Lipid droplets: biophysics of the first steps of biogenesis

MURATORI BREST PC; CROSIO, M; N. WILKE. .; B. CARUSO

Congreso; L Reunión Anual SAB; 2022

"Lipid droplets” (LDs) are intracellular structures that bud from the endoplasmic reticulummembrane (ERM) and are formed by a neutral lipid (NL) nucleus surrounded by a single layer ofphospholipids (PLs) and proteins. They are recognized as key organelles in intracellularphysiology because of their multiple roles within cell biology; playing a role in several diseasessuch as dengue, coronavirus and non-viral infections, cancer and obesity. The dynamics of LDsamong them vary greatly, but these differences can be accounted for by their assembly anddisassembly processes. This study aimed to contribute to this objective from a biophysicalapproach, focusing on the molecular mechanisms that govern the first stages of its biogenesis;particularly, those that trigger the accumulation and budding of NL within the ERM. For thispurpose, we used model monolayers (Langmuir films) and bilayers (Giant Unilamellar Vesicles)made of triolein (TO) as NL and PLs with different spontaneous curvatures (POPE (-), POPC (0)and LysoPC (+)) to study their influence on the stability and topology of the TO structures formed.We also took advantage of the solvatochromic properties of the Nile Red (NR) fluorescent probeto evidence the presence of TO blisters inside the bilayer, while observing the effect of aninduced bilayer compression on their emission spectra. Results on monolayers show that PL'scurvature affects the height but not the diameter or density of the TO lenses formed. In turn, thevesicles were successfully shrinked (>10% diameter) by osmotic shock. However, the emissionspectra of NR in the bilayers did not evidence the accumulation of TO aggregates, even underbilayer compression. Furthermore, when GUVs where over-irradiated (lex 488 and 543 nm), thespectra of NR in the bilayers exhibited different populations, even in the absence of TO.Therefore, the incorporation of non-aggregated TO molecules into the bilayer is being studied byits bending rigidity properties.