Release of Small RNA-containing Exosome-like Vesicles from the Human Filarial Parasite Brugia malayi

Abstract

Lymphatic filariasis (LF) is a socio-economically devastating mosquito-borne Neglected Tropical Disease caused by parasitic filarial nematodes. The interaction between the parasite and host, both mosquito and human, during infection, development and persistence is dynamic and delicately balanced. Manipulation of this interface to the detriment of the parasite is a promising potential avenue to develop disease therapies but is prevented by our very limited understanding of the host-parasite relationship. Exosomes are bioactive small vesicles (30–120 nm) secreted by a wide range of cell types and involved in a wide range of physiological processes. Here, we report the identification and partial characterization of exosome-like vesicles (ELVs) released from the infective L3 stage of the human filarial parasite Brugia malayi. Exosome-like vesicles were isolated from parasites in culture media and electron microscopy and nanoparticle tracking analysis were used to confirm that vesicles produced by juvenile B. malayi are exosome-like based on size and morphology. We show that loss of parasite viability correlates with a time-dependent decay in vesicle size specificity and rate of release. The protein cargo of these vesicles is shown to include common exosomal protein markers and putative effector proteins. These Brugia-derived vesicles contain small RNA species that include microRNAs with host homology, suggesting a potential role in host manipulation. Confocal microscopy shows J774A.1, a murine macrophage cell line, internalize purified ELVs, and we demonstrate that these ELVs effectively stimulate a classically activated macrophage phenotype in J774A.1. To our knowledge, this is the first report of exosome-like vesicle release by a human parasitic nematode and our data suggest a novel mechanism by which human parasitic nematodes may actively direct the host responses to infection. Further interrogation of the makeup and function of these bioactive vesicles could seed new therapeutic strategies and unearth stage-specific diagnostic biomarkers.

Functional genomics in Brugia malayi reveal diverse muscle nAChRs and differences between cholinergic anthelmintics

“…Future phenotypic anthelmintic screens for drug development should include growth and developmental assays as well as release of excretory substances and exosomes assay (54)(55)(56) in addition to motility screens.…”

Host Manipulation by Parasites: Cases, Patterns, and Remaining Doubts

“…Unfortunately, the mechanisms and the net fitness effects remain to be investigated for virtually all described cases of host manipulation. Multiple parasites of insects have been speculated to secrete chemical compounds for host manipulation (Libersat et al, 2009), T. gondii secretes peptides that interact in multiple ways with the host immune system (Leroux et al, 2015), and even the release of small RNAcontaining vesicles has been reported for the filarial parasite Brugia malayi (Zamanian et al, 2015). However, the detailed nature of these molecules and their modes of action in the host remain to be identified.…”

Extracellular vesicle-mediated communication in host-parasite interactions: insight from Fasciola hepatica

“…Whilst EVs secreted by helminths can be internalized by host cells and regulate host immune and inflammatory responses (2)(3)(4)(5)10), it is unclear to what extent Fasciola EVs contribute to maintaining a Th2/regulatory environment that is permissive to fluke survival and reproduction. Once we gain a better understanding of these issues, the selective disruption of key pathways involved in EV biogenesis, or blocking the EV-driven delivery of parasite immunomodulators to host cells, might prove to be an efficient way to achieve parasite control in the future.…”

“…Indeed, perturbing EV production to modulate their pathological effects is an attractive therapeutic option that has been successful in a number of diseases, including cancer (1). To the same extent, several studies have described the contribution of parasite-derived EVs to the modulation of the host immune system (2)(3)(4) or the pathological effects on host cells (5). Tools such as transcriptomics and proteomics, have been particularly useful for identification of the immunomodulatory molecules that parasites package into EVs (6).…”