Triglyceride lenses at the air-water interface as a model for studying lipid droplets?

B. CARUSO, N. WILKE, MA PERILLO, MARÍA.

Tucumán

Congreso; Reunión conjunta: III LAFeBS, IX Iberoamerican Congress of Biophysics, XLV SAB.; 2016

Lipid Droplets (LD) are intracelular structures consisting on an apolarlipid core -composed mainly of triglycerides (TG) and steryl esterswhichis surrounded by a phospholipid and protein monolayer. LDsoriginate in the ER bilayer, where TG synthesis concludes. The mechanismsunderlying TG nucleation, size maduration and budding-off fromthe ER membrane are a matter of current investigations and the roleof dewetting from cytosolic-bilayer interface appears to play a criticalrole [1]. Here, we study phospadilcholine (PC) / triglycerides mixturesat the air-water interface as Langmuir and collapsed monolayersin order to gain insight into those factors that may affect the stabilityof TG bulk structures in contact with interfaces. PC/TG form stable monolayers which, under lateral compression, collapse at a surfacepressure () dependent on composition. Observation under BrewsterAngle Microscopy (BAM) revealed the appearance of microscopicstructures at beyond collapse, whose size (3 2 microns radius) didnot vary with composition. Contrary to dpPC/TG mixtures, pure TGand EPC/TG compression isotherms are reversible after collapse, andBAM confirmed this behavior. Furthermore, identical results were obtainedwhen monolayers where spread on the interface up to a higherthan collapse. The fluorescent probe Nile Red (NR), commonly used tostain lipid droplets, was able to reveal these structures. Comparison ofBAM and fluorescence microscopy indicate that these collapsed structurescorresponde to TG liquid phase which are known as interfasial?lenses?. Latest theoretical models propose nanometer-sized structuresto dewet an dettach from the bilayer. Being in equilibrium and with amicroscopic size, these lenses suggest that dewetting of TG adyacent toa PC monolayer (eventually hemilayer) is enough to reach such lateralsize.