title: Starvation of low-density lipoprotein-derived cholesterol induces bradyzoite conversion in Toxoplasma gondii.
abstract: BACKGROUND
  Lacking enzymes for sterol synthesis, the intracellular protozoan Toxoplasma gondii scavenges cholesterol from host cells to multiply. T. gondii has a complex life cycle consisting of two asexual stages; the proliferative stage (tachyzoite), and the latent stage characterized by tissue cysts (bradyzoite). In vitro, bradyzoite development can be induced by mimicking host immune response stressors through treatment with IFN-γ, heat shock, nitric oxide, and high pH. However, the extent to which host nutrients contribute to stage conversion in T. gondii is unknown. In this study, we examined the impact of host cholesterol levels on stage conversion in this parasite.
  
  
  METHODS
  Growth of T. gondii tachyzoites (ME49 strain) was investigated in Chinese hamster ovary (CHO) cells using various concentrations of low-density lipoprotein (LDL), oleic acid, or glucose. Squalestatin, which is an inhibitor of squalene synthase and is, therefore, an inhibitor of sterol synthesis, was used to treat the CHO cells. Tachyzoite to bradyzoite conversion rates were analyzed by indirect fluorescent antibody tests.
  
  
  RESULTS
  Parasite growth was significantly enhanced by addition of exogenous LDL, whereas no such enhancement occurred with oleic acids or glucose. In ME49, growth inhibition from squalestatin treatment was not obvious. Although growth of the RH strain was unaffected by squalestatin in the presence of lipoprotein, in its absence growth of this strain was suppressed. The frequency of BAG1-positive vacuoles in ME49 increased under lipoprotein-free conditions. However, addition of exogenous LDL did not increase tachyzoite to bradyzoite conversion in this strain. Furthermore, treatment with squalestatin did not enhance stage conversion.
  
  
  CONCLUSIONS
  Our results suggest that LDL-derived cholesterol levels play a crucial role in bradyzoite conversion in T. gondii.
authors.forename: Fumiaki
authors.initials: F
authors.lastname: Ihara
authors.affiliation: National Research Center for Protozoan Diseases, Obihiro University of Agriculture and Veterinary Medicine, Inada-cho, Obihiro Hokkaido 080-8555, Japan. nisikawa@obihiro.ac.jp.
authors.forename: Yoshifumi
authors.initials: Y
authors.lastname: Nishikawa
mesh_terms: D000818:Animals; D000924:Anticholesteremic Agents / Q000494:pharmacology; D019086:Bridged Bicyclo Compounds, Heterocyclic / Q000494:pharmacology; D016466:CHO Cells; D008078:Cholesterol, LDL / Q000378:metabolism*; D006224:Cricetinae; D003412:Cricetulus; D005227:Fatty Acids; D005947:Glucose / Q000378:metabolism; D008018:Life Cycle Stages; D014122:Toxoplasma / Q000502:physiology*; D014233:Tricarboxylic Acids / Q000494:pharmacology
chemical_list: D000924:Anticholesteremic Agents; D019086:Bridged Bicyclo Compounds, Heterocyclic; D008078:Cholesterol, LDL; D005227:Fatty Acids; D014233:Tricarboxylic Acids; D005947:Glucose