Publications by authors named "Margarete Lechleitner"

6 Publications

  • Page 1 of 1

Endothelial Lipase Modulates Paraoxonase 1 Content and Arylesterase Activity of HDL.

Int J Mol Sci 2021 Jan 13;22(2). Epub 2021 Jan 13.

Gottfried Schatz Research Center for Cell Signaling, Metabolism and Aging, Molecular Biology and Biochemistry, Medical University of Graz, Neue Stiftingtalstraße 6/6, 8010 Graz, Austria.

Endothelial lipase (EL) is a strong modulator of the high-density lipoprotein (HDL) structure, composition, and function. Here, we examined the impact of EL on HDL paraoxonase 1 (PON1) content and arylesterase (AE) activity in vitro and in vivo. The incubation of HDL with EL-overexpressing HepG2 cells decreased HDL size, PON1 content, and AE activity. The EL modification of HDL did not diminish the capacity of HDL to associate with PON1 when EL-modified HDL was incubated with PON1-overexpressing cells. The overexpression of EL in mice significantly decreased HDL serum levels but unexpectedly increased HDL PON1 content and HDL AE activity. Enzymatically inactive EL had no effect on the PON1 content of HDL in mice. In healthy subjects, EL serum levels were not significantly correlated with HDL levels. However, HDL PON1 content was positively associated with EL serum levels. The EL-induced changes in the HDL-lipid composition were not linked to the HDL PON1 content. We conclude that primarily, the interaction of enzymatically active EL with HDL, rather than EL-induced alterations in HDL size and composition, causes PON1 displacement from HDL in vitro. In vivo, the EL-mediated reduction of HDL serum levels and the consequently increased PON1-to-HDL ratio in serum increase HDL PON1 content and AE activity in mice. In humans, additional mechanisms appear to underlie the association of EL serum levels and HDL PON1 content.
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http://dx.doi.org/10.3390/ijms22020719DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7828365PMC
January 2021

Reduced expression of adipose triglyceride lipase decreases arachidonic acid release and prostacyclin secretion in human aortic endothelial cells.

Arch Physiol Biochem 2017 Oct 3;123(4):249-253. Epub 2017 Apr 3.

a Institute of Molecular Biology and Biochemistry , Center of Molecular Medicine , Graz , Austria.

Background: Vascular endothelial cells represent an important source of arachidonic acid (AA)-derived mediators involved in the generation of anti- or proatherogenic environments. Evidence emerged (in mast cells), that in addition to phospholipases, neutral lipid hydrolases as adipose triglyceride lipase (ATGL) also participate in this process.

Objective: To examine the impact of ATGL on AA-release from cellular phospholipids (PL) and on prostacyclin secretion in human aortic endothelial cells (HAEC).

Methods And Results: siRNA-mediated silencing of ATGL promoted lipid droplet formation and TG accumulation in HAEC (nile red stain). ATGL knockdown decreased the basal and A23187 (calcium ionophore)-induced release of C-AA from (C-AA-labeled) HAEC. In A23187-stimulated ATGL silenced cells, this was accompanied by a decreased content of C-AA in cellular PL and a decreased secretion of prostacyclin (determined by 6-keto PGF1α EIA).

Conclusions: In vascular endothelial cells, the efficiency of stimulus-induced AA release and prostacyclin secretion is dependent on ATGL.
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http://dx.doi.org/10.1080/13813455.2017.1309052DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5942144PMC
October 2017

Acyl chain-dependent effect of lysophosphatidylcholine on endothelium-dependent vasorelaxation.

PLoS One 2013 31;8(5):e65155. Epub 2013 May 31.

Institute of Molecular Biology and Biochemistry, Center of Molecular Medicine, Medical University Graz, Graz, Austria.

