LIPID DROPLET BIOGENESIS AND HYDROPHOBIC BLISTERS INSIDE BILAYERS STUDIED USING MONOLAYER WETTING BY LIQUID LENSES

MILAGRO MOTTOLA; NATALIA WILKE; BENJAMÍN CARUSO; MARÍA ANGÉLICA PERILLO

Buenos Aires

Congreso; Reunión conjunta de Sociedades de Biociencias; 2017

Comité Organizador Reunión Conjunta de Sociedades de BioCiencias

The biogenesis of triglyceride (TG) Lipid Droplets and the encapsulationof apolar substances, such as vaseline (V), in bilayers involvea dewetting process and the formation of blisters containing abulk phase of the hydrophobic molecule (HM). To gain insight intothe factors affecting the stability of the bulk structure in contact withphospholipids (PC) we studied Langmuir films of PC with HM whichform (TG) or do not form (V) stable monolayers. Then, we evaluatedTG-blister formation using microscopy, calorimetry (DSC) andFluorescence Anisotropy (FA). PC/TG and PC/V monolayers collapseat a composition-dependent surface pressure (SP) producingmicrometric lenses (observed by BAM and fluorescence with Nilered probe) interpreted as bulk HM phase. PC/TG compression isothermsare reversible after collapse (lenses disappeared at SP belowthe collapse pressure). On the contrary, in PC/V, once formed, Vlenses remain on the surface. To analyze the monolayer wettability,HM lenses height was calculated assuming refractive indexes similarto those for bulk TG and V. We found that TG lenses were thickerthan V lenses. Knowing the thickness allowed estimating contactangles, interfacial tensions and spreading tendencies, and thus obtainingcoefficients which, together with wettability arguments, indicatedthat segregated TG would form discrete structures whereas V,alike other hydrocarbons (e.g. n-decane and squalene), would tendto spread along the intrabilayer space. Free standing bilayers of PC/TG did not exhibit microscopic blisters. However, DSC of PC/TGvesicles at compositions where TG remains in the bilayer showed athermotropic behavior similar to that of pure PC, suggesting a phaseseparation inside a global bilayer structure. FA of PC/TG vesiclesusing DPH and TMA-DPH (hycrocarbon chain and polar head regionsprobes) are coherent with XTG~TG solubility defined in monolayersand suggest TG segregation inside the bilayer (blisters) upto XTG=0.25.