Unit:
Τομέας Βασικών ΕπιστημώνLibrary of the School of Health Sciences
Author:
Μαρκάκης Κωνσταντίνος
Dissertation committee:
Αναπληρώτρια Καθηγήτρια Ε. Κοτσιφάκη (επιβλέπουσα), Εργαστήριο Πειραματικής Φυσιολογίας, Ιατρική Σχολή Πανεπιστημίου Αθηνών, Καθηγητής Κ. Δημόπουλος, Εργαστήριο Βιοχημείας, Τμήμα Χημείας Πανεπιστημίου Αθηνών, Επίκουρη Καθηγήτρια Σ. Γραμμένου – Σαββόγλου, Τμήμα Παθολογικής Φυσιολογίας, Ιατρική Σχολή Πανεπιστημίου Αθηνών
Original Title:
Διερεύνηση του ρόλου της συνδεδεμένης με τις λιποπρωτεΐνες φωσφολιπάσης Α2 (Lp-PLA2) στην πρόσληψη της οξειδωμένης LDL από τα μακροφάγα
Translated title:
Investigation of the role of lipoprotein associated phospholipase A2 (Lp-PLA2) in the uptake of oxidized LDL by macrophages
Summary:
Recognition and uptake of oxLDL by scavenger receptors of macrophages and foam
cell formation are mediated by the oxidatively modified apolipoprotein B (ApoB)
and the lipid moiety of oxLDL. A great amount of oxidized phosphatidylcholine
of oxLDL is hydrolyzed at the sn-2 position to lysophosphatidylcholine and
small products of hydrolysis by Lp-PLA2 activity which progressively decreases
during oxidation. The remaining Lp-PLA2 activity after 6 h oxidation with 5μM
CuSO4 is ~40–50%, and after 24 h only 10–15% of the initial activity has been
preserved.
The role of Lp-PLA2 in the binding and the uptake of oxLDL by macrophages was
examined using LDL with intact or inhibited Lp-PLA2 activity. Additionally, LDL
oxidized for 6 h (moderately oxidized LDL, MoxLDL) or 24 h (heavily oxidized
LDL, HoxLDL) was used to assess the possible difference between a shorter
oxidation with the major percentage of Lp-PLA2 activity present and a longer
oxidation during which Lp-PLA2 activity was significantly attenuated.
Binding and uptake of oxLDL were assessed by incubation with mouse peritoneal
macrophages at 40C or 370C respectively. The inhibition of Lp-PLA2 resulted in
increased binding and uptake by ~30% regarding MoxLDL and ~20% regarding
HoxLDL.
The implication of ApoB was examined by assessing the binding and the uptake of
ApoB-liposome conjugates containing ApoB isolated from oxLDL. The inhibition of
Lp-PLA2 activity had no effect on the uptake of ApoB-liposomes conjugates
prepared with ApoB isolated from MoxLDL or HoxLDL.
The role of Lp-PLA2 in the binding and the uptake of oxLDL via the lipid moiety
was investigated using liposomes prepared from the lipid extract of oxLDL. The
binding and the uptake of these liposomes exhibited a similar pattern to that
of the corresponding lipoproteins. The inhibition of Lp-PLA2 resulted in
increased binding and uptake by ~40% regarding the liposomes from MoxLDL lipids
and ~30% regarding the liposomes from HoxLDL lipids. The examination of several
phospholipids, their oxidized and lyso derivatives, regarding their ability to
mediate binding and uptake, revealed the oxidized
1-palmitoyl-2-arachidonoyl-sn-glycero-3-phosphocholine (oxPAPC) as particularly
strong ligand for macrophage receptors.
The results of this study support the conclusion that the progressive
inactivation of Lp-PLA2 during LDL oxidation leads to an increased recognition
of oxLDL by macrophage receptors which could be primarily attributed to the
increased recognition of the oxidized phospholipids, especially oxPAPC,
enriched lipid moiety of oxLDL.
Keywords:
Lipoprotein associated phospholipase A2 (Lp-PLA2), Oxidized LDL, Macrophage, Apolipoprotein B100, 1-palmitoyl-2-arachidonoyl-sn-glycero-3-phosphocholine (PAPC)l
Number of references:
591
