Abstract Tu0016: The Impact of Proteolytic Modifications on Lipoprotein Metabolism

Introduction: LDL and HDL are clinical biomarkers used for predicting risk of atherosclerotic CVD. Both of these lipoproteins are susceptible to posttranslational modifications that can affect their function and their relationship with the development of atherosclerosis. For example, centrifugally isolated LDL and HDL have been reported to be degraded by neutrophil elastase in vitro . However, the impact of elastase on plasma lipoproteins in vivo has not been reported. Furthermore, in human plasma LDL and HDL bind the elastase inhibitor Alpha-1-antitrypsin (AAT) suggesting a possible physiological importance of protecting lipoproteins from elastolytic modification. Objectives: 1) Characterize the effect of elastase-mediated proteolysis on lipoproteins in plasma in vitro . 2) Use the recently-developed Serpina1 -/- (AAT-deficient) mouse model to determine the impact of AATD on lipoprotein metabolism in vivo . Results: We first characterized the impact of human neutrophil elastase (HNE) treatment on lipoproteins in whole plasma in vitro . Western blotting revealed dose-dependent HNE-mediated degradation of apolipoproteins in plasma from wild type and Serpina1 -/- mice. Serpina1 -/- plasma proteins were more susceptible to HNE treatment than wild type. Interestingly, Apob and Apoa1 were more susceptible to proteolysis than other plasma proteins suggesting a possible preference of elastase for lipoprotein-associated proteins. Elastase treatment of human plasma in vitro resulted an HDL shift towards larger fractions, suggesting elastase may cause HDL aggregation or impaired reverse cholesterol transport. Lipoprotein profile analysis in Serpina1 -/- mice revealed an altered lipoprotein profile characterized by reduced triglyceride in VLDL and increased HDL-cholesterol, similar to that observed in AATD human patients. Administration of an HDL-targeting AAT-mimetic peptide to Serpina1 -/- mice partially corrected this dyslipidemia, suggesting that alterations in circulating lipoproteins are caused by elevated circulating elastase activity in this strain. Conclusions: Serpina1 -/- mice display an altered lipid profile which may be driven by increased circulating elastase activity. Proteolytic modifications may influence lipoprotein metabolism and impact atherosclerosis risk. Understanding how AAT and elastase impact lipoprotein metabolism and function and influence CVD risk could offer insight for new biomarkers or therapeutic approaches.