests that CSF-1R inhibitors (CSF-1Ri) can be helpful in preclinical models of neurodegenerative diseases. This review article also summarises the most recent developments of CSF-1Ri-based therapy for AD.

Inflammatory biomarkers in patients with painful knee osteoarthritis: exploring the potential link to chronic postoperative pain after total knee arthroplasty-a secondary analysis

ABSTRACT

Total knee arthroplasty (TKA) is the end-stage treatment of knee osteoarthritis (OA), and approximately 20% of patients experience chronic postoperative pain. Studies indicate that inflammatory biomarkers might be associated with pain in OA and potentially linked to the development of chronic postoperative pain after TKA. This study aimed to (1) evaluate preoperative serum levels of inflammatory biomarkers in patients with OA and healthy control subjects, (2) investigate preoperative differences of inflammatory biomarker profiles in subgroups of patients, and (3) compare subgroups of patients with and without postoperative pain 12 months after surgery. Serum samples from patients with OA scheduled for TKA (n = 127) and healthy participants (n = 39) were analyzed. Patients completed the Knee-injury-and-Osteoarthritis-Outcome-Score (KOOS) questionnaire and rated their clinical pain intensity using a visual analog scale (VAS) before and 12 months after TKA. Hierarchical cluster analysis and Orthogonal Partial Least Squares Discriminant Analysis were used to compare groups (patients vs control subjects) and to identify subgroups of patients in relation to postoperative outcomes. Difference in preoperative and postoperative VAS and KOOS scores were compared across subgroups. Twelve inflammatory markers were differentially expressed in patients when compared with control subjects. Cluster analysis identified 2 subgroups of patients with 23 proteins being significantly different ( P < 0.01). The 12-months postoperative VAS and KOOS scores were significantly different between subgroups of patients ( P < 0.05). This study identified differences in specific inflammatory biomarker profiles when comparing patients with OA and control subjects. Cluster analysis identified 2 subgroups of patients with OA, with one subgroup demonstrating comparatively worse 12-month postoperative pain intensity and function scores.

Repeated Activation of Pyramidal Neurons in the Prefrontal Cortex Alters Microglial Phenotype in Male Mice

Aberrant neuronal activity in the cortex alters microglia phenotype and function in several contexts, including chronic psychologic stress and neurodegenerative disease. Recent findings even suggest that heightened levels of neuronal activity spur microglia to phagocytose synapses, with potential impacts on cognition and behavior. Thus, the present studies were designed to determine if activation of neurons alone-independent of disease or dysfunction-is sufficient to alter microglial phenotype in the medial prefrontal cortex (mPFC), a brain region critical in emotion regulation and cognition. In these studies, we used both an adeno-associated virus-mediated and Cre-dependent chemogenetic [designer receptors exclusively activated by designer drugs (DREADD)] approach to repeatedly activate excitatory pyramidal neurons (CaMKIIa+) neurons in the mPFC. Various molecular, cytometric, and behavioral endpoints were examined. Recurrent DREADD-induced neuronal activation led to pronounced changes in microglial density, clustering, and morphology in the mPFC and increased microglia-specific transcripts implicated in synaptic pruning (e.g., Csf1r, Cd11b). Further analyses revealed that the magnitude of DREADD-induced neuronal activation was significantly correlated with measures of microglial morphology in the mPFC. These alterations in microglial phenotype coincided with an increase in microglial lysosome volume in the mPFC and selective deficits in working memory function. Altogether, these findings indicate that repeated neuronal activation alone is sufficient to drive changes in microglia phenotype and function in the mPFC. Future studies using optogenetic and chemogenetic approaches to manipulate neural circuits need to consider microglial and other nonneuronal contributions to physiologic and behavioral outcomes. SIGNIFICANCE STATEMENT: Microglia are highly attuned to fluctuations in neuronal activity. Here we show that repeated activation of pyramidal neurons in the prefrontal cortex induces broad changes in microglia phenotype; this includes upregulation of pathways associated with microglial proliferation, microglia-neuron interactions, and lysosome induction. Our findings suggest that studies using chemogenetic or optogenetic approaches to manipulate neural circuits should be mindful of indirect effects on nonneuronal cells and their potential contribution to measured outcomes.