Colony-stimulating factor 1 receptor signaling in the central nervous system and the potential of its pharmacological inhibitors to halt the progression of neurological 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.

Bioinformatics data combined with single-cell analysis reveals patterns of immunoinflammatory infiltration and cell death in melanoma

BACKGRUOND

Melanoma is a common cancer in dermatology, but its molecular mechanisms remain poorly explained.

AIM

Utilizing single-cell analytics and bioinformatics, the work sought to discover the immunological infiltration and cellular molecular mechanisms of melanoma.

METHODS

Melanoma genes databases were downloaded from GeneCards, and gene expression profiles were chosen from the Gene Expression Omnibus (GSE244889). Establishing and analyzing protein-protein interaction networks for functional enrichment made use of the Kyoto Encyclopedia of Genes and Genomes (KEGG) and Gene Ontology (GO) databases. The process assesses the immunological cell infiltration variations between normal and malignant samples by Immune Cell AI software program. Different cell type differences were clarified by cell quality control, filtration, removal of batch effects and cell clustering analysis using single cell analysis techniques.

RESULTS

Using a variety of machine learning techniques, 20 differentially expressed hub genes were found; among these, TP53, HSP90AB1, HSPA4, RHOA, CCND1, CYCS, PPARG, NFKBIA, CAV1, ANXA5, ENO1, ITGAM, YWHAZ, RELA, SOD1, and VDAC1 were found to be significantly significant. The results of enrichment analysis demonstrated that immune response and inflammatory response were strongly associated with melanoma. Animal mitophagy, ferroptosis, the PI3K-Akt signaling pathway, and the HIF-1 signaling pathway were the primary signaling pathways implicated. Cells of immunity, T-cells, lymphocytes, B-cells, NK-cells, monocytes, and macrophages were shown to be significantly infiltrated in melanoma patients, according to analysis. Single cell analysis also demonstrated that ferroptosis is a significant mechanism of cell death that contributes to the advancement of melanoma and that macrophages are important in the disease.

CONCLUSION

In summary, different immune cell infiltrations-particularly macrophages-have a significant impact on the onset and course of melanoma, and our findings may help direct future investigations into melanoma macrophages.

Ethanol-activated microglial exosomes induce MCP1 signaling mediated death of stress-regulatory proopiomelanocortin neurons in the developing hypothalamus

BACKGROUND

Microglia, a type of resident immune cells within the central nervous system, have been implicated in ethanol-activated neuronal death of the stress regulatory proopiomelanocortin (POMC) neuron-producing β-endorphin peptides in the hypothalamus in a postnatal rat model of fetal alcohol spectrum disorders. We determined if microglial extracellular vesicles (exosomes) are involved in the ethanol-induced neuronal death of the β-endorphin neuron via secreting elevated levels of the chemokine monocyte chemoattractant protein 1 (MCP1), a key regulator of neuroinflammation.

METHODS

We employed an in vitro model, consisting of primary culture of hypothalamic microglia prepared from postnatal day 2 (PND2) rat hypothalami and treated with or without 50 mM ethanol for 24 h, and an in vivo animal model in which microglia were obtained from hypothalami of PND6 rats fed daily with 2.5 mg/kg ethanol or control milk formula for five days prior to use. Exosomes were extracted and characterized with nanosight tracking analysis (NTA), transmission electron microscopy and western blot. Chemokine multiplex immunoassay and ELISA were used for quantitative estimation of MCP1 level. Neurotoxic ability of exosome was tested using primary cultures of β-endorphin neurons and employing nucleosome assay and immunocytochemistry. Elevated plus maze, open field and restraint tests were used to assess anxiety-related behaviors.

RESULTS

Ethanol elevated MCP1 levels in microglial exosomes both in vitro and in vivo models. Ethanol-activated microglial exosomes when introduced into primary cultures of β-endorphin neurons, increased cellular levels of MCP1 and the chemokine receptor CCR2 related signaling molecules including inflammatory cytokines and apoptotic genes as well as apoptotic death of β-endorphin neurons. These effects of microglial exosomes on β-endorphin neurons were suppressed by a CCR2 antagonist RS504393. Furthermore, RS504393 when injected in postnatal rats prior to feeding with ethanol it reduced alcohol-induced β-endorphin neuronal death in the hypothalamus. RS504393 also suppressed corticosterone response to stress and anxiety-like behaviors in postnatally alcohol-fed rats during adult period.

