Circulating brain‐enriched microRNAs as peripheral biomarkers of neurodegeneration

Abstract

AbstractBackgroundMinimally invasive diagnostic tools are needed to better characterize heterogeneous groups of patients with mild cognitive impairment (MCI), pre‐MCI, and dementia. At DiamiR, we developed an approach based on targeted selection and quantitative analysis of microRNAs enriched in specific brain regions, present in synapses, and detectable in blood plasma. microRNAs are short, non‐coding regulatory molecules whose levels change in disease.MethodConcentrations of 24 brain‐enriched and inflammation‐associated microRNAs (Table 1) were analyzed in plasma samples of 200 study participants with the following clinical diagnoses at the time of blood draw: 76 cognitively unimpaired (CU), 85 MCI, and 39 Alzheimer’s disease (AD). The demographic characteristics and clinical data of the study participants are summarized in Table 2. The plasma samples were collected at the Penn Alzheimer’s Disease Research Center (ADRC). Based on amyloid status (Abeta+/‐), APOE genotype (APOE4 +/‐), and sex, each sample was assigned to a specific subgroup. RNA from plasma samples was isolated using the MagMAX mirVana kit (ThermoFisher). microRNA concentrations were measured by qPCR using custom plates (Qiagen) pre‐plated with lyophilized miRCURY LNA‐based primers for a 24‐microRNA panel. Differentiation of subgroups by microRNA pairs and their combinations (classifiers) was evaluated using a proprietary software program developed at DiamiR.ResultUsing the ratio between two microRNAs as a biomarker (“pair” approach) reduces variability and enhances specificity and sensitivity. Effective microRNA pairs were combined into classifiers. Data on the differentiation of subgroups using one, two, and three microRNA pairs are presented in Table 3.In line with our prior results, sex‐stratified analysis yielded higher AUC values for females and males as compared to the combined group. Interestingly, microRNAs differ in effective pairs for female and male subgroups. For example, levels of inflammation‐associated miR‐146a were higher in female MCI/AD study participants. However, sex‐stratified groups were relatively small and further assessment is required.ConclusionThese data support the development of assays based on the analysis of circulating brain‐enriched and inflammation‐associated microRNAs for better characterization of MCI/AD patients and understanding of AD‐associated processes. Further, combining these microRNAs with other factors, such as amyloid and APOE, may enhance a biomarker algorithm.