Protective role of TLR9‐induced macrophage/microglia phagocytosis after experimental intracerebral hemorrhage in mice

• Published in: CNS neuroscience & therapeutics 2022-11, Vol.28 (11), p.1800-1813
• Main Authors: Wei, Jialiang, Dai, Shuhui, Pu, Chen, Luo, Peng, Yang, Yuefan, Jiang, Xiaofan, Li, Xia, Lin, Wei, Fei, Zhou
• Format: Article
• Language: English
• Subjects: Antibodies; Bisphosphonates; Blood & organ donations; Brain; Brain injury; Cell lines; Clodronic acid; Drug dosages; Experiments; Hematoma; Hemorrhage; Immune system; Injection; intracerebral hemorrhage; Iron; macrophage/microglia; Macrophages; Microglia; Morbidity; Original; Pathogens; Phagocytes; Phagocytosis; Proteins; TLR9 protein; Toll-like receptors; toll‐like receptor 9
• ISSN: 1755-5930; 1755-5949
• DOI: 10.1111/cns.13919

Introduction Intracerebral hemorrhage (ICH) causes devastating morbidity and mortality, and studies have shown that the toxic components of hematomas play key roles in brain damage after ICH. Recent studies have found that TLR9 participates in regulating the phagocytosis of peripheral macrophages. The current study examined the role of TLR9 in macrophage/microglial (M/M) function after ICH. Methods RAW264.7 (macrophage), BV2 (microglia), and HT22# (neurons) cell lines were transfected with lentivirus for TLR9 overexpression. Whole blood from C57BL/6 or EGFPTg/+ mice was infused for phagocytosis and injury experiments, and brusatol was used for the experiments. Intraperitoneal injection of the TLR9 agonist ODN1826 or control ODN2138 was performed on days 1, 3, 5, 7, and 28 after ICH to study the effects of TLR9 in mice. In addition, clodronate was coinjected in M/M elimination experiments. The brains were collected for histological and protein experiments at different time points after ICH induction. Cellular and histological methods were used to measure hematoma/iron residual, M/Ms variation, neural injury, and brain tissue loss. Behavioral tests were performed premodeling and on days 1, 3, 7, and 28 post‐ICH. Results Overexpression of TLR9 facilitated M/M phagocytosis and protected neurons from blood‐derived hazards in vitro. Furthermore, ODN1826 boosted M/M activation and phagocytic function, facilitated hematoma/iron resolution, reduced brain injury, and improved neurological function recovery in ICH mice, which were abolished by clodronate injection. The experimental results indicated that the Nrf2/CD204 pathway participated in TLR9‐induced M/M phagocytosis after ICH. Conclusion Our study suggests a protective role for TLR9‐enhanced M/M phagocytosis via the Nrf2/CD204 pathway after ICH. Our findings may serve as potential targets for ICH treatment. Experimental Procedures: The WT C57BL/6 mouse or EGFPTg/+ mouse whole blood was injected into BV2 and RAW264.7 cell lines with or without TLR9 overexpression for phagocytosis experiments. Male C57BL/6 mice were injected with autologous blood with or without clodronate liposome, and received TLR9 agonist ODN1826 or negative control ODN2138. The neurological, histological, and protein experiments were conducted at different time points after ICH modeling. Molecular Mechanism Diagram: TLR9 expression was upregulated after ICH in M/M and astrocyte. Post‐ICH, TLR9 activation facilitated M/M activation, enhanced M