CONCLUSION

These data suggest that alcohol exposures during the developmental period elevates MCP1 levels in microglial exosomes that promote MCP1/CCR2 signaling to increase the apoptosis of β-endorphin neurons and resulting in hormonal and behavioral stress responses.

An update on novel and emerging therapeutic targets in Parkinson's disease

Parkinson's Disease (PD) remains a significant focus of extensive research aimed at developing effective therapeutic strategies. Current treatments primarily target symptom management, with limited success in altering the course of the disease. This shortfall underscores the urgent need for novel therapeutic approaches that can modify the progression of PD.This review concentrates on emerging therapeutic targets poised to address the underlying mechanisms of PD. Highlighted novel and emerging targets include Protein Abelson, Rabphilin-3 A, Colony Stimulating Factor 1-Receptor, and Apelin, each showing promising potential in preclinical and clinical settings for their ability to modulate disease progression. By examining recent advancements and outcomes from trials focusing on these targets, the review aims to elucidate their efficacy and potential as disease-modifying therapies.Furthermore, the review explores the concept of multi-target approaches, emphasizing their relevance in tackling the complex pathology of PD. By providing comprehensive insights into these novel targets and their therapeutic implications, this review aims to guide future research directions and clinical developments toward more effective treatments for PD and related neurodegenerative disorders.

Targeting the CSF-1/CSF-1R Axis: Exploring the Potential of CSF1R Inhibitors in Neurodegenerative Diseases

We report herein the potential of colony-stimulating factor-1 receptor (CSF1R) inhibitors as therapeutic agents in neuroinflammatory diseases, with a focus on Alzheimer's disease (AD). Employing a carefully modified scaffold, N-(4-heterocycloalkyl-2-cycloalkylphenyl)-5-methylisoxazole-3-carboxamide, we identify highly selective and potent CSF1R inhibitors─7dri and 7dsi. Molecular docking studies shed light on the binding modes of these key compounds within the CSF1R binding site. Remarkably, kinome-wide selectivity assessment underscores the impressive specificity of 7dri for CSF-1R. Notably, 7dri emerges as a potent CSF-1R inhibitor with favorable cellular activity and minimal cytotoxicity among the synthesized compounds. Demonstrating efficacy in inhibiting CSF1R phosphorylation in microglial cells and successfully mitigating neuroinflammation in an in vivo LPS-induced model, 7dri establishes itself as a promising antineuroinflammatory agent.

Discovery of N-(5-amido-2-methylphenyl)-5-methylisoxazole-3-carboxamide as dual CSF-1R/c-Kit Inhibitors with improved stability and BBB permeability

This study explores the potential of CSF-1R inhibitors as therapeutic agents for neurodegenerative diseases. CSF-1R, a receptor tyrosine kinase primarily expressed in macrophage lineages, plays a pivotal role in regulating various cellular processes. Recent research highlights the significance of CSF-1R inhibition in mitigating neuroinflammation, particularly in Alzheimer's disease, where microglial overactivation contributes to neurodegeneration. The research reveals a series of N-(5-amido-2-methylphenyl)-5-methylisoxazole-3-carboxamide CSF-1R inhibitors, where compounds 7d, 7e, and 9a exhibit outstanding inhibitory activities and selectivity, with IC50 values of 33, 31, and 64 nM, respectively. These most promising compounds in this series were profiled for cellular potency and subjected to in vitro pharmacokinetic profiling. These inhibitors exhibit minimal cytotoxicity, even at higher concentrations, and possess promising blood-brain barrier permeability, making them potential candidates for central nervous system diseases. The investigation into the in vitro ADME properties, including plasma and microsomal stability, reveals that these CSF-1R inhibitors maintain their structural integrity and plasma concentration. This resilience positions them for further development as therapeutic agents for neurodegenerative diseases.

Diagnostic signatures and immune cell infiltration characteristics in anti-GABABR encephalitis

PURPOSE

Anti-gamma-aminobutyric acid B receptor (GABABR) encephalitis is an uncommon form of autoimmune encephalitis associated with a poor prognosis and a high fatality rate. We aim to find diagnostic markers for anti- GABABR encephalitis as well as the effects of immune cell infiltration on this pathology.

