Abstract
Osteopontin (encoded by secreted phosphoprotein 1) is a multifunctional matricellular phosphoglycoprotein that has emerged as an important mediator in the aging nervous system. During aging, osteopontin interacts with microglial priming, vascular remodeling, myelin repair, and innate immune responses and is consistently implicated in major late-life neurological disorders. However, its biological effects are highly context dependent. Depending on its cellular source, proteolytic processing, receptor interactions, anatomical distribution, and disease stage, osteopontin may either exacerbate chronic neuroinflammation and tissue injury or promote phagocytic clearance, neuronal survival, remyelination, neuroplasticity, and tissue repair. This review critically synthesizes studies indexed in PubMed and Google Scholar through 3 April 2026 on the role of osteopontin in brain aging, Alzheimer's disease and related dementias, Parkinson's disease and Lewy body disorders, cerebrovascular disease, vascular cognitive impairment, cerebral small vessel disease, and amyotrophic lateral sclerosis. In Alzheimer's disease, cerebrospinal fluid and plasma osteopontin concentrations increase from the prodromal to symptomatic stages, whereas microglial or perivascular secreted phosphoprotein 1 expression correlates with amyloid pathology, synaptic remodeling, and cognitive decline. However, under specific conditions, osteopontin also enhances macrophage-mediated amyloid-beta clearance. In stroke, elevated circulating osteopontin predicts poor clinical outcomes, whereas experimental studies demonstrate that appropriately timed exogenous osteopontin, regulatory T cell-derived osteopontin, and osteopontin-mediated autophagic and reparative pathways promote white-matter repair, peri-infarct plasticity, and blood–brain barrier integrity. Evidence from Parkinson's disease, Lewy body disease, frontotemporal dementia, and amyotrophic lateral sclerosis further supports the role of osteopontin as both a candidate biomarker and a regulator of selective neuronal vulnerability. Rather than being uniformly detrimental or protective, osteopontin should be regarded as a context-dependent regulator of age-related neuroimmune remodeling. This perspective reconciles seemingly conflicting findings and supports the development of therapeutic strategies that are tailored to disease stage, protein fragment, and cell type rather than broadly targeting osteopontin.