Contributor:

Kamińska-Kaczmarek, Bożena (1961– ) : Supervisor ; Jankowski, Aleksander : Auxiliary supervisor

Publisher:

Nencki Institute of Experimental Biology PAS

Place of publishing:

Warsaw

Description:

114 pages : illustrations ; 30 cm ; Bibliography ; Summary in Polish

Degree name:

PhD in Biological Sciences

Degree discipline :

Biological Sciences

Degree grantor:

Nencki Institute of Experimental Biology PAS ; degree obtained: 17.04.2026

Type of object:

Thesis

Abstract:

Microglia, the resident immune cells of the central nervous system (CNS), are critical for maintaining neuronal homeostasis, supporting synaptic plasticity, and mounting immune responses to injury and disease. Unlike most CNS-resident cell populations, microglia possess a unique regenerative capacity: following depletion, they are able to repopulate the brain and restore density within days. Microglia viability is regulated by colony stimulating factor 1 receptor (CSF1R) signaling. However, whether these repopulated microglia fully reacquire the functional heterogeneity and homeostatic states of their counterparts, and how this process is influenced by aging, remains poorly understood. In this study, we combined pharmacological depletion using the CSF1R inhibitor BLZ-945 with single-cell RNA sequencing (scRNA-seq) of CD11b+ cells to examine the molecular programs underlying microglial repopulation in both young and aged mice. Complete depletion was achieved after 21 days of BLZ-945 treatment, and repopulation occurred within 7 days following withdrawal of the inhibitor. The analyses of the acquired dataset revealed that repopulated microglia reestablish many of the transcriptional states observed in control animals, but only after passing through distinct, transiently activated phenotypes (Act-MG1, Act- MG2, Act-MG3). These activation states were marked by expression of genes involved in proliferation (Mki67, Top2a), motility and cytoskeletal remodeling (Rac1, P2ry12), extracellular matrix (ECM) degradation (Cstb, Ctsd), and inflammatory cytokine signaling (Il1b, Tnf, Il6). Trajectory analyses demonstrated that repopulated microglia originate from proliferating precursors and move through activated states before reaching a homeostatic phenotype. Age emerged as a major determinant of repopulation efficiency and outcome. While young mice successfully generated homeostatic microglia following transient activation, aged mice displayed impaired maturation of repopulated cells. Repopulated microglia from older animals exhibited heightened proliferation, persistent inflammatory signaling, and reduced representation of homeostatic clusters. Bulk RNA sequencing (RNA-seq) further confirmed downregulation of core homeostatic genes (P2ry12, Tmem119, Trem2) and upregulation of pro-apoptotic and senescence-associated genes in repopulated microglia from aged mice. Pathway-level analysis implicated dysregulation of RhoA-ROCK signaling, which regulates microglial motility, cytoskeletal dynamics, and inflammatory responses, as a central feature of the aging-associated deficits. Comparative analysis revealed striking similarities between the transient Act-MG states of repopulated microglia and the transcriptional programs of glioma-associated microglia. Integration of the presented scRNA-seq dataset with CITE-seq data from murine glioma models identified overlapping clusters enriched for migratory, phagocytic, and inflammatory signatures. These results suggest that microglia repopulation recapitulates transcriptional programs exploited in pathological contexts, highlighting conserved mechanisms of microglial plasticity. These findings have several implications. First, they demonstrate that repopulation is not a simple return to baseline but a dynamic, multi-stage process requiring activation, migration, and eventual resolution to homeostasis. Second, they reveal that aging disrupts this trajectory, leaving microglia in maladaptive states that may compromise neuronal support and increase vulnerability to neurodegeneration. Third, the shared transcriptional features between repopulated and glioma- associated microglia suggest that cellular programs enabling regeneration may also predispose microglia to pathological reprogramming in disease. In conclusion, our study establishes a comprehensive transcriptional framework for microglial repopulation in young and aged brains.(...)

Detailed Resource Type:

PhD Dissertations

Resource Identifier:

oai:rcin.org.pl:262628

Source:

IBD PAN, call no. 20928

Language:

eng

Language of abstract:

pol

Rights:

Rights Reserved - Free Access

Terms of use:

Copyright-protected material. May be used within the limits of statutory user freedoms

Copyright holder:

Publication made available with the written permission of the author

Digitizing institution:

Nencki Institute of Experimental Biology of the Polish Academy of Sciences

Original in:

Library of the Nencki Institute of Experimental Biology PAS

Access:

Open