Description
- Abstract:
- Trypanosomes are the causative agent of human African sleeping sickness and nagana in cattle. The bovine parasite, Trypanosoma brucei brucei (T. b. brucei), is unable to infect humans because of a small subclass of High Density Lipoprotein (HDL) known as trypanosome lytic factor (TLF). TLF is composed of several proteins including apolipoprotein A-1 (ApoA-1), apolipoprotein L-1 (ApoL-1), and haptoglobin-related protein (Hpr). Both ApoL-1 and Hpr have been shown to be trypanolytic. When these two proteins are reconstituted into an HDL particle, the lytic activity increases 100-fold, indicating that the proteins have a synergistic relationship. Furthermore, Hpr and ApoL-1 co-purify from plasma when an antibody to either Hpr or ApoL-1 is used, suggesting that the proteins co-assemble. Our findings suggest, however, that Hpr and ApoL-1 do not have direct interactions. To understand how Hpr and ApoL-1 are co-assembled, we have examined the biogenesis of TLF in human liver cells. Hpr and ApoL-1 localize to the surface of liver cells. Addition of HDL to the media results in scavenging of Hpr. We propose that Hpr and ApoL-I traffic to the cell surface of liver cells, where they are scavenged by HDL. Once co-assembled, Hpr and ApoL-1 containing HDL are still not lytic in vitro. Only after TLF binds Hb is TLF "armed" for killing. We show that Hb is required for binding and endocytosis of TLF. In addition, an iron chelator and free radical scavenger inhibit lysis by TLF-Hb. Using 500 kDa dextrans, we also show that TLF-Hb causes lysosomal membrane breakdown. Taken together, TLF-Hb generates free radicals by an iron dependent mechanism. The free radicals lead to lipid peroxidation and membrane breakdown. We now have a model of TLF that begins with its biogenesis and ends with its killing of trypanosomes. Hpr and ApoL-1 are assembled into HDL by a cell-mediated process. Upon infection by T. b. brucei, an acute phase response causes severe hemolysis. Hpr binds hemoglobin, activating the toxin. TLF is then endocytosed by the parasite, leading to cell death and clearance of the infection.
- Notes:
- Thesis (Ph.D.) -- Brown University (2008)
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Citation
Widener, Justin W.,
"Biogenesis of Trypanosome Lytic Factor and Mechanism of Trypanosome Killing"
(2008).
Biology and Medicine Theses and Dissertations, Pathobiology Theses and Dissertations.
Brown Digital Repository. Brown University Library.
https://doi.org/10.7301/Z0WS8RGG
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Biology and Medicine Theses and Dissertations
Theses and Dissertations for the Biology and Medicine department.... -