MicroRNA Expression Levels Are Altered in the Cerebrospinal Fluid of Patients with Young-Onset Alzheimer's Disease.

Clinical diagnosis of Alzheimer's disease (AD) prior to the age of 65 years is classified as young-onset (YOAD), whereas diagnosis after the age of 65 years is considered late-onset (LOAD). Although rare autosomal mutations more commonly associate with YOAD, most YOAD and LOAD cases are sporadic. YOAD and LOAD share amyloid and tau pathology, but many YOAD patients show increased disease severity and rate of progression. The current study examined the microRNA (miRNA) expression profile from exosomes isolated from the cerebrospinal fluid (CSF) of YOAD patients with biomarker-confirmed AD. Results uncovered miR-16-5p, miR-125b-5p, miR-451a, and miR-605-5p as differentially expressed in the CSF-derived exosomes of YOAD patients when compared with healthy controls (HC). In a cohort of LOAD patients, miR-125b-5p, miR-451a, and miR-605-5p were similarly altered in expression, but miR-16-5p showed similar expression to control. Analysis of the mRNA targets of these miRNAs revealed transcripts enriched in biological processes relevant to the post-mortem posterior cingulate cortex transcriptome in YOAD from a previously published microarray study, including those related to neuron projections, synaptic signaling, metabolism, apoptosis, and the immune system. Hence, these miRNAs represent novel targets for uncovering disease mechanisms and for biomarker development in both YOAD and LOAD.