Publications by authors named "Melanie Korbelius"

12 Publications

  • Page 1 of 1

Tissue-Specific Landscape of Metabolic Dysregulation during Ageing.

Biomolecules 2021 02 7;11(2). Epub 2021 Feb 7.

Gottfried Schatz Research Center for Cell Signaling, Metabolism and Ageing, Molecular Biology and Biochemistry, Medical University of Graz, 8010 Graz, Austria.

The dysregulation of cellular metabolism is a hallmark of ageing. To understand the metabolic changes that occur as a consequence of the ageing process and to find biomarkers for age-related diseases, we conducted metabolomic analyses of the brain, heart, kidney, liver, lung and spleen in young (9-10 weeks) and old (96-104 weeks) wild-type mice [mixed genetic background of 129/J and C57BL/6] using NMR spectroscopy. We found differences in the metabolic fingerprints of all tissues and distinguished several metabolites to be altered in most tissues, suggesting that they may be universal biomarkers of ageing. In addition, we found distinct tissue-clustered sets of metabolites throughout the organism. The associated metabolic changes may reveal novel therapeutic targets for the treatment of ageing and age-related diseases. Moreover, the identified metabolite biomarkers could provide a sensitive molecular read-out to determine the age of biologic tissues and organs and to validate the effectiveness and potential off-target effects of senolytic drug candidates on both a systemic and tissue-specific level.
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http://dx.doi.org/10.3390/biom11020235DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7914945PMC
February 2021

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

Spatially Resolved Activity-based Proteomic Profiles of the Murine Small Intestinal Lipases.

Mol Cell Proteomics 2020 12 6;19(12):2104-2115. Epub 2020 Oct 6.

Institute of Chemical Technologies and Analytics, Vienna University of Technology, Vienna, Austria; Diagnostic and Research Institute of Pathology, Medical University Graz, Graz, Austria; BioTechMed-Graz, Graz, Austria. Electronic address:

Despite the crucial function of the small intestine in nutrient uptake our understanding of the molecular events underlying the digestive function is still rudimentary. Recent studies demonstrated that enterocytes do not direct the entire dietary triacylglycerol toward immediate chylomicron synthesis. Especially after high-fat challenges, parts of the resynthesized triacylglycerol are packaged into cytosolic lipid droplets for transient storage in the endothelial layer of the small intestine. The reason for this temporary storage of triacylglycerol is not completely understood. To utilize lipids from cytosolic lipid droplets for chylomicron synthesis in the endoplasmic reticulum, stored triacylglycerol has to be hydrolyzed either by cytosolic lipolysis or lipophagy. Interestingly, triacylglycerol storage and chylomicron secretion rates are unevenly distributed along the small intestine, with the proximal jejunum exhibiting the highest intermittent storage capacity. We hypothesize that correlating hydrolytic enzyme activities with the reported distribution of triacylglycerol storage and chylomicron secretion in different sections of the small intestine is a promising strategy to determine key enzymes in triacylglycerol remobilization. We employed a serine hydrolase specific activity-based labeling approach in combination with quantitative proteomics to identify and rank hydrolases based on their relative activity in 11 sections of the small intestine. Moreover, we identified several clusters of enzymes showing similar activity distribution along the small intestine. Merging our activity-based results with substrate specificity and subcellular localization known from previous studies, carboxylesterase 2e and arylacetamide deacetylase emerge as promising candidates for triacylglycerol mobilization from cytosolic lipid droplets in enterocytes.
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http://dx.doi.org/10.1074/mcp.RA120.002171DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7710144PMC
December 2020

Intestine-specific DGAT1 deficiency improves atherosclerosis in apolipoprotein E knockout mice by reducing systemic cholesterol burden.

Atherosclerosis 2020 10 10;310:26-36. Epub 2020 Aug 10.

