Discipline: Biological Sciences
Subcategory: Cell and Molecular Biology
Yasmine Oprea - CUNY Hunter College
Co-Author(s): Daphne Ko, CUNY Hunter College, New York, New York; Joey Verdi, CUNY Graduate Center, New York, New York; Jayne Raper, CUNY Hunter College, New York, New York
African trypanosomes are extracellular parasites that cause African trypanosomiasis, or sleeping sickness. They are transmitted by infected tsetse flies to mammalian hosts, but humans and certain primates are able to resist infection by Trypanosoma brucei brucei because of innate immune factors known as trypanosome lytic factors (TLFs). TLFs are high-density lipoproteins that contain the trypanolytic protein Apolipoprotein L-1 (APOL1). APOL1 forms cation channels in the plasma membrane of the trypanosome, causing ion flux across the plasma membrane. After channel formation in the membrane, there is an initial influx of sodium ions, followed by chloride influx and a loss of osmoregulation resulting from uncontrolled ion flux. We hypothesize that the initial sodium influx is counterbalanced by potassium ion efflux through potassium leak channels. Trypanosomes have a genetically encoded heterodimeric plasma membrane potassium channel that is essential to survival, and we hypothesize that blocking this channel would accelerate lysis by forcing chloride influx to occur earlier. To investigate this, we used the potassium channel blocker barium chloride to block the transport of potassium ions across the plasma membrane and performed TLF-mediated trypanolysis assays using TLF-containing high-density lipoprotein isolated from human plasma. We observed that TLF kills parasites more rapidly in the presence of barium, although barium itself does not kill the parasites. However, barium is not entirely specific for potassium channels. Thus, we would like to confirm these biochemical experiments by using reverse genetics via targeted knockdown of the potassium channel in the presence of TLF and repeating these trypanolysis assays. This would help us better understand the mechanism by which APOL1-mediated trypanolysis occurs. References: 1. del Pilar Molina-Portela, M., Lugli, E. B., Recio-Pinto, E. & Raper, J.Trypanosome lytic factor, a subclass of high-density lipoprotein, forms cation-selective pores in membranes. Mol. Biochem. Parasitol. 144, 218–226 (2005). 2. Steinmann M.E., González-Salgado A., Bütikofer P., Mäser P., Sigel E. A heteromeric potassium channel involved in the modulation of the plasma membrane potential is essential for the survival of African trypanosomes. FASEB J., 29 (2015), pp. 3228-3237 3. Thomson R, Finkelstein A. Human trypanolytic factor APOL1 forms pH-gated cation-selective channels in planar lipid bilayers: relevance to trypanosome lysis. Proc Natl Acad Sci U S A. 2015;112(9):2894–9.
Funder Acknowledgement(s): Funding was provided by a National Science Foundation grant to Jayne Raper and by the McNulty Foundation.
Faculty Advisor: Dr. Jayne Raper, Jayne.Raper@nyumc.org
Role: I conducted all trypanolysis assays using the potassium channel blocker to determine its effect on the rate of lysis. I performed all data analysis for these assays as well.