Cholesterol uptake in Tetrahymena thermophila

GABRIELLI M; UTTARO AD; HERNÁNDEZ J

Paraná

Congreso; LIV Reunión anual de la SAIB; 2018

SAIB

The ciliate T. thermophila incorporates exogenous cholesterol and converts it into 7,22 bisdehydrocholesterol, replacing tetrahymanol (acholesterol surrogate) on the cell membranes. This process is accompanied by repression of tetrahymanol synthesis, and induction of genesinvolved in sterol bioconversion. By fluorescent microscopy, it was previously found that cholesteryl esters were mainly incorporated byphagocytosis. In a preliminary study, using a mutant strain defective in phagocytosis (II8GIA), we observed by GC-MS a reduction ofcholesterol uptake and a negligible bioconversion, compared to a wild type strain (CU428). Nonetheless, II8GIA treated with cholesterol showeda significant upregulation of genes involved in bioconversion, indicating that these cells certainly respond to the presence of cholesterol. Wefollowed the uptake of radiolabeled cholesterol over time in both strains and traced its modification to cholesteryl esters by TLC. Consistentlywith previous results, the kinetics of sterol incorporation indicated a rapid and massive intake in CU428 cells but it was slower in II8GIA. Inaddition, treatment with Cytochalasin D, which impairs phagocytosis, resulted in a delayed uptake of cholesterol in CU428 but also inhibited itsincorporation in II8GIA, suggesting the involvement of several actin-dependent and independent mechanisms. Our results corroborate thehypothesis that cholesterol uptake is mainly due to phagocytosis, but also indicate that, at least, a secondary path of internalization exists and ithas an associated signaling that affects gene expression.