Leishmania Hijacks microRNA Import-Export Machinery of Infected Macrophage and Survives by Cross-Communicating Host miR-146a to Subjugate HuR and miR-122 in Neighbouring cells

Leishmania donovani, the causative agent of visceral leishmaniasis, infects and resides within tissue macrophage cells of the mammalian host. It is not clear how the parasite infected cells cross-talk with the non-infected cells in the infection niche to regulate the infection process. Interestingly, miRNAs, the regulatory small RNAs of the host, could get trafficked into and out of infected cells as part of extracellular vesicles to ensure exchange of the epigenetic signals and can regulate the expression of their target genes in both donor and recipient cells. Leishmania, for its survival in host macrophage, adopts a dual strategy to regulate the intercellular transport of host miRNAs. The parasite, by preventing mitochondrial function of the host cells, restricts the entry of liver cell derived miR-122 containing extracellular vesicles in infected macrophage to curtail the inflammatory response by miR-122. The parasite reciprocally upregulates the extracellular export of anti-inflammatory miR-146a from the infected cells. The exported miR-146a restricts miR-122 production in liver cells and polarizes neighbouring naive macrophages to the M2 state. miR-146a upregulates IL-10 in neighbouring macrophages where miR-146a dominates the RNA binding and miRNA suppressor protein HuR to inhibit the expression of proinflammatory cytokine mRNAs having HuR-interacting AU-rich elements and polarized the recipient cells to M2 stage. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=116 SRC="FIGDIR/small/459146v1_ufig1.gif" ALT="Figure 1"> View larger version (22K): org.highwire.dtl.DTLVardef@32e32dorg.highwire.dtl.DTLVardef@e0d3c6org.highwire.dtl.DTLVardef@6f77e6org.highwire.dtl.DTLVardef@289e49_HPS_FORMAT_FIGEXP M_FIG C_FIG Key FindingsO_LILeishmania stops vesicular entry of inflammatory miR-122 in infected cells by causing mitochondrial depolarization C_LIO_LILeishmania secrets miR-146a from infected cells to stop miR-122 production in neighbouring hepatocytes C_LIO_LImiR-146a containing vesicles secreted by infected cells stops inflammatory response in recipient naive macrophage C_LIO_LImiR-146 targets RNA binding protein HuR to stop inflammatory cytokine production C_LI