Hepatic Proteome and Lipid Profiling of Wild Type and Lipocalin-2-Deficient Mice in Experimental Steatosis

A Asimakopoulou; A Fülöp; E Borkham-Kamphorst; N Gassler; T Berger; TW Mak; C Hopf; C Henkel; R Weiskirchen

doi:10.1055/s-0035-1567952

Zeitschrift für Gastroenterologie, Inhaltsverzeichnis

Hepatic Proteome and Lipid Profiling of Wild Type and Lipocalin-2-Deficient Mice in Experimental Steatosis

A Asimakopoulou ¹, A Fülöp ², E Borkham-Kamphorst ¹, N Gassler ³, T Berger ⁴, TW Mak ⁵, C Hopf ², C Henkel ⁶, R Weiskirchen ¹

¹RWTH University Hospital Aachen, Institute of Molecular Pathobiochemistry, Experimental Gene Therapy and Clinical Chemistry, Aachen, Germany
²Mannheim University of Applied Sciences, Applied Research Center in Biomedical Mass Spectrometry (ABIMAS), Instrumental Analysis and Bioanalysis, Mannheim, Germany
³Klinikum Braunschweig, Institute of Pathology, Braunschweig, Germany
⁴University Health Network, The Campbell Family Institute for Breast Cancer Research, Toronto, Canada
⁵Ontario Cancer Institute, Ontario Cancer Institute, Toronto, Canada
⁶ISAS – e.V., Leibniz-Institut für Analytische Wissenschaften, Dortmund, Germany

Abstract

Background: Lipocalin-2 (LCN2) or neutrophil gelatinase-associated lipocalin (NGAL) is a small secreted adipokine belonging to the lipocalin family [1]. It binds and transports small hydrophobic molecules and limits bacterial growth by sequestering iron-containing siderophores. In the liver, LCN2 plays a protective role in inflammation, infection, and cellular stress. Recently, we demonstrated that LCN2 regulates lipid droplet protein Perilipin 5 (PLIN5) expression in primary hepatocytes and showed that LCN2 animals are more prone to hepatic inflammation and steatosis [2 – 4]. Methods: We here comparatively analyzed the proteome (label-free proteomics or 2D-DIGE protein expression profiling) of wild type and Lcn2-deficient mice fed either a standard-chow and a methionine- and choline-deficient (MCD) diet. The differential expression was confirmed by Western blot analysis and quantitative real-time PCR. We further employed comparative MALDI-TOF Imaging Mass Spectrometry to monitor the spatial distribution of a broad range of lipids in liver tissue sections of respective groups. Results: We identified a multitude of genes that are either upregulated during hepatic steatosis or differentially induced or repressed in mice lacking LCN2. Differentially expressed proteins were BRIT1/MCPH1, FABP5, HMGB1, HBB2, and L-FABP. In addition, we identified significantly altered m/z signal intensities for several sphingomyelins, triglycerides, and phospholipid species. Most notably, phosphatidylinositol phosphates were substantially elevated in MCD-fed mice, indicating chronic activation of phosphatidylinositol phosphate-dependent signaling pathways, and this alteration was unaffected by LCN2 deletion. Moreover, the abundance of some 20:4 lipids were elevated in the livers of Lcn2-deficient mice suggesting that this gene disruption might interfere with arachidonic acid and eicosanoid metabolism. Conclusion: In summary, our data indicate that LCN2 is a key switch influencing triglyceride balance, reactive oxidative stress formation, inflammatory response, and cellular apoptosis.

References cited:

[1] Asimakopoulou A, Weiskirchen R. Lipocalin 2 in the pathogenesis of fatty liver disease and non-alcoholic steatohepatitis. Clinical Lipidol. 2015;10:47 – 67.

[2] Borkham-Kamphorst E, van de Leur E, Zimmermann HW, Karlmark KR, Tihaa L, Haas U, Tacke F, Berger T, Mak TW, Weiskirchen R. Protective effects of lipocalin-2 (LCN2) in acute liver injury suggest a novel function in liver homeostasis. Biochim Biophys Acta 2013;1832:660 – 73.

[3] Asimakopoulou A, Borkham-Kamphorst E, Henning M, Yagmur E, Gassler N, Liedtke C, Berger T, Mak TW, Weiskirchen R. Lipocalin-2 (LCN2) regulates PLIN5 expression and intracellular lipid droplet formation in the liver. Biochim Biophys Acta 2014;1842:1513 – 24.

[4] Asimakopoulou A, Borkham-Kamphorst E, Tacke F, Weiskirchen R. Lipocalin-2 (NGAL/LCN2), a "HELP-ME" signal in organ inflammation. Hepatology 2015; Jun 5 [Epub ahead of print]

Corresponding author: Weiskirchen, Ralf

E-Mail: rweiskirchen@ukaachen.de