Toxoplasma gondii Exploits Host Low-Density Lipoprotein Receptor-Mediated Endocytosis for Cholesterol Acquisition

Abstract

The obligate intracellular protozoan Toxoplasma gondii resides within a specialized parasitophorous vacuole (PV), isolated from host vesicular traffic. In this study, the origin of parasite cholesterol was investigated. T. gondii cannot synthesize sterols via the mevalonate pathway. Host cholesterol biosynthesis remains unchanged after infection and a blockade in host de novo sterol biosynthesis does not affect parasite growth. However, simultaneous limitation of exogenous and endogenous sources of cholesterol from the host cell strongly reduces parasite replication and parasite growth is stimulated by exogenously supplied cholesterol. Intracellular parasites acquire host cholesterol that is endocytosed by the low-density lipoprotein (LDL) pathway, a process that is specifically increased in infected cells. Interference with LDL endocytosis, with lysosomal degradation of LDL, or with cholesterol translocation from lysosomes blocks cholesterol delivery to the PV and significantly reduces parasite replication. Similarly, incubation of T. gondii in mutant cells defective in mobilization of cholesterol from lysosomes leads to a decrease of parasite cholesterol content and proliferation. This cholesterol trafficking to the PV is independent of the pathways involving the host Golgi or endoplasmic reticulum. Despite being segregated from the endocytic machinery of the host cell, the T. gondii vacuole actively accumulates LDL-derived cholesterol that has transited through host lysosomes.

Host cell manipulation by the human pathogen Toxoplasma gondii

“…T. gondii is an auxotroph for tryptophan [19][20][21], arginine [22,23], polyamines [24], purines [25,26], cholesterol [27,28], iron [23,29], and other essential nutrients [30]. Although parasites surrounded by the PVM are protected against the acidification from the fusion of endocytic vesicle, this non-fusion state deprives parasites of an abundant source of nutrients from the host's endocytic and exocytic system.…”

“…Host cell cholesterol is crucial for T. gondii invasion and intracellular replication of [27]. Indeed, the diminution of the cholesterol at the host cell plasma membrane appears to disrupt the release of microneme and rhoptry contents during the invasion by the parasite [28].…”

“…T. gondii does not synthesize its own cholesterol and instead scavenges it from the host. Parasite growth is enhanced by addition of free cholesterol or cholesterol bound to low-density lipoprotein (LDL) particles to the extracellular medium [27]. Also, extracellular parasites and parasites inside the purified PV can incorporate free cholesterol, suggesting the existence of cholesterol acquisition machinery at the plasma membrane and PVM [49].…”

Lipidomics of host–pathogen interactions

“…Lysobisphosphatidic acid and phosphoinositides regulate release of VSV nucleocapsid into cytoplasm [13] SigD/SopB is a type III bacterial derived phosphoinositide phosphatase [29,112] Molecular species of phosphatidylcholine and phosphatidylethanolamine are altered in host plasmamembrane after Plasmodium infection [116] GP Ethanolamine phospholipids required for Sindbis virus production [111] Intracellular mycobacteria release a heterogeneous mixture of lipids [27,113] Growth arrest of Plasmodium [117] and Toxoplasma [85] by disruption of phosphatidylcholine synthesis Semliki Forest virus mRNA capping enzyme requires association with anionic membrane phospholipids for activity [14] Phosphatidylinositol mannosides stimulate fusion of early endosomes with mycobacterial phagosomes [30] Glycosylated phosphatidylinositol causes phagosome maturation arrest [114] SapM, a mycobacterial derived phosphatase hydrolyses PI3P contributing to inhibition of phagolysosome maturation [115] Sphingosine 1-kinase is recruited to nascent phagosomes [118] Inhibition of sphingolipid biosynthesis in T. gondii blocks replication [119] SP Sphingomyelin metabolism important for P. falciparum development [120] Inhibition of cholesterol biosynthesis inhibits Hepatitis C virus RNA replication [15] Inhibition of cholesterol acquisition by the host lowers T. gondii replication [40] ST Cholesterol esterification essential for optimal T. gondii proliferation [121,122] Isopreonoid synthesis inhibitors with anti-malarial [123] and anti-T. gondii activity [124] PR Block of protein farnesylation as antiapicomplexan therapies [125] 5…”

“…As obligate intracellular pathogens Plasmodium and Toxoplasma are dependent on nutrient access [40]. Phospholipid and neutral lipids are currently at a center stage of attention at intracellular stages of Toxoplasma but also of other parasites which feed small molecular metabolites from their hosts ( Table 1).…”