CRISPR/Cas9-mediated deletion of a kinetoplast-associated gene attenuates virulence in Leishmania major parasites.

Abstract

We employed a CRISPR/Cas9 technique in Leishmania major to evaluate its efficiency in editing a kDNA-associated gene, the universal minicircle sequence binding protein (UMSBP), which is involved in mitochondrial respiration and kinetoplast division. Using this toolkit, we generated UMSBP mNG-tagged and single knockout L. major (LmUMSBP^+/-) parasites, which were confirmed by PCR, confocal microscopy and Western blot analyses. The growth rate of promastigotes in culture and their infectivity in macrophages were analysed in vitro. Mice were immunized with the LmUMSBP^+/- mutant strain, and lesion size and parasite burden were measured upon challenge with wild-type (WT) L. major. Cytokines were quantified in supernatants of lymph node cell cultures. The results suggested successful expression and localization of the UMSBP mNG-tagged protein within the kinetoplast in both promastigote and intracellular amastigote forms, confirming the consistency of fluorescence tagging throughout various stages of the Leishmania life cycle. Attenuated LmUMSBP^+/- parasites showed significantly reduced growth in culture (P < 0.05), increased apoptosis (P < 0.05) and downregulation of tryparedoxin peroxidase (TXNPx) and trypanothione synthetase (TryS) gene expression compared to WT L. major. LmUMSBP^+/- mutant strains did not cause lesions in a susceptible BALB/c mouse model. Furthermore, immunization with LmUMSBP^+/- parasites elicited a Th1 immune response, characterized by significantly higher IFN-γ and lower IL-4 production in cell culture (P < 0.001), which was associated with partial protection against WT L. major challenge, as evidenced by reduced parasite burden and lesion development in BALB/c mice. In this study, we successfully validated a practical CRISPR/Cas9 toolkit in L. major, targeting the kinetoplast-associated gene UMSBP. Our findings suggest that the UMSBP single-allele knockout mutant holds promise as a valuable tool for studying the role of the kinetoplast in Leishmania biology and as a potential candidate for further investigation as a live-attenuated vaccine against Leishmania infection.