Neutral lipid demixing from a bilayer

Neutral lipid demixing from a bilayer

By In PhD proposals 2018 On April 3, 2018

Project: Neutral lipid demixing from a bilayer

Laboratory: Laboratoire de Physique Statistique

Affiliation: Ecole Normale Supérieure de Paris
Address: 24 rue Lhomond

LAB Director
Name: Jorge Kurchan
Phone number: 0144323363

Name: Abdou Rachid THIAM
Phone number: 0144323363

Subject Keywords: Lipid droplet, metabolism, emulsion, dewetting, nucleation
Summary of lab’s interests: Lipid droplets (LDs) are the organelles regulating cellular energy metabolism. They represent dynamic intracellular oil-in-water emulsion droplets, interacting with nearly all organelles to supply them with lipids or proteins. LD biology is tightly linked to how it is formed in the cell, but this step remains very elusive. Our team studies mechanisms of LD formation and has made key contributions in understanding how it is regulated. Our strategy is to develop model emulsion droplets that mimic cellular LDs at a given metabolic state and identify minimal parameters controlling LD dynamics. These parameters are next modulated in cells to alter metabolism.
Project summary: Lipid droplets (LDs) are organelles playing a central role in cellular energy metabolism and homeostasis (1). They are implicated in many biological processes other than in metabolism; they are implicated in viral infections, embryo development, and neurodegeneration (2). LD function is particularly determined during LD biogenesis (1,3), which starts in the endoplasmic reticulum (ER) bilayer where specific enzymes convert excess energy into neutral lipids (4). These lipids are dispersed and mobile in the inter-monolayer space of the bilayer. At a critical concentration they demix to nucleate a lipid lens, which grows by accumulating more lipids and become a spherical LD that buds off from the bilayer (5). Currently, it is not known how and where LD nucleation occurs, and this is an important step to resolve for understanding and modulating lipid metabolism for medical and industrial avails.
This project propose to use in vitro reconstitutions assays, based on emulsion droplets and vesicles, to study the impact of lipids and membrane proteins on LD nucleation. This approach will enable to identify the minimal biophysical parameters controlling LD nucleation. We will then modulate these parameters in cells to confirm our in vitro findings, modulate LD nucleation and alter metabolism.

1 Thiam, Abdou Rachid, and Mathias Beller. “The why, when and how of lipid droplet diversity.” J Cell Sci 130.2 (2017): 315-324.
2 Welte, Michael A. “Expanding roles for lipid droplets.” Current biology 25.11 (2015): R470-R481.
3 Pol, Albert, Steven P. Gross, and Robert G. Parton. “Biogenesis of the multifunctional lipid droplet: Lipids, proteins, and sites.” J Cell Biol 204.5 (2014): 635-646.
4 Buhman, Kimberly K., Hubert C. Chen, and Robert V. Farese. “The enzymes of neutral lipid synthesis.” Journal of Biological Chemistry 276.44 (2001): 40369-40372.
5 Thiam, Abdou Rachid, and Lionel Forêt. “The physics of lipid droplet nucleation, growth and budding.” Biochimica et Biophysica Acta (BBA)-Molecular and Cell Biology of Lipids1861.8 (2016): 715-722.

Interdisciplinary aspect of the project: The question raised in this project is at the crossroad between emulsion science, membrane biophysics, lipid droplet biology and metabolism. This is why we will combine various biophysics techniques, based on emulsion formulation, giant unilamellar vesicles (GUVs) fabrication and modulation, proteo-GUVs fabrication, with genetic modulation of cells. These approaches are highly complementary. They will enable to unveil the physical-chemistry conditions upon which neutral lipid oil molecules in a bilayer demix, and then, based upon these findings, modulate these parameters in a cellular context so as to modulate lipid droplet formation and metabolism.
Funding: applying FDV funding