Alzheimer’s Disease-Associated Molecular Abnormalities in White Matter Glia and Related Pathologies Detected in Unfractionated and O4-Selected Serum Exosomes Using a Liquid Biopsy Approach

<b>Background/Objectives</b>: White matter degeneration is a significant and early mediator of cognitive impairment in Alzheimer's disease (AD), yet the critical pathologic features remain poorly understood, under-detected, and therapeutically untargeted. Herein, we characterize molecular features of white matter glial cells in AD brains and assess the utility of non-invasive approaches for detecting related abnormalities in extracellular vesicles (EVs) isolated from serum (SEV). In addition, results from unfractionated (SEV-T) and O4 sulfatide-selected SEVs were compared to determine whether white matter abnormalities were detected with greater sensitivity in oligodendrocyte-specific SEVs (SEV-O4). <b>Methods</b>: Oligodendrocyte glycoprotein and astrocyte mRNA levels were measured in postmortem human AD and control frontal lobe white matter by RT-PCR. Immunoreactivity to oligodendrocyte glycoproteins, astrocyte structural proteins, neurofilament light chain (NfL), and aspartyl-asparaginyl-β-hydroxylase (ASPH) was measured by ELISA in SEV-T and SEV-O4 from patients with moderate AD or normal aging. <b>Results</b>: AD brain pathology was associated with significantly reduced mRNA expression of multiple oligodendrocyte glycoproteins and increased mRNA expression of astrocytic structural genes. SEV analyses demonstrated significantly increased immunoreactivity to 2',3'-cyclic nucleotide 3' phosphodiesterase (CNPase), myelin-associated glycoprotein 1 (MAG1), astrocyte proteins, and ASPH, a potent activator of Notch and myelin-regulated homeostatic functions. There were no significant benefits of measuring SEV-O4 compared with SEV-T immunoreactivity. <b>Conclusions</b>: AD is associated with significant molecular abnormalities in oligodendrocyte and astrocyte function in brain tissue. The abnormalities detected in SEVs likely reflect oligodendrocyte injury and degeneration, as well as astrocytic activation. The findings suggest that low-invasive SEV approaches, including the novel analysis of ASPH upregulation, can be used to detect and monitor AD white matter degeneration.