Gottfried Schatz Research Center, Medical University of Graz, Graz, Austria; BioTechMed-Graz, Graz, Austria. Electronic address:

Background And Aims: Acyl-CoA:diacylglycerol acyltransferase 1 (DGAT1) is the rate-limiting enzyme catalyzing the final step of triglyceride synthesis by esterifying a diglyceride with a fatty acid. We have previously shown that apolipoprotein E-knockout (ApoE) mice lacking Dgat1 have reduced intestinal cholesterol absorption and potentiated macrophage cholesterol efflux, and consequently, exhibit attenuated atherogenesis. However, hematopoietic Dgat1 deficiency lacked beneficial effects on atherosclerosis. Due to our recent results on the critical role of intestinal Dgat1 in murine cholesterol homeostasis, we delineated whether intestinal Dgat1 deficiency regulates atherogenesis in mice.

Methods: We generated intestine-specific Dgat1 mice on the ApoE background (iDgat1ApoE) and determined cholesterol homeostasis and atherosclerosis development.

Results: When fed a Western-type diet, iDgat1ApoE mice exhibited a substantial decrease in fasting plasma cholesterol content in ApoB-containing lipoproteins. Although lipid absorption was delayed, iDgat1ApoE mice had reduced acute and fractional cholesterol absorption coupled with an elevated fecal caloric loss. In line, increased appearance of i.v. administered [³H]cholesterol in duodena and stool of iDgat1ApoE animals suggested potentiated cholesterol elimination. Atherosclerotic lesions were markedly smaller with beneficial alterations in plaque composition as evidenced by reduced macrophage infiltration and necrotic core size despite unaltered collagen content, indicating improved plaque stability.

Conclusions: Disruption of Dgat1 activity solely in the small intestine of ApoE mice strongly decreased plasma cholesterol levels by abrogating the assimilation of dietary cholesterol, partly by reduced absorption and increased excretion. Consequently, the reduced cholesterol burden significantly attenuated atherogenesis and improved the lesion phenotype in iDgat1ApoE mice.
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http://dx.doi.org/10.1016/j.atherosclerosis.2020.07.030DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7116265PMC
October 2020

ATGL/CGI-58-Dependent Hydrolysis of a Lipid Storage Pool in Murine Enterocytes.

Cell Rep 2019 08;28(7):1923-1934.e4

Gottfried Schatz Research Center, Molecular Biology and Biochemistry, Medical University of Graz, 8010 Graz, Styria, Austria; BioTechMed-Graz, 8010 Graz, Styria, Austria. Electronic address:

As circulating lipid levels are balanced by the rate of lipoprotein release and clearance from the plasma, lipid absorption in the small intestine critically contributes to the maintenance of whole-body lipid homeostasis. Within enterocytes, excessive triglycerides are transiently stored as cytosolic lipid droplets (cLDs), and their mobilization sustains lipid supply during interprandial periods. Using mice lacking adipose triglyceride lipase (ATGL) and its coactivator comparative gene identification-58 (CGI-58) exclusively in the intestine (intestine-specific double KO [iDKO]), we show that ATGL/CGI-58 are not involved in providing substrates for chylomicron synthesis. Massive intestinal cLD accumulation in iDKO mice independent of dietary lipids together with inefficient lipid incorporation into cLDs in the early absorption phase demonstrate the existence of a secretion/re-uptake cycle, corroborating the availability of two diverse cLD pools. This study identified ATGL/CGI-58 as critical players in the catabolism of basolaterally (blood) derived lipids and highlights the necessity to modify the current model of intestinal lipid metabolism.
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http://dx.doi.org/10.1016/j.celrep.2019.07.030DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6713565PMC
August 2019

Lysosomal acid lipase regulates fatty acid channeling in brown adipose tissue to maintain thermogenesis.

Biochim Biophys Acta Mol Cell Biol Lipids 2018 Apr 31;1863(4):467-478. Epub 2018 Jan 31.

