Lipocalin-2 (LCN2) expression during transdifferentiation of rat hepatic stellate cells and its potential impact on liver fibrogenesis

Background and aims: The lipocalin protein family contains a group of small secreted extracellular proteins with the ability to bind small hydrophobic molecules. They are involved in the regulation of the immune response and cell homeostasis. Lipocalin-2 (LCN2), also known as Neutrophil gelatinase-associated lipocalin (NGAL), is an inflammatory marker abundantly expressed in adipose tissue and liver and induced by oxidative stress [1, 2]. Additionally, we have previously shown that the expression of LCN2 is TGF-β1-dependent in hepatic stellate cells (HSC) [3]. Methods: HSC were isolated from Sprague-Dawley rats by the Pronase-collagenase method and cultured in DMEM. The cells were harvested after several days, extracted and the protein lysates analysed by Western blot. Simultaneously, RNA for cDNA synthesis was isolated. The time-dependent expression of LCN2 was monitored during transdifferentiation and in different models of hepatic fibrogenesis. Also, the expression level of LCN2 in different liver cells was semi-quantitatively determined by RT-PCR and Western blot. The distribution of hepatic LCN2 expression in normal and fibrotic livers was determined by immunohistochemistry. Results: Both, the Western blot and the RT-PCR experiments revealed that the expression of LCN2 decreased during activation and transdifferentiation of HSC. The expression was inversely correlated to the expression of typical fibrogenic markers and the situation in hepatocytes. Hepatic LCN2 levels were further elevated in animals that underwent bile duct ligation and in animals that received repeatedly doses of CCl4. The number of LCN2 positive cells strongly increased during ongoing hepatic fibrogenesis. Conclusions: LCN2 is a fibrogenic marker gene that is closely related to inflammation and fibrosis in liver. Therefore, measurement of LCN2 in serum or tissue specimen might be useful as a clinical marker to assess the severity of liver injury during ongoing fibrogenesis.