METHODS

For quantitative proteomic analysis, isobaric tags for relative and absolute quantitation were used in conjunction with LC-MS/MS analysis. To conduct functional correlation analyses, differentially expressed proteins (DEPs) were identified. Following that, we used bioinformatics analysis to screen for and determine the diagnostic signatures of anti- GABABR encephalitis. ROC curves were used to evaluate the diagnostic values. To assess the inflammatory status of anti- GABABR encephalitis, we used cell-type identification by estimating relative subsets of the RNA transcript (CIBERSORT) and explored the link between diagnostic markers and infiltrating immune cells.

RESULTS

Overall, 108 robust DEPs (47 upregulated and 61 downregulated) were identified, of which 11 were immune related. The most impressively enriched pathways were complemented and coagulation cascades, actin cytoskeleton regulation, and cholesterol metabolism; GSEA revealed that the enriched pathways were considerably differentially connected to immune modulation. Eleven immune-related DEPs were chosen for further investigation. We developed a novel diagnostic model based on CSF1R and AZGP1 serum levels using ROC analysis (area under the ROC curve = 1). M1 macrophages and activated natural killer cells are likely to play a role in course of anti- GABABR encephalitis.

CONCLUSION

We identified CSF1R and AZGP1 are possible anti-GABABR encephalitis diagnostic indicators, and immune cell infiltration may have a significant impact on the development and occurrence of anti- GABABR encephalitis.

Implicative role of Cytokines in Neuroinflammation mediated AD and associated signaling pathways: Current Progress in molecular signaling and therapeutics

Alzheimer's Disease (AD) is one of the most devastating age-related disorder causing significant social and economic burden worldwide. It affects the cognitive and social behavior of individuals and characterized by accumulation of Aβ, phosphorylated tau and cytokines formation. The synthesis and release of cytokines are regulated by specific groups of immune and non-immune cells in response to microglia or astrocyte activation through multiple pathways. Physiologically, microglia assert an anti-inflammatory, quiescent state with minimal cytokine expression and little phagocytic activity in motion to carry out their housekeeping role to eliminate pathogens, aggregated Aβ and tau protein. However, they develop a phagocytic nature and overexpress cytokine gene modules in response to certain stimuli in AD. Microglia and astrocytes upon chronic activation release an enormous amount of inflammatory cytokines due to interaction with formed Aβ and neurofibrillary tangle. Gut microbiota dysbiosis also stimulates the release of inflammatory cytokines contributing to AD pathogenesis. In addition, the dysregulation of few signaling pathways significantly influences the development of disease, and the pace of advancement also rises with age. This review sheds light on multiple pathways results into neuroinflammation triggered by activated cytokines worsening AD pathology and making it an appropriate target for AD treatment. This review also included drugs targeting different neuroinflammation pathways under clinical and preclinical studies that are found to be effective in attenuating the disease pathology.

Microglial INPP5D limits plaque formation and glial reactivity in the PSAPP mouse model of Alzheimer's disease

INTRODUCTION

The inositol polyphosphate-5-phosphatase D (INPP5D) gene encodes a dual-specificity phosphatase that can dephosphorylate both phospholipids and phosphoproteins. Single nucleotide polymorphisms in INPP5D impact risk for developing late onset sporadic Alzheimer's disease (LOAD).

METHODS

To assess the consequences of inducible Inpp5d knockdown in microglia of APPKM670/671NL /PSEN1Δexon9 (PSAPP) mice, we injected 3-month-old Inpp5dfl/fl /Cx3cr1CreER/+ and PSAPP/Inpp5dfl/fl /Cx3cr1CreER/+ mice with either tamoxifen (TAM) or corn oil (CO) to induce recombination.

RESULTS

At age 6 months, we found that the percent area of 6E10+ deposits and plaque-associated microglia in Inpp5d knockdown mice were increased compared to controls. Spatial transcriptomics identified a plaque-specific expression profile that was extensively altered by Inpp5d knockdown.

DISCUSSION

These results demonstrate that conditional Inpp5d downregulation in the PSAPP mouse increases plaque burden and recruitment of microglia to plaques. Spatial transcriptomics highlighted an extended gene expression signature associated with plaques and identified CST7 (cystatin F) as a novel marker of plaques.

