Periostin Promotes Scar Formation through the Interaction between Pericytes and Infiltrating Monocytes/Macrophages after Spinal Cord Injury

Scar formation is a prominent pathological feature of traumatic central nervous system (CNS) injury, which has long been implicated as a major impediment to the CNS regeneration. However, the factors affecting such scar formation remain to be elucidated. We herein demonstrate that the extracellular matrix protein periostin (POSTN) is a key player in scar formation after traumatic spinal cord injury (SCI). Using high-throughput RNA sequencing data sets, we found that the genes involved in the extracellular region, such as POSTN, were significantly expressed in the injured spinal cord. The expression of POSTN peaked at 7 days after SCI, predominantly in the scar-forming pericytes. Notably, we found that genetic deletion of POSTN in mice reduced scar formation at the lesion site by suppressing the proliferation of the pericytes. Conversely, we found that recombinant POSTN promoted the migration capacity of the monocytes/macrophages and increased the expression of tumor necrosis factor-a from the monocytes/macrophages in vitro, which facilitated the proliferation of pericytes. Furthermore, we revealed that the pharmacological blockade of POSTN suppressed scar formation and improved the long-term functional outcome after SCI. Our findings suggest a potential mechanism whereby POSTN regulates the scar formation after SCI and provide significant evidence that POSTN is a promising therapeutic target for CNS injury.