Temporal and Spatial Gene Expression Dynamics in Neonatal HI Hippocampus with Focus on Arginase

Area of Science:

• Neuroscience
• Immunology
• Developmental Biology

Background:

• Hypoxic-ischemic (HI) brain injury induces complex microglial responses, including efferocytosis and scar formation.
• Arginase-1 (ARG1) is crucial for tissue repair, but its role in neonatal microglia post-HI is unclear.
• This study investigates ARG1-linked pathways in neonatal microglia during the acute and fibrotic phases following HI.

Purpose of the Study:

• To characterize the temporal dynamics of ARG1-related pathways in neonatal microglia after HI.
• To identify distinct microglial states and molecular programs involved in efferocytosis and fibrotic remodeling.
• To uncover potential therapeutic targets for mitigating HI-induced brain damage.

Main Methods:

• Neonatal mice (P9) underwent HI using the Vannucci model.
• Spatially resolved single-cell transcriptomics (seqFISH) analyzed microglial gene expression at 24 hours (D1) and 5 days (D5) post-HI.
• Bioinformatic analyses (Navigator, Seurat) identified cell populations, spatial organization, and differential gene expression.

Main Results:

• Spatial transcriptomics revealed 12 distinct microglial populations and preserved neuroanatomy.
• HI led to microglial and astrocyte expansion, with significant loss of neurons by D5.
• Microglia exhibited early regenerative and profibrotic programs (e.g., TGF-β, PI3K-Akt) and later adopted a collagen-rich fibrotic phenotype.

Conclusions:

• Neonatal microglia transition through efferocytic and fibrotic phases post-HI.
• Persistent activation of PI3K-Akt, TGF-β, and Wnt/FZD4 pathways drives this transition.
• Microglia are key regulators of neonatal scar formation, offering potential therapeutic targets within ARG1-signaling pathways.