Regulation of Macrophage Heterogeneity and Activation

Abstract

Macrophage heterogeneity arises from both ontogenic determinism and context-dependent plasticity. This thesis investigates how these two regulatory dimensions—(1) temporal transitions in brain-resident macrophages and (2) internal metabolic regulation under fixed stimuli—shape macrophage identity. In the first part, we analyzed single-cell RNA sequencing data from mouse brains at embryonic day 16 (E16), postnatal day 8 (P8), and postnatal day 28 (P28) to profile immune cell composition and microglial maturation. Microglia exhibited a stepwise transcriptional progression through distinct inter- mediate states, accompanied by enrichment of gene programs related to RNA regulation and chromatin remodeling. These findings suggest that microglial development is primarily guided by intrinsic and temporally regulated programs, with limited responsiveness to inflammatory signals during the early postnatal stages. In the second part, we examined whether macrophage responses to identical cytokine stimuli diverge depending on their internal metabolic state. We focused on O-GlcNAc transferase (OGT), a nutrient- sensitive enzyme that links metabolic status to gene regulation. In vitro stimulation of Ogt-deficient macrophages with IL-4 revealed disrupted expression of transcriptional regulators, despite retention of surface markers. In an in vivo model of chronic inflammation, OGT deficiency modestly attenuated joint swelling, suggesting a context-dependent role for OGT in supporting transcriptional stability during macrophage activation. Together, these findings delineate two distinct regulatory modes underlying macrophage heterogene- ity—developmental programming and metabolic modulation—and highlight how intrinsic and extrinsic signals coordinately shape macrophage function across time and tissue environments.