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

GABRIELLI, M; UTTARO, AD; ALTABE, SG

Virtual

Congreso; LVII Reunión Anual de la Sociedad Argentina de Investigación en Bioquímica y Biología Molecular; 2021

Sociedad Argentina de Investigación en Bioquímica y Biología Molecular (SAIB) y Asociación Civil de Microbiología General (SAMIGE)

The filasterean protist Capsaspora owczarzaki is a closeunicellular relative of metazoans which has become an important model to studythe origins of animal multicellularity. Its life cycle includes anadherent filopodial stage, an aggregative-multicellular stage and a cysticstage. In order to further characterize this organism and to understand therole of lipids during its life cycle we started to study the fatty acidcomposition at the different stages. In the present work we focus on thefilopodial and cystic stages. Wecompared the profiles of fatty-acids (as FAMEs) of filopodial and cystic cells obtainedby GC/MS. Cysts showed a higher percentage of unsaturated fatty acids, mainlycharacterized by increased levels of arachidonic acid (20:4, n-6) concomitantlywith a decrease of palmitic acid (16:0) and stearic acid (18:0). Thisobservation led us to the hypothesis that arachidonic acid may be involved inthe transition from the filopodial to the cystic stage. To test whetherarachidonic acid (AA) could trigger such transition we incubated filopodiatedcells with different concentrations of this fatty acid. After 24 - 48 h notablemorphological changes were observed at 50 to 200 µM AA: treated cells becomeslightly larger and more refringent than control cells, and this effect wasmore evident at the higher concentrations. However, no differentiation to thecystic stage could be detected at the moment. Fluorescence microscopy using thelipophilic stains Bodipy 493/503 and Nile Red revealed that these morphologicalchanges were associated with to an increase in the number and size ofintracellular lipid droplets (LDs). A similar effect was observed with oleicacid (18:1, n-9) and linoleic acid (18:2, n-6), although to a lesser extent. Usingradiolabeled cholesterol and following its incorporation and esterification bythin layer chromatography we found that in the presence of 100 µM AA the sterolwas preferentially incorporated in steryl-esters, despite a reduced uptake.Similarly, radiolabeled acetate was converted to fatty acids that were mostlyfound in triglycerides. These effects are in keeping with the accumulation ofLDs induced by AA.