A group of microorganisms known as kinetoplastids include the parasites that cause devastating diseases such as African sleeping sickness, Chagas disease, and leishmaniasis. They share an ability to attach to the insides of their insect hosts, using a specialized protein structure. But what if scientists could prevent the parasite from joining? Would the parasites pass right through the vectors, unable to be transmitted to humans?
That's the idea behind a new study led by Michael Povelones of Penn State School of Veterinary Medicine and Megan L. Povelones of Penn State Brandywine. Using a kinetoplastid species non-causing disease called Crithidia fasciculata, this husband-wife duo and their research team identified a number of genes involved in adhesion in its mosquito host.
The parasite must keep itself from going through it. It needs to retain itself in the intestine to multiply and eventually pass on. These mechanisms of incorporation appear to be [shared] across kinetoplastid species, so the hope is that our understanding of Crithidia will tell us something about adherence in the medicinal species. "
Michael Povelones, assistant professor of pathobiology, Penn Vet
The study appears in the newspaper PLOS Neglected Tropical Diseases.
Scientists have long turned to Crithidia fasciculata as a biochemical model for understanding features of parasitic disease, as it is easy to grow in a laboratory. Megan Povelones, whose specialty is African trypanosomiasis, knew it from her doctoral studies at Johns Hopkins University, and the topic came up in conversations with her husband.
"Sometimes we talk shop at home," says Michael Povelones, whose own research has focused on ways to harness the power of the mosquito's own immune defenses to stop them from transmitting disease. "I was amazed at the fact that Crithidia infects mosquitoes, but is not a human or animal pathogen, little has been known about its life cycle, and that some electron microscope studies have been done that show that the parasite actually attaches to the mosquito's intestine. a specific kind of structure that people have described as a hemidesmosome. I felt like I had to explore some fascinating cell biology. "
Together, they began investigating what is going on to enable the parasite to "hold on" inside the mosquito, a feature believed to be critical for the transmission of disease.
In the lab, the researchers were able to replicate what other scientists found previously: Crithidia parasites both exist in a swim-like shape, with a tail-like appendix called a flagellum, and an adherent form that even clings to the surface of the. plastic dishes in which they were grown in the lab. The swimming-shaped shape was favored when the cultured dishes were placed on a shaft, while the aderal shape, which split to form rosette structures, developed more when the plates were stopped. Interestingly, they noticed that the parasitic parasites in the rosettes sometimes give rise to swimming versions.
In order to focus on the adept parasites, the researchers would wait to see rosettes appear and then remove the swimming parasite. They could then focus on probing the genetics of the two types.
"One question we had was really simple," says Michael Povelones, "which was," What were the transcriptional differences between the swimming cells versus those allowed to grow like rosettes? "
Notably, that two forms of the same species grow in the same medium, the researchers found a significant range of variation in gene expression between the two.
"The adhesion process has transformed its transcription in a really dramatic way," says Michael Povelones.
When the researchers infected mosquito laboratories with Crithidia, they found that the parasites adhering to the mosquitoes, especially in their postglacial region, resembled the adept form they cultivated in the lab, giving them confidence that studying their labs could reveal important information about what happened in the insect hosts of the parasites.
Among the genes with enhanced expression was a group known as GP63s, which have been implicated in adhesion to immune cells in the Leishmania parasite.
The team hopes to conduct further research on adhesion using Crithidia as a tool, looking specifically at genes involved in the process, which are known to be divided between kinetoplastid species and which may, one day, serve as a target for blocking vector-borne transmission. diseases.
University of Pennsylvania
Reference journal reference:
Filosa, J.N.L et al. (2019) Dramatic changes in gene expression in different forms of Crithidia fasciculata reveal possible mechanisms for insect-specific adhesion in kinetoplastid parasites. PLOS Neglected Tropical Diseases. doi.org/10.1371/journal.pntd.0007570.