SPP1 and multiple sclerosis: OPN has been shown to act as a chemoattractant for microglia, macrophages, and astrocytes during glial scar formation after ischemic injury in adult rodent models [21] and to play a role in neurodegeneration and demyelination diseases such as multiple sclerosis [12, 15, 18, 44, 76] as well as in re-myelination [55].