CCN1 orchestrates region-specific microglial distribution in brain development
Insights into how CCN1 regulates neural stem cell-microglia signaling to shape region-specific brain development
image: (A) Immunohistochemistry analysis of CCN1 in wild type (WT) and conditional knockout (CKO) brains at E13.5, E16.5, and P0. Scale bar: 50 μm. (B) Expression of Ccn1 in NSPCs of the mouse brain at E16.5, P0, and P2 from published data. (C) CCN1 is highly expressed in NSCs at E17.5 and P2, as confirmed by co-immunostaining of CCN1 (green) and SOX2 (silver). Scale bar: 50 μm. (D) Schematic diagram of the generation of Ccn1-CKO mice using Nestin-Cre. (E, F) Confirmed the expression specificity and CKO efficiency of Ccn1 in WT and CKO mouse brains at E17.5 (E) and P2 (F), as validated by scRNA-seq.(G) CCN1 expression is nearly absent in E17.5 and P2 CKO mouse brains, as shown by co-immunostaining of DAPI (blue) and CCN1 (red). Scale bar: 50 μm. (H) The percentage of microglia was significantly reduced at E17.5 and P2 according to scRNA-seq analysis. (I) The proportion of microglia in the brain was significantly decreased upon Ccn1 depletion in NSPCs at E17.5 and P2, as determined by FACS analysis using *tmem119-tdTomato; Nestin-cre; Ccn1flox/flox* mice (n = 6 brains per group; E17.5, P = 0.0071; P2, P < 0.0001). (J, K) Microglia were markedly reduced in the ventricular zone (VZ), as shown by immunofluorescence of the microglial marker IBA1 (J) and statistical analysis of IBA1+ nuclei in the VZ (K) (n = 6 mice per group; E17.5, P < 0.001; P2, P < 0.0001). Scale bar: 50 μm. Data information: In (I) and (K), data are presented as mean ± SEM. Unpaired Student’s t-test (two-tailed) was used: ∗∗P < 0.01, ∗∗∗P < 0.001, ∗∗∗∗P < 0.0001.
Credit: Zhile Bai, Zhanhe Chang, Shuguang Wang, Jiangli Zheng, Huan Wu, Hanyu Liu, Yalin Zhang, Jiayang Xie, Qingran Bai, Jiqing Yin, You Wu, Qin Shen, Shaorong Gao, Yawei Gao
The development of the central nervous system (CNS) depends on the coordinated interactions between neural stem cells (NSCs) and resident immune cells to regulate neurogenesis, tissue organization, and brain maturation. Among these immune cells, microglia play essential roles in maintaining developmental homeostasis, yet the molecular mechanisms governing their spatial distribution remain poorly understood.
In a recent study published in Genes & Diseases, researchers from Tongji University, Shanghai Institute of Stem Cell Research and Clinical Translation, Tsinghua University, and Sycamore Research Institute of Life Sciences investigated the role of cellular communication network factor 1 (CCN1), a matricellular protein secreted by neural stem cells, in regulating microglial localization through region-specific cellular interactions during brain development.
Using CNS-specific Ccn1 knockout (cKO) mice generated via the Nestin-Cre system, the researchers integrated single-cell RNA sequencing (scRNA-seq) and high-resolution spatial transcriptomics to elucidate the molecular mechanisms governing these multicellular dynamics.
Single-cell analysis at embryonic stage E17.5 and postnatal day P2 revealed that Ccn1 is predominantly expressed in NSPCs, including NSCs and astrocyte precursor cells, making it a critical factor in the germinal regions of the telencephalon. Ccn1 deletion led to a significant reduction in the overall proportion of microglia in the brain. Immunostaining and FACS analysis confirmed that this decrease was spatially restricted, primarily occurring within the ventricular zone (VZ) at both late embryonic and early postnatal stages, while microglia accumulated in the rostral lateral septal region (LSR). Furthermore, Ccn1 deficiency induced substantial transcriptional alterations in microglia, particularly the upregulation of genes associated with autophagy, apoptosis, and immune activation, such as Atg7, Ctsl, Ms4a6d, and Cd86.
This region-specific redistribution was accompanied by an increased expression of activation-associated gene modules and markers such as Spp1 and Lpl in LSR microglia. The authors identified that Ccn1 deletion in NSCs—rather than astrocytes—was the primary driver of this phenomenon, as NSCs exhibit region-specific dysregulation of key signaling ligands, namely Csf1 and Il2.
Ccn1 deficiency in NSCs increases Il2 expression and alters regional Csf1 signaling, with activation in the LSR and suppression in the VZ, accompanied by an elevated expression of their corresponding receptors and downstream target genes in microglia. These changes affect NSC-microglia communication through the CSF1-CSF1R and IL2-CD53 pathways, leading to transcriptional remodeling and abnormal microglial distribution. Reduced CSF1 secretion in the VZ and its accumulation in the LSR promote microglial migration toward the LSR, causing microglial depletion in the VZ. Concurrently, elevated IL2 expression in the LSR drives microglial overactivation and enhanced autophagy, contributing to region-specific alterations in microglial function and localization. These findings highlight the importance of neural stem cell-derived molecular cues in establishing region-specific developmental microenvironments and demonstrate that neural stem cells actively regulate immune cell behavior through spatially restricted signaling networks during brain development.
In conclusion, this study identifies CCN1 as a critical regulator of neural cell-microglia communication, demonstrating that its loss disrupts region-specific microglial distribution and activation through altered Csf1 and Il2 signaling. These findings advance the understanding of neuroimmune regulation during brain development and provide a molecular framework for investigating how disrupted spatial cellular interactions may contribute to neurodevelopmental and neurological disorders.
Reference
Title of the original paper: Revealed the regulatory role of CCN1 to microglia distribution through region-specific cellular interactions
Journal: Genes & Diseases
Genes & Diseases is a journal for molecular and translational medicine. The journal primarily focuses on publishing investigations on the molecular bases and experimental therapeutics of human diseases. Publication formats include full length research article, review article, short communication, correspondence, perspectives, commentary, views on news, and research watch.
DOI: https://doi.org/10.1016/j.gendis.2025.101969
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