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

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.

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.