Description of work

In humans, fat cell hypertrophy has emerged as the central adipose parameter associated with metabolic and cardiovascular complications. The volume of the unilocular LD is the main determinant of adipocyte size. Furthermore, the LD is a complex organelle that determines adipocyte lipid turnover, the latter being casually linked to a number of relevant metabolic disturbances. We therefore hypothesize that the molecular determinants of adipocyte LD size explain the pernicious impact of adipocyte hypertrophy.

Through the development of beyond-state-of-the-art models and methods as well as use of the most advanced technologies in our respective fields, the objectives of SPHERES are:
- to decipher the mechanisms governing adipocyte unilocular LD growth and shrinkage;
- to identify the major protein and lipid determinants of adipocyte LD dynamics;
- to determine the factors explaining inter-individual variations in adipocyte LD size.

By addressing these points, we will obtain novel insights and a significantly better understanding of how LD hypertrophy impacts adipocyte dysfunction and the consequences there of at the whole body level (B1 Fig. 1).

A major challenge in studies of mature adipocytes is that they are short-lived in vitro, fragile and float in suspension. This constitutes a major bottleneck in LD research. SPHERES circumvents this hurdle by developing new and beyond-state-of-the-art research tools that will allow studies of adipocyte function with a granularity that has hitherto been impossible to do. From a clinical perspective, it is imperative to investigate both human and murine fat cells because of qualitative species differences in triglyceride metabolism. For ethical and practical reasons, the focus in our clinical studies is on subcutaneous abdominal WAT. However, various white fat depots will be investigated in mouse models, which also allow investigation of causality at whole body level. This WP will focus on five specific areas of development in human and mouse fat cells as well as reconstitution systems.

LD-associated proteins (PLIN/CIDEs/lipases) and their protein interactomes have a critical role in determining LD size and adipocyte function. To decipher the importance of these proteins, we will use the innovative WP1 technologies and combine them with established techniques/models and unique clinical material.

In addition to the proteins present on the LDs, the lipid composition of the LD (both the surface and inner core) may also have pathophysiological relevance. Even in healthy subjects, there are large variations in the fatty acid profiles of triglycerides. The abundance of 14:0, 16:0, 18:0, 18:1 and 18:3 fatty acids varies up to 3-fold between individuals. It is likely but still not known how the fatty acid profile of triglycerides and phospholipids might influence elementary biochemical reactions occurring on unilocular LDs, including coating by PLINs, hydrolysis by HSL, and CIDEmediated LD fusion. The aim of this WP is to study the impact of the lipid composition on the fate and function of unilocular LDs in both physiological and in pathological contexts.