Abstract 415: Role of Proteolysis in the Remodeling of High-Density Lipoprotein
Introduction: Both quantity and quality of the circulating HDL determine their optimal anti-atherogenic potential. During atherogenesis, various cell types in the arterial intima release enzymes into the intimal fluid, which modify HDL proteins and lipids that adversely affect HDL functionality.
Hypothesis: The emerging paradigm for the in vivo proteolytic inactivation of HDL is centered on pre-beta-HDL. Over 90% of the major HDL proteins, apoA-I and apoA-II, circulate on mature HDL. Although binding to HDL protects these proteins from proteolysis, such proteolysis cannot be completely excluded, and its effects on HDL functionality remain unknown.
Methods: Human plasma HDL were subjected to mild proteolysis with plasmin, a protease active in atherosclerotic lesions. The proteolytic products were analyzed by SDS-PAGE and Western blotting. HDL remodeling was monitored under near-physiological conditions by size-exclusion chromatography and gel electrophoresis.
Results: HDL treatment with plasmin caused no significant structural remodeling of lipoprotein particles. Interestingly, plasmin cleaved apoA-I and apoA-II on HDL. The major protein fragments were observed in the 10-12 kDa range. Western blotting indicated that these fragments were derived from both apoA-I and apoA-II. Next, intact and plasmin-treated HDL were incubated at 37 oC, pH 7.5 for 6-12 h. Intact HDL showed dissociation of a fraction of lipid-free apoA-I without significant changes in the particle size. In contrast, plasmin-treated HDL underwent fusion with release of full-length and fragmented apoA-I and apoA-II, indicating lipoprotein destabilization.
Conclusion: Our results reveal that plasmin, can cleave HDL-bound forms of apoA-I and apoA-II and thereby destabilize HDL under near-physiological conditions, resulting in HDL disintegration and dissociation of lipid-free proteins. For the first time, we demonstrate that proteolysis can render not only lipid-free but also HDL-bound proteins dysfunctional. Destabilization of HDL via proteolytic modifications may contribute to the recently observed excessive accumulation of lipid-free apoA-I in the arterial intima, which probably contributes to the progression of atherosclerosis.
Author Disclosures: S. Jayaraman: None.
- © 2014 by American Heart Association, Inc.