Chronic heat-shock treatment driven differentiation induces apoptosis in Leishmania donovani

The present study investigates the role of apoptosis in the regulation of cell numbers of Leishmania donovani during the in vitro differentiation of promastigote stage to amastigote stage in axenic conditions. We report that apoptosis is induced in Leishmania donovani due to chronic heat-shock treatment of 37 ^°C that also mediates the differentiation of promastigotes to amastigotes. This is characterized by the fragmentation of DNA, blebbing in the parasite cell membrane, nuclear condensation, formation of preapoptotic bodies and involvement of Ca⁺⁺ in the apoptotic process. The flowcytometric analysis shows an early and steep rise in percentage apoptotic nuclei till 48-hour stage of differentiation and then a gradual decline, suggesting synergistic action of Ca⁺⁺ ATPase and probably Hsp70. Hsp70 might be rescuing cells from apoptosis in the death signaling pathway. Incubation of the culture with Ca⁺⁺ chelator EGTA (1 mM) brings down the percentage of apoptotic nuclei considerably showing thereby that calcium is needed for the process of cell death here that occurs by apoptosis. The survival of the infective individuals appears to be decided by the parasite in the early stages of its differentiation. Our studies show the potential of the physiological temperature of 37 ^°C in inducing apoptosis in Leishmania donovani and the therapeutic use it can be put to.