The relationship between macrophage polarization and glial scar formation in mouse model of spinal cord injury

The study aimed to investigate the relationship between macrophage polarization and glial scar formation in mice model of spinal cord injury (SCI).

A total of 40 specific pathogen-free male C57BL/6 mice were randomly divided into the model (n=20) and control (n=20) groups. The model group was divided into 1-d, 7-d, 14-d, and 28-d post-model groups, with 5 mice in each group. SCI at T9-10 levels was produced by freely dropping a 10 g weight from a height of 5 cm onto the T9-10 spinal segment. The control group underwent the same procedures without damaging the spinal cord. Spinal cord tissue samples were obtained at 1d, 7d, 14d, and 28d after SCI, HE and immunohistochemical staining were used to observe glial scar formation following SCI. RT-qPCR and ELISA assay were used to detect the expression of M1 markers TNF-a, IL-1β, and M2 markers Arginase-1, IL-10.

HE and immunohistochemical staining showed glial scar formation in the model group, while no glial scar formation was observed in the control group. Results from RT-qPCR and ELISA showed that the expression of IL-1β and TNF-α in the model group were significantly higher compared with the control group at each time point (both p <0.01). Highest expression of IL-1β and TNF-α was observed on days 7, which gradually decreased, and remained stable on day 28 day after SCI in the model group. No significant change in IL-1β and TNF-α expresseion was obsreved in the control groups. the expression of IL-10 and Arginase-1 in the model group were significantly higher compared with the control group at each time point (both P <0.01). IL-10 and Arginase-1 expression reached its maximum level on day 14, then gradually decreased, and remained stable on day 28 day after SCI in the model group. No significant change in IL-10 and Arginase-1expression was observed in the control group at each time point.

Macrophages were are mainly polarized to M1 phenotype in the first 7 days during glia scar formation after SCI, which were then gradually polarized into M2 phenotype at 7 days, and tended to be stabilized at 28 days after SCI.