Leishmaniasis, a disease caused by the Leishmania spp. parasite, affects 700 000 to 1 million people annually worldwide and causes chronic, severe skin and mucocutaneous ulcers1. Specific Leishmania species, such as Leishmania donovani, cause chronic spleen, liver and bone marrow infection which if left untreated leads to a fatal visceral infection resulting in 25 000 - 65 000 deaths globally each year1. Current visceral leishmaniasis treatments are expensive, have severe side effects, and with the rise of drug resistance and no available vaccine, there is an unmet need for novel therapeutics1.
Intracellular pathogens, such as Leishmania spp. manipulate host cell survival and cell death signalling pathways in order to survive, replicate and disseminate. We therefore hypothesise that therapeutic approaches that specifically target the host, rather than the pathogen itself present a valid therapeutic option to reduce parasite burden and ultimately, treat visceral leishmaniasis.
The aim of this project was to use L. donovani as a model organism of visceral leishmania in both in vivo and in vitro systems to explore the role of different cell death pathways in infection.
Using gene-targeted mice as well as therapeutic compounds targeting the host cell apoptotic and necroptotic machinery, we determined parasitic burden, cell death and protein expression through microscopy, live cell imaging, flow cytometry and immunoblotting upon infection with L. donovani.
Our results suggest that there is no role for necroptosis in L. donovani infection as MLKL-/- or RIPK3-/- mice showed no difference in parasite burden compared to C57Bl/6 controls. Furthermore, pharmacological induction of intrinsic apoptosis using BCL-2 and BCL-XL inhibitors also do not affect parasite burdens.
However, extrinsic apoptosis appears to play a central role in vivo as mice infected with L. donovani and treated with SMAC mimetics have a reduced parasite replicative reservoir due to apoptosis, a reduction in liver granulomas and in the associated symptom; hepatosplenomegaly. Using live cell imaging and flow cytometry we have shown that we can induce extrinsic apoptosis of infected BMDMs in vitro, resulting in parasite death.
We are currently exploring improved SMAC mimetic treatment regiments and the immunological consequences of therapeutic targeting in vivo.