Previously we identified palmitoyl-, oleoyl-, linoleoyl-, and arachidonoyl-lysophosphatidylcholine (LPC 16:0, 18:1, 18:2 and 20:4) as the most prominent LPC species generated by endothelial lipase (EL). In the present study, we examined the impact of those LPC on acetylcholine (ACh)- induced vascular relaxation. All tested LPC attenuated ACh-induced relaxation, measured ex vivo, using mouse aortic rings and wire myography. The rank order of potency was as follows: 18:2>20:4>16:0>18:1. The attenuating effect of LPC 16:0 on relaxation was augmented by indomethacin-mediated cyclooxygenase (COX)-inhibition and CAY10441, a prostacyclin (PGI2)- receptor (IP) antagonist. Relaxation attenuated by LPC 20:4 and 18:2 was improved by indomethacin and SQ29548, a thromboxane A2 (TXA2)- receptor antagonist. The effect of LPC 20:4 could also be improved by TXA2- and PGI2-synthase inhibitors. As determined by EIA assays, the tested LPC promoted secretion of PGI2, TXA2, PGF2α, and PGE2, however, with markedly different potencies. LPC 16:0 was the most potent inducer of superoxide anion production by mouse aortic rings, followed by LPC 18:2, 20:4 and 18:1, respectively. The strong antioxidant tempol recovered relaxation impairment caused by LPC 18:2, 18:1 and 20:4, but not by LPC 16:0. The tested LPC attenuate ACh-induced relaxation through induction of proconstricting prostanoids and superoxide anions. The potency of attenuating relaxation and the relative contribution of underlying mechanisms are strongly related to LPC acyl-chain length and degree of saturation.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0065155PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3669280PMC
January 2014

Impact of endothelial lipase on cellular lipid composition.

Biochim Biophys Acta 2012 Jul 6;1821(7):1003-11. Epub 2012 Apr 6.

Institute of Molecular Biology and Biochemistry, Center of Molecular Medicine, Medical University Graz, Graz, Austria.

Using mass spectrometry (MS), we examined the impact of endothelial lipase (EL) overexpression on the cellular phospholipid (PL) and triglyceride (TG) content of human aortic endothelial cells (HAEC) and of mouse plasma and liver tissue. In HAEC incubated with the major EL substrate, HDL, adenovirus (Ad)-mediated EL overexpression resulted in the generation of various lysophosphatidylcholine (LPC) and lysophosphatidylethanolamine (LPE) species in cell culture supernatants. While the cellular phosphatidylethanolamine (PE) content remained unaltered, cellular phosphatidylcholine (PC)-, LPC- and TG-contents were significantly increased upon EL overexpression. Importantly, cellular lipid composition was not altered when EL was overexpressed in the absence of HDL. [(14)C]-LPC accumulated in EL overexpressing, but not LacZ-control cells, incubated with [(14)C]-PC labeled HDL, indicating EL-mediated LPC supply. Exogenously added [(14)C]-LPC accumulated in HAEC as well. Its conversion to [(14)C]-PC was sensitive to a lysophospholipid acyltransferase (LPLAT) inhibitor, thimerosal. Incorporation of [(3)H]-Choline into cellular PC was 56% lower in EL compared with LacZ cells, indicating decreased endogenous PC synthesis. In mice, adenovirus mediated EL overexpression decreased plasma PC, PE and LPC and increased liver LPC, LPE and TG content. Based on our results, we conclude that EL not only supplies cells with FFA as found previously, but also with HDL-derived LPC and LPE species resulting in increased cellular TG and PC content as well as decreased endogenous PC synthesis.
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http://dx.doi.org/10.1016/j.bbalip.2012.03.006DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3460414PMC
July 2012

Docosahexaenoic acid-induced unfolded protein response, cell cycle arrest, and apoptosis in vascular smooth muscle cells are triggered by Ca²⁺-dependent induction of oxidative stress.

Free Radic Biol Med 2012 May 3;52(9):1786-95. Epub 2012 Mar 3.

Institute of Molecular Biology and Biochemistry, Center for Molecular Medicine, Austria.

