Lipocalin 2 (LCN2) in hepatic inflammation

Background: Lipocalin-2 (LCN2), also known as neutrophil gelatinase-associated lipocalin (NGAL), is a small secreted adipokine that belongs to the family of lipocalins that are known for binding and transporting small hydrophobic molecules such as fatty acids, steroids and iron [1]. In the liver, LCN2 plays a protective role in inflammation, infection, injury and other forms of cellular stress. This was proven in the bile duct ligation and the carbon tetrachloride model [2]. Recently, we demonstrated that LCN2 regulates perilipin 5 (PLIN5) expression in primary hepatocytes [3]. Material and Methods: In the present study, we analysed the role of LCN2 in an experimental model of non-alcoholic steatohepatitis (NASH). A methionine- and choline-deficient (MCD) diet was fed in wild type (WT) and LCN2-deficient (Lcn2-/-) mice for four to six weeks as an experimental model for NASH. Hepatic inflammation, injury and fibrosis were scored in specimen subjected to Haematoxylin and Eosin stain, Sirius Red stain, and by immunohistochemistry using antibodies specific for the common leukocyte marker CD45 and Myeloperoxidase (MPO) representing a marker for neutrophil granulocytes. Moreover, we comparatively analysed the mRNA expression of inflammatory cytokines such as IL-6, TNF-α, IL-1β, CCL2 and CCR2. Furthermore, the expression and phosphorylation of the STAT1 and STAT3 proteins was investigated. Results: WT mice developed more severe liver inflammation than the Lcn2-/-. They had significant more multiple leukocyte and bigger neutrophil infiltrates, showed higher expression of CD45 and MPO. Strong upregulation of LCN2 during administration of the MCD diet was observed in the WT mice. In addition, a significant stronger activation of STAT3 and STAT1 was observed in WT mice. In summary, inflammation at 4 weeks and fibrosis scores at 6 weeks in animals fed with MCD diet were higher in WT animals. Conclusions: Our data indicate that the biological activity of LCN2 in experimentally- induced liver injury depends on the model analysed. While LCN2 acts protectively in models that are commonly used to induce liver cirrhosis, the presence of LCN2 during MCD diet results in more severe liver damage. References cited: [1] Flower DR. The lipocalin protein family: structure and function. Biochem. J. 1996;318:1 – 14. [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;1841:1513 – 24. Corresponding author: Weiskirchen, Ralf E-Mail: rweiskirchen@ukaachen.de