Gottfried Schatz Research Center, Medical University of Graz, Graz, Austria; BioTechMed-Graz, Graz, Austria. Electronic address:

Lysosomal acid lipase (LAL) is the only known enzyme, which hydrolyzes cholesteryl esters and triacylglycerols in lysosomes of multiple cells and tissues. Here, we explored the role of LAL in brown adipose tissue (BAT). LAL-deficient (Lal-/-) mice exhibit markedly reduced UCP1 expression in BAT, modified BAT morphology with accumulation of lysosomes, and mitochondrial dysfunction, consequently leading to regular hypothermic events in mice kept at room temperature. Cold exposure resulted in reduced lipid uptake into BAT, thereby aggravating dyslipidemia and causing life threatening hypothermia in Lal-/- mice. Linking LAL as a potential regulator of lipoprotein lipase activity, we found Angptl4 mRNA expression upregulated in BAT. Our data demonstrate that LAL is critical for shuttling fatty acids derived from circulating lipoproteins to BAT during cold exposure. We conclude that inhibited lysosomal lipid hydrolysis in BAT leads to impaired thermogenesis in Lal-/- mice.
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http://dx.doi.org/10.1016/j.bbalip.2018.01.011DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5839464PMC
April 2018

Lysosomal lipid hydrolysis provides substrates for lipid mediator synthesis in murine macrophages.

Oncotarget 2017 Jun;8(25):40037-40051

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

Degradation of lysosomal lipids requires lysosomal acid lipase (LAL), the only intracellular lipase known to be active at acidic pH. We found LAL to be expressed in murine immune cells with highest mRNA expression in macrophages and neutrophils. Furthermore, we observed that loss of LAL in mice caused lipid accumulation in white blood cells in the peripheral circulation, which increased in response to an acute inflammatory stimulus. Lal-deficient (-/-) macrophages accumulate neutral lipids, mainly cholesteryl esters, within lysosomes. The cholesteryl ester fraction is particularly enriched in the PUFAs 18:2 and 20:4, important precursor molecules for lipid mediator synthesis. To investigate whether loss of LAL activity affects the generation of lipid mediators and to eliminate potential systemic effects from other cells and tissues involved in the pronounced phenotype of Lal-/- mice, we treated macrophages from Wt mice with the LAL-specific inhibitor LAListat-2. Acute inhibition of LAL resulted in reduced release of 18:2- and 20:4-derived mediators from macrophages, indicating that lipid hydrolysis by LAL is an important source for lipid mediator synthesis in macrophages. We conclude that lysosomes should be considered as organelles that provide precursor molecules for lipid mediators such as eicosanoids.
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http://dx.doi.org/10.18632/oncotarget.16673DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5522325PMC
June 2017

Monoglyceride lipase deficiency affects hepatic cholesterol metabolism and lipid-dependent gut transit in ApoE-/- mice.

Oncotarget 2017 May;8(20):33122-33136

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

Monoglyceride lipase (MGL) hydrolyzes monoglycerides (MGs) to glycerol and fatty acids. Among various MG species MGL also degrades 2-arachidonoylglycerol (2-AG), the most abundant endocannabinoid and potent activator of cannabinoid receptors (CBR) 1 and 2. MGL-knockout (-/-) mice exhibit pronounced 2-AG accumulation, but lack central cannabimimetic effects due to CB1R desensitization. We have previously shown that MGL affects plaque stability in apolipoprotein E (ApoE)-/- mice, an established animal model for dyslipidemia and atherosclerosis. In the current study, we investigated functional consequences of MGL deficiency on lipid and energy metabolism in ApoE/MGL double knockout (DKO) mice. MGL deficiency affected hepatic cholesterol metabolism by causing increased cholesterol elimination via the biliary pathway. Moreover, DKO mice exhibit lipid-triggered delay in gastric emptying without major effects on overall triglyceride and cholesterol absorption. The observed phenotype of DKO mice is likely not a consequence of potentiated CB1R signaling but rather dependent on the activation of alternative signaling pathways. We conclude that MGL deficiency causes complex metabolic changes including cholesterol metabolism and regulation of gut transit independent of the endocannabinoid system.
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http://dx.doi.org/10.18632/oncotarget.16529DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5464855PMC
May 2017

Lysosomal acid lipase regulates VLDL synthesis and insulin sensitivity in mice.