Proliferation of vascular smooth muscle cells is a characteristic of pathological vascular remodeling and represents a significant therapeutic challenge in several cardiovascular diseases. Docosahexaenoic acid (DHA), a member of the n-3 polyunsaturated fatty acids, was shown to inhibit proliferation of numerous cell types, implicating several different mechanisms. In this study we examined the molecular events underlying the inhibitory effects of DHA on proliferation of primary human smooth muscle cells isolated from small pulmonary artery (hPASMCs). DHA concentration-dependently inhibited hPASMC proliferation, induced G1 cell cycle arrest, and decreased cyclin D1 protein expression. DHA activated the unfolded protein response (UPR), evidenced by increased mRNA expression of HSPA5, increased phosphorylation of eukaryotic initiation factor 2α, and splicing of X-box binding protein 1. DHA altered cellular lipid composition and led to increased reactive oxygen species (ROS) production. DHA-induced ROS were dependent on both intracellular Ca(2+) release and entry of extracellular Ca(2+). Overall cellular ROS and mitochondrial ROS were decreased by RU360, a specific inhibitor of mitochondrial Ca(2+) uptake. DHA-induced mitochondrial dysfunction was evidenced by decreased mitochondrial membrane potential and decreased cellular ATP content. DHA triggered apoptosis as found by increased numbers of cleaved caspase-3- and TUNEL-positive cells. The free radical scavenger Tempol counteracted DHA-induced ROS, cell cycle arrest, induction of UPR, and apoptosis. We conclude that Ca(2+)-dependent oxidative stress is the central and initial event responsible for induction of UPR, cell cycle arrest, and apoptosis in DHA-treated hPASMCs.
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http://dx.doi.org/10.1016/j.freeradbiomed.2012.02.036DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3482662PMC
May 2012

Endothelial lipase (EL) and EL-generated lysophosphatidylcholines promote IL-8 expression in endothelial cells.

Atherosclerosis 2011 Feb 13;214(2):338-44. Epub 2010 Nov 13.

Institute of Molecular Biology and Biochemistry, Harrachgasse 21/III, Medical University Graz, 8010 Graz, Austria.

Objective: Previously we identified palmitoyl-lysophosphatidylcholine (LPC 16:0), as well as linoleoyl-, arachidonoyl- and oleoyl-LPC (LPC 18:2, 20:4 and 18:1) as the most prominent LPC species generated by the action of endothelial lipase (EL) on high-density lipoprotein (HDL). In the present study, the impact of EL and EL-generated LPC on interleukin-8 (IL-8) synthesis was examined in vitro in primary human aortic endothelial cells (HAEC) and in mice.

Methods And Results: Adenovirus-mediated overexpression of the catalytically active EL, but not its inactive mutant, increased endothelial synthesis of IL-8 mRNA and protein in a time- and HDL-concentration-dependent manner. While LPC 18:2 was inactive, LPC 16:0, 18:1 and 20:4 promoted IL-8 mRNA- and protein-synthesis, differing in potencies and kinetics. The effects of all tested LPC on IL-8 synthesis were completely abrogated by addition of BSA and chelation of intracellular Ca(2+). Underlying signaling pathways also included NFkB, p38-MAPK, ERK, PKC and PKA. In mice, adenovirus-mediated overexpression of EL caused an elevation in the plasma levels of MIP-2 (murine IL-8 analogue) accompanied by a markedly increased plasma LPC/PC ratio. Intravenously injected LPC also raised MIP-2 plasma concentration, however to a lesser extent than EL overexpression.

Conclusion: Our results indicate that EL and EL-generated LPC, except of LPC 18:2, promote endothelial IL-8 synthesis, with different efficacy and kinetics, related to acyl-chain length and degree of saturation. Accordingly, due to its capacity to modulate the availability of the pro-inflammatory and pro-adhesive chemokine IL-8, EL should be considered an important player in the development of atherosclerosis.
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http://dx.doi.org/10.1016/j.atherosclerosis.2010.11.007DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3034026PMC
February 2011