Introduction: Arginase (ARG) is a regulator of pro-repair microglial polarization, efferocytosis, oxidative stress, extracellular matrix remodeling, and tissue scar formation. We have used novel FISHseq (Sequential Florescence In Situ Hybridization) technology to characterize spatial gene changes triggered by neonatal brain hypoxia-ischemia (HI) in our murine model. Methods: Neonatal HI was induced in the mice at postnatal day 10 by permanent coagulation of left common carotid artery to induce ischemia, a one-hour recovery period, and exposure to 10% oxygen/balance nitrogen at 37°C for 50 minutes to induce hypoxia. The mouse brains were hybridized with the Spatial Genomics Mouse Brain Mapper Panel, supplemented with additional genes related to the ARG1 pathway. Results: While focusing on hippocampal microglia, ARG1 was predominantly expressed on day 1 after HI, while ARG2 was expressed on days 1 and 5. P2RY12, homeostatic microglial marker, was significantly downregulated following injury. Genes involved in efferocytosis showed a temporal pattern with upregulation of STAT6 on day 1 and Rac1 on day 5 after HI, reflecting active apoptotic cell clearance. Genes associated with pro-fibrotic pathways (TGFB1, COL1A2) were expressed on day 1 suggesting early activation of fibrosis signaling. On day 5, TGFB1 and COL1A2 were still highly expressed, indicating persistent activation of fibrotic and inflammatory pathways. Conclusions: HI induces differential expression of ARG1 and ARG2 in microglia. Therapies targeting pro-fibrotic pathways in HI may need to be initiated early due to their early activation.
Natarajan et al. (Sun,) studied this question.