Summary
The goal to prevent Plasmodium falciparum transmission from
humans to mosquitoes requires the identification of targetable metabolic processes in the
mature (stage V) gametocytes, the sexual stages circulating in the bloodstream. This task
is complicated by the apparently low metabolism of these cells, which renders them
refractory to most antimalarial inhibitors and constrains the development of specific and
sensitive cell-based assays. Here we identify and functionally characterize the regulatory
regions of the P. falciparum gene PF3D7_1234700, encoding a CPW-WPC
protein and named here Upregulated in Late Gametocytes (ULG8), which we
have leveraged to express reporter genes in mature male and female gametocytes. Using
transgenic parasites containing a pfULG8-luciferase cassette, we
investigated the susceptibility of stage V gametocytes to compounds specifically affecting
redox metabolism. Our results reveal a high sensitivity of mature gametocytes to the
glutathione reductase inhibitor and redox cycler drug methylene blue (MB). Using
isobologram analysis, we find that a concomitant inhibition of the parasite enzyme
glucose-6-phosphate dehydrogenase-6-phosphogluconolactonase, a key component of NADPH
synthesis, potently synergizes MB activity. These data suggest that redox metabolism and
detoxification activity play an unsuspected yet vital role in stage V gametocytes,
rendering these cells exquisitely sensitive to decreases in NADPH concentration.