Erythrocyte microRNAs show biomarker potential and implicate multiple sclerosis susceptibility genes

BACKGROUND: Multiple sclerosis is a demyelinating autoimmune disease, for which there is no blood‐borne biomarker. Erythrocytes may provide a source of such biomarkers as they contain microRNAs. MicroRNAs regulate protein translation through complementary binding to messenger RNA. As erythrocytes are transcriptionally inactive, their microRNA profiles may be less susceptible to variation. The aim of this study was to assess the biomarker potential of erythrocyte microRNAs for multiple sclerosis and assess the potential contribution of erythrocyte‐derived extracellular vesicle microRNAs to pathology. METHODS: Erythrocytes were isolated from whole blood by density gradient centrifugation. Erythrocyte microRNAs of a discovery cohort (23 multiple sclerosis patients and 22 healthy controls) were sequenced. Increased expression of miR‐183 cluster microRNAs (hsa‐miR‐96‐5p, hsa‐miR‐182‐5p and hsa‐miR‐183‐5p) was validated in an independent cohort of 42 patients and 45 healthy and pathological (migraine) controls. Erythrocyte‐derived extracellular vesicles were created ex vivo and their microRNAs were sequenced. Targets of microRNAs were predicted using miRDIP. RESULTS: Hsa‐miR‐182‐5p and hsa‐miR‐183‐5p were able to discriminate relapsing multiple sclerosis patients from migraine patients and/or healthy controls with 89‐94% accuracy and around 90% specificity. Hsa‐miR‐182‐5p and hsa‐miR‐183‐5p expression correlated with measures of physical disability and hsa‐miR‐96‐5p expression correlated with measures of cognitive disability in multiple sclerosis. Erythrocytes were found to selectively package microRNAs into extracellular vesicles and 34 microRNAs were found to be differentially packaged between healthy controls and multiple sclerosis patients. Several gene targets of differentially expressed and packaged erythrocyte microRNAs overlapped with multiple sclerosis susceptibility genes. Gene enrichment analysis indicated involvement in nervous system development and histone H3‐K27 demethylation. CONCLUSIONS: Erythrocyte miR‐183 cluster members may be developed into specific multiple sclerosis biomarkers that could assist with diagnosis and disability monitoring. Erythrocyte and their extracellular microRNAs were shown to target multiple sclerosis susceptibility genes and may be contributing to the pathophysiology via previously identified routes.