“I always said there were two things I’d never do:
parasites and metabolism!”
Professor Ariel Silber, from the University of São Paulo (USP), the NTD Network hub leader for South America, laughs as he recalls himself as an impetuous undergraduate. Ariel is a specialist in trypanosomes (Tryps); single-celled parasites causing the neglected tropical diseases (NTDs) Chagas disease, leishmaniasis and sleeping sickness. We are catching up over a coffee during his visit with Durham NTD Network members.
When asked how he became interested in parasitology, Ariel laughs again, and shakes his head. Initially, he explains, he dreamed of studying ‘something important’; development, or neuroscience, or possibly cancer. He explains, “I was in love with molecular biology! Parasites were way too boring!” However, a short undergraduate course in molecular laboratory techniques, involving Trypanosoma cruzi (the cause of Chagas disease), radically changed his mind.
“I realised that, to begin to understand this parasite,
I had to ‘burn’ all my undergraduate textbooks!”
Ariel’s PhD at the University of Buenos Aires investigated how T. cruzi gains entry into mammalian cells. Later, in 2000, he moved to USP for post-doctoral studies. His supervisor, Professor Maria Julia Manso Alves, supported him to develop his own independent research investigating the role of amino acids in Tryp biology. This mentoring was crucial to his gaining funding from the Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) to set up his own lab. In the same spirit as Maria Julia and FAPESP, Ariel generously encourages his brilliant students to follow their curiosity, and develop independence in their ideas and research career.
It was curiosity that led Ariel from ‘dabbling’ with metabolism to embracing it fully, in 2004, “…although,” he adds, “I’m still not sure its love!” He wanted to work with trypanosome genetics using RNA interference (RNAi), a routine tool used to ‘knock down’ (prevent the action of) individual genes. This proved difficult, as some Tryps, specifically T. cruzi1 and most Leishmania species2 (causing leishmaniasis), lack the cellular machinery needed for RNAi.3,4 Fortunately, the technique can be used in a genetically similar trypanosome; T. brucei,5 the cause of sleeping sickness. This prompted Ariel to collaborate with Dr Alvaro Acosta Serrano at the Liverpool School of Tropical Medicine, a specialist in T. brucei and its relationship with its insect host, the tsetse fly (Glossinia spp). Tsetse flies are vectors for sleeping sickness, spreading the infection to humans and other mammals.
Together with Ariel’s students, Lisvane Silva Paes and Brian Suárez Mantilla, Ariel and Alvaro began genetic manipulation studies in T. brucei. They choose to work with genes from a familiar biochemical pathway found in all living cells, involved in the conversion (metabolism) of the amino acid proline into another amino acid, glutamate. They began to ‘knock down’ genes in T. brucei to infer the role of the equivalent gene from T. cruzi.
The data from their early experiments shows how familiarity can create the illusion that we understand something The proline-to-glutamate pathway involves two enzymes, proline dehydrogenase (ProDH) and Δ1-pyrroline-5-carboxylate dehydrogenase (P5CDH). Ariel and Alvaro initially found that T cruzi’s version of ProDH, although peculiar, is not especially unusual. However their results showed that T. cruzi’s P5CDH, needed for its familiar metabolic role, was also vital for T. brucei to survive in its tsetse fly host, and for T. cruzi to reproduce and infect its mammalian host!6,7 Ariel’s eyes widen as he explains, “I realised that P5CHD was barely characterised in any organism!”
Today, the genetic techniques used in Ariel’s lab include the routine shuttling genes between three Tryps (‘TriTryps’) – mainly T. cruzi and T. brucei and to a lesser extent Leishmania major, using each as a system to investigate the action of genes taken from the others. These genetic methods, replacing genes in one Tryp with genes taken from another, are now valuable methods which allow his team to study in depth the intricacies of Tryp metabolism.
“Trypanosomes show us that another biological logic is possible… and it works!”
In addition, a body of work on TriTryps now shows that these parasites use amino acids in various ways beyond their well-known roles as energy sources and the building blocks of proteins.8 In adapting to the range of environments encountered inside their varied insect and mammal hosts, Tryps have evolved their own, novel biological rules and solutions. This is “wild” in scientific terms. Crucially, Ariel’s research also highlights the possibility that key metabolic enzymes may prove useful as potential targets for new drugs to treat Chagas disease and leishmaniasis in humans.9 As a result, the sign on the Silber laboratory door reads, “Drugs (for neglected diseases), metabolism, and rock and roll”.
Ariel now describes himself as ‘…a cartographer’, an idea taken from his collaborator, Professor Fred Bringaud (Université Bordeaux, France). These colleagues now seek to map all of the biochemical pathways used in Tryp metabolism. Ariel’s priorities are now:
1. To figure out ‘how the TriTryp machines work’
2. To identify potential new drug targets
These aims are complementary. Understanding parasite metabolism highlights potential new targets for much-needed drug treatments against Chagas disease and leishmaniasis, whilst drugs are also vital as tools for research, enabling the easy modification of parasite metabolism in the laboratory.
I ask Ariel for his dream now as a scientist. He laughs again, confessing that he hopes, eventually, “…to understand a little bit about this very odd organism”.
- DaRocha WD, et al. Molec Biochem Parasitol 2004; 133: 175–186.
- Robinson KA and Beverley SM. Molec Biochem Parasitol 2003; 128: 217–228.
- El-Sayed NM, et al. Science 2005; 309(5733): 409–415.
- Ivens AC, et al. Science. 2005; 309(5733): 436–442.
- Ngô H, et al. Proc Natl Acad Sci USA 1998: 95:14687–14692.
- Mantilla BS, et al. J Biol Chem 2015; 290: 7767-7790.
- Mantilla BS, et al. PLoS Pathogens 2017; 13: e1006158.
- Marchese L, et al. Pathogens 2018; 7: 36.
- Silber AM, et al. Curr DrugTargets Infect Disord 2005; 5(1): 53–64