SPP1 and Cerebral ischemia: As a key ECM mineralization modulator, OPN exerts pleiotropic regulatory effects in neurotrauma, cerebrovascular ischemia, and neurodegenerative pathologies.182,183 Basal CNS OPN expression localizes predominantly to olfactory bulb mitral cells, cerebellar Purkinje neurons, and pontomedullary nuclei, exhibiting rostral-caudal expression gradients.