title: Trypanosome Lytic Factor-1 Initiates Oxidation-stimulated Osmotic Lysis of Trypanosoma brucei brucei.
abstract: Human innate immunity against the veterinary pathogen Trypanosoma brucei brucei is conferred by trypanosome lytic factors (TLFs), against which human-infective T. brucei gambiense and T. brucei rhodesiense have evolved resistance. TLF-1 is a subclass of high density lipoprotein particles defined by two primate-specific apolipoproteins: the ion channel-forming toxin ApoL1 (apolipoprotein L1) and the hemoglobin (Hb) scavenger Hpr (haptoglobin-related protein). The role of oxidative stress in the TLF-1 lytic mechanism has been controversial. Here we show that oxidative processes are involved in TLF-1 killing of T. brucei brucei. The lipophilic antioxidant N,N'-diphenyl-p-phenylenediamine protected TLF-1-treated T. brucei brucei from lysis. Conversely, lysis of TLF-1-treated T. brucei brucei was increased by the addition of peroxides or thiol-conjugating agents. Previously, the Hpr-Hb complex was postulated to be a source of free radicals during TLF-1 lysis. However, we found that the iron-containing heme of the Hpr-Hb complex was not involved in TLF-1 lysis. Furthermore, neither high concentrations of transferrin nor knock-out of cytosolic lipid peroxidases prevented TLF-1 lysis. Instead, purified ApoL1 was sufficient to induce lysis, and ApoL1 lysis was inhibited by the antioxidant DPPD. Swelling of TLF-1-treated T. brucei brucei was reminiscent of swelling under hypotonic stress. Moreover, TLF-1-treated T. brucei brucei became rapidly susceptible to hypotonic lysis. T. brucei brucei cells exposed to peroxides or thiol-binding agents were also sensitized to hypotonic lysis in the absence of TLF-1. We postulate that ApoL1 initiates osmotic stress at the plasma membrane, which sensitizes T. brucei brucei to oxidation-stimulated osmotic lysis.
authors.affiliation: From the Department of Biochemistry and Molecular Biology, University of Georgia, Athens, Georgia 30602.
authors.forename: Amy Styer
authors.initials: AS
authors.lastname: Greene
authors.affiliation: From the Department of Biochemistry and Molecular Biology, University of Georgia, Athens, Georgia 30602 shajduk@bmb.uga.edu.
authors.forename: Stephen L
authors.initials: SL
authors.lastname: Hajduk
mesh_terms: D000075944:Apolipoprotein L1; D001053:Apolipoproteins / Q000378:metabolism / Q000494:pharmacology; D002462:Cell Membrane / Q000235:genetics / Q000378:metabolism*; D005609:Free Radicals / Q000378:metabolism; D055785:Gene Knockdown Techniques; D006801:Humans; D008075:Lipoproteins, HDL / Q000378:metabolism / Q000494:pharmacology*; D009997:Osmotic Pressure / Q000187:drug effects*; D010084:Oxidation-Reduction / Q000187:drug effects; D018384:Oxidative Stress / Q000187:drug effects*; D015800:Protozoan Proteins / Q000235:genetics / Q000378:metabolism; D014346:Trypanosoma brucei brucei / Q000235:genetics / Q000378:metabolism*
chemical_list: C108666:APOL1 protein, human; D000075944:Apolipoprotein L1; D001053:Apolipoproteins; D005609:Free Radicals; D008075:Lipoproteins, HDL; D015800:Protozoan Proteins; C434063:TLF1 protein, human
keywords: Trypanosoma brucei; cell death; innate immunity; osmotic swelling; oxidative stress; parasite; trypanosome