Increased erythrocyte microRNA-183 cluster expression during relapse - A potential new MS-specific marker for disease activity?

Multiple Sclerosis (MS) research has largely emphasised the role of immune and neuronal cells yet erythrocytes may be involved in antioxidant capacity and haemorheological alterations. Erythrocytes contain a range of RNA transcripts, including microRNAs (miRNAs). MiRNAs may silence translation through complementary base pairing. Some miRNAs are transcribed as clusters and may exert increased control over genes in the same pathway. Erythrocyte miRNAs were sequenced in a discovery cohort of 11 relapsing-remitting MS (RRMS), 12 secondary progressive MS (SPMS), and 22 healthy controls (HCs). Differentially expressed miRNAs were further assessed with a targeted assay (RT-qPCR) in an independent cohort of 21 RRMS (remission), 14 RRMS (relapse), 11 SPMS, 25 HCs, and 20 migraine patients (MPs) as pathological controls. Next-generation sequencing revealed 13 differentially expressed miRNAs between RRMS patients and HCs, 3 of which (miR183-5p, miR-96-5p, miR-18a-5p) were validated by RT-qPCR. Both miR-183-5p and miR-96-5p belong to the miR-183 cluster, so all 3 members were investigated. During relapse both miR-183-5p and miR-182-5p showed increased expression compared to remission (miR-183-5p: 3.15- fold, p< 0.001; miR-182-5p: 2.44-fold, p< 0.001), HCs (miR183-5p: 5.22-fold, p=2.2E-07; miR-182-5p: 3.46-fold, p=2.2E-07) and MPs (miR-183-5p: 3.15-fold, p=3.9E-05; miR182-5p: 2.83-fold, p=3.8E-06). Trends of increased expression of all miR-183 cluster miRNAs were also observed in remission compared to MPs and HCs. Further, expression of all miR-183 cluster members correlated with extended disability status scale scores (miR-183-5p: r=0.53, p< 0.01; miR-182-5p: r=0.44, p< 0.05; miR-96-5p: r=0.62, p< 0.001) and age-related MS severity scores (miR-183-5p: r=0.57, p< 0.01; miR-182-5p: r=0.44, p< 0.05; miR-96-5p: r=0.45, p< 0.05) in remission. Expression of all cluster miRNAs correlated with each other (r=0.63-0.94, p< 2.2E-16). The erythrocyte miRNA-183 cluster shows coordinated expression and appears to be increased during relapse, as well as correlated with MS severity; yet increased expression was not observed in other neurological conditions (migraine). The potential this cluster may have as a disease activity and severity marker should be further explored. While erythrocytes are translationally inactive, erythrocyte miRNA-183 cluster miRNAs may be involved in intercellular communication through extracellular vesicles, which have been reported to be increased in MS.