Non-Canonical Ago Loading of EV-Derived Exogenous miRNA Generates Foreign miRNPs on Endosomes to Arbitrate Gene Expression in Recipient Cells

Abstract

MicroRNAs, the tiny regulators of gene expression, can be transferred between neighbouring cells via Extracellular Vesicles (EV) to control the expression of genes in both donor and recipient cells. How the Extracellular Vesicles-derived miRNAs are getting internalized and become functional in target cells is an unresolved question. We found that EV-associated miRNAs are primarily single stranded and, to become functional, get loaded with the Ago proteins present in the recipient cells without requiring host Dicer1. Following endocytosis of miRNA-containing extracellular vesicles, loading of host Ago occurs on the endosomal membrane where pH-dependent membrane fusion triggers the release of internalized miRNAs to form exogenous miRNP pool. In addition, loading of exogenous miRNA to host Ago also depends on the mitochondrial activity of recipient cells. Internalization of hepatocyte derived miR-122 containing EVs in macrophage activates the recipient cell by targeting cytokine expression. Leishmania donovani, a protozoan parasite known to affect endocytosis and to cause mitochondrial depolarization in infected macrophages, restricts the EV-internalization process and thereby preventing inflammatory cytokine expression and ensuring internalized pathogen survival in macrophage.