ROS regulate differentiation of visceralizing Leishmania species into the virulent amastigote form

Leishmania virulence and disease development critically depends on the ability of Leishmania promastigotes to infect, differentiate into amastigote forms and replicate inside mammalian host macrophages. Understanding changes associated with amastigote differentiation in axenic culture conditions is key to identifying virulence factors. Here we compared efficiency of the conventional pH-temperature-dependent shift method to induce amastigote differentiation with the recently identified trigger for differentiation mediated by mitochondrial reactive oxygen species (ROS). Using two different visceral leishmaniasis species, L. infantum and. L. donovani, we show that ROS-generating methods such as iron deprivation or exposure to sub-lethal concentrations of H₂O₂ or menadione are significantly more effective in promoting promastigoteamastigote differentiation than the low pH-high temperature shift, leading to higher survival rates, morphological changes and gene expression patterns characteristic of the amastigote stage. Notably, both H₂O₂ and menadione-mediated differentiation did not require up-regulation of the mitochondrial electron transport chain (ETC)-associated protein p27, suggesting that treatment with oxidants bypasses the necessity to upregulate mitochondrial activity, a precondition for mROS generation. Our findings confirm that ROS-induced differentiation occurs in multiple Leishmania species, including the medically important visceralizing species, and provide mechanistic rationale for earlier reports demonstrating markedly increased virulence of L. infantum promastigotes pre-treated with oxidative reagents.