A novel pathway of functional microRNA uptake and mitochondria delivery

Abstract

AbstractExtracellular miRNAs serve as signal molecules in the recipient cells. Uptake of extracellular miRNAs by the recipient cells and their intracellular transport, however, remains elusive. Here we show RNA phase separation as a novel pathway of miRNA uptake. In the presence of serum, synthetic miRNAs rapidly self-assembly into ∼110nm discrete nanoparticles which enable miRNAs’ entry into different cells. Depleting serum cationic proteins prevents the formation of such nanoparticles and thus blocks miRNA uptake. Different from lipofectamine-mediated miRNA transfection in which the majority of miRNAs are in lysosomes of transfected cells, nanoparticles-mediated miRNA uptake predominantly delivers miRNAs into mitochondria in a polyribonucleotide nucleotidyltransferase 1-dependent manner. Functional assays further show that the internalized miR-21 via miRNA phase separation enhances mitochondrial translation of Cytochrome b, leading to increase in ATP and ROS reduction in HEK293T cells. Our findings reveal a previously unrecognized mechanism for uptaking and delivering functional extracellular miRNAs into mitochondria.SynopsisRNA phase separation-based extracellular miRNA uptake and PNPT1-mediated mitochondrial delivery of internalized miRNAsmiRNAs can self-assembly into ∼110nm nanoparticles to enter various cells in the presence of serummiRNA phase separation is mediated by serum cationic proteinsInternalized miRNAs via this nanoparticle pathway are predominantly delivered to mitochondriaMitochondrial delivery of the internalized miRNAs is mediated by PNPT1