Wednesday, February 5, 2025
2/5/2025
Title of Project: “Solving longstanding mysteries in plasma triglyceride metabolism” PROJECT SUMMARY/ABSTRACT The objective of this Multiple Principal Investigator (PI) R01 grant is to solve persistent mysteries in the molecular physiology of plasma triglyceride (TG) metabolism. The PIs, Loren Fong (UCLA) and Michael Ploug (Finsen Laboratory, Copenhagen), are international leaders in TG metabolism. Fong, a cell biologist and physiologist, discovered that GPIHBP1, an endothelial cell (EC) protein, captures LPL within the interstitial spaces (where it is secreted by parenchymal cells) and moves it to the capillary lumen. Ploug, a physiologist and protein chemist with specialized expertise in biophysical methods, quantified GPIHBP1–LPL interactions; showed that GPIHBP1 stabilizes LPL; and discovered that ANGPTL4 inhibits LPL activity by catalyzing unfolding of LPL’s hydrolase domain. For 11 years, the UCLA and Finsen Laboratory groups have collaborated on the physiology and biophysics of TG metabolism, publishing 21 papers in top-tier journals. They discovered that LPL is active as a monomer, dispelling dogma that it is a homodimer; solved the atomic structure of the GPIHBP1–LPL complex; elucidated the function of GPIHBP1’s acidic domain; and discovered a new human disease (chylomicronemia from GPIHBP1 autoantibodies). The latter discovery has saved lives. They are now focusing on longstanding mysteries in TG metabolism. In Specific Aim 1, they will define the function of apolipoprotein regulators of LPL activity (APOA5, APOC2). They will build on their discovery that APOA5 deficiency reduces intracapillary LPL levels and a recent in vitro discovery (by their collaborator Robert Konrad) that APOA5 suppresses the ability of ANGPTL3/8 to inhibit LPL activity. They will test the ability of recombinant APOA5 to increase intracapillary LPL levels, and they will define the molecular basis for APOA5–ANGPTL3/8 and ANGPTL3/8–LPL interactions. They will also build on their discovery that APOC2 stabilizes the conformational integrity of LPL’s hydrolase domain— even in the presence of ANGPTL4. They will now test whether APOC2 protects LPL from inhibition by ANGPTL3 and ANGPTL3/8, and they will define the impact of APOC2 on LPL’s lid, which regulates substrate entry into LPL’s catalytic pocket. In Specific Aim 2, they will use stable isotope labeling to study the turnover of GPIHBP1 and LPL in tissues and determine the extent to which LPL turnover is altered by fasting/refeeding and APOA5 deficiency. They will test the hypothesis that GPIHBP1 is a long-lived protein that moves bidirectionally across ECs and that LPL has a short half-life and largely moves unidirectionally (towards the capillary lumen). In Specific Aim 3, they will investigate LPL expression in lower vertebrates (where GPIHBP1 is absent) with the goal of better understanding mammalian LPL biology. They will explore the hypothesis that LPL in lower vertebrates is produced by capillary ECs (obviating a requirement for GPIHBP1) and that LPL production in capillary ECs has been retained in mammals. Fong and Ploug are ideally positioned, with outstanding collaborators and unique tool chests of reagents and experimental methods, to solve each of the three longstanding mysteries in plasma TG metabolism. They expect that their work will transform textbook descriptions of intravascular lipolysis.
HHS’ Tracking Accountability in Government Grants System (TAGGS) website provides access to detailed descriptions of grants, loans, aggregated direct payments and other types of financial assistance awarded by the HHS Operating Divisions (OPDIVs) and the Office of the Secretary Staff Divisions (STAFFDIVs).