Mechanism of lipid droplet formation at the endoplasmic reticulum

• Applicant: Dr. Henning Arlt
• Subject Area: Cell Biology ; Biochemistry
• Term: from 2017 to 2019
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 387469234

Cellular lipid droplets (LDs) are versatile organelles with a variety of essential functions ranging from energy storage and membrane synthesis to viral replication and protein storage. Perturbations of LD function cause severe disease, such as type-2 diabetes, fatty liver disease and atherosclerosis. Despite these observations, the molecular machinery that orchestrates LD biogenesis, homeostasis and degradation are only beginning to be understood.The overarching question of my research is to determine how LDs are formed. The biogenesis of this organelle represents a key aspect of LD biology that determines the cellular location and number of LDs in cells. However, insights on the mechanisms underlying formation are lacking. I will focus my efforts on the molecular mechanism of LD formation, capitalizing on the discovery that endoplasmic reticulum (ER) structure and LD formation are functionally connected. LDs originate from the ER by synthesis of neutral lipids, such as triacylglycerol (TG). The ER is a multifunctional organelle composed of a variety of domains that are characterized by differences in membrane curvature. This complex architecture is regulated by a specific set of proteins that change the local curvature and connectivity of the membrane. The current model of LD formation indicates that specific sites in the ER exist where TG accumulates and LD formation is initiated, but the molecular machinery has not been identified.Previous studies could show that proteins involved in ER structure affect LD morphology and could even localize to LDs. Our preliminary results indicate that knockdown of atlastin, which is a well known factor in ER membrane connectivity, resulted in increased number of LDs early during LD formation. This surprising finding now provides us with molecular tools to determine how ER structure and specific ER proteins contribute to the organization of LD formation. I will test the hypotheses that LD formation occurs at specific sites in the ER. Capitalizing on the connection between ER structure and LD formation, I will further test the hypothesis that atlastin stabilizes LD formation sites. To achieve this, I will pursue the following specific aims: 1) determine the location and time-course of LD formation with high spatial and temporal resolution, and 2) elucidate the role of atlastin in LD formation. The exceptional environment at Harvard will provide me with all the resources and expertise to perform these experiments and make rapid progress.This proposal addresses the cell biology of LDs, but mechanistic insights on LD formation will reveal the basic biology that underlies severe human diseases that are connected to neutral lipid metabolism.

• DFG Programme: Research Fellowships
• International Connection: USA
• Host: Professor Tobias Walther, Ph.D.