Macrophages play a leading role in determining the direction of astrocytic migration in spinal cord injury via ADP-P2Y1R axis

Abstract

After spinal cord injury (SCI), inflammatory cells such as macrophages infiltrate the injured area, and astrocytes migrate, forming a glial scar around macrophages. The glial scar inhibits axonal regeneration, resulting in significant permanent disability. However, the mechanism by which glial scar-forming astrocytes migrate to the injury site has not been clarified. Here we show that migrating macrophages attract reactive astrocytes toward the center of the lesion after SCI. Chimeric mice with bone marrow lacking IRF8, which controls macrophage centripetal migration after SCI, showed widely scattered macrophages in injured spinal cord with the formation of a huge glial scar around the macrophages. To determine whether astrocytes or macrophages play a leading role in determining the directions of migration, we generated chimeric mice with reactive astrocyte-specific Socs3−/− mice, which showed enhanced astrocyte migration, and bone marrow from IRF8−/− mice. In this mouse model, macrophages were widely scattered, and a huge glial scar was formed around the macrophages as in wild-type mice that were transplanted with IRF8−/ bone marrow. In addition, we revealed that macrophage-secreted ATP-derived ADP attracts astrocytes via the P2Y1 receptor. Our findings revealed a mechanism in which migrating macrophages attracted astrocytes and affected the pathophysiology and outcome after SCI.

Galectin-3 inhibition reduces fibrotic scarring and promotes functional recovery after spinal cord injury in mice

“…Every 5th 16-µm frozen sagittal section that included the entire injured spinal cord was quanti ed. To evaluate spatiotemporal changes in PDGFRβ + broblasts and Galectin-3 + macrophages, the maximum range of the positive cells spanning the craniocaudal range at the center of the injury site was quanti ed for broblasts and macrophages at 3-56 dpi [23]. To determine the source of Galectin-3 after SCI, the percentage of Galectin-3 + macrophages relative to the total number of F4/80 + macrophages at the injured spinal cord was quanti ed.…”