Resident microglia and infiltrating macrophages inflammatory, metabolic and sex-dependent gene-regulatory dynamics in the neonatal hippocampus after hypoxia-ischemia.
Neonatal hypoxia-ischemia (HI) is a major cause of perinatal death and long-term disabilities worldwide. Post-ischemic neuroinflammation, characterized by resident and infiltrating immune cells, plays a pivotal role in HI pathophysiology. However, the specific modulatory roles of resident microglia and blood-derived macrophages remain poorly understood. In the present study, we investigated the temporal dynamics of microglia (CX3CR1GFP/+) and infiltrating macrophages (CCR2RFP/+) in the hippocampi of mice subjected to HI at postnatal day (PND) 9. We reveal an increase of CX3CR1GFP+ resident cells in the injured hippocampi soon after HI, peaking at three days post injury. In contrast, infiltration of CCR2RFP/+ cells peaked one day after HI and gradually decreased over time. Transcriptomic signatures of CX3CR1GFP/+ and CCR2RFP/+ cells isolated from hippocampi showed a partial convergence at day 3, through cell type - specific dynamics. Using inflammatory pathway and transcription factor analyses, we identify a distinct post-ischemic response in CCR2RFP/+ cells characterized by differential gene expression in sensome, homeostatic, matrisome, lipid metabolic and inflammatory molecular signatures as consequence of HI. Finally, we identified a sexual dimorphism in CX3CR1GFP/+ cells, where microglia unique genes in males but not in females returned to homeostatic levels comparable to controls three days after HI. In conclusion, our results indicate that CX3CR1GFP/+ and CCR2RFP/+ cells have diverse roles in orchestrating the inflammatory cascade after HI, and that infiltrating macrophages drive post-ischemic inflammation.