Clathrin-dependent pathways and the cytoskeleton network are involved in ceramide endocytosis by a parasitic protozoan, Giardia lamblia

Abstract

Although identified as an early-diverged protozoan, Giardia lamblia shares many similarities with higher eukaryotic cells, including an internal membrane system and cytoskeleton, as well as secretory pathways. However, unlike many other eukaryotes, Giardia does not synthesize lipids de novo, but rather depends on exogenous sources for both energy production and organelle or membrane biogenesis. It is not known how lipid molecules are taken up by this parasite and if endocytic pathways are involved in this process. In this investigation, we tested the hypothesis that highly regulated and selective lipid transport machinery is present in Giardia and necessary for the efficient internalization and intracellular targeting of ceramide molecules, the major sphingolipid precursor. Using metabolic and pathway inhibitors, we demonstrate that ceramide is internalized through endocytic pathways and is primarily targeted into perinuclear/endoplasmic reticulum membranes. Further investigations suggested that Giardia uses both clathrin-dependent pathways and the actin cytoskeleton for ceramide uptake, as well as microtubule filaments for intracellular localization and targeting. We speculate that this parasitic protozoan has evolved cytoskeletal and clathrin-dependent endocytic mechanisms for importing ceramide molecules from the cell exterior for the synthesis of membranes and vesicles during growth and differentiation.

Role the Employee of Some Biological Stains in Detecting Giardia lamblia among Internal Iraqi Displaced Peoples in Kirkuk Province

“…In addition to staining proteins in the cytoplasm, it can be used to stain collagen and muscle fibers for examination under the microscope (Weller,et al, 1988). The high rate of positivity might be due to high contents of proteins in the cell wall that will show high affinity to eosin stain particularly the microtubules in flagellum of Giardia parasite that anchored it to kinetoplast beneath the wall in posterior region of the trophozoite that will extend to link with flagella within a shaft in the cell wall (Hernandez, et al, 2007).…”

Glucosylceramide synthesis inhibition affects cell cycle progression, membrane trafficking, and stage differentiation in Giardia lamblia

“…Lipid neosynthesis is limited in G. lamblia , and the parasite is thought to rely on lipids taken up from the environment, namely, the host intestinal content. Indeed, in vitro analyses showed negligible incorporation of lipid precursors, such as acetate and glycerol ( 11 ), while robust incorporation of exogenous radiolabeled fatty acids (12)(13)(14), phospholipids ( 14 ), ceramide, and gangliosides ( 15,16 ) could be demonstrated. In addition, uptake of fl uorescent sphingolipid analogs, including ceramide and sphingomyelin, has been reported ( 12,14,15 ).…”

Lysosomal protein trafficking in Giardia lamblia common and distinct features

“…Several groups have presented evidence for a role of clathrin in endocytosis in Giardia (12,(32)(33)(34). However, neither typical membrane-associated clathrin lattices nor emerging clathrin-coated pits have been observed in this parasite.…”