We recently demonstrated that microRNA-218 (miR-218) is greatly enriched in motor neurons and is released extracellularly in amyotrophic lateral sclerosis model rats. To determine if the released, motor neuron-derived miR-218 may have a functional role in amyotrophic lateral sclerosis, we examined the effect of miR-218 on neighbouring astrocytes. Surprisingly, we found that extracellular, motor neuron-derived miR-218 can be taken up by astrocytes and is sufficient to downregulate an important glutamate transporter in astrocytes [excitatory amino acid transporter 2 (EAAT2)]. The effect of miR-218 on astrocytes extends beyond EAAT2 since miR-218 binding sites are enriched in mRNAs translationally downregulated in amyotrophic lateral sclerosis astrocytes. Inhibiting miR-218 with antisense oligonucleotides in amyotrophic lateral sclerosis model mice mitigates the loss of EAAT2 and other miR-218-mediated changes, providing an important in vivo demonstration of the relevance of microRNA-mediated communication between neurons and astrocytes. These data define a novel mechanism in neurodegeneration whereby microRNAs derived from dying neurons can directly modify the glial phenotype and cause astrocyte dysfunction.
Hoye ML, Regan MR, Jensen LA, Lake AM, Reddy LV, Vidensky S, Richard JP, Maragakis NJ, Rothstein JD, Dougherty JD, Miller TM. Motor neuron-derived microRNAs cause astrocyte dysfunction in amyotrophic lateral sclerosis. Brain. 2018 Sep 1;141(9):2561-2575. doi: 10.1093/brain/awy182. PMID: 30007309; PMCID: PMC6113638.