Role of clathrin-mediated endocytosis in Giardia lamblia encystation

FELIZIANI, CONSTANZA; RIVERO, MARIA ROMINA; ROPOLO, ANDREA ; TOUZ, MARÍA CAROLINA

Simposio; XXXII Reunión Anual de la Sociedad Argentina de Protozoología; 2020

One way that cells have to exchange material and information with their environmentis through cell surface receptors involved in processes that range from nutrient uptaketo signaling responses. Consequently, endocytosis constitutes a powerful mechanismto regulate both events. During growth, the protozoa parasite G. lamblia acquirescholesterol from the environment through receptor-mediated endocytosis of LDLlipoprotein and chylomicrons. However, during encystation, there is a decrease inavailable cholesterol that triggers the differentiation from trophozoites to cysts. In thiswork, we reveal the involvement of the endocytic machinery in the cell differentiationprocess of G. lamblia to its resistant form, the cyst. By using wild-type as well as stablenegative of knock-down strains for the clathrin adaptors GlAP2 (for G. lamblia AdaptorProtein 2) and GlENTHp (for G. lamblia ENTH protein), immunofluorescence assays,and confocal microscopy, we found that GlAP2 colocalize with ESV (for EncystationSpecific vesicles) while the GlENTHp seems not to be colocalized with those vesicles.Moreover, GlAP2 knock-down trophozoites were unable to complete thedifferentiation process, while GlENTHp knock-down trophozoites accomplished theencystation similarly to wild-type cells. When the number of viable cysts wasdetermined by counting with a haemocytometer, we observed a decrease in cystproduction only in GlAP2 knock-down mutants. Also, different expression patterns ofGlAP2 and GlENTHp were found during encystation when their mRNAs were analyzedby microarrays. Our results support the hypothesis that it is not the endocytosismechanism per se that is involved in the generation of cysts but rather the role ofGlAP2 in the transport of cyst wall proteins to the surface, for cyst development.However, the restricted localization of GlAP2 may also be important in endocytosis ofcyst wall molecules during post-release membrane recycling.