Apoptosis-like cell death pathways in the unicellular parasite Toxoplasma gondii following treatment with apoptosis indu
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ORIGINAL PAPER
Apoptosis-like cell death pathways in the unicellular parasite Toxoplasma gondii following treatment with apoptosis inducers and chemotherapeutic agents: a proof-of-concept study Ayu Dewi Ni Nyoman • Carsten G. K. Lu¨der
Published online: 7 March 2013 Ó The Author(s) 2013. This article is published with open access at Springerlink.com
Abstract Ancient pathways of an apoptosis-like cell death have been identified in unicellular eukaryotes including protozoan parasites. Here, we examined programmed cell death in the apicomplexan Toxoplasma gondii which is a common intracellular pathogen of humans and warm-blooded animals. Treatment of extracellular T. gondii with various pro-apoptotic stimuli significantly induced DNA strand breaks as revealed by TUNEL and flow cytometry. Using staurosporine or miltefosine as pro-apoptotic stimuli, parasites also presented a reduced cell size, i.e. pyknosis and externalized phosphatidylserine while the plasma membrane remained intact. Importantly, staurosporine also induced DNA strand breaks in intracellular T. gondii. Data mining of the Toxoplasma genome resource identified 17 putative cell death-associated genes encoding proteases, a nuclease and several apoptosis regulators. Staurosporine-treated parasites but not controls strongly up-regulated several of these genes in a time-dependent fashion with a putative PDCD2 protein being more than 100-fold up-regulated. However, the mitochondrial membrane potential (DWm) remained intact and caspase-like activity increased only slightly during staurosporine-triggered cell death. As compared to staurosporine, the transcriptional response of parasites to miltefosine was more restricted but PDCD2 was again
A. D. Ni Nyoman C. G. K. Lu¨der (&) Institute for Medical Microbiology, University Medical Center, Georg-August-University, Kreuzbergring 57, 37075, Go¨ttingen, Germany e-mail: [email protected] A. D. Ni Nyoman Department of Biochemistry, Faculty of Medicine and Health Sciences, Udayana University, Sudirman Denpasar, 80232 Bali, Indonesia
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strongly induced. Furthermore, T. gondii lost their DWm and rapidly presented strong caspase-like activity during miltefosine treatment. Consequently, protease inhibitors abrogated miltefosine-induced but not staurosporineinduced Toxoplasma cell death. Finally, toxoplasmacidal drugs triggered DNA strand breaks in extracellular T. gondii. Interestingly, clindamycin also induced markers of an apoptosis-like cell death in intracellular parasites. Together, the data indicate that T. gondii possesses ancient apoptosis-like cell death machinery which can be triggered by chemotherapeutic agents. Keywords Toxoplasma gondii Unicellular parasite Apoptosis Therapeutics Mitochondria Protease
Introduction Apoptosis is a form of programmed cell death (PCD) that until recently was thought to be confined to metazoans. A form of cellular suicide in single-celled organisms indeed appeared counter-intuitive and evolutionary not favorable. This view has been challenged with the detection of m
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