Diabetologia 2016 08 6;59(8):1743-52. Epub 2016 May 6.

Institute of Molecular Biology and Biochemistry, Center of Molecular Medicine, Medical University of Graz, Harrachgasse 21, 8010, Graz, Austria.

Aims/hypothesis: Lysosomal acid lipase (LAL) hydrolyses cholesteryl esters and triacylglycerols (TG) within lysosomes to mobilise NEFA and cholesterol. Since LAL-deficient (Lal (-/-) ) mice suffer from progressive loss of adipose tissue and severe accumulation of lipids in hepatic lysosomes, we hypothesised that LAL deficiency triggers alternative energy pathway(s).

Methods: We studied metabolic adaptations in Lal (-/-) mice.

Results: Despite loss of adipose tissue, Lal (-/-) mice show enhanced glucose clearance during insulin and glucose tolerance tests and have increased uptake of [(3)H]2-deoxy-D-glucose into skeletal muscle compared with wild-type mice. In agreement, fasted Lal (-/-) mice exhibit reduced glucose and glycogen levels in skeletal muscle. We observed 84% decreased plasma leptin levels and significantly reduced hepatic ATP, glucose, glycogen and glutamine concentrations in fed Lal (-/-) mice. Markedly reduced hepatic acyl-CoA concentrations decrease the expression of peroxisome proliferator-activated receptor α (PPARα) target genes. However, treatment of Lal (-/-) mice with the PPARα agonist fenofibrate further decreased plasma TG (and hepatic glucose and glycogen) concentrations in Lal (-/-) mice. Depletion of hepatic nuclear factor 4α and forkhead box protein a2 in fasted Lal (-/-) mice might be responsible for reduced expression of microsomal TG transfer protein, defective VLDL synthesis and drastically reduced plasma TG levels.

Conclusions/interpretation: Our findings indicate that neither activation nor inactivation of PPARα per se but rather the availability of hepatic acyl-CoA concentrations regulates VLDL synthesis and subsequent metabolic adaptations in Lal (-/-) mice. We conclude that decreased plasma VLDL production enhances glucose uptake into skeletal muscle to compensate for the lack of energy supply.
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http://dx.doi.org/10.1007/s00125-016-3968-6DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4930475PMC
August 2016

Active autophagy but not lipophagy in macrophages with defective lipolysis.

Biochim Biophys Acta 2015 Oct 2;1851(10):1304-1316. Epub 2015 Jul 2.

Institute of Molecular Biology & Biochemistry, Center of Molecular Medicine, Medical University of Graz, Harrachgasse 21, 8010 Graz, Austria.

During autophagy, autophagosomes fuse with lysosomes to degrade damaged organelles and misfolded proteins. Breakdown products are released into the cytosol and contribute to energy and metabolic building block supply, especially during starvation. Lipophagy has been defined as the autophagy-mediated degradation of lipid droplets (LDs) by lysosomal acid lipase. Adipose triglyceride lipase (ATGL) is the major enzyme catalyzing the initial step of lipolysis by hydrolyzing triglycerides (TGs) in cytosolic LDs. Consequently, most organs and cells, including macrophages, lacking ATGL accumulate TGs, resulting in reduced intracellular free fatty acid concentrations. Macrophages deficient in hormone-sensitive lipase (H0) lack TG accumulation albeit reduced in vitro TG hydrolase activity. We hypothesized that autophagy is activated in lipase-deficient macrophages to counteract their energy deficit. We therefore generated mice lacking both ATGL and HSL (A0H0). Macrophages from A0H0 mice showed 73% reduced neutral TG hydrolase activity, resulting in TG-rich LD accumulation. Increased expression of cathepsin B, accumulation of LC3-II, reduced expression of p62 and increased DQ-BSA dequenching suggest intact autophagy and functional lysosomes in A0H0 macrophages. Markedly decreased acid TG hydrolase activity and lipid flux independent of bafilomycin A1 treatment, however, argue against effective lysosomal degradation of LDs in A0H0 macrophages. We conclude that autophagy of proteins and cell organelles but not of LDs is active as a compensatory mechanism to circumvent and balance the reduced availability of energy substrates in A0H0 macrophages.
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http://dx.doi.org/10.1016/j.bbalip.2015.06.005DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4562370PMC
October 2015

Endoplasmic reticulum stress impairs cholesterol efflux and synthesis in hepatic cells.

