Arachidonic acid induces lipid droplet formation in Capsaspora owczarzaki filopodial stage cells

GABRIELLI M; ALTABE, SG; UTTARO AD

Congreso; . LVII Reunión anual de la SAIB; 2021

The filasterean protist Capsaspora owczarzaki is a close unicellular relative of metazoans which has become an importantmodel to study the origins of animal multicellularity. Its life cycle includes an adherent filopodial stage, an aggregativemulticellular stage and a cystic stage. In order to further characterize this organism and to understand the role of lipids duringits life cycle we started to study the fatty acid composition at the different stages. In the present work we focus on the filopodialand cystic stages. We compared the profiles of fatty-acids (as FAMEs) of filopodial and cystic cells obtained by GC/MS. Cystsshowed a higher percentage of unsaturated fatty acids, mainly characterized by increased levels of arachidonic acid (20:4, n6) concomitantly with a decrease of palmitic acid (16:0) and stearic acid (18:0). This observation led us to the hypothesis thatarachidonic acid may be involved in the transition from the filopodial to the cystic stage. To test whether arachidonic acid(AA) could trigger such transition we incubated filopodiated cells with different concentrations of this fatty acid. After 24 -48 h notable morphological changes were observed at 50 to 200 µM AA: treated cells become slightly larger and morerefringent than control cells, and this effect was more evident at the higher concentrations. However, no differentiation to thecystic stage could be detected at the moment. Fluorescence microscopy using the lipophilic stains Bodipy 493/503 and NileRed revealed that these morphological changes were associated with to an increase in the number and size of intracellular lipiddroplets (LDs). A similar effect was observed with oleic acid (18:1, n-9) and linoleic acid (18:2, n-6), although to a lesserextent. Using radiolabeled cholesterol and following its incorporation and esterification by thin layer chromatography wefound that in the presence of 100 µM AA the sterol was preferentially incorporated in steryl-esters, despite a reduced uptake.Similarly, radiolabeled acetate was converted to fatty acids that were mostly found in triglycerides. These effects are in keepingwith the accumulation of LDs induced by AA.