Exosome RNA Exosome RNA Research & Industry News
Leishmaniasis is caused by Leishmania parasites, which can survive inside macrophages, immune cells that normally help destroy invading microorganisms. Researchers are increasingly finding that one way the parasite may manipulate these cells is through exosomes, small extracellular vesicles that transport proteins, RNA, and other molecules between cells.
A research team from the Department of Medicine at the University of British Columbia, Canada have investigated how small RNA molecules carried by Leishmania exosomes can alter host macrophages. The researchers focused on two tRNA-derived fragments, Ld-tRF-Asp and Ld-tRF-Leu.
Hypothetical model of Leishmania tRFs mediating modulation
of host macrophage gene expression
Leishmania tRFs are delivered into the host cell cytosol via exosomes secreted within the phagolysosome of the Leishmania-infected host cell or via secreted exosomes released by infected bystander cells. Leishmania tRFs released from exosomes could be preferentially loaded onto host Ago1, which does not require complete complementarity to target mRNA. Ago1, together with other proteins, forms the RISC. The RISC then regulates gene expression post-transcriptionally by targeting mRNAs. tRF-loaded Ago1 could also enter the nucleus, leading to nascent RNA silencing. As Ago-independent mechanisms, tRFs directly interact with other RNA-binding proteins to regulate host gene expression.
Exosomes as parasite delivery vehicles
Exosomes can act as biological delivery systems, carrying molecular cargo from one cell to another. Leishmania exosomes contain small noncoding RNAs that may influence gene regulation after entering host cells.
The researchers examined tRNA-derived fragments, or tRFs, which are small pieces of transfer RNA that can function as regulatory molecules rather than simply being products of RNA breakdown.
To determine how these parasite-derived RNAs affect macrophages, the researchers used quantitative proteomics to measure changes in the proteins produced by the cells.
Ld-tRF-Asp altered 20 macrophage proteins, while Ld-tRF-Leu affected 18. Several of these changes appeared to favor Leishmania survival, suggesting that exosome-delivered RNAs may help the parasite create a more favorable environment inside host cells.
Using the host’s gene-regulation machinery
The researchers also investigated how the tRNA fragments produce these effects.
They found that both Ld-tRF-Asp and Ld-tRF-Leu associated with Argonaute proteins, which are important components of RNA-based gene regulation. Small regulatory RNAs can bind to Argonaute proteins and help direct them toward specific messenger RNA targets.
Additional experiments showed that Ld-tRF-Leu selectively interacted with Argonaute 1, suggesting that the parasite-derived RNA may use the macrophage’s own molecular machinery to influence host gene expression.
This is an important example of how pathogens can exploit normal cellular processes. Instead of supplying all of the machinery needed to regulate host genes, Leishmania may deliver regulatory RNAs through exosomes and then use proteins already present in the host cell.
Understanding parasite-host communication
Macrophages are supposed to eliminate microorganisms, yet Leishmania can survive and reproduce inside them. Understanding how the parasite changes macrophage biology could help reveal new therapeutic targets.
These findings suggest that exosomal tRNA fragments are one mechanism by which Leishmania may manipulate host cells. By altering macrophage protein production and interacting with Argonaute proteins, these small RNAs may help create conditions that support parasite survival.
Further research will be needed to identify the specific genes targeted by these RNAs and determine how important these interactions are during infection. More broadly, the findings demonstrate how extracellular vesicles can serve as active communication systems between pathogens and host cells.
