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Updated: Sep 25, 2025
Quantification of Intracellular Growth Inside Macrophages is a Fast and Reliable Method for Assessing the Virulence of Leishmania Parasites
Published on: March 16, 2018
FRB domain of human TOR protein induces compromised proliferation and mitochondrial dysfunction in Leishmaniadonovani
Sudipta Chakraborty1, Soumyajit Mukherjee2, Priyam Biswas2
1Department of Biochemistry, University of Calcutta, India; Department of Microbiology, Bidhannagar College, Kolkata, India.
Abstract:
Visceral leishmaniasis (VL) or Kala-azar, the second-largest parasitic killer worldwide, is caused by Leishmania donovani. The drugs to treat VL are toxic and expensive. Moreover, their indiscriminate use gave rise to resistant strains. The high rate of parasite proliferation within the host macrophage cells causes pathogenesis. In the proliferative pathway, FRB domain of TOR protein is ubiquitously essential. Although orthologues of mTOR protein are reported in trypanosomatids and Leishmania but therein depth molecular characterization is yet to be done. Considerable protein sequence homology exists between the TOR of kinetoplastidas and mammals. Interestingly, exogenous human FRB domain was shown to block G1 to S transition in mammalian cancer cells. Thus, we hypothesized that expression of human FRB domain would inhibit the proliferation of Leishmaniadonovani. Indeed, promastigotes stably expressing wild type human FRB domain show 4.7 and 1.5 folds less intra- and extra-cellular proliferations than that of untransfected controls. They also manifested 2.65 times lower rate of glucose stimulated oxygen consumption. The activities of all respiratory complexes were compromised in the hFRB expressing promastigotes. In these cells, depolarized mitochondria were 2-fold more than control cells. However, promastigotes expressing its mutant version (Trp2027-Phe) has shown similar characteristics like untransfected cells. Thus, this study reveals greater insights on the conserved role of TOR in the regulation of the respiratory complexes in L. donovani. The slow growing variant of FRB expressing promastigotes will have great potential to be exploited as a prophylactic agent against leishmaniasis.
Insights
Researchers explored inhibiting Leishmania donovani proliferation using the human FRB domain, a key part of the TOR protein. Expressing this domain significantly reduced parasite growth and affected cellular respiration, offering potential for new leishmaniasis treatments.
Area of Science:
- Parasitology
- Molecular Biology
- Drug Discovery
Background:
- Visceral leishmaniasis (VL), caused by Leishmania donovani, is a major parasitic disease with limited treatment options.
- Existing VL drugs are toxic, expensive, and face growing resistance due to parasite proliferation within host macrophages.
- The FRB domain of the TOR protein is crucial for parasite proliferation, with conserved homology between kinetoplastids and mammals.
Purpose of the Study:
- To investigate the potential of expressing the human FRB domain to inhibit Leishmania donovani proliferation.
- To understand the molecular mechanisms underlying TOR's role in regulating parasite growth and cellular respiration.
Main Methods:
- Stable expression of wild-type and mutant human FRB domain in Leishmania donovani promastigotes.
- Quantification of intra- and extra-cellular parasite proliferation.
- Measurement of glucose-stimulated oxygen consumption and respiratory complex activities.
- Mitochondrial membrane potential assessment.
Main Results:
- Promastigotes expressing wild-type human FRB showed significantly reduced intra- and extra-cellular proliferation (4.7 and 1.5 folds, respectively).
- FRB-expressing parasites exhibited decreased glucose-stimulated oxygen consumption (2.65 times lower) and compromised respiratory complex activities.
- Mitochondria in FRB-expressing cells were depolarized (2-fold higher), while mutant FRB expression had no significant effect.
- These findings highlight the conserved role of TOR in regulating respiratory complexes in L. donovani.
Conclusions:
- The human FRB domain effectively inhibits Leishmania donovani proliferation by disrupting cellular respiration and mitochondrial function.
- The conserved nature of the TOR pathway suggests a potential therapeutic target for leishmaniasis.
- FRB-expressing Leishmania donovani variants show promise as prophylactic agents against visceral leishmaniasis.
