The malaria parasite Plasmodium falciparum has a complex life cycle involving two hosts. P. falciparum gametocytes are the form of the parasite which undertakes the transition from the human to the mosquito host. The developmental changes required for this transition are poorly understood. There is, however, some evidence for a shift in metabolic energy generation from glycolysis in the human host to respiration in the mosquito host. The primary goal of the proposed study is to test the hypothesis that P. falciparum mitochondria undergo developmental changes during gametocytogenesis that allow them to become functionally competent for respiration. A secondary goal is to determine if the timing of biochemical changes in developing gametocyte mitochondria correlate with changes in P. falciparum sensitivity to the antimalarial drug primaquine. The long-term goal of this study is to elucidate the mechanisms by which gametocytes regulate changes in metabolism in preparation for the shift in hosts. There are three specific aims for the proposed study. The first specific aim is to develop assays to measure the expression of marker proteins representing the three major mitochondrial activities. The marker proteins selected are cytochrome b, which is required for electron transport, mitochondrial malate dehydrogenase, which is required for the tricarboxylic acid (TCA) cycle and for the malate shuttle, and cytoplasmic malate dehydrogenase, which is required for the malate shuttle. These assays will require preparation of nucleic acid and antibody probes for each marker protein. The second specific aim is to characterize the biochemical changes in P. falciparum mitochondrial during the transition from the human to the mosquito host. To accomplish this, the expression of the marker proteins will be measured in asexual erythrocytic parasites, in parasites in early stages of gametocyte development, in parasites in late stages of gametocyte development and in zygotes. The third specific aim is to determine if there is a correlation between the biochemical changes in developing gametocyte mitochondria and the development of primaquine sensitivity. To accomplish this, a vital dye will be used to first determine how mitochondrial structure and transmembrane potential change during asexual and sexual developmental stages. Then the vital dye will be used to assay these same stages for the effects of primaquine on mitochondrial potential and cell viability. These studies will increase our understanding of the role of P. falciparum mitochondrial biogenesis in the transition from a human to a mosquito host.