HIGHLIGHTS

Inpp5d knockdown increases plaque burden and plaque-associated microglia number. Spatial transcriptomics identifies an expanded plaque-specific gene expression profile. Plaque-induced gene expression is altered by Inpp5d knockdown in microglia. Our plaque-associated gene signature overlaps with human Alzheimer's disease gene networks.

Microbial neuraminidase induces TLR4-dependent long-term immune priming in the brain

Innate immune memory explains the plasticity of immune responses after repeated immune stimulation, leading to either enhanced or suppressed immune responses. This process has been extensively reported in peripheral immune cells and also, although modestly, in the brain. Here we explored two relevant aspects of brain immune priming: its persistence over time and its dependence on TLR receptors. For this purpose, we used an experimental paradigm consisting in applying two inflammatory stimuli three months apart. Wild type, toll-like receptor (TLR) 4 and TLR2 mutant strains were used. The priming stimulus was the intracerebroventricular injection of neuraminidase (an enzyme that is present in various pathogens able to provoke brain infections), which triggers an acute inflammatory process in the brain. The second stimulus was the intraperitoneal injection of lipopolysaccharide (a TLR4 ligand) or Pam3CSK4 (a TLR2 ligand). One day after the second inflammatory challenge the immune response in the brain was examined. In wild type mice, microglial and astroglial density, as well as the expression of 4 out of 5 pro-inflammatory genes studied (TNFα, IL1β, Gal-3, and NLRP3), were increased in mice that received the double stimulus compared to those exposed only to the second one, which were initially injected with saline instead of neuraminidase. Such enhanced response suggests immune training in the brain, which lasts at least 3 months. On the other hand, TLR2 mutants under the same experimental design displayed an enhanced immune response quite similar to that of wild type mice. However, in TLR4 mutant mice the response after the second immune challenge was largely dampened, indicating the pivotal role of this receptor in the establishment of immune priming. Our results demonstrate that neuraminidase-induced inflammation primes an enhanced immune response in the brain to a subsequent immune challenge, immune training that endures and that is largely dependent on TLR4 receptor.

Two Novel Intronic Mutations in the CSF1R Gene in Two Families With CSF1R-Microglial Encephalopathy

Objective: To describe two novel heterozygous splicing variants of the CSF1R gene responsible for CSF1R-microglial encephalopathy in two unrelated Han Chinese families and further explore the relationship between the pathological and neuroimaging findings in this disease.

Methods: The demographic data, detailed medical history, and clinical manifestations of two unrelated Han families with CSF1R-microglial encephalopathy were recorded. Some family members also underwent detailed neuropsychological evaluation, neuroimaging, and genetic testing. The probands underwent whole-exome sequencing (WES) or next-generation sequencing (NGS) to confirm the diagnosis. The findings were substantiated using Sanger sequencing, segregation analysis, and phenotypic reevaluation.

Results: Both families presented with a dominant hereditary pattern. Five of 27 individuals (four generations) from the first family, including the proband and his sister, father, uncle, and grandmother, presented with cognitive impairments clinically during their respective lifetimes. Brain magnetic resonance imaging (MRI) depicted symmetric, confluent, and diffuse deep white matter changes, atrophy of the frontoparietal lobes, and thinning of the corpus callosum. The proband’s brother remained asymptomatic; brain MRI revealed minimal white matter changes, but pseudo-continuous arterial spin labeling (pCASL) demonstrated a marked reduction in the cerebral blood flow (CBF) in the bilateral deep white matter and corpus callosum. Seven family members underwent WES, which identified a novel splice-site heterozygous mutation (c.2319+1C>A) in intron 20 of the CSF1R gene in four members. The proband from the second family presented with significant cognitive impairment and indifference; brain MRI depicted symmetric diffuse deep white matter changes and thinning of the corpus callosum. The proband’s mother reported herself to be asymptomatic, while neuropsychological evaluation suggested mild cognitive impairment, and brain MRI demonstrated abnormal signals in the bilateral deep white matter and corpus callosum. NGS of 55 genes related to hereditary leukodystrophy was performed for three members, which confirmed a novel splice-site heterozygous mutation (c.1858+5G>A) in intron 13 of the CSF1R gene in two members.

Conclusions: Our study identified two novel splicing mutation sites in the CSF1R gene within two independent Chinese families with CSF1R-microglial encephalopathy, broadening the genetic spectrum of CSF1R-microglial encephalopathy and emphasizing the value of pCASL for early detection of this disease.