Deciphering the role of phospholipid homeostasis in physiology and disease

PROJECT SUMMARY Choline is a vitamin-like metabolite that is indispensable for cellular and organismal viability which must be obtained through diet. Once imported into the cell, choline has multiple metabolic fates influencing diverse cellular processes ranging from membrane biosynthesis to epigenetics. Choline it is a key constituent of phospholipids, acetylcholine, and betaine which in turn impacts S-adenosylmethionine (SAM) and DNA methylation. Despite the influence of choline on diverse cellular processes, the identity of a high affinity choline transporter ubiquitously expressed across mammalian tissues was unknown. In our recently published preliminary data, we utilized genome-wide association studies (GWAS) of serum metabolites to identify a poorly characterized plasma membrane protein, feline leukemia virus subgroup C cellular receptor 1 (FLVCR1), as the predominant choline transporter in mammals. In human cells and the developing mouse embryo, FLVCR1 loss severely impacts choline metabolism resulting in depletion of betaine and phosphatidylcholine (PC) – the predominant phospholipid species in cellular and organellar membranes. Mechanistically, FLVCR1 directly transports choline into cells and we have recently used CryoEM to identify the residue necessary for transport. In this effort, we also discovered that FLVCR1 can also transport ethanolamine, suggesting that it may also affect phosphatidylethanolamine (PE) synthesis, the second most abundant membrane phospholipid. Taken together, these data suggest that FLVCR1 is a crucial transporter for phospholipid metabolism. Broadly, this proposal seeks to investigate the influence of phospholipid metabolism on cellular and organismal physiology. Utilizing a conditional knockout mouse, in Aim 1, we will study the role of FLVCR1 in organismal physiology and metabolism and assess the efficacy of FLVCR1 as a target in metabolic disease. Our preliminary data suggest that mitochondrial stress and activation of the integrated stress response are defining features of cells and embryos lacking FLVCR1. In Aim 2 we will study how FLVCR1 loss and phospholipid metabolism impacts mitochondrial function and the subsequent cellular stress response. In Aim 3 we seek to understand how phospholipid homeostasis is maintained and regulated. Spanning basic biochemistry to mouse modeling, this application will address outstanding fundamental questions in cellular metabolism and seek to apply these findings to the possible treatment of human disease. The innovative studies proposed in this application in addition to the personalized training plan, will provide rigorous scientific training and professional development which will enable my transition to independence and start my own laboratory as a tenure-track professor.