University of North Carolina at Chapel Hill Graduate School
Doi
Abstract
Lipoprotein lipase (LPL) is required for the clearance of triglycerides (TG) from the bloodstream. LPL is anchored to the walls of blood vessels where it undergoes conformational changes to engage TG-rich lipoprotein particles, hydrolyze TG within the particle, and release free fatty acids. LPL activity is tightly regulated in a nutrient-dependent manner to coordinate the delivery of free fatty acids to specific tissues. The unique ability of LPL to directly control plasma TG levels makes it a good target for specific TG-lowering therapeutics. However, directly targeting LPL may be a difficult as it has several regulatory partners and disruption of activators or its endothelial anchor will abolish LPL activity. Alternatively, pharmacologic modulation of proteins that regulate LPL has been shown to dramatically lower plasma TG levels in both preclinical animal models and human clinical trials. One approach is to inactivate a subset of LPL inhibitory proteins, known as angiopoietin-like protein 3 or 4 (ANGPTL3, 4). Despite not knowing the molecular mechanism for how ANGPTL3 inhibits LPL, anti-ANGPTL3 monoclonal antibodies have shown great promise in clinical trials for severe HTG. The molecular mechanism for ANGPTL4-mediated inhibition of LPL has been more thoroughly investigated; however, therapeutic strategies that result in complete loss of ANGPTL4 have not been successful in preclinical animal models. This thesis aims to better understand the molecular mechanism of LPL inhibition by ANGPTL3 and ANGPTL4 and use this information to enhance the activity of LPL in vivo. To better understand the molecular mechanisms of ANGPTL-mediated inhibition of LPL, we i) performed biophysical experiments to compare ANGPTL3 and ANGPTL4 in vitro, ii) looked for differences in LPL inhibition and iii) identified ANGPTL4 binding sites on LPL. Lastly, we sought to improve upon existing ANGPTL4 inhibitors by generating a domain-specific inhibitor of ANGPTL4 to prevent LPL inhibition. Overall, we have identified LPL variants with ANGPTL4 resistance and an anti-ANGPTL4 single domain antibody for inactivation of the N-terminal domain of ANGPTL4. These results could have implications for future biologic-based therapeutics for hypertriglyceridemia and acute pancreatitis.Doctor of Philosoph
