Development and context-dependent plasti city of brain macrophages

Prof. Dr. Josef Priller

• A11N
• B07
• IRTG

Prof. Dr. Marco Prinz

• A01
• B07

Project Summary

Microglia and central nervous system (CNS)-associated macrophages (CAMs) are the key immune effector cells of the CNS. They mostly originate from primitive c-kit⁺ erythromyeloid precursors in the yolk sac. Microglia development strongly depends on colony stimulating factor 1 receptor (CSF1R) signalling. Mice deficient in the fms-intronic regulatory element (FIRE) in the Csf1r locus (Csf1r^{ΔFIRE/ΔFIRE} mice) completely lack microglia and display reduced numbers of CAMs throughout life. It is not clear at which stage of prenatal development and postnatal life the progenitors of microglia and CAMs diff erenti ally rely on CSF1R signalling. We will address these questions and potential sex differences using single-cell RNA sequencing (scRNA-seq), CUT & Tag, spatial transcriptomics and proteomics in Csf1r^{ΔFIRE/ΔFIRE} mice compared with Csf1r^ΔFIRE/+ mice and Csf1r^+/+ mice (Aim 1). We hypothesize that microglia and CAMs are shaped by both environment and ontogeny, and we will therefore isolate GFP-expressing microglia and CAMs from the brains of young and old mice and transplant these cells into the brains of age/sex-matched or -mismatched Csf1r^{ΔFIRE/ΔFIRE} mice. Additional groups of mice will receive injecti ons of GFP-expressing peripheral blood monocytes and vehicle.
The transplanted animals will be assessed at 1-20 months after grafting of microglia, CAMs, or monocytes. We will perform motor, cognitive and behavioural testing; electrophysiological recordings from hippocampal granule cells and determination of spine density and morphology, immunohistochemistry, cytokine arrays, single-cell/single-nucleus RNAseq, CUT & Tag, spatial transcriptomics and proteomics (Aim 2). In a translational approach, we will study post-mortem brain tissue from humans with CSF1R-related leukencephalopathy due to heterozygous mutations of CSF1R (Aim 3). The results will provide a comprehensive characterisation of the influence of age and microenvironment on CNS myeloid cells, and of their impact on neural cells across the life span.