Osteopontin: A novel marker of pre‐symptomatic sporadic Alzheimer's disease

Abstract INTRODUCTION We investigate the role of osteopontin (OPN) in participants with Pre‐symptomatic Alzheimer's disease (AD), mild cognitive impairment (MCI), and in AD brains. METHODS Cerebrospinal fluid (CSF) OPN, AD, and synaptic biomarker levels were measured in 109 cognitively unimpaired (CU), parental‐history positive Pre‐symptomatic Evaluation of Experimental or Novel Treatments for Alzheimer's Disease (PREVENT‐AD) participants, and in 167 CU and 399 participants with MCI from the Alzheimer's Disease Neuroimaging Initiative (ADNI) cohort. OPN levels were examined as a function of amyloid beta (Aβ) and tau positivity. Survival analyses investigated the link between OPN and rate of conversion to AD. RESULTS In PREVENT‐AD, CSF OPN was positively correlated with synaptic biomarkers. In PREVENT‐AD and ADNI, OPN was elevated in CSF Aβ 42/40 (+)/total tau(+) and CSF Aβ 42/40 (+)/phosphorylated tau181(+) individuals. In ADNI, OPN was increased in Aβ(+) positron emission tomography (PET) and tau(+) PET individuals, and associated with an accelerated rate of conversion to AD. OPN was elevated in autopsy‐confirmed AD brains. DISCUSSION Strong associations between CSF OPN and key markers of AD pathophysiology suggest a significant role for OPN in tau neurobiology, particularly in the early stages of the disease. Highlights In the Pre‐symptomatic Evaluation of Experimental or Novel Treatments for Alzheimer's Disease cohort, we discovered that cerebrospinal fluid (CSF) osteopontin (OPN) levels can indicate early synaptic dysfunction, tau deposition, and neuronal loss in cognitively unimpaired elderly with a parental history. CSF OPN is elevated in amyloid beta(+) positron emission tomography (PET) and tau(+) PET individuals. Elevated CSF OPN is associated with an accelerated rate of conversion to Alzheimer's disease (AD). Elevated CSF OPN is associated with an accelerated rate of cognitive decline on the Alzheimer's Disease Assessment Scale‐Cognitive subscale 13, Montreal Cognitive Assessment, Mini‐Mental State Examination, and Clinical Dementia Rating Scale Sum of Boxes. OPN mRNA and protein levels are significantly upregulated in the frontal cortex of autopsy‐confirmed AD brains.