Osteopontin in post-subarachnoid hemorrhage pathologies

Rupture of intracranial aneurysms causes subarachnoid hemorrhage (SAH), of which the treatment remains the most difficult among cerebrovascular disorders even in this modern medical era. Following successful surgical ablation of ruptured intracranial aneurysms, other conditions may be encountered including delayed cerebral ischemia and chronic hydrocephalus, in addition to early brain injury. Osteopontin (OPN) is one of matricellular proteins that have cytokine-like effect on various cells and act as secretory extracellular matrix proteins between cells. The complexity of OPN functions is attributed to its several isoforms, cleavage sites and functional changes determined by its differing isoforms following various cleavages or other post-translational modifications. Notably, OPN functions beneficially or harmfully in accordance with the context of OPN upregulation. In the field of aneurysmal SAH, OPN has exerted neuroprotective effects against early brain injury and delayed cerebral ischemia by suppressing apoptosis of neurons, disruption of blood-brain barrier, and/or cerebrovascular constriction, while excessive and prolonged secretion of OPN can be harmful through the occurrence of chronic hydrocephalus requiring shunt surgery. This is a review article that is focused on OPN's potential roles in post-SAH pathologies.