J Lipid Res 2014 Jan 31;55(1):94-103. Epub 2013 Oct 31.

Institute of Medical Chemistry, Center for Pathobiochemistry and Genetics, Medical University of Vienna, Vienna, Austria.

Metabolic disorders such as type 2 diabetes cause hepatic endoplasmic reticulum (ER) stress, which affects neutral lipid metabolism. However, the role of ER stress in cholesterol metabolism is incompletely understood. Here, we show that induction of acute ER stress in human hepatic HepG2 cells reduced ABCA1 expression and caused ABCA1 redistribution to tubular perinuclear compartments. Consequently, cholesterol efflux to apoA-I, a key step in nascent HDL formation, was diminished by 80%. Besides ABCA1, endogenous apoA-I expression was reduced upon ER stress induction, which contributed to reduced cholesterol efflux. Liver X receptor, a key regulator of ABCA1 in peripheral cells, was not involved in this process. Despite reduced cholesterol efflux, cellular cholesterol levels remained unchanged during ER stress. This was due to impaired de novo cholesterol synthesis by reduction of HMG-CoA reductase activity by 70%, although sterol response element-binding protein-2 activity was induced. In mice, ER stress induction led to a marked reduction of hepatic ABCA1 expression. However, HDL cholesterol levels were unaltered, presumably because of scavenger receptor class B, type I downregulation under ER stress. Taken together, our data suggest that ER stress in metabolic disorders reduces HDL biogenesis due to impaired hepatic ABCA1 function.
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http://dx.doi.org/10.1194/jlr.M043299DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3927476PMC
January 2014

Identification of the transcription factor HOXB4 as a novel target of miR-23a.

Genes Chromosomes Cancer 2013 Aug 30;52(8):709-15. Epub 2013 Apr 30.

Institute of Pathology, Medical University of Graz, Auenbruggerplatz 25, 8036, Graz, Austria.

The transcription factor HOXB4 not only plays a role during nephrogenesis, but displays also oncogenic characteristics in different malignant neoplasms. An in-silico analysis revealed HOXB4 as a new target of microRNA-23a (miR-23a). Nephroblastomas are malignant embryonal renal neoplasms of childhood resembling developing kidney morphologically and genetically. In our study we verified HOXB4 as a target of miR-23a and furthermore examined the expression of HOXB4 and miR-23a in nephroblastomas. We investigated binding of miR-23a to the 3'UTR of HOXB4 by a luciferase assay. Effects on protein levels of HOXB4 were analysed in Western blot experiments. Expression of HOXB4 in nephroblastomas was assessed by quantitative REALtime PCR (qRT PCR) and immunohistochemistry. The luciferase reporter assay showed a statistically significant downregulation of activity by 72,5% demonstrating direct binding of miR-23a to the 3'UTR of HOXB4. In addition, miR-23a reduced the protein expression of HOXB4 statistically significantly by 65.1%. All 21 nephroblastomas investigated had statistically significantly decreased expression levels of miR-23a. A high level of HOXB4 mRNA was found in five out of 33 nephroblastomas including mixed, blastema-type and stroma-type tumors. Protein expression of HOXB4 was stronger in 15 out of 27 nephroblastomas of all subtypes in a semiquantitative comparison to normal kidney parenchyma. Our study demonstrates for the first time the regulation of HOXB4 by miR-23a. In comparison to mature kidney, nephroblastomas had low levels of miR-23a, and in a majority of them a stronger protein expression in comparison to mature kidney was found.
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http://dx.doi.org/10.1002/gcc.22066DOI Listing
August 2013