Roles of endoplasmic reticulum subdomains in regulating intracellular lipid distribution and organelle biogenesis

Project Summary/Abstract The endoplasmic reticulum (ER) plays a central role in many cellular processes, including lipid metabolism. The ER network is formed from a single membrane and yet contains functionally distinct subdomains that allows the ER to regulate lipid metabolism and respond to stress. How this functional diversity is mechanistically achieved is not well understood. One type of ER subdomain are regions of the ER in close contact with other organelles, called membrane contact sites (MCSs). They play important roles in cellular lipid homeostasis, signaling, and stress responses. Other subdomains are regions where some organelles are formed. One is lipid droplets (LDs), which are lipid storage depots that have many roles in cell physiology. Here, I take a multidisciplinary approach to address key gaps in our knowledge about the formation and function of ER subdomains. Central to the projects in this proposal is the question of how cells control the distribution of lipids within the ER and how this contributes to cellular lipid homeostasis. There are three directions in the proposal. 1) Direction one addresses key gaps in our understanding of how LD biogenesis occurs and goes awry in disease. We will leverage a novel in vitro LD biogenesis assay we have developed to investigate mechanism of LD formation and the roles LD biogenesis proteins. We will also determine how disease-causing mutations in these proteins alters their functions. 2) Direction two addresses the mechanism and functions of a recently described new family of tube- like lipid transport proteins that operate MCSs. 3) Direction three addresses a key gap in our knowledge of how the hydrophobic metabolite Coenzyme Q (CoQ) exits mitochondria and reaches the ER and other compartment and how export is regulated in response to oxidative stress. Capitalizing on a novel genetic screen we conducted, we will identify proteins that facilitate and regulate CoQ interorganelle transport. Collectively, these directions will provide mechanistic insights into the formation and functions of ER subdomains and how defects in these processes contribute to various diseases.