Journal of Lipid Research (Feb 2015)

Discovery of an ergosterol-signaling factor that regulates Trypanosoma brucei growth[S]

  • Brad A. Haubrich,
  • Ujjal K. Singha,
  • Matthew B. Miller,
  • Craigen R. Nes,
  • Hosanna Anyatonwu,
  • Laurence Lecordier,
  • Presheet Patkar,
  • David J. Leaver,
  • Fernando Villalta,
  • Benoit Vanhollebeke,
  • Minu Chaudhuri,
  • W. David Nes

Journal volume & issue
Vol. 56, no. 2
pp. 331 – 341

Abstract

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Ergosterol biosynthesis and homeostasis in the parasitic protozoan Trypanosoma brucei was analyzed by RNAi silencing and inhibition of sterol C24β-methyltransferase (TbSMT) and sterol 14α-demethylase [TbSDM (TbCYP51)] to explore the functions of sterols in T. brucei growth. Inhibition of the amount or activity of these enzymes depletes ergosterol from cells at <6 fg/cell for procyclic form (PCF) cells or <0.01 fg/cell for bloodstream form (BSF) cells and reduces infectivity in a mouse model of infection. Silencing of TbSMT expression by RNAi in PCF or BSF in combination with 25-azalanosterol (AZA) inhibited parasite growth and this inhibition was restored completely by adding synergistic cholesterol (7.8 μM from lipid-depleted media) with small amounts of ergosterol (1.2 μM) to the medium. These observations are consistent with the proposed requirement for ergosterol as a signaling factor to spark cell proliferation while imported cholesterol or the endogenously formed cholesta-5,7,24-trienol act as bulk membrane components. To test the potential chemotherapeutic importance of disrupting ergosterol biosynthesis using pairs of mechanism-based inhibitors that block two enzymes in the post-squalene segment, parasites were treated with AZA and itraconazole at 1 μM each (ED50 values) resulting in parasite death. Taken together, our results demonstrate that the ergosterol pathway is a prime drug target for intervention in T. brucei infection.

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