S. Gannavaram, A. Debrabant, Laboratory of Bacterial Parasitic and Unconventional Agents, Division of Emerging and Transfusion Transmitted Diseases, CBER, FDA, Bethesda, MD 20892
Apoptosis is a physiological process critical for normal cellular development and tissue homeostasis in multicellular organisms but also in population control of unicellular organisms such as Leishmania and Trypanosoma which are responsible for a variety of human parasitic diseases (e.g. leishmaniasis, Chagas disease, African sleeping sickness). Although evident in several protozoan organisms, programmed cell death (PCD) pathway is not adequately exploited for developing strategies to control these important human parasites. We sought to identify components of protozoan PCD pathway as a means of parasite elimination. One of the hallmarks of apoptosis is the cleavage of chromatin into oligonucleosomal-sized fragments. Biochemical and genetic studies have identified at least two endonucleases involved in mammalian DNA fragmentation during apoptosis, the DNA fragmentation factor and endonuclease G (EndoG). We identified homologues of mammalian EndoG in Leishmania and Trypanosoma genomes. Overexpression of EndoG in Leishmania resulted in increased DNA damage, leading to parasite death. In addition, parasites overexpressing EndoG displayed heightened sensitivity to H2O2 induced PCD. In contrast, selective depletion of EndoG mRNA by RNA-interference in Trypanosoma brucei rendered the parasites more resistant to H2O2 induced PCD. We conclude that EndoG is an important component of protozoan PCD pathway. Understanding of the PCD pathway may contribute to better understanding of the biology and pathogenesis of trypanosomatid parasites and also in devising control strategies against these blood borne pathogens.