Medizinische Universität Graz Austria/Österreich - Forschungsportal - Medical University of Graz
Gewählte Publikation:
Schilcher, I.
IMPACT OF ENDOTHELIAL LIPASE ON STRUCTURAL AND FUNCTIONAL PROPERTIES OF SERUM AND HIGH-DENSITY LIPOPROTEIN
PhD-Studium (Doctor of Philosophy); Humanmedizin; [ Dissertation ] Graz Medical University; 2018. pp. 116
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- Autor*innen der Med Uni Graz:
- Betreuer*innen:
- Frank Sasa
- Kratky Dagmar
- Marsche Gunther
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- Abstract:
- HDL exhibits numerous atheroprotective properties including the promotion of reverse cholesterol transport (RCT) and the protection against LDL oxidation. Endothelial lipase (EL) is a strong negative regulator of HDL plasma levels as well as a modulator of the structural and functional properties of HDL. In the present study, first the impact of EL on the composition and cholesterol efflux capacity (CEC) of serum, apolipoprotein B-depleted serum (apoB-DS) and HDL isolated from EL-modified serum was investigated, using appropriate in vitro and in vivo approaches. EL overexpression in vitro was achieved by adenoviral transduction of cultured cells and in mice by adenoviral tail vein injection. CEC was analyzed in 3H-cholesterol labeled J774 macrophages under basal conditions or with upregulation of ABCA1. Incubation of human and mouse serum with EL overexpressing cells resulted in an enhanced CEC of serum and apoB-DS and decreased CEC of isolated HDL, accompanied by the formation of lipid-poor ApoA-I, alterations in the lipid composition as well as decreased size of human but not mouse HDL. In contrast, overexpression of human and mouse EL in mice impaired CEC of serum without altering CEC of isolated HDL. This was accompanied by reduced HDL-C and ApoA-I serum levels, markedly altered lipid composition of serum and HDL as well as unaltered HDL size. The impact of EL on the CEC of serum and HDL reflects structural and compositional features as well as abundance of EL-modified HDL. Results of our study highlight the complexity of the interaction between EL and HDL, clearly showing the role of experimental models on the structural and functional properties of EL-modified HDL. We show that EL by acting on human and mouse serum in vitro results in accumulation of lipid-poor ApoA-I, a potent cholesterol acceptor. The relevance of these findings for human (patho)physiology needs to be addressed in future studies. Second, the relationship between composition, structure and the antioxidative capacity by measuring the capacity to attenuate CuCl2 induced LDL oxidation and MDA formation of in vitro generated EL-HDL has been investigated. Compared to control, EL-HDL had significantly increased antioxidative capacity reflected by a prolonged lag phase and less MDA accumulation. HDL particles were smaller in size and had altered lipid composition upon EL overexpression. Interestingly, despite a better antioxidative activity, EL-HDL had reduced PON1 content and activity as well as decreased LCAT and PAF-AH mass. Incubation of HDL with cells overexpressing enzymatically inactive EL resulted in an increased HDL-PON1 content and activity, indicating the importance of EL lipolytic activity in displacing PON1 from HDL. Small EL-HDL particles showed higher antioxidative capacity compared to large EL-HDL particles, whereby the smallest particles exhibited the lowest PON1 content. Modification of HDL with EL in the presence of bovine serum albumin yielded EL-HDL with markedly lower content of lipolytic products and profoundly decreased antioxidative capacity. The rate of ApoA-I Met136 oxidation was higher in EL-HDL compared to control HDL, indicating a higher antioxidative activity of that residue in EL-HDL compared to control HDL. Chloramine T abolished the capacity of EL-HDL and control HDL to protect LDL from oxidation, without affecting the difference between EL-HDL and EV-HDL. The EL induced alteration in HDL size, structure and lipid composition, in particular the enrichment of lipolytic products in EL-HDL, augment the antioxidative capacity of EL-HDL, independent of HDL